Author: "Costa B" / Publication Type: Reports - Searchworks@Jio Institute Digital Library Search Results

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1. Benchmarking the design of the cryogenics system for the underground argon in DarkSide-20k

Author: Collaboration, DarkSide-20k, Acerbi, F., Adhikari, P., Agnes, P., Ahmad, I., Albergo, S., Albuquerque, I. F. M., Alexander, T., Alton, A. K., Amaudruz, P., Angiolilli, M., Aprile, E., Ardito, R., Corona, M. Atzori, Auty, D. J., Ave, M., Avetisov, I. C., Azzolini, O., Back, H. O., Balmforth, Z., Olmedo, A. Barrado, Barrillon, P., Batignani, G., Bhowmick, P., Blua, S., Bocci, V., Bonivento, W., Bottino, B., Boulay, M. G., Buchowicz, A., Bussino, S., Busto, J., Cadeddu, M., Cadoni, M., Calabrese, R., Camillo, V., Caminata, A., Canci, N., Capra, A., Caravati, M., Cárdenas-Montes, M., Cargioli, N., Carlini, M., Castellani, A., Castello, P., Cavalcante, P., Cebrian, S., Ruiz, J. Cela, Chashin, S., Chepurnov, A., Cifarelli, L., Cintas, D., Citterio, M., Cleveland, B., Coadou, Y., Cocco, V., Colaiuda, D., Vilda, E. Conde, Consiglio, L., Costa, B. S., Czubak, M., D'Aniello, M., D'Auria, S., Rolo, M. D. Da Rocha, Darbo, G., Davini, S., De Cecco, S., De Guido, G., Dellacasa, G., Derbin, A. V., Devoto, A., Di Capua, F., Di Ludovico, A., Di Noto, L., Di Stefano, P., Dias, L. K., Mairena, D. Díaz, Ding, X., Dionisi, C., Dolganov, G., Dordei, F., Dronik, V., Elersich, A., Ellingwood, E., Erjavec, T., Diaz, M. Fernandez, Ficorella, A., Fiorillo, G., Franchini, P., Franco, D., Gatti, H. Frandini, Frolov, E., Gabriele, F., Gahan, D., Galbiati, C., Galiński, G., Gallina, G., Gallus, G., Garbini, M., Abia, P. Garcia, Gawdzik, A., Gendotti, A., Ghisi, A., Giovanetti, G. K., Casanueva, V. Goicoechea, Gola, A., Grandi, L., Grauso, G., di Cortona, G. Grilli, Grobov, A., Gromov, M., Guerzoni, M., Gulino, M., Guo, C., Hackett, B. R., Hallin, A., Hamer, A., Haranczyk, M., Harrop, B., Hessel, T., Hill, S., Horikawa, S., Hu, J., Hubaut, F., Hucker, J., Hugues, T., Hungerford, E. V., Ianni, A., Ippolito, V., Jamil, A., Jillings, C., Jois, S., Kachru, P., Keloth, R., Kemmerich, N., Kemp, A., Kendziora, C. L., Kimura, M., Kish, A., Kondo, K., Korga, G., Kotsiopoulou, L., Koulosousas, S., Kubankin, A., Kunzé, P., Kuss, M., Kuźniak, M., Kuzwa, M., La Commara, M., Lai, M., Guirriec, E. Le, Leason, E., Leoni, A., Lidey, L., Lissia, M., Luzzi, L., Lychagina, O., Macfadyen, O., Machulin, I. N., Manecki, S., Manthos, I., Mapelli, L., Marasciulli, A., Mari, S. M., Mariani, C., Maricic, J., Martinez, M., Martoff, C. J., Matteucci, G., Mavrokoridis, K., McDonald, A. B., Mclaughlin, J., Merzi, S., Messina, A., Milincic, R., Minutoli, S., Mitra, A., Moharana, A., Moioli, S., Monroe, J., Moretti, E., Morrocchi, M., Mroz, T., Muratova, V. N., Murphy, M., Murra, M., Muscas, C., Musico, P., Nania, R., Nessi, M., Nieradka, G., Nikolopoulos, K., Nikoloudaki, E., Nowak, J., Olchanski, K., Oleinik, A., Oleynikov, V., Organtini, P., de Solórzano, A. Ortiz, Pallavicini, M., Pandola, L., Pantic, E., Paoloni, E., Papi, D., Pastuszak, G., Paternoster, G., Peck, A., Pegoraro, P. A., Pelczar, K., Pellegrini, L. A., Perez, R., Perotti, F., Pesudo, V., Piacentini, S. I., Pino, N., Plante, G., Pocar, A., Poehlmann, M., Pordes, S., Pralavorio, P., Price, D., Puglia, S., Bazetto, M. Queiroga, Ragusa, F., Ramachers, Y., Ramirez, A., Ravinthiran, S., Razeti, M., Renshaw, A. L., Rescigno, M., Retiere, F., Rignanese, L. P., Rivetti, A., Roberts, A., Roberts, C., Rogers, G., Romero, L., Rossi, M., Rubbia, A., Rudik, D., Sabia, M., Salomone, P., Samoylov, O., Sandford, E., Sanfilippo, S., Santone, D., Santorelli, R., Santos, E. M., Savarese, C., Scapparone, E., Schillaci, G., Schuckman II, F. G., Scioli, G., Semenov, D. A., Shalamova, V., Sheshukov, A., Simeone, M., Skensved, P., Skorokhvatov, M. D., Smirnov, O., Smirnova, T., Smith, B., Sotnikov, A., Spadoni, F., Spangenberg, M., Stefanizzi, R., Steri, A., Stornelli, V., Stracka, S., Sulis, S., Sung, A., Sunny, C., Suvorov, Y., Szelc, A. M., Taborda, O., Tartaglia, R., Taylor, A., Taylor, J., Tedesco, S., Testera, G., Thieme, K., Thompson, A., Thorpe, T. N., Tonazzo, A., Torres-Lara, S., Tricomi, A., Unzhakov, E. V., Vallivilayil, T. J., Van Uffelen, M., Velazquez-Fernandez, L., Viant, T., Viel, S., Vishneva, A., Vogelaar, R. B., Vossebeld, J., Vyas, B., Wada, M., Walczak, M. B., Wang, H., Wang, Y., Westerdale, S., Williams, L., Wojaczyński, R., Wojcik, M., Wojcik, M. M., Wright, T., Xiao, X., Xie, Y., Yang, C., Yin, J., Zabihi, A., Zakhary, P., Zani, A., Zhang, Y., Zhu, T., Zichichi, A., Zuzel, G., and Zykova, M. P.
Subjects: Physics - Instrumentation and Detectors, High Energy Physics - Experiment
Abstract: DarkSide-20k (DS-20k) is a dark matter detection experiment under construction at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy. It utilises ~100 t of low radioactivity argon from an underground source (UAr) in its inner detector, with half serving as target in a dual-phase time projection chamber (TPC). The UAr cryogenics system must maintain stable thermodynamic conditions throughout the experiment's lifetime of >10 years. Continuous removal of impurities and radon from the UAr is essential for maximising signal yield and mitigating background. We are developing an efficient and powerful cryogenics system with a gas purification loop with a target circulation rate of 1000 slpm. Central to its design is a condenser operated with liquid nitrogen which is paired with a gas heat exchanger cascade, delivering a combined cooling power of >8 kW. Here we present the design choices in view of the DS-20k requirements, in particular the condenser's working principle and the cooling control, and we show test results obtained with a dedicated benchmarking platform at CERN and LNGS. We find that the thermal efficiency of the recirculation loop, defined in terms of nitrogen consumption per argon flow rate, is 95 % and the pressure in the test cryostat can be maintained within $\pm$(0.1-0.2) mbar. We further detail a 5-day cool-down procedure of the test cryostat, maintaining a cooling rate typically within -2 K/h, as required for the DS-20k inner detector. Additionally, we assess the circuit's flow resistance, and the heat transfer capabilities of two heat exchanger geometries for argon phase change, used to provide gas for recirculation. We conclude by discussing how our findings influence the finalisation of the system design, including necessary modifications to meet requirements and ongoing testing activities., Comment: 45 pages, 24 figures
Published: 2024

2. DarkSide-20k sensitivity to light dark matter particles

Author: Collaboration, DarkSide-20k, Acerbi, F., Adhikari, P., Agnes, P., Ahmad, I., Albergo, S., Albuquerque, I. F. M., Alexander, T., Alton, A. K., Amaudruz, P., Angiolilli, M., Aprile, E., Ardito, R., Corona, M. Atzori, Auty, D. J., Ave, M., Avetisov, I. C., Azzolini, O., Back, H. O., Balmforth, Z., Olmedo, A. Barrado, Barrillon, P., Batignani, G., Bhowmick, P., Blua, S., Bocci, V., Bonivento, W., Bottino, B., Boulay, M. G., Buchowicz, A., Bussino, S., Busto, J., Cadeddu, M., Cadoni, M., Calabrese, R., Camillo, V., Caminata, A., Canci, N., Capra, A., Caravati, M., Cárdenas-Montes, M., Cargioli, N., Carlini, M., Castellani, A., Castello, P., Cavalcante, P., Cebrian, S., Ruiz, J. M. Cela, Chashin, S., Chepurnov, A., Cifarelli, L., Cintas, D., Citterio, M., Cleveland, B., Coadou, Y., Cocco, V., Colaiuda, D., Vilda, E. Conde, Consiglio, L., Costa, B. S., Czubak, M., D'Aniello, M., D'Auria, S., Rolo, M. D. Da Rocha, Darbo, G., Davini, S., De Cecco, S., De Guido, G., Dellacasa, G., Derbin, A. V., Devoto, A., Di Capua, F., Di Ludovico, A., Di Noto, L., Di Stefano, P., Dias, L. K., Mairena, D. Díaz, Ding, X., Dionisi, C., Dolganov, G., Dordei, F., Dronik, V., Elersich, A., Ellingwood, E., Erjavec, T., Diaz, M. Fernandez, Ficorella, A., Fiorillo, G., Franchini, P., Franco, D., Gatti, H. Frandini, Frolov, E., Gabriele, F., Gahan, D., Galbiati, C., Galiński, G., Gallina, G., Gallus, G., Garbini, M., Abia, P. Garcia, Gawdzik, A., Gendotti, A., Ghisi, A., Giovanetti, G. K., Casanueva, V. Goicoechea, Gola, A., Grandi, L., Grauso, G., di Cortona, G. Grilli, Grobov, A., Gromov, M., Guerzoni, M., Gulino, M., Guo, C., Hackett, B. R., Hallin, A., Hamer, A., Haranczyk, M., Harrop, B., Hessel, T., Hill, S., Horikawa, S., Hu, J., Hubaut, F., Hucker, J., Hugues, T., Hungerford, E. V., Ianni, A., Ippolito, V., Jamil, A., Jillings, C., Jois, S., Kachru, P., Keloth, R., Kemmerich, N., Kemp, A., Kendziora, C. L., Kimura, M., Kondo, K., Korga, G., Kotsiopoulou, L., Koulosousas, S., Kubankin, A., Kunzé, P., Kuss, M., Kuźniak, M., Kuzwa, M., La Commara, M., Lai, M., Guirriec, E. Le, Leason, E., Leoni, A., Lidey, L., Lissia, M., Luzzi, L., Lychagina, O., Macfadyen, O., Machulin, I. N., Manecki, S., Manthos, I., Mapelli, L., Marasciulli, A., Mari, S. M., Mariani, C., Maricic, J., Martinez, M., Martoff, C. J., Matteucci, G., Mavrokoridis, K., McDonald, A. B., Mclaughlin, J., Merzi, S., Messina, A., Milincic, R., Minutoli, S., Mitra, A., Moioli, S., Monroe, J., Moretti, E., Morrocchi, M., Mroz, T., Muratova, V. N., Murphy, M., Murra, M., Muscas, C., Musico, P., Nania, R., Nessi, M., Nieradka, G., Nikolopoulos, K., Nikoloudaki, E., Nowak, J., Olchanski, K., Oleinik, A., Oleynikov, V., Organtini, P., de Solórzano, A. Ortiz, Pallavicini, M., Pandola, L., Pantic, E., Paoloni, E., Papi, D., Pastuszak, G., Paternoster, G., Peck, A., Pegoraro, P. A., Pelczar, K., Pellegrini, L. A., Perez, R., Perotti, F., Pesudo, V., Piacentini, S. I., Pino, N., Plante, G., Pocar, A., Poehlmann, M., Pordes, S., Pralavorio, P., Price, D., Puglia, S., Bazetto, M. Queiroga, Ragusa, F., Ramachers, Y., Ramirez, A., Ravinthiran, S., Razeti, M., Renshaw, A. L., Rescigno, M., Retiere, F., Rignanese, L. P., Rivetti, A., Roberts, A., Roberts, C., Rogers, G., Romero, L., Rossi, M., Rubbia, A., Rudik, D., Sabia, M., Salomone, P., Samoylov, O., Sandford, E., Sanfilippo, S., Santone, D., Santorelli, R., Santos, E. M., Savarese, C., Scapparone, E., Schillaci, G., Schuckman II, F. G., Scioli, G., Semenov, D. A., Shalamova, V., Sheshukov, A., Simeone, M., Skensved, P., Skorokhvatov, M. D., Smirnov, O., Smirnova, T., Smith, B., Sotnikov, A., Spadoni, F., Spangenberg, M., Stefanizzi, R., Steri, A., Stornelli, V., Stracka, S., Sulis, S., Sung, A., Sunny, C., Suvorov, Y., Szelc, A. M., Taborda, O., Tartaglia, R., Taylor, A., Taylor, J., Tedesco, S., Testera, G., Thieme, K., Thompson, A., Tonazzo, A., Torres-Lara, S., Tricomi, A., Unzhakov, E. V., Vallivilayil, T. J., Van Uffelen, M., Velazquez-Fernandez, L., Viant, T., Viel, S., Vishneva, A., Vogelaar, R. B., Vossebeld, J., Vyas, B., Walczak, M. B., Wang, Y., Wang, H., Westerdale, S., Williams, L., Wojaczyński, R., Wojcik, M., Wojcik, M. M., Wright, T., Xie, Y., Yang, C., Yin, J., Zabihi, A., Zakhary, P., Zani, A., Zhang, Y., Zhu, T., Zichichi, A., Zuzel, G., and Zykova, M. P.
Subjects: High Energy Physics - Experiment, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: The dual-phase liquid argon time projection chamber is presently one of the leading technologies to search for dark matter particles with masses below 10 GeV/c$^2$. This was demonstrated by the DarkSide-50 experiment with approximately 50 kg of low-radioactivity liquid argon as target material. The next generation experiment DarkSide-20k, currently under construction, will use 1,000 times more argon and is expected to start operation in 2027. Based on the DarkSide-50 experience, here we assess the DarkSide-20k sensitivity to models predicting light dark matter particles, including Weakly Interacting Massive Particles (WIMPs) and sub-GeV/c$^2$ particles interacting with electrons in argon atoms. With one year of data, a sensitivity improvement to dark matter interaction cross-sections by at least one order of magnitude with respect to DarkSide-50 is expected for all these models. A sensitivity to WIMP--nucleon interaction cross-sections below $1\times10^{-42}$ cm$^2$ is achievable for WIMP masses above 800 MeV/c$^2$. With 10 years exposure, the neutrino fog can be reached for WIMP masses around 5 GeV/c$^2$., Comment: submitted to Nature Communications
Published: 2024

3. A new hybrid gadolinium nanoparticles-loaded polymeric material for neutron detection in rare event searches

Author: Collaboration, DarkSide-20k, Acerbi, F., Adhikari, P., Agnes, P., Ahmad, I., Albergo, S., Albuquerque, I. F., Alexander, T., Alton, A. K., Amaudruz, P., Angiolilli, M., Aprile, E., Ardito, R., Corona, M. Atzori, Auty, D. J., Ave, M., Avetisov, I. C., Azzolini, O., Back, H. O., Balmforth, Z., Olmedo, A. Barrado, Barrillon, P., Batignani, G., Bhowmick, P., Bocci, V., Bonivento, W., Bottino, B., Boulay, M. G., Buchowicz, A., Bussino, S., Busto, J., Cadeddu, M., Cadoni, M., Calabrese, R., Camillo, V., Caminata, A., Canci, N., Capra, A., Caravati, M., Cárdenas-Montes, M., Cargioli, N., Carlini, M., Castellani, A., Castello, P., Cavalcante, P., Cavallo, D., Cebrian, S., Ruiz, J. Cela, Chashin, S., Chepurnov, A., Cifarelli, L., Cintas, D., Citterio, M., Cleveland, B., Coadou, Y., Cocco, V., Colaiuda, D., Vilda, E. Conde, Consiglio, L., Costa, B. S., Czubak, M., D'Auria, S., Rolo, M. D. Da Rocha, Darbo, G., Davini, S., De Cecco, S., De Guido, G., Dellacasa, G., Derbin, A. V., Devoto, A., Di Capua, F., Di Ludovico, A., Di Noto, L., Di Stefano, P., Dias, L. K., Mairena, D. Díaz, Ding, X., Dionisi, C., Dolganov, G., Dordei, F., Dronik, V., Elersich, A., Ellingwood, E., Erjavec, T., Diaz, M. Fernandez, Ficorella, A., Fiorillo, G., Franchini, P., Franco, D., Gatti, H. Frandini, Frolov, E., Gabriele, F., Gahan, D., Galbiati, C., Galinski, G., Gallina, G., Garbini, M., Abia, P. Garcia, Gawdzik, A., Gendotti, A., Ghisi, A., Giovanetti, G. K., Casanueva, V. Goicoechea, Gola, A., Grandi, L., Grauso, G., di Cortona, G. Grilli, Grobov, A., Gromov, M., Guerzoni, M., Gulino, M., Guo, C., Hackett, B. R., Hallin, A., Hamer, A., Haranczyk, M., Harrop, B., Hessel, T., Hill, S., Horikawa, S., Hu, J., Hubaut, F., Hucker, J., Hugues, T., Hungerford, E. V., Ianni, A., Ippolito, V., Jamil, A., Jillings, C., Keloth, R., Kemmerich, N., Kemp, A., Kendziora, C. L., Kimura, M., Kondo, K., Korga, G., Kotsiopoulou, L., Koulosousas, S., Kubankin, A., Kuss, M., Kuzniak, M., Kuzwa, M., La Commara, M., Lai, M., Guirriec, E. Le, Leason, E., Leoni, A., Lidey, L., Lissia, M., Luzzi, L., Lychagina, O., Macfadyen, O., Machulin, I. N., Manecki, S., Manthos, I., Mapelli, L., Marasciulli, A., Mari, S. M., Mariani, C., Maricic, J., Marini, A., Martinez, M., Martoff, C. J., Matteucci, G., Mavrokoridis, K., McDonald, A. B., Mclaughlin, J., Merzi, S., Messina, A., Milincic, R., Minutoli, S., Mitra, A., Moharana, A., Moioli, S., Monroe, J., Moretti, E., Morrocchi, M., Mroz, T., Muratova, V. N., Murphy, M., Murra, M., Muscas, C., Musico, P., Nania, R., Nessi, M., Nieradka, G., Nikolopoulos, K., Nikoloudaki, E., Nowak, J., Olchanski, K., Oleinik, A., Oleynikov, V., Organtini, P., de Solórzano, A. Ortiz, Pallavicini, M., Pandola, L., Pantic, E., Paoloni, E., Papi, D., Pastuszak, G., Paternoster, G., Peddis, D., Pegoraro, P. A., Pelczar, K., Pellegrini, L. A., Perez, R., Perotti, F., Pesudo, V., Piacentini, S. I., Pino, N., Plante, G., Pocar, A., Poehlmann, M., Pordes, S., Pralavorio, P., Price, D., Puglia, S., Bazetto, M. Queiroga, Ragusa, F., Ramachers, Y., Ramirez, A., Ravinthiran, S., Razeti, M., Renshaw, A. L., Rescigno, M., Retiere, F., Rignanese, L. P., Rivetti, A., Roberts, A., Roberts, C., Rogers, G., Romero, L., Rossi, M., Rubbia, A., Rudik, D., Sabia, M., Sadashivajois, S., Salomone, P., Samoylov, O., Sandford, E., Sanfilippo, S., Santone, D., Santorelli, R., Santos, E. M., Savarese, C., Scapparone, E., Schillaci, G., Schuckman II, F. G., Scioli, G., Semenov, D. A., Sheshukov, A., Simeone, M., Skensved, P., Skorokhvatov, M. D., Slimani, S., Smirnov, O., Smirnova, T., Smith, B., Sotnikov, A., Spadoni, F., Spangenberg, M., Stefanizzi, R., Steri, A., Stornelli, V., Stracka, S., Sulis, S., Sung, A., Sunny, C., Suvorov, Y., Szelc, A. M., Taborda, O., Tartaglia, R., Taylor, A., Taylor, J., Tedesco, S., Testera, G., Thieme, K., Thompson, A., Tonazzo, A., Torres-Lara, S., Tosi, S., Tricomi, A., Unzhakov, E. V., Vallivilayil, T. J., Van Uffelen, M., Velazquez-Fernandez, L., Viant, T., Vicini, S., Viel, S., Vishneva, A., Vogelaar, R. B., Vossebeld, J., Vyas, B., Wada, M., Walczak, M. B., Wang, H., Wang, Y., Westerdale, S., Williams, L., Wojaczynski, R., Wojcik, M. M., Wojcik, M., Wright, T., Xie, Y., Yang, C., Yin, J., Zabihi, A., Zakhary, P., Zani, A., Zhang, Y., Zhu, T., Zichichi, A., Zuzel, G., and Zykova, M. P.
Subjects: Physics - Instrumentation and Detectors, High Energy Physics - Experiment
Abstract: Experiments aimed at direct searches for WIMP dark matter require highly effective reduction of backgrounds and control of any residual radioactive contamination. In particular, neutrons interacting with atomic nuclei represent an important class of backgrounds due to the expected similarity of a WIMP-nucleon interaction, so that such experiments often feature a dedicated neutron detector surrounding the active target volume. In the context of the development of DarkSide-20k detector at INFN Gran Sasso National Laboratory (LNGS), several R&D projects were conceived and developed for the creation of a new hybrid material rich in both hydrogen and gadolinium nuclei to be employed as an essential element of the neutron detector. Thanks to its very high cross-section for neutron capture, gadolinium is one of the most widely used elements in neutron detectors, while the hydrogen-rich material is instrumental in efficiently moderating the neutrons. In this paper results from one of the R&Ds are presented. In this effort the new hybrid material was obtained as a poly(methyl methacrylate) (PMMA) matrix, loaded with gadolinium oxide in the form of nanoparticles. We describe its realization, including all phases of design, purification, construction, characterization, and determination of mechanical properties of the new material.
Published: 2024
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4. Connecting the Unstable Region of the Entropy to the Pattern of the Fisher's Zeros Map

Author: Rocha, J. C. S. and Costa, B. V.
Subjects: Condensed Matter - Statistical Mechanics, Physics - Computational Physics
Abstract: Phase transitions are one of the most interesting natural phenomena. For finite systems, one of the concerns in the topic is how to classify a specific transition as being of first, second, or even of a higher order, according to the Ehrenfest classification. The partition function provides all the thermodynamic information about the physical systems, and a phase transition can be identified by the complex temperature where it is equal to zero. In addition, the pattern of the zeros on the complex temperature plane can provide evidence of the order of the transition. In this manuscript, we present an analytical and simulational study connecting the microcanonical analysis of the unstable region of the entropy to the canonical partition function zeros. We show that, for the first-order transition, the zeros accumulate uniformly in a vertical line on the complex inverse temperature plane as discussed in previous works. We illustrate our calculation using the $147$ particles Lennard-Jones cluster., Comment: 19 pages, 8 figures
Published: 2023
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5. Pushing the limits of EPD zeros method

Author: Rodrigues, R. G. M., Costa, B. V., and Mól, L. A. S.
Subjects: Condensed Matter - Statistical Mechanics, Physics - Computational Physics
Abstract: The use of partition function zeros in the study of phase transition is growing in the last decade mainly due to improved numerical methods as well as novel formulations and analysis. In this paper the impact of different parameters choice for the energy probability distribution (EPD) zeros recently introduced by Costa et al is explored in search for optimal values. Our results indicate that the EPD method is very robust against parameter variations and only small deviations on estimated critical temperatures are found even for large variation of parameters, allowing to obtain accurate results with low computational cost. A proposal to circumvent potential convergence issues of the original algorithm is presented and validated for the case where it occurs.
Published: 2021
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6. Phase Diagram of Flexible Polymers with Quenched Disordered Charged Monomers

Author: Rodrigues, B. B., Rocha, J. C. S., and Costa, B. V.
Subjects: Condensed Matter - Soft Condensed Matter, 82D60
Abstract: Recent advances in Generalized Ensemble simulations and microcanonical analysis allowed the investigation of structural transitions in polymer models over a broad range of local bending and torsion strengths. It is reasonable to argue that electrostatic interactions play a significant role in stabilizing and mediating structural transitions in polymers. We propose a bead-spring polymer model with randomly distributed charged monomers interacting via a screened Coulomb potential. By combining the Replica Exchange Wang-Landau (REWL) method with energy-dependent monomer updates, we constructed the hyperphase diagram as a function of temperature ($T$) and charged monomer concentration ($\eta$). The coil-globule and globular-solid transitions are respectively second and first order for the entire concentration range. However, above a concentration threshold of $\eta=80\%$, electrostatic repulsion hinders the formation of solid and liquid globules, and the interplay between enthalpic and entropic interactions leads to the formation of liquid pearl-necklace ad solid helical structures. The probability distribution, $P(E,T)$, indicates that at high $\eta$, the pearl-necklace liquid phase freezes into a stable solid helix-like structure with a free energy barrier higher than the freezing globule transition at low $\eta$., Comment: 10 pages, 8 figures
Published: 2021
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7. Correlations in a polymeric structure immersed in a magnetic solution

Author: Costa, B. V.
Subjects: Condensed Matter - Soft Condensed Matter
Abstract: Polymers are among the most important materials in the modern society being found almost in every activity of our daily life. Understanding their chemical and physical properties lead to improvements of their usage. The correlation functions are one of most important quantities to understand a physical system. The characteristic way it behaves describe how the system fluctuates, and much of the progress achieved to understand complex systems has been due to their study. Of particular interest in polymer science are the space correlations which describe its mechanical behavior. In this work I study the stiffness of a polymer immersed in a magnetic medium and trapped in an optical tweezers. Using Monte Carlo simulations the correlation function along the chain and the force in the tweezers are obtained as a function of temperature and density of magnetic particles. The results show that the correlation decay has two regimes: an initial very fast decay of order the monomer-monomer spacing and a power law in the long distance regime. The power law exponent has a minimum at a temperature $T_{min}$ for any non zero density of magnetic particles indicating that the system is more correlated in this region. Using a formula for the persistence length derived from the WLC theory one observed that it has a maximum at the same temperature. These results suggest that the correlations in the system may be a combination of exponential and power law., Comment: Magnetism, Polymers
Published: 2021

8. The fully frustrated XY model revisited: A new universality class

Author: Lima, A. B. and Costa, B. V.
Subjects: Condensed Matter - Statistical Mechanics
Abstract: The two-dimensional ($2d$) fully frustrated Planar Rotator model on a square lattice has been the subject of a long controversy due to the simultaneous $Z_2$ and $O(2)$ symmetry existing in the model. The $O(2)$ symmetry being responsible for the Berezinskii - Kosterlitz - Thouless transition ($BKT$) while the $Z_2$ drives an Ising-like transition. There are arguments supporting two possible scenarios, one advocating that the loss of $Ising$ and $BKT$ order take place at the same temperature $T_{t}$ and the other that the $Z_2$ transition occurs at a higher temperature than the $BKT$ one. In the first case an immediate consequence is that this model is in a new universality class. Most of the studies take hand of some order parameter like the stiffness, Binder's cumulant or magnetization to obtain the transition temperature. Considering that the transition temperatures are obtained, in general, as an average over the estimates taken about several of those quantities, it is difficult to decide if they are describing the same or slightly separate transitions. In this paper we describe an iterative method based on the knowledge of the complex zeros of the energy probability distribution to study the critical behavior of the system. The method is general with advantages over most conventional techniques since it does not need to identify any order parameter \emph{a priori}. The critical temperature and exponents can be obtained with good precision. We apply the method to study the Fully Frustrated Planar Rotator ($PR$) and the Anisotropic Heisenberg ($XY$) models in two dimensions. We show that both models are in a new universality class with $T_{PR}=0.45286(32)$ and $T_{XY}=0.36916(16)$ and the transition exponent $\nu=0.824(30)$ ($\frac{1}{\nu}=1.22(4)$).
Published: 2018
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9. On the use of the energy probability distribution zeros in the study of phase transitions

Author: Mól, L A S, Rodrigues, R G M, Stancioli, R A, Rocha, J C S, and Costa, B V
Subjects: Condensed Matter - Statistical Mechanics, Physics - Computational Physics
Abstract: This contribution is devoted to cover some technical aspects related to the use of the recently proposed energy probability distribution zeros in the study of phase transitions. This method is based on the partial knowledge of the partition function zeros and has been shown to be extremely efficient to precisely locate phase transition temperatures. It is based on an iterative method in such a way that the transition temperature can be approached at will. The iterative method will be detailed and some convergence issues that has been observed in its application to the 2D Ising model and to an artificial spin ice model will be shown, together with ways to circumvent them., Comment: 11 pages, 8 figures, proceeding of the IX BMSP
Published: 2017

10. Contributions of the Cherenkov Telescope Array (CTA) to the 6th International Symposium on High-Energy Gamma-Ray Astronomy (Gamma 2016)

Author: Consortium, The CTA, Abchiche, A., Abeysekara, U., Abril, Ó., Acero, F., Acharya, B. S., Adams, C., Agnetta, G., Aharonian, F., Akhperjanian, A., Albert, A., Alcubierre, M., Alfaro, J., Alfaro, R., Allafort, A. J., Aloisio, R., Amans, J. -P., Amato, E., Ambrogi, L., Ambrosi, G., Ambrosio, M., Anderson, J., Anduze, M., Angüner, E. O., Antolini, E., Antonelli, L. A., Antonucci, M., Antonuccio, V., Antoranz, P., Aramo, C., Aravantinos, A., Araya, M., Arcaro, C., Arezki, B., Argan, A., Armstrong, T., Arqueros, F., Arrabito, L., Arrieta, M., Asano, K., Ashley, M., Aubert, P., Singh, C. B., Babic, A., Backes, M., Bais, A., Bajtlik, S., Balazs, C., Balbo, M., Balis, D., Balkowski, C., Ballester, O., Ballet, J., Balzer, A., Bamba, A., Bandiera, R., Barber, A., Barbier, C., Barcelo, M., Barkov, M., Barnacka, A., de Almeida, U. Barres, Barrio, J. A., Basso, S., Bastieri, D., Bauer, C., Becciani, U., Becherini, Y., Tjus, J. Becker, Beckmann, V., Bednarek, W., Benbow, W., Ventura, D. Benedico, Berdugo, J., Berge, D., Bernardini, E., Bernardini, M. G., Bernhard, S., Bernlöhr, K., Bertucci, B., Besel, M. -A., Beshley, V., Bhatt, N., Bhattacharjee, P., Bhattacharyya, W., Bhattachryya, S., Biasuzzi, B., Bicknell, G., Bigongiari, C., Biland, A., Bilinsky, A., Bilnik, W., Biondo, B., Bird, R., Bird, T., Bissaldi, E., Bitossi, M., Blanch, O., Blasi, P., Blazek, J., Bockermann, C., Boehm, C., Bogacz, L., Bogdan, M., Bohacova, M., Boisson, C., Boix, J., Bolmont, J., Bonanno, G., Bonardi, A., Bonavolontà, C., Bonifacio, P., Bonnarel, F., Bonnoli, G., Borkowski, J., Bose, R., Bosnjak, Z., Böttcher, M., Bousquet, J. -J., Boutonnet, C., Bouyjou, F., Bowman, L., Braiding, C., Brantseg, T., Brau-Nogué, S., Bregeon, J., Briggs, M., Brigida, M., Bringmann, T., Brisken, W., Bristow, D., Britto, R., Brocato, E., Bron, S., Brook, P., Brooks, W., Brown, A. M., Brügge, K., Brun, F., Brun, P., Brunetti, G., Brunetti, L., Bruno, P., Buanes, T., Bucciantini, N., Buchholtz, G., Buckley, J., Bugaev, V., Bühler, R., Bulgarelli, A., Bulik, T., Burton, M., Burtovoi, A., Busetto, G., Buson, S., Buss, J., Byrum, K., Cadoux, F., Tovar, J. Calvo, Cameron, R., Canelli, F., Canestrari, R., Capalbi, M., Capasso, M., Capobianco, G., Caproni, A., Caraveo, P., Cardenzana, J., Cardillo, M., Carius, S., Carlile, C., Carosi, A., Carosi, R., Carquín, E., Carr, J., Carroll, M., Carter, J., Carton, P. -H., Casandjian, J. -M., Casanova, S., Cascone, E., Casiraghi, M., Castellina, A., Mora, J. Castroviejo, Catalani, F., Catalano, O., Catalanotti, S., Cauz, D., Cavazzani, S., Cerchiara, P., Chabanne, E., Chadwick, P., Chaleil, T., Champion, C., Chatterjee, A., Chaty, S., Chaves, R., Chen, A., Chen, X., Cheng, K., Chernyakova, M., Chiappetti, L., Chikawa, M., Chinn, D., Chitnis, V. R., Cho, N., Christov, A., Chudoba, J., Cieślar, M., Ciocci, M. A., Clay, R., Colafrancesco, S., Colin, P., Colley, J. -M., Colombo, E., Colome, J., Colonges, S., Conforti, V., Connaughton, V., Connell, S., Conrad, J., Contreras, J. L., Coppi, P., Corbel, S., Coridian, J., Cornat, R., Corona, P., Corti, D., Cortina, J., Cossio, L., Costa, A., Costantini, H., Cotter, G., Courty, B., Covino, S., Covone, G., Crimi, G., Criswell, S. J., Crocker, R., Croston, J., Cuadra, J., Cumani, P., Cusumano, G., Da Vela, P., Dale, Ø., D'Ammando, F., Dang, D., Dang, V. T., Dangeon, L., Daniel, M., Davids, I., Dawson, B., Dazzi, F., Costa, B. de Aguiar, De Angelis, A., Cardoso, R. F. de Araujo, De Caprio, V., Anjos, R. de Cássia dos, De Cesare, G., De Franco, A., De Frondat, F., Pino, E. M. de Gouveia Dal, de la Calle, I., De Lisio, C., Lopez, R. de los Reyes, De Lotto, B., De Luca, A., Neto, J. R. 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M., Greenshaw, T., Grenier, I., Griffiths, S., Grillo, A., Grondin, M. -H., Grube, J., Grudzinska, M., Grygorczuk, J., Guarino, V., Guberman, D., Gunji, S., Gyuk, G., Hadasch, D., Hagedorn, A., Hagge, L., Hahn, J., Hakobyan, H., Hara, S., Hardcastle, M. J., Hassan, T., Hatanaka, K., Haubold, T., Haupt, A., Hayakawa, T., Hayashida, M., Heller, M., Heller, R., Helo, J. C., Henault, F., Henri, G., Hermann, G., Hermel, R., Llorente, J. Herrera, Herrero, A., Hervet, O., Hidaka, N., Hinton, J., Hirai, W., Hirotani, K., Hnatyk, B., Hoang, J., Hoffmann, D., Hofmann, W., Holch, T., Holder, J., Hooper, S., Horan, D., Hörandel, J., Hörbe, M., Horns, D., Horvath, P., Hose, J., Houles, J., Hovatta, T., Hrabovsky, M., Hrupec, D., Huet, J. -M., Huetten, M., Hughes, G., Hui, D., Humensky, T. B., Hussein, M., Iacovacci, M., Ibarra, A., Ikeno, Y., Illa, J. 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B., Kihm, T., Kimeswenger, S., Kisaka, S., Kishida, S., Kissmann, R., Klepser, S., Kluźniak, W., Knapen, J., Knapp, J., Knödlseder, J., Koch, B., Köck, F., Kocot, J., Kohri, K., Kokkotas, K., Kolitzus, D., Komin, N., Kominis, I., Kong, A., Konno, Y., Kosack, K., Koss, G., Kossatz, M., Kowal, G., Koyama, S., Kozioł, J., Kraus, M., Krause, J., Krause, M., Krawzcynski, H., Krennrich, F., Kretzschmann, A., Kruger, P., Kubo, H., Kudryavtsev, V., Mezek, G. Kukec, Kuklis, M., Kuroda, H., Kushida, J., La Barbera, A., La Palombara, N., La Parola, V., La Rosa, G., Laffon, H., Lahmann, R., Lakicevic, M., Lalik, K., Lamanna, G., Landriu, D., Landt, H., Lang, R. G., Lapington, J., Laporte, P., Fèvre, J. -P. Le, Flour, T. Le, Sidaner, P. Le, Lee, S. -H., Lee, W. H., Lees, J. -P., Lefaucheur, J., Leffhalm, K., Leich, H., de Oliveira, M. A. 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C., Shibata, T., Shigenaka, A., Shilon, I., Shum, E., Sidoli, L., Sidz, M., Sieiro, J., Siejkowski, H., Silk, J., Sillanpää, A., Simone, D., Simpson, H., Singh, B. B., Sinha, A., Sironi, G., Sitarek, J., Sizun, P., Sliusar, V., Smith, A., Sobczyńska, D., Sol, H., Sottile, G., Sowiński, M., Spanier, F., Spengler, G., Spiga, R., Stadler, R., Stahl, O., Stamerra, A., Stanič, S., Starling, R., Staszak, D., Stawarz, Ł., Steenkamp, R., Stefanik, S., Stegmann, C., Steiner, S., Stella, C., Stephan, M., Stergioulas, N., Sternberger, R., Sterzel, M., Stevenson, B., Stinzing, F., Stodulska, M., Stodulski, M., Stolarczyk, T., Stratta, G., Straumann, U., Stringhetti, L., Strzys, M., Stuik, R., Sulanke, K. -H., Suomijärvi, T., Supanitsky, A. D., Suric, T., Sushch, I., Sutcliffe, P., Sykes, J., Szanecki, M., Szepieniec, T., Szwarnog, P., Tacchini, A., Tachihara, K., Tagliaferri, G., Tajima, H., Takahashi, H., Takahashi, K., Takahashi, M., Takalo, L., Takami, S., Takata, J., Takeda, J., Talbot, G., Tam, T., Tanaka, M., Tanaka, S., Tanaka, T., Tanaka, Y., Tanci, C., Tanigawa, S., Tavani, M., Tavecchio, F., Tavernet, J. -P., Tayabaly, K., Taylor, A., Tejedor, L. A., Telezhinsky, I., Temme, F., Temnikov, P., Tenzer, C., Terada, Y., Terrazas, J. C., Terrier, R., Terront, D., Terzic, T., Tescaro, D., Teshima, M., Testa, V., Tezier, D., Thayer, J., Thornhill, J., Thoudam, S., Thuermann, D., Tibaldo, L., Tiengo, A., Timpanaro, M. C., Tiziani, D., Tluczykont, M., Peixoto, C. J. Todero, Tokanai, F., Tokarz, M., Toma, K., Tomastik, J., Tomono, Y., Tonachini, A., Tonev, D., Torii, K., Tornikoski, M., Torres, D. F., Torres, M., Torresi, E., Toso, G., Tosti, G., Totani, T., Tothill, N., Toussenel, F., Tovmassian, G., Toyama, T., Travnicek, P., Trichard, C., Trifoglio, M., Pujadas, I. Troyano, Trzeciak, M., Tsinganos, K., Tsujimoto, S., Tsuru, T., Uchiyama, Y., Umana, G., Umetsu, Y., Upadhya, S. S., Uslenghi, M., Vagelli, V., Vagnetti, F., Valdes-Galicia, J., Valentino, M., Vallania, P., Valore, L., van Driel, W., van Eldik, C., van Soelen, B., Vandenbroucke, J., Vanderwalt, J., Vasileiadis, G., Vassiliev, V., Vázquez, J. R., Acosta, M. L. Vázquez, Vecchi, M., Vega, A., Vegas, I., Veitch, P., Venault, P., Venema, L., Venter, C., Vercellone, S., Vergani, S., Verma, K., Verzi, V., Vettolani, G. P., Veyssiere, C., Viana, A., Viaux, N., Vicha, J., Vigorito, C., Vincent, P., Vincent, S., Vink, J., Vittorini, V., Vlahakis, N., Vlahos, L., Voelk, H., Voisin, V., Vollhardt, A., Volpicelli, A., von Brand, H., Vorobiov, S., Vovk, I., Vrastil, M., Vu, L. V., Vuillaume, T., Wagner, R., Wagner, S. J., Wakely, S. P., Walstra, T., Walter, R., Walther, T., Ward, J. E., Ward, M., Warda, K., Warren, D., Wassberg, S., Watson, J. J., Wawer, P., Wawrzaszek, R., Webb, N., Wegner, P., Weiner, O., Weinstein, A., Wells, R., Werner, F., Wetteskind, H., White, M., White, R., Więcek, M., Wierzcholska, A., Wiesand, S., Wijers, R., Wilcox, P., Wild, N., Wilhelm, A., Wilkinson, M., Will, M., Williams, D. A., Williams, J. T., Willingale, R., Wilson, N., Winde, M., Winiarski, K., Winkler, H., Winter, M., Wischnewski, R., Witt, E., Wojcik, P., Wolf, D., Wood, M., Wörnlein, A., Wu, E., Wu, T., Yadav, K. K., Yamamoto, H., Yamamoto, T., Yamane, N., Yamazaki, R., Yanagita, S., Yang, L., Yelos, D., Yoshida, A., Yoshida, M., Yoshida, T., Yoshiike, S., Yoshikoshi, T., Yu, P., Zabalza, V., Zaborov, D., Zacharias, M., Zaharijas, G., Zajczyk, A., Zampieri, L., Zandanel, F., Sanchez, R. Zanmar, Zaric, D., Zavrtanik, D., Zavrtanik, M., Zdziarski, A., Zech, A., Zechlin, H., Zhao, A., Zhdanov, V., Ziegler, A., Ziemann, J., Ziętara, K., Zink, A., Ziółkowski, J., Zitelli, V., Zoli, A., Zorn, J., and Żychowski, P.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: List of contributions from the Cherenkov Telescope Array (CTA) Consortium presented at the 6th International Symposium on High-Energy Gamma-Ray Astronomy (Gamma 2016), July 11-15, 2016, in Heidelberg, Germany., Comment: Index of CTA conference proceedings for the Gamma 2016, Heidelberg, Germany
Published: 2016

11. Energy Probability Distribution Zeros: A Route to Study Phase Transitions

Author: Costa, B. V., Mól, L. A. S., and Rocha, J. C. S.
Subjects: Condensed Matter - Statistical Mechanics
Abstract: In the study of phase transitions a very few models are accessible to exact solution. In the most cases analytical simplifications have to be done or some numerical technique has to be used to get insight about their critical properties. Numerically, the most common approaches are those based in Monte Carlo simulations together finite size scaling analysis. The use of Monte Carlo techniques requires the estimate of quantities like the specific heat or susceptibilities in a wide range of temperature or the construction of the density of states in large intervals of energy. Although many of these techniques are well developed they may be very time consuming when the system size becomes large enough. It should be suitable to have a method that could surpass those difficulties. In this work we present an iterative method to study the critical behavior of a system based on the partial knowledge of the complex Fisher zeros set of the partition function. The method is general with advantages over most conventional techniques since it does not need to identify any order parameter \emph{a priori}. The critical temperature and exponents can be obtained with great precision even in the most unamenable cases like the two dimensional $XY$ model. To test the method and to show how it works we applied it to some selected models where the transitions are well known: The 2D Ising, Potts and XY models and to a homopolymer system. Our choice cover systems with first order, continuous and Berezinskii-Kosterlitz-Thouless transitions as well as the homopolymer that has two pseudo-transitions. The strategy can easily be adapted to any model, classical or quantum, once we are able to build the corresponding energy probability distribution., Comment: 9 pages, 11 figures, 5 tables
Published: 2016
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12. CTA Contributions to the 34th International Cosmic Ray Conference (ICRC2015)

Author: Consortium, The CTA, Abchiche, A., Abeysekara, U., Abril, Ó., Acero, F., Acharya, B. S., Actis, M., Agnetta, G., Aguilar, J. A., Aharonian, F., Akhperjanian, A., Albert, A., Alcubierre, M., Alfaro, R., Aliu, E., Allafort, A. J., Allan, D., Allekotte, I., Aloisio, R., Amans, J. -P., Amato, E., Ambrogi, L., Ambrosi, G., Ambrosio, M., Anderson, J., Anduze, M., Angüner, E. O., Antolini, E., Antonelli, L. A., Antonucci, M., Antonuccio, V., Antoranz, P., Aramo, C., Aravantinos, A., Argan, A., Armstrong, T., Arnaldi, H., Arnold, L., Arrabito, L., Arrieta, M., Asano, K., Asorey, H. G., Aune, T., Singh, C. B., Babic, A., Backes, M., Bais, A., Bajtlik, S., Balazs, C., Balbo, M., Balis, D., Balkowski, C., Ballester, O., Ballet, J., Balzer, A., Bamba, A., Bandiera, R., Barber, A., Barbier, C., Barceló, M., Barnacka, A., de Almeida, U. Barres, Barrio, J. A., Basso, S., Bastieri, D., Bauer, C., Baushev, A., Becciani, U., Becherini, Y., Tjus, J. Becker, Beckmann, V., Bednarek, W., Benbow, W., Ventura, D. Benedico, Berdugo, J., Berge, D., Bernardini, E., Bernhard, S., Bernlöhr, K., Bertucci, B., Besel, M. -A., Bhatt, N., Bhattacharjee, P., Bhattachryya, S., Biasuzzi, B., Bicknell, G., Bigongiari, C., Biland, A., Billotta, S., Bilnik, W., Biondo, B., Bird, T., Birsin, E., Bissaldi, E., Biteau, J., Bitossi, M., Bigas, O. Blanch, Blasi, P., Boehm, C., Bogacz, L., Bogdan, M., Bohacova, M., Boisson, C., Gargallo, J. Boix, Bolmont, J., Bonanno, G., Bonardi, A., Bonifacio, P., Bonnoli, G., Borkowski, J., Bose, R., Bosnjak, Z., Bottani, A., Böttcher, M., Bousquet, J. -J., Boutonnet, C., Bouyjou, F., Braiding, C., Brandt, L., Brau-Nogué, S., Bregeon, J., Bretz, T., Briggs, M., Brigida, M., Bringmann, T., Brisken, W., Brocato, E., Brook, P., Brown, A. M., Brun, P., Brunetti, G., Brunetti, L., Bruno, P., Bryan, M., Buanes, T., Bucciantini, N., Buchholtz, G., Buckley, J., Bugaev, V., Bühler, R., Bulgarelli, A., Bulik, T., Burton, M., Burtovoi, A., Busetto, G., Buson, S., Buss, J., Byrum, K., Cameron, R., Camprecios, J., Canelli, F., Canestrari, R., Cantu, S., Capalbi, M., Capasso, M., Capobianco, G., Caraveo, P., Cardenzana, J., Carius, S., Carlile, C., Carmona, E., Carosi, A., Carosi, R., Carr, J., Carroll, M., Carter, J., Carton, P. -H., Caruso, R., Casandjian, J. -M., Casanova, S., Cascone, E., Casiraghi, M., Castellina, A., Catalano, O., Catalanotti, S., Cavazzani, S., Cazaux, S., Cefalà, M., Cerchiara, P., Cereda, M., Cerruti, M., Chabanne, E., Chadwick, P., Champion, C., Chaty, S., Chaves, R., Cheimets, P., Chen, A., Chen, X., Chernyakova, M., Chiappetti, L., Chikawa, M., Chinn, D., Chitnis, V. R., Cho, N., Christov, A., Chudoba, J., Cieślar, M., Cillis, A., Ciocci, M. A., Clay, R., Cohen-Tanugi, J., Colafrancesco, S., Colin, P., Colombo, E., Colome, J., Colonges, S., Compin, M., Conforti, V., Connaughton, V., Connell, S., Conrad, J., Contreras, J. L., Coppi, P., Corbel, S., Coridian, J., Corona, P., Corti, D., Cortina, J., Cossio, L., Costa, A., Costantini, H., Cotter, G., Courty, B., Covino, S., Covone, G., Crimi, G., Criswell, S. J., Crocker, R., Croston, J., Cusumano, G., Da Vela, P., Dale, Ø., D'Ammando, F., Dang, D., Daniel, M., Davids, I., Dawson, B., Dazzi, F., Costa, B. de Aguiar, De Angelis, A., Cardoso, R. F. de Araujo, De Caprio, V., De Cesare, G., De Franco, A., De Frondat, F., Pino, E. M. de Gouveia Dal, de la Calle, I., De La Vega, G. A., Lopez, R. de los Reyes, De Lotto, B., De Luca, A., Neto, J. R. T. de Mello, de Naurois, M., Wilhelmi, E. de Oña, De Palma, F., de Souza, V., Decock, G., Deil, C., Del Santo, M., Delagnes, E., Deleglise, G., Delgado, C., della Volpe, D., Deloye, P., Depaola, G., Detournay, M., Dettlaff, A., Di Girolamo, T., Di Giulio, C., Di Paola, A., Di Pierro, F., Di Sciascio, G., Díaz, C., Dick, J., Dickinson, H., Diebold, S., Diez, V., Digel, S., Dipold, J., Disset, G., Distefano, A., Djannati-Ataï, A., Doert, M., Dohmke, M., Domainko, W., Dominik, N., Prester, D. Dominis, Donat, A., Donnarumma, I., Dorner, D., Doro, M., Dournaux, J. -L., Doyle, K., Drake, G., Dravins, D., Drury, L., Dubus, G., Dumas, D., Dumm, J., Durand, D., D'Urso, D., Dwarkadas, V., Dyks, J., Dyrda, M., Ebr, J., Echaniz, J. C., Edy, E., Egberts, K., Eger, P., Einecke, S., Eisch, J., Eisenkolb, F., Eleftheriadis, C., Elsässer, D., Emmanoulopoulos, D., Engelbrecht, C., Engelhaupt, D., Ernenwein, J. -P., Errando, M., Eschbach, S., Etchegoyen, A., Evans, P., Fairbairn, M., Falcone, A., Fantinel, D., Farakos, K., Farnier, C., Farrell, E., Farrell, S., Fasola, G., Fegan, S., Feinstein, F., Ferenc, D., Fernandez, A., Fernandez-Alonso, M., Ferreira, O., Fesquet, M., Fetfatzis, P., Fiasson, A., Filipčič, A., Filipovic, M., Fink, D., Finley, C., Finley, J. P., Finoguenov, A., Fioretti, V., Fiorini, M., Curcoll, R. Firpo, Fleischhack, H., Flores, H., Florin, D., Föhr, C., Fokitis, E., Font, L., Fontaine, G., Fontes, B., Forest, F., Fornasa, M., Förster, A., Fortin, P., Fortson, L., Fouque, N., Franckowiak, A., Franco, F. J., Frankowski, A., Frega, N., Albuquerque, I. Freire Mota, Coromina, L. 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S., Gotz, D., Grabarczyk, T., Graciani, R., Grandi, P., Grañena, F., Granot, J., Grasseau, G., Gredig, R., Green, A. J., Green, A. M., Greenshaw, T., Grenier, I., Grillo, A., Grondin, M. -H., Grube, J., Grudzinska, M., Grygorczuk, J., Guarino, V., Guberman, D., Gunji, S., Gyuk, G., Hadasch, D., Hagedorn, A., Hahn, J., Hakansson, N., Heras, N. Hamer, Hanabata, Y., Hara, S., Hardcastle, M. J., Harris, J., Hassan, T., Hatanaka, K., Haubold, T., Haupt, A., Hayakawa, T., Hayashida, M., Heller, M., Heller, R., Henault, F., Henri, G., Hermann, G., Hermel, R., Llorente, J. Herrera, Herrero, A., Hervet, O., Hidaka, N., Hinton, J., Hirai, W., Hirotani, K., Hoard, D., Hoffmann, D., Hofmann, W., Hofverberg, P., Holch, T., Holder, J., Hooper, S., Horan, D., Hörandel, J. R., Hormigos, S., Horns, D., Hose, J., Houles, J., Hovatta, T., Hrabovsky, M., Hrupec, D., Huet, J. -M., Hütten, M., Humensky, T. B., Huovelin, J., Huppert, J. -F., Iacovacci, M., Ibarra, A., Idźkowski, B., Ikawa, D., Illa, J. M., Impiombato, D., Incorvaia, S., Inome, Y., Inoue, S., Inoue, T., Inoue, Y., Iocco, F., Ioka, K., Iori, M., Ishio, K., Israel, G. L., Jablonski, C., Jacholkowska, A., Jacquemier, J., Jamrozy, M., Janecek, P., Janiak, M., Jankowsky, F., Jean, P., Jeanney, C., Jegouzo, I., Jenke, P., Jimenez, J. J., Jingo, M., Jocou, L., Jogler, T., Johnson, C. A., Journet, L., Juffroy, C., Jung, I., Kaaret, P. E., Kagaya, M., Kakuwa, J., Kalekin, O., Kalkuhl, C., Kankanyan, R., Karastergiou, A., Kärcher, K., Karczewski, M., Karkar, S., Karn, P., Kasperek, J., Katagiri, H., Kataoka, J., Katarzyński, K., Katz, U., Kaufmann, S., Kawanaka, N., Kawashima, T., Kazanas, D., Kelley-Hoskins, N., Kellner-Leidel, B., Kendziorra, E., Kersten, J., Khélifi, B., Kieda, D. 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Leigui, Lelas, D., Lemière, A., Lemoine-Goumard, M., Lenain, J. -P., Leonard, R., Leoni, R., Lessio, L., Leto, G., Leveque, A., Lieunard, B., Limon, M., Lindemann, R., Lindfors, E., Liolios, A., Lipniacka, A., Lockart, H., Lohse, T., Loiseau, D., Łokas, E., Lombardi, S., Longo, F., Longo, G., Lopatin, A., Lopez, M., López-Coto, R., López-Oramas, A., Loreggia, D., Louge, T., Louis, F., Lu, C. -C., Lucarelli, F., Lucchesi, D., Lüdecke, H., Luque-Escamilla, P. L., Luz, O., Lyard, E., Maccarone, M. C., Maccarone, T. J., Mach, E., Madejski, G. M., Madonna, A., Mahabir, M., Maier, G., Majumdar, P., Makariev, M., Malaguti, G., Malaspina, G., Mallot, A. K., Maltezos, S., Mancilla, A., Mandat, D., Maneva, G., Manigot, P., Mankushiyil, N., Mannheim, K., Maragos, N., Marano, D., Marchegiani, P., Marcomini, J. A., Marcowith, A., Mariotti, M., Marisaldi, M., Markoff, S., Marszałek, A., Martens, C., Martí, J., Martin, J. -M., Martin, P., Martínez, G., Martínez, M., Martínez, O., Marx, R., Massimino, P., Mastichiadis, A., Mastroianni, S., Mastropietro, M., Masuda, S., Matsumoto, H., Matsuoka, S., Mattiazzo, S., Maurin, G., Maxted, N., Maya, J., Mayer, M., Mazin, D., Mazureau, E., Mazziotta, M. N., Comb, L. Mc, McCann, A., McCubbin, N., McHardy, I., McKay, R., McKinney, K., Meagher, K., Medina, C., Mehrez, F., Melioli, C., Melkumyan, D., Melo, D., Melse, T., Mereghetti, S., Mertsch, P., Meyer, M., Meyrelles jr, J. L., Miccichè, A., Michałowski, J., Micolon, P., Mientjes, P., Mignot, S., Mihailidis, A., Mineo, T., Minuti, M., Mirabal, N., Mirabel, F., Miranda, J. M., Mirzoyan, R., Mistò, A., Mitchell, A., Mizuno, T., Moderski, R., Mognet, I., Mohammed, M., Moharana, R., Molinari, E., Monmarthe, E., Monnier, G., Montaruli, T., Monte, C., Monteiro, I., Moore, P., Olaizola, A. Moralejo, Morello, C., Moretti, E., Mori, K., Morlino, G., Morselli, A., Mottez, F., Moudden, Y., Moulin, E., Mrusek, I., Mueller, S., Mukherjee, R., Munar-Adrover, P., Mundell, C., Muraishi, H., Murase, K., Muronga, A., Murphy, A., Nagataki, S., Nagayoshi, T., Nagesh, B. K., Naito, T., Nakajima, D., Nakamori, T., Nakayama, K., Naumann, D., Nayman, P., Nellen, L., Nemmen, R., Neronov, A., Neustroev, V., Neyroud, N., Nguyen, T., Nicastro, L., Nicolau-Kukliński, J., Niederwanger, F., Niedźwiecki, A., Niemiec, J., Nieto, D., Nievas, M., Nikolaidis, A., Nishijima, K., Nishikawa, K. -I., Noda, K., Nogues, L., Nolan, S., Northrop, R., Nosek, D., Nozka, L., Nunio, F., Oakes, L., O'Brien, P., Occhipinti, G., de Bhroithe, A. O'Faolain, Ogino, M., Ohira, Y., Ohishi, M., Ohm, S., Ohoka, H., Okumura, A., Olive, J. -F., Olszowski, D., Ong, R. A., Ono, S., Orienti, M., Orito, R., Orlati, A., Osborne, J., Ostrowski, M., Otero, L. A., Ottaway, D., Otte, N., Oya, I., Ozieblo, A., Padovani, M., Pagano, I., Paiano, S., Paizis, A., Palacio, J., Palatka, M., Pallotta, J., Panagiotidis, K., Panazol, J. -L., Paneque, D., Panter, M., Panzera, M. R., Paoletti, R., Paolillo, M., Papayannis, A., Papyan, G., Paravac, A., Paredes, J. M., Pareschi, G., Park, N., Parsons, D., Paśko, P., Pavy, S., Arribas, M. Paz, Pech, M., Peck, A., Pedaletti, G., Peet, S., Pelassa, V., Pelat, D., Peres, C., Perez, M. d. C., Perri, L., Persic, M., Petrashyk, A., Petrucci, P. -O., Peyaud, B., Pfeifer, M., Pfeiffer, G., Piano, G., Pichel, A., Pieloth, D., Pierbattista, M., Pierre, E., de Pinho, F. Pinto, García, C. Pio, Piret, Y., Pita, S., Planes, A., Platino, M., Platos, Ł., Platzer, R., Podkladkin, S., Pogosyan, L., Pohl, M., Poinsignon, P., Ponz, J. D., Porcelli, A., Potter, W., Poulios, S., Poutanen, J., Prandini, E., Prast, J., Preece, R., Profeti, F., Prokhorov, D., Prokoph, H., Prouza, M., Proyetti, M., Pruchniewicz, R., Pueschel, E., Pühlhofer, G., Puljak, I., Punch, M., Pyzioł, R., Queiroz, F., Quel, E. J., Quinn, J., Quirrenbach, A., Racero, E., Räck, T., Rafalski, J., Rafighi, I., Rainò, S., Rajda, P. J., Rameez, M., Rando, R., Rannot, R. C., Rataj, M., Rateau, S., Ravel, T., Ravignani, D., Razzaque, S., Reardon, P., Reimann, O., Reimer, A., Reimer, O., Reitberger, K., Renaud, M., Renner, S., Reposeur, T., Rettig, R., Reville, B., Rhode, W., Ribeiro, D., Ribó, M., Richards, G., Richer, M. G., Rico, J., Ridky, J., Rieger, F., Ringegni, P., Ristori, P. R., Rivière, A., Rivoire, S., Roache, E., Rodeghiero, G., Rodriguez, J., Fernandez, G. Rodriguez, Vázquez, J. J. Rodríguez, Rogers, T., Rojas, G., Romano, P., Rodriguez, M. P. Romay, Romeo, G., Romero, G. E., Roncadelli, M., Rose, J., Rosen, S., Lees, S. Rosier, Ross, D., Rossiter, P., Rouaix, G., Rousselle, J., Rovero, A. C., Rowell, G., Roy, F., Royer, S., Różańska, A., Rudak, B., Rugliancich, A., Rulten, C., Rupiński, M., Russo, F., Rutkowski, K., Saavedra, O., Sabatini, S., Sacco, B., Saemann, E. O., Saggion, A., Saha, L., Sahakian, V., Saito, K., Saito, T., Sakaki, N., Salega, M., Salek, D., Salgado, J., Salini, A., Sanchez, D., Sanchez, F., Sanchez-Conde, M., Sandaker, H., Sandoval, A., Sangiorgi, P., Sanguillon, M., Sano, H., Santander, M., Santangelo, A., Santos, E. M., Santos-Lima, R., Sanuy, A., Sapozhnikov, L., Sarkar, S., Satalecka, K., Savalle, R., Sawada, M., Sayède, F., Schafer, J., Schanne, S., Schanz, T., Schioppa, E. J., Schlenstedt, S., Schlickeiser, R., Schmidt, T., Schmoll, J., Schneider, M., Schovanek, P., Schubert, A., Schultz, C., Schultze, J., Schulz, A., Schulz, S., Schure, K., Schussler, F., Schwab, T., Schwanke, U., Schwarz, J., Schweizer, T., Schwemmer, S., Schwendicke, U., Schwerdt, C., Segreto, A., Seiradakis, J. -H., Sembroski, G. H., Semikoz, D., Serre, N., Servillat, M., Seweryn, K., Shafi, N., Sharma, M., Shayduk, M., Shellard, R. C., Shibata, T., Pandeni, K. Shiningayamwe, Shukla, A., Shum, E., Sidoli, L., Sidz, M., Sieiro, J., Siejkowski, H., Silk, J., Sillanpää, A., Simone, D., Singh, B. B., Sinha, A., Sironi, G., Sitarek, J., Sizun, P., Slyusar, V., Smith, A., Smith, J., Sobczyńska, D., Sol, H., Sottile, G., Sowiński, M., Spanier, F., Spengler, G., Spiga, D., Stadler, R., Stahl, O., Stamatescu, V., Stamerra, A., Stanič, S., Starling, R., Stawarz, Ł., Steenkamp, R., Stefanik, S., Stegmann, C., Steiner, S., Stella, C., Stergioulas, N., Sternberger, R., Sterzel, M., Stevenson, B., Stinzing, F., Stodulska, M., Stodulski, M., Stolarczyk, T., Straumann, U., Strazzeri, E., Stringhetti, L., Strzys, M., Stuik, R., Sulanke, K. -H., Supanitsky, A. D., Suric, T., Sushch, I., Sutcliffe, P., Sykes, J., Szanecki, M., Szepieniec, T., Szwarnog, P., Tacchini, A., Tachihara, K., Tagliaferri, G., Tajima, H., Takahashi, H., Takahashi, K., Takahashi, M., Takalo, L., Takami, H., Talbot, G., Tammi, J., Tanaka, M., Tanaka, S., Tanaka, T., Tanaka, Y., Tanci, C., Tarantino, E., Tavani, M., Tavecchio, F., Tavernet, J. -P., Tayabaly, K., Tejedor, L. A., Telezhinsky, I., Temme, F., Temnikov, P., Tenzer, C., Terada, Y., Terrier, R., Tescaro, D., Teshima, M., Testa, V., Tezier, D., Thayer, J., Thomas, V., Thornhill, J., Thuermann, D., Tibaldo, L., Tibolla, O., Tiengo, A., Tijsseling, G., Timpanaro, M. C., Tluczykont, M., Peixoto, C. J. Todero, Tokanai, F., Tokarz, M., Toma, K., Tomastik, J., Tomono, Y., Tonachini, A., Tonev, D., Torii, K., Tornikoski, M., Torres, D. F., Torres, M., Torresi, E., Toscano, S., Toso, G., Tosti, G., Totani, T., Tothill, N., Toussenel, F., Tovmassian, G., Townsley, C., Toyama, T., Travnicek, P., Trifoglio, M., Pujadas, I. Troyano, Trzeciak, M., Tsinganos, K., Tsubone, Y., Tsuchiya, Y., Tsujimoto, S., Tsuru, T., Uchiyama, Y., Umana, G., Umetsu, Y., Underwood, C., Upadhya, S. S., Uslenghi, M., Vagnetti, F., Valdes-Galicia, J., Vallania, P., Vallejo, G., Valore, L., van Driel, W., van Eldik, C., van Soelen, B., Vandenbroucke, J., Vanderwalt, J., Vasileiadis, G., Vassiliev, V., Acosta, M. L. Vázquez, Vecchi, M., Vegas, I., Veitch, P., Venema, L., Venter, C., Vercellone, S., Vergani, S., Verma, K., Verzi, V., Vettolani, G. P., Viana, A., Vicha, J., Videla, M., Vigorito, C., Vincent, P., Vincent, S., Vink, J., Vittorini, V., Vlahakis, N., Vlahos, L., Voelk, H., Vogler, P., Voisin, V., Vollhardt, A., Volpicelli, A., Vorobiov, S., Vovk, I., Vu, L. V., Wagner, R., Wagner, R. M., Wagner, R. G., Wagner, S. J., Wakely, S. P., Walter, R., Walther, T., Ward, J. E., Ward, M., Warda, K., Warwick, R., Wassberg, S., Watson, J., Wawer, P., Wawrzaszek, R., Webb, N., Wegner, P., Weinstein, A., Weitzel, Q., Wells, R., Werner, F., Werner, M., Wetteskind, H., White, M., White, R., Więcek, M., Wierzcholska, A., Wiesand, S., Wijers, R., Wild, N., Wilhelm, A., Wilkinson, M., Will, M., Williams, D. A., Williams, J. T., Willingale, R., Winde, M., Winiarski, K., Winkler, H., Wischnewski, R., Wojcik, P., Wolf, D., Wood, M., Wörnlein, A., Wu, E., Wu, T., Yadav, K. K., Yamamoto, H., Yamamoto, T., Yamazaki, R., Yanagita, S., Yang, L., Yebras, J. M., Yelos, D., Yeung, W., Yoshida, A., Yoshida, T., Yoshiike, S., Yoshikoshi, T., Yu, P., Zabalza, V., Zacharias, M., Zaharijas, G., Zajczyk, A., Zampieri, L., Zandanel, F., Zanin, R., Sanchez, R. Zanmar, Zavrtanik, D., Zavrtanik, M., Zdziarski, A., Zech, A., Zechlin, H., Zhao, A., Ziegler, A., Ziemann, J., Ziętara, K., Ziółkowski, J., Zitelli, V., Zoli, A., Zurbach, C., and Żychowski, P.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: List of contributions from the CTA Consortium presented at the 34th International Cosmic Ray Conference, 30 July - 6 August 2015, The Hague, The Netherlands., Comment: Index of CTA conference proceedings at the ICRC2015, The Hague (The Netherlands). v1: placeholder with no arXiv links yet, to be replaced once individual contributions have been all submitted; v2: final with arXiv links to all CTA contributions and full author list
Published: 2015

13. Using zeros of the canonical partition function map to detect signatures of a Berezinskii-Kosterlitz-Thouless transition

Author: Rocha, J. C. S., Mól, L. A. S., and Costa, B. V.
Subjects: Condensed Matter - Statistical Mechanics
Abstract: Using the two dimensional $XY-(S(O(3))$ model as a test case, we show that analysis of the Fisher zeros of the canonical partition function can provide signatures of a transition in the Berezinskii-Kosterlitz-Thouless ($BKT$) universality class. Studying the internal border of zeros in the complex temperature plane, we found a scenario in complete agreement with theoretical expectations which allow one to uniquely classify a phase transition as in the $BKT$ class of universality. We obtain $T_{BKT}$ in excellent accordance with previous results. A careful analysis of the behavior of the zeros for both regions $\mathfrak{Re}(T) \leq T_{BKT}$ and $\mathfrak{Re}(T) > T_{BKT}$ in the thermodynamic limit show that $\mathfrak{Im}(T)$ goes to zero in the former case and is finite in the last one.
Published: 2015
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14. Debye temperature of nanocrystalline Fe-Cr alloys obtained by mechanical alloying

Author: Dubiel, S. M., Costa, B. F. O., Cieslak, J., and Batista, A. C.
Subjects: Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science
Abstract: A series on nanocrystalline Fe100-xCrx alloys prepared by mechanical alloying was investigated with X-ray diffraction (XRD), scanning electron microscopy (SEM) and M\"ossbauer spectroscopy (MS) techniques. XRD and SEM were used to structurally characterize the samples whereas MS permitted phase analysis as well as determination of the Debye temperature, Theta_D. Concerning the latter, an enhancement relative to bulk Theta_D-values was revealed in the range of ca. 40 < x <50. In a sample of Fe55.5Cr44.5 two phases were detected viz. (1) crystalline and magnetic with Theta_D=572(56) K and (2) amorphous and paramagnetic with Theta_D=405(26) K., Comment: 11 pages, 7 figures, 36 references
Published: 2015
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15. The phase transition in the anisotropic Heisenberg model with long range dipolar interactions

Author: Mól, L. A. S. and Costa, B. V.
Subjects: Condensed Matter - Statistical Mechanics
Abstract: In this work we have used extensive Monte Carlo calculations to study the planar to paramagnetic phase transition in the two-dimensional anisotropic Heisenberg model with dipolar interactions (AHd) considering the true long-range character of the dipolar interactions by means of the Ewald summation. Our results are consistent with an order-disorder phase transition with unusual critical exponents in agreement with our previous results for the Planar Rotator model with dipolar interactions. Nevertheless, our results disagrees with the Renormalization Group results of Maier and Schwabl [PRB, 70, 134430 (2004)] and the results of Rapini et. al. [PRB, 75, 014425 (2007)], where the AHd was studied using a cut-off in the evaluation of the dipolar interactions. We argue that besides the long-range character of dipolar interactions their anisotropic character may have a deeper effect in the system than previously believed. Besides, our results shows that the use of a cut-off radius in the evaluation of dipolar interactions must be avoided when analyzing the critical behavior of magnetic systems, since it may lead to erroneous results., Comment: Accepted for publication in the Journal of Magnetism and Magnetic Materials. arXiv admin note: substantial text overlap with arXiv:1109.1840
Published: 2013
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16. Phase transition in two-dimensional magnetic systems with dipolar interactions

Author: Mól, L. A. S. and Costa, B. V.
Subjects: Condensed Matter - Statistical Mechanics
Abstract: In this work we have used extensive Monte Carlo calculations to study the planar to paramagnetic phase transition in the two-dimensional anisotropic Heisenberg model with dipolar interactions (AHd) considering the true long-range character of the dipolar interactions by means of the Ewald summation. Our results are consistent with an order-disorder phase transition with unusual critical exponents in agreement with our previous results for the Planar Rotator model with dipolar interactions. Nevertheless, our results disagrees with the Renormalization Group results of Maier and Schwabl [PRB, 70, 134430 (2004)] and the results of Rapini et. al. [PRB, 75, 014425 (2007)], where the AHd was studied using a cut-off in the evaluation of the dipolar interactions. We argue that besides the long-range character of dipolar interactions their anisotropic character may have a deeper effect in the system than previously believed. Besides, our results shows that the use of a cut-off radius in the evaluation of dipolar interactions must be avoided when analyzing the critical behavior of magnetic systems, since it may lead to erroneous results., Comment: 14 pages, 4 figures, 1 table
Published: 2011

17. Phase diagram of the antiferromagnetic XY model in two dimensions in a magnetic field

Author: Pires, A. S. T., Costa, B. V., and Dias, R. A.
Subjects: Condensed Matter - Statistical Mechanics, Physics - Computational Physics
Abstract: The phase diagram of the quasi-two-dimensional easy-plane antiferromagnetic model, with a magnetic field applied in the easy plane, is studied using the self-consistent harmonic approximation. We found a linear dependence of the transition temperature as a function of the field for large values of the field. Our results are in agreement with experimental data for the spin-1 honeycomb compound BaNi_2V_2O_3, Comment: 3 pages
Published: 2010
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18. Static and dynamic simulation in the classical two-dimensional anisotropic Heisenberg model

Author: Costa, J. E. R. and Costa, B. V.
Subjects: Condensed Matter - Statistical Mechanics, Physics - Computational Physics
Abstract: By using a simulated annealing approach, Monte Carlo and molecular-dynamics techniques we have studied static and dynamic behavior of the classical two-dimensional anisotropic Heisenberg model. We have obtained numerically that the vortex developed in such a model exhibit two different behaviors depending if the value of the anisotropy $\lambda$ lies below or above a critical value $\lambda_c$ . The in-plane and out-of-plane correlation functions ($S^{xx}$ and $S^{zz}$) were obtained numerically for $\lambda < \lambda_c$ and $\lambda > \lambda_c$ . We found that the out-of-plane dynamical correlation function exhibits a central peak for $\lambda > \lambda_c$ but not for $\lambda < \lambda_c$ at temperatures above $T_{BKT}$ ., Comment: 7 pages
Published: 2010

19. A model for vortex formation in magnetic nanodots

Author: Leonel, S. A., Marques, I. A., Coura, P. Z., and Costa, B. V.
Subjects: Condensed Matter - Statistical Mechanics, Physics - Computational Physics
Abstract: We use Monte Carlo simulation to study the vortex nucleation on magnetic nanodots at low temperature. In our simulations, we have considered a simple microscopic two-dimensional anisotropic Heisenberg model with term to describe the anisotropy due to the presence of the nanodot edge. We have considered the thickness of the edge, which was not considered in previous works, introducing a term that controls the energy associated to the edge. Our results clearly show that the thickness of the edge has a considerable influence in the vortex nucleation on magnetic nanodots. We have obtained the hysteresis curve for several values of the surface anisotropy and skin depth parameter ($\xi$). The results are in excellent agreement with experimental data.
Published: 2010
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20. Phase transition in ultrathin magnetic films with long-range interactions: Monte Carlo simulation of the anisotropic Heisenberg model

Author: Rapini, M., Dias, R. A., and Costa, B. V.
Subjects: Condensed Matter - Statistical Mechanics, Physics - Computational Physics
Abstract: Ultrathin magnetic films can be modeled as an anisotropic Heisenberg model with long-range dipolar interactions. It is believed that the phase diagram presents three phases: An ordered ferromagnetic phase I, a phase characterized by a change from out-of-plane to in-plane in the magnetization II, and a high-temperature paramagnetic phase III. It is claimed that the border lines from phase I to III and II to III are of second order and from I to II is first order. In the present work we have performed a very careful Monte Carlo simulation of the model. Our results strongly support that the line separating phases II and III is of the BKT type., Comment: 7 pages
Published: 2010
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21. Diagram for vortex formation in quasi-two-dimensional magnetic dots

Author: Rocha, J. C. S., Coura, P. Z., Leonel, S. A., Dias, R. A., and Costa, B. V.
Subjects: Condensed Matter - Statistical Mechanics, Physics - Computational Physics
Abstract: The existence of nonlinear objects of the vortex type in two-dimensional magnetic systems presents itself as one of the most promising candidates for the construction of nanodevices, useful for storing data, and for the construction of reading and writing magnetic heads. The vortex appears as the ground state of a magnetic nanodisk whose magnetic moments interact via dipole-dipole potential?. In this work it is investigated the conditions for the formation of vortices in nanodisks in triangular, square, and hexagonal lattices as a function of the size of the lattice and of the strength of the dipole interaction D. Our results show that there is a "transition" line separating the vortex state from a capacitor like state. This line has a finite size scaling form depending on the size, L, of the system as Dc=D0 +1/A(?1+B*L^2)?. This behavior is obeyed by the three types of lattices. Inside the vortex phase it is possible to identify two types of vortices separated by a constant, D=Dc, line: An in-plane and an out-of-plane vortex. We observed that the out-of-plane phase does not appear for the triangular lattice. In a two layer system the extra layer of dipoles works as an effective out-of-plane anisotropy inducing a large S^z component at the center of the vortex. Also, we analyzed the mechanism for switching the out-of-plane vortex component. Contrary to some reported results, we found evidences that the mechanism is not a creation-annihilation vortex anti-vortex process., Comment: 5 pages
Published: 2010
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22. Debye temperature of disordered bcc-Fe-Cr alloys

Author: Dubiel, S. M., Cieslak, J., and Costa, B. F. O.
Subjects: Condensed Matter - Materials Science
Abstract: Debye temperature, TD, of Fe100-xCrx disordered alloys with 0~95 the Debye temperature is smaller than the one for the metallic iron, with a local minimum at x=~55 at which the relative decrease of TD amounts to ~12%. The first maximum coincides quite well with that found for the spin-waves stiffness coefficient, D0, while the pretty steep decrease observed for x>~95 which is indicative of a decoupling of the probe Fe atoms from the underlying chromium matrix is likely related to the spin-density waves which constitute the magnetic structure of chromium in that interval of composition. The harmonic force constant calculated from the Debye temperature of the least Fe-concentrated alloy (x>99.9) amounts to only 23% of the one characteristic of a pure chromium., Comment: 15 pages, 7 figures, 26 references
Published: 2009
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23. Phase transition in the two-dimensional dipolar Planar Rotator model

Author: Mól, L. A. S. and Costa, B. V.
Subjects: Condensed Matter - Statistical Mechanics
Abstract: In this work we have used extensive Monte Carlo simulations and finite size scaling theory to study the phase transition in the dipolar Planar Rotator model (dPRM), also known as dipolar XY model. The true long-range character of the dipolar interactions were taken into account by using the Ewald summation technique. Our results for the critical exponents does not fit those from known universality classes. We observed that the specific heat is apparently non-divergent and the critical exponents are $\nu=1.277(2)$, $\beta=0.2065(4)$ and $\gamma=2.218(5)$. The critical temperature was found to be $T_c=1.201(1)$. Our results are clearly distinct from those of a recent Renormalization Group study from Maier and Schwabl [PRB 70, 134430 (2004)] and agrees with the results from a previous study of the anisotropic Heisenberg model with dipolar interactions in a bilayer system using a cut-off in the dipolar interactions [PRB 79, 054404 (2009)]., Comment: 6 pages, 8 figures, Submitted to Journal of Physics: Condensed Matter
Published: 2009
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24. Anomalous behavior of the Debye temperature in Fe-rich Fe-Cr alloys

Author: Costa, B. F. O., Cieslak, J., and Dubiel, S. M.
Subjects: Condensed Matter - Materials Science
Abstract: Debye temperature, $\Theta_D$, of Fe-rich Fe$_{100-x}$Cr$_x$ disordered alloys with $0\le x \le 22.3$ was determined from the temperature dependence of the central shift of M\"ossbauer spectra recorded in the temperature range of 60 -- 300 K. Its compositional dependence shows a maximum at $x \approx 5$ with a relative increase of $\sim 30$% compared to a pure iron. The composition at which the effect occurs correlates well with that at which several other quantities, e. g. the Curie temperature and the spin-wave stiffness coefficient, $D_0$, show their maxima, but the enhancement of $\Theta_D$ is significantly greater and comparable with the enhancement of the hyperfine field (spin-density of itinerant $s$-like electrons) in the studied system. The results suggest that the electron-phonon interaction is important in this alloy system.
Published: 2008
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25. Magnetic monopole and string excitations in a two-dimensional spin ice

Author: Mol, L. A. S., Silva, R. L., Silva, R. C., Pereira, A. R., Moura-Melo, W. A., and Costa, B. V.
Subjects: Condensed Matter - Materials Science, Condensed Matter - Other Condensed Matter
Abstract: We study the magnetic excitations of a square lattice spin-ice recently produced in an artificial form, as an array of nanoscale magnets. Our analysis, based upon the dipolar interaction between the nanomagnetic islands, correctly reproduces the ground-state observed experimentally. In addition, we find magnetic monopole-like excitations effectively interacting by means of the usual Coulombic plus a linear confining potential, the latter being related to a string-like excitation binding the monopoles pairs, what indicates that the fractionalization of magnetic dipoles may not be so easy in two dimensions. These findings contrast this material with the three-dimensional analogue, where such monopoles experience only the Coulombic interaction. We discuss, however, two entropic effects that affect the monopole interactions: firstly, the string configurational entropy may loose the string tension and then, free magnetic monopoles should also be found in lower dimensional spin ices; secondly, in contrast to the string configurational entropy, an entropically driven Coulomb force, which increases with temperature, has the opposite effect of confining the magnetic defects., Comment: 8 pages. Accepted by Journal of Applied Physics (2009)
Published: 2008
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26. Possibility of a new universality class: The anisotropic Heisenberg model with dipolar interactions

Author: Mól, L. A. S. and Costa, B. V.
Subjects: Condensed Matter - Statistical Mechanics, Condensed Matter - Other Condensed Matter
Abstract: This paper has been withdrawn by the authors due to a possible inconsistency in the program code., Comment: This paper has been withdrawn
Published: 2008

27. Velocity, temperature and normal force dependence on friction: An analytical and molecular dynamic study

Author: Dias, R. A., Coura, P. Z., Rapini, M., and Costa, B. V.
Subjects: Physics - Computational Physics, Physics - Classical Physics
Abstract: In this work we propose an extension to the analytical one-dimensional model proposed by E. Gnecco (Phys. Rev. Lett. 84:1172) to describe friction. Our model includes normal forces and the dependence with the angular direction of movement in which the object is dragged over a surface. The presence of the normal force in the model allow us to define judiciously the friction coefficient, instead of introducing it as an {\sl a posteriori} concept. We compare the analytical results with molecular dynamics simulations. The simulated model corresponds to a tip sliding over a surface. The tip is simulated as a single particle interacting with a surface through a Lennard-Jones $(6-12)$ potential. The surface is considered as consisting of a regular BCC(001) arrangement of particles interacting with each other through a Lennard-Jones $(6-12)$ potential. We investigate the system under several conditions of velocity, temperature and normal forces. Our analytical results are in very good agreement with those obtained by the simulations and with experimental results from E. Riedo (Phys. Rev. Lett. 91:084502) and Eui-Sung Yoon (Wear 259:1424-1431) as well.
Published: 2007

28. Temperature Dependent Molecular Dynamic Simulation of Friction

Author: Dias, R. A., Rapini, M., Coura, P. Z., and Costa, B. V.
Subjects: Physics - Computational Physics
Abstract: In this work we present a molecular dynamics simulation of a FFM experiment. The tip-sample interaction is studied by varying the normal force in the tip and the temperature of the surface. The friction force, cA, at zero load and the friction coefficient, $\mu$, were obtained. Our results strongly support the idea that the effective contact area, A, decreases with increasing temperature and the friction coefficient presents a clear signature of the premelting process of the surface., Comment: 5 pages, 25 figures
Published: 2006
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29. Magnetic friction due to vortex fluctuation

Author: Dias, R. A., Rapini, M., Coura, P. Z., and Costa, B. V.
Subjects: Physics - Computational Physics
Abstract: We use Monte Carlo and molecular dynamics simulation to study a magnetic tip-sample interaction. Our interest is to understand the mechanism of heat dissipation when the forces involved in the system are magnetic in essence. We consider a magnetic crystalline substrate composed of several layers interacting magnetically with a tip. The set is put thermally in equilibrium at temperature T by using a numerical Monte Carlo technique. By using that configuration we study its dynamical evolution by integrating numerically the equations of motion. Our results suggests that the heat dissipation in this system is closed related to the appearing of vortices in the sample., Comment: 6 pages, 41 figures
Published: 2006
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30. Monte Carlo Simulations of Ultrathin Magnetic Dots

Author: Rapini, M., Dias, R. A., Landau, D. P., and Costa, B. V.
Subjects: Physics - Computational Physics, Physics - General Physics
Abstract: In this work we study the thermodynamic properties of ultrathin ferromagnetic dots using Monte Carlo simulations. We investigate the vortex density as a function of the temperature and the vortex structure in monolayer dots with perpendicular anisotropy and long-range dipole interaction. The interplay between these two terms in the hamiltonian leads to an interesting behavior of the thermodynamic quantities as well as the vortex density., Comment: 10 figures
Published: 2006
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31. Phase transition in ultrathin magnetic films with long range interactions

Author: Rapini, M., Dias, R. A., and Costa, B. V.
Subjects: Physics - Computational Physics
Abstract: Ultrathin magnetic films can be modeled as an anisotropic Heisenberg model with long range dipolar interactions. It is believed that the phase diagram presents three phases: A ordered ferromagnetic phase (I), a phase characterized by a change from out-of-plane to in-plane in the magnetization (II), and a high temperature paramagnetic phase (III). It is claimed that the border lines from phase I to III and II to III are of second order and from I to II is first order. In the present work we have performed a very careful Monte Carlo simulation of the model. Our results strongly support that the line separating phase II and III is of the BKT type., Comment: 7 pages, 21 figures
Published: 2006

32. Vortex behavior near a spin vacancy in 2D XY-magnets

Author: Pereira, A. R., Mol, L. A. S., Leonel, S. A., Coura, P. Z., and Costa, B. V.
Subjects: Condensed Matter
Abstract: The dynamical behavior of anisotropic two dimensional Heisenberg models is still a matter of controversy. The existence of a central peak at all temperatures and a rich structure of magnon peaks are not yet understood. It seems that the central peaks are related, in some way, to structures like vortices. In order to contribute to the discussion of the dynamical behavior of the model we use Monte Carlo and spin dynamics simulations as well analytical calculations to study the behavior of vortices in the presence of nonmagnetic impurities. Our simulations show that vortices are attracted and trapped by the impurities. Using this result we show that if we suppose that vortices are not very much disturbed by the presence of the impurities, then they work as an attractive potential to the vortices explaining the observed behavior in our simulations., Comment: 4 pages, 6 figures
Published: 2003
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33. Monte Carlo study of the critical temperature for the planar rotator model with nonmagnetic impurities

Author: Leonel, S. A., Coura, Pablo Zimmermann, Pereira, A. R., Mól, L. A. S., and Costa, B. V.
Subjects: Condensed Matter
Abstract: We performed Monte Carlo simulations to calculate the Berezinskii-Kosterlitz-Thouless (BKT) temperature $T_{BKT}$ for the two-dimensional planar rotator model in the presence of nonmagnetic impurity concentration $(\rho)$. As expected, our calculation shows that the BKT temperature decreases as the spin vacancies increase. There is a critical dilution $\rho_c \approx 0.3$ at which $T_{BKT} =0$. The effective interaction between a vortex-antivortex pair and a static nonmagnetic impurity is studied analytically. A simple phenomenological argument based on the pair-impurity interaction is proposed to justify the simulations., Comment: 5 pages, 5 figures, Revetex file
Published: 2002
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34. Molecular dynamic simulation of directional crystal growth

Author: Costa, B. V., Coura, P. Z., and Mesquita, O. N.
Subjects: Condensed Matter - Statistical Mechanics, Condensed Matter - Materials Science
Abstract: We use molecular dynamic to simulate the directional growth of binary mixtures. our results compare very well with analitical and experimental results. This opens up the possibility to probe growth situations which are difficult to reach experimentally, being an important tool for further experimental and theoretical developments in the area of crystal growth., Comment: 6 pages, 5 figures. Computer Simulation Studies in Condensed Matter Physics XII, edited by D.P. Landau, et al. (Springer, Heidelberg, in press)
Published: 1999

35. Language and Area Studies: A Contribution to the Debate.

Author: da Costa, B. Gomes
Abstract: This article examines the range of language and area studies courses now offered in British universities and polytechnic institutes. Four types of language programs are reviewed: (1) the conventional "culture" model, (2) basic skills courses, (3) joint honors programs, and (4) an area studies model. Advantages of the area studies approach are detailed. (RL)
Published: 1972

36. German Language Attainment: A Sample Survey of Universities and Colleges in the UK.

Author: Gomes da Costa, B.
Abstract: This report presents the findings of a survey carried out in 1970 on nearly 200 degree students in England and Wales studying German as their main subject. The objectives of the survey were to: (1) determine the ranges of language proficiency attained by British graduates in German at various universities and other colleges; (2) interpret these proficiency levels in absolute terms which could be readily understood; (3) study the inter-relationships between certain aspects of foreign language attainment and other factors; and (4) discover those factors associated with the different levels of attainment. Other factors to be measured were: (1) language learning aptitude, (2) intelligence, (3) home and school background, (4) college curriculum, and (5) student's career and study interests. Some of the conclusions were: (1) the overall level of foreign language attainment within the educational system is not high; (2) measured intelligence has a closer association with the passive than with the active language skills; (3) there is a considerable disparity between the aims of degree courses and the students' aims; (4) time spent abroad is the most powerful determiner of high level language attainment; (5) integrative motivation is a necessary condition for high level language attainment; (6) instrumental motivation operates against high level language attainment; (7) language teaching in Great Britain fails to achieve the declared official aims. (CFM)
Published: 1975

37. The Design and Execution of a Language Testing Programme at University Level in the United Kingdom.

Author: Council of Europe, Strasbourg (France). and Gomes da Costa, B.
Abstract: This paper describes an experimental testing program in England which parallels a broader, 1967 study concerning second language acquisition in the United States. The earlier study, conducted by John Carroll, concentrated on determining proficiency of language majors in five foreign languages. This experiment limits the field of study to German majors engaged in the British Honours Degree programs at several universities. Phase 1 is based on the MLA Advanced Proficiency Tests and the Carroll-Sapon Modern Language Aptitude Test. Additionally, Alice Heim's "AH5 Group Test of High Grade Intelligence" and a comprehensive questionnaire devised by the author were also administered to some 400 students. Conclusive results were not obtained for various reasons explained by the author. (RL)
Published: 1970

38. Factors of soil erosion in the Córrego Rico watershed, São Paulo, Brazil

Author: De Oliveira Costa, B., De Oliveira, G. S., Pissarra, T. C. T., Campos, S., Werner, Armin, Santos, J. P., and Vanzela, E. L. S.
Published: 2016
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