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Orientador: Vera Lucia da Silveira Nantes Button Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação Resumo: o objetivo deste trabalho foi aprimorar o processo de apodização de discos de cerâmica piezoelétrica utilizado no LUS (Laboratório de Ultra-Som, DEB/FEEC e CEB, UNlCAMP), buscando estabelecer uma melhor relação entre tempo de aplicação do campo elétrico e a temperatura do banho de óleo isolante usado no processo. A apodização das cerâmicas piezoelétricas é utilizada para reduzir a difração no campo acústico gerado por transdutores de ultra-som, como já foi comprovado no LUS em trabalhos anteriores. Buscou-se reduzir o tempo de aplicação do campo elétrico através do ensaio de temperaturas diferentes do óleo mineral que banha o disco cerâmico e verificando em quais ensaios foi obtida uma boa apodização. Foram utilizadas cerâmicas piezoelétricas PZT-5A de 12,7mm de diâmetro, com 0,885mm (EDO Acoustics) e lmm (APCI) de espessura. O campo elétrico aplicado foi de 2kV/mm de espessura de cerâmica, e um eletrodo esférico de 5mm de raio foi usado para formatar o campo elétrico de apodização. Foram utilizados dois tipos de óleo mineral: o Nujol, que acima de 160°C evapora rapidamente e o óleo da CooperPower, que permitiu utilizar temperaturas até 250°C, com pouca evaporação. Os discos cerâmicos apodizados para os quais o coeficiente eletromecânico do modo espessura, kt, resultou em valores acima de 0,37, foram considerados bem apodizados. O óleo isolante foi aquecido a temperaturas diferentes entre 120°C e 250°C e o campo elétrico foi aplicado por períodos de 2 minutos até 4 horas e 30 minutos (tempo necessário para a temperatura do óleo resfriar até 25°C). Este estudo também incluiu a avaliação do efeito de sucessivas despolarizações e repolarlzações nos modos de vibração da cerâmica piezoelétrica. Os resultados confirmaram que, usando temperaturas mais altas (acima de 200°C), o campo elétrico precisa ser aplicado durante um período menor. Apodizações que utilizaram temperatura igual a 160°C, só mostraram acoplamentos bons quando o campo permaneceu aplicado enquanto o óleo resfriava até 25°C. Apodizações em que o óleo foi aquecido a temperaturas inferiores a 160°C não apresentaram bons resultados, independentemente do tempo de aplicação do campo elétrico. Os resultados também mostraram que o efeito de aplicar o campo elétrico ainda antes do óleo ser aquecido foi um aumento do acoplamento eletromecânico obtido, comparando com o resultado de um processo de apodização semelhante, mas em que o campo elétrico só foi aplicado depois do aquecimento do óleo. O mesmo efeito não foi observado com as apodizações em que utilizou-se a temperatura mais alta possível, 250°C, usando o óleo mineral da Copper Power. Concluiu-se que, usando a temperatura igual a 250°C, foi possível reduzir o tempo de aplicação do campo elétrico de apodização, com resultados satisfatórios, de mais de 4 horas para apenas 2 minutos. No entanto, o processo que utiliza uma dada relação tempo de aplicação do campo/temperatura do óleo, e que apodiza satisfatoriamente uma cerâmica com lmm de espessura, pode resultar na polarização convencional (linear) de uma cerâmica mais fina, como a cerâmica com espessura igual a O,885mm. Algumas das cerâmicas apodizadas foram usadas para construir transdutores de ultra-som. Os campos acústicos gerados pelos transdutores construidos foram mapeados, confirmando o aumento da profundidade do campo acústico, como conseqüência da redução da difração acústica, obtida a partir da apodização da polarização das cerâmicas piezoelétricas Abstract: The objective of this work was to optimize the process of apodization of piezoelectric ceramics disks, looking for the better relation between the insulating oil bath temperature and the smaIlest period of time through which the poling field must be applied. The apodization of the piezoelectric ceramic is performed to reduce the diffraction in the acoustic field generated by ultrasonic transducers. We looked for the best initial temperature of the insulating mineral oil that surrounds the piezoelectric ceramic, and how long the poling electric field must be applied to the ceramic to achieve a good apodization. We used 12.7mm diameter, 0.885mm and lmm thickness PZT-5A ceramic disks. The non-uniform poling electric field (2kV/mm) has been shaped by a 5mm radius spherica1 electrode. The apodized ceramic disks which showed piezoelectric coupling coefficient values larger than 0.37, were considered well apodizated. We used oil temperatures from 120°C to above 200°C and the electric field was applied for periods of at least 2 minutes to up to 4 hours and third minutes (until the oil temperature cooled down to 25°C). This study a1so inc1uded the ceramic disk evaluation after successive depolarizations and repolarizations. The results showed that using higher temperatures (above 200°C) we needed to apply the poling field for a shorter time. Temperature equa1160°C was efficient on1y ifthe poling field was applied until the oil was cooled down to 25°C (4 hours and thirty minutes). The results also showed that if the poling electric field was applied to the piezoelectric ceramic even before the oil was heated, we obtained larger piezoelectric coupling coefficients, compared to the poling processes where the electric field was applied to the ceramic on1y afier the oil was heated. This was not necessary if we used higher temperatures (250°C). We concluded that using higher temperatures (250°C) it was possible to reduce the apodization process, with good results, from more than 4 hours to on1y 2 minutes. Ultrasound transducers were built; their acoustic fields were mapped in a water tank, and the results confirmed the increasing of the depth of the acoustic field, as consequence of the acoustic difraction reduction Mestrado Engenharia Biomédica Mestre em Engenharia Elétrica

Recently, researchers have adapted Bioelectrical Impedance Analysis (BIA) as a new approach to objectively monitor wounds. They have indicated various BIA parameters associated to specific wound types can be linked to wound healing through trend analysis relative to time. However, these studies are conducted using wet electrodes which have been identified as possessing several shortcomings, such as unstable measurements. Thus, the adaption of e-textile electrodes has become an area of interest in measuring biosignals. E-textile electrodes are known to possess a significantly large polarization impedance (Z p ) that potentially influences these biosignal measurements. In this study we aim to identify the suitability of e-textile electrodes to monitor wounds using BIA methodologies. By adapting suggested methodologies conducted in-vivo from previous studies, we used an ex-vivo model to observe the behaviour of e-textile electrodes relative to time. This was compared to common clinical wet electrodes, specifically Ag/AgCl. The objective of this study was to identify the BIA parameters that can be used to monitor wounds with e-textile electrodes. By analysing the BIA parameters relative to time, we observed the influence of Z p on these parameters.

Agradecimentos: The Authors acknowledge financial support from the Brazilian funding agencies Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) (Finance Code 001), and the Brazilian National Institute for Science and Technology of Quantum Information (INCT-IQ). A.O.J. acknowledges financial support by the Foundation for Polish Science through TEAM-NET project (Contract No. POIR.04.04.00-00-17C1/18-00) Abstract: The Solovay-Kitaev theorem allows us to approximate any single-qubit gate to arbitrary accuracy with a finite sequence of fundamental operations from a universal set of gates. Inspired by this decomposition, we present a quantum channel simulator capable of implementing any completely positive trace-preserving map. Our realization consists of one ancillary qubit, encoded in the transverse mode of a laser beam (orbital degree of freedom), one qubit system, encoded in its polarization (spin), one spin-orbit CNOT gate, and four single-qubit operations performed with prisms and polarization components. Our results describe the implementation of arbitrary single-qubit channels on the photon polarization using the transverse mode as the ancillary qubit CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO CARLOS CHAGAS FILHO DE AMPARO À PESQUISA DO ESTADO DO RIO DE JANEIRO - FAPERJ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Fechado

The orthoferrites with the general formula RFeO3 (R = Ho, Er, Lu, Sc, and Y) have recently attracted a great deal of attention because they are promising candidates for a second generation of multiferroic materials. In this computational work, the structural, ferroelectric and optical properties of the YFeO3 perovskite oxide (YFO) and a Bi‐doped YFeO3 were analyzed. Bi‐substitution in YFO leads to an increase of its lattice parameters by virtue of the larger ionic radius of Bi3+. Both compounds exhibit a G‐type antiferromagnetic ground state. The calculations disclose a significant spontaneous polarization along the [101] direction of YFO‐Bi, which originates in the asymmetric distribution of the charges around the Bi3+ ions, as a result of the Bi‐6s electrons. The electric polarizability of YFO is increased upon Bi3+‐doping and the more significant components of the real permittivity tensor of YFO‐Bi are those associated with the direction along which the maximum value of spontaneous polarization is observed. The spontaneous polarization of YFO‐Bi found in this work reveals that this compound holds the potential for the next generation of multi ferroic materials.

Sizing natural or engineered single nanoscale objects is fundamental in many areas of science and technology. To achieve it several advanced microscopic techniques have been developed, mostly based on electron and scanning probe microscopies. Still for soft and poorly adhered samples the existing techniques face important challenges. Here, we propose an alternative method to size single nanoscale objects based on the measurement of its electric polarization. The method is based on Electrostatic Force Microscopy measurements combined with a specifically designed multiparameter quantification algorithm, which gives the physical dimensions (height and width) of the nanoscale object. The proposed method is validated with ~50 nm diameter silver nanowires, and successfully applied to ~10 nm diameter bacterial polar flagella, an example of soft and poorly adhered nanoscale object. We show that an accuracy comparable to AFM topographic imaging can be achieved. The main advantage of the proposed method is that, being based on the measurement of long-range polarization forces, it can be applied without contacting the sample, what is key when considering poorly adhered and soft nanoscale objects. Potential applications of the proposed method to a wide range of nanoscale objects relevant in Material, Life Sciences and Nanomedicine is envisaged.

The often used simplistic correlations between molecular electronic parameters and experimentally determined corrosion inhibition efficiencies are critically evaluated for a set of 24 heterocyclic organic compounds, tested as corrosion inhibitors for copper in 3 wt.% NaCl aqueous solution. Twelve different molecular electronic descriptors—such as ionization potential, electron affinity, HOMO–LUMO gap, dipole moment—are tested and it is shown that none of them displays any noticeable correlation with the inhibition efficiency. Our results, therefore, cast serious doubt on reported correlations between such parameters and inhibition efficiency, obtained for only a few inhibitors, which are abundant in the literature. We also discuss some pros and cons of inhibition efficiency as a metric for evaluating the performance of corrosion inhibitors, and introduce a new metric termed inhibition power that uses the universal logarithmic scale and dimensionless decibel (dB) units., info:eu-repo/semantics/published

International audience; Couette-Taylor-Poiseuille flow CTPF consists on the superposition of Couette-Taylor flow to an axial flow. The CTPF flow hydrodynamics studies remain rather qualitative or numerical or are restricted to relatively low Taylor and/or axial Reynolds numbers. For more comprehensive and control of CTPF, especially for relatively high Taylor numbers and high axial Reynolds numbers, we investigated experimentally CTF with and without an axial flow, using the electro-diffusion ED method. This technique requires the use of Electro-Diffusion ED probe which allows the determination of the local mass transfer rate from the Limiting Diffusion current measurement delivered by the ED probe while it is polarized by a polarization voltage. From the local mass transfer (the Sherwood number), we determined the wall shear rate using different approaches. The results illustrate that low axial flow can generate a stabilizing effect on the CT flow. The time-evolutions of the local mass transfer and the wall shear rate are periodic. These evolutions characterize the waviness or the stretching of the vortices. However, Taylor Wavy Vortex Flow TWVF is destabilized under the effect of relatively important axial flow. The time-evolutions of wall shear rate are no longer periodic. Indeed, Taylor vortices are overlapped or completely destructed.

This Letter addresses the statistical modeling of dual-polarized MIMO-LMS fading channels. In the absence of accurate experimental results, a statistical model for the characterization of MIMO-LMS channels is proposed based on consolidation of available experimental results for SISO-LMS and MIMO wireless channels as well as on their extrapolation to the MIMO-LMS case of interest. Moreover, a step-by-step methodology for the simulation and time-series generation of the proposed MIMO-LMS channel model is provided, which is useful for the design and performance assessment of MIMOLMS transmission systems. The proposed model incorporates the effects of all relevant critical channel aspects in a flexible and fully-parameterized way.

In the present work, we have computed the energy and hardness profiles for a series of inter and intramolecular conformational changes at several levels of calculation. All processes studied have in common the fact that the choice of a weak methodology or a poor basis set results in the presence of spurious stationary points in the energy profile. At variance with the energy profiles, the hardness profiles calculated as the difference between the vertical ionization potential and electron affinity always show the correct number of stationary points independently of the basis set and methodology used. For this reason, we have concluded that hardness profiles can be used to check the reliability of the energy profiles for those chemical systems that, because of their size, cannot be treated with high level ab initio methods.

Electrical property derivative expressions are presented for the nuclear relaxation contribution to static and dynamic (infinite frequency approximation) nonlinear optical properties. For CF4 and SF6, as opposed to HF and CH4, a term that is quadratic in the vibrational anharmonicity (and not previously evaluated for any molecule) makes an important contribution to the static second vibrational hyperpolarizability of CF4 and SF6. A comparison between calculated and experimental values for the difference between the (anisotropic) Kerr effect and electric field induced second-harmonic generation shows that, at the Hartree–Fock level, the nuclear relaxation/infinite frequency approximation gives the correct trend (in the series CH4, CF4, SF6) but is of the order of 50% too small.

Agradecimentos: This work was supported by FAPESP (Grants 2008/11527-1, 2009/0947-3, 2009/10264-0, 2012/04870-7, 2012/10675-2), CNPq, and CAPES-Brazil. The authors thank the XRD2-LNLS staff for technical support and the LNLS for the beam time (proposals 8808, 10069, and 11045) Abstract: In this work we have determined the magnetic structure of R2CoGa8 (R = Gd, Tb, and Dy) intermetallic compounds using x-ray resonant magnetic scattering in order to study the evolution of the anisotropic magnetic properties along the series for R = Gd-Tm. The three compounds have a commensurate antiferromagnetic spin structure with a magnetic propagation vector (tau) over right arrow = (1/2, 1/2, 1/2) and a Neel temperature of approximately 20, 28.5, and 15.2 K for R = Gd, Tb, and Dy, respectively. The critical exponent beta obtained from the temperature dependence of the magnetic peaks suggest a three-dimensional universality class for the three compounds. Comparing the simulated and integrated intensities we conclude that the magnetic moment direction is in the ab plane for the Gd2CoGa8 compound and parallel to the c axis for the Tb2CoGa8 and Dy2CoGa8 compounds. The evolution of the magnetic properties of the R2CoGa8 series for R = Gd-Tm is discussed taking into account the indirect Ruderman-Kittel-Kasuya-Yoshida interaction and crystalline-electric field effects. The comparison between the reported magnetic properties of the Ga-based compounds with those for the In-based isostructural family reveals differences in their exchange couplings that contribute to the understanding of the role of the f-electronmagnetism in these classes of materials FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Aberto

An Euler-Lagrange-type equation is solved to different orders for a plane metallic system perturbed by the external operator Q^ used previously in a sum-rule calculation. This approach managed to reproduce to within a few percent the multipole surface-plasmon energies. The jellium model is used for the positive ionic background and local-density functionals for the Hamiltonian. From the zeroth-order Euler-Lagrange equation a self-consistent ground-state density is obtained and used in the first-order equation to obtain the induced density. From the induced density, several aspects of the system response are considered and special attention is focused on the static polarizability.

Ab initio Hartree–Fock and MP2 calculations of the longitudinal (hyper)polarizability—including the static electronic, static zero-point vibrational average (ZPVA), and pure vibrational (static and dynamic) contributions—have been carried out on a set of seven typical medium size conjugated nonlinear optical (NLO) molecules. The ZPVA is obtained through first-order in mechanical plus electrical anharmonicity. Based on physical “nuclear relaxation” considerations the individual (square bracket) terms that contribute to the pure vibrational (hyper)polarizability are then taken into account through third-, fourth-, or fifth-order depending upon the type of term. In order to carry out the correlated treatment, field-induced coordinates and a special finite field technique are utilized. Correlation leads to very substantial differences in the absolute and relative values of the various contributions. In comparison to the electronic term the ZPVA correction is usually small but in one case is over two-thirds as large. On the other hand, both static and dynamic pure vibrational contributions are commonly of a magnitude that is comparable to, or are larger than, the electronic term. The higher-order pure vibration terms are often large. For dynamic processes they can be almost as important as the lowest-order terms; for static (hyper)polarizabilities they can be more important. Thus, for typical NLO molecules, the initial convergence behavior of the perturbation series in mechanical and electrical anharmonicity requires further investigation.

Our new simple method for calculating accurate Franck-Condon factors including nondiagonal (i.e., mode-mode) anharmonic coupling is used to simulate the C2H4+X2B 3u←C2H4X̃1 Ag band in the photoelectron spectrum. An improved vibrational basis set truncation algorithm, which permits very efficient computations, is employed. Because the torsional mode is highly anharmonic it is separated from the other modes and treated exactly. All other modes are treated through the second-order perturbation theory. The perturbation-theory corrections are significant and lead to a good agreement with experiment, although the separability assumption for torsion causes the C2 D4 results to be not as good as those for C2 H4. A variational formulation to overcome this circumstance, and deal with large anharmonicities in general, is suggested

We present a theoretical investigation on positron scattering by N2O. Elastic differential and integral cross sections at both the static and static plus correlation-polarization levels of approximation are calculated and reported in the 0.1-100 eV. Calculations were performed using two theoretical methods, namely, the Schwinger multichannel method and the method of continued fractions. Also, two different schemes were used to treat correlation-polarization effects. The comparison between our calculated results and the existing experimental data is encouraging CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Aberto

Nonlocal approximations for the electronic exchange and correlation effects are used to compute, within density-functional theory, the polarizability and surface-plasma frequencies of small jelliumlike alkali-metal clusters. The results are compared with those obtained using the local-density approximation and with available experimental data, showing the relevance of these effects in obtaining an accurate description of the surface response of metallic clusters.

Agradecimentos: The authors acknowledge support from Brazilian agency Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). One of the authors (M.H.F.B) acknowledges support from the Paraná state agency Fundação Araucária and from FINEP (under Project No. CT-Infra 1) and computational support from Professor Carlos M. de Carvalho at DF-UFPR and from CENAPAD-SP Abstract: The authors report integral, differential and momentum transfer cross sections for elastic scattering of low-energy electrons by C4H4O (furan) molecules. Their calculations employed the Schwinger multichannel method with pseudopotentials and were performed in the static-exchange and in the static-exchange plus polarization approximations. The authors found two shape resonances located around 2.1 and 4.2 eV that belong to the B-1 and A(2) symmetries of the C-2v group, respectively. The authors' results are consistent with recent measurements of vertical electron attachment energies CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO ARAUCÁRIA DE APOIO AO DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO DO ESTADO DO PARANÁ - FAPPR FINANCIADORA DE ESTUDOS E PROJETOS - FINEP Fechado

Agradecimentos: The work was supported in part by a Grant-in-Aid, the Ministry of Education, Science, Technology, Sport and Culture, Japan, the Japan Society for the Promotion of Science (JSPS), and the Japan Atomic Energy Research Institute (JAERI). One of the authors (C.M.) is also grateful to the JSPS for financial support under Grant No. P04064. Another author (H.T.) acknowledges Dr. T. Ozeki of the JAERI for his encouragement and support during this work. This work was also done under the International Atomic Energy Agency (IAEA) project for three of the authors (C.M., M.H., and H.T.). Two of the authors (M.H.F.B. and M.A.P.L.) acknowledge support from the Brazilian agency Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). MHFB also acknowledges support from the Paraná state agency Fundação Araucária and from FINEP (under Project No. CT-Infra 1). One of the authors (M.H.F.B.) also acknowledges Professor Carlos M. de Carvalho for computational support at Departamento de Física-UFPR. These calculations were made at CENAPAD-SP and a DF-UFPR Abstract: 1,1-difluoroethylene (1,1-C2H2F2) molecules have been studied for the first time experimentally and theoretically by electron and positron impact. 0.4-1000 eV electron and 0.2-1000 eV positron impact total cross sections (TCSs) were measured using a retarding potential time-of-flight apparatus. In order to probe the resonances observed in the electron TCSs, a crossed-beam method was used to investigate vibrational excitation cross sections over the energy range of 1.3-49 eV and scattering angles 90 degrees and 120 degrees for the two loss energies 0.115 and 0.381 eV corresponding to the dominant C-H (nu(2) and nu(9)) stretching and the combined C-F (nu(3)) stretching and CH2 (nu(11)) rocking vibrations, respectively. Electron impact elastic integral cross sections are also reported for calculations carried out using the Schwinger multichannel method with pseudopotentials for the energy range from 0.5 to 50 eV in the static-exchange approximation and from 0.5 to 20 eV in the static-exchange plus polarization approximation. Resonance peaks observed centered at about 2.3, 6.5, and 16 eV in the TCSs have been shown to be mainly due to the vibrational and elastic channels, and assigned to the B-2, B-1, and A(1) symmetries, respectively. The pi* resonance peak at 1.8 eV in C2H4 is observed shifted to 2.3 eV in 1,1-C2H2F2 and to 2.5 eV in C2F4; a phenomenon attributed to the decreasing C=C bond length from C2H4 to C2F4. For positron impact a conspicuous peak is observed below the positronium formation threshold at about 1 eV, and other less pronounced ones centered at about 5 and 20 eV CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO ARAUCÁRIA DE APOIO AO DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO DO ESTADO DO PARANÁ - FAPPR FINANCIADORA DE ESTUDOS E PROJETOS - FINEP Fechado

Agradecimentos: The authors acknowledge support from Brazilian agency Conselho Nacional de Desenvolvimento Cientíifico e Tecnológico (CNPq). MHFB also acknowledges support from the Paraná state agency Fundação Araucária and from FINEP (under project CT-Infra 1) and computational support from Professor Carlos M de Carvalho at DF-UFPR and from CENAPAD–SP Abstract: We report elastic integral, differential and momentum transfer cross sections for low-energy electron collisions with the two isomers of C4H10, butane and isobutane. We employ the Schwinger multichannel method with pseudopotentials at the static-exchange-polarization approximation, and cover energies from 1 eV to 20 eV. We investigate the influence of polarization on the isomer effect comparing the cross sections of these isomers and concluded that polarization has a small influence in that effect. We also compare our computed elastic cross sections with available total cross sections. Total ionization cross sections by electron impact are computed using the binary-encounter-Bethe (BEB) model and the results compared with available experimental data. The ionization cross sections for butane and isobutane are similar, showing that they also have a small isomer effect in the ionization process CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO ARAUCÁRIA DE APOIO AO DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO DO ESTADO DO PARANÁ - FAPPR FINANCIADORA DE ESTUDOS E PROJETOS - FINEP Fechado

In previous works, we have shown that bond length alternation vibrational modes in -conjugated organic molecules may break the minimum polarizability principle (MPP). To arrive at this conclusion, we have developed a method that diagonalizes the polarizability Hessian matrix with respect to the vibrational nontotally symmetric normal coordinates. The vibrational motions that disobey the MPP in -conjugated molecules are distortions of the equilibrium geometry that produce a reduction of the polarizability due to the localization of -electrons. For aromatic species, this electronic localization is responsible for the subsequent reduction of the aromaticity of the system. In the present work, we apply our methodology to calculate the nontotally symmetric distortions that produce the maximum breakdown of the MPP in a series of twenty polycyclic aromatic hydrocarbons. It is shown that the nuclear displacements that break the MPP have larger components in those rings that possess the highest local aromaticity. Thus, these vibrational motions can be use as an indicator of local aromaticity Support for this work from the Spanish Ministerio de Ciencia y Tecnología (projects No. BQU2002-04112-C02-02 and BQU2002-03334), from the DURSI (Generalitat de Catalunya) (project 2001SGR-00290), and the use of the computational facilities of the Catalonia Supercomputer Center (CESCA) are gratefully acknowledged. M. T.-S. is financed through CIRIT Project No. FI/01-000699 from the Generalitat de Catalunya. M. S. thanks the DURSI for financial support through the Distinguished University Research Promotion, 2001

A variational approach for reliably calculating vibrational linear and nonlinear optical properties of molecules with large electrical and/or mechanical anharmonicity is introduced. This approach utilizes a self-consistent solution of the vibrational Schrodinger equation for the complete field-dependent potential-energy surface and, then, adds higher-level vibrational correlation corrections as desired. An initial application is made to static properties for three molecules of widely varying anharmonicity using the lowest-level vibrational correlation treatment (i.e., vibrational Møller-Plesset perturbation theory). Our results indicate when the conventional Bishop-Kirtman perturbation method can be expected to break down and when high-level vibrational correlation methods are likely to be required. Future improvements and extensions are discussed.

[spa] El trabajo realizado en esta tesis doctoral tiene como objetivo mejorar las metodologías de la química teórica y computacional en la descripción de los efectos del entorno en sistemas químicos. La primera parte se centra en el efecto del solvente, en concreto en el desarrollo de modelos cuánticos continuos de solvatación, y en la derivación de modelos de solvatación fraccional obtenidos a partir de métodos continuos capaces de descomponer energías libres de solvatación y de transferencia entre solventes en contribuciones asociadas a fragmentos químicos de una molécula. Esto permite obtener el perfil tridimensional de las regiones hidrofóbicas/hidrofílicas de una molécula a partir de sus contribuciones fraccionales a la solvatación, siendo esta información muy útil en el establecimiento de relaciones cuantitativas estructura-actividad para el desarrollo de nuevos fármacos, o en la definiciones de índices de similaridad hidrofóbicos, basados en la similitud de este perfil tridimensional entre dos compuestos. Con este objetivo se ha parametrizado satisfactoriamente el modelo continuo MST para la predicción de coeficientes de partición octanol/agua y de energías libres de solvatación en agua, cloroformo, tetracloruro de carbono y octanol, tanto a nivel ab initio HF/6-31G(d) como a niveles semiempíricos AM1 y PM3. También se ha parametrizado el modelo MST para el estudio de especies iónicas en solución. Finalmente, se ha llevado a cabo una comparación entre la respuesta electrostática obtenida a partir de diferentes modelos continuos SCRF (MST, SM5.42R y MPE), ilustrando las grandes diferencias que se pueden encontrar entre las contribuciones electrostáticas y no electrostáticas según sea el modelo usado, y poniendo así de manifiesto la estrecha relación que hay que considerar entre estas contribuciones a la solvatación y la parametrización específica de cada modelo continuo. La metodología de solvatación fraccional usada ha permitido además ilustrar la dependencia de estas contribuciones fragmentales respecto a efectos electrónicos, estéricos o tautoméricos. La segunda parte de este trabajo se centra en el desarrollo de metodologías eficientes y precisas para la descripción de las fuerzas de polarización en campos de fuerzas clásicos. Se han estudiado dos metodologías, una basada en un tratamiento implícito de estas fuerzas a partir de un modelo de doble carga, que permite describir satisfactoriamente la distribución de carga de una molécula en un entorno aislado, y frente a la acción de un campo externo, respectivamente, permitiendo reproducir de forma adecuada las energías de polarización para una serie de complejos por puente de hidrógeno y catión-pi. También se ha estudiado la inclusión de los efectos de polarización mediante dipolos puntuales inducidos. En este sentido, se ha profundizado en una metodología capaz de obtener modelos distribuidos de polarizabilidades atómicas isotrópicas muy eficiente computacionalmente y que permite reproducir de forma precisa la polarizabilidad global de las moléculas para la serie de derivados bencénicos estudiados, así como la contribución de polarización en sus energías de interacción catión-pi con un catión de sodio., [eng] The objective of this work is the improvement of the methodologies available in the field of theoretical and computacional chemistry for the description of the effects of environment in chemical systems. First, it is presented a set of studies on the effect of the solvent, in particular on the development of quantum continuum solvation models and the decomposition of free energies of solvation and transfer into contributions associated to chemical fragments of a molecule. In this way, it can be obtained a 3D picture of the hydrophobic/hydrophylic regions of a molecule, and this information is very valuable in the establishment of quantitative structure-activity relationships for the development of new drugs, and permits also the definition of a hydrophobic similarity index based on the the hydrophobic profile of two different compounds. The parametrization of the MST model presented is able to satisfactorily reproduce octanol/water partition coefficients and free energies of solvation in water, chloroform, carbon tetrachloride and octanol, both at the ab initio HF/6-31G(d) and semiempirical AM1 and PM3 levels of theory. The hydration of ionic species has also been revised in the framework of the MST model. Finally, a comparison of the electrostatic response obtained from different SCRF continuum models (MST, SM5.42R and MPE) is presented. A different balance between the electrostatic and nonelectrostatic contributions has been obtained from the different models, and show that it is necessary to mantain a close correspondece between each SCRF formalism and the specific details of its parametrization. Finally, the transferability of fragmental contributions to solvation has been explored. The second part of this work is aimed at the development of efficient methodologies for the description of polarization forces in classical force fields. Two methodologies has been explored. The first is based on an implicit treatment of these forces through a dual charge model, that represent the charge distribution of a molecule alone and in response to an external field, respectively. Finally, the explicit treatment of polarization effects through induced point dipoles has been studied. In particular, it has been explored an efficient methodology to obtain distributed models of atomic isotropic polarizabilities.

Manipulation of yeast cell polarity by external electric fields reveals electrochemical pathways that influence the distribution of membrane lipids and the polarity regulator Cdc4p., Cells are naturally surrounded by organized electrical signals in the form of local ion fluxes, membrane potential, and electric fields (EFs) at their surface. Although the contribution of electrochemical elements to cell polarity and migration is beginning to be appreciated, underlying mechanisms are not known. Here we show that an exogenous EF can orient cell polarization in budding yeast (Saccharomyces cerevisiae) cells, directing the growth of mating projections towards sites of hyperpolarized membrane potential, while directing bud emergence in the opposite direction, towards sites of depolarized potential. Using an optogenetic approach, we demonstrate that a local change in membrane potential triggered by light is sufficient to direct cell polarization. Screens for mutants with altered EF responses identify genes involved in transducing electrochemical signals to the polarity machinery. Membrane potential, which is regulated by the potassium transporter Trk1p, is required for polarity orientation during mating and EF response. Membrane potential may regulate membrane charges through negatively charged phosphatidylserines (PSs), which act to position the Cdc42p-based polarity machinery. These studies thus define an electrochemical pathway that directs the orientation of cell polarization., Author Summary The ability of cells to orient towards spatial cues is critical for processes such as migration, wound healing, and development. Although the role of electrochemical signals is well characterized in processes such as neuronal signaling, their function in cell polarity is much less understood or appreciated. Application of exogenous electric fields can direct cell polarization in many cell types, and electric fields of similar magnitude surround cells and tissues naturally. However, the significance and mechanism of these responses remain poorly understood. Here, we introduce budding yeast (Saccharomyces cerevisiae) as a powerful model system to study electrochemical regulation of cell polarity. We show that application of electric fields causes budding yeast to polarize in particular directions. We begin to identify key proteins involved in this response, which implicate an electrochemical pathway involving membrane potential, membrane charge, and an ion channel, which ultimately regulate the central polarity factor Cdc42p. These key proteins are not only needed for response to electric fields, but also contribute to cell polarity more generally. To test whether a change in membrane potential is sufficient to control cell polarization, we introduce a light-sensitive ion channel into yeast and show that we can now control the site of polarization simply by using a focused laser beam. Thus, our study shows that electrochemical regulation is an integral component of cell polarity pathways.

The most important contribution to nonresonant vibrational nonlinear optical properties arises from nuclear relaxation (NR). In previous work a set of static field-induced vibrational coordinates (FICs) has been developed to simplify calculation of the NR contribution within the infinite optical frequency approximation. Although the number of FICs is small and independent of molecular size, these coordinates form a complete set. However, the infinite optical frequency approximation does not take into account the frequency dispersion, which we evaluate for three conjugated organic molecules that span a range of polarity and valence-bond/charge transfer characteristics. Our results show that dispersion can be significant and that, in such cases, frequency-dependent FICs (FD-FICs) are necessary for an adequate treatment. A complete, though still small, set of FD-FICs is presented for this purpose. Computational tests reveal that a reduced subset, together with an harmonic approximation, can be used to achieve high accuracy outside the infrared (IR) region. That subset is complete for the electro-optic and Pockels and Kerr effects though not for other common properties.

In the finite field (FF) treatment of vibrational polarizabilities and hyperpolarizabilities, the field-free Eckart conditions must be enforced in order to prevent molecular reorientation during geometry optimization. These conditions are implemented for the first time. Our procedure facilities identification of field-induced internal coordinates that make the major contribution to the vibrational properties. Using only two of these coordinates, quantitative accuracy for nuclear relaxation polarizabilities and hyperpolarizabilities is achieved in π-conjugated systems. From these two coordinates a single most efficient natural conjugation coordinate (NCC) can be extracted. The limitations of this one coordinate approach are discussed. It is shown that the Eckart conditions can lead to an isotope effect that is comparable to the isotope effect on zero-point vibrational averaging, but with a different mass-dependence.

Compact expressions, complete through second order in electrical and/or mechanical anharmonicity, are given for the dynamic dipole vibrational polarizability and dynamic first and second vibrational hyperpolarizabilities. Certain contributions not previously formulated are now included.

In this study we report on the electronic and vibrational (hyper)polarizabilities of donor–acceptorsubstituted azobenzene. It is observed that both electronic and vibrational contributions to the electric dipole first hyperpolarizability of investigated photoactive molecule substantially depend on the conformation. The contributions to the nuclear relaxation first hyperpolarizability are found to be quite important in the case of two considered isomers (cis and trans). Although the double-harmonic term is found to be the largest in terms of magnitude, it is shown that the total value of the nuclear relaxation contribution to vibrational first hyperpolarizability is a result of subtle interplay of higher-order contributions. As a part of the study, we also assess the performance of long-range-corrected density functional theory in determining vibrational contributions to electric dipole (hyper)polarizabilities. In most cases, the applied long-range-corrected exchange correlation potentials amend the drawbacks of their conventional counterparts

The overvoltage that is produced in the cells under operation limits the capacity and power they can deliver. A detailed study about the mechanisms that contribute to that overvoltage—and thus to their lifetime—is required for optimizing the use of batteries as well as their manufacturing process. We investigate galvanostatic discharge at low and moderate rates in an LCO-NMC/graphite cell in order to quantify the ohmic voltage drop and activation and concentration polarizations. For doing so, we compare half-cells to full cell overvoltages. We find that the ohmic drop and concentration polarization dominate at high rates and low rates, respectively. Moreover, we track the evolution of concentration polarization with State-of-Charge (SoC) and we observe that there exists a relationship between diffusion and phase transformations. Specifically, we validate experimentally that initial stages of a phase formation are not dominated by diffusion. Phase transitions are commonly evaluated by incremental capacity analysis. However, we determine that it is more appropriate to obtain that information from the full cells by the overvoltage analysis. Furthermore, we suggest that the working SoC range can be optimized from the overvoltage analysis by avoiding the particular SoCs at which the most detrimental phase transitions take place.

A theoretical model was implemented to obtain the total specular reflection of a variable external multicavity for out of normal incidence and different polarisations. The model was theoretically and experimentally validated and a further analysis was applied to the study of the stability of the SMI signal. It was found that out of normal incidence, or the use of different polarisations does not affect the quality of the signal in a relevant manner.

This thesis is a part of a project started in December 2016 in collaboration with Prof. Jorge Alcalá Cabrelles (UPC, Barcelona) and Dr. Jan Ocenasek (ZCU institute, Czech Republic) aiming to perform piezoelectric and flexoelectric studies in barium titanate by means of molecular dynamics simulations. The specific objective of this work is to gain expertise on molecular dynamics simulations of piezoelectric response, develop several analytical tools and characterize the basic thermodynamic and electric properties through a core-shell model of barium titanate fitted from first principle calculations. With the emergence of increasingly powerful and cheap supercomputing, atomistic simulations are quickly becoming a very attractive and reliable method for testing materials at the nanoscale and mesoscale. This thesis provides a literature review regarding the basics of molecular dynamics simulations performed to investigate dielectric properties of barium titanate, which is a key archetypal material used in sensors and memory storage devices as well as in the development of new supercapacitors. This work comprises a series of 13 simulations of barium titanate aimed to characterize the spontaneous polarization developing in the ferroelectric phases, study the effect of externally applied electric fields, build the temperature versus pressure phase diagram, estimate the piezoelectric coefficients of the tetragonal phase, calculate the hysteresis loops, identify ferroelectric switching and analyze the paraelectricity of the cubic phase. Furthermore, the limitations of simulating barium titanate using periodic boundary conditions are described and alternatives are given in the context of the investigation of flexoelectric response. Phonon dispersion is introduced as a key aspect to elucidate the underlying mechanisms in phase transformations. Finally, considerable amount of software has been developed to facilitate tracking, measuring and analysis of the physical properties in each simulation

We employ a classical, nonlinear Lorentz-Duffing oscillator model to predict third harmonic conversion efficiencies in the ultrafast regime, from a variety of metal nanostructures, including smooth, isolated metal layers, a metal-dielectric photonic band gap structure, and a metal grating. As expected, the plasmonic grating yields the largest narrow-band conversion efficiencies. However, interference phenomena at play within the multilayer stack yield comparable, broadband conversion. The method includes both linear and nonlinear material dispersions that in turn sensitively depend on linear oscillator parameters. Concurrently, and unlike other techniques, the integration scheme is numerically stable. By design, one thus avoids the introduction of explicit, third-order nonlinear coefficients and also takes into account linear and nonlinear material dispersions simultaneously, elements that are often necessary to fully understand many of the subtleties of the interaction of light with matter.

Medium-voltage cross-linked polyethylene (MV-XLPE) cables have an important role in the electrical power distribution system. For this reason, the study of XLPE insulation may lead to improve cable features and lifetime. Although relaxational analysis yield a lot of information about XLPE properties, sometimes their results are difficult to interpret. To overcome this handicap, we have used a combination of thermally stimulated depolarization currents (TSDC) and isothermal depolarization currents (IDC) techniques. In order to discard spurious effects from the semiconductor interfaces, preliminary measurements have been done on specially prepared cables. TSDC have been performed using conventional poling between 140°C and 40°C. IDC measurements also have been carried out at temperatures between 90°C and 110°C in 2°C steps. The TSDC spectra are dominated by a broad peak of uncertain origin. On the other hand, IDC show a combination of power and exponential currents. Exponential currents are fitted to a KWW model. The relaxation times obtained from the model present an Arrhenius behavior with Ea = 1.32 eV and τ0 = 3.29×10-16 s. The KWW parameter obtained is β = 0.8. The calculated depolarization current given by the exponential relaxation matches the predominant peak of TSDC spectra. Therefore, we conclude that in the MV cables studied the most visible peak of the TSDC spectrum has a dipolar origin.

This paper presents the results of a pioneering exploration of the physical origins of vibrational contributions to the interaction-induced electric properties of molecular complexes. In order to analyze the excess nuclear relaxation (hyper)polarizabilities, a new scheme was proposed which relies on the computationally efficient Bishop-Hasan-Kirtman method for determining the nuclear relaxation contributions to electric properties. The extension presented herein is general and can be used with any interaction-energy partitioning method. As an example, in this study we employed the variational-perturbational interaction-energy decomposition scheme (at the MP2/aug-cc-pVQZ level) and the extended transition state method by employing three exchange-correlation functionals (BLYP, LC-BLYP, and LC-BLYP-dDsC) to study the excess properties of the HCN dimer. It was observed that the first-order electrostatic contribution to the excess nuclear relaxation polarizability cancels with the negative exchange repulsion term out to a large extent, resulting in a positive value of Δαnr due to the contributions from the delocalization and the dispersion terms. In the case of the excess nuclear relaxation first hyperpolarizability, the pattern of interaction contributions is very similar to that for Δαnr, both in terms of their sign as well as relative magnitude. Finally, our results show that the LC-BLYP and LC-BLYP-dDsC functionals, which yield smaller values of the orbital relaxation term than BLYP, are more successful in predicting excess properties R. Z. gratefully acknowledges support from the National Science Centre, Poland (Grant No. 2015/19/B/ST4/01881). M. G.-B. and J. M. L. thank the Spanish Ministerio de Economía y competividad (MINECO, CTQ2014-52525-P) and the Generalitat de Catalunya project number 2014SGR931). M. M. acknowledges the financial support of the Slovak Research and Development Agency (project No. APVV-15-0105)

Semipermanently polarized hydroxyapatite, named SP/HAp(w), is obtained by applying a constant dc electric field of 1–10 kV/cm at 300–850 °C to the samples previously sintered in water vapor, while permanently polarized hydroxyapatite, PP/HAp(a), is produced by applying a dc electric field of 3 kV/cm at 1000 °C to the samples sintered in air. SP/HAp(w) has been used for biomedical applications, while PP/HAp(a) has been proved to be a valuable catalyst for N2 and CO2 fixation. In this work, structural differences between SP/HAp(w) and PP/HAp(a) have been ascertained using Raman microscopy, wide-angle X-ray diffraction, scanning electronic microscopy, high-resolution transmission electron microscopy, and grazing incidence X-ray diffraction. Results prove the existence of crystal distortion in the form of amorphous calcium phosphate and ß-tricalcium phosphate (ß-TCP) phases close to the surface because of the atmosphere used in the sintering process. The existence of an amorphous layer in the surface and the phase transition through ß-TCP of SP/HAp(w) are the structural factors responsible for the differences with respect to PP/HAp(a). Moreover, a superstructure has been identified in PP/HAp(a) samples, which could be another structural factor associated with enhanced conductivity, permanent polarization, and catalytic activity of this material