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3. Asteroseismology of solar-type stars with K2

Author

Chaplin, W. J., Lund, M. N., Handberg, R., Basu, S., Buchhave, L. A., Campante, T. L., Davies, G. R., Huber, D., Latham, D. W., Latham, C. A., Serenelli, A., Antia, H. M., Appourchaux, T., Ball, W. H., Benomar, O., Casagrande, L., Christensen-Dalsgaard, J., Coelho, H. R., Creevey, O. L., Elsworth, Y., Garc, R. A., Gaulme, P., Hekker, S., Kallinger, T., Karoff, C., Kawaler, S. D., Kjeldsen, H., Lundkvist, M. S., Marcadon, F., Mathur, S., Miglio, A., Mosser, B., R, C., Roxburgh, I. W., Aguirre, V. Silva, Stello, D., Verma, K., White, T. R., Bedding, T. R., Barclay, T., Buzasi, D. L., Deheuvels, S., Gizon, L., Houdek, G., Howell, S. B., Salabert, D., and Soderblom, D. R.

Subjects
Astrophysics - Solar and Stellar Astrophysics
Abstract

We present the first detections by the NASA K2 Mission of oscillations in solar-type stars, using short-cadence data collected during K2 Campaign\,1 (C1). We understand the asteroseismic detection thresholds for C1-like levels of photometric performance, and we can detect oscillations in subgiants having dominant oscillation frequencies around $1000\,\rm \mu Hz$. Changes to the operation of the fine-guidance sensors are expected to give significant improvements in the high-frequency performance from C3 onwards. A reduction in the excess high-frequency noise by a factor of two-and-a-half in amplitude would bring main-sequence stars with dominant oscillation frequencies as high as ${\simeq 2500}\,\rm \mu Hz$ into play as potential asteroseismic targets for K2., Comment: Accepted for publication in PASP; 16 pages, 2 figures

Published
2015
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4. The effect of dipole-dipole interactions between atoms in an active medium

Author

Berezovsky, V. V., Men'shikov, L. I., Oberg, S., and Latham, C. D.

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Other Condensed Matter
Abstract

Based on the results of numerical modeling, it is shown that dipole-dipole interactions among atoms in the active medium influences strongly the character of the associated superradiation. The main effect is to make the nuclear subsystem behave chaotically. Its strength increases with the atom density, and leads to the suppression of distant collective correlations and superradiation. Near correlations between the atoms are established, causing a confinement effect: a shielding of radiation in the active medium., Comment: 8 pages, 7 figures

Published
2007
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9. Conduction electron interactions in sodium and potassium studied by magnetic resonance techniques

Author

Latham, C. D., J E Cousins, and J R Sambles

Subjects
546, Sodium/potassium NMR studies
Abstract

Conduction electron interactions in sodium and potassium studied by magnetic resonance techniques Christopher D. Latham Department of Physics, Stocker Road, University of Exeter, EX4 4QL, UK. Abstract Pure sodium consists of a mixture of body centred cubic (BCC) and hexagonal close packed (HCP) crystals at low temperatures and these two phases exhibit subtly di?erent many body e?ects despite their almost identical conduction electron densities. This thesis represents a ?rst attempt to unravel the di?erences in the values of the many body parameters which characterize the description of the two phases in terms of the Fermi liquid theory. Fresh theoretical estimates of several many body parameters are presented and shortcomings in earlier theoretical work are highlighted. It has been found that the cause of these e?ects can be attributed to the di?erent and anisotropic phonon spectra in the two crystal phases. This has little e?ect on the lowest order many body parameters; the cyclotron e?ective masss, m * c, the paramagnetic susceptibility, ?p and the Landau-Silin Fermi liquid theory spin coe?cient, B0; but the second spin coe?cient B1 is very di?erent in the two crystal phases; it also seems likely that it is highly anisotropic. This di?erence leads to the observation of splittings in the microwave transmission spin wave spectra and di?erent spin wave coalescence angles for the two phases. Experimental results of measurements on sodium are presented. The conduction electron spin resonance (CESR), observed by the 35 GHz microwave transmission spectometer at Exeter, is split into two distinct lines which can be identi?ed with the two crystal phases present. A continuum region between the lines indicates that there is some averaging of electron spins among crystal grains or there may be some sodium present in an intermediate, faulted crystal phase in the samples. These observations con?rm the earlier work of Myler (1982), who used re?ection methods, and demonstrate with exceptional clarity, the presence of the two crystal phases. Analysis of the microwave transmission spectra, in various ?eld orientations, of spin waves, Gantmakher-Kaner oscillations, and cyclotron wave signals shows no observable di?er¬ences between the two phases of the quantities m * c, ?p and B0. The estimated values, con?rmed by spin wave measurements, of B1 are -0.01 ± 0.01 in BCC sodium and -0.05 ± 0.01 in HCP sodium at 5 K. The strong possibility of anisotropy in B1 may result in ambiguity in the values obtained from spin wave measurements depending on the details of the methods used to solve for the various quantities. For the ?rst time the microwave frequency size e?ect (MFSE) has been properly identi?ed and measured for potassium metal. This is the microwave frequency version of the radio frequency size e?ect but with the additional complication that the time of ?ight of the conduction electrons across the sample is comparable with the period of the microwaves. The electron orbits are identi?ed as being the symmetrical “type II” orbits, in the terminology of size e?ect studies. Unusually high quality spectra obtained during the early test work on the 35 GHz spectrometer enabled this study to be made. August 1987

Published
1987

11. The influence of structural characteristics on the electronic and thermal properties of GaN/AlN core/shell nanowires.

Author

Pavloudis, Th., Termentzidis, K., Komninou, Ph., Latham, C. D., Briddon, P. R., and Kioseoglou, J.

Subjects
INTERATOMIC distances, MOLECULAR dynamics, AB initio quantum chemistry methods, NANOWIRES, THERMAL analysis
Abstract

Interatomic potential based molecular dynamics and ab initio calculations are employed to investigate the structural, thermal, and electronic properties of polar GaN/AlN core/shell nanowires. Nanowire models for the molecular dynamics simulations contain hundreds of thousands of atoms with different shell-to-nanowire ratios. The energetic and structural properties are evaluated through a detailed examination of the strain, the stress, and the displacement fields. It is found that the relaxation of the AlN shell is initiated at the edges, with the shell becoming increasingly stress free when the shell-to-nanowire ratio is increased. The basal lattice parameter a of the AlN shell is found to have a smaller value than the value predicted by the elasticity theory. The stresses on the GaN core are strongly influenced by the shell. The core retains the a lattice parameter of bulk GaN only up to a shell-to-nanowire ratio equal to 0.10 and is significantly compressed beyond this point. Concerning the thermal properties, the molecular dynamics simulations conclude that there is a linear relationship between the thermal conductivity and the shell-to-core area ratio of the GaN/AlN core/shell nanowires. The bandgaps of the nanowires are calculated through ab initio calculations of 103 atoms and the influence of the structural characteristics on the electronic properties is investigated. A well-defined relationship that predicts the bandgap of the GaN/AlN nanowires, follows the 2nd order Vegard's law and taking into account the shell-to-nanowire ratio, is established. Finally, the valence band maximum is found to be dominated by the surface N-2p levels, while the conduction band minimum is dominated by the core and interface Ga-3s, and the surface Al-2s levels. [ABSTRACT FROM AUTHOR]

Published
2016
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12. Structural and electronic properties of GaN nanowires with embedded InxGa1-xN nanodisks.

Author

Kioseoglou, J., Pavloudis, Th., Kehagias, Th., Komninou, Ph., Karakostas, Th., Latham, C. D., Rayson, M. J., Briddon, P. R., and Eickhoff, M.

Subjects
ELECTRICAL conductivity measurement, ELECTRICAL conductors, QUANTUM electronics, NANOWIRE optical sensors, NANOSTRUCTURED materials
Abstract

In the present study, the effects of various types of strain and indium concentration on the total energy and optoelectronic properties of GaN nanowires (NWs) with embedded InxGa1-xN nanodisks (NDs) are examined. In particular, the bi-axial, hydrostatic, and uniaxial strain states of the embedded InxGa1-xN NDs are investigated for multiple In concentrations. Density functional theory is employed to calculate the band structure of the NWs. The theoretical analysis finds that the supercell-size-dependent characteristics calculated for our 972-atom NW models are very close to the infinite supercell-size limit. It is established that the embedded InxGa1-xN NDs do not induce deep states in the band gap of the NWs. A bowing parameter of 1.82?eV is derived from our analysis in the quadratic Vegard's formula for the band gaps at the various In concentrations of the investigated InxGa1-xN NDs in GaN NW structures. It is concluded that up to ~10% of In, the hydrostatic strain state is competitive with the bi-axial due to the radial absorption of the strain on the surfaces. Above this value, the dominant strain state is the bi-axial one. Thus, hydrostatic and bi-axial strain components coexist in the embedded NDs, and they are of different physical origin. The bi-axial strain comes from growth on lattice mismatched substrates, while the hydrostatic strain originates from the lateral relaxation of the surfaces. [ABSTRACT FROM AUTHOR]

Published
2015
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16. 43 Evaluation of Dietary Trace Mineral Source on Markers of Cartilage Metabolism in Weanling Horses Challenged with Lipopolysaccharide.

Author

Millican, A A, primary, Leatherwood, J L, additional, Coverdale, J A, additional, Arnold, C E, additional, Bradbery, A N, additional, Fikes, K, additional, Goehring, M S, additional, Dickson, E C, additional, Latham, C M, additional, Hartz, C J, additional, Paulk, C B, additional, Welsh, T H, additional, White, S H, additional, Larson, C K, additional, Lamprecht, E D, additional, and Wickersham, T A, additional

Published
2018
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19. Evaluation of dietary trace mineral source on growth in weanling horses

Author

Millican, A.A., primary, Coverdale, J.A., additional, Leatherwood, J.L., additional, Bradbery, A.N., additional, Goehring, M.S., additional, Fikes, K., additional, Dickson, E.C., additional, Latham, C., additional, Hartz, C.J., additional, White, S.H., additional, Larson, C.K., additional, Lamprecht, E., additional, and Wickersham, T.A., additional

Published
2017
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22. Asteroseismology of solar-type stars with K2:detection of oscillations in C1 Data

Author

Chaplin, W. J., Lund, M. N., Handberg, Rasmus, Basu, S., Buchhave, Lars A., Campante, T. L., Davies, G. R., Huber, D., Latham, D. W., Latham, C. A., Serenelli, A., Antia, H. M., Appourchaux, T., Ball, W. H., Benomar, O., Casagrande, L., Christensen-Dalsgaard, J., Coelho, H. R., Creevey, O. L., Elsworth, Y., García, R. A., Gaulme, P., Hekker, S., Kallinger, T., Karoff, C., Kawaler, S. D., Kjeldsen, H., Lundkvist, M. S., Marcadon, F., Mathur, S., Miglio, A., Mosser, B., Régulo, C., Roxburgh, I. W., Aguirre, V. Silva, Stello, D., Verma, K., White, T. R., Bedding, T. R., Barclay, T., Buzasi, D. L., Dehuevels, S., Gizon, L., Houdek, G., Howell, S. B., Salabert, D., Soderblom, D. R., Chaplin, W. J., Lund, M. N., Handberg, Rasmus, Basu, S., Buchhave, Lars A., Campante, T. L., Davies, G. R., Huber, D., Latham, D. W., Latham, C. A., Serenelli, A., Antia, H. M., Appourchaux, T., Ball, W. H., Benomar, O., Casagrande, L., Christensen-Dalsgaard, J., Coelho, H. R., Creevey, O. L., Elsworth, Y., García, R. A., Gaulme, P., Hekker, S., Kallinger, T., Karoff, C., Kawaler, S. D., Kjeldsen, H., Lundkvist, M. S., Marcadon, F., Mathur, S., Miglio, A., Mosser, B., Régulo, C., Roxburgh, I. W., Aguirre, V. Silva, Stello, D., Verma, K., White, T. R., Bedding, T. R., Barclay, T., Buzasi, D. L., Dehuevels, S., Gizon, L., Houdek, G., Howell, S. B., Salabert, D., and Soderblom, D. R.

Published
2015

23. Antimicrobial and immune modulatory effects of lactic acid and short chain fatty acids produced by vaginal microbiota associated with eubiosis and bacterial vaginosis

Author

Aldunate, M., Srbinovski, D., Hearps, A., Latham, C., Ramsland, Paul, Gugasyan, R., Cone, R., Tachedjian, G., Aldunate, M., Srbinovski, D., Hearps, A., Latham, C., Ramsland, Paul, Gugasyan, R., Cone, R., and Tachedjian, G.

Abstract

Lactic acid and short chain fatty acids (SCFAs) produced by vaginal microbiota have reported antimicrobial and immune modulatory activities indicating their potential as biomarkers of disease and/or disease susceptibility. In asymptomatic women of reproductive-age the vaginal microbiota is comprised of lactic acid-producing bacteria that are primarily responsible for the production of lactic acid present at ~110 mM and acidifying the vaginal milieu to pH ~3.5. In contrast, bacterial vaginosis (BV), a dysbiosis of the vaginal microbiota, is characterized by decreased lactic acid-producing microbiota and increased diverse anaerobic bacteria accompanied by an elevated pH>4.5. BV is also characterized by a dramatic loss of lactic acid and greater concentrations of mixed SCFAs including acetate, propionate, butyrate, and succinate. Notably women with lactic acid-producing microbiota have more favorable reproductive and sexual health outcomes compared to women with BV.Regarding the latter, BV is associated with increased susceptibility to sexually transmitted infections (STIs) including HIV. In vitro studies demonstrate that lactic acid produced by vaginal microbiota has microbicidal and virucidal activities that may protect against STIs and endogenous opportunistic bacteria as well as immune modulatory properties that require further characterization with regard to their effects on the vaginal mucosa. In contrast, BV-associated SCFAs have far less antimicrobial activity with the potential to contribute to a pro-inflammatory vaginal environment. Here we review the composition of lactic acid and SCFAs in respective states of eubiosis (non-BV) or dysbiosis (BV), their effects on susceptibility to bacterial/viral STIs and whether they have inherent microbicidal/virucidal and immune modulatory properties. We also explore their potential as biomarkers for the presence and/or increased susceptibility to STIs.

Published
2015

24. Asteroseismology of Solar-Type Stars withK2: Detection of Oscillations in C1 Data

Author

Chaplin, W. J., primary, Lund, M. N., additional, Handberg, R., additional, Basu, S., additional, Buchhave, L. A., additional, Campante, T. L., additional, Davies, G. R., additional, Huber, D., additional, Latham, D. W., additional, Latham, C. A., additional, Serenelli, A., additional, Antia, H. M., additional, Appourchaux, T., additional, Ball, W. H., additional, Benomar, O., additional, Casagrande, L., additional, Christensen-Dalsgaard, J., additional, Coelho, H. R., additional, Creevey, O. L., additional, Elsworth, Y., additional, García, R. A., additional, Gaulme, P., additional, Hekker, S., additional, Kallinger, T., additional, Karoff, C., additional, Kawaler, S. D., additional, Kjeldsen, H., additional, Lundkvist, M. S., additional, Marcadon, F., additional, Mathur, S., additional, Miglio, A., additional, Mosser, B., additional, Régulo, C., additional, Roxburgh, I. W., additional, Silva Aguirre, V., additional, Stello, D., additional, Verma, K., additional, White, T. R., additional, Bedding, T. R., additional, Barclay, T., additional, Buzasi, D. L., additional, Dehuevels, S., additional, Gizon, L., additional, Houdek, G., additional, Howell, S. B., additional, Salabert, D., additional, and Soderblom, D. R., additional

Published
2015
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27. Vacancy diffusion and coalescence in graphene directed by defect strain fields

Author

Trevethan, T, Latham, C, Heggie, MI, Briddon, PR, Rayson, MJ, Trevethan, T, Latham, C, Heggie, MI, Briddon, PR, and Rayson, MJ

Abstract

The formation of extended defects in graphene from the coalescence of individual mobile vacancies can significantly alter its mechanical, electrical and chemical properties. We present the results of ab initio simulations which demonstrate that the strain created by multi-vacancy complexes in graphene determine their overall growth morphology when formed from the coalescence of individual mobile lattice vacancies. Using density functional theory, we map out the potential energy surface for the motion of mono-vacancies in the vicinity of multi-vacancy defects. The inhomogeneous bond strain created by the multi-vacancy complexes strongly biases the activation energy barriers for single vacancy motion over a wide area. Kinetic Monte Carlo simulations based on rates from ab initio derived activation energies are performed to investigate the dynamical evolution of single vacancies in these strain fields. The resultant coalescence processes reveal that the dominant morphology of multi-vacancy complexes will consist of vacancy lines running in the two primary crystallographic directions, and that more thermodynamically stable structures, such as holes, are kinetically inaccessible from mono-vacancy aggregation alone.

Published
2014

31. Comment on “Increase in specific heat and possible hindered rotation of interstitial C2 moleculesin neutron-irradiated graphite”

Author

Latham, C., Haffenden, G., Heggie, M., Suarez-Martinez, Irene, Ewels, C., Latham, C., Haffenden, G., Heggie, M., Suarez-Martinez, Irene, and Ewels, C.

Abstract

Iwata and Watanabe’s model for the observed low-temperature specific heat of neutron-irradiated graphite [T. Iwata and M. Watanabe, Phys. Rev. B 81, 014105 2010] assumes that self-interstitial atoms exist as clusters of nearly free C2 molecules. We suggest that their hypothesis is not supported by other experiments and theory, including our own calculations. Not only is it inconsistent with the long-known kinetics of interstitial prismatic dislocation loop formation, density-functional theory shows that the di-interstitial is covalently bonded to the host crystal. In such calculations no prior assumptions are made about the nature of the bonding, covalent or otherwise.

Published
2010

32. To be fair, no one promised 10GBase-T would work on Category 6

Author

Latham, C. Donald, Jr.

Subjects
Computers -- Management, Ethernet -- Service introduction, Microcomputers -- Analysis, Ethernet, Company business management, Company service introduction, Business, Electronics and electrical industries, Mass communications
Abstract

If a desktop computer had the capability to transmit data at 10 Gigabits per second, one could transfer an entire DVD movie in 30 seconds--a movie that otherwise would require [...]

Published
2006

33. The di-interstitial in graphite

Author

Latham, C., Heggie, M., Gamez, J., Suarez-Martinez, Irene, Ewels, C., Briddon, P., Latham, C., Heggie, M., Gamez, J., Suarez-Martinez, Irene, Ewels, C., and Briddon, P.

Published
2008

40. The di-interstitial in graphite

Author

Latham, C D, primary, Heggie, M I, additional, Gámez, J A, additional, Suárez-Martínez, I, additional, Ewels, C P, additional, and Briddon, P R, additional

Published
2008
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43. Asteroseismology of Solar-Type Stars with K2: Detection of Oscillations in C1 Data.

Author

CHAPLIN, W. J., LUND, M. N., HANDBERG, R., BASU, S., BUCHHAVE, L. A., CAMPANTE, T. L., DAVIES, G. R., HUBER, D., LATHAM, D. W., LATHAM, C. A., SERENELLI, A., ANTIA, H. M., APPOURCHAUX, T., BALL, W. H., BENOMAR, O., CASAGRANDE, L., CHRISTENSEN-DALSGAARD, J., COELHO, H. R., CREEVEY, O. L., and ELSWORTH, Y.

Subjects
SPACE flight, SOLAR oscillations, PHOTOMETRY, DETECTORS
Abstract

We present the first detections by the NASA K2 mission of oscillations in solar-type stars, using short-cadence data collected during K2 Campaign 1 (C1). We understand the asteroseismic detection thresholds for C1-like levels of photometric performance, and we can detect oscillations in subgiants having dominant oscillation frequencies around 1000 μHz. Changes to the operation of the fine-guidance sensors are expected to give significant improvements in the high-frequency performance from C3 onwards. A reduction in the excess high-frequency noise by a factor of 2.5 in amplitude would bring main-sequence stars with dominant oscillation frequencies as high as ≃2500 μHz into play as potential asteroseismic targets for K2. [ABSTRACT FROM AUTHOR]

Published
2015
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48. International Standards 101

Author

Bjorkman, S., primary, Bjorkman, J., additional, Penrose, H.W., additional, O'Brien, D., additional, Bjorkman, M., additional, and Latham, C., additional

Published
2003
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