726 research outputs found
Subaerial bone weathering and other taphonomic changes in a temperate climate
Thesis (M.S.)--Boston UniversityDetermining the postmortem interval in forensic cases becomes problematic at advanced stages when the decomposition of soft tissue ceases (generally less than six months) and radiocarbon dating cannot be applied (prior to AD 1950). Further research into bone weathering rates and patterns can aid in filling this large postmortem interval gap. Similar to soft tissue decomposition studies, the rate at which osseous weathering occurs needs to be studied regionally due to the significant effects of temperature fluctuations, sun exposure, and precipitation. This study investigates bone weathering rates and other taphonomic changes in New England. Other taphonomic changes that were investigated include carnivore scavenging patterns and tooth marks, rodent gnawing, and sources of color staining. The first part of this research was carried out in the White Mountain National Forest, NH on a sample of whole-carcass moose (Alces alces) deposited throughout the year due to vehicle collisions. Observations were made monthly and took place from December 2011 through October 2012. The second part of this research was conducted at the Boston University Outdoor Research Facility (ORF) in Holliston, MA on a sample of white-tailed deer (Odocoileus virginianus) long bones that were placed in three different microhabitats (grassland, wetland margin, and forest).
Field observations took place from February 2012 through February 2013. The hypotheses being tested were that the rate of weathering is dependent on seasonality and that it will vary among different regions and between various microhabitats. In both the White Mountain National Forest, NH and Holliston ORF, weathering stage 1 was first observed five months after deposition. Advancement in weathering was greatest during the Fall and Spring months when temperature fluctuations above and below freezing occurred most frequently. At this time, the results from Holliston ORF indicate that microhabitat is not a statistically significant factor of osseous weathering when examined 50 weeks after deposition ( p=0.53). However, longer term data collection is needed in order to gather more meaningful information. Due to the short nature of this study in relation to weathering, this research will serve as a preliminary investigation and is intended to be carried out through the coming years
Specific heat of MgB_2 after irradiation
We studied the effect of disorder on the superconducting properties of
polycrystalline MgB_2 by specific-heat measurements. In the pristine state,
these measurements give a bulk confirmation of the presence of two
superconducting gaps with 2 Delta 0 / k_B T_c = 1.3 and 3.9 with nearly equal
weights. The scattering introduced by irradiation suppresses T_c and tends to
average the two gaps although less than predicted by theory. We also found that
by a suitable irradiation process by fast neutrons, a substantial bulk increase
of dH_{c2}/dT at T_c can be obtained without sacrificing more than a few
degrees in T_c. The upper critical field of the sample after irradiation
exceeds 28 T at T goes to 0 K.Comment: 11 pages text, 6 figures, accepted by Journal of Physics: Condensed
Matte
Inequivalent representations of commutator or anticommutator rings of field operators and their applications
Hamiltonian of a system in quantum field theory can give rise to infinitely
many partition functions which correspond to infinitely many inequivalent
representations of the canonical commutator or anticommutator rings of field
operators. This implies that the system can theoretically exist in infinitely
many Gibbs states. The system resides in the Gibbs state which corresponds to
its minimal Helmholtz free energy at a given range of the thermodynamic
variables. Individual inequivalent representations are associated with
different thermodynamic phases of the system. The BCS Hamiltonian of
superconductivity is chosen to be an explicit example for the demonstration of
the important role of inequivalent representations in practical applications.
Its analysis from the inequivalent representations' point of view has led to a
recognition of a novel type of the superconducting phase transition.Comment: 25 pages, 6 figure
Specific heat of single crystal MgB_2: a two-band superconductor with two different anisotropies
Heat-capacity measurements of a 39 microgramm MgB_2 single crystal in fields
up to 14 T and below 3 K allow the determination of the low-temperature linear
term of the specific heat, its field dependence and its anisotropy. Our results
are compatible with two-band superconductivity, the band carrying the small gap
being isotropic, that carrying the large gap having an anisotropy of ~ 5. Three
different upper critical fields are thus needed to describe the superconducting
state of MgB2.Comment: 4 pages, 4 figures - V2: Bibliography updated and some typo
corrected. One reference added - V3: version accepted for publication in PRL,
changes made in the tex
Specific heat of heavy fermion CePd2Si2 in high magnetic fields
We report specific heat measurements on the heavy fermion compound CePd2Si2
in magnetic fields up to 16 T and in the temperature range 1.4-16 K. A sharp
peak in the specific heat signals the antiferromagnetic transition at T_N ~ 9.3
K in zero field. The transition is found to shift to lower temperatures when a
magnetic field is applied along the crystallographic a-axis, while a field
applied parallel to the tetragonal c-axis does not affect the transition. The
magnetic contribution to the specific heat below T_N is well described by a sum
of a linear electronic term and an antiferromagnetic spin wave contribution.
Just below T_N, an additional positive curvature, especially at high fields,
arises most probably due to thermal fluctuations. The field dependence of the
coefficient of the low temperature linear term, gamma_0, extracted from the
fits shows a maximum at about 6 T, at the point where an anomaly was detected
in susceptibility measurements. The relative field dependence of both T_N and
the magnetic entropy at T_N scales as [1-(B/B_0)^2] for B // a, suggesting the
disappearance of antiferromagnetism at B_0 ~ 42 T. The expected suppression of
the antiferromagnetic transition temperature to zero makes the existence of a
magnetic quantum critical point possible.Comment: to be published in Journal of Physics: Condensed Matte
Observation of Magnetic Flux Generated Spontaneously During a Rapid Quench of Superconducting Films
We report observations of spontaneous formation of magnetic flux lines during
a rapid quench of YBaCuO films through T. This
effect is predicted according to the Kibble-Zurek mechanism of creation of
topological defects of the order parameter during a symmetry-breaking phase
transition. Our previous experiment, at a quench rate of 20K/sec, gave null
results. In the present experiment, the quench rate was increased to
\TEXTsymbol{>} 10 K/sec. Within experimental resolution, the dependence
of the measured flux on the cooling rate is consistent with the prediction
Superconducting Diamagnetic Fluctuations in MgB2
The fluctuating diamagnetic magnetization Mfl at constant field H as a
function of temperature and the isothermal magnetization Mfl vs H are measured
in MgB2, above the superconducting transition temperature. The expressions for
Mfl in randomly oriented powders are derived in the Gaussian approximation of
local Ginzburg-Landau theory and used for the analysis of the data. The scaled
magnetization Mfl/H^{1/2}*T is found to be field dependent. In the limit of
evanescent field the behaviour for Gaussian fluctuations is obeyed while for
H>~ 100 Oe the field tends to suppress the fluctuating pairs, with a field
dependence of Mfl close to the one expected when short wavelength fluctuations
and non-local electrodynamic effects are taken into account. Our data, besides
providing the isothermal magnetization curves for T>Tc(0) in a BCS-type
superconductor such as MgB2, evidence an enhancement of the fluctuating
diamagnetism which is related to the occurrence in this new superconductor of
an anisotropic spectrum of the superconducting fluctuations.Comment: Tex file, 4 pages, 3 ps figures, submitted to Phys. Rev. Let
La santé des aînés : portrait de la santé et de ses déterminants sociaux en ville de Lausanne
L'influence du vieillissement démographique se ressent dans divers secteurs de la société. Le financement des assurances sociales, l'organisation des soins et l'accueil destiné aux aînés doivent être repensés. Une récente analyse de l'Office fédéral de la statistique suggère que l'on vieillit en meilleure santé, avec une meilleure qualité de vie que par le passé. La mise en place de programmes pour un vieillissement en bonne santé s'impose en même temps qu'évolue notre système de santé. Les données actuelles décrivant la population des Lausannois de 65 ans et plus (la cohorte Lc65+) nous invitent à réfléchir à la question. Le présent document est le premier de trois rapports qui présenteront les données de la cohorte Lc65+. Il se fonde principalement sur les informations recueillies durant les années 2010 et 2011, et présentera avant tout les problèmes de santé d'une population âgée entre 68 et 77 ans. Les aspects de la santé seront mis en perspective avec des facteurs sociaux structurels, les déterminants sociaux de la santé. Le rapport se divise en deux parties. La première donne un aperçu de l'état de santé dans la population des seniors domiciliés à Lausanne; les fréquences relatives à chaque indicateur ont été calculées et les résultats présentés sous forme de graphiques ou tableaux. La seconde partie s'attache à évaluer le lien entre les variables de santé et les facteurs socio-économiques. La significativité statistique de l'association (brute, puis ajustée sur le sexe et le groupe d'âge) entre les facteurs socio-économiques et les variables de santé a été testée par des tests du" chi" d'indépendance
Critical dynamics, duality, and the exact dynamic exponent in extreme type II superconductors
The critical dynamics of superconductors is studied using renormalization
group and duality arguments. We show that in extreme type II superconductors
the dynamic critical exponent is given exactly by . This result does not
rely on the widely used models of critical dynamics. Instead, it is shown that
follows from the duality between the extreme type II superconductor and
a model with a critically fluctuating gauge field. Our result is in agreement
with Monte Carlo simulations.Comment: 7 pages, no figures; version accepted for publication in PR
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