4,169 research outputs found
Magnetic phase diagram and transport properties of FeGe_2
We have used resistivity measurements to study the magnetic phase diagram of
the itinerant antiferromagnet FeGe_2 in the temperature range from 0.3->300 K
in magnetic fields up to 16 T. In contrast to theoretical predictions, the
incommensurate spin density wave phase is found to be stable at least up to 16
T, with an estimated critical field \mu _0H_c of ~ 30 T. We have also studied
the low temperature magnetoresistance in the [100], [110], and [001]
directions. The transverse magnetoresistance is well described by a power law
for magnetic fields above 1 T with no saturation observed at high fields. We
discuss our results in terms of the magnetic structure and the calculated
electronic bandstructure of FeGe_2. We have also observed, for the first time
in this compound, Shubnikov-de Haas oscillations in the transverse
magnetoresistance with a frequency of 190 +- 10 T for a magnetic field along
[001].Comment: 13 pages, RevTeX, 7 postscript figures, to appear in Journal of
Physics: Condensed Matte
Risk factors for feline infectious peritonitis in Australian cats
Objective: To determine whether patient signalment (age, breed, sex, and neuter status) are associated with naturally occurring feline infectious peritonitis (FIP) in cats in Australia. Design: A retrospective comparison of the signalment between cats with confirmed FIP and the general cat population. Results: The patient signalment of 382 FIP confirmed cases were compared with the Companion Animal Register of NSW and the general cat population of Sydney. Younger cats were significantly over-represented amongst FIP cases. Domestic crossbred, Persian, and Himalayan cats were significantly under-represented in the FIP cohort while several breeds were over-represented including British Shorthair, Devon Rex, and Abyssinian. A significantly higher proportion of male cats had FIP compared to female cats. Conclusion: This study provides further evidence that FIP is primarily a disease of young cats and that significant breed and sex predilections exist in Australia. This opens further avenues to investigate the role of genetic factors in FIP
Risk factors for feline infectious peritonitis in Australian cats
Objective: To determine whether patient signalment (age, breed, sex, and neuter status) are associated with naturally occurring feline infectious peritonitis (FIP) in cats in Australia.
Design: A retrospective comparison of the signalment between cats with confirmed FIP and the general cat population.
Results: The patient signalment of 382 FIP confirmed cases were compared with the Companion Animal Register of NSW and the general cat population of Sydney. Younger cats were significantly over-represented amongst FIP cases. Domestic crossbred, Persian, and Himalayan cats were significantly under-represented in the FIP cohort while several breeds were over-represented including British Shorthair, Devon Rex, and Abyssinian. A significantly higher proportion of male cats had FIP compared to female cats.
Conclusion: This study provides further evidence that FIP is primarily a disease of young cats and that significant breed and sex predilections exist in Australia. This opens further avenues to investigate the role of genetic factors in FIP
DeWitt-Schwinger Renormalization and Vacuum Polarization in d Dimensions
Calculation of the vacuum polarization, , has seen a recent resurgence, notably
for black hole spacetimes. To date, most calculations of this type have been
done only in four dimensions. Extending these calculations to dimensions
includes -dimensional renormalization. Typically, the renormalizing terms
are found from Christensen's covariant point splitting method for the
DeWitt-Schwinger expansion. However, some manipulation is required to put the
correct terms into a form that is compatible with problems of the vacuum
polarization type. Here, after a review of the current state of affairs for
calculations and a thorough introduction to
the method of calculating and for certain spacetimes is discussed, with application to four and
five dimensions.Comment: 21 pages, 2 tables, 3 figures. References added, rewritten to clarify
some points, corrections performed, our claim in the first version that there
is an error in Anderson's calculations is incorrec
Three-dimensional flux states as a model for the pseudogap phase of transition metal oxides
We propose that the pseudogap state observed in the transition metal oxides
can be explained by a three-dimensional flux state, which exhibits
spontaneously generated currents in its ground state due to electron-electron
correlations. We compare the energy of the flux state to other classes of mean
field states, and find that it is stabilized over a wide range of and
. The signature of the state will be peaks in the neutron diffraction
spectra, the location and intensity of which are presented. The dependence of
the pseudogap in the optical conductivity is calculated based on the parameters
in the model.Comment: submitted to Phys. Rev. B on January 8, 200
Impurity-induced transition and impurity-enhanced thermopower in the thermoelectric oxide NaCo_{2-x}Cu_x$O_4
Various physical quantities are measured and analysed for the Cu-substituted
thermoelectric oxide NaCo_{2-x}Cu_xO_4. As was previously known, the
substituted Cu enhances the thermoelectric power, while it does not increase
the resistivity significantly. The susceptibility and the electron
specific-heat are substantially decreased with increasing x, which implies that
the substituted Cu decreases the effective-mass enhancement. Through a
quantitative comparison with the heavy fermion compounds and the valence
fluctuation systems, we have found that the Cu substitution effectively
increases the coupling between the conduction electron and the magnetic
fluctuation. The Cu substitution induces a phase transition at 22 K that is
very similar to a spin-density-wave transition.Comment: 8 pages, 7 figures, submitted to Phys. Rev.
Enhancement of the electronic contribution to the low temperature specific heat of Fe/Cr magnetic multilayer
We measured the low temperature specific heat of a sputtered
magnetic multilayer, as well as separate
thick Fe and Cr films. Magnetoresistance and magnetization
measurements on the multilayer demonstrated antiparallel coupling between the
Fe layers. Using microcalorimeters made in our group, we measured the specific
heat for and in magnetic fields up to for the multilayer. The
low temperature electronic specific heat coefficient of the multilayer in the
temperature range is . This is
significantly larger than that measured for the Fe or Cr films (5.4 and respectively). No magnetic field dependence of was
observed up to . These results can be explained by a softening of the
phonon modes observed in the same data and the presence of an Fe-Cr alloy phase
at the interfaces.Comment: 20 pages, 5 figure
The influence of surface stress on the equilibrium shape of strained quantum dots
The equilibrium shapes of InAs quantum dots (i.e., dislocation-free, strained
islands with sizes >= 10,000 atoms) grown on a GaAs (001) substrate are studied
using a hybrid approach which combines density functional theory (DFT)
calculations of microscopic parameters, surface energies, and surface stresses
with elasticity theory for the long-range strain fields and strain relaxations.
In particular we report DFT calculations of the surface stresses and analyze
the influence of the strain on the surface energies of the various facets of
the quantum dot. The surface stresses have been neglected in previous studies.
Furthermore, the influence of edge energies on the island shapes is briefly
discussed. From the knowledge of the equilibrium shape of these islands, we
address the question whether experimentally observed quantum dots correspond to
thermal equilibrium structures or if they are a result of the growth kinetics.Comment: 7 pages, 8 figures, submitted to Phys. Rev. B (February 2, 1998).
Other related publications can be found at
http://www.rz-berlin.mpg.de/th/paper.htm
Automated underwriting in life insurance: Predictions and optimisation
© Springer International Publishing AG, part of Springer Nature 2018. Underwriting is an important stage in the life insurance process and is concerned with accepting individuals into an insurance fund and on what terms. It is a tedious and labour-intensive process for both the applicant and the underwriting team. An applicant must fill out a large survey containing thousands of questions about their life. The underwriting team must then process this application and assess the risks posed by the applicant and offer them insurance products as a result. Our work implements and evaluates classical data mining techniques to help automate some aspects of the process to ease the burden on the underwriting team as well as optimise the survey to improve the applicant experience. Logistic Regression, XGBoost and Recursive Feature Elimination are proposed as techniques for the prediction of underwriting outcomes. We conduct experiments on a dataset provided by a leading Australian life insurer and show that our early-stage results are promising and serve as a foundation for further work in this space
Magnetic phase diagram of cubic perovskites SrMn_1-xFe_xO_3
We combine the results of magnetic and transport measurements with Mossbauer
spectroscopy and room-temperature diffraction data to construct the magnetic
phase diagram of the new family of cubic perovskite manganites SrMn_1-xFe_xO_3.
We have found antiferromagnetic ordering for lightly and heavily Fe-substituted
material, while intermediate substitution leads to spin-glass behavior. Near
the SrMn_0.5Fe_0.5O_3 composition these two types of ordering are found to
coexist and affect one another. The spin glass behavior may be caused by
competing ferro- and antiferromagnetic interactions among Mn^4+ and observed
Fe^3+ and Fe^5+ ions.Comment: 8 pages, 10 figures, revtex, accepted to Phys. Rev.
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