239 research outputs found
The dielectric constant of PbTe at 4.2 K and =84.15 cm, 96.97 cm, 103.60 cm
The dielectric constant of a PbTe epitaxial layer has been measured by surface wave spectroscopy using an optically pumped far-infrared laser and the technique of attenuated total reflection
New Electronic Phase Transitions in \alpha-(BEDT-TTF)2KHg(SCN)4
\alpha-(BEDT-TTF)2KHg(SCN)4 is considered to be in the charge-density-wave
(CDW) state below 8 K. We present new magnetoresistance data suggesting that
the material undergoes a series of field-induced CDW (FICDW) transitions at
pressures slightly exceeding the critical pressure Pc at which the zero-field
CDW state is destroyed. Further, we argue that a novel kind of FICDW
transitions, entirely determined by a superposition of the strong Pauli and
quantizing orbital effects of magnetic field on the CDW wavevector, arises when
the field is strongly tilted towards the conducting layers. These new
transitions can take place even in the case of a relatively well nested Fermi
surface. Finally we report on the superconducting (SC) state and its
coexistence with the CDW in the title compound under quasi-hydrostatic
pressure. Below Pc the material is most likely a heterogeneous SC/CDW mixture,
with the SC phase persisting down to ambient pressure. The SC onset temperature
appears to drastically increase upon entering the SC/CDW coexistence region.Comment: 7 pages, 6 figures; invited talk at ISCOM'2003, 21-26.09.2003, Port
Bourgenay, France to be published in J. Phys. IV Franc
Magnetoresistance of UPt3
We have performed measurements of the temperature dependence of the
magnetoresistance up to 9 T in bulk single crystals of UPt3 with the magnetic
field along the b axis, the easy magnetization axis. We have confirmed previous
results for transverse magnetoresistance with the current along the c axis, and
report measurements of the longitudinal magnetoresistance with the current
along the b axis. The presence of a linear term in both cases indicates broken
orientational symmetry associated with magnetic order. With the current along
the c axis the linear term appears near 5 K, increasing rapidly with decreasing
temperature. For current along the b axis the linear contribution is negative.Comment: 6 pages, 3 figures, submitted to Quantum Fluids and Solids Conference
(QFS 2006
Fundamental parameter-free solutions in Modified Gravity
Modified Gravity (MOG) has been used successfully to explain the rotation
curves of galaxies, the motion of galaxy clusters, the Bullet Cluster, and
cosmological observations without the use of dark matter or Einstein's
cosmological constant. We now have the ability to demonstrate how these
solutions can be obtained directly from the action principle, without resorting
to the use of fitted parameters or empirical formulae. We obtain numerical
solutions to the theory's field equations that are exact in the sense that no
terms are omitted, in two important cases: the spherically symmetric, static
vacuum solution and the cosmological case of an homogeneous, isotropic
universe. We compare these results to selected astrophysical and cosmological
observations.Comment: 11 pages, 8 figures; accepted for publication in CQ
Effect of Pressure on Tiny Antiferromagnetic Moment in the Heavy-Electron Compound URu_2Si_2
We have performed elastic neutron-scattering experiments on the
heavy-electron compound URu_2Si_2 for pressure P up to 2.8 GPa. We have found
that the antiferrmagnetic (100) Bragg reflection below T_m ~ 17.5 K is strongly
enhanced by applying pressure. For P < 1.1 GPa, the staggered moment mu_o at
1.4 K increases linearly from ~ 0.017(3) mu_B to ~ 0.25(2) mu_B, while T_m
increases slightly at a rate ~ 1 K/GPa, roughly following the transition
temperature T_o determined from macroscopic anomalies. We have also observed a
sharp phase transition at P_c ~ 1.5 GPa, above which a 3D-Ising type of
antiferromagnetic phase (mu_o ~ 0.4 mu_B) appears with a slightly reduced
lattice constant.Comment: RevTeX, 4 pages, 4 eps figures, accepted for publication in Phys.
Rev. Let
Superconductivity in the charge-density-wave state of the organic metal \alpha-(BEDT-TTF)2KHg(SCN)4
The superconducting transition in the layered organic compound
\alpha-(BEDT-TTF)_2KHg(SCN)_4 has been studied in the two hydrostatic pressure
regimes where a charge-density wave is either present or completely suppressed.
Within the charge-density-wave state the experimental results reveal a network
of weakly coupled superconducting regions. This is especially seen in a strong
enhancement of the measured critical field and the corresponding positive
curvature of its temperature dependence. Further, it is shown that on lowering
the pressure into the density-wave state traces of a superconducting phase
already start to appear at a much higher temperature.Comment: 8 pages, 9 figures, Phys. Rev. B, in pres
Low Temperature Properties of Anisotropic Superconductors with Kondo Impurities
We present a self-consistent theory of superconductors in the presence of
Kondo impurities, using large- slave-boson methods to treat the impurity
dynamics. The technique is tested on the s-wave case and shown to give good
results compared to other methods for . We calculate low temperature
thermodynamic and transport properties for various superconducting states,
including isotropic s-wave and representative anisotropic model states with
line and point nodes on the Fermi surface.Comment: 21 pages, RevTeX 3.0, 12 figures available upon request, UF preprin
Genetic selection for bovine chromosome 18 haplotypes associated with divergent somatic cell score affects postpartum reproductive and metabolic performance
The susceptibility of animals to periparturient diseases has a great effect on the economic efficiency of dairy industries, on the frequency of antibiotic treatment, and on animal welfare. The use of selection for breeding cows with reduced susceptibility to diseases offers a sustainable tool to improve dairy cattle farming. Several studies have focused on the association of distinct bovine chromosome 18 genotypes or haplotypes with performance traits. The aim of this study was to test whether selection of Holstein Friesian heifers via SNP genotyping for alternative paternal chromosome 18 haplotypes associated with favorable (Q) or unfavorable (q) somatic cell scores influences postpartum reproductive and metabolic diseases. Thirty-six heifers (18 Q and 18 q) were monitored from 3 wk before calving until necropsy on d 39 (± 4 d) after calving. Health status and rectal temperature were measured daily, and body condition score and body weight were assessed once per week. Blood samples were drawn twice weekly, and levels of insulin, nonesterified fatty acids, insulin-like growth factor-I, growth hormone, and β-hydroxybutyrate were measured. Comparisons between the groups were performed using Fisher's exact test, chi-squared test, and the GLIMMIX procedure in SAS. Results showed that Q-heifers had reduced incidence of metritis compared with q-heifers and were less likely to develop fever. Serum concentrations of β-hydroxybutyrate were lower and insulin-like growth factor-I plasma concentrations were higher in Q- compared with q-heifers. However, the body condition score and withers height were comparable between haplotypes, but weight loss tended to be lower in Q-heifers compared with q-heifers. No differences between the groups were detected concerning retained fetal membranes, uterine involution, or onset of cyclicity. In conclusion, selection of chromosome 18 haplotypes associated with a reduced somatic cell score resulted in a decreased incidence of postpartum reproductive and metabolic diseases in this study. The presented data add to the existing knowledge aimed at avoiding negative consequences of genetic selection strategies in dairy cattle farming. The underlying causal mechanisms modulated by haplotypes in the targeted genomic region and immune competence necessitate further investigation
Superconductivity in heavy-fermion U(Pt,Pd)3 and its interplay with magnetism
The effect of Pd doping on the superconducting phase diagram of the
unconventional superconductor UPt3 has been measured by (magneto)resistance,
specific heat, thermal expansion and magnetostriction. Experiments on single-
and polycrystalline U(Pt1-xPdx)3 for x<= 0.006 show that the superconducting
transition temperatures of the A phase, Tc+, and of the B phase, Tc-, both
decrease, while the splitting DTc increases at a rate of 0.30(2)K/at.%Pd. We
find that DTc(x) correlates with an increase of the weak magnetic moment m(x)
upon Pd doping. This provides further evidence for Ginzburg-Landau scenarios
with magnetism as the symmetry breaking field, i.e. the 2D E representation and
the 1D odd parity model. Only for small splittings DTc is proportional to
m^2(Tc+) (DTc<= 0.05 K) as predicted. The results at larger splittings call for
Ginzburg-Landau expansions beyond 4th order. The tetracritical point in the B-T
plane persists till at least x= 0.002 for B perpendicular to c, while it is
rapidly suppressed for B||c. Upon alloying the A and B phases gain stability at
the expense of the C phase.Comment: 25 pages text (PS), 8 pages with 14 figures (PS), submitted to
Phys.Rev.
The SLUGGS survey: probing the supermassive blackhole connection with bulges and haloes using red and blue globular cluster systems
Understanding whether the bulge or the halo provides the primary link to the growth of supermassive black holes has strong implications for galaxy evolution and supermassive black hole formation itself. In this paper, we approach this issue by investigating extragalactic globular cluster (GC) systems, which can be used to probe the physics of both the bulge and the halo of the host galaxy. We study the relation between the supermassive black hole masses (MBH) and the GC system velocity dispersions (σGC) using an updated and improved sample of 21 galaxies. We exploit the dichotomy of GC system colours, to test if the blue and red GCs correlate differently with black hole mass. This may be expected if they trace the potentially different formation history of the halo and of the bulge of the host galaxy, respectively. We find that MBH correlates with the total GC system velocity dispersion, although not as strongly as claimed by recent work of Sadoun & Colin. We also examine the MBH-σGC relation for barred/barless and core/non-core galaxies, finding no significant difference, and for the first time we quantify the impact of radial gradients in the GC system velocity dispersion profile on the MBH-σGC relation. We additionally predict MBH in 13 galaxies, including dwarf elliptical galaxies and the cD galaxy NGC 3311. We conclude that our current results cannot discriminate between the bulge/halo scenarios. Although there is a hint that the red GC velocity dispersion might correlate better with MBH than the blue GC velocity dispersion, the number statistics are still too low to be certain
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