433 research outputs found
Magnetism in Nb(1-y)Fe(2+y) - composition and magnetic field dependence
We present a systematic study of transport and thermodynamic properties of
the Laves phase system NbFe. Our measurements confirm that
Fe-rich samples, as well as those rich in Nb (for ), show
bulk ferromagnetism at low temperature. For stoichiometric NbFe, on the
other hand, magnetization, magnetic susceptibility and magnetoresistance
results point towards spin-density wave (SDW) order, possibly helical, with a
small ordering wavevector \AA. Our results suggest that on
approaching the stoichiometric composition from the iron-rich side,
ferromagnetism changes into long-wavelength SDW order. In this scenario,
changes continuously from 0 to small, finite values at a Lifshitz point in the
phase diagram, which is located near . Further reducing the Fe content
suppresses the SDW transition temperature, which extrapolates to zero at
. Around this Fe content magnetic fluctuations dominate the
temperature dependence of the resistivity and of the heat capacity which
deviate from their conventional Fermi liquid forms, inferring the presence of a
quantum critical point. Because the critical point is located between the SDW
phase associated with stoichiometric NbFe and the ferromagnetic order which
reemerges for very Nb-rich NbFe, the observed temperature dependences could
be attributed both to proximity to SDW order or to ferromagnetism.Comment: 13 pages, 20 figure
Improving thermoelectric performance of TiNiSn by mixing MnNiSb in the half-Heusler structure
The thermoelectric properties of n type semiconductor, TiNiSn is optimized by
partial substitution with metallic, MnNiSb in the half Heusler structure.
Herein, we study the transport properties and intrinsic phase separation in the
system. The Ti1-xMnxNiSn1-xSbx alloys were prepared by arc-melting and were
annealed at temperatures obtained from differential thermal analysis and
differential scanning calorimetry results. The phases were characterized using
powder X-ray diffraction patterns, energy dispersive X-ray spectroscopy, and
differential scanning calorimetry. After annealing the majority phase was
TiNiSn with some Ni rich sites and the minority phases was majorly Ti6Sn5, Sn,
and MnSn2. Ni rich sites were caused by Frenkel defects, this led to a
metal-like behavior of the semiconducting specimens at low temperature. For x
up to 0.05 the samples showed an activated conduction, whereas for x>0.05 they
showed metallic character. The figure of merit for x=0.05 was increased by 61%
(ZT=0.45) in comparison to the pure TiNiSn.Comment: 7 pages and 5 figures. Submitted to Physical Chemistry Chemical
Physics - RSC Publishing on 6th of October, 201
Radial Velocity Studies of Southern Close Binary Stars.I
Radial-velocity measurements and sine-curve fits to the orbital velocity
variations are presented for nine contact binaries, V1464 Aql, V759 Cen, DE
Oct, MW Pav, BQ Phe, EL Aqr, SX Crv, VZ Lib, GR Vir; for the first five among
these, our observations are the first available radial velocity data. Among
three remaining radial velocity variables, CE Hyi is a known visual binary,
while CL Cet and V1084 Sco are suspected to be multiple systems where the
contact binary is spectrally dominated by its companion (which itself is a
binary in V1084 Sco). Five additional variables, V872 Ara, BD Cap, HIP 69300,
BX Ind, V388 Pav, are of unknown type, but most are pulsating stars; we give
their mean radial velocities and Vsini.Comment: to appear in AJ October 2006; 3 figure
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From Colossal to Zero: Controlling the Anomalous Hall Effect in Magnetic Heusler Compounds via Berry Curvature Design
Since the discovery of the anomalous Hall effect (AHE), the anomalous Hall conductivity (AHC) has been thought to be zero when there is no net magnetization. However, the recently found relation between the intrinsic AHE and the Berry curvature predicts other possibilities, such as a large AHC in noncolinear antiferromagnets with no net magnetization but net Berry curvature. Vice versa, the AHE in principle could be tuned to zero, irrespective of a finite magnetization. Here, we experimentally investigate this possibility and demonstrate that the symmetry elements of Heusler magnets can be changed such that the Berry curvature and all the associated properties are switched while leaving the magnetization unaffected. This enables us to tune the AHC from 0 Ω-1 cm-1 up to 1600 Ω-1 cm-1 with an exceptionally high anomalous Hall angle up to 12%, while keeping the magnetization the same. Our study shows that the AHC can be controlled by selectively changing the Berry curvature distribution, independent of the magnetization
Radial Velocity Studies of Close Binary Stars. XI
Radial-velocity measurements and sine-curve fits to the orbital radial
velocity variations are presented for ten close binary systems: DU Boo, ET Boo,
TX Cnc, V1073 Cyg, HL Dra, AK Her, VW LMi, V566 Oph, TV UMi and AG Vir. By this
contribution, the DDO program has reached the point of 100 published radial
velocity orbits. The radial velocities have been determined using an improved
fitting technique which uses rotational profiles to approximate individual
peaks in broadening functions.
Three systems, ET Boo, VW LMi and TV UMi, were found to be quadruple while AG
Vir appears to be a spectroscopic triple. ET Boo, a member of a close visual
binary with years, was previously known to be a multiple
system, but we show that the second component is actually a close,
non-eclipsing binary. The new observations enabled us to determine the
spectroscopic orbits of the companion, non-eclipsing pairs in ET Boo and VW
LMi. The particularly interesting case is VW LMi, where the period of the
mutual revolution of the two spectroscopic binaries is only 355 days.
While most of the studied eclipsing pairs are contact binaries, ET Boo is
composed of two double-lined detached binaries and HL Dra is single-lined
detached or semi-detached system. Five systems of this group were observed
spectroscopically before: TX Cnc, V1073 Cyg, AK Her (as a single-lined binary),
V566 Oph, AG Vir, but our new data are of much higher quality than the previous
studies.Comment: Accepted by AJ, August 2006, 10 figures, 3 table
Evidence of a Massive Black Hole Companion in the Massive Eclipsing Binary V Puppis
Up to now, most stellar-mass black holes were discovered in X-ray emitting
binaries, in which the black holes are formed through a common-envelope evolu
tion. Here we give evidence for the presence of a massive black hole candidate
as a tertiary companion in the massive eclipsing binary V Puppis. We found that
the orbital period of this short-period binary (P=1.45 days) shows a periodic
variation while it undergoes a long-term increase. The cyclic period
oscillation can be interpreted by the light-travel time effect via the presence
of a third body with a mass no less than 10.4 solar mass. However, no spectral
lines of the third body were discovered indicating that it is a massive black
hole candidate. The black hole candidate may correspond to the weak X-ray
source close to V Puppis discovered by Uhuru, Copernicus, and ROSAT satellites
produced by accreting materials from the massive binary via stellar wind. The
circumstellar matter with many heavy elements around this binary may be formed
by the supernova explosion of the progenitor of the massive black hole. All of
the observations suggest that a massive black hole is orbiting the massive
close binary V Puppis with a period of 5.47 years. Meanwhile, we found the
central close binary is undergoing slow mass transfer from the secondary to the
primary star on a nuclear time scale of the secondary component, revealing that
the system has passed through a rapid mass-transfer stage.Comment: Accepted for publication in ApJ
Navy Prototype Optical Interferometer Imaging of Line Emission Regions of beta Lyrae Using Differential Phase Referencing
We present the results of an experiment to image the interacting binary star
beta Lyrae with data from the Navy Prototype Optical Interferometer (NPOI),
using a differential phase technique to correct for the effects of the
instrument and atmosphere on the interferometer phases. We take advantage of
the fact that the visual primary of beta Lyrae and the visibility calibrator we
used are both nearly unresolved and nearly centrally symmetric, and
consequently have interferometric phases near zero. We used this property to
detect and correct for the effects of the instrument and atmosphere on the
phases of beta Lyrae and to obtain differential phases in the channel
containing the Halpha emission line. Combining the Halpha-channel phases with
information about the line strength, we recovered complex visibilities and
imaged the Halpha emission using standard radio interferometry methods. We find
that the results from our differential phase technique are consistent with
those obtained from a more-standard analysis using squared visibilities
(V^2's). Our images show the position of the Halpha emitting regions relative
to the continuum photocenter as a function of orbital phase and indicate that
the major axis of the orbit is oriented along p.a.=248.8+/-1.7 deg. The orbit
is smaller than previously predicted, a discrepancy that can be alleviated if
we assume that the system is at a larger distance from us, or that the
contribution of the stellar continuum to the Halpha channel is larger than
estimated. Finally, we also detected a differential phase signal in the
channels containing HeI emission lines at 587.6 and 706.5nm, with orbital
behavior different from that of the Halpha, indicating that it originates from
a different part of this interacting system.Comment: Submitted to Ap
Genome-wide association and HLA fine-mapping studies identify risk loci and genetic pathways underlying allergic rhinitis
Allergic rhinitis is the most common clinical presentation of allergy, affecting 400 million people worldwide, with increasing incidence in westernized countries1,2. To elucidate the genetic architecture and understand the underlying disease mechanisms, we carried out a meta-analysis of allergic rhinitis in 59,762 cases and 152,358 controls of European ancestry and identified a total of 41 risk loci for allergic rhinitis, including 20 loci not previously associated with allergic rhinitis, which were confirmed in a replication phase of 60,720 cases and 618,527 controls. Functional annotation implicated genes involved in various immune pathways, and fine mapping of the HLA region suggested amino acid variants important for antigen binding. We further performed genome-wide association study (GWAS) analyses of allergic sensitization against inhalant allergens and nonallergic rhinitis, which suggested shared genetic mechanisms across rhinitis-related traits. Future studies of the identified loci and genes might identify novel targets for treatment and prevention of allergic rhinitis
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