1,871 research outputs found
Uniaxial pressure dependencies of the phase boundary of TlCuCl_3
We present a thermal expansion and magnetostriction study of TlCuCl_3, which
shows a magnetic-field induced transition from a spin gap phase to a Neel
ordered phase. Using Ehrenfest relations we derive huge and strongly
anisotropic uniaxial pressure dependencies of the respective phase boundary,
e.g. the transition field changes by about GPa depending on the
direction of uniaxial pressure.Comment: 2 pages, e figures; presented at SCES200
Magnetoelastic Coupling in the Spin-Dimer System TlCuCl
We present high-resolution measurements of the thermal expansion and the
magnetostriction of TlCuCl which shows field-induced antiferromagnetic
order. We find pronounced anomalies in the field and temperature dependence of
different directions of the lattice signaling a large magnetoelastic coupling.
The phase boundary is extremely sensitive to pressure, e.g. the transition
field would change by about +/- 185$%/GPa under uniaxial pressure applied along
certain directions. This drastic effect can unambiguously be traced back to
changes of the intradimer coupling under uniaxial pressure. The interdimer
couplings remain essentially unchanged under pressure, but strongly change when
Tl is replaced by K.Comment: 4 pages with 4 figures include
Testing black hole no-hair theorem with OJ287
We examine the ability to test the black hole no-hair theorem at the 10%
level in this decade using the binary black hole in OJ287. In the test we
constrain the value of the dimensionless parameter q that relates the scaled
quadrupole moment and spin of the primary black hole: q2 = -q 2 . At the
present we can say that q = 1 \pm 0.3 (one), in agreement with General
Relativity and the no-hair theorems. We demonstrate that this result can be
improved if more observational data is found in historical plate archives for
the 1959 and 1971 outbursts. We also show that the predicted 2015 and 2019
outbursts will be crucial in improving the accuracy of the test. Space-based
photometry is required in 2019 July due the proximity of OJ287 to the Sun at
the time of the outburst. The best situation would be to carry out the
photometry far from the Earth, from quite a different vantage point, in order
to avoid the influence of the nearby Sun. We have considered in particular the
STEREO space mission which would be ideal if it has a continuation in 2019 or
LORRI on board the New Horizons mission to Pluto.Comment: 14 pages, 14 figure
Sex differences in the association of postural control with indirect measures of body representations
Besides anthropometric variables, high-order body representations have been hypothesised to influence postural control. However, this has not been directly tested before. Moreover, some studies indicate that sex moderates the relationship of anthropometry and postural control. Therefore, as a proof of concept we investigated the association of body representations with postural control as well as the influence of participants’ sex/gender. Body image measures were assessed with a figural drawing task. Body schema was tested by a covert and an overt task. Body sway was measured during normal bipedal quiet standing with eyes closed (with/without neck extended). Statistical analysis consisted of hierarchical multiple linear regressions with the following regression steps: (1) sensory condition, (2) sex/gender, (3) age, (4) anthropometry, (5) body schema, (6) body image, (7) sex/gender-interactions. Across 36 subjects (19 females), body schema was significantly associated with body sway variability and open-loop control, in addition to commonly known influencing factors, such as sensory condition, gender, age and anthropometry. While in females, also body image dissatisfaction substantially was associated with postural control, this was not the case in males. Sex differences and possible causes why high-order body representations may influence concurrent sensorimotor control of body sway are discussed
Hydrographic, chemical and planktological data from the north-west African upwelling area obtained from February to April 1983 : ("Ostatlantik-Biozirkel")
Evidence of reduced surface electron-phonon scattering in the conduction band of Bi_{2}Se_{3} by non-equilibrium ARPES
The nature of the Dirac quasiparticles in topological insulators calls for a
direct investigation of the electron-phonon scattering at the \emph{surface}.
By comparing time-resolved ARPES measurements of the TI Bi_{2}Se_{3} with
different probing depths we show that the relaxation dynamics of the electronic
temperature of the conduction band is much slower at the surface than in the
bulk. This observation suggests that surface phonons are less effective in
cooling the electron gas in the conduction band.Comment: 5 pages, 3 figure
The momentum and photon energy dependence of the circular dichroic photoemission in the bulk Rashba semiconductors BiTeX (X = I, Br, Cl)
Bulk Rashba systems BiTeX (X = I, Br, Cl) are emerging as important
candidates for developing spintronics devices, because of the coexistence of
spin-split bulk and surface states, along with the ambipolar character of the
surface charge carriers. The need of studying the spin texture of strongly
spin-orbit coupled materials has recently promoted circular dichroic Angular
Resolved Photoelectron Spectroscopy (cd-ARPES) as an indirect tool to measure
the spin and the angular degrees of freedom. Here we report a detailed photon
energy dependent study of the cd-ARPES spectra in BiTeX (X = I, Br and Cl). Our
work reveals a large variation of the magnitude and sign of the dichroism.
Interestingly, we find that the dichroic signal modulates differently for the
three compounds and for the different spin-split states. These findings show a
momentum and photon energy dependence for the cd-ARPES signals in the bulk
Rashba semiconductor BiTeX (X = I, Br, Cl). Finally, the outcome of our
experiment indicates the important relation between the modulation of the
dichroism and the phase differences between the wave-functions involved in the
photoemission process. This phase difference can be due to initial or final
state effects. In the former case the phase difference results in possible
interference effects among the photo-electrons emitted from different atomic
layers and characterized by entangled spin-orbital polarized bands. In the
latter case the phase difference results from the relative phases of the
expansion of the final state in different outgoing partial waves.Comment: 6 pages, 4 figure
Understanding Deer, Bear, and Forest Trends in the North Georgia Mountains: The Value of Long-term Data
Most state wildlife agencies collect harvest data to inform management decisions. However, these data are typically considered across relatively short time periods and are rarely revisited. We present a case study using historical records to investigate potential agents (i.e., harvest, predation, and forest change) influencing the declining white-tailed deer (Odocoileus virginianus) population in the north Georgia mountains. We used long-term black bear (Ursus americanus) and deer harvest data, and indices of forest stand conditions from 1979–2015 on eight Wildlife Management Areas (WMAs) in the north Georgia mountains. During 1979–2015, harvest of male and female deer declined by 85% and 97%, respectively. Over the same time period, mean yearling male deer body weight increased by 21%, mean antler diameter increased by 62%, and mean antler beam length increased by 92%. We observed a 97% reduction in availability of early successional forests (0–10 years old) and a 53% increase in volume of large diameter (\u3e27.9 cm) oak species, suggesting increasing homogeneity/maturation of forest stands across all eight WMAs. Concomitantly, the U.S. Forest Service increased the acreage under prescribed fire management from 2,916 to 5,629 ha during 2003–2015. Black bear populations grew at an annual rate of 1.07 for males and 1.08 for females. Our analyses indicated that despite the reduction in early successional habitats as illustrated by the reduction in young forests (0–10 years old), deer condition indices have improved suggesting that a habitat-driven change in fecundity was not the likely primary driver of the deer population decline. However, increasing fawn predation, coupled with a decline in available fawning cover may be reducing recruitment rates and should be investigated as potential causes for the observed population decline. Our research also illustrates the importance of maintaining longterm data, especially the value offered to evaluate trends over time
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