322 research outputs found
Satellite and ground radiotracking of elk
Radiotracking and monitoring of free-living animals in natural environments is providing an effective new technique for acquiring information on biological processes, including animal orientation and navigation. To test the practicability of extending the technique by using satellite systems for tracking animals, a female elk was instrumented with an electronic collar. It contained both the Interrogation Recording Location System (IRLS) transponder and a Craighead-Varney ground-tracking transmitter. The elk was successfully tracked and monitored by satellite during month of April 1970. This was the first time an animal had been tracked by satellite on the surface of the earth
Electron acceleration by turbulent plasmoid reconnection
In space and astrophysical plasmas, like in planetary magnetospheres, as that
of Mercury,energetic electrons are often found near current sheets (CSs), which
hints at electron acceleration by magnetic reconnection. Unfortunately,
electron acceleration by reconnection is not well understood, yet. In
particular, acceleration by turbulent plasmoid reconnection. We have
investigated electron acceleration by turbulent plasmoid reconnection,
described by MHD simulations, via test particle calculations. In order to avoid
resolving all relevant turbulence scales down to the dissipation scales, a
mean-field turbulence model is used to describe the turbulence of sub-grid
scales (SGS) and their effects via a turbulent electromotive force (EMF). The
mean-field model describes the turbulent EMF as a function of the mean values
of current density, vorticity, magnetic field as well as of the energy,
cross-helicity and residual helicity of the turbulence. We found that, mainly
around X-points of turbulent reconnection, strongly enhanced localized EMFs
most efficiently accelerated electrons and caused the formation of power-law
spectra. Magnetic-field-aligned EMFs, caused by the turbulence, dominate the
electron acceleration process. Scaling the acceleration processes to parameters
of the Hermean magnetotail, electron energies up to 60 keV can be reached by
turbulent plasmoid reconnection through the thermal plasma.Comment: 2018PhPl...25d2904
Disorder-induced Spin Gap in the Zigzag Spin-1/2 Chain Cuprate Sr_{0.9}Ca_{0.1}CuO_2
We report a comparative study of 63Cu Nuclear Magnetic Resonance spin lattice
relaxation rates, T_1^{-1}, on undoped SrCuO_2 and Ca doped
Sr_{0.9}Ca_{0.1}CuO_2 spin chain compounds. A temperature independent T_1^{-1}
is observed for SrCuO_2 as expected for an S=1/2 Heisenberg chain.
Surprisingly, we observe an exponential decrease of T_1^{-1} for T < 90,K in
the Ca-doped sample evidencing the opening of a spin gap. The data analysis
within the J_1-J_2 Heisenberg model employing density-matrix renormalization
group calculations suggests an impurity driven small alternation of the
J_2-exchange coupling as a possible cause of the spin gap.Comment: 4 pages, 4 figure
Liquid Limits: The Glass Transition and Liquid-Gas Spinodal Boundaries of Metastable Liquids
The liquid-gas spinodal and the glass transition define ultimate boundaries
beyond which substances cannot exist as (stable or metastable) liquids. The
relation between these limits is analyzed {\it via} computer simulations of a
model liquid. The results obtained indicate that the liquid - gas spinodal and
the glass transition lines intersect at a finite temperature, implying a glass
- gas mechanical instability locus at low temperatures. The glass transition
lines obtained by thermodynamic and dynamic criteria agree very well with each
other.Comment: 5 pages, 4 figures, to appear in Phys. Rev. Let
Non-Fermi-liquid scattering rates and anomalous band dispersion in ferropnictides
Angle-resolved photoemission spectroscopy (ARPES) is used to study the band
dispersion and the quasiparticle scattering rates in two ferropnictides
systems. Our ARPES results show linear-in-energy dependent scattering rates
which are constant in a wide range of control parameter and which depend on the
orbital character of the bands. We demonstrate that the linear energy
dependence gives rise to weakly dispersing band with a strong mass enhancement
when the band maximum crosses the chemical potential. In the superconducting
phase the related small effective Fermi energy favors a
Bardeen-Cooper-Schrieffer (BCS)\,\cite{Bardeen1957}-Bose-Einstein
(BE)\,\cite{Bose1924} crossover state.Comment: 5 pages, 4 figures Supplement 4 pages, 6 figure
Thermodynamic and structural aspects of the potential energy surface of simulated water
Relations between the thermodynamics and dynamics of supercooled liquids
approaching a glass transition have been proposed over many years. The
potential energy surface of model liquids has been increasingly studied since
it provides a connection between the configurational component of the partition
function on one hand, and the system dynamics on the other. This connection is
most obvious at low temperatures, where the motion of the system can be
partitioned into vibrations within a basin of attraction and infrequent
inter-basin transitions. In this work, we present a description of the
potential energy surface properties of supercooled liquid water. The dynamics
of this model has been studied in great details in the last years.
Specifically, we locate the minima sampled by the liquid by ``quenches'' from
equilibrium configurations generated via molecular dynamics simulations. We
calculate the temperature and density dependence of the basin energy,
degeneracy, and shape. The temperature dependence of the energy of the minima
is qualitatively similar to simple liquids, but has anomalous density
dependence. The unusual density dependence is also reflected in the
configurational entropy, the thermodynamic measure of degeneracy. Finally, we
study the structure of simulated water at the minima, which provides insight on
the progressive tetrahedral ordering of the liquid on cooling
Universal linear-temperature dependence of static magnetic susceptibility in iron-pnictides
A universal linear-temperature dependence of the uniform magnetic
susceptibility has been observed in the nonmagnetic normal state of
iron-pnictides. This non-Pauli and non-Curie-Weiss-like paramagnetic behavior
cannot be understood within a pure itinerant picture. We argue that it results
from the existence of a wide antiferromagnetic fluctuation window in which the
local spin-density-wave correlations exist but the global directional order has
not been established yet.Comment: 4 pages, 2 figure
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