390 research outputs found
Satellite animal tracking feasibility studies
A study was initiated in Tsavo National Park to determine movements and home ranges of individual elephants and their relations to overall distribution patterns and environmental factors such as rainfall. Methods used were radio tracking and observations of visually identifiable individuals. Aerial counts provided data on overall distribution. Two bulls and two cows were radio-tagged in Tsavo West and two bulls and four cows in Tsavo East, providing home range and movement data. The movements of individuals were useful in interpreting relatively major shifts in elephant distribution. Results point to the following preliminary conclusions: (1) elephants in the Tsavo area undertook long distance movements in fairly direct response to localized rainfall; (2) a subdivision of the overall population into locally distinct units may exist during the dry season but did not occur after significant rainfall; and (3) food appears to be the primary factor governing movements and distribution of elephants in the area
Satellite (IRLS) tracking of elk
The practicability of tracking free roaming animals in natural environments by satellite systems is reported. Satellite systems combine continuous tracking with simultaneous monitoring of physiological and environmental parameters through a combination of radio tracking and biotelemetric ground systems that lead to a better understanding of animal behavior and migration patterns
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
Lattice Expansion in Seamless Bi layer Graphene Constrictions at High Bias
Our understanding of sp2 carbon nanostructures is still emerging and is
important for the development of high performance all carbon devices. For
example, in terms of the structural behavior of graphene or bi-layer graphene
at high bias, little to nothing is known. To this end we investigated bi-layer
graphene constrictions with closed edges (seamless) at high bias using in situ
atomic resolution transmission electron microscopy. We directly observe a
highly localized anomalously large lattice expansion inside the constriction.
Both the current density and lattice expansion increase as the bi-layer
graphene constriction narrows. As the constriction width decreases below 10 nm,
shortly before failure, the current density rises to 4 \cdot 109 A cm-2 and the
constriction exhibits a lattice expansion with a uniaxial component showing an
expansion approaching 5 % and an isotropic component showing an expansion
exceeding 1 %. The origin of the lattice expansion is hard to fully ascribe to
thermal expansion. Impact ionization is a process in which charge carriers
transfer from bonding states to antibonding states thus weakening bonds. The
altered character of C-C bonds by impact ionization could explain the
anomalously large lattice expansion we observe in seamless bi-layer graphene
constrictions. Moreover, impact ionization might also contribute to the
observed anisotropy in the lattice expansion, although strain is probably the
predominant factor.Comment: to appear in NanoLetter
Photoemission induced gating of topological insulator
The recently discovered topological insulators exhibit topologically
protected metallic surface states which are interesting from the fundamental
point of view and could be useful for various applications if an appropriate
electronic gating can be realized. Our photoemission study of Cu intercalated
Bi2Se3 shows that the surface states occupancy in this material can be tuned by
changing the photon energy and understood as a photoemission induced gating
effect. Our finding provides an effective tool to investigate the new physics
coming from the topological surface states and suggests the intercalation as a
recipe for synthesis of the material suitable for electronic applications.Comment: + resistivity data and some discussio
Anomalously enhanced photoemission from the Dirac point and symmetry of the self-energy variations for the surface states in Bi2Se3
Accurate analysis of the photoemission intensity from the surface states of
Bi2Se3 reveals two unusual features: spectral line asymmetry and anomalously
enhanced photoemission from the Dirac point. The former indicates a certain
symmetry of a scattering process, which results in strongly k\omega-dependent
contribution to the imaginary part of the self-energy that changes sign while
crossing both the dispersion curves and the energy of the Dirac point. The
latter is hard to describe by one particle spectral function while a final
state interference seems to be plausible explanation
Signatures of superconducting and pseudogap phases in ultrafast transient reflectivity of Ca(Fe0.927Co0.073)2As2
We present femtosecond time-resolved pump-probe spectroscopic studies of a
pseudogap (PG) along with the superconducting (SC) gap in an overdoped iron
pnictide Ca(Fe0.927Co0.073)2As2. It is seen that the temperature evolution of
the photoexcited quasiparticle (QP) relaxation dynamics, coherently excited
A1g-symmetric optical phonon and two acoustic phonon dynamics behave
anomalously in the vicinity of the superconducting transition temperature Tc. A
continuous change in the sign of the experimentally measured transient
differential reflectivity Delta_R/R signal at the zero time-delay between the
pump and probe pulses at a temperature of ~200 K is inferred as an evidence of
the emergence of the PG phase around that temperature. This behavior is
independent of the pump photon energy and occurs for crystals without the spin
density wave phase transition.Comment: EPL (2014
Magnetic excitations in two-leg spin 1/2 ladders: experiment and theory
Magnetic excitations in two-leg S=1/2 ladders are studied both experimentally
and theoretically. Experimentally, we report on the reflectivity, the
transmission and the optical conductivity sigma(omega) of undoped La_x Ca_14-x
Cu_24 O_41 for x=4, 5, and 5.2. Using two different theoretical approaches
(Jordan-Wigner fermions and perturbation theory), we calculate the dispersion
of the elementary triplets, the optical conductivity and the momentum-resolved
spectral density of two-triplet excitations for 0.2 <=
J_parallel/J_perpendicular <= 1.2. We discuss phonon-assisted two-triplet
absorption, the existence of two-triplet bound states, the two-triplet
continuum, and the size of the exchange parameters.Comment: 6 pages, 7 eps figures, submitted to SNS 200
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