5,952 research outputs found
Survey of the adequacy of existing conserved areas in relation to wild animal species
The following mammals larger than the silver fox (Vulpes Chama) were considered to be endangered within South and South West Afric
Shell-model test of the rotational-model relation between static quadrupole moments Q(2^+_1), B(E2)'s, and orbital M1 transitions
In this work, we examine critically the relation between orbital magnetic
dipole (scissors mode) strength and quadrupole deformation properties. Assuming
a simple K=0 ground state band in an even-even nucleus, the quantities Q(2^+_1)
(i.e., the static quadrupole moment) and B(E2)_{0_1 \to 2_1} both are described
by a single parameter--the intrinsic quadrupole moment Q_0. In the shell model,
we can operationally define Q_0(Static) and Q_0(BE2) and see if they are the
same. Following a brief excursion to the sd shell, we perform calculations in
the fp shell. The nuclei we consider ({44,46,48}Ti and {48,50}Cr) are far from
being perfect rotors, but we find that the calculated ratio
Q_0(Static)/Q_0(BE2) is in many cases surprisingly close to one. We also
discuss the collectivity of orbital magnetic dipole transitions. We find that
the large orbital B(M1) strength in {44}Ti relative to {46}Ti and {48}Ti cannot
be explained by simple deformation arguments.Comment: 12 pages, RevTeX4. Sections II (Quadrupole properties in the
sd-shell) and V (Random interaction studies) added. Minor changes throughout
the text and 48Cr added to present Table IV, as well as results for the
lowest 100 state
Tunable Fano Resonances in Transport through Microwave Billiards
We present a tunable microwave scattering device that allows the controlled
variation of Fano line shape parameters in transmission through quantum
billiards. Transport in this device is nearly fully coherent. By comparison
with quantum calculations, employing the modular recursive Green's-function
method, the scattering wave function and the degree of residual decoherence can
be determined. The parametric variation of Fano line shapes in terms of
interacting resonances is analyzed.Comment: 5 pages, 4 figures, submitted to Phys. Rev.
Does the East Greenland Current exist in the northern Fram Strait?
Warm Atlantic Water (AW) flows around the Nordic Seas in a cyclonic boundary
current loop. Some AW enters the Arctic Ocean where it is transformed to
Arctic Atlantic Water (AAW) before exiting through the Fram Strait. There the AAW
is joined by recirculating AW. Here we present the first summer synoptic
study targeted at resolving this confluence in the Fram Strait which forms the
East Greenland Current (EGC). Absolute geostrophic velocities and hydrography
from observations in 2016, including four sections crossing the east
Greenland shelf break, are compared to output from an eddy-resolving
configuration of the sea ice–ocean model FESOM. Far offshore (120 km at
80.8° N) AW warmer than 2 °C is found in the northern Fram
Strait. The Arctic Ocean outflow there is broad and barotropic, but gets
narrower and more baroclinic toward the south as recirculating AW increases
the cross-shelf-break density gradient. This barotropic to baroclinic
transition appears to form the well-known EGC boundary current flowing along
the shelf break farther south where it has been previously described. In this
realization, between 80.2 and 76.5° N, the southward transport along
the east Greenland shelf break increases from roughly 1 Sv to about 4 Sv and
the proportion of AW to AAW also increases fourfold from 19±8 % to
80±3 %. Consequently, in the southern Fram Strait, AW can propagate
into the Norske Trough on the east Greenland shelf and reach the large
marine-terminating glaciers there. High instantaneous variability observed in both
the synoptic data and the model output is attributed to eddies, the
representation of which is crucial as they mediate the westward transport of
AW in the recirculation and thus structure the confluence forming the EGC.</p
Realistic description of electron-energy loss spectroscopy for One-Dimensional SrCuO
We investigate the electron-energy loss spectrum of one-dimensional undoped
CuO chains within an extended multi-band Hubbard model and an extended
one-band Hubbard model, using the standard Lanczos algorithm. Short-range
intersite Coulomb interactions are explicitly included in these models, and
long-range interactions are treated in random-phase approximation. The results
for the multi-band model with standard parameter values agree very well with
experimental spectra of SrCuO. In particular, the width of the main
structure is correctly reproduced for all values of momentum transfer. It is
shown for both models that intersite Coulomb interactions mainly lead to an
energy shift of the spectra. We find no evidence for enhanced intersite
interactions in SrCuO.Comment: 4 pages, 4 figure
Practical solution to the Monte Carlo sign problem: Realistic calculations of 54Fe
We present a practical solution to the "sign problem" in the auxiliary field
Monte Carlo approach to the nuclear shell model. The method is based on
extrapolation from a continuous family of problem-free Hamiltonians. To
demonstrate the resultant ability to treat large shell-model problems, we
present results for 54Fe in the full fp-shell basis using the Brown-Richter
interaction. We find the Gamow-Teller beta^+ strength to be quenched by 58%
relative to the single-particle estimate, in better agreement with experiment
than previous estimates based on truncated bases.Comment: 11 pages + 2 figures (not included
Development of a device to simulate tooth mobility
Objectives: The testing of new materials under simulation of oral conditions is essential in medicine. For simulation of fracture strength different simulation devices are used for test set-up. The results of these in vitro tests differ because there is no standardization of tooth mobility in simulation devices. The aim of this study is to develop a simulation device that depicts the tooth mobility curve as accurately as possible and creates reproducible and scalable mobility curves. Materials and methods: With the aid of published literature and with the help of dentists, average forms of tooth classes were generated. Based on these tooth data, different abutment tooth shapes and different simulation devices were designed with a CAD system and were generated with a Rapid Prototyping system. Then, for all simulation devices the displacement curves were created with a universal testing machine and compared with the tooth mobility curve. With this new information, an improved adapted simulation device was constructed. Results: A simulations device that is able to simulate the mobility curve of natural teeth with high accuracy and where mobility is reproducible and scalable was developed
The magnetic susceptibility of disordered non-diffusive mesoscopic systems
Disorder-induced spectral correlations of mesoscopic quantum systems in the
non-diffusive regime and their effect on the magnetic susceptibility are
studied. We perform impurity averaging for non-translational invariant systems
by combining a diagrammatic perturbative approach with semiclassical
techniques. This allows us to study the entire range from clean to diffusive
systems. As an application we consider the magnetic response of non-interacting
electrons in microstructures in the presence of weak disorder. We show that in
the ballistic case (elastic mean free path larger than the system size)
there exist two distinct regimes of behaviour depending on the relative
magnitudes of and an inelastic scattering length . We present
numerical results for square billiards and derive approximate analytical
results for generic chaotic geometries. The magnetic field dependence and
dependence of the disorder-induced susceptibility is qualitatively
similar in both types of geometry.Comment: 11 pages, 7 eps figures, to be published in Phys. Rev.
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