15,098 research outputs found
Magnetic order in Ce0.95Nd0.05CoIn5: the Q-phase at zero magnetic field
We report neutron scattering experiment results revealing the nature of the
magnetic order occurring in the heavy fermion superconductor Ce0.95Nd0.05CoIn5,
a case for which an antiferromagnetic state is stabilized at a temperature
below the superconducting transition one. We evidence an incommensurate order
and its propagation vector is found to be identical to that of the magnetic
field induced antiferromagnetic order occurring in the stoichiometric
superconductor CeCoIn5, the so-called Q-phase. The commonality between these
two cases suggests that superconductivity is a requirement for the formation of
this kind of magnetic order and the proposed mechanism is the enhancement of
nesting condition by d-wave order parameter with nodes in the nesting area.Comment: submitted to Phys. Rev. Lett. on June 30th, 201
Testing the cooling flow model in the intermediate polar EX Hydrae
We use the best available X-ray data from the intermediate polar EX Hydrae to
study the cooling-flow model often applied to interpret the X-ray spectra of
these accreting magnetic white dwarf binaries. First, we resolve a
long-standing discrepancy between the X-ray and optical determinations of the
mass of the white dwarf in EX Hya by applying new models of the inner disk
truncation radius. Our fits to the X-ray spectrum now agree with the white
dwarf mass of 0.79 Msun determined using dynamical methods through
spectroscopic observations of the secondary. We use a simple isobaric cooling
flow model to derive the emission line fluxes, emission measure distribution,
and H-like to He-like line ratios for comparison with the 496 ks Chandra High
Energy Transmission Grating observation of EX Hydrae. We find that the H/He
ratios are not well reproduced by this simple isobaric cooling flow model and
show that while H-like line fluxes can be accurately predicted, fluxes of
lower-Z He-like lines are significantly underestimated. This discrepancy
suggests that some extra heating mechanism plays an important role at the base
of the accretion column, where cooler ions form. We thus explored more complex
cooling models including the change of gravitational potential with height in
the accretion column and a magnetic dipole geometry. None of these
modifications to the standard cooling flow model are able to reproduce the
observed line ratios. While a cooling flow model with subsolar (0.1 )
abundances is able to reproduce the line ratios by reducing the cooling rate at
temperatures lower than K, the predicted line-to-continuum
ratios are much lower than observed. We discuss and discard mechanisms such as
photoionization, departures from constant pressure, resonant scattering,
different electron-ion temperatures, and Compton cooling. [Abridged]Comment: Accepted in Astronomy & Astrophysics, modified version after referee
comments and proof correction
Sea turtle nesting activity along Eglin Air Force Base on Cape San Blas and Santa Rosa Island, Florida from 1994 to 1997.
Along EAFB on Cape San BIas, the only sea turtle species nest observed has been
the loggerhead turtle. The first green turtle nest documented along the Florida panhandle
coast was observed on EAFB property, however (D. Atencio, EAFB, pers. comm). Santa
Rosa Island, located approximately 150 miles west of Cape San BIas supports a small but
consistent, group of nesting green turtles (Fig. 2). Although erosion is not as severe along
Santa Rosa Island as it is on Cape San BIas, and vehicular traffic is not permitted, sea
turtles nesting on this barrier island must survive severe tropical storms, predation, and
artificial lighting to be successful. Because this area supports a rare group of nesting green
turtles and is disturbed by intense artificial lighting from Air Force missions and adjacent
resort towns, continued monitoring is necessary. The sea turtle species that nest along this
barrier island, and the human activities that disturb those sea turtles present unique
circumstances for management ofthis area. Protection ofthe significant nesting
populations of sea turtles on EAFB properties on Cape San BIas and Santa Rosa Island
requires yearly monitoring of the nesting activity and the natural and human disturbances
influencing the nesting females.
The objectives ofthis study were to monitor sea turtle nesting along EAFB on
Cape San BIas to determine number of nests and hatching success, assess disturbances,
and determine proper management to ensure successful nesting and hatching.(56 page document
Effects of shear on eggs and larvae of striped bass, morone saxatilis, and white perch, M. americana
Shear stress, generated by water movement, can kill fish eggs and larvae by causing rotation or deformation. Through the use of an experimental apparatus, a series of shear
(as dynes/cm2)-mortality equations for fixed time exposures were generated for striped bass and white perch eggs and larvae. Exposure of striped bass eggs to a shear level of 350 dynes/cm2 kills 36% of the eggs in 1 min; 69% in 2 min, and 88% in 4 min; exposure of larvae to 350 dynes/cm2 kills 9.3% in 1 min, 30.0% in 2 min, and 68.1% in 4 min. A shear level of 350 dynes/cm2 kills 38% of the white perch eggs in 1 min, 41% in 2 min, 89% in 5 min, 96% in 10 min, and 98% in 20 min. A shear level of 350 dynes/cm2 applied to white perch larvae destroys 38% of the larvae in 1 min, 52% in 2 min, and 75% in 4 min. Results are experimentally used in conjunction with the determination of shear levels in the Chesapeake and Delaware Canal and ship movement for the estimation of fish egg and larval mortalities in the field
Quantum phase transition using quantum walks in an optical lattice
We present an approach using quantum walks (QWs) to redistribute ultracold
atoms in an optical lattice. Different density profiles of atoms can be
obtained by exploiting the controllable properties of QWs, such as the variance
and the probability distribution in position space using quantum coin
parameters and engineered noise. The QW evolves the density profile of atoms in
a superposition of position space resulting in a quadratic speedup of the
process of quantum phase transition. We also discuss implementation in
presently available setups of ultracold atoms in optical lattices.Comment: 7 pages, 8 figure
The Cape San Blas Ecological Study
Eglin AFB on Cape San Blas consists of approximately 250 acres located about
180 miles east of the main Eglin reservation. This area lies on the S1. Joseph peninsula,
part of a dynamic barrier island chain that extends across the northern Gulf of Mexico.
Due to the natural forces that formed Cape San Blas and those that maintain this area, St.
Joseph Peninsula has experienced severe land form change over time (see GIS land form
change maps). These changes allow for fluctuations in habitat types along Cape San Blas
(see GIS land cover change maps)that influence the floral and faunal species using this
area.
The dynamic environment along Cape San Blasincludes flatwoods, interdunal
swale, rosemary scrub, and beachfront. These habitats support a wide array of species,
including several threatened and endangered species such as the loggerhead sea turtle
(Caretta caretta), PipingPlover (Charadnus melodus), Least Tern (Sterna antillarum),
and Bald Eagle (Haliaeetus leucocephalus). Proper management of these species and their
habitats require knowledge of their abundance and distribution, and the effects
disturbances have on their survival.
In addition to threatened and endangered flora and fauna, Cape San Blas also
supports tourists and recreationists. Although Gulf County is sparsely populated, with
approximately 13,000 inhabitants throughout 578 square miles, summer tourism and heavy
recreational use of beaches for fishing, crabbing, and shelling place continued and
increasing pressure on the natural resources of these areas (Rupert 1991). Gulf County is
also one of the few remaining counties in Florida that permits vehicular traffic on its
beaches, including Cape San Blas. In addition to recreational use of these habitats;EAFB
also uses the area for military missions. Air Force property on Cape San Blas is primarily
used for radar tracking of flying missions over the Gulf of Mexico, although in recent
years it has been used for missile launchings and other various military activities.
To allow continued military and public use of Air Force property while also
protecting the unique flora and fauna of the area,EAFB proposed a characterization of the
resources found along Cape San Blas. A complete inventory of the physical features of the
area included investigating topography, soil chemistry, hydrology, archeology, and the
dynamics of land mass and land cover change over time. Various thematic layers within a
geographic information system (GIS) were used to spatially portray georeferenced data.
Large scale changes over time were assessed using stereo aerial photography. Vegetation
transects, soil samples, elevation transects, an archeological survey, freshwater wells, and
a tidal monitor were used to investigate the remaining features. (247 page document
Suppression of hidden order in URu2Si2 under pressure and restoration in magnetic field
We describe here recent inelastic neutron scattering experiments on the heavy
fermion compound URu2Si2 realized in order to clarify the nature of the hidden
order (HO) phase which occurs below T_0 = 17.5 K at ambient pressure. The
choice was to measure at a given pressure P where the system will go, by
lowering the temperature, successively from paramagnetic (PM) to HO and then to
antiferromagnetic phase (AF). Furthermore, in order to verify the selection of
the pressure, a macroscopic detection of the phase transitions was also
achieved in situ via its thermal expansion response detected by a strain gauge
glued on the crystal. Just above P_x = 0.5 GPa, where the ground state switches
from HO to AF, the Q_0 = (1, 0, 0) excitation disappears while the excitation
at the incommensurate wavevector Q_1 = (1.4, 0, 0) remains. Thus, the Q_0 = (1,
0, 0) excitation is intrinsic only in the HO phase. This result is reinforced
by studies where now pressure and magnetic field can be used as tuning
variable. Above P_x, the AF phase at low temperature is destroyed by a magnetic
field larger than H_AF (collapse of the AF Q_0 = (1, 0, 0) Bragg reflection).
The field reentrance of the HO phase is demonstrated by the reappearance of its
characteristic Q_0 = (1, 0, 0) excitation. The recovery of a PM phase will only
be achieved far above H_AF at H_M approx 35 T. To determine the P-H-T phase
diagram of URu2Si2, macroscopic measurements of the thermal expansion were
realized with a strain gauge. The reentrant magnetic field increases strongly
with pressure. Finally, to investigate the interplay between superconductivity
(SC) and spin dynamics, new inelastic neutron scattering experiments are
reported down to 0.4 K, far below the superconducting critical temperature T_SC
approx 1.3 K as measured on our crystal by diamagnetic shielding.Comment: 5 pages, 7 figures, ICN 2009 conference proceeding
Topological constraints on spiral wave dynamics in spherical geometries with inhomogeneous excitability
We analyze the way topological constraints and inhomogeneity in the
excitability influence the dynamics of spiral waves on spheres and punctured
spheres of excitable media. We generalize the definition of an index such that
it characterizes not only each spiral but also each hole in punctured,
oriented, compact, two-dimensional differentiable manifolds and show that the
sum of the indices is conserved and zero. We also show that heterogeneity and
geometry are responsible for the formation of various spiral wave attractors,
in particular, pairs of spirals in which one spiral acts as a source and a
second as a sink -- the latter similar to an antispiral. The results provide a
basis for the analysis of the propagation of waves in heterogeneous excitable
media in physical and biological systems.Comment: 5 pages, 6 Figures, major revisions, accepted for publication in
Phys. Rev.
Characteristics of ion flow in the quiet inner plasma sheet
Abstract
We use AMPTE/IRM and ISEE 2 data to study the properties of the high beta (βi \u3e 0.5) plasma sheet, the inner plasma sheet (IPS). Bursty bulk flows (BBFs) are excised from the two databases, and the average flow pattern in the non-BBF (quiet) IPS is constructed. At local midnight this ensemble-average flow is predominantly duskward; closer to the flanks it is mostly earthward. The flow pattern agrees qualitatively with calculations based on the Tsyganenko [1987] model (T87), where the earthward flow is due to the ensemble-average cross tail electric field and the duskward flow is the diamagnetic drift due to an inward pressure gradient. The IPS is on the average in pressure equilibrium with the lobes. Because of its large variance the average flow does not represent the instantaneous flow field. Case studies also show that the non-BBF flow is highly irregular and inherently unsteady, a reason why earthward convection can avoid a pressure balance inconsistency with the lobes. The ensemble distribution of velocities is a fundamental observable of the quiet plasma sheet flow field
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