1,486 research outputs found
Dynamic Responses of Calving Caribou to Oilfields in Northern Alaska
Past research has suggested that during the calving period, caribou (Rangifer tarandus) in Arctic Alaska generally avoid areas within 1 km of oilfield roads with traffic. However, avoidance is not absolute, and caribou may habituate to infrastructure (e.g., buildings, roads, well pads) and human activity. We conducted road-based surveys of caribou in oilfields on Alaska’s Arctic Coastal Plain during the late calving and post-calving periods of June in 2000–02. We recorded location, composition, and behavior of caribou groups located less than 1 km from active gravel roads and production pads. Caribou groups with calves were on average distributed farther from oilfield infrastructure than were groups without calves, but habituation to oilfield activities, indicated by decreased avoidance, occurred at similar rates for groups with and without calves. During the calving period, sighting rates were greater in areas of low human activity, and calf percentages tended to be greater at night when oilfield activity was reduced. Caribou groups were on average closer to infrastructure during the post-calving periods than during the calving periods in 2000 and 2001, but not in 2002. In 2002, when snow melted early, caribou groups were closer to infrastructure during the calving period than in 2000 and 2001, when snow melted later, emphasizing the importance of examining environmental variables when investigating the dynamic interactions of caribou and oilfields. Overall, caribou appeared to habituate to active oilfield infrastructure after the calving period in 2000, late in the calving period in 2001, and likely before our sampling period in 2002. The timing of annual rehabituation was positively correlated with timing of spring snowmelt. Land and wildlife managers can use information from this study to develop calving period-specific mitigation measures that are more effective and flexible.Selon des recherches antérieures, pendant sa période de vêlage, le caribou (Rangifer tarandus) de l’Alaska arctique évite généralement les régions se trouvant à l’intérieur d’un kilomètre des routes où circulent des véhicules menant aux chantiers pétroliers. Cependant, cet évitement n’est pas absolu, et le caribou peut s’accoutumer aux infrastructures (comme les bâtiments, les routes et les chantiers) et à l’activité humaine. Nous avons effectué le dénombrement des caribous près des routes des champs de pétrole de la plaine côtière arctique de l’Alaska vers la fin de la période de vêlage et après la période de vêlage de juin 2000 à 2002. Nous avons consigné l’emplacement, la composition et le comportement des groupes de caribous se trouvant à moins d’un kilomètre des routes de gravier et des chantiers de production en activité. En moyenne, les caribous qui avaient des petits se tenaient plus loin des infrastructures pétrolières que les groupes de caribous qui n’avaient pas de petits. Cela dit, l’accoutumance aux activités pétrolières, dénotée par un moins grand évitement, survenait à des taux semblables pour les groupes qui avaient des petits et les groupes qui n’en avaient pas. Pendant la période de vêlage, les taux d’observation de caribous étaient plus élevés dans les régions où il y avait peu d’activité humaine, et les pourcentages de petits avaient tendance à être plus élevés la nuit, lorsqu’il y avait peu de va-et-vient aux chantiers. En moyenne, les groupes de caribous s’approchaient plus des infrastructures pendant les périodes suivant le vêlage des années 2000 et 2001, mais pas en 2002. En 2002, quand la neige a fondu plus tôt que d’habitude, les groupes de caribous s’approchaient plus des infrastructures pendant la période de vêlage qu’en 2000 et 2001, lorsque la neige a fondu plus tard. Cela fait ressortir l’importance de tenir compte des variables environnementales lorsque nous faisons des enquêtes sur les interactions dynamiques entre les caribous et les champs de pétrole. Dans l’ensemble, les caribous semblaient s’accoutumer aux infrastructures pétrolières en activité après la période de vêlage en 2000, puis vers la fin de la période de vêlage en 2001, et vraisemblablement avant notre période d’échantillonnage en 2002. Le moment de l’accoutumance annuelle coïncidait positivement avec le moment de la fonte des neiges au printemps. Les gestionnaires des terres et de la faune peuvent se servir de l’information émanant de cette étude pour élaborer des mesures d’atténuation tenant compte de la période de vêlage, mesures qui sont plus efficaces et qui présentent plus de souplesse
Entanglement, measurement, and conditional evolution of the Kondo singlet interacting with a mesoscopic detector
We investigate various aspects of the Kondo singlet in a quantum dot (QD)
electrostatically coupled to a mesoscopic detector. The two subsystems are
represented by an entangled state between the Kondo singlet and the
charge-dependent detector state. We show that the phase-coherence of the Kondo
singlet is destroyed in a way that is sensitive to the charge-state information
restored both in the magnitude and in the phase of the scattering coefficients
of the detector. We also introduce the notion of the `conditional evolution' of
the Kondo singlet under projective measurement on the detector. Our study
reveals that the state of the composite system is disentangled upon this
measurement. The Kondo singlet evolves into a particular state with a fixed
number of electrons in the quantum dot. Its relaxation time is shown to be
sensitive only to the QD-charge dependence of the transmission probability in
the detector, which implies that the phase information is erased in this
conditional evolution process. We discuss implications of our observations in
view of the possible experimental realization.Comment: Focus issue on "Interference in Mesoscopic Systems" of New J. Phy
High-fidelity simulations of CdTe vapor deposition from a new bond-order potential-based molecular dynamics method
CdTe has been a special semiconductor for constructing the lowest-cost solar
cells and the CdTe-based Cd1-xZnxTe alloy has been the leading semiconductor
for radiation detection applications. The performance currently achieved for
the materials, however, is still far below the theoretical expectations. This
is because the property-limiting nanoscale defects that are easily formed
during the growth of CdTe crystals are difficult to explore in experiments.
Here we demonstrate the capability of a bond order potential-based molecular
dynamics method for predicting the crystalline growth of CdTe films during
vapor deposition simulations. Such a method may begin to enable defects
generated during vapor deposition of CdTe crystals to be accurately explored
Entanglement dynamics of two qubits under the influence of external kicks and Gaussian pulses
We have investigated the dynamics of entanglement between two spin-1/2 qubits
that are subject to independent kick and Gaussian pulse type external magnetic
fields analytically as well as numerically. Dyson time ordering effect on the
dynamics is found to be important for the sequence of kicks. We show that
"almost-steady" high entanglement can be created between two initially
unentangled qubits by using carefully designed kick or pulse sequences
Single-qubit gates and measurements in the surface acoustic wave quantum computer
In the surface acoustic wave quantum computer, the spin state of an electron
trapped in a moving quantum dot comprises the physical qubit of the scheme. Via
detailed analytic and numerical modeling of the qubit dynamics, we discuss the
effect of excitations into higher-energy orbital states of the quantum dot that
occur when the qubits pass through magnetic fields. We describe how
single-qubit quantum operations, such as single-qubit rotations and
single-qubit measurements, can be performed using only localized static
magnetic fields. The models provide useful parameter regimes to be explored
experimentally when the requirements on semiconductor gate fabrication and the
nanomagnetics technology are met in the future.Comment: 13 pages, 10 figures, submitted to Phys. Rev.
Strong "quantum" chaos in the global ballooning mode spectrum of three-dimensional plasmas
The spectrum of ideal magnetohydrodynamic (MHD) pressure-driven (ballooning)
modes in strongly nonaxisymmetric toroidal systems is difficult to analyze
numerically owing to the singular nature of ideal MHD caused by lack of an
inherent scale length. In this paper, ideal MHD is regularized by using a
-space cutoff, making the ray tracing for the WKB ballooning formalism a
chaotic Hamiltonian billiard problem. The minimum width of the toroidal Fourier
spectrum needed for resolving toroidally localized ballooning modes with a
global eigenvalue code is estimated from the Weyl formula. This
phase-space-volume estimation method is applied to two stellarator cases.Comment: 4 pages typeset, including 2 figures. Paper accepted for publication
in Phys. Rev. Letter
Report on the May-June 2002 Englebright Lake deep coring campaign
This report describes the May-June 2002 Englebright Lake coring project. Englebright Lake is a 14-km-long reservoir on the Yuba River of northern California, impounded by Englebright Dam, which was completed in 1940. The sediments were cored to assess the current conditions in the reservoir as part of the California Bay-Delta Authority’s Upper Yuba River Studies Program. Sediment was collected using both hydraulic-piston and rotational coring equipment mounted on a floating drilling platform. Thirty boreholes were attempted at 7 sites spaced along the longitudinal axis of the reservoir. Complete sedimentary sections were recovered from 20 boreholes at 6 sites. In total, 335 m of sediment was cored, with 86% average recovery. The core sections (each up to 1.5 m long) were processed using a standard set of laboratory techniques, including geophysical logging of physical properties, splitting, visual descriptions, digital photography, and initial subsampling. This report presents the results of these analyses in a series of stratigraphic columns. Using the observed stratigraphy as a guide, several series of subsamples were collected for various sedimentologic, geochemical, and geochronological analyses. The results of laboratory analyses of most of these subsamples will be presented in future reports and articles
Facility for testing ice drills
The Rapid Access Ice Drill (RAID) is designed for subsurface scientific
investigations in Antarctica. Its objectives are to drill rapidly through
ice, to core samples of the transition zone and bedrock, and to leave behind
a borehole observatory. These objectives required the engineering and
fabrication of an entirely new drilling system that included a modified
mining-style coring rig, a unique fluid circulation system, a rod skid, a
power unit, and a workshop with areas for the storage of supplies and
consumables. An important milestone in fabrication of the RAID was the
construction of a North American Test (NAT) facility where we were able to
test drilling and fluid processing functions in an environment that is as
close as possible to that expected in Antarctica. Our criteria for site
selection was that the area should be cold during the winter months, be
located in an area of low heat flow, and be at relatively high elevation. We
selected a site for the facility near Bear Lake, Utah, USA.
The general design of the NAT well (NAT-1) started with a 27.3 cm (10.75 in.)
outer casing cemented in a 152 m deep hole. Within that casing, we
hung a 14 cm (5.5 in.) casing string, and, within that casing, a column of
ice was formed. The annulus between the 14 and 27.3 cm casings provided the
path for circulation of a refrigerant. After in-depth study, we chose to use
liquid CO2 to cool the hole. In order to minimize the likelihood of the
casing splitting due to the volume increase associated with freezing water,
the hole was first cooled and then ice was formed in increments from the
bottom upward. First, ice cubes were placed in the inner liner and then
water was added. Using this method, a column of ice was incrementally
prepared for drilling tests. The drilling tests successfully demonstrated
the functioning of the RAID system. Reproducing such a facility for testing
of other ice drilling systems could be advantageous to other research
programs in the future
Exact limiting relation between the structure factors in neutron and x-ray scattering
The ratio of the static matter structure factor measured in experiments on
coherent X-ray scattering to the static structure factor measured in
experiments on neutron scattering is considered. It is shown theoretically that
this ratio in the long-wavelength limit is equal to the nucleus charge at
arbitrary thermodynamic parameters of a pure substance (the system of nuclei
and electrons, where interaction between particles is pure Coulomb) in a
disordered equilibrium state. This result is the exact relation of the quantum
statistical mechanics. The experimental verification of this relation can be
done in the long wavelength X-ray and neutron experiments.Comment: 7 pages, no figure
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