1,431 research outputs found
The performance and application of high speed long life LH2 hybrid bearings for reusable rocket engine turbomachinery
Data are presented for two different experimental programs which were conducted to investigate the characteristics of a hybrid (hydrostatic/ball) bearing operating in liquid hydrogen. The same bearing design was used in both programs. Analytical predictions were made of the bearing characteristics and are compared with the experimental results when possible. The first program used a bearing tester to determine the steady state, transient, and cyclic life characteristics of the bearing over a wide range of operating conditions. The second program demonstrated the feasibility of applying hybrid bearings to an actual high speed turbopump by retrofitting and then testing an existing liquid hydrogen turbopump with the bearings
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
Application of quantum Darwinism to a structured environment
Quantum Darwinism extends the traditional formalism of decoherence to explain the emergence of classicality in a quantum universe. A classical description emerges when the environment tends to redundantly acquire information about the pointer states of an open system. In light of recent interest, we apply the theoretical tools of the framework to a qubit coupled with many bosonic subenvironments. We examine the degree to which the same classical information is encoded across collections of (i) complete subenvironments and (ii) residual “pseudomode” components of each subenvironment, the conception of which provides a dynamic representation of the reservoir memory. Overall, significant redundancy of information is found as a typical result of the decoherence process. However, by examining its decomposition in terms of classical and quantum correlations, we discover classical information to be nonredundant in both cases i and ii. Moreover, with the full collection of pseudomodes, certain dynamical regimes realize opposite effects, where either the total classical or quantum correlations predominantly decay over time. Finally, when the dynamics are non-Markovian, we find that redundant information is suppressed in line with information backflow to the qubit. By quantifying redundancy, we concretely show it to act as a witness to non-Markovianity in the same way as the trace distance does for nondivisible dynamical maps
Entanglement Evolution in the Presence of Decoherence
The entanglement of two qubits, each defined as an effective two-level, spin
1/2 system, is investigated for the case that the qubits interact via a
Heisenberg XY interaction and are subject to decoherence due to population
relaxation and thermal effects. For zero temperature, the time dependent
concurrence is studied analytically and numerically for some typical initial
states, including a separable (unentangled) initial state. An analytical
formula for non-zero steady state concurrence is found for any initial state,
and optimal parameter values for maximizing steady state concurrence are given.
The steady state concurrence is found analytically to remain non-zero for low,
finite temperatures. We also identify the contributions of global and local
coherence to the steady state entanglement.Comment: 12 pages, 4 figures. The second version of this paper has been
significantly expanded in response to referee comments. The revised
manuscript has been accepted for publication in Journal of Physics
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
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Bridge-specific fragility analysis: when is it really necessary?
In seismic assessment of bridges the research focus has recently shifted on the derivation of bridge-specific fragility curves that account for the effect of different geometry, structural system, component and soil properties, on the seismic behaviour. In this context, a new, component-based methodology for the derivation of bridge-specific fragility curves has been recently proposed by the authors, with a view to overcoming the inherent difficulties in assessing all bridges of a road network and the drawbacks of existing methodologies, which use the same group of fragility curves for bridges within the same typological class. The main objective of this paper is to critically assess the necessity of bridge-specific fragility analysis, starting from the effect of structure-specific parameters on component capacity (limit state thresholds), seismic demand, and fragility curves. The aforementioned methodology is used to derive fragility curves for all bridges within an actual road network, with a view to investigating the consistency of adopting generic fragility curves for bridges that fall within the same class and quantifying the degree of over- or under-estimation of the probability of damage when generic bridge classes are considered. Moreover, fragility curves for all representative bridges of the analysed concrete bridge classes are presented to illustrate the differentiation in bridge fragility for varying structural systems, bridge geometry, total bridge length and maximum pier height. Based on the above, the relevance of bridge-specific fragility analysis is assessed, and pertinent conclusions are drawn
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
Suppression of decoherence by bath ordering
The dynamics of two coupled spins-1/2 coupled to a spin-bath is studied as an
extended model of the Tessieri-Wilkie Hamiltonian \cite{TWmodel}. The pair of
spins served as an open subsystem were prepared in one of the Bell states and
the bath consisted of some spins-1/2 is in a thermal equilibrium state from the
very beginning. It is found that with the increasing the coupling strength of
the bath spins, the bath forms a resonant antiferromagnetic order. The
polarization correlation between the two spins of the subsystem and the
concurrence are recovered in some extent to the isolated subsystem. This
suppression of the subsystem decoherence may be used to control the quantum
devices in practical applications.Comment: 32 pages, Chinese Physics (accepted
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