30,763 research outputs found
Power and cross-power spectrum analysis by hybrid computers
Power and cross power spectrum analysis by hybrid computer
Design zero-voltage switching DC-DC buck converter
This report proposes an integrated, high switching frequency, zero-voltage-switching
dc-dc buck converter for battery charger application. The design and analysis of dc�dc buck converter with integrated inductor is presented. The converter has been
optimized to convert 12V input voltage to 5V at 1.5A maximum load current at
50MHz switching frequency. The converter has been simulated using an ORCAD
16.5 based simulation tool and result show that the switching losses using zero�voltage-switching technique is less compared to conventional buck converter
Sensitivity of Space Station alpha joint robust controller to structural modal parameter variations
The photovoltaic array sun tracking control system of Space Station Freedom is described. A synthesis procedure for determining optimized values of the design variables of the control system is developed using a constrained optimization technique. The synthesis is performed to provide a given level of stability margin, to achieve the most responsive tracking performance, and to meet other design requirements. Performance of the baseline design, which is synthesized using predicted structural characteristics, is discussed and the sensitivity of the stability margin is examined for variations of the frequencies, mode shapes and damping ratios of dominant structural modes. The design provides enough robustness to tolerate a sizeable error in the predicted modal parameters. A study was made of the sensitivity of performance indicators as the modal parameters of the dominant modes vary. The design variables are resynthesized for varying modal parameters in order to achieve the most responsive tracking performance while satisfying the design requirements. This procedure of reoptimization design parameters would be useful in improving the control system performance if accurate model data are provided
Quantum random number generation for 1.25 GHz quantum key distribution systems
Security proofs of quantum key distribution (QKD) systems usually assume that
the users have access to source of perfect randomness. State-of-the-art QKD
systems run at frequencies in the GHz range, requiring a sustained GHz rate of
generation and acquisition of quantum random numbers. In this paper we
demonstrate such a high speed random number generator. The entropy source is
based on amplified spontaneous emission from an erbium-doped fibre, which is
directly acquired using a standard small form-factor pluggable (SFP) module.
The module connects to the Field Programmable Gate Array (FPGA) of a QKD
system. A real-time randomness extractor is implemented in the FPGA and
achieves a sustained rate of 1.25 Gbps of provably random bits.Comment: 6 pages, 8 figure
Destructive physical analysis results of Ni/H2 cells cycled in LEO regime
Six 48-Ah individual pressure vessel (IPV) Ni/H2 cells containing 26 and 31 percent KOH electrolyte were life cycle tested in low Earth orbit. All three cells containing 31 percent KOH failed (3729, 4165, and 11,355 cycles), while those with 26 percent KOH were cycled over 14,000 times in the continuing test. Destructive physical analysis (DPA) of the failed cells included visual inspections, measurements of electrode thickness, scanning electron microscopy, chemical analysis, and measurements of nickel electrode capacity in an electrolyte flooded cell. The cycling failure was due to a decrease of nickel electrode capacity. As possible causes of the capacity decrease, researchers observed electrode expansion, rupture, and corrosion of the nickel electrode substrate, active material redistribution, and accumulation of electrochemically undischargeable active material with cycling
Measurement of Spin Polarization by Andreev Reflection in Ferromagnetic In1-xMnxSb Epilayers
We carried out Point Contact Andreev Reflection (PCAR) spin spectroscopy
measurements on epitaxially-grown ferromagnetic In1-xMnxSb epilayers with a
Curie temperature of ~9K. The spin sensitivity of PCAR in this material was
demonstrated by parallel control studies on its non-magnetic analog,
In1-yBeySb. We found the conductance curves of the Sn point contacts with
In1-yBeySb to be fairly conventional, with the possible presence of
proximity-induced superconductivity effects at the lowest temperatures. The
experimental Z-values of interfacial scattering agreed well with the estimates
based on the Fermi velocity mismatch between the semiconductor and the
superconductor. These measurements provided control data for subsequent PCAR
measurements on ferromagnetic In1-xMnxSb, which indicated spin polarization in
In1-xMnxSb to be 52 +- 3%
Learning Points and Routes to Recommend Trajectories
The problem of recommending tours to travellers is an important and broadly
studied area. Suggested solutions include various approaches of
points-of-interest (POI) recommendation and route planning. We consider the
task of recommending a sequence of POIs, that simultaneously uses information
about POIs and routes. Our approach unifies the treatment of various sources of
information by representing them as features in machine learning algorithms,
enabling us to learn from past behaviour. Information about POIs are used to
learn a POI ranking model that accounts for the start and end points of tours.
Data about previous trajectories are used for learning transition patterns
between POIs that enable us to recommend probable routes. In addition, a
probabilistic model is proposed to combine the results of POI ranking and the
POI to POI transitions. We propose a new F score on pairs of POIs that
capture the order of visits. Empirical results show that our approach improves
on recent methods, and demonstrate that combining points and routes enables
better trajectory recommendations
Enhancement of plasticity in Ti-based metallic glass matrix composites by controlling characteristic and volume fraction of primary phase
In this study, Ti-based metallic glass matrix composites with high plasticity have been developed by controlling characteristic and volume fraction of primary phase embedded in the glass matrix. By careful alloy design procedure, the compositions of Ăź/glass phases, which are in metastable equilibrium have been properly selected, therefore the mechanical properties can be tailored by selecting the alloy compositions between the composition of Ăź and glass phases. The relation between the compressive yield strength and volume fraction of Ăź phase is well described using the rule of mixtures
Density dependence of the Ionization Avalanche in ultracold Rydberg gases
We report on the behaviour of the ionization avalanche in an ensemble of
ultracold 87Rb atoms coupled to a high lying Rydberg state and investigate
extensions to the current model by including the effects of three-body
recombination and plasma expansion. To separate the two effects we study the
time dependence of the plasma formation at various densities as well as for
different nS and nD states. At medium densities and low n we observe the onset
of the avalanche as has been reported in other experiments, as well as a
subsequent turn-off of the avalanche for longer excitation times, which we
associate with plasma expansion. At higher densities and for higher lying
Rydberg states we observe a disappearance of the avalanche signature, which we
attribute to three-body recombination.Comment: 5 pages, 4 figure
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