6,079 research outputs found
Thermal behavior of Quantum Cellular Automaton wires
We investigate the effect of a finite temperature on the behavior of logic
circuits based on the principle of Quantum Cellular Automata (QCA) and of
ground state computation. In particular, we focus on the error probability for
a wire of QCA cells that propagates a logic state. A numerical model and an
analytical, more approximate, model are presented for the evaluation of the
partition function of such a system and, consequently, of the desired
probabilities. We compare the results of the two models, assessing the limits
of validity of the analytical approach, and provide estimates for the maximum
operating temperature.Comment: 15 pages, 7 figures, uses revte
Virtual integration platform for computational fluid dynamics
Computational Fluid Dynamics (CFD) tools used in shipbuilding industry involve multiple disciplines, such as resistance, manoeuvring, and cavitation. Traditionally, the analysis was performed separately and sequentially in each discipline, which often resulted in conflict and inconsistency of hydrodynamic prediction. In an effort to solve such problems for future CFD computations, a Virtual Integration Platform (VIP) has been developed in the University of Strathclyde within two EU FP6 projects - VIRTUE and SAFEDOR1. The VIP provides a holistic collaborative environment for designers with features such as Project/Process Management, Distributed Tools Integration, Global Optimisation, Version Management, and Knowledge Management. These features enhance collaboration among customers, ship design companies, shipyards, and consultancies not least because they bring together the best expertise and resources around the world. The platform has been tested in seven European ship design companies including consultancies. Its main functionalities along with advances are presented in this paper with two industrial applications
How matters:End-of-life communication with family members of critically ill neonates, children, and adults
End-of-life decisions, more specifically decisions about whether to continue or discontinue the patientâs life-sustaining treatment, are among the most difficult decisions to make. Decision-making is emotionally overwhelming and complex for all involved in the communication- and decision-making process, especially when it concerns life and death decisions for another human being. These situations confront healthcare providers and family members of critically ill patients with the limitations of medical possibilities and human knowledge. In these situations, there is no way out but rather only a way through. As such, how matters.How physicians and family members of critically ill patients together make end-of-life decisions, how they communicate about these decisions, and how physicians learn to conduct such complex end-of-life conversations, can significantly impact the experiences and outcomes for patients, family members, and healthcare providers. In this thesis, we therefore obtained in-depth insights into end-of-life communication- and decision-making practices in intensive care units. We aimed to increase knowledge and awareness of how physicians actually communicate with the family members of critically ill neonates, children, and adults during real-life end-of-life conversations. Additionally, we explored how physicians perceive their own communication and how they (wish to) learn to communicate with family members of critically ill patients in end-of-life conversations. Based on our overall conclusions, we propose three âshiftsâ in communication. We also propose corresponding learning methods, to not only move toward effective end-of-life communication with families but also to move toward a valuing communication culture in intensive care medicine
Precise Measurements of the Kilohertz Quasi-Periodic Oscillations in 4U 1728-34
We have analyzed seventeen observations of the low-mass X-ray binary and
atoll source 4U 1728-34, carried out by the Rossi X-ray Timing Explorer in 1996
and 1997. We obtain precise measurements of the frequencies of the two
simultaneous kilohertz quasi-periodic oscillations (kHz QPOs) in this source.
We show that the frequency separation between the two QPO, , is
always significantly smaller than the frequency of the nearly-coherent
oscillations seen in this source during X-ray bursts, even at the lowest
inferred mass accretion rate, when seems to reach its maximum
value. We also find that decreases significantly, from Hz to Hz, as the frequency of the lower frequency kHz QPO
increases from 615 to 895 Hz. This is the first time that variations of the kHz
QPO peak separation are measured in a source which shows nearly-coherent
oscillations during bursts.Comment: Accepted for publication in The Astrophysical Journal Letters. Uses
AAS LaTex v4.0 (5 pages plus 4 postscript figures
Correlated X-ray spectral and fast-timing behaviour of 4U 1636-53
We present a study of the persistent X-ray emission from the low-mass X-ray
binary 4U 1636-53 based ont he entire archival EXOSAT ME data set. We per-
formed a homogeneous analysis of all five EXOSAT observations in terms of the
correlated rapid X-ray variability and X-ray spectral properties by means of
power spectra, and colour-colour and hardness-intensity diagrams, respectively.
Over the years we find similar patterns in the colour-colour and
hardness-intensity diagrams, but small shifts in their postions occur. We find
one case of an island-banana transition. On all but one occasion the
differences in colour are smaller than 5%. Between the two 'island state' data
sets, we find a shift of 8 % in the soft colour, which must be at least partly
intrinsic. Clear correlations are present between the X-ray colours (which are
governed by the mass accretion rate) and the power spectrum. With increasing
mass accretion rate the fractional rms amplitude of the power-law shaped power
spectral component that dominates the power spectra below ~1 Hz rises, while
the band-limited noise component at higher frequencies drops. The cut-off
frequency of the band-limited component increases whn its amplitude decreases.
This is reminiscent of the behaviour of black hole candidates in the low state.Comment: Accepted by Astronomy and Astrophysics, 10 pages, Latex, uses l-aa,
full version (including 8 figures) available at
http://www.astro.uva.nl/preprints/preprints.html, AIAP preprint nr 6
Spin-dependent transport in metal/semiconductor tunnel junctions
This paper describes a model as well as experiments on spin-polarized tunnelling with the aid of optical spin orientation. This involves tunnel junctions between a magnetic material and gallium arsenide (GaAs), where the latter is optically excited with circularly polarized light in order to generate spin-polarized carriers. A transport model is presented that takes account of carrier capture in the semiconductor surface states, and describes the semiconductor surface in terms of a spin-dependent energy distribution function. The so-called surface spin-splitting can be calculated from the balance of the polarized electron and hole flow in the semiconductor subsurface region, the polarized tunnelling current across the tunnel barrier between the magnetic material and the semiconductor surface, and the spin relaxation at the semiconductor surface.
Measurements are presented of the circular-polarization-dependent photocurrent (the so-called helicity asymmetry) in thin-film tunnel junctions of Co/Al2O3/GaAs. In the absence of a tunnel barrier, the helicity asymmetry is caused by magneto-optical effects (magnetic circular dichroism). In the case where a tunnel barrier is present, the data cannot be explained by magneto-optical effects alone; the deviations provide evidence that spin-polarized tunnelling due to optical spin orientation occurs. In Co/Ï-MnAl/AlAs/GaAs junctions no deviations from the magneto-optical effects are observed, most probably due to the weak spin polarization of Ï-MnAl along the tunnelling direction; the latter is corroborated by bandstructure calculations. Finally, the application of photoexcited GaAs for spin-polarized tunnelling in a scanning tunnelling microscope is discussed.
An automated thermal-relaxation calorimeter for operation at low temperature (0.5 K <T <10 K)
The authors describe an automated calorimeter for measurement of the sp. heats at 10 > T > 0.5 K. It uses sample of moderate size (100-1000 mg), has a moderate precision and accuracy (2%-5%), is easy to operate and the measurements can be done quickly with He4. The accuracy of this calorimeter was checked by measurement of sp. heat of copper and that of aluminum near its superconducting transition temp. [on SciFinder (R)
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