1,297 research outputs found
Analysis of a communication satellite for lunar far-side exploration
Analysis of communication satellite for lunar far-side exploration relaying color television, voice, high-bit-rate telemetry data, and ranging code from command and service, and lunar module
Radiation testing of composite materials, in situ versus ex situ effects
The effect of post irradiation test environments on tensile properties of representative advanced composite materials (T300/5208, T300/934, C6000/P1700) was investigated. Four ply (+ or - 45 deg/+ or - 45 deg) laminate tensile specimens were exposed in vacuum up to a bulk dose of 1 x 10 to the 10th power rads using a mono-energetic fluence of 700 keV electrons from a Van de Graaff accelerator. Post irradiation testing was performed while specimens were being irradiated (in situ data), in vacuum after cessation of irradiation (in vacuo data), and after exposure to air (ex situ data). Room temperature and elevated temperature effects were evaluated. The radiation induced changes to the tensile properties were small. Since the absolute changes in tensile properties were small, the existance of a post irradiation test environment effect was indeterminate
Ground state spin and Coulomb blockade peak motion in chaotic quantum dots
We investigate experimentally and theoretically the behavior of Coulomb
blockade (CB) peaks in a magnetic field that couples principally to the
ground-state spin (rather than the orbital moment) of a chaotic quantum dot. In
the first part, we discuss numerically observed features in the magnetic field
dependence of CB peak and spacings that unambiguously identify changes in spin
S of each ground state for successive numbers of electrons on the dot, N. We
next evaluate the probability that the ground state of the dot has a particular
spin S, as a function of the exchange strength, J, and external magnetic field,
B. In the second part, we describe recent experiments on gate-defined GaAs
quantum dots in which Coulomb peak motion and spacing are measured as a
function of in-plane magnetic field, allowing changes in spin between N and N+1
electron ground states to be inferred.Comment: To appear in Proceedings of the Nobel Symposium 2000 (Physica
Scripta
Pre-hospital emergency nurse specialist's experiences in caring for patients with non-specific chief complaints in the ambulance - A qualitative interview study
Background: Pre-hospital emergency nurse (PEN) specialists are faced with patients presenting with non-specific chief complaints (NSC) to the emergency medical service (EMS) on a daily basis. These patients are often elderly and one in three has a serious condition and their acuity is not recognized. Objective: The aim of the current study was to explore PEN specialists' experiences in caring for patients presenting with non-specific chief complaints. Design: A qualitative study design with eleven individual interviews of PENs, between 2018 and 2020. Qualitative content analysis was used. Results: The analyses generated three categories including subcategories. The categories were "Unexplained suffering". "Systematic approach and experience enhances medical safety". "Organizational processes can be optimized". The relation between the categories compiled as 'In-depth systematic assessment is perceived to reduce suffering and increases patient safety. Conclusion: The PENs experiences in caring for patients presenting with non-specific chief complaints show that an in-depth systematic assessment may lead to a meaningful caring encounter which enables the identification of the cause of the chief complaint. Experience and a systematic approach were considered as essential to enhance medical safety. This could be strengthened through feedback on the nurse's care provided by care managers and employers. To optimize organizational processes, the development of the opportunity to convey the patient to different levels of care can be an important component.Peer reviewe
Interactions and Disorder in Quantum Dots: Instabilities and Phase Transitions
Using a fermionic renormalization group approach we analyse a model where the
electrons diffusing on a quantum dot interact via Fermi-liquid interactions.
Describing the single-particle states by Random Matrix Theory, we find that
interactions can induce phase transitions (or crossovers for finite systems) to
regimes where fluctuations and collective effects dominate at low energies.
Implications for experiments and numerical work on quantum dots are discussed.Comment: 4 pages, 1 figure; version to appear in Phys Rev Letter
Spin and e-e interactions in quantum dots: Leading order corrections to universality and temperature effects
We study the statistics of the spacing between Coulomb blockade conductance
peaks in quantum dots with large dimensionless conductance g. Our starting
point is the ``universal Hamiltonian''--valid in the g->oo limit--which
includes the charging energy, the single-electron energies (described by random
matrix theory), and the average exchange interaction. We then calculate the
magnitude of the most relevant finite g corrections, namely, the effect of
surface charge, the ``gate'' effect, and the fluctuation of the residual e-e
interaction. The resulting zero-temperature peak spacing distribution has
corrections of order Delta/sqrt(g). For typical values of the e-e interaction
(r_s ~ 1) and simple geometries, theory does indeed predict an asymmetric
distribution with a significant even/odd effect. The width of the distribution
is of order 0.3 Delta, and its dominant feature is a large peak for the odd
case, reminiscent of the delta-function in the g->oo limit. We consider finite
temperature effects next. Only after their inclusion is good agreement with the
experimental results obtained. Even relatively low temperature causes large
modifications in the peak spacing distribution: (a) its peak is dominated by
the even distribution at kT ~ 0.3 Delta (at lower T a double peak appears); (b)
it becomes more symmetric; (c) the even/odd effect is considerably weaker; (d)
the delta-function is completely washed-out; and (e) fluctuation of the
coupling to the leads becomes relevant. Experiments aimed at observing the T=0
peak spacing distribution should therefore be done at kT<0.1 Delta for typical
values of the e-e interaction.Comment: 15 pages, 4 figure
How close are we to complete annotation of metabolomes?
The metabolome describes the full complement of the tens to hundreds of thousands of low molecular weight metabolites present within a biological system. Identification of the metabolome is critical for discovering the maximum amount of biochemical knowledge from metabolomics datasets. Yet no exhaustive experimental characterisation of any organismal metabolome has been reported to date, dramatically contrasting with the genome sequencing of thousands of plants, animals and microbes. Here we review the status of metabolome annotation and describe advances in the analytical methodologies being applied. In part through new international coordination, we conclude that we are now entering a new era of metabolome annotation
Kondo effect in real quantum dots
Exchange interaction within a quantum dot strongly affects the transport
through it in the Kondo regime. In a striking difference with the results of
the conventional model, where this interaction is neglected, here the
temperature and magnetic field dependence of the conductance may become
non-monotonic: its initial increase follows by a drop when temperature and
magnetic field are lowered
Discrete charging of metallic grains: Statistics of addition spectra
We analyze the statistics of electrostatic energies (and their differences)
for a quantum dot system composed of a finite number of electron islands
(metallic grains) with random capacitance-inductance matrix , for which the
total charge is discrete, (where is the charge of an electron and
is an integer). The analysis is based on a generalized charging model,
where the electrons are distributed among the grains such that the
electrostatic energy E(N) is minimal. Its second difference (inverse
compressibility) represents the spacing between
adjacent Coulomb blockade peaks appearing when the conductance of the quantum
dot is plotted against gate voltage. The statistics of this quantity has been
the focus of experimental and theoretical investigations during the last two
decades. We provide an algorithm for calculating the distribution function
corresponding to and show that this function is piecewise
polynomial.Comment: 21 pages, no figures, mathematical nomenclature (except for Abstract
and Introduction
Mesoscopic Tunneling Magnetoresistance
We study spin-dependent transport through
ferromagnet/normal-metal/ferromagnet double tunnel junctions in the mesoscopic
Coulomb blockade regime. A general transport equation allows us to calculate
the conductance in the absence or presence of spin-orbit interaction and for
arbitrary orientation of the lead magnetizations. The tunneling
magnetoresistance (TMR), defined at the Coulomb blockade conductance peaks, is
calculated and its probability distribution presented. We show that mesoscopic
fluctuations can lead to the optimal value of the TMR.Comment: 5 pages, 3 eps figures included using epsf.sty. Revised text and
improved notation, fig. 2 removed, explicit equations for the GSE case adde
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