1,210 research outputs found
Radiation from carbon in a rocket plume mixing region with coupled convective and radiative energy fluxes and general optical thickness
Carbon radiant heat transfer from plume mixing region to base of rocket vehicl
Computation of unsteady transonic flows through rotating and stationary cascades. 3: Acoustic far-field analysis
A small perturbation type analysis has been developed for the acoustic far field in an infinite duct extending upstream and downstream of an axial turbomachinery stage. The analysis is designed to interface with a numerical solution of the near field of the blade rows and, thereby, to provide the necessary closure condition to complete the statement of infinite duct boundary conditions for the subject problem. The present analysis differs from conventional inlet duct analyses in that a simple harmonic time dependence was not assumed, since a transient signal is generated by the numerical near-field solution and periodicity is attained only asymptotically. A description of the computer code developed to carry out the necessary convolutions numerically is included, as well as the results of a sample application using an impulsively initiated harmonic signal
Diffusion-limited reactions and mortal random walkers in confined geometries
Motivated by the diffusion-reaction kinetics on interstellar dust grains, we
study a first-passage problem of mortal random walkers in a confined
two-dimensional geometry. We provide an exact expression for the encounter
probability of two walkers, which is evaluated in limiting cases and checked
against extensive kinetic Monte Carlo simulations. We analyze the continuum
limit which is approached very slowly, with corrections that vanish
logarithmically with the lattice size. We then examine the influence of the
shape of the lattice on the first-passage probability, where we focus on the
aspect ratio dependence: Distorting the lattice always reduces the encounter
probability of two walkers and can exhibit a crossover to the behavior of a
genuinely one-dimensional random walk. The nature of this transition is also
explained qualitatively.Comment: 18 pages, 16 figure
Estimates for practical quantum cryptography
In this article I present a protocol for quantum cryptography which is secure
against attacks on individual signals. It is based on the Bennett-Brassard
protocol of 1984 (BB84). The security proof is complete as far as the use of
single photons as signal states is concerned. Emphasis is given to the
practicability of the resulting protocol. For each run of the quantum key
distribution the security statement gives the probability of a successful key
generation and the probability for an eavesdropper's knowledge, measured as
change in Shannon entropy, to be below a specified maximal value.Comment: Authentication scheme corrected. Other improvements of presentatio
Complete physical simulation of the entangling-probe attack on the BB84 protocol
We have used deterministic single-photon two qubit (SPTQ) quantum logic to
implement the most powerful individual-photon attack against the
Bennett-Brassard 1984 (BB84) quantum key distribution protocol. Our measurement
results, including physical source and gate errors, are in good agreement with
theoretical predictions for the Renyi information obtained by Eve as a function
of the errors she imparts to Alice and Bob's sifted key bits. The current
experiment is a physical simulation of a true attack, because Eve has access to
Bob's physical receiver module. This experiment illustrates the utility of an
efficient deterministic quantum logic for performing realistic physical
simulations of quantum information processing functions.Comment: 4 pages, 5 figure
Mechanical ventilation: lessons from the ARDSNet trial
The acute respiratory distress syndrome (ARDS) is an inflammatory disease of the lungs characterized clinically by bilateral pulmonary infiltrates, decreased pulmonary compliance and hypoxemia. Although supportive care for ARDS seems to have improved over the past few decades, few studies have shown that any treatment can decrease mortality for this deadly syndrome. In the 4 May 2000 issue of New England Journal of Medicine, the results of an NIH-sponsored trial were presented; they demonstrated that the use of a ventilatory strategy that minimizes ventilator-induced lung injury leads to a 22% decrease in mortality. The implications of this study with respect to clinical practice, further ARDS studies and clinical research in the critical care setting are discussed
The Critical Coupling Likelihood Method: A new approach for seamless integration of environmental and operating conditions of gravitational wave detectors into gravitational wave searches
Any search effort for gravitational waves (GW) using interferometric
detectors like LIGO needs to be able to identify if and when noise is coupling
into the detector's output signal. The Critical Coupling Likelihood (CCL)
method has been developed to characterize potential noise coupling and in the
future aid GW search efforts. By testing two hypotheses about pairs of
channels, CCL is able to identify undesirable coupled instrumental noise from
potential GW candidates. Our preliminary results show that CCL can associate up
to of observed artifacts with , to local noise sources,
while reducing the duty cycle of the instrument by . An approach
like CCL will become increasingly important as GW research moves into the
Advanced LIGO era, going from the first GW detection to GW astronomy.Comment: submitted CQ
Polyclonal Infections Due to Mycobacterium Avium Complex in Patients with AIDS Detected by Pulsed-field Gel Electrophoresis of Sequential Clinical Isolates.
Invasive infection with organisms of the Mycobacterium avium complex (MAC) is common among patients with advanced human immunodeficiency virus infection. In previous studies, we analyzed multiple individual colonies of MAC isolated from specimens obtained at the same time and observed that 14 to 20% of patients are simultaneously infected with more than one strain. In this study, we examined sequential isolates from 12 patients with AIDS who had two or more MAC isolates available from clinical specimens collected more than 1 week apart; the intervals between the first and last specimens ranged from 8 to 192 (median, 46) days. For each isolate, restriction digests of genomic DNA were analyzed by pulsed-field gel electrophoresis; DNA was prepared by using a protocol, described here in detail, which had been optimized for conditions of bacterial growth and lysis. The pulsed-field gel electrophoresis analysis identified four patients (33%) infected with two different MAC strains. Both M. avium and M. intracellulare were cultured from blood specimens from two patients. In each of the four patients, the second strain was identified from a culture taken within 14 days of the initial study isolate, and in three of these patients, the first strain was detected again in a subsequent culture. These observations suggest that the presence of two different strains among isolates from sequential cultures may reflect ongoing polyclonal infection. We conclude that polyclonal infection with MAC is common among patients with AIDS. The identification of such infections may be critical in the development of effective treatments
Cost-benefit analysis for commissioning decisions in GEO600
Gravitational wave interferometers are complex instruments, requiring years
of commissioning to achieve the required sensitivities for the detection of
gravitational waves, of order 10^-21 in dimensionless detector strain, in the
tens of Hz to several kHz frequency band. Investigations carried out by the
GEO600 detector characterisation group have shown that detector
characterisation techniques are useful when planning for commissioning work. At
the time of writing, GEO600 is the only large scale laser interferometer
currently in operation running with a high duty factor, 70%, limited chiefly by
the time spent commissioning the detector. The number of observable
gravitational wave sources scales as the product of the volume of space to
which the detector is sensitive and the observation time, so the goal of
commissioning is to improve the detector sensitivity with the least possible
detector down time. We demonstrate a method for increasing the number of
sources observable by such a detector, by assessing the severity of
non-astrophysical noise contaminations to efficiently guide commissioning. This
method will be particularly useful in the early stages and during the initial
science runs of the aLIGO and adVirgo detectors, as they are brought up to
design performance.Comment: 17 pages, 17 figures, 2 table
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