6,729 research outputs found
Development of microwave NDT inspection techniques for large solid propellant rocket motors Final report
Microwave nondestructive testing techniques for large solid propellant rocket engine
Discovery of Pulsed X-ray Emission from the SMC Transient RX J0117.6-7330
We report on the detection of pulsed, broad-band, X-ray emission from the
transient source RX J0117.6-7330. The pulse period of 22 seconds is detected by
the ROSAT/PSPC instrument in a 1992 Sep 30 - Oct 2 observation and by the
CGRO/BATSE instrument during the same epoch. Hard X-ray pulsations are
detectable by BATSE for approximately 100 days surrounding the ROSAT
observation (1992 Aug 28 - Dec 8). The total directly measured X-ray luminosity
during the ROSAT observation is 1.0E38 (d/60 kpc)^2 ergs s-1. The pulse
frequency increases rapidly during the outburst, with a peak spin-up rate of
1.2E-10 Hz s-1 and a total frequency change 1.8%. The pulsed percentage is
11.3% from 0.1-2.5 keV, increasing to at least 78% in the 20-70 keV band. These
results establish RX J0117.6-7330 as a transient Be binary system.Comment: 17 pages, Latex, aasms, accepted for publication in ApJ Letter
The use of disjunct eddy sampling methods for the determination of ecosystem level fluxes of trace gases
The concept of disjunct eddy sampling (DES)
for use in measuring ecosystem-level micrometeorological
fluxes is re-examined. The governing equations are discussed
as well as other practical considerations and guidelines concerning
this sampling method as it is applied to either the
disjunct eddy covariance (DEC) or disjunct eddy accumulation
(DEA) techniques. A disjunct eddy sampling system
was constructed that could either be combined with relatively
slow sensors (response time of 2 to 40 s) to measure
fluxes using DEC, or could also be used to accumulate samples
in stable reservoirs for later laboratory analysis (DEA
technique). Both the DEC and DEA modes of this sampler
were tested against conventional eddy covariance (EC) for
fluxes of either CO2 (DEC) or isoprene (DEA). Good agreement
in both modes was observed relative to the EC systems.
However, the uncertainty in a single DEA flux measurement
was considerable (40%) due to both the reduced statistical
sampling and the analytical precision of the concentration
difference measurements. We have also re-investigated
the effects of nonzero mean vertical wind velocity on accumulation
techniques as it relates to our DEA measurements.
Despite the higher uncertainty, disjunct eddy sampling can
provide an alternative technique to eddy covariance for determining
ecosystem-level fluxes for species where fast sensors
do not currently exist
Timing Features of the Accretion--driven Millisecond X-Ray Pulsar XTE J1807--294 in 2003 March Outburst
In order to probe the activity of the inner disk flow and its effect on the
neutron star surface emissions, we carried out the timing analysis of the Rossi
X-Ray Timing Explorer (RXTE) observations of the millisecond X-ray pulsar XTE
J1807--294, focusing on its correlated behaviors in X-ray intensities, hardness
ratios, pulse profiles and power density spectra. The source was observed to
have a serial of broad "puny" flares on a timescale of hours to days on the top
of a decaying outburst in March 2003. In the flares, the spectra are softened
and the pulse profiles become more sinusoidal. The frequency of kilohertz
quasi-periodic oscillation (kHz QPO) is found to be positively related to the
X-ray count rate in the flares. These features observed in the flares could be
due to the accreting flow inhomogeneities. It is noticed that the fractional
pulse amplitude increases with the flare intensities in a range of , comparable to those observed in the thermonuclear bursts of the
millisecond X-ray pulsar XTE J1814--338, whereas it remains at about 6.5% in
the normal state. Such a significant variation of the pulse profile in the
"puny" flares may reflect the changes of physical parameters in the inner disk
accretion region. Furthermore, we noticed an overall positive correlation
between the kHz QPO frequency and the fractional pulse amplitude, which could
be the first evidence representing that the neutron-star surface emission
properties are very sensitive to the disk flow inhomogeneities. This effect
should be cautiously considered in the burst oscillation studies.Comment: Accepted by ApJ, 23 pages, 7 figures, 3 table
Stochastic Process Associated with Traveling Wave Solutions of the Sine-Gordon Equation
Stochastic processes associated with traveling wave solutions of the
sine-Gordon equation are presented. The structure of the forward Kolmogorov
equation as a conservation law is essential in the construction and so is the
traveling wave structure. The derived stochastic processes are analyzed
numerically. An interpretation of the behaviors of the stochastic processes is
given in terms of the equation of motion.Comment: 12 pages, 9 figures; corrected typo
Key inflammatory pathway activations in the MCI stage of Alzheimer's disease
OBJECTIVE:
To determine the key inflammatory pathways that are activated in the peripheral and CNS compartments at the mild cognitive impairment (MCI) stage of Alzheimer's disease (AD).
METHODS:
A cross-sectional study of patients with clinical and biomarker characteristics consistent with MCI-AD in a discovery cohort, with replication in the Alzheimer's Disease Neuroimaging Initiative (ADNI) cohort. Inflammatory analytes were measured in the CSF and plasma with the same validated multiplex analyte platform in both cohorts and correlated with AD biomarkers (CSF Aβ42, total tau (t-tau), phosphorylated tau (p-tau) to identify key inflammatory pathway activations. The pathways were additionally validated by evaluating genes related to all analytes in coexpression networks of brain tissue transcriptome from an autopsy confirmed AD cohort to interrogate if the same pathway activations were conserved in the brain tissue gene modules.
RESULTS:
Analytes of the tumor necrosis factor (TNF) signaling pathway (KEGG ID:4668) in the CSF and plasma best correlated with CSF t-tau and p-tau levels, and analytes of the complement and coagulation pathway (KEGG ID:4610) best correlated with CSF Aβ42 levels. The top inflammatory signaling pathways of significance were conserved in the peripheral and the CNS compartments. They were also confirmed to be enriched in AD brain transcriptome gene clusters.
INTERPRETATION:
A cell-protective rather than a proinflammatory analyte profile predominates in the CSF in relation to neurodegeneration markers among MCI-AD patients. Analytes from the TNF signaling and the complement and coagulation pathways are relevant in evaluating disease severity at the MCI stage of AD
Solar Magnetic Tracking. I. Software Comparison and Recommended Practices
Feature tracking and recognition are increasingly common tools for data
analysis, but are typically implemented on an ad-hoc basis by individual
research groups, limiting the usefulness of derived results when selection
effects and algorithmic differences are not controlled. Specific results that
are affected include the solar magnetic turnover time, the distributions of
sizes, strengths, and lifetimes of magnetic features, and the physics of both
small scale flux emergence and the small-scale dynamo. In this paper, we
present the results of a detailed comparison between four tracking codes
applied to a single set of data from SOHO/MDI, describe the interplay between
desired tracking behavior and parameterization of tracking algorithms, and make
recommendations for feature selection and tracking practice in future work.Comment: In press for Astrophys. J. 200
Nanorheology of viscoelastic shells: Applications to viral capsids
We study the microrheology of nanoparticle shells [Dinsmore et al. Science
298, 1006 (2002)] and viral capsids [Ivanovska et al. PNAS 101, 7600 (2004)] by
computing the mechanical response function and thermal fluctuation spectrum of
a viscoelastic spherical shell that is permeable to the surrounding solvent. We
determine analytically the damped dynamics of the shear, bend, and compression
modes of the shell coupled to the solvent both inside and outside the sphere in
the zero Reynolds number limit. We identify fundamental length and time scales
in the system, and compute the thermal correlation function of displacements of
antipodal points on the sphere and the mechanical response to pinching forces
applied at these points. We describe how such a frequency-dependent antipodal
correlation and/or response function, which should be measurable in new
AFM-based microrheology experiments, can probe the viscoelasticity of these
synthetic and biological shells constructed of nanoparticles.Comment: 17 page
Orthogonal, solenoidal, three-dimensional vector fields for no-slip boundary conditions
Viscous fluid dynamical calculations require no-slip boundary conditions.
Numerical calculations of turbulence, as well as theoretical turbulence closure
techniques, often depend upon a spectral decomposition of the flow fields.
However, such calculations have been limited to two-dimensional situations.
Here we present a method that yields orthogonal decompositions of
incompressible, three-dimensional flow fields and apply it to periodic
cylindrical and spherical no-slip boundaries.Comment: 16 pages, 2 three-part figure
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