31,803 research outputs found
Modular and standardized GAS payload hardware
The benefits of the standardized hardware included in the Get Away Special (GAS) space shuttle payloads are discussed. Payload requirements within the GAS program are summarized
A causal multifractal stochastic equation and its statistical properties
Multiplicative cascades have been introduced in turbulence to generate random
or deterministic fields having intermittent values and long-range power-law
correlations. Generally this is done using discrete construction rules leading
to discrete cascades. Here a causal log-normal stochastic process is
introduced; its multifractal properties are demonstrated together with other
properties such as the composition rule for scale dependence and stochastic
differential equations for time and scale evolutions. This multifractal
stochastic process is continuous in scale ratio and in time. It has a simple
generating equation and can be used to generate sequentially time series of any
length.Comment: Eur. Phys. J. B (in press
A spatially resolved limb flare on Algol B observed with XMM-Newton
We report XMM-Newton observations of the eclipsing binary Algol A (B8V) and B
(K2III). The XMM-Newton data cover the phase interval 0.35 - 0.58, i.e.,
specifically the time of optical secondary minimum, when the X-ray dark B-type
star occults a major fraction of the X-ray bright K-type star. During the
eclipse a flare was observed with complete light curve coverage. The decay part
of the flare can be well described with an exponential decay law allowing a
rectification of the light curve and a reconstruction of the flaring plasma
region. The flare occurred near the limb of Algol B at a height of about 0.1R
with plasma densities of a few times 10^11 cm^-3 consistent with spectroscopic
density estimates. No eclipse of the quiescent X-ray emission is observed
leading us to the conclusion that the overall coronal filling factor of Algol B
is small.Comment: 8 pages, 7 figures, accepted by A&
Time dependent intrinsic correlation analysis of temperature and dissolved oxygen time series using empirical mode decomposition
In the marine environment, many fields have fluctuations over a large range
of different spatial and temporal scales. These quantities can be nonlinear
\red{and} non-stationary, and often interact with each other. A good method to
study the multiple scale dynamics of such time series, and their correlations,
is needed. In this paper an application of an empirical mode decomposition
based time dependent intrinsic correlation, \red{of} two coastal oceanic time
series, temperature and dissolved oxygen (saturation percentage) is presented.
The two time series are recorded every 20 minutes \red{for} 7 years, from 2004
to 2011. The application of the Empirical Mode Decomposition on such time
series is illustrated, and the power spectra of the time series are estimated
using the Hilbert transform (Hilbert spectral analysis). Power-law regimes are
found with slopes of 1.33 for dissolved oxygen and 1.68 for temperature at high
frequencies (between 1.2 and 12 hours) \red{with} both close to 1.9 for lower
frequencies (time scales from 2 to 100 days). Moreover, the time evolution and
scale dependence of cross correlations between both series are considered. The
trends are perfectly anti-correlated. The modes of mean year 3 and 1 year have
also negative correlation, whereas higher frequency modes have a much smaller
correlation. The estimation of time-dependent intrinsic correlations helps to
show patterns of correlations at different scales, for different modes.Comment: 35 pages with 22 figure
Lagrangian Cascade in Three-Dimensional Homogeneous and Isotropic Turbulence
In this work, the scaling statistics of the dissipation along Lagrangian
trajectories are investigated by using fluid tracer particles obtained from a
high resolution direct numerical simulation with . Both the
energy dissipation rate and the local time averaged
agree rather well with the lognormal distribution hypothesis.
Several statistics are then examined. It is found that the autocorrelation
function of and variance of
obey a log-law with scaling exponent
compatible with the intermittency parameter . The
th-order moment of has a clear power-law on the inertial
range . The measured scaling exponent agrees
remarkably with where is the scaling exponent
estimated using the Hilbert methodology. All these results suggest that the
dissipation along Lagrangian trajectories could be modelled by a multiplicative
cascade.Comment: 10 pages with 7 figures accepted for Journal of Fluid Mechanics as
Rapid
The moon: An abundant source of clean and safe fusion fuel for the 21st century
It is shown how helium-3 can be obtained from the moon and how its use in fusion reactors can benefit the inhabitants of this planet. The physics and technology issues associated with the use of He-3 is addressed. A description is given of He-3 distribution on the moon and of methods which could be used to retrieve it
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