13,314 research outputs found
Speed of light on rotating platforms
It is often taken for granted that on board a rotating disk it is possible to
operate a \QTR{it}{global}3+1 splitting of space-time, such that both lengths
and time intervals are \QTR{it}{uniquely} defined in terms of measurements
performed by real rods and real clocks at rest on the platform. This paper
shows that this assumption, although widespread and apparently trivial, leads
to an anisotropy of the velocity of two light beams travelling in opposite
directions along the rim of the disk; which in turn implies some recently
pointed out paradoxical consequences undermining the self-consistency of the
Special Theory of Relativity (SRT). A correct application of the SRT solves the
problem and recovers complete internal consistency for the theory. As an
immediate consequence, it is shown that the Sagnac effect only depends on the
non homogeneity of time on the platform and has nothing to do with any
anisotropy of the speed of light along the rim of the disk, contrary to an
incorrect but widely supported idea.Comment: Latex, 2 figure
Combining visible and infrared radiometry and lidar data to test simulations in clear and ice cloud conditions
Measurements taken during the 2003 Pacific THORPEX Observing System Test (P-TOST) by the MODIS Airborne Simulator (MAS), the Scanning High-resolution Interferometer Sounder (S-HIS) and the Cloud Physics Lidar (CPL) are compared to simulations performed with a line-by-line and multiple scattering modeling methodology (LBLMS). Formerly used for infrared hyper-spectral data analysis, LBLMS has been extended to the visible and near infrared with the inclusion of surface bi-directional reflectance properties. A number of scenes are evaluated: two clear scenes, one with nadir geometry and one cross-track encompassing sun glint, and three cloudy scenes, all with nadir geometry. <br><br> CPL data is used to estimate the particulate optical depth at 532 nm for the clear and cloudy scenes and cloud upper and lower boundaries. Cloud optical depth is retrieved from S-HIS infrared window radiances, and it agrees with CPL values, to within natural variability. MAS data are simulated convolving high resolution radiances. The paper discusses the results of the comparisons for the clear and cloudy cases. LBLMS clear simulations agree with MAS data to within 20% in the shortwave (SW) and near infrared (NIR) spectrum and within 2 K in the infrared (IR) range. It is shown that cloudy sky simulations using cloud parameters retrieved from IR radiances systematically underestimate the measured radiance in the SW and NIR by nearly 50%, although the IR retrieved optical thickness agree with same measured by CPL. <br><br> MODIS radiances measured from Terra are also compared to LBLMS simulations in cloudy conditions, using retrieved cloud optical depth and effective radius from MODIS, to understand the origin for the observed discrepancies. It is shown that the simulations agree, to within natural variability, with measurements in selected MODIS SW bands. <br><br> The impact of the assumed particles size distribution and vertical profile of ice content on results is evaluated. Sensitivity is much smaller than differences between measured and simulated radiances in the SW and NIR. <br><br> The paper dwells on a possible explanation of these contradictory results, involving the phase function of ice particles in the shortwave
Spacetime metric from linear electrodynamics
The Maxwell equations are formulated on an arbitrary (1+3)-dimensional
manifold. Then, imposing a (constrained) linear constitutive relation between
electromagnetic field and excitation , we derive
the metric of spacetime therefrom.Comment: 4 pages' latex-scrip
Heat flux evaluation in high temperature ring-on-ring contacts
A comprehensive methodology to investigate heat flux in a ring-on-ring tribometer is presented. Thermal fluxes under high contact pressures and temperature differences were evaluated through an experimental campaign and by a numerical procedure of inverse analysis applied to surface temperature measurements. An approximation of a two-dimensional time-dependent analytical solution for the temperature distribution was first developed and subsequently adapted to mimic the specific testing configuration characteristics; the problem was finally simplified to enable further inverse analysis. Experiments were performed using an innovative high temperature ring-on-ring tribometer. The evaluated contact heat transfer rates were reported as a function of normal load and temperature difference between the discs under steady-state conditions; the results reported here show that, in the present test configuration, the temperature difference has stronger influence than the applied load in terms of heat transfer induced by contact
Interplanetary space-A new laboratory for rarefied gas dynamics
Interplanetary space provides simultaneously the best vacuum available to man and, because of the solar wind, a tenuous and unsteady high-speed outflow of predominantly hydrogen gas from the sun, a remarkable variety of rarefied gasdynamics phenomena, to observe. A review is provided of these phenomena, and of the way in which the present level of understanding has been achieved
The fitting of multifunctions : an approach to nonparametric multimodal regression.
In the last decades a lot of research has been devoted to
smoothing in the sense of nonparametric regression. However, this
work has nearly exclusively concentrated on fitting regression
functions. When the conditional distribution of y|x is
multimodal, the assumption of a functional relationship y = m(x)
+ noise might be too restrictive. We introduce a nonparametric
approach to fit multifunctions, allowing to assign a set of
output values to a given x. The concept is based on
conditional mean shift, which is an easily implemented tool to
detect the local maxima of a conditional density function. The
methodology is illustrated by environmental data examples
Quantum Interference Effects in Spacetime of Slowly Rotating Compact Objects in Braneworld
The phase shift a neutron interferometer caused by the gravitational field
and the rotation of the earth is derived in a unified way from the standpoint
of general relativity. General relativistic quantum interference effects in the
slowly rotating braneworld as the Sagnac effect and phase shift effect of
interfering particle in neutron interferometer are considered. It was found
that in the case of the Sagnac effect the influence of brane parameter is
becoming important due to the fact that the angular velocity of the locally non
rotating observer must be larger than one in the Kerr space-time. In the case
of neutron interferometry it is found that due to the presence of the parameter
an additional term in the phase shift of interfering particle emerges
from the results of the recent experiments we have obtained upper limit for the
tidal charge as . Finally, as an example, we
apply the obtained results to the calculation of the (ultra-cold neutrons)
energy level modification in the braneworld.Comment: 12 pages, 2 figure
The Martian bow wave - Theory and observation
Relationship between Mariner 4 space probe trajectory and calculated location of proposed Martian bow wav
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