25,586 research outputs found
LANDSAT-D Thematic Mapper image dimensionality reduction and geometric correction accuracy
Principal components transformations was applied to a Walnut Creek, Texas subscene to reduce the dimensionality of the multispectral sensor data. This transformation was also applied to a LANDSAT 3 MSS subscene of the same area acquired in a different season and year. Results of both procedures are tabulated and allow for comparisons between TM and MSS data. The TM correlation matrix shows that visible bands 1 to 3 exhibit a high degree of correlation in the range 0.92 to 0.96. Correlation for bands 5 to 7 is 0.93. Band 4 is not highly correlated with any other band, with corrections in the range 0.13 to 0.52. The thermal band (6) is not highly correlated with other bands in the range 0.13 to 0.46. The MSS correlation matrix shows that bands 4 and 5 are highly correlated (0.96) as are bands 6 and 7 with a correlation of 0.92
Disentanglement and Decoherence without dissipation at non-zero temperatures
Decoherence is well understood, in contrast to disentanglement. According to
common lore, irreversible coupling to a dissipative environment is the
mechanism for loss of entanglement. Here, we show that, on the contrary,
disentanglement can in fact occur at large enough temperatures even for
vanishingly small dissipation (as we have shown previously for decoherence).
However, whereas the effect of on decoherence increases exponentially with
time, the effect of on disentanglement is constant for all times,
reflecting a fundamental difference between the two phenomena. Also, the
possibility of disentanglement at a particular increases with decreasing
initial entanglement.Comment: 3 page
Reply to Comment on "Completely positive quantum dissipation"
This is the reply to a Comment by R. F. O'Connell (Phys. Rev. Lett. 87 (2001)
028901) on a paper written by the author (B. Vacchini, ``Completely positive
quantum dissipation'', Phys.Rev.Lett. 84 (2000) 1374, arXiv:quant-ph/0002094).Comment: 2 pages, revtex, no figure
Landsat D Thematic Mapper image dimensionality reduction and geometric correction accuracy
To characterize and quantify the performance of the Landsat thematic mapper (TM), techniques for dimensionality reduction by linear transformation have been studied and evaluated and the accuracy of the correction of geometric errors in TM images analyzed. Theoretical evaluations and comparisons for existing methods for the design of linear transformation for dimensionality reduction are presented. These methods include the discrete Karhunen Loeve (KL) expansion, Multiple Discriminant Analysis (MDA), Thematic Mapper (TM)-Tasseled Cap Linear Transformation and Singular Value Decomposition (SVD). A unified approach to these design problems is presented in which each method involves optimizing an objective function with respect to the linear transformation matrix. From these studies, four modified methods are proposed. They are referred to as the Space Variant Linear Transformation, the KL Transform-MDA hybrid method, and the First and Second Version of the Weighted MDA method. The modifications involve the assignment of weights to classes to achieve improvements in the class conditional probability of error for classes with high weights. Experimental evaluations of the existing and proposed methods have been performed using the six reflective bands of the TM data. It is shown that in terms of probability of classification error and the percentage of the cumulative eigenvalues, the six reflective bands of the TM data require only a three dimensional feature space. It is shown experimentally as well that for the proposed methods, the classes with high weights have improvements in class conditional probability of error estimates as expected
LANDSAT-D thematic mapper image dimensionality reduction and geometric correction accuracy
When principal component analysis of a subscene of a section of the Sacramento River showed lower correlation among the TM spectral components that were observed for the MSS spectral components, principal component analysis was applied to a LANDSAT 2 MSS subscene of the same area for comparison purposes. Correlation coefficient matrices indicate the pairwise similarity and correlation of the data for the spectral components. The principal components transformation matrix, indicates the weights applied to the original components to generate the transformed components. The first two TM components can be described as visible and near infrared. For the MSS data, the first transformed component is roughly the average of the four original components. The second transformed component is roughly the difference between the visible and infrared components. Tables show that 97.0% of the variance in an MSS image is contained in only two transformed components
Stochastic Spacetime and Brownian Motion of Test Particles
The operational meaning of spacetime fluctuations is discussed. Classical
spacetime geometry can be viewed as encoding the relations between the motions
of test particles in the geometry. By analogy, quantum fluctuations of
spacetime geometry can be interpreted in terms of the fluctuations of these
motions. Thus one can give meaning to spacetime fluctuations in terms of
observables which describe the Brownian motion of test particles. We will first
discuss some electromagnetic analogies, where quantum fluctuations of the
electromagnetic field induce Brownian motion of test particles. We next discuss
several explicit examples of Brownian motion caused by a fluctuating
gravitational field. These examples include lightcone fluctuations, variations
in the flight times of photons through the fluctuating geometry, and
fluctuations in the expansion parameter given by a Langevin version of the
Raychaudhuri equation. The fluctuations in this parameter lead to variations in
the luminosity of sources. Other phenomena which can be linked to spacetime
fluctuations are spectral line broadening and angular blurring of distant
sources.Comment: 15 pages, 3 figures. Talk given at the 9th Peyresq workshop, June
200
Using ACIS on the Chandra X-ray Observatory as a particle radiation monitor II
The Advanced CCD Imaging Spectrometer is an instrument on the Chandra X-ray
Observatory. CCDs are vulnerable to radiation damage, particularly by soft
protons in the radiation belts and solar storms. The Chandra team has
implemented procedures to protect ACIS during high-radiation events including
autonomous protection triggered by an on-board radiation monitor. Elevated
temperatures have reduced the effectiveness of the on-board monitor. The ACIS
team has developed an algorithm which uses data from the CCDs themselves to
detect periods of high radiation and a flight software patch to apply this
algorithm is currently active on-board the instrument. In this paper, we
explore the ACIS response to particle radiation through comparisons to a number
of external measures of the radiation environment. We hope to better understand
the efficiency of the algorithm as a function of the flux and spectrum of the
particles and the time-profile of the radiation event.Comment: 10 pages, 5 figures, to be published in Proc. SPIE 8443, "Space
Telescopes and Instrumentation 2012: Ultraviolet to Gamma Ray
Casimir Force between a Dielectric Sphere and a Wall: A Model for Amplification of Vacuum Fluctuations
The interaction between a polarizable particle and a reflecting wall is
examined. A macroscopic approach is adopted in which the averaged force is
computed from the Maxwell stress tensor. The particular case of a perfectly
reflecting wall and a sphere with a dielectric function given by the Drude
model is examined in detail. It is found that the force can be expressed as the
sum of a monotonically decaying function of position and of an oscillatory
piece. At large separations, the oscillatory piece is the dominant
contribution, and is much larger than the Casimir-Polder interaction that
arises in the limit that the sphere is a perfect conductor. It is argued that
this enhancement of the force can be interpreted in terms of the frequency
spectrum of vacuum fluctuations. In the limit of a perfectly conducting sphere,
there are cancellations between different parts of the spectrum which no longer
occur as completely in the case of a sphere with frequency dependent
polarizability. Estimates of the magnitude of the oscillatory component of the
force suggest that it may be large enough to be observable.Comment: 18pp, LaTex, 7 figures, uses epsf. Several minor errors corrected,
additional comments added in the final two sections, and references update
- …