8,765 research outputs found
Quantum properties of a non-Gaussian state in the large-N approximation
We study the properties of a non-Gaussian density matrix for a O(N) scalar
field in the context of the incomplete description picture. This is of
relevance for studies of decoherence and entropy production in quantum field
theory. In particular, we study how the inclusion of the simplest non-Gaussian
correlator in the set of measured observables modifies the effective (Gaussian)
description one can infer from the knowledge of the two-point functions only.
We compute exactly the matrix elements of the non-Gaussian density matrix at
leading order in a 1/N-expansion. This allows us to study the quantum
properties (purity, entropy, coherence) of the corresponding state for
arbitrarily strong nongaussianity. We find that if the Gaussian and the
non-Gaussian observers essentially agree concerning quantum purity or
correlation entropy, their conclusion can significantly differ for other, more
detailed aspects such as the degree of quantum coherence of the system.Comment: 14 pages, 7 figures. Published version (Phys. Rev. D, minor
corrections
A Theory of Soft Capture
Capture of regulatory agencies by firms or other stakeholders has given rise to a rich literature, much of which is dominated by models in which the motivation for the welfare-reducing behavior is found in side-contracting (bribes, corruption), threats (blackmail, political support) or corresponding mechanisms for repeated games (reputation, career concerns, signaling for promotion). Notwithstanding, the empirical support for monetary corruption and 'revolving doors' is scarce and inconclusive. We propose an alternative and more intuitive model for regulatory capture that is based on information transmission and asymmetric information. In a three-tier model, a regulator is charged by a political principal to provide a signal for the type of a regulated firm. Only the firm can observe his type and the production of a correlated signal with a given accuracy is costly for the regulator. The firm can costlessly provide an alternative signal of lower accuracy that is presented to the regulator. In a self-enforcing equilibrium, the regulator transmits the firm-produced signal, internalizes its own savings in information cost and the firm enjoys higher information rents. The main feature of soft capture is that it is not based on a reciprocity of favors but on a congruence of interests between the firm and the regulator.
Report of the sensor cooler technology panel
The Sensor Cooler Technology Panel identified three major areas in which technology development must be supported in order to meet the system performance requirements for the Astrotech 21 mission set science objectives. They are: long life vibration free refrigerators; mechanical refrigeration for 2 K to 5 K; and flight testing of emerging prototype refrigerators. A development strategy and schedule were recommended for each of the three areas
Pattern recognition of satellite cloud imagery for improved weather prediction
The major accomplishment was the successful development of a method for extracting time derivative information from geostationary meteorological satellite imagery. This research is a proof-of-concept study which demonstrates the feasibility of using pattern recognition techniques and a statistical cloud classification method to estimate time rate of change of large-scale meteorological fields from remote sensing data. The cloud classification methodology is based on typical shape function analysis of parameter sets characterizing the cloud fields. The three specific technical objectives, all of which were successfully achieved, are as follows: develop and test a cloud classification technique based on pattern recognition methods, suitable for the analysis of visible and infrared geostationary satellite VISSR imagery; develop and test a methodology for intercomparing successive images using the cloud classification technique, so as to obtain estimates of the time rate of change of meteorological fields; and implement this technique in a testbed system incorporating an interactive graphics terminal to determine the feasibility of extracting time derivative information suitable for comparison with numerical weather prediction products
Limits of flexural wave absorption by open lossy resonators: reflection and transmission problems
The limits of flexural wave absorption by open lossy resonators are
analytically and numerically reported in this work for both the reflection and
transmission problems. An experimental validation for the reflection problem is
presented. The reflection and transmission of flexural waves in 1D resonant
thin beams are analyzed by means of the transfer matrix method. The hypotheses,
on which the analytical model relies, are validated by experimental results.
The open lossy resonator, consisting of a finite length beam thinner than the
main beam, presents both energy leakage due to the aperture of the resonators
to the main beam and inherent losses due to the viscoelastic damping. Wave
absorption is found to be limited by the balance between the energy leakage and
the inherent losses of the open lossy resonator. The perfect compensation of
these two elements is known as the critical coupling condition and can be
easily tuned by the geometry of the resonator. On the one hand, the scattering
in the reflection problem is represented by the reflection coefficient. A
single symmetry of the resonance is used to obtain the critical coupling
condition. Therefore the perfect absorption can be obtained in this case. On
the other hand, the transmission problem is represented by two eigenvalues of
the scattering matrix, representing the symmetric and anti-symmetric parts of
the full scattering problem. In the geometry analyzed in this work, only one
kind of symmetry can be critically coupled, and therefore, the maximal
absorption in the transmission problem is limited to 0.5. The results shown in
this work pave the way to the design of resonators for efficient flexural wave
absorption
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