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Effect of Gravitation on Noninteracting Trapped Fermions

A report presents a theoretical study of the thermodynamics of an ultralow-temperature gas of fermions that interact with a gravitational field and with an externally imposed trapping potential but not with each other. The gravitational field is taken to define the z axis and the trapping potential to be of the form (m/2) (ωxx2+ωyy2+ωzz2), where m is the mass of a fermion; x, y, and z are Cartesian coordinates originating at the center of the trap; and the ω values denote effective harmonic- oscillator angular frequencies with respect to motion along the respective coordinate axes. The single-particle energy is found from the solution of the time-dependent Schroedinger equation for a Hamiltonian that includes kinetic energy plus the gravitational and trapping potentials. The equation for the single-particle energy is combined with Fermi statistics to obtain equations for the chemical potential, internal energy, and specific heat of the gas; the number of trapped fermions; and the spatial distribution of fermions at zero temperature. The equations reveal the ways in which the Fermi energy, the specific heat, and the shape of the Fermion cloud are affected by the gravitational field and the anisotropy of the trapping field.

Posted in: Briefs, TSP

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New Technique Improves Cirrus Cloud Characterization

Radiometric measurements at submillimeter-wavelength accurately characterize cirrus cloud properties. A new technique for retrieving cirrus properties from radiometric measurements at submillimeter wavelengths has been developed. The technique can accurately measure the amount of ice present in cirrus clouds, determine the median crystal size, and constrain crystal shape. The retrieval algorithm improves upon prior algorithms by also retrieving middle and upper tropospheric water-vapor profiles in concert with cloud properties. This joint-analysis method corrects for retrieval errors introduced by water vapor in and near the cloud.

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Study of Inertial and Gravitational Masses of a Boson

A report presents a theoretical study of the relationship between the inertial mass (mi) and gravitational mass (mg) of a self-interacting neutral scalar boson in a heat bath. The question of whether these masses differ arises in modern physics. In quantum field theory, the mass of a particle appears as a parameter that, as a result of interaction with fields, is changed to a renormalizable, physically reliable value (mR). The interaction of a particle with fields also has a thermal character. Thus, a boson in a heat bath in a gravitational field gains an acceleration different from the gravitational acceleration. The study utilizes a simple approximate Lagrangian model that is well suited for analysis of temperature- and gravitation-related effects.

Posted in: Briefs, TSP

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Metal/Dielectric Color Filters for Flat Panel Displays

A report expands on the proposal described in “Low-Absorption Color Filters for Flat Panel Display Devices” (NPO-20435) NASA Tech Briefs, Vol. 23, No. 12 (December 1999), page 34. To recapitulate: The dye pixel color filters in a conventional liquid-crystal or other display device would be replaced with interference filters, which are less absorptive, and optics would be configured so that light reflected from the filters would be reused as illumination. The overall effect would be to increase brightness and efficiency. The present report adds specificity by proposing that the interference filters be of the type described in “Metal/Dielectric-Film Interference Color Filters” (NPO-20217), NASA Tech Briefs, Vol. 23, No. 2 (February 1999), page 70: Each filter would be made of three thin metal films interspersed with two thin dielectric films. In comparison with conventional multilayer all-dielectric filters, the proposed filters would contain fewer layers, and therefore could be fabricated more easily and at lower cost.

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Multiphase-Flow Model of Fluidized-Bed Pyrolysis of Biomass

A report presents additional information about the subject matter of “Model of Pyrolysis of Biomass in a Fluidized- Bed Reactor” (NPO-20708) NASA Tech Briefs, Vol. 25, No. 6 (June 2001), page 59. The model is built on equations for the dynamics of three components — gas, sand, and biomass — partly by taking suitable ensemble averages of the coupled conservation equations for the gas, and for the biomass and sand particles. Equations for exchanges of mass, momentum, and energy between phases are included. Equations for transport of the solid phase are closed by use of separate distribution functions for sand and biomass particles. Interparticle collisions are described in the framework of the kinetic theory of dense gases, using inelastic- rigid-sphere models.

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Tiger Fibers for Enhanced Optical Sensing of Volatiles

Striped polymer coats on optical fibers would induce gratings upon exposure to analytes. Improved fiber-optic transducers, denoted tiger fibers, have been proposed for sensing volatile compounds. Tiger fibers are so named because, as described below, their sensitive portions would be coated with periodically alternating stripes of different polymers, reminiscent of a tiger’s stripes.

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Using Laser Diodes to Characterize Force and Pressure Sensors

A proposed method of characterizing microphones and other pressure and force sensors would exploit the temporally varying forces of impingement of amplitude-modulated light beams from inexpensive laser diodes. What makes the method likely to be practical is the surprising fact that these forces, albeit small, are nevertheless large enough to enable quantification of the noise floors, sensitivities, and frequency responses of many modern pressure sensors. The time-averaged force of impingement of a pulsed beam of light on a surface is given by F = SDP/c, where S ranges from 1 for a totally absorptive (black) to 2 for a perfectly reflective surface, D is the pulse duty cycle, P is the peak power of the beam, and c is the speed of light. Hence, if one knows S, D, and P, it may be possible to determine the absolute sensitivity of the sensor. Even if one does not know one or more of these parameters, it should be possible to determine the relative sensitivities of different sensors by measuring their responses to the same modulated beam, or to determine the relative frequency response of a given sensor by measuring its output while sweeping the modulation frequency.

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