Physical Sciences

Microelectromechanical Sensors Based on Magnetoresistance

These would offer advantages over similar sensors based on quantum-mechanical tunneling of electrons.Microelectromechanical sensors based on magnetoresistance have been proposed. Like other microelectromechanical sensors, these would be used to measure physical quantities that can be made to manifest themselves in small mechanical displacements. Potential applications for microelectromechanical sensors include accelerometers, magnetometers, bolometers, pressure sensors, seismometers, Golay cells, and microphones. Potential markets include the aerospace, biomedical, semiconductor, automotive, and defense industries.

Posted in: Briefs, TSP, Physical Sciences, Microelectromechanical devices, Sensors and actuators


Model of Pyrolysis of Biomass in a Fluidized-Bed Reactor

Complex dynamics and heat transfer are represented more realistically than in prior models.A mathematical model has been formulated to describe the pyrolysis of biomass in a bubbling fluidized-bed reactor. The reactor is a vertical cylinder that contains a mixture of biomass particles and sand. Superheated steam enters the reactor through holes in the bottom and flows out freely at the top. The sand is a high heat capacity medium used for heating the biomass. The biomass particles, initially at room temperature, are introduced into the already hot reactor and become heated primarily through contact with the sand. Upon reaching a threshold temperature, the biomass particles undergo chemical reactions, the gaseous products of which are carried away by the flow of steam. The "bubbles" are regions of the fluidized bed that are mostly devoid of particles; these regions occur as a result of the interaction of the turbulent gaseous flow with the particles.

Posted in: Briefs, TSP, Physical Sciences, Thermodynamics, Biomaterials, Chemicals, Gases, Test equipment and instrumentation


System for Delivering Gas Samples to Multiple Instruments

A system that samples gases at multiple remote locations and delivers the gases to two or possibly more gas-monitoring instruments (e.g., mass spectrometers) has been developed. The system includes a transport (suction) pump that draws the gases from the sampling locations, through transport tubes, into a plenum, which is large enough to act as a buffer against changes in pressure in the transport tubes. Connected to each transport tube at a location near the plenum are two or more sample tubes that are, in turn, connected to manifolds of sample-selector valves through which gases are drawn into the instruments. Each instrument is equipped with a sampling (suction) pump that draws gas from one of the transport tubes that has been selected by opening the corresponding sample-selector valve. Each sampling pump is operated under feedback flow and pressure control to maintain a steady instrument-inlet pressure needed to ensure stable instrument readings. The sample flow thus diverted from the transport tube is kept to one-fifth or less of the transport flow in order to minimize the perturbation of the transport flow and thus, further, minimize any effect of one instrument on the other.

Posted in: Briefs, TSP, Physical Sciences, Gases, Test equipment and instrumentation, Spacecraft


Atmospheric Source of Atomic Oxygen for Cleaning Paintings

A vacuum chamber is no longer necessary.A portable apparatus that operates at atmospheric pressure generates a beam of monatomic oxygen. The apparatus is designed to be used in a dry, noncontact process for removing organic contaminants from the surfaces of paintings. Organic contaminants that can be wholly or partly removed by use of this apparatus include some deposited in acts of defacement (e.g., lipstick and marks left by felt-tip and ball-point pens) and some deposited from fire (e.g., soot and charred binder). In some cases, this apparatus may make it possible to restore works of art that were previously counted as lost.

Posted in: Briefs, TSP, Physical Sciences, Maintenance, repair, and service operations, Oxygen


General-Purpose Wavelet Program

This program affords a variety of capabilities that are especially useful in wavelet analysis."S+Wavelets" is the name of a computer program that implements a suite of mathematical "tools" for wavelet analysis of signals (including two-dimensional signals that represent images.) Wavelets, being localized in both time and frequency (or space and wave number), serve as means for transforming and extracting information from signals that have temporally or spatially varying properties. In a sense, wavelet methods combine the best features of time and frequency methods (e.g., Fourier-transform methods). Modern wavelet research began in the mid-1980s, but until now, there has been no commercially available, general-purpose software to support rapid prototyping for research on, and application of, wavelets. S+Wavelets satisfies the need for such a computer code.

Posted in: Briefs, Information Sciences, Physical Sciences, Mathematical analysis, Rapid prototyping, Computer software and hardware, Imaging and visualization


Simple Fiber-Optic Coupling for Microsphere Resonators

The "pigtailed" ultra-high-Q microcavities make a novel building block for fiber-optic systems.Simple fiber-optic couplers have been devised for use in coupling light into and out of the "whispering-gallery" electromagnetic modes of transparent microspheres. The need for this type of coupling arises in conjunction with the use of transparent microspheres as compact, high-Q (where Q is the resonance quality factor) resonators, delay lines for optoelectronic oscillators (including microlasers), and narrow-band-pass filters.

Posted in: Briefs, TSP, Physical Sciences, Fiber optics


Surface Gratings for Optical Coupling With Microspheres

Far-field coupling offers advantages over near-field coupling.A diffraction grating consisting of a periodic gradient in the index of refraction of a thin surface layer has been shown to be effective as a means of far-field coupling of monochromatic light into or out of the "whispering-gallery" electromagnetic modes of a transparent microsphere. This far-field coupling can be an alternative to the near-field (evanescent-wave) coupling afforded by prism- and fiber-optic couplers described in the immediately preceding article. Far-field coupling is preferable to near-field coupling in applications in which there are requirements for undisturbed access to the entire surfaces of microspheres. Examples of such applications include (1) a proposed atomic cavity in which cold atoms would orbit in a toroidal trap around a microsphere and (2) a photonic quantum logic gate based on coupling between a high-Q (where Q is the resonance quality factor) microsphere and trapped individual resonant ions.

Posted in: Briefs, TSP, Physical Sciences, Architecture, Optics, Milling, Refractory materials


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