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Chen, T. C.

Publications and source records attributed to Chen, T. C..

10 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Integrated Electron-tunneling Refrigerator and TES Bolometer for Millimeter Wave Astronomy

We describe progress in the development of a close-packed array of bolometers intended for use in photometric applications at millimeter wavelengths from ground- based telescopes. Each bolometer in the may uses a proximity-effect Transition Edge Sensor (TES) sensing element and each will have integrated Normal-Insulator-Superconductor (NIS) refrigerators to cool the bolometer below the ambient bath temperature. The NIS refrigerators and acoustic-phonon-mode-isolated bolometers are fabricated on silicon. The radiation-absorbing element is mechanically suspended by four legs, whose dimensions are used to control and optimize the thermal conductance of the bolometer. Using the technology developed at NIST, we fabricate NIS refrigerators at the base of each of the suspension legs. The NIS refrigerators remove hot electrons by quantum-mechanical tunneling and are expected to cool the biased (approx.10 pW) bolometers to <170 mK while the bolometers are inside a pumped 3He-cooled cryostat operating at approx.280 mK. This significantly lower temperature at the bolometer allows the detectors to approach background-limited performance despite the simple cryogenic system.

Silverberg, R. F.↗
NASA NTRS2003

An Array of Frequency Selective Bolometers (FSB) for the Spectral Energy Distribution (SPEED) Camera

The SPEED camera is being developed to study the spectral energy distributions of high redshift galaxies using the Heinrich Hertz Telescope (HHT) in Arizona. SPEED requires a small cryogenic detector array of 2x2 pixels with each pixel having four frequency bands in the 150-350 GHz range. Here we describe the development of the detector array of these high efficiency FSBs. The FSB design provides the multi-pixel multi-spectral band capability required for SPEED in a compact stackable array. The SPEED bolometers will use proximity effect superconducting transition edge sensors as their temperature-sensing element allowing for higher levels of multiplexing in future applications.

Silverberg, R. F.↗
NASA NTRS1993

High latitude field aligned light ion flows in the topside ionosphere deduced from ion composition and plasma temperatures

Using a comprehensive ionospheric data set comprised of all available ion composition and plasma temperature measurements from satellites, the vertical distributions of ion composition and plasma temperatures are defined from middle latitudes up into the polar cap for summer conditions for altitudes below about 1200 km. These data are sufficient to allow a numerical estimation of the latitudinal variation of the light ion outflows from within the plasmasphere to the polar wind regions. The altitude at which significant light ion outflow begins is found to be lower during solar minimum conditions than during solar maximum. The H(+) outward speeds are of the order of 1 km/s near 1100 km during solar maximum but attain several km/s speeds for solar minimum. He(+) shows a similar altitude development of flow but attains polar cap speeds much less than 1 km/s at altitudes below 1100 km, particularly under solar maximum conditions. Outward flows are also found in the topside F-region for noontime magnetic flux tubes within the plasmasphere.

Grebowsky, J. M.↗
NASA NTRS1985

A comparison study of spectral energetics analysis using varius FGGE 3b data

The atmospheric spectral energetics studies performed before the First GARP Global Experiment (FGGE) were reviewed, and the deficiencies of these studies were pointed out. The data generated by the FGGE IIIb analyses of the European Center for Medium Range Weather Forecasts, the Geophysical Fluid Dynamics Laboratory, and the Goddard Laboratory for Atmospheric Sciences over the entire globe during the FGGE summer and winter are used to analyze the atmospheric spectral energetics. Comparisons were made between the results using three FGGE IIIb analyses, and between previous and current studies with the spectral energetics of the Southern Hemisphere.

Chen, T. C.↗
NASA NTRS1984

Analysis of Diabatic Heating During FGGE

The objective is to examine the maintenance of momentum and thermal fields in the Southern Hemisphere and the diabatic heating and generation of available potential energy of the entire global atmosphere. The data generated by the Goddard Laboratory for Atmospheric Sciences First GARP Global Experiment (FGGE) III-b analysis for SOP1 and SOP2 are used for this effort. It is observed that the atmospheric circulation of the Southern Hemisphere exhibits a double jet structure (subtropical jet and polar jet) in winter and a single jet in summer during the FGGE year. The geographic distribution of standard deviation in the height field at 500 mb indicates that the major eddy activities occur in the downstream side of the polar jet and poleward side of the subtropic jet in winter. However, the major eddy activites go hand-in-hand with the jet stream in summer. The momentum transport is essentially carried out by the transient eddies in both seasons. The distribution of the temperature field is more axisymmetric in the Southern Hemisphere than in the Northern Hemisphere. The sensible heat is mainly transported poleward by transient eddies along the strong baroclinic zone where the jet streams are located. In other seasons, it is shown from the geographic distribution of the divergence of transient eddy sensible heat flux that the Antarctic continent acts as a heat sink to consume the sensible heat converged toward the polar area from the middle and low latitudes.

Chen, T. C.↗
NASA NTRS1981

A study of the extended-range forecasting problem blocking

Wavenumber frequency spectral analysis of a 90 day winter (Jan. 15 - April 14) wind field simulated by a climate experiment of the GLAS atmospheric circulation model is made using the space time Fourier analysis which is modified with Tukey's numerical spectral analysis. Computations are also made to examine how the model wave disturbances in the wavenumber frequency domain are maintained by nonlinear interactions. Results are compared with observation. It is found that equatorial easterlies do not show up in this climate experiment at 200 mb. The zonal kinetic energy and momentum transport of stationary waves are too small in the model's Northern Hemisphere. The wavenumber and frequency spectra of the model are generally in good agreement with observation. However, some distinct features of the model's spectra are revealed. The wavenumber spectra of kinetic energy show that the eastward moving waves of low wavenumbers have stronger zonal motion while the eastward moving waves of intermediate wavenumbers have larger meridional motion compared with observation. Furthermore, the eastward moving waves show a band of large spectral value in the medium frequency regime.

Chen, T. C.↗
NASA NTRS1978

Multiprocessing tradeoffs and the wind-tunnel simulation problem

The architecture tradeoff issue is discussed, concentrating on an oversimplified version of the multiprocessing aspect. A degree of symmetric multiprocessing is unavoidable; the choice is either complete symmetric multiprocessing or a number of identical pipelines. The processing elements can be geared to do either plane-multiprocessing, or line-multiprocessing. Other important design choices are the number notation, word length, main memory size, cache memory size, and different means to implement data transport.

Chen, T. C.↗
NASA NTRS1976

The influence of the diabatic heating in the troposphere on the stratosphere

In order to simulate the seasonal variation of the stratospheric circulation in a zonal mean circulation model, a Newtonian heating function and a detailed heating function were applied to the troposphere and stratosphere, respectively. The purpose of this study was to investigate the response of stratospheric circulation to alterations of the radiative equilibrium temperature of the troposphere.

Turner, R. E.↗