Engineering topics

Gupta, M. C.

Publications and source records attributed to Gupta, M. C..

4 records

NASA NTRS1983

Fluorescence from polystyrene - Photochemical processes in polymeric systems, 7

Results are presented for measurements of the fluorescence spectra of polystyrene in dilute solution and in pure solid films. It is determined that a major potential source of experimental error is the concurrent photooxidative degradation in air which may obscure fluorescence emission from monomeric sites in solid films at 25 C. The fluorescence spectra of oriented films are evaluated in terms of the monomer to excimer fluorescence intensity ratio and the excimer 'red shift'. The monomer to excimer fluorescence intensity ratio is determined to be significantly higher in fluid solution than in solid film.

Gupta, M. C.↗

NASA NTRS1980

Thermal diffusivity measurements using a pulsed dual-beam thermal lens technique

A novel pulsed dual-beam thermal lens technique for the determination of thermal diffusivity of liquids and solids was developed. In this technique a transient thermal lens is formed in the test specimen by using a dye laser pulse as a heating source and the thermal lens decay is monitored by means of a CW He-Ne laser. The technique is fast and contactless and avoids some of the major difficulties of conventional methods. Thermal diffusivities for water and a polycarbonate plastic were measured and found to be in agreement with literature values. Considerable simplification and minimization of certain errors was achieved by use of a reference material.

Gupta, M. C.↗

NASA NTRS1979

Static compression of Al2O3 to 1.2 Mbars /120 GPa/

Pressures up to 120 GPa were generated when a diamond indentor of radius 10.0 micrometers was pressed against a very thin sample of Al2O3 on a diamond flat. The thin film of Al2O3 was prepared by sputtering of aluminum in an oxygen atmosphere. From the measurement of the electrical resistance of Al2O3 as a function of pressure it was found that Al2O3 remains an insulator at the highest pressure studied, namely, 120 GPa.

Gupta, M. C.↗

NASA NTRS1979

Studies of the high pressure transition in sulfur

High-pressure transition in crystalline orthorhombic sulfur has been investigated, using a diamond indentor pressed against a diamond flat to produce pressures up to 300 kbar and an opposed-anvil apparatus to obtain lower pressures. The first indication of sulfur transition using the indentor technique was seen when resistance measured 3 times 10 to the 12th ohm. Transition was found to be sluggish and highly time-dependent.

Ruoff, A. L.↗