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Yang, Lily

Publications and source records attributed to Yang, Lily.

18 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Optical spectroscopy of site-controlled quantum dots in a Schottky diode

The optical quality of site-controlled quantum dots is typically assessed by off-resonant photoluminescence spectroscopy, and emission linewidth is the most common figure of merit. Here, we combine photoluminescence and resonance fluorescence spectroscopy to obtain a more complete picture of site-controlled quantum dots embedded in a charge injection device. Although resonant and non-resonant linewidths are nearly as small as those of randomly nucleated dots, other optical properties show clear evidence of influence from defects introduced by the nanofabrication process. We demonstrate optical spin pumping and spin-flip Raman processes, which are important functions for use in quantum information applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1999

A Fast Code for Jupiter Atmospheric Entry Analysis

A fast code was developed to calculate the forebody heating environment and heat shielding that is required for Jupiter atmospheric entry probes. A carbon phenolic heat shield material was assumed and, since computational efficiency was a major goal, analytic expressions were used, primarily, to calculate the heating, ablation and the required insulation. The code was verified by comparison with flight measurements from the Galileo probe's entry. The calculation required 3.5 sec of CPU time on a work station, or three to four orders of magnitude less than for previous Jovian entry heat shields. The computed surface recessions from ablation were compared with the flight values at six body stations. The average, absolute, predicted difference in the recession was 13.7% too high. The forebody's mass loss was overpredicted by 5.3% and the heat shield mass was calculated to be 15% less than the probe's actual heat shield. However, the calculated heat shield mass did not include contingencies for the various uncertainties that must be considered in the design of probes. Therefore, the agreement with the Galileo probe's values was satisfactory in view of the code's fast running time and the methods' approximations.

Tauber, Michael E.↗
NASA NTRS1998

A Fast Code for Jupiter Atmospheric Entry

A fast code was developed to calculate the forebody heating environment and heat shielding that is required for Jupiter atmospheric entry probes. A carbon phenolic heat shield material was assumed and, since computational efficiency was a major goal, analytic expressions were used, primarily, to calculate the heating, ablation and the required insulation. The code was verified by comparison with flight measurements from the Galileo probe's entry; the calculation required 3.5 sec of CPU time on a work station. The computed surface recessions from ablation were compared with the flight values at six body stations. The average, absolute, predicted difference in the recession was 12.5% too high. The forebody's mass loss was overpredicted by 5.5% and the heat shield mass was calculated to be 15% less than the probe's actual heat shield. However, the calculated heat shield mass did not include contingencies for the various uncertainties that must be considered in the design of probes. Therefore, the agreement with the Galileo probe's values was considered satisfactory, especially in view of the code's fast running time and the methods' approximations.

Tauber, Michael E.↗
NASA NTRS1997

JAE: A Jupiter Atmospheric Entry Probe Heating Code

The strong gravitational attraction of Jupiter on probes approaching the planet results in very high atmospheric entry velocities. The values relative to the rotating atmosphere can vary from about 47 to 60 km/sec, depending on the latitude of the entry. Therefore, the peak heating rates and heat shield mass fractions exceed those for any other atmospheric entries. For example, the Galileo probe's heat shield mass fraction was 50%, of which 45% was devoted to the forebody. Although the Galileo probe's mission was very successful, many more scientific questions about the Jovian atmosphere remain to be answered and additional probe missions are being planned. Recent developments in microelectronics have raised the possibility of building smaller and less expensive probes than Galileo. Therefore, it was desirable to develop a code that could quickly compute the forebody entry heating environments when performing parametric probe sizing studies. The Jupiter Atmospheric Entry (JAE) code was developed to meet this requirement. The body geometry consists of a blunt-nosed conical shape of arbitrary nose and base radius and cone angles up to about 65 deg at zero angle of attack.

Wercinski, Paul F.↗
NASA NTRS1992

Study Of Spacecraft Capsule Reentering The Atmosphere

Report describes computational study of heating and deceleration of crew capsule of spacecraft entering atmosphere of Earth upon return from Mars. Issues pertaining to heating and deceleration considered in context of related issues pertaining to navigation, maneuverability of spacecraft, and safety.

Tauber, Michael↗
NASA NTRS1991

Thermal protection for hypervelocity flight in earth's atmosphere by use of radiation backscattering ablating materials

A heat-shield-material response code predicting the transient performance of a material subject to the combined convective and radiative heating associated with the hypervelocity flight is developed. The code is dynamically interactive to the heating from a transient flow field, including the effects of material ablation on flow field behavior. It accomodates finite time variable material thickness, internal material phase change, wavelength-dependent radiative properties, and temperature-dependent thermal, physical, and radiative properties. The equations of radiative transfer are solved with the material and are coupled to the transfer energy equation containing the radiative flux divergence in addition to the usual energy terms.

Howe, John T.↗
NASA NTRS1990

Earth atmospheric entry studies for manned Mars missions

Decelerations, heating rates, and total heat loads encountered when returning from Mars to earth at entry speeds of 12 km/sec to 16 km/sec are studied. For entry at 14 km/sec, it is found that a lift/drag ratio (L/D) of 0.5 is required to provide a guidance corridor margin near 1 deg for the specified deceleration limit of 5 g. For a blunted, raked cone with an L/D = 0.5, the peak heating rate near the aft end of the forebody varies from 0.14 to 0.23 kW/sq cm for laminar flow. If ablation triggers boundary layer transition, the peak heating can rise to 0.5 or up to 0.72 kW/sq cm. All heating rates are sufficiently high to make ablative heat shields necessary.

Tauber, M. E.↗
NASA NTRS1989

Atmospheric environment during maneuvering descent from Martian orbit

This paper presents an analysis of the atmospheric maneuvering capability of a vehicle designated to land on the Martian surface, together with an analysis of the entry environment encountered by the vehicle. A maximum lift/drag ratio of 2.3 was used for all trajectory calculations. The maximum achievable lateral ranges varied from about 3400 km to 2500 km for entry velocities of 5 km/s (from a highly elliptical Martian orbit) and 3.5 km/s (from a low-altitude lower-speed orbit), respectively. It is shown that the peak decelerations are an order of magnitude higher for the 5-km/s entries than for the 3.5-km/s entries. The vehicle entering at 3.5 km/s along a gliding trajectory encountered a much more benign atmospheric environment. In addition, the glider's peak deceleration was found to be only about 0.7 earth g, making the shallow flight path ideal for manned vehicles whose crews might be physically weakened by the long voyage to Mars.

Tauber, Michael E.↗
NASA NTRS1989

The use of atmospheric braking during Mars missions

The use of a high-lift, winged atmospheric entry-glide vehicle by an early Mars manned mission lasting 14-16 months allows the effective use of atmospheric braking to decelerate upon arrival at Mars. Following nearly-constant deceleration, the vehicle skips out of the atmosphere into a low planetary orbit. The maximum atmospheric heating rate thus generated is of the order of 100 W/sq cm at the stagnation point for a fully catalytic surface; the corresponding equilibrium wall temperature was 2150 K. The vehicle envisioned could be radiatively cooled to an entry speed of over 8 km/sec.

Tauber, M. E.↗
NASA NTRS1988

The heating environment during Martian atmospheric descent

It has been shown that a vehicle with a lift/drag ratio of 2.3 entering the Martian atmosphere at parabolic speed of 5 km/sec, or from a low orbit at 3.5 km/sec, has a very large landing footprint. At the 5-km/sec entry speed, the trajectory exhibits large skipping motions; however, a lateral range of up to 3300 km is attainable. The entries from low satellite orbit yield a gliding lateral range of 2500 km. The distances correspond to latitude changes of 57 and 42 deg, respectively. The high-speed, skipping entries were accompanied by the most intense heating. The peak stagnation point convective rates varied from 59 W/sq cm to 88 W/sq cm for partially and fully catalytic walls, respectively; the corresponding equilibrium wall temperatures were 1900 K and 2100 K. The peak heating at a wing leading-edge point reached 50 W/sq cm because of the presence of a transitional boundary layer. The lower-speed, gliding entries experienced much milder heating with a peak stagnation point rate of about 14 W/sq cm, resulting in a wall temperature near 1300 K. However, the longer duration of the gliding entries resulted in comparable heat loads for both entry speeds. The highest heat loads approached values experienced by the Shuttle orbiter stagnation point during a typical entry.

Tauber, Michael E.↗
NASA NTRS1988

Entry aeromaneuvering capabilities of transatmospheric vehicles

The landing footprint of a conceptual high-lift transatmospheric vehicle is defined for aeromaneuvering entry from a typical low-earth orbit. The flight strategy for trajectory construction to maximize the landing area by extending downrange and crossrange as far as possible is developed in four phases by optimal programming of the vehicle's roll angle. Trajectories that reach any given landing site were calculated with the corresponding heating rates at three critical vehicle locations (stagnation point, wing leading edge, and body centerline). An optimization methodology was developed that demonstrates the trades between crossrange, peak heating and total heat loads as a function of three key flight parameters (altitude, flight-path angle, and vehicle roll angle). The maximum extent of the landing footprint was found to be 29,690 km downrange and 6560 km crossrange. Large variations in the ballistic coefficient had negligible effect on the extent of the footprint but could significantly affect heating. However, the footprint's longitude was displaced downstream or upstream with increasing or decreasing ballistic coefficient, respectively.

Menees, Gene P.↗
NASA NTRS1988

Atmospheric maneuvering during Martian entry

A comparative-advantages study is made of two different Martian atmospheric entry maneuvers, on the basis of calculation results for the case of a vehicle with a maximum L/D ratio of 2.3. Entries from a highly elliptical Martian orbit at 5 km/sec are more difficult than those from a lower altitude and speed orbit at 3.5 km/sec, due to their more stringent guidance requirements. Efforts to reduce the deceleration for the higher speed entry by lift-modulation achieved a 40-percent reduction, but at the cost of a 50-percent decrease in lateral range. The lower-speed entry's gliding trajectory is noted to encounter a far more benign atmospheric environment.

Tauber, Michael E.↗
NASA NTRS1987

Performance comparisons of maneuvering vehicles returning from orbit

In the present study of maneuvering reentry vehicles employing skipping and gliding flight paths, attention is given to aerodynamic heating pulses during longitudinal flight and lateral maneuvers. While skipping vehicles can achieve longer ranges than gliding ones, the deceleration loads can be an order of magnitude higher and involve heating rates 4-5 times higher, even for shallow entries, therefore requiring much heavier structural components and heavier thermal protection systems than gliders. A total lateral range of 8000 km is noted to be achievable by a gliding aerodynamic maneuver involving a 90-deg turn initiated at entry.

Tauber, Michael E.↗
NASA NTRS1987

Prebiotic synthesis of imidazole-4-acetaldehyde and histidine

The prebiotic synthesis of imidazole-4-acetaldehyde and imidazole-4-glycol from erythrose and formamidine has been demonstrated as well as the prebiotic synthesis of imidazole-4-ethanol and imidazole-4-glycol from erythrose, formaldehyde, and ammonia. The maximum yields of imidazole-4-acetaldehyde, imidazole-4-ethanol, and imidazole-4-glycol obtained in these reactions are 1.6, 5.4, and 6.8 percent respectively, based on the erythrose. Imidazole-4-acetaldehyde would have been converted to histidine on the primitive earth by a Strecker synthesis, and several prebiotic reactions would convert imidazole-4-glycol and imidazole-4-ethanol to imidazole-4-acetaldehyde.

Shen, Chun↗