[NASA's Manned Flight Programs- Gemini and Apollo] News Release

Manned space flight research projects - Gemini and Apoll

High Mobility SiGe/Si n-Type Structures and Field Effect Transistors on Sapphire Substrates

SiGe/Si n-type modulation doped field effect transistors (MODFETs) fabricated on sapphire substrates have been characterized at microwave frequencies for the first time. The highest measured room temperature electron mobility is 1380 sq cm/V-sec at a carrier density of 1.8 x 10(exp 12)/sq cm for a MODFET structure, and 900 sq cm/V-sec at a carrier density of 1.3 x 10/sq cm for a phosphorus ion implanted sample. A two finger, 2 x 200 micron gate n-MODFET has a peak transconductance of 37 mS/mm at a drain to source voltage of 2.5 V and a transducer gain of 6.4 dB at 1 GHz

Intrinsic response time of graphene photodetectors

Graphene-based photodetectors are promising new devices for high-speed optoelectronic applications. However, despite recent efforts, it is not clear what determines the ultimate speed limit of these devices. Here, we present measurements of the intrinsic response time of metal-graphene-metal photodetectors with monolayer graphene using an optical correlation technique with ultrashort laser pulses. We obtain a response time of 2.1 ps that is mainly given by the short lifetime of the photogenerated carriers. This time translates into a bandwidth of ~262 GHz. Moreover, we investigate the dependence of the response time on gate voltage and illumination laser power

Hot Carrier Transport and Photocurrent Response in Graphene

Strong electron-electron interactions in graphene are expected to result in multiple-excitation generation by the absorption of a single photon. We show that the impact of carrier multiplication on photocurrent response is enhanced by very inefficient electron cooling, resulting in an abundance of hot carriers. The hot-carrier-mediated energy transport dominates the photoresponse and manifests itself in quantum efficiencies that can exceed unity, as well as in a characteristic dependence of the photocurrent on gate voltages. The pattern of multiple photocurrent sign changes as a function of gate voltage provides a fingerprint of hot-carrier-dominated transport and carrier multiplication.Comment: 4 pgs, 2 fg

Civilian casualties and public support for military action: Experimental evidence

In contrast to the expansive literature on military casualties and support for war, we know very little about public reactions to foreign civilian casualties. This article, based on representative sample surveys in the US and Britain, reports four survey experiments weaving information about civilian casualties into vignettes about Western military action. These produce consistent evidence of civilian casualty aversion: where death tolls were higher, support for force was invariably and significantly lower. Casualty effects were moderate in size but robust across our two cases and across different scenarios. They were also strikingly resistant to moderation by other factors manipulated in the experiments, such as the framing of casualties or their religious affiliation. The importance of numbers over even strongly humanizing frames points towards a utilitarian rather than a social-psychological model of casualty aversion. Either way, civilian casualties deserve a more prominent place in the literature on public support for war

Photo-Thermoelectric Effect at a Graphene Interface Junction

We investigate the optoelectronic response of a graphene interface junction, formed with bilayer and single-layer graphene, by photocurrent (PC) microscopy. We measure the polarity and amplitude of the PC while varying the Fermi level by tuning a gate voltage. These measurements show that the generation of PC is by a photo-thermoelectric effect. The PC displays a factor of ~10 increase at the cryogenic temperature as compared to room temperature. Assuming the thermoelectric power has a linear dependence on the temperature, the inferred graphene thermal conductivity from temperature dependent measurements has a T^{1.5} dependence below ~100 K, which agrees with recent theoretical predictions

6-Hydroxydopamine Treatments Enhance Behavioral Responses to Intracerebral Microinjection of D1- and D2-Dopamine Agonists into Nucleus Accumbens and Striatum Without Changing Dopamine Antagonist Binding

Behavioral responses to D1 and D2-dopamine agonists are enhanced when these agonists are administered systemically to 6-hydroxydopamine (6-OHDA)-lesioned rats. In the present investigation, microinjection of SKF-38393, a D1-dopamine agonist, into the nucleus accumbens of adult rats lesioned as neonates with 6-OHDA produced a dose-related increase in locomotor activity that was enhanced markedly compared to control. LY-171555, a D2-agonist, elicited less locomotor activity than did SKF-38393 after microinjection into this site. Administration of SKF-38393 or LY-171555 into the nucleus accumbens did not increase locomotion in unlesioned rats at the doses administered to lesioned animals. In adult-6-OHDA-lesioned rats, microinjection of SKF-38393 into the nucleus accumbens also increased locomotion more than did LY-171555. As described previously, systemic administration of SKF-38393 produced little locomotion in adult-6-OHDA-lesioned rats, whereas LY-171555 produced a markedly enhanced response. Administration of SKF-38393 or LY-171555 into the caudate nucleus of neonatally and adult-6-OHDA-lesioned rats produced negligible locomotor activity, but did induce stereotypic behaviors similar to those observed after systemic treatment with these drugs. Stereotypic behaviors occurred to a greater degree in the 6-OHDA-lesioned rats than in unlesioned controls. A regional specificity for certain behaviors induced by dopamine agonist administration was observed. In spite of the enhanced behavioral responses of D1 and D2-dopamine agonists after microinjection into the brain of 6-OHDA-lesioned rats, binding of [3H]spiperone (D2-receptor antagonist ligand) and [3H]SCH 23390 (D1-receptor antagonist ligand) to tissue from striatum and nucleus accumbens was not altered significantly. In contrast to this lack of change in binding characteristics in 6-OHDA-lesioned rats, blockade of dopaminergic transmission with haloperidol treatment caused an elevation of [3H]spiperone binding sites in striatum without affecting affinity for the site. However, chronic haloperidol treatment did not alter significantly [3H]SCH 23390 binding to striatal membranes. These latter findings suggest that chronic dopamine receptor blockade need not produce the same adaptive mechanisms as destruction of dopamine-containing neurons. Thus, a change in receptor characteristics as measured by dopamine antagonist binding does not account for the behavioral supersensitivity observed after D1- and D2-dopamine agonist administration to neonatally or adult-6-OHDA-treated rats

Scaling Rule for Nonperturbative Radiation in a Class of Event Shapes

We discuss nonperturbative radiation for a recently introduced class of infrared safe event shape weights, which describe the narrow-jet limit. Starting from next-to-leading logarithmic (NLL) resummation, we derive an approximate scaling rule that relates the nonperturbative shape functions for these weights to the shape function for the thrust. We argue that the scaling reflects the boost invariance implicit in NLL resummation, and discuss its limitations. In the absence of data analysis for the new event shapes, we compare these predictions to the output of the event generator PYTHIA.Comment: 23 pages, 3 figures, uses JHEP3.cls (included); v2 - version to appear in JHE