1,311 research outputs found
Spacecraft ram glow and surface temperature
Space shuttle glow intensity measurements show large differences when the data from different missions are compared. In particular, on the 41-G mission the space shuttle ram glow was observed to display an unusually low intensity. Subsequent investigation of this measurement and earlier measurements suggest that there was a significant difference in temperature of the glow producing ram surfaces. The highly insulating properties coupled with the high emissivity of the shuttle tile results in surfaces that cool quickly when exposed to deep space on the night side of the orbit. The increased glow intensity is consistent with the hypothesis that the glow is emitted from excited NO2. The excited NO2 is likely formed through three body recombination (OI + NO + M = NO2*) where ramming of OI interacts with weakly surface bound NO. The NO is formed from atmospheric OI and NI which is scavenged by the spacecraft moving through the atmosphere. It is postulated that the colder surfaces retain a thicker layer of NO thereby increasing the probability of the reaction. It has been found from the glow intensity/temperature data that the bond energy of the surface bound precursor, leading to the chemical recombination producing the glow, is approximately 0.14 eV. A thermal analysis of material samples of STS-8 was made and the postulated temperature change of individual material samples prior to the time of glow measurements above respective samples are consistent with the thermal effect on glow found for the orbiter surface
Evidence for Non-perturbative String Symmetries
String theory appears to admit a group of discrete field transformations --
called dualities -- as exact non-perturbative quantum symmetries.
Mathematically, they are rather analogous to the better-known duality
symmetries, which hold perturbatively. In this talk the evidence for
duality is reviewed and some speculations are presented.Comment: Error corrected and reference added; 10 pages, latex, no figures,
conference Repor
NUV/Blue spectral observations of sprites in the 320-460 nm region: (2PG) Emissions
A near-ultraviolet (NUV) spectrograph (320-460 nm) was flown on the EXL98
aircraft sprite observation campaign during July 1998. In this wavelength range
video rate (60 fields/sec) spectrographic observations found the NUV/blue
emissions to be predominantly N2 (2PG). The negligible level of N2+ (1NG)
present in the spectrum is confirmed by observations of a co-aligned, narrowly
filtered 427.8 nm imager and is in agreement with previous ground-based
filtered photometer observations. The synthetic spectral fit to the
observations indicates a characteristic energy of ~1.8 eV, in agreement with
our other NUV observations.Comment: 7 pages, 2 figures, 1 table, JGR Space Physics "Effects of
Thunderstorms and Lightning in the Upper Atmosphere" Special Sectio
Alternative Signature of TeV Strings
In string theory, it is well known that any hard scattering amplitude
inevitably suffers exponential suppression. We demonstrate that, if the string
scale is M_s < 2TeV, this intrinsically stringy behavior leads to a dramatic
reduction in the QCD jet production rate with very high transverse momenta p_T
> 2TeV at LHC. This suppression is sufficient to be observed in the first year
of low-luminosity running. Our prediction is based on the universal behavior of
string theory, and therefore is qualitatively model-independent. This signature
is alternative and complementary to conventional ones such as Regge resonance
(or string ball/black hole) production.Comment: a note added; version to appear in Phys. Rev. D; 11 pages, 1 eps
figure, LaTeX2e; BibTeX with utphys style use
Technology ready use of single layer graphene as a transparent electrode for hybrid photovoltaic devices
Graphene has been used recently as a replacement for indium tin oxide (ITO)
for the transparent electrode of an organic photovoltaic device. Due to its
limited supply, ITO is considered as a limiting factor for the
commercialization of organic solar cells. We explored the use of large-area
graphene grown on copper by chemical vapor deposition (CVD) and then
transferred to a glass substrate as an alternative transparent electrode. The
transferred film was shown by scanning Raman spectroscopy measurements to
consist of >90% single layer graphene. Optical spectroscopy measurements showed
that the layer-transferred graphene has an optical absorbance of 1.23% at a
wavelength of 532 nm. We fabricated organic hybrid solar cells utilizing this
material as an electrode and compared their performance with ITO devices
fabricated using the same procedure. We demonstrated power conversion
efficiency up to 3.98%, higher than that of the ITO device (3.86%), showing
that layer-transferred graphene promises to be a high quality, low-cost,
flexible material for transparent electrodes in solar cell technology.Comment: 6 pages, 3 figure
Recommended from our members
Gq/11-Mediated Signaling and Hypertrophy in Mice with Cardiac-Specific Transgenic Expression of Regulator of G-Protein Signaling 2
Cardiac hypertrophy is a well-established risk factor for cardiovascular morbidity and mortality. Activation of -mediated signaling is required for pressure overload-induced cardiomyocyte (CM) hypertrophy to develop. We previously showed that among Regulators of G protein Signaling, RGS2 selectively inhibits signaling and its hypertrophic effects in isolated CM. In this study, we generated transgenic mice with CM-specific, conditional RGS2 expression (dTG) to investigate whether RGS2 overexpression can be used to attenuate -mediated signaling and hypertrophy in vivo. Transverse aortic constriction (TAC) induced a comparable rise in ventricular mass and ANF expression and corresponding hemodynamic changes in dTG compared to wild types (WT), regardless of the TAC duration (1-8 wks) and timing of RGS2 expression (from birth or adulthood). Inhibition of endothelin-1-induced -mediated phospholipase C β activity in ventricles and atrial appendages indicated functionality of transgenic RGS2. However, the inhibitory effect of transgenic RGS2 on -mediated PLCβ activation differed between ventricles and atria: (i) in sham-operated dTG mice the magnitude of the inhibitory effect was less pronounced in ventricles than in atria, and (ii) after TAC, negative regulation of signaling was absent in ventricles but fully preserved in atria. Neither difference could be explained by differences in expression levels, including marked RGS2 downregulation after TAC in left ventricle and atrium. Counter-regulatory changes in other -regulating RGS proteins (RGS4, RGS5, RGS6) and random insertion were also excluded as potential causes. Taken together, despite ample evidence for a role of RGS2 in negatively regulating signaling and hypertrophy in CM, CM-specific RGS2 overexpression in transgenic mice in vivo did not lead to attenuate ventricular -mediated signaling and hypertrophy in response to pressure overload. Furthermore, our study suggests chamber-specific differences in the regulation of RGS2 functionality and potential future utility of the new transgenic model in mitigating signaling in the atria in vivo
Targeting atypical protein kinase C iota reduces viability in glioblastoma stem-like cells via a notch signaling mechanism
In a previous study, Protein Kinase C iota (PRKCI) emerged as an important candidate gene for glioblastoma (GBM) stem-like cell (GSC) survival. Here, we show that PKCι is overexpressed and activated in patient derived GSCs compared with normal neural stem cells and normal brain lysate, and that silencing of PRKCI in GSCs causes apoptosis, along with loss of clonogenicity and reduced proliferation. Notably, PRKCI silencing reduces tumor growth in vivo in a xenograft mouse model. PKCι has been intensively studied as a therapeutic target in non-small cell lung cancer, resulting in the identification of an inhibitor, aurothiomalate (ATM), which disrupts the PKCι/ERK signaling axis. However, we show that, although sensitive to pharmacological inhibition via a pseudosubstrate peptide inhibitor, GSCs are much less sensitive to ATM, suggesting that PKCι acts along a different signaling axis in GSCs. Gene expression profiling of PRKCI-silenced GSCs revealed a novel role of the Notch signaling pathway in PKCι mediated GSC survival. A proximity ligation assay showed that Notch1 and PKCι are in close proximity in GSCs. Targeting PKCι in the context of Notch signaling could be an effective way of attacking the GSC population in GBM
VaporSPOT : parallel synthesis of oligosaccharides on membranes
Automated chemical synthesis has revolutionized synthetic access to biopolymers in terms of simplicity and speed. While automated oligosaccharide synthesis has become faster and more versatile, the parallel synthesis of oligosaccharides is not yet possible. Here, a chemical vapor glycosylation strategy (VaporSPOT) is described that enables the simultaneous synthesis of oligosaccharides on a cellulose membrane solid support. Different linkers allow for flexible and straightforward cleavage, purification, and characterization of the target oligosaccharides. This method is the basis for the development of parallel automated glycan synthesis platforms
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