1,859 research outputs found
Space-Time Uncertainty and Noncommutativity in String Theory
We analyze the nature of space-time nonlocality in string theory. After
giving a brief overview on the conjecture of the space-time uncertainty
principle, a (semi-classical) reformulation of string quantum mechanics, in
which the dynamics is represented by the noncommutativity between temporal and
spatial coordinates, is outlined. The formalism is then compared to the
space-time noncommutative field theories associated with nonzero electric
B-fields.Comment: 10 pages with one figure. Written version of talks presented at the
Strings 2000 (Michigan, July, 2000) and the Summer Workshop on Branes (KIAS,
Seoul, June, 2000
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
The measurements of vehicle glow on the Space Shuttle
From the combined data set of glow observations on STS-3, STS-4 and STS-5 some of the properties of the shuttle glow were observed. Comparison of the STS-3 (240 km) and STS-5 (305 km) photographs show that the intensity of the glow is about a factor of 3.5 brighter on the low altitude (STS-3) flight. The orbiter was purposely rotated about the x axis in an experiment on STS-5 to observe the dependence of the intensity on the angle of incidence between the spacecraft surface normal and the velocity vector. For a relatively large angle between the velocity vector and the surface normal there is an appreciable glow, provided the surface is not shadowed by some other spacecraft structure. As the angle becomes less the glow intensifies. The grating experiments (STS-4 photography only, STS-5 image intensifier photography) provided a preliminary low resolution spectra of the spacecraft glow. Accurate wavelength calibrations of the STS-5 instrument permitted measuring of the spectrum and intensity of the Earth's airglow
Specific and reversible activation and inactivation of the mitochondrial phosphate carrier by cardiolipin and nonionic detergents, respectively
AbstractThe phosphate carrier of pig heart mitochondria was solubilized with Triton X-100 and purified by chromatography on hydroxylapatite. Incubation of the phosphate carrier fraction with cardiolipin stimulated the reconstituted [32P]phosphate exchange activity in liposomes, whereas increased Triton X-100 concentrations inhibited it. The effects of cardiolipin and Triton X-100 are reversible. The activation by cardiolipin is highly specific and could not be obtained with any other applied phospholipid
Penentuan Persediaan Bahan Baku Kopra Pada PT. Salim Ivomas Pratama Tbk Dengan Pendekatan Epq (Economic Production Quantity)
One of the factor to minimize the total cost is increasing the efficiency staples of copra, to avoid raw materials shortage that will make the production process stopped or the company will paying more for storage when the raw materials is excessive. This research is applying EPQ (Economic Production Quantity) method to determine the quantity and the period of staples ordering in a palm oil industries, using PT. Salim Ivomas Pratama Tbk as a case study. By using EPQ method, the company could anticipating the gradually arrival of raw materials. Financially, EPQ method is more optimal in ordering the raw materials. The calculation resulted, the value of Q0 (order quantity) is 79.539,90 tons and T0 (order period) is 1,29 months. Applying EPQ will profit the company
Pengukuran Kesenjangan Kinerja Antara Supplier Dengan Customer Pada Rantai Pasokan Jasa Pendidikan Tinggi Menggunakan Metode Servqual
Performance is the key to measure the quality of service. On the other side an increase in the quality of service is one of the keys to winning the competition.The purpose of this study is measuring the service quality of services at the college using SERVQUAL. SERVQUAL method itself is a method to measure services through five dimensions namely Tangibels, Empathy, Reliability, Responsiveness and Assurance.The results of using SERVQUAL method from 25 variables obtained dimensions that has the biggest gap is Tangibels, Empathy, and Responsiveness
Graphene formed on SiC under various environments: Comparison of Si-face and C-face
The morphology of graphene on SiC {0001} surfaces formed in various
environments including ultra-high vacuum, 1 atm of argon, and 10^-6 to 10^-4
Torr of disilane is studied by atomic force microscopy, low-energy electron
microscopy, and Raman spectroscopy. The graphene is formed by heating the
surface to 1100 - 1600 C, which causes preferential sublimation of the Si
atoms. The argon atmosphere or the background of disilane decreases the
sublimation rate so that a higher graphitization temperature is required, thus
improving the morphology of the films. For the (0001) surface, large areas of
monolayer-thick graphene are formed in this way, with the size of these areas
depending on the miscut of the sample. Results on the (000-1) surface are more
complex. This surface graphitizes at a lower temperature than for the (0001)
surface and consequently the growth is more three-dimensional. In an atmosphere
of argon the morphology becomes even worse, with the surface displaying
markedly inhomogeneous nucleation, an effect attributed to unintentional
oxidation of the surface during graphitization. Use of a disilane environment
for the (000-1) surface is found to produce improved morphology, with
relatively large areas of monolayer-thick graphene.Comment: 22 pages, 11 figures, Proceedings of STEG-2 Conference; eliminated
Figs. 4 and 7 from version 1, for brevity, and added Refs. 18, 29, 30, 31
together with associated discussio
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