Active rendezvous between a low-earth orbit user spacecraft and the Space Transportation System (STS) shuttle

Active rendezvous of an unmanned spacecraft with the Space Transportation System (STS) Shuttle is considered. The various operational constraints facing both the maneuvering spacecraft and the Shuttle during such a rendezvous sequence are discussed. Specifically, the actively rendezvousing user spacecraft must arrive in the generic Shuttle control box at a specified time after Shuttle launch. In so doing it must at no point violate Shuttle separation requirements. In addition, the spacecraft must be able to initiate the transfer sequence from any point in its orbit. The four-burn rendezvous sequence incorporating two Hohmann transfers and an intermediate phasing orbit as a low-energy solution satisfying the above requirements are discussed. The general characteristics of the four-burn sequence are discussed, with emphasis placed on phase orbit altitude and delta-velocity requirements. The planning and execution of such a sequence in the operational environment are then considered. Factor crucial in maintaining the safety of both spacecraft, such as spacecraft separation and contingency analysis, are considered in detail

Gamma Rays From The Galactic Center and the WMAP Haze

Recently, an analysis of data from the Fermi Gamma Ray Space Telescope has revealed a flux of gamma rays concentrated around the inner ~0.5 degrees of the Milky Way, with a spectrum that is sharply peaked at 2-4 GeV. If interpreted as the products of annihilating dark matter, this signal implies that the dark matter consists of particles with a mass between 7.3 and 9.2 GeV annihilating primarily to charged leptons. This mass range is very similar to that required to accommodate the signals reported by CoGeNT and DAMA/LIBRA. In addition to gamma rays, the dark matter is predicted to produce energetic electrons and positrons in the Inner Galaxy, which emit synchrotron photons as a result of their interaction with the galactic magnetic field. In this letter, we calculate the flux and spectrum of this synchrotron emission assuming that the gamma rays from the Galactic Center originate from dark matter, and compare the results to measurements from the WMAP satellite. We find that a sizable flux of hard synchrotron emission is predicted in this scenario, and that this can easily account for the observed intensity, spectrum, and morphology of the "WMAP Haze".Comment: 5 pages, 4 figure

Analytical and experimental study of the dynamics of a single-tube counterflow boiler

Experimental and analytical study of dynamics of single tube counterflow boile

Primordial Black Holes, Hawking Radiation and the Early Universe

The 511 keV gamma emission from the galactic core may originate from a high concentration ($\sim 10^{22}$) of primordial black holes (PBHs) in the core each of whose Hawking radiation includes $\sim 10^{21}$ positrons per second. The PBHs we consider are taken as near the lightest with longevity greater than the age of the universe (mass $\sim 10^{12}$ kg; Schwarzschild radius $\sim 1$ fm). These PBHs contribute only a small fraction of cold dark matter, $\Omega_{PBH} \sim 10^{-8}$. This speculative hypothesis, if confirmed implies the simultaneous discovery of Hawking radiation and an early universe phase transition.Comment: 4 Page

Sensing using differential surface plasmon ellipsometry

Copyright © 2004 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Journal of Applied Physics 96 (2004) and may be found at http://link.aip.org/link/?JAPIAU/96/3004/1In this work a differential ellipsometric method utilizing surface plasmons (SPs) for monitoring refractive index changes, which could be used in chemical and biological sensors, is presented. The method is based upon determining the azimuth of elliptically polarized light reflected from a Kretschmann SP system, resulting from linearly polarized light containing both p and s components incident upon it. The sensitivity of this azimuth to the refractive index of a dielectric on the nonprism side of the metal film is demonstrated both experimentally and theoretically. The smallest refractive index change which is resolvable is of the order of 10–7 refractive index units, although it is believed that this could be improved upon were it not for experimental constraints due to atmospheric changes and vibrations. The method requires the Kretschmann configuration to be oriented at a fixed angle, and the SP to be excited at a fixed wavelength. With no moving parts this method would be particularly robust from an application point of view

Behavioral Risk Elicits Selective Activation of the Executive System in Adolescents: Clinical Implications

We investigated adolescent brain processing of decisions under conditions of varying risk, reward, and uncertainty. Adolescents (n = 31) preformed a Decision–Reward Uncertainty task that separates decision uncertainty into behavioral and reward risk, while they were scanned using functional magnetic resonance imaging. Behavioral risk trials involved uncertainty about which action to perform to earn a fixed monetary reward. In contrast, during reward risk the decision that might lead to a reward was known, but the likelihood of earning a reward was probabilistically determined. Behavioral risk trials evoked greater activation than the reward risk and no risk conditions in the anterior cingulate, medial frontal gyrus, bilateral frontal poles, bilateral inferior parietal lobe, precuneus, bilateral superior-middle frontal gyrus, inferior frontal gyrus, and insula. Our results were similar to those of young adults using the same task (Huettel, 2006) except that adolescents did not show significant activation in the posterior supramarginal gyrus during behavioral risk. During the behavioral risk condition regardless of reward outcome, overall mean frontal pole activity showed a positive correlation with age during the behavioral and reward risk conditions suggesting a developmental difference of this region of interest. Additionally, reward response to the Decision–Reward Uncertainty task in adolescents was similar to that seen in young adults (Huettel, 2006). Our data did not show a correlation between age and mean ventral striatum activity during the three conditions. While our results came from a healthy high functioning non-maltreated sample of adolescents, this method can be used to address types of risks and reward processing in children and adolescents with predisposing vulnerabilities and add to the paucity of imaging studies of risk and reward processing during adolescence

Strongly coupled surface plasmons on thin shallow metallic gratings

Z. Chen, Ian R. Hooper, and J. Roy Sambles, Physical Review B, Vol. 77, article 161405(R) (2008). Copyright © 2008 by the American Physical Society.The optical response of a thin metallic film with shallow corrugations on both surfaces is explored and the structure is found to support a strongly coupled surface plasmon polariton when transverse magnetic radiation is incident in a plane parallel to the grating grooves. Modeling confirms that this strongly excited mode is the short range surface plasmon polariton and its presence is confirmed experimentally in the visible part of the spectrum

Making Tunnel Barriers (Including Metals) Transparent

Ian R. Hooper, T. W. Preist, and J. Roy Sambles, Physical Review Letters, Vol. 97, article 053902 (2006). "Copyright © 2006 by the American Physical Society."The classical "brick wall," which may, according to quantum mechanics, leak via tunneling, is here shown to be completely transparent when appropriate impedance matching media are placed both in front of and behind the "wall." Optical experiments involving beyond-critical-angle-tunnel barriers in the frustrated total internal reflection scheme which mimic quantum mechanical systems provide convincing proof of this remarkable effect. The same mechanism also allows vastly enhanced transmission through unstructured thin metal films without the need for surface wave excitation

ASCA and contemporaneous ground-based observations of the BL Lacertae objects 1749+096 and 2200+420 (BL Lac)

We present ASCA observations of the radio-selected BL Lacertae objects 1749+096 (z=0.32) and 2200+420 (BL Lac, z=0.069) performed in 1995 Sept and Nov, respectively. The ASCA spectra of both sources can be described as a first approximation by a power law with photon index Gamma ~ 2. This is flatter than for most X-ray-selected BL Lacs observed with ASCA, in agreement with the predictions of current blazar unification models. While 1749+096 exhibits tentative evidence for spectral flattening at low energies, a concave continuum is detected for 2200+420: the steep low-energy component is consistent the high-energy tail of the synchrotron emission responsible for the longer wavelengths, while the harder tail at higher energies is the onset of the Compton component. The spectral energy distributions from radio to gamma-rays are consistent with synchrotron-self Compton emission from a single homogeneous region shortward of the IR/optical wavelengths, with a second component in the radio domain related to a more extended emission region. For 2200+420, comparing the 1995 Nov state with the optical/GeV flare of 1997 July, we find that models requiring inverse Compton scattering of external photons provide a viable mechanism for the production of the highest (GeV) energies during the flare. An increase of the external radiation density and of the power injected in the jet can reproduce the flat gamma-ray continuum observed in 1997 July. A directly testable prediction of this model is that the line luminosity in 2200+420 should vary shortly after (~1 month) a non-thermal synchrotron flare.Comment: 28 pages,6 figures, 5 tables; LaTeX document. accepted for publication in the Astrophysical Journa