7,513 research outputs found
Advanced electric propulsion system concept for electric vehicles. Addendum 1: Voltage considerations
The two electric vehicle propulsion systems that best met cost and performance goals were examined to assess the effect of battery pack voltage on system performance and cost. A voltage range of 54 to 540 V was considered for a typical battery pack capacity of 24 k W-hr. The highest battery specific energy (W-hr/kg) and the lowest cost (0.057/km and for the flywheel system was $0.037/km
The optical and near-infrared properties of nearby groups of galaxies
We present a study of the optical (BRI) and near-infrared (JHK) luminosity
fuctions (LFs) of the GEMS sample of 60 nearby groups of galaxies between
0<z<0.04, with our optical CCD photometry and near-IR photometry from the 2MASS
survey. The LFs in all filters show a depletion of galaxies of intermediate
luminosity, two magnitudes fainter than L*, within 0.3 R{500} from the centres
of X-ray faint groups. This feature is not as pronounced in X-ray bright
gropus, and vanishes when LFs are found out to R{500}, even in the X-ray dim
groups. We argue that this feature arises due to the enhanced merging of
intermediate-mass galaxies in the dynamically sluggish environment of low
velocity-dispersion groups, indicating that merging is important in galaxy
evolution even at z~0.Comment: to appear in the proceedings of the ESO workshop "Groups of Galaxies
in the Nearby Universe", Santiago, Dec 5-9, 2005. Eds. I. Saviane, V. Ivanov,
& J. Borissova (Springer Verlag); 5 page
Orbiting astronomical observatory Final report /including status reports for 1 Dec. 1967 - 30 Jun. 1968 and 1 Jul. 1968 - 31 Mar. 1969/
Research activities of Lunar and Planetary Laborator
Physics-based derivation of a formula for the mutual depolarization of two post-like field emitters
Recent analyses of the field enhancement factor (FEF) from multiple emitters
have revealed that the depolarization effect is more persistent with respect to
the separation between the emitters than originally assumed. It has been shown
that, at sufficiently large separations, the fractional reduction of the FEF
decays with the inverse cube power of separation, rather than exponentially.
The behavior of the fractional reduction of the FEF encompassing both the range
of technological interest ( being the separation and is
the height of the emitters) and , has not been predicted by
the existing formulas in field emission literature, for post-like emitters of
any shape. In this letter, we use first principles to derive a simple
two-parameter formula for fractional reduction that can be of interest for
experimentalists to modeling and interpret the FEF from small clusters of
emitters or arrays in small and large separations. For the structures tested,
the agreement between numerical and analytical data is
Dust and ionized gas in active radio elliptical galaxies
The authors present broad and narrow bandwidth imaging of three southern elliptical galaxies which have flat-spectrum active radio cores (NGC 1052, IC 1459 and NGC 6958). All three contain dust and extended low excitation optical line emission, particularly extensive in the case of NGC 1052 which has a large H alpha + (NII) luminosity. Both NGC 1052 and IC 1459 have a spiral morphology in emission-line images. All three display independent strong evidence that a merger or infall event has recently occurred, i.e., extensive and infalling HI gas in NGC 1052, a counter-rotating core in IC 1459 and Malin-Carter shells in NGC 6958. This infall event is the most likely origin for the emission-line gas and dust, and the authors are currently investigating possible excitation mechanisms (Sparks et al. 1990)
Prospects for the Characterization and Confirmation of Transiting Exoplanets via the Rossiter-McLaughlin Effect
The Rossiter-McLaughlin (RM) effect is the distortion of stellar spectral
lines that occurs during eclipses or transits, due to stellar rotation. We
assess the future prospects for using the RM effect to measure the alignment of
planetary orbits with the spin axes of their parent stars, and to confirm
exoplanetary transits. We compute the achievable accuracy for the parameters of
interest, in general and for the 5 known cases of transiting exoplanets with
bright host stars. We determine the requirements for detecting the effects of
differential rotation. For transiting planets with small masses or long periods
(as will be detected by forthcoming satellite missions), the velocity anomaly
produced by the RM effect can be much larger than the orbital velocity of the
star. For a terrestrial planet in the habitable zone of a Sun-like star found
by the Kepler mission, it will be difficult to use the RM effect to confirm
transits with current instruments, but it still may be easier than measuring
the spectroscopic orbit.Comment: 18 pages, 8 figures, one table. Minor changes. Accepted to ApJ, to
appear in the Jan 20, 2007 issue (v655
Quantum Evaporation from Superfluid Helium at Normal Incidence
We study the scattering of atoms, rotons and phonons at the free surface of
He at normal incidence and calculate the evaporation, condensation and
reflection probabilities. Assuming elastic one-to-one processes and using
general properties of the scattering matrix, such as unitarity and time
reversal, we argue that all nonzero probabilities can be written in terms of a
single energy-dependent parameter. Quantitative predictions are obtained using
linearized time dependent density functional theory.Comment: 12 pages, REVTeX, 2 postscript figures, available also at
http://anubis.science.unitn.it/~dalfovo/papers/papers.htm
Satellite accelerometer measurements of neutral density and winds during geomagnetic storms
A new thermospheric wind measurement technique is reported which is based on a Satellite Electrostatic Triaxial Accelerometer (SETA) system capable of accurately measuring accelerations in the satellite's in-track, cross-track and radial directions. Data obtained during two time periods are presented. The first data set describes cross-track winds measured between 170 and 210 km during a 5-day period (25 to 29 March 1979) of mostly high geomagnetic activity. In the second data set, cross-track winds and neutral densities from SETA and exospheric temperatures from the Millstone Hill incoherent scatter radar are examined during an isolated magnetic substorm occurring on 21 March 1979. A polar thermospheric wind circulation consisting of a two cell horizontal convection pattern is reflected in both sets of cross-track acceleration measurements. The density response is highly asymmetric with respect to its day/night behavior. Latitude structures of the density response at successive times following the substorm peak suggest the equatorward propagation of a disturbance with a phase speed between 300 and 600 m/s. A deep depression in the density at high latitudes (less than 70 deg) is evident in conjunction with this phenomenon. The more efficient propagation of the disturbance to lower latitudes during the night is probably due to the midnight surge effect
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