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Comet C/2007 H2 (Skiff)

  • April 2007
Authors:
B. A. Skiff
B. A. Skiff
B. A. Skiff
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L. Bittesini
L. Bittesini
L. Bittesini
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Ginevra Virginia Lombardi at University of Florence
Ginevra Virginia Lombardi
E. Pettarin
E. Pettarin
E. Pettarin
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Abstract

IAUC 8831 available at Central Bureau for Astronomical Telegrams.
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Circular No. 8831
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT@CFA.HARVARD.EDU (science)
URL http://www.cfa.harvard.edu/iau/cbat.html ISSN 0081-0304
Phone 617-495-7440/7244/7444 (for emergency use only)
COMET C/2007 H2 (SKIFF)
B. A. Skiff, Lowell Observatory, reports his discovery of a comet on
CCD images taken by himself with the 0.59-m LONEOS Schmidt tele-
scope (discovery observation tabulated below), a 1000 coma noted as being
moderately condensed with a narrow tail extending 3000 in p.a. 250o. Fol-
lowing posting on the Minor Planet Center’s ‘NEOCP’ webpage, numerous
other CCD astrometric observers have remarked on the objects cometary
appearance, including L. Bittesini, G. Lombardi, E. Pettarin, F. Piani,
and G. Cralli (Farra d’Isonzo, Italy, 0.40-m f/4.5 reflector, Apr. 19.84 UT;
diffuse coma of diameter ∼1000 and a tail ∼5000 long in p.a. 230o); A.
Kn¨ofel (Schoenbrunn, Germany, 0.5-m f/5 reflector, Apr. 19.9; short tail
visible); L. Donato, M. Gonano, V. Gonano, E. Guido, and G. Sostero
(Remanzacco, Italy, 0.45-m f/4.4 reflector, Apr. 19.83–19.91; co-adding of
sixty unfiltered 60-s exposures reveals the presence of a coma nearly 2000
in diameter and a narrow tail extending almost 20toward p.a. 235o); J. J.
M¨uller (Irmtraut, Germany, 0.31-m f/4.8 reflector, Apr. 19.9; coma diam-
eter 500); P. Birtwhistle (Great Shefford, Berkshire, England, 0.40-m f/6.0
Schmidt-Cassegrain reflector, Apr. 19.9; diffuse coma of diameter 900 with
central condensation and a tail 2000 long — possibly up to 3000 long — in
p.a. 230o); J. Lacruz, Madrid, Spain, 0.30-m Schmidt-Cassegrain reflector,
Apr. 19.96–19.98; condensed, elongated coma of diameter 800 with a fan-
shaped tail 2800 –3000 long spanning p.a. 223o–235o); M. Pietschnig (Vienna,
0.35-m f/7 Schmidt-Cassegrain reflector, Apr. 19.96-19.98; 2000 tail in p.a.
239o); G. Hug (Scranton, KS, 0.30-m Schmidt-Cassegrain reflector, Apr.
20.26; narrow tail extending ∼10in p.a. ∼220o); and R. E. Hill (Mount
Lemmon 1.5-m reflector, Apr. 20.3; four 30-s stacked images in 200-300 see-
ing show a well-condensed nuclear condensation of diameter ∼1000 and a
broad, fan-shaped tail ∼10long toward p.a. ∼225o).
2007 UT α2000 δ2000 Mag.
Apr. 19.25649 13h
40
m
08s
.95 −0o2601500
.3 18.1
The available astrometry, the following preliminary parabolic orbital ele-
ments, and an ephemeris appear on MPEC 2007-H33.
T= 2007 Feb. 17.409 TT ω= 319o
.448
Ω = 203.789 ¾2000.0
q= 1.41383 AU i=52.638
2007 April 20 c
°Copyright 2007 CBAT Daniel W. E. Green
Study of individual phonon scattering mechanisms and the validity of Matthiessen's rule in a gate-all-around silicon nanowire transistor
Article
  • Jan 2013
In this paper, we investigate the impact of different phonon scattering mechanisms on the performance of a small silicon gate-all-around nanowire field effect transistor. The Non-equilibrium Green's function (NEGF) framework in the effective mass approximation is used to describe the carrier transport in a wide range of bias conditions. For all gate bias conditions, acoustic phonons are found to be the most important scattering mechanism. At low drain bias, the total impact of the phonons increases monotonically with the gate bias as all the contributions from different phonons increase, but at high drain bias the drain current reduction remains almost constant. At high gate bias conditions, the calculations show a different behaviour for acoustic phonons at low and high drain bias, which substantially influences the total impact of phonon scattering at high gate biases. The drain current reduction, including all phonons, is in agreement with previous simulations using a tight-binding/NEGF approach [M. Luisier and G. Klimeck, Phys. Rev. B 80, 155430 (2009)]. We find a violation of Matthiessen's rule of 13%. A value of 16% is obtained through the use of a Green-Kubo formula, which includes a self-consistent calculation of the retarded Green's function. However, an overestimation of 23% is found if a semi-classical Kubo expression is used.
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