107,750 research outputs found
On varieties of almost minimal degree I: Secant loci of rational normal scrolls
To complete the classification theory and the structure theory of varieties
of almost minimal degree, that is of non-degenerate irreducible projective
varieties whose degree exceeds the codimension by precisely 2, a natural
approach is to investigate simple projections of varieties of minimal degree.
Let be a variety of minimal degree and
of codimension at least 2, and consider where . By
\cite{B-Sche}, it turns out that the cohomological and local properties of
are governed by the secant locus of with
respect to .
Along these lines, the present paper is devoted to give a geometric
description of the secant stratification of , that is of the
decomposition of via the types of secant loci. We show
that there are exactly six possibilities for the secant locus , and we precisely describe each stratum of the secant stratification of
, each of which turns out to be a quasi-projective variety.
As an application, we obtain the classification of all non-normal Del Pezzo
varieties by providing a complete list of pairs where is a variety of minimal degree, is a closed
point in and is a Del Pezzo variety.Comment: 20 page
Germanium:gallium photoconductors for far infrared heterodyne detection
Highly compensated Ge:Ga photoconductors have been fabricated and evaluated for high bandwidth heterodyne detection. Bandwidths up to 60 MHz have been obtained with corresponding current responsivity of 0.01 A/W
D1 and D5-Brane Actions in AdS_m x S^n
The kappa-invariant and supersymmetric actions of D1 and D5-branes in AdS_3 x
S^3 are investigated, as well as the action of a D5-brane in an AdS_5 x S^5
background. The action of a D5-brane lying totally in an AdS_3 x S^3 background
is found. Some progress was made towards finding the action for the D5-brane
free to move in the whole AdS_3 x S^3 x T^4 space, however the supersymmetric
action found here is not kappa-invariant and the reasons the method used did
not find a kappa-invariant solution are discussed.Comment: 17pp, Latex, improved explanations, a definition adde
Statistical Mechanics of Three-dimensional Kerr-de Sitter Space
The statistical computation of the (2+1)-dimensional Kerr-de Sitter space in
the context of the {\it classical} Virasoro algebra for an asymptotic isometry
group has been a mystery since first, the degeneracy of the states has the
right value only at the infinite boundary which is casually disconnected from
our universe, second, the analyses were based on the unproven Cardy's formula
for complex central charge and conformal weight. In this paper, I consider the
entropy in Carlip's "would-be gauge" degrees of freedom approach instead. I
find that it agree with the Bekenstein-Hawking entropy but there are no the
above problems. Implications to the dS/CFT are noted.Comment: Added comments about diffeomorphism generators and Wheeler-de Witt
equation; Added references; Accpected in CQ
Gamma-Rays Produced in Cosmic-Ray Interactions and the TeV-band Spectrum of RX J1713.7-3946
We employ the Monte Carlo particle collision code DPMJET3.04 to determine the
multiplicity spectra of various secondary particles (in addition to 's)
with 's as the final decay state, that are produced in cosmic-ray
('s and 's) interactions with the interstellar medium. We derive an
easy-to-use -ray production matrix for cosmic rays with energies up to
about 10 PeV. This -ray production matrix is applied to the GeV excess
in diffuse Galactic -rays observed by EGRET, and we conclude the
non- decay components are insufficient to explain the GeV excess,
although they have contributed a different spectrum from the -decay
component. We also test the hypothesis that the TeV-band -ray emission
of the shell-type SNR RX J1713.7-3946 observed with HESS is caused by hadronic
cosmic rays which are accelerated by a cosmic-ray modified shock. By the
statistics, we find a continuously softening spectrum is strongly
preferred, in contrast to expectations. A hardening spectrum has about 1%
probability to explain the HESS data, but then only if a hard cutoff at 50-100
TeV is imposed on the particle spectrum.Comment: 3 pages; 4 figures; Contribution to the First GLAST Symposium,
Standord, 200
Light mixed sneutrinos as thermal dark matter
In supersymmetric models with Dirac neutrino masses, a left-right mixed
sneutrino can be a viable dark matter candidate. We examine the
MSSM+ parameter space where this is the case with particular
emphasis on light sneutrinos with masses below 10 GeV. We discuss implications
for direct and indirect dark matter searches, including the relevant
uncertainties, as well as consequences for collider phenomenology.Comment: 33 pages, 14 figures; one figure and references adde
Objectification theory predicts college womenâs attitudes toward cosmetic surgery
This study investigated cosmetic surgery attitudes
within the framework of objectification theory. One hundred
predominantlyWhite, British undergraduate women completed
self-report measures of impression management, global selfesteem,
interpersonal sexual objectification, self-surveillance,
body shame, and three components of cosmetic surgery
attitudes. As expected, each of the objectification theory
variables predicted greater consideration of having cosmetic
surgery in the future. Also, as expected, sexual objectification
and body shame uniquely predicted socialmotives for cosmetic
surgery, whereas self-surveillance uniquely predicted intrapersonal
motives for cosmetic surgery. These findings suggest that
womenâs acceptance of cosmetic surgery as a way to
manipulate physical appearance can be partially explained by
the degree to which they view themselves through the lenses of
sexual and self-objectification
On Minimum Violations Ranking in Paired Comparisons
Ranking a set of objects from the most dominant one to the least, based on
the results of paired comparisons, proves to be useful in many contexts. Using
the rankings of teams or individuals players in sports to seed tournaments is
an example. The quality of a ranking is often evaluated by the number of
violations, cases in which an object is ranked lower than another that it has
dominated in a comparison, that it contains. A minimum violations ranking (MVR)
method, as its name suggests, searches specifically for rankings that have the
minimum possible number of violations which may or may not be zero. In this
paper, we present a method based on statistical physics that overcomes
conceptual and practical difficulties faced by earlier studies of the problem.Comment: 10 pages, 10 figures; typos corrected (v2
Detection of an exoplanet around the evolved K giant HD 66141
Aims. We have been carrying out a precise radial velocity (RV) survey for K
giants to search for and study the origin of the lowamplitude and long-periodic
RV variations.
Methods. We present high-resolution RV measurements of the K2 giant HD 66141
from December 2003 to January 2011 using the fiber-fed Bohyunsan Observatory
Echelle Spectrograph (BOES) at Bohyunsan Optical Astronomy Observatory (BOAO).
Results. We find that the RV measurements for HD 66141 exhibit a periodic
variation of 480.5 +/- 0.5 days with a semi-amplitude of 146.2 +/- 2.7 m/s. The
Hipparcos photometry and bisector velocity span (BVS) do not show any obvious
correlations with RV variations. We find indeed 706.4 +/- 35.0 day variations
in equivalent width (EW) measurements of H_alpha line and 703.0 +/- 39.4 day
variations in a space-born measurements 1.25{\mu} flux of HD 66141 measured
during COBE/DIRBE experiment. We reveal that a mean value of long-period
variations is about 705 +/- 53 days and the origin is a rotation period of the
star and variability that is caused by surface inhomogeneities. For the 480 day
periods of RV variations an orbital motion is the most likely explanation.
Assuming a stellar mass of 1.1 +/- 0.1 M_Sun? for HD 66141, we obtain a minimum
mass for the planetary companion of 6.0 +/- 0.3 M_Jup with an orbital
semi-major axis of 1.2 +/- 0.1 AU and an eccentricity of 0.07 +/- 0.03.Comment: 7 pages, 10 figures, 3 tables, accepted for publisation in Astronomy
& Astrophysic
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