3,139 research outputs found
Random Projections For Large-Scale Regression
Fitting linear regression models can be computationally very expensive in
large-scale data analysis tasks if the sample size and the number of variables
are very large. Random projections are extensively used as a dimension
reduction tool in machine learning and statistics. We discuss the applications
of random projections in linear regression problems, developed to decrease
computational costs, and give an overview of the theoretical guarantees of the
generalization error. It can be shown that the combination of random
projections with least squares regression leads to similar recovery as ridge
regression and principal component regression. We also discuss possible
improvements when averaging over multiple random projections, an approach that
lends itself easily to parallel implementation.Comment: 13 pages, 3 Figure
First Lunar Occultation Results from the 2.4 m Thai National Telescope equipped with ULTRASPEC
The recently inaugurated 2.4\,m Thai National Telescope (TNT) is equipped,
among other instruments, with the ULTRASPEC low-noise, frame-transfer EMCCD
camera. At the end of its first official observing season, we report on the use
of this facility to record high time resolution imaging using small detector
subarrays with sampling as fast as several \,Hz. In particular, we have
recorded lunar occultations of several stars which represent the first
contribution to this area of research made from South-East Asia with a
telescope of this class. Among the results, we discuss an accurate measurement
of ~Cnc, which has been reported previously as a suspected close
binary. Attempts to resolve this star by several authors have so far met with a
lack of unambiguous confirmation. With our observation we are able to place
stringent limits on the projected angular separation (<0\farcs003) and
brightness () of a putative companion. We also present a
measurement of the binary {HR~7072}, which extends considerably the time
coverage available for its yet undetermined orbit. We discuss our precise
determination of the flux ratio and projected separation in the context of
other available data. We conclude by providing an estimate of the performance
of ULTRASPEC at TNT for lunar occultation work. This facility can help to
extend the lunar occultation technique in a geographical area where no
comparable resources were available until now.Comment: Accepted for publication in Astronomical Journa
An observational test of common-envelope evolution
By analysing and modelling the change in the abundance ratio of
C/C and O/O on the surface of the lower mass star
of a binary during the common-envelope (CE) phase of evolution, we propose a
simple observational test of the CE scenario. The test is based on the infrared
measurement of either the C/C or O/O ratio of red
dwarfs in post-common envelope binaries (PCEB's). In certain cases
(main-sequence red dwarf secondaries in PCEB's without planetary nebulae), as
well as determining whether or not accretion has occurred during the CE phase,
we can determine the amount of mass accreted during the CE phase and hence the
initial mass of the red dwarf component prior to the CE phase. In the other
cases considered (low-mass red dwarfs in PCEB's and red dwarf's in PCEB's with
planetary nebulae) we can only say whether or not accretion has occurred during
the CE phase.Comment: uuencoded compressed postscript. The preprint are also available at
URL http://www.ast.cam.ac.uk/preprint/PrePrint.htm
Seed dormancy and endogenous growth substances in Anab-e-Shahi grapes
Auxin, gibberellin and inhibitor contents were estimated in the freshly extracted seeds as well as in those moist stratified for 30, 45, 60, 75 and 90 days. The maximum seed germination was obtained when the seeds were stratified for 60 days. Auxin activity increased with the increase in the period of stratification and was found to be at its maximum in the germinating seeds. Fully ripe freshly extracted seeds did not show any gibberellin-like activity. It was maximum in the extracts of the seeds moist-stratified for 60 days. Abscisic acid-like inhibitor was present in the extracts of the fully ripe fresh seeds. Its quantity decreased with the period of stratification and was minimum when the seeds were stratified for 45 and 90 days. From these studies, it may be postulated that the seed germination in grapes is regulated by the appearance of growth promoting substances like auxins and gibberellins during stratification and disappearance of inhibitors like abscisic acid. In all the cultivars, stratification for 60 days was sufficient to create these conditions for the best seed germination.Samenruhe und endogene Wachstumsregulatoren bei der Rebensorte Anab-e-ShahiDer Gehalt an Auxin, Gibberellin und Hemmstoffen in frisch isolierten Samen von Anab-e-Shahi sowie in Samen, die 30, 45, 60, 75 und 90 Tage lang feucht stratifiziert worden waren, wurde bestimmt. Durch 60tägige Stratifikation wurde die Keimung am stärksten gefördert. Mit der Dauer der Stratifikation nahm auch die Auxinaktivität zu, um ihr Maximum in den keimenden Samen zu erreichen. Voll ausgereifte, frisch isolierte Samen zeigten keinerlei Gibberellin-artige Aktivität. Eine solche war in den Extrakten von Samen, die 60 Tage lang feucht stratifiziert worden waren, im Maximum vorhanden. In den Extrakten voll ausgereifter, frischer Samen trat ein Abscisinsäure-artiger Hemmstoff auf. Seine Konzentration nahm mit fortschreitender Stratifikation ab und erreichte ihr Minimum nach 45 und 90 Tagen. Aufgrund der vorliegenden Untersuchungen kann angenommen werden, daß die Samenkeimung bei Reben durch das verstärkte Auftreten wachstumsfördernder Substanzen wie Auxine und Gibberelline im Laufe der Stratifikation und den Rückgang Abscisinsäure-artiger Hemmstoffe reguliert wird. Auch bei anderen Rebensorten genügte durchweg eine 60tägige Stratifikation, um die bestmöglichen Bedingungen für die Samenkeimung zu schaffen
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Aggressive digital papillary adenocarcinoma and sentinel node biopsy: A case report and literature review.
Aggressive digital papillary adenocarcinomas (ADPA) are malignant tumours of the sweat gland. Due to the high tendency to recur and metastasise, wide local resection of the lesion is recommended. However, there are a limited number of cases reporting the use of sentinel node biopsy in the management of ADPA, thus its effectiveness remains unclear. We present a case of ADPA of the right middle finger treated with digital amputation and sentinel node biopsy, and review the current literature focusing on the usefulness of sentinel node biopsy
Infrared spectroscopy of cataclysmic variables: III. Dwarf novae below the period gap and novalike variables
We present K-band spectra of the short-period dwarf novae YZ Cnc, LY Hya, BK
Lyn, T Leo, SW UMa and WZ Sge, the novalike variables DW UMa, V1315 Aql, RW
Tri, VY Scl, UU Aqr and GP Com, and a series of field dwarf stars with spectral
types ranging from K2-M6.
The spectra of the dwarf novae are dominated by emission lines of HI and HeI.
The large velocity and equivalent widths of these lines, in conjunction with
the fact that the lines are double-peaked in the highest inclination systems,
indicate an accretion disc origin. In the case of YZ Cnc and T Leo, for which
we obtained time-resolved data covering a complete orbital cycle, the emission
lines show modulations in their equivalent widths which are most probably
associated with the bright spot (the region where the gas stream collides with
the accretion disc). There are no clear detections of the secondary star in any
of the dwarf novae below the period gap, yielding upper limits of 10-30% for
the contribution of the secondary star to the observed K-band flux. In
conjunction with the K-band magnitudes of the dwarf novae, we use the derived
secondary star contributions to calculate lower limits to the distances to
these systems.
The spectra of the novalike variables are dominated by broad, single-peaked
emission lines of HI and HeI - even the eclipsing systems we observed do not
show the double-peaked profiles predicted by standard accretion disc theory.
With the exception of RW Tri, which exhibits NaI, CaI and 12CO absorption
features consistent with a M0V secondary contributing 65% of the observed
K-band flux, we find no evidence for the secondary star in any of the novalike
variables. The implications of this result are discussed.Comment: 13 pages, 5 figures, to appear in MNRA
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