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 $10^2$\,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 $\alpha$~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 ($\Delta{\rm m} > 5$) 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 $^{12}$C/$^{13}$C and $^{16}$O/$^{17}$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 $^{12}$C/$^{13}$C or $^{16}$O/$^{17}$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

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