374 research outputs found
The ESO-Sculptor Faint Galaxy Redshift Survey: The Photometric Sample
We present the photometric sample of a faint galaxy survey carried out in the
southern hemisphere, using CCDs on the 3.60m and NTT-3.5m telescopes at La
Silla (ESO). The survey area is a continuous strip of 0.2 deg x 1.53 deg
located at high galactic latitude (-83 deg) in the Sculptor constellation. The
photometric survey provides total magnitudes in the bands B, V (Johnson) and R
(Cousins) to limiting magnitudes of 24.5, 24.0, 23.5 respectively. To these
limits, the catalog contains about 9500, 12150, 13000 galaxies in B, V, R bands
respectively and is the first large digital multi-colour photometric catalog at
this depth. This photometric survey also provides the entry catalog for a
fully-sampled redshift survey of ~ 700 galaxies with R < 20.5 (Bellanger et al.
1995). In this paper, we describe the photometric observations and the steps
used in the data reduction. The analysis of objects and the star-galaxy
separation with a neural network are performed using SExtractor, a new
photometric software developed by E. Bertin (1996). The photometric accuracy of
the resulting catalog is ~ 0.05 mag for R < 22. The differential galaxy number
counts in B, V, R are in good agreement with previously published CCD studies
and confirm the evidence for significant evolution at faint magnitudes as
compared to a standard non evolving model (by factors 3.6, 2.6, 2.1). The
galaxy colour distributions B-R, B-V of our sample show a blueing trend of ~
0.5 mag between 21 < R < 23.5 in contrast to the V-R colour distribution where
no significant evolution is observed.Comment: LATEX, 18 Postscript figures, 20 pages. To appear July 1997. Modified
version of article. Abstract corrected for missing lin
Interacting Binaries with Eccentric Orbits. Secular Orbital Evolution Due To Conservative Mass Transfer
We investigate the secular evolution of the orbital semi-major axis and
eccentricity due to mass transfer in eccentric binaries, assuming conservation
of total system mass and orbital angular momentum. Assuming a delta function
mass transfer rate centered at periastron, we find rates of secular change of
the orbital semi-major axis and eccentricity which are linearly proportional to
the magnitude of the mass transfer rate at periastron. The rates can be
positive as well as negative, so that the semi-major axis and eccentricity can
increase as well as decrease in time. Adopting a delta-function mass-transfer
rate of 10^{-9} M_\sun {\rm yr}^{-1} at periastron yields orbital evolution
timescales ranging from a few Myr to a Hubble time or more, depending on the
binary mass ratio and orbital eccentricity. Comparison with orbital evolution
timescales due to dissipative tides furthermore shows that tides cannot, in all
cases, circularize the orbit rapidly enough to justify the often adopted
assumption of instantaneous circularization at the onset of mass transfer. The
formalism presented can be incorporated in binary evolution and population
synthesis codes to create a self-consistent treatment of mass transfer in
eccentric binaries.Comment: 16 pages, 8 figures, Accepted by The Astrophysical Journa
Correcting systematic effects in a large set of photometric lightcurves
We suggest a new algorithm to remove systematic effects in a large set of
lightcurves obtained by a photometric survey. The algorithm can remove
systematic effects, like the ones associated with atmospheric extinction,
detector efficiency, or PSF changes over the detector. The algorithm works
without any prior knowledge of the effects, as long as they linearly appear in
many stars of the sample. The approach, which was originally developed to
remove atmospheric extinction effects, is based on a lower rank approximation
of matrices, an approach which was already suggested and used in chemometrics,
for example. The proposed algorithm is specially useful in cases where the
uncertainties of the measurements are unequal. For equal uncertainties the
algorithm reduces to the Principal Components Analysis (PCA) algorithm. We
present a simulation to demonstrate the effectiveness of the proposed algorithm
and point out its potential, in search for transit candidates in particular.Comment: 6 pages, 2 figure
PACS: 33.20.Fb, 33.20.Kf, 32.50.+d, 61.46.Df, 73.20.Mf, 78.67.Bf, 87
The enhancing properties of silver nanoparticles in surface-enhanced Raman scattering (SERS) and metalenhanced uorescence (MEF) are studied in this work. The obtained results conrm that the partial aggregation of nanoparticles leads to a great increase of Raman scattering cross-section but there are signicant dierences in SERS-activity of colloidal silver treated with various aggregating compounds. The dierences are interpreted through the analysis of both experimental and computational results. The same silver colloid covered with silica shell preventing the uorescence quenching makes possible a several-fold increase in uorescence emission. The eect strongly depends on thickness of the outer layer of nanoparticles. Geometrical parameters of nanoparticles (radius or radius and thickness of the adsorption layer in core-shell systems) are determined on the basis of the dynamic light scattering (DLS) data and extinction spectra analysis
Photometric Solutions for Detached Eclipsing Binaries: selection of ideal distance indicators in the SMC
Detached eclipsing binary stars provide a robust one-step distance
determination to nearby galaxies. As a by-product of Galactic microlensing
searches, catalogs of thousands of variable stars including eclipsing binaries
have been produced by the OGLE, MACHO and EROS collaborations. We present
photometric solutions for detached eclipsing binaries in the Small Magellanic
Cloud (SMC) discovered by the OGLE collaboration. The solutions were obtained
with an automated version of the Wilson-Devinney program. By fitting mock
catalogs of eclipsing binaries we find that the normalized stellar radii
(particularly their sum) and the surface brightness ratio are accurately
described by the fitted parameters and estimated standard errors, despite
various systematic uncertainties. In many cases these parameters are well
constrained. In addition we find that systems exhibiting complete eclipses can
be reliably identified where the fractional standard errors in the radii are
small. We present two quantitatively selected sub-samples of eclipsing binaries
that will be excellent distance indicators. These can be used both for
computation of the distance to the SMC and to probe its structure. One
particularly interesting binary has a very well determined solution, exhibits
complete eclipses, and is comprised of well detached G-type, class giants.Comment: 29 pages, 12 figures. To be published in Ap
Estimated Assessment of the Potential Impact of Driverassistance Systems Used in Automated Vehicles on the Level of Road Safety in Poland
Strengthening road safety in the face of the enormous development of the automotive in recent decades is crucial. The safety benefits of automated vehicles are paramount. Automated vehicles have the potential to remove human error in road traffic, which will help protect drivers and passengers, as well as pedestrians and bicyclists. The carried-out forecasts are pioneering for Polish road traffic conditions. In England, studies have been carried out to determine the estimated impact of autonomous vehicles on road safety in simulated traffic conditions on the motorway. In Poland, preliminary forecasts of the reduction in the number of road accidents were made; however, they were based on other assumptions. Therefore, estimating the impact of using autonomous vehicles in order to increase the level of road safety is an innovative activity for Polish road conditions. For the purposes of this article, available statistical data on vehicles registered in Poland, their equipment with advanced driver-assistance systems as well as accident data and their causes were analyzed. A diagnosis of Road Safety in Poland in 2018 (base year for further estimations) was made, taking into account the trend of recent years together with an indication of the most common causes of road accidents. These data were compiled with statistical data from other countries about the influence of driversupport systems on traffic safety. Possible potential for increasing Road Safety in Poland by the year 2030 was estimated. The analyses were prepared assuming different types of processes related to traffic, road safety, and the recent development of the passenger car fleet in Poland. Presented results show four scenarios of road safety change, where the number of accidents is reduced with statistical average of 5000 reduction in the year 2030. These expectations are based on various predictable factors connected with upgrade of car fleet quality and take into account changes in road safety observed in recent years. Based on the current trend of driving automation and rapid development of driver-support systems, the provided estimations were found reliable and likely. The conducted research shows the benefits and the need for the use of driver-assistance systems in vehicles as they can measurably affect the level of road safety
User Requirements for Autonomous Vehicles – a Comparative Analysis of Expert and Non-expert-based Approach
Given the rapid progress being made in the design and development of autonomous vehicles, society is reaching the situation whereby customers will be able to access a range of semi-autonomous vehicles. These vehicles have the capability to drive autonomously in certain circumstances, with minimal input from the driver, except situations when a Request to Intervene is issued. While user requirements differ across and between types of users, there is no unified set of user requirements which will be acceptable to all drivers. Motivated by the recent explosion of interest around autonomous mobility, the authors made an attempt to extract, rank and compare the requirements that should be met according to different types of users - experts and non-experts. An initial set of user requirements was obtained, recognizing that drivers will have different priorities and preferences in this most critical of handover scenarios
IPHAS J062746.41+014811.3: a deeply eclipsing intermediate polar
We present time-resolved photometry of a cataclysmic variable discovered in
the Isaac Newton Telescope Photometric Halpha Survey of the northern galactic
plane, IPHAS J062746.41+014811.3 and classify the system as the fourth deeply
eclipsing intermediate polar known with an orbital period of Porb=8.16 h, and
spin period of Pspin=2210 s. The system shows mild variations of its
brightness, that appear to be accompanied by a change in the amplitude of the
spin modulation at optical wavelengths, and a change in the morphology of the
eclipse profile. The inferred magnetic moment of the white dwarf is mu_wd = 6-7
x 10^33 Gcm^3, and in this case IPHAS J0627 will either evolve into a
short-period EX Hya-like intermediate polar with a large Pspin\Porb ratio, or,
perhaps more likely, into a synchronised polar. Swift observations show that
the system is an ultraviolet and X-ray source, with a hard X-ray spectrum that
is consistent with those seen in other intermediate polars. The ultraviolet
light curve shows orbital modulation and an eclipse, while the low
signal-to-noise ratio X-ray light curve does not show a significant modulation
on the spin period. The measured X-ray flux is about an order of magnitude
lower than would be expected from scaling by the optical fluxes of well-known
X-ray selected intermediate polars.Comment: 34 pages, 9 figures, accepted for publication in Ap
Energy state distributions of the P(b) centers at the (100), (110), and (111) Si/SiO(2) interfaces investigated by Laplace deep level transient spectroscopy
The energy distribution of the P(b) centers at the Si/SiO(2) interface has been determined using isothermal laplace deep level transient spectroscopy. For the (111) and (110) interface orientations, the distributions are similar and centered at 0.38 eV below the silicon conduction band. This is consistent with only P(b0) states being present. For the (100) orientation, two types of the interface states are observed: one similar to the (111) and (110) orientations while the other has a negative-U character in which the emission rate versus surface potential dependence is qualitatively different from that observed for P(b0) and is presumed to be P(b1). (C) 2008 American Institute of Physics. (DOI: 10.1063/1.2939001
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