304 research outputs found
Constraining RRc candidates using SDSS colours
The light variations of first-overtone RR Lyrae stars and contact eclipsing
binaries can be difficult to distinguish. The Catalina Periodic Variable Star
catalog contains several misclassified objects, despite the classification
efforts by Drake et al. (2014). They used metallicity and surface gravity
derived from spectroscopic data (from the SDSS database) to rule out binaries.
Our aim is to further constrain the catalog using SDSS colours to estimate
physical parameters for stars that did not have spectroscopic data.Comment: 2 pages, 1 figure, proceedings of the RRL2015 - High-Precision
Studies of RR Lyrae Stars conference, to appear in the Communications from
the Konkoly Observator
Target selection of classical pulsating variables for space-based photometry
In a few years the Kepler and TESS missions will provide ultra-precise
photometry for thousands of RR Lyrae and hundreds of Cepheid stars. In the
extended Kepler mission all targets are proposed in the Guest Observer (GO)
Program, while the TESS space telescope will work with full frame images and a
~15-16th mag brightness limit with the possibility of short cadence
measurements for a limited number of pre-selected objects. This paper
highlights some details of the enormous and important work of the target
selection process made by the members of Working Group 7 (WG#7) of the Kepler
and TESS Asteroseismic Science Consortium.Comment: 4 pages, 1 figure, proceedings of the RRL2015 - High-Precision
Studies of RR Lyrae Stars conference, to appear in the Communications from
the Konkoly Observator
Quasi-classical Approach to Bose Condensation in a Finite Potential Well
We treat the problem of self-consistently interacting bosons in the presence
of a finite (but macroscopic) potential well within a quasi-classical
approximation for the normal component and the order parameter. We solve the
equilibrium problem and show, that actually condensation occurs in two steps.
One already at low densities with Bose condensation only in the well and
another one corresponding to the usual condensation in bulk. The peak and width
of the distribution of trapped particles in the well display a distinct
signature of the local condensation. A possible connection to recent
experiments with excitons is discussed
Kinetics of four-wave mixing for a 2D magneto-plasma in strong magnetic fields
We investigate the femtosecond kinetics of an optically excited 2D
magneto-plasma at intermediate and high densities under a strong magnetic field
perpendicular to the quantum well (QW). We assume an additional weak lateral
confinement which lifts the degeneracy of the Landau levels partially. We
calculate the femtosecond dephasing and relaxation kinetics of the laser pulse
excited magneto-plasma due to bare Coulomb potential scattering, because
screening is under these conditions of minor importance. In particular the
time-resolved and time-integrated four-wave mixing (FWM) signals are calculated
by taking into account three Landau subbands in both the valance and the
conduction band assuming an electron-hole symmetry. The FWM signals exhibit
quantum beats mainly with twice the cyclotron frequency. Contrary to general
expectations, we find no pronounced slowing down of the dephasing with
increasing magnetic field. On the contrary, one obtains a decreasing dephasing
time because of the increase of the Coulomb matrix elements and the number of
states in a given Landau subband. In the situation when the loss of scattering
channels exceeds these increasing effects, one gets a slight increase at the
dephasing time. However, details of the strongly modulated scattering kinetics
depend sensitively on the detuning, the plasma density, and the spectral pulse
width relative to the cyclotron frequency.Comment: 13 pages, in RevTex format, 10 figures, Phys. Rev B in pres
Effect of drought on yield components of maize hybrids : Zea mays L
When investigating drought tolerance, it must not be forgotten that drought stress is a complex phenomenon exhibiting quite different characters in different years and locations. For this reason, the plant response to drought is also a complex process. In our study, 83 maize hybrids originating from various countries were investigated over a period of two years, under irrigated and non-irrigated conditions. The drought tolerance of plants in the non-irrigated plots was analysed in terms of flowering synchrony and yield components. It could be concluded from the results that in response to long-term water deficit the period between tasselling and silking became longer, while the analysis of yield components revealed the greatest reductions in the number of kernels per ear and in the proportion of seed set. As the degree of proterandry increased, there was a decline in the grain yield, confirming that the analysis of this trait could be a way of predicting drought tolerance. Considerable differences in drought tolerance were observed between the genetic materials included in the analysis, suggesting the presence among these parental lines and hybrids of genotypes resistant to long-term water deficit, suitable for cultivation under dry conditions. An analysis of correlations between the traits revealed that proterandry should be treated as a priority trait when investigating drought stress tolerance, as better predictions can be made of both drought tolerance and potential yields, leading to more reliable selection for higher yields
Coherent Control for a Two-level System Coupled to Phonons
The interband polarizations induced by two phase-locked pulses in a
semiconductor show strong interference effects depending on the time tau_1
separating the pulses. The four-wave mixing signal diffracted from a third
pulse delayed by tau is coherently controlled by tuning tau_1. The four-wave
mixing response is evaluated exactly for a two-level system coupled to a single
LO phonon. In the weak coupling regime it shows oscillations with the phonon
frequency which turn into sharp peaks at multiples of the phonon period for a
larger coupling strength. Destructive interferences between the two
phase-locked pulses produce a splitting of the phonon peaks into a doublet. For
fixed tau but varying tau_1 the signal shows rapid oscillations at the
interband-transition frequency, whose amplitude exhibits bursts at multiples of
the phonon period.Comment: 4 pages, 4 figures, RevTex, content change
Size-dependent bandgap and particle size distribution of colloidal semiconductor nanocrystals
A new analytical expression for the size-dependent bandgap of colloidal
semiconductor nanocrystals is proposed within the framework of the finite-depth
square-well effective mass approximation in order to provide a quantitative
description of the quantum confinement effect. This allows one to convert
optical spectroscopic data (photoluminescence spectrum and absorbance edge)
into accurate estimates for the particle size distributions of colloidal
systems even if the traditional effective mass model is expected to fail, which
occurs typically for very small particles belonging to the so-called strong
confinement limit. By applying the reported theoretical methodologies to CdTe
nanocrystals synthesized through wet chemical routes, size distributions are
inferred and compared directly to those obtained from atomic force microscopy
and transmission electron microscopy. This analysis can be used as a
complementary tool for the characterization of nanocrystal samples of many
other systems such as the II-VI and III-V semiconductor materials.Comment: 9 pages, 5 figure
- …