1,370 research outputs found
Determination of Stellar Ellipticities in Future Microlensing Surveys
We propose a method that can determine the ellipticities of source stars of
microlensing events produced by binary lenses. The method is based on the fact
that the products of the caustic-crossing timescale, , and the cosine
of the caustic incidence angle of the source trajectory, , of the
individual caustic crossings are different for events involving an elliptical
source, while the products are the same for events associated with a circular
source. The product corresponds to the
caustic-crossing timescale when the incidence angle of the source trajectory is
. For the unique determination of the source ellipticity, resolutions
of at least three caustic crossings are required. Although this requirement is
difficult to achieve under the current observational setup based on
alert/follow-up mode, it will be possible with the advent of future lensing
experiments that will survey wide fields continuously at high cadence. For
typical Galactic bulge events, the difference in between
caustic crossings is of the order of minutes depending on the source
orientations and ellipticities. Considering the monitoring frequency of the
future lensing surveys of times/hr and the improved photometry
especially of the proposed space-based survey, we predict that ellipticity
determinations by the proposed method will be possible for a significant
fraction of multiple caustic-crossing binary lens events involving source stars
having non-negligible ellipticities.Comment: 6 pages, 4 figures, ApJ, submitte
Sub-band level-assisted photoconduction in epitaxial BiFeO3 films
Sub-band level assisted conduction mechanisms are well known in the field of semiconducting materials. In this work, we explicitly show the validity of such a mechanism in the multiferrroic material BiFeO3 (BFO). Our study is based on two different systems of epitaxial thin films of BFO, relaxed and strained. By analyzing the spectral distribution of the photoresponse from both the systems, the role of the sub-band levels in the photoconductive phenomena becomes evident. Additionally, the influence of epitaxial strain on the trapping activity of these levels is also observed. A model is proposed by taking into account the reversal of the role of a sub-band gap level, i.e., from a trapping to a ground state
Further genetic heterogeneity for autosomal dominant human sutural cataracts
A unique sutural cataract was observed in a 4-generation German family to be transmitted as an isolated autosomal, dominant trait. Since mutations in the gamma-crystallin encoding CRYG genes have previously been demonstrated to be the most frequent reason for isolated congenital cataracts, all 4 active CRYG genes have been sequenced. A single base-pair change in the CRYGA gene has been shown, leading to a premature stop codon. This was not observed in 170 control individuals. However, it did not segregate with the disease phenotype. This is the first truncating mutation in an active CRYG gene without a dominant phenotype. As the CRYGA mutation did not explain the cataract, several other candidate loci (CCV, GJA8, CRYBB2, BFSP2, MIP, GJA8, central pouch-like, CRYBA1) were investigated by micro-satellite markers and linkage analysis, but they were excluded based on the combination of haplotype analysis and two-point linkage analysis. The phenotype in this family is due to a mutation in another sutural cataract gene yet to be identified
Roles of dark energy perturbations in the dynamical dark energy models: Can we ignore them?
We show the importance of properly including the perturbations of the dark
energy component in the dynamical dark energy models based on a scalar field
and modified gravity theories in order to meet with present and future
observational precisions. Based on a simple scaling scalar field dark energy
model, we show that observationally distinguishable substantial differences
appear by ignoring the dark energy perturbation. By ignoring it the perturbed
system of equations becomes inconsistent and deviations in (gauge-invariant)
power spectra depend on the gauge choice.Comment: 5 pages, 4 figure
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