6,602 research outputs found
Analysis of the Early-time Optical Spectra of SN 2011fe in M101
The nearby Type Ia supernova (SN Ia) SN 2011fe in M101 (cz = 241 km s^(–1)) provides a unique opportunity to study the early evolution of a "normal" SN Ia, its compositional structure, and its elusive progenitor system. We present 18 high signal-to-noise spectra of SN 2011fe during its first month beginning 1.2 days post-explosion and with an average cadence of 1.8 days. This gives a clear picture of how various line-forming species are distributed within the outer layers of the ejecta, including that of unburned material (C+O). We follow the evolution of C II absorption features until they diminish near maximum light, showing overlapping regions of burned and unburned material between ejection velocities of 10,000 and 16,000 km s^(–1). This supports the notion that incomplete burning, in addition to progenitor scenarios, is a relevant source of spectroscopic diversity among SNe Ia. The observed evolution of the highly Doppler-shifted O I λ7774 absorption features detected within 5 days post-explosion indicates the presence of O I with expansion velocities from 11,500 to 21,000 km s^(–1). The fact that some O I is present above C II suggests that SN 2011fe may have had an appreciable amount of unburned oxygen within the outer layers of the ejecta
Investigation of laser ablated ZnO thin films grown with Zn metal target: a structural study
High quality ZnO thin films were gown using the pulsed laser deposition
technique on (0001) AlO substrates in an oxidizing atmosphere, using a
Zn metallic target. We varied the growth conditions such as the deposition
temperature and the oxygen pressure. First, using a battery of techniques such
as x-rays diffraction, Rutherford Backscattering spectroscopy and atomic force
microscopy, we evaluated the structural quality, the stress and the degree of
epitaxy of the films. Second, the relations between the deposition conditions
and the structural properties, that are directly related to the nature of the
thin films, are discussed qualitatively. Finally, a number of issues on how to
get good-quality ZnO films are addressed.Comment: To be published in Jour. Appl. Phys. (15 August 2004
Expected characteristics of the subclass of Supernova Gamma-ray Bursts (S-GRBs)
The spatial and temporal coincidence between the gamma-ray burst (GRB) 980425
and supernova (SN) 1998bw has prompted speculation that there exists a class of
GRBs produced by SNe (``S-GRBs''). Robust arguments for the existence of a
relativistic shock have been presented on the basis of radio observations. A
physical model based on the radio observations lead us to propose the following
characteristics of supernovae GRBs (S-GRBs): 1) prompt radio emission and
implied brightness temperature near or below the inverse Compton limit, 2) high
expansion velocity of the optical photosphere as derived from lines widths and
energy release larger than usual, 3) no long-lived X-ray afterglow, and 4) a
single pulse (SP) GRB profile. Radio studies of previous SNe show that only
type Ib and Ic potentially satisfy the first condition. Accordingly we have
investigated proposed associations of GRBs and SNe finding no convincing
evidence (mainly to paucity of data) to confirm any single connection of a SN
with a GRB. If there is a more constraining physical basis for the burst
time-history of S-GRBs beyond that of the SP requirement, we suggest the 1% of
light curves in the BATSE catalogue similar to that of GRB 980425 may
constitute the subclass. Future optical follow-up of bursts with similar
profiles should confirm if such GRBs originate from some fraction of SN type
Ib/Ic.Comment: 11 pages of LaTeX with 1 figure. Submitted to the Astrophysical
Journal Letter
Pulsations of the Low Mass ZZ Ceti Star HS 1824+6000
Measuring g-mode pulsations of isolated white dwarfs can reveal their
interior properties to high precision. With a spectroscopic mass of ~0.51
M_{\odot} (log g = 7.82), the DAV white dwarf HS 1824+6000 is near the
transition between carbon/oxygen core and helium core white dwarfs, motivating
our photometric search for additional pulsations from the Palomar 60-inch
telescope. We confirmed (with much greater precision) the three frequencies:
2.751190 +/- 0.000010 mHz (363.479 sec), 3.116709 +/- 0.000006 mHz (320.851
sec), 3.495113 +/- 0.000009 mHz (286.114 sec), previously found by B. Voss and
collaborators, and found an additional pulsation at 4.443120 +/- 0.000012 mHz
(225.067 sec). These observed frequencies are similar to those found in other
ZZ Ceti white dwarfs of comparable mass (e.g. log g < 8). We hope that future
observations of much lower mass ZZ Ceti stars (< 0.4 M_{\odot}) will reveal
pulsational differences attributable to a hydrogen covered helium core.Comment: 8 Pages; 4 Figures; Accepted to PASP (scheduled to appear in October
issue
Optical Detection of Two Intermediate Mass Binary Pulsar Companions
We report the detection of probable optical counterparts for two Intermediate
Mass Binary Pulsar (IMBP) systems, PSR J1528-3146 and PSR J1757-5322. Recent
radio pulsar surveys have uncovered a handful of these systems with putative
massive white dwarf companions, thought to have an evolutionary history
different from that of the more numerous class of Low Mass Binary Pulsars
(LMBPs) with He white dwarf companions. The study of IMBP companions via
optical observations offers us several new diagnostics: the evolution of main
sequence stars near the white-dwarf-neutron star boundary, the physics of white
dwarfs close to the Chandrasekhar limit, and insights into the recycling
process by which old pulsars are spun up to high rotation frequencies. We were
unsuccessful in our attempt to detect optical counterparts of PSR J1141-6545,
PSR J1157-5112, PSR J1435-6100, and PSR J1454-5846.Comment: 9 pages, 2 figures, accepted for publication in ApJ
Differential binding of RNA polymerase to the wild type Mu mom promoter and its C independent mutant: a theoretical analysis
Using the theoretical model for DNA bending we have analyzed the Mu mom promoter wild type and its mutant tin7 which showed differential binding to the RNA polymerase. We have demonstrated here the structural change as a result of the point mutation which may be responsible for the altered binding of RNA polymerase. Analysis using both sets of parameters essentially gives the same result
Continued Radio Monitoring of the Gamma Ray Burst 991208
We present radio observations of the afterglow of the bright gamma-ray burst
GRB 991208 at frequencies of 1.4, 4.9 and 8.5 GHz, taken between two weeks and
300 days after the burst. The well-sampled radio light curve at 8.5 GHz shows
that the peak flux density peaked about 10 days after the burst and decayed
thereafter as a power-law t^-1.07. This decay rate is more shallow than the
optical afterglow with t^-2.2, which was measured during the first week. These
late-time data are combined with extensive optical, millimeter and centimeter
measurements and fitted to the standard relativistic blast wave model. In
agreement with previous findings, we find that an isotropic explosion in a
constant density or wind-blown medium cannot explain these broadband data
without modifying the assumption of a single power-law slope for the electron
energy distribution. A jet-like expansion provides a reasonable fit to the
data. In this case, the flatter radio light curve compared to the optical may
be due to emission from an underlying host galaxy, or due to the blastwave
making a transition to non-relativistic expansion. The model that best
represents the data is a free-form model in which it is assumed that the
broadband emission originates from a synchrotron spectrum, while the
time-evolution of the break frequencies and peak flux density are solved for
explicitly. Although the decay indices for most of the synchrotron parameters
are similar to the jet model, the evolution of the cooling break is unusually
rapid, and therefore requires some non-standard evolution in the shock.
(abridged)Comment: ApJ, in pres
Application of artificial neural networks for prokaryotic transcription terminator prediction
Artificial neural networks (ANN) to predict terminator sequences, based on a feed-forward architecture and trained using the error back propagation technique, have been developed. The network uses two different methods for coding nucleotide sequences. In one the nucleotide bases are coded in binary while the other uses the electron-ion interaction potential values (EIIP) of the nucleotide bases. The latter strategy is new, property based and substantially reduces the network size. The prediction capacity of the artificial neural network using both coding strategies is more than 95%
Enhancing gynaecological care: the obstetrics and gynaecological distress measurement scale
Background: Gynaecological patients are evaluated using a few scales that are not population-targeted, so a targeted tool was required, particularly for the Indian population where these problems are prevalent.
Methods: A short interview was done after a top-down survey. Then, from the results of the pilot study, some items were retained after the deletion of others.
Results: Using Cronbach's alpha, a reliability coefficient of 0.907 was obtained. With a value of 0.867, the split-half coefficient demonstrated a good degree of internal consistency. Convergent validity was 0.62.
Conclusions: The OGDMS is a useful tool for detecting possible psychological distress in pregnant women. OGDMS is a standardised instrument which can be used by psychologists, physicians, and patients to pinpoint probable mental health-related problem areas
The obstetrics and gynaecological distress measurement scale: a promising tool for improving obstetrics care
Background: Screening done on obstetrics patients is based on a few scales which are not targeted towards the population, thus a need for a targeted tool was necessary especially for the Indian population where these issues are high and care provided lacks in quality.
Methods: A top down survey was conducted followed by a brief interview. A pilot study was then done out of which specific items were selected.
Results: Cronbach's alpha yielded a reliability coefficient of 0.907. Split-half coefficient yielded a high level of internal consistency with a value of 0.867. The convergent validity was 0.62.
Conclusions: The OGDMS is a valuable tool for identifying potential psychological distress in women needing obstetrics care. OGDMS is a unified tool for doctors, psychologists, and patients to identify potential problem areas related to mental health
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