422 research outputs found
Bond Properties and Molecular Conformation from Vibrational Intensity Analysis
Experimental vibrational intensities in infrared spectra can be
transformed into quantities characterizing bond properties fol-
lowing the formalism of the bond polar parameters model. The
theory is briefly presented. An optimized set of bond polar parameters for hydrocarbons is obtained following constraints derived
from experimental spectral data and ab initio MO calculations.
The set of intensity parameters together with transferable force
constants is used in predicting the infrared spectra of individual
conformers and equilibrium conformer mixtures of n-butane-do,
n-pentane-d, n-pentane-djj and n-hexane-d, The influence of
rotational isomerism on infrared intensities in these systems is discussed
Polarimetry and the Long Awaited Superoutburst of BZ UMa
BZ UMa is a cataclysmic variable star whose specific classification has
eluded researchers since its discovery in 1968. It has outburst and spectral
properties consistent with both U Gem class dwarf novae and intermediate
polars. We present new photometric and polarimetric measurements of recent
outbursts, including the first detected superoutburst of the system.
Statistical analysis of these and archival data from outbursts over the past 40
years present a case for BZ UMa as a non-magnetic, U Gem class, SU-UMa subclass
dwarf novae.Comment: Accepted by PASP for the November, 2009 issu
Atomic Tunneling from a STM/AFM tip: Dissipative Quantum Effects from Phonons
We study the effects of phonons on the tunneling of an atom between two
surfaces. In contrast to an atom tunneling in the bulk, the phonons couple very
strongly, and qualitatively change the tunneling behavior. This is the first
example of {\it ohmic} coupling from phonons for a two-state system. We propose
an experiment in which an atom tunnels from the tip of an STM, and show how its
behavior would be similar to the Macroscopic Quantum Coherence behavior
predicted for SQUIDS. The ability to tune and calculate many parameters would
lead to detailed tests of the standard theories. (For a general intro to this
work on the on the World-Wide-Web: http://www.lassp.cornell.edu. Click on
``Entertaining Science Done Here'' and ``Quantum Tunneling of Atoms'')Comment: 12 pages, ReVTex3.0, two figures (postscript). This is a
(substantially) revised version of cond-mat/9406043. More info (+ postscript
text) at : http://www.lassp.cornell.edu/ardlouis/publications.htm
Taxonomy of GRB optical light-curves: identification of a salient class of early afterglows
The temporal behaviour of the early optical emission from Gamma-Ray Burst
afterglows can be divided in four classes: fast-rising with an early peak,
slow-rising with a late peak, flat plateaus, and rapid decays since first
measurement. The fast-rising optical afterglows display correlations among peak
flux, peak epoch, and post-peak power-law decay index that can be explained
with a structured outflow seen off-axis, but the shock origin (reverse or
forward) of the optical emission cannot be determined. The afterglows with
plateaus and slow-rises may be accommodated by the same model, if observer
location offsets are larger than for the fast-rising afterglows, or could be
due to a long-lived injection of energy and/or ejecta in the blast-wave. If
better calibrated with more afterglows, the peak flux-peak epoch relation
exhibited by the fast and slow-rising optical light-curves could provide a way
to use this type of afterglows as standard candles.Comment: 8 pages, submitted to MNRA
Dust and Metal Column Densities in Gamma-Ray Burst Host Galaxies
In this paper we present the results from the analysis of a sample of 28
gamma-ray burst (GRB) afterglow spectral energy distributions, spanning the
X-ray through to near-infrared wavelengths. This is the largest sample of GRB
afterglow spectral energy distributions thus far studied, providing a strong
handle on the optical depth distribution of soft X-ray absorption and
dust-extinction systems in GRB host galaxies. We detect an absorption system
within the GRB host galaxy in 79% of the sample, and an extinction system in
71% of the sample, and find the Small Magellanic Cloud (SMC) extinction law to
provide an acceptable fit to the host galaxy extinction profile for the
majority of cases, consistent with previous findings. The range in the soft
X-ray absorption to dust-extinction ratio, N_{H,X}/Av, in GRB host galaxies
spans almost two orders of magnitude, and the typical ratios are significantly
larger than those of the Magellanic Clouds or Milky Way. Although dust
destruction could be a cause, at least in part, for the large N_{H,X}/Av
ratios, the good fit provided by the SMC extinction law for the majority of our
sample suggests that there is an abundance of small dust grains in the GRB
environment, which we would expect to have been destroyed if dust destruction
were responsible for the large N_{H,X}/Av ratios. Instead, our analysis
suggests that the distribution of N_{H,X}/Av in GRB host galaxies may be mostly
intrinsic to these galaxies, and this is further substantiated by evidence for
a strong negative correlation between N_{H,X}/Av and metallicity for a
subsample of GRB hosts with known metallicity. Furthermore, we find the
N_{H,X}/Av ratio and metallicity for this subsample of GRBs to be comparable to
the relation found in other more metal-rich galaxies.Comment: 23 pages, 10 figures, accepted for publication in MNRA
Trans-ethyl methyl ether in space - A new look at a complex molecule in selected hot core regions
An extensive search for the complex molecule trans-ethyl methyl ether towards
several hot core regions has been performed. Using the IRAM 30m telescope and
the SEST 15m we looked at several frequencies where trans-ethyl methyl ether
has strong transitions, as well as lines which are particularly sensitive to
the physical conditions in which the molecule can be found. We included G34.26,
NGC6334(I), Orion KL, and W51e2 which have previously been proven to have a
rich chemistry of complex molecules. Our observations cannot confirm the
tentative Orion KL detection made by Charnley et al. (2001) within their stated
column density limits, but we confirm the existence of the trans-ethyl methyl
ether towards W51e2 with a column density of 2x10^14 cm-2. The dimethyl
ether/methanol ratio of 0.6 as well as the newly found ethyl methyl
ether/ethanol ratio of 0.13 indicate relative high abundances of ethers toward
W51e2. Furthermore, the observation of ethyl methyl ether also confirms the
importance of ethanol as a grain mantle constituent. We present new upper
limits of around 8x10^13 cm-2 for the column densities of the molecule toward
Orion KL, G34.26, NGC6334(I) and estimate the column density towards SgrB2(N)
to be of the same order. The W51e2 observations are discussed in more detail.Comment: accepted by A&
Ispitivanje kompatibilnosti nateglinida s pomoćnim tvarima u razvoju tableta nateglinida za trenutno oslobađanje
Experiments were done to assess the compatibility of nateglinide with selected excipients in the development of immediate release tablets of nateglinide by thermal and isothermal stress testing (IST) techniques. To evaluate the drug-excipient compatibility, different techniques such as differential scanning calorimetric (DSC) study, infra-red (IR) spectrophotometric study and isothermal stress testing were adopted. The results of DSC study showed that magnesium stearate exhibited some interaction with nateglinide. However, the results of IR, and IST studies showed that all the excipients used in the formula were compatible with nateglinide. Optimized formulations developed using the compatible excipients were found to be stable over 3 months of accelerated stability studies (40 ± 2 C and 75 ± 5 % RH). Overall, compatibility of excipients with nateglinide was successfully evaluated using a combination of thermal and IST methods and the formulations developed using the compatible excipients were found to be stable.Koristeći termičke metode kao što su diferencijalna pretražna kalorimetrija (DSC) i infra-crvena spektrofotometrija (IR), te izotermička stres-testiranja (IST) ispitana je kompatibilnost nateglinida s izabranim ekscipiensima u razvoju tableta nateglinida za trenutno oslobađanje. Rezultati DSC ispitivanja pokazala su da magnezijev stearat stupa u određenu interakciju s nateglinidom. Međutim, IR i IST ispitivanja pokazuju da su svi upotrijebljeni ekscipiensi kompatibilni s nateglinidom. Optimirana formulacija bila je stabilna preko 3 mjeseca u testovima ubrzanog starenja (40 ± 2 C i 75 ± 5 % RH). Kompatibilnost ekscipiensa s nateglinidom uspješno je evaluirana koristeći kombinaciju termičke i IST metode, a formulacije razvijene koristeći kompatibilne ekscipiense bile su stabilne
Novel Mouse Xenograft Models Reveal a Critical Role of CD4+ T Cells in the Proliferation of EBV-Infected T and NK Cells
Epstein-Barr virus (EBV), a ubiquitous B-lymphotropic herpesvirus, ectopically infects T or NK cells to cause severe diseases of unknown pathogenesis, including chronic active EBV infection (CAEBV) and EBV-associated hemophagocytic lymphohistiocytosis (EBV-HLH). We developed xenograft models of CAEBV and EBV-HLH by transplanting patients' PBMC to immunodeficient mice of the NOD/Shi-scid/IL-2RÎłnull strain. In these models, EBV-infected T, NK, or B cells proliferated systemically and reproduced histological characteristics of the two diseases. Analysis of the TCR repertoire expression revealed that identical predominant EBV-infected T-cell clones proliferated in patients and corresponding mice transplanted with their PBMC. Expression of the EBV nuclear antigen 1 (EBNA1), the latent membrane protein 1 (LMP1), and LMP2, but not EBNA2, in the engrafted cells is consistent with the latency II program of EBV gene expression known in CAEBV. High levels of human cytokines, including IL-8, IFN-Îł, and RANTES, were detected in the peripheral blood of the model mice, mirroring hypercytokinemia characteristic to both CAEBV and EBV-HLH. Transplantation of individual immunophenotypic subsets isolated from patients' PBMC as well as that of various combinations of these subsets revealed a critical role of CD4+ T cells in the engraftment of EBV-infected T and NK cells. In accordance with this finding, in vivo depletion of CD4+ T cells by the administration of the OKT4 antibody following transplantation of PBMC prevented the engraftment of EBV-infected T and NK cells. This is the first report of animal models of CAEBV and EBV-HLH that are expected to be useful tools in the development of novel therapeutic strategies for the treatment of the diseases
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