752 research outputs found
A 33 year constancy of the X-ray coronae of AR Lac and eclipse diagnosis of scale height
Extensive X-ray and extreme ultraviolet (EUV) photometric observations of the
eclipsing RS CVn system AR Lac were obtained over the years 1997 to 2013 with
the Chandra X-ray Observatory Extreme Ultraviolet Explorer. During primary
eclipse, HRC count rates decrease by ~40%. A similar minimum is seen during one
primary eclipse observed by EUVE but not in others owing to intrinsic source
variability. Little evidence for secondary eclipses is present in either the
X-ray or EUV data, reminiscent of earlier X-ray and EUV observations. Primary
eclipses allow us to estimate the extent of a spherically symmetric corona on
the primary G star of about 1.3Rsun, or 0.86Rstar, and indicate the G star is
likely brighter than the K component by a factor of 2-5. Brightness changes not
attributable to eclipses appear to be dominated by stochastic variability and
are generally non-repeating. X-ray and EUV light curves cannot therefore be
reliably used to reconstruct the spatial distribution of emission assuming only
eclipses and rotational modulation are at work. Moderate flaring is observed,
where count rates increase by up to a factor of three above quiescence.
Combined with older ASCA, Einstein, EXOSAT, ROSAT and Beppo-SAX observations,
the data show that the level of quiescent coronal emission at X-ray wavelengths
has remained remarkably constant over 33 years, with no sign of variation due
to magnetic cycles. Variations in base level X-ray emission seen by Chandra
over 13 years are only ~10%, while variations back to pioneering Einstein
observations in 1980 amount to a maximum of 45% and more typically about 15%.Comment: To appear in the Astrophysical Journa
Sensitive and selective spectrophotometric determination of pantoprazole sodium in pharmaceuticals using permanganate
A simple visible spectrophotometric method is described for the determination of pantoprazole sodium sesquihydrate (PSS). The method is based on the formation of a brown colored product on treating PSS with permanganate in neutral medium, the absorbance being measured at 350 nm. The experimental conditions for the assay were optimized. The absorbance is found to increase linearly with the concentration of PSS and the calibration graph is linear in the range of 2.5-40.0 μg ml-1 with a linear regression coefficient of 0.998. The calculated molar absorptivity value is 1.27x104 l mol-1 cm-1 and the corresponding Sandel sensitivity is 0.0341 µg cm-2. The limits of detection (LOD) and quantification (LOQ) are calculated to be 0.49 and 1.47 µg ml-1, respectively. Intra-day and inter-day accuracy expressed as relative error were better than 2.0% and the corresponding precision (RSD) was less than 2.5 %. The developed and validated method was applied to the determination of the active ingredient in a tablet dosage form and the results obtained agreed well with those of the reference method. The accuracy and reliability of the method were ascertained by performing recovery experiments via standard-addition procedure
SIMPLE AND SENSITIVE SPECTROPHOTO¬METRIC ASSAY OF OFLOXACIN IN PHARMACEUTICALS BASED ON ION-PAIR REACTION
Two simple, sensitive, economical and extraction-free spectrophotometric methods have been developed for the determination of ofloxacin (OFX) in pure form and in tablets. The methods are based on the interaction of OFX with two sulphonphthalein dyes, namely, bromothymol blue (method A) and bromophenol blue (method B) in dichloromethane medium to form stable, yellow-colored ion–pair complexes peaking at 410 nm. Under the optimum conditions, OFX could be assayed in the concentration ranges 1.25-20 and 1.0-16 µg mL-1 OFX by methods A and B, respectively, with correlation coefficient of 0.999 in both methods. The apparent molar absorptivity values are calculated to be 1.74104 and 2.18104, L moL-1 cm-1, for method A and B, respectively, with corres¬pond¬ing Sandell sensitivity values of 0.021 and 0.017 µg cm-2. The limits of detec¬tion (LOD) and quantification (LOQ) are also reported. The stoichiometry of the reaction was found to be 1:1 in both cases and the conditional stability cons¬tants (Kf) of the complexes have also been reported. The intra-day and inter-day variation was assessed. The methods were applied to determine OFX from marked tablet formulations. Statistical analysis proved that the proposed methods were both accurate and precise
Performance metrics for the evaluation of hyperspectral chemical identification systems
Remote sensing of chemical vapor plumes is a difficult but important task for many military and civilian applications. Hyperspectral sensors operating in the long-wave infrared regime have well-demonstrated detection capabilities. However, the identification of a plume’s chemical constituents, based on a chemical library, is a multiple hypothesis testing problem which standard detection metrics do not fully describe. We propose using an additional performance metric for identification based on the so-called Dice index. Our approach partitions and weights a confusion matrix to develop both the standard detection metrics and identification metric. Using the proposed metrics, we demonstrate that the intuitive system design of a detector bank followed by an identifier is indeed justified when incorporating performance information beyond the standard detection metrics.United States. Defense Threat Reduction Agency (Air Force contract FA8721-05-C-0002
Parity Fluctuations Between Coulomb Blockaded Superconducting Islands
We find that if two superconducting islands of different number parity are
linked by a tunnel junction the unpaired electron in the odd island has a
tendency to tunnel into the even island. This process leads to fluctuations in
time of the number parity of each island, giving rise to a random telegraph
noise spectrum with a characteristic frequency that has an unusual temperature
dependence. This new phenomenon should be observable in a Cooper-pair pump and
similar single-electron tunneling devices.Comment: 4 pages, self-unpacking uuencoded gz-compressed postscript file with
3 figures included; also available at
http://www.lassp.cornell.edu/janko/publications.htm
Favorable Outcomes of LVAD as Bridge to Simultaneous Heart-Kidney Transplantation
Background
Chronic kidney disease (CKD) is an established risk factor for incident cardiovascular disease and progression of heart failure disease state, and is associated with decreased survival after left ventricular assist device (LVAD) therapy or heart transplantation (HT). Combined heart-kidney transplantation (HKT) compared with isolated HT recently has been shown to have survival advantage among patients whose estimated glomerular filtration rate is less than 37 ml/min/m2. Data on LVAD to HKT are limited.
Methods
At our center, a total of 803 patients have received HT, 594 patients LVAD therapy, and 23 patients HKT from single donors; of those 23, 15 were without the use of LVAD and 8 were after support with LVAD.
Results
Kaplan-Meier survival analysis found LVAD-supported patients with CKD stages 4 or 5 had statistically worse 24-month survival after HT as compared with those with CKD stage 1, 2, and 3 (58% vs 88%, p=0.01). Patients who received combined HKT after LVAD had comparable 24-month survival with those who received HKT without LVAD (87% and 85%, p=NS); both groups had numerically better survival compared with those who had CKD (stage 4-5) with isolated HT (58%).
Conclusions
Patients supported with LVAD who demonstrate advanced CKD (stage 4-5) have worse 24-month post-HT survival compared with those with less advanced CKD (stage 1-3). Combined HKT after LVAD support is feasible and confers comparable 24-month survival compared with HKT without prior LVAD therapy. Our study supports combined HKT for select LVAD patients with advanced CKD (stage 4-5)
Andreev Scattering and the Kondo Effect
We examine the properties of an infinite- Anderson impurity coupled to
both normal and superconducting metals. Both the cases of a quantum dot and a
quantum point contact containing an impurity are considered; for the latter, we
study both one and two-channel impurities. Using a generalization of the
noncrossing approximation which incorporates multiple Andreev reflection, we
compute the impurity spectral function and the linear-response conductance of
these devices. We find generically that the Kondo resonance develops structure
at energies corresponding to the superconducting gap, and that the magnitude of
the resonance at the Fermi energy is altered. This leads to observable changes
in the zero-bias conductance as compared to the case with no superconductivity.Comment: 8 pages, 7 figures; expanded version to appear in PR
Acetyl-CoA synthetase 2 promotes acetate utilization and maintains cancer cell growth under metabolic stress
A functional genomics study revealed that the activity of acetyl-CoA synthetase 2 (ACSS2) contributes to cancer cell growth under low-oxygen and lipid-depleted conditions. Comparative metabolomics and lipidomics demonstrated that acetate is used as a nutritional source by cancer cells in an ACSS2-dependent manner, and supplied a significant fraction of the carbon within the fatty acid and phospholipid pools. ACSS2 expression is upregulated under metabolically stressed conditions and ACSS2 silencing reduced the growth of tumor xenografts. ACSS2 exhibits copy-number gain in human breast tumors, and ACSS2 expression correlates with disease progression. These results signify a critical role for acetate consumption in the production of lipid biomass within the harsh tumor microenvironment
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