We present the calibration and background model for the Large Area X-ray Proportional Counter (LAXPC) detectors on-board AstroSat. LAXPC instrument has three nominally identical detectors to achieve large collecting area. These detectors are independent of each other and in the event analysis mode, they record the arrival time and energy of each photon that is detected. The detectors have a time-resolution of 10 µs and a dead-time of about 42 µs. This makes LAXPC ideal for timing studies. The energy resolution and peak channel to energy mapping were obtained from calibration on ground using radioactive sources coupled with GEANT4 simulations of the detectors. The response matrix was further refined from observations of the Crab after launch. At around 20 keV the energy resolution of detector is 10-15%, while the combined effective area of the 3 detectors is about 6000 cm 2 .
Several potentially experimentally accessible lithiated heterocyclic and heteroatom compounds with planar tetracoordinate carbons (ptC) have been predicted computationally. These utilize the strong electron-donating ability and the bridging proclivity of lithium to achieve the ptC preferences. As the p orbitals on the central carbons are only partially occupied, their electronic structures are similar to those of the related carbenes, e.g. imidazole-2-ylidene, rather than to the other ptC compounds such as dilithiocyclopropane.
Hydnocarpin
(Hy) is a flavonoid isolated and purified from the
seeds of Hydnocarpus wightiana Blume.
Herein, we have developed a built-in semi-synthetic modification on
Hy by one-pot multi-component reaction and a [3 + 2] cycloaddition
strategy to append five membered isoxazole and isoxazolone as new
phytochemical entities (NPCEs). Two selected NPCEs viz Hy-ISO-VIII
and Hy-ISO-G from the library of 20 newly synthesized derivatives
after in vitro screening unveiled promising cytotoxicity and induced
caspase-mediated apoptosis against the human lung and melanoma cancer
cells which were well supported by virtual screening based on ligand
binding affinity and molecular dynamic simulations. As a new insight,
we introduced surface-enhanced Raman spectroscopy to identify the
chemo-marker molecular fingerprint to confirm the cellular uptake,
cytochrome c release, and DNA fragmentation in a
label-free manner. The present findings throw up a surfeit of seminal
reasons behind the semi-synthetic modification of Hy, stepping forward
to cancer chemotherapy.
Abstract. Large Area X-ray Propositional Counter (LAXPC) instrument on AstroSat is aimed at providing high time resolution X-ray observations in 3-80 keV energy band with moderate energy resolution. To achieve large collecting area, a cluster of three co-aligned identical LAXPC detectors, is used to realize an effective area in access of ∼6000 cm 2 at 15 keV. The large detection volume of the LAXPC detectors, filled with xenon gas at ∼2 atmosphere pressure, results in detection efficiency greater than 50%, above 30 keV. In this article, we present salient features of the LAXPC detectors, their testing and characterization in the laboratory prior to launch and calibration in the orbit. Some preliminary results on timing and spectral characteristics of a few X-ray binaries and other type of sources, are briefly discussed to demonstrate that the LAXPC instrument is performing as planned in the orbit.
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