54 research outputs found
Effect of Mg Doping on the Structural and Optical Properties of CdS Nanoparticles Synthesized by co-Precipitation Method
Cd1 – xMgxS (x = 0.00, 0.05, 0.10, 0.15 and 0.20) nanoparticles were synthesized by co-precipitation method for the first time. Compositional, morphological, structural and optical studies of the as prepared samples were carried out by X-ray diffraction (XRD), Energy dispersive analysis of X-rays (EDAX), Scanning electron microscopy (SEM), Diffuse reflectance spectroscopy (DRS) and Photoluminescence (PL) techniques. XRD studies revealed the structural phase transition from cubic to hexagonal and increase in the average grain size of the nanoparticles (lie in the range 1.4 nm to 2.8 nm) with increasing Mg content. EDAX spectra rules out the existence of impurities in the samples. Bandgap widening was observed in all the samples compared to bulk CdS (2.42 eV). Decrease in bandgap (3.02 eV to 2.54 eV), luminescence quenching and red shift of luminescence peak position were observed with increasing Mg in Cd1 – xMgxS.
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Isospectrality in Chaotic Billiards
We consider a modification of isospectral cavities whereby the classical
dynamics changes from pseudointegrable to chaotic. We construct an example
where we can prove that isospectrality is retained. We then demonstrate this
explicitly in microwave resonators.Comment: 5 pages, 7 figure
From chiral vibration to static chirality in ^{135}Nd
Electromagnetic transition probabilities have been measured for the intra-
and inter-band transitions in the two sequences in the nucleus ^{135}Nd that
were previously identified as a composite chiral pair of rotational bands. The
measurements are in good agreement with results of a new combination of TAC and
RPA calculations. The chiral character of the bands is affirmed and it is shown
that their behavior is associated with a transition from a vibrational into a
static chiral regime.Comment: Accepted for publication in the Physical Review Letters. Small
modifications to fit the length limits of the journal. 10 pages, 4 figure
Astrophysical S_{17}(0) factor from a measurement of d(7Be,8B)n reaction at E_{c.m.} = 4.5 MeV
Angular distribution measurements of H(Be,Be)H and
H(Be,B) reactions at ~4.5 MeV were performed to
extract the astrophysical factor using the asymptotic normalization
coefficient (ANC) method. For this purpose a pure, low emittance Be beam
was separated from the primary Li beam by a recoil mass spectrometer
operated in a novel mode. A beam stopper at 0 allowed the use of a
higher Be beam intensity. Measurement of the elastic scattering in the
entrance channel using kinematic coincidence, facilitated the determination of
the optical model parameters needed for the analysis of the transfer data. The
present measurement significantly reduces errors in the extracted
Be(p,) cross section using the ANC method. We get
~(0)~=~20.7~~2.4 eV~b.Comment: 15 pages including 3 eps figures, one figure removed and discussions
updated. Version to appear in Physical Review
Electromagnetic transition rates in high-spin bands in Nd136
Lifetimes have been measured for transitions in the two multiquasiparticle rotational bands in the nucleus Nd136. The extracted transition probabilities are compared with results of tilted-axis cranking and random-phase approximation calculations. The bands are identified as being built on two distinct quasiparticle configurations, with very different associated transition rates. These findings are contrary to an earlier suggestion that the bands form a chiral-band pair in this even-even nucleus
Transverse wobbling in Pr 135
A pair of transverse wobbling bands is observed in the nucleus Pr135. The wobbling is characterized by ΔI=1, E2 transitions between the bands, and a decrease in the wobbling energy confirms its transverse nature. Additionally, a transition from transverse wobbling to a three-quasiparticle band comprised of strong magnetic dipole transitions is observed. These observations conform well to results from calculations with the tilted axis cranking model and the quasiparticle rotor model
Role of Active Site Rigidity in Activity: MD Simulation and Fluorescence Study on a Lipase Mutant
Relationship between stability and activity of enzymes is maintained by underlying conformational flexibility. In thermophilic enzymes, a decrease in flexibility causes low enzyme activity while in less stable proteins such as mesophiles and psychrophiles, an increase in flexibility is associated with enhanced enzyme activity. Recently, we identified a mutant of a lipase whose stability and activity were enhanced simultaneously. In this work, we probed the conformational dynamics of the mutant and the wild type lipase, particularly flexibility of their active site using molecular dynamic simulations and time-resolved fluorescence techniques. In contrast to the earlier observations, our data show that active site of the mutant is more rigid than wild type enzyme. Further investigation suggests that this lipase needs minimal reorganization/flexibility of active site residues during its catalytic cycle. Molecular dynamic simulations suggest that catalytically competent active site geometry of the mutant is relatively more preserved than wild type lipase, which might have led to its higher enzyme activity. Our study implies that widely accepted positive correlation between conformation flexibility and enzyme activity need not be stringent and draws attention to the possibility that high enzyme activity can still be accomplished in a rigid active site and stable protein structures. This finding has a significant implication towards better understanding of involvement of dynamic motions in enzyme catalysis and enzyme engineering through mutations in active site
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