276 research outputs found
PHYSICAL MUTAGENESIS BASED STRAIN IMPROVEMENT OF ASPERGILLUS SP. FOR ENHANCED PRODUCTION OF LOVASTATIN
Objective: The present investigation aimed towards the strain improvement of lovastatin maximum yielding wild-type fungal strains (Aspergillus terreus-MTCC 11045, Aspergillus terreus-MTCC 11395 and Aspergillus flavus-MTCC 11396) through physical mutagenesis by applying UV random mutations.Methods: Revival of fungal cultures on PDA plates followed by a screening of their morphological and microscopic properties. Strain improvement of screened fungi by UV (255 nm) random mutagenesis, selection of mutants based on morphological variations further submerged fermentation of selected (SmF) mutants, subsequently extraction of lovastatin from the spent broth and the extracts were analyzed for the presence of lovastatin by TLC and UV spectrophotometer scans (200-300 nm).Results: Out of eighteen screened mutant samples seven showed positive results for the lovastatin production. Among these seven positive cultures, Aspergillus terreus 11045-90 found to yield the maximum amount of lovastatin (3912 mg/l).Conclusion: The present study concludes by reporting the evidence of raised in the lovastatin titre by three-fold compared to the yield of the wild-type strain (996 mg/l) and confirms the achievement of strain improvement by UV random mutagenesis.Keywords: Aspergillus terreus, Lovastatin, UV Random mutations, Strain improvement, Submerged fermentatio
Interference effects in the counting statistics of electron transfers through a double quantum dot
We investigate the effect of quantum interferences and Coulomb interaction on
the counting statistics of electrons crossing a double quantum dot in a
parallel geometry using a generating function technique based on a quantum
master equation approach. The skewness and the average residence time of
electrons in the dots are shown to be the quantities most sensitive to
interferences and Coulomb coupling. The joint probabilities of consecutive
electron transfer processes show characteristic temporal oscillations due to
interference. The steady-state fluctuation theorem which predicts a universal
connection between the number of forward and backward transfer events is shown
to hold even in the presence of Coulomb coupling and interference.Comment: 11 pages, 12 figure
Many-body Green's function approach to attosecond nonlinear X-ray spectroscopy
Closed expressions are derived for resonant multidimensional X-ray
spectroscopy using the quasiparticle nonlinear exciton representation of
optical response. This formalism is applied to predict coherent four wave
mixing signals which probe single and two core-hole states. Nonlinear X-ray
signals are compactly expressed in terms of one- and two- particle Green's
functions which can be obtained from the solution of Hedin-like equations at
the level.Comment: 10 pages and 3 figures (To appear in Physical Review B
Nonlinear optical spectroscopy of single, few, and many molecules; nonequilibrium Green's function QED approach
Nonlinear optical signals from an assembly of N noninteracting particles
consist of an incoherent and a coherent component, whose magnitudes scale \sim
N and \sim N(N-1), respectively. A unified microscopic description of both
types of signals is developed using a quantum electrodynamical (QED) treatment
of the optical fields. Closed nonequilibrium Green's function expressions are
derived that incorporate both stimulated and spontaneous processes. General
(n+1)-wave mixing experiments are discussed as an example of spontaneously
generated signals. When performed on a single particle, such signals cannot be
expressed in terms of the nth order polarization, as predicted by the
semiclassical theory. Stimulated processes are shown to be purely incoherent in
nature. Within the QED framework, heterodyne-detected wave mixing signals are
simply viewed as incoherent stimulated emission, whereas homodyne signals are
generated by coherent spontaneous emission.Comment: article: 33 pages (preprint format!) ''paper.tex'' figures: 17
figures (.eps) in folder ``figures'
Quantum master equation for electron transport through quantum dots and single molecules
A quantum master equation (QME) is derived for the many-body density matrix
of an open current-carrying system weakly coupled to two metal leads. The
dynamics and the steady-state properties of the system for arbitrary bias are
studied using projection operator techniques, which keep track of number of
electrons in the system. We show that coherences between system states with
different number of electrons, n, (Fock space coherences) do not contribute to
the transport to second order in system-lead coupling.
However, coherences between states with the same n may effect transport
properties when the damping rate is of the order or faster then the system Bohr
frequencies.
For large bias, when all the system many-body states lie between the chemical
potentials of the two leads, we recover previous results. In the rotating wave
approximation (when the damping is slow compared to the Bohr frequencies of the
system), the dynamics of populations and the coherences in the system
eigenbasis are decoupled. The QME then reduces to a birth and death master
equation for populations.Comment: 22 pages, 8 figures, paper accepted in Phys. Rev.
Zone center phonons of the orthorhombic RMnO3 (R = Pr, Eu, Tb, Dy, Ho) perovskites
A short range force constant model (SRFCM) has been applied for the first
time to investigate the phonons in RMnO3 (R = Pr, Eu, Tb, Dy, Ho) perovskites
in their orthorhombic phase. The calculations with 17 stretching and bending
force constants provide good agreement for the observed Raman frequencies. The
infrared frequencies have been assigned for the first time.
PACS Codes: 36.20.Ng, 33.20.Fb, 34.20.CfComment: 8 pages, 1 figur
Improving Reliability of High Power Quasi-CW Laser Diode Arrays for Pumping Solid State Lasers
Most Lidar applications rely on moderate to high power solid state lasers to generate the required transmitted pulses. However, the reliability of solid state lasers, which can operate autonomously over long periods, is constrained by their laser diode pump arrays. Thermal cycling of the active regions is considered the primary reason for rapid degradation of the quasi-CW high power laser diode arrays, and the excessive temperature rise is the leading suspect in premature failure. The thermal issues of laser diode arrays are even more drastic for 2-micron solid state lasers which require considerably longer pump pulses compared to the more commonly used pump arrays for 1-micron lasers. This paper describes several advanced packaging techniques being employed for more efficient heat removal from the active regions of the laser diode bars. Experimental results for several high power laser diode array devices will be reported and their performance when operated at long pulsewidths of about 1msec will be described
BiLaWO6: Er3+/Tm3+/Yb3+ phosphor: study of multiple fluorescence intensity ratiometric thermometry at cryogenic temperatures
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The question concerning human rights and human rightlessness: disposability and struggle in the Bhopal gas disaster
In the midst of concerns about diminishing political support for human rights, individuals and groups across the globe continue to invoke them in their diverse struggles against oppression and injustice. Yet both those concerned with the future of human rights and those who champion rights activism as essential to resistance, assume that human rights – as law, discourse and practices of rights claiming – can ameliorate rightlessness. In questioning this assumption, this article seeks also to reconceptualise rightlessness by engaging with contemporary discussions of disposability and social abandonment in an attempt to be attentive to forms of rightlessness co-emergent with the operations of global capital. Developing a heuristic analytics of rightlessness, it evaluates the relatively recent attempts to mobilise human rights as a frame for analysis and action in the campaigns for justice following the 3 December 1984 gas leak from Union Carbide Corporation’s (UCC) pesticide manufacturing plant in Bhopal, India. Informed by the complex effects of human rights in the amelioration of rightlessness, the article calls for reconstituting human rights as an optics of rightlessness
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