719 research outputs found
Coherent control of magnetization precession in ferromagnetic semiconductor (Ga,Mn)As
We report single-color, time resolved magneto-optical measurements in
ferromagnetic semiconductor (Ga,Mn)As. We demonstrate coherent optical control
of the magnetization precession by applying two successive ultrashort laser
pulses. The magnetic field and temperature dependent experiments reveal the
collective Mn-moment nature of the oscillatory part of the time-dependent Kerr
rotation, as well as contributions to the magneto-optical signal that are not
connected with the magnetization dynamics.Comment: 6 pages, 3 figures, accepted in Applied Physics Letter
Phospholipase A2Mechanism Of Interfacial Activation,An Interdiscliplinary Approach
Phospholipase A2 (PLA2) is an enzyme that hydrolyzes the sn-2-ester bond of membrane phospholipids and liberates arachidonic acid, which is converted to eicosanoids that act as potent mediators of inflammation and allergy. As such this enzyme plays a crucial role in many homeostatic physiological and immunologic processes and disease progression. PLA2s undergo substantial increase in activity upon binding to cellular membranes. This effect of interfacial activation is well recognized, yet its structural and physical aspects are poorly understood. In this work, we have employed the interdisciplinary methods of molecular biology, biochemistry, biophysics, bioinformatics and computational biology, in order to elucidate the structure-function relationships mediating the interfacial activation of human group IIA and group IB PLA2 isoforms. We have evaluated the structural and functional consequences of two conservative, single residue substitutions, located at key membrane-binding and substrate-binding positions of hIIA PLA2. We have also evaluated a human group IB fragment (hIBΔN10), missing the first 10 N-terminal residues which make up the N-terminal alpha helix, as well as a chimeric enzyme substituting the N-terminal alpha helix of hIB PLA2 with that from hIIA PLA2 (hIIA/IB PLA2). We have compared the engineered proteins against both the hIIA and hIB PLA2 native enzymes and their N-terminal peptides, N10-hIB and N10-hIIA, respectively. We have developed and used a novel multidisciplinary approach in order to position the segmentally labeled hIB PLA2 and hIIA/IB chimeric PLA2s at the membrane surface. The results of this work provide significant insight into the understanding of the physical aspects of interfacial activation by determining the precise membrane binding modes of PLA2 isoforms and identifying certain amino acid residues and whole protein segments that play key roles in membrane binding, activation, and involved allosteric conformational effects in PLA2s
Stellar impact on disequilibrium chemistry and on observed spectra of hot Jupiter atmospheres
In this work we study the effect of disequilibrium processes on mixing ratio
profiles of neutral species and on the simulated spectra of a hot Jupiter
exoplanet that orbits stars of different spectral types. We also address the
impact of stellar activity that should be present to a different degree in all
stars with convective envelopes. We used the VULCAN chemical kinetic code to
compute number densities of species. The temperature-pressure profile of the
atmosphere was computed with the HELIOS code. We also utilized the -ReX
forward model to predict the spectra of planets in primary and secondary
eclipses. In order to account for the stellar activity we made use of the
observed solar XUV spectrum taken from Virtual Planetary Laboratory (VPL) as a
proxy for an active sun-like star. We find large changes in mixing ratios of
most chemical species in planets orbiting A-type stars that radiate strong XUV
flux inducing a very effective photodissociation. For some species, these
changes can propagate very deep into the planetary atmosphere to pressures of
around 1 bar. To observe disequilibrium chemistry we favor hot Jupiters with
temperatures Teq=1000 K and ultra-hot Jupiters with Teq=3000$ K that also have
temperature inversion in their atmospheres. On the other hand, disequilibrium
calculations predict little changes in spectra of planets with intermediate
temperatures. We also show that stellar activity similar to the one of the
modern Sun drives important changes in mixing ratio profiles of atmospheric
species. However, these changes take place at very high atmospheric altitudes
and thus do not affect predicted spectra. We estimate that the effect of
disequilibrium chemistry in planets orbiting nearby bright stars could be
robustly detected and studied with future missions with spectroscopic
capabilities in infrared such as, e.g., JWST and ARIEL.Comment: 17 pages, 12 figure
Continuum variational and diffusion quantum Monte Carlo calculations
This topical review describes the methodology of continuum variational and
diffusion quantum Monte Carlo calculations. These stochastic methods are based
on many-body wave functions and are capable of achieving very high accuracy.
The algorithms are intrinsically parallel and well-suited to petascale
computers, and the computational cost scales as a polynomial of the number of
particles. A guide to the systems and topics which have been investigated using
these methods is given. The bulk of the article is devoted to an overview of
the basic quantum Monte Carlo methods, the forms and optimisation of wave
functions, performing calculations within periodic boundary conditions, using
pseudopotentials, excited-state calculations, sources of calculational
inaccuracy, and calculating energy differences and forces
Focal Monomorphic Ventricular Tachycardia As The First Manifestation Of Amyloid Cardiomyopathy
52-year-old patient presented with palpitation and well tolerated monomorphic ventricular tachycardia. He had normal echocardiogram and coronary angiogram 3 months prior to presentation. Surface EKG revealed regular wide-complex tachycardia with right bundle branch block morphology and right inferior axis. In conjunction with recent negative cardiac evaluation, this suggested idiopathic focal ventricular tachycardia from anterolateral basal left ventricle. CARTO based activation mapping confirmed the presence of VT focus in that area. Radiofrequency ablation at the site of perfect pacemap resulted in a partial suppression of the focus. Echocardiogram was subsequently performed because of progressive dyspnea. It revealed asymmetrical thickening of posterolateral left ventricle, with delayed enhancement on contrast magnetic resonance imaging. Fine needle aspiration of abdominal fat stained with Congo red confirmed the diagnosis of systemic AL amyloidosis due to IgG λ-light chain deposition. Consequently, the patient underwent placement of implantable defibrillator and hematopoetic stem cell transplantation. He remains in excellent functional status 18 months after presentation
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