Alignment-Dependent Ionization of N2_2, O2_2, and CO2_2 in Intense Laser Fields

The ionization probability of N$_2$, O$_2$, and CO$_2$ in intense laser fields is studied theoretically as a function of the alignment angle by solving the time-dependent Schr\"odinger equation numerically assuming only the single-active-electron approximation. The results are compared to recent experimental data [D.~Pavi{\v{c}}i{\'c} et al., Phys.\,Rev.\,Lett.\ {\bf 98}, 243001 (2007)] and good agreement is found for N$_2$ and O$_2$. For CO$_2$ a possible explanation is provided for the failure of simplified single-active-electron models to reproduce the experimentally observed narrow ionization distribution. It is based on a field-induced coherent core-trapping effect.Comment: 5 pages, 2 figure

Deconstructing the D0-D6 system

We find the complete classical moduli space of two-centered supersymmetric solutions carrying D0 and D6 brane charge in the STU model delimited by walls of marginal stability of co-dimension one. U-duality guarantees our conclusions hold for any BPS state with negative quartic invariant. The analysis explicitly shows that the conditions of marginal stability, i.e. the integrability conditions, are generically insufficient to provide a regular supergravity solution in this model.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65085/2/1126-6708_2009_05_078.pd

Metallicity dependence of turbulent pressure and macroturbulence in stellar envelopes

Macroturbulence, introduced as a fudge to reproduce the width and shape of stellar absorption lines, reflects gas motions in stellar atmospheres. While in cool stars, it is thought to be caused by convection zones immediately beneath the stellar surface, the origin of macroturbulence in hot stars is still under discussion. Recent works established a correlation between the turbulent-to-total pressure ratio inside the envelope of stellar models and the macroturbulent velocities observed in corresponding Galactic stars. To probe this connection further, we evaluated the turbulent pressure that arises in the envelope convective zones of stellar models in the mass range 1-125 Msun based on the mixing-length theory and computed for metallicities of the Large and Small Magellanic Cloud. We find that the turbulent pressure contributions in models with these metallicities located in the hot high-luminosity part of the Hertzsprung-Russel (HR) diagram is lower than in similar models with solar metallicity, whereas the turbulent pressure in low-metallicity models populating the cool part of the HR-diagram is not reduced. Based on our models, we find that the currently available observations of hot massive stars in the Magellanic Clouds appear to support a connection between macroturbulence and the turbulent pressure in stellar envelopes. Multidimensional simulations of sub-surface convection zones and a larger number of high-quality observations are necessary to test this idea more rigorously.Comment: Accepted A&A, 8 p

Role of Fiber Orientation in Atrial Arrythmogenesis

Electrical wave-front propagation in the atria is determined largely by local fiber orientation. Recent study suggests that atrial fibrillation (AF) progresses with enhanced anisotropy. In this work, a 3D rabbit atrial anatomical model at 20 × 20 × 20 μm3 resolution with realistic fiber orientation was constructed based on the novel contrast-enhanced micro-CT imaging. The Fenton-Karma cellular activation model was adapted to reproduce rabbit atrial action potential period of 80 ms. Diffusivities were estimated for longitudinal and transverse directions of the fiber orientation respectively. Pacing was conducted in the 3D anisotropic atrial model with a reducing S2 interval to facilitate initiation of atrial arrhythmia. Multiple simulations were conducted with varying values of diffusion anisotropy and stimulus locations to evaluate the role of anisotropy in initiating AF. Under physiological anisotropy conditions, a rapid right atrial activation was followed by the left atrial activation. Excitation waves reached the atrio-ventricular border where they terminated. Upon reduction of conduction heterogeneity, re-entry was initiated by the rapid pacing and the activation of both atrial chambers was almost simultaneous. Myofiber orientation is an effective mechanism for regulating atrial activation. Modification of myoarchitecture is proarrhythmic

Kinetics of 5-aminolevulinic acid-induced fluorescence in organ cultures of bronchial epithelium and tumor

Background: 5-Aminolevulinic acid (5-ALA)-induced protoporphyrin IX (PPIX) fluorescence improves the differentiation of tumor and normal tissue in the bladder, skin and brain. Objective: The kinetics of 5-ALA-induced protoporphyrin IX (PPIX) fluorescence in organ cultures of normal human bronchial epithelium and cocultures of bronchial epithelium and tumor have been studied. Methods: Cultured biopsies of bronchial epithelium were exposed for 5 or 15 min, or continuously to 5-ALA. PPIX fluorescence was quantified for up to 300 min by spectroscopy. Cocultures of normal bronchial epithelium and a non-small-cell lung cancer cell line (EPLC-32M1) were incubated with 5-ALA. Space-resolved fluorescence microscopy was used to quantify PPIX fluorescence kinetics in the tumor and normal epithelium. Results: In cultures of normal epithelium, PPIX fluorescence kinetics were shown to depend on the duration of exposure to 5-ALA. There was a trend to higher fluorescence intensities with longer exposure times. In cocultures of bronchial epithelium and tumor, increases of fluorescence intensity were significantly greater in the tumor. Best tumor/normal tissue fluorescence ratios were found between 110 and 160 min after exposure to 5-ALA. Conclusion: Data obtained in this coculture system of bronchial epithelium and tumor is valuable to optimize modalities of fluorescence bronchoscopy for the diagnosis of early bronchial carcinoma. Copyright (C) 2002 S. Karger AG, Basel

Effects of Cardiac Structural Remodelling During Heart Failure on Cardiac Excitation – Insights from a Heterogeneous 3D Model of the Rabbit Atria

Heart failure is a leading cause of morbidity and mortality in the western world. One of the effects of heart failure is the structural remodelling of cardiac tissue, including tissue dilation and development of fibrosis. It is therefore important to study these changes and their effect on cardiac activity, in order to gain a better understanding of the underlying mechanisms in arrhythmogenesis, which will hopefully enable us to develop better treatments for heart failure. In this study we developed biophysically detailed models of the rabbit atria for normal and heart failure conditions. These models were used to study the effects of structural remodelling of heart failure on cardiac excitation wave conduction. Anatomical reconstructions of the control and heart failure hearts were based on contrast enhanced micro-CT imaging. Fibre orientation was extracted from the control and heart failure datasets. Effects of heart failure geometry on the activation pattern of atrial excitation waves were analyzed. It was found that atrial activation time increased from the control to the heart failure case in both isotropic and anisotropic conditions, which is attributed primarily to the dilation of tissue caused by heart failure

Intracellular trafficking of prohormones and proneuropeptides: Cell type-specific sorting and targeting

Hormones and neuropeptides are usually synthesized as large precursor molecules which must undergo a series of post-translational modifications before they are released from secretory vesicles after stimulation by specific secretagogues. The classical vectorial transport of precursors and mature peptide products from the endoplasmic reticulum (ER) to their site of release has been the subject of intensive studies during the past 25 years, but there are a number of unresolved issues which still challenge cell biologists. The main issues are: (i) the molecular mechanisms underlying targeting and sorting of prohormones within the eukaryotic secretory pathway; (ii) further identification and intracellular site of action of post-translational processing enzymes; (iii) tissue-specific processing of hormone and neuropeptide precursors; and (iv) molecular mechanisms underlying intracellular transport ofl hormone and neuropeptide precursors and their cleavage products to alternative intracellular compartments besides the secretory pathway.Fil: Perone, Marcelo Javier. Universidad Austral. Facultad de Ciencias Biomédicas. Instituto de Investigaciones en Medicina Traslacional. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Medicina Traslacional; Argentina. University of Manchester; Reino UnidoFil: Windeatt, Simon. University of Manchester; Reino UnidoFil: Castro, Maria G.. University of Manchester; Reino Unid

Water molecules in ultrashort intense laser fields

Ionization and excitation of water molecules in intense laser pulses are studied theoretically by solvingthe three-dimensional time-dependent electronic Schrödinger equation within the single-active-electronapproximation. The possibility to image orbital densities by measurement of the orientation-dependentionization of H2O in few-cycle, 800 nm linear-polarized laser pulses is investigated. While the highest-occupied molecular orbital 1b1is found to dominate the overall ionization behavior, contributions fromthe energetically lower lying 3a1orbital dominate the ionization yield in the nodal plane of the 1b1orbi-tal. The ratio of the ionization yields of the two orbitals depends on the intensity. Furthermore, even forlaser pulses as long as 8 cycles the orientation-dependent ion yield depends on the carrier-envelopephase. In the interpretation of the orientation-dependent ionization as an imaging tool these effects haveto be considered

Multiwavelength study of the fast rotating supergiant high-mass X-ray binary IGR J16465-4507

Since its launch, the X-ray and gamma-ray observatory INTEGRAL satellite has revealed a new class of high-mass X-ray binaries (HMXB) displaying fast flares and hosting supergiant companion stars. Optical and infrared (OIR) observations in a multi-wavelength context are essential to understand the nature and evolution of these newly discovered celestial objects. The goal of this multiwavelength study (from ultraviolet to infrared) is to characterise the properties of IGR J16465-4507, to confirm its HMXB nature and that it hosts a supergiant star. We analysed all OIR, photometric and spectroscopic observations taken on this source, carried out at ESO facilities. Using spectroscopic data, we constrained the spectral type of the companion star between B0.5 and B1 Ib, settling the debate on the true nature of this source. We measured a high rotation velocity of v = 320 +/- 8 km/s from fitting absorption and emission lines in a stellar spectral model. We then built a spectral energy distribution from photometric observations to evaluate the origin of the different components radiating at each energy range. We finally show that, having accurately determined the spectral type of the early-B supergiant in IGR J16465-4507, we firmly support its classification as an intermediate supergiant fast X-ray transient (SFXT).Comment: A&A in press, 14 pages, 15 tables, 13 figure