On the role of continuum-driven eruptions in the evolution of very massive stars and Population III stars

We suggest that the mass lost during the evolution of very massive stars may be dominated by optically thick, continuum-driven outbursts or explosions, instead of by steady line-driven winds. In order for a massive star to become a WR star, it must shed its H envelope, but new estimates of the effects of clumping in winds indicate that line driving is vastly insufficient. We discuss massive stars above roughly 40-50 Msun, for which the best alternative is mass loss during brief eruptions of luminous blue variables (LBVs). Our clearest example of this phenomenon is the 19th century outburst of eta Car, when the star shed 12-20 Msun or more in less than a decade. Other examples are circumstellar nebulae of LBVs, extragalactic eta Car analogs (``supernova impostors''), and massive shells around SNe and GRBs. We do not yet fully understand what triggers LBV outbursts, but they occur nonetheless, and present a fundamental mystery in stellar astrophysics. Since line opacity from metals becomes too saturated, the extreme mass loss probably arises from a continuum-driven wind or a hydrodynamic explosion, both of which are insensitive to metallicity. As such, eruptive mass loss could have played a pivotal role in the evolution and fate of massive metal-poor stars in the early universe. If they occur in these Population III stars, such eruptions would profoundly affect the chemical yield and types of remnants from early SNe and hypernovae.Comment: 4 pages, 1 figure, accepted by ApJ Letter

Coherent radiation from neutral molecules moving above a grating

We predict and study the quantum-electrodynamical effect of parametric self-induced excitation of a molecule moving above the dielectric or conducting medium with periodic grating. In this case the radiation reaction force modulates the molecular transition frequency which results in a parametric instability of dipole oscillations even from the level of quantum or thermal fluctuations. The present mechanism of instability of electrically neutral molecules is different from that of the well-known Smith-Purcell and transition radiation in which a moving charge and its oscillating image create an oscillating dipole. We show that parametrically excited molecular bunches can produce an easily detectable coherent radiation flux of up to a microwatt.Comment: 4 page

Enhancing Acceleration Radiation from Ground-State Atoms via Cavity Quantum Electrodynamics

When ground state atoms are accelerated through a high Q microwave cavity, radiation is produced with an intensity which can exceed the intensity of Unruh acceleration radiation in free space by many orders of magnitude. The cavity field at steady state is described by a thermal density matrix under most conditions. However, under some conditions gain is possible, and when the atoms are injected in a regular fashion, the radiation can be produced in a squeezed state

Stable mode-locked pulses from mid-infrared semiconductor lasers

We report the unequivocal demonstration of mid-infrared mode-locked pulses from a semiconductor laser. The train of short pulses was generated by actively modulating the current and hence the optical gain in a small section of an edge-emitting quantum cascade laser (QCL). Pulses with pulse duration at full-width-at-half-maximum of about 3 ps and energy of 0.5 pJ were characterized using a second-order interferometric autocorrelation technique based on a nonlinear quantum well infrared photodetector. The mode-locking dynamics in the QCLs was modelled and simulated based on Maxwell-Bloch equations in an open two-level system. We anticipate our results to be a significant step toward a compact, electrically-pumped source generating ultrashort light pulses in the mid-infrared and terahertz spectral ranges.Comment: 26 pages, 4 figure

Instabilities in the Envelopes and Winds of Very Massive Stars

The high luminosity of Very Massive Stars (VMS) means that radiative forces play an important, dynamical role both in the structure and stability of their stellar envelope, and in driving strong stellar-wind mass loss. Focusing on the interplay of radiative flux and opacity, with emphasis on key distinctions between continuum vs. line opacity, this chapter reviews instabilities in the envelopes and winds of VMS. Specifically, we discuss how: 1) the iron opacity bump can induce an extensive inflation of the stellar envelope; 2) the density dependence of mean opacity leads to strange mode instabilities in the outer envelope; 3) desaturation of line-opacity by acceleration of near-surface layers initiates and sustains a line-driven stellar wind outflow; 4) an associated line-deshadowing instability leads to extensive small-scale structure in the outer regions of such line-driven winds; 5) a star with super-Eddington luminosity can develop extensive atmospheric structure from photon bubble instabilities, or from stagnation of flow that exceeds the "photon tiring" limit; 6) the associated porosity leads to a reduction in opacity that can regulate the extreme mass loss of such continuum-driven winds. Two overall themes are the potential links of such instabilities to Luminous Blue Variable (LBV) stars, and the potential role of radiation forces in establishing the upper mass limit of VMS.Comment: 44 pages, 13 figures. Chapter to appear in the book "Very Massive Stars in the Local Universe", Springer, J.S. Vink, e

Density correlations and dynamical Casimir emission of Bogoliubov phonons in modulated atomic Bose-Einstein condensates

We present a theory of the density correlations that appear in an atomic Bose-Einstein condensate as a consequence of the dynamical Casimir emission of pairs of Bogoliubov phonons when the atom-atom scattering length is modulated in time. Different regimes as a function of the temporal shape of the modulation are identified and a simple physical picture of the phenomenon is discussed. Analytical expressions for the density correlation function are provided for the most significant limiting cases. This theory is able to explain some unexpected features recently observed in numerical calculations of Hawking radiation from analog black holes

Current status of turbulent dynamo theory: From large-scale to small-scale dynamos

Several recent advances in turbulent dynamo theory are reviewed. High resolution simulations of small-scale and large-scale dynamo action in periodic domains are compared with each other and contrasted with similar results at low magnetic Prandtl numbers. It is argued that all the different cases show similarities at intermediate length scales. On the other hand, in the presence of helicity of the turbulence, power develops on large scales, which is not present in non-helical small-scale turbulent dynamos. At small length scales, differences occur in connection with the dissipation cutoff scales associated with the respective value of the magnetic Prandtl number. These differences are found to be independent of whether or not there is large-scale dynamo action. However, large-scale dynamos in homogeneous systems are shown to suffer from resistive slow-down even at intermediate length scales. The results from simulations are connected to mean field theory and its applications. Recent work on helicity fluxes to alleviate large-scale dynamo quenching, shear dynamos, nonlocal effects and magnetic structures from strong density stratification are highlighted. Several insights which arise from analytic considerations of small-scale dynamos are discussed.Comment: 36 pages, 11 figures, Spa. Sci. Rev., submitted to the special issue "Magnetism in the Universe" (ed. A. Balogh

Origin of Galactic and Extragalactic Magnetic Fields

A variety of observations suggest that magnetic fields are present in all galaxies and galaxy clusters. These fields are characterized by a modest strength (10^{-7}-10^{-5} G) and huge spatial scale (~Mpc). It is generally assumed that magnetic fields in spiral galaxies arise from the combined action of differential rotation and helical turbulence, a process known as the alpha-omega dynamo. However fundamental questions concerning the nature of the dynamo as well as the origin of the seed fields necessary to prime it remain unclear. Moreover, the standard alpha-omega dynamo does not explain the existence of magnetic fields in elliptical galaxies and clusters. The author summarizes what is known observationally about magnetic fields in galaxies, clusters, superclusters, and beyond. He then reviews the standard dynamo paradigm, the challenges that have been leveled against it, and several alternative scenarios. He concludes with a discussion of astrophysical and early Universe candidates for seed fields.Comment: 67 pages, 17 figures, accepted for publication in Reviews of Modern Physic

МЕСТОРОЖДЕНИЕ ВЛАДИМИРСКОЕ (ВОСТОЧНЫЙ САЯН): ВОЗРАСТ ДАЙКОВЫХ КОМПЛЕКСОВ И ОСОБЕННОСТИ ЛОКАЛИЗАЦИИ ЗОЛОТОГО ОРУДЕНЕНИЯ

The Vladimirskoe deposit is one of the largest gold ore deposits in the southeastern part of the Eastern Sayan. This work is devoted to the localization of mineralized zones and the determination of the formation time of gold mineralization.The geological and structural analysis has shown that second-order discontinuous disturbances accompanied by zones of beresitization, calcification, sulfidization and dyke bodies are the main ore-controlling structures of gold mineralization. For the first time, the age of rocks of dyke complexes and ore mineralized zones of the deposit has been established by 40Ar/39Ar dating methods.Месторождение Владимирское является одним из крупных золоторудных месторождений в юго-восточной части Восточного Саяна. Данная работа посвящена вопросам структурного контроля жильно-прожилковых золоторудных минерализованных зон и определению времени формирования золотого оруденения.В результате геолого-структурного анализа установлено, что разрывные нарушения второго порядка, сопровождаемые зонами березитизации, окварцевания, сульфидизации, как и дайковые тела, являются основными рудоконтролирующими структурами золотого оруденения. Впервые методом 40Ar/39Ar датирования установлен возраст пород дайковых комплексов и рудных жильно-прожилковых зон месторождения

Количественная оценка проницаемости гематомиокардиального барьера для полиацетатных комплексов Gd при ишемической и воспалительной патологии миокарда

Purpose. We developed and applied for quantification of microvascular permeability in damaged myocardium a model - based approach employing the dynamic acquisition of magnetic resonance imaging of paramagnetic diffusion to damaged myocardium and kinetic Gjedde-Rutlend-Patlak (GRP) analysis of blood clearance of the contrast concomitantly with it’s rise in the damaged tissue, in ischemic or inflamed tissue.Material and methods. The model is based on the passive gradient-driven diffusion, unidirectional for first minutes after injection of the contrast, used as Gjedd-Rutland-Patlak technique. If the Cmyoc - depicts the concentration of the paramagnetic in the blood, and the Cblood -means the blood level of the contrast agent, whereas the kblood–myocardium – is the index of diffusion of the contrast from blood to myocardium, then assuming the diffusion unidirectional for first minutes post injection we can plot the ratio {(∫Cblood(t)dt) / Cblood} – as abscissa X, and {Cmyoc /Cblood} – as ordinata Y, kblood-myocardium can be obtained then from such linear plot as it’s slope. We substituted the concentrations themselves with the values of intensities of the echo-planar ECG-synchronized scans of the heart and validated this approach with comparison of MRI intensity data over LV cavity to Gd content in blood samples.MRI of the heart with contrast enhancement was carried out using dynamic scannig, after bolus injection of 2 ml of 0.5 M of paramagnetic contrast (Gadoversetamide -TMOptimark) per 10 Kg of BW. TR = 3.4 ms, TE = 1.7 ms, inversion time 176.0 ms, deviation angle = 40 deg, scanning field 38 х 38 cm, slice thickness = 8-10 мм, acqu-sition matrix 256 х 256, or 192 х 192, echo train length = 1. The groups of patients comprised twenty one persons with acute myocardial infarction treated clically successfully with intravenous thrombolysis and coronary stenting and also nine persons with firstly revealed inflammatory myocarditis. Uptake kinetics to the myocardium was imaged using protocols with fat supression for up to 12 minutes after bolus injection and then processed using RadiAnt software (Medixant, Poznan, Polska), and also original software for dynamic data analysis written using MATLAB 6.1 (SCILAB also), with output of plots of MRI signal intensities over time for various myocardial regions and also of GRP plots and calculation of  kblood-myocardium values.Results. The physiological sence of the kblood–myocardiumdiffusion koefficient means this value depicts the clearance of paramagnetic to myocardium, i.e. the amount of blood cleared from the paramagnetic due to paramagnetic’ diffusion to damaged myocardium, per minute, per unit of myocardial volume. The value of the kblood–myocardiumdiffusion koefficient was, respectively, as high as 3.09 ± 1.32 (2.36-11.9) ml/min/100 g of tissue, in myocardial infarction although treated successfully with thrombolysis and stenting (n = 21) and 1.78 ± 0.67 (0.50-2.42) ml/min/100 g of tissue -in inflammatory myocarditis damage of myocardium (n = 9); In normal controls kblood–myocardium was close to zero values and namely as low as 0.09 ± 0.06 (<0.2) (ml/min/100 g of tissue). Use of this dynamic protocol provided highly significant separation of ishemic and iflammatory conditions.Conclusion. Dynamic MRI echo-planar ECG-synchro-nised contrast-enhanced echo-planar study of the heart can be successfully carried out using both high- and middle-field MRI scanner. The model-based indexes of diffusion of paramagnetic to the infarction or inflammation are significantly different and deliver additional object-based characteristics of the vascular permeability of the damaged haematomyocardial barrier.Цель исследования: разработать и апробировать в клинике методику количественного расчета сосудистой проницаемости гистогематического барьера миокарда для контраста-парамагнетика на основе математической модели Гьедде-Рутланда-Патлака (ГРП) с оценкой роста содержания контраста в миокарде и его клиренса из крови по данным динамической МРТ.Материал и методы. В основе модели накопления парамагнетика в поврежденном миокарде - принцип Гьедде-Рутланд-Патлака (1977). Если Смиок - содержание контраста в миокарде, Скровь - содержание в крови, а ккрть_мтрд - показатель скорости диффузии “кровь-миокард”, считая транспорт парамагнетика однонаправленным в течение первых минут после инъекции, то откладывая {(∫Cкровь(t)dt) / Cкровь} по оси X, а {Cмиок /Cкровь} -по оси Y, kкровь–миокард получается тогда как линейный наклон такого графика.Были обследованы пациенты с острым инфарктом миокарда с успешным тромболизисом (n = 21) и впервые выявленной воспалительной патологией (n = 9). МРТ с парамагнитным контрастным усилением проводилась с помощью динамического протокола FFE1.7.ssfp330k МР-томографа Toshiba Titan Vantage. Динамика поглощения парамагнетика миокардом в ишемических региогнах фиксировалась при введении 2 мл 0,5 M раствора гадоверсетамида на 10 кг массы тела с помощью быстрого протокола в матрицу 256 х 256 элементов изображения, с показателями: время повторения TR = 3,4 мс, время эхо TE = 1,7 мс, время инверсии 176,0 мс, угол отклонения 40°, область сканирования 38 х 38 см, толщина среза 8-10 мм, матрица записи 192 х 192 или 256 х 256, при однократном усреднении, показателе длины эхо (echo train length) равном 1, собственно длительность записи группы из 4 срезов в средней трети левого желудочка 210-300 мс. Запись данных велась на протяжении до 12 мин с частотой 1 кадр в 30 с и затем обрабатывалась с помощью программы RadiAnt (Medixant, Познань, Польша), а также оригинальной программы динамического анализа на MATLAB и SCILAB с построением зависимостей содержания контраста в крови и миокарде от времени, графика ГРП и расчетом показателя kкровь-миокардРезультаты. Физиологический смысл показателя ккровь-миокард в том, что эта величина представляет собой клиренс крови по Gd-ДТПА в миокард, т.е. количество крови, очищаемое от парамагнетика за минуту единицей объема ткани миокарда. Показатель ккровь -миокард составил в зависимости от характера патологии: у пациентов с острым инфарктом миокарда с успешным тромболизистом и ЧКВ (n = 21) 3,09 ± 1,32 (2,3611,9) мл/мин/100 г ткани, тогда как у пациентов с воспалительными поражениями - хроническим миокардитом в стадии обострения или впервые выявленным острым миокардитом (n = 9) 1,78 ± 0,67 (0,50-2,42) мл/мин/100 г ткани. В норме ккровь-миокард слабо отличался от нулевых величин и составлял 0,09 ± 0,06 (<0,2) (мл/мин/100 г ткани). Использование динамического протокола позволило высокодостоверно дифференцировать ишемическое и воспалительное поражение.Заключение. Динамическое МРТ-исследование сердца с парамагнитным контрастным усилением может быть успешно выполнено с помощью как высокопольного, так и среднепольного МР-томографа. Получаемые при математическом моделировании показатели диффузии парамагнетика в ткань ишемического повреждения и воспалительного некоронарогенного очага значительно различаются в зависимости от характера процесса и позволяют получить дополнительную объективную характеристику сосудистой проницаемости пораженного гематомиокардиального барьера