Tidal accelerations in general relativity

We derive the kinematical magnification of tidal accelerations which occurs for test bodies in highly relativistic orbits preferentially aligned with respect to repeated principal null rays of algebraically special spacetimes. Some examples of astrophysical importance are discussed. A general expression for computing tidal accelerations in the Newman-Penrose formalism is given.     

Tidal activity in the middle atmosphere

Summary Recent progress in the study of tides in the middle atmosphere ((10÷120) km) includes: i) development of more realistic thermal excitation and numerical simulation models; ii) observational efforts which delineate average seasonal, latitudinal and vertical structures of tides and shorter term variations of these. A survey is presented here of the variation with time and height of atmospheric tides observed at Budrio (45° N, 12° E) in the wind field between 75 and 115 km of altitude during the period 1978–82. Thermal excitation of the tides is mainly due to absorption of solar incident flux by ozone in the stratosphere and water vapour in the troposphere, release of latent heat in clouds, and heat conduction at the ground. The spectral analysis of wind data, obtained at Budrio in a few days of each month of 1978, shows that the semi-diurnal tide is the most easily observable by its regularity and amplitude: consistent amplitudes (around 20 m/s) are recorded in Summer and Winter months at 95 km. The vertical profiles of amplitudes of the diurnal, semi-diurnal and terdiurnal tide observed in zonal winds in some periods of 1979 (January 11–26, March 14–28, July 26–August 4, and September 11–23) demonstrate the great variability of tides not only over a large time scale (seasonal variations) but also on a reduced scale (variations in a few days).

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Riassunto I recenti progressi nello studio delle maree nell'atmosfera media ((10÷120) km), includono i) lo sviluppo di modelli piú realistici di eccitazione termica e modelli di simulazione numerica, ii) osservazioni che delineano strutture medie stagionali, latitudini e verticali di maree nonché le loro variazioni a piú breve periodo. Si presenta qui una rassegna delle variazioni nel tempo e con l'altezza delle maree atmosferiche osservate a Budrio (45° N, 12° E) nel campo dei venti tra 75 e 115 km di quota durante il periodo 1978–1982. La sorgente di eccitazione termica di queste oscillazioni è principalmente l'assorbimento del fluosso di energia solare incidente da parte dell'ozono nella stratosfera e del vapor d'acqua nella troposfera, il rilascio di calore latente nelle nubi, e la conduzione di calore al suolo. L'analisi spettrale dei dati di vento, osservato a Budrio nel corso di alcuni giorni di ogni mese dell'anno 1978, mostra che la marea semidiurna è la componente piú facilmente osservabile per la sua regolarità ed ampiezza: ampiezze consistenti (circa 20 m/s) sono registrate nei mesi estivi ed invernali a 95 km. I profili verticali delle ampiezze delle maree diurna, semidiurna e terdiurna osservate nel campo dei venti zonali in alcuni periodi del 1979 (11–25 gennaio, 14–28 marzo, 26 luglio–4 agosto e 11–23 settembre) mettono in evidenza la grande variabilità delle maree non solo su ampia scala temporale (variazioni stagionali), ma anche su scala ridotta (variazioni nell'arco di alcuni giorni).

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Резюме Недавний прогресс в исследовании приливов в средней атмосфере ((10÷120) км) включает: 1) развитиye более реалистического теплового возбуждения и численных моделей для моделирования; 2) результаты наблюдений, которые описывают усредненные сезонные, щиротные и вертикальные структуры приливов и более краткосрочные изменения этих структур. В работе предлагается обзор изменений во времени и по высоте атмосферных приливов, наблюденные в Будрио (45° N, 12° E) в поле ветров в интервале от 75 до 115 км, в течение 1978–82 г.г. Тепловое возбуждение приливов, в основном, обусловлено поглощением потока солнечной радиации озоном в стратосфере и водяным паром в тропосфере, высвобождением скрытой теплоты в облаках и теплопроводностью на Земле. Спектральный анализ данных для ветра, полученных в Будрио в течение нескольких дней каждого месяца 1978 г., показывает, что полусуточный прилив наиболее легко наблюдается ив-за регулярности и амплитуды: соответствуюшие амплитуды (около 20 м/с) регистрируются в летние и зимние месяцы на высоте 95 км. Вертикальные профили амплитуд суточных, полусуточных и восьмичасовых приливов, наблюденные в зональных ветрах в некоторые периоды 1979 г. (11–26 января, 14–28 марта, 26 июля–4 августа, 11–23 сентября) обнаруживают значительную изменчивость не только на протяжении больщого промежутка времени (сезонные изменения), но с меньщим временным масщтабом (изменения в течение нескольких дней).

     

黑洞潮汐撕裂恒星事件及其回响

超大质量黑洞普遍存在于星系中心,当星系中一颗恒星运动足够靠近黑洞时,会被黑洞的潮汐力撕裂瓦解,产生一个主要能量在软X 射线到紫外的耀发事件,称为恒星潮汐撕裂事件(TDE)。作为黑洞特殊的爆发性吸积事件,TDE正成为蓬勃发展的时域天文的主要研究目标之一。虽然TDE很罕见,但它蕴含的巨大科学价值逐渐引起了人们的兴趣和关注,有助于理解黑洞吸积相关的物理。除此之外,TDE照射在黑洞周围星际介质上还会产生气体和尘埃的回响信号,不仅为探测星系核区的星际介质环境提供了有效手段,还揭示了一种全新的探测TDE的途径,尤其是被尘埃遮蔽的源。作者基于此做出了一系列开创性的前沿研究。     

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利用TSC程序非刚性、可变形等离子体模型的特点，对EAST装置等离子体由于发生垂直位移事件而产生破裂的过程进行了模拟，计算了halo电流和真空室应力在破裂过程中的变化情况，对不同初始条件的破裂情况进行了比较，并模拟了利用杀手弹丸注入快速熄灭等离子体的过程。     

Tidal Dissipation in the System WASP-46

The change in the orbital period of the system WASP-46 due to quasi-static and dynamical tidal interactions is investigated. Various dissipation mechanisms are studied. In the case of quasi-static tides, dissipation is assumed to occur due to turbulent viscosity, while in the case of dynamical tides, two limiting cases are considered: the regime of moderately large dissipation and the regime of weak dissipation due to radiative viscosity. The change in the orbital period of WASP-46 is calculated and compared with observations. The regime of moderately large dissipation is shown to describe best the observations.     

Tidal Effects in Some Regular Black Holes

This paper is aimed to study the tidal forces produced by a class of regular black holes. We consider the radial infall of test particle and find radial as well as angular components of tidal forces by taking geodesic deviation equations. We also compute geodesic deviation vector by solving geodesic deviation equation numerically. It is concluded that a particle undergos either compression or stretching in radial or angular direction due to tidal forces.     

Tidal effects and the proximity decay of nuclei

We examine the decay of the 3.03 MeV state of (8)Be evaporated from an excited projectilelike fragment following a peripheral heavy-ion collision. The relative energy of the daughter alpha particles exhibits a dependence on the decay angle of the (8)Be(*), indicative of a tidal effect. A comparison of the measured tidal effect with a model suggests a measurable nuclear proximity interaction.     

Time and Events

Time plays a special role in Standard QuantumTheory. The concept of time observable causes manycontroversies there. In Event-Enhanced Quantum Theory(EEQT) Schrodinger's differential equation is replaced by a piecewise deterministic algorithm thatdescribes also the timing of events. This allows us torevisit the problem of time of arrival in quantumtheory.     

Tidal dynamics of relativistic flows near black holes

We point out novel consequences of general relativity involving tidal dynamics of ultrarelativistic relative motion. Specifically, we use the generalized Jacobi equation and its extension to study the force‐free dynamics of relativistic flows near a massive rotating source. We show that along the rotation axis of the gravitational source, relativistic tidal effects strongly decelerate an initially ultrarelativistic flow with respect to the ambient medium, contrary to Newtonian expectations. Moreover, an initially ultrarelativistic flow perpendicular to the axis of rotation is strongly accelerated by the relativistic tidal forces. The astrophysical implications of these results for jets and ultrahigh energy cosmic rays are briefly mentioned.     

Characteristic of Disruption on HL-2A Tokamak

The tokamak disruption is a dramatic event in which the plasma confinement is suddenly destroyed. Detailed experimental studies of disruptions have been made in many machines. During disruption, the plasma current and plasma thermal energy content collapse in an uncontrollable way, thereby applying mechanical forces and heat loads onto the vacuum vessel components. For that reason, the disruptions in a tokamak must be investigated and the physical processes leading to and occurring at the disruption need to be understood.     

Disruption of light coherence by matte glass surfaces

The present paper concerns a study of the degree of disruption of the coherence of light transmitted by matter surfaces of various roughnesses moistened with water, cedar oil, and glycerine. The dependence of the visibility of the interference pattern on the degree of specimen roughness and on the difference between the refractive indices of the glass and immersion liquids was investigated. The measurements were carried out photoelectrically on a setup similar to that employed in Young's experiment.