Gamma-ray Flares and VLBI Outbursts of Blazars

A model is developed for the time dependent electromagnetic - radio to gamma-ray - emission of active galactic nuclei, specifically, the blazars, based on the acceleration and creation of leptons at a propagating discontinuity or {\it front} of a Poynting flux jet. The front corresponds to a discrete relativistic jet component as observed with very-long-baseline-interferometry (VLBI). Equations are derived for the number, momentum, and energy of particles in the front taking into account synchrotron, synchrotron-self-Compton (SSC), and inverse-Compton processes as well as photon-photon pair production. The apparent synchrotron, SSC, and inverse-Compton luminosities as functions of time are determined. Predictions of the model are compared with observations in the gamma, optical and radio bands. The delay between the high-energy gamma-ray flare and the onset of the radio is explained by self-absorption and/or free-free absorption by external plasma. Two types of gamma-ray flares are predicted depending on pair creation in the front.Comment: 11 pages, submitted to ApJ. 10 figures can be obtained from R. Lovelace by sending postal address to [email protected]

Relativistic Poynting Jets from Accretion Disks

A model is developed for relativistic Poynting jets from the inner region of a disk around a rotating black hole. The disk is initially threaded by a dipole-like magnetic field. The model is derived from the special relativistic equation for a force-free electromagnetic field. The ``head'' of the Poynting jet is found to propagate outward with a velocity which may be relativistic. The Lorentz factor of the head (Gamma) is found to be dependent on the magnetic field strength close to the black hole, B_0, the density of the external medium n_ext, and on the ratio R=r_0/r_g >1, where r_g is the gravitational radius of the black hole, and r_0 is the radius of the O-point of the initial dipole field threading the disk. For conditions pertinent to an active galactic nuclei, Gamma is approximately equal to 8 (10/R)^(1/3) (B_0/10^3 Gauss)^(1/3) (1/cm^3/n_ext)^(1/6). This model offers an explanation for the observed Lorentz factors which are of the order of 10 for the parsec-scale radio jets measured with very long baseline interferometry.Comment: 4 pages, 1 figur

VHF scintillations, orientation of the anisotropy of F-region irregularities and direction of plasma convection in the polar cap

Scintillation data recorded at the polar cap station Barentsburg are shown to occasionally exhibit two or more peaks in the latitudinal profiles of the amplitude dispersion. Comparison with concurrent SuperDARN radar convection maps indicates that multiple peaks occur when Barentsburg is located within the area of strong changes in the plasma flow direction. When parameters of the ionospheric irregularities are inferred from the scintillation data, the orientation of the irregularity anisotropy in a plane perpendicular to the magnetic field is found to coincide well with the <I><b>E</b></I>×<I><B>B</B></I> flow direction, individually for each peak of the scintillation data. The differences were found to be mostly less than 20° for a data set comprised of 104 events. The conclusion is made that analysis of scintillation data allows one to infer the direction of plasma flow with a certain degree of detail

Orientation of the cross-field anisotropy of small-scale ionospheric irregularities and direction of plasma convection

The relationship between the orientation of the small-scale ionospheric irregularity anisotropy in a plane perpendicular to the geomagnetic field and the direction of plasma convection in the F region is investigated. The cross-field anisotropy of irregularities is obtained by fitting theoretical expectations for the amplitude scintillations of satellite radio signals to the actual measurements. Information on plasma convection was provided by the SuperDARN HF radars. Joint satellite/radar observations in both the auroral zone and the polar cap are considered. It is shown that the irregularity cross-field anisotropy agrees quite well with the direction of plasma convection with the best agreement for events with quasi-stationary convection patterns

The analysis of magnetic field measurements of T Tau

It is shown that the existence of hot accretion spots at the surface of T Tau practically has no effect on the accuracy of estimation of its magnetic field strength at photospheric level. We also found that one can interpret results of T Tau's photospheric magnetic field strength measurements carried out via different methods in the frame of the following alternative: 1) if T Tau's inclination angle $i\le 10^\circ,$ then magnetic field of the star may be dipolar with the angle between rotational and magnetic axes is near $85^\circ;$ 2) if it will be found (e.g. from interferometric observations) that $i>10^\circ,$ then magnetic field of T Tau is essentially non-dipolar or/and non-stationary.Comment: 4 figure

Syntactic Features of Proper Names: The Generativist Approach(es) to Properhood

The paper presents an overview of the generativist approaches to the syntactic analysis of proper names which are only very little known in the field of onomastics. The authors start with the general outline of basic theoretical ideas of generative grammar pertaining to the syntactic nature of words and phrases, the nature of the determiner phrase, and the main issues of transformational semantic syntax. The authors further proceed to present the cornerstone theories related to proper names within the generativist paradigm: Giuseppe Longobardi’s idea of proper names as determiner phrase projections, followed by Hagit Borer who elaborated a detailed analysis of nominal functional sequences; Ora Matushansky’s analysis of constructions of naming and nominating, and its critique by Alexandra Cornilescu. The overview leads the authors to conclude that, although generativism does not offer a unified syntactic theory of proper names, in some respects it can be a more promising theoretical framework than constructivism which now constitutes the basis for the modern “pragmatic” theory of properhood. Unlike constructivism, generativism considers proper names as a part of universal grammar seeking for explanations that would have crosslinguistic relevance. However, the approaches discussed in this paper clearly demonstrate the contribution of the syntactic environment to the interpretation of a noun as a proper or common name, which is a strong argument in favour of the “pragmatic” theory of properhood. The authors show that the generativist framework may also be used in the future for creating a more comprehensive description of some specifically proprial syntactic constructions.Настоящая статья представляет собой обзор малоизвестных среди ономастов подходов к синтаксическому анализу имен собственных, сложившихся в рамках генеративной грамматики. В начале статьи авторы излагают основные идеи генеративной грамматики, связанные с синтаксической природой слов и фраз, статусом группы детерминатора, а также обсуждают основные вопросы трансформационного семантического синтаксиса. Затем авторы представляют ключевые генеративные теории, относящиеся к изучению имен собственных, а именно: концепцию Джузеппе Лонгобарди об именах собственных как проекции группы детерминатора, развитую позднее Хагит Борер, которая разработала более детальный подход к описанию функциональной структуры именных групп; анализ конструкций именования и назначения, предложенный Орой Матушански, а также критику этого подхода в работах Александры Корнилеску. Обзор позволяет авторам заключить, что хотя генеративизм не предлагает целостной теории имен собственных, в ряде отношений он может обеспечить даже более многообещающую методологию для анализа синтаксических свойств имен собственных, чем конструктивизм, который сегодня составляет основу современной «прагматической» теории проприальности. В противоположность конструктивизму генеративизм рассматривает имена собственные как часть универсальной грамматики, пытаясь найти объяснения, одинаково хорошо работающие для разных языков. Рассмотренные в статье подходы однозначно показывают значение синтаксического окружения для проприальной или апеллятивной интерпретации существительного, что само по себе является сильным аргументом в пользу прагматической теории проприальности. Авторы также показывают, что генеративизм может в будущем выступить хорошим теоретическим фундаментом для более детального описания некоторых специфических проприальных синтаксических конструкций

Mechanical Aspects of Nonhomogeneous Deformation of Aluminum Single Crystals under Compression along [100] and [110] Directions

The deformation behavior of aluminum single crystals subjected to compression along the [100] and [110] directions is numerically examined in terms of crystal plasticity. A constitutive model taking into account slip geometry in face-centered cubic crystals is developed using experimental data for the single-crystal samples with lateral sides coplanar to certain crystal planes. Two sets of calculations are performed using ABAQUS/Explicit to examine the features of plastic strain evolution in perfectly plastic and strain-hardened crystals. Special attention is given to the discussion of mechanical aspects of crystal fragmentation. Several distinct deformation stages are revealed in the calculations. In the first stage, narrow solitary fronts of plastic deformation are alternately formed near the top or bottom surfaces and then propagate towards opposite ends to save the symmetry of the crystal shape. The strain rate within the fronts is an order of magnitude higher than the average strain rate. The first stage lasts longer in the strain-hardened crystals, eventually giving way to an intermediate stage of multiple slips in different crystal parts. Finally, the crystal shape becomes asymmetrical, but no pronounced macroscopic strain localization has been revealed at any deformation stage. The second stage in perfectly plastic crystals relates to abrupt strain localization within a through-thickness band-shaped region, accompanied by macroscale crystal fragmentation. Stress analysis has shown that pure compression took place only in the first deformation stage. Once the crystal shape has lost its symmetry, the compressive stress in some regions progressively decreases to zero and eventually turns tensile

Relativistic Jets from Accretion Disks

The jets observed to emanate from many compact accreting objects may arise from the twisting of a magnetic field threading a differentially rotating accretion disk which acts to magnetically extract angular momentum and energy from the disk. Two main regimes have been discussed, hydromagnetic jets, which have a significant mass flux and have energy and angular momentum carried by both matter and electromagnetic field and, Poynting jets, where the mass flux is small and energy and angular momentum are carried predominantly by the electromagnetic field. Here, we describe recent theoretical work on the formation of relativistic Poynting jets from magnetized accretion disks. Further, we describe new relativistic, fully-electromagnetic, particle-in-cell simulations of the formation of jets from accretion disks. Analog Z-pinch experiments may help to understand the origin of astrophysical jets.Comment: 7 pages, 3 figures, Proc. of High Energy Density Astrophysics Conf., 200