Alfven waves as a driving mechanism in stellar winds

Alfven waves have been invoked as an important mechanism of particle acceleration in stellar winds of cool stars. After their identification in the solar wind they started to be studied in winds of stars located in different regions of the FIR diagram. We discuss here some characteristics of these waves and we present a direct application in the acceleration of late-type stellar winds. (C) 2009 COSPAR. Published by Elsevier Ltd. All rights reserved.

Moho map of South America from receiver functions and surface waves

We estimate crustal structure and thickness of South America north of roughly 40 degrees S. To this end, we analyzed receiver functions from 20 relatively new temporary broadband seismic stations deployed across eastern Brazil. In the analysis we include teleseismic and some regional events, particularly for stations that recorded few suitable earthquakes. We first estimate crustal thickness and average Poisson`s ratio using two different stacking methods. We then combine the new crustal constraints with results from previous receiver function studies. To interpolate the crustal thickness between the station locations, we jointly invert these Moho point constraints, Rayleigh wave group velocities, and regional S and Rayleigh waveforms for a continuous map of Moho depth. The new tomographic Moho map suggests that Moho depth and Moho relief vary slightly with age within the Precambrian crust. Whether or not a positive correlation between crustal thickness and geologic age is derived from the pre-interpolation point constraints depends strongly on the selected subset of receiver functions. This implies that using only pre-interpolation point constraints (receiver functions) inadequately samples the spatial variation in geologic age. The new Moho map also reveals an anomalously deep Moho beneath the oldest core of the Amazonian Craton.

Contributions to the theory of magnetorotational instability and waves in a rotating plasma

The one-fluid magnetohydrodynamic (MHD) theory of magnetorotational instability (MRI) in an ideal plasma is presented. The theory predicts the possibility of MRI for arbitrary 0, where 0 is the ratio of the plasma pressure to the magnetic field pressure. The kinetic theory of MRI in a collisionless plasma is developed. It is demonstrated that as in the ideal MHD, MRI can occur in such a plasma for arbitrary P. The mechanism of MRI is discussed; it is shown that the instability appears because of a perturbed parallel electric field. The electrodynamic description of MRI is formulated under the assumption that the dispersion relation is expressed in terms of the permittivity tensor; general properties of this tensor are analyzed. It is shown to be separated into the nonrotational and rotational parts. With this in mind, the first step for incorporation of MRI into the general theory of plasma instabilities is taken. The rotation effects on Alfven waves are considered.

BREAKING WAVES IN AN IDEAL QUARK GLUON PLASMA

We study the propagation of perturbations in the energy density in a quark gluon plasma. Expanding the Euler and continuity equations of relativistic hydrodynamics around equilibrium configurations we obtain a nonlinear differential equation called the breaking wave equation. We solve it numerically and follow the time-evolution of initially localized pulses. We find that, quite unexpectedly, these pulses live for a very long time (compared to the reaction time-scales) before breaking. In practice, they mimick the Korteweg-de Vries solitons. Their existence may have some observable consequences.

Sound waves and solitons in hot and dense nuclear matter

Assuming that nuclear matter can be treated as a perfect fluid, we study the propagation of perturbations in the baryon density. The equation of state is derived from a relativistic mean field model, which is a variant of the non-linear Walecka model. The expansion of the Euler and continuity equations of relativistic hydrodynamics around equilibrium configurations leads to differential equations for the density perturbation. We solve them numerically for linear and spherical perturbations and follow the propagation of the initial pulses. For linear perturbations we find single soliton solutions and solutions with one or more solitons followed by ""radiation"". Depending on the equation of state a strong damping may occur. We consider also the evolution of perturbations in a medium without dispersive effects. In this case we observe the formation and breaking of shock waves. We study all these equations also for matter at finite temperature. Our results may be relevant for the analysis of RHIC data. They suggest that the shock waves formed in the quark gluon plasma phase may survive and propagate in the hadronic phase. (C) 2009 Elseiver. B.V. All rights reserved.

Stability of periodic travelling shallow-water waves determined by Newton`s equation

We study the existence and stability of periodic travelling-wave solutions for generalized Benjamin-Bona-Mahony and Camassa-Holm equations. To prove orbital stability, we use the abstract results of Grillakis-Shatah-Strauss and the Floquet theory for periodic eigenvalue problems.

Reflection of matter waves in potential structures

In this paper the behavior of matter waves in suddenly terminated potential structures is investigated numerically. It is shown that there is no difference between a fully quantum mechanical treatment and a semiclassical one with regards to energy redistribution. For the quantum case it is demonstrated that there can be substantial reflection at the termination. The neglect of backscattering by the semiclassical method brings about major differences in the case of low kinetic energies. A simple phenomenological model is shown to partially explain the observed backscattering using dynamics of reduced dimensionality.

Localization in splitting of matter waves

In this paper we present an analysis of how matter waves, guided as propagating modes in potential structures, are split under adiabatic conditions. The description is formulated in terms of localized states obtained through a unitary transformation acting on the mode functions. The mathematical framework results in coupled propagation equations that are decoupled in the asymptotic regions as well before as after the split. The resulting states have the advantage of describing propagation in situations, for instance matter-wave interferometers, where local perturbations make the transverse modes of the guiding potential unsuitable as a basis. The different regimes of validity of adiabatic propagation schemes based on localized versus delocalized basis states are also outlined. Nontrivial dynamics for superposition states propagating through split potential structures is investigated through numerical simulations. For superposition states the influence of longitudinal wave-packet extension on the localization is investigated and shown to be accurately described in quantitative terms using the adiabatic formulations presented here.

Single-mode acceleration of matter waves in circular waveguides

Ultracold gases in ring geometries hold promise for significant improvements of gyroscopic sensitivity. Recent experiments have realized atomic and molecular storage rings with radii in the centimeter range, sizes whose practical use in inertial sensors requires velocities significantly in excess of typical recoil velocities. We use a combination of analytical and numerical techniques to study the coherent acceleration of matter waves in circular waveguides, with particular emphasis on its impact on single-mode propagation. In the simplest case we find that single-mode propagation is best maintained by the application of time-dependent acceleration force with the temporal profile of a Blackmann pulse. We also assess the impact of classical noise on the acceleration process.

Propagation characteristics of lamb waves in stringer-stiffened panels

Stringer-stiffened plate-like structure is a typical engineering structure and its structural integrity is critical. A guided Lamb wave-based damage identification scheme and an online structural health monitoring (SHM) system with an integrated PZT-sensor network were developed. In the previous studies, the specimens were relatively simple. In this paper, the above mentioned method was extended to the stiffened plate-like structure—a flat plate reinforced by stringer. FE dynamic simulation was applied to investigate the Lamb wave propagation characteristics due to the existence of stringer with the consideration of its material and geometric configurations.

Cinema's new waves : an interview with Albie Thoms

Albie Thomas is a seminal figure in the history of Avant-Garde film in Australia. In the mid-1960s he helped found UBU Films, the precursor of the Sydney Film-Makers' Co-operative, and he has made a number of short and feature-length experimental films. Thoms has written on film and film cultures for an array of journals and maintains an active involvement with aspects of the surf film industry in Australia. In this interview, Thoms discusses his early UBU films, and the connections between those films and Palm Beach (1979). Styles of surf film and the influences on Thoms' filmmaking are also discussed.

1948 and 1968 Czech refugee settlers in Australia : a comparison of the settlement and integration processes among two waves of settlers

Nearly eighteen years ago when I first became interested in the history and sociology of Australian immigration, I was particularly attracted by the fact and opportunity to incorporate immigration settlement, experience and accomplishments in my history teaching in secondary school. In particular it was the area of the settlement of Australia that needed a fuller understanding in the teaching of Australian history. By that I mean it was needed to show that there were many other ethnic groups besides the Anglo-Saxon group which had participated in the development of Australia since 1788. Since the end of World War II, the Australian population has doubled, the population structure and characteristics have changed and knowledge about the diverse groups forming the Australian nation is now sought. Sane ethnic groups, mainly the numerically large, have been studied and numerous reports are available. But many of the smaller groups have attracted little interest among Australian scholars. This was one of the reasons that I decided to research the behaviour of one of the smaller groups - the Czechs - to find out about their immigration history to Australia; their immigration processes such as re-settlement and re-establishment; and their community life since World War II. Because of the scarcity of written materials on Czechs in Australia, I had to rely on interviews, personal reminiscenses, letters and documents translated from the Czech language. I should like to express my gratitude to all people and officials of Czech ethnic organisations and clubs in Australia, who agreed to be interviewed and who provided me with documentary material so important for my work. Respecting the wishes of my interviewees their anonymity had to be preserved. In the course of my research, I have received substantial help and the encouragement from the Editor of the now extinct Czech language paper Newspaper Hlas domova, Mr. F.V., whose co-operation is gratefully recognised. I am also grateful to Associate Professor William D. Rubinstein for his help and encouragement in all stages of my work. The introductory part of the study is covered in Chapter One. She reasons for the need to increase Australia's population after World War II and an analysis of the development of settlement in Australia between 1947 and 1984 are discussed. The emigration of Czechs into Australia and their place in the post-war immigration scheme is introduced. To obtain an overview of how Czechs have emigrated around the world, the literature describing their settlement is compared. Also discussed in the literature on Czech settlement in Australia from an historical point of view. The studies on the concept of ethnicity and settlement in Australia are used to document the theoretical issues for an understanding of Australian society. This chapter also contains aspects of sources and research, shewing the processes of documentary research, interviews and related matters. In Chapter Two the history of Czech emigration is discussed, covering the period from the seventeenth to the twentieth century. The first contacts with Australia are highlighted, continuing into the inter-war period and finally the re-settlement of Czechs after World War II. To understand why Czechs left their ancestral country after World War II, the political situation in Czechoslovakia is analysed. The third chapter concentrates mainly in the 1948 wave of settlers, who left Czechoslovakia after the communist take-over in 1948. Their means of departure from their homeland, selection of Australia as a new homeland and their re-settlement and re-establishment are discussed. Their attitudes after their arrival and their later stages of their settlement are analysed. The formation of numerous Czech ethnic organisations which mushroomed between 1950 and 1954 led to an active community life which began to change about five years after their arrival. These charges led to disorganisation of Czech community's life. The causes of these changes which were influential for the failure of the 1948 group to establish a viable community in Australia are analysed. In Chapter Four the wave of 1968 is viewed, their arrival and settling is covered. The study of their group attitudes and formation of group institutions is the main part of this section. A comparison of my data of the two waves, 1948 and 1968, reveals the information that these two groups did not develop the harmonious relationship expected of them as members of the one ethnic group. Chapter Five discusses immigration typologies and concentrates on the differences between legal and illegal emigrants from the Czechoslovak point of view. The integration processes of Czechs and their incorporation into Australian society are discussed. The sixth chapter sums up the findings of this disertation and states the influences which were responsible for the divisions in Czech ethnic life in Australia in the 1980s.

On the influence of building design, occupants and heat waves on comfort and greenhouse gas emissions in naturally ventilated offices. A study based on the EN 15251 adaptive thermal comfort model in Athens, Greece

According to the Intergovernmental Panel on Climate Change the buildings sector has the largest mitigation potential for CO2 emissions. Especially in office buildings, where internal heat loads and a relatively high occupant density occur at the same time with solar heat gains, overheating has become a common problem. In Europe the adaptive thermal comfort model according to EN 15251 provides a method to evaluate thermal comfort in naturally ventilated buildings. However, especially in the context of the climate change and the occurrence of heat waves within the last decade, the question arises, how thermal comfort can be maintained without additional cooling, especially in warm climates. In this paper a parametric study for a typical cellular naturally ventilated office room has been conducted, using the building simulation software EnergyPlus. It is based on the Mediterranean climate of Athens, Greece. Adaptive thermal comfort is evaluated according to EN 15251. Variations refer to different building design priorities, and they consider the variability of occupant behaviour and internal heat loads by using an ideal and worst case scenario. The influence of heat waves is considered by comparing measured temperatures for an average and an exceptionally hot year within the last decade. Since the use of building controls for shading affects thermal as well as visual comfort, daylighting and view are evaluated as well. Conclusions are drawn regarding the influence and interaction of building design, occupants and heat waves on comfort and greenhouse gas emissions in naturally ventilated offices, and related optimisation potential.