FLUTTER SUPPRESSION USING DISTRIBUTED PIEZOELECTRIC ACTUATORS

The Flutter suppression using distributed piezoelectric actuators has been analyzed and tested. In constructing the finite element equation, effects of piezoelectric matrices are investigated. LQG method is used in designing the control law. In reducing the order of the control law, both balance realization and LK methods are used. For the rational approximation of the unsteady aerodynamic forces LS method is improved. In determining the piezoelectric constants d31 a new dynamic response method is developed. Laser vibrameter is used to pick up the model response and in ground resonance test the model is excited by piezoelectric actuators. Reasonable agreement of the wind tunnel flutter suppression test with calculated results is obtained.     

M. Ostrowski,M. Sikora,G. Madejski and M. Begelman (eds.), Relativistic Jets in AGN's; M. Ostrowski and R. Schlickeiser (eds.), Plasma Turbulence and Energetic Particles in Astrophysics

Space Science Reviews -     

基于PC-BUS的通用可编程A/D转换组件的设计方法探讨

本文介绍了以ＨＡＤＣ５７４２（或ＡＤ１６７４）为核心的基于ＰＣ－ＢＵＳ的通用可编程Ａ／Ｄ转换组件的原理，介绍了Ａ／Ｄ转换组件的设计方法、工作方式、时序分析及其注意事项，对于特殊的可编程Ｉ／Ｏ组件和智能接口卡的设计具有借鉴意义。     

Planck-LFI 44 GHz back end module

This work describes the principle of operation, assembly and performance of one branch of the 44 GHz back end module (BEM) for the Planck low frequency instrument (LFI). This subsystem constitutes a fully representative branch of the qualification-model version (QM). It includes waveguide to microstrip transition, GaAs pseudomorphic high electron mobility transistor (PHEMT) low noise amplifiers (LNA), bandpass filter, square-law detector and dc amplifier. The fundamentals of the design of the RF part are described and all of the components have been tested individually before integration. Using single tone and wideband noise stimuli, the output voltage has been measured for several input powers, in order to obtain the sensitivity factor of the complete BEM. The effective bandwidth and the equivalent noise temperature have been calculated from the measurements, taking into account the frequency dependence on the noise source and the BEM. Finally, the low frequency output power spectrum has been obtained and a maximum 1/f knee frequency around 200 Hz has been measured with a 3 dB output signal video bandwidth above 50 KHz.     

Large solar event of September 29, 1989: ten years after

Out of the 56 Ground Level Enhancements (GLEs) of solar cosmic rays (SCRs) observed since 1942 until the present, 15 events were recorded in the 22nd cycle of solar activity (1986–1996). Solar proton events (SPEs) in that cycle displayed some peculiarities, which may need an interpretation on a new concept base. The event of September 29, 1989 is of special interest. Since the well-known event of February 23, 1956, it proved to be the most intense in the relativistic range of proton energies. This GLE affords a unique opportunity to study the propagation of SCRs over a wide range of rigidity.In spite of its occurrence behind the western solar limb, the originating major flare could be observed over a wide range of the wavelengths and particle energy spectra – from gamma rays to decametric radio waves, from >2 MeV electrons to multi-GeV protons; there were also measurements of the energy spectra and charge states of solar heavy nuclei. The flare was followed by some energetic solar phenomena (large magnetic loops, coronal eruptions and mass ejections, shocks, etc.). Due to the very hard rigidity spectrum, this was the first GLE recorded by underground muon detectors. The event also has a number of other unusual features, for example, an extended component of gamma-ray emission and the change in direction of the probable particle source during the event's initial stage. In addition, the intensity-time profile of the GLE is notable for its non-classic shape, showing a two-peak structure. The latter implies the possibility of a two-component (or two-source) ejection of accelerated particles from the Sun.The available observational data for the event is described in detail, the main focus of this paper is concentrated on different attempts to interpret the data within the framework of traditional and non-traditional concepts: shock and/or post-eruption acceleration, two-component (dual) ejection, two-source model of particle acceleration in large (extended) coronal structures, etc. None of the models put forward for explaining this event is exhaustive. The rigidity spectrum of ejected protons is estimated and the problem of the maximum rigidity, R _m, of the accelerated particles is discussed. In the relativistic range, this event proved to be by 1–2 orders less intense than the event of February 23, 1956. It is also shown that the event of September 29, 1989 could not have been recorded with the present-day neutrino detectors.     

Can a double component outflow explain the X-ray and optical lightcurves of Swift Gamma-Ray Bursts?

An increasing sample of Gamma-Ray Bursts (GRBs) observed by Swift show evidence of ‘chromatic breaks’, i.e. breaks that are present in the X-ray but not in the optical. We find that in a significant fraction of these GRB afterglows the X-ray and the optical emission cannot be produced by the same component. We propose that these afterglow lightcurves are the result of a two-component jet, in which both components undergo energy injection for the whole observation and the X-ray break is due to a jet break in the narrow outflow. Bursts with chromatic breaks also explain another surprising finding, the paucity of late achromatic breaks. We propose a model that may explain the behaviour of GRB emission in both X-ray and optical bands. This model can be a radical and noteworthy alternative to the current interpretation for the ‘canonical’ XRT and UVOT lightcurves, and it bears fundamental implications for GRB physics.     

Radiometric estimation of water vapor content over Brazil

A multi-channel microwave radiometre (make: Radiometrics Corporation) is installed at Instituto Nacional de Pesquisas Espaciais–INPE, Brazil (22°S). The radiometric output of two channels of the radiometer in the form of brightness temperature at 23.834 GHz and 30 GHz, initially, were used to find out the ambient water vapor content and the non-precipitable cloud liquid water content. The necessary algorithm was developed for the purpose. The best results were obtained using the hinge frequency 23.834 GHz and 30 GHz pair having an r.m.s. error of only 2.64. The same methodology was then adopted exploiting 23.034 GHz and 30 GHz pair. In that case the r.m.s. error was 3.42. These results were then compared with those obtained over Kolkata (22°N), India, by using 22.234 GHz and 31.4 GHz radiometric data. This work conclusively suggests the use of a frequency should not be at the water vapor resonance line. Instead, while measuring the vapor content for separation of vapor and cloud liquid, one of them should be a few GHz left or right from the resonance line i.e., at 23.834 GHz and the other one should be around 30 GHz.     

Nonlinear development of MHD waves in coronal loops

The solar corona, modelled by a low β, resistive plasma slab sustains MHD wave propagations due to footpoint motions in the photosphere. The numerical simulation presents the evolution of MHD waves and the formation of current sheets. Steep gradients at the slab edges, which are signatures of resonance layers are observed. Singularities are removed by the inclusion of finite resistivity. The fast waves develop kink modes. As the plasma evolves the current sheets which provide heating at the edges fragment into two current sheets at each edge which in turn come closer when the twist is enhanced.     

Photochemical synthesis of citric acid cycle intermediates based on titanium dioxide

The emergence of the citric acid cycle is one of the most remarkable occurrences with regard to understanding the origin and evolution of metabolic pathways. Although the chemical steps of the cycle are preserved intact throughout nature, diverse organisms make wide use of its chemistry, and in some cases organisms use only a selected portion of the cycle. However, the origins of this cycle would have arisen in the more primitive anaerobic organism or even back in the proto-metabolism, which likely arose spontaneously under favorable prebiotic chemical conditions. In this context, we report that UV irradiation of formamide in the presence of titanium dioxide afforded 6 of the 11 carboxylic acid intermediates of the reductive version of the citric acid cycle. Since this cycle is the central metabolic pathway of contemporary biology, this report highlights the role of photochemical processes in the origin of the metabolic apparatus.