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Abstract: We study the damping rate of massless Dirac fermions due to the gauge field in -dimensional quantum electrodynamics. In the absence of a Maxwell term for the gauge field, the fermion damping rate is found to diverge in both perturbative and self-consistent results. In the presence of a Maxwell term, there is still divergence in the perturbative results for . Once the Maxwell term is included into the self-consistent equations for fermion self-energy and vacuum polarization functions, the fermion damping rate is free of divergence and exhibits non-Fermi liquid behavior: . [Copyright &y& Elsevier]

The validity of approximating radiative heating rates in the middle atmosphere by a local linear relaxation to a reference temperature state (i.e., “Newtonian cooling”) is investigated. Using radiative heating rate and temperature output from a chemistry–climate model with realistic spatiotemporal variability and realistic chemical and radiative parameterizations, it is found that a linear regression model can capture more than 80% of the variance in longwave heating rates throughout most of the stratosphere and mesosphere, provided that the damping rate is allowed to vary with height, latitude, and season. The linear model describes departures from the climatological mean, not from radiative equilibrium. Photochemical damping rates in the upper stratosphere are similarly diagnosed. Three important exceptions, however, are found. The approximation of linearity breaks down near the edges of the polar vortices in both hemispheres. This nonlinearity can be well captured by including a quadratic term. The use of a scale-independent damping rate is not well justified in the lower tropical stratosphere because of the presence of a broad spectrum of vertical scales. The local assumption fails entirely during the breakup of the Antarctic vortex, where large fluctuations in temperature near the top of the vortex influence longwave heating rates within the quiescent region below. These results are relevant for mechanistic modeling studies of the middle atmosphere, particularly those investigating the final Antarctic warming. [ABSTRACT FROM AUTHOR]

High resolution observations in the region of the Hα, HeII λ 4686, and Hγ lines in the spectrum of the symbiotic binary Z And were performed during a small-amplitude flare at the end of 2002. The profiles of the hydrogen lines were double-peaked, and suggest that the lines may be emitted mainly by an optically thin accretion disk. Since the Hα line is strongly contaminated by emission from the envelope, the Hγ line is used to investigate the properties of the accretion disk. The Hα line has broad wings, believed to be determined mostly by radiation damping, although the high-velocity stellar wind from the compact object in the system may also contribute. The Hγ line has a broad emission component, assumed to be emitted mainly from the inner part of the accretion disk. The HeIIλ 4686 line also has a broad emission component, but is believed to arise in a region of high-velocity stellar wind. The outer radius of the accretion disk can be calculated from the shift between the peaks. Assuming that the orbital inclination can range from 47° to 76°, we estimate the outer radius to be 20–50 R⨀. The behavior of the observed lines can be interpreted in the model proposed for the line spectrum during the first large 2000–2002 flare of this binary. [ABSTRACT FROM AUTHOR]

Abstract: The scientific literature contains reports of external magnetic fields affecting the fundamental properties and structure of water, including a report of the rotational motion of water molecules being slowed due to increased hydrogen bonding resulting from magnetic treatment. To investigate such a change in molecular motion, 1H spin–lattice relaxation times of water were measured at increasing magnetic field strengths. Strong radiation damping was observed at each magnetic field strength when using inversion-recovery experiments. To measure the relaxation times in the presence of radiation damping, several experimental methods of saturation recovery to measure spin–lattice relaxation were applied to a 90% H2O sample to obtain results as a function of field strength for proton frequencies from 300 to 800MHz. [Copyright &y& Elsevier]

The article discusses a paper which examined the mechanics of a charged matter particle in general relativity. The study deduced the fundamental equations of mechanics from Einstein's equations for gravitation. It calculated divergences and investigated the mechanical equations with radiation damping. It suggested to substitute in an equation in order to avoid the obstacles arising from the affinity of an integrand.

Scattering of radiation by a system on N quasi-point like dipoles located on a circle (equidistantly in the polar angle) in two spatial dimensions is considered. The coupling of the dipoles is taken into account exactly. A closed-form expression for the electric fields at the points where the dipoles are located is given via the partial wave decomposition. Scattering and focusing properties are investigated for both dielectric and metallic scatterers. [ABSTRACT FROM AUTHOR]

It is proposed to place the actuators to maximize the mean value of energy transmitted from or dissipated by the actuators, while the sensor location should maximize the mean square value of system output, which also maximizes the signal-to-noise ratio. By using explicit expressions for controllability and observability grammians as well as modal energies, it is shown that the approaches based on the system responses to transient and persistent disturbances are closely related, and are equivalent for structures which damping is small and the natural frequencies of which are well spaced. The method of actuator and sensor optimal location via grammians was proposed and compared it with results given by the method of matrix norms. [ABSTRACT FROM AUTHOR]

A model of ultrasonic radiation damping is presented to describe the dissipation of ultrasonic vibration energy in a solid processing system on the basis of vibration damping theory. Four kinds of polyethylene particles, with diameters varying from 0.15 to 0.85 mm and bulk densities varying from 499.6 to 252.5 kg·m-3, are put in a Plexiglas storage bin inserted with a Plexiglas bar, as powder material. Ultrasonic energies absorbed by these kinds of particles were detected by receivers at different levels. The results show that when distance between receiver and source of ultrasonic vibration is lengthened, the AE energy absorption increases, and it also increases when the bulk density of powder material is increased. It is also found that the ultrasonic vibration energy dissipates much more along the inserted bar than along the wall of a storage bin, because the inserted bar has greater radiation area. The results of experiments are accurately predicted by the radiation damping model presented in this article with a fairly good accuracy. Furthermore, a method of level gauging is developed to meet the requirements of different applications, such as online measurement of the particle material, to replace other level gauging methods. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a study of the nonlinear dynamic behavior of a gearshift cable and more specifically of the associated tizzing phenomenon. A gearshift cable is composed of an inner wire that can slide freely in an outer composite housing. When undergoing harmonic excitation, the inner wire interacts with the housing. Hammer and swept sine shaker tests are first used to estimate the characteristics of the two main components. It is shown that the behavior of the outer housing is nonlinear and depends on the amplitude of the excitation. The assembled gearshift cable is then set up on the shaker and the nonlinear vibro-impacting phenomenon is studied. Finally a finite element model, based on the Euler–Bernoulli beams and the Rayleigh damping coefficients, proves to offer good correlation with the measured data for different excitation frequencies. A period doubling bifurcation is observed both experimentally and numerically. [Copyright &y& Elsevier]

Abstract: This paper presents a macro-element to simulate dynamic Soil-Structure Interaction (SSI). This new numerical tool is suitable for dynamic (seismic) loadings on structures with shallow foundations. It takes into account the plasticity of the soil, the uplift of the foundation, effects and the radiation damping. The foundation is supposed infinitely rigid while its movement is entirely described by a system of global variables (forces and displacements) defined in its center. The nonlinear behavior of the soil and the uplift of the foundation are reproduced using the classical theory of plasticity. Uplift and plasticity are combined using the theory of multi-mechanisms. Failure is described by an interaction diagram of the ultimate bearing capacity of the foundation under combined loads. The performance of the macro-element is validated using the experimental results of the structure Camus IV. Furthermore, a parametric study on the behavior of a seven-story building shows the capability of the macro-element to consider different types of soils. Based on the results obtained it seems now possible to use this approach to investigate numerically the behavior of a wider variety of configurations. [Copyright &y& Elsevier]

Abstract: The long-term variability of stationary and traveling planetary waves in the lower stratosphere has been investigated using the data of NCEP/NCAR reanalysis. The results obtained show that during the last decades winter-mean amplitude of the stationary planetary wave with zonal wave number 1 (SPW1) increases at the higher middle latitudes of the Northern Hemisphere. It has been suggested that the observed increase in the SPW1 amplitude should be accompanied by the growth in the magnitude of the stratospheric vacillations. The analysis of the SPW1 behavior in the NCEP/NCAR data set supports this suggestion and shows a noticeable increase with time in the SPW1 intra-seasonal variability. The amplitudes of the long-period normal atmospheric modes, the so-called 5-, 10- and 16-day waves, diminish. It is supposed that one of the possible reasons for this decrease can be a growth of radiative damping rate caused, for instance, by the increase of . To investigate a possible climatic change of the middle atmosphere dynamics caused by observed changes in the tropospheric temperature, two sets of runs (using zonally averaged temperature distributions in the troposphere typical for January 1960 and 2000) with the middle and upper atmosphere model (MUAM) have been performed. The results obtained show that on average the calculated amplitude of the SPW1 in the stratosphere increased in 2000 and there is also an increase of its intra-seasonal variability conditioned by nonlinear interaction with the mean flow. This increase in the amplitudes of stratospheric vacillations during the last four decades allows us to suggest that stratospheric dynamics becomes more stochastic. [Copyright &y& Elsevier]

Abstract: We show that radiation generated in optical parametric down-conversion with losses and noise is entangled for all times if the coupling coefficient is higher than half of damping constant and the product of damping constant and mean number of noise photons. For the process stimulated by means of chaotic light there is a saturable bound of its intensity for the generation of nonclassical light. Otherwise the quantum behaviour and entanglement are fully reduced. Under some restrictions for noise nonclassical light can also be generated at and below the threshold. [Copyright &y& Elsevier]

We study the collision of two fast solitons for the nonlinear Schrödinger equation in the presence of a slowly varying external potential. For a high initial relative speed || v|| of the solitons, we show that, up to times of order || v|| after the collision, the solitons preserve their shape (in L2-norm), and the dynamics of the centers of mass of the solitons is approximately determined by the external potential, plus error terms due to radiation damping and the extended nature of the solitons. We remark on how to obtain longer time scales under stronger assumptions on the initial condition and the external potential. [ABSTRACT FROM AUTHOR]

Radiation damping due to wave propagation in unbounded domains may cause a significant reduction of structural vibrations when excited near resonance. Here a novel matrix-valued algebraic Padé-like stiffness formulation in the frequency-domain and a corresponding state equation in the time domain are elaborated for a soil-structure interaction problem with a layered soil excited in a transient manner by a flexible rotor during startup and shutdown. The contribution of radiation damping caused by 'a soil-layer upon a rigid bedrock is characterized by the corresponding amount of critical damping as it is used in structural dynamics. [ABSTRACT FROM AUTHOR]

Abstract: It is found experimentally that there exist some harmonic peaks in one-dimensional NMR spectra of solution samples with two dominant solvents. Theoretical analysis indicates that such harmonic peaks result from the interaction between two radiation damping fields induced by the dominant solvents. Using a homo-nuclear decoupling pulse as a radiation damping field, a novel detection approach is proposed to investigate these harmonic peaks without interferences caused by the nonlinear amplification of the receiver. The results presented herein give a new insight into the radiation damping effects in samples with solvent mixtures (e.g. natural products) at high fields. [Copyright &y& Elsevier]

Abstract: In this study, two different earthquake input models are introduced, i.e. massless foundation model and viscous-spring boundary input model considering radiation damping. Linear elastic and nonlinear contraction joint opening analyses of the 210m high Dagangshan arch dam under construction in China are performed using the two different earthquake input models. First, the responses of the three-dimensional (3-D) canyon without the dam are analyzed, respectively, with massless-truncated foundation and with viscous-spring boundary; second, linear and nonlinear analyses of the dam–foundation system are performed and compared by using the two input models. Hydrodynamic effects are considered using finite element discretization for incompressible reservoir fluid. It is concluded that stresses and displacements and contraction joint opening in the dam are significantly reduced both in linear and nonlinear analyses when using viscous-spring boundary model. Interestingly, in the case of linear analysis of the Dagangshan, the massless foundation input model with a relatively higher damping ratio of 10% leads to a comparable response of the dam to that using viscous-spring boundary model. In addition, the maximum tensile stresses from nonlinear analysis are 10–25% larger than that of the corresponding linear cases due to a partial release of the arch action. [Copyright &y& Elsevier]

As a stepping stone towards understanding acoustic resonances in axial flow compressors, acoustic resonances are computed numerically in fixed single and tandem plate cascades in an infinitely long annular duct. Applying perfectly matched layer absorbing boundary conditions in the form of the complex scaling method of atomic and molecular physics to approximate the radiation condition the resonance problem is transformed into an eigenvalue problem. Of particular interest are resonances with zero radiation damping (trapped modes) or very small radiation damping (nearly trapped modes). Such resonances can be excited by wakes from compressor cascades or struts. If the shedding frequency is sufficiently close to an acoustic resonant frequency, the latter may control the vortex shedding causing high-intensity tonal noise or occasionally even blade failure. All resonances are computed for zero mean flow approximating low-Mach-number flows. The influence of various cascade parameters on the resonant frequencies is studied and, whenever possible, our numerical results are compared with published experimental findings. [ABSTRACT FROM AUTHOR]

Abstract: The nonlinear dynamic behaviour of preloaded traditional multilayer plates incorporating visco-hyperelastic materials is investigated. The visco-hyperelastic material was confined between stiff layers and worked as a damping layer. The full structure is submitted to shear vibrations under a compression preload. We present herein a nonlinear model describing the tangent dynamic shear modulus as function of both preload and frequency. A Navier approach is used to calculate the stress and the deformation fields which are written by a transfer matrix formulation. The dynamic shear modulus for elastomers is expressed by a nonlinear visco-hyperelastic model based on a deformation energy density. The effects of the elastomer''s nonlinear behaviour, the frequency and the preload on the structure''s overall dynamic shear modulus is the main object of this study. Verification of the model is performed on visco-hyperelastic multilayer through a series of dynamic shear tests under various compression preload levels. A comparison with both finite element calculations and discreet models is discussed. [Copyright &y& Elsevier]

Abstract: Accurately estimating a structure''s broadband response is highly dependent on a proper characterization of the system''s internal damping as well as induced (or effective) damping when coupled systems are considered. In many aerospace and related applications a primary or master structure is loaded with equipment or substructures. The effects of these attachments on the master structure are often poorly understood and frequently overlooked, but in many cases can dominate the master structure''s response. In this work various measures of damping of a lightweight aerospace panel (aluminum sandwich honeycomb core panel) with simple (lumped mass) and complex (electronic equipment) attachments are investigated using experimental techniques and simple statistical energy analysis models. The panel''s various measures of damping in steady-state conditions are defined and explored. The panels with simple and complex attachments are experimentally evaluated using power injection methods. The results show that at different frequencies the simple panel''s response is controlled by internal and then acoustic radiation damping. The complex attachment''s induced damping effects, however, can far exceed both the structure internal and acoustic radiation components. A range of complex attachment configurations are evaluated and general design assessment procedures developed for use by designers. Future work is planned to explore the systems transient response and derived parameters, as well as investigate the effects when the attachment mass varies over a greater range of values, a realistic condition applicable to many aerospace systems. [Copyright &y& Elsevier]

Abstract: In order to study the effects of coastline on wave power absorption, we describe here a linearized theory of an oscillating water column (OWC) installed on a straight coast. The sea depth is assumed to be constant and the coast is a vertical cliff. The column is a vertical circular cylinder half embedded in the cliff and open on the seaside. Forced by incident waves from any direction, the water surface inside pushes the dry air above through a Wells turbine system to generate power. Carrying out the linearized theories of radiation and diffraction analytically, we calculate the coefficients of apparent mass and radiation damping, and the chamber pressure. Optimum absorption efficiency is examined under the constraint of constant chamber volume. Results are compared with a parallel study of an OWC installed either offshore or at the tip of a thin breakwater. [Copyright &y& Elsevier]

Abstract: We have systematically investigated the line shapes observed in proton nuclear spin-noise spectra which depend in a complex way on the properties of the resonance circuit, the number of spins present, transverse relaxation, inhomogeneous broadening, and radiation damping. Using highly sensitive high resolution probes these dependencies are investigated by way of high resolution 1H noise power NMR spectra of liquid samples. Significant deviations from intuitive expectations are observed. Simulations based on an adapted Nyquist noise equation are used to understand and interpret the experimental findings. [Copyright &y& Elsevier]

Glyben is an artificial soil comprising bentonite mixed with glycerin that has been used recently in scaled model tests to study seismic soil structure interaction. In spite of recent interest in glyben, factors affecting the dynamic properties of this material have not been well established. This paper presents the results of vane shear tests, cyclic triaxial tests, resonant column tests and bender element tests undertaken to characterize the dynamic properties of glyben. The results show that the modulus ratio of glyben decreases with increasing shear strain amplitude similar to that observed for natural clays. However, there are significant thixotropic changes in the properties of glyben after mixing bentonite with glycerin. In addition, glyben exhibits time-dependent volumetric compression after the application of isotropic consolidation pressure, the damping ratio of glyben is higher than that of natural clays and the dynamic properties of glyben are strongly influenced by temperature. These factors should be considered when interpreting the results of scaled physical model tests using glyben. [ABSTRACT FROM AUTHOR]

Abstract: Chaotic dynamics of a water magnetization in a 600MHz NMR spectrometer was generated by a radiation damping-based electronic feedback. Erratic induction signal was observed for several tens of seconds. The analysis of the data shows that this chaotic behaviour can be ascribed to spin turbulence in the sample and that a simpler model based on the three-dimensional Bloch equations modified to include a feedback field may not account for the experimental data. [Copyright &y& Elsevier]

In this study, a nonlinear model is presented for analysis of damage-cracking behavior in arch dams during strong earthquakes using different seismic input mechanisms. The nonlinear system includes a plastic-damage model for cyclic loading of concrete considering strain softening and a contact boundary model of contraction joint opening. Two different earthquake input mechanisms are used for comparison, including massless foundation input model and viscous-spring boundary model considering radiation damping due to infinite canyon. The results demonstrate that effects of seismic input mechanism and radiation damping on nonlinear response and damage-cracking of the dam are significant. Compared with the results of using massless foundation input model, the damage-cracking region and contraction joint opening are substantially reduced when using viscous-spring boundary model to take into account radiation damping. However, if the damping ratio of the dam is artificially increased to about 10%–15% for massless foundation input model, the joint opening and damage-cracking of the dam are comparable to the results obtained from the viscous-spring boundary model. [ABSTRACT FROM AUTHOR]

A number of vertical array records during eight destructive earthquakes in Japan are utilized, after discussing criteria for desirable requirements of vertical arrays, to formulate seismic amplification between ground surface and outcrop base for seismic zonation. A correlation between peak spectrum amplification and Vs (S-wave velocity) ratio (base Vs/surface Vs) was found to clearly improve by using Vs in an equivalent surface layer wherein predominant frequency or first peak is exerted, though the currently used average Vs in top 30 m is also meaningful, correlating positively with the amplification. We also found that soil nonlinearity during strong earthquakes has only a marginal effect even in soft soil sites on the amplification between surface and outcrop base except for ultimate soil liquefaction failure, while strong nonlinearity clearly appears in the vertical array amplification between surface and downhole base. Its theoretical basis has been explained by a simple study on a two-layered system in terms of radiation damping and strain-dependent equivalent nonlinearity. [ABSTRACT FROM AUTHOR]

Abstract: A self-centering designed bridge model that can eliminate residual deformations after earthquakes was constructed and tested by a shaking table. The bridge model consists of two precast RC bridge columns post-tensioned to the concrete deck and foundations by high strength rods. The concrete deck moves horizontally and columns rock on the foundation surface under the excitation of earthquakes. Research parameters include materials used in the rocking interface (plastic or steel), anchoring states and forms of ground shaking. Through the shaking table tests, the seismic performance of the bridge model with variable parameters was evaluated in terms of deck displacement, deck acceleration, vibrating frequency and damping ratio. Test results showed that the bridge model rocked up to at least 5% of the column rotation without damage or residual deformation. Seismic energy dissipated through each impact of column rocking was used to evaluate the radiation damping of the bridge system based on a previous study. Analytical damping of each test was calculated and compared with tested damping estimated from the modified response spectra and the measured displacement and acceleration at the concrete deck. [Copyright &y& Elsevier]

Abstract: Results are presented from detailed study of inverse processes of photoionization and electron-ion recombination of (hν +Al XI⇋Al XII+e), (hν +Al XII⇋Al XIII+e), (hν +Si XII⇋Si XIII+e), and (hν +Si XIII⇋Si XIV+e) using ab initio unified method. These are the first results on photoionization cross-sections (σ PI(nSLJ)) with autoionizing resonances and level-specific recombination rate coefficients, incorporating both the radiative and dielectronic recombination, for these ions. All fine structure levels with n ⩽10 and 0⩽ l ⩽9 are considered. A total of 98 fine structure levels with 1/2⩽ J ⩽17/2 for Al XI and Si XII, and 190 for Al XII and 189 for Si XIII with 0⩽ J ⩽10 are found. σ PI(nSLJ) show background enhancements due to core excitations and narrow high-peak resonances. Level-specific recombination rates show smooth decay with a small bump at high temperature. Present total recombination rate coefficients with temperature (α R(T)) show good agreement with available rates. Recombination rates over photoelectron energy (α R(E)) are presented for astrophysical and laboratory plasma applications. Total recombination rates for H-like Al XIII and Si XIV are given for completeness. Calculations are carried out in the relativistic Breit-Pauli R-matrix method using coupled channel wavefunctions. Inclusion of important atomic effects such as radiation damping, channel couplings, interference of DR and RR, and relativistic fine structure effects should provide accuracy within 10–15%. The comprehensive datasets are applicable for various models such as for ionization balance and recombination-cascade for UV and X-ray lines. [Copyright &y& Elsevier]

Quantum space-time nonlocality, i.e. retardation of the interaction between an electron and its own radiation field at distances about the Compton wavelength, is established. By taking into account a finite variance of electron-coordinate increment in the intrinsic coordinate system, the radiative damping coefficient is obtained as a divergence-free function of frequency that is not subject to the well-known paradoxes of the classical theory of radiative damping. A relation between radiative damping and the electromagnetic mass of the electron is found. [ABSTRACT FROM AUTHOR]

A computer model is developed to analyze the steady-state and transient responses of circular grating-coupled distributed feedback (CGC DFB) lasers. The model solved the time-dependent coupled-mode equations and carrier rate equation self-consistently by using a modified time-domain finite-difference method. The nonuniform distributions of carrier concentration and refractive index are taken into calculation. Using the model, the temporal and spatial variations of electric field and carrier concentration of the CGC DFB lasers are examined. It is found that the laser performance would be underestimated if the carrier-induced index change is ignored in the calculation. On the other hand, it is noted that the output power and resonant oscillation frequency as well as damping rate of the lasers could be maximized simultaneously by an optimal design for the grating. [ABSTRACT FROM AUTHOR]

We study the dynamics of an electron weakly coupled to a phonon gas. The initial state of the electron is the superposition of two spatially localized distant bumps moving towards each other, and the phonons are in a thermal state. We investigate the dynamics of the system in the kinetic regime and show that the time evolution makes the non-diagonal terms of the density matrix of the electron decay, destroying the interference between the two bumps. We show that such a damping effect is exponential in time, and the related decay rate is proportional to the total scattering cross section of the electron-phonon interaction. [ABSTRACT FROM AUTHOR]

Abstract: By using spin-noise type measurement we show that the resonance frequency of the reception circuit of classical NMR spectrometers does not match the Larmor frequency even if, in emission, the electronic circuit is perfectly tuned at the Larmor frequency and matches the amplifier impedance. We also show that this spin-noise method can be used to ensure a match between the Larmor frequency and the reception circuit resonance frequency. In these conditions, (i) the radiation damping field is in perfect quadrature to the magnetization and (ii) the NMR signal level and potentially the signal-to-noise ratio, are enhanced. This choice induces a change of the probe resonance frequency by several hundreds of kHz for 500 or 700MHz spectrometer. We show that the resulting mismatch condition for emission can be removed by adding other tuning and matching degrees of freedom located on the excitation line (or by symmetry on the reception line) decoupled to the probe resonance circuit by the crossed diodes. [Copyright &y& Elsevier]

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One of the main concerns regarding a decrease in stratospheric ozone is the consequential increase in the amount of ultraviolet (UV) radiation that reaches the lower atmosphere and the Earth's surface. Radiation at UV wavelengths where ozone absorbs strongly is detrimental to most biological species, including human beings, so a decrease in stratospheric ozone could have a significant impact on the biosphere. This concern has led to a significant increase in surface UV radiation research over the last two decades since the ratification of the Montreal Protocol. Studies include investigations into understanding the complicated absorption and scattering processes involved in the radiative transfer of UV through the atmosphere as well as research on the impacts of changes in UV radiation. Factors affecting surface UV radiation will be discussed, resources used to study surface UV radiation will be described and progress made in our understanding of surface UV radiation over the past two decades will be reviewed.[Traduit par la rédaction] L'une des principales inquiétudes concernant une diminution de l'ozone stratosphérique est l'augmentation consécutive de la quantité de rayonnement ultraviolet (UV) qui atteint la basse atmosphère et la surface de la terre. Le rayonnement de longueurs d'onde UV dans la région où il se trouve fortement absorbé par l'ozone est préjudiciable à la plupart des espèces biologiques, y compris les ětres humains, de sorte qu'une diminution de l'ozone stratosphérique pourrait avoir des conséquences importantes sur la biosphère. Cette inquiétude a mené à une augmentation importante de la recherche sur le rayonnement UV à la surface au cours des deux dernières décennies, depuis la ratification du Protocole de Montréal. Les études comprennent des investigations visant à comprendre les processus compliqués d'absorption et de diffusion qui jouent un rôle dans le transfert radiatif de l'UV à travers l'atmosphère de měme que des recherches sur les conséquences de changements dans le rayonnement UV. Nous discuterons des facteurs ayant une influence sur le rayonnement UV à la surface, nous décrirons les ressources utilisées pour étudier le rayonnement UV à la surface et nous examinerons les progrès réalisés dans la compréhension du rayonnement UV à la surface au cours des deux dernières décennies. [ABSTRACT FROM AUTHOR]

This paper uses a 3-D finite-difference time-domain method to accurately calculate the single-scattering properties of randomly oriented leaves and evaluate the influence of vegetation water content (VWC) on these properties at frequencies of 19.35 and 37.0 GHz. The studied leaves are assumed to be thin elliptical disks with two different sizes and have various VWC values. Although leaf moisture causes considerable absorption in the scattering process, the effective efficiencies of extinction and scattering of leaves essentially linearly increase with VWC, which is critical for forest remote sensing. Calculated asymmetry factors and phase functions also indicate that there is a significant amount of scattered energy at large scattering angles at microwave wavelengths. This paper can improve the modeling of the radiative transfer by vegetation canopies at the higher frequencies of the microwave spectrum, which is important for passive microwave remote sensing. [ABSTRACT FROM AUTHOR]

Abstract: The evolution of a propagating kink in a Sine-Gordon lattice is studied asymptotically using an averaged Lagrangian formulation appropriately coupled to the effect of the radiation. We find that unlike the continuum case the interaction with the Goldstone mode is important to explain the acceleration of the kink as it hops along the lattice. We develop a discrete WKB type solution to study the interaction of the kink and the radiation. In particular using this solution we show how to calculate the effect of the Peyrard and Kruskal resonant radiation in the energy loss of the kink. We obtain a set of modulation equation which explains qualitatively the evolution of the kink with remarkable quantitative agreement. [Copyright &y& Elsevier]

Abstract: A parametric study was carried out to investigate the hydrodynamics of a cylindrical wave energy absorber. Established methods of hydrodynamic analysis were applied to the case of a damped vertically oriented cylinder pivoted near the sea floor in intermediate depth water. The simple geometry provides a canonical reference for more complex structure shapes and configurations that may be considered for either wave energy conversion or wave energy absorption. The study makes use of the relative velocity Morison equation, with force coefficients derived from radiation and diffraction theory. Viscous effects were accounted for by including a drag term with an empirically derived coefficient, C D. A non-linear first-order formulation was used to calculate the cylinder motion response in regular waves. It was found that the non-linear drag term, which is often neglected in studies on wave energy conversion, has a large effect on performance. Results from the study suggest a set of design criteria based on Keulegan–Carpenter (KC) number, ratio of cylinder radius to water depth (a/h), and ratio of water depth to wavelength (h/L). Respectively, these parameters account for viscous, wave radiation, and water depth effects, and optimal ranges are provided. [Copyright &y& Elsevier]

A closed-loop control system for damping undesired longitudinal oscillations of particle bunches in heavy-ion synchrotrons is presented. The system is based on technologies like digital signal processors (DSPs), modern field programmable gate arrays (FPGAs), and direct digital synthesis (DDS). After describing the technological challenges, the design of the system is presented, and some theoretical background is given. Finally, measurement results are presented which are in good agreement with simulations and theoretical predictions. [ABSTRACT FROM AUTHOR]

The article discusses correction factors for theoretical exposure models used to determine the dose rates for radioactive patients. Patients with thyroid diseases are often treated with Na131I, creating an exposure risk for other people following therapy. Evaluation of the potentially absorbed dose is used to limit radiation exposure but theoretical exposure models can overestimate exposure rates. A study was conducted with patients treated with a radioiodine protocol. Theoretical exposure rates were compared with exposure amounts measured by a detector. The scattering of radiation can affect exposure rate measurement. A correction factor was developed from comparisons of exposure rates.

Abstract: Mathematical and computer methods have been used by others to predict the seismic behaviour of viscous damped structures, yet most analyses have not accounted for the influence of an unbounded foundation. In order to better understand the motional behaviour of structures during earthquakes, this study considers the effects of radiation damping and flexibility when characterizing the interaction between damped structures and unbounded soil media. Two numerical methods, the consistent-infinitesimal finite element cell method and a new quiet boundary method, are introduced here. Also, computer simulation is used to demonstrate the effects of radiation damping for far field, unbounded media. The differences in seismic responses of structures with and without consideration of radiation damping are significant. The results also make clear the importance of accounting for such effects when, for example, structural engineers incorporate structural control devices into their designs. [Copyright &y& Elsevier]

A mechanism of damped oscillations of a coronal loop is investigated. The loop is treated as a thin toroidal flux rope with two stationary photospheric footpoints, carrying both toroidal and poloidal currents. The forces and the flux-rope dynamics are described within the framework of ideal magnetohydrodynamics (MHD). The main features of the theory are the following: i) Oscillatory motions are determined by the Lorentz force that acts on curved current-carrying plasma structures and ii) damping is caused by drag that provides the momentum coupling between the flux rope and the ambient coronal plasma. The oscillation is restricted to the vertical plane of the flux rope. The initial equilibrium flux rope is set into oscillation by a pulse of upflow of the ambient plasma. The theory is applied to two events of oscillating loops observed by the Transition Region and Coronal Explorer (TRACE). It is shown that the Lorentz force and drag with a reasonable value of the coupling coefficient ( c d ) and without anomalous dissipation are able to accurately account for the observed damped oscillations. The analysis shows that the variations in the observed intensity can be explained by the minor radial expansion and contraction. For the two events, the values of the drag coefficient consistent with the observed damping times are in the range c d ≈2 – 5, with specific values being dependent on parameters such as the loop density, ambient magnetic field, and the loop geometry. This range is consistent with a previous MHD simulation study and with values used to reproduce the observed trajectories of coronal mass ejections (CMEs). [ABSTRACT FROM AUTHOR]

Several current particle-antiparticle collider designs require the beams to collide at a small angle. In order. to make the luminosity comparable to that of beams colliding head-on, transverse deflecting cavities known as crab cavities will be used. Additional modes, other than the required "crabbing" mode are excited by the beam and if these are excited resonantly then an appreciable dilution of the beam emittance will occur. We provide a singlemode analysis of the damping requirements on the dipole modes which will minimize the resulting angular kicks to the beams, by deriving an explicit solution for the frequency offset of the mode from a bunch harmonic for maximum deflection of bunches, using a novel analytical technique. [ABSTRACT FROM AUTHOR]

In large structures, the excitation energy produced by an impact force may not be sufficient to spread throughout the structure and excite global modes. Thus, one may be interested in the dynamic characterization of the excited part of the structure by taking into consideration the wave propagation through its boundaries. This radiation damping is a source of local damping and, as a consequence, causes modal complexity. The spectral element method is adopted here to describe the modal characteristics of a system with radiation damping. A semi-infinite Euler-Bernoulli beam+ whose span is interrupted by a spring with translational and rotational stiffness, is used as an example to illustrate the main features of the phenomenon characterized by modal complexity and to obtain a simple but meaningful experimental confirmation. This method could be useful in the modal characterization of a part of a structure. [ABSTRACT FROM AUTHOR]

This work is focused on the evolution of the dominant air–sea coupled mode in the equatorial and southeastern tropical Atlantic and the associated physical processes. It is shown that in June–August (JJA) the evolution of the dominant mode is mainly dynamically driven and displays a coherent warming or cooling pattern extending from the Angola coast toward the equator in the Gulf of Guinea. For anomalies peaking in JJA, the warming (cooling) is initiated near the Angola coast in March–May. It is suggested that SST anomalies along the coast and near the equator are physically connected. The air–sea interaction along the coast may be a major factor in triggering the development of SST anomalies near the equator, which is intensified by local positive feedbacks that may include Bjerknes and Ekman processes. In return, the warming or cooling near the equator weaken the SST anomalies along the coast by changing the direction of anomalous wind. Slow westward Rossby wave propagation may also play a role in stimulating the equatorial feedback. The thermodynamic processes affect the evolution of this mode. On average, the net surface latent heat flux anomalies are the leading damping factor, and the net surface sensible heat flux plays the same role on a smaller scale, while the net surface shortwave (longwave) radiation heating has a negative (positive) contribution to the SST variation. However, although on average the surface heat flux damps the SST anomalies, the role played by the heat flux varies with regions and components. Spatially, the latent and sensible heat flux as well as the longwave radiation damp air–sea coupling in the eastern South Atlantic near the Gulf of Guinea and amplify the coupling in the western equatorial ocean. The situation is opposite for the solar radiation. [ABSTRACT FROM AUTHOR]

Abstract: The strength of static magnetic field and the sensitivity of probe increase with the technique development of modern nuclear magnetic resonance (NMR) spectrometer. Radiation damping effect thus can no longer be neglected in solution NMR experiments with abundant spins. The cooperative effects of radiation damping and distant dipolar field (DDF) generate spin turbulence, which makes the evolution of magnetization unpredictable by traditional NMR theory and causes the uncertainty of acquired signals. The chaos phenomena can be described by introducing a radiation damping term into the Bloch equations. In this paper, we used two kinds of feedback control method to suppress the chaotic process. Numerical simulation indicates their feasibility and efficiency. [Copyright &y& Elsevier]

Abstract: In this paper, the dam–reservoir interaction problem is solved directly in the time-domain by modelling a part of the reservoir as a semi-infinite fluid-channel. Radiation damping is taken into account rigorously using an analytical solution with respect to the direction of wave propagation. The key step of the method consists of approximating the resulting modal flux–pressure relationship by a rational function in iΩ, which can be replaced by a system of linear equations in the frequency-domain. Two algorithms for the calculation of the coefficients of the rational function are described and compared. Finally, a system of first-order differential equations in the time-domain is obtained which completely represents the semi-infinite fluid-channel and can be coupled to the equations of motion of a dam and a bounded reservoir. The proposed strategy is verified considering a rigid dam. Moreover, the results of an earthquake analysis of a coupled flexible dam–reservoir system are presented. [Copyright &y& Elsevier]

Abstract: The presence and diagnosis of radiation damping could have major implications in NMR experiments with hyperpolarised gases, where accurate knowledge of the flip angle is imperative. In this work radiation damping was observed and investigated in a low-pass birdcage resonator (Q =250) with samples of hyperpolarised 3He at 1.5T. With an initially highly polarised (P =38%) sample of 3He in a spherical cell, the observed FID had a distorted line shape with a spectral line width that was three times that of the same sample in a virtually depolarised state (1Hz line width for P <1%). Moreover a linear relation between the sample’s magnetisation (M 0) and the line width of the spectrum was observed which is indicative of radiation damping. With highly polarised samples, significant radiation damping was observed and the effect was a lower than expected rate of depletion of M 0 in RF flip angle calibration experiments, which led to significant underestimate of the RF flip angle. To our knowledge this is the first report of radiation damping in a birdcage resonator with samples hyperpolarised or otherwise. Experimental observation of radiation damping could be used as means of measuring coil efficiency as an alternative to the geometrical filling factor (η) the definition of which is open to question for a birdcage resonator. Estimates of the birdcage filling factor from the measured damping time constants (η RD =0.4%) are compared to those derived from electromagnetic energy ratios (η E =1.6%) and metallic sphere frequency shift methods (η fs =1.4%). These figures are much lower than the simple volume geometrical upper limit of η v =3.7% derived from the ratio of cell volume to total coil volume (shield included). The physical explanation for this shortfall is that the bulk of the magnetic energy stored in the birdcage is spatially distributed predominantly between the rungs and the shield, and not in the coil centre where the sample is placed and where the field has its highest spatial homogeneity. [Copyright &y& Elsevier]

The radiation damping rate of plasmon resonances in pairs of spherical gold nanoparticles is calculated. The radiative line width of the plasmon resonance indicates significant far-field coupling between the nanoparticles over distances many times the particle diameter. The radiation damping of the coupled particle−plasmon mode alternates between superradiant and subradiant behavior when the particle spacing is varied. At small particle spacings where near-field coupling occurs, the radiation damping rate lies far below that of an isolated particle. [ABSTRACT FROM AUTHOR]