bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determinants of fruit removal in Geonoma pauciflora, an understory palm of neotropical forests
Authors: Pizo Marco Aurélio , Almeida‐Neto Mário 
Published: March 2009

AbstractCompetition for seed dispersers is supposedly a selective force that drives the evolution of plant reproductive traits. In the understory of tropical forests, such competition should be especially severe among bird‐dispersed plant species because (i) the production of copious fruit crops is limited by low light availability; (ii) there usually is a high density of fleshy fruited plants, and (iii) understory frugivorous birds are not abundant. In this paper, we took advantage of a high‐density population of Geonoma pauciflora, a bird‐dispersed palm species growing in the understory of the Brazilian Atlantic forest, to investigate the influence of plant traits and its immediate neighborhood on fruit removal. Intrinsic (crop and fruit sizes) and extrinsic traits (related to light availability) affected the fruit removal of G. pauciflora. Crop size had a greater influence than fruit size on the absolute number of fruits removed, whereas none of the investigated traits influenced decisively fruit removal efficiency (i.e., the proportion of an individual's crop removed). The influence of light availability was mostly indirect, through its positive influence on fruit production. A significant positive spatial autocorrelation in removal efficiency occurred among neighboring plants within a 7‐m radius, which is indicative of facilitation among neighboring individuals. The consequence of such positive spatial autocorrelation in removal efficiency for clonal plants such as G. pauciflora is that by attracting a frugivore a given ramet may promote the removal of fruits of other ramets, thus enhancing the reproductive output of the genet as a whole.
Cylindrical plasma equilibria maintained by means of a rotating magnetic field
Authors: Hugrass W. N. 
Published: March 2009

The equilibrium of a plasma cylinder confined by means of a steady axial magnetic field, Bα, and a transverse magnetic field, Bω, which rotates about the axis of the cylinder is analysed using a two-fluid model. It is shown that the electron fluid is tied to the rotating field provided that
The rotating field does not impart a steady azimuthal motion to the ions provided that However, the ion fluid acquires a steady azimuthal velocity due to electron-ion collisions. A self-consistent radial electric field is produced; this field plays an important role in establishing the steady ion flow.
Properties of Alfvén Solitons in a Finite-Beta Plasma J. Plasma Phys. vol. 27, 1982, p. 193
Authors: Spangler Steven R. , Sheerin James P. 
Published: March 2009

In the aforementioned paper we obtained an equation for non-linear Alfvén waves in a finite-β plasma, and investigated envelope soliton solutions thereof. The purpose of this note is to point out an error in the derivation of the soliton envelopes, and present corrected expressions for these solitons.The error arises from our assumption of translational invariance of both the envelope and phase of an envelope soliton expressed in equations (16) and (17). Rather, the phase is related to the amplitude by

where y ≡ x — VEt is a comoving co-ordinate, and all other quantities are defined in the above paper.
A modified truncation procedure for the BBGKY hierarchy
Authors: Myerscough C. J. 
Published: March 2009

The approximations usually made to truncate the BBGKY hierarchy for a plasma are discussed; their failure at small inter-particle separations leads to divergence of the Balescu—Lenard collision integral. A number of authors have obtained convergent kinetic equations, often by rather complicated methods.It is shown here that, if the standard truncation procedure is modified in a way which makes it less obviously inconsistent for close approaches, the standard methods maybe closely followed in deriving a convergent collision integral which agrees to dominant order with the ‘cutoff’ Balescu—Lenard integral and with the other work on the problem. In fact, the kinetic equation obtained is identical with the Balescu—Lenard equation except that the Coulomb potential is replaced by another that is non-singular at the origin. A physical interpretation of this result is suggested.
Ion density and current distributions in a propagating current sheet, determined by microwave reflection technique
Authors: Ellis W. R. , Jahn R. G. 
Published: March 2009

Electron and ion density distributions and the problem of electron/ion current partitioning are studied in a large radius Z-pinch in argon. Radial scans of the electron density and temperature proffles in the propagating sheet are obtained with a multi-purpose microwave interferometer which measures the complex refiexion coefficient from the plasma. At 70 GHz the probe resolves densities up to 1017 cm−3 over dimensions of ˜ 4 mm. Proffles of the electric and magnetic field components are obtained using standard probe techniques, and these data are used to calculate ion and electron current components in the sheet.Within the approximations of MHD theory, calculations show that the overall axial current pattern is built up of four interior zones alternately dominated by electron or ion current. This structure is observed to be closely correlated with variations of the Hall parameter, Wb/vc, about the value of unity through the sheet, which suggests that this parameter might be used as a guide to the relative importance of ion conduction in pinch discharge current sheets.
The growth and decay of resonant plasma oscillations excited by a small pulsed dipole
Authors: Fejer J. A. , Yu Wai-Mao 
Published: March 2009

The application of integration by the method of stationary phase to resonant oscillations excited by a small pulsed dipole is outlined. Both the growth and the decay of the oscillations near the plasma frequency are determined by this method at a fixed distance from the dipole, first in the absence and then in the presence of an external magnetic field. It is shown that Landau damping must be taken into account in the calculation of the growth but not of the decay. The oscillations are shown to spread out with a speed that is about half the mean thermal speed of electrons.Only the decay, not the growth, of the oscifiations near harmonics of the cyclotron frequency can be calculated by the same method. It is shown, moreover, that the amplitude, calculated for an observation point that moves away with sateffite velocity in an ionospheric environment, is only valid for time delays longer than about a minute. Such a result is therefore of no practical interest because the resonances observed from sateffites only last a few milliseconds. The erroneous nature of using such a result and the need for a different approach, such as that used in earlier work by the first author, are thus demonstrated.
Higher order resonances in a plasma
Authors: Lewak G. J. , Chen C. S. 
Published: March 2009

Resonances of a plasma driven into a weakly non-linear régime are investigated by two different models.(1) A cold plasma driven by an extended wave source is considered. It is found that resonances can occur at fractions as well as multiples of the normal mode resonances. For the fractional resonances the response amplitude grows linearly with time, whereas for the harmonic resonances it grows exponentially with time.(2) An unmagnetized Vlasov plasma is excited by a two-grid source below the plasma frequency. A resonance is shown to occur when the driving frequency approaches one half the plasma frequency. It is argued that such non-linear resonances may be responsible for the Alouette II observations of resonances at fractions of the plasma frequency.
A note on the semi-Lagrangian formulation of the Vlasov equation
Authors: Lewak G. J. 
Published: March 2009

In a previous paper [Lewak (1969), see also Pflrsch (1966) for related treatment], it was shown that the Vlasov equation in the Semi-Lagrangian (S.L.) formulation, may be written in a form resembling the fluid equations.plus Maxwell's equations with the source terms given bywhere n is the determinant of the tensor Tij = ∂gi/∂ζj, and N is the constant mean number density of electrons. The averaging notation < > here is defined bywhere f(σ) is the electron distribution function to be specified. The equations assume for simplicity a uniform fixed ion background, although this is not a necessary restriction and equations (1) and (2) need only an obvious modification to account for ions. The force fields in (1) are related to the electric field E and magnetic field B in the plasma by
.
Study of the oscillations stimulated at the upper hybrid resonance by a pulsed dipole antenna in a weakly inhomogeneous plasma
Authors: Graff Philippe 
Published: March 2009

The oscillations, excited by a pulsed dipole antenna at the upper hybrid resonance in a weakly inhomogeneous plasma, are investigated by the Wentzel—Kramers—Brillouin (WKB) approximation. In addition to a direct component, the field at a given distance from the transmitter is shown to consist in two obliquely reflected rays when the upper hybrid frequency WT is less than twice the electron gyro-frequency WH. The analytical expressions of the frequencies of the echoes intercepted by a moving receiver are given and the influence of the reception time t, the velocity VS of the receiver and the parameters of the plasma are thus pointed out.As distinct from previous studies, the static magnetic field B0, the velocity of the receiver, and the gradient of the electron density ∂N/∂X, are here vectors of arbitrary directions. The choice of such a general model makes it possible to interpret most of the experimental data concerning the upper hybrid resonance in the ionosphere.
Non-linear electrostatic plasma waves
Authors: Schamel Hans 
Published: March 2009

A solution of the one-dimensional time-independent Vlasov–Poisson system, including the condition of no net current, is constructed for a large class of electric potential functions φ(x), including periodic and solitary waves, as well as monotonic transitions. Displaced Maxwell distributions for the free particles, and an unshifted Maxwell distribution for the trapped ions, are used. The condition of positiveness of the unknown distribution function for the trapped electrons (which can be split into two parts, one depending solely on the chosen wave, the other on the given distributions) is examined. It is shown, for a non-linear wavethat this condition plays no rôle when the thickness l of the wave considerably exceeds the Debye length λD(l ≫ λD). If, however, l lies in the neighbourhood of λD(l ≳ λD), there exist limits for the free parameters. The smallest thickness lmin results if the Mach number M lies in the range 1 > M > 2 and the electronion—temperature ratio θ = Te/Ti exceeds 10. This confirms the view that the wave is a steepened ion-acoustic wave. lmin decreases with decreasing amplitude ϕmax of the wave and decreasing number of trapped ions, but does not lie below the Debye length as long as the wave is non-linear. In the linear case, the condition of positiveness imposes no restrictions.
Effect of the plasma inhomogeneity on the nonlinear damping of monochromatic waves
Authors: Asseo E. , Laval G. , Pellat R. , Welti R. , Roux A. 
Published: March 2009

We study the resonant interaction of particles with a monochromatic wave in an inhomogeneous plasma. The effects of the inhomogeneity are represented by a variable phase velocity of the wave. This introduces, in the wave frame, an inertial force due to the non-Galilean transformation of co-ordinates. Asymptotic expressions are obtained for the spatial damping coefficient of the wave in two physically different cases.(i) When the inertial force is greater than the force due to the trapping (strong inhomogeneity case) instead of the null asymptotic behaviour that one obtains in the homogeneous case, the spatial nonlinear damping coefficient behaves asymptotically like the linear Landau damping coefficient.(ii) When the inertial force is lower than the trapping force (weakinhomogeneity case), the spatial nonlinear damping coefficient for short distances is proportional to the ratio of the inertial force to the trapping force. For long distances, this coefficient is proportional to the square of the preceding ratio multiplied by the number of trapping lengths. In both cases, the proportionality coefficient is the linear spatial Landau damping rate.
Ion turbulence and thermal transport in laser-produced plasmas
Authors: Barr H. C. , Boyd T. J. M. 
Published: March 2009

In the interaction of high-intensity lasers with target plasmas the transport of thermal enelgy from the region in which the radiation is absorbed, to the cold dense plasma in the interior of the target, is an issue of central importance. It is also one of great complexity and as such is still largely unresolved. Ion-acoustic turbulence, self-generated magnetic fields and the inadequacy of classical transport theory have all been widely canvassed by way of explaining the observations which show thermal transport much reduced below what would be expected from conventional arguments.In this paper the role of ion turbulence as a flux limiter is addressed with particular regard to recent experiments in which target plasmas were irradiated by 1·06 µm neodymium laser light at irradiances of 1015W cm−2 and greater. Saturation levels of the ion-acoustic turbulence driven by a combination of a suprathermal electron current and a heat flux have been calculated on the basis of perturbed orbit theory.The levels of turbulence are found to be markedly lower than those commonly estimated from simple trapping arguments and too low to explain the thermal flux inhibition observed in the experiments used as a basis for the model.
Nonlinear interaction between two electrostatic harmonics in a plasma
Authors: Verheest Frank , Lewak G. J. 
Published: March 2009

The problem of harmonic and subharmonic generation of electrostatic waves in a general collisionless plasma, or in some other electromagnetic medium, is treated anew, using coupled-mode theory based on two time scales. A novel feature is that one of the two interacting waves may be a negative energy wave. Furthermore, the model describing the medium need not be specified, only a general linear and nonlinear conductivity or an equivalent description is required. Just by invoking wave energy conservation, the coupled-mode equations are obtained in such a way that unequivocal conclusions can be drawn.When both waves have positive energy, they exchange part of it in a periodic fashion, provided they both have some energy initially. If initially all the energy is in the fundamental, then all of it will eventually end up (irreversibly) in thesecond harmonic. If, on the other hand, all the energy is in the harmonic initially, then no generation of the fundamental (or subharmonic) will take place. If one of the two waves is a negative-energy wave, however, an explosive instability develops, and this regardless of initial values. For comparable conditions, the instability time depends on whether the negative energy wave is in the fundamental or in the upper harmonic.
Nonlinear Rayleigh–Taylor instability in hydromagnetics
Authors: Kalra G. L. , Kathuria S. N. 
Published: March 2009

Nonlinear theory of Rayleigh—Taylor instability in plasma supported by a vacuum magnetic field shows that the growth rate of the mode, unstable in the linear theory, increases if the wavelength of perturbation π lies betweenand 2πcrit. This might have an important bearing on the proposed thermonuclear MHD power generation experiments.
Theory and computer simulation of electron beam-plasma interactions in unbounded systems
Authors: Cuperman S. , Roth I. , Bernstein W. 
Published: March 2009

Computer simulation experiments of linear and nonlinear collisionless interactions between electron beams and background plasmas, for conditions relevant to active magnetospheric experiments, were carried out. Both electrostatic and electromagnetic interactions were simultaneously considered. The beam-plasma systems were infinite and homogeneous.The relative beam concentrations considered were ε ≡ nb/np, = 1, 0·1 and 0·01. In all cases, the background plasma (1 eV thermal energy) was penetrated by an electron beam of 1 keV streaming energy and 5 % thermal spread in the streaming direction.The paper presents a full description of the results and a brief discussion of their relevance to magnetospheric active experiments.The off-angle propagation case in unmagnetized plasmas is also briefly discussed.
Electrostatic plasma turbulence Part 2. The nonlinear dispersion relation and fluctuation spectrum
Authors: Barr H. C. , Boyd T. J. M. 
Published: March 2009

This paper complements an earlier one in which we considered the diffusion and drift across a magnetic field induced by a turbulent spectrum of fluctuations. We examine here the effects of these on the propagation of an unstable spectrum of modes. In the first paper a nonlinear dispersion relation is derived in a general closed form. This is then examined in the limint of short wavelengths (i.e.wavelengths much less than the gyroradii) and results of other authors are retrieved. In particular it is found that modes supported by the magnetic field are quashed whenever a particle may diffuse a wavelength per gyroperiod. For instance, in the context of current-driven instabilities (current across the magnetic field), electron cyclotron instabilities are quashed but not the ion-acoustic. The dispersion characteristics of the latter are unchanged except in that the drift which sustains the instability is altered by the presence of a turbulent (E × B) type drift. Depending on the level of fluctuations and magnetic field strength, this may amount simply to a rotation of the cone of unstable modes or may form a countercurrent which in turn suppresses the original current driving the instability.In the second half of the paper the problem of calculating the fluctuation spectrum of the electric field is addressed since this is essential for a self-consistent computation of the diffusion tensor and turbulent drift appearing in the nonlinear dispersion relation.
Electrostatic instabilities in anti-loss-cone plasma
Authors: Bhatia K. G. , Lakhina G. S. 
Published: March 2009

It is shown that both lower hybrid and modified electron acoustic instabilities can be excited in a hot anti-loss-cone plasma co-existing with a rarefied cold plasma, provided the anti-loss-cone factor, ρ, exceeds a value Tm/Tt, where Tm and Tt are the parallel temperatures of missing and trapped electrons respectively. These instabilities are excited in a bounded range of wavenumbers and the growth rates are enhanced with the increase of cold plasma density. ForTm/Tt < ρ > (Tm/Tt)½both the instabilities are of resonant type whereas for ρ > (Tm/Tt)½ both may be converted into non-resonant types. These instabilities are expected to give rise to the heating of protons as well as electrons in the magnetosphere beyond the plasmapause.
Stability of a plasma stream in a magnetic field
Authors: Lamont A. , Taylor J. C. , Laing E. W. 
Published: March 2009

The system studied is a plasma streaming parallel to a uniform magnetic field with a velocity which varies in a transverse direction. The flow is bounded at y =± a by perfectly conducting planes.The Poisson-Vlasov equations are used to derive an integro-differential equation for ø the Fourier transform of the electrostatic potential. The kernel of this equation is expanded using a small Larmor radius expansion for ø and for the equilibrium distribution function f0.
Absolute maxmum growth rates and enhancement of unstable electromagnetic ion–cyclotron waves in mixed warm–cold plasmas
Authors: Cuperman S. , Gomberoff L. , Sternlieb A. 
Published: March 2009

SummaryWe calculated relative and absolute maximum linear growth rates of the electromagnetic ion–cyclotron instability produced by the addition of cold plasma to an infinite uniform anisotropic plasma. In this, both accurate numerical solution of the linearized dispersion relation, and approximate analytic calculations, were carried out, and the results were compared critically.Qualitatively, results similar to those obtained in the past for the right-hand polarized electron–cyclotron electromagnetic (whistler) waves (Cuperman & Landau 1974) are found also for the left-hand polarized waves considered in this paper. Specifically, the electromagnetic ion–cyclotron instability in a warm, anisotropic proton plasma, characterized by Pp ≡ βP,A2p(Ap + 1) ≲ 1, may be significantly enhanced by addition of cold plasma.
The biophysics of ligand–receptor interactions
Authors: DeLisi Charles 
Published: March 2009

For the cells of an organism to act in the coordinated fashion necessary for complex functioning, they must be able to receive and transmit information. Information transfer is mediated by molecules released by the cells and may be local, as in the case of neurotransmitters, or long range, as in the case of hormones. It is apparent, however, that irrespective of the range of interaction, a cell must be able to distinguish, with a high degree of precision, the signals relevant to it from an enormous flow of background noise.Molecular recognition at the cell surface is mediated by receptors: cell surface glycoproteins that usually form an integral part of the plasma membrane (see, for example, Cuatrecasas & Greaves, 1978). Typically, receptors bind the ligands they are designed to recognize with affinities of the order of 108M-1, and they translate that interaction into a sequence of signals that ultimately lead to biological activity.
The application of fluorescent probes in membrane studies
Authors: Azzi Angelo 
Published: March 2009

Fluorescence has been used in biochemical studies for many years but only recently has the information content and the practical applicability of the fluorescence method been fully realized.Following the early studies of Newton (1954) and Weber (11954) and after the initial utilization of fluorescent probes by Chance and coworkers (Azziet al.1969) and Tasakiet al.(1968), in the study of membranes, the use of fluorescence to provide structural information at microscopic or molecular levels in biological membranes has become widespread. widespread. The application of the fluorescence technique to biological systems has progressed parallel to the development of a theoretical basis for fluorescence data interpretation and the synthesis of a large number of fluorescent probes, organic molecules having fluorescence characteristics that are dependent on their environment.
A comparison of X-ray small-angle scattering results to crystal structure analysis and other physical techniques in the field of biological macromolecules
Authors: Kratky O. , Pilz I. 
Published: March 2009

In principle, there exist two ways to contribute to structure determination of macromolecules by X-ray diffraction: (a) by analysing diffraction data obtained from the crystalline state, and (b) by interpretation of X-ray small-angle scattering from particles in solution.The brilliant achievements of X-ray crystal-structure analysis of macromolecules, initiated by the works of Perutz on heamoglobin and Kendrew on myoglobin, are well known and it is evident that its detailed elution of secondary, tertiary and quaternary structure cannot be matched by any other means. However, a number of necessary prerequisites for a successful application, as, for example, the availability of well-defined crystals and heavy atom labelled derivatives thereof to surmount the problem of phase determination are not always given.