Specific features of the distribution of protons at small altitudes in near-equatorial latitudes according to data of satellite experiments. I. Energy spectrum

The spectra of protons with energies from 10 keV to 1 MeV as measured in experiments conducted at satellites and the MIR orbital station are presented. These data were obtained in the area of the geomagnetic equator at L < 1.15 and at altitudes up to 1000 km. The proton spectrum was determined during periods of geomagnetic perturbations and quite periods. These spectra were approximated using a kappa-function. The proton spectra in the near-equatorial area and in the ring current are compared. The proton’s life time in the near-equatorial area is estimated, taking into account charge exchange and Coulomb scattering. It is confirmed that the ring current is a main source of protons in the near-equatorial area at low altitudes.     

Analysis of thunderstorm neutron fluxes in the generation region and at orbital altitudes

Thunderstorm neutron generation and transport are modeled using the known properties of terrestrial gamma-ray flashes. The spectra of the neutron fluxes in the generation area and at orbital altitudes are analyzed and compared to the neutron albedo background, demonstrating the possibility of detecting thunderstorm neutrons in principle.     

Ion irradiation of TNOs: from the fluxes measured in space to the laboratory experiments

Cosmic ion irradiation is believed to be one of the processes driving the evolution of the surface materials on TNOs. We review the laboratory simulations of radiation effects induced in likely TNO materials. In particular the production of new molecular species, the formation of refractory organics, and the spectral changes induced in icy targets and in natural bitumens are described. In order to establish if the effects seen in the laboratory are in fact responsible for the surface properties of the TNOs, the present knowledge of the ion fluxes is reviewed. For objects at selected solar distances, dosage time is given versus depth into the material. As suggested by recent experiments, the contribution of the electronic energy loss and that due to knock-on collisions are given separately. The relevance of ion-irradiation for the physico-chemical properties of TNOs is demonstrated, and the need for future investigations is outlined. To cite this article: G. Strazzulla et al., C. R. Physique 4 (2003).     

Femtosecond filamentation in air at low pressures. Part II: Laboratory experiments

We present experimental studies of filamentation of a femtosecond laser pulse in air at low pressures. The evolution of the filament has been studied by measuring along the propagation axis the conductivity and the sub-THz emission from the plasma channel. We show experimentally that the filamentation process occurs at pressures as low as 0.2 atm in agreement with numerical simulations. Experimental and numerical results [A. Couairon, M. Franco, G. Méchain, T. Olivier, B. Prade, A. Mysyrowicz, Opt. Commun., submitted for publication] are compared and the possible sources of discrepancy are discussed.     

Application of proton radiography in experiments of relevance to inertial confinement fusion

Multi-Mev proton beams generated by target normal sheath acceleration (TNSA) during the interaction of an ultra intense laser beam (I≥10¹⁹ W/cm²) with a thin metallic foil (thickness of the order of a few tens of microns) are particularly suited as a particle probe for laser plasma experiments. The proton imaging technique employs a laser-driven proton beam in a point-projection imaging scheme as a diagnostic tool for the detection of electric fields in such experiments. The proton probing technique has been applied in experiments of relevance to inertial confinement fusion (ICF) such as laser heated gasbags and laser-hohlraum experiments. The data provides direct information on the onset of laser beam filamentation and on the plasma expansion in the hohlraum’s interior, and confirms the suitability and usefulness of this technique as an ICF diagnostic.     

The dynamics of clusters of flexible cylinders in axial flow: Theory and experiments

This paper presents an outline of the theory for the dynamics of clusters of independently supported flexible cylinders in axial flow, and an extensive discussion of the behaviour of such systems with increasing flow velocity, with special emphasis placed on the modal forms of free coupled motions of the cylinders and on the onset of instabilities. Results of an experimental study of the problem are also presented, involving systems of two, three or four cylinders supported at both ends and positioned symmetrically in the cylindrical test section of a water tunnel; experiments were conducted with different inter-cylinder gaps and support conditions. Both theory and experiment show that with increasing flow the system loses stability by buckling in one of its coupled modes, commonly in a pattern where cylinders move towards one another symmetrically, maximum displacement occurring just downstream of their midpoints. With increasing flow, theory predicts that other buckling instabilities are superimposed on the first; in the experiments the system remains buckled, changing modal patterns constantly; some of them correspond to those predicted by theory. At sufficiently high flow, oscillatory motion is observed, corresponding to theoretical flutter. Theory and experiment agree qualitatively in most essential features of the dynamical behaviour of the system, and quantitative agreement in the critical flow velocities for the onset of the first buckling instability is remarkably good.     

About estimations of a one-photon background in neutrino-oscillation experiments at low neutrino energies

The possible sources of one-photon radiation as a background for the quasi-elastic reaction ν _μ + n → μ⁻ + p are considered. They are relevant in experiments on determination of oscillation parameters at low neutrino energies (E _ν ∼ 1 GeV). The estimation for the cross section of the reaction ν _μ + n → μ ⁻ + p + γ is given at E _ν ^lab = 0.7 GeV as 0.65% of the corresponding cross section of quasielastic reaction. The mechanisms of quasi-elastic reaction are also considered at low neutrino energies on a quark level. The text was submitted by the authors in English.     

Soft and hard Pomeron in the structure function of the proton at low x and low Q^2

We study inclusive electroproduction on the proton at low x and low using a soft and a hard Pomeron. The contribution of the soft Pomeron is based on the Stochastic Vacuum Model, in which a nonperturbative dipole-dipole cross section can be calculated by means of a gauge invariant gluon field strength correlator. To model the hard Pomeron exchange we phenomenologically extend the leading order evolution of a power-behaved structure function, , proposed by López and Ynduráin. This extension allows to consider both the case and the region of higher on the basis of the same parametrization. A good simultaneous fit to the data on and on the cross section of real photoproduction is obtained for . With four parameters we achieve a for 222 data points. In addition, we use our model of the inclusive interaction to compute the longitudinal structure function . Received: 6 December 1998 / Revised version: 19 April 1999 / Published online: 18 June 1999     

Vibro-acoustic radiation of rigid bodies oscillating at large amplitude and low Mach number: Modelling and experiments

The acoustic radiation of vibrating bodies can usually be considered as a linear phenomenon as in most cases the vibration amplitudes of oscillating bodies are small compared to their dimension. However, in case of large amplitude and small Mach number, the large displacement amplitude of a vibrating body gives rise to geometric nonlinear acoustic effects. In this paper it is shown that the nonlinearity causes an asymmetry in the time signal of the radiated pressure as observed at a fixed position, resulting in harmonic distortion of the radiated sound field. These nonlinear effects can be analysed by the finite element method, using a linear fluid behaviour in combination with a moving mesh approach. This approach is implemented and used to predict the nonlinear sound radiation of lithographic stages oscillating at large amplitude and low Mach number. Acoustic experiments prove the validity of the analysis technique for the geometrical nonlinear phenomena. In addition the structural response of a nearby body excited by the nonlinear acoustic radiation of the stage is calculated and verified experimentally.     

Probability distribution of random paths in the Ising model at low temperature

Communications in Mathematical Physics - The random walk representation of then-dimensional Ising model exhibits the 2-point correlation function 〈σ(x) σ(y)〉 as a sum of...     

Pseudo-classical narrowing of the proton NMR absorption line at low temperature in the tunneling methyl system

The lineshape of the NMR absorption of a methyl group was measured down to 4.2 K for trichloromethylsilane, tetramethylsilane, and tetramethylpyrazine. A small reduction of the linewidth was observed at 30–50 K, which was attributed to averaging of the contribution of intermethyl dipole interactions by tunnel rotation of methyl groups. The mechanism of narrowing is discussed in relation to the magnitude of tunnel splitting and correlation frequency of fluctuation of the dipole interaction.     

The structural and dynamics neutron study of proton conductors: Difficulties and improvement procedures in protonated perovskite

With the expected development of Hydrogen as energy vector, there is a great impetus on the study of thermally stable proton conductors, the core of fuel cells, electrolysers and potential CO₂ converters. Prior to a successful industrial application one should first well determine their extremely complex physical and chemical behaviour related to the unique character of the proton. The difficulties in comprehension of the nature of mobile protonic species, their location (especially the differentiation between bulk and surface species) as well as local and long range dynamics are different as a function of the hydration level: i) in hydrates the number of protons not really involved in the conduction is much larger than that of protonic conducting species, ii) in non-hydrated materials, the total amount of conducting protons can be very small, as dopants in semiconductors, and similar to that arising from surface water and physisorbed protonic moieties. The attempts and difficulties to locate and identify the protonic species and their dynamics using the neutron techniques are discussed in the light of representative examples, with emphasis on proton conducting perovskites.     

Design of proton beam optics to realize beam distribution transformation in C-ADS HTBT

The linac to the transmuter beam transport line (LTBT) connecting the end of the linac to the spallation target is a critical sub-system in the accelerator driven system (ADS). It has the function of transporting the accel-erated high power proton beam to the target with a beam footprint satisfying the special requirements of the minor actinide (MA) transmuter. In this paper, a preliminary conceptual design of the hurling magnet to transmuter beam transport section (HTBT), as a part of the LTBT, for the China ADS (C-ADS) system is proposed and developed. In this design, a novel hurling magnet with a two dimensional amplitude modulation (AM) of 1 kHz and scanning of more than 10 kHz at 360 in transverse directions is used to realize a 300 mm diameter uniform distribution of beam on target. The preliminary beam optics design of C-ADS HTBT optimized to minimize the beam loss on the vacuum chamber and the radiation damage caused by back-scattering neutrons will be reported.     

Decondensation behavior of DNA chains induced by multivalent cations at high salt concentrations:Molecular dynamics simulations and experiments

Using molecular dynamics simulations and atomic force microscopy(AFM), we study the decondensation process of DNA chains induced by multivalent cations at high salt concentrations in the presence of short cationic chains in solutions.The typical simulation conformations of DNA chains with varying salt concentrations for multivalent cations imply that the concentration of salt cations and the valence of multivalent cations have a strong influence on the process of DNA decondensation. The DNA chains are condensed in the absence of salt or at low salt concentrations, and the compacted conformations of DNA chains become loose when a number of cations and anions are added into the solution. It is explicitly demonstrated that cations can overcompensate the bare charge of the DNA chains and weaken the attraction interactions between the DNA chains and short cationic chains at high salt concentrations. The condensation-decondensation transitions of DNA are also experimentally observed in mixing spermidine with λ-phage DNA at different concentrations of Na Cl/Mg Cl2 solutions.     

Modeling of stress distribution in granular piles: Comparison with centrifuge experiments

The classical method to compute stress and strain distributions in granular materials is recalled using continuum mechanics approach, and different rheological laws described. It is recalled that granular materials exhibit highly nonlinear response such as nonlinear elasticity, dilatancy and plastic flow. Finite element technique is used to predict the stress field distribution below a conic and a triangular pile. The dependence of the stress distribution on the rheological law, the bottom boundary condition and the building process (horizontal or inclined strata) is demonstrated. These results are compared to experimental data obtained in centrifuge. (c) 1999 American Institute of Physics.