Selection of modes by time reversal in a shallow sea

Modes of the waveguide are selected from signals of individual receivers by time reversing them with the use of the frequency response of a plane wave. The experimental distribution of the modes on the “arrival time — mode number” plane corresponds to the model of an ideal waveguide, differing in that higher modes advance lower ones in the experiment. A modification of the frequency response, which eliminates that contradiction, is proposed, the modification accounting for the dependence of the effective thickness of the waveguide on the frequency. As a result, a method of determining the distance between the sound source and receiver is proposed and tested, and the interpretation of the noise immunity of signal reception on the basis of the time reversal is presented. The experimental data are obtained in the Barents Sea, at depths of about 100 m and distances of 7, 10.5, and 12 km, with the signals in a band of 100–300 Hz.     

Quantum effects for parametric X-ray radiation during channeling: Theory and first experimental observation

The theory of X-ray radiation from relativistic channeled electrons at the Bragg angles—parametric X-ray radiation (PXR) during channeling (PXRC)—is developed while accounting for two quantum effects: the initial population of bound states of transverse motion and the transverse “form-factor” of channeled electrons. An experiment was conducted using a 255 MeV electron beam from a linac at the SAGA Light Source. We have identified a difference in the angular distributions of PXR and PXRC and obtained a fairly good agreement between the theoretical and experimental results.     

Measurement of gas solutions in small samples of intermetallic alloys

This article describes a measuring system that was proposed so as to enable measurement of the content of dissolved gas in samples, whose shape is determined by the specific requirements of the simultaneous measurements and cannot be modified to satisfy the requirements on solubility measurements. The apparatus — a dynamic UHV vacuum system — consists of a measuring chamber fitted with a heater based on electron bombardment, which permits a change in the sample temperature according to the selected schedule. The design of the heater permits reduction of additional heating in the actual measuring chamber, so that the increase in pressure caused by the action of the heater can be neglected. The measuring part of the system permits recording of changes in the overall pressure and partial pressures of selected gases in the measuring chamber. The lowest detectable amount of dissolved gas is less than 10⁻⁵ Pa m³. The results of measurement of the solubility of hydrogen in Ti and Fe aluminides in samples that are simultaneously used to measure the electrical conductivity are given as an example of the suitability of the apparatus for such measurements. This work is a part of research plan MSM 0021620834 financed by the Ministry of Education, Youth and Sports of the Czech Republic.     

Long-distance electron tunneling in proteins: A new challenge for time-resolved spectroscopy

Long-distance electron tunneling is a fundamental process which is involved in energy generation in cells. The tunneling occurs between the metal centers in the respiratory enzymes, typically over distances up to 20 or 30 such distances, the tunneling time—i.e., the time during which an electron passes through the body of the protein molecule from one metal center to another—is of the order of 10 fs. Here the process of electron tunneling in proteins is reviewed, and a possibility of experimental observation of real-time electron tunneling in a single protein molecule is discussed.     

Limitations to testing the equivalence principle with satellite laser ranging

We consider the possibility of testing the equivalence principle (EP) in the gravitational field of the Earth from the orbits of LAGEOS and LAGEOS II satellites, which are very accurately tracked from ground by laser ranging. The orbital elements that are affected by an EP violation and can be used to measure the corresponding dimensionless parameter η are semimajor axis and argument of pericenter. We show that the best result is obtained from the semimajor axis, and it is limited—with all available ranging data to LAGEOS and LAGEOS II—to η ≃ 2 × 10⁻⁹, more than 3 orders of magnitude worse than experimental results provided by torsion balances. The experiment is limited because of the non uniformity of the gravitational field of the Earth and the error in the measurement of semimajor axis, precisely in the same way as they limit the measurement of the product GM of the Earth. A better use of the pericenter of LAGEOS II can be made if the data are analyzed searching for a new Yukawa-like interaction with a distance scale of one Earth radius. It is found that the pericenter of LAGEOS II is 3 orders of magnitude more sensitive to a composition dependent new interaction with this particular scale than it is to a composition dependent effect expressed by the η parameter only. Nevertheless, the result is still a factor 500 worse than EP tests with torsion balances in the gravitational field of the Earth (i.e. at comparable distance), though a detailed data analysis has yet to be performed. While EP tests with satellite laser ranging are not competitive, laser ranging to the Moon has been able to provide a test of the EP almost 1 order of magnitude better than torsion balances. We show that this is due to the much greater distance of the test masses (the Earth and the Moon) from the primary body (the Sun) and the correspondingly smaller gradients of its gravity field. We therefore consider a similar new experiment involving the orbit of LAGEOS: testing LAGEOS and the Earth for an EP violation in the gravitational field of the Sun. We show that this test may be of interest, though it is a factor 300 less sensitive than in the case of the Moon due to the fact that LAGEOS is closer to the Earth than the Moon and consequently its orbit is less affected by the Sun. The limitations we have pointed out for laser ranging can be overcome by flying in low Earth orbit a spacecraft carrying concentric test masses of different composition with the capability, already demonstrated in ground laboratories, to accurately sense in situ any differential effects between them. An erratum to this article can be found at     

Polarization effects in Drell-Yan processes

Effects of polarization of hadrons and constituent quarks in Drell-Yan processes are considered; they are one of the most efficient tools for investigation of the quark structure of hadrons. Special attention is paid to such important parton distribution functions as the transversity and T-odd Sivers and Boer—Mulders functions whose study is necessary for understanding the effects connected with the nonzero transverse component of the quark momentum. An original method for direct extraction of transversity and Boer—Mulders function in the proton from the data on Drell—Yan processes, in which a maximum of one hadron in the initial state is transversely polarized, is presented. This method possesses a number of important advantages. The method is applied both to Drell—Yan processes with a valence antiquark (antiproton-proton and pion-proton collisions) and with a sea antiquark (proton-proton, proton-deuteron, and deuteron-deuteron collisions). Theoretical estimates of asymmetries and cross sections for setups at RHIC (BNL, US), NICA (JINR, Russia), COMPASS (CERN, Switzerland), PAX (GSI, Germany), and J-PARC (Japan) are presented for evaluation of the measurability of transversity and T-odd distributions. These theoretical estimates are accompanied by calculations of statistical uncertainties for measured asymmetries using the new Monte Carlo generator of Drell—Yan events. The duality of Drell—Yan processes and those of production of J/Φ resonance is studied, and it may allow one to considerably reduce statistical uncertainties of parton distributions. Kinematical conditions, for which this duality can be observed, are evaluated.     

Aggregating block copolymers as model systems to study polymer brush dynamics

Summary A-B block copolymers in a selective solvent—good for the B-species and bad for the A-species—form micellar aggregates with a compact A-core with a corona (brush) of B ?hairs? reaching into the solvent. Whereas polystyrene(PS)-polyisoprene(PI) in decane forms spherical micelles with a PS core of about 10 nm radius, polyethylene(PE)-polyethylenepropylene(PEP) forms micellar platelets, the shape of which is goverend by the habitus of PE crystallites forming the core. These planar aggregates have large (several hundred nanometers) lateral extension and a core thickness in the range of 10 nm. Both systems are model systems for polymer brushes, either on a spherical surface or planar. Neutron spin-echo experiments allow for the investigation of the dynamics of the brushes which reflects their viscoelastic properties. Results of neutron small-angle and spin-echo investigations are reported. The brush dynamics is explained using a model based on an idea of de Gennes describing the brush properties in terms of scaling relations for osmotic pressure and viscosity of a semi-dilute solution with inhomogeneous density. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Muon implantation in alkali metal hydrides

Zero, longitudinal and transverse field μSR measurements have been made on LiH, LiD and NaH. The primary motivation for the study was to elucidate the behaviour of the muons in the diamagnetic state and analysis of the time‐dependent zero field relaxation data suggests that negatively charged muonium, Mu^-, is formed and takes up a H^- vacancy site in these materials. Evidence is presented for a small (approximately 2%) reduction in the Mu^-–Li distance relative to the unperturbed nearest neighbour anion‐cation distances in the pure crystal lattices. This revised version was published online in August 2006 with corrections to the Cover Date.     

Evolution of large-scale correlations in a strongly nonequilibrium Bose condensation process

The evolution of off-diagonal correlation functions (for the example of a single-particle density matrix) in the process of Bose condensation of an initially nonequilibrium interacting gas is discussed. Special attention is given to the character of the decay of the density matrix at distances much greater than the size of the quasicondensate region. Specifically, it is shown that the exponential decay of the density matrix necessarily presupposes the presence of a chaotic vortex structure — a tangle of vortex lines — in the system. When topological order is established but there is no off-diagonal long-range order, the density matrix decays with distance according to a power law. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 7, 495–501 (10 April 1998)     

Impurity transport in percolation media

An equation describing the impurity transport in a percolation medium is obtained and the inferences drawn from this equation are analyzed based on the scale invariance concept. A determining part in this analysis is allowance for the sinks inherent in such media. At distances shorter than the correlation length, the particles are transferred in the regime of subdiffusion; at large distances, the concentration asymptotics exhibits a characteristic “tail” shape. In the medium occurring in the state above the percolation threshold, the impurity transport over time periods longer than the characteristic time related to the correlation length is well described by the classical equation with a renormalized diffusion coefficient. In this case, the concentration tail has a Gaussian shape at moderate distances and tends to subdiffusion asymptotics at very long distances. A relation is established between the factor determining renormalization of the diffusion coefficient and the factor determining a decrease in the number of active impurity particles at large times.     

Thermally activated muonium formation in Al2O3 and BaF2

Direct evidence is presented for thermally activated muonium formation in Al₂O₃ and BaF₂. In each case the signature of the transition is a transverse field depolarization rate of the prompt diamagnetic component which is much too large to be attributable to muon-nuclear dipolar couplings. Longitudinal field decoupling measurements in Al₂O₃ support the interpretation that the initial diamagnetic fraction converts into a state with a stongly coupled electron —-i.e., muonium.     

Sounding of an artificially perturbed ionosphere by means of an ionosonde/position finder with chirp modulation of the signal

We describe the operation of an ionosonde/position finder with chirp modulation of the signal. The first results of measuring the characteristics of short-wave radio signals scattered by artificial small-scale inhomogeneities, which were obtained by means of an ionosonde/position finder on the IZMIRAN—“SURA”—Rostov-on-Don path are presented. It was found that under certain ionospheric conditions, the angular and frequency selection of the scattered signals take place, in which case the signals are observed simultaneously in several frequency intervals (mainly, in three, namely, 6–9.5 MHz, 10–12 MHz, and 15–18 MHz) with different angles of incidence of radio waves in the vertical plane. In this case, the incidence angles were 20◦–35◦, 18◦–32◦, and 10◦–20◦ from the horizon for the first, second, and third frequency interval, respectively. Ionograms of oblique sounding were modeled allowing for the scattering of radio waves by artificial small-scale inhomogeneities. It is shown that at frequencies from 10 to 12 MHz, aspect conditions are fulfilled for the signals ducting along the high-angle beam (Pedersen mode). At frequencies 15–18 MHz (higher than the maximum observable frequency of the forward signal on the path IZMIRAN—Rostov-on-Don), aspect scattering conditions are fulfilled for the signals incident on a scattering area in the ascending part of the trajectory. At low frequencies 6–9.5 MHz (below the maximum observed frequency of the forward signal on the IZMIRAN—Rostov-on-Don path), the observable additional signals are caused by the scattering of radio waves by artificial inhomogeneities with subsequent relfection of the scattered signal from the Earth on the “SURA”—Rostov-on-Don path. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 4, pp. 267–278, April 2009.     

Cosmic microwave background and first molecules in the early universe

Besides the Hubble expansion of the universe, the main evidence in favor of the big-bang theory was the discovery, by Penzias and Wilson, of the cosmic microwave background (hereafter CMB) radiation. In 1990, the COBE satellite (Cosmic Background Explorer) revealed an accurate black-body behavior with a temperature around 2.7 K. Although the microwave background is very smooth, the COBE satellite did detect small variations—at the level of one part in 100 000—in the temperature of the CMB from place to place in the sky. These ripples are caused by acoustic oscillations in the primordial plasma. While COBE was only sensitive to long-wavelength waves, the Wilkinson Microwave Anisotropy Probe (WMAP)—with its much higher resolution—reveals that the CMB temperature variations follow the distinctive pattern predicted by cosmological theory. Moreover, the existence of the microwave background allows cosmologists to deduce the conditions present in the early stages of the big bang and, in particular, helps to account for the chemistry of the universe. This report summarizes the latest measurements and studies of the CMB with the new calculations about the formation of primordial molecules. The PLANCK mission—planned to be launched in 2009—is also presented.     

Methods of determining the magnetic penetration depth of high-κ superconductors fromμ + SR measurementsSR measurements

This paper explores several different methods of determining the magnetic penetration depth of high-κ superconductors from transverse field muon spin rotation (TFμ ⁺ SR) measurements. The methods include fitting the theoretical magnetic field distribution directly to the distribution of muon precession frequencies and calculating the penetration depth from the second or third moments of the field distribution. These three methods are discussed critically in the light of experimental noise and the effect of the superconductor's flux line lattice being distorted.     

Features of interaction of a narrow light beam with a smectic OCBP. Memory effect

1. A memory effect was observed in a smectic liquid crystal without artificially increasing its absorption in a wide temperature interval — from the nematic-phase temperature (t ≤ 35°C) to room temperature (t ⋍ 21–22°C). 2. We have shown that a narrow light beam produces in the crystal an optical inhomogeneity indicative of transverse anisotropy.     

Electron-hole pair condensation in a graphene bilayer

The pairing of electrons and holes due to their Coulomb attraction in two parallel, independently gated graphene layers separated by a barrier is considered. At a weak coupling, there exists the BCS-like pair-condensed state. Despite the fact that electrons and holes behave like massless Dirac fermions, the problem of BCS-like electron—hole pairing in the graphene bilayer turns out to be rather similar to that in usual coupled semiconductor quantum wells. The distinctions are due to the Berry phase of electronic wavefunctions and different screening properties. We estimate the values of the gap in a one-particle excitation spectrum for different interlayer distances and carrier concentrations. The influence of the disorder is discussed. At a large enough dielectric susceptibility of the surrounding medium, the weak coupling regime holds at arbitrarily small carrier concentrations. Localized electron—hole pairs are absent in graphene, thus the behavior of the system versus the coupling strength is cardinally different from usual BCS—BEC crossover. The text was submitted by the authors in English.     

Jet absorption and the corona effect at RHIC: Extracting collision geometry from experimental data

The possible existence of a finite formation time of strongly interacting plasma in nuclear collisions at RHIC is demonstrated from recent experimental data. To show this, we use a simple model based on Monte Carlo simulation of nucleus-nucleus collisions with realistic nuclear density distribution. The most striking feature of the experimental data—an absence of absorption of high transverse momentum pions in the reaction plane direction for mid-peripheral collisions—points to the presence of a surface zone with no absorption and strong suppression in the inner core. A natural interpretation of such a zone could be the plasma formation time T ~ 2–3 fm/c. The existence of a formation time could dramatically change our understanding of many experimentally observed features. With this assumption, we describe the angular anisotropy of high transverse momentum pions with respect to the reaction plane and the centrality dependence of the nuclear modification factor in Au + Au and Cu + Cu collisions. The text was submitted by the author in English.     

Microwave radiation of the atmosphere induced by a pulsed gamma source

The model problem of the perturbation of the atmosphere by an isotropic gamma source (pulse width Δτ ≤ 100 ns) situated at various altitudes (0 ≤ h ≤ 100 km) and assumed to be a “point” source was solved. The action of emitted gamma quanta caused the formation of a spatial region in the atmosphere containing highly excited atoms and molecules, the emission from which was recorded over a certain microwave range (0.8–1.0 GHz). The amplitudes of the electric component intensity of the field of noise Rydberg radiation over the range specified were calculated. Rydberg radiation duration, type, and the degree of polarization were estimated. The shape of the emission line and the character of broadening of signals received by two receivers situated at an altitude of H ₁ = 20000 km and on the surface of the Earth (H ₁ = 0 km) were analyzed. During measurements, both receivers were situated on the axis perpendicular to the surface of the Earth.     

1D stability analysis of filtering and controlling the solitons in Bose-Einstein condensates

We present one-dimensional (1D) stability analysis of a recently proposed method to filter and control localized states of the Bose–Einstein condensate (BEC), based on novel trapping techniques that allow one to conceive methods to select a particular BEC shape by controlling and manipulating the external potential well in the three-dimensional (3D) Gross–Pitaevskii equation (GPE). Within the framework of this method, under suitable conditions, the GPE can be exactly decomposed into a pair of coupled equations: a transverse two-dimensional (2D) linear Schr?dinger equation and a one-dimensional (1D) longitudinal nonlinear Schr?dinger equation (NLSE) with, in a general case, a time-dependent nonlinear coupling coefficient. We review the general idea how to filter and control localized solutions of the GPE. Then, the 1D longitudinal NLSE is numerically solved with suitable non-ideal controlling potentials that differ from the ideal one so as to introduce relatively small errors in the designed spatial profile. It is shown that a BEC with an asymmetric initial position in the confining potential exhibits breather-like oscillations in the longitudinal direction but, nevertheless, the BEC state remains confined within the potential well for a long time. In particular, while the condensate remains essentially stable, preserving its longitudinal soliton-like shape, only a small part is lost into “radiation”.     

Cosmic rays in the heliosphere

Summary This is a rapporteur paper for the XXIV International Cosmic-Ray Conference covering topics of anomalous cosmic rays, shock acceleration, modulation and transport theory, cosmic-ray gradients, corotating interaction regions, coronal-mass ejections, and solar neutrinos. Among the highlights of the meeting are —conclusive proof that most anomalous cosmic rays are singly charged,—undisputed detection of anomalous cosmic-ray hydrogen,—discovery of unexpectedly large anisotropies of pickup ions,—observation of pronounced solar rotational modulation of cosmic-ray fluxes to the highest heliolatitudes (∼80°) probed by the Ulysses spacecraft, and—new measurements of modulation effects sensitive to particle charge sign. Rapporteur talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.