Long-range sound propagation in the northeastern Atlantic

Experimental data on the long-range propagation of explosion-generated signals are analyzed. The experiments were performed in the northeastern Atlantic under the conditions of a two-axis underwater sound channel. The sound field in the upper channel was governed by the vertical redistribution of the ray structure and sound energy under the influence of a smooth increase in the depth of the channel’s axis along the propagation path. The explosions were produced in the upper sound channel at a depth of 200 m, which was constant along the path. The time structure of the sound field is analyzed for the upper channel (a reception depth of 200 m) and for deeper layers lying somewhat below the boundary between the upper and lower sound channels (a reception depth of 1200 m). The deviation of the decay law obtained for the sound field level in the upper channel from the cylindrical law is used to estimate the attenuation coefficient. The low-frequency (several hundreds of hertz) attenuation coefficients experimentally determined with allowance for the sound field redistribution agree well with the calculated sound absorption in seawater. The attenuation coefficients determined by the differential method also agree well with the absorption calculated by the formulas proposed earlier. The analysis of the time structure of the sound field near the boundary between the upper and lower channels reveals a permanent insonification of this horizon by weak water-path signals propagating with the velocity typical of the signals traveling in the upper channel.     

Long-range sound propagation in the norwegian sea

The data of repeated experiments on the long-range propagation of explosion-generated and cw signals in the Norwegian Sea in summer conditions (with a fully-developed underwater sound channel) are presented. These data are used to analyze the spatial and time structures of the sound field, as well as to estimate the attenuation coefficient at frequencies within 63–630 Hz and to determine its frequency dependence. The spatial variability of the propagation conditions is analyzed on the basis of the experimental data obtained for the propagation of explosion-generated signals along a 815-km-long path crossing the Norwegian and Lofoten Hollows.     

Long-range dependence in interest rates and monetary policy

This Letter studies the dynamics of Brazilian interest rates for short-term maturities. The Letter employs developed techniques in the econophysics literature and tests for long-range dependence in the term structure of these interest rates for the last decade. Empirical results suggest that the degree of long-range dependence has changed over time due to changes in monetary policy, specially in the short-end of the term structure of interest rates. Therefore, we show that it is possible to identify monetary arrangements using these techniques from econophysics.     

Investigation of the zenith angle dependence of cosmic-ray muons at sea level

Angular distribution of cosmic-ray muons at sea level has been investigated using the Geant4 simulation package. The model used in the simulations was tested by comparing the simulation results with the measurements made using the Berkeley Lab cosmic ray detector. Primary particles’ energy and fluxes were obtained from the experimental measurements. Simulations were run at each zenith angle starting from θ?=?0° up to θ?=?70° with 5° increment. The angular distribution of muons at sea level has been estimated to be in the form I(θ)?=?I(0°) cos ⁿ (θ), where I(0°) is the muon intensity at 0° and n is a function of the muon momentum. The exponent n?=?1.95±0.08 for muons with energies above 1 GeV is in good agreement, within error, with the values reported in the literature.     

Long-range dependence in the volatility of commodity futures prices: Wavelet-based evidence

Commodity futures have long been used to facilitate risk management and inventory stabilization. The study of commodity futures prices has attracted much attention in the literature because they are highly volatile and because commodities represent a large proportion of the export value in many developing countries. Previous research has found apparently contradictory findings about the presence of long memory or more generally, long-range dependence. This note investigates the nature of long-range dependence in the volatility of 14 energy and agricultural commodity futures price series using the improved Hurst coefficient (H) estimator of Abry, Teyssière and Veitch. This estimator is motivated by the ability of wavelets to detect self-similarity and also enables a test for the stability of H. The results show evidence of long-range dependence for all 14 commodities and of a non-stationary H for 9 of 14 commodities.     

Long-range dependence and multifractality in the term structure of LIBOR interest rates

In this paper we present evidence of long-range dependence in LIBOR interest rates. We study a data set from 2000 to 2005, for six different currencies and various maturities. Empirical results suggest that the degree of long-range dependence decreases with maturity, with the exception of interest rates on Japanese Yen and on Indonesian Rupiah. Furthermore, interest rates have a multifractal nature and the degree of multifractality is much stronger for Indonesia (emerging market). These findings suggest that interest rates derivatives should take these features into account. Furthermore, fixed income risk and portfolio management should incorporate long-range dependence in the modeling of interest rates.     

Pinkness of the North Atlantic Oscillation signal revisited

The long episode of negative values in the North Atlantic Oscillation (NAO) index during the winter season 2009-2010 has attracted more attention to its predictability. Previous analyses (Fernández et al. (2003) [16] and Caldeira et al. (2007) [25]) by this same author group have established that the NAO signal behaves as a slightly red noise and therefore the prediction of the phenomenon must rely upon a deeper understanding of the underlying Physics. In this paper the authors address a predictability study of the NAO index by applying the “detrended fluctuation analysis” (DFA) to a composite series, completed with a bootstrap spectral analysis. The DFA provides a quantitative measure of predictability by computing several piecewise fits, either linear or higher degree polynomial ones, to a cumulative series of fluctuations associated to the original series. These newer measurements agree with the previous results.     

Parity dependence of nuclear level densities

A simple formula for the ratio of the number of odd- and even-parity states as a function of temperature is derived. This formula is used to calculate the ratio of level densities of opposite parities as a function of excitation energy. We test the formula with quantum Monte Carlo shell model calculations in the (pf+g(9/2)) shell. The formula describes well the transition from low excitation energies where a single parity dominates to high excitations where the two densities are equal.     

A chronological test of ocean-bottom spreading in the North Atlantic

Fission-track and K-Ar dating of basaltic glass from the Mid-Atlantic Ridge gives results which are consistent with the proposal of ocean-floor spreading. Correlation exists between the magnetic anomaly patterns over the Crest Mountains at 45°N and the age of the outcropping basalts. The observed sequences of ages progressing outward from the Median Valley 11,000, 230,000, 310,000, 750.000, 8,000,000, and 16,000,000 years constitute strong, direct support for the idea of ocean-bottom spreading.     

On the flavour dependence of polarized sea in the nucleon

We performed a phenomenological fit in order to get quark parton polarized distributions in the nucleon. The data on inclusive and semi-inclusive spin asymmetries measured on nucleon targets were used. We present the results for the flavour dependence of polarized sea inside a nucleon. An excellent agreement between inclusive and semiinclusive data was found in our model.     

Isospin dependence of the nuclear level density

Experiments on $\text{(ft)}{}^{\mathrm{+}}\text{/(}\text{ft)}{}^{\mathrm{?}}$ for mirror Gamow-Teller β-decay are reanalyzed in the light of recent work and new values for the Kubodera, Delorme and Rho second class parameters are deduced: ξ = ? (0.8 ± 2.0) × 10^?3MeV^?1; λ = (3.4 ± 3.9) × 10^?3. These values are compared with recent correlation experiments.     

Angular dependence of centimeter-band radar scattering by sea surface

Dependences of radar-scattering intensity on local slope of wind waves on the sea surface are obtained under real-sea conditions at a frequency of 20 GHz. To calculate the dependences, we use the fine structure of Doppler spectrum of backscattering. The results are qualitatively compatible with model calculations within the framework of the theory of perturbations on a two-scale surface and allow us to estimate the inhomogeneity of short gravity waves and gravity-capillary ripple, which are modulated by large-scale waves.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 5, pp. 538–546, May, 1996.The author thanks V. G. Makarov and A. Yu. Gurulev of the laboratory of geophysical hydrodynamics at the Pacific Institute for Oceanology for assistance in numerical processing of the data.This work was supported by the Russian Foundation for Fundamental Research (grant No 94-05016630).     

Carrier injection level dependence of post-breakdown metastability in semi-insulating GaAs

Recently, a room temperature electrically induced metastability in semi-insulating (SI)-GaAs has been reported in which the normally high resistance state of SI-GaAs converts into a low resistance state when breakdown electric fields are applied to the metal/SI-GaAs/metal system. The low resistance state continues to persist when the electric field is lowered below the breakdown bias and as such may be treated as metastable state of the material. This phenomenon is believed to be closely related to the ‘lock-on’ effect utilized in high power photoconductive semiconductor switches made from SI-GaAs. The present study seeks to understand the mechanism for this electrically induced metastability by studying the influence of the injection current on the metastable phase. The data favor an interpretation of the high current state of the SI-GaAs in terms of double carrier injection and the sustaining of an internal electron-hole plasma in the material.     

Interannual variability of the sea level at Trieste

Summary Some aspects of the interannual variability of the sea level at Trieste are studied by investigating the monthly arrangement of sea level peaks and their evolution from 1939 to 1991. The analysis is carried out by means of level thresholds, which allow to select sets of marked low and high daily mean sea level events. Extreme events correspond to well-defined weather synoptic configurations. As a result, the events tend to be concentrated in the first and last three months of the year, respectively, and their time evolution is sensitive to that of the annual mean sea level. Finally, the different mean duration of low- and high-level episodes is pointed out. Paper presented at the IX Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 8–10, 1992, Rome.     

Blue whale (Balaenoptera musculus) sounds from the North Atlantic

Sounds of blue whales were recorded from U.S. Navy hydrophone arrays in the North Atlantic. The most common signals were long, patterned sequences of very-low-frequency sounds in the 15-20 Hz band. Sounds within a sequence were hierarchically organized into phrases consisting of one or two different sound types. Sequences were typically composed of two-part phrases repeated every 73 s: a constant-frequency tonal "A" part lasting approximately 8 s, followed 5 s later by a frequency-modulated "B" part lasting approximately 11 s. A common sequence variant consisted only of repetitions of part A. Sequences were separated by silent periods averaging just over four minutes. Two other sound types are described: a 2-5 s tone at 9 Hz, and a 5-7 s inflected tone that swept up in frequency to ca. 70 Hz and then rapidly down to 25 Hz. The general characteristics of repeated sequences of simple combinations of long-duration, very-low-frequency sound units repeated every 1-2 min are typical of blue whale sounds recorded in other parts of the world. However, the specific frequency, duration, and repetition interval features of these North Atlantic sounds are different than those reported from other regions, lending further support to the notion that geographically separate blue whale populations have distinctive acoustic displays.     

Energy dependence of the rotational enhancement factor in the level density

The one-shell SU(3) energies are given and the corresponding level density is calculated approximately by use of a distribution function for the SU(3) quantum numbers. The calculation is extended to include many shells by a renormalization procedure and an effective one-shell interaction. The traditional level density is then obtained from the related mean-field hamiltonian which corresponds to a deformed harmonic oscillator potential. Various rotational enhancement factors are considered. Numerical results, are obtained and comparisons between the SU(3) and the traditional level densities allow the first computation of the energy dependence of the rotational enhancement factor. A transition from axial to spherical level density is found. A simple parametrization is suggested in terms of a deformation-dependent half-value energy and a transition width.     

Understanding the time dependence of atomic level populations in evolving plasmas

The time dependence of atomic level populations in evolving plasmas is studied using an eigenfunction expansion of the non-LTE rate equations. The work aims to develop understanding without the need for, and as an aid to, numerical solutions. The discussion is mostly limited to linear systems, especially those for optically thin plasmas, but the implicitly non-linear case of non-LTE radiative transfer is briefly discussed. Eigenvalue spectra for typical atomic systems are examined using results compiled by Hearon. Diagonal dominance and sign symmetry of rate matrices show that just one eigenvalue is zero (corresponding to the equilibrium state), that the remaining eigenvalues have negative real parts, and that oscillations, if any, are necessarily damped. Gershgorin's theorems are used to show that many eigenvalues are determined by the radiative lifetimes of certain levels, because of diagonal dominance. With other properties, this demonstrates the existence of both “slow” and “fast” time-scales, where the “slow” evolution is controlled by properties of meta-stable levels. It is shown that, when collisions are present, Rydberg states contribute only “fast” eigenvalues. This justifies use of the quasi-static approximation, in which atoms containing just meta-stable levels can suffice to determine the atomic evolution on time-scales long compared with typical radiative lifetimes. Analytic solutions for two- and three-level atoms are used to examine the basis of earlier intuitive ideas, such as the “ionizing plasma” approximation. The power and limitations of Gershgorin's theorems are examined through examples taken from the solar atmosphere. The methods should help in the planning and interpretation of both experimental and numerical experiments in which atomic evolution is important. While the examples are astrophysical, the methods and results are applicable to plasmas in general.     

Scale dependence and localization of the deformation of Arctic sea ice

A scaling analysis of the deformation of Arctic sea ice over a 3-day time period is performed for scales of 10 to 1000 km. The deformation field is derived from satellite radar data; it allows us to study how a very large solid body-the Arctic sea-ice cover-deforms under the action of heterogeneous forcing winds and ocean currents. The deformation is strongly localized at small scales, and can be characterized as multifractal. This behavior is well known for turbulent flows, and is here also observed for a deforming solid. A multiscaling extrapolation to the meter scale (laboratory scale) shows that, at the 3-day time scale, about 15% of the deformation is larger than 10(-4) s(-1), implying brittle failure, over 0.2% of the total area.     

Long-range forces in the universe

Possible existence of new long range forces and their interaction strength are critically analyzed and reviewed.