Self-initiating MUSIC-based direction finding in underwateracoustic particle velocity-field beamspace

This paper introduces a novel blind MUSIC-based (MUltiple SIgnal Classification) source localization algorithm applicable to an arbitrarily spaced three-dimensional array of vector hydrophones, each of which comprises two or more co-located and orthogonally oriented velocity hydrophones plus an optional pressure hydrophone. This proposed algorithm: (1) exploits the incident sources' angular diversity in the underwater acoustic particle velocity field; (2) adaptively forms velocity-field beams at each vector-hydrophone; (3) uses ESPRIT to self-generate coarse estimates of the sources' arrival angles to start off its MUSIC-based iterative search with no a priori source information; and (4) automatically pairs the x-axis direction-cosine estimates with the y-axis direction-cosine estimates. Simulation results verify the efficacy of this proposed scheme     

A Detailed Study on the Equal Arrival Time Surface Effect in Gamma-Ray Burst Afterglows

Due to the relativistic motion of gamma-ray burst remnant and its deceleration in the circumburst medium, the equal arrival time surfaces at any moment are not spherical, rather, they are distorted ellipsoids. This will leave some imprints in the afterglows. We study the effect of equal arrival time surfaces numerically for various circumstances, i.e., isotropic fireballs, collimated jets, density jumps and energy injection events. For each case, a direct comparison is made between including and not including the effect. For isotropic fireballs and jets viewed on axis, the effect slightly hardens the spectra and postpones the peak time of the afterglows, but does not change the shapes of the spectra and light curves significantly. In the cases of a density jump or an energy injection, the effect smears out the variations in the afterglows markedly.     

Investigating the impact of the Chi‐Chi earthquake on the occurrence of debris flows using artificial neural networks

Debris flows have caused enormous losses of property and human life in Taiwan during the last two decades. An efficient and reliable method for predicting the occurrence of debris flows is required. The major goal of this study is to explore the impact of the Chi‐Chi earthquake on the occurrence of debris flows by applying the artificial neural network (ANN) that takes both hydrological and geomorphologic influences into account. The Chen‐Yu‐Lan River watershed, which is located in central Taiwan, is chosen for evaluating the critical rainfall triggering debris flows. A total of 1151 data sets were collected for calibrating model parameters with two training strategies. Significant differences before and after the earthquake have been found: (1) The size of landslide area is proportioned to the occurrence of debris flows; (2) the amount of critical rainfall required for triggering debris flows has reduced significantly, about half of the original critical rainfall in the study case; and (3) the frequency of the occurrence of debris flows is largely increased. The overall accuracy of model prediction in testing phase has reached 96·5%; moreover, the accuracy of occurrence prediction is largely increased from 24 to 80% as the network trained with data from before the Chi‐Chi earthquake sets and with data from the lumped before and after the earthquake sets. The results demonstrated that the ANN is capable of learning the complex mechanism of debris flows and producing satisfactory predictions. Copyright © 2009 John Wiley & Sons, Ltd.     

A ultraluminous X-ray source associated with a cloud collision in M 99

The Sc galaxy M 99 in the Virgo Cluster has been strongly affected by tidal interactions and recent close encounters, responsible for an asymmetric spiral pattern and a high star formation rate. Our XMM–Newton study shows that the inner disc is dominated by hot plasma at kT ≈ 0.30 keV, with a total X-ray luminosity of ≈10⁴¹ erg s⁻¹ in the 0.3–12 keV band. At the outskirts of the galaxy, away from the main star-forming regions, there is an ultraluminous X-ray source (ULX) with an X-ray luminosity of ≈2 × 10⁴⁰ erg s⁻¹ and a hard spectrum well fitted by a power law of photon index Γ≈ 1.7. This source is close to the location where a massive H  i cloud appears to be falling on to the M 99 disc at a relative speed of >100 km s⁻¹. We suggest that there may be a direct physical link between fast cloud collisions and the formation of bright ULXs, which may be powered by accreting black holes with masses ∼100 M_⊙. External collisions may trigger large-scale dynamical collapses of protoclusters, leading to the formation of very massive (≳200 M_⊙) stellar progenitors; we argue that such stars may later collapse into massive black holes if their metal abundance is sufficiently low.     

The stability of molecular iodine in seawater

Both theoretical considerations and laboratory studies suggest that molecular iodine undergoes rapid hydrolysis to form hypoiodite when it is added to seawater. Previous experimental designs were not suitable for studying the fate of molecular iodine in seawater.     

A study of three extraction methods for hydrocarbons in marine sediment

Three methods for the extraction of hydrocarbons from surface sediments were studied. The methods were: (1) digestion by methanolic-KOH and extraction with methanol; (2) Soxhlet extraction with chloroform and (3) Soxhlet extraction with carbon tetrachloride. Results are presented and compared.     

High resolution aerosol optical thickness retrieval over the Pearl River Delta region with improved aerosol modelling

Aerosol retrieval algorithms for the MODerate Resolution Imaging Spectroradiometer (MODIS) have been developed to estimate aerosol and microphysical properties of the atmosphere, which help to address aerosol climatic issues at global scale. However, higher spatial resolution aerosol products for urban areas have not been well researched mainly due to the difficulty of differentiating aerosols from bright surfaces in urban areas. Here, a new aerosol retrieval algorithm using the MODIS 500 m resolution image...     

First incoherent scatter radar observations of ionospheric heating on the second electron gyro-harmonic

We report first results from a unique experiment performed at the HIPAS ionospheric modification facility in conjunction with the Poker Flat incoherent scatter radar in Alaska. High-power radio waves at 2.85 MHz, which corresponds to the second electron gyro-harmonic at ~245 km altitude, were transmitted into the nighttime ionosphere. Clear evidence of F-region ionospheric electron temperature enhancements were found, for the first time at this pump frequency, maximizing when the pump frequency is close to the second gyro-harmonic and double resonance. This is consistent with previous pump-enhanced artificial optical observations. We estimate the plasma heating efficiency to be approximately double that for higher pump frequencies.     

海南海莲红树林土壤CH4的产生及其某些影响因素

全球CH₄预算的估算表明,湿地是大气CH₄最大的生物排放源[1].旨在估算全球大气CH₄湿地源强的工作大多集中在内陆淡水环境,因为在此环境的CH₄通量较大[2].国外对海岸盐沼的CH₄排放也有一些报道,发现其通量变化范围较大,并进而研究了温度、土壤湿度、盐度以及土壤有机碳含量等因素对CH₄排放的影响[3].     

How nature uses overland flow regime to maximize equilibrium detention storage and flood attenuation

Equilibrium detention storage is an important parameter as it has a proportional effect on flood attenuation. In this paper, based on the kinematic wave theory, a working formula for the equilibrium detention storage of an overland plane with upstream inflow has been derived. Since the flow regime over a concrete plane can vary throughout the entire range laminar to turbulent, this case has been selected to examine the effect of flow regime on the equilibrium detention storage. In the examination, the derived formula has been applied to four flow regimes: (a) laminar, (b) transitional, (c) near turbulent, and (d) turbulent. The examination shows that for planes with a small discharge, laminar flow gives the maximum detention storage. For planes with a medium discharge, transitional flow gives the maximum detention storage, and for planes with a large discharge, near turbulent flow gives the maximum detention storage. The flow regime can cause more than two‐fold increase in detention storage. All these results can be attributed to the respective flow resistance, and have been endorsed with analyses of the water surface profile and the rising limb of the hydrograph. Finally, relating the results to real‐life situations, it shows that the flow regime that gives the maximum detention storage is also the dominating flow regime in nature. Hence, extraordinarily, the flow regimes that exist in nature in fact provide maximum flood attenuation. Copyright © 2008 John Wiley & Sons, Ltd.