Baryon loading and the Weibel instability in gamma-ray bursts

The dynamics of two counter-streaming electron–positron–ion unmagnetized plasma shells with zero net charge is analysed in the context of magnetic field generation in gamma-ray burst internal shocks due to the Weibel instability. The effects of large thermal motion of plasma particles, arbitrary mixture of plasma species and space charge effects are taken into account. We show that, although thermal effects slow down the instability, baryon loading leads to a non-negligible growth rate even for large temperatures and different shell velocities, thus guaranteeing the robustness and the occurrence of the Weibel instability for a wide range of scenarios.     

Modeling households’ decisions on reconstruction of houses damaged by earthquakes––Japanese case study

In this study, households’ decisions on reconstruction of damaged houses were modeled, using questionnaire data in Japan. Characteristics of households’ decisions were investigated using parameter estimation results. The effects of subsidizing policy were evaluated as follows. First, subsidy for rebuilding may be effective for the households whose houses were heavily damaged. Second, there is a possibility that subsidy accelerated rebuilding of houses by the households having children. Third, subsidy for rebuilding may not be effective for elderly people’s households and households in depopulated areas.     

Dynamic properties of green water event in the overtopping of extreme waves on a fixed dock

A statistical model is developed to predict wave overtopping volume and rate of extreme waves on a fixed deck. The probability density function for the volume and rate of overtopping water are formulated based on the truncated Weibull distribution with the assumption of local sinusoidal profile for small amplitude waves. Sensitivity to the wave nonlinearity parameter and deck clearance is discussed. The statistical model is compared to laboratory data of the instantaneous free surface elevation measured in front of a fixed deck, and overtopping volume and overtopping rate measured at the leading edge of the deck. The statistical theory compared well with the measured exceedance probability seaward of the deck. The model prediction of the exceedance probability of deck overtopping gave qualitatively good agreement for large overtopping values.     

Abyssal current along the northern periphery of Shikoku Basin

Abyssal currents along the northern periphery of the Shikoku Basin south of Japan were measured by current meters moored off Cape Daio-zaki, Cape Shiono-misaki and Cape Ashizuri-misaki and on the eastern foot of the northernmost part of the Kyushu-Palau Ridge. Total length of observation off Cape Shiono-misaki was about five years including the periods of the Kuroshio large meander and no meander. Analyses of current data show:

1. Mean currents with a magnitude of 5–10 cm sec^?1 were observed during the whole observation period at all of current meters which were set 400 m above the sea bottom that was deeper than 4,500 m. The mean current for each current meter was parallel to the local bottom contour arond each station and was toward a direction looking the Nankai Trough (a trough located along the northern end of the Shikoku Basin) to the left.
2. At each station located above the shelf toe off Cape Daio-zaki and off Cape Shiono-misaki and on the foot of the Kyushu-Palau Ridge, the mean current increases with depth (a bottomward intensification of the mean current), and the vertical extent of the mean current is estimated to be about 2,000 m above the sea bottom.
3. At a station located at 2,600 m depth on the continental slope off Cape Shiono-misaki, no bottom-ward intensification of currents was observed.

These results strongly suggest that a steady abyssal flow exists in the depths deeper than about 3,000 m along the northern and northwestern peripheries of the Shikoku Basin. Existence of the abyssal circulation system is also suggested, at least, in the north of the Shikoku Basin.     

A Preliminary Study of Oceanic Bomb Radiocarbon Inventory in the North Pacific during the Last Two Decades

Radiocarbon and total carbonate data were obtained near the 1973 GEOSECS stations in the North Pacific along 30°N and along 175°E between 1993 and 1994. In these stations, we estimated radiocarbon originating from atomic bomb tests using tritium, trichlorofluoromethane and silicate contents. The average penetration depth of bomb radiocarbon during the two decades has deepened from 900 m to 1300 m. Bomb radiocarbon inventories above the average value for the whole North Pacific were found widely in the western subtropical region around 30°N both in the 1970s and 1990s, and its area in the 1990s was broader than that in the 1970s. In most of the North Pacific, while the bomb radiocarbon has decreased above 25.4, the bomb radiocarbon flux below 25.4 was over 1 × 10¹² atom m^-2yr^-1 in the subtropical region around 30°N. In the tropical area south of 20°N, the bomb radiocarbon inventory below 25.4 increased from zero to over 10 × 10¹² atom m^-2 during the last three decades. These distributions suggest that the bomb radiocarbon removed from the surface is currently accumulated with bomb ¹⁴C flux of over 1 × 10¹² atom m^-2yr^-1 below 25.4 in the subtropical region, mainly by advection from the higher latitude, and that part of the accumulated bomb ¹⁴C gradually spread southward with about 30 years.     

Hydrographic structure in association with deep boundary current in the north of the Shikoku Basin

High quality CTD data were collected in the north of the Shikoku Basin where an abyssal boundary current has been observed through direct current measurements. Analyses of hydrographic data showed:

1. Colder and saltier water (heavier water) compared to surrounding waters is found above the continental shelf-toe and the eastern flank of the Kyushu-Palau Ridge where the existence of the abyssal boundary current has been expected. The heavier water has a horizontal extent of about 50 km.
2. The heavier water has the vertical scale of 2000 m from the sea bottom, and is associated with a thermal wind shear which enhances a component of the flow toward a direction looking the Nankai Trough (a trough located along the northern end of the Shikoku Basin) to the left in the abyss. The assumed “level of no motion” at about 2500 m depth gives the geostrophically estimated current in a good agreement with the directly measured current.

A volume transport associated with the colder and higher salinity water is estimated to be about 2 Sv off Cape Shiono-misaki which may include a recirculation above the Nankai Trough. This is about twice of the transport estimated in the interior of the Shikoku Basin through a vorticity balance between the stretching term and latitudinal variation of the planetary vorticity.     

Effects of high-order nonlinear interactions on unidirectional wave trains

Numerical simulations of gravity waves with high-order nonlinearities in two-dimensional domain are performed by using the pseudo spectral method. High-order nonlinearities more than third order excite apparently chaotic evolutions of the Fourier energy in deep water random waves. The high-order nonlinearities increase kurtosis, wave height distribution and H_max/H_1/3 in deep water and decrease these wave statistics in shallow water. Moreover, they can generate a single extreme high wave with an outstanding crest height in deep water. High-order nonlinearities (more than third order) can be regarded as one cause of freak waves in deep water.     

Biomarkers of Exposure and Effects for Assessing Toxicological Risk of Endocrine Disrupters in Top Predators of the Mediterranean Sea

Abstract. Endocrine Disrupting Chemicals (EDCs) have the potential to alter hormone pathways that regulate reproductive processes in wildlife and fisheries. In this research the unexplored hypothesis that Mediterranean top predator species (such as large pelagic fish and marine mammals) are potentially at risk due to EDCs is investigated. In the Mediterranean environment, top predators accumulate high concentrations of polyhalogenated aromatic hydrocarbons (PHAHs) and toxic metals, incurring high toxicological risk. Here we illustrate the need to develop sensitive biomarkers for evaluation of toxicological risk in top marine predators (Xiphias gladius, Thunnus thynnus thynnus) and non-lethal techniques, such as non-destructive biomarkers, for the hazard assessment of threatened species exposed to EDCs, such as marine mammals ( Stenella coeruleoalba, Tursiops truncatus, Delphinus delphis and Balaenoptera physalus ).     

Bedrock structure in Adapazari, Turkey—a possible cause of severe damage by the 1999 Kociaeli earthquake

The 1999 Kocaeli earthquake brought serious damage to downtown of Adapazari. To study why strong motions were generated at the town, a bedrock structure was investigated on the basis of Bouguer gravity anomaly, and SPAC and H/V analyses of microseisms. It was revealed that, the basin consists of three narrow depressions of bedrock with very steep edges, extending in E–W or NE–SW directions along the North Anatolia faults, and the depth to bedrock reaches 1000 m or more. Downtown of Adapazari is located 1–2 km apart from the basin-edge. It is considered that, the specific configuration of bedrock amplifies ground motions at the downtown area by focusing of seismic waves and/or interference between incident S-waves and surface-waves secondarily generated at the basin-edge. Studying 3D bedrock structure is an urgent issue for microzoning an urban area in a sedimentary basin.