A numerical study of the contributions of dust source regions to the global dust budget

Contributions of the nine potential dust source regions (North and South Africa, the Arabian Peninsula, Central Asia, eastern and western China, North and South America, and Australia) to the global dust budget are investigated with a global dust transport model. A six-year simulation (1990 to 1995) indicates that the greatest contributor to the global dust budget is found to be North Africa (the Sahara Desert), which accounts for 58% of the total global dust emission and 62% of the total global dust load in the atmosphere. Australian dust dominates the southern hemisphere. The dust emission and atmospheric dust load originating from East Asia (eastern and western China) are estimated to be 214 Tg yr^− 1 and 1.1 Tg, respectively, which are 11% and 6% of the total global dust emission and dust load. Dust from East Asia dominates the atmospheric load over China and Mongolia (about 70%), Korea (60%), Japan (50%), and the North Pacific Ocean (40%). The contribution of dust originating from regions other than East Asia to the dust load over these East Asian countries and the North Pacific Ocean cannot be ignored. The simulated total dust deposition flux on Greenland suggests a possible overestimation of the Saharan dust and an underestimation of the East Asian dust in the Arctic region, which may be a common problem with global dust transport models. Possible reasons for the underestimation of the East Asian dust are discussed.     

Experimental study on countermeasure against liquefaction-induced flotation of manhole using recycled materials packed in sandbags

The 2004 Niigata-ken Chuetsu earthquake in Japan caused serious damage to sewage facilities such as uplift of manholes and settlement of pavement above backfill soil for pipes.This paper deals with shake table tests in a 1 g gravity field on application of recycled materials for ground improvement to mitigation of liquefaction-induced flotation of manhole during earthquakes.The recycled materials used in tests were tire chips made of waste tires and crushed gravels made of waste reinforced concrete,and they were packed in sandbags.From the test results,it was confirmed that the recycled materials packed in sandbags could be treated as one of the countermeasures to restrain the flotation of manholes and settlement of ground surrounded by sandbags.     

Kinematic dynamos associated with large scale fluid motions

Abstract

A standard approach to the kinematic dynamo problem is that pioneered by Bullard and Gellman (1954), which utilizes the toroidal-poloidal separation and spherical harmonic expansion of the magnetic and velocity fields. In these studies, the velocity field is given as a combination of small number of toroidal and poloidal harmonics, with their radial dependences prescribed by some physical considerations. Starting from the original paper of Bullard and Gellman (1954), a number of authors repeated such analyses on different combination of velocity fields, including the most recent and comprehensive effort by Dudley and James (1989). In this paper, we re-examine the previous kinematic dynamo models, using the computer algebra approach initiated by Kono (1990). This method is particularly suited to this kind of research since different velocity fields can be treated by a single program. We used the distribution of magnetic energies in various harmonics to infer the convergence of the results.

The numerical results obtained in this study for the models of Bullard and Gellman (1954), Lilley (1970), Gubbins (1973), Pekeris et al. (1973), Kumar and Roberts (1975), and Dudley and James (1989) are consistent with the previously reported results, in particular, with the extensive calculation of Dudley and James. In addition, we found that the combination of velocities used by Lilley can support the dynamo action if the radial dependence of the velocity is modified.

We also examined the helicity distributions in these dynamo models, to see if there is any correlation between the helicity and the efficiency of dynamo action. A successful dynamo can result both from the cases in which the helicity distributions are symmetric or antisymmetric with respect to the equator. In both cases, it appears that the dynamo action is efficient if the volume integral of helicity over a hemisphere is large.     

Distinctive copepod community of the estuarine turbidity maximum: comparative observations in three macrotidal estuaries (Chikugo, Midori, and Kuma Rivers), southwestern Japan

Copepods are considered to be a vital component connecting the unique macrotidal environment to the high productivity and high biodiversity of the Ariake Sea. To examine the spatiotemporal succession of copepod communities, we conducted monthly sampling (vertical hauls of a 100-μm mesh plankton net) in three neighboring macrotidal estuaries between 2005 and 2006. Irrespective of the season, three copepod communities were recognized in relation to the relatively long gradients of salinity and turbidity along the Chikugo and Midori River estuaries. The oligohaline community (salinity 1–10) was observed at higher turbidities (>100 NTU), whereas the freshwater (salinity <1) and meso/polyhaline (salinity >10) communities were associated with lower turbidities (<100 NTU). The oligohaline calanoid Sinocalanus sinensis occurred only in the Chikugo River estuary, maintaining a large biomass (dry weight >10 mg m^?3) in or close to the well-developed estuarine turbidity maximum (ETM) throughout the year. In the Midori River estuary, the oligohaline community lacked S. sinensis and showed a minimum biomass during winter (<10 mg m^?3). In both estuaries, the freshwater community always remained at a small biomass (<1 mg m^?3), whereas the meso/polyhaline community showed marked seasonal changes in biomass (0.1–657 mg m^?3). The prevalence of higher salinities allowed only the meso/polyhaline community to occur in the Kuma River estuary. In summary, S. sinensis characterized the copepod community distinctive of the well-developed ETM, potentially serving as an important link to higher trophic levels during winter when copepods are scarce in other areas.     

Waste loading in shrimp and fish processing effluents: potential source of hazards to the coastal and nearshore environments

On average, only 30-40% of the global fishery production is consumed fresh and the rest 60-70% is processed for human consumption and other purposes. Although the proportion of the total fishery production that are processed remained relatively stable over the last decade, the total bulk of processed fishery commodity increased due to the steady increase in the total fishery production. Processing of large bulk of fish, shrimp and other aquatic organisms produces a corresponding large bulk of by-products and wastes. Although recent trend shows that much of these wastes are made into various value added products, considerable quantities are discharged as the processing effluents with large volume of waters used in processing. Reports suggest that fish and shrimp processing effluents are very high in biological oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), fat-oil-grease (FOG), pathogenic and other microflora, organic matters and nutrients, etc. Fish and shrimp processing effluents are, therefore, highly likely to produce adverse effects on the receiving coastal and marine environments. Although substantial reduction of the waste loads is possible by applying available simple techniques, this is not in practice in most part of the world due to lack of proper managerial and regulatory approach. The present paper reviews the characteristics of fish and shrimp processing effluents as a potential source of coastal and marine pollution and, using the existing data, analyzes the global production and discharge of waste loads from the processing plants and discusses available options for waste treatment and management.     

Paleoseismological evidence for non-characteristic behavior of surface rupture associated with the 2004 Mid-Niigata Prefecture earthquake, central Japan

The 2004 Mid-Niigata Prefecture earthquake sequence (mainshock magnitude, M_JMA 6.8), which occurred in an active fold-and-thrust belt in northern central Japan, generated a small thrust surface rupture (< 20 cm of vertical displacement) along a previously unmapped northern extension of the active Muikamachi–Bonchi–Seien fault zone, on the eastern margin of the epicentral region. To better understand past seismic behavior of the rupture, we conducted a paleoseismic trenching study across the 10-cm-high west-side-up surface rupture at the foot of a pre-existing 1.8-m-high east-facing scarp, which probably resulted from past earthquake(s). A well-defined west-dipping thrust fault zone accompanied by drag folding and displacing the upper Pliocene to lower Pleistocene strata and the unconformably overlying upper Pleistocene (?) to Holocene strata was exposed. The principal fault zone is connected directly to the 2004 surface rupture. From the deformational characteristics of the strata and radiocarbon dating, we inferred that two large paleoseismic events occurred during the past 9000 years prior to the 2004 event. These two pre-2004 events have a nearly identical fault slip (at minimum, 1.5 m), which is ≥ 15 times that of the 2004 event (∼ 10 cm). These paleoseismic data, coupled with the geological and geomorphological features, suggest that the 2004 event represented non-characteristic behavior of the fault, which can potentially generate a more destructive earthquake accompanied by meter-scale surface displacement. This study provides insight into the interpretation of past faulting events and increases our understanding of rupture behavior.     

Intergalactic ionized hydrogen in nearby groups of galaxies

Stability of the nearest 14 groups of galaxies is investigated by means of Jacobi's criterion. In this way these groups are found strongly unstable, except perhaps two. The result is unaltered when we discuss the validity of the assumptions needed for the computations and when we take into account the inaccuracy of the data. This apparent instability is tentatively explained by presence of intergalactic ionized hydrogen in each group. Physical parameters of the gas are derived by means of the general modified form of the virial theorem and through the assumption of the equiparatition among several modes of energy.The main results are the following: the ratios of the gas mass to the sum of the masses of the member galaxies are of the order of 10, densitiesg of the gas are about 10^–29 to 10^–28 g cm^–3, and temperatures are of the order of 10⁵K. Values of each physical parameter of the gas show little change from one group to the next. As significant correlation:G g ^0.9 is obtained betweeng and the densityG of the visible matter for the various groups; it may be compatible with the assumption that the intergalactic gas is a remnant of the condensation of the galaxies. Then it is shown that, at present, the observations are not opposed to our treatment. Finally, it is noticed that detection of intergalactic gas in the groups investigated will be very difficult, except if this gas is strongly cloudy.     

Geological prognosis ahead of a tunnel face

The locations of a specific geological boundary and aquifer were predicted, prior to reaching them, by a reflection method and the measurement of geothermic temperature. The determination was performed during tunnelling work which passed through the Median Tectonic Line in central Japan. The reflection method procedure was as follows. A P-wave was produced on the tunnel face by a small blasting. The location of the velocity layer boundary was predicted by the travel time of the direct wave and the reflected wave. The geothermic temperature was measured by a thermocouple which was set in the borehole at the face. The location of the aquifer was predicted by the thermal deviation between the measured value and the theoretical value that was determined from a mean geothermal gradient. Also, a water quality survey is performed, discussing the quality of the fissure water. In addition, we were able to confirm, using the Seismic Tomography method, that the sheared zone found, was the layer including lens-shaped low-velocity zone. The methods considered proved to be simple and effective for geological prognosis from within the tunnel.     

Influence of partial pressure of oxygen on thermoremanent magnetization of basalts

An electric furnace with oxygen-fugacity control was constructed. Oxygen partial pressure inside the furnace is controlled by flowing H₂ and CO₂ gas mixtures in different ratios. The system is set up inside a three-layer permalloy shield and a solenoid coil to produce an axial magnetic field. Oxygen fugacities are directly measured by an yttriadoped zirconia probe. The difference between the predicted and measured values of fugacities was small at 1,200°C, but a substantial discrepancy was observed at 780°C. Thermoremanent magnetization (TRM) was produced in various gas mixtures by heating the samples of recent basaltic lavas of Oshima (Japan) and Hawaii to 600 or 800°C for 1 h and cooling in a 0.4-Oe field. In general, the TRM is larger when produced in an oxidizing atmosphere and smaller in a reducing atmosphere. Alternating field demagnetization shows that the coercivity is also increased (decreased) when the TRM is acquired in oxidizing (reducing) conditions. However, these properties depend also on the previous heat treatments of the samples.