Cascade processes in the surface layers of pulsars

The influence of the Landau-Pomeranchuk effect on the development of a shower generated by ultrarelativistic particles bombarding the surface of a pulsar is discussed. Because of this effect, the path length of the shower increases while low-energy photon generation is strongly suppressed. In view of this, the mechanism of pair production suggested by Cheng, Ruderman, and Jones for the pulsar magnetosphere, may be essential only for pulsars whose magnetic field intensity at the surface lies in a relatively narrow range of aroundB 10¹² G.     

Bidirectional Type III Solar Radio Bursts

Bidirectional coronal type III bursts are modeled by combining a model of coronal electron heating and beam generation via time-of-flight effects with semiquantitative estimates of quasilinear relaxation. Electromagnetic emissivities are estimated by extending the recently developed theory of interplanetary type III bursts to coronal emissions, including its features of stochastic Langmuir-wave growth and three-wave interactions. The results are investigated for heating on open and closed coronal field lines and are compared with observations of normal, reverse-slope, bidirectional, and inverted-J and -U coronal type III radio bursts. Harmonic emission is predicted to dominate at plasma frequencies above roughly 100 MHz where the efficiency of fundamental emission falls off steeply, while its free-free reabsorption rises. The model also explains the observed trends in the likelihood of occurrence of normal, reverse-slope, and bidirectional coronal type III bursts.     

多维体视方法论及其在地球科学研究中的意义

本文阐述”多维体视方法论”,主张立体透视与动态、多维地看问题;它起源于医学CT(计算机层析学)透视成像、核磁共振(MRI)等体视学方法研究疾病的生理解剖结构、病理特征、监测人体有关器官的各种变化,是行之有效的方法;已成功地应用于检测工业器械、航天器及地下结构等物体的内部结构,从而发展和演绎出来的认识论方法。在医学领域将CT、MRI所得二维信息和断面图像、对病灶区引入“体显示”和“面显示”等可视化技术,将能充分反映不同疾病的病理、药理特征;在航天、地学等领域同样应用着CT多维“可视化技术”。本文试图发扬综合预测的学术思想,将医学临床应用CT、核磁共振、体视学方法结合研究其他制约因素指标,从而区分出疾病的原发、继发分期,导致绝症的进程和前兆,概括为“多维体视预测方法”;也适用于地震孕育、强震发生与火山喷发预测的研究。     

Magnetic stratigraphy observed in ferromanganese crust

Summary. A sample of ferromanganese crust deposit (SCHW-1D) was cut into two sets of 1 mm slices for palaeomagnetic study. Alternating field and thermal demagnetization, and isothermal remanent magnetization analyses were performed on each thin slice. The results reveal the presence of a stable magnetism and both normal and reversed polarity intervals in the specimens. The observed polarity intervals cannot be confidently correlated with the geomagnetic polarity time-scale of the last 10 Myr due to the polarity overlap inherent in the sampling technique. But the results confirm the slow accretion rate of ferromanganese deposit determined by ¹⁰Be method and suggest potential use of ferromanganese deposits in palaeomagnetic and tectonic studies.     

Global comparison of the regional rainfall results of enhanced greenhouse coupled and mixed layer ocean experiments: Implications for climate change scenario development

The extent of agreement amongst current global climate models (GCMs) on the global pattern of rainfall change simulated under enhanced greenhouse conditions is assessed. We consider the results of five experiments which use a simple mixed layer ocean formulation and five which use a fully dynamic ocean model (coupled experiments). For many regions of the northern hemisphere there is strong agreement amongst both mixed layer and coupled experiments on the sign of simulated rainfall change. However, in the southern hemisphere there are large, and apparently systematic, differences between the coupled and mixed layer experiments. In particular, whereas the mixed layer experiments agree on simulated rainfall increase in summer in the tropics and subtropics of the Australian sector, the coupled experiments agree (although more weakly) on rainfall decreases. These differences appear to relate to the much reduced warming simulated by the coupled experiments in the high latitudes of the southern hemisphere. However, recent oceanographie evidence suggests that this suppressed warming may be considerably overestimated. We conclude therefore that despite the in-principle advantages of coupled models, it may be too soon to base some regionally specific climate change scenarios solely on the results of coupled experiments.     

Estuarine Habitat and Demographic Factors Affect Juvenile Chinook (<Emphasis Type="Italic">Oncorhynchus tshawytscha</Emphasis>) Growth Variability in a Large Freshwater Tidal Estuary

Estuarine rearing has been shown to enhance within watershed biocomplexity and support growth and survival for juvenile salmon (Oncorhynchus sp.). However, less is known about how growth varies across different types of wetland habitats and what explains this variability in growth. We focused on the estuarine habitat use of Columbia River Chinook salmon (Oncorhynchus tshawytscha), which are listed under the Endangered Species Act. We employed a generalized linear model (GLM) to test three hypotheses: (1) juvenile Chinook growth was best explained by temporal factors, (2) habitat, or (3) demographic characteristics, such as stock of origin. This study examined estuarine growth rate, incorporating otolith microstructure, individual assignment to stock of origin, GIS habitat mapping, and diet composition along ~130 km of the upper Columbia River estuary. Juvenile Chinook grew on average 0.23 mm/day in the freshwater tidal estuary. When compared to other studies in the basin our growth estimates from the freshwater tidal estuary were similar to estimates in the brackish estuary, but ~4 times slower than those in the plume and upstream reservoirs. However, previous survival studies elucidated a possible tradeoff between growth and survival in the Columbia River basin. Our GLM analysis found that variation in growth was best explained by habitat and an interaction between fork length and month of capture. Juvenile Chinook salmon captured in backwater channel habitats and later in the summer (mid-summer and late summer/fall subyearlings) grew faster than salmon from other habitats and time periods. These findings present a unique example of the complexity of understanding the influences of the many processes that generate variation in growth rate for juvenile anadromous fish inhabiting estuaries.     

Estimation of sedimentary thickness in the Godavari basin

A major portion of the southern part of the Indian subcontinent is classified as a stable continental region. However, a few segments in this region are punctuated by rifts and shear zones that are seismically active. The Godavari rift that sutures the eastern Dharwar and the Bastar cratons is one such region, prone to seismic hazard. Estimation of the sedimentary thickness in these seismically active regions assumes importance since locales of thick and soft sediments are vulnerable to destruction due to surface waves generated by earthquakes. In the present study, data from five broadband seismological stations are utilized to estimate the average sedimentary thickness of the Godavari region using the difference in travel times of the direct S and converted Sp phases from local earthquakes. The thickness of sediments varies between 0.32 and 4.32 km. Also, the site-specific response in terms of the fundamental resonance frequency and the corresponding amplifications are estimated using the well-established Nakamura technique. The predominant frequencies are in the range of 1.3–4.61 Hz, and the amplifications are higher (>1.5) for the stations inside the Godavari basin. Both the thickness and amplification values clearly indicate that the sediments tend to get thicker toward the center of the basin, in good agreement with the geological distribution of the sedimentary units.     

Impact of adsorbed petroleum hydrocarbons on marine organisms

Adsorptions of south Louisiana crude oil from seawater by clays, non-clay minerals and sediments were conducted in the laboratory. Effect of sediment-adsorbed and water dispersed crude oil on adult oysters were investigated in aquaria. Hydrocarbons in oyster tissues and surrounding water were identified by gas chromatography. Field specimens from an area of a new oil spill and an area five months after an oil spill were also analysed. Evidence of secondary chemical effect of aged oil in sediments on oyster mortality is presented. Oil coated asbestos surfaces severely reduced recruitment of sedentary larval organisms.