High critical current density and enhanced irreversibility field in superconducting MgB2 thin films

The discovery of superconductivity at 39 K in magnesium diboride offers the possibility of a new class of low-cost, high-performance superconducting materials for magnets and electronic applications. This compound has twice the transition temperature of Nb3Sn and four times that of Nb-Ti alloy, and the vital prerequisite of strongly linked current flow has already been demonstrated. One possible drawback, however, is that the magnetic field at which superconductivity is destroyed is modest. Furthermore, the field which limits the range of practical applications-the irreversibility field H*(T)-is approximately 7 T at liquid helium temperature (4.2 K), significantly lower than about 10 T for Nb-Ti (ref. 6) and approximately 20 T for Nb3Sn (ref. 7). Here we show that MgB2 thin films that are alloyed with oxygen can exhibit a much steeper temperature dependence of H*(T) than is observed in bulk materials, yielding an H* value at 4.2 K greater than 14 T. In addition, very high critical current densities at 4.2 K are achieved: 1 MA cm-2 at 1 T and 105 A cm-2 at 10 T. These results demonstrate that MgB2 has potential for high-field superconducting applications.     

Gigantic jets between a thundercloud and the ionosphere

Transient luminous events in the atmosphere, such as lighting-induced sprites and upwardly discharging blue jets, were discovered recently in the region between thunderclouds and the ionosphere. In the conventional picture, the main components of Earth's global electric circuit include thunderstorms, the conducting ionosphere, the downward fair-weather currents and the conducting Earth. Thunderstorms serve as one of the generators that drive current upward from cloud tops to the ionosphere, where the electric potential is hundreds of kilovolts higher than Earth's surface. It has not been clear, however, whether all the important components of the global circuit have even been identified. Here we report observations of five gigantic jets that establish a direct link between a thundercloud (altitude approximately 16 km) and the ionosphere at 90 km elevation. Extremely-low-frequency radio waves in four events were detected, while no cloud-to-ground lightning was observed to trigger these events. Our result indicates that the extremely-low-frequency waves were generated by negative cloud-to-ionosphere discharges, which would reduce the electrical potential between ionosphere and ground. Therefore, the conventional picture of the global electric circuit needs to be modified to include the contributions of gigantic jets and possibly sprites.     

Integrated Quay Crane and Yard Truck Schedule Problem in Container Terminals

Quay crane and yard truck scheduling are two important subproblems in container terminal operations which have been studied separately in previous research. This paper proposes a new problem for the integrated quay crane and yard truck scheduling for inbound containers. The problem is formulated as a mixed integer programming (MIP) model. Due to the intractability, a genetic algorithm (GA) and a modified Johnson's Rule-based heuristic algorithm (MJRHA) are used for the problem solution. In addition, two closed form lower bounds are given to evaluate the solution accuracy. Computational experiments show that the solution algorithm can efficiently handle the scheduling problem and that the integrated methods are very useful.     

Structural basis of water-specific transport through the AQP1 water channel.

Water channels facilitate the rapid transport of water across cell membranes in response to osmotic gradients. These channels are believed to be involved in many physiological processes that include renal water conservation, neuro-homeostasis, digestion, regulation of body temperature and reproduction. Members of the water channel superfamily have been found in a range of cell types from bacteria to human. In mammals, there are currently 10 families of water channels, referred to as aquaporins (AQP): AQP0-AQP9. Here we report the structure of the aquaporin 1 (AQP1) water channel to 2.2 A resolution. The channel consists of three topological elements, an extracellular and a cytoplasmic vestibule connected by an extended narrow pore or selectivity filter. Within the selectivity filter, four bound waters are localized along three hydrophilic nodes, which punctuate an otherwise extremely hydrophobic pore segment. This unusual combination of a long hydrophobic pore and a minimal number of solute binding sites facilitates rapid water transport. Residues of the constriction region, in particular histidine 182, which is conserved among all known water-specific channels, are critical in establishing water specificity. Our analysis of the AQP1 pore also indicates that the transport of protons through this channel is highly energetically unfavourable.     

Improved D-IDS using the federated peer-to-peer architecture

A number of IDSs have been proposed for a networked or distributed environment. A modified D-IDS using federated peer-to-peer architecture, MCR (Multicast Reflector) and modified shaker protocol were proposed. The suggested scheme can be implemented easily and performs the information sharing between low-level IDS agents. As all users within a group monitor each other's, the common control server can perform detect intrusions with less cost and support the detection of the inside intruders.     

长白山区次生林恢复过程中天然更新的动态

以长白山区天然次生林为研究对象,采用空间代替时间的方法,分别对不同年度进行择代后形成的天然次生林进行群落学调查,分析择伐后28年恢复期间高度小于3m的幼苗幼树的天然更新过程及特点。结果表明,恢复初期更新幼苗幼树的树种出现比率较低,随着次生林恢复时间的增加,更新幼苗幼树的树种出现比率超过75％,且15年后变化相对较小;次生林内更新幼苗幼树的分布密度随着恢复时间的增加呈增加的趋势,恢复15年时分布密度达7500株／hm^2,此后分布密度的变化相对较小;在次生林内幼苗幼树主要是集中分布在距最近立木1．5～3．5m的范围内,随着次生林恢复时间的增加,幼树的分布范围相对靠近立木,幼苗的分布范围则相对远离立木。     

Pathological changes in olfactory neurons in patients with Alzheimer's disease

Alzheimer's disease is a central nervous system disorder characterized by the presence of neurofibrillary tangles, neuritic plaques and dystrophic neurites in susceptible areas of the brain. Investigation of the mechanism and development of the disease has been hampered by the lack of an animal model and the inaccessibility of neural tissue during the illness. Deficits in odour detection and discrimination are among the signs of Alzheimer's and previous anatomical studies suggest that olfactory pathways may be involved early in the illness. Neurons in the olfactory epithelium, which are of central origin, are relatively accessible for biopsy and could be used as a source of living nerve cells for the study of Alzheimer's disease if they can be shown to have characteristics of this disease. As these neurons have the unusual property of arising from stem cells throughout the life of the organism, they are good candidates for the development of cell cultures or cell lines which may express the disorder from living patients. We report here that nasal epithelium tissue taken at autopsy shows unique pathological changes in morphology, distribution and immunoreactivity of neuronal structures in patients with Alzheimer's disease.