冲模块在线切割过程的开裂及变形分析

１引言在冲模制造中，一些厚（大）件（如高度为６０～８０ｍｍ的凸模及凸凹模等）在线切割过程突然开裂的现象时有发生。还有一些零部件在切割过程中发生扭曲、弯曲变形。据了解，９０％以上的工模具制造者把问题归咎于热处理，还有少数人认为是原材料先天性缺陷或锻造缺...

Initiation and evolution of the South China Sea: an overview

Different models have been proposed for the formation and tectonic evolution of the South China Sea （SCS）, including extrusion of the Indochina Peninsula, backarc extension, two-stage opening, proto-SCS dragging, extension induced by a mantle plume, and integrated models that combine diverse factors. Among these, the extrusion model has gained the most attention. Based on simplified physical experiments, this model proposes that collision between the Indian and Eurasian Plates resulted in extrusion of the Indochina Peninsula, which in turn led to opening of the SCS. The extrusion of the Indochina Peninsula, however, should have led to preferential open- ing in the west side of the SCS, which is contrary to observations. Extensional models propose that the SCS was a backarc basin, rifted off the South China Block. Most of the backarc extension models, however, are not compatible with observations in terms of either age or subduction direction. The two-stage extension model is based on extensional basins surrounding the SCS. Recent dating results indeed show two-stage opening in the SCS, but the Southwest Subbasin of the SCS is much younger, which contradicts the two-stage extension model. Here we pro- pose a refined backarc extension model. There was a wide Neotethys Ocean between the Australian and Eurasian Plates before the Indian-Eurasian collision. The ocean floorstarted to subduct northward at ~ 125 Ma, causing backarc extension along the southem margin of the Eurasian Plate and the formation of the proto-SCS. The Neotethys sub- duction regime changed due to ridge subduction in the Late Cretaceous, resulting in fold-belts, uplifting, erosion, and widespread unconformities. It may also have led to the subduction of the proto-SCS. Flat subduction of the ridge may have reached further north and resulted in another backarc extension that formed the SCS. The rollback of the fiat subducting slab might have occurred ~ 90 Ma ago; the second backarc extension may have initiated between 50 and 45 Ma. The opening of the Southwest Subbasin is roughly simultaneous with a ridge jump in the East Sub- basin, which implies major tectonic changes in the sur- rounding regions, likely related to major changes in the extrusion of the Indochina Peninsula.

A New Model of Lithosphere Deformation Beneath the Okinawa Trough Based on Gravity Data

The Ryukyu trench-arc system can be divided into two types according to its subduction model. The normal subduction in the northern part of the Philippine Sea plate creates a hinge sedimentary wedge with large deformation at the collision front, while the oblique subduction in the southern part gives rise to a smaller accretion with small deformation than that in the northern part. The mechanisms that cause the distinction between these two types have been analysed and calculated by using gravity data based on the lithosphere rheology and the stress state of the lithosphere in the subduction boundary. The two types of subduction model are associated with the internal extension in the southern Okinawa Trough and the small extension in the northern part. The difference of the stress state between the two types of subduction model is also manifested in other tectonic features, such as topography, volcanic activity and crust movement. Modeling bathymetric and gravity data from this area suggests that the oblique subduction of low angle, together with smooth geometry of the overlying plate crust, results in small stress released on the south of the trench by the subduction plate. The intraplate faults in the southern Okinawa Trough behind the trench stand in surplus intensive stress. On the other hand, the normal subduction of high angle, together with strong undulation geometry of the overlying crust, results in more intensive stress released in the northern Ryukyu Trench than that in the south. The intraplate faults in the northern Okinawa Trough behind the northern Ryukyu Trench stand in small stress.

Design and Performances of High-Current Modular Pulsed Power

A design of the high-current modular pulsed power generator and results of the test of this generator are presented. The generator is based on two capacitors each of 2.5μF and 50 kV maximum charging voltage. Two multi-gaps gas spark switches with capacitive coupled triggering are used to discharge stored energy into the load. The triggering pulse with amplitude up to 70 kV and rise time of-50 ns is supplied by three-stage Marx-generator. The output of each capacitor with multi-gaps spark switch is connected to the load by eight coaxial cables -1 m in length. The total inductance of the generator does not exceed 200 nil. At 40 kV charging voltage this generator produces 180 kA with a quarter of period of 1.6 μs at short circuit load of-15 nil. The generator has been used in the research of underwater electrical wire explosion. The space separation of the load and modules of generator allows one to avoid possible damages of the generator by shock waves produced during the wire explosion. In addition, this modular generator design allows to increase easily the number of modules and to reach several hundreds of kiloamperes in the load.

A Practical Online Approach to Protecting Kernel Heap Buffers in Kernel Modules

Heap overflow attack is one of the major memory corruption attacks that have become prevalent for decades. To defeat this attack,many protection methods are proposed in recent years. However,most of these existing methods focus on user-level heap overflow detection. Only a few methods are proposed for kernel heap protection. Moreover,all these kernel protection methods need modifying the existing OS kernel so that they may not be adopted in practice. To address this problem,we propose a lightweight virtualization-based solution that can protect the kernel heap buffers allocated for the target kernel modules. The key idea of our approach is to combine the static binary analysis and virtualization technology to trap a memory allocation operation of the target kernel module,and then add one secure canary word to the end of the allocated buffer. After that,a monitor process is launched to check the integrity of the canaries. The evaluations show that our system can detect kernel heap overflow attacks effectively with minimal performance cost.