抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).

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Diamond-like amorphous carbon

Rapid progress in the synthesis and processing of materials with structure on nanometer length scales has created a demand for greater scientific understanding of thermal transport in nanoscale devices, individual nanostructures, and nanostructured materials. This review emphasizes developments in experiment, theory, and computation that have occurred in the past ten years and summarizes the present status of the field. Interfaces between materials become increasingly important on small length scales. The thermal conductance of many solid–solid interfaces have been studied experimentally but the range of observed interface properties is much smaller than predicted by simple theory. Classical molecular dynamics simulations are emerging as a powerful tool for calculations of thermal conductance and phonon scattering, and may provide for a lively interplay of experiment and theory in the near term. Fundamental issues remain concerning the correct definitions of temperature in nonequilibrium nanoscale systems. Modern Si microelectronics are now firmly in the nanoscale regime—experiments have demonstrated that the close proximity of interfaces and the extremely small volume of heat dissipation strongly modifies thermal transport, thereby aggravating problems of thermal management. Microelectronic devices are too large to yield to atomic-level simulation in the foreseeable future and, therefore, calculations of thermal transport must rely on solutions of the Boltzmann transport equation; microscopic phonon scattering rates needed for predictive models are, even for Si, poorly known. Low-dimensional nanostructures, such as carbon nanotubes, are predicted to have novel transport properties; the first quantitative experiments of the thermal conductivity of nanotubes have recently been achieved using microfabricated measurement systems. Nanoscale porosity decreases the permittivity of amorphous dielectrics but porosity also strongly decreases the thermal conductivity. The promise of improved thermoelectric materials and problems of thermal management of optoelectronic devices have stimulated extensive studies of semiconductor superlattices; agreement between experiment and theory is generally poor. Advances in measurement methods, e.g., the 3ω method, time-domain thermoreflectance, sources of coherent phonons, microfabricated test structures, and the scanning thermal microscope, are enabling new capabilities for nanoscale thermal metrology.

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Nanoscale thermal transport

Electromigration (EM) study at temperatures from 325-400/spl deg/C and current densities from 1-2 MA/cm/sup 2/ has determined the failure time characteristics and failure behavior of submicron dual-damascene Cu/oxide interconnects. The test structures used are based on statistical concepts potentially suitable to address the early failure issue in sub-/spl mu/m interconnects and are designed to examine failures occurring only in dual-damascene interconnects. A combination of single and repeated (N=1, 10, 50, and 100) serial chains of nominally identical interconnects are used in conjunction with statistical analysis based on weakest-link concepts (Nelson, 1990) to identify differences in the failure distribution as larger collections of interconnect elements are sampled. In total, nearly 10,000 interconnects were tested using this configuration. Through the use of these multiply-linked interconnect ensembles, statistical evidence of two distinct (weak and strong) failure modes in dual-damascene Cu/oxide interconnects is first reported. The bimodal failures have also been identified with distinct void formation mechanisms that appear characteristic of the dual-damascene interconnect architecture. The weak mode is found to be void formation within the dual-damascene via, while the strong mode is associated with voiding in the dual-damascene trench. The weak mode activation energy is found to be about 1 eV and seems consistent with void formation controlled by interface diffusion between Cu metal and Ta diffusion barrier. These observations using this type of testing methodology confirm the utility of the multi-link approach in electromigration reliability analysis and the detection of early failures.

Statistics of electromigration early failures in Cu/oxide dual-damascene interconnects

Grain-boundary melting transition in an atomistic simulation model

Evidence for vacancy mechanism in grain boundary diffusion in bcc iron: A molecular-dynamics study

The solid‐state reaction of thin Pd films with GaAs substrates has been investigated using Auger sputter profiling, x‐ray diffraction, He‐ion backscattering, and sheet‐resistivity measurements. Fast diffusion and dissolution were observed for both As and Ga into Pd, which slowed down after distinct compound layers were formed. The kinetics of Pd penetration into GaAs was found to be controlled by diffusion with an activation energy of 1.4 eV. The As and Ga compounds formed as a result of contact reactions were identified to be PdAs2 and PdGa at 250 °C; PdAs2, PdGa, and Pd2Ga at 350 °C; and PdGa at 500 °C. For each annealing temperature a ’’steady‐state’’ time is reached when there is no measurable change in the backscattering spectra. The sheet resistivity of the contact was found to increase with time under isothermal annealing and eventually reached a saturation value. The saturation time of resistivity change is well correlated to the steady‐state time. To determine the effect of the contact reaction on device performance, p‐n junction solar cells fabricated by diffusing Zn into an n‐type GaAs wafer with Pd and Ag contact layers have been tested. An onset of shunting was observed on the solar devices after heat treatments above 200 °C. Results indicated that shunting is most probably due to Pd penetration through localized defects in the p layer of GaAs.

Contact reactions in Pd/GaAs junctions

A series of electromigration (EM) tests were performed as a function of temperature and current density to investigate lifetime statistics and damage evolution for Pb-free solder joints with Cu and Ni under-bump-metallizations (UBMs). The EM lifetime was found to depend on the failure criterion used, so the results were compared based on the first resistance jump and conventional open-failure criterion. Solder joints with Cu UBM had a longer lifetime than Ni UBM based on the open-failure criterion, but the lifetime with Ni UBM became comparable when the first resistance jump criterion was applied. To determine the temperature in solder joints, the Joule heating effect was investigated with experiments and finite element analysis. The temperature of solder joints was determined to be approximately 15°C higher than that at the Si die surface when 1 A of current was applied. With the appropriate temperature correction, the activation energies and the current density exponents were found to be Q = 1.11 eV, n = 3.75 and Q = 0.86 eV, n = 2.1 based on the open-failure criterion for solder joints with Cu and Ni UBM, respectively. Based on the first resistance jump criterion, Q = 1.05 eV, n = 1.45 for Cu UBM and Q = 0.94 eV, n = 2.2 for Ni UBM, respectively. For solder joints with Cu UBM, voids were formed initially at the Cu6Sn5/solder interface while the final open failure occurred at the Cu3Sn/Cu6Sn5 interface. For Ni UBM, voids were formed initially at the Ni3Sn4/solder interface leading to failure at the same interface. The formation of intermetallic compounds (IMCs) was enhanced under current stressing, which followed linear growth kinetics with time. The IMC growth was accompanied by volume shrinkage, which accelerated damage evolution under EM.

Paul S. Ho

Papers

Statistics of electromigration early failures in Cu/oxide dual-damascene interconnects

Grain-boundary melting transition in an atomistic simulation model

Evidence for vacancy mechanism in grain boundary diffusion in bcc iron: A molecular-dynamics study

Contact reactions in Pd/GaAs junctions

Electromigration statistics and damage evolution for Pb-free solder joints with Cu and Ni UBM in plastic flip-chip packages