Sintering silver paste has attracted ever-increasing attention in the electronic packaging field due to high melting point, excellent thermal conductivity and ease of process, which is even considered as the most promising mainstream bonding material for WBG power devices. However, the high current density and high-power density of WBG power devices lead to the generation of large amounts of heat, which brings about thermal stress between sintered silver layer and die/substrate, and sintered silver joints easily suffer reliability problem. In this paper, the effect of Young's modulus on the reliability of sintered silver will be systematically investigated from two aspects: simulation and experiment. In terms of simulation, a sequential thermodynamic coupling method based on finite element analysis (FEA) is used to investigate the reliability of sintered silver. We obtained data on the evolution of Mises stress and plastic strain for sintered silver with different Young's modulus under power cycles (PC), and firstly found three plastic strain cumulative trends corresponding to the three Young's modulus ranges for sintered silver and analyzed the effect of Young's modulus on reliability based on them. Experimentally, we can obtain various microporous sintered silver with different Young's modulus and different shear strengths by changing the sintering parameters, and their porosity and pore size distribution are counted in detail. We systematically and orderly analyze the correlation between sintering parameters, microstructure, Young's modulus and reliability of sintered silver.
There have been some significant advances in direct joining of dissimilar materials over recent years for enabling multi-material lightweight structures. As such, both dissimilar material joint design and structural integrity evaluation call for engineering fracture mechanics solutions to bi-material interface crack problems involving finite bond line length. This paper presents a novel elastic foundation modeling approach to address a set of two-dimensional bi-material interface crack problems. The analytical formulation presented enables the extraction of important length-scale parameters for supporting quantitative joint sizing and interrelating the mixed-mode energy release rates to the classical mode-mixity defined by bi-material crack tip singularity fields. The modeling results can be directly used for analyzing some common test configurations, e.g., "lap-shear" (LS) and "coach-peel" (CP) widely used by industry for ensuring optimal bond line sizing for both satisfactory mechanical performance and easy dis-assembly. To demonstrate the practical implications of this research, a group of bi-material (aluminum to steel) lap-shear fracture tests are modeled through a linear superposition of the solutions of the elementary load cases.
Sphere decoding (SD) is an efficient algorithm for Multiple-input Multiple-output (MIMO) digital communications. It has been showed to achieve near Maximum Likelihood (ML) performance with low complexity. However, the complexity of conventional SD algorithm is high under the specific environment. The performance and the computation complexity of SD algorithm is highly dependent on the initial choice of sphere radius. Thus, it is important to design a proper initial radius scheme for SD which improve the performance and reduce the computation complexity. In this paper, we propose a novel scheme base on the knowledge of statistical probability and the constellation energy to design a new initial radius scheme. The performance and algorithmic efficiency of this scheme are increased by application of a factor constellation energy E. The simulation results show under the low signal-to-noise ratio (SNR) condition. The proposed scheme can achieve the aim that save more operation time than the conventional SD algorithm. At the same time, the performance gap compared to conventional SD algorithm can be restricted to a certain level.
The empiric initial antibiotic regimen (IAR) for treatment of febrile neutropenia (FN) relies on a knowledge of epidemiology and susceptibility patterns of bacterial bloodstream infections (BSI), especially in high-risk patient populations, i.e., those receiving chemotherapy for hematologic malignancies (HM) or undergoing hematopoietic stem cell transplant (HCT). As the last US national survey of BSI epidemiology in cancer patients was published in 2003, we sought to update these data focusing exclusively on high-risk patients with attention to IARs used and their concordance with susceptibilities of isolated bloodstream pathogens. A prospective ongoing survey among 14 high-volume US cancer centers submitting clinical and microbiologic data from consecutive HM patients with BSI during first FN after cytotoxic chemotherapy or HCT. Concordance between antibiotic and BSI was determined by investigator (AZ, AF) interpretation of susceptibility reports provided by each center compared with IAR used, for single organism bacteremias only. Among 294 FN bacteremic episodes (93 HCT), there were 336 bacterial pathogens (48.5% Gram negative [GN] 46.5% Gram positive [GP] and 6% anaerobes), with 88% monomicrobial episodes. E. coli and viridans group Streptococci (VGS) were the most commonly isolated GN and GP, respectively, each accounting for nearly 25% of total organisms identified. IARs included cefepime 61%, piperacillin–tazobactam 24%, and meropenem 8%. Isolates were nonsusceptible to the IAR in 38/227 (17%) of FN episodes. Antibiotic mismatch was more likely to occur with a non-VGS GP (37%) vs. GN (13%) or VGS (2%) P < 0.001. This is the first US national survey of high-risk BSI in FN. Although mismatch between BSI and IAR occurs in 17% of FN bacteremia episodes, this is driven primarily by non-VGS GP isolates such as CoNS and MRSA. Currently used IARs, comprised primarily of cefepime and piperacillin–tazobactam, generally provide reliable coverage for GN isolates across the United States (87%) but careful tracking of this rate is essential to identify further erosion of coverage in the current era of antimicrobial resistance. A. Zimmer, Merck: Investigator, Research grant. A. G. Freifeld, Merck: Investigator, Research grant. S. Pergam, Merck: Consultant, Consulting fee; Chimerix: Consultant, Consulting fee. K. V. Rolston, Merck: Investigator, Research grant; JMI Laboratories: Investigator, Research grant; Shionogi (Japan): Investigator, Research grant. S. Shoham, Merck: Investigator and Scientific Advisor, Consulting fee and Grant recipient; Astellas: Investigator, Grant recipient; Shionogi (Japan): Investigator, Grant recipient; Gilead: Investigator, Grant recipient; Shire: Investigator, Grant recipient. T. J. Walsh, Merck: Grant Investigator, Research grant; Atellas: Consultant, Grant Investigator and Scientific Advisor, Consulting fee and Research grant; Gilead: Scientific Advisor, Consulting fee; Allergan: Grant Investigator and Scientific Advisor, Consulting fee and Research grant; Scynexis: Grant Investigator, Research grant; Amplyx: Grant Investigator, Research grant; Shionogi: Scientific Advisor, Consulting fee. J. A. Young, GSK: Investigator, The University of Minnesota is reimbursed for contract costs associated with conducting clinical trials of vaccine. I receive no personal financial benefit.. J. Meza, Merck: Investigator, Research grant. Y. Zhang, Merck: Investigator, Research grant.
A software self-recovery technique was proposed to mitigate the effect of multi-bit upsets(MBUs) on on-board computers to guarantee satellite safety.This technique takes advantages of the inherent multi-bit error detection capability of hardware EDAC(error detection and correction) and self-recovery feature of fault-tolerant technology to capture MBU and selectively starts system self-recovery to prevent on-board computer problems caused by MBUs.Key data index is set up to refrain from unnecessary self-recoveries.A division hash table and a novel moderate recovering strategy are applied to minimize the interrupt processing time.SEU(single event upset) hazard analysis and flight data show that the proposed technique can decrease the probability of satellite failures caused by SEUs by more than 90%.The technique has been successfully applied to XX02 satellites.
The quasi-static and dynamic compressive mechanical properties of a bullet composite are investigated using the scattered spot technique, an electronic universal testing machine, and a Split—Hopkinson pressure bar. The stress-strain curves under static and dynamic loading are also obtained, and the strain rate effect is analyzed. The rupture structure is observed under a scanning electron microscope, and the microscopic damage mechanism of the bullet composite is examined. Results show that the composite is sensitive to the strain rate, such that the compressive strength of the composite increases with increased strain rate. The relationship of the compressive strength and elastic modulus with the logarithmic strain rate is nonlinear.
In this paper,coseismic response waves recorded by 4 strainmeter of borehole in Fujian province were compared and analyzed,characteristics of volume strain of Fujian province was researched.The results show,range of volume strain was direct proportion to earthquake magnitude,and response delay time was direct proportion to epicentral distance.In this paper,the relation between characteristics of volume strain of seismic station in Fujian province to strong teleseismic in Indonesia and fault were discussed.
Complex structural wells have the advantages of increasing drainage area,effectively connecting reservoir cracks and increasing the flow conductivity of reservoir.The results of developing low permeability reservoirs through two kinds of complex structural wells—fractured horizontal well and multilateral horizontal well are analyzed and the relationship between earth stress based on the investigation of the domestic and overseas present situation of low-permeability reservoir development,and the parameters of the cracks are studied.The results show that the multilateral horizontal well is superior to fractured horizontal well for the development of the low permeability reservoirs,and it is necessary to consider the relationship between the earth stress and the trend of horizontal borehole in the design of two kinds of complex structural wells.It is reasonable that the trend of horizontal borehole is vertical to the direction ofthe largest horizontal principal stress.
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