108 research outputs found
Parallel and distributed computing techniques in biomedical engineering
Master'sMASTER OF ENGINEERIN
High-voltage ESD structures and ESD protection concepts in smart power technologies
Electro-static discharge (ESD) event can cause upset or permanent damage of integrated circuits (IC) and electrical systems. The risk of ESD fails needs to be mitigated or prevented. ESD robustness of IC products and electrical systems is specified, verified and qualified according to respective ESD standards. For high-voltage IC products based on smart power semiconductor technologies for industrial, power and automotive applications, design of effective and cost-efficient ESD protection is a big challenge, demanding wide and deep technical knowledge throughout high-frequency and high-power characterization techniques, semiconductor device physic, circuit design as well as modeling and simulation.
The required measurement setups and tester components are developed and introduced. The characterization of ESD protection devices, IC and off-chip circuit elements is enabled and improved. The rise-time filters are important for the study of rise-time dependent ESD robustness. The human metal model (HMM) tester as an alternative to IEC ESD generators provides voltage waveform measurement with good quality in addition to current waveform measurement. It can be used for wafer-level or package-level device characterization. The measurement results of HMM tester and IEC ESD generator are compared.
The on-chip ESD protection design relies on proper choice of different types of ESD protection devices and structures, depending on ESD specifications and IC applications. Typical on-chip ESD protection, whether snapback or non-snapback, single device or ESD circuit is introduced. The failure levels studies give a systematic benchmark of the ESD protection devices and structures, concerning device area, clamping voltage and other relevant parameters. The trade-off between those parameters and limitation of different ESD protection is discussed. Moreover, understanding of ESD failure modes is the key to implement effective ESD design. A unique ESD failure mode of smart power semiconductor device is discovered and investigated in detail. In the scope of finding ESD solutions, new active ESD clamps have been further developed in this work.
The study of ESD protection is extended to the system-level involving on- and off-chip ESD protection elements. The characteristics of typical off-chip elements as well as the interaction between IC and off-chip protection elements plays essential role on the system robustness. A system-level ESD simulation incorporating IC and off-chip protection elements is desired for system efficient ESD design (SEED). A behavioral ESD model is developed which reproduces pulse-energy-dependent failure levels and self-heating effects. This modeling methodology can be used for assessment of system robustness even beyond ESD time-domain. The validation of the models is given by representative application examples.
Several main challenges of high-voltage ESD design in smart power technologies have been addressed in this work, which can serve as guidance for ESD development and product support in future power semiconductor technologies
Constructing Tree-based Index for Efficient and Effective Dense Retrieval
Recent studies have shown that Dense Retrieval (DR) techniques can
significantly improve the performance of first-stage retrieval in IR systems.
Despite its empirical effectiveness, the application of DR is still limited. In
contrast to statistic retrieval models that rely on highly efficient inverted
index solutions, DR models build dense embeddings that are difficult to be
pre-processed with most existing search indexing systems. To avoid the
expensive cost of brute-force search, the Approximate Nearest Neighbor (ANN)
algorithm and corresponding indexes are widely applied to speed up the
inference process of DR models. Unfortunately, while ANN can improve the
efficiency of DR models, it usually comes with a significant price on retrieval
performance.
To solve this issue, we propose JTR, which stands for Joint optimization of
TRee-based index and query encoding. Specifically, we design a new unified
contrastive learning loss to train tree-based index and query encoder in an
end-to-end manner. The tree-based negative sampling strategy is applied to make
the tree have the maximum heap property, which supports the effectiveness of
beam search well. Moreover, we treat the cluster assignment as an optimization
problem to update the tree-based index that allows overlapped clustering. We
evaluate JTR on numerous popular retrieval benchmarks. Experimental results
show that JTR achieves better retrieval performance while retaining high system
efficiency compared with widely-adopted baselines. It provides a potential
solution to balance efficiency and effectiveness in neural retrieval system
designs.Comment: 10 pages, accepted at SIGIR 202
4-{2-[2-(4-Formylphenoxy)ethoxy]ethoxy}benzaldehyde
The title compound, C18H18O5, was obtained by the reaction of 4-hydroxybenzaldehyde with bis(2,2-dichloroethyl) ether in dimethylformamide. In the crystal, the molecule lies on a twofold rotation axis that passes through the central O atom of the aliphatic chain, thus leading to one half-molecule being present per asymmetric unit. The carbonyl, aryl and O—CH2—CH2 groups are almost coplanar, with an r.m.s. deviation of 0.030 Å. The aromatic rings are approximately perpendicular to each other, forming a dihedral angle of 78.31 sh;H⋯O hydrogen bonds and C—H⋯π interactions help to consolidate the three-dimensional network
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Response of Electric Field in Terrestrial Magnetosphere to Interplanetary Shock
Electric field impulses generated by interplanetary shocks can cause a series of dynamic processes in the Earth's magnetosphere and were previously explained by either fast-mode wave propagation or flow related to compression of the magnetopause. Based on a Space Weather Modeling Framework simulation, we suggest a new scenario in which the evolution of the impulse is due to both the propagation of the fast-mode wave and the compression of the magnetopause, which can explain the simulation and observations in previous related studies. The onset of the electric field impulse is determined by the propagation of the fast-mode wave in the magnetosphere while the peak of the impulse is determined by the propagation of the compression of the magnetopause. The new understanding of the impulse is important for the generation of subsequent ultralow frequency waves through the coupling of the fast-mode to Alfvén waves and field line resonances and related radiation-belt electron acceleration.
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The polygalacturonase gene BcMF2 from Brassica campestris is associated with intine development
Brassica campestris Male Fertility 2 (BcMF2) is a putative polygalacturonase (PG) gene previously isolated from the flower bud of Chinese cabbage (Brassica campestris L. ssp. chinensis Makino, syn. B. rapa ssp. chinensis). This gene was found to be expressed specifically in tapetum and pollen after the tetrad stage of anther development. Antisense RNA technology was used to study the function of BcMF2 in Chinese cabbage. Scanning and transmission electron microscopy revealed that there were deformities in the transgenic mature pollen grains such as abnormal location of germinal furrows. In addition, the homogeneous pectic exintine layer facing the exterior seemed to be overdeveloped and predominantly occupied the intine, thus reversing the normal proportional distribution of the internal endintine layer and the external exintine layer. Since it is a continuation of the intine layer, the pollen tube wall could not grow normally. This resulted in the formation of a balloon-like swelling structure in the pollen tube tip in nearly 80% of the transgenic pollen grains. Premature degradation of tapetum was also found in these transgenic plants, which displayed decreased expression of the BcMF2 gene. BcMF2 might therefore encode a new PG with an important role in pollen wall development, possibly via regulation of pectin's dynamic metabolism
Accelerated similarity searching and clustering of large compound sets by geometric embedding and locality sensitive hashing
Motivation: Similarity searching and clustering of chemical compounds by structural similarities are important computational approaches for identifying drug-like small molecules. Most algorithms available for these tasks are limited by their speed and scalability, and cannot handle today's large compound databases with several million entries
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