分段尝试法研究碱金属对铁氧化物还原的影响北大核心CSCD

为了研究碱金属在高炉内对Fe2O3还原的影响,采用热重分析方法研究含有不同碱金属含量的Fe2O3在不同温度下的还原特性。通过分析试样的还原度曲线,讨论温度和碱金属含量对还原过程的影响,发现随着温度的升高,反应速率增加,试样的还原度增加,接近完全还原的反应时间缩短;Na2O对Fe2O3的还原有抑制作用,抑制作用随着Na2O含量增加而加强,但这种抑制作用随着Na2O含量增加不是均匀增长的,会存在饱和点。针对还原过程的特点,采用分段尝试法建立了前期化学反应控速的未反应核模型和后期收缩核内扩散模型,并对实验数据进行分段拟合,求得相关动力学参数,同时定量地给出了不同的温度条件下2种控制转换的时间点。从拟合结果看,实验数据和模型取得了很好的吻合,说明所建模型与实际情况相符。     

搅拌摩擦焊温度场最新研究进展

早期的搅拌摩擦焊温度场模型只考虑了摩擦产热，而忽略了塑性变形产热。在刚结束的第五届搅拌摩擦焊国际会议上，有许多学者就塑性变形产热对其温度场的影响进行了研究，本文对此作了概括地介绍分析。     

High-frequency nonlinearity analysis of common-emitter anddifferential-pair transconductance stages

Equations describing the high-frequency nonlinear behavior of common-emitter and differential-pair transconductance stages are derived. The equations show that transconductance stages using inductive degeneration are more linear than those using capacitive or resistive degeneration, and that the common-emitter transconductance stages are more linear than the differential-pair transconductance stages with the same bias current and transconductance. The nonlinearity equations can also be used to explain the class AB behavior of the common-emitter transconductance stage with inductive degeneration     

I. Yeast sequencing reports. Sequencing of chromosome I of Saccharomyces cerevisiae: Analysis of the 42 kbp SP07-CENI-CDC15 region

Determination of the DNA sequence and preliminary functional analysis of a 42 kbp centromeric section of chromosome I have been completed. The section spans the SPO7-CEN1-CDC15 loci and contains 19 open reading frames (ORFs). They include an apparently inactive Ty1 retrotransposon and eight new ORFs with no known homologs or function. The remaining ten genes have been previously characterized since this part of the yeast genome has been studied in an unusually intensive manner. Our directed sequencing allows a complete ordering of the region. The sequence has been deposited in the GenBank data library under Accession Number L22015.     

Structure of FokI has implications for DNA cleavage

FokI is a member an unusual class of restriction enzymes that recognize a specific DNA sequence and cleave nonspecifically a short distance away from that sequence. FokI consists of an N-terminal DNA recognition domain and a C-terminal cleavage domain. The bipartite nature of FokI has led to the development of artificial enzymes with novel specificities. We have solved the structure of FokI to 2.3 A resolution. The structure reveals a dimer, in which the dimerization interface is mediated by the cleavage domain. Each monomer has an overall conformation similar to that found in the FokI-DNA complex, with the cleavage domain packing alongside the DNA recognition domain. In corroboration with the cleavage data presented in the accompanying paper in this issue of Proceedings, we propose a model for FokI DNA cleavage that requires the dimerization of FokI on DNA to cleave both DNA strands.     

Theoretical predictions on the effective piezoelectric coefficients of 0–3 PZT/Polymer composites

Two explicit formulae for the effective piezoelectric coefficients (d ₃₁ and d ₃₃) of 0–3 composite have been derived by taking into account the interaction effects between the inclusions and are expressed directly in terms of the properties of the constituents. Predictions using these two formulae are compared with published experimental data of 0–3 composite systems having three different polarization states: only the inclusion phase is polarized; both phases are polarized in the same direction and the two phases are polarized in opposite directions. In addition, the predictions using Wong et al.’s scheme (Wong CK, Poon YM, Shin FG (2001) J Appl Phys 90:4690) and Furukawa et al.’s model (Furukawa T, Fujino K, Fukada E (1976) Jpn J Appl Phys 15:2119) are included for comparison. For the first two cases, the results show that both our model and Wong et al.’s scheme have comparable performance. However, for the last case, our model gives more favorable predictions than theirs.     

Tracking and Vibration Control of Flexible Robots Using Shape Memory Alloys

This paper considers the tracking control problem for flexible robots with active vibration suppression by shape memory alloys (SMAs). With a singular perturbation technique, the flexible modes and joint angles are modeled as fast and slow variables, respectively. The fast subsystem comprising the nonlinear SMA dynamics is obtained in a strict feedback form feasible for the backstepping design. The SMA actuators are configured in redundant pairs for an active suppression of vibrations. For the slow subsystem, asymptotically stable tracking is ensured, while for the fast subsystem, uniform exponential stability is guaranteed. By invoking Tikhonov's theorem, it is shown that the error arising from the nonideal time-scale separation in the singular perturbation model is small. Simulation demonstrates the effectiveness of the proposed control     

Engineering a human bone marrow model: a case study on ex vivo erythropoiesis

Theoretical and practical problems related to the dosimetric data verification for recovery workers at the Chernobyl NPP are considered. The distinctions in definitions epsilon-entropy in paper [1] and delta-entropy in [2] are considered. In a certain measure this distinctions explain distinction in conclusions, made in these papers. Method of dosimetric data collection, used by Institute of Biophysics and its difference from the method of data acquisition, used in national Medical-dosimetric registers is described. Results on determination of a share of participants given for various clean-up worker divisions, contained in pointed delta-shape peaks, received by two various methods, stated in [2] and [6], are compared and their satisfactory conformity with one another is established.