非共沸混合工质自复叠热泵循环试验研究

单级压缩式热泵冷凝温度与蒸发温度之差一般为40~50℃,非共沸混合工质自复叠循环具有工作温差大的优点,将其应用于热泵循环,则可产生较大的供热温差。该文通过搭建一个空气源自复叠热泵实验台,利用NIST公司的制冷剂物性数据库Refprop7,绘制出了混合工质的温度-浓度图。经过实验,分析了自复叠热泵循环工作温差的影响因素,得出了自复叠热泵气液分离器简单分离对增大工作温差的作用有限,增加工质的相对挥发度也不能显著改善热泵的运行性能等结论。并进一步得出了增设分凝设施可显著增大工作温差的结论。     

The Effect of Dia2 Protein Deficiency on the Cell Cycle,Cell Size,and Recruitment of Ctf4 Protein in Saccharomyces cerevisiae

Cells have evolved elaborate mechanisms to regulate DNA replication machinery and cell cycles in response to DNA damage and replication stress in order to prevent genomic instability and cancer. The E3 ubiquitin ligase SCF^Dia2 in S. cerevisiae is involved in the DNA replication and DNA damage stress response, but its effect on cell growth is still unclear. Here, we demonstrate that the absence of Dia2 prolongs the cell cycle by extending both S- and G2/M-phases while, at the same time, activating the S-phase checkpoint. In these conditions, Ctf4—an essential DNA replication protein and substrate of Dia2—prolongs its binding to the chromatin during the extended S- and G2/M-phases. Notably, the prolonged cell cycle when Dia2 is absent is accompanied by a marked increase in cell size. We found that while both DNA replication inhibition and an absence of Dia2 exerts effects on cell cycle duration and cell size, Dia2 deficiency leads to a much more profound increase in cell size and a substantially lesser effect on cell cycle duration compared to DNA replication inhibition. Our results suggest that the increased cell size in dia2∆ involves a complex mechanism in which the prolonged cell cycle is one of the driving forces.     

Novel Substituted Purine Isosteres: Synthesis,Structure-Activity Relationships and Cytotoxic Activity Evaluation

A number of pyrrolo[2,3-c]pyridines, pyrrolo[3,2-d]pyrimidines and pyrazolo[4,3-d]pyrimidines were designed and synthesized as antiproliferative agents. The target compounds possessed selected substituents in analogous positions on the central scaffold that allowed the extraction of interesting SARs. The cytotoxic activity of the new derivatives was evaluated against prostatic (PC-3) and colon (HCT116) cell lines, and the most potent analogues showed IC₅₀ values in the nM to low µM range, while they were found to be non-toxic against normal human fibroblasts (WI-38). Flow cytometric analysis of DNA content revealed that the most promising derivative 14b caused a statistically significant accumulation of PC-3 cells at G₂/M phase and induced apoptosis in PC-3 cells.     

Multiple cover time

Motivated by applications in Markov estimation and distributed computing, we define the blanket time of an undirected graph G to be the expected time for a random walk to hit every vertex of G within a constant factor of the number of times predicted by the stationary distribution. Thus the blanket time is, essentially, the number of steps required of a random walk in order that the observed distribution reflect the stationary distribution. We provide substantial evidence for the following conjecture: that the blanket time of a graph never exceeds the cover time by more than a constant factor. In other words, at the cost of a multiplicative constant one can hit every vertex often instead of merely once. We prove the conjecture in the case where the cover time and maximum hitting time differ by a logarithmic factor. This case includes almost all graphs, as well as most “natural” graphs: the hypercube, k-dimensional lattices for k ≥ 2, balanced k-ary trees, and expanders. We further prove the conjecture for perhaps the most natural graphs not falling in the above case: paths and cycles. Finally, we prove the conjecture in the case of independent stochastic processes. © 1996 John Wiley & Sons, Inc. Random Struct. Alg., 9 , 403–411 (1996)     

Coexistence of the chaos and the periodic solutions in planar fluid flows

This paper discusses the dynamic behavior of the Kelvin-Stuart cat’s eye flow underperiodic perturbations.By means of the Melnikov method the conditions to havebifurcations to subharmonics of even order for the oscillating orbits and to have bifurcationsto subharmonics of any order for the rotating orbits are given,and further,the coexistencephenomena of the chaotic motions and periodic solutions are presented.     

Asymptotic solution of Brusselator limit cycle in biochemistry

In this paper,two kinds of asymptotic analytic expression of the Brusselator limitcycle are given by means of two simple methods.To some extem,they are better thanthe analytic expression in [2].     

Singular perturbation of boundary value problem for a vector fourth order nonlinear differential equation

We study the vector boundary value problem with boundary perturbations: ε~2y~((4))=f(x,y,y″,ε, μ) ( μ<χ<1-μ) y(χ,ε,μ)l_(χ-μ)= A_1(ε,μ), y(χ,ε,μ)l_(χ-1-μ)=B_1(ε,μ) y″(χ,ε,μ)l_(χ-μ)=A_2(ε,μ),y″(χ,ε,μ)l_(χ-1-μ)=B_2(ε,μ)where yf, A_j and B_j (j=1,2) are n-dimensional vector functions and ε,μ are two small positive parameters. This vector boundary value problem does not appear to have been studied, although the scalar boundary value problem has been treated. Under appropriate assumptions, using the method of differential inequalities we find a solution of the vector boundary value problem and obtain the uniformly valid asymptotic expansions.     

Vertex-Disjoint Cycles Containing Specified Edges

Dirac and Ore-type degree conditions are given for a graph to contain vertex disjoint cycles each of which contains a previously specified edge. One set of conditions is given that imply vertex disjoint cycles of length at most 4, and another set of conditions are given that imply the existence of cycles that span all of the vertices of the graph (i.e. a 2-factor). The conditions are shown to be sharp and give positive answers to conjectures of Enomoto in [3] and Wang in [5]. Revised: July 28, 1999     

Increased biotic metabolism of the biosphere inferred from observed data and models

A 35 year record ot production and respiration in tne Northern Hemisphere bas been derived from monthly records of atmospheric concentration, fossil fuel combustion, and oceanic absorption of carbon dioxide using a method developed by Hall et al. The original conclusion of Hall et al. that there was no significant change in biotic metabolism, is confirmed by measuring both production and respiration from 1958 to 1972. But the analysis of the subsequent record shows that both production and respiration have been enhanced since the early 1970s by some large scale global change, probably of human origin. Our results also show that high-latitude regions in the Northern Hemisphere are changing more than regions further south. Nevertheless, the ratio of production to respiration (P/R) remains unchanged during the time period examined. Thus, no argument can be made for net carbon storage of or release from the biosphere from this analysis, although the turnover rate of the biosphere appears to be enhanced.     

关于(Ⅱ)类方程极限环个数问题

本文利用Ｄｕｌａｃ函数构造（Ⅱ类方程的不变集［１］,研究此类方程极限环的个数,给出了判别准则,回答了文［２］中提出的问题．