Density-functional study of lanthanum, ytterbium, and lutetium dimers

La-2, Yb-2, and Lu-2 have been studied by use of the density-functional methods B3LYP, BLYP, B3PW91, BHLYP, BP86, B3P86, MPW1PW91, and PBE1PBE. In these density-functional methods, the exchange functional is from either Becke's three-parameter HF-DFT hybrid exchange functional (B3), pure DFT exchange functional of 1988 (B), a modification of the half-and-half HF/DFT hybrid method (BH), Perdew-Wang 1991 (PW91), or Barone's modified PW91 (MPW1), while the correlation functional is from either Lee, Yang, and Parr (LYP), Perdew-Wang 1991 (PW91), or Perdew 86 (P86). PBE1PBE is the generalized-gradient-approximation exchange-correlation functional of Perdew, Burke, and Ernzerhof. For La-2, the calculated bond distance is in reasonable agreement with the experiment, but the calculated vibrational frequency is underestimated significantly compared with the experiment. Only BP86 and B3P86 have the best performance in reproducing the experimental dissociation energy for La-2. For the van der Waals dimer Yb-2, three functionals, B3LYP, BLYP, and BHLYP have excellent performance in reproducing the spectroscopic constants compared with both the experiment and previous theoretical studies.

Ground state of lutetium dimer by density functional methods

Bond distances, vibrational frequencies and dissociation energies for the ground state of Lu-2 were studied by density functional methods B3LYP, B3PW91, BLYP, BHLYP, BP86, B3P86, MPW1PW91, PBE1PBE and SVWN with CEP-121G and SDD basis sets. Singlet state is predicted to be the most stable. CEP-121G has a better overall performance than SDD. At CEP-121G basis set, all density functional methods used in this study perform well in reproducing the spectroscopic constants.

Self-assembly of star block copolymers by dynamic density functional theory

The dynamic mean-field density functional method, driven from the generalized time-dependent Ginzburg-Landau equation, was applied to the mesoscopic dynamics of the multi-arms star block copolymer melts in two-dimensional lattice model. The implicit Gaussian density functional expression of a multi-arms star block copolymer chain for the intrinsic chemical potentials was constructed for the first time. Extension of this calculation strategy to more complex systems, such as hyperbranched copolymer or dendrimer, should be straightforward. The original application of this method to 3-arms block copolymer melts in our present works led to some novel ordered microphase patterns, such as hexagonal (HEX) honeycomb lattice, core-shell HEX lattice, knitting pattern, etc. The observed core-shell HEX lattice ordered structure is qualitatively in agreement with the experiment of Thomas [Macromolecules 31, 5272 (1998)].

Real-time immunoassay of antibody activity in serum by surface plasmon resonance biosensor

A surface plasmon resonance biosensor has been used to determine antibody activity in serum. As a model system, the interaction of mouse IgG and sheep anti-mouse IgG polyclonal antibody was investigated in real time. The factors, including pH value, ionic strength, protein concentration, influencing electrostatic adsorption of mouse IgG protein onto carboxylated dextran-coated sensor chip surface, were studied. The procedures of mouse IgG protein immobilization and immune reaction were monitored in real time. The regeneration effect using the different elution reagents was also investigated. The same mouse IgG immobilized surface can be used for 100 cycles of binding and elution with only 0.38% loss per regeneration in reactivity. The results show that the surface plasmon resonance biosensor is a rapid, simple, sensitive, accurate and reliable detection technique for real-time immunoassay of antibody activity. The assay allows antibodies to be detected and studied in their native form without any purification. (C) 2000 Elsevier Science B.V. All rights reserved.

Prediction of C-13-nuclear magnetic resonance chemical shifts for aliphatic amines

Prediction of C-13-nuclear magnetic resonance chemical shifts for aliphatic amines is performed. The topological, geological and electronic descriptors are generated. To reduce the variables, the best subsets of the descriptors are obtained by using leaps-and-bounds regression analysis. The model is achieved using multiple regression with satisfactory results.

Electrostatic layer-by-layer assembly of polycation and DNA multilayer films by real-time surface plasmon resonance technique

The assembly of alternating DNA and positively charged poly(dimethyldiallylammonium chloride) (PDDA) multilayer films by electrostatic layer-by-layer adsorption has been studied. Real time surface plasmon resonance (BIAcore) technique was used to characterize and monitor the formation of multilayer films in solution in real time continuously. The results indicate that the uniform multilayer can be obtained on the poly(ethylenimine) (PEI) coated substrate surface. The kinetics of the adsorption of DNA on PDDA surface was also studied by real-time BIAcore technique, and the observed rate constant was calculated using a Langmuir model (k(obs) = (1.28 +/- 0.08) x 10(-2) s(-1)).

NMR titration and molecular model MOPAC calculation of protonation processes of two MRI ligands

The protonation process of two DTPA bis(amide) derivatives, DTPA-BDMA and DTPA-BDEA, was studied by using H-1 NMR titration and MOPAC calculation. Their protonation process was proposed in the order of the central amine, the terminal amines, the central carboxyl, the terminal carboxyl, the other terminal carboxyl and central amine. During the protonation of the terminal amine, there existed a large fraction of proton transfer from the central amine to the other terminal amine.

Sequence analysis and functional study of thymidylate synthase from zebrafish, Danio rerio

The thymidylate synthase (TS), an important target for many anticancer drugs, has been cloned from different species. But the cDNA property and function of TS in zebrafish are not well documented. In order to use zebrafish as an animal model for screening novel anticancer agents, we isolated TS cDNA from zebrafish and compared its sequence with those from other species. The open reading frame (ORF) of zebrafish TS cDNA sequence was 954 nucleotides, encoding a 318-amino acid protein with a calculated molecular mass of 36.15 kDa. The deduced amino acid sequence of zebrafish TS was similar to those from other organisms, including rat, mouse and humans. The zebrafish TS protein was expressed in Escherichia coli and purified to homogeneity. The purified zebrafish TS showed maximal activity at 28 degrees C with similar K-m value to human TS. Western immunoblot assay confirmed that TS was expressed in all the developmental stages of zebrafish with a high level of expression at the 1-4 cell stages. To study the function of TS in zebrafish embryo development, a short hairpin RNA (shRNA) expression vector, pSilencer 4.1-CMV/TS, was constructed which targeted the protein-coding region of zebrafish TS mRNA. Significant change in the development of tail and epiboly was found in zebrafish embryos microinjected pSilencer4.1-CMV/TS siRNA expression vector.

A mechanistic model of algal photoinhibition induced by photodamage to Photosystem-II

Photoinhibition is a central problem for the understanding of plasticity in photosynthesis vs. irradiance response. It effectively reduces the photosynthetic rate. In this contribution, we present a mechanistic model of algal photoinhibition induced by photodamage to photosystem-II. Photosystem-IIs (PSIIs) are assumed to exist in three states: open, closed and inhibited. Photosynthesis is closely associated with the transitions between the three states. The present model is defined by four parameters: effective cross section of PSII, number of PSIIs, turnover time of electron transfer chains and the ratio of rate constant of damage to that of repair of D1 proteins in PSIIs. It gives a photosynthetic response curve of phytoplankton to irradiance (PI-curve). Without photoinhibition, the PI-curve is in hyperbola with the first three parameters. The PI-curve with photoinhibition can be simplified to the same form as the hyperbola by replacing either the number of PSIIs with the number of functional PSIIs or the turnover time of electron transfer chains with the average turnover time.

直接驱动机器人关节加速度反馈解耦控制

以利用线加速度传感器实际测量转动关节的加速度为基础 ,分析了机器人关节加速度反馈控制的开环模型 ,以及影响其闭环稳定性的主要因素 ;提出了闭环控制策略的设计准则 .在一台三自由度直接驱动机器人上的实验结果证明了该文分析的正确性 ,与不具备加速度反馈控制时的实验结果相比较 ,显示出这种方法的有效性

阿片药物依赖的神经机制---内侧前额叶与药物的心理依赖

Mental dependence, characterized by craving and impulsive seeking behavior, is the matter of intensive study in the field of drug addiction. The mesolimbic dopamine system has been suggested to play an important role in rewarding of drugs and relapse. Although chronic drug use can induce neuroadaptations of the mesolimbic system and changes of drug reinforcement, these mechanisms cannot fully account for the craving and the compulsive drug-using behavior of addicts. Acknowledging the reinforcement effects of drugs, most previous studies have studied the impact of environmental cues and conditioned learning on addiction behavior, often using established classical or operant conditioning model. These studies, however, paid little attention to the role of cognitive control and emotion in addiction. These mental factors that are believed to have an important influence on conditioned learning. The medial prefrontal cortex (mPFC) has close anatomic and functional connections with the mesolimbic dopamine system. A number of the cognitive neurological studies demonstrate that mPFC is involved in motivation, emotional regulation, monitoring of responses and other executive functions. Thus we speculated that the function of abnormality in mPFC following chronic drug use would cause related to the abnormal behavior in addicts including impulse and emotional changes. In the present study of a series of experiments, we used functional magnetic resonance imaging to examine the hemodynamic response of the mPFC and related circuits to various cognitive and emotional stimuli in heroin addicts and to explore the underlying dopamine neuromechnism by microinjection of tool drugs into the mPFC in laboratory animals. In the first experiment, we found that heroin patients, relative to the normal controls, took a much shorter time and committed more errors in completing the more demanding of cognitive regulation in the reverse condition of the task, while the neural activity in anterior cingulate cortex (ACC) was attenuated. In the second experiment, the scores of the heroin patients in self-rating depression scale (SDS) and Self-rating anxiety scale (SAS) were significantly higher than the normal controls and they rated the negative pictures more aversive than the normal controls. Being congruent with the behavioral results, hemodynamic response to negative pictures showed significant difference between the two groups in bilateral ventral mPFC (VMPFC), amygdala, and right thalamus. The VMPFC of patients showed increased activation than normal controls, whereas activation in the amygdala of patients was weaker than that in normal subjects. Our third experiment showed that microinjection of D1 receptor agonist SKF38393 into the mPFC of rats decreased hyperactivity, which was induced by morphine injection, in contrast, D1 receptor antagonist SCH23390 increased the hyperactivity, These findings suggest: (1) The behavior and neural activity in ACC of addicts changed in chronic drug users. Their impulsive behavior might result from the abnormal neural activity in the mPFC especially the ACC. (2) Heroine patients were more depress and anxiety than normal controls. The dysfunction of the mPFC---amygdala circuit of heroine addicts might be related to the abnormal emotion response. (3) Dopamine in the mPFC has an inhibitory effect on morphine induced behavior. The hyperactivity induced by chronic morphine was reduced by dopamine increase with D1 receptor agonist, confirm the first experiment that the neuroadaption of mPFC system induced by chronic morphine administration appears to be the substrate the impulse behavior of drug users.

心算年老化的认知心理机制及功能磁共振成像研究

Mechanisms underlying cognitive psychology and cerebral physiological of mental arithmetic with increasing are were studied by using behavioral methods and functional magnetic resonance imaging (fMRI). I. Studies on mechanism underlying cognitive psychology of mental arithmetic with increasing age These studies were accomplished in 172 normal subjects ranging from 20 to 79 years of age with above 12 years of education (Mean = 1.51, SD = 1.5). Five mental arithmetic tasks, "1000-1", "1000-3", "1000-7", "1000-13", "1000-17", were designed with a serial calculation in which subjects sequentially subtracted the same prime number (1, 3, 7, 13, 17) from another number 1000. The variables studied were mental arithmetic, age, working memory, and sensory-motor speed, and four studies were conducted: (1) Aging process of mental arithmetic with different difficulties, (2) mechanism of aging of mental arithmetic processing. (3) effects of working memory and sensory-motor speed on aging process of mental arithmetic, (4) model of cognitive aging of mental arithmetic, with statistical methods such as MANOVA, hierarchical multiple regression, stepwise regression analysis, structural equation modelling (SEM). The results were indicated as following: Study 1: There was an obvious interaction between age and mental arithmetic, in which reaction time (RT) increased with advancing age and more difficult mental arithmetic, and mental arithmetic efficiency (the ratio of accuracy to RT) deceased with advancing age and more difficult mental arithmetic; Mental arithmetic efficiency with different difficulties decreased in power function: Study 2: There were two mediators (latent variables) in aging process of mental arithmetic, and age had an effect on mental arithmetic with different difficulties through the two mediators; Study 3: There were obvious interactions between age and working memory, working memory and mental arithmetic; Working memory and sensory-motor speed had effects on aging process of mental arithmetic, in which the effect of working memory on aging process of mental arithmetic was about 30-50%, and the effect of sensory-motor speed on aging process of mental arithmetic was above 35%. Study 4: Age, working memory, and sensory-motor speed had effects on two latent variables (factor 1 and factor 2), then had effects on mental arithmetic with different difficulties through factor 1 which was relative to memory component, and factor 2 which relative to speed component and had an effect on factor 1 significantly. II. Functional magnetic resonance imaging study on metal arithmetic with increasing age This study was accomplished in 14 normal right-handed subjects ranging from 20 to 29 (7 subjects) and 60 to 69 (7 subjects) years of age by using functional magnetic resonance imaging apparatus, a superconductive Signa Horizon 1.5T MRI system. Two mental arithmetic tasks, "1000-3" and "1000-17", were designed with a serial calculation in which subjects sequentially subtracted the same prime number (3 or 17) from another number 1000 silently, and controlling task, "1000-0", in which subjects continually rehearsed number 1000 silently, was regarded as baseline, based on current "baseline-task" OFF-ON subtraction pattern. Original data collected by fMRI apparatus, were analyzed off-line in SUN SPARC working station by using current STIMULATE software. The analytical steps were composed of within-subject analysis, in which brain activated images about mental arithmetic with two difficulties were obtained by using t-test, and between-subject analysis, in which features of brain activation about mental arithmetic with two difficulties, the relationship between left and right hemisphere during mental arithmetic, and age differences of brain activation in young and elderly adults were examined by using non-parameter Wilcoxon test. The results were as following: