First-principles investigation of pressure-induced changes in structural and electronic properties of Y 2C3 superconductor

The structural and electronic properties of Y ₂C₃ superconductor under different external pressures were calculated by employing the first-principles method. This shows that the lattice constants as well as the lengths of C-C dimers decrease with the pressure. Results of band structure calculations indicate that the Fermi level advances to the bonding zone with an increase in pressure; meantime, the valence and conduction bands intersect more deeply with the Fermi level. Moreover, the Fermi level is found to shift from the valley bottom of the density of states (DOS) curve to the shoulder, which means an increase in N(E_F), and therefore the critical temperature, T_c. The calculations verify that the critical temperature is directly related to the electronic structure.     

Chaotic attractor transforming control of hybrid Lorenz-Chen system

Based on passive theory, this paper studies a hybrid chaotic dynamical system from the mathematics perspective to implement the control of system stabilization. According to the Jacobian matrix of the nonlinear system, the stabilization control region is gotten. The controller is designed to stabilize fast the minimum phase Lorenz-Chen chaotic system after equivalently transforming from chaotic system to passive system. The simulation results show that the system not only can be controlled at the different equilibria, but also can be transformed between the different chaotic attractors.     

The magnetic and dielectric properties of multiferroic Sr- substituted Zn2-Y hexagonal ferrites

The magnetic and dielectric properties of Sr-substituted Zn2-Y hexagonal ferrites （Ba2-x SrxZn2Fe12O22, 1.0 〈 x ≤ 1.5） are studied in this paper. Sr substitution will lead to the variation of cation occupation, which influences both the magnetic and electric properties. As Sr content x rises from 1.0 to 1.5, magnetic hysteresis loop gets wider gradually and the permeability drops rapidly due to the transformation from ferrimagnetic to antiferromagnetic phase. Moreover, permittivity rises with increasing Sr content. Under a certain external magnetic field, the phase transition of helical spin structure of Ba0.5Srl.5Zn2Fe12O22 at about 295 K seems to open a possibility for the room-temperature ferroelectricity induced by magnetic field. But its low resistivity prevents the observation of ferroelectric and magnetoelectric properties at room-temperature.     

Design of the target type flowmeter based on fiber Bragg grating and experiment

The target type flowmeter based on fiber Bragg gratings （FBGs） is experimentally studied. The relationship between the central wavelength shift of FBG and the flux is derived and the analytic expression is also given. Simulation and preliminary experiments have been carried out, and experimental validation of the water further proves the feasibility of the sensor. The experimental results verify the proposed sensor which can measure flux range from 200 to 1200 cm^3/s. And on this basis, the improvement program is raised.     

Porous polymer films and honeycomb structures based on amphiphilic dendronized block copolymers

Fabrication of honeycomb patterned films from our synthesized amphiphilic dendronized block copolymer by "on-solid surface spreading" method and "on-water spreading" method was reported for the first time in this paper. The comparison of the two methods indicated honeycomb-patterned films with smaller size, and larger surface density of micropores can be fabricated by spreading on water but with lower regular arrangement. Furthermore, several influencing factors on the formation of the honeycomb structure and the different morphologies, such as the concentration of the copolymer solution and the relative humidity in the atmosphere and the substrates, were investigated. The results showed that comparably high relative humidity from 80% to 95% was needed, and the mica plate as a spreading substrate was suitable to form orderly porous films for such a copolymer. The best ordered pattern could be formed from the copolymer with concentration of 1.00 mg/mL at the relative humidity of 85% using a mica plate. Besides, strong periodicity, regularity, and a large, defect-free area were notable, which made this structure extremely interesting for applications for templated molecular objects formed via intramolecular metal or metal oxide synthesis.     

Solution route to single crystalline SnO platelets with tunable shapes

Square and round single crystalline SnO platelets have been prepared in a solution-based chemical route aided with sonication at room temperature.     

Ordered thin films of alkyloxy-substituted benzaldehydes on a graphite surface studied by scanning tunneling microscopy

The molecular assembly of three different trialkyloxy-substituted benzaldehydes on graphite has been studied using scanning tunneling microscopy (STM). It is found that these benzaldehydes, which do not have intermolecular hydrogen bonding, could form a lamella arrangement in which the headgroups are aligned side by side. The effect due to the alkyl chain length on the lamella structure is also presented. Received: 21 January 2002 / Accepted: 22 March 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +86-10/6255-7908     

Structure and thermal behaviors of organic crystals based on substituted 1,3,4-thiadiazoles

The crystalline structure of some compounds containing the 1,3,4-thiadiazole moiety, (1) 5-ethyl-2-amino-1,3,4- thiadiazole (EATZ), (2) 5-benzylsulfany-2-amino-1,3,4-thiadiazole (BSATZ) and (3) 2,5-bis-benzylsulfanyl-1,3,4-thiadiazole (BBSTZ) were determined. Both EATZ and BBSTZ show orthorhombic structures with space group Pbca and BSATZ a monoclinic system with space group C2/c. The lattice parameters: a=0.72280 (14), b=1.0811 (2), c=1.6210 (3) nm for 1, a=2.5282 (5), b=0.59083 (12), c=1.5390 (3) nm for 2 and a=0.87530 (18), b=1.0365 (2), c=3.6098 (7) nm for 3. To compare the intra- and intermolecular interactions in thiadiazole containing organic crystals, thermal analysis studies on each crystal is performed using DSC and TG in N₂ atmosphere to describe the thermal behaviors. Based on the results, the changing regularity of melting point and decomposition temperature of these compounds is educed     

A versatile approach to PI(3,4)P2, PI(4,5)P2, and PI(3,4,5)P3 from L-(-)-quebrachitol

[reaction: see text] A versatile synthesis of PI(3,4)P2, PI(4,5)P2, and PI(3,4,5)P3 is disclosed, starting from L-(-)-quebrachitol, a byproduct of latex production. The crystalline nature of most intermediates and the utilization of inexpensive protecting groups facilitate this synthetic route and its scale-up.     

焦斑形态精细化设计及其性能分析

 对实现焦斑形态控制的衍射光学器件进行了精细化设计,模拟计算结果表明,可同时满足洞口附近旁瓣光强峰值不超过主瓣平均光强的0.01%,且主瓣顶部不均匀性小于10%。选取不同的采样间隔对比说明了精细化设计相对于传统设计,能真实准确地获得焦斑形态的性能参数。最后,采用功率谱密度(PSD)方法初步分析了器件几何结构与焦斑性能,特别是旁瓣间的对应关系。