The storage and its stability of space charge in poly(ethylene naphthalene-2, 6-dicarboxylate)

Poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) is an aromatic polyester with molecular structure similar to that of poly(ethylene terephthalate)(PET). In this paper, the space charge storage ability and its stability in corona charged PEN were studied by measurement of surface potential decay under different storage conditions including dif- ferent temperatures and relative humidities, and analysis of open circuit thermally stimu- lated discharge (TSD) current spectra and charge TSD curves. The comparison between the charge stability of PEN and PET was carried out. The results point out that the charge stability of PEN is markedly better than that of PET under different environmental condi- tions. By means of isothermal depolarization program, the space charge lifetimes (effec- tive time constant) τ at room temperature of positively and negatively charged PEN are estimated to be 90 y. The results offer theoretical and technical support for the use of PEN as the chip of high quality electret condenser microphone due to its excellent dielectric, mechanical and thermal properties.     

The Dual Probability Sieve Method and the Distribution fo Primes (Revision)——On the Goldbach conjecture,the 8th problem of Hilbert and the YU Xin-he conjecture

~~The Dual Probability Sieve Method and the Distribution fo Primes (Revision)——On the Goldbach conjecture,the 8th problem of Hilbert and the YU Xin-he conjecture~~     

The Theoretical Study of O_2 Adsorption on NiTi (100) and (110) Surfaces

1　IntroductionNiTishapememoryalloyhaswidelybeenusedinmanyfieldsduetoitsexcellentmechanicalproperties ,uniqueshapememoryeffectandsuperelasticity .In 1970’s ,thegoodbiocompatibilityofNiTialloywasdiscoveredanditwasfurtherusedforvariousbiomedicalapplica tions ,suchasorthopaedicsurgery ,cardiovascularandgas trointestinalsurgery[1-4] .Thehighmechanicalpropertiesandbiocompatibilityofthebiomedicalmaterialsarenec essaryfortheirefficientuseinhumanbody .Thecorrosionresistanceofthealloyandthetoxicityo…     

From the Journal of University of Science and Technology Beijing (in Chinese)

Evaluation on Structure Damage Due to Heavy Rain in Hard Composite Rock-mass in Subsidence Area Based on the displacement.stree and energy coupled monitoring technique.the trends of subsi     

Effect of PVA Fiber on the Dynamic and Static Mechanical Properties of Concrete under Freeze-thaw Cycles at Extremely Low Temperature(-70 ℃)

In order to study the effect of PVA fiber on the dynamic and static mechanical properties of low-temperature freeze-thaw concrete under the saturated surface dry state, different contents of PVA fiber were added to prepare concrete in this experiment. The concrete was subjected to compression, flexural and SHPB impact tests combined with scanning electron microscopy for microstructure analysis, after different times of freeze-thaw cycles in the temperature range of 20--70℃. The experimental resu...     

ABSTRACTS--From the Journal of University of Science and Technology Beijing (in Chinese)

Mineral Study on forecasting strong mining-induced earthquake Tie Li, Meifeng Cai, Hongguang Ji, Shiyu Li, Xuesong He Based on field observations of the high-density digital seismograph and tidal deformation network of a meso-scale seismological experimental site, the data of strong mining-induced earthquake process were analyzed by the seismological method and wavelet tool. Believable b values and ηvalues     

Research on seismic performance and design method of combined steel lead energy dissipation structure(Ⅰ)

A new combined steel lead damper (NCSLD) was presented. Construction and working mechanism of NCSLD were introduced,pseudo-static tests of the small size dampers which would be used in the subsequent shaking table tests were carried out for the study of mechanical properties of NCSLD using electro-hydraulic servo press-shear machine. Processing technology of the damper was improved. Shaking table tests under two-dimensional excitation on structural aseismic control of a one-story structure model were carried out using the small size NCSLD; parameters of the structure and shaking table were also introduced. Results indicate that process improvement is beneficial to the implementation of working mechanism of the damper,NCSLD has full hysteresis loop which takes on bilinearity,NCSLD has obvious energy dissipation effect and it can control structural seismic response effectively.     

Coalescence of the crystallites under hydrothermal conditions (II)

Cuprite (Cu₂O) particles are synthesized by hydrothermal method. Most crystalline particles have long column morphology. Particles which are regarded as assembling of the crystallites in definite directions are observed. The typical example is the particles formed by assembling six columns in three perpendicular directions. The cone surfaces are visible at the tops of the columns. The results revealed that the coalescence of the crystallites did happen under hydrothermal conditions in which the crystallite connected with other crystallite on certain structure compatible surfaces to form a crystalline particle with a special morphology. This phenomenon is called the second kind of coalescence. The Cu₂O structure unit is determined by its crystal structure. It is concluded that the tetragonal prism and three tetragonal prism-like growth units are the favorable units after stability energy calculation was performed on different kinds of growth units. It is believed that the first kind of coalescence exists commonly. The second kind of coalescence is unlikely to occur for all crystallites under hydrothermal conditions. The occurrence is dependent on the crystal structure.     

The growth units and hydrothermal preparation of lead tungstate (PbWO4) crystallites

The crystal structure of lead tungstate (PbWO4) can be regarded as ordered combination of the tungsten oxide tetrahedrons (WO4) and lead ions (Pb2 ). According to the growth unit model, the growth units of lead tungstate are the aggregations of the tungsten oxide tetrahedrons and lead cations with various geometry configurations. It is suggested that the favorable growth units of lead tungstate crystal are pyramidal, tetragonal prism and quadrangular units corresponding to geometric orientations of the simple forms of the crystal. Under low restricted growth conditions, the growth form of lead tungstate crystallites is the aggregation of the geometric configurations of these favorable growth units. The above conclusions are completely confirmed by the experiment on hydrothermal preparation of lead tungstate crystallites.     

Formation mechanism of barium titanate nanocrystalis under hydrothermal conditions

Growth units and the crystallization habit of BaTiO3 nanocrystals have been investigated. It has been proposed that the growth units of BaTiO3 were surface hydroxylated Ti(OH)62- octahedra. The relationship between crystal morphology and the variation of the current intensity in the solution has been obtained through the measurement of the OH in the solution and the hydrothermal experiment with superimposed direct electric field. Based on the computation of the stability energy of the growth units, the relationship between the crystallized morphology of crystallites and the most favorable growth units under different conditions has been derived. It has been found that there is structure similarity between anatase (TiO2) and BaTiO3 from the crystal chemistry viewpoint, so they are soluble in each other, which can serve as a reasonable explanation for the abnormal phenomenon of the retention of cubic substable phase at room temperature.     

Formation mechanism of barium titanate nanocrystals under hydrothermal conditions

Growth units and the crystallization habit of BaTiO₃ nanocrystals have been investigated. It has been proposed that the growth units of BaTiO₃ were surface hydroxylated Ti(OH)₆²⁻ octahedra. The relationship between crystal morphology and the variation of the current intensity in the solution has been obtained through the measurement of the OH⁻ in the solution and the hydrothermal experiment with superimposed direct electric field. Based on the computation of the stability energy of the growth units, the relationship between the crystallized morphology of crystallites and the most favorable growth units under different conditions has been derived. It has been found that there is structure similarity between anatase (TiO₂) and BaTiO₃ from the crystal chemistry viewpoint, so they are soluble in each other, which can serve as a reasonable explanation for the abnormal phenomenon of the retention of cubic substable phase at room temperature. Project supported by the National Natural Science Foundation of China.     

关于系统零解完全稳定与渐近稳定的一个问题

讨论了系统在零解在经常扰动下稳定推出零解一致指数型渐近稳定的条件，并在这个条件下证明了系统的零解一致指数型渐近稳定，则零解在经常扰动下稳定。     

Synthesis of ZnO fibers and nanometer powders by hydrothermal method

Ｎａｎｏｍｅｔｅｒｐｏｗｄｅｒｉｓｓｍａｌｌｐａｒｔｉｃｌｅｓｗｉｔｈｔｈｅｓｉｚｅｏｆｌｅｓｓｔｈａｎ100ｎｍ.Ｂｅｃａｕｓｅｏｆｉｔｓｕｎｉｑｕｅｓｔｒｕｃｔｕｒｅ,ｉｔｈａｓａｌｏｔｏｆｃｈａｒａｃｔｅｒｉｓｔｉｃｓｄｉｆｆｅｒｅｎｔｆｒｏｍｇｅｎｅｒａｌｐｏｗｄｅｒｓ.Ｓｔｕｄｙａｂｏｕｔｔｈｅｐｒｅｐａｒａｔｉｏｎａｎｄａｐｐｌｉｃａｔｉｏｎｏｆｎａｎｏｍｅｔｅｒｐｏｗｄｅｒｉｓｕｎｄｅｒｗａｙ.Ｈｙｄｒｏｔｈｅｒｍａｌｍｅｔｈｏｄ[1]ｉｓｏｎｅｏｆｔｈｅｍｏｓｔｉｍｐｏｒｔａｎｔｗｅｔｃｈ…     

Phase field simulation of the interface morphology evolution and its stability during directional solidification of binary alloys

The influences of pulling speed V and temperature gradient G on morphology evolution, concentration distribution, solute trapping and interface stability during directional solidification of binary alloys have been studied with the B-S phase field model. Simulated results reproduced the morphology transitions of deep cell to shallow cell and shallow cell to plane front. The primary cellular spacing, depth of groove and effective solute redistribution coefficient for different V and G are compared. The absolute stability under high pulling speed and high temperature gradient has also been predicted, which is in agreement with the Mullins-Sekerka (M-S) stability theory. Supported by the National Natural Science Foundation of China (Grant No. 50401013)     

水热前驱溶液pH值对Sm2O3微晶相组成及显微结构的影响

以SmCl3·6H2O和NaOH为起始原料,采用水热法可控制备了Sm2O3微晶．利用X-射线衍射仪（XRD）、扫描电子显微镜（SEM）分别对产物的物相和形貌进行了表征．结果表明：在水热条件下,反应温度为200℃,前驱溶液PH为9时,水热产物主晶相为Sm2O3,杂相为Sm（OH）2C1,呈现细棒状结构．在800℃下煅烧,保温1h均可得到纯的Sm2O3立方相微晶．随着pH值的增大,所制备的Sm2O3微晶的形貌变成规则的棒状结构,当pH为9时,棒状结构尺寸约为0．2～0．3μm．     

Preparation and thermal stability of Pd_(40.5)Ni_(40.5)SixP_(19-x) bulk metallic glasses

With the addition of Si to replace some P,Pd_(40.5)Ni_(40.5)Si_xP_(19-x)(x=0,2.5,5,9.5,14,and 19 in atomic number fraction) bulk glassy samples with the diameter of about 5 mm were successfully prepared by use of flux treatment and water quenching technology.With the increase of Si content,the glass forming ability of Pd_(40.5)Ni_(40.5)Si-xP_(19-x) increases first for low Si content and then decreases for high Si content (Si≥9.5at%).The Pd_(40.50Ni_(40.5)Si_5P_(14) glassy alloy possesses the largest supe...     

Effect of Fe(III) impurity on the electrochemical performance of LiFePO_4 prepared by hydrothermal process

Lithium iron phosphate (LiFePO4) was synthesized from LiOH, FeSO4 and H3PO4 by a hydrothermal process at 180℃. The samples were characterized by X-ray diffraction, scanning electron microscopy and chemical analysis. Electrochemical performance of the samples was tested in terms of charge-discharge capacity and cycling behavior. The results indicated that Fe(III) impurity had obvi- ously effect on the electrochemical properties of LiFePO4, and the formation of Fe3 was caused by the oxidation of Fe2 in the dissolving and feeding processes accompanying the increase of pH value. It was found that the precipitation separation was effective in decreasing the content of Fe3 in the solu- tion of FeSO4 and the sealed feeding was useful in preventing the conversion of Fe2 to Fe3 . When the content of Fe3 < 0.5 wt%, the hydrothermally synthesized LiFePO4 calcined at 750℃ with sucrose as carbon source exhibited an initial discharge capacity of 154.9 mAh·g-1 at the rate of 0.1 C (1 C = 150 mA·g-1) and the cycling retention rate could reach 98% after 50 cycles at room temperature.