Characterization of cocrystals formed by grinding amino acids through terahertz time-domain spectroscopy

In this paper,we used terahertz time-domain spectroscopy(THz-TDS)over a range of 0.3–2.5 THz to investigate the formation of solid-state cocrystals of amino acids,formed by grinding mixtures of two different kinds of amino acids.For comparison,we prepared dual-layer samples,combined by pressing two single-component pellets together without grinding.In the ground-mixture samples,some extra absorption peaks appeared,different from the characteristic peaks of the pure components,but these peaks did not appear in the dual-layer samples.Thus,these extra absorption peaks in the THz range are unique features of cocrystals.From our results,we believe that THz-TDS is a promising technique to characterize cocrystals.     

Long-chain branched/cyclic alkanes in recent sediment of Lake Fuxian and their environmental implications

Lake Fuxian is a large, deep, and oligotrophic freshwater lake. In recent sediment of this lake, a series of branched and cyclic alkanes, including branched alkanes with one or two quaternary carbon atoms （C2n compounds）, alkylcycloheptane, and alkylcyclohexane, were detected in high abundance. For each homolog of long-chain branched/ cyclic alkanes, molecules with only an odd or even carbon number were present in the sediment. The abundance vari- ation of each compound homolog corresponded to those of other compound homolog in the section, indicating the same origin of these compounds. The concentrations of long-chain branched/cyclic alkanes in the sediment profile exhibited variations similar to those of phytoplankton biomarkers, such as 3-methylJalkanes, short-chain odd carbon n-alkanes, hopene, polyunsaturated fatty acids, phytol, sterols, and long-chain alkyl diols, but slightly different from those of long-chain odd carbon n-alkanes, which are ubiquitous biomarkers for higher plants. Therefore, the Can compounds and long-chain cyclic alkanes in the lake sediment were most likely produced by algae and bacteria in the water, primarily, by the heterotrophic bacteria in the moderately oxygenated waters, which flourishing might be the results of specific water environments in Lake Fuxian.     

On design of physical random access channel in high-speed railway LTE systems

For the uplink in the long-term evolution （LTE） systems, the physical random access channel （PRACH） adopts Zadoff-Chu （ZC） sequences as preamble sequences, and each user can choose a unique cyclic shift for user identification. In high-mobility scenario, the Doppler fre- quency shift raises up the false alarm probability by inducing the correlation peak offsetting at the receiver side. Traditional detection method utilizes multiple search win- dows for searching the potential uplink users. When the Doppler frequency shift is larger than the subcarrier spac- ing, the energy of correlation peak leaks outside the search window and increases the false alarm probability. In this paper, we present a novel design for PRACH preamble sequence for high-speed railway scenario. Through numerical observation, we find out that the offset of the correlation peaks only depends on the initial root sequence number and the length of ZC sequences. Therefore, the root number of ZC sequences should be carefully designed to generate a preamble sequence to fight against the Doppler frequency shift. Consequently, those offsets of the corre- lation peaks are concentrated within a single search win- dow, resulting in lower complexity of detection and lower probability of false alarm for random access in LTE uplink.     

微孔玻璃的制备及其吸附分离N_2/CO_2研究

吸附法脱除二氧化碳的关键在于开发高效的吸附剂.采用溶胶-凝胶法制备微孔玻璃,首先通过控制pH值、乙醇用量、温度等参数来得到适宜的干凝胶,干凝胶在高温下熔融形成玻璃体后,依次进行分相和酸浸析处理后得到微孔玻璃.结果表明:在pH值1~2、凝胶温度50℃、熔融温度1 175℃条件下,可以得到孔径集中在0.7~2.0 nm的微孔玻璃;随着盐酸浓度的升高,微孔玻璃的平均孔径逐渐增大,而孔体积和比表面积则逐渐减小;微孔玻璃对N2/CO2具有较高的吸附选择性,分离因子可达8.4以上.     

颗粒物质三维直剪实验的数值模拟

为了获取断层物质的受压剪切特性,用离散元法生成5种非规则颗粒单元来模拟自然条件下断层物质的直剪过程,以实验数据为参数,探讨了不同法向应力、摩擦系数、颗粒形状、试样颗粒组构对断层物质的剪应力的影响。结果表明,剪应力随法向应力、摩擦系数、非规则颗粒含量的增加而增大,不同法向应力、颗粒形状、试样组构下孔隙率的变化反映了剪应力的变化。     

晶体管混合π模型与网络Y参数模型的等效变换

Y参数模型是晶体管高频小信号放大电路分析中常采用的网络参数模型,以共射组态晶体管为例,通过电路转换及Y参数的定义,获得了共射组态晶体管Y参数与混合π型参数之间的关系.     

Joining of Si3N4 ceramic using PdCo(Ni SiB)–V system brazingfi ller alloy and interfacial reactions

The wettability of V-active PdCo-based alloys on Si3N4ceramic was studied with the sessile drop method. And the alloy of Pd50.0–Co33.7–Ni4.0–Si2.0–B0.7–V9.6(wt%),was developed for Si3N4ceramic joining in the present investigation. The rapidly-solidified brazing foils were fabricated by the alloy Pd50.0–Co33.7–Ni4.0–Si2.0–B0.7–V9.6. The average room-temperature three-point bend strength of the Si3N4/Si3N4joints brazed at 1453 K for 10 min was 205.6 MPa,and the newly developed braze gives joint strengths of 210.9 MPa,206.6 MPa and 80.2 MPa at high temperatures of 973 K,1073 K and 1173 K respectively. The interfacial reaction products in the Si3N4/Si3N4joint brazed at 1453 K for10 min were identified to be VN and Pd2Si by XRD analysis. Based on the XEDS analysis result,the residual brazing alloy existing at the central part of the joint was verified as Co-rich phases,in which the concentration of element Pd was high up to 18.0–19.1 at%. The mechanism of the interfacial reactions was discussed. Pd should be a good choice as useful alloying element in newer high-temperature braze candidates for the joining of Si-based ceramics.     

Φ6250土压平衡盾构机出渣能力设计计算

简要介绍了土压平衡盾构的排渣系统,指出了保持其土仓压力平衡的重要性。并以太重Φ6250土压平衡盾构机为考察依据,对该盾构机的螺旋输送机的排渣能力和皮带运输机的运输能力进行了设计核算。     

Force modeling for needle insertion into soft tissue based on mechanical properties and geometric parameters

The force model during needle insertion into soft tissue is important for accurate percutaneous intervention.In this paper,a force model for needle insertion into a tissue-equivalent material is presented and a series of experiments are conducted to acquire data from needle soft-tissue interaction process.In order to build a more accurate insertion force model,the interaction force between a surgical needle and soft tissue is divided into three parts：stiffness force,friction force,and cutting force.The stiffness force is modeled on the basis of contact mechanics model.The friction force model is presented using a modified Winkler＇s foundation model.The cutting force is viewed as a constant depending on a given tissue.The proposed models in the paper are established on the basis of the mechanical properties and geometric parameters of the needle and soft tissue.The experimental results illustrate that the force models are capable of predicting the needle-tissue interaction force.The force models of needle insertion can provide real-time haptic feedback for robot-assisted procedures,thereby improving the accuracy and safety of surgery.     

Design and research of torque tube used in HTS motor

In order to improve the overall performance of high temperature superconducting （HTS） motor, a radial connection torque tube with high strength and low thermal leakage has been designed. Firstly, fiberglass epoxy composite is chosen as con- struction material. The structural size of the torque tube is obtained by means of load analysis and theoretical calculation. Secondly, thermal leakage of the torque tube is calculated with both theo- retical method and 3D finite-element analysis （FEA）. According to the result of the thermal analysis and mechanical loads, the struc- tural stresses of the torque tube are also obtained by FEA method. Lastly, a low temperature test platform is developed to verify the strength and the thermal leakage of the torque tube. The results show that the maximal shear stress of the torque tube is 24.3 MPa and thermal leakage of torque tube is 10.5 W, which satisfy the design requirements of the HTS motor. The torque tube also works in good condition at full-power and full-torque testing of the motor. The design method is also applicable for other similar design of torque tube in other applications.