废旧橡胶的催化裂解工艺

介绍了催化裂解技术对废旧橡胶回收再利用的处理工艺。废旧橡胶细块与催化剂A在400℃发生催化裂解反应,生成合成橡胶原始状态的产物,经分离得裂解气、石油馏分及炭黑产品。其生产过程能耗低,产品质量好,无污染物排放,产品具有综合利用价值。     

老化对丁羟推进剂燃速性能影响的试验研究

试验研究了贮存老化对HTPB复合固体推进剂燃速性能影响。分别采用自然老化和加速老化的试验方法,对HTPB推进剂在贮存过程中燃速的变化规律进行了对照分析。自然老化采用库房中贮存的方坯,加速老化采用热加速老化方法,燃速测定为水下声发射方法。试验结果表明,HTPB推进剂在贮存过程中燃速有随时间下降趋势,但变化不明显。自然老化与加速老化结论比较一致,具有可比性,这初步表明加速老化试验可以用于推算HTPB推进剂的燃速老化性能,所获得结论可以为固体火箭发动机进一步寿命评估作参考。分析了老化过程引起燃速性能变化的2种机理:化学老化引起的推进剂组分分解和物理老化引起的裂纹和空洞。前者使燃速产生减小的趋势,后者使燃速有增加的趋势,但总体而言,化学老化是主要的,老化的长期效应是燃速略有减小。     

The influence of publication delays on three ISI indicators

Summary Based on the transform function model of the observed citing process, the analytical expression of the age distribution of citations is deduced, and it is theoretically proved that the peak value of the citation distribution curve would fall and shift backward along with increasing the average publication delay and the peak age has a direct proportion relation with the pure delay and would be prolonged along with increasing the delay or decreasing the aging rate. The influence of the average publication delay on three ISI indicators impact factor, immediacy index and cited half-life are studied; in one subject discipline, the bigger the delay, the lower the three indicators of journals. Using the sensitivity theory, sensitivity formulae of the three indicators to publication delay parameters are deduced and it is found that responses of these indicators to changes of publication delays are different according to different time constant of the aging process; The faster the aging rate of a discipline literature is, the worse the influence of publication delays on the indicators of journals in the discipline.     

Structure–property relationships in polyurethanes derived from soybean oil

Two types of soy polyols have been prepared, one with secondary OH groups resulted from epoxidation of soybean oil followed by methanolysis (polyol type I) and the other with primary OH groups created from hydroformylation of soybean oil followed by hydrogenation (polyol type II). Cast polyurethane resins were prepared from these two types of polyols with Isonate 2143L, and rigid polyurethane foams were prepared from a blend of soy polyol and glycerol with PAPI 2901. Polyol II is much more reactive than polyol I towards polyurethane formation. This is evidenced from studies on polyurethane gel-times, glass transitions and rigid foam mechanical strengths. The reaction for the polyurethane formation is more complete for polyol II resulted from its higher reactivity than polyol I, although a less rigid polyurethane material is resulted from polyol II than from polyol I. Polyol type II also requires lower amounts of catalysts for rigid foam formulation. Both rigid foam systems produce foams having the required mechanical strength. The polyol II foam system behaves much like conventional rigid foam systems where the strength are proportional to system OH content, while the less reactive polyol I system does not.     

Micromechanical modeling of local field distribution for a planar composite under plastic deformation

Summary Due to statistical distribution of local material property, local stress and strain fields in a composite are random in nature. Classical micromechanical methods can only predict the average value of these local fields in different phases. An analytical method, which combines the maximum entropy theory and secant moduli method, is proposed in this paper. The distribution of the local field for a planar composite with plastic deformation is examined by the proposed method. The results show that with increase of plastic deformation the stress field in the matrix becomes more and more inhomogeneous. The predicted results on the stress distribution are in reasonable agreement with finite element simulation. Some salient features near the elastic and plastic deformation transition revealed by finite element simulation are also discussed.     

Piezoelectromagnetic waves guided by the surface of a ceramic cylinder

Summary The propagation of shear horizontal (SH) waves over the surface of a circular cylinder of polarized ceramics is studied from the three-dimensional equations of linear piezoelectromagnetism with full electromagnetic coupling. An exact solution is obtained.     

Molecular Dynamics Simulation for Ultrafine Machining

This article surveys the advances of molecular dynamics (MD) simulation in the research of ultrafine machining and related technologies. Modeling methods, including interatomic potentials and boundary conditions, are addressed. Algorithm strategies for MD simulations are discussed. By applying simulations with Tersoff potential, a case study of the material removal mechanism of the polishing based on coupling vibrations of liquid (PCVL) is presented.     

Local thermal property analysis by scanning thermal microscopy of an ultrafine-grained copper surface layer produced by surface mechanical attrition treatment

Scanning thermal microscopy (SThM) was used to map thermal conductivity images in an ultrafine-grained copper surface layer produced by surface mechanical attrition treatment (SMAT). It is found that the deformed surface layer shows different thermal conductivities that strongly depend on the grain size of the microstructure: the thermal conductivity of the nanostructured surface layer decreases obviously when compared with that of the coarse-grained matrix of the sample. The role of the grain boundaries in thermal conduction is analyzed in correlation with the heat conduction mechanism in pure metal. A theoretical approach, based on this investigation, was used to calculate the heat flow from the probe tip to the sample and then estimate the thermal conductivities at different scanning positions. Experimental results and theoretical calculation demonstrate that SThM can be used as a tool for the thermal property and microstructural analysis of ultrafine-grained microstructures.     

A proximate-time-optimal-control design and its application to a hard disk drive dual-stage actuator system

We propose a compensator-based strategy for design of a track-seeking and track-following control system for a dual-stage servo actuator in hard disk drives. A well-known decoupling structure is employed to disconnect the control of the primary voice coil motor (VCM) actuator from the loop for a secondary high-bandwidth actuator. The compensator is placed in the secondary loop and suitably combined with a saturation nonlinearity in order to obtain actuator signal boundedness. The design procedure consists of four steps: 1) design of an established nonlinear seek-settle-track following controller for the VCM; 2) design of a linear track following controller for the secondary actuator; 3) observer design; and 4) design of a compensator to retain global stability and to improve performance. The proposed control system improves performance of both long-span seeking (proximate-time-optimal controller) and short-span seeking. In addition, it achieves high-bandwidth track following performance. The experimental results show good track-following performance, and short-span/long-span-seeking performance with fast settling time. The overshoot during track seeking can be made negligible for a suitably tuned VCM-actuator control loop.