The assessment of particle friction of a drug substance and a drug carrier substance

The centrifuge technique, which has been previously used in adhesion experiments, has been modified for use in single particle friction studies. Both flat compacted surfaces and large single particles were used as substrate surfaces to allow assessment of drug-drug, drug-drug carrier and drug carrier-drug carrier friction forces. Particle size, particle shape and surface roughness were identified as main factors influencing the change from a static into a dynamic friction process and the division between friction due to adhesion and ploughing. The forces of adhesion and friction were found to be proportional to the reversible energy of adhesion. The ratio between the force of adhesion and the press-on force applied and the ratio between the force of friction and the press-on force can be related to the yield stress and the reduced Young's modulus of the materials in contact.     

Effect of a hard artificial asperity on the crack closure behavior in an annealed SAE 1015 steel

The load-crack opening displacement (COD) curves and deformation characteristics in the vicinity of a hard artificial asperity in an annealed SAE 1015 steel were studied. The artificial asperity was found to have a significant effect on the trend of the load-COD curves. The lower portion of the load-COD curves in the unloading phase exhibited a convex shape without the asperity, but a concave shape with the asperity. The concave shape, signifying the acceleration in the COD decrease, was further verified by varying the size of the asperity, conducting special compression tests and elastic-plastic load-COD tests. The plastic deformation in the vicinity of both asperity and crack tip was studied via microhardness tests, etching techniques, and finite element analysis. Based on the experimental observations, a modified crack closure process model was proposed, where three stages of the unloading curve was defined: (i) the asperity does not contact the upper crack face, (ii) a process where both the asperity and the specimen material deform elastically, and the elastic-wedge model is applicable, and (iii) the plastic deformation of the specimen material adjacent to the asperity occurs, thus resulting in the concavely shaped load-COD curves. An equation was proposed to estimate the COD values, in which the plastic deformation both at the crack tip and at the asperity was considered. The residual COD calculated from the proposed equation was found to be consistent with the experimental results.     

Simulation studies of the hydrodynamics in high-temperature solutions for crystal growth. V. Shape of the crystal/liquid interface in the presence of simultaneous free and forced convections

The formation conditions of a concave, convex or flat crystal/liquid interface in the presence of simultaneous free and forced convections have been investigated using model liquids. Simultaneous free and forced convections with both the same and opposite flow directions have been considered. The interface shape was found to depend on the direction and rate of the resultant convection flow under the crystal. The formation conditions of a flat interface for liquids having kinematic viscosities of 0.001·10^?3 – 0.5·10^?3 m²/s and for crystal diameters of 10, 15 and 20 mm, respectively, have been established. These conditions have been compared with the optimum conditions found experimentally by other authors for the growth of several kinds of crystals from high-temperature solutions by the TSSG method and from melts by the Czochralski method. The comparison has shown that the model proposed describes well the real processes.     

Simulation studies of the hydrodynamics in high-temperature solutions for crystal growth. I. Forced convection

Investigations on forced convection have been carried out in model liquids (glycerol and glycerol-water containing 70, 80, 90 and 95 vol.% glycerol) with parameters corresponding to those of high-temperature solutions for crystal growth. Dependences between the rate of convection flow and the system parameters have been found for different interface shapes (flat, concave and convex). The explicit form of these functions has been established.     

Coating deposition and adhesion enhancements by laser surface texturing—metallic particles on different classes of substrates in cold spraying process

A nonsystematic study of metallic particle deposition behavior in kinetic spray process for three classes of substrate materials was performed (metallic, polymer, and ceramic). The particle–substrate contact time, temperature, and area upon impact were estimated for different topographies by numerical analysis. The results indicated that the deformation and the resultant bonding were dependent on the contact shape area. Laser surface texturing was used as a surface prior treatment to create specific topographies. The deposition efficiency and the adhesion strength were evaluated and compared with the numerical results. First, metal–metal couples investigated large adiabatic shear instability at the interface causing intimate adhesive bonds. It was maximized for cavities because the interface temperature and contact area were larger at the interface. Besides, the mechanical anchoring was more efficient with laser gripping zones. Then, metal deposition on polymer was a challenge. Particle embedded in the substrate only if the particle kinetic energy was sufficient to penetrate as far as its diameter. Cold spray process needed to be studied. However, concave shape indicated a larger deposition efficiency by minimizing bounces. Also, metallization of ceramic by cold spray demonstrated a problem due to a nondeformation of the substrate. So, particle compressive states were the key for mechanical anchoring, and it was provided by laser surface texturing. Finally, cold spray parameters and surface topography were dependant. A methodology was established with particle states and particle/substrate properties to adapt the surface topography to enhance deposition efficiency and adhesion. The window of deposition was larger for laser-treated surface. Laser surface texturing enabled an adapted surface structuration for many applications.     

Influence of circumferential curve shapes and surface options on curve length and volume of axisymmetric components in modelling for reverse engineering applications

In this work axisymmetric components are scanned using Coordinate Measuring Machine (CMM) and modeled using circular section/boundary curves. Surface options such as Surfaces of revolution, lofted surface and coons surface are considered in modelling. The curve length and volume are numerically evaluated for various surface options. The error percentage is obtained for curve length and volume by taking the values measured from the components as reference values. Result are presented for six different circumferential curves shapes viz., parallel (cylindrical), inclined upwards (inverted frustum), inclined downwards (frustum), convex (barrel), concave (sand-clock shape) and combined convex-concave shape. The results show that percentage error is negligible only for Surfaces of revolution and lofted surface in modelling convex, concave and combined convex-concave shapes. In modelling parallel and inclined shapes all three surface options fit well. In modelling convex, concave and combined convex-concave shapes, coons surface does not fit well. The suggestion to designers is to use surfaces of revolution and lofted surface rather than using coons surface. Otherwise the shapes of components will be different from the designed shape. Also the volume of components will be different from the designed volume. In such cases the designed components fail to meet the shape and volume requirements.     

非完整形态KH2PO4晶体薄表面层生长特性

实时观察了非完整形态的KH2PO4 (KDP)晶体在过饱和溶液中以薄表面层生长形式恢复其结晶学形态的过程.提出了晶体形态恢复的“最小多面体原理”,即:在自由生长系统中,对于非完整形态的KDP晶体,当其以薄表面层形式恢复其结晶学完整形态时,薄表面层将选择相应的奇异面方向生长,使晶体形态最终恢复为一个由各结晶学显露面所围成的体积最小的凸多面体.利用PBC理论分析了生长基元在非结晶学显露面上的附着情况并阐述了锥顶处薄表面层倒垂生长的原因.结果表明,薄表面层形成与晶体非完整结晶学形态及不均匀水动力学条件相关联.柱面凹角与非正常棱边及Z切片正常棱角均可诱发产生薄表面层,且薄表面层生长终止于其所在奇异面的正常结晶学晶棱.     

All-sky camera with a concave mirror

The characteristics of an all-sky camera with a concave mirror are analyzed. A differential equation for a concave aspheric mirror with constant angular magnification is derived for the general dependence of the camera image height on the camera field angle. This equation is solved in parametric form for the case of a concave mirror with a constant angular magnification. The explicit equations for the shape of the aspheric mirror are given for some particular values of the angular magnification. Parametric equations of the surface shape for sevenfold angular magnification are developed into a power series that is used to analyze the imaging performance of such a mirror. The performance of the concave aspheric mirror is compared with that of a spherical mirror. The minimal camera-to-mirror distance is determined as a function of the blur allowed and the camera lens aperture. Some characteristics of convex mirrors are also presented for comparison.     

Simple yet accurate noncontact device for measuring the radius of curvature of a spherical mirror

An easily reproducible device is demonstrated to be capable of measuring the radii of curvature of spherical mirrors, both convex and concave, without resorting to high-end interferometric or tactile devices. The former are too elaborate for our purposes, and the latter cannot be used due to the delicate nature of the coatings applied to mirrors used in high-power CO(2) laser applications. The proposed apparatus is accurate enough to be useful to anyone using curved optics and needing a quick way to assess the values of the radii of curvature, be it for entrance quality control or trouble shooting an apparently malfunctioning optical system. Specifically, the apparatus was designed for checking 50 mm diameter resonator (typically flat or tens of meters concave) and telescope (typically some meters convex and concave) mirrors for a high-power CO(2) laser, but it can easily be adapted to any other type of spherical mirror by a straightforward resizing.     

Adherent jet along a curved surface

The problem of a flat jet traveling along a curved surface has been solved numerically and the results are discussed here. The characteristics of a developing boundary layer as well as the frictional stresses at a convex and at a concave surface are shown.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol.22, No. 5, pp. 881–884, May, 1972.     

Chemical-assisted laser parallel nanostructuring of silicon in optical near fields

The authors present a simple and efficient technique for producing hexagonal arrays of nanostructures on silicon surfaces in chemical solutions. It utilizes the effect of optical near-field enhancement by self-assembled particle-lens arrays and a thermally induced chemical reaction with an alkaline solution. About 10(8) features can be produced simultaneously by one single laser pulse. Furthermore, the shape of the structures was found to be controllable, from concave holes to convex bumps, by means of a post-etching process, in the same chemical solution.     

Heat transfer and flow in spiral channels and coils

An analysis of the experimental results for heat transfer on convex and concave walls of slotted spiral channels as well as for local heat transfer around the periphery and along the tube of the coils is presented. Great attention is paid to examining surface friction and its pulsations on the hydrodynamic entrance section and under stabilized coil flow conditions. The transition from laminar to turbulent flow on the convex and concave walls of slotted spiral channels and around the periphery of the tube of different-curvature coils is analyzed.Lithuanian Power Engineering Institute. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 64, No. 6, pp. 670–680, June, 1993.     

The response of small scale rigid targets to shallow buried explosive detonations

Experimental and computational investigations were performed in order to better understand the mechanical response of rigid targets with various geometries to the detonation of shallow buried explosives. The motion of the targets was measured by use of high-speed digital video photography. This work involved flat targets, targets that were downwardly convex, and targets that were downwardly concave with explosive charges located at various positions beneath the targets. It was observed that, in general, angled hulls - whether downwardly concave or convex - tended to reduce the amount of momentum imparted to the center of mass of the targets. Computations were performed by use of an arbitrary Langrangian-Eulerian treatment in a nonlinear finite element code. A model based on quasi-static test evaluations of wet concrete sand was used for prediction of the soil behavior. The computational technique provided very good agreement between computation and experiment.     

Contact problem for a half plane with cracks subjected to the action of a rigid punch on its boundary

We consider a contact problem of the theory of elasticity for an isotropic half plane with a system of curvilinear cracks and a rigid punch pressed into the half plane. We assume that the base of the punch has an arbitrary convex shape, that either the punch interacts with the half plane via friction forces or they are rigidly engaged, and that the crack lips are under the conditions of smooth contact. The problem is reduced to singular integral equations in unknown derivatives of singular displacements on the crack contours and contact forces under the punch. These equations are solved by the method of mechanical quadratures. We present the results of numerical analysis of the stressed state of the half plane with internal vertical crack under pressure of a flat punch without friction on the boundary of the half plane.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 6, pp. 7–16, November – December, 1995.     

Surface contact and design of fibrillar ‘friction pads’ in stick insects (Carausius morosus): mechanisms for large friction coefficients and negligible adhesion

Many stick insects and mantophasmids possess tarsal ‘heel pads’ (euplantulae) covered by arrays of conical, micrometre-sized hairs (acanthae). These pads are used mainly under compression; they respond to load with increasing shear resistance, and show negligible adhesion. Reflected-light microscopy in stick insects (Carausius morosus) revealed that the contact area of ‘heel pads’ changes with normal load on three hierarchical levels. First, loading brought larger areas of the convex pads into contact. Second, loading increased the density of acanthae in contact. Third, higher loads changed the shape of individual hair contacts gradually from circular (tip contact) to elongated (side contact). The resulting increase in real contact area can explain the load dependence of friction, indicating a constant shear stress between acanthae and substrate. As the euplantula contact area is negligible for small loads (similar to hard materials), but increases sharply with load (resembling soft materials), these pads show high friction coefficients despite little adhesion. This property appears essential for the pads’ use in locomotion. Several morphological characteristics of hairy friction pads are in apparent contrast to hairy pads used for adhesion, highlighting key adaptations for both pad types. Our results are relevant for the design of fibrillar structures with high friction coefficients but small adhesion.     

Three-dimensional aspects of boundary-layer transition

A review is made in this paper of the three-dimensional nature of instability leading to transition in a two-dimensional flow on a flat plate (Blasius boundary layer) or between parallel plates (plane Poiseuille flow), with additional reference to the flow on a concave wall. Instability and transition in a three-dimensional boundary layer are then reviewed, with particular attention to the flow due to a rotating disk and the flow perturbed by a three-dimensional roughness element on a flat plate. The growth of a turbulent spot is discussed as a phenomenon exhibiting a similar feature of instability. Only the flow of an incompressible fluid is considered.     

Reflow of phosphorous silicate glass layer formed on textured Si surface in crystalline Si solar cells

We have investigated the reflow behavior of phosphorus silicate glass (PSG) layer formed on textured Si surface using transmission electron microscopy and simulation. For conventional wet oxidation process, stress-dependent surface reaction and stress-dependent oxidant diffusion led to the oxidation retardation in both convex and concave regions of the textured Si surface, respectively. However, PSG film formed by POCl3-diffusion underwent reflow, resulting in the formations of thinner and thicker PSG films in convex and concave regions, respectively. Simulation results showed that the reflow of PSG films causes lateral thermal mismatch stresses to increase and decrease in convex and concave regions, respectively.     

Convex–concave nanostructure transition on highly oriented pyrolitic graphite surface induced by atomic force microscope tip under bias voltage

Convex and concave nanoscale dots were formed on a highly oriented pyrolitic graphite surface in air by an atomic force microscope tip under positively applied bias voltage. It was found that the increasing amplitude or duration of the bias voltage over threshold values can change the convex profiles into concave ones. The threshold voltage duration for the profile transition increases sharply with decreasing amplitude of the voltage and a nonlinear relationship between them was obtained. For enough long duration, there exists a threshold voltage amplitude, about 4.1–5?V in this study, for the profile transition as well.     

基于正交试验的枕型空气衬垫优选方法

目的 基于正交试验的方法,探究枕型空气衬垫的规格、初始充气压强、温度、压缩速率在准静态压缩试验下对其缓冲性能影响的主次关系,得到一组使衬垫缓冲性能优良稳定的试验变量和一种枕型空气衬垫的优选方法.方法 采用正交试验的方法设计L9=(34)的正交试验,以枕型空气衬垫为研究对象进行准静态压缩试验,将试验结果归纳整理并进行极差分析和综合优选,判断所研究因素对枕型空气衬垫缓冲性能影响的主次关系,综合优选缓冲性能最优的枕型空气衬垫.结果 通过极差分析,得到了影响枕型空气衬垫缓冲性能的主次因素,由主到次依次为枕型空气衬垫规格、初始充气压强、温度、压缩速率,继而结合试验的易操作性综合优选了枕型空气衬垫的规格为100 mm×150 mm,初始充气压强为5 kPa,温度为30℃,压缩速率为100 mm/min,确定了一组使衬垫缓冲性能优良稳定的试验因素.结论 采用正交试验方法综合优选缓冲性能最优的枕型空气衬垫这一方法是可行的,结果也明确了4个试验变量对枕型空气衬垫缓冲性能影响的主次关系,这种思路能够为后续类似缓冲包装试验研究设计提供参考.     

模具结构对箔板电磁微成形的影响

对T2紫铜箔板进行电磁微成形实验,研究不同模具结构对材料成形性能的影响.采用激光共聚焦显微镜及轮廓仪研究不同模具结构对箔板电磁微成形的影响规律,分析模具结构对材料流动规律的影响.研究结果表明:随着电压的升高坯料出现不同程度的翘曲现象,采用凸型模具更有利于凹模内气体的排除,使得坯料能够迅速贴模;随着电压的升高材料成形性不断提高,采用凹型模具比采用凸型模具更加有利于微槽精度的提高;电磁成形制件应变分布均匀,凸型模具成形制件壁厚最小值出现在微槽侧壁,成形过程以拉深成形为主;凹型模具成形制件最小壁厚出现在微槽底部,成形过程以胀形为主.