Electron beam-induced changes in vitreous sections of biological samples

Nonpretreated high pressure frozen samples of Zea mays, cartilage and human erythrocytes were cryosectioned and observed at 110 K in a cryoelectron microscope. Changes induced by medium doses of electron irradiation (< 10 ke nm^?2) are described. After some ke nm^?2, the most conspicuous cutting artefacts are erased to a large extent and the visibility of the cell organelles is improved. The sections, compressed in the cutting direction by the sectioning process, shrink once more, in the same direction, when irradiated. This shrinkage depends on the section support and on how the section is adsorbed to it. Shrinkage is not uniform; it is most pronounced in mitochondria, condensed chromatin and nucleolus. This differential shrinkage improves the visibility of major structures on the section and, as a result, ‘nicer’ images are recorded. However, this apparent improvement is a beam-induced artefact that must be paired with a loss of high resolution information.     

Recrystallization and ice-crystal growth in a biological specimen,as shown by a simple freeze substitution method

The sensory hairs of the silkmoth, Bombyx mori, are suitable test objects to check for recrystallization and secondary freezing damage in a biological object, because cryofixation by immersion into propane (90 K) routinely yields well-preserved specimens without noticeable freezing damage. After rewarming the frozen specimens for 10 min to 230 K (boiling propane), the tissue preservation has not deteriorated, and even after 45 min at 230 K, ice-crystal ghosts rarely exceed 50 nm. Two minutes at 250 K (in deep freezer) produced moderate freezing damage with ice-crystal ghosts of 30–75 nm, whereas 90 min at 250 K resulted in severe damage with ice-crystal ghosts well over 100 nm. Secondary freezing damage by ice-crystal growth upon rewarming well-frozen biological specimens, therefore, is a relatively slow process, depending not only on the temperature, but also on the exposure time. Moreover, with some biological specimens, secondary ice-crystal growth starts at much higher temperatures than previously guessed, and with short exposure times rarely should become a hazard in fine structure work.     

The relative efficiency of cryogenic fluids used in the rapid quench cooling of biological samples

The heat transfer characteristics of various cryogenic fluids used in the rapid quench cooling of biological samples are examined. It is concluded that cryofixation should be achieved during the initial plunge stage of the cooling. Liquid nitrogen maintained near its melting point of 63·1 K at a pressure in excess of the critical value of 33·5 atm will produce the quickest cooling. Nitrogen could also provide the best ultrastructure at atmospheric pressure if the minimum plunge depth and velocity criteria are satisfied. Plunging bare thermocouples into cryogenic fluids will lead to erroneous conclusions about the relative cooling efficiencies of various liquids for cryofixation. A qualitative explanation for the results obtained by Silvester et al. (1982) during the rapid cooling of water drops in various fluids is proposed.     

Liquid nitrogen-based quick freezing: Experiences with bounce-free delivery of cholinergic nerve terminals to a metal surface

The limitations of chemical fixation in permitting the 1:1 quantitative correlations required for convincing ultrastructural explanations of cell biological processes are noted. We describe techniques for obtaining highly reproducible direct quick freezing on the polished surface of pure copper bars dipping into a static dewar of liquid N₂. The importance and the ease of testing and obtaining bounce suppression with commerically available equipment is emphasized. Artefacts caused by tissue damage and bad freezing are illustrated, and a hitherto unrecognized population of presynaptic membrane attached vesicles is described in Torpedine electric organ. Between 15 and 20% of the synaptic vesicles are attached to ca. 30% of the cytoplasmic face of the presynaptic terminal membrane. There is a close correlation between the occurrence of such attachments and the application of electrocyte basal lamina to the external face. We suggest that these vesicles are the ‘membrane operators,’ ‘vesigates,’ and ‘highly active subpopulation’ of vesicles whose existence has been invoked to explain biochemical data in other laboratories. We further speculate that relatively selective Ca pumping by this immediately submembranous population leads to displacement of acetylcholine (ACh) and reloading with newly synthesized ACh. The preferential release of the latter would then be expected.     

The effect of the additive concentration in emulsions to the tribological behavior of a cold rolling tube under sliding contact

The industrial steel tube in the cold rolling processes under liquid lubrication was simulated in a recovered cutting machine to study the tribological performances of an emulsion with four different concentrations of an emulsifier. The test machine was equipped with a device to measure the electrical contact resistance (ECR) between the rubbing surfaces of a steel tube and a roller. The ECR readings were useful to identify the existence of a surface absorption layer (a boundary layer film) between the contact surfaces and thus to realize the tribological effects. The tribological properties, including the friction coefficient, the electrical contact resistance, the wear loss of the tube and the worn surface area, were evaluated at these emulsifier concentrations. The displacement energy and the spraying coefficients for these emulsifier concentrations were applicable to interpret their relationships with the wear loss of the steel tube. The measures of the ECR are found to have a tendency more related to the values of the friction coefficient. Stribeck curves were also established for four emulsions; they are useful for assisting in the explanation for why a high friction coefficient in some cases does not necessarily produce a high wear loss. They were also provided to investigate the effects of the emulsifier concentrations on the friction coefficients at various lubrication stages. The emulsion with a dilute ratio of 50:1 proved to be the optimum choice of the four emulsifier concentrations because it leads to the lowest friction coefficient, the smallest wear loss and the worn surface as to the test time of 60 minutes.     

Fretting corrosion of materials for orthopaedic implants: a study of a metal/polymer contact in an artificial physiological medium

The fretting corrosion behaviour of a 316L SS flat against a PMMA counterface has been investigated in an artificial physiological medium. A specific device has been used to visualize the in situ degradation at the contact interface. Simultaneous analysis of the coefficient of friction and free corrosion potential has shown four distinct stages during fretting experiments. An energy-oriented approach to the fretting process was conducted in tandem with measurement of wear. This method has shown a linear progression in the wear volume of the samples as a function of the interfacial energy dissipated during fretting. The presence of chlorides contributes to a considerable acceleration of the degradation of the stainless steel surface. This process was explained by a mechanism related to crevice corrosion activated by friction.     

水浴加热王水提取ICP-MS法测量地质样品中微量银

水浴加热王水提取地质样品中的微量银,银被完全溶解,一些样品提取液中对银产生质谱干扰的锆元素溶解量很低,实现了目标元素与干扰元素的初步分离,使用 ICP-MS 采用¹⁰⁷Ag 同位素对银的含量可以直接进行测试。对于其他一些地质样品,提取液中锆含量较高,目标元素与干扰元素未分离,需要利用质谱校正方程 I_107Ag=I_{107Ag 表观}-K^*I_94Zr对银的测试结果进行校正。本实验建立的方法,检出限为 0. 0025μg/g,精密度为 1. 2%～3. 2%,准确度好,适合于分析测试大批量地质样品中的微量银。     

Tensionless contact of a flexible plate and annulus with a smooth half-space under axisymmetric loads by integral equations

In this paper, a new hybrid method of analysis is presented for the problem of a frictionless circular plate or annulus in tensionless contact with a half-space. By virtue of a set of analytically explicit Green's functions for the two interacting continua, an exact but compact integral equation formulation with closed-form kernels is derived. With the incorporation of a newly developed adaptive-gradient (AG) element capable of capturing regular-to-singular solution transitions smoothly, an accurate numerical procedure is developed and validated in a number of benchmark cases of nonlinear plate–annulus–half-space interaction. From the simplicity and rate of convergence demonstrated, the hybrid method is apt to be an attractive analytical–numerical platform that can be extended to a large class of contact problems.     

Calculation of actual area in the contact of a single microasperity modeled by a cone with a smooth surface of the part

The present paper represents dependences for determining the approach and actual area of the contact on a single microasperity with the conical shape with the surface of a part. It is shown that loads may differ significantly under defined contact conditions at equal actual contact areas of the microasperity with spherical and conical shapes.     

Numerical study of droplet motion in a microchannel with different contact angles

The droplet motion in a microchannel with different contact angles, which is applicable to a typical proton exchange membrane fuel cell (PEMFC), was studied numerically by solving the equations governing the conservation of mass and momentum. The gas-liquid interface or droplet shape was determined by a level set method which was modified to treat the static and dynamic contact angles. The matching conditions at the interface were accurately imposed by incorporating the ghost fluid approach based on a sharp-interface representation. Based on the numerical results, the droplet dynamics including the sliding and detachment of droplets was found to depend significantly on the contact angle. Also, the effects of inlet flow velocity, droplet size and side wall on the droplet motion were investigated. This paper was recommended for publication in revised form by Associate Editor Haecheon Choi Gihun Son received a B.S. and M.S. degree in Mechanical Engineering from Seoul National University in 1986 and 1988, respectively. He then went on to receive his Ph.D. degrees from UCLA in 1996. Dr. Son is currently a Professor of Mechanical Engineering at Sogang University in Seoul, Korea. Dr. Son’s research interests are in the area of multiphase dynamics, heat transfer, and power system simulation. Jiyoung Choi received a B.S. degree in Mechanical Engineering from Sogang University in 2005. He is a graduate student of Mechanical Engineering at Sogang University in Seoul, Korea. Choi’s research interests are in the area of PEM fuel cell and microfluidics.     

Creating internal conductivity in dry biological SEM samples by a simple vapour treatment

Internal sample conductivity in scanning electron microscopy can be a valuable alternative to metal coating. Proton conductivity may be used for this purpose. Many solid materials with active hydrogen atoms, such as hydrogen‐ and ammonium‐salts, organic acids, and even ice, are protonic conductors or semiconductors. Here we present a method to generate proton conductivity in dry biological materials. A simple treatment with hydrogen chloride gas or hydrochloric acid vapour for a few minutes provides sufficient conductivity for many samples. After a removal of excess hydrogen chloride vapour with a vacuum desiccator, the objects may be examined in the SEM without metal coating. The use of internally conductive samples extends the range of easy‐to‐perform SEM preparation techniques. It is advantageous for material contrast imaging of uncoated samples, and it can be used in combination with metal coating to enhance conductivity on difficult samples with complex overlapping surfaces, where simple metal coating does not reliably eliminate charging problems.     

A new HPF specimen carrier adapter for the use of high‐pressure freezing with cryoscanning electron microscope: two applications: stearic acid organization in a hydroxypropyl methylcellulose matrix and mice myocardium

Cryogenic transmission electron microscopy of high‐pressure freezing (HPF) samples is a well‐established technique for the analysis of liquid containing specimens. This technique enables observation without removing water or other volatile components. The HPF technique is less used in scanning electron microscopy (SEM) due to the lack of a suitable HPF specimen carrier adapter. The traditional SEM cryotransfer system (PP3000T Quorum Laughton, East Sussex, UK; Alto Gatan, Pleasanton, CA, USA) usually uses nitrogen slush. Unfortunately, and unlike HPF, nitrogen slush produces water crystal artefacts. So, we propose a new HPF specimen carrier adapter for sample transfer from HPF system to cryogenic‐scanning electronic microscope (Cryo‐SEM). The new transfer system is validated using technical two applications, a stearic acid in hydroxypropyl methylcellulose solution and mice myocardium. Preservation of samples is suitable in both cases. Cryo‐SEM examination of HPF samples enables a good correlation between acid stearic liquid concentration and acid stearic occupation surface (only for homogeneous solution). For biological samples as myocardium, cytoplasmic structures of cardiomyocyte are easily recognized with adequate preservation of organelle contacts and inner cell organization. We expect this new HPF specimen carrier adapter would enable more SEM‐studies using HPF.     

Coefficient of friction for aluminum in contact with a carbon fiber epoxy composite

In bolted joints, a large part of the load is transferred by friction. The objective of this investigation is to measure the coefficient of friction for carbon fiber epoxy matrix composite, HTA-6376, in contact with aluminum, 3637-77, in reciprocal sliding. During testing, the coefficient of friction increased initially with number of cycles and after reaching a maximum, slowly decreased. The initial coefficient of friction is approximately 0.23 and the peak coefficient of friction after wear in is approximately 0.68. The coefficient of friction is independent of normal load. During wear, cracks are formed at the fiber–matrix interface, which causes the matrix layer on the original composite surface to break off in pieces. It also causes single fibers or groups of fibers to be broken off and removed from the surface. Pieces of carbon fiber caused depressions in the aluminum surface. The wear debris is reattached to the composite surface but not to the aluminum surface.     

Estimation of real contact area in a wheel-rail system by means of ultrasonic waves

The application of an ultrasonic technique to estimate the Real Contact Area (RCA) in a wheel-rail system is proposed. The method is based on the analysis of the reflection of ultrasonic waves which are sent over the contact region and reflected by it according to the state of contact. The interaction of the experimental data with a theoretical model formulated in the early 1990s by Krolikowski allows us to calculate the RCA for the area illuminated by the ultrasonic beam. By varying the external load and the surface conditions of the contacting elements, it is possible to obtain the trend of the RCA with increasing load (for a certain roughness) as well to explore changes in RCA for different roughness while the load is kept fixed. Results showed that RCA grows almost linearly with the applied load and that an increase of one order of magnitude in combined roughness of the wheel-rail system leads to a roughly sevenfold reduction in RCA under a given load.     

气相色谱法测定岩石样品中的水含量

研究建立了一种使用高分辨弹性毛细柱+TCD气相色谱仪快速检测岩石样品中的水含量的方法,该方法通过使用无水乙醇密闭加热超声对岩石样品中的水萃取,用毛细色谱柱对混合物进行分离,在TCD检测器中检测,采用外标法进行定量。该方法具有需用岩石量少、检测周期短、准确度高、重复性好等特点。使用该方法建立的标准曲线,其相关系数都达0.999以上,检测岩石样品中水含量的相对标准偏差达0.1%以上,可以满足研究的需要。     

单色光干涉面接触润滑膜厚在线测量

提出了滑块-玻璃盘形成的面接触润滑油膜厚度光干涉在线测量方法。以单色激光为光源,根据油膜厚度变化引起平行干涉条纹平移的物理特征,基于光流和动态时间规整技术构造复合算法,测量干涉图像相邻帧空间域上一维光强曲线的位移,从而得到相邻帧之间的油膜厚度差。从零速度开始记录每一帧干涉图像对应的膜厚变化,实时计算出当前帧对应的膜厚,实现了膜厚的在线测量。当前算法的测量结果与离线膜厚测量结果进行了对比,验证了该系统的测量准确性。进行了阶跃载荷、匀加速及匀减速工况下的膜厚测量,揭示了膜厚变化规律。     

Estimation of contact stiffness at interfaces in machine structures by a beam model on an elastic foundation

The dynamic properties of machine structures are significantly influenced by an interaction at the mating surfaces of machine elements. This interaction is called contact stiffness, and the development of a simple method for contact stiffness estimation is an important tribological objective. In this paper the contact stiffness is estimated by a beam model vibrating on an elastic foundation. The effects of clamping condition and mating surface topography on the contact stiffness obtained are quantitatively and accurately represented by experimental equations.     

Axial effects investigation in fixed-end circular bars under torsion with a finite deformation model based on logarithmic strain

In this paper the torsion problem of a circular bar with fixed ends is solved using a finite deformation constitutive model based on the corotational rates of the logarithmic strain. The logarithmic, Green–Naghdi and Eulerian corotational rates of the logarithmic strain are used in the model. The solution is based on a von Mises type yield function that incorporates isotropic and kinematic hardenings. For the kinematic hardening, a modified Armstrong–Fredrick hardening model with the corotational rate of the logarithmic strain is used. Assuming incompressible behavior, the fixed-end torsion problem is simplified to the simple shear problem. Solving the problem, the stress components are integrated to calculate the torque and axial force. It is qualitatively shown that the results based on the logarithmic corotational rate are in good agreement with the experimental results.     

Localization of strain in metal matrix composites studied by a scanning electron microscope-based grating method

The deformation characteristics of the metal matrix composites Ag/Ni and Al/Al₂O₃ are studied at microstructural level by a scanning electron microscope based grating method and finite element (FE) simulation. The measured strain was found to localize in narrow bands in the ductile matrix of both composites. In the case of the Al/Al₂O₃ composite, the bands are preferentially initiated in Al regions adjacent to the interface of large Al₂O₃ particles, leading to local strain maxima. The band positions found in the Ag/Ni composite are also affected by the less deformable Ni phase, but strain localization first occurs by sliding of single Ag grains sometimes located away from the Ni phase. Using a FE model of real phase geometry and measured border displacements as boundary conditions, the simulation agrees reasonably with the experiment. The differences in the case of the Al/Al₂O₃ composite are due to particle cracks and voids at the particle/matrix interface. This effect was found in the experiment but not considered in modelling. For the Ag/Ni composite the band positions agree fairly well. However, the level and gradient of strain is clearly different as the crystallographic orientation of the Ag grains was not accounted for in modelling.