A nonlinear analysis of spatial compliant parallel modules: Multi-beam modules

This paper presents normalized, nonlinear and analytical models of spatial compliant parallel modules—multi-beam modules with a large range of motion. The models address the non-linearity of load-equilibrium equations, applied in the deformed configuration, under small deflection hypothesis. First, spatial nonlinear load-displacement equations of the tip of a beam, conditions of geometry compatibility and load-equilibrium conditions for a spatial three-beam module are derived. The nonlinear and analytical load-displacement equations for the three-beam module are then solved using three methods: approximate analytical method, improved analytical method and numerical method. The nonlinear-analytical solutions, linear solutions and large-deflection FEA solutions are further analyzed and compared. FEA verifies that the accuracy of the proposed nonlinear-analytical model is acceptable. Moreover, a class of multi-beam modules with four or more beams is proposed, and their general nonlinear load-displacement equations are obtained based on the approximate load-displacement equations of the three-beam module. The proposed multi-beam modules and their nonlinear models have potential applications in the compliant mechanism design. Especially, the multi-beam modules can be regarded as building blocks of novel compliant parallel mechanisms.     

Three-dimensional contact model for numerically analyzing pressure distribution in wear

Although FEM is adequate in solving most elastic and rough surface contact problems with acceptable accuracy, its requirement for a large number of elements jeopardizes its effective use in analyzing real surface contacts, the contact stresses and the surface profile over a finite area between two rough contact surfaces. To overcome this problem, a technique, for constructing 3D surface in a computer by modifying the available 2D finite impulse response (FIR) digital filter methods and using the fast Fourier transform (FFT) procedure, is proposed, by referring to SEM morphology and experimental results. The technique, incorporating the variatonal approach in minimizing the stored contact energy, eliminates the additional iteration needed in determining contact area. It can be used to predict: (i) the contact pressure distribution and contact statistics of 3D real rough surfaces, (ii) the real contact stresses between a rigid flat and various coated specimens, (iii) the contact stress distribution profile, (iv) the role of friction and stress distribution in wear process. This revised version was published online in August 2006 with corrections to the Cover Date.     

Evidence for Chemicals Intermingling at Silicon/Titanium Oxide (TiOx) Interface and Existence of Multiple Bonding States in Monolithic TiOx

Metal oxides (MOs) are used in photovoltaics and microelectronics as surface passivating layers and gate dielectrics, respectively. The effectiveness of MOs predominantly depends on their structure and the nature of the semiconductor/MO (S/MO) interface. While some efforts are made to analyze interface behavior of a few MOs, greater fundamental understanding on the interface and structural behaviors of emerging MOs is yet to be established for enhanced scientific and technological developments. Here, the structure of atomic layer deposited titanium oxide (TiO_x) and the nature of the c‐Si/TiO_x interface on the atomic‐ to nanoscale are probed. A new breed of mixed oxide (SiO_x+TiO_x) interfacial layer with a thickness of ≈1.3 nm at the c‐Si/TiO_x interface is discovered, and its thickness further increases to ≈1.5 nm after postdeposition annealing. It is observed that both as‐deposited and annealed monolithic TiO_x films comprise multiple bonding states at varying film thickness, with an oxygen‐deficient TiO_x layer located close to the mixed oxide/TiO_x interface. The stoichiometry of this layer improves when reaching the middle and near surface regions of the TiO_x layer, respectively. This work uncovers several critical structural and interface aspects of TiO_x, and thus creates opportunities to control and design improved photovoltaic and electronic devices for future development.     

Antecedents to Government Relationship Building and the Institutional Contingencies in a Transition Economy

• This study argues that the government-relationship building efforts by foreign invested enterprises (FIEs) depend on the perceived level of regulatory uncertainties, which, in turn, is conditioned by the institutional distances between their home and host countries.
• The regulatory antecedents (regulatory complexity and enforcement uncertainty) to government-relationship building by foreign-invested enterprises and the moderating effects of institutional distance (regulative and cultural distances) in the context of the large transition economy of China are examined using a sample of 424 foreign-invested enterprises.
• The results show that they tend to actively engage in government-relationship building when regulatory uncertainties (complexity and enforcement uncertainties) are high. The moderating analyses reveal the strengthening effects of regulative distances on the relationship between regulatory uncertainties and government-relationship building and the mixed effects of cultural distance.

     

Experimental demonstration of Klyshko’s advanced-wave picture using a coincidence-count based,camera-enabled imaging system

The Klyshko advanced-wave picture is a well-known tool useful in the conceptualisation of parametric down-conversion (SPDC) experiments. Despite being well-known and understood, there have been few experimental demonstrations illustrating its validity. Here, we present an experimental demonstration of this picture using a time-gated camera in an image-based coincidence measurement. We show an excellent agreement between the spatial distributions as predicted by the Klyshko picture and those obtained using the SPDC photon pairs. An interesting speckle feature is present in the Klyshko predictive images due to the spatial coherence of the back-propagated beam in the multi-mode fibre. This effect can be removed by mechanically twisting the fibre, thus degrading the spatial coherence of the beam and time-averaging the speckle pattern, giving an accurate correspondence between the predictive and SPDC images.     

Molecular dynamics simulation model for the quantitative assessment of tool wear during single point diamond turning of cubic silicon carbide

Silicon carbide (SiC) is a material of great technological interest for engineering applications concerning hostile environments where silicon-based components cannot work (beyond 623 K). Single point diamond turning (SPDT) has remained a superior and viable method to harness process efficiency and freeform shapes on this harder material. However, it is extremely difficult to machine this ceramic consistently in the ductile regime due to sudden and rapid tool wear. It thus becomes non trivial to develop an accurate understanding of tool wear mechanism during SPDT of SiC in order to identify measures to suppress wear to minimize operational cost.In this paper, molecular dynamics (MD) simulation has been deployed with a realistic analytical bond order potential (ABOP) formalism based potential energy function to understand tool wear mechanism during single point diamond turning of SiC. The most significant result was obtained using the radial distribution function which suggests graphitization of diamond tool during the machining process. This phenomenon occurs due to the abrasive processes between these two ultra hard materials. The abrasive action results in locally high temperature which compounds with the massive cutting forces leading to sp³-sp² order-disorder transition of diamond tool. This represents the root cause of tool wear during SPDT operation of cubic SiC. Further testing led to the development of a novel method for quantitative assessment of the progression of diamond tool wear from MD simulations.     

Measures of functional status in community-dwelling elders

OBJECTIVE: To evaluate two performance-based measures of functional status and assess their correlation with self-report measures. DESIGN: Cross-sectional study. PARTICIPANTS: Of the 363 community-dwelling elders enrolled in a trial of comprehensive geriatric assessment who participated, all had at least one of four target conditions (urinary incontinence, depression, impaired functional status, or history of falling). MEASUREMENTS: Two performance-based measures, National Institute on Aging (NIA) Battery, and Physical Performance Test (PPT), and three self-report functional status measures, basic and intermediate activities of daily living and the Short-Form-36 (SF-36) physical functioning subscale, were used. Measures of restricted activity days, patient satisfaction and perceived efficacy were also used. MAIN RESULTS: All measures were internally consistent. There was a high correlation between the NIA and PPT (kappa = 0.71), while correlations between the performance-based and self-report measures ranged from 0.37 to 0.50. When patients with values above the median on the two performance-based measures were compared with those below, there were significant differences (p 相似文献   

Helix‐Grafted Pleckstrin Homology Domains Suppress HIV‐1 Infection of CD4‐Positive Cells

The size, functional group diversity and three‐dimensional structure of proteins often allow these biomolecules to bind disease‐relevant structures that challenge or evade small‐molecule discovery. Additionally, folded proteins are often much more stable in biologically relevant environments compared to their peptide counterparts. We recently showed that helix‐grafted display—extensive resurfacing and elongation of an existing solvent‐exposed helix in a pleckstrin homology (PH) domain—led to a new protein that binds a surrogate of HIV‐1 gp41, a validated target for inhibition of HIV‐1 entry. Expanding on this work, we prepared a number of human‐derived helix‐grafted‐display PH domains of varied helix length and measured properties relevant to therapeutic and basic research applications. In particular, we showed that some of these new reagents expressed well as recombinant proteins in Escherichia coli, were relatively stable in human serum, bound a mimic of pre‐fusogenic HIV‐1 gp41 in vitro and in complex biological environments, and significantly lowered the incidence of HIV‐1 infection of CD4‐positive cells.     

Microengineered dynamometer for microfan thrust measurement

The fabrication, development and thrust testing of a microengineered three-beam suspended structure manufactured in nickel is described. The structure is intended to be used as a support for axial-flow microfans and microturbines. The purpose of the test device is to measure torsional friction drag as a function of thrust force in configurations where microfans have cup-shaped bearings