Study of gas film quality in electrochemical discharge machining

Electrochemical Discharge Machining (ECDM) has been demonstrated to be an alternative spark-based micromachining method for fabricating microholes and microchannels in non-conductive brittle materials. However, the mechanism for attaining accurate control of the contour shape and dimensions remains to be explored. In ECDM process, the gas film on the electrode surface is used as the dielectric medium required for discharge generation. Quality of gas film is the dominant factor that determines the machining qualities such as geometric accuracy, surface roughness and repeatability. Nevertheless, it is difficult to assess the gas film quality of ECDM. In this study, current signals and machined contours were taken as indexes of gas film quality. Experimental results showed that a stable and dense gas film could be obtained when the applied voltage exceeded the critical voltage and reached a specific level, which is called the “transition voltage” in this study. At the transition voltage, a stable electrochemical discharge activity could be generated, thus producing the smallest deviation of contour dimensions. Moreover, when the drilling process reached a certain critical depth, bubbles inside the hole could not easily escape. In order to reduce the interface energy between bubbles, a thicker gas film is formed at the hole entrance, resulting in unstable discharge performance that undermined machining results. In summary, information provided by current signals can shed light on the changes in gas film structure, which serve as useful reference for varying process parameters to achieve better efficiency and accuracy.     

An RMVT-Based Finite Rectangular Prism Method for the 3D Analysis of Sandwich FGM Plates with Various Boundary Conditions

A Reissner's mixed variational theorem (RMVT)-based finite rectangular prism method (FRPM) is developed for the three-dimensional (3D) analysis of sandwich functionally graded material (FGM) plates subjected to mechanical loads, in which the edge conditions of the plates are such that one pair of opposite edges is simply supported and the other pair may be combinations of free, clamped or simply supported edges. The sandwich FGM plate considered consists of two thin and stiff homogeneous material face sheets combined with an embedded thick and soft FGM core, the material properties of which are assumed to obey the powerlaw distributions of the volume fractions of the constituents. In this formulation, the plate is divided into a number of finite rectangular prisms, in which the trigonometric functions and Lagrange polynomials are used to interpolate the y-direction and x-ζ plane variations of the primary field variables of each individual prism, respectively. Because an h-refinement process is adopted to yield the convergent solutions in this analysis, the prism-wise either linear or quadratic function distribution through the x-ζ plane is assumed for the related field variables. A unified formulation of these FRPMs with freely-chosen orders for assorted field variables is presented. It is shown that these quadratic FRPM solutions of simply supported, multilayered composite plates and sandwich FGM ones are in excellent agreement with the exact 3D solutions available in the literature, and those of multilayered composite plates with various boundary conditions closely agree with the solutions obtained using the ANSYS commercial software.     

All-solution-processed inverted polymer solar cells on granular surface-nickelized polyimide

In this study, we prepared all-solution-processed inverted polymer solar cells (PSCs) incorporating two solution-processed electrodes – surface-nickelized polyimide films (NiPI films) as cathodes and high-conductivity poly(3,4-ethylenedioxythiophene)/poly(styrene-sulfonate) (PEDOT:PSS) films as anodes – and an active layer with a bulk heterojunction morphology of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C₆₁-buytyric acid methyl ester (PCBM). The granular Ni thin films, which exhibited good adhesion and high-conductivity (ca. 2778 S cm^?1) on the polyimide (PI) substrates and possessed a work function different from that of pure Ni metal (WF, 5.4 eV). Using ultraviolet photoelectron spectroscopy, we determined that the WF of the NiPI films was ca. 3.9 eV. Prior to the coating of the photoactive layer, the surface of the NiPI films were treated with titanium(diisopropoxide)bis(2,4-pentanedionate) (TIPD) solution to facilitate the deposition of high-quality active layer and further as a hole blocking layer. The solution processed anodes (solvent-modified PEDOT:PSS films) were further coated and subjected to mild oxygen plasma treatment on the active layer. Short exposure (5 s) to the plasma improved the quality of the surface of the active layer for PEDOT:PSS deposition. These inverted PSCs on flexible granular NiPI films provided a power conversion efficiency of 2.4% when illuminated under AM 1.5 conditions (100 mW cm^?2). The phenomenon of light absorption enhancement in those inverted PSCs was observed as indicated in reflective UV–vis, haze factor and external quantum efficiency (EQE) responses. The resulting fill factor (FF) of 0.43 is still significantly lower than the FF of 0.64 for standard devices. When compared to the planar structure, the improvement of absorbance of light and good haze factors was obtained for granular structure which suggests NiPI as a better back contact electrode through enhancing the light trapping and scattering in inverted PSCs.     

Transistor-and Circuit-Design Optimization for Low-Power CMOS

CMOS-technology scaling has moved to a power-constrained condition regardless of the application segments. Power management in advanced CMOS technology drives the need to conciliate scaling-driven fundamental material limitations with product and application evolution requirements. Flexible CMOS technologies and tighter interaction between process development and circuit/system design are needed to efficiently realize systems on a chip. This paper reviews issues associated with transistor scaling and co-optimization for power-management circuit-design schemes for active-and leakage-power control. This paper also addresses the derived trends and implications on I/O and analog-transistor scaling.     

A meshless collocation method based on the differential reproducing kernel interpolation

A differential reproducing kernel (DRK) interpolation-based collocation method is developed for solving partial differential equations governing a certain physical problem. The novelty of this method is that we construct a set of differential reproducing conditions to determine the shape functions of derivatives of the DRK interpolation function, without directly differentiating the DRK interpolation function. In addition, the shape function of the DRK interpolation function at each sampling node is separated into a primitive function processing Kronecker delta properties and an enrichment function constituting reproducing conditions, so that the nodal interpolation properties are satisfied. A point collocation method based on the present DRK interpolation is developed for the analysis of one-dimensional bar problems, two-dimensional potential problems, and plane problems of elastic solids. It is shown that the present DRK interpolation-based collocation method is indeed a truly meshless approach, with excellent accuracy and fast convergence rate.     

Associations between family structure, family functioning, and substance use among Hispanic/Latino adolescents.

This study examined the role of family structure and functioning in predicting substance use among Hispanic/Latino adolescents, surveyed in 9th and 10th grade. The sample (N = 1433) was half female, mostly of Mexican descent, and the majority was born in the United States. Living with a single father was associated with less parental monitoring and less family cohesion (γ = ?0.07, ?0.06, respectively). Living with a single mother was associated with less parental monitoring (γ = ?0.10). Living with neither parent was associated with less communication (γ = ?0.08), less parental monitoring (γ = ?0.09), more family conflict (γ = 0.06), and less family cohesion (γ = ?0.06). Less monitoring was associated with substance use at follow-up (β = ?0.17). Low rates of parental monitoring appear to mediate the association between parental family structure and substance use. Results suggest that improving basic parenting skills and offering additional social support and resources to assist parents in monitoring adolescents may help prevent substance use. These interventions may be particularly beneficial for single parents. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Exact Solutions for the Stability and Free Vibration of Multilayered Functionally Graded Material Hollow Cylinders under Axial Compression

Exact three-dimensional stability and free vibration analyses of simply-supported, multilayered functionally graded material (FGM) circular hollow cylinders and laminated composite ones under axial compression are presented. The material properties of each FGM layer are assumed to obey a power-law distribution of the volume fractions of constituents through the thickness coordinate. The Pagano method, which is based on the principle of virtual displacement and is conventionally used for the analysis of laminated composite structures, is modified to be feasible for the study of multilayered FGM cylinders, in which Reissner's mixed variational theorem, the successive approximation and transfer matrix methods, and the transformed real-valued solutions of the system equations are used. The present modified Pagano solutions for laminated composite cylinders are in excellent agreement with the exact 3D ones available in the literature, and those for sandwich FGM cylinders may be used as the benchmark solutions to assess the ones obtained using various two-dimensional theories and numerical models. The influence of some effects on the lowest critical load parameters of multilayered FGM cylinders and laminated composite ones is investigated, such as the derivation between using von Karman nonlinearity and full kinematic one, and the difference between using the uniform stress assumption and the uniform strain one. In addition, a parametric study with regard to some effects on the lowest frequency parameters of axially loaded, multilayered FGM cylinders is carried out, such as the magnitude of the applied compressive loads, the radius-to-thickness, length-to-radius and orthotropic ratios, and the material-property gradient index.     

Differential quadrature solution for the free vibration analysis of laminated conical shells with variable stiffness

The free vibration analysis of laminated conical shells with variable stiffness is presented using the method of differential quadrature (DQ). The stiffness coefficients are assumed to be functions of the circumferential coordinate that may be more close to the realistic applications. The first-order shear deformation shell theory is used to account for the effects of transverse shear deformations. In the DQ method, the governing equations and the corresponding boundary conditions are replaced by a system of simultaneously algebraic equations in terms of the function values of all the sampling points in the whole domain. These equations constitute a well-posed eigenvalue problem where the total number of equations is identical to that of unknowns and they can be solved readily. By vanishing the semivertex angle (α) of the conical shell, we can reduce the formulation of laminated conical shells to that of laminated cylindrical shells of which stiffness coefficients are the constants. Besides, the present formulation is also applicable to the analysis of annular plates by letting α=π/2. Illustrative examples are given to demonstrate the performance of the present DQ method for the analysis of various structures (annular plates, cylindrical shells and conical shells). The discrepancies between the analyses of laminated conical shells considering the constant stiffness and the variable stiffness are mainly concerned.