Investigation of elastic modulus of nanoporous alumina membrane

Nanoporous alumina membranes containing parallel regular pores of uniform size and normal to substrate surface were fabricated by anodically oxidizing high purity aluminum foils in acid solutions and their elastic modulus was investigated. The continuous out-of-plane displacement and current load of the porous membranes were obtained through bulge test combining real-time ESPI (electronic speckle pattern interferometry) observation system. Then the elastic modulus was calculated through an analytical model and the pore distortion after load was characterized by HRSEM (high resolution scan electron microscope). Measurement of mechanical properties indicates unusual mechanical behavior of these anodic alumina films compared with bulk alumina materials. This observation may help shed light on fracture mechanism of these films with nanopore arrays and bring further understanding on connecting of micro-meso structure and mechanical properties.     

FEM for evaluation of weight functions for SIF, COD and higher-order coefficients with application to a typical wedge splitting specimen

In the evaluation of accurate weight functions for the coefficients of first few terms of the linear elastic crack tip fields and the crack opening displacement (COD) using the finite element method (FEM), singularities at the crack tip and the loading point need to be properly considered. The crack tip singularity can be well captured by a hybrid crack element (HCE), which directly predicts accurate coefficients of first few terms of the linear elastic crack tip fields. A penalty function technique is introduced to handle the point load. With the use of these methods numerical results of a typical wedge splitting (WS) specimen subjected to wedge forces at arbitrary locations on the crack faces are obtained. With the help of appropriate interpolation techniques, these results can be used as weight functions. The range of validity of the so-called Paris equation, which is widely used in the evaluation of the COD from the stress intensity factors (SIFs), is established.     

Derivation of applied stress-crack opening displacement relationships for the evaluation of effective stress intensity factor range

Linear elastic fracture mechanics (LEFM) integrated with the interference of fracture surface asperities has been formulated. The asperities are considered to simulate the influence of the microstructures and possibly oxide debris. The applied stress/load-crack opening displacement (COD) relationships in several cases have been derived. In the original LEFM, the stress-COD relationship is represented by a straight line passing through the origin of the stress-COD plot. The insert of one asperity results in a deviation of the stress-COD response from the LEFM relationship, leading to the exhibition of an inflection point (first contact point, σ_op), a larger slope, and a residual COD. In the case of two asperities, the slope and the residual COD of the stress-COD relationship become further larger, and two inflection points emerge. A general stress-COD expression in the case of multiple asperities has been derived. The slope of the stress-COD equation, the residual COD, and the minimum COD all increase with increasing number of asperities for a given loading condition, resulting in a smaller ΔCOD and Δσ_eff. The number of the inflection points is the same as that of the asperities. To the authors' knowledge, this paper is the first to derive analytically an applied stress-COD curve with a gradual variation below σ_op, caused by the asperity-/roughness-, or oxide-induced crack closure.     

"Missing is useful": missing values in cost-sensitive decision trees

Many real-world data sets for machine learning and data mining contain missing values and much previous research regards it as a problem and attempts to impute missing values before training and testing. In this paper, we study this issue in cost-sensitive learning that considers both test costs and misclassification costs. If some attributes (tests) are too expensive in obtaining their values, it would be more cost-effective to miss out their values, similar to skipping expensive and risky tests (missing values) in patient diagnosis (classification). That is, "missing is useful" as missing values actually reduces the total cost of tests and misclassifications and, therefore, it is not meaningful to impute their values. We discuss and compare several strategies that utilize only known values and that "missing is useful" for cost reduction in cost-sensitive decision tree learning.     

A refined beam theory based on the refined plate theory

Summary Based on the refined plate theory, a refined theory of rectangular beams is derived by using the Papkovich-Neuber solution and Lur’e method without ad hoc assumptions. It is shown that the displacements and stresses of the beam can be represented by the angle of rotation and the deflection of the neutral surface. The solutions based on the new theory are the same as the exact solutions of elasticity theory. In three examples it is shown that the new theory provides as good or better results than Levinson’s beam theory when compared to those obtained from the linear theory of elasticity.     

Mechanical and electrical characterization of /spl beta/-Ga/sub 2/O/sub 3/ nanostructures for sensing applications

Single crystalline /spl beta/-Ga/sub 2/O/sub 3/ nanowire and nanoribbon materials were synthesized, and electrical and mechanical properties were studied for sensing applications. The structural analysis showed that the Ga/sub 2/O/sub 3/ nanomaterials were stoichiometric and had the same crystal lattice structure as the /spl beta/ phase Ga/sub 2/O/sub 3/ crystal. The mechanical study on individual Ga/sub 2/O/sub 3/ nanowires and nanoribbons showed that they had a bending modulus of around 300 GPa, are flexible (in bending and twisting), and are easy to be cleaved along their crystal lattice. The current-voltage electrical characterization through the thickness of nanoribbon and along the length of nanowire confirmed their semiconducting characteristic. A two-terminal device fabricated with an individual Ga/sub 2/O/sub 3/ nanowire showed good sensing response to ethanol gas at low-operating temperature, which revealed the potential of using such nanostructures for effective sensing applications.     

Effect of prolactin suppression on gonadotrophic secretion in the puerperium

Serum levels of prolactin (PRL), FSH, LH and oestradiol-17 beta were determined by radioimmunoassay in 57 lactating women and in 20 women in whom lactation was inhibited by ergocryptine (CS-154). Women who breast fed their infants exhibited high PRL levels which abruptly declined within 48 h post-partum, and remained low for the duration of the study. Serum FSH was undetectable during the first week post-partum in lactating as well as in CB-154 treated women. Thereafter, lactating women showed increasing FSH levels which reached a maximum by the third week post-partum. These FSH values were higher in lactating women than in the CBS-154 treated group. In contrast, LH levels were higher in those women receiving CB-154. Serum oestradiol-17 beta remained in low levels throughout the study, and no difference was observed between the two groups of subjects. From these results it seems that: 1) inhibition of PRL secretion leads to a faster recovery of gonadotrophin secretion toward the "menstrual type", and 2) PRL suppression produces no effect on the ovarian oestrogen production.     

Investigation into the surface morphology of nanosized silicate and hybrid films by optical and atomic-force microscopy

This paper reports on the results of investigations into the surface morphology of hybrid organic-inorganic films prepared by the sol-gel method on single-crystal semiconductor silicon. The spin-on-glass films are coated from sols based on tetraethoxysilane. The chemical composition of the films is modified by introducing inorganic compounds (dopants), namely, boric acid and gadolinium nitrate, into the sols. For the purpose of increasing the film thickness, the sols are modified by small amounts (～1 wt %) of polyols that have linear and branched structures, different molecular weights, and different numbers of active functional groups. A substantial change in the surface morphology of the spin-coated films, i.e., the formation of a specific structure of the films under the action of the above dopants and modifiers, is revealed using optical and atomic-force microscopy.     

Synthetic chemistry for ultrapure, processable, and high-mobility organic transistor semiconductors

An essential aspect of the development of organic-based electronics is the synthetic chemistry devised for the preparation of the semiconductor materials responsible for the activity of organic field-effect transistors. Access to organic semiconductors in sufficient purity and variety has led to breakthroughs in solid-state physics and circuit realization. In this Account, we review the synthetic methods that have been most useful for preparing a range of semiconductors, including thiophene-based oligomers, several kinds of fused rings, and polymers. The tradeoff between process efficiency and target purity is emphasized.