Isothermal Gas Forming of Mg Alloy AZ31 Sheet

There have been reports on sheet forming of Mg alloy in industry via the punch and die method;this paper is probably the first formal one for studying the sheet formability of AZ31 employing pressurized gas to press the sheet into a female die cavity at various elevated temperatures.The results indicate it is feasible to form a rectangular box via pressurized gas from extruded sheets of 0.5 and 1.7 mm thick.The formed box has 1:2 depth over width ratio,which should be large enough when dealing with realistic industrial sheet forming parts.Presently,forming a sheet of 0.5 mm thick is considered a technical challenge by industry,and it is conquered as demonstrated in this paper.Gas forming technique applied to Mg alloy is unprecedented and shows potential for industrial utilization.     

Photothermal radiometric detection and imaging of surface cracks

This paper discusses surface crack detection by photothermal radiometric imaging (PRI). In PRI, also called dynamic infrared scanning, a surface is scanned with a spot of heat. Imperfections are detected by radiometrically sensing changes in the surface temperature of a small area in the vicinity of this spot. In the work described, cracks narrower than 25 µm (0.001 in.) in a lightly rusted steel surface have been detected. Indiscrete scanning an amplitude modulated heating beam is moved in steps, remaining at each location long enough to measure amplitude and phase of the AC temperature. Incontinuous scanning a constant intensity heating beam is moved continuously while the temperature deviations are measured. This paper presents methods of calculating amplitude and phase of surface temperature for discrete scanning and instantaneous temperature for continuous scanning across a surface crack. For a steel surface scanned by a watt-level laser beam, predicted surface temperature deviations when crossing the crack are several degrees Celsius, with expected radiometrically detected power several orders of magnitude above the detector noise. In experiments performed, both techniques easily detected narrow cracks in a smooth, clean surface. Discolorations and pits, on the other hand, generate a disturbing type of surface noise. This noise was minimized by differential detection. Based on results obtained, continuously scanned PRI with a fan-type heating beam and array detection could become a viable way of mapping surface cracks at practical scanning speeds.     

Modification of a carbon/carbon composite with a thermosetting resin precursor as a matrix by the addition of carbon black

Carbon/carbon composites were made through the pyrolysis of stabilized PAN felt and phenolic resin with the addition of 5 or 10 wt % carbon black to the matrix and then heat treatment at 600–2500°C. The effects of adding carbon black to the matrix precursor on the physical properties, microstructure, and mechanical properties of the resultant composites were investigated. Adding carbon black not only reduced the weight loss but also limited the shrinkage of the resultant composites. Adding carbon black also accelerated the formation of carbon basal planes in the matrix. At 2500°C, the crystalline stacking height in the composite with 10 wt % added carbon black was 200% greater than that with no additive. The flexural strength of the composite also increased from 15 to 42 MPa (almost 300%). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 333–337, 2006     

A simple practical analytic design method for multiloop‐controlled PWM switching regulators

Abstract

In this paper, a simple practical analytic method is proposed for designing multiloop‐controlled pulse width modulation (PWM) switching regulators. First, an equivalent single loop gain is presented and an approximate optimal set of closed‐loop poles is suggested according to the given specification such that the familiar design concept of a single‐loop second order system can be applied directly. In particular, closed form expressions of the feedback gains and the unknown parameters of the standard implemented circuit are derived. This renders the implementation problem surprisingly simple. Finally, some experimental results are also presented to demonstrate the effectiveness of the proposed method.     

On building a medical diagnostic system of acute exanthemas

Abstract

In this paper, we present a multi‐purpose medical diagnostic system named AEA — the Acute Exanthem Advisor, and the methodologies of its implementation. AEA provides an accurate diagnosis of acute exanthemas and a complete environment including a user‐friendly interface, reviewing function, record keeping function and explanation function. Therefore, it may serve as an assistant, a record keeper or an educational tool. A prediction program is also provided which is capable of predicting the number of potential patients who are going to have acute exanthemas in the near future. To illustrate the processes of the consultation and the prediction of the AEA, an example is given. Finally, for the 25 different test cases given to the diagnosticians and the AEA, the answers are almost the same, so we can conclude that the performance of the AEA is satisfactory. Now, we are trying to extend the AEA system to be a medical diagnostic net for acute exanthemas, which will be able to be remote accessed through network communications.     

Effect of carbon nanotube dispersion on the complex permittivity and absorption of nanocomposites in 2–18 GHz ranges

The effect of dispersion processes on complex permittivity and microwave absorption in 2?18 GHz ranges is presented for nanocomposites loaded with different amounts of carbon nanotubes (CNTs) ranging from 1 to 5 wt %. The ultrasonic sonication (US) method and the three‐roll mill (TRM) method were performed for the manufacturing of the CNT/epoxy absorbers with different dispersing levels. Microscopic observations revealed that the CNT agglomerates were reduced after the TRM process, and individual CNTs were uniformly dispersed in the epoxy resin. For the same weight content of CNT fillers, the percentage increase of between US and TRM samples varies from 35.5% to 101.7% while the corresponding increment of (dielectric loss) varies from 79.6% to 248.8%. A minimum reflection loss for the US sample with 2 wt % CNTs is only ?7.8 dB at 11.3 GHz while the corresponding TRM sample is greatly improved to reach ?37.4 dB at 7.76 GHz for the same matching thickness of 3 mm. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40963.     

Sharing multiple secrets in visual cryptography

The secret sharing schemes in conventional visual cryptography are characterized by encoding one shared secret into a set of random transparencies which reveal the secret to the human visual system when they are superimposed. In this paper, we propose a visual secret sharing scheme that encodes a set of x 2 secrets into two circle shares such that none of any single share leaks the secrets and the x secrets can be obtained one by one by stacking the first share and the rotated second shares with x different rotation angles. This is the first true result that discusses the sharing ability in visual cryptography up to any general number of multiple secrets in two circle shares.     

Processing and failure behavior of carbon‐nanotube composites in sheet forms

In their original forms, carbon nanotubes (CNT) are spatially entangled. To make CNT papers (CNTPs), the CNT agglomerates must be dispersed and re‐entangled into a planar sheet. The processing characteristics are very different from those of traditional buck‐form nanocomposites. This article examines the processing, micro‐structures, and failure behavior of the CNTP composites. The CNTPs were first made by a dispersion and filtering process. Then, an epoxy resin was added into the CNTP by using a vacuum bag method. Different CNT weights were employed to make the CNTPs with different thicknesses and areal weights. The CNTP allows direct resin impregnation along the thickness direction and avoids the difficulty of dispersing CNTs in the viscous resin. The CNT content can be much higher than that attainable in traditional bulk CNT composites. Both tensile and tearing tests were conducted, and the fracture behaviors were examined. POLYM. COMPOS., 37:1564–1571, 2016. © 2014 Society of Plastics Engineers