Threshold Fluence Measurement for Laser Liftoff of InP Thin Films by Selective Absorption

We explore conditions for achieving laser liftoff in epitaxially grown heterojunctions, in which single crystal thin films can be separated from their growth substrates using a selectively absorbing buried intermediate layer. Because this highly non‐linear process is subject to a variety of process instabilities, it is essential to accurately characterize the parameters resulting in liftoff. Here, we present an InP/InGaAs/InP heterojunction as a model system for such characterization. We show separation of InP thin films from single crystal InP growth substrates, wherein a ≈10 ns, Nd:YAG laser pulse selectively heats a coherently strained, buried InGaAs layer. We develop a technique to measure liftoff threshold fluences within an inhomogeneous laser spatial profile, and apply this technique to determine threshold fluences of the order 0.5 J cm^?2 for our specimens. We find that the fluence at the InGaAs layer is limited by non‐linear absorption and InP surface damage at high powers, and measure the energy transmission in an InP substrate from 0 to 8 J cm^?2. Characterization of the ejected thin films shows crack‐free, single crystal InP. Finally, we present evidence that the hot InGaAs initiates a liquid phase front that travels into the InP substrate during liftoff.

     

Analyzing the efficiency of nanostructured Sm3+- and Gd3+-doped TiO2 and constructing DSSCs using efficacious photoanodes

The rare earth elements, gadolinium and samarium, are doped with TiO₂ by hydrothermal synthesis technique to study the photoconversion performance of a photoanode in a dye-sensitized solar cell (DSSC). The obtained materials are subjected to the characterizations XRD, HR-TEM, UV–Vis spectroscopy, and XPS. DSSCs are fabricated using N719 dye, redox electrolyte, and platinum counter electrode. Charge-transfer ability was investigated using electrochemical impedance spectroscopy (EIS) on DSSCs. The efficiencies of DSSCs are influenced by the electron transport within the TiO₂–dye–electrolyte system. After the fabrication and simulation, among the two, Gd³⁺-doped TiO₂ gives the desired outcomes and higher efficiency (5.542%) than the pure and Sm³⁺-doped TiO₂ and thus it proves to be a superior solar cell anode material.

     

Autoclave cure simulation of composite structures applying implicit and explicit FE techniques

Simulation of the autoclave manufacturing technique of composites can yield a preliminary estimation of induced residual thermal stresses and deformations that affect component fatigue life, and required tolerances for assembly. In this paper, an approach is proposed to simulate the autoclave manufacturing technique for unidirectional composites. The proposed approach consists of three modules. The first module is a thermo-chemical model to estimate the temperature and the degree of cure distributions in the composite part during the cure cycle. The second and third modules are a sequential stress analysis using FE-implicit and FE-explicit respectively. User-material subroutine is used to model the viscoelastic properties of the material based on theory of micromechanics.     

The effect of investment materials on the surface of cast fluorcanasite glasses and glass–ceramics

Modified fluorcanasite glass–ceramics were produced by controlled two stage heat-treatment of as-cast glasses. Castability was determined using a spiral castability test and the lost-wax method. Specimens were cast into moulds formed from gypsum and phosphate bonded investments to observe their effect on the casting process, surface roughness, surface composition and biocompatibility. Both gypsum and phosphate bonded investments could be successfully used for the lost-wax casting of fluorcanasite glasses. Although the stoichiometric glass composition had the highest castability, all modified compositions showed good relative castability. X-ray diffraction showed similar bulk crystallisation for each glass, irrespective of the investment material. However, differences in surface crystallisation were detected when different investment materials were used. Gypsum bonded investment discs showed slightly improved in vitro biocompatibility than equivalent phosphate bonded investment discs under the conditions used.     

Degradative transport of cationic amphiphilic drugs across phospholipid bilayers

Drug molecules must cross multiple cell membrane barriers to reach their site of action. We present evidence that one of the largest classes of pharmaceutical drug molecules, the cationic amphiphilic drugs (CADs), does so via a catalytic reaction that degrades the phospholipid fabric of the membrane. We find that CADs partition rapidly to the polar-apolar region of the membrane. At physiological pH, the protonated groups on the CAD catalyse the acid hydrolysis of the ester linkage present in the phospholipid chains, producing a fatty acid and a single-chain lipid. The single-chain lipids rapidly destabilize the membrane, causing membranous fragments to separate and diffuse away from the host. These membrane fragments carry the drug molecules with them. The entire process, from drug adsorption to drug release within micelles, occurs on a time-scale of seconds, compatible with in vivo drug diffusion rates. Given the rate at which the reaction occurs, it is probable that this process is a significant mechanism for drug transport.     

Optimization of multiple responses using a fuzzy-rule based inference system

The optimization of multiple responses (or performance characteristics) has received increasing attention over the last few years in many manufacturing organizations. Many Taguchi practitioners have employed past experience and engineering knowledge or judgement when dealing with multiple responses. This approach brings an element of uncertainty to the decision-making process and therefore is not recommended for optimization of multiple responses. The approach presented in this paper takes advantage of both the Taguchi method and a fuzzy-rule based inference system, which forms a robust and practical methodology in tackling multiple response optimization problems. The paper also presents a case study to illustrate the potential of this powerful integrated approach for tackling multiple response optimization problems. The variance analysis is also an integral part of the study, which identifies the most critical and statistically significant parameters.     

Modified analytic hierarchy process to incorporate uncertainty and managerial aspects

The analytic hierarchy process (AHP) is a powerful multiple-criteria decision analysis technique for dealing with complex problems. Traditional AHP forces decision-makers to converge vague judgements to single numeric preferences in order to estimate the pairwise comparisons of all pairs of objectives and decision alternatives required in the AHP. The resultant rankings of alternatives cannot be tested for statistical significance and it lacks a systematic approach that addresses managerial/soft aspects. To overcome the above limitations, the present paper presents a modified analytic hierarchy process, which incorporates probabilistic distributions to include uncertainty in the judgements. The vector of priorities is calculated using Monte Carlo simulation. The final rankings are analysed for rank reversal using analysis of variance, and managerial aspects (stake holder analysis, soft system methods, etc.) are introduced systematically. The focus is on the actual methodology of the modified analytic hierarchy process, which is illustrated by a brief account of a case study.     

High speed insertion of bone fracture fixation pins: a finite element penetration model with experimental comparisons

A new method of bone fracture fixation is considered in which small pins/darts are dynamically inserted into bone to prevent translation and rotation at the fracture site. An ABAQUS model was developed to analyze dart penetration in cortical and cancellous bone for varying dart diameter, material, and velocity, and cortical thickness. The method is advocated for bioresorbable darts, so polylactide (PLA) and magnesium are the materials examined in this study. Numerical results showed that magnesium darts can achieve full penetration in bone while suffering little damage. The PLA darts penetrated thin bone well, but substantial deformation was seen as the cortical thickness increased, especially for small diameter darts. As partial validation, prototype PLA fixation darts were fired into cadaveric bone with a custom nailer. As in the model, the PLA darts could penetrate thin cortices but saw gross deformation when impacted against thicker bone.