Analysis and shape optimization in incompressible flows with unstructured grids

The aim of this study is to develop and validate numerical methods that perform shape optimization in incompressible flows using unstructured meshes. The three-dimensional Euler equations for compressible flow are modified using the idea of artificial compressibility and discretized on unstructured tetrahedral grids to provide estimates of pressure distributions for aerodynamic configurations. Convergence acceleration techniques like multigrid and residual averaging are used along with parallel computing platforms to enable these simulations to be performed in a few minutes. This computational frame-work is used to analyze sail geometries. The adjoint equations corresponding to the “incompressible” field equations are derived along with the functional form of gradients. The evaluation of the gradients is reduced to an integral around the boundary to circumvent hurdles posed by adjoint-based gradient evaluations on unstructured meshes. The reduced gradient evaluations provide major computational savings for unstructured grids and its accuracy and use for canonical and industrial problems is a major contribution of this study. The design process is driven by a steepest-descent algorithm with a fixed step-size. The feasibility of the design process is demonstrated for three inverse design problems, two canonical problems and one industrial problem.     

A test method for determining adhesion forces and Hamaker constants of cementitious materials using atomic force microscopy

A method for determining Hamaker constant of cementitious materials is presented. The method involved sample preparation, measurement of adhesion force between the tested material and a silicon nitride probe using atomic force microscopy in dry air and in water, and calculating the Hamaker constant using appropriate contact mechanics models. The work of adhesion and Hamaker constant were computed from the pull-off forces using the Johnson–Kendall–Roberts and Derjagin–Muller–Toropov models. Reference materials with known Hamaker constants (mica, silica, calcite) and commercially available cementitious materials (Portland cement (PC), ground granulated blast furnace slag (GGBFS)) were studied. The Hamaker constants of the reference materials obtained are consistent with those published by previous researchers. The results indicate that PC has a higher Hamaker constant than GGBFS. The Hamaker constant of PC in water is close to the previously predicted value C₃S, which is attributed to short hydration time (≤ 45 min) used in this study.     

Rubbers Based on Conjugated Soybean Oil: Synthesis and Characterization

A range of bio‐based rubbery thermosets have been synthesized by the cationic copolymerization of conjugated soybean oil, styrene, and 1,5‐hexadiene or isoprene as flexible crosslinkers. The thermal, and mechanical properties, as well as the wear behavior, of these new bio‐rubbers are reported. The amount of styrene and the type of diene incorporated have the greatest influence on the properties of the final materials. The largest variations are found in glass transition temperature, storage modulus, tan δ values, crosslink density, and abrasive wear depth, while thermal degradation and extraction analyses showed minimal variations with changes in composition.

     

Quantification of extreme thermal gradients during in situ transmission electron microscope heating experiments

Studies on materials affected by large thermal gradients and rapid thermal cycling are an area of increasing interest, driving the need for real time observations of microstructural evoultion under transient thermal conditions. However, current in situ transmission electron microscope (TEM) heating stages introduce uniform temperature distributions across the material during heating experiments. Here, a methodology is described to generate thermal gradients across a TEM specimen by modifying a commercially available MEMS-based heating stage. It was found that a specimen placed next to the metallic heater, over a window, cut by FIB milling, does not disrupt the overall thermal stability of the device. Infrared thermal imaging (IRTI) experiments were performed on unmodified and modified heating devices, to measure thermal gradients across the device. The mean temperature measured within the central viewing area of the unmodified device was 3–5% lower than the setpoint temperature. Using IRTI data, at setpoint temperatures ranging from 900 to 1,300°C, thermal gradients at the edge of the modified window were calculated to be in the range of 0.6 × 10⁶ to 7.0 × 10⁶°C/m. Additionally, the Ag nanocube sublimation approach was used, to measure the local temperature across a FIB-cut Si lamella at high spatial resolution inside the TEM, and demonstrate “proof of concept” of the modified MEMS device. The thermal gradient across the Si lamella, measured using the latter approach was found to be 6.3 × 10⁶°C/m, at a setpoint temperature of 1,000°C. Finally, the applicability of this approach and choice of experimental parameters are critically discussed.     

Emerging chemical and physical disinfection technologies of fruits and vegetables: a comprehensive review

Abstract

With a growing demand for safe, nutritious, and fresh-like produce, a number of disinfection technologies have been developed. This review comprehensively examines the working principles and applications of several emerging disinfection technologies. The chemical treatments, including chlorine dioxide, ozone, electrolyzed water, essential oils, high-pressure carbon dioxide, and organic acids, have been improved as alternatives to traditional disinfection methods to meet current safety standards. Non-thermal physical treatments, such as UV-light, pulsed light, ionizing radiation, high hydrostatic pressure, cold plasma, and high-intensity ultrasound, have shown significant advantages in improving microbial safety and maintaining the desirable quality of produce. However, using these disinfection technologies alone may not meet the requirement of food safety and high product quality. Several hurdle technologies have been developed, which achieved synergistic effects to maximize lethality against microorganisms and minimize deterioration of produce quality. The review also identifies further research opportunities for the cost-effective commercialization of these technologies.     

Generate‐map‐reduce: An extension to map‐reduce to support shared data and recursive computations

It is difficult to express the parallelism present in complex computations by using existing higher level abstractions such as MapReduce and Dryad. These computations include applications from wide variety of domains, like Artificial Intelligence, Decision Tree Algorithms, Association Rule Mining, Recommender Systems, Graph Algorithms, Clustering Algorithms, Compute Intensive Scientific Workflows, Optimization Algorithms, and so forth. Their execution graphs introduce new challenges in terms of programmer expressibility and runtime performance such as iterative and recursive computations, shared communication model, and so forth. We propose an extension to MapReduce, called Generate‐Map‐Reduce (GMR), targeted towards modeling these applications. GMR introduces a new Generate abstraction into the MapReduce framework that captures recursive computations. The runtime also supports iterative jobs and a distributed communication model by using shared data structures. We illustrate recursive computations with GMR by modeling complex applications such as simulated annealing, A* search, and adaptive quadrature computation that require recursive spawning of new tasks to handle variable degree of parallelism. GMR runtime supports caching of common data across iterations in memory and local disks. We illustrate how this caching helps in achieving significant speedup for iterative computations by modeling k‐means clustering. Copyright © 2013 John Wiley & Sons, Ltd.     

Analytical model of hot carrier degradation in uniaxial strained triple-gate FinFET for circuit simulation

The triple-gate (TG) SOI FinFET has well suppressed short-channel effects compared to planar MOSFET due to increased gate voltage controllability. However, the hot carrier injection (HCI) is a serious reliability issue for nanoscale FinFET and this should be taken care for reliable circuit design. The introduction of uniaxial strain in the channel of FinFET to enhance the performance further limits the reliable design of VLSI circuits. Hence, there is a great need to capture these device-level variations in circuits through physics-based models. In this paper, one such analytical model of hot carrier (HC) degradation in uniaxial strained TG FinFET based on reaction–diffusion mechanism is developed, considering various geometrical aspects of the device, for the first time. The developed model is validated using experimentally calibrated Sentaurus TCAD simulation results. The results show that the strain in the channel worsens the degradation of threshold voltage due to HCI. The developed model is integrated in Cadence circuit simulator, and the impact of HC degradation in strained TG FinFET-based CMOS NAND logic circuit is analyzed.     

Impact of compression ratio analysis in waste cooking oil biodiesels–diesel blends as fuel

ABSTRACT

The objective of this study is to investigate the effect of compression ratio on combustion characteristics of diesel engine with waste cooking oils methyl ester–diesel blends as fuel. The DI engine fuelled with Waste Cooking Rice Bran Methyl Ester (WCRBME) and Waste Cooking Cotton Seed Oil Methyl Ester (WCCSME) prepared by the transesterification process was investigated for its combustion and then compared with petroleum-based diesel fuel (PBDF). Experiments were conducted at a constant speed of 1500?rpm and maintained at a full-load condition for the compression ratio of 17:1, 18:1 and 19:1 and blending ratios B20, B40, B60 and B80.The fuel properties were strictly measured as per ASTM testing methods and these observed properties are verified to be well within the limits of ASTM D 6751 biodiesel standards. The combustion characteristics of heat release rate and combustion pressure of WCRBME & WCCSME were found closer to diesel.     

Optimal conditions for protein array deposition using continuous flow

Optimal conditions for depositing protein microarrays using a continuous-flow microfluidic device, the continuous-flow microspotter (CFM), have been determined using a design of experiments approach. The amount of protein deposited on the surface depends on the rates of convective and diffusive transport to the surface and binding at the surface. These rates depend on parameters such as the flow rate, time, and capture mechanism at the surface. The process parameters were optimized, and uniform protein spots were obtained at a protein concentration of 10 microg/mL and even at 0.4 microg/mL. A 150-fold dilution in protein concentration in the sample solution decreased surface concentration by a factor of only 16. If the capture mechanism of the protein on the substrate is nonspecific, optimal deposition is obtained at higher flow rates for short periods of time. If the capture mechanism is specific, such as biotin-avidin, deposition is optimal at medium flow rates with little advantage beyond 30 min. The CFM can be used to deposit protein arrays with good spot morphology, spot-to-spot uniformity and enhanced surface concentration. The CFM was used to deposit an array of various antibodies, and their interactions with an antigen were studied using surface plasmon resonance (SPR). Affinity values were obtained at low antibody concentrations (5 microg/mL) with low coefficients of variation. Thus, the CFM can be used to effectively capture proteins and antibodies from dilute samples while depositing multiple spots, thereby increasing the quality of spots in protein microarrays and especially improving screening throughput of SPR.