Amplification Effects of Soil Stratification on Ground Stress Waves

An analytical model is presented for the prediction of the amplification of compressional and shear waves produced by an explosion, or any other shock impact on the surface of a stratified soil deposit. This amplification is caused by multiple reflections of waves between the ground surface and an underlying parallel soil layer possessing different density and seismic velocity. The model developed may be easily applied for the protection of both buried and aboveground structures with the aid of suitable diagrams prepared in this work, which give, in a simple way, the enhancement factors by which particle velocities of direct waves should be multiplied to estimate the resultant particle velocities. The soil parameters that are taken into account in the analytical model and its simplified graphical solution are density, attenuation factor, and compressional- and shear-wave propagation velocities for the first two soil layers. Other parameters encountered are depth of the top soil layer, depth of burial of the structure, horizontal distance of the structure from the source, and trinitrotoluene equivalent of the source. The cube root scaling is considered for the attenuation of waves in soil with distance.     

Finite Element Modelling of TRIP Steels

A constitutive model that describes the mechanical behaviour of steels exhibiting “Transformation Induced Plasticity” (TRIP) during martensitic transformation is presented. Multiphase TRIP steels are considered as composite materials with a ferritic matrix containing bainite and retained austenite, which gradually transforms into martensite. The effective properties and overall behaviour of TRIP steels are determined by using homogenization techniques for non‐linear composites. The developed constitutive model considers the different hardening behaviour of the individual phases and estimates the apportionment of plastic strain and stress between the individual phases of the composite. A methodology for the numerical integration of the resulting elastoplastic constitutive equations in the context of the finite element method is developed and the constitutive model is implemented in a general‐purpose finite element program. The prediction of the model in uniaxial tension agrees well with the experimental data. The problem of necking of a bar in uniaxial tension is studied in detail.     

Bimorph actuator with monolithically integrated CMOS OFET control

We present an electrostrictive polymer bimorph controllable with low voltage through an integrated CMOS OFET control system. We have actuated the device by applying voltages up to 400 V to the control system, and can actuate the control with 60 V switching. The electrostrictor material was used both as the substrate for the transistors and as the dielectric layer for the control circuitry. This allows for a reduction in the number of layers in the structure, minimizing the clamping effect that would compromise the strain capabilities of the device. We have characterized the macroscopic displacement of the structure through a radius of curvature measurement, ranging from 11.4 mm to 7.5 mm depending on the supply voltage provided. The architecture proposed can be scaled to larger system with higher supply voltages.     

On the performance of two-hop message spreading in DTNs

In this paper, a Delay Tolerant Network environment is considered where the source is in full control of the two-hop spreading mechanism by setting key parameters such as the number of copies allowed to be spread in the network and the delay bound of the messages. The introduced analysis allows for a differentiation between the source of the message and the intermediate nodes (in terms of e.g. transmission power, speed or cooperation degree). Analytical expressions for the cumulative distribution function (cdf) of the delivery delay and the induced overhead are extracted, taking into account the fact that the source node may continue spreading copies after the message delivery. In addition, a fairly accurate approximate expression for the cdf of the delivery delay is also derived and validated through simulations.     

Image-based gating of intravascular ultrasound pullback sequences

Intravascularultrasound (IVUS) sequences recorded in vivo are subject to a wide array of motion artifacts as the majority of these studies are performed within the coronary arteries of a beating heart. To eliminate these artifacts, an electrocardiogram (ECG) signal is typically used to gate (collect) those frames recorded at the points in time associated with a particular fraction of the cardiac cycle. However, this technique may be suboptimal for a number of reasons, among which is the difficulty of determining the optimal fraction at which to gate. This value is generally nonobvious. To circumvent this problem, we introduce a frame-gating method for IVUS pullbacks that mimics ECG (i.e., in the sense that it selects only one frame per cardiac cycle), but will automatically choose the fraction of the cycle that renders the most stable gated frame set. Stability here is gauged by measuring interframe similarity. Our method operates exclusively on the imagery data and does not require ECG or any form of image segmentation or other high-level image analysis. To validate our algorithm, we compare its behavior versus true ECG gating.     

In-depth analysis and evaluation of diffusive glioma models

Glioma is one of the most aggressive types of brain tumor. Several mathematical models have been developed during the past two decades, toward simulating the mechanisms that govern the development of glioma. The most common models use the diffusion-reaction equation (DRE) for simulating the spatiotemporal variation of tumor cell concentration. Nevertheless, despite the applications presented, there has been little work on studying the details of the mathematical solution and implementation of the 3-D diffusion model and presenting a qualitative analysis of the algorithmic results. This paper presents a complete mathematical framework on the solution of the DRE using different numerical schemes. This framework takes into account all characteristics of the latest models, such as brain tissue heterogeneity, anisotropic tumor cell migration, chemotherapy, and resection modeling. The different numerical schemes presented have been evaluated based upon the degree to which the DRE exact solution is approximated. Experiments have been conducted both on real datasets and a test case for which there is a known algebraic expression of the solution. Thus, it is possible to calculate the accuracy of the different models.     

Experimental Determination of Energy Content of Unknown Organics in Municipal Wastewater Streams

A bomb calorimetry method has been used for the first time to measure the energy content of raw municipal wastewater. The method was first validated using standard compounds (arginine, glucose, and propionic acid) and then tested with municipal sludge samples, with the results compared to previously published values. By drying a large enough sample to yield approximately 0.5 g of solid residue and using benzoic acid in a 1:1 ratio as a combustion aid, an accurate and precise measurement of the energy content of raw municipal wastewater can be made. The energy content measurements indicate that for the full-scale treatment facility examined, the potential energy available in the raw waste-water exceeds the electricity requirements of the treatment process by a factor of 9.3.     

Matrices are forever: On applied mathematics and computing in chemical engineering

In the 1960s, Industrial and Engineering Chemistry published a sequence of Fundamentals Reviews (several authored or co-authored by Leon Lapidus) documenting annual progress in mathematics and computers in the field of chemical engineering. These reviews included detailed lists of all publications in the profession that had something to do with applied mathematical and computational techniques and their application to reaction engineering, transport, control and design. Far from such a detailed account, in our tracing of the impact of applied mathematics and computing developments in chemical engineering research through the last 50 years we find two main trends, at very different professional levels. The first is in basic graduate education, where modeling (and the tools to exploit it) forms the basis and the common language of a research/problem solving culture. The second is at the forefront of research, where the time span between mathematical/computational developments and their fruitful adoption, modification and exploitation in chemical engineering is constantly narrowing.     

Effects of mastication on the distribution of molecular weights and on the mechanical properties of native and commercial dental gutta percha (trans-polyisoprene)

Mastication of gutta percha (trans-polyisoprene) resulted in the selective scission of molecules, producing a narrower distribution of lower molecular weights. The mechanical properties of the samples also underwent a significant change due to mastication. The greater the content of incompatible substances (salts and oxides) in commercial gutta percha. the more substantial were these effects. The atmosphere (air, N₂, O₂) in which the experiments were conducted yielded significantly different results. The decrease in molecular weight was far greater in an O₂ atmosphere than under a current of nitrogen or air, owing to the combination of double bonds with O₂.