Mesh insensitive formulation for initiation and growth of shear bands using mixed finite elements

An Implicit Nonlinearly Consistent (INC) numerical solution of a partial differential equation (PDE) model for shear bands, which includes a thermo-visco-plastic flow rule and finite thermal conductivity, is presented, and is found to be insensitive to mesh size. Insensitivity is achieved through the use of finite thermal conductivity in the PDE model in conjunction with the INC numerical solver. Finite thermal conductivity gives rise to an inherent physical length scale in the PDE model, governed by competition between shear heating and diffusion. This length scale serves as a localization limiter and will regularize the problem in the strain softening regime. This occurs since diffusion removes heat from the shearband more quickly as localization becomes more severe (i.e. as temperature gradients steepen). The INC solver leaves no splitting error at the end of a time step and is accurate even during phases for which the solution is evolving very rapidly. A key point in this paper is the analytical derivation of the system Jacobian by differentiation of the weak form of the PDE model, thus avoiding the use of numerical approximation formulas. In contrast, solution of the same continuous model using an operator split solution scheme is seen to lead to unreasonably slow convergence. One and two dimensional implementations of the algorithm are presented. For two dimensions, a mixed quadrilateral using discontinuous bilinear functions for plastic strain, and the interpolants associated with the Pian-Sumihara element for the stress is implemented.     

Effect of Congeneric Chemical Signals of Different Ages on Foraging Response and Food Choice in the Field by Golden Spiny Mice (Acomys russatus)

The common spiny mice Acomys dimidiatus and golden spiny mice Acomys russatus coexist in the extreme warm and dry parts of the Rift Valley in Israel. However, they are temporally segregated in that the former is nocturnal, whereas the latter is diurnal. Daily rhythms of physiological and behavioral variables in A. russatus responded to semiochemical signals released by A. dimidiatus (in the urine and feces). Both species feed upon the same food items but at different times of the 24-hr cycle. The main aim of the present study was to test under field conditions the foraging response of A. russatus to odors of different ages released by A. dimidiatus. Various feeding and behavioral variables were compared in three groups of A. russatus. The results show that fresh semiochemical signals released by A. dimidiatus decrease the feeding efficiency and increase the rate of smelling from a distance in A. russatus. These results support the idea that temporal segregation between the two coexisting species is at least partly through semiochemicals present in the urine and feces.     

Numerical Study of Particle Motion in Jet Milling

Jet mills are common devices used in industry for fine milling of dry particulate materials. The size reduction is caused by repeated events of impacts between particles. Although many parameters affect the performance of a jet mill, only a few of them were investigated. Particles' motions in a jet mill have great influence on the comminution process and energy consumption. Therefore, as a first step for a full simulation of the jet-mill process, it was decided to investigate the particle motion inside the jet mill by neglecting particle-particle interaction and particle breakage. In this way, the numerical simulations provide a better understanding of the classification process. In the present study, three-dimensional numerical simulations of particle motion in an industrial full-scale jet mill were conducted. The predictions of the numerical simulations were compared with experimental data and used to analyze the flow field characteristics.     

Super-resolution in PET imaging

This paper demonstrates a super-resolution method for improving the resolution in clinical positron emission tomography (PET) scanners. Super-resolution images were obtained by combining four data sets with spatial shifts between consecutive acquisitions and applying an iterative algorithm. Super-resolution attenuation corrected PET scans of a phantom were obtained using the two-dimensional and three-dimensional (3-D) acquisition modes of a clinical PET/computed tomography (CT) scanner (Discovery LS, GEMS). In a patient study, following a standard 18F-FDG PET/CT scan, a super-resolution scan around one small lesion was performed using axial shifts without increasing the patient radiation exposure. In the phantom study, smaller features (3 mm) could be resolved axially with the super-resolution method than without (6 mm). The super-resolution images had better resolution than the original images and provided higher contrast ratios in coronal images and in 3-D acquisition transaxial images. The coronal super-resolution images had superior resolution and contrast ratios compared to images reconstructed by merely interleaving the data to the proper axial location. In the patient study, super-resolution reconstructions displayed a more localized 18F-FDG uptake. A new approach for improving the resolution of PET images using a super-resolution method has been developed and experimentally confirmed, employing a clinical scanner. The improvement in axial resolution requires no changes in hardware.     

Incorporating agglomeration economies in transport cost-benefit analysis: The case of the proposed light-rail transit in the Tel-Aviv metropolitan area

Abstract.  The economic evaluation of transport projects relies primarily on the impact of the project on road users. Economic benefits are calculated from a reduction in the aggregate value of time saved by the users, as well as from savings on vehicle-operation and maintenance costs, reducion in traffic accidents, and more recently the negative environmental impacts that ensued. Most often the analysis assumes fixed demand. Major mass-transit systems, like the new Light Rail Transit (LRT) currently proposed for the Tel-Aviv Metropolitan Area (TAMA) in Israel, are expected to generate substantial new (induced) traffic. This development will most likely enhance the agglomeration forces at work in major urban concentrations. Agglomeration economies could lead to an upward shift in the production function of the metropolitan area, thus generating substantial additional benefits for the transport project. This article presents the methodology used to estimate the benefits derived from agglomeration economies induced by the aforementioned proposed new LRT in the TAMA. An estimate is made of the increase in the number of employees in the CBD owing to the proposed LRT and their potential contribution to the total annual production of the CBD. Agglomeration economies could add a significant amount of additional benefit to the transport project. In our case study the extent of these benefits increased the benefit-cost ratio from 1.15 to 1.40.     

Reconstruction in diffraction ultrasound tomography using nonuniform FFT

We show an iterative reconstruction framework for diffraction ultrasound tomography. The use of broad-band illumination allows significant reduction of the number of projections compared to straight ray tomography. The proposed algorithm makes use of forward nonuniform fast Fourier transform (NUFFT) for iterative Fourier inversion. Incorporation of total variation regularization allows the reduction of noise and Gibbs phenomena while preserving the edges. The complexity of the NUFFT-based reconstruction is comparable to the frequency-domain interpolation (gridding) algorithm, whereas the reconstruction accuracy (in sense of the L2 and the L(infinity) norm) is better.     

Near-field effects in multilayer inductive metal meshes

The transmittance of inductive single-layer and multilayer cross-shaped metal meshes has been calculated with the Micro-Stripes software program. The effect of symmetric and asymmetric alignment of the crosses of one mesh with respect to another was studied and compared with transmission line theory, which presents the nonaligned case. Significant differences are found for small spacing at approximately 1/5 the periodicity constant, whereas the differences disappear for large spacing. A pair of coupled surface waves is used to represent the mode of a single mesh. The resulting modes corresponding to the transmittance of multilayer metal meshes are interpreted by modes composed of resonance modes of a single mesh coupled by Fabry-Perot modes depending on the separation.     

Self‐Assembled Hybrid Materials Based on Organic Nanocrystals and Carbon Nanotubes

Organic crystalline materials are used as dyes/pigments, pharmaceuticals, and active components of photonic and electronic devices. There is great interest in integrating organic crystals with inorganic and carbon nanomaterials to create nanocomposites with enhanced properties. Such efforts are hampered by the difficulties in interfacing organic crystals with dissimilar materials. Here, an approach that employs organic nanocrystallization is presented to fabricate solution‐processed organic nanocrystal/carbon nanotube (ONC/CNT) hybrid materials based on readily available organic dyes (perylene diimides (PDIs)) and carbon nanotubes. The hybrids are prepared by self‐assembly in aqueous media to afford free‐standing films with tunable CNT content. These exhibit excellent conductivities (as high as 5.78 ± 0.56 S m^?1), and high thermal stability that are superior to common polymer/CNT hybrids. The color of the hybrids can be tuned by adding various PDI derivatives. ONC/CNT hybrids represent a novel class of nanocomposites, applicable as optoelectronic and conductive colorant materials.     

I/O Efficient Dynamic Data Structures for Longest Prefix Queries

We present an efficient data structure for finding the longest prefix of a query string q in a dynamic database of strings. When the database strings are prefixes of IP-addresses then this is the IP-lookup problem. Our data structure is I/O efficient. It supports a query with a string q using $O(\log_{B}(n)+\frac{|q|}{B})$ I/O operations, where B is the size of a disk block. It also supports an insertion and a deletion of a string q with the same number of I/Os. The data structure requires O(n/B) blocks, and the running time for each operation is O(Blog _B (n)+|q|).     

Least square projection: a fast high-precision multidimensional projection technique and its application to document mapping

The problem of projecting multidimensional data into lower dimensions has been pursued by many researchers due to its potential application to data analysis of various kinds. This paper presents a novel multidimensional projection technique based on least square approximations. The approximations compute the coordinates of a set of projected points based on the coordinates of a reduced number of control points with defined geometry. We name the technique Least Square Projections (LSP). From an initial projection of the control points, LSP defines the positioning of their neighboring points through a numerical solution that aims at preserving a similarity relationship between the points given by a metric in mD. In order to perform the projection, a small number of distance calculations is necessary and no repositioning of the points is required to obtain a final solution with satisfactory precision. The results show the capability of the technique to form groups of points by degree of similarity in 2D. We illustrate that capability through its application to mapping collections of textual documents from varied sources, a strategic yet difficult application. LSP is faster and more accurate than other existing high quality methods, particularly where it was mostly tested, that is, for mapping text sets.