Imposing Dirichlet boundary conditions with Nitsche's method and spline‐based finite elements

A key challenge while employing non‐interpolatory basis functions in finite‐element methods is the robust imposition of Dirichlet boundary conditions. The current work studies the weak enforcement of such conditions for B‐spline basis functions, with application to both second‐ and fourth‐order problems. This is achieved using concepts borrowed from Nitsche's method, which is a stabilized method for imposing constraints on surfaces. Conditions for the stability of the system of equations are derived for each class of problem. Stability parameters in the Nitsche weak form are then evaluated by solving a local generalized eigenvalue problem at the Dirichlet boundary. The approach is designed to work equally well when the grid used to build the splines conforms to the physical boundary of interest as well as to the more general case when it does not. Through several numerical examples, the approach is shown to yield optimal rates of convergence. Copyright © 2010 John Wiley & Sons, Ltd.     

Senescence of spatial chromatic contrast sensitivity. I. Detection under conditions controlling for optical factors

Chromatic contrast thresholds for spatially varying patterns of various spatial frequencies (0.5, 1, 2, and 4 cycles per degree) were measured for ten older (65-77 yr of age) and ten younger (18-30 yr of age) observers. The stimuli were Gabor patches modulated along S-varying or (L - M)-varying chromatic axes. Thresholds were determined for two sets of stimuli. For one set of stimuli, the mean chromaticity and luminance were equated at the cornea for all observers. The second set of stimuli was corrected for ocular media density differences to equate stimulation of each of the three cone types at the retina for each individual. Chromatic contrast thresholds were higher for older observers for all stimuli tested. The magnitude of this difference showed little dependence on spatial frequency. When stimuli were equated at the cornea, this difference was greater for S-varying stimuli. When stimuli were equated at the retina, the age-related difference in thresholds for S-varying stimuli was reduced. Both optical and neural factors contribute to these age-related losses in spatial chromatic contrast sensitivity.     

ED-SWE: Event detection based on scoring and word embedding in online social networks for the internet of people

Online social media networks are gaining attention worldwide, with an increasing number of people relying on them to connect, communicate and share their daily pertinent event-related information. Event detection is now increasingly leveraging online social networks for highlighting events happening around the world via the Internet of People. In this paper, a novel Event Detection model based on Scoring and Word Embedding (ED-SWE) is proposed for discovering key events from a large volume of data streams of tweets and for generating an event summary using keywords and top-k tweets. The proposed ED-SWE model can distill high-quality tweets, reduce the negative impact of the advent of spam, and identify latent events in the data streams automatically. Moreover, a word embedding algorithm is used to learn a real-valued vector representation for a predefined fixed-sized vocabulary from a corpus of Twitter data. In order to further improve the performance of the Expectation-Maximization (EM) iteration algorithm, a novel initialization method based on the authority values of the tweets is also proposed in this paper to detect live events efficiently and precisely. Finally, a novel automatic identification method based on the cosine measure is used to automatically evaluate whether a given topic can form a live event. Experiments conducted on a real-world dataset demonstrate that the ED-SWE model exhibits better efficiency and accuracy than several state-of-art event detection models.     

The technology assessment and forecast program of the United States patent and trademark office

Often overlooked is the wealth of information in patents that makes patents useful to public policy making agencies and corporate management, among others. The source of this information is the bibliographic and classification data associated with each patent. much of which is required by law and hence is extremely accurate. These data serve to fingerprint the increment of technological activity disclosed in a patent. Possible ways of using the data include: — identification of emerging technologies — Monotoring foreign activity — identification of “actors” in the technology — tracking applications and impacts of a technologyThe objective of the technology assessment and forecast program of the United States Patent and Trademark Office is to stimulate the use of the patent file of the Office. The Office of Technology Assessment and Forecast (OTAF), which administers the program has assembled a master data base covering all U.S. patents. It periodically updates this base and adds new data items to it.     

Impurities block the alpha to omega martensitic transformation in titanium

Impurities control phase stability and phase transformations in natural and man-made materials, from shape-memory alloys to steel to planetary cores. Experiments and empirical databases are still central to tuning the impurity effects. What is missing is a broad theoretical underpinning. Consider, for example, the titanium martensitic transformations: diffusionless structural transformations proceeding near the speed of sound. Pure titanium transforms from ductile alpha to brittle omega at 9 GPa, creating serious technological problems for beta-stabilized titanium alloys. Impurities in the titanium alloys A-70 and Ti-6Al-4V (wt%) suppress the transformation up to at least 35 GPa, increasing their technological utility as lightweight materials in aerospace applications. These and other empirical discoveries in technological materials call for broad theoretical understanding. Impurities pose two theoretical challenges: the effect on the relative phase stability, and the energy barrier of the transformation. Ab initio methods calculate both changes due to impurities. We show that interstitial oxygen, nitrogen and carbon retard the transformation whereas substitutional aluminium and vanadium influence the transformation by changing the d-electron concentration. The resulting microscopic picture explains the suppression of the transformation in commercial A-70 and Ti-6Al-4V alloys. In general, the effect of impurities on relative energies and energy barriers is central to understanding structural phase transformations.     

Fracture behaviour of composite maritime T-joints

This paper outlines a study on the fracture behaviour of a glass fibre reinforced polymer T-joint commonly used in composite marine vessels. Finite element analysis was conducted using the virtual crack closure technique (VCCT) to investigate the fracture behaviour of the structure. The structure analysed contained initial disbond in various locations with various sizes under a straight pull-off load. The strain energy release rate (SERR) at the disbond tips were used to predict the failure loads and crack growth mechanism of the structure. The experimental results validated the VCCT as a tool for assessing the fracture behaviour and damage criticality of such structures. It was also discovered that skewed loading affected the SERR at the crack tips which altered the fracture behaviour of such structures, therefore sensitivity analysis is recommended to enhance the prediction accuracy.     

DEPP functionally graded piezoceramics via micro-fabrication by co-extrusion

This paper introduces the Dual Electro/Piezo Property (DEPP) gradient technique via Micro-Fabrication through Co-eXtrusion (MFCX) which pairs a high displacement lead zirconate titanate (PZT) piezoceramic with a high permittivity barium titanate (BT) dielectric. By grading with this material combination spatially across an actuator, the electric field is concentrated in the more active region for improved efficiency, higher displacements, and complex motions. To aid in synthesis and analysis of any gradient profile, compositional maps are provided for key material properties (density, stiffness, permittivity, and piezoelectric coefficients). The DEPP technique was validated, independent of the MFCX process, by powder pressing a conventional bimodal gradient beam which demonstrated through experiments high displacement capabilities at lower driving potentials than comparable functionally graded piezoceramic actuators. For more complex gradients, the MFCX process was adapted to the DEPP gradient technique and illustrated by the fabrication of a linearly graded prototype whose monolithic nature and gradual material variation significantly reduces internal stresses, improves reliability, and extends service lifetime.     

Struktur und Eigenschaften gepfropfter Kartoffelstärke. III. Mikrostruktur und Bindungsverhältnisse in der Pfropf-co-polymer-Phase

Structure and Properties of Grafted Potatoe Starch. III. Microstructure and Interchain Bonds in the Graft-Copolymer-Phase Graft copolymers of polyacrylic acid and polymethacrylic acid, grafted according to the Scott-xanthation process were investigated. By combining different optical methods information could be obtained about interchain bonds in the copolymer phase. From frequency, shape and intensity of different infra-red absorption bands it could be concluded that there are hydrogen bridges from the carboxylic groups of the side chain polymer to the hydroxyl groups of the backbone-polysaccharid. These bonds lead to a crystalline copolymer phase which is different from starch and have an influence on the configuration of the polysaccharid chains in solution.     

Modulated pulse laser with pseudorandom coding capabilities for underwater ranging, detection, and imaging

Optical detection, ranging, and imaging of targets in turbid water is complicated by absorption and scattering. It has been shown that using a pulsed laser source with a range-gated receiver or an intensity modulated source with a coherent RF receiver can improve target contrast in turbid water. A blended approach using a modulated-pulse waveform has been previously suggested as a way to further improve target contrast. However only recently has a rugged and reliable laser source been developed that is capable of synthesizing such a waveform so that the effect of the underwater environment on the propagation of a modulated pulse can be studied. In this paper, we outline the motivation for the modulated-pulse (MP) concept, and experimentally evaluate different MP waveforms: single-tone MP and pseudorandom coded MP sequences.