Combined MR data acquisition of multicontrast images using variable acquisition parameters and K-space data sharing

A new technique to reduce clinical magnetic resonance imaging (MRI) scan time by varying acquisition parameters and sharing k-space data between images, is proposed. To improve data utilization, acquisition of multiple images of different contrast is combined into a single scan, with variable acquisition parameters including repetition time (TR), echo time (TE), and echo train length (ETL). This approach is thus referred to as a "combo acquisition." As a proof of concept, simulations of MRI experiments using spin echo (SE) and fast SE (FSE) sequences were performed based on Bloch equations. Predicted scan time reductions of 25%-50% were achieved for 2-contrast and 3-contrast combo acquisitions. Artifacts caused by nonuniform k-space data weighting were suppressed through semi-empirical optimization of parameter variation schemes and the phase encoding order. Optimization was assessed by minimizing three quantitative criteria: energy of the "residue point spread function (PSF)," energy of "residue profiles" across sharp tissue boundaries, and energy of "residue images." In addition, results were further evaluated by quantitatively analyzing the preservation of contrast, the PSF, and the signal-to-noise ratio. Finally, conspicuity of lesions was investigated for combo acquisitions in comparison with standard scans. Implications and challenges for the practical use of combo acquisitions are discussed.     

Comparison of the electrical conductivity of bulk and film Ce1–xZrxO2–δ in oxygen-depleted atmospheres at high temperatures

Journal of Materials Science - Featuring high levels of achievable oxygen non-stoichiometry δ, Ce1?xZrxO2?δ solid solutions (CZO) are crucial for application as...     

Beschichtungen für Zahnräder

Coatings for gear wheels In order to optimize the goal, steel gear wheels regarding load‐carrying capacity and wear, thin film coatings were tested. Different coating systems were examined numerically with the software ELASTICA® for their suitability. The characteristics of the coating systems were determined dependent on the material, its surface treatment as well as the diameters of relevant rolling partners. Differences were made between macroscopic rolling contacts between the teeth profiles and microscopic contacts with surface roughness and abrasion particles. First the four best suitable coating systems were deposited on simplified rollers and examined under different conditions. Two coating systems were determined, which show special suitability for the coating of the gear wheels. The first system is an a:C‐H coating with an CrN interlayer. The second system is an a:C‐H coating wtih an CrN interlayer on a plasma‐nitrided substrat (Duplex‐process). In order to protect the coatings on the teeth, their involute profile was provided with a tip relief. As gear wheel materials 16MnCr5, 42CrMo4 as well as the special steel ETG®88 were used. Two kinds of flow fats were used as lubricants and additional the unlubricated operation was examined. The gear wheels were tested at three different speeds on a test machine especially built for it. The testing routine was carried out in so‐called power‐stages. Each stage means a defined number of contacts and a certain Hertzian stress on the teeth profiles. With each stage the Hertzian stress was increased. The end of operation time is the beginning of cavitation pitting. The test results showed that in particular with the steel 16MnCr5 and 42CrMo4 the used Duplex‐systems leads to considerable increases of the load‐carrying capacity of the tooth flanks and the wear resistance. This increase was observed both with fat‐lubricated and with unlubricated gear wheels. The results for the special steel ETG®88 were less promising. An unlubricated operation could be made possible by the described coatings, which would not have been possible without the coatings. However the results are not as good as the results of uncoated gear wheels wih use of minimum fat lubrication. The reason could be an insufficient nitriding‐depth. For the selected steel the plasma‐nitriding parameters were investigated with the goal of optimized nitriding‐depth. Unfortunately up to the end of this project the gear wheels could not be treated with the optimized Duplex‐Process. At present the attempts with optimally plasma‐nitrided gear wheels are carried out. After that it would be possible to give recommendations for the plasma‐nitriding process and the necessary coating as well as the selection of the fat.     

An adaptive singular finite element in nonlinear fracture mechanics

In the case of nonlinear fracture mechanics the type of singularity induced by the crack tip is commonly not known. This results in a poor approximation of the near crack tip fields in a finite element setting and induces so called spurious—or residual—discrete material forces in the vicinity of the crack tip. Thus the numerical calculation of the crack driving material force in nonlinear fracture is often not that precise as in linear elasticity where we can use special crack tip elements and/or path independency. To overcome this problem we propose an adaptive singular element, which adapts automatically to the type of singularity. The adaption is based on an optimisation procedure using a variational principle.     

The focus of light—linear polarization breaks the rotational symmetry of the focal spot

Abstract

We experimentally demonstrate for the first time that a linearly polarized beam is focused to an asymmetric spot when using a high-numerical aperture focusing system. This asymmetry was predicted by Richards and Wolf in 1959 and can only be measured when a polarization-insensitive sensor is placed in the focal region. We used a specially modified photodiode in a knife-edge-type set-up to obtain highly resolved images of the total electric energy density distribution at the focus. The results are in good agreement with the predictions of a vectorial focusing theory.     

Theoretical and experimental properties of a binary linear beam-splitting element with a large fan angle

Abstract

Diffractive beam-splitting elements with a large fan angle of about 45° were realized as binary phase elements for application in a commercial laser device operating at the wavelength of 635 nm. The fan-out elements designated to split a laser beam into a line of 43 equal power spots were fabricated in silica by means of microstructuring techniques and replicated in acrylate by ultraviolet curing. Two different gratings have been designed using scalar unidirectional iterative methods, based on the iterative discrete on-axis and on the direct binary search algorithms. The optical properties of both gratings obtained by these scalar methods were compared with simulations based on rigorous electromagnetic calculations in order to verify and control the application-relevant specifications. The experimentally measured optical performance of the replicated fan-out elements is in good agreement with the theoretical predictions. The complete procedure for realizing the linear beam splitters, that is the design method, the fabrication of the master, and the replication process, will be presented. The optical properties and characteristic data of the replicas will be compared with scalar simulations as well as rigorous calculations; the results will be discussed.     

Do lead articles signal higher quality in the digital age? Evidence from finance journals

Citations are regarded as measures of quality yet citation rates vary widely within each of the top finance journals. Since article ordering is at the discretion of editors, lead articles can be interpreted as signals of quality that academics can use to allocate their attention and assert the value of their publications. Advances in electronic journal access allow researchers to directly access articles, suggesting article ordering may be less relevant today. We confirm the past importance of lead articles by examining citation rates from published papers as well as the wider source of papers that are listed in Google Scholar. Our findings also confirm using Google Scholar as a citation source provides congruent results to using citations from articles published in ISI-listed journals, with the additional benefit of it potentially being more timely since it includes wider citation sources, inclusive of working and conference papers.     

Social-cognitive predictors of health behavior: Action self-efficacy and coping self-efficacy.

The effects of social-cognitive variables on preventive nutrition and behavioral intentions were studied in 580 adults at 2 points in time. The authors hypothesized that optimistic self-beliefs operate in 2 phases and made a distinction between action self-efficacy (preintention) and coping self-efficacy (postintention). Risk perceptions, outcome expectancies, and action self-efficacy were specified as predictors of the intention at Wave 1. Behavioral intention and coping self-efficacy served as mediates linking the 3 predictors with low-fat and high-fiber dietary intake 6 months later at Wave 2. Covariance structure analysis yielded a good model fit for the total sample and 6 subsamples created by a median split of 3 moderators: gender, age, and body weight. Parameter estimates differed between sample; the importance of perceived self-efficacy increased with age and weight. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Towards a VLSI Architecture for Interpolation-Based Soft-Decision Reed-Solomon Decoders

The Koetter-Vardy algorithm is an algebraic soft-decision decoder for Reed-Solomon codes which is based on the Guruswami-Sudan list decoder. There are three main steps: (1) multiplicity calculation, (2) interpolation and (3) root finding. The Koetter-Vardy algorithm seems challenging to implement due to the high cost of interpolation. Motivated by a VLSI implementation viewpoint we propose an improvement to the interpolation algorithm that uses a transformation of the received word to reduce the number of iterations. We show how to reduce the memory requirements and give an efficient VLSI implementation for the Hasse derivative.