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51.
Abstract An optimal control problem for a two-dimensional elliptic equation with pointwise control constraints is investigated. The
domain is assumed to be polygonal but non-convex. The corner singularities are treated by a priori mesh grading. Approximations
of the optimal solution of the continuous optimal control problem are constructed by a projection of the discrete adjoint
state. It is proved that these approximations have convergence order h2.
Keywords Linear-quadratic optimal control problems, error estimates, elliptic equations, non-convex domains, corner singularities,
control constraints, superconvergence.
Mathematics Subject Classification (2000): 49K20, 49M25, 65N30, 65N50 相似文献
52.
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54.
Janet Feigenspan Christian Kästner Sven Apel Jörg Liebig Michael Schulze Raimund Dachselt Maria Papendieck Thomas Leich Gunter Saake 《Empirical Software Engineering》2013,18(4):699-745
Software-product-line engineering aims at the development of variable and reusable software systems. In practice, software product lines are often implemented with preprocessors. Preprocessor directives are easy to use, and many mature tools are available for practitioners. However, preprocessor directives have been heavily criticized in academia and even referred to as “#ifdef hell”, because they introduce threats to program comprehension and correctness. There are many voices that suggest to use other implementation techniques instead, but these voices ignore the fact that a transition from preprocessors to other languages and tools is tedious, erroneous, and expensive in practice. Instead, we and others propose to increase the readability of preprocessor directives by using background colors to highlight source code annotated with ifdef directives. In three controlled experiments with over 70 subjects in total, we evaluate whether and how background colors improve program comprehension in preprocessor-based implementations. Our results demonstrate that background colors have the potential to improve program comprehension, independently of size and programming language of the underlying product. Additionally, we found that subjects generally favor background colors. We integrate these and other findings in a tool called FeatureCommander, which facilitates program comprehension in practice and which can serve as a basis for further research. 相似文献
55.
Ivancevich NM Dahl JJ Trahey GE Smith SW 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2006,53(8):1432-1439
We tested the feasibility of using adaptive imaging, namely phase-aberration correction, with two-dimensional (2-D) arrays and real-time, 3-D ultrasound. Because of the high spatial frequency content of aberrators, 2-D arrays, which generally have smaller pitch and thus higher spatial sampling frequency, and 3-D imaging show potential to improve the performance of adaptive imaging. Phase-correction algorithms improve image quality by compensating for tissue-induced errors in beamforming. Using the illustrative example of transcranial ultrasound, we have evaluated our ability to perform adaptive imaging with a real-time, 3-D scanner. We have used a polymer casting of a human temporal bone, root-mean-square (RMS) phase variation of 45.0 ns, full-width-half-maximum (FWHM) correlation length of 3.35 mm, and an electronic aberrator, 100 ns RMS, 3.76 mm correlation, with tissue phantoms as illustrative examples of near-field, phase-screen aberrators. Using the multilag, least-squares, cross-correlation method, we have shown the ability of 3-D adaptive imaging to increase anechoic cyst identification, image brightness, contrast-to-speckle ratio (CSR), and, in 3-D color Doppler experiments, the ability to visualize flow. For a physical aberrator skull casting we saw CSR increase by 13% from 1.01 to 1.14, while the number of detectable cysts increased from 4.3 to 7.7. 相似文献
56.
Clinical applications of glass-ceramics in dentistry 总被引:3,自引:0,他引:3
Höland W Rheinberger V Apel E van 't Hoen C Höland M Dommann A Obrecht M Mauth C Graf-Hausner U 《Journal of materials science. Materials in medicine》2006,17(11):1037-1042
Glass-ceramics featuring special properties can be used as a basis to develop biomaterials. It is generally differentiated
between highly durable biomaterials for restorative dental applications and bioactive glass-ceramics for medical use, for
example, bone replacements. In detail, this paper presents one biomaterial from each of these two groups of materials.
In respect to the restorative dental biomaterials, the authors give an overview of the most important glass-ceramics for clinical
applications. Leucite, leucite-apatite, lithium disilicate and apatite containing glass-ceramics represent biomaterials for
these applications. In detail, the authors report on nucleation and crystallization mechanisms and properties of leucite-apatite
glass-ceramics. The mechanism of apatite nucleation is characterized by a heterogeneous process. Primary crystal phases of
α - and β -NaCaPO4 were determined.
Rhenanite glass-ceramics represent biomaterials with high surface reactivity in simulated body fluid, SBF, and exhibit reactive
behaviour in tests with bone cells. Cell adhesion phenomena and cell growth were observed. Suitable colonization and proliferation
and differentiation of cells as a preliminary stage in the development of a material for bone regeneration applications was
established. The authors conclude that the processes of heterogeneous nucleation and crystallization are important for controlling
the required reactions in both biomaterial groups. 相似文献
57.
Gutiérrez Lezama I Nakano M Minder NA Chen Z Di Girolamo FV Facchetti A Morpurgo AF 《Nature materials》2012,11(9):788-794
Organic semiconductors based on small conjugated molecules generally behave as insulators when undoped, but the heterointerfaces of two such materials can show electrical conductivity as large as in a metal. Although charge transfer is commonly invoked to explain the phenomenon, the details of the process and the nature of the interfacial charge carriers remain largely unexplored. Here we use Schottky-gated heterostructures to probe the conducting layer at the interface between rubrene and PDIF-CN(2) single crystals. Gate-modulated conductivity measurements demonstrate that interfacial transport is due to electrons, whose mobility exhibits band-like behaviour from room temperature to ~150 K, and remains as high as ~1 cm(2) V(-1) s(-1) at 30 K for the best devices. The electron density decreases linearly with decreasing temperature, an observation that can be explained quantitatively on the basis of the heterostructure band diagram. These results elucidate the electronic structure of rubrene/PDIF-CN(2) interfaces and show the potential of Schottky-gated organic heterostructures for the investigation of transport in molecular semiconductors. 相似文献
58.
Huila MF Lukin N Parussulo AL Oliveira PV Kyohara PK Araki K Toma HE 《Analytical chemistry》2012,84(7):3067-3069
The acid protection effect promoted by traces of PdCl(2) in [Ni(dmgH)(2)] spot tests was elucidated from confocal Raman microscopy imaging, which revealed the formation of protecting layers of [Pd(dmgH)(2)] closing the extremities of the [Ni(dmgH)(2)] filaments. 相似文献
59.
Kelly C. da Silva RodriguesMíriam A. Apel Amélia T. HenriquesArthur G. Fett-Neto 《Biomass & bioenergy》2011,35(10):4442-4448
Oleoresin biomass production by trees of Pinus elliottii, which is a source of terpenes for the chemical and pharmaceutical industries, was investigated. Trees were individually analyzed for oleoresin yield using the bark streak method of wounding for stimulation of resin flow. Controls included plain wounding and wounding followed by application of commercial stimulant paste, based on sulfuric acid and synthetic precursors of the phytohormone ethylene. Metal cofactors of terpene synthases and ethylene receptors applied locally as adjuvants of the oleoresin stimulant paste on wounded bark tissue improved resin yields. The use of potassium, copper, and iron did not affect significantly the composition of semiochemical monoterpenes, which are involved with pine - bark beetle interactions, and are important as oleoresin-derived products. Some adjuvants, particularly potassium, were capable of supporting oleoresin yields equivalent to those obtained with current commercial stimulant paste, even with removal of ethylene precursor, the most expensive adjuvant. 相似文献
60.
Nikolas Esposito David W. Konas Nina M. Goodey 《Chembiochem : a European journal of chemical biology》2022,23(2):e202100314
Tuberculosis (TB), caused by the pathogen Mycobacterium tuberculosis, affects millions of people worldwide. Several TB drugs have lost efficacy due to emerging drug resistance and new anti-TB targets are needed. Recent research suggests that indole-3-glycerol phosphate synthase (IGPS) in M. tuberculosis (MtIGPS) could be such a target. IGPS is a (β/α)8-barrel enzyme that catalyzes the conversion of 1-(o-carboxyphenylamino)-1-deoxyribulose 5’-phosphate (CdRP) into indole-glycerol-phosphate (IGP) in the bacterial tryptophan biosynthetic pathway. M. tuberculosis over expresses the tryptophan pathway genes during an immune response and inhibition of MtIGPS allows CD4 T-cells to more effectively fight against M. tuberculosis. Here we review the published data on MtIGPS expression, kinetics, mechanism, and inhibition. We also discuss MtIGPS crystal structures and compare them to other IGPS structures to reveal potential structure-function relationships of interest for the purposes of drug design and biocatalyst engineering. 相似文献