排序方式: 共有42条查询结果,搜索用时 15 毫秒
31.
Adam D. Helfer 《Physics letters. A》1990,150(8-9):342-344
Using the approach initiated by Penrose, we calculate the flux of angular momentum emitted by a gravitational system. In appropriate circumstances, we recover the formula Ashtekar and Streubel derived for the total emitted angular momentum. 相似文献
32.
The role of perceived spatial separation in the unmasking of speech 总被引:12,自引:0,他引:12
Freyman RL Helfer KS McCall DD Clifton RK 《The Journal of the Acoustical Society of America》1999,106(6):3578-3588
Spatial separation of speech and noise in an anechoic space creates a release from masking that often improves speech intelligibility. However, the masking release is severely reduced in reverberant spaces. This study investigated whether the distinct and separate localization of speech and interference provides any perceptual advantage that, due to the precedence effect, is not degraded by reflections. Listeners' identification of nonsense sentences spoken by a female talker was measured in the presence of either speech-spectrum noise or other sentences spoken by a second female talker. Target and interference stimuli were presented in an anechoic chamber from loudspeakers directly in front and 60 degrees to the right in single-source and precedence-effect (lead-lag) conditions. For speech-spectrum noise, the spatial separation advantage for speech recognition (8 dB) was predictable from articulation index computations based on measured release from masking for narrow-band stimuli. The spatial separation advantage was only 1 dB in the lead-lag condition, despite the fact that a large perceptual separation was produced by the precedence effect. For the female talker interference, a much larger advantage occurred, apparently because informational masking was reduced by differences in perceived locations of target and interference. 相似文献
33.
Dra Barczikai Judit Domokos Dra Szab Kristof Molnar David Juriga Eniko Krisch Krisztina S. Nagy Laszlo Kohidai Carin A. Helfer Angela Jedlovszky-Hajdu Judit E. Puskas 《Molecules (Basel, Switzerland)》2021,26(17)
This paper presents the results of the first part of testing a novel electrospun fiber mat based on a unique macromolecule: polyisobutylene (PIB). A PIB-based compound containing zinc oxide (ZnO) was electrospun into self-supporting mats of 203.75 and 295.5 g/m2 that were investigated using a variety of techniques. The results show that the hydrophobic mats are not cytotoxic, resist fibroblast cell adhesion and biofilm formation and are comfortable and easy to breathe through for use as a mask. The mats show great promise for personal protective equipment and other applications. 相似文献
34.
Marijke WA de Backer Maike AD Brans Mieneke CM Luijendijk Keith M Garner Dianne MA van den Heuvel R Jeroen Pasterkamp Roger AH Adan 《BMC neuroscience》2010,11(1):94
Background
Multiple neuropeptides, sometimes with opposing functions, can be produced from one precursor gene. To study the roles of the different neuropeptides encoded by one large precursor we developed a method to overexpress minigenes and establish local secretion. 相似文献35.
Carin A. Helfer Donghai Chen Wayne L. Mattice Barry L. Farmer 《Journal of polymer science. Part A, Polymer chemistry》2005,43(8):886-896
A coarse-grained model has been developed for asymmetrically substituted poly(silylenemethylene)s in which the side chain is a flexible spacer terminated by a biphenyl unit. Each monomer unit is represented by four coarse-grained beads that interact via a Lennard–Jones potential and are subject to the first- and second-order interactions deduced from the atomistically detailed model. Metropolis Monte Carlo simulations were performed for isolated syndiotactic, isotactic, and atactic chains. Snapshots from the equilibrated coarse-grained chain on the discrete space of a high coordination lattice were reverse-mapped to atomistically detailed structures in continuous space. At 373 K, the chains were disordered independent of the stereochemical composition. The occupancy of bond pairs depended on the stereochemical composition, with the trans-gauche (tg) sequence being favored by the isotactic chain. When the simulation was performed with the backbone constrained to specific periodic structures, the g helix was the lowest energy structure for either the atactic or isotactic chains. For the syndiotactic chain, the g and gt helices were favored. The appearance of the g helix as the favored periodic structure of the isolated chain was consistent with the chain conformation reported previously for the smectic phase of this polymer in the bulk state. The g helix was disrupted when the backbone was allowed to access nonhelical conformations, even though these conformations may have been slightly higher in energy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 886–896, 2005 相似文献
36.
A mathematical model is proposed for the process of vacuum superplasticforming. The model exploits the fact that in most industrialapplications the sheet aspect ratio (thickness/sheet width)is small. After an initial consideration of some of the moregeneral properties and the literature of superplastic materials,the elastic/plastic deformation of an internally-inflated thin-walledcylinder is examined. Plates of arbitrary geometry are thenconsidered. A quasisteady model in which the sheet moves througha sequence of steady states is developed. Some simplified closed-formsolutions are examined, but for general cases a system of nonlinearpartial differential equations must be solved numerically. Anefficient and accurate semi-explicit numerical scheme is proposedand a simplified stability analysis is presented; the methodis then used to compute properties of superplastic vacuum mouldedsheets in a number of practically motivated cases. 相似文献
37.
Adam D. Helfer 《General Relativity and Gravitation》1985,17(2):133-147
A holomorphic connection on (1, 0)-vector fields which is intrinsically defined on any curved twistor space is described. Although it is a local operator, it is given in terms of the nonlocal geometry of the twistor space corresponding to the local geometry of the spacetime. The connection is represented in local coordinates by a system ofnonlinear first-order partial differential operators. It has torsion but no curvature. A parallelism is given explicitly, and an example is computed. 相似文献
38.
H. Lawrence Helfer Robert L. McCrory Hugh M. Van Horn 《Journal of statistical physics》1984,37(5-6):577-588
Very accurate Monte Carlo calculations for the one-component plasma (OCP) have been compared with the results of Slattery, Doolen, and DeWitt.(1,2) We confirm their results and also find a slight dependence of the calculation of the internal energy per particle uponN, the number of particles. A detailed investigation forN=108 permits us to evaluate the Helmholtz free energy for an OCP fcc lattice. As is usually believed, we find that the bcc lattice is more stable than the fcc lattice. The transition from the liquid to the fcc lattice phase occurs when
fcc = 196 ± 1. A three-dimensional modified cubic procedure, capable of achieving high accuracy in using tables of two-particle interaction potentials, is described in Appendix B. 相似文献
39.
Wayne L. Mattice Carin A. Helfer Sagar S. Rane Ernst D. Von Meerwall Barry L. Farmer 《Journal of Polymer Science.Polymer Physics》2005,43(11):1271-1282
Coarse‐grained chains can be designed so that they successfully capture subtle effects arising from the local covalent structure of real chains. Constraining the conformations of the coarse‐grained chains with an appropriate rotational isomeric state model can achieve this objective. This claim has been documented by simulations of the dependence of the mixing behavior of polypropylene melts on the stereochemical composition of the chains; atactic polypropylene and isotactic polypropylene are miscible, but the replacement of either component with syndiotactic polypropylene can lead to immiscibility. This has also been documented by a comparison of simulations and infrared–visible sum frequency generation spectroscopy studies of the surface structures of atactic polystyrene and random copolymers of ethylene and propylene. The success of this method when the stereochemical composition is defined by side chains as small as CH3 suggests that it should also be applicable to other problems in which the influence of the stereochemical composition is less subtle because the stereochemistry is defined by larger side chains. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1271‐1282, 2005 相似文献
40.
To elucidate the reasons underlying the poor penetration of non-viral vectors in tissues, relating transport properties to
physico-chemical parameters of vectors may be crucial. These properties can be influenced by the presence of multiples labels
that are used. Therefore utilizing a vector with minimum of labels preferably not more than one is important to studying penetration
in tissues. The cell impermeant bisintercalating dye YOYO-1 was found suitable to both monitor the formation of complexes
between DNA and an amphipathic peptide LK15 and, to track their penetration in HCT116 spheroids by confocal microscopy. The
results revealed a limited decrease of fluorescence ascribed to the high affinity of YOYO-1 to bind DNA. The residual fluorescence
of complexes can be exploited to monitor penetration into spheroids, after correction for YOYO-1 attenuation, and to revealing
hyaluronidase-induced reduced binding. Hence high affinity dyes such as YOYO-1 with inefficiently quenched fluorescence may
be important to establish a relation between novel medicines characteristics and penetration in tissues. 相似文献