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181.
The parity violating effective interaction in models based on the SU(2)L × SU(2)R × U(1) gauge group is shown to have the same structure, at zero momentum transfer, as in the Weinberg-Salam model, apart from a constant scale factor. 相似文献
182.
183.
Costa AC Composto RJ Vlcek P Geoghegan M 《The European physical journal. E, Soft matter》2005,18(2):159-166
Using neutron reflectometry, the adsorption of diblock copolymers from a neutral polystyrene (PS) matrix is studied as a function
of substrate type and non-adsorbing block degree of polymerization. The block copolymer is poly(deutero styrene)-block-poly(methyl methacrylate) and the substrates are silicon oxide, SiOx, and SiOx functionalized with (3-aminopropyl)triethoxysilane (APTES). We have determined the equilibrium volume fraction-depth profiles
for such films, and compared them with volume fraction profiles generated by self-consistent mean-field (SCMF) theory and
find good agreement between the experimental and theoretical data. SCMF calculations show that the segmental interaction energy
between PS matrix chains and APTES is two orders of magnitude stronger than that between PS and SiOx. 相似文献
184.
L?da Fontoura Costa G.?TraviesoEmail author C. A.?Ruggiero 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,44(1):119-128
This article investigates the functional properties of complex
networks used as grid computing systems. Complex networks following
the Erdös-Rényi model and other models with a preferential
attachment rule (with and without growth) or priority to the
connection of isolated nodes are studied. Regular networks are also
considered for comparison. The processing load of the parallel
program executed on the grid is assigned to the nodes on demand, and
the efficiency of the overall computation is quantified in terms of
the parallel speedup. It is found that networks with preferential
attachment allow lower computing efficiency than networks with
uniform link attachment. At the same time, considering only node
clusters of the same size, preferential attachment networks display
better efficiencies. The regular networks, on the other hand,
display a poor efficiency, due to their implied larger internode
distances. A correlation is observed between the topological
properties of the network, specially average cluster size, and their
respective computing efficiency. 相似文献
185.
Pessoa JC Correia I Galvão A Gameiro A Felix V Fiuza E 《Dalton transactions (Cambridge, England : 2003)》2005,(13):2312-2321
Several Ni(II) complexes derived from (S)-o-N-(N-benzylprolyl)aminobenzophenone ((S)-BBP) and amino acids of general formula [Ni((S)-BBP-L-(or D-)-aa)] were prepared. The crystal and molecular structures of [Ni((S)-BBP-Gly)], [Ni((S)-BBP-L-Ser)] and [Ni((S)-BBP-L-aaIm)](aaIm =L-2-amino-3-(imidazol-1-yl)propanoate were determined by X-ray diffraction analysis. In the three complexes the nickel atoms display a square-planar coordination and the overall structure around the metal indicates that the entire Schiff-base ligands form quite rigid frameworks. Molecular mechanics calculations were carried out for complexes [Ni((S)-BBP-Gly)], [Ni((S)-BBP-Ser)] and [Ni((S)-BBP-aaIm)] containing either the L- or D-amino acid forms, and the factors controlling the stereoselectivity are discussed. Several other [Ni((S)-BBP-L-aa)] complexes are also prepared and their circular dichroism spectra in solution and of the solids dispersed in KBr disks are measured and discussed. In agreement with other studies in solution with similar [Ni((S)-BBP-aa)] complexes, the Cotton effects for the bands with lambda(max) at 520--530 nm are positive when the amino acids have the L-configuration at the alpha-carbon. The same is observed in this work for the solid-state CD spectra of all compounds. 相似文献
186.
We present model studies of the ground state for magnetic dimers on metal surfaces. We find it can be neither ferromagnetic nor antiferromagnetic, but is often canted for nearest neighbors. Thus, the system cannot be described using bilinear exchange. We give a criterion which can be used quite generally to interrogate the local stability of ferromagnetically or antiferromagnetically aligned dimers, and which also may be used to infer the canting angle when canted states are stable. 相似文献
187.
Helmholtz electrically induced extra mass inside a charged hollow sphere, recently evidenced by Mikhailov, is analogous to Machs inertial mass. Existence of a corresponding magnetically induced extra mass in an electron flying around an autistic magnet is derived. The overall electro-magnetic effect can be covariantly expressed. 相似文献
188.
Costa DP Crocker DE Gedamke J Webb PM Houser DS Blackwell SB Waples D Hayes SA Le Boeuf BJ 《The Journal of the Acoustical Society of America》2003,113(2):1155-1165
Changes in the diving behavior of individual free-ranging juvenile northern elephant seals, Mirounga angustirostris, exposed to the acoustic thermometry of the ocean climate (ATOC) sound source were examined using data loggers. Data loggers were attached to the animals and measured swim speed, maximum depth of dive, dive duration, surface interval, descent and ascent rate, and descent and ascent angle along with sound pressure level (SPL). The ATOC sound source was at a depth of 939 m and transmitted at 195 dB re: 1 microPa at 1 m centered at 75 Hz with a 37.5-Hz bandwidth. Sound pressure levels (SPL) measured at the seal during transmissions averaged 128 dB and ranged from 118 to 137 dB re: 1 microPa for the 60-90 Hz band, in comparison to ambient levels of 87-107 dB within this band. In no case did an animal end its dive or show any other obvious change in behavior upon exposure to the ATOC sound. Subtle changes in diving behavior were detected, however. During exposure, deviations in descent rate were greater than 1 s.d. of the control mean in 9 of 14 seals. Dive depth increased and descent velocity increased in three animals, ascent velocity decreased in two animals, ascent rate increased in one animal and decreased in another, and dive duration decreased in only one animal. There was a highly significant positive correlation between SPL and descent rate. The biological significance of these subtle changes is likely to be minimal. This is the first study to quantify behavioral responses of an animal underwater with simultaneous measurements of SPL of anthropogenic sounds recorded at the animal. 相似文献
189.
Costa PR Sun B Griffin RG 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,164(1):92-103
The solid state NMR technique of rotational resonance (R2) has been used extensively to measure distances approaching 5-6 A between 13C nuclei in a variety of compounds including amyloidogenic peptides and membrane proteins. The accuracy of the distance information extracted from the time-dependent spin dynamics at R2 is often limited by the accuracy with which the relevant zero-quantum lineshape parameters are estimated. Here we demonstrate that measurement of spinning frequency dependent magnetization exchange dynamics provides data from which both distance and zero-quantum relaxation parameters can be extracted independently. In addition to providing more accurate distance information, this technique allows examination of the zero-quantum lineshape, which can indicate the presence of correlated relaxation or chemical shift distributions between dipolar-coupled sites. With this approach we have separated the contribution of dipolar couplings and zero quantum relaxation to R2 exchange curves. Thus, we have significantly improved the accuracy of the measurement of the intramolecular, internuclear distances between a pair of 13C's in two model compounds (N-acetyl-D,L-valine and glycylglycine.HCl) that lie in the distance range 4.6-4.7 A. 相似文献
190.
Duarte MF Martins F Fernandez MT Langley GJ Rodrigues P Barros MT Costa ML 《Rapid communications in mass spectrometry : RCM》2003,17(9):957-962
A series of derivatives of 2-azidoacetic acid and 2-azidoacetone were synthesized and their behaviour under electron ionization conditions was investigated. This paper reports the electron ionization fragmentation mechanisms for five aliphatic alpha-carbonyl azides, which were clarified by accurate mass measurements and B/E linked scans. The substituent influences the abundance and the nature of the ions resulting from the molecular ion fragmentation. 相似文献