1,114 research outputs found
Dynamic surface scaling behavior of isotropic Heisenberg ferromagnets
The effects of free surfaces on the dynamic critical behavior of isotropic
Heisenberg ferromagnets are studied via phenomenological scaling theory,
field-theoretic renormalization group tools, and high-precision computer
simulations. An appropriate semi-infinite extension of the stochastic model J
is constructed, the boundary terms of the associated dynamic field theory are
identified, its renormalization in d <= 6 dimensions is clarified, and the
boundary conditions it satisfies are given. Scaling laws are derived which
relate the critical indices of the dynamic and static infrared singularities of
surface quantities to familiar static bulk and surface exponents. Accurate
computer-simulation data are presented for the dynamic surface structure
factor; these are in conformity with the predicted scaling behavior and could
be checked by appropriate scattering experiments.Comment: 9 pages, 2 figure
On baryon-antibaryon coupling to two photons
We discuss recent claims that may be described
by a generalized parton picture. We propose that quark-hadron duality provides
a justification for the effective dominance of the "handbag" diagram assumed in
recent literature, and that handbag diagrams may dominate phenomena in
kinematic regions far more extensive than that might be expected from pQCD
alone.Comment: 11 pages, 2 eps figures, minor modifications made, version to appear
on Phys. Lett.
Implant-Supported Overdentures: Current Status and Preclinical Testing of a Novel Attachment System
Numerous attachment systems exist for implant-supported overdentures, with each having
specific limitations in terms of retention, cost, wear, maintenance and cleanability. A retrospective
analysis of patients restored with implant-supported overdentures using bars, telescopic crowns and
Locator-type attachments was performed and the patients were interviewed. An in vitro strain gauge
study compared telescopic crowns, Locator-type attachments and a novel flexible attachment system
employing a shape memory alloy (NiTi) with respect to peri-implant strain development during
insertion, loading and removal of an overdenture. A significantly lower number of attachment-related
complications was observed in bars as compared to telescopic crowns (p = 0.00007) and Locator-type
attachments (p = 0.00000), respectively. Greater overall patient satisfaction was noted in bar-retained
restorations while Locator-type attachments led to lower levels of satisfaction regarding prosthesis
retention. In vitro, telescopic crowns caused maximum strain development during prosthesis insertion and loading, while during removal this was observed in Locators with white retentive inserts.
NiTi attachments caused significantly lower strain development during insertion as compared to
telescopic crowns (p = 0.027). During loading, NiTi attachments caused significantly lower strain
development than Locators with blue retentive inserts (p = 0.039). During removal, NiTi attachments
caused significantly less strain development as compared to Locators with white retentive inserts
(p = 0.027). Positional discrepancies between male and female attachment parts affected the retention
and reaction force between both components, which may be minimized by using the novel NiTi
attachment system. This may be beneficial in terms of component wear and implant loading
Critical adsorption at chemically structured substrates
We consider binary liquid mixtures near their critical consolute points and
exposed to geometrically flat but chemically structured substrates. The
chemical contrast between the various substrate structures amounts to opposite
local preferences for the two species of the binary liquid mixtures. Order
parameters profiles are calculated for a chemical step, for a single chemical
stripe, and for a periodic stripe pattern. The order parameter distributions
exhibit frustration across the chemical steps which heals upon approaching the
bulk. The corresponding spatial variation of the order parameter and its
dependence on temperature are governed by universal scaling functions which we
calculate within mean field theory. These scaling functions also determine the
universal behavior of the excess adsorption relative to suitably chosen
reference systems
The Antimonous-Antimonic Complex in Hydrochloric Acid
A successful theory systematizing or correlating the color of inorganic complexes has not yet been advanced. Linus Pauling in his Richards Medal address (7) listed such a theory as one of the puzzling unsolved problems of structural chemistry . The colors developed by solutions containing the same element in different valence states is particularly interesting, in that the color of the mixture may be radically different from that of either component. Cuprous chloride in concentrated hydrochloric acid is colorless, cupric chloride in a similar solution is green; present together they produce a dark brown or black solution (3). Similarly, a hydrochloric acid solution of antimony trichloride is colorless, of antimony pentachloride a pale yellow; a mixture of the two, however, possesses an intense red-brown color. Although ferrous hydroxide is white and ferric hydroxide brown, the ferrous-ferric hydroxide resulting from partial air oxidation of freshly precipitated ferrous hydroxide is black. Again, colorless tervalent ytterbium on reduction with metallic zinc to green, bivalent ytterbium passes through a purple stage, again probably a mixed valence complex(2). In the present paper a more detailed study is reported of the antimonous chloride-antimonic chloride-hydrochloric acid system
Spatial Distribution of Nucleosynthesis Products in Cassiopeia A: Comparison Between Observations and 3D Explosion Models
We examine observed heavy element abundances in the Cassiopeia A supernova
remnant as a constraint on the nature of the Cas A supernova. We compare bulk
abundances from 1D and 3D explosion models and spatial distribution of elements
in 3D models with those derived from X-ray observations. We also examine the
cospatial production of 26Al with other species. We find that the most reliable
indicator of the presence of 26Al in unmixed ejecta is a very low S/Si ratio
(~0.05). Production of N in O/S/Si-rich regions is also indicative. The
biologically important element P is produced at its highest abundance in the
same regions. Proxies should be detectable in supernova ejecta with high
spatial resolution multiwavelength observations.Comment: To appear in the Conference Proceedings for the "10th Symposium on
Nuclei in the Cosmos (NIC X)", July 27 - August 1 2008, Mackinack Island,
Michigan, US
- …