17,850 research outputs found
Adaptations of the surfgrass phyllospadix to hard marine substrates: tests of anatomical differentiation and carbon isotope fractionation hypotheses
Thesis (Ph.D.) University of Alaska Fairbanks, 1987The study examined adaptation in the seagrass genus Phyllospadix to rocky substrates, habitats not generally exploited by seagrasses. One hypothesis tested whether the genus exhibits anatomical features distinguishing it from other seagrasses. A corollary predicted that individual Phyllospadix species show additional specialization, based on observations that three species are distinctly zoned where they occur together. A second hypothesis tested a model of carbon assimilation that predicts that submerged aquatic plants growing on hard substrates, such as Phyllospadix species and most marine algae, experience less transport resistances to inorganic carbon uptake than rooted and rhizoidal plants. As a consequence, it was predicted that Phyllospadix species would show enzymatic discrimination against carbon-13 similar to marine algae and dissimilar to other seagrasses. Carbon isotopic variability in Phyllospadix serrulatus and Phyllospadix torreyi was compared with that of the algae Egregia menziesii and Halosaccion amerlcanum growing at the same location. Carbon isotopic variability in eelgrass. Zostera marina, was also examined to provide a basis of comparison to sediment rooted seagrasses. Comparison with Z. marina was useful in defining anatomical features in Phyllospadix that are adaptations to rocky littoral environments. These features include greater hypodermal fiber and roothair development, thickened rhizomes, and smaller lacunae. Comparison among Phyllospadix spp. for microhabitat adaptations was less fruitful. Phyllospadix spp. show carbon isotopic discriminatory patterns distinct from Z. marina and marine algae. Although marine algae and Phyllospadix spp. overlapped isotopically, only the seagrasses became isotopically lighter with increasing intertidal height, probably through atmospheric carbon dioxide incorporation. Carbon isotope ratios in submerged seagrasses did not appear to be affected by water motion, as predicted by boundary layer considerations. An observed correlation between leaf thickness and leaf isotopic ratios also indicated complications to simple models of carbon assimilation in submerged aquatic plants
The maximal tubes under the deformations of a class of 3-dimensional hyperbolic cone-manifolds
Recently, Hodgson and Kerckhoff found a small bound on Dehn surgered
3-manifolds from hyperbolic knots not admitting hyperbolic structures using
deformations of hyperbolic cone-manifolds. They asked whether the area
normalized meridian length squared of maximal tubular neighborhoods of the
singular locus of the cone-manifold is decreasing and that summed with the cone
angle squared is increasing as we deform the cone-angles. We confirm this near
0 cone-angles for an infinite family of hyperbolic cone-manifolds obtained by
Dehn surgeries along the Whitehead link complements. The basic method is based
on explicit holonomy computations using the A-polynomials and finding the
maximal tubes. One of the key tool is the Taylor expression of a geometric
component of the zero set of the A-polynomial in terms of the cone-angles. We
also show a sequence of Taylor expressions for Dehn surgered manifolds
converges to one for the limit hyperbolic manifold.Comment: 27 pages, 10 figure
Comment: Complex Federal Civil Litigation-Can Jury Trials Be Constitutionally Avoided?
The seventh amendment to the United States Constitution affords the right to a jury trial to parties to a common law action when the value in controversy exceeds twenty dollars. In a select group of extremely lengthy cases involving complex factual and legal issues, however, several United States appellate and district courts have refused to permit trial by jury. This comment reviews and evaluates different theories that may be applied to preclude the granting of a jury trial. In addition, guidelines are proposed that may be utilized by a federal district court judge in determining whether a case is so complex and lengthy that a request for a jury trial should be denied
Almost-zero-energy Eigenvalues of Some Broken Supersymmetric Systems
For a quantum mechanical system with broken supersymmetry, we present a
simple method of determining the ground state when the corresponding energy
eigenvalue is sufficiently small. A concise formula is derived for the
approximate ground state energy in an associated, well-separated, asymmetric
double-well-type potential. Our discussion is also relevant for the analysis of
the fermion bound state in the kink-antikink scalar background.Comment: revised version, to be pubilshed in PR
Coulomb Explosion Dynamics of Chlorocarbonylsulfenyl Chloride
The Coulomb explosion dynamics following strong field ionization of chlorocarbonylsulfenyl chloride was studied using multimass coincidence detection and covariance imaging analysis, supported by density functional theory calculations. These results show evidence of multiple dissociation channels from various charge states. Double ionization to low-lying electronic states leads to a dominant C-S cleavage channel, while higher states can alternatively correlate to the loss of Cl+. Triple ionization leads to a double dissociation channel, the observation of which is confirmed via three-body covariance analysis, while further ionization leads primarily to atomic or diatomic fragments whose relative momenta depend strongly on the starting structure of the molecule
Optical investigations on : Electronic structure evolutions related to the metal-insulator transition
Optical conductivity spectra of cubic pyrochlore
(0.0{\it x}2.0) compounds are investigated. As a metal-insulator
transition (MIT) occurs around {\it x}0.8, large spectral changes are
observed. With increase of {\it x}, the correlation-induced peak between the
lower and the upper Hubbard bands seems to be suppressed, and a strong
mid-infrared feature is observed. In addition, the charge transfer peak
shifts to the lower energies. The spectral changes cannot be explained by
electronic structural evolutions in the simple bandwidth-controlled MIT
picture, but are consistent with those in the filling-controlled MIT picture.
In addition, they are also similar to the spectral changes of
YCaRuO compounds, which is a typical
filling-controlled system. This work suggests that, near the MIT, the Ru bands
could be doped with the easily polarizable Bi cations.Comment: 5 figure
Non-locality and Medium Effects in the Exclusive Photoproduction of Eta Mesons on Nuclei
A relativistic model for the quasifree exclusive photoproduction of
mesons on nuclei is extended to include both non-local and medium effects. The
reaction is assumed to proceed via the dominant contribution of the
S(1535) resonance. The complicated integrals resulting from the
non-locality are simplified using a modified version of a method given by
Cooper and Maxwell. The non-locality effects are found to affect the magnitude
of the cross section. Some possibilities reflecting the effects of the medium
on the propagation and properties of the intermediate S resonance are
studied. The effects of allowing the S to interact with the medium via
mean field scalar and vector potentials are considered. Both broadening of
width and reduction in mass of the resonance lead to a suppression of the
calculated cross sections.Comment: 19 pages, 7 figure
Irreversible reorganization in a supercooled liquid originates from localised soft modes
The transition of a fluid to a rigid glass upon cooling is a common route of
transformation from liquid to solid that embodies the most poorly understood
features of both phases1,2,3. From the liquid perspective, the puzzle is to
understand stress relaxation in the disordered state. From the perspective of
solids, the challenge is to extend our description of structure and its
mechanical consequences to materials without long range order. Using computer
simulations, we show that the localized low frequency normal modes of a
configuration in a supercooled liquid are causally correlated to the
irreversible structural reorganization of the particles within that
configuration. We also demonstrate that the spatial distribution of these soft
local modes can persist in spite of significant particle reorganization. The
consequence of these two results is that it is now feasible to construct a
theory of relaxation length scales in glass-forming liquids without recourse to
dynamics and to explicitly relate molecular properties to their collective
relaxation.Comment: Published online: 20 July 2008 | doi:10.1038/nphys1025 Available from
http://www.nature.com/nphys/journal/v4/n9/abs/nphys1025.htm
Electron and orbital correlations in Ca_{2-x}Sr_{x}RuO_{4} probed by optical spectroscopy
The doping and temperature dependent optical conductivity spectra of the
quasi-two-dimensional Ca_{2-x}Sr_xRuO_4 (0.0=<x=<2.0) system were investigated.
In the Mott insulating state, two electron correlation-induced peaks were
observed around 1.0 and 1.9 eV, which could be understood in terms of the
3-orbital Hubbard model. The low frequency peak showed a shift toward higher
frequency as temperature was lowered, which indicated that electron-phonon
interactions play an important role in the orbital arrangements. From the
systematic analysis, it was suggested that the antiferro-orbital and the
ferro-orbital ordering states could coexist.Comment: 12 pages, 4 figure
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