3,131 research outputs found
Construing the Pelly and Packwood-Magnuson Amendments: The D.C. Circuit Court Harpoons Executive Discretion—American Cetacean Society v. Baldridge, 768 F.2d 425 (D.C. Cir. 1985), cert. granted sub nom. Japan Whaling Association v. American Cetacean Society, 106 S. Ct. 787 (1986) (Nos. 85-954, 955)
The court declared that the Secretary of Commerce has no discretion to refuse certifying the Japanese for exceeding the IWC sperm whaling quota. The court permanently enjoined the Secretary from agreeing not to certify, and from failing to certify, any Japanese whaling activities exceeding IWC quotas. The court ordered the Secretary to certify the Japanese sperm whaling under both the Pelly and the Packwood-Magnuson Amendments. On appeal, the District of Columbia Circuit Court of Appeals affirmed the district court decision on slightly different grounds. The Supreme Court granted certiorari and will hear the case during the 1985-86 term. A careful examination of the whaling agreement, the Pelly and the Packwood-Magnuson Amendments, and the circuit court decision suggests that the Supreme Court should reverse the appellate court\u27s decision because the agreement is consistent with the amendments and the Secretary of Commerce had discretion not to certify the Japanese in this case
Topological Solitons and Folded Proteins
We propose that protein loops can be interpreted as topological domain-wall
solitons. They interpolate between ground states that are the secondary
structures like alpha-helices and beta-strands. Entire proteins can then be
folded simply by assembling the solitons together, one after another. We
present a simple theoretical model that realizes our proposal and apply it to a
number of biologically active proteins including 1VII, 2RB8, 3EBX (Protein Data
Bank codes). In all the examples that we have considered we are able to
construct solitons that reproduce secondary structural motifs such as
alpha-helix-loop-alpha-helix and beta-sheet-loop-beta-sheet with an overall
root-mean-square-distance accuracy of around 0.7 Angstrom or less for the
central alpha-carbons, i.e. within the limits of current experimental accuracy.Comment: 4 pages, 4 figure
Fractal dimension of domain walls in the Edwards-Anderson spin glass model
We study directly the length of the domain walls (DW) obtained by comparing
the ground states of the Edwards-Anderson spin glass model subject to periodic
and antiperiodic boundary conditions. For the bimodal and Gaussian bond
distributions, we have isolated the DW and have calculated directly its fractal
dimension . Our results show that, even though in three dimensions
is the same for both distributions of bonds, this is clearly not the case for
two-dimensional (2D) systems. In addition, contrary to what happens in the case
of the 2D Edwards-Anderson spin glass with Gaussian distribution of bonds, we
find no evidence that the DW for the bimodal distribution of bonds can be
described as a Schramm-Loewner evolution processes.Comment: 6 pages, 5 figures. Accepted for publication in PR
Stability of the Magnetic Monopole Condensate in three- and four-colour QCD
It is argued that the ground state of three- and four-colour QCD contains a
monopole condensate, necessary for the dual Meissner effect to be the mechanism
of confinement, and support its stability on the grounds that it gives the
off-diagonal gluons an effective mass sufficient to remove the unstable ground
state mode.Comment: jhep.cls, typos corrected, references added, some content delete
Elastic energy of proteins and the stages of protein folding
We propose a universal elastic energy for proteins, which depends only on the
radius of gyration and the residue number . It is constructed using
physical arguments based on the hydrophobic effect and hydrogen bonding.
Adjustable parameters are fitted to data from the computer simulation of the
folding of a set of proteins using the CSAW (conditioned self-avoiding walk)
model. The elastic energy gives rise to scaling relations of the form
in different regions. It shows three folding stages
characterized by the progression with exponents , which we
identify as the unfolded stage, pre-globule, and molten globule, respectively.
The pre-globule goes over to the molten globule via a break in behavior akin to
a first-order phase transition, which is initiated by a sudden acceleration of
hydrogen bonding
Absorption/Expulsion of Oligomers and Linear Macromolecules in a Polymer Brush
The absorption of free linear chains in a polymer brush was studied with
respect to chain size and compatibility with the brush by means of
Monte Carlo (MC) simulations and Density Functional Theory (DFT) /
Self-Consistent Field Theory (SCFT) at both moderate, , and
high, , grafting densities using a bead-spring model.
Different concentrations of the free chains are
examined. Contrary to the case of when all species are almost
completely ejected by the polymer brush irrespective of their length , for
we find that the degree of absorption (absorbed amount)
undergoes a sharp crossover from weak to strong () absorption,
discriminating between oligomers, , and longer chains. For a
moderately dense brush, , the longer species, ,
populate predominantly the deep inner part of the brush whereas in a dense
brush they penetrate into the "fluffy" tail of the dense
brush only. Gyration radius and end-to-end distance of absorbed
chains thereby scale with length as free polymers in the bulk. Using both
MC and DFT/SCFT methods for brushes of different chain length , we demonstrate the existence of unique {\em critical} value of
compatibility . For the energy of free
chains attains the {\em same} value, irrespective of length whereas the
entropy of free chain displays a pronounced minimum. At all density
profiles of absorbing chains with different intersect at the same distance
from the grafting plane. The penetration/expulsion kinetics of free chains into
the polymer brush after an instantaneous change in their compatibility
displays a rather rich behavior. We find three distinct regimes of penetration
kinetics of free chains regarding the length : I (), II (), and III (), in which the time of absorption grows with
at a different rate. During the initial stages of penetration into the
brush one observes a power-law increase of with power
whereby penetration of the free chains into the
brush gets {\em slower} as their concentration rises
Binding branched and linear DNA structures: from isolated clusters to fully bonded gels
The proper design of DNA sequences allows for the formation of well defined
supramolecular units with controlled interactions via a consecution of
self-assembling processes. Here, we benefit from the controlled DNA
self-assembly to experimentally realize particles with well defined valence,
namely tetravalent nanostars (A) and bivalent chains (B). We specifically focus
on the case in which A particles can only bind to B particles, via
appropriately designed sticky-end sequences. Hence AA and BB bonds are not
allowed. Such a binary mixture system reproduces with DNA-based particles the
physics of poly-functional condensation, with an exquisite control over the
bonding process, tuned by the ratio, r, between B and A units and by the
temperature, T. We report dynamic light scattering experiments in a window of
Ts ranging from 10{\deg}C to 55{\deg}C and an interval of r around the
percolation transition to quantify the decay of the density correlation for the
different cases. At low T, when all possible bonds are formed, the system
behaves as a fully bonded network, as a percolating gel and as a cluster fluid
depending on the selected r.Comment: 15 pages, 11 figure
Polymer Brushes in Cylindrical Pores: Simulation versus Scaling Theory
The structure of flexible polymers endgrafted in cylindrical pores of
diameter D is studied as a function of chain length N and grafting density
\sigma, assuming good solvent conditions. A phenomenological scaling theory,
describing the variation of the linear dimensions of the chains with \sigma, is
developed and tested by Molecular Dynamics simulations of a bead-spring model.Comment: 35 pages, 38 figure
Cooperative Dynamics in Unentangled Polymer Fluids
We present a Generalized Langevin Equation for the dynamics of interacting
semiflexible polymer chains, undergoing slow cooperative dynamics. The
calculated Gaussian intermolecular center-of-mass and monomer potentials, wich
enter the GLE, are in quantitative agreement with computer simulation data. The
experimentally observed, short-time subdiffusive regime of the polymer
mean-square displacements, emerges here from the competition between the
intramolecular and the intermolecular mean-force potentials.Comment: 9 pages, latex, 3 figure
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