7,104 research outputs found
Antifouling bastadin congeners target blue mussel phenoloxidase and complex copper(II) ions
Synthetically prepared congeners of spongederived bastadin derivatives such as 5,5'-dibromohemibastadin- 1 (DBHB) that suppress the settling of barnacle larvae were identified in this study as strong inhibitors of blue mussel phenoloxidase that is involved in the firm attachment of mussels to a given substrate. The IC50 value of DBHB as the most active enzyme inhibitor encountered in this study amounts to 0.84 mu M. Inhibition of phenoloxidase by DBHB is likely due to complexation of copper(II) ions from the catalytic centre of the enzyme by the a-oxo-oxime moiety of the compound as shown here for the first time by structure activity studies and by X-ray structure determination of a copper(II) complex of DBHB.Biotechnology & Applied MicrobiologyMarine & Freshwater BiologySCI(E)EI0ARTICLE61148-11581
Current carrying capacity of carbon nanotubes
The current carrying capacity of ballistic electrons in carbon nanotubes that
are coupled to ideal contacts is analyzed. At small applied voltages, where
electrons are injected only into crossing subbands, the differential
conductance is . At applied voltages larger than
( is the energy level spacing of first non crossing subbands),
electrons are injected into non crossing subbands. The contribution of these
electrons to current is determined by the competing processes of Bragg
reflection and Zener type inter subband tunneling. In small diameter nanotubes,
Bragg reflection dominates, and the maximum differential conductance is
comparable to . Inter subband Zener tunneling can be non negligible as
the nanotube diameter increases because is inversely
proportional to the diameter. As a result, with increasing nanotube diameter,
the differential conductance becomes larger than , though not
comparable to the large number of subbands into which electrons are injected
from the contacts. These results may be relevant to recent experiments in large
diameter multi-wall nanotubes that observed conductances larger than .Comment: 12 pages, 4 figure
On The Assembly History of Dark Matter Haloes
(abridged) We study the mass assembly history (MAH) of dark matter haloes. We
compare MAHs obtained using (i) merger trees constructed with the extended
Press-Schechter (EPS) formalism, (ii) numerical simulations, and (iii) the
Lagrangian perturbation code PINOCCHIO. We show that the PINOCCHIO MAHs are in
excellent agreement with those obtained using numerical simulations. Using a
suite of 55 PINOCCHIO simulations, with 256^3 particles each, we study the MAHs
of 12,924 cold dark matter haloes in a \LambdaCDM concordance cosmology. We
show that haloes less massive than the characteristic non-linear mass scale
establish their potential wells much before they acquire most of their mass.
The time when a halo reaches its maximum virial velocity roughly divides its
mass assembly into two phases, a fast accretion phase which is dominated by
major mergers, and a slow accretion phase dominated by minor mergers. Each halo
experiences about 3 \pm 2 major mergers since its main progenitor had a mass
equal to one percent of the final halo mass. This major merger statistic is
found to be virtually independent of halo mass. However, the average redshift
at which these major mergers occur, is strongly mass dependent, with more
massive haloes experiencing their major mergers later.Comment: 15 pages, 13 figures (with 2 new), accepted by MNRA
Three-dimensional coupled mode analysis of internal-wave acoustic ducts
A fully three-dimensional coupled mode approach is used in this paper to describe the physics of low frequency acoustic signals propagating through a train of internal waves at an arbitrary azimuth. A three layer model of the shallow water waveguide is employed for studying the properties of normal modes and their coupled interaction due to the presence of nonlinear internal waves. Using a robust wave number integration technique for Fourier transform computation and a direct global matrix approach, an accurate three-dimensional coupled mode full field solution is obtained for the tonal signal propagation through straight and parallel internal waves. This approach provides accurate results for arbitrary azimuth and includes the effects of backscattering. This enables one to provide an azimuthal analysis of acoustic propagation and separate the effects of mode coupled transparent resonance, horizontal reflection and refraction, the horizontal Lloyd's mirror, horizontal ducting and anti-ducting, and horizontal tunneling and secondary ducting.United States. Office of Naval Research (Grant N00014-11-1-0195)United States. Office of Naval Research (Grant N00014-11-1-0701
Constraints on the relationship between stellar mass and halo mass at low and high redshift
We use a statistical approach to determine the relationship between the
stellar masses of galaxies and the masses of the dark matter halos in which
they reside. We obtain a parameterized stellar-to-halo mass (SHM) relation by
populating halos and subhalos in an N-body simulation with galaxies and
requiring that the observed stellar mass function be reproduced. We find good
agreement with constraints from galaxy-galaxy lensing and predictions of
semi-analytic models. Using this mapping, and the positions of the halos and
subhalos obtained from the simulation, we find that our model predictions for
the galaxy two-point correlation function (CF) as a function of stellar mass
are in excellent agreement with the observed clustering properties in the SDSS
at z=0. We show that the clustering data do not provide additional strong
constraints on the SHM function and conclude that our model can therefore
predict clustering as a function of stellar mass. We compute the conditional
mass function, which yields the average number of galaxies with stellar masses
in the range [m, m+dm] that reside in a halo of mass M. We study the redshift
dependence of the SHM relation and show that, for low mass halos, the SHM ratio
is lower at higher redshift. The derived SHM relation is used to predict the
stellar mass dependent galaxy CF and bias at high redshift. Our model predicts
that not only are massive galaxies more biased than low mass ones at all
redshifts, but the bias increases more rapidly with increasing redshift for
massive galaxies than for low mass ones. We present convenient fitting
functions for the SHM relation as a function of redshift, the conditional mass
function, and the bias as a function of stellar mass and redshift.Comment: 21 pages, 17 figures, discussion enlarged, one more figure, updated
references, accepted for publication in Ap
A simple variational approach to the quantum Frenkel-Kontorova model
We present a simple and complete variational approach to the one-dimensional
quantum Frenkel-Kontorova model. Dirac's time-dependent variational principle
is adopted together with a Hatree-type many-body trial wavefunction for the
atoms. The single-particle state is assumed to have the Jackiw-Kerman form. We
obtain an effective classical Hamiltonian for the system which is simple enough
for a complete numerical solution for the static ground state of the model.
Numerical results show that our simple approach captures the essence of the
quantum effects first observed in quantum Monte Carlo studies.Comment: 12 pages, 2 figure
Projection decomposition in multiplier algebras
In this paper we present new structural information about the multiplier
algebra Mult (A) of a sigma-unital purely infinite simple C*-algebra A, by
characterizing the positive elements a in Mult(A) that are strict sums of
projections belonging to A. If a is not in A and is not a projection, then the
necessary and sufficient condition for a to be a strict sum of projections
belonging to A is that the norm ||a||>1 and that the essential norm ||a||_ess
>=1.
Based on a generalization of the Perera-Rordam weak divisibility of separable
simple C*-algebras of real rank zero to all sigma-unital simple C*-algebras of
real rank zero, we show that every positive element of A with norm greater than
1 can be approximated by finite sums of projections. Based on block
tri-diagonal approximations, we decompose any positive element a in Mult(A)
with ||a||>1 and ||a||_ess >=1 into a strictly converging sum of positive
elements in A with norm greater than 1.Comment: To appear in Mathematische Annale
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