532 research outputs found
The genus Boccardia (Polychaeta: Spionidae) associated with mollusc shells on the south coast of South Africa
Three species of Boccardia (B. polybranchia, B. pseudonatrix and B. proboscidea) were associated with mollusc shells on the south and south-east coasts of South Africa. Boccardia polybranchia was widely distributed along the coast and falls within the known distribution range of this species. Comparisons with material from other, international, locations showed that some specimens have been misidentified. No characters could be found to characterize distinct species for different regions within the range of B. polybranchia, as currently recognized. Boccardia pseudonatrix was found only at the most eastern site, increasing its known distribution range. Boccardia proboscidea, a non-indigenous species, was found only on abalone farms and was most abundant in the west
A crib-shaped triplet pairing gap function for an orthogonal pair of quasi-one dimensional Fermi surfaces in SrRuO
The competition between spin-triplet and singlet pairings is studied
theoretically for the tight-binding - bands in SrRuO,
which arise from two sets of quasi-one dimensional Fermi surfaces. Using
multiband FLEX approximation, where we incorporate an anisotropy in the spin
fluctuations as suggested from experiments, we show that (i) the triplet can
dominate over the singlet (which turns out to be extended s), and (ii) the
triplet gap function optimized in the Eliashberg equation has an unusual, very
non-sinusoidal form, whose time-reversal-broken combination exhibits a
crib-shaped amplitude with dips.Comment: 5 pages, RevTeX, to appear in Phys.Rev.B (Rapid Communications
Motion of rotatory molecular motor and chemical reaction rate
We examine the dependence of the physical quantities of the rotatory
molecular motor, such as the rotation velocity and the proton translocation
rate, on the chemical reaction rate using the model based only on diffusion
process. A peculiar behavior of proton translocation is found and the energy
transduction efficiency of the motor protein is enhanced by this behavior. We
give a natural explanation that this behavior is universal when certain
inequalities between chemical reaction rates hold. That may give a clue to
examine whether the motion of the molecular motor is dominated by diffusion
process or not.Comment: 12 pages, 8 figure
Magnetic ordering in Sr2RuO4 induced by nonmagnetic impurities
We report unusual effects of nonmagnetic impurities on the spin-triplet
superconductor Sr2RuO4. The substitution of nonmagnetic Ti4+ for Ru4+ induces
localized-moment magnetism characterized by unexpected Ising anisotropy with
the easy axis along the interlayer c direction. Furthermore, for x(Ti) > 0.03
magnetic ordering occurs in the metallic state with the remnant magnetization
along the c-axis. We argue that the localized moments are induced in the Ru4+
and/or oxygen ions surrounding Ti4+ and that the ordering is due to their
interaction mediated by itinerant Ru-4d electrons with strong spin
fluctuations.Comment: 5 pages, 4figure
Dissipative collisions in O + Al at E=116 MeV
The inclusive energy distributions of fragments (3Z7) emitted in
the reaction O + Al at 116 MeV have been measured in
the angular range = 15 - 115. A non-linear
optimisation procedure using multiple Gaussian distribution functions has been
proposed to extract the fusion-fission and deep inelastic components of the
fragment emission from the experimental data. The angular distributions of the
fragments, thus obtained, from the deep inelastic component are found to fall
off faster than those from the fusion-fission component, indicating shorter
life times of the emitting di-nuclear systems. The life times of the
intermediate di-nuclear configurations have been estimated using a diffractive
Regge-pole model. The life times thus extracted (
Sec.) are found to decrease with the increase in the fragment charge. Optimum
Q-values are also found to increase with increasing charge transfer i.e. with
the decrease in fragment charge.Comment: 9 pages, 4 figures, 1 tabl
Notes on the algebraic curves in (p,q) minimal string theory
Loop amplitudes in (p,q) minimal string theory are studied in terms of the
continuum string field theory based on the free fermion realization of the KP
hierarchy. We derive the Schwinger-Dyson equations for FZZT disk amplitudes
directly from the W_{1+\infty} constraints in the string field formulation and
give explicitly the algebraic curves of disk amplitudes for general
backgrounds. We further give annulus amplitudes of FZZT-FZZT, FZZT-ZZ and ZZ-ZZ
branes, generalizing our previous D-instanton calculus from the minimal unitary
series (p,p+1) to general (p,q) series. We also give a detailed explanation on
the equivalence between the Douglas equation and the string field theory based
on the KP hierarchy under the W_{1+\infty} constraints.Comment: 61 pages, 1 figure, section 2.5 and Appendix B added, references
added, final version to appear in JHE
Super-Hubble de Sitter Fluctuations and the Dynamical RG
Perturbative corrections to correlation functions for interacting theories in
de Sitter spacetime often grow secularly with time, due to the properties of
fluctuations on super-Hubble scales. This growth can lead to a breakdown of
perturbation theory at late times. We argue that Dynamical Renormalization
Group (DRG) techniques provide a convenient framework for interpreting and
resumming these secularly growing terms. In the case of a massless scalar field
in de Sitter with quartic self-interaction, the resummed result is also less
singular in the infrared, in precisely the manner expected if a dynamical mass
is generated. We compare this improved infrared behavior with large-N
expansions when applicable.Comment: 33 pages, 4 figure
Spin fluctuations in nearly magnetic metals from ab-initio dynamical spin susceptibility calculations:application to Pd and Cr95V5
We describe our theoretical formalism and computational scheme for making
ab-initio calculations of the dynamic paramagnetic spin susceptibilities of
metals and alloys at finite temperatures. Its basis is Time-Dependent Density
Functional Theory within an electronic multiple scattering, imaginary time
Green function formalism. Results receive a natural interpretation in terms of
overdamped oscillator systems making them suitable for incorporation into spin
fluctuation theories. For illustration we apply our method to the nearly
ferromagnetic metal Pd and the nearly antiferromagnetic chromium alloy Cr95V5.
We compare and contrast the spin dynamics of these two metals and in each case
identify those fluctuations with relaxation times much longer than typical
electronic `hopping times'Comment: 21 pages, 9 figures. To appear in Physical Review B (July 2000
Transport by molecular motors in the presence of static defects
The transport by molecular motors along cytoskeletal filaments is studied
theoretically in the presence of static defects. The movements of single motors
are described as biased random walks along the filament as well as binding to
and unbinding from the filament. Three basic types of defects are
distinguished, which differ from normal filament sites only in one of the
motors' transition probabilities. Both stepping defects with a reduced
probability for forward steps and unbinding defects with an increased
probability for motor unbinding strongly reduce the velocities and the run
lengths of the motors with increasing defect density. For transport by single
motors, binding defects with a reduced probability for motor binding have a
relatively small effect on the transport properties. For cargo transport by
motors teams, binding defects also change the effective unbinding rate of the
cargo particles and are expected to have a stronger effect.Comment: 20 pages, latex, 7 figures, 1 tabl
Josephson current in s-wave superconductor / Sr_2RuO_4 junctions
The Josephson current between an s-wave and a spin-triplet superconductor
SrRuO (SRO) is studied theoretically. In spin-singlet / spin-triplet
superconductor junctions, there is no Josephson current proportional to in the absence of the spin-flip scattering near junction interfaces,
where is a phase-difference across junctions. Thus a dominant term of
the Josephson current is proportional to . The spin-orbit
scattering at the interfaces gives rise to the Josephson current proportional
to , which is a direct consequence of the chiral paring symmetry in
SRO
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