24,877 research outputs found
Microscopic two-fluid theory of rotational constants of the OCS-H complex in He droplets
We present a microscopic quantum analysis for rotational constants of the
OCS-H complex in helium droplets using the local two-fluid theory in
conjunction with path integral Monte Carlo simulations. Rotational constants
are derived from effective moments of inertia calculated assuming that motion
of the H molecule and the local non-superfluid helium density is rigidly
coupled to the molecular rotation of OCS and employing path integral methods to
sample the corresponding H and helium densities. The rigid coupling
assumption for H-OCS is calibrated by comparison with exact calculations of
the free OCS-H complex. The presence of the H molecule is found to
induce a small local non-superfluid helium density in the second solvation
shell which makes a non-negligible contribution to the moment of inertia of the
complex in helium. The resulting moments of inertia for the OCS-H complex
embedded in a cluster of 63 helium atoms are found to be in good agreement with
experimentally measured values in large helium droplets. Implications for
analysis of rotational constants of larger complexes of OCS with multiple H
molecules in helium are discussed.Comment: 11 pages, 5 figures, accepted for publication in J. Chem. Phy
Fractional ac Josephson effect in p- and d-wave superconductors
For certain orientations of Josephson junctions between two p_x-wave or two
d-wave superconductors, the subgap Andreev bound states produce a 4pi-periodic
relation between the Josephson current I and the phase difference phi: I
sin(phi/2). Consequently, the ac Josephson current has the fractional frequency
eV/h, where V is the dc voltage. In the tunneling limit, the Josephson current
is proportional to the first power (not square) of the electron tunneling
amplitude. Thus, the Josephson current between unconventional superconductors
is carried by single electrons, rather than by Cooper pairs. The fractional ac
Josephson effect can be observed experimentally by measuring frequency spectrum
of microwave radiation from the junction. We also study junctions between
singlet s-wave and triplet p_x-wave, as well as between chiral p_x + ip_y-wave
superconductors.Comment: v. 5: minor update of references in proofs; v.4: minor improvements;
v.3: major expansion to 13 pages, 6 figures; v.2: significantly expanded to 6
pages; v.1: 4 pages, 2 figures, RevTeX
Towards Distributed Convoy Pattern Mining
Mining movement data to reveal interesting behavioral patterns has gained
attention in recent years. One such pattern is the convoy pattern which
consists of at least m objects moving together for at least k consecutive time
instants where m and k are user-defined parameters. Existing algorithms for
detecting convoy patterns, however do not scale to real-life dataset sizes.
Therefore a distributed algorithm for convoy mining is inevitable. In this
paper, we discuss the problem of convoy mining and analyze different data
partitioning strategies to pave the way for a generic distributed convoy
pattern mining algorithm.Comment: SIGSPATIAL'15 November 03-06, 2015, Bellevue, WA, US
Extending Romanovski polynomials in quantum mechanics
Some extensions of the (third-class) Romanovski polynomials (also called
Romanovski/pseudo-Jacobi polynomials), which appear in bound-state
wavefunctions of rationally-extended Scarf II and Rosen-Morse I potentials, are
considered. For the former potentials, the generalized polynomials satisfy a
finite orthogonality relation, while for the latter an infinite set of
relations among polynomials with degree-dependent parameters is obtained. Both
types of relations are counterparts of those known for conventional
polynomials. In the absence of any direct information on the zeros of the
Romanovski polynomials present in denominators, the regularity of the
constructed potentials is checked by taking advantage of the disconjugacy
properties of second-order differential equations of Schr\"odinger type. It is
also shown that on going from Scarf I to Scarf II or from Rosen-Morse II to
Rosen-Morse I potentials, the variety of rational extensions is narrowed down
from types I, II, and III to type III only.Comment: 25 pages, no figure, small changes, 3 additional references,
published versio
Electronic structures of doped anatase : (M=Co, Mn, Fe, Ni)
We have investigated electronic structures of a room temperature diluted
magnetic semiconductor : Co-doped anatase . We have obtained the
half-metallic ground state in the local-spin-density approximation(LSDA) but
the insulating ground state in the LSDA++SO incorporating the spin-orbit
interaction. In the stoichiometric case, the low spin state of Co is realized
with the substantially large orbital moment. However, in the presence of oxygen
vacancies near Co, the spin state of Co becomes intermediate. The
ferromagnetisms in the metallic and insulating phases are accounted for by the
double-exchange-like and the superexchange mechanism, respectively. Further,
the magnetic ground states are obtained for Mn and Fe doped ,
while the paramagnetic ground state for Ni-doped .Comment: 5 pages, 4 figure
Anomalous double peak structure in Nb/Ni superconductor/ferromagnet tunneling DOS
We have experimentally investigated the density of states (DOS) in Nb/Ni
(S/F) bilayers as a function of Ni thickness, . Our thinnest samples show
the usual DOS peak at , whereas intermediate-thickness samples
have an anomalous ``double-peak'' structure. For thicker samples ( nm), we see an ``inverted'' DOS which has previously only been reported in
superconductor/weak-ferromagnet structures. We analyze the data using the
self-consistent non-linear Usadel equation and find that we are able to
quantitatively fit the features at if we include a large amount
of spin-orbit scattering in the model. Interestingly, we are unable to
reproduce the sub-gap structure through the addition of any parameter(s).
Therefore, the observed anomalous sub-gap structure represents new physics
beyond that contained in the present Usadel theory.Comment: 4 pages, 3 figure
Condensation phase transitions of symmetric conserved-mass aggregation model on complex networks
We investigate condensation phase transitions of symmetric conserved-mass
aggregation (SCA) model on random networks (RNs) and scale-free networks (SFNs)
with degree distribution . In SCA model, masses diffuse
with unite rate, and unit mass chips off from mass with rate . The
dynamics conserves total mass density . In the steady state, on RNs and
SFNs with for , we numerically show that SCA
model undergoes the same type condensation transitions as those on regular
lattices. However the critical line depends on network
structures. On SFNs with , the fluid phase of exponential mass
distribution completely disappears and no phase transitions occurs. Instead,
the condensation with exponentially decaying background mass distribution
always takes place for any non-zero density. For the existence of the condensed
phase for at the zero density limit, we investigate one
lamb-lion problem on RNs and SFNs. We numerically show that a lamb survives
indefinitely with finite survival probability on RNs and SFNs with ,
and dies out exponentially on SFNs with . The finite life time
of a lamb on SFNs with ensures the existence of the
condensation at the zero density limit on SFNs with at which
direct numerical simulations are practically impossible. At ,
we numerically confirm that complete condensation takes place for any on RNs. Together with the recent study on SFNs, the complete condensation
always occurs on both RNs and SFNs in zero range process with constant hopping
rate.Comment: 6 pages, 6 figure
A superfluid hydrodynamic model for the enhanced moments of inertia of molecules in liquid 4He
We present a superfluid hydrodynamic model for the increase in moment of
inertia, , of molecules rotating in liquid He. The static
inhomogeneous He density around each molecule (calculated using the Orsay-Paris
liquid He density functional) is assumed to adiabatically follow the
rotation of the molecule. We find that the values created by the
viscousless and irrotational flow are in good agreement with the observed
increases for several molecules [ OCS, (HCN), HCCCN, and HCCCH ]. For
HCN and HCCH, our model substantially overestimates . This is likely
to result from a (partial) breakdown of the adiabatic following approximation.Comment: 4 pages, 1 eps figure, corrected version of published paper. Erratum
has been submitted for change
Neutron-rich rare isotope production from projectile fission of heavy beams in the energy range of 20 MeV/nucleon
We investigate the possibilities of producing neutron-rich nuclides in
projectile fission of heavy beams in the energy range of 20 MeV/nucleon
expected from low-energy facilities. We report our efforts to theoretically
describe the reaction mechanism of projectile fission following a multinucleon
transfer collision at this energy range. Our calculations are mainly based on a
two-step approach: the dynamical stage of the collision is described with
either the phenomenological Deep-Inelastic Transfer model (DIT), or with the
microscopic Constrained Molecular Dynamics model (CoMD). The
deexcitation/fission of the hot heavy projectile fragments is performed with
the Statistical Mul- tifragmentation Model (SMM). We compared our model
calculations with our previous experimental projectile-fission data of 238U (20
MeV/nucleon)+208Pb and 197Au (20 MeV/nucleon)+197Au and found an overall
reasonable agreement. Our study suggests that projectile fission following
periph- eral heavy-ion collisions at this energy range offers an effective
route to access very neutron-rich rare isotopes toward and beyond the
astrophysical r-process path
- …