3,450 research outputs found
Point-contact Andreev reflection spectroscopy of heavy-fermion-metal/superconductor junctions
Our previous point-contact Andreev reflection studies of the heavy-fermion
superconductor CeCoIn using Au tips have shown two clear features: reduced
Andreev signal and asymmetric background conductance [1]. To explore their
physical origins, we have extended our measurements to point-contact junctions
between single crystalline heavy-fermion metals and superconducting Nb tips.
Differential conductance spectra are taken on junctions with three
heavy-fermion metals, CeCoIn, CeRhIn, and YbAl, each with different
electron mass. In contrast with Au/CeCoIn junctions, Andreev signal is not
reduced and no dependence on effective mass is observed. A possible explanation
based on a two-fluid picture for heavy fermions is proposed. [1] W. K. Park et
al., Phys. Rev. B 72 052509 (2005); W. K. Park et al., Proc. SPIE-Int. Soc.
Opt. Eng. 5932 59321Q (2005); W. K. Park et al., Physica C (in press)
(cond-mat/0606535).Comment: 2 pages, 2 figures, submitted to the SCES conference, Houston, Texas,
USA, May 13-18, 200
Phase transition classes in triplet and quadruplet reaction diffusion models
Phase transitions of reaction-diffusion systems with site occupation
restriction and with particle creation that requires n=3,4 parents, whereas
explicit diffusion of single particles (A) is present are investigated in low
dimensions by mean-field approximation and simulations. The mean-field
approximation of general nA -> (n+k)A, mA -> (m-l)A type of lattice models is
solved and novel kind of critical behavior is pointed out. In d=2 dimensions
the 3A -> 4A, 3A -> 2A model exhibits a continuous mean-field type of phase
transition, that implies d_c<2 upper critical dimension. For this model in d=1
extensive simulations support a mean-field type of phase transition with
logarithmic corrections unlike the Park et al.'s recent study (Phys. Rev E {\bf
66}, 025101 (2002)). On the other hand the 4A -> 5A, 4A -> 3A quadruplet model
exhibits a mean-field type of phase transition with logarithmic corrections in
d=2, while quadruplet models in 1d show robust, non-trivial transitions
suggesting d_c=2. Furthermore I show that a parity conserving model 3A -> 5A,
2A->0 in d=1 has a continuous phase transition with novel kind of exponents.
These results are in contradiction with the recently suggested implications of
a phenomenological, multiplicative noise Langevin equation approach and with
the simulations on suppressed bosonic systems by Kockelkoren and Chat\'e
(cond-mat/0208497).Comment: 8 pages, 10 figures included, Updated with new data, figures, table,
to be published in PR
Efficient magneto-optical trapping of Yb atoms with a violet laser diode
We report the first efficient trapping of rare-earth Yb atoms with a
high-power violet laser diode (LD). An injection-locked violet LD with a 25 mW
frequency-stabilized output was used for the magneto-optical trapping (MOT) of
fermionic as well as bosonic Yb isotopes. A typical number of
atoms for Yb with a trap density of cm was
obtained. A 10 mW violet external-cavity LD (ECLD) was used for the
one-dimensional (1D) slowing of an effusive Yb atomic beam without a Zeeman
slower resulting in a 35-fold increase in the number of trapped atoms. The
overall characteristics of our compact violet MOT, e.g., the loss time of 1 s,
the loading time of 400 ms, and the cloud temperature of 0.7 mK, are comparable
to those in previously reported violet Yb MOTs, yet with a greatly reduced cost
and complexity of the experiment.Comment: 5 pages, 3 figures, 1 table, Phys. Rev. A (to be published
Little Higgs Models and Precision Electroweak Data
We study the low energy limit of Little Higgs models. The method consists in
eliminating the heavy fields using their classical equations of motion in the
infinite mass limit. After the elimination of the heavy degrees of freedom we
can directly read off deviations from the precision electroweak data. We also
examine the effects on the low energy precision experiments.Comment: Misprint in eps3 for the custodial model corrected and additional
discussion of the triplet higg
Dynamics-dependent criticality in models with q absorbing states
We study a one-dimensional, nonequilibrium Potts-like model which has
symmetric absorbing states. For , as expected, the model belongs to the
parity conserving universality class. For the critical behaviour depends
on the dynamics of the model. Under a certain dynamics it remains generically
in the active phase, which is also the feature of some other models with three
absorbing states. However, a modified dynamics induces a parity conserving
phase transition. Relations with branching-annihilating random walk models are
discussed in order to explain such a behaviour.Comment: 5 pages, 5 eps figures included, Phys.Rev.E (accepted
Sample sequence analysis uncovers recurrent horizontal transfers of transposable elements among grasses
Limited genome resources are a bottleneck in the study of horizontal transfer (HT) of DNA in plants. To solve this issue, we tested the usefulness of low-depth sequencing data generated from 19 previously uncharacterized panicoid grasses for HT investigation. We initially searched for horizontally transferred LTR-retrotransposons by comparing the 19 sample sequences to 115 angiosperm genome sequences. Frequent HTs of LTR-retrotransposons were identified solely between panicoids and rice (Oryza sativa). We consequently focused on additional Oryza species and conducted a non-targeted investigation of HT involving the panicoid genus Echinochloa, which showed the most HTs in the first set of analyses. The comparison of nine Echinochloa samples and ten Oryza species identified recurrent HTs of diverse transposable element (TE) types at different points in Oryza history, but no confirmed cases of HT for sequences other than TEs. One case of HT was observed from one Echinochloa species into one Oryza species with overlapping geographic distributions. Variation among species and datasets highlights difficulties in identifying all HT, but our investigations showed that sample sequence analyses can reveal the importance of HT for the diversification of the TE repertoire of plants
Ni/HZSM-5 catalyst preparation by deposition-precipitation. Part 2. Catalytic hydrodeoxygenation reactions of lignin model compounds in organic and aqueous systems
Nickel metal supported on HZSM-5 (zeolite) is a promising catalyst for lignin depolymerization. In this work, the ability of catalysts prepared via deposition-precipitation (DP) to perform hydrodeoxygenation (HDO) on two lignin model compounds in organic and aqueous solvents was evaluated; guaiacol in dodecane and 2-phenoxy-1-phenylethanol (PPE) in aqueous solutions. All Ni/HZSM-5 catalysts were capable of guaiacol HDO into cyclohexane at 523 K. The role of the HZSM-5 acid sites was confirmed by comparison with Ni/SiO2 (inert support) which exhibited incomplete deoxygenation of guaiacol due to the inability to perform the cyclohexanol dehydration step. The catalyst prepared with 15 wt% Ni, a DP time of 16 h, and a calcination temperature of 673 K (Ni(15)/HZSM-5 DP16_Cal673), performed the guaiacol conversion with the greatest selectivity towards HDO products, with an intrinsic rate ratio (HDO rate to conversion rate) of 0.31, and 90% selectivity to cyclohexane. Catalytic activity and selectivity of Ni/HZSM-5 (15 wt%) in aqueous environments (water and 0.1 M NaOH solution) was confirmed using PPE reactions at 523 K. After 30 min reaction time in water, Ni/HZSM-5 exhibited ~100% conversion of PPE, and good yield of the desired products; ethylbenzene and phenol (~35% and 23% of initial carbon, respectively). Ni/HZSM-5 in NaOH solution resulted in significantly higher ring saturation compared to the Ni/HZSM-5 in water or the NaOH solution control
Hyperons analogous to the \Lambda(1405)
The low mass of the hyperon with , which is
higher than the ground state mass by 290 MeV, is difficult to
understand in quark models. We analyze the hyperon spectrum in the bound state
approach of the Skyrme model that successfully describes both the
and the . This model predicts that several
hyperon resonances of the same spin but with opposite parity form parity
doublets that have a mass difference of around 300 MeV, which is indeed
realized in the observed hyperon spectrum. Furthermore, the existence of the
and the of is predicted by this model.
Comments on the baryons and heavy quark baryons are made as well.Comment: 4 pages, talk presented at the Fifth Asia-Pacific Conference on
Few-Body Problems in Physics 2011 (APFB2011), Aug. 22-26, 2011, Seoul, Kore
Chiral radiative corrections and D_s(2317)/D(2308) mass puzzle
We show that one loop chiral corrections for heavy-light mesons in potential
model can explain the small mass of D_s(2317) as well as the small mass gap
between D_s(2317) and D(2308).Comment: To appear in EPJC. A figure and references addede
Multifractal current distribution in random diode networks
Recently it has been shown analytically that electric currents in a random
diode network are distributed in a multifractal manner [O. Stenull and H. K.
Janssen, Europhys. Lett. 55, 691 (2001)]. In the present work we investigate
the multifractal properties of a random diode network at the critical point by
numerical simulations. We analyze the currents running on a directed
percolation cluster and confirm the field-theoretic predictions for the scaling
behavior of moments of the current distribution. It is pointed out that a
random diode network is a particularly good candidate for a possible
experimental realization of directed percolation.Comment: RevTeX, 4 pages, 5 eps figure
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