11,147 research outputs found
Possible indicators for low dimensional superconductivity in the quasi-1D carbide Sc3CoC4
The transition metal carbide Sc3CoC4 consists of a quasi-one-dimensional (1D)
structure with [CoC4]_{\inft} polyanionic chains embedded in a scandium
matrix. At ambient temperatures Sc3CoC4 displays metallic behavior. At lower
temperatures, however, charge density wave formation has been observed around
143K which is followed by a structural phase transition at 72K. Below T^onset_c
= 4.5K the polycrystalline sample becomes superconductive. From Hc1(0) and
Hc2(0) values we could estimate the London penetration depth ({\lambda}_L ~=
9750 Angstroem) and the Ginsburg-Landau (GL) coherence length ({\xi}_GL ~= 187
Angstroem). The resulting GL-parameter ({\kappa} ~= 52) classifies Sc3CoC4 as a
type II superconductor. Here we compare the puzzling superconducting features
of Sc3CoC4, such as the unusual temperature dependence i) of the specific heat
anomaly and ii) of the upper critical field H_c2(T) at T_c, and iii) the
magnetic hysteresis curve, with various related low dimensional
superconductors: e.g., the quasi-1D superconductor (SN)_x or the 2D
transition-metal dichalcogenides. Our results identify Sc3CoC4 as a new
candidate for a quasi-1D superconductor.Comment: 4 pages, 5 figure
The role of the pion pair term in the theory of the weak axial meson exchange currents
The structure of the weak axial pion exchange current is discussed in various
models. It is shown how the interplay of the chiral invariance and the double
counting problem restricts uniquely the form of the pion potential term, in the
case when the nuclear dynamics is described by the Schroedinger equation with
the static nucleon-nucleon potential.Comment: 17 pages, 1 figure, 2 tables, stylistic changes of the tex
Lithographic band gap tuning in photonic band gap crystals
We describe the lithographic control over the spectral response of three-dimensional photonic crystals. By precise microfabrication of the geometry using a reproducible and reliable procedure consisting of electron beam lithography followed by dry etching, we have shifted the conduction band of crystals within the near-infrared. Such microfabrication has enabled us to reproducibly define photonic crystals with lattice parameters ranging from 650 to 730 nm. In GaAs semiconductor wafers, these can serve as high-reflectivity (> 95%) mirrors. Here, we show the procedure used to generate these photonic crystals and describe the geometry dependence of their spectral response
Probing new physics in electroweak penguins through B_d and B_s decays
An enhanced electroweak penguin amplitude due to the presence of unknown new
physics can explain the discrepancies found between theory and experiment in
the B -> pi K decays, in particular in A_CP(B^- -> pi^0 K^-) - A_CP(\bar{B}^0
-> pi^+ K^-), but the current precision of the theoretical and experimental
results does not allow to draw a firm conclusion. We argue that the \bar{B}_s
-> phi rho^0 and \bar{B}_s -> phi pi^0 decays offer an additional tool to
investigate this possibility. These purely isospin-violating decays are
dominated by electroweak penguins and we show that in presence of a new physics
contribution their branching ratio can be enhanced by about an order of
magnitude, without violating any constraints from other hadronic B decays. This
makes them very interesting modes for LHCb and future B factories. In
arXiv:1011.6319 we have performed both a model-independent analysis and a study
within realistic New Physics models such as a modified-Z^0-penguin scenario, a
model with an additional Z' boson and the MSSM. In this article we summarise
the most important results of our study.Comment: 8 pages, 5 figures, LaTeX. Talk given at Discrete2010, Rome, 6-11
December 2010; References adde
Alaska\u27s Tribal Trust Lands: A Forgotten History
Since the enactment of the Alaska Native Claims Settlement Act in 1971, there has been significant debate over whether the Secretary of the Interior should accept land in trust for the benefit of federally recognized tribes in Alaska. A number of legal opinions have considered the issue and have reached starkly different conclusions. In 2017, the United States accepted in trust a small parcel of land in Craig, Alaska. This affirmative decision drew strong reactions from both sides of the argument. Notably absent from the conversation, however, was any mention or discussion of Alaska’s existing trust parcels. Hidden in plain sight, their stories reflect the complicated history of federal Indian policy in Alaska, and inform the debate over the consequences of any future acquisitions
Crossover from Single-Ion to Coherent Non-Fermi Liquid Behavior in CeLaNiGe
We report specific heat and magneto-resistance studies on the compound
CeLaNiGe for various concentrations over the entire
stoichiometric range. Our data reveal single-ion scaling with Ce-concentration
between and 0.95. Furthermore, CeNiGe turns out to have
the largest ever recorded value of the electronic specific heat 5.5 J at K which was found in Cerium
f-electron lattice systems. In the doped samples increases
logarithmically in the temperature range between 3 K and 50 mK typical for
non-Fermi liquid (nFl) behavior, while exhibits a Kondo-like minimum
around 30 K, followed by a single-ion local nFl behavior. In contrast to this,
CeNiGe flattens out in below 300 mK and displays a
pronounced maximum in the resistivity curve at 1.5 K indicating a coherent
heavy fermion groundstate. These properties render the compound
CeLaNiGe a unique system on the borderline between
Fermi liquid and nFl physics.Comment: 2 pages, 3 figures, SCES0
The effects of age on the perception of frequency in noise
Difficulty understanding speech in the presence of background noise is one of the most common complaints of older adults, both with and without hearing loss. One possible contributing factor is an age-related decline in neural synchrony (e.g., phase locking). Tones-in-noise were used in an attempt to disrupt rate-place coding of frequency and to encourage participants to use phase-locked, temporal representations of frequency during a behavioral frequency discrimination task. Fourteen adults participated in the study (five younger, aged 21-29; four middle aged, 41-50; and five older, aged 61-80). Participants had clinically normal hearing sensitivity (≤ 25 dB HL at octave frequencies 250 – 8000 Hz). Tone-in-noise detection thresholds and frequency discrimination limens (FDLs) were obtained at 500 and 1000 Hz, separately. FDLs were tested in quiet and noise conditions. The Words-in-Noise test was used to assess speech-in-noise understanding. Results indicated that tone-in-noise detection thresholds were not significantly different across age groups. Frequency discrimination limens were significantly poorer (larger) in the presence of noise; however, no significant age effects were found. Frequency discrimination results indicated that the presence of noise worsened FDLs, consistent with the effect expected with reduced neural coding strategies available in noise. Speech-in-noise understanding was not significantly different across age groups. It is believed that the presence of noise may reduce the effectiveness of some neural coding strategies available to listeners
Direct picosecond time resolution of unimolecular reactions initiated by local mode excitation
The concept of local mode (LM) states [1] in large molecules raises the possibilty of inducing chemical reactions from a well-defined initial state (bond-selective chemistry). The results of linewidth and energy measurements in gases, [2(a)] and low temperature solids, [2(b)] however, indicate that the relaxation times for such high energy (> 15000 cm^-1) states can be extremely short, < 1ps. Because of the lack of direct time-resolved measurements, the following fundamental questions have not been unequivocally answered: What are the homogeneous linewidths of LM states and what are the rates of energy relaxation or reaction out of these states? Over the past five years we have made several attempts to observe the picosecond dynamics of LM states. Due to the inherent difficulties associated with making these measurements, such as the very small oscillator strength (σ < 10^-23 cm^2), an extremely sensitive probing technique becomes imperative
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