7,283 research outputs found
Simulation of Cu-Mg metallic glass: Thermodynamics and Structure
We have obtained effective medium theory (EMT) interatomic potential
parameters suitable for studying Cu-Mg metallic glasses. We present
thermodynamic and structural results from simulations of such glasses over a
range of compositions. We have produced low-temperature configurations by
cooling from the melt at as slow a rate as practical, using constant
temperature and pressure molecular dynamics. During the cooling process we have
carried out thermodynamic analyses based on the temperature dependence of the
enthalpy and its derivative, the specific heat, from which the glass transition
temperature may be determined. We have also carried out structural analyses
using the radial distribution function (RDF) and common neighbor analysis
(CNA). Our analysis suggests that the splitting of the second peak, commonly
associated with metallic glasses, in fact has little to do with the glass
transition itself, but is simply a consequence of the narrowing of peaks
associated with structural features present in the liquid state. In fact the
splitting temperature for the Cu-Cu RDF is well above . The CNA also
highlights a strong similarity between the structure of the intermetallic
alloys and the amorphous alloys of similar composition. We have also
investigated the diffusivity in the supercooled regime. Its temperature
dependence indicates fragile-liquid behavior, typical of binary metallic
glasses. On the other hand, the relatively low specific heat jump of around
indicates apparent strong-liquid behavior, but this can
be explained by the width of the transition due to the high cooling rates.Comment: 12 pages (revtex, two-column), 12 figures, submitted to Phys. Rev.
Current dependence of grain boundary magnetoresistance in La_0.67Ca_0.33MnO_3 films
We prepared epitaxial ferromagnetic manganite films on bicrystal substrates
by pulsed laser ablation. Their low- and high-field magnetoresistance (MR) was
measured as a function of magnetic field, temperature and current. At low
temperatures hysteretic changes in resistivity up to 70% due to switching of
magnetic domains at the coercitive field are observed. The strongly non-ohmic
behavior of the current-voltage leads to a complete suppression of the MR
effect at high bias currents with the identical current dependence at low and
high magnetic fields. We discuss the data in view of tunneling and mesoscale
magnetic transport models and propose an explicit dependence of the spin
polarization on the applied current in the grain boundary region.Comment: 5 pages, to appear in J. Appl. Phy
Transcription and the Pitch Angle of DNA
The question of the value of the pitch angle of DNA is visited from the
perspective of a geometrical analysis of transcription. It is suggested that
for transcription to be possible, the pitch angle of B-DNA must be smaller than
the angle of zero-twist. At the zero-twist angle the double helix is maximally
rotated and its strain-twist coupling vanishes. A numerical estimate of the
pitch angle for B-DNA based on differential geometry is compared with numbers
obtained from existing empirical data. The crystallographic studies shows that
the pitch angle is approximately 38 deg., less than the corresponding
zero-twist angle of 41.8 deg., which is consistent with the suggested principle
for transcription.Comment: 7 pages, 3 figures; v2: minor modifications; v3: major modifications
compared to v2. Added discussion about transcription, and reference
IDENTIFYING AND PREDICTING INTENTION TO QUIT USING JUUL AMONG EMERGING ADULTS
Objectives: (1) Describe intention to quit, (2) identify relationships between sociodemographic factors or social influences and intention to quit, (3) explore if Theory of Planned Behavior-informed constructs can predict intention to quit as well as identify which construct best predicts, and (4) discover if descriptive norms strengthen a predictive model of intention to quit among emerging adults currently using Juul. Participants: Full-time, first-year students currently using Juul, an e-cigarette product, at a large university in the southeastern United States (N = 182). Methods: A November 2018 online survey assessed sociodemographic characteristics, social influences, patterns of use, quit intention, and attitudes, norms, and perceived behavioral control toward Juul. Results: A quarter of participants reported current use, with nearly half intending to quit within six months. Recent quit attempts was the only factor related to intention. Two models were created that successfully predicted intention to quit, but only perceived behavioral control was individually significant as a predictor. Conclusions: Cessation-focused campaigns and interventions are needed on college campuses and could be less tailored than prevention to save time and money
Photon Parameterisation for Robust Relaxation Constraints
This paper presents a novel approach to detecting and preserving fine illumination structure within photon maps. Data derived from each photon's primal trajectory is encoded and used to build a high-dimensional kd-tree. Incorporation of these new parameters allows for precise differentiation between intersecting ray envelopes, thus minimizing detail degradation when combined with photon relaxation. We demonstrate how parameter-aware querying is beneficial in both detecting and removing noise. We also propose a more robust structure descriptor based on principal components analysis that better identifies anisotropic detail at the sub-kernel level. We illustrate the effectiveness of our approach in several example scenes and show significant improvements when rendering complex caustics compared to previous methods
Fiber Fabry-Perot cavity with high finesse
We have realized a fiber-based Fabry-Perot cavity with CO2 laser-machined
mirrors. It combines very small size, high finesse F>=130000, small waist and
mode volume, and good mode matching between the fiber and cavity modes. This
combination of features is a major advance for cavity quantum electrodynamics
(CQED), as shown in recent CQED experiments with Bose-Einstein condensates
enabled by this cavity [Y. Colombe et al., Nature 450, 272 (2007)]. It should
also be suitable for a wide range of other applications, including coupling to
solid-state emitters, gas detection at the single-particle level, fiber-coupled
single-photon sources and high-resolution optical filters with large stopband.Comment: Submitted to New J. Phys
- …