1,771 research outputs found
2,4-Dinitrophenylhydrazones of 2,4-dihydroxybenzaldehyde, 2,4-dihydroxyacetophenone and 2,4-dihydroxybenzophenone
In 2,4-dihydroxybenzaldehyde 2,4-dinitrophenylhydrazone N,N-dimethylformamide solvate (or 4-[(2,4-dinitrophenyl)-hydrazonomethyl]benzene-1,3-diol N,N-dimethylformamide solvat
Ac transport studies in polymers by a resistor network and transfer matrix approaches: application to polyaniline
A statistical model of resistor network is proposed to describe a polymer
structure and to simulate the real and imaginary components of its ac
resistivity. It takes into account the polydispersiveness of the material as
well as intrachain and interchain charge transport processes. By the
application of a transfer matrix technique, it reproduces ac resistivity
measurements carried out with polyaniline films in different doping degrees and
at different temperatures. Our results indicate that interchain processes
govern the resistivity behavior in the low frequency region while, for higher
frequencies, intrachain mechanisms are dominant.Comment: LaTeX file, 15 pages, 5 ps figures, to appear in Phys. Rev.
Connective tissue disease related interstitial lung diseases and idiopathic pulmonary fibrosis: provisional core sets of domains and instruments for use in clinical trials
Rationale Clinical trial design in interstitial lung diseases (ILDs) has been hampered by lack of consensus on appropriate outcome measures for reliably assessing treatment response. In the setting of connective tissue diseases (CTDs), some measures of ILD disease activity and severity may be confounded by non-pulmonary comorbidities. Methods The Connective Tissue Disease associated Interstitial Lung Disease (CTD-ILD) working group of Outcome Measures in Rheumatology—a non-profit international organisation dedicated to consensus methodology in identification of outcome measures—conducted a series of investigations which included a Delphi process including >248 ILD medical experts as well as patient focus groups culminating in a nominal group panel of ILD experts and patients. The goal was to define and develop a consensus on the status of outcome measure candidates for use in randomised controlled trials in CTD-ILD and idiopathic pulmonary fibrosis (IPF). Results A core set comprising specific measures in the domains of lung physiology, lung imaging, survival, dyspnoea, cough and health-related quality of life is proposed as appropriate for consideration for use in a hypothetical 1-year multicentre clinical trial for either CTD-ILD or IPF. As many widely used instruments were found to lack full validation, an agenda for future research is proposed. Conclusion Identification of consensus preliminary domains and instruments to measure them was attained and is a major advance anticipated to facilitate multicentre RCTs in the field
Light Curves of the Neutron Star Merger GW170817/SSS17a: Implications for R-Process Nucleosynthesis
On 2017 August 17, gravitational waves were detected from a binary neutron
star merger, GW170817, along with a coincident short gamma-ray burst,
GRB170817A. An optical transient source, Swope Supernova Survey 17a (SSS17a),
was subsequently identified as the counterpart of this event. We present
ultraviolet, optical and infrared light curves of SSS17a extending from 10.9
hours to 18 days post-merger. We constrain the radioactively-powered transient
resulting from the ejection of neutron-rich material. The fast rise of the
light curves, subsequent decay, and rapid color evolution are consistent with
multiple ejecta components of differing lanthanide abundance. The late-time
light curve indicates that SSS17a produced at least ~0.05 solar masses of heavy
elements, demonstrating that neutron star mergers play a role in r-process
nucleosynthesis in the Universe.Comment: Accepted to Scienc
Effect of heterogeneity on the elastic properties of auxetic materials
Copyright © 2003 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Journal of Applied Physics 94 (2003) and may be found at http://link.aip.org/link/?jap/94/6143Auxetic materials are gaining practical interest for their unusual and sometimes extreme mechanical response. The process of modeling these materials so far has highlighted a number of microstructural properties that are key to these materials. However these models often rely on the assumption of homogeneity and order within the materials. Practically, a homogeneous auxetic material such as foam is unlikely to be manufactured. This work seeks to analyze the effect of fluctuations within the microstructure of the material. Numerical results show the effect of fluctuations in an auxetic granular substance and analytical work indicates the relation between microscale fluctuations and the elastic moduli for a general auxetic material
Early Spectra of the Gravitational Wave Source GW170817: Evolution of a Neutron Star Merger
On 2017 August 17, Swope Supernova Survey 2017a (SSS17a) was discovered as
the optical counterpart of the binary neutron star gravitational wave event
GW170817. We report time-series spectroscopy of SSS17a from 11.75 hours until
8.5 days after merger. Over the first hour of observations the ejecta rapidly
expanded and cooled. Applying blackbody fits to the spectra, we measure the
photosphere cooling from K to K,
and determine a photospheric velocity of roughly 30% of the speed of light. The
spectra of SSS17a begin displaying broad features after 1.46 days, and evolve
qualitatively over each subsequent day, with distinct blue (early-time) and red
(late-time) components. The late-time component is consistent with theoretical
models of r-process-enriched neutron star ejecta, whereas the blue component
requires high velocity, lanthanide-free material.Comment: 33 pages, 5 figures, 2 tables, Accepted to Scienc
Observational Constraints on the Ultra-high Energy Cosmic Neutrino Flux from the Second Flight of the ANITA Experiment
The Antarctic Impulsive Transient Antenna (ANITA) completed its second
long-duration balloon flight in January 2009, with 31 days aloft (28.5 live
days) over Antarctica. ANITA searches for impulsive coherent radio Cherenkov
emission from 200 to 1200 MHz, arising from the Askaryan charge excess in
ultra-high energy neutrino-induced cascades within Antarctic ice. This flight
included significant improvements over the first flight in the payload
sensitivity, efficiency, and a flight trajectory over deeper ice. Analysis of
in-flight calibration pulses from surface and sub-surface locations verifies
the expected sensitivity. In a blind analysis, we find 2 surviving events on a
background, mostly anthropogenic, of 0.97+-0.42 events. We set the strongest
limit to date for 1-1000 EeV cosmic neutrinos, excluding several current
cosmogenic neutrino models.Comment: 6 pages, 5 figures, submitted to Phys. Rev.
Carbon Nanotubes as Nanoelectromechanical Systems
We theoretically study the interplay between electrical and mechanical
properties of suspended, doubly clamped carbon nanotubes in which charging
effects dominate. In this geometry, the capacitance between the nanotube and
the gate(s) depends on the distance between them. This dependence modifies the
usual Coulomb models and we show that it needs to be incorporated to capture
the physics of the problem correctly. We find that the tube position changes in
discrete steps every time an electron tunnels onto it. Edges of Coulomb
diamonds acquire a (small) curvature. We also show that bistability in the tube
position occurs and that tunneling of an electron onto the tube drastically
modifies the quantized eigenmodes of the tube. Experimental verification of
these predictions is possible in suspended tubes of sub-micron length.Comment: 8 pages, 5 eps figures included. Major changes; new material adde
Understanding the nature of "superhard graphite"
Numerous experiments showed that on cold compression graphite transforms into
a new superhard and transparent allotrope. Several structures with different
topologies have been proposed for this phase. While experimental data are
consistent with these models, the only way to solve this puzzle is to find
which structure is kinetically easiest to form. Using state-of-the-art
molecular-dynamics transition path sampling simulations, we investigate kinetic
pathways of the pressure-induced transformation of graphite to various
superhard candidate structures. Unlike hitherto applied methods for elucidating
nature of superhard graphite, transition path sampling realistically models
nucleation events necessary for physically meaningful transformation kinetics.
We demonstrate that nucleation mechanism and kinetics lead to -carbon as the
final product. -carbon, initially competitor to -carbon, is ruled out by
phase growth. Bct-C structure is not expected to be produced by cold
compression due to less probable nucleation and higher barrier of formation
- …