18,227 research outputs found
Modelling mechanical percolation in graphene-reinforced elastomer nanocomposites
Graphene is considered an ideal filler for the production of multifunctional
nanocomposites; as a result, considerable efforts have been focused on the
evaluation and modeling of its reinforcement characteristics. In this work, we
modelled successfully the mechanical percolation phenomenon, observed on a
thermoplastic elastomer (TPE) reinforced by graphene nanoplatelets (GNPs), by
designing a new set of equations for filler contents below and above the
percolation threshold volume fraction (Vp). The proposed micromechanical model
is based on a combination of the well-established shear-lag theory and the
rule-of-mixtures and was introduced to analyse the different stages and
mechanisms of mechanical reinforcement. It was found that when the GNPs content
is below Vp, reinforcement originates from the inherent ability of individual
GNPs flakes to transfer stress efficiently. Furthermore, at higher filler
contents and above Vp, the nanocomposite materials displayed accelerated
stiffening due to the reduction of the distance between adjacent flakes. The
model derived herein, was consistent with the experimental data and the reasons
why the superlative properties of graphene cannot be fully utilized in this
type of composites, were discussed in depth.Comment: 29 pages, 12 figure
Entropy of the FRW universe based on the generalized uncertainty principle
The statistical entropy of the FRW universe described by time-dependent
metric is newly calculated using the brick wall method based on the general
uncertainty principle with the minimal length. We can determine the minimal
length with the Plank scale to obtain the entropy proportional to the area of
the cosmological apparent horizon.Comment: 10 pages, accepted in Modern Physics Letters
Long range magnetic ordering in NaIrO
We report a combined experimental and theoretical investigation of the
magnetic structure of the honeycomb lattice magnet NaIrO, a strong
candidate for a realization of a gapless spin-liquid. Using resonant x-ray
magnetic scattering at the Ir L-edge, we find 3D long range
antiferromagnetic order below T=13.3 K. From the azimuthal dependence of
the magnetic Bragg peak, the ordered moment is determined to be predominantly
along the {\it a}-axis. Combining the experimental data with first principles
calculations, we propose that the most likely spin structure is a novel
"zig-zag" structure
Direct amplification of nodD from community DNA reveals the genetic diversity of Rhizobium leguminosarum in soil
Sequences of nodD, a gene found only in rhizobia, were amplified from total community DNA isolated from a pasture soil. The polymerase chain reaction (PCR) primers used, Y5 and Y6, match nodD from Rhizobium leguminosarum biovar trifolii, R. leguminosarum biovar viciae and Sinorhizobium meliloti. The PCR product was cloned and yielded 68 clones that were identified by restriction pattern as derived from biovar trifolii [11 restriction fragment length polymorphism (RFLP) types] and 15 clones identified as viciae (seven RFLP types). These identifications were confirmed by sequencing. There were no clones related to S. meliloti nodD. For comparison, 122 strains were isolated from nodules of white clover (Trifolium repens) growing at the field site, and 134 from nodules on trap plants of T. repens inoculated with the soil. The nodule isolates were of four nodD RFLP types, with 77% being of a single type. All four of these patterns were also found among the clones from soil DNA, and the same type was the most abundant, although it made up only 34% of the trifolii-like clones. We conclude that clover selects specific genotypes from the available soil population, and that R. leguminosarum biovar trifolii was approximately five times more abundant than biovar viciae in this pasture soil, whereas S. meliloti was rare
Investigating fragmentation of gas structures in OB cluster-forming molecular clump G33.92+0.11 with 1000 AU resolution observations of ALMA
We report new, 1000 AU spatial resolution observations of 225 GHz dust
continuum emission towards the OB cluster-forming molecular clump G33.92+0.11.
On parsec scales, this molecular clump presents a morphology with several
arm-like dense gas structures surrounding the two central massive (100
) cores. From the new, higher resolution observations, we identified
28 localized, spatially compact dust continuum emission sources, which may be
candidates of young stellar objects. Only one of them is not embedded within
known arm-like (or elongated) dense gas structures. The spatial separations of
these compact sources can be very well explained by Jeans lengths. We found
that G33.92+0.11 may be consistently described by a marginally centrifugally
supported, Toomre unstable accretion flow which is approximately in a face-on
projection. The arm-like overdensities are natural consequence of the Toomre
instability, which can fragment to form young stellar objects in shorter time
scales than the timescale of the global clump contraction. On our resolved
spatial scales, there is not yet evidence that the fragmentation is halted by
turbulence, magnetic field, or stellar feedback.Comment: 24 pages, 18 figures. Accepted to publish on December 04, 2018;
updated to arXiv on December 05, 201
Simulation of photodetection using finite-difference time-domain method with application to near-field subwavelength imaging based on nanoscale semiconductor photodetector array
Simulation of detecting photoelectrons using multi-level multi-electron
(MLME) finite-difference time-domain (FDTD) method with an application to
near-field subwavelength imaging based on semiconductor nanophotodetector (NPD)
array is reported. The photocurrents from the photodiode pixels are obtained to
explore the resolution of this novel NPD device for subwavelength imaging. One
limiting factor of the NPD device is the optical power coupling between
adjacent detector pixels. We investigate such power coupling in the presence of
absorbing media as well as the spatial distributions of the electric field and
photoelectron density using the MLME FDTD simulation. Our results show that the
detection resolution is about one tenth of the operating wavelength, which is
comparable to that of a near-field scanning optical microscope based on metal
clad tapered fiber.Comment: 7 pages, 4 figure
Ultracold Neutron Production in a Pulsed Neutron Beam Line
We present the results of an Ultracold neutron (UCN) production experiment in
a pulsed neutron beam line at the Los Alamos Neutron Scattering Center. The
experimental apparatus allows for a comprehensive set of measurements of UCN
production as a function of target temperature, incident neutron energy, target
volume, and applied magnetic field. However, the low counting statistics of the
UCN signal expected can be overwhelmed by the large background associated with
the scattering of the primary cold neutron flux that is required for UCN
production. We have developed a background subtraction technique that takes
advantage of the very different time-of-flight profiles between the UCN and the
cold neutrons, in the pulsed beam. Using the unique timing structure, we can
reliably extract the UCN signal. Solid ortho-D is used to calibrate UCN
transmission through the apparatus, which is designed primarily for studies of
UCN production in solid O. In addition to setting the overall detection
efficiency in the apparatus, UCN production data using solid D suggest that
the UCN upscattering cross-section is smaller than previous estimates,
indicating the deficiency of the incoherent approximation widely used to
estimate inelastic cross-sections in the thermal and cold regimes
Crystallization of hepatocyte nuclear factor 4α (HNF4α) in complex with the HNF1α promoter element
Sample preparation, characterization, crystallization and preliminary X-ray analysis are reported for the HNF4뱉DNA binary complex
Multiwavelength Observations of Small-Scale Reconnection Events triggered by Magnetic Flux Emergence in the Solar Atmosphere
The interaction between emerging magnetic flux and the pre-existing ambient
field has become a "hot" topic for both numerical simulations and
high-resolution observations of the solar atmosphere. The appearance of
brightenings and surges during episodes of flux emergence is believed to be a
signature of magnetic reconnection processes. We present an analysis of a
small-scale flux emergence event in NOAA 10971, observed simultaneously with
the Swedish 1-m Solar Telescope on La Palma and the \emph{Hinode} satellite
during a joint campaign in September 2007. Extremely high-resolution G-band,
H, and \ion{Ca}{2} H filtergrams, \ion{Fe}{1} and \ion{Na}{1}
magnetograms, EUV raster scans, and X-ray images show that the emerging region
was associated with chromospheric, transition region and coronal brightenings,
as well as with chromospheric surges. We suggest that these features were
caused by magnetic reconnection at low altitude in the atmosphere. To support
this idea, we perform potential and linear force-free field extrapolations
using the FROMAGE service. The extrapolations show that the emergence site is
cospatial with a 3D null point, from which a spine originates. This magnetic
configuration and the overall orientation of the field lines above the emerging
flux region are compatible with the structures observed in the different
atmospheric layers, and remain stable against variations of the force-free
field parameter. Our analysis supports the predictions of recent 3D numerical
simulations that energetic phenomena may result from the interaction between
emerging flux and the pre-existing chromospheric and coronal field.Comment: In press for Ap
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