367 research outputs found
Influence of carbon nanotubes on the rheology and dynamic mechanical properties of polyamide-12 for laser sintering
The rheological behaviour of polymer nanocomposites is very important for polymer processing and understanding the structure-properties relationship. In this paper, the rheological properties of a polyamide 12 (PA12) - carbon nanotube (CNT) nanocomposite for laser sintering were studied. Compared to neat PA12, the presence of CNTs resulted in higher storage modulus (G′), loss modulus (G″) and viscosity (η). With an increase in temperature, viscosity showed an unusual increase for both PA12 and the PA12-CNT nanocomposites, which is likely to result from incomplete melting of powder particles. Dynamic mechanical analysis was carried out to examine the effect the CNTs were having on the laser sintered parts. The laser sintered PA12-CNT nanocomposite had an increased elastic modulus compared to that of neat PA12. The CNT and polymer matrix interaction hindered the chain motions, which resulted in higher loss modulus and decreased the thermal expansion coefficient
Primordial non-Gaussianity in the Bispectrum of the Halo Density Field
The bispectrum vanishes for linear Gaussian fields and is thus a sensitive
probe of non-linearities and non-Gaussianities in the cosmic density field.
Hence, a detection of the bispectrum in the halo density field would enable
tight constraints on non-Gaussian processes in the early Universe and allow
inference of the dynamics driving inflation. We present a tree level derivation
of the halo bispectrum arising from non-linear clustering, non-linear biasing
and primordial non-Gaussianity. A diagrammatic description is developed to
provide an intuitive understanding of the contributing terms and their
dependence on scale, shape and the non-Gaussianity parameter fNL. We compute
the terms based on a multivariate bias expansion and the peak-background split
method and show that non-Gaussian modifications to the bias parameters lead to
amplifications of the tree level bispectrum that were ignored in previous
studies. Our results are in a good agreement with published simulation
measurements of the halo bispectrum. Finally, we estimate the expected signal
to noise on fNL and show that the constraint obtainable from the bispectrum
analysis significantly exceeds the one obtainable from the power spectrum
analysis.Comment: 34 pages, 15 figures, (v3): matches JCAP published versio
Relativistic effects and primordial non-Gaussianity in the galaxy bias
When dealing with observables, one needs to generalize the bias relation
between the observed galaxy fluctuation field to the underlying matter
distribution in a gauge-invariant way. We provide such relation at second-order
in perturbation theory adopting the local Eulerian bias model and starting from
the observationally motivated uniform-redshift gauge. Our computation includes
the presence of primordial non-Gaussianity. We show that large scale-dependent
relativistic effects in the Eulerian bias arise independently from the presence
of some primordial non-Gaussianity. Furthermore, the Eulerian bias inherits
from the primordial non-Gaussianity not only a scale-dependence, but also a
modulation with the angle of observation when sources with different biases are
correlated.Comment: 12 pages, LaTeX file; version accepted for publication in JCA
Possible large phase in psi(2S) -> 1-0- Decays
The strong and the electromagnetic amplitudes are analyzed on the basis of
the measurements of J/psi, psi(2S) -> 1-0- in e+e- experiments. The currently
available experimental information is revised with inclusion of the
contribution from e+e- -> gamma * -> 1-0- . The study shows that a large phase
around minus 90 degree between the strong and the electromagnetic amplitudes
could not be ruled out by the experimental data for psi(2S).Comment: 4 page
A New Finite-lattice study of the Massive Schwinger Model
A new finite lattice calculation of the low lying bound state energies in the
massive Schwinger model is presented, using a Hamiltonian lattice formulation.
The results are compared with recent analytic series calculations in the low
mass limit, and with a new higher order non-relativistic series which we
calculate for the high mass limit. The results are generally in good agreement
with these series predictions, and also with recent calculations by light cone
and related techniques
Self-assembly of quantum dots: effect of neighbor islands on the wetting in coherent Stranski-Krastanov growth
The wetting of the homogeneously strained wetting layer by dislocation-free
three-dimensional islands belonging to an array has been studied. The array has
been simulated as a chain of islands in 1+1 dimensions. It is found that the
wetting depends on the density of the array, the size distribution and the
shape of the neighbor islands. Implications for the self-assembly of quantum
dots grown in the coherent Stranski-Krastanov mode are discussed.Comment: 4 pages, 6 figures, accepted version, minor change
Coherent \pi^0 threshold production from the deuteron at Q^2 = 0.1 GeV^2/c^2
First data on coherent threshold \pi^0 electroproduction from the deuteron
taken by the A1 Collaboration at the Mainz Microtron MAMI are presented. At a
four-momentum transfer of q^2=-0.1 GeV^2/c^2 the full solid angle was covered
up to a center-of-mass energy of 4 MeV above threshold. By means of a
Rosenbluth separation the longitudinal threshold s wave multipole and an upper
limit for the transverse threshold s wave multipole could be extracted and
compared to predictions of Heavy Baryon Chiral Perturbation Theory.Comment: 7 pages, 7 figures, latex2
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