10,076 research outputs found
Kovacs Effect in a Fragile Glass Model
The Kovacs protocol, based on the temperature shift experiment originally
conceived by A.J. Kovacs for glassy polymers, is implemented in an exactly
solvable dynamical model. This model is characterized by interacting fast and
slow modes represented respectively by spherical spins and harmonic oscillator
variables. Due to this fundamental property, the model reproduces the
characteristic non-monotonic evolution known as the ``Kovacs effect'', observed
in polymers, in granular materials and models of molecular liquids, when
similar experimental protocols are implemented.Comment: 8 pages, 6 figure
The rich frequency spectrum of the triple-mode variable AC And
Fourier analysis of the light curve of AC And from the HATNet database
reveals the rich frequency structure of this object. Above 30 components are
found down to the amplitude of 3 mmag. Several of these frequencies are not the
linear combinations of the three basic components. We detect period increase in
all three components that may lend support to the Pop I classification of this
variable.Comment: Poster presented at IAU Symposium 301, "Precision Asteroseismology -
Celebration of the Scientific Opus of Wojtek Dziembowski", 19-23 August 2013,
Wroclaw, Polan
Development and characterisation of injection moulded, all-polypropylene composites
In this work, all-polypropylene composites (all-PP composites) were manufactured by injection moulding. Prior
to injection moulding, pre-impregnated pellets were prepared by a three-step process (filament winding, compression
moulding and pelletizing). A highly oriented polypropylene multifilament was used as the reinforcement material, and a
random polypropylene copolymer (with ethylene) was used as the matrix material. Plaque specimens were injection
moulded from the pellets with either a film gate or a fan gate. The compression moulded sheets and injection moulding
plaques were characterised by shrinkage tests, static tensile tests, dynamic mechanical analysis and falling weight impact
tests; the fibre distribution and fibre/matrix adhesion were analysed with light microscopy and scanning electron
microscopy. The results showed that with increasing fibre content, both the yield stress and the perforation energy significantly
increased. Of the two types of gates used, the fan gate caused the mechanical properties of the plaque specimens to
become more homogeneous (i.e., the differences in behaviour parallel and perpendicular to the flow direction became negligible)
Thermally conductive polymer compounds for injection moulding: The synergetic effect of hexagonal boron-nitride and talc
The aim of the research project was to investigate and maximize the thermal conductivity of polymer compounds with low filler content (<30âvol%). The study focused on the effect of the matrix material, the filler type, the processing method and the interaction of the fillers. It was concluded that compression-moulded samples have higher thermal conductivity than injection-moulded samples due to the segregation effect and the orientation of the anisotropic fillers. Conductivity can be improved by adding fillers with higher thermal conductivity, and also by combining, or hybridizing the fillers. A synergetic behaviour between hexagonal boron-nitride and talc which improved thermal conductivity was found. </jats:p
Waterborne GPR survey for estimating bottom-sediment variability: A survey on the Po River, Turin, Italy
We conducted an integrated geophysical survey on a stretch of the river Po in order to check the GPR ability to discriminate the variability of riverbed sediments through an analysis of the bottom reflection amplitudes. We conducted continuous profiles with a 200-MHzGPR system and a handheld broadband EM sensor.Aconductivity meter and a TDR provided punctual measurements of water conductivity, permittivity, and temperature. The processing and interpretation of the GEM-2 and GPR data were enhanced by reciprocal results and by integration with the punctual measurements of the EM properties of the water. We used a processing flow that improved the radargram images and preserved the amplitude ratios among the different profiles and the frequency content at the bottom reflection signal.We derived the water attenuation coefficient both from the punctual measurements using the Maxwell formulas and from the interpretation of the GPR data, finding an optimal matching between the two values. The GPR measurements provided maps of the bathymetry and of the bottom reflection amplitude. The high reflectivity of the riverbed, derived from the GPR interpretation, agreed with the results of the direct sampling campaign that followed the geophysical survey. The variability of the bottom-reflection-amplitudes map, which was not confirmed by the direct sampling, could also have been caused by scattering phenomena due to the riverbed clasts which are dimensionally comparable to the wavelength of the radar pulse
A multi-color and Fourier study of RR Lyrae variables in the globular cluster NGC 5272 (M3)
We have performed a detailed study of the pulsational and evolutionary
characteristics of 133 RR Lyrae stars in the globular cluster NGC5272 (M3)
using highly accurate BVI data taken on 5 separate epochs. M3 seems to contain
no less than ~32% of Blazhko stars, and the occurrence and characteristics of
the Blazhko effect have been analyzed in detail. We have identified a good
number (~ 14%) of overluminous RR Lyrae stars that are likely in a more
advanced evolutionary stage off the Zero Age Horizontal Branch (ZAHB). Physical
parameters (i.e. temperature, luminosity, mass) have been derived from (B--V)
colors and accurate color-temperature calibration, and compared with Horizontal
Branch evolutionary models and with the requirements of stellar pulsation
theory. Additional analysis by means of Fourier decomposition of the V light
curves confirms, as expected, that no metallicity spread is present in M3.
Evolution off the ZAHB does not affect [Fe/H] determinations, whereas Blazhko
stars at low amplitude phase do affect [Fe/H] distributions as they appear more
metal-rich. Absolute magnitudes derived from Fourier coefficients might provide
useful average estimates for groups of stars, if applicable, but do not give
reliable {\em individual} values. Intrinsic colors derived from Fourier
coefficients show significant discrepancies with the observed ones, hence the
resulting temperatures and temperature-related parameters are unreliable.Comment: 86 pages, 19 figures, 13 tables, in press A
Chaos control with ion propulsion
The escape dynamics around the triangular Lagrangian point L-5 in the real Sun-Earth-Moon-Spacecraft system is investigated. Appearance of the finite-time chaotic behavior suggests that widely used methods and concepts of dynamical system theory can be useful in constructing a desired mission design. Existing chaos control methods are modified in such a way that we are able to protect a test particle from escape. We introduce initial condition maps (ICMs) in order to have a suitable numerical method to describe the motion in high-dimensional phase space. Results show that the structure of ICMs can be split into two well-defined domains. One of these two parts has a regular contiguous shape and is responsible for long-time escape; it is a long-lived island. The other one shows a filamentary fractal structure in the ICMs. The short-time escape is governed by this object. This study focuses on a low-cost method that successfully transfers a reference trajectory between these two regions using an appropriate continuous control force. A comparison of the Earth-Moon transfer is also presented to show the efficiency of our method
Injection molding of ceramic filled polypropylene: The effect of thermal conductivity and cooling rate on crystallinity
Cores, filaments, and bundles: hierarchical core formation in the L1495/B213 Taurus region
(Abridged) Context. Core condensation is a critical step in the
star-formation process, but is still poorly characterized observationally.
Aims. We have studied the 10 pc-long L1495/B213 complex in Taurus to
investigate how dense cores have condensed out of the lower-density cloud
material. Results. From the NH emission, we identify 19 dense cores,
some starless and some protostellar. They are not distributed uniformly, but
tend to cluster with relative separations on the order of 0.25 pc. From the
CO emission, we identify multiple velocity components in the gas. We
have characterized them by fitting gaussians to the spectra, and by studying
the distribution of the fits in position-position-velocity space. In this
space, the CO components appear as velocity-coherent structures, and we
have identified them automatically using a dedicated algorithm (FIVe: Friends
In Velocity). Using this algorithm, we have identified 35 filamentary
components with typical lengths of 0.5 pc, sonic internal velocity dispersions,
and mass-per-unit-length close to the stability threshold of isothermal
cylinders at 10 K. Core formation seems to have occurred inside the filamentary
components via fragmentation, with a small number of fertile components with
larger mass-per-unit-length being responsible for most cores in the cloud. At
large scales, the filamentary components appear grouped into families, which we
refer to as bundles. Conclusions. Core formation in L1495/B213 has proceeded by
hierarchical fragmentation. The cloud fragmented first into several pc-scale
regions. Each of these regions later fragmented into velocity-coherent
filaments of about 0.5 pc in length. Finally, a small number of these filaments
fragmented quasi-statically and produced the individual dense cores we see
today.Comment: 23 pages, 20 figures. Accepted for publication in Astronomy and
Astrophysic
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