7,830 research outputs found
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
Chopped basalt fibres: A new perspective in reinforcing poly(lactic acid) to produce injection moulded engineering composites from renewable and natural resources
This paper focuses on the reinforcing of Poly(lactic acid) with chopped basalt fibres by using silane treated and
untreated basalt fibres. Composite materials with 5â10â15â20â30â40 wt% basalt fibre contents were prepared from silane
sized basalt fibres using extrusion, and injection moulding, while composites with 5â10â15 wt% basalt fibre contents were
also prepared by using untreated basalt fibres as control. The properties of the injection moulded composites were extensively
examined by using quasi-static (tensile, three-point bending) and dynamic mechanical tests (notched and unnotched
Charpy impact tests), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), heat deflection temperature
(HDT) analysis, dimensional stability test, as well as melt flow index (MFI) analysis and scanning electron microscopic
(SEM) observations. It was found that silane treated chopped basalt fibres are much more effective in reinforcing
Poly(lactic acid) than natural fibres; although basalt fibres are not biodegradable but they are still considered as natural (can
be found in nature in the form of volcanic rocks) and biologically inert. It is demonstrated in this paper that by using basalt
fibre reinforcement, a renewable and natural resource based composite can be produced by injection moulding with excellent
mechanical properties suitable even for engineering applications. Finally it was shown that by using adequate drying of
the materials, composites with higher mechanical properties can be achieved compared to literature data
Application of the Trend Filtering Algorithm on the MACHO Database
Due to the strong effect of systematics/trends in variable star observations,
we employ the Trend Filtering Algorithm (TFA) on a subset of the MACHO database
and search for variable stars. TFA has been applied successfully in planetary
transit searches, where weak, short-lasting periodic dimmings are sought in the
presence of noise and various systematics (due to, e.g., imperfect flat
fielding, crowding, etc). These latter effects introduce colored noise in the
photometric time series that can lead to a complete miss of the signal. By
using a large number of available photometric time series of a given field, TFA
utilizes the fact that the same types of systematics appear in several/many
time series of the same field. As a result, we fit each target time series by a
(least-square-sense) optimum linear combination of templates and
frequency-analyze the residuals. Once a signal is found, we reconstruct the
signal by employing the full model, including the signal, systematics and
noise. We apply TFA on the brightest ~5300 objects from subsets of each of the
MACHO Large Magellanic Cloud fields #1 and #79. We find that the Fourier
frequency analysis performed on the original data detect some 60% of the
objects as trend-dominated. This figure decreases essentially to zero after
using TFA. Altogether, We detect 387 variables in the two fields, 183 of which
would have remained undetected without using TFA. Where possible, we give
preliminary classification of the variables found.Comment: 12 pages, 15 figures, 3 tables with online material; to appear in
Astronomy and Astrophysic
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)
Dust formation, evolution, and obscuration effects in the very high-redshift universe
The evolution of dust at redshifts z>9, and consequently the dust properties,
differs greatly from that in the local universe. In contrast to the local
universe, core collapse supernovae (CCSNe) are the only source of
thermally-condensed dust. Because of the low initial dust-to-gas mass ratio,
grain destruction rates are low, so that CCSNe are net producers of
interstellar dust. Galaxies with large initial gas mass or high mass infall
rate will therefore have a more rapid net rate of dust production comported to
galaxies with lower gas mass, even at the same star formation rate. The dust
composition is dominated by silicates, which exhibit a strong rise in the UV
opacity near the Lyman break. This "silicate-UV break" may be confused with the
Lyman break, resulting in a misidentification of a galaxies' photometric
redshift. In this paper we demonstrate these effects by analyzing the spectral
energy distribution (SED) of MACS1149-JD, a lensed galaxy at z=9.6. A potential
2mm counterpart of MACS1149-JD has been identified with GISMO. While additional
observations are required to corroborate this identification, we use this
possible association to illustrate the physical processes and the observational
effects of dust in the very high redshift universe.Comment: Accepted for publication in ApJ Letter
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
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Az 1.3 fejezet a szelektĂv lĂ©zer szinterezĂ©s, ezen belĂŒl is a DMLS (Direct Metal Laser Sintering)
technolĂłgiĂĄval foglalkozik, bemutatja az eljĂĄrĂĄs jellemzĆit, elĆnyeit Ă©s korlĂĄtait formakövetĆ
hƱtĆcsatornĂĄval rendelkezĆ fröccsöntĆ szerszĂĄmbetĂ©tek gyĂĄrtĂĄsĂĄban
The Metallicity Dependence of the Fourier Components of RR Lyrae Light Curves is the Oosterhoff/Arp/Preston Period Ratio Effect in Disguise
The correlation of particular Fourier components of the light curves of RR
Lyrae variables with metallicity, discovered by Simon and later by Kovacs and
his coworkers, is shown to have the same explanation as the period ratios
(period shifts in log P) between RRab Lyrae variables that have the same
colors, amplitudes, and light-curve shapes but different metallicities. A
purpose of this paper is to demonstrate that the model which predicts the
period-metallicity relations is the mediating parameters of colors, amplitudes,
and light-curve shapes also explains the Simon/Kovacs et al. correlation
between period, Phi_31, and metallicity. The proof is made by demonstrating
that the combination of the first and third phase terms in a Fourier
decomposition of RRab light curves, called Phi_31 by Simon and Lee, varies
monotonically across the RR Lyrae instability strip in the same way that
amplitude, color, and rise time vary with period within the strip. The premise
of the model is that if horizontal branches at the RR Lyrae strip are stacked
in luminosity according to the metallicity, then there necessarily must be a
log period shift between RR Lyraes with different metallicities at the same
Phi_31 values. However, there are exceptions to the model. (...)Comment: 17 pages, 8 figures, 1 table. Accepted for publication in The A
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