411 research outputs found
Development of environmentally friendly composite matrices from epoxidized cottonseed oil
The continuous rise in oil prices has led to the use of other ways to obtain polymer materials. This paper proposes a methodology to obtain a thermosetting resin from cottonseed oil by epoxidation process. The cottonseed oil contains as most representative fatty acids: 52.5% of linoleic acid (C18: 2), 23.9% of palmitic acid (C16: 0) and 17.6% of oleic acid (C18: 1); the real iodine index, which is indicative of the number of double bonds, has a value of 107. Epoxidized cottonseed oil (ECSO) has been successfully obtained using conventional epoxidation process with hydrogen peroxide, acetic acid and sulfuric acid, maintaining a constant temperature of 70 °C with homogeneous magnetic stirring. Average oxirane oxygen content (OOC) of 5.32% can be obtained by conventional epoxidation process which represents a yield over 83%. The epoxidized oil has been crosslinked with mixtures of two cyclic anhydrides to tailor different properties on final crosslinked thermosetting resins: on the one hand, methyl nadic anhydride (MNA) which is characterized by a rigid molecular structure and on the other hand, dodecenylsuccinic anhydride (DDSA) with a long side chain that can confer flexibility. The crosslinking process has been followed by dynamic differential scanning calorimetry (DSC), ionic mobility and oscillatory rheometry (OR) as well as gel time determination. The effect of the hardener mixture (wt.% DDSA:MNA) on mechanical performance of cured materials has been followed by flexural and impact tests as well as the evolution of the storage modulus (G′) by dynamic mechanical analysis (DMA) in torsion mode. By selecting the appropriate hardener mixture, it is possible to obtain crosslinked materials with different properties ranging from stiff matrices for ECSO crosslinked with MNA to flexible matrices for ECSO cured with DDSA. This has occurred with other thermosetting resins like epoxidized soy bean oil (ESBO) or epoxidized linseed oil (ELO). (C) 2014 Elsevier Ltd. All rights reserved.Authors thank Conselleria d'Educacio, Cultura i Esport (Generalitat Valenciana) Ref: GV/2014/008 for financial support.Carbonell Verdú, A.; Bernardi, L.; García García, D.; Sánchez Nacher, L.; Balart Gimeno, RA. (2015). Development of environmentally friendly composite matrices from epoxidized cottonseed oil. European Polymer Journal. 63:1-10. doi:10.1016/j.eurpolymj.2014.11.043S1106
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Adults with probable Developmental Coordination Disorder selectively process early visual, but not tactile information during action preparation. An electrophysiological study.
Developmental coordination disorder (DCD) is a neurodevelopmental condition affecting motor coordination in children and adults. Here, EEG signals elicited by visual and tactile stimuli were recorded while adult participants with and without probable DCD (pDCD) performed a motor task. The task cued reaching movements towards a location in visible peripersonal space as well as an area of unseen personal space. Event-related potentials elicited by visual and tactile stimuli revealed that visual processing was strongly affected by movement preparation in the pDCD group, even more than in controls. However, in contrast to the controls, tactile processing in unseen space was unaffected by movement preparation in the pDCD group. The selective use of sensory information from vision and proprioception is fundamental for the adaptive control of movements, and these findings suggest that this is impaired in DCD. Additionally, the pDCD group showed attenuated motor rhythms (beta: 13-30Hz) over sensorimotor regions following cues to prepare movements towards unseen personal space. The results reveal that individuals with pDCD exhibit differences in the neural mechanisms of spatial selection and action preparation compared to controls, which may underpin the sustained difficulties they experience. These findings provide new insights into the neural mechanisms potentially disrupted in this highly prevalent disorder
Verificacion del grado de regularidad del cuero de fabricación nacional
Se realizaron ensayos físicos y mecánicos sobre muestras periódicas de cueros para empeine curtidos al cromo, recurtidos, flor corregida, elaborados por 6 curtiembres locales. Los resultados tabulados y los gráficos respectivos muestran: el nivel medio () de cada propiedad y para cada curtiembre; las variaciones de los promedios muéstrales () con respecto al nivel medio (); la magnitud del recorrido medio () y las oscilaciones del recorrido muestral () con respecto al recorrido medio ().
Los datos obtenidos permiten a cada fabricante conocer los límites de los cuales oscilan el valor de cada una de las propiedades y de su posición en el conjunto. Se ha logrado además una información útil para la redacción de especificacionesA quality control of chrome retanned corrected grain upper leathers produced by six local tanneries is reported. Samples were taken monthly with sizes ranging from 2-4 units; total sampling lasted from 6-12 months.
The average levels for each property examined and each tannery; its monthly fluctuations and variations within the sample are indicated. The average range and its fluctuations are also informed.
Data as a whole reveals the quality level and regularity of each tannery
Characterizing Signal Loss in the 21 cm Reionization Power Spectrum: A Revised Study of PAPER-64
The Epoch of Reionization (EoR) is an uncharted era in our Universe's history
during which the birth of the first stars and galaxies led to the ionization of
neutral hydrogen in the intergalactic medium. There are many experiments
investigating the EoR by tracing the 21cm line of neutral hydrogen. Because
this signal is very faint and difficult to isolate, it is crucial to develop
analysis techniques that maximize sensitivity and suppress contaminants in
data. It is also imperative to understand the trade-offs between different
analysis methods and their effects on power spectrum estimates. Specifically,
with a statistical power spectrum detection in HERA's foreseeable future, it
has become increasingly important to understand how certain analysis choices
can lead to the loss of the EoR signal. In this paper, we focus on signal loss
associated with power spectrum estimation. We describe the origin of this loss
using both toy models and data taken by the 64-element configuration of the
Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER).
In particular, we highlight how detailed investigations of signal loss have led
to a revised, higher 21cm power spectrum upper limit from PAPER-64.
Additionally, we summarize errors associated with power spectrum error
estimation that were previously unaccounted for. We focus on a subset of
PAPER-64 data in this paper; revised power spectrum limits from the PAPER
experiment are presented in a forthcoming paper by Kolopanis et al. (in prep.)
and supersede results from previously published PAPER analyses.Comment: 25 pages, 18 figures, Accepted by Ap
PAPER-64 Constraints On Reionization II: The Temperature Of The z=8.4 Intergalactic Medium
We present constraints on both the kinetic temperature of the intergalactic
medium (IGM) at z=8.4, and on models for heating the IGM at high-redshift with
X-ray emission from the first collapsed objects. These constraints are derived
using a semi-analytic method to explore the new measurements of the 21 cm power
spectrum from the Donald C. Backer Precision Array for Probing the Epoch of
Reionization (PAPER), which were presented in a companion paper, Ali et al.
(2015). Twenty-one cm power spectra with amplitudes of hundreds of mK^2 can be
generically produced if the kinetic temperature of the IGM is significantly
below the temperature of the Cosmic Microwave Background (CMB); as such, the
new results from PAPER place lower limits on the IGM temperature at z=8.4.
Allowing for the unknown ionization state of the IGM, our measurements find the
IGM temperature to be above ~5 K for neutral fractions between 10% and 85%,
above ~7 K for neutral fractions between 15% and 80%, or above ~10 K for
neutral fractions between 30% and 70%. We also calculate the heating of the IGM
that would be provided by the observed high redshift galaxy population, and
find that for most models, these galaxies are sufficient to bring the IGM
temperature above our lower limits. However, there are significant ranges of
parameter space that could produce a signal ruled out by the PAPER
measurements; models with a steep drop-off in the star formation rate density
at high redshifts or with relatively low values for the X-ray to star formation
rate efficiency of high redshift galaxies are generally disfavored. The PAPER
measurements are consistent with (but do not constrain) a hydrogen spin
temperature above the CMB temperature, a situation which we find to be
generally predicted if galaxies fainter than the current detection limits of
optical/NIR surveys are included in calculations of X-ray heating.Comment: companion paper to Ali et al. (2015), ApJ 809, 61; matches version
accepted to ApJ; 11 pages, 7 figure
Optical and Radio Properties of Extragalactic Sources Observed by the FIRST and SDSS Surveys
We discuss the optical and radio properties of 30,000 FIRST sources
positionally associated with an SDSS source in 1230 deg of sky. The
majority (83%) of the FIRST sources identified with an SDSS source brighter
than r=21 are optically resolved. We estimate an upper limit of 5% for the
fraction of quasars with broad-band optical colors indistinguishable from those
of stars. The distribution of quasars in the radio flux -- optical flux plane
supports the existence of the "quasar radio-dichotomy"; 8% of all quasars with
i<18.5 are radio-loud and this fraction seems independent of redshift and
optical luminosity. The radio-loud quasars have a redder median color by 0.08
mag, and a 3 times larger fraction of objects with red colors. FIRST galaxies
represent 5% of all SDSS galaxies with r<17.5, and 1% for r<20, and are
dominated by red galaxies. Magnitude and redshift limited samples show that
radio galaxies have a different optical luminosity distribution than non-radio
galaxies selected by the same criteria; when galaxies are further separated by
their colors, this result remains valid for both blue and red galaxies. The
distributions of radio-to-optical flux ratio are similar for blue and red
galaxies in redshift-limited samples; this similarity implies that the
difference in their luminosity functions, and resulting selection effects, are
the dominant cause for the preponderance of red radio galaxies in flux-limited
samples. We confirm that the AGN-to-starburst galaxy number ratio increases
with radio flux, and find that radio emission from AGNs is more concentrated
than radio emission from starburst galaxies (abridged).Comment: submitted to AJ, color gif figures, PS figures available from
[email protected]
The Murchison Widefield Array
It is shown that the excellent Murchison Radio-astronomy Observatory site
allows the Murchison Widefield Array to employ a simple RFI blanking scheme and
still calibrate visibilities and form images in the FM radio band. The
techniques described are running autonomously in our calibration and imaging
software, which is currently being used to process an FM-band survey of the
entire southern sky.Comment: Accepted for publication in Proceedings of Science [PoS(RFI2010)016].
6 pages and 3 figures. Presented at RFI2010, the Third Workshop on RFI
Mitigation in Radio Astronomy, 29-31 March 2010, Groningen, The Netherland
Galaxy Clustering in Early SDSS Redshift Data
We present the first measurements of clustering in the Sloan Digital Sky
Survey (SDSS) galaxy redshift survey. Our sample consists of 29,300 galaxies
with redshifts 5,700 km/s < cz < 39,000 km/s, distributed in several long but
narrow (2.5-5 degree) segments, covering 690 square degrees. For the full,
flux-limited sample, the redshift-space correlation length is approximately 8
Mpc/h. The two-dimensional correlation function \xi(r_p,\pi) shows clear
signatures of both the small-scale, ``fingers-of-God'' distortion caused by
velocity dispersions in collapsed objects and the large-scale compression
caused by coherent flows, though the latter cannot be measured with high
precision in the present sample. The inferred real-space correlation function
is well described by a power law, \xi(r)=(r/6.1+/-0.2 Mpc/h)^{-1.75+/-0.03},
for 0.1 Mpc/h < r < 16 Mpc/h. The galaxy pairwise velocity dispersion is
\sigma_{12} ~ 600+/-100 km/s for projected separations 0.15 Mpc/h < r_p < 5
Mpc/h. When we divide the sample by color, the red galaxies exhibit a stronger
and steeper real-space correlation function and a higher pairwise velocity
dispersion than do the blue galaxies. The relative behavior of subsamples
defined by high/low profile concentration or high/low surface brightness is
qualitatively similar to that of the red/blue subsamples. Our most striking
result is a clear measurement of scale-independent luminosity bias at r < 10
Mpc/h: subsamples with absolute magnitude ranges centered on M_*-1.5, M_*, and
M_*+1.5 have real-space correlation functions that are parallel power laws of
slope ~ -1.8 with correlation lengths of approximately 7.4 Mpc/h, 6.3 Mpc/h,
and 4.7 Mpc/h, respectively.Comment: 51 pages, 18 figures. Replaced to match accepted ApJ versio
The velocity dispersion function of early-type galaxies
The distribution of early-type galaxy velocity dispersions, phi(sigma), is
measured using a sample drawn from the SDSS database. Its shape differs
significantly from that which one obtains by simply using the mean correlation
between luminosity, L, and velocity dispersion, sigma, to transform the
luminosity function into a velocity function: ignoring the scatter around the
mean sigma-L relation is a bad approximation. An estimate of the contribution
from late-type galaxies is also made, which suggests that phi(sigma) is
dominated by early-type galaxies at velocities larger than ~ 200 km/s.Comment: Minor changes, matches version to appear in ApJ, 1 September 200
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