366 research outputs found
Frictorq, tribómetro para avaliação objectiva de superfícies texteis
Muitos materiais têxteis, senão mesmo a sua grande maioria, são usados ou então em contacto com o ser humano. são inumeras as aplicações em que os materiais estão em contacto com o corpo e as mãos, como é o caso do vestuário e dos têxteis lar, e mesmo os têxtais técnicos em algumas aplicações especiais, entre outras. O conceito de vestuário, assim visto como a nossa segunda pele, está intimamente relacionado com enorme variedade de tecidos, que surgem, naturalmente, em função das exigencias e das voluções da moda. neste sentido, e com especial ênfase no vestuário, existem vários parâmetros que permitem avaliar a qualidade e a aplicabilidade de tecidos. o coeficiente de atrito é um desses parâmetros, sendo um dos principais indicadores para avaliação objectiva de um conceito vulgarmente conhecido por toque. Este artigo pretende rever os principais desenvolvimentos que conduziram à concepção, construção e aperfeiçoamento de um aparelho para a medição do coeficiente de atrito de tecidos, que fosse de utilização simples, preciso e com um custo aceitável. de acordo com os ultimos desenvolvimentos, também aqui analisados e discutidos, é possivel concluir que o protótipo concebido é preciso e fiável, mostrando os resultados obtidos um comportamento comparável com outro instrumento com reconhecimento mundial, o sistema japonês Kes(Kawabata Evaluation System
Radio asymmetry in 3C99
The N-galaxy 3C99, a Compact Steep-spectrum Source showing a triple
asymmetric structure, has been observed with several arrays of radio telescopes
at sub-arcsecond resolution. New images from MERLIN, European VLBI Network and
the Very Long Baseline Array show that the source components detected in the
central region of 3C99 have steep spectral indices, making it difficult to
determine which of them is the core. The asymmetric radio structure of 3C99 is
explained using the Scheuer-Baldwin continuous streaming model with a rather
large difference in the interstellar medium density on the two sides of the
central region. The age of 3C99 has been estimated; the source is found younger
than 10^6 years.Comment: 18 pages, plain tex, plus 8 figures, accepted by A&
Catalyzing sustainable urban transformations towards smarter, healthier cities through urban ecological infrastructure, regenerative development, eco towns and regional prosperity
published_or_final_versio
Do South African Consumers have an Appetite for an Origin-based Certification System for Meat Products? A Synthesis of Studies on Perceptions, Preferences and Experiments
The introduction of Protected Designation of Origin (PDO) type certification schemes in countries outside Europe is a recent phenomenon as the philosophy of origin based foods obtains global traction. It is therefore interesting to understand whether consumers in these countries have a similar appreciation for these certification schemes and whether they are willing to pay a premium if the origin of the product is guaranteed. The Karoo Lamb case in South Africa provides an ideal opportunity to explore this question. At the same time the paper illustrates that the results and interpretation of consumer studies are sensitive to the methodology applied. We illustrate this argument by benefitting from a range of consumer studies that was undertaken over a period of five years in order to understand the South African consumers’ perceptions about the Karoo region and their preferences and willingness to pay for the meat product from the Karoo. The studies which we compare and synthesise in this paper used different techniques such as perception analysis; stated preference methods (through a conjoint analysis); and a range of revealed preference methods including, an experimental auction and a retail store experiment. In essence the paper synthesises and compares the results from the different studies and illustrates how different techniques bring different results and conclusions. We then try to establish whether there is consistency in the results across methods to help us getting to a conclusive position on the consumer value of this product. From these results we are able – in a more comprehensive way - to tell whether PDO-type products are likely to be of value to South African consumers
Spitzer Observations of 3C Quasars and Radio Galaxies: Mid-Infrared Properties of Powerful Radio Sources
We have measured mid-infrared radiation from an orientation-unbiased sample
of 3CRR galaxies and quasars at redshifts 0.4 < z < 1.2 with the IRS and MIPS
instruments on the Spitzer Space Telescope. Powerful emission (L_24micron >
10^22.4 W/Hz/sr) was detected from all but one of the sources. We fit the
Spitzer data as well as other measurements from the literature with synchrotron
and dust components. The IRS data provide powerful constraints on the fits. At
15 microns, quasars are typically four times brighter than radio galaxies with
the same isotropic radio power. Based on our fits, half of this difference can
be attributed to the presence of non-thermal emission in the quasars but not
the radio galaxies. The other half is consistent with dust absorption in the
radio galaxies but not the quasars. Fitted optical depths are anti-correlated
with core dominance, from which we infer an equatorial distribution of dust
around the central engine. The median optical depth at 9.7 microns for objects
with core-dominance factor R > 10^-2 is approximately 0.4; for objects with R <
10^-2, it is 1.1. We have thus addressed a long-standing question in the
unification of FR II quasars and galaxies: quasars are more luminous in the
mid-infrared than galaxies because of a combination of Doppler-boosted
synchrotron emission in quasars and extinction in galaxies, both
orientation-dependent effects.Comment: 42 pages, 14 figures plus two landscape tables. Accepted for
publication in Ap
Heat transfer and rheology of stirred yoghurt during cooling in plate heat exchangers
http://www.sciencedirect.com/science/journal/02608774In the present work an experimental investigation was conducted to obtain a correlation for the determination of convective heat transfer coefficients of stirred yoghurt in a plate heat exchanger. A rheological study was carried out in order to characterise the stirred yoghurt flow behaviour, evaluating its dependency both on shear rate and temperature. A shift in the temperature dependency was evidenced at 25 ºC. It is also shown that the material shows a complex flow behaviour, changing from a Bingham fluid to a power-law fluid at shear stresses in excess of approximately 6.7 Pa. As regards the heat transfer behaviour of the non-Newtonian stirred yoghurt a correlation for the convective heat transfer coefficient was obtained that reveals the large effects of the thermal entry length due to the high Prandtl numbers and to the short length of the plate heat exchanger
Dust tori in radio galaxies
We investigate the validity of the quasar - radio galaxy unification scenario
and detect dust tori within radio galaxies of various types. Using VISIR on the
VLT, we acquired sub-arcsecond (~0.40") resolution N-band images, at a
wavelength of 11.85 micron, of the nuclei of a sample of 27 radio galaxies of
four types in the redshift range z=0.006-0.156. The sample consists of 8
edge-darkened, low-power Fanaroff-Riley class I (FR-I) radio galaxies, 6
edge-brightened, class II (FR-II) radio galaxies displaying low-excitation
optical emission, 7 FR-IIs displaying high-excitation optical emission, and 6
FR-II broad emission line radio galaxies. Out of the sample of 27 objects, 10
nuclei are detected and several have constraining non-detections at
sensitivities of 7 mJy, the limiting flux a point source has when detected with
a signal-to-noise ratio of 10 in one hour of source integration. On the basis
of the core spectral energy distributions of this sample we find clear
indications that many FR-I and several low-excitation FR-II radio galaxies do
not contain warm dust tori. At least 57+-19 percent of the high-excitation
FR-IIs and almost all broad line radio galaxies display excess infrared
emission, which must be attributed to warm dust reradiating accretion activity.
The FR-I and low-excitation FR-II galaxies all possess low efficiencies,
calculated as the ratio of bolometric and Eddington luminosity log
(L_bol/L_Edd) < -3. This suggests that thick tori are absent at low accretion
rates and/or low efficiencies. We argue that the unification viewing angle
range 0-45 degrees of quasars should be increased to ~60 degrees, at least at
lower luminosities.Comment: 17 pages, 9 figures, published in Astronomy and Astrophysics. Version
2 matches published version
Gradients of absorption-line strengths in elliptical galaxies
© 1999. The American Astronomical Society. All rights reserved. This is the final published version of the work, which was originally published at https://doi.org/10.1086/308092We have restudied line-strength gradients of 80 elliptical galaxies. Typical metallicity gradients of elliptical galaxies are Delta[Fe/H]/Delta log r similar or equal to -0.3, which is flatter than the gradients predicted by monolithic collapse simulations. The metallicity gradients do not correlate with any physical properties of galaxies, including central and mean metallicities, central velocity dispersions sigma(0), absolute B magnitudes M-B, absolute effective radii R-e, and dynamical masses of galaxies. By using the metallicity gradients, we have calculated mean stellar metallicities for individual ellipticals. Typical mean stellar metallicities are [[Fe/H]] similar or equal to -0.3 and range from [[Fe/H]] similar or equal to -0.8 to +0.3, which is contrary to what Gonzalez & Gorgas claimed; the mean metallicities of ellipticals are not universal. The mean metallicities correlate well with sigma(0) and dynamical masses, though relations for M-B and R-e include significant scatters. We find fundamental planes defined by surface brightnesses SBe, [[Fe/H]], and R-e (or M-B), the scatters of which are much smaller than those of the [[Fe/H]]-R-e (or [[Fe/H]]-M-B) relations. The [[Fe/H]]-log sigma(0) relation is nearly parallel to the [Fe/H](0)-log sigma(0) relation but systematically lower by 0.3 dex; thus the mean metallicities are about one-half of the central values. The metallicity-mass relation or, equivalently, the color-magnitude relation of ellipticals holds not only for the central parts of galaxies but also for entire galaxies. Assuming that Mg-2 and Fe-1 give [Mg/H] and [Fe/H], respectively, we find [[Mg/Fe]] similar or equal to +0.2 in most of elliptical galaxies. [[Mg/Fe]] shows no correlation with galaxy mass tracers such as sigma(0), in contrast to what was claimed for the central [Mg/Fe]. This can be most naturally explained if the star formation had stopped in elliptical galaxies before the bulk of Type Ia supernovae began to occur. Elliptical galaxies can have significantly different metallicity gradients and [[Fe/H]], even if they have the same galaxy mass. This may result from galaxy mergers, but no evidence is found from presently available data to support the same origin for metallicity gradients, the scatters around the metallicity-mass relation, and dynamical disturbances. This may suggest that the scatters have their origin at the formation epoch of galaxies.Peer reviewe
On the Evolution of and High-Energy Emission from GHz-Peaked-Spectrum Sources
Here we discuss evolution and broad-band emission of compact (< kpc) lobes in
young radio sources. We propose a simple dynamical description for these
objects, consisting of a relativistic jet propagating into a uniform gaseous
medium in the central parts of an elliptical host. In the framework of the
proposed model, we follow the evolution of ultrarelativistic electrons injected
from a terminal hotspot of a jet to expanding lobes, taking into account their
adiabatic energy losses as well as radiative cooling. This allows us to discuss
the broad-band lobe emission of young radio sources. In particular, we argue
that the observed spectral turnover in the radio synchrotron spectra of these
objects cannot originate from the synchrotron self-absorption process but is
most likely due to free-free absorption effects connected with neutral clouds
of interstellar medium engulfed by the expanding lobes and photoionized by
active centers. We also find a relatively strong and complex high-energy
emission component produced by inverse-Compton up-scattering of various
surrounding photon fields by the lobes' electrons. We argue that such high
energy radiation is strong enough to account for several observed properties of
GHz-peaked-spectrum (GPS) radio galaxies at UV and X-ray frequencies. In
addition, this emission is expected to extend up to GeV (or possibly even TeV)
photon energies and can thus be probed by several modern gamma-ray instruments.
In particular, we suggest that GPS radio galaxies should constitute a
relatively numerous class of extragalactic sources detected by GLAST.Comment: 32 pages, 3 figures included. Revised version, accepted for
publication in Ap
A Study of 3CR Radio Galaxies from z = 0.15 to 0.65. II. Evidence for an Evolving Radio Structure
Radio structure parameters were measured from the highest quality radio maps
available for a sample of 3CR radio galaxies in the redshift range 0.15 < z <
0.65. Combined with similar data for quasars in the same redshift range, these
morphology data are used in conjunction with a quantification of the richness
of the cluster environment around these objects (the amplitude of the
galaxy-galaxy spatial covariance function, Bgg) to search for indirect evidence
of a dense intracluster medium (ICM). This is done by searching for confinement
and distortions of the radio structure that are correlated with Bgg.
Correlations between physical size and hot spot placement with Bgg show
evidence for an ICM only at z 0.4,
suggesting an epoch of z ~ 0.4 for the formation of an ICM in these Abell
richness class 0-1, FR2-selected clusters. X-ray selected clusters at
comparable redshifts, which contain FR1 type sources exclusively, are
demonstrably richer than the FR2-selected clusters found in this study. The
majority of the radio sources with high Bgg values at z < 0.4 can be described
as ``fat doubles'' or intermediate FR2/FR1s. The lack of correlation between
Bgg and bending angle or Bgg and lobe length asymmetry suggests that these
types of radio source distortion are caused by something other than interaction
with a dense ICM. Thus, a large bending angle cannot be used as an unambiguous
indicator of a rich cluster around powerful radio sources. These results
support the hypothesis made in Paper 1 that cluster quasars fade to become
FR2s, then FR1s, on a timescale of 0.9 Gyrs (for H0 = 50 km s^-1 Mpc^-1).Comment: 44 pages, 8 figures, 2 tables; to be published in the September 2002
issue of The Astronomical Journa
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