707 research outputs found
Further development of feedback control of cavity flow using experimental based reduced order model
In our recent work we presented preliminary results for subsonic cavity flow control using a reduced-order model based feedback control derived from experimental measurements. The model was developed using the Proper Orthogonal Decomposition of PIV images in conjunction with the Galerkin projection of the Navier-Stokes equations onto the resulting spatial eigenfunctions. A linear-quadratic optimal controller was designed to reduce cavity flow resonance by controlling the time coefficient and tested in the experiments. The stochastic estimation method was used for real-time estimation of the corresponding time coefficients from 4 dynamic surface pressure measurements. The results obtained showed that the controller was capable of reducing the cavity flow resonance at the design Mach 0.3 flow, as well as at other flows with slightly different Mach number. In the present work we present several improvements made to the method. The reduced order model was derived from a larger set of PIV measurements and we used 6 sensors for the stochastic estimation of the instantaneous time coefficients. The reduced order model so obtained shows a better convergence of the time coefficients. This combined with the 6-sensor estimation improves the control performance while using a scaling factor closer to the theoretically expected value. The controller also performed better in off design flow conditions
The importance of knowledge and trust for ethical fashion consumption
Purpose. The clothing industry is one of the most polluting industries in the world, although manufacturers and retailers are trying to revert this tendency by applying ethical fashion principles. Drawing on the knowledge-attitude-behavior (KAB) model or practice, this study aims to predict Chinese consumers' purchase intention of ethical fashion by employing and extending the theory of planned behavior (TPB).
Design/methodology/approach. The extended TPB model incorporates knowledge of ethical fashion and trust in the fashion industry and two critical variables in ethical fashion literature to explain the purchase intention of ethical fashion. Primary data from 245 Chinese respondents were collected in 2019. The model was tested and analyzed through structural equation modeling (SEM).
Findings. Results show that the extended TPB model has higher predictability than the original TPB model. Attitude toward ethical fashion and subjective norm significantly predicts purchase intention while perceived behavioral control (PBC) does not. In addition, trust of ethical fashion is positively related to attitude toward ethical fashion and purchase intention, whereas knowledge of ethical fashion plays a significant role in predicting trust and the three TPB factors. The subjective norm was found to have the most significant impact on consumers' intention to purchase ethical fashion, which shows that social pressure from one individual's reference group is the most dominant factor in forming consumer's purchase intention on ethical fashion.
Originality/value. The findings enrich the past literature on ethical fashion that trusting belief is a salient determinant of consumers' attitude toward ethical fashion and purchase intention of ethical fashion products. The findings also supported the applicability of KAB and TPB in the domain of ethical consumption in the context of a developing country
Bimodal Formation Time Distribution for Infall Dark Matter Halos
We use a 200 h-1Mpc a-side N-body simulation to study the mass accretion history (MAH) of dark matter halos to be accreted by larger halos, which we call infall halos. We define a quantity \u3b1nf 61 (1 + zf) (1 + zpeak) to characterize the MAH of infall halos, where zpeakand zfare the accretion and formation redshifts, respectively. We find that, at given zpeak, their MAH is bimodal. Infall halos are dominated by a young population at high redshift and by an old population at low redshift. For the young population, the anf distribution is narrow and peaks at about 1.2, independent of zpeak, while for the old population, the peak position and width of the \u3b1nfdistribution both increase with decreasing zpeakand are both larger than those of the young population. This bimodal distribution is found to be closely connected to the two phases in the MAHs of halos. While members of the young population are still in the fast accretion phase at zpeak, those of the old population have already entered the slow accretion phase at zpeak. This bimodal distribution is not found for the whole halo population, nor is it seen in halo merger trees generated with the extended Press-Schechter formalism. The infall halo population at zpeakare, on average, younger than the whole halo population of similar masses identified at the same redshift. We discuss the implications of our findings in connection to the bimodal color distribution of observed galaxies and to the link between central and satellite galaxies
Effects of Simulated Nitrogen Deposition on the Bacterial Community of Urban Green Spaces
Continuing nitrogen (N) deposition has a wide-ranging impact on terrestrial ecosystems. To test the hypothesis that, under N deposition, bacterial communities could suffer a negative impact, and in a relatively short timeframe, an experiment was carried out for a year in an urban area featuring a cover of Bermuda grass (Cynodon dactylon) and simulating environmental N deposition. NH4NO3 was added as external N source, with four dosages (N0 = 0 kg N haâ2 yâ1, N1 = 50 kg N haâ2 yâ1, N2 = 100 kg N haâ2 yâ1, N3 = 150 kg N haâ2 yâ1). We analyzed the bacterial community composition after soil DNA extraction through the pyrosequencing of the 16S rRNA gene amplicons. N deposition resulted in soil bacterial community changes at a clear dosage-dependent rate. Soil bacterial diversity and evenness showed a clear trend of time-dependent decline under repeated N application. Ammonium nitrogen enrichment, either directly or in relation to pH decrease, resulted in the main environmental factor related to the shift of taxa proportions within the urban green space soil bacterial community and qualified as a putative important driver of bacterial diversity abatement. Such an impact on soil life induced by N deposition may pose a serious threat to urban soil ecosystem stability and surrounding areas
Signatures of reionization on Lyman alpha emitters
We use a semi-analytic model of Lyman alpha emitters (LAEs) to constrain the
reionization history. By considering two physically motivated scenarios in
which reionization ends either early (ERM, z_i ~ 7) or late (LRM, z_i ~ 6), we
fix the global value of the IGM neutral fraction (e.g. chi_{HI}=3 times
10^{-4}, 0.15 at z=6.56 for the ERM and LRM, respectively) leaving only the
star formation efficiency and the effective escape fraction of Lya photons as
free parameters. The ERM fits the observed LAE luminosity function (LF) at
z=5.7 and 6.56 requiring no redshift evolution or mass dependence of the star
formation efficiency, and LAE star formation rates (SFR) of 3-103 solar
masses/year, contributing approximately 8% of the cosmic SFR density at z=5.7.
The LRM requires a physically uncomfortable drop of approximately 4.5 times in
the SFR of the emitters from z=6.5 to 5.7. Thus, the data seem to imply that
the Universe was already highly ionized at z=6.56. The mass-dependent Lya
transmissivity is between 0.36-0.51 (ERM) and less than 0.26 (LRM) at z=6.56.
The LF data at z=4.5 imply an extra Lya line damping factor of approximately
0.25 possibly due to dust; the presence of a (clumpy) dust component with
E(B-V) ~ 0.28 is also required to reproduce the observed large Lya equivalent
widths at the same redshift. Additional useful information can be extracted
from the line profile (weighted) skewness, found to be S_W=10-17 Angstrom for
the two reionization models, which shows an interesting L_alpha-chi_{HI}
anti-correlation, holding under the model assumptions. The shortcomings of the
model and strategies to overcome them are discussed.Comment: 15 pages, 10 figures, Accepted to MNRA
Towards a Concordant Model of Halo Occupation Statistics
We use the conditional luminosity function (CLF) and data from the 2dFGRS to
constrain the average relation between light and mass in a LCDM cosmology with
Omega_m=0.23 and sigma_8=0.74 (hereafter WMAP3 cosmology). Reproducing the
observed luminosity dependence of the galaxy two-point correlation function
results in average mass-to-light ratios that are about 35 percent lower than in
a LCDM cosmology with Omega_m=0.3 and sigma_8=0.9 (hereafter WMAP1 cosmology).
This removes an important problem with previous halo occupation models which
had a tendency to predict cluster mass-to-light ratios that were too high. For
the WMAP3 cosmology our model yields average mass-to-light ratios, central
galaxy luminosities, halo occupation numbers, satellite fractions, and
luminosity-gap statistics, that are all in excellent agreement with those
obtained from a 2dFGRS group catalogue and from other independent studies. We
also use our CLF model to compute the probability distribution P(M|L_cen), that
a central galaxy of luminosity L_cen resides in a halo of mass M. We find this
distribution to be much broader than what is typically assumed in HOD models,
which has important implications for the interpretation of galaxy-galaxy
lensing data. Finally, reproducing the luminosity dependence of the pairwise
velocity dispersions in the 2dFGRS requires relatively low mass-to-light ratios
for clusters and a satellite fraction that decreases strongly with increasing
luminosity. This is only marginally consistent with our CLF constraints. We
argue that a cosmology with parameters between those of the WMAP1 and WMAP3
cosmologies is likely to yield results with a higher level of consistency.Comment: 23 pages, 11 figures. Submitted for publication in MNRA
Limits on Dust and Metallicity Evolution of Lya Forest Clouds from COBE
We consider possible observational consequences of dust and metals in \lya
forest clouds. We relate the dust content, , to the metal
evolution of the absorbers and assume that dust is heated by the ultraviolet
background radiation and by the CMB. We find that the dust temperature deviates
from by at most 10% at redshift . The \lya cloud dust opacity to
redshift sources around the observed wavelength m is , and could affect observations of the distant universe in
that band. The expected CMB spectral distortions due to high- dust in \lya
clouds is smaller than the current COBE upper limit, depending
on the metallicity evolution of the clouds. If \lya clouds are clustered, the
corresponding CMB anisotropy due to dust is on angular scales
\theta \simlt 10'' at frequencies probed by various future/ongoing FIR
missions, which makes these fluctuations potentially detectable in the near
future. Emission from CII fine-structure transitions could considerably
contribute to submm range of the FIR background radiation. Depending on the
ionization of carbon and on the density of metal enriched regions, this
contribution can be comparable with the observed residual flux at
mm, after CMB subtraction. We argue that constraints on
metal evolution versus redshift can be obtained from the observed flux in that
range.Comment: 8 pages, 3 figures, MNRAS, in pres
The Asiago-ESO/RASS QSO Survey. III. Clustering analysis and its theoretical interpretation
This is the third paper of a series describing the Asiago-ESO/RASS QSO survey
(AERQS), a project aimed at the construction of an all-sky statistically
well-defined sample of relatively bright QSOs (B<15) at z<0.3. We present here
the clustering analysis of the full spectroscopically identified database (392
AGN). The clustering signal at 0.02<z<0.22 is detected at a 3-4 sigma level and
its amplitude is measured to be r_0=8.6\pm 2.0 h^{-1} Mpc (in a LambdaCDM
model). The comparison with other classes of objects shows that low-redshift
QSOs are clustered in a similar way to Radio Galaxies, EROs and early-type
galaxies in general, although with a marginally smaller amplitude. The
comparison with recent results from the 2QZ shows that the correlation function
of QSOs is constant in redshift or marginally increasing toward low redshift.
We discuss this behavior with physically motivated models, deriving interesting
constraints on the typical mass of the dark matter halos hosting QSOs, M_DMH=
10^{12.7} h^{-1} M_sun (10^{12.0}-10^{13.5}h^{-1} M_sun at 1 sigma confidence
level). Finally, we use the clustering data to infer the physical properties of
local AGN, obtaining M_BH=2 10^8 h^{-1} M_sun (10^7-3 10^9 h^{-1} M_sun) for
the mass of the active black holes, tau_{AGN}= 8 10^6 yr (2 10^{6}-5 10^{7} yr)
for their life-time and eta = 0.14 for their efficiency (always for a LambdaCDM
model).Comment: 37 pages, Astronomical Journal in press. Changes to match the referee
comment
Towards a concordant model of halo occupation statistics
We use the conditional luminosity function (CLF) and data from the 2-degree Field Galaxy Redshift Survey (2dFGRS) to constrain the average relation between light and mass in a Lambda cold dark matter (ÎCDM) cosmology with Ωm= 0.23 and Ï8= 0.74 (hereafter WMAP3 cosmology). Reproducing the observed luminosity dependence of the galaxy two-point correlation function results in average mass-to-light ratios that are âŒ35 per cent lower than those in a ÎCDM cosmology with Ωm= 0.3 and Ï8= 0.9 (hereafter WMAP1 cosmology). This removes an important problem with previous halo occupation models which had a tendency to predict cluster mass-to-light ratios that were too high. For the WMAP3 cosmology, our model yields average mass-to-light ratios, central galaxy luminosities, halo occupation numbers, satellite fractions and luminosity-gap statistics, that are all in excellent agreement with those obtained from a 2dFGRS group catalogue and from other independent studies. We also use our CLF model to compute the probability distribution P(Mâ|âLcen), that a central galaxy of luminosity Lcen resides in a halo of mass M. We find this distribution to be much broader than what is typically assumed in halo occupation distribution models, which has important implications for the interpretation of satellite kinematics and galaxy-galaxy lensing data. Finally, reproducing the luminosity dependence of the pairwise peculiar velocity dispersions in the 2dFGRS requires relatively low mass-to-light ratios for clusters and a satellite fraction that decreases strongly with increasing luminosity. This is only marginally consistent with the constraints obtained from the luminosity dependence of the galaxy two-point correlation function. We argue that a cosmology with parameters between those of the WMAP1 and WMAP3 cosmologies is likely to yield results with a higher level of consistenc
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