1,133 research outputs found
Direct upgrading of fast pyrolysis lignin vapor over the HZSM-5 catalyst
Continuous fast pyrolysis of lignin and direct upgrading of pyrolysis vapor by the HZSM-5 catalyst produce renewable aromatics.</p
Identification of two bright z>3 submillimeter galaxy candidates in the COSMOS field
We present high-resolution interferometric Submillimeter Array (SMA) imaging
at 890 microns (~2" resolution) of two millimeter selected galaxies --
MMJ100015+021549 and MMJ100047+021021 -- discovered with the Max-Planck
Millimeter Bolometer (MAMBO) on the IRAM 30 m telescope and also detected with
Bolocam on the CSO, in the COSMOS field. The first source is significantly
detected at the ~11 sigma level, while the second source is tentatively
detected at the ~4 sigma level, leading to a positional accuracy of ~0.2-0.3".
MM100015+021549 is identified with a faint radio and K-band source.
MMJ100047+021021 shows no radio emission and is tentatively identified with a
very faint K-band peak which lies at ~1.2" from a clumpy optical source. The
submillimeter-to-radio flux ratio for MM100015+021549 yields a redshift of
~4.8, consistent with the redshift implied by the UV-to-submillimeter
photometry, z~3.0-5.0. We find evidence for warm dust in this source with an
infrared luminosity in the range ~0.9-2.5x10^{13} L_sun, supporting the
increasing evidence for a population luminous submillimeter galaxies at z>3.
Finally, the lack of photometric data for MMJ100047+021021 does not allow us to
investigate its properties in detail, however its submillimeter-to-radio ratio
implies z>3.5.Comment: Accepted for publication in ApJ letter
Children's exposure to environmental pollutants and biomarkers of genetic damage. I. Overview and critical issues.
In the last decade, molecular epidemiological studies have provided new perspectives on studying environmental risks in
pediatric populations, based on the growing understanding that children may be more susceptible to toxicants than adults.
Protecting children’s health is a social priority, and specific research programs have been initiated with this purpose in the United States and Europe. These programs address the development of (i) less invasive methods for biological specimens collection, (ii) specific tools for interpretation and validation of biomarkers, (iii) methods for translating biomarker results into intervention strategies and for integrating them with environmental monitoring and health data, (iv) optimal ways to obtain consent and provide information to children and/or their parents participating in the studies and (v) techniques for the effective communication with policy makers and the public. Critical issues in children’s environmental research discussed in this paper include specific needs of study design, exposure assessment, sample collection and ethics. Special consideration is given to the autonomy of the child in giving consent, the details and nature of the information provided, and the need to warrant controlled access to sensitive information. The use of incentives such as gifts and payment to ensure the participation of school-aged children is specifically discussed. Examples of field studies that are focused on the effects of pesticides, air pollution and
formaldehyde are used to illustrate advantages and limitations of biomarker studies in children
Classic and spatial shift-share analysis of state-level employment change in Brazil
This paper combines classic and spatial shift-share decompositions of 1981 to 2006 employment change across the 27 states of Brazil. The classic shift-share method shows higher employment growth rates for underdeveloped regions that are due to an advantageous industry-mix and also due to additional job creation, commonly referred to as the competitive effect. Alternative decompositions proposed in the literature do not change this broad conclusion. Further examination employing exploratory spatial data analysis (ESDA) shows spatial correlation of both the industry-mix and the competitive effects. Considering that until the 1960s economic activities were more concentrated in southern regions of Brazil than they are nowadays, these results support beta convergence theories but also find evidence of agglomeration effects. Additionally, a very simple spatial decomposition is proposed that accounts for the spatially-weighted growth of surrounding states. Favourable growth in northern and centre-western states is basically associated with those states’ strengths in potential spatial spillover effect and in spatial competitive effect
Modeling the evolution of infrared galaxies: A Parametric backwards evolution model
We aim at modeling the infrared galaxy evolution in an as simple as possible
way and reproduce statistical properties among which the number counts between
15 microns and 1.1 mm, the luminosity functions, and the redshift
distributions. We then aim at using this model to interpret the recent
observations (Spitzer, Akari, BLAST, LABOCA, AzTEC, SPT and Herschel), and make
predictions for future experiments like CCAT or SPICA.
This model uses an evolution in density and luminosity of the luminosity
function with two breaks at redshift ~0.9 and 2 and contains the two
populations of the Lagache et al. (2004) model: normal and starburst galaxies.
We also take into account the effect of the strong lensing of high-redshift
sub-millimeter galaxies. It has 13 free parameters and 8 additional calibration
parameters. We fit the parameters to the IRAS, Spitzer, Herschel and AzTEC
measurements with a Monte-Carlo Markov chain.
The model ajusted on deep counts at key wavelengths reproduces the counts
from the mid-infrared to the millimeter wavelengths, as well as the
mid-infrared luminosity functions. We discuss the contribution to the cosmic
infrared background (CIB) and to the infrared luminosity density of the
different populations. We also estimate the effect of the lensing on the number
counts, and discuss the recent discovery by the South Pole Telescope (SPT) of a
very bright population lying at high-redshift. We predict confusion level for
future missions using a P(D) formalism, and the Universe opacity to TeV photons
due to the CIB.Comment: 25 pages, 10 tables, 18 figures, accepted for publication in A&
Genesis of the dusty Universe: modeling submillimetre source counts
We model the evolution of IR galaxies using a phenomenological approach to
match the observed source counts at different IR wavelengths. We introduce a
new algorithm for reproducing source counts based on direct integration of
probability distributions rather than Monte-Carlo sampling. We construct a
simple model for the evolution of the luminosity function and the colour
distribution of IR galaxies which utilizes a minimum number of free parameters.
Moreover we analyze how each of these parameters is constrained by
observational data. The model is based on pure luminosity evolution and adopts
the Dale & Helou SED templates. We find that the 850um source counts and their
redshift distribution depend strongly on the shape of the luminosity evolution
function, but only weakly on the details of the SEDs. We derive the best-fit
evolutionary model using the 850um counts and redshift distribution as
constraints. Moreover our best-fit shows a flattening of the faint end of the
luminosity function towards high redshifts and requires a colour evolution
which implies the typical dust temperatures of objects with the same
luminosities to decrease with redshift. We compare our best-fit model to
observed source counts at shorter and longer wavelengths which indicates our
model reproduces the 70um and 1100um source counts remarkably well, but
under-produces the counts at intermediate wavelengths. Analysis reveals that
the discrepancy arises at low redshifts, indicating that revision of the
adopted SED library towards lower dust temperatures (at a fixed infrared
luminosity) is required. This modification is equivalent to a population of
cold galaxies existing at low redshifts, as also indicated by recent Herschel
results, which are underrepresented in IRAS sample. We show that the modified
model successfully reproduces the source counts in a wide range of IR and submm
wavelengths.Comment: 21 pages, 11 figures, 2 tables. Accepted for publication in MNRAS.
Supplementary information could be found at
http://www.strw.leidenuniv.nl/genesis
The Far-Infrared--Radio Correlation at High Redshifts: Physical Considerations and Prospects for the Square Kilometer Array
(Abridged) I present a predictive analysis for the behavior of the FIR--radio
correlation as a function of redshift in light of the deep radio continuum
surveys which may become possible using the SKA. To keep a fixed ratio between
the FIR and predominantly non-thermal radio continuum emission of a normal
star-forming galaxy requires a nearly constant ratio between galaxy magnetic
field and radiation field energy densities. While the additional term of IC
losses off of the cosmic microwave background (CMB) is negligible in the local
Universe, the rapid increase in the strength of the CMB energy density (i.e.
suggests that evolution in the FIR-radio correlation should
occur with infrared (IR; 8-1000 \micron)/radio ratios increasing with
redshift. At present, observations do not show such a trend with redshift;
radio-quiet QSOs appear to lie on the local FIR-radio correlation
while a sample of and SMGs exhibit ratios that are a
factor of 2.5 {\it below} the canonical value. I also derive a 5
point-source sensitivity goal of 20 nJy (i.e. nJy) requiring that the SKA specified be m K; achieving this sensitivity should enable the detection
of galaxies forming stars at a rate of \ga25 M_{\sun} {\rm yr}^{-1}, at all
redshifts if present. By taking advantage of the fact that the non-thermal
component of a galaxy's radio continuum emission will be quickly suppressed by
IC losses off of the CMB, leaving only the thermal (free-free) component, I
argue that deep radio continuum surveys at frequencies \ga10 GHz may prove to
be the best probe for characterizing the high- star formation history of the
Universe unbiased by dust.Comment: 16 pages, 8 figures, accepted for publication in Ap
A backward evolution model for infrared surveys: the role of AGN- and Color-L_TIR distributions
Empirical "backward" galaxy evolution models for infrared bright galaxies are
constrained using multi-band infrared surveys. We developed a new Monte-Carlo
algorithm for this task, implementing luminosity dependent distribution
functions for the galaxies' infrared spectral energy distributions (SEDs) and
for the AGN contribution, allowing for evolution of these quantities. The
adopted SEDs take into account the contributions of both starbursts and AGN to
the infrared emission, for the first time in a coherent treatment rather than
invoking separate AGN and star-forming populations. In the first part of the
paper we consider the quantification of the AGN contribution for local universe
galaxies, as a function of total infrared luminosity. It is made using a large
sample of LIRGs and ULIRGs for which mid-infrared spectra are available in the
Spitzer archive. In the second part we present the model. Our best-fit model
adopts very strong luminosity evolution, , up to , and
density evolution, , up to , for the population of
infrared galaxies. At higher , the evolution rates drop as and
respectively. To reproduce mid-infrared to submillimeter number
counts and redshift distributions, it is necessary to introduce both an
evolution in the AGN contribution and an evolution in the
luminosity-temperature relation. Our models are in plausible agreement with
current photometry-based estimates of the typical AGN contribution as a
function of mid-infrared flux, and well placed to be compared to upcoming
Spitzer spectroscopic results. As an example of future applications, we use our
best-fitting model to make predictions for surveys with Herschel.Comment: Model available at: (http://www.physics.ubc.ca/~valiante/model) ApJ
accepte
On the evolution of clustering of 24um-selected galaxies
This paper investigates the clustering properties of a complete sample of
1041 24um-selected sources brighter than F[24um]=400 uJy in the overlapping
region between the SWIRE and UKIDSS UDS surveys. We have concentrated on the
two (photometric) interval ranges z=[0.6-1.2] (low-z sample) and z>1.6 (high-z
sample) as it is in these regions were we expect the mid-IR population to be
dominated by intense dust-enshrouded activity such as star formation and black
hole accretion. Investigations of the angular correlation function produce a
correlation length are r0~15.9 Mpc for the high-z sample and r0~8.5 Mpc for the
low-z one. Comparisons with physical models reveal that the high-z sources are
exclusively associated with very massive (M>~10^{13} M_sun)haloes, comparable
to those which locally host groups-to-clusters of galaxies, and are very common
within such (rare) structures. Conversely, lower-z galaxies are found to reside
in smaller halos (M_min~10^{12} M_sun) and to be very rare in such systems.
While recent studies have determined a strong evolution of the 24um luminosity
function between z~2 and z~0, they cannot provide information on the physical
nature of such an evolution. Our clustering results instead indicate that this
is due to the presence of different populations of objects inhabiting different
structures, as active systems at z<~1.5 are found to be exclusively associated
with low-mass galaxies, while very massive sources appear to have concluded
their active phase before this epoch. Finally, we note that the small-scale
clustering data seem to require steep profiles for the distribution of galaxies
within their halos. This is suggestive of close encounters and/or mergers which
could strongly favour both AGN and star-formation activity.Comment: 13 pages, 8 figures, to appear in MNRA
A Census of the High-Density Molecular Gas in M82
We present a three-pointing study of the molecular gas in the starburst
nucleus of M82 based on 190 - 307 GHz spectra obtained with Z-Spec at the
Caltech Submillimeter Observatory. We present intensity measurements,
detections and upper limits, for 20 transitions, including several new
detections of CS, HNC, C2H, H2CO, and CH3CCH lines. We combine our measurements
with previously-published measurements at other frequencies for HCN, HNC, CS,
C34S, and HCO+ in a multi-species likelihood analysis constraining gas mass,
density and temperature, and the species' relative abundances. We find some 1.7
- 2.7 x 10^8 M_sun of gas with n_H2 between 1 - 6 x 10^4 cm^-3 and T > 50 K.
While the mass and temperature are comparable to values inferred from mid-J CO
transitions, the thermal pressure is a factor of 10 - 20 greater. The molecular
interstellar medium is largely fragmented and is subject to ultraviolet
irradiation from the star clusters. It is also likely subject to cosmic rays
and mechanical energy input from the supernovae, and is warmer on average than
the molecular gas in the massive star formation regions in the Milky Way. The
typical conditions in the dense gas in M82's central kpc appear unfavorable for
further star formation; if any appreciable stellar populations are currently
forming, they are likely biased against low mass stars, producing a top-heavy
initial mass function.Comment: 15 pages (using emulateapj.cls), 6 figures, Astrophysical Journal, in
pres
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