1,992 research outputs found
Radio Wavelength Constraints on the Sources of the Far Infrared Background
The cosmic far infrared background detected recently by the COBE-DIRBE team
is presumably due, in large part, to the far infrared (FIR) emission from all
galaxies. We take the well-established correlation between FIR and radio
luminosity for individual galaxies and apply it to the FIR background. We find
that these sources make up about half of the extragalactic radio background,
the other half being due to AGN. This is in agreement with other radio
observations, which leads us to conclude that the FIR-radio correlation holds
well for the very faint sources making up the FIR background, and that the FIR
background is indeed due to star-formation activity (not AGN or other possible
sources). If these star-forming galaxies have a radio spectral index between
0.4 and 0.8, and make up 40 to 60% of the extragalactic radio background, we
find that they have redshifts between roughly 1 and 2, in agreement with recent
estimates by Madau et al. of the redshift of peak star-formation activity. We
compare the observed extragalactic radio background to the integral over the
logN-logS curve for star-forming radio sources, and find that the slope of the
curve must change significantly below about 1 microjansky. At 1 microjansky,
the faint radio source counts predict about 25 sources per square arcminute,
and these will cause SIRTF to be confusion limited at 160micron.Comment: 10 pages including 1 figure, AASTeX, accepted by Ap
Pemanfaatan Limbah Alkali Industri Rumput Laut Dan Limbah Pickling Industri Pelapisan Logam Sebagai Pupuk Anorganik
Limbah cair dari industri rumput laut (Eucheuma cottoni) yang dalam proses pengolahannya menggunakan Kalium Hidroksida (KOH) mempunyai kandungan Kalium. Sedangkan dari proses pickling di industri lapis listrik dihasilkan limbah cair sekitar 2 m3 untuk setiap 1000 m2 benda yang dilapis. Limbah cair ini mengandung FeCl2/FeCl3, jika tidak dikelola dengan baik akan menyebabkan pencemaran lingkungan. Dengan dimanfaatkannya secara bersama limbah pickling dan limbah cair dari rumput laut, maka lingkungan akan tetap terjaga.Tujuan penelitian ini adalah memanfaatkan limbah cair dari industri rumputlaut dan limbah cair dari proses pickling di industri elektroplating untuk pembuatan pupuk Anorganik sebagai salah satu upaya pengelolaan lingkungan.Keluaran dari kegiatan ini adalah penanganan limbah secara integrasi dari limbah cair industri rumput laut dan proses pickling yang dapat dimanfaatkan sebagai pupuk. Limbah cair dari industri rumput laut dapat dimanfaatkan secara bersama dengan limbah cair dari proses pickling di industri electroplating untuk dijadikan pupuk buatan yang memenuhi persyaratan Pupuk KCl yang mengacu pada SNI 02 – 2805:2005. Kadar kalium sebagai K2O dari hasil pengolahan limbah cair industri rumput laut tersebut berkisar antara 0,08 - 0,12 % (800 – 1200 ppm) nilai tersebut lebih tinggi dari pada nilai standard sesuai SNI 02 – 2805: 2005 sebesar 600 ppm
The Variability of Seyfert 1.8 and 1.9 Galaxies at 1.6 microns
We present a study of Seyfert 1.5-2.0 galaxies observed at two epochs with
the Hubble Space Telescope (HST) at 1.6 microns. We find that unresolved
nuclear emission from 9 of 14 nuclei varies at the level of 10-40% on
timescales of 0.7-14 months, depending upon the galaxy. A control sample of
Seyfert galaxies lacking unresolved sources and galaxies lacking Seyfert nuclei
show less than 3% instrumental variation in equivalent aperture measurements.
This proves that the unresolved sources are non-stellar and associated with the
central pc of active galactic nuclei. Unresolved sources in Seyfert 1.8 and 1.9
galaxies are not usually detected in HST optical surveys, however high angular
resolution infrared observations will provide a way to measure time delays in
these galaxies.Comment: accepted by ApJLetters (emulateapj latex
The 1<z<5 Infrared Luminosity Function of Type I Quasars
We determine the rest-frame 8 micron luminosity function of type I quasars
over the redshift range 1<z<5. Our sample consists of 292 24 micron sources
brighter than 1 mJy selected from 7.17 square degrees of the Spitzer Space
Telescope MIPS survey of the NOAO Deep Wide-Field Survey Bootes field. The AGN
and Galaxy Evolution Survey (AGES) has measured redshifts for 270 of the R<21.7
sources and we estimate that the contamination of the remaining 22 sources by
stars and galaxies is low. We are able to select quasars missed by ultra-violet
excess quasar surveys, including reddened type I quasars and 2.2<z<3.0 quasars
with optical colors similar to main sequence stars. We find reddened type I
quasars comprise 20% of the type I quasar population. Nonetheless, the shape,
normalization, and evolution of the rest-frame 8 micron luminosity function is
comparable to that of quasars selected from optical surveys. The 8 micron
luminosity function of type I quasars is well approximated by a power-law with
index -2.75(+/-0.14). We directly measure the peak of the quasar space density
to be at z=2.6(+/-0.3).Comment: Accepted for publication in the ApJ, 19 pages, 12 figure
LBT and Spitzer Spectroscopy of Star-Forming Galaxies at 1 < z < 3: Extinction and Star Formation Rate Indicators
We present spectroscopic observations in the rest-frame optical and near- to
mid-infrared wavelengths of four gravitationally lensed infrared (IR) luminous
star-forming galaxies at redshift 1 < z < 3 from the LUCIFER instrument on the
Large Binocular Telescope and the Infrared Spectrograph on Spitzer. The sample
was selected to represent pure, actively star-forming systems, absent of active
galactic nuclei. The large lensing magnifications result in high
signal-to-noise spectra that can probe faint IR recombination lines, including
Pa-alpha and Br-alpha at high redshifts. The sample was augmented by three
lensed galaxies with similar suites of unpublished data and observations from
the literature, resulting in the final sample of seven galaxies. We use the IR
recombination lines in conjunction with H-alpha observations to probe the
extinction, Av, of these systems, as well as testing star formation rate (SFR)
indicators against the SFR measured by fitting spectral energy distributions to
far-IR photometry. Our galaxies occupy a range of Av from ~0 to 5.9 mag, larger
than previously known for a similar range of IR luminosities at these
redshifts. Thus, estimates of SFR even at z ~ 2 must take careful count of
extinction in the most IR luminous galaxies. We also measure extinction by
comparing SFR estimates from optical emission lines with those from far-IR
measurements. The comparison of results from these two independent methods
indicates a large variety of dust distribution scenarios at 1 < z < 3. Without
correcting for dust extinction, the H-alpha SFR indicator underestimates the
SFR; the size of the necessary correction depends on the IR luminosity and dust
distribution scenario. Individual SFR estimates based on the 6.2 micron PAH
emission line luminosity do not show a systematic discrepancy with extinction,
although a considerable, ~0.2 dex scatter is observed.Comment: Accepted for publication in The Astrophysical Journal; 14 pages, 8
figure
The Initial Mass Function of Low-Mass Stars and Brown Dwarfs in Young Clusters
We have obtained images of the Trapezium Cluster (140" x 140"; 0.3 pc x 0.3
pc) with the Hubble Space Telescope Near-Infrared Camera and Multi-Object
Spectrometer (NICMOS). Combining these data with new ground-based K-band
spectra (R=800) and existing spectral types and photometry and the models of
D'Antona & Mazzitelli, we find that the distributions of ages of comparable
samples of stars in the Trapezium, rho Oph, and IC 348 indicate median ages of
\~0.4 Myr for the first two regions and ~1-2 Myr for the latter. The low-mass
IMFs in these sites of clustered star formation are similar over a wide range
of stellar densities and other environmental conditions. With current data, we
cannot rule out modest variations in the substellar mass functions among these
clusters. We then make the best estimate of the true form of the IMF in the
Trapezium by using the evolutionary models of Baraffe et al. and an empirically
adjusted temperature scale and compare this mass function to recent results for
the Pleiades and the field. All of these data are consistent with an IMF that
is flat or rises slowly from the substellar regime to about 0.6 Msun, and then
rolls over into a power law that continues from about 1 Msun to higher masses
with a slope similar to or somewhat larger than the Salpeter value of 1.35. For
the Trapezium, this behavior holds from our completeness limit of ~0.02 Msun
and probably, after a modest completeness correction, even from 0.01-0.02 Msun.
These data include ~50 likely brown dwarfs. We test the predictions of theories
of the IMF against various properties of the observed IMF.Comment: 34 pages, 13 figures, for color image see
http://cfa-www.harvard.edu/~kluhman/trap/colorimage.jp
Optimizing information flow in small genetic networks. I
In order to survive, reproduce and (in multicellular organisms)
differentiate, cells must control the concentrations of the myriad different
proteins that are encoded in the genome. The precision of this control is
limited by the inevitable randomness of individual molecular events. Here we
explore how cells can maximize their control power in the presence of these
physical limits; formally, we solve the theoretical problem of maximizing the
information transferred from inputs to outputs when the number of available
molecules is held fixed. We start with the simplest version of the problem, in
which a single transcription factor protein controls the readout of one or more
genes by binding to DNA. We further simplify by assuming that this regulatory
network operates in steady state, that the noise is small relative to the
available dynamic range, and that the target genes do not interact. Even in
this simple limit, we find a surprisingly rich set of optimal solutions.
Importantly, for each locally optimal regulatory network, all parameters are
determined once the physical constraints on the number of available molecules
are specified. Although we are solving an over--simplified version of the
problem facing real cells, we see parallels between the structure of these
optimal solutions and the behavior of actual genetic regulatory networks.
Subsequent papers will discuss more complete versions of the problem
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