17,632 research outputs found
Application of vascular aquatic plants for pollution removal, energy and food production in a biological system
Vascular aquatic plants such as water hyacinths (Eichhornia crassipes) (Mart.) Solms and alligator weeds (Alternanthera philoxeroides) (Mart.) Griesb., when utilized in a controlled biological system (including a regular program of harvesting to achieve maximum growth and pollution removal efficiency), may represent a remarkably efficient and inexpensive filtration and disposal system for toxic materials and sewage released into waters near urban and industrial areas. The harvested and processed plant materials are sources of energy, fertilizer, animal feed, and human food. Such a system has industrial, municipal, and agricultural applications
Temperature effects on the 15-85-micron spectra of olivines and pyroxenes
Far-infrared spectra of laboratory silicates are normally obtained at room
temperature even though the grains responsible for astronomical silicate
emission bands seen at wavelengths >20 micron are likely to be at temperatures
below ~150 K. In order to investigate the effect of temperature on silicate
spectra, we have obtained absorption spectra of powdered forsterite and
olivine, along with two orthoenstatites and diopside clinopyroxene, at 3.5+-0.5
K and at room temperature (295+-2K). To determine the changes in the spectra
the resolution must be increased from 1 to 0.25 cm^-1 at both temperatures
since a reduction in temperature reduces the phonon density, thereby reducing
the width of the infrared peaks. Several bands observed at 295 K split at 3.5
K. At 3.5 K the widths of isolated single bands in olivine, enstatites and
diopside are ~ 90% of their 295 K-widths. However, in forsterite the
3.5-K-widths of the 31-, 49- and 69-micron bands are, respectively, 90%, 45%
and 31% of their 295 K widths. Due to an increase in phonon energy as the
lattice contracts, 3.5-K-singlet peaks occur at shorter wavelengths than do the
corresponding 295-K peaks; the magnitude of the wavelength shift increases from
\~ 0-0.2 micron at 25 micron to ~0.9 micron at 80 micron. Changes in the
relative absorbances of spectral peaks are also observed. The temperature
dependence of lambda_pk and bandwidth shows promise as a means to deduce
characteristic temperatures of mineralogically distinct grain populations. In
addition, the observed changes in band strength with temperature will affect
estimates of grain masses and relative mineral abundances inferred using
room-temperature laboratory data.Comment: 11 pages, 7 figures including figures 3a and 3b. includes latex and
eps files. Accepted by MNRAS on 15th March 200
Optimizing information flow in small genetic networks. II: Feed forward interactions
Central to the functioning of a living cell is its ability to control the
readout or expression of information encoded in the genome. In many cases, a
single transcription factor protein activates or represses the expression of
many genes. As the concentration of the transcription factor varies, the target
genes thus undergo correlated changes, and this redundancy limits the ability
of the cell to transmit information about input signals. We explore how
interactions among the target genes can reduce this redundancy and optimize
information transmission. Our discussion builds on recent work [Tkacik et al,
Phys Rev E 80, 031920 (2009)], and there are connections to much earlier work
on the role of lateral inhibition in enhancing the efficiency of information
transmission in neural circuits; for simplicity we consider here the case where
the interactions have a feed forward structure, with no loops. Even with this
limitation, the networks that optimize information transmission have a
structure reminiscent of the networks found in real biological systems
Variability Tests for Intrinsic Absorption Lines in Quasar Spectra
Quasar spectra have a variety of absorption lines whose origins range from
energetic winds expelled from the central engines to unrelated, intergalactic
clouds. We present multi-epoch, medium resolution spectra of eight quasars at
z~2 that have narrow ``associated'' absorption lines (AALs, within 5000 km
s^{-1} of the emission redshift). Two of these quasars were also known
previously to have high-velocity mini-broad absorption lines (mini-BALs). We
use these data, spanning ~17 years in the observed frame with two to four
observations per object, to search for line strength variations as an
identifier of absorption that occurs physically near (``intrinsic'' to) the
central AGN.
Our main results are the following: Two out of the eight quasars with narrow
AALs exhibit variable AAL strengths. Two out of two quasars with high-velocity
mini-BALs exhibit variable mini-BAL strengths. We also marginally detect
variability in a high-velocity narrow absorption line (NAL) system, blueshifted
\~32,900 km s^{-1}$ with respect to the emission lines. No other absorption
lines in these quasars appeared to vary. The outflow velocities of the variable
AALs are 3140 km s^{-1} and 1490 km s^{-1}. The two mini-BALs identify much
higher velocity outflows of ~28,400 km s^{-1} and ~52,000 km s^{-1}. Our
temporal sampling yields upper limits on the variation time scales from 0.28 to
6.1 years in the quasar rest frames. The corresponding minimum electron
densities in the variable absorbers, based on the recombination time scale, are
\~40,000 cm^{-3} to ~1900 cm^{-3}. The maximum distances of the absorbers from
the continuum source, assuming photoionization with no spectral shielding,
range from ~1.8 kpc to ~7 kpc.Comment: 16 pages, 4 figures, ApJ, accepte
Variability in Quasar Broad Absorption Line Outflows I. Trends in the Short-Term versus Long-Term Data
Broad absorption lines (BALs) in quasar spectra identify high velocity
outflows that likely exist in all quasars and could play a major role in
feedback to galaxy evolution. The variability of BALs can help us understand
the structure, evolution, and basic physical properties of the outflows. Here
we report on our first results from an ongoing BAL monitoring campaign of a
sample of 24 luminous quasars at redshifts 1.2<z<2.9, focusing on C IV 1549 BAL
variability in two different time intervals: 4 to 9 months (short-term) and 3.8
to 7.7 years (long-term) in the quasar rest-frame. We find that 39% (7/18) of
the quasars varied in the short-term, whereas 65% (15/23) varied in the
long-term, with a larger typical change in strength in the long-term data. The
variability occurs typically in only portions of the BAL troughs. The
components at higher outflow velocities are more likely to vary than those at
lower velocities, and weaker BALs are more likely to vary than stronger BALs.
The fractional change in BAL strength correlates inversely with the strength of
the BAL feature, but does not correlate with the outflow velocity. Both the
short-term and long-term data indicate the same trends. The observed behavior
is most readily understood as a result of the movement of clouds across the
continuum source. If the crossing speeds do not exceed the local Keplerian
velocity, then the observed short-term variations imply that the absorbers are
<6 pc from the central quasar.Comment: 14 pages, 7 figures, accepted for publication in MNRA
Atomic and molecular interstellar absorption lines toward the high galactic latitude stars HD~141569 and HD~157841 at ultra-high resolution
We present ultra-high resolution (0.32 km/s) spectra obtained with the 3.9m
Anglo-Australian Telescope (AAT) and Ultra-High-Resolution Facility (UHRF), of
interstellar NaI D1, D2, Ca II K, K I and CH absorption toward two high
galactic latitude stars HD141569 and HD157841. We have compared our data with
21-cm observations obtained from the Leiden/Dwingeloo HI survey. We derive the
velocity structure, column densities of the clouds represented by the various
components and identify the clouds with ISM structures seen in the region at
other wavelengths. We further derive abundances, linear depletions and H2
fractional abundances for these clouds, wherever possible. Toward HD141569, we
detect two components in our UHRF spectra : a weak, broad component at - 15
km/s, seen only in CaII K absorption and another component at 0 km/s, seen in
NaI D1, D2, Ca II K, KI and CH absorption. In the case of the HD157841
sightline, a total of 6 components are seen on our UHRF spectra in NaI D1, D2
Ca II K, K I and CH absorption. 2 of these 6 components are seen only in a
single species.Comment: 16 pages, Latex, 4 figures, ps files Astrophysical Journal (in press
SwSt 1: an O-rich planetary nebula around a C-rich central star
The hydrogen-deficient carbon-rich [WCL] type central star HD167362 and its
oxygen-rich planetary nebula (PN) SwSt~1 are investigated. The nebular
chemistry might indicate a recent origin for the carbon-rich stellar spectrum.
Its stellar and nebular properties might therefore provide further
understanding of the origin of the [WCL] central star class. The UV-IR stellar
spectra are modelled with state of the codes and show ~40kK central star with a
wind and a C/O~3, indicative of efficient third dredge-up. The synthetic
stellar flux distribution is used to model the high density, compact PN, which
has a solar C/O ratio, is still enshrouded by 1200K and 230K dust shells and,
reported here for the first time, in molecular hydrogen. Although it appears
that the change in C/O ratio has been recent, the published spectroscopy since
1895 has been re-examined and no clear spectral change is seen. If an event
occurred that has turned it into a hydrogen-deficient central star, it did not
happen in the last 100 years.Comment: 31 pages, 19 figures (some are gif files), MNRAS in pres
A model for the generic alpha relaxation of viscous liquids
Dielectric measurements on molecular liquids just above the glass transition
indicate that alpha relaxation is characterized by a generic high-frequency
loss varying as , whereas deviations from this come from one or
more low-lying beta processes [Olsen et al, Phys. Rev. Lett. {\bf 86} (2001)
1271]. Assuming that long-wavelength fluctuations dominate the dynamics, a
model for the dielectric alpha relaxation based on the simplest coupling
between the density and dipole density fields is proposed here. The model,
which is solved in second order perturbation theory in the Gaussian
approximation, reproduces the generic features of alpha relaxation
Palmitate-induced impairment of glucose-stimulated insulin secretion by pancreatic beta cells is disconnected from concomitant mitochondrial respiratory defects
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