592 research outputs found
Changes in the algal composition, bacterial metabolic activity and element content of biofilms developed on artificial substrata in the early phase of colonization
Changes in the algal composition and metabolic profiles of bacterial communities as well as the inorganic components were studied on artificial substrata during the early phase of biofilm formation under laboratory conditions in September 2002 and 2003. Sterile Perspex and polished quartz glass discs with a diameter of 3 cm were placed into a
Perspex rack, which was immersed vertically in an aquarium containing water from a shallow soda lake. The temperature was kept constant and sufficient oxygen supply was provided. The samples were illuminated for 12 hours a day. Periphyton communities were sampled from 2 to 126 hours of exposure. In both experiments, the alteration of the number of algal species and cells as well as the carbon source utilization of microbial communities was logarithmic. In the two years, considerable differences were revealed in the magnitude of algal cell numbers. The proportion of benthic and planktonic algae showed an undulating pattern in the second experiment. One of the dominant benthic species was the diatom Achnanthidium minutissimum KĂŒtz., while that of the planktonic, the cyanobacterium Microcystis aeruginosa KĂŒtz. During the experiments an increase in the bacterial
activities could be observed; the higher the microbial diversity and abundance that was detected, the more BIOLOG carbon sources were utilized. The examined element contents indicated interactions among algae and bacteria in the biofilms from the beginning of the colonization processes
Simultaneous Multicolor Detection of Faint Galaxies in the Hubble Deep Field
We present a novel way to detect objects when multiband images are available.
Typically, object detection is performed in one of the available bands or on a
somewhat arbitrarily co-added image. Our technique provides an almost optimal
way to use all the color information available. We build up a composite image
of the N passbands where each pixel value corresponds to the probability that
the given pixel is just sky. By knowing the probability distribution of sky
pixels (a chi-square distribution with N degrees of freedom), the data can be
used to derive the distribution of pixels dominated by object flux. From the
two distributions an optimal segmentation threshold can be determined. Clipping
the probability image at this threshold yields a mask, where pixels unlikely to
be sky are tagged. After using a standard connected-pixel criterion, the
regions of this mask define the detected objects. Applying this technique to
the Hubble Deep Field data, we find that we can extend the detection limit of
the data below that possible using linearly co-added images. We also discuss
possible ways of enhancing object detection probabilities for certain well
defined classes of objects by using various optimized linear combinations of
the pixel fluxes (optimal subspace filtering).Comment: 8 pages, 5 figures (4 postscript, 1 JPEG). To be published in A
Mass loss and longevity of gravitationally bound oscillating scalar lumps (oscillatons) in D-dimensions
Spherically symmetric oscillatons (also referred to as oscillating soliton
stars) i.e. gravitationally bound oscillating scalar lumps are considered in
theories containing a massive self-interacting real scalar field coupled to
Einstein's gravity in 1+D dimensional spacetimes. Oscillations are known to
decay by emitting scalar radiation with a characteristic time scale which is,
however, extremely long, it can be comparable even to the lifetime of our
universe. In the limit when the central density (or amplitude) of the
oscillaton tends to zero (small-amplitude limit) a method is introduced to
compute the transcendentally small amplitude of the outgoing waves. The results
are illustrated in detail on the simplest case, a single massive free scalar
field coupled to gravity.Comment: 23 pages, 2 figures, references on oscillons added, version to appear
in Phys. Rev.
What does a strongly excited 't Hooft-Polyakov magnetic monopole do?
The time evolution of strongly exited SU(2) Bogomolny-Prasad-Sommerfield
(BPS) magnetic monopoles in Minkowski spacetime is investigated by means of
numerical simulations based on the technique of conformal compactification and
on the use of hyperboloidal initial value problem. It is found that an
initially static monopole does not radiate the entire energy of the exciting
pulse toward future null infinity. Rather, a long-lasting quasi-stable
`breathing state' develops in the central region and certain expanding shell
structures -- built up by very high frequency oscillations -- are formed in the
far away region.Comment: 4 pages, 6 figure
Density Functional Molecular Study on the Full Conformational Space of the S-4-(2-Hydroxypropoxy)carbazol Fragment of Carvedilol (1-(9HâCarbazol-4-yloxy)-3- [2-(2-methoxyphenoxy)ethylamino]-2-propanol) in Vacuum and in Different Solvent Media
Density functional theory (DFT) conformational analysis was carried out
on the potential energy hypersurface (PEHS) of the carbazole-containing
molecular fragment, S-4-(2-hydroxypropoxy)-carbazol, of the chiral
cardiovascular drug molecule carvedilol,
(1-(9H-carbazol-4-yloxy)-3-[2-(2-methoxy-phenoxy)ethylamino]-2-propanol)
. The PEHS was computed in vacuum, chloroform, ethanol, DMSO, and water
at the B3LYP/6-31G(d) level of theory. The carbazole ring system was
confirmed to be planar, and the resultant PEHS in vacuum contained 19
converged minima, of which the global minima possessed a conformation
with chi(1), chi(2), and chi(3) in the anti position and chi(10) in the
g position. Conformer stability for the S-4-(2-hydroxypropoxy)carbazol
PEHS was influenced by intramolecular hydrogen bonding. Tomasi PCM
reaction-field calculations revealed that the lowest SCF energies,
relative conformer energies, and solvation free energies (DeltaG
(solvation)) for the S-4-(2-hydroxypropoxy)carbazol PEHS were in protic
solvents, ethanol and water, because of the larger hydrogen bond donor
values of these solvents, which aid in stabilization of the dipole
moment created by the carbazole ring system and the oxygen and nitrogen
atoms. However, solvent effects contributed most significantly to the
stabilization of S-4-(2-hydroxypropoxy)carbazol conformers that
contained no internal hydrogen bonding, whereas solvent effects were
not as important for conformers that contained intramolecular hydrogen
bonding
N-acetyl-l-aspartic acid-N'-methylamide with side-chain orientation capable of external hydrogen bonding
In this study, we generated and analyzed the side-chain conformational
potential energy hyper-surfaces for each of the nine possible backbone
conformers for N-acetyl-L-aspartic acid-N' methylamide. We found a
total of 27 out of the 81 possible conformers optimized at the
B3LYP/6-31G(d) level of theory. The relative energies, as well as the
stabilization energies exerted by the side-chain on the backbone, have
been calculated for each of the 27 optimized conformers at this level
of theory. Various backbone-backbone (N-(HO)-O-...=C) and
backbone-side-chain (N-(HO)-O-...=C; N-(HOH)-O-...) hydrogen bonds were
analyzed. The appearance of the notoriously absent epsilon(L) backbone
conformer may be attributed to such side-chain-backbone (SC/BB) and
backbone-backbone (BB/BB) hydrogen bonds
Dust Reddening in SDSS Quasars
We explore the form of extragalactic reddening toward quasars using a sample
of 9566 quasars with redshifts 0<z<2.2, and accurate optical colors from the
Sloan Digital Sky Survey (SDSS). We confirm that dust reddening is the primary
explanation for the red ``tail'' of the color distribution of SDSS quasars. Our
fitting to 5-band photometry normalized by the modal quasar color as a function
of redshift shows that this ``tail'' is well described by SMC-like reddening
but not by LMC-like, Galactic, or Gaskell et al. (2004) reddening. Extension to
longer wavelengths using a subset of 1886 SDSS-2MASS matches confirms these
results at high significance. We carry out Monte-Carlo simulations that match
the observed distribution of quasar spectral energy distributions using a
Lorentzian dust reddening distribution; 2% of quasars selected by the main SDSS
targeting algorithm (i.e., which are not extincted out of the sample) have
E_{B-V} > 0.1; less than 1% have E_{B-V} > 0.2, where the extinction is
relative to quasars with modal colors. Reddening is uncorrelated with the
presence of intervening narrow-line absorption systems, but reddened quasars
are much more likely to show narrow absorption at the redshift of the quasar
than are unreddened quasars. Thus the reddening towards quasars is dominated by
SMC-like dust at the quasar redshift.Comment: 29 pages including 8 figures. AJ, September 2004 issu
Exploration of the four-dimensional-conformational potential energy hypersurface of N-acetyl-L-aspartic acid N'-methylamide with its internally hydrogen bonded side-chain orientation
Can NO2+ exist in bent or cyclic forms?
Calculations of NO2+ at HF, CBS-4, CASSCF, MBPT(2), MBPT(3), and
MBPT(4) theory levels, using 3-21G and 6-31G(d) basis sets, found two
C-2V structures along with the linear geometry. Computations using
MBPT(2) and CCSD(T) approaches and the aug-cc-pvtz basis set confirmed
these results. Harmonic vibrational frequency calculations, performed
with MBPT(2) and CCSD(T) theories, indicated that the linear structure
was the global minimum while one of the bent structures (angle ONO = 80
degrees) was a higher energy local minimum. The second C-2V structure
(angle ONO = 45 degrees) exhibited a large imaginary vibrational
frequency along the asymmetric stretching (B-2) mode, indicating its
saddle point nature. (C) 2001 Elsevier Science B.V. All rights reserved
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