435 research outputs found
Fly ash-derived MCM-41 as a low-cost silica support for polyethyleneimine in post-combustion CO2 capture
The mesoporous silicate molecular sieve, MCM-41, has been synthesized from pulverized coal fly ash (PFA), where the silicate filtrate used is a by-product from hydrothermal zeolite production. Rice husk ash was also used for comparison but fusion with sodium hydroxide was used to prepare the silicate filtrate, along similar lines to earlier reports of using PFA as a precursor for MCM-41 synthesis. The MCM-41 samples are chemically and mineralogically similar to a commercially available sample, but with higher pore volumes dominated by mesopores (0.92â1.13 cf. 0.88 cm3 gâ1). After polyethyleneimine (PEI) impregnation for CO2 capture, the ash derived MCM-41 samples displayed higher uptakes than the commercial sample with the maximum achievable PEI loading of 60 Wt.% PEI (dry basis) before particle agglomeration occurs, approximately 13 compared to 11 Wt.%, respectively, the latter being comparable to earlier reports in the literature. The PFA sample that displays the fastest kinetics to achieve 90% of the equilibrium uptake had the largest mesopore volume of 1.13 cm3 gâ1. Given the PFA-derived MCM-41 uses a waste silicate solution for hydrothermal preparation and no prior preparation is needed, production costs are estimated to be considerable lower where silicate solutions need to be prepared by base treatment, even if ash is used, as for the RHA derived MCM-41 used here
Inflationary Cosmological Perturbations of Quantum-Mechanical Origin
This review article aims at presenting the theory of inflation. We first
describe the background spacetime behavior during the slow-roll phase and
analyze how inflation ends and the Universe reheats. Then, we present the
theory of cosmological perturbations with special emphasis on their behavior
during inflation. In particular, we discuss the quantum-mechanical nature of
the fluctuations and show how the uncertainty principle fixes the amplitude of
the perturbations. In a next step, we calculate the inflationary power spectra
in the slow-roll approximation and compare these theoretical predictions to the
recent high accuracy measurements of the Cosmic Microwave Background radiation
(CMBR) anisotropy. We show how these data already constrain the underlying
inflationary high energy physics. Finally, we conclude with some speculations
about the trans-Planckian problem, arguing that this issue could allow us to
open a window on physical phenomena which have never been probed so far.Comment: Review Article, 47 pages, 3 figures. Lectures given at the 40th
Karpacz Winter School on Theoretical Physics (Poland, Feb. 2004), submitted
to Lecture Notes in Physic
Generating --cosmologies with perfect fluid in dilaton gravity
We present a method for generating exact diagonal -cosmological
solutions in dilaton gravity coupled to a radiation perfect fluid and with a
cosmological potential of a special type. The method is based on the symmetry
group of the system of -field equations. Several new classes of explicit
exact inhomogeneous perfect fluid scalar-tensor cosmologies are presented.Comment: 10 pages, LaTe
The No-defect Conjecture: Cosmological Implications
When the topology of the universe is non trivial, it has been shown that
there are constraints on the network of domain walls, cosmic strings and
monopoles. I generalize these results to textures and study the cosmological
implications of such constraints. I conclude that a large class of
multi-connected universes with topological defects accounting for structure
formation are ruled out by observation of the cosmic microwave background.Comment: 4 pages, 1 figure, accepted for publication as a brief report in
Phys. Rev.
Inflationary Perturbations: the Cosmological Schwinger Effect
This pedagogical review aims at presenting the fundamental aspects of the
theory of inflationary cosmological perturbations of quantum-mechanical origin.
The analogy with the well-known Schwinger effect is discussed in detail and a
systematic comparison of the two physical phenomena is carried out. In
particular, it is demonstrated that the two underlying formalisms differ only
up to an irrelevant canonical transformation. Hence, the basic physical
mechanisms at play are similar in both cases and can be reduced to the
quantization of a parametric oscillator leading to particle creation due to the
interaction with a classical source: pair production in vacuum is therefore
equivalent to the appearance of a growing mode for the cosmological
fluctuations. The only difference lies in the nature of the source: an electric
field in the case of the Schwinger effect and the gravitational field in the
case of inflationary perturbations. Although, in the laboratory, it is
notoriously difficult to produce an electric field such that pairs extracted
from the vacuum can be detected, the gravitational field in the early universe
can be strong enough to lead to observable effects that ultimately reveal
themselves as temperature fluctuations in the Cosmic Microwave Background.
Finally, the question of how quantum cosmological perturbations can be
considered as classical is discussed at the end of the article.Comment: 49 pages, 6 figures, to appear in a LNP volume "Inflationary
Cosmology
A covariant and gauge-invariant analysis of cosmic microwave background anisotropies from scalar perturbations
We present a new, fully covariant and manifestly gauge-invariant expression
for the temperature anisotropy in the cosmic microwave background radiation
resulting from scalar perturbations. We pay particular attention to gauge
issues such as the definition of the temperature perturbation and the placing
of the last scattering surface. In the instantaneous recombination
approximation, the expression may be integrated up to a Rees-Sciama term for
arbitrary matter descriptions in flat, open and closed universes. We discuss
the interpretation of our result in the baryon-dominated limit using numerical
solutions for conditions on the last scattering surface, and confirm that for
adiabatic perturbations the dominant contribution to the anisotropy on
intermediate scales (the location of the Doppler peaks) may be understood in
terms of the spatial inhomogeneity of the radiation temperature in the baryon
rest frame. Finally, we show how this term enters the usual Sachs-Wolfe type
calculations (it is rarely seen in such analyses) when subtle gauge effects at
the last scattering surface are treated correctly.Comment: 20 pages, 2 Postscript figure
Population Dynamics and Angler Exploitation of the Unique Muskellunge Population in Shoepack Lake, Voyageurs National Park, Minnesota
A unique population of muskellunge Esox masquinongy inhabits Shoepack Lake in Voyageurs National Park, Minnesota. Little is known about its status, dynamics, and angler exploitation, and there is concern for the long-term viability of this population. We used intensive sampling and markârecapture methods to quantify abundance, survival, growth, condition, age at maturity and fecundity and angler surveys to quantify angler pressure, catch rates, and exploitation. During our study, heavy rain washed out a dam constructed by beavers Castor canadensis which regulates the water level at the lake outlet, resulting in a nearly 50% reduction in surface area. We estimated a population size of 1,120 adult fish at the beginning of the study. No immediate reduction in population size was detected in response to the loss of lake area, although there was a gradual, but significant, decline in population size over the 2-year study. Adults grew less than 50 mm per year, and relative weight (W r) averaged roughly 80. Anglers were successful in catching, on average, two fish during a full day of angling, but harvest was negligible. Shoepack Lake muskellunge exhibit much slower growth rates and lower condition, but much higher densities and angler catch per unit effort (CPUE), than other muskellunge populations. The unique nature, limited distribution, and location of this population in a national park require special consideration for management. The results of this study provide the basis for assessing the long-term viability of the Shoepack Lake muskellunge population through simulations of long-term population dynamics and genetically effective population size
HST/STIS spectroscopy of the exposed white dwarf in the short-period dwarf nova EK TrA
We present high resolution Hubble Space Telescope ultraviolet spectroscopy of
the dwarf nova EK TrA obtained in deep quiescence. The Space Telescope Imaging
Spectrograph data reveal the broad Ly-alpha absorption profile typical of a
moderately cool white dwarf, overlayed by numerous broad emission lines of He,
C, N, and Si and by a number of narrow absorption lines, mainly of CI and SiII.
Assuming a white dwarf mass in the range 0.3-1.4Msun we derive
Teff=17500-23400K for the primary in EK TrA; Teff=18800K for a canonical mass
of 0.6Msun. From the narrow photospheric absorption lines, we measure the white
dwarf rotational velocity, v*sin i=200+-100kms. Even though the strong
contamination of the photospheric white dwarf absorption spectrum by the
emission lines prevents a detailed quantitative analysis of the chemical
abundances of the atmosphere, the available data suggest slightly sub-solar
abundances. The high time resolution of the STIS data allows us to associate
the observed ultraviolet flickering with the emission lines, possibly
originating in a hot optically thin corona above the cold accretion disk.Comment: 6 pages A&A-Latex, 5 Figures, accepted for publication in A&
The role of functional single nucleotide polymorphisms of the human glucocorticoid receptor gene NR3C1 in Polish patients with bronchial asthma
N363S and ER22/23EK polymorphisms observed within glucocorticoid receptor gene (NR3C1) may play an important role in the development of bronchial asthma. NR3C1 gene is associated with an altered sensitivity to GCs. The aim of the research project was to study the correlation between this NR3C1 gene polymorphisms and occurrence of asthma in the population of Polish asthmatics. Peripheral blood was obtained from 207 healthy volunteers and 221 asthma patients. Genotyping was carried out with PCR-RFLP method. In the groups of patients with uncontrolled moderate asthma and uncontrolled severe disease, the genotype distribution for the investigated polymorphisms was as follows: N363S-AA, AG, GG occurring with 0.881/0.073/0.046 frequency and ER22/23EK-GG, GA, AA occurring with 0.963/0.037/0.000 frequency. Chi-square analysis revealed a significantly different (PÂ <Â 0.05) distribution between cases and controls for the N363S polymorphisms. The N363S polymorphism of NR3C1 gene is significantly associated with bronchial asthma, susceptibility to the development of moderate to severe form of uncontrolled bronchial asthma
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