9,649 research outputs found
Hydraulic and Electrokinetic Delivery of Remediants for In-situ Remediation
Nano-scale zero valent iron (nZVI) has shown promising mobility and in-situ reactivity with chlorinated volatile organic compounds when injected into saturated porous media. The current study evaluated nZVI mobility and subsequent reactivity with in-situ contaminants in a variably saturated porous media. The nZVI particles, synthesized onsite at subzero temperatures, demonstrated complete trichloroethene (TCE) degradation within the target area. Furthermore, a three dimensional finite difference model (CompSim) was utilized to investigate nZVI mobility in variably saturated zones. Model predicted well head data were in very good agreement with field observations. Simulation results showed that the injected slurry migrated radially outward from the injection well and that nZVI travel distance increases were not proportional to the increase in injected nZVI volume. This study suggested that the numerical simulator can be a practical tool for optimal design of nZVI field applications.
The second study aimed at alleviating back diffusion from low permeability porous media observed at numerous field studies. Experiments were conducted in a two-dimensional sandbox with alternate vertical layers of coarse sand and silt flooded with TCE at aqueous solubility. Electrokinetics (EK) was used to enhance permanganate delivery through the silt layers. The suite of experiments demonstrated that EK was able to drive more permanganate at a faster rate throughout the silt layers in comparison to no-EK experiments. The combined EK and permanganate application resulted in 4.4 orders of magnitude reduction in TCE concentrations compared to a 3.5 orders of magnitude reduction without EK application. This experiment demonstrated that EK coupled with permanganate application can be used to remediate low permeability strata.
The third study investigated a novel approach of EK assisted persulfate delivery followed by electrical resistance heating (ERH) for persulfate activation for low permeability soil remediation. The study showed that EK delivered persulfate throughout the silt. The application of ERH was successfully able to activate the persulfate within the porous matrix leading to complete in-situ tetrachlorothene (PCE) degradation. To the authors’ knowledge, this study was the first to combine EK and ERH for persulfate delivery and activation for low permeability soil remediation
The CWKB particle production and classical condensate in de Sitter spacetime
The complex time WKB approximation is an effective tool in studying particle
production in curved spacetime. We use it in this work to understand the
formation of classical condensate in expanding de Sitter spacetime. The CWKB
leads to the emergence of thermal spectrum that depends crucially on horizons
(as in de Sitter spacetime) or observer dependent horizons (as in Rindler
spacetime). A connection is sought between the horizon and the formation of
classical condensate. We concentrate on de Sitter spacetime and study the
cosmological perturbation of mode with various values of . We find
that for a minimally coupled free scalar field for , the one-mode
occupation number grows more than unity soon after the physical wavelength of
the mode crosses the Hubble radius and soon after diverges as , where . The results substantiates the previous works in this
direction. We also find the correct oscillation and behaviour of at
small from a single expression using CWKB approximation for various values
of . We also discuss decoherence in relation to the formation of
classical condensate. We also find that the squeezed state formalism and CWKB
method give identical results.Comment: 19 pages, revtex, 5 figure
Distribution of dwell times of a ribosome: effects of infidelity, kinetic proofreading and ribosome crowding
Ribosome is a molecular machine that polymerizes a protein where the sequence
of the amino acid residues, the monomers of the protein, is dictated by the
sequence of codons (triplets of nucleotides) on a messenger RNA (mRNA) that
serves as the template. The ribosome is a molecular motor that utilizes the
template mRNA strand also as the track. Thus, in each step the ribosome moves
forward by one codon and, simultaneously, elongates the protein by one amino
acid. We present a theoretical model that captures most of the main steps in
the mechano-chemical cycle of a ribosome. The stochastic movement of the
ribosome consists of an alternating sequence of pause and translocation; the
sum of the durations of a pause and the following translocation is the time of
dwell of the ribosome at the corresponding codon. We derive the analytical
expression for the distribution of the dwell times of a ribosome in our model.
Whereever experimental data are available, our theoretical predictions are
consistent with those results. We suggest appropriate experiments to test the
new predictions of our model, particularly, the effects of the quality control
mechanism of the ribosome and that of their crowding on the mRNA track.Comment: This is an author-created, un-copyedited version of an article
accepted for publication in Physical Biology. IOP Publishing Ltd is not
responsible for any errors or omissions in this version of the manuscript or
any version derived from it. The definitive publisher authenticated version
is available online at DOI:10.1088/1478-3975/8/2/02600
Intertwining Relations for the Deformed D1D5 CFT
The Higgs branch of the D1D5 system flows in the infrared to a
two-dimensional N=(4,4) SCFT. This system is believed to have an "orbifold
point" in its moduli space where the SCFT is a free sigma model with target
space the symmetric product of copies of four-tori; however, at the orbifold
point gravity is strongly coupled and to reach the supergravity point one needs
to turn on the four exactly marginal deformations corresponding to the blow-up
modes of the orbifold SCFT. Recently, technology has been developed for
studying these deformations and perturbing the D1D5 CFT off its orbifold point.
We present a new method for computing the general effect of a single
application of the deformation operators. The method takes the form of
intertwining relations that map operators in the untwisted sector before
application of the deformation operator to operators in the 2-twisted sector
after the application of the deformation operator. This method is
computationally more direct, and may be of theoretical interest. This line of
inquiry should ultimately have relevance for black hole physics.Comment: latex, 23 pages, 3 figure
Doping Dependence of Thermal Oxidation on n-type 4H-SiC
The doping dependence of dry thermal oxidation rates in n-type 4H-SiC was
investigated. The oxidation was performed in the temperature range 1000C to
1200C for samples with nitrogen doping in the range of 6.5e15/cm3 to
9.3e18/cm3, showing a clear doping dependence. Samples with higher doping
concentrations displayed higher oxidation rates. The results were interpreted
using a modified Deal-Grove model. Linear and parabolic rate constants and
activation energies were extracted. Increasing nitrogen led to an increase in
linear rate constant pre-exponential factor from 10-6m/s to 10-2m/s and the
parabolic rate constant pre-exponential factor from 10e9m2/s to 10e6m2/s. The
increase in linear rate constant was attributed to defects from doping-induced
lattice mismatch, which tend to be more reactive than bulk crystal regions. The
increase in the diffusion-limited parabolic rate constant was attributed to
degradation in oxide quality originating from the doping-induced lattice
mismatch. This degradation was confirmed by the observation of a decrease in
optical density of the grown oxide films from 1.4 to 1.24. The linear
activation energy varied from 1.6eV to 2.8eV, while the parabolic activation
energy varied from 2.7eV to 3.3eV, increasing with doping concentration. These
increased activation energies were attributed to higher nitrogen content,
leading to an increase in effective bond energy stemming from the difference in
C-Si (2.82eV) and Si-N (4.26eV) binding energies. This work provides crucial
information in the engineering of SiO2 dielectrics for SiC MOS structures,
which typically involve regions of very different doping concentrations, and
suggests that thermal oxidation at high doping concentrations in SiC may be
defect mediated.Comment: 13 pages. 9 figures, accepted as a transiction in IEEE electron
device. TED MS#8035
Excitations in the deformed D1D5 CFT
We perform some simple computations for the first order deformation of the
D1D5 CFT off its orbifold point. It had been shown earlier that under this
deformation the vacuum state changes to a squeezed state (with the further
action of a supercharge). We now start with states containing one or two
initial quanta and write down the corresponding states obtained under the
action of deformation operator. The result is relevant to the evolution of an
initial excitation in the CFT dual to the near extremal D1D5 black hole: when a
left and a right moving excitation collide in the CFT, the deformation operator
spreads their energy over a larger number of quanta, thus evolving the state
towards the infrared.Comment: 26 pages, Latex, 4 figure
A (Running) Bolt for New Reasons
We construct a four-parameter family of smooth, horizonless, stationary
solutions of ungauged five-dimensional supergravity by using the
four-dimensional Euclidean Schwarzschild metric as a base space and
"magnetizing" its bolt. We then generalize this to a five-parameter family
based upon the Euclidean Kerr-Taub-Bolt. These "running Bolt" solutions are
necessarily non-static. They also have the same charges and mass as a
non-extremal black hole with a classically-large horizon area. Moreover, in a
certain regime their mass can decrease as their charges increase. The existence
of these solutions supports the idea that the singularities of non-extremal
black holes are resolved by low-mass modes that correct the singularity of the
classical black hole solution on large (horizon-sized) scales.Comment: 25 pages, 3 figures, LaTeX; v2: minor changes, references adde
Deforming the D1D5 CFT away from the orbifold point
The D1D5 brane bound state is believed to have an `orbifold point' in its
moduli space which is the analogue of the free Yang Mills theory for the D3
brane bound state. The supergravity geometry generated by D1 and D5 branes is
described by a different point in moduli space, and in moving towards this
point we have to deform the CFT by a marginal operator: the `twist' which links
together two copies of the CFT. In this paper we find the effect of this
deformation operator on the simplest physical state of the CFT -- the Ramond
vacuum. The twist deformation leads to a final state that is populated by pairs
of excitations like those in a squeezed state. We find the coefficients
characterizing the distribution of these particle pairs (for both bosons and
fermions) and thus write this final state in closed form.Comment: 30 pages, 4 figures, Late
Chlorinated Pesticide Residue Status in Tomato, Potato and Carrot
A study was carried out to identify the bioaccumulation and the ascertain level of chlorinated pesticide residues in some vegetables collected from market baskets of New market, Dhaka, Bangladesh namely potato, tomato and carrot. The samples were randomly collected from different shops and analyzed by capillary column of Gas Chromatograph Mass Spectrometry (GCMS) with Electron Impact Ionization (EI) method for the detection of chlorinated pesticide. The results of the study revealed that collected samples of potato, tomato, red amaranth and spinach were contaminated with some chlorinated substances. But Indian spinach and carrot were free of contamination with organochlorine pesticide
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