1,394 research outputs found
Surface Passivation of Mercury-Cadmium-Telluride Infrared Detectors
The theoretical considerations and practical aspects of passivating insulator films, in the context of their use on high-performance mercury cadmium telluride (MCT) infrared detectors are reviewed. The methods of growth, the interface properties and the applications of both native and deposited passivant films have been discussed. Native films include anodic, chemical, photochemical, and plasma oxides as well as anodic sulphides and fluoro-oxides. Deposited films include ZnS, photo-CVD-grown SiO2, CDTe, and SiN/sub x/. The properties of all these passivant films on MCT have been summarized
Order preserving pattern matching on trees and DAGs
The order preserving pattern matching (OPPM) problem is, given a pattern
string and a text string , find all substrings of which have the
same relative orders as . In this paper, we consider two variants of the
OPPM problem where a set of text strings is given as a tree or a DAG. We show
that the OPPM problem for a single pattern of length and a text tree
of size can be solved in time if the characters of are
drawn from an integer alphabet of polynomial size. The time complexity becomes
if the pattern is over a general ordered alphabet. We
then show that the OPPM problem for a single pattern and a text DAG is
NP-complete
α-pinene photooxidation under controlled chemical conditions – Part 2: SOA yield and composition in low- and high-NO_x environments
The gas-phase oxidation of α-pinene produces a large amount of secondary organic aerosol (SOA) in the atmosphere. A number of carboxylic acids, organosulfates and nitrooxy organosulfates associated with α-pinene have been found in field samples and some are used as tracers of α-pinene oxidation. α-pinene reacts readily with OH and O_3 in the atmosphere followed by reactions with both HO_2 and NO. Due to the large number of potential reaction pathways, it can be difficult to determine what conditions lead to SOA. To better understand the SOA yield and chemical composition from low- and high-NO_x OH oxidation of α-pinene, studies were conducted in the Caltech atmospheric chamber under controlled chemical conditions. Experiments used low O_3 concentrations to ensure that OH was the main oxidant and low α-pinene concentrations such that the peroxy radical (RO_2) reacted primarily with either HO_2 under low-NO_x conditions or NO under high-NO_x conditions. SOA yield was suppressed under conditions of high-NO_x. SOA yield under high-NO_x conditions was greater when ammonium sulfate/sulfuric acid seed particles (highly acidic) were present prior to the onset of growth than when ammonium sulfate seed particles (mildly acidic) were present; this dependence was not observed under low-NO_x conditions. When aerosol seed particles were introduced after OH oxidation, allowing for later generation species to be exposed to fresh inorganic seed particles, a number of low-NO_x products partitioned to the highly acidic aerosol. This indicates that the effect of seed acidity and SOA yield might be under-estimated in traditional experiments where aerosol seed particles are introduced prior to oxidation. We also identify the presence of a number of carboxylic acids that are used as tracer compounds of α-pinene oxidation in the field as well as the formation of organosulfates and nitrooxy organosulfates. A number of the carboxylic acids were observed under all conditions, however, pinic and pinonic acid were only observed under low-NO_x conditions. Evidence is provided for particle-phase sulfate esterification of multi-functional alcohols
Secondary organic aerosol formation from photooxidation of naphthalene and alkylnaphthalenes: implications for oxidation of intermediate volatility organic compounds (IVOCs)
Current atmospheric models do not include secondary
organic aerosol (SOA) production from gas-phase reactions
of polycyclic aromatic hydrocarbons (PAHs). Recent
studies have shown that primary emissions undergo oxidation
in the gas phase, leading to SOA formation. This
opens the possibility that low-volatility gas-phase precursors
are a potentially large source of SOA. In this work,
SOA formation from gas-phase photooxidation of naphthalene,
1-methylnaphthalene (1-MN), 2-methylnaphthalene (2-
MN), and 1,2-dimethylnaphthalene (1,2-DMN) is studied in
the Caltech dual 28-m^3 chambers. Under high-NO_x conditions
and aerosol mass loadings between 10 and 40μgm^(−3),
the SOA yields (mass of SOA per mass of hydrocarbon reacted)
ranged from 0.19 to 0.30 for naphthalene, 0.19 to 0.39
for 1-MN, 0.26 to 0.45 for 2-MN, and constant at 0.31 for
1,2-DMN. Under low-NO_x conditions, the SOA yields were
measured to be 0.73, 0.68, and 0.58, for naphthalene, 1-
MN, and 2-MN, respectively. The SOA was observed to be
semivolatile under high-NO_x conditions and essentially nonvolatile
under low-NO_x conditions, owing to the higher fraction
of ring-retaining products formed under low-NO_x conditions.
When applying these measured yields to estimate
SOA formation from primary emissions of diesel engines
and wood burning, PAHs are estimated to yield 3–5 times
more SOA than light aromatic compounds over photooxidation
timescales of less than 12 h. PAHs can also account for
up to 54% of the total SOA from oxidation of diesel emissions,
representing a potentially large source of urban SOA
Chemical Composition of Gas- and Aerosol-Phase Products from the Photooxidation of Naphthalene
The current work focuses on the detailed evolution of the chemical composition of both the gas- and aerosol-phase constituents produced from the OH-initiated photooxidation of naphthalene under low- and high-NO_x conditions. Under high-NO_x conditions ring-opening products are the primary gas-phase products, suggesting that the mechanism involves dissociation of alkoxy radicals (RO) formed through an RO_2 + NO pathway, or a bicyclic peroxy mechanism. In contrast to the high-NO_x chemistry, ring-retaining compounds appear to dominate the low-NO_x gas-phase products owing to the RO_2 + HO_2 pathway. We are able to chemically characterize 53−68% of the secondary organic aerosol (SOA) mass. Atomic oxygen-to-carbon (O/C), hydrogen-to-carbon (H/C), and nitrogen-to-carbon (N/C) ratios measured in bulk samples by high-resolution electrospray ionization time-of-flight mass spectrometry (HR-ESI-TOFMS) are the same as the ratios observed with online high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS), suggesting that the chemical compositions and oxidation levels found in the chemically-characterized fraction of the particle phase are representative of the bulk aerosol. Oligomers, organosulfates (R-OSO_3), and other high-molecular-weight (MW) products are not observed in either the low- or high-NO_x SOA; however, in the presence of neutral ammonium sulfate seed aerosol, an organic sulfonic acid (R-SO_3), characterized as hydroxybenzene sulfonic acid, is observed in naphthalene SOA produced under both high- and low-NO_x conditions. Acidic compounds and organic peroxides are found to account for a large fraction of the chemically characterized high- and low-NO_x SOA. We propose that the major gas- and aerosol-phase products observed are generated through the formation and further reaction of 2-formylcinnamaldehyde or a bicyclic peroxy intermediate. The chemical similarity between the laboratory SOA and ambient aerosol collected from Birmingham, Alabama (AL) and Pasadena, California (CA) confirm the importance of PAH oxidation in the formation of aerosol within the urban atmosphere
Molecular Study of Glycoprotein (G) Gene Region of Rabies Virus from Spotted Deer, Delhi, India
Rabies is a viral zoonotic disease of public health importance in India. The disease is usually transmitted by a rabid animal bite, scratches and licks on broken skin and mucous membrane. Rabies is reported from all continents except Antarctica although prevalence is more in Asia and Africa. India is endemic for rabies virus (RABV) throughout the country except for islands of Lakshadweep, Andaman & Nicobar. In the present study, brain samples of clinically suspected animals obtained during the RABV outbreak at National Zoological Park, New Delhi, India, in 2016 were initially tested for rabies antigen by DFAT. All the 32 DFAT positive brain samples were then processed for RNA isolation. The extracted RNA was amplified for glycoprotein (G) gene of 590 bp by RT-PCR followed by nucleotide sequencing. Nucleotide alignment revealed only substitutions without any insertion or deletion. Amino acid alignment revealed replacement at four positions namely L244I, T264A, M310I and N375K. The amino acid change at position where Leucine is replaced by Isoleucine has not been observed in available RABV references of the G gene region either from India or other countries. This mutation was observed in all the samples included in the present study. A phylogenetic tree showed that all the study sequences belonged to Arctic like 1a lineage, in RABV genotype 1. In conclusion, RABV in the study region is acquiring genetic variation; which may have effect on the pathogenicity. This indicates that continued molecular surveillance of the circulating rabies virus strains should be carried out
Correlation Exponent and Anomalously Localized States at the Critical Point of the Anderson Transition
We study the box-measure correlation function of quantum states at the
Anderson transition point with taking care of anomalously localized states
(ALS). By eliminating ALS from the ensemble of critical wavefunctions, we
confirm, for the first time, the scaling relation z(q)=d+2tau(q)-tau(2q) for a
wide range of q, where q is the order of box-measure moments and z(q) and
tau(q) are the correlation and the mass exponents, respectively. The influence
of ALS to the calculation of z(q) is also discussed.Comment: 6 pages, 3 figure
Size-selective concentration of chondrules and other small particles in protoplanetary nebula turbulence
Size-selective concentration of particles in a weakly turbulent
protoplanetary nebula may be responsible for the initial collection of
chondrules and other constituents into primitive body precursors. This paper
presents the main elements of this process of turbulent concentration. In the
terrestrial planet region, both the characteristic size and size distribution
of chondrules are explained. "Fluffier" particles would be concentrated in
nebula regions which were at a lower gas density and/or more intensely
turbulent. The spatial distribution of concentrated particle density obeys
multifractal scaling}, suggesting a close tie to the turbulent cascade process.
This scaling behavior allows predictions of the probability distributions for
concentration in the protoplanetary nebula to be made. Large concentration
factors (>10^5) are readily obtained, implying that numerous zones of particle
density significantly exceeding the gas density could exist. If most of the
available solids were actually in chondrule sized particles, the ensuing
particle mass density would become so large that the feedback effects on gas
turbulence due to mass loading could no longer be neglected. This paper
describes the process, presenting its basic elements and some implications,
without including the effects of mass loading.Comment: 34 pages, 7 figures; in press for Astrophys. J; expected Jan 01 2001
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Multifractal analysis of the metal-insulator transition in anisotropic systems
We study the Anderson model of localization with anisotropic hopping in three
dimensions for weakly coupled chains and weakly coupled planes. The eigenstates
of the Hamiltonian, as computed by Lanczos diagonalization for systems of sizes
up to , show multifractal behavior at the metal-insulator transition even
for strong anisotropy. The critical disorder strength determined from the
system size dependence of the singularity spectra is in a reasonable agreement
with a recent study using transfer matrix methods. But the respective spectrum
at deviates from the ``characteristic spectrum'' determined for the
isotropic system. This indicates a quantitative difference of the multifractal
properties of states of the anisotropic as compared to the isotropic system.
Further, we calculate the Kubo conductivity for given anisotropies by exact
diagonalization. Already for small system sizes of only sites we observe
a rapidly decreasing conductivity in the directions with reduced hopping if the
coupling becomes weaker.Comment: 25 RevTeX pages with 10 PS-figures include
Influence of cytoplasmic-nuclear male sterility systems on microsporogenesis in pearl millet (Pennisetum glaucum (L.) R. Br.)
Influence of a range of cytoplasms on microsporogenesis and anther development in pearl millet was studied using six isonuclear A-lines having five cytoplasms (A1, A2, A3, A4 and Av) and the nuclear genome of 81B. 81B was used as a male-fertile control. Microsporogenesis and anther development were normal in 81B. However, pollen mother cell (PMC)/microspore/pollen degeneration in the six A-lines occurred at different stages of anther development. Each cytoplasm had its unique influence on microsporogenesis and anther development as evidenced by different developmental paths followed by them leading to pollen abortion. The cause of pollen abortion differed from line to line, from floret to floret within a spikelet, from anther to anther within a floret, and in some cases even from locule to locule within an anther. Events that led to male sterility included anomalies in tapetum and callose behaviour, persistence of tapetum, endothecium thickness, and other unknown causes. The present study also indicated that anther/pollen development was more irregular in Pb 406A3. In 81A4 and 81A1 > 95% of anther locules followed a definite developmental path to pollen abortion. In the other A-lines many developmental paths were observed within the line and pollen degeneration occurred at various stages. This could be one of the reasons for greater instability of male sterility in the A2 and A3 systems and greater stability of male sterility in the A1 and A4 systems
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