7,327 research outputs found
Xe 4d photoionization in Xe@C60, Xe@C240, and Xe@C60@C240
Re-evaluated parameters for the square-well potential model for
photoionization of endo-fullerenes are proposed and employed to reveal the
spectacular modifications in the Xe 4d photoionization giant resonance along
the path from Xe@C60 to Xe@C240 to multi-walled Xe@[email protected]: 1 page, 1 figure. 2011 International Conference on Photonic,
Electronic, and Atomic Collisions (Belfast, UK, 2011), abstract Tue13
Twin prime correlations from the pair correlation of Riemann zeros
We establish, via a formal/heuristic Fourier inversion calculation, that the
Hardy-Littlewood twin prime conjecture is equivalent to an asymptotic formula
for the two-point correlation function of Riemann zeros at a height on the
critical line. Previously it was known that the Hardy-Littlewood conjecture
implies the pair correlation formula, and we show that the reverse implication
also holds. A smooth form of the Hardy-Littlewood conjecture is obtained by
inverting the limit of the two-point correlation
function and the precise form of the conjecture is found by including
asymptotically lower order terms in the two-point correlation function formula.Comment: 11 page
On the variance of sums of arithmetic functions over primes in short intervals and pair correlation for L-functions in the Selberg class
We establish the equivalence of conjectures concerning the pair correlation
of zeros of -functions in the Selberg class and the variances of sums of a
related class of arithmetic functions over primes in short intervals. This
extends the results of Goldston & Montgomery [7] and Montgomery & Soundararajan
[11] for the Riemann zeta-function to other -functions in the Selberg class.
Our approach is based on the statistics of the zeros because the analogue of
the Hardy-Littlewood conjecture for the auto-correlation of the arithmetic
functions we consider is not available in general. One of our main findings is
that the variances of sums of these arithmetic functions over primes in short
intervals have a different form when the degree of the associated -functions
is 2 or higher to that which holds when the degree is 1 (e.g. the Riemann
zeta-function). Specifically, when the degree is 2 or higher there are two
regimes in which the variances take qualitatively different forms, whilst in
the degree-1 case there is a single regime
Reionization in Technicolor
We present the Technicolor Dawn simulations, a suite of cosmological
radiation-hydrodynamic simulations of the first 1.2 billion years. By modeling
a spatially-inhomogeneous UVB on-the-fly with 24 frequencies and resolving dark
matter halos down to within 12 Mpc volumes, our
simulations unify observations of the intergalactic and circumgalactic media,
galaxies, and reionization into a common framework. The only empirically-tuned
parameter, the fraction of ionizing photons that
escape the interstellar medium, is adjusted to match observations of the
Lyman- forest and the cosmic microwave background. With this single
calibration, our simulations reproduce the history of reionization; the stellar
mass-star formation rate relation of galaxies; the number density and
metallicity of damped Lyman- absorbers (DLAs) at ; the
abundance of weak metal absorbers; the ultraviolet background (UVB) amplitude;
and the Lyman- flux power spectrum at . The galaxy stellar mass
and UV luminosity functions are underproduced by , suggesting an
overly vigorous feedback model. The mean transmission in the Lyman-
forest is underproduced at , indicating tension between measurements of
the UVB amplitude and Lyman- transmission. The observed SiIV column
density distribution is reasonably well-reproduced ( low). By
contrast, CIV remains significantly underproduced despite being boosted by an
intense Ryd UVB. Solving this problem by increasing metal yields would
overproduce both weak absorbers and DLA metallicities. Instead, the observed
strength of high-ionization emission from high-redshift galaxies and absorption
from their environments suggest that the ionizing flux from conventional
stellar population models is too soft.Comment: 24 pages, 17 figures, accepted to MNRA
Automatic Digital Processing for Calibration Data of Open Skies Treaty Sensors
The Open Skies Treaty provides guidelines allowing participants to fly in air space over other participants\u27 countries to monitor strategic military placement and development. The treaty restricts the ground size of the smallest detail recorded by these aerial imaging systems to any size larger than 30 cm. This restriction is enforced by placing a lower limit on the altitude at which a participating aircraft can fly and it is computed as the value of Hmin. Current techniques rely on human photographic interpreters to select the value of Hmin for every calibration pass and is very resource intensive. The Open Skies participants are investigating machine based techniques to supplement the traditional human role in an effort to increase the objectiveness of the measurement. This thesis presents a software tool called, ADiM, a man-in-the-loop, algorithm which manipulates image statistics to identify the orientation and width of individual target bar groups from digitized images of aerial photographs of Open Skies Treaty calibration triple bar target. ADiM Hmin results achieved an 88.6 percent correlation with the Open Skies Media Processing Facility\u27s Hmin computations
Cold adaptation and replicable microbial community development during long-term low temperature anaerobic digestion treatment of synthetic sewage
The development and, activity of a cold-adapting microbial community was monitored during low temperature anaerobic digestion (LtAD) treatment of wastewater. Two replicate hybrid anaerobic sludge bed-fixed-film reactors treated a synthetic sewage wastewater at 12°C, at organic loading rates of 0.25–1.0 kg Chemical Oxygen Demand (COD) m−3 d−1, over 889 days. The inoculum was obtained from a full-scale AD reactor, which was operated at 37˚C. Both LtAD reactors readily degraded the influent with COD removal efficiencies regularly exceeding 78% for both the total and soluble COD fractions. The biomass from both reactors was sampled temporally and tested for activity against hydrolytic and methanogenic substrates at 12˚C and 37˚C. Data indicated that significantly enhanced low-temperature hydrolytic and methanogenic activity developed in both systems. For example, the hydrolysis rate constant (K) at 12°C had increased 20–30-fold by comparison to the inoculum by day 500. Substrate affinity also increased for hydrolytic substrates at low temperature. Next generation sequencing demonstrated that a shift in community structure occurred over the trial, involving a 1-log-fold change in 25 SEQS (OTU-free approach) from the inoculum. Microbial community structure changes and process performance were replicable in the LtAD reactors
Ozone reference models for the middle atmosphere (new CIRA)
Models of ozone vertical structure were generated that were based on multiple data sets from satellites. The very good absolute accuracy of the individual data sets allowed the data to be directly combined to generate these models. The data used for generation of these models are from some of the most recent satellite measurements over the period 1978 to 1983. A discussion is provided of validation and error analyses of these data sets. Also, inconsistencies in data sets brought about by temporal variations or other factors are indicated. The models cover the pressure range from from 20 to 0.003 mb (25 to 90 km). The models for pressures less than 0.5 mb represent only the day side and are only provisional since there was limited longitudinal coverage at these levels. The models start near 25 km in accord with previous COSPAR international reference atmosphere (CIRA) models. Models are also provided of ozone mixing ratio as a function of height. The monthly standard deviation and interannual variations relative to zonal means are also provided. In addition to the models of monthly latitudinal variations in vertical structure based on satellite measurements, monthly models of total column ozone and its characteristic variability as a function of latitude based on four years of Nimbus 7 measurements, models of the relationship between vertical structure and total column ozone, and a midlatitude annual mean model are incorporated in this set of ozone reference atmospheres. Various systematic variations are discussed including the annual, semiannual, and quasibiennial oscillations, and diurnal, longitudinal, and response to solar activity variations
Attitude determination of the spin-stabilized Project Scanner spacecraft
Attitude determination of spin-stabilized spacecraft using star mapping techniqu
Quantum chaotic resonances from short periodic orbits
We present an approach to calculating the quantum resonances and resonance
wave functions of chaotic scattering systems, based on the construction of
states localized on classical periodic orbits and adapted to the dynamics.
Typically only a few of such states are necessary for constructing a resonance.
Using only short orbits (with periods up to the Ehrenfest time), we obtain
approximations to the longest living states, avoiding computation of the
background of short living states. This makes our approach considerably more
efficient than previous ones. The number of long lived states produced within
our formulation is in agreement with the fractal Weyl law conjectured recently
in this setting. We confirm the accuracy of the approximations using the open
quantum baker map as an example.Comment: 4 pages, 4 figure
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