6,830 research outputs found
Observations of HNO3, ΣAN, ΣPN and NO2 fluxes: evidence for rapid HOx chemistry within a pine forest canopy
Measurements of exchange of reactive nitrogen oxides between the atmosphere and a ponderosa pine forest in the Sierra Nevada Mountains are reported. During winter, we observe upward fluxes of NO<sub>2</sub>, and downward fluxes of total peroxy and peroxy acyl nitrates (ΣPNs), total gas and particle phase alkyl and multifunctional alkyl nitrates (ΣANs<sub>(g+p)</sub>), and the sum of gaseous HNO<sub>3</sub> and semi-volatile NO<sub>3</sub><sup>−</sup> particles (HNO<sub>3(g+p)</sub>). We use calculations of the vertical profile and flux of NO, partially constrained by observations, to show that net midday ΣNO<sub>yi</sub> fluxes in winter are –4.9 ppt m s<sup>−1</sup>. The signs and magnitudes of these wintertime individual and ΣNO<sub>yi</sub> fluxes are in the range of prior measurements. In contrast, during summer, we observe downward fluxes only of ΣANs<sub>(g+p)</sub>, and upward fluxes of HNO<sub>3(g+p)</sub>, ΣPNs and NO<sub>2</sub> with signs and magnitudes that are unlike most, if not all, previous observations and analyses of fluxes of individual nitrogen oxides. The results imply that the mechanisms contributing to NO<sub>y</sub> fluxes, at least at this site, are much more complex than previously recognized. We show that the observations of upward fluxes of HNO<sub>3(g+p)</sub> and σPNs during summer are consistent with oxidation of NO<sub>2</sub> and acetaldehyde by an OH x residence time of 1.1×10<sup>10</sup> molec OH cm<sup>−3</sup> s, corresponding to 3 to 16×10<sup>7</sup> molecules cm<sup>−3</sup> OH within the forest canopy for a 420 to 70 s canopy residence time. We show that ΣAN<sub>(g+p)</sub> fluxes are consistent with this range in OH if the reaction of OH with ΣANs produces either HNO<sub>3</sub> or NO<sub>2</sub> with a 6–30% yield. Calculations of NO fluxes constrained by the NO<sub>2</sub> observations and the inferred OH indicate that NO<sub>x</sub> fluxes are downward into the canopy because of the substantial conversion of NO<sub>x</sub> to HNO<sub>3</sub> and σPNs in the canopy. Even so, we derive that NO<sub>x</sub> emission fluxes of ~15 ng(N) m<sup>−2</sup> s<sup>−1</sup> at midday during summer are required to balance the NO<sub>x</sub> and NO<sub>y</sub> flux budgets. These fluxes are partly explained by estimates of soil emissions (estimated to be between 3 and 6 ng(N) m<sup>−2</sup> s<sup>-1</sup>). One possibility for the remainder of the NO<sub>x</sub> source is large HONO emissions. Alternatively, the 15 ng(N) m<sup>−2</sup> s<sup>−1</sup> emission estimate may be too large, and the budget balanced if the deposition of HNO<sub>3</sub> and σPNs is slower than we estimate, if there are large errors in either our understanding of peroxy radical chemistry, or our assumptions that the budget is required to balance because the fluxes do not obey similarity theory
Development of a three-dimensional time-dependent flow field model
A three-dimensional, time-dependent mathematical model to represent Mobile Bay was developed. Computer programs were developed which numerically solve the appropriate conservation equations for predicting bay and estuary flow fields. The model is useful for analyzing the dispersion of sea water into fresh water and the transport of sediment, and for relating field and physical model data
Random polynomials, random matrices, and -functions
We show that the Circular Orthogonal Ensemble of random matrices arises
naturally from a family of random polynomials. This sheds light on the
appearance of random matrix statistics in the zeros of the Riemann
zeta-function.Comment: Added background material. Final version. To appear in Nonlinearit
Effects of Neutron Irradiation on Carbon Doped MgB2 Wire Segments
We have studied the evolution of superconducting and normal state properties
of neutron irradiated Mg(BC) wire segments as a function
of post exposure annealing time and temperature. The initial fluence fully
suppressed superconductivity and resulted in an anisotropic expansion of the
unit cell. Superconductivity was restored by post-exposure annealing. The upper
critical field, H(T=0), approximately scales with T starting with an
undamaged T near 37 K and H(T=0) near 32 T. Up to an annealing
temperature of 400 C the recovery of T tends to coincide with a
decrease in the normal state resistivity and a systematic recovery of the
lattice parameters. Above 400 C a decrease in order along the c- direction
coincides with an increase in resistivity, but no apparent change in the
evolution of T and H. To first order, it appears that carbon doping
and neutron damaging effect the superconducting properties of MgB
independently
Quantifying the Likelihood of Regional Cimate Change: A hybridized Approach
The growing need for risk-based assessments of impacts and adaptation to climate change calls for
increased capability in climate projections: the quantification of the likelihood of regional outcomes
and the representation of their uncertainty. Herein, we present a technique that extends the latitudinal
projections of the 2-D atmospheric model of the MIT Integrated Global System Model (IGSM) by
applying longitudinally resolved patterns from observations, and from climate-model projections
archived from exercises carried out for the 4th Assessment Report (AR4) of the Intergovernmental
Panel on Climate Change (IPCC). The method maps the IGSM zonal means across longitude using a
set of transformation coefficients, and we demonstrate this approach in application to near-surface
air temperature and precipitation, for which high-quality observational datasets and model
simulations of climate change are available. The current climatology of the transformation
coefficients is observationally based. To estimate how these coefficients may alter with climate, we
characterize the climate models’ spatial responses, relative to their zonal mean, from transient
increases in trace-gas concentrations and then normalize these responses against their corresponding
transient global temperature responses. This procedure allows for the construction of meta-ensembles
of regional climate outcomes, combining the ensembles of the MIT IGSM—which produce global and
latitudinal climate projections, with uncertainty, under different global climate policy scenarios—with
regionally resolved patterns from the archived IPCC climate-model projections. This approach also
provides a hybridization of the climate-model longitudinal projections with the global and latitudinal
patterns projected by the IGSM, and can be applied to any given state or flux variable that has the
sufficient observational and model-based information.U.S. Department of Energy’s Abrupt Climate Change program, grant
# DE-FG02-08ER64597
The Elections of 2000: Politics, Culture and Economics in North America
The essays in this collection are the product of a conversation among scholars, spanning national borders and disciplinary boundaries, about the increasing integration of Canada, Mexico, and the United States and the development of a “continental perspective.” This conversation has been underway for some time, reflecting the causes, challenges, and consequences of economic, cultural, and political integration in North America. The conjunction of national elections in all three of the great North American democracies in 2000 offered us the opportunity to deepen this conversation and engage in scholarly discourse from a “continental perspective.” Taken together, the essays in this book provide a vivid portrait of North American democracies at the turn of the century.https://ideaexchange.uakron.edu/elections_of_2000/1000/thumbnail.jp
Adaptive time-varying detrended fluctuations analysis: a new method for characterizing time-varying scaling parameters in physiological time series
Information Flow through a Chaotic Channel: Prediction and Postdiction at Finite Resolution
We reconsider the persistence of information under the dynamics of the
logistic map in order to discuss communication through a nonlinear channel
where the sender can set the initial state of the system with finite
resolution, and the recipient measures it with the same accuracy. We separate
out the contributions of global phase space shrinkage and local phase space
contraction and expansion to the uncertainty in predicting and postdicting the
state of the system. Thus, we determine how the amplification parameter, the
time lag, and the resolution influence the possibility for communication. A
novel representation for real numbers is introduced that allows for a
visualization of the flow of information between scales.Comment: 14 pages, 13 figure
Statistical Properties of Share Volume Traded in Financial Markets
We quantitatively investigate the ideas behind the often-expressed adage `it
takes volume to move stock prices', and study the statistical properties of the
number of shares traded for a given stock in a fixed time
interval . We analyze transaction data for the largest 1000 stocks
for the two-year period 1994-95, using a database that records every
transaction for all securities in three major US stock markets. We find that
the distribution displays a power-law decay, and that the
time correlations in display long-range persistence. Further, we
investigate the relation between and the number of transactions
in a time interval , and find that the long-range
correlations in are largely due to those of . Our
results are consistent with the interpretation that the large equal-time
correlation previously found between and the absolute value of
price change (related to volatility) are largely due to
.Comment: 4 pages, two-column format, four figure
On the Floquet Theory of Delay Differential Equations
We present an analytical approach to deal with nonlinear delay differential
equations close to instabilities of time periodic reference states. To this end
we start with approximately determining such reference states by extending the
Poincar'e Lindstedt and the Shohat expansions which were originally developed
for ordinary differential equations. Then we systematically elaborate a linear
stability analysis around a time periodic reference state. This allows to
approximately calculate the Floquet eigenvalues and their corresponding
eigensolutions by using matrix valued continued fractions
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