364 research outputs found
X-Ray Synchrotron White Beam Excitation of Auger Electrons
Auger electron spectra have been measured at the Cornell High Energy Synchrotron Source (CHESS), using the full white beam x-ray spectrum as the excitation source. Ordinary Auger spectra obtained in the laboratory with an electron beam source must employ derivative techniques to distinguish the Auger structures from the large background due to the excitation beam. The synchrotron white beam eliminates this source of background and produces signal rates as high as 107 cps. Superior signal-to-background ratios are found for Auger peaks above a few hundred eV, and count rates are large enough to suggest microprobe applications. X-ray induced Auger satellite peaks were observed with intensities much greater than the electron-induced counterpart; this anomaly is not completely understood
Relationship of stream flow regime in the western Lake Superior basin to watershed type characteristics
To test a conceptual model of non-linear response of hydrologic regimes to watershed characteristics, we selected 48 secondand third-order study sites on the North and South Shores of western Lake Superior, MN(USA) using a random-stratified design based on hydrogeomorphic region, fraction mature forest, and fraction watershed storage (lakeCwetland area/watershed area). We calculated several commonly used hydrologic indices from discharge and velocity estimates, including daily flow indices, overall flood indices, low flow variables, and ratios or ranges of flow percentiles reflecting the nature of cumulative frequency distributions. Four principal components (PCs) explained 85.9 and 88.6% of the variation of flow metrics among second- and third-order stream sites, respectively. Axes of variation corresponded to a runoff vs. baseflow axis, flow variability, mean flow, and contrasts between flood duration and frequency. Analysis of velocity metrics for third-order streams yielded four PCs corresponding to mean or maximum velocity, Froude number, and inferred shear velocity, as well as spate frequencies vs. intervals associated with different velocity ranges. Using discriminant function analysis, we could discriminate among watershed classes based on region, mature forest, or watershed storage as a function of flow metrics. For second-order streams, median flow (Qs50) increased as watershed storage increased. North Shore streams showed a more skewed distribution and greater spread of discharge values than did South Shore streams for both stream orders, while third-order North Shore streams exhibited a higher frequency of spates. Independent of regional differences, loss of mature forest increased the range of variation between baseflow and peak flows, and depressed baseflow. Consistent with our initial model for watershed classification, Classification and Regression Tree (CART) analysis confirmed significant thresholds of change in flow metrics averaging between 0.506 and 0.636 for fraction mature forest and between 0.180 and 0.258 for fraction watershed storage
An Alternative Interpretation of Statistical Mechanics
In this paper I propose an interpretation of classical statistical mechanics that centers on taking seriously the idea that probability measures represent complete states of statistical mechanical systems. I show how this leads naturally to the idea that the stochasticity of statistical mechanics is associated directly with the observables of the theory rather than with the microstates (as traditional accounts would have it). The usual assumption that microstates are representationally significant in the theory is therefore dispensable, a consequence which suggests interesting possibilities for developing non-equilibrium statistical mechanics and investigating inter-theoretic answers to the foundational questions of statistical mechanics
Emergence: Key physical issues for deeper philosophical inquiries
A sketch of three senses of emergence and a suggestive view on the emergence
of time and the direction of time is presented. After trying to identify which
issues philosophers interested in emergent phenomena in physics view as
important I make several observations pertaining to the concepts, methodology
and mechanisms required to understand emergence and describe a platform for its
investigation. I then identify some key physical issues which I feel need be
better appreciated by the philosophers in this pursuit. I end with some
comments on one of these issues, that of coarse-graining and persistent
structures.Comment: 16 pages. Invited Talk at the Heinz von Foerster Centenary
International Conference on Self-Organization and Emergence: Emergent Quantum
Mechanics (EmerQuM11). Nov. 10-13, 2011, Vienna, Austria. Proceedings to
appear in J. Phys. (Conf. Series
Particulate matter concentrations in residences: an intervention study evaluating standâalone filters and air conditioners
This study, a randomized controlled trial, evaluated the effectiveness of freeâstanding air filters and window air conditioners (ACs) in 126 lowâincome households of children with asthma. Households were randomized into a control group, a group receiving a freeâstanding HEPA filter placed in the childâs sleeping area, and a group receiving the filter and a windowâmounted AC. Indoor air quality (IAQ) was monitored for weekâlong periods over three to four seasons. High concentrations of particulate matter (PM) and carbon dioxide were frequently seen. When IAQ was monitored, filters reduced PM levels in the childâs bedroom by an average of 50%. Filter use varied greatly among households and declined over time, for example, during weeks when pollutants were monitored, filter use was initially high, averaging 84â±â27%, but dropped to 63â±â33% in subsequent seasons. In months when households were not visited, use averaged only 34â±â30%. Filter effectiveness did not vary in homes with central or room ACs. The study shows that measurements over multiple seasons are needed to characterize air quality and filter performance. The effectiveness of interventions using freeâstanding air filters depends on occupant behavior, and strategies to ensure filter use should be an integral part of interventions. Practical Implications Environmental tobacco smoke (ETS) increased particulate matter (PM) levels by about 14âÎŒg/m 3 and was often detected using ETSâspecific tracers despite restrictions on smoking in the house as reported on questionnaires administered to caregivers. PM concentrations depended on season, filter usage, relative humidity, air exchange ratios, number of children, outdoor PM levels, sweeping/dusting, and presence of a central air conditioner (AC). Freeâstanding air filters can be an effective intervention that provides substantial reductions in PM concentrations if the filters are used. However, filter use was variable across the study population and declined over the study duration, and thus strategies are needed to encourage and maintain use of filters. The variability in filter use suggests that exposure misclassification is a potential problem in intervention studies using filters. The installation of a room AC in the bedroom, intended to limit air exchange ratios, along with an air filter, did not lower PM levels more than the filter alone.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91183/1/j.1600-0668.2011.00761.x.pd
Emergence: Key physical issues for deeper philosophical inquiries
A sketch of three senses of emergence and a suggestive view on the emergence
of time and the direction of time is presented. After trying to identify which
issues philosophers interested in emergent phenomena in physics view as
important I make several observations pertaining to the concepts, methodology
and mechanisms required to understand emergence and describe a platform for its
investigation. I then identify some key physical issues which I feel need be
better appreciated by the philosophers in this pursuit. I end with some
comments on one of these issues, that of coarse-graining and persistent
structures.Comment: 16 pages. Invited Talk at the Heinz von Foerster Centenary
International Conference on Self-Organization and Emergence: Emergent Quantum
Mechanics (EmerQuM11). Nov. 10-13, 2011, Vienna, Austria. Proceedings to
appear in J. Phys. (Conf. Series
Holographic analysis of diffraction structure factors
We combine the theory of inside-source/inside-detector x-ray fluorescence
holography and Kossel lines/x ray standing waves in kinematic approximation to
directly obtain the phases of the diffraction structure factors. The influence
of Kossel lines and standing waves on holography is also discussed. We obtain
partial phase determination from experimental data obtaining the sign of the
real part of the structure factor for several reciprocal lattice vectors of a
vanadium crystal.Comment: 4 pages, 3 figures, submitte
Steel and bone: Mesoscale modeling and middle-out strategies in physics and biology
Mesoscale modeling is often considered merely as a practical strategy used when information on lower-scale details is lacking, or when there is a need to make models cognitively or computationally tractable. Without dismissing the importance of practical constraints for modeling choices, we argue that mesoscale models should not just be considered as abbreviations or placeholders for more âcompleteâ models. Because many systems exhibit different behaviors at various spatial and temporal scales, bottom-up approaches are almost always doomed to fail. Mesoscale models capture aspects of multi-scale systems that cannot be parameterized by simple averaging of lower-scale details. To understand the behavior of multi-scale systems, it is essential to identify mesoscale parameters that âcode forâ lower-scale details in a way that relate phenomena intermediate between microscopic and macroscopic features. We illustrate this point using examples of modeling of multi-scale systems in materials science (steel) and biology (bone), where identification of material parameters such as stiffness or strain is a central step. The examples illustrate important aspects of a so-called âmiddle-outâ modeling strategy. Rather than attempting to model the system bottom-up, one starts at intermediate (mesoscopic) scales where systems exhibit behaviors distinct from those at the atomic and continuum scales. One then seeks to upscale and downscale to gain a more complete understanding of the multi-scale systems. The cases highlight how parameterization of lower-scale details not only enables tractable modeling but is also central to understanding functional and organizational features of multi-scale systems
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