226 research outputs found
Hydrologic response of a semi-arid watershed to spatial and temporal characteristics of convective rain cells
Rain can be measured and represented in many ways such as point data from rain gauges, grid data from meteorological radar, or interpolated data. In this paper we represent rain fields by implementing a rain cell model of convective rain cells. The rain fields are used as an input to a hydrological model to test the watershed response to spatial and temporal characteristics of the rain cells. As a case study we tested an extreme storm event over a semi-arid watershed in southern Israel. The rain cell model was found to simulate the rain storm adequately. The use of these modeled cells allowed us to test the sensitivity of the watershed hydrological response to rain cell characteristics and it was found that the watershed is mainly sensitive to the starting location of the rain cell. Relatively small changes in the rain cell's location, speed and direction may increase watershed peak discharge by three-fold
Why Physical Understanding Should Precede the Mathematical Formalism—Conditional Quantum Probabilities as a Case-Study
Conditional probabilities in quantum systems which have both initial and final boundary conditions are commonly evaluated using the Aharonov–Bergmann–Lebowitz rule. In this short note, we present a seemingly disturbing paradox that appears when applying the rule to systems with slightly broken degeneracies. In these cases, we encounter a singular limit—the probability “jumps” when going from perfect degeneracy to negligibly broken one. We trace the origin of the paradox and solve it from both traditional and modern perspectives in order to highlight the physics behind it: the necessity to take into account the finite resolution of the measuring device. As a practical example, we study the application of the rule to the Zeeman effect. The analysis presented here may stress the general need to first consider the governing physical principles before heading to the mathematical formalism, in particular, when exploring puzzling quantum phenomena
Why physical understanding should precede the mathematical formalism - conditional quantum probabilities as a case-study
Conditional probabilities in quantum systems which have both initial and
final boundary conditions are commonly evaluated using the
Aharonov-Bergmann-Lebowitz rule. In this short note we present a seemingly
disturbing paradox that appears when applying the rule to systems with slightly
broken degeneracies. In these cases we encounter a singular limit - the
probability "jumps" when going from perfect degeneracy to negligibly broken
one. We trace the origin of the paradox and solve it from both traditional and
modern perspectives in order to highlight the physics behind it: the necessity
to take into account the finite resolution of the measuring device. As a
practical example, we study the application of the rule to the Zeeman effect.
The analysis presented here may stress the general need to first consider the
governing physical principles before heading to the mathematical formalism, in
particular when exploring puzzling quantum phenomena.Comment: Slightly revised versio
Local/Non-Local Complementarity in Topological Effects
In certain topological effects the accumulation of a quantum phase shift is
accompanied by a local observable effect. We show that such effects manifest a
complementarity between non-local and local attributes of the topology, which
is reminiscent but yet different from the usual wave-particle complementarity.
This complementarity is not a consequence of non-commutativity, rather it is
due to the non-canonical nature of the observables. We suggest that a
local/non-local complementarity is a general feature of topological effects
that are ``dual'' to the AB effect.Comment: 4 page
Quantum interference experiments, modular variables and weak measurements
We address the problem of interference using the Heisenberg picture and
highlight some new aspects through the use of pre-selection, post-selection,
weak measurements, and modular variables, We present a physical explanation for
the different behaviors of a single particle when the distant slit is open or
closed: instead of having a quantum wave that passes through all slits, we have
a localized particle with non-local interactions with the other slit(s). We
introduce a Gedankenexperiment to measure this non-local exchange. While the
Heisenberg picture and the Schrodinger pictures are equivalent formulations of
quantum mechanics, nevertheless, the results discussed here support a new
approach which has led to new insights, new intuitions, new experiments, and
even the possibility of new devices that were missed from the old perspective
Analysis of the Karmarkar-Karp Differencing Algorithm
The Karmarkar-Karp differencing algorithm is the best known polynomial time
heuristic for the number partitioning problem, fundamental in both theoretical
computer science and statistical physics. We analyze the performance of the
differencing algorithm on random instances by mapping it to a nonlinear rate
equation. Our analysis reveals strong finite size effects that explain why the
precise asymptotics of the differencing solution is hard to establish by
simulations. The asymptotic series emerging from the rate equation satisfies
all known bounds on the Karmarkar-Karp algorithm and projects a scaling
, where . Our calculations reveal subtle
relations between the algorithm and Fibonacci-like sequences, and we establish
an explicit identity to that effect.Comment: 9 pages, 8 figures; minor change
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Constraining surface carbon fluxes using in situ measurements of carbonyl sulfide and carbon dioxide
Understanding the processes that control the terrestrial exchange of carbon is critical for
assessing atmospheric CO₂ budgets. Carbonyl sulfide (COS) is taken up by vegetation during
photosynthesis following a pathway that mirrors CO₂ but has a small or nonexistent emission component,
providing a possible tracer for gross primary production. Field measurements of COS and CO₂ mixing ratios
were made in forest, senescent grassland, and riparian ecosystems using a laser absorption spectrometer
installed in a mobile trailer. Measurements of leaf fluxes with a branch-bag gas-exchange system were made
across species from 10 genera of trees, and soil fluxes were measured with a flow-through chamber. These
data show (1) the existence of a narrow normalized daytime uptake ratio of COS to CO₂ across vascular
plant species of 1.7, providing critical information for the application of COS to estimate photosynthetic
CO₂ fluxes and (2) a temperature-dependent normalized uptake ratio of COS to CO₂ from soils. Significant
nighttime uptake of COS was observed in broad-leafed species and revealed active stomatal opening prior
to sunrise. Continuous high-resolution joint measurements of COS and CO₂ concentrations in the boundary
layer are used here alongside the flux measurements to partition the influence that leaf and soil fluxes
and entrainment of air from above have on the surface carbon budget. The results provide a number of
critical constraints on the processes that control surface COS exchange, which can be used to diagnose the
robustness of global models that are beginning to use COS to constrain terrestrial carbon exchange.Keywords: surface fluxes, carbonyl sulfide, laser absorption spectrometry, carbon budget, instrument developmen
Transcriptome-wide association study of schizophrenia and chromatin activity yields mechanistic disease insights
Genome-wide association studies (GWAS) have identified over 100 risk loci for schizophrenia, but the causal mechanisms remain largely unknown. We performed a transcriptome-wide association study (TWAS) integrating a schizophrenia GWAS of 79,845 individuals from the Psychiatric Genomics Consortium with expression data from brain, blood, and adipose tissues across 3,693 primarily control individuals. We identified 157 TWAS-significant genes, of which 35 did not overlap a known GWAS locus. Of these 157 genes, 42 were associated with specific chromatin features measured in independent samples, thus highlighting potential regulatory targets for follow-up. Suppression of one identified susceptibility gene, mapk3, in zebrafish showed a significant effect on neurodevelopmental phenotypes. Expression and splicing from the brain captured most of the TWAS effect across all genes. This large-scale connection of associations to target genes, tissues, and regulatory features is an essential step in moving toward a mechanistic understanding of GWAS
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