1,335 research outputs found
Mean First Passage Time in Periodic Attractors
The properties of the mean first passage time in a system characterized by
multiple periodic attractors are studied. Using a transformation from a high
dimensional space to 1D, the problem is reduced to a stochastic process along
the path from the fixed point attractor to a saddle point located between two
neighboring attractors. It is found that the time to switch between attractors
depends on the effective size of the attractors, , the noise, ,
and the potential difference between the attractor and an adjacent saddle point
as: ; the
ratio between the sizes of the two attractors affects . The
result is obtained analytically for small and confirmed by numerical
simulations. Possible implications that may arise from the model and results
are discussed.Comment: 14 pages, 3 figures, submitted to journal of physics
Monte Carlo simulations of pulse propagation in massive multichannel optical fiber communication systems
We study the combined effect of delayed Raman response and bit pattern
randomness on pulse propagation in massive multichannel optical fiber
communication systems. The propagation is described by a perturbed stochastic
nonlinear Schr\"odinger equation, which takes into account changes in pulse
amplitude and frequency as well as emission of continuous radiation. We perform
extensive numerical simulations with the model, and analyze the dynamics of the
frequency moments, the bit-error-rate, and the mutual distribution of amplitude
and position. The results of our numerical simulations are in good agreement
with theoretical predictions based on the adiabatic perturbation approach.Comment: Submitted to Physical Review E. 8 pages, 5 figure
Calculations of time-dependent observables in non-Hermitian quantum mechanics: The problem and a possible solution
The solutions of the time independent Schrodinger equation for non-Hermitian
(NH) Hamiltonians have been extensively studied and calculated in many
different fields of physics by using L^2 methods that originally have been
developed for the calculations of bound states. The existing non-Hermitian
formalism breaks down when dealing with wavepackets(WP). An open question is
how time dependent expectation values can be calculated when the Hamiltonian is
NH ? Using the F-product formalism, which was recently proposed, [J. Phys.
Chem., 107, 7181 (2003)] we calculate the time dependent expectation values of
different observable quantities for a simple well known study test case model
Hamiltonian. We carry out a comparison between these results with those
obtained from conventional(i.e., Hermitian) quantum mechanics (QM)
calculations. The remarkable agreement between these results emphasizes the
fact that in the NH-QM, unlike standard QM, there is no need to split the
entire space into two regions; i.e., the interaction region and its
surrounding. Our results open a door for a type of WP propagation calculations
within the NH-QM formalism that until now were impossible.Comment: 20 pages, 5 Postscript figures. To be Published in Physical Review
Groundwater Quality and Its Health Impact: An Assessment of Dental Fluorosis in Rural Inhabitants of the Main Ethiopian Rift
This study aims to assess the link between fluoride content in groundwater and its impact on dental health in rural communities of the Ethiopian Rift. A total of 148 water samples were collected from two drainage basins within the Main Ethiopian Rift (MER). In the Ziway-Shala basin in particular, wells had high fluoride levels (mean: 9.4 ± 10.5 mg/L; range: 1.1 to 68 mg/L), with 48 of 50 exceeding the WHO drinking water guideline limit of 1.5 mg/L. Total average daily intake of fluoride from drinking groundwater (calculated per weight unit) was also found to be six times higher than the No-Observed-Adverse-Effects-Level (NOAEL) value of 0.06 mg/kg/day. The highest fluoride levels were found in highly alkaline (pH of 7 to 8.9) groundwater characterized by high salinity; high concentrations of sodium (Na+), bicarbonate (HCO3â), and silica (SiO2); and low concentrations of calcium (Ca2+). A progressive Ca2+ decrease along the groundwater flow path is associated with an increase of fluoride in the groundwater. The groundwater quality problem is also coupled with the presence of other toxic elements, such as arsenic (As) and uranium (U). The health impact of fluoride was evaluated based on clinical examination of dental fluorosis (DF) among local residents using the Thylstrup and Fejerskov index (TFI). In total, 200 rural inhabitants between the ages of 7 and 40 years old using water from 12 wells of fluoride range of 7.8â18 mg/L were examined. Signs of DF (TF score of â„ 1) were observed in all individuals. Most of the teeth (52%) recorded TF scores of 5 and 6, followed by TF scores of 3 and 4 (30%), and 8.4% had TF scores of 7 or higher. Sixty percent of the teeth exhibited loss of the outermost enamel. Within the range of fluoride contents, we did not find any correlation between fluoride content and DF. Finally, preliminary data suggest that milk intake has contributed to reducing the severity of DF. The study highlights the apparent positive role of milk on DF and emphasizes the importance of nutrition in management efforts to mitigate DF in the MER and other parts of the world
The Effect of Non-fluoride Factors on Risk of Dental Fluorosis: Evidence from Rural Populations of the Main Ethiopian Rift
Elevated level of fluoride (Fâ) in drinking water is a well-recognized risk factor of dental fluorosis (DF). While considering optimization of region-specific standards for Fâ, it is reasonable, however, to consider how local diet, water sourcing practices, and non-Fâ elements in water may be related to health outcomes. In this study, we hypothesized that non-Fâ elements in groundwater and lifestyle and demographic characteristics may be independent predictors or modifiers of the effects of Fâ on teeth. Dental examinations were conducted among 1094 inhabitants from 399 randomly selected households of 20 rural communities of the Ziway-Shala lake basin of the Main Ethiopian Rift. DF severity was evaluated using the Thylstrup-Fejerskov Index (TFI). Household surveys were performed and water samples were collected from community water sources. To consider interrelations between the teeth within individual (in terms of DF severity) and between Fâ and non-Fâ elements in groundwater, the statistical methods of regression analysis, mixed models, and principal component analysis were used. About 90% of study participants consumed water from wells with Fâ levels above the WHO recommended standard of 1.5 mg/l. More than 62% of the study population had DF. Fâ levels were a major factor associated with DF. Age, sex, and milk consumption (both cowâs and breastfed) were also statistically significantly (p \u3c 0.05) associated with DF severity; these associations appear both independently and as modifiers of those identified between Fâ concentration and DF severity. Among 35 examined elements in groundwater, Ca, Al, Cu, and Rb were found to be significantly correlated with dental health outcomes among the residents exposed to water with excessive Fâ concentrations. Quantitative estimates obtained in our study can be used to explore new water treatment strategies, water safety and quality regulations, and lifestyle recommendations which may be more appropriate for this highly populated region
Normal scaling in globally conserved interface-controlled coarsening of fractal clusters
Globally conserved interface-controlled coarsening of fractal clusters
exhibits dynamic scale invariance and normal scaling. This is demonstrated by a
numerical solution of the Ginzburg-Landau equation with a global conservation
law. The sharp-interface limit of this equation is volume preserving motion by
mean curvature. The scaled form of the correlation function has a power-law
tail accommodating the fractal initial condition. The coarsening length
exhibits normal scaling with time. Finally, shrinking of the fractal clusters
with time is observed. The difference between global and local conservation is
discussed.Comment: 4 pages, 3 eps figure
Molecular and Cellular Profiling of Scalp Psoriasis Reveals Differences and Similarities Compared to Skin Psoriasis
Scalp psoriasis shows a variable clinical spectrum and in many cases poses a great therapeutic
challenge. However, it remains unknown whether the immune response of scalp psoriasis
differs from understood pathomechanisms of psoriasis in other skin areas. We sought
to determine the cellular and molecular phenotype of scalp psoriasis by performing a comparative
analysis of scalp and skin using lesional and nonlesional samples from 20 Caucasian
subjects with untreated moderate to severe psoriasis and significant scalp involvement
and 10 control subjects without psoriasis. Our results suggest that even in the scalp, psoriasis
is a disease of the inter-follicular skin. The immune mechanisms that mediate scalp psoriasis
were found to be similar to those involved in skin psoriasis. However, the magnitude
of dysregulation, number of differentially expressed genes, and enrichment of the psoriatic
genomic fingerprint were more prominent in skin lesions. Furthermore, the scalp transcriptome
showed increased modulation of several gene-sets, particularly those induced by
interferon-gamma, compared with that of skin psoriasis, which was mainly associated with
activation of TNFα/L-17/IL-22-induced keratinocyte response genes. We also detected differences
in expression of gene-sets involving negative regulation, epigenetic regulation,
epidermal differentiation, and dendritic cell or Th1/Th17/Th22-related T-cell processes
Occurrence and sources of radium in groundwater associated with oil fields in the southern San Joaquin Valley, California
Author Posting. © American Chemical Society, 2019. This is an open access article published under an ACS AuthorChoice License. The definitive version was published in Environmental Science and Technology 53(16), (2019): 9398-9406, doi:10.1021/acs.est.9b02395.Geochemical data from 40 water wells were used to examine the occurrence and sources of radium (Ra) in groundwater associated with three oil fields in California (Fruitvale, Lost Hills, South Belridge). 226Ra+228Ra activities (range = 0.010â0.51 Bq/L) exceeded the 0.185 Bq/L drinking-water standard in 18% of the wells (not drinking-water wells). Radium activities were correlated with TDS concentrations (p < 0.001, Ï = 0.90, range = 145â15,900 mg/L), Mn + Fe concentrations (p < 0.001, Ï = 0.82, range = <0.005â18.5 mg/L), and pH (p < 0.001, Ï = â0.67, range = 6.2â9.2), indicating Ra in groundwater was influenced by salinity, redox, and pH. Ra-rich groundwater was mixed with up to 45% oil-field water at some locations, primarily infiltrating through unlined disposal ponds, based on Cl, Li, noble-gas, and other data. Yet 228Ra/226Ra ratios in pond-impacted groundwater (median = 3.1) differed from those in oil-field water (median = 0.51). PHREEQC mixing calculations and spatial geochemical variations suggest that the Ra in the oil-field water was removed by coprecipitation with secondary barite and adsorption on MnâFe precipitates in the near-pond environment. The saline, organic-rich oil-field water subsequently mobilized Ra from downgradient aquifer sediments via Ra-desorption and Mn/Fe-reduction processes. This study demonstrates that infiltration of oil-field water may leach Ra into groundwater by changing salinity and redox conditions in the subsurface rather than by mixing with a high-Ra source.This article was improved by the reviews of John Izbicki and anonymous reviewers for the journal. This work was funded by the California State Water Resources Control Boardâs Regional Groundwater Monitoring in Areas of Oil and Gas Production Program and the USGS Cooperative Water Program. A.V., A.J.K., and Z.W were supported by USDA-NIFA grant (#2017-68007-26308). Any use of trade, firm, or product names is for description purposes only and does not imply endorsement by the U.S. Government
Different paths to the modern state in Europe: the interaction between domestic political economy and interstate competition
Theoretical work on state formation and capacity has focused mostly on early modern Europe and on the experience of western European states during this period. While a number of European states monopolized domestic tax collection and achieved gains in state capacity during the early modern era, for others revenues stagnated or even declined, and these variations motivated alternative hypotheses for determinants of fiscal and state capacity. In this study we test the basic hypotheses in the existing literature making use of the large date set we have compiled for all of the leading states across the continent. We find strong empirical support for two prevailing threads in the literature, arguing respectively that interstate wars and changes in economic structure towards an urbanized economy had positive fiscal impact. Regarding the main point of contention in the theoretical literature, whether it was representative or authoritarian political regimes that facilitated the gains in fiscal capacity, we do not find conclusive evidence that one performed better than the other. Instead, the empirical evidence we have gathered lends supports to the hypothesis that when under pressure of war, the fiscal performance of representative regimes was better in the more urbanized-commercial economies and the fiscal performance of authoritarian regimes was better in rural-agrarian economie
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