3,663 research outputs found
The effective conductivity of a periodic lattice of circular inclusions
We determine the effective conductivity of a two-dimensional composite
consisting of a doubly periodic array of identical circular cylinders within a
homogeneous matrix. We obtain an exact analytic expression for the effective
conductivity tensor as well as its expansion in terms of volume fraction of the
cylinders. Results are illustrated by examples.Comment: 21 pages, 5 figure
Developing conceptual hydrogeological model for Potsdam sandstones in southwestern Quebec, Canada
A hydrogeological study was conducted in Potsdam sandstones on the international border between Canada (Quebec) and the USA (New York). Two sandstone formations, arkose and conglomerate (base) and well-cemented quartz arenite (upper), underlie the study area and form the major regional aquifer unit. Glacial till, littoral sand and gravel, and marine silt and clay discontinuously overlie the aquifer. In both sandstone formations, sub-horizontal bedding planes are ubiquitous and display significant hydraulic conductivities that are orders of magnitude more permeable than the intact rock matrix. Aquifer tests demonstrate that the two formations have similar bulk hydrologic properties, with average hydraulic conductivities ranging from 2Ă10â5 to 4Ă10â5 m/s. However, due to their different lithologic and structural characteristics, these two sandstones impose rather different controls on groundwater flow patterns in the study area. Flow is sustained through two types of fracture networks: sub-horizontal, laterally extensive fractures in the basal sandstone, where hydraulic connectivity is very good horizontally but very poor vertically and each of the water-bearing bedding planes can be considered as a separate planar two-dimensional aquifer unit; and the more fractured and vertically jointed system found in the upper sandstone that promotes a more dispersed, three-dimensional movement of groundwater. Une Ă©tude hydrogĂ©ologique a Ă©tĂ© entreprise dans les grĂšs de Potsdam, sur la frontiĂšre entre le Canada (QuĂ©bec) et les Etats-Unis (New York). Sous le secteur dâĂ©tude, deux formations grĂ©seuses, les arkoses et conglomĂ©rats (base) et les arĂ©nites quartzeuses cimentĂ©es (sommet), forment une unitĂ© aquifĂšre majeure Ă lâĂ©chelle rĂ©gionale. Les moraines glaciaires, les sables et graviers littoraux, et les argiles et silts marins recouvrent lâaquifĂšre de maniĂšre discontinue. Dans les deux formations grĂ©seuses, les litages sub-horizontaux sont omniprĂ©sents, et prĂ©sentent des conductivitĂ©s hydrauliques significatives, supĂ©rieures de plusieurs ordres de grandeur Ă celles de la matrice rocheuse intacte. Les pompages dâessai dĂ©montrent que les deux formations ont des propriĂ©tĂ©s hydrologiques apparentes comparables, avec notamment des conductivitĂ©s hydrauliques comprises entre 2Ă10â5 et 4Ă 10â5 m/s. Cependant, du fait de leurs lithologies et de leurs caractĂ©ristiques structurales contrastĂ©es, ces deux formations grĂ©seuses imposent des contrĂŽles diffĂ©rents sur les Ă©coulements souterrains dans le secteur dâĂ©tude. LâĂ©coulement est soutenu par deux types de rĂ©seaux de fractures : des fractures latĂ©ralement extensives subhorizontales dans les grĂšs de base, oĂč la connectivitĂ© hydraulique est trĂšs bonne horizontalement mais mĂ©diocre verticalement, et oĂč chacun des plans aquifĂšres peut ĂȘtre considĂ©rĂ© comme une unitĂ© aquifĂšre isolĂ©e plane bidimensionnelle, et un systĂšme fissurĂ© verticalement et plus fracturĂ© situĂ© dans les grĂšs supĂ©rieurs, qui favorise des Ă©coulements souterrains tridimensionnels et plus dispers
Algorithmic decidability of Engel's property for automaton groups
We consider decidability problems associated with Engel's identity
( for a long enough commutator sequence) in groups
generated by an automaton. We give a partial algorithm that decides, given
, whether an Engel identity is satisfied. It succeeds, importantly, in
proving that Grigorchuk's -group is not Engel. We consider next the problem
of recognizing Engel elements, namely elements such that the map
attracts to . Although this problem seems intractable in
general, we prove that it is decidable for Grigorchuk's group: Engel elements
are precisely those of order at most . Our computations were implemented
using the package FR within the computer algebra system GAP
Revisiting stress-corrosion cracking and hydrogen embrittlement in 7xxx-Al alloys at the near-atomic-scale
Poly(4-vinyl pyridine) radiografted PVDF track etched membranes as sensors for monitoring trace mercury in water
International audiencePoly-4-vinyl pyridine chains were radiografted inside the etched-tracks of PVDF nanoporous membrane. P4VP grafting was found to be localized on the solid PVDF surface. Coating of these PVDF-g-P4VP membranes with a very thin layer of gold results in an ASV electrochemical sensor. Functionalized ion track-etched PVDF-g-P4VP sensors were found very selective and highly sensitive for mercury LOD 5 ng/L. a b s t r a c t By a radiation-induced grafting technique, we have functionalized track-etched nanoporous polymer membranes with mercury sensitive poly-4-vinyl pyridine (P4VP). Coating of these membranes with a very thin layer of gold results in an electrochemical sensor that is very selective and highly sensitive for mercury LOD 5 ng/L â well below the norms for water (0.015 mg/L potable water and 0.5 mg/L residual waters-French water norms of 27 October 2011). E-beam irradiation permitted optimization of the radiografting synthesis on PVDF thin films prior to ion-track grafting. Synthesis and characterization by EPR, FESEM and FTIR are described in detail. A comparison between FTIR in ATR and transmission modes enabled us to localize the grafting on the surface of the e-beam irradiated PVDF films allowing us to extrapolate what happens on the etched tracks. Using Square Wave Anodic Stripping Voltammetry (SW-ASV), mercury concentrations of 1 mg/L are detected in 2 h and low ng/L concentrations are detected after 24 h of adsorption. The adsorption is passive so sensors do not require instrumentation and the analysis takes only 3â4 min. Also, the P4VP functionalized sensor appears insensitive to pH variations (pHs 3â9), high salt concentrations (up to 1 g/ L) and the presence of other heavy metals in the same solution.
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Interfacial Engineering of a Carbon Nitride-Graphene Oxide-Molecular Ni Catalyst Hybrid for Enhanced Photocatalytic Activity
Abstract can be found here: https://doi.org/10.1021/acscatal.8b0196
Modeling long-range cross-correlations in two-component ARFIMA and FIARCH processes
We investigate how simultaneously recorded long-range power-law correlated
multi-variate signals cross-correlate. To this end we introduce a two-component
ARFIMA stochastic process and a two-component FIARCH process to generate
coupled fractal signals with long-range power-law correlations which are at the
same time long-range cross-correlated. We study how the degree of
cross-correlations between these signals depends on the scaling exponents
characterizing the fractal correlations in each signal and on the coupling
between the signals. Our findings have relevance when studying parallel outputs
of multiple-component of physical, physiological and social systems.Comment: 8 pages, 5 figures, elsart.cl
A prospective study of cumulative job stress in relation to mental health
BACKGROUND: This study tests associations between psychosocial stress at work measured by the effort-reward imbalance model in a dynamic perspective, and multiple indicators of poor mental health, in a prospective design. METHODS: 1986 male and female employees from four Belgian enterprises were followed-up over one year within the framework of the Somstress study. Based on two consecutive measurements, an index of cumulative job stress was constructed and its associations with five indicators of mental health were studied, excluding caseness at entry (for depression, anxiety, somatisation, chronic fatigue and psychotropic drug consumption respectively). Taking into account the longitudinal design, four categories of job stress are defined: 1) employees free from stress at both measures, 2) job stress present at first measure but not at the second one, 3) recent onset of job stress as evidenced by second measure 4) workers exposed to stress at both measures. Multivariate logistic regression with appropriate adjustments was applied. RESULTS: In bivariate analysis, a clear graded association of cumulative job stress with all five mental health indicators is observed, both in men and women. In multivariate logistic regression analysis, recent onset of stress is strongly associated with poor mental health among men (odds ratios ranging from 1.8 to 4.6), while cumulative stress shows strongest effects on mental health in women (odds ratios ranging from 1.4 to 7.1). CONCLUSION: Cumulative experience and recent onset of job stress in terms of high effort spent and low reward received is associated with elevated risk of all five indicators of poor mental health at follow-up in a large cohort of employees
The impact of asking intention or self-prediction questions on subsequent behavior: a meta-analysis
The current meta-analysis estimated the magnitude of the impact of asking intention and self-prediction questions on rates of subsequent behavior, and examined mediators and moderators of this questionâbehavior effect (QBE). Random-effects meta-analysis on 116 published tests of the effect indicated that intention/prediction questions have a small positive effect on behavior (d+ = 0.24). Little support was observed for attitude accessibility, cognitive dissonance, behavioral simulation, or processing fluency explanations of the QBE. Multivariate analyses indicated significant effects of social desirability of behavior/behavior domain (larger effects for more desirable and less risky behaviors), difficulty of behavior (larger effects for easy-to-perform behaviors), and sample type (larger effects among student samples). Although this review controls for co-occurrence of moderators in multivariate analyses, future primary research should systematically vary moderators in fully factorial designs. Further primary research is also needed to unravel the mechanisms underlying different variants of the QBE
Flow Reorganization in an Anthropogenically Modified Tidal Channel Network: An Example From The Southwestern Ganges-Brahmaputra-Meghna Delta
We examine variations in discharge exchange between two parallel, 1â to 2âkmâwide tidal channels (the Shibsa and the Pussur) in southwestern Bangladesh over springâneap, and historical timescales. Our objective is to evaluate how largeâscale, interconnected tidal channel networks respond to anthropogenic perturbation. The study area spans the boundary between the pristine Sundarbans Reserved Forest, where regular inundation of the intertidal platform maintains the fluvially abandoned delta plain, and the anthropogenically modified region to the north, where earthen embankments sequester large areas of formerly intertidal landscape. Estimates of tidal response to the embankmentâdriven reduction in basin volume, and hence tidal prism, predict a corresponding decrease in size of the mainstem Shibsa channel, yet the Shibsa is widening and locally scouring even as the interconnected Pussur channel faces rapid shoaling. Rather, the Shibsa has maintained or even increased its preâpolder tidal prism by capturing a large portion of the Pussur\u27s basin via several transverse channels that are themselves widening and deepening. We propose that an enhanced tidal setup in the Pussur and the elimination of an effective ShibsaâPussur flow barrier are driving this basin capture event. These results illustrate previously unrecognized channel interactions and emphasize the importance of flow reorganization in response to perturbations of interconnected, multichannel tidal networks that characterize several large tidal delta plains worldwide
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