Thresholds, switches and hysteresis in hydrology from the pedon to the catchment scale: a non-linear systems theory

International audienceHysteresis is a rate-independent non-linearity that is expressed through thresholds, switches, and branches. Exceedance of a threshold, or the occurrence of a turning point in the input, switches the output onto a particular output branch. Rate-independent branching on a very large set of switches with non-local memory is the central concept in the new definition of hysteresis. Hysteretic loops are a special case. A self-consistent mathematical description of hydrological systems with hysteresis demands a new non-linear systems theory of adequate generality. The goal of this paper is to establish this and to show how this may be done. Two results are presented: a conceptual model for the hysteretic soil-moisture characteristic at the pedon scale and a hysteretic linear reservoir at the catchment scale. Both are based on the Preisach model. A result of particular significance is the demonstration that the independent domain model of the soil moisture characteristic due to Childs, Poulavassilis, Mualem and others, is equivalent to the Preisach hysteresis model of non-linear systems theory, a result reminiscent of the reduction of the theory of the unit hydrograph to linear systems theory in the 1950s. A significant reduction in the number of model parameters is also achieved. The new theory implies a change in modelling paradigm

Effective renormalized multi-body interactions of harmonically confined ultracold neutral bosons

We calculate the renormalized effective 2-, 3-, and 4-body interactions for N neutral ultracold bosons in the ground state of an isotropic harmonic trap, assuming 2-body interactions modeled with the combination of a zero-range and energy-dependent pseudopotential. We work to third-order in the scattering length a defined at zero collision energy, which is necessary to obtain both the leading-order effective 4-body interaction and consistently include finite-range corrections for realistic 2-body interactions. The leading-order, effective 3- and 4-body interaction energies are U3 = -(0.85576...)(a/l)^2 + 2.7921(1)(a/l)^3 + O[(a/l)^4] and U4 = +(2.43317...)(a/l)^3 + O[(a\l)^4], where w and l are the harmonic oscillator frequency and length, respectively, and energies are in units of hbar*w. The one-standard deviation error 0.0001 for the third-order coefficient in U3 is due to numerical uncertainty in estimating a slowly converging sum; the other two coefficients are either analytically or numerically exact. The effective 3- and 4-body interactions can play an important role in the dynamics of tightly confined and strongly correlated systems. We also performed numerical simulations for a finite-range boson-boson potential, and it was comparison to the zero-range predictions which revealed that finite-range effects must be taken into account for a realistic third-order treatment. In particular, we show that the energy-dependent pseudopotential accurately captures, through third order, the finite-range physics, and in combination with the multi-body effective interactions gives excellent agreement with the numerical simulations, validating our theoretical analysis and predictions.Comment: Updated introduction, correction of a few typos and sign error

Movement demands and perceived wellness associated with preseason training camp in NCAA Division I college football players

The aims of this study were to examine the movement demands of preseason practice in National Collegiate Athletic Association Division I college football players using portable global positioning system (GPS) technology and to assess perceived wellness associated with preseason practice to determine whether GPS-derived variables from the preceding day influence perceived wellness the following day. Twenty-nine players were monitored using GPS receivers (Catapult Innovations, Melbourne, Australia) during 20 preseason practices. Individual observations (n = 550) were divided into offensive and defensive position groups. Movement variables including low-, medium-, high-intensity, and sprint distance, player load, and acceleration and deceleration distance were assessed. Perceived wellness ratings (n = 469) were examined using a questionnaire which assessed fatigue, soreness, sleep quality, sleep quantity, stress, and mood. A 1-way analysis of variance for positional movement demands and multilevel regressions for wellness measures were used, followed by post hoc testing to evaluate the relational significance between categorical outcomes of perceived wellness scores and movement variables. Results demonstrated significantly (p ≤ 0.05) greater total, high-intensity, and sprint distance, along with greater acceleration and deceleration distances for the defensive back and wide receiver position groups compared with their respective offensive and defensive counterparts. Significant (p ≤ 0.05) differences in movement variables were demonstrated for individuals who responded more or less favorably on each of the 6 factors of perceived wellness. Data from this study provide novel quantification of the position-specific physical demands and perceived wellness associated with college football preseason practice. Results support the use of position-specific training and individual monitoring of college football players

The use of information in online healthcare provider choice

In order to evaluate and facilitate the provision of health information online, we must first understand how it is perceived by those who use it. Two important considerations in research on patients’ information use in online healthcare provider choice are the need for a conceptual framework for studying information types and methods for studying information use. Therefore, our first contribution lies in using Donabedian's structure-process-outcome model of healthcare quality to identify specific patterns of preference and information use in online healthcare provider choice, and differences in information use between two healthcare provider types. Our second contribution lies in identifying differences in results between data collection methods (importance rating/selection, concurrent self-report of online information use and retrospective information use) in relation to choice tasks. In a mixed-methods design, provider type (primary and secondary care) was systematically varied during participants’ use of the infomediary NHS Choices. Participants preferred process topics over structure topics, in contrast with the results of concurrent and retrospective self-report. We conclude that the differences in results between the types of data collection method reflect underlying differences in choice task. Future research should address the use of novel infomediary user-interfaces, and infomediaries in relation to the use of other information sources and (e-)health literacy

Cosmology on a Mesh

An adaptive multi grid approach to simulating the formation of structure from collisionless dark matter is described. MLAPM (Multi-Level Adaptive Particle Mesh) is one of the most efficient serial codes available on the cosmological 'market' today. As part of Swinburne University's role in the development of the Square Kilometer Array, we are implementing hydrodynamics, feedback, and radiative transfer within the MLAPM adaptive mesh, in order to simulate baryonic processes relevant to the interstellar and intergalactic media at high redshift. We will outline our progress to date in applying the existing MLAPM to a study of the decay of satellite galaxies within massive host potentials.Comment: 3 pages, 2 figures, to appear in the proceedings of "The IGM/Galaxy Connection - The Distribution of Baryons at z=0", ed. M. Putman & J. Rosenber

Temperature dependence of metal film growth via low‐energy electron diffraction intensity oscillations: Pt/Pd(100)

A commercial, conventional low‐energy electron diffraction apparatus is used to monitor Bragg intensity oscillations during the growth of Pt on Pd(100). The effect of substrate temperature between 80 and 400 K is investigated. Between 80 and 300 K, two to three Bragg oscillations are observed. The oscillation amplitude damps out quickly as film coverage increases at fixed temperature, but damp out less quickly at the higher substrate temperatures. Above ∼350 K, reconstruction of the Pt overlayer interferes with the oscillations. These data indicate that a kinetic barrier, most probably the barrier to surface diffusion,inhibits the system from achieving macroscopic equilibrium, and that the true equilibrium growth mode for this system is layer‐by‐layer. A new, analytical procedure is used to determine the coverage distribution within the layers from the Bragg intensities during growth. Bragg oscillations are predicted to occur at low substrate temperatures where surface diffusion is minimal and deposition is essentially random, but restricted to the fourfold hollow adsorption sites