Analysis of Surface Runoff

A mathematical model of surface runoff is presented which is of use in building a model of erosion processes. The method used for deriving the conceptual model of surface runoff is based on the mathematical expression of the basic laws of movement of water -- the equation of continuity and the equation of motion. Both equations form a system of nonlinear partial differential equations with two unknown functions expressing the depth and velocity of the movement of water along the slope, in dependence on their location on the slope, and time. The input variables of the model are the intensity and direction of the impinging raindrops, the intensity of infiltration and the physical characteristics of the slope (gradient, length and properties of soil surface). Extensive laboratory experiments have been carried out to determine the functional dependence of tangential stress on the depth and rate of runoff from different types of soil surfaces. Further, the conceptual model of surface runoff has been simplified to a kinematic one by using a simple relation between depth and rate of surface runoff instead of the equation of motion. Two empirical parameters of this relation have been determined by using data from the above mentioned laboratory experiments during calibration of the kinematic model. The kinematic model is recommended because of its simplicity with regard to simulation of the surface runoff formation from individual slopes within the watershed. The model is a multipurpose one. It may be used either for hydrological purposes (simulation of surface runoff characteristics) or for soil conservation purposes. The model outputs are surface characteristics (depth, velocity, rate). It is possible by comparing the surface runoff velocity with the critical nonscouring velocity for given field conditions to determine the critical slope length which is the basis for planning efficient soil conservation measures

INVESTIGATING THE RELATION BETWEEN COMMON CAUSE COUPLING FACTORS AND AGEING

Usually, probabilistic safety analyses are using the assumption of the constant component failure rate, and the assumption that the probability associated to common cause failure (CCF) will be constant in time. Still, as ageing phenomena could have some influence on components or systems performances, is probable that it could influence the probability of occurrence of CCFs also. This paper is devoted to investigation of the most important CCFs initiating factors from point of view of relation to ageing phenomena. The connections between CCF potential and ageing phenomena, as the influence of the individual prevention factors against CCF were evaluated. A questionnaire has been developed on this topic and all the inputs provided were summarized, compared and commented. The analysis has not been limited only to the list of negative factors that would increase the CCF potential, it has included also positive factors representing the prevention and correction measures applied with the aim to avoid occurrence and recurrence of CCF events, whether related to ageing or not. Two main topics were discussed: a) the strength of relation between the individual CCF coupling factors (contributing to total CCF potential) and ageing phenomena; b) the effect of CCF prevention measures on the coupling factors versus ageing relation (estimated for those CCF coupling factors that were evaluated as coincident with ageing phenomena, with at least medium level of coincidence).JRC.F.5-Nuclear Reactor Safety Assessmen

Is the daily use of public transport facilities an enhanced epidemiological risk for diagnosing COVID-19 among healthcare workers with mild respiratory symptoms?

Introduction: Many people in Switzerland think that the daily use of the public transport facilities, during a pandemic peak wave, could be associated with an enhanced risk for Covid-19. Objectives: To investigate the association between the daily use of the public transport and acquisition of Covid-19 in Zurch during a peak wave of the pandemics. Methods: Retrospective cohort analysis of hospital-own databases at the Balgrist University Hospital in Zurich, between 1 October and 31 December 2020. We specifically interviewed our healthcare workers (HCW) about the use of public transport (with mandatory masking). Results: During the three most intensive months of the 2nd wave, we investigated 376 episodes of Covid-19-compatible respiratory symptoms and exposures among our HCW (median age 37 years), of which 94 (25%) revealed a positive PCR result for Covid-19. Overall, 225 HCW (225/376;60%) reportedly used the public transport (train, bus, tramway). In group comparison, the HCWs using the public transport system acquired no more Covid-19 than using a private transport (58/225 vs. 36/151;Pearson-chi2-test;p = 0.67). We added a logistic regression model with the outcome “Covid-19 infection” to adjust for the case-mix of different localizations or opportunities of potential contamination such as a documented exposure in the hospital, among the team members, in the family, or after a close contact to a PCR-confirmed case. In the multivariate results, using the public transport was irrelevant concerning the acquisition of Covid- 19 (odds ratio (OR) 0.98, 95%CI 0.59-1.62), in contrast, for example, to being exposed to a sick team member (OR 2.28, 95%CI 1.20-4.34). Conclusion: In Zurich, the daily use of public transport was not associated with an additional risk of being diagnosed with Covid-19 among the young population of HCWs, not even during the peak of a pandemic wave. Other factors are more relevant

"Riesenrad" Ion Gantry for Hadron Therapy, 3

When using accelerator beams for cancer therapy, the three-dimensional freedom afforded by a gantry helps the treatment planner to spread out surface doses, avoid directions that intercept vital organs and irradiate a volume that is conformal with the tumour. The general preference is for an iso-centric gantry turning 360° in the vertical plane around the patient bed with sufficient space to be able to orientate the patient through 360° in the horizontal plane. For hadrontherapy, gantries are impressive structures of the order of 10 m in diameter and 100 tons in weight and to date only proton gantries have been demonstrated to operate satisfactorily. The increased magnetic rigidity of say carbon ions will make ion gantries more difficult and costly to build. For this reason, exo-centric gantries and, in particular the so-called 'Riesenrad' gantry with a single 90° bending magnet, merit further attention. The power consumption is reduced and the heavy magnets with their counterbalance weight are reduced and are kept close to the axis. The treatment room, which is lighter, is positioned at a larger radius, but only the patient bed requires careful alignment. An optics module called a 'rotator' is needed to match an incoming dispersion vector to the gantry in order to have an achromatic beam at the patient. A practical design is described that assumes the beam is derived from a slow-extraction scheme in a synchrotron and that the beam sizes are controlled by modules in the transfer line. Magnetic scanning is integrated into the gantry optics for both transverse directions

Bone Marrow Cell Colonization Of, and Extracellular Matrix Expression On, Biodegradable Polymers

Poly(DL-lactide-co-glycolide)s (PLGAs) have been proposed as substrata for bone tissue engineering. In the experiments reported herein, we sought to identify the optimum lactide to glycolide ratio, from the series 85:15, 75:25, 50:50, or poly-(DL-lactide) (PLA), for the elaboration of bone matrix by cultured rat bone marrow cells (RBMC) on two-dimensional substrates. Having identified PLGA 75:25 as the optimum for bone matrix elaboration by RBMC, we produced three dimensional foams from this copolymer. For the two dimensional substrata, glass coverslips were spin-coated with one of the PLGAs, or PLA. Cultures were maintained for two weeks. We employed a new technique to label the elaborated bone matrix with the fluorescent antibiotic tetracycline. Bone matrix was present to a varying degree dependent on substrate composition: PLGA 75:25 = TCP \u3e PLGA 85:15 \u3e \u3e PLA. No bone matrix was observed on PLGA 50:50 or on uncoated glass coverslips. Cell proliferation was similar on each surface except PLA on which they did not proliferate. Cell morphology was assessed by scanning electron microscopy. Based on these results, three dimensional devices were produced from PLGA 75:25. Our results demonstrate that the copolymer ratios that maximize cell proliferation are not identical to the that optimize bone matrix elaboration. Furthermore, despite the intended use of three dimensional matrices for connective tissue engineering applications, bone marrow-derived cells produced only a superficial matrix layer that did not invade the scaffold, whether produced by either the salt leaching or freeze-drying procedures employed

Erosion and Water Quality as Modeled by Creams: A Case Study of the Sedlicky Catchment

In the process of verifying and validating the models of agricultural nonpoint source pollution at IIASA, a study was made of the Sedlicky brook (Bohemia, Czechoslovakia) case. The CREAMS model, verified at the Samsin research area (Czechoslovakia) has been used as the mathematical instrument. The validation results of the CREAMS model for the boundary conditions between the field level and the watershed level seem to show that under certain conditions, it can be applied to small watersheds. For large watersheds, modification of the hydrology submodel is necessary in order to describe the comprehensive hydrologic phenomena, particularly, the interflow and some of the subsurface flow