Alleviation of pressure pulse effects for trains entering tunnels. Volume 1: Summary

The degree to which it is possible to attenuate the effects of pressure pulses on the passengers in trains entering tunnels by modifying the normally abrupt portal of a constant-diameter single track tunnel was investigated. Although the suggested modifications to the tunnel entrance portal may not appreciably decrease the magnitude of the pressure rise, they are very effective in reducing the discomfort to the human ear by substantially decreasing the rate of pressure rise to that which the normal ear can accommodate. Qualitative comparison was made of this portal modification approach with other approaches: decreasing the train speed or sealing the cars. The optimum approach, which is dependent upon the conditions and requirements of each particular rail system, is likely to be the portal modification one for a rapid rail mass transit system

Hamming weights and Betti numbers of Stanley-Reisner rings associated to matroids

To each linear code over a finite field we associate the matroid of its parity check matrix. We show to what extent one can determine the generalized Hamming weights of the code (or defined for a matroid in general) from various sets of Betti numbers of Stanley-Reisner rings of simplicial complexes associated to the matroid

LiDAR mapping of tidal marshes for ecogeomorphological modelling in the TIDE project

The European research project TIDE (Tidal Inlets Dynamics and Environment) is developing and validating coupled models describing the morphological, biological and ecological evolution of tidal environments. The interactions between the physical and biological processes occurring in these regions requires that the system be studied as a whole rather than as separate parts. Extensive use of remote sensing including LiDAR is being made to provide validation data for the modelling. This paper describes the different uses of LiDAR within the project and their relevance to the TIDE science objectives. LiDAR data have been acquired from three different environments, the Venice Lagoon in Italy, Morecambe Bay in England, and the Eden estuary in Scotland. LiDAR accuracy at each site has been evaluated using ground reference data acquired with differential GPS. A semi-automatic technique has been developed to extract tidal channel networks from LiDAR data either used alone or fused with aerial photography. While the resulting networks may require some correction, the procedure does allow network extraction over large areas using objective criteria and reduces fieldwork requirements. The networks extracted may subsequently be used in geomorphological analyses, for example to describe the drainage patterns induced by networks and to examine the rate of change of networks. Estimation of the heights of the low and sparse vegetation on marshes is being investigated by analysis of the statistical distribution of the measured LiDAR heights. Species having different mean heights may be separated using the first-order moments of the height distribution

Temporal acceleration of a turbulent channel flow

We report new laboratory experiments of a flow accelerating from an initially turbulent state following the opening of a valve, together with large eddy simulations of the experiments and extended Stokes first problem solutions for the early stages of the flow. The results show that the transient flow closely resembles an accelerating laminar flow superimposed on the original steady turbulent flow. The primary consequence of the acceleration is the temporal growth of a boundary layer from the wall, gradually leading to a strong instability causing transition. This extends the findings of previous direct numerical simulations of transient flow following a near-step increase in flow rate. In this interpretation, the initial turbulence is not the primary characteristic of the resulting transient flow, but can be regarded as noise, the evolution of which is strongly influenced by the development of the boundary layer. We observe the spontaneous appearance of turbulent spots and discontinuities in the velocity signals in time and space, revealing rich detail of the transition process, including a striking contrast between streamwise and wall-normal fluctuating velocities

Applicability of frozen-viscosity models of unsteady wall shear stress

The validity of assumed frozen-viscosity conditions underpinning an important class of theoretical models of unsteady wall shear stress in transient flows in pipes and channels is assessed using detailed computational fluid dynamics (CFD) simulations. The need for approximate one-dimensional ð1DÞfx; tg models of the wall stress is unavoidable in analyses of transient flows in extensive pipe networks because it would be economically impracticable to use higher order methods of analysis. However, the bases of the various models have never been established rigorously. It is shown herein that a commonly used approach developed by the first authors is flawed in the case of smoothwall flows although it is more plausible for rough-wall flows. The assessment process is undertaken for a particular, but important, unsteady flow case, namely, a uniform acceleration from an initially steady turbulent flow. First, detailed predictions from a validated CFD method are used to derive baseline solutions with which predictions based on approximate models can be compared. Then, alternative solutions are obtained using various prescribed frozen-viscosity distributions. Differences between these solutions and the baseline solutions are used to determine which frozen-viscosity distributions are the most promising starting points for developing 1Dfx; tg models of unsteady components of wall shear stress. It is shown that no frozen-viscosity distribution performs well for large times after the commencement of an acceleration. However, even the simplest approximation (laminar) performs well for short durations—which is when the greatest amplitudes of the unsteady components occu

Developments in unsteady pipe flow friction modelling

This paper reviews a number of unsteady friction models for transient pipe flow. Two distinct unsteady friction models, the Zielke and the Brunone models, are investigated in detail. The Zielke model, originally developed for transient laminar flow, has been selected to verify its effectiveness for "low Reynolds number" transient turbulent flow. The Brunone model combines local inertia and wall friction unsteadiness. This model is verified using the Vardy's analytically deduced shear decay coefficient C* to predict the Brunone's friction coefficient k rather than use the traditional trial and error method for estimating k. The two unsteady friction models have been incorporated into the method of characteristics water hammer algorithm. Numerical results from the quasi-steady friction model and the Zielke and the Brunone unsteady friction models are compared with results of laboratory measurements for water hammer cases with laminar and low Reynolds number turbulent flows. Conclusions about the range of validity for the three friction models are drawn. In addition, the convergence and stability of these models are addressed.Anton Bergant, Angus Ross Simpson, John Vìtkovsk

Exploring the literacy related behaviours and feelings of pupils eligible for free school meals in relation to their use of, and access to, school libraries

Although it has been argued that school libraries are important for supporting the reading engagement of pupils who receive free school meals, to date there has been little analysis of the extent to which use of school library spaces is related to these pupils' reading behaviors. We analyzed data from 6,264 UK children and young people entitled to FSM who completed the 2019 National Literacy Trust Annual Literacy Survey, to understand the extent to which these pupils' engagement with reading and writing is related to access to or use of their school library. We found their enjoyment of both reading and writing, their confidence in their own abilities, and the frequency with which they read or wrote for pleasure outside of school was significantly higher for those pupils eligible for FSM who used their school libraries relative to both those who did not, and those who had no school library. Consistent with this, children eligible for FSM who used their school library engaged with a greater diversity of reading material and writing than those who were not school library users. We argue that school library provision appears to be a significant resource in supporting low income children's engagement with self-motivated literacy practices

Material insecurity predicts greater commitment to moralistic and less commitment to local deities: a cross-cultural investigation

The existential security hypothesis predicts that in the absence of more successful secular institutions, people will be attracted to religion when they are materially insecure. Most assessments, however, employ data sampled at a state-level with a focus on world religions. Using individual-level data collected in societies of varied community sizes with diverse religious traditions including animism, shamanism, polytheism, and monotheism, we conducted a systematic cross-cultural test (N = 1820; 14 societies) of the relationship between material insecurity (indexed by food insecurity) and religious commitment (indexed by both beliefs and practices). Moreover, we examined the relationship between material security and individuals’ commitment to two types of deities (moralistic and local), thus providing the first simultaneous test of the existential security hypothesis across co-existing traditions. Our results indicate that while material insecurity is associated with greater commitment to moralistic deities, it predicts less commitment to local deity traditions

Turbulence in a transient channel flow with a wall of pyramid roughness

A direct numerical simulation investigation of a transient flow in a channel with a smooth top wall and a roughened bottom wall made of close-packed pyramids is presented. An initially stationary turbulent flow is accelerated rapidly to a new flow rate and the transient flow behaviour after the acceleration is studied. The equivalent roughness heights of the initial and final flows are $k_{s}^{+}=14.5$k+s=14.5 and 41.5, respectively. Immediately after the acceleration ends, the induced change behaves in a ‘plug-flow’ manner. Above the roughness crests, the additional velocity due to the perturbation flow is uniform; below the crest, it reduces approximately linearly to zero at the bottom of the roughness elements. The interaction of the perturbation flow with the rough wall is characterised by a series of events that resemble those observed in roughness-induced laminar–turbulent transitions. The process has two broad stages. In the first of these, large-scale vortices, comparable in extent to the roughness wavelength, develop around each roughness element and high-speed streaks form along the ridge lines of the elements. After a short time, each vortex splits into two, namely (i) a standing vortex in front of the element and (ii) a counter-rotating hairpin vortex behind it. The former is largely inactive, but the latter advects downstream with increasing strength, and later lifts away from the wall. These hairpin vortices wrap around strong low-speed streaks. The second stage of the overall process is the breakdown of the hairpin vortices into many smaller multi-scale vortices distributed randomly in space, leading eventually to a state of conventional turbulence. Shortly after the beginning of the first stage, the three components of the r.m.s of the velocity fluctuation all increase significantly in the near-wall region as a result of the vortical structures, and their spectra bear strong signatures of the surface topology. During the second stage, the overall turbulence energy in this region varies only slightly, but the spectrum evolves significantly, eventually approaching that of conventional turbulence. The direct effect of roughness on the flow is confined to a region up to approximately three element heights above the roughness crests. Turbulence in the core region does not begin to increase until after the transition near the wall is largely complete. The processes of transition over the smooth and rough walls of the channel are practically independent of each other. The flow over the smooth wall follows a laminar–turbulent transition and, as known from previous work, resembles a free-stream turbulence-induced boundary layer bypass transition

Are German patients burdened by the practice charge for physician visits ('Praxisgebuehr')? A cross sectional analysis of socio-economic and health related factors

<p>Abstract</p> <p>Background</p> <p>In 2004, a practice charge for physician visits ('Praxisgebuehr') was implemented in the German health care system, mainly in order to reduce expenditures of sickness funds by reducing outpatient physician visits. In the statutory sickness funds, all adults now have to pay € 10 at their first physician visit in each 3 month period, except for vaccinations and preventive services. This study looks at the effect of this new patient fee on delaying or avoiding physician visits, with a special emphasis on different income groups.</p> <p>Methods</p> <p>Six representative surveys (conducted between 2004 and 2006) of the Bertelsmann Healthcare Monitor were analysed, comprising 7,769 women and men aged 18 to 79 years. The analyses are based on stratified analyses and logistic regression models, including a focus on the subgroup having a chronic disease.</p> <p>Results</p> <p>Two results can be highlighted. First, avoiding or delaying a physician visit due to this fee is seen most often among younger and healthier adults. Second, those in the lowest income group are much more affected in this way than the better of. The multivariate analysis in the subgroup of respondents having a chronic disease shows, for example, that this reaction is reported 2.45 times more often in the lowest income group than in the highest income group (95% CI: 1.90–3.15).</p> <p>Conclusion</p> <p>The analyses indicate that the effects of the practice charge differ by socio-economic group. It would be important to assess these effects in more detail, especially the effects on health care quality and health outcomes. It can be assumed, however, that avoiding or delaying physician visits jeopardizes both, and that health inequalities are increasing due to the practice charge.</p