Modeling of transitional flows

An effort directed at developing improved transitional models was initiated. The focus of this work was concentrated on the critical assessment of a popular existing transitional model developed by McDonald and Fish in 1972. The objective of this effort was to identify the shortcomings of the McDonald-Fish model and to use the insights gained to suggest modifications or alterations of the basic model. In order to evaluate the transitional model, a compressible boundary layer code was required. Accordingly, a two-dimensional compressible boundary layer code was developed. The program was based on a three-point fully implicit finite difference algorithm where the equations were solved in an uncoupled manner with second order extrapolation used to evaluate the non-linear coefficients. Iteration was offered as an option if the extrapolation error could not be tolerated. The differencing scheme was arranged to be second order in both spatial directions on an arbitrarily stretched mesh. A variety of boundary condition options were implemented including specification of an external pressure gradient, specification of a wall temperature distribution, and specification of an external temperature distribution. Overall the results of the initial phase of this work indicate that the McDonald-Fish model does a poor job at predicting the details of the turbulent flow structure during the transition region

Digging deeper: How do different types of organic consumers influence the increasing organic market share?

The purpose of this paper is to investigate how sub markets with different degrees of maturity develop during a period of general organic growth, and how different consumer segments behave on these sub markets. The paper uses actual purchasing behaviour of six consumer segments with different attitudes towards food in general and organic production and products in particular. The data is from the Danish market for organic foods, which is one of the most mature markets in the world. The segmentation splits consumers into a positive and a non-positive half, each half consisting of three different segments. The estimations show that the development in general organic consumption varies between segments, and that their behaviour varies between sub markets. The positive half of the population has driven the overall growth in organic budget share at the Danish market over the period 2005 to 2007, while the other half have not changed their consumption significantly. The results indicate that for the most dedicated organic consumers, the organic budget share may be approaching a saturation point for some types of food, but also identifies other types of food which still have a growing organic budget share, even among the most dedicated consumers. The combination of attitudes and actual behaviour for a large number of consumers is new, and the results provide a valuable contribution to the ongoing investigation of organic consumers, and provide new nuances to the understanding of the latest organic growth.organic budget shares, organic consumers, consumer segments, latent class analysis, demand

An MDL approach to the climate segmentation problem

This paper proposes an information theory approach to estimate the number of changepoints and their locations in a climatic time series. A model is introduced that has an unknown number of changepoints and allows for series autocorrelations, periodic dynamics, and a mean shift at each changepoint time. An objective function gauging the number of changepoints and their locations, based on a minimum description length (MDL) information criterion, is derived. A genetic algorithm is then developed to optimize the objective function. The methods are applied in the analysis of a century of monthly temperatures from Tuscaloosa, Alabama.Comment: Published in at http://dx.doi.org/10.1214/09-AOAS289 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Theory of second harmonic generation in few-layered MoS2

Recent experimental results have demonstrated the ability of monolayer MoS$_2$ to efficiently generate second harmonic fields with susceptibilities between 0.1 and 100 nm/V. However, no theoretical calculations exist with which to interpret these findings. In particular, it is of interest to theoretically estimate the modulus of the second harmonic response, since experimental reports on this differ by almost three orders of magnitude. Here, we present single-particle calculations of the second harmonic response based on a tight-binding band structure. We compare directly with recent experimental findings and include in the discussion also spectral features and the effects of multiple layers

A computational study of thrust augmenting ejectors based on a viscous-inviscid approach

A viscous-inviscid interaction technique is advocated as both an efficient and accurate means of predicting the performance of two-dimensional thrust augmenting ejectors. The flow field is subdivided into a viscous region that contains the turbulent jet and an inviscid region that contains the ambient fluid drawn into the device. The inviscid region is computed with a higher-order panel method, while an integral method is used for the description of the viscous part. The strong viscous-inviscid interaction present within the ejector is simulated in an iterative process where the two regions influence each other en route to a converged solution. The model is applied to a variety of parametric and optimization studies involving ejectors having either one or two primary jets. The effects of nozzle placement, inlet and diffuser shape, free stream speed, and ejector length are investigated. The inlet shape for single jet ejectors is optimized for various free stream speeds and Reynolds numbers. Optimal nozzle tilt and location are identified for various dual-ejector configurations

Effekt av surt aluminiumsrikt vann på atferd hos karuss og laks

Sammendrag Jeg ønsket med mine forsøk å rette søkelyset på fisks atferd når det ble utsatt stabil og ustabil Al-kjemi. Høye Al-konsentrasjoner i vannet forårsakes av sur nedbør, og er en viktig årsak til fiskedød. Aluminium er mest toksisk for fisk ved relativt høy pH (5-6), særlig dersom vannkjemien er ustabil med en høy grad av Al-polymerisering. Jeg ville derfor se på om fisk kunne oppdage forskjeller i Al-toksistet og endre atferd basert på dette. Jeg utførte 3 forsøk med karuss (Carassius carassius) og et forsøk med laks (Salmo salaris). I hvert forsøk ble det satt ut 10 fisk i hver av tre forskjellig renner. En med stabil Al-kjemi, en med ustabil Al-kjemi og en kontrollrenne. Jeg observerte deretter atferdsendringer ved plassering under forsøket, samt aktivitet. Ved observasjon av karuss viste det seg at de endret oppholdssted under Al-eksponering i forhold til før og etter eksponering. De visste også en forhøyet aktivitet som et resultat av Al-eksponering. Laksen viste ingen endring av oppholdssted som et resultat av Al-eksponering. Aktiviteten for laks var høyere før og etter Al-eksponering og sank under Al-eksponeringen. Det fremkom ingen statistisk signifikante sammenhenger mellom Al-kjemi og atferd i mine studier

Immunobiology of ovine γδ T cells

αßδγδγδ T cells have been found in every species so far examined yet no function has been attributed to this population of lymphocytes. WC1 is a cell surface glycoprotein expressed exclusively by γδ T cells in ruminants. The function of this protein is unknown. The γδ TCR molecule is similar to the TCR expressed on αß T cells. αß T cells recognise foreign antigen which is presented on the surface of antigen presenting cells in association with MHC class I or MHC class II molecules. It has been a general assumption that γδ T cells, because of the similarity of the antigen receptor molecules, may recognise antigen, and therefore function in a similar manner to αß T cells. This however has not yet been shown to be the case.In this thesis, the expression of the WC1 protein on ovine γδ T cells was analysed. A large number of monoclonal antibodies exist which recognise epitopes of this molecule in the bovine species. Their reactivity with ovine WC1 proticn was examined, both at a cellular level and protein level. The results in this thesis, along with those published by others during the course of the thesis, identified WC1 as a protein complex with great diversity at the genetic level, and possibly at the post-transciptional or post-translational level. Work in this thesis also confirmed that, with respect to the expression of WC1 proteins, γδ T cell immunochcmistry in the ovine species is similar in some, but not all, respects to that seen in the bovine species.γδ T cells are more prevelant in the ovine species than in either the human or murine species. This may imply that sheep have a greater requirement for γδ T cells than either the human or murine species. The in vitro activation and proliferative response of ovine γδ T cells, following in vitro culture with mitogen or antigen, was examined and compared to the responses of ovine αß T cells. The responses by γδ T cells to both antigen and mitogen were different to the responses by αß T cells. All γδ T cells expressed markers of activation within 8hrs of culture with mitogen, in contrast, it took 24hrs for all αß T cells to express the same markers. In addition, all γδ T cells expressed markers of activation following culture with antigen whereas there was little change in the expression of these markers on αß T cells. Purified γδ T cells proliferated following culture with mitogen but did not proliferate in response to culture with antigen. In addition, purified γδ T cells did not proliferate following culture with allogeneic lymphocytes. These result implied that the function of γδ T cells within the immune system may be markedly different to the function of αß T cells

British Wildlife Law Before the American Revolution: Lessons from the Past

Early legislation may excite the condescending interest ·that Dr. Johnson directed toward a dog walking on its hind legs: It is not done well; but you are surprised to find it done at all. British wildlife law, however, merits more respect. As long ago as the Middle Ages, man\u27s appetite for meat endowed legislators with at least an ambling competence at wildlife management. Nor has the passage of time made their efforts wholly irrelevant. Early methods of controlling habitat, for example, may still be appropriate since historical change has not altered the needs of animals as it has those of men. This is not to say that within the bestiary of early British law there does not run many a droll species of regulation, amusing only because of its ludicrous appearance. Indeed, within the following discussion of the goals and methods of those laws, a kind of carnival fever may appear at times to have overtaken the legislators. But such are the parallels between early problems and those faced today that in the end, to a surprising degree, the stock of old laws can still provide exemplary service

Fast time variations of supernova neutrino fluxes and their detectability

In the delayed explosion scenario of core-collapse supernovae (SNe), the accretion phase shows pronounced convective overturns and a low-multipole hydrodynamic instability, the standing accretion shock instability (SASI). These effects imprint detectable fast time variations on the emerging neutrino flux. Among existing detectors, IceCube is best suited to this task, providing an event rate of ~1000 events per ms during the accretion phase for a fiducial SN distance of 10 kpc, comparable to what could be achieved with a megaton water Cherenkov detector. If the SASI activity lasts for several hundred ms, a Fourier component with an amplitude of 1% of the average signal clearly sticks out from the shot noise. We analyze in detail the output of axially symmetric hydrodynamical simulations that predict much larger amplitudes up to frequencies of a few hundred Hz. If these models are roughly representative for realistic SNe, fast time variations of the neutrino signal are easily detectable in IceCube or future megaton-class instruments. We also discuss the information that could be deduced from such a measurement about the physics in the SN core and the explosion mechanism of the SN.Comment: 14 pages, 11 figures. Final version accepted in PRD. Section on astrophysical relevance and several references adde