Modelling hazardous distances for large-scale liquid hydrogen pool releases

Abstract An analysis has been carried out using a CFD model (FLACS) to simulate large-scale liquid hydrogen (LH2) pool releases to examine their behaviour and predict the LH2 pool size, downwind hazardous distance, and flammable mass of the hydrogen-air clouds formed for different environmental conditions and release scenarios. The FLACS pool model reproduces similar qualitative trends with regard to the effect of spill rate, spill duration and wind speed on the flammable cloud extent to those observed in the NASA WSTF experimental tests, although significant quantitative differences in the results are also apparent. FLACS simulations were also performed for a number of different transient and continuous LH2 spill release rates to predict the maximum downwind hazardous distances as a function of the LH2 spill release rate. The results are intended to assist with assessing the safety of future LH2 aircraft and airport LH2 storage facilities, being considered as part of the EU ENABLEH2 project

The challenges of titanium metal injection moulding

Published ArticleTitanium has fired the imagination of engineers and designers for decades by its 'ideal' combination of high strength, low density and good corrosion resistance. However, its application has unfortunately been limited to those niche markets where performance is more important than cost, such as in the aerospace, military, medical and off-shore oil drilling fields. Extensive efforts have been and still are being expended on ways to make this metal cheaper. There are promising new processes but these have yet to be demonstrated commercially. Nevertheless, there has been a global surge in interest in titanium over the past decade, and in South Africa the government has recently made this a particular focus for research and development funding. With the increased availability of higher quality titanium powder, metal injection moulding offers an attractive method for producing small, intricate components at a reasonable cost. This paper will present an overview of the metal injection moulding process and discuss the particular challenges related to the use of titanium and titanium alloy powders. The state of the global and local industry and markets will also be reviewed

Geographic Variation In Resource Dominance Discovery In Brazilian Ant Communities

A predictive framework for the ecology of species invasions requires that we learn what limits successful invaders in their native range. The red imported fire ant (Solenopsis invicta) is invasive in the United States, Puerto Rico, Australia, New Zealand, and China, Solenopsis invicta appears to be a superior competitor in its introduced range, where it can cause the local extirpation of native species, but little is known about its competitive ability in its native range in South America. Here we examine the competitive ability of S. invicta for food resources in three widely separated Brazilian ant communities. Each of these communities contains 20-40 ant species, 8-10 of which were common and frequently interacted with S. invicta. S. invicta at all three sites was attacked by several species-specific phorid parasitoids, and at one site, two other species were attacked by their own specialized parasitoids. We examined interactions in these local communities for evidence that trade-offs among ant species between resource dominance and resource discovery, and between resource dominance and parasitoid vulnerability facilitate local coexistence. The trade-off between resource dominance and resource discovery was strong and significant only at Santa Genebra, where parasitoids had no effect on the outcome of confrontations at resources. At Bonito, parasitoids significantly reduced the ability of S. invicta, which was the top-ranked behavioral dominant, from defending and usurping food resources from subordinate species. In the Pantanal, S. invicta ranked behind three other ant species in a linear hierarchy of behavioral dominance, and lost the majority of its interactions with a fourth more subordinate species, Paratrechina fulva, another invasive species. Parasitoids of S. invicta were uncommon in the Pantanal, and did not affect its low position in the hierarchy relative to the other two sites. Parasitoids, however, did affect the ability of Linepithema angulation, the top-ranked behavioral dominant in this community, from defending and usurping resources from behavioral subordinates. These results indicate that both interspecific competition and trait-mediated indirect effects of phorid parasitoids affect the ecological success of the red imported fire ant in its native range, but that the relative importance of these factors varies geographically. © 2008 by the Ecological Society of America.89718241836Adler, F.R., The balance of terror: An alternative mechanism for competitive tradeoffs and its implications for invading species (1999) American Naturalist, 154, pp. 497-509Adler, F.R., LeBrun, E.G., Feener Jr., D.H., Maintaining diversity in an ant community: Modeling, extending, and testing the dominance-discovery trade-off (2007) American Naturalist, 169, pp. 323-333Allen, C.R., Lutz, R.S., Demaris, S., Red imported fire ant impacts on northern bobwhite populations (1995) Ecological Applications, 5, pp. 632-638Allen, C.R., Willey, R.D., Myers, P.E., Horton, P.M., Buffa, J., Impact of red imported fire ant infestation on northern bobwhite quail abundance trends in southeastern United States (2000) Journal of Agricultural and Urban Entomology, 17, pp. 43-51Bestelmeyer, B.T., The trade-off between thermal tolerance and behavioural dominance in a subtropical South American ant community (2000) Journal of Animal Ecology, 69, pp. 998-1009Callaway, R.M., Aschehoug, E.T., Invasive plants versus their new and old neighbors: A mechanism for exotic invasion (2000) Science, 290, pp. 521-523Cerdá, X., Retana, J., Cros, S., Thermal disruption of transitive hierarchies in Mediterranean ant communities (1997) Journal of Animal Ecology, 66, pp. 363-374Cerdá, X., Retana, J., Cros, S., Critical thermal limits in Mediterranean ant species: Trade-off between mortality risk and foraging performance (1998) Functional Ecology, 12, pp. 45-55Cerdá, X., Retana, J., Manzaneda, A., The role of competition by dominants and temperature in the foraging of subordinate species in mediterranean ant communities (1998) Oecologia, 117, pp. 404-412Chase, J.M., Abrams, P.A., Grover, J.P., Diehl, S., Chesson, P., Holt, R.D., Richards, S.A., Case, T.J., The interaction between predation and competition: A review and synthesis (2002) Ecology Letters, 5, pp. 302-315Chase, J.M., Leibold, M.A., (2003) Ecological niches: Linking classical and contemporary approaches, , University of Chicago Press, Chicago, Illinois, USAColley, W.N., (2002) Colley's bias free college football ranking method: The Colley matrix explained, , http://www.colleyrankings.com/matrate.pdfCytel. 2005. StatXact. Version 7. Cytel, Cambridge, Massachusetts, USADavidson, D.W., Resource discovery versus resource domination in ants: A functional mechanism for breaking the trade-off (1998) Ecological Entomology, 23, pp. 484-490de Vries, H., An improved test of linearity in dominance hierarchies containing unknown or tied relationships (1995) Animal Behaviour, 50, pp. 1375-1389de Vries, H., Finding a dominance order most consistent with a linear hierarchy: A new procedure and review (1998) Animal Behaviour, 55, pp. 827-843de Vries, H., Netto, W.J., Hanegraaf, P.L.H., MatMan: A program for the analysis of sociometric matrices and behavioral transition matrices (1993) Behaviour, 125, pp. 157-175Feener Jr., D.H., Is the assembly of ant communities mediated by parasitoids? (2000) Oikos, 90, pp. 79-88Fellers, J.H., Interference and exploitation in a guild of woodland ants (1987) Ecology, 68, pp. 1466-1478Folgarait, P.J., D'Adamo, P., Gilbert, L.E., A grassland ant community in Argentina: The case of Solenopsis richteri and Camponotus punctulatus (Hymenoptera: Formicidae) attaining high densities in their native ranges (2004) Annals of the Entomological Society of America, 97, pp. 450-457Giraud, T., Pedersen, J.S., Keller, L., Evolution of supercolonies: The Argentine ants of southern Europe (2002) Proceedings of the National Acadcmv of Sciences, 99, pp. 6075-6079. , USAHölldobler, B., Wilson, E.O., (1990) The ants, , Harvard University Press, Cambridge, Massachusetts, USAHolway, D.A., Effect of Argentine ant invasions on ground-dwelling arthropods in northern California riparian woodlands (1998) Oecologia, 116, pp. 252-258Holway, D.A., Competitive mechanisms underlying the displacement of native ants by the invasive Argentine ant (1999) Ecology, 80, pp. 238-251Holway, D.A., Lach, L., Suarez, A.V., Tsutsui, N.D., Case, T.J., The causes and consequences of ant invasions (2002) Annual Review of Ecology and Systematics, 33, pp. 181-233Hook, A.W., Porter, S.D., Destruction of harvester ant colonies by invading fire ants in South-central Texas (Hymenoptera: Formicidae) (1990) Southwestern Naturalist, 35, pp. 477-478Keane, R.M., Crawley, M.J., Exotic plant invasions and the enemy release hypothesis (2002) Trends in Ecology and Evolution, 17, pp. 164-170Kneitel, J.M., Chase, J.M., Trade-offs in community ecology: Linking spatial scales and species coexistence (2004) Ecology Letters, 7, pp. 69-80Kopachena, J.G., Buckley, A.J., Potts, G.A., Effects of the red imported fire ant (Solenopsis invicta) on reproductive success of barn swallows (Hirundo rustica) in northeast Texas (2000) Southwestern Naturalist, 45, pp. 477-482LeBrun, E.G., Who is the top dog in ant communities? Resources, parasitoids, and multiple competitive hierarchies (2005) Oecologia, 142, pp. 643-652LeBrun, E.G., Feener, D.H., Linked indirect effects in ant-phorid interactions: Impacts on ant assemblage structure (2002) Oecologia, 133, pp. 599-607LeBrun, E.G., Feener, D.H., When trade-offs interact: Balance of terror enforces dominance discovery-trade-off in a local ant assemblage (2007) Journal of Animal Ecology, 76, pp. 58-64LeBrun, E.G., Tillberg, C.V., Suarez, A.V., Folgarait, P., Smith, C.R., Holway, D.A., An experimental study of competitive interactions between red imported fire ants and Argentine ants in a region of native-range sympatry (2007) Ecology, 88, pp. 63-75Lockwood, J.L., McKinney, M.L., (2001) Biotic homogenization, , Kluwer Academic Publishers, New York, New York, USALodge, D.M., Biological invasions: Lessons for ecology (1993) Trends in Ecology and Evolution, 8, pp. 133-137Mann, C.C., Fire ants parlay their queens into a threat to biodiversity (1994) Science, 263, pp. 1560-1561Mattos, M.R., Orr, M.R., Two new species of Pseudacteon (Diptera: Phoridae) of ants in the genus Linepithema (Hymenoptera: Formicidae) in Brazil (2002) Studia Dipterologia, 9, pp. 283-288Mescher, M.C., Ross, K.G., Shoemaker, D.D., Keller, L., Krieger, M.J.B., Distribution of the two social forms of the fire ant Solenopsis invicta (Hymenoptera: Formicidae) in the native South American range (2003) Annals of the Entomological Society of America, 96, pp. 810-817Morrison, L.W., Community organization in a recently assembled fauna: The case of Polynesian ants (1996) Oecologia, 107, pp. 243-256Morrison, L.W., Long-term impacts of an arthropod-community invasion by the imported fire ant, Solenopsis invicta (2002) Ecology, 83, pp. 2337-2345Morrison, L.W., Kawazoe, E.A., Guerra, R., Gilbert, L.E., Ecological interactions of Pseudacteon parasitoids and Solenopsis ant hosts: Environmental correlates of activity and effects on competitive hierarchies (2000) Ecological Entomology, 25, pp. 433-444Noldus Information Technology, 2002. MatMan. Version 1.1. Noldus Information Technology, Sterling, Virginia, USAOlden, J.D., Poff, N.L., Toward a mechanistic understanding and prediction of biotic homogenization (2003) American Naturalist, 162, pp. 442-460Olden, J.D., Poff, N.L., Ecological processes driving biotic homogenization: Testing a mechanistic model using fish faunas (2004) Ecology, 85, pp. 1867-1875Orr, M.R., Dahlsten, D.L., Benson, W.W., Ecological interactions among ants in the genus Linepithema, their parasitoids (Diptera: Phoridae), and their ant competitors (2003) Ecological Entomology, 28, pp. 203-210Orr, M.R., Seike, S.H., Gilbert, L.E., Foraging ecology and patterns of diversification in dipteran parasitoids of fire ants in south Brazil (1997) Ecological Entomology, 22, pp. 305-314Porter, S.D., Fowler, H.G., Mackay, W.P., Fire ant mound densities in the United States and Brazil (Hymenoptera: Formicidae) (1992) Journal of Economic Entomology, 85, pp. 1154-1161Porter, S.D., Savignano, D.A., Invasion of polygyne fire ants decimates native ants and disrupts arthropod community (1990) Ecology, 71, pp. 2095-2106Porter, S.D., Williams, D.F., Patterson, R.S., Fowler, H.G., Intercontinental differences in the abundance of Solenopsis fire ants (Hymenoptera: Formicidae): an escape from natural enemies? (1997) Environmental Entomology, 26, pp. 373-384Qian, H., Ricklefs, R.E., The role of exotic species in homogenizing the North American flora (2006) Ecology Letters, 9, pp. 1293-1298R Development Core Team. 2006. R: a language and environment for statistical computing. Version 2.3.1. R Foundation for Statistical Computing, Vienna, AustriaRetana, J., Cerdá, X., Patterns of diversity and composition of Mediterranean ground ant communities tracking spatial and temporal variability in the thermal environment (2000) Oecologia, 123, pp. 436-444Ross, K.G., Vargo, E.L., Keller, L., Social evolution in a new environment: The case of introduced fire ants (1996) Proceedings of the National Academy of Sciences (USA), 93, pp. 3021-3025Seike, S.H., (2002) Ecologica da interaçáo entre formigas invasoras e moscas parasitóides, , Dissertation. Universidade Estadual de Campinas, Campinas, BrazilShea, K., Chesson, P., Community ecology theory as a framework for biological invasions (2002) Trends in Ecology and Evolution, 17, pp. 170-176Trager, J.C., A revision of the fire ants, Solenopsis geminata group (Hymenoptera: Formicidae: Myrmicinae) (1991) Journal of the New York Entomological Society, 99, pp. 141-198Tschinkel, W.R., Distribution of the fire ants Solenopsis invicta and S. geminata (Hymenoptera: Formicidae) in northern Florida in relation to habitat and disturbance (1988) Annals of the Entomological Society of America, 81, pp. 76-81Tschinkel, W.R., (2006) The fire ants, , Belknap Press, Cambridge, Massachusetts, USATsutsui, N.D., Suarez, A.V., Holway, D.A., Case, T.J., Reduced genetic variation and the success of an invasive species (2000) Proceedings of the National Academy of Sciences (USA), 97, pp. 5948-5953Vepsäläinen, K., Pisarski, B., Assembly of island ant communities (1982) Annales Zoologici Fennici, 19, pp. 327-335Wolfe, L.M., Why alien invaders succeed: Support for the escape-from-enemv hypothesis (2002) American Naturalist, 160, pp. 705-71

Optimising a nonlinear utility function in multi-objective integer programming

In this paper we develop an algorithm to optimise a nonlinear utility function of multiple objectives over the integer efficient set. Our approach is based on identifying and updating bounds on the individual objectives as well as the optimal utility value. This is done using already known solutions, linear programming relaxations, utility function inversion, and integer programming. We develop a general optimisation algorithm for use with k objectives, and we illustrate our approach using a tri-objective integer programming problem.Comment: 11 pages, 2 tables; v3: minor revisions, to appear in Journal of Global Optimizatio

Aldehyde dehydrogenase-1a1 induces oncogene suppressor genes in B cell populations

AbstractThe deregulation of B cell differentiation has been shown to contribute to autoimmune disorders, hematological cancers, and aging. We provide evidence that the retinoic acid-producing enzyme aldehyde dehydrogenase 1a1 (Aldh1a1) is an oncogene suppressor in specific splenic IgG1+/CD19− and IgG1+/CD19+ B cell populations. Aldh1a1 regulated transcription factors during B cell differentiation in a sequential manner: 1) retinoic acid receptor alpha (Rara) in IgG1+/CD19− and 2) zinc finger protein Zfp423 and peroxisome proliferator-activated receptor gamma (Pparg) in IgG1+/CD19+ splenocytes. In Aldh1a1−/− mice, splenic IgG1+/CD19− and IgG1+/CD19+ B cells acquired expression of proto-oncogenic genes c-Fos, c-Jun, and Hoxa10 that resulted in splenomegaly. Human multiple myeloma B cell lines also lack Aldh1a1 expression; however, ectopic Aldh1a1 expression rescued Rara and Znf423 expressions in these cells. Our data highlight a mechanism by which an enzyme involved in vitamin A metabolism can improve B cell resistance to oncogenesis

Coherent transition radiation produced by a 1.2 MeV electron beam

We describe a method of generating very high-frequency coherent radiation using an electron beam source with a maximum beam energy of 1.2 MeV. We show that, though the high frequency cutoff for the radiation generated when the beam impacts a target at normal incidence is reduced by transverse beam size effects, it is nevertheless possible to generate much higher frequencies by a judicious choice of the angles of incidence and observation. 5 refs., 4 figs., 1 tab

An entangled two photon source using biexciton emission of an asymmetric quantum dot in a cavity

A semiconductor based scheme has been proposed for generating entangled photon pairs from the radiative decay of an electrically-pumped biexciton in a quantum dot. Symmetric dots produce polarisation entanglement, but experimentally-realised asymmetric dots produce photons entangled in both polarisation and frequency. In this work, we investigate the possibility of erasing the `which-path' information contained in the frequencies of the photons produced by asymmetric quantum dots to recover polarisation-entangled photons. We consider a biexciton with non-degenerate intermediate excitonic states in a leaky optical cavity with pairs of degenerate cavity modes close to the non-degenerate exciton transition frequencies. An open quantum system approach is used to compute the polarisation entanglement of the two-photon state after it escapes from the cavity, measured by the visibility of two-photon interference fringes. We explicitly relate the two-photon visibility to the degree of Bell-inequality violation, deriving a threshold at which Bell-inequality violations will be observed. Our results show that an ideal cavity will produce maximally polarisation-entangled photon pairs, and even a non-ideal cavity will produce partially entangled photon pairs capable of violating a Bell-inequality.Comment: 16 pages, 10 figures, submitted to PR

Helioseismic Holography of an Artificial Submerged Sound Speed Perturbation and Implications for the Detection of Pre-Emergence Signatures of Active Regions

We use a publicly available numerical wave-propagation simulation of Hartlep et al. 2011 to test the ability of helioseismic holography to detect signatures of a compact, fully submerged, 5% sound-speed perturbation placed at a depth of 50 Mm within a solar model. We find that helioseismic holography as employed in a nominal "lateral-vantage" or "deep-focus" geometry employing quadrants of an annular pupil is capable of detecting and characterizing the perturbation. A number of tests of the methodology, including the use of a plane-parallel approximation, the definition of travel-time shifts, the use of different phase-speed filters, and changes to the pupils, are also performed. It is found that travel-time shifts made using Gabor-wavelet fitting are essentially identical to those derived from the phase of the Fourier transform of the cross-covariance functions. The errors in travel-time shifts caused by the plane-parallel approximation can be minimized to less than a second for the depths and fields of view considered here. Based on the measured strength of the mean travel-time signal of the perturbation, no substantial improvement in sensitivity is produced by varying the analysis procedure from the nominal methodology in conformance with expectations. The measured travel-time shifts are essentially unchanged by varying the profile of the phase-speed filter or omitting the filter entirely. The method remains maximally sensitive when applied with pupils that are wide quadrants, as opposed to narrower quadrants or with pupils composed of smaller arcs. We discuss the significance of these results for the recent controversy regarding suspected pre-emergence signatures of active regions

Eye-movements reveal attention to social information in autism spectrum disorder

Autism spectrum disorder (ASD) is a neurodevelopmental condition in which children show reduced attention to social aspects of the environment. However in adults with ASD, evidence for social attentional deficits is equivocal. One problem is that many paradigms present social information in an unrealistic, isolated way. This study presented adults and adolescents, with and without ASD, with a complex social scene alongside another, non-social scene, and measured eye-movements during a 3-s viewing period. Analyses first identified viewing time to different regions and then investigated some more complex issues. These were: the location of the very first fixation in a trial (indicating attentional priority); the effect of a task instruction on scan paths; the extent to which gaze-following was evident; and the degree to which participants’ scan paths were influenced by the low-level properties of a scene. Results indicate a superficially normal attentional preference for social information in adults with ASD. However, more sensitive measures show that ASD does entail social attention problems across the lifespan, supporting accounts of the disorder which emphasise lifelong neurodevelopmental atypicalities. These subtle abnormalities may be sufficient to produce serious difficulties in real-life scenarios

Core Structure of Global Vortices in Brane World Models

We study analytically and numerically the core structure of global vortices forming on topologically deformed brane-worlds with a single toroidally compact extra dimension. It is shown that for an extra dimension size larger than the scale of symmetry breaking the magnitude of the complex scalar field at the vortex center can dynamically remain non-zero. Singlevaluedness and regularity are not violated. Instead, the winding escapes to the extra dimension at the vortex center. As the extra dimension size decreases the field magnitude at the core dynamically decreases also and in the limit of zero extra dimension size we reobtain the familiar global vortex solution. Extensions to other types of defects and gauged symmetries are also discussed.Comment: 6 two column pages, 3 figure