Solid-state combustion synthesis of ceramics and alloys in reduced gravity

Possible microgravity effects are explored in the combustion synthesis of ceramics and alloys from their constituent elements. Molten intermediates are typically present during the combustion process, thereby offering the chance for natural convection to take place. Numerical simulations suggest that the combustion front in concert with gravity may act as a partial zone-refinement mechanism which is attempting to sweep out porosity in the sample. Contrary to suggestions by dimensional analysis, no effects on the combustion rate are seen. An analytical model of the combustion velocity as a function of the gravitational field and the spreading rate of molten material gives the correct order of magnitude of the gravity effect as measured by centrifuge experiments

Potential of a Neutrino Detector in the ANDES Underground Laboratory for Geophysics and Astrophysics of Neutrinos

The construction of the Agua Negra tunnels that will link Argentina and Chile under the Andes, the world longest mountain range, opens the possibility to build the first deep underground labo- ratory in the Southern Hemisphere. This laboratory has the acronym ANDES (Agua Negra Deep Experiment Site) and its overburden could be as large as \sim 1.7 km of rock, or 4500 mwe, providing an excellent low background environment to study physics of rare events like the ones induced by neutrinos and/or dark matter. In this paper we investigate the physics potential of a few kiloton size liquid scintillator detector, which could be constructed in the ANDES laboratory as one of its possible scientific programs. In particular, we evaluate the impact of such a detector for the studies of geoneutrinos and galactic supernova neutrinos assuming a fiducial volume of 3 kilotons as a reference size. We emphasize the complementary roles of such a detector to the ones in the Northern Hemisphere neutrino facilities through some advantages due to its geographical location.Comment: 20 pages, 16 figures and 9 table

What does transit oriented development mean in a South African context? A multiple stakeholder perspective from Johannesburg

Car dependency is increasing in South African cities, and apartheid spatial patterns continue to be observed in the accommodation of public transport captive communities at low densities on the fringes. It has been argued in many contemporary plans and strategies that Transit Oriented Development (TOD) offers a potentially useful concept to drive the restructuring of South African socio-spatial patterns. The 2011 National Development Plan, in particular, calls for ?the internationally accepted principles? of TOD to be employed. The concept of TOD is rooted in North American attempts to overcome the predominant use of private cars, and the inefficiencies of urban sprawl. This paper aims to explore what TOD means in a South African context. It is argued that identifying and adopting internationally accepted principles of TOD design is fairly straight forward, and it is clear that South African TOD strategies have largely been informed by these. However, the international experience highlights that the implementation of these principles encounters many complex challenges, amongst which divergent stakeholder interests are particularly important. Adopting narrow physical and urban design principles, without paying attention to attendant complex implementation challenges, is unlikely to achieve success. Drawing from (n=11) qualitative practitioner interviews in Johannesburg, the paper highlights that local TOD stakeholders often have contradictory and competing interests and understandings. This poses a risk to achieving TOD objectives. It is concluded that greater effort is required to understand local TOD stakeholder dynamics, and that local governments need to provide frameworks and associated strategies through which competing interests can be resolved.Paper presented at the 34th Annual Southern African Transport Conference 6-9 July 2015 "Working Together to Deliver - Sakha Sonke", CSIR International Convention Centre, Pretoria, South Africa.The Minister of Transport, South AfricaTransportation Research Board of the US

Weak Long-Ranged Casimir Attraction in Colloidal Crystals

We investigate the influence of geometric confinement on the free energy of an idealized model for charge-stabilized colloidal suspensions. The mean-field Poisson-Boltzmann formulation for this system predicts pure repulsion among macroionic colloidal spheres. Fluctuations in the simple ions' distribution provide a mechanism for the macroions to attract each other at large separations. Although this Casimir interaction is long-ranged, it is too weak to influence colloidal crystals' dynamics.Comment: 5 pages 2 figures ReVTe

Technical design and commissioning of the KATRIN large-volume air coil system

The KATRIN experiment is a next-generation direct neutrino mass experiment with a sensitivity of 0.2 eV (90% C.L.) to the effective mass of the electron neutrino. It measures the tritium $\beta$-decay spectrum close to its endpoint with a spectrometer based on the MAC-E filter technique. The $\beta$-decay electrons are guided by a magnetic field that operates in the mT range in the central spectrometer volume; it is fine-tuned by a large-volume air coil system surrounding the spectrometer vessel. The purpose of the system is to provide optimal transmission properties for signal electrons and to achieve efficient magnetic shielding against background. In this paper we describe the technical design of the air coil system, including its mechanical and electrical properties. We outline the importance of its versatile operation modes in background investigation and suppression techniques. We compare magnetic field measurements in the inner spectrometer volume during system commissioning with corresponding simulations, which allows to verify the system's functionality in fine-tuning the magnetic field configuration. This is of major importance for a successful neutrino mass measurement at KATRIN.Comment: 32 pages, 16 figure

c-Jun reprograms Schwann cells of injured nerves to generate a repair cell essential for regeneration.

The radical response of peripheral nerves to injury (Wallerian degeneration) is the cornerstone of nerve repair. We show that activation of the transcription factor c-Jun in Schwann cells is a global regulator of Wallerian degeneration. c-Jun governs major aspects of the injury response, determines the expression of trophic factors, adhesion molecules, the formation of regeneration tracks and myelin clearance and controls the distinctive regenerative potential of peripheral nerves. A key function of c-Jun is the activation of a repair program in Schwann cells and the creation of a cell specialized to support regeneration. We show that absence of c-Jun results in the formation of a dysfunctional repair cell, striking failure of functional recovery, and neuronal death. We conclude that a single glial transcription factor is essential for restoration of damaged nerves, acting to control the transdifferentiation of myelin and Remak Schwann cells to dedicated repair cells in damaged tissue

Synthesis of refractory-oxide materials by skull melting

Skull melting is a cold-crucible technique for obtaining high-purity melts of refractory materials, particularly oxides. This technique has been used to synthesize high-purity minerals and to prepare single crystals of uraninite (UO/sub 2/) and thorianite (ThO/sub 2/) directly from the melt. A description of the crystal-growing technique is discussed. Los Alamos is also interested in developing the skull-melting technique to zone-refine spent UO/sub 2/ nuclear reactor fuel pins. Since metallic fission products and actinides will behave as solute impurities in a UO/sub 2/ solvent, the success of the zone-refining process will depend on the distribution of the impurities between molten and solid UO/sub 2/. An effective distribution coefficient for Y/sub 2/O/sub 3/ segregated between molten and solid UO/sub 2/ was experimentally determined by zone melting. An effective distribution coefficient of k = 0.75 +- 0.05 was obtained, in good agreement with an equilibrium value of k/sub 0/ = 0.6, estimated from the Y/sub 2/O/sub 3/-UO/sub 2/ phase diagram

The viscosity of shoshonitic melts (Vulcanello Peninsula, Aeolian Islands, Italy): insight on the magma ascent in dikes

The viscosity of shoshonitic melts from Vulcanello Peninsula (Vulcano Island, Italy) is experimentally determined at temperatures between 733 K and 1673 K. The water content of the melts varies from 0.03 to 4.75 wt% H2O. The micropenetration technique is employed at ambient pressure in the high viscosity range (109-1012 Pa·s). Falling sphere(s) experiments are performed at 500 and 2000 MPa in the low viscosity range (100.5-103 Pa·s). Results show a decrease of about 2 orders of magnitude in viscosity if ~ 3 wt% of water is added to the dry melt at 1300 K. At high temperature the viscosity of Vulcanello melts is intermediate between that of andesitic and basaltic melts. In contrast, at low temperatures (≤1050 K), the shoshonitic melt is characterized by a lower viscosity with respect to the two previous melts. Based on our new data set, a calculation model is proposed to predict the viscosity of the shoshonitic melts as a function of temperature and water content. The viscosity data are used to constrain the ascent velocity of shoshonitic magmas from Vulcanello within dikes. Using petrological data (temperature and crystal content of the magma) and volcanological information (geometrical parameters of the eruptive fissure and depth of magma storage), we estimate the time scale for the ascent of magma from the main reservoir to the surface. Results show time scales in the order of hours to few days. We conclude that the rapid ascent of poorly evolved melts from Moho depths should be taken into account for the hazard assessment of Vulcano Island

When lithics hit bones: Evaluating the potential of a multifaceted experimental protocol to illuminate Middle Palaeolithic weapon technology

Recent zooarchaeological and isotope analyses have largely settled the debate surrounding Neanderthal hunting capacities, repeatedly demonstrating their successful acquisition of large ungulates. Nevertheless, the functional identification of individual tools as hunting weapons remains a methodological challenge. In-depth studies have focussed mainly on small subsets of lithic artefacts from selected assemblages assessing features of breakage patterns, retouch, shape and use wear. Studies focussing on associated hunting lesions are rarer and often focus on reconstructing very specific bone surface marks encountered in the archaeological record. This study aims to add to our understanding of the formation and characteristics of projectile impact marks (PIMs) on bone through a series of highly monitored, replicative experiments, using thrusting and throwing spears with replica Levallois points into two wild pig carcasses. In total, 152 shots were made, and for each a series of attributes was recorded, including velocity and location of impact. Subsequent quantitative analyses focussed on understanding the various factors underlying the formation of different types of projectile impact marks. These experiments demonstrate that PIM formation results from the properties of both the impacting projectile and bone element. PIMs can signal impacts caused by different delivery methods but only on some parts of the skeleton. These results are contextualised in relation to the occurrence and recognition of Palaeolithic PIMs and patterns of Neanderthal behaviour. These experiments are only a first step in improving the recognition of these signatures in the archaeological record and providing better insights into understanding of the mechanisms of Neanderthal hunting

Cost risk benefit analysis to support chemoprophylaxis policy for travellers to malaria endemic countries

BACKGROUND: In a number of malaria endemic regions, tourists and travellers face a declining risk of travel associated malaria, in part due to successful malaria control. Many millions of visitors to these regions are recommended, via national and international policy, to use chemoprophylaxis which has a well recognized morbidity profile. To evaluate whether current malaria chemo-prophylactic policy for travellers is cost effective when adjusted for endemic transmission risk and duration of exposure. a framework, based on partial cost-benefit analysis was used. METHODS: Using a three component model combining a probability component, a cost component and a malaria risk component, the study estimated health costs avoided through use of chemoprophylaxis and costs of disease prevention (including adverse events and pre-travel advice for visits to five popular high and low malaria endemic regions) and malaria transmission risk using imported malaria cases and numbers of travellers to malarious countries. By calculating the minimal threshold malaria risk below which the economic costs of chemoprophylaxis are greater than the avoided health costs we were able to identify the point at which chemoprophylaxis would be economically rational. RESULTS: The threshold incidence at which malaria chemoprophylaxis policy becomes cost effective for UK travellers is an accumulated risk of 1.13% assuming a given set of cost parameters. The period a travellers need to remain exposed to achieve this accumulated risk varied from 30 to more than 365 days, depending on the regions intensity of malaria transmission. CONCLUSIONS: The cost-benefit analysis identified that chemoprophylaxis use was not a cost-effective policy for travellers to Thailand or the Amazon region of Brazil, but was cost-effective for travel to West Africa and for those staying longer than 45 days in India and Indonesia