Dense packing on uniform lattices

We study the Hard Core Model on the graphs ${\rm {\bf \scriptstyle G}}$ obtained from Archimedean tilings i.e. configurations in $\scriptstyle \{0,1\}^{{\rm {\bf G}}}$ with the nearest neighbor 1's forbidden. Our particular aim in choosing these graphs is to obtain insight to the geometry of the densest packings in a uniform discrete set-up. We establish density bounds, optimal configurations reaching them in all cases, and introduce a probabilistic cellular automaton that generates the legal configurations. Its rule involves a parameter which can be naturally characterized as packing pressure. It can have a critical value but from packing point of view just as interesting are the noncritical cases. These phenomena are related to the exponential size of the set of densest packings and more specifically whether these packings are maximally symmetric, simple laminated or essentially random packings.Comment: 18 page

Scattering of a longitudinal wave by a circular crack in a fluid-saturated porous medium

Physical properties of many natural and man-made materials can be modelled using the concept of poroelasticity. Some porous materials, in addition to the network of pores, contain larger inhomogeneities such as inclusions, cavities, fractures or cracks. A common method of detecting such inhomogeneities is based on the use of elastic wave scattering. We consider interaction of a normally incident time-harmonic longitudinal plane wave with a circular crack imbedded in a porous medium governed by Biot's equations of dynamic poroelasticity. The problem is formulated in cylindrical co-ordinates as a system of dual integral equations for the Hankel transform of the wave field, which is then reduced to a single Fredholm integral equation of the second kind. It is found that the scattering that takes place is predominantly due to wave inducedfluid flow between the pores and the crack. The scattering magnitude depends on the size of the crack relative to the slow wave wavelength and has it's maximum value when they are of the same order

Evolution of Models to Support Community and Policy Action with Science: Balancing Pastoral Livelihoods and Wildlife Conservation in Savannas of East Africa

We developed a “continual engagement” model to better integrate knowledge from policy makers, communities, and researchers with the goal of promoting more effective action to balance poverty alleviation and wildlife conservation in 4 pastoral ecosystems of East Africa. The model involved the creation of a core boundary-spanning team, including community facilitators, a policy facilitator, and transdisciplinary researchers, responsible for linking with a wide range of actors from local to global scales. Collaborative researcher–facilitator community teams integrated local and scientific knowledge to help communities and policy makers improve herd quality and health, expand biodiversity payment schemes, develop land-use plans, and fully engage together in pastoral and wildlife policy development. This model focused on the creation of hybrid scientific–local knowledge highly relevant to community and policy maker needs. The facilitation team learned to be more effective by focusing on noncontroversial livelihood issues before addressing more difficult wildlife issues, using strategic and periodic engagement with most partners instead of continual engagement, and reducing costs by providing new scientific information only when deemed essential. We conclude by examining the role of facilitation in redressing asymmetries in power in researcher–community–policy maker teams, the role of individual values and character in establishing trust, and how to sustain knowledge-action links when project funding ends

Origins of the Ambient Solar Wind: Implications for Space Weather

The Sun's outer atmosphere is heated to temperatures of millions of degrees, and solar plasma flows out into interplanetary space at supersonic speeds. This paper reviews our current understanding of these interrelated problems: coronal heating and the acceleration of the ambient solar wind. We also discuss where the community stands in its ability to forecast how variations in the solar wind (i.e., fast and slow wind streams) impact the Earth. Although the last few decades have seen significant progress in observations and modeling, we still do not have a complete understanding of the relevant physical processes, nor do we have a quantitatively precise census of which coronal structures contribute to specific types of solar wind. Fast streams are known to be connected to the central regions of large coronal holes. Slow streams, however, appear to come from a wide range of sources, including streamers, pseudostreamers, coronal loops, active regions, and coronal hole boundaries. Complicating our understanding even more is the fact that processes such as turbulence, stream-stream interactions, and Coulomb collisions can make it difficult to unambiguously map a parcel measured at 1 AU back down to its coronal source. We also review recent progress -- in theoretical modeling, observational data analysis, and forecasting techniques that sit at the interface between data and theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue connected with a 2016 ISSI workshop on "The Scientific Foundations of Space Weather." 44 pages, 9 figure

Hypoxic Pulmonary Vasoconstriction in Humans:Tale or Myth

Hypoxic Pulmonary vasoconstriction (HPV) describes the physiological adaptive process of lungs to preserves systemic oxygenation. It has clinical implications in the development of pulmonary hypertension which impacts on outcomes of patients undergoing cardiothoracic surgery. This review examines both acute and chronic hypoxic vasoconstriction focusing on the distinct clinical implications and highlights the role of calcium and mitochondria in acute versus the role of reactive oxygen species and Rho GTPases in chronic HPV. Furthermore it identifies gaps of knowledge and need for further research in humans to clearly define this phenomenon and the underlying mechanism

Combating piracy off the coast of Somalia: current legal challenges

The ongoing maritime operations against piracy off the coast of Somalia have not only put naval enforcement against piracy at sea in the spotlight, but also the legal aftermath of what to do with pirates after their capture. While warships at sea within the current legal framework of UNCLOS and the UN Security Council amplifications specifically adopted for the case of Somalia can effectively perform their tasks, the question of what to do with the pirate suspects is still not satisfactorily resolved. As a consequence, attacks against merchant vessels and international trade run the risk of being ‘consequence free’, in which the perpetrators are not being held accountable. Participating nations are confronted with the fact that military operations against piracy, which is essentially a criminal offence, need a comprehensive approach to ensure accountability. To counter this criminal activity at sea nations try to strengthen the judicial infrastructure through national prosecution or transfer suspects for prosecution in the Horn of Africa region. As these options are not considered to be enough, and hampered by other non-legal factors, some nations call for an international court as a possible long term solution

Gas sampling efficiencies and aerodynamic characteristics of a laboratory wind tunnel for odour measurement

The rate of odour emission depends on meteorological factors, such as wind speed, humidity and temperature, but no wind tunnels control these factors adequately. A novel laboratory wind tunnel was developed that can control airflow rate. The gas recovery efficiency of the tunnel was evaluated and the aerodynamic characteristics were then examined to further assess its performance. Gas recovery efficiencies ranged from 62 to 107% with an average of 81%. The optimal performance of the tunnel (gas recovery efficiency of 89%) occurred at an airflow rate and CO supply rate of 1.68m3 min-1 and 10.0 l min-1, respectively. The vertical and cross-sectional wind speed profiles exhibited a substantial degree of non-uniformity. The airflow was turbulent, although Reynolds numbers were low indicating it to be close to laminar. The non-uniform wind speed profiles and CO concentration profiles illustrate the difficulty in obtaining representative samples from which to calculate emission rates. Further work is required to improve aerodynamic characteristics and hence performance of the tunnel