1,038 research outputs found
Reflections on Zimbabwe’s past and future: Tradeoffs between the Lexus and the Baobab tree
Abstract. In early 2018, President Mnangagwa seemingly struck a new tone to the Western world that was welcoming, rather than antagonistic to business investment (Mnangagwa, 2018). Nonetheless, recent and continued land expropriations, continued deficit spending and a severe shortage of cash liquidity have made any recovery a very challenging prospect. Outside observers now have differing outlooks on Zimbabwe, ranging from uniformly “negative” to “mixed”, “neutral” or “cautiously optimistic” (World Bank, 2018; Mining Review Africa, 2018; Mdzungairi, 2018) My recent take on the country in an op-ed for The Wall Street Journal sided with the cautiously optimistic group (Richardson, 2018), but it appears I was too sanguine.Keywords. Reflections, Baobab tree, Zimbabwe, Tradeoffs.JEL. B1, B50, F11, F13, G10
Relating Spectral Observations of the Agricultural Landscape to Crop Yield
Remote sensing and microscopy share several common concerns including wavelength and sensor selection, signal processing, and image analysis. For crop yield assessments, multispectral observations are acquired photographically, videographically, or with opticalmechanical scanners from aircraft and spacecraft. Sensors are chosen at wavelengths of high atmospheric transmission and maximum contrast between the soil background and the vegetation growing out of it. Vegetation indices have been developed that maximize the information about the photosynthetic size of the vegetation in the landscape and, hence, about crop stresses and yield . Three such indices that reduce the multispectral observations to a single numerical index are described and software for one general procedure that pennits characterization of each major spectral component of multiband scenes is appended. Microscopists may encounter analogous si tuat ions for which the techniques developed in agricultural remote sensing can be useful
The dynamics of single spike-evoked adenosine release in the cerebellum
The purine adenosine is a potent neuromodulator in the brain, with roles in a number
of diverse physiological and pathological processes. Modulators such as adenosine are difficult
to study as once released they have a diffuse action (which can affect many neurones) and,
unlike classical neurotransmitters, have no inotropic receptors. Thus rapid postsynaptic currents
(PSCs) mediated by adenosine (equivalent to mPSCs) are not available for study. As a result
the mechanisms and properties of adenosine release still remain relatively unclear. We have
studied adenosine release evoked by stimulating the parallel fibres in the cerebellum. Using
adenosine biosensors combined with deconvolution analysis and mathematical modelling, we
have characterised the release dynamics and diffusion of adenosine in unprecedented detail.
By partially blocking K+ channels, we were able to release adenosine in response to a single
stimulus rather than a train of stimuli. This allowed reliable sub-second release of reproducible
quantities of adenosine with stereotypic concentration waveforms that agreed well with predictions
of a mathematical model of purine diffusion. We found no evidence for ATP release
and thus suggest that adenosine is directly released in response to parallel fibre firing and does
not arise from extracellular ATP metabolism. Adenosine release events showed novel short-term
dynamics, including facilitated release with paired stimuli at millisecond stimulation intervals
but depletion-recovery dynamics with paired stimuli delivered over minute time scales. These
results demonstrate rich dynamics for adenosine release that are placed, for the first time, on a
quantitative footing and show strong similarity with vesicular exocytosis
Interferometric Constraints on Quantum Geometrical Shear Noise Correlations
Final measurements and analysis are reported from the first-generation
Holometer, the first instrument capable of measuring correlated variations in
space-time position at strain noise power spectral densities smaller than a
Planck time. The apparatus consists of two co-located, but independent and
isolated, 40 m power-recycled Michelson interferometers, whose outputs are
cross-correlated to 25 MHz. The data are sensitive to correlations of
differential position across the apparatus over a broad band of frequencies up
to and exceeding the inverse light crossing time, 7.6 MHz. By measuring with
Planck precision the correlation of position variations at spacelike
separations, the Holometer searches for faint, irreducible correlated position
noise backgrounds predicted by some models of quantum space-time geometry. The
first-generation optical layout is sensitive to quantum geometrical noise
correlations with shear symmetry---those that can be interpreted as a
fundamental noncommutativity of space-time position in orthogonal directions.
General experimental constraints are placed on parameters of a set of models of
spatial shear noise correlations, with a sensitivity that exceeds the
Planck-scale holographic information bound on position states by a large
factor. This result significantly extends the upper limits placed on models of
directional noncommutativity by currently operating gravitational wave
observatories.Comment: Matches the journal accepted versio
Dynamics of simple liquids at heterogeneous surfaces : Molecular Dynamics simulations and hydrodynamic description
In this paper we consider the effect of surface heterogeneity on the slippage
of fluid, using two complementary approaches. First, MD simulations of a
corrugated hydrophobic surface have been performed. A dewetting transition,
leading to a super-hydrophobic state, is observed for pressure below a
``capillary'' pressure. Conversely a very large slippage of the fluid on this
composite interface is found in this superhydrophobic state. Second, we propose
a macroscopic estimate of the effective slip length on the basis of continuum
hydrodynamics, in order to rationalize the previous MD results. This
calculation allows to estimate the effect of a heterogeneous slip length
pattern on the composite interface. Comparison between the two approaches are
in good agreement at low pressure, but highlights the role of the exact shape
of the liquid-vapor interface at higher pressure. These results confirm that
small variations in the roughness of a surface can lead to huge differences in
the slip effect. On the basis of these results, we propose some guidelines to
design highly slippery surfaces, motivated by potential applications in
microfluidics.Comment: submitted to EPJ
Low Friction Flows of Liquids at Nanopatterned Interfaces
With the recent important development of microfluidic systems,
miniaturization of flow devices has become a real challenge. Microchannels,
however, are characterized by a large surface to volume ratio, so that surface
properties strongly affect flow resistance in submicrometric devices. We
present here results showing that the concerted effect of wetting . properties
and surface roughness may considerably reduce friction of the fluid past the
boundaries. The slippage of the fluid at the channel boundaries is shown to be
drastically increased by using surfaces that are patterned at the nanometer
scale. This effect occurs in the regime where the surface pattern is partially
dewetted, in the spirit of the 'superhydrophobic' effects that have been
recently discovered at the macroscopic scales. Our results show for the first
time that, in contrast to the common belief, surface friction may be reduced by
surface roughness. They also open the possibility of a controlled realization
of the 'nanobubbles' that have long been suspected to play a role in
interfacial slippag
Modeling Pipe to Soil Potentials From Geomagnetic Storms in Gas Pipelines in New Zealand
Gas pipelines can experience elevated pipe to soil potentials (PSPs) during geomagnetic disturbances due to the induced geoelectric field. Gas pipeline operators use cathodic protection to keep PSPs between −0.85 and −1.2 V to prevent corrosion of the steel pipes and disbondment of the protective coating from the pipes. We have developed a model of the gas pipelines in the North Island of New Zealand to identify whether a hazard exists to these pipelines and how big this hazard is. We used a transmission line representation to model the pipelines and a nodal admittance matrix method to calculate the PSPs at nodes up to 5 km apart along the pipelines. We used this model to calculate PSPs resulting from an idealized 100 mVkm−1 electric field, initially to the north and east. The calculated PSPs are highest are at the ends of the pipelines in the direction of the applied electric field vector. The calculated PSP follows a characteristic curve along the length of the pipelines that matches theory, with deviations due to branchlines and changes in pipeline direction. The modeling shows that the PSP magnitudes are sensitive to the branchline coating conductance with higher coating conductances decreasing the PSPs at most locations. Enhanced PSPs produce the highest risk of disbondment and corrosion occurring, and hence this modeling provides insights into the network locations most at risk
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