77,697 research outputs found
Food Reserve Stocks and Critical Food Shortages - a Proposal Based on the Needs of Sub-Saharan Africa
This working paper examines the food security policy, where food security means ensuring an adequate supply of food for hungry people. In particular, the recommendations of FAO are being used as a measuring rod against which food security policies are assessed. By means of FAO's database a statistical analysis of all Sub-Saharan Africa countries with respect to measuring the incidence and severity of critical food shortages are carried out. Stock policies seem to have been the answer when issues of ensuring adequate supplies have surfaced. In the paper, an estimate of the costs of keeping stocks is provided, and the costs are quite staggering. Based on the statistical analysis an estimate of the number and volume of acute food shortages per year in Sub-Saharan Africa is achieved. Upon this number a much cheaper alternative to keeping stocks for security purposes is proposed. It is proposed that a financial fund is set up with the sole purpose of purchasing grains on the open market when acute food shortages occur. In order for the fund to achieve its goals it must be completely independent of politics, and the financing and replenishing of the fund must be automatic. The advantages are that a lot of costs are saved which could be used to improve food security policies in developing countries. Furthermore, the supply of food aid is done via a global fund, and is not the result of political considerations in donor (big exporting) countries. The reservations voiced by some developing countries that further liberalisations in agricultural policies in the WTO round of negotiations could jeopardise food security is answered by this fund. Liberalisations of agricultural policies may lead to lower food stocks in the big exporting countries, but the proposed financial fund does not rely on such stocks. It is found that the purchases the fund would have to conduct only comprise a small fraction of the world trade in cereals.Food, stocks, shortages, uncertainty, Sub-Saharan Africa, Food Security and Poverty,
Sensitivity to initial conditions in self-organized critical systems
We discuss sensitivity to initial conditions in a model for avalanches in
granular media displaying self-organized criticality. We show that damage, due
to a small perturbation in initial conditions, does not spread. The damage
persists in a statistically time-invariant and scale-free form. We argue that
the origin of this behavior is the Abelian nature of the model, which
generalizes our results to all Abelian models, including the BTW model and the
Manna model. An ensemble average of the damage leads to seemingly time
dependent damage spreading. Scaling arguments show that this numerical result
is due to the time lag before avalanches reach the initial perturbation.Comment: 4 pages, 4 figures, submitted to Physical Review Letter
Symmetry and anti-symmetry of the CMB anisotropy pattern
Given an arbitrary function, we may construct symmetric and antisymmetric
functions under a certain operation. Since statistical isotropy and homogeneity
of our Universe has been a fundamental assumption of modern cosmology, we do
not expect any particular symmetry or antisymmetry in our Universe. Besides
fundamental properties of our Universe, we may also figure our contamination
and improve the quality of the CMB data products, by matching the unusual
symmetries and antisymmetries of the CMB data with known contaminantions.
Noting this, we have investigated the symmetry and antisymmetry of CMB
anisotropy pattern, which provides the deepest survey. If we let the operation
to be a coordinate inversion, the symmetric and antisymmetric functions have
even and odd-parity respectively. The investigation on the parity of the recent
CMB data shows a large-scale odd-parity preference, which is very unlikely in
the statistical isotropic and homogeneous Universe. We have investigated the
association of the WMAP systematics with the anomaly, but not found a definite
non-cosmological cause. Additionally, we have investigated the phase of even
and odd multipole data respectively, and found the behavior distinct from each
other. Noting the odd-parity preference anomaly, we have fitted a cosmological
model respectively to even and odd multipole data, and found significant
parametric tension. Besides anomalies explicitly associated with parity, there
are anomalous lack of large-scale correlation in CMB data. Noting the
equivalence between the power spectrum and the correlation, we have
investigated the association between the lack of large-angle correlation and
the odd-parity preference of the angular power spectrum. From our analysis, we
find that the odd-parity preference at low multipoles is, in fact,
phenomenologically identical with the lack of large-angle correlation.Comment: review articl
Nanoscale electrochemical patterning reveals the active sites for catechol oxidation at graphite surfaces
Graphite-based electrodes (graphite, graphene, and nanotubes) are used widely in electrochemistry, and there is a long-standing view that graphite step edges are needed to catalyze many reactions, with the basal surface considered to be inert. In the present work, this model was tested directly for the first time using scanning electrochemical cell microscopy reactive patterning and shown to be incorrect. For the electro-oxidation of dopamine as a model process, the reaction rate was measured at high spatial resolution across a surface of highly oriented pyrolytic graphite. Oxidation products left behind in a pattern defined by the scanned electrochemical cell served as surface-site markers, allowing the electrochemical activity to be correlated directly with the graphite structure on the nanoscale. This process produced tens of thousands of electrochemical measurements at different locations across the basal surface, unambiguously revealing it to be highly electrochemically active, with step edges providing no enhanced activity. This new model of graphite electrodes has significant implications for the design of carbon-based biosensors, and the results are additionally important for understanding electrochemical processes on related sp2-hybridized materials such as pristine graphene and nanotubes
Limit Your Consumption! Finding Bounds in Average-energy Games
Energy games are infinite two-player games played in weighted arenas with
quantitative objectives that restrict the consumption of a resource modeled by
the weights, e.g., a battery that is charged and drained. Typically, upper
and/or lower bounds on the battery capacity are part of the problem
description. Here, we consider the problem of determining upper bounds on the
average accumulated energy or on the capacity while satisfying a given lower
bound, i.e., we do not determine whether a given bound is sufficient to meet
the specification, but if there exists a sufficient bound to meet it.
In the classical setting with positive and negative weights, we show that the
problem of determining the existence of a sufficient bound on the long-run
average accumulated energy can be solved in doubly-exponential time. Then, we
consider recharge games: here, all weights are negative, but there are recharge
edges that recharge the energy to some fixed capacity. We show that bounding
the long-run average energy in such games is complete for exponential time.
Then, we consider the existential version of the problem, which turns out to be
solvable in polynomial time: here, we ask whether there is a recharge capacity
that allows the system player to win the game.
We conclude by studying tradeoffs between the memory needed to implement
strategies and the bounds they realize. We give an example showing that memory
can be traded for bounds and vice versa. Also, we show that increasing the
capacity allows to lower the average accumulated energy.Comment: In Proceedings QAPL'16, arXiv:1610.0769
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Visible light-mediated gold-catalysed carbon(sp2)-carbon(sp) cross-coupling.
A dual photoredox and gold-catalysed cross-coupling reaction of alkynyltrimethylsilanes and aryldiazonium tetrafluoroborates is described. The reaction proceeds through visible-light mediated oxidative addition of aryldiazoniums, transmetalation of alkynyltrimethylsilanes and aryl-alkynyl reductive elimination. Exclusive selectivity for silyl-substituted alkynes is observed, with no reactivity observed for terminal alkynes
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