168 research outputs found
Purely competitive evolutionary dynamics for games
We introduce and analyze a purely competitive dynamics for the evolution of
an infinite population subject to a 3-strategy game. We argue that this
dynamics represents a characterization of how certain systems, both natural and
artificial, are governed. In each period, the population is randomly sorted
into pairs, which engage in a once-off play of the game; the probability that a
member propagates its type to its offspring is proportional only to its payoff
within the pair. We show that if a type is dominant (obtains higher payoffs in
games with both other types), its 'pure' population state, comprising only
members of that type, is globally attracting. If there is no dominant type,
there is an unstable 'mixed' fixed point; the population state eventually
oscillates between the three near-pure states. We then allow for mutations,
where offspring have a non-zero probability of randomly changing their type. In
this case, the existence of a dominant type renders a point near its pure state
globally attracting. If no dominant type exists, a supercritical Hopf
bifurcation occurs at the unique mixed fixed point, and above a critical
(typically low) mutation rate, this fixed point becomes globally attracting:
the implication is that even very low mutation rates can stabilize a system
that would, in the absence of mutations, be unstable.Comment: 13 pages, 6 figure
The introductory astronomy course at the University of Cape Town: probing student perspectives
We report on research carried out to improve teaching and student engagement
in the introductory astronomy course at the University of Cape Town. This
course is taken by a diverse range of students, including many from
educationally disadvantaged backgrounds. We describe the development of an
instrument, the Introductory Astronomy Questionnaire (IAQ), which we
administered as pre- and post-tests to students enrolled in the course. The
instrument comprised a small number of questions which probed three areas of
interest: student motivation and expectations, astronomy content, and
worldview. Amongst our findings were that learning gains were made in several
conceptual areas, and that students appeared to develop a more nuanced view of
the nature of astronomy. There was some evidence that the course had a positive
impact on students' worldviews, particularly their attitudes towards science.
We also identified a promising predictor of course success that could in future
be used to identify students requiring special teaching intervention.Comment: 19 pages, 2 figures. Accepted for publication in Physical Review
Special Topics - Physics Educatio
Pinning down the mass of Kepler-10c: the importance of sampling and model comparison
Initial RV characterisation of the enigmatic planet Kepler-10c suggested a
mass of M, which was remarkably high for a planet with radius
R; further observations and subsequent analysis hinted at a
(possibly much) lower mass, but masses derived using RVs from two different
spectrographs (HARPS-N and HIRES) were incompatible at a -level. We
demonstrate here how such mass discrepancies may readily arise from sub-optimal
sampling and/or neglecting to model even a single coherent signal (stellar,
planetary, or otherwise) that may be present in RVs. We then present a
plausible resolution of the mass discrepancy, and ultimately characterise
Kepler-10c as having mass M, and mean density
g cm.Comment: 7 pages, 4 figures. Accepted for publication in MNRAS Letter
Ground water quality assessment for irrigation in Palwal block of Palwal district, Haryana, India
The present study examined the quality of groundwater for agriculture purpose in a 49785 ha region comprising Palwal block of Palwal district of Haryana state by focusing on spatial variability of electrical conductivity (EC), cationic and anionic composition of CO32-, HCO3-, Cl-, SO42-, Ca2+, Mg2+, Na+ and K+ of the ground water. It was found 75% of the samples showed EC values up to 4 dS/m and the maximum value of EC was found as 10.55 dS/m. Out of one hundred thirty three ground water samples 34.8 % were of good quality, 49.2 % saline and 16.0 % alkali in nature. Out of the saline water, 24.2, 1.5 and 23.5 % were marginally saline, saline and high SAR saline, respectively. In alkali group, 2.3, 2.3 and 11.4 % were marginally alkali, alkali and high alkali, respectively. Residual sodium carbonate (RSC) and sodium adsorption ratio (SAR) varied from nil to 5.50 me L-1 and 2.50 to 23.41 (m mol L-1)½, respectively. Counter map maps of EC, SAR, RSC and water quality of groundwater used for irrigation in the block were prepared through GIS to study spatial variability
Inferring probabilistic stellar rotation periods using Gaussian processes
Variability in the light curves of spotted, rotating stars is often
non-sinusoidal and quasi-periodic --- spots move on the stellar surface and
have finite lifetimes, causing stellar flux variations to slowly shift in
phase. A strictly periodic sinusoid therefore cannot accurately model a
rotationally modulated stellar light curve. Physical models of stellar surfaces
have many drawbacks preventing effective inference, such as highly degenerate
or high-dimensional parameter spaces. In this work, we test an appropriate
effective model: a Gaussian Process with a quasi-periodic covariance kernel
function. This highly flexible model allows sampling of the posterior
probability density function of the periodic parameter, marginalising over the
other kernel hyperparameters using a Markov Chain Monte Carlo approach. To test
the effectiveness of this method, we infer rotation periods from 333 simulated
stellar light curves, demonstrating that the Gaussian process method produces
periods that are more accurate than both a sine-fitting periodogram and an
autocorrelation function method. We also demonstrate that it works well on real
data, by inferring rotation periods for 275 Kepler stars with previously
measured periods. We provide a table of rotation periods for these 1132 Kepler
objects of interest and their posterior probability density function samples.
Because this method delivers posterior probability density functions, it will
enable hierarchical studies involving stellar rotation, particularly those
involving population modelling, such as inferring stellar ages, obliquities in
exoplanet systems, or characterising star-planet interactions. The code used to
implement this method is available online.Comment: Submitted to MNRAS. Replaced 27/06/2017: corrections made to
koi_periods.cs
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Agricultural Information's Impact on the Adaptive Capacity of Ghana's Smallholder Cocoa Farmers
Ghanaian smallholders grow one quarter of the world's cocoa, but climate change, individual extreme weather events, such as droughts, as well as deforestation increasingly threaten cocoa production. Pertinent information could bolster adaptive capacity. However, in Ghana's cocoa sector, relevant agricultural information is not available to all farmers, which can exacerbate power asymmetries. This paper focuses on how (i) agricultural and drought-adaptive information and (ii) socio-economic characteristics shape a cocoa farmer's adaptive capacity. We conducted our study in the aftermath of 2015–16's prolonged El Niño-induced drought that negatively impacted the livelihoods of cocoa smallholders across Ghana. In 48 semi-structured interviews and 12 focus groups, we asked smallholders how they responded to the drought to decipher how adaptive capacity compares between farmers receiving four different sources of agricultural information, and of diverse socio-economic status. Overall, agricultural information improved cocoa farmers' adaptive capacity compared to those who received no formal agricultural information. Smallholders detailed adaptive techniques that would be accessible to, and thus replicable by, other poorly-resourced cocoa farmers. Shade tree management and income diversification were identified as pertinent adaptive actions. However, we identified a divergence between exposure to agricultural information and its transformation into substantive adaptive action. Additionally, informal information sharing between smallholders represents an underutilized resource by extension programmes. We found that adaptive capacity is also determined by socio-economic characteristics: particularly gender, and to a lesser extent formal education level, proximity to asphalt roads, and land tenure. Finally, we present evidence that framing adaptive techniques in relatable terms that resonate with farmers' immediate livelihood concerns could narrow the adaptation deficit prevalent in Ghana's cocoa sector
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Coffee certification in Brazil: compliance with social standards and its implications for social equity
© 2018, The Author(s). This paper addresses the relationship between compliance with social performance criteria (the social outcomes that must be achieved for certification) and procedural (management) criteria and this relationship’s significance for social equity at both farm and wider landscape levels. We consider social performance compliance to be pertinent to farm-level equity, and the relative compliance of small versus large farms to be pertinent to landscape-level equity. Certification’s management requirements are often deemed disproportionately burdensome for small, resource-poor producers, and hence a barrier to landscape-level equity. There is a lack of research examining how management criteria impact the ability of different sized farms to meet certification’s social performance requirements. We analysed 435 certification audits, covering all Brazilian coffee farms that sought Rainforest Alliance certification from 2006 to 2014 inclusive: 80 individual farms and 23 groups of farms. In principle, undergoing group certification permits smallholders to benefit from economies of scale. Our analysis revealed a statistically significant, positive correlation between compliance with procedural (managing sustainability plans) and social performance criteria. This correlation was stronger for groups than individual farms. Group farms’ compliance was statistically equivalent to that of individual farms, suggesting that group certification is achieving its intended purpose of socio-economic levelling of certified farmers. Over time, certified farms’ average compliances improved. Our findings suggest that management requirements play an important role in improving smallholders’ overall social sustainability performance and that group certification may help resource-poor smallholders achieve those requirements. Further work is required to understand causal mechanisms underlying the relationships we present
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