73 research outputs found
Accuracy assessment of ISI-MIP modelled flows in the Hidukush-Karakoram-Himalayan basins
Large Asian rivers heading in the Hindukush-Karakoram-Himalayan mountains, and whose streamflow includes significant snow-melt and glacier-melt components, may be highly susceptible to climate warming and pattern changes. Millions of people depend on these streamflows for agriculture and power generation. Reliable predictions of future water availability are therefore needed for planning under a changing climate, and depend on the quality of hydro-climatic modelling. ISI-MIP provides global hydrological modelling results, and need validation at regional scale. This study evaluates the accuracy of modelled flows from the hydrological models used in ISI-MIP, in various sub-basins of the Upper Indus Basin (UIB) and for the reference period 1985-1998. The modelled flows are based on six hydrological models, which are: i) H08, ii) VIC, iii) WaterGAP, iv) WBM, v) MPI-HM, vi) PCR-GLOBWB. Of these models, H08 and VIC are energy-based hydrological models, while the others are temperature-based hydrological models. WBM and MPI are not suitable for the UIB, due to significant under-estimation (by 70-90%) of measured flows by their modelled flows. The remaining four models provide consistent, but still significantly under-estimated flows (up to 60% of measured flows) in all sub-basins, except the Kharmong basin. Monthly differences between modelled and measured flows vary between sub-basins, but with noticeable over-estimation in winter-spring months and under-estimation during summer months. Accuracy of the bias-corrected precipitation data sets (based on five GCMs) used in the ISI-MIP hydrological models has been assessed, using a basin-wide water balance assessment method. This method shows that all precipitation data sets significantly under-estimate precipitation in the UIB, particularly in the Karakoram sub-basins. The selected ISI-MIP hydrological models have used precipitation data which are under-estimates, which may be a main reason
for under-estimated flows. ISI-MIP hydrological modelling needs to use the best available precipitation data for the UIB, but other input data and calibration parameters also need revision. An important message from this study is that caution must be exercised in selecting precipitation data sets and hydrological models in alpine regions such as the Hindukush-Karakoram-Himalayas
Generalized coupling in the Kuramoto model
We propose a modification of the Kuramoto model to account for the effective
change in the coupling constant among the oscillators, as suggested by some
experiments on Josephson junction, laser arrays and mechanical systems, where
the active elements are turned on one by one. The resulting model is
analytically tractable and predicts that both first and second order phase
transitions are possible, depending upon the value of a new parameter that
tunes the coupling among the oscillators. Numerical simulations of the model
are in accordance with the analytical estimates, and in qualitative agreement
with the behavior of Josephson junctions coupled via a cavity
Identifying gaps in HIV policy and practice along the HIV care continuum: evidence from a national policy review and health facility surveys in urban and rural Kenya
The last decade has seen rapid evolution in guidance from the WHO concerning the provision of HIV services along the diagnosis-to-treatment continuum, but the extent to which these recommendations are adopted as national policies in Kenya, and subsequently implemented in health facilities, is not well understood. Identifying gaps in policy coverage and implementation is important for highlighting areas for improving service delivery, leading to better health outcomes. We compared WHO guidance with national policies for HIV testing and counselling, prevention of mother-to-child transmission, HIV treatment and retention in care. We then investigated implementation of these national policies in health facilities in one rural (Kisumu) and one urban (Nairobi) sites in Kenya. Implementation was documented using structured questionnaires that were administered to in-charge staff at 10 health facilities in Nairobi and 34 in Kisumu. Policies were defined as widely implemented if they were reported to occur in > 70% facilities, partially implemented if reported to occur in 30–70% facilities, and having limited implementation if reported to occur in < 30% facilities. Overall, Kenyan national HIV care and treatment policies were well aligned with WHO guidance. Policies promoting access to treatment and retention in care were widely implemented, but there was partial or limited implementation of several policies promoting access to HIV testing, and the more recent policy of Option B+ for HIV-positive pregnant women. Efforts are needed to improve implementation of policies designed to increase rates of diagnosis, thus facilitating entry into HIV care, if morbidity and mortality burdens are to be further reduced in Kenya, and as the country moves towards universal access to antiretroviral therapy
Understanding historical coastal spit evolution : a case study from Spurn, East Yorkshire, UK
Globally sandy coastlines are threatened by erosion driven by climatic changes and increased storminess. Understanding how they have responded to past storms is key to help manage future coastal changes. Coastal spits around the world are particularly dynamic and therefore potentially vulnerable coastal features. Therefore, how they have evolved over the last few centuries is of great importance. To illustrate this, this study focuses on the historical evolution of a spit at Spurn on the east coast of the UK, which currently provides critical protection to settlements within the Humber estuary. Through the combination of digitized historical mapping and luminescence dating, this study shows that Spurn has been a consistent coastal feature over at least the past 440 years. No significant westward migration was observed for the last 200 years. Results show a long‐term extension of the spit and a decrease in its overall area, particularly in the last 50 years. Breaches of the neck cause temporary sediment pathway changes enabling westward extension of the head. Use of digitized historical maps in GIS combined with OSL dating has allowed a more complete understanding of long‐term spit evolution and sediment transport modes at Spurn. In doing so it helps inform future possible changes linked to pressures, such as increases in storm events and sea‐level rise
Symmetry breaking perturbations and strange attractors
The asymmetrically forced, damped Duffing oscillator is introduced as a
prototype model for analyzing the homoclinic tangle of symmetric dissipative
systems with \textit{symmetry breaking} disturbances. Even a slight fixed
asymmetry in the perturbation may cause a substantial change in the asymptotic
behavior of the system, e.g. transitions from two sided to one sided strange
attractors as the other parameters are varied. Moreover, slight asymmetries may
cause substantial asymmetries in the relative size of the basins of attraction
of the unforced nearly symmetric attracting regions. These changes seems to be
associated with homoclinic bifurcations. Numerical evidence indicates that
\textit{strange attractors} appear near curves corresponding to specific
secondary homoclinic bifurcations. These curves are found using analytical
perturbational tools
Computational Method for Phase Space Transport with Applications to Lobe Dynamics and Rate of Escape
Lobe dynamics and escape from a potential well are general frameworks
introduced to study phase space transport in chaotic dynamical systems. While
the former approach studies how regions of phase space are transported by
reducing the flow to a two-dimensional map, the latter approach studies the
phase space structures that lead to critical events by crossing periodic orbit
around saddles. Both of these frameworks require computation with curves
represented by millions of points-computing intersection points between these
curves and area bounded by the segments of these curves-for quantifying the
transport and escape rate. We present a theory for computing these intersection
points and the area bounded between the segments of these curves based on a
classification of the intersection points using equivalence class. We also
present an alternate theory for curves with nontransverse intersections and a
method to increase the density of points on the curves for locating the
intersection points accurately.The numerical implementation of the theory
presented herein is available as an open source software called Lober. We used
this package to demonstrate the application of the theory to lobe dynamics that
arises in fluid mechanics, and rate of escape from a potential well that arises
in ship dynamics.Comment: 33 pages, 17 figure
Tecnologias sociais: as organizações não governamentais no enfrentamento das mudanças climáticas e na promoção de desenvolvimento humano
De acordo com o quarto relatório do Intergovernmental Panel on Climate Change (IPCC), as regiões semiáridas do mundo estarão entre as mais afetadas pelos impactos das mudanças climáticas globais. Estudos realizados pelo Ministério do Meio Ambiente (MMA), em 2007, confirmam que, no Nordeste brasileiro, não apenas choverá menos e mais irregularmente, mas, também, haverá mais secas, devido ao aquecimento da temperatura. Diante dos diversos impactos sociais, ambientais e econômicos possíveis nesses cenários, é de fundamental importância a verificação de alternativas sustentáveis para o semiárido brasileiro. Este artigo tem por objetivo avaliar o potencial de algumas das tecnologias sociais (TS) de convivência com o semiárido, desenvolvidas por diversas organizações, para a mitigação das mudanças climáticas e a promoção de desenvolvimento humano. Constata-se que as TS tem grande potencial para auxiliar na mitigação e na adaptação das mudanças climáticas, ao mesmo tempo que promovem melhorias na qualidade de vida das localidades onde estão sendo desenvolvidas
Third-Party Strategy under Plurality Rule: The British Liberal Democrats and the New Zealand Social Credit Party
This paper examines the strategic options facing small centrist third parties in two-party parliamentary systems operating under the single-member district plurality (SMDP) electoral system. It uses a spatial model to show that centrist third parties are better off targeting the 'safe' districts of a major party rather than marginal districts. Furthermore, it is optimal to target one party's districts, not both, to benefit from tactical and protest voting. The paper also questions the implicit conclusion of the median-legislator theorem that pivotality-seeking is the best strategy for a third party, at least under SMDP, because that would usurp voters' ability to select the executive directly, a key feature of two-partism. Finally, the paper shows that third parties can damage themselves if they 'flip' from opposition to one major party to support for it. Evidence is provided for the British Liberal Democrats and New Zealand?s historic Social Credit Party
- …