3,150 research outputs found
Misrepresenting the Jordan River Basin
This article advances a critique of the UN Economic and Social Commission for West Asia’s (ESCWA’s) representation of the Jordan River Basin, as contained in its recently published Inventory of Shared Water Resources in Western Asia. We argue that ESCWA’s representation of the Jordan Basin is marked by serious technical errors and a systematic bias in favour of one riparian, Israel, and against the Jordan River’s four Arab riparians. We demonstrate this in relation to ESCWA’s account of the political geography of the Jordan River Basin, which foregrounds Israel and its perspectives and narratives; in relation to hydrology, where Israel’s contribution to the basin is overstated, whilst that of Arab riparians is understated; and in relation to development and abstraction, where Israel’s transformation and use of the basin are underplayed, while Arab impacts are exaggerated. Taken together, this bundle of misrepresentations conveys the impression that it is Israel which is the main contributor to the Jordan River Basin, Arab riparians its chief exploiters. This impression is, we argue, not just false but also surprising, given that the Inventory is in the name of an organisation of Arab states. The evidence discussed here provides a striking illustration of how hegemonic hydro-political narratives are reproduced, including by actors other than basin hegemons themselves
Buffering volatility : storage investments and technology-specific renewable energy support
Mitigating climate change will require integrating large amounts of highly intermittent renewable energy (RE) sources in future electricity markets. Considerable uncertainties exist about the cost and availability of future large-scale storage to alleviate the potential mismatch between demand and supply. This paper examines the suitability of regulatory (public policy) mechanisms for coping with the volatility induced by intermittent RE sources, using a numerical equilibrium model of a future wholesale electricity market. We find that the optimal RE subsidies are technology-specific reflecting the heterogeneous value for system integration. Differentiated RE subsidies reduce the curtailment of excess production, thereby preventing costly investments in energy storage. Using a simple cost-benefit framework, we show that a smart design of RE support policies significantly reduces the level of optimal storage. We further find that the marginal benefits of storage rapidly decrease for short-term (intra-day) storage and are small for long-term (seasonal) storage independent of the storage level. This suggests that storage is not likely to be the limiting factor for decarbonizing the electricity sector
Term Graph Representations for Cyclic Lambda-Terms
We study various representations for cyclic lambda-terms as higher-order or
as first-order term graphs. We focus on the relation between
`lambda-higher-order term graphs' (lambda-ho-term-graphs), which are
first-order term graphs endowed with a well-behaved scope function, and their
representations as `lambda-term-graphs', which are plain first-order term
graphs with scope-delimiter vertices that meet certain scoping requirements.
Specifically we tackle the question: Which class of first-order term graphs
admits a faithful embedding of lambda-ho-term-graphs in the sense that: (i) the
homomorphism-based sharing-order on lambda-ho-term-graphs is preserved and
reflected, and (ii) the image of the embedding corresponds closely to a natural
class (of lambda-term-graphs) that is closed under homomorphism?
We systematically examine whether a number of classes of lambda-term-graphs
have this property, and we find a particular class of lambda-term-graphs that
satisfies this criterion. Term graphs of this class are built from application,
abstraction, variable, and scope-delimiter vertices, and have the
characteristic feature that the latter two kinds of vertices have back-links to
the corresponding abstraction.
This result puts a handle on the concept of subterm sharing for higher-order
term graphs, both theoretically and algorithmically: We obtain an easily
implementable method for obtaining the maximally shared form of
lambda-ho-term-graphs. Also, we open up the possibility to pull back properties
from first-order term graphs to lambda-ho-term-graphs. In fact we prove this
for the property of the sharing-order successors of a given term graph to be a
complete lattice with respect to the sharing order.
This report extends the paper with the same title
(http://arxiv.org/abs/1302.6338v1) in the proceedings of the workshop TERMGRAPH
2013.Comment: 35 pages. report extending proceedings article on arXiv:1302.6338
(changes with respect to version v2: added section 8, modified Proposition
2.4, added Remark 2.5, added Corollary 7.11, modified figures in the
conclusion
Non-equilibrium steady state of a driven levitated particle with feedback cooling
Laser trapped nanoparticles have been recently used as model systems to study
fundamental relations holding far from equilibrium. Here we study, both
experimentally and theoretically, a nanoscale silica sphere levitated by a
laser in a low density gas. The center of mass motion of the particle is
subjected, at the same time, to feedback cooling and a parametric modulation
driving the system into a non-equilibrium steady state. Based on the Langevin
equation of motion of the particle, we derive an analytical expression for the
energy distribution of this steady state showing that the average and variance
of the energy distribution can be controlled separately by appropriate choice
of the friction, cooling and modulation parameters. Energy distributions
determined in computer simulations and measured in a laboratory experiment
agree well with the analytical predictions. We analyse the particle motion also
in terms of the quadratures and find thermal squeezing depending on the degree
of detuning.Comment: Submitted to the New Journal of Physic
Non-invasive imaging of hypoxia in tissue engineering
In tissue engineering, cells are grown on biomaterials in vitro and subsequently implanted. A critical parameter in effective proliferation and differentiation is the availability of nutrients. Few tools are currently available to monitor the nutritional status of cells. In this study, we have employed A4-4 cells [1], a Chinese hamster ovary cell line stably transfected with a luciferase gene driven by the hypoxia responsive element (HRE) from the promoter region of the VEGF gene [2, 3]. HRE activity, and thus luciferase activity, directly correlates with decreasing cellular O2 levels.The aim of this study is to investigate whether the HREluciferase construct can be used for non-invasive imaging of hypoxia in tissue engineering
Force measurement in the presence of Brownian noise: Equilibrium distribution method vs. Drift method
The study of microsystems and the development of nanotechnologies require new
techniques to measure piconewton and femtonewton forces at microscopic and
nanoscopic scales. Amongst the challenges, there is the need to deal with the
ineluctable thermal noise, which, in the typical experimental situation of a
spatial diffusion gradient, causes a spurious drift. This leads to a correction
term when forces are estimated from drift measurements [Phys. Rev. Lett. 104,
170602 (2010)]. Here, we provide a systematic study of such effect comparing
the forces acting on various Brownian particles derived from equilibrium
distribution and drift measurements. We discuss the physical origin of the
correction term, its dependence on wall distance, particle radius, and its
relation to the convention used to solve the respective stochastic integrals.
Such correction term becomes more significant for smaller particles and is
predicted to be in the order of several piconewtons for particles the size of a
biomolecule.Comment: 10 pages, 13 figure
Expressibility in the Lambda Calculus with Letrec
We investigate the relationship between finite terms in lambda-letrec, the
lambda calculus with letrec, and the infinite lambda terms they express. As
there are easy examples of lambda-terms that, intuitively, are not unfoldings
of terms in lambda-letrec, we consider the question: How can those infinite
lambda terms be characterised that are lamda-letrec-expressible in the sense
that they can be obtained as infinite unfoldings of terms in lambda-letrec?
For 'observing' infinite lambda-terms through repeated 'experiments' carried
out at the head of the term we introduce two rewrite systems (with rewrite
relations) -reg-> and -reg+-> that decompose the term, and produce 'generated
subterms' in two notions. Thereby the sort of the step can be observed as well
as its target, a generated subterm. In both systems there are four sorts of
decomposition steps: -lambda-> steps (decomposing a lambda-abstraction), -@0>
and -@1> steps (decomposing an application into its function and argument), and
respectively, -del-> steps (delimiting the scope of an abstraction, for
-reg->), and -S-> (delimiting of scopes, for -reg+->). These steps take place
on infinite lambda-terms furnished with a leading prefix of abstractions for
gathering previously encountered lambda-abstractions and keeping the generated
subterms closed. We call an infinite lambda-term 'regular'/'strongly regular'
if its set of -reg-> -reachable / -reg-> -reachable generated subterms is
finite. Furthermore, we analyse the binding structure of lambda-terms with the
concept of 'binding-capturing chain'.
Using these concepts, we answer the question above by providing two
characterisations of lambda-letrec-expressibility. For all infinite
lambda-terms M, the following statements are equivalent: (i) M is
lambda-letrec-expressible; (ii) M is strongly regular; (iii) M is regular, and
it only has finite binding-capturing chains.Comment: 79 pages, 25 figure
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