85,413 research outputs found
Numerical P Systems with Thresholds
Numerical P systems are a class of P systems inspired both from the structure of living cells and from economics. In this work, a control of using evolution programs is introduced into numerical P systems: a threshold is considered and a program can be applied only when the values of the variables involved in the production function of the program are greater than/equal to (lower-threshold) or smaller than/equal to (upper-threshold) the threshold. The computational power of numerical P systems with lower-threshold or upper-threshold is investigated. It is proved that numerical P systems with a lower-threshold, with one membrane and linear production functions, working both in the all-parallel mode and in the one-parallel mode are universal. The result is also extended to numerical P systems with an upperthreshold, by proving the equivalence of the numerical P systems with lower- and upper-thresholds
Upscaling Low Salinity Waterflooding in Heterogeneous Reservoirs
Imperial Users onl
Distributed machining control and monitoring using smart sensors/actuators
The study of smart sensors and actuators led, during the past few years, to the development of facilities which improve traditional sensors and actuators in a necessary way to automate production systems. In an other context, many studies are carried out aiming at defining a decisional structure for production activity control and the increasing need of reactivity leads to the autonomization of decisional levels close to the operational system. We suggest in this paper to study the natural convergence between these two approaches and we propose an integration architecture dealing with machine tool and machining control that enables the exploitation of distributed smart sensors and actuators in the decisional system
Regime change thresholds in flute-like instruments: influence of the mouth pressure dynamics
Since they correspond to a jump from a given note to another one, the mouth
pressure thresholds leading to regime changes are particularly important
quantities in flute-like instruments. In this paper, a comparison of such
thresholds between an artificial mouth, an experienced flutist and a non player
is provided. It highlights the ability of the experienced player to
considerabily shift regime change thresholds, and thus to enlarge its control
in terms of nuances and spectrum. Based on recent works on other wind
instruments and on the theory of dynamic bifurcations, the hypothe- sis is
tested experimentally and numerically that the dynamics of the blowing pressure
influences regime change thresholds. The results highlight the strong influence
of this parameter on thresholds, suggesting its wide use by experienced
musicians. Starting from these observations and from an analysis of a physical
model of flute-like instruments, involving numerical continuation methods and
Floquet stability analysis, a phenomenological modelling of regime change is
proposed and validated. It allows to predict the regime change thresholds in
the dynamic case, in which time variations of the blowing pressure are taken
into account
A graphical theory of competition on spatial resource gradients
Resource competition is a fundamental interaction in natural
communities.However little is known about competition in spatial environments
where organisms are able to regulate resource distributions. Here, we analyze
the competition of two consumers for two resources in a one-dimensional habitat
in which the resources are supplied from opposite sides. We show that the
success of an invading species crucially depends on the slope of the resource
gradients shaped by the resident. Our analysis reveals that parameter
combinations which lead to coexistence in a uniform environment may favor
alternative stable states in a spatial system, and vice versa. Furthermore,
differences in growth rate, mortality or dispersal abilities allow a consumer
to coexist stationarily with - or even outcompete - a competitor with lower
resource requirements. Applying our theory to a phytoplankton model, we explain
shifts in the community structure that are induced by environmental changes
A framework for the selection of the right nuclear power plant
Civil nuclear reactors are used for the production of electrical energy. In the nuclear industry vendors propose several nuclear reactor designs with a size from 35–45 MWe up to 1600–1700 MWe. The choice of the right design is a multidimensional problem since a utility has to include not only financial factors as levelised cost of electricity (LCOE) and internal rate of return (IRR), but also the so called “external factors” like the required spinning reserve, the impact on local industry and the social acceptability. Therefore it is necessary to balance advantages and disadvantages of each design during the entire life cycle of the plant, usually 40–60 years. In the scientific literature there are several techniques for solving this multidimensional problem. Unfortunately it does not seem possible to apply these methodologies as they are, since the problem is too complex and it is difficult to provide consistent and trustworthy expert judgments. This paper fills the gap, proposing a two-step framework to choosing the best nuclear reactor at the pre-feasibility study phase. The paper shows in detail how to use the methodology, comparing the choice of a small-medium reactor (SMR) with a large reactor (LR), characterised, according to the International Atomic Energy Agency (2006), by an electrical output respectively lower and higher than 700 MWe
Tree-Grass interactions dynamics and Pulse Fires: mathematical and numerical studies
Savannas are dynamical systems where grasses and trees can either dominate or
coexist. Fires are known to be central in the functioning of the savanna biome
though their characteristics are expected to vary along the rainfall gradients
as observed in Sub-Saharan Africa. In this paper, we model the tree-grass
dynamics using impulsive differential equations that consider fires as discrete
events. This framework allows us to carry out a comprehensive qualitative
mathematical analysis that revealed more diverse possible outcomes than the
analogous continuous model. We investigated local and global properties of the
equilibria and show that various states exist for the physiognomy of
vegetation. Though several abrupt shifts between vegetation states appeared
determined by fire periodicity, we showed that direct shading of grasses by
trees is also an influential process embodied in the model by a competition
parameter leading to bifurcations. Relying on a suitable nonstandard finite
difference scheme, we carried out numerical simulations in reference to three
main climatic zones as observable in Central Africa.Comment: 51 pages, 7 figure
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