390 research outputs found
Indirect forces between impurities in one-dimensional quantum liquids
We investigate the indirect interaction between two isolated impurities in a
Luttinger liquid described by a microscopic lattice model. To treat the
electron-electron interaction U the functional renormalization group method is
used. For comparison we also study the U=0 case. We find that for a wide range
of impurity parameters the impurity interaction V_{12} as a function of their
separation r oscillates with decaying amplitude between being attractive and
repulsive. For half-filling of the band and in a crossover regime between weak
and strong impurities the interaction becomes purely attractive. For U=0 and
independent of the impurity strength the amplitude of the interaction energy
falls off as 1/r. For U>0 the decay for small separations and weak to
intermediate impurities is governed by a U dependent exponent larger than -1,
which crosses over to -1 for large r. The crossover scale depends on the
impurity strength and U. We present simple pictures which explain our results
in the limits of weak and strong impurities. We finally also consider
attractive interactions U<0.Comment: 8 pages, 9 figures include
A comparative analysis of built environment and open terrain wind data by higher order statistics and performance evaluation of 5 kW HAWT using FAST
Small wind turbines (SWT) that are designed as per the IEC 61400-2 standard suffer structural and operational complexities when operating in the built environment, because such environments impose stochastic variations in wind speed and turbulence. The wind conditions in flat terrain of Östergarnsholm (OG) Island, Sweden and built environment of Port Kennedy (PK), Australia are compared for turbulence intensity (TI) and intermittency. The TI of the PK wind field was 24% at mean wind speed of 15 m/s, which was higher than the Normal Turbulence Model (NTM) indicated in IEC 61400-2. The TI in the open terrain was below 18% for all mean wind speeds. Similarly, for three chosen wind speed bins within a SWT's operating range, the urban wind field had higher intermittency for smaller timescales but resulted in smaller intermittency as the time lag increased. The effect of these measured wind fields on the performance and loading of a turbine was studied at the three chosen wind speed bins using an aeroelastic model of a 5 kW SWT that was developed in FAST. The predicted output statistics using measured wind fields were compared with the assumed wind fields in the IEC 61400-2 standard. The rotor thrust and blade flapwise bending moment with PK wind data were higher than that of the IEC standard due to the increased turbulence in the inflowing wind indicating the inadequacy in the current wind standard applied for such SWTs for urban installations
Dynamics of Dengue epidemics using optimal control
We present an application of optimal control theory to Dengue epidemics. This
epidemiologic disease is an important theme in tropical countries due to the
growing number of infected individuals. The dynamic model is described by a set
of nonlinear ordinary differential equations, that depend on the dynamic of the
Dengue mosquito, the number of infected individuals, and the people's
motivation to combat the mosquito. The cost functional depends not only on the
costs of medical treatment of the infected people but also on the costs related
to educational and sanitary campaigns. Two approaches to solve the problem are
considered: one using optimal control theory, another one by discretizing first
the problem and then solving it with nonlinear programming. The results
obtained with OC-ODE and IPOPT solvers are given and discussed. We observe that
with current computational tools it is easy to obtain, in an efficient way,
better solutions to Dengue problems, leading to a decrease of infected
mosquitoes and individuals in less time and with lower costs.Comment: Submitted to Mathematical and Computer Modelling 25/Oct/2009;
accepted for publication, after revision, 22/June/201
Combining the regularization strategy and the SQP to solve MPCC - A MATLAB implementation
Mathematical Program with Complementarity Constraints (MPCC) plays a very
important role in many fields such as engineering design, economic equilibrium,
multilevel game, and mathematical programming theory itself. In theory its constraints
fail to satisfy a standard constraint qualification such as the linear independence
constraint qualification (LICQ) or the Mangasarian-Fromovitz constraint
qualification (MFCQ) at any feasible point. As a result, the developed nonlinear
programming theory may not be applied to MPCC class directly. Nowadays, a natural
and popular approach is try to find some suitable approximations of an MPCC
so that it can be solved by solving a sequence of nonlinear programs.
This work aims to solve the MPCC using nonlinear programming techniques,
namely the SQP and the regularization scheme. Some algorithms with two iterative
processes, the inner and the external, were developed. A set of AMPL problems
from MacMPEC database [7] were tested. The algorithms performance comparative
analysis was carried out
CEDIM Risk Explorer ? a map server solution in the project "Risk Map Germany"
International audienceThe project "Risk Map Germany" at the Center for Disaster Management and Risk Reduction Technology (CEDIM) aims at visualizing hazards, vulnerabilities and risks associated with natural and man made hazards. CEDIM as an interdisciplinary project unified various expertise like earthquake, storm and flood disaster research. Our aim was to visualize the manifold data exploration in thematic maps. The implemented Web-GIS solution "CEDIM Risk Explorer" represents the map visualizations of the different risk research. This Web-GIS integrates results from interdisciplinary work as maps of hazard, vulnerability and risk in one application and offers therefore new cognitions to the user by enabling visual comparisons. The present paper starts with a project introduction and a literature review of distributed GIS environments. Further the methods of map realization and visualization in the selected technical solution is worked out. Finally, the conclusions give the perspectives for future developments to the "CEDIM Risk Explorer"
Incompressible image registration using divergence-conforming B-splines
Anatomically plausible image registration often requires volumetric
preservation. Previous approaches to incompressible image registration have
exploited relaxed constraints, ad hoc optimisation methods or practically
intractable computational schemes. Divergence-free velocity fields have been
used to achieve incompressibility in the continuous domain, although, after
discretisation, no guarantees have been provided. In this paper, we introduce
stationary velocity fields (SVFs) parameterised by divergence-conforming
B-splines in the context of image registration. We demonstrate that sparse
linear constraints on the parameters of such divergence-conforming B-Splines
SVFs lead to being exactly divergence-free at any point of the continuous
spatial domain. In contrast to previous approaches, our framework can easily
take advantage of modern solvers for constrained optimisation, symmetric
registration approaches, arbitrary image similarity and additional
regularisation terms. We study the numerical incompressibility error for the
transformation in the case of an Euler integration, which gives theoretical
insights on the improved accuracy error over previous methods. We evaluate the
proposed framework using synthetically deformed multimodal brain images, and
the STACOM11 myocardial tracking challenge. Accuracy measurements demonstrate
that our method compares favourably with state-of-the-art methods whilst
achieving volume preservation.Comment: Accepted at MICCAI 201
Optimal topological simplification of discrete functions on surfaces
We solve the problem of minimizing the number of critical points among all
functions on a surface within a prescribed distance {\delta} from a given input
function. The result is achieved by establishing a connection between discrete
Morse theory and persistent homology. Our method completely removes homological
noise with persistence less than 2{\delta}, constructively proving the
tightness of a lower bound on the number of critical points given by the
stability theorem of persistent homology in dimension two for any input
function. We also show that an optimal solution can be computed in linear time
after persistence pairs have been computed.Comment: 27 pages, 8 figure
On the Production of Pairs in pp Collisions at 0.8 GeV
Data accumulated recently for the exclusive measurement of the reaction at a beam energy of 0.793 GeV using the COSY-TOF
spectrometer have been analyzed with respect to possible events from the reaction channel. The latter is expected to be the only
production channel, which contains no major contributions from
resonance excitation close to threshold and hence should be a good testing
ground for chiral dynamics in the production process. No single event
has been found, which meets all conditions for being a candidate for the reaction. This gives an upper limit for the cross section of
0.16 b (90% C.L.), which is more than an order of magnitude smaller than
the cross sections of the other two-pion production channels at the same
incident energy
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