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Flow measurement inside a zinc-nickel flow cell battery using FBG based sensor system
Downloading of the abstract is permitted for personal use only. A detailed knowledge of the internal flow distribution inside a zinc-nickel flow battery is of critical importance to ensure smooth flow of the electrolyte through the battery cell and better operation of the device. Information of this type can be used as a useful means of early detection of zinc deposition and dendrite formation inside the cell, negative factors which affect the flow and thus which can lead to internal short circuiting, this being a primary failure mode of these types of batteries. This deposition occurs at low pH levels when zinc reacts with the electrolyte to form solid zinc oxide hydroxides. Traditionally, manual inspection is conducted, but this is time consuming and costly, only providing what are often inaccurate results-overall it is an impractical solution especially with the wider use of batteries in the very near future. Fibre Bragg grating (FBG) sensors integrated inside the flow cell offer the advantage of measuring flow changes at multiple locations using a single fibre and that then can be used as an indicator of the correlation between the internal flow distribution and the deposition characteristics. This work presents an initial study, where two networks of FBGs have been installed and used for flow change detection in an active zinc-nickel flow battery. Data have been obtained from the sensor networks and information of battery performance completed and summarized in this paper. The approach shows promising results and thus scope for the future research into the development of this type of sensor system
Quantum computing on encrypted data
The ability to perform computations on encrypted data is a powerful tool for
protecting privacy. Recently, protocols to achieve this on classical computing
systems have been found. Here we present an efficient solution to the quantum
analogue of this problem that enables arbitrary quantum computations to be
carried out on encrypted quantum data. We prove that an untrusted server can
implement a universal set of quantum gates on encrypted quantum bits (qubits)
without learning any information about the inputs, while the client, knowing
the decryption key, can easily decrypt the results of the computation. We
experimentally demonstrate, using single photons and linear optics, the
encryption and decryption scheme on a set of gates sufficient for arbitrary
quantum computations. Because our protocol requires few extra resources
compared to other schemes it can be easily incorporated into the design of
future quantum servers. These results will play a key role in enabling the
development of secure distributed quantum systems
Quench dynamics across quantum critical points
We study the quantum dynamics of a number of model systems as their coupling
constants are changed rapidly across a quantum critical point. The primary
motivation is provided by the recent experiments of Greiner et al. (Nature 415,
39 (2002)) who studied the response of a Mott insulator of ultracold atoms in
an optical lattice to a strong potential gradient. In a previous work
(cond-mat/0205169), it had been argued that the resonant response observed at a
critical potential gradient could be understood by proximity to an Ising
quantum critical point describing the onset of density wave order. Here we
obtain numerical results on the evolution of the density wave order as the
potential gradient is scanned across the quantum critical point. This is
supplemented by studies of the integrable quantum Ising spin chain in a
transverse field, where we obtain exact results for the evolution of the Ising
order correlations under a time-dependent transverse field. We also study the
evolution of transverse superfluid order in the three dimensional case. In all
cases, the order parameter is best enhanced in the vicinity of the quantum
critical point.Comment: 10 pages, 6 figure
UNDERSTANDING TECHNOLOGY ADOPTION THROUGH SYSTEM DYNAMICS MODELING: IMPLICATIONS FOR AGRIBUSINESS MANAGEMENT
This work demonstrates the utility of sophisticated simulation tools in aiding agribusiness managers' decision making. The system dynamics model developed here provides insight into the use of such models to evaluate potential adoption rates and diffusion patterns of yield mapping and monitoring technologies. The model allows for comparative analyses of the possible effects of different profit assumptions on adoption and diffusion.Agribusiness, Research and Development/Tech Change/Emerging Technologies,
An Unsplit, Cell-Centered Godunov Method for Ideal MHD
We present a second-order Godunov algorithm for multidimensional, ideal MHD.
Our algorithm is based on the unsplit formulation of Colella (J. Comput. Phys.
vol. 87, 1990), with all of the primary dependent variables centered at the
same location. To properly represent the divergence-free condition of the
magnetic fields, we apply a discrete projection to the intermediate values of
the field at cell faces, and apply a filter to the primary dependent variables
at the end of each time step. We test the method against a suite of linear and
nonlinear tests to ascertain accuracy and stability of the scheme under a
variety of conditions. The test suite includes rotated planar linear waves, MHD
shock tube problems, low-beta flux tubes, and a magnetized rotor problem. For
all of these cases, we observe that the algorithm is second-order accurate for
smooth solutions, converges to the correct weak solution for problems involving
shocks, and exhibits no evidence of instability or loss of accuracy due to the
possible presence of non-solenoidal fields.Comment: 37 Pages, 9 Figures, submitted to Journal of Computational Physic
Metal-superconductor transition at zero temperature: A case of unusual scaling
An effective field theory is derived for the normal metal-to-superconductor
quantum phase transition at T=0. The critical behavior is determined exactly
for all dimensions d>2. Although the critical exponents \beta and \nu do not
exist, the usual scaling relations, properly reinterpreted, still hold. A
complete scaling description of the transition is given, and the physics
underlying the unusual critical behavior is discussed. Quenched disorder leads
to anomalously strong T_c-fluctuations which are shown to explain the
experimentally observed broadening of the transition in low-T_c thin films.Comment: 4 pp., no figs, final version as publishe
Wiener Reconstruction of Large-Scale Structure from Peculiar Velocities
We present an alternative, Bayesian method for large-scale reconstruction
from observed peculiar velocity data. The method stresses a rigorous treatment
of the random errors and it allows extrapolation into poorly sampled regions in
real space or in k-space. A likelihood analysis is used to determine the
fluctuation power spectrum, followed by a Wiener Filter (WF) analysis to obtain
the minimum-variance mean fields of velocity and mass density. Constrained
Realizations (CR) are then used to sample the statistical scatter about the WF
mean field. The WF/CR method is applied as a demonstration to the Mark III data
with 1200 km/s, 900 km/s, and 500 km/s resolutions. The main reconstructed
structures are consistent with those extracted by the POTENT method. A
comparison with the structures in the distribution of IRAS 1.2Jy galaxies
yields a general agreement. The reconstructed velocity field is decomposed into
its divergent and tidal components relative to a cube of +/-8000 km/s centered
on the Local Group. The divergent component is very similar to the velocity
field predicted from the distribution of IRAS galaxies. The tidal component is
dominated by a bulk flow of 194 +/- 32 km/s towards the general direction of
the Shapley concentration, and it also indicates a significant quadrupole.Comment: 28 pages and 8 GIF figures, Latex (aasms4.sty), submitted to ApJ.
Postscript version of the figures can be obtained by anonymous ftp from:
ftp://alf.huji.ac.il/pub/saleem
Fluctuating loops and glassy dynamics of a pinned line in two dimensions
We represent the slow, glassy equilibrium dynamics of a line in a
two-dimensional random potential landscape as driven by an array of
asymptotically independent two-state systems, or loops, fluctuating on all
length scales. The assumption of independence enables a fairly complete
analytic description. We obtain good agreement with Monte Carlo simulations
when the free energy barriers separating the two sides of a loop of size L are
drawn from a distribution whose width and mean scale as L^(1/3), in agreement
with recent results for scaling of such barriers.Comment: 11 pages, 4 Postscript figure
Density Matrix Renormalization Group Method for the Random Quantum One-Dimensional Systems - Application to the Random Spin-1/2 Antiferromagnetic Heisenberg Chain -
The density matrix renormalization group method is generalized to one
dimensional random systems. Using this method, the energy gap distribution of
the spin-1/2 random antiferromagnetic Heisenberg chain is calculated. The
results are consistent with the predictions of the renormalization group theory
demonstrating the effectiveness of the present method in random systems. The
possible application of the present method to other random systems is
discussed.Comment: 13 pages, 3 figures upon reques
Modified TAP equations for the SK spin glass
The stability of the TAP mean field equations is reanalyzed with the
conclusion that the exclusive reason for the breakdown at the spin glass
instability is an inconsistency for the value of the local susceptibility. A
new alternative approach leads to modified equations which are in complete
agreement with the original ones above the instability. Essentially altered
results below the instability are presented and the consequences for the
dynamical mean field equations are discussed.Comment: 7 pages, 2 figures, final revised version to appear in Europhys. Let
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