140 research outputs found
Factorization of the current algebra and integrable top-like systems
A hierarchy of integrable hamiltonian nonlinear ODEs is associated with any
decomposition of the Lie algebra of Laurent series with coefficients being
elements of a semi-simple Lie algebra into a sum of the subalgebra consisting
of the Taylor series and some complementary subalgebra. In the case of the Lie
algebra our scheme covers all classical integrable cases in the
Kirchhoff problem of the motion of a rigid body in an ideal fluid. Moreover,
the construction allows us to generate integrable deformations for known
integrable models.Comment: 21 page
Integrable matrix equations related to pairs of compatible associative algebras
We study associative multiplications in semi-simple associative algebras over
C compatible with the usual one. An interesting class of such multiplications
is related to the affine Dynkin diagrams of A, D, E-type. In this paper we
investigate in details the multiplications of the A-type and integrable matrix
ODEs and PDEs generated by them.Comment: 12 pages, Late
Optical Conductivity of the Trellis-Lattice t-J Model: Charge Fluctuations in NaV_2O_5
Optical conductivity of the trellis lattice t-J model at quarter filling is
calculated by an exact-diagonalization technique on small clusters, whereby the
valence state of V ions of NaV_2O_5 is considered. We show that the
experimental features at \sim 1 eV, including peak positions, presence of
shoulders, and anisotropic spectral weight, can be reproduced in reasonable
range of parameter values, only by assuming that the system is in the charge
disproportionated ground state. Possible reconciliation with experimental data
suggesting the presence of uniform ladders at T>T_c is discussed.Comment: 4 pages, 4 gif figures. Minor revisions have been made. Hardcopies of
figures (or the entire manuscript) can be obtained by e-mail request to
[email protected]
"Doubled" generalized Landau-Lifshiz hierarchies and special quasigraded Lie algebras
Using special quasigraded Lie algebras we obtain new hierarchies of
integrable nonlinear vector equations admitting zero-curvature representations.
Among them the most interesting is extension of the generalized Landau-Lifshitz
hierarchy which we call "doubled" generalized Landau-Lifshiz hierarchy. This
hierarchy can be also interpreted as an anisotropic vector generalization of
"modified" Sine-Gordon hierarchy or as a very special vector generalization of
so(3) anisotropic chiral field hierarchy.Comment: 16 pages, no figures, submitted to Journal of Physics
Design of Scalable Continuous Media Servers with Dynamic Replication
Multimedia applications place high demands for quality-of-service (QoS),
performance, and reliability on systems. These stringent requirements
make design of cost-effective and scalable systems difficult.
Therefore efficient adaptive and dynamic resource management techniques
in conjunction with data placement techniques can be of great help in
improving performance, scalability and reliability of such systems.
In this paper, we first focus on data placement.
In the recent past, a great deal of work has focused on "wide" data
striping as a way of dealing with load imbalance problems caused by
skews in data access patterns. Another approach to dealing with load imbalance
problems is replication. The appropriate compromise between the degree
of striping and the degree of replication is key to the design of
scalable continuous media (CM) servers. In this work we focus on evaluation
of this compromise in the context of a hybrid CM server design.
Changes in data access patterns lead to other questions:
(1) when should the system alter the number of copies of a CM object, and
(2) how to accomplish this change. We address (1) through an adaptive
threshold-based approach, and we use dynamic replication policies in
conjunction with a mathematical model of user behavior to address (2).
We do this without any knowledge of data access patterns and with
provisions for full use of VCR functionality. Through a performance
study, we show that not only does the use of this mathematical model
in conjunction with dynamic resource management policies improves the
system's performance but that it also facilitates reduced sensitivity
to changes in:(a) workload characteristics, (b) skewness of data access
patterns, and (c) frequency of changes in data access patterns.
We believe that not only is this a desirable property for a CM server,
in general, but that furthermore, it suggests the usefulness of these
techniques across a wide range of continuous media applications.
(Cross-referenced as UMIACS-TR-2001-21
From AKNS to derivative NLS hierarchies via deformations of associative products
Using deformations of associative products, derivative nonlinear Schrodinger
(DNLS) hierarchies are recovered as AKNS-type hierarchies. Since the latter can
also be formulated as Gelfand-Dickey-type Lax hierarchies, a recently developed
method to obtain 'functional representations' can be applied. We actually
consider hierarchies with dependent variables in any (possibly noncommutative)
associative algebra, e.g., an algebra of matrices of functions. This also
covers the case of hierarchies of coupled DNLS equations.Comment: 22 pages, 2nd version: title changed and material organized in a
different way, 3rd version: introduction and first part of section 2
rewritten, taking account of previously overlooked references. To appear in
J. Physics A: Math. Ge
High frequency dielectric and magnetic anomaly at the phase transition in NaV2O5
We found anomalies in the temperature dependence of the dielectric and the
magnetic susceptibiliy of NaV_2O_5 in the microwave and far infrared frequency
ranges. The anomalies occur at the phase transition temperature T_c, at which
the spin gap opens. The real parts of the dielectric constants epsilon_a and
epsilon_c decrease below T_c. The decrease of epsilon_a (except for the narrow
region close to T_c) is proportional to the intensity of the x-ray reflection
appearing at T_c. The dielectric constant anomaly can be explained by the
zigzag charge ordering in the ab-plane appearing below T_c. The anomaly of the
microwave magnetic losses is probably related to the coupling between the spin
and charge degrees of freedom in vanadium ladders.Comment: 3 PS-figures, LATEX-text, new experimental data added, typos
correcte
Postpandemic rebound of adeno-associated virus type 2 (AAV2) infections temporally associated with an outbreak of unexplained severe acute hepatitis in children in the United Kingdom
Over 1000 cases of unexplained severe acute hepatitis in children have been reported to date worldwide. An association with adeno-associated virus type 2 (AAV2) infection, a human parvovirus, prompted us to investigate the epidemiology of AAV in the United Kingdom. Three hundred pediatric respiratory samples collected before (April 03, 2009–April 03, 2013) and during (April 03, 2022) the COVID-19 pandemic were obtained. Wastewater samples were collected from 50 locations in London (August 2021–March 2022). Samples were tested for AAV using real-time polymerase chain reaction followed by sequencing. Selected adenovirus (AdV)-positive samples were also sequenced. The detection frequency of AAV2 was a sevenfold higher in 2022 samples compared with 2009–2013 samples (10% vs. 1.4%) and highest in AdV-positive samples compared with negatives (10/37, 27% vs. 5/94, 5.3%, respectively). AAV2-positive samples displayed high genetic diversity. AAV2 sequences were either very low or absent in wastewater collected in 2021 but increased in January 2022 and peaked in March 2022. AAV2 was detected in children in association with AdV of species C, with a highest frequency in 2022. Our findings are consistent with the expansion of the population of children unexposed to AAV2, leading to greater spread of the virus once distancing restrictions were lifted
Folded modes in the infrared spectra of the spin-Peierls phase of CuGeO_3
Polarized far-infrared transmittance spectra of CuGeO_3 single crystals were
measured at different temperatures (6K < T < 300K). Two spectral lines, at
284.2 cm-1 in E||c polarization and at 311.7 cm-1 in E||b polarization, appear
at the temperature of the spin-Peierls transition and grow in intensity with
decreasing temperature. Both of them are, most probably, folded modes of the
dimerized lattice. We discuss a possible role of the spin-phonon interaction in
the formation of the 311.7 cm-1 feature.Comment: 4 pages, 5 figures, 1 table; Submitted to Phys.Rev.B Second revision.
Figures and text were slightly change
One-dimensional dynamics of the d-electrons in -NaVO
We have studied the electronic properties of the ladder compound
-NaVO, adopting a joint experimental and theoretical
approach. The momentum-dependent loss function was measured using electron
energy-loss spectroscopy in transmission. The optical conductivity derived from
the loss function by a Kramers-Kronig analysis agrees well with our results
from LSDA+U band-structure calculations upon application of an
antiferromagnetic alignment of the V~3 spins along the legs and an
on-site Coulomb interaction U of between 2 and 3 eV. The decomposition of the
calculated optical conductivity into contributions from transitions between
selected energy regions of the DOS reveals the origin of the observed
anisotropy of the optical conductivity. In addition, we have investigated the
plasmon excitations related to transitions between the vanadium states within
an effective 16 site vanadium cluster model. Good agreement between the
theoretical and experimental loss function was obtained using the hopping
parameters derived from the tight binding fit to the band-structure and
moderate Coulomb interactions between the electrons within the ab plane.Comment: 23 pages, 8 figures; submitted to PR
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