163 research outputs found
R-Matrix Formulation of KP Hierarchies and their Gauge Equivalence
The Adler-Kostant-Symes -bracket scheme is applied to the algebra of
pseudo-differential operators to relate the three integrable hierarchies: KP
and its two modifications, known as nonstandard integrable models. All three
hierarchies are shown to be equivalent and connection is established in the
form of a symplectic gauge transformation. This construction results in a new
representation of the W-infinity algebras in terms of 4 bosonic fields.Comment: 13 pages, Latex, CERN-TH.6627/9
Comparison of Destructive Methods to Appraise the Mechanical Integrity of a Concrete Surface
peer reviewedDepending on the technique being used, the concrete removal operation prior to repair can be harmful to the residual concrete skin left on the structure. Whenever a tight bond between the repair and the old concrete is required, the soundness of the prepared surface should thus be assessed. Although this is widely recognized, there is no standard method intended to characterize the integrity of a concrete substrate after concrete removal. This paper presents the results of an investigation intended to assess and compare quantitatively different test methods, namely the Schmidt rebound hammer, the pull-out test and the pull-off test, to evaluate superficial mechanical integrity of a substrate after concrete removal operations. Although it does not yield a precise evaluation of compressive strength, the Schmidt rebound hammer test is recognized as a useful tool for performing quick surveys to assess concrete uniformity. The pull-off test is very well correlated with the splitting-tensile test, but it is not suited for vertical and overhead surfaces. The Capo pull-out test has limited interest for surface preparation, as it is applicable to flat surfaces only. Conversely, the accelerated pull-out test showed interesting potential as a simple and relatively rapid means for assessing the mechanical integrity of a concrete surface prior to repair for any type of concrete surface. More work is definitely required to refine the procedures and develop performance criteria. Nevertheless, it appears from the results generated in this study that the combination Schmidt hammer / pull-off test could fill the needs for the evaluation of horizontal surfaces after concrete removal, while the combination Schmidt hammer / accelerated pull-out test could be used effectively on vertical and overhead surfaces.Coopération scientifique WBI/Québe
Induced Gravity as a WZNW Model
We derive the explicit form of the Wess-Zumino quantum effective action of
chiral \Winf-symmetric system of matter fields coupled to a general chiral
\Winf-gravity background. It is expressed as a geometric action on a
coadjoint orbit of the deformed group of area-preserving diffeomorphisms on
cylinder whose underlying Lie algebra is the centrally-extended algebra of
symbols of differential operators on the circle. Also, we present a systematic
derivation, in terms of symbols, of the "hidden" SL(\infty;\IR) Kac-Moody
currents and the associated SL(\infty;\IR) Sugawara form of energy-momentum
tensor component as a consequence of the SL(\infty;\IR) stationary
subgroup of the relevant \Winf coadjoint orbit
Integrable Perturbations of and WZW Models
We present a new class of 2d integrable models obtained as perturbations of
minimal CFT with W-symmetry by fundamental weight primaries. These models are
generalisations of well known -perturbed Virasoro minimal models. In the
large (number of minimal model) limit they coincide with scalar
perturbations of WZW theories. The algebra of conserved charges is discussed in
this limit. We prove that it is noncommutative and coincides with twisted
affine algebra represented in a space of asymptotic states. We conjecture
that scattering in these models for generic is described by -matrix of
the -deformed - algebra with being root of unity.Comment: 10p., LaTeX, preprint SISSA 19/94/FM (references added
Concrete repair bond: evaluation and factors of influence
peer reviewedRepair and strengthening of existing concrete structures are among the biggest challenges civil
engineers are facing today and will have to face in the years to come. Present concerns of sustainable
development emphasizing repair instead of new construction will only strengthen this trend. Concerted efforts
towards improving the durability of concrete repairs are still needed from scientists and engineers. One of the
critical aspects of durability of concrete repairs and overlays is lasting and sufficient interfacial bond between repair material and existing concrete substrate. This paper summarizes some of the findings of a collaborative study devoted to the most significant factors influencing bond in repairs (roughness, degree of saturation and carbonation of the substrate) and its field evaluation (type of loading, device misalignment). Based on the test results collected in different test programs, guideline-type recommendations for surface preparation prior to repair were issued
Randomly coupled minimal models
Using 1-loop renormalisation group equations, we analyze the effect of
randomness on multi-critical unitary minimal conformal models. We study the
case of two randomly coupled models and found that they flow in two
decoupled models, in the infra-red limit. This result is then extend
to the case with randomly coupled models, which will flow toward
decoupled .Comment: 12 pages, latex, 1 eps figures; new results adde
Cellular IP<sub>6</sub> Levels Limit HIV Production while Viruses that Cannot Efficiently Package IP<sub>6</sub> Are Attenuated for Infection and Replication
Summary: HIV-1 hijacks host proteins to promote infection. Here we show that HIV is also dependent upon the host metabolite inositol hexakisphosphate (IP6) for viral production and primary cell replication. HIV-1 recruits IP6 into virions using two lysine rings in its immature hexamers. Mutation of either ring inhibits IP6 packaging and reduces viral production. Loss of IP6 also results in virions with highly unstable capsids, leading to a profound loss of reverse transcription and cell infection. Replacement of one ring with a hydrophobic isoleucine core restores viral production, but IP6 incorporation and infection remain impaired, consistent with an independent role for IP6 in stable capsid assembly. Genetic knockout of biosynthetic kinases IPMK and IPPK reveals that cellular IP6 availability limits the production of diverse lentiviruses, but in the absence of IP6, HIV-1 packages IP5 without loss of infectivity. Together, these data suggest that IP6 is a critical cofactor for HIV-1 replication
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