365 research outputs found
Algebra of Non-Local Charges in Supersymmetric Non-Linear Sigma Models
We propose a graphic method to derive the classical algebra (Dirac brackets)
of non-local conserved charges in the two dimensional supersymmetric non-linear
sigma model. As in the purely bosonic theory we find a cubic Yangian
algebra. We also consider the extension of graphic methods to other integrable
theories.Comment: LateX file, 19 pages, figures included with epsf; file with figures
has been replace
Classical and quantum N=1 super -algebras
We construct higher-spin N=1 super algebras as extensions of the super
Virasoro algebra containing generators for all spins . We find two
distinct classical (Poisson) algebras on the phase super space. Our results
indicate that only one of them can be consistently quantized.Comment: 10 pages, latex, no figure
Superloop Equations and Two Dimensional Supergravity
We propose a discrete model whose continuum limit reproduces the string
susceptibility and the scaling dimensions of -minimal superconformal
models coupled to -supergravity. The basic assumption in our presentation
is a set of super-Virasoro constraints imposed on the partition function. We
recover the Neveu-Schwarz and Ramond sectors of the theory, and we are also
able to evaluate all planar loop correlation functions in the continuum limit.
We find evidence to identify the integrable hierarchy of non-linear equations
describing the double scaling limit as a supersymmetric generalization of KP
studied by Rabin.Comment: 34 page
The Algebra of Non-Local Charges in Non-Linear Sigma Models
We obtain the exact Dirac algebra obeyed by the conserved non-local charges
in bosonic non-linear sigma models. Part of the computation is specialized for
a symmetry group . As it turns out the algebra corresponds to a cubic
deformation of the Kac-Moody algebra. The non-linear terms are computed in
closed form. In each Dirac bracket we only find highest order terms (as
explained in the paper), defining a saturated algebra. We generalize the
results for the presence of a Wess-Zumino term. The algebra is very similar to
the previous one, containing now a calculable correction of order one unit
lower.Comment: 27 pages + figures available via ftp, Plain TeX, IFUSP/P-106
READMISSION COSTS RELATED TO INTENSIVE CARE AFTER CARDIAC SURGERY. ANALYSIS OF RISK FACTORS AND COSTS WITHIN SIX MONTHS AFTER DISCHARGE USING AN ADMINISTRATIVE REGISTRY
Higher spin constraints and the super algebra in the super eigenvalue model
We show that the partition function of the super eigenvalue model satisfies
an infinite set of constraints with even spins . These
constraints are associated with half of the bosonic generators of the super
algebra. The
simplest constraint is shown to be reducible to the super Virasoro
constraints, previously used to construct the model. All results hold for
finite .Comment: 14 pages, latex, no figure
High entropy alloys obtained by field assisted powder metallurgy route: SPS and microwave heating
The aim of this work was to investigate the field assisted powder metallurgy route for producing HEAs at equimolar composition, i.e. FeCoNiCrAl, starting from metal powders. Both mixed, mechanically activated and mechanically alloyed powders have been used. The powders obtained by mechanical alloying were synthesized only by SPS, whereas the remaining ones were sintered by SPS or microwave heating. The investigated field assisted sintering techniques allowed an extremely short alloying time, high energy density on the load and negligible contamination by the surrounding environment. Both the conducted sintering-synthesis technology resulted not definitive to produce chemical homogeneity and to obtain a single stable structure. Thus a subsequently heat treatment was required. The post heat treatment, indeed, led to a single crystalline structure (FCC) and the material was fully recrystallized. After heat treatment samples are isomorphic: they exhibit two different phases with the same FCC cell, but different chemical composition, in detail Fe-Cr richer and Al-Ni richer. SPS-ed samples present a reduced porosity, while microwave processed ones are much more porous and this is reflected in the mechanical properties
Sviluppo di un acciaio per lavorazione a caldo rinforzato tramite alligazione meccanica
I compositi a matrice metallica combinano elevata durezza e buona tenacità offrendo la possibilità di modularele loro proprietà attraverso la scelta più opportuna del tipo, frazione e dimensioni del rinforzo. La produzione dicompositi a matrice metallica basati su acciai per lavorazioni a caldo è stata poco sviluppata in letteratura. Inquesto lavoro è stata investigata la possibilità di produrre un acciaio per lavorazioni a caldo AISI H13 rinforzatocon particelle ceramiche di diversa natura quali carburi (TiC), nitruri (TiN) e boruri (TiB2). Questi compostirisultano particolarmente promettenti per applicazioni ad alta temperatura data la loro elevata stabilità termica.Le polveri composite sono state prodotte tramite macinazione meccanica, ottenendo un affinamento dellamicrostruttura e una fine distribuzione delle particelle di rinforzo. Le polveri composite sono state sinterizzatetramite la tecnica Spark Plasma, in modo da preservare la fine microstruttura prodotta durante macinazionee limitare l’interazione tra matrice e particelle rinforzanti. Il composito con il 20%vol di TiB2 mostra la migliordensificazione raggiungendo quasi densità teorica. L’analisi diffrattometrica ai raggi-x di questo materialeevidenzia però la formazione di composti secondari, quali Fe2B e TiC, indicando una parziale decomposizione delTiB2. Tra i materiali sinterizzati, il composito il TiC mostra il maggior incremento di durezza
SPS-assisted Synthesis of SICp reinforced high entropy alloys: reactivity of SIC and effects of pre-mechanical alloying and post-annealing treatment
In this work a traditional high entropy alloy (FeCoNiCrAl) was reinforced by uniformly distributed reactive silicon carbide (SiC) particles by a powder metallurgy synthetic route, using as precursors simply mixed powders or mechanically prealloyed ones. The reactive sintering produced a single isomorphic BCC structure. The sample microstructure resulted equiassic, more homogenous in samples based on prealloyed powders. The instability of SiC in the presence of metal precursors resulted in the formation of more stable carbides and silicides, as well as in carbon diffusion in the high entropy alloy matrix and partially unreacted SiC particles. The formation of these newly formed fine precipitates, as well as the presence of residual SiC were useful to increase the hardness of the alloy
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