28,932 research outputs found
Hamiltonian Reduction of -theories at the Level of Correlators
Since the work of Bershadsky and Ooguri and Feigin and Frenkel it is well
known that correlators of current algebra for admissible
representations should reduce to correlators for conformal minimal models. A
precise proposal for this relation has been given at the level of correlators:
When primary fields are expressed as with being
a variable to keep track of the representation multiplet (possibly
infinitely dimensional for admissible representations), then the minimal model
correlator is supposed to be obtained simply by putting all . Although
strong support for this has been presented, to the best of our understanding a
direct, simple proof seems to be missing so in this paper we present one based
on the free field Wakimoto construction and our previous study of that in the
present context. We further verify that the explicit correlators we
have published in a recent preprint reduce in the above way, up to a constant
which we also calculate. We further discuss the relation to more standard
formulations of hamiltonian reduction.Comment: 13 pages, LaTe
Extended Superconformal Algebras from Classical and Quantum Hamiltonian Reduction
We consider the extended superconformal algebras of the Knizhnik-Bershadsky
type with -algebra like composite operators occurring in the commutation
relations, but with generators of conformal dimension 1, and 2,
only. These have recently been neatly classified by several groups, and we
emphasize the classification based on hamiltonian reduction of affine Lie
superalgebras with even subalgebras . We reveiw the situation
and improve on previous formulations by presenting generic and very compact
expressions valid for all algebras, classical and quantum. Similarly generic
and compact free field realizations are presented as are corresponding
screening charges. Based on these a discussion of singular vectors is
presented. (Based on talk by J.L. Petersen at the Int. Workshop on "String
Theory, Quantum Gravity and the Unification of the Fundamental Interactions",
Rome Sep. 21-26, 1992)Comment: 30 pages, NBI-HE-92-8
Turbojet blade vibration data acquisition design and feasibility testing
A turbojet blade vibration data acquisition system was designed to allow the measurement of blade vibration. The data acquisition system utilizing 96 microprocessors to gather data from optical probes, store, sort and transmit to the central computer is described. Areas of high technical risk were identified and a two-microprocessor system was breadboarded and tested to investigate these areas. Results show that the system was feasible and that low technical risk would be involved in proceeding with the complete system fabrication
Introduction to the Maldacena Conjecture on AdS/CFT
These lectures do not at all provide a general review of this rapidly growing field. Instead a rather detailed account is presented of a number of the most elementary aspects
A new approach to hierarchical data analysis: Targeted maximum likelihood estimation for the causal effect of a cluster-level exposure
We often seek to estimate the impact of an exposure naturally occurring or
randomly assigned at the cluster-level. For example, the literature on
neighborhood determinants of health continues to grow. Likewise, community
randomized trials are applied to learn about real-world implementation,
sustainability, and population effects of interventions with proven
individual-level efficacy. In these settings, individual-level outcomes are
correlated due to shared cluster-level factors, including the exposure, as well
as social or biological interactions between individuals. To flexibly and
efficiently estimate the effect of a cluster-level exposure, we present two
targeted maximum likelihood estimators (TMLEs). The first TMLE is developed
under a non-parametric causal model, which allows for arbitrary interactions
between individuals within a cluster. These interactions include direct
transmission of the outcome (i.e. contagion) and influence of one individual's
covariates on another's outcome (i.e. covariate interference). The second TMLE
is developed under a causal sub-model assuming the cluster-level and
individual-specific covariates are sufficient to control for confounding.
Simulations compare the alternative estimators and illustrate the potential
gains from pairing individual-level risk factors and outcomes during
estimation, while avoiding unwarranted assumptions. Our results suggest that
estimation under the sub-model can result in bias and misleading inference in
an observational setting. Incorporating working assumptions during estimation
is more robust than assuming they hold in the underlying causal model. We
illustrate our approach with an application to HIV prevention and treatment
Anomalous Chiral Action from the Path-Integral
By generalizing the Fujikawa approach, we show in the path-integral
formalism: (1) how the infinitesimal variation of the fermion measure can be
integrated to obtain the full anomalous chiral action; (2) how the action
derived in this way can be identified as the Chern-Simons term in five
dimensions, if the anomaly is consistent; (3) how the regularization can be
carried out, so as to lead to the consistent anomaly and not to the covariant
anomaly. Our method uses Schwinger's ``proper-time'' representation of the
Green's function and the gauge invariant point-splitting technique. We find
that the consistency requirement and the point-splitting technique allow both
an anomalous and a non-anomalous action. In the end, the nature of the vacuum
determines whether we have an anomalous theory, or, a non-anomalous theoryComment: 28 page
Free field realizations of 2D current algebras, screening currents and primary fields
In this paper we consider Wakimoto free field realizations of simple affine Lie algebras, a subject already much studied. We present three new sets of results, (i) Based on quantizing differential operator realizations of the corresponding Lie algebras we provide general universal very simple expressions for all currents, more compact than has been established so far. (ii) We supplement the treatment of screening currents of the first kind, known in the literature, by providing a direct proof of the properties for screening currents of the second kind. Finally (iii) we work out explicit free field realizations of primary fields with general non-integer weights. We use a formalism where the (generally infinite) multiplet is replaced by a generating function primary operator. These results taken together allow setting up integral representations for correlators of primary fields corresponding to non-integrable degenerate (in particular admissible) representations
Satellite detection of vegetative damage and alteration caused by pollutants emitted by a zinc smelter
The author has identified the following significant results. Field observations and data collected by low flying aircraft were used to verify the accuracy of maps produced from the satellite data. Although areas of vegetation as small as six acres can accurately be detected, a white pine stand that was severely damaged by sulfur dioxide could not be differentiated from a healthy white pine stand because spectral differences were not large enough. When winter data were used to eliminate interference from herbaceous and deciduous vegetation, the damage was still undetectable. The analysis was able to produce a character map that accurately delineated areas of vegetative alteration due to high zinc levels accumulating in the soil. The map depicted a distinct gradient of less damage and alteration as the distance from the smelter increased. Although the satellite data will probably not be useful for detecting small acreages of damaged vegetation, it is concluded that the data may be very useful as an inventory tool to detect and delineate large vegetative areas possessing differing spectral signatures
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