597 research outputs found
Background Field Equations for the Duality Symmetric String
This paper describes the background field equations for strings in T-duality
symmetric formalisms in which the dimension of target space is doubled and the
sigma model supplemented with constraints. These are calculated by demanding
the vanishing of the beta-functional of the sigma model couplings in the
doubled target space. We demonstrate the equivalence with the background field
equations of the standard string sigma model.Comment: 26 pages, latex, v2 typos correcte
State Leadership Development Policies An Analysis of 50 States and Territories
State education systems to support leadership development have received relatively scant attention and resources, despite the demonstrated importance of leadership to school improvement. This need spurred the National Association of State Boards of Education (NASBE) to form a study group with its members and partner with the Consortium for Policy Research in Education (CPRE) to examine the problem from a state policy perspective; to offer a framework, guidance, and resources to help states develop and keep effective leaders; provide examples of practices for states; and share insights from partner organizations. The report, Successful Leaders for Successful Schools: Building and Maintaining a Quality Workforce, details findings that emerged from this work. As a companion piece to this work, State Leadership Development Policies -An Analysis of 50 States and Territories, presents a comprehensive picture of school leadership development policies across all 50 states and US territories. CPRE Researchers Bobbi Newman, Jonathan Supovitz, and Greg Collins, in collaboration with NASBE\u27s Robert Hull and Stephen Prociw, produced an interactive report that seeks to operationalize the framework developed for state education agencies to improve the school leadership pipeline.
Researchers interviewed state board members and staff members from state education agencies to learn about their states\u27 school leadership development policies and practices. Data collection questions focused on identifying the organizational and individual supports that states have established. State Leadership Development Policies -An Analysis of 50 States and Territories provides a wealth of information for state leaders interested in learning about a sample of each state\u27s policies and programs that support the school leadership pipeline
Double Field Theory
The zero modes of closed strings on a torus --the torus coordinates plus dual
coordinates conjugate to winding number-- parameterize a doubled torus. In
closed string field theory, the string field depends on all zero-modes and so
can be expanded to give an infinite set of fields on the doubled torus. We use
the string field theory to construct a theory of massless fields on the doubled
torus. Key to the consistency is a constraint on fields and gauge parameters
that arises from the L_0 - \bar L_0=0 condition in closed string theory. The
symmetry of this double field theory includes usual and 'dual diffeomorphisms',
together with a T-duality acting on fields that have explicit dependence on the
torus coordinates and the dual coordinates. We find that, along with gravity, a
Kalb-Ramond field and a dilaton must be added to support both usual and dual
diffeomorphisms. We construct a fully consistent and gauge invariant action on
the doubled torus to cubic order in the fields. We discuss the challenges
involved in the construction of the full nonlinear theory. We emphasize that
the doubled geometry is physical and the dual dimensions should not be viewed
as an auxiliary structure or a gauge artifact.Comment: 51 pages. v2: Corrected typo in eqn. (2.48) and very minor typos
elsewhere. Added ref. [9] to M. Van Raamsdon
Non-geometric backgrounds, doubled geometry and generalised T-duality
String backgrounds with a local torus fibration such as T-folds are naturally
formulated in a doubled formalism in which the torus fibres are doubled to
include dual coordinates conjugate to winding number. Here we formulate and
explore a generalisation of this construction in which all coordinates are
doubled, so that the doubled space is a twisted torus, i.e. a compact space
constructed from identifying a group manifold under a discrete subgroup. This
incorporates reductions with duality twists, T-folds and a class of flux
compactifications, together with the non-geometric backgrounds expected to
arise from these through T-duality. It also incorporates backgrounds that are
not even locally geometric, and suggests a generalisation of T-duality to a
more general context. We discuss the effective field theory arising from such
an internal sector, give a world-sheet sigma model formulation of string theory
on such backgrounds and illustrate our discussion with detailed examples.Comment: 81 page
dS/CFT correspondence on a brane
We study branes moving in an AdS Schwarzschild black hole background. When
the brane tension exceeds a critical value, the induced metric on the brane is
of FRW type and asymptotically de Sitter. We discuss the relevance of such
configurations to dS/CFT correspondence. When the black hole mass reaches a
critical value that depends on the brane tension, the brane interpolates in the
infinite past and future between a dS space and a finite space of zero Hubble
constant. This corresponds to a cosmological evolution without a Big Bang or a
Big Crunch. Moreover, the central charge of the CFT dual to the dS brane enters
the Cardy-Verlinde formula that gives the entropy of the thermal CFT dual to
the bulk AdS black hole.Comment: 15 pages, 1 figure, v2 references adde
Geometric Transitions, Flops and Non-Kahler Manifolds: I
We construct a duality cycle which provides a complete supergravity
description of geometric transitions in type II theories via a flop in
M-theory. This cycle connects the different supergravity descriptions before
and after the geometric transitions. Our construction reproduces many of the
known phenomena studied earlier in the literature and allows us to describe
some new and interesting aspects in a simple and elegant fashion. A precise
supergravity description of new torsional manifolds that appear on the type IIA
side with branes and fluxes and the corresponding geometric transition are
obtained. A local description of new G_2 manifolds that are circle fibrations
over non-Kahler manifolds is presented.Comment: Harvmac, 79 pages, 1 .eps figure; v4: Text further expanded with
additional results, typos corrected and references adde
Relating the Cosmological Constant and Supersymmetry Breaking in Warped Compactifications of IIB String Theory
It has been suggested that the observed value of the cosmological constant is
related to the supersymmetry breaking scale M_{susy} through the formula Lambda
\sim M_p^4 (M_{susy}/M_p)^8. We point out that a similar relation naturally
arises in the codimension two solutions of warped space-time varying
compactifications of string theory in which non-isotropic stringy moduli induce
a small but positive cosmological constant.Comment: 7 pages, LaTeX, references added and minor changes made, (v3) map
between deSitter and global cosmic brane solutions clarified, supersymmetry
breaking discussion improved and references adde
Analytical Derivation of a Coupled-circuit Model of a Claw-pole Alternator with Concentrated Stator Windings
A lumped-parameter coupled-circuit model of a claw-pole alternator is derived. To derive the model, analytical techniques are used to define a three-dimensional (3-D) Fourier-series representation of the airgap flux density. Included in the series expansion are the harmonics introduced by rotor saliency, concentrated stator windings, and stator slots. From the airgap flux density waveform, relatively simple closed-form expressions for the stator and rotor self- and mutual-inductances are obtained. The coupled-circuit model is implemented in the simulation of an alternator/rectifier system using a commercial state-model-based circuit analysis program. Comparisons with experimental results demonstrate the accuracy of the model in predicting both the steady-state and transient behavior of the machin
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