8,669 research outputs found
On higher-order corrections in M theory
A theoretical analysis of higher-order corrections to D=11 supergravity is
given in a superspace framework. It is shown that any deformation of D=11
supergravity for which the lowest-dimensional component of the four-form
vanishes is trivial. This implies that the equations of motion of D=11
supergravity are specified by an element of a certain spinorial cohomology
group and generalises previous results obtained using spinorial or pure spinor
cohomology to the fully non-linear theory. The first deformation of the theory
is given by an element of a different spinorial cohomology group with
coefficients which are local tensorial functions of the massless supergravity
fields. The four-form Bianchi Identities are solved, to first order and at
dimension , in the case that the lowest-dimensional component of
is non-zero. Moreover, it is shown how one can calculate the first-order
correction to the dimension-zero torsion and thus to the supergravity equations
of motion given an explicit expression for this object in terms of the
supergravity fields. The version of the theory with both a four-form and a
seven-form is discussed in the presence of the five-brane anomaly-cancelling
term. It is shown that the supersymmetric completion of this term exists and it
is argued that it is the unique anomaly-cancelling invariant at this dimension
which is at least quartic in the fields. This implies that the first
deformation of the theory is completely determined by the anomaly term from
which one can, in principle, read off the corrections to all of the superspace
field strength tensors.Comment: 32 pages. v2: Two references added in the text; footnote adde
Improved current-regulated delta modulator for reducing switching frequency and low-frequency current error in permanent magnet brushless AC drives
The conventional current-regulated delta modulator (CRDM) results in a high current ripple and a high switching frequency at low rotational speeds, and in low-frequency current harmonics, including a fundamental current error, at high rotational speeds. An improved current controller based on CRDM is proposed which introduces a zero-vector zone and a current error correction technique. It reduces the current ripple and switching frequency at low speeds, without the need to detect the back-emf, as well as the low-frequency error at high speeds. The performance of the modulator is verified by both simulation and measurements on a permanent magnet brushless ac drive
The Threebrane Soliton of the M-Fivebrane
We discuss the supersymmetry algebra of the M theory fivebrane and obtain a
new threebrane soliton preserving half of the six-dimensional supersymmetry.
This solution is dimensionally reduced to various D-p-branes.Comment: 10 pages, phyzz
A New Massive Type IIA Supergravity From Compactification
We consider the most general form for eleven dimensional supersymmetry
compatible with on-shell superfields. This allows for the introduction of a
conformal Spin(1,10) connection. In eleven dimensional Minkowski space this
modification is trivial and can be removed by a field redefinition, however,
upon compactification on S^1 it is possible to introduce a non-trivial `Wilson
line'. The resulting ten dimensional supergravity has massive 1-form and 3-form
potentials and a cosmological constant. This theory does not possess a
supersymmetric eightbrane soliton but it does admit a supersymmetric non-static
cosmological solution.Comment: 13 pages, phyzzx. The introduction is clarifed and a reference adde
L-branes
The superembedding approach to -branes is used to study a class of
-branes which have linear multiplets on the worldvolume. We refer to these
branes as L-branes. Although linear multiplets are related to scalar multiplets
(with 4 or 8 supersymmetries) by dualising one of the scalars of the latter to
a -form field strength, in many geometrical situations it is the linear
multiplet version which arises naturally. Furthermore, in the case of 8
supersymmetries, the linear multiplet is off-shell in contrast to the scalar
multiplet. The dynamics of the L-branes are obtained by using a systematic
procedure for constructing the Green-Schwarz action from the superembedding
formalism. This action has a Dirac-Born-Infeld type structure for the -form.
In addition, a set of equations of motion is postulated directly in superspace,
and is shown to agree with the Green-Schwarz equations of motion.Comment: revised version, minor changes, references added, 22 pages, no
figures, LaTe
Volume-reflecting dielectric heat shield
White, volume-reflecting dielectric material absorbs essentially none of the incident radiant energy, and continues to reflect even though in severe environment its surface is melted and is being vaporized. Process of overall reflectance in dielectric material, involving internal refractions and reflections, is similar to process of reflection in paints
The deformed M2-brane
The superembedding formalism is used to study correction terms to the
dynamics of the M2 brane in a flat background. This is done by deforming the
standard embedding constraint. It is shown rigorously that the first such
correction occurs at dimension four. Cohomological techniques are used to
determine this correction explicitly. The action is derived to quadratic order
in fermions, and the modified \k-symmetry transformations are given.Comment: 38 pages, 3 figure
Cyclic-averaging for high-speed analysis of resonant converters
AbstractâThe paper describes the development and application
of a cyclic-averaging technique for the rapid analysis of
high-order resonant power converters. To provide a focus to the paper, particular emphasis is given to a 3rd-order LCC voltage output converter topology. The proposed methodology predicts steady-state voltages and currents throughout the circuit, and provides estimates of the stresses on the resonant circuit components. State-space simulations and experimental results from a 350 V-input/150 V-output converter are used to demonstrate a prediction accuracy comparable with time-domain integration-based
techniques is achievable, while requiring only 1/10,000th of the computation time. In addition, a comparison with Spice simulation results shows that cyclic averaging provides commensurate predictions of voltage and current stresses on the resonant circuit components. Issues arising from the stray capacitance associated with the resonant inductor, and the corresponding sensitivity of the predicted output voltage, are also considered
On the covariance of the Dirac-Born-Infeld-Myers action
A covariant version of the non-abelian Dirac-Born-Infeld-Myers action is
presented. The non-abelian degrees of freedom are incorporated by adjoining to
the (bosonic) worldvolume of the brane a number of anticommuting fermionic
directions corresponding to boundary fermions in the string picture. The
proposed action treats these variables as classical but can be given a matrix
interpretation if a suitable quantisation prescription is adopted. After
gauge-fixing and quantisation of the fermions, the action is shown to be in
agreement with the Myers action derived from T-duality. It is also shown that
the requirement of covariance in the above sense leads to a modified WZ term
which also agrees with the one proposed by Myers.Comment: 18 pages. Minor alterations to the text; references adde
Einstein-Weyl structures and Bianchi metrics
We analyse in a systematic way the (non-)compact four dimensional
Einstein-Weyl spaces equipped with a Bianchi metric. We show that Einstein-Weyl
structures with a Class A Bianchi metric have a conformal scalar curvature of
constant sign on the manifold. Moreover, we prove that most of them are
conformally Einstein or conformally K\"ahler ; in the non-exact Einstein-Weyl
case with a Bianchi metric of the type or , we show that the
distance may be taken in a diagonal form and we obtain its explicit
4-parameters expression. This extends our previous analysis, limited to the
diagonal, K\"ahler Bianchi case.Comment: Latex file, 12 pages, a minor modification, accepted for publication
in Class. Quant. Gra
- âŠ