57 research outputs found
Multidimensional Classical and Quantum Cosmology with Intersecting p-branes
Multidimensional cosmological model describing the evolution of n+1 Einstein
spaces in the theory with several scalar fields and forms is considered. When a
(electro-magnetic composite) p-brane Ansatz is adopted the field equations are
reduced to the equations for Toda-like system. The Wheeler-De Witt equation is
obtained. In the case when n "internal" spaces are Ricci-flat, one space M_0
has a non-zero curvature, and all p-branes do not "live" in M_0, the classical
and quantum solutions are obtained if certain orthogonality relations on
parameters are imposed. Spherically-symmetric solutions with intersecting
non-extremal p-branes are singled out. A non-orthogonal generalization of
intersection rules corresponding to (open, closed) Toda lattices is obtained. A
chain of bosonic D > 11 models (that may be related to hypothetical higher
dimensional supergravities and F-theories) is suggested.Comment: 26 pages, Latex. Submit. to J. Math. Phy
Solutions with intersecting p-branes related to Toda chains
Solutions in multidimensional gravity with m p-branes related to Toda-like
systems (of general type) are obtained. These solutions are defined on a
product of n+1 Ricci-flat spaces M_0 x M_1 x...x M_n and are governed by one
harmonic function on M_0. The solutions are defined up to the solutions of
Laplace and Toda-type equations and correspond to null-geodesics of the
(sigma-model) target-space metric. Special solutions relating to A_m Toda
chains (e.g. with m =1,2) are considered.Comment: 20 pages, Latex, to be submit. to JM
On avoiding cosmological oscillating behavior for S-brane solutions with diagonal metrics
In certain string inspired higher dimensional cosmological models it has been
conjectured that there is generic, chaotic oscillating behavior near the
initial singularity -- the Kasner parameters which characterize the asymptotic
form of the metric "jump" between different, locally constant values and
exhibit a never-ending oscillation as one approaches the singularity. In this
paper we investigate a class of cosmological solutions with form fields and
diagonal metrics which have a "maximal" number of composite electric S-branes.
We look at two explicit examples in D=4 and D=5 dimensions that do not have
chaotic oscillating behavior near the singularity. When the composite branes
are replaced by non-composite branes chaotic oscillatingComment: Corrected typos, published in Phys. Rev. D72, 103511 (2005
Curved branes from string dualities
We describe a simple method for generating new string solutions for which the
brane worldvolume is a curved space. As a starting point we use solutions with
NS-NS charges combined with 2-d CFT's representing different parts of
space-time. We illustrate our method with many examples, some of which are
associated with conformally invariant sigma models. Using U-duality, we also
obtain supergravity solutions with RR charges which can be interpreted as
D-branes with non-trivial worldvolume geometry. In particular, we discuss the
case of a D5-brane wrapped on AdS_3 x S^3, a solution interpolating between
AdS_3 x S^3 x R^5 and AdS_3 x S^3 x S^3 x R, and a D3-brane wrapped over S^3 x
R or AdS_2 x S^2. Another class of solutions we discuss involves NS5-branes
intersecting over a 3-space and NS5-branes intersecting over a line. These
solutions are similar to D7-brane or cosmic string backgrounds.Comment: 21 pages, harvmac; misprint correcte
Billiard Representation for Multidimensional Cosmology with Intersecting p-branes near the Singularity
Multidimensional model describing the cosmological evolution of n Einstein
spaces in the theory with l scalar fields and forms is considered. When
electro-magnetic composite p-brane ansatz is adopted, and certain restrictions
on the parameters of the model are imposed, the dynamics of the model near the
singularity is reduced to a billiard on the (N-1)-dimensional Lobachevsky
space, N = n+l. The geometrical criterion for the finiteness of the billiard
volume and its compactness is used. This criterion reduces the problem to the
problem of illumination of (N-2)-dimensional sphere by point-like sources. Some
examples with billiards of finite volume and hence oscillating behaviour near
the singularity are considered. Among them examples with square and triangle
2-dimensional billiards (e.g. that of the Bianchi-IX model) and a 4-dimensional
billiard in ``truncated'' D = 11 supergravity model (without the Chern-Simons
term) are considered. It is shown that the inclusion of the Chern-Simons term
destroys the confining of a billiard.Comment: 27 pages Latex, 3 figs., submit. to Class. Quantum Gra
Toda p-brane black holes and polynomials related to Lie algebras
Black hole generalized p-brane solutions for a wide class of intersection
rules are obtained. The solutions are defined on a manifold that contains a
product of n - 1 Ricci-flat internal spaces. They are defined up to a set of
functions H_s obeying non-linear differential equations equivalent to Toda-type
equations with certain boundary conditions imposed. A conjecture on polynomial
structure of governing functions H_s for intersections related to semisimple
Lie algebras is suggested. This conjecture is proved for Lie algebras: A_m,
C_{m+1}, m > 0. For simple Lie algebras the powers of polynomials coincide with
the components of twice the dual Weyl vector in the basis of simple coroots.
The coefficients of polynomials depend upon the extremality parameter \mu >0.
In the extremal case \mu = 0 such polynomials were considered previously by H.
L\"u, J. Maharana, S. Mukherji and C.N. Pope. Explicit formulas for
A_2-solution are obtained. Two examples of A_2-dyon solutions, i.e. dyon in D =
11 supergravity with M2 and M5 branes intersecting at a point and Kaluza-Klein
dyon, are considered.Comment: 24 pages, Latex, typos are eliminated, a correct relation on
parameters of special block-orthogonal solution is added in third line after
eq. (4.10
МАШИННО-ТРАНСФОРМАТОРНИЙ АГРЕГАТ ДЛЯ ВІТРОЕНЕРГЕТИЧНИХ УСТАНОВОК
Background. Electric generators of wind turbines must meet the following requirements: they must be multi-pole; to have a minimum size and weight; to be non-contact, but controlled; to ensure the maximum possible output voltage when working on the power supply system. Multipole and contactless are relatively simply realized in the synchronous generator with permanent magnet excitation and synchronous inductor generator with electromagnetic excitation; moreover the first one has a disadvantage that there is no possibility to control the output voltage, and the second one has a low magnetic leakage coefficient with the appropriate consequences. Purpose. To compare machine dimensions and weight of the transformer unit with induction generators and is an opportunity to prove their application for systems with low RMS-growth rotation. Methodology. A new design of the electric inductor machine called in technical literature as machine-transformer unit (MTU) is presented. A ratio for estimated capacity determination of such units is obtained. Results. In a specific example it is shown that estimated power of MTU may exceed the same one for traditional synchronous machines at the same dimensions. The MTU design allows placement of stator coil at some distance from the rotating parts of the machine, namely, in a closed container filled with insulating liquid. This will increase capacity by means of more efficient cooling of coil, as well as to increase the output voltage of the MTU as a generator to a level of 35 kV or more. The recommendations on the certain parameters selection of the MTU stator winding are presented. The formulas for copper cost calculating on the MTU field winding and synchronous salient-pole generator are developed. In a specific example it is shown that such costs in synchronous generator exceed 2.5 times the similar ones in the MTU.В работе предложена новая конструкция индукторной электрической машины, которая в технической литературе называется – машинно-трансформаторный агрегат (МТА). Для такого агрегата получено соотношение для определения расчетной мощности. На конкретном примере показано, что при одинаковых габаритах расчетная мощность МТА может превышать таковую для обычных синхронных машин. Конструкция МТА позволяет разместить катушки обмотки статора на некотором расстоянии от подвижных элементов машины, а именно, в закрытой емкости, заполненной электроизоляционной жидкостью. Это позволит увеличить мощность за счет более эффективного охлаждения обмотки, а также повысить выходное напряжение МТА как генератора до уровня 35 кВ и более.В роботі запропонована нова конструкція індукторної електричної машини, яка в технічній літературі називається – машинно-трансформаторним агрегатом (МТА). Для такого агрегату отримано співвідношення для визначення розрахункової потужності. На конкретному прикладі показано, що при однакових габаритах розрахункова потужність МТА може перевищувати таку для звичайних синхронних машин. Конструкція МТА дозволяє розмістити котушки обмотки статора на деякій відстані від рухомих елементів машини, а саме, у закритій ємності, заповненій електроізоляційною рідиною. Це дасть змогу збільшити потужність за рахунок більш ефективного охолодження обмотки, а також підвищити вихідну напругу МТА як генератора до рівня 35 кВ і більше
- …