Is there a news function for an infinite cosmic string?

A special form of the Bondi news function can be associated with an infinite static cosmic string. In case of a radiaing isolated system pierced by an infinite cosmic string, the total news function will be composed of two parts — one characterizing the radiation field, the other the string. Some examples are discussed and related to a recently given solution, which was interpreted as an outgoing gravitational wave due to the splitting of an infinite cosmic string.     

Quantum string theory in curved space-times

A general method to quantize strings in curved space-times is exposed. It treats the space-time metric exactly and the string excitations small as compared with the energy scale of the geometry. The method is applied to cosmological (de Sitter) and black-hole (Schwarzschild) geometries. The critical dimension decreases in one for de Sitter and stays unaltered for black-holes as compared with flat space-time values. Bogoliubov transformations in the context of string theory are derived and the Bogoliubov coefficients describing elastic and inelastic scattering and excitation of modes are computed explicitely. The string-black-hole cross section is derived and a pair mode creation phenomena is found. The quantization and scattering of strings in shockwave geometries (ultrarelativistic boosted black-holes or Aichelburg-Sexl space time) is found to be exactly solvable.     

Cosmic strings and strings in gravitational waves

We consider strings with the Nambu action as extremal surfaces in a given space-time, thus, we ignore their back reaction. Especially, we look for strings sharing one symmetry with the underlying space-time. If this is a non-null symmetry the problem of determining ihc motion of the string can be dimensionally reduced. We get exact solutions for the following cases: straight and circle-like strings in a Friedmann background, straight strings in an anisotropic Kasner background, different types of strings in the metric of a gravitational wave. The solutions will be discussed. Wir betrachten Strings mit der Nambu-Wirkung als Extremalflächen in einer gegebenen Raum-Zeit, d. h., wir ignorieren ihre Rückwirkung. Wir interessieren uns dabei besonders für solche Strings, die eine Isometrie mit der unterliegenden Raum-Zeit gemeinsam haben. Handelt es sich dabei um eine nicht-lichtartige Symmetrie, so läß Bt sich das Problem der Bestimmung der Stringbewegung dimensionsreduzieren. Wir erhalten exakte Lösungen für die folgenden Fälle: gerade und kreisrunde Strings im Friedmann-Hintergrund, gerade Strings im anisotropen Kasner-Hintergrund sowie verschiedene Stringtypen in der Metrik einer Gravitationswelle. Die Lösungen werden diskutiert.     

Axially Symmetric Cosmic Strings in a Scalar-Tensor Theory

Axially symmetric cosmological models with cosmic string source are obtained in a scalar-tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A113, 467, 1985). The models obtained give us axially symmetric geometric (Nambu) string, p-string and Reddy string (Astrophys. Space Sci. 286, 2003b) in Saez-Ballester theory. Some physical properties of the models are also discussed.     

Bianchi type-IX cosmic strings in a scalar-tensor theory of gravitation

Bianchi type-IX space-time is considered in the presence of cosmic string source in the frame work of a scalar- tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1985). Exact cosmological models representing geometric (Nambu) string, p string and baratropic string are discussed in this theory. Some physical and kinematical properties of the models are also studied.     

Plane Symmetric Cosmic Strings In Lyra Manifold

Static and non-static plane symmetric string cosmological models are obtained in Lyra [Mathematische Zeitsehrift 54, 52, 1951] manifold. Some properties of the models are also discussed.     

Strange quark matter attached to string cloud in Bianchi type-III space time

We have obtained Bianchi type-III cosmological model with strange quark matter attached to the string cloud in general relativity. For solving the Einstein’s field equations the relation [C=A ⁿ ] between metric coefficients C and A is used. Also, some physical and kinematic properties of the model are discussed.The results are analogous to results obtained by Yilmaz (Gen. Rel. Grav. 38:1397–1406, 2006).     

套管短口袋技术的应用探讨

介绍了短口袋技术可以提高固井质量及避免钻井掉块等优点,阐述了保证井身质量优良、井底少沉沙、套管长度与井眼深度的一致和套管居中等使用短口袋的技术要求.通过该技术在埕北古A井的应用,说明优选钻具组合和钻进参数,使用优质钻井液、通井和套管居中等技术措施可以满足要求,并成功地实现套管短口袋.     

N-dimensional string cosmological model in Brans–Dicke theory of gravitation

A spatially homogeneous and anisotropic Bianchi type-I cosmological model is examined with N-dimensions in Brans–Dicke (Phys. Rev. 124, 925, 1961) scalar-tensor theory of gravitation. Some properties of the model are also studied.      

Cosmic strings and viscous matter in a Kantowski-Sachs universe

We study the dynamics of a universe where the matter content is represented by a radially directed distribution of cosmic strings plus matter admitting both shear and bulk viscosity. We assume specific forms for the equation of state of both the strings and matter and discuss the cosmological solutions obtained.