The Krein-Gupta-Bleuler Quantization in de Sitter Space-time; Casimir Energy-Momentum Tensor for a Curved Brane

In this paper, vacuum expectation value (VEV) of the energy-momentum tensor for a conformally coupled scalar field in de Sitter space-time is investigated through the Krein-Gupta-Bleuler construction. This construction has already been successfully applied to the de Sitter minimally coupled massless scalar field and massless spin-2 field to obtain a causal and fully covariant quantum field on the de Sitter background. We also consider the effects of boundary conditions. In this respect, Casimir energy-momentum tensor induced by Dirichlet boundary condition on a curved brane is evaluated.Comment: 9 page

A Group Theoretical Approach to Graviton Two-Point Function

Respecting the group theoretical approach, it is debated that the theory of linear conformal gravity should be formulated through a tensor field of rank-3 and mixed symmetry \cite{binegar}. Pursuing this path, such a field equation was obtained in de Sitter space \cite{takook}. In present work, considering the de Sitter ambient space notation, a proper solution to the physical part of this field equation is obtained. We have also calculated the related two-point function, which is interestingly de Sitter invariant and free of infrared divergence.Comment: 10 page

Hemomediastinum and bilateral hemothorax with extensive angiomatosis of anterior mediastinum

Angiomatosis is a rare, benign but clinically extensive and serious vascular lesion of soft tissue. Hereby, we report a case of diffuse angiomatosis of mediastinum, presenting with hemomediastinum and bilateral massive hemothorax in a 19-year old boy. On medical imaging, mediastinal widening along with enhanced small vessels and capillaries were detected. On operation, hemorrhagic sponge-like vascular tissue patches were seen extensively in pericardium, pleura, lymph node and thymus as well. The lesion was debulked. The pathologic evaluation revealed characteristic features of soft tissue angiomatosis involving thymus, lymph node, pleura, pericardium and its fibrofatty tissue. Diffuse angiomatosis should be considered for differential diagnosis of vascular lesions of anterior mediastinum

Virtual prototyping of a semi-active transfemoral prosthetic leg

This article presents a virtual prototyping study of a semi-active lower limb prosthesis to improve the functionality of an amputee during prosthesis–environment interaction for level ground walking. Articulated ankle–foot prosthesis and a single-axis semi-active prosthetic knee with active and passive operating modes were considered. Data for level ground walking were collected using a photogrammetric method in order to develop a base-line simulation model and with the hip kinematics input to verify the proposed design. The simulated results show that the semi-active lower limb prosthesis is able to move efficiently in passive mode, and the activation time of the knee actuator can be reduced by approximately 50%. Therefore, this semi-active system has the potential to reduce the energy consumption of the actuators required during level ground walking and requires less compensation from the amputee due to lower deviation of the vertical excursion of body centre of mass

Conformal linear gravity in de Sitter space II

From the group theoretical point of view, it is proved that the theory of linear conformal gravity should be written in terms of a tensor field of rank-3 and mixed symmetry [Binegar, et al, Phys. Rev. D 27, (1983) 2249]. We obtained such a field equation in de Sitter space [Takook, et al, J. Math. Phys. 51, (2010) 032503]. In this paper, a proper solution to this equation is obtained as a product of a generalized polarization tensor and a massless scalar field and then the conformally invariant two-point function is calculated. This two-point function is de Sitter invariant and free of any pathological large-distance behavior.Comment: 16 pages, no figure, published versio

Auxiliary "massless" spin-2 field in de Sitter universe

For the tensor field of rank-2 there are two unitary irreducible representation (UIR) in de Sitter (dS) space denoted by $\Pi^{\pm}_{2,2}$ and $\Pi^{\pm}_{2,1}$ [1]. In the flat limit only the $\Pi^{\pm}_{2,2}$ coincides to the UIR of Poincar\'e group, the second one becomes important in the study of conformal gravity. In the pervious work, Dirac's six-cone formalism has been utilized to obtain conformally invariant (CI) field equation for the "massless" spin-2 field in dS space [2]. This equation results in a field which transformed according to $\Pi^{\pm}_{2,1}$, we name this field the auxiliary field. In this paper this auxiliary field is considered and also related two-point function is calculated as a product of a polarization tensor and "massless" conformally coupled scalar field. This two-point function is de Sitter invariant.Comment: 16 page

Multiparty, Multimedia Communications Systems

In recent years, there has been a growing interest in multimedia computer systems and applications. We will explore the important challenges that multimedia systems pose to system and application developers, and describe the main issues involved. An overview of the current systems and research in the area and how they have addressed some of these challenges will be provided, with emphasis on the Xphone Multimedia application development toolkit, developed at Columbia University. 1. INTRODUCTION In recent years, there has been a growing interest in multimedia computer systems and applications. Early systems were limited to logical (as opposed to physical) integration of different media and to stand-alone systems. With the rapid advances witnessed in the computing and networking technologies over the last decade, fully integrated multimedia systems distributed over a network have become a reality. Applications of such systems include videoconferencing [1], group editing [2, 3], multimed..