Minkowski Brane in Asymptotic dS5_5 Spacetime without Fine-tuning

We discuss properties of a 3-brane in an asymptotic 5-dimensional de-Sitter spacetime. It is found that a Minkowski solution can be obtained without fine-tuning. In the model, the tiny observed positive cosmological constant is interpreted as a curvature of 5-dimensional manifold, but the Minkowski spacetime, where we live, is a natural 3-brane perpendicular to the fifth coordinate axis.Comment: 6 pages, Latex fil

Optimization Strategy & Energy Savings Of Water-Cooled Chiller Plant System

Water-cooled chiller cooling systems are commonly used for air conditioning purposes in tropical countries like Malaysia. Chillers need to be optimized to increase the performance of the system and achieve energy savings. Understanding the interaction between each sub systems and exploiting their strength is the key to system optimization. The significance of this study is to provide more insight on how to optimize the water-cooled chiller system. For that, a thermodynamic model is developed to evaluate the energy saving opportunities in the system. Using an iterative procedure on finding the thermodynamic properties and equations of the system, data on the performance and energy savings of the system can be calculated for every part load conditions. From the results of the paper, there is improvement in the performance of the chiller plant system when variable speed pumps are used. Using a cooling load profile of a typical office building, electricity can be saved up to 80% for pump power and 18% for the total plant energy usage. Application of variable speed pump in the system can save significant amount of energy that conventional chiller plant system used in excess nowaday

Spatial damping of propagating sausage waves in coronal cylinders

Sausage modes are important in coronal seismology. Spatially damped propagating sausage waves were recently observed in the solar atmosphere. We examine how wave leakage influences the spatial damping of sausage waves propagating along coronal structures modeled by a cylindrical density enhancement embedded in a uniform magnetic field. Working in the framework of cold magnetohydrodynamics, we solve the dispersion relation (DR) governing sausage waves for complex-valued longitudinal wavenumber $k$ at given real angular frequencies $\omega$. For validation purposes, we also provide analytical approximations to the DR in the low-frequency limit and in the vicinity of $\omega_{\rm c}$, the critical angular frequency separating trapped from leaky waves. In contrast to the standing case, propagating sausage waves are allowed for $\omega$ much lower than $\omega_{\rm c}$. However, while able to direct their energy upwards, these low-frequency waves are subject to substantial spatial attenuation. The spatial damping length shows little dependence on the density contrast between the cylinder and its surroundings, and depends only weakly on frequency. This spatial damping length is of the order of the cylinder radius for $\omega \lesssim 1.5 v_{\rm Ai}/a$, where $a$ and $v_{\rm Ai}$ are the cylinder radius and the Alfv\'en speed in the cylinder, respectively. We conclude that if a coronal cylinder is perturbed by symmetric boundary drivers (e.g., granular motions) with a broadband spectrum, wave leakage efficiently filters out the low-frequency components.Comment: 6 pages, 2 figures, to appear in Astronomy & Astrophysic