Analysis of mean packet delay for upstream transmissions in passive optical networks with sleep mode

The sleep mode has been introduced to improve the energy efficiency of passive optical networks (PONs) with interleaved polling with adaptive cycle time (IPACT) as a medium access control (MAC) scheme. For energy saving, the sleep mode of each optical network unit (ONU) is activated based on the packet queue length for upstream traffic. We model such a PON as an N-user M/G/1 queue with reservations and vacations. Based on the framework of M/G/1 queueing analysis with some modification made to incorporate the nature of IPACT as well as the sleep mode, we derive a closed form expression of the mean packet delay. A unique challenge in our analysis is that certain quantities such as the residual time of an on-going sleep period for the upstream channel must be considered from the network's viewpoint while the delay due to the sleep mode experienced by a packet must be considered from the ONU's viewpoint. Simulation experiments are conducted to validate the analytical results and to show that the results are relatively insensitive to packet arrival statistics for large sleep periods. Finally, we demonstrate how a sleep period can be chosen given the quality-of-service (QoS) requirement on the mean packet delay.     

A novel ray tracing on general paraboloids of revolution for UTDapplications

Analytical expressions have been obtained for the ray-geometry parameters on the general paraboloid of revolution (GPOR) using a novel technique known as the geodesic constant method. These ray parameters are in a one-parameter form and can be readily employed in high-frequency EM antenna scattering problems. As an example, the uniform theory of diffraction (UTD) mutual admittance results are presented for two antennas located on the GPOR arbitrarily, in three dimensions     

The Linux operating system

The enormous consumer market for IBM PCs and compatibles has made them affordable. Now, with a free operating system called Linux, these inexpensive machines can be converted into powerful workstations for teaching, research and software development. For professionals who use Unix-based workstations at work, Linux permits virtually identical working environments on their personal home machines. For cost-conscious educational institutions-especially in developing nations-Linux can create world-class computing environments from inexpensive, easily maintained PC clones. And for university students-especially in science and engineering-Linux provides an essentially cost-free path into Unix and X Windows     

A novel image encryption scheme based on Arnold scrambling and Lucas series

Secure data transmission over the public channels have high impact and increasingly important due to theft and manipulation in contents. The requirement of public/ private organizations to develop an efficient scheme to provide security to their contents. We developed a digital contents encryption scheme based Arnold scrambling and Lucas series, which is very simple to implement but almost impossible to breach in this article. We perform encryption at standard images by using Lucas series at different iterations of scrambled images of Arnold transform. Numerical simulation analyses performed to analyze the efficiency and effectiveness of the projected structure.

     

Steady-state thermal hydraulic analysis of the equilibrium core of Pakistan research reactor-1

Steady-state thermal hydraulic analysis of Pakistan Research Reactor-1 (PARR-1) has been carried out. RELAP5/Mod 3.4 (a best-estimate system code) was employed. PARR-1 is a swimming pool type research reactor using MTR (Material Testing Reactor) type fuel. It uses low enriched uranium (<20%) fuel with light water flowing from top to bottom under gravity. Standard correlations were employed to compute various parameters, which include: coolant velocity distribution in the core; critical velocity; pressure drop; saturation temperature; temperature distribution in the core, OFI (onset of flow instability) and DNB (departure from nucleate boiling).     

Performance evaluation/analysis of Pakistan Research Reactor-1 (PARR-1) current core configuration

Neutronic and thermal hydraulic analyses have been carried out for current core of Pakistan Research Reactor-1 (PARR-1). Comparison was made between calculated and measured key neutronic parameters. Reactor core parameters important for reactor operation and safety have been calculated. Calculated neutronic parameters include: excess reactivity, shut down margin, control rod worth, peak power density location, criticality position, peaking factors, neutron flux in fuel elements and neutron flux at irradiation sites in the core. Calculated thermal hydraulic parameters include: steady-state temperatures and peak temperatures at fuel centerline, clad surface and in water coolant. In order to determine safety margins, heat fluxes at Onset of Nucleate Boiling (ONB), Onset of Flow Instability (OFI) and Departure from Nucleate Boiling (DNB) were determined using standard correlations. After assembling the core, performance of the core was also evaluated by experimentation. The core was assembled and some of the core parameters namely: excess reactivity, shut down margin, control rod worth and flux profile at in-core irradiation sites have been measured. On comparison with experimental data, reasonable agreement has been found between the calculated and the measured parameters.