Impacts Of Nonlinear Stimulated Raman Scattering On The Performance Of Optical Codedivision Multiple-Access Transmission Systems

Code-division multiple access (CDMA) is a well-known scheme for multiplexing communication channels that is based on the method of directsequence spread spectrum. This concept was introduced into fiber optic communication systems in the middle of 1980’s as optical CDMA (OCDMA), where encoding and decoding operations are all performed in optical domain using optical devices and large number of users with asynchronous access capability. In addition to the good performance at high number of users and asynchronous access to the network, OCDMA systems provide the users with high security by coding the data before transmission and at the same time using this code to recover the data at the receiver. However, there are various nonlinear effects that limit the performance of OCDMA systems. In particular, nonlinear stimulated Raman scattering (SRS) causes the optical power from one mode to be transferred in the forward direction to the same, or other modes, at a different frequency. The process of SRS can severely limit the performance of multi-channel communication systems through the transfer of energy between the signals at different wavelengths. The main motivation behind this research is the need to understand signal distortion due to SRS in OCDMA transmission systems. Specially, there is no real attention paid to investigate this issue in OCDMA systems while most of researches that study nonlinear effects are based on wavelength-division multiplexing (WDM) systems. Therefore, this work is attempting to understand SRS effects on the performance of OCDMA systems as a function of system design parameters (i.e. power per chip, transmission distance, and number of users), and hence, to determine the fundamental transmission limits in OCDMA systems in the presence of SRS nonlinear effects. The system performance is evaluated by measuring the bit-error-rate (BER) and tilt ratio which indicates the power transfer between the chips at different wavelength. It is demonstrated through numerical simulations that the performance of OCDMA systems, at high input powers, large number of users and/or long transmission distances, is significantly degraded due to SRS effects. Furthermore, the transmission limits to keep the performance of the system under study within acceptable levels in the presence of SRS effects is estimated according to the BER threshold of 10-9 and 10-12

An Integrated Firewall System Model In A Multiclient-Server Environment

As the Internet grows, and the use of computers is getting more common, the need to secure networks and protect them from the Internet, while still being able to access it, is increasing. The easiest way to achieve a lot of this protection is through firewalls. Firewall technology is the most widely deployed security technology on the Internet. Firewalls have been around for several years. They are a fact of life on the Internet and it is not likely they will disappear in the future. Ongoing development and research in the field of firewall technology have shown a continually addition of features and services to conventional firewall systems.This thesis introduces a new concept for applying the security policy rules by both firewall administrators and users. The proposed firewall system solves some known problems which arise with the use of conventional firewalls residing at the networks perimeter. The developed firewall system integrates the main network firewall and the second-line firewalls into one system by the use of client/server technology to facilitate firewall configuration in a way that affords more convenience to users providing the new integrated firewall using multiclient-server scheme. It centralizes security functions in a single point, simplifying configuration and administration. The new system makes it easier to configure and administrate a firewall in a way in which it is not a source of annoyance to users which offering them higher level of flexibility by giving them the chance to participate in the process of configuration of the firewall using the client side of the system and without affecting the network security policy. It also makes the progress of configuration and administration of the firewall system smoother by reducing the administrator efforts to maintain the system. Good results have been achieved by using the program package. Results show that this system helps keeping the network traffic as low as possible, increasing the efficiency of the network and reducing the threats of malicious data passing in the network. It reduces the efforts and cost of overall system administration and maintenance as well. In addition, it affords users a system which is acceptable and preferable more than conventional firewall systems

Proton and Neutron Pairing Properties within a mixed volume-surface pairing force using SKI3-HFB Theory

This work aims at a systematic investigations of the pairing properties and Fermi properties from the proton drip-line to the neutron drip-line. In order to provide more accurate mass formula with skyrme SKI3 force, the global descriptive power of the SKI3-HFB model for pairing properties are made in this study. Systematic Skyrme SKI3-Hartree-Fock-Bogoliubov calculations with a mixed volume-surface pairing force are carried out to study the ground-state neutron and proton pairing gap, neutron and proton pairing energy and neutron and proton Fermi energy for about 2095 even-even nuclei ranging from $2\le{Z}\le110$ to $2\le{N}\le236$. The calculated results of neutron and proton pairing gap are compared with experimental data using the difference-point formulas $\Delta^{(3)}, \Delta^{(4)}$ and $\Delta^{(5)}$, and also compared with the neutron and proton pairing gap of Lipkin-Nogami model. It is shown that the Skyrme-SKI3 functional with the mixed volume-surface pairing force can be successfully used for describing the ground-state pairing and Fermi properties of the investigated nuclei, in particularly the neutron-rich nuclei and the exotic nuclei near the neutron drip-line. On the other hand, the calculated neutron and proton pairing gap are in good agreement with the available experimental values of the neutron and proton pairing gap of the difference-point formulas $\Delta^{(3)}, \Delta^{(4)}$ and $\Delta^{(5)}$ and with the data of Lipkin-Nogami model over the whole nuclear chart.Comment: 18 pages, 9 figure

Particle-Particle Collective Excitations of Sn isotopes

In this paper, energy-level schemes and reduced electric transition strengths of neutron-rich Tin isotopes 102, 110, 116, 120, 122Sn (Z=50) are studied using collective models, that is, particle-particle Tamm-Dancoff Approximation and particle-particle Random Phase Approximation. According to these models, the excited states of closed-core A+2 systems with multipolarity J and isospin T can be described as a linear combination of particle-particle pairs. In our investigation, the low-lying states of the investigated isotopes 102, 110, 116, 120, 122Sn are described by acting two-particle operators on a correlated core 100Sn, 108Sn, 114Sn, 118Sn, and 120Sn, respectively. The Hamiltonian is diagonalized within the model space include {1g7/2, 2d5/2, 2d3/2, 3s1/2 and 1h11/2} orbits, using the matrix elements of neutron-neutron interaction and modified surface delta interaction. The calculated values are checked by using the resultant eigenvalues and eigenvectors to calculate the excitation energies and reduced electric transition strengths. Our calculated results are compared to the available experimental data, and these comparisons led to reasonable agreements. Effective charges are also used to account for the core polarization effect

Teaching English at Elementary Level: Quality Differences between Theory and Practice

This study examines the perceptions of the Kuwaiti elementary school teacher trainees of EFL (English as a Foreign Language) and an attempt to identify areas that need to be improved in the elementary English teachers’ program at the CBE (College of Basic Education). The participants in this paper are one hundred and twenty six Kuwaiti teacher trainees of English who currently teach EFL through a practicum course in elementary public schools located in six school districts in the State of Kuwait. The data was collected through out the school year 2010/2012 by using a questionnaire which was filled out by the main classroom teachers as they were observing the EFL teachers' trainees in their classrooms. Based on the findings, the study has reported that teacher trainees with delight had the opportunity to work alongside a true mentor (classroom teacher), and most teacher trainees were satisfied with their performance. Key Words: Teacher trainee, Elementary stage, Practice, EFL Teachers, Curriculu

Screening of high risk infants for metabolic disease in a metropolitan hospital

Screening of symptomatic infants for metabolic diseases is described which led to an improved detection rate because of better awareness and case selection, as well as the use of a test for urinary organic acids.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147121/1/jimd0081.pd

A theoretical model for exciton binding energies in rectangular and parabolic spherical finite quantum dots

. Using the variational method in real space and the effective-mass theory, we present quite an advanced semi-analytic approach susceptible for calculating the binding energy Eb of Wannier excitons in semiconductor quantum dot structures with rectangular and parabolic shapes of the confining potential in the so-called strong-confinement regime. Illustration is given for CdS, ZnSe, CdSe, GaAs structures of crystallites for both rectangular and parabolic quantum dots, and it displays a very good agreement between the experimental and theoretical results reported in literature