الفلك، الفيزياء

This paper describes a new method of simulation for inverter circuits by using the interpreted Petri-nets (IPN). This method begins with a formalization stage which culminates in a set of IPN and mathematical equations which translate the requirements of the performance specifications sheet pertinent both to the control strategies to be guaranteed in relation to the status of the process, and to characteristics of these specifications and requirements. The algorithms of the simulation are written directly from these sets of IPN. This method facilitates and organizes writing the simulation algorithms. A single-phase half-bridge inverter circuit is used to validate this method.

The low density, the cohesion-less nature, high percentage of voids, and other undesirable properties of volcanic ash materials in their natural state necessitate their improvement prior to any construction. This study was conducted on natural volcanic ash in order to assess the performance of lime-stabilized mixture (lime-volcanic ash and fine materials). The volcanic ash was mixed with two different types of fine soils individually to improve the grading of the volcanic ash, cohesion properties and to reduce the amount of required lime. Different variables influencing the performances of ash-soil-lime mixture were studied. These variables included water content, lime content, fine soil plasticity, soil content, and curing duration. The laboratory program adopted in this investigation includes material characterization, compaction, deformation properties and strength. Strength characteristics using unconfined compressive strength were studied and recommended values of lime content for specified conditions of road bases and sub-bases are presented in this paper.

A mathematical "Sediment Yield" model has been developed and integrated with Rainfall-Runoff Model NAXOS [1] for estimating upland delivery rates of individual storm resulting from rainfall and runoff at the outlet of the catchment area of Wadi Surdud (2370 km2), Tihama, Yemen. The erosion and sedimentation processes of the upland watersheds have to be assessed by means which do not rely on historical storm flow data. Methods that depend on available or measurable representative data were developed for a deterministic approach of the erosion process. Considering the present state of knowledge of the system analysis, GIS techniques offer a unique opportunity for the appraisal of the complex interactions of erosion and sedimentation factors (rainfall, runoff, watershed, physical and land use characteristics) as well as sediment load contributions of the upland watershed. To apply the model, the watershed is divided into 242 subwatersheds using TOPAZ (Topographic Parameterization) [2]. Sediment yield is computed for each of 242 sub-basins using a steady state Sediment Continuity Equation [3] by routing mobilized sediment through a series of linear reservoir [5]. The Model uses a mass balance equation to compute sediment transport, erosion and deposition over the land surface as direct throughfall, leaf drainage and streamflow. Sediment transport is considered as the erosion rate in the plane reduced by the deposition rate within the reach. The erosion occurs due to raindrop impact as well as surface shear. The model may serve as a tool for design of soil conservation measures. The following results were obtained: " Identification of hazard areas for soil erosion, " Assessment of sediment transport at a given point within the basin, " The basis for planning of soil conservation measures. Keywords: erosion modeling; wadi Surdud; sediment yield, GIS

The sharp increase in the cost of new generating capacity, uncertain load growth, increasing fuel prices, and other environmental and siting constraints have led to increasing interest by utilities in load management (LM) programs. LM means reducing the electric power consumption and shifting some loads from the peak hours to the off-peak ones. This work deals with an LM program to demonstrate the potential and cost effectiveness of implementing direct load control (DLC) scheme in Jordan's electrical power system. The DLC approach focuses on cycling some of consumer appliances such as air conditioning (A/C) and water heaters (W/H's) to reduce their load during the peak hours, and shifting some of the water pumping system load from peak to off-peak hours. This is done by the utility through remote switching control against an incentive paid to the consumers participating in the program. A computer program was developed for the DLC scheme and applied to the Jordanian system. The results reflect the benefits of implementing the LM program. Based on these results some recommendations were made to the Jordanian electric utility.

Wadi Zabid is one of the main agricultural Wadis in the Tihama Plain. Wide ranges of crops have been cultivated such as cereals, vegetables, fruits, and some cash crops like cotton, sesame and tobacco. It has provided the country with high valued food basket as well as exporting to the neighboring countries. The government realized the importance of Wadi Zabid and started in 1979 constructing diversion works and canals to maximize the agricultural output of the Wadi. During the past twenty years of operations, sediment deposition in front of the diversion works and along the canal system posed serious threats to the project network. Sediment deposition caused many problems such as blocking the off take pipes and gates, raising canal beds and reducing canals slope, increasing the field levels and reducing canal flow capacity. This study would assess the changes in canal sections and profiles at which the present canal profiles and sections are drawn and compared with the canal profiles and sections of the previous years to provide sound basis for problems assessment. Laboratory experiments and sieve analysis were conducted to analyze canal bed samples in order to draw recent grading curves and compared it with the previous grading curves of the canals. This study exposed the fact that canal sections and profiles are changed greatly due to the accumulation of sediments in the upper reaches of the canals whilst equilibrium sections and profiles existed in the middle parts with section erosion in the lower parts of the canal reaches. It also indicated that greater sediments sizes were deposited in the canal upper reaches, which meant that canal behavior is changed and does not work as it was designed for.

Design Patterns have proven valuable in the creation of flexible and reusable object-oriented designs. In recent years there has been much interest in this topic and several catalogues of design patterns have been created. However, the issue of the application of a design pattern to an existing program has not received much attention. Applying a design pattern to a program may involve a large amount of code restructuring and extension. This paper refactors a traditional and important problem of sorting data based on design patterns and parallelism. This refactoring process passes through three stages: Setting Common Ontology, Partitioning using Divide and Conquer, and Building using Design Patterns.

Water shortage is one of the major problems that face Yemen and in certain areas it is becoming critical . Most people in several areas rely on collectable water in ponds and mountain hides which is normally not sufficient for their need . The water supply in some places comes from wells . This is true in most parts of Yemen. In some areas the wells are as deep as 100 meters . In the majority of locations where water pumping is required out of wells or up along steep mountains the means to power pumps are not available or they are difficult and costly to provide. Photovoltaic power or wind power has been proposed as viable alternatives to conventional power . This work has been carried out with the aim of evaluating PV pumping system. The system under study is made up of a submersible pump type Grundfos SP1A-28 with 100 - 200m head driven by 3x65 V , 550 W motor . The power is delivered from 24 PV modules , each rated at 50 Wp coupled through 1500VA dc/ac inverter . The system is used to pump water out of well to an overall height of 54 meters . The location chosen for the test is at Al-Jarahi Lat 14deg N , Al-Hodeidah Governate , 30 km inland from the Red Sea coast. Our observation of the system over the last five months has shown that the average daily pumping capacity was 8.5 m3 /day, the highest pumping was seen to be 10.4 m3/day and the minimum to be 5.9 m3 / day. The maximum pumping rate was achieved at an insolation of 750 W/m2 on inclined modules: Thus for a normal clear day the utilization of the available solar energy was 75 % .

This paper introduces a simple method in measuring small inductances ( in nanohenery) not usually measurable in conventional measuring instruments The idea is summarized by the slight change in the frequency of oscillation of a Colpitts oscillator caused by the unknown inductance Analogue and digital circuits have been designed for implementing this project together with a PC which calculates and displays the measured inductance value