فهرست مطالب شهریار کابلی

Holding short-term skill enhancement workshops can be a good opportunity to increase the performance and develop the abilities of experts for the all-round growth and development of society. The purpose of the present research is to investigate the effectiveness of holding short-term skill enhancement workshops for automatic transmission repairs for three years and for a statistical population of 142 people. First, the requirements and preparations for holding a standard skill enhancement workshop at four levels of needs assessment, planning, implementation and evaluation of training effectiveness were carried out. After that, by selecting qualified instructors and training them and obtaining the required specialized qualifications, 142 people who participated in these workshops were trained and monitored over a period of three years. The results show that only 42% of this statistical population continued to work in the aforementioned specialized field and 58% stopped working for various reasons. Only 22% managed to achieve good and excellent scores based on Kirkpatrick’s evaluation model. 20% of the people are still working in this specialized field, while their evaluation scores remain weak and average, and they have no motivation to improve their evaluation level.

Engineering education is based on the technical methods in the present form. Information revolution causes to access the technical education materials as a widely spread form by the students. These materials are more effective than the traditional engineering education. Thus, it is necessary to change the engineering education methods from the classical form. General workshop is a first-year course for the engineering students and it is an introduction on the engineering regulations. Nowadays, this course is run to teach the practical training. However, this goal cannot be achieved because of the short period of the course, various topics of the course and improper education methods. In this paper, this course is revised based on the teaching of engineering concepts to the students. Various engineering concepts are explained which can be educated in this course without considerable changes in practice but with magnificent change in the course prospective. It is expected that this new design helps the students more to be familiar with the engineering concepts and methods.

The ceramic fracture in output RF1 window is one of the most important failure factors in high power vacuum tubes. Fast protection systems are used to protect the tube. These protection systems are activated with some measured variables such as the level of backward RF power. On the other hand, a fast protection system can be activated with noise. Therefore, a tradeoff must be done between the response time of the protection system and its sensitivity to the noise. There are many methods to determine the response time of the protection system. The level of allowable power loss in the tube failure process is one of the conventional figures of merit for protection response time determination. However, these methods are conservative and the resulted response time is usually less than the critical time which is necessary for protecting the tube. In this paper, an experimental investigation is presented about the relation between the response time of the tube protection system and the crack growth in the ceramic of RF window. It is shown that the twin growth in ceramic can be a reliable figure of merit for the response time calculation of the tube protection system.

Blumlein bipolar pulse former is a widely used bipolar pulse generator with good performance. This structure produces a bipolar pulse from a unipolar pulse using the reflection theorem of the waves in transmission lines. Practical considerations in the design process of Blumlein bipolar pulse former is an important issue from the view point of output voltage waveform quality and construction cost. In this paper, a Blumlein bipolar pulse former has been simulated and analyzed to investigate the effect of different physical parameters on the output voltage waveform. The results of simulations can be used to design a bipolar pulse generator with acceptable output voltage waveform.

Nowadays, producing high voltage ultra-narrow bipolar pulse is considered in many applications. Considering the antenna or load, a bipolar pulse generator has many advantages compared to a unipolar pulse generator. Therefore, a high-power bipolar pulse generator has become a goal in the field of pulsed power. To achieve this goal, producing a bipolar pulse from a unipolar pulse is an important issue. Blumlein pulse generator is a widely used bipolar pulse generator with good performance. One of the issues in this pulse generator is the effect of spark gaps’ shape on the waveform of the output pulse. In this paper, a Blumlein bipolar pulse former has been considered, simulated and analyzed with different spark gap types. The effect of parasitic capacitance of these spark gaps in the transmission lines has been considered. The results of simulations can be used to design a bipolar pulse generator with acceptable output voltage waveform.

In this paper, a high power tetrode tube (TH781-200kW, cw) modulator is designed and implemented. This modulator is used for a part of RF system of the first Iranian high power electron accelerator project with similar structure to Rhodotron accelerator. Regarding to the level of sensitive and importance of TH781 tube the modulator system designed with high accuracy. So beside of power supplies design the control circuits for protection of the tube have been considered. The results of test and operation of this system that have been constructed in Iran for fist time is very satisfactory.