NN Final-State Interaction in the Helicity Dependence of Inclusive π−\pi^- Photoproduction from the Deuteron

The helicity dependence of the inclusive $\pi^-$ photoproduction reaction from the deuteron in the $\Delta$(1232)-resonance region is investigated with inclusion of final-state nucleon-nucleon rescattering ($NN$-FSI). For the elementary $\pi$-production operator an effective Lagrangian model which includes the standard pseudovector Born terms and a contribution from the $\Delta$-resonance is used. The half-off-shell $NN$-scattering matrix is obtained from a separable representation of a realistic $NN$-interaction. The differential polarized cross-section difference for parallel and antiparallel helicity states is predicted and compared with experiment. We find that the effect of $NN$-FSI is much less important in the helicity difference than in the previously studied unpolarized differential cross section. Furthermore, the contribution of $\vec d(\vec\gamma,\pi^-)pp$ to the deuteron spin asymmetry is explicitly evaluated with inclusion of $NN$-FSI. It has been found that the effect of $NN$-FSI is much larger in the asymmetry than in the total cross section, and this leads to an appreciable reduction of the spin asymmetry in the $\Delta$-region. Inclusion of such effect also leads to improved and quite satisfactory agreement with existing experimental data.Comment: 13 pages, 6 eps figures, published in Prog. Theor. Phys. 113 (2005) 169-18

UPS system: How can future technology and topology improve the energy efficiency in data centers?

A Data Center can consist of a large group of networked servers and associated power distribution, networking, and cooling equipment. All these applications consume enormous amounts of energy which result in a significant increase in energy inefficiency problems. One of the causes of Data Center energy inefficiency power distribution is from the uninterruptible power supply (UPS). The UPS system is an alternate or backup source of power linking between mains power supply and end critical loads in order to provide back-up power and protection for the sensitive load. This study attempts to answer the question of how can future UPS topology and technology improve the efficiency of Data Center. In order to analyze the impact of different UPS technologies and their operating efficiencies, a model for a medium size Data Centre is developed, and load schedules and worked schematics were created to analyze and test the components of each of the UPS system topologies

Power loss investigation in HVDC for cascaded H-bridge multilevel inverters (CHB-MLI)

In the last decade, the use of voltage-source multilevel inverters in industrial and utility power applications has been increased significantly mainly due to the many advantages of multilevel inverters, compared to conventional two level inverters. These advantages include: 1) higher output voltage at low switching frequency, 2) low voltage stress (dv/dt), 3) lower total harmonic distortion (THD), 4) less electro-magnetic interference (EMI), 5) smaller output filter, and 6) higher fundamental output. However, the computation of multilevel inverter power losses is much more complicated compared to conventional two level inverters. This paper presents a detailed investigation of CHB-MLI losses for HVDC. Different levels, and IGBT switching devices have been considered in the study. The inverter has been controlled using selective harmonic elimination in which the switching angles were determined using the Genetic Algorithm (GA). MATLAB-SIMULINK is used for the modelling and simulation. This investigation should result in a deeper knowledge and understanding of the performance of CHB-MLI using different IGBT switching devices

Online control of AC/AC converter based SHEPWM technique

Conventional online control of AC/AC converter controlled by the selective harmonic elimination pulse width modulation technique (SHEPWM) is based on storing the offline calculated switching angle values in a form of lookup table. Then the required switching pattern of certain modulation index (M) is searched through the lookup table. This methodology suffers from limited system flexibility. This paper introduces a novel implementation scheme based on real-time calculation of the required SHEPWM switching pattern with linear control of the fundamental voltage component magnitude based on curve fitting technique for the exact switching angle trajectories. The accuracy of the derived polynomials is evaluated by calculating converter performance parameters using the approximated switching angles solutions obtained from the introduced method and the exact switching angles solutions. Detail of the introduced methodology is presented. Simulation and experimental results have been carried out to confirm the validity of the introduced algorithm

Modular OrCAD simulation approach in teaching power electronics

In this paper the authors present a new technique which can be used in simulating multi power electronic circuits at the same time in a very accurate way without the worries of the circuit analysis being diverted during the simulation. In this technique each circuits is simulated alone and the output current/voltage waveform(s) of this circuit is presented as a 'wave-form' generator. Then the final multi circuit design will be a collection of these 'wave-form' generators. This technique can be used in teaching power electronics system design for undergraduate as well as postgraduate levels and can also be used in the industry. A UPS system is used as an example in demonstrating this technique but this approach could equally be applicable to other multi circuit design configurations

Voltage regulation considerations for the design of hybrid distribution transformers

The future substation depends on finding a way to mitigate the effects of the drawbacks of the conventional legacy by employing the efficiency of the solid state switches [1]. This paper discusses the considerations of designing a distribution transformer that provides additional functions in regulating the voltage and controlling the reactive power that is injected in the distribution network, using a fractional rated converter attached partially with the windings of the transformer. This approach aims mainly to enhance the unit with more flexibility in controlling the voltage at the last mile of the network, in order to decrease the losses and meet the future expectations for low voltage networks modifications, and that by using a power electronic (PE) approach has less losses and more functionality (depending on the reliability of transformer and intelligence of PE). The design of a hybrid distribution transformer is detailed and its functionality in regulating the voltage is discussed as a combination between the features of one of the most reliable network devices, the transformer, and the effect of PE existence with less losses in both switching and conduction losses. Reduced ratings PE are used in this approach, whereby the solid state switches are controlled according to the immediate need for voltage control in low voltage (LV) networks

A new control technique for active power filters using a combined genetic algorithm/conventional analysis

In this paper, the computational problems associated with the optimization techniques used to evaluate the switching patterns for controlling variable-characteristics active power filters are presented and critically analyzed. Genetic algorithms (GAs) are introduced in this paper to generate a fast and accurate initial starting point in the highly nonlinear optimization space of mathematical optimization techniques. GAs tend to speed up the initialization process by a factor of 13. A combined GA/conventional technique is also proposed and implemented to reduce the associated computational burden associated with the control and, consequently, increasing the speed of response of this class of active filters. Comparisons of these techniques are discussed and presented in conjunction with simulation and practical results for the filter operation