DYNAMIC DAMPING IN OPTICAL RECEIVERS

Today's telecommunications involves ever-increasing amounts of optical communication. Besides being an important component of the long-haul network, optical communications are also being used in data centers, circuit boards, integrated circuits, and the next generation of mobile networks. This thesis proposes an optical receiver in which the damping factor of both the transimpedance and post amplifiers is modulated synchronously with incoming data. Modulation of the damping factor allows the fast response of the low-damping factor while mitigating the intersymbol interference (ISI) associated with underdamped systems. To investigate the modulated damping shunt-feedback transimpedance amplifier (SF-TIA), some methods, including switching the feedback resistor and modulating the damping factor by a sine wave, are used. Due to damping factor value limitation by changing the shunt-feedback and complexity of producing appropriate value of the sine wave with proper DC offset, amplitude and phase, damping factor modulation by a rail-to-rail square wave signal is presented where only phase adjustment is necessary and has better noise performance, Vertical Eye Opening (VEO) gain and gain to power ratio. The extension of dynamic damping to the post amplifier is investigated through simulation at 10 Gb/s. A shunt-feedback TIA with cross-coupled inverters at the output, optimized to reach minimum input-referred noise is used as a reference for creating SF-TIA and Cherry-Hooper post-amplifier (CH-PA) blocks. By modulating the damping factor in both blocks, the proposed system achieves more than three times the VEO and lower input-referred noise compared to the optimized reference. Alternatively, an equal-gain modulated system has 40 % lower power consumption compared to the reference design

Innovations in Rotary Drill Bit Design to Reduce Vibration and Improve Durability

Well drilling is an important process for extracting oil, natural gas, water, and mineral materials. Opening wells requires boring through earth formations, which can range from very soft to very hard. Penetrating into such formations requires specialized tools and operation procedures which should be employed based on the environment and application. Rotary drilling, in which a drill bit is used to crush the rock and penetrate into the formation, is one of the main methods of well drilling. Rotary cone bits are one of the main types of drill bits used for rotary drilling. There are two main problems encountered when drilling with rotary cone bits. Excessive vibration can cause damage to the entire system and can decrease efficiency of the drilling process. Failure of the bit’s bearings and seals can also result in damage to the bit and cessation of the drilling process. In recent years, a great deal of research has been undertaken to address these problems and find appropriate solutions to improve drilling efficiency and production rate while reducing the overall cost of drilling. In this thesis, a new design for rotary cone bits, with the objective of improving overall drilling performance, is presented. First, a new pattern for distribution of inserts over the cone is presented, which results in reduced vibration of the drillstring. Second a new design for the bit’s bearings is introduced that is capable of operating in harsh environments. Finally, an experimental set-up is introduced to evaluate the performance of the proposed designs

Mitigation of Seismic Deformation of Anchored Quay Wall by Compacting

The anchored quay walls or bulkheads are commonly used in coastal areas. Previous studies on the seismic behavior of these quay walls have shown a significant effect of the liquefaction on the performance of the walls. Considerable length of an anchored sheet pile wall in Rajaii port, Iran, has been embedded in liquefiable sand. This study tries to clarify failure mechanism of the wall during earthquake and to identify more effective zone for improvement of the wall stability. Numerical modeling by DIANA software and physical modeling by shake table were presented. Results show that the main reason for extensive deformation of the system is the liquefaction of the soil adjacent to the root of the wall. The compaction of this zone improves the performance of the system and prevents large displacements. The mitigation plan was proven by comparison among the measured results, including the final shape, displacements and excess pore water pressure ratio

Determination of chromosomes that control physiological traits associated with salt tolerance in barley at the seedling stage

Salt stress is one of the most important abiotic stresses, and plays an important role in reducing the yield of crops worldwide. It is now recognized that tolerance to salinity is genetically and physiologically complex and also inherited quantitatively. Barley is a short-season, early maturing, diploid and self pollinating crop, thus it is an ideal model plant for genetic and physiological studies of salinity tolerance. In order to map the genes/QTLs for salinity tolerance in barley, 72 doubled-haploid lines derived from a cross between ‘Steptoe’ and ‘Morex’ were used in an experiment using a randomized complete factorial design with three replications. The phenotypic traits under study included: chlorophyll contents, chlorophyll fluorescence (Fo, Fv, Fv/Fm), proline and carbohydrate rates, relative water content (RWC) and dry and wet weight of plant. Analysis of variance results showed that there were significant differences among the lines and different levels of salinity for all the traits. The strongest correlation was observed between dry and wet weight of plant (r = 0.95**). QTL analysis was performed using the genetic linkage map derived from 327 RFLP molecular markers and QTL cartographer software with the composite interval mapping method. Phenotypic variations that were explained by these QTLs, ranged from 10.64 to 24.20. The highest and lowest phenotypic variances were related to chlorophyll content (Q3cls) and Fv/Fm (Q1fv/fms), respectively. LOD values ranged from 2.77 to 6.33. The highest LOD scores were attained for Fv/Fm on chromosome 2H. Physiological traits associated with salt tolerance in this population were mapped to chromosomes 1H, 2H, 5H and 7H.Key words: Barley, QTL, salinity, stress, tolerance

A Direct Elliptic Solver Based on Hierarchically Low-rank Schur Complements

A parallel fast direct solver for rank-compressible block tridiagonal linear systems is presented. Algorithmic synergies between Cyclic Reduction and Hierarchical matrix arithmetic operations result in a solver with $O(N \log^2 N)$ arithmetic complexity and $O(N \log N)$ memory footprint. We provide a baseline for performance and applicability by comparing with well known implementations of the $\mathcal{H}$-LU factorization and algebraic multigrid with a parallel implementation that leverages the concurrency features of the method. Numerical experiments reveal that this method is comparable with other fast direct solvers based on Hierarchical Matrices such as $\mathcal{H}$-LU and that it can tackle problems where algebraic multigrid fails to converge

Mixed Convection Heat Transfer of Al2O3 Nanofluid on the Elliptical Shapes: Numerical Study of Irreversibility

In this study the 2D laminar and steady water-based Al2O3 nanofluid flow over a cylinder with circular, horizontal and vertical elliptical cross section by constant surface temperature boundary condition has been studied. The main goal of this research is to investigate the effects of different natural and mixed convection heat transfer mechanisms on the convective heat transfer coefficient, and the entropy generation due to the thermal and frictional origination. Conservation equations of the mass, momentum and energy under the assumption of incompressible, Newtonian nanofluid, by using the homogeneous single phase method have been solved. The impact of considered parameters in this study (alteration in cross section, convective flow direction and volume fraction of nano particles) in enhancing the heat transfer rate is studied in association with the entropy generated value in each case. Based on the results, the vertical elliptical cross section, in comparison with others, shows the highest entropy generation value and the heat transfer coefficient in all considered mechanisms. Moreover, mixed convection heat transfer type 2, in which the force flow is perpendicular to the buoyant flow direction, has the highest entropy generation and heat transfer rate for all cross sections. In addition, in all cases in the presence of the nanoparticles, the heat transfer rate and entropy generation increases

Control of Road Settlement around Stone-Arch Bridges by Material Modification and Embankment

Occurrence of road settlement around bridges is considered as one of the common problems of road operations. In buried bridges, especially in deep valleys, where it is not possible to use soil compaction machinery, significant settlement is observed after road operation. Such settlement mainly reduces the ride quality as well as the safety of the crossing. Based on experience, the deeper the valley and the weaker the soil, the greater the settlement created in these embankments. In this paper, in addition to field assessment of settlement in buried bridges, a suitable method has been presented for embankment around these bridges. In this regard, by finite element method, a sample of bridges buried in deep valleys has been modeled in which the settlement was calculated. The results of the finite element method were compared with the field values of the settlement at one of the studied bridges. The results showed that the settlement was directly related to the width and depth of the valley, the volume of the embankment and the soil type. Also, the results of numerical studies by finite element method showed that the created settlement was strongly affected by the modulus of elasticity of the soil compared to other parameters. If the modulus of elasticity of the materials reduces, the settlement will increase significantly. In this study, a suitable method for embankment around buried bridges in deep valleys has been presented. The results of using this method showed a significant reduction in settlement around buried bridges

Experimental Study of Subcooled Boiling Heat Transfer of Axial and Swirling Flows inside Mini Annular Gaps

An experimental study of the subcooled boiling heat transfer of axial and swirling upward flows inside vertical mini annular gaps was conducted using deionized water. The subcooled boiling heat transfer coefficients and the boiling curves of the flow inside mini annular gaps with different gap sizes have been investigated. The experimental results both for the single phase heat transfer and subcooled boiling heat transfer inside mini annular gaps showed very good agreement with correlations in the literature. The results showed that the subcooled boiling heat transfer coefficient for a given heat flux increases as the size of the annular gap is decreased. The maximum wall superheat is also influenced negligibly by mass flux. Furthermore, the effects of swirl flow by using spring insets inside the mini annuli on the single phase and subcooled boiling heat transfer have been studied. The results showed that the single phase and subcooled boiling heat transfer coefficients are increased by having swirl flow inside mini annuli using spring inserts. The obtained results also showed that the heat transfer enhancement by having swirl flow inside the annuli using spring inserts decreases as the applied heat flux is increased in the subcooled boiling heat transfer region