619 research outputs found
The Evolution of Grain Policy Beyond Europe: Ottoman Grain Administration in the Late Eighteenth Century
No full textDuring the second half of the eighteenth century, the Ottoman policy-makers adopted a more liberal attitude towards price formation in the Ottoman grain markets. This was accompanied by the fiscal and administrative centralization of the grain trade. These seemingly contradictory policy changes could, in part, be explained in the context of conjectural changes in grain demand and supply, which rendered pre-emptive privileges and price controls less effective. The policy change, however, was not only a practical response to the strains on the pre-existing supply network but also reflected a new concern with the state of agricultural production along with the emergence of emulation as a development strategy.Ottoman economic institutions, grain markets, liberalization
THE USE OF MEAN-VARIANCE FOR COMMODITY FUTURES AND OPTIONS HEDGING DECISIONS
No full textThis study provides additional evidence of the usefulness of mean-variance procedures in the presence of options which can truncate and skew the returns distribution. Using a simulation analysis, price hedging decisions are examined for hog producers when options are available. Mean-variance results are contrasted with optimal decisions based on negative exponential and Cox-Rubinstein utility functions over 56 ending price scenarios and two levels of risk aversion. The findings from our simulation, which considers discrete contracts, basis risk, lognormality in prices, transactions costs, and alternative utility specifications, affirm the usefulness of mean-variance framework.Marketing,
Inertia emulation control of VSC-HVDC transmission system
No full textThe increasing penetration of power electronics interfaced renewable generation (e.g. offshore wind) has been leading to a reduction in conventional synchronous-machine based generation. Most converter-interfaced energy sources do not contribute to the overall power system inertia; and therefore cannot support the system during system transients and disturbances. It is therefore desirable that voltage-source-converter (VSC) based high voltage direct current (HVDC) interfaces, which play an important role in delivery of renewable power to AC systems, could contribute a virtual inertia and provide AC grid frequency support. In this paper, an inertia emulation control (IEC) system is proposed that allows VSC-HVDC system to perform an inertial response in a similar fashion to synchronous machines (SM), by exercising the electro-static energy stored in DC shunt capacitors of the HVDC system. The proposed IEC scheme has been implemented in simulations and its performance is evaluated using Matlab/Simulink
An analysis of the correspondence and hagiographical works of Philip of Harvengt
No full textFor every famous author of the twelfth-century renaissance, there are numerous lesser-known writers. Despite being overshadowed by more brilliant scholars or those closer to the centre of important events, their voices add depth to the study of the intellectual history of this period. A founding member of one of the earliest Premonstratensian houses; a highly-educated and prolific author, much in demand as a hagiographer; and a vigorous defender of the clerical order, Philip of Harvengt is one such writer, and a worthy subject for study. This thesis examines two bodies of Philip’s works – his letters and his hagiographical writings – analysing the predominant and recurrent concerns and ideals expressed in them, and the means by which they are expressed.
The letters are carefully crafted works, examples of the literary labour which Philip writes is incumbent upon the cleric. The first part of this thesis approaches these letters in chapters on four themes: the role of the ecclesiastical prelate; the importance of learning; the relationship between religious orders; and Philip’s use of the motif of friendship. His hagiographical works, too, are examples of literary artistry, to move as well as to educate the audience. In the second part of the thesis, these will be discussed individually, with the first chapter analysing his vita of Oda, a nun attached to his own house, whom he portrays as a martyr. The succeeding chapters consider Philip’s rewritings of earlier vitae, and show how he managed his sources in order to produce vitae depicting their subjects according to his ideal model of sanctity.
Philip’s letters express concerns shared by contemporaries, reflecting anxieties surrounding roles and ideal forms of living in a period immediately following the first fervour of religious renewal. His hagiographies articulate ideals of sanctity, clarifying these when they are not made sufficiently explicit in earlier works, for the better edification of an audience pursuing this vita perfecta. Both letters and hagiographies are designed to exhort and instruct the reader or listener: above all, Philip is a teacher
THE ECONOMICS OF CLEANING WINTER WHEAT FOR EXPORT: AN EVALUATION OF PROPOSED FEDERAL "CLEAN GRAIN" STANDARDS
No full textBuyer complaints about poor quality U.S. wheat have led to proposals to enforce minimum dockage standards for exports. An economic-engineering approach is used to evaluate costs and benefits of cleaning wheat in order to meet these standards for 13 possible cleaning configurations. These results are used in an optimization framework to estimate costs and benefits of cleaning all U.S. export wheat. The estimates indicate that cleaning U.S. export winter wheat to .35% dockage would cost an average of 1 cent/bu., requiring an initial capital investment of $28 million. Value of wheat lost in cleaning is a significant cost that previously has been overlooked.Agricultural and Food Policy,
Transient fault analysis of a VSC-based multi-terminal HVDC scheme
No full textSubmitted in fulfilment of the requirements for the degree of Master of Engineering: Electrical Engineering, Durban University of Technology, Durban, South Africa, 2020.A multiterminal HVDC system includes the connection of different HVDC terminals to a common grid. Most of the MTDC networks are realized in voltage source converter (VSC) high voltage direct current (HVDC). Over long distances, HVDC transmission is preferred to high voltage direct current (HVAC). Furthermore, HVDC is subjected to minimal harmonics oscillation problems due to the absence of frequency. HVDC enables the interconnection of systems at different frequencies, and the system becomes free of angular stability problems. VSCs employ insulated gate bipolar transistors (IGBTs) switches, and High-frequency pulse width modulation is used to operate the IGBTs in order to achieve high-speed control of active and reactive power. The growth of MTDC networks may require a new type of VSCs topology, which is resilient and efficient to dc and ac network fault. This research investigation focuses on the transient dc-side fault analysis in a two-level Monopolar VSC- Based Multi-Terminal HVDC Scheme consisting of four asynchronous terminals sharing a rated 400kV DC-grid was carried out in PSCAD software. During dc-side fault analysis, a pole-to-ground fault was taken into consideration as it’s more likely to occur, although it is less severe compared to pole-to-pole. The converters are interconnected through 100 km dc cables placed 0.5 gm apart and at a depth of 1.5 m underground. It was observed that during the steady-state analysis, the dc voltage in the grid was maintained at the rated value 400 kV, the currents measured at the converters bus was 0.5 kA, and the current flowing through the cables was 0.25 kA. Under the fault condition, the dc voltage drop needs to be maintained to a closed range to avoid the grid to collapse. The voltage droop technique was incorporated in the dc voltage controller to keep the dc voltage at the narrow range. Depending on the value and nature of ground fault resistance, the fault current magnitude varies, and distance variation along the cable has a significant contribution in the fault current. It is observed that fault close to the converter (5 km’s measured 9 kA) results in high fault currents compared to fault away from the converter (50 km’s measured 7.8 kA). The protection design of the VSC needs to be able to detect whether its ground fault or short circuit since the location of the fault needs to be identified and repaired. Another observation made when the fault is inserted 50 kms away from the converter, meaning the fault is at the center of the two converters, the outcome results in high currents in both converters. The isolation of the fault should be fast and selective as the critical time is very short. The dc circuit breakers are mostly recommended to be used as primary protection; however, different protection techniques need to be incorporated with dc circuit breaker in order to quickly identify, select and reliable isolate the faulted line. Moreover, the protection should be able to isolate the line before the fault reaches the maximum fault current to avoid the damage in the converter components.
Interview with Robert Gordon
No full textThis interview with Robert Gordon, Illinois Tech architecture alumnus, architect, planner, artist, and author, was conducted on June 6, 2017 by Ralph Pugh and Adam Strohm
Quasi two-level operation of a five-level diode clamped converter
No full textEThOS - Electronic Theses Online ServiceGBUnited Kingdo
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