Wess-Zumino-Novikov-Witten Models Based on Lie Superalgebras

The affine current algebra for Lie superalgebras is examined. The bilinear invariant forms of the Lie superalgebra can be either degenerate or non-degenerate. We give the conditions for a Virasoro construction, in which the currents are primary fields of weight one, to exist. In certain cases, the Virasoro central charge is an integer equal to the super dimension of the group supermanifold. A Wess-Zumino-Novikov-Witten action based on these Lie superalgebras is also found.Comment: 10 pages, Latexfile, BONN-TH-94-0

Multilayer optimisation for day-ahead energy planning in microgrids

In the search for low carbon, reliable and affordable ways to provide electricity, an increased attention is going to the microgrid, a small-scale power system that uses a combination of energy generation and storage devices to serve local customers. The most promising feature of the microgrid is its flexibility to act as a standalone source of electricity for remote communities, and to be connected to the main power system, selling and purchasing power as required. Additionally, a microgrid can be considered as a coordinated system approach for incorporating intermittent renewable sources of energy. Microgrid customers can have power from their batteries or distributed generators, they can buy it from the utility grid, or they can reduce their consumption.When designing a new optimal planning tool for a microgrid, a major challenge (and opportunity) is to decide on what units to operate in order to meet the demand. The question is what mix will provide the performance needed at the lowest cost, or with the lowest possible emissions. Unfortunately, both objectives are often contradictory. Generally, low costs mean high emissions, and vice versa. A microgrid system operator may care more about achieving lower costs rather than lower emissions. Given the preferences, the operator needs to decide how to configure and operate the microgrid while satisfying all technical requirements, such as voltage stability and power balance. In order to control and manage the microgrid units in real-time while fully exploiting the benefit of long-term prediction, an off-line optimisation approach imposes itself to devise the online microgrid management. In this PhD thesis, an efficient multilayer control approach is developed which obtains a day-ahead unit commitment method to provide an economically and environmentally viable unit commitment (UC) that is physically feasible in terms of voltage violations. With the multilayer control approach, the future operational states of the controllable units within the microgrid are determined ahead of time. The proposed concept follows the idea of a day-ahead coordination including the unit commitment problem (scheduling layer), an off-line power flow calculation (executive layer) and a security check with feedback control (adjustment layer). Since the complete multilayer control concept works on a day-ahead time scale, the model can be considered as an off-line optimisation approach. The power reference set points provided by the multilayer control approach can, in turn, be used for an online microgrid implementation to achieve real-time system state updates

W-Strings from Affine Lie Algebras

The most disappointing aspect of \W-strings is probably the fact that at least for the known models one does not recover a physical spectrum that differs much from that of ordinary string theory. It is hoped that this is not an intrinsic shortcoming of \W-string theory, but rather that it is a consequence of the \W-algebra realizations that have been chosen. In this note we point out a whole new class of possible \W-strings built from representations of affine Lie algebras via (quantum) Drinfel'd-Sokolov reduction. Explicitly, we construct a BRST operator in terms of $\widehat{sl}_3$ currents which computes the physical spectrum of a \W_3-string. As a special case of this construction, if we take a free-field realization of $\widehat{sl}_3$, we recover the 2-scalar \W_3-string. These results generalize to any \W-algebra which can be obtained via quantum Drinfel'd-Sokolov reduction from an affine algebra.Comment: 12 document pages (6 physical pages), uuencoded compressed .dvi file (uses AmsFonts eu* msa* msb*), QMW-PH-93-3

Study of the lateral boundary condition temporal resolution problem and a proposed solution by means of boundary error restarts

To properly utilize coupled limited-area models (LAMs), the time scales of the cross-boundary fluxes in the available lateral boundary data must be assessed. In current operational practice, the update frequencies of these data are usually determined by common sense guesswork and by technical constraints. This paper quantifies the required temporal resolution of the lateral boundary conditions. For a mesoscale LAM it is concluded that in standard forecast cases, coupling updates of about 3 h are sufficient. However, in rare cases of severe storms, this can lead to errors in the coupling data of about 10 hPa. To avoid such errors, it is found that one should update the coupling fields with the period given by the time step of the model that provides the coupling data. However, in most existing operational applications this is not feasible. For those cases, it is shown that the forecast can be substantially improved by restarting the model run at a forecast range when the storm has entered the domain. The proper restart time can be detected in an operational suite by an existing strategy of monitoring the coupling update frequency. Additionally, it is argued that the forecast should then be initialized by a scale-selective digital filter

An integrated decision support tool for the prediction and evaluation of efficiency, environmental impact and total social cost of forestry projects in the framework of the Kyoto Protocol

For the implementation of the Kyoto Protocol, governments of annex I countries need to develop strategies and policies for greenhouse gas reduction. Land use, land use change and forestry (LULUCF) offer CO2 emission reduction opportunities both home and abroad. Selection of effective forestry opportunities is a complex decision process based on multiple information concerning the greenhouse gas emission reduction potential, the environmental impacts and the cost efficiency of potential scenarios. In this paper, a decision support framework to evaluate forestry scenarios for greenhouse gas emission reduction was presented and tested on five different scenarios (existing and new multifunctional forest in Flanders, Belgium, energy crop with short rotation poplar, energy crop with annually harvested Miscanthus, forest plantation in the subtropics, and conservation of tropical rainforest). The framework is organized as a serial connection of a carbon accounting module, an environmental module and an economic module. Modules include a combination of models and quantitative assessments procedures. In order to make scenarios comparable, the environmental and economic modules calculate their outputs on a functional unit basis of 1 ton CO2 emission reduction. The framework is universally applicable, straightforward, transparent and quantitative. Data requirements are medium, but applicability is fairly complex due to the interdisciplinary character of the tool. Further developments would require automated data flows between models and a user interface. As to the results of the scenario analysis, the only attractive possibility for sinks in Flanders is the establishment of new multifunctional forests. This even yields a net benefit because it replaces the generally loss-making agriculture and, in addition, yields other environmental and recreational benefits. The establishment of bioenergy plantations is a very efficient way of reducing CO2 as far as land occupation and environmental impacts are concerned. However, it also turns out to be a very expensive option. Plantation forestry in the tropics is advantageous when evaluated over longer periods of time. Conservation of tropical forest does not come into consideration as a CDM project, but is nevertheless economically attractive for Flanders since the cost per ton CO2 emission reduction is in the neighborhood of the world market price.CO2 emission reduction, carbon balance, Life Cycle Assessment, Land use impact, Cost benefit analysis