Innovative concepts for aerodynamic control of wind turbine rotors

New systems for the aerodynamic control of wind turbine rotors are being studied in various projects funded by the UK Department of Energy. Results from a current project, ongoing at the National Wind Turbine Test Centre (NWTC) in Scotland are presented. These systems show the promise of much cheaper and more affective active control of horizontal axis wind turbines than has been achieved with full span and partial span pitching systems

Marketing export grapes

IN RECENT years there have been many changes in the buying power and of the availability of fresh fruit on our principal overseas grape market, Singapore. The market has become highly competitive and trade acceptance today demands that only grapes having a large berry size for the particular variety be exported, and that the grapes arrive in sound condition

Trends in viticultural production

The viricultural industries are in one of their cyclical downturns. This is nothing new! What is new is that new factors are coming into play whose exact significance is unknown but will have an important bearing on the economics of a viticultural enterprise

Potential markets for a satellite-based mobile communications system

The objective of the study was to define the market needs for improved land mobile communications systems. Within the context of this objective, the following goals were set: (1) characterize the present mobile communications industry; (2) determine the market for an improved system for mobile communications; and (3) define the system requirements as seen from the potential customer's viewpoint. The scope of the study was defined by the following parameters: (1) markets were confined to U.S. and Canada; (2) range of operation generally exceeded 20 miles, but this was not restrictive; (3) the classes of potential users considered included all private sector users, and non-military public sector users; (4) the time span examined was 1975 to 1985; and (5) highly localized users were generally excluded - e.g., taxicabs, and local paging

Cryogenic propellant management: Integration of design, performance and operational requirements

The integration of the design features of the Shuttle elements into a cryogenic propellant management system is described. The implementation and verification of the design/operational changes resulting from design deficiencies and/or element incompatibilities encountered subsequent to the critical design reviews are emphasized. Major topics include: subsystem designs to provide liquid oxygen (LO2) tank pressure stabilization, LO2 facility vent for ice prevention, liquid hydrogen (LH2) feedline high point bleed, pogo suppression on the Space Shuttle Main Engine (SSME), LO2 low level cutoff, Orbiter/engine propellant dump, and LO2 main feedline helium injection for geyser prevention

DOWNHILL DOMINATION IN GRAPHS

A path π = (v1, v2, . . . , vk+1) iun a graph G = (V, E) is a downhill path if for every i, 1 ≤ i ≤ k, deg(vi) ≥ deg(vi+1), where deg(vi) denotes the degree of vertex vi ∈ V. The downhill domination number equals the minimum cardinality of a set S ⊆ V having the property that every vertex v ∈ V lies on a downhill path originating from some vertex in S. We investigate downhill domination numbers of graphs and give upper bounds. In particular, we show that the downhill domination number of a graph is at most half its order, and that the downhill domination number of a tree is at most one third its order. We characterize the graphs obtaining each of these bounds

Truncating and Oversampling OFDM Signals in White Gaussian Noise Channels

This work introduces a modified version of the orthogonal frequency division multiplexing (OFDM) signal by truncating OFDM symbols in the time domain. Sub-carriers are no longer orthogonally packed in the frequency domain as time samples are only partially transmitted, leading to improved spectral efficiency. In this work, mathematical expressions are derived for the newly proposed Truncated OFDM (TOFDM) signal, followed by interference analysis and performance comparisons. We also consider optimal and practical decoder architectures. Results from a Sphere Decoder-based decoder indicate that truncation length can significantly affect the error performance. With short truncation length, using a purpose designed detector, signals can be recovered even with truncated symbol transmission