1,135 research outputs found
Problem of the slotted wing : a communication from the Aerodynamic Institute of the Aachen Technical High School
It is to be expected that the advantageous properties, hitherto discovered in many slotted wing sections, depend very largely on the contour of the slot and the structural details of the wing. It is therefore of interest, aside from measurements on wings of constant cross-section along the span, to measure also wing models in which the structural details have already been given practical consideration
Indirect observation of unobservable interstellar molecules
It is suggested that the abundances of neutral non-polar interstellar molecules unobservable by radio astronomy can be systematically determined by radio observation of the protonated ions. As an example, observed N2H(+) column densities are analyzed to infer molecular nitrogen abundances in dense interstellar clouds. The chemistries and expected densities of the protonated ions of O2, C2, CO2, C2H2 and CH4 are then discussed. Microwave transition frequencies fo HCO2(+) and C2H3(+) are estimated, and a preliminary astronomical search for HCO2(+) is described
Investigation of the Forces Acting on Gliders in Automobile-pulley-winch and Airplane Towed Flight
The magnitude, the direction, and the fluctuation of towing forces exerted upon gliders by towing them aloft behind an automobile, by means of a winch, and by airplane were measured under a variety of conditions covering a range from gentle to severe types of operation. For these tests the towing forces did not exceed 92 percent of the gross weight of the glider. The results indicate that in pulley and winch towing the towing forces are of about the same magnitude as in automobile towing. Speed increases in the accelerated phases of the towing jerks encountered in airplane towing can readily become critical as speeds in excess of placard speeds can be attained. Passage through the slipstream of the towing airplane can be equivalent to a severe gust that, at high speed, may impose high wing loads and require large control moments
A case for heuristic optimization methods in forestry
With rising competition for scarce resources, forest managers are increasingly concerned with estimating optimal solutions to complex problems. Heuristic procedures are often useful in solving such problems
Thinning optimization in mixed-species forests
An approach is summarized for estimating optimal thinning and final harvest age for existing, mixed-species stands. The method involves stand-table projection with upgrowth and mortality equations, formulated as an integer-nonlinear programming problem. Random search methods are proposed for estimating optimal cutting prescriptions. Such solution methods warrant further study in forestry, since their use enables broad application of stand-specific modeling results
Estimating Optimal Thinning and Rotation for Mixed-Species Timber Stands Using a Random Search Algorithm
The problem of optimal density over time for even-aged, mixed-species stands is formulated as a nonlinear-integer programming problem with numbers of trees cut by species and diameter class as decision variables. The model is formulated using a stand-table projection growth model to predict mixed-speciesg rowth and stand-structureO. ptimal thinning and final harvest age are estimated simultaneously using heuristic random search algorithms. For sample problemsw ith two speciesr, andom searchm ethodsp rovide near-optimalc uttings trategiesw ith very little computer time or memory. Optimal solutions are estimated for problems with eight initial species/diameter class groups, projected for up to three discrete growth periods. Such solution methods merit further study for evaluating complex stand- and forest-level decisions. FOREST Scl. 31:303-315
Solving Strong-Substitutes Product-Mix Auctions
This paper develops algorithms to solve strong-substitutes product-mix
auctions. That is, it finds competitive equilibrium prices and quantities for
agents who use this auction's bidding language to truthfully express their
strong-substitutes preferences over an arbitrary number of goods, each of which
is available in multiple discrete units. (Strong substitutes preferences are
also known, in other literatures, as -concave, matroidal and
well-layered maps, and valuated matroids). Our use of the bidding language, and
the information it provides, contrasts with existing algorithms that rely on
access to a valuation or demand oracle to find equilibrium.
We compute market-clearing prices using algorithms that apply existing
submodular minimisation methods. Allocating the supply among the bidders at
these prices then requires solving a novel constrained matching problem. Our
algorithm iteratively simplifies the allocation problem, perturbing bids and
prices in a way that resolves tie-breaking choices created by bids that can be
accepted on more than one good. We provide practical running time bounds on
both price-finding and allocation, and illustrate experimentally that our
allocation mechanism is practical
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