Validating a GIS-based multi-criteria method for potential road identification

This paper investigated the validation of a multi-criteria method for identifying potential roads, and demonstrated the capability of analyzing GPS vehicle tracking data for identifying vehicle movement patterns and potential roads. The multi-criteria method was evaluated by comparing the predictions to the site visit results on 34 selected road segments meeting different criteria levels. Results show that locations meeting higher criteria levels have higher possibilities to be roads: an approximately 91% possibility of road existence for the locations meeting all five criteria; 55% for the locations meeting four criteria; and 14% for those meeting criteria level two or three. This approach provides an opportunity for land managers to update existing GIS roads map, or identify newly formed roads that may need either rehabilitation or inclusion into the roads maintenance program.     

Buckling load optimization of beams

In this paper, shape optimization is used to optimize the buckling load of a Euler–Bernoulli beam having constant volume. This is achieved by varying appropriately the beam cross section so that the beam buckles with the maximum or a prescribed buckling load. The problem is reduced to a nonlinear optimization problem under equality and inequality constraints as well as specified lower and upper bounds. The evaluation of the objective function requires the solution of the buckling problem of a beam with variable stiffness subjected to an axial force. This problem is solved using the analog equation method for the fourth-order ordinary differential equation with variable coefficients. Besides its accuracy, this method overcomes the shortcomings of a possible FEM solution, which would require resizing of the elements and recomputation of their stiffness properties during the optimization process. Several example problems are presented that illustrate the method and demonstrate its efficiency.     

Method of homogenization applied to dispersion in porous media

The theory of homogenization which is a rigorous method of averaging by multiple scale expansions, is applied here to the transport of a solute in a porous medium. The main assumption is that the matrix has a periodic pore structure on the local scale. Starting from the pores with the Navier-Stokes equations for the fluid motion and the usual convective-diffusion equation for the solute, we give an alternative derivation of the three-dimensional macroscale dispersion tensor for solute concentration. The original result was first found by Brenner by extending Brownian motion theory. The method of homogenization is an expedient approach based on conventional continuum equations and the technique of multiple-scale expansions, and can be extended to more complex media involving three or more contrasting scales with periodicity in every but the largest scale.     

Control of circular-disk stability with membrane stresses

Membrane stresses alter the dynamic behavior and stability of circular-disk elements, such as circular saws and grinding wheels, by shifting the disk's natural frequency spectrum. Such shifts are directly related to variation in the critical rotation speed at which standing-wave-resonance instability occurs. Negative critical-speed variations reduce the disk stability, and positive critical-speed variations increase stability. The present paper theoretically and experimentally investigates the relationship between the state of disk-membrane stress, critical rotation speed, and the frequency spectrum in radially symmetric disk problems. The observed critical-speed variations are theoretically predictable and well understood. The approach of a shifting critical-speed instability can be predicted by monitoring the disk-frequency spectrum.     

Experimental study of the Kolmogorov refined similarity variable

Recently Thoroddsen and Van Atta (1992, Phys. Fluids A4, 2592) showed that Kolmogorov's refined similarity hypothesis (1962, J. Fluid Mech. 13, 77; 82) is supported by experimental data from a wind-tunnel study of a cylinder wake, at Re_λ of 550. We show here that the probability density of the Kolmogorov similarity variable approaches a Gaussian distribution. The data also suggest that it may obey an even more demanding conditional similarity, which leads to important conclusions regarding the scaling exponents.     

Carrier testing program in a high-risk cystic fibrosis population from northeastern Italy. Active recruitment of relatives via probands' parents

OBJECTIVE: To assess the practicability and monitor the results of an active carrier testing program among relatives of cystic fibrosis (CF) patients. METHODS: Parents of CF patients in the Veneto and Trentino regions of northeastern Italy were asked to help recruit relatives aged between 18 and 45 years for CF mutation testing. RESULTS: Of 409 enrolled CF parents, 59.6% agreed to send to the CF Center family composition data of relatives up to the third degree, and 28.8% recruited relatives to carrier testing, providing names and addresses of those who, being contacted, expressed a willingness to be tested. The participation of parents was higher if they were young and had a child recently diagnosed with CF. Recruiting parents indicated 333 close relatives (59%) for testing. When contacted by the CF Center, 170 of these 333 (51%) attended for testing. The percentage of close relatives who spontaneously asked for the test was 5.4% before the carrier testing program started; it rose to 25.3% following the introduction of the active strategy. CONCLUSIONS: The participation of the parents of CF patients is an important factor affecting the utilization of testing by relatives. Besides this, the influence of a favorable medical and cultural context (participation of gynecologists and family doctors in testing programs, genetic education of the general population) has to be considered.     

Zur Bestimmung der Verwölbungen und Profilverformungen von elastischen Stäben mit beliebigen und dünnwandigen Querschnitten

Übersicht Eine bereits vorgestellte Theorie, die eine schrittweise Bestimmung der Verwölbungen und Profilverformungen von Stäben mit beliebiger Querschnittsform ermöglicht, wird zusammengefaßt und hinsichtlich des Problems gekoppelter Biegung und Torsion erweitert. Dabei wird auf einer allgemeinen Approximationsstufe die Lage des Schub und Drillruhepunkts für das zugehörige Verwölbungsproblem angegeben und die Einführung von Hilfskräften zur Erzeugung von Gleichgewichtszuständen für das zugehörige Profilverformungsproblem erörtert. Die Theorie wird anschließend auf Stäbe mit dünnwandigen Querschnitten spezialisiert, Beispiele aus der Ingenieurpraxis sollen die Anwendbarkeit des Verfahrens zeigen.

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On the determination of cross-sectional warpings and distortions of bars with arbitrary and thin-walled cross-sections

Summary An already presented theory which allows for a stepwise determination of cross-sectional warpings and distortions of bars with arbitrary cross-sections is summarized and extended with respect to the problem of coupled bending and torsion. On a general approximation level the locations of the shear centers due to bending and torsion are given for the corresponding warping problem and the introduction of auxiliary forces in order to get equilibrated states of stress is discussed for the corresponding distortional problem. The theory is then specialized to bars with thin-walled cross-sections. Examples from the engineering practice shall demonstrate the applicability of the method.

     

Vibrations and stability of cylindrical panels with elliptical cross section

Summary The free vibrations of cylindrical panels with elliptical cross section subjected to an initial stress state are investigated. The buckling problem of the panel under the stress state considered is studied as special case of the free vibration problem.

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Übersicht Es wird die freie Schwingung offener Zylinderschalen mit elliptischem Querschnitt behandelt, die sich in einem Anfangspannungszustand befinden. Das Schalenbeulproblem wird als Spezialfall der freien Schwingung untersucht.

     

A generalized force measure of conditions at crack tips

A tentative measure of the forces tending to cause crack growth—the apparent crack extension force—is defined within the framework of continuum mechanics. By an associated fracture criterion initiation of growth may be predicted as well as the direction of preferred growth. The theory is specialized to elastic, viscoelastic and elastic-plastic materials. Under specified conditions the apparent crack extension force may be expressed by surface integrals over the boundary of an arbitrary part of the body for quasi-static deformation and for steady-state propagation of the crack. For plane deformation and for infinitesimal deformation under plane stress conditions these surface integrals reduce to path independent line integrals which include the J integral by Rice[1] and the G integral by Sih[2] as special cases.