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Height H (height + h)

Distribution by Scientific Domains

Engineering	80%

Selected Abstracts

Experimental study of stick-slip behaviour

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 6 2004
Florence Adjemian
Abstract Simple axi-symmetric uni-axial compression tests have been realized on dry loose samples of glass beads (diameters d: d=0.2 ± 0.05 mm, 0.75 ± 0.1 mm, or 3 mm) and on Hostun sand under small lateral confinement, ,3<60 kPa, using different sample sizes. The experiments with the two smallest spheres (d=0.2 and 0.75 mm) exhibit stick-slips, which are characterized by (i) a rapid release ,q of the deviatoric stress q and by (ii) the strain ,,1 separating two events. The samples which exhibit stick-slip also present a weakening of strength q(,1) as the rate of deformation d,1/dt is increased. No stick-slip is generated during the first part of the q,,1 curve, i.e. when q grows fast with ,1. Four different parameters helped us determine the statistics of ,q and ,,: the lateral pressure ,3,, the rate of deformation d,1/dt, the sample height H, and the diameter D. The statistics do not depend on rate history. They look like exponentials in small samples and/or in (large sample+fast d,1/dt), and they look like Poissonian or Gaussian in (Large sample+small d,1/dt). This change in statistics is attributed to a varying of triggering process starting from a single random event in small samples to multiple random events. We have interpreted this change of statistics as due to some finite size effect so that the representative elementary volume shall contain at least (200)3 grains. Localization of deformation is visible at the end of compression but cannot be detected from stick-slip statistics nor from q vs , curve. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Geometric parameters of isotropic ensembles of right cylinders from the small-angle-scattering correlation function

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2010
Wilfried Gille
The scattered intensity of ensembles of right homogeneous quasi-diluted cylinders with constant oval right section (RS) and volume fraction , are analyzed using the small-angle-scattering (SAS) correlation function (CF) ,(r) = ,(r, ,) in the isotropic two-phase approximation. A relation between the CF of the cylinder RS, ,0(r), and the CF of the single cylinder of height H, ,0(r, H), allows the calculation of the explicit cylinder parameters of height, surface area, RS surface area, RS perimeter and volume. This is accomplished by evaluating the first two derivatives of ,0(r) at r = 0. Without the assumption of an oval RS, neither H nor the RS surface area can be uniquely determined. [source]

What is the best way to represent surface conductance for a range of vegetated sites?

HYDROLOGICAL PROCESSES, Issue 9 2007
Hikaru Komatsu
Abstract Surface conductance Gs is a significant parameter for indicating the evaporative and photosynthetic properties of a vegetated surface. When comparing Gs values between different observation sites, some studies have used Gsmax and others have used ,smax (where Gsmax is the maximum Gs value measured during the measurement period, and ,smax is the maximum Gs value obtained with a vapour pressure deficit (VPD) of , 1·0 kPa during the measurement period). In this study, we demonstrate a clear justification for using ,smax instead of Gsmax when comparing Gs values between different sites. We examined whether both ,smax and Gsmax lead to the same conclusions in classifying vegetated sites. Komatsu (2003b) [Hydrological Processes 17: 2503,2512] reported a clear relationship between canopy height h and ,smax for coniferous forests with a projected leaf area index (LAI) of , 3·0. We examined not only the relationship between h and ,smax but also the relationship between h and Gsmax for coniferous forests with a projected LAI of , 3·0. Both ,smax and Gsmax decreased with increasing h. However, the relationship between h and Gsmax was less well defined than the relationship between h and ,smax because of biased Gsmax data. Consequently, we conclude that ,smax is a more appropriate index than Gsmax to represent Gs for sites with different vegetation. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Interior point optimization and limit analysis: an application

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 10 2003
Joseph Pastor
Abstract The well-known problem of the height limit of a Tresca or von Mises vertical slope of height h, subjected to the action of gravity stems naturally from Limit Analysis theory under the plane strain condition. Although the exact solution to this problem remains unknown, this paper aims to give new precise bounds using both the static and kinematic approaches and an Interior Point optimizer code. The constituent material is a homogeneous isotropic soil of weight per unit volume ,. It obeys the Tresca or von Mises criterion characterized by C cohesion. We show that the loading parameter to be optimized, ,h/C, is found to be between 3.767 and 3.782, and finally, using a recent result of Lyamin and Sloan (Int. J. Numer. Meth. Engng. 2002; 55: 573), between 3.772 and 3.782. The proposed methods, combined with an Interior Point optimization code, prove that linearizing the problem remains efficient, and both rigorous and global: this point is the main objective of the present paper. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Short helical antenna with extremely small pitch angle

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2007
Ze-Hai Wu
Abstract A 2-turn helical antenna with small pitch angle between 0.6° and 3° has been studied as a radiation element of circular polarization waves in this article. The antenna with pitch angle 2° exhibits a 3-dB axial ratio bandwidth of 9.8%, and the optimal axial ratio of 0.1 dB. When the pitch angle decreases to 0.6°, the 3-dB axial ratio bandwidth and the best axial ratio are 5% and 0.15 dB, respectively. Variation of on-axis axial ratio as a function of the straight wire height h has been computed, and the current along the helix is also given. Experimental verification of the antenna performance is presented. The antenna with low profile and high polarization purity characteristics is suitable for application of array antenna. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 17,19, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22054 [source]