295,252 research outputs found
Foliations of small tubes in Riemannian manifolds by capillary minimal discs
No full textLetting Γ be an embedded curve in a Riemannian manifold M, we prove the existence of minimal disc-type surfaces centered at Γ inside the surface of revolution of M around Γ, having small radius, and intersecting it with constant angles. In particular we obtain that small tubular neighborhoods can be foliated by minimal discs. © 2008 Elsevier Ltd. All rights reserved
Hardy-Poincaré inequalities with boundary singularities
No full textLet Ω be a bounded
domain in R^N (N≥2) such that 0 is in the boundary of Ω. In this paper we
study the Hardy-Poincare' inequality for maps vanishing on ∂Ω.
In particular we give sufficient and some necessary conditions
so that the best constant is achieved
Minimal disc-type surfaces embedded in a perturbed cylinder
No full textIn the present note, we deal with small perturbations of an infinite cylinder in three-dimensional Euclidian space. We find minimal disc-type surfaces embedded in the cylinder and intersecting its boundary perpendicularly. The existence and localization of those minimal discs is a consequence of a non-degeneracy condition for the critical points of a functional related to the oscillations of the cylinder from the flat configuration
Sharp nonexistence results for a linear elliptic inequality involving Hardy and Leray potentials
Get PDFWe deal with nonnegative distributional supersolutions for a class of linear elliptic equations involving inverse-square potentials and logarithmic weights. We prove sharp nonexistence results
The computer simulation and prediction of rock fall
Get PDFThis thesis deals with the study of rock falls using a mathematical model, codified for computer use, entitled GeoFall. GeoFall, which was developed by the author, allows predictions to be made of rock fall trajectories, run out distances and kinetic energies for a rock of any arbitrary shape. Its main purpose is to assist in the design of remedial works. The mathematical model is based on rigid body mechanics, and analyses a fall in 2D space using a new theory of impact dynamics developed by Brach (1991). The main features and algorithms of the program are presented in this thesis. The performance of GeoFall was evaluated by comparing actual rock fall events described in several published papers with the output created by GeoFall. Also the output from GeoFall has been compared with the output from other rock fall simulation programs used to simulate the documented rockfalls. A new rock slope inventory system entitled the Rock Fall Risk Assessment System (RFRAS) has been developed by the author to determine the rock fall risk at specific rock fall sites. It consists of three phases of inspection, the slope survey, and the preliminary and detailed rating phases. The detailed rating phase uses 13 parameters that when assessed, evaluated and totalled, numerically differentiates slopes from the least to the most hazardous producing an overall rating in the range 21-1926. It not only allows the relative risk of rockfall between slopes to be assessed but it also categorises the rock fall risk and the potential number of future rockfalls. It has been tested on 18 slopes at ten locations in County Durham. The final part of the thesis details a new laboratory based procedure that can be used to determine the coefficients of restitution for any type of rock material. The normal coefficient of restitution has been determined for seven different types of rock, and the tangential coefficient of restitution has been determined for a local sandstone. Some tentative correlations between the normal coefficient of restitution and the rocks physical properties, such as its Unconfined Compressive Strength (UCS) have been presented
The density, construction and drag coefficient of electrostatic volcanic ash aggregates.
Get PDFRecent laboratory experiments have demonstrated that electrostatic charges generated during the fragmentation of volcanic pumice cause rapid aggregation of the silicate particles produced. Here, we present measurements of the mass and component particle size distribution of individual, electrostatically bound aggregates produced during these experiments. Particles produced by fracturing pumice aggregated as they fell ∼1.5 m within an enclosed fall chamber. Aggregate mass measurements indicate aggregate densities of ∼200 kg m−3 or less. The component particle size analysis demonstrates exponential-type cumulative distributions which are dominated (on a volume basis) by particles ∼10–40 μm in diameter and contain few particles >70 μm. By representing these particles as disks of 5 μm thickness the calculated aggregate densities are in agreement with those derived from the aggregate mass measurements and indicate a relatively constant aggregate density with size (in contrast with previous results from fall velocities). Combining the density measurements with fall velocity data allows the drag coefficient of aggregates to be determined. Empirical equations developed to describe the particle size distribution within aggregates are used to derive relative aggregation coefficients for the electrostatic aggregation process. Our results can be used within numerical models of volcanic plumes in order to improve their representation of electrostatic aggregation processes
A multi-method approach to study the stability of natural slopes and landslide susceptibility mapping
No full textIn this paper, a multi-method approach for the assessment of the stability of natural slopes and landslide hazard mapping applied to the Dakar coastal region is presented. This approach is based oil the effective combination of geotechnical field and laboratory works, of GIS, and of mechanical (deterministic and numerical) stability analysis. By using this approach, valuable results were gained regarding instability factors, landslide kinematics, simulation of slope failure and coastal erosion. This led to a thorough assessment and strong reduction in the subjectivity of the slope stability and hazard assessment and to the development of an objective landslide danger map of the SW coast of Dakar. Analysis of the results shows that the slides were influenced by the geotechnical properties of the soil, the weathering, the hydrogeological situation, and the erosion by waves. The landslide susceptibility assessment based on this methodological approach has allowed for an appropriate and adequate consideration of the multiple factors affecting the stability and the optimization of planning and investment for land development in the city. (C) 2005 Elsevier B.V. All rights reserved
An investigation of fall protection systems in the roofing industry
Get PDFThesis Chair, Dr. Sang D. Choi.
This file was last viewed in Adobe Reader 7.0Construction is one of most dangerous industries in the United States. One of the most hazardous areas within the construction industry is roofing. Concern for safety in roofing construction has continued to spread, as a result of falls that make up the greatest rate of fatalities in the construction industry. Previous research has found that falls have been one of the leading categories under type of occupational death and that fall protection systems are not consistently used to prevent fall accidents in the roofing industry. Research is needed in order to analyze falls and other potential hazards in roofing. The main goal for this study is to analyze commercial and residential roofers’ behaviors, attitudes, and beliefs on the fall protection systems. A survey was distributed to commercial and residential roofers in the Midwest. Information collected from roofers was compared and analyzed to find differences between residential and commercial roofers. A total of 129 roofing contractors participated in this study. The results of the survey showed that while most of commercial roofers did use fall protection devices, a significant number of residential roofers did not comply with fall protection regulations and guidelines. Two main reasons of noncompliance with fall protection regulations and guidelines in roofing construction were found: (1) fall protection devices decrease productivity; (2) fall protection equipment makes roofers uncomfortable. Results from this study revealed that personal fall arrest system (PFAS) was the most prevalent fall protection device used among residential and commercial roofers. PFAS was also the most preferred fall protection equipment among the two groups of roofers. For both residential and commercial roofing, there is a significant (p = 0.05 and p = 0.01) negative relationship between enforcing roofers to wear or install fall protection devices and having falls from roofs. In both residential and commercial roofing, there is a very significant (p= 0.001 and p = 0.001) positive relationship between the enforcement and the actual usage of fall protection equipment. This thesis presents the results of the investigation of fall protection systems in roofing construction and recommendations that ultimately would reduce fall accidents
Texas A&M Law Review Fall 2020 Symposium: Containing Covid Catastrophes: Addressing The Effects Of Covid-19 On The Agricultural Industry Texas A&M University School Of Law
Get PDFTranscript from Fall 2020 Symposium, Containing Covid Catastrophes: Addressing The Effects Of Covid-19 On The Agricultural Industry Texas A&M University School Of Law
Featuring Panelists: Jim Bradbury & Greg Ibac
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