October 1992 nPerils of sand production. At worst, sand production threatens a well. Voids can form behind the pipe, causing formation subsidence and casing collapse. The well may also fill with sand and cease flowing. Or the surface equipment may be catastrophically damaged by erosion or plugging. For help in preparation of this article, thanks to: Bob Elder, Chevron UK Ltd., London, England; ...

This paper addresses issues in the design of wheel grousers for planetary rovers. It has been shown in prior and related work that grousers on wheel rims can improve traveling performance of rovers on loose soils. However, the main focus of these studies, so far, has been limited to straight grousers and to straight line motion of the wheels. This work extends such studies to include chevron-sh...

We consider a simplified model of the chevron structure observed in thin cells of ferroelectric smectic liquid crystals, based on a generalization of the "uniaxial" (or "nematic") approximation of orientation elasticity. This model allows for the conciliation of the continuous nature of the layers with the matching conditions postulated by Clark, and takes large rotations of the c-director into...

The reduction of phosphorus and sulfur in engine oil are the main topics of this paper. Very reproducible boundary lubrication tests were conducted as part of Design of Experiment software (DOE) to study the behavior of fluorinated catalyst iron fluoride (FeF3), and polutetrafluoroethylene or Teflon (PTFE) in developing environmentally friendly (reduced P and S) anti-wear additives for future e...

BACKGROUND Hallux valgus deformity is a common chronic problem with a reported prevalence of 28.4% and its chief complaint is pain. Thus far, different surgical procedures with their proposed indications have been introduced. This study compared three current procedures, namely the chevron and scarf osteotomies and the McBride procedure. METHODS This retrospective cohort was conducted at the ...

Celestite/barite−replaced and phosphate−replicated tubes of Early Cambrian anabaritids from the northern part of the Si− berian Platform (Anabar Shield) give new evidence on the wall−structure of these enigmatic fossils. The walls consist of fibres, interpreted as reflecting an original aragonitic fabric. Bundles of fibres are arranged in growth lamellae, and the latter form an angle of at leas...