253 research outputs found
On a theory of sandwich construction
The theory of sandwich construction developed in
this paper proceeds from the simple assumption that the filling
has only transverse direct and shear stiffnesses, corresponding
to its functional requirements (§1). This supposition permits
integration of the equilibrium equations for the filling (§2).
The resulting integrals are used to study the compression
buckling of a flat sandwich plate (§3). The formulae obtained
are complex, but may be simplified in practical cases (§4). A
second approach to sandwich problems is made in §5, where a
theory of "bending" of plates is outlined. This generalises the
usual theory, making allowance for flexibility in sheer. This
approach is applied to overall compression buckling of a plate
in §6, and agreement with the previous calculations is found.
This suggests the possibility of calculating buckling loads for
curved sandwich shells. A simple example, the symmetrical
buckling of a circular cylinder in compression is worked out in
§7. The theory developed would seem applicable to all cases of
buckling of not too short a wave length (§8)
Notes on the problem of the optimum design of structures
The urgent need for a systematic approach to the problems of
the optimum design of structures is stressed and ideal formulations
of these problems are considered. Differential equations and a
variational principle are derived for the case of plates loaded in
their own planes; these can form the basis for approximate
solutions, in the form of optimum distributions of plate thickness
and the corresponding stress distributions which are required to
equilibrate given systems of external loads
Plastic buckling of a plate in shear
This note derives the mathematical equations for
the analysis of the shear buckling of a plate, in the case where
the initial stresses exceed the elastic limit of the material.
It is hoped at a later stage to apply this theory to test
results, which are being obtained using rectangular torsion boxes
Solution of a load diffusion problem by relaxation methods
SUMMARY
The need. to generalise the usual assumptions made in
the analysis of load diffusion problems has been emphasised by
recent experimental work (Ref. 3)1 which has shown the importance
of bending of the edge members. Direct mathematical
solution of the plate problems, which arise, is hardly feasible
and so in this report a numerical solution using the 'relaxation
method' is carried out. Results show the method to be suitable
for design purposes/ but comparison with experiment still shows
the need for further physical generalisations. These will
form the subject of future work
Optimum structures
The design of the best structure for a given purpose
depends upon the criterion used for optimisation. Structures
may be designed to safely transmit a given system of forces using
the least weight of material.. They may also be designed to have
maximum stiffness of a certain type for a given weight or
alternatively to have the greatest possible fundamental
frequency of vibration. These problems, although in general
distinct from one another, are closely related and much can be
achieved towards maximisation of stiffness and frequency by the
use of minimum weight designs. In fact it can be shown that a
minimum weight framework is the stiffest structure of that weight
for the force system, which it is designed to carry.x
The present report is concerned exclusively with the problem of
the design of structures of minimum weight, which are required
to transmit specified forces. Some attention will be given to
frameworks because, in particular, methods of approximate
numerical analysis are more readily formulated for this type of
structure, but the main emphasis will be placed upon the design
of structures formed from plates of variable thickness reinforced
by direct load carrying members.
See para,l.
Características de plantas em genótipos de feijão carioca relacionadas à habilidade competitiva com plantas daninhas.
Interferência de plantas daninhas em diferentes cultivares de feijão do grupo carioca.
O objetivo desse trabalho foi avaliar a habilidade competitiva de cultivares de feijão do grupo carioca com plantas daninhas. As perdas de produtividade de grãos em cultivares de feijão carioca, decorrentes da interferência exercida pelas plantas daninhas, variaram de 42,2 a 61,2 %, sendo que as cultivares que apresentaram as menores perdas de produtividade também suprimiram em maior grau o crescimento das plantas daninhas. Não foi possível identificar, de forma consistente, características de plantas associadas à redução de produtividade de grãos em função da interferência de plantas daninhas
Sidewall Buckling of Equal-width RHS Truss X-Joints
This paper presents a new design methodology for equal-width rectangular hollow section (RHS) X-joints failing by sidewall buckling. In the new approach, a slenderness parameter is defined based on the elastic local buckling stress of the sidewall, idealized as an infinitely long plate under patch loading. A Rayleigh-Ritz approximation is thereby used to obtain a closed-form solution. The proposed design equation is verified against experimental results over a wide range of wall slenderness values obtained from the literature and complemented by a brief experimental program carried out by the authors. It is demonstrated that the new design equation yields excellent results against the experimental data. Finally, a reliability analysis is performed within the framework of both the Eurocode and the AISI standards to ensure that the proposed design equation possesses the required level of safety. The newly proposed equation strongly outperforms the current Comité International pour le Développement et l’Etude de la Construction Tubulaire (CIDECT) design rule for sidewall buckling and also further extends the range of applicability to a wall slenderness ratio of up to 50
Genome of the epsilonproteobacterial chemolithoautotroph Sulfurimonas denitrificans
Author Posting. © American Society for Microbiology, 2008. This article is posted here by permission of American Society for Microbiology for personal use, not for redistribution. The definitive version was published in Applied and Environmental Microbiology 74 (2008): 1145-1156, doi:10.1128/AEM.01844-07.Sulfur-oxidizing epsilonproteobacteria are common in a variety of sulfidogenic environments. These autotrophic and mixotrophic sulfur-oxidizing bacteria are believed to contribute substantially to the oxidative portion of the global sulfur cycle. In order to better understand the ecology and roles of sulfur-oxidizing epsilonproteobacteria, in particular those of the widespread genus Sulfurimonas, in biogeochemical cycles, the genome of Sulfurimonas denitrificans DSM1251 was sequenced. This genome has many features, including a larger size (2.2 Mbp), that suggest a greater degree of metabolic versatility or responsiveness to the environment than seen for most of the other sequenced epsilonproteobacteria. A branched electron transport chain is apparent, with genes encoding complexes for the oxidation of hydrogen, reduced sulfur compounds, and formate and the reduction of nitrate and oxygen. Genes are present for a complete, autotrophic reductive citric acid cycle. Many genes are present that could facilitate growth in the spatially and temporally heterogeneous sediment habitat from where Sulfurimonas denitrificans was originally isolated. Many resistance-nodulation-development family transporter genes (10 total) are present; of these, several are predicted to encode heavy metal efflux transporters. An elaborate arsenal of sensory and regulatory protein-encoding genes is in place, as are genes necessary to prevent and respond to oxidative stress.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory, University of California, under contract W-7405-ENG-48. Genome closure was funded in part by a USF Innovative Teaching Grant (K.M.S.). S.M.S. received partial support through a fellowship from the Hanse Wissenschaftskolleg in Delmenhorst, Germany (http://www.h-w-k.de), and NSF grant OCE-0452333. K.M.S. is grateful for support from NSF grant MCB-0643713. M.H. was supported by a WHOI postdoctoral scholarship. M.G.K. was supported in part by incentive funds provided by the UofL-EVPR office, the KY Science and Engineering Foundation (KSEF-787-RDE-007), and the National Science Foundation (EF-0412129)
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