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1.
PAPER CURRENT
Bifurcation in rolling of non-spherical grains and fluctuations in macroscopic friction (2014)
Publication Date: 2014-04-18
Description: Abstract The presence of granular matter between the sliding blocks (such as for example gouge in rock joints and faults) considerably affects friction. The effect of grain movement and rolling is often modelled by considering them as spherical. This paper investigates the influence of the grain/particle shape. We found that rolling of non-spherical particles leads to an apparent friction reduction related to the effect of the moment equilibrium about a point of contact. The collective behaviour of rolling non-spherical particles is affected by their interaction by the elasticity of the material of the sliding blocks. In the case of identical and symmetrical particles, there exists a uniform solution whereby all particles undergo identical displacements. This solution is, however, unstable; at certain magnitudes of the friction force and the corresponding values of the displacement the solution bifurcates such that different particles show different displacements. When many particles of different sizes are rolling without interaction, the friction force fluctuates, and as the displacement increases, the fluctuations reach a steady state. The amplitudes of the fluctuations depend upon the shape factor; they are the smallest when the particles have a square shape and considerably increase as the period of particle rolling approaches the diameter.
Print ISSN: 0001-5970
Electronic ISSN: 1619-6937
Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
Published by Springer
2.
PAPER CURRENT
Unsteady Hydromagnetic Flow of Radiating Fluid Past a Convectively Heated Vertical Plate with the Navier Slip (2014)
Publication Date: 2014-04-18
Description: This paper investigates the unsteady hydromagnetic-free convection of an incompressible electrical conducting Boussinesq’s radiating fluid past a moving vertical plate in an optically thin environment with the Navier slip, viscous dissipation, and Ohmic and Newtonian heating. The nonlinear partial differential equations governing the transient problem are obtained and tackled numerically using a semidiscretization finite difference method coupled with Runge-Kutta Fehlberg integration technique. Numerical data for the local skin friction coefficient and the Nusselt number have been tabulated for various values of parametric conditions. Graphical results for the fluid velocity, temperature, skin friction, and the Nusselt number are presented and discussed. The results indicate that the skin friction coefficient decreases while the heat transfer rate at the plate surface increases as the slip parameter and Newtonian heating increase.
Print ISSN: 1687-9120
Electronic ISSN: 1687-9139
Topics: Mathematics , Physics
Published by Hindawi
3.
PAPER CURRENT
Edelen’s dissipation potentials and the visco-plasticity of particulate media (2014)
Publication Date: 2014-04-18
Description: Abstract Following is an elaboration on D. G. B. Edelen’s (1972–1973) nonlinear generalization of the classical Rayleigh-Onsager dissipation potentials and the implications for the models of viscoplasticity. A brief derivation is given via standard vector calculus of Edelen’s potentials and the associated non-dissipative or “gyroscopic” forces and fluxes. It is also shown that certain extensions of Edelen’s formulae can be obtained by means of a recently proposed source-flux relation or “inverse divergence,” a generalization of the classical Gauss-Maxwell construct. The Legendre–Fenchel duality of Edelen’s potentials is explored, with important consequences for rate-independent friction or plasticity. The use of dissipation potentials serves to facilitate the development of viscoplastic constitutive equations, a point illustrated here by the special cases of Stokesian fluid-particle suspensions and granular media. In particular, we consider inhomogeneous systems with particle migration coupled to gradients in particle concentration, strain rate, and fabric. Employing a mixture-theoretic treatment of Stokesian suspensions, one is able to identify particle stress as the work conjugate of the global deformation of the particle phase. However, in contrast to past treatments, this stress is not assumed to be a privileged driving force for particle migration. A comparison is made with models based on extremal dissipation or entropy production. It is shown that such models yield the correct dissipative components of force or flux but generally fail to capture certain non-dissipative, but mechanically relevant components. The significance of Edelen’s gyroscopic forces and their relation to reactive constraints or other reversible couplings is touched upon. When gyroscopic terms are absent, one obtains a class of strongly dissipative or hyperdissipative materials whose quasi-static mechanics are governed by variational principles based on dissipation potential. This provides an interesting analog to elastostatic variational principles based on strain energy for hyperelastic materials and to the associated material instabilities arising from loss of convexity.
Print ISSN: 0001-5970
Electronic ISSN: 1619-6937
Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
Published by Springer
4.
PAPER CURRENT
The role of coffee agroforestry in the conservation of tree diversity and community composition of native forests in a Biosphere Reserve (2014)
Publication Date: 2014-04-18
Description: Publication date: 1 May 2014 Source:Agriculture, Ecosystems & Environment, Volume 189 Author(s): Vivian Valencia , Luis García-Barrios , Paige West , Eleanor J. Sterling , Shahid Naeem Agroforestry is considered a promising alternative to conventional agriculture that can both conserve biodiversity and support local livelihoods. Coffee agroforestry may be particularly important for sustaining trees of conservation concern and late-successional stage, but this possibility remains unclear. Here, we examined whether coffee agroforestry systems can serve as conservation reservoirs of tree species native to nearby forests. We compared tree diversity, composition and structure between coffee agroforests and forests in La Sepultura Biosphere Reserve in Chiapas, Mexico. We found that, although at the landscape level the full set of coffee agroforests appears to conserve comparable tree species richness to nearby native forests, the species composition that is being conserved is different. Coffee agroforests had a lower proportion of trees of conservation concern, a higher proportion of pioneer trees, were dominated by Inga spp., harbored lower tree species diversity at the plot level, and were composed of different tree species compared to native forests. We suggest that conservation practitioners and policy makers seeking to promote coffee agroforestry as a conservation strategy should consider how such agroforestry systems differ in species diversity and composition from the native forests of conservation interest. Further, promoting different coffee agroforest management strategies, such as discouraging the replacement of diverse agroforest canopies with Inga-dominated canopies, would help improve the conservation value of coffee agroforests through more sustainable practices.
Print ISSN: 0167-8809
Electronic ISSN: 1873-2305
Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Published by Elsevier
5.
PAPER CURRENT
Ecosystem Services in Urban Landscapes: Practical Applications and Governance Implications (2014)
Publication Date: 2014-04-18
Description: Abstract Urban landscapes are the everyday environment for the majority of the global population, and almost 80 % of the Europeans live in urban areas. The continuous growth in the number and size of urban areas along with an increasing demand on resources and energy poses great challenges for ensuring human welfare in cities while preventing an increasing loss of biodiversity. The understanding of how urban ecosystems function, provide goods and services for urban dwellers; and how they change and what allows and limits their performance can add to the understanding of ecosystem change and governance in general in an ever more human-dominated world. This Special Issue aims at bridging the knowledge gap among urbanization, demand creation, and provisioning of ecosystem services in urban regions on the one hand and schemes of urban governance and planning on the other.
Print ISSN: 0044-7447
Electronic ISSN: 1654-7209
Topics: Energy, Environment Protection, Nuclear Power Engineering
Published by Springer on behalf of The Royal Swedish Academy of Sciences.
6.
PAPER CURRENT
Normal Incidence of Sound Transmission Loss from Perforated Plates with Micro and Macro Size Holes (2014)
Publication Date: 2014-04-18
Description: This paper studies the sound transmission loss of perforated panels and investigates the effect ofthe hole diameter on the sound insulation performance under normal incidence of acoustic loading. The hole diameters are distinguished into micro (submillimeter) and macro (millimeter) sizes. In general, the transmission loss reduces as the perforation ratio is increased. However, by retaining the perforation ratio, it is found that the transmission loss increases as the hole diameter is reduced for a perforate with micro holes due to the effect of resistive part in the hole impedance, which iscontrary to the results for those with the macro holes. Both show similar trend at high frequency where the fluid behavior inside the hole is inertial. Simple analytical formulae for engineering purpose are provided. Validation of the models with measurement data also gives good agreement.
Print ISSN: 1687-6261
Electronic ISSN: 1687-627X
Topics: Physics
Published by Hindawi
7.
PAPER CURRENT
A Quantitative Review of Urban Ecosystem Service Assessments: Concepts, Models, and Implementation (2014)
Publication Date: 2014-04-18
Description: Abstract Although a number of comprehensive reviews have examined global ecosystem services (ES), few have focused on studies that assess urban ecosystem services (UES). Given that more than half of the world’s population lives in cities, understanding the dualism of the provision of and need for UES is of critical importance. Which UES are the focus of research, and what types of urban land use are examined? Are models or decision support systems used to assess the provision of UES? Are trade-offs considered? Do studies of UES engage stakeholders? To address these questions, we analyzed 217 papers derived from an ISI Web of Knowledge search using a set of standardized criteria. The results indicate that most UES studies have been undertaken in Europe, North America, and China, at city scale. Assessment methods involve bio-physical models, Geographical Information Systems, and valuation, but few study findings have been implemented as land use policy.
Print ISSN: 0044-7447
Electronic ISSN: 1654-7209
Topics: Energy, Environment Protection, Nuclear Power Engineering
Published by Springer on behalf of The Royal Swedish Academy of Sciences.
8.
PAPER CURRENT
A Modified Three-Level Average Linear-Implicit Finite Difference Method for the Rosenau-Burgers Equation (2014)
Publication Date: 2014-04-18
Description: We introduce a new technique, a three-level average linear-implicit finite difference method, for solving the Rosenau-Burgers equation. A second-order accuracy on both space and time numerical solution of the Rosenau-Burgers equation is obtained using a five-point stencil. We prove the existence and uniqueness of the numerical solution. Moreover, the convergence and stability of the numerical solution are also shown. The numerical results show that our method improves the accuracy of the solution significantly.
Print ISSN: 1687-9120
Electronic ISSN: 1687-9139
Topics: Mathematics , Physics
Published by Hindawi
9.
PAPER CURRENT
Adaptive Fractional Differentiation Harris Corner Detection Algorithm for Vision Measurement of Surface Roughness (2014)
Publication Date: 2014-04-18
Description: The Harris algorithm via fractional order derivative (the adaptive fractional differentiation Harris corner detection algorithm), which adaptively adjusts the fractal dimension parameter, has been investigated for an analysis of image processing relevant to surface roughness by vision measurements. The comparative experiments indicate that the algorithm allows the edge information in the high frequency areas to be enhanced, thus overcoming shortcomings. The algorithm permits real-time measurements of surface roughness to be performed with high precision, superior to the conventional Harris algorithm.
Print ISSN: 1687-9120
Electronic ISSN: 1687-9139
Topics: Mathematics , Physics
Published by Hindawi
10.
PAPER CURRENT
An airborne actinobacteria Nocardiopsis alba isolated from bioaerosol of a mushroom compost facility (2014)
Publication Date: 2014-04-18
Description: Abstract Actinobacteria are widely distributed in many environments and represent the most important trigger to the occupant respiratory health. Health complaints, including hypersensitivity pneumonitis of the workers, were recorded in a mushroom compost facility (MCF). The studies on the airborne bacteria were carried out to find a possible microbiological source of these symptoms. Culture analysis of compost bioaerosols collected in different location of the MCF was performed. An assessment of the indoor microbial exposure revealed bacterial flora of bioaerosol in the mushroom compost facility represented by Bacillus, Geobacillus, Micrococcus, Pseudomonas, Staphylococcus spp., and actinobacterial strain with white aerial mycelium. The thermotolerant actinobacterial strain of the same morphology was repeatedly isolated from many locations in MCF: air, compost sample, and solid surface in production hall. On the base of complex morphological, chemotaxonomic, and phylogenetic characteristics, the isolate has been classified as Nocardiopsis alba. Dominant position of N. alba in microbial environment of the mushroom compost facility may represent an indicator microorganism in compost bioaerosol. The bioavailability of N. alba in mushroom compost facility creates potential risk for the health of workers, and the protection of respiratory tract and/or skin is strongly recommended.
Print ISSN: 0393-5965
Electronic ISSN: 1573-3025
Topics: Biology
Published by Springer