23,197 research outputs found
Quantum interference in deformed carbon nanotube waveguides
Quantum interference (QI) in two types of deformed carbon nanotubes (CNTs),
i.e., axially stretched and AFM tip-deformed CNTs, has been investigated by the
pi-electron only and four-orbital tight-binding (TB) method. It is found that
the rapid conductance oscillation (RCO) period is very sensitive to the applied
strains, and decreases in an inverse proportion to the deformation degree,
which could be used as a powerful experimental tool to detect precisely the
deformation degree of the deformed CNTs. Also, the sigma-pi coupling effect is
found to be negligible under axially stretched strain, while it works on the
transport properties of the tip-deformed CNTs.Comment: 14 pages and 5 figure
Felix Alexandrovich Berezin and his work
This is a survey of Berezin's work focused on three topics: representation
theory, general concept of quantization, and supermathematics.Comment: LaTeX, 27 page
The Average Temperature of Energy Piles
The geotechnical design of energy piles requires confirmation that the foundations can continue to carry safely the required load from the overlying structure and that no detrimental effects from the additional imposed temperature changes will occur. These additional design checks require assumptions to be made about the temperature changes within the pile. However, there is no universal approach for determining these, and routine application of over-conservative pile temperatures can lead to unrealistically adverse geotechnical design scenarios. This paper considers how the average temperature of a pile can be determined based on the analysis steps already carried out for the thermal design. The aim is to be able use the calculated fluid temperatures, along with readily available pile and ground parameters, to provide better assessments of the actual pile temperature so that the outputs of the geotechnical design can be improved. Two dimensional numerical simulations are used to determine the average pile temperature for different pipe, pile and concrete properties. The results of the simulations are compared with analytical approaches, allowing these to be validated for use on a routine basis. It is shown that the temperature of the center of the pile, which can be determined easily by analytical methods, can be used as a proxy for the average pile temperature
Optimal Design Approach of Solar Powered Rural Water Distribution Systems in Developing Countries
This is the author accepted manuscript.In many rural parts of the developing world reliable access to clean water and electrical power is constrained. In this
study, methods of integrating estimations of power outputs from solar photovoltaic arrays into gravity-fed water distribution
network modelling are investigated. The effects of powering a rural water distribution system that is replenished with groundwater
pumps that use solar power, and the effect of this on other network design decisions, are investigated. A rural community of an
estimated 2,800 people with 28 standpipes from a borehole was chosen to develop the optimisations. The water storage tank and
pipework were the focus on the water distribution system. EPANET and generic algorithms were used to run network optimisation
simulations of: water tank location, elevation and volume; pipe diameter and configuration; and optimal system design in terms of
cost. Different scenarios were included producing supply, demand and required water storage curves, which could have practical
application for rural water distribution system design. Indicative costs for theoretical water distribution networks for rural
communities in The Gambia were generated
Error analysis of the thermal cell for soil thermal conductivity measurement
Soil thermal conductivity is an important factor in the design of energy foundations and other ground heat exchanger systems. Laboratory tests in a thermal cell are often used to determine the thermal conductivity of soil specimens. Two interpretation methods have been suggested. Analysis can be based on the assumption of one-directional heat flow and the thermal conductivity calculated using Fourier's law. Alternatively the lumped capacitance method can be employed, using results generated as a specimen cools. In this study, six samples of London Clay were tested using a thermal cell. A finite-element model of the tests was then used to determine the validity of the assumptions made in analysis. The model showed substantial heat loss through the sides of the specimens, which would have a significant impact on the calculated thermal conductivity. The conditions required for the lumped capacitance method to be valid were also found not to be met. Consequently neither analysis method is recommended. A better approach would be to pursue apparatus with fewer heat losses or transient testing techniques
An Integrated Optimal Approach for Solar Powered Rural Water Distribution Systems in the Gambia
This is the final version. Available on open access from Scientific Research Publishing via the DOI in this recordIn the Gambia and across sub-Saharan Africa, reliable access to clean water and electrical power is constrained. As many rural water supply systems are already built, enhanced understanding of efficiencies and optimisation is required. Here, methods of integrating estimations of power outputs from solar photovoltaic arrays into gravity-fed water distribution network modelling are investigated. The effects of powering a rural water distribution system that is replenished with groundwater pumps that use solar power are investigated, along with the effect of this on other network design decisions. The water storage tank and pipework of a rural community with an estimated 2800 people and 28 standpipes from a borehole was selected. EPANET modelling software and genetic algorithms were used to run network optimisation simulations of: water tank location, elevation and volume; pipe diameter and configuration; and optimal system design in terms of cost. Different scenarios included producing supply, demand and required water storage curves, which could have practical application for rural water distribution system design. Indicative costs for theoretical water distribution networks will be useful for decision makers and planners
Giant urinary bladder calculus: Case report
A vertical calculus weighing more than 100 g is categorised as a giant urinary bladder stone. Giant urinary bladder stones are very rare and very few cases have been reported in English literature and only one case from Africa. This is a case report of a patient with a giant urinary bladder calculus presenting as a rectal tumour. The stone was removed by open cystolithotomy. Possible etiological factors and imaging modalities are discussed
Fokker-Planck equation with variable diffusion coefficient in the Stratonovich approach
We consider the Langevin equation with multiplicative noise term which
depends on time and space. The corresponding Fokker-Planck equation in
Stratonovich approach is investigated. Its formal solution is obtained for an
arbitrary multiplicative noise term given by , and the
behaviors of probability distributions, for some specific functions of %
, are analyzed. In particular, for , the physical
solutions for the probability distribution in the Ito, Stratonovich and
postpoint discretization approaches can be obtained and analyzed.Comment: 6 pages in LATEX cod
Gaussian Effective Potential and the Coleman's normal-ordering Prescription : the Functional Integral Formalism
For a class of system, the potential of whose Bosonic Hamiltonian has a
Fourier representation in the sense of tempered distributions, we calculate the
Gaussian effective potential within the framework of functional integral
formalism. We show that the Coleman's normal-ordering prescription can be
formally generalized to the functional integral formalism.Comment: 6 pages, revtex; With derivation details and an example added. To
appear in J. Phys.
Structural and electronic properties of the metal-metal intramolecular junctions of single-walled carbon nanotubes
Several intramolecular junctions (IMJs) connecting two metallic (11, 8) and
(9, 6) carbon nanotubes along their common axis have been realized by using a
layer-divided technique to the nanotubes and introducing the topological
defects. Atomic structure of each IMJ configuration is optimized with a
combination of density-functional theory (DFT) and the universal force field
(UFF) method, based upon which a four-orbital tight-binding calculation is made
on its electronic properties. Different topological defect structures and their
distributions on the IMJ interfaces have been found, showing decisive effects
on the localized density of states, while the sigma-pi coupling effect is
negligible near Fermi energy (EF). Finally, a new IMJ model has been proposed,
which probably reflects a real atomic structure of the M-M IMJ observed in the
experiment [Science 291, 97 (2001)].Comment: 11 pages and 3 figure
- …