33,843 research outputs found
Delivery of broadband services to SubSaharan Africa via Nigerian communications satellite
Africa is the least wired continent in the world in terms of robust telecommunications infrastructure and systems to cater for its more than one billion people. African nations are mostly still in the early stages of Information Communications Technology (ICT) development as verified by the relatively low ICT Development Index (IDI) values of all countries in the African region. In developing nations, mobile broadband subscriptions and penetration between 2000-2009 was increasingly more popular than fixed broadband subscriptions. To achieve the goal of universal access, with rapid implementation of ICT infrastructure to complement the sparsely distributed terrestrial networks in the hinterlands and leveraging the adequate submarine cables along the African coastline, African nations and their stakeholders are promoting and implementing Communication Satellite systems, particularly in Nigeria, to help bridge the digital hiatus. This paper examines the effectiveness of communication satellites in delivering broadband-based services
Thermodynamical Properties of Hall Systems
We study quantum Hall effect within the framework of a newly proposed
approach, which captures the principal results of some proposals. This can be
established by considering a system of particles living on the non-commutative
plane in the presence of an electromagnetic field and quantum statistical
mechanically investigate its basic features. Solving the eigenvalue equation,
we analytically derive the energy levels and the corresponding wavefunctions.
These will be used, at low temperature and weak electric field, to determine
the thermodynamical potential \Omega^{nc} and related physical quantities.
Varying \Omega^{nc} with respect to the non-commutativity parameter \theta, we
define a new function that can be interpreted as a \Omega^{nc} density.
Evaluating the particle number, we show that the Hall conductivity of the
system is \theta-dependent. This allows us to make contact with quantum Hall
effect by offering different interpretations. We study the high temperature
regime and discuss the magnetism of the system. We finally show that at
\theta=2l_B^2, the system is sharing some common features with the Laughlin
theory.Comment: 20 pages, misprints correcte
Solidification processing of alloys using an applied electric field
A method is provided for obtaining an alloy having an ordered microstructure which comprises the steps of heating the central portion of the alloy under uniform temperature so that it enters a liquid phase while the outer portions remain solid, applying a constant electric current through the alloy during the heating step, and solidifying the liquid central portion of the alloy by subjecting it to a temperature-gradient zone so that cooling occurs in a directional manner and at a given rate of speed while maintaining the application of the constant electric current through the alloy. The method of the present invention produces an alloy having superior characteristics such as reduced segregation. After subsequent precipitation by heat-treatment, the alloys produced by the present invention will have excellent strength and high-temperature resistance
Memory-Controlled Diffusion
Memory effects require for their incorporation into random-walk models an
extension of the conventional equations. The linear Fokker-Planck equation for
the probability density is generalized to include non-linear and
non-local spatial-temporal memory effects. The realization of the memory
kernels are restricted due the conservation of the basic quantity . A
general criteria is given for the existence of stationary solutions. In case
the memory kernel depends on polynomially the transport is prevented. Owing
to the delay effects a finite amount of particles remains localized and the
further transport is terminated. For diffusion with non-linear memory effects
we find an exact solution in the long-time limit. Although the mean square
displacement shows diffusive behavior, higher order cumulants exhibits
differences to diffusion and they depend on the memory strength
Analysis of the Relaxation Period of a Multivibrator
An improved mathematical analysis of the relaxation periods of a free
running symmetrical multivibrator has been made showing expressions for different electrode potentials and time periods. The theoretical values obtained have been compared with experimental data, part of which is also presented here
Multiscale approaches to high efficiency photovoltaics
While renewable energies are achieving parity around the globe, efforts to
reach higher solar cell efficiencies becomes ever more difficult as they
approach the limiting efficiency. The so-called third generation concepts
attempt to break this limit through a combination of novel physical processes
and new materials and concepts in organic and inorganic systems. Some examples
of semi-empirical modelling in the field are reviewed, in particular for
multispectral solar cells on silicon (french ANR project MULTISOLSI). Their
achievements are outlined, and the limits of these approaches shown. This
introduces the main topic of this contribution, which is the use of multiscale
experimental and theoretical techniques to go beyond the semi-empirical
understanding of these systems. This approach has already led to great advances
at modelling which have led to modelling software which is widely known. Yet a
survey of the topic reveals a fragmentation of efforts across disciplines,
firstly, such as organic and inorganic fields, but also between the high
efficiency concepts such as hot carrier cells and intermediate band concepts.
We show how this obstacle to the resolution of practical research obstacles may
be lifted by inter-disciplinary cooperation across length scales, and across
experimental and theoretical fields, and finally across materials systems. We
present a European COST Action MultiscaleSolar kicking off in early 2015 which
brings together experimental and theoretical partners in order to develop
multiscale research in organic and inorganic materials. The goal of this
defragmentation and interdisciplinary collaboration is to develop understanding
across length scales which will enable the full potential of third generation
concepts to be evaluated in practise, for societal and industrial applications.Comment: Draft paper accompanying a plenary presentation to the World
Renewable Energy Conference WREC 2015, June 2015, Bucharest. In press (IOP
Optimization of an Alkylpolyglucoside-Based Dishwashing Detergent Formulation.
The aim of this work was to formulate and optimize the washing performance of an alkylpolyglucoside-based dishwashing detergent. The liquid detergent was formulated with five ingredients of commercial origin: anionic (linear sodium alkylbenzenesulfonate and sodium laurylethersulfate), nonionic (C12–C14 alkylpolyglucoside) and zwitterionic (a fatty acid amide derivative with a betaine structure) surfactants, and NaCl for viscosity control. In addition to the plate test, other properties were investigated including ‘‘cloud point’’, viscosity, and emulsion stability. Statistical analysis software was used to generate a central composite experimental design. Then, a second order design and analysis of experiments approach, known as the Response Surface Methodology, was set up to investigate the effects of the five components of the formulation on the studied properties in the region covering plausible component ranges. The method proved to be efficient for locating the domains of concentrations where the desired properties were met
A proposal for testing Quantum Gravity in the lab
Attempts to formulate a quantum theory of gravitation are collectively known
as {\it quantum gravity}. Various approaches to quantum gravity such as string
theory and loop quantum gravity, as well as black hole physics and doubly
special relativity theories predict a minimum measurable length, or a maximum
observable momentum, and related modifications of the Heisenberg Uncertainty
Principle to a so-called generalized uncertainty principle (GUP). We have
proposed a GUP consistent with string theory, black hole physics and doubly
special relativity theories and have showed that this modifies all quantum
mechanical Hamiltonians. When applied to an elementary particle, it suggests
that the space that confines it must be quantized, and in fact that all
measurable lengths are quantized in units of a fundamental length (which can be
the Planck length). On the one hand, this may signal the breakdown of the
spacetime continuum picture near that scale, and on the other hand, it can
predict an upper bound on the quantum gravity parameter in the GUP, from
current observations. Furthermore, such fundamental discreteness of space may
have observable consequences at length scales much larger than the Planck
scale. Because this influences all the quantum Hamiltonians in an universal
way, it predicts quantum gravity corrections to various quantum phenomena.
Therefore, in the present work we compute these corrections to the Lamb shift,
simple harmonic oscillator, Landau levels, and the tunneling current in a
scanning tunneling microscope.Comment: v1: 10 pages, REVTeX 4, no figures; v2: minor typos corrected and a
reference added. arXiv admin note: has substantial overlap with
arXiv:0906.5396 , published in a different journa
Fire Safety in High-Rise Buildings: Is the Stay-Put Tactic a Misjudgement or Magnificent Strategy?
Historically, fire incidents in high-rise buildings reveal that Fire and Rescue Services frequently rely on the stay-put tactic (i.e., occupants of high-rise buildings should remain in their apartments) during an inferno. Recent fire occurrences in high-rise buildings reveal that there are two opposing viewpoints on the stay-put tactic. First, the understanding that the stay-put tactic is a beneficial practice used to protect, control, and facilitate smooth evacuation of occupants during fire incidents. Second, the argument that the stay-put tactic is a misjudgement and futile strategy that leads to fatalities, particularly in high-rise buildings. The aim of this study was to provide awareness and understanding of fire and rescue services use of the stay-put tactic in high-rise buildings. We attempted to answer the questions: is the stay-put tactic a misjudgement or magnificent strategy? The study adopted phenomenological research strategies with various focus groups consisting of seasoned firefighters and survivors with first-hand accounts of stay-put instructions in high-rise buildings. The study also scrutinised three case studies of fire incidents in high-rise buildings in two countries. The study revealed that the stay-put tactic is obsolete; with the potential to cause catastrophic misjudgement, mostly during conflagrations in high-rise buildings. There is a need to advance research on the use of artificial intelligence communication systems and infrared image detectors camera to enhance quick and smooth fire evacuation in high-rise buildings
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