2,134 research outputs found
Spectrum occupancy measurement: a case for cognitive radio network in lagos, Nigeria
The proliferation in technologies and with the recent introduction of new paradigm for wireless communication, the demand for wireless devices has increased drastically in recent years. This therefore, posed a major threat on the available frequency spectrum and as a result, an efficient method for the utilisation of the limited frequency spectrum is required. As the scarcity of frequency spectrum is a major problem in the telecommunication field, cognitive radio technology has been identified as a promising solution to this problem. Cognitive radio allows the opportunistic access of licensed bands by unlicensed users without causing harmful interference to the licensed user. There is a need to evaluate the utilisation level of the licensed bands in order to identify which frequency bands can be used for cognitive radio implementation. Nevertheless, spectrum measurement campaigns have been conducted mostly in USA and a few other locations around the world. In this paper, the results of the measurement campaign conducted in Ikeja, the capital city of Lagos, Nigeria covering the range of frequency 700 MHz up to 2.2 GHz is presented. The measurement results are analysed and compared to the frequency allocation table published by the Nigerian Communications Commission. The results obtained show that the frequency spectrum is underutilised and therefore a significant amount of spectrum is available for the future implementation of cognitive radio networks
Mini-DSAEK for Macro Corneal Perforations
PURPOSE: We present a technique that preserves good vision in paracentral macroperforations and avoids challenges of tectonic lamellar or penetrating keratoplasty in eyes with poor visual potential. METHOD: A wet laboratory was implemented for mini-Descemet stripping endothelial keratoplasty to seal macroperforations ab interno. This included a suture support technique designed to prevent graft herniation. We also present 3 cases who were treated successfully with this technique. RESULTS: The laboratory test confirmed that mini-Descemet stripping endothelial keratoplasty can successfully seal macroperforations without the need of large incisions. The minidisc is introduced through the perforation, and a double mattress suture prevents graft herniation. The technique allowed us to preserve 20/15 unaided vision in a case with paracentral macroperforation. It also restored eye globe integrity and achieved long-term stability in 2 cases with limbal stem-cell deficiency. CONCLUSIONS: Mini-Descemet stripping-automated endothelial keratoplasty technique can be an alternative approach to avoid poor visual outcomes of tectonic keratoplasty in paracentral perforations. It also offers host tissue preservation in eyes with high risk of rejection for tectonic grafts
Robots, computer algebra and eight connected components
Answering connectivity queries in semi-algebraic sets is a long-standing and
challenging computational issue with applications in robotics, in particular
for the analysis of kinematic singularities. One task there is to compute the
number of connected components of the complementary of the singularities of the
kinematic map. Another task is to design a continuous path joining two given
points lying in the same connected component of such a set. In this paper, we
push forward the current capabilities of computer algebra to obtain
computer-aided proofs of the analysis of the kinematic singularities of various
robots used in industry. We first show how to combine mathematical reasoning
with easy symbolic computations to study the kinematic singularities of an
infinite family (depending on paramaters) modelled by the UR-series produced by
the company ``Universal Robots''. Next, we compute roadmaps (which are curves
used to answer connectivity queries) for this family of robots. We design an
algorithm for ``solving'' positive dimensional polynomial system depending on
parameters. The meaning of solving here means partitioning the parameter's
space into semi-algebraic components over which the number of connected
components of the semi-algebraic set defined by the input system is invariant.
Practical experiments confirm our computer-aided proof and show that such an
algorithm can already be used to analyze the kinematic singularities of the
UR-series family. The number of connected components of the complementary of
the kinematic singularities of generic robots in this family is
Chern-Simons Solitons, Toda Theories and the Chiral Model
The two-dimensional self-dual Chern--Simons equations are equivalent to the
conditions for static, zero-energy solutions of the -dimensional gauged
nonlinear Schr\"odinger equation with Chern--Simons matter-gauge dynamics. In
this paper we classify all finite charge solutions by first
transforming the self-dual Chern--Simons equations into the two-dimensional
chiral model (or harmonic map) equations, and then using the Uhlenbeck--Wood
classification of harmonic maps into the unitary groups. This construction also
leads to a new relationship between the Toda and chiral model
solutions
Space Climate Manifestation in Earth Prices - from Medieval England Up to Modern Usa
In this study we continue to search for possible manifestations of space
weather influence on prices of agricultural products and consumables. We note
that the connection between solar activity and prices is based on the causal
chain that includes several nonlinear transition elements. These non-linear
elements are characterized by threshold sensitivity to external parameters and
lead to very inhomogeneous local sensitivity of the price to space weather
conditions. It is noted that "soft type" models are the most adequate for
description of this class of connections. Two main observational effects
suitable for testing causal connections of this type of sensitivity are
considered: burst-like price reactions on changes in solar activity and price
asymmetry for selected phases of the sunspot cycle. The connection, discovered
earlier for wheat prices of Medieval England, is examined in this work on the
basis of another 700-year data set of consumable prices in England. Using the
same technique as in the previous part of our work (Pistilnik and Yom Din 2004)
we show that statistical parameters of the interval distributions for price
bursts of consumables basket and for sunspot minimum states are similar one to
another, like it was reported earlier for wheat price bursts. Possible sources
of these consistencies between three different multiyear samples are discussed.
For search of possible manifestations of the "space weather - wheat market"
connection in modern time, we analyze dynamics of wheat prices in the USA in
the twentieth century. We show that the wheat prices revealed a maximum/minimum
price asymmetry consistent with the phases of the sunspot cycle. We discuss
possible explanations of this observed asymmetry, unexpected under conditions
of globalization of the modern wheat market.Comment: First International Symposium on Space Climate: Direct and Indirect
Observations of Long-Term Solar Activity, 20-23 June 2004, Oulu, Finlan
CP^{N-1} models and the Quantized 2D Black Holes
We have examined the coupled system of the dilaton gravity and the
theory known as a model of the confinement of massive scalar quarks. After the
quantization of the system, we could see the quantum effect of the gravitation
on the coupling constant of model and how the coupling constant of
dynamically induced gauge field changes near the black hole configuration.Comment: 12 pages, Late
A Special Homotopy Continuation Method For A Class of Polynomial Systems
A special homotopy continuation method, as a combination of the polyhedral
homotopy and the linear product homotopy, is proposed for computing all the
isolated solutions to a special class of polynomial systems. The root number
bound of this method is between the total degree bound and the mixed volume
bound and can be easily computed. The new algorithm has been implemented as a
program called LPH using C++. Our experiments show its efficiency compared to
the polyhedral or other homotopies on such systems. As an application, the
algorithm can be used to find witness points on each connected component of a
real variety
Manganese pigmented anodized copper as solar selective absorber
The study concerns the optical and structural properties of layers obtained by a new efficient surface treatment totally free of chromium species. The process is made up of an anodic oxidation of copper in an alkaline solution followed by an alkaline potassium permanganate dipping post-treatment. Coatings, obtained at the lab and pilot scales, are stable up to 220 °C in air and vacuum, present low emissivity (0.14 at 70 °C) and high solar absorptivity (0.96), i.e. a suitable thermal efficiency (0.84 at 70 °C)
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Effect of different storage conditions on analytical and sensory quality of thermally processed milk based germinated Foxtail millet porridge
Foxtail millet porridge was prepared using germinated grains and milk and was evaluated for its storage stability after thermal processing at Ultra High Temperatures (UHT) of 142 oC for 5 s and Retort processing temperatures of 121.5 oC for 15 min. Various physical, chemical and microbial changes of the porridge were studied for a storage period of 180 days at 25 ± 1 oC. Using consumer perception and survival analysis, the predicted shelf life of the UHT treated and retort processed foxtail millet porridge samples stored at 25 ± 1 oC was found to be 186 ± 9 days and 245 ± 15 days, respectively. Also, data from consumer liking, profiling, physical, chemical and microbial parameters showed significant changes (p < 0.05) in the thermally treated packaged porridge samples over time. As the consumer overall acceptability decreased, the detection of positive attributes (Thick and uniformly coloured texture and appearance; grainy mouth texture; caramel taste and aroma) in the porridge decreased, while the detection of negative attributes (Uneven, decoloured, and curdled texture and appearance; sticky mouth texture; cooked, sour and off smell; cooked, sour and off taste) increased. The present study could establish a significant difference (p < 0.05) in the storage induced properties of UHT and retort processed porridge samples. The analytical evaluation of foxtail millet porridge found that UHT treated porridge was better in quality, but consumers preferred retort processed porridge
Acesso ao desempenho de irrigação na cultura da mangueira na região semi-árida do Nordeste do Brasil.
Parâmetros hídricos foram estimados em um cultivo comercial de mangueira durante dois ciclos produtivos. A evapotranspiração atual ( ET) foi obtida pelo método das correlações turbulentas, enquanto para a de referência ( ET0), a equação de Penman Monteith (FAO 56) foi aplicada. O valor acumulado médio de ET para os dois ciclos foi de 1333 mm, correspondendo a uma taxa diária de 3,5 mm dia 1 e coeficientes de cultura baseados na evapotranspiração ( Kc) e transpiração ( Kcb) de 0,87 e 0,78, respectivamente. A fração média de depleção de água ( FD) no solo foi de 0,80 e o déficit hídrico médio ( DH) médio foi de 118 mm, representando em geral um bom desempenho de irrigação. A produtividade de água ( PA) foi em torno de 4.5, 3,4 e 5 kg m 3 quando baseada na irrigação, evapotranspiração e transpiração, respectivamente. Os valores monetários correspondentes foram 4,60, 3,50 e 5,20 US$ m 3, o que indicou um elevado rendimento com o cultivo irrigado da cultura da mangueira na região semiárida do Brasil
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