745 research outputs found
Mixture Detectors for Improved Spectrum Sensing
No full textThe energy detector and the sphericity test are two widely used spectrum sensing techniques that utilize different properties of the signal received at the secondary user terminal. In this paper we use meta analysis to combine these two techniques and derive two novel mixture detectors that outperform both techniques. Since the spectrum sensing capability of the energy detector is limited by the uncertain knowledge of the noise power, first, we analyze the performance of the energy detector with estimated noise power. We derive analytical expressions for the false alarm and the detection probabilities when the secondary user terminal is equipped with multiple antennas. Next, we apply meta analysis to combine the outputs of the energy detector and the sphericity test to derive two mixture detectors, namely, Fisher's method and the weighted -transform method. Furthermore, we extend our analysis to consider cooperative spectrum sensing where multiple secondary user terminals cooperatively detect the presence of primary users. Based on the mixture detectors, we propose two new cooperative spectrum sensing techniques and derive simple analytical expressions for false alarm probabilities. Extensive numerical examples are used to illustrate the accuracy of our analysis and to highlight the performance gains obtained by the mixture detectors
The dissolution of gold colloids in aqueous thiosulfate solutions
No full textThe kinetics of the dissolution of gold and silver colloids in ammoniacal thiosulfate solutions has been studied using oxygen, copper(II) or oxygenated copper(II) as oxidants at pH 9 - 11 and temperature 22oC to 48oC. The effects of the concentration of the main reagents such as copper(II), ammonia and thiosulfate as well as various background reagents have been investigated. Gold and silver colloids have characteristic absorption peaks at 530 nm and 620 nm respectively. Thus, the extent of gold or silver dissolution in different lixiviant systems was monitored using an ultraviolet-visible spectrophotometer. A comparison of the behaviour of gold colloids and powders has also been made. The beneficial or detrimental effects of silver colloid, and background reagents such as silver nitrate, and sodium salts of nitrate, carbonate, sulfite, sulfate, trithionate, tetrathionate anions have also been investigated.
Experimental results show that the relative rates and the extent of gold colloid dissolution at 25ºC in different lixiviant systems in a given time interval are in the order: oxygen-cyanide > copper(II)-ammonia-thiosulfate ≈ oxygen-copper(II)- ammonia-thiosulfate > oxygen ammonia-thiosulfate ≥ oxygen-ammonia > copper(II) ammonia. The analysis of electrode potentials shows that Au(S2O3)23- is the predominant gold(I) species in the lixiviant solutions containing oxygen or copper(II) as oxidant and thiosulfate or mixed ammonia-thiosulfate as ligands. During the reaction of copper(II) with thiosulfate in ammoniacal solution without oxygen, the measured potential using a platinum electrode represent the redox couple Cu(NH3)n2+/Cu(S2O3)m1-2m (n = 4 or 3, m = 3 or 2) depending on the concentrations of thiosulfate and ammonia.
The initial dissolution rates of gold colloid by oxygen in copper-free solutions show a reaction order of 0.28 with respect to the concentration of dissolved oxygen, but independent of the concentration of ammonia and thiosulfate. The reaction activation energy of 25 kJ/mol in the temperature range 25°C to 48°C indicated a diffusion controlled reaction.
The initial dissolution rates of gold colloid by oxidation with copper(II) in oxygenfree solutions show reaction orders of 0.41, 0.49, 0.60, 0.15 and 0.20 with respect to the concentrations of copper(II), thiosulfate, ammonia, chloride and silver respectively. The presence of silve (I) or chloride ions enhances the rate of gold dissolution, indicating their involvement in the surface reaction, possibly by interfering with or preventing a passivating sulfur rich film on gold surface. An activation energy of 40-50 kJ/mol for the dissolution of gold by oxidation with copper(II) in the temperature range 22°C to 48°C suggests a mixed chemically/diffusion controlled reaction. The dissolution of gold by oxidation with copper(II) in oxygen-free solutions appears to be a result of the reaction between gold, thiosulfate ions and the mixed complex Cu(NH3)p(S2O3)0. The half order reactions support electrochemical mechanisms in some cases.
The initial dissolution rates of gold colloid, massive gold and gold-silver alloys by oxygenated copper(II) solutions also suggest a reaction that is first order with respect to copper(II) concentration. High oxygen concentration in solutions has a negative effect on the initial rate of gold dissolution and overall percentage of gold dissolution, indicating that oxygen affects the copper(II), copper(I) or sulfur species which in turn affects the gold dissolution. The surface reaction produces Au(NH3)(S2O3)- and Cu(NH3)p+. The mixed complexes Au(NH3)(S2O3)- and Cu(NH3)p+ re-equilibrate to the more stable complexes Au(S2O3)23- and Cu(S2O3)35- in solution.
The dissolution of gold powder by oxidation with copper(II) in oxygen-free solutions shows the same trends as that of gold colloid. The presence of silver(I) or chloride ions enhances the initial rate and percentage dissolution of gold colloid and powder. The dissolution kinetics of gold powder and colloid follow a shrinking sphere kinetic model in solutions of relatively low concentrations of thiosulfate and ammonia, with apparent rate constants being inversely proportional to particle radius.
The best system for dissolving gold based on the results of this work is the copper(II)-ammonia-thiosulfate solution in the absence of oxygen or in the presence of oxygen. In the absence of oxygen, copper(II) 1.5-4.5 mM, thiosulfate 20-50 mM, ammonia 120-300 mM and pH 9.3-10 are the best conditions. The presences of carbonate and sulfite have a significant negative effect on the dissolution of gold. The presence of sodium trithionate shows a beneficial effect in the first two hours, while sodium tetrathionate or lead nitrate have a small negative effect and sodium nitrate showed no effect on the dissolution of gold. Silver nitrate and sodium chloride also show beneficial effects. In the presence of oxygen, copper(II) 2.0-3.0 mM, thiosulfate 50 mM, ammonia 240 mM and pH 9.3-9.5 are the best conditions
The Impact of Channel Type on Spectrum Sensing
No full textIn this letter, we investigate the impact of channel correlation and line-of-sight (LOS) on the performance of spectrum sensing, focusing on energy detection (ED) with estimated noise power and the sphericity test (ST). We derive the expected value and variance of the test statistic for ED with estimated noise power, showing that detection probability decreases with channel correlation but increases with LOS propagation. For the ST, we show that detection improves with increased LOS, but the effects of correlation are complex. Depending on the system parameters correlation can improve or degrade detection performance. The analysis is corroborated by means of simulations for correlated Rayleigh, Ricean and ray-based channel models. Finally, we leverage these results to investigate the performance of the recently proposed mixture detector (MD)
Catering to Domain (Genomics) specific eResearch needs
No full textProviding eResearch capability and training catered to a specific domain such as
Genomics presents its own set of challenges and opportunities. The advancement of
sequencing technologies and decreasing cost is responsible in creating an avalanche of
genomics data across multiple sub-domains. This data deluge demands an
interdisciplinary approach to face the associated challenges such as data storage,
parallel and high-performance computing solutions for data analysis, scalability, security
and data integration. Ability to deliver solutions to these needs will result in converting
highly granular, unstructured genomics data into real scientific insights which will
accelerate the advances being made in genomics assisted precision medicine,
eukaryotic conservation programmes, etc. Also, implementing eResearch training tools
such as genomics virtual labs will assist beginners’ level bioinformaticians/computationalbiologists to acquire advance skills within an interactive environment which will assist
them in their search to understand the rules of life. ABOUT THE AUTHOR(S)Nooriyah Lohani
- A background in bioinformatics and past roles as a bioinformatician at Pacific Edge in
Dunedin and the Bioinformatics Institute at the University of Auckland has exposed me to
both the commercial and academic research spaces. Currently as NeSI’s Research
Communities Advisor, my aim is to help bring the right digital tools to meet researchers
needs.Dinindu Senanayake
- An Applications Support Specialist at NeSI with a particular interest in Genomics and
Bioinformatics. Joined NeSI following half a decade of research experience gained in the
field of Cancer Genetics, Chemical Genetics and Bioinformatics. </div
HPC for life sciences: handling the challenges posed by a domain that relies on big data
No full textThe advancement of sequencing technologies, proteomics, microscopy (High throughput
high content), etc. and decreasing cost is responsible in creating an avalanche of data across
multiple sub-domains that fall under life sciences. This data deluge demands an
interdisciplinary approach to face the associated challenges such as data storage, parallel
and high-performance computing solutions for data analysis, scalability, security and data
integration. Ability to deliver solutions to these needs will result in converting highly
granular, unstructured data into real scientific insights which will accelerate the advances
being made assisted precision medical treatment based on an individual’s genetic makeup,
developing drugs with minimum side effects, species conservation programmes, etc.New Zealand eScience Infrastructure (NeSI) is focused on delivering these tools that are
required by our researchers who might need a “huge” amount of memory to assemble a
large genome, simulate the Newtonian equations of motion in biochemical molecules like
proteins, nucleic acids in parallel, facilitate the ever increasing requirement of data storage
(from day to day to “Sensitive”) and deploying efficient methods for end-to-end data
transfers. Also, NeSI’s partnership with Genomics Aotearoa had been instrumental in
introducing training tools such as virtual machines and an extensive number of workshops
hosted on these machine which are proving to assist beginners’ level
bioinformaticians/computational biologists to acquire advance skills within a short period to
be used in their search to understand the rules of life.ABOUT THE AUTHOR(S) Dinindu Senanayake is an Applications Support Specialist at NeSI with a particular interest in Bioinformatics
and Computational Biology. Joined NeSI following half a decade of research
experience gained in the field of Cancer Genetics, Chemical Genetics and
Bioinformatics </div
The influence of Hall currents, plasma viscosity and electron inertia on magnetic reconnection solutions
No full textAbstract
This thesis examines magnetic reconnection in the solar corona. Magnetic reconnection is the only mechanism which allows the magnetic topology of magnetized plasmas to be changed. Many of the dynamic processes in the Sun's atmosphere are believed to be driven by magnetic reconnection and studying the behaviour of such phenomena is a key step to understanding the reconnection mechanism. In Chapters 1 to 3, we discuss the physical and mathematical framework on which current magnetohydrodynamic
reconnection models are based.
The aim of the thesis is to investigate theoretical models of magnetic reconnection using variety of analytic and numerical techniques within the theoretical frame work of magnetohydrodynamics (MHD).
In Chapter 4 we use a line-tied X-point collapse model for compressible plasmas to investigate the role of viscosity on the energy release mechanism. This model also provides the basis for the investigation of Chapter 5 which explores the impact of Hall currents in the transient X-point energy dissipation.
Chapter 6 is concerned with how reconnection is modified in the presence of generalized Ohm's law which includes both Hall current and electron inertia contributions. In contrast to the closed X-point collapse geometry adopted for compressible plasmas previously, we find it more convenient to explore this problem using an open incompressible geometry in which plasma is continually entering and exiting the reconnection region. Specially, we find the scaling of the Hall-MHD system size analytically, rather than numerically as in the X-point problem of Chapter 5. Chapter 7 summarizes the results of investigations in Chapters 4, 5 and 6
Methods for the automatic alignment of colour histograms
No full textColour provides important information in many image processing tasks such as object identification and
tracking. Different images of the same object frequently yield different colour values due to undesired
variations in lighting and the camera. In practice, controlling the source of these fluctuations is difficult,
uneconomical or even impossible in a particular imaging environment. This thesis is concerned with the
question of how to best align the corresponding clusters of colour histograms to reduce or remove the
effect of these undesired variations.
We introduce feature based histogram alignment (FBHA) algorithms that enable flexible alignment
transformations to be applied. The FBHA approach has three steps, 1) feature detection in the colour
histograms, 2) feature association and 3) feature alignment. We investigate the choices for these three
steps on two colour databases : 1) a structured and labeled database of RGB imagery acquired under controlled
camera, lighting and object variation and 2) grey-level video streams from an industrial inspection
application. The design and acquisition of the RGB image and grey-level video databases are a key contribution
of the thesis. The databases are used to quantitatively compare the FBHA approach against
existing methodologies and show it to be effective. FBHA is intended to provide a generic method for
aligning colour histograms, it only uses information from the histograms and therefore ignores spatial
information in the image. Spatial information and other context sensitive cues are deliberately avoided
to maintain the generic nature of the algorithm; by ignoring some of this important information we gain
useful insights into the performance limits of a colour alignment algorithm that works from the colour
histogram alone, this helps understand the limits of a generic approach to colour alignment
FIGURE 3 in The status of Myriangiaceae (Dothideomycetes)
No full textFIGURE 3. Ascostratum insigne (holotype). a–c. Herbarium material. d–f. Ascostromata on host surface. g–i. Cross section of ascostromata. j–l. Immature asci with distinct, short pedicel in j. m. Asci with ascospores. n–r. Ascospores. Scale bars: d = 1000 µm, e–f = 200 µm, g = 50 µm, h–i = 20 µm, j–r = 10 µm.Published as part of Dissanayake, Asha J., Jayawardena, Ruvishika S., Boonmee, Saranyaphat, Thambugala, Kasun M., Tian, Qing, Mapook, Ausana, Senanayake, Indunil C., Yan, Jiye, Li, Yan Mei, Li, Xinghong, Chukeatirote, Ekachai & Hyde, Kevin D., 2014, The status of Myriangiaceae (Dothideomycetes), pp. 219-237 in Phytotaxa 176 (1) on page 226, DOI: 10.11646/phytotaxa.176.1.22, http://zenodo.org/record/514434
Spread of the h-index for each manipulative and non-manipulative author (as absolute values) in the first simulation scenario.
No full text<p>For authors of similar seniority, the ‘manipulative’ author group has a clear advantage.</p
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