Optimising the Structure of Metal-Insulator-Metal Diodes for Rectenna Applications

The work in this thesis investigates the design and fabrication of metal-insulator-metal (MIM) diodes using an ultrathin organic insulator. The organic insulating layer was found to be compact, highly conformal, and uniform, effectively overcoming the main design challenge in MIM diodes. The fabricated diodes have strong nonlinear current-voltage characteristics with a zero-bias curvature coefficient and a voltage responsivity among the best values reported in the available literature. The fabrication process is simple and carried out at low temperature, which is cost effective, and can potentially be ported to large-area roll-to-roll manufacturing. An encapsulation method to prevent MIM junctions’ degradation has also been developed. Following the successful production of these MIM devices on a rigid substrate, with the fabrication only requiring low-temperature processing, the diodes were successfully fabricated on a flexible substrate with results similar to those fabricated on a rigid substrate. The flexible substrate diodes show no significant degradation in performance when stressed in a one-off bending experiment, although extreme mechanical stress testing does produce some loss in quality. Also, an elegant method for matching the impedance of an antenna to that of a MIM diode was successfully developed, for optimal external conversion efficiency where the diodes are used in a rectenna device. The responsivity of the impedance-matched rectenna is approaching an order of magnitude higher than that of a control device without a matching network. The fabrication, electrical characterisation and physical analysis of both the MIM diodes and rectennas are discussed in detail in this thesis

CO 2 Migration Monitoring Methodology in the Shallow Subsurface: Lessons Learned From the CO 2 FIELDLAB Project

International audienceA CO 2 migration field laboratory for testing of monitoring methods has been established in the glaciofluvial-glaciomarine Holocene deposits of the Svelvik ridge, near Oslo. A shallow CO 2 injection experiment was conducted in September 2011 in which approximately 1700 kg of CO 2 was injected at 18 m depth below surface. The objectives of this experiment were to (i) detect and, where possible, quantify migrated CO 2 concentrations, (ii) evaluate the sensitivity of the monitoring tools and (iii) study the impact of the vadose zone on measurements. This paper describes the injection, discusses the joint interpretation of the results and suggests some recommendations for further work

Electrochemical neasurement of crevice corrosion of type AISI 304 stainless steel

Crevice corrosion is a form of galvanic corrosion that occurs when a metal is exposed to different environments. This occurs when the oxygen within the crevice gets depleted, thus acting as the anodic site for metal dissolution reaction. The anodic site thus encourages the migration of Cl- ions into the crevice leading to the development of an aggressive local solution. The acidic conditions present in the crevice reaches a critical crevice solution composition and results in the loss of stability of the passive film which further leads to a rapid breakdown of these films on the metal thus indicating the onset of active corrosion. In this research, it is hypothesized that the onset of crevice corrosion can be detected by measuring the galvanic coupling current between electrodes in a crevice and an external metal surface composed of the same material as the electrodes. To prove this hypothesis an engineered crevice was designed to measure IR controlled crevice currents along the crevice length of AISI 304 stainless steel immersed in a 0.5 M solution and a 1 M NaCl solution. Varying crevice openings were used to determine the effect of crevice gap (G) on the initiation of crevice corrosion and the position of the accelerated attack within the crevice. Multiplexed corrosion potential measurement and galvanic corrosion measurement techniques were used to measure the change in the open circuit potential (OCP) and the galvanic current for the four channels along the crevice length of the galvanic couple. The results obtained from the MGC test for the 100 µm crevice width immersed in 0.5 M NaCl solution showed good results with high anodic current at approximately 1 cm from the crevice mouth. This finding was in close agreement with the peak pH value observed at the position closest to the crevice mouth in the work of Alavi and Cottis (1987) and the model prediction of Kennell et al. 2009. However, for test samples with crevice width ≥ 200 µm, there was no initiation of crevice corrosion and the results obtained were discarded. The Linear polarization resistance scan and Potentiodynamic polarization scan carried out along the crevice to measure the polarization resistance, Rp , and to obtain the region of passivity along an AISI 304 SS crevice did not yield good results. Low corrosion rate in the range of 0.06 mm/yr was calculated for the AISI 304 stainless steel crevice

Speeding-up Evolutionary Algorithms to solve Black-Box Optimization Problems

Population-based evolutionary algorithms are often considered when approaching computationally expensive black-box optimization problems. They employ a selection mechanism to choose the best solutions from a given population after comparing their objective values, which are then used to generate the next population. This iterative process explores the solution space efficiently, leading to improved solutions over time. However, these algorithms require a large number of evaluations to provide a quality solution, which might be computationally expensive when the evaluation cost is high. In some cases, it is possible to replace the original objective function with a less accurate approximation of lower cost. This introduces a trade-off between the evaluation cost and its accuracy. In this paper, we propose a technique capable of choosing an appropriate approximate function cost during the execution of the optimization algorithm. The proposal finds the minimum evaluation cost at which the solutions are still properly ranked, and consequently, more evaluations can be computed in the same amount of time with minimal accuracy loss. An experimental section on four very different problems reveals that the proposed approach can reach the same objective value in less than half of the time in certain cases

Assessing the Impact of Boko Haram's Terrorist Activities in the North East Region of Nigeria

This paper examined the impact Boko Haram in Northeast with special reference to the Lake Chad Basin (LCB). It will focus on the growing climate of insecurity in the region owing to the emergence of terrorism across the country particularly in the Northeast geopolitical zone. The analytical foundations was built upon the meaning of security, insecurity, tensions in the Northeast making reference to (LCB), the impacts on socio-political and economic relations among the occupants of the region such as high rate of death, unemployment, poverty as well as malnutrition in the North East Nigeria. It will proceed to the causes and the sustaining factors driving the insecurity in the region, the difficulties and failure facing Nigerian government to eliminate the Boko-Haram. The work uses secondary sources of data collection such as journal articles, newspaper, magazine, internet materials, books and others. This paper applied social identity and structural functionalism theories to better explain and analyze factors that aided the terrorist group. The paper discovered that the reason for the continuous attack of the Northeast region by the Bokoharam sect includes religious indoctrination, existence of porous border etc. the paper recommend that government should provide adequate border security and that there should be a campaign for the de orientation of religious radicalism in the region

Human Health Risk Assessment of PAHs in Fish and Shellfish from Amariaria Community, Bonny River, Nigeria

The concentration of polycyclic aromatic hydrocarbons (PAHs) in Fish (Mullet fish-Mugil cephalus) and Shellfish (Tiger prawn-Penaeus Monodon and crab-Uca tangeri) samples from fishing areas in Amariaria Community, downstream of Bonny River, Southern Nigeria, were assessed to determine possible human health risk associated with consumption. Mean levels (mg/kg) of total PAHs ranged from 0.059 to 0.126 in fish, 0.015 to 0.106 in prawn and 0.057 to 0.063 in crab. A considerable predominance of the 3 and 4-rings PAHs in all the matrices was observed with benzo (a) anthracene dominating in all three species. Estimated daily intake (EDI) of PAHs through consumption of fish ranged from 0 to 0.0005 mg/kg/day, for prawn, 0 to 0.0002 mg/kg/day and for crab, 0 to 0.0002 mg/kg/day. EDI values were, however, lower than the reference dose (RfD) indicating low risk from consumption. Results of the estimated excess cancer risk (ECR) for Benzo (a) anthracene in fish, however, suggests that lifetime exposure to Benzo (a) anthracene through fish consumption would result in cancer risk

Principals’ management practices and organizational effectiveness of teachers in public secondary schools: A quantitative assessment

Introduction: Past studies have assessed widely the teachers' involvement in school-based decision-making. However, some studies have associated it with subject choices and teacher variables. Purpose: The thrust of this study was to determine the relationship between management practices and organizational effectiveness of teachers in public secondary schools. Methodology: The research was conducted in Calabar South Local Government Area of Cross River State, Nigeria. To give direction to this study, three hypotheses arising from the three specific purposes of the study were formulated. The correlation research design was adopted in this study. The study conducted a census on the entire population of 431 public secondary school teachers. The instrument for data collection was titled “Management Practices and Organizational Effectiveness of Teachers Questionnaire (MPOETQ)”. The null hypotheses formulated for the study were tested at the .05 level of significance using Pearson Product Moment Correlation. Results: It was found that principals' communication, motivation and participatory decision-making practices had a significant and positive relationship with the organizational effectiveness of teachers in terms of punctuality, completion of scheme of work/diary, preparation of lesson plans, classroom management, lesson delivery, assessment of students, administration of examinations, involvement in PTA, involvement in extra-curricular activities and preparation/issuance of terminal results to students respectively. Recommendations/Classroom Implications: Based on these findings, it was recommended that school principals, as well as the government, should ensure that there is an effective display of situational management practices where a situation in the school system should warrant the application of management practice that suits such a situation

On the Fair Comparison of Optimization Algorithms in Different Machines

An experimental comparison of two or more optimization algorithms requires the same computational resources to be assigned to each algorithm. When a maximum runtime is set as the stopping criterion, all algorithms need to be executed in the same machine if they are to use the same resources. Unfortunately, the implementation code of the algorithms is not always available, which means that running the algorithms to be compared in the same machine is not always possible. And even if they are available, some optimization algorithms might be costly to run, such as training large neural-networks in the cloud. In this paper, we consider the following problem: how do we compare the performance of a new optimization algorithm B with a known algorithm A in the literature if we only have the results (the objective values) and the runtime in each instance of algorithm A? Particularly, we present a methodology that enables a statistical analysis of the performance of algorithms executed in different machines. The proposed methodology has two parts. First, we propose a model that, given the runtime of an algorithm in a machine, estimates the runtime of the same algorithm in another machine. This model can be adjusted so that the probability of estimating a runtime longer than what it should be is arbitrarily low. Second, we introduce an adaptation of the one-sided sign test that uses a modified p-value and takes into account that probability. Such adaptation avoids increasing the probability of type I error associated with executing algorithms A and B in different machines

Challenges of Human Capacity Development in Federal Universities in Akwa Ibom and Cross River States, Nigeria

The study investigated the challenges of human capacity development in Universities and the possible strategies for improvement. Three research questions were posed to guide the study. A survey design was adopted and simple random sampling technique was used to select a sample of 500 lecturers from a population of 1,819 academic staff from two Federal Universities in Nigeria. The instrument for data collection was a questionnaire developed by the researchers and was titled “Challenges of Human Capacity Development Questionnaire (CHCDQ)”. The instrument was a 5-point Likert scale. Cronbach alpha reliability method was used to ascertain the reliability of the instrument and a reliability coefficient of 0.88 was obtained.  Data collected were analyzed using descriptive statistics – means, standard deviations, frequencies and percentages. Results of the study revealed that inadequate funding, corruption/examination malpractice, lack of effective monitoring/supervision of teaching and learning, lack of committed teachers, students’ poor attitude towards learning, inadequate facilities and certificate racketeering were identified as constraints to  human capacity development in Universities. Male and female lecturers did not differ in their mean rating of the challenges of human capacity building. In the light of these findings, it was recommended among other things that the government should adequately fund federal Universities in Nigeria to enhance quality human capacity building and lecturers should be given adequate incentives to motivate them to be committed to the training of students for quality outputs. Key words: Challenges, Human Capacity, Development, University , Education

Genetic Algorithms and Genetic Programming on Comparison Sorting

[EUS] Lan honetan Algoritmo Genetikoen teoriaren errepaso arin bat egin ostean, hiru algoritmo genetikoren berri ematen da. Lehenengoa, simpleena, funtzio baten maximoa aurkitzen duen algoritmoa da. Bigarrena funtzio bat urbiltzeko asmoz, polinomio baten interpolazio puntu optimoak kalkulatzen ditu, eta azkenak, tamainu txikiko listak ordenatzen ditu programazio genetiko lineala eta "Holland's Broadcast Language" erabiliz.[EN] In this dissertation, we first introduce a very brief introduction to Genetic Algorithms. Then, we show our implementation of three Genetic Algorithms, the first one, tries to find the global maximum of a given function. The second algorithm, approximates a given function by finding the optimal interpolating points of a polynomial. Finally, the last algorithm learns to sort small lists by using Hollands Broadcast Language and linear genetic programming