Self-optimizing control methodology for mixed integer programming problems: a case study of refinery production scheduling

Problem formulation as mixed integer nonlinear programming (MINLP) is one of the most challenging task in refinery scheduling optimization. In most of the work reported in refinery scheduling, uncertainties from design point of view predominate. However, there is also a need to consider operational uncertainties (disturbances) as they affect the accuracy and robustness of the overall schedule. This study proposed a novel approach under self- optimizing control (SOC) framework to deal with multi-period refinery scheduling problems under uncertain conditions. The goal is to maintain global optimum by controlling the gradient of the cost function at zero via approximating necessary conditions of optimality (NCO) over the whole uncertain parameter space. A regression model for the plant expected revenue (profit) as a function of independent variables using optimal operation data was obtained and a feedback input (manipulated variable) was derived. The performance of the proposed approach was tested using case studies. The first case assumed a system with no disturbance with the base case model giving an optimal profit of $56,696,407 while the proposed approach yields$50,523,054, translating to 10.888 % loss. The percentage loss for the second, third and fourth cases with disturbances are 5.807 %, 4.409% and 7.898% respectively. The results obtained have shown that the idea presented was able to effectively deal with the situation at hand with percentage loss within a reasonable degreeKeywords: Refinery scheduling scheduling, MINLP formulation, Operational uncertainty (disturbances), Necessary condition of optimality, Feedback contro

Biosynthesis, characterization and antimicrobial study of silver nanoparticles (agNPs)

In this paper, biological synthesis of silver nanoparticles (AgNPs) using Syzygium guineenses stem extract with 1mM, 2mM and 3mM AgNO3 concentrations has been presented. The plant extract was prepared with distilled water. The characterization and morphological composition of the synthesized AgNPs were determined by UV-visible spectroscopy and SEM respectively, while FTIR analysis was performed to identify the presence of the possible functional groups in the synthesized nano particles. It was observed from the UV and SEM analyses that the particles formed have diameters in the range of 23.5nm - 89.3nm, which is the range of nanoparticle size. Antibacterial test was carried out on the sample with six pathogenic microbes (Methicillin Resistant Staphylococus aureas, Vancomycin Resistant Entrococci, Staphylococcus aureas, Bacillus sublitis, Escherichia coli, and Pseudomonas aeruginosa) to ascertain the antimicrobial activity of the synthesized AgNPs. Both the characterization and antimicrobial activity test were very successful and could lead to significant economic viability, as well as being environmentally friendly for treatment of some infectious diseases.Keywords: Syzygium guineenses, Green Chemistry, Spectroscopy, Optoelectronics, Biomedical Sensor

Correlates of postpartum sexual activity and contraceptive use in Kano, northern Nigeria

Practices related to resumption of coitus after childbirth remains poorly documented in Nigeria. This study examined factors associated with sexual intercourse, delivery-coitus interval, and contraceptive use among postpartum women attending a tertiary centre in Kano, northern Nigeria. A cross section of 317 women attending immunization, postnatal and family planning clinics within 12 months of childbirth was interviewed using a structured questionnaire. Vaginal intercourse was resumed by most women (n=212; 66.9%, 95% Confidence Interval (CI) = 61.8%, 72.2%) with delivery-coitus resumption interval (mean ± SD) of 9.6±5.2 weeks postpartum. The majority (67.9%) resumed sexual activity within 8 weeks of delivery. Nearly two-thirds 65.6% (n=139/212) of the sexually active women reported current use of contraceptives. Onset of postpartum sexual activity was independently associated with mode of delivery adjusted odds ratio (AOR) (95%CI)= 1.10 (1.03,1.78), baby‘s age AOR (95%CI) =2.10 (1.27, 8.70), number of living children AOR (95%CI)=1.21 (1.07,1.79), onset of menstruation AOR (95%CI)=0.34 (0.17,0.69) and co-habitation AOR (95%CI)=0.47 (0.016, 0.14). Contraceptive use was predicted by educational status, sexual activity, baby‘s age and menstruation. Most women attending maternal and child health clinics resumed sexual intercourse within 2 months of delivery, but only two-thirds used modern contraceptive methods. Contraceptive counseling should commence early, preferably during pregnancy.Keywords: sexual intercourse, postpartum, contraceptive use, predictors, Nigeri

Behavioral Characteristics of Photovoltaic Cell with Different Irradiation in Matlab/Simulink/Simscape Environment

Photovoltaic technology is one of the fastest growing energy among the different type of renewable energies that are available for electricity generation. This is due to the availability of the natural sun rise, and the non polluted energy that is free from emission of carbon dioxide (CO2). This paper presents a typical modeling of photovoltaic cell under different irradiations level, in order to monitor the behavior of the (Voltage-Current) V-I and (Power-Voltage) P-V characteristics. The simulation of the proposed model was performed in MATLAB/SIMULINK and Simscape environment. Single diode model of the PV system was presented in the mathematical modeling of the proposed system. Simulation results of different I-V and P-V characteristics were also presented. DOI: 10.5901/ajis.2014.v3n7p5

Determination of morphological features and molecular interactions of Nigerian bentonitic clays using Scanning Electron Microscope (SEM)

This research focused on identifying the morphological features and molecular  interactions of the Nigerian Bentonitic clays using Scanning Electron Microscope (SEM) characterisation technique. The SEM microstructure images indicated that the bentonite samples are generally moderately dispersive to dispersive with some large flocs which were apparently separate and dispersed from one another rather than located on the totality of the image. This property is more pronounced on the sodium (Na) activated and the treated samples than in the raw samples, which could be due to quartz removal and Na activation on the raw Bentonitic samples. Dispersive sample surfaces consist of loose flakes with no definitive mass structures observed on the treated samples due to added poly anionic cellulose (PAC) to the samplesKey words: SEM, microstructure, images, bentonite, flocs and PA

Urbanization and carbon dioxide emissions in Singapore: evidence from the ARDL approach

The main aim of this article is to examine empirically the impact of urbanization on carbon dioxide emissions in Singapore from 1970 to 2015. The autoregressive distributed lags (ARDL) approach is applied within the analysis. The main finding reveals a negative and significant impact of urbanization on carbon emissions in Singapore, which means that urban development in Singapore is not a barrier to the improvement of environmental quality. Thus, urbanization enhances environmental quality by reducing carbon emissions in the sample country. The result also highlighted that economic growth has a positive and significant impact on carbon emissions, which suggests that economic growth reduces environmental quality through its direct effect of increasing carbon emissions in the country. Despite the high level of urbanization in Singapore, which shows that 100 % of the populace is living in the urban center, it does not lead to more environmental degradation. Hence, urbanization will not be considered an obstacle when initiating policies that will be used to reduce environmental degradation in the country. Policy makers should consider the country’s level of economic growth instead of urbanization when formulating policies to reduce environmental degradation, due to its direct impact on increasing carbon dioxide emissions

The Emergence of Anisotropic Superconductivity in the Nodal-line Semi-metal TlTaSe2

TlTaSe2 is a non-centrosymmetric quasi-2D crystal semi-metal hosting nodal-line topological features protected by mirror-reflection symmetry. Here, we investigated the superconducting properties of TlTaSe2 using the first-principles anisotropic Migdal-Eliashberg theory. The Fermi surface hosts well gapped multiband features contributed by the Ta 5d and Tl 6p orbitals. Moreso, anisotropic superconducting gaps were found to exist at 2.15 and 4.5 meV around the in-plane orbitals, coupling effectively with the in-plane phonons of the Ta and Tl atoms. Using the Allen-Dynes-modified McMillan formula, we found a superconducting transition temperature of 6.67 K, accompanied by a robust electron-phonon coupling constant {\lambda} of 0.970. This investigation provides valuable insights into the mechanisms underlying anisotropic superconductivity in TlTaSe2.Comment: 17 pages, 5 figure

Effects of Operating Conditions on Gas Release Thermal Consequences: a case study of the Trans- Saharan Gas Pipeline

A recent study concluded that militant activities/insurgency constitutes the biggest threat to the proposed Trans-Saharan Gas Pipeline (TSGP) intended to traverse Nigeria, Niger and Algeria. Hence gas release is a credible source of concern. Using the potential leak of inventory from the TSGP as a case study; this paper assesses the Simplex Source Term and Multivariate Consequence Modelling approaches. Aspen HYSYS® platform was used to determine the average Molecular Weight and Lower Heat of Combustion of the gas mixture. Thereafter, the gas discharge rates for various leak scenarios were evaluated. The gas release rates and the flame length of the potential jet fires were initially estimated using Simplex Source Term Models which pay limited attention to operating conditions. Finally a more detailed follow-up study, accounting for a range of practical factors was conducted. A number of useful risk management metrics were determined. For example, the release rate for the 100mm leak is about 130.50 kg/s and 162.13 kg/s for scenarios with and without modifiers respectively. Similarly, the maximum flame lengths were found to be significantly different with values of 8m and 142m with and without modifiers respectively. The results show that the direct approach could be overly conservative, hence more expensive to implement