Generator Maintenance Scheduling Models in Power Systems. Integrated Cost Models for Generator Maintenance Strategy under Market Environment.

Change from a regulated to deregulated structure means that, the centralized maintenance system is not valid any more. In the surveyed published literature, there is not a single model which incorporates all maintenance cost components to analyze the effect of different maintenance strategies for generator companies (GENCOs). The work enclosed in this thesis demonstrates that there is a considerable requirement for accurately modelling cost components of the maintenance model, to be used in maintenance scheduling for deregulated power system, in order to attain a superior schedule with major financial and operational impact. This research investigates and models most cost factors that affect the maintenance activities of the deregulated GENCOs, and demonstrates the utilization of the developed cost models in maintenance scheduling. It also presents the data gathering process for the developed maintenance cost model. A generator maintenance scheduling model that considers direct and indirect maintenance costs, opportunity costs (i.e. loss of customer goodwill), effective maintenance strategies, failures, and interruptions is developed. A Genetic Algorithm (GA) based approach is employed to achieve maintenance schedules to various generators maintenance scenarios. An Analytical Hierarchy Process (AHP) approach is proposed for modelling customer goodwill. The maintenance model was redeveloped under the Reliability Centred Maintenance (RCM) strategy to analyze the effect of a maintenance strategy on maintenance costs. Case studies are presented to demonstrate the utilisation of the developed models.The investigation shows that the market prices, opportunity costs and maintenance strategy have an effect on the final maintenance schedule. The research demonstrates that the cost components are critical factors to achieve an effective maintenance schedule, and they must be considered and carefully modelled in order to reflect more realistic situation for maintenance scheduling of generator units in deregulation environment

Herpes Zoster Infections in SLE in a University Hospital in Saudi Arabia: Risk Factors and Outcomes

Patients with SLE carry an increased risk of infection that account for 11–23% of all hospitalized patients and 50% of all SLE patients develop major infections during the course of their disease. Globally Herpes Zoster has been reported as the most frequent viral infection in SLE patients. We determined the clinical spectrum, disease sequelae and the risk factors associated with the development of Herpes Zoster in patients with SLE and their outcomes. Retrospective case control study of Herpes Zoster infections was done in SLE patients between 1982 and 2006. Cases were matched 1:2 to controls for age, race, sex and duration of follow up. Clinical features of the cases from the time of lupus diagnosis to the time of Zoster were compared to their respective controls over similar time periods. Thirty two SLE cases were compared to sixty four controls. Cases were more likely to have received cyclophosphamide (P = .0223) and intravenous methylprednisolone pulse therapy (P = .0026), MMF (P < .02), had leucopenia (P = .0407) and hemolytic anemia (P = .0344). More cases than controls had lupus nephritis, cerebritis, thrombocytopenia but the differences did not reach statistical significance. The mean oral prednisolone dose and proportion of patients receiving immunosuppressives including pulse methylprednisolone therapy, IV Cyclophosphamide and mycophenolate was significantly higher in patients with active SLE compared to patients with SLE in remission at the time of Herpes Zoster (P < .05). Disseminated Zoster developed in patients with active SLE (7/9) compared to patients with SLE in remission (0/23). None of the patients had postherpetic neuralgia or bacterial super infection. Immunosuppressive medications were discontinued at the time of diagnosis of Zoster in 19 of 32 patients and all patients received antiviral medications.There were no permanent neurologic deficits or deaths. We conclude that Herpes Zoster infections occur at increased frequency among patients with SLE and carry significant morbidity. Immunosuppressive therapy and severe manifestations of lupus may be risk factors for the development of Herpes Zoster although not necessarily at the time of disease flare or immunosuppressive therapy. Our study suggests that although Herpes Zoster occurs frequently in patients with SLE, it has a relatively benign course

Maintenance cost models in deregulated power systems under opportunity costs.

Maintenance costs in deregulated power systems play an important role. This mainly includes direct costs associated with material and labor costs; and indirect costs associated with spare parts inventory, shipment, test equipment cost, indirect labor, and opportunity costs. The cost function is used as the sole or main component of the objective function in maintenance scheduling and planning activities. The cost has been modeled in literature with several representations for centralized power systems. With deregulation of power industries in many countries the costs representation to be used within the maintenance model in the decentralized power systems has become an important research question. This paper presents modeling of different components of maintenance costs that can be used within the main objective function of the maintenance scheduling and planning problem for the deregulated environment

First Order Phase Transformation in Amorphous Ge25Se75 – xSbx Glasses

Non-isothermal Differential scanning calorimetry (DSC) technique was used to study the kinetics of first order phase transformation in Ge25Se75 – xSbx glasses. The X-ray diffraction (XRD) technique was employed to investigate the amorphous and crystalline phases in Ge25Se75 – xSbx glasses. From the heating rate dependences of crystallization temperature; the activation energy for crystallization and other kinetics parameters were derived. The temperature difference (Tc – Tg) and Tc is highest for the samples with 6 % of Sb. Hence, Ge25Se69Sb6 glass is most stable. The enthalpy released is found to be less for Ge25Se69Sb6 glass which further confirms its maximum stability. The activation energy of crystallization (Ec) is found to vary with compositions indicating a structural change due to the addition of Sb. The crystallization data are interpreted in terms of recent analyses developed for non-isothermal conditions. The present investigation indicates that both the glass transition and the crystallization processes occur in a single stage. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3101

Reflection and Transmission of an Incident Progressive Wave by Obstacles in Homogeneous Shallow Water

The influence of a suspended fixed obstacle on an incident progressive wave inside an ideal homogeneous shallow water is studied in two dimensions. The fluid occupies an infinite channel of a constant depth, and a fixed obstacle of a small horizontal extent is partially submerged without contact with the bottom of the channel. An asymptotic double series expansion for the solution is used. The procedure enables us to calculate analytic expressions for the local perturbations up to the second order. The results of the first-order approximation indicate that no reflections exist. The second-order approximation of the solution is found to be the superposition of a progressive wave and local perturbations. For approximations of order higher than two, a secular term which increases monotonically with time and distance appears in the expressions for the progressive wave. This unacceptable result is due to a certain aspects in the mathematical procedure used. For this reason, the procedure is modified by using a suitable transformation of variables which reduces the determination of the transmitted wave to the solution of the KdV equation. As an illustration, the special case of the incident uniform flow is considered and the stream lines of the resulting flow are drawn

Evaluation of the protective efficacy of immunoglobulin Y (IgY- antibodies) prepared against Walterinnesia aegyptia snake venom in Saudi Arabia

Four groups of eight chickens were immunized intramuscularly with Walterinnesia aegyptia snake venoms mixed with Freund's complete adjuvant during the period from 1st October 2009 to 1st October 2011 at the Center of Excellence in Biotechnology Research, King Saud University, Saudi Arabia. Three weeks later, the injections were repeated with the venoms in incomplete Freund's adjuvant. Three boosters were given with the venoms at three weeks intervals. The immunoglobulin Y (IgY)-antibodies was extracted by ammonium sulphate-caprylic acid method, the antibody titer were tested by enzyme linked immunosorbant assay and the protective efficacies of the extracted immunoglobulins were performed. IgY-preparation extracted by ammonium sulphate-caprylic acid method showed lack of low molecular weight bands (non-immunoglobulin proteins) and the bands representing IgY-antibodies, which have molecular weights ranging from 180 to 200 kDa, appeared sharp and clear. Moreover, evaluation of the protective value of the IgY - antibodies prepared revealed that, one milliliter of extracted IgY-antibodies containing 15 mg/ml anti-W. aegyptia venom specific IgY could produce 100% protection against 50 LD50 and 75% protection against 60 LD50. Laying hens could be used as an alternative source of polyclonal antibodies against W. aegyptia snake venoms due to several advantages as compared with mammals traditionally used for such purpose.Keywords: Snake venom, Walterinnesia aegyptia, immunoglobulins Y, protective efficacy, caprylic aci

Synthesis of Multiwalled Carbon Nanotubes-Titania Nanomaterial for Desulfurization of Model Fuel

This work reported on the development of novel nanomaterials of multiwalled carbon nanotubes doped with titania (CNT/TiO2) for the adsorptive desulfurization of model fuel oils. Various analytical techniques such as field emission scanning electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDX), and Fourier transform infrared spectroscopy (FTIR) were used for the characterization of the nanomaterials. The initial results indicated the effectiveness of the prepared CNT/TiO2 nanomaterials in removing sulfur compounds from model fuel oil. The adsorption of DBT, BT, and thiophene from model fuel onto the derived sorbents was performed using batch mode system. These CNT/TiO2 nanomaterials initially afforded approximately 45% removal of DBT, 55% BT, and more than 65% thiophene compounds from model fuels. The CNT/TiO2 nanomaterials provided an excellent activity towards interaction with organosulfur compounds. More experiments are underway to optimize the parameters for the adsorptive desulfurization processes. We believe that these nanomaterials as adsorbents will find useful applications in petroleum industry because of their operational simplicity, high efficiency, and high capacity

Characterization of tungstophosphoric acid supported on MCM-41 mesoporous silica by using n-hexane cracking, benzene adsorption, and xray diffraction.

MCM-41 with all-silica composition was synthesized with unit cell parameters a=b=60Å. The material was characterized by X-ray powder diffraction and benzene adsorption. Combinations of unit cell parameter, benzene adsorption and crystal density determination have given values for the pore diameter and wall thickness in the ab-plane of the unit cell. The unit cell size shrank upon impregnation of the material with tungstophosphoric acid.The catalytic activity of tungstophosphoric acid (HPW) supported on the all-silica mesoporous MCM-41 material has been evaluated for the cracking of n-hexane. The catalyst showed a very high activity of n-hexane cracking at a temperature as low as 200oC, at very low space velocity. However, the catalyst deactivated rapidly due to coke deposition on the acid sites. At higher temperature the activity declined, most likely because of the heteropoly-acid thermal instability. Both X-ray powder diffraction and infra-red spectroscopy have shown evidence for the heteropolyacid instability starting at 300oC.The type of the solvent used in the impregnation affected the dispersion of HPW on the MCM-41 material as indicated by benzene adsorption measurement, but it did not influence the catalytic performance for nhexane cracking. In the case of aqueous solution, the benzene adsorption was lower than that of the parent MCM-41 material. The reduced adsorption capacity was probably due to the presence of the HPW at the pore mouth of the cylindrical channels, causing narrowing and blocking of some sections of the channels. Moreover, the adsorption isotherm showed a micropore characteristic supporting the pore narrowing proposal. In the case of using methanol solvent for the impregnation, the full adsorption capacity was retained, indicating a much higher dispersion of the HPW throughout the channels of the MCM-41 material. The benzene adsorption isotherm also showed the characteristic of mesoporosity and the adsorption capacity was not appreciably reduced.Characterization of the spent catalyst after n-hexane cracking test showed additional reduction in the benzene adsorption capacity for the aqueous impregnated catalyst. Again the methanol-impregnated catalyst had almost a full adsorption capacity

Characterization of tungstophosphoric acid supported on MCM-41 mesoporous silica by using n-hexane cracking, benzene adsorption, and xray diffraction.

MCM-41 with all-silica composition was synthesized with unit cell parameters a=b=60Å. The material was characterized by X-ray powder diffraction and benzene adsorption. Combinations of unit cell parameter, benzene adsorption and crystal density determination have given values for the pore diameter and wall thickness in the ab-plane of the unit cell. The unit cell size shrank upon impregnation of the material with tungstophosphoric acid.The catalytic activity of tungstophosphoric acid (HPW) supported on the all-silica mesoporous MCM-41 material has been evaluated for the cracking of n-hexane. The catalyst showed a very high activity of n-hexane cracking at a temperature as low as 200oC, at very low space velocity. However, the catalyst deactivated rapidly due to coke deposition on the acid sites. At higher temperature the activity declined, most likely because of the heteropoly-acid thermal instability. Both X-ray powder diffraction and infra-red spectroscopy have shown evidence for the heteropolyacid instability starting at 300oC.The type of the solvent used in the impregnation affected the dispersion of HPW on the MCM-41 material as indicated by benzene adsorption measurement, but it did not influence the catalytic performance for nhexane cracking. In the case of aqueous solution, the benzene adsorption was lower than that of the parent MCM-41 material. The reduced adsorption capacity was probably due to the presence of the HPW at the pore mouth of the cylindrical channels, causing narrowing and blocking of some sections of the channels. Moreover, the adsorption isotherm showed a micropore characteristic supporting the pore narrowing proposal. In the case of using methanol solvent for the impregnation, the full adsorption capacity was retained, indicating a much higher dispersion of the HPW throughout the channels of the MCM-41 material. The benzene adsorption isotherm also showed the characteristic of mesoporosity and the adsorption capacity was not appreciably reduced.Characterization of the spent catalyst after n-hexane cracking test showed additional reduction in the benzene adsorption capacity for the aqueous impregnated catalyst. Again the methanol-impregnated catalyst had almost a full adsorption capacity