1,325 research outputs found
Control aspects of synchronous machines in power systems applications
No full textDevelopments in control design methods for power systems have continually been made during the last ten years, and the present thesis seeks to make its contribution to this pattern of work. In so doing, it develops electrical machine mathematical models on which the subsequent designs are based. The formulations relate specifically to those from which computer programs may be readily developed and particular importance has been attached to the systematic marshalling of plant and network equations for the subsequent and efficient solution by computer methods. Methods of model reduction and state transformation are described and these are used to manipulate the system models into the form appropriate to the regulator design algorithm. The regulator-design algorithm is described in which a systematic numerical technique is used to predetermine the performance criterionJ = C(xtQx + u )dt. The constraints imposed on the system response by the design specification are associated with the movement of the eigenvalue locations to give actual values for the elements of Q. The algorithm described, for the linear single-input system, is based on the sensitivity of the elements of Q to shifts in the eigenvalue locations to produce a performance criterion for improved system stability. The resulting algorithm is applied to the design of an a.c. turbo generator excitation control and is shown to give a system that has advantages over a controller designed using conventional techniques. The thesis is supported by four published papers in which the author of the present thesis is joint author. One reports on the development of the design algorithm and the others deal with computational aspects of control design and its-application to power systems; computer listings are presented in the papers. In addition, the author's work has been presented at two conferences for which published records exist.</p
A pilot-scale trial comparing mesophilic and thermophilic digestion for the stabilisation of source segregated kitchen waste
No full textSource segregated food waste was collected from domestic properties and its composition determined together with the average weight produced per household, which was 2.91 kg per week. The waste was fed over a trial period lasting 58 weeks to an identical pair of 1.5 m3 anaerobic digesters, one at a mesophilic (36.5 oC) and the other at a thermophilic temperature (56 oC). The digesters were monitored daily for gas production, solids destruction and regularly for digestate characteristics including alkalinity, pH, volatile fatty acid (VFA) and ammonia concentrations. Both digesters showed high VFA and ammonia concentrations but in the mesophilic digester the pH remained stable at around 7.4, buffered by a high alkalinity of 13,000 mg l-1; whereas in the thermophilic digester VFA levels reached 45,000 mg l-1 causing a drop in pH and digester instability. In the mesophilic digester volatile solids (VS) destruction and specific gas yield were favourable, with 67% of the organic solids being converted to biogas at a methane content of 58% giving a biogas yield of 0.63 m3 kg-1 VS added. Digestion under thermophilic conditions showed potentially better VS destruction at 70% VS and a biogas yield of 0.67 m3 kg-1 VS added, but the shifts in alkalinity and the high VFA concentrations required a reduced loading to be applied. The maximum beneficial loading that could be achieved in the mesophilic digester was 4.0 kg VS m-3 d-1
A pilot-scale comparison of mesophilic and thermophilic digestion of source segregated domestic food waste
No full textSource segregated food waste was collected from domestic properties and its composition determined together with the average weight produced per household, which was 2.91 kg per week. The waste was fed over a trial period lasting 58 weeks to an identical pair of 1.5 m3 anaerobic digesters, one at a mesophilic (36.5°C) and the other at a thermophilic temperature (56°C). The digesters were monitored daily for gas production, solids destruction and regularly for digestate characteristics including alkalinity, pH, volatile fatty acid (VFA) and ammonia concentrations. Both digesters showed high VFA and ammonia concentrations but in the mesophilic digester the pH remained stable at around 7.4, buffered by a high alkalinity of 13,000 mg l-1; whereas in the thermophilic digester VFA levels reached 45,000 mg l-1 causing a drop in pH and digester instability. In the mesophilic digester volatile solids (VS) destruction and specific gas yield were favourable, with 67% of the organic solids being converted to biogas at a methane content of 58% giving a biogas yield of 0.63 m3 kg-1 VSadded. Digestion under thermophilic conditions showed potentially better VS destruction at 70% VS and a biogas yield of 0.67 m3 kg-1 VSadded, but the shifts in alkalinity and the high VFA concentrations required a reduced loading to be applied. The maximum beneficial loading that could be achieved in the mesophilic digester was 4.0 kg VS m-3 d-1
Metalorganic chemical vapor deposition of GaAsN epilayers: microstructures and optical properties
No full textIn this article, we investigate the parameters used in the MOCVD growth of GaAsN epilayers on GaAs substrates and some of their microstructures and optical properties. The N incorporation was found to mainly depend on the growth temperature and the fractional 1,1-dimethylhydrazine molar flow. A thin highly strained interface layer was observed between GaAsN and GaAs, which, contrary to previously published results, was not N enriched. The low-temperature (10 K) photoluminescence spectra were composed of several emissions that we attribute to a combination of interband transition and transitions involving localized defect states. (C) 2004 Elsevier B.V. All rights reserved
Allen C. Jones Camp of the United Confederate Veterans in Greensboro, Alabama.
No full textFirst row, left to right (numbers 1 through 11): T. J. Kinnaird; William N. Knight; W. C. Tunstall; R. B. Waller; H. T. Waller; Charles E. Waller; George Nabors; N. B. Jones; R. H. Jackson; A. J. Moore; and S. M. Hosmer. Second row, left to right (numbers 12 through 21): John H. Turpin; H. T. Stringfellow; W. G. Britton; T. J. Crawford; Cud Jones; J. A. Ellerbe; Bell [?] Singley; J. Huggins; W. C. Christian; and John G. Apsey
XIV Modern Literature:Section 3(b) Fiction Post-2000
No full textThis chapter has eight sections 1. General. 2. Fiction Pre-1945; 3. Fiction Post-1945; 4. Drama Pre-1950; 5. Drama Post-1950; 6. British Poetry Pre-1950; 7. British Poetry Post-1950; 8. Modern Irish Poetry. Section 1 is by Jennifer Sorensen; section 2(a) is by Chris Mourant; section 2(b) will resume in 2023; section 2(c) is delayed by parental leave and will resume in 2023; section 2(d) is by Joshua Phillips; section 3(a) is by Katherine Parsons; section 3(b) is by Rebecca Roach, with thanks to Samuel Cooper, and covers work in 2020 and 2021; section 4(a) is by Sophie Stringfellow; section 4(b) is by Gustavo A. Rodríguez Martín; section 5 is by Catriona Fallow; section 6(a) will resume in 2023; section 6(b) is by Joshua Richards; section 7 is by Alex Niven and covers work in 2020 and 2021; section 8 is by David Wheatley
XIV Modern Literature
No full textThis chapter has eight sections 1. General. 2. Fiction Pre-1945; 3. Fiction Post-1945; 4. Drama Pre-1950; 5. Drama Post-1950; 6. British Poetry Pre-1950; 7. British Poetry Post-1950; 8. Modern Irish Poetry. Section 1 is by Shawna Ross; section 2(a) is by Chris Mourant; section 2(b) will resume in 2023; section 2(c) is by Tiana M. Fischer; section 2(d) will resume in 2023; section 2(e) is by Joshua Phillips; section 3(a) is by Katherine Parsons; section 3(b) will resume in 2023; section 4(a) is by Sophie Stringfellow; section 4(b) is by Gustavo A. Rodríguez Martín; section 5 is by Graham Saunders; section 6(a) will resume in 2023, section 6(b) is by Joshua Richards; section 7 will resume in 2023; section 8 is by Jack Quin
Increased personal protective equipment litter as a result of COVID-19 measures
No full textUse of personal protective equipment (PPE) increased during the COVID-19 pandemic to reduce virus transmission. Here, we quantitatively analyse emergence of PPE and COVID-19-related litter over 14 months for 11 countries using the litter collection application Litterati. The proportion of masks in litter increased by >80-fold as a result of COVID-19 legislation, from <0.01% to >0.8%. Gloves and wipes, more prevalent at ~0.2% of litter before the pandemic, doubled to 0.4%, but this has since fallen. Glove litter increased in the initial stages of the pandemic but fell after the introduction of facemask policies, whereupon there was an increase of facemask litter. National COVID-19 policy responses and international World Health Organization announcements and recommendations are a probable driver of PPE litter dynamics, especially the implementation of facemask policies. Waste management should be incorporated in designing future pandemic policies to avoid negative environmental legacies of mismanaged PPE.</p
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