3,577 research outputs found
A direct A.C. to A.C. regenerative frequency and voltage converter
No full textIncludes bibliographical references.The reliable variable speed operation of an a. c. machine over a wide speed range is a problem that has received attention for some time. In this thesis a system to permit such operation from a fixed frequency fixed voltage supply is proposed, under the name of the asynchronous modulation converter. This converter is of the cycloconverter family, but is force-commutated and is not synchronised with the supply frequency. The power switching element comprises a power transistor in a diode bridge, coupled to the control circuitry by opto-isolators. The output of the a-mod converter is produced by a "chopper" modulation process and this results in the harmonics present being at frequencies well removed from the fundamental. A feedback system to ensure smooth commutation of the output current from the power switches is described. This feedback system operates by sensing the rate of rise of the inductive voltage surge on the load when a switch is opened to operate a freewheel path switch
Zane Grey with Orange A.C. baseball team
No full textThis photograph shows Ohio native Zane Grey with the Orange A.C. Baseball Team, ca. 1896-1904. Prior to becoming a well-known author of western novels, Zane Grey was also a dentist and a semi-professional baseball player, with teams including the Orange Athletic Club and the Newark (New Jersey) Colts
Experimental research on spatial distribution of overtopping
No full textThe overtopping empirical formulas calculate the discharge only at the top of the crest of a coastal protection structure. On the other hand, the tolerable overtopping discharges are defined at certain points behind the crest where the total overtopping is reduced. The scope of this thesis is to find an empirical formula to describe the distribution of overtopping at the space behind the crest. This thesis comes as a further investigation on the work conducted by v.Kester [2009] for regular waves. In this research, a physical model was developed on which irregular waves are tested. Because of the duration of the tests and the amount of collected water (significant lose of water during the test), a completely new measuring system was designed. Five influencing parameters (variables) are considered on this research: wave height, wave period/steepness, slope angle, crest freeboard and crest permeability. The entire overtopping process is analysed separately for the total overtopping discharge, the overtopping discharge directly behind the crest and the distribution of overtopping behind the structure. In the analysis of the data collected from the measurements, the impact of the varying parameters is investigated leading to useful conclusions and better understanding of the entire process. Additionally, the experimental findings are analysed and compared to the relative existing methods. Based on the TAW [2002] method which is proposed by the EurOtop Manual [2007], a prediction formula is developed. This formula is a generic version of TAW [2002] formula in which a new reduction factor ?c is introduced in order to describe the decay of the overtopping and thus predict the discharge at any certain distance behind the crest. Other relevant methods are also analysed (Juul Jensen [1984], Steenaard [2002], Besley [1999] and v.Kester [2009]) and conclusions for their applicability are drawn leading to suggested improvements or corrections. Apart from the distribution of overtopping, on this thesis the determination of crest freeboard (which is an ambiguous issue) is also investigated. Finally, suggestions of further research on this topic are discussed. The entire work has been perfomed in close cooperation with van Oord.Hydraulic EngineeringCivil Engineering and Geoscience
Flow over partially liquid filled cavity
No full textExperiments have been carried out to investigate the effect of liquid cavity filling on the behavior of the gas flow over a flat plate cavity. PIV measurements in the gas phase reveal that cavity filling can affect vortex shedding in the cavity mouth. Shear layer vortices can break-up into smaller vortices, thereby losing their periodic interaction with the aft wall and, hence, their sound producing potential. Expected is that this is one of the mechanisms causing sound mitigation in corrugated pipes with liquid addition, observed in literature
On modular lattices generated by chains
No full textDe La Maza, A.C. (reprint author). Instituto de Matematica y Fisica, Universidad de Talca. Casilla 747, Talca, Chile.We describe the free modular lattice generated by two chains and a single point, under the assumption that there are few meets
Quantized current steps due to the a.c. coherent quantum phase-slip effect
No full text| openaire: EC/H2020/862660/EU//QUANTUM E-LEAPS Funding Information: This work was supported by European Union’s Horizon 2020 Research and Innovation Programme under grant agreement no. 862660/QUANTUM E-LEAPS and Engineering and Physical Sciences Research Council (EPSRC) grant no. EP/T004088/1. Publisher Copyright: © 2022, The Author(s), under exclusive licence to Springer Nature Limited.The a.c. Josephson effect predicted in 19621 and observed experimentally in 19632 as quantized ‘voltage steps’ (the Shapiro steps) from photon-assisted tunnelling of Cooper pairs is among the most fundamental phenomena of quantum mechanics and is vital for metrological quantum voltage standards. The physically dual effect, the a.c. coherent quantum phase slip (CQPS), photon-assisted tunnelling of magnetic fluxes through a superconducting nanowire, is envisaged to reveal itself as quantized ‘current steps’3,4. The basic physical significance of the a.c. CQPS is also complemented by practical importance in future current standards, a missing element for closing the quantum metrology triangle5,6. In 2012, the CQPS was demonstrated as superposition of magnetic flux quanta in superconducting nanowires 7. However, the direct flat current steps in superconductors, the only unavailable basic effect of superconductivity to date, was unattainable due to lack of appropriate materials and challenges in circuit engineering. Here we report the direct observation of the dual Shapiro steps in a superconducting nanowire. The sharp steps are clear up to 26 GHz frequency with current values 8.3 nA and limited by the present set-up bandwidth. The current steps were theoretically predicted in small Josephson junctions 30 years ago5. However, unavoidable broadening in Josephson junctions prevents their direct experimental observation8,9. We solve this problem by placing a thin NbN nanowire in an inductive environment.Peer reviewe
Semi-Automatic Identification of Humpback Whales
No full textThis paper describes current work on a photo-id system for humpback whales. Individuals of this
species can be uniquely identied by the light and dark pigmentation patches on their tails. We propose
semi-automatic algorithm based on marker-controlled watershed transformation for segmenting
the animal's tail from the surrounding sea. We propose tting an afne invariant coordinate grid to
the resulting segmentation. The grid can be adjusted according to the level of occlusion by the sea.
A numerical feature vector capturing the patch-distribution with respect to the grid is then automatically
extracted and used to match the individual against the database of similarly processed images
Stabiliteit van het achtertalud van een rubble mound golfbreker
No full textCivil Engineering and Geoscience
Interview with A.C. Salaam by Tessa Desmond, September 27, 2023
No full textA.C. Salaam reflects on her time attending medical school in the Caribbean and discusses how that experience led her to the practice of plant healing. She shares stories of plant medicines and how she uses them throughout the interview. She reflects on her family's food practices and the role of sufficiency. Salaam touches on the importance of sustenance, and connects this value to her work in the Farmville, NC, community garden
Questionnaire severity measures for depression: a threat to the doctor-patient relationship?
No full textBackground Since 2006 the Quality Outcomes Framework (QOF) has rewarded GPs for carrying out standardised assessments of the severity of symptoms of depression in newly diagnosed patients. Aim To gain understanding of GPs' opinions and perceived impact on practice of the routine introduction of standardised questionnaire measures of severity of depression through the UK general practice contract QOF. Design of study Semi-structured qualitative interview study, with purposive sampling and constant comparative analysis. Setting Thirty-four GPs from among 38 study general practices in three sites in England, UK: Southampton, Liverpool, and Norfolk. Method GPs were interviewed at a time convenient to them by trained interviewers. Interviews were audiorecorded and transcribed verbatim in preparation for thematic analysis, to identify key views. Results Analysis of the interviews suggested that the use of severity questionnaires posed an intrusion into the consultation. GPs discursively polarised two technologies: formal assessment versus personal enquiry, emphasising the need to ensure the scores are used sensitively and as an aid to clinical judgement rather than as a substitute. Importantly, these challenges implicitly served a function of preserving GPs' identities as professionals with expertise, constructed as integral to the process of diagnosis. Conclusion GP accounts indicated concern about threats to patient care. Contention between using severity questionnaires and delivering individualised patient care is significantly motivated by GP concerns to preserve professional expertise and identity. It is important to learn from GP concerns to help establish how best to optimise the use of severity questionnaires in depression
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