3,221 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
Obtaining information from eyewitnesses : effects of retrieval support in eyewitness interviews
No full textIn many police cases eyewitness statements are the only available evidence. Hence, whether a crime can be solved may critically depend on the statement quality. Seeking to improve the reliability of eyewitness statements, the thesis examined the effectiveness of retrieval support during the interview when the witnessing conditions were suboptimal (e.g., experience of stress during the crime), as well as retrieval support through repeated interviews. Retrieval support refers to techniques that help witnesses get access to their recollections (e.g., asking the witness to picture the incident in his/her mind). The results showed that retrieval support improves recall performance only after some suboptimal conditions. Furthermore, recall performance can be enhanced when witnesses are interviewed several times. Unfortunately, police detectives in the Netherlands are not aware of the latter, as this research has shown. Therefore, interview trainings need to be revised to improve police detectives’ knowledge about human memory
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
Das Eigenständige Vernehmungsprotokoll für Augenzeugen: Ein neues Verfahren, mit dem Zeugen sich selbst vernehmen können
No full textIn order to obtain a comprehensive and accurate eyewitness statement eyewitnesses should be interviewed as soon as possible after the crime. When an interview is conducted with a considerable delay, the quality of the witnesses' statements is likely to have suffered due to the forgetting of information or the influence of misinformation. This can be hindering for the police investigation. In order to counteract these problems, the self-administered interview (SAI) was developed. It is based upon the Cognitive Interview and is distributed to the witnesses by the police directly after the crime. Witnesses can independently complete the interview. It is the aim of the present article to present this recall tool as well as first research results. The latter indicate that the SAI elicits a comprehensive recall and, more importantly, is able to preserve memory for a subsequent interview. Additionally, the SAI provides a number of practical advantages for police work which are also discussed
Would you recognize the perpetrator? What do you need to know when you have to make an identification from a lineup?
No full text
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
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