98 research outputs found
Lecture 6: Torsional Interharmonic Interaction Study of 75 MW Direct-Driven VSDS Motor Compressor Trains for LNG Duty
No full textLecturepg. 57-66In all-electric-driven liquefied natural gas (LNG) plants, converter-fed synchronous motors up to a power of 100 MW are being offered. During operation of compressor trains by a variable speed drive system (VSDS), integer and noninteger harmonics are generated in the converter. Intersection of integer harmonics with relevant torsional natural frequencies of the system can generally be avoided within the operating-speed range. The intersections of the noninteger excitation frequencies with torsional natural frequencies within to operating-speed range cannot be eliminated if the train is designed to operate below and above a motor supply frequency of approximate grid frequency. The generated harmonic torque excitation may have an essential impact on the torsional behavior and the reliability of the entire train and ultimately the reliability of the whole LNG plant. Due to this fact a traditional torsional analysis and specified in API 617, Seventh Edition (2002), is an obligatory task. This analysis normally considers the VSDS train operating as an individual mechanical train, including motor, coupling, and compressor, even if it is installed in a multiunit plant. As a further simplification, the torsional model does not include the full electrical/mechanical interaction.To ensure reliable operation of a 75 MW refrigerant-compressor train in an LNG plant, the effect of the full coupled electrical and mechanical VSDS train, including the electrical grid had to be investigated. In addition, with respect to torsional oscillations, two or more identical trains in parallel operation have been investigated in detail to determine the interaction. This paper details multiple issues associated with the electrical and mechanical interaction and additionally the interaction of two or more identical trains in parallel operation with respect to torsional oscillations during converter operation. The paper also provides a comparative overview of the torsional design with regard to results of the individual mechanical system, without electrical/mechanical interaction and the results of the full coupled electrical-mechanical model. The detailed analytical investigation of the behavior of the torsional system has been carried out to demonstrate the integrity of such kind of projected plant configurations of LNG duty
Precuneus connectivity and symptom severity in chronic depression<sup>✰</sup>
No full textAlthough abnormal resting state connectivity within several brain networks has been repeatedly reported in depression, little is known about connectivity in patients with early onset chronic depression. We compared resting state connectivity in a homogenous sample of 32 unmedicated patients with early onset chronic depression and 40 healthy control participants in a seed-to-voxel-analysis. According to previous meta-analyses on resting state connectivity in depression, 12 regions implicated in default mode, limbic, frontoparietal and ventral attention networks were chosen as seeds. We also investigated associations between connectivity values and severity of depression. Patients with chronic depression exhibited stronger connectivity between precuneus and right pre-supplementary motor area than healthy control participants, possibly reflecting aberrant information processing and emotion regulation deficits in depression. Higher depression severity scores (Hamilton Rating Scale for Depression) were strongly and selectively associated with weaker connectivity between the precuneus and the subcallosal anterior cingulate. Our findings correspond to results obtained in studies including both episodic and chronic depression. This suggests that there may be no strong differences between subtypes of depression regarding the seeds analyzed here. To further clarify this issue, future studies should directly compare patients with different courses of depression.</p
AI in breast screening mammography : breast screening readers' perspectives
Get PDFAcknowledgements We would like to thank all the survey respondents for their time and input. We would also like to thank the Scottish Breast Radiology Forum (SBRF) and British Society of Breast Radiology (BSBR) for their aid in dissemination of the survey. Furthermore, we would like to thank Dr Rumana Newlands for her advice on how to perform content analysis and report its results. iCAIRD Radiology Collaboration team members: Harrison D (iCAIRD Director), University of St Andrews. Black C, Murray A and Wilde K, University of Aberdeen. Blackwood JD, NHS Greater Glasgow and Clyde. Butterly C and Zurowski J, University of Glasgow. Eilbeck J and McSkimming C, NHS Grampian. Canon Medical Research Europe Ltd. – SHAIP platform. Funding This work is supported by the Industrial Centre for Artificial Intelligence Research in Digital Diagnostics (iCAIRD) which is funded by Innovate UK on behalf of UK Research and Innovation (UKRI) [project number: 104690]. The funding source was not involved in study design; collection, analysis and interpretation of data; writing of the report; or in the decision to submit the article for publication. Author infoPeer reviewe
Trajectory planning for space manipulators
Get PDFThe angular momentum of a free-flying multibody system in space is a conserved quantity. This conservation law acts as a nonholonomic constraint and manifests itself when cyclic motion of the articulated joints of an on board manipulator produces a net change in the orientation of the whole system. This poses two important and coupled problems: (a) the motion planning problem of the manipulator for attitude reorientation of the space structure using internal motion of the joints, and (b) planning the manipulator joint trajectories that produce repeatable motion of all the configuration variables. We have adopted a surface integral approach to come up with algorithms for these nonholonomic motion planning problems. .Approved for public release; distribution is unlimited.Lieutenant, United States Navyhttp://archive.org/details/trajectoryplanni109453976
Thermogravimetric investigation of thermal decomposition of copper(II) complexes with methylpyrido[2,3-d]imidazole derivatives
No full text
- …
