Evaluating the impact of superconducting fault current limiters on distribution network protection schemes

Rising fault levels are becoming increasingly problematic in the UK distribution network, with large sections of the network operating near to its designed fault level capability. With the increase in penetration of distributed generation that is expected in the coming years, this situation is becoming more pressing. Traditional methods of dealing with the issue may not be appropriate - upgrading plant is expensive and disruptive, while network reconfiguration can compromise security of supply. Superconducting Fault Current Limiters (SFCLs) are emerging as a potential solution, with installations now taking place in several locations worldwide. The integration of an SFCL into a network involves a number of challenges, particularly concerning the coordination of protection systems. The operation of existing protection schemes may be compromised due to the increased resistance in the network during a fault (in the case of a resistive SFCL). Furthermore, the reduction in fault levels, although desirable, can have a detrimental impact on protection operating times. This paper will consider an existing medium voltage network in the UK, which incorporates distributed generation capacity. The performance of IDMT overcurrent and distance protection schemes will be examined when an SFCL is installed in this network. In particular, the increased operating time of overcurrent relays will be discussed along with grading implications. The impact on distance protection reach will also be examined. A variety of network operational scenarios including SFCL placement and fault conditions will be considered and compared. Recommendations will be made in terms of protection settings and SFCL placement in order to mitigate the aforementioned issues

Inductive learning: Does interleaving exemplars affect long-term retention?

Purpose: The present study investigated whether or not the benefi ts of interleaving of exemplars from several categories vary with retention interval in inductive learning. Methodology: Two experiments were conducted using paintings (Experiment 1) and textual materials (Experiment 2), and the experiments used a mixed factorial design. Forty students participated in each experiment for course credit. In each experiment, participants studied a series of exemplars from several categories which were presented massed and interleaved, and later their induction was tested either shortly after the study phase (short-term retention) or after a week's delay (long- term retention). Findings: Consistent with fi ndings from previous studies, the interleaving effect was found in the short-term retention condition, and crucially, the present study provided the initial evidence that interleaving of exemplars also affected long-term retention. Interestingly, massing was judged to be more effective than spacing (interleaving) in most groups, even when actual performance showed the opposite. Significance: The present study shows that interleaved exemplars have considerable potential in improving inductive learning in the long term. For example, induction is used in case-based reasoning which requires one to start with learning from specifi c cases, and then form generalizations of these cases by identifying the commonalities between them. In order to enhance long-term retention, educators may want to consider using interleaved presentation rather than massed presentation in teaching examples or cases from a particular category or concept

Are word representations abstract or instance-based? Effects of spelling inconsistency in orthographic learning

In Experiment 1, 62 10-year-old children studied printed pseudowords with semantic information. The items were later represented in a different format for reading, with half of the items spelled in the same way as before and half displayed in a new phonologically equivalent spelling. In a dictation test, the exposure to an alternative spelling substantially increased the number of errors that matched the alternative spelling, especially in good spellers. Orthographic learning predicted word identification when accuracy on orthographic choice for words was controlled. In Experiment 2, the effects on dictation responses of exposure to a misspelling versus the correct spelling, and the interactive effect of spelling ability, were confirmed relative to a no-exposure control in adults. The results support a single-lexicon view of reading and spelling and have implications for abstractionist and instance-based theories of orthographic representations

A 4-Planet System Orbiting the K0V Star HD 141399

We present precision radial velocity (RV) data sets from Keck-HIRES and from Lick Observatory's new Automated Planet Finder Telescope and Levy Spectrometer on Mt. Hamilton that reveal a multiple-planet system orbiting the nearby, slightly evolved, K-type star HD 141399. Our 91 observations over 10.5 years suggest the presence of four planets with orbital periods of 94.35, 202.08, 1070.35, and 3717.35 days and minimum masses of 0.46, 1.36, 1.22, and 0.69 Jupiter masses respectively. The orbital eccentricities of the three inner planets are small, and the phase curves are well sampled. The inner two planets lie just outside the 2:1 resonance, suggesting that the system may have experienced dissipative evolution during the protoplanetary disk phase. The fourth companion is a Jupiter-like planet with a Jupiter-like orbital period. Its orbital eccentricity is consistent with zero, but more data will be required for an accurate eccentricity determination.Comment: 11 pages, 13 figures, To appear in the Astrophysical Journa

Hexafluorosilicate and tetrafluoroborate coordination to lead(II) di- and tri-imine complexes – Unusual fluoroanion coordination modes

AbstractLead(II) tetrafluoroborate and hexafluorosilicate complexes with 2,2′-bipyridyl, 1,10-phenathroline and 2,2′:6′,2″-terpyridyl have been prepared from the ligand and lead salt in aqueous/MeCN. Crystal structures are reported for [Pb(bipy)2(SiF6)], [Pb(phen)2(SiF6)] and [Pb(bipy)2(BF4)2] which are dinuclear with each lead coordinated “cis” to the two diimines and with the bridging fluoroanions completing eight or nine-coordination. [Pb(phen)2(BF4)2] is eight-coordinate and mononuclear with “cis” diimines and two κ2-BF4− groups. [Pb(phen)2(H2O)2(SiF6)] is also mononuclear with a κ2-SiF62− group and two coordinated water molecules. Reaction of Pb(BF4)2 with 2,2′:6′,2″-terpyridyl gave only [Pb(terpy)3][BF4]2, but Pb(SiF6) produced [Pb(terpy)(H2O)(SiF6)], which is a chain polymer with bridging SiF62− groups and significant π-stacking of the imine rings. The work has identified a number of coordination modes of the SiF62− anion, which has been little used in coordination chemistry but proves to be versatile and also stable (to decomposition/hydrolysis)

Astro2020 Science White Paper: Toward Finding Earth 2.0: Masses and Orbits of Small Planets with Extreme Radial Velocity Precision

Having discovered that Earth-sized planets are common, we are now embarking on a journey to determine if Earth-like planets are also common. Finding Earth-like planets is one of the most compelling endeavors of the 21st century - leading us toward finally answering the question: Are we alone? To achieve this forward-looking goal, we must determine the masses of the planets; the sizes of the planets, by themselves, are not sufficient for the determination of the bulk and atmospheric compositions. Masses, coupled with the radii, are crucial constraints on the bulk composition and interior structure of the planets and the composition of their atmospheres, including the search for biosignatures. Precision radial velocity is the most viable technique for providing essential mass and orbit information for spectroscopy of other Earths. The development of high quality precision radial velocity instruments coupled to the building of the large telescope facilities like TMT and GMT or space-based platforms like EarthFinder can enable very high spectral resolution observations with extremely precise radial velocities on minute timescales to allow for the modeling and removal of radial velocity jitter. Over the next decade, the legacy of exoplanet astrophysics can be cemented firmly as part of humankind's quest in finding the next Earth - but only if we can measure the masses and orbits of Earth-sized planets in habitable zone orbits around Sun-like stars.Comment: Science White Paper Submitted to the Astro2020 Decadal Survey (35 co-signers in addition to co-authors

Racial Microaggressions within the Advisor-advisee Relationship: Implications for Engineering Research, Policy, and Practice

The underrepresentation of Black men in engineering highlights a missing segment of the population who could contribute to the knowledge economy.1 An increase in Black men in engineering could lead to an increase in Black faculty members - and in general, role models - who cold teach and inspire future generations of students in science, technology, engineering, and mathematics (STEM). To address this national concern, stakeholders must first identify prevailing issues such as racial microaggressions, which threaten the long-term participation of Black men in science and engineering