5,870 research outputs found
A historical comment about the GVT in short interval
No full textIn this article, the author introduces the history, progress and method in the Goldbach-Vinogradov Theorem in short interval by which every sufficiently large odd integer could be expressed as the sum of three almost equal prime numbers.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000183488400018&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701MathematicsCPCI-S(ISTP)
Investigation on the DC CB Performance during a Current Interruption Failure at First Current Zero
No full textThe vacuum interrupter is used as the key component of an active DCCB due to its excellent interruption and dielectric recovery characteristics after current zero. The vacuum interrupter can only interrupt the fault currents below the limitation of a critical di/dt and TIV, otherwise it causes a reignition and the interruption failure. In this paper, a detailed active injection DC CB model is developed, considering operation delay of switches, parasitic parameters of switches and thorough control logic. The limitation dielectric strength between the vacuum gap is defined by the cold break down voltage. Based on the numerical modelling, investigation will be performed to see the performance of DC CB with a failure interruption on the first current zero. The simulation results can help to optimize the injection circuit parameters when DC CB has a failure on the first current zero and has to interrupt in the next current zeros. This algorithm will consider predefined threshold of di/dt, chopping current and variable operation time in different scenarios.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Intelligent Electrical Power Grid
Quantitative comparison of METEOSAT-based thunderstorm detektion and nowcastin with in-situ reports in the European Severe Weather Database (ESWD)
No full textSevere thunderstorms constitute a major weather hazard in Europe, with an estimated total damage of € 5-8 billion each year. Yet a pan-European database of severe weather reports in a homogeneous data format has become available only recently: the European Severe Weather Database (ESWD). We demonstrate the large potential of ESWD applications for storm detection and forecast evaluation purposes and complement an earlier case-based study. The analysis of all warm-season (JJA) severe weather days in Europe in 2008 corroborated our earlier findings. There is a good agreement between ESWD reports and Cb-TRAM detected thunderstorms, even though no exact correspondence between ESWD reports and Cb-TRAM cells is required (e.g. due to storm morphology). Correspondingly, a large portion of ESWD reports regarded as misses by our strict in/out-of-Cb-TRAM-polygon criterion were still located close to a Cb-TRAM cell. Quantitatively, only the probability of detection (POD) can be evaluated due to the different characteristics of the two data sources. The POD for storm detection was 0.24 on average, with maximum values up to 0.58. The respective analysis for the 30 and 60 minutes nowcasts yielded average POD values of 0.11 and 0.08, respectively, with maximum values of POD exceeding 0.4 on 3 days for the 30 minutes nowcast and on one day for the 60 minutes nowcast
Improved thunderstorm weather information for pilots through ground and satellite based observing systems
No full textToday’s weather information for pilots on thunderstorm conditions on their flight path is insufficient. Weather charts provided by the World Area Forecasting Centres and taken onboard by pilots before take-off are based on forecasts of large scale weather models which are initialized only twice a day. The information of the charts is therefore outdated, at least with respect to thunderstorm occurrence, at the time of use. They can only provide a rough estimation of thunderstorm hazards for relatively large areas. In contrast, thunderstorms develop quickly within tenths of minutes up to an hour and their exact time of occurrence and location is more or less impossible to predict deterministically hours in advance.
In this paper, the value of the satellite information on thunderstorm detection over the oceans is demonstrated by applying the DLR Cb-TRAM cloud tracker (Zinner et al., 2009) to last years occurrences of aircraft accident and incident over the Atlantic. In addition, two incidents over the European area with severe turbulence and hail encounter are investigated by satellite, radar and lighting data. The aim of the study is to demonstrate the improved information pilots would gain once the thunderstorm analyses and forecasts of the satellite and ground based systems would be brought, i.e. up-linked, to the cockpit during flight.
Today, pilots have information on thunderstorm activity through onboard radar equipment which provides quite good indication on thunderstorm activity within the close range part in flight direction, about 50 miles or so, provided there is precipitation within the convective up-droughts, strong enough to give radar returns. However, the radar returns are strongly attenuated when precipitation cells are large and intense, or several cells behind one another, due to the short wave length of the radars which operate at 3 cm. In that case the pilot’s information of the situation is quite incomplete which makes it difficult for them to choose a proper path around thunderstorm cells or through a thunderstorm line. In addition there are cases where thunderstorm cells are just about to develop with weak or no returns on the radar, yet they can produce convective turbulence which can propagate to levels above the developing cells. In that case the aircraft might experience sudden turbulence without any pre-warning. Also, at high flight levels through tropical storms over the oceans, radar returns might be weak due to small droplet sizes, thereby giving a wrong indication of the severity of the storm.
In contrast to this onboard radar information, remote sensing by satellite, ground based radar and lightning can provide a more complete picture of the thunderstorm situation. Ground based systems have been developed which use this data to inspect cells from above, below and multiple viewing angles thereby providing a more complete picture of the thunderstorm situation (e.g.; Tafferner et al., 2009; Sénési et al., 2009). Thunderstorms can well be detected from satellite due to their cold cloud tops and characteristic cloud shape at already early development stage, the precipitation they produce can well be detected by radar and lightning discharges by lightning detectors.
References
Sénési, S., Y. Guillou, A. Tafferner, and C. Forster, 2009: Cb nowcasting in FLYSAFE: Improving flight safety regarding thunderstorm hazards. WMO Symposium on Nowcasting , 30 August - 4 September 2009 , Whistler, B.C., Canada
Tafferner, A. , C. Forster, S. Sénési, Y. Guillou, P. Tabary, P. Laroche, A. Delannoy, B. Lunnon, D. Turp, T. Hauf, and D. Markovic, 2009: Nowcasting thunderstorm hazards for flight operations: the CB WIMS approach in FLYSAFE. European Air and Space Conference (CEAS) , 26 - 29 Oct. 2009, Manchester, UK
Zinner, T., Mannstein, H., Tafferner, A. , 2008: Cb-TRAM: Tracking and monitoring severe convection from onset over rapid development to mature phase using multi-channel Meteosat-8 SEVIRI data. Meteorol. Atmos. Phys. 101, 191–21
Technical performance of different DC CB technologies for future HVDC Grids
No full textMultiterminal dc (MTDC) network is preferred due to its reliability, security of supply and flexibility. However, MTDC network also comes with the protection challenges resulting from dc faults. Hence, the dc circuit breaker (DC CB) is imperative in such a network. In these recent years, several DC CB technologies have been proposed and demonstrated by different manufacturers. Besides, these DC CB technologies differ from each other in terms of the speed of operation, interruption capability and costs. Hence, for the optimal performance of the MTDC network, a study of the co-ordinative operation of different DC CB technologies is required. In this thesis, two typical types of DC CBs are modelled in detail and implemented in a 4-terminal MTDC network in PSCAD environment, by considering operation time, interruption capability and interruption characteristics. The obtained results are used for DC CB’s selection optimization methodology for the future MTDC networks. Similarly, a scaled model of DC CB has to be analysed in terms of its interruption capability in MTDC network considering various scenarios. Therefore, in this master thesis, technical performance of DC CB technologies is conducted for a test and multiterminal dc network in EMT based software environment.The DC CB is the key to unlock the reliable operation of a Multi-terminal direct current network, whereas fast, effective and accurate models are frequently needed for system-level studies. Due to higher subsystem components in DC CB, a detailed DC CB model creates a bottleneck in the network analysis. This thesis also proposes and compares, an average model with a detailed model of Voltage source converter Assisted Resonant Current (VARC) and Mechanical DC CB in MTDC Network in terms of their performance and computation time for two typical simulation cases. The average and detailed model is modelled and simulated on the PSCAD/EMTDC electromagnetic transient platform. Decisively, this thesis concludes by presenting an accurate response of the average model during the fast transient event, showing additional computational advantage.<br/
Preparation and Characterization of Radar Wave Absorbing CB/PP Fibers
No full textThe compound fibers were melt-spun by co-extrusion of polypropylene and polypropylene/ fillers master-batches. The melt-spun fibers were characterized by DSC, SEM and MSERA. Crystallinity of compound fibers with carbon black (CB) was more than that of PP alone. SEM results showed that inorganic particles in fibers had relatively good dispersibility. The electrical resistance of fibers containing CB particles reached minimum at the 10 Wt% CB content. Fibers with CB showed the good radar absorption effects and the absorption property was improved with the increase in CB content.</jats:p
Nowcasting Thunderstorms for Munich Airport
No full textThe successful demonstration and assessment of the DLR thunderstorm nowcasting algorithms at Munich Airport during two campaigns in the summers of 2010 and 2011 are described. The algorithms Cb-TRAM and Rad-TRAM, that detect, monitor, and forecast up to one hour (nowcast) thunderstorm cells from satellite and radar data, run in real time and provided new thunderstorm products for users at the airport. The products were presented on displays the users were already familiar with as well as on webpages designed by DLR. On the webpages, also additional information like measurements with DLR’s polarimetric radar and model forecasts was shown. Moreover, thunderstorm warnings were is-sued and sent via email to the users whenever a thunderstorm was detected in the terminal manoeu-vring area of the airport of Munich. The nowcasting skills of Rad-TRAM and Cb-TRAM are encouraging, especially for lead times up to 30 minutes, and the user feedback on the DLR thunderstorm products was very positive. The Rad-TRAM and Cb-TRAM products provide a good overview on the situation and its future development, and the thunderstorm warnings were very helpful for the collaborative decision making at the airport. However, some suggestions for improvements were made like the demand for nowcasts beyond one hour. This will be considered within the integrated weather forecast system, WxFUSION, which has been further developed during the campaigns
The characteristics of the polish CB-language
No full textThe paper analyzes the language used by drivers on the Citizens’ Band radio (CB radio). The
users of the radio communicate only in speech, their communication is highly pragmatic and
based on partnership. The utterances alternate between formal and informal ones, which
determines the range and register of vocabulary. Drivers often use diminutives and polite
addresses thus creating the atmosphere of mutual respect and cordiality, which can be
comforting and reassuring for strangers who happen to establish a casual contact. The specific
language used on the CB radio fulfils two basic functions: it creates a sense of community
among drivers and protects the information passed on as warnings. At the end of the paper,
the author appends a comprehensive glossary of the CB language
Modelling of GO/PPy/CB and rGO/PPy/CB nanocomposite supercapacitors using an electrical equivalent circuit
No full textIn this study, supercapacitor device performances of graphene oxide (GO), reduced graphene oxide (rGO), polypyrrole (PPy), and ternary nanocomposites of GO, PPy, and carbon black (CB) as GO/PPy/CB and rGO/PPy/CB were firstly prepared using the in situ polymerization method. The obtained composite materials were characterized by scanning electron microscopy energy–dispersive X-ray (SEM–EDX), Fourier-transform infrared-attenuated transmission reflectance (FTIR-ATR), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), atomic force microscopy (AFM), Brunauer–Emmett–Teller (BET) surface area analysis, cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopic (EIS) methods. The highest specific capacitance (Csp) of the rGO/PPy/CB nanocomposite was obtained as Csp = 39, 48, and 27.86 F × g?1 by three methods of CV, GCD, and EIS, respectively. Two equivalent circuit models of Rs(CdlRct) and LRs(QRct) were presented to compare equivalent circuit parameters. Theoretical and experimental values are compatible with each other. Graphical abstract: [Figure not available: see fulltext.]. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.Trakya ÜniversitesiThis work is a part of the research project NKUBAP.01.?NAP.19.213 approved by the Scientific and Research Project Unit (Tekirdag Namik Kemal University). This research grant is gratefully acknowledged. We thank Prof. Dr. Murat Turkyilmaz and Ozan Yoruk (PhD student) for TGA and BET measurements (TUTAGEM, Trakya University, Turkey)
CB[7]- and CB[8]-Based [2]-(Pseudo)rotaxanes with Triphenylphosphonium-Capped Threads: Serendipitous Discovery of a New High-Affinity Binding Motif
No full textThe synthesis of
new triphenylphosphonium-capped cucurbit[7]uril
(CB[7])- and cucurbit[8]uril (CB[8])-based [2]rotaxanes was achieved
by a simultaneous threading-capping strategy. While the use of CB[7]
produced the designed [2]rotaxane, attempts to obtain the CB[8] analogue
were unsuccessful due to the unexpected strong interaction found between
the host and the phosphonium caps leading to pseudo-heteroternary
host–guest complexes. This unusual binding motif has been extensively
studied experimentally, with results in good agreement with those
obtained by dispersion-corrected DFT methods
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