Providing dc fault ride-through capability to H-bridge MMC-based HVDC Networks

E. Kontos,R. Teixeira Pinto,P. Bauer 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

This paper proposes a framework to achieve dc fault ride-through capability in multi-terminal dc networks (MTdc), when H-bridge multilevel modular converters (MMC) are used. The studied network consists of four voltage-source converters (VSC) for high voltage direct current (HVdc) transmission. Two of these VSC converters connect two offshore wind farms (OWF) to the main HVdc link between two asynchronous onshore grids, in a radial configuration. In case of a dc fault, H-bridge MMCs are able to block the fast developing currents and drive them to zero, allowing for fast mechanical disconnectors to isolate the faulty cable segment and reconfigure the grid layout. In this paper, the effect of the dc fault location to the grid behavior is analysed both at the fault isolation phase, as well as at the grid restoration phase. Moreover, the worst-case dc fault scenario for the studied network is identified. Finally, the total fault recovery time of the MTdc network is estimated. The study showed that Hbridge MMCs are unable to isolate the faulty part of the network without de-energizing the MTdc grid. However, the proposed framework allows for fast grid restoration within 3.6 s without the need for expensive dc breakers.

A Season-Long Examination of Injuries Among Female High School Varsity Soccer Players

( Anthony P. Kontos ),( Eugene W. Brown ) 한국스포츠정책과학원(구 한국스포츠개발원) 2000 International Journal of Applied Sports Sciences Vol.12 No.1

The participation of female high school soccer players has not been examined in relation to rate, type, site, and severity of injuries. Therefore, a prospective investigation of injuries among 92 female players participating in varsity high school soccer was conducted. An overall injury rate of 15.9/1000 hours of participation was reported. The injury rate for matches (29/1000 hours) was much higher than for practices (7.9/1000 hours). The average injury resulted in 2.17 days away from competition. The lower extremity accounted for 86.7% of all injuries. The ankle (27.9%) was the most frequently injured area. Contusions (39.4%), strains (30.7%), and sprains (22.1%) were the most common types of injuries. Self-perceived levels of physical condition and soccer skill levels were positively related to the number of injuries. Participants` self-perceived levels of physical condition and experience (number of years) were positively related to the severity of injuries. Overall, the injury rate in this study was lower than in previous studies of female soccer players, suggesting that female high school soccer is relatively safe sport.

Nanospintronics with carbon nanotubes

Cottet, A,Kontos, T,Sahoo, S,Man, H T,Choi, M-S,Belzig, W,Bruder, C,Morpurgo, A F,Schö,nenberger, C Institute of Physics 2006 Semiconductor science and technology Vol.21 No.11

<P>One of the actual challenges of spintronics is the realization of a spin transistor allowing control of spin transport through an electrostatic gate. In this paper, we report on different experiments which demonstrate gate control of spin transport in a carbon nanotube connected to ferromagnetic leads. We also discuss some theoretical approaches which can be used to analyse spin transport in these systems. We emphasize the roles of the gate-tunable quasi-bound states inside the nanotube and the coherent spin-dependent scattering at the interfaces between the nanotube and its ferromagnetic contacts.</P>

AC fault clearing within an MMC-based DC hub

M. Poikilidis,E. Kontos,P. Bauer 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

As the number of high voltage (HVDC) installations is increasing, there is a growing need for interconnection to create more efficient grids. To tackle the main challenges in HVDC grids, a multiport DC-DC converter, often referred to as DC hub, is considered a solution. This paper provides a methodology for the clearing of AC faults within the DC hub and the protection of the system during a fault. A methodology is also presented for the safe connection or disconnection of additional ports from the DC hub without affecting the operation of the other ports. A design based on modular multilevel converters (MMC) is chosen due to their inherent advantages and its control operation is described. A DC hub was modelled in Matlab/Simulink and was tested in a case study including the interconnection of three DC lines in symmetric monopolar configuration, operating at different voltage levels.

Comparison of the Incidences of Selected Events Performed by Youth Players in Regulation and Modified Soccer Games

( Eugene W. Brown ),( David M. Wisner ),( Anthony Kontos ) 한국스포츠정책과학원(구 한국스포츠개발원) 2000 International Journal of Applied Sports Sciences Vol.12 No.1

Videotape data were collected on youth soccer games played under two conditions: 11 players per side on α regulation field and 7 players per side on α smaller field. Multivariate analysis of variance (MANOVA) was used to analyze selected incidences of events per ten minutes of game time per field player. Comparisons were made between the two field/player combinations, between boys and girls, and between second-grade and fourth-grade players. Significant differences were found between regulation and modified play (F(3,16)=47.93, p=0.004), with nearly all measures for modified play being significantly greater, suggesting that modified play offers greater exposure to game events and thus greater opportunity for learning and skill development. No significant differences were found between boys and girls (F(3,16)= 4.86, p=0.109). Significant differences were found between second-grade and fourth-grade players (F(3,16)=60.49, p=0.003), mostly favoring older players. The amount of time the ball remained in play was also analyzed. Under both field/player combinations the ball remained in play less than 60 percent of the total game time.

A Fast Steady-State Loss Model of a Modular Multilevel Converter for Optimization Purposes

A. Papadopoulos,S. Rodrigues,E. Kontos,T. Todorcevic,P. Bauer 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

Lesnicar and Marquardt introduced a Modular Multilevel Converter (MMC) topology back in 2003. Although this topology has received a great deal of attention in recent years by both the research community and industry, hitherto no steadystate model has been developed which accurately captured all the relevant power losses while being computationally light. Hence, the aim of this paper is to introduce a fast MMC loss model which captures the key sources of power losses in steady-state operation. The model only requires information which is known a priori, e.g. datasheet information of the components. The proposed model was compared to a loss model developed by Marquardt. Both models presented similar results under the same assumptions. However, the proposed model captures the switching losses more realistically and considers the temperature of operation of the electronics, as well as the losses of the inductors and cooling system in the overall efficiency of the MMC. To validate these new additions, the proposed steady-state model was compared to a dynamic model. Once again the proposed model was able to capture the different sources of power losses. Nonetheless, results demonstrated that the balancing strategy greatly influences the efficiency of the MMC. Therefore, information regarding the envisioned control strategy is necessary to accurately calculate the efficiency curve of the MMC.

Trimethylsulfonium Lead Triiodide: An Air-Stable Hybrid Halide Perovskite

Kaltzoglou, Andreas,Stoumpos, Constantinos C.,Kontos, Athanassios G.,Manolis, Georgios K.,Papadopoulos, Kyriakos,Papadokostaki, Kyriaki G.,Psycharis, Vasilis,Tang, Chiu C.,Jung, Young-Kwang,Walsh, Aro ACS AMERICAN CHEMICAL SOCIETY 2017 Inorganic Chemistry Vol.56 No.11

<P>We report on the synthesis, characterization, and optoelectronic properties of the novel trimethylsulfonium lead triiodide perovskite, (CH3)(3)SPbI3. At room temperature, the air-stable compound adopts a hexagonal crystal structure with a 1D network of face-sharing [PbI6] octahedra along the c axis. UV-vis reflectance spectroscopy on a pressed pellet revealed a band gap of 3.1 eV, in agreement with first-principles calculations, which show a small separation between direct and indirect band gaps. Electrical resistivity measurements on single crystals indicated that the compound behaves as a semiconductor. According to multi-temperature single-crystal X-ray diffraction, synchrotron powder X-ray diffraction, Raman spectroscopy, and differential scanning calorimetry, two fully reversible structural phase transitions occur at -5 and ca. -100 degrees C with reduction of the unit cell symmetry to monoclinic as temperature decreases. The role of the trimethylsulfonium cation regarding the chemical stability and optoelectronic properties of the new compound is discussed in comparison with APbI(3) (A = Cs, methylammonium, and formamidinium cation), which are most commonly used in perovskite solar cells</P>

Multifocal Bilateral Breast Cancer and Breast Follicular Lymphoma: A Simple Coincidence?

Adamantios Michalinos,Theodoros Vassilakopoulos,Georgia Levidou,Penelope Korkolopoulou,Michalis Kontos 한국유방암학회 2015 Journal of breast cancer Vol.18 No.3

Breast cancer coexisting with lymphoma is a rare condition with various diagnostic and therapeutic implications. In this report, we describe the case of a 55-year-old Caucasian woman who presented with simultaneous ductal carcinoma in situ of the right breast, and follicular lymphoma involving an inguinal lymph node and the left breast. The patient underwent local excision and radiotherapy for the ductal carcinoma in situ, while a watch and wait strategy was adopted for the lymphoma. Two years later, the patient presented with multifocal ductal carcinoma of the left breast and reappearance of the lymphoma in the left axillary lymph nodes. She underwent bilateral mastectomy, left sentinel node biopsy, and chemotherapy. Synchronous follicular lymphoma and bilateral metachronous breast carcinoma has not been described previously. Diagnosis is based on tissue histology after excision or a needle biopsy. Treatment for these two diseases is distinct, and a multidisciplinary approach should be adopted.

Influence of pyridine ligand nature and the corresponding ruthenium(II) dye molecular structure on the performance of dye-sensitized solar cells

Konti, Georgia,Chatzivasiloglou, Evaggelia,Likodimos, Vlassis,Kantonis, Georgios,Kontos, Athanassios G.,Philippopoulos, Athanassios I.,Falaras, Polycarpos Korean Society of Photoscience 2009 Photochemical & photobiological sciences Vol.8 No.5

cis-$[Ru(bpy)_2(L^n)]Cl_2$ (n = 1, $L^1$ = 4-carboxy-2-(2'-pyridyl)quinoline (2); n = 2, $L^2$ = 2,2'-pyridine-4,4'-dicarboxylic acid (4)); and cis-$[Ru(bpy)_2(L')_2)]Cl_2$ (L' = 4-pyridinecarboxylic acid (6)) complexes, with surface anchoring groups, are prepared from the reaction of cis-[$Ru(bpy)_2Cl_2$] (1) with the appropriate ligand ($L^1$, $L^2$, L'). Ion exchange in aqueous solution with $NH_4PF_6$ gives the corresponding bis(hexafluorophosphate) derivatives cis-$[Ru(bpy)_2(L^1)](PF_6)_2$ (3), cis-$[Ru(bpy)_2(L^2)](PF_6)_2$ (5) and cis-$[Ru(bpy)_2(L')_2](PF_6)_2$ (7), respectively. The photo-electrochemical properties of the dyes (2-7) are investigated and the efficiency of the corresponding dye sensitized solar cells is compared to a N719 sensitized device, under similar fabrication and testing conditions.

Observation of the frozen charge of a Kondo resonance

Desjardins, M. M.,Viennot, J. J.,Dartiailh, M. C.,Bruhat, L. E.,Delbecq, M. R.,Lee, M.,Choi, M.-S.,Cottet, A.,Kontos, T. Macmillan Publishers Limited, part of Springer Nat 2017 Nature Vol.545 No.7652

<P>The ability to control electronic states at the nanoscale has contributed to our modern understanding of condensed matter. In particular, quantum dot circuits represent model systems for the study of strong electronic correlations, epitomized by the Kondo effect(1-3). We use circuit quantum electrodynamics architectures to study the internal degrees of freedom of this many-body phenomenon. Specifically, we couple a quantum dot to a highquality- factor microwave cavity to measure with exceptional sensitivity the dot's electronic compressibility, that is, its ability to accommodate charges. Because electronic compressibility corresponds solely to the charge response of the electronic system, it is not equivalent to the conductance, which generally involves other degrees of freedom such as spin. Here, by performing dual conductance and compressibility measurements in the Kondo regime, we uncover directly the charge dynamics of this peculiar mechanism of electron transfer. The Kondo resonance, visible in transport measurements, is found to be ` transparent' to microwave photons trapped in the high-quality cavity, thereby revealing that (in such a many-body resonance) finite conduction is achieved from a charge frozen by Coulomb interaction. This freezing of charge dynamics(4-6) is in contrast to the physics of a free electron gas. We anticipate that the tools of cavity quantum electrodynamics could be used in other types of mesoscopic circuits with many-body correlations7,8, providing a model system in which to perform quantum simulation of fermion-boson problems.</P>