1,720,980 research outputs found
Methicillin-resistant Staphylococcus aureus CC22-MRSA-IV as an agent of dairy cow intramammary infections
Full text linkMethicillin-resistant S. aureus (MRSA) lineages have become major responsible of healthcare- and community-associated infections in human population. Bovine MRSA are sporadically detected in the dairy herd, but its presence enhances the risk of zoonosis. Some lineages are able to lose the specific host tropism, being easily transmitted from animals to humans and vice-versa. The present study aims at clarifying the epidemiology of MRSA intramammary infections in a closed dairy herd, which was running a mastitis control program since years. Quarter milk samples were collected from all lactating cows once a week for 9 weeks and bacteriologically tested. At the end of the follow-up period, also a self-taken nasal swab of the milker was analysed. Three cows (12.5%) were MRSA positive, a fourth showed a transient infection and MRSA was isolated also from the milker's nose. Somatic cell counts of infected quarters fluctuated from 1000 to 1,800,000 cells/mL. The isolates were genotyped using DNA microarrays and identified as the epidemic UK-EMRSA-15 grouping in CC22. All strains carried the genes for β-lactam and macrolide resistance. The milker isolate differed from cow isolates mainly for the absence of the untruncated β-haemolysin and the presence of the immune evasion cluster. The milker had been volunteering in a nursing home since months, thus playing the role of MRSA vector into the herd. Our results showed the adaptive capacity of such MRSA to the bovine host. Therefore, we suggest that CC22-MRSA should be regarded as a potential cause of reverse zoonosis in dairy cattle herds
Frequency domain studies for the Malta-Sicily interconnector
No full textVery long HV and EHV submarine ac cable lines can be an effective solution for bulk power transmission systems at distances up to 100 km, as demonstrated by several recent projects like the Malta-Sicily and the Mallorca-Ibiza interconnections. However the introduction of very long HV cable system can cause significant interaction between the existing network and the cable system itself. Most recent literature focuses about two main issues:
• Switching transients, mainly due to the distributed nature of the line.
• Low-order harmonic resonances, mainly due to the interaction of the cable capacitance with the (inductive) network impedance.
Even if the first issue could be counteracted by proper selection of line-end surge arresters (SAs), the latter could result in temporary overvoltages, typically as a consequence of switching manoeuvres, especially troublesome to above mentioned SAs. The relative weakness of one or both interconnected networks, in terms of short circuit current, exacerbates the above issues; very long cable lines connecting weak nodes (such as offshore windfarms or small isolated networks) should thus be investigated by means of time and frequency domain studies, also due to the current lack of information about operating results of similar projects, most of which are presently under construction.
The paper deals with the detailed frequency domain studies for the 118 km Malta-Sicily line, which will be the longest 245 kV cable in the world
Collegamenti in cavo sottomarino nel Mar Mediterraneo: Aspetti tecnologici e di sistema
No full textIl crescente interesse nelle interconnessioni tra stati e nelle centrali eoliche offshore ha portato a significativi miglioramenti nella tecnologia dei cavi sottomarini ad alta tensione.
L’articolo tratta le caratteristiche tecnologiche e le problematiche di sistema tipiche dei collegamenti elettrico sottomarini nel mare Mediterraneo, esaminando i recenti sviluppi tecnologici nei convertitori HVDC e nei cavi sottomarini.
Viene inoltre discusso lo stato dell’arte della tecnologia per le connessioni sottomarine e vengono presentati le principali problematiche relative alle connessioni sia in corrente alternata, sia in corrente continua, tenendo in conto i recenti sviluppi delle de tecnologie come ad esempio lo sviluppo di cavi tripolari isolati in XLPE di grande sezione.
La massima lunghezza e potenza trasmissibile per collegamenti in corrente alternata sono discussi in dettaglio, così come una stima delle perdite per i sistemi HVDC ed HVAC , al fine di valutare la convenienza dell’una o dell’altra soluzione per un dato progetto. Più in particolare è stato esaminato l’effetto del profilo di corrente e potenza reattiva sui cavi in c.a.The growing interest in international interconnection lines as well as offshore-located energy generation has led to the improvement of high voltage submarine transmission technology. The paper deals with the technology and system challenges typical of submarine cable links in the Mediterranean Sea. Recent developments in HVDC converters technology and submarine cables are summarized. An overview of the state-of-the-art for submarine transmission technology is provided and major issues concerning DC and AC connections, taking into account both HVDC-VSC and recent AC advances, such as large cross-section, XLPE-insulated three-core cables are outlined. Attention is focused on the assessment of actual limits of transmissible power and length of AC links and calculation of losses in HVDC and HVAC systems, aiming at the evaluation of the most convenient choice. In particular, the effect of non-uniform reactive power and current profiles along AC cables is studied
Compatibilità tra linee elettriche di trasmissione HVDC e nuove infrastrutture ferroviarie
No full textLo sviluppo della rete di trasmissione europea ha un interesse strategico per incrementare la sicurezza dell'alimentazione elettrica e per garantire ai vari operatori un accesso più facile al mercato elettrico paneuropeo. A ciò si aggiunga che le forti opposizioni per la costruzione di nuove linee aeree in altissima tensione spingono verso un uso più razionale delle infrastrutture esistenti.
L'articolo esamina la possibilità di utilizzare un tunnel ferroviario di 65 km per installare una linea elettrica di potenza nominale pari a 1000 MW [1]. Lo studio (che rientra in un'analisi più ampia che contempla oltre all'infrastruttura ferroviaria anche quella stradale) ha preso come riferimento il collegamento tra Italia e Francia in quanto, nel caso specifico, il progetto dell'alta velocità ferroviaria prevede la costruzione di due canne separate: conseguentemente il collegamento di potenza dovrebbe trovare collocazione all'interno di uno dei due tunnel ferroviari a differenza di altre casistiche (già esaminate nel caso del tunnel del Brennero [2, 3]) che prevedono invece di installare il collegamento elettrico nel tunnel pilota (o di prospezione) o in un tunnel d'emergenza.
Ciò rappresenta una vera e propria sfida ingegneristica per molteplici ragioni: gli spazi disponibili, le problematiche di accesso al tunnel, i vincoli sull'esercizio e la manutenzione dovuti a quelli prioritari dell'esercizio ferroviario, la necessità di garantire condizioni di assoluta sicurezza. Partendo dalle conclusioni dello studio di compatibilità geometrica, che ha indagato sulle varie opzioni tecnologiche (cavi c.a. ad isolamento estruso o gassoso, cavi c.c.) all'interno di un tunnel fortemente sovraccarico di servizi, la soluzione HVDC sembra essere l'unica possibile, soprattutto per gli stringenti vincoli spaziali. Lo studio di fattibilità individua inoltre nella configurazione bipolare con ritorno metallico quella con maggiori margini di disponibilità. Vengono quindi messe in evidenza le scelte tecniche e le problematiche emerse durante lo studio di fattibilità. In particolare:
le due tecnologie scelte per i cavi di polo: una più tradizionale con isolamento in carta impregnata a 500 kV e una più innovativa con isolamento in polietilene a 300 kV;
il cavo di ritorno metallico;
il calcolo delle perdite elettriche del collegamento al fine di valutarne la compatibilità termica all'interno della galleria;
le problematiche legate alla sicurezza in caso di corto circuito su un cavo di polo all'interno della galleria: approccio teorico e validazione sperimentale su spezzoni di cavo a 300 kV e 450 kV;
l'impatto elettromagnetico considerando le due opzioni di un polo per galleria o entrambi in un'unica galleria;
la compatibilità elettromagnetica tra l'alimentazione ferroviaria e il collegamento c.c. considerando la presenza di un certo contenuto armonico sul lato corrente continua e l'effetto schermante fornito dagli schermi metallici dei cavi;
valutazioni teoriche sul comportamento al fuoco dei cavi all'interno del tunnel.
La comunità europea ha co-finanziato tale studio nell'ambito del TEN-ENERGY Programme con il titolo "Studies for a new interconnection between France and Italy: Integration of Electricity and Rail Transport in the Lyon-Turin High Speed Railway French-Italian Tunnel"
An integrated transformer-shunt reactor operation device for the connection of off-shore wind-farms
No full textSteady-State And Transient Ehv Ac Cable Shunt Reactive Compensation Assessment
No full textIn recent years attention towards underground cables (UGCs) has been stimulated by the development and performance enhancement of XLPE-insulated cables at HV and EHV level. The liberalisation of the energy market with the related need to connect new power plants and strengthen the grid, in conjunction with public opposition to the construction of new overhead lines, are increasingly prompting the installation of underground HV and EHV a.c transmission lines. The possibility of integrating power transmission and other services (i.e. railway and highway transport, bridges, galleries) in the same corridor or in the same "structure" is another significant technical challenge favouring underground technologies. This field has been advocated by Cigré which has investigated the topic by means of several working groups [1-4].
The paper analyzes some issues related to the electrical behaviour of long EHV a.c. cable lines both in steady-state and in transient conditions. In particular, the paper deals with the choice of the shunt reactive compensation degree from a twofold standpoint, that is, steady-state operation and network transients. The capability charts are a useful tool for highlighting the steady-state operating characteristics of a cable link, giving an immediate outlook of admissible active and reactive power flows along the link. The same charts also show regimes associated to undesirable voltages, and can be used to estimate the needed shunt compensation.
The size of shunt compensation, lumped and equally shared at cable line terminals, can be evaluated in closed-form, based on steady-state line no-load energization/load rejection constraints. The paper points out that the rated line- and cable-charging breaking current of standard EHV circuit breakers should be checked as it may set significant minimum shunt compensation requirements, even in powerful meshed networks. It is also of interest to perform transient analyses of the cable line, aimed at verifying shunt reactor preliminary rating and determine other required characteristics of shunt reactors.
With the increasing use of cables in the EHV network the likelihood of low-order harmonic resonance, owing to the large cable capacitance, is becoming of more concern. The low order harmonic resonance can give rise to temporary overvoltages, dangerous to line apparatuses due to their sustained nature. Notably, the energy absorption withstand capability of commonly adopted surge arresters can be exceeded.
The paper shows that the feasibility of a long UGC line depends, besides the steady-state operation, on its interaction with the network in various operating conditions
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
