297 research outputs found
Full scale impact testing of ski safety barriers using an instrumented anthropomorphic dummy
No full textThe results of full scale testing on type A nets and mattresses are reported. Tests were performed after using an anthropomorphic dummy wearing boots, skis and helmets, developed for the scope. The tests were performed in the field by means of a tower pendulum of 18 m height. Maximum impact speed was 66 km/hr: head and chest deceleration values measured by means of tri-axial accelerometers were evaluated together with high speed video taken from the top of the impact area. The method can be applied for the validation of safety barriers in skiing and for the evaluation of protective equipments
Electric Drives with Permanent Magnet Synchronous Machines Connected to Internal Combustion Engines
No full textIn recent years, the increasing cost of oil and Earth global warming due to greenhouse gases have pushed the scientific research, the governments and thus the markets in the direction of a higher efficiency of the systems in order to reduce the use of this fuel and therefore its associated emissions of CO2.
Nowadays, the most involved sectors of this technological revolution are the fields of electricity generation and the transportation. In fact, these two sectors are the main accountable of CO2 global emission, that are associated for about 45% to electricity generation and for about 30% to transport. Moreover, it should be noted that although the oil is not a renewable energy source, currently about 40% of the production world energy depends on oil and the level of dependence rises to about 80% in the transportation sector where the majority of vehicles is powered by an engine fueled by oil derivatives.
For these reasons, the scientific research in the last decade was focusing on these issues in particular in emerging fields such as distributed cogeneration and hybrid electric vehicles. In particular, new systems of distributed energy are studied, which are capable to increase the energy efficiency of the plant because the electrical and thermal energy are produced in combined way and directly in the site where they are required. In this way the losses of the network can be reduced. Instead, in the field of hybrid electric vehicles the use of the electric machine can help to increase the efficiency of the power-train in the various working points. These hybrid systems allow to reduce up to 30% the fuel consumption and associated emissions compared to a conventional vehicle.
With this historical context this thesis is focused in the study of a power-train structure of domestic cogeneration system or a vehicle, namely the analysis of a system composed by an internal combustion engine directly connected to an electric machine. The two principal tasks of the electric machine are: startup of the internal combustion engine and generate on electric energy. In the case of a hybrid electric vehicle, in addition to those listed above, there are other two operation modes that are: increase the engine torque during the acceleration and recovering the energy during braking phase. Among the various types of electrical machines existing in the market, the permanent magnet synchronous machines take up an important position in the cogeneration and
hybrid vehicle fields. In fact, this kind of electric machine allows to obtain: a high performance, high torque density, high overload capacity, a good robust construction, compact volume, and therefore low weight. Furthermore this type of electric machine can work at variable speeds and operate as motor and as generator with comparable performance.
For this reason in this Ph.D. thesis the electrical drives composed by an internal combustion engines direct connected to permanent magnet synchronous electric machines will be presented.
The author’s doctoral thesis has been carried out at the Electric Drive Laboratory of University of Padova, which since more than twenty years is active in the design of electrical machines and their control through research projects with industrial partners and scientific publications in journals and in international conferences. Therefore, although in the literature there are several books discussing an electric drives, thanks to the experience acquired in this laboratory the author intention is to emphasize with greater detail the aspects and basic notions which in his opinion are fundamental to the design of on electric drive devoted to the applications subject of this work.
In addition, in the opinion of the author, unlike a paper on journal or conference the doctoral thesis should be reasonably self-contained and should be understandable even by a non expert of this field of research; therefore also basic aspects of an electric drive and its control have been reported with detail.
So the work reported in this thesis is essentially composed by two parts, the first part is made up by the first four Chapters and the second one is composed by the last two Chapters.
In the first part of Ph.D. thesis the basic aspects, that are required for a good knowledge on the electric drives field, have been reported. In particular the design aspects and fundamental characteristics of electric machine control, operating limits of a permanent magnet synchronous machine, and power converter have been pointed out. The second part of Ph.D. thesis is focused on the design aspects of electric drive for a domestic cogeneration system and for hybrid electric motorcycle. In particular for CHP system some effective techniques, that can help to reduce the vibration and noise problems due to the internal combustion engine, have been described. In the field of hybrid electric motorcycle the main design choices carried out in order to achieve a hybrid electric motorcycle prototype with good performance are reported.In questi ultimi anni l’aumento del costo del petrolio e il riscaldamento globale della terra dovuto ai gas serra ha spinto il settore scientifico, i governi e quindi il mercato nella direzione di una più alta efficienza dei sistemi con lo scopo di ridurre l’utilizzo di questo combustibile e quindi le sue emissioni di CO2 associate. Oggigiorno i settori più coinvolti in questa rivoluzione tecnologica sono il settori della generazione di energia elettrica e il settore dei trasporti. Infatti questi due settori sono
i principali responsabili di emissioni di CO2 globali della terra che sono associate per circa il 45% alla generazione elettrica e per circa 30% ai trasporti. Inoltre va ricordato che sebbene il petrolio non sia una fonte di energia rinnovabile attualmente circa il 40% dell’energia mondiale dipende dal petrolio e questo livello di dipendenza sale a circa 80% nel settore dei trasporti dove la maggior parte dei veicoli è spinta da un motore alimentato da derivati del petrolio.
Per questi motivi la ricerca scientifica negli ultimi dieci anni si sta concentrando su questi problematiche in particolare nei settori emergenti quali cogenerazione distribuita e veicoli ibridi. In particolare vengono studiati nuovi impianti di energia distribuita capaci di aumentare l’efficienza energetica producendo in maniera combinata energia elettrica e termica direttamente dove richiesta e solo se necessaria in questo modo si riducendo le perdite di rete. Nel settore dei veicoli ibridi invece l’utilizzo del motore elettrico può aiutare ad aumentare l’efficienza del motore termico nei vari punti di lavoro, questi sistemi consentono infatti di migliorare fino al 30% le prestazioni in termini di consumi ed emissioni rispetto ad un veicolo tradizionale.
Con questo contesto storico la tesi si è focalizzata nello studio di una struttura della catena di potenza di un veicolo o di un sistema di cogenerazione di piccola taglia ossia l’analisi di un sistema composto da un motore endotermico direttamente calettato con una macchina elettrica. La macchina elettrica viene generalmente utilizzata con due funzioni principali: avviare il motore a combustione e generare energia elettrica. Nel caso di un veicolo ibrido vi sono altre due funzioni che si aggiungono a quelle appena elencate ossia la fase di incremento di coppia durante le accelerazioni e una fase di recupera di energia durante le frenate.
Tra le varie tipologie di macchine elettriche esistenti nel mercato, le macchine sincrone a magnete permanente occupano un posto di rilievo in questi settori. Infatti questa tipologia di macchina elettrica consente di ottenere: un alto rendimento, un’alta densità di coppia, notevole capacità di sovraccarico, una buona robustezza costruttiva, volumi compatti e quindi peso ridotto. Inoltre questo tipo di macchina può lavorare a velocità variabile e può operare con prestazioni aragonabili sia come motore che come generatore.
Per questo motivo nella tesi verranno presentati azionamenti elettrici basati su motori a combustione interna calettati a macchine elettriche sincrone a magneti permanenti.
La tesi di dottorato dell’autore è stata svolta presso il laboratorio di azionamenti elettrici di Padova, il quale da più di venti anni è attivo nel campo della progettazione di macchine elettriche e del loro controllo mediante progetti di ricerca con partner industriali e pubblicazioni scientifiche su riviste e su conferenze internazionali. Quindi sebbene siano presenti in letteratura molti libri che parlano di azionamenti elettrici grazie all’esperienza dell’autore maturata in questo laboratorio l’autore ha voluto enfatizzare con maggiore dettaglio gli aspetti e le nozioni che secondo la sua opinione sono
fondamentali per la progettazione di un azionamento elettrico.
Inoltre secondo il parere dell’autore al tesi di dottorato a differenza di un articolo su conferenza o su rivista deve essere autonoma e deve poter essere compresa anche da un non esperto del settore pertanto sono stati riportati con dettaglio anche aspetti base di una azionamento elettrico e del controllo motore. Quindi il lavoro riportato in questa tesi di dottorato è diviso sostanzialmente in due parti la prima composta dai primi quattro capitoli e la seconda parte composta dagli ultimi due capitoli. Nella prima parte sono state riportate le nozioni fondamentali necessarie per una buona conoscenza sul settore degli azionamenti elettrici in particolare nella parte di controllo motore, limiti di funzionamento di un motore sincrono a magneti permanenti e inverter di potenza.
Mentre la seconda parte si è focalizzata sulla descrizione della progettazione di un azionamento per un sistema di cogenerazione domestica e per motociclette ibride.
Nell’ambito della cogenerazione sono state descritte alcune tecniche che consentono di ridurre il problema delle vibrazioni dovute al motore a combustione interna. Nel settore della motocicletta ibrida sono state mostrate le principali scelte di progettazione effettuate per realizzare un prototipo efficace e funzionante di motocicletta ibrida
Capacitance-based sensor for monitoring bees passing through a tunnel
No full textA sensor has been developed to monitor objects passing through tunnels using a capacitance bridge. While the sensor concept is easily adaptable to a wide range of objects or organisms which pass through an enclosed area, our version of the sensor was designed specifically for monitoring bumblebee colonies. Other bee sensors have been developed based on optical methods of detection. The capacitance sensor provides all the information of the optical sensors and additional information on the bee size and velocity. The sensor is expected to provide entomologists with more efficient methods of studying the foraging activities of bees.PT: J; CR: BRITTAIN WH, 1933, CAN DEP AGR B, V162, P119 BROMENSHENK J, 2005, 6910941, US BUCKLEY GA, 1978, BRIT J PHARMACOL, V64, P475 DEVILLERS J, 2004, COMPUT ELECTRON AGR, V42, P87 ELTZ T, 2001, P M EUR SECT IUSSI B FABERGE AC, 1943, J SCI INSTRUM, V20, P28 GREENBERG B, 1981, ENVIRON ENTOMOL, V10, P600 JARIMOPAS B, 2005, POSTHARVEST BIOL TEC, V35, P25 LIU C, 1990, J APICULT RES, V29, P20 MORANDIN LA, 2001, CAN ENTOMOL, V133, P883 MORANDIN LA, 2001, J ECON ENTOMOL, V94, P462 PHAMDELEGUE MH, 2002, APIDOLOGIE, V33, P425 STRUYE MH, 7 INT S ICPBR BEE PR, P269 STRUYE MH, 1991, P EXP APPL ENT AMST, V2, P150 STRUYE MH, 1994, APIDOLOGIE, V25, P384 TAPP HS, 2003, SENSOR ACTUAT B-CHEM, V92, P17; NR: 16; TC: 0; J9: MEAS SCI TECHNOL; PG: 8; GA: 994MISource type: Electronic(1
Analysis of the structural behaviour of ski helmets during impact and penetration tests
No full textlo scopo del lavoro è l'analisi del comportamento meccanico dei caschi da sci in prove di impatto e penetrazione secondo la normativa EN1077. Sono state confrontate le differenze presenti tra caschi di normale produzione, tramite l'acquisizione delle accelerazioni e delle forze durante gli urti. Successivamente è stato analizzato il fenomeno di assorbemento dell'energia da parte dei materialiembargoed_20281230Embargo per motivi di segretezza e/o di proprietà dei risultati e informazioni di enti esterni o aziende private che hanno partecipato alla realizzazione del lavoro di ricerca relativo alla tes
Photodynamic therapy for the treatment of infected wound skin: systematic review and meta-analysis from randomized clinical trials
No full textIn the present study, the author will evaluated the efficacy of photodynamic therapy (PDT) for the treatment of infected wound skin. A systematic review and metaanalysis will be perform
The coefficient of homophily (<i>α</i>′) was slightly less positive when calculated for two-author papers only, relative to papers with longer author lists.
No full textThe individual points, whose distribution is summarised by the violin plots, correspond to individual journals. The larger white points show the mean for each group (and its 95% CIs), as calculated by a Bayesian meta-regression model accounting for repeated measures of α′ within journals, as well as the precision with which α′ was estimated.</p
The Wahlund effect can make it appear as if authors publish with same-gendered colleagues disproportionately often, even if collaboration is completely random with respect to gender.
No full textHere, coloured circles represent male and female authors, and coauthors are linked with lines. Across the whole set of ten papers, there is an apparent excess of same-gender collaborations: there are six same-gender papers and only four mixed-gender papers, which is fewer than the 10 × 2 × 0.5 × 0.5 = 5 mixed-gender papers expected under the null hypothesis that authors assort randomly. However, within each subset, there is no evidence that authors prefer to publish with same-gendered individuals (if anything, this small dataset suggests gender heterophily). The Wahlund effect will tend to inflate the frequency of same-gender coauthorships whenever the data is composed of two or more disconnected subsets of literature with different author gender ratios; these subsets could be research disciplines, older versus newer papers, or papers from authors based in different countries. The example countries and disciplines were selected based on data in [5].</p
Offshore oil and gas, and operational sheen occurrence: is there potential harm to marine birds?
No full textHydrocarbon discharges into the ocean, both regulated and accidental, occur from offshore drilling and production operations, and can result in oil sheen (â ¤ 3 Âľm thick) and slick (> 3 Âľm thick) formation, potentially harming marine birds. Sheens may commonly occur around offshore oil and gas platforms in Atlantic Canada, however, there is little information on regularity of occurrence. Further, there are few direct studies on potential impacts of sheens associated with offshore oil and gas operations, on marine birds. We reviewed potential sources and frequency of hydrocarbon accumulation on sea surfaces from offshore oil and gas operations in Atlantic Canada, and likelihood of overlap with marine birds. We conducted a literature review on lethal and sub-lethal effects of low-levels of oil contact and ingestion on marine birds, focusing on studies that describe measured dosages of oil. We extrapolated from these data on low-dose oil exposure in order to link possible effects to marine birds resulting from exposure to sheens. We found that sheens occur around production operations in Atlantic Canada at allowable levels of oil concentrations in produced water. Frequency and extent of occurrence can not be estimated from current monitoring practices. While immediate lethal effects to seabirds likely are not common from external oiling of feathers from sheens, added stressors such as cold weather can result in external oiling from sheens having significant impact on seabird metabolic rate and can be ultimately lethal. Ingestion of small amounts of oil, doses that realistically could be expected from exposure to sheens, in some cases resulted in sub-lethal effects to adult seabirds, primarily affecting metabolic rate, sub-lethal health impacts, and reproductive output. Nestlings and eggs do not come in direct contact with sheens, yet these life stages are highly sensitive to oil, and transfer of oil from adults exposed to sheens likely is above tolerance levels at times. Negative effects to reproductive output from small doses of ingested oil could be causing undetected impact to marine birds and marine bird populations. Lack of standardized monitoring of marine bird contact with sheens and potential harm make assessments of magnitude and extent of impact problematic.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
Measurement of the Xi(-)(b) and Omega(-)(b) baryon lifetimes
No full textUsing a data sample of pp collisions corresponding to an integrated luminosity of 3 fb−1, the Ξ−b and Ω−b baryons are reconstructed in the Ξ−b → J/ψΞ− and Ω−b → J/ψΩ− decay modes and their lifetimes measured to be
τ(Ξ−b) = 1.55+0.10−0.09 (stat) ± 0.03 (syst) ps,
τ(Ω−b) = 1.54+0.26−0.21 (stat) ± 0.05 (syst) ps.
These are the most precise determinations to date. Both measurements are in good agreement with previous experimental results and with theoretical predictions
Effective lifetime measurements in the B-s(0) -> K+K-, B-0 -> K+pi(-) and B-s(0) -> pi K-+(-) decays
No full textMeasurements of the effective lifetimes in the View the MathML source, B0→K+π− and View the MathML source decays are presented using 1.0 fb−1 of pp collision data collected at a centre-of-mass energy of 7 TeV by the LHCb experiment. The analysis uses a data-driven approach to correct for the decay time acceptance.
This is the most precise determination to date of the effective lifetime in the View the MathML source decay and provides constraints on contributions from physics beyond the Standard Model to the View the MathML source mixing phase and the width difference ΔΓs
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