Iskanje po katalogu digitalne knjižnice

Opis: Prediction of the expected milk yield is important for the management of the primiparous cows (PPC) with a few or no data on their own milk productivity. We developed a system of regression equations for predicting milk yields in standard lactation. The models include the systematic effects of the calving season, the five-year rolling herd average of milk yield of PPC, the breeding values of the parents for milk production, and daily milk recordings. A total of 21,901 lactations of Holstein PPC were collected during the regular monthly milk recordings of cows in the Republic of Slovenia. By including daily milk recordings in the model, the coefficients of determination of regression models for the prediction of milk yield increase: without known recordings (M0) R 2 =0.80; with one recording (M1) R 2 =0.82; with two first consecutive recordings (M2) R 2 =0.86; and with three recordings (M3) R 2 =0.89. Deviations of milk yield up to 500 kg in a standard lactation (<1.6 kg/day) were as follows: with the model M0, they occurred in 53.4% of PPC; with M1, they occurred in 56.3% of PPC; with M2, they occurred in 64.5% of PPC; and with M3, they occurred in 70.9% of PPC. We concluded that the developed system of regression models is an appropriate method for milk yield prediction of PPC.
Ključne besede: primiparous cows, milk yield, prediction, lactation curves, regression equations
Objavljeno v DKUM: 24.07.2017; Ogledov: 1364; Prenosov: 519
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Opis: V doktorski disertaciji je predstavljen srednje-frekvenčni sistem za uporovno točkovno varjenje (UTV) s katerim se v industriji varijo pločevine. Tak sistem je sestavljen iz frekvenčnega pretvornika, transformatorja, diodnega usmernika in varilnih klešč ter varjenih pločevin. S frekvenčnim pretvornikom lahko generiramo poljubne dolžine pulzov napetosti, s katero nato napajamo transformator. Posledično pa lahko uporabimo različne metode generiranja pulzov napajalne napetosti. V industriji se v ta namen najpogosteje uporablja pulzno-širinska modulacija, ki ji moramo definirati modulacijsko frekvenco, ki je pogosto konstantna. Ker lahko generiramo poljubne dolžine pulzov napajalne napetosti, pa lahko te prožimo tudi glede na potrebe procesa UTV. V disertaciji je tako predstavljen algoritem histereznega vodenja sistema za UTV, ki transformator napaja z minimalno frekvenco napajalne napetosti, ki jo sistem potrebuje, da lahko zagotovi želen bremenski tok. Pri tem pa se lahko frekvenca napajalne napetosti med obratovanjem tudi spremeni, kar ni značilno za pulzno-širinsko modulacijo. Zaradi spreminjanja frekvence napajalne napetosti v disertaciji obravnavamo število pulzov napajalne napetosti v enako dolgih varilnih ciklih. Spreminjanje frekvence pa vpliva na tako imenovane dinamične izgube sistema za UTV, ki so odvisne od frekvence napajalne napetosti. Med te izgube uvrščamo stikalne izgube frekvenčnega pretvornika, izgube povezane s kožnim pojavom v navitjih transformatorja in histerezne izgube železnega jedra transformatorja za UTV. Z zmanjšanjem frekvence se te običajno zmanjšajo, kar smo potrdili tudi v primeru sistema za UTV. Pri uporabi algoritma histereznega vodenja, ki transformator napaja z minimalno frekvenco napajalne napetosti pa naraste valovitost bremenskega toka. Ta je lahko še posebej velika pri varjenju pločevin z nizko vrednostjo nadomestne varilne upornosti. Za tak primer smo pripravili tudi algoritem vodenja, ki zmanjša valovitost bremenskega toka na polovico tako, da maksimalno dolžino pulza napajalne napetosti prepolovi. Pri tem algoritem vodenja samodejno določi dolžino pulza napajalne napetosti na podlagi prvega pulza napajalne napetosti, ki vrednost gostote magnetnega pretoka spremeni od ene točke nasičenja do druge. Oba razvita algoritma pa lahko uporabljamo tudi pri DC-DC pretvornikih, ki vsebujejo transformator. V disertaciji pa smo analizirali tudi vplive bremenskega toka, nadomestne upornosti bremena in napetosti enosmernega vodila na obremenitev sistema. Od obremenitve je namreč odvisno koliko bo lahko algoritem vodenja znižal frekvenco oziroma zmanjšal število pulzov napajalne napetosti. Na podlagi te analize lahko izberemo tak nabor varilnih parametrov, pri katerih bo izkoristek sistema za UTV največji. Vrednosti varilnih parametrov lahko namreč tudi nekoliko spremenimo, pri tem pa se kvaliteta nastalega spoja ne spremeni.
Ključne besede: uporovno točkovno varjenje, regulacija, histerezna regulacija, nasičenje, algoritem vodenja, minimalna frekvenca, izgube, izkoristek, valovitost bremenskega toka, frekvenčni pretvornik
Objavljeno v DKUM: 05.07.2017; Ogledov: 1901; Prenosov: 88
Celotno besedilo (9,12 MB)

Opis: The introduction of contemporary procedures to fleet management processes has recently changed the work planning and supervision of driver's work activities. Tendencies to control the implementation of driver's work have been present in modem professional practice for quite a long time; however, the equipment available on the market limited its implementation. The intensified development of digital tachographs has, in technical terms, ensured such equipment considerably before the legislative groundwork was prepared for its practical implementation. The Commission Regulation (EC) No. 561/2006 (implementation of Social legislation relating to Road Transport) does not bring any essential novelties in terms of permitted workload. Consistent monitoring of drivers activities, made possible by digital tachographs, will have impact on the existing working methods. The topic of the present paper is in deep analysis of the impact of the mentioned regulation with special emphasis on the conditions for the regulation of the current stage of drivers work and on the expected consequences. The essential importance lies on the expected change in the mentality and approach to planning the driver's activities in the transport process on the part of the carrier: the outcome will eventually result in the efficiency of each individual carrier.
Ključne besede: fleet management, driver's work planning, digital tachographs
Objavljeno v DKUM: 06.06.2017; Ogledov: 1223; Prenosov: 573
Celotno besedilo (2,98 MB)
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Opis: The ropeway transportation system plays a major role in mountain resorts. In order to provide a sustainable development of the entire mountain resort system, the real capacity of the ropeway transportation system was set. The real capacity of the ropeway transportation system is one of the indicators of the development harmonisation level of single system elements. The research into this field was carried out at the Road Traffic Centre of the Faculty of Civil Engineering, University of Maribor. The paper deals with the basic points of the topic and the methods used. The know-how transfer of experiences into the Slovenian environment is presented together with the obtained results.
Ključne besede: traffic management, traffic, transport, ropeway, capacity
Objavljeno v DKUM: 05.06.2017; Ogledov: 1325; Prenosov: 199
Celotno besedilo (2,01 MB)
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Opis: The paper is based on the question whether the existing (legislation determined) method for determining the visibility length on passive protected level railroad crossings insures the relevant level of traffic safety. It has been recognised that using of such method does not provide stopping of road driver vehicles in front of railroad crossing in all conditions. Based on such conclusion a new approach to determining visibility length on passive protected level railroad crossing is proposed. The new approach is based on the assumption that it is necessary, primarily on level railroad crossings with local roads to recognize the worst possible and expected road and weather conditions. The testing of the proposed method in the real environment has shown that at lower speeds of road vehicles there is almost no difference, and that important benefits are recognised for the speeds of 30 and 50km/h where longer stopping distances of road vehicles have been detected (road vehicle can stop safely in front of a rail crossing) with almost the same visibility lengths. The use of the proposed method could have important impact on the increase of traffic safety on passive protected level railroad crossings.
Ključne besede: traffic safety, visibility field, level railroad crossings
Objavljeno v DKUM: 05.06.2017; Ogledov: 1426; Prenosov: 501
Celotno besedilo (892,41 KB)
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