Switching converters with wide DC conversion range

In dc-to-dc conversion applications that require a large range of input and/or output voltages, conventional PWM converter topologies must operate at extremely low duty ratios, which limits the operation to lower switching frequencies because of the minimum ON-time of the transistor switch. This is eliminated in a new class of single-transistor PWM converters featuring voltage conversion ratios with quadratic dependence on duty ratio. Practical circuit examples operating at 0.5 MHz are described

A unified analysis of PWM converters in discontinuous modes

Three discontinuous operating modes of PWM (pulsewidth modulated) converters are considered: the discontinuous inductor current mode (DICM), the discontinuous capacitor voltage mode (DCVM), and a previously unidentified mode called the discontinuous quasi-resonant mode (DQRM). DC and small-signal AC analyses are applicable to all basic PWM converter topologies. Any particular topology is taken into account via its DC conversion ratio in the continuous conduction mode. The small-signal model is of the same order as the state-space averaged model for the continuous mode, and it offers improved predictions of the low-frequency dynamics of PWM converters in the discontinuous modes. It is shown that converters in discontinuous modes exhibit lossless damping similar to the effect of the current-mode programming

A general approach to synthesis and analysis of quasi-resonant converters

A method for systematic synthesis of quasi-resonant (QR) topologies by addition of resonant elements to a parent pulse-width modulation (PWM) converter network is proposed. It is found that there are six QR classes with two resonant elements, including two novel classes. More complex QR converters can be generated by a recursive application of the synthesis method. Topological definitions of all known and novel QR classes follow directly from the synthesis method and topological properties of PWM parents. The synthesis of QR converters is augmented by a study of possible switch realizations and operating modes. In particular, it is demonstrated that a controllable rectifier can be used to accomplish the constant-frequency control in all QR classes. Links between the QR converters and the underlying PWM networks are extended to general DC and small-signal AC models in which the model of the PWM parent is explicitly exposed. Results of steady-state analyses of selected QR classes and operating modes include boundaries of operating regions, DC characteristics, a comparison of switching transitions and switch stresses, and a discussion of relevant design trade-offs

Constant-frequency control of quasi-resonant converters

An additional independent control needed to eliminate the undesirable variable switching frequency of quasi-resonant converters can be obtained if the output rectifier is replaced by an active switch. The concept is applicable to all classes of quasi-resonant converters. It is demonstrated that in addition to operation at constant switching frequency, selected classes of constant-frequency quasi-resonant (CF-QR) topologies feature extended range of accessible conversion ratios and load currents. A practical example of a constant-frequency multi-resonant (CF-MR) buck converter operating at 2 MHz is described

HERITABILITY AND REPEATABILITY OF FERTILITY TRAITS OF HOLSTEIN-FRIESIAN BULLS MONITORED IN PROGENY TESTING

To test the variability of fertility traits of Holstein-Friesian bulls monitored in progeny test, reproduction data of 342 cows, daughters of 15 bulls were used. Cows have been in production in seven farms of Agricultural Corporation "Belgrade" in the period from 2004 to 2012. The study included the following fertility traits: the average calving age, service period and calving interval. To analyze the influence of genetic and non-genetic sources of variability a mixed model with random effect of bull - sire, the fixed effects of farm, year, season and order of calving was used. The sire is present in variability of all the observed fertility traits (p <0.01), whereas the fixed factors manifested their influence at different levels of statistical significance. The heritability of fertility traits was low: the average calving age – 0.224, service period – 0.087, calving interval – 0.085. Repeatability of mentioned traits was 0.258, 0.111, 0.102, respectively

Surface plasmon - Polariton assisted metal-dielectric multilayers as passband filters for ultraviolet range

We designed and fabricated metal-dielectric multilayers intended for passband filters in the ultraviolet range. We determined the dispersion characteristics by the Bloch approach to evanescent wave resonant coupling and calculated the spectral characteristics using the transfer matrix method while taking into account real dispersion and absorptive losses. We considered the influence of nanoscale interface roughness as a means to couple evanescent electromagnetic field to the propagating far field modes. In our structures both propagating and evanescent modes contribute to the overall performance, resulting in an enhanced transmission in the desired range, while retaining a strong suppression of undesired frequencies of more than four orders of magnitude. In our experiments we used radiofrequent sputtering of silver and silica and characterized our multilayers by UV-vis spectroscopy

Variability and heritability of milk traits of holstein - frisian bull dams and their progeny

The research was performed on Holstein-Friesian and Black and White bull dams reared on five farms of Agricultural Corporation of Belgrade - PKB. The study included 575 lactations of cows selected as bull dams and their progeny calved in the period from 2007 - 2014 and represent progeny of 24 bulls. The following dairy traits were analysed in a standard lactation (305 days): milk yield (kg) - MY, milk fat content (%) - % MF, milk fat yield (kg) - MFY, protein content (%) - % PC and protein yield (kg) - PY. Holstein-Friesian bull dams and their progeny, in standard lactation, produced on average 9239.84 +/- 1607.64 kg of milk, with a milk fat content of 3.44 +/- 0.20 and protein content of 3.21 +/- 0.12. The impact of bull - sire, year of birth, lactation order, farm, year and calving season was present at different levels of statistical significance on yield traits, while the genetic group had no influence on any of the milk traits. Bull sire, year of birth, lactation order and calving season did not influence the variability of milk fat and protein content. Heritability of observed milk traits was medium to low. The content of milk fat and protein had the lowest values of heritability, 0.014, and 0.024, respectively. The heritability of milk yield, milk fat yield and protein yield was 0.293, 0.319 and 0.273, respectively

Procena koeficijenta naslednosti za osobine porasta kod ovaca

The objective of this research paper was to estimate heritability coefficients (heritability) of growth traits in the lambs of indigenous Sjenicka Pramenka breed. The research was conducted on a sample which included 421 lambs the descendants of 15 sires and 187 sheep-dams, raised on 3 private farms in Kolubarski district, Serbia. The effect of fixed factors was studied while the values of heritability coefficients were estimated within the frame of SAS software package. A statistically highly significant (**=P lt 0.01) effect on studied traits had following parameters: sex, year of lambing, type of lambing, farm and method of applied reproductive technology. By means of REML method and using the sire model the values of heritability coefficients were determined for the following traits: average lamb birth weight (BW0), average lamb body weight at 30 days (BW30) and average lamb body weight at 90 days (BW90) being: 0.0355; 0.4642 and 0.3018, respectively.Cilj rada bio je da se procene koeficijenti naslednosti (heritabilitet) osobina porasta kod jagnjadi sjeničke pramenke. Istraživanje je sprovedeno na uzorku od 421 jagnjadi, potomaka 15 očeva i 187 ovaca-majki sa 3 privatne farme u Kolubarskom okrugu. Ispitan je uticaj fiksnih faktora i procenjene su vrednosti koeficijenata naslednosti u okviru SAS softverskog paketa. Visoko statistički značajan (**=P lt 0,01) uticaj na ispitivane osobine imali su: pol, godina jagnjenja, tip jagnjenja, farma i metod primenjene reproduktivne tehnologije. Metodom intraklasne korelacije polusrodnika po ocu utvrđene su vrednosti koeficijenta naslednosti za osobine: prosečna telesna masa jagnjadi na rođenju (BW0), prosečna telesna masa jagnjadi sa 30 dana starosti (BW30) i prosečna telesna masa jagnjadi sa 90 dana starosti (BW90) i iznosile su: 0,0355; 0,4642 i 0,3018, respektivno

Fenotipske korelacije linearnih ocena tipa i proizvodnih osobina krava simentalske rase

Determining the degree of correlation between two or more traits depends to a large extent on their manifestation. The knowledge of genetic and phenotypic correlations between body characteristics of the animal and product characteristics can help define the breeding goal, but also to define and harmonize the assessment criteria. Although the phenotypic and genetic correlations between the traits of body development and type and the milk yield show different degrees of variation, they should be taken into account in the final assessment of the breeding value of the animal so that the selection programs are more comprehesively defined. The examination of phenotypic correlations of linear assessment scores of the type, milk and fertility traits was performed on a total of 303 cows of the Simental breed in the first three lactations. The examination of phenotypic correlations included the following milk performance properties in the first three standard lactations: milk yield, milk fat content, milk fat yield, yield of 4% corrected milk; also fertility traits: age at current calving and service period in each lactation; while the linear type scoring included a group of traits: type or frame, muscularity, fundament, udder.Poznavanje fenotipske povezanosti osobina mlečnosti i plodnosti, sa linearnim ocenama tipa je veoma značajno u selekcijskom radu, gde se pored visoke proizvodnje, očekuje dobro zdravlje kao i dug produktivni život grla u stadu. U ovom istraživanju medjusobna pozitivna i potpuna fenotipska povezanost prinosa mleka, mlečne masti i 4% mast korigovanog mleka ustanovljena je u sve tri laktacije, kao i niska i uglavnom pozitivna povezanost pokazatelja prinosa i sadržaja mlečne masti. Niska i uglavnom pozitivna fenotipska povezanost utanovljena je u sve tri laktacije i za pokazatelje mlečnosti i plodnosti, ali i za pokazatelje plodnosti i tipa. Fenotipska povezanost pokazatelja mlečnosti i prosečnih ocena tipa je bila srednje jaka i uglavnom pozitivna za osobine prinosa i slaba i uglavnom negativna izmedju osobina tipa i sadržaja mlečne masti. Fenotipska povezanost ispitivanih osobina pokazuje da se prilikom odabira kako priplodnih junica, tako i semena za oplodnju krava i junica, mora povesti računa i o tipskim karakteristikama, jer će to pored odabira po mlečnosti doprineti ostvarenju veće proizvodnje mleka i bržem genetskom unapredjenju naše populacije

Cattle Herd book and Record Keeping in Central Serbia

Serbia has a tradition of cattle production, and the area of Central Serbia, as a hilly region is suitable for farming of the combined Simmental and dairy Holstein-Friesian breed. The first Herd Book of Serbia was founded in 1935. The high quality breeding animals registered in the main register and the herd book are under the control of production performance. According to the expert report of the Institute for Animal Husbandry and the results of the implementation of the breeding program in 2017, on the territory of Central Serbia, there were 147,997 high quality breeding animals of the Simmental and 17,192 of Holstein-Friesian breed in the main/parent herd. Both breeds of national interest for rearing in the territory of Central Serbia are included in the breeding – selection programs for cattle for milk production, which are implemented through the cooperation of farmers and local breeding organizations in the field. In the territory of Central Serbia there are 157 registered local breeding organizations that are carrying out the activities of cattle recording/registering and selection. In this paper the data of the Main Breeding Organization in cattle breeding, the Institute for Animal Husbandry, and its annual report are used. A tabular analysis and a five-year trend of animals are presented according to: the number of registered animals, linearly evaluated first calving females, the realized yield of milk, milk fat and protein, as well as the trend of the number of bull dams in the population. Based on the analysis of the results of work on the selection of bovine animals, it can be concluded that some progress has been made in the production of milk of both breeds. It is important to emphasize that the mentioned results are reflected on the productivity of the entire population of cattle in Central Serbia