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  • Author: Katarzyna Pietrzak x
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Open access

K. Pietrzak, W. Olesinska, D. Kalinski and A. Strojny-Nedza

Abstract

The effect of phase transformations induced in the surface layer of alumina ceramics during its direct joining with copper activated with oxygen or titanium on the mechanical strength of the ceramic/copper joints was examined. The materials used in the experiments were an alumina single crystal, alumina ceramics (97.5 wt% Al2O3), the cermet mixtures: Cu-Cu2O with 10-50 wt% of Cu2O, copper with 5 wt% of Ti, and copper with 5 wt% of Ti and 10 wt% of Ag. The microstructure of the transition layer was examined by the X-ray diffraction method (XRD), scanning electron microscopy method (SEM) and energy dispersive x-ray spectroscopy (EDX). The mechanical strength of the joints was measured using the three-point bending method. The amount of oxygen optimal for the joining process was determined. It has been demonstrated that the cohesion of the joints depends not only on the formation of the individual phases but also, or even primarily, on the microstructure of the transition layer formed between them.

Open access

Sławomir Pietrzak, Tomasz Próchniak, Katarzyna Kozak-Jurek and Angelika Zapała

Abstract

Breeding value of sport horses in Poland is estimated on the basis of, among others, results of the 100-day performance test of young stallions in the training centres. However recently, a drastic decrease has been reported in the number of stallions undergoing this way of assessment in Poland with an increase in foreign breeds in equestrian competitions. The objective of the study was to determine variability level of stallion traits evaluated in the training centres and to identify factors affecting stallion performance value assessment during the stationary performance test. The study included 503 stallions subjected to the 100-day training followed by the performance test in the years 2004-2013 at the training centres. There were computed statistical characteristics of 16 performance traits which were scored by the trainer of the training centre, judging commission and test riders. Influence of identified factors on each evaluation was established using the GLM procedure. The rank correlations served to estimate phenotypic interdependencies between the scores and performance value indices. It was stated that the studied group of stallions showed low variation within the body basic measurements and the conformation correctness evaluated on the 100-point scale was also found within an average value (78.86 pts), quite close to minimum value for young stallions in Poland (78 pts). The highest variation was observed for the scores given by the test riders and the main factor differentiating the performance value of horses was their origin-breed group. The horses of the German breeds (HANN, OLDBG, HOLST) earned the highest scores, while Wielkopolska horses got the lowest scores for performance test. Insufficient consistency between the individual evaluation made by the trainer of training centre and the judging commission may imply completely different period of assessment (trainer - 100 days, judging commission - 2 days) or unsatisfactory competencies of examiners.

Open access

K. Pietrzak, A. Gładki, K. Frydman, D. Wójcik-Grzybek, A. Strojny-Nędza and T. Wejrzanowski

Abstract

The main current of publication is focused around the issues and problems associated with the formation of composite materials with Cu matrix and reinforcing phases in the various carbon nanoforms. The core of the research has been focused on thermal conductivity of these composites types. This parameter globally reflects the state of the structure, quality of raw materials and the technology used during the formation of composite materials. Vanishingly low affinity of copper for carbon, multilayered forms of graphene, the existence of critical values of graphene volume in the composite are not conducive to the classic procedures of composites designing. As a result, the expected, significant increase in thermal conductivity of composites is not greater than for pure copper matrix. Present paper especially includes: (i) data of obtaining procedure of copper/graphene mixtures, (ii) data of sintering process, (iii) the results of structure investigations and of thermal properties. Structural analysis revealed the homogenous distribution of graphene in copper matrix, the thermal analysis indicate the existence of carbon phase critical concentration, where improvement of thermal diffusivity to pure copper can occur.

Open access

Jerzy Rojek, Szymon Nosewicz, Katarzyna Pietrzak and Marcin Chmielewski

Abstract

This paper presents numerical simulation of powder sintering. The numerical model introduced in this work employs the discrete element method which assumes that material can be modelled by a large assembly of discrete elements (particles) of spherical shape interacting among one another. Modelling of sintering requires introduction of the cohesive interaction among particles representing interparticle sintering forces. Numerical studies of sintering have been combined with experimental studies which provided data for calibration and validation of the model. In the laboratory tests evolution of microstructure and density during sintering have been studied. Comparison of numerical and experimental results shows a good performance of the numerical model developed

Open access

Katarzyna Pietrzak, Wiesława Olesińska, Cezary Strąk, Robert Siedlec and Andrzej Gładki

Abstract

The aim of the work presented in the article was to clarify controversial comments about anti-corrosion and mechanical properties of graphene coatings, deposited on copper substrates. It was designed special experimental cycle comprising: preparation of graphene forms and copper, the observation of layers Cu / GO (rGO) after the thermal reduction processes and oxidative test in air at 150°C temperature and 350 h in time. The resulting coatings and graphene layers were subjected to tribological test for hardness. The observed differences in the continuity of the coverage copper surface by graphene forms, allowed to understand the macroscopic effect of increased hardness and wear resistance layers rGO/Cu.

Open access

Monika Michalczuk, Monika Łukasiewicz, Jan Niemiec, Julitta Gajewska, Justyna Bartosik, Dorota Pietrzak and Katarzyna Sikorska

Abstract

The experiment was conducted on 480 Hubbard Flex chickens (fast-growing) reared to 42 days of age and 480 Hubbard JA 957 chickens (slow-growing) reared to 63 day of age. Day-old chicks were randomly assigned to the three following groups according to the type of coccidiostat: C (control - no coccidiostat in the diet and birds not vaccinated against coccidiosis), A (plant coccidiostat adiCox® AP), and M (monensin coccidiostat). At the end of rearing period the results of the controlled production were presented, the chickens were slaughtered and samples of their intestines were collected for microflora composition analyses. The obtained results show that rearing time influenced the composition of enteric microflora (small intestine and blind gut). Moreover, a higher total count of bacteria was stated in intestinal digesta of the slow-growing chickens that were kept for three weeks longer than the Hubbard Flex chickens.

The study also proved a positive influence of the diet on the quantitative composition of enteric microflora. The lowest count of mesophilic bacteria and those from the Enterobacteriaceae family was observed in the chickens receiving adiCox® AP compared to the chickens of the control group and those receiving monensin.

Open access

Katarzyna Więckowska, Lech Dudarewicz, Hanna Moczulska, Maciej Słodki, Zbigniew Pietrzak and Maria Respondek-Liberska

Abstract

The primary aim of this study was to determine the predictive value of prenatal ultrasound and echocardiography for prognosis in congenital heart disease (CHD) with coexisting diaphragmatic hernia (DH) in a tertiary care center. Eleven records from the database of the Department for Diagnoses and Prevention of Congenital Malformations, Polish Mother’s Memorial Hospital Research Institute, were reviewed. The mean maternal age was 29,2 ± 5,1 years, and the mean gestational age at the time of diagnosis was 28,4 ± 6,7 weeks. No information was available for children discharged from hospital. Data of eight cases of prenatal DH and complex heart disease from the literature were also analyzed. Three fetuses survived the neonatal period. In each of these, CHD was other than the urgent or critical type, defined as not requiring cardiac surgical intervention in the first day or month of life. Both sets of data collected from our center and the published literature confirmed the unfavorable prognosis for fetuses with severe or critical CHD with coexisting DH.