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Search Results: 1 - 10 of 461941 matches for " A. Chojnowska-Michalik "
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Symmetric Ornstein-Uhlenbeck Semigroups and their Generators
A. Chojnowska-Michalik,B. Goldys
Mathematics , 2002,
Abstract: We provide necessary and sufficient conditions for a Hilbert space-valued Ornstein-Uhlenbeck process to be reversible with respect to its invariant measure $\mu$. For a reversible process the domain of its generator in $L^p(\mu )$ is characterized in terms of appropriate Sobolev spaces thus extending the Meyer equivalence of norms to any symmetric Ornstein-Uhlenbeck operator. We provide also a formula for the size of the spectral gap of the generator. Those results are applied to study the Ornstein-Uhlenbeck process in a chaotic environment. Necessary and sufficient conditions for a transition semigroup $(R_t)$ to be compact, Hilbert-Schmidt and strong Feller are given in terms of the coefficients of the Ornstein-Uhlenbeck operator. We show also that the existence of spectral gap implies a smoothing property of $R_t$ and provide an estimate for the (appropriately defined) gradient of $R_t\phi$. Finally, in the Hilbert-Schmidt case, we show that for any $\phi\in L^p(\mu)$ the function $R_t\phi$ is an (almost) classical solution of a version of the Kolmogorov equation.
Optimisation of the lacquering process
K. Michalik,A. Pusz
Archives of Materials Science and Engineering , 2008,
Abstract: Purpose: The topic of this research is estimation of coat parameters generate by paint robots. The purpose of this article is to present results of optimization of the varnishing process.Design/methodology/approach: After theoretical analysis of the methods of the optimization, in examinations was used multicriterial with method of the optimization. This method allows for diagnosing the problem of the lacquering process.Findings: Optimization of the process with multicriterial method let for selecting right parameters of the process of painting. The possibility of the optimum technological process choice was proposed. The optimization methods should have more and more meaning in the materials engineering. It is because of many possible technical problems to solutions.Research limitations/implications: The method of optimization such as multicriterial depend on degree of complexity of physical and technical relations of the analysed lacquering processes.Practical implications: The work is an example of analysis of chosen technological process in aspect of its efficiency. It could be helpful to improve a level of total productivity of technological processes by using multicriterial method.Originality/value: This paper is obtained original model for experimental domain of forming parameters and identification of parameters influence in that model.
Examining the hardness of the high density polyethylene with method of the cone
A. Pusz,K. Michalik
Archives of Materials Science and Engineering , 2007,
Abstract: Purpose: The purpose of this article is to present results of examining the hardness of the high density polyethylene with method of the cone.Design/methodology/approach: In the article a method of the cone was used for examining the hardness of the polythene of high density. Findings: The method of the cone it is possible to examine small samples and he allows for more exact measurements than different methods of examining the hardness.Research limitations/implications: The methods presented in this paper differ in the size and the shape of the indenter. The choice of the method of the measurement of the hardness in case of crystalline polymers is difficult since none of known methods has the right measuring resolution. The method of the cone is solving in the case of examining polymers. The method of the cone isn’t limited only to polymer materialsPractical implications: Presented method can be applied for other materials in the future.Originality/value: The expressed method can be applied in the future for developing the research on the hardness of polymers.
Creep damage mechanisms in gas pipes made of high density polyethylene
A. Pusz,K. Michalik
Archives of Materials Science and Engineering , 2009,
Abstract: Purpose: The purpose of this article is to present results of creep damage mechanisms in gas pipes made of high density polyethylene [HDPE]. High density polyethylene has been widely used in the piping industry as raw material. Even though there are large numbers of experimental and analytical investigations on HDPE, few of them have examined the effects of manufacturing techniques on the small and finite deformation behaviors of HDPE. Since HDPE is semi-crystalline polymeric material the rate of crystallinity, molecular morphologies and molecular structure extensively influence its mechanical behaviors.Design/methodology/approach: Tensile creep experiments on HDPE with a duration of examinations from four till nine days were performed at temperature of 20°C.Findings: In this study, findings are indicating differences of the property in individual layers walls of the pipe.Research limitations/implications: Applying this method is limited to thermoplastic materials.Practical implications: Presented method can be applied for other thermoplastic materials in the future.Originality/value: The expressed method can be applied in the future for developing the research on the process with creeping of polymers.
Fractographic study of high-density polyethylene gas pipe following Small Scale Steady State test
A. Pusz,K. Michalik
Journal of Achievements in Materials and Manufacturing Engineering , 2010,
Abstract: Purpose: The present work attempts to examine the failure performance of high density polyethylene [HDPE] gas pipe through a fractographic study of the fracture morphology following Small Scale Steady State test (S4). Failure mechanisms are discussed based on the fracture morphologies resulting from these tests. There are many instances where the rapid propagation of cracks is the result of fluid pressure acting on piping structures. This problem is recognized as one of the most important issues of dynamic fracture mechanics. A fractographic study of the HDPE type of a gas pipe has been undertaken.Design/methodology/approach: Scanning electron microscopic (SEM) observations were used to identify elementary process involved in the crack initiation and propagation.Findings: Based on an investigation of the Small Scale Steady State (S4) test, in order to assess the fracture behaviour of polyethylene (PE) gas distribution pipe material during rapid crack propagation (RCP). Failure mechanisms are discussed based on the fracture morphologies resulting from these tests. The influence of molecular architecture on the rapid crack propagation (RCP) resistance of high-density polyethylene pipes was investigated. It was concluded that high molecular weight, high crystallinity and a relatively narrow molecular weight distribution are important architectural attributes for RCP resistance.Research limitations/implications: Applying S4 test is limited to thermoplastic materials.Practical implications: Presented method can be applied for other thermoplastic materials in the future.Originality/value: The expressed method can be applied in the future for developing the research on the process with rapid crack propagation of polymers.
Impact of Age on Surgical Outcomes after Robot Assisted Laparoscopic Hysterectomies  [PDF]
A. Eddib, S. Hughes, M. Aalto, A. Eswar, M. Erk, C. Michalik, V. Krovi, P. Singhal
Surgical Science (SS) , 2014, DOI: 10.4236/ss.2014.53018
Abstract:

Objective: To estimate the impact of patient’s age on surgical outcomes in patients undergoing robotic hysterectomy. Methods: A retrospective review of prospectively collected cohort data for a consecutive series of patients undergoing gynecologic robotic surgery. Patient’s age and perioperative variables were collected from the database, charts, and other hospital records of all patients undergoing robotic hysterectomy. Results: 399 patients underwent robotic surgery for gynecologic disease. 370 patients who were under age 70 were compared with 29 patients who were over age 70. When comparing all patients under age 70 with patients over age 70, the mean age was 48.4 and 77 (P < 0.05), mean BMI was 32.1 and 28.3 kg/m2 (P < 0.05), mean procedure time was 185 and 211 minutes (min) (P = 0.09), mean console time was 123 and 148 min (P = 0.056), mean OR (Operating room) time was 237 and 273, mean EBL (Estimated blood loss) was 71 and 65 ml (P = 0.74), Hb (Hemoglobin) drop was 1.4 and 1.2 (P = 0.45), uterine weight was 212 and 95 gm (P = 0.98), and length of stay was 1.4 and 1.6 days (P = 0.33) (Table 1). The patients over age 70, when procedures were combined, had a statistically significant lower mean BMI, uterine weight and longer Operating room (OR) time. However, when stratified by the type of procedure performed, there was no difference in surgery times among those under 70 and over 70 years of age. The elderly patients were more likely to have cancer, which was in almost half the elderly patients, and thus necessitate staging. Thus adding the performance of lymph node dissection likely resulted in the increased length of the surgery time that was noted in the combined group (Tables 1,

Topography and the structure of the surface of polyamide - glass composites after the ageing process
A. Pusz,M. Szymiczek,K. Michalik
Journal of Achievements in Materials and Manufacturing Engineering , 2011,
Abstract: Purpose: Polymers have found applications in such diverse biomedical fields as tissue engineering, implantation of medical devices and artificial organs, prostheses, ophthalmology, dentistry, bone repair and many other medical fields. The requirements for materials used in the construction of removable dentures are becoming more and more demanding. The introduction of improved flexible materials has been a considerable advance. The aim of this work was to determine how the structure of thermoplastic materials changes over time in terms of weight changes and artificial saliva sorption. Purpose of this paper was to evaluate the influence of the ageing process on structure of polyamide - glass composites applied in dentistry.Design/methodology/approach: Polyamide samples about the diversified content of the glass fibre were produced with method of the injection moulding. Denotation the absorbency of artificial saliva was performed on standardized samples according to the norm. Samples were dried off to fixed mass, and then they were soaked in artificial saliva. Three temperatures of examination were applied 20oC, 35oC and 50oC.Findings: Examinations allowed to show that the absorbency of artificial saliva through composite is dependent on the temperature.Research limitations/implications: To fully evaluate the influence of the ageing process on mechanical properties of polyamide - glass composites applied in human body environment it is planned to continue described research. Simultaneous influence of the ageing process on mechanical properties of polyamide - glass composites will be tested.Originality/value: Applying strengthened thermoplastics with glass fibre on dentures is a new look at materials applied in dentistry.
Ageing process influence on mechanical properties of polyamide - glass composites applied in dentistry
A. Pusz,M. Szymiczek,K. Michalik
Journal of Achievements in Materials and Manufacturing Engineering , 2010,
Abstract: Purpose: The application of polymeric materials for medical purposes is growing very fast. Polymers have found applications in such diverse biomedical fields as tissue engineering, implantation of medical devices and artificial organs, prostheses, ophthalmology, dentistry, bone repair and many other medical fields. The requirements for materials used in the construction of removable dentures are becoming more and more demanding. The introduction of improved flexible materials has been a considerable advance. The aim of this work was to determine how the properties of thermoplastic materials change over time in terms of weight changes and artificial saliva sorption. Purpose of this paper was to evaluate the influence of the ageing process on mechanical properties of polyamide - glass composites applied in dentistry.Design/methodology/approach: Polyamide samples about the diversified content of the glass fibre were produced with method of the injection moulding. Denotation of the absorbency of artificial saliva was performed on standardized samples according to the norm. Samples were dried up to fixed mass, and then they were soaked in artificial saliva. Two temperatures of examination were applied 23°C and 30°C.Findings: An influence of the absorbability on mechanical properties of composites was determined. Examinations allowed to show that the absorbency of artificial saliva through composite is dependent on the temperature.Research limitations/implications: To fully evaluate the influence of the ageing process on mechanical properties of polyamide - glass composites applied in human body environment it is planned to continue described research. Simultaneous influence of the ageing process on mechanical properties of polyamide - glass composites shall be tested.Originality/value: Applying strengthened thermoplastics with glass fibre on dentures is a new look at materials applied in dentistry.
Swagelining as a method of trenchless piplines rehabilitation
G. Wróbel,A. Pusz,M. Szymiczek,K. Michalik
Journal of Achievements in Materials and Manufacturing Engineering , 2009,
Abstract: Purpose: The present study outlines the advantages of using trenchless methods for the rehabilitation of pipelines made of steel, concrete, cast iron etc. The authors describe causes of carrier pipe ageing and methods of their inspection and renovation. The technical aspects of choosing the renovation methods are also presented. The paper includes a decision-making flowchart for choosing the carrier pipes renovations.Design/methodology/approach: The 1980’s and 1990’s saw an explosion of new pipe installation and repair techniques which minimize the need to dig continuous trenches to bury the pipeline, so called ‘trenchless technologies’. The trenchless technologies have been widely applied for the rehabilitation of various pipelines such as sewage systems, gas pipelines or water supply systems. There has been characterized the swagelining technology which is based on one of the metal working technologies and namely the sinking of pipes.Findings: The PE pipe stress in the drawing die zone has been analyzed and an attempt has been made to analyze the mechanisms causing the elastic recovery of PE pipes. There have also been presented the diameter changes as the parameter of the elastic recovery which is a result of our own research conducted in accordance with the program developed.Research limitations/implications: Each pipeline renovation method has its advantages and disadvantages, possibilities and limitations, depending on the application.Practical implications: The work is an example of analysis of chosen trenchless renovation on the example of swageling technology.Originality/value: The trenchless renovation of pipelines certainly will be more readily used in the future because of wearing out of pipelines. The other reason is the lack of space for new utilities, increasing costs and road-surface restoration requirements.
Distribution of plant communities as a function of the relative insolation of the Czy ówki rocky ridge in the Ojców National Park
Stefan Michalik
Acta Societatis Botanicorum Poloniae , 1991, DOI: 10.5586/asbp.1991.025
Abstract: Highly significant dependences were found between the distribution of plant communities and the relative insolation on a small rocky ridge with relief and microclimatic conditions varying to a very great degree. The dependences are presented in graphical and numerical forms, and their significance is tested using non-parametric statistics.
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