Wyniki wyszukiwania

Filtruj wyniki

  • Czasopisma
  • Autorzy
  • Słowa kluczowe
  • Data
  • Typ

Wyniki wyszukiwania

Wyników: 45
Wyników na stronie: 25 50 75
Sortuj wg:

Abstrakt

This paper presents and analyses the results of a simulation of the acoustic field distribution in sectors of a 1024-element ring array, intended for the diagnosis of female breast tissue with the use of ultrasonic tomography. The array was tested for the possibility to equip an ultrasonic tomograph with an additional modality - conventional ultrasonic imaging with the use of individual fragments (sections) of the ring array. To determine the acoustic field for sectors of the ring array with a varying number of activated ultrasonic transducers, a combined sum of all acoustic fields created by each elementary transducer was calculated. By the use of MATLAB software, a unique algorithm was developed, for a numerical determination of the distribution of pressure of an ultrasonic wave on any surface or area of the medium generated by the concave curvilinear structure of rectangular ultrasound transducers with a geometric focus of the beam. The analysis of the obtained results of the acoustic field distribution inside the ultrasonic ring array used in tomography allows to conclude that the optimal number of transducers in a sector enabling to obtain ultrasound images using linear echographic scanning is 32 ≤ n ≤ 128, taking into account that due to an increased temporal resolution of ultrasonic imaging, this number should be as low as possible.

Przejdź do artykułu

Autorzy i Afiliacje

Wiktor Staszewski
Tadeusz Gudra
Krzysztof J. Opieliński

Abstrakt

In this work we present the design and the manufacturing processes, as well as the acoustics standardization tests, of an acoustic barrier formed by a set of multi-phenomena cylindrical scatterers. Periodic arrangements of acoustic scatterers embedded in a fluid medium with different physical properties are usually called Sonic Crystals. The multiple scattering of waves inside these structures leads to attenuation bands related to the periodicity of the structure by means of Bragg scattering. In order to design the acoustic barrier, two strategies have been used: First, the arrangement of scatterers is based on fractal geometries to maximize the Bragg scattering; second, multi-phenomena scatterers with several noise control mechanisms, as resonances or absorption, are designed and used to construct the periodic array. The acoustic barrier reported in this work provides a high technological solution in the field of noise control.

Przejdź do artykułu

Autorzy i Afiliacje

Sergio Castiñeira-Ibáñez
Constanza Rubio
Vicent Romero-García
Juan Vicente Sánchez-Pérez
Luís Miguel García-Raffi

Abstrakt

Research over a three year period indicated that P. ramorum occurred rarely in Poland on Rhododendron spp., in spite of established monitoring in nurseries, trade stands, forest and water from early spring to late autumn each year. The pathogen was not found in forests on Vaccinium vitisidaea, Calluna vulgaris, Fagus sylvatica and Quercus rubra, proving its limited spread. The species was detected, however, from 2 rivers. P. citricola was isolated from most of surveyed plants. Besides this P. cactorum, P. cinnamomi, P.citrophthora and P. nicotianae var. nicotianae were isolated from diseased plants. Additionally Pestalotia sydowiana, species of Fusarium, Botrytis cinerea and Trichoderma were often found in diseased plant tissues. Laboratory and glasshouse research showed slight differences in colonization of plants by P. ramorum and P. citricola. However, taking into account the range of host plants, and frequency of pathogen occurrence in infected plant material and water, it became clear that P. citricola poses a much greater danger than P. ramorum to the natural environment in Poland.

Przejdź do artykułu

Autorzy i Afiliacje

Leszek B. Orlikowski
Tomasz Oszako
Aleksandra Trzewik
Teresa Orlikowska

Abstrakt

Foam fractionation process for concentration of laccases from two Basidiomycete strains under different process conditions was investigated. Culture supernatants of Cerrena unicolor and Pleurotus sapidus containing active laccase were used with and without surfactant additives. Two surfactants: cationic cetrimonium bromide (CTAB) and non-ionic Polysorbate 80 were applied in the range from 0.2 mM to 1.5 mM. The pH levels ranging from 3 to 10 were examined with particular attention to pH=4, which is close to the pI of the enzymes. Results show that the source of the enzyme is significant in terms of partitioning efficiency in a foam fractionation process. Laccase from Cerrena unicolor showed the best activity partitioning coefficients between foamate and retentate of almost 200 with yields reaching 50% for pH 7.5 and concentration of CTAB cCTAB = 0.5 mM, whereas laccase from Pleurotus sapidus showed partitioning coefficients of up to 8 with 25% yield for pH 4 and cCTAB = 0.5 mM.

Przejdź do artykułu

Autorzy i Afiliacje

Michał Blatkiewicz
Stanisław Ledakowicz
Anna Antecka
Andrzej Górak

Abstrakt

In this paper, we estimate the upper limit of the transmission data rate in airborne ultrasonic communications, under condition of the optimal power allocation. The presented method is based on frequency response of a channel in case of single-path LOS propagation under different climatic conditions and AWGN background noise model, and it can be easily extended to the case of frequency-dependent noise. The obtained results go beyond the discrete distances for which experimental SNR values were available, and are more accurate than the previous calculations in the literature, due to the inclusion of the channel frequency response and its changes over the distance. The impact of air temperature, relative humidity and the atmospheric pressure on the channel capacity is also investigated. The presented results can serve as a reference during the design of airborne ultrasonic communication systems operating in the far-field region.

Przejdź do artykułu

Autorzy i Afiliacje

Gustaw Mazurek

Abstrakt

This article discusses the main points in the Bertrand Russell and Frederick Copleston’s debate about the existence of God. Copleston defended the cosmological argument based on a sufficient reason and argued against radical contingency in explaining the origin of the world. During the debate, the understanding of necessity was discussed, whether the word ‘God’ is a proper name or a description, whether the universe as a whole can have a cause, and the arguments about the origin of the world formulated in modern physics. The whole debate is an excellent example of the difference between a theist and an atheist with regard to Leibnizian type of the cosmological argument.i
Przejdź do artykułu

Autorzy i Afiliacje

Ryszard Mordarski
1
ORCID: ORCID

  1. Uniwersytet Kazimierza Wielkiego w Bydgoszczy, Instytut Filozofii, ul. Ogińskiego 16, 85-092 Bydgoszcz

Abstrakt

W wieloaspektowej pracy Utwór muzyczny i sprawa jego tożsamości Romana Ingardena na czoło wysuwają się zagadnienia ontologiczne: kwestia kategorii ontycznej i istoty utworu muzycznego. W niniejszym artykule koncepcja Ingardena poddana jest krytyce wewnętrznej i zewnętrznej. W krytyce wewnętrznej rozwiązanie Ingardena rozpatrzone zostało przez pryzmat przyjętych przez niego założeń. W krytyce zewnętrznej poddane rewizji są same te założenia. Ingarden opiera swe badania na elitarnym korpusie analitycznym (rozpatruje wybitne utwory muzyki zachodniej XVIII i XIX w.) i liberalnych założeniach ontologicznych (dopuszcza istnienie wielu różnych typów przedmiotów). Przy tych założeniach rozwiązanie Ingardena, tj. uznanie utworu muzycznego za schematyczny przedmiot czysto intencjonalny, wydaje się optymalne. Perspektywa zmienia się, gdy wykroczymy poza ów elitarny korpus lub przyjmiemy bardziej restrykcyjne założenia ontologiczne.
Przejdź do artykułu

Autorzy i Afiliacje

Anna Brożek
1

  1. Uniwersytet Warszawski, Wydział Filozofii, ul. Krakowskie Przedmieście 3, 00-927 Warszawa

Abstrakt

In the paper selected methods of measuring the thermal resistance of an IGBT (Insulated Gate Bipolar Transistor) are presented and the accuracy of these methods is analysed. The analysis of the measurement error is performed and operating conditions of the considered device, at which each measurement method assures the least measuring error, are pointed out. Theoretical considerations are illustrated with some results of measurements and calculations.
Przejdź do artykułu

Autorzy i Afiliacje

Krzysztof Górecki
Paweł Górecki

Abstrakt

In the paper there has been made an advantage of the non-classical operational calculus to determination of the response of the certain discrete time-systems. The Z-transform is often used to analysis of the stationary discrete time-systems. However, the use of the Z-transform to determination of the response especially of the non-stationary discrete time-systems is doubtful or may cause complications. This method leads to differential equations of n-th order of variable coefficients, whose solutions are very difficult or impossible. The non-classical operational calculus can be used to analysis both of the stationary and non-stationary discrete time-systems. The presented method with the use of the Heaviside operator soon leads to the target without unnecessary differential equations.

Przejdź do artykułu

Autorzy i Afiliacje

E. Mieloszyk
A. Milewska
M. Magulska

Abstrakt

The chaotic phenomena of coronary artery systems are hazardous to health and may induce illness development. From the perspective of engineering, the potential harm can be eliminated by synchronizing chaotic coronary artery systems with a normal one. This paper investigates the chaos synchronization problem in light of the methodology of sliding mode control (SMC). Firstly, the nonlinear dynamics of coronary artery systems are presented. Since the coronary artery systems suffer from uncertainties, the technique of derivative-integral terminal SMC is employed to achieve the chaos synchronization task. The stability of such a control system is proven in the sense of Lyapunov. To verify the feasibility and effectiveness of the proposed method, some simulation results are illustrated in comparison with a benchmark.

Przejdź do artykułu

Autorzy i Afiliacje

D.W. Qian
Y.F. Xi
S.W. Tong

Abstrakt

In this paper a DC-link voltage balancing strategy for multilevel Cascaded H-Bridge (CHB) converter is proposed. Presented solution bases on optimal choice of active vector durations in Space-Vector Pulse Width Modulation (SV-PWM). It makes it possible to DC-link voltages control and to properly generate the output voltage vector in the case of DC-link voltage unbalance. Results of simulation and experimental researches on proposed control strategy are presented in the paper.
Przejdź do artykułu

Autorzy i Afiliacje

Arkadiusz Lewicki

Abstrakt

Some physical concepts important for a hysteresis model (effective field, anhysteretic magnetization) are discussed on the example of Jiles-Atherton model. The Jiles-Atherton model reveals some drawbacks, which make this model more difficult to be applied in electrical engineering. In particular, it does not describe accurately the magnetization curves after a reversal, moreover complex magnetization cycles are poorly represented. On the other hand, the phenomenological description proposed by Takács seems to be a valuable alternative to the Jiles-Atherton formalism. The concept of effective field may be easily incorporated in the description.

Przejdź do artykułu

Autorzy i Afiliacje

Krzysztof Chwastek

Abstrakt

New echinoid material from the Oligocene Chlamys Ledge Member (uppermost part of the Polonez Cove Formation) on King George Island, West Antarctica, includes the “regular” echinoid Caenopedina aleksandrabitnerae sp. n. and poorly preserved spatangoids, here tentatively identified as members of the genus Abatus . Caenopedina aleksandrabitnerae sp. n. is characterized by fully tuberculate genital plates, which sets it apart from most other species in the genus, by the uneven periproctal margin which indicates that periproctal plates were incorporated into the apical disc, and by moderately wide interambulacral plates with a height/width ratio of 1:3. Among the modern Caenopedina species it is closest to the Australian and New Zealand representatives, which is in contrast to previous reviews of Cenozoic Antarctic echinoid faunas that suggested limited relationship to the Australasian region. This is the first record of Caenopedina from Antarctica; it considerably extends its historical distribution to the south.
Przejdź do artykułu

Autorzy i Afiliacje

Andreas Kroh

Abstrakt

In this article, the fracture behavior of functionally graded thick-walled cylinder under thermo-mechanical shock is investigated. For this purpose, classical coupled thermoelastic equations are used in calculations. First, these equations are discretized with extended finite element method (XFEM) in the space domain and then they are solved by the Newmark method in the time domain. The most general form of interaction integral is extracted for axially symmetric circumferential crack in a cylinder under thermal and mechanical loads in functionally graded materials and is used to calculate dynamic stress intensity factors (SIFs). The problem solution has been implemented in MATLAB software.

Przejdź do artykułu

Autorzy i Afiliacje

Mohammad Reza Ghafoor Elahi
Masoud Mahdizadeh Rokhi

Abstrakt

The joined wing concept is an unconventional airplane configuration, known since the mid-twenties of the last century. It has several possible advantages, like reduction of the induced drag and weight due to the closed wing concept. The inverted joined wing variant is its rarely considered version, with the front wing being situated above the aft wing. The following paper presents a performance prediction of the recently optimized configuration of this airplane. Flight characteristics obtained numerically were compared with the performance of two classical configuration airplanes of similar category. Their computational fluid dynamics (CFD) models were created basing on available documentation, photographs and some inverse engineering methods. The analysis included simulations performed for a scale of 3-meter wingspan inverted joined wing demonstrator and also for real-scale manned airplanes. Therefore, the results of CFD calculations allowed us to assess the competitiveness of the presented concept, as compared to the most technologically advanced airplanes designed and manufactured to date. At the end of the paper, the areas where the inverted joined wing is better than conventional airplane were predicted and new research possibilities were described.

Przejdź do artykułu

Autorzy i Afiliacje

Adam Sieradzki
Adam Dziubiński
Cezary Galiński

Abstrakt

Friction stir welding is a solid state innovative joining technique, widely being used for joining aluminium alloys in aerospace, marine automotive and many other applications of commercial importance. The welding parameters and tool pin profile play a major role in deciding the weld quality. In this paper, an attempt has been made to understand the influences of welding speed and pin profile of the tool on friction stir welded joints of AA6082-T6 alloy. Three different tool pin profiles (tapered cylindrical four flutes, triangular and hexagonal) have been used to fabricate the joints at different welding speeds in the range of 30 to 74 mm/min. Microhardness (HV) and tensile tests performed at room temperature were used to evaluate the mechanical properties of the joints. In order to analyse the microstructural evolution of the material, the weld’s cross-sections were observed optically and SEM observations were made of the fracture surfaces. From this investigation it is found that the hexagonal tool pin profile produces mechanically sound and metallurgically defect free welds compared to other tool pin profiles.

Przejdź do artykułu

Autorzy i Afiliacje

Hiralal Subhash Patil
Sanjay N. Soman

Abstrakt

The social and political transformations Russia underwent in the 20th century were also reflected in the sphere of imagery. This also refers to the imagery of movement and means of transport. The process of linking the imagery of means of transportation with the political doctrine in force is mostly visible in the period of Soviet rule, in particular in the interwar period when the foundations of this rule were laid. Then, aviation was to become one of the strongly ideologized means of transport. The ideologization process occurred at various levels, starting from onomastic procedures through advertising and linking aviation and Soviet rule within artistic and literary conceptualisations. In Soviet culture, an aeroplane or a rocket were not merely means of transport but the means by which the expansion of communist ideology globally was supposed to be facilitated.

Przejdź do artykułu

Autorzy i Afiliacje

Roman Bobryk

Abstrakt

The article is devoted to contemporary studies on the nineteenth century memoirs written by Russian women. In the nineteenth century women’s memoirs were underestimated and neglected by researchers. Recently, there has been a signifi cant increase in research interest in memoirs written by women. This subject has been taken up by literary scholars, historians, experts on cultural studies and anthropologists. A. Bielova, I. Savkina, W. Laszczak, K. Kosowska, N. Pushkariova, A. Fieduta, W. Ponomarieva, L. Khoroshilova, J. Prikazchikova, A. Stankewich, J. Samofalova, O. Mamaieva, S. Tatarkina are among those who are interested in it. Memoirs are a valuable source of information about the epoch, historical events, outstanding leaders, event-making fi gures, Russian intellectual elites, aristocracy as well as the everyday life of the Russian gentry. They also provide some insight into the way female memoirists expressed themselves in their writings, their views on femininity and the role of women in society.

Przejdź do artykułu

Autorzy i Afiliacje

Daria Ambroziak

Ta strona wykorzystuje pliki 'cookies'. Więcej informacji