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B. Zieliński

Efficiency analysis of IEEE 802.11 protocol with block acknowledge and frame aggregation

The article presents data transmission methods in IEEE 802.11 wireless LAN standard, including transmission efficiency improving methods like block acknowledge and two variants of frame aggregation. On the basis of their operation, an analytical model is derived which allows for estimation of protocol efficiency and effective throughput under perfect conditions for various protocol parameters. With this model, all transmission methods are analysed for their efficiency for two currently used physical layers, namely, OFDM (802.11a/g) and HT (802.11n). The calculation results are presented on graphs and discussed. Finally, so-called throughput upper limit is calculated for all the methods considered in the paper.

Open access

B. Zieliński

Abstract

AX.25 protocol belongs to the HDLC protocols family and is used, among others, as a data link layer in an amateur Packet Radio network. The paper presents a simple analytical model developed on the basis of protocol frame exchange rules. Then, we compare analytical results to the experimental ones achieved using various different types of TNC controllers that act as network interfaces for Packet Radio network. In the experimental part we focus on both hardware and software properties of TNC that have influence on the effective throughput of the network.

Open access

A. Zieliński, W. Serbiński, B. Majkowska, M. Jażdżewska and I. Skalski

Influence of laser remelting at cryogenic conditions on corrosion resistance of non-ferrous alloys

The main reason for laser remelting of the components made of aluminium, copper and titanium alloys is to obtain high hardness and corrosion resistance at the surface for longer lifetime as result of the rapid solidification. The final microstructure, phase composition and properties of aluminium, copper and titanium alloys depend on the laser process parameters and obviously on the nature of the equilibrium system.

The effect of laser surface remelting at cryogenic conditions on the microstructure and corrosion characteristics of the AlSi13Mg1CuNi, SUPERSTON and Ti-6Al-4V alloys are presented. The beneficial effects of laser treatment on the microstructure and corrosion behaviour of those alloys used for different products are observed.

Open access

A. Zieliński, S. Sobieszczyk, T. Seramak, W. Serbiński, B. Świeczko-Żurek and A. Ossowska

Biocompatibility and Bioactivity of Load-Bearing Metallic Implants

The main objective of here presented research is to develop the titanium (Ti) alloy base composite materials possessing better biocompatibility, longer lifetime and bioactivity behaviour for load-bearing implants, e.g. hip joint and knee joint endoprosthesis. The development of such materials is performed through: modeling the material behaviour in biological environment in long time and developing of new procedures for such evaluation; obtaining of a Ti alloy with designed porosity; developing of an oxidation technology resulting in high corrosion resistance and bioactivity; developing of technologies for hydroxyapatite (HA) deposition aimed at composite bioactive coatings; developing of technologies of precipitation of the biodegradable core material placed within the pores.

The examinations of degradation of Ti implants are carried out in order to recognize the sources of both early allergies and inflammation, and of long term degradation. The theoretical assessment of corrosion is made assuming three processes: electrochemical dissolution through imperfections of the anodic oxide layer, diffusion of metallic ions through the oxide layer, and dissolution of oxides themselves.

In order to increase the biocompatibility, the toxic elements, aluminium (Al) and vanadium (V) are eliminated. The experiments have shown that titanium - zirconium - niobium (Ti-Zr-Nb) alloy may be a such a material which can also be prepared by both powder metallurgy (P/M) technique and selective laser melting. The porous (scaffold) Ti-Zr-Nb alloy is now obtained by powder metallurgy, classical and with space holders used before melting and decomposed, or remained during melting and removed by subsequent water dissolution. The oxidation of porous materials is performed either by electrochemical technique in special electrolytes or by chemical and/or hydrothermal method in order to obtain the optimal oxide layer well adjacent to an interface, preventing the base metal against corrosion and bioactive because of its nanotubular structure, permitting injection of some species into the pores. The Ca, O and N ion implantation or deposition of zirconia sublayers may be used to increase the biocompatibility, bioactivity and corrosion resistance. The HA coating obtained by either electrophoretic, biomimetic or by sol-gel deposition should result in gradient structure similar to bone structure, possessing high adhesion strength. The core material of the porous material should result in a biodegradable material, allowing slower dissolution followed by stepwise growth of bone tissue and angiogenesis, preventing local inflammation processes, sustaining the mechanical strength close to that of non-porous material.

Open access

B. Majkowska, M. Jażdżewska, E. Wołowiec, W. Piekoszewski, L. Klimek and A. Zieliński

Abstract

The purpose of this paper is to show results of laser treatment at cryogenic conditions of the Ti6Al4V alloy used for orthopedic applications. That modification process ought to bring beneficial changes of microstructure and residual stresses in the surface layer. The paper presents the abrasive wear of the base and laser remelted material in association with ceramics Al2O3. Despite the surface cracking after laser treatment the tribological properties in simulated body fluid have been substantially improved.

Open access

M. Kozarski, P. Suwalski, K. Zieliński, K. Górczyńska, B. Szafron, K.J. Pałko, R. Smoczyński and M. Darowski

Abstract

In most cases of diseased heart valves, they can be repaired or replaced with biological or mechanical prostheses. Biological prostheses seem to be safer than mechanical ones and are applied with good clinical outcomes. Their disadvantage, when compared with mechanical valves, is durability. In the development and application of mechanical and biological heart valves, a significant role can be played by a Hybrid (Hydro-Numerical) Circulatory Model. The aim of this paper is to demonstrate the opportunities created by the hybrid model for investigations of mechanical heart valves and their computer models under conditions similar to those of the circulatory system. A diode-resistor numerical valve model and three different design mechanical aortic valves were tested. To perform their investigations, computer applications were developed under RT LabView to be run on a PC. Static and dynamic characteristics of the valves were measured and registered - pressure in the numerical time-varying elastance left ventricle (pLV), in the aorta (pas) and flow (f), proving, among other factors, that 1) time delay of pas with respect to pLV is mainly related to the valve’s opening time, and 2) the valves of substantially different designs tested under identical hydrodynamic conditions reveal nearly the same dynamic performance.

Open access

Aleksander Brzeziński, Mieczysław Jóźwik, Marek Kaczorowski, Maciej Kalarus, Damian Kasza, Wiesław Kosek, Jolanta Nastula, Zbigniew Szczerbowski, Małgorzata Wińska, Roman Wronowski, Ryszard Zdunek and Janusz B. Zieliński

Abstract

The Department of Planetary Geodesy of the Space Research Centre PAS has been conducting research on a broad spectrum of problems within a field of global dynamics of the Earth. In this report we describe the investigations on selected subjects concerning polar motion (modeling and geophysical interpretation of the Chandler wobble, hydrological excitation of seasonal signals, search for optimal prediction methods), tectonic activity in the region of the Książ Geodynamic Laboratory of the SRC, and finally the new joint Polish-Italian project GalAc analyzing feasibility and usefulness of equipping second-generation Galileo satellites with accelerometers.