Different viscoelastic models and characteristics are commonly used to describe, analyze, compare and improve the mechanical properties of polymers. A time-dependent linear relaxation modulus next to frequency-domain storage and loss moduli are the basic rheological material functions of polymers. The exponential Maxwell model and the exponential stretched Kohlrausch–Williams–Watts model are, probably, the most known linear rheological models of polymers. There are different identification methods for such models, some of which are dedicated to specific models, while others are general in nature. However, the identification result, i.e., the best model, always depends on the specific experimental data on the basis of which it was determined. When the rheological stress relaxation test is performed, the data are composed of the sampling instants used in the test and on the measurements of the relaxation modulus of the real material. To build a relaxation modulus model that does not depend on sampling instants is a fundamental concern. The problem of weighted least-squares approximation of the real relaxation modulus is discussed when only the noise-corrupted time-measurements of the relaxation modulus are accessible for identification. A wide class of models, that are continuous, differentiable and Lipschitz with respect to parameters, is considered for the relaxation modulus approximation. The main results concern the models that are selected asymptotically as the number of measurements tends to infinity. It is shown that even when the true relaxation modulus description is completely unknown, the approximate optimal model parameters can be derived from the measurement data that are obtained for sampling instants that are selected randomly due to the appropriate randomization introduced whenever certain conditions regarding the adopted class of models are satisfied. It is shown that the most commonly used stress relaxation models, the Maxwell and Kohlrausch–Williams–Watts models, satisfy these conditions. Since the practical problems of the identification of relaxation modulus models are usually ill posed, Tikhonov regularization is applied to guarantee the stability of the regularized solutions. The approximate optimal model is a strongly consistent estimate of the regularized model that is optimal in the sense of the deterministic integral weighted square error. An identification algorithm leading to the best regularized model is presented. The stochastic-type convergence analysis is conducted for noise-corrupted relaxation modulus measurements, and the exponential convergence rate is proved. Numerical studies for different models of the relaxation modulus used in the polymer rheology are presented for the material described by a bimodal Gauss-like relaxation spectrum. Numerical studies have shown that if appropriate randomization is introduced in the selection of sampling instants, then optimal regularized models of the relaxation modulus being asymptotically independent of these time instants can be recovered from the stress relaxation experiment data. The robustness of the identification algorithm to measurement noises was demonstrated both by analytical and numerical analyses.

The paper presents analysis of the processes taking place in fuel systems which lead to damage of injection devices in farm machines. The most frequent reasons of failure of traditional injection systems and Common Rail high pressure systems which are caused inter alia by an improper quality of diesel oil were described and discussed. Microscopic tests of the surface of worn plungers of the plunger and barrel assemby of Motorpal injection pumps used in Zetor tractors were carried out. Types of damage to elements of the injection pump and electromagnetic injectors used in Common Rail systems CP4 type based on the tests on the group of 126 on-site repairs were assessed. Repairs were made in the repair centres in Podkarpackie Voivodeship and centres dealing with repair of injection systems. Metallographic tests were carried out in the Laboratory of Materials of Rzeszow University of Technology with the use of electrone scanning microscope Hitachi S-3400N.

Viscoelastic relaxation time and frequency spectra are useful for describing, analyzing, comparing, and improving the mechanical properties of materials. The spectra are typically obtained using the stress or oscillatory shear measurements. Over the last 80 years, dozens of mathematical models and algorithms were proposed to identify relaxation spectra models using different analytical and numerical tools. Some models and identification algorithms are intended for specific materials, while others are general and can be applied for an arbitrary rheological material. The identified relaxation spectrum model always depends on the identification method applied and on the specific measurements used in the identification process. The stress relaxation experiment data consist of the sampling times used in the experiment and the noise-corrupted relaxation modulus measurements. The aim of this paper is to build a model of the spectrum that asymptotically does not depend on the sampling times used in the experiment as the number of measurements tends to infinity. Broad model classes, determined by a finite series of various basis functions, are assumed for the relaxation spectra approximation. Both orthogonal series expansions based on the Legendre, Laguerre, and Chebyshev functions and non-orthogonal basis functions, like power exponential and modified Bessel functions of the second kind, are considered. It is proved that, even when the true spectrum description is entirely unfamiliar, the approximate sampling-times-independent spectra optimal models can be determined using modulus measurements for appropriately randomly selected sampling times. The recovered spectra models are strongly consistent estimates of the desirable models corresponding to the relaxation modulus models, being optimal for the deterministic integral weighted square error. A complete identification algorithm leading to the relaxation spectra models is presented that requires solving a sequence of weighted least-squares relaxation modulus approximation problems and a random selection of the sampling times. The problems of relaxation spectra identification are ill-posed; solution stability is ensured by applying Tikhonov regularization. Stochastic convergence analysis is conducted and the convergence with an exponential rate is demonstrated. Simulation studies are presented for the Kohlrausch–Williams–Watts spectrum with short relaxation times, the uni- and double-mode Gauss-like spectra with intermediate relaxation times, and the Baumgaertel–Schausberger–Winter spectrum with long relaxation times. Models using spectrum expansions on different basis series are applied. These studies have shown that sampling times randomization provides the sequence of the optimal spectra models that asymptotically converge to sampling-times-independent models. The noise robustness of the identified model was shown both by analytical analysis and numerical studies.

The present article contains an analysis of issues concerning logistics of agricultural tractors distribution. Programmes and the level of utilization of means...

The oversized cargo transportation market in Poland actively participates in developing the economy, providing services necessary for implementing large infrastructure and industrial projects on a national and European scale. Development and functioning of this sector in the EU and globally requires overcoming many organisational, technical and administrative barriers and difficulties, and the authors of several publications indicate how these services are developing. The current study contains a detailed analysis of data from 2001-2022. The paper characterises the changes in particular years, indicating the main causes of the occurring processes, and defines the existing trends. It presents the legal framework that regulates the functioning of the domestic market. Moreover, it discusses the number of permits and the value of fees for issuing permits collected by the General Directorate for National Roads and Motorways (Generalna Dyrekcja Dróg Krajowych i Autostrad, GDDKiA) over two decades. The article also evaluates trends concerning the number of licenses more than 50% decrease compared to the maximum in 2008. It assesses the course of changes in values, which in 2021 reached their highest level during the period under assessment. Furthermore, it discusses the differences that occurred in the number of permits issued and applications submitted in the years 2014-2022. It describes the structure of the number of permits issued in categories IV-VII in 2014-2020 and categories III-V in 2021-2022. It characterises the course of the largest operation in the history of Polish road haulage - the transport of an abnormally-sized TBM (Tunnel Boring Machine) - in terms of requirements and problems that occurred during the preparation and fulfilment of this order and were typical for the functioning of the sector. The evaluation provides the basis for summaries and conclusions on the Development and condition of the oversized cargo transportation sector in Polish road transport sector.

Wydawnictwo SIGMA-NOT wydaje czasopisma fachowe informuj?ce swoich czytelnik?w o najnowszych osi?gni?ciach naukowych i nowoczesnych rozwi?zaniach technicznych w Polsce i na ?wiecie, popularyzuje problemy techniczne oraz poszerza wiedz? i kultur? techniczn?.