Lodz University of Technology
Recent publications
Leishmaniasis is a group of contagious diseases having high surveillance among dogs. According to World Health Organization (WHO), ninety-two territories were infected around the world in 2018. One billion dogs live in areas endemic for Leishmaniasis and are at risk of infection. Almost one million cases are reported annually. The dog's population is categorized into five classes like susceptible (S), latent (L), infectious (I), uninfected (R), and infected (Q). The Leishmaniasis delayed model is developed to analyze and control its spread. Equilibria, positivity, boundedness, reproduction number, and parameter sensitivity are the model's essential features. The stability of the model is investigated in a local and global sense with the help of the Routh Hurwitz criterion and Lyapunov theory. In the end, simulations are presented to verify the theoretical analysis of the delayed model.
One of the major applications of chitosan is based on its ability to bind ions. In essence, the presence of active hydroxyl groups (-OH) and amino groups (-NH2), chitosan coordinates easily e.g. with transition metal ions, meanwhile it has a weak adsorption properties towards to alkaline earth metals. In this paper, a batch adsorption system was applied to study the adsorption of Ca(II) ions from aqueous solution by thermosensitive chitosan hydrogels. Due to the presence of sodium β-glycerophosphate (β-GP) in the sol structure, chitosan salts respond with phase transition and obtain thermosensitive properties, including changes in sorption abilities. Experimental research (the maximum adsorption capacity obtained 1.157 g g⁻¹) and theoretical investigation on sorption of calcium in range of concentrations of CaCl2 solution, has been studied. Equilibria were described by Langmuir, Freundlich, Toth, Redlich-Peterson, Dubinin-Radushkevich, Radke-Praushnitz, Fritz-S, Langmuir-Freundlich, Marczewski-Jaroniec, Bi-Langmuir isotherm equations. Whereas, to describe sorption kinetics an original model was proposed, which combine chemical reaction on sorbent surface and intraparticle diffusion. The process of sorption was described by two parameters: diffusion coefficient DAB = 2.967·10⁻⁹ m² s⁻¹ and surface process rate constant kv = 9.129·10⁻⁵ s⁻¹.
Electroactive polymers (EAPs) are functional materials that, stimulated by an electric field, change its composition or molecular structure so that the material expands, contracts, or bends (Guzmán et al. in J Appl Polymer Sci 112:3284–32931, 2009) and (Rappaport et al. in A glucose fuiel cell for implantable brain machine interfaces, Massachusetts Institute of Technology, Cambridge, 2012). The literature has shown that Chitin and Chitosan are considerably versatile and promising biomaterials to be used as EAPs in medical and biomedical applications as cochlear implant, and due to its chemical structure, is considered a biocompatible, bio-adhesive and biodegradable polymer (Falguni et al. in Proceedings of the 2010 IEEE Students Technology Simposium, IIT Kharagpur, 2010). Their amino and hydroxyl groups can be easily modified by organic (Younes et al. in Process Biochem 47:2032–2039, 2012) or cross-linked reactions, to obtain sophisticated functional medical devices (Wongpaint et al. in Micromol Biosci 5:1001–1012, 2005). This research collaboration aims to prove that Chitosan-based membranes could be synthetized as EAPs; as well as determine that there are useful ionic flow and movement responses on them. Chitosan-based membranes were prepared by the film-casting traditional method, treated with Tetraammineplatinum (II) chloride hydrate and Silver Nitrate by the ion exchange polymer method; and then cast with Sodium and Potassium Chloride as conductive salts. Membranes were tested at different voltages, as well as the chemical tests as FTIR, XRD, TGA and tensile strength and elongation as a function of the treatment applied. Film properties depended on its morphology, which is affected by Molecular Weight, degree of N-acetylation (DDA%), solvent evaporation and free amine regenerating mechanism (Younes et al. in Process Biochem 47:2032–2039, 2012) and (Wongpaint et al. in Micromol Biosci 5:1001–1012, 2005). Samples exhibited good displacement increasing as the applied voltage increased; best tip displacement was located as 17 mm at 7 V; and best theoretical δ value is found at 29.6 mm.
To solve large number of digital signal processing problems, such as on-board radar-location or hydro-acoustic systems, it is necessary to perform discrete trigonometric transforms over intensive data flows in real time with the constraints on size and power consumption. To solve this problem, the hardware implementation in the form of the VLSI has been proposed. In particular, we improve an algorithm for the fast cosine and sine Fourier transforms with a focus on the parallel-streaming hardware implementation. A flow graph of the improved algorithm has been developed on the basis of addition, subtraction and multiplication of real numbers with the relation scheme of algorithms. A linear projection of the improved algorithm for fast cosine and sine Fourier transforms on the axis parallel to the data transmission has been obtained. This makes it possible to change the type and dimensions of the transforms. Further, we develop a structure of 2-4-8-16-point processor for fast cosine and sine Fourier transforms. Such an implementation provides a reduction of the dimensions, energy consumption and performance of the transforms in real time.
This work presents a novel cluster based optimization procedure for estimating parameter values that yield stable, periodic responses with desired amplitude in nonlinear vibrating systems. The parameter values obtained by conventional nonlinear optimization schemes, with minimization of amplitude as the objective, may not furnish periodic and stable responses. Moreover, global optimization strategies may converge to isolated optima that are sensitive to parametric perturbations. In practical engineering systems, unstable or isolated optimal orbits are not practically realizable. To overcome these limitations, the proposed method tries to converge to a cluster in the r-dimensional parameter space in which the design specifications including the specified optimality, periodicity, stability and robustness are satisfied. Thus, it eliminates the need for computationally expensive bifurcation studies to locate stable, periodic parameter regimes before optimization. The present method is based on a hybrid scheme which involves the algebraic form of the governing equations in screening phase and its differential form in the selection phase. In the screening phase, force and energy balance conditions are used to rephrase the nonlinear governing equations in terms of the design parameter vector. These rephrased equations are reduced to algebraic form using a harmonic balance procedure which also specifies the desired amplitude and frequency of the response. An error norm based on this algebraic form is defined and is used to contract the search bounds in the parameter space leading to convergence to a cluster. The selection phase of the algorithm uses shooting method coupled with evaluation of Floquet multipliers to retain only those vectors in the arrived cluster yielding stable periodic solutions. The method is validated with Den Hartog's vibration absorbers and is then applied to vibration absorbers with material nonlinearity and vibration isolators with geometric nonlinearity. In both the cases, the converged cluster is shown to yield stable, periodic responses satisfying the amplitude condition. Parametric perturbation studies are conducted on the cluster to illustrate its robustness. The use of algebraic form of governing equations in the screening phase drastically reduces the computational time needed to converge to the cluster. The fact that the present method converges to a cluster in the parameter space rather than to a single parameter value offers the designer more freedom to choose the design vector from inside the cluster. It also ensures that the design is robust to small changes in parameter values.
Among inorganic salts, sodium sulfate is considered as one of the most dangerous to porous building materials. The pores of building materials are usually occupied by aqueous salt solution. Hence, the phase transitions of both, water and salt should be considered simultaneously during temperature decrease. In the present paper we describe an extensive experimental study devoted to the analysis of combined salt crystallization and water freezing in the Na2SO4–H2O system confined in the pores of sandstone and red clay brick induced by temperature variation. Salt and water phase transition patterns were investigated using differential scanning calorimetry. Saturated samples were subjected to 20 cooling-heating scans, where the initial temperature was changed in each cycle. Such a procedure enabled us to define three different crystallization paths of Na2SO4 hydrates and ice depending on the initial conditions. Based on the recorded heat flow, the crystallization enthalpies of hepta- and decahydrate of sodium sulfate were estimated.
The reliability of the usage of a splitter plate (passive control device) downstream of the obstacle, in suppressing the fluid forces on a circular obstacle of diameter D=0.1m is studied in this paper. The first parameter of the current study is the attachment of a splitter plate of various lengths (Li) with the obstacle, whereas the gap separation (Gi) between the splitter plate and the obstacle, is used as a second parameter. The control elements of the first and second parameters are varied from 0.1 to 0.3. For the attached splitter plates of lengths 0.2 and 0.3, the oscillatory behavior of transient flow at Re=100 is successfully controlled. For the gap separation, 0.1 and 0.2 similar results are obtained. However, it is observed that a splitter plate of too short length and a plate located at the inappropriate gap from the obstacle, are worthless. A computational strategy based on the finite element method is utilized due to the complicated representative equations. For a clear physical depiction of the problem, velocity and pressure plots have been provided. Drag and lift coefficients the hydrodynamic benchmark values are also evaluated in a graphical representation surrounding the obstacle’s peripheral surface as well as the splitter plate. In a conclusion, a splitter plate can function to control fluid forces whether it is attached or detached, based on plate length and gap separation between obstacle and plate, respectively.
Analytical methods based on the use of thermal analysis techniques were and still are very popular and often used in the study of plastics. These techniques enable the determination of thermal properties of polymeric materials, such as the glass transition temperature, melting temperature and heat of fusion, temperature and heat of crystallization, and specific heat. The effect of high temperature on polymers can lead to their depolymerization and degradation related to the release of low‐molecular‐weight decomposition products. Measurement of the material mass change as a function of temperature allows to determine the thermal stability of plastics. The most commonly used research techniques in this field include thermogravimetric analysis (TGA) and dynamic‐mechanical thermal analysis (DMTA), in addition to differential scanning calorimetry (DSC). Particularly, TGA is a very rapid accurate technique which, given that the connection between TGA and long‐term life testing can be established, should provide proper kinetic expressions and corresponding apparent activation energy of degradation values that can be used to predict the thermal lifetime of polymeric materials. The polymer industry is in fact split between the need to expand and implement a variety of applications and new materials, as well as to protect and maintain their functional properties, and the need for easy disposal or recycling after use. Therefore, the study on the thermal properties of polymers is crucial to improving their recyclability or providing a viable alternative. In particular, lifetime predictions play a key role in facilitating both the design stage and the final disposition. However, thermal analysis methods are not only used to study polymer materials for their desired thermal parameters, degradation, flammability, or development of more effective recycling methods after use. They are also readily applied for the analysis of raw materials, including auxiliaries and additives necessary and widely used in the production and processing of polymeric materials. The additives most often used in the processing of polymeric materials include stabilizers, flame retardants, (nano)fillers, pigments, and processing aids. The following chapter provides an insight into the role of thermal analysis methods in characterization of some polymer additives, both pristine and used as components of polymer composites.
Paper is devoted to the effective stationary heat conductivity for the fibre composite materials. We are aimed on getting on analytical expression for effective thermal conductivity coefficient. Asymptotic homogenization approach, based on the multiple scale perturbation method, is used. This allows to reduce the original boundary value problem in multiply connected domain to the sequence of boundary value problems in simply connected domains. These problems include: the local problem for the periodically repeated cell and homogenized problem with effective coefficient. It is shown that for densely packed and high contrast fibre composites, the cell problem can be solved analytically. For this aim, lubrication approach (asymptotics of thin layer) has been employed. We also generalise obtained solution to the case of medium‐sized inclusions in the framework of the Padé approximants.
Extending the concept of level measure μ({f⩾a}) we introduce a generalized level measure based on a family of conditional aggregations operators. As a recent research direction, conditional aggregation operators extend aggregation operators in order to model the dependence of function on a conditional set. Generalized level measures then provide a new insight into behaviour of level-dependent (monotone) measures and the related processes. We investigate in detail several basic properties of the generalized level measure, including connections with the family of level measures, the extension of the survival function μ({f>a}) and the transformation of monotone measures to hyperset. Applications in scientometrics and information science are described.
Financial misconduct has come into the spotlight in recent years, causing market regulators to increase the reach and severity of interventions. We show that at times the economic benefits of illicit financial activity outweigh the costs of litigation. We illustrate our argument with data from the US Securities and Exchanges Commission and a case of investment misconduct. From the neoclassical economic paradigm, which follows utilitarian thinking, it is rational to engage in misconduct. Still, the majority of professionals refrain from misconduct, foregoing economic rewards. We suggest financial activity could be reimagined taking into account intrinsic and prosocial motivations. A virtue ethics framework could also be applied, linking financial behavior to the quest for moral excellence and shared flourishing. By going beyond utilitarian thinking and considering alternative models, we offer a fuller account of financial behavior and a better perspective from which to design deterrence methods.
In this paper, bidirectional-coupled neurons through an asymmetric electrical synapse are investigated. These coupled neurons involve 2D Hindmarsh–Rose (HR) and 2D FitzHugh–Nagumo (FN) neurons. The equilibria of the coupled neurons model are investigated, and their stabilities have revealed that, for some values of the electrical synaptic weight, the model under consideration can display either self-excited or hidden firing patterns. In addition, the hidden coexistence of chaotic bursting with periodic spiking, chaotic spiking with period spiking, chaotic bursting with a resting pattern, and the coexistence of chaotic spiking with a resting pattern are also found for some sets of electrical synaptic coupling. For all the investigated phenomena, the Hamiltonian energy of the model is computed. It enables the estimation of the amount of energy released during the transition between the various electrical activities. Pspice simulations are carried out based on the analog circuit of the coupled neurons to support our numerical results. Finally, an STM32F407ZE microcontroller development board is exploited for the digital implementation of the proposed coupled neurons model.
The paper is devoted to the study of a family of complex-valued holomorphic functions and a family of holomorphic mappings in $${\mathbb {C}}^{n}.$$ C n . More precisely, the article concerns a Bavrin’s family of functions defined on a bounded complete n -circular domain $${\mathcal {G}}$$ G of $${\mathbb {C}}^{n}$$ C n and a family of biholomorphic mappings on the Euclidean open unit ball in $${\mathbb {C}}^{n}.$$ C n . The presented results include some estimates of a combination of the Fréchet differentials at the point $$z=0,$$ z = 0 , of the first and second order for Bavrin’s functions, also of the second and third order for biholomorphic close-to-starlike mappings in $${\mathbb {C}}^{n},$$ C n , respectively. These bounds give a generalization of the Fekete–Szegö coefficients problem for holomorphic functions of a complex variable on the case of holomorphic functions and mappings of several variables.
An autapse is a particular synapse with its axon and dendrites interconnected. In this contribution, the effect of a memristive autapse is investigated on the dynamics of a 2D Hindmarsh-Rose neuron. The Hamilton energy of the proposed model is established using the Helmholtz theorem. It is found after monitoring the parameters that the frequency of the external current has no effect on the energy while only the memristive autapse strength and the amplitude of the stimuli are able to affect the energy released by the considered neuron. The study of the dynamics of the proposed model revealed exotic neuronal behaviors such as reverse period doubling route to chaos, and the phenomenon of interior and exterior crises. In addition, the striking phenomenon of homogeneous extreme multistability is captured. It is characterized by the coexistence of firing patterns with identical shapes for the same set of parameters. Of particular interest, a non-invasive control method exploiting a temporal feedback term is applied to enable the basin of attraction of all the undesired dynamics to merge with the desired one for a suitable value of the controller coupling strength. The electronic circuit of the proposed model is constructed and simulated in the PSpice environment. The obtained results match well with those from the direct investigations of the mathematical model of the introduced neuron.
In this mini-review, we discuss implantable cardiovascular devices (ICVDs)-associated biofilm infections that have caused huge healthcare challenges, and their treatment not only has caused serious threats to human health, but it also imposed an exorbitant cost on communities worldwide. Solutions toward better managing biofilm formation on ICVDs will be provided, both in vitro and in vivo or in clinical trials. Furthermore, we provide expert recommendations to move the field of ICVDs towards more sustainable and durable surfaces on implantable devices that can significantly reduce both the imposed cost on healthcare (by reducing the rate of hospitalization, re-surgery, etc.) and patients suffering from prolonged medical care. Finally, we discuss the promises and pitfalls along with the solutions in the use of ICVDs for cardiovascular disease therapeutics and diagnostics.
This work describes two new synthetic methods for the efficient preparation of isoflavones following the Ni‐catalysed domino arylation reactions of the vast range of ortho‐hydroxyarylenaminones utilising aromatic bromides as well as carboxylic acids. The presented protocols tolerated significant variation of all coupling partners and enabled synthesis of isoflavone library of twenty‐three representatives. This is the first communicated precedent where the mechanic energy was utilised in the synthesis of isoflavones following the domino cyclisation mode.
Friction-induced stick–slip vibration has been identified as the main reason for various types of disc brake noises like creep groan, squeak and creak. In this work, we investigate the suppression of stick–slip vibrations in disc brakes due to the application of a small-amplitude normal harmonic force on the brake pad. The discontinuity induced bifurcations that lead to such suppression are studied in detail. The frequency range of the normal force in which suppression of stick–slip vibration occur is identified. A 3 DoF discontinuous model of the disc brake is considered. The discontinuous oscillator is modelled as a Filippov system with smooth vector fields separated by a discontinuity surface. It is shown that the normal harmonic force entrains the non-smooth limit cycle even for very small forcing amplitudes. Different frequency intervals exhibiting harmonic, super-harmonic, and sub-harmonic entrainments are identified. It is demonstrated that the initiation and termination of these entrainment intervals are associated with Neimark-Sacker bifurcations. It is also shown that discontinuity induced grazing-sliding mechanism brings about these bifurcations. Switching-sliding bifurcations happening in the entrainment region give rise to a sub-interval which is associated with suppression of stick–slip vibrations. We also report interesting discontinuity induced bifurcation scenarios in higher order entrainment regimes like grazing-sliding involving different orbit loops at lower and upper limits of the interval and splitting-merging of the sliding surface.
In this work, the mechanical properties of thermo-oxidative aged and thermally stabilized high consistency silicone rubber were investigated. The thermal oxidative stabilization is achieved by titanium oxide based fillers that were incorporated at different concentrations into the silicone compounds. Besides a pure titanium oxide filler, AEROXIDE® TiO2 P25, also an iron oxide doped heat stabilizer, AEROXIDE® TiO2 PF 2, was studied. The addition of the AEROXIDE® TiO2 fillers significantly improves the thermal stability of the compounds and maintains the mechanical properties on a good level after thermal aging. The thermal stabilization depends on the type and concentration of the AEROXIDE® TiO2 fillers. Due to iron oxide doping, the efficiency of AEROXIDE® TiO2 PF 2 is higher in comparison to AEROXIDE® TiO2 P25. However, a too high concentration, especially of AEROXIDE® TiO2 PF 2, induces a catalytic effect and favors the thermal degradation of the silicone. Therefore, the optimum concentration depends on the behavior of the heat stabilizer, its catalytic effect, and the thermal-oxidative conditions applied to the silicone. This study has revealed that titanium oxide based fillers are efficient heat stabilizers to preserve the mechanical properties of silicone rubber on a good level during applications at elevated temperatures.
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4,355 members
Grzegorz Liśkiewicz
  • Institute of Turbomachinery
Jolanta Prywer
  • Institute of Physics
Tomasz Kapitaniak
  • Department of Dynamics
Żeromskiego 116, 90-924, Łódź, Poland
Head of institution
Sławomir Wiak