Gdansk University of Technology
  • Gdańsk, Pomeranian Voivodeship, Poland
Recent publications
In this study, the effects of soluble readily biodegradable COD (sCOD) and particulate slowly biodegradable COD (pCOD) on anammox process were investigated. The results of the long-term experiment indicated that a low sCOD/N ratio of 0.5 could accelerate the anammox and denitrification activity, to reach as high as 84.9%±2.8% TN removal efficiency. Partial denitrification-anammox (PDN/anammox) and denitrification were proposed as the major pathways for nitrogen removal, accounting for 91.3% and 8.7% of the TN removal, respectively. Anammox bacteria could remain active with high abundance of anammox genes to maintain its dominance. Candidatus Kuenenia and Thauera were the predominant genera in the presence of organic matter. Compared with sCOD, batch experiments showed that the introduction of pCOD had a negative effect on nitrogen removal. The contribution of denitrification to nitrogen removal decreased from approximately 14% to 3% with increasing percentage of pCOD. In addition, the analysis result of the process data using an optimized ASM1 model indicated that high percentage of pCOD resulted in serious N2O emission (the peak value up to 0.25 mg N/L), which was likely due to limited mass diffusion and insufficient available carbon sources for denitrification. However, a high sCOD/N ratio was beneficial for alleviating N2O accumulation.
The thermoelectric generator (TEG) system has attracted extensive attention because of its applications in centralized solar heat utilization and recoverable heat energy. The operating efficiency of the TEG system is highly affected by operating conditions. In a series-parallel structure, due to diverse temperature differences, the TEG modules show non-linear performance. Due to the non-uniform temperature distribution (NUTD) condition, several maximum power points (MPPs) appear on the P/V curve. In multiple MPPs, the true global maximum power points (GMPP) are very important for optimum action. The existing conventional technologies have slow tracking speed, low productivity, and unwanted fluctuations in voltage curves. To overcome the TEG system behavior and shortcomings, A novel control technology for the TEG system is proposed, which utilizes the improved generalized regression neural network and fitness dependent optimization (GRNNFDO) to track the GMPP under dynamic operating conditions. Conventional TEG system control techniques are not likely to trace true GMPP. Our novel GRNNFDO can trace the true GMPP for NUTD and under varying temperature conditions. In this article, some major contributions in the area of the TEG systems are investigated by solving the issues such as NUTD global maxima tracking, low efficiency of TEG module due to mismatch, and oscillations around optimum point. The results of GRNNFDO are compared with the Cuckoo-search algorithm (CSA), and grasshopper optimization (GHO) algorithm and particle swarm optimization (PSO) algorithm. Results of GRNNFDO are verified with experiments and authenticated with MATLAB/SIMULINK. The proposed GRNNFDO control technique generates up to 7% more energy than PSO and 60% fast-tracking than metaheuristic algorithms.
The aim of and inspiration behind this paper was to explain the reasons, also observed by other researchers, of the discrepancy in the results of experimental free convection, which for small Rayleigh and Nusselt numbers in the initial phase of research can sometimes reach several hundred percent. These discrepancies decrease with increasing heating power and plate surface temperature, in proportion to the increase in Ra and Nu, reaching typical values for this type of research. To explain this phenomenon, a comprehensive theoretical and experimental analysis of the influence of the physical properties of a fluid (air and water) as well as primary (tw and t∞) and secondary (tav and Δt) temperatures on the Rayleigh number was carried out. The impact was found to be unequal. The plate temperature tw is of greater importance, which is much higher than the much lower and almost constant temperature t∞ of the undisturbed area, especially since it causes convective movement, generating differences in fluid density and thus driving the phenomenon. Similarly, the direct contribution of the temperature difference Δt to Ra suggests that it has a greater influence on convective heat transfer than the average temperature of the medium tav. By analysing the effect of each of these temperatures separately, it was possible to show that their mutual, compatible or opposite interaction (tw/t∞) causes a different scattering of results, or may even lead to unusual Rayleigh numbers (Ra temperature dualism). This study led not only to a better understanding of the phenomenon, but even to a prediction of its unusual behaviour, unheard of in typical experimental studies of free convection. For example, if we consider the theoretical convective heat transfer from a plate l = 0.15 m in air in the context of the interaction of tav and Δt, it turns out that for the same Δt = 40 K, the Rayleigh number may assume, depending on tav = (tw + t∞)/2, different values. So, for tw = 50 °C, t∞ = 10 °C and tav = 30 °C, Ra = 1.213.10⁷, whereas for tw = 90 °C, t∞ = 50 °C and tav = 70 °C it is ≈ 1.7 times smaller (Ra = 0.687.10⁷). This hypothetical phenomenon, unheard of in typical experimental studies, which could occur, and maybe even does occur in smelting, thermal energy, etc., forces us to think about the values of Nusselt numbers, heat transfer coefficients and heat fluxes for these two cases. This lies beyond the scope of the present paper, but it is a topic for possible future research.
Christopher Alexander, a British-American scholar, famously differentiated an old (natural) city from a new (planned) one in structure. The former resembles a “semilattice”, or a complex system encompassing many interconnected sub-systems. The latter is shaped in a graph-theoretical “tree”, which lacks the structural complexity as its sub-systems are compartmentalized into a single hierarchy. This structural distinction can explain, or perhaps determine “the patina of life” in old urban districts and the lack of such in new ones. Alexander's idea, although widely influential, remains contested for its lack of empirical support. Subsequent literature failed to distinguish the structural differences between the old and new cities in systematic ways, nor is his asserted structure-life relationship verified with rigor. This study aims to test Alexander’s urban structural theory under a comprehensive research framework. We translated his constructs and premises into a mathematically testable form. The structural qualities of an urban street network, conceived as “semilattice”, “complex network” and “living structure”, were measured using graph-topological indicators. Urban life was captured using a combination of Twitter activities, Point-Of-Interests, and walking trips, aggregated at the district level. The structure-life relationship was tested statistically, after controlling for urban form and socio-demographic confounders, including land use, density, block size, parks, income, age, and demographics. This research design was implemented in London, New York, Hong Kong, and Gdansk. Our results support Alexander's early works that an old urban district contains more “semilattice” than new ones. This quality can be captured by Meshedness Coefficient, a graph-network indicator for a semilattice-shaped street network and a strong predictor for urban life. The same cannot be observed for “complex network” with consistency, and we found no independent associations between “living structure” and life, contrary to existing literature. The study shed light on the hidden relationships between urban spatial structure and behaviors, in both the virtual and physical world. We uncovered the British-American predilection of Alexander’s theory, which is well-supported by observations in London and New York yet less so in Hong Kong or Gdansk, suggesting the need for a locally-sensitive approach. The analytical tools developed can be of value for planning research and practice.
The Photovoltaic (PV) module converts only a small portion of irradiance into electrical energy. Most of the solar energy is wasted as heat, resulting in a rise in PV cell temperature and a decrease in solar cell efficiency. One way to harvest this freely available solar thermal energy and improve PV cell efficiency is by integrating PV systems with thermoelectric generators (TEG). This cogeneration approach of the hybrid PV-TEG system uses waste heat as an energy production source, resulting in higher output power density. Furthermore, as hybrid PV-TEG systems are frequently used in dynamic environments with temperature and irradiance variations, it is critical to modify the electrical operating points effectively and precisely to maximize the collected power, a process known as maximum power point tracking (MPPT). Under stochastic environmental conditions, a properly chosen MPPT technique can improve the generation efficiency from 10 to 15%. Therefore, in this study a novel implementation of atomic orbital search optimization algorithm is presented for MPPT tracking. Several case studies are designed to test AOS based MPPT algorithm performance under stochastic operating conditions. The effectiveness of the proposed algorithm is validated by comparing it with the conventional Perturb and Observe (P&O) algorithm and other highly-efficient metaheuristic algorithms such as Grasshopper Optimization (GHO), Particle swarm optimization (PSO), and Grey Wolf Optimization (GWO). AOS based controller extracts 6% more energy and tracks optimal power at an efficiency of 99.984% under various test scenarios. The tracking time is improved by 616.48% as compared to PSO. Experimental, quantitative, comparative, and statistical results demonstrate the AOS-based proposed technique's superior performance under various practical conditions.
The principal focus of software product management is to ensure the economic success of the product, which means to prolong the product life as much as possible with modest expenditures to maximizs profits. Software product managers play an important role in the software development organization while being responsible for the strategy, business case, product roadmap, high-level requirements, product deployment (release-management), and retirement plan. This article explores the problems that affect the software product management process, their perceived frequency and perceived severity. The data were collected by a systematic literature review (5 main databases were analyzed), interviews (10 software product managers from IT companies), and surveys (89 participants). 95 software product management problems assigned nonexclusively to 7 areas were identified. 27 commonly mentioned software product management problems were evaluated for their perceived frequency and perceived severity. The problems perceived as the most frequent are: determining the true value of the product that the customer needs, strategy and priorities change frequently, technical debt, working in silos, and balancing between reactive and proactive work. In total, 95 problems have been identified which have been narrowed down to 27 problems based on their occurrence in at least 3 interviews. These selected problems were prioritized by perceived frequency and perceived severity. Some of the identified problems spanned beyond the software product management process itself, but they all affect the work of software product managers.
Thermally activated persulfate (TAP) finds application in Advanced Oxidation Processes for the removal of pollutants from contaminated water and soil. This paper reviewed the various cases of TAP in the environmental remediation. The pollutants such as individual pharmaceuticals, biocides, cyclic organic compounds, and dyes are considered in this review. It is interesting to note that most of the organic compounds undergo complete degradation at a high temperature of 70°C with a first-order reaction kinetics. The influence of operating parameters such as temperature, persulfate concentration, initial pH, and degradation behavior in the presence of natural water constituents are also discussed. In addition, several processes to reduce the temperature of TAP are highlighted.
This paper aims to study the effect of asynchronous axial-torsional strain-controlled loading histories on fracture surface behavior of thin-walled tubular X5CrNi18-10 (304/304L) austenitic steel specimens. Tests under pure axial loading and pure torsional loading are also conducted to better segregate the effect of multiaxiality. The fractures surface topographies were examined through the profiles over the entire surface with the support of an optical measurement system. Then, features of the post-failure fractures were related to the loading conditions and the fatigue life. The outcomes indicate that the multiaxial loading path significantly affects the surface topography. Overall, fracture surface parameters increase for higher fatigue lives. Based on the dialectic relationship, a fatigue damage model able to estimate the fatigue lifetime under asynchronous axial-torsional loading histories has been successfully developed. The fracture surface topology parameters collected from both sides of the same specimen lead to comparable results which reinforces the applicability of the proposed approach.
In 2008, Hedetniemi et al. introduced the concept of (1,k)‐domination and obtained some interesting results for (1,2) ‐domination. Obviously every (1,1) ‐dominating set of a graph (known as 2‐dominating set) is (1,2) ‐dominating; to distinguish these concepts, we define a proper (1,2) ‐dominating set of a graph as follows: a subset D is a proper (1,2) ‐dominating set of a graph if D is (1,2) ‐dominating and it is not a (1,1) ‐dominating set of a graph. In particular, we introduce proper (1,2) ‐domination parameters and study their relations with (1,2) ‐domination parameters and the classical domination numbers.
The current study is the first attempt to prepare nanocomposites of Eleocharis dulcis biochar (EDB) with nano zero-valent Copper (nZVCu/EDB) and magnetite nanoparticles (MNPs/EDB) for batch and column scale sequestration of Congo Red dye (CR) from synthetic and natural water. The adsorbents were characterized with advanced analytical techniques. The impact of EDB, MNPs/EDB and nZVCu/EDB dosage (1–4 g/L), pH (4–10), initial concentration of CR (20–500 mg/L), interaction time (180 min) and material type to remove CR from water was examined at ambient temperature. The CR removal followed sequence of nZVCu/EDB > MNPs/EDB > EDB (84.9–98% > 77–95% > 69.5–93%) at dosage 2 g/L when CR concentration was increased from 20-500 mg/L. The MNPs/EDB and nZVCu/EDB showed 10.9% and 20.1% higher CR removal than EDB. The adsorption capacity of nZVCu/EDB, MNPs/EDB and EDB was 212, 193 and 174 mg/g, respectively. Freundlich model proved more suitable for sorption experiments while pseudo 2nd order kinetic model well explained the adsorption kinetics. Fixed bed column scale results revealed excellent retention of CR (99%) even at 500 mg/L till 2 h when packed column was filled with 3.0 g nZVCu/EDB, MNPs/EDB and EDB. These results revealed that nanocomposites with biochar can be applied efficiently for the decontamination of CR contaminated water.
In this investigation, a computational analysis is conducted to study a magneto-thermoelastic problem ‎for an isotropic perfectly conducting half space medium. The medium is subjected to a periodic heat flow in the presence of a continuous longitude magnetic field. Based on Moore-Gibson- Thompson equation (MGTE) a new generalized model has been investigated to address the considered problem. ‎The introduced model can be formulated by combining the Green-Naghdi-Type III and Lord-Shulman models. Eringen's non-local theory has also been applied to demonstrate the effect of ‎thermoelastic materials which depends on small-scale. Some special cases as well as previous thermoelasticity ‎models are deduced from the presented approach. In the domain of the Laplace transform, the system ‎of equations is expressed and the problem is solved using state space method. The converted ‎physical expressions are numerically reversed by Zakian's computational algorithm. The analysis ‎indicates the significant influence on field variables of non-local modulus and magnetic field with larger ‎values. Moreover, with the established literature, the numerical results are satisfactorily examined.
Galerkin weighted residual method (GWRM) is applied and implemented to address the axial stability and bifurcation point of a functionally graded (FG) piezomagnetic structure containing flexomagneticity (FM) in a thermal environment. The continuum specimen involves an exponential mass distributed in a heterogeneous media with a constant square cross-section. The physical neutral plane is investigated to postulate functionally graded material (FGM) close to reality. Mathematical formulations concern the Timoshenko shear deformation theory. Small scale and atomic interactions are shaped as maintained by the nonlocal strain gradient elasticity approach. Since there is no bifurcation point for FGMs, whenever both boundary conditions are rotational and the neutral surface does not match the mid-plane, the clamp configuration is examined only. The fourth-order ordinary differential stability equations will be converted into the sets of algebraic ones utilizing the GWRM whose accuracy was proved before. After that, by simply solving the achieved polynomial constitutive relation, the parametric study can be started due to various predominant and overriding factors. It was found that the flexomagneticity is further visible if the ferric nanobeam is constructed by FGM technology. In addition to this, shear deformations are also efficacious to make the FM detectable.
A combination of dual-frequency acoustic cavitation (acoustic cavitation) and UV assisted advanced oxidation processes (AOPs) reaction system was developed for desulfurization of raw naphtha used to produce aviation fuels. Various types of oxidants in hybrid systems including hydrogen peroxide, acetic acid, acetone, air and ozone were compared. At optimum oxidant to sulfur compounds molar ratio (rox) of 5.0, the hybrid process of acoustic cavitation /acetic acid/hydrogen peroxide (acoustic cavitation/peracetic acid) was the most effective treatment process with synergistic index of 7.55 and desulfurization efficiency of 100% (highest reaction rate constant of 0.1337 min-1) for all sulfur compounds present in naphtha within the short reaction time of 30 min. At rox of 0.5 and 1.0, the synergy coefficients of 3.77 and 5.41 corresponding to the desulfurization efficiencies of 93.07 and 95.10% were obtained in 180 min, respectively. Comparatively, at the rox of 5.0, the efficiency of acoustic cavitation combined with hydrogen peroxide alone and acetic acid alone was 63.68 and 47.36%, respectively. Alternative treatment process of acoustic cavitation /UV/acetone/water can be used for the complete desulfurization (100%) of specific sulphur compounds including dibutyl sulfide, di-tert butyl disulfide, 1,4-butanedithiol and benzyl thiol considering the optimum acetone to water ratio of 2:1. All acoustic cavitation-based treatment systems followed the pseudo first order kinetic model. The most expensive process was ozone-aided acoustic cavitation with treatment costs exceeding 100 USD m-3. The peracetic acid-based system was the most economic process with a treatment cost of 15 USD/m³ with electric energy consumption of 100.17 kWh/m³.
In this paper, the fracture behavior and fatigue crack growth rate of the 2024-T351 aluminum alloy has been investigated. At first, the 2024-T351 aluminum alloys have been welded using friction stir welding procedure and the fracture toughness and fatigue crack growth rate of the CT specimens have been studied experimentally based on ASTM standards. After that, in order to predict fatigue crack growth rate and fracture toughness, artificial neural network is used. To obtain the best neuron number in the hidden layer of the artificial neural network, different neuron numbers are tested and the best network based on the performance is selected. Then the fitting method is applied and the fitted surfaces that illustrate the behavior of welding are shown and the results of artificial neural network and fitting method are compared. Also, multi-objective optimization algorithm is used to obtain the best welding parameters and finally sensitivity analysis is applied to measure the effect of rotational and traverse speeds on the fracture toughness and fatigue crack growth rate.
Since the first bacterial inhabitants of the human gastrointestinal tract were identified, a lot of research into the study of the human microbiome and its effects on health has been conducted. Currently, it is accepted that humans have a symbiotic relationship with the gut microbiome, though the specifics of this relationship are not well understood. The microbiome of neonates constantly changes and appears to influence many facets of the infant’s health and predisposition later in life. This review aims to show how the microbiome develops over time. We discuss its composition, origins and stages of development of microbiota, the possible health benefits of a proper neonatal microbiome, and the dangers associated with dysbiosis. We emphasize the shielding, modulating, and stimulating effects breast milk has on the infant microbiota. The methods commonly used for the study of microbiota are also discussed.
Based on transformation optics (TO), this paper uses geometric divisions and linear coordinate transformations to design “shrinking-shifting—and reshaping”, and “amplifying-shifting—and reshaping” devices. The proposed devices can reshape the sizes and locations of the wrapped-objects inside the core-region. The shrinking-shifting device shrinks the larger object into a smaller one and shifts it to different location, whereas the shrinking-reshaping device can generate a smaller-size image with different shape located at different location. In contrast to previously designed shrinking devices, the real object wrapped inside the proposed core-region and the transformed object contains the same material properties, and the location-shifting is another feature. Here, the shifting-region is located inside the physical-space boundaries to achieve the non-negative, homogeneous, and anisotropic material properties of the proposed device, which are easier for real implementations. Thus, we further verified this concept with the amplifying-shifting and -reshaping devices for visually transformation of smaller object into bigger one placed at different location and position. We also applied active scatterer to further validate the working functionality of proposed devices. In addition, the proposed devices behave like the concentrator and (or) rotator effect in the absence of any scatterer. Our findings highlight the role of TO, suggesting directions for future research on bi-functional devices that will be useful for shrinking and amplifying devices, illusion optics, camouflage, and object protection etc.
Due to the key role of nitrite in novel nitrogen removal systems, nitrite oxidizing bacteria (NOB) have been receiving increasing attention. In this study, the coexistence and interactions of nitrifying bacteria were explored at decreasing solids retention times (SRTs). Four 5-week washout experiments were carried out in laboratory-scale (V=10 L) sequencing batch reactors (SBRs) with mixed liquor from two full-scale activated sludge systems (continuous flow vs SBR). During the experiments, the SRT was gradually reduced from the initial value of 4.0 d to approximately 1.0 d. The reactors were operated under limited dissolved oxygen conditions (set point of 0.6 mg O2/L) and two process temperatures: 12℃ (winter) and 20℃ (summer). At both temperatures, the progressive SRT reduction was inefficient for the out-selection of both canonical NOB and comammox Nitrospira. However, the dominant NOB switched from Nitrospira to Ca. Nitrotoga, whereas the dominant AOB was always Nitrosomonas. The results of this study are important for optimizing NOB suppression strategies in the novel N removal processes, which are based on nitrite accumulation.
In this study, a mathematical model was proposed to analyze the performance of storm overflows. The model included the influence of rainfall genesis on the duration of storm overflow, its volume, and the maximum instantaneous flow. The multinomial logistic regression model, which has not been used so far to model objects located in a stormwater system, was proposed to simulate the duration of storm overflow. The Iman–Conover method, using the theoretical cumulative distributions determined on the basis of 45 – year rainfall sequences, was adopted to simulate the rainfall characteristics describing the overflow performance (total and maximum 30-min rainfall depth and duration). The simulations showed a significant impact of rainfall genesis on the parameters of the storm overflow. The model and the results presented in this study can be used at the stage of dimensioning storm overflows and to create an early warning system against undesirable phenomena in the stormwater system within urban catchments.
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5,398 members
Magdalena Olczyk
  • Faculty of Management and Economics
Monika Padariya
  • Department of Pharmaceutical Technology and Biochemistry
Srinivasu Kunuku
  • Department of Metrology and Optoelectronics
Hanna Staroszczyk
  • Department of Chemistry, Technology and Biochemistry of Food
Marek Blok
  • Department of Teleinformation Networks
Narutowicza 11/12, 80-233, Gdańsk, Pomeranian Voivodeship, Poland