University of Niš: Facta Universitatis (E-Journals) / Универзитет у Нишу
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A MONITORING METHOD OF MILLING CHATTER BASED ON OPTIMIZED HYBRID NEURAL NETWORK WITH ATTENTION MECHANISM
Full text linkMachining chatter is a self-excited vibration between the cutting tool and the workpiece, which can reduce surface quality and tool life, and even endanger the safety of operators in severe cases. Considering that milling chatter has multi-scale features and the debugging of neural network hyperparameters heavily relies on experience, a milling chatter monitoring method based on an optimized hybrid neural network with an attention mechanism (MISSA-MSCNN-BiLSTM-ATM) is proposed. Firstly, the harmonic of the spindle rotation frequency is filtered out using the spindle rotation frequency removal technique (SFT). Then, an improved sparrow search algorithm (MISSA) is proposed based on multiple strategies including improved circle chaotic mapping, golden sine strategy, and enhanced Lévy flight. Subsequently, MISSA is utilized to optimize the hyperparameters of the milling chatter classification hybrid neural network model, combining multi-scale convolutional neural networks (MSCNN), bidirectional long short-term memory (BiLSTM), and attention mechanism (ATM). In numerical simulations with CEC2005 complex functions, MISSA demonstrates better optimization accuracy, stability, and shorter computation time compared to other intelligent algorithms. Compared with other milling chatter classification models, the proposed method exhibits significant improvements in accuracy and stability
STABILITY ANALYSIS OF THE SECOND-ORDER DPCM PREDICTION FILTER AND CORRELATION WITH SIGNAL-TO-QUANTIZATION NOISE RATIO
Full text linkThe stability study of the differential pulse code modulation system with the special focus on a predictor is given in this paper. Moreover, sufficient stability conditions for a linear prediction (recursive) filter are derived. The corresponding mathematical inequalities for the commonly used second-order predictor are derived. A method off probability estimation for the predictor coefficients is given, both deterministic and stochastic. It allows the design of the differential pulse code modulation system with the linear predictor whose coefficients meet the technical requirements. Finally, the probability of stability values for the specific second-order predictor are computed and compared with the corresponding values of the Signal-to-Quantization Noise Ratio (SQNR). The correlation between these values is verified for different frame lengths. This could be crucial for the optimal choice of predictor coefficients. Useful conclusions are drawn regarding the stability and performances of the system
STAVOVI O OCENJIVANJU KOD STUDENATA I AKTIVNIH NASTAVNIKA FIZIČKOG VASPITANJA
No full textAssessing and grading students’ performance in class is an essential part of teaching as a profession. Compared to other classroom-based subjects, Physical Education (PE) teachers usually handle grading practices in the motor learning domain and in a gym-based environment (Rink, 2013). Pre-service and in-service teachers may have different views on handling grading in PE according to differences in teaching experience, and theoretical and practical knowledge (Alkharusi, Kazem, & Al-Musawai, 2011; Schempp et al., 1998). This study aims to investigate in-service PE teachers’ (ISPET) perspectives of teaching practices in grading and compare them to the respective pre-service PE teachers’ (PSPET) perspectives. To find a common set of teaching practices for grading in PE that fits knowledge and experience scopes of both in-service and pre-service PE teachers, essential aspects of grading were extracted out of systematic research on PE teachers’ stress factors (König, 2004). Communicative and pragmatic validity of selected items were ensured by group discussion with selected pre-service and in-service PE teachers. 132 pre-service PE teachers and 134 in-service PE teachers were surveyed using a questionnaire consisting of personal data and previously developed items on teaching practices in grading. Results showed statistically significant differences in slightly more than a half of the respective attitudes on grading practices (e.g., “I assess and grade student performance frequently, because students learn well under pressure.”). ANOVA showed significant differences regarding study/teaching experience in both groups in regard to some attitudes on grading. PE teacher education programs and PE teachers’ continuing professional development may emphasize the change in teaching practices in grading to increase awareness.Procena i ocenjivanje uspeha učenika na času su ključni deo rada nastavnika. U poređenju sa drugim predmetima koji su vezani za učionicu, nastavnici fizičkog vaspitanja (FV) se obično bave praksama ocenjivanja u domenu motoričkog učenja i u sali za vežbanje (Rink, 2013). Budući nastavnici i aktivni nastavnici mogu imati različite stavove prema ocenjivanju u FV zbog razlika u nastavnom iskustvu, kao i teoretskom i praktičnom znanju (Alkharusi, Kazem, & Al-Musawai, 2011; Schempp et al., 1998). Ovaj rad ima za cilj da istraži perspektive aktivnih nastavnika fizičkog vaspitanja (ANFV) o praksama ocenjivanja i uporedi ih sa stavovima budućih nastavnika fizičkog vaspitanja (BNFV). Da bi se pronašao zajednički skup nastavnih praksi ocenjivanja u FV, koji odgovara obimu znanja i iskustva i budućih i aktivnih nastavnika fizičkog vaspitanja, ključni aspekti ocenjivanja izdvojeni su iz sistematskog istraživanja o faktorima stresa kod nastavnika FV (König, 2004). Komunikativna i pragmatička validnost odabranih stavki osigurana je grupnom diskusijom sa odabranim budućim i aktivnim nastavnicima FV. Anketirano je 132 budućih i 134 aktivnih nastavnika FV pomoću upitnika koji je sadržao stavke vezane za prikupljanje ličnih podataka i prethodno razvijene stavke o praksama ocenjivanja. Rezultati su pokazali statistički značajne razlike u nešto više od polovine stavova o praksama ocenjivanja (npr. „Često procenjujem i ocenjujem učenički učinak, jer učenici dobro uče pod pritiskom.“). ANOVA je pokazala značajne razlike u vezi sa studijskim/nastavnim iskustvom u obe grupe u pogledu nekih stavova o ocenjivanju. Programi obrazovanja nastavnika FV i kontinuirani profesionalni razvoj nastavnika FV mogu obratiti više pažnje na promenu nastavnih praksi ocenjivanja kako bi se povećala svest o njima
TEMPERATURE DEPENDENCE OF THE ELECTRONIC BAND GAP OF CsPbBr3 QUANTUM WELLS OBTAINED USING K•P METHOD
Full text linkWe calculated the electronic structure of CsPbBr3 quantum wells using the k•p model with parameters extracted from hybrid functional based DFT calculations supplemented with self-energy corrections arising from the electron-phonon interaction. We obtained the temperature dependence of the band gap for different sizes of the quantum well. The results show that the temperature dependence in quantum wells is similar to the one found in bulk phase for all sizes of the well that were considered
ENSURING AN ACOUSTICALLY UNPOLLUTED LIVING ENVIRONMENT
Full text linkHuman beings are always concerned with living in an unpolluted environment. Noise pollution is one type of pollution that can arise. To address this issue, the acoustic properties of the environment are studied. This is done through periodic measurements, identifying the sources of pollution at the same time. The impact on the environment is then evaluated based on the collected data. Based on this, pollution reduction measures are established, and measures to reduce pollution are implemented accordingly. The methodology, measurement procedures, development of reduction strategies, and their effectiveness are thoroughly outlined
SOUND INSULATION PARADOX OF MASSIVE CAVITY WALLS IN BUILDINGS
Full text linkIn literature, the "box-in-box" system is described as a solution for achieving the highest possible sound insulation in a room. The system involves double walls separating a room from the surroundings in all directions, without any lateral pass for sound. This approach doubles the number of discontinuities in the material through which sound energy travels, thus providing higher sound insulation. Based on such an idea, some dwelling houses were designed with massive cavity walls between apartments with the expectation of better sound insulation. The concept was further motivated by the need to achieve adequate thermal insulation between apartments using insulation material in the cavity. However, in buildings where this was implemented, residents complained about inadequate sound insulation. Measurements showed that the sound reduction index of the double brick wall was lower than expected, even less than that of a wall where the two thinner layers were combined into a single thicker brick wall without an internal cavity. This was surprising, leading to research aimed at finding an explanation. It was concluded that in buildings there is the influence of sound paths through the wall’s lateral junctions, which is more pronounced with two thinner layers. With a cavity wall, the transmission of sound energy through lateral junctions and further by flanking transmission is more pronounced than with a single wall of the same surface mass. Additionally, the high seismic zone in Serbia requires certain adjustments in construction, invisible in architectural drawings, that further diminish the effect of the increased number of discontinuities in the wall. All of this makes the massive cavity wall in the building, contrary to expectations, less effective than a single wall made of the same quantity of material, making it acoustically and financially unreasonable. Research also revealed that material in the cavity has no influence on the sound reduction index value of the wall
STRATEGIC NOISE MAP FOR BELGRADE NIKOLA TESLA AIRPORT
Full text linkEnvironmental noise management is a critical aspect of public health policy, particularly within the European Union, which established Directive 2002/49/EC to standardize noise assessment and mitigation efforts across member states. Serbia has integrated the Directive's provisions through its Law on Environmental Noise Protection and accompanying by-laws. This paper presents the strategic noise mapping process for Belgrade Nikola Tesla Airport, Serbia's largest international airport, marking a significant milestone as it is the first time a strategic noise map is being developed for a major airport in Serbia. The legal framework, methodology, and results of this mapping process are discussed in detail. Utilizing the CNOSSOS-EU:2015 method and the Aviation Environmental Design Tool (AEDT) for acoustic calculations, the study defines the affected areas, noise indicators, and population exposure based on 2023 air traffic data. The results indicate that the Lden noise levels exceeding 55 dB impacted 24,223 residents, while the Lnight noise levels exceeding 50 dB affected 7,493 residents. The analysis also includes the estimated number of dwellings, schools, hospitals, and people affected by different noise levels, providing necessary data for developing action plans aimed at mitigating noise pollution. Additionally, the study examines the potential health impacts, including population annoyance and sleep disturbance, using dose-effect relationships as defined by the European Commission. The results underline the importance of ongoing noise monitoring and the need for timely revisions of strategic noise maps and action plans to ensure compliance with both national and EU regulations. This research contributes to the broader effort of environmental noise management, offering insights into the methodologies and challenges of strategic noise mapping for airports in Serbia
BIBLIOMETRIC ANALYSIS OF ARTIFICIAL INTELLIGENCE APPLICATIONS IN HIGHER EDUCATION USING WEB OF SCIENCE DATABASE
Full text linkArtificial intelligence (AI) is becoming increasingly important in higher education, which has resulted in the accelerated development of research in this area. This paper conducts a bibliometric analysis of scientific papers researching AI applications in higher education, using the Web of Science database. The analysis covers the period from 1996 to February 2024 and focuses on the most cited works in this field, a total of 82 papers, with 1011 citations (944 without self-citations). Our analysis shows that interest in AI has increased significantly over the past few years, with the most dominant research in the fields of education, computer science, and engineering. The largest number of papers was published in 2023, which indicates the growing importance of this topic. These results provide a foundation for future research on the impact of AI on educational practices, its challenges, and its potential to transform education in the future
IMPROVING THE ABILITY OF VOCAL INTERPRETATION OF CHILDREN'S SONGS AMONG STUDENTS PRESCHOOL TEACHERS WITHIN PROJECT ACTIVITIES
Full text linkMusic education plays a pivotal role in shaping a child's personality. Educators with comprehensive musical knowledge are crucial. Vocal and instrumental instruction, including music theory, solfeggio, and piano training, is highly valuable. Specific songs and exercises effectively teach music theory concepts to future educators, showcasing a practical and comprehensive approach. Mastering vocal and instrumental interpretation techniques enables the seamless integration of musical elements into educational activities, enriching new knowledge and experiences. Music fosters better integration among activities and forms a cohesive whole within thematic projects
VEŠTAČKE NEURONSKE MREŽE U PROJEKTOVANJU I OCENI STABILNOSTI ZIDANIH KONSTRUKCIJA: SVEOBUHVATAN PREGLED (1999–2024)
No full textMasonry structures, both historically and in contemporary construction, are widely utilized due to the availability and diversity of their constituent materials. Throughout their service life, masonry walls are subjected to various types of loading conditions, making the accurate determination of their load-bearing capacity a fundamental yet challenging aspect of both design and rehabilitation processes. This complexity arises from the composite nature of masonry, characterized by anisotropic and inhomogeneous properties. In recent years, Artificial Neural Networks (ANNs) have emerged as a powerful tools in structural engineering, providing advanced solutions in areas such as structural design, performance prediction, optimization, data analysis, and decision-making support. The objective of this paper is to provide a comprehensive review and critical analysis of existing literature on the application of ANNs in evaluating the load-bearing capacity of masonry structures. The review aims to highlight current methodologies, identify research gaps, and propose directions for future research in this evolving field.Zidane konstrukcije, kako u istorijskom, tako i u savremenom građevinarstvu, široko se primenjuju zahvaljujući dostupnosti i raznovrsnosti materijala od kojih se izrađuju. Tokom svog eksploatacionog veka, zidovi od zidanih elemenata izloženi su različitim vrstama opterećenja, što čini precizno određivanje njihove noseće sposobnosti osnovnim, ali i složenim zadatkom u fazama projektovanja i sanacije. Ova složenost proističe iz kompozitne prirode zidane konstrukcije, koju karakterišu anizotropna i nehomogena mehanička svojstva. U poslednjim godinama, veštačke neuronske mreže (VNM) su se afirmisale kao moćan alat u oblasti građevinskog inženjerstva, omogućavajući napredna rešenja u projektovanju konstrukcija, predikciji ponašanja, optimizaciji, obradi podataka i donošenju inženjerskih odluka. Cilj ovog rada je da pruži sveobuhvatan pregled i kritičku analizu postojeće literature koja se bavi primenom VNM u oceni noseće sposobnosti zidanih konstrukcija. Pregled ima za cilj da istakne postojeće metodologije, identifikuje praznine u istraživanjima i predloži pravce za buduća istraživanja u ovoj razvijajućoj oblasti