Please login first

List of accepted submissions

Show results per page
Find papers
  • Open access
  • 58 Reads
Ab initio study of three phases of zirconium oxide ZrO2 and fuorite-related zirconium oxynitride Zr2ON2
Published: 01 December 2022 by MDPI in 3rd International Electronic Conference on Applied Sciences session Posters

In recent years, there has been a growing interest in replacing metallic parts in heat engines by structural ceramics such as zirconium dioxide (ZrO2). However, the high-temperature form of ZrO2 with the fluorite structure and high oxide ion mobility is unstable at room temperature. One approach to stabilise the fluorite structure of ZrO2 is aliovalent substitution of Zr4+ by Y3+ or Ca2+. As well as stabilising the fluorite structure, this introduces anion vacancies enhancing the oxide ion conductivity. A second approach is to make an anion substitution of O2- by N3- to make a series of zirconium oxynitrides which will have anion vacancies.

The band structures, density of states and optical properties of zirconium dioxide (ZrO2) in the cubic, the tetragonal and the monoclinic phases and the fuorite-related zirconium oxynitride (Zr2ON2) have been calculated using the density functional theory with the generalized gradient approximation (GGA) parameterized with the revised Perdew-Burke-Ernzerh for solids (PBESOL) as an exchange correlation function. Band gaps of 3.30, 4.01, 3.97 and 1.55 eV are obtained respectively for these phases. The underestimation of band gaps by DFT is common, which exists due to the limitation of predicting conduction band properties. As a result, the conduction band minimum of Zr2ON2 is reduced compred to ZrO2, which makes Zr2ON2 active under visible light irradiation.

For the ZrO2 structures, the valence bands and the lower conduction bands are all quite similar but become more fiat in going from the cubic to the monoclinic phase. The valence bands are composed with an higher mixed O 2p, Zr 4d orbitals of about 4 -6 eV width. The conduction band is mainly derived from the Zr 4d orbitals. For the Zr2ON2 fluorite structure, the valence band maximum mostly consists of O 2p and N 2p states which are strongly hybridized with Zr 4d orbitals, while the bottom of the conduction band is composed of a Zr 4d state overlap with O 2p and N 2p. Strong hybridization means potential covalent bonding and a less ionic character. A covalent bond between O or N and the Zr atom can be seen when the O 2p and N 2p states hybridized with Zr 4d between -5.5 eV and 0.0 eV.

The optical properties of ZrO2 and Zr2ON2 are calculated by the dielectric function ε(ω) = ε1(ω)+Iε2(ω). The Kramer–Kronig relation is used to obtain the real parts of the dielectric function from imaginary ones. Optical properties such as reflectivity R(ω), energy loss function L(ω), refractive index n(ω) and extinction coefficient k(ω) are calculated from the dielectric constant.

The average value of the refractive index of Zr2ON2 is 1.7 at the static limit, naverage(0), and 2.0 at 650 nm. Our calculations show better agreement with the experimental value, 2.2 at 650 nm, than another theoretical value. The refractive indices increased beyond the zero frequency limits and reached their maximum values. Beyond the maximum value they start to decrease and with a few oscillations they go beyond unity

The energy loss function and extinction coefficient were also calculated. The peaks in the energy loss function represent a reduction in the trailing edges of the reflectivity spectrum.

  • Open access
  • 35 Reads
Regeneration and Rehabilitation of Sarafa Bazaar: A Study for Sustainable Heritage and Future Cities
Published: 01 December 2022 by MDPI in 3rd International Electronic Conference on Applied Sciences session Posters

The goal of the project is to revitalize the historic core of the city of Multan to encourage sustainable environmental protection and socio-economic development. This case study focuses on the implementation of an intervention is 'Sarafa Bazaar'. The objective of the project is to restore the structure and provide a framework for the development of the local community. The other goal of the intervention is to improve the tourist experience and promote energy efficiency. This type of project is carried out through a process that aims to identify and address the social and urban issues that affect the development of the city. The selected section of 'Sarafa Bazaar' is approximately 80 meters from the Musafir Khana building and is connected to the other side of the bazaar. The walls of the Sarafa Bazaar are being renovated and conserved. Laser scanner was used to identify the quantity of materials and steel reinforcement was used to balance the settled facade. The renovation of the façades of the Sarafa Bazaar is being carried out to improve the overall appearance of the area. The project has been carried out through the establishment of an integrated system for the development of the city's urban area. It involves the renovation of the façades of the Sarafa Bazaar and the establishment of public spaces.

  • Open access
  • 53 Reads
Motion planning of triple links robotic system

The Robogymnast is a complex system formed from a triple-inverted pendulum and mimics the action of a gymnast as they hang by their hands from the high bar and perform progressive upswings to eventually rotate completely around the bar. The three links of the Robogymnast can be compared to the lower limbs, torso, and upper limbs of a gymnast, with a single passive joint and two further stepper-motor powered joints. There is sensor equipment attached to the different links to gather data and control signals. While this system has been 11 physically constructed previously, the current paper describes the approach to automating the 3 link pendulum, as well as describing the system, its parts and set-up. Following this, STM32 is applied for programming, system operation and to present results

  • Open access
  • 24 Reads
A neural circuit model of the striatum resolves the conflict between context and dominance apparent in the prefrontal cortex
Published: 01 December 2022 by MDPI in 3rd International Electronic Conference on Applied Sciences session Student Session

Neural selectivity is essential to organize information in the brain. Being able to filter the relevant information and to combine different aspects of a task is key to accomplish goal-directed behavior.

In a recent study [1], the authors recorded prefrontal neurons of macaque monkeys performing an attention task. The monkeys needed to respond to a relevant stimulus dimension (orientation or color, defined by a previously presented cue) to obtain reward. Results from the study showed that prefrontal cells synchronized their activity at beta frequencies during stimulus presentation. Selectivity in the prefrontal cortex (PFC) to either stimulus dimension (orientation or color) was apparent because coherence at beta frequencies was modulated by two distinct aspects: context and dominance. Context was correlated physiologically with a boost in coherence in the population encoding the relevant dimension. In addition, neural recordings also showed a dominance of orientation against color. In orientation trials, context and dominance modulations were aligned for orientation-selective cells, which was behaviorally correlated with shorter response times. In contrast, in color trials no apparent difference was present between the patterns of activity of color- and orientation-selective cells in PFC due to the disalignment between context and dominance, despite the fact that monkeys performed the task similarly well. Interestingly, the study also reported the presence of pre-stimulus alpha-oscillatory activity in orientation-selective cells, which appeared at the cue onset informing about color trials.

Thus, a conflict was apparent in color trials at the level of PFC between dominance (favoring orientation) and context (favoring color). The fact that monkeys performed the task equally well seems indicative that color trials may be resolved elsewhere in the brain. The role of pre-stimulus alpha oscillations in orientation-selective cells of the PFC remains a puzzling observation.

Here, we designed a striatal circuit model, based on [2], to test the hypothesis that the conflict between context and dominance is resolved downstream in the striatum. D1 and D2 striatal cells in our model inherit color and orientation selectivity from cortical inputs. Further additions to [2] are: Inhibitory inputs between cells sharing the same selectivity, i.e., same population, were assumed to be weaker than across populations. Cortical inputs were increased to compensate for the overall increase in inhibition. Orientation and color trials were simulated based on [1]. Color trials included not only beta-band cortical inputs but also the pre-stimulus alpha-band input to orientation-selective cells.

Results from our computational model show that, in color trials, pre-stimulus alpha inputs from cortex activate synaptic depression in orientation-selective cells. Later, during the stimulus presentation, despite that equally strong beta inputs target both striatal populations, their responses become transiently different: orientation-selective striatal neurons become depressed, but color-selective neurons do not. This creates a window of opportunity to propagate the activation of the color response through inhibitory control that resolves the conflict between dominance and context present in the PFC.

[1] Buschman et al. Neuron, 76(4):838–46, 2012.
[2] Ardid et al. Proceedings of the National Academy of Sciences, 116(17):8564–69, 2019.

  • Open access
  • 30 Reads
Spectral Properties of Tunable Privacy Window Films Made of Polymer-Dispersed Liquid Crystals

Modern applications of polymer-dispersed liquid crystals (PDLC) made of liquid crystal droplets dispersed in polymer matrices continue to grow. They include privacy and smart windows, flexible diffusers, advanced displays, energy storage and energy harvesting devices, to name a few. An electrically controlled switching between opaque and transparent states of PDLC films enables their numerous applications. An applied electric field reorients an average director of a liquid crystal droplet resulting in a gradual transition from an opaque to a transparent state. A fully transparent state is observed if the refractive index matching is achieved. As a rule, electro-optical characterization of polymer dispersed liquid crystals is performed using a laser. As a result, basic physical parameters such as switching times, the steepness of the switching curve, contrast ratio, and transmittance are obtained for a single wavelength of light. Even though the spectral dependence of electro-optical properties of PDLC films was mentioned in several papers, systematic studies reporting the dependence of contrast ratio, transmittance, and steepness of the switching curve of PDLC films on the wavelength of light are still missing. In this paper, electrically controlled spectral properties of PDLC films are reported. The obtained dependence of the contrast ratio and transmittance on the wavelength of light can be used for the optimization of electro-optical performance of polymer-dispersed liquid crystals.

  • Open access
  • 44 Reads
Preparation of alginate hydrogels with carbonated water for wound dressings application
Published: 01 December 2022 by MDPI in 3rd International Electronic Conference on Applied Sciences session Student Session

Hydrogels are known to properly promote wound healing by providing a moist environment on wound sites. Alginate, a polysaccharide extracted from brown algae, reacts with Ca2+ to form hydrogels with high biocompatibility. The most common method of preparing alginate hydrogels is to preliminarily mix CaCO3 with an alginate solution and subsequently add an acid agent such as glucono-δ-lactone to ionize CaCO3 for gelation gradually. However, to accelerate the gelation rate, adding an excessive amount of acidic agent is necessary, which leads to acidification of hydrogels and unsolicited tissue damage. Rapid gelation of hydrogels expands the applicability of hydrogels, including in situ gelation at wound sites. In this study, we prepared the alginate hydrogels with carbonated water, which promotes the dissolution of CaCO3 and volatilizes to the atmosphere after gelation. The carbonated water transiently decreased the pH of the alginate/CaCO3 solution at pH ~5.5 and accelerated the gel transition within 3 min. After the gelation, CO2 in the hydrogels volatilized through the gel surface, and the final pH of hydrogels converged at a pH of ~8.5, which is supposed to be suitable for fibroblast proliferation and wound closure. The physicochemical properties of the prepared hydrogels were determined to be excellent concerning transparency, absorb physiological saline, and possess a high-water content (approximately 99%). The hydrogel prepared in this study showed excellent wound healing effects by in vivo evaluations of full-thickness skin wound healing in mice. These results demonstrate that alginate hydrogels prepared with carbonated water are promising for wound care.

  • Open access
  • 38 Reads
Electronic structures and photovoltaic properties of copper-, sodium- and ethylammonium-added CH3NH3PbI3 perovskite compound
, , , , , ,
Published: 01 December 2022 by MDPI in 3rd International Electronic Conference on Applied Sciences session Student Session

CH3NH3PbI3 perovskite solar cells are expected to be the next generation solar cells due to their low cost and easy fabrication process. The purpose of the present work is to investigate the effects of co-adding copper (Cu), sodium (Na) and ethylammonium (EA) to the CH3NH3PbI3 perovskite compound. The conversion efficiencies were enhanced by the addition of Cu and Na to CH3NH3PbI3. The first-principles calculations showed formation of a shallow band of Cu d-orbitals, which functions as an acceptor level, would promote the carrier generation. The additional excitation process from Cu d-orbitals to Na s-orbitals would suppress the carrier recombination, thus improving the photovoltaic properties. Furthermore, the stability of the crystals increased by the EA substitution at the CH3NH3 site from the results of the total energy calculations, which would lead to suppression of formation of lattice defects. The further addition of EA also improved the conversion efficiencies, which indicates the EA substitution would stabilize the crystal structure even in the presence of Cu and Na.

  • Open access
  • 45 Reads
Robust Nonlinear control of Maximum Power Point Tracking in PV solar energy system under real environmental conditions
Published: 01 December 2022 by MDPI in 3rd International Electronic Conference on Applied Sciences session Student Session

Optimization of the operational performance PV systems require tracking the PV operating point at which maximum power is available. Given that, in practice the PV system is subjected to environmental parameters, which are random in nature, continuous tracking of this point, the Maximum Power Point (MPP), becomes an absolute necessity. Numerous techniques for Maximum Power Point Tracking (MPPT) have been reported in the literature. However, these techniques suffer from numerous problems such as oscillation around the maximum power point and robust inabilities. Taking into account the nonlinear nature of the PV coupled to the nonlinear time variant nature of power electronics converters interfaced in PV systems, nonlinear control becomes a vital strategy to guarantee both an oscillation free and a robust PV-MPPT system. This work presents a nonlinear robust strategy for MPPT control of PV system using a Boost DC-DC converter. The nonlinear strategy is based on the Integral Backstepping Controller. The control system uses a trained Artificial Neural Network (ANN) to generate a reference voltage that is injected in the closed system for reference tracking. The stability of the closed system has been verified using Lyapunov functions. To ensure an effective and robust response of the closed loop system, mathematical equations derived by initializing tuning goals in the control law, have been developed . Therefore, the closed loop system formed a Robust Integral Backstepping (RIBS) control. The performance of the RIBS-MPPT system has been investigated in real environmental conditions under light as well as heavy load variations, perceived by the nonlinear controller as disturbances, while benchmarking its performance against the conventional perturb and observe (P&O). It was noted that the RIBS outperformed the P&O under all test conditions. An interesting feature of the proposed RIBS lies in its high reference tracking and zero steady-state oscillations potential under heavy disturbances in real environmental conditions. Therefore, the proposed nonlinear control scheme is suitable for effective and efficient optimization of PV systems

  • Open access
  • 79 Reads
The air quality and the influence of Etesians on pollution levels in the Rhodes city, the case of July 2022

In July 2022 strong and high-frequency northern sector winds blew over the Aegean Sea. The low tropospheric circulation in combination with the air quality and human comfort are of great importance for the climate and human health. This study investigates the variation of pollutants’ concentrations (PM10, NO2, O3 and SO2), meteorological factors (temperature, relative humidity, wind speed and direction) and discomfort index in Rhodes city during July, 2022. Additionally, the impact of Etesians on pollution levels is studied. The strength of the Etesian flow is quantified by calculating a statistical index that takes under consideration the July pressure gradient (ΔP) over Aegean Sea. For the analysis, pollutants concentration recordings from a mobile air quality monitoring system during July 2022 and, mean sea level pressure (MSLP) data from ERA5 reanalysis during July for the period from 1980 to 2022 are analyzed. Results indicate that traffic affects the pollution level although the pollution limits, according to the European directive for air quality (2008/50/EC), are not exceeded. Findings also reveal an increase in ΔP, about 1.8hPa, during 2022 compared to the period from 1980 to 2022 and the dipole of high (over Balkans) and low (over eastern Mediterranean) pressure centers also strengthens, leading to stronger winds over Aegean Sea. The ΔP is strongly correlated (0.8) to the first principal component of MSLP over the eastern Mediterranean. Finally, study shows that the Etesian flow tends to reduce the concentration of PM10, NO2 and O3 improving the air quality in Rhodes city.

  • Open access
  • 49 Reads
Band gap closure in MnS under pressure

Manganese chalcogenides are being actively studied both experimentally and theoretically because of metal-to-insulator transition under pressure and possible catalytic, optical and magnetic applications [1,2,3]. In particular, binary manganese sulphide MnS was found in several crystal phases: α – γ-MnS. The α-MnS phase crystallizes in cubic structure (Space Group Fmm), γ-MnS – in hexagonal structure (SG P63mc). It is known that γ-MnS is metastable when heated to 200-300° C, it becomes the α-MnS phase [1]. We carried our theoretical studies of this compound taking into account antiferromagnetic ordering of the manganese ions at the ambient conditions and in compressed unit cells. To study the electronic structure of MnS, our calculations were done in the Quantum ESPRESSO software package [4] using the DFT+U method [5] for the Pedew-Burke-Ernsenhof (PBE) form of exchange-correlation functional [6]. MnS is a wide-band insulator in environmental conditions. In the course of the study, it was found out that in order to reproduce a wide gap, strong electronic correlations should be taken into account. Thus, to obtain the experimental value of the band gap, the values of the Coulomb interaction parameter U = 6.9 eV and the exchange interaction J = 0.86 eV were taken. It is also worth noting that taking into account electronic correlations affects the γ-MnS more strongly and when the maximum parameter of the Coulomb interaction parameter U = 6.9 eV is reached, the width of the electron gap of the γ-MnS reaches about 2 eV, while the α-MnS has a band gap width of no more than 1 eV. For compressed volumes of the unit cell, it was found that with increasing pressure on the unit cell, the band gap width decreases and finally closes for the cell volume, which is about 50% of the ambient volume. Thus, the closure of the energy gap and the increase in metallic states at Fermi energy demonstrate the experimentally observed transition from insulator to metal in MnS.The work was supported by RFBR grant (project 20-02-00234).

[1] X. Yang, et al., J. Phys. Chem. C, 116, 3292 (2012).
[2] A.A. Dyachenko, et al., Phys. Rev. 98, 085139 (2018).
[3] P. Wang, et al., Chem. Mater. 34, 3931 (2022).
[4] P. Giannozzi, et al., J. Phys. Condens. Matter. 21, 395502 (2009).
[5] V. Anisimov, O. Gunnarsson, Phys. Rev. 43, 7570 (1991).
[6] J. Perdew, et al., Phys. Rev. Lett. 9, 767 (1996).