Hasil untuk "Chemistry"

A. S.

Junjun Pei, Jianbin Liu, Kaixing Fu et al.

Abstract In this study, we introduce a highly effective non-metallic iodine single-atom catalyst (SAC), referred to as I-NC, which is strategically confined within a nitrogen-doped carbon (NC) scaffold. This configuration features a distinctive C-I coordination that optimizes the electronic structure of the nitrogen-adjacent carbon sites. As a result, this arrangement enhances electron transfer from peroxymonosulfate (PMS) to the active sites, particularly the electron-deficient carbon. This electron transfer is followed by a deprotonation process that generates the peroxymonosulfate radical (SO5 •−). Subsequently, the SO5 •− radical undergoes a disproportionation reaction, leading to the production of singlet oxygen (1O2). Furthermore, the energy barrier for the rate-limiting step of SO5 •− generation in I-NC is significantly lower at 1.45 eV, compared to 1.65 eV in the NC scaffold. This reduction in energy barrier effectively overcomes kinetic obstacles, thereby facilitating an enhanced generation of 1O2. Consequently, the I-NC catalyst exhibits remarkable catalytic efficiency and unmatched reactivity for PMS activation. This leads to a significantly accelerated degradation of pollutants, evidenced by a relatively high observed kinetic rate constant (k obs ~ 0.436 min− 1) compared to other metallic SACs. This study offers valuable insights into the rational design of effective non-metallic SACs, showcasing their promising potential for Fenton-like reactions in water treatment applications.

Napolean Bonaparte Thanapaul, Shrijana Bista, Panlada Tittabutr et al.

Mustafa Sevindik, Ayşenur Gürgen, Aras Fahrettin Korkmaz et al.

In this study, extraction conditions were optimized to maximize the biological activities of extracts obtained from <i>Paralepista flaccida</i>, an edible mushroom species. Extraction processes were carried out using an ultrasonically assisted system, and two different optimization approaches were used as follows: Response Surface Methodology (RSM) and Artificial Neural Network–Genetic Algorithm (ANN-GA). The antioxidant potentials of the optimized extracts were evaluated using DPPH, FRAP, TAS, TOS, and OSI parameters; anticholinesterase activities were measured against AChE and BChE enzymes; and antiproliferative activities were investigated in A549, MCF-7, and DU-145 human cancer cell lines. In addition, phenolic contents were determined by LC-MS/MS analysis. The findings revealed that the extracts obtained by the RSM method exhibited a superior biological profile compared to ANN-GA extracts in terms of antioxidant, anticholinesterase, and antiproliferative activities. The high cytotoxicity observed, particularly in the MCF-7 line, supports the anticancer potential of this extract. These results demonstrate that optimization strategies are crucial for increasing not only extract yield but also biological functionality.

Xiao Chen, Chengdi Li, Shuangxia Zhu et al.

This study employs numerical simulations and experiments to examine the cold spray deposition of nanostructured hydroxyapatite (Ca₁₀(PO4)₆(OH)₂, HA)/70wt.%Ti composite particles under different processing conditions, based on the features of nanocomposites that strengthen interfacial adhesion and improve coating interfacial strength. Using ABAQUS/CAE combined with LS-PrePost 4.9-x64 software, the deposition behavior of the composite particles during deposition under various impact velocities was analyzed, along with the stress of the HA and Ti particles within the composite particle. The deposition behavior of both single and multiple composite particles under different gas temperatures was studied through cold spray experiments, and composite coatings were fabricated. The microstructure and phase composition were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that the numerical simulations were consistent with the experimental analyses. As the particle velocity or gas temperature increased, the degree of particle deformation upon deposition became more pronounced, accompanied by phenomena such as cracking or fragmentation and splashing rebound. At a gas temperature of 700 °C, both the bonding density of individual particles and the bonding effectiveness of multi-particle deposits were lower than those achieved at 500 °C. The coating prepared at a gas temperature of 500 °C exhibited a flatter surface, better overall bonding with the Ti interlayer, and higher internal density.

I. S. Young, P. Baran

Gábor Hosszú

Abstract This paper introduces the concept of pattern systems that evolve, with a focus on scripts, a specific type of pattern system. The study analyses the development of different script systems, known as scriptinformatics, with a focus on the historical Rovash scripts used in the Eurasian steppe. The aim is to assess the traditional classification of historical inscriptions, referred to as script relics, into distinct Rovash scripts. Clustering and ordination techniques were used to perform multivariate analyses on Rovash scripts and inscriptions. The study presents two new measures, the script-specific holophyletic index and the joint holophyletic index, for evaluating trees produced by hierarchical clustering. The results indicate that holophyletic indices can validate the traditional assignment of inscriptions to scripts through phylogenetic tree evaluation. This method can be extended to include pattern systems with evolutionary properties and graph sequences derived from them, as well as additional scripts and inscriptions.

H. V. Leland, James E. Moore, S. Ramamoorthy

Chuqi He, Yucheng Yang, Mi Zhang et al.

Using plant-based polysaccharide gels to produce hard capsules is a novel application of this technology in the medicinal field, which has garnered significant attention. However, the current manufacturing technology, particularly the drying process, limits its industrialization. The work herein employed an advanced measuring technique and a modified mathematical model to get more insight into the drying process of the capsule. Low field magnetic resonance imaging (LF-MRI) technique is adopted to reveal the distribution of moisture content in the capsule during drying. Furthermore, a modified mathematical model is developed by considering the dynamic variation of the effective moisture diffusivity (<i>D</i>_eff) according to Fick’s second law, which enables accurate prediction of the moisture content of the capsule with a prediction accuracy of ±15%. The predicted <i>D</i>_eff ranges from 3 × 10⁻¹⁰ to 7 × 10⁻¹⁰ m²·s⁻¹, which has an irregular variation with a time extension. Moreover, as temperature increases or relative humidity decreases, there is an increased acceleration of moisture diffusion. The work provides a fundamental understanding of the drying process of the plant-based polysaccharide gel, which is crucial for enhancing the industrial preparation of the HPMC-based hard capsules.

R. Ruska, B. Berzina, J. Cipa et al.

Luminescence processes resulting in 600 nm emission of Mn2+ ions in AlN:Mn ceramics were studied based on investigations of photoluminescence and its excitation spectra, luminescence kinetics and long-lasting luminescence (PersL) properties. For AlN:Mn2+ nanopowders, the photoluminescence spectra and PersL were studied. Luminescence properties were examined and compared after the samples were irradiated with 520 nm light, resulting in direct excitation of Mn2+ ions, thus causing the intra-center luminescence, or with 263 nm light. As known, in the last case, the oxygen-related defects are primarily excited with the following energy transfer to Mn2+ ions and 600 nm emission, thus forming the recombination luminescence (RecL). Two types of excitations of the 600 nm RecL were used. In the first case, the luminescence response was detected during the sample irradiation with 263 nm light. It was found that at RT, the decay of the RecL is fast and its decay constant τ = 1.2 ms coincides with the value obtained for the intra-center luminescence. A time-dependent rise of the 600 nm luminescence intensity under 263 nm excitation was observed. In the other case, the 600 nm RecL was detected when irradiation of the sample with 263 nm light was ceased, and spectra and decay of PersL were studied. It was found that the decay of 600 nm PersL spectra could be described using three exponential functions, thus manifesting a variety of luminescence processes. The results allow tracing of the luminescence processes and proposal of the mechanisms resulting in the 600 nm light emission of Mn2+ ions. An energy level scheme of AlN:Mn2+ was constructed to elucidate of the luminescence processes and mechanisms.

E. Constable

C. Jiménez-González, P. Poechlauer, Q. Broxterman et al.

Xinwei Li, Zhishu Yao, Xianwen Huang et al.

The newly built shaft in the western region needs to pass through the deep Cretaceous stratum, where the pores and fissures are developed, the cementation ability is poor, and the surrounding rock is rich in water. Under the coupling effect of the stress field and seepage field, the surrounding rock is easy to deteriorate and loses stability. The hydraulic coupling test of Cretaceous red sandstone was carried out by using the TAW-2000 rock mechanics testing system, and the characteristic strength evolution law of red sandstone was analyzed; Mohr’s circle and strength envelope were obtained by the M–C criterion, and the influence mechanism seepage pressure on red sandstone was explored; and combined with the effective stress principle and M–C strength criterion, a constitutive model under hydraulic coupling was established. Confining pressure limits the development of cracks and strengthens the mechanical properties. The results revealed that red sandstone has the characteristics of low less clay, loose particles, and weak cementation capacity; under the action of water pressure, the cement between particles disintegrates and loses the cementation strength, resulting in a significant decrease in cohesion, and the loss of cementation strength is the internal reason for the softening of red sandstone. The constitutive model based on the effective principle and M–C criterion can better reflect the mechanical behavior of red sandstone under hydraulic coupling. This paper provides a research basis for understanding the microscopic characteristics and hydraulic coupling characteristics of Cretaceous weakly cemented sandstone.

Ce Zhang, Wei-Gong Lv, Sheng Sheng et al.

From the perspective of FDR (fault detection rate), which is an indispensable component in reliability modeling, this paper proposes two kinds of reliability models under imperfect debugging. This model is a relatively flexible and unified software reliability growth model. First, this paper examines the incomplete phenomenon of debugging and fault repair and established a unified imperfect debugging framework model related to FDR, which is called imperfect debugging type I. Furthermore, it considers the introduction of new faults during debugging and establishes a unified imperfect debugging framework model that supports multiple FDRs, called imperfect debugging type II. Finally, a series of specific reliability models are derived by integrating multiple specific FDRs into two types of imperfect debugging framework models. Based on the analysis of the two kinds of imperfect debugging models on multiple public failure data sets, and the analysis of model performance differences from the perspective of fitting metrics and prediction research, a fault detection rate function that can better describe the fault detection process is found. By incorporating this fault detection rate function into the two types of imperfect debugging models, a more accurate model is obtained, which not only has excellent performance and is superior to other models but also describes the real testing process more accurately and will guide software testers to quantitatively improve software reliability.

J. Mallinson, I. Collins

Radovan Černý, Matteo Brighi, Fabrizio Murgia

The crystal structures of inorganic hydroborates (salts and coordination compounds with anions containing hydrogen bonded to boron) except for the simplest anion, borohydride BH4−, are analyzed regarding their structural prototypes found in the inorganic databases such as Pearson’s Crystal Data [Villars and Cenzual (2015), Pearson’s Crystal Data. Crystal Structure Database for Inorganic Compounds, Release 2019/2020, ASM International, Materials Park, Ohio, USA]. Only the compounds with hydroborate as the only type of anion are reviewed, although including compounds gathering more than one different hydroborate (mixed anion). Carbaborane anions and partly halogenated hydroborates are included. Hydroborates containing anions other than hydroborate or neutral molecules such as NH3 are not discussed. The coordination polyhedra around the cations, including complex cations, and the hydroborate anions are determined and constitute the basis of the structural systematics underlying hydroborates chemistry in various variants of anionic packing. The latter is determined from anion–anion coordination with the help of topology analysis using the program TOPOS [Blatov (2006), IUCr CompComm. Newsl. 7, 4–38]. The Pauling rules for ionic crystals apply only to smaller cations with the observed coordination number within 2–4. For bigger cations, the predictive power of the first Pauling rule is very poor. All non-molecular hydroborate crystal structures can be derived by simple deformation of the close-packed anionic lattices, i.e., cubic close packing (ccp) and hexagonal close packing (hcp), or body-centered cubic (bcc), by filling tetrahedral or octahedral sites. This review on the crystal chemistry of hydroborates is a contribution that should serve as a roadmap for materials engineers to design new materials, synthetic chemists in their search for promising compounds to be prepared, and materials scientists in understanding the properties of novel materials.

David Salgado-Chavarría , Joaquín Palacios-Alquisira

Science Education International ¦ Volume 32 ¦ Issue 2 107 ORIGINAL ARTICLE INTRODUCTION The problem-based learning (PBL) methodology is a student-centered approach that is related to the learning process that occurs when students deal with real world problems, while working in teams to find and develop a solution, with teachers/instructors acting as facilitators (Nagarajan and Overton, 2019). Some elements seem to be common to PBL: Learning is student centered (as mentioned before), problems are structured and authentic, teachers act as advisors, and students work in small groups (Cowden and Santiago, 2016). Although, the elements are in constant interaction, students are responsible of their learning, implying that they have the main role in the cognitive process and should work actively, in group, to solve a problem. On the other hand, instructors act as coaches, they incite group discussion, and they are in charge of monitoring the process. Students are the main characters, since PBL methodology emerged from constructivist learning theories and it was developed as an alternative to conventional teaching (Loyens et al., 2006). Constructivism suggests that humans build knowledge from their experiences and, contrary to traditional education, where students receive knowledge like empty vessels to be filled, in constructivist, students are encouraged to confront what they know (Bada and Olusegun, 2015). It is evident that, long-term memorability is enhanced by PBL, because it fosters the utilization of previous knowledge to solve a new problem and demands students to put in practice what they have already been taught, therefore, facilitating the comprehension of the concepts (Schmidt et al., 2011). Other benefits that come along with PBL include the improvement of student’s creative thinking, self-regulated skills, and self-evaluation (Jansson et al., 2015; Yoon et al., 2014). Therefore, to improve chemistry student’s learning experience, the PBL approach can be used for a better comprehension of the importance of Green Chemistry. According to the U.S. Environmental Protection Agency (EPA, 1990), Green Chemistry is the design of chemical products and processes that reduce or eliminate the use or generation of hazardous substances; this designing process can be assisted by the Twelve Principles of Green Chemistry (Lancaster, 2002). The principles are qualitative, and their aim is to minimize the impact of chemical activities on human health and environment without compromising the chemical process (Ribeiro and Machado, 2013). There is a commitment to green chemistry education (Armstrong et al., 2018), and efforts have been made to implement it, at the undergraduate level (Timmer et al., 2018; Kennedy, 2016; Manchanayakage, 2013), but there is an uneven development of green chemistry curricular materials, since there have been few comprehensive reforms for general chemistry lecture or laboratory curricula (Armstrong et al., 2019). For example, Green Chemistry has not been covered extensively by chemistry A problem-based learning (PBL) methodology was implemented to a project, whose main objectives were to discuss and apply the Twelve Principles of Green Chemistry to the study of poly(vinyl alcohol)’s cross-linking reaction with dicarboxylic acids. The five participating students were oriented to be responsible for their own learning and the professor participated as an advisor. The problem was proposed and students planned all their activities to accomplish the objectives and goals, reviewed recent information in scientific literature and summarized it, made experimental work, prepared written reports, and were evaluated in seminars. The results obtained by the students were assessed through the generation of a final report and also with a final oral presentation in front of faculty members. The experience lived by the collaborative workgroup during the development and execution of the project, is described. This research is an example of how the PBL methodology can motivate the active participation of students when solving problems. The next step is to introduce this tool to teachers and students of other undergraduate courses or laboratories, since it causes a difference in the way education is being perceived in our university, because it emphasizes the application and understanding of concepts over simple memorization.

V. P. (Bill) Evangelou

D. Ferraris