Preparation and characterization of biocompatible magnetic carbon nanotubes

Magnetic carbon nanotubes consisting of multi-wall carbon nanotubes (MWNTs) core and Fe₃O₄ shell were successfully prepared by in situ thermal decomposition of Fe(acac)₃ or FeCl₃ or Fe(CO)₅ in 2-pyrrolidone containing acid treated MWNTs at 240 °C with the protection of nitrogen gas. The samples were characterized by TEM, XRD, SEAD, XPS and superconducting quantum interference device. Also, their biocompatibility was compared with naked carbon nanotubes. The results showed that after coated with Fe₃O₄ nanoparticles, the obtained magnetic carbon nanotubes show superparamagnetic characteristic at room temperature, and their blocking temperature is about 80 K. The magnetic properties of the nanotubes are relevant to the content of magnetic particles, increasing content of magnetic nanoparticles leads to higher blocking temperature and saturation magnetization. The results of antimicrobial activities to bacterial cells (Escherichia coli) showed that the MWNTs have antimicrobial activity, while the magnetic nanotubes are biocompatible even with a higher concentration than that of MWNTs.     

Requirements in mathematics textbooks: a five-dimensional analysis of textbook exercises and examples

Mathematics textbooks play a very important role in mathematics education and textbook tasks are used by students for practice to a large extent. Since the nature of the tasks may influence the way students think it is important that the textbooks provide a balance of a variety of tasks. The analyses of the requirements in textbook tasks contain the usual dimensions of content, cognitive demands, question type and contextual features. The aim of this study is to embed a new fifth dimension into the framework: mathematical activities. This addresses the question of what a student should do in a particular textbook task: to represent, to compute, to interpret or to use argumentation. The analysis encompassed more than 22,000 tasks from the most commonly used Croatian mathematics textbooks in the 6th, 7th and 8th grade. The results show that the textbooks do not provide a full range of task types. There is an emphasis on computation, while argumentation and interpretation activities, reflective thinking and open answer tasks are underrepresented. The study revealed that incorporating mathematical activities into the multidimensional framework of textbook tasks may help to better understand the opportunities to learn which are afforded students by using mathematics textbooks.     

Calculus demonstrations using MATLAB

The note discusses ways in which technology can be used in the calculus learning process. In particular, five MATLAB programs are detailed for use by instructors or students that demonstrate important concepts in introductory calculus: Newton's method, differentiation and integration. Two of the programs are animated. The programs and the graphical user interface have been specifically designed to help the student understand the processes behind these important introductory concepts. Each program has a series of demonstrations that show unusual, difficult or important cases.     

The development of children's understanding of mathematical patterns through mathematical activities

In this paper we report how children (aged 8) developed their mathematical understanding through number tasks based on the Fibonacci sequence (Bamboo numbers) used in the context of a Substantial Learning Environment (SLE), which is designed to be mathematically rich, have a clear purpose and give opportunities to utilise mathematical thinking. The flexible nature of the SLEs makes it possible for teachers and children to explore various mathematical patterns. To capture children's activities when working within SLEs, we make particular reference to Pegg and Tall's work in 2005, and consider a theoretical framework based on the SOLO taxonomy (Biggs and Collis 1982) and the developmental process of understanding mathematical concepts. It was found that the key progression to be made through learning using our Bamboo number-based SLEs is from Multi-structural to Relational levels. It was also suggested that it is difficult for many children to understand the structural aspects of number patterns.     

Piezoelectric activities and domain patterns of orthorhombic Ba(Zr,Ti)O3 ceramics

Ba(Zr_xTi_1?x)O₃ (0.025 ≤ x ≤ 0.065) ceramics were prepared by conventional solid-state reaction method. Crystalline structures were analyzed by X-ray diffraction. It was shown that all the Ba(Zr_xTi_1?x)O₃ (0.025 ≤ x ≤ 0.065) ceramics were of orthorhombic phase at room temperature. Piezoelectric activities and domain patterns were investigated and compared with those of BaTiO₃ ceramic. All the Ba(Zr_xTi_1?x)O₃ ceramics showed nearly the same d₃₃ values of about 265 pC/N and the same domain width of about 220 nm. By comparing the grain sizes and domain width of the Ba(Zr_xTi_1?x)O₃ ceramics with those of BaTiO₃ ceramic, it is speculated that the variation of domain width with grain sizes in orthorhombic Ba(Zr_xTi_1?x)O₃ ceramics may be different with that in tetragonal BaTiO₃ ceramic. Besides domain width, the effective inertia mass of domain wall is also considered to be a very important factor that impacts the piezoelectric activities of the Ba(Zr_xTi_1?x)O₃ ceramics.     

Multiple levels of metacognition and their elicitation through complex problem-solving tasks

Building on prior efforts, we re-conceptualize metacognition on multiple levels, looking at the sources that trigger metacognition at the individual level, the social level, and the environmental level. This helps resolve the paradox of metacognition: metacognition is personal, but it cannot be explained exclusively by individualistic conceptions. We develop a theoretical model of metacognition in collaborative problem solving based on models and modeling perspectives. The theoretical model addresses several challenges previously found in the research of metacognition. This paper illustrates how metacognition was elicited, at the environmental level, through problems requiring different problem-solving processes (definition building and operationalizing definitions), and how metacognition operated at both the individual level and the social level during complex problem solving. The re-conceptualization of metacognition has the potential to guide the development of metacognitive activities and effective instructional methods to integrate them into existing curricula that are necessary to engage students in active, higher-order learning.     

Naturally occurring furofuran lignans: structural diversity and biological activities

Furofuran lignans containing the 2,6-diaryl-3,7-dioxabicyclo[3.3.0]octane skeleton, represent one of the major subclasses of the lignan family of natural products. Furofuran lignans feature a wide variety of structures due to different substituents at aryl groups and diverse configurations at furofuran ring. Moreover, they exhibit a wide range of significant biological activities, including antioxidant, anti-inflammatory, cytotoxic, and antimicrobial activities. This review summarizes source, phytochemistry, and biological activities of 137 natural furofuran lignans isolated from 53 species in 41 genera of 27 plant families for the last 20 years, which provides a comprehensive information for further research of these furofuran lignans as potential pharmaceutical agents.     

Phytochemical profile and biological activities of Deverra tortuosa (Desf.)DC.: a desert aromatic shrub widespread in Northern Region of Saudi Arabia

The present study describes the chemical composition of the essential oil of different plant parts of Devrra tortuosa; in vivo and in vitro biological activities of plant extract and essential oils. Apiol was found to be the major component of the oil (between 65.73% and 74.41%). The best antioxidant activities were observed for the oil of flowers (IC50 = 175 μg/ml). The samples of stems and roots exhibit lower antioxidant activity (IC50 = 201 μg/ml and 182 μg/ml, respectively). The values of IC50 showed that the extracts of methanol exhibit the highest antioxidants activities (IC50 = 64.8 102 μg/ml). EOs showed excellent antifungal activity against yeasts with low azole susceptibilities (i.e. Malassezia spp. and Candida krusei). The MIC values of oils varied between 2.85 mg/mL and 27 mg/mL. The obtained results also showed that the plant extracts inhibited the germination and the shoot and root growth of Triticum æstivum seedlings.     

Preparation,characterization, mechanical and barrier properties investigation of chitosan-kaolinite nanocomposite

The purpose of this study was to prepare a novel Clay Bio-Polymer Nanocomposite (CBPN) films by mixing polymer (chitosan, C) with exfoliated nanoclay (kaolinite, k). DRX has shown that the mechano-chemical treatment of kaolinite allows its exfoliation and the significant reduction of its particles size. Physicochemical properties namely thickness, water solubility, color, light transmission and transparency of the films were studied. Fourier transform infrared analysis (FTIR) was to study the interaction between chitosan and kaolinite. Differential scanning calorimetry (DSC) scans showed that the transition temperature (Tg) of films depends on the film's composition. The surface morphology of the films was also studied by scanning electron microscopy (SEM). Results showed that water solubility (Ws) decrease with the increase of the amount of clay. In addition, the presence of clay in the said films increases the mechanical strength. All prepared films were tested for their antimicrobial activities against gram-positive and gram-negative bacteria (strain). It was found that all CBPN films showed good inhibitory activity against all the tested bacteria. The above analysis suggested that the CBPN films could be used as potential candidates for therapeutic application.     

Surface antimicrobial modification of polyamide by poly(hexamethylene guanidine) hydrochloride

Antimicrobial polyamide (PA) received much attention for the demand of packaging and biomedical fields. In this paper, an antimicrobial PA6 membrane was prepared via a surface chemical reaction. A highly effective antibacterial component (PHMG‐E) with terminal epoxy group was firstly synthesized via a reaction between polyhexamethylene guanidine hydrochloride (PHMG) and ethylene glycol diglycidyl ether (EGDE). Then, PHMG‐E was bonded on the surface of PA6 membrane with secondary amine reduced by borane‐tetrahydrofuran (BH₃‐THF). The antimicrobial rates of surface‐modified PA6 membrane (PA6‐PHMG) against Escherichia coli and Staphylococcus aureus were both higher than 99.99%, and the PHMG was non‐leaching due to the chemical bonding. The hydrophilicity of antibacterial PA6 membrane was also significantly improved and the mechanical performance became better.