Composite hydroxyapatite/TiO2 materials for photocatalytic oxidation of NOx

Hydroxyapatite/TiO₂ composite photocatalysts were obtained from sol–gel prepared TiO₂ and commercial hydroxyapatite (HA) powders. Composites with different HA/TiO₂ ratio were studied to assess the influence of HA on the morphology and the photocatalytic behavior of the materials. Morphological SEM analysis revealed that the presence of HA diminishes the aggregation of TiO₂ particles and leads to their higher dispersion in the composites that was confirmed by the N₂ adsorption–desorption isotherms and Barret–Joyner–Halenda analysis. The photocatalytic activity of the prepared catalysts was examined by monitoring photocatalytic oxidation of NO_x model gases over catalysts under UV illumination. The NO_x oxidation over the composite catalysts was improved in comparison with pure TiO₂ powder. Moreover, the decrease of the TiO₂ content, which is the photocatalytically active component in the composites, resulted in enhanced NO_x removal. Maximum activity was recorded for composites with HA/TiO₂ ratios 1 and 2 that was related to improved TiO₂ dispersion and NO₂ trapping by the composite materials.     

Phase transitions of liquid crystalline polyesters: Poly(heptane-1,7-diyl-4,4′-biphenyldicarboxylate)

Wide-angle X-ray scattering was applied to investigate the non-isothermal and isothermal phase transitions of poly(heptane-1,7-dyil-4,4′-biphenyldicarboxylate). It is suggested that the isotropic–smectic (I–S) transition is controled by a nanophase separation with a critical point T_ns=151 °C. Nanophase separation is followed by a first-order S–Cr (crystal) transition. At isothermal conditions above T_ns only S phase exists, whereas below it the S phase appears first and the Cr phase grows from the S by nucleation and three-dimensional crystal growth.     

Study of thermomechanical,structural and antibacterial properties of poly(lactic acid) reinforced with graphene oxide nanoparticles via melt mixing

Addition of graphene oxide (GO) to poly(l ‐lactic acid) (PLLA) offers an alternative approach for tuning its crystallinity, improving its mechanical properties and transfusing an antibacterial behavior. GO/PLLA nanocomposites were prepared by melt extrusion, thus avoiding the potentially toxic, for biomedical applications, residue of organic solvents. Fourier transform infrared spectroscopy verified the formation of intermolecular hydrogen bonds. Using differential scanning calorimetry experiments concerning the isothermal crystallization of PLLA and PLLA containing 0.4 wt% GO, a two‐dimensional disc‐like geometry of crystal growth was determined, whereas at 125 and 130 °C the nanocomposite developed three‐dimensional spherulitic growth. Higher crystallization rate constant values suggest that the incorporation of 0.4 wt% GO accelerated the crystallization of PLLA. The lowest crystallization half‐time for PLLA was observed at 115 °C, while at 110 °C GO caused its highest decrease, accompanied by the highest increase in melting enthalpy (ΔH_m), as compared to that of PLLA, after completion of isothermal crystallization. Their ΔH_m values increased with T_ic, whereas multiple melting peaks transited to a single one with increasing T_ic. GO improved the PLLA thermal stability, tensile strength and Young's modulus. Incorporation of 0.8 wt% GO endowed PLLA with another potential application as a biomaterial since the derived composite presented good thermomechanical properties and effective prohibition of Escherichia coli bacteria attachment and proliferation. This effect was more prominent under simulated sunlight exposure than in the dark. The preparation method did not compromise the intrinsic properties of GO. © 2020 Society of Chemical Industry     

Investigation on the kinetics of the adsorption process of aliphatic amidpolyamine on cellulose

Investigation has been carried out on the kinetic dependences of the adsorption process of aliphatic amidpolyamine (lamide-1, L-1) on three kinds of bleached pulp (sulfate pulp of hard wood and sulfate and sulfite pulp of soft wood) at temperatures of 0, 20, 40, and 60°C within a concentration interval of 0.030 g/liter + 0.500 g/liter. It has been established that the kinetic process can be described by the Elovich–Tyomkin exponential kinetic equation. The activation energy is of the order of 4.12–4.42 kJ/mol and the entropy factors substantially affect the process speed. The coefficients of the correlations describing the effect of the L-1 solution concentrations on the coefficient of heterogeneity (α) and the initial adsorption speed (V₀) have been determined.     

A fair resource allocation protocol for multimedia wireless networks

Wireless networks are expected to support real-time interactive multimedia traffic and must be able, therefore, to provide their users with quality-of-service (QoS) guarantees. Although the QoS provisioning problem arises in wireline networks as well, mobility of hosts and scarcity of bandwidth makes QoS provisioning a challenging task in wireless networks. It has been noticed that multimedia applications can tolerate and gracefully adapt to transient fluctuations in the QoS that they receive from the network. The additional flexibility afforded by the ability of multimedia applications to tolerate and adapt to transient changes in QoS can be exploited by protocol designers to significantly improve the overall performance of wireless systems. This paper presents a fair resource allocation protocol for multimedia wireless networks that uses a combination of bandwidth reservation and bandwidth borrowing to provide network users with QoS in terms of guaranteed bandwidth, call blocking, and call dropping probabilities. Our view of fairness was inspired by the well-known max-min fairness allocation protocol for wireline networks. Simulation results are presented that compare our protocol to similar schemes.     

Effect of metal cyanourates on some properties of PVC

The effects of barium, lead and calcium cyanourate on the properties of poly(vinyl chloride) and its compositions were investigated. In concentrations up to 2 vol. % they decreased the T_g and T_m of the polymer. Physical and mechanical properties (tensile strength, impact strength, and hardness) are improved. The thermostability (dynamic and static) increases with increasing concentration.     

Metastable diamond synthesis from vitreous carbon and other disordered or nano-dispersed carbon materials

A new method for growth of diamond seed crystals at metastable conditions is described. The process is realized isothermally (at temperatures in the range of 1000 K to 1400 K) in the closed volume of a quartz ampoule, via appropriate chemical transport reactions or in a CVD-apparatus. Vitreous carbon materials and other non-equilibrium forms of carbon, representing state of frozen-in disorder, increased thermodynamic potential and chemical affinity, are used as a constant driving force of isothermal crystallization.The experiments are based on the detailed analysis of the thermodynamic properties of carbon modifications and on the influence of dispersity and the degree of disorder on their thermodynamic potential. Additional kinetic factors, influencing the diamond growth, like introduction of active substrates and mechanism of incorporation of carbon atoms in growing diamond face are also analyzed discussed in their possible technical application.     

Mechanical performance of re‐extruded and aged graphene/polypropylene nanocomposites

In the present research polypropylene/expanded graphite (PP/ExpG) and polypropylene/graphene nanoplatelet (PP/GNP) composites were prepared by melt blending and their morphology and tensile properties were investigated. Although both reinforcements improved the elastic modulus of PP, PP/GNP composite presented better dispersion of the nanofiller in the polymer matrix and it was selected for further re‐extrusion and ageing experiments. The re‐extrusion affected the content of crystal phases of PP in pure PP and in its nanocomposite with GNP and increased their elastic modulus. The ageing of one and five times re‐extruded PP caused an increase of the β‐crystal phase and the formation of voids in the cross‐section. GNPs seem to protect the PP matrix from ageing as in Fourier transform IR spectra of PP/GNP nanocomposite, both one and five times extruded, the peak corresponding to carbonyl degradation products of PP was barely visible. The tensile properties of aged nanocomposites, one and five times re‐extruded, were similar to those of the corresponding non‐aged composites, whereas in aged PP the tensile strength and strain decreased significantly compared to non‐aged PP. The anti‐ageing effect of graphene can prolong the life of the PP matrix. © 2017 Society of Chemical Industry     

Mutagenic effect of freezing on nuclear DNA of Saccharomyces cerevisiae

Although fragmentation of DNA has been observed in cells undergoing freezing procedures, a mutagenic effect of sub‐zero temperature treatment has not been proved by induction and isolation of mutants in nuclear DNA (nDNA). In this communication we supply evidence for mutagenicity of freezing on nDNA of Saccharomyces cerevisiae cells. In the absence of cryoprotectors, cooling for 2 h at +4°C and freezing for 1 h at ?10°C and 16 h at ?20°C, with a cooling rate of 3°C/min, resulted in induction of frame‐shift and reverse mutations in microsatellite and coding regions of nDNA. The sub‐zero temperature exposure also has a strong recombinogenic effect, evidenced by induction of gene‐conversion and crossing‐over events. Freezing induces mutations and enhances recombination with a frequency equal to or higher than that of methylmethanesulphonate at comparable survival rates. The signals for the appearance of nDNA lesions induced by freezing are detected and transduced by the DNA damage pathway. Extracellular cryoprotectors did not prevent the mutagenic effect of freezing, while accumulation of trehalose inside cells reduced nDNA cryodamage. Freezing of cells is accompanied by generation of high ROS levels, and the oxidative stress raised during the freeze–thaw process is the most likely reason for the DNA damaging effect. Experiments with mitochondrial rho^– mutants or scavengers of ROS indicated that mutagenic and recombinogenic effects of sub‐zero temperatures can be decreased but not eliminated by reduction of ROS level. The complete protection against cryodamage in nDNA required simultaneous usage of intracellular cryoprotector and ROS scavenger during the freeze–thaw process. Copyright © 2012 John Wiley & Sons, Ltd.     

新兴城市背景下的绿道 乌托邦还是创新良机

以保加利亚的索菲亚市绿道为对象,旨在探讨绿道在新兴城市下的发展潜力。通过整合案例研究、当地规划、统计数据和法律框架等规划初期所需的理论知识与索菲亚区域内的实时现状,提出从绿色射线到特色绿轴的总体规划和"8+1战略方针",并指出对规划途径的反思和革新,都将有助于新兴城市发展趋势的本质转变,使其向着更为负责和可持续的方向发展。