Viscoelastic properties of plasticized methylcellulose and chemically crosslinked methylcellulose

Films of methylcellulose (MC), poly(ethylene glycol)400 (PEG400) plasticized MC, and MC gels (MC crosslinked with glutaraldehyde (GA)) were prepared by casting from aqueous solutions. The swelling test has shown that the MC gels were insoluble in water and that their crosslinking density increased with increasing GA and HCl concentrations. The effect of the addition of PEG400 or GA to MC was investigated through dynamic mechanical analysis (DMA). The DMA analysis of PEG400/MC blends has shown that PEG400 was compatible with MC and was an effective plasticizer since the curves of tan δ against temperature exhibited single peaks (corresponding to a single glass transition temperature), which were displaced to lower values with increasing PEG400 content. The thermogravimetric analysis (TGA) indicated that the thermal stability of MC was not affected by the chemical crosslinking. The tensile strength was slightly increased through crosslinking while the elongation was slightly decreased. The presence of moisture in MC hydrogels decreased the tensile strength and enhanced the elongation while the addition of PEG400 decreased the tensile strength but sharply increased the elongation.     

Flexural and Dynamic Mechanical Properties of Alkali-Treated Coir/Pineapple Leaf Fibres Reinforced Polylactic Acid Hybrid Biocomposites

Polylactic acid(PLA)possesses good mechanical and biodegradability properties which make it a suitable material for polymer composites whereas brittleness and high costs limit its utilization in various applications.The reinforcement of natural fibres with biopolymers has been formed to be an efficient technique to develop composites having the ability to be fully biodegradable.This study concerns with the incorporation of various percentages of untreated and alkali-treated Coir Fibres(CF)and pineapple leaf fibres(PALF)in PLA biocomposites and characterizations of flexural,morphological and dynamic mechanical properties.Flexural properties showed that the treated C1P1 hybrid composites(C1P1A)displayed highest flexural strength(35.81 MPa)and modulus(5.28 GPa)among all hybrid biocomposites.Scanning Electron Micros-copy(SEM)revealed a behaviour of fibre-matrix adhesion in untreated treated biocomposites.SEM observation revealed good dispersion of the fillers in PLA.Dynamic mechanical analysis revealed that C1P1A showed highest glass transition temperature(Tg)and storage modulus(E')while untreated C3P7 displayed the least Tg and E'.Overall findings showed that alkali-treated hybrid biocomposites(CF/PALF/PLA)especially C1P1A have improved flexural properties,dynamic and morphological properties over untreated biocomposites.Success of these findings will provide attracting consideration of these hybrid biocomposites for various lightweight uses in a broad selection of industrial applications such as biomedical sectors,automobile,construction,electronics equipment,and hardware tools.     

D201—GM大孔树脂吸附交联固定菊粉酶的研究

克鲁维酵母Ｙ－８５产生的胞内菊粉酶,以Ｄ２０１－ＧＭ大孔径阴离子交换树脂吸附交联法固定化,其制备固定化酶（ＩＥ）的适宜条件：树脂吸附酶时ｐＨ６．５、温度３０℃、时间３ｈ;交联时戊二醛浓度０．０３％、温度４℃、时间３ｈ。上述条件下制得ＩＥ的活性产率可达６２％,水解菊粉底物的最适温度５５℃,对热的稳定性和贮存稳定性均有明显提高,用ＩＥ填充床反应器连续降解菊粉抽提液（总糖４．５％）的实验结果表明,进料空     

Crosslinked polyethylenimine: An enzyme carrier with spacers of various lengths introduced in crosslinking reaction

Polyethylenimine (PEI) reacted with epichlorhydrin to various degrees of crosslinking was further activated with thiophosgene or with succinic anhydride; the carboxyl derivatives obtained were converted to hydrazide derivatives. d-Glucose oxidase (β-d-glucose:oxygen 1-oxidoreductase, EC 1.1.3.4), glucoamylase (exo-1,4-α-d-glucosidase, 1,4-α-d-glucan glucohydrolase, EC 3.2.1.3) and cholinesterase (acetyl-, butyryl-) [acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7), butyryl cholinesterase (acylcholine acylhydrolase, EC 3.1.1.8)] were bound in their native forms to the first two types of carriers, while in the case of the hydrazide derivative of crosslinked PEI this occurred just after periodate oxidation of a glycoenzyme. The PEI derivatives prepared from the crosslinked PEI with the lowest degree of crosslinking, i.e. from that having the longest mean length of the spacer (～ 11.1 Å), revealed the best binding properties towards low-molecular thiols, amino acids and proteins/enzymes. After enzyme coupling, the isothiocyanate derivatives of crosslinked PEI gave preparations with the highest residual activities.     

Esterification crosslinking structures of rayon fibers with 1,2,3,4-butanetetracarboxylic acid and their water-responsive properties

1,2,3,4-Butanetetracarboxylic acid (BTCA) was applied to crosslink amorphous regions of cotton-type rayon fibers via anhydride-mediated esterification for the purpose of enhanced mechanical properties. Crosslinking was conducted under a series of curing temperature with the presence of sodium hypophosphite (SHP) as the effective catalyst for anhydride formation. The conversion rate based on Fourier transform infrared (FTIR) spectra was in good agreement with that from the direct calculation based on titrated carboxyl groups and ester linkages. Crosslinking degree increased linearly with the curing temperature. The optimal tensile properties were derived from the curing temperature of 180 °C with an intermediate crosslinking degree. Moreover, the crosslinked structures of the rayon fibers had a great impact on absorption of liquid and gaseous water. The liquid water retention capacity diminished substantially with the crosslinking degree, while interaction between moisture and the fibers revealed that sorption–desorption cycles and concomitant hystereses were scarcely affected by the crosslinked fiber structures.     

Dynamic and extensional properties of starch in aqueous dimethylsulfoxide

The effect of starch composition and concentration on the rheological properties of starch in a mixed solvent, water–DMSO, was investigated in dynamic shear and extensional mode. High amylose corn starch containing 70% amylose and 30% amylopectin, common corn starch containing 25% amylose and 75% amylopectin, and waxy corn starch containing about 99% amylopectin were used in this study. Concentrations of 2, 4, 6, and 8% (w/v) in 10% water-90% DMSO (v/v) were used for each starch type. An increase in the amylopectin content of starch from 30 to 99% caused a change in behavior from semidilute solution to viscoelastic solid at a concentration of 8% (w/v). At a concentration of 2%, an increase in the amylopectin content of starch from 30 to 99% caused a change from Newtonian to incipient gel-like behavior. Behavior at intermediate concentrations of 4 and 6% (w/v) varied from semidilute to critical gel-like with increasing amylopectin content. A power-law relaxation was observed for all concentrations of common and waxy corn starches with the slope decreasing with increase in concentrations. A 2% waxy corn starch solution displayed extension thinning behavior, while a 2% high amylose corn starch solution displayed Newtonian behavior.     

Radionuclide-induced evolution of DNA and the origin of life

Summary Artesian groundwaters of high radionuclide concentration are ubiquitous and may have provided the large, sustained energy sources that were required to drive the multistage process of DNA and primordial cell evolution. The rapid, early development of the genetic code as well as its degeneracy can be attributed to exceptionally high radiation-induced mutation rates in this unique environment. The ability of double-strand DNA to direct enzymatic repair of radiation damage to single strands contributed importantly to its selective evolution. It is postulated that the polymerization of nucleotides took place at elevated temperatures within -particle tracks of high ion and free-radical density, followed by rapid quenching to ambient conditions. It also is evident that radiation resistance and ploidy were important selection factors in cellular evolution.     

Protein dynamics: conformational disorder,vibrational coupling and anharmonicity in deoxy-hemoglobin and myoglobin

In this work we study the temperature dependence of the Soret band lineshape of deoxymyoglobin and deoxyhemoglobin, in the range 300–20 K. To fit the measured spectra we use an approach originally proposed by Champion and coworkers (Srajer et al. 1986; Srajer and Champion 1991). The band profile is modelled as a Voigt function that accounts for the coupling with low frequency vibrational modes, whereas the coupling with high frequency modes is responsible for the vibronic structure of the spectra. Moreover, owing to the position of the iron atom out of the mean heme plane, inhomogeneous broadening brings about a non-Gaussian distribution of 0–0 electronic transition frequencies. The reported analysis enables us to isolate the various contributions to the overall bandwidth, and their temperature dependence points out the relevance of low frequency vibrations and of large scale anharmonic motions starting at temperatures higher than 170 K. Information on the mean iron-heme plane distance and on its temperature dependence, as well as on the heme pocket conformational disorder, is also obtained.Abbreviations Cc Carbon monoxide - Hb Human deoxyhemoglobin A - HbCO human carbonmonoxyhemoglobin A - SWMb spermwhale deoxymyoglobin - SWMbCO spermwhale carbonmonoxymyoglobin - HbO₂ human oxyhemoglobin A - SWMb³⁺-H₂O spermwhale aquometmyoglobin     

A novel technique for the study of bacterial cell mechanical properties

A micromanipulation method is described for measuring the bursting forces of bacteria and relating them to cell size. At a compression speed of 6.2 m s^–1, bursting forces of three samples of rapidly growing Staphylococcus epidermis from a batch culture varied from 3 to 34 N with an average value of 13.8 N (standard error 0.8 N). Escherichia coli grown in continuous culture at a specific growth rate of 0.5 h^–1 had bursting forces varying from 1 to 9 N with an average value of 3.6 N (standard error 0.4 N). In squeeze-hold experiments, force relaxation was observed, which was attributed to water loss from the cells, or viscoelasticity, or both. At high compression speed, such as 6.2 m s^–1, this relaxation could be neglected. Micromanipulation strength measurements might be used in studies of cell mechanical disruption and of the dependence of cell strength on cell physiology.     

Application of artificial intelligence technique for modelling elastic properties of 2D nanoscale material

A novel computational approach is proposed to investigate the shear modulus of graphene nanostructures. In this approach, the factors that affect the shear modulus of graphene structures are analysed using an integrated artificial intelligence (AI) cluster comprising molecular dynamics (MD) and gene expression programming. The MD-based-AI approach has the ability to formulate the explicit relationship of shear modulus graphene nanostructure with respect to aspect ratio, temperature, number of atomic planes and vacancy defects. In addition, the shear modulus of graphene predicted using an integrated MD-based-AI model is in good agreement with that of experimental results obtained from the literature. The sensitivity and parametric analysis were further conducted to find out specific influence and variation of each of the input system parameters on the shear modulus of two graphene structures. It was found that the number of defects has the most dominating influence on the shear modulus of graphene nanostructure.     

不同食性哺乳动物及人的牙釉质微结构对比研究

根据动物食性将搜集于西藏、新疆、江苏和吉林4省和自治区16种哺乳动物的581颗牙齿分为食草、杂食和食肉3类,设计了录像-截图-测量-定标4步微米量级牙釉质结构测量方法,测量得到牙釉质的颊面厚度和舌面厚度比、臼齿外轮廓平均牙釉质厚度比等牙釉质分布规律,观测到不同哺乳动物釉柱的组装直径均在100 μm 左右,但柱间晶体的宽度不同,发现3类哺乳动物牙釉柱与釉牙本质界夹角的规律:人和食肉动物狗的釉柱角度最大,接近90°,杂食动物猪釉柱角度约为70°,而食草动物釉柱角度在54°～68°之间.研究表明,不同食性哺乳动物牙齿外在和内在结构都和其生物力学功能密切相关,牙釉质的异型结构是使得釉质具有优异的力学性能的优化结构模式.     

First principles investigation of pressure dependent stability,phonon, Debye temperature,physical, mechanical and thermodynamic properties of Rh3Al intermetallic compound

ABSTRACT

Pressure dependence of stability, phonon, Debye temperature, physical, mechanical and thermodynamic properties of Rh₃Al intermetallic compound were investigated by first-principles The calculated cohesive energy (E_c), formation enthalpy (ΔH) show that Rh₃Al is a thermodynamically stable compound. Properties related to the phonons of Rh₃Al were also obtained. In addition, the transverse sound velocity (ν_s), longitudinal sound velocity (ν_l), average sound velocity (ν_m) and Debye temperature (Θ_D) of Rh₃Al were calculated by using the VRH method along with pressure range from 0 to 60?GPa. The values of lattice parameters, bulk modulus and its first-order pressure derivative are consistent well with other works. The band structure indicates that Rh₃Al compound exhibits a metallic character. Moreover, the total density of states, partial density of states, Mulliken charges and electron density difference have been analysed to explain the physical properties. Based on the stress–strain approach and the Born stability criteria, the mechanical properties were evaluated by elastic constants (C_ij), other modulus (B, E, G), (B/G) ratio, Poisson’s ratio (ν), the anisotropic index (A), hardness (H) and compressibility (K) for this intermetallic compound. Finally, the thermodynamic properties, including enthalpy, free energy, entropy and heat capacity are discussed range from 0 to 1000?K.     

Evaluation of dynamic response and biomechanical properties of isolated blood vessels

In this study we present the experimental and mathematical model for a precise assessment of isolated blood vessels dynamic response under a sudden change of blood pressure. Only the end points within the time interval of the considered dynamic response of the blood vessel, or so-called “alternate steady states” of the processes, were usually considered in various studies. These studies do not provide an insight how the process variables change between these alternate steady states. Isolated blood vessels (rat abdominal aorta) were used to determine how the process dynamics can be described in detailed quantitative terms by mathematical parameters. The experimental model and mathematical procedures presented in this study describe precisely (at a high sensitivity level) the time history of the pressure and the diameter change in between alternate steady states, when an abrupt change of blood pressure occurs at the vessel outlet. Also, the experimental model and mathematical procedures were used to determine changes in the stress–strain law, caused by the action of L-arginine. The presented experimental design and mathematical model can be used for assessment of isolated blood vessel dynamic responses under different stimuli, such as drug effects, electrostimulation etc.