Limit cycles of a three-dimensional bio-reactor with inhibition responses

By using a relation connecting the global stability and Hopf bifurcation, the existence of limit cycles in a three-dimensional bio-reactor model of exploitative competition of two predator organisms with inhibition responses for the same renewable organism with reproductive properties is obtained. We also correct the proof of the main result in a previous paper of the same model (Su et al., J. Math. Chem., 2007).     

Global behavior and asymptotic reduction of a chemical kinetics system with continua of equilibria

We consider a model chemical kinetics system describing the dynamics of species concentrations taking part is consecutive-competitive reaction in a continuopusly stirred tank reactor. Corresponding dynamical system has a continua of equilibria. Particular equilibrium to which the solution of the system tends depends on the initial conditions. The global behavior of the system and its reductions via the invariant manifold and the boundary function methods are studied.AMS Subject Classification: 34D15, 34D35, 37C10     

A simple, universal theory and method for computer plotting of stable equilibrium phase diagrams of a multisystem——SFM method

A new easy method has been presented to calculate the variable intervals corresponding to the stable univariant curves and to discriminate the stabilities of invariant points. This method and the one reported previously constitute a simple and universal theory for the computer-plotting of the equilibrium phase diagrams of a multisystem——sign function matrix (SFM) discrimination method. Its main steps are: determining the stable univariant scheme according to the derivative (or difference) of △rGm; grouping the univariant curves by comparisons of the mutual relations among them; determining the existing intervals of the variables for the stable curves by comparisons of coordinate values of the curves about the invariant point; determining the stabilities of invariant points by comparisons of relations between the common curves and the invariant points. This method is suitable for any kind of phase diagram of closed or open systems in a phase diagram "space" with either 2 or more than 2 dimensions.     

High-temperature stability of a novel phenylethynyl liquid-crystalline thermoset

We report the synthesis of a new high-temperature liquid-crystalline thermoset based on the phenylethynyl functional group. The monomer was a nematic thermotropic liquid crystal with a melting temperature of 268 °C. The extrapolated onset of the cure exotherm occurred at 313 °C. The cured thermoset retained the nematic liquid-crystalline order of the parent monomer. The monomer and crosslinked resin were characterized by differential scanning calorimetry, optical microscopy, and thermogravimetric analysis. The thermal stability of the crosslinked resin was determined in both air and nitrogen atmospheres at various heating rates. The onset of weight loss in air and nitrogen atmospheres was determined to be 397 and 422 °C, respectively, for a heating rate of 10 °C/min. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4184–4190, 1999     

Building a Global Culture of Science—The Vietnam Experience

We detail the lessons learned, challenges, achievements, and outlook in building a chemistry research center in Vietnam. Through the principles of “global science”, we provide specific insight into the process behind establishing an internationally‐competitive research program—a model that is scalable and adaptable to countries beyond Vietnam. Furthermore, we highlight the prospects for success in advancing global science education, research capacity building, and mentorship.     

Global minimum geometries of acetylene clusters (HCCH)n with n ≤ 55 obtained by a heuristic method combined with geometrical perturbations

Geometry optimization of acetylene clusters (HCCH)_n in the range of n ≤ 55 was carried out with a recently proposed intermolecular potential consisting of Morse potentials, damped dispersion terms, and damped Coulomb terms. The heuristic method developed by the present author was used in the optimization: optimal geometries were searched by using geometry perturbations and subsequent local optimizations. The calculations were repeated until the global minimum was found for each cluster at least three times. The obtained results were analyzed to examine structural evolution of the clusters. The geometries of the clusters with n ≥ 25 were similar to the geometry in the cubic crystal of acetylene whereas smaller clusters take icosahedron‐based geometries. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Theoretical study of a novel organic electride with large nonlinear optical responses

The design of stable organic electrides with high nonlinear optical (NLO) properties is a challenge in organic and materials chemistry. Here we theoretically design of a novel organic molecular electride model, Li⁺(C₂₀H₁₅Li₅)e⁻, by modifying the lithiation and Li-doping based on dodecahedrane (C₂₀H₂₀). Its electride characteristic is verified by the quantum theory of atoms in molecules and electron localization function analyses. For the first time, the strategy of steric protection is applied to improve the stability of the organic electride Li⁺@(C₂₀H₁₅Li₅)e⁻, in which the closed C₂₀ cage serves not only as the ligand with a negative inner electric field to stabilize the Li cation but also as a barrier to prevent the Li cation from escaping. Meanwhile, the released excess electron is firmly captured in the cavity of Li₅. Moreover, Li⁺(C₂₀H₁₅Li₅)e⁻ displays a remarkably large first hyperpolarizability of 1.4 × 10⁴ au with potential application in organic second-order NLO materials.     

Biocompatibility and structural stability of a laminin biopolymer

Polylaminin (polyLM) is a polymerized form of the extracellular matrix protein laminin obtained upon pH acidification. Here microscopy and spectroscopic tools are used to study the cell compatibility and the structural stability of polyLM, aiming at establishing its robustness as a biopolymer for therapeutic use. PolyLM is cell compatible as judged by the efficiency of attachment and neuritogenesis. It is resistant to low temperature. Addition of urea or an increase in hydrostatic pressure leads to polymer disassembly. PolyLM biofilms remain stable for 48 h in contact with cell culture medium. The sedimented polymer recovered after centrifugation and adsorbed on a glass coverslip preserved its original structure and its biological properties.

     

Thermal stability of a HAN-based liquid gun propellant

Experiments to determine the effect of surface area, head space, and containment on liquid gun propellant degradation at temperatures of 100 and 148°C were conducted. The conclusions from these tests are that an increased surface area in LP containment can significantly increase the rate of LP decomposition. The head space is not a significant factor in altering the rate of degradation, but if the gaseous products are allowed to escape, the degradation rate is significantly lowered.     

含季戊四醇磷酸酯阻燃剂的合成与表征

采用1-氧代-4-羟甲基-2,6,7-三氧杂-1-磷杂双环[2.2.2]辛烷(PEPA)、三氯氧磷、双酚A和双酚S为反应物,合成了两个新型添加型阻燃剂:双酚A双[二(1-氧代-1-磷杂-2,6,7-三氧杂双环辛烷-4-亚甲基)]磷酸酯(BAPP)和双酚S双[二(1-氧代-1-磷杂-2,6,7-三氧杂双环辛烷-4-亚甲基)]磷酸酯(BSPP),通过元素分析、FT-IR和1H NMR等表征了标题化合物的结构,结果表明,所合成的标题化合物的结构与预期一致。热失重分析结果证明,BAPP和BSPP质量损失5%(wt)时的温度分别为343.6℃和352.3℃,600℃残余量分别达46.6%和55.5%,具有较高的热稳定性和结炭性能。阻燃性能实验证明,E-51环氧树脂中分别添加质量分数为18.2%(wt)的BAPP和BSPP时,极限氧指数分别为32.2%和31.8%,均能达到UL 94 V-0级。     

Molecular dynamics simulation for studying the stability of structure H clathrate-hydrates of argon and large guest molecules

The aim of present paper is to study the stability of (argon + large guest molecules) structure H clathrate-hydrates by using molecular dynamics simulations and with employing the COMPASS force field to consider the molecular interactions. The simulations are performed by embedding the structure H clathrate-hydrates in a simulation cell under isobaric-isothermal (NPT) conditions. The obtained equilibrium lattice parameters are compared with the experimental data, where a good consistency is observed. The results show that the size and dipole moment of the guest molecules enclosed in the hydrate cages play the main role in the interactions between the guest molecules and the water molecules, which constitute the surrounding walls of the hydrate cage and these interactions would stabilize the hydrate structure. The characteristics of the clathrate-hydrate structure are analyzed by evaluating the radial distribution function, where the agreement between the results obtained in this work and other similar theoretical and experimental investigations validates the simulation procedure and related interpretations.     

Thermodynamic stability and hydration enthalpy of strontium cerate doped with yttrium

The standard molar enthalpy of formation of SrY_0.05Ce_0.95O_2.975 has been derived by combining the enthalpy of solution in 1 M HCl + 0.1 KI with auxiliary literature data, Δ_fH° (SrY_0.05Ce_0.95O_2.975, s, 298.15 K) = −1720.4 ± 3.4 kJ/mol. The formation enthalpy of SrY_0.05Ce_0.95O_2.975 from the mixture of binary oxides is Δ_oxH° (298.15 K) = −45.9 ± 3.4 kJ/mol and the enthalpy of reaction of SrY_0.05Ce_0.95O_2.975 with water forming Sr(OH)₂, CeO₂, and Y₂O₃ is Δ_rH° (298.15 K) = −85.5 ± 3.4 kJ/mol. Our data and the entropies of different substances show that SrY_0.05Ce_0.95O_2.975 is thermodynamically stable with respect to a mixture of SrO, Y₂O₃, CeO₂ and that the reaction of SrY_0.05Ce_0.95O_2.975 with water is thermodynamically favourable.     

The effect of trimethylamine N-oxide on RNase a stability

The thermal stability of bovine pancreatic ribonuclease (RNase A) has been investigated in the presence of trimethylamine N-oxide (TMAO), a naturally occurring osmolyte, by means of differential scanning calorimetry (DSC) and circular dichroism (CD) measurements at neutral and acid pH conditions. It is well known that compatible osmolytes such as TMAO are effective in stabilizing protein structure and counteracting the denaturing the effect of urea and guanidinium hydrochloride (GuHCl). Calorimetric results show that TMAO stabilizes RNase A at pH 7.0 and does not stabilize the protein at pH 4.0. RNase A thermal denaturation in the presence of TMAO is a reversible two-state N ⇆ D process. We also show that TMAO counteracts the urea and GuHCl denaturing effect at neutral pH, whereas the counteracting ability is lost at acid pH.     

Global cluster geometry optimization by a phenotype algorithm with Niches: Location of elusive minima,and low-order scaling with cluster size

The problem of global geometry optimization of clusters is addressed with a phenotype variant of the method of genetic algorithms, with several novel performance enhancements. The resulting algorithm is applied to Lennard–Jones clusters as benchmark system, with up to 150 atoms. The well-known, difficult cases involving nonicosahedral global minima can be treated reliably using the concept of niches. The scaling of computer time with cluster size is approximately cubic, which is crucial for future applications to much larger clusters. © 1999 John Wiley & Sons, Inc. J Comput Chem 20: 1752–1759, 1999     

Colloidal stability of sulfonated polystyrene model colloids. Correlation with electrokinetic data

In this work we describe the colloid stability of functionalized latexes: two sulfonated polystyrene model colloids with the same particle size and different surface charge densities. The critical coagulation concentration (ccc) was determined in the presence of two electrolytes (11 and 22), being around 0.75 M and 0.075 M, respectively. By the DLVO theory the electrokinetic and colloid stability data were correlated to calculate the Hamaker constant at both experimental conditions. By comparing the experimental and theoretical values of the Hamaker constant, it is possible to get more information about the colloidal stabilization mechanism of functionalized latexes. In the case of sulfonated latexes, the electrostatic and seric contributions occur, with different influence for each latex depending of their surface electric charge.     

Mechanical stability of two immiscible liquid drops resting on a solid substrate

The mechanical stability of two immiscible liquid drops of water and mercury resting on a polypropylene solid substrate was attained. It is found that the mechanical stability and the complete encapsulation of mercury drop, by a Millipore water drop, depends severely on the volume of the droplets. The merging of four phases along a single contact line as claimed by Mahadevan et al. [L. Mahadevan, M. Adda-Bedia, and Y. Pomeau, J. Fluid Mech. 451, 411 (2002)] is experimentally shown to be invalid.     

Molecular structure and conformational stability of allylisocyanate—post-Hartree–Fock and density functional theory studies

The molecular structure and conformational stability of allylisocyanate (CH₂CHCH₂NCO) molecule was studied using the ab initio and DFT methods. The geometries of possible conformers, C-gauche (δ=120°, θ=0°) (δ=C=C–C–N and θ=C–C–N=C) and C-cis N-trans (δ=0° and θ=180°) were optimized employing HF/6-31G^*, MP2/6-31G^* levels of theory of ab initio and BLYP, B3LYP, BPW91 and B3PW91 methods of DFT implementing the atomic basis set 6-311+G(d,p). The structural and physical parameters of the above conformers were discussed with the experimental and theoretical values of the related molecules, methylisocyanate and 3-fluoropropene. It has been found that the N=C=O bond angle is not linear as the experimental result for both the conformers and the theoretical bond angle is 173°. The rotational potential energy surfaces have been performed at the HF/6-31G^*, and MP2/6-31G^* levels of theory. The Fourier decomposition potentials were analysed at the HF/6-31G^*, and MP2/6-31G^* levels of theory. The HF/6-31G^* level of theory predicted that the C-gauche conformer is more stable than the C-cis N-trans conformer by 0.41 kJ/mol, but the MP2 and DFT methods predicted the C-cis N-trans conformer is found to be more stable than the C-gauche conformer. The calculated chemical hardness value at the HF/6-31G^* level of theory predicted the C-cis N-trans form is more stable than C-gauche form, whereas the chemical hardness value at the MP2/6-31G^* level of theory favours the slight preference towards the C-gauge conformer.     

Unbiased Fuzzy Global Optimization of Morse Clusters with Short-Range Potential for N < 400

Global optimization of Morse clusters with short-range potential is a great challenge. Here, we apply our recently developed unbiased fuzzy global optimization method to systematically study Morse clusters with the potential range \begin{document}$ \rho $\end{document} = 14 and the number of atoms \begin{document}$ N $\end{document} up to 400. All the putative global minima reported in the literature have been successfully reproduced with relatively high success ratios. Compared to the available results for \begin{document}$ N $\end{document}\begin{document}$ \leq $\end{document}240 and several larger Morse clusters, new global minima (and local minima) with lower energies have been found out for \begin{document}$ N $\end{document} = 164, 175, 188, 193, 194, 197, 239, 246, 260, 318, and 389. Clusters with magic numbers are figured out through fitting the size-dependent global minimum energies. The cluster structures tend to be close-packed for short-range potential with large \begin{document}$ N $\end{document}.     

提高漆酶稳定性的化学修饰方法的研究

天然漆酶在其应用条件下容易失活,因此如何提高漆酶的稳定性显得尤为重要和紧迫.以目前广泛应用的商品化漆酶DeniLite ⅡS为研究对象,采用邻苯二甲酸酐(PA)、丁二酸酐(SA)及马来酸酐(MA)对漆酶进行化学修饰,根据修饰酶的酶活和热稳定性的变化确定SA为漆酶的最佳修饰剂.采用L9(34)正交设计表研究了磷酸盐缓冲液...