Studies on the second reciprocal derivative constant-current stripping analysis

Theoretical and experimental investigation have been made on a method called the second reciprocal derivative constant-current stripping analysis (SRD-CCSA). The SRD-CCSA is based on the measurement of the d(2)t/dE(2) signal given by the curve of (d(2)t/dE(2)) versus the electrode potential (E). The d(2)t/dE(2)-E curve gives a maximum value (d(2)t/dE(2))(max) and a maximum value ((d(2)t/dE(2)))(min), which show as two peaks on the curve. Either of the heights of the peaks and the sum of absolute values of the two peaks are proportional to the bulk concentration of the analyte in solution, and they are much larger than (dt/dE)(p) in the first reciprocal derivative constant-current stripping analysis (FRD-CCSA). The ratio of peak-peak height in the SRD-CCSA to peak height in the FRD-CCSA is about 43n (where n represents the number of electrons transferred during the electrode process for the analyte). Potential difference (W(pp)) between the two peaks is 48.2 mV n(-1) at 25 degrees C in the SRD-CCSA, which is noticeably smaller than the half-height width W(p/2), 65.5 mv n(-1), in the FRD-CCSA. The theory was verified with a home-made multireciprocal derivative measuring instrument. The experimental results were in good agreement with the theoretical ones.     

A superhard orthorhombic carbon with all six-membered-ring in sp3 bonding networks

We identify by first-principles calculations a new diamond-like carbon phase with a 16-atom orthorhombic primitive cell in $Pbcn$ (${D_{2h}}^{14}$) symmetry. This new carbon allotrope consists of all $s{p}^3$ six-membered rings like as the reported BC8, BC12 and R16 carbon, while energetically more stable than these carbon phases. Its dynamical stability has been confirmed by phonon mode analysis and molecular dynamics simulations. The calculated bulk modulus (435 GPa) and Vickers hardness (93 GPa) are comparable to that of diamond, showing as a superhard carbon material. Electronic band calculations reveal that it is an insulator with an indirect band gap of 4.35 eV. Simulated X-ray diffraction spectrum presents a complicated pattern, showing an amorphous form of diamond, reflecting its structural complexity stemming from its multiple bond lengths and bond angles, but matches well with the diffractions peaks found in the diamond-rich coatings on stainless steel substrate. These findings lay a foundation for further study of this new diamond-like carbon allotrope and its outstanding properties.     

非晶合金剪切带动力学行为研究

剪切带是一种材料塑性变形高度局域化的变形模式, 广泛存在于非晶体系的形变中, 控制着这些无序体系失稳、灾难性断裂行为.传统的非晶体系如岩石, 胶体, 玻璃和聚合物等因较差的力学性能以及过于复杂的结构而不利于剪切带的实验研究. 近几十年来, 非晶合金的出现极大丰富了剪切带的研究, 推进了对剪切带的认识. 通过大量非晶合金中剪切带的实验和理论研究, 人们发现剪切带行为具有空间不均匀性和时间不连续性的特征, 表现出复杂的动力学特征, 和自然界以及物理系统中许多复杂体系的动力学行为相似.同时, 剪切带的性质尤其是其动力学行为对非晶合金的宏观力学行为和性能有重要的影响, 对理解这类材料的微观变形机理也起着重要的作用.本文结合团队近年来在非晶合金剪切带行为方面的研究结果, 对剪切带的运动行为和物理机制进行介绍, 包剪切带间歇性运动行为、以及间歇性运动在表征其动力学性质中的作用以及物理机制, 以及剪切带的自组织临界行为、物理机制等.最后对非晶合金剪切带行为研究中亟需解决的问题进行了总结和展望.      

Measurement and correlation of phase equilibrium data of the mixtures consisting of butyric acid,water, cyclohexanone at different temperatures

In this work, experimental solubility and tie-line data for the (water + butyric acid + cyclohexanone) system were obtained at T = (298.2, 308.2, and 318.2) K and atmospheric pressure. The ternary system investigated exhibits type-1 behavior of LLE. The experimental tie-line data were compared with those correlated by the UNIQUAC and NRTL models. The consistency of the experimental tie-line data was determined through the Othmer Tobias and Hand correlation equations. Distribution coefficients and separation factors were evaluated over the immiscibility regions. A comparison of the extracting capability of the solvent at different temperatures was made with respect to separation factors. The Katritzky and Kamlet–Abboud–Taft multiparameter scales were applied to correlate distribution coefficients and separation factors in this ternary system. The LSER models values were interpreted in terms of intermolecular interactions.     

Global examination of the 12C + 12C reaction data at low and intermediate energies

We examine the ¹²C + ¹²C elastic scattering over a wide energy range from 32.0 to 70.7 MeV in the laboratory system within the framework of the optical model and the coupled-channels formalism. The ¹²C + ¹²C system has been extensively studied within and over this energy range in the past. These efforts have been futile in determining the shape of the nuclear potential in the low energy region and in describing the individual angular distributions, single-angle 50° to 90° excitation functions and reaction cross-section data simultaneously. In order to address these problems systematically, we propose a potential that belongs to a family other than the one used to describe higher energy experimental data and show that it is possible to use it over this wide energy range. This potential also predicts the resonances at correct energies with reasonable widths.     

Biocomposites based on poly(butylene succinate) and curaua: Mechanical and morphological properties

Biocomposites based on poly(butylene succinate) (PBS) and curaua fibers have been produced by compression molding, and investigated as a function of fiber length and amount. Mechanical tests, water uptake and morphology studies were carried out in order to assess the composite features according to the characteristics of the reinforcing agents. It turns out that the impact and flexural strengths increase with fiber content. Moreover, the fiber length, varying from 1 to 4 cm for the composite reinforced with 20 wt% of fiber, influences impact strength, which is higher for shorter than for longer fibers. However, flexural strength is not greatly influenced by the length of the fibers. Water uptake studies reveal a higher sensitivity of the material to fiber content rather than fiber size. Biocomposites, which are characterized by enhanced mechanical properties as compared to PBS, can have different applications, for example in rigid packaging or interior car parts.     

On the influence of inter-layer time and energy density on selected critical-to-quality properties of PA12 parts produced via laser sintering

Laser Sintering (LS) of polymers is an Additive Manufacturing technique progressively used to produce functional parts. However, LS parts still present a certain quality variability. Efficient consolidation of the polymeric powder, necessary to obtain a dense part, mainly depends on the viscosity of the molten polymer and on the time given for the polymer to coalesce. The polymer viscosity is a function of the temperature and, consequently, of the energy density (ED) input by the laser. The sintering time strongly depends on the surface area to be laser-scanned in each layer, which in turn is strongly related to the product complexity and the number of parts within one build. The aim of this work is to investigate how this thermo-temporal effect, influenced by the ED and the inter-layer time, influences the resulting LS PA12 part quality at both micro-level (e.g., porosity, crystallinity) and macro-level (e.g., dimensional accuracy, mechanical performance).     

Molecular structure of propargylgermane (2-propynylgermane) determined by gas-phase electron diffraction and quantum chemical calculations

The molecular structure of propargylgermane, HCCCH₂GeH₃, has been determined by gas-phase electron diffraction. The electron-diffraction investigation has been supported by density functional theory and ab initio calculations. The r_a value of the bond lengths (pm) are: r(C–Ge)=197.2(1); r(C–C)=143.9(2); r(CC)=123.1(1); r(H–C_acetylene)=108.5(3); r(C–H)=111.6(3) and r(Ge–H_average)=153.7(2). The Ge–C–C angle is 111.7(1)° and the C–CC angle is 178.3(4)°. The uncertainties are one standard deviation from the least-squares refinement.     

A note on coordination in decentralized assembly systems with uncertain component yields

Gurnani and Gerchak [H. Gurnani, Y. Gerchak, Coordination in decentralized assembly systems with uncertain component yields, European Journal of Operational Research 176 (2007) 1559–1576] study coordination of a decentralized assembly system in which the demand of the assembler is deterministic and the component yields are random. They present incentive alignment control mechanisms under which system coordination is achieved. In this note, we extend Gurnani and Gerchak’s model to the case of positive salvage value and n asymmetric suppliers, and show that the shortage penalty contract which can coordinate Gurnani and Gerchak’s model no longer coordinates the extended model. Furthermore, we present a new kind of contract, surplus subsidy contract, to coordinate the extended model and prove that the profit of the supply chain under coordination can be arbitrarily divided between the component suppliers and the assembler.