Cure Characterization of a New Bismaleimide Resin using Differential Scanning Calorimetry

The cure characterization of a new BMI resin was investigated to ascertain a suitable cure model for the material. A series of isothermal differential scanning calorimetry (DSC) runs from 170°C to 220°C provided information about the cure characterization. All “kinetic triplet” (i. e., Arrhenius parameters A, activation energy E, and the reaction model, f(α)) of this new BMI system were calculated. It was found that the cure characterization of this new BMI could be expressed by nth‐order cure reaction.     

Geometry of Hasimoto Surfaces in Minkowski 3-Space

In this paper, we investigate the Hasimoto surfaces in Minkowski 3-space. We discussed the geometric properties of Hasimoto surfaces in \(\mathbb {M}^{3}\) for three cases. The Gaussian and mean curvature of Hasimoto surface are found for each case. Then, we give the characterization of parameter curves of Hasimoto surfaces in \(\mathbb {M}^{3}.\)      

呋虫胺衍生物杀虫活性的理论研究

基于Chem3D Ultra 7.0软件中的MOPAC半经验方法 AM1,计算了13种呋虫胺衍生物的19个量子化学和理化参数(包括ELUMO、EHOMO、△E=ELUMO-EHOMO、QC1、QC2、QN、QN1~QN4、QO、QO、μ、Hf、Ve、E0、Cv、Sm等)。采用最佳变量子集回归方法,建立呋虫胺衍生物对褐飞虱杀虫活性与上述结构参数的定量构效关系模型。结果表明,呋虫胺衍生物对褐飞虱杀虫活性的大小与ELUMO、QN1呈负相关,而与QC2正相关。所建的最优三变量模型具有良好的预报能力(R2=0.928、Rcv2=0.805、Rcv-22=0.797)和较高的稳健性(Radj2、F、VIF、t、AIC和FIT等检验)。设计与预测了4种新颖化合物的杀虫活性,在浓度为500mg/dm3下,它们的杀虫活性预测值均超过115%。所建模型可为化学工作者合成新型高效新烟碱类化合物提供理论参考。     

Characterization of highly porous polymeric materials with pore diameters larger than 100 nm by mercury porosimetry and X-ray scattering methods

Highly porous polymeric materials with pore sizes ranging from 100 nm to 1 microm are a very challenging class of materials not only to prepare synthetically (due to the high capillary pressures generated upon solvent removal) but also to characterize structurally. Through the examples of three different types of porous compounds synthesized in our laboratory (i) high-density melamine-based "MF-hd" with monomodal pore diameters around 500-900 nm, (ii) low-density melamine-based "MF-ld" with bimodal pore size distribution and average diameters around 2.3 microm and 350 nm, (iii) highly porous polyurethane "PU" with monomodal pore sizes around 150 nm, we confirm the limitations of mercury porosimetry as a means to investigate the architecture of materials with very high porosity (>80 vol %) and low compressive strength. Instead, a combination of high-resolution scanning electron microscopy and small-angle and ultrasmall-angle X-ray scattering (SAXS and USAXS, respectively) studies of these three types of materials helps in determining both the network and the pore structures. This work elucidates the need and applicability of the SAXS/USAXS techniques in characterizing such porous materials. For instance, the polyurethane specimens can only be quantitatively characterized by scattering techniques, the results of which are corroborated by high-resolution scanning electron microscopy observations.     

Molecular structure and vibrational spectra of 1,3-bis(4-pyridyl)propane by quantum chemical calculations

The experimental and theoretical study on the structures and vibrations of 1,3-bis(4-pyridyl)propane are presented. The FT-IR and Raman spectra of molecule have been measured. The optimized geometric bond lengths have been obtained by DFT show the best agreements with experimental values. The harmonic vibrational frequencies were calculated and scaled values have been compared with experimental FT-IR and FT-Raman spectra. Majority of the computed wavenumbers were found to be in good agreement with experimental observations. A complete assignment of the fundamentals was proposed based on the total energy distribution (TED) calculation.     

Forecasting financial failure using a Kohonen map: A comparative study to improve model stability over time

This study attempts to show how a Kohonen map can be used to improve the temporal stability of the accuracy of a financial failure model. Most models lose a significant part of their ability to generalize when data used for estimation and prediction purposes are collected over different time periods. As their lifespan is fairly short, it becomes a real problem if a model is still in use when re-estimation appears to be necessary. To overcome this drawback, we introduce a new way of using a Kohonen map as a prediction model. The results of our experiments show that the generalization error achieved with a map remains more stable over time than that achieved with conventional methods used to design failure models (discriminant analysis, logistic regression, Cox’s method, and neural networks). They also show that type-I error, the economically costliest error, is the greatest beneficiary of this gain in stability.     

Radically perfect prime ideals in polynomial rings

We call an ideal I of a commutative ring R radically perfect if among the ideals of R whose radical is equal to the radical of I the one with the least number of generators has this number of generators equal to the height of I. Let R be a Noetherian integral domain of Krull dimension one containing a field of characteristic zero. Then each prime ideal of the polynomial ring R[X] is radically perfect if and only if R is a Dedekind domain with torsion ideal class group. We also show that over a finite dimensional Bézout domain R, the polynomial ring R[X] has the property that each prime ideal of it is radically perfect if and only if R is of dimension one and each prime ideal of R is the radical of a principal ideal.