The Use of a Modified Resin for Studying the Internal Structure of Microcrystalline Cellulose Particles

The use of a modified resin which allows the study of the internal structure of microcrystalline cellulose is described. Electron probe microanalysis and elemental X-ray mapping suggest that it is possible to identify cellulose within cross-sectioned microcrystalline cellulose particles.     

Fluorescent Molecular Logic Gates and Pourbaix Sensors in Polyacrylamide Hydrogels

Polyacrylamide hydrogels formed by free radical polymerisation were formed by entrapping anthracene and 4-amino-1,8-naphthalimide fluorescent logic gates based on photoinduced electron transfer (PET) and/or internal charge transfer (ICT). The non-covalent immobilisation of the molecules in the hydrogels resulted in semi-solid YES, NOT, and AND logic gates. Two molecular AND gates, examples of Pourbaix sensors, were tested in acidic aqueous methanol with ammonium persulfate, a strong oxidant, and displayed greater fluorescence quantum yields than previously reported. The logic hydrogels were exposed to aqueous solutions with chemical inputs, and the fluorescence output response was viewed under 365 nm UV light. All of the molecular logic gates diffuse out of the hydrogels to some extent when placed in solution, particularly those with secondary basic amines. The study exemplifies an effort of taking molecular logic gates from homogeneous solutions into the realm of solid-solution environments. We demonstrate the use of Pourbaix sensors as pE-pH indicators for monitoring oxidative and acidic conditions, notably for excess ammonium persulfate, a reagent used in the polymerisation of SDS-polyacrylamide gels.     

箱形梁剪力滞效应分析中的翘曲位移函数及广义内力研究

以薄壁箱梁的弯曲计算理论为基础,从分析翼缘板的面内剪切变形和弯曲剪力流的分布规律入手,从理论上证明二次抛物线是箱形梁剪力滞效应分析中的合理翘曲位移函数。选取剪力滞效应引起的附加挠度作为广义位移,用基于最小势能原理的能量变分法建立箱形梁剪力滞效应分析的控制微分方程和边界条件。对箱梁横截面上新出现的广义内力给出严密定义,并建立了剪力滞翘曲应力的简便计算公式,它与初等梁弯曲应力公式具有相同的形式。对一个简支箱梁模型的计算表明,计算值与实测值吻合良好,从而证实了本文的分析方法和建立的公式是正确的。不同于弯矩的分布,剪力滞广义力矩具有快速衰减的分布特征。对集中荷载作用下的简支箱梁算例,剪力滞效应使其跨中挠度增大达12%,工程实践中必须认真对待。     

Principal parametric and three-to-one internal resonances of flexible beams undergoing a large linear motion

A set of nonlinear differential equations is established by using Kane‘s method for the planar oscillation of flexible beams undergoing a large linear motion. In the case of a simply supported slender beam under certain average acceleration of base, the second natural frequency of the beam may approximate the tripled first one so that the condition of 3 : 1 internal resonance of the beam holds true. The method of multiple scales is used to solve directly the nonlinear differential equations and to derive a set of nonlinear modulation equations for the principal parametric resonance of the first mode combined with 3 : 1 internal resonance between the first two modes. Then, the modulation equations are numerically solved to obtain the steady-state response and the stability condition of the beam. The abundant nonlinear dynamic behaviors, such as various types of local bifurcations and chaos that do not appear for linear models, can be observed in the case studies. For a Hopf bifurcation,the 4-dimensional modulation equations are reduced onto the central manifold and the type of Hopf bifurcation is determined. As usual, a limit cycle may undergo a series of period-doubling bifurcations and become a chaotic oscillation at last.     

Non-linear interactions in imperfect beams at veering

Non-linear interactions in a hinged-hinged uniform moderately curved beam with a torsional spring at one end are investigated. The two-mode interaction is a one-to-one autoparametric resonance activated in the vicinity of veering of the frequencies of the lowest two modes and results from the non-linear stretching of the beam centerline. The excitation is a base acceleration that is involved in a primary resonance with either the first mode only or with both modes. The ensuing non-linear responses and their stability are studied by computing force- and frequency-response curves via bifurcation analysis tools. Both the sensitivity of the internal resonance detuning—the gap between the veering frequencies—and the linear modal structure are investigated by varying the rise of the beam half-sinusoidal rest configuration and the torsional spring constant. The internal and external resonance detunings are varied accordingly to construct the non-linear system response curves. The beam mixed-mode response is shown to undergo several bifurcations, including Hopf and homoclinic bifurcations, along with the phenomenon of frequency island generation and mode localization.     

芦笋中化学成分的内部萃取电喷雾电离质谱检测

选择芦笋(Asparagus Officinalis L)新鲜茎块和两种干燥茎块为代表性植物组织样品,建立了一种直接检测芦笋中多种化学成分的内部萃取电喷雾电离质谱(iEESI-MS)分析方法。在正离子检测模式下,选择甲醇(CH₃OH)作萃取溶剂,在无需样品预处理的条件下对芦笋组织样品进行直接质谱分析,获得了组织样品在m/z 50~1000范围内的化学指纹谱图,并通过目标离子的碰撞诱导解离(CID)实验,鉴定了对药物和自然产品研发具有重要意义的糖类、氨基酸、生物碱以及芦丁等多种代表性的营养成分。 本方法具有无需样品预处理、样品耗量少、操作简便、分析速度快(单个样品的分析时间少于1 min)等优点,为食源性植物组织样品的快速分析提供了一种质谱分析新方法。     

Application of Internal Standard for Micro Extraction– Spectrophotometric Determination of Bismuth in Pharmaceutical Formulations

 A micro extraction – spectrophotometric procedure is developed for the determination of bismuth in pharmaceutical formulations. The procedure is based on the extraction of tetraiodobismuthate(III) ion paired with benzyltributylammonium cation into chloroform. The application of Nile Blue as internal standard (IS) enabled good analytical performance for micro-scale analysis. The ratio between the absorbances measured at 491 nm (bismuth complex) and at 632 nm (IS) was taken as the analytical signal. The procedure was carried out in Eppendorf tubes, lowering significantly the use of reagents and the volume of organic solvent. In the calibration range up to 60 mgċl⁻¹, the linear regression coefficient was 0.9999, the CV for 15 mgċl⁻¹ and for 50 mgċl⁻¹ Bi were 1.6% and 0.7% respectively. The results obtained in the analysis of pharmaceutical formulations were in good agreement with the results of EDTA titration method. Received November 25, 1999. Revision February 14, 2000.     

Application of torsion angle molecular dynamics for efficient sampling of protein conformations

We investigate the application of torsion angle molecular dynamics (TAMD) to augment conformational sampling of peptides and proteins. Interesting conformational changes in proteins mainly involve torsional degrees of freedom. Carrying out molecular dynamics in torsion space does not only explicitly sample the most relevant degrees of freedom, but also allows larger integration time steps with elimination of the bond and angle degrees of freedom. However, the covalent geometry needs to be fixed during internal coordinate dynamics, which can introduce severe distortions to the underlying potential surface in the extensively parameterized modern Cartesian-based protein force fields. A "projection" approach (Katritch et al. J Comput Chem 2003, 24, 254-265) is extended to construct an accurate internal coordinate force field (ICFF) from a source Cartesian force field. Torsion crossterm corrections constructed from local molecular fragments, together with softened van der Waals and electrostatic interactions, are used to recover the potential surface and incorporate implicit bond and angle flexibility. MD simulations of dipeptide models demonstrate that full flexibility in both the backbone phi/psi and side chain chi1 angles are virtually restored. The efficacy of TAMD in enhancing conformational sampling is then further examined by folding simulations of small peptides and refinement experiments of protein NMR structures. The results show that an increase of several fold in conformational sampling efficiency can be reliably achieved. The current study also reveals some complicated intrinsic properties of internal coordinate dynamics, beyond energy conservation, that can limit the maximum size of the integration time step and thus the achievable gain in sampling efficiency.     

用板式电势差计测量电池的电动势和内阻实验的改进

分析了在“用板式电势差计测量电池的电动势和内阻”实验中 ,由于待测干电池的电动势和内阻在实验过程中均不为恒定值而引起的误差 ,依据电化学理论和电阻构成解释了实验现象 ,并给出了实验改进方案 .     

金属磁记忆效应的第一性原理计算与实验研究

为研究铁磁材料应力集中区域金属磁记忆信号的产生机理及其变化规律, 采用基于密度泛函理论的第一性原理平面波赝势法, 建立了磁记忆效应的磁力学模型; 计算分析了力与磁记忆自发漏磁信号的定量变化关系. 研究结果表明:力作用导致晶格畸变是磁记忆自发漏磁信号产生的根本原因; 常温下, 磁记忆信号随应力近似线性变化的规律与X70钢管水压爆破实验结果具有很好的一致性. 研究结果有助于金属磁记忆检测机理的研究. 关键词： 金属磁记忆 第一性原理 漏磁信号