关于稳定单变度曲线自动判别的一种简便的普适性方法

无变度点周围各单变度曲线稳定性的自动判别,是多体系稳定平衡相图计算机成图理论中十分关键而棘手的问题。它既令化学家感兴趣,更为地质地球化学家、冶金学家、材料学家所关注。在这方面,已有不少学者做过探讨,其基本依据是“等温等压下达到平衡时体系的Ｇｉｂｂｓ自...     

The perceptual nature of vocal register change

This study focuses on the perceptual nature of chest and falsetto registers as a function of various production tokens and methods of perceptual evaluation. Fifteen target tones, ranging from G#3 to A#4, were sung by a male and a female subject in the context of ascending and descending sequences on the vowels /a/ and /i/. Register transitions were elicited by setting strict constraints on production. Segments of 1-s duration were extracted from the target notes, digitized, and acoustically analyzed. These excerpts were presented to ten trained listeners in four different perceptual tasks. Identification and discrimination tasks yielded nearly identical results, suggesting that the primary registers are perceived as distinct entities. The marked change from chest to falsetto as well as the locus of the transition between these registers did not vary systematically as a function of production token or perceptual task. Mean register shift-point frequencies of the male and female subjects were perceived at 320 Hz and 353 Hz, respectively. Multidimensional scaling and hierarchical clustering analyses were utilized to capture the dimensionality and the internal structure of perceptual data sets derived from the pair-wise similarity ratings. Optimal spatial representation of these data required no more than two orthogonal dimensions, with the quality attribute represented by the dominant dimension. The representation of pitch differences was reflected only in the internal ordering of the stimuli within registers, but did not affect the perceptual discontinuity between registers.     

Chirale Erkennung bei Trisdiimin-Metallkomplexen: 3. Adsorption von Tris-(3,3′-bi-1,2,4-triazin)eisen(II)-Komplexen an Montmorillonit

Summary Adsorptionisotherms of tris-(3,3-bi-1,2,4-triazine)iron(II) complexes onto a well characterized montmorillonite are discussed in respect to the relative charge densities of adsorbent and adsorbat. While the adsorption capacities for trisbipyridyl and trisphenanthroline complexes differ for the racemates and the enantiomers they are equal for these complexes. Adsorption is limited to a monolayer. This backs the proposal that the observed chiral recognition phenomena are founded solely in the lateral interactions between adsorbats.

     

Theoretical study of chiral discrimination in the hydrogen bonding complexes of the hydrazine dimer

In this work, the discrimination of different chiral forms of the hydrazine dimer were investigated using Density Functional Theory (DFT) and second‐order Moller–Plesset Perturbation (MP2) theory at basis set levels from 6‐31g to 6‐31++g(d,p). Four chiral structures were studied. The optimized geometric parameters, interaction energies, and chirodiastatic energy for various isomers at different levels were estimated. Finally, the solvent effects on the geometries of the hydrazine dimers were also investigated using self‐consistent reaction‐field (SCRF) calculations at the B3LYP/6‐31++g(d,p) level. The results indicate that the polarity of the solvent has played an important role in the structures and relative stabilities of different isomers. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

The comparative spreading behavior of enantiomeric and racemic tyrosine amphiphiles

Several derivatives of tyrosine or its methyl ester have been synthesized in which the para hydroxyl group on the aromatic side chain has been converted to a long chain alkyl ether or urethane. The surface behavior of these compounds is discussed. Enantiomeric discrimination, the ability of a chiral molecule to distinguish between mirror-image stereoisomers, has been investigated for the urethane derivates by comparing the surface pressure-area isotherms of the enantiomer with that of the racemic compound. Enantiomeric discrimination was demonstrated for the methyl ester analog, but was not conclusively observed for the zwitterionic compounds. Possible structural requirements for enantiomeric discrimination in a chiral molecule are discussed.     

Multi‐Channel Surface Acoustic Wave Sensors Based on Principal Component Analysis (PCA) and Linear Discriminate Analysis (LDA) for Organic Vapors

A multi‐channel surface acoustic wave (SAW) detection system which is employed to detect various organic molecules in a static system was prepared using 315 MHz one‐port quartz resonators and a home‐made computer interface for signal acquisition and data process. The oscillating frequency of the quartz crystal decreases on adsorption of organic molecules on the coating materials. The principal component analysis (PCA) method with SAS software was applied to select the appropriate coating materials onto the SAW crystals for organic vapors, e.g. hexane, 1‐hexene, 1‐hexyne, 1‐propanol, propionaldehyde, propionic acid, and 1‐propylamine. A dataset for a multi‐channel sensor with 19 SAW crystals for 7 analyses was collected after comparing the correlation between the 19 coating materials and the first six principal component (PC) factor. Furthermore, linear discriminate analysis (LDA) with SPSS software and a profile discrimination map were also applied and discussed for the discrimination of these organic vapors. These organic molecules could be clearly distinguished by the six‐channel SAW static sensor. The effect of concentration for various organic vapors was investigated and discussed.     

Chiral discrimination of quinine and quinidine based on notable room temperature phosphorescence lifetime differences with γ-cyclodextrin as chiral selector

Upon addition of small amount of bromocyclohexane (BrCH), quinine (QN) and quinidine (QD) display strong room temperature phosphorescence (RTP) in γ-cyclodextrin (γ-CD) solution without deoxygenation. The associated phosphorescence decay curves can be best fitted to biexponential patterns and quite different RTP lifetimes are obtained for QN (86.9 and 12.5 ms) and QD (12.1 and 4.17 ms), indicating a distinct chiral discrimination of γ-CD toward this pair of pseudo-enantiomers. The corresponding association constants evaluated for QN/γ-CD/BrCH and QD/γ-CD/BrCH are 3.47 × 10⁵ and 4.67 × 10⁴ L mol⁻¹, respectively. It can be inferred that their different ability to form complexes with the chiral γ-CD is accounted for the notable difference in RTP lifetimes between QN and QD.     

Chiral discrimination in biliverdin (S)-amino acids,II: Structural variations of the amino acid functional groups

The Biliverdin-(S)-amino acid derivatives2–21 have been synthesized, and are subject to a thorough c. d. and u. v.-vis. electronic absorption analysis in the bilatriene chromophoric region. It is shown that the extent of chiral discrimination of the bilatriene helices is particularly sensitive towards structural variations of the amino acids bound to the propionic side chains. Thus, a pronounced decrease of chiral induction occurs if hydrogen bonding between one of the two essential coordination sites of the amino acid entity and the bilatriene backbone is disturbed. Accordingly, derivatives of (S)-amino acidt-butyl esters (3,5,7,16 and17) andN-substituted (S)-amino acids (8–10, 20 and21) generally display weak c. d. spectra. If additional polar groups are present in bis(amino acid) derivatives mutual interferences of the adjacent side chains must be taken into account. The attenuations of -values observed for the bis(serine) and bis(aspartic acid) compounds14 and15 thus are mainly due to intramolecular interchain interactions. The results provide evidence in support of the proposed mechanism of chiral discrimination in biliverdin amino acids.Dedicated to Prof. Dr.Kurt L. Komarek on the occasion of his 60th birthday.     

Improved quantitative capillary GC by the use of CO2 as secondary coolant in cold on-column injection

A comparison is made between air and carbon dioxide as secondary cooling gases in cold on-column injection into capillary columns. Because CO₂ is a more effective coolant than air, the injection zone can be kept at a colder temperature, thus preventing loss of sample vapor through the open injector even as the initial oven temperatures because greater than the boiling point of the solvent. Sample loss at these elevated temperatures is shown as a reduction in peak area as functions of column temperature during injection and different injection zone temperatures. The maximum allowable oven temperature during injection is significantly higher when CO₂ is used as secondary coolant rather than air.     

关于类质同晶与同质多晶判断的札记

当个主要依据X光等衍射方法测定晶体结构以判断类质同晶和同质多晶现象。在形式化学式相同或相似的前提下，关键在于正确判断晶体的空间群。本文通过实例枚举类质同晶和同质多晶这一常见现象以及由于空间群指定失误等原因导致有关判断的不同结论。