Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Analysis of two-dimensional photonic band gap structure with a rhombus lattice

The relative band gap for a rhombus lattice photonic crystal is studied by plane wave expansion method and high frequency structure simulator (HFSS) simulation. General wave vectors in the first Briliouin zone are derived. The relative band gap as a function of air-filling factor and background material is investigated, respectively, and the nature of photonic band gap for different lattice angles is analyzed by the distribution of electric energy. These results would provide theoretical instruction for designing optical integrated devices using photonic crystal with a rhombus lattice.     

Studies on structural requirements for atropisomerism in N-phenyl γ-lactams

We prepared a series of substituted N-phenyl γ-lactams to investigate the structural requirements for forming atropisomers. NMR spectroscopic and X-ray crystallographic data as well as chiral HPLC analyses proved that ortho-F, Cl-disubstituted N-phenyl γ-lactams (i.e., RS-4 and SS-4) yielded separable atropisomers. Computational studies using the conformational data derived from crystal structures showed that conformational variations in the γ-lactam ring had negligible impacts on the rotational barriers of the N-phenyl group around the central CN bond. Atropisomerism in N-phenyl γ-lactams was depended solely on the steric interactions between bulky ortho-substituents on the N-phenyl group and the adjacent CH₂ and CO groups in the γ-lactam.     

Optisch aktive aromatische Spirane, 19. Mitt. Ermittlung von optimalen λ-Werten bei tri- bis polysubstituierten 2,2′-Spirobiindanen

Summary Nearly all ligand parameters which were empirically determined from disubstituted 2,2-spirobiindanes proved to be inaccurate for the calculation of the optical rotations of the title compounds by means of the so-called shortened approach, especially in the case ofo-alkylsubstituted carbonyl derivates. The modified parameters were now determined either by comparison of a series of similar substituted spirocompounds or — for the carbonyl derivates — from the torsional angles calculated from their¹³C NMR data.

Herrn Prof. Dr.K. Schlögl anläßlich seiner Emeritierung gewidmet     

Towards better multi-class parametric-decomposition approximations for open queueing networks

Methods are developed for approximately characterizing the departure process of each customer class from a multi-class single-server queue with unlimited waiting space and the first-in-first-out service discipline. The model is (GT _i /GI _i )/1 with a non-Poisson renewal arrival process and a non-exponential service-time distribution for each class. The methods provide a basis for improving parametric-decomposition approximations for analyzing non-Markov open queueing networks with multiple classes. For example, parametric-decomposition approximations are used in the Queueing Network Analyzer (QNA). The specific approximations here extend ones developed by Bitran and Tirupati [5]. For example, the effect of class-dependent service times is considered here. With all procedures proposed here, the approximate variability parameter of the departure process of each class is a linear function of the variability parameters of the arrival processes of all the classes served at that queue, thus ensuring that the final arrival variability parameters in a general open network can be calculated by solving a system of linear equations.     

Predicting nucleic acid torsion angle values using artificial neural networks

By means of an error back-propagation artificial neural network, a new method to predict the torsion angles , and from torsion angles , , and for nucleic acid dinucleotides is introduced. To build a model, training sets and test sets of 163 and 81 dinucleotides, respectively, with known crystal structures, were assembled. With 7 hidden units in a three-layered network a model with good predictive ability is constructed. About 70 to 80% of the residuals for predicted torsion angles are smaller than 10 degrees. This means that such a model can be used to construct trial structures for conformational analysis that can be refined further. Moreover, when reasonable estimates for , , and are extracted from COSY experiments, this procedure can easily be extended to predict torsion angles for structures in solution.     

Synthesis, separation and configuration determination of diastereoisomers of (R,S)-1-methyl-3-[3-(aryl)-1,2,4-oxadiazol-5-yl] propyl 2,3-dideoxy-α-d-erythro-hex-2-enopyranosides

For synthesizing title compounds, first we carried out the Ferrier's rearrangement involving tri-O-acetyl-d-glucal 1 and alcohols 2a-e using Montmorillonite K-10 as a catalyst. This reaction gave diastereoisomeric mixture of 3a-e and 4a-e. Basic hydrolysis of each pair of diastereoisomeric mixture furnished title compounds 5a-e and 6a-e, which were separated very carefully over a silica gel column yielding all diastereoisomers in the pure form. One of them 5d was subjected to a single crystal X-ray analysis to determine the correct configuration at the asymmetric carbon atom of the aglycone. The methyl signals of the diastereomers helped to assign the configuration of each diastereoisomer. Molecular orbital calculations of 5d using the semi-empirical method (AM1) has been performed to compare its results with the crystallographic data. We have also determined the rotational barrier of C(8) and O(9) bond in both (R) and (S) enantiomers of compounds 5a and 6a.     

Studies on the electrical double layer structure at the water/air interface

Effective dipole moments (calculated from experimental data of surface tension and electric surface potential) of some homologous normal alcohols and carboxylic acid were found to vary linearly with the number of carbon atoms in the hydrocarbon chain. Values of effective dipole moments were used for the determination of the effective dipole moments of water molecules , and the dielectric permittivity of the water subphase (₁), as well as in the vicinity of the hydrophobic part of adsorbed molecule (₂). The latter was found to decrease with the increase of the hydrocarbon chain length. Knowing the effective dipole moment of surface water dipoles, the average orientation angle () of water molecules at the inteface was estimated. The calculated potential drop of water varies within the range –0.038 to –2.38 V for two extreme orientations of water dipoles at the surface.     

Applicability of MNDO techniques AM1 and PM3 to ring-structured polymers

Semiempirical Hartree‐Fock techniques are widely used to study properties of long ring‐structured chains, although these types of systems were not included in the original parametrization ensembles. These techniques are very useful for an ample class of studies, and their predictive power should be tested. We present here a study of the applicability of some techniques from the NDDO family (MNDO, AM1, and PM3) to the calculation of the ground state geometries of a specific set of molecules with the ring‐structure characteristic. For this we have chosen to compare results against ab initio Restricted Hartree‐Fock 6‐31G(d,p) calculations, extended to Møller‐Plesset 2 perturbation theory for special cases. The systems investigated comprise the orthobenzoquinone (O₂C₆H₄) molecule and dimers (O₂C₆H₄)₂, as well as trimers of polyaniline, which present characteristics that extend to several systems of interest in the field of conducting polymers, such as ring structure and heterosubstitution. We focus on the torsion between rings, because this angle is known to affect strongly the electronic and optical properties of conjugated polymers. We find that AM1 is always in qualitative agreement with the ab initio results, and is thus indicated for further studies of longer, more complicated chains. © 2002 Wiley Periodicals, Inc. J Comput Chem 23: 1135–1142, 2002     

Problems of contact angle and solid surface free energy determination

The current general problems of formulation and determination of surface free energy are discussed. So far several theories and approaches have been proposed, but formulation of surface and interfacial free energy, as regards its components, is still a very debatable issue. However, as long as no method for determination of real surface free energy quantities is known, even relative values charged with many simplified assumptions are useful for better understanding of the wetting processes. In this paper special focus is concentrated on powdered solids for which direct measurement of the contact angles is not possible. For such solids the porous layer imbibition techniques are most frequently applied. Then, using the wicking results the contact angle is calculated from Washburn's equation. However, such a procedure leads to overestimated contact angle values in comparison to those measured directly on smooth surfaces of the same solid, if such surface can be obtained at all. As a consequence, the solid surface free energy components calculated via such overestimated contact angles are significantly lower than those obtained from contact angles measured directly. Methodologies to avoid this problem are also described.