Non-symmetric Structure Research Articles

Pyroelectric organo-metallic langmuir-blodgett films

Abstract Organic materials are highly efficient non-linear media and can be prepared in a non-symmetric structure using the simple yet elegant deposition process termed the Langmuir-Blodgett technique. In this paper the pyroelectric behaviour of novel organo-metallic/behenic acid superlattices, prepared using this method, are reported. The largest pyroelectric coefficients (3 μCm−2K−1) were obtained from a ruthenium [(η5-cyclopentadienyl)-(bis-triphenylphosphine)] hexafluorophosphate complexed with a cyano (poly) phenyl liquid crystal. The influence of the phenyl rings and the effects of electron donating groups have been investigated to give an insight into the origins of the pyroelectric effect. The low dielectric loss and relative permittivity exhibited by these materials suggest a possible application as a thin film infra-red detector layer.

ChemInform Abstract: Nature of Carbon‐Lithium Bonding in Dilithiated Polynuclear Aromatics: An MNDO Study

Abstract(nonsym.

Spectroscopic investigations on the structure and fluxionality of the trihaptocycloheptatrienyl complexes [MX(CO) 2(LL)(η 3-C 7H 7)] (M  Mo, W; X  I, Cl; LL  bisphosphine or diamine) and synthesis of the tetracyanoethene adducts [WI(CO) 2{Ph 2P(CH 2) nPPh 2}{η 3-C 9H 7(CN) 4}] ( n = 1 or 2)

Spectroscopic investigations, including 31P, 1H and 13C NMR studies, on the formally 6-coordinate bisphosphine complexes [MX(CO) 2{Ph 2P(CH 2) n PPh 2}(η 3-C 7H 7)] (M  Mo, W; X  I, Cl; n = 2 (dppe), n = 1 (dppm); C 7H 7  cycloheptatrienyl) reveal a structure with no molecular plane of symmetry in which inequivalent P-donor atoms are arranged cis-cis and cis-trans to the two mutually cis-carbonyl groups. The dppe complexes exhibit a fluxional process which interconverts inequivalent phosphorus environments. Low temperature 1H and 13C NMR studies on the diamine derivatives [MCl(CO) 2(H 2NCH 2CH 2NH 2)(η 3-R)] (M  Mo, W, R  C 7H 7; M  Mo, R  C 3H 5 (allyl)) imply that the non-symmetric structure of the bisphosphine analogues is adopted. The adducts [WI(CO) 2{Ph 2P(CH 2) n -PPh 2} {η 3-C 9H 7(CN) 4}] ( n = 1 or 2) are formed by tetracyanoethene addition to the trihapto-bonded cycloheptatrienyl ring of the tungsten complexes [WI(CO) 2-{Ph 2P(CH 2) n PPh 2}(η 3-C 7H 7)] ( n = 1 or 2).

High-voltage poly-Si TFTs with multichannel structure

High-voltage (>100-V) and large-transconductance poly-Si thin-film transistors (TFTs) have been fabricated on quartz substrates by the use of laser-recrystallized multiple-strip poly-Si films as semiconductors in the channel regions. The TFTs have an offset gate structure between the source and the gate (L/sub OFF,1/), and between the gate and the drain (L/sub OFF,2/). With the nonsymmetric offset gate structure at L/sub OFF,1/=3 mu m and L/sub OFF,2/=15 mu m, the TFTs have a large transconductance of 520 mu S and exhibit low-threshold n-channel enhancement-mode characteristics. Simultaneously, a very large ON/OFF current ratio (above 10/sup 7/) and a low leakage current of 2*10/sup -10/ A occur at the high drain voltage of V/sub D/=100 V. The breakdown voltage V/sub BD/ of the TFT depends strongly on L/sub OFF,2/, so V/sub BD/ can increase with increasing L/sub OFF,2/ to 110 V at L/sub OFF,2/=10 mu m, 130 V at L/sub OFF,2/=15 mu m, and 170 V at L/sub OFF,2/=20 mu m.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis and results of cooperative magnetographic measurements. I. Correction, comparison and discussion of measurements

AbstractOn June 24, 1983 cooperative magnetographic measurements were made with the vectormagnetographs of the Sayan Observatory (Irkutsk) and the Potsdam Solar Observatory “Einsteinturm” and with the longitudinal magnetograph of the Ondrejov Observatory. Additionally, the maximum field strengths in the sunspot were measured with the photographic method. Using the photographically measured field strengths as reference values we provide a method to eliminate the influences of stray light in a time series of vectormagnetograms. A comparison of nearly simultaneous magnetograms shows a good correspondence in general. The deviations of the zero points as well as the scales are comparable with the results of other authors. Regarding the magnetic field distribution the magnetograms reflect a substantial nonsymmetric structure in the spot under study. The magnetic field lines tend to concentrate into several flux tube clusters. In one region of the penumbra we find a magnetic field with nearly longitudinal character in close neighbourhood of a strong, nearly horizontal flux tube bundle. This indicates a strong nonradial horizontal field gradient in the penumbra.

Nature of carbon-lithium bonding in dilithiated polynuclear aromatics: an MNDO study

An MNDO study shows that the nonsymmetric crystal structures of dilithionaphthalene and dilithioanthracene are not the result of crystal-packing forces, but rather reflect the internal minimum energy arrangement of the molecules considered. On the other hand, the optimal structures of the complexes of the respective dianions with two positive charge are symmetrical. This difference suggests that partial covalency of the carbon-lithium bonding may be responsible for the nonsymmetric arrangement becoming the most stable in the crystal state.

Stereochemical studies on cyclic peptides. XIII. Energy minimization studies on cyclic hexapeptides having hydrogen bonds*

The basic cyclic hexapeptide conformations which accommodate hydrogen bonded β and γ turns in the backbone have been worked out using stereochemical criteria and energy minimization procedures. It was found that cyclic hexapeptides can be made up of all possible combinations of 4 ± 1 hydrogen bonded types I, I', II and II' β turns, giving rise to symmetric conformations having twofold and inversion symmetries as well as nonsymmetric structures. Conformations having exclusive features of 3 ± 1 hydrogen bonded γ turns were found to be possible in threefold and S6 symmetric cyclic hexapeptides. The results show that the cyclic hexapeptides formed by the linking of two β turn tripeptide fragments differ mainly in (a) the hydrogen bonding scheme present in the β turn tripeptides and (b) the conformation at the α‐carbon atoms where the two tripeptide fragments link. The different hydrogen bonding schemes found in the component β turns are: 1) a β turn with only a 4 ± 1 hydrogen bond, 2) a type I or I' β turn with 4 ± 1 and 3 ± 1 hydrogen bonds occurring in a bifurcated form and 3) a type II or II' β turn having both the 4 ± 1 and the 3 ± 1 hydrogen bonds with the same acceptor oxygen atom. The conformation at the linking α‐carbon atoms was found to lie either in the extended region or in the 3 ± 1 hydrogen bonded γ turn or inverse γ turn regions. Further, the threefold and the S6 symmetric conformations have three γ turns interleaved by three extended regions or three inverse γ turns, respectively. The feasibility of accommodating alanyl residues of both isomeric forms in the CHP minima has been explored. Finally, the available experimental data are reviewed in the light of the present results.

Edge-projection tomography

A biological structure can be reconstructed in three dimensions from a series of transmission electron microscope (TEM) images taken as a support grid is tilted over a large angle. A back-projection (tomographic) algorithm using a radially weighted Fourier transform of each tilted image can be used for this purpose. The accuracy of reconstructing a nonsymmetric structure is limited by the number of micrographs that can be taken, and by the total tilt angle that can be achieved. Thirty independent views of a nonsymmetric structure (taken over a total tilt angle of ∼180 degrees) are needed to resolve a nonsymmetric structure to ∼3nm.

Ring-opening polymerization of norbornene catalysed by W(CO) 3Cl 2(AsPh 3) 2 in the presence of other olefins

The steric course of ring-opening polymerization catalysed by W(CO) 3Cl 2(AsPh 3) 2 is strongly influenced by the presence of other cyclic or linear olefins, such as cyclooctene, cyclohexene, 1-hexene and 1,7-octadiene. The blockiness of the polymer increases linearly with the overall olefin concentration in the reaction mixture. This effect of the individual olefins is independent of whether or not they participate in the cross-metathesis reaction to a detectable extent. The results are in agreement with the existence of two major kinetically-distinct propagating metallacarbene species, one cis- and one trans-directing. Terminal olefins act as chain transfer agents. Based on polymer fractionation, 13C NMR and GC-MS studies, two more kinds of selectivity of the catalyst was found besides the increase of σ c and r c r t , of the polymer: 1. The formation, exclusively, of oligomers of a nonsymmetric structure; 2. The lack of detectable products of the homometathesis of linear chain olefins. The results are explained by the reluctance to form CH 2 carbenes and the relatively high reaction rate of propagation, chain transfer and degenerate metathesis, compared to the productive metathesis of the terminal olefins.

On the geometrical interpretation of 'non-symmetric' space-time field structures

Using the framework of affine differential geometry, which is related to the gauge theory of the Poincare group, the author discusses the geometric interpretation of the non-symmetric field structure originally proposed by Einstein and Straus (1946).

Energetics and structure of the hydrated gaseous halide anions

AbstractEnergetics and geometries for the hydrated gaseous halide anions have been computed from a simple model in which the molecular dipole of water was composed of two parts, one due to a lone pair on oxygen (60%) and the rest to formal charges on the nuclei. The calculations were made for both the symmetric and nonsymmetric structures. A variety of structures were used to compute potential energies and distances with up to six water molecules. The total energy consisted of a sum of electrostatic, polarization, dispersion, and repulsion terms. Various sets of repulsive potential parameters, ranging from those determined from molecular beam experiments to those determined using experimental ion–water distances or energies, have been employed to compute repulsive interaction energies. It was found that the range parameters play a significant role in deciding the magnitudes of the distances and energies, as the latter are most sensitive to them. It was also shown that with a simple correlation scheme the consistency of the experimental energies and distances can be tested separately without using repulsive potential parameters from other sources. It also suggests that a range of parameters can be used to compute repulsion energies. Despite the fact that the model is greatly simplified, the agreement of both the predicted ion‐oxygen distances and energies with both experiment and other calculations is excellent. A detailed analysis of our calculation suggests that the negative ion clusters with one to three water molecules contain symmetric orientation of water molecules, while those with more than three may contain asymmetric orientations of water molecules or a mixture of both. From the log–log plots of hydration energies versus (R + radius of water molecule), we have proposed empirical expressions of the type ΔEn−1,n = 10·0x (R + 1.38)−y with both Pauling's and Ladd's radii for univalent ions with which stepwise hydration energies of the latter can be predicted if we know thier radii. The values predicted for the alkali cations are in excellent agreement with the experimental and theoretical values, indicating the consistency of the simple model.

Theoretical study of the allyl radical: structure and vibrational analysis

The electronic structure of the allyl CH/sub 2/CHCH/sub 2/ and its vibrational spectrum have been calculated from ab initio multiconfiguration Hartee-Fock (MCHF) wave functions. While the Hartree-Fock (HF) model incorrectly predicts a nonsymmetric structure, the MCHF calculations indicate that the allyl radical has C/sub 2..nu../ symmetry in accord with ESR evidence. Harmonic vibrational frequencies of all the normal modes are reported for the allyl radical and various deuterium-substituted analogues. Most noteworthy are the out-of-plane bending mode frequencies calculated at 760-790 cm/sup -1/ which are predicted to give rise to a very intense and characteristic band of the allyl radical.

Coupling Characteristics of Planar Dielectric Waveguides of Rectangular Cross Section

An approximate analytical method based on experimental results for predicting the coupling characteristics of various coupling structures is described. Expressions for the propagation constants were derived using the generalized effective dielectric constant method. For nonsymmetric coupling structures, the theoretical coupling coefficients were modified by a correction factor. Comparisons between experimental and theoretical results are presented.

Optoelectrical study of bubble propagation in field access devices

Bubble propagation on several field access structures is studied with an optoelectrical method. Measurements were performed with a 40-Oe, 10-kHz rotating field on closed-loop shift registers that were fabricated on Bi-substituted garnet films having either 7 μm or 2.7 μm bubbles. The effect of increasing the interelement gap for several nonsymmetrical structures is discussed.

New theory of gravitation

A new theory of gravity is proposed in which the geometry of space-time is determined by a nonsymmetric field structure. The theory satisfies the following requirements: (1) general covariance, (2) (weak) principle of equivalence, (3) the field equations are derivable from a Lagrangian action principle, (4) the theory agrees with all the classical (weak gravitational field) tests of Einstein's general relativity. The field equations for the nonsymmetric Hermitian ${g}_{\ensuremath{\mu}\ensuremath{\nu}}$ lead to a rigorous static spherically symmetric solution for the gravitational field in empty space that excludes the essential singularity at $r=0$ from physical space-time. It is expected that the predictions of the theory will differ significantly from Einstein's theory of gravitation for compact sources or supermassive stars. Matter undergoing gravitational collapse is prevented from forming a black hole (in physical space-time) of the kind predicted in Einstein's theory, when a new gravitational parameter $l$ that appears as a constant of integration in the solution satisfies $l&gt;2m$.

Space-time structure in a generalization of gravitation theory

A generalized theory of gravitation, formulated recently in terms of a nonsymmetric field structure, is derived from a variational principle, and its relation to the Einstein-Maxwell theory is studied in detail. The physical interpretation of a new universal constant $k$ that occurs in the theory is considered, and reasons are given to choose the constant to be $|k|=\ensuremath{\hbar}\frac{G}{{c}^{3}}e=\frac{{L}^{2}}{e}$, where $L={(\ensuremath{\hbar}\frac{G}{{c}^{3}})}^{\frac{1}{2}}$ is the Planck length. The exact static spherically symmetric solution of the theory is shown to be world-line complete. The timelike and null (radial and nonradial) physical paths of test particles are deflected away from a sphere $S$ with a radius ${r}_{s}\ensuremath{\sim}L$. A discussion is given of the implications of the nonsingular solution of the theory for large- and small-scale physical phenomena.

Chiral non-symmetric structures functions in asymptotically free theories

The asymptotic behaviour of the chiral symmetry violating structure functions W 4 and W 5 of neutrino-hadron scattering is studied in asymptotically free gauge theories of the strong interactions. Use is made of Weinberg's improved renormalisation group equation. The validity of results previously obtained in the parton and vector gluon models is discussed.

On the theory of sandwich plates of nonsymmetric structure with orthotropic layers

On the theory of sandwich plates of nonsymmetric structure with orthotropic layers

The perturbation of linearly and circularly polarized geomagnetic fields by a non-symmetric two-island structure at three periods.

The perturbation of alternating geomagnetic fields by a three-dimensional conductivity model is studied by a numerical technique. The model is a nonsymmetric island structure embedded in a layered half-space. Linearly polarized source fields of two different directions as well as a circularly polarized source field are studied. Three source field frequencies are considered. The results are presented as amplitude contours of the various field components over the surface plane. It is found that the perturbations in the fields are greater for shorter period. Also, the various maxima and minima in the amplitude contours associated with the island structure are dependent on the orientation of the source field. The results for the different polarization fields are compared, and the amplitude contours for the circularly polarized source field vary considerably from the linearly polarized cases.

Application of the Matrix Displacement Method to the Analysis of Pressure Vessels

The matrix displacement approach of the finite element method is applied to the analysis of deformations and stresses in pressure-vessel type structures. Particular reference is made to structures with rotational symmetry, both under axisymmetric and unsymmetric loading and temperature distribution, for which two classes of structural elements for the idealization of solids and membrane shells are described. A survey of some finite elements used for the analysis of more general pressure vessel structures is conducted. Several examples of axisymmetric and nonsymmetric structures are included to demonstrate the versatility and power of the method.