Short-range Orientation Research Articles

"NONCRYSTALLOGRAPHIC" SYMMETRY AND QUASICRYSTALS

After the sensational discovery of the icosahedral quasicrystals, two dimensional quasicrystals with 8,10 and 12 fold rotational symmetries have also been found in various rapidly solidified alloys and experimental evidence will be presented here. Since these rotational symmetries are not compatible with the Bravais space lattices, they were called "noncrystallographic" point group symmetry in the past. However, it is argued that the long-range periodic translation order is only one of the results of the propagation of short-range orientation order and that the Bravais space lattice might not be a prerequisite of a crystal. During rapid solidification short-range orientation order predominates and therefore quasicrystals might occur with rotational symmetries not hitherto encountered.

Monte Carlo Simulations of the Chemical Potential and Free Energy for Trimer and Hexamer Rings

Abstract The chemical potential of a trimer and hexamer model ring system was determined by computer simulation over a range of temperatures and densities. Such ring molecules are important as model aromatic and naphthenic hydrocarbons. Thermodynamic integration of the pressure along a reversible path, Widom's ghost particle insertion method and Kirkwood's charging parameter method were used over a molecular density range of 0.05 to 0.30. Data were obtained by Monte Carlo simulation of a 96 molecule system that was modelled with a Lennard-Jones 6-12 truncated potential. The original insertion method, which does not take into account the orientation of the molecule when it is inserted, gives results for the chemical potential which deviate from that obtained using the thermodynamic pressure integration. At high density or temperature the deviation is significant. We have modified the Widom insertion technique to account for this short range orientation and find good agreement between this technique and the...

Molecular dynamics simulation of polymer liquid and glass. II. Short range order and orientation correlation

Molecular dynamics simulation has been performed with an assembly of n-alkane-like chains subject to potentials restricting bond lengths, bond angles, and trans–gauche dihedral angles and interacting with neighboring chains according to a truncated Lennard-Jones potential. The system, on stepwise cooling under constant pressure, undergoes a transition exhibiting characteristics of glass transition observable with laboratory polymers. The short range order in the system was monitored by evaluating the radial distribution function gk(r), where r is the distance between two short subchains, each comprising k consecutive CH2 units. The orientation correlations between neighboring subchains were monitored by evaluating the function Sk (r), giving the average cosine square of the angle between the end-to-end vectors of two neighboring subchains of k CH2 units separated by a scalar distance r. Integration of Sk(r), weighted by gk(r), gives the correlation volume. Both the short range order and the orientation correlation are seen to improve steadily as the temperature is lowered. This increased order is brought about as a result of increased density, reduced thermal motion, and more extended chain conformation. Extrapolation of the orientation correlation against temperature predicts an isotropic–nematic transition temperature Tc, as suggested by the Landau–deGennes theory. Isothermal annealing just below the predicted Tc indeed produces a highly ordered structure.

Spatial arrangement of orientations in rolled copper

The spatial arrangement of 205 individual orientations in 95% reversed rolled copper, which had been determined using selected area diffraction transmission electron microscopy on two sections perpendicular to the transverse and rolling directions respectively and also the orientation differences between neighbouring sites are presented in detail. The complete orientation distribution function (ODF) (including even and odd series expansion terms) was determined for each of the sections. The local arrangement of orientations is analysed from the point of view of long-range and short-range orientation relationships. The orientation differences between each pair of neighbours, expressed as rotation axes, represent in misorientation space the misorientation distribution. Two features of this distribution are considered in greater detail: (i) the distribution of rotation axes with minimal rotation angles ( ω min axes) and (ii) the distribution of rotation axes with respect to specific crystallographic directions or specimen axes (coincidence of rotation axes). The ODF shows for both sections the main components of the rolling texture for copper; their relative proportions, however, are different. This is explained by the fact that the probability of the section-cutting anisotropic regions is different (the cutting effect). The misorientation distribution shows, using the specimen reference system, clearly preferred positions. Using the crystal reference system there were no accumulations apart from those caused by the position of symmetry axes. The implication of these results is discussed.

Orientation to Landmarks within the Preferred Habitat by Peromyscus leucopus

A field study was conducted in two woodlots to identify the major physical features of the habitat that Peromyscus leucopus uses in short-range orientation and navigation, and to which it is responsive in the process of habitat selection. In one woodlot, landmarks used for short-range orientational and navigational aids were trees, logs (fallen branches and tree trunks), rocks, stone fences, and rock piles. In the other woodlot, trees (particularly those of large diameter) were important but logs and rocks were avoided to some extent. For both woodlots, areas with high densities of woody stems were avoided; logs were not important as refuge sites.

Evidence for short range orientation effects in pure liquid SO2 from vibrational Raman spectroscopy

AbstractIn the Raman spectrum of pure liquid SO2 a difference is observed between the wavenumbers of the isotropic and anisotropic components of the totally symmetric vibrations ν1 and ν2, the anisotropic component being at a higher frequency than the isotropic one. The separations are Δν1 = 5 cm−1, Δν2 ≃ 3.5 cm−1. This effect is approximately independent of temperature in the range −60 to +40°C. It disappears with dilution of SO2 in an inert solvent. The same shift is observed in solid SO2. Mirone and Fini2 and Josien3 have observed and interpreted such an effect in the case of larger molecules. They assume the liquid to be composed of clusters in which the molecules are partially ordered. In the case of SO2 our calculations based on such a model are in good agreement with the experimental results for ν2 but not for ν1.

The flight activity of the sheep headfly,Hydrotaea irritans(Fallén) (Diptera:Muscidae)

AbstractThe flight activity ofHydrotaea irritans(Fall.) was investigated in western Scotland using an unbaited suction trap, a carbon-dioxide-baited suction trap and a Manitoba trap. Consistently more female flies were caught than males. Trapping experiments showed that carbon dioxide and visual or thermal stimuli influence long-range attraction and short-range orientation in host-seeking flies. The seasonal activity of adults was determined from the geometric means of catches from a suction trap baited with carbon dioxide and a Manitoba trap.H. irritanswas shown to be univoltine. The activity of females was greatest in the middle of July and declined sharply in the first week of August. Male activity reached a peak at the same time as that of the females, then declined until no males were caught after mid-August. Females were most active between 10.00 and 18.00 h B.S.T., with a peak about 13.00 h. There was no variation in sex ratio during the day. Multiple regression equations of climatic and seasonal factors with log catches of flies were very similar for the two types of trap. Radiant temperature, illumination, wind speed and date were shown to influence activity of females and, with the exception of illumination, male activity also. Seasonal activity curves calculated from the regression equations were plotted for both sexes in the two traps.

Short-range orientation effects in dipolar aprotic liquids—III. Intermolecular coupling of vibrations in sulfoxides, sulfones, nitriles and other compounds

In the Raman spectrum of dipolar aprotic liquids the anisotropic component of bands arising from totally symmetric vibrations falls at a higher frequency than the isotropic component. The corresponding i.r. band maximum appears at about the same frequency as the Raman anisotropic component. These effects disappear with dilution in an inert solvent. This behaviour can be explained by assuming that these liquids are composed of clusters inside which the molecules are oriented in a partially ordered way.

Evidence for short-range orientation effects in dipolar aprotic liquids from vibrational spectroscopy. Part 2.—Carbonyl compounds

In the Raman spectrum of pure liquids, the anisotropic component of the CO stretching band falls at a higher frequency than the isotropic component. In the same liquids the infra-red band maximum appears at almost the same frequency as the Raman anisotropic component. In some cases the infra-red band may be resolved into two components, the stronger coinciding with the anisotropic, the weaker with the isotropic Raman band. These effects disappear with dilution and are reduced with increasing temperature.This behaviour is explained in terms of a model which assumes that dipolar aprotic liquids are composed of clusters of molecules oriented in an (at least partially) ordered way.

Feeding Behavior of Larvae of Plodia interpunctella1 , 2

The feeding behavior of Plodia interpunctella (Hubner) larvae was analyzed by using separate bioassays for stimuli eliciting short-range orientation responses and for stimuli involved in the maintenance of feeding. Nonpolar and polar extracts of wheat, corn (maize), and peanuts elicited both orientation and feeding responses in this polyphagous insect. When the role of carbohydrates in larval feeding behavior was studied, sucrose, fructose, glucose, maltose, fucose, and melibiose were powerful feeding stimulants. Also, tests with combinations of active and inactive sugars demonstrated that the total concentration of sugar directly influenced larval feeding. Thus, behaviorally inactive sugars could affect feeding behavior positively in a synergistic manner or by increasing the total concentration. Amino acids had little effect on feeding, even when used in combination with sucrose. Fatty acids and sterols had no effect by themselves, but when linoleic, oleic, and palmitic acids were used in combination with subthreshold levels of sucrose, a definite synergistic feeding effect occurred.

Evidence for short-range orientation effects in dipolar aprotic liquids from vibrational spectroscopy. Part 1.—Ethylene and propylene carbonates

The CO stretching frequency of liquid ethylene and propylene carbonates is higher in the infrared than in the Raman spectrum. The difference amounts to 13 cm–1 for ethylene carbonate at 313 K. This effect is explained as the consequence of a coupling between the transition dipoles of neighbouring molecules, which is made possible by some degree of alignment of molecular dipoles due to the high dipole moment of these molecules (about 16 × 10–30 C m). A study of dilution and temperature effects confirms this interpretation.

A Sex Pheromone of the Female Face Fly, Musca autumnalis,1 and Its Role in Sexual Behavior2

Data obtained from olfactometer tests demonstrated the presence of a sex pheromone in the hexane extract of 5-day-old virgin female face flies, Musca antumnalis De Geer (Diptera: Muscidae). Results of chromatography and simple chemical procedures suggest that the pheromone is an unsaturated hydrocarbon. The sex pheromone of the female face fly probably influences the behavior of the male in 2 ways, by attracting him to the pheromone source and by sexually stimulating him to initiate copulation. Apparently, both visual and olfactory stimuli are involved in the orientation mechanism of the male to the female face fly. The pheromone is perhaps operative over a relatively great distance whereas vision is probably used by pheromonestimulated males for only short-range orientation.

Magnetic circular dichroism studies of polystyrene solutions

AbstractThe magnetic circular dichroism (MCD) spectra of “atactic” and isotactic polystyrene solutions have been found to be sensitive to configurational and conformational differences. The ratio of B terms for “atactic” polystyrene (predominantly syndiotactic) to that of cumene was found to pass through a minimum as the coil expanded in various solvents. The ratio of dipole strengths D also passed through a minimum. For isotactic polystyrene and cumene the ratio of B terms increased with increasing coil size in the range of solvents utilized. The ratio of B terms of isotactic polystyrene over atactic polystyrene was found to go through a maximum as the coil expanded whereas the ratio of dipole strengths was found to continuously decrease. These results have been interpreted on the basis of the change in short range and long range orientation and interaction distances between chromophores during coil expansion. It is concluded that the microscopic conformation of isotactic and atactic polystyrene are very different in very good solvents. The B/D ratio for cumene was found generally to decrease with increasing solvent power.

Further Biological and Chemical Aspects of Host Selection by Scolytus multistriatus1

By use of a newly developed bioassay technique, biting responses by Scolytus multistriatus (Marsham) were oriented and initiated by the sublimable fraction of a benzene extract of elm twig bark at distances up to 17.5 mm on sucrose-treated discs. The residue (nonsublimable fraction) was significantly less active than either the original benzene extract or the sublimate. However, feeding on discs treated directly with the benzene extract or the nonsublimable fraction was much greater than on discs so treated with the sublimate fraction. Thus, the sublimate, while evoking strong orientation responses by the beetles, contained very little of the feeding stimulant properties of the benzene extract. Therefore, chemicalsin healthy elm bark show a broad array of biologicalactivity (i.e., short-range orientation, feeding incitation, feeding stimulation, etc.). Interpretation of the experimental results provided new levels of insight to the continuum of behavioral responses by S. multistriatus to these chemicals.

�ber die biologie blutsaugender simuliiden (diptera)

Swarming behaviour of the mammalophilic simuliids Wilhelmia equina, W. salopiensis and Boophthora erythrocephala is closely related to sex-finding. Long-range orientation occurs by optically directed swarming of the ♂♂ towards a dark marker above them contrasting with the bright sky. ♀♀ flying directly to the same marker or the bigger object carrying it, e.g. a tree, are visually recognized by the ♂♂ at a short distance (short-range orientation).