Asymmetric Phenomena Research Articles

On the effect of the local overall interaction on the postbuckling of uniformly compressed channels

On the basis of the general theory of elastic stability due to Koiter, postbuckling analysis of simply supported channels under uniform compression is performed. Attention is essentially focused on local/eularian and local/flexural-torsional simultaneous bucklin modes interaction. The column is treated as a plate assemblage. Linearized expressions for the displacement field are employed while assuming strain-displacements relationships that are linear for the curvatures and up to second order terms for the in-plane strains. The total potential energy is hence written up to third order terms in order to investigate asymmetric buckling phenomena. A discrete model is developed through an automatic procedure of algebraic manipulation, and an extensive parametric analysis is performed. After determining the range of geometric parameters which characterize different types of interaction, it is found that in the postbuckling range the local/eulerian interaction is more dangerous than the local/flexural-torsional one, due to the column higher imperfection sensitivity.

Directional hypothesis: Late stage preearthquake loading may often be asymmetric

Spatial patterns of seismicity before some mainshocks appear skewed to one side or toward one end of the pending surface of rupture. Several examples of thrust‐type earthquakes, for example, indicate stronger patterns of prior seismicity within the overthrusting block. Similarly some aftershock patterns appear skewed to one side of the rupture surface or in a direction away from the location of prior seismicity. For some earthquakes, therefore, the zones of most significant activity before and after the mainshock do not coincide and, thus, are difficult to explain in terms of loading processes or physical properties that are completely symmetric about the plane of rupture. Furthermore, there are some indications that these asymmetric phenomena may repeat in the same or in nearby locations. These observations appear to be explainable in terms of either: (1) an asymmetric distribution of rock properties about the fault zone with consequent asymmetric seismic response to stress accumulation, or (2) a fundamental directionality to the process of tectonic loading resulting possibly from earlier crustal or plate movement in a nearby region. These two explanations are not incompatible and may in fact be related.

Metal catalysis in organic reactions. 12. Asymmetric induction phenomena in the isomerization of racemic 1-alkenes by chiral aluminum solvate-nickel systems

Metal catalysis in organic reactions. 12. Asymmetric induction phenomena in the isomerization of racemic 1-alkenes by chiral aluminum solvate-nickel systems

Alkyl metal asymmetric reduction. 11. The reaction of α,β-unsaturated ketones with β-branched trialkylaluminium compounds.

The reduction of a series of α,β-unsaturated ketones has been studied under various experimental conditions, by using β-branched trialkylalanes. Asymmetric induction phenomena are observed when optically active trialkylalanes are used.

Optically active alternating copolymers of maleic acid and alkylvinylethers

Alternating copolymers of maleic acid (MAc) with optically active alkylvinylethers (RVE)[R = (S)-1-methylpropyl, (R)-1-methylbutyl, (S)-2-methylbutyl, (S)-3-methylpentyl, (S)-4-methylhexyl, (S)-1-methylheptyl and (S)-3,7-dimethyloctyl] were obtained by hydrolysis in aqueous alkaline medium of the corresponding copolymers with maleic anhydride (MAn). i.r. Absorption spectra, viscosity and potentiometric titration curves are described as well as u.v., ORD and CD spectra recorded in ethanol and water. Conductometric titrations in non-aqueous medium confirm the alternance of dicarboxylic and ethereal structural units. It is shown that the nature of alkyl substituents strongly affects the ionization process of the first carboxylic group. The u.v. bands connected with the n → π ∗ electronic transitions of carboxylic chromophores are optically active and the ellipticities of the dichroic bands around 215 nm depend on the position of the asymmetric carbon atoms present in the side chain. Moreover for copolymers with ethereal structural unit containing an asymmetric carbon atom α with respect to the oxygen atom, the rotatory strength of such bands is dependent on the length of the alkyl substituents for measurements carried out in water, whilst no significant dependence is evident in measurements performed in ethanol. No ordered secondary structure is considered to account for these features which are probably due to asymmetric induction phenomena involving optically active side chains.

Characteristics of Ovonic Threshold Switches with Crystalline Semiconductor Electrodes

The letter describes asymmetric threshold-switching phenomena observed on thin films of Te40As37Ge7Si18 (0.2–1.9 μ), deposited by flash evaporation on crystalline Ge, and surface probed by means of a pyrolytic graphite counterelectrode. ``Dynamically tristable'' systems can be made in this way. The asymmetries are reversed for n- and p-type Ge. Suitably biased systems can be switched by illumination. The differences between the present results and those obtained on conventional threshold switches with two graphite electrodes call for an interpretation in terms of electronic-interface phenomena.

New Dynamic Aspects of Intertropical F2 Ionization

Diurnal changes in F2 ionization distribution as measured during June and July 1966 over the Tamanrasset meridian reveal two types of asymmetric phenomena distorting the crest‐and‐trough system (formerly known as the equatorial F2 ionization anomaly). The first type corresponds to a general time variation of the latitude asymmetry. Our observations yield four independent parameters of this asymmetry; for 80% of the time, the variation can be attributed to ion drag due to a time‐varying meridian air wind. Magnetic activity is correlated with the amplitude of this wind, and the low‐altitude thermospheric circulation is discussed. Day‐to‐day fluctuations of the diurnal evolution pattern suggest a possible long‐term control of the equatorial electric field by the general dynamo current system. A second type of asymmetry shows more intense, local, and short‐lived phases superimposed on the fountain and neutral wind fluctuations. It has the character of a transitory forced‐diffusion process. We believe that the factor responsible is electron temperature gradients produced by conjugate photoelectron heating.

On the polarisation of X-rays compared with their power of exciting high velocity cathode rays

1. The discovery of polarisation of Röntgen rays was suggested by the ether pulse theory, and gave this theory a good support. But, on the other hand, the theory meets with many difficulties when we are going to account for a number of other properties of these rays which recent investigation has brought to light. Sir J. J. Thomson has tried to make the ether pulse theory consistent with observations by introducing new properties for the pulse-medium, and assumes that the ether has a structure, and that the energy radiating from the pulse centre is transmitted along “lines of force” with undiminished intensity. Prof. W. H. Bragg has assumed, in the so-called “neutral pair theory,” that the rays are of a corpuscular nature. For a fuller discussion of the arguments in favour of this view I must refer to Prof. Bragg’s papers. I shall here confine myself to mentioning that one of the chief difficulties on the ether pulse theory is to explain the properties of secondary cathode rays, as the latter, on account of the relation existing between their velocity and the hardness of the bulb, must be supposed to get their energy from the exciting X-rays. What may be said to offer some difficulty to the neutral pair theory is the existence of polarisation, and although Bragg has called attention to the fact that the neutral pairs possess all properties which are necessary to produce asymmetric phenomena of the kind termed polarisation, there still remains some difficulty in explaining that the polarisation is able to make itself felt already in the primary beam, and to explain why certain directions of spin of the doublet should be more likely to occur than others.