Dislocations in uniaxial lamellar phases of liquid crystals, polymers and amphiphilic systems

Dislocations in soft condensed matter systems such as lamellar systems of polymers, liquid crystals and ternary mixtures of oil, water and surfactant (amphiphilic systems) are described in the framework of continuum elastic theory. These systems are the subject of studies of physics, chemistry and biology. They also find applications in the industry. Here we will discuss in detail the influence of dislocations on the bulk and surface properties of these lamellar phases. Especially the latter properties have only been recently studied in detail. We will present the experimental evidence of the existence of screw and edge dislocations in the systems and study their static properties such as: energy, line tension and core structure. Next we will show how does the surface influence the equilibrium position of dislocations in the system. We will give the theoretical predictions and present the experimental results on thin copolymer films, free standing films of liquid crystals and smectic droplets shapes. The surface is deformed by dislocations. These deformations are known as edge profiles. Surface deformations induce elastic interactions between edge dislocations. A new phenonenon discussed in our paper is the fluctuations induced interactions between edge dislocations.At suitable conditions edge dislocations can undergo an unbinding transition. Also a single dislocation loop in a smectic freely suspended film can undergo an unbinding transition. We shall also compute the equilibrium size of the loop contained between two hard walls. Finally we will discuss the dynamical bulk properties of dislocations such as: mobility (climb and glide),permeation, and helical instability of screw dislocations. Lubrication theory will also be discussed.Comment: plain TeX, 65 pages, review for International Journal of Modern Physics

Influence of the electric field on edge dislocations in smectics

The electric field applied perpendicularly to smectic layers breaks the rotational symmetry of the system. Consequently, the elastic energy associated with distortions induced by an edge dislocation diverges logarithmically with the size of the system. In freely suspended smectic films the dislocations in the absence of the electric field are located exactly in the middle of the film. The electric field above a certain critical value can shift them towards the surface. This critical field squared is a linear function of the surface tension and is inversly proportional to the thickness of the film. The equilibrium location of a dislocation in the smectic film subjected to the field is also calculated.Comment: Tex, 13 pages, submitted to J. de Physique II. (permanent e-mail address: [email protected]

Vibration in Planetary Gear Systems with Unequal Planet Stiffnesses

An algorithm suitable for a minicomputer was developed for finding the natural frequencies and mode shapes of a planetary gear system which has unequal stiffnesses between the Sun/planet and planet/ring gear meshes. Mode shapes are represented in the form of graphical computer output that illustrates the lateral and rotational motion of the three coaxial gears and the planet gears. This procedure permits the analysis of gear trains utilizing nonuniform mesh conditions and user specified masses, stiffnesses, and boundary conditions. Numerical integration of the equations of motion for planetary gear systems indicates that this algorithm offers an efficient means of predicting operating speeds which may result in high dynamic tooth loads

Electron capture to continuum in collisions of bare projectiles with Ne targets

Abstract. We have investigated the cusp resulting from electron capture to the continuum of 1.25-5 MeV m u- ' fully stripped hydrogen and oxygen as a function of the collision energy and the detector angular resolution B o. It is revealed that the characteristic cusp shape parameters depend strongly on the experimental resolution. Our experimental data are "pared with the second-order Born theory and the impulse approximation. Both theories mnhrm the 8, dependence of the shape parameters and gjve a reasonable descrip-lion of the cusp asymmetry. However, theory tends to overestimate the absolute cross sections, in particular in the case of oxygen. 1

Seasonal Assessment of Oral Reading Rate Obtained by Rural Elementary Students

Seasonal assessments of oral reading rates were obtained from rural first and second grade elementary students. The rates were obtained by administering reading probes selected from the school\u27s curriculum and administered during the fall, winter, and spring months. The obtained rates were then compared to establish prescriptive for frustration, instructional, and mastery level reading standards. The results indicated that the first grade participants were significantly below frustration and mastery reading levels for the fall and winter assessments respectively. However, the first grade participants\u27 were significantly above the mastery level prescriptive during the spring assessment. The second grade participants were at the frustration level during the fall assessment. At the winter assessment, second grade participants\u27 oral reading rates did not differ significantly from the recommended mastery level prescriptive. However, the spring assessment revealed oral reading rates significantly above the suggested prescriptive for mastery level. Also, changes in seasons were associated with equal increases in oral reading rate. A rationale was presented for why the standard normal learning curve was obtained

Site Factors Influence on Herbaceous Understory Diversity in East Texas Pinus palustris savannas

Longleaf pine (Pinus palustris) savannas were once dominant across the southeastern U.S., including East Texas and parts of western and central Louisiana. The diverse understory associated with these historical savannas may occasionally be seen today, but not often in longleaf pine ecosystems. This project aimed to define east Texas site characteristics that are necessary to support these ecosystems with a dense and diverse herbaceous understory with little to no midstory cover. Fifty-nine plots across three study sites were established to evaluate the influence of overstory cover, basal area, aspect, elevation, and slope on the number of plant genera present. Forest structure and site characteristics had significant effects on the number of plant genera found. The number of genera increased with higher elevation and slope; as elevation increased, there was a decline in basal area and overstory cover, leading to a more diverse, understory layer. In order to re-establish and maintain a diverse, herbaceous understory in longleaf pine savannas, sites with more open canopies and on slopes with the most solar exposure should be given priority, particularly when planting desired understory species