Polymer nematic liquid crystals :: disclination structure and interaction/

Disclinations and inversion walls in the director field of nematic thermotropic liquid crystal polymers (TLCP\u27s) are imaged at high resolution using the lamellar decoration technique of Wood and Thomas. The utility of the lamellar decoration technique has also been greatly extended by using an etch and replication technique to image the director in sections of a bulk sample. The interaction of disclinations in the presence of an applied magnetic or extensional flow field which tends to align the director is studied. At intermediate field strengths, where the disclination separation is comparable to the characteristic length for director field distortions, pairwise interaction no longer dominates, but clusters of disclinations are observed to form. The applied field suppresses fluctuations of the disclination positions which increase the topological dipole moment of a cluster while enhancing those that preserve zero dipole. The applied field tends to minimize the long range distortional energy which is proportional to the square of the dipole moment. As a result, quadrupolar (Lehmann) clusters of disclinations are commonly observed in either magnetically or extensionally flow aligned samples. Many-bodied interaction of disclinations in the absence of an applied field is studied via computer simulation, and the results agree favorably with recent experimental work. The structure of the cores of disclinations has been observed. The core size is on the order of a few molecular lengths, and its structure depends upon polymer architecture. A rigid polymer splays more within the core of a $\pi$ wedge disclination, and an excess of chain ends aggregates. A semi-flexible polymer, in contrast, bends more within the core. Hairpins are not thought to be abundant in the semi-flexible TLCP. The morphology of the TLCP semi-crystalline state has also been examined. It is observed to depend upon the relative primary crystal nucleation and crystal growth rates. The lamellar decoration morphology, where the crystalline lamellae are everywhere perpendicular to the director of the precursor nematic, is favored by rapid nucleation and slow growth. This morphology is unique to TLCP\u27s, but other morphologies are possible. Spherulites have also been grown from the nematic melt. Their growth is favored by slow nucleation and rapid growth

A New Taxonomy of Thin Markets

The traditional conception of a thin market based on transactions volume remains relevant in many agricultural markets but does not adequately frame emerging thin market issues. As non-price means of pricing goods becomes more common, some cash commodity markets have become residual markets. In some of these markets, not only the volume of transactions but also the representativeness of transactions to those on the related contract market is an important issue. This paper develops a concept of thin markets that accounts for this dimension of market thinness and proposes a research agenda related to this topic.Marketing,

The Impacts of Market Structure and Contracts on Agricultural Markets

Experimental markets were used to isolate the effects of market structure and contract design on market outcomes. Preliminary results suggest that market structure drives outcomes, and not necessarily contract design. Future research will replicate experiments and add dimensions of market information.Political Economy,

Perceptual and Adaptation Implications with Display 3-D Spatial Location: Retrofit of HUD on a Tactical Airlift Platform

The retrofitting of a cockpit with a Head-Up-Display (HUD) raises potential accommodation and perceptual issues for pilots that must be addressed. For maximum optical efficiency, the goal is to be able to place every pilot’s eye into the HUD Eye Motion Box (EMB) given a seat adjustment range. Initially, the Eye Reference Point (ERP) of the EMB should theoretically be located on the aircraft’s original cockpit Design Eye Point (DEP) while horizontal and vertical seat adjustment would allow pilots to position their eyes inside the EMB. However, human postures vary, and HUD systems may not be optimally placed. In reality there is a distribution of pilot eyes around the DEP (which is dominant eye dependent) therefore this must be accounted for in order to obtain appropriate visibility of all of the symbology based on photonic characteristics of the HUD. Pilot size and postural variation need to be taken into consideration when positioning the HUD system to ensure proper vision of all HUD symbology in addition to meeting the basic physical accommodation requirements of the cockpit. The innovative process and data collection methods for maximizing accommodation and pilot perception on a new “tactical airlift” platform are discussed as well as the related neurocognitive factors and the effects of information display design on cognitive phenomena

Asteroid 1986 DA: Radar evidence for a metallic composition

Radar observations of the near-Earth asteroid 1986 DA were carried out at the Arecibo Observatory in April 1986, two months after its discovery. Radar results are consistent with the hypothesis that 1986 HA is a piece of NiFe metal derived from the interior of a much larger object that melted, differentiated, cooled and subsequently was disrupted in a catastrophic collision. This 2-km asteroid might be (or have been part of) the parent body of some iron meteorites. Or 1986 DA might share the parentage and/or part of the dynamical history of some meteorites without ever having contributed any of its own ejecta to our meteorite sample. Analysis of the samples returned from 1986 DA might ultimately involve economic considerations. Meteoritic metal is mostly iron with about 8 percent nickel, but also contains substantial concentrations of precious and strategic metals, including approx. 1 ppm of gold and approx. 10 ppm of platinum group elements. If these abundances apply to 1986 DA, it contains some 10(exp 16) g of iron, 10 (exp 15) g of nickel, 10(exp 11) g of platinum group metals, and 10(exp 10) g of gold

Interfacial effects on droplet dynamics in poiseuille flow

Many properties of emulsions arise from interfacial rheology, but a theoretical understanding of the effect of interfacial viscosities on droplet dynamics is lacking. Here we report such a theory, relating to isolated spherical drops in a Poiseuille flow. Stokes flow is assumed in the bulk phases, and a jump in hydrodynamic stress at the interface is balanced by Marangoni and surface viscous forces according to the Boussinesq–Scriven constitutive law. Our model employs a linear equation of state for the surfactant. Our analysis predicts slip, cross-stream migration and droplet-circulation velocities. These results and the corresponding interfacial parameters are separable: e.g., cross-stream migration occurs only if gradients in surfactant concentration are present; slip velocity depends on viscosity contrast and dilatational properties, but not on shear Boussinesq number. This separability allows a new and advantageous means to measure surface viscous and elastic forces directly from the drop interface

We are what we (think we) eat: The effect of expected satiety on subsequent calorie consumption

Varying expected satiety (ES) for equi-calorie portions of different foods can affect subsequent feelings of hunger and fullness and alter consumption. To our knowledge, no study has manipulated ES for an equal portion of the same solid food, appetite has not been measured >3 h and studies have not consistently measure later consumption. It is also unclear whether changes in hunger, fullness or later consumption are related to a physiological response. The aims of this study were to use the same solid food, to measure participants' response over a 4-h inter-meal period, to measure later consumption and to assess whether any effect of ES was related to a physiological (i.e. total ghrelin) response. Using a within-subjects design, 26 healthy participants had their ES for omelettes manipulated experimentally, believing that a 3-egg omelette contained either 2 (small condition) or 4 (large condition) eggs. When ES was higher (large condition) participants ate significantly fewer calories at a lunchtime test meal (mean difference = 69 kcal [± 95% CI 4–136]) and consumed significantly fewer calories throughout the day (mean difference = 167 kcal [± 95% CI 26–309]). As expected, there was a main effect of time on hunger and fullness, but no main effect of ‘portion size’ (p > .05). There was also a significant interaction between time and portion size for hunger. There was no evidence for any significant differences being the result of changes in total ghrelin. Overall, the data suggest that ES for a solid food can be manipulated and that, when given at breakfast, having a higher ES for a meal reduces lunchtime and whole day caloric consumption

High quality waveguides for the mid-infrared wavelength range in a silicon-on-sapphire platform

We report record low loss silicon-on-sapphire nanowires for applications to mid infrared optics. We achieve propagation losses as low as 0.8dB/cm at 1550nm, 1.1 to 1.4dB/cm at 2080nm and < 2dB/cm at = 5.18 microns.Comment: 9 pages, 6 figures, 18 reference