Anomalous magnetotransport in wide quantum wells

We present magneto transport experiments of quasi 3D PbTe wide quantum wells. A plateau-like structure in the Hall resistance is observed, which corresponds to the Shubnikov de Haas oscillations in the same manner as known from the quantum Hall effect. The onsets of plateaux in Rxy do not correspond to 2D filling factors but coincide with the occupation of 3D (bulk-) Landau levels. At the same time a non-local signal is observed which corresponds to the structure in Rxx and Rxy and fulfils exactly the Onsager-Casimir relation (Rij,kl(B) = Rkl,ij(-B)). We explain the behaviour in terms of edge channel transport which is controlled by a permanent backscattering across a system of "percolative EC - loops" in the bulk region. Long range potential fluctuations with an amplitude of the order of the subband splitting are explained to play an essential role in this electron system.Comment: postscript file including 3 figs, 5 page

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]

Conductance Fluctuations in PbTe Wide Parabolic Quantum Wells

We report on conductance fluctuations which are observed in local and non-local magnetotransport experiments. Although the Hall bar samples are of macroscopic size, the amplitude of the fluctuations from the local measurements is close to e^2/h. It is shown that the fluctuations have to be attributed to edge channel effects.Comment: postscript file including 3 figs, 3 pages, Paper presented at 3rd Int. Symposium on "New Phenomena in Mesoscopic Structures" in Maui, Hawaii 199

Initial Development of Surface Fuel Models for The Netherlands

Estimating the spread of wildland fire is growing concern in the Netherlands, where fire events at the wildland urban interface is a growing concern with a changing climate. A multi-year project was initiated in 2012 to obtain field-based fuel measurements to be used to estimate wildland fire spread for surface fire. The overall objective was to develop either custom fuel models or utilize existing Northern American fuel models to fuel conditions in some of the hazardous vegetation in the Netherlands. Over a four-year period, 96 plots were established, a wide variety of fuel parameters measured, and ANOVA (p ≤ 0.1) and Duncan’s MRT used to place these into 56 different vegetation communities. Following multiple permutations in Behaveplus, the 56 communities were consolidated into 28 different fuel models. It was then attempted to use these fuel models as input variables in a Dutch-developed wildland fire spread model. Some fuel models produced similar fire spread, and since they were within relatively similar communities, were combined, resulting in 21 working fuel models. The results of this project will provide land managers, fire brigades and landowners more accurate wildland fire spread estimations, improving safety of the public in this densely populated country. The results of this project will contribute to more accurate and detailed calculations of the NBVM (Dutch wildfire spreadmodel). The NBVM will provide necessary information, to be able to reduce the risk on uncontrollable wildfires, via wildfire prevention measurements and during an incident, to support decision making

Lehmann rotation of cholesteric droplets subjected to a temperature gradient: role of the concentration of chiral molecules

International audienceWe present a systematic study of the Lehmann rotation of cholesteric droplets subjected to a temperature gradient when the concentration of chiral molecules is changed. The liquid crystal chosen is an eutectic mixture of 8CB and 8OCB doped with a small amount of the chiral molecule R811. The angular velocity of the droplets strongly depend on their size and on the concentration of chiral molecules. The Lehmann coefficient is estimated by using three different methods. Our results are consistent with a Lehmann coefficient proportional to the concentration of chiral molecules. We additionally show the existence of a critical size of the droplets below which they change texture and stop rotating

Forage Yields in Turkey Hill Wilderness in East Texas for White-tailed Deer

Wilderness areas are often considered quality areas where natural processes occur without human activity. It is often assumed that these unmanaged areas will provide and support quality wildlife habitat. The objective of this study was to evaluate the forage production and stocking potential of an unmanaged wilderness area in east Texas. Four different community types were evaluated for forage yield, forage availability, and browse utilization for white-tailed deer. Results show that although a wide range of forage yields were measured in the spring, summer forage yield did not differ among the various communities. Availability also differed between community types, but utilization within each community appears to be lower than what could be supported

Plastid redox state and sugars: Interactive regulators of nuclear-encoded photosynthetic gene expression

Feedback regulation of photosynthesis by carbon metabolites has long been recognized, but the underlying cellular mechanisms that control this process remain unclear. By using an Arabidopsis cell culture, we show that a block in photosynthetic electron flux prevents the increase in transcript levels of chlorophyll a/b-binding protein and the small subunit of Rubisco that typically occurs when intracellular sugar levels are depleted. In contrast, the expression of the nitrate reductase gene, which is induced by sugars, is not affected. These findings were confirmed in planta by using Arabidopsis carrying the firefly luciferase reporter gene fused to the plastocyanin and chlorophyll a/b-binding protein 2 gene promoters. Transcription from both promoters increases on carbohydrate depletion. Blocking photosynthetic electron transport with 3-(3',4'-dichlorophenyl)-1,1'-dimethylurea prevents this increase in transcription. We conclude that plastid-derived redox signaling can override the sugar-regulated expression of nuclear-encoded photosynthetic genes. In the sugar-response mutant, sucrose uncoupled 6 (sun6), plastocyanin-firefly luciferase transcription actually increases in response to exogenous sucrose rather than decreasing as in the wild type. Interestingly, plastid-derived redox signals do not influence this defective pattern of sugar-regulated gene expression in the sun6 mutant. A model, which invokes a positive inducer originating from the photosynthetic electron transport chain, is proposed to explain the nature of the plastid-derived signal

Efficient reconstruction of dispersive dielectric profiles using time domain reflectometry (TDR)

We present a numerical model for time domain reflectometry (TDR) signal propagation in dispersive dielectric materials. The numerical probe model is terminated with a parallel circuit, consisting of an ohmic resistor and an ideal capacitance. We derive analytical approximations for the capacitance, the inductance and the conductance of three-wire probes. We couple the time domain model with global optimization in order to reconstruct water content profiles from TDR traces. For efficiently solving the inverse problem we use genetic algorithms combined with a hierarchical parameterization. We investigate the performance of the method by reconstructing synthetically generated profiles. The algorithm is then applied to retrieve dielectric profiles from TDR traces measured in the field. We succeed in reconstructing dielectric and ohmic profiles where conventional methods, based on travel time extraction, fail

Dynamic measurements of gear tooth friction and load

As part of a program to study fundamental mechanisms of gear noise, static and dynamic gear tooth strain measurements were made on the NASA gear-noise rig. Tooth-fillet strains from low-contact ratio-spur gears were recorded for 28 operating conditions. A method is introduced whereby strain gage measurements taken from both the tension and compression sides of a gear tooth can be transformed into the normal and frictional loads on the tooth. This technique was applied to both the static and dynamic strain data. The static case results showed close agreement with expected results. For the dynamic case, the normal-force computation produced very good results, but the friction results, although promising, were not as accurate. Tooth sliding friction strongly affected the signal from the strain gage on the tensionside of the tooth. The compression gage was affected by friction to a much lesser degree. The potential of the method to measure friction force was demonstrated, but further refinement will be required before this technique can be used to measure friction forces dynamically with an acceptable degree of accuracy