Experience with statically-generated proxies for facilitating Java runtime specialisation

Issues pertaining to mechanisms which can be used to change the behaviour of Java classes at runtime are discussed. The proxy mechanism is compared to, and contrasted with other standard approaches to this problem. Some of the problems the proxy mechanism is subject to are expanded upon. The question of whether statically-developed proxies are a viable alternative to bytecode rewriting was investigated by means of the JavaCloak system, which uses statically-generated proxies to alter the runtime behaviour of externally-developed code. The issues addressed include ensuring the type safety, dealing with the self problem, object encapsulation, and issues of object identity and equality. Some performance figures are provided which demonstrate the load the JavaCloak proxy mechanism places on the system

Radiation trapping in coherent media

We show that the effective decay rate of Zeeman coherence, generated in a Rb87 vapor by linearly polarized laser light, increases significantly with the atomic density. We explain this phenomenon as the result of radiation trapping. Our study shows that radiation trapping must be taken into account to fully understand many electromagnetically induced transparency experiments with optically thick media

Environments Explored: An In-Depth Analysis of Soil Movement in Northern Iceland

The initial colonization of Iceland in the late 9th century had a profound impact on the fragile environment of the North Atlantic island. Settlement and the introduction of livestock resulted in widespread erosion and the replacement of woodlands with meadows and heaths. Changes in the environment are assumed to have played a role in determining settlement patterning and subsistence strategies. While marginal highland areas were most seriously affected, resulting in farmstead abandonment, the nature of changes in lowland areas and their impact on the productivity of individual farms is poorly understood. Local patterns of landscape change in Iceland could be highly varied as erosion in one area often resulted in soil accumulation in another. Focusing on the lowland region of Hegranes in northern Iceland, this thesis examined patterns of erosion and sediment accumulation in relation to fluctuations in farmstead size during three periods of occupation: pre-1104 A.D., 1104-1300 A.D., and post-1300 A.D. This study considers when and where soil erosion and accumulation occurred and its implications for farmstead activity and the long-term viability and productivity of individual farms and households

Phosphorus Fertilization for Wheat Production on Blackland and Grand Prairie Soils.

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Phosphorus Fertilization for Grain Sorghum Production in the Texas Blacklands.

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Spectral Narrowing via Quantum Coherence

We have studied the transmission of an optically thick Rb vapor that is illuminated by monochromatic and noise broaden laser fields in Lambda configuration. The spectral width of the beat signal between the two fields after transmission through the atomic medium is more than 1000 times narrower than the spectral width of this signal before the medium.Comment: 4 pages, 4 figure

Applying robotics to HAZMAT

The use of robotics in situations involving hazardous materials can significantly reduce the risk of human injuries. The Emergency Response Robotics Project, which began in October 1990 at the Jet Propulsion Laboratory, is developing a teleoperated mobile robot allowing HAZMAT (hazardous materials) teams to remotely respond to incidents involving hazardous materials. The current robot, called HAZBOT III, can assist in locating characterizing, identifying, and mitigating hazardous material incidents without risking entry team personnel. The active involvement of the JPL Fire Department HAZMAT team has been vital in developing a robotic system which enables them to perform remote reconnaissance of a HAZMAT incident site. This paper provides a brief review of the history of the project, discusses the current system in detail, and presents other areas in which robotics can be applied removing people from hazardous environments/operations

Light scattering study of the “pseudo-layer” compression elastic constant in a twist-bend nematic liquid crystal

The nematic twist-bend (TB) phase, exhibited by certain achiral thermotropic liquid crystalline (LC) dimers, features a nanometer-scale, heliconical rotation of the average molecular long axis (director) with equally probable left- and right-handed domains. On meso to macroscopic scales, the TB phase may be considered as a stack of equivalent slabs or “pseudo-layers”, each one helical pitch in thickness. The long wavelength fluctuation modes should then be analogous to those of a smectic-A phase, and in particular the hydrodynamic mode combining “layer” compression and bending ought to be characterized by an effective layer compression elastic constant Beff and average director splay constant Keff1. The magnitude of Keff1 is expected to be similar to the splay constant of an ordinary nematic LC, but due to the absence of a true mass density wave, Beff could differ substantially from the typical value of ∼10⁶ Pa in a conventional smectic-A. Here we report the results of a dynamic light scattering study, which confirms the “pseudo-layer” structure of the TB phase with Beff in the range 10³–10⁴ Pa. We show additionally that the temperature dependence of Beff at the TB to nematic transition is accurately described by a coarse-grained free energy density, which is based on a Landau-deGennes expansion in terms of a heli-polar order parameter that characterizes the TB state and is linearly coupled to bend distortion of the director