A novel synthetic route to ether-Free metal alkyl precursors

A new synthetic route to metal alkyl precursors has been developed, eliminating ether solvents which have been shown to result in unintentional oxygen incorporation in epitaxial AlGaAs layers. The synthesis is performed in a trialkylamine solvent and the need for an additional adduct purification step is eliminated. The products of triisopropylgallium synthesis solvated by either ethyldimethylamine or triethylamine have been assessed as potential growth precursors for chemical beam epitaxy by¹H NMR spectroscopy, vapor pressure measurements and GaAs growth rate measurements.     

Propagation model for ultrafast signals on superconductingdispersive striplines

The algorithm suitable for the computer-aided design of transmission lines is used to model the propagation of picosecond and subpicosecond electrical signals on superconducting planar transmission lines. Included in the computation of a complex propagation factor are geometry-dependent modal dispersion and the frequency-dependent attenuation and phase velocity which arise as a result of the presence of a superconductor in the structure. The results of calculations are presented along with a comparison to experimental data. The effects of modal dispersion and the complex surface conductivity of the superconductor are demonstrated, with the conclusion that it is necessary to incorporate both phenomena for accurate modeling of transient propagation in strip transmission lines     

Visualizing Time‐Specific Hurricane Predictions,with Uncertainty,from Storm Path Ensembles

The U.S. National Hurricane Center (NHC) issues advisories every six hours during the life of a hurricane. These advisories describe the current state of the storm, and its predicted path, size, and wind speed over the next five days. However, from these data alone, the question “What is the likelihood that the storm will hit Houston with hurricane strength winds between 12:00 and 14:00 on Saturday?” cannot be directly answered. To address this issue, the NHC has recently begun making an ensemble of potential storm paths available as part of each storm advisory. Since each path is parameterized by time, predicted values such as wind speed associated with the path can be inferred for a specific time period by analyzing the statistics of the ensemble. This paper proposes an approach for generating smooth scalar fields from such a predicted storm path ensemble, allowing the user to examine the predicted state of the storm at any chosen time. As a demonstration task, we show how our approach can be used to support a visualization tool, allowing the user to display predicted storm position – including its uncertainty – at any time in the forecast. In our approach, we estimate the likelihood of hurricane risk for a fixed time at any geospatial location by interpolating simplicial depth values in the path ensemble. Adaptivelysized radial basis functions are used to carry out the interpolation. Finally, geometric fitting is used to produce a simple graphical visualization of this likelihood. We also employ a non‐linear filter, in time, to assure frame‐to‐frame coherency in the visualization as the prediction time is advanced. We explain the underlying algorithm and definitions, and give a number of examples of how our algorithm performs for several different storm predictions, and for two different sources of predicted path ensembles.     

Decentralised detection of periodic encounter communities in opportunistic networks

We tackle the problem of individuals being able to self-detect the encounter communities within which they periodically occur. This has widespread applicability, not least for future communication systems where content can be locally shared via wireless opportunistic networking when devices carried by participants come into close range. In this paper, we introduce a comprehensive model and decentralised algorithm to accomplish the detection of periodic communities in opportunistic networks. To the best of our knowledge, this is the first decentralised algorithm for the detection of periodic communities. We investigate the behaviour of our approach both analytically and with real-world data.     

Defensive Spiroketals from Asceles glaber (Phasmatodea): Absolute Configuration and Effects on Ants and Mosquitoes

Insects are the largest and most diverse group of organisms on earth, with over 1,000,000 species identified to date. Stick insects (“walkingsticks” or “phasmids”, Order Phasmatodea) are known for and name-derived from their camouflage that acts as a primary line of defense from predation. However, many species also possess a potent chemical defense spray. Recently we discovered that the spray of Asceles glaber contains spiroketals [a confirmed major component: (2S,6R)-(?)(E)-2-methyl-1,7-dioxaspiro[5.5]undecane, and a tentatively identified minor component: 2-ethyl-1,6-dioxaspiro[4.5]decane] and glucose. In this paper, we: 1) illustrate the identification of spiroketals and glucose in the defense spray of A. glaber by using Nuclear Magnetic Resonance (NMR), Gas Chromatography/Mass Spectrometry (GC/MS), and comparison with a synthetic reference sample; 2) provide the elucidation of the absolute configuration of the major spiroketal in that defense spray; and 3) demonstrate the effect of this compound and its enantiomer on both fire ants (Solenopsis invicta) and mosquitoes (Aedes aegypti).     

Escher: A New Technology Transitioning Model

The Escher model relies on a mix of government and industry funding to identify cross-industry needs and select technologies for maturation and transitioning. The Escher organization serves as a thin layer of management to join end users and the research community in setting standards, directing users to available sites, using uniform community-established criteria to monitor software's effectiveness, and taking advantage of user feedback to identify bugs and other software problems. Additionally, we foresee that Escher increasingly provide a common meeting place where stakeholders can develop a roadmap for the future and discuss common concerns and needs in NESS evolution     

Effect of Various Lubricants and Base Materials on Friction at Ultrahigh Loads

A series of high load, low-speed sliding friction tests was made on eight greases and eighteen dry lubricants at normal unit loads from 10,000 psi to 150,000 psi. Four different substrate materials were used having a range of hardnesses from Rockwell C 18 to Rockwell C 55. The ultimate load capability of both greases and dry films is a function of substrate hardness with the best ultimate load capability being provided by inorganically bonded molybdenum disulfide films with small amounts of graphite added. The coefficient of friction of the greases appears to be an inverse function of substrate hardness and a direct function of the normal load. The coefficient of friction of the dry lubricants is an inverse function of the normal load, but does not appear to be related to the substrate hardness.     

Alkyldimethylpyrazines in the Defensive Spray of <Emphasis Type="Italic">Phyllium westwoodii</Emphasis>: A First for Order Phasmatodea

Phyllium westwoodii is a phasmid insect (Order Phasmatodea) belonging to the Family Phylliidae (leaf insects). These rather large and ornate creatures are known for their morphological resemblance to plant leaves for camouflage. Pyrazines are a common class of compounds used or produced by a wide variety of organisms, even humans. When an individual of P. westwoodii is disturbed, it sprays an opaque liquid from a pair of prothoracic glands, which are utilized by other phasmid species for defense. The current study has found that this liquid contains glucose and a mixture of 3-isobutyl-2,5-dimethylpyrazine, 2,5-dimethyl-3-(2-methylbutyl)pyrazine, and 2,5-dimethyl-3-(3-methylbutyl)pyrazine. This is the first report of pyrazines found in the defensive gland spray of phasmid insects, and the first chemical analysis of glandular material from family Phylliidae.     

利用环境产生电能 创造无电池无线传感器

本文介绍了基于最新半导体器件提供极低的静态电流和一种高效率能量收集解决方案,使分布式传感器网络更易于部署。传感器现在可以用在远程地点,而无需担忧电池寿命。     

An investigation into microwave bonding mechanisms via a study of silicon carbide and zirconia

It is known that the glassy grain-boundary phase present in low-purity aluminas has two primary functions during direct microwave bonding. Firstly, it increases the dielectric loss of the host ceramic, allowing heating to occur; secondly, the bonding mechanism itself has been found to be based on viscous flow of the glassy grain-boundary phase. However, some evidence has also been found for the bonding of individual grains where they come into direct contact across the join line. To investigate the role of grain-boundary phases further, the microwave bonding of two different grades of silicon carbide and one grain of zirconia has been studied. A single-mode resonant cavity operating at 2450 MHz was used for both studies. The temperature and axial pressure were varied and the bonding time was kept to a minimum. Analysis of the resultant bonds indicated that both reaction-bonded silicon carbide and partially stabilized zirconia could be successfully joined using microwave energy with bonding times typically 10 min or less. For reaction-bonded silicon carbide ceramics, the silicon grain-boundary phase softened at the bonding temperature, allowing the butting faces to be "glued" together. Unlike the glassy grain-boundary phase for alumina ceramics, the silicon phase did not allow grain motion but always formed a discrete and continuous layer at the interface, even under optimum joining conditions. The work with zirconia confirmed that it is possible to join ceramics without the presence of a substantial grain-boundary phase. The mechanism is thought to be either solid-state diffusion and/or grain-boundary sliding. © 1998 Kluwer Academic Publishers