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Historically, alloy development with better radiation performance has been focused on traditional alloys with one or two principal element(s) and minor alloying elements, where enhanced radiation resistance depends on microstructural or nanoscale features to mitigate displacement damage. In sharp contrast to traditional alloys, recent advances of single-phase concentrated solid solution alloys (SP-CSAs) have opened up new frontiers in materials research. In these alloys, a random arrangement of multiple elemental species on a crystalline lattice results in disordered local chemical environments and unique site-to-site lattice distortions. Based on closely integrated computational and experimental studies using a novel set of SP-CSAs in a face-centered cubic structure, we have explicitly demonstrated that increasing chemical disorder can lead to a substantial reduction in electron mean free paths, as well as electrical and thermal conductivity, which results in slower heat dissipation in SP-CSAs. The chemical disorder also has a significant impact on defect evolution under ion irradiation. Considerable improvement in radiation resistance is observed with increasing chemical disorder at electronic and atomic levels. The insights into defect dynamics may provide a basis for understanding elemental effects on evolution of radiation damage in irradiated materials and may inspire new design principles of radiation-tolerant structural alloys for advanced energy systems.
The general adaptations of the species are described in relation to the environment of its natural distribution and are shown to be well suited to its use as an exotic in forestry. What is known of natural stand dynamics has little relevance to the cultivation of the species in pure plantations but the interaction with climate and soils is important in determining the limits to its growth and in prediction of productivity. Atmospheric humidity, windiness and accumulated temperature appear to be the most influential climatic variables and, given adequate soil conditions, can be used to give good estimates of potential production. Sitka spruce flowers freely and regenerates readily, demonstrating its ability to survive unaided in British conditions.
Alnus rubra growing in the field in Scotland is nodulated effectively by local strains of Frankia. Strains which have been isolated from Alnus rubra at Lennox Forest show different growth medium requirements and colony morphology compared with isolates from Alnus glutinosa and several different strains have been isolated from the same locality. Preliminary evidence suggests that some spore negative, northwest American Frankia strains may be more effective than local spore positive crushed nodule inoculum for nitrogen-fixation in Alnus rubra.
On the moderately fertile clay soil of Lennox Forest, a mixed plantation of alternate Picea silchensis and Alnus rubra showed no improvement in growth of spruce compared with pure spruce plots. However, the presence of alder increased upper soil nitrogen status by 585 kg ha ' which approximates the standard 150 kg N ha 'of fertiliser nitrogen applied in practice to nitrogen deficient stands at about 5-year intervals. Although the alder had penetrated the subsoil, there was no apparent effect on spruce rooting depth in the mixed stands in this high clay soil. In addition to nitrogen content, the total phosphorus of the upper soil horizons was improved in the mixed plots by an estimated 3–6 kg ha -1 y 1 and it is suggested that this phosphorus may be brought from the subsoil by the deeper rooting alder and deposited on the surface in its litter.
Although improved growth of spruce in mixture with Alnus rubra is only likely where pure spruce stands are stressed for nutrients, the potential benefits of symbiotic nitrogen-fixation in silvicultural practice make it desirable to investigate other species and provenances of Alnus suited to British conditions, to achieve maximum symbiotic fixation of nitrogen by selection and inoculation with superior strains of Frankia and to include such plants in trials of mixtures on sites where nitrogen-availability may be critical.
The dogwhelk Nucella lapillus experienced localized extinction in the 1980s and 1990s due to the use of tributyltin (TBT) antifoulants, causing imposex in females. The aim of this study was to establish the extent of the return of the species across the mainland coast of central southern England as TBT use has been progressively restricted, and to quantify the extent of imposex impact on the populations present. We surveyed from Poole to Selsey where isolated populations had become extinct, and the Isle of Wight where some populations had persisted. We found evidence that since TBT restrictions, recolonization and colonization by N. lapillus has been rapid. By 2007–2008, of the eleven surveyed mainland sites, seven were colonized, although indications of reduced imposex impacts were mixed. Distribution had also extended on the Isle of Wight and populations were larger with less imposex impact in sites with long term populations. The lack of continuous suitable habitat blocks and the hydrodynamic complexity of the region, leads us to hypothesize that recovery has been facilitated by man-made structures which may be acting as ‘stepping stones’. Populations that have become established on engineered structures such as sea walls, breakwaters and rock groynes demonstrate accelerated recovery in the region as TBT in the environment has generally declined. Sites with suitable substrates and food sources near to ports were either not recolonized or had small populations with imposex evident. For species with a short pelagic larval stage or with direct development, population connectivity between patches of harder substrata along hydrodynamically complex coastlines may be greater than previously thought.
Reaction of chlorosilanes with sheet silicates, such as the naturally occurring apophyllite, [Ca4Si8O2O(F, OH).8H2O] results in the formation of sheet organofunctional siloxane polymers. Similarly, reaction of chlorosilanes with the tube silicate K2CuSi4O10results in the formation of tube organofunctional siloxane polymers. Representative polymers have been characterized by XRD, KR, XPS and solid state 29Si NMR. The interlayer spacing of the sheet polymers varies with the type of the group pendent on the sheet. When the organofunctional pendent groups of the sheet polymers contain reactive sites, further reactivity can be demonstrated with heterogeneous reactions such as hydrosilation. The sheet polymers behave as very effective thickeners of siloxane fluids. Dispersions of them in siloxane fluids exhibit thixotropic properties. The organosilicon polymers have the potential to show useful chemical, thermal, rheological and mechanical properties
High flux composite hollow fiber membranes for brackish water desalination based on the interfacial polymerization of a cross-linked polyamide salt rejecting layer onto a semi-permeable hollow fiber support have been developed. These hollow fiber membranes exploit the advantages of using a thin-film composite reverse osmosis membrane (higher flux and salt rejection) with the higher surface area/volume ratio of hollow fiber membrane elements. The composite hollow fiber membranes were prepared by coating a polysulfone hollow fiber with a polyamide salt rejecting layer based on the interfacial polymerization reaction between m-phenylenediamine and trimesoyl chloride/isophthaloyl dichloride. The RO figures-of-merit of these composite polyamide hollow fiber membranes were evaluated for the desalination of a synthetic brackish water feed (2,000 ppm NaCl) at 225 psi over a 60 hour period. After an initial break-in period in which the flux declined 30% due to membrane compaction, the stabilized RO figures-of-merit for these hollow fiber membranes were a water flux of 280 L/m2·day and a salt rejection of 99.1%. Based on the water flux and packing density of the membrane, it is estimated that the stable production of potable water of a hollow fiber membrane element containing these composite membranes will be between 20 and 30% greater than that of a similarly sized spiral wound brackish water membrane element.
Demand for integration of optoelectronic functionality (e.g., optical interconnects) with silicon complementary metal oxide semiconductor (CMOS) technology has for many years motivated the investigation of low temperature (∼ 450°C) germanium deposition processes that may be integrated in to the back-end CMOS process flow. A common challenge to improving the germanium quality is the thermal budget of the in-situ bake, which is used to reduce defect forming oxygen and carbon surface residues. Typical cleaning temperatures to remove significant concentrations of oxygen and carbon have been reported to be approximately 750°C for thermal hydrogen bakes in standard chemical vapor deposition chambers. Germanium device performance using lower peak in-situ cleans (i.e., ∼450°C) has been hampered by additional crystal defectivity, although epitaxy is possible with out complete removal of oxygen and carbon at lower temperatures.
Plasma enhanced chemical vapor deposition (PECVD) is used to reduce the processing temperature. Hydrogen plasma assisted in-situ surface preparation of epitaxy has been shown to reduce both carbon and oxygen concentrations and enable epitaxial growth at temperatures as low as ∼150°C. The hydrogen is believed to help produce volatile Si-O and H2O species in the removal of oxygen, although typically this is not reported to occur rapidly enough to completely clear the surface of all oxygen until ∼550°C. In this paper, we describe the use of an in-situ argon/germane high density plasma to help initiate germanium epitaxy on silicon using a peak temperature of approximately 460°C. Germanium is believed to readily break Si-O bonds to form more volatile Ge-O, therefore, argon/germane plasmas offer the potential to reduce the necessary in-situ clean temperature while obtaining similar results as hydrogen in-situ cleans. To the authors knowledge this report is also the first demonstration of germanium epitaxy on silicon using this commercially available high density plasma chamber configuration instead of, for example, remote or electron cyclotron resonance configurations.
Middle Archaic earthen mound complexes in the lower Mississippi valley are remote antecedents of the famous but much younger Poverty Point earthworks. Watson Brake is the largest and most complex of these early mound sites. Very extensive coring and stratigraphic studies, aided by 25 radiocarbon dates and six luminescence dates, show that minor earthworks were begun here at ca. 3500 B.C. in association with an oval arrangement of burned rock middens at the edge of a stream terrace. The full extent of the first earthworks is not yet known. Substantial moundraising began ca. 3350 B.C. and continued in stages until some time after 3000 B.C. when the site was abandoned. All 11 mounds and their connecting ridges were occupied between building bursts. Soils formed on some of these temporary surfaces, while lithics, fire-cracked rock, and fired clay/loam objects became scattered throughout the mound fills. Faunal and floral remains from a basal midden indicate all-season occupation, supported by broad-spectrum foraging centered on nuts, fish, and deer. All the overlying fills are so acidic that organics have not survived. The area enclosed by the mounds was kept clean of debris, suggesting its use as ritual space. The reasons why such elaborate activities first occurred here remain elusive. However, some building bursts covary with very well-documented increases in El Niño/Southern Oscillation events. During such rapid increases in ENSO frequencies, rainfall becomes extremely erratic and unpredictable. It may be that early moundraising was a communal response to new stresses of droughts and flooding that created a suddenly more unpredictable food base.
We report the clinical, microbiological, and epidemiological features of an emerging serotype, Shigella boydii 20. We interviewed patients about symptoms, and history of travel and visitors during the week before illness onset. Seventy-five per cent of the 56 patients were Hispanic. During the week before illness onset, 18 (32%) travelled abroad; 17 (94%) had visited Mexico. Eight (21%) out of 38 who had not travelled had foreign visitors. There were eight closely related patterns by PFGE with XbaI. S. boydii 20 may be related to travel to Mexico and Hispanic ethnicity. Prompt epidemiological investigation of clusters of S. boydii 20 infection may help identify specific vehicles and risk factors for infection.
In 1995, Salmonella Enteritidis (SE) cases in the state of Utah increased fivefold. Isolates were
identified as phage type 4 (PT4). Risk factors and sources of infection were investigated in two
case-control studies, a traceback of implicated foods, and environmental testing. Forty-three
patients with sporadic infections and 86 controls were included in a case-control study of risk
factors for infection. A follow-up case-control study of 25 case and 19 control restaurants
patronized by case and control patients examined risks associated with restaurant practices. In
the first case-control study, restaurant dining was associated with illness (P = 0·002). In the
follow-up case-control study, case restaurants were likelier to use > 2000 eggs per week
(P < 0·02), to pool eggs (P < 0·05), and to use eggs from cooperative ‘A’ (P < 0·009). Eggs
implicated in separately investigated SE PT4 outbreaks were traced to cooperative ‘A’, and SE
PT4 was cultured from one of the cooperative's five local farms. We conclude that SE PT4
transmitted by infected eggs from a single farm caused a fivefold increase in human infections
The central theme of this session is the changing relationship between “orthodox” (i.e., mainstream, neoclassical) and “heterodox” economics, especially in the USA, during the past two or three decades. Economics is such a large and heterogeneous discipline that it cannot be characterized both briefly and accurately. Alongside the growth of formalization and mathematization, and the high degree of uniformity in the undergraduate and graduate curricula and in the leading textbooks, there are also within the subject a number of dissenting or deviant doctrinal schools, rival methodological approaches, and innovative developments designed to remedy its defects and/or overcome its limitations. Moreover, many of the outspoken criticisms of the status quo, proposed remedies, and innovations, originate with or are endorsed by prominent economists with impeccable professional credentials. Indeed, in some cases their contributions threaten the discipline's foundations and can, therefore, be considered a species of “orthodox subversion.”