Dielectric Properties of the "Twinned" 8H-Hexagonal Perovskite Ba8Nb4Ti3O24

The dielectric properties of dense ceramics of the "twinned" 8H-hexagonal perovskite Ba₈Nb₄Ti₃O₂₄ are reported. Single-phase powders were obtained from the mixed-oxide route at 1325°C and ceramics (>92% of the theoretical X-ray density) by sintering in air or flowing O₂ at 1400°–1450°C. The ceramics are dc insulators with a band gap >3.4 eV that resonate at microwave frequencies with relative permittivity, ɛ_r∼44–48, quality factor, Q × f _r∼21 000–23 500 GHz (at f _r∼5.5 GHz) and temperature coefficient of resonant frequency, TC _f,∼+115 ppm/K.     

Defining a synthetic pheromone blend attractive to male Heliothis subflexa under wind tunnel conditions

Heliothis subflexa males were flown in a wind tunnel to a variety of combinations of synthetic pheromone components admixed on a filter paper disk. Blends containing (Z)-11-hexadecenal (Z11–16:Ald, 1000 ng), (Z)-9-hexadecenal (Z9–16:Ald, 500 ng) and (Z)-11-hexadecenol (Z11–16:OH, 10–500 ng) elicited upwind flight and source contact in 52–69% of males. All these compounds have previously been isolated and identified from female H. subflexa gland extracts and volatile pheromone emissions. Males were not attracted by blends in which Z9–16:Ald was omitted (0% source contact). Similarly, blends lacking Z11–16:OH were unattractive to male H. subflexa (3% or less source contact). Males were extremely sensitive to the presence of Z11–16:OH; however, responding in high numbers (57–69% source contact) to blends containing a dosage of 1% (10 ng) or greater Z11–16:OH. Males were unresponsive to blends in which Z9–16:Ald was replaced with a variety of dosages of (Z)-9-tetradecenal, a secondary component of a closely-related congeneric species, Heliothis virescens. Another compound present in the blend emitted by conspecific females, (Z)-11-hexadecenyl acetate (Z11–16:Ac), did not inhibit H. subflexa males (69% source contact) when added to the three-component mixture (1:0.5:0.1) at a ratio of 0.1 (100 ng) with respect to Z11–16:Ald. These results indicate that Z9–16:Ald and Z11–16:OH are required in addition to Z11–16:Ald to elicit significant levels of upwind flight in H. subflexa males. The effects of Z11–16:Ac are more subtle, but at the dosage tested in these experiments, this compound does not have an antagonistic effect on upwind flight and source location by H. subflexa males.     

Cellulose-binding domains: potential for purification of complex proteins

The endoglucanase CenA and the exoglucanase Cex from Cellulomonasfimi each contain a discrete cellulose-binding domain (CBD),at the amino-terminus or carboxyl-terminus respectively. Thegene fragment encoding the CBD can be fused to the gene of aprotein of interest. Using this approach hybrid proteins canbe engineered which bind reversibly to cellulose and exhibitthe biological activity of the protein partner. Alkaline phosphatase(PhoA) from Escherichia coli, and a ß-glucosidase(Abg) from an Agrobacterium sp. are dimeric proteins. The fusionpolypeptides CenA-PhoA and Abg-CBC_cex are sensitive to proteolysisat the junctions between the fusion partners. Proteolysis resultsin a mixture of homo- and heterodimers; these bind to celluloseif one or both of the monomers carry a CBD, e.g. CenA-PhoA/CenA-PhoAand CenA-PhoA/PhoA. CBD fusion polypeptides could be used inthis way to purify polypeptides which associate with the fusionpartner.     

Synthesis,structure, and characterization of the thorium zirconolite CaZr1-xThxTi2O7 system

A series of zirconolite ceramics with composition CaZr_1-xTh_xTi₂O₇ (Δx = 0.10) were reactively sintered at 1350°C for 20 h, in air (0 ≤ x ≤ 0.60) and 5% H₂/N₂ (0 ≤ x ≤ 0.40). A sample with composition corresponding to x = 0.20 was also produced by hot isostatic pressing (HIP) at 1300°C and 100 MPa for 4 hours. Th⁴⁺ immobilization was most readily achieved under oxidizing conditions, with Th⁴⁺ preferentially incorporated within a pyrochlore-structured phase in the range 0.10 ≤ x ≤ 0.50, yet formation of the zirconolite-4M polytype was not observed. We report the novel synthesis of single-phase pyrochlore with nominal composition CaZr_0.40Th_0.60Ti₂O₇ when targeting x = 0.60. Th⁴⁺ incorporation under reducing conditions produced a secondary Th-bearing perovskite, comprising 24.2 ± 0.6 wt% of the phase assemblage when targeting x = 0.40, alongside 8.8 ± 0.3 wt% undigested ThO₂. Under reducing conditions, powder XRD data were consistent with zirconolite adopting the 3T polytype structure. The sample produced by HIP presented a nonequilibrium phase assemblage, yielding a major phase of zirconolite-2M alongside accessory Th⁴⁺-bearing phases ThTi₂O₆, ThO₂, and perovskite. These data highlight the efficacy of Th⁴⁺ as a Pu⁴⁺ surrogate, with implications for the formation of Zr-stabilized Th-pyrochlore phases as matrices for waste with elevated Th⁴⁺ content.     

An investigation of methods for the on-line estimation of tool wear

The paper examines the use of the measurements of spindle motor power for the estimation of wear and the detection of the end of effective tool life for a vertical milling machine. The measurements are analysed using spectral analysis and the effectiveness of using moving averages, running-means and cumulative sum of the power spectrum values to estimate wear is evaluated. For a specific machine tool (Beaver NC5), workpiece material (stainless steel) and under a particular set of cutting conditions it is shown that (a) there is a strong correlation between the cumulative sum of the power spectral energies and the total flank wear, and (b) the residuals obtained from computing a least squares linear fit to the plot of cumulative sums of the power spectral energies against cutting time clearly indicates when the tool is entering the region of high wear.     

The oxidation behavior of the nimonic alloy PE16 in carbon dioxide at 700–800°C

The oxidation behavior of the nimonic alloy PE16 in carbon dioxide has been examined, at 700–800° C, for periods up to 10,250 hr duration. At all temperatures the oxidation kinetics were pseudoparabolic. The chromium-rich and titanium-bearing oxide scale was adherent, except at 800° C, when 10% spalled. Intergranular oxidation beneath the outer scale resulted in the formation of alumina and to a lesser depth, titanium oxide. The penetration increased parabolically with time and also with temperature, the activation energy being 50 kcal/mole. After oxidation at all temperatures the carbon profiles across the oxidized alloys were determined by nuclear microprobe analysis and indicated three distinct regions. From the gas interface carbon was picked up increasingly in the oxide scale, with a peak concentration (0.1–0.34 wt. %) at the oxide-alloy interface. The carbon level then fell sharply and to the depth of the titanium-bearing intergranular oxide the alloy was decarburized. At this juncture carbon had entered the alloy to a maximum concentration of 0.23–0.50 wt. % and a depth which increased both with temperature and exposure. Carburization is attributed to a crevice corrosion mechanism.     

Predicting the health risks related to whole-body vibration and shock: a comparison of alternative assessment methods for high-acceleration events in vehicles

In this paper, alternative assessment methods for whole-body vibration and shocks are compared by means of 70 vibration samples measured from 13 work vehicles, deliberately selected to represent periods containing shocks. Five methodologies (ISO 2631-1:1997, BS 6841:1987, ISO 2631-5:2004, DIN SPEC 45697:2012 and one specified by Gunston [2011], ‘G-method’) were applied to the vibration samples. In order to compare different evaluation metrics, limiting exposures were determined by calculating times to reach the upper limit thresholds given in the methods. Over 10-fold shorter times to exposure thresholds were obtained for the tri-axial VDV (BS 6841) than for the dominant r.m.s. (ISO 2631-1) when exposures were of high magnitude or contained substantial shocks. Under these exposure conditions, the sixth power approaches (ISO 2631-5, DIN SPEC, G-method) are more stringent than a fourth power VDV method. The r.m.s. method may lead to misleading outcomes especially if a lengthy measurement includes a small number of severe impacts. In conclusion, methodologies produce different evaluations of the vibration severity depending on the exposure characteristics, and the correct method must be selected.     

The natural history and fisheries ecology of Lake Chilwa,southern Malawi

Lake Chilwa produces between zero and 24,000 metric tons of fish per year, making it one of the most productive but variable lakes in Africa. The size of the lake varies seasonally and among years, sometimes drying completely. Its surrounding wetland and floodplain provide habitat for a diversity of birds and economically valuable grasses and reeds. When the lake has water, there is considerable activity on its shores and temporary fishing villages spring up. People move in and out of the lake basin in concert with these seasonal and longer term changes. This paper examines the environmental dynamics of Lake Chilwa and its surrounding wetlands, presents an overview of the socio-economic context of the area and discusses threats to this resilient system that might occur as a result of climate change. We conclude that management of Lake Chilwa must place the lake in the wider economic and ecological system in which it is situated. Ultimately, land-use practices within the basin present more of a threat to the resilience of the fishery and people's livelihoods than overfishing or a strict focus on the lake's resources. These perspectives present significant challenges to conventional fisheries governance.     

Adiabatic quantum optimization with qudits

Most realistic solid state devices considered as qubits are not true two-state systems. If the energy separation of the upper energy levels from the lowest two levels is not large, then these upper states may affect the evolution of the ground state over time and therefore cannot be neglected. In this work, we study the effect of energy levels beyond the lowest two energy levels on adiabatic quantum optimization in a device with a double-well potential as the basic logical element. We show that the extra levels can be modeled by adding additional ancilla qubits coupled to the original logical qubits, and that the presence of upper levels has no effect on the final ground state. We also study the influence of upper energy levels on the minimum gap for a set of 8-qubit spin glass instances.