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We present simultaneous multiwavelength observations of the intermediate polar PQ Gem (Mason et al. 1992) obtained on 1993 February 18 and 19 using the Hatfield Polarimeter on UKIRT.
The data are folded on the 13.9 m spin period in Fig. 1. The light curves are double peaked at long wavelengths, with dips at phase ~ 0.15 and phase ~0.65, but almost sinusoidal in the U and B bands where the phase ~0.65 dip is absent. The percentage of circular polarisation also varies with the spin cycle, most notably in the I band, with both positive and negative excursions. The peaks in the positive and negative polarisation occur at phase ~ 0.15 and phase ~ 0.65 respectively, approximately coincident with the two intensity dips.
HST UV observations of V795 Her reveal a strong 2.6-h orbital variation in the prominent UV lines, in contrast to earlier (IUE) evidence of a 4.8-h period. Only the C IV line contains a strong blue-shifted, wind formed absorption component. Several lines exhibit a ‘narrow’ absorption feature near rest velocity which may originate in the disk, and a blue-shifted emission feature which accounts for most of the line profile variability.
An overview of the Czech national R&D project HiLASE (High average power pulsed laser) is presented. The project focuses on the development of advanced high repetition rate, diode pumped solid state laser (DPSSL) systems with energies in the range from mJ to 100 J and repetition rates in the range from 10 Hz to 100 kHz. Some applications of these lasers in research and hi-tech industry are also presented.
III Zw2 was observed with XMM-Newton in July 2000. Its X-ray spectrum can be described by a power law of photon index Γ≈1.7 with a Gaussian line at 6.7 KeV. There is no significant evidence of intrinsic absorption within the source or of a soft X-ray excess. Multi-wavelength light curves over a period of 25 years show related variations from the radio to X-rays. We interpret the radio to optical emission as synchrotron radiation, self-absorbed in the radio/millimetre region, and the X-rays as mainly due to Compton up-scattering of low energy photons by the population of high energy electrons that give rise to the synchrotron radiation.
The use of nanoparticle precursors for electronic materials including sulfides, selenides, oxides and the elements has potentially wide ranging implications for improving device properties and substantially reducing the deposition costs. To realize this goal the complex interfacial chemistry of these small particles must be controlled. In this paper we present a number of cases demonstrating the complexity of this chemistry. These include CuInSe2 where the kinetics of phase formation dominate the sintering process; CdTe where sintering proceeds with and without the sintering enhancement of CdCl2, but produces materials different electronically than bulk materials; and the use of compound and elemental nanoparticles ( Ag, Al, Hg-Cu-Te and Sb-Te) for contacts to elemental and compound semiconductors (Si and CdTe).
Acrolepiopsis assectella (Zeller), leek moth, is a widespread and common pest of species of Allium L. (Liliaceae) in the western Palaearctic subregion. The establishment of A. assectella in eastern North America has resulted in economic losses to garlic (Allium sativum L.), leek (Allium porrum L.), and onion (Allium cepa L.) growers, especially to organic producers in eastern Ontario and southern Quebec. Acrolepiopsis assectella was first recorded in the Ottawa area in 1993. By 2010, A. assectella had expanded its range into eastern Ontario, southwestern Quebec, Prince Edward Island, and New York. A bioclimate model, using CLIMEX simulation software, was developed to produce mapped results that closely approximated known distributions for A. assectella in central Europe. This model was then validated with recorded distribution records in eastern Europe, Asia, and North America. Model output predicted that A. assectella will readily survive in southeastern Canada and the eastern United States of America. Other areas potentially suitable for A. assectella include coastal regions of the Pacific Northwest, the interior of southern British Columbia, and north-central Mexico. The continued range expansion of A. assectella into other Allium-growing areas of eastern North America appears to be inevitable. Establishment in these areas presents the risk of substantial production losses to Allium spp. producers.
Impedance spectra (5Hz ‐ 13MHz) were collected during the solid state reaction of Yba2Cu2O6+y from large monosized CuO particles imbedded in a finely divided Y2 O3 /BaCO3 matrix. No particle size effect was observed, but a large temperature effect was observed corresponding to an activation energy of approximately 1.8eV (175kJ/mol) over the range 700‐900°C.
Two β-NiAl plus α -Re alloys with near eutectic composition were produced by rapid solidification and then consolidated through a powder extrusion process. Microstructures of the rapidly solidified, as-consolidated, and deformed alloys were characterized by transmission electron microscopy. Both compression and tensile properties of these alloys were determined over the temperature range of 300–1300 K. The Re additions were found to greatly enhance low and intermediate temperature yield strengths when compared to other β-NiA1 alloys. This enhancement was attributed to a combination of solid solution strengthening, precipitate hardening, and grain size refinement. Above 1200K the strength of these Re-modified alloys was comparable to the binary β-NiAl compound.
Recent results on the diffuse scattering from single crystals of Fe1−xO at high temperatures reveal that the defect structure is in striking agreement with embedded cluster calculations by Ellis et al. The dominant defect is an imperfect 7:2 cluster. Mixtures of this and a larger complex (13:4) can explain the electrical properties. XANES studies of this oxide are in agreement with Ellis' theoretical work. However, in both FOx and MnxO it is not possible to use the shift of the cation K absorption edge to characterize valence. In fact in the latter case the shift passes through a minimum, perhaps indicating the onset of clustering.
Fracture mechanisms in calcium aluminate macro-defect-free-cement were studied by in situ deformation in the TEM. Fracture occurred predominantly at the cement / polymer interface. The toughening mechanism involved crack bridging at the interphase / polymer interface. XPS studies of the chemistry of the interphase revealed it to be made up of an AlOC complex in addition to the amorphous hydration product phase.
Measurements of the bulk electrical properties of cement pastes were made using impedance spectroscopy (IS) and are useful for studying hydration. Normalization of these quantities by dividing out changes in the pore fluid reveals information pertinent to the microstructural development of these materials. In this study, observations are made on the influence of accelerators, retarders and silica fume (SF) on pastes of white and ordinary portland cements (OPC). All systems show variations in the normalized electrical properties at the same degree of hydration, as compared to a control. Changes in the microstructure that are implied by these measurements are consistent with the observations of others.
Layered copper-oxide superconductors exhibit the highest critical transition temperatures of any materials. Yet all of the known double perovskites A′A″B′B″O6 containing copper have a random or rock salt distribution of the B cations with the exception of the unique layered arrangement found in La2CuSnO6. Only the layered arrangement contains the CuO22- planes which are necessary for high-temperature superconductivity. The occurrence of layered or two dimensional structures increases markedly when vacancies are introduced on the oxygen sublattice, as evidenced in Ln2AEmCu2TimO5+3m (Ln = lanthanide, Y: AE = Ba, Ca: 2 ≤ m ≤ 4). Similarities among oxygen-deficient structures, especially those with two-dimensional solid-state features, are discussed. Combined conductivity and thermopower analysis are presented to elucidate their unique internal chemistry, defect structure, and conduction parameters. In particular, data for La2-xSrxCuSnO6 are presented and related to the crystal chemistry of the copper-oxygen layer. These data are compared with La2Ba2Cu2Sn2O11 and La2Ba2Cu2Ti2O11 to illustrate the significance of oxygen vacancies on the properties of the copper oxygen planes. New layered cuprates are discussed including the mixed A-site stoichiometries Ln′Ln″AEmCu2TimO5+3m (Ln = lanthanide, Y: AE = Ba, Ca: 2 ≤ m ≤ 4) which contain the smaller lanthanide (Ln″) ordered between the closely spaced, facing sheets of Cu-O square pyramids.
In-situ high temperature electrical conductivity and thermopower have been measured simultaneously on a number of ordered perovskite-like oxides containing double CUO4/2 sheets. Equilibrium measurements have been conducted as a function of oxygen partial pressure, temperature and chemical substitution in order to understand the relationships between the chemical architecture and the transport and defect properties. Data for LaBa2Cu2NbO8 and LaCa2Cu2GaO7 are presented and compared with those of known triple perovskite superconductors, Y1−xCaxSr2Cu2GaO7 and YBa2Cu3O7−δ, and several quadruple perovskites, Ln′Ln″Ba2Cu2M2O11 (Ln = Lanthanide, Y; M = Sn, Ti). These materials belong to a general family of superconductors which are constructed from similar ‘active’ layers (double perovskite blocks of square-pyramidal copper-oxygen sheets), and interleaved with fixed valence cations in perovskite-like ‘conditioning’ layers. Similarities in the transport properties of the non-superconducting and superconducting materials at elevated temperatures are illustrated, and the amount and types of defects, including carrier concentrations, are correlated with the internal chemistry and inner architecture of each material.
Single phase, pure monocalcium aluminate (CaAl2O4) powders are chemically synthesized at temperatures as low as 900°C. The powders have a specific surface area of approximately 10 m2/g. The hydration kinetics of CaAl2O4 and the morphology of the hydrates are analyzed using electron microscopy techniques
In the microcrystalline regime, the behavior of grain boundary-controlled electroceramics is well described by the “brick layer model” (BLM). In the nanocrystalline regime, however, grain boundary layers can represent a significant volume fraction of the overall microstructure and simple layer models are no longer valid. This work describes the development of a pixel-based finite-difference approach to treat a “nested cube model” (NCM), which more accurately calculates the current distribution in polycrystalline ceramics when grain core and grain boundary dimensions become comparable. Furthermore, the NCM approaches layer model behavior as the volume fraction of grain cores approaches unity (thin boundary layers) and it matches standard effective medium treatments as the volume fraction of grain cores approaches zero. Therefore, the NCM can model electroceramic behavior at all grain sizes, from nanoscale to microscale. It can also be modified to handle multi-layer grain boundaries and property gradient effects (e.g., due to space charge regions).
Using resistor-capacitor networks, sources of experimental artifacts in impedance spectroscopy were investigated, such sources include machine limitations, rig/cabling contributions at high frequencies, and artifacts due to high impedance reference electrodes and their geometrical placement. In the instance of electrode placement, computer simulations with a pixel-based model were in agreement with the experimental observations. Remedies for these artifacts such as rig shielding/grounding, geometrical adjustments, and null corrections are also discussed.
Electrical/dielectric properties of nanocrystalline cerium oxide have been studied using impedance spectroscopy, thermopower, and DC 4-point conductivity. The combined techniques identified the effect of poor electroding on impedance spectra. Incomplete contact between the specimen and the electrode induces an additional arc in the impedance spectra. The additional high resistance feature results from the geometric constriction of current flow at the specimen/electrode interface and can be misinterpreted as a grain boundary response. The defect chemistry, nonstoichiometry, and transport properties were investigated in nanoscale ceria and compared with those of microcrystalline material.
We investigated an international outbreak of Salmonella Agona with a distinct PFGE pattern associated with an Irish Food company (company X) producing pre-cooked meat products sold in various food outlet chains in Europe. The outbreak was first detected in Ireland. We undertook national and international case-finding, food traceback and microbiological investigation of human, food and environmental samples. We undertook a matched case-control study on Irish cases. In total, 163 cases in seven European countries were laboratory-confirmed. Consumption of food from food outlet chains supplied by company X was significantly associated with being a confirmed case (mOR 18·3, 95% CI 2·2–149·2) in the case-control study. The outbreak strain was isolated from the company's pre-cooked meat products and production premises. Sufficient evidence was gathered to infer the vehicles of infection and sources of the outbreak and to justify the control measures taken, which were plant closure and food recall.