Effects of Medial Septal Lesions on Action-Outcome Associations in Rats Under Conditions of Delayed Reinforcement.

In operant tasks, control rats maintain high response rates under positive contingencies, when the probability of reinforcement is greater following a response (contingent reinforcement) than during the absence of that response. However, as contingencies approach zero, response rates decrease. In this experiment, under immediate contingent reinforcement, rats with medial septal lesions reduced their response rates, just like controls, when contingencies were shifted from positive toward zero. However, the septal rats were less sensitive to this contingency shift, compared with controls, when there was a 5-s delay between lever presses and contingent reinforcements. This lesion effect appeared to be due to a failure of voluntary response memory, which impaired sensitivity to operant contingencies when there was a delay between action and outcome. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The ESA/NASA SOHO mission interruption: using the STAMP accident analysis technique for a software related ‘mishap’

Mishap investigations provide important information about adverse events and are intended to help avoid any recurrence of previous failures. However, the complexity of many safety critical systems poses new challenges for mishap analysis. Similarly, the recognition that many failures have complex, systemic causes has helped to widen the scope of many mishap investigations. A new generation of mishap analysis techniques has been proposed to help investigators address these problems. For instance, Leveson has recently developed the Systems Theory Accident Modelling and Process (STAMP) approach to address some of the weaknesses associated with previous ‘chain of event’ approaches that can miss the systemic causes of adverse events. There are relatively few examples of the STAMP approach. This paper, therefore, presents the results obtained when two analysts performed an independent application of this technique to analyse the causes, including software problems, which led to the mission interruption of the joint European Space Agency (ESA) and National Aeronautics and Space Administration (NASA) Solar and Heliocentric Observatory (SOHO). Copyright © 2003 John Wiley & Sons, Ltd.     

The composition of beeswax alkyl esters

The alkyl esters of beeswax, after isolation from the unhydrolyzed wax by preparative layer chromatography (PLC), have been analyzed directly by high temperature GLC using 1.5% OV1 as liquid phase. In two commercial wax samples examined the ester homologues are predominantly even carbon numbered ranging from C₃₆ to C₅₄. The principal alkyl esters are C₄₀, C₄₂, C₄₄, C₄₆ and C₄₈. The GLC analysis of the ester hydrolysis products revealed that the variations in ester chain length are produced by variations in the esterified primary alcohol chain lengths. The esterified fatty acid is chiefly hexadecanoic acid. The esterified fatty acids differ in composition from the free fatty acids which are also present in the wax.     

Requirements for an effective reverberation chamber: unloaded or loaded

In this paper, we present two versions of a threshold metric for the purpose of accessing the effectiveness of a reverberation chamber. One metric is based on the chamber quality factor (Q), and the other is based on the volume of the loaded reverberation chamber. These metrics are baseline quantities that must be exceeded in order to have an effective reverberation chamber. These threshold metrics are obtained from two different approaches. The first approach is based on a free-space transmission formulation and the scalar mean power density associated with the "stirred energy" in the chamber and requires that the stirred energy exceeds the unstirred energy throughout most of the chamber volume. The second approach is obtained by requiring that the amplitude of the electric (or magnetic) field satisfies the expected Rayleigh probability density function throughout most of the chamber volume. We present an application of these metrics for the case of a reverberation chamber loaded with spheres composed of lossy materials.     

Efficient and Photostable ZnS‐Passivated CdS:Mn Luminescent Nanocrystals

Efficient and photostable ZnS‐passivated CdS:Mn (CdS:Mn/ZnS core/shell) nanocrystals were synthesized using reverse micelle chemistry. CdS:Mn/ZnS core/shell nanocrystals exhibited much improved luminescent properties (quantum yield and photostability) over organically (n‐dodecanethiol‐) capped CdS:Mn nanocrystals. This is the result of effective, robust passivation of CdS surface states by the ZnS shell and consequent suppression of non‐radiative recombination transitions. The dependence of photoluminescence (PL) intensity has been observed as a function of UV irradiation time for both organically and inorganically capped CdS:Mn nanocrystals. Whereas organically capped CdS:Mn nanocrystals exhibit a significant reduction of PL intensity, CdS:Mn/ZnS core/shell nanocrystals exhibit an increased PL intensity with UV irradiation. XPS (X‐ray photoelectron spectroscopy) studies reveal that UV irradiation of CdS:Mn/ZnS nanocrystals in air atmosphere induces the photo‐oxidation of the ZnS shell surface, leading to the formation of ZnSO₄. This photo‐oxidation product is presumably responsible for the enhanced PL emission, serving as a passivating layer.     

Natural emissions of CO2 from the geosphere and their bearing on the geological storage of carbon dioxide

Carbon dioxide (CO₂) capture and storage has the potential to reduce CO₂ emissions from fossil fuel combustion. Although leakage from monitored CO₂ injection sites has been minimal to non-existent, experience from the natural gas storage industry suggests that, if it becomes a widely deployed technology, leaks may be expected from some storage sites. Natural occurrences of CO₂ in the geosphere, some of which have been exploited, provide insights into the types of emissions that might be expected from anthropogenic CO₂ storage sites. CO₂ emission sites are commonly found in clusters in CO₂-prone geological provinces: the most common natural emissions sites in sedimentary basins consist of carbonated springs and mofettes. These represent at worst only a local hazard. In volcanic and hydrothermal provinces, more energetic emissions may occur due to active supply from degassing magma. These include rare, sudden emissions from fissures and craters that have caused fatalities. It is unlikely that such provinces would be considered for CO₂ storage Major lake overturn events such as occurred at Lake Nyos in 1986 are considered highly unlikely to occur as a result of CO₂ storage, not least because CO₂ levels in lake waters can be monitored and remediated. Natural CO₂ fields indicate that under favourable conditions CO₂ can be retained in the subsurface for millions of years. The main risk from man-made CO₂ storage sites that does not have any close analogy in nature is considered to be a well blowout. A blowout that took place at a natural CO₂ field provides some indication of the likely hazard.     

Sub-wavelength resonators: on the use of metafilms to overcome the λ size limit

Metamaterials - in particular, double negative materials - have been used in the design of electromagnetic resonators as a means to overcome the classical lambda/2 size limitation. The surface equivalent of a metamaterial is a so-called metafilm - a surface distribution of suitably chosen electrically small scatterers. In this paper we illustrate how metafilms can be used to overcome the lambda/2 size limit in order to design resonators of very small dimension. We present expressions that relate the polarisability densities of the scatterers of the metafilm needed to achieve in principle any desired resonator size. To validate the analytical results, comparisons to full-wave simulations of resonators containing various metafilms are shown. The effect of loss is investigated, and it is shown that smaller resonator size is achieved at the expense of lower Q (quality factor). The results can be scaled; that is, the dimensions of the scatterers can range from relatively large to relatively small, depending on the frequencies of interest.     

Salt roasting of suncor oil sands fly ash

Fly ash samples from 25 years of Suncor’s oil sands upgrading operations were tested to determine the effects of time, temperature, and salt addition on vanadium recovery by salt roasting and water leaching. The optimum roasting conditions for “carbon-free” ash were determined to be 2 to 3 hours roasting at 850 °C to 900 °C with NaCl additions of 20 to 30 pct that resulted in vanadium extractions of 75 to 85 pct for all samples tested. Leach solutions contained less than 150 mg/L Al, Fe, Ni, Si, and Ti and typically analyzed 12–20 g/L V, 0.3 to 0.6 g/L Mo, 3.2 g/L K, and 10 g/L Na. Sodium carbonate (100 g/L) was also a selective lixiviant for vanadium and produced 2 to 7 pct higher extractions than water leaching. Characterization tests showed that most of the mineral matter in the Suncor fly ash is initially present as a poorly crystalline aluminosilicate glass, but crystallizes on heating with NaCl to form distinct aluminosilicate (albite and hauyne) and iron-titanium (pseudobrookite and hematite) phases. Water-soluble vanadium and molybdenum compounds are likely formed by reacting with NaCl during this crystallization. These tests indicate that insoluble vanadium and molybdenum are associated with the aluminosilicates and that nickel is associated with the iron-titanium minerals.     

Photoluminescence from terbium doped silica-titania prepared by a sol-gel method

Terbium doped (0.5 at.%) TiO₂-SiO₂ (30%/70%) was prepared by a sol-gel method. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the powder calcined at two different temperatures. At a low temperature of 550 °C an amorphous phase was obtained, but at a higher temperature of 1000 °C, the anatase TiO₂ phase was crystallized in the amorphous SiO₂ phase. Green photoluminescence from ultraviolet excitation was detected after heating to either temperature, but the amorphous sample heated to 550 °C exhibited a higher intensity. X-ray diffraction and photoluminescence excitation data are discussed to explain these observations.     

Diffusion characteristics of boron and phosphorus in polycrystalline silicon

Grain boundary diffusion of dopants (boron and phosphorous) in silicon is discussed. The appropriate models and equations are presented both for semi-infinite and for thin film boundary conditions. Data reported in the literature for both thick and thin samples have generally been analyzed using models appropriate to diffusion in a homogeneous semi-infinite substrate. These data were reanalyzed using the appropriate boundary conditions and a more realistic model of the inhomogeneous nature of diffusion in polycrystalline samples. It was shown that, even though the relation between diffusion depth and time may be the same from bulk and grain boundary models, the diffusion coefficients determined from assuming the homogeneous semi-infinite solid may be several orders of magnitude in error for the pre-exponential factor, and the activation energy will also be wrong. Grain boundary diffusion coefficients for arsenic, boron and phosphorus in silicon were determined.