High-Tc bolometers with silicon-nitride spiderwebsuspension for far-infrared detection

High-Tc GdBa2Cu3O7-δ (GBCO) superconducting transition edge bolometers with operating temperatures near 90 K have been made with both closed silicon-nitride membranes and patterned silicon-nitride (SiN) spiderweb-like suspension structures. As a substrate silicon-on-nitride (SON) wafers are used which are made by fusion bonding of a silicon wafer to a silicon wafer with a silicon-nitride top layer. The resulting monocrystalline silicon top layer on the silicon-nitride membranes enables the epitaxial growth of GBCO. By patterning the silicon-nitride the thermal conductance G is reduced from about 20 to 3 μW/K. The noise of both types of bolometers is dominated by the intrinsic noise from phonon fluctuations in the thermal conductance G. The optical efficiency in the far infrared is about 75% due to a goldblack absorption layer. The noise equivalent power NEP for FIR detection is 1.8 pW/√Hz, and the detectivity D* is 5.4×1010 cm √Hz/W. Time constants are 0.1 and 0.6 s, for the closed membrane and the spiderweb like bolometers respectively. The effective time constant can be reduced with about a factor 3 by using voltage bias. Further reduction necessarily results in an increase of the NEP due to the 1/f noise of the superconductor

Effects of environmental enrichment on behavioral responses to novelty, learning, and memory, and the circadian rhythm in cortisol in growing pigs

Previously we showed that pigs reared in an enriched environment had higher baseline salivary cortisol concentrations during the light period than pigs reared under barren conditions. In the present experiment, it was investigated whether these higher baseline salivary cortisol concentrations were a real difference in cortisol concentration or merely represented a phase difference in circadian rhythm. The effects of different cortisol concentrations on the behavioral responses to novelty and learning and long-term memory in a maze test were also studied in enriched and barren housed pigs. At 9 weeks of age enriched and barren housed pigs did not differ in baseline salivary cortisol concentrations nor in circadian rhythm, but at 22 weeks of age barren housed pigs had a blunted circadian rhythm in salivary cortisol as compared to enriched housed pigs. The differences in baseline salivary cortisol concentrations between enriched- and barren-housed pigs are age-dependent, and become visible after 15 weeks of age. Enriched- and barren-housed piglets did not differ in time spent on exploration in the novel environment test. Barren-housed pigs had an impaired long-term memory in the maze test compared to enriched-housed pigs; however, no differences in learning abilities between enriched- and barren-housed pigs were found. Because blunted circadian cortisol rhythms are often recorded during states of chronic stress in pigs and rats or during depression in humans, it is suggested that the blunted circadian rhythm in cortisol in barren-housed pigs similarily may reflect decreased welfare.

Analysing the effects of travel information on public transport traveller’s decision making and learning

This thesis examines the effect of travel information on a public transport traveller’s decision making over time. It investigates whether the effect of information is sustained over time and is affected by its type and reliability. It is postulated that the traveller will attain better decision outcomes over time, and this process is reinforced when given information. It is postulated that dynamic information would produce the best outcomes, followed by static information and no information. A series of computer-based experiments, in which the participants made hypothetical trips by public bus under various travel information and operating conditions, were conducted. At the aggregate level, the hypothesised relationships are not observed at a statistically significant level. At the disaggregate level, day-to-day decisions are shown to relate significantly to the outcome of the previous day, with the participant more likely to seek a more rewarding but riskier choice if the previous day sees no adverse outcome, and vice-versa. When the information is static, decision changes are few and incremental. When it is dynamic, these changes are more frequent and pronounced, with choices ‘anchored’ around values provided by the information. Nonetheless, a significant proportion of participants made no or few changes, regardless of information or operating conditions. The findings suggest a higher propensity for some travellers to use dynamic information over static information over time, regardless of reliability. On the other hand, those who acquire information do not necessarily maximise their utility, implying that they do so for other less quantifiable factors. The benefits of information provision could also be further circumscribed by the heterogeneity of responses. This set of findings suggests that assuming travellers respond to information in a utility-maximising and homogeneous manner may over-estimate the effect of information

The Low Quiescent X-Ray Luminosity of the Transient X-Ray Burster EXO 1747-214

We report on X-ray and optical observations of the X-ray burster EXO 1747-214. This source is an X-ray transient, and its only known outburst was observed in 1984-1985 by the EXOSAT satellite. We re-analyzed the EXOSAT data to derive the source position, column density, and a distance upper limit using its peak X-ray burst flux. We observed the EXO 1747-214 field in 2003 July with the Chandra X-ray Observatory to search for the quiescent counterpart. We found one possible candidate just outside the EXOSAT error circle, but we cannot rule out the possibility that the source is unrelated to EXO 1747-214. Our conclusion is that the upper limit on the unabsorbed 0.3-8 keV luminosity is L < 7E31 erg/s, making EXO 1747-214 one of the faintest neutron star transients in quiescence. We compare this luminosity upper limit to the quiescent luminosities of 19 neutron star and 14 black hole systems and discuss the results in the context of the differences between neutron stars and black holes. Based on the theory of deep crustal heating by Brown and coworkers, the luminosity implies an outburst recurrence time of >1300 yr unless some form of enhanced cooling occurs within the neutron star. The position of the possible X-ray counterpart is consistent with three blended optical/IR sources with R-magnitudes between 19.4 and 19.8 and J-magnitudes between 17.2 and 17.6. One of these sources could be the quiescent optical/IR counterpart of EXO 1747-214.Comment: 7 pages, accepted by the Astrophysical Journa

Low noise far-infrared detection at 90 K using high-T(c) superconducting bolometers with silicon-nitride beam suspension

High-T(c) GdBa2Cu3O7-d (GBCO) superconducting transition edge bolometers with operating temperatures near 90 K and receiving area of 1 mm2 have been made with both closed silicon-nitride membranes and patterned silicon-nitride (Si(x)N(y)) spiderweb-like suspension structures. To enable epitaxial growth of the GBCO layer, a thin monocrystalline Si layer is prepared on the silicon-nitride base, using fusion bonding techniques. By pattering the silicon-nitride supporting membrane the thermal conductance G is reduced from 20 to 3.5 μW/K. The noise of both types of bolometers is fully dominated by the intrinsic noise from phonon fluctuations in the thermal conductance G. The optical efficiency in the far infrared is about 75% due to a gold black absorption layer. The optical noise equivalent power (NEP) is 1.8 pW/√Hz, and the detectivity D* is 5.4x1010 cm√Hz/W. Time constants are 0.1 and 0.6 s, for the closed membrane and the spiderweb like bolometers respectively. We have observed an empirical limit for the NEP for this type of bolometers. The effective timeconstant can be reduced with a factor of 3 by using an electronic feedback system or by using voltage bias. A further reduction necessarily results in an increase of the NEP due to the 1/f noise of the superconductor

Bird observations in Severnaya Zemlya, Siberia

Fieldwork in different parts of Severnaya Zemlya in 1985, 1991, 1992 and 1993 and aerial surveys in 1994 revealed a limited bird fauna with a total of 17 breeding species. The most numerous breeding birds are cliff-nesting seabirds, comprising little auk (Alle alle), 10 000-80 000 pairs; kittiwake (Rissa tridactyla), 5000-10 000; black guillemot (Cepphus grylle), 1000-5000; ivory gull (Pagophila eburnea), 1000-2000; and glaucous gull (Larus hyperboreus), 500-1000. They breed all over the archipelago, usually in rather small mixed- or single-species colonies. Arctic tern (Sterna paradisaea) 100-500, and herring gull (Larus argentatus) 1-10, breed as solitary pairs or with a few pairs together. Of tundra birds, only brent goose (Branta bernicla), purple sandpiper (Calidris maritima) and snow bunting (Plectrophenax nivalis) are found breeding on most of the major islands. The other tundra species-red-throated diver (Gavia stellata), king eider (Somateria spectabilis), sanderling (Calidris alba), Arctic skua (Stercorarius parasiticus), long-tailed skua (Stercorarius longicaudus), snowy owl (Nyctea scandiaca) and Lapland bunting (Calcarius lapponicus)-breed in small numbers and in limited areas, often not every year. Of the even fewer mammal species, reindeer (Rangifer tarandus) occurs occasionally, while Arctic fox (Alopex lagopus) and collared lemming (Dicrostonyx torquatus) are locally common in some years

Ultrasensitive TES Bolometers for Space Based FIR Astronomy

We present results from the development of a background limited transition edge sensor (TES) bolometer for the wavelength band 30–60 μm. The bolometer consists of a Ti/Au superconducting thermometer and a Ta radiation absorber deposited on a 200μm×300μm200μm×300μm membrane of SixNySixNy suspended on long, narrow legs. This device is voltage biased and the current through the device is measured by a SQUID amplifier. The thermometer has transition temperature Tc = 108 mKTc = 108 mK and the device is operated from a 70 mK base plate. FIR radiation is coupled into a multimodc horn with entrance aperture of 450 μm, length 4.5 mm and exit aperture of 45 μm, which feeds a metal integrating cavity containing the detector. The radiation band is defined by a pair of lowpass and highpass mesh filters in front of the horn. Here we present measurements of optical noise equivalent power (NEP), optical efficiency, dynamic range and time constant. The results show that measured TES detectors are close to meeting the requirement of the “Band 3” of SAFARI FTS imaging instrument [1] on the SPICA mission [2]

Teleworking practice in small and medium-sized firms: Management style and worker autonomy

In an empirical study of teleworking practices amongst small and medium-sized enterprises (SMEs) in West London, organisational factors such as management attitudes, worker autonomy and employment flexibility were found to be more critical than technological provision in facilitating successful implementation. Consequently, we argue that telework in most SMEs appears as a marginal activity performed mainly by managers and specialist mobile workers

Effect of smoke-free legislation on the incidence of sudden circulatory arrest in the Netherlands

Objective To investigate whether smoke-free legislation in the Netherlands led to a decreased incidence of out-of-hospital sudden circulatory arrest (SCA). Smoke-free legislation was implemented in two phases: a workplace ban in 2004 and an extension of this ban to the hospitality sector on 1 July 2008. Design Weekly incidence data on SCA were obtained from the ambulance registry of South Limburg, the Netherlands. Three time periods were distinguished: the pre-ban period (1 January 2002-1 January 2004), the first post-ban period (1 January 2004-1 July 2008) and the second post-ban period (1 July 2008-1 May 2010). Trends in absolute SCA incidence were analysed using Poisson regression, adjusted for population size, ambient temperature, air pollution and influenza rates. Results A total of 2305 SCA cases were observed (mean weekly incidence 5.3 +/- 2.3 SD). The adjusted Poisson regression model showed a small but significant increase in SCA incidence during the pre-ban period (+0.20% cases per week, p = 0.044). This trend changed significantly after implementation of the first ban (with -0.24% cases per week, p = 0.043), translating into a 6.8% (22 cases) reduction in the number of SCA cases after 1 year of smoke-free legislation. No further decrease was seen after the second smoking ban. Conclusions After introduction of a nationwide workplace smoking ban in 2004, a significant decrease in the incidence of out-of-hospital SCA was seen in South Limburg. Poor enforcement of the 2008 hospitality sector ban may account for the fact that no further decrease in the incidence of SCA was seen at this time