Search

Ba0.5Sr0.5TiO3 (BST) thin-film capacitor structures with various thicknesses, (50–1200 nm) and different strain conditions (on lanthanum strontium cobalt oxide La0.5Sr0.5CoO3 and strontium ruthenate SrRuO3 buffer layers) were made using pulsed laser deposition, and characterized by x-ray diffraction. The out-of-plane lattice parameter was followed as a function of temperature within the 100–300 K temperature interval. The phase sequence (cubic-tetragonal-orthorhombic-rhombohedral) known to exist in the bulk analog is shown to be strongly affected by both the stress conditions imposed by the buffer layer and the thickness of the BST film itself. Thus, no phase transition was found for the in-plane compressed BST films. On the stress-free BST films, on the contrary, more phase transitions were observed. It appeared that the complexity of structural phase transitions increased as the film thickness in this system was reduced. [ABSTRACT FROM AUTHOR]

Thin film Au/Ba[sub 0.5]Sr[sub 0.5]TiO[sub 3]/SrRuO[sub 3] capacitor structures, with a thickness of dielectric varying between ∼70 and ∼950 nm, were deposited on {001} MgO single-crystal substrates using pulsed laser deposition. Low-field dielectric measurements were performed as a function of temperature and frequency. At all temperatures and frequencies, the dielectric response as a function of thickness was found to adhere reasonably well to the so-called “series capacitor model,” from which nominal “bulk” and “interfacial” capacitance components could be extracted. The bulk component showed weak frequency dependence but strong temperature dependence, with a peak in permittivity and dielectric loss around 250 K and 150 K, respectively. Well above 250 K, reasonable Curie–Weiss behavior was evident. Overall, the extracted bulk component behaved much as would be expected in real bulk ceramics or single crystals lending confidence as to the general applicability of the series capacitor model. The functional behavior of the extracted interfacial capacitance was rationalized as being due to a combination of a thermally independent background, and thermally activated space charge. The activation energy of the space charge (∼0.6 eV) is commensurate with the detrapping of electrons from shallow level traps associated with oxygen vacancies. Importantly, since this component acts in series with the bulk component, the functional analysis performed here implies that the oxygen vacancies lie in a plane parallel to the electrodes. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Thin film parallel-plate capacitor structures with Ba[sub 0.5]Sr[sub 0.5]TiO[sub 3] as the dielectric layer were fabricated using pulsed-laser deposition. The thickness of the dielectric was varied between 7.5 nm and 1.4 µm. Low-field measurements of the dielectric constant showed the system to possess a nonzero interfacial capacitance. Since there is considerable debate about the origin of interfacial capacitance, further functional analysis was performed: zero-field dielectric susceptibility information was extracted using Landau-Ginzburg-Devonshire fitting of saturated polarization loops. This analysis revealed that the zero-field dielectric susceptibility extracted from P-E loops does not possess a finite interfacial component. The origin of interfacial capacitance therefore disappears (albeit temporarily) after a significant field has been applied and then removed during the P-E loop measurement cycle. [ABSTRACT FROM AUTHOR]

Ba0.5Sr0.5TiO3 (BST) thin-films with various thicknesses and different strain conditions were made using pulsed laser deposition and characterized by x-ray diffraction. No phase-transition was found for the in-plane compressed BST films, on the contrary more phase transitions were observed on the stress-free BST films.

Thin film Ba0.5Sr0.5 TiO3 (BST) capacitors of thickness ∼75 nm to ∼1200 nm, with Au top electrodes and SrRuO3 (SRO) or (La, Sr)CoO3 (LSCO) bottom electrodes were fabricated using Pulsed Laser Deposition. Implementing the "series capacitor model," bulk and interfacial capacitance properties were extracted as a function of temperature and frequency. 'Bulk' properties demonstrated typical ceramic behaviour, displaying little frequency dependence and a permittivity and loss peak at 250 K and 150 K respectively. The interfacial component was found to be relatively temperature and frequency independent for the LSCO/BST capacitors, but for the SRO/BST configuration the interfacial capacitance demonstrated moderate frequency and little temperature dependence below T ∼ 300 K but a relatively strong frequency and temperature dependence above T ∼ 300 K. This was attributed to the thermal activation of a space charge component combined with a thermally independent background. The activation energy for the space charge was found to be EA ∼ 0.6 eV suggesting de-trapping of electrons from shallow level traps associated with a thin interfacial layer of oxygen vacancies, parallel to the electrodes. [ABSTRACT FROM AUTHOR]

Background: In response to the COVID-19 pandemic, most countries have introduced non-pharmaceutical interventions, such as stay-at-home orders, to reduce person-to-person contact and break trains of transmission. The aim of this systematic review was to assess the effect of different public health restrictions on mobility across different countries and cultures. The University of Bern COVID-19 Living Evidence database of COVID-19 and SARS-COV-2 publications was searched for retrospective or prospective studies evaluating the impact of COVID-19 public health restrictions on Google Mobility. Titles and abstracts were independently screened by two authors. Information from included studies was extracted by one researcher and double checked by another. Risk of bias of included articles was assessed using the Newcastle Ottowa Scale. Given the heterogeneous nature of the designs used, a narrative synthesis was undertaken. From the search, 1672 references were identified, of which 14 were included in the narrative synthesis. All studies reported data from the first wave of the pandemic, with Google Mobility Scores included from January to August 2020, with most studies analysing data during the first two months of the pandemic. Seven studies were assessed as having a moderate risk of bias and seven as a low risk of bias. Countries that introduced more stringent public health restrictions experienced greater reductions in mobility, through increased time at home and reductions in visits to shops, workplaces and use of public transport. Stay-at-home orders were the most effective of the individual strategies, whereas mask mandates had little effect of mobility., Conclusions: Public health restrictions, particularly stay-at-home orders have significantly impacted on transmission prevention behaviours. Further research is required to understand how to effectively address pandemic fatigue and to support the safe return back to normal day-to-day behaviours., Competing Interests: The authors have declared that no competing interests exist.

This study addressed the hypotheses that exposure to chronic hypoxia (CH) and chronic hypercapnia (CHC) would modify the acute hypercapnic ventilatory response in the cane toad (Rhinella marina; formerly Bufo marinus or Chaunus marinus) and its regulation by NMDA-mediated processes. Cane toads were exposed to 10 days of CH (10% O(2)) or CHC (3.5% CO(2)) followed by acute in vivo hypercapnic breathing trials, conducted before and after an injection of the NMDA-receptor channel blocker, MK801 into the dorsal lymph sac. CH, CHC and MK801 did not alter ventilation under acute normoxic normocapnic conditions. CH blunted the increase in breathing frequency during acute hypercapnia while CHC had no effect. The effect of CH on breathing frequency was mediated by a decrease in the number of breaths per breathing episode. Neither CH nor CHC altered breath area (volume). MK801 augmented breathing frequency (via an increase in breaths per episode) and total ventilation during acute hypercapnia in control toads and toads exposed to CH; there was no effect of MK801 on the increase in breathing frequency or total ventilation, during acute hypercapnia in toads exposed to CHC. The results indicate that CH and CHC differentially alter breathing pattern. Furthermore, they indicate an absence of NMDA-mediated glutamatergic tone during normoxic normocapnia but that NMDA-mediated processes attenuate the increase in breathing frequency during acute hypercapnia under control conditions and following CH but not following CHC. Given that MK801 was administered systemically, the effects could be acting anywhere in the reflex pathway from CO(2)-sensing to respiratory motor output.

This study examines the bushfire (wildland fire) risk to the built environment in Australia. The most salient result is that the annual probability of building destruction has remained almost constant over the last century despite large demographic and social changes as well as improvements in fire fighting technique and resources. Most historical losses have taken place in a few extreme fires which if repeated are likely to overwhelm even the most professional of fire services. We also calculate the average annual probability of a random home on the urban-bushland interface being destroyed by a bushfire to be of the order of 1 in 6500, a factor 6.5 times lower than the ignition probability of a structural house fire. Thus on average and if this risk was perceived rationally, the incentive for individual homeowners to mitigate and reduce the bushfire danger even further is low. This being the case and despite predictions of an increasing likelihood of conditions favouring bushfires under global climate change, we suspect that building losses due to bushfires are unlikely to alter materially in the near future.

Previous studies have shown that exposure to chronic hypoxia (CH) and chronic hypercapnia (CHC) alone have opposite effects on central respiratory-related pH/CO(2) chemosensitivity in the cane toad (Bufo marinus). This study examined the effects of chronic hypoxic hypercapnia (CHH) on central pH/CO(2) chemosensitivity. Cane toads were maintained at 10% O(2) and 3.5% CO(2) for 10 days. Changes in central pH/CO(2)-sensitive fictive breathing were measured using in vitro brainstem-spinal cord preparations. Whole animal experiments examined the effects of CHH on in vivo ventilatory responses. In vitro, CHH augmented fictive breathing frequency but attenuated the integrated fictive breath area such that total fictive breathing was not altered. The effects on frequency were mediated by changes in the number of episodes/min rather than breaths/episode. In vivo, CHH blunted the ventilatory response to severe hypoxia and moderate hypercapnia. The results indicate that CHH alters breathing pattern in response to central chemoreceptor stimulation in vitro and modifies in vivo ventilatory chemoreflexes.

This study examined the effects of chronic hypoxia (CH) and mid-brain transection on central respiratory-related pH/CO(2) chemosensitivity in cane toads (Bufo marinus). Toads were exposed to 10 days of CH (10% O(2)) following which in vitro brainstem-spinal cord preparations, with the mid-brain attached, were used to examine central pH/CO(2) chemosensitivity. A reduction in artificial cerebral spinal fluid (aCSF) pH increased fictive breathing frequency (fR) and total fictive ventilation. CH reduced fictive fR and total fictive ventilation, compared to controls. Mid-brain transection caused an increase in fictive fR, at the lower aCSF pH levels, in both control and CH preparations. In the CH preparations, mid-brain transection restored fictive breathing to control levels. In both groups, mid-brain transection eliminated fictive breath clustering. The data indicate that CH attenuates central pH/CO(2)-sensitive fictive breathing but a mid-brain transection in the middle of the optic lobes abolishes this attenuation. The results suggest that CH induces inhibition of central pH/CO(2) chemoreceptor function via descending inputs from the mid-brain region.

A series of experiments has been undertaken to understand more about the fundamental origin of the thickness-induced permittivity collapse often observed in conventional thin film ferroelectric heterostructures. The various experiments are discussed, highlighting the eventual need to examine permittivity collapse in thin film single crystal material. It has been seen that dielectric collapse is not a direct consequence of reduced size, and neither is it a consequence of unavoidable physics associated with the ferroelectric-electrode boundary. Research on three-dimensional shape-constrained ferroelectrics, emphasizing self-assembled structures based on nanoporous alumina templates and on FIB-milled single crystals, is also presented, and appears to represent an exciting area for ongoing research.

This study examined whether a hypoxia-tolerant amphibian, the Cane toad, undergoes mammalian-like ventilatory acclimatisation to hypoxia (VAH) and whether chronic hypoxia (CH) alters NMDA-mediated regulation of the acute hypoxic ventilatory response (HVR). Toads were exposed to 10 days of CH (10% O2) followed by acute hypoxic breathing trials or an intra-arterial injection of NaCN. Trials were conducted before and after i.p. treatment with an NMDA-receptor channel blocker (MK801). CH blunted the acute HVR but did not alter resting breathing. MK801 did not alter resting ventilation. In control animals, MK801 augmented breathing frequency (fR) during acute hypoxia by increasing the number of breaths per episode. This effect was attenuated following CH although MK801 did enhance the number of episodes per minute during acute hypoxia. MK801 enhanced the fR response to NaCN in both groups. The results indicate that CH did not produce mammalian-like VAH (i.e. increased resting ventilation and an augmented acute HVR) but did alter MK801-sensitive regulation of breathing pattern and the acute HVR.