Evidence for compliance controlled oxygen vacancy and metal filament based resistive switching mechanisms in RRAM

We present electrical evidence on asymmetric metal-insulator-semiconductor (MIS) based test structures in support of the presence of two different independent switching mechanisms in a resistive random access memory (RRAM) device. The valid mechanism for switching depends on the compliance capping (I_gl) for forming/SET transition. Our results convincingly show that low compliance based switching only involves reversible oxygen ion drift to and from oxygen gettering gate electrodes, while high compliance switching involves formation and rupture of conductive metallic nanofilaments, as verified further by our physical analysis investigations. We have observed this unique dual mode switching mechanism only in NiSi-based gate electrodes, which have a moderate oxygen solubility as well as relatively low melting point.     

Exercise testing in children: an alternative approach

In recent years there has been a call for new methods of evaluating the cardiorespiratory responses of children to exercise that complement their everyday exercise patterns. One potential method would be to use a sub-maximal, intermittent, pseudo-random binary sequence (PRBS) exercise test protocol to measure oxygen uptake kinetics (VO_{2 kinetics}). Ten children of mean (SD) age 10.8 (± 1.5) years completed a 20–50 W cycle ergometer protocol of 17-min duration. An estimate of alveolar oxygen uptake (VO₂) was calculated on a breath-by-breath basis. The VO₂ kinetic parameters were expressed in the frequency domain as amplitude ratio and phase delay using standard Fourier techniques. Analysis was restricted to the frequency range 2.2 to 8.9 mHz. The mean (SD) amplitude ratio responses decreased from 10.33 (± 0.73) to 7.42 (± 0.99) ml min^?1 W^?1 and the mean phase delay increased from -26.78° (± 6.37°) to -81.93° (± 10.45°) over the frequency range 2.2-8.9 mHz. Significant correlations (p<0.05) were found between chronological age and amplitude ratio (r= 0.68 and 0.62), and chronological age and phase delay (r= -0.62 and -0.69) at the frequencies of 2.2 and 4.4 mHz, respectively. No significant correlations were found between VO_{2 kinetics} and stature or VO_{2 kinetics} and body mass. The observations demonstrated the use of the PRBS technique to measure VO_{2 kinetics} in the frequency domain in children. This approach may be a useful addition to the tests that are used to quantify the oxygen uptake responses to exercise in children.     

Physiological and subjective measures of workload when shovelling with a conventional and two-handled (‘levered’) shovel

Previous studies have suggested that the two-handled (levered) shovel is advantageous over the conventional spade from a biomechanical point of view. The aim of this experiment was to determine whether less energy was consumed while shovelling a load of sand with this shovel compared to a conventional tool. Accordingly, an experiment was designed in which subjects (n = 10) shovelled 1815 kg sand under laboratory conditions using either a conventional or a levered shovel. Heart rate and oxygen consumption were measured continuously during the trial and subjective data on perceived exertion, general fatigue and body discomfort were recorded after the trial. Although total energy expenditure was similar under both conditions (120±20 and 125±25 kcal; conventional versus two-handled spade), average heart rate was 4% higher when the two-handled &lt;. shovel was used (p<0 05). In addition, the mass of sand per scoop was 4% less &lt;. with the two-handled shovel (p<0 05). In conclusion, subjects used similar energy expenditure to shovel 1815 kg sand with the conventional shovel and the twohandled tool despite lower mass of sand per scoop with the latter. This can be explained by the fact that the increased mass of the additional handle compensated for the lower mass of sand per scoop. The higher average heart rate while shovelling with the two-handled shovel can be explained by the more erect posture.     

Maximal oxygen uptake during cycling is reduced in moving environments; consequences for motion-induced fatigue

In previous studies on physical fatigue during simulated ship movements, the apparent exhaustion of subjects after experimentation suggested that the traditional index of physical workload, oxygen consumption expressed as the percentage of peak oxygen consumption ([Vdot]O_2-peak) measured in a separate graded exercise test (GXT), underestimates workload in a moving environment. In these studies, the GXT was carried out in a stationary environment, as is standard practice. To explain the underestimation, it was hypothesized that [Vdot]O_2-peak might have been less if the GXT had been carried out in the moving environment. This paper reports on three experimental tests of this hypothesis, performed with a ship motion simulator and aboard a ship at sea. In all three experiments, [Vdot]O_2-peak was indeed significantly reduced when the GXT was carried out in the moving environment. Theoretical reasons for this phenomenon are discussed and investigated, but a clear explanation is still lacking.     

Estimation of temporal changes in oxidation rates of sulphides in copper mine tailings at Laver, Northern Sweden

Tailings containing pyrrhotite were deposited in an impoundment at a copper mine at Laver, Northern Sweden, which operated between 1936 and 1946. Since then the oxidation of sulphides has acidified recipient water courses and contaminated them with metals. Measurements from surface water sampled in 1993, 2001 and 2004-05 from a brook into which the tailing impoundment drains indicate that the amounts of sulphide-associated elements such as Cu, S and Zn released into the brook have decreased over time, while pH has increased. The mass transport of S in the brook during 1993 and 2001 corresponded well with the amount of S estimated to be released from the tailings by oxidation. Secondary precipitates such as covellite and gypsum, which can trap sulphur, were shown in earlier studies to be present in only low amounts. The annual release of elements from the tailings was estimated from the volume of tailings assumed to oxidise each year, which depends on movement of the oxidation front with time. The results indicate that the oxidation rate in the tailings has decreased over time, which may be due to the increased distance over which oxygen needs to diffuse to reach unoxidised sulphide grains, or their cores, in the tailings.     

Facile synthesis of cobalt-doped (Zn,Ni)(O,S) as an efficient photocatalyst for hydrogen production

Cobalt-doped (Zn,Ni)(O,S) or Co-(Zn,Ni)(O,S) was facilely synthesized at low temperature below 100 °C with different cobalt precursor contents for photocatalytic hydrogen production. The X-ray pattern and elemental mapping proved that cobalt was successfully doped into zinc sites in the (Zn,Ni)(O,S) host lattice. We found the incorporation with a small amount of cobalt into (ZnNi)(O,S) enhanced its photo activity for hydrogen production. The best hydrogen production was achieved for 2.5% Co-(ZnNi)(O,S) with a rate of 8,527 μmol/g·h during a span of 5 h in a 20% (v/v) ethanol/water solution. Based on the results of optical characterizations, the enhancement of hydrogen production was caused by the slow electron-hole recombination and the low charge transfer resistance. A different photocatalytic kinetic mechanism for hydrogen generation from the conventional one with the simultaneous formation of hydrogen and oxygen gases is proposed, based upon the activated surface oxygen anion to initiate or trigger the key reaction of oxidation for water splitting to proceed. Our strategy in preparing catalyst at low process temperature and in doping to activate catalyst is for weakening the lattice oxygen bonding on the catalyst surface in order to firstly initiate the oxidation reaction and the formation of oxygen vacancies. These freshly formed oxygen vacancies play a critical role to trap the water and weaken its OH bonding to form hydrogen gas through the reduction reaction.     

High efficiency process for the production of pure oxygen based on solid oxide fuel cell–solid oxide electrolyzer technology

This paper presents a novel system for production of pure oxygen based on the integration of a solid oxide fuel cell (SOFC) and a solid oxide electrolyzer (SOEC). In the proposed arrangement, the SOFC provides electricity, heat and H₂O in vapour phase to the SOEC which carries out the inverse reactions of the SOFC, that is the separation of H₂O into H₂ (used as a fuel for the SOFC) and O₂ (representing the yield of the system). Simulations carried out in different operating conditions show that when the integrated SOFC–SOEC device runs at low current densities (less than 1000 A m⁻²), pure oxygen can be generated with an electric consumption comparable to mid-size cryogenic air separation units, and significantly lower than small scale systems based on the PSA technology.     

Oriented colloidal-crystal thin films of polystyrene spheres via spin coating

We developed a simple and inexpensive synthesis of a large-scale close-packed monolayer of polystyrene sphere arrays, which have a variety of applications. The influence of three step spin speeds, spinning time, solution quantity and relative humidity is studied in order to achieve a large area close-packed monolayer.A relatively high surface coverage and uniform monolayer of PS spheres in the range of 85%–90% are achieved by appropriate control of the preparative parameters. Also the effect of the oxygen plasma etching process on the reduction of PS spheres has been studied. We conclude that it can be useful in industrial applications, because of the fabrication speed, surface coverage, control over PS spheres and cost of the process.