Power laws, memory capacity, and self-tuned critical branching in an LIF model with binary synapses

Both fluctuations and distributions of spontaneous neural spiking activity have been observed to closely follow a variety of power laws. Multiple explanations have been offered for each observation, but few lead to mechanisms that encompass their widespread occurrence. A canonical, leaky integrate-and-fire model is presented in which synapses are updated based on the timing of pre- and post-synaptic spikes in order to maintain a state of critical branching. Results showed that 1) the self-tuning algorithm maintained critical branching under a range of parameters; 2) power laws were obtained in spiking activity fluctuations (1/f scaling), size distributions of network bursts (neural avalanches), and temporal correlations in interspike intervals (Allan factor); 3) power laws disappeared once the self-tuning algorithm was disabled; and 4) critical branching was adaptive in that it maximized the network’s memory capacity when assessed as a liquid state machine

Median price changes: an alternative approach to measuring current monetary inflation

An analysis concluding that inflation measures based on median price changes are a better indicator than measures based on mean price changes.Inflation (Finance) ; Consumer price indexes

Price Discovery in Canadian Government Bond Futures and Spot Markets

In this paper we look at the relative information content of cash and futures prices for Canadian Government bonds. We follow the information-share approaches introduced by Hasbrouck (1995) and Harris et al (1995), applying the techniques in Gonzalo-Granger (1995), to evaluate the relative contributions of trading in the cash and futures markets to the price discovery process. Both approaches estimate a vector error correction model that permits the separation of long-run price movements from short-run market microstructure effects. As well, we follow Yan and Zivot (2004) who introduce size measures of a market's adjustment to a new equilibrium during the price discovery process. We find that, on an average day, just over 70% of price discovery occurs on the futures market where bid-ask spreads are lower and trading activity is higher. The size of the responses to shocks and the time taken to adjust to a new equilibrium are found to be significantly larger for the cash market.Financial markets; Market structure and pricing

Correlating Electrochemical Performance with In Situ Optical Spectroscopy in Solid Oxide Fuel Cells

Solid oxide fuel cells are versatile electrochemical devices that can operate with a wide variety of carbon containing fuels. However, SOFCs operate at high temperatures (650ªC) making in situ characterization of material properties and reaction mechanisms, associated with electrochemical fuel oxidation, difficult to perform. Experiments described employed in situ vibrational spectroscopy and standard electrochemical methods to characterize the properties of SOFC electrolytes and anodes at temperatures up to 715ªC. Collectively these methods address long standing questions about fuel oxidation and degradation mechanisms. One investigation coupled in situ Raman with surface specific EIS measurements to show that yttria stabilized zirconia electrolytes form a slightly conductive, surface reduced layer under anodic conditions commonly encountered during SOFC operation. Polarizing the SOFC further depleted oxide ion concentrations close to the three phase boundary. Additional ex situ XAS measurements confirmed that only zirconium, in the crystal structure, plays a role in the formation of conductive surface states in reduced YSZ. A second project combined electrochemical measurements with kinetically resolved in situ spectroscopic data to compare the performance and oxidation mechanisms of SOFCs operating with methanol and methane. Methanol exhibited higher percentages in utilization and conversion at the anode as compared to methane. Results emphasized that this increase in reactivity enabled the methanol fuel to pyrolyze into carbon deposits on the anode at a faster rate and significant amounts leading to greater degradation in electrochemical performance than compared to methane. The final project investigated the internal oxidative and steam reforming of methane and ethanol using in situ Raman, real time electrochemical, and FTIR exhaust measurements. EIS data show that direct methane and ethanol lead to anode degradation that correlates directly with the appearance of aggressive carbon deposits on the anode surface. Ex situ FTIR measurements revealed that methane doesn¡&hibar;t undergo pyrolysis but when reformers were introduced into the fuel, a mixture of H2, CO, CO2, and H2O was created. These same measurements show a decrease in acetylene when H2O was introduced into ethanol. In situ Raman measurements showed that carbon formation could be completely suppressed in the presence of these reformers, especially at high cell overpotentials

Sublimation Rate of Paradichlorobenzene Spheres in a Natural Convection Environment

Spherical paradichlorobenzene specimens were cast, then allowed to sublimate in a natural convection environment. The mass loss over time was recorded, suspending the specimens by a weigh bellow hook attached to a balance, which was required to obtain the sublimation rate. The diameters tested in this study were 3 cm, 4 cm, 5 cm, and 5.8 cm. A total of three data sets for each sized sphere were recorded to ensure accuracy. The results were used to determine the Schmidt, Grashoff, Sherwood, and Rayleigh numbers. After finding these values, an emperical equation was found relating the Sherwood number as a function of the Rayleigh number. Using this technique and these results it is possible to determine heat transfer coefficients via the heat mass transfer analogy. This method is not only bound to spheres and natural convection, for it can be used to analyze more complex geometries as well as forced convection environments

An Analysis of Helicopter EMS Accidents using HFACS: 2000-2012

In 1972, the first hospital based civilian helicopter emergency medical service (HEMS) in the United States began operations. While the use of helicopters to transport medical casualties started decades previously, St. Anthony Flight for Life represented the start of an industry that would grow rapidly in the years to follow, both in the US and around the world (Flight for Life Colorado, n.d.). Helicopters provide a valuable contribution to the field of medicine. They are faster than ground-based transportation and able to reach areas considered otherwise remote or impassible. They are highly manoeuvrable, unhindered by traffic, and can land in confined spaces. Further advancements, such as the use of advanced life support equipment and flight medical personnel have further improved patient outcomes. After a decade of growth, a disturbing trend emerged in the air ambulance sector. In the early 1980s, the National Transportation Safety Board (NTSB) observed a marked rise in aviation accidents involving ambulance helicopters. Since then it has been observed that there are a disproportionate number of accidents in HEMS flying compared to other types of flying, including fixed-wing EMS. This phenomenon has been the subject of numerous articles, government reports, and news stories (e.g. NTSB, 1988; Harris, 1994; Wright, 2004; Veilette, 2005; and Negroni, 2009). By its nature, HEMS operations pose more risks than other types of flying. Unscheduled flights into unfamiliar areas and semi-prepared landing surfaces ostensibly increase the chance of an accident or incident. However, examination of HEMS operations in other countries show that the risk is more pronounced in the US than other countries (Table 1). The US had an accident rate in 2000-09 that was both higher than other countries and the previous decade. It also has the highest fatal accident rate, considering that the Australian rate in 2000-09 was the result of a single HEMS crash in 2003