Drag reductions obtained by modifying a box-shaped ground vehicle

A box-shaped ground vehicle was used to simulate the aerodynamic drag of high volume transports, that is, delivery vans, trucks, or motor homes. The coast-down technique was used to define the drag of the original vehicle, having all square corners, and several modifications of the vehicle. Test velocities ranged up to 65 miles per hour, which provided maximum Reynolds numbers of 1 times 10 to the 7th power based on vehicle length. One combination of modifications produced a reduction in aerodynamic drag of 61 percent as compared with the original square-cornered vehicle

Parameter estimation and forecasting for multiplicative log-normal cascades

We study the well-known multiplicative log-normal cascade process in which the multiplication of Gaussian and log normally distributed random variables yields time series with intermittent bursts of activity. Due to the nonstationarity of this process and the combinatorial nature of such a formalism, its parameters have been estimated mostly by fitting the numerical approximation of the associated non-Gaussian probability density function to empirical data, cf. Castaing et al. [Physica D 46, 177 (1990)]. More recently, alternative estimators based upon various moments have been proposed by Beck [Physica D 193, 195 (2004)] and Kiyono et al. [Phys. Rev. E 76, 041113 (2007)]. In this paper, we pursue this moment-based approach further and develop a more rigorous generalized method of moments (GMM) estimation procedure to cope with the documented difficulties of previous methodologies. We show that even under uncertainty about the actual number of cascade steps, our methodology yields very reliable results for the estimated intermittency parameter. Employing the Levinson-Durbin algorithm for best linear forecasts, we also show that estimated parameters can be used for forecasting the evolution of the turbulent flow. We compare forecasting results from the GMM and Kiyono et al.’s procedure via Monte Carlo simulations.We finally test the applicability of our approach by estimating the intermittency parameter and forecasting of volatility for a sample of financial data from stock and foreign exchange markets

Rapid Changes of Potassium Concentration at the Outer Surface of Exposed Single Neurons during Membrane Current Flow

K+-sensitive liquid ion-exchanger microelectrodes are shown to be capable of measuring concentration changes which occur on a millisecond time scale. However, some quaternary ammonium ions, such as tetraethylammonium and acetylcholine, are able to block electrode function when present in concentrations as low as 10-4 to 10-3 M. Changes in extracellular potassium concentration caused by spike activity or voltage clamp pulses of exposed single neurons of the snail Helix pomatia may be measured by these electrodes. Quantitative analysis shows that the total amount of excess potassium found in the vicinity of the cell a short time after a clamp pulse, is in relatively good agreement with the amount of potassium carried by the membrane current

Auction fever: the unrecognized effects of incidental arousal

Despite countless anecdotes about emotionally-charged bidding in auctions, there is little research to help understand what causes auction fever and why it persists. Because research has only considered how integral arousal (i.e., arousal from within the auction) affects bidding, the current research considered whether incidental arousal (i.e., arousal from outside the auction) also increases bidding. With two different manipulations of arousal, Experiments 1 and 2 showed that incidental arousal increased bidding in live auctions with monetary stakes. Experiment 1 also measured arousal physiologically to demonstrate its role in bidding. Experiment 3 utilized a third manipulation of incidental arousal and found that individuals were unaware of its effects. Overall, the current research demonstrates how bidders are potentially subject to many different sources of arousal that have nothing to do with auctions, all of which can unwittingly increase individuals’ bidding