Radial transonic shock solutions of Euler-Poisson system in convergent nozzles

Given constant data of density $\rho_0$, velocity $-u_0{\bf e}_r$, pressure $p_0$ and electric force $-E_0{\bf e}_r$ for supersonic flow at the entrance, and constant pressure $p_{\rm ex}$ for subsonic flow at the exit, we prove that Euler-Poisson system admits a unique transonic shock solution in a two dimensional convergent nozzle, provided that $u_0>0$, $E_0>0$, and that $E_0$ is sufficiently large depending on $(\rho_0, u_0, p_0)$ and the length of the nozzle

Primary Seat Belt Laws and Offsetting Behavior: Empirical Evidence from Individual Accident Data.

According to the offsetting effect theory, since drivers wearing seat belts feel more secure, they tend to drive less carefully and may cause more accidents, including those involving pedestrians. Most previous studies have used only state-level accident data, which cannot control for individual characteristics of drivers, vehicles, and the environmental factors surrounding the accidents. This paper uses individual-level accident data to analyze how drivers respond to the laws exploiting changes in the seat belt laws in a number of US states in the last decade. I find that the laws do not cause less careful behavior by drivers. In fact, they drive more carefully when more stringent seat belt laws are in effect, and this leads to less involvement of pedestrians in accidents. These results show that the offsetting effects do not exist when all accidents, including fatal accidents, are considered.Offsetting Effects, Safety Regulation, Seat Belt Laws, Vehicle Accidents

Do Vehicle Recalls Reduce the Number of Accidents? The Case of the U.S. Car Market

The number of automobile recalls in the U.S. has sharply increased in the last decade and a half, and the number of units involved in these recalls are often counted in the millions. In 2006 alone, over 10.6 million vehicles were recalled in the United States. However, there is no quantitative evidence of the effect of recalls on safety. Without that evidence, the government and insurance companies have been reluctant to request and use more detailed recall information to increase correction rates. In this paper we empirically quantify the effect of vehicle recalls on safety using repeated cross-sections on accidents of individual drivers and aggregate vehicle recall data, to construct synthetic panel data on individual drivers of a particular vehicle model. We estimate the effect of recalls on the number of accidents, and find that a 10% increase in the recall rate of a particular model will reduce the accidents of that model by around 2%. Recalls classified as .hazardous,. and those initiated by foreign manufacturers are more effective in reducing accidents. We also find that vehicle models with recalls with higher correction rates have on average less accidents in the years following a recall, which indicates the importance of the role of drivers' behavior regarding recalls, on safety. The latter suggests that society as a whole, individual drivers, and insurance companies, could benefit from an initiative to take into account recall correction behavior when pricing auto insurance.Vehicle Recalls, Car accidents, Synthetic Panel Data, Auto Insurance. Classification-JEL : L62, C23

The Effects of Automobile Recalls on the Severity of Accidents

The number of automobile recalls in the U.S. has substantially increased over the last two decades, and after a record of over 30 million cars recalled in 2004, in the last few years it has consistently reached between 15 and 17 million, and in 2009 alone 16.4 million cars were recalled. Toyota's recall crisis in 2010 illustrates how recalls can affect a large number of American drivers and the defects connected to them can result in loss of life and serious accidents. However, in spite of the increase in public concern over recalls and the loss of property and life attached to them, there is no empirical evidence of the effect of vehicle recalls on safety. This paper investigates whether vehicle recalls reduce accidental harm measured by the severity of injuries in vehicle accidents. The results of our analysis show that if a recall for a new-year model is issued, then the severity of injuries of accidents continuously diminishes during the rst year after the recall, something we do not nd among cars not subject to recalls. This is because defects are repaired over time but also because drivers react by driving more carefully until the defects are fixed. To minimize the losses attached to having dangerously defective cars on our roads, both quick and timely recall issuance are needed and more detailed information on defects should be delivered to owners of defective vehicles. The latter can be made possible through simple but important policy changes by the U.S. government regarding recall information sharing with drivers and insurance companies.Automobile Recalls, Safety Regulation, Vehicle Defects, Car Accidents.

A study on the turbulent transport of an advective nature in the fluid plasma

Advective nature of the electrostatic turbulent flux of plasma energy is studied numerically in a nearly adiabatic state. Such a state is represented by the Hasegawa-Mima equation that is driven by a noise that may model the destabilization due to the phase mismatch of the plasma density and the electric potential. The noise is assumed to be Gaussian and not to be invariant under reflection along a direction $\hat s$. It is found that the flux density induced by such noise is anisotropic: While it is random along $\hat s$, it is not along the perpendicular direction ${\hat s}_\perp$ and the flux is not diffusive. The renormalized response may be approximated as advective with the velocity being proportional to $(k\rho_s)^2$ in the Fourier space $\vec k$

Protein kinase CK2 phosphorylates and activates p21-activated kinase 1

Activation of the p21-activated kinase 1 (PAK1) is achieved through a conformational change that converts an inactive PAK1 dimer to an active monomer. In this paper, we show that this change is necessary but not sufficient to activate PAK1 and that it is, rather, required for CK2-dependent PAK1S223 phosphorylation that converts a monomeric PAK1 into a catalytically active form. This phosphorylation appears to be essential for autophosphorylation at specific residues and overall activity of PAK1. A phosphomimetic mutation (S223E) bypasses the requirement for GTPases in PAK1 activation, whereas the constitutive activity of the PAK1 mutant (PAK1H83,86L), postulated to mimic GTPase-induced structural changes, is abolished by inhibition of S223 phosphorylation. Thus, S223 is likely accessible to CK2 upon conformational changes of PAK1 induced by GTPase-dependent and GTPase-independent stimuli, suggesting that S223 phosphorylation may play a key role in the final step of the PAK1 activation process. The physiological significance of this phosphorylation is reinforced by the observations that CK2 is responsible for epidermal growth factor–induced PAK1 activation and that inhibition of S223 phosphorylation abrogates PAK1-mediated malignant transformation of prostate epithelial cells. Taken together, these findings identify CK2 as an upstream activating kinase of PAK1, providing a novel mechanism for PAK1 activation