Close calls

Social monitoring via close calls in meerkats.

Social monitoring of the actions of group members is thought to be a key development associated with group living. Humans constantly monitor the behaviour of others and respond to them in a flexible way depending on past interactions and the current social context. While other primates have also been reported to change their behaviour towards other group members flexibly based on the current st...

Close calls in patient safety: should we be paying closer attention?

Implied volatility explosions: European calls and implied volatilities close to expiry in exponential Lévy models

We examine the small expiry behaviour of the price of call options in models of exponential Lévy type. In most cases of interest, it turns out that E ( (Sτ −K) ) − (S0 −K) ∼ { τ ∫ R (S0e x −K)+ ν(dx), S0 < K, τ ∫ R (K − S0e) ν(dx), S0 > K, as τ → 0+, i.e. as time to expiry goes to zero. (We have written ν for the Lévy measure of the driving Lévy noise.) In “complete generality”, however, we can...

False Alarms and Close Calls: A Conceptual Model of Warning Accuracy

The false alarm rate (FAR) measures the fraction of forecasted events that did not occur, and it remains one of the key metrics for verifying National Weather Service (NWS) weather warnings. The national FAR for tornado warnings in 2003 was 0.76, indicating that only one in four tornado warnings was verified. The NWS’s goal for 2010 is to reduce this value to 0.70. Conventional wisdom is that f...

Close to close packing ∗

For various lattice gas models with nearest neighbour exclusion (and, in one case, second-nearest neighbour exclusion as well), we obtain lower bounds on m, the average number of particles on the non-excluded lattice sites closest ∗We dedicate this work to the memory of Ann Stell, beloved friend of OP and beloved wife of GS.