Positively Radical

Thinking positively

How to come up with numerical PD estimates if there are no default observations? Katja Pluto and Dirk Tasche propose a statistically based methodology to derive non-zero probabilities of default for credit portfolios with none or very few observed defaults. Their most prudent estimation principle delivers results for any desired degree of conservatism, and can be applied to both uncorrelated an...

Positively-deflected anomaly mediation

We generalize the so-called “deflected anomaly mediation” scenario to the case where threshold corrections of heavy messengers to the sparticle squared-masses are positive. A concrete model realizing this scenario is also presented. The tachyonic slepton problem can be fixed with only a pair of messengers. The resultant sparticle mass spectrum is quite different from that in the conventional de...

Parity is Positively Useless

We give the first examples of non-trivially positively-useless predicates subject only to P 6= NP. In particular, for every constraint function Q : {−1, 1}4 → R, we construct Contraint-SatisfactionProblem (CSP) instances without negations which have value at least 1 − ε when evaluted for the arity-four odd-parity predicate, yet it is NP-hard to find a solution with value significantly better th...

Positively spin coherent

98 nature materials | VOL 7 | FEBRUARY 2008 | www.nature.com/naturematerials fact that dislocation plasticity is much more discrete at the nanoscale. !eir observations of inhomogeneous dislocation nucleation under the surface of the loading platen — where the indenter contacts the specimen — and the occurrence of discrete dislocation bursts provide valuable insight into how plasticity occurs in...

Positively Dependent Random