Sigref – A Symbolic Bisimulation Tool Box

We present a uniform signature-based approach to compute the most popular bisimulations. Our approach is implemented symbolically using BDDs, which enables the handling of very large transition systems. Signatures for the bisimulations are built up from a few generic building blocks, which naturally correspond to efficient BDD operations. Thus, the definition of an appropriate signature is the key for a rapid development of algorithms for other types of bisimulation. We provide experimental evidence of the viability of this approach by presenting computational results for many bisimulations on real-world instances. The experiments show cases where our framework can handle state spaces efficiently that are far too large to handle for any tool that requires an explicit state space description. This work was partly supported by the German Research Council (DFG) as part of the Transregional Collaborative Research Center “Automatic Verification and Analysis of Complex Systems” (SFB/TR 14 AVACS). See www.avacs.org for more information

Hit or Miss? The Effect of Assassinations on Institutions and War

Assassinations are a persistent feature of the political landscape. Using a new data set of assassination attempts on all world leaders from 1875 to 2004, we exploit inherent randomness in the success or failure of assassination attempts to identify assassination's effects. We find that, on average, successful assassinations of autocrats produce sustained moves toward democracy. We also find that assassinations affect the intensity of small-scale conflicts. The results document a contemporary source of institutional change, inform theories of conflict, and show that small sources of randomness can have a pronounced effect on history.

Drugs for exceptionally rare diseases: a commentary on Hughes et al

Recently in this journal, Hughes and colleagues discussed special funding status to ultra-orphan drugs. They concluded that there should be a uniform policy for the provision of orphan drugs across Europe; that complete restriction was impractical, and that UK policy should aspire to the values of the EU directive on orphan drugs. We critically assess these arguments, demonstrating that they failed to justify special status for treatments for rare diseases

Concepts of inhomogeneous illumination of area-based light modulators for high-resolution headlamps

Adaptive headlamps with innovative lighting functionalities can increase traffic safety. Subtractive light modulators such as Digital-Micromirror-Devices (DMD), liquid crystal displays (LCD) or liquid crystal on silicon devices (LCoS) are considered to be used as an implementation with a high resolution. In order to realize the regulated light distribution as well as to improve the optical efficiency and on-road projection quality of such headlamp systems, an inhomogeneous illumination on the modulator and whereafter low distortion projection optics are considered. In this paper we present simulation results of an optical concept of inhomogeneous illumination for headlamps

Relativistic model of hidden bottom tetraquarks

The relativistic model of the ground state and excited heavy tetraquarks with hidden bottom is formulated within the diquark-antidiquark picture. The diquark structure is taken into account by calculating the diquark-gluon vertex in terms of the diquark wave functions. Predictions for the masses of bottom counterparts to the charm tetraquark candidates are given.Comment: 6 page

Thermodynamic interpretation of the scaling of the dynamics of supercooled liquids

The recently discovered scaling law for the relaxation times, tau=f(T,V^g), where T is temperature and V the specific volume, is derived by a revision of the entropy model of the glass transition dynamics originally proposed by Avramov [I. Avramov, J. Non-Cryst. Solids 262, 258 (2000).]. In this modification the entropy is calculated by an alternative route, while retaining the approximation that the heat capacity is constant with T and P. The resulting expression for the variation of the relaxation time with T and V is shown to accurately fit experimental data for several glass-forming liquids and polymers over an extended range encompassing the dynamic crossover. From this analysis, which is valid for any model in which the relaxation time is a function of the entropy. we find that the scaling exponent g can be identified with the Gruneisen constant.Comment: 24 pages, 7 figure

Are the Collatz and abc conjectures related?

The Collatz and $abc$ conjectures, both well known and thoroughly studied, appear to be largely unrelated at first sight. We show that assuming the $abc$ conjecture true is helpful to improve the lower bound of integers initiating a particular type of Collatz sequences, namely finite sequences of a given length where all terms but one are odd with the usual ``shortcut'' form. To obtain sharper bounds in this context, we are led to consider a small subset of the $abc$-hits. Then, it turns out that Collatz iterations as well as Wieferich primes may be used to find large triples in this subset