Kodaira dimension of irregular varieties

Let f:X→Y be an algebraic fiber space with general fiber F. If Y is of maximal Albanese dimension, we show that κ(X)≥κ(Y)+κ(F).     

Solving the post enrolment course timetabling problem by ant colony optimization

In this work we present a new approach to tackle the problem of Post Enrolment Course Timetabling as specified for the International Timetabling Competition 2007 (ITC2007), competition track 2. The heuristic procedure is based on Ant Colony Optimization (ACO) where artificial ants successively construct solutions based on pheromones (stigmergy) and local information. The key feature of our algorithm is the use of two distinct but simplified pheromone matrices in order to improve convergence but still provide enough flexibility for effectively guiding the solution construction process. We show that by parallelizing the algorithm we can improve the solution quality significantly. We applied our algorithm to the instances used for the ITC2007. The results document that our approach is among the leading algorithms for this problem; in all cases the optimal solution could be found. Furthermore we discuss the characteristics of the instances where the algorithm performs especially well.     

An integral equation arising in a convective heat (mass) transfer problem through a boundary layer

A problem of Lighthill and Levich, where convective heat (mass) transfer occurs through a boundary layer, is considered. This gives rise to a certain integral equation. The unique L₂ solution of a generalized version of this integral equation is obtained providing the solution, in closed form, of the original problem.     

A Class of Integrable Non-QRT Mappings and Their Deautonomisation

We study classes of mappings which do not belong to the QRT family. We obtain several integrable non-autonomous forms of these mappings extending previous results where only linearisable cases were found. Using our recently introduced method of singularity confinement with full deautonomisation, we analyse a mapping which, while non-integrable, does possess confined singularities and show that our method makes it possible to obtain the exact value of its algebraic entropy.     

Dynamic Lone Pair Expression as Chemical Bonding Origin of Giant Phonon Anharmonicity in Thermoelectric InTe

Loosely bonded (“rattling”) atoms with s² lone pair electrons are usually associated with strong anharmonicity and unexpectedly low thermal conductivity, yet their detailed correlation remains largely unknown. Here we resolve this correlation in thermoelectric InTe by combining chemical bonding analysis, inelastic X-ray and neutron scattering, and first principles phonon calculations. We successfully probe soft low-lying transverse phonons dominated by large In¹⁺ z-axis motions, and their giant anharmonicity. We show that the highly anharmonic phonons arise from the dynamic lone pair expression with unstable occupied antibonding states induced by the covalency between delocalized In¹⁺ 5s² lone pair electrons and Te 5p states. This work pinpoints the microscopic origin of strong anharmonicity driven by rattling atoms with stereochemical lone pair activity, important for designing efficient materials for thermoelectric energy conversion.     

Unprecedented alkene complex of zinc(II): structures and bonding of divinylzinc complexes

This report describes the solid-state structures of a series of divinylzinc complexes, one of which represents the only structurally characterized zinc(II) pi-complex. Vinylzinc reagents, Zn[C(Me)=CH2]2 (1) and Zn[C(H)=CMe2]2 (2), have been synthesized and isolated as white crystalline solids in 66 and 72% yield, respectively. Each compound exhibits an infinite polymeric architecture in the solid state via a series of zinc-pi (1) and zinc-sigma-bonded (2) bridging interactions. Addition of chelating ligands to these divinylzinc compounds allowed isolation of the monomeric adducts (bipy)Zn[C(Me)=CH2]2 (1.bipy), (tmeda)Zn[C(Me)=CH2]2 (1*tmeda), (bipy)Zn[C(H)=CMe2]2 (2*bipy), and (tmeda)Zn[C(H)=CMe2]2 (2*tmeda), of which 1*bipy, 2*bipy, and 2*tmeda have been characterized crystallographically.     

Preparative scale mass spectrometry: A brief history of the calutron

Calutrons were developed in the laboratory of E. O. Lawrence at the University of California at Berkeley. They were a modification of the cyclotrons he had invented and used in his Noble Prize winning investigations of the atomic nucleus. At the time their construction was undertaken, calutrons represented the only certain means of preparing enriched uranium isotopes for the construction of a fission bomb. The effort was successful enough that every atom of the 42 kg of ²³⁵U used in the first uranium bomb had passed through at least one stage of calutron separation. At peak production, the first stage separators, α tanks, yielded an aggregate 258-g/d ²³⁵U enriched to about 10 at. % from its natural abundance level of 0. 72 at. %. The second stage separators, β tanks, used the 10 at. % material as feedstock and produced a total 204-g/d ²³⁵U enriched to at least 80 at. %. The latter, weapons grade, material was used in fission bombs. Under typical operating conditions, each α tank operated at a uranium beam intensity at the collectors of approximately 20 mA and each β tank at a beam intensity of approximately 215 mA at the collectors. Bulk separation of isotopes for bomb production ceased in 1945. Since that time calutrons have been used to separate stable isotopes, but on a more limited scale than wartime weapons production. Stable isotope separations since 1960 have taken place using one modified beta tank.