Reconstructing the Deep Population History of Central and South America

We report genome-wide ancient DNA from 49 individuals forming four parallel time transects in Belize, Brazil, the Central Andes, and the Southern Cone, each dating to at least 9,000 years ago. The common ancestral population radiated rapidly from just one of the two early branches that contributed to Native Americans today. We document two previously unappreciated streams of gene flow between North and South America. One affected the Central Andes by 4,200 years ago, while the other explains an affinity between the oldest North American genome associated with the Clovis culture and the oldest Central and South Americans from Chile, Brazil, and Belize. However, this was not the primary source for later South Americans, as the other ancient individuals derive from lineages without specific affinity to the Clovis-associated genome, suggesting a population replacement that began at least 9,000 years ago and was followed by substantial population continuity in multiple regions

Advanced In-Core Fuel Cycles for the Gas Turbine-Modular Helium Reactor

In 1789 a German chemist, Martin Heinrich Klaproth, announced the discovery of a new element: uranium; few years later, the head of father of the modern chemistry, Antoine Lavoisier, was swept away by guillotine: a new era was destined to be opened, either where energy would have been produced in large scale by nuclear processes delivering hundreds of times the energy of chemical processes or where a mass of people, revolutionary or not, would have been melted down into a couple of seconds. After a quite long time, on the 2nd December 1942, the first nuclear reactor has been put into operation by Enrico Fermi in Chicago; few years later, came also the dark side utilization of fissile materials in Hiroshima and Nagasaki. Since those moments, three power plants generations succeeded, until the current one which is the generation IV of nuclear reactors. The latter has the goal of generating electricity in a safe manner, for the core is designed to provide an effective passive cooling of the decay heat. Amid generation IV of nuclear power plants, the Gas Turbine – Modular Helium Reactor, designed by General Atomics, is the only core with an energy conversion efficiency of 50%; the above consideration, coupled to construction and operation costs lower than ordinary Light Water Reactors, renders the Gas Turbine – Modular Helium reactor rather unequaled. In the present studies we investigated the possibility to operate the GT-MHR with two types of fuels: LWRs waste and thorium; since thorium is made of only fertile 232Th, we tried to mix it with pure 233U, 235U or 239Pu; ex post facto, only uranium isotopes allow the reactor operation, that induced us to examine the possibility to use a mixture of uranium, enriched 20% in 235U, and thorium. We performed all calculations by the MCNP and MCB codes, which allowed to model the reactor in a very detailed threedimensional geometry and to describe the nuclides transmutation in a continuous energy approach; finally, we completed our studies by verifying the influence of the major nuclear data libraries, JEFF, JENDL and ENDF/B, on the obtained results.QC 20100922</p

On line maintainance of a solution for bin-packing

The classical on-line bin-packing problem, unlike typical on-line problems, does not admit any reorganization of its data, i.e. no element can be moved from the bin it was first inserted. In this paper we introduce a new model for this problem, in which an element can possibly be moved in correspondence of the arrival of another element, but the number of movements performed is explicitly considered in the complexity analysis. In the framework of this paradigm, we introduce a new class of O(n log n) - time and O(n) - space algorithms, HARMONIC_REL(M) (where M > 2 is an integer), that, for each prefix of the input list, obtain a new bin assignment performing a limited reorganization of the previous solution, making, at most, cn element movements (c = 2 for M = 3). All of the algorithms in this class present an 1.5 asymptotic approximation ratio (and an 1.5 OPT + (M - 1) absolute ratio), that goes beyond the theoretical 1.536... lower bound for on-line bin-packing in the restricted model

New Algorithms for on-line bin-packing

In this paper, two new algorithms for on-line bin packing are given, under the assumption that each element can be moved for a constant number of times after its first assignment to some bin. The first algorithm presents linea time and space complexities with a 1.5 approximation ratio, while the second one is a O(n log n) time and linear space one with a 1.33... approximation ratio. Both algorithms present an approximation rate less than the 1.53 lower bound for on-line bin-packing without element movements