146,967 research outputs found
Modelling incomplete fusion dynamics of weakly-bound nuclei at near-barrier energies
The classical dynamical model for reactions induced by weakly-bound nuclei at
near-barrier energies is developed further. It allows a quantitative study of
the role and importance of incomplete fusion dynamics in asymptotic
observables, such as the population of high-spin states in reaction products as
well as the angular distribution of direct alpha-production. Model calculations
indicate that incomplete fusion is an effective mechanism for populating
high-spin states, and its contribution to the direct alpha production yield
diminishes with decreasing energy towards the Coulomb barrier. It also becomes
notably separated in angles from the contribution of no-capture breakup events.
This should facilitate the experimental disentanglement of these competing
reaction processes.Comment: 12 pages, 7 figures (for better resolution figures please contact the
author), Accepted in Journal of Physics
Two dimensional Sen connections and quasi-local energy-momentum
The recently constructed two dimensional Sen connection is applied in the
problem of quasi-local energy-momentum in general relativity. First it is shown
that, because of one of the two 2 dimensional Sen--Witten identities, Penrose's
quasi-local charge integral can be expressed as a Nester--Witten integral.Then,
to find the appropriate spinor propagation laws to the Nester--Witten integral,
all the possible first order linear differential operators that can be
constructed only from the irreducible chiral parts of the Sen operator alone
are determined and examined. It is only the holomorphy or anti-holomorphy
operator that can define acceptable propagation laws. The 2 dimensional Sen
connection thus naturally defines a quasi-local energy-momentum, which is
precisely that of Dougan and Mason. Then provided the dominant energy condition
holds and the 2-sphere S is convex we show that the next statements are
equivalent: i. the quasi-local mass (energy-momentum) associated with S is
zero; ii.the Cauchy development is a pp-wave geometry with pure
radiation ( is flat), where is a spacelike hypersurface
whose boundary is S; iii. there exist a Sen--constant spinor field (two spinor
fields) on S. Thus the pp-wave Cauchy developments can be characterized by the
geometry of a two rather than a three dimensional submanifold.Comment: 20 pages, Plain Tex, I
Floriculture world wide; production, trade and consumption patterns show market opportunities and challenges
Floricultural production contains a wide variety of products. The production value world wide has been rising from 11 billion to 60 billion dollars in 2003 (estimate). Europe is traditionally a large producer and trader, with a stable production value of about 10 billion dollars (2002). North America has a production value of about 6,5 billion dollars. In Asia production capacity is growing rapidly in several countries. In Africa the production has emerged enormously, but in a risky environment. Oceania is a small producer. Looking a inter- and intra continental trade in 2002 the following view occurs. Europe and USA have the largest intra continental trade. Latin America, Africa, Asia and Europe export to these continents. Of the existing markets USA has emerged the last decade. Further more the consumption per capita has been rising due to rise of income and developments in culture in countries in Europe, USA and Japan. Asia and Easter Europe have big potential as new markets because the level of prosperity is rising. Totally the worldwide demand has grown. For high volume bulky product we see a South-North pattern. For high quality product there are niche markets world wide. While we see the international trade increasing, the regional supply will be leading. Parallel WTO liberalises the world trade, non-trade barriers occur. This, together with changing from a product driven to a demand driven market, requires strategies for market access. Co-operation in supply chains offers possibilities.Production, Crop Production/Industries,
Mechanism Deduction from Noisy Chemical Reaction Networks
We introduce KiNetX, a fully automated meta-algorithm for the kinetic
analysis of complex chemical reaction networks derived from semi-accurate but
efficient electronic structure calculations. It is designed to (i) accelerate
the automated exploration of such networks, and (ii) cope with model-inherent
errors in electronic structure calculations on elementary reaction steps. We
developed and implemented KiNetX to possess three features. First, KiNetX
evaluates the kinetic relevance of every species in a (yet incomplete) reaction
network to confine the search for new elementary reaction steps only to those
species that are considered possibly relevant. Second, KiNetX identifies and
eliminates all kinetically irrelevant species and elementary reactions to
reduce a complex network graph to a comprehensible mechanism. Third, KiNetX
estimates the sensitivity of species concentrations toward changes in
individual rate constants (derived from relative free energies), which allows
us to systematically select the most efficient electronic structure model for
each elementary reaction given a predefined accuracy. The novelty of KiNetX
consists in the rigorous propagation of correlated free-energy uncertainty
through all steps of our kinetic analyis. To examine the performance of KiNetX,
we developed AutoNetGen. It semirandomly generates chemistry-mimicking reaction
networks by encoding chemical logic into their underlying graph structure.
AutoNetGen allows us to consider a vast number of distinct chemistry-like
scenarios and, hence, to discuss assess the importance of rigorous uncertainty
propagation in a statistical context. Our results reveal that KiNetX reliably
supports the deduction of product ratios, dominant reaction pathways, and
possibly other network properties from semi-accurate electronic structure data.Comment: 36 pages, 4 figures, 2 table
Quantum many-body systems out of equilibrium
Closed quantum many-body systems out of equilibrium pose several
long-standing problems in physics. Recent years have seen a tremendous progress
in approaching these questions, not least due to experiments with cold atoms
and trapped ions in instances of quantum simulations. This article provides an
overview on the progress in understanding dynamical equilibration and
thermalisation of closed quantum many-body systems out of equilibrium due to
quenches, ramps and periodic driving. It also addresses topics such as the
eigenstate thermalisation hypothesis, typicality, transport, many-body
localisation, universality near phase transitions, and prospects for quantum
simulations.Comment: 7 pages, review and perspectives article, updated to journal version
after embarg
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