148 research outputs found
Elastic effects on relaxation volume tensor calculations
Relaxation volume tensors quantify the effect of stress on diffusion of
crystal defects. Continuum linear elasticity predicts that calculations of
these parameters using periodic boundary conditions do not suffer from
systematic deviations due to elastic image effects and should be independent of
supercell size or symmetry. In practice, however, calculations of formation
volume tensors of the interstitial in Stillinger-Weber silicon
demonstrate that changes in bonding at the defect affect the elastic moduli and
result in system-size dependent relaxation volumes. These vary with the inverse
of the system size. Knowing the rate of convergence permits accurate estimates
of these quantities from modestly sized calculations. Furthermore, within the
continuum linear elasticity assumptions the average stress can be used to
estimate the relaxation volume tensor from constant volume calculations.Comment: 31 pages, 6 figures, submitted to Phys. Rev.
Non-equilibrium emission of complex fragments from p+Au collisions at 2.5 GeV proton beam energy
Energy and angular dependence of double differential cross sections
d/ddE was measured for reactions induced by 2.5 GeV protons
on Au target with isotopic identification of light products (H, He, Li, Be, and
B) and with elemental identification of heavier intermediate mass fragments (C,
N, O, F, Ne, Na, Mg, and Al). It was found that two different reaction
mechanisms give comparable contributions to the cross sections. The
intranuclear cascade of nucleon-nucleon collisions followed by evaporation from
an equilibrated residuum describes low energy part of the energy distributions
whereas another reaction mechanism is responsible for high energy part of the
spectra of composite particles. Phenomenological model description of the
differential cross sections by isotropic emission from two moving sources led
to a very good description of all measured data. Values of the extracted
parameters of the emitting sources are compatible with the hypothesis claiming
that the high energy particles emerge from pre-equilibrium processes consisting
in a breakup of the target into three groups of nucleons; small, fast and hot
fireball of 8 nucleons, and two larger, excited prefragments, which
emits the light charged particles and intermediate mass fragments. The smaller
of them contains 20 nucleons and moves with velocity larger than the CM
velocity of the proton projectile and the target. The heavier prefragment
behaves similarly as the heavy residuum of the intranuclear cascade of
nucleon-nucleon collisions. %The mass and charge dependence of the total
production cross %sections was extracted from the above analysis for all
observed %reaction products. This dependence follows the power low behavior
%(A or Z)
Species and abundance of ectoparasitic flies (Diptera) in pied flycatcher nests in Fennoscandia
Peer reviewe
The choice for EU theorists: Establishing a common framework for analysis
European Union (EU) studies have entered a highly contentious and, arguably, creative phase. A range of theoretical perspectives, seemingly quite highly differentiated from one another, now compete for influence and lsquospacersquo. However, the questions remain: is EU studies developing theories which are truly competing theories? Or is it developing theories that do not compete so much as they aim to explain distinctly different pieces of the EU puzzle? This paper responds directly to these two questions, while reviewing recent literature on EU governance. It argues, first, that we lack theories of EU governance that are true rivals; and, second, that leading models explain different outcomes at different levels in a multi-level system of governance. The result is somewhat phoney debates between compatible theories masquerading as rivals, and between lsquocomparative politicsrsquo and lsquointernational relationsrsquo approaches. Above all, perhaps, we find middle range theories posing as general or lsquometa-theoriesrsquo. In the absence of a plausible general theory of EU governance, theorists must choose precisely which type of outcome theywish to explain
Balanço de nitrogênio, concentrações de ureia e síntese de proteína microbiana em caprinos alimentados com dietas contendo cana-de-açúcar tratada com óxido de cálcio
The Luminescent Inhomogeneity and the Distribution of Zinc Vacancy-Related Acceptor-Like Defects in N-Doped ZnO Microrods
Digital image watermarking using fast parametric transforms
This paper proposes a novel method for digital image watermarking, in which watermarks are embedded in the domain of fast para-metric transforms based on known spread spectrum approaches. Fast parametric transforms have the ability to adapt the forms of base vectors, which enables automatic selection of the domain of watermarking in relation to the pair: a marked image – a watermarking attack. The process of adapting the forms of fast parametric transforms is carried out with aid of the classical genetic algorithm with the fitting function based on the known measure of separability of watermarks. The effectiveness of the proposed method has been verified experimentally on the basis of the images of two classes, i.e. natural images and technical diagrams. The results taking into account both the efficiency of watermark embedding and the generated distortions in the marked images are summarized in tables and accompanied by an appropriate commentary
Ground-State Phase Diagram of the Extended Ising Model on the Shastry-Sutherland Lattice
The ground-state phase diagram of the Ising model on the Shastry-Sutherland lattice with the first (), second (), third () and fourth () nearest neighbour spin couplings is studied using the exact and well controlled numerical method. It is shown that switching on of the and interactions (in addition to usually considered and interactions) leads to stabilization of the following dominant magnetic phases with m/=1/9, 1/6, 4/9, 1/2 and 5/9, which is manifested in appearance of new magnetization plateaus on the magnetization curve of the model at given values of m/. The obtained results are consistent with experimental measurements of magnetization curves in selected rare-earth tetraborides
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