Comment on current correlators in QCD at finite temperature

We address some criticisms by Eletsky and Ioffe on the extension of QCD sum rules to finite temperature. We argue that this extension is possible, provided the Operator Product Expansion and QCD-hadron duality remain valid at non-zero temperature. We discuss evidence in support of this from QCD, and from the exactly solvable two- dimensional sigma model O(N) in the large N limit, and the Schwinger model.Comment: 10 pages, LATEX file, UCT-TP-208/94, April 199

Lattice thermal conductivity of graphene nanostructures

Non-equilibrium molecular dynamics is used to investigate the heat current due to the atomic lattice vibrations in graphene nanoribbons and nanorings under a thermal gradient. We consider a wide range of temperature, nanoribbon widths up to 6nm and the effect of moderate edge disorder. We find that narrow graphene nanorings can efficiently suppress the lattice thermal conductivity at low temperatures (~100K), as compared to nanoribbons of the same width. Remarkably, rough edges do not appear to have a large impact on lattice energy transport through graphene nanorings while nanoribbons seem more affected by imperfections. Furthermore, we demonstrate that the effects of hydrogen-saturated edges can be neglected in these graphene nanostructures

Experimental evidence of delocalized states in random dimer superlattices

We study the electronic properties of GaAs-AlGaAs superlattices with intentional correlated disorder by means of photoluminescence and vertical dc resistance. The results are compared to those obtained in ordered and uncorrelated disordered superlattices. We report the first experimental evidence that spatial correlations inhibit localization of states in disordered low-dimensional systems, as our previous theoretical calculations suggested, in contrast to the earlier belief that all eigenstates are localized.Comment: 4 pages, 5 figures. Physical Review Letters (in press

Implications of the ALEPH tau-Lepton Decay Data for Perturbative and Non-Perturbative QCD

We use ALEPH data on hadronic $\tau$ decays in order to calculate Euclidean coordinate space correlation functions in the vector and axial-vector channels. The linear combination $V-A$ receives no perturbative contribution and is quantitatively reproduced by the instanton liquid model. In the case of $V+A$ the instanton calculation is in good agreement with the data once perturbative corrections are included. These corrections clearly show the evolution of $\alpha_s$. We also analyze the range of validity of the Operator Product Expansion (OPE). In the $V-A$ channel we find a dimension $d=6$ contribution which is comparable to the original SVZ estimate, but the instanton model provides a different non-singular term of the same magnitude. In the $V+A$ case both the OPE and the instanton model predict the same $d=4$ power correction induced by the gluon condensate, but it is masked by much larger perturbative contributions. We conclude that the range of validity of the OPE is limited to x\lsim0.3 fm, whereas the instanton model describes the data over the entire range.Comment: 4 pages, 6 figure

Review of the ELI-NP-GBS low level rf and synchronization systems

The Gamma Beam System (GBS) of ELI-NP is a linac based gamma-source in construction at Magurele (RO) by the European consortium EuroGammaS led by INFN. Photons with tunable energy and with intensity and brilliance well beyond the state of the art will be produced by Compton back-scattering between a high quality electron beam (up to 740 MeV) and a 515 nm intense laser pulse. Production of very intense photon flux with narrow bandwidth requires multi-bunch operation at 100 Hz repetition rate. A total of 13 klystrons, 3 S-band (2856 MHz) and 10 C-band (5712 MHz) will power a total of 14 Travelling Wave accelerating sections (2 S-band and 12 C-band) plus 3 S-band Standing Wave cavities (a 1.6 cell RF gun and 2 RF deflectors). Each klystron is individually driven by a temperature stabilized LLRF module, for a maximum flexibility in terms of accelerating gradient, arbitrary pulse shaping (e.g. to compensate beam loading effects in multi-bunch regime) and compensation of long-term thermal drifts. In this paper, the whole LLRF system architecture and bench test results, the RF reference generation and distribution together with an overview of the synchronization system will be described

Calculation of gluon and four-quark condensates from the operator expansion

The magnitudes of gluon and four-quark condensates are found from the analysis of vector mesons consisting of light quarks (the families of $\rho$ and $\omega$ mesons) in the 3 loops approximation. The QCD model with infinite number of vector mesons is used to describe the function $R(s)$. This model describes well the experimental function $R(s)$. Polarization operators calculated with this model coincide with the Wilson operator expansion at large $Q^2$. The improved perturbative theory, such that the polarization operators have correct analytical properties, is used. The result is $<0 | (\alpha_s/\pi) G^2 | 0 > = 0.062 \pm 0.019 GeV^4$. The electronic widths of $\rho(1450)$ and $\omega(1420)$ are calculated.Comment: 18 pages, latex, changed content slightl

Is there evidence for dimension-two corrections in QCD two-point functions?

The ALEPH data on the (non-strange) vector and axial-vector spectral functions, extracted from tau-lepton decays, is used in order to search for evidence for a dimension-two contribution, $C_{2 V,A}$, to the Operator Product Expansion (other than $d=2$ quark mass terms). This is done by means of a dimension-two Finite Energy Sum Rule, which relates QCD to the experimental hadronic information. The average $C_{2} \equiv (C_{2V} + C_{2A})/2$ is remarkably stable against variations in the continuum threshold, but depends rather strongly on $\Lambda_{QCD}$. Given the current wide spread in the values of $\Lambda_{QCD}$, as extracted from different experiments, we would conservatively conclude from our analysis that $C_{2}$ is consistent with zero.Comment: A misprint in Eq. (14) has been corrected. No other changes. Paper to appear in Phys. Rev.

Avaliação de metodologias para a determinação do teor de carbono e de matéria orgânica em fertilizantes líquidos à base de ácidos húmicos.

Este trabalho tem como objetivo avaliar diferentes metodologias para a determinação dos teores de carbono e de matéria orgânica em fertilizantes orgânicos líquidos à base de ácidos húmicos, observando-se o coeficiente de variação de cada método e o número mínimo de repetições necessárias para a obtenção de um resultado confiável. A determinação de padrões e desvios para os diferentes atributos avaliados para o controle de processos e avaliação da variabilidade entre lotes do produto Vitaplus® é também objetivo deste trabalho.bitstream/CNPS-2010/14901/1/bpd85-avaliacao-metodologias.pd