265 research outputs found
Irrelevant operators in the two-dimensional Ising model
By using conformal-field theory, we classify the possible irrelevant
operators for the Ising model on the square and triangular lattices. We analyze
the existing results for the free energy and its derivatives and for the
correlation length, showing that they are in agreement with the conformal-field
theory predictions. Moreover, these results imply that the nonlinear scaling
field of the energy-momentum tensor vanishes at the critical point. Several
other peculiar cancellations are explained in terms of a number of general
conjectures. We show that all existing results on the square and triangular
lattice are consistent with the assumption that only nonzero spin operators are
present.Comment: 32 pages. Added comments and reference
Correction induced by irrelevant operators in the correlators of the 2d Ising model in a magnetic field
We investigate the presence of irrelevant operators in the 2d Ising model
perturbed by a magnetic field, by studying the corrections induced by these
operators in the spin-spin correlator of the model. To this end we perform a
set of high precision simulations for the correlator both along the axes and
along the diagonal of the lattice. By comparing the numerical results with the
predictions of a perturbative expansion around the critical point we find
unambiguous evidences of the presence of such irrelevant operators. It turns
out that among the irrelevant operators the one which gives the largest
correction is the spin 4 operator T^2 + \bar T^2 which accounts for the
breaking of the rotational invariance due to the lattice. This result agrees
with what was already known for the correlator evaluated exactly at the
critical point and also with recent results obtained in the case of the thermal
perturbation of the model.Comment: 28 pages, no figure
Progress of the Felsenkeller shallow-underground accelerator for nuclear astrophysics
Low-background experiments with stable ion beams are an important tool for
putting the model of stellar hydrogen, helium, and carbon burning on a solid
experimental foundation. The pioneering work in this regard has been done by
the LUNA collaboration at Gran Sasso, using a 0.4 MV accelerator. In the
present contribution, the status of the project for a higher-energy underground
accelerator is reviewed. Two tunnels of the Felsenkeller underground site in
Dresden, Germany, are currently being refurbished for the installation of a 5
MV high-current Pelletron accelerator. Construction work is on schedule and
expected to complete in August 2017. The accelerator will provide intense, 50
uA, beams of 1H+, 4He+, and 12C+ ions, enabling research on astrophysically
relevant nuclear reactions with unprecedented sensitivity.Comment: Submitted to the Proceedings of Nuclei in the Cosmos XIV, 19-24 June
2016, Niigata/Japa
Injector fouling and its impact on engine emissions and spray characteristics in gasoline direct injection engines
In Gasoline Direct Injection engines, direct exposure of the injector to the flame can cause combustion products to accumulate on the nozzle, which can result in increased particulate emissions. This research observes the impact of injector fouling on particulate emissions and the associated injector spray pattern and shows how both can be reversed by utilising fuel detergency. For this purpose multi-hole injectors were deliberately fouled in a four-cylinder test engine with two different base fuels. During a four hour injector fouling cycle particulate numbers (PN) increased by up to two orders of magnitude. The drift could be reversed by switching to a fuel blend that contained a detergent additive. In addition, it was possible to completely avoid any PN increase, when the detergent containing fuel was used from the beginning of the test. Microscopy showed that increased injector fouling coincided with increased particulate emissions. Based on these results a selection of the injectors was installed in a laboratory injection chamber and the spray patterns were investigated with a high speed camera. Injectors corresponding to the largest PN drift produced the thinnest spray jets with the deepest penetration. These factors amplify the risk of wall wetting and provide an explanation for the increase of PN. The positive effect of the detergent was also reflected in the spray pattern analysis, which illustrates the potential benefits of such fuel additives
Recycling bins, garbage cans or think tanks? Three myths regarding policy analysis institutes
The phrase 'think tank' has become ubiquitous â overworked and underspecified â in the political lexicon. It is entrenched in scholarly discussions of public policy as well as in the 'policy wonk' of journalists, lobbyists and spin-doctors. This does not mean that there is an agreed definition of think tank or consensual understanding of their roles and functions. Nevertheless, the majority of organizations with this label undertake policy research of some kind. The idea of think tanks as a research communication 'bridge' presupposes that there are discernible boundaries between (social) science and policy. This paper will investigate some of these boundaries. The frontiers are not only organizational and legal; they also exist in how the 'public interest' is conceived by these bodies and their financiers. Moreover, the social interactions and exchanges involved in 'bridging', themselves muddy the conception of 'boundary', allowing for analysis to go beyond the dualism imposed in seeing science on one side of the bridge, and the state on the other, to address the complex relations between experts and public policy
Global public policy, transnational policy communities, and their networks
Public policy has been a prisoner of the word "state." Yet, the state is reconfigured by globalization. Through "global publicâprivate partnerships" and "transnational executive networks," new forms of authority are emerging through global and regional policy processes that coexist alongside nation-state policy processes. Accordingly, this article asks what is "global public policy"? The first part of the article identifies new public spaces where global policies occur. These spaces are multiple in character and variety and will be collectively referred to as the "global agora." The second section adapts the conventional policy cycle heuristic by conceptually stretching it to the global and regional levels to reveal the higher degree of pluralization of actors and multiple-authority structures than is the case at national levels. The third section asks: who is involved in the delivery of global public policy? The focus is on transnational policy communities. The global agora is a public space of policymaking and administration, although it is one where authority is more diffuse, decision making is dispersed and sovereignty muddled. Trapped by methodological nationalism and an intellectual agoraphobia of globalization, public policy scholars have yet to examine fully global policy processes and new managerial modes of transnational public administration
DivergĂȘncia genĂ©tica dos atributos sensoriais de clones de Coffea canephora cultivados na AmazĂŽnia ocidental.
O objetivo deste trabalho foi avaliar a qualidade de bebida de genĂłtipos do cafeeiro Coffea canephora cultivados em dois ambientes contrastantes da AmazĂŽnia Ocidental. Foram avaliados 15 clones comercializados em domĂnio pĂșblico nos ambientes de Porto Velho e SĂŁo Felipe dâOeste, ISSN: 16799844 â InterSciencePlace â International Scientific Journal Page 34 RondĂŽnia. A classificação da bebida foi realizada conforme o Protocolo de Degustação de Robusta Finos que quantifica a qualidade a partir de nota que varia de 0 a 100 pontos, destacando as nuances dos clones. O desempenho dos clones em diferentes ambientes foi analisado considerando anĂĄlises de variĂąncia simples e conjunta, estimativas de parĂąmetros genĂ©ticos e a dispersĂŁo no plano dos valores genĂ©ticos. Observou-se efeito significativo da interação genĂłtipo x ambientes, o que indica que os clones apresentaram desempenho diferenciado entre os ambientes cultivados. Estimativas dos parĂąmetros genĂ©ticos indicaram boa condução experimental e predomĂnio do efeito genotĂpico na expressĂŁo dos atributos sensoriais. Dez genĂłtipos apresentaram notas acima de 80 pontos e, portanto, foram classificados como Robustas Finos. Os demais clones foram classificados como de bebida muito boa com notas superiores a 76 pontos. Os clones AS7, AS1, N8(G8), L1, R152, AS5, LB15 e R152 apresentaram maior adaptabilidade e estabilidade tendo sido avaliados com notas acima de 80 pontos nos dois ambientes. Os clones WP6, GB7, N16 e R22 apresentaram menor previsibilidade de desempenho tendo apresentado nota acima de 80 pontos em apenas um dos ambientes avaliados. JĂĄ os clones AR106 e N13 se caracterizaram pela maior estabilidade e menor adaptabilidade, tendo apresentado notas abaixo de 80 pontos nos dois ambientes avaliados. Os clones estudados apresentaram ampla variabilidade genĂ©tica, sendo possĂvel selecionar clones com desempenho superior para a qualidade de bebida
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