581 research outputs found
Soft Covariant Gauges on the Lattice
We present an exploratory study of a one-parameter family of covariant,
non-perturbative lattice gauge-fixing conditions, that can be implemented
through a simple Monte Carlo algorithm. We demonstrate that at the numerical
level the procedure is feasible, and as a first application we examine the
gauge dependence of the gluon propagator.Comment: 11 pages, Latex, epsf.sty included + 5 PostScript picture
Gluon Propagator in the Infrared Region
The gluon propagator is calculated in quenched QCD for two different lattice
sizes (16^3x48 and 32^3x64) at beta=6.0. The volume dependence of the
propagator in Landau gauge is studied. The smaller lattice is instrumental in
revealing finite volume and anisotropic lattice artefacts. Methods for
minimising these artefacts are developed and applied to the larger lattice
data. New structure seen in the infrared region survives these conservative
cuts to the lattice data. This structure serves to rule out a number of models
that have appeared in the literature. A fit to a simple analytical form
capturing the momentum dependence of the nonperturbative gluon propagator is
also reported.Comment: 13 pages, 9 figures, using RevTeX. Submitted to Phys. Rev. D. This
and related papers can also be obtained from
http://www.physics.adelaide.edu.au/~jskuller/papers
Gluon mass generation in the PT-BFM scheme
In this article we study the general structure and special properties of the
Schwinger-Dyson equation for the gluon propagator constructed with the pinch
technique, together with the question of how to obtain infrared finite
solutions, associated with the generation of an effective gluon mass.
Exploiting the known all-order correspondence between the pinch technique and
the background field method, we demonstrate that, contrary to the standard
formulation, the non-perturbative gluon self-energy is transverse
order-by-order in the dressed loop expansion, and separately for gluonic and
ghost contributions. We next present a comprehensive review of several subtle
issues relevant to the search of infrared finite solutions, paying particular
attention to the role of the seagull graph in enforcing transversality, the
necessity of introducing massless poles in the three-gluon vertex, and the
incorporation of the correct renormalization group properties. In addition, we
present a method for regulating the seagull-type contributions based on
dimensional regularization; its applicability depends crucially on the
asymptotic behavior of the solutions in the deep ultraviolet, and in particular
on the anomalous dimension of the dynamically generated gluon mass. A
linearized version of the truncated Schwinger-Dyson equation is derived, using
a vertex that satisfies the required Ward identity and contains massless poles
belonging to different Lorentz structures. The resulting integral equation is
then solved numerically, the infrared and ultraviolet properties of the
obtained solutions are examined in detail, and the allowed range for the
effective gluon mass is determined. Various open questions and possible
connections with different approaches in the literature are discussed.Comment: 54 pages, 24 figure
Neural correlates of enhanced visual short-term memory for angry faces: An fMRI study
Copyright: © 2008 Jackson et al.Background: Fluid and effective social communication requires that both face identity and emotional expression information are encoded and maintained in visual short-term memory (VSTM) to enable a coherent, ongoing picture of the world and its players. This appears to be of particular evolutionary importance when confronted with potentially threatening displays of emotion - previous research has shown better VSTM for angry versus happy or neutral face identities.Methodology/Principal Findings: Using functional magnetic resonance imaging, here we investigated the neural correlates of this angry face benefit in VSTM. Participants were shown between one and four to-be-remembered angry, happy, or neutral faces, and after a short retention delay they stated whether a single probe face had been present or not in the previous display. All faces in any one display expressed the same emotion, and the task required memory for face identity. We find enhanced VSTM for angry face identities and describe the right hemisphere brain network underpinning this effect, which involves the globus pallidus, superior temporal sulcus, and frontal lobe. Increased activity in the globus pallidus was significantly correlated with the angry benefit in VSTM. Areas modulated by emotion were distinct from those modulated by memory load.Conclusions/Significance: Our results provide evidence for a key role of the basal ganglia as an interface between emotion and cognition, supported by a frontal, temporal, and occipital network.The authors were supported by a Wellcome Trust grant (grant number 077185/Z/05/Z) and by BBSRC (UK) grant BBS/B/16178
Rate Equations for Graphs
In this paper, we combine ideas from two different scientific traditions: 1)
graph transformation systems (GTSs) stemming from the theory of formal
languages and concurrency, and 2) mean field approximations (MFAs), a
collection of approximation techniques ubiquitous in the study of complex
dynamics. Using existing tools from algebraic graph rewriting, as well as new
ones, we build a framework which generates rate equations for stochastic GTSs
and from which one can derive MFAs of any order (no longer limited to the
humanly computable). The procedure for deriving rate equations and their
approximations can be automated. An implementation and example models are
available online at https://rhz.github.io/fragger. We apply our techniques and
tools to derive an expression for the mean velocity of a two-legged walker
protein on DNA.Comment: to be presented at the 18th International Conference on Computational
Methods in Systems Biology (CMSB 2020
Evaluation of the Self-healing Capability of Ultra-High-Performance Fiber-Reinforced Concrete with Nano-Particles and Crystalline Admixtures by Means of Permeability
[EN] Self-healing is the capability of a material to repair its damage autonomously. Ultra-High-Performance Fiber Reinforced Concrete (UHPFRC) has potentially higher self-healing properties than conventional concrete because of its lower water/binder content and controlled microcracking due to the high fiber content. This work uses a novel methodology based on the permeability to evaluate autogenous self-healing of UHPFRC and enhanced self-healing, incorporating several additions. To this purpose, one UHPFRC was selected and modified to include alumina nanofibers in 0.25% by the cement weight, nanocellulose (nanocrystals and nanofibers), in a dosage of 0.15% by the cement weight, and 0.8-1.6% of a crystalline admixture. The results obtained show that the methodology proposed allows the evaluation of the self-healing capability of different families of concrete mixes that suffered a similar level of damage using permeability tests adapted to the specific properties of UHPFRC.The authors would like to acknowledge the European UnionÂżs Horizon
2020 ReSHEALience project (Grant Agreement No. 760824).Doostkami, H.; Roig-Flores, M.; Negrini, A.; Mezquida-Alcaraz, EJ.; Serna Ros, P. (2020). Evaluation of the Self-healing Capability of Ultra-High-Performance Fiber-Reinforced Concrete with Nano-Particles and Crystalline Admixtures by Means of Permeability. Springer. 489-499. https://doi.org/10.1007/978-3-030-58482-5_45489499Homma, D., Mihashi, H., Nishiwaki, T.: Self-healing capability of fibre reinforced cementitious composites. J. Adv. Concr. Technol. 7(2), 217â228 (2009)Maes, M., Snoeck, D., De Belie, N.: Chloride penetration in cracked mortar and the influence of autogenous crack healing. Constr. Build. Mater. 115, 114â124 (2016)Edvardsen, C.: Water Permeability and Autogenous Healing of Cracks in Concrete, vol. 96 (1999)De Belie, N., et al.: A review of self-healing concrete for damage management of structures. Adv. Mater. Interfaces 5(17) (2018)Wang, H.L., Dai, J.G., Sun, X.Y., Zhang, X.L.: Characteristics of concrete cracks and their influence on chloride penetration. Constr. Build. Mater. 107, 216â225 (2016)Wang, K., Jansen, D.C., Shah, S.P., Karr, A.F.: Permeability study of cracked concrete. Cem. Concr. Res. (1997)Ć avija, B., Schlangen, E.: Autogeneous healing and chloride ingress in cracked concrete. Heron 61(1), 15â32 (2016)Ismail, M., Toumi, A., François, R., GagnĂ©, R.: Effect of crack opening on the local diffusion of chloride in cracked mortar samples. Cem. Concr. Res. 38(8â9), 1106â1111 (2008)Habel, K., Gauvreau, P.: Response of ultra-high performance fiber reinforced concrete (UHPFRC) to impact and static loading. Cem. Concr. Compos. 30(10), 938â946 (2008)DenariĂ©, E., BrĂŒhwiler, E.: Strain-hardening ultra-high performance fibre reinforced concrete: deformability versus strength optimization. Restor. Build. Monum. 17(6), 397â410 (2014)Granger, S., Pijaudier-Cabot, G., Loukili, A.: Mechanical behavior of self-healed ultra high performance concrete: from experimental evidence to modeling. In: Proceedings of the 6th International Conference on Fracture Mechanics of Concrete and Concrete Structures, vol. 3, pp. 1827â1834 (2007)Escoffres, P., Desmettre, C., Charron, J.P.: Effect of a crystalline admixture on the self-healing capability of high-performance fiber reinforced concretes in service conditions. Constr. Build. Mater. 173, 763â774 (2018)Sisomphon, K., Copuroglu, O., Koenders, E.A.B.: Self-healing of surface cracks in mortars with expansive additive and crystalline additive. Cem. Concr. Compos. 34(4), 566â574 (2012)Roig-Flores, M., Moscato, S., Serna, P., Ferrara, L.: Self-healing capability of concrete with crystalline admixtures in different environments. Constr. Build. Mater. 86, 1â11 (2015)Roig-Flores, M., Pirritano, F., Serna, P., Ferrara, L.: Effect of crystalline admixtures on the self-healing capability of early-age concrete studied by means of permeability and crack closing tests. Constr. Build. Mater. 114, 447â457 (2016)Ferrara, L., Krelani, V., Carsana, M.: A âfracture testingâ based approach to assess crack healing of concrete with and without crystalline admixtures. Constr. Build. Mater. 68, 535â551 (2014)Ferrara, L., Krelani, V., Moretti, F.: On the use of crystalline admixtures in cement based construction materials: from porosity reducers to promoters of self healing. Smart Mater. Struct. 25(8), 1â17 (2016)Cuenca, E., Cislaghi, G., Puricelli, M., Ferrara, L.: Influence of self-healing stimulated via crystalline admixtures on chloride penetration. In: America Concrete Institute, vol. 2018(SP 326), pp. 1â10. ACI Spec. Publ. (2018)Borg, R.P., Cuenca, E., Gastaldo Brac, E.M., Ferrara, L.: Crack sealing capacity in chloride-rich environments of mortars containing different cement substitutes and crystalline admixtures. J. Sustain. Cem. Mater. 7(3), 141â159 (2018)LĂłpez, J.Ă., Serna, P., Navarro-Gregori, J., Camacho, E.: An inverse analysis method based on deflection to curvature transformation to determine the tensile properties of UHPFRC. Mater. Struct. 48(11), 3703â3718 (2014). https://doi.org/10.1617/s11527-014-0434-0LĂłpez, J.Ă.: Characterisation of the Tensile Behaviour of UHPFRC By Means of Four-Point Bending Tests, March 2017Negrini, A., Roig-Flores, M., Mezquida-Alcaraz, E.J., Ferrara, L., Serna, P.: Effect of crack pattern on the self-healing capability in traditional, HPC and UHPFRC concretes measured by water and chloride permeability. In: MATEC Web Conference, vol. 289, p. 01006 (2019
From Africa to Europe and back: refugia and range shifts cause high genetic differentiation in the Marbled White butterfly Melanargia galathea
<p>Abstract</p> <p>Background</p> <p>The glacial-interglacial oscillations caused severe range modifications of biota. Thermophilic species became extinct in the North and survived in southern retreats, e.g. the Mediterranean Basin. These repeated extinction and (re)colonisation events led to long-term isolation and intermixing of populations and thus resulted in strong genetic imprints in many European species therefore being composed of several genetic lineages. To better understand these cycles of repeated expansion and retraction, we selected the Marbled White butterfly <it>Melanargia galathea</it>. Fourty-one populations scattered over Europe and the Maghreb and one population of the sibling taxon <it>M. lachesis </it>were analysed using allozyme electrophoresis.</p> <p>Results</p> <p>We obtained seven distinct lineages applying neighbour joining and STRUCTURE analyses: (i) Morocco, (ii) Tunisia, (iii) Sicily, (iv) Italy and southern France, (v) eastern Balkans extending to Central Europe, (vi) western Balkans with western Carpathian Basin as well as (vii) south-western Alps. The hierarchy of these splits is well matching the chronology of glacial and interglacial cycles since the GĂŒnz ice age starting with an initial split between the <it>galathea </it>group in North Africa and the <it>lachesis </it>group in Iberia. These genetic structures were compared with past distribution patterns during the last glacial stage calculated with distribution models.</p> <p>Conclusions</p> <p>Both methods suggest climatically suitable areas in the Maghreb and the southern European peninsulas with distinct refugia during the last glacial period and underpin strong range expansions to the North during the Postglacial. However, the allozyme patterns reveal biogeographical structures not detected by distribution modelling as two distinct refugia in the Maghreb, two or more distinct refugia at the Balkans and a close link between the eastern Maghreb and Sicily. Furthermore, the genetically highly diverse western Maghreb might have acted as source or speciation centre of this taxon, while the eastern, genetically impoverished Maghreb population might result from a relatively recent recolonisation from Europe via Sicily.</p
A Lattice Study of the Gluon Propagator in Momentum Space
We consider pure glue QCD at beta=5.7, beta=6.0 and beta=6.3. We evaluate the
gluon propagator both in time at zero 3-momentum and in momentum space. From
the former quantity we obtain evidence for a dynamically generated effective
mass, which at beta=6.0 and beta=6.3 increases with the time separation of the
sources, in agreement with earlier results. The momentum space propagator G(k)
provides further evidence for mass generation. In particular, at beta=6.0, for
k less than 1 GeV, the propagator G(k) can be fit to a continuum formula
proposed by Gribov and others, which contains a mass scale b, presumably
related to the hadronization mass scale. For higher momenta Gribov's model no
longer provides a good fit, as G(k) tends rather to follow an inverse power
law. The results at beta=6.3 are consistent with those at beta=6.0, but only
the high momentum region is accessible on this lattice. We find b in the range
of three to four hundred MeV and the exponent of the inverse power law about
2.7. On the other hand, at beta=5.7 (where we can only study momenta up to 1
GeV) G(k) is best fit to a simple massive boson propagator with mass m. We
argue that such a discrepancy may be related to a lack of scaling for low
momenta at beta=5.7. {}From our results, the study of correlation functions in
momentum space looks promising, especially because the data points in Fourier
space turn out to be much less correlated than in real space.Comment: 19 pages + 12 uuencoded PostScript picture
Prediagnostic sex steroid hormones in relation to male breast cancer risk
Purpose Although previous studies have implicated a variety of hormone-related risk factors in the etiology of male breast cancers, no previous studies have examined the effects of endogenous hormones. Patients and Methods Within the Male Breast Cancer Pooling Project, an international consortium comprising 21 case-control and cohort investigations, a subset of seven prospective cohort studies were able to contribute prediagnostic serum or plasma samples for hormone quantitation. Using a nested case-control design, multivariable unconditional logistic regression analyses estimated odds ratios and 95% CIs for associations between male breast cancer risk and 11 individual estrogens and androgens, as well as selected ratios of these analytes. Results Data from 101 cases and 217 matched controls were analyzed. After adjustment for age and date of blood draw, race, and body mass index, androgens were found to be largely unrelated to risk, but circulating estradiol levels showed a significant association. Men in the highest quartile had an odds ratio of 2.47 (95% CI, 1.10 to 5.58) compared with those in the lowest quartile (trend P = .06). Assessment of estradiol as a ratio to various individual androgens or sum of androgens showed no further enhancement of risk. These relations were not significantly modified by either age or body mass index, although estradiol was slightly more strongly related to breast cancers occurring among younger (age < 67 years) than older men. Conclusion Our results support the notion of an important role for estradiol in the etiology of male breast cancers, similar to female breast cancers
NEMO: A Project for a km Underwater Detector for Astrophysical Neutrinos in the Mediterranean Sea
The status of the project is described: the activity on long term
characterization of water optical and oceanographic parameters at the Capo
Passero site candidate for the Mediterranean km neutrino telescope; the
feasibility study; the physics performances and underwater technology for the
km; the activity on NEMO Phase 1, a technological demonstrator that has
been deployed at 2000 m depth 25 km offshore Catania; the realization of an
underwater infrastructure at 3500 m depth at the candidate site (NEMO Phase 2).Comment: Proceeding of ISCRA 2006, Erice 20-27 June 200
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