Stress field around arbitrarily shaped cracks in two-dimensional elastic materials

The calculation of the stress field around an arbitrarily shaped crack in an infinite two-dimensional elastic medium is a mathematically daunting problem. With the exception of few exactly soluble crack shapes the available results are based on either perturbative approaches or on combinations of analytic and numerical techniques. We present here a general solution of this problem for any arbitrary crack. Along the way we develop a method to compute the conformal map from the exterior of a circle to the exterior of a line of arbitrary shape, offering it as a superior alternative to the classical Schwartz-Cristoffel transformation. Our calculation results in an accurate estimate of the full stress field and in particular of the stress intensity factors K_I and K_{II} and the T-stress which are essential in the theory of fracture.Comment: 7 pages, 4 figures, submitted for PR

Environment and harvest time affects the combustion qualities of Miscanthus genotypes

Miscanthus spp. are high-yielding perennial C4 grasses, native to Asia, that are being investigated in Europe as potential biofuels. Production of economically viable solid biofuel must combine high biomass yields with good combustion qualities. Good biomass combustion quality depends on minimizing moisture, ash, K, chloride, N, and S. To this end, field trials at five sites in Europe from Sweden to Portugal were planted with 15 different genotypes including M. x giganteus, M. sacchariflorus, M. sinensis, and newly bred M. sinensis hybrids. Yield and combustion quality at an autumn and a late winter/ early spring harvest were determined in the third year after planting when the stands had reached maturity. As expected, delaying the harvest by three to four months improved the combustion quality of all genotypes by reducing ash (from 40 to 25 g kg-1 dry matter), K (from 9 to 4 g kg-1 dry matter), chloride (from 4 to 1 g kg-1 dry matter), N (from 5 to 4 g kg-1 dry matter), and moisture (from 564 to 291 g kg-1 fresh matter). However, the delayed harvest also decreased mean biomass yields from 17 to 14 t ha-1. There is a strong interaction among yield, quality, and site growing conditions. Results show that in northern regions of Europe, M. sinensis hybrids can be recommended for high yields (yielding up to 25 t ha-1), but M. sinensis (nonhybrid) genotypes have higher combustion qualities. In mid- and south Europe, M. giganteus (yielding up to 38 t ha-1) or specific high-yielding M. sinensis hybrids (yielding up to 41 t ha-1) are more suitable for biofuel production

Space-time evolution of hadronization

Beside its intrinsic interest for the insights it can give into color confinement, knowledge of the space-time evolution of hadronization is very important for correctly interpreting jet-quenching data in heavy ion collisions and extracting the properties of the produced medium. On the experimental side, the cleanest environment to study the space-time evolution of hadronization is semi-inclusive Deeply Inelastic Scattering on nuclear targets. On the theoretical side, 2 frameworks are presently competing to explain the observed attenuation of hadron production: quark energy loss (with hadron formation outside the nucleus) and nuclear absorption (with hadronization starting inside the nucleus). I discuss recent observables and ideas which will help to distinguish these 2 mechanisms and to measure the time scales of the hadronization process.Comment: 6 pages, 4 figures. Based on talks given at "Hot Quarks 2006", Villasimius, Italy, May 15-20, 2006, and at the "XLIV internataional winter meeting on nuclear physics", Bormio, Italy, Jan 29 - Feb 5, 2006. To appear in Eur.Phys.J.

Restricting quark matter models by gravitational wave observation

We consider the possibilities for obtaining information about the equation of state for quark matter by using future direct observational data on gravitational waves. We study the nonradial oscillations of both fluid and spacetime modes of pure quark stars. If we observe the $f$ and the lowest $w_{\rm II}$ modes from quark stars, by using the simultaneously obtained radiation radius we can constrain the bag constant $B$ with reasonable accuracy, independently of the $s$ quark mass.Comment: To appear in Phys. Rev.

Sexual dimorphism in the size and shape of the raptorial pedipalps of Giant Whip Spiders (Arachnida: Amblypygi)

Sexual dimorphism in the form of elaborate crests, horns and swellings can be a clear indicator of the differing evolutionary pressures to which males and females are subject. However, dimorphism can also be expressed in more subtle shape differences not outwardly obvious to the observer. Whip spiders (Amblypygi) possess a unique pair of spined pedipalps hypothesized to primarily function in prey capture, but also serving multiple other functions. Little is known regarding the intraspecific shape variation of these limbs and its potential causes. Because a role during courtship and male contest has also been hypothesized, sexual selection may contribute to shape differences. As such, we hypothesize that sexual dimorphism will be present in the size and shape of amblypygid pedipalps, with male contest selecting for longer and thicker pedipalps, and larger spines in males. This study aims to test this hypothesis, by quantifying the contribution of ontogeny and sexual dimorphism to shape within the raptorial pedipalps of Damon variegatus. Discriminant function analysis using GMM landmark data reveals statistically significant sexual shape dimorphism in both the tibia and femur of the pedipalp. Contrary to our hypothesis, males display a more gracile pedipalp morphology with reduced spination. Sex differences in the allometric slope and overall size were also found in a number of linear appendicular metrics using Type-II regression. Males have statistically longer pedipalp tibiae, whip femora, and leg two femora. We propose that males have evolved a longer pedipalps in the context of display contest rather than physical aggression. The elongation of structures used in display-based contest and courtship found herein further emphasizes the contribution of visual cues to the evolution of morphology more broadly

Soft Photons in Hadron-Hadron Collisions: Synchrotron Radiation from the QCD Vacuum?

We discuss the production of soft photons in high energy hadron-hadron collisions. We present a model where quarks and antiquarks in the hadrons emit ``synchrotron light'' when being deflected by the chromomagnetic fields of the QCD vacuum, which we assume to have a nonperturbative structure. This gives a source of prompt soft photons with frequencies $\omega <= 300 MeV$ in the c.m. system of the collision in addition to hadronic bremsstrahlung. In comparing the frequency spectrum and rate of ``synchrotron'' photons to experimental results we find some supporting evidence for their existence. We make an exclusive--inclusive connection argument to deduce from the ``synchrotron'' effect a behaviour of the neutron electric formfactor $G_E^n(Q^2)$ proportional to $(Q^2)^{1/6}$ for $Q^2 < 20 fm^{-2}$. We find this to be consistent with available data. In our view, soft photon production in high energy hadron-hadron and lepton-hadron collisions as well as the behaviour of electromagnetic hadron formfactors for low $Q^2$ are thus sensitive probes of the nonperturbative structure of the QCD vacuum.Comment: Heidelberg preprint HD-THEP-94-36, 31 pages, LaTeX + ZJCITE.sty (included), 12 figures appended as uuencoded compressed ps-fil

Self-help interventions for anxiety disorders: An overview.

Anxiety disorders are highly prevalent and are associated with a marked impairment in quality of life and a huge economic cost to society. Unfortunately, a considerable number of people who struggle with anxiety do not seek or receive adequate treatment. Self-help interventions have been proposed to constitute a relatively cheap, effective, efficient, and low-threshold intervention for anxiety disorders. This paper offers a critical discussion of their advantages and disadvantages and the evidence for their effectiveness. We conclude that guided self-help can play a major role in mental health care for patients with anxiety disorders. However, several research questions need to be answered before broad-scale dissemination is possible. The Internet will continue to play a prominent role in the further development of this field of research and clinical practice

Multimessenger astronomy with the Einstein Telescope

Gravitational waves (GWs) are expected to play a crucial role in the development of multimessenger astrophysics. The combination of GW observations with other astrophysical triggers, such as from gamma-ray and X-ray satellites, optical/radio telescopes, and neutrino detectors allows us to decipher science that would otherwise be inaccessible. In this paper, we provide a broad review from the multimessenger perspective of the science reach offered by the third generation interferometric GW detectors and by the Einstein Telescope (ET) in particular. We focus on cosmic transients, and base our estimates on the results obtained by ET's predecessors GEO, LIGO, and Virgo.Comment: 26 pages. 3 figures. Special issue of GRG on the Einstein Telescope. Minor corrections include

Grain Surface Models and Data for Astrochemistry

AbstractThe cross-disciplinary field of astrochemistry exists to understand the formation, destruction, and survival of molecules in astrophysical environments. Molecules in space are synthesized via a large variety of gas-phase reactions, and reactions on dust-grain surfaces, where the surface acts as a catalyst. A broad consensus has been reached in the astrochemistry community on how to suitably treat gas-phase processes in models, and also on how to present the necessary reaction data in databases; however, no such consensus has yet been reached for grain-surface processes. A team of ∼25 experts covering observational, laboratory and theoretical (astro)chemistry met in summer of 2014 at the Lorentz Center in Leiden with the aim to provide solutions for this problem and to review the current state-of-the-art of grain surface models, both in terms of technical implementation into models as well as the most up-to-date information available from experiments and chemical computations. This review builds on the results of this workshop and gives an outlook for future directions