The strange quark condensate in the nucleon in 2+1 flavor QCD

We calculate the "strange quark content of the nucleon", , which is important for interpreting the results of some dark matter detection experiments. The method is to evaluate quark-line disconnected correlations on the MILC lattice ensembles, which include the effects of dynamical strange quarks. After continuum and chiral extrapolations, the result is <N |s s_bar |N> = 0.69 +- 0.07(statistical) +- 0.09(systematic), in the modified minimal subtraction scheme (2 GeV), or for the renormalization scheme invariant form, m_s partial{M_N}/partial{m_s} = 59(6)(8) MeV.Comment: Added figures and references, especially for fit range choice. Other changes for clarity. Version to appear in publicatio

BIOMECHANICS OF PROPULSION AND DRAG IN FRONT CRAWL SWIMMING

Peak performances in sport require the full deployment of all powers an athlete possesses. How factors like force, technique, and endurance each on itself, but also in concert determine swimming performance is subject of inquiry. The accent in this overview of swimming biomechanics is with 2 performance factors: (i) drag encountered by the body during swimming, and (ii) the generation of propulsion in water

AN ALTERNATIVE FLUID DYNAMIC EXPLANATION FOR PROPULSION IN FRONT CRAWL SWIMMING

Calculation of propulsion in front crawl swimming relies on the quasi-steady assumption that the fluid dynamic behaviour of a hand model in a flow channel (constant velocity and orientation) is similar to that of a hand of a real swimmer swimming the front crawl. It has been shown that quasi-steady calculations cannot account for the observed propulsive forces during front crawl swimming. Using woollen tufts the flow pattern around the arm and hand during the front crawl stroke was visualised. The flow direction varied strongly throughout the stroke and a strong, accelerating axial flow, not in the direction of the arm movement, was observed. These observations discredit the quasi-steady analysis of front crawl swimming. Instead, it is proposed that rotation of the arm leads to a proximo-distal pressure gradient, inducing axial flow. Such axial flow along the trailing side of the arm could greatly enhance the pressure difference over the hand, thus assisting propulsion by paddling

A General Criterion for Liquefaction in Granular Layers with Heterogeneous Pore Pressure

International audienceFluid-saturated granular and porous layers can undergo liquefaction and lose their shear resistance when subjected to shear forcing. In geosystems, such a process can lead to severe natural hazards of soil liquefaction, accelerating slope failure, and large earthquakes. Terzaghi's principle of effective stress predicts that liquefaction occurs when the pore pressure within the layer becomes equal to the applied normal stress on the layer. However, under dynamic loading and when the internal permeability is relatively small the pore pressure is spatially heterogeneous and it is not clear what measurement of pore pressure should be used in Terzaghi's principle. Here, we show theoretically and demonstrate using numerical simulations a general criterion for liquefaction that applies also for the cases in which the pore pressure is spatially heterogeneous. The general criterion demands that the average pore pressure along a continuous surface within the fluid-saturated granular or porous layer is equal to the applied normal stress

Chiral nature of magnetic monopoles in artificial spin ice

Micromagnetic properties of monopoles in artificial kagome spin ice systems are investigated using numerical simulations. We show that micromagnetics brings additional complexity into the physics of these monopoles that is, by essence, absent in spin models: besides a fractionalized classical magnetic charge, monopoles in the artificial kagome ice are chiral at remanence. Our simulations predict that the chirality of these monopoles can be controlled without altering their charge state. This chirality breaks the vertex symmetry and triggers a directional motion of the monopole under an applied magnetic field. Our results also show that the choice of the geometrical features of the lattice can be used to turn on and off this chirality, thus allowing the investigation of chiral and achiral monopoles.Comment: 10 pages, 4 figure

Critical Behavior at the Chiral Phase Transition

Quantum chromodynamics with two zero mass flavors is expected to exhibit a phase transition with O(4) critical behavior. Fixing the universality class is important for phenomenology and for facilitating the extrapolation of simulation data to physical quark mass values. At Lattice '96 the Tsukuba and Bielefeld groups reported results from new simulations with dynamical staggered quarks at $N_t = 4$, which suggested a departure from the expected critical behavior. We report observations of similar deviations and discuss efforts in progress to understand this phenomenon.Comment: 3 pp, LaTeX with 6 encapsulated Postscript figures. Lattice '97 proceeding

High density QCD with static quarks

We study lattice QCD in the limit that the quark mass and chemical potential are simultaneously made large, resulting in a controllable density of quarks which do not move. This is similar in spirit to the quenched approximation for zero density QCD. In this approximation we find that the deconfinement transition seen at zero density becomes a smooth crossover at any nonzero density, and that at low enough temperature chiral symmetry remains broken at all densities.Comment: LaTeX, 18 pages, uses epsf.sty, postscript figures include