16,732 research outputs found
ICT as Technical Change in the Matching and Production Functions of a Pissarides-Dixit-Stiglitz model
No full textIn this paper we integrate two workhorse models in economics: Themonopolistic competition model of Dixit and Stiglitz and the search unemploymentmodel of Pissarides. Information and communication technology (ICT) is interpretedas i) technical progress in the matching function of the Pissarides labour marketsearch model where it is increasing the probability of filling a vacancy, and ii) astechnical change in the production function of the Dixit-Stiglitz goods market modelwhere it is increasing fixed costs and decreasing variable costs. All effects together,modelled as a permanent once-and-for-all ICT and Internet shock, increase thevacancy/ unemployment ratio, decrease the long-run equilibrium unemployment rate,and increase wages. Keywords: ICT, Monopolistic competition, unemployment.macroeconomics ;
Ausslegung des hundert und neunten Psalms Dixit Dominus domino meo
No full textA reprint of an early work by Luther which comments on the 110th Psalm (Vulgate 109).
Full title: Auszlegung des hu[n]dert vnd neundten psalmen. Dixit D[omi]n[u]s domino meo. / Doctoris Martini Luther Augustiner zu Witte[n]bergk ; zu herr Hieronymo Ebner Loszunger zu Nurnbergk
Find this item in the library catalog.https://digitalcommons.usm.maine.edu/spcrb_howardbs/1016/thumbnail.jp
Near Wall PIV-Measurements on the Windward Slope of a Hill
No full textThe turbulent flow over periodic hills was measured near to the wall, using planar Particle-Image-Velocimetry (PIV) at high spatial resolution. Our focus is on the near wall turbulence structure on the windward slope of the hill. For large-eddy simulation (LES) we suspect that, if this was not predicted accurately, it affects the prediction of the velocity profiles over the hill crest which in turn will affect the recirculation length downstream of the hill. Regarding the time averaged velocities, we were able to resolve the linear viscous region of the boundary layer. The velocity distribution and also the Reynolds stress does not comply with the law of the wall as it is valid for a turbulent boundary layer at equilibrium
Real-space Manifestations of Bottlenecks in Turbulence Spectra
No full textAn energy-spectrum bottleneck, a bump in the turbulence spectrum between the inertial and dissipation ranges, is shown to occur in the non-turbulent, one-dimensional, hyperviscous Burgers equation and found to be the Fourier-space signature of oscillations in the real-space velocity, which are explained by boundary-layer-expansion techniques. Pseudospectral simulations are used to show that such oscillations occur in velocity correlation functions in one- and three-dimensional hyperviscous hydrodynamical equations that display genuine turbulence
Universal Statistical Properties of Inertial-particle Trajectories in Three-dimensional, Homogeneous, Isotropic, Fluid Turbulence
No full textWe obtain new universal statistical properties of heavy-particle trajectories in three-dimensional, statistically steady, homogeneous, and isotropic turbulent flows by direct numerical simulations. We show that the probability distribution functions (PDFs) P(Φ), of the angle Φ between the Eulerian velocity u and the particle velocity v, at a point and time, scales as P(Φ) ∼Φ−, with a new universal exponent ≃ 4
Turbulent bands in a planar shear flow without walls
No full textThe banded structure of turbulence is observed immediately beyond transition in shear flows with two unconstrained directions (e.g. TCF, PCF, PPF). Yet despite its ubiquitous nature, the mechanisms underpinning bands are not understood to the level of localized turbulence in pipe flow. To this aim we investigate turbulent bands in Waleffe flow, a sinusoidal shear flow, U(y)=sin(pi/2 * y), with stress-free boundary conditions at y=+-1. The existence of turbulent bands in this system demonstrates that walls are not necessary to induce the phenomenon. The sinusoidal nature of the base forcing means the dominant features of bands can be viewed through a small number of Fourier modes in y. Utilizing this simple dependence we examine the emergence of turbulent bands from uniform turbulence
Assessing late-time singular behaviour in symmetry-plane models of 3D Euler flow
No full textMotivated by work on stagnation-point type exact solutions of the 3D Euler fluid equations by Gibbon [Gibbon et. al. Phys. D, 132, 497, (1999)] and the subsequent demonstration of finite-time blowup by Constantin [Constantin, Math. Res. Notices, 9, 455, (2000)] we introduce a one-parameter family of models of the 3D Euler equations on a 2D symmetry plane. These models provide a collection of blow-up scenarios which admit analytical solutions and are computationally inexpensive in comparison to the full 3D Euler equations. We take advantage of these features to examine the efficacy of novel methods which aid the assessment of finite-time blow-up in numerical simulations. The principal of these is the mapping to regular systems [Bustamante, Phys. D, 240, 1092, (2011)]; a bijective nonlinear mapping of time and the prognostic variables based on a Beale-Kato-Majda (BKM) type supremum norm regularity condition [Beale et. al. Commun. Math. Phys. 94, 61, (1984)]. We show a 3 order of magnitude increase of accuracy of the singularity time when employing the mapping with negligible additional computational expense. An investigation of the spectra of the primary field (vortex stretching rate) allows us to confirm a power law decrement of the analyticity-strip width with time in agreement with rigorous bounds bridging between the global spatial behaviour and BKM theorems [Bustamante & Brachet, Phys. Rev. E. 86, (2012)]
Weak decays of the axial-vector tetraquark Tbb;(u)over-bar(d)over-bar(-)
No full textAzizi, Kazem (Dogus Author)The weak decays of the axial-vector tetraquark T-bb;(u) over bar(d) over bar(-) to the scalar state Z(bc;(u) over bar(d) over bar)(0) are investigated using the QCD three-point sum rule approach. In order to explore the process T-bb;(u) over bar(d) over bar(-) -> Z(bc;(u) over bar(d) over bar)(0)l (nu) over bar (l), we recalculate the spectroscopic parameters of the tetraquark T-bb;(u) over bar(d) over bar(-) and find the mass and coupling of the scalar four-quark system Z(bc;(u) over bar(d) over bar)(0), which are important ingredients of calculations. The spectroscopic parameters of these tetraquarks are computed in the framework of the QCD two-point sum rule method by taking into account various condensates up to dimension ten. The mass of the T-bb;(u) over bar(d) over bar(-) state is found to be m = (10035 +/- 260) MeV, which demonstrates that it is stable against the strong and electromagnetic decays. The full width Gamma and mean lifetime tau of T-bb;(u) over bar(d) over bar(-) are evaluated using its semileptonic decay channels T-bb;(u) over bar(d) over bar(-) -> Z(bc;(u) over bar(d) over bar)(0)l (nu) over bar (l), l = e, mu, and tau. The obtained results, Gamma = (7.17 +/- 1.23) x 10(-8) MeV and tau = 9.18(-1.34)(+1.90) fs, can be useful for experimental investigations of the doubly-heavy tetraquarks
Dynamics of finite-sized light spheres in turbulence
No full textWe report experimental results on the Lagrangian dynamics of finite-size light particles in turbulence. Using an orthogonal camera setup and 3D particle tracking, we study the velocity and acceleration statistics of rigid light spheres in a water tunnel with nearly homogeneous and isotropic turbulence. The Reynolds number (ReY) is varied from 180 to 300, and the study covers a range of size ratios (4 < D/η < 16) for marginally light spheres. We find that the normalised acceleration PDF decreases in intermittency with increasing size ratio - in qualitative agreement with the predictions of the Faxén corrected model. We also present preliminary results on the rotational dynamics of large light spheres in turbulence
Logarithmic variance profiles and the corresponding f-1 spectra of temperature fluctuations in turbulent Rayleigh-Bénard convection
No full textWe report experimental results for the temperature variance 2(z) and the corresponding frequency spectra P(f) in turbulent Rayleigh-Bénard convection (RBC) in a cylindrical sample of aspect ratioT= D/L = 1:00 (D = 1:12 m is the diameter and L = 1:12 m the height). The measurements were conducted in the Rayleigh-number range 1011 < Ra < 1:35 1014 and Pr ' 0:8. For Ra = 1:35x1014, 2(z) could be described well by a logarithmic dependence on the vertical position z in a range of z 1 < z < z 2 with z 1 ' 70 and z 2 = 0:1L. Here L=(2Nu) is the thickness of a thin thermal sublayer adjacent to the horizontal plate where the heat flux (denoted by the Nusselt number Nu) is carried mostly by thermal diffusion. In the log layer, we found that the temperature spectra had a significant frequency range over which P(f) f with close to 1. As Ra decreased, increased so that the log layer became thinner. At Ra = 2:05 1011, z 2 < z 1 and therefore there was no range for a log layer. Correspondingly, the temperature spectrum near the horizontal plate did not have the f1 scaling form either
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