1,255 research outputs found
Numerical study of supersonic turbulent flow over small protuberances
Supersonic turbulent boundary layers over two-dimensional protuberances are investigated, using the numerical finite difference alternating direction implicit (ADI) method. The turbulence is modeled mathematically. The turbulence is represented here by the eddy viscosity approach. The turbulent boundary layer structure as well as an interest in thick boundary layers and much larger protuberance heights than in the laminar case lead to new difficulties. The problems encountered and the means to remove them are discussed
Interacting turbulent boundary layer over a wavy wall
The two dimensional supersonic flow of a thick turbulent boundary layer over a train of relatively small wave-like protuberances is considered. The flow conditions and the geometry are such that there exists a strong interaction between the viscous and inviscid flow. The problem cannot be solved without inclusion of interaction effects due to the occurrence of the separation singularity in classical boundary layer methods. The interacting boundary layer equations are solved numerically using a time-like relaxation method with turbulence effects represented by the inclusion of the eddy viscosity model. Results are presented for flow over a train of up to six waves for Mach numbers of 10 and 32 million/meter, and wall temperature rations (T sub w/T sub 0) of 0.4 and 0.8. Limited comparisons with independent experimental and analytical results are also given. Detailed results on the influence of small protuberances on surface heating by boundary layers are presented
Supersonic separated turbulent boundary - layer over a wavy wall
A prediction method is developed for calculating distributions of surface heating rates, pressure and skin friction over a wavy wall in a two-dimensional supersonic flow. Of particular interest is the flow of thick turbulent boundary layers. The surface geometry and the flow conditions considered are such that there exists a strong interaction between the viscous and inviscid flow. First, using the interacting turbulent boundary layer equations, the problem is formulated in physical coordinates and then a reformulation of the governing equations in terms of Levy-Lees variables is given. Next, a numerical scheme for solving interacting boundary layer equations is adapted. A number of modifications which led to the improvement of the numerical algorithm are discussed. Finally, results are presented for flow over a train of up to six waves at various flow conditions
The separated turbulent boundary layer over a wavy wall
A study and application of the fourth order spline collocation procedure, numerical solution of boundary layer like differential equations, is presented. A simple inversion algorithm for the simultaneous solution of the resulting difference equations is given. Particular attention is focused on the boundary condition representation for the spline second derivative approximations. Solutions using the spline procedure, as well as the three point finite difference method, are presented for several model problems in order to assess and improve the spline numerical scheme. Application of the resulting algorithm to the incompressible laminar self similar boundary layer equations is presented
Exact Self-consistent Particle-like Solutions to the Equations of Nonlinear Scalar Electrodynamics in General Relativity
Exact self-consistent particle-like solutions with spherical and/or
cylindrical symmetry to the equations governing the interacting system of
scalar, electromagnetic and gravitational fields have been obtained. As a
particular case it is shown that the equations of motion admit a special kind
of solutions with sharp boundary known as droplets. For these solutions, the
physical fields vanish and the space-time is flat outside of the critical
sphere or cylinder. Therefore, the mass and the electric charge of these
configurations are zero.Comment: 17 pages, Submitted to the International Journal of Theoretical
Physic
Agrin isoforms and their role in synaptogenesis
Agrin is thought to mediate the motor neuron-induced aggregation of synaptic proteins on the surface of muscle fibers at neuromuscular junctions. Recent experiments provide direct evidence in support of this hypothesis, reveal the nature of agrin immunoreactivity at sites other than neuromuscular junctions, and have resulted in findings that are consistent with the possibility that agrin plays a role in synaptogenesis throughout the nervous system
DeWitt Wallace Library Annual Report 2016-2017
Summary of library and media services activities for 2016-201
LUX -- A Laser-Plasma Driven Undulator Beamline
The LUX beamline is a novel type of laser-plasma accelerator. Building on the
joint expertise of the University of Hamburg and DESY the beamline was
carefully designed to combine state-of-the-art expertise in laser-plasma
acceleration with the latest advances in accelerator technology and beam
diagnostics. LUX introduces a paradigm change moving from single-shot
demonstration experiments towards available, stable and controllable
accelerator operation. Here, we discuss the general design concepts of LUX and
present first critical milestones that have recently been achieved, including
the generation of electron beams at the repetition rate of up to 5 Hz with
energies above 600 MeV and the generation of spontaneous undulator radiation at
a wavelength well below 9 nm.Comment: submitte
The morphological transformation of ram pressure stripped galaxies: a pathway from late to early galaxy types
We investigate how the ageing of stellar populations can drive a
morphological transformation in galaxies whose star formation (SF) activity has
been quenched on short timescales, like in cluster galaxies subject to ram
pressure stripping from the intracluster medium. For this purpose, we use a
sample of 91 galaxies with MUSE data from the GASP program and of their
spatially resolved SF history derived with the spectral modelling software
SINOPSIS. We simulate the future continuation of the SF activities by exploring
two quenching scenarios: an instantaneous truncation of the SF across the whole
disc, and an outside-in quenching with typical stripping timescales of 0.5 Gyr
and 1 Gyr. For each scenario we produce mock MUSE spectroscopic datacubes and
optical images for our galaxies during their evolution, and classify their
morphology using a new diagnostic tool, calibrated on cluster galaxies from the
OmegaWINGS Survey. We find that, in all scenarios considered, the initial
galaxy population dominated by blue-cloud spirals (90%) evolves into a mixed
population mostly composed by red-sequence spirals (50-55%) and lenticulars
(~40%). The morphology transformation is completed after just 1.5-3.5 Gyr,
proceeding faster in more efficient quenching scenarios. Our results indicate
that, even without accounting for dynamical processes, SF quenching caused by
the harsh environment of a cluster can significantly affect the morphology of
the infalling galaxy population on timescales of a few Gyr.Comment: 19 pages, 11 figures, accepted for publication in MNRA
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