7,532 research outputs found
Three flow regimes of viscous jet falling onto a moving surface
A stationary viscous jet falling from an oriented nozzle onto a moving
surface is studied, both theoretically and experimentally. We distinguish three
flow regimes and classify them by the convexity of the jet shape (concave,
vertical and convex). The fluid is modeled as a Newtonian fluid, and the model
for the flow includes viscous effects, inertia and gravity. By studying the
characteristics of the conservation of momentum for a dynamic jet, the boundary
conditions for each flow regime are derived, and the flow regimes are
characterized in terms of the process and material parameters. The model is
solved by a transformation into an algebraic equation. We make a comparison
between the model and experiments, and obtain qualitative agreement
Falling of a viscous jet onto a moving surface
We analyze the stationary flow of a jet of Newtonian fluid that is drawn by
gravity onto a moving surface. The situation is modeled by a third-order ODE on
a domain of unknown length and with an additional integral condition; by
solving part of the equation explicitly we can reformulate the problem as a
first-order ODE, again with an integral constraint. We show that there are two
flow regimes, and characterize the associated regions in the three-dimensional
parameter space in terms of an easily calculable quantity. In a qualitative
sense the results from the model are found to correspond with experimental
observations.Comment: 16 pages, 11 figure
Calculations of the thermodynamic and kinetic properties of LiV3O8
The phase behavior and kinetic pathways of Li1+xV3O8 are investigated by
means of density functional theory (DFT) and a cluster expansion (CE)
methodology that approximates the system Hamiltonian in order to identify the
lowest energy configurations. Although DFT calculations predict the correct
ground state for a given composition, both GGA and LDA fail to obtain phase
stability consistent with experiment due to strongly localized vanadium 3d
electrons. A DFT+U methodology recovers the correct phase stability for an
optimized U value of 3.0eV. GGA+U calculations with this value of U predict
electronic structures that qualitatively agree with experiment. The resulting
calculations indicate solid solution behavior from LiV3O8 to Li2.5V3O8 and
two-phase coexistence between Li2.5V3O8 and Li4V3O8. Analysis of the lithiation
sequence from LiV3O8 to Li2.5V3O8 reveals the mechanism by which lithium
intercalation proceeds in this material. Calculations of lithium migration
energies for different lithium concentrations and configurations provides
insight into the relevant diffusion pathways and their relationship to
structural properties
N=8 Supergravity on the Light Cone
We construct the generating functional for the light-cone superfield
amplitudes in a chiral momentum superspace. It generates the n-point particle
amplitudes which on shell are equivalent to the covariant ones. Based on the
action depending on unconstrained light-cone chiral scalar superfield, this
functional provides a regular d=4 QFT path integral derivation of the Nair-type
amplitude constructions.
By performing a Fourier transform into the light-cone chiral coordinate
superspace we find that the quantum corrections to the superfield amplitudes
with n legs are non-local in transverse directions for the diagrams with the
number of loops smaller than n(n-1)/2 +1. This suggests the reason why UV
infinities, which are proportional to local vertices, cannot appear at least
before 7 loops in the light-cone supergraph computations. By combining the E7
symmetry with the supersymmetric recursion relations we argue that the
light-cone supergraphs predict all loop finiteness of d=4 N=8 supergravity.Comment: 38
Understanding the central kinematics of globular clusters with simulated integrated-light IFU observations
The detection of intermediate mass black holes in the centres of globular
clusters is highly controversial, as complementary observational methods often
deliver significantly different results. In order to understand these
discrepancies, we develop a procedure to simulate integral field unit (IFU)
observations of globular clusters: Simulating IFU Star Cluster Observations
(SISCO). The input of our software are realistic dynamical models of globular
clusters that are then converted in a spectral data cube. We apply SISCO to
Monte Carlo cluster simulations from Downing et al. (2010), with a realistic
number of stars and concentrations. Using independent realisations of a given
simulation we are able to quantify the stochasticity intrinsic to the problem
of observing a partially resolved stellar population with integrated-light
spectroscopy. We show that the luminosity-weighted IFU observations can be
strongly biased by the presence of a few bright stars that introduce a scatter
in the velocity dispersion measurements up to 40% around the expected
value, preventing any sound assessment of the central kinematic and a sensible
interpretation of the presence/absence of an intermediate mass black hole.
Moreover, we illustrate that, in our mock IFU observations, the average
kinematic tracer has a mass of 0.75 solar masses, only slightly lower
than the mass of the typical stars examined in studies of resolved
line-of-sight velocities of giant stars. Finally, in order to recover unbiased
kinematic measurements we test different masking techniques that allow us to
remove the spaxels dominated by bright stars, bringing the scatter down to a
level of only a few percent. The application of SISCO will allow to investigate
state-of-the-art simulations as realistic observations.Comment: 13 pages, 9 figures, 1 table. Accepted for publication in MNRA
Load-depth sensing of isotropic, linear viscoelastic materials using rigid axisymmetric indenters
An indentation experiment involves five variables: indenter shape, material
behavior of the substrate, contact size, applied load and indentation depth.
Only three variable are known afterwards, namely, indenter shape, plus load and
depth as function of time. As the contact size is not measured and the
determination of the material properties is the very aim of the test; two
equations are needed to obtain a mathematically solvable system.
For elastic materials, the contact size can always be eliminated once and for
all in favor of the depth; a single relation between load, depth and material
properties remains with the latter variable as unknown.
For viscoelastic materials where hereditary integrals model the constitutive
behavior, the relation between depth and contact size usually depends also on
the (time-dependent) properties of the material. Solving the inverse problem,
i.e., determining the material properties from the experimental data, therefore
needs both equations. Extending Sneddon's analysis of the indentation problem
for elastic materials to include viscoelastic materials, the two equations
mentioned above are derived. To find the time dependence of the material
properties the feasibility of Golden and Graham's method of decomposing
hereditary integrals (J.M. Golden and G.A.C. Graham. Boundary value problems in
linear viscoelasticity, Springer, 1988) is investigated and applied to a single
load-unload process and to sinusoidally driven stationary state indentation
processes.Comment: 116 pages, 29 figure
L’avenir de la théologie empirique, évalué à partir d’une analyse critique de son passé : I. D’aujourd’hui à hier
- …