To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Energy stability theory has been used to study BBnard convection in one- and two-component horizontal fluid layers heated from below or above when there is a deformable upper surface. To a first approximation in the crispation number, we provide sufficient conditions for stability of the motionless state of the layer, and delineate regions of possible subcritical instability.
Long term research in low activation materials is being pursued in
fusion programs and the assessment of allowable elements and/or
impurities from safety and repository reasons are being studied at
Instituto Fusión Nuclear (DENIM), using ACAB code, for national
ignition facility (NIF) and inertial fusion energy (IFE) reactors.
Uncertainties in nuclear data are being considered, and experiments for
validation of modeling will be presented. Multiscale simulation of
radiation damage is now starting to be compared with experiments, and
results on the simplest material can be reported as a function of
impurities, temperature, and dose. Molecular dynamics (MD) allows us to
identify stress-strain curve of FeCr ferritic steels under irradiation,
and macroscopic conclusions can be advanced using simple models. However,
a neutron source of enough intensity and adequate energy spectrum is
needed which will be very peculiar in the case of pulsed IFE, as we
claimed in past years. Development of international fusion materials
irradiation facility (IFMIF) will be commented and compared with solutions
such as spallation, and others using ultra-intense lasers for obtaining
required irradiation magnitudes. Research on radiation damage in SiC
composite is being pursued at macroscopic level, but basic knowledge is
scarce. A systematic identification of type of stable defects is being
presented with a new tight binding MD technique. Our research on
simulation of silica irradiation damage will also be presented. The role
of tritium, when elemental tritium (HT) and titrated water (HTO) derive in
organically bound tritium (OBT) will be explained. The deposition and
absorption processes are now being considered in our calculations giving
more precision and accuracy to our conclusions of dosimetry effects. The
role of HT versus HTO and the importance of re-emission process will be
remarked, together with the long-term role of OBT.
We analyse the regularized reduced model derived in Part 1 (Ruyer-Quil et al. 2005). Our investigation is two-fold: (i) we demonstrate that the linear stability properties of the model are in good agreement with the Orr–Sommerfeld analysis of the linearized Navier–Stokes/energy equations; (ii) we show the existence of nonlinear solutions, namely single-hump solitary pulses, for the widest possible range of parameters. We also scrutinize the influence of Reynolds, Prandtl and Marangoni numbers on the shape, speed, flow patterns and temperature distributions for the solitary waves obtained from the regularized model. The hydrodynamic and Marangoni instabilities are seen to reinforce each other in a non-trivial manner. The transport of heat by the flow has a stabilizing effect for small-amplitude waves but promotes the instability for large-amplitude waves when a recirculating zone is present. Nevertheless, in this last case, by increasing the shear in the bulk and thus the viscous dissipation, increasing the Prandtl number decreases the amplitude and speed of the waves.
We consider the dynamics of a thin liquid film falling down a uniformly heated wall. The heating sets up surface tension gradients that induce thermocapillary stresses on the free surface, thus affecting the evolution of the film. We model this thermocapillary flow by using a gradient expansion combined with a Galerkin projection with polynomial test functions for both velocity and temperature fields. We obtain equations for the evolution of the velocity and temperature amplitudes at first- and second-order in the expansion parameter. These equations are fully compatible close to criticality with the Benney long-wave expansion. Models of reduced dimensionality for the evolution of the local film thickness, flow rate and interfacial temperature only, are proposed.
We consider a thin layer of a viscous fluid flowing down a uniformly heated planar wall. The heating generates a temperature distribution on the free surface which in turn induces surface tension gradients. We model this thermocapillary flow by using the Shkadov integral-boundary-layer (IBL) approximation of the Navier–Stokes/energy equations and associated free-surface boundary conditions. Our linear stability analysis of the flat-film solution is in good agreement with the Goussis & Kelly (1991) stability results from the Orr–Sommerfeld eigenvalue problem of the full Navier–Stokes/energy equations. We numerically construct nonlinear solutions of the solitary wave type for the IBL approximation and the Benney-type equation developed by Joo et al. (1991) using the usual long-wave approximation. The two approaches give similar solitary wave solutions up to an $O(1)$ Reynolds number above which the solitary wave solution branch obtained by the Joo et al. equation is unrealistic, with branch multiplicity and limit points. The IBL approximation on the other hand has no limit points and predicts the existence of solitary waves for all Reynolds numbers. Finally, in the region of small film thicknesses where the Marangoni forces dominate inertia forces, our IBL system reduces to a single equation for the film thickness that contains only one parameter. When this parameter tends to zero, both the solitary wave speed and the maximum amplitude tend to infinity.
Simultaneous capillary–gravity solitary waves (simultons or quadratic solitons) are
shown to be possible in a rectangular liquid channel of arbitrary finite depth bounded
below by a solid plate and above with a free deformable surface with constant surface
tension. A second-harmonic resonance between two waveguide modes (fundamental
and second-harmonic waves) is studied with the inclusion of dispersion in the system.
The nonlinearly coupled amplitude equations for the two slowly varying envelopes
of the fundamental and the second-harmonic wave components are derived using
the method of multiple scales. Two types of capillary–gravity simulton solutions are
explicitly obtained and an experiment for observing such hydrodynamic simultons is
The usual model of intermittent hypoxia (sleep apnoea) corresponds to repeated episodes of hypoxia from a few seconds to a few hours interspersed with episodes of normoxia. The aim of this study was to evaluate in rats the effect of two periods of intermittent exposure for 2 months to hypoxia (IHX1, 24 h in hypoxia (428 Torr), 24 h in normoxia; IHX2, 48 h in hypoxia (428 Torr), 24 h in normoxia) as a new model of hypoxia simulating intermittent exposure to high altitude experienced by Andean miners. We assessed the haematological parameters, time course of resting heart rate and systolic blood pressure. We also evaluated the expression of adrenergic and muscarinic receptors. IHX1 and IHX2 produced an increase in haematocrit, haemoglobin concentration and mean corpuscular volume as previously seen in most hypoxic models. IHX1 and IHX2 induced a similar sustained elevation of systolic blood pressure (132 ± 2 and 135 ± 3 mmHg, respectively, vs. the control level of 121 ± 16 mmHg) after 10 days of exposure without change in heart rate. Right ventricular (RV) hypertrophy (225 ± 13 and 268 ± 15 mg g−1, vs. 178 ± 7 mg g−1) and downregulation of α1-adrenoceptor (RV: 127 ± 21 and 94 ± 16 fmol mg−1vs. 157 ± 8 fmol mg−1; left ventricle (LV): 141 ± 5 and 126 ± 9 fmol mg−1vs. 152 ± 5 fmol mg−1) have been found in both groups, with right ventricular hypertrophy being greater and α1-adrenoceptor density being lower in IHX2 than in HX1 groups. These data indicate that both parameters are related to the time of exposure to hypoxia. IHX1 and IHX2 produced the same magnitude of upregulation of muscarinic receptors (LV, 60%; RV, 40%), and no change in β-adrenoceptors. In conclusion, exposure to intermittent hypoxia led to polycythaemia and RV hypertrophy as observed in other types of hypoxia. A specific cardiovascular response was seen, that is an increase in blood pressure without change in heart rate, which was different from the one observed in episodic and chronic hypoxia. Furthermore, this model involved specific modifications of α1-adrenergic and muscarinic expression.
An oscillatory instability mechanism is identified for a horizontal liquid layer with
undeformable open surface heated from the air side. Although buoyancy and surface
tension gradients are expected to play a stabilizing role in this situation, we show that,
acting together, they may lead to the instability of the motionless state of the system.
The instability is a consequence of the coupling between internal and surface waves,
whose resonant interaction and resulting mode mixing are discussed. Predictions
amenable to experimental test are given together with a thorough analytical and
numerical study of the problem.
A derivation is given of the amplitude equations governing pattern
surface tension gradient-driven Bénard–Marangoni
convection. The amplitude equations
are obtained from the continuity, the Navier–Stokes and the Fourier
equations in the
Boussinesq approximation neglecting surface deformation and buoyancy. The
is a shallow liquid layer heated from below, confined below by a rigid
above with a free surface whose surface tension linearly depends on temperature.
amplitude equations of the convective modes are equations of the Ginzburg–Landau
type with resonant advective non-variational terms. Generally, and in agreement
experiment, above threshold solutions of the equations correspond to an
convective structure in which the fluid rises in the centre of the cells.
analytically study the dynamics of pattern formation leading not only to
but also to squares or rolls depending on the various dimensionless parameters
Prandtl number, and the Marangoni and Biot numbers at the boundaries. We
that a transition from an hexagonal structure to a square pattern is possible.
also determine conditions for alternating, oscillatory transition between
rolls. Moreover, we also show that as the system of these amplitude equations
non-variational the asymptotic behaviour (t→∞)
may not correspond to a steady
convective pattern. Finally, we have determined the Eckhaus band for hexagonal
and we show that the non-variational terms in the amplitude equations enlarge
this band of allowable modes. The analytical results have been checked
integration of the amplitude equations in a square container. Like in experiments,
numerics shows the emergence of different hexagons, squares and rolls according
values given to the parameters of the system.
New improvements in the atomic physics models for numerically treating high density plasmas, typical of ICF, together with new algorithms for multigroup radiation transport are presented.
The performance of Large High Aspect Ratio Targets has been numerically determined by using those models implemented in a one-dimensional hydro code. Some differences from experiments are identified, and a comparative analysis with other numerical codes is given.
In this article the current capabilities at DENIM for the analysis of directly driven targets are presented. These include theoretical, computational and applied physical studies and developments of detailed simulation models for the most relevant processes in ICF. The simulation of directly driven ICF targets is carried out with the one-dimensional NORCLA code developed at DENIM. This code contains two main segments: NORMA and CLARA, able to work fully coupled and in an iterative manner. NORMA solves the hydrodynamic equations in a lagrangian mesh. It has modular programs coupled to it to treat the laser or particle beam interaction with matter. Equations of state, opacities and conductivities are taken from a DENIM atomic data library, generated externally with other codes that will also be explained in this work. CLARA solves the transport equation for neutrons, (Boltzmann), as well as for charged particles, and suprathermal electrons (Fokker-Planck), using discrete ordinates and finite element methods in the computational procedure. Parametric calculations of multilayered single-shell targets driven by heavy ion beams are also analyzed. Finally, conclusions are focused on the ongoing developments in the areas of interest such as: radiation transport, atomic physics, particle in cell method, charged particle transport, two-dimensional calculations and instabilities.
Email your librarian or administrator to recommend adding this to your organisation's collection.