2,062 research outputs found
Paramagnetic tunneling state concept of the low-temperature magnetic anomalies of multicomponent insulating glasses
A generalized tunneling model of multicomponent insulating glasses is
formulated, considering tunneling states to be paramagnetic centers of the
electronic hole type. The expression for magnetic field dependent contribution
into the free energy is obtained. The derivation is made of the expression for
the nonmonotonic magnetic field dependence of dielectric susceptibility,
recently observed in amorphous BaO-Al_2O_3-SiO_2 in sub-Kelvin temperature
range.Comment: submitted to Physica
The characterization and evaluation of accidental explosions
Accidental explosions are discussed from a number of viewpoints. First, all accidental explosions, intentional explosions and natural explosions are characterized by type. Second, the nature of the blast wave produced by an ideal (point source or HE) explosion is discussed to form a basis for describing how other explosion processes yield deviations from ideal blast wave behavior. The current status blast damage mechanism evaluation is also discussed. Third, the current status of our understanding of each different category of accidental explosions is discussed in some detail
Terminal energy distribution of blast waves from bursting spheres
The calculation results for the total energy delivered to the surroundings by the burst of an idealized massless sphere containing an ideal gas are presented. The logic development of various formulas for sphere energy is also presented. For all types of sphere bursts the fraction of the total initial energy available in the sphere that is delivered to the surroundings is shown to lie between that delivered for the constant pressure addition of energy to a source region and that delivered by isentropic expansion of the sphere. The relative value of E sub/Q increases at fixed sphere pressure/surrounding pressure as sphere temperature increases because the velocity of sound increases
Behavior of the lean methane-air flame at zero-gravity
A special rig was designed and constructed to be compatible with the NASA Lewis Research Center Airborne Research Laboratory to allow the study of the effect of gravity on the behavior of lean limit in a standard 50.4 mm (2 in.) internal diameter tube when the mixtures are ignited at the open end and propagate towards the closed end of the tube. The lean limit at zero gravity was found to be 5.10% methane and the flame was found to extenguish in a manner previously observed for downward propagating flames at one g. It was observed that g-jitter could be maintained at less than + or 0.04 g on most zero g trajectories. All of propagating lean limit flames were found to be sporadically cellularly unstable at zero g. There was no observable correlation between the occurrence of g-jitter and the lean limit, average propagation speed of the flame through the tube or the occurrence of cellular instability
The Use of a Laser Doppler Velocimeter in a Standard Flammability Tube
The use of the Laser Doppler Velocimeter, (LDV), to measure the flow associated with the passage of a flame through a standard flammability limit tube (SFLT) was studied. Four major results are presented: (1) it is shown that by using standard ray tracing calculations, the displacement of the LDV volume and the fringe rotation within the experimental error of measurement can be predicted; (2) the flow velocity vector field associated with passage of an upward propagating flame in an SFLT is determined; (3) it is determined that the use of a light interruption technique to track particles is not feasible; and (4) it is shown that a 25 mW laser is adequate for LDV measurements in the Shuttle or Spacelab
Untersuchungen an Leptocephali und adulten Exemplaren der Ordnung Anguilliformes aus dem Iberischen Becken und dem Seegebiet vor Nordwestafrika
Effect of thermal expansion on the linear stability of planar premixed flames for a simple chain-branching model: The high activation energy asymptotic limit
The linear stability of freely propagating, adiabatic, planar premixed
ames is investigated in the context of a simple chain-branching
chemistry model consisting of a chain-branching reaction step and a completion reaction step. The role of chain-branching is governed
by a crossover temperature. Hydrodynamic effects, induced by thermal expansion, are taken into account and the results compared and
contrasted with those from a previous purely thermal-di�usive constant density linear stability study. It is shown that when thermal
expansion is properly accounted for, a region of stable
ames predicted by the constant density model disappears, and instead the
ame
is unstable to a long-wavelength cellular instability. For a pulsating mode, however, thermal expansion is shown to have only a weak
e�ect on the critical fuel Lewis number required for instability. These e�ects of thermal expansion on the two-step chain-branching
ame
are shown to be qualitatively similar to those on the standard one-step reaction model. Indeed, as found by constant density studies, in
the limit that the chain-branching crossover temperature tends to the adiabatic
ame temperature, the two-step model can be described
to leading order by the one-step model with a suitably de�ned e�ective activation energy
Regularization of the inverse medium problem : on nonstandard methods for sparse reconstruction
In this thesis, we investigate nonstandard methods for the stable solution of the inverse medium problem. Particularly, we consider the linearization of the model of the scattering process given by the Born approximation and investigate regularization methods that are designed for sparse reconstruction. In numerical experiments we demonstrate that sparsity constraints contribute to meaningful reconstructions from synthetic and even measurement data. In our investigations, we consider both iterative and variational methods for the solution of the inverse problem. Starting from the Landweber iteration, we discuss existing variants of this approach and develop a novel sparsity-enforcing method which is based on the Bregman projection. Furthermore, we consider a variational regularization scheme. First, we develop a novel parameter choice rule based on the L-curve criterion designed for sparse reconstruction. We then propose to replace the variational problem by some smooth approximation and provide an exhaustive investigation regarding stability of this approach. The theoretical investigations of each of the methods proposed in this work are complemented by a numerical evaluation
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