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Point source
About: Point source is a research topic. Over the lifetime, 5077 publications have been published within this topic receiving 94091 citations.
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TL;DR: In this article, the authors study the dynamics of small spherical flame kernels whose evolution is triggered in a lean mixture of a light mobile reactant by a time-dependent point source of energy.
Abstract: We study the dynamics of small spherical flame kernels whose evolution is triggered in a lean mixture of a light mobile reactant by a time-dependent point- source of energy. For simplicity, the analysis is conducted in the framework of a one-reactant flame model, with a one-step Arrhenius overall kinetics. Using the method of matched asymptotic expansion for large activation energies, we show that: The concentration and temperature fields split into quasi-steady regions, inside and around the flame kernel, and an unsteady far-field; in both regions convection effects may be neglected. Match ing the near - and far-fields furnishes a parameter-free, non-linear evolution equation for the flame radius ; in addition to memory effects of diffusive origin, it includes explicitly the functional form of the chemical rate and the instan taneous power of the point source of energy we used as ignition device. Through a numerical integration of this equation, flame front trajectories and critical energies are...
72 citations
TL;DR: In this paper, the linear response of two-dimensional amorphous elastic bodies to an external delta force is determined in analogy with recent experiments on granular aggregates, and strong relative fluctuations of order 1 close to the source, which, however, average out readily to the classical predictions of isotropic continuum elasticity.
Abstract: The linear response of two-dimensional amorphous elastic bodies to an external delta force is determined in analogy with recent experiments on granular aggregates. For the generated forces, stress, and displacement fields, we find strong relative fluctuations of order 1 close to the source, which, however, average out readily to the classical predictions of isotropic continuum elasticity. The stress fluctuations decay (essentially) exponentially with distance from the source. Only beyond a surprisingly large distance, $b\ensuremath{\approx}30$ interatomic distances, self-averaging dominates, and the quenched disorder becomes irrelevant for the response of an individual configuration. We argue that this self-averaging length $b$ also sets the lower wavelength bound for the applicability of classical eigenfrequency calculations. Particular attention is paid to the displacements of the source, allowing a direct measurement of the local rigidity. The algebraic correlations of these displacements demonstrate the existence of domains of slightly different rigidity without, however, revealing a characteristic length scale, at least not for the system sizes we are able to probe.
72 citations
TL;DR: The optical vortex coronagraph (OVC) as discussed by the authors is a high contrast imaging system which has the potential to completely extinguish light from an on-axis point source, allowing glare-free, high throughput imaging of off-axis targets.
Abstract: An optical vortex coronagraph is a high contrast imaging system which has the potential to completely extinguish light from an on-axis point source, allowing glare-free, high throughput imaging of off-axis targets. An important application is the direct detection of exoplanets orbiting distant stars. The optical physics of the OVC is reviewed, a heuristic argument describing its operation is presented for the first time, and performance limitations are explored.
70 citations
TL;DR: In this paper, the transition points to line source or plane source behavior of the sound attenuation with distance are shown to be simply related to the characteristic dimensions of the source, which can be used to make a universal attenuation template.
70 citations
TL;DR: In this work, a laser line source was modeled and verified experimentally by measuring the ultrasonic shear wave signal generated in aluminum with a broadband laser generation/electromagnetic acoustic transducer (EMAT)-detection system.
Abstract: Modeling the ultrasound generated by a laser source is critical for using noncontact laser-generated ultrasonic systems for the characterization of material properties. In this work, a laser line source was modeled and verified experimentally by measuring the ultrasonic shear wave signal generated in aluminum with a broadband laser generation/electromagnetic acoustic transducer (EMAT)-detection system. Results of calculations and experiments show that the amplitude directivity of a laser line source is identical to that of a point source in the plane perpendicular to the line axis while the temporal dependence differs.
70 citations