A study of high frequency nonlinear combustion instability in baffled annular liquid propellant rocket motors

Computer program contains mathematical model which provides relationship between engine gas dynamics and combustion processes. Mathematically simulated explosions initiate gas disturbances. Design methods for damping disturbances can be studied to prevent future engine shutdown or destruction

Cooperation, Proximity, and Social Innovation: Three Ingredients for Industrial Medium-Sized Towns’ Renewal?

Over several decades, medium-sized industrial towns have suffered from a combination of economic and political processes: Deindustrialization, metropolization, and withdrawal of public services. After two decades in which they have been somewhat neglected (in favor of metropolises), there have recently been State and European public policies aimed at them. Medium-sized cities are not homogeneous and present several trajectories. Based on quantitative approach in France, we highlight the very diverse socio-economic dynamics of French medium-sized industrial towns. Thus, far from widespread decline or shrinking dynamics, some of these cities are experiencing an economic rebound. This is the case of Romans-sur-Isère, a medium-sized town located in the south-east of France. Focusing our qualitative analyze on this city, we try to understand this type of process. In this medium-sized town, former capital of the shoe industry, local stakeholders, private, and public try to support a productive renewal. The results of our case study highlight the role that cooperation, spatial and organizational proximity, and social innovation could play in the renewal of productive economy in medium-sized industrial towns. Even if the economic situation remains difficult for many medium-sized cities in France as in Europe, we argue that they could have a productive future making and ultimately take advantages of their “medium-sized” attributes. Over several decades, medium-sized industrial towns have suffered from a combination of economic and political processes: Deindustrialization, metropolization, and withdrawal of public services. After two decades in which they have been somewhat neglected (in favor of metropolises), there have recently been State and European public policies aimed at them. Medium-sized cities are not homogeneous and present several trajectories. Based on quantitative approach in France, we highlight the very diverse socio-economic dynamics of French medium-sized industrial towns. Thus, far from widespread decline or shrinking dynamics, some of these cities are experiencing an economic rebound. This is the case of Romans-sur-Isère, a medium-sized town located in the south-east of France. Focusing our qualitative analyze on this city, we try to understand this type of process. In this medium-sized town, former capital of the shoe industry, local stakeholders, private, and public try to support a productive renewal. The results of our case study highlight the role that cooperation, spatial and organizational proximity, and social innovation could play in the renewal of productive economy in medium-sized industrial towns. Even if the economic situation remains difficult for many medium-sized cities in France as in Europe, we argue that they could have a productive future making and ultimately take advantages of their “medium-sized” attributes. &nbsp

The Cuspy LINER Nucleus of the S0/a Galaxy NGC 2681

The nucleus of the bulge-dominated, multiply-barred S0/a galaxy NGC 2681 is studied in detail, using high resolution Hubble Space Telescope FOC and NICMOS imaging and FOS spectroscopy. The ionised gas central velocity dispersion is found to increase by a factor ~2 when narrowing the aperture from R~1.5" (ground) to R~0.1" (FOS). Dynamical modeling of these velocity dispersions suggests that NGC 2681 does host a supermassive black hole (BH) for which one can estimate a firm mass upper limit M_BH < 6*10^7 Solar Masses. This upper limit is consistent with the relation between the central BH mass and velocity dispersion M_BH - sigma known for other galaxies. The emission line ratios place the nucleus of NGC 2681 among LINERs. It is likely that the emission line region comes from a rather mild, but steady, feeding of gas to the central BH in this galaxy. The inner stellar population lacks any measurable color gradient (to a radius of 0.6 kpc) from the infrared to the ultraviolet, consistently with FOC, FOS and IUE data, all indicating that this system underwent a starburst ~1 Gyr ago that encompassed its whole interior, down to its very center. The most likely source of such a widely-distributed starburst is the dumping of tidally-extruded gas from a galaxy neighbor. If so, then NGC 2681 can be considered as the older brother of M82, seen face-on as opposed to the edge-on view we have for M82.Comment: 25 pages, LaTeX, with 10 PostScript figures, to appear in The Astrophysical Journa

Spontaneous emission of radiation by metallic electrons in the presence of electromagnetic fields of surface plasmon oscillations

The spontaneous emission of radiation of metallic electrons embedded in a high-intensity enhanced surface plasmon field is considered analytically. The electrons are described by exact dressed quantum states which contain the interaction with the plasmon field non-perturbatively. Considerable deviations from the pertubative behaviour have been found in the intensity dependence of the emitted fundamental and the second harmonic signals, even at moderate incoming laser intensities. The theoretical predictions deduced from the formalism are in good qualitative agreement with the experimental results.Comment: 23 pages, 6 figure

A non-Markovian quantum trajectory approach to radiation into structured continuum

We present a non-Markovian quantum trajectory method for treating atoms radiating into a reservoir with a non-flat density of states. The results of an example numerical simulation of the case where the free space modes of the reservoir are altered by the presence of a cavity are presented and compared with those of an extended system approach

Observation of Collective Excitations of the Dilute 2D Electron System

We report inelastic light scattering measurements of dispersive spin and charge density excitations in dilute 2D electron systems reaching densities less than 10^{10} cm^{-2}. In the quantum Hall state at nu=2, roton critical points in the spin inter--Landau level mode show a pronounced softening as r_s is increased. Instead of a soft mode instability predicted by Hartree--Fock calculations for r_s ~ 3.3, we find evidence of multiple rotons in the dispersion of the softening spin excitations. Extrapolation of the data indicates the possibility of an instability for r_s >~ 11.Comment: Submitted to Physical Review Letter

An HST/WFPC2 survey of bright young clusters in M31. I. VdB0, a massive star cluster seen at t ≃ 25 Myr

Aims. We introduce our imaging survey of possible young massive globular clusters in M31 performed with the Wide Field and Planetary Camera 2 (WFPC2) on the Hubble Space Telescope (HST). We obtained shallow (to B ~ 25) photometry of individual stars in 20 candidate clusters. We present here details of the data reduction pipeline that is being applied to all the survey data and describe its application to the brightest among our targets, van den Bergh 0 (VdB0), taken as a test case. Methods. Point spread function fitting photometry of individual stars was obtained for all the WFPC2 images of VdB0 and the completeness of the final samples was estimated using an extensive set of artificial stars experiments. The reddening, the age and the metallicity of the cluster were estimated by comparing the observed color magnitude diagram (CMD) with theoretical isochrones. Structural parameters were obtained from model-fitting to the intensity profiles measured within circular apertures on the WFPC2 images. Results. Under the most conservative assumptions, the stellar mass of VdB0 is M> 2.4 x 10^4 M_☉ , but our best estimates lie in the range ≃4-9 x 10^4 M_☉. The CMD of VdB0 is best reproduced by models having solar metallicity and age ≃25 Myr. Ages less than ≃12 Myr and greater than ≃60 Myr are clearly ruled out by the available data. The cluster has a remarkable number of red super giants (≳18) and a CMD very similar to Large Magellanic Cloud clusters usually classified as young globulars such as NGC 1850, for example. Conclusions. VdB0 is significantly brighter (≳1 mag) than Galactic open clusters of similar age. Its present-day mass and half-light radius ((r_h = 7.4 pc) are more typical of faint globular clusters than of open clusters. However, given its position within the disk of M31, it is expected to be destroyed by dynamical effects, in particular by encounters with giant molecular clouds, within the next ~4 Gyr