Estimation of shock induced vorticity on irregular gaseous interfaces: a wavelet-based approach

We study the interaction of a shock with a density-stratified gaseous interface (Richtmyer–Meshkov instability) with localized jagged and irregular perturbations, with the aim of developing an analytical model of the vorticity deposition on the interface immediately after the passage of the shock. The jagged perturbations, meant to simulate machining errors on the surface of a laser fusion target, are characterized using Haar wavelets. Numerical solutions of the Euler equations show that the vortex sheet deposited on the jagged interface rolls into multiple mushroom-shaped dipolar structures which begin to merge before the interface evolves into a bubble-spike structure. The peaks in the distribution of x-integrated vorticity (vorticity integrated in the direction of the shock motion) decay in time as their bases widen, corresponding to the growth and merger of the mushrooms. However, these peaks were not seen to move significantly along the interface at early times i.e. t < 10 τ, where τ is the interface traversal time of the shock. We tested our analytical model against inviscid simulations for two test cases – a Mach 1.5 shock interacting with an interface with a density ratio of 3 and a Mach 10 shock interacting with a density ratio of 10. We find that this model captures the early time (t/τ ∼ 1) vorticity deposition (as characterized by the first and second moments of vorticity distributions) to within 5% of the numerical results. PACS 47.40.Nm; 47.20.Ma     

Mass transfer with chemical reaction in a laminar falling film

Zusammenfassung Es wird eine analytische Lösung für die Absorption in einem laminaren Rieselfilm mit homogener und heterogener chemischer Reaktion 1. Ordnung vorgestellt, wobei der Stofftransportwiderstand auf der Gasseite liegt. Die Lösung ist eine Funktion von drei dimensionslosen ParameternBi, und, welche die BiotZahl und einen homogenen bzw. heterogenen Reaktionsparameter darstellen. Es wird gezeigt, daß für feste Werte vonBi und die Absorptionsrate (bezogen auf die Breite 1 des Rieselfilms) über eine gewisse Länge (dimensionslos) des Rieselfilms unabhängig von ist, wenn, < 0,6 ist. Die laufende Länge wird von der Stelle aus gemessen, an der die Absorption beginnt. Für b 0,6 nimmt der FlußQ mit zu, erreicht aber einen Sättigungswert bei=10, wonachQ nurmehr sehr langsam anwächst. Jedoch für ein gegebenes und ohne Übergangswiderstand im Film (Bi ) nimmtQ mit für alle 0 zu.

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Mass transfer with chemical reaction in a laminar falling film

An analytical solution is presented for gas absorption in a laminar falling film with first-order homogeneous and heterogeneous chemical reaction and external gas-phase mass transfer resistance. The solution depends on three dimensionless parametersBi, and, wich represent the Biot number, homogeneous and heterogeneous reaction parameters, respectively. It is shown that for fixed values ofBi and, the rate of gas absorption (per unit breadth) over a certain length; (dimensionless) along the falling film measured from the point where surface absorption begins is independent of if < 0.6. For 0.6, this fluxQ increases with but reaches a saturation value at=10 beyond whichQ increases very slowly. But for given and zero gas film resistance (Bi ),Q increases with for all 0.

     

An equilibrium solution for a fluid saturated porous elastic solid

This work concerns the behavior of a binary mixture of a fluid and an isotropic elastic solid in static equilibrium. The displacements are assumed to be small. Thus, the governing partial differential equations are linear. The physical model is sufficiently general to allow for a nonconstant fluid pressure when the mixture is in static equilibrium. The model is applied to the problem of an arbitrary pressure distribution on an isothermal half-space. Among the results of this calculation is an explicit formula for the surface porosity. This parameter gives the fraction of the applied pressure transmitted to the fluid.

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Zusammenfassung Diese Arbeit behandelt das Verhalten einer binären Mischung eines Flüssigkeit und eines isotropen elastischen Festkorgers im statischen Gleichgewicht. Deformationen sind als klein angenommen. Die beschreibenden partiellen Differentialgleichungen sind dadurch linear. Das physikalische Modell ist allgemein genügend um einen nichtkonstanten Druck zuzulassen, wenn die Mischung im statischen Gleichgewicht ist. Das Modell wird auf das Problem einer willkürlichen druckverteilung auf dem isothermen halbraum angewandt. Unter den Ergebnissen dieser Berechnung ist eine explizite Formel für die Oberflächen porosität. Dieser Parameter gibt den Bruchteil des ausgeübten Druckes an, der auf die Flüssigkeit übertragen wird.

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Presently employed at Johnson Space Center National Aeronautics and Space Administration Houston, Texas.     

On estimating site damping with soil non-linearity from earthquake recordings

This study proposes an approach for estimating the damping factor of non-linear soil and its role in seismic wave responses at soil sites from earthquake recordings. In particular, the paper first reviews the Fourier-based approach to characterizing the dynamic features of soil sites in seismic ground motion and shows the deficiencies for assessing non-linear site amplification and damping. It then offers an alternative approach, i.e., the Hilbert-Huang transform (HHT) for non-linear and non-stationary data process, in addressing the non-linearity issues. This study focuses on discerning the signature of non-linear site damping from the general non-linear features in the motion that are typically shown in the frequency-dependent site amplification. As a result, the study proposes an HHT-based approach to estimate site damping with non-linear soil from earthquake recordings and to measure the influences in the motion at soil sites. With the use of recordings from the mainshock and aftershock of the 2001 Nisqually earthquakes, this study shows that the proposed approach is able to assess appropriately the site damping that can be used to estimate the influences of soil damping in non-linear site responses.     

TRANSIENT RESPONSE OF COPLANAR INTERFACIAL CRACKS BETWEEN TWO DISSIMILAR PIEZOELECTRIC STRIPS UNDER ANTI-PLANE MECHANICAL AND IN-PLANE ELECTRICAL IMPACTS

The dynamic response of multiple coplanar interface cracks between two dissimilar piezoelectric strips subjected to mechanical and electrical impacts is investigated. Solutions to two kinds of electric boundary conditions on crack surfaces, i.e. electric impermeable and electric permeable, are obtained. Laplace and Fourier transforms and dislocation density functions are employed to reduce the mixed boundary value problem to Cauchy singular integral equations,which can be solved numerically. The effects of electrical load, geometry criterion of piezoelectric strips, relative location of cracks and material properties on the dynamic energy release rate are examined.     

Nitrogen-doped carbon spheres: an X-ray absorption near-edge structure spectroscopy study

Carbon spheres (CSs) and low content nitrogen (2.5 and 3.5 at%) doped carbon spheres (NCSs) were synthesized by a pyrolysis process at 900 °C using $\mathrm{C}_{2}\mathrm{H}_{2}$ and CH₃CN. The electronic structure and chemical bonding of CSs and NCSs were studied using Raman spectroscopy, valence-band photoemission spectroscopy (VBPES) and X-ray absorption near-edge structure spectroscopy (XANES). XANES spectroscopy showed the effect of carbon and nitrogen bonds and graphitic as well as pyridinic structures on the NCS structure. For the spheres VBPES showed the effect of nitrogen on the spectral shape of the density of states and confirmed the role played by the $\pi$ bonds in controlling the electronic and structural properties of the NCSs. VBPES also showed that both $\pi$ and $\sigma$ bands shift towards higher binding energies after N-doping which is consistent with the XANES data. The consistency of the spherical geometry, chemical purity, suitable electronic/bonding structure and the availability of macroscopic quantities of the N–CSs makes these spheres promising new materials for different applications.     

Wearable electrochemical sensors for in situ analysis in marine environments

The development of wearable screen-printed electrochemical sensors on underwater garments comprised of the synthetic rubber neoprene is reported. These wearable sensors are able to determine the presence of environmental pollutants and security threats in marine environments. Owing to its unique elastic and superhydrophobic morphology, neoprene is an attractive substrate for thick-film electrochemical sensors for aquatic environments and offers high-resolution printing with no apparent defects. The neoprene-based sensor was evaluated for the voltammetric detection of trace heavy metal contaminants and nitroaromatic explosives in seawater samples. We also describe the first example of enzyme (tyrosinase) immobilization on a wearable substrate towards the amperometric biosensing of phenolic contaminants in seawater. Furthermore, the integration of a miniaturized potentiostat directly on the underwater garment is demonstrated. The wearable sensor-potentiostat microsystem provides a visual indication and alert if the levels of harmful contaminants have exceeded a pre-defined threshold. The concept discussed here is well-suited for integration into dry- and wetsuits worn by divers and recreational surfers/swimmers, thereby providing them with the ability to continuously assess their surroundings for environmental contaminants and security hazards.     

Langevin-Bloch equations for a spin bath

We derive the Bloch equations for a two-level system coupled to a spin bath of infinitely many two-level atoms to examine phase and energy relaxation of an optically excited system. We show that increasing temperature assists coherence. This is reflected in a number of anomalous features of relaxation of the system, e.g., decrease of integrated absorption coefficient with temperature, nonlinear variation of linewidth with incident power. We also predict that thermally induced coherence may result in anomalous narrowing of linewidth, reminiscent (but distinct) of "motional narrowing" of spectral line. The theoretical results are discussed in the light of absorption-emission experiments on single quantum dots.