Roll waves in mud

The stability of a viscoplastic fluid film falling down an inclined plane is explored, with the aim of determining the critical Reynolds number for the onset of roll waves. The Herschel–Bulkley constitutive law is adopted and the fluid is assumed two-dimensional and incompressible. The linear stability problem is described for an equilibrium in the form of a uniform sheet flow, when perturbed by introducing an infinitesimal stress perturbation. This flow is stable for very high Reynolds numbers because the rigid plug riding atop the fluid layer cannot be deformed and the free surface remains flat. If the flow is perturbed by allowing arbitrarily small strain rates, on the other hand, the plug is immediately replaced by a weakly yielded ‘pseudo-plug’ that can deform and reshape the free surface. This situation is modelled by lubrication theory at zero Reynolds number, and it is shown how the fluid exhibits free-surface instabilities at order-one Reynolds numbers. Simpler models based on vertical averages of the fluid equations are evaluated, and one particular model is identified that correctly predicts the onset of instability. That model is used to describe nonlinear roll waves

High-order harmonic generation from diatomic molecules with large internuclear distance: The effect of two-center interference

In the present paper, we investigate the high-order harmonic generation (HHG) from diatomic molecules with large internuclear distance using a strong field approximation (SFA) model. We find that the hump and dip structure emerges in the plateau region of the harmonic spectrum, and the location of this striking structure is sensitive to the laser intensity. Our model analysis reveals that two-center interference as well as the interference between different recombination electron trajectories are responsible for the unusual enhanced or suppressed harmonic yield at a certain order, and these interference effects are greatly influenced by the laser parameters such as intensity.Comment: 5 pages,4 figure

Complex Dynamics of Correlated Electrons in Molecular Double Ionization by an Ultrashort Intense Laser Pulse

With a semiclassical quasi-static model we achieve an insight into the complex dynamics of two correlated electrons under the combined influence of a two-center Coulomb potential and an intense laser field. The model calculation is able to reproduce experimental data of nitrogen molecules for a wide range of laser intensities from tunnelling to over-the-barrier regime, and predicts a significant alignment effect on the ratio of double over single ion yield. The classical trajectory analysis allows to unveil sub-cycle molecular double ionization dynamics.Comment: 5 pages, 5 figures. to appear in Phys. Rev. Lett.(2007

Improved Chebyshev series ephemeris generation capability of GTDS

An improved implementation of the Chebyshev ephemeris generation capability in the operational version of the Goddard Trajectory Determination System (GTDS) is described. Preliminary results of an evaluation of this orbit propagation method for three satellites of widely different orbit eccentricities are also discussed in terms of accuracy and computing efficiency with respect to the Cowell integration method. An empirical formula is deduced for determining an optimal fitting span which would give reasonable accuracy in the ephemeris with a reasonable consumption of computing resources

Surrogate Brands - The pull to adopt an ‘Other’ nation; via sports merchandise

A growing number of consumers are choosing to wear sporting merchandise, from an ‘other’ nation – whom they have no geographic or ethnic affiliation with. In addition, nation sports branding appears to have scaled pandemic heights; by reaching fever pitch, when actively carrying its message across boarders. Consumer preferences are being driven past simple behavioural characteristics; towards more transient psychographic and emotional constructs. In short, nation branded sporting uniform is no longer viewed as demanding restrictive monogamous loyalty. Ownership of a uniform largely suggests exclusivity and encouraged competition. However, manufactures, national teams, athletes and sponsors are entering symbiotic brand relationships - where they are actively seeking publics, open to multiple adopted nationalities. This phenomenon draws consumers towards embracing temporal national identities, which are converted into an over-arching cross-border identity; ultimately gifting sports brands more significance. The following paper explores consumers’ entry into relationships with another nation, in preference to their own - in manner that has been likened to a form of surrogacy; by the authors. The aim is to stimulate further thinking in a field; which transcends national and cultural boundaries - in the interests of developing new insight, and to provide a platform for marketers to develop more effective communication

Gravitational Lensing and Anisotropies of CBR on the Small Angular Scales

We investigate the effect of gravitational lensing, produced by linear density perturbations, for anisotropies of the Cosmic Background Radiation (CBR) on scales of arcminutes. In calculations, a flat universe ($\Omega=1$) and the Harrison-Zel'dovich spectrum ($n=1$) are assumed. The numerical results show that on scales of a few arcminutes, gravitational lensing produces only negligible anisotropies in the temperature of the CBR. Our conclusion disagrees with that of Cay\'{o}n {\it et al.} who argue that the amplification of $\Delta T/T$ on scales $\le 3'$ may even be larger than 100\%.Comment: Accepted by MNRAS. 16 pages, 2 figures, tarred, compressed and uuencoded Postscript file

Advances and challenges in commercializing radiative cooling

Radiative cooling (RC) dissipates terrestrial heat to outer space through the atmospheric window, without external energy input and production of environmental pollutants. More and more efforts have been devoted to this clean promising cooling technology; thus diverse radiative coolers have emerged. However, the performance, cost, and effectiveness of various radiative coolers are not exactly the same. In addition, the large-scale application of RC technology is impeded by the low energy density, uncontrollable cooling power, and limited sky-facing area. Here, we critically review the recent progress of RC technology, evaluate the cooling performance of various radiative coolers, and discuss the challenges and feasible solutions to commercialize RC technology. Furthermore, valuable insights are provided to make new breakthroughs in this field