Stability of Periodic, Traveling-Wave Solutions to the Capillary-Whitham Equation

Recently, the Whitham and capillary-Whitham equations were shown to accurately model the evolution of surface waves on shallow water. In order to gain a deeper understanding of these equations, we compute periodic, traveling-wave solutions to both and study their stability. We present plots of a representative sampling of solutions for a range of wavelengths, wave speeds, wave heights, and surface tension values. Finally, we discuss the role these parameters play in the stability of the solutions

Instability of Near-Extreme Solutions to the Whitham Equation

The Whitham equation is a model for the evolution of small-amplitude, unidirectional waves of all wavelengths on shallow water. It has been shown to accurately model the evolution of waves in laboratory experiments. We compute $2\pi$-periodic traveling-wave solutions of the Whitham equation and numerically study their stability with a focus on solutions with large steepness. We show that the Hamiltonian oscillates as a function of wave steepness when the solutions are sufficiently steep. We show that a superharmonic instability is created at each extremum of the Hamiltonian and that between each extremum the stability spectra undergo similar bifurcations. Finally, we compare these results with those from the Euler equations

GOING GAGA: POP FANDOM AS ONLINE COMMUNITY OF PRACTICE

Among various fan sites dedicated to pop stars, GagaDaily is one prominent online collective that centers around Lady Gaga. This study is a piece of ethnographic research focused on two claims – GagaDaily constitutes a Community of Practice (Eckert, 2006) in an online setting, and the regular use of humor by users fulfills social and pragmatic roles in the discourse. Communicative phenomena (both textual and graphic) that characterize the linguistic repertoire of GagaDaily members were catalogued from the first 100 pages of one thread within the forums. These data were grouped into categories corresponding to different dimensions of language use as well as media/literary devices. Alongside a quantitative analysis of various tokens and types of data, a qualitative examination of selected excerpts from the sample confirm the veracity of the two main claims. When analyzed with regard to Wenger’s definition of a Community of Practice (Wenger, 2009), GagaDaily meets all three of his requirements. Likewise, the analysis of humor reveal that GagaDaily users regularly engage in the first dichotomy of the tactics of intersubjectivity, adequation and distinction (Bucholtz & Hall, 2004) and incorporate GIF images in their humor to express their alignment with stance objects (DuBois, 2007) and other members

Markerless View Independent Gait Analysis with Self-camera Calibration

We present a new method for viewpoint independent markerless gait analysis. The system uses a single camera, does not require camera calibration and works with a wide range of directions of walking. These properties make the proposed method particularly suitable for identification by gait, where the advantages of completely unobtrusiveness, remoteness and covertness of the biometric system preclude the availability of camera information and use of marker based technology. Tests on more than 200 video sequences with subjects walking freely along different walking directions have been performed. The obtained results show that markerless gait analysis can be achieved without any knowledge of internal or external camera parameters and that the obtained data that can be used for gait biometrics purposes. The performance of the proposed method is particularly encouraging for its appliance in surveillance scenarios

Observation of a possible superflare on Proxima Centauri

We report the observation on UT 2017 July 1 of an unusually powerful flare detected in near-infrared continuum photometry of Proxima Centauri. During a campaign monitoring the star for possible exoplanet transits, we identified an increase in Sloan i' flux leading to an observed peak at BJD 2457935.996 that was at least 10 per cent over pre-flare flux in this band. It was followed by a two-component rapid decline in the first 100 s that became a slower exponential decay with time constant of 1350 s. A smaller flare event 1300 s after the first added an incremental peak flux increase of 1 per cent of pre-flare flux. Since the onset of the flare was not fully time resolved at a cadence of 62 s, its actual peak value is unknown but greater than the time average over a single exposure of 20 s. The i' band is representative of broad optical and near-IR continuum flux over which the integrated energy of the flare is 100 times the stellar luminosity. This meets the criteria that established the concept of superflares on similar stars. The resulting implied ultraviolet flux and space weather could have had an extreme effect on the atmospheres of planets within the star's otherwise habitable zone

A Prototype National Drought Alert Strategic Information System for Australia

Defining and categorizing drought in a quantitative and scientific manner are important national issues for Australian state and Commonwealth governments, landholders, and agribusiness. The challenge for modelers of Australia’s grasslands is to integrate biological models, geographic information systems (GIS), satellite imagery, economics, climatology, and visual high-performance computing into an Internet-deliverable application that can provide easily understood monitoring and prediction advice in near real-time— a national drought alert strategic information system. Although NOAA satellite-derived imagery has been somewhat useful in the broad-scale spatial assessment of green cover, especially the spatial response of vegetation to rainfall events (Smith, 1994; Dudgeon et al., 1990; Filet et al., 1990), it has inherent limitations in providing a total solution for drought and rangeland monitoring; biomass relationships are not good, tree cover confounds the signal, and a future projection of the current situation is not inherent. Also, the interpretation of the imagery does not usually consider the effects of soil type, vegetation structure, or rangeland “condition.” Similarly, rainfall analyses alone do not necessarily reflect the quantity and quality of pasture available on the ground. In the recent 1991–95 record-breaking drought in Queensland, rainfall analyses did not map the drought-declared southwestern areas of the state as droughted, and, conversely, coastal areas of the state were classed as droughted by rainfall analyses, when there was no community push for their declaration. Measures of rainfall effectiveness expressed as measures of plant biomass are required for drought definition. Improved assessments of the quantity and quality of biomass are needed, as well as consideration of herbivore densities and future climatic scenarios