Double-ionization dynamics of laser-driven helium

We report a new method which allows sequential and non-sequential double-ionization rates in laser-driven helium to be distinguished and calculated separately. The method is applied to calculate such rates for two laser pulses, one of 0.236 au frequency and 8.0 × 1015 W cm-2 peak intensity, the other of 1.0 au frequency and also of 8.0 × 1015 W cm-2 peak intensity.

Half-precessional dynamics of monsoon rainfall near the East African Equator

External climate forcings-such as long-term changes in solar insolation-generate different climate responses in tropical and high latitude regions(1). Documenting the spatial and temporal variability of past climates is therefore critical for understanding how such forcings are translated into regional climate variability. In contrast to the data-richmiddle and high latitudes, high-quality climate-proxy records from equatorial regions are relatively few(2-4), especially from regions experiencing the bimodal seasonal rainfall distribution associated with twice-annual passage of the Intertropical Convergence Zone. Here we present a continuous and well-resolved climate-proxy record of hydrological variability during the past 25,000 years from equatorial East Africa. Our results, based on complementary evidence from seismic-reflection stratigraphy and organic biomarker molecules in the sediment record of Lake Challa near Mount Kilimanjaro, reveal that monsoon rainfall in this region varied at half-precessional (similar to 11,500-year) intervals in phase with orbitally controlled insolation forcing. The southeasterly and northeasterly monsoons that advect moisture from the western Indian Ocean were strengthened in alternation when the inter-hemispheric insolation gradient was at a maximum; dry conditions prevailed when neither monsoon was intensified and modest local March or September insolation weakened the rain season that followed. On sub-millennial timescales, the temporal pattern of hydrological change on the East African Equator bears clear high-northern-latitude signatures, but on the orbital timescale it mainly responded to low-latitude insolation forcing. Predominance of low-latitude climate processes in this monsoon region can be attributed to the low-latitude position of its continental regions of surface air flow convergence, and its relative isolation from the Atlantic Ocean, where prominent meridional overturning circulation more tightly couples low-latitude climate regimes to high-latitude boundary conditions.

The challenge of revealing and tailoring the dynamics of radio-frequency plasmas

The complex dynamics of ionization and excitation mechanisms in capacitively coupled radio-frequency plasmas is discussed for single- and dual-frequency operations in low-pressure and atmospheric pressure plasmas. Electrons are energized through the dynamics of electric fields in the vicinity of the plasma boundary sheaths. Distinctly different power dissipation mechanisms can either co-exist or initiate mode transitions exhibiting characteristic spatio-temporal ionization structures. Phase resolved optical emission spectroscopy, in combination with adequate modelling of the population dynamics of excited states, and numerical simulations reveal dissipation associated with sheath expansion, sheath collapse, transient electron avalanches and wave–particle interactions. In dual-frequency systems the relative phase between the two frequency components provides additional strategies to tailor the plasma dynamics.

Liquid Structure and Dynamics of Aqueous Isopropanol over gamma-Alumina

The liquid structures of thin films of aqueous solutions of 0, 7, 19, 50, and 100 mol % isopropanol above O/Al-terminated gamma-alumina surfaces have been investigated by means of classical molecular dynamics simulations. The structuring effect of the oxide oil the liquid mixtures is strong and heavily dependent on the local structure of the oxide. Two distinct re-ions are found oil the oxide Surface characterized by the degree of coordination of Al atoms. Above octahedral Al atoms, water and isopropanol molecules adsorb via the oxygen atoms to maximize the electrostatic interaction, whereas above tetrahedral Al sites the solvent molecules adsorb via hydrogen atoms with the oxygen atoms away front the surface. More mobility is found in the second layer compared with the first; however, its structure is still influenced significantly by the orientation of molecules in the first adsorbed layer. Qualitatively, the displacement of water from the surface by the adsorption of isopropanol occurs with 2.6 Water molecules lost for every alcohol molecule present based on the effective surface areas of the two species calculated from the pure simulations.

Music, Magic, and the Mythic: The Dynamics of Visual and Aural Discourse in Souleymane Cissé’s Yeelen

The 1980s saw a wave of African films that aimed to represent, on both local and international screens, a sophisticated pre-colonial Africa, thus debunking notions of the continent as primitive. Toward this aim the films inscribed the conventions of oral performance within their visual styles, denying spectator identification with the protagonists and emphasising the presence of the narrator. However, some critics argued that these films exoticised Africa, while their use of oral performance’s distancing effect echoed the ‘scientific’ distance structured by the ethnographic film, in which African societies were represented as ‘the other’. Souleymane Cissé’s Yeelen exemplifies this tension, transposing into cinematic form oral storytelling techniques in the depiction of a power struggle within the covert cult of the komo, a Bambara initiation society unfamiliar to most non-Bambara viewers. This paper demonstrates how the film negotiates this tension via music, which interpellates the international spectator by eliciting a greater identification with the protagonists than that determined at a visual level, while encoding a verisimilitude to rituals that may otherwise be read as the superstitious practices of ‘the other’. In this way, music and image in Yeelen operate as parallel, though often overlapping, discourses, bridging the gap between the film’s culturally specific narrative and formal components, and its international spectators.

The feeding dynamics of broiler chickens

Contrary to a commonly held belief that broiler chickens need more space, there is increasing evidence that these birds are attracted to other birds. Indeed, commercially farmed birds exhibit a range of socially facilitated behaviours, such as increased feeding and preening in response to the presence of other birds. Social facilitation can generate feedback loops, whereby the adoption of a particular behaviour can spread rapidly and suddenly through the population. Here, by measuring the rate at which broiler chickens join and leave a feeding trough as a function of the number of birds already there, we quantify social facilitation. We use these measurements to parameterize a simulation model of chicken feeding behaviour. This model predicts, and further observations of broiler chickens confirm, that social facilitation leads to excitatory and synchronized patterns of group feeding. Such models could prove a powerful tool in understanding how feeding patterns depend on broiler house design.

Dynamics of Gompertzian tumour growth under environmental fluctuations

We investigate the effect of correlated additive and multiplicative Gaussian white noise oil the Gompertzian growth of tumours. Our results are obtained by Solving numerically the time-dependent Fokker-Planck equation (FPE) associated with the stochastic dynamics. In Our numerical approach we have adopted B-spline functions as a truncated basis to expand the approximated eigenfunctions. The eigenfunctions and eigenvalues obtained using this method are used to derive approximate solutions of the dynamics under Study. We perform simulations to analyze various aspects, of the probability distribution. of the tumour cell populations in the transient- and steady-state regimes. More precisely, we are concerned mainly with the behaviour of the relaxation time (tau) to the steady-state distribution as a function of (i) of the correlation strength (lambda) between the additive noise and the multiplicative noise and (ii) as a function of the multiplicative noise intensity (D) and additive noise intensity (alpha). It is observed that both the correlation strength and the intensities of additive and multiplicative noise, affect the relaxation time.