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Abstract. The statistical properties of acoustic signals re ected by a randomly layered medium are analyzed when a pulsed spherical wave issuing from a point source is incident u p o n i t . The asymptotic analysis of stochastic equations and geometrical acoustics is used to arrive at a set of transport equations that characterize multiply scattered signals observed at the surface of the layered medium. The results of extensive n umerical simulations are presented, illustrating the scope of the theory. A n umber of inverse problems for randomly layered media are also formulated where we recover large scale properties of the sound speed pro le from the statistics of re ected signals.

When deep-water surface gravity waves traverse an area with a curved or otherwise variable current, the current can act analogously to an optical lens, to focus wave action into a caustic region. In this region, waves of surprisingly large size, alternatively called freak, rogue, or giant waves are produced. We show how this mechanism produces freak waves at random locations when ocean swell traverses an area of random current. When the current has a constant (possibly zero) mean with small random fluctuations, we show that the probability distribution for the formation of a freak wave is universal, that is, it does not depend on the statistics of the current, but only on a single distance scale parameter, provided that this parameter is finite and non-zero. Our numerical simulations show excellent agreement with the theory, even for current standard deviation as large as 1.0 m s −" . Since many of these results are derived for arbitrary dispersion relations with certain general properties, they include as a special case previously published work on caustics in geometrical optics.

Currently, the training of the future work force presents challenging problems to higher education. This training, in the form of practical and theoretical knowledge can come from multiple platforms, channels and means, both formal and informal. In addition, it is quite difficult to assess the knowledge skill level that a student has acquired to optimize their chances for future employability. This, together with the need to still manage academic curricula on paper, the problems of confidence when validating these documents and contrasting them with real knowledge, etc., means that management in higher education requires revolutionary new tools. This work evaluates the benefits of the blockchain (or distributed ledger) technology and advocates a decentralised model of confidence for transactions based on an academic crypto currency. In this approach blockchain is used to manage transactions of content, teaching and competencies, assessed by consensus by students, trainers and employers, to eliminate once and for all the "gap" between the academic world and the working world. This paper aims to address the current challenges of an increasingly dispersed, open and ubiquitous higher education. The proposed model can be implemented in any training institution to adapt its teaching to the specific needs of professional profiles validated by employers in the sector. This model has been validated by means of a prototype with more than acceptable results.

Here, we report, for what we believe to be the first time, on the modification of a low cost sensor, designed for the smartphone camera market, to develop an ultraviolet (UV) camera system. This was achieved via adaptation of Raspberry Pi cameras, which are based on back-illuminated complementary metal-oxide semiconductor (CMOS) sensors, and we demonstrated the utility of these devices for applications at wavelengths as low as 310 nm, by remotely sensing power station smokestack emissions in this spectral region. Given the very low cost of these units, ≈ USD 25, they are suitable for widespread proliferation in a variety of UV imaging applications, e.g., in atmospheric science, volcanology, forensics and surface smoothness measurements.

We predict that anomalously long localization lengths -which in some special cases diverge -can be expected for p-polarized light propagating through one-dimensional disordered structures under certain conditions. We give a physical argument for the existence of such anomalies, and support it by a longwavelength theory and Monte Carlo calculations. 108

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Following continuous-time random-walk dynamics, we consider particle diffusion and trapping on fractals, and study the interplay of the spatial (a) and temporal (y) stochastic aspects. At long times and for broad waiting-time distributions the mean squared displacement behaves as (r 2 (t)) ~ t ay , whereas the particle decay is algebraic, 0(0 ~~ t~y.PACS numbers: 05.40.H-j, 66.30.-h, 72.80.Ng A very successful description of the dynamics of carrier diffusion and recombination in disordered media is provided by the continuous-time randomwalk (CTRW) method. 1 " 5 For wide classes of materials the decay law due to recombination is highly nonexponential in time: Denoting by 4>(0 the survival probability of the carrier at time / one finds that at longer times(see Refs. 5-7 and citations therein). Moreover, in these materials the diffusion is dispersive, i.e., the diffusion coefficient D{t) tends to zero for large t, generally following an algebraic law, 5 " 7 DU)-d{T 2 (t))ldt-r y } 0