Stability of additive-free water-in-oil emulsions

We calculate ion distributions near a planar oil-water interface within non-linear Poisson-Boltzmann theory, taking into account the Born self-energy of the ions in the two media. For unequal self-energies of cations and anions, a spontaneous charge separation is found such that the water and oil phase become oppositely charged, in slabs with a typical thickness of the Debye screening length in the two media. From the analytical solutions, the corresponding interfacial charge density and the contribution to the interfacial tension is derived, together with an estimate for the Yukawa-potential between two spherical water droplets in oil. The parameter regime is explored where the plasma coupling parameter exceeds the crystallization threshold, i.e. where the droplets are expected to form crystalline structures due to a strong Yukawa repulsion, as recently observed experimentally. Extensions of the theory that we discuss briefly include numerical calculations on spherical water droplets in oil, and analytical calculations of the linear PB-equation for a finite oil-water interfacial width.Comment: 9 pages, 4 figures, accepted by JPCM for proceedings of LMC

Boxed pervasive games: an experience with user-created pervasive games

Pervasive games are rapidly maturing - from early research experiments with locative games we now start to see a range of commercial projects using locative and pervasive technology to create technology-supported pervasive games. In this paper we report on our experiences in transferring the successful involvement of players in computer games to modding for pervasive games. We present the design process, the enabling tools and two sample games provided in boxes to end users. Finally we discuss how our findings inform the design of modding tools for a pervasive game community of the future

The Analysis of Polystyrene and Polystyrene Aggregates into the Mega Dalton Mass Range by Cryodetection MALDI TOF MS

Mass spectra of atactic polystyrene were collected into the mega-dalton mass range with a matrix-assisted laser desorption ionization time of flight (MALDI TOF) mass spectrometer, which incorporates a cryodetector comprised of an array of 16 superconducting tunnel junctions (STJ). The STJ cryodetector, theoretically, has no loss in signal response at any mass compared with the reduced signal found at high mass when using a conventional secondary-ionization detector. Since ion detection at high m/z is one of the fundamental limitations of mass spectrometry (MS), the cryodetector was used to explore the high m/z limit of the MALDI TOF technique for the analysis of two polymer types. Mass spectra were collected for polystyrene at Mn 170, 400, 900, and 2000 kDa and polymethyl methacrylate (PMMA) at Mn 62.6 kDa and 153.7 kDa. For polystyrene, the data showed a trend toward increased aggregation and charge state with mass. The Mn 2 MDa polystyrene data revealed a peak at m/z 2.2 MegaTh and a charge state analysis revealed that these ions were primarily polystyrene aggregates with a mass of ∼4 MDa. This aggregate assignment was possible because the cryodetector response allows for the determination of a charge state up to about four. The contribution of each charge state for a selected peak can be determined in this fashion. This analysis revealed the preferential formation of doubly charged even-numbered aggregates over odd-numbered aggregates for high molecular mass polystyrene. A potential mechanism for the aggregation process for doubly charged species is discussed

Active Brownian Motion Models and Applications to Ratchets

We give an overview over recent studies on the model of Active Brownian Motion (ABM) coupled to reservoirs providing free energy which may be converted into kinetic energy of motion. First, we present an introduction to a general concept of active Brownian particles which are capable to take up energy from the source and transform part of it in order to perform various activities. In the second part of our presentation we consider applications of ABM to ratchet systems with different forms of differentiable potentials. Both analytical and numerical evaluations are discussed for three cases of sinusoidal, staircase-like and Mateos ratchet potentials, also with the additional loads modeled by tilted potential structure. In addition, stochastic character of the kinetics is investigated by considering perturbation by Gaussian white noise which is shown to be responsible for driving the directionality of the asymptotic flux in the ratchet. This \textit{stochastically driven directionality} effect is visualized as a strong nonmonotonic dependence of the statistics of the right versus left trajectories of motion leading to a net current of particles. Possible applications of the ratchet systems to molecular motors are also briefly discussedComment: 12 pages, 17 figure

Irreversible and reversible modes of operation of deterministic ratchets

We discuss a problem of optimization of the energetic efficiency of a simple rocked ratchet. We concentrate on a low-temperature case in which the particle's motion in a ratchet potential is deterministic. We show that the energetic efficiency of a ratchet working adiabatically is bounded from above by a value depending on the form of ratchet potential. The ratchets with strongly asymmetric potentials can achieve ideal efficiency of unity without approaching reversibility. On the other hand we show that for any form of the ratchet potential a set of time-protocols of the outer force exist under which the operation is reversible and the ideal value of efficiency is also achieved. The mode of operation of the ratchet is still quasistatic but not adiabatic. The high values of efficiency can be preserved even under elevated temperatures

Transition from Secondary school CLIL to EMI at University: Initial evidence from research in Italy

Through vocabulary tests, interviews with students and recordings of classes/lectures, we measured students' English vocabulary knowledge against the vocabulary in the teachers' talk, the nature of classroom interaction in the two settings and the students' approaches to their learning in general and their in-class listening strategies in particular. In this way we aimed to identify the challenges students faced in English-medium education in the secondary and tertiary educational phases

Shear Viscosity of Clay-like Colloids in Computer Simulations and Experiments

Dense suspensions of small strongly interacting particles are complex systems, which are rarely understood on the microscopic level. We investigate properties of dense suspensions and sediments of small spherical Al_2O_3 particles in a shear cell by means of a combined Molecular Dynamics (MD) and Stochastic Rotation Dynamics (SRD) simulation. We study structuring effects and the dependence of the suspension's viscosity on the shear rate and shear thinning for systems of varying salt concentration and pH value. To show the agreement of our results to experimental data, the relation between bulk pH value and surface charge of spherical colloidal particles is modeled by Debye-Hueckel theory in conjunction with a 2pK charge regulation model.Comment: 15 pages, 8 figure

Multiple current reversals in forced inhomogeneous ratchets

Transport properties of overdamped Brownian paricles in a rocked thermal ratchet with space dependent friction coefficient is studied. By tuning the parameters, the direction of current exhibit multiple reversals, both as a function of the thermal noise strength as well as the amplitude of rocking force. Current reversals also occur under deterministic conditions and exhibits intriguing structure. All these features arise due to mutual interplay between potential asymmetry,noise, driving frequency and inhomogeneous friction.Comment: 6 figure

Mirror symmetry breaking through an internal degree of freedom leading to directional motion

We analyze here the minimal conditions for directional motion (net flow in phase space) of a molecular motor placed on a mirror-symmetric environment and driven by a center-symmetric and time-periodic force field. The complete characterization of the deterministic limit of the dissipative dynamics of several realizations of this minimal model, reveals a complex structure in the phase diagram in parameter space, with intertwined regions of pinning (closed orbits) and directional motion. This demonstrates that the mirror-symmetry breaking which is needed for directional motion to occur, can operate through an internal degree of freedom coupled to the translational one.Comment: Accepted for publication in Phys. Rev.