The Institute of Physics (IOP) is a UK-based learned society and professional body that works to advance physics education, research and application.It was founded in 1874 and has a worldwide membership of over 20,000. The IOP is the Physical Society for the UK and Ireland and supports physics in education, research and industry. In addition to this, the IOP provides services to its members including careers advice and professional development and grants the professional qualification of Chartered Physicist (CPhys), as well as Chartered Engineer (CEng) as a nominated body of the Engineering Council. The IOP's publishing company, IOP Publishing, publishes 85 academic titles.
We study directed transport in a two-dimensional suspension of repulsively interacting colloids driven by a stochastic asymmetric piecewise-linear flashing ratchet using large-scale molecular dynamics simulations. The driving frequency and the ratchet asymmetry offer two independent ways of controlling the particle current, but they affect the suspension differently. At fixed asymmetry, the current shows a resonance with ratcheting frequency that is set by the collective relaxation dynamics of the interacting particles. The resulting increase in transport is accompanied by defect-mediated structural changes, showing density-dependent hexatic and solid-like states, with larger currents generally associated with weaker ordering. By contrast, at fixed frequency, changing the ratchet asymmetry mainly alters the strength of the directed bias and can significantly enhance the current while leaving the hexatic order largely unchanged. Near the equilibrium hexatic-melting regime, this makes it possible to generate substantial directed currents without strongly disrupting sixfold orientational order. These results show that frequency tuning couples transport to structural reorganization, whereas asymmetry tuning primarily controls transport leaving the structure largely unaltered, providing distinct and complementary routes for manipulating transport and order in driven colloidal suspensions.
Context. Dusty discs detected around main-sequence stars are thought to be signs of planetesimal belts in which the dust distribution is shaped by collisional and dynamical processes, including interactions with gas if present. The debris disc around the young A-type star HD 131835 is composed of two dust rings at similar to 65 au and similar to 100 au, a third unconstrained innermost component, and a gaseous component centred at similar to 65 au. New ALMA observations show that the inner of the two dust rings is brighter than the outer one, in contrast with previous observations in scattered light. Aims. We explore two scenarios that could explain these observations: the two dust rings might represent distinct planetesimal belts with different collisional properties, or only the inner ring might contain planetesimals while the outer ring consists entirely of dust that has migrated outwards due to gas drag. Methods. To explore the first scenario, we employed a state-of-the-art collisional evolution code. To test the second scenario, we used a simple dynamical model of dust grain evolution in an optically thin gaseous disc. In each case we identified the parameters of the planetesimal and the gaseous disc that best reproduce the observational constraints. Results. Collisional models of two planetesimal belts cannot fully reproduce the observations by only varying their dynamical excitation, and matching the data through a different material strength requires an extreme difference in dust composition. The gas-driven scenario can reproduce the location of the outer ring and the brightness ratio of the two rings from scattered light observations, but the resulting outer ring is too faint overall in both scattered light and sub-millimetre emission. Conclusions. The dust rings in HD 131835 could be produced from two planetesimal belts, although how these belts would attain the required extremely different properties needs to be explained. The dust-gas interaction is a plausible alternative explanation and deserves further study using a more comprehensive model.
Human social behavior follows stratified, hierarchical networks, with support groups of about 5 members scaling proportionally up to approximately 150 frequent interactions per individual, as posited by the Social Brain Hypothesis. The number of close contacts per individual aligns with psychological and neurological evidence given by the Big Five personality traits, which span a five-dimensional space of traits necessary for a thorough social life. The fractal network framework elucidates social phenomena such as information propagation and socioeconomic output generated in urban areas. This study models socioeconomic interactions using fractal networks, where group sizes scale by a fixed factor, to analyze consensus formation. Employing q-calculus, the model reveals how hierarchical structures influence information spread, exhibiting universal power-law behaviors. The results yield q-Gaussian distributions with heavy tails, aligning with observed socioeconomic inequalities globally, consistent with the fractal structure of social networks.
The Cu2S-Ag2S-GeS2 (A) system is of interest for the preparation of copper–silver-substituted solid solutions based on ternary compounds possessing a number of interesting functional properties. This paper presents the results of a detailed experimental study of phase equilibria in this system using the DTA/DSC and X-ray diffraction methods. A new refined version of the T-x diagram of the Ag2S-GeS2 boundary system is presented. A new picture of phase equilibria in the system (A) is obtained, including diagrams of solid-phase equilibria at 300 K and 750 K, a projection of the liquidus surface of the system, as well as some polythermal sections and isothermal sections of the phase diagram at 1200, 1100 and 1000 K. It is established that the quasi-binary system Ag2S-GeS2 is characterized by the formation of two intermediate compounds, Ag8GeS6 and Ag2GeS3. The first melts congruently at 1220 K and undergoes a polymorphic transformation at 495 K. The second is formed as a result of a peritectic reaction at 895 K. System (A) is characterized by the formation of continuous solid solutions between the high-temperature cubic modifications of Cu8GeS6 and Ag8GeS6, limited solid solutions based on their low-temperature modifications, and Cu2GeS3 and Ag2GeS3 compounds. In the subsolidus region of system (A), phase transformations associated with the polymorphism of binary and ternary compounds are observed.
The discoveries of the hidden-charm P-c pentaquarks by the LHCb Collaboration have been not confirmed by other experiments yet. It is desirable to investigate the feasibility of observing them in other experiments. We present an order-of-magnitude estimate of the cross section of the e(+)e(-) -> J/psi p (p) over bar process, where the hidden-charm pentaquarks may be searched for, and find it to be of O(4 fb) when the e(+)e(-) c.m. energy is about between 6 and 7 GeV. The cross section for e(+)e(-) - P-c(p) over bar is then estimated to be less than or similar to O(0.1 pb). Thus, it is promising to search for P at the future high-luminosity super tau-charm facilities with annual integrated luminosity about 1 ab(-1). We also predict the branching fraction of Upsilon- J/psi p (p) over bar to be of O(2 x 10(-6)), which can be tested at B factories.
