Dynamics of a vortex dipole in a holographic superfluid

We use holography to investigate the dynamics of a vortex-anti-vortex dipole in a strongly coupled superfluid in 2+1 dimensions. The system is evaluated in numerical real-time simulations in order to study the evolution of the vortices as they approach and eventually annihilate each other. A tracking algorithm with sub-plaquette resolution is introduced which permits a high-precision determination of the vortex trajectories. With the increased precision of the trajectories it becomes possible to directly compute the vortex velocities and accelerations. We find that in the holographic superfluid the vortices follow universal trajectories independent of their initial separation, indicating that a vortex-anti-vortex pair is fully characterized by its separation. Subtle non-universal effects in the vortex motion at early times of the evolution can be fully attributed to artifacts due to the numerical initialization of the vortices. We also study the dependence of the dynamics on the temperature of the superfluid.

Pentiptycene-based ladder polymers with configurational free volume for enhanced gas separation performance and physical aging resistance

Polymers of intrinsic microporosity (PIMs) have shown promise in pushing the limits of gas separation membranes, recently redefining upper bounds for a variety of gas pair separations. However, many of these membranes still suffer from reductions in permeability over time, removing the primary advantage of this class of polymer. In this work, a series of pentiptycene-based PIMs incorporated into copolymers with PIM-1 are examined to identify fundamental structure–property relationships between the configuration of the pentiptycene backbone and its accompanying linear or branched substituent group. The incorporation of pentiptycene provides a route to instill a more permanent, configuration-based free volume, resistant to physical aging via traditional collapse of conformation-based free volume. PPIM-ip-C and PPIM-np-S, copolymers with C- and S-shape backbones and branched isopropoxy and linear n-propoxy substituent groups, respectively, each exhibited initial separation performance enhancements relative to PIM-1. Additionally, aging-enhanced gas permeabilities were observed, a stark departure from the typical permeability losses pure PIM-1 experiences with aging. Mixed-gas separation data showed enhanced CO2/CH4 selectivity relative to the pure-gas permeation results, with only ∼20% decreases in selectivity when moving from a CO2 partial pressure of ∼2.4 to ∼7.1 atm (atmospheric pressure) when utilizing a mixed-gas CO2/CH4 feed stream. These results highlight the potential of pentiptycene’s intrinsic, configurational free volume for simultaneously delivering size-sieving above the 2008 upper bound, along with exceptional resistance to physical aging that often plagues high free volume PIMs.

Control of produced water with highly corrosive medium in oil-gas production

The construction of middle oil-gathering facility, in which technological processes are managed in a closed medium is necessary for environmental protection to control highly corrosive medium in oil and gas production. Associated gas separated from the fluid in initial separation unit within middle oil-gathering facility enters gas-gathering point with low pressure, and the liquid - into the pig of oil, water and sand, which should be constructed from iron concrete for cleaning from mechanical impurities sediments and salt as well. The liquid charge from the separation unit and pig of oil, water and sand is based upon the law of communicating vessels. To supply long-life for reservoirs, the inner and outer walls should be covered with a special coating and additionally, electrochemical protection should be provided as well.

Dynamic behavior of chloride ion-electrically charged open carbon nanocone oscillators: A molecular dynamics study

This paper is intended to study the dynamic oscillatory behavior of chloride ion inside electrically charged open carbon nanocones (CNCs) using the molecular dynamics (MD) simulations. The small and wide ends of nanocone are assumed to be identically and uniformly charged with positive electric charges. In the simulation, the Tersoff-Brenner (TB) and the Lennard-Jones (LJ) potential functions are employed to evaluate the interatomic interactions between carbon atoms and the van der Waals (vdW) interactions between the ion and the nanocone, respectively. The Coulomb potential is also adopted to evaluate the electrostatic interactions between the ion and the electric charges distributed at both ends of nanocone. Numerical results are presented to examine the effects of magnitude of electric charges, initial separation distance and initial velocity on the mechanical oscillatory behavior of system and the obtained results are also compared with the ones related to an uncharged nanocone. It is found that operating frequency as well as escape velocity enhance considerably as a result of electrostatic interactions. It is further found that regardless of the value of electric charges, optimal oscillation frequency is achievable when no initial velocity is imposed on the ion initially located inside of nanocone with an offset of 2 Å from its small end.

Relative Dispersion on the Inner Shelf: Evidence of a Batchelor Regime

Oceanographic relative dispersion (based on drifter separations r) has been extensively studied mostly finding either Richardson-Obukhov ( ~ t3) or enstrophy cascade ( ~ exp(t)) scaling. Relative perturbation dispersion (, based on perturbation separation r − r0 where r0 is the initial separation) has a Batchelor scaling ( ~ t2) for times less than the r0-dependent Batchelor time. Batchelor scaling has received little oceanographic attention. GPS-equipped surface drifters were repeatedly deployed on the Inner Shelf off of Pt. Sal, CA in water depths ≤ 40 m. From 12 releases of ≈ 18 drifters per release, perturbuation and regular relative dispersion over ≈ 4 h are calculated for 250 ≤ r0 ≤ 1500 m for each release and the entire experiment. The perturbation dispersion is consistent with Batchelor scaling for the first 1000-3000 s with larger r0 yielding stronger dispersion and larger Batchelor times. At longer times, and scale-dependent diffusivities begin to suggest Richardson-Obukhov scaling. This applies to both experiment averaged and individual releases. For individual releases, nonlinear internal waves can modulate dispersion. Batchelor scaling is not evident in as the correlations between initial and later separations are significant at short time scaling as ~ t Thus, previous studies investigating are potentially aliased by initial separation effects not present in the perturbation dispersion . As the underlying turbulent velocity wavenumber spectra is inferred from the dispersion power law time dependence, analysis of both and is critical.

The Influence of the Interference Effects on the Aerodynamic Characteristics of the Reentry Vehicle and Its Parachute System Structural Elements During Their Separation

This work considers the aerodynamic characteristics of the reentry vehicle (RV) of a segmental-conical shape, and the parachute container hatch cover (PCHC) during its separation. Due to the aerodynamic interference, the hatch may collide with the RV. The authors propose a method of studying the aerodynamic characteristics of the PCHC and RV based on modelling using the dynamic mesh technology in the FlowVision software package. Stationary flow around the RV until the hatch cover separation, flow around the hatch cover and free flow are calculated. As the result of the calculations, the PCHC trajectories (excluding gravitational forces) under various initial separation conditions, as well as the aerodynamic characteristics of the RV are obtained. The cases when the hatch cover collides with the RV are identified.

The timing of breeding and independence for snow leopard females and their cubs

Significant knowledge gaps persist on snow leopard demography and reproductive behavior. From a GPS-collared population in Mongolia, we estimated the timing of mating, parturition and independence. Based on three mother–cub pairs, we describe the separation phase of the cub from its mother as it gains independence. Snow leopards mated from January–March and gave birth from April–June. Cubs remained with their mother until their second winter (20–22 months of age) when cubs started showing movements away from their mother for days at a time. This initiation of independence appeared to coincide with their mother mating with the territorial male. Two female cubs remained in their mothers’ territory for several months after initial separation, whereas the male cub quickly dispersed. By comparing the relationship between body size and age of independence across 11 solitary, medium-to-large felid species, it was clear that snow leopards have a delayed timing of separation compared to other species. We suggest this may be related to their mating behavior and the difficulty of the habitat and prey capture for juvenile snow leopards. Our results, while limited, provide empirical estimates for understanding snow leopard ecology and for parameterizing population models.