Triaqua­(2,2′-bipyridine)(5-nitro­isophthal­ato-κO)nickel(II) monohydrate

In the title compound, [Ni(C8H3NO6)(C10H8N2)(H2O)3]·H2O, the NiII cation is six-coordinated by a chelating 2,2′-bipyridine ligand, one carboxyl­ate O atom from a 5-nitro­isophthalate dianion and three water mol­ecules, with a slightly distorted cis-NiN2O4 octa­hedral geometry. The neutral complex is isolated, in contrast to coordination polymers formed by MnII, CoII and CuII with the same ligand set, but forms an extensive network of O—H⋯O hydrogen bonds between the coordinated and uncoordinated water mol­ecules and carboxyl­ate groups of the 5-nitro­isophthalate ions

Synergy of slippery surface and pulse flow: An anti-scaling solution for direct contact membrane distillation

Recent progress on mitigating scaling on hydrophobic membrane distillation (MD) membrane focuses on the design of superhydrophobic/omniphobic surface and process optimization. However, the rationale for scaling resistance is not yet complete. We attempted in this work to unravel the correlation of scaling resistance based on the synergy of slippery surface (via chem-physical engineering) and pulse flow (process engineering). Superhydrophobic micro-pillared polyvinylidene fluoride (MP-PVDF) and CF4 plasma modified MP-PVDF (CF4-MP-PVDF) were utilized as the model membranes. We proposed rheometry as a simple quantitative measure for the wetting state in a hydrodynamic environment. Results showed that MP-PVDF possessed pinned wetting and prone to scaling (2000 mg/L CaSO4 solution) in both steady and pulse flow. In contrast, the CF4-MP-PVDF showed suspended wetting and excellent scaling resistance (at water recovery of 60%, the CF4-MP-PVDF surface was still clean without any crystals) under pulse flow, but not at steady flow. At steady flow, feed over-pressure changes the suspended wetting to pinned wetting by pushing the water-gas interface into the pillars, thereby resulting in scaling for CF4-MP-PVDF. At pulse flow, rhythmic fluctuation in the water-gas interface for CF4-MP-PVDF led to sustained scaling resistance. For the first time, we experimentally demonstrated a scaling resistance in DCMD via engineering surface wetting state and process. We envision that this rationale would pave the forward-looking strategy for a robust stable MD process in the near future

Slippery for scaling resistance in membrane distillation: a novel porous micropillared superhydrophobic surface

Scaling in membrane distillation (MD) is a key issue in desalination of concentrated saline water, where the interface property between the membrane and the feed become critical. In this paper, a slippery mechanism was explored as an innovative concept to understand the scaling behavior in membrane distillation for a soluble salt, NaCl. The investigation was based on a novel design of a superhydrophobic polyvinylidene fluoride (PVDF) membrane with micro-pillar arrays (MP-PVDF) using a micromolding phase separation (μPS) method. The membrane showed a contact angle of 166.0 ± 2.3° and the sliding angle of 15.8 ± 3.3°. After CF4 plasma treatment, the resultant membrane (CF4-MP-PVDF) showed a reduced sliding angle of 3.0o. In direct contact membrane distillation (DCMD), the CF4-MP-PVDF membrane illustrated excellent anti-scaling in concentrating saturated NaCl feed. Characterization of the used membranes showed that aggregation of NaCl crystals occurred on the control PVDF and MP-PVDF membranes, but not on the CF4-MP-PVDF membrane. To understand this phenomenon, a “slippery” theory was introduced and correlated the sliding angle to the slippery surface of CF4-MP-PVDF and its anti-scaling property. This work proposed a well-defined physical and theoretical platform for investigating scaling problems in membrane distillation and beyond

Unprecedented scaling/fouling resistance of omniphobic polyvinylidene fluoride membrane with silica nanoparticle coated micropillars in direct contact membrane distillation

Recent development of omniphobic membranes shows promise in scaling/fouling mitigation in membrane distillation (MD), however, the fundamental understanding is still under dispute. In this paper, we report a novel omniphobic micropillared membrane coated by silica nanoparticles (SiNPs) (SiNPs-MP-PVDF) with dual-scale roughness prepared by a micromolding phase separation (μPS) and electrostatic attraction. This membrane was used as a model for analysis of scaling behavior by calcium sulfate (CaSO4) scaling and fouling behavior by protein casein in comparison with commercial (C-PVDF) and micropillared (MP-PVDF) membranes. Unprecedented scaling/fouling resistance to CaSO4 and casein was observed in direct contact membrane distillation (DCMD) for SiNPs-MP-PVDF membrane. Similar scaling and fouling occurred for commercial PVDF and micropillared PVDF membranes. The observation corresponds well to the wetting state of all membranes as SiNPs-MP-PVDF shows suspended wetting, but MP-PVDF shows pinned wetting. From a hydrodynamic view, the suspended wetting attributes a slippery surface which reduces the direct contact of foulants to solid membrane part and leads to significantly reduced fouling and scaling. However, a pinned (or metastable) wetting state leads to a stagnant interfacial layer that is prone to severe fouling and scaling. This work highlights that both scaling and fouling resistance are indeed of suspended wetting state and slippage origin

Evolutionary Programming Based on Non-Uniform Mutation 1)

Abstract. A new evolutionary programming algorithm (NEP) using the non-uniform mutation operator instead of Gaussian or Cauchy mutation operators is proposed. NEP has the merits of “long jumps ” of the Cauchy mutation operator at the early stage of the algorithm and “fine-tunings ” of the Gaussian mutation operator at the later stage. Comparisons with the recently proposed sequential and parallel evolutionary algorithms are made through comprehensive experiments. NEP significantly outperforms the adaptive LEP for most of the benchmarks. NEP outperforms some parallel GAs and performs comparably to others in terms of the solution quality and algorithmic robustness. We give a detailed theoretical analysis of NEP. The probability convergence is proved. The expected step size of the non-uniform mutation is calculated. Based on this, the key property of NEP with “long jumps ” at the early stage and “fine-tunings ” at the later stage is proved strictly

Understanding the fouling/scaling resistance of superhydrophobic/omniphobic membranes in membrane distillation

Membrane distillation has shown great promises in desalinating various water streams. Significant progresses have been made in the past decades owing to the development of advanced membrane materials, such as superhydrophobic and omniphobic membranes. However, fouling and scaling remains a critical issue for stable operation. This account summarizes contemporary theories in fouling and scaling formation and their limitations in explaining the fouling resistance of superhydrophobic and omniphobic membranes. A new understanding is proposed based on hydrodynamics where non-slip boundary conditions play a critical role. By distinguishing a pinned and suspended wetting state, it is suggested that a superhydrophobic or omniphobic membrane correlates to a suspended wetting state, consequently a slip surface leading to scaling/fouling resistance. A new framework for analyzing the fouling/scaling behavior of MD membrane is provided to identify the wetting and hydrodynamic character of the membrane. A novel concept of treating the highly saline waste streams is suggested to cover membrane synthesis, module design and process optimization. The present work will be of interest to scientists and engineers searching for solutions to the MD fouling issues

BiT: Robustly Binarized Multi-distilled Transformer

Modern pre-trained transformers have rapidly advanced the state-of-the-art in machine learning, but have also grown in parameters and computational complexity, making them increasingly difficult to deploy in resource-constrained environments. Binarization of the weights and activations of the network can significantly alleviate these issues, however is technically challenging from an optimization perspective. In this work, we identify a series of improvements which enables binary transformers at a much higher accuracy than what was possible previously. These include a two-set binarization scheme, a novel elastic binary activation function with learned parameters, and a method to quantize a network to its limit by successively distilling higher precision models into lower precision students. These approaches allow for the first time, fully binarized transformer models that are at a practical level of accuracy, approaching a full-precision BERT baseline on the GLUE language understanding benchmark within as little as 5.9%

Anisotropic performance of a superhydrophobic polyvinyl difluoride membrane with corrugated pattern in direct contact membrane distillation

A novel surface-corrugated superhydrophobic polyvinylidene fluoride (PVDF) membrane (C-PVDF) was prepared for direct contact membrane distillation (DCMD) using a micromolding phase separation (μPS) method. The membrane showed a static contact angle of 159.0 ± 4.0°. However, dynamic measurements of the sliding angles revealed a lower value of 9.1 ± 0.8° when a water droplet slides in parallel to the ridge, and a higher value of 14.6 ± 1.6° if perpendicular to the ridge. This anisotropic property was also reflected in the DCMD fluxes for both feed of deionized water and 4.0 wt% NaCl solution: in case the feed flows in parallel to the ridge, a higher flux is resulted than it flows perpendicular to the ridge. Anisotropic MD performance cannot be explained by the Dusty-Gas model because the average characteristics of the membrane in the model are intrinsically the same for both flow modes. Instead, anisotropic wetting and sliding in the parallel and perpendicular orientation revealed that the MD performance has both thermodynamic and hydrodynamic origins