A biomimetic nanofluidic diode based on surface-modified polymeric carbon nitride nanotubes

A controllable ion transport including ion selectivity and ion rectification across nanochannels or porous membranes is of great importance because of potential applications ranging from biosensing to energy conversion. Here, a nanofluidic ion diode was realized by modifying carbon nitride nanotubes with different molecules yielding an asymmetric surface charge that allows for ion rectification. With the advantages of low-cost, thermal and mechanical robustness, and simple fabrication process, carbon nitride nanotubes with ion rectification have the potential to be used in salinity-gradient energy conversion and ion sensor systems

General, metal-free synthesis of carbon nanofiber assemblies from plant oils

Synthesis of carbon nanofibers suffers in classical approaches from either costs or the introduction of metallic impurities, and a more simple method of synthesis based on affordable and accessible educts would be highly welcomed. For that, we rationally designed a metal-free approach based on ketene chemistry using phosphorus pentoxide (P2O5) and vegetable oil. Based on the characterization of intermediates, P2O5-oil reaction yielded most possibly alkylketenes, which polymerized into poly(ketene) with abundant enol groups. The enol groups further reacted with P2O5, forcing the poly(ketene) to assemble into a nano-sized preassembly structure. Moderate heating transforms these soft assembly structures into carbonaceaus nanofibers. Moreover, this approach is applicable to other chemicals with similar structure to vegetable oil, which demonstrates the generality of methodology. The carbon nanofibers with P-O-C functionalization show relatively high graphitization degree and promising textural properties (e.g., well-developed porosity, negatively-charged surface). The C-O-P environment accounts for 66 at% of the total P and create a superior thermal stability of carbon nanofibers as compared with unfunctionalized all-carbon nanotubes. As a model application, a CDI system built of a carbon nanofibers-based electrode countered by an activated carbon-based electrode exhibited exceptional performance: a NaCl adsorption capacity ~30 mg g-1 at applied voltage of 1.2 V was reached, with very stable adsorption-desorption cycles. This research opens a promising path to large-scale and low-cost synthesis of 1-dimensional carbon nanofibers from sustainable carbon sources without using metal catalysts or expensive equipment

Cascade communication in disordered networks of enzyme-loaded microdroplets

Regulation of chemical reactivity in reaction cascades is critical to the functioning and survival of living organisms. In nature, an asymmetry in chemical communication is often controlled by compartmentalizing active species, e.g. enzymes, within cells or subcellular organelles. In this work, we describe an artificial droplet network that exhibits programmed and directional communication capable to perform a multistep enzymatic cascade reaction across multiple droplets. More specifically, a non-reciprocal transfer of substrates between enzyme-containing aqueous emulsion droplets is realized by (biochemically) induced osmolarity gradients and concomitant concentration gradients then direct an enzymatic cascade reaction across different droplets. Given the generalizable nature of this approach, we believe the herein developed guidelines can be extended to other enzymes and enzyme-linked assays thereby increasing the specificity in chemotactic signaling cascades

Multigrid algorithms for hp-version interior penalty discontinuous Galerkin methods on polygonal and polyhedral meshes

In this paper we analyze the convergence properties of two-level and W-cycle multigrid solvers for the numerical solution of the linear system of equations arising from hp-version symmetric interior penalty discontinuous Galerkin discretizations of second-order elliptic partial differential equations on polygonal/polyhedral meshes. We prove that the two-level method converges uniformly with respect to the granularity of the grid and the polynomial approximation degree p, provided that the number of smoothing steps, which depends on p, is chosen sufficiently large. An analogous result is obtained for the W-cycle multigrid algorithm, which is proved to be uniformly convergent with respect to the mesh size, the polynomial approximation degree, and the number of levels, provided the latter remains bounded and the number of smoothing steps is chosen sufficiently large. Numerical experiments are presented which underpin the theoretical predictions; moreover, the proposed multilevel solvers are shown to be convergent in practice, even when some of the theoretical assumptions are not fully satisfied

A Unified Analysis of Balancing Domain Decomposition by Constraints for Discontinuous Galerkin Discretizations

The BDDC algorithm is extended to a large class of discontinuous Galerkin (DG) discretizations of second order elliptic problems. An estimate of C(1 + log(H/h))2 is obtained for the condition number of the preconditioned system where C is a constant independent of h or H or large jumps in the coefficient of the problem. Numerical simulations are presented which confirm the theoretical results. A key component for the development and analysis of the BDDC algorithm is a novel perspective presenting the DG discretization as the sum of element-wise “local” bilinear forms. The element-wise perspective allows for a simple unified analysis of a variety of DG methods and leads naturally to the appropriate choice for the subdomain-wise local bilinear forms. Additionally, this new perspective enables a connection to be drawn between the DG discretization and a related continuous finite element discretization to simplify the analysis of the BDDC algorithm.Boeing CompanyMassachusetts Institute of Technology (Zakhartchenko Fellowship

Recent experiments performed at "Carlo Novero" lab at INRIM on Quantum Information and Foundations of Quantum Mechanics

In this paper we present some recent work performed at "Carlo Novero" lab on Quantum Information and Foundations of Quantum Mechanics.Comment: Contribution to III international workshop "Recent advances in Foundations of Quantum Mechanics and Quantum Information. In memory of Carlo Novero

New Organic Semiconducting Scaffolds by Supramolecular Preorganization: Dye Intercalation and Dye Oxidation and Reduction

The assembly of melamine and 2,5-dihydroxy-1,4-benzoquinone results in new “sheet-like” supramolecular crystals that by controlled thermal condensation can be converted to photoactive materials at relativity low temperatures. The condensation temperature alters the materials properties from polymer-like to carbon materials alongside their morphology and elemental ratio. This new method opens the possibility for the synthesis of new organic, photoactive carbon–nitrogen based frameworks at low calcination temperatures with great simplicity. Photodegradation experiments of methylene blue reveal that the obtained materials can perform dye reduction photochemically with visible photons, while at the same time the photogenerated holes oxidize the dye toward small molecular fragments

Spline Upwind for space--time Isogeometric Analysis of cardiac electrophysiology

We present an elaboration and application of Spline Upwind (SU) stabilization method, designed in space--time Isogeometric Analysis framework, in order to make this stabilization as suitable as possible in the context of cardiac electrophysiology. Our aim is to propose a formulation as simple and efficient as possible, effectual in preventing spurious oscillations present in plain Galerkin method and also reasonable from the computational cost point of view. For these reasons we validate the method's capability with numerical experiments, focusing on accuracy and computational aspects

Unidirectional ion transport in nanoporous carbon membranes with a hierarchical pore architecture

The transport of fluids in channels with diameter of 1-2 nm exhibits many anomalous features due to the interplay of several genuinely interfacial effects. Quasi-unidirectional ion transport, reminiscent of the behavior of membrane pores in biological cells, is one phenomenon that has attracted a lot of attention in recent years, e.g., for realizing diodes for ion-conduction based electronics. Although ion rectification has been demonstrated in many asymmetric artificial nanopores, it always fails in the high-concentration range, and operates in either acidic or alkaline electrolytes but never over the whole pH range. Here we report a hierarchical pore architecture carbon membrane with a pore size gradient from 60 nm to 1.4 nm, which enables high ionic rectification ratios up to 104 in different environments including high concentration neutral (3 M KCl), acidic (1 M HCl), and alkaline (1 M NaOH) electrolytes, resulting from the asymmetric energy barriers for ions transport in two directions. Additionally, light irradiation as an external energy source can reduce the energy barriers to promote ions transport bidirectionally. The anomalous ion transport together with the robust nanoporous carbon structure may find applications in membrane filtration, water desalination, and fuel cell membranes