Search results for "Concentration gradient"
showing 10 items of 11 documents
Photophysical Properties of Charged Cyclometalated Ir(III) Complexes: A Joint Theoretical and Experimental Study
2011
The photophysical properties of a series of charged biscyclometalated [Ir(ppy)(2)(N boolean AND N)](1+) complexes, where ppyH is 2-phenylpyridine and N boolean AND N is 2,2'-bipyridine (bpy), 6-phenyl-2,2'-bipyridine (pbpy), and 6,6'-dipheny1-2,2'-bipyridine (dpbpy) for complexes 1, 2, and 3, respectively, have been investigated in detail. The photoluminescence performance in solution decreases from 1 to 3 upon attachment of phenyl groups to the ancillary ligand. The absorption spectra recorded over time suggest that complex 3 is less stable compared to complexes 1 and 2 likely due to a nucleophilic-assisted ancillary ligand-exchange reaction. To clarify this behavior, the temperature depen…
Ion size effects on the electrokinetic flow in nanoporous membranes caused by concentration gradients
2003
The space charge model (SCM) relies on the Poisson−Boltzmann (PB) equation, and hence on the assumption of negligible ion size effects, to calculate the radial distribution of the electrical potent...
Magnetically enhancing the Seebeck coefficient in ferrofluids.
2019
The influence of the magnetic field on the Seebeck coefficient (Se) was investigated in dilute magnetic nanofluids (ferrofluids) composed of maghemite magnetic nanoparticles dispersed in dimethyl-sulfoxide (DMSO). A 25% increase in the Se value was found when the external magnetic field was applied perpendicularly to the temperature gradient, reminiscent of an increase in the Soret coefficient (ST, concentration gradient) observed in the same fluids. In-depth analysis of experimental data, however, revealed that different mechanisms are responsible for the observed magneto-thermoelectric and -thermodiffusive phenomena. Possible physical and physico-chemical origins leading to the enhancemen…
The first operating thermolytic reverse electrodialysis heat engine
2020
Abstract Thermolytic reverse electrodialysis heat engine (t-RED HE) has been recently proposed as a technology for converting low-temperature waste heat into electricity. The construction and operation of the first world lab-scale prototype unit are reported. The system consists of: (i) a reverse electrodialysis unit where, the concentration gradient between two solutions of thermolytic salts is converted into electricity and (ii) a thermally-driven regeneration unit where low-temperature heat is used to restore the initial conditions of the two feed streams. Regeneration is based on a degradation process of salts into gaseous ammonia and carbon dioxide, which can be removed almost entirely…
Conoscopic Studies of Optical Homogeneity of the LiNbO3:Mg Crystals
2012
An essential modification of the method to observe large-scale conoscopic images is proposed. Divergent beam of wide-aperture radiation is formed by a diffuser placed before entrance of a lithium niobate crystal. The optical homogeneity of LiNbO3:Mg crystals is studied in a wide range of the admixture concentrations (0.01 – 5.5 mol.%). An inhomogeneous distribution of the admixture is found to increase with the admixture concentration being accompanied by growth bands, micro-defects, such as micro-domains, domain boundaries, and block structures particularly in parts of higher concentration gradients at the boundaries of the growth bands.
Model calculations of ion transport against its concentration gradient when the driving force is a pH difference across a charged membrane
1997
Model calculations of the steady-state ion transport against its external concentration gradient when the driving force of this transport is a pH difference across a charged membrane are presented. We have solved numerically the exact Nernst-Planck equations without any additional simplifying approximation, such as the Goldman constant field assumption within the membrane. The validity of this assumption for a broad range of pH values, and salt and membrane fixed charge concentrations was analyzed critically. The membrane characteristics studied are the ionic fluxes and the membrane potential. Special attention is paid to the physical mechanism which leads to the ion transport against the c…
Electrical Pumping of Potassium Ions Against an External Concentration Gradient in a Biological Ion Channel
2013
We show experimentally and theoretically that significant currents can be obtained with a biological ion channel, the OmpF porin of Escherichia coli, using zero-average potentials as driving forces. The channel rectifying properties can be used to pump potassium ions against an external concentration gradient under asymmetric pH conditions. The results are discussed in terms of the ionic selectivity and rectification ratio of the channel. The physical concepts involved may be applied to separation processes with synthetic nanopores and to bioelectrical phenomena. (C) 2013 AIP Publishing LLC.
Asymmetric nanopore rectification for ion pumping, electrical power generation, and information processing applications
2011
Single-track, asymmetric nanopores can currently be functionalised with a spatially inhomogeneous distribution of fixed charges and a variety of pore tip shapes. Optimising the asymmetric nanopore characteristics is crucial for practical applications in nanofluidics. We have addressed here this question for three cases based on different input/output chemical and electrical signals: (i) ion pumping up a concentration gradient by means of a periodic, time-dependent bias potential, (ii) information processing with a single nanopore acting as the nanofluidic diode of a logic gate, and (iii) electrical energy harvesting using a nanopore that separates two solutions of different salt concentrati…
Experimental investigation and modeling of diffusion dialysis for HCl recovery from waste pickling solution
2019
Abstract Hydrochloric acid recovery from pickling solutions was studied by employing a batch diffusion dialysis (DD) laboratory test-rig equipped with Fumasep membranes. The effect of main operating parameters such as HCl concentration (0.1–3 M) and the presence of Fe2+ (up to 150 g/l) was investigated to simulate the system operation with real industrial streams. The variation of HCl, Fe2+ and water flux was identified. When only HCl is present, a recovery efficiency of 100% was reached. In the presence of FeCl2, higher acid recovery efficiencies, up to 150%, were observed due to the so-called “salt effect”, which promotes the passage of acid even against its concentration gradient. A 7% l…
Hunting active Brownian particles: Learning optimal behavior
2021
We numerically study active Brownian particles that can respond to environmental cues through a small set of actions (switching their motility and turning left or right with respect to some direction) which are motivated by recent experiments with colloidal self-propelled Janus particles. We employ reinforcement learning to find optimal mappings between the state of particles and these actions. Specifically, we first consider a predator-prey situation in which prey particles try to avoid a predator. Using as reward the squared distance from the predator, we discuss the merits of three state-action sets and show that turning away from the predator is the most successful strategy. We then rem…