Kalium rhodopsins: Natural light-gated potassium channels

We report a family of K+ channels, kalium channelrhodopsins (KCRs) from a fungus-like protist. Previously known potassium channels, widespread and mainly ligand- or voltage-gated, share a conserved pore-forming domain and K+-selectivity filter. KCRs differ in that they are light-gated and they have independently evolved an alternative K+ selectivity mechanism. The KCRs are potent, highly selective of K+ over Na+, and open in less than 1 millisecond following photoactivation. Their permeability ratio PK/PNa of ∼ 20 make KCRs powerful hyperpolarizing tools that suppress excitable cell firing upon illumination, demonstrated here in mouse cortical neurons. KCRs enable specific optogenetic photocontrol of K+ gradients promising for the study and potential treatment of potassium channelopathies such as epilepsy, Parkinson’s disease, and long-QT syndrome and other cardiac arrhythmias.One-Sentence SummaryPotassium-selective channelrhodopsins long-sought for optogenetic research and therapy of neurological and cardiac diseases.

A Unified Parameter to Represent Reservoir Heterogeneity

We aim to find a universal method and/or parameter to quantify impact of overall heterogeneity on waterflood performance. For this purpose, we combined the Lorenz coefficient, horizontal permeability to vertical permeability ratio, and thief zone permeability to average permeability ratio, with a radar chart. The area of the radar chart serves as a single parameter to rank reservoirs according to heterogeneity, and correlates to waterflood performance. The parameters investigated are vertical and horizontal permeability. Average porosity, initial water saturation, and initial diagonal pressure ratio are kept constant. Computer based experiments are used over the course of this entire research. We conducted permeability studies that demonstrate the effects of thief zones and crossflow. After normalizing these parameters into a number between 0 and 1, we then plot them on a radar chart. A reservoir's overall degree of heterogeneity can be inferred using the radar chart area procedure discussed in this study. In general, our simulations illustrate that the larger the radar chart area, the more heterogenous the reservoir is, which in turn yields higher water cut trends and lower recovery factors. Computer simulations done during this study also show that the higher the Lorenz coefficient, the higher the probability of a thief zone to exist. Simulations done to study crossflow also show certain trends with respect to under tonguing and radar chart area.

Modelling the Molecular Permeation through Mixed-Matrix Membranes Incorporating Tubular Fillers

Membrane-based processes are considered a promising separation method for many chemical and environmental applications such as pervaporation and gas separation. Numerous polymeric membranes have been used for these processes due to their good transport properties, ease of fabrication, and relatively low fabrication cost per unit membrane area. However, these types of membranes are suffering from the trade-off between permeability and selectivity. Mixed-matrix membranes, comprising a filler phase embedded into a polymer matrix, have emerged in an attempt to partly overcome some of the limitations of conventional polymer and inorganic membranes. Among them, membranes incorporating tubular fillers are new nanomaterials having the potential to transcend Robeson’s upper bound. Aligning nanotubes in the host polymer matrix in the permeation direction could lead to a significant improvement in membrane permeability. However, although much effort has been devoted to experimentally evaluating nanotube mixed-matrix membranes, their modelling is mostly based on early theories for mass transport in composite membranes. In this study, the effective permeability of mixed-matrix membranes with tubular fillers was estimated from the steady-state concentration profile within the membrane, calculated by solving the Fick diffusion equation numerically. Using this approach, the effects of various structural parameters, including the tubular filler volume fraction, orientation, length-to-diameter aspect ratio, and permeability ratio were assessed. Enhanced relative permeability was obtained with vertically aligned nanotubes. The relative permeability increased with the filler-polymer permeability ratio, filler volume fraction, and the length-to-diameter aspect ratio. For water-butanol separation, mixed-matrix membranes using polydimethylsiloxane with nanotubes did not lead to performance enhancement in terms of permeability and selectivity. The results were then compared with analytical prediction models such as the Maxwell, Hamilton-Crosser and Kang-Jones-Nair (KJN) models. Overall, this work presents a useful tool for understanding and designing mixed-matrix membranes with tubular fillers.

Analysis of formation damage and fracture choking in hydraulically induced fractured reservoirs due to asphaltene deposition

Hydraulically induced fractures provide a significant fraction of oil supply to the world from unconventional reservoirs due to their high permeability. However, these fractures might choke because of the deposition of organic and in-organic particles. Among organic particles, asphaltene deposition severely reduces reservoir permeability causing an exponential drop in production. In this work, a simulator is developed that predicts the performance of fractured reservoirs by solving the fluid flow governing equations for matrix and fractures. These flow equations were then incorporated with asphaltene deposition equations. Primarily, a numerical model is developed to predict the rate of asphaltene deposition and fracture choking in a radial geometry. It is found that asphaltene deposition could partially or completely choke fractures. Finally, the results are compared with the experimental data and determined various factors affecting fracture choking. From the detailed analysis, it is found that fracture choking is a few percent, but it increases with long production time. The sensitivity analysis was performed to investigate the effect of different influential parameters on permeability alteration of fractured reservoirs by asphaltene deposition. These parameters include fracture-to-matrix permeability ratio, production time, and asphaltene concentration. It is observed that, low fracture-to-matrix permeability ratio has a negligible effect on permeability of a reservoir. The developed model assumes negligible gravity and capillary forces. However, these forces might increase fracture choking in unconventional fractured reservoirs.

Filtration studies of polymer solution applied in flow deviation technologies in Kazakhstan fields

The paper deals with the results of laboratory experiments on filtration characteristics of cross-linked polymer systems (CPS) based on the “FP-307” PAA polymer solution and A grade crosslinker of acetate-chrome applied in flow deviation technologies. The studies on the estimation of CPS filtration characteristics have been carried out on the linear two-layer formation model with different interlayer permeability. Obtained results justified that the higher is formation homogeneity (permeability ratio of high permeability and low permeability interlayers), the more CPS enter into the high permeability interlayer. As a result of formation of flow deviation screen in high permeability interlayers, a regulation possibility of filtration flows direction and logging into the operation of low-permeable interlayers appears.

KINETIC AND STRUCTURAL CHARACTERISTICS OF ULTRAFILTRATIONAL MEMBRANES AT SEPARATION OF SOLUTIONS CONTAINING SODIUM LAURYLSULPHATE

In work the generalized analysis of literary data on a research of relative permeability ratio of various types of porous organic and inorganic membranes was submitted. Application of a method of X-ray analysis of samples of the semipermeable ultrafiltrational membranes on a diffractometer of DRON-3 and a specific output flow on a flat-chamber ultrafiltration unit is shown. In materials of work the pilot and theoretical studies on isokinetic zones and structural characteristics of polymeric semipermeable membranes in the course of ultrafiltrational separation of the technological solutions containing the anionic and fissile surface substances are conducted. It is experimentally confirmed that kinetic curves on a specific output flow have two isokinetic zones. The first zone, the stage of the ultrafiltration process, proceeds quickly, lasts only a few minutes - 7.8 min and 13.05 min, the second zone is slower with duration of about 30 min and 60 min for ultrafiltration cellulose acetate membranes of the UAM-100 and UAM-50 series, respectively. The revealed isokinetic zones differ in characteristic times, which differ by orders of magnitude, and, as a result, the final kinetic dependence has an exponential form. The comparative analysis of roentgenograms allows to note coincidence of angles of diffraction, but significant redistribution of intensity of reflexes in air-dried and working sapless in the range of scattering angles 2θ from 8°-35°. The obtained experimental data and their comparison with literary, indicate the same set of the diffraction reflexes at corners 2θ = 17°; 22°; 25° for both samples of membranes that corresponds to the crystal reflexes of membranes created from polyamide fibers (nylon).

Study on Distribution Characteristics and Displacement Mechanism of Microscopic Residual Oil in Heterogeneous Low Permeability Reservoirs

In order to explore the development methods suitable for heterogeneous low permeability reservoirs and study the distribution characteristics of residual oil, photoetched glass and artificial core models with three permeability ratios of 1, 6, and 9 were prepared in this research. Three displacement schemes including polymeric surfactant flooding, polymeric surfactant with binary flooding, and binary flooding were designed at the same expenses to obtain the displacement mechanism of various residual oil saturations. The results show that the best displacement efficiency can be achieved by polymeric surfactant flooding, followed by polymeric surfactant with binary flooding, and binary flooding for the models with the same permeability ratio. Binary flooding mainly activates cluster and oil drop residual oils, polymeric surfactant with binary flooding mainly activates cluster, oil film, and column residual oils, whereas polymeric surfactant flooding mainly activates cluster, oil drop, and column residual oils. In addition, with the increase of the model permeability ratio, the recovery ratio of water flooding decreases, whereas the enhanced oil recovery and the variations in residual oil saturation gradually increase after carrying out different displacement measures. The viscoelastic and shearing effects of the polymeric surfactant flooding system can better displace the residual oil, assisting in the further development of heterogeneous low permeability reservoirs.

Dynamic change of electrostatic field in TMEM16F permeation pathway shifts its ion selectivity

TMEM16F is activated by elevated intracellular Ca2+, and functions as a small-conductance ion channel and as a phospholipid scramblase. In contrast to its paralogs, the TMEM16A/B calcium-activated chloride channels, mouse TMEM16F has been reported as a cation-, anion-, or non-selective ion channel, without a definite conclusion. Starting with the Q559K mutant that shows no current rundown and less outward rectification in excised patch, we found that the channel shifted its ion selectivity in response to the change of intracellular Ca2+ concentration, with an increased permeability ratio of Cl- to Na+ (PCl-/PNa+) at a higher Ca2+ level. The gradual shift of relative ion permeability did not correlate with the channel activation state. Instead, it was indicative of an alteration of electrostatic field in the permeation pathway. The dynamic change of ion selectivity suggests a charge-screening mechanism for TMEM16F ion conduction, and it provides hints to further studies of TMEM16F physiological functions.