Cation and anion transport through hydrophilic pores in lipid bilayers

To understand the origin of transmembrane potentials, formation of transient pores, and the movement of anions and cations across lipid membranes, we have performed systematic atomistic molecular dynamics simulations of palmitoyl-oleoyl-phosphatidylcholine (POPC) lipids. A double bilayer setup was employed and different transmembrane potentials were generated by varying the anion (Cl−)(Cl−) and cation (Na+)(Na+) concentrations in the two water compartments. A transmembrane potential of ∼ 350 mV∼350mV was thereby generated per bilayer for a unit charge imbalance. For transmembrane potential differences of up to ∼ 1.4 V∼1.4V, the bilayers were stable, over the time scale of the simulations (10–50 ns)(10–50ns). At larger imposed potential differences, one of the two bilayers breaks down through formation of a water pore, leading to both anion and cation translocations through the pore. The anions typically have a short residence time inside the pore, while the cations show a wider range of residence times depending on whether they bind to a lipid molecule or not. Over the time scale of the simulations, we do not observe the discharge of the entire potential difference, nor do we observe pore closing, although we observe that the size of the pore decreases as more ions translocate. We also observed a rare lipid flip-flop, in which a lipid molecule translocated from one bilayer leaflet to the opposite leaflet, assisted by the water pore.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87872/2/074901_1.pd

Implementation of Fault-tolerant Quantum Logic Gates via Optimal Control

The implementation of fault-tolerant quantum gates on encoded logic qubits is considered. It is shown that transversal implementation of logic gates based on simple geometric control ideas is problematic for realistic physical systems suffering from imperfections such as qubit inhomogeneity or uncontrollable interactions between qubits. However, this problem can be overcome by formulating the task as an optimal control problem and designing efficient algorithms to solve it. In particular, we can find solutions that implement all of the elementary logic gates in a fixed amount of time with limited control resources for the five-qubit stabilizer code. Most importantly, logic gates that are extremely difficult to implement using conventional techniques even for ideal systems, such as the T-gate for the five-qubit stabilizer code, do not appear to pose a problem for optimal control.Comment: 18 pages, ioptex, many figure

Modelling of a thin film thermoelectric micro-Peltier module

A micro Peltier cooler/heater module has been modelled. The module consists of n-type bismuth telluride and p-type antimony telluride thermoelectric materials. The commercial software package CFD-ACE+ has been used to implement and analyse the model. A two-dimensional coupled electrical and thermal simulation was performed. This software includes the possibility to incorporate the Peltier effect. The temperature, electric field intensity and wall heat flux distributions were simulated for different applied potentials. The variation in temperature difference with respect to the Seebeck coefficient of the material was calculated and analysed

Rubidium recovery using potassium cobalt hexacyanoferrate sorbent

© 2016 Balaban Desalination Publications. All rights reserved. Rubidium (Rb) is a highly valued and economically important metal present in large quantities in many natural and wastewaters. However, its recovery is hampered by its low concentration and extracting agents’ limited selectivity. A batch sorption study showed that a potassium cobalt hexacyanoferrate (KCoFC) sorbent had much higher sorption capacities for Rb and caesium (Cs) than for lithium (Li), sodium (Na) and calcium (Ca). Equilibrium sorption data at pH 7 and 24 ± 1°C for Rb and Cs satisfactorily fitted to the Langmuir model with sorption maxima of 96 and 61 mg/g, respectively. A fixed-bed column (12 cm height) containing a mixture of 2.2 g KCoFC and 19.8 g granular activated carbon had a breakthrough sorption capacity of 61 mg/g when a solution containing 5 mg Rb/L was passed through the column at a velocity of 2.5 m/h (0.7 L/h). When 1 and 5 mg Cs/L were added to the Rb solution, Rb sorption capacity dropped to 46 and 41 mg/g, respectively. During Rb sorption, K from the KCoFC lattice was released. Leaching the column containing sorbed Rb with 0.1 M KCl for 60 min at a velocity of 10 m/h desorbed 99% of sorbed Rb. A process for recovering Rb from sea water reverse osmosis brine is presented

Morphological adaptation in an energy efficient vibration-based robot

Morphological computation is a concept relevant to robots made of soft and elastic materials. It states that robot's rich dynamics can be exploited to generate desirable behaviors, which can be altered when their morphology is adapted accordingly. This paper presents a low-cost robot made of elastic curved beam driven by a motor, with morphological computation and adaptation ability. Simply by changing robot's shape and the rotating frequency of the motor that vibrates the robot's body, the robot is able to shift its behavior from showing a tendency to slide when it needs to perform tasks like going under confined space, to have more tendency to hop diagonally forward when the robot stands upright. It will also be shown that based on the proposed mechanism, the energy efficiency of the robot locomotion can be maximized

Stark tuning of the charge states of a two-donor molecule in silicon

Gate control of phosphorus donor based charge qubits in Si is investigated using a tight-binding approach. Excited molecular states of P2+ are found to impose limits on the allowed donor separations and operating gate voltages. The effects of surface (S) and barrier (B) gates are analyzed in various voltage regimes with respect to the quantum confined states of the whole device. Effects such as interface ionization, saturation of the tunnel coupling, sensitivity to donor and gate placement are also studied. It is found that realistic gate control is smooth for any donor separation, although at certain donor orientations the S and B gates may get switched in functionality. This paper outlines and analyzes the various issues that are of importance in practical control of such donor molecular systems.Comment: 8 pages, 9 figure

Determination of Cr, Pb and Ni in water, sludge and plants from settling ponds of a sewage treatment works

Wastewater from a sewage treatment works is channelled through a series of inter-connected settling ponds into a stream. Furthermore, leachates from a domestic and industrial landfill site are disposed into the first pond. From the variety of plants growing in the ponds, A. sessilis, P. stratiotes, R. steudelii and T. capensis were investigated for their ability to uptake chromium, lead and nickel (these metals are toxic to humans while nickel is also involved in plant growth). The levels of the metals in the water, plants and sludge were determined using an inductively coupled plasma-mass spectrometer (ICP-MS). For the plants, the amounts of the metals in roots, stems and leaves were also measured. In general it was found that the plants accumulated up to 15% of the level of metals in the water and that accumulation depends on the plant species as well as on the organ of the plant. The concentrations of metals in the water in the last pond were found to be well within the limits set by the South African National Water Act of 1998 for discharge of water into rivers. Furthermore, the results of this study, which involved a real system, were compared with those from model studies where conditions of the system could be controlled by the investigator.Keywords: uptake, heavy metals, plants, wastewater treatmen

Fractures of metacarpal bone: evaluation of functional outcome of open reduction and internal fixation with mini locking plate: a hospital based study

Background: Metacarpal bones fracture is very common. Management of metacarpal fractures varies from conservative to percutaneous pinning to various surgical methods. We endeavour to evaluate the functional outcome of metacarpal fractures in patients managed with open reduction and internal fixation with mini locking plate.Methods: A total of 32 patients with extra-articular metacarpal bones fracture were recruited for the study. After open reduction the fractures were fixed with the mini locking plate, postoperative day 3, plaster removed and active and passive exercises started. The Michigan hand score was used for functional evaluation, grip strength, visual analogue scale score, range of motion evaluated at follow up till six months.Results: All the 32 patients achieved union, 31 had full union at 6 weeks whereas 1 patient has delayed union. The Michigan hand outcome questionnaire score of 97.5 % at 6 months in all 32 patients. A total of 5 out of 32 patients had complications, the most common being finger stiffness followed by superficial infection and delayed union.Conclusions: We concluded that metacarpal plating with mini locking plate is a good option to achieve and maintain a rigid fixation and this method produces a better outcome in unstable fractures of metacarpal bones