Tunable Flux Research Articles

Development of PVDF Membrane Nanocomposites via Various Functionalization Approaches for Environmental Applications.

Membranes are finding wide applications in various fields spanning biological, water, and energy areas. Synthesis of membranes to provide tunable flux, metal sorption, and catalysis has been done through pore functionalization of microfiltration (MF) type membranes with responsive behavior. This methodology provides an opportunity to improve synthetic membrane performance via polymer fabrication and surface modification. By optimizing the polymer coagulation conditions in phase inversion fabrication, spongy polyvinylidene fluoride (PVDF) membranes with high porosity and large internal pore volume were created in lab and full scale. This robust membrane shows a promising mechanical strength as well as high capacity for loading of adsorptive and catalytic materials. By applying surface modification techniques, synthetic membranes with different functionality (carboxyl, amine, and nanoparticle-based) were obtained. These functionalities provide an opportunity to fine-tune the membrane surface properties such as charge and reactivity. The incorporation of stimuli-responsive acrylic polymers (polyacrylic acid or sodium polyacrylate) in membrane pores also results in tunable pore size and ion-exchange capacity. This provides the added benefits of adjustable membrane permeability and metal capture efficiency. The equilibrium and dynamic binding capacity of these functionalized spongy membranes were studied via calcium ion-exchange. Iron/palladium catalytic nanoparticles were immobilized in the polymer matrix in order to perform the challenging degradation of the environmental pollutant trichloroethylene (TCE).

Conformational changes during permeation of Na+ through a modified cyclic peptide nanotube promote energy landscape roughness.

Using a metadynamics approach, we investigate the potential of mean force for Na+ permeation inside a cyclic peptide nanotube (CPN) with modified interior as a function of ion position, coordination number, and lumen chemistry. We show that functionalizing the lumen of a CPN with a methyl-benzoic acid group introduces non-periodic variations in the internal energy of the nanotube, which dictate the overall free energy roughness during the permeation of Na+. These non-periodic variations arise from the structural dynamics of the functional group, where changes in the dihedral angles induced by the proximity of the ion give rise to conformational changes that increase landscape roughness and thereby decrease transport rate. Our computational framework emphasizes the advantages of using the coordination number as a collective variable to investigate the available conformations during ion permeation through CPNs, and reveals new structure-function relations for chemically tunable CPNs, paving the way for rational design of nano-porous systems with tunable selectivity and flux.

A Non-Rare-Earth Doubly Salient Flux Controllable Motor Capable of Fault-Tolerant Control

Facing the price fluctuation and unstable supply of rare-earth material, motors that do not employ rare-earth permanent magnets (PMs) have been gaining research popularity recently. This paper proposes a non-rare-earth doubly salient flux controllable (DSFC) motor that incorporates the flux tunable characteristics of AlNiCo PMs and the hybrid excitation function of dc windings, realizing the goal of high power density and wide speed range simultaneously. Furthermore, the AlNiCo PMs can be fully demagnetized in the fault condition, and the DSFC motor will operate as a switched reluctance motor, which provides a high fault-tolerant capability. The simulation results illustrate that the output torque of DSFC motor with hybrid excitation is able to match that of a rare-earth doubly salient PM motor, while the speed range of the former is superior to the latter because of the tunable flux. In addition, the simulation and experimental results of flux control and fault-tolerant operation verify the flux weakening and fault-tolerant capability of the DSFC motor.

Circuit analog of quadratic optomechanics

We propose a superconducting electrical circuit that simulates a quadratic optomechanical system. A capacitor placed between two transmission-line (TL) resonators acts like a semi-transparent membrane, and a superconducting quantum interference device (SQUID) that terminates a TL resonator behaves like a movable mirror. Combining these circuit elements, it is possible to simulate a quadratic optomechanical coupling whose coupling strength is determined by the coupling capacitance and the tunable bias flux through the SQUIDs. Estimates using realistic parameters suggest that an improvement in the coupling strength could be realized, to five orders of magnitude from what has been observed in membrane-in-the-middle cavity optomechanical systems. This leads to the possibility of achieving the strong-coupling regime of quadratic optomechanics.

Absence of the Aharonov-Bohm effect of chiral Majorana fermion edge states

Majorana fermions in a superconductor hybrid system are charge neutral zero-energy states. For the detection of this unique feature, we propose an interferometry of a chiral Majorana edge channel, formed along the interface between a superconductor and a topological insulator under an external magnetic field. The superconductor is of a ring shape and has a Josephson junction that allows the Majorana state to enclose continuously tunable magnetic flux. Zero-bias differential electron conductance between the Majorana state and a normal lead is found to be independent of the flux at zero temperature, manifesting the Majorana feature of a charge neutral zero-energy state. In contrast, the same setup on graphene has no Majorana state and shows Aharonov-Bohm effects.

Charge-Related SQUID and Tunable Phase-Slip Flux Qubit

A phase-slip flux qubit, exactly dual to a charge qubit, is composed of a superconducting loop interrupted by a phase-slip junction. We propose a tunable phase-slip flux qubit by replacing the phase-slip junction with a charge-related superconducting quantum interference device (SQUID) consisting of two phase-slip junctions connected in series with a superconducting island. This charge-SQUID acts as an effective phase-slip junction controlled by the applied gate voltage and can be used to tune the energy-level splitting of the qubit. In addition, we show that a large inductance inserted in the loop can reduce the inductance energy and consequently suppress the dominating flux noise of the phase-slip flux qubit. This enhanced phase-slip flux qubit is exactly dual to a transmon qubit.

Arrays of microplasmas for the controlled production of tunable high fluxes of reactive oxygen species at atmospheric pressure

The atmospheric-pressure generation of singlet delta oxygen (O2(a 1Δg)) by microplasmas was experimentally studied. The remarkable stability of microcathode sustained discharges (MCSDs) allowed the operation of dc glow discharges, free from the glow-to-arc transition, in He/O2/NO mixtures at atmospheric pressure. From optical diagnostics measurements we deduced the yield of O2(a 1Δg). By operating arrays of several MCSDs in series, O2(a 1Δg) densities higher than 1.0 × 1017 cm−3 were efficiently produced and transported over distances longer than 50 cm, corresponding to O2(a 1Δg) partial pressures and production yields greater than 5 mbar and 6%, respectively. At such high O2(a 1Δg) densities, the fluorescence of the so-called O2(a 1Δg) dimol was observed as a red glow at 634 nm up to 1 m downstream. Parallel operation of arrays of MCSDs was also implemented, generating O2(a 1Δg) fluxes as high as 100 mmol h−1. In addition, ozone (O3) densities up to 1016 cm−3 were obtained. Finally, the density ratio of O2(a 1Δg) to O3 was finely and easily tuned in the range [10−3–10+5], through the values of the discharge current and NO concentration. This opens up opportunities for a large spectrum of new applications, making this plasma source notably very useful for biomedicine.

Novel device for continuous spatial control and temporal delivery of nitric oxide for in vitro cell culture

Nitric oxide (NO) is an ubiquitous signaling molecule of intense interest in many physiological processes. Nitric oxide is a highly reactive free radical gas that is difficult to deliver with precise control over the level and timing that cells actually experience. We describe and characterize a device that allows tunable fluxes and patterns of NO to be generated across the surface upon which cells are cultured. The system is based on a quartz microscope slide that allows for controlled light levels to be applied to a previously described photosensitive NO-releasing polydimethylsiloxane (PDMS). Cells are cultured in separate wells that are either NO-releasing or a chemically similar PDMS that does not release NO. Both wells are then top coated with DowCorning RTV-3140 PDMS and a polydopamine/gelatin layer to allow cells to grow in the culture wells. When the waveguide is illuminated, the surface of the quartz slide propagates light such that the photosensitive polymer is evenly irradiated and generates NO across the surface of the cell culture well and no light penetrates into the volume of the wells where cells are growing. Mouse smooth muscle cells (MOVAS) were grown in the system in a proof of principle experiment, whereby 60% of the cells were present in the NO-releasing well compared to control wells after 17h. The compelling advantage of illuminating the NO-releasing polymers with the waveguide system is that light can be used to tunably control NO release while avoiding exposing cells to optical radiation. This device provides means to quantitatively control the surface flux, timing and duration of NO cells experience and allows for systematic study of cellular response to NO generated at the cell/surface interface in a wide variety of studies.

The hydrodynamic permeability and surface property of polyethersulfone ultrafiltration membranes with mussel-inspired polydopamine coatings

Abstract In this paper, the characters of hydrodynamic permeability, surface property, and blood compatibility of polydopamine (PDA) coated polyethersulfone (PES) ultrafiltration (UF) membranes were investigated in detail. We presented a general protocol to improve the hydrodynamic permeability and blood compatibility of PES UF membranes by a simple biomimetic strategy. The chemical structure and surface morphology of the PDA coated membranes were studied in detail; meanwhile, the influence of the coated PDA nano-layer on water contact angle and water flux of the modified membranes was investigated. It was found that the water flux of the pure PES membrane decreased dramatically, approach to 0 ml/(m2 h mmHg), after a few hours of PDA coating. To avoid the dramatic decline of water flux, the method of pre-adding pore-forming reagent was taken to fabricate the PDA coated PES membranes with tunable water flux. Moreover, the anti-fouling property, platelet adhesion, and blood coagulation time of the PDA modified PES membranes were studied, and the results indicated that the PDA modified PES UF membranes showed enhanced blood compatibility.

Tunable Gauge Potential for Neutral and Spinless Particles in Driven Optical Lattices

We present a universal method to create a tunable, artificial vector gauge potential for neutral particles trapped in an optical lattice. The necessary Peierls phase of the hopping parameters between neighboring lattice sites is generated by applying a suitable periodic inertial force such that the method does not rely on any internal structure of the particles. We experimentally demonstrate the realization of such artificial potentials, which generate ground-state superfluids at arbitrary nonzero quasimomentum. We furthermore investigate possible implementations of this scheme to create tunable magnetic fluxes, going towards model systems for strong-field physics.

Tuned Transition from Quantum to Classical for Macroscopic Quantum States

The boundary between the classical and quantum worlds has been intensely studied. It remains fascinating to explore how far the quantum concept can reach with use of specially fabricated elements. Here we employ a tunable flux qubit with basis states having persistent currents of 1 μA carried by a million pairs of electrons. By tuning the tunnel barrier between these states we see a crossover from quantum to classical. Released from nonequilibrium, the system exhibits spontaneous coherent oscillations. For high barriers the lifetime of the states increases dramatically while the tunneling period approaches the phase coherence time and the oscillations fade away.

Tunable magnetic flux sensor using a metallic Rashba ring with half-metal electrodes

We propose a magnetic field sensor consisting of a square ring made of metal with a strong Rashba spin–orbital coupling (RSOC) and contacted to half-metal electrodes. Due to the Aharonov–Casher effect, the presence of the RSOC imparts a spin-dependent geometric phase to conduction electrons in the ring. The combination of the magnetic flux emanating from the magnetic sample placed below the ring, and the Aharonov–Casher effect due to RSOC results in spin interference, which modulates the spin transport in the ring nanostructure. By using the tight-binding nonequilibrium Green’s function formalism to model the transport across the nanoring detector, we theoretically show that with proper optimization, the Rashba ring can function as a sensitive and tunable magnetic probe to detect magnetic flux.

Coherent oscillations in a superconducting tunable flux qubit manipulated without microwaves

We experimentally demonstrate coherent oscillations of a tunable superconducting flux qubit by manipulating its energy potential with a nanosecond-long pulse of magnetic flux. The occupation probabilities of two persistent current states oscillate at a frequency ranging from 6 GHz to 21 GHz, tunable by changing the amplitude of the flux pulse. The demonstrated operation mode could allow quantum gates to be realized in less than 100 ps, which is much shorter than gate times attainable in other superconducting qubits. Another advantage of this type of qubit is its immunity to both thermal and magnetic field fluctuations.

A Novel Rotating Magnetic Field Generator for Driving Magnetic Micro-Machine

In order to make magnetic micro-machine swim more flexibly, we designed a rotating magnetic field generator with tunable angular frequency and magnetic flux density in arbitrary spatial plane by computation and simulation. A device which consists of power supply and three pairs of Helmholtz coils which are pair-wise orthogonal would be applied. Triphase sinusoidal currents were chosen to obtain a rotating magnetic field with an arbitrary rotation axis. The magnetic flux density, angular frequency and rotation axis can be modulated by tuning the amplitude and frequency of each phase current. The device can achieve a rotating magnetic field with arbitrary rotation axis to drive magnetic micro-machine. And through driving experiments, the generator can rotate magnetic micro-machine and move.

Functionalized membranes and environmental applications

The development of separation processes with reduced energy consumption and minimal environmental impact is critical for sustainable operation. Membrane processes provide a highly flexible separation technique for selective solute separation/concentration, and permeate recycling and reuse (Bhattacharyya et al. 2003; Ho et al. 1992; Bhattacharyya and Shah 2005). The special features for membrane processes that make them attractive for industrial applications are their compactness, ease of fabrication, operation, and modular design (Meyer et al. 2006). Although membrane processes such as, Reverse Osmosis, Nanofiltration, Ultrafiltration, and Microfiltration have provided many successful applications ranging from highquality water production to material recovery, but incorporation of biological aspects in membranes should add immense value in the area of separations and material capture. The questions are, Can we make membranes which can capture toxic metals at high capacity? Can we add functional moiety in pores which can go through conformation changes and results in tunable separations? Can we make layer-by-assembly in pores to immobilize proteins and enzymes? Can we synthesize nanosized metals in membranes to detoxify toxic organics at room temperature? The answers to all of these are yes if we can integrate life science field with synthetic membranes to make tunable and functionalized materials. Membranes functionalized with appropriate macromolecules (Decher 1997; Hollman and Bhattacharyya 2002, 2004; Ritchie et al. 1999; Ito et al. 2000; Smuleac et al. 2005) can indeed provide applications ranging from tunable flux and separations, toxic metal capture, to nanoparticle synthesis for toxic organic dechlorination. If the selected macromolecule is a biomolecule, such as, polypeptide (for e.g., poly-glutamic or poly-aspartic acid) then in addition to creating a highly charged field in the membrane pores, conformational changes (such as, helix-coil) can be utilized to conduct tunable nanofiltration type separations or metal capture at high capacity with macroporous membranes at low pressures. The metal sorption results indicated not only high capacity but also rapid uptake rate. Metal sorption with polypeptide functionalized membranes is extremely high (>1 g metal/g for Pb) compared with conventional ion exchange (50–100 mg/g). Helix-coil formation ability of the attached polypeptides can also be used for selective metal regeneration. We have extended the approach to create pore-assembled charged multilayers for nanofiltration-type separations. In addition, one can fabricate charged multilayer assemblies inside of the membrane pores for subsequent incorporation of enzymes for biocatalysis. Traditionally, microfiltration (MF) membrane separations have been performed on the basis of size exclusion and are typically used for filtration of suspended solids, bacteria, viruses, etc. However, microfiltration membranes (e.g., cellulosics, silica, polysulfone, polycarbonate) can be functionalized with a variety of reagents. Depending on the types of functionalized groups (such as, chain length, charge of groups, biomolecule, etc.) and number of layers, these microfiltration membranes could be used in applications ranging from metal (or oxyanions) separation to biocatalysis. The conformation properties dependence on pH and provide tunable separation properties (Hollman and D. Bhattacharyya (&) Department of Chemical and Materials Engineering, University of Kentucky, Lexington, KY 40506, USA e-mail: db@engr.uky.edu

Double SQUID tunable flux qubit manipulated by fast pulses: operation requirements, dissipation and decoherence

A double SQUID manipulated by fast magnetic flux pulses can be used as a tunable flux qubit. In this paper we study the requirements for the qubit operation, and evaluate dissipation and decoherence due to the manipulation for a typical system. Furthermore, we discuss the possibility to use an integrated Rapid Single Flux Quantum logic for the qubit control.

Rf SQUID system as tunable flux qubit

We present a fully integrated rf SQUID-based system as flux qubit with a high control of the flux transfer function of the superconducting transformer modulating the coupling between the flux qubit and the readout system. The control of the system is possible by including into the superconducting flux transformer a vertical two-Josephson-junctions interferometer (VJI) in which the Josephson current is precisely modulated from a maximum to zero by a transversal magnetic field parallel to the flux transformer plane. The proposed system can be also used in a more general configuration to control the off-diagonal terms in the Hamiltonian of the flux qubit and to turn on and off the coupling between two or more qubits.

Experimental Demonstration of an Oscillator Stabilized Josephson Flux Qubit

We experimentally demonstrate the use of a superconducting transmission line, shorted at both ends, to stabilize the operation of a tunable flux qubit. Using harmonic-oscillator stabilization and pulsed dc operation, we have observed Larmor oscillations with a single shot visibility of 90%. In another qubit, the visibility was 60% and there was no measurable visibility reduction after 35 ns.

Superconducting tunable flux qubit with direct readout scheme

We describe a simple and efficient scheme for the readout of a tunable flux qubit, andpresent preliminary experimental tests for the preparation, manipulation and final readoutof the qubit state, performed in the incoherent regime at liquid helium temperature. Thetunable flux qubit is realized by a double SQUID with an extra Josephson junction insertedin the large superconducting loop, and the readout is performed by applying a currentramp to the junction and recording the value for which there is a voltage response,depending on the qubit state. This preliminary work indicates the feasibility and efficiencyof the scheme.

Rotating Permanent Magnetic Fields Exposure System for In Vitro Study

For the bioeffect study of the rotating magnetic fields, a permanent magnet of two layer magic rings driven by a motor was designed to produce a rotating magnetic field with tunable frequency (0-10 Hz) and tunable magnetic flux density (4-300 mT). In the design a simple 3D computing method was adopted to do the optimization. The actual results proved the efficiency of the method. The finished magnet fully satisfied the requirements of the bioelectromagnetic study.