Transition Of Coil Research Articles

Flexibility, size and hydrophobicity of alkyl side groups in methoxy-poly (ethylene glycol)-polypeptide for the nano-assembly and thermo-sensitivity

Tailoring of amino acid residues is a feasible strategy to design the structure of peptide for special application. We selected poly(ethylene glycol) and α-amino acids with hydrophobic alkyl side group (L-alanine，L-valine and L-leucine) to synthesize di-block co-polypeptide. The copolymers with methyl side group self-assembled into random coil in majority and aggregated further into stable spherical nanoarchitectures with a little filament owing to the small size, less flexibility and less hydrophobicity of methyl group. By lengthening peptide block, the copolymer self-organized into overwhelming β-sheet and ordered nanorods or nanofibers due to the strengthening hydrophobicity as the copolymers with isopropyl side group did. The copolymers with isobutyl side groups showed cloudy solutions and irregular morphology because the flexibility and large size of isobutyl groups hampered the regular stacking of β-plated sheets and agglomerated into micro-sized precipitates despite of the most hydrophobicity. As temperature rising, both the transition of random coil to β-sheet and PEG dehydration contributed to the sol-gel transition for the copolymers with methyl side group, while PEG dehydration was the primary reason of sol-gel transition for the copolymers with isopropyl side group. In this article, we first disclosed the self-organization process of mPEG-b-polypeptide, which would lay the foundation for the designing of polypeptide-related materials with well-defined properties.

Use of Specific Properties of Poly-N-vinylcaprolactam in Immunochemical Reactions

Principal possibility of using a smart polymer, poly-N-vinylcaprolactam, for immobilization of biopharmaceuticals (antibodies and antigens) in the course of phase transition of a soluble coil into an insoluble globule was demonstrated. A procedure for preparing a hydrosol stable at room temperature in the presence of a stabilizer was examined. The hydrosol obtained, in which the collapsed polymer with the captured antigen acts as a solid support, can be used for agglutination with a complementary antibody, i.e., the immunochemical reaction can be evaluated visually.

REBCO コイルにおける熱暴走のメカニズムと対策

REBCO conductors were commercialized only recently in 2009 and therefore the magnet technology for REBCO conductors remains undeveloped. The major technological problems for REBCO coils encountered thus far are (a) degradation in the superconducting performance for mechanical reasons, (b) difficulty in protecting the magnet in the case of a super-normal transition of the REBCO coil and (c) the enormous effect of a screening-current-induced magnetic field. In this paper, the basic mechanism of premature thermal runaway in the REBCO superconductor is investigated through experiments and numerical simulations on small model coils. Effective remedies for suppressing the premature thermal runaway are discussed.

REBCO コイルにおける遮蔽電流磁場のメカニズムと抑制方法

REBCO conductors were commercialized only recently in 2009 and therefore the magnet technology for REBCO conductors remains undeveloped. The major technological problems for REBCO coils encountered thus far are (a) degradation in the superconducting performance for mechanical reasons, (b) difficulty in protecting the magnet in the case of a super-normal transition of the REBCO coil and (c) the enormous effect of a screening-current-induced magnetic field. In this paper, the basic mechanism of the screening-current-induced magnetic field and effective remedies for suppressing the screening field is investigated through experiments and numerical simulations.

Current Limiting and Recovery Characteristics Under Load of Transformer Type SFCL with Rewound Structure Using BSCCO Wire in Model Power System

Abstract We have proposed new design of a transformer type SFCL with primary and secondary superconducting coils which has rewound structure. For not so large fault current, the proposed SFCL limits the current by the inductive component by the normal transition of the flux shielding coil (secondary), and for larger fault current, it can give the resistive component additively by the normal transition of the primary coil. The recovery characteristics under load condition and repetitive limiting operation were experimentally investigated in a laboratory scale power system. The SFCL limited twice repetitive faults current and recovered quickly under load condition.

Electrospun Silk Fibroin Mats for Tissue Engineering

AbstractProcessing Silk Fibroin (SF) with electrospinning (ES) offers a very attractive opportunity for producing a variety of 2D and 3D matrices with great potential for tissue regeneration and repair due to the superior biocompatibility and mechanical properties of SF. Different combinations of ES parameters were explored to investigate the best experimental set‐up related to the dimension and uniformity of the fibers in the electrospun silk fibroin (ES‐SF) mats. Using SEM it was found that the ES‐SF mats contain uniform fibers with a diameter in the nanometric range obtained by electrospinning a 7.5 % w/v SF solution in formic acid, with an electric field of 2.4 kV/cm and a spinneret‐collector distance of 10 cm. FT‐IR and DSC analyses were performed to investigate the structure of the ES‐SF mats before and after immersion in methanol for different times (5, 10, and 15 min). The methanol treatment was able to promote the crystallization of SF by conformational transition of random coil and other poorly ordered conformations (turns and bends) to the β‐sheet structure. The degree of crystallinity was enhanced as shown by the trend of both the FT‐IR crystallinity index and the melting/decomposition peak temperature (from DSC). To study the cytocompatibility of ES‐SF mats, tests with L929 murine fibroblasts were carried out. Samples were seeded with the cells and incubated for 1, 3, and 7 days at 37 °C. At each time point, SEM investigations and Alamar blue tests were performed. The SEM images showed cell adhesion and proliferation just after 1 day and cell confluence at 7 days. Alamar blue test demonstrated that there were very low differences between cell viability on ES‐SF mats and the tissue culture plastic control.

Non-Inductive Variable Reactor Design and Computer Simulation of Rectifier Type Superconducting Fault Current Limiter

A rectifier type superconducting fault current limiter with noninductive reactor has been proposed by the authors. The concept behind this SFCL is that the high impedance generated during superconducting to normal state of the trigger coil limits the fault current. In the hybrid bridge circuit of the SFCL, two superconducting coils: a trigger coil and a limiting coil are connected in anti-parallel. Both the coils are magnetically coupled with each other and could have the same value of self inductance so that they can share the line current equally. At fault time when the trigger coil current reaches a certain level, the trigger coil changes from superconducting state to normal state. This super to normal transition of the trigger coil changes the current ratio of the coils and therefore the flux inside the reactor is no longer zero. So, the equivalent impedance of both the coils is increased and limits the fault current. We have carried out computer simulation using PSCAD/EMTDC and observed the results. Both the simulation and preliminary experiment shows good results. The advantage of using hybrid bridge circuit is that the SFCL can also be used as circuit breaker.

α-Helix Formation Is Required for High Affinity Binding of Human Apolipoprotein A-I to Lipids

Apolipoprotein (apo) A-I is thought to undergo a conformational change during lipid association that results in the transition of random coil to alpha-helix. Using a series of deletion mutants lacking different regions along the molecule, we examined the contribution of alpha-helix formation in apoA-I to the binding to egg phosphatidylcholine (PC) small unilamellar vesicles (SUV). Binding isotherms determined by gel filtration showed that apoA-I binds to SUV with high affinity and deletions in the C-terminal region markedly decrease the affinity. Circular dichroism measurements demonstrated that binding to SUV led to an increase in alpha-helix content, but the helix content was somewhat less than in reconstituted discoidal PC.apoA-I complexes for all apoA-I variants, suggesting that the helical structure of apoA-I on SUV is different from that in discs. Isothermal titration calorimetry showed that the binding of apoA-I to SUV is accompanied by a large exothermic heat and deletions in the C-terminal regions greatly decrease the heat. Analysis of the rate of release of heat on binding, as well as the kinetics of quenching of tryptophan fluorescence by brominated PC, indicated that the opening of the N-terminal helix bundle is a rate-limiting step in apoA-I binding to the SUV surface. Significantly, the correlation of thermodynamic parameters of binding with the increase in the number of helical residues revealed that the contribution of alpha-helix formation upon lipid binding to the enthalpy and the free energy of the binding of apoA-I is -1.1 and -0.04 kcal/mol per residue, respectively. These results indicate that alpha-helix formation, especially in the C-terminal regions, provides the energetic source for high affinity binding of apoA-I to lipids.

Proposal of rectifier type superconducting fault current limiter with non-inductive reactor (SFCL)

A rectifier type superconducting fault current limiter (SFCL) with non-inductive reactor has been proposed. The concept behind this SFCL is the appearance of high impedance during non-superconducting state of the coil. In a hybrid bridge circuit, two superconducting coils connected in anti-parallel: a trigger coil and a limiting coil. Both the coils are magnetically coupled with each other and have same number of turns. There is almost zero flux inside the core and therefore the total inductance is small during normal operation. At fault time when the trigger coil current reaches to a certain level, the trigger coil changes from superconducting state to normal state. This super-to-normal transition of the trigger coil changes the current ratio of the coils and therefore the flux inside the reactor is no longer zero. So, the equivalent impedance of both the coils increased thus limits the fault current. We have carried out computer simulation using EMTDC and observed the results. A preliminary experiment has already been performed using copper wired reactor with simulated super-to-normal transition resistance and magnetic switches. Both the simulation and preliminary experiment shows good results. The advantage of using hybrid bridge circuit is that the SFCL can also be used as circuit breaker. Two separate bridge circuit can be used for both trigger coil and the limiter coil. In such a case, the trigger coil can be shutdown immediately after the fault to reduce heat and thus reduce the recovery time. Again, at the end of fault when the SFCL needs to re-enter to the grid, turning off the trigger circuit in the two-bridge configuration the inrush current can be reduced. This is because the current only flows through the limiting coil. Another advantage of this type of SFCL is that no voltage sag will appear during load increasing time as long as the load current stays below the trigger current level.

Nematic ordering problem as the polymer problem of the excluded volume

AbstractBased on a solution of the polymer excluded volume problem, a technique is proposed to estimate some parameters at the isotropic-nematic liquid crystal phase transition (the product of the volume fraction of hard sticks and the ratio of the stick length, L, to its diameter, D; the maximum value of this ratio at which one cannot regard the stick as hard). The critical exponents are estimated. The transition of a swelling polymer coil to ideal is revealed as the polymerization degree of a macromolecule increases. The entanglement concentration obtained agrees with experimental data for polymers with flexible chains. The number of monomers between neighbor entanglements is assumed to be the ratio L/D. A comparison of the theory with other ones and recent experimental data is made.

Excitation test results on a single inner vertical coil for the Large Helical Device

Excitation experiments on a single inner vertical coil for the Large Helical Device (LHD) were carried out to confirm its performance. The coil is one of the LHD's poloidal field coils and consists of a forced-flow Nb-Ti cable-in-conduit conductor (CICC). After cooldown for 250 hours, the superconducting transition of the whole coil was confirmed. Pressure drops were measured during the cooldown to determine the coil's hydraulic characteristics. Then, the coil was successfully energized up to the specified current, 20.8 kA. In the experiments, heat generation of joints, radial displacement and acoustic emission (AE) were measured.

Fluorescence Spectroscopic Study of the Aggregation Behavior of Non-Cross-Linked and Cross-Linked Poly(alkylmethyldiallylammonium bromides) Having Decyl, Octyl, and Hexyl Side Chains in Aqueous Solution

The conformational state of a series of non-cross-linked and cross-linked poly(alkylmethyldiallylammonium bromides) bearing decyl, octyl, and hexyl side chains ((CL)-CopolC1-10, (CL)-CopolC1-8, and (CL)-CopolC1-6, respectively) in aqueous solutions were investigated by fluorescence spectroscopy using pyrene as a probe. Photophysical studies show that the conformational transition of random coil non-cross-linked and cross-linked copolymers to compact coils is strongly side chain length dependent. (CL)CopolC1-10 with sufficient n-decyl side chains was found to form hydrophobic microdomains in compact coil conformations in aqueous solution. Much less efficient intramolecular micellization was observed for (CL)-CopolC1-8 in a similar concentration range. No conformational transition to compact coils was found in the case of(CL)-CopolC1-6 as indicated by the absence of pyrene binding to the macromolecule. The presence of sodium bromide facilitates the formation of compact coil conformations for (CL)-CopolC1-10 in aqueous solution. There are significant effects of side chain length and alkyl group content on the critical aggregation concentration(cac). The cac for (CL)-CopolC1-10 in aqueous solution decreased strongly with increasing total hydrophobicity of the n-decyl side chains in the polysoaps. The cross-linked copolymers CL-CopolC1-10 exhibited lower cac's than the corresponding non-cross-linked copolymer analogues. A minimum in the cac for (CL)-CopolC1-10 in aqueous solution was found at about 0.20%(w/w) cross-linking agent.

Experimental results on an hybrid superconducting current limiter

The superconducting current limiter, a device without classical equivalent, appears to be one of the most promising and innovative applied superconducting devices for electric power systems. Its operation is based on the ultra-fast and natural transition of a superconducting coil when the current oversteps a predetermined threshold value. The authors propose a hybrid device consisting of a resistive series transformer and superconducting coils. The superconducting coils trigger the limitation. The latter is ensured by the primary self inductance of the transformer. This design allows the reduction of the current through the superconducting cable, the volume of superconductor and the cryogenic losses under normal operation. These advantages are brought about by a transformer whose magnetic coupling between the windings changes accordingly to the mode of operation. To study this device experimentally, a 150 V-50 A model has been developed. This model has been exposed to a number of tests under normal and fault operations. The results have demonstrated the satisfactory performance of this hybrid device, at least at a reduced scale. With a view to an industrial device, a 63 kV-1250 A system has been theoretically designed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Neuronal membrane conductance activated by amyloid β peptide: importance of peptide conformation

Whole-cell voltage-clamp recording and circular dichroism (CD) spectroscopy were used to assess the importance of amyloid β peptide (A β) conformation for eliciting homeostatically disruptive membrane conductances in embryonic rat hippocampal neurons. A β that assumed a random coil conformation when freshly dissolved in water did not alter cell resting (‘leak’) membrane conductances. In contrast, after several days incubation (‘aging’), the same peptide samples became capable of activating a large, rapid onset and potentially toxic increase in leak membrane conductance that coincided temporally with a transition in peptide conformation from random coil to β-sheet. Interestingly, this membrane activity was not mimicked with chemically equivalent A βs that immediately adopted a β-sheet conformation in water (‘pre-aged’). These findings suggest that, under conditions that allow for a gradual transition of random coil A β to β-sheet structures, peptide conformation may be an important determinant of the toxic consequences of A β-mediated membrane conductances.

Force‐length relations in deformed coils above and below the theta state. Possible bimodality in the chain distribution function

AbstractStretching of flexible macromolecules by an external force, acting on the chain ends, in solvents of variable quality was simulated by the Monte Carlo method on a tetrahedral lattice. The forcelength relations and the stress‐induced changes in the population of the gauche conformers were calculated for coils in theta and athermal solvents. In poor solvents, the stretching of a collapsed coil involves a rather abrupt upturn of the force‐length curve explained as a transition of a globular coil into an extended coil. In conformity with this interpretation, a bimodal shape of the chain vector distribution function P(R) was found in the intermediate range of deformation of collapsed coils. The significance of the results to the stress‐strain behavior of networks with pronounced interaction (such as collapsed gels) are discussed.

Stability of the helical conformation of random L-alanine-L-lysine copolymers in aqueous solution.

AbstractThe potentiometric titration of random copolymers of L‐lysine and L‐alanine containing 0–35% alanine was carried out. The standard free‐energy change for the transition of coil to helix was calculated from the titration curve, and was treated by taking account of first‐neighbor interactions. For uncharged lysine ΔG° = −140 cal/mole, and for alanine ΔG° = −50 cal/mole in 0.06M NaBr at 25°C, indicating that the alanine helix is thermodynamically less stable than the lysine helix. The randomness in co‐polymerization was confirmed by trypsin treatment.