Ideal Coil Research Articles

Structural basis of α-catenin recognition by EspB from enterohaemorrhagic E. coli based on hybrid strategy using low-resolution structural and protein dissection.

Enterohaemorrhagic E. coli (EHEC) induces actin reorganization of host cells by injecting various effectors into host cytosol through type III secretion systems. EspB is the natively partially folded EHEC effector which binds to host α-catenin to promote the actin bundling. However, its structural basis is poorly understood. Here, we characterize the overall structural properties of EspB based on low-resolution structural data in conjunction with protein dissection strategy. EspB showed a unique thermal response involving cold denaturation in the presence of denaturant according to far-UV circular dichroism (CD). Small angle X-ray scattering revealed the formation of a highly extended structure of EspB comparable to the ideal random coil. Various disorder predictions as well as CD spectra of EspB fragments identified the presence of α-helical structures around G41 to Q70. The fragment corresponding to this region indicated the thermal response similar to EspB. Moreover, this fragment showed a high affinity to C-terminal vinculin homology domain of α-catenin. The results clarified the importance of preformed α-helix of EspB for recognition of α-catenin.

Ballistic energy transport along PEG chains: distance dependence of the transport efficiency

Dual-frequency relaxation-assisted two-dimensional infrared (RA 2DIR) spectroscopy was used to investigate energy transport in polyethylene glycol (PEG) oligomers of different length, having 0, 4, 8, and 12 repeating units and end-labeled with azido and succinimide ester moieties (azPEGn). The energy transport initiated by excitation of the N≡N stretching mode of the azido group in azPEGn in CCl(4) at ca. 2100 cm(-1) was recorded by probing the C=O stretching modes (reporters) of the succinimide ester moiety. Sensitive to the excess energy delivered to the reporter modes, RA 2DIR permits observation of both the through-bond and through-solvent energy transport contributions. The cross-peak data involving the reporter modes with different thermal sensitivity and the data for mixtures of compounds permitted concluding that through-bond energy transport is the dominant mechanism for most cross peaks in all four azPEGn compounds. The through-bond energy transport time, evaluated as the waiting time at which the cross peak maximum is reached, was found to be linearly dependent on the chain length of up to 60 Å, suggesting a ballistic energy transport regime. The through-bond energy transport speed determined from the chain-length dependence of T(max) in CCl(4) is found to be ca. 450 m s(-1). The cross-peak amplitude at the maximum decays exponentially with the chain length; a characteristic decay distance is found to be 15.7 ± 1 Å. The cross-peak amplitude at zero waiting time, determined by the end-to-end distance distribution, is found to decay with the chain length (L) as ∼L(-1.4), which is close to predictions of the free flight chain model. The match indicates that the end-group interaction does not strongly perturb the end-to-end distribution, which is close to the ideal random coil distribution with the Gaussian probability density.

Single Molecule Study of the Intrinsically Disordered FG-Repeat Nucleoporin 153

Nucleoporins (Nups), which are intrinsically disordered, form a selectivity filter inside the nuclear pore complex, taking a central role in the vital nucleocytoplasmic transport mechanism. These Nups display a complex and nonrandom amino-acid architecture of phenylalanine glycine (FG)-repeat clusters and intra-FG linkers. How such heterogeneous sequence composition relates to function and could give rise to a transport mechanism is still unclear. Here we describe a combined chemical biology and single-molecule fluorescence approach to study the large human Nup153 FG-domain. In order to obtain insights into the properties of this domain beyond the average behavior, we probed the end-to-end distance (RE) of several ∼50-residues long FG-repeat clusters in the context of the whole protein domain. Despite the sequence heterogeneity of these FG-clusters, we detected a reoccurring and consistent compaction from a relaxed coil behavior under denaturing conditions (RE/RE,RC = 0.99 ± 0.15 with RE,RC corresponding to ideal relaxed coil behavior) to a collapsed state under native conditions (RE/RE,RC = 0.79 ± 0.09). We then analyzed the properties of this protein on the supramolecular level, and determined that this human FG-domain was in fact able to form a hydrogel with physiological permeability barrier properties.

Microstructure Investigation on Micropore Formation in Microporous Silica Materials Prepared via a Catalytic Sol–Gel Process by Small Angle X–Ray Scattering

The so-called sol-gel technique has been shown to be a template-free, efficient way to create functional porous silica materials having uniform micropores. This appears to be closely linked with a postulation that the formation of weakly branched polymer-like aggregates in a precursor solution is a key to the uniform micropore generation. However, how such a polymer-like structure can precisely be controlled, and further, how the generated low-fractal dimension solution structure is imprinted on the solid silica materials still remain elusive. Here we present fabrication of microporous silica from tetramethyl orthosilicate (TMOS) using a recently developed catalytic sol-gel process based on a nonionic hydroxyacetone (HA) catalyst. Small angle X-ray scattering (SAXS), nitrogen adsorption porosimetry, and transmission electron microscope (TEM) allowed us to observe the whole structural evolution, ranging from polymer-like aggregates in the precursor solution to agglomeration with heat treatment and microporous morphology of silica powders after drying and hydrolysis. Using the HA catalyst with short chain monohydric alcohols (methanol or ethanol) in the precursor solution, polymer-like aggregates having microscopic correlation length (or mesh-size) < 2 nm and low fractal dimensions ∼2, which is identical to that of an ideal coil polymer, can selectively be synthesized, yielding the uniform micropores with diameters <2 nm in the solid materials. In contrast, the absence of HA or substitution of 1-propanol led to considerably different scattering behavior reflecting the particle-like aggregate formation in the precursor solution, which resulted in the formation of mesopores (diameter >2 nm) in the solid product due to apertures between the particle-like aggregates. The data demonstrate that the extremely fine porous silica architecture comes essentially from a gaussian polymer-like nature of the silica aggregates in the precursor having the microscopic mesh-size and their successful imprint on the solid product. The result offers a general but significantly efficient route to creating precisely designed fine porous silica materials under mild condition that serve as low refractive index and efficient thermal insulation materials in their practical applications.

Self‐Consistent Theory of Structures and Transitions in Weak Polyampholytes

AbstractWeak polyampholytes are charged polymers, where the charge asymmetry can be tuned by varying the solution pH. We determine the size of a randomly charged weak polyampholyte in dilute solution as a function of charge asymmetry, Bjerrum length, salt concentration, pH, and degree of polymerization, using a self‐consistent method. It is known that in the limiting cases of low and high charge asymmetries, polyampholytes behave as neutral polyampholytes and polyelectrolytes, respectively. We explore in detail the regime of intermediate charge asymmetry where a polyampholyte show non‐monotonic change in the chain size as a function of Bjerrum length. A hierarchy of structures exists at different length scales, ranging from ideal coils at low Bjerrum length, extended rod‐like state at intermediate Bjerrum length to globular states at high Bjerrum length. The transition between ideal coil and rod‐like states is continuous, while that between rod‐like and globular states is discontinuous. The addition of salt changes the nature of the rod‐to‐globule transition from discontinuous to continuous. The effective free energy shows a double minimum at intermediate charge asymmetry, indicating the coexistence of globules and extended states. The size as a function of the solution pH shows a minimum at the isoelectric point. The size of neutral polyampholytes at the isoelectric pH increases with the increase in the salt concentration. The size of charge excess polyampholytes far away from the isoelectric pH decreases with the increase in the salt concentration. magnified image

An efficient impedance method for induced field evaluation based on a stabilized Bi-conjugate gradient algorithm

This paper presents a stabilized Bi-conjugate gradient algorithm (BiCGstab) that can significantly improve the performance of the impedance method, which has been widely applied to model low-frequency field induction phenomena in voxel phantoms. The improved impedance method offers remarkable computational advantages in terms of convergence performance and memory consumption over the conventional, successive over-relaxation (SOR)-based algorithm. The scheme has been validated against other numerical/analytical solutions on a lossy, multilayered sphere phantom excited by an ideal coil loop. To demonstrate the computational performance and application capability of the developed algorithm, the induced fields inside a human phantom due to a low-frequency hyperthermia device is evaluated. The simulation results show the numerical accuracy and superior performance of the method.

An Improved Quasi-Static Finite-Difference Scheme for Induced Field Evaluation Based on the Biconjugate Gradient Method

This paper presents a biconjugate gradient (BiCG) method that can significantly improve the performance of the quasi-static finite-difference scheme, which has been widely used to model field induction phenomena in voxel phantoms. The proposed BiCG method offers remarkable computational advantages in terms of convergence performance and memory consumption over the conventional iterative, successive overrelaxation algorithm. The scheme has been validated against other known solutions on a lossy, multilayered ellipsoid phantom excited by an ideal coil loop. The wide application capability and computational performance of the BiCG method is demonstrated by modeling the exposure of MRI healthcare workers to fields produced by pulsed field gradients. This is an important topic of research in light of the Physical Agents Directive 2004/40/EC because a variety of realistic operator postures near the bore entrance of an MRI system are modeled.

Broad Band Modeling of a Superconducting Magnetic Energy Storage (SMES) Coil

In this paper, we compute with accuracy the impedance parameters of a superconducting magnetic energy storage (SMES) system. We do this by using a three-dimensional integral formulation of the full set of frequency domain Maxwell's equations in the quasistatic limit. The impedance parameter allows the construction of a time domain equivalent circuit to be used for the simulation of the overall SMES system. The numerical model is based on a volume integral formulation where the unknown is the total current density J, expressed as the sum of its solenoidal and non-solenoidal components. This separation allows to avoid the ill-conditioning of the relevant stiffness matrix at low frequencies, being essential for developing a numerical model accurately working where the SMES resonances are located. The model is applied to the case of an ideal model coil consisting of an 18-layers solenoid.

A round robin test for pre-standardization of a saddle-shaped pickup coil method to measure AC losses in Bi-2223 Ag-sheathed tapes

We performed a round robin test to measure AC losses in Bi-2223 Ag-sheathed tapes with saddle-shaped pickup coils in an alternating perpendicular magnetic field at liquid nitrogen temperature. Two laboratories participated in the round robin test with each system of the pickup coil and the measurement circuit. Short specimens of a Bi-2223 tape and a copper magnet to generate the alternating magnetic field were used for common conditions in the test. The saddle-shaped pickup coils were made under recommended conditions for the structure and the sizes that give a calibration coefficient around unity. The signals of the magnetic moment from the pickup coils were calibrated by using a standard hairpin copper tape. AC losses of the common specimen of the Bi-2223 tape were measured in the round robin test in the ranges of frequency up to 60 Hz and the amplitude up to 0.2 T of perpendicular magnetic field. While we had only two participants in the test, we obtained the following results in a pre-standardization process of the AC loss measurement with the saddle-shaped pickup coil (i) it was suggested from the calibration procedure using hairpin copper tape that the deviations from numerical simulation for an ideal pickup coil and a sufficiently long specimen is within 3% on an average, (ii) the values of COV for the AC losses measured at 1 Hz and 10 Hz are less than about 3% in the range of the field amplitude between 0.02 T and 0.2 T.

Ideal coil shape for combined function superconducting magnets

Coil shapes for generating the perfect field in superconducting dipoles, quadrupoles and sextupoles are known. However, for combined function superconducting magnets coil shapes are not available in the literature. Here we provide the coil shapes which can generate mixed dipole–quadrupole and dipole–sextupole fields.

Real polymer size from the ideal chain molecules model in a diffusive Minkowskian spacetime

The universal exponent ( ν r ) of the real polymer size (i.e., the excluded volume chain) is derived from constraining the ideal coil model ( ν i = 1 2 ) to a Minkowski-type diffusive spacetime. The square end-to-end distance was expanded in wavenumber power series, whence the leading contribution is extracted according to previously proposed Lorentz transforms acting in Brownian media. In the end, it turns out ν i ≃ ν r sin ( 1 ) , in good agreement with predictions of the phase transition theory for critical phenomena.

Dynamic covalent chemistry on self-templating peptides: formation of a disulfide-linked beta-hairpin mimic.

Dynamic covalent chemistry on self-templating peptides: formation of a disulfide-linked beta-hairpin mimic.

Asymptotical and mapping methods in study of ergodic divertor magnetic field in a toroidal system

Asymptotical and mapping methods to study the structure of magnetic field perturbations and magnetic field line dynamics in a tokamak ergodic divertor in toroidal geometry are developed. The investigation is applied to the Dynamic Ergodic Divertor under construction for the Torus Experiment for the Technology Oriented Research (TEXTOR-94) Tokamak at Jülich [Fusion Eng. Design 37, 337 (1997)]. An ideal coil configuration designed to create resonant magnetic perturbations at the plasma edge is considered. In cylindrical geometry, the analytical expressions for the vacuum magnetic field perturbations of such a coil system are derived, and its properties are studied. Corrections to the magnetic field due to the toroidicity are presented. The asymptotical analysis of transformation of magnetic perturbation into the Hamiltonian perturbation in toroidal geometry is carried out, and the asymptotic formulas for the spectrum of the Hamiltonian perturbations are found. A new method of integration of Hamiltonian equations is developed. It is based on a canonical transformation of variables that replaces the dynamics of a continuous Hamiltonian system by a symplectic mapping. The form of the mapping is established in the first order of perturbation theory. It is shown that the mapping well reproduces Poincaré sections of field lines, as well as their statistical properties in an ergodic zone obtained by the numerical integration of field line equations. The mapping is applied to study, in particular, the formation of a stochastic layer and the statistical properties of field lines at the plasma edge.

Magnetic field topology and field lines structure in the Dynamic Ergodic Divertor of TEXTOR-94

An analytical model of the magnetic field perturbations and the mapping technique to study field line dynamics in an ergodic divertor tokamak are developed. The analytical formulas for the vacuum magnetic field perturbations of ideal divertor coil configuration are derived. The Hamiltonian representation in toroidal geometry is discussed, and asymptotic formulas for it are found. The so-called symmetric perturbed twist mapping is derived and applied to the formation of a stochastic layer and statistical properties of field lines at the plasma edge.

Benchmark problems for defect size and shape determination in eddy-current nondestructive evaluation

A set of four benchmark problems is presented for verification of theoretical calculations of defect size and shape in eddy-current nondestructive evaluation. The benchmark problems are based on careful measurements of the change in coil impedance as a function of frequency for a circular air-cored coil which is scanned along the axis of an electrodischarge machined slot in a thick aluminum alloy plate. Slots of (i) semi-elliptical, and (ii) double-peaked profiles are considered. Deviations from ideal coil behavior are identified and corrected so that the final impedance data and experimental parameters can be directly used to verify theoretical inversion algorithms.

Single-chain statistics and the upper wave-vector cutoff in polymer blends.

We derive the equation for the single-chain correlation function in polymer blends. The chains in the incompressible blend have a radius of gyration smaller than the radius of gyration for ideal chains. The chains shrink progressively as we approach the critical temperature ${\mathit{T}}_{\mathit{c}}$. The correction responsible for shrinking is proportional to 1/ \ensuremath{\surd}N , where N is the polymerization index. At T=${\mathit{T}}_{\mathit{c}}$ and for N=1000, the size of the chain has been estimated to be 10% smaller than the size of the ideal coil. The estimate relies on the appropriate cutoff. In the limit of N\ensuremath{\rightarrow}\ensuremath{\infty} the chains approach the random walk limit. Additionally, we propose in this paper a self-consistent determination of the radius of gyration and the upper wave-vector cutoff. Our model is free from any divergences such as were encountered in the previous mean-field studies; we make an estimate of the chain size at the true critical temperature and not the mean-field one.

Dissecting the Disulphide-coupled Folding Pathway of Bovine Pancreatic Trypsin Inhibitor: Forming the First Disulphide Bonds in Analogues of the Reduced Protein

The kinetics of disulphide bond formation and breakage have been measured in five analogues of the single-disulphide intermediates that occur in folding of bovine pancreatic trypsin inhibitor (BPTI), in which the cysteine residues not involved in disulphide bonds have been replaced by serine residues. Only a single disulphide bond can be made in each analogue, allowing the rates and equilibrium constants of the corresponding microscopic steps to be determined. These steps cannot be characterized in normal BPTI with six cysteine residues, as only the total overall rate of forming all 15 possible disulphide bonds can be measured.The intramolecular rate of forming each disulphide bond was found in the dithiol forms of reduced BPTI to be approximately proportional inversely to the size of the disulphide loop formed. On this basis, the 30-51 disulphide bond is not formed preferentially in the fully reduced protein, even though it predominates amongst the one-disulphide intermediates as a result of rapid intramolecular disulphide rearrangements. It is found to be more stable than the other one-disulphide intermediates because its disulphide is more stable to reduction than the others. This is undoubtedly due to the stable partially folded structure of (30-51), as the other intermediates are much less structured under folding conditions.Urea (8 M) uniformly decreased by a factor of 5 the effective concentrations of cysteine thiol groups in the analogues and in reduced BPTI, suggesting that reduced BPTI under normal refolding conditions is not an ideal random coil; any non-random conformations do not, however, favour formation of any specific disulphide bonds.Findings from these studies have led to further refinement and development of various approaches to measuring and interpreting the intramolecular rates of disulphide bond formation and breakage in proteins.

A comparison of the conductor requirements for energy storage devices made with ideal coil geometries

Superconducting magnetic energy storage (SMES) plants have previously been proposed in both solenoidal and toroidal geometries. The former is efficient in terms of the quantity of superconductor required per unit of stored energy. For applications where a fringe field could be a problem, the toroidal geometry, which requires at least a factor of two more material, has been proposed. In addition to the solenoid and toroid, other geometries are possible, such as linear multipoles and spherical coils. These geometries have been considered for use in applications other than energy storage. Here the effectiveness (quantity of superconductor/stored energy) is calculated for various coil geometries. >

Impedance of a loop surrounding a conducting cylinder

The change in complex impedance between an ideal one-turn coil surrounding and coaxial with an infinitely long circular cylinder of conductivity δ and permeability μ and a similar coil without the core has been calculated. From the exact expression, a power series in the quantity δ/b (δ=skin depth; b=radius of core) has been developed. From this result, the change in impedance of a physically realistic multiturn coil can be estimated. The theory permits a rational approach to optimization of the design of eddy-current test coils and provides a possible means of detecting changes in the radius and conductivity of the cylinder.

熱疲労試験における高周波加熱コイルの形状と試験片の温度分布

On the high frequency heating apparatus used for thermal fatigue tests, the relation between the shape of heating coils and the temperature distribution of specimens was experimentally examined for SUS 304 stainless steel. This report describes the relation between heating coil dimensions and heating rate, the most ideal coil shape for various specimen types, and the effects of temperature range and specimen shape on temperature distribution.The results obtained are as follows:(1) The heating rate increases with decreasing distance from specimen surface to heating coil and with increasing coil tube diameter.(2) For the general cylindrical and hour glass type specimens, the most ideal coil shapes are a separate type and a parallel type coil, respectively, as judged from the point of temperature distribution.