Anomalous Susceptibility Research Articles

An Update on the Structure of hERG.

The human voltage-sensitive K+ channel hERG plays a fundamental role in cardiac action potential repolarization, effectively controlling the QT interval of the electrocardiogram. Inherited loss- or gain-of-function mutations in hERG can result in dangerous “long” (LQTS) or “short” QT syndromes (SQTS), respectively, and the anomalous susceptibility of hERG to block by a diverse range of drugs underlies an acquired LQTS. A recent open channel cryo-EM structure of hERG should greatly advance understanding of the molecular basis of hERG channelopathies and drug-induced LQTS. Here we describe an update of recent research that addresses the nature of the particular gated state of hERG captured in the new structure, and the insight afforded by the structure into the molecular basis for high affinity drug block of hERG, the binding of hERG activators and the molecular basis of hERG's peculiar gating properties. Interpretation of the pharmacology of natural SQTS mutants in the context of the structure is a promising approach to understanding the molecular basis of hERG inactivation, and the structure suggests how voltage-dependent changes in the membrane domain may be transmitted to an extracellular “turret” to effect inactivation through aromatic side chain motifs that are conserved throughout the KCNH family of channels.

Fragility and anomalous susceptibility of weakly interacting networks.

Percolation is a fundamental concept that has brought new understanding of the robustness properties of complex systems. Here we consider percolation on weakly interacting networks, that is, network layers coupled together by much fewer interlinks than the connections within each layer. For these kinds of structures, both continuous and abrupt phase transitions are observed in the size of the giant component. The continuous (second-order) transition corresponds to the formation of a giant cluster inside one layer and has a well-defined percolation threshold. The abrupt transition instead corresponds to the merger of coexisting giant clusters among different layers and is characterized by a remarkable uncertainty in the percolation threshold, which in turns causes an anomalous behavior of the observed susceptibility. We develop a simple mathematical model able to describe this phenomenon, using a susceptibility measure that defines the range where the abrupt transition is more likely to occur. Finite-size scaling analysis in the abrupt region supports the hypothesis of a genuine first-order phase transition.

Pressure effects on spin-lattice coupling of CdCr2S4

Results of DC magnetization and x-ray diffraction measurements under hydrostatic pressure are reported for the CdCr2S4 spinel compound. Magnetization measurements were performed in a polycrystalline sample up to 14 kbar in the 20–220 K temperature range. At low applied magnetic fields an anomalous susceptibility behavior, associated to magnetic clusters, persists up to 14 kbar. X-ray synchrotron diffraction spectra acquired under pressure show a strong linear correlation between the variation of lattice parameters under pressure and the variation of the Cr–Cr distance. In contrast, the S-Cr-S angles remain constant. Clearly, the CdCr2S4 magnetic properties are strongly sensitive to pressure variations and the Cr local distortions observed in this compound promote a competition between direct antiferromagnetic and super-exchange ferromagnetic interactions within such short-range magnetic clusters.

Modeling and Inversion of Magnetic Anomalies Caused by Sediment–Basement Interface Using Three-Dimensional Cauchy-Type Integrals

This letter introduces a new method for the mod- eling and inversion of magnetic anomalies caused by crystalline basements. The method is based on the 3-D Cauchy-type inte- gral representation of the magnetic field. Traditional methods use volume integrals over the domains occupied by anomalous susceptibility and on the prismatic representation of the volumes with an anomalous susceptibility distribution. Such discretization is computationally expensive, particularly in 3-D cases. The tech- nique of Cauchy-type integrals makes it possible to represent the magnetic field as surface integrals, which is particularly significant in solving problems of the modeling and inversion of magnetic data for the depth to the basement. In this letter, a novel method is proposed, which only requires discretizing the magnetic contrast surface for modeling and inversion. We demonstrate the method using several synthetic models. The results show that the new method is fast and capable of providing high-resolution depth estimation for the sediment-basement interface. Index Terms—Basement depth, Cauchy-type integral, inversion, magnetic.

Manipulation of the magnetic properties in Er1−xCo2 compounds by atomic vacancies

ErCo2 compound is a well-known magnetocaloric material which shows giant magnetocaloric effect in the vicinity of first-order phase transition. We demonstrate a new way of fine tuning its crystal structure and magnetic properties. Er atomic vacancies are introduced in order to manipulate the local atomic environment, the phase transition characteristics, and the magnetocaloric effect as well. Er1−xCo2 can be stable over a narrow homogenous range, and maintain the cubic structure. The Bragg peaks shift upward to higher angles, and the unit cell volume contracts with reduction of the Er content. The Curie temperatures in low magnetic field increase from 32K (ErCo2) to 46K (Er0.97Co2), and linearly change with the magnetic field in nearly same slope. Er1−xCo2 compounds exhibit anomalous susceptibility behaviors in the paramagnetic state, and deviate from the Curie–Weiss law at around 100K. The temperature range of anomalous susceptibility behaviors also move upward to higher temperature with reduction of Er content. Er1−xCo2 compounds also show anomalous coercivity behavior in the vicinity of phase transition. Er1−xCo2 compounds exhibit large magnetocaloric effect and good refrigerant capacity in the vicinity of ferrimagnetic–paramagnetic phase transition.

First measurements of hydrodynamic instability growth in indirectly driven implosions at ignition-relevant conditions on the National Ignition Facility.

Ignition experiments have shown an anomalous susceptibility to hydrodynamic instability growth. To help understand these results, the first hydrodynamic instability growth measurements in indirectly driven implosions on the National Ignition Facility were performed at ignition conditions with peak radiation temperatures up to ∼300 eV. Plastic capsules with two-dimensional preimposed, sinusoidal outer surface modulations of initial wavelengths of 240 (corresponding to a Legendre mode number of 30), 120 (mode 60), and 80 μm (mode 90) were imploded by using actual low-adiabat ignition laser pulses. The measured growth was in excellent agreement, validating 2D hydra simulations for the most dangerous modes in the acceleration phase. These results reinforce confidence in the predictive capability of calculations that are paramount to illuminating the path toward ignition.

분해능 모델 제한자를 사용하는 자력탐사자료의 2차원 역산

새로운 2차원 자력탐사자료 역산 방법을 개발하였다. 중,자력탐사와 같은 포텐셜 자료의 역산에서 가장 문제가 되는 점은 비유일해 문제이다. 일반적으로 자력탐사 자료의 역산은 모델변수의 수가 자료의 수보다 훨씬 많은 불충분 문제이며, 이는 비유일해 문제를 더욱 심화시키게 된다. 일반적인 최소자승법을 자력탐사자료의 역산에 적용하게 되면, 이 상대가 지표면에 집중되는 결과를 초래한다. 본 연구에서는 이러한 비유일해 문제를 극복하기 위하여 모델분해능에 근거한 새로운 모델제한자를 제안하였다. 이 모델제한자는 분해능이 높은 모델변수에는 큰 제한을 가하고, 작은 모델변수에는 약한 제한을 가하게 된다. 따라서 분해능이 낮은 심부의 모델변수도 효과적으로 추정할 수 있다. 개발된 역산 알고리듬을 이용하여, 전형적인 모델에 대한 이론자료의 역산에 적용하였다. 또한 옥천대에서 얻어진 항공자력탐사자료 역산에 적용하였다. We developed a method for inverting magnetic data to image 2D susceptibility models. The major difficulty in the inversion of the potential data is the nonuniqueness. Furthermore, generally the number of inversion blocks are greater than the number of the magnetic data available, and thus the magnetic inversion leads to under-determined problem, which aggravates the nonuniqueness. When the magnetic data were inverted by the general least-squares method, the anomalous susceptibility would be concentrated near the surface in the inverted section. To overcome this nonuniqueness problem, we propose a new resolution model constraint that is calculated from the parameter resolution. The model constraint imposes large penalty on the model parameter with good resolution, on the other hand small penalty on the model parameter with poor resolution. Thus, the deep-seated model parameter, generally having poor resolution, can be effectively resolved. The developed inversion algorithm is applied to the inversion of the synthetic data for typical models of magnetic anomalies and is tested on real airborne data obtained at the Okcheon belt of Korea.

High-resolution transmission electron microscopy and bulk magnetometry study of LaFe11.5Si1.5 compound

This paper studies the microstructural and magnetic properties of LaFe11.5Si1.5 compound by means of high-resolution transmission electron microscope and bulk magnetometry measurements. The crystalline structure is accompanied with the noncrystalline and nanocrystalline structures. This characteristic is the reflection of the crystalline process held by quenching. The inverse susceptibilities diverge and deviate from Curie–Weiss law under low applied magnetic fields. This paper proposes the possible mechanism between the anomalous susceptibilities and microstructure, and offers a perspective on the magnetic properties of metastable intermetallic compounds.

Magnetic survey of topsoils in Windsor–Essex County, Canada

Windsor–Essex County is a major cross-border truck and transportation route, with significant localized industrialization as well as rural and farming areas. Magnetic property measurements (in-field and laboratory susceptibility, frequency-dependent susceptibility, hysteresis properties, thermomagnetic and thermosusceptibility curves, anhysteretic and isothermal magnetizations) were made in order to determine the potential for using such variables to distinguish between natural and anthropogenic pollutants. In-field magnetic susceptibility measured on 324 soil sampling sites on a 0.5–2 km grid spacing through Windsor–Essex County ranged from 3.7 × 10 − 6 to 305.2 × 10 − 6 SI (average 36.2 ± 35.8 × 10 − 6 SI), and showed that high magnetic susceptibility values were obtained on soil sampling sites in and around the cities/towns of Windsor, Harrow, Olinda and Oakland and near the beaches of Point Pelee National Park (PPNP) and Deerbrook, whereas lower susceptibility values were observed in near the towns of Lakeshore and Essex. On this grid spacing, Highway 401 (the major truck route) did not show anomalous susceptibility values; however, closer (1–3 m) sampling on other roads did show anomalously high values, suggesting that the coarser grid spacing may have missed anomalies. Laboratory measurements indicated that the dominant magnetic mineral in the Windsor–Essex County soils is magnetite; however, the grain size is variable. Pseudo-single domain (PSD)–multidomain (MD) magnetite is generally found on beaches and in PPNP, whereas single domain (SD)–PSD magnetite has been found near the City of Windsor and other towns. While certain correlations exist between some anthropogenic activities and the measured magnetic susceptibility and magnetic property values, no overall correlation can be made. A variety of geologic and anthropogenic factors must be considered when interpreting the origin of the magnetic signal in a particular area.

Static magnetic susceptibility in the SDW phase of (TMTSF) 2X

We report on the static susceptibility in the SDW phase of (TMTSF) 2AsF 6 with field parallel to the a-axis. Anomalous susceptibility was observed around 4K. In this field direction, the susceptibility is given by the canting of anti-ferromagnetically ordering spins. This anomaly indicates the difference of the spin canting between above and below the critical temperature which divide the SDW phase.

ＹＢａ２Ｃｏ３Ｏｙの結晶構造と磁性

YBa2Co3Oy prepared at 1200 K under reduced pressure forms a cubic perovskite type oxide with a superstructure (a = 1.24 [nm] : E phase). Heat treatments of the E phase oxide in oxygen of 0.106 [MPa] at 1100 [K], 1200 [K], and 1320 [K] formed a tetragonal oxide (a = 1.22 [nm], c = 1.25 [nm] : C phase), an orthorombic oxide (a = 0.389 [nm], b = 0.365 [nm], c = 1.253 [nm] : D phase), and a tetragonal oxide (a = 0.39 [nm], c = 1.13 [nm] : A' phase) with a small amount of other oxides, respectively. The magnetic susceptibilities of the E and C phases oxides are expressed as a sum of a temperature-independent term and the Curie-Weiss term. The D phase oxide is a ferromagnet with magnetization σ = 0.63 μB/Co and Curie temperature Tc = 57 [K]. The A' phase oxide is a paramagnet with anomalous susceptibility maximum at 170 [K]. The electrical resistances of the four oxide phases are semiconductive and, in addition, only the E phase oxide shows a remarkable resistance decrease below 200 [K].

Anomalous Second-Order Nonlinear Optical Response of In-Plane Poled Glassy Polymers. Spectroscopic and Theoretical Support for the Importance of Charged Chromophore Aggregates

We report here measurements of the orientational and frequency dependence of the anomalously large second-order nonlinear optical (NLO) susceptibilities observed in guest−host DANS [4-(N,N-dimethylamino)-4‘-nitrostilbene]/PMMA [poly(methyl methacrylate)] films poled in an “in-plane” electrode configuration. The resonant response is sharply peaked (fwhm decreases by a factor of 4) in comparison to identical samples poled by standard corona field techniques. Additionally, these anomalous susceptibilities, which are oriented normal to the electric poling field, exhibit unusually strong features at long wavelengths where the linear absorption is low. We also report the first direct experimental EPR evidence for nitrogen-centered cation radicals, hence the creation of charged chromophores trapped in the polymeric matrix by charge injection from the poling electrodes. These observations are in qualitative agreement with the very large NLO response magnitudes and distinct spectral features predicted by sum-over-...

Nonlinear conduction and anomalous susceptibility of sliding electronic crystals: Charge and spin density waves

Metastable plastic deformations of sliding electronic crystals determine their low frequency dielectric susceptibility ε( T, ω), long time relaxation and nonlinear I – V characteristics. We present a theory of plastic deformations due to the pinning induced dislocation loops which originate the local metastable state. Within the same model we describe the two remarkable features which became commonly observed in Charge and Spin Density Waves (DW). There are both the anomalous peak of ε( T, ω = const) and the characteristic I – V curve with second threshold field in sliding regime. Namely the features of ε( T) result from a competition of the local relaxation with the collective pinning effected by freezing of the Coulomb screening. The upper critical field in I – V curves is reached when the shortest life time configurations are accessed by the fast moving DW.

Anomalous susceptibility of low-dissipation bistable systems

The time-asymptotic behavior of a bistable system under conditions of a nonequilibrium phase transition of displacement type was studied. Anomalous behavior of the susceptibility of this system is observed with increase in the noise intensity. It is inferred that the effect of stochastic resonance can be observed in such systems.

Structural freedom, topological disorder, and the irradiation-induced amorphization of ceramic structures

The susceptibility to irradiation-induced loss of long-range translational and orientational order during amorphization of crystalline solids, a process which usually amounts to topological disordering, can be understood on the basis of available structural freedom which depends on the redundancies present in structural connectivity. A surprisingly good correlation has been established between the critical accumulated energy deposited per atom — or displacements per atom (dpa) — required for amorphization during ion irradiation and the calculated structural freedom for the structure type irradiated over a wide range of non-metal structural types. These include AO, AO 2, A 2O 3, ABO 3, ABO 4, A 2B 2O 7 and A 2BO 4 compact structure types, in which weakest links can often be identified, as well as less-compact network structures. The present contribution specifically compares the order of susceptibility to amorphization — in these more complex oxide structures and in the simpler network structures Si 3N 4, SiC, Be 2SiO 4, AlPO 4, Si, SiO 2, P 2O 5 and graphite — on the basis of structural connectivity and discusses the anomalous susceptibility of SiC.

Scaling in spin susceptibility of high-Tc cuprates: A model with nondegenerate fermions.

We propose that the anomalous spin susceptibility {chi}{sub {ital s}}({ital T}) and specific heat {ital C}{sub {ital V}}({ital T}) in the high-{ital T}{sub {ital c}} cuprates have origin in a {ital nondegenerate} electron component. This arises when the chemical potential {mu} is tuned near the top of a two-dimensional band submerged just below the Fermi surface. The important role of the charge reservoir is also taken into account. The model predicts a {ital scaling} in {chi}{sub {ital s}}({ital T}) and {ital C}{sub {ital V}}({ital T}) of bilayer cuprates. We demonstrate this scaling in the {chi}{sub {ital s}}({ital T},{ital x}) data on TlSr{sub 2}(Lu{sub 1{minus}{ital x}}Ca{sub {ital x}})Cu{sub 2}O{sub {ital y}}. {copyright} {ital 1996 The American Physical Society.}

Transient spin structures at the antiferro-to-paramagnetic phase boundary of FeBr2

Excess magnetization and anomalous susceptibility loss is observed on antiferromagnetic FeBr2 in an axial field H below and above its H-T-phase boundary between the multicritical temperature (Tm = 4.6 K) and the Néel temperature (TN = 14.1 K). These and other unusual properties of FeBr2 are attributed to frustration-induced intraplanar non-critical spin fluctuations, which can be simulated within the framework of a triaxial version of the 2D-ANNNI model.

Spin-Orbit Interaction in Small Metallic Particles

The conduction electron spin susceptibility of small metallic particles with electrons of even number vanishes at T =0. Using NMR, we observed the recovery of this anomalous susceptibility in small particles of Cu when the spin-orbit interaction is enhanced by adding Au impurities. The result is similar to what happens with magnetic impurities, although the mechanisms are substantially different.

Anomalies of dielectric properties of the incommensurate phase of Rb2ZnCl4crystals under mechanical and electrical actions

Abstract A behaviour of the anomalous dielectric susceptibility ϵ y of Rb2ZnCl4 crystal under combined thermal, mechanical and electrical actions has been studied in the vicinity of incommensurate-commensurate phase transition. An anomalous change in ϵ y critically dependent of the sequence of the external electrical and mechanical actions is found. It is shown that this effect has the same origin as the well known anomalous temperature hysteresis of ϵ y and is due to the crystal “memory” conditioned by the soliton pinning on lattice inhomogeneities.

Magnetic characteristics of superconducting RBa 2Cu 3O 6+y ( R = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm and Yb)

Magnetic properties of superconducting RBa 2Cu 3O 6+y compounds ( R = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm and Yb) have been studied by using a SQUID magnetometer in the temperature range of 3 – 400 K. The susceptibility data of most of the samples can be well described by the Curie-Weiss relation. The rare earth ions exhibit essentially the full magnetic moments expected for the R 3+ states, while the superconducting transition temperature remains in the 88 – 94 K range. The rare earth moments are generally found to interact antiferromagnetically. However, no magnetic order is observed in the temperature range studied. The Eu samples exhibited anomalous susceptibilities which we ascribe to the low-lying states of the 7F J manifold of Eu 3+.