Multidomain Region Research Articles

Synthesis and characterization of Pt3Co alloy magnetic nanoparticles in multidomain region for oxygen reduction reaction catalysts in PEMFCs

The structural and electrochemical characteristics of Pt3Co alloy nanoparticles as novel magnetic catalysts are investigated experimentally to improve the performance of the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFCs). Pt3Co alloy nanoparticles are synthesized using a wet chemical reduction and seed-mediated method. The synthesized Pt3Co alloy nanoparticles are annealed at 400 °C (Pt3Co-400) and 700 °C (Pt3Co-700) to increase the remanent magnetizations. The synthesized Pt3Co alloy nanoparticles for magnetic catalysts are characterized using physicochemical and electrochemical methods. Physicochemical tests confirm that the Pt3Co alloy nanoparticles are properly synthesized with the desired atomic ratio for magnetization in the multidomain region. The remanent magnetizations of the Pt3Co alloy nanoparticles substantially increase after annealing at 400 °C. For the rotating ring-disk electrode tests, the electrocatalytic performance improvement of Pt3Co alloy nanoparticles by magnetization is very small under the liquid electrolyte condition. However, the performances of PEMFCs using Pt3Co-400 alloy nanoparticles are substantially improved after magnetization owing to the enhanced ORR activities and oxygen diffusivity. In addition, the optimal operating conditions for PEMFCs using Pt3Co-400 magnetic catalysts are determined to be a higher reactant flow rate and lower operating temperature with a Pt-to-Pt3Co-400 mass ratio of 8:2.

Dynamic reorganization of cortical structure in multi-domain regions after capsular and pontine stroke

Subcortical stroke may cause widespread structural changes to the cerebral cortex in multiple domains; however, the details of this process remain unclear. In this prospective observational study, we acquired two datasets to investigate the effect of lesion location on cortical structure. One was cross-sectional, comprising 269 patients with chronic stroke, either capsular stroke (CS) or pontine stroke (PS), and the other was longitudinal, comprising 119 patients with CS or PS. In the chronic-stage data, both CS and PS exhibited reduced cortical thickness in the precentral gyrus and increased cortical thickness and area in the frontal, temporal, occipital and insular cortices. Cortical thicknesses were correlated with motor outcomes in the precentral and lingual gyri, and early impairment of the corticospinal tract was associated with cortical thickness in the middle frontal gyrus. In the longitudinal dataset, CS showed gradually decreasing cortical thickness in the precentral gyrus, and both CS and PS showed gradually increasing cortical thickness and area in regions with significant structural reorganization. Subcortical stroke can therefore cause complex cortical structural changes in multi-domain regions involved in motor, primary and higher cognitive areas and have different evolution patterns depending on the subcortical level of the lesion affecting the motor pathways.

Effect of TbF3 diffusion on the demagnetization behavior and domain evolution of sintered Nd–Fe–B magnets by electrophoretic deposition

We studied the magnetic properties and domain evolution of annealed and TbF3-diffused sintered Nd–Fe–B magnets using the electrophoretic deposition method. After TbF3 diffusion, the coercivity increased significantly by 9.9 kOe and microstructural analysis suggested that Tb favored the formation of the (Nd, Tb)2Fe14B shell phase in the outer region of the matrix grains. The first magnetization reversal and the dynamic successive domain propagation process were detected with a magneto-optical Kerr microscope. For the TbF3-diffused magnet, the magnetization reversal appeared at a larger applied field and the degree of simultaneous magnetization reversal decreased compared with an annealed magnet. During demagnetization after full magnetization, the occurrence of domain wall motion (DWM) in the reproduced multi-domain regions was observed by the step method. The maximum polarization change resulting from the reproduced DWM was inversely related to the coercivity. The increased coercivity for the diffused magnet was mainly attributed to the more difficult nucleation of the magnetic reversed region owing to the improved magneto-crystalline anisotropy field as a result of Tb diffusion.

Identification of the domains within the N2A region of titin that regulate binding to actin

Titin, the largest muscle protein, plays an important role in passive tension, sarcomeric integrity and cell signaling within the muscle. Recent work has also highlighted a role for titin in active muscle and the N2A region found in skeletal muscle titin and in some isoforms of cardiac titin has been linked to this function. The N2A region is a multi-domain region composed of four immunoglobulin domains (I80–I83) and a disordered region called the insertion sequence. Previously, our lab has shown that the N2A region binds F-actin in a calcium dependent manner, but it is not known which domains within this region are critical for this binding to occur. In this work, we have used co-sedimentation to demonstrate that only constructs containing the I80 domain are capable of binding F-actin. In addition, binding was only observed in constructs containing at least 3 immunoglobulin domains suggesting a length-dependence to binding. Finally, the calcium-dependence of N2A binding is lost when I83 is not present, consistent with the calcium stabilization that has been reported for this domain. Based on these results, we propose that I80 is critical for initiating binding to F-actin and that I83 is responsible for the calcium dependence.

Regulation of the EphA2 receptor intracellular region by phosphomimetic negative charges in the kinase-SAM linker

Eph receptor tyrosine kinases play a key role in cell-cell communication. Lack of structural information on the entire multi-domain intracellular region of any Eph receptor has hindered understanding of their signaling mechanisms. Here, we use integrative structural biology to investigate the structure and dynamics of the EphA2 intracellular region. EphA2 promotes cancer malignancy through a poorly understood non-canonical form of signaling involving serine/threonine phosphorylation of the linker connecting its kinase and SAM domains. We show that accumulation of multiple linker negative charges, mimicking phosphorylation, induces cooperative changes in the EphA2 intracellular region from more closed to more extended conformations and perturbs the EphA2 juxtamembrane segment and kinase domain. In cells, linker negative charges promote EphA2 oligomerization. We also identify multiple kinases catalyzing linker phosphorylation. Our findings suggest multiple effects of linker phosphorylation on EphA2 signaling and imply that coordination of different kinases is necessary to promote EphA2 non-canonical signaling.

Fuzzy Bit-Plane-Dependence Region Competition

This paper presents a novel variational model based on fuzzy region competition and statistical image variation modeling for image segmentation. In the energy functional of the proposed model, each region is characterized by the pixel-level color feature and region-level spatial/frequency information extracted from various image domains, which are modeled by the windowed bit-plane-dependence probability models. To efficiently minimize the energy functional, we apply an alternating minimization procedure with the use of Chambolle’s fast duality projection algorithm, where the closed-form solutions of the energy functional are obtained. Our method gives soft segmentation result via the fuzzy membership function, and moreover, the use of multi-domain statistical region characterization provides additional information that can enhance the segmentation accuracy. Experimental results indicate that the proposed method has a superior performance and outperforms the current state-of-the-art superpixel-based and deep-learning-based approaches.

Effect of heat treatment on structural and magnetic properties of Li–Ni ferrite prepared via sol–gel auto-combustion method

Nanocrystalline Li0.35Ni0.3Fe2.35O4 ferrites were prepared at different annealing temperatures by sol–gel auto-combustion method. The effects of the annealing temperature on the structure and magnetic properties of the synthesized Li–Ni ferrites were characterized by X-ray diffraction (XRD), scanning electron microscopy, Fourier transform infrared spectra and Vibrating Sample Magnetometer, and X-ray photoelectron spectrometer. Rietveld refinement of the XRD data confirmed the occurrence of phase transition from α-spinel to β-spinel, from which the ideal cation occupation and lattice parameter can be obtained. The grain size increased significantly with annealing temperature. The variation of saturation magnetization can be well explained in terms of the occupation of ions in tetrahedron and octahedron. The coercivity initially increased and later decreased significantly from 115 to 37 Oe with the increase of annealed temperature which could be attributed the fact that the 600 °C-annealed grain size is close to transition size from single- to multi-domain region.

Leptospiral Immunoglobulin-Like Domain Proteins: Roles in Virulence and Immunity.

The virulence mechanisms required for infection and evasion of immunity by pathogenic Leptospira species remain poorly understood. A number of L. interrogans surface proteins have been discovered, lying at the interface between the pathogen and host. Among these proteins, the functional properties of the Lig (leptospiral immunoglobulin-like domain) proteins have been examined most thoroughly. LigA, LigB, and LigC contain a series of, 13, 12, and 12 closely related domains, respectively, each containing a bacterial immunoglobulin (Big) -like fold. The multidomain region forms a mostly elongated structure that exposes a large surface area. Leptospires wield the Lig proteins to promote interactions with a range of specific host proteins, including those that aid evasion of innate immune mechanisms. These diverse binding events mediate adhesion of L. interrogans to the extracellular matrix, inhibit hemostasis, and inactivate key complement proteins. These interactions may help L. interrogans overcome the physical, hematological, and immunological barriers that would otherwise prevent the spirochete from establishing a systemic infection. Despite significant differences in the affinities of the LigA and LigB proteins for host targets, their functions overlap during lethal infection of hamsters; virulence is lost only when both ligA and ligB transcription is knocked down simultaneously. Lig proteins have been shown to be promising vaccine antigens through evaluation of a variety of different adjuvant strategies. This review serves to summarize current knowledge of Lig protein roles in virulence and immunity and to identify directions needed to better understand the precise functions of the Lig proteins during infection.

Cr content-dependent modification of structural, magnetic properties and bandgap in green synthesized Co–Cr nano-ferrites

Honey green synthesis of CoCrxFe2−xO4 (x = 0.0 − 1.0) ferrites with increasing Cr content was done by sol-gel auto-combustion method, without any post-preparation thermal treatment. Nanocrystalline nature (grain diameter range between 12.2 nm and 27.9 nm) of the studied samples is confirmed by X-ray diffraction (XRD) data. Observed modification of magnetic properties can be understood in terms of Cr addition induced changes in degree of inversion, modification of disorder affecting A–A, A–B, B–B interaction, re-distribution of cations on A, B sites in the spinel lattice. Grain size (D)-dependent coercivity (Hc) shows that the studied samples lie in the region with overlap between single- and multi-domain regions. Achieved magnetic properties in the studied honey green synthesized samples have significance for self-regulating hyperthermia applications. Results as well reveal modification of bandgap, and would be of use for applications, where minor bandgap tuning is required. Antistructure modeling provides information on the types of surface-active centers.

HspB1 phosphorylation regulates its intramolecular dynamics and mechanosensitive molecular chaperone interaction with filamin C.

Mechanical force-induced conformational changes in proteins underpin a variety of physiological functions, typified in muscle contractile machinery. Mutations in the actin-binding protein filamin C (FLNC) are linked to musculoskeletal pathologies characterized by altered biomechanical properties and sometimes aggregates. HspB1, an abundant molecular chaperone, is prevalent in striated muscle where it is phosphorylated in response to cues including mechanical stress. We report the interaction and up-regulation of both proteins in three mouse models of biomechanical stress, with HspB1 being phosphorylated and FLNC being localized to load-bearing sites. We show how phosphorylation leads to increased exposure of the residues surrounding the HspB1 phosphosite, facilitating their binding to a compact multidomain region of FLNC proposed to have mechanosensing functions. Steered unfolding of FLNC reveals that its extension trajectory is modulated by the phosphorylated region of HspB1. This may represent a posttranslationally regulated chaperone-client protection mechanism targeting over-extension during mechanical stress.

Crystal Structure and Magnetic Properties of Magnesium Ferrite (MgFe2O4) Nanoparticles Synthesized by Coprecipitation Method

MgFe2O4 has been successfully synthesized by coprecipitation method. The Precursors used are MgCl2.6H2O (magnesium chloride hexa-hydrate, Mr = 203.205 g/mol) and FeCl3. 6H2O (ferric chloride hexa-hydrate, Mr = 270.19 g/mol) and NaOH (sodium hydroxide, Mr = 39.99 g/mol) as coprecipitant. This synthesis process was done by varying the NaOH concentration, the synthesis temperature and the stirring duration. XRD analysis results showed that the grain size increases with synthesis temperature and decreases with the increase in the concentration of NaOH and the duration of stirring. The smallest grain size is 2.1 nm and the largest grain size is 10 nm. Analysis of magnetic properties MgFe2O4 by Vibrating Sample Magnetometer (VSM) showed that nanoparticles MgFe2O4 can be assumed in multidomain region, with relationships. Sample with the smallest particle size 2.1 nm, has highest Hc value 133.9 Oe. The maximum magnetization at H = 15 kOe and remanent magnetization (Mr) increase with the degree of crystallinity of the sample. Although there is also the effect of the presence of hematite phase (α-Fe2O3) and the grain size. Magnesium ferrite magnetic nanoparticles (MgFe2O4) has great potential to be applied as adsorption, sensors, drug delivery, semiconductor materials and other magnetic technology

Polarization reversal in lithium niobate using electrodes of dendrite shape created by drying drops of protein-NaCl solution

ABSTRACTWe present a new technique of fabricating the extended-shape electrodes with dendrite channels for formation of the multi-domain state in lithium niobate (LN). The dendrite structure of NaCl created by drying drops of protein-NaCl solution was used for electrode patterning. The linear dependence of the dendrite sizes on drying time has been revealed. The high resolution visualization of the static domain structures created using dendrite electrodes allowed revealing formation of quasi-periodic domain arrays. The produced LN plates with multi-domain regions will be used for manufacturing of the pyroelectric field generators with focusing effect for bioprinting.

Superconducting gap anisotropy sensitive to nematic domains in FeSe

The structure of the superconducting gap in unconventional superconductors holds a key to understand the momentum-dependent pairing interactions. In superconducting FeSe, there have been controversial results reporting nodal and nodeless gap structures, raising a fundamental issue of pairing mechanisms of iron-based superconductivity. Here, by utilizing polarization-dependent laser-excited angle-resolved photoemission spectroscopy, we report a detailed momentum dependence of the gap in single- and multi-domain regions of orthorhombic FeSe crystals. We confirm that the superconducting gap has a twofold in-plane anisotropy, associated with the nematicity due to orbital ordering. In twinned regions, we clearly find finite gap minima near the vertices of the major axis of the elliptical zone-centered Fermi surface, indicating a nodeless state. In contrast, the single-domain gap drops steeply to zero in a narrow angle range, evidencing for nascent nodes. Such unusual node lifting in multi-domain regions can be explained by the nematicity-induced time-reversal symmetry breaking near the twin boundaries.

Reproduced multi-domain regions during demagnetization in Nd2Fe14B sintered magnets with different average grain sizes

We prepared five Nd2Fe14B sintered magnets with similar saturation polarizations (Js) of 1.38–1.43 T and anisotropy fields (Ha) of 6.76–8.52 T, but different grain sizes (DAV) of 3.1–8.4 μm in diameter and obviously different coercivities (μ0Hc) of 0.8–1.6 T. The observed difference in coercivity could not be explained by the Kronmüller equation, because of the similar Ha values and similar chemical compositions and microstructures resulting from similar preparation method except DAV. The Hc values themselves, however, are inversely proportional to DAV. During demagnetization after magnetization in a 5 T pulse field, domain wall motion (DWM) was observed except in the sample with μ0Hc = 1.6 T by using our step method. The DWM was also confirmed by susceptibility measurements using a custom-built vibrating sample magnetometer, and DWM was generated in the reproduced multi-domain regions (RMDR) during demagnetization. The magnitude of DWM as a polarization change in the RMDR was inversely proportional to the coercivities of the samples. Therefore, it should be considered that the propagation of the nucleated region through the grain boundary, which corresponds to the expansion process in previous studies, was different caused by, first, the difference in DAV, and, second, in grain boundary state which was varied by difference in final annealing temperature.

Genetic Structure and Molecular Variability Analysis of Citrus sudden death-associated virus Isolates from Infected Plants Grown in Brazil.

Citrus sudden death-associated virus (CSDaV) is a monopartite positive-sense single-stranded RNA virus that was suggested to be associated with citrus sudden death (CSD) disease in Brazil. Here, we report the first study of the genetic structure and molecular variability among 31 CSDaV isolates collected from both symptomatic and asymptomatic trees in CSD-affected areas. Analyses of partial nucleotide sequences of five domains of the CSDaV genomic RNA, including those encoding for the methyltransferase, the multi-domain region (MDR), the helicase, the RNA-dependent RNA polymerase and the coat protein, showed that the MDR coding region was the most diverse region assessed here, and a possible association between this region and virus adaption to different host or plant tissues is considered. Overall, the nucleotide diversity (π) was low for CSDaV isolates, but the phylogenetic analyses revealed the predominance of two main groups, one of which showed a higher association with CSD-symptomatic plants. Isolates obtained from CSD-symptomatic plants, compared to those obtained from asymptomatic plants, showed higher nucleotide diversity, nonsynonymous and synonymous substitution rates and number of amino acid changes on the coding regions located closer to the 5’ end region of the genomic RNA. This work provides new insights into the genetic diversity of the CSDaV, giving support for further epidemiological studies.

Magnetic study of a mixture of magnetite and metallic iron in indoor dust samples

Magnetite in mixture with metallic iron in indoor dust samples was examined using several magnetic analyses, thermomagnetic curves of the magnetic susceptibility and the induced magnetization vs. temperature, hysteresis loops, and first-order reversal curves. The study of the magnetic properties was supplemented by the analysis of chemical elements and electron microscopic observation. The metallic iron in the mixture affects the values of hysteresis parameters, decreasing coercivity (Bc) and increasing saturation magnetization (Ms), and it is responsible for the magnetic enhancement of magnetic susceptibility. The thermomagnetic curves show several distinct features: the first Curie temperature of magnetite, the second one (∼764 °C) of iron, and the rapid decrease on the heating curves (between 600 and 750 °C) caused by the oxidation of iron to magnetite. Two magnetochemical processes appear during the thermal treatment of indoor dust: the oxidation of iron to magnetite and the neo-formation of magnetite as a result of chemical transformation of non-magnetic minerals. The shift of the hysteresis parameter ratios from the multi-domain (MD) region towards the single-domain (SD) region on the Day-Dunlop plot is controlled by the oxidation of iron in the thermally induced process and the grain size of the new formed magnetite. The magnetic properties of indoor dust are a potential indicator of indoor air pollution. Elemental iron plays an important role in the development of inflammation in humans via oxidative stress, so that the presence of metallic Fe in indoor dust can affect human health.

Optical Characterization and Lasing in Three-Dimensional Opal-Structures

The lasing properties of dye-permeated opal pyramidal structures are compared with the lasing properties of opal films. The opal-structures studied were made by sedimentation of micro-spheres and by sol-gel inversion of the direct-opals. Forced-sedimentation by centrifugation inside wet-etched pyramidal pits on silicon surfaces was used to improve the structural quality of the direct-opal structures. Single crystalline pyramids with the base length of ∼ 100 µm were formed by centrifuged sedimentation. The lasing of dyes in the well-ordered crystalline and poly-crystalline structures showed a distinct multi-modal spectrum. Gain via a distributed feedback was responsible for the lasing since the photonic band gap was negligible in a low refractive index contrast medium; the indices of silica and ethylene glycol are 1.46 and 1.42, respectively. A disordered lasing spectrum was observed from opal films with structural defects and multi-domain regions. The three dimensional structural quality of the structures was assessed by in situ optical diffraction and confocal fluorescence. A correlation between the lasing spectrum and the three-dimensional structural quality was established. Lasing threshold of a sulforhodamine dye in a silica opal was controlled via Forster mechanism by addition of a donor rhodamine 6G dye. The lasing spectrum had a well-ordered modal structure which was spectrally stable at different excitation powers. The sharp lasing threshold characterized by a spontaneous emission coupling ratio β ' 10−2 was obtained.

Function of polyketide synthases from the SAXS structure of a complete module

The modular polyketide synthases (PKS), common to many bacterial antibiotic-producers, are huge multienzyme, multidomain systems which can be likened to molecular assembly lines.1 An understanding of the structural and mechanistic aspects which underpin interdomain cooperation during biosynthesis by modular PKS is crucial to ongoing efforts to re-engineer these systems for the production of novel compounds of medicinal value.2 Previous attempts to solve the structures of PKS modules by X-ray crystallography have been unsuccessful, likely due to the high, inherent flexibility of the multienzymes. Here, we have employed an alternative technique, small-angle X-ray scattering (SAXS), in combination with NMR structure elucidation and homology modelling of individual domains, to obtain the first low-resolution structural data on an entire apo PKS module. The model system comprises a multidomain region of the virginiamycin M1 PKS from Streptomyces virginiae, a target of relevance for its involvement in production of the commercial antibiotic dalfopristin. The investigated region, which comprises a ketosynthase (KS) and two consecutive acyl carrier protein (ACP) domains, interacts with a wide range of protein partners, including notably, a complex of discrete enzymes responsible for β-methylation of the polyketide, and the N-terminus of the downstream PKS protein, VirFG.3 In our solved structure (Fig. 1), the homodimeric KS, which is flanked by well-folded linker regions, occupies the center of the module. While the first ACP is located close to the KS, the second is situated at the end of a flexible linker, and mobile. Taken together, these data provide a physical explanation for the functional non-equivalence previously observed for certain tandem ACPs of this class of PKS. Furthermore, the overall open shape of the module renders the second ACP highly accessible, which may be critical for its interaction with its multiple in trans catalytic partners. Finally, our analysis redefines the function of a putative dimerization motif of tandem ACPs as a docking domain, suggesting that the module likely adopts a more closed form in order to affect transfer of the chain extension intermediate to the subsequent module.

Structural, IR, and Magnetic Studies of Annealed Li-Ferrite Nanoparticles

Nanoparticles of spinel Li-ferrite, Li0.5Fe2.5O4, were prepared by sol-gel autocombustion technique and annealed at different temperatures (Ta = 673, 873, and 1073 K), i.e., at relatively low annealing temperatures to control the crystallite size. The saturation magnetization (Ms) increased, and the surface area decreased by increasing the crystallite size, while Curie temperature (TC) remained almost constant. The critical crystallite size (Ds), 74 nm, which corresponds to a maximum value of coercivity was determined. Samples with crystallite sizes ≤ Ds had low initial permeability μi, while the other samples lying in the multidomain region showed very high μi values indicating a reversible domain wall displacement mechanism. Hence, the crystallite size plays an important role in changing the physical and magnetic properties of Li-ferrite.

Andreev Current and Subgap Conductance of Spin-Valve SFF Structures

The Andreev current and the subgap conductance in a superconductor/insulator/ferromagnet (SIF) structure in the presence of a small spin-splitting field show novel interesting features (Ozaeta et al. in Phys. Rev. B 86:060509(R), 2012). For example, the Andreev current at zero temperature can be enhanced by a spin-splitting field h, smaller than the superconducting gap Δ, as has been recently reported by the authors. Also at finite temperatures, the Andreev current has a peak for values of the spin-splitting field close to the superconducting gap, h≈Δ. Finally, the differential subgap conductance at low temperatures shows a peak at the bias voltage eV=h. In this paper, we investigate the Andreev current and the subgap conductance in SFF structures with arbitrary direction of magnetization of the F layers. We show that all the aforementioned features occur now at the value of the “effective field”, which is the field acting on the Cooper pairs in the multi-domain ferromagnetic region, averaged over the decay length of the superconducting condensate into a ferromagnet. We also briefly discuss the heat transport and electron cooling in the considered structures.