Isotropic Orientation Research Articles

Investigating Longitudinal Continuity of Persistent White Matter Alterations in Sport-related Concussion Using Individualized Analyses

Background: Sport-related concussion (SRC) has been shown to lead to acute and long-term alterations in white matter (WM) organization. The Centers for Disease Control estimates around 283,000 children each year seek medical attention for SRC/recreation-related traumatic brain injury. However, literature on subject-specific longitudinal WM abnormalities in SRC is limited.Purpose: Given the heterogeneous nature of SRC on WM microstructure, the goal of this study is to investigate the longitudinal continuity of persistent white matter alterations using a subject-specific approach.
 Methods: MRI is a non-invasive imaging modality suitable for detecting neuropathophysiological changes after SRC. Compared to conventional anatomical MRI, using diffusion MRI to probe WM microarchitecture may provide additional sensitivity.The diffusion MRI data from 50 participants were obtained from the CARE consortium, a prospective multisite study examining the natural history of concussion. Each concussed athlete underwent MRI scan at three time points: (1) 24-48 hours after concussion, (2) asymptomatic state, and (3) 7-days after returned to play. Diffusion tensor imaging (DTI) and neurite orientation dispersion and density imaging (NODDI) metrics were computed and Z-scored based on a normal distribution template created from non-contact sport controls. Potential WM alterations indicated by extreme deviations of Z-score maps were calculated for all diffusion metrics in each concussed participant and time point.
 Results: WM alterations persistent across all three timepoints manifested in 76%, 62%, and 82% of the participants as quantified by increases of mean, axial, and radial diffusivity, respectively. 58% of the participants had fractional anisotropy decreases. For NODDI metrics, 82% and 86% of the participants showed increases of isotropic volume fraction and orientation dispersion index, respectively.
 Conclusion: This study demonstrated that by applying subject-specific analysis, extreme Z-score voxels can be identified across time in the same or spatially proximal brain regions suggesting persistent WM abnormalities beyond apparent clinical recovery.

Six-Dimensional Single-Molecule Imaging with Isotropic Resolution using a Multi-View Reflector Microscope.

Imaging both the positions and orientations of single fluorophores, termed single-molecule orientation-localisation microscopy, is a powerful tool to study biochemical processes. However, the limited photon budget associated with single-molecule fluorescence makes high-dimensional imaging with isotropic, nanoscale spatial resolution a formidable challenge. Here, we realise a radially and azimuthally polarized multi-view reflector (raMVR) microscope for the imaging of the 3D positions and 3D orientations of single molecules, with precision of 10.9 nm and 2.0° over a 1.5 μm depth range. The raMVR microscope achieves 6D super-resolution imaging of Nile red (NR) molecules transiently bound to lipid-coated spheres, accurately resolving their spherical morphology despite refractive-index mismatch. By observing the rotational dynamics of NR, raMVR images also resolve the infiltration of lipid membranes by amyloid-beta oligomers without covalent labelling. Finally, we demonstrate 6D imaging of cell membranes, where the orientations of specific fluorophores reveal heterogeneity in membrane fluidity. With its nearly isotropic 3D spatial resolution and orientation measurement precision, we expect the raMVR microscope to enable 6D imaging of molecular dynamics within biological and chemical systems with exceptional detail.

The mystery in Gaia DR3 triples: occurrence rates, orientations, and eccentricities of wide tertiaries around close binaries

ABSTRACT The formation of close binaries has been an open question for decades. A large fraction of close binaries are in triple systems, suggesting that their formation may be associated with the Kozai–Lidov mechanism. However, this picture remains under debate because the configurations of many observed triples are unlikely to trigger the Kozai–Lidov mechanism. In this paper, we use the close binary samples, including eclipsing, spectroscopic, and astrometric binaries, from Gaia Data Release 3 to investigate the mysterious connection between inner binaries and their wide tertiaries. We show that the wide tertiary (at 103–104 au) fraction increases with decreasing orbital periods of the inner binaries. The wide tertiary fraction of eclipsing binaries (a median orbital period of 0.41 d) is 2.33 ± 0.11 times higher than the field wide binary fraction. Furthermore, there is a tentative excess at ∼104 au for tertiaries of eclipsing binaries. Using the v − r angle distributions, we show that wide tertiaries have isotropic orientations with respect to the inner binaries, and the co-planar orbits can be ruled out. The inferred eccentricity distribution of wide tertiaries is consistent (<1σ) with being thermal (f(e) ∝ e), similar to wide binaries at similar separations. The dynamical unfolding scenario is disfavoured because it predicts highly eccentric wide tertiaries, which is inconsistent with our findings. For the Kozai–Lidov mechanism to be effective for wide tertiaries at >103 au, the initial separations of the inner binaries need to be >3 au. Future theoretical investigations are needed to explore the parameter space at these large initial separations and large tertiary separations.

Eco-friendly and scalable strategy to design electrically insulating boron nitride/polymer composites with high through-plane thermal conductivity

Hexagonal boron nitride (h-BN)/epoxy composites with high through-plane thermal conductivity were successfully fabricated using core-shell h-BN/epoxy (e-BN) microspheres which were synthesized using a simple one-pot emulsion polymerization process in an eco-friendly aqueous medium. e-BN microspheres covered with self-assembled h-BN flakes (1 μm lateral size) on the surface of the epoxy microspheres facilitated the effective alignment and distribution of the flakes in the epoxy matrix. The e-BN/BN/epoxy composites fabricated by mixing the e-BN microspheres with the h-BN flakes (17 μm lateral size) exhibited far higher through-plane thermal conductivity than the BN/epoxy composites (without e-BN microspheres) with the same h-BN flake content. In particular, the e-BN/BN/epoxy composite with 50 wt% (33 vol%) h-BN flakes exhibited excellent through-plane thermal conductivity of 4.27 W/mK, which was approximately 3.7 times that of the BN/epoxy composite (1.17 W/mK), owing to a more random or isotropic orientation of the h-BN flakes in the e-BN/BN/epoxy composite. The experimentally measured thermal conductivities were well matched to those obtained from micromechanical estimations using the modified Mori-Tanaka method. We expect that this eco-friendly and scalable fabrication process of e-BN microspheres and e-BN/BN/epoxy composites could provide an innovative strategy for manufacturing electrically insulating polymer composites with high through-plane thermal conductivity.

Exceeding 30 % External Quantum Efficiency in Non-doped OLEDs Utilizing Solution Processable TADF Emitters with High Horizontal Dipole Orientation via Anchoring Strategy.

Strategies to enhance the ratio of the molecular horizontal emitting dipole orientation (Θ∥ ) for thermally activated delayed fluorescence (TADF) emitters have unlocked the full potential of efficiencies for the evaporated devices, which, however, remain elusive for the solution-processed ones. Here, a strategic molecular design for solution processable TADF emitters featuring high Θ∥ s is proposed by attaching flexible chains ended with bipolar 9,9'-spirobi[fluorene] subunits as anchoring groups onto TADF emitting core. It's unveiled that the anchoring groups not only enhance the horizontal orientation via enlarging molecular planarity, but also benefit the high photoluminescence in pristine films. The corresponding non-doped solution processable OLEDs substantiate an unprecedented maximum external quantum efficiency (EQEmax )>30 %. Meanwhile, combining these compounds as TADF sensitizers, and multiple resonance final emitter, solution-processed OLEDs achieve an EQEmax of 25.6 % with a narrow full width at half maximum of 29 nm.

Elastic wave velocities in a granitic geothermal reservoir

AbstractGeothermal resources have potential for providing cost‐effective and sustainable energy. Monitoring of production‐induced changes in geothermal reservoirs using seismic waves requires understanding of the elastic properties of the rock and how they change due to injection of fluids and opening and closing of natural and hydraulic fractures. P‐ and S‐wave velocities measured in a granitic geothermal reservoir using sonic logging are systematically lower than those predicted using the composition of the rock. Cracks may occur in granitic rocks from tectonic stresses and from the thermal expansion mismatch between differently oriented anisotropic crystals. An isotropic orientation distribution of microcracks causes a significant reduction in both the P‐ and S‐velocities, consistent with the observed sonic P‐ and S‐velocities. Vertical fractures cause a difference in the velocity of vertically propagating shear waves polarized parallel and perpendicular to the fractures. An assumption that the lower measured velocities are caused by the presence of vertical fractures is inconsistent with the sonic data. This is because vertical fractures cause a decrease in slow S‐wave velocity that greatly exceeds the decrease in P‐wave velocity, in contrast to the observed data. The growth of vertical fractures in the geothermal reservoir may be monitored using the difference in velocity of the fast and slow shear waves, while the change in P‐velocity in a crossplot of measured P‐ and slow S‐velocities is useful for estimating the ratio of the normal‐to‐shear compliance of the fractures.

Preparation of graphene oxide-silica nanohybrid/poly(lactic acid) biaxially oriented films with enhanced mechanical properties

Poly(lactic acid) (PLA) biaxially stretched films and graphene oxide-silica nanohybrids (GO-SiO2)/PLA nanocomposite biaxially stretched films (PGSi) with different stretching ratios were prepared by simultaneous biaxial stretching. The structural changes during biaxial stretching have a direct impact on the properties of the biaxially stretched films. Therefore, this work mainly studies the effect of the presence of filler (i.e., GO-SiO2) on the structural evolution of PLA during biaxial stretching, and establishes a bridge between structural changes and property changes. Through wide-angle X-ray diffraction (WAXD) and atomic force microscopy (AFM), it was found that GO-SiO2 facilitates the isotropic orientation of molecular chains during biaxial stretching and attenuates the degree of preferred orientation. As a result, the mechanical properties of PGSi biaxially oriented films are inferior to those of PLA biaxially oriented films. However, the synergistic effect of the excellent barrier property of GO-SiO2 and biaxial stretching make the barrier property of PGSi biaxially stretched films even better. In addition, when the tensile force is stronger than the interfacial force between GO-SiO2 and PLA, GO-SiO2 will precipitate out of PLA under the condition of a large stretching ratio, resulting in the generation of defects, which is not conducive to the improvement of PLA performance.

Imaging the Infection Cycle of T7 at the Single Virion Level.

T7 phages are E. coli-infecting viruses that find and invade their target with high specificity and efficiency. The exact molecular mechanisms of the T7 infection cycle are yet unclear. As the infection involves mechanical events, single-particle methods are to be employed to alleviate the problems of ensemble averaging. Here we used TIRF microscopy to uncover the spatial dynamics of the target recognition and binding by individual T7 phage particles. In the initial phase, T7 virions bound reversibly to the bacterial membrane via two-dimensional diffusive exploration. Stable bacteriophage anchoring was achieved by tail-fiber complex to receptor binding which could be observed in detail by atomic force microscopy (AFM) under aqueous buffer conditions. The six anchored fibers of a given T7 phage-displayed isotropic spatial orientation. The viral infection led to the onset of an irreversible structural program in the host which occurred in three distinct steps. First, bacterial cell surface roughness, as monitored by AFM, increased progressively. Second, membrane blebs formed on the minute time scale (average ~5 min) as observed by phase-contrast microscopy. Finally, the host cell was lysed in a violent and explosive process that was followed by the quick release and dispersion of the phage progeny. DNA ejection from T7 could be evoked in vitro by photothermal excitation, which revealed that genome release is mechanically controlled to prevent premature delivery of host-lysis genes. The single-particle approach employed here thus provided an unprecedented insight into the details of the complete viral cycle.

Polar alignment of a massive retrograde circumbinary disc around an eccentric binary

ABSTRACT A test particle orbit around an eccentric binary has two stationary states in which there is no nodal precession: coplanar and polar. Nodal precession of a misaligned test particle orbit centres on one of these stationary states. A low-mass circumbinary disc undergoes the same precession and moves towards one of these states through dissipation within the disc. For a massive particle orbit, the stationary polar alignment occurs at an inclination less than 90°, which is the prograde-polar stationary inclination. A sufficiently high angular momentum particle has an additional higher inclination stationary state, the retrograde-polar stationary inclination. Misaligned particle orbits close to the retrograde-polar stationary inclination are not nested like the orbits close to the other stationary points. We investigate the evolution of a gas disc that begins close to the retrograde-polar stationary inclination. With hydrodynamical disc simulations, we find that the disc moves through the unnested crescent shape precession orbits and eventually moves towards the prograde-polar stationary inclination, thus increasing the parameter space over which circumbinary discs move towards polar alignment. If protoplanetary discs form with an isotropic orientation relative to the binary orbit, then polar discs may be more common than coplanar discs around eccentric binaries, even for massive discs. This has implications for the alignment of circumbinary planets.

A new semi-analytical method for estimation of anisotropic hydraulic conductivity of three-dimensional fractured rock masses

• A semi-analytical method based on Snow's peameability tensor model is proposed. • The new method can predict anisotropic hydraulic conductivity of complex DFNs. • The new method can deal with engineering level problems with low computational cost. The hydraulic characteristics of rock masses usually show strong anisotropy due to the existence of oriented structure planes. A new semi-analytical method is proposed for estimation of the anisotropic hydraulic conductivity of fractured rock masses based on the discrete fracture network (DFN) description and the Snow’s model ( Snow, 1969 ). In this method, the number of intersections on a fracture is a key parameter to construct correction coefficient, which are used to adjust the contribution of each individual fracture to the macro hydraulic conductivity tensor. In this way, the initial Snow’s model is extended from infinite connectivity conditions to finite connectivity conditions. The correction coefficient is determined by using a mathematical optimization method in the condition of networks following isotropic orientation distribution and polydisperse size distribution. Then, the new method is applied to estimate the directional hydraulic conductivity of engineering rock masses with complex anisotropic oriented fracture networks. The results show that the directional hydraulic conductivities predicted by the proposed semi-analytical method are in good agreement with the referential numerical results. The proposed semi-analytical model can be used to predict the anisotropic hydraulic conductivity of complex fractured rock masses with less processing time and lower memory requirements than numerical models.

Thermodynamic perturbation theory coefficients for hard spherocylinders and cylinders

Thermodynamic perturbation theories are indispensable in the development of equations of state based on Statistical Mechanics. Recently, a new statistical thermodynamic model has been proposed in which molecules are represented as cylindrically symmetric hard bodies (ellipsoids of revolution, spherocylinders, and cylinders) interacting with identical neighboring molecules through a spherically symmetric square-well potential. This novel equation of state embeds at least two approximations to the Onsager’s second virial theory: one restrains the equation of state to systems with an isotropic (disordered) orientation distribution, while the other decouples the translational and orientational degrees of freedom, being only valid at low densities. Using canonical Monte Carlo simulations, we investigated the feasibility of such approximations by determining the uniaxial nematic order parameter of the systems and calculating the first- and second-order perturbation coefficients of the high-temperature series expansion (HTSE) of the Helmholtz free energy. Our results indicate that both approximations are reasonable for a certain range of packing fractions and molecular anisotropies. We have also calculated the full Helmholtz free energy of the perturbed system, which can be used for determining high-order perturbation terms to improve the predictive capability of the equation of state.

Structural evolution and related physical properties of machine direction oriented poly(butylene succinate-co-adipate) films

This study sheds light on the microstructural change of uniaxially oriented poly(butylene succinate-co-adipate) (PBSA) copolymer, and the consequent gas permeabilities, as well as tensile and optical properties. Uniaxial stretching at 62 °C takes place by means of a machine direction orientation (MDO) with varied draw ratios and annealing near the melting temperature. The PBSA precursor sheet favorably melt-crystallizes in the form of α-PBS crystals with isotropic in-plane orientation. MDO-PBSA films with and without annealing exhibit preferential orientation of the α-PBS crystal parallel to the stretching direction (MD), with an increased degree of crystallinity according to the increased draw ratio and applied annealing. This was evident from two-dimensional wide-angle X-ray diffraction patterns and X-ray diffraction profiles. Additionally, MDO stretching above the crystallization temperature simultaneously induces rigid amorphous fraction, in particular, by a high draw ratio (5 × ) and chain relaxation during annealing near the melting temperature. From the determined Herman's orientation function, the c-axis of the α-PBS crystal is parallel to the MD, thereby resulting in decreased diffusion path tortuosity. Consequently, oxygen and water vapor permeation are promoted. Furthermore, Young's modulus and tensile strength of MDO-PBSA films drastically increase with high ductility, and are approximately two and four times higher than those of non-oriented PBSA, respectively. MDO-PBSA films exhibit high clarities above 94% while yielding low haze values.

Evidence for widely-separated binary asteroids recorded by craters on Mars

Over the last decades, a significant number of small asteroids (diameter <10km) having a satellite in orbit around them have been discovered. This population of binary asteroids has very specific properties (secondary-to-primary diameter ratio of about 0.3, semi-major axis to primary diameter ratio around 2 and an obliquity of the system close to either 0∘ or 180∘) pointing at formation by YORP-induced spin-up and rotational fission. When impacting the surface of terrestrial bodies, those exotic objects lead to the formation of binary craters, exhibiting various morphologies depending on the configuration of the system at the moment of the impact. Planetary surfaces constitutes therefore the best (if not the only one) record of binary asteroid population through time. In contrast to the Moon or Mercury, a large fraction of impact craters on Mars exhibits thick ejecta layers due to the presence of volatile material at the moment of the impact (e.g., water ice). The martian surface represents thus the ideal case to survey for the existence of binary craters, as the ejecta morphology can attest of a synchronous impact. From a survey of 87% of Mars surface, we identify 150 binary craters (0.5% of the total), likely formed by the impact of binary asteroids. The properties of these craters contrast with those of the population of binary asteroids: size ratio close to unity, large separation, and isotropic orientation on the surface. We run numerical simulations of impacts to test whether tidal effects on the impact trajectory can explain these discrepancies. Our results suggest that a population of similarly-sized and well-separated binary asteroids with non-zero obliquity remains to be observed.

Photon efficient orientation estimation using polarization modulation in single-molecule localization microscopy.

Combining orientation estimation with localization microscopy opens up the possibility to analyze the underlying orientation of biomolecules on the nanometer scale. Inspired by the recent improvement of the localization precision by shifting excitation patterns (MINFLUX, SIMFLUX), we have adapted the idea towards the modulation of excitation polarization to enhance the orientation precision. For this modality two modes are analyzed: i) normally incident excitation with three polarization steps to retrieve the in-plane angle of emitters and ii) obliquely incident excitation with p-polarization with five different azimuthal angles of incidence to retrieve the full orientation. Firstly, we present a theoretical study of the lower precision limit with a Cramér-Rao bound for these modes. For the oblique incidence mode we find a favorable isotropic orientation precision for all molecular orientations if the polar angle of incidence is equal to degrees. Secondly, a simulation study is performed to assess the performance for low signal-to-background ratios and how inaccurate illumination polarization angles affect the outcome. We show that a precision, at the Cramér-Rao bound (CRB) limit, of just 2.4 and 1.6 degrees in the azimuthal and polar angles can be achieved with only 1000 detected signal photons and 10 background photons per pixel (about twice better than reported earlier). Lastly, the alignment and calibration of an optical microscope with polarization control is described in detail. With this microscope a proof-of-principle experiment is carried out, demonstrating an experimental in-plane precision close to the CRB limit for signal photon counts ranging from 400 to 10,000.

Orientation anisotropies in macaque visual areas

In mammals, a larger number of neurons in V1 are devoted to cardinal (horizontal and vertical) orientations than to oblique orientations. However, electrophysiological results from the macaque monkey visual cortex are controversial. Both isotropic and anisotropic orientation distributions have been reported. It is also unclear whether different visual areas along the visual hierarchy have different orientation anisotropies. We analyzed orientation maps in a large set of intrinsic signal optical imaging data and found that both V1 and V4 exhibited significant orientation anisotropies. However, their overrepresented orientations were very different: in V1, both cardinal and radial orientations were overrepresented, while in V4, only cardinal bias was presented. These findings suggest that different cortical areas have evolved to emphasize different features that are suitable for their functional purposes, a factor that needs to be considered when efforts are made to explain the relationships between the visual environment and the cortical representation and between the cortical representation and visual perception.

Time‐Resolved Orientation and Phase Analysis of Lead Halide Perovskite Film Annealing Probed by In Situ GIWAXS

AbstractScalable thin‐film deposition methods are increasingly important for hybrid lead halide perovskite thin films. Understanding the structure evolution during non‐equilibrium processes helps to find suitable materials and processing parameters to produce films with well‐performing optoelectronic properties. Here, spin‐cast and slot‐die coated bilayers of lead iodide (PbI2) and methylammonium iodide (MAI) are investigated by in situ grazing‐incidence wide‐angle X‐ray scattering during the thermal annealing process, which converts the bilayer into methylammonium lead iodide (MAPI). Photoluminescence (PL) and UV/Vis measurements show increasing crystallinity during the annealing process and a slight PL red‐shift of the spin‐cast film, attributed to crystallite coalescence that is not prominent for the slot‐die coated film. The disintegration of the solvent‐precursor complex (MA)2(Pb3I8) ⋅ 2 DMSO and conversion into perovskite are followed in situ and differences in the morphology and time evolution are observed. In both, spin‐cast and slot‐die coated thin‐films, the isotropic orientation is dominant, however, in the slot‐die coated films, the perovskite crystallites have an additional face‐on orientation ((110) parallel to substrate) that is not detected in spin‐cast films. An Avrami model is applied for the perovskite crystal growth that indicates reduced dimensionality of the growth for the printed thin films.

Characterization of the Interfacial Orientation and Molecular Conformation in a Glass-Forming Organic Semiconductor.

The ability to control structure in molecular glasses has enabled them to play a key role in modern technology; in particular, they are ubiquitous in organic light-emitting diodes. While the interplay between bulk structure and optoelectronic properties has been extensively investigated, few studies have examined molecular orientation near buried interfaces despite its critical role in emergent functionality. Direct, quantitative measurements of buried molecular orientation are inherently challenging, and many methods are insensitive to orientation in amorphous soft matter or lack the necessary spatial resolution. To overcome these challenges, we use polarized resonant soft X-ray reflectivity (p-RSoXR) to measure nanometer-resolved, molecular orientation depth profiles of vapor-deposited thin films of an organic semiconductor Tris(4-carbazoyl-9-ylphenyl)amine (TCTA). Our depth profiling approach characterizes the vertical distribution of molecular orientation and reveals that molecules near the inorganic substrate and free surface have a different, nearly isotropic orientation compared to those of the anisotropic bulk. Comparison of p-RSoXR results with near-edge X-ray absorption fine structure spectroscopy and optical spectroscopies reveals that TCTA molecules away from the interfaces are predominantly planar, which may contribute to their attractive charge transport qualities. Buried interfaces are further investigated in a TCTA bilayer (each layer deposited under separate conditions resulting in different orientations) in which we find a narrow interface between orientationally distinct layers extending across ≈1 nm. Coupling this result with molecular dynamics simulations provides additional insight into the formation of interfacial structure. This study characterizes the local molecular orientation at various types of buried interfaces in vapor-deposited glasses and provides a foundation for future studies to develop critical structure-function relationships.

Mechanochemistry Advances High-Performance Perovskite Solar Cells.

A prerequisite for commercializing perovskite photovoltaics is to develop a swift and eco-friendly synthesis route, which guarantees the mass production of halide perovskites in the industry. Herein, a green-solvent-assisted mechanochemical strategy is developed for fast synthesizing a stoichiometric δ-phase formamidinium lead iodide (δ-FAPbI3 ) powder, which serves as a high-purity precursor for perovskite film deposition with low defects. The presynthesized δ-FAPbI3 precursor possesses high concentration of micrometer-sized colloids, which are in favor of preferable crystallization by spontaneous nucleation. The resultant perovskite films own preferred crystal orientations of cubic (100) plane, which is beneficial for superior carrier transport compared to that of the films with isotropic crystal orientations using "mixture of PbI2 and FAI" as precursors. As a result, high-performance perovskite solar cells with a maximum power conversion efficiency of 24.2% are obtained. Moreover, the δ-FAPbI3 powder shows superior storage stability for more than 10 months in ambient environment (40± 10% relative humidity), being conducive to a facile and practical storage for further commercialization.

Molecular simulation of molecular and surface properties of random copolymer nanoparticle

Random copolymer nanoparticles were studied by Monte Carlo simulation of coarse-grained models on the high coordination lattice. Molecular and surface properties of free-standing nanoparticle were characterized at fixed 50% co-monomer content as a function of the interaction strength between co-monomer units. Intramolecular interaction for all copolymer chains were treated by the Rotational Isomeric State (RIS) model of polyethylene (PE). To simulate the copolymer model, the non-bonded interactions for comonomer units were described by different parameter sets of the Lennard-Jones energy. When the co-monomer interaction was stronger, the bulk densities of nanoparticles were increased and the interfacial widths were narrower. Near the surface, end beads of copolymer chains were segregated and the bond orientation was preferably perpendicular to the surface. Molecular shape and molecular size of copolymer chains were slightly changed as a function of co-monomer interaction strength and most of which occurs close to the surface. For chain orientation, the largest principal axis tended to orient parallelly to the surface, and then changed toward randomly isotropic orientation for weaker co-monomer interaction. The intrachain energies were decreased at the surface region implying more trans conformation while the non-bonded energies were increased due to better monomer packing at the surface region. The change of system energetics was more apparent as a function of the co-monomer interaction.

Splitting of the Magnetic Loss Peak of Composites under External Magnetic Field

Composite materials filled with ferromagnetic inclusions are useful in the development of various microwave devices. The performance of such devices is determined both by material properties (such as the saturation magnetization and the permeability) and by the demagnetization effects. The paper is devoted to the study of the demagnetization effect on the permeability measurements of composites under external magnetic bias. The microwave permeability of composites filled with flake sendust (Fe-Si-Al alloy) particles is measured as a function of frequency and the external magnetic field. The measurements are carried out by the Nicolson–Ross–Weir technique in a 7/3 coaxial line in the frequency range of 0.1 to 20 GHz by a vector network analyzer. It is found that the magnetic loss peak is split under external fields of more than 1.5 kOe. The main aim of this paper is to study the causes of this splitting and to interpret the observed magnetic loss peaks. To study this effect, the samples of various thicknesses and the samples with isotropic and anisotropic orientations of particles are measured. The particles in the anisotropic samples are oriented by a strong uniform magnetic field. At a small fraction of inclusions, the permanent magnetic field is demagnetized on the individual particles rather than the whole sample. The splitting of the magnetic loss peak of the isotropic sample is caused by different orientations of particles in the sample. At a high fraction of inclusions, the permanent magnetic field is demagnetized on the whole sample and the magnetic loss peak of the isotropic sample is not split. The saturation magnetization of the material is found by measurements under the external magnetic field of the anisotropic sample.