Parallel Alignment Research Articles

Topochemical Polymerization of a Diacetylene in a Chalcogen‐Bonded (ChB) Assembly

AbstractThe successful topochemical polymerization of bis(selenocyanatomethyl)butadyine 1 is achieved upon association in a 1 : 1 co‐crystal with 1,2‐bis(2‐pyridyl)ethylene (2‐bpen) through strong and linear (NC)−Se⋅⋅⋅NPy chalcogen bonding (ChB) interactions, allowing for an appropriate parallel alignment of the diacetylene moieties toward the solid‐state reaction. Co‐crystal 1⋅(2‐bpen) undergoes polymerization upon heating at 100 °C. The reaction progress was monitored by IR, DSC and PXRD. An enhancement of the polymer conductivity by 8 orders of magnitude is observed upon iodine doping. Strikingly, the course of polymerization is accompanied with sublimation of the ChB acceptor molecules 2‐bpen, providing the polymer in a pure form with full recovery of the co‐former, at variance with the usual hydrogen‐bonded co‐crystal strategies toward polydiacetylenes.

Topochemical Polymerization of a Diacetylene in a Chalcogen-Bonded (ChB) Assembly.

The successful topochemical polymerization of bis(selenocyanatomethyl)butadyine 1 is achieved upon association in a 1 : 1 co-crystal with 1,2-bis(2-pyridyl)ethylene (2-bpen) through strong and linear (NC)-Se⋅⋅⋅NPy chalcogen bonding (ChB) interactions, allowing for an appropriate parallel alignment of the diacetylene moieties toward the solid-state reaction. Co-crystal 1⋅(2-bpen) undergoes polymerization upon heating at 100 °C. The reaction progress was monitored by IR, DSC and PXRD. An enhancement of the polymer conductivity by 8 orders of magnitude is observed upon iodine doping. Strikingly, the course of polymerization is accompanied with sublimation of the ChB acceptor molecules 2-bpen, providing the polymer in a pure form with full recovery of the co-former, at variance with the usual hydrogen-bonded co-crystal strategies toward polydiacetylenes.

Magnetotransport and magnetic textures in Ho/FeCoGd/ β -W multilayers

The enhancement of interfacial Dzyaloshinskii-Moriya Interaction (DMI) in magnetic multilayers results in the stabilization of topological spin textures such as chiral domain walls and skyrmions. Here we report on the evaluation of interface-driven magnetic interactions in a uniquely designed multilayer where each magnetic layer of two antiferromagnetically coupled sublattices of $3d$ and $4f$ moments is sandwiched between the layers of \ensuremath{\beta}-tungsten and holmium whose spin Hall angles are large but opposite in sign. The atomic and magnetic periodicity of these multilayers is established by polarized neutron reflectivity measurements and the presence of a labyrinth domain spin texture of zero remanence with x-ray photoelectron microscopy. Measurements of the Hall resistivity $[{\ensuremath{\rho}}_{xy}(T,H)]$ together with static magnetization [$M$($T, H$)] over a broad range of temperature ($T$) and magnetic field ($H$) indicate impending compensation between $3d$ and $4f$ sublattices at $T>350\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. These multilayers are characterized by a small (0.04%) but positive magnetoresistance indicative of interface enhanced scattering, and a large (40 n\ensuremath{\Omega} m) and negative anomalous ${\ensuremath{\rho}}_{xy}(T,H)$ which results from a parallel alignment of $4f$ moments with the external magnetic field. No distinct scaling is seen between ${\ensuremath{\rho}}_{xy}(T,H), {\ensuremath{\rho}}_{xx}(T,H)$, and $M$($T, H$) at temperatures above 200 K where the magnetization develops out of plane anisotropy. The field scans of ${\ensuremath{\rho}}_{xy}$ at $T>200\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ show a distinct cusp in the vicinity of magnetic saturation. These Hall data have been analyzed in the framework of a model where a distinct topological contribution to ${\ensuremath{\rho}}_{xy}$ rides over the anomalous Hall resistivities of the $3d$ and $4f$ magnetic sublattices. It is suggested that this apparent topological effect results from an interfacial DMI and dominates ${\ensuremath{\rho}}_{xy}(T,H)$ in the temperature regime where the $3d$ and $4f$ lattices are nearly compensated.

The effect of temperature on water desorption and oxide formation in MoS2 coatings and its impact on tribological properties

Molybdenum disulfide (MoS2) is used extensively in aerospace applications, where liquid lubricants are not suitable. MoS2 has excellent tribological properties in vacuum, however, further research is required to fully understand the mechanisms taking place when exposed to varying temperatures in ambient atmosphere due to storage and on-ground testing. MoS2 coatings were deposited on AISI 440C steel substrates, friction and wear tests were conducted at increasing temperatures, up to 75 °C, determining the effect of temperature on wear mechanisms in air. It was found that the detected surface oxides do not impact tribological properties in MoS2 at temperatures around 75 °C. The water molecules at room temperature hinder the alignment of MoS2 layers leaving some active edge sites exposed to contacting surfaces, leading to high friction and wear. Desorption of water molecules promote parallel alignment of layers, reducing shear strength, friction and wear.

Parallel multiple DNA sequence alignment using genetic algorithm and asynchronous advantage actor critic model

Multiple sequence alignment plays a crucial role in bioinformatics field. In this process, sequences are compared by establishing residue-residue correspondence among related sequences. In this paper, we present a novel framework that uses genetic algorithm and asynchronous advantage actor critic model to look for the optimal multiple DNA sequence alignment. In the first step, we generate initial alignments by applying the T-COFFEE method. Then, we recursively use a genetic algorithm to find the optimal fragmentation of the pre-aligned sequences. At this stage, the obtained short sub alignments are introduced to the A3C model for parallel alignments. So, the optimal multiple alignment of the original sequences represents the fusion of sub-alignments. To evaluate the performances of the proposed approach, we used the Balibase 3.0 benchmark and compared to TCOFFEE, MAFFT and RLALIGN methods. The obtained experimental results show that the proposed approach can achieve solutions of competitive quality.

Analysis of Difficulty on Bimanual Rotational Movements in Sagittal Plane

It is thought that interference of motor commands, task goals, and visual information between the left and right hands sides may contribute to the difficulty of bimanual movement. If both hands are controlled in mirror alinement at the midline, muscle control is the same in both hands. On the other hand, if both hands are controlled in parallel alignment at the midline, muscle control is not the same in both hands. The visual movements of hands in the horizontal and frontal plane are the same even in the parallel condition, although they are also not the same in the sagittal plane. It was hypothesized that such incongruency of muscle control and visual movements in the sagittal plane induces difficulty of motor control. In this study, rotational movements in the horizontal, frontal, and sagittal planes were measured. Movement direction of a right hand was designed as an experimental condition, mirror condition and non-mirror condition. As a result, in the sagittal plane, the errors and phase deviations between the left and right hands trajectories were greater in the non-mirror image condition than in the mirror condition than in the other motion planes. Therefore, it is suggested that it is more difficult to generate non-mirror image bimanual rotational movement in the sagittal plane than in the frontal and horizontal planes.

Real-Time Switching Dynamics in STT-MRAM

In this paper a new experimental technique for measuring the switching dynamics and extracting the energy consumption of Spin Transfer Torque MRAM (STTMRAM) device is presented. This technique is performed by a real-time current reading while a pulsed bias is applied. The switching from a high resistive state, anti-parallel (AP) alignment, to a low resistive state, parallel (P) alignment, is investigated as well as the impact of the cell diameter on the switching parameters. We demonstrate that preswitching and switching times and energies have a log-linear relationship with the applied voltage. Increasing the applied voltage leads to a higher spin torque on the free layer in a shorter time. This decreases the time needed to change the magnetization orientation of this layer, thus the time required before the switching occurs. We have also shown that for a given applied voltage, the smaller the cell the longer the time before switching. For low applied voltages, the preswitching time increases exponentially dominating the whole reversal time. The longer switching times can be explained by a lower Joule heating not sufficient to induce the thermally activated reversal process. This phenomenon is accentuated for smaller cells, where the heating is more significant and the time before switching is shorter than for larger cells.

Magnetic-field-free spin–orbit torque-driven magnetization dynamics in CoFeB/β-W-based nanoelements

A full numerical analysis, which takes into account the effects of the spin Hall effect, interfacial Dzyaloshinskii–Moriya interaction, and thermal fluctuations, is carried out in in-plane magnetized CoFeB/MgO/CoFeB/high-resistivity tungsten (β-W) nanoelements. The analysis is focused on the investigation of the underlying mechanisms of magnetic-field-free spin–orbit torque (SOT)-driven magnetization reversal process on subnanosecond time scales. It is found that the magnetization in the free magnetic layer can be electrically toggled between the parallel and antiparallel alignment with respect to the fixed magnetic layer without the assistance of an external magnetic field, in which the out-of-plane canting of the magnetic moments at the element edges plays a significant role in the nucleation and subsequent expansion of the reversed magnetization. Furthermore, the thermally activated magnetization process combined with the SOT effect is found to significantly reduce the effective energy barrier to the magnetization reversal and alter the details of the SOT-driven magnetization process in nanomagnets.

Tuning the dielectric response in a nanocomposite material through nanoparticle morphology.

Ceramic materials such as metal oxides, mixed metal oxides and silicates, constitute a broadly-used, high-performance technology for electronic insulators. The introduction of metal cluster dopants and molecular-scale inclusions in a dielectric matrix provides an opportunity for manufacturing new high-κ solid-state dielectrics with tunable field–response properties. The quantum properties of these metallic nanoparticles depend strongly on their size and shape, a characteristic that can be exploited in changing the response properties of a material, whereas the small nanoparticle size can help limit the issues of conduction and current leakage. Here, we model the polarization of molecular-scale silver inclusions in a magnesium oxide matrix, using the Modern Theory of Polarization and Car–Parrinello Molecular Dynamics (CPMD). Details of the implementation are laid out, including handling of current jumps due to the distortion of the matrix during the simulation. Several trends in the dielectric response are considered in this work, including the effects of nanoparticle size, shape and orientation relative to the applied field. Dielectric permittivity enhancements of 30–100% are observed with inclusion sizes varying from 8 to 32 atoms, considering both rod-like and disk-like inclusions, with alignment either parallel or perpendicular to the external field.

Large scale alignment of alumina platelets en route to porous nacre-like alumina by ice-templating

Ice templating, being a highly versatile technique contributes largely to the development of biomimetic structures. Biomimetic materials are the synthetic materials that possess one or more design and functional aspects of natural materials like abalone nacre, bone, wood. The present research aimed to replicate the inorganic part of nacre, by taking as-synthesized alpha-alumina platelets as primary building blocks. Ice templating was carried out under large vertical temperature gradient in a custom-built setup, that resulted in large-scale ordered lamellar structure; mainly due to the fast and straightforward self-assembly of platelets during directional solidification. The structural wavelength and lamella thickness, the critical parameters to define the ordered lamellar microstructure, were measured to be 16.23 ± 2.0 μm and 2.79 ± 1.0 μm respectively. The resultant green scaffold was subsequently pressed (i.e. cold-compaction) in a direction perpendicular to the ice-front growth and sintered at 1550 °C/4h. Although the nature of the compression response (before and after intermediate cold compaction step) did not change considerably, but large differences in the strength, work of fracture and modulus were obtained. This is mainly due to the large reduction of porosity as well as large-scale alignment of alumina platelets in bulk, resulted from the additional intermediate cold-compaction step. The microstructure of the sintered specimen displayed large-scale parallel alignment of anisotropic alumina platelets, closely resembles to the inorganic counterpart of natural nacre.

Synergistic effect of 2[V2P2O14]∞ layers and hydrogen bonds inducing large birefringence in M(VO)2(PO4)2·4H2O (M = Ca, Sr, Ba) systems

The parallel alignment of zigzag 2[V2P2O14]∞ layers and the binding force of hydrogen bonds result in the large birefringence of M(VO)2(PO4)2·4H2O (M = Ca, Sr, Ba) compounds.

Field-free spintronic terahertz emitters based on IrMn/Fe/Pt exchage bias heterostructures

Spintronic terahertz (THz) emitter has more advantages such as lower cost, broader spectrum and easier operation than the commercial THz emitters, and thus has become a focus of research towards the next-generation THz source. However, in such a spintronic THz emitter, an external magnetic field is technologically required to align the orientation of the magnetization, which is detrimental for practical applications. Here, a spintronic terahertz emitter based on IrMn/Fe/Pt exchange bias structure is presented. By means of ultrafast spin injection on Fe/Pt interface followed by the spin-to-charge conversion in Pt, plus the effective magnetic field originating from the IrMn/Fe interface, the THz pulse with considerable intensity can be generated in such a structure without the assistance of external field. Besides, the remanent magnetization for thin Fe layer is enhanced by inserting an ultrathin Cu layer between the IrMn surface and the Fe surface, which is beneficial to the field-free THz emission. The range of obtained dynamic THz spectrum exceeds 60 dB and the positive saturation field can reach up to ~ –10 mT by optimizing the multilayer thickness, meeting the standard for commercial application. By rotating the sample, it is found that the polarization direction of the generated THz wave circulates simultaneously and keeps perpendicular to the direction of exchange bias field in the film plane. Moreover, we design a spin valve THz emitter based on the structure of IrMn/Fe/Pt/Fe by adding a free ferromagnetic Fe layer into the exchange bias multilayers. The emitted THz pulse amplitude is larger for the antiparallel alignment of the Fe layers at zero field than for the parallel alignment or exchange bias structure. The present work shows that the spin terahertz emitter based on IrMn/Fe/Pt exchange bias structure can produce the considerable terahertz signals without external field. Furthermore, the polarization direction of the emitted THz signal can be easily manipulated by rotating the sample. Because of this series of advantages, such exchange bias heterostructures are expected to play an important role in designing the next-generation THz source.

Spin valve effect in two-dimensional VSe[formula omitted] system

Vanadium based dichalcogenides, VSe2, are two-dimensional materials in which magnetic Vanadium atoms are arranged in a hexagonal lattice and are coupled ferromagnetically within the plane. However, adjacent atomic planes are coupled antiferromagnetically. This provides new and interesting opportunities for application in spintronics and data storage and processing technologies. A spin valve magnetoresistance may be achieved when magnetic moments of both atomic planes are driven to parallel alignment by an external magnetic field. The resistance change associated with the transition from antiparallel to parallel configuration is qualitatively similar to that observed in artificially layered metallic magnetic structures. Detailed electronic structure of VSe2 was obtained from DFT calculations. Then, the ballistic spin-valve magnetoresistance was determined within the Landauer formalism. In addition, we also analyze thermal and thermoelectric properties. Both phases of VSe2, denoted as H and T, are considered.

Origin of Ferroelectric Domain Wall Alignment with Surface Trenches in Ultrathin Films.

Engraving trenches on the surfaces of ultrathin ferroelectric (FE) films and superlattices promises control over the orientation and direction of FE domain walls (DWs). Through exploiting the phenomenon of DW-surface trench (ST) parallel alignment, systems where DWs are known for becoming electrical conductors could now become useful nanocircuits using only standard lithographical techniques. Despite this clear application, the microscopic mechanism responsible for the alignment phenomenon has remained elusive. Using ultrathin PbTiO_{3} films as a model system, we explore this mechanism with large scale density functional theory simulations on as many as 5,136 atoms. Although we expect multiple contributing factors, we show that parallel DW-ST alignment can be well explained by this configuration giving rise to an arrangement of electric dipole moments which best restore polar continuity to the film. These moments preserve the polar texture of the pristine film, thus minimizing ST-induced depolarizing fields. Given the generality of this mechanism, we suggest that STs could be used to engineer other exotic polar textures in a variety of FE nanostructures as supported by the appearance of ST-induced polar cycloidal modulations in this Letter. Our simulations also support experimental observations of ST-induced negative strains which have been suggested to play a role in the alignment mechanism.

Effect of texture and grain size on the compressive creep of Ti3SiC2 MAX phase ceramics

The sintering and simultaneous texturing of Ti3SiC2 MAX phase ceramics have been reported. The degree of orientation of Ti3SiC2 grains were quantified with X-ray diffraction for the bulk crystallographic texture and electron back scattered diffraction for local and morphological texture. Analysis revealed that the basal plane of Ti3SiC2 was aligned perpendicular to the direction of applied external force during sintering. The textured MAX phase was subjected to high temperature annealing to induce grain growth which resulted in a duplex microstructure. The ceramics with fine (∼1 µm) and duplex (500 µm wide elongated grains in a matrix of equiaxed 1 µm grains) microstructure were subjected to compressive creep tests at high temperature (1000–1300 °C) in different directions with respect the orientation of the crystals in the bulk Ti3SiC2. The creep resistance was highest for fine grained Ti3SiC2 with basal planes aligned perpendicular to the direction of applied stress, whereas the ceramics with duplex microstructure and basal plane aligned parallel to the direction of applied stress suffered the highest creep deformation. A probable mechanism for the creep response of the different grades of Ti3SiC2 has been proposed.

Heteromolecular H –bond interaction forces and dielectric parameters: Time domain reflectometry studies

H – bond interactions between acetonitrile(AN)/dimethyl sulfoxide(DMSO) and acetylacetone (AcAc) have been investigated using time domain reflectometry studies. The relaxation time values confirm that 1:1 complex has been formed between AN/DMSO and AcAc, and both the keto and enol forms of AcAc exist as monomers. Antiparallel and parallel alignment of AN/DMSO – AcAc H – bonded dipoles in AN/DMSO and AcAc rich solutions, respectively, have been identified. The gf values indicate that non-classical H – bond interactions are operative in AN/DMSO – AcAc solutions. The εEvsϕ2 suffers quantitatively a large change from the εEvsX2 plot but, they qualitatively agree each other.

The psychoanalysis of Mam's character in the narrative of Mam and Zin based on Rogers's humanist model

Abstract Humanism is considered as one of the novel trends in Psychology which deals with the human innate inclinations and his needs. Karl Ruggers is one of the humanist psychologists who has a positive perspective towards human potentials and creativities. In his works, Ruggers has a special inclination towards the idea of ‘superman’ and the ways that human being could pave the way to make this historical dream come true. The development of Zin’s round identity is one of the essential ideas in Mam and Zin that could be discussed and analyzed via Ruggers’ theory and is carried out in this research. The essence of human perfection is one of the coral arguments that Khani attempts to develop authentically from Mam’s perspective. Therefore, Ruggers’ humanist theory could analyze Khani’s thoughts in a great deal. Such a parallel alignment of Ruggers’ theories and Khani’s psychological thematic inclinations could lead to great conclusions that Khani as a Kurdish classic writer has delt with psychological development of his characters that analyzing them requires advanced contemporary knowledge in humanism and psychology. The results of the research vividly illustrate that Khani through his emphasis on Mam’s dynamic and round character attempts to provide his addressees with a perfect psychological model of the ‘superman’ and has done everything logically possible to characterize Mam; a character that shares a lot with Ruggers’ model of ‘superman’ celebrating the thinker’s psychological traits of a psychologically perfect human such as the potential of acquiring new experiences, living a purposeful life, dependance of self-organism, freedom, and creativity.

All are aromatic: A 3D globally aromatic cage containing five types of 2D aromatic macrocycles

All are aromatic: A 3D globally aromatic cage containing five types of 2D aromatic macrocycles

Non-Aqueous electro-deposition of novel one-dimensional Sm2Co17 nanostructures and magnetic field annealing effect on structural and magnetic properties

Through a versatile and quite economical technique of DC electro-deposition, Sm2Co17 nanowires (NWs) have been fabricated into the nanochannels of anodic aluminum oxide (AAO) templates by using non-aqueous electrolyte. The average diameter and length of NWs are 80 nm and 3 µm respectively. The structural and magnetic properties of NWs have been investigated before and after magnetic field (MF) annealing with magnetic field strength of 1 T applied parallel to the NWs axis at temperature of 300 °C. SEM and TEM have been employed to observe the morphology of NWs after partial and full etching respectively. Deposition of SmCo alloy has been confirmed through EDX analysis whereas XRD peaks shows hexagonal closed packed (hcp-P63/mmc) as the dominant phase with (203) preferred orientation. After MF annealing the crystallinity got improved as manifested by the increase in peak sharpness. Furthermore, after the said field assisted heat treatment the magnetic parameters including coercivity (Hc) from 91 to 527 Oe for θ = 0°, from 101 to 151 Oe for θ = 90° and squareness (SQ) from 0.040 to 0.16 for θ = 0°, from 0.037 to 0.032 for θ = 90° have been observed through VSM. A switching of magnetization reversal mechanism from curling to coherent rotation has been observed after MF annealing due to the stronger inter-wire coupling which leads to parallel alignment of magnetic moments of adjacent NWs. Temperature dependent study has been carried out employing PPMS manifesting gradual increase in Hc from 67 to 440 Oe, Ms from 5.4 × 10−3 to 6.1 × 10−3 emu and SQ from 0.19 to 0.25 with the decrease in temperature up to 5 K.

Universal Protoplanetary Disk Size under Complete Nonideal Magnetohydrodynamics: The Interplay between Ion-neutral Friction, Hall Effect, and Ohmic Dissipation

Abstract The role of nonideal magnetohydrodynamics has been proven critical during the formation of protoplanetary disks, particularly in regulating their sizes. We provide a simple model to predict the disk size under the interplay among ambipolar diffusion, the Hall effect, and ohmic dissipation. The model predicts a small disk size of around 20 au that depends only sublinearly on disk parameters, for a wide range of initial conditions of subsolar mass and moderate magnetization. It is able to explain phenomena manifested in existing numerical simulations, including the bimodal disk behavior under parallel and antiparallel alignment between the rotation and magnetic field. In the parallel configuration, the disk size decreases and eventually disappears. In the antiparallel configuration, the disk has an outer partition (or pseudodisk), which is flat, shrinking, and short-lived, as well as an inner partition, which grows slowly with mass and is long-lived. Even with significant initial magnetization, the vertical field in the disk can only dominate at the early stage when the mass is low, and the toroidal field eventually dominates in all disks.