Needle Domain Research Articles

Modelling needle domains with dislocations: A dislocation pile-up model and comparison with synchrotron experiment

The shape and strain field of a needle domain in a barium titanate single crystal are modelled using a distribution of dislocations and line charges. The arrangement of these dislocations and charges is a result of the balance of modified Peach–Koehler forces acting among the dislocations and a lattice friction assumed to act at each dislocation site. Based on measurements of needle shape by synchrotron X-ray diffraction, dislocation pile-up theory is used to compute the distribution of discrete dislocations along the needle and hence estimate the lattice friction. It is found that the lattice friction in this model is proportional to the opening angle of a wedge-shape needle domain and consistent with the observed magnitude of stress required to mobilize needle domains. The microstrain distribution around an a-a needle domain tip, obtained from X-ray diffraction measurement, is further used to test the dislocation model, with a similar pattern and magnitude of strains identified in the model and the experiment.

Influence of dislocations on domain walls in perovskite ferroelectrics: Phase-field simulation and driving force calculation

Dislocations in ferroelectrics cause domain wall pinning and nucleation of ferroelectric domains, which significantly influence the electromechanical properties of ferroelectrics. To have an in-depth understanding of the role of dislocations in ferroelectrics, this work presents a finite element analysis of the driving force on domain walls and their interaction with dislocations. The phase-field model coupled with the non-singular continuum dislocation theory and the generalized configurational force theory are derived for dislocated ferroelectrics. In particular, by making use of the driving force on domain walls and dislocations, we propose a new approach to evaluate the critical electric field for domain walls to break through dislocations. It is shown to be computationally much more efficient than the brute force approach of scanning all electric fields. The influences of dislocations on the 180° and 90° domain walls are analyzed numerically. The dislocation-induced stress field causes fluctuation of the polarization, which results in multiple equilibrium positions of the domain wall. Increased polarization was observed on the tensile side of the dislocation, which is responsible for the strong pinning strength of the dislocation. The needle domain nucleated from the dislocation core also causes the pinning of domain walls, and the interaction between the domain wall and the needle domain results in nonlinear dependency of the critical electric field on the Burgers vector.

Multiple direction needle-path planning and inverse dose optimization for robotic low-dose rate brachytherapy

PurposeRobotic systems to assist needle placements for low-dose rate brachytherapy enable conformal dose planning only restricted to path planning around risk structures. We report a treatment planning system (TPS) combining multiple direction needle-path planning with inverse dose optimization algorithms. MethodsWe investigated in a path planning algorithm to efficiently locate needle injection points reaching the target volume without puncturing risk structures. A candidate needle domain with all combinations of trajectories is used for the optimization process. We report a modular algorithm for inverse radiation plan optimization. The initial plan with V100>99% is generated by the “greedy optimizer”. The “remove-seed algorithm” reduces the number of seeds in the high dose regions. The “depth-optimizer” varies the insertion depth of the needles. The “coverage-optimizer” locates under-dosed areas in the target volume and supports them with an additional amount of seeds. The dose calculation algorithm is benchmarked on an image set of a phantom with a liver metastasis (prescription dose Dpr=100 Gy) and is re-planned in a commercial CE-marked TPS to compare the calculated dose grids using a global gamma analysis. The inverse optimizer is benchmarked by calculating 10 plans on the same phantom to investigate the stability and statistical variability of the dose parameters. ResultsThe path planning algorithm efficiently removes 72.5% of all considered injection points. The candidate needle domain consists of combinations of 1971 tip points and 827 injection points. The global gamma analysis with gamma 1%=2.9 Gy, 1 mm showed a pass rate of 98.5%. The dose parameters were V100=99.1±0.3%, V150=76.4±2.5%, V200=44.5±5.5% and D90=125.9±3.6 Gy and 10.7±1.3 needles with 34.0±0.8 seeds were used. The median of the TPS total running time was 4.4minutes. ConclusionsThe TPS generates treatment plans with acceptable dose coverage in a reasonable amount of time. The gamma analysis shows good accordance to the commercial TPS. The TPS allows taking full advantage of robotic navigation tools to enable a new precise and safe method of minimally invasive low-dose-rate brachytherapy.

Co-carbonization behavior of the blended heavy oil and low temperature coal tar for the preparation of needle coke

Needle coke is mainly used in high-power electrode material for electric arc furnace, the economy of material cost and the quality of co-carbonized products are widely concerned. Low temperature coal tar (LCT) and heavy oil (HO) were used to prepare needle coke by liquid phase carbonization, and the co-carbonization behavior as well as structural evolution of blended materials were also studied. It was concluded that the derived needle coke pyrolyzed from the blended HO and LCT showed obvious structural separation interfaces between the anisotropic acicular structure and isotropic matrix. The abundant primary quinoline insolubles (QI) in LCT prevented the penetration of smaller molecules. The removal of primary QI in LCT improved the compatibility of HO and LCT-derived structure and eliminated the obvious structural separation interfaces. The furfural extraction significantly regulates the molecular composition distribution which is conductive to promote interactions within compositions and improve the order of structural evolution. The sample extracted at 60℃ after removing QI (LCTE60) contained 25.7 wt% of alkanes and naphthenes, and the total content of bicyclic aromatics, tricyclic aromatics and tetracyclic aromatics occupied 45.3 wt%. The derived needle coke prepared from blended HO and LCTE60 with the proportion of 50:50 obtained the needle domain content of 60 wt% and the optical texture index (OTI) of 71.66. This study provides theoretical basis for the co-carbonization of needle coke production.

P.591 Orexin-A ameliorates lasting effects of postnatal dysfunctioning of muscarinic cholinergic system on sleep-wakefulness

Needle domains are thin, lamellar domains that can appear as fine lines or stripes in a ferroelectric crystal. They affect the poling, switching, and other properties of ferroelectrics. A model is established to study the stress and electric fields caused by needle domains and their interaction. Considering the electrical and mechanical compatibility conditions at the tip of a needle domain, the fields are represented using equivalent edge dislocations and line charges. Accordingly, the dislocation fields derived by Barnett and Lothe for anisotropic piezoelectric media are employed. A modified Peach–Koehler force and calculations of the total energy due to the needle domains are used to study the formation, interaction and stability of needle patterns, taking full account of the strong anisotropy and electromechanical coupling present.The interaction of pairs of needle domains in an infinite piezoelectric with properties of barium titanate is found to be dominated by the electrostatic terms. This makes comb-like arrays of needle domains unstable if perfectly insulating properties are assumed. By considering redistribution of charge, stable equilibrium states for arrays of needle domains are found; these agree well with experimental observations. The model explains the stability of various observed needle patterns and also how unstable patterns evolve.

Modelling and interaction of needle domains in barium titanate single crystals

Needle domains are thin, lamellar domains that can appear as fine lines or stripes in a ferroelectric crystal. They affect the poling, switching, and other properties of ferroelectrics. A model is established to study the stress and electric fields caused by needle domains and their interaction. Considering the electrical and mechanical compatibility conditions at the tip of a needle domain, the fields are represented using equivalent edge dislocations and line charges. Accordingly, the dislocation fields derived by Barnett and Lothe for anisotropic piezoelectric media are employed. A modified Peach–Koehler force and calculations of the total energy due to the needle domains are used to study the formation, interaction and stability of needle patterns, taking full account of the strong anisotropy and electromechanical coupling present.The interaction of pairs of needle domains in an infinite piezoelectric with properties of barium titanate is found to be dominated by the electrostatic terms. This makes comb-like arrays of needle domains unstable if perfectly insulating properties are assumed. By considering redistribution of charge, stable equilibrium states for arrays of needle domains are found; these agree well with experimental observations. The model explains the stability of various observed needle patterns and also how unstable patterns evolve.

Formation of polarization needle-like domain and its unusual switching in compositionally graded ferroelectric thin films: an improved phase field model.

Compositionally graded ferroelectrics (cgFEs), which possess a spatial variation in material composition, exhibit anomalous or even unprecedented properties. Despite several breakthroughs having been achieved in experiments, there surprisingly is a lack of an effective simulation approach for cgFEs, thereby greatly hindering a deep understanding about underlying mechanisms hidden behind the observed phenomena. In this study, an improved phase field model is proposed for a cgFE made of PbZr(1−x)TixO3 based on the Ginzburg–Landau theory. The improved approach enables us to capture several key phenomena occurring in the cgFE PbZr0.8Ti0.2O3 ⇔ PbZr0.2Ti0.8O3 thin film that are observed from experiments, such as the formation of needle-like domains with curved domain walls, ferroelastic switching under an electric field, and the voltage offset of the hysteresis loop. Results obtained from the improved approach indicate that the high elastic energy near the needle-tip of an a-domain gives rise to a deflection of the domain wall from the regular a/c domain wall, while the high concentration of the depolarization field shrinks a part of the a-domain near the needle-tip and terminates the a-domain within the cgFE thin film. These facilitate the stabilization of needle-like domains with curved domain walls in the cgFE thin film. Furthermore, the flexoelectricity is proven to play an important role in the voltage offset of the hysteresis loop. On the other hand, the ferroelectric switching process in the cgFE thin film exhibits a vastly different response in comparison to that in homogeneous ferroelectric thin films, including local switching initiation and formation and annihilation of vortex–antivortex pairs during the switching. The present study, therefore, provides an incisive approach for investigations on cgFEs, which may bring new understanding and unique insights into these complex materials, as well as novel potential applications.

Photoinduced in Vivo Magnetic Resonance Imaging (MRI) with Rapid CO Release from an MnCO-Protein Needle Composite.

Construction of an artificial protein needle (PN), which includes the membrane puncturing needle domain of bacteriophage T4 conjugated to Mn carbonyl (MnCO) complexes, is reported. The responsiveness to visible light of the MnCO complex makes it useful as a photoinduced in vivo magnetic resonance imaging contrast reagent (MRI CR), because the PN carrier has the potential to deliver the MnCO complex into mouse tumors with retention of coordination structure within the in vivo environment. Moreover, the composite has higher relaxivity and longer circulation as an MRI CR than the corresponding MnCO complex. These results demonstrate construction of a responsive in vivo MRI CR by using an artificial metalloprotein.

In-situ observation of needle domain evolution in barium titanate single crystals

Abstract We report in-situ optical observations of the ferroelastic switching in a barium titanate single crystal under compressive stress. Optical micrographs were captured in two regions showing distinct arrangements of domains. Coarsely spaced needle domains in a matrix consisting of a differently oriented large single domain were found to retreat under the application of compressive stress of around 1–2 MPa. However, a comb of closely spaced needle domains was found to be more stable, retreating only slightly under a similar magnitude of applied load. The observations show that the pattern of needle domains influences the ferroelastic switching process and the observed coercive stress can depend strongly on domain arrangement.

Interfacial Properties and Critical Avalanche Exponents of Shape Memory Alloys and Related Materials

Interfaces in martensites and ferroelastic crystals show internal structures which are not simply the interpolation of the two adjacent domains. These structures can influence solitary front propagation as observed for large depinning forces. They also contribute to local pinning of walls when the applied forces are close to the depinning threshold. Under these conditions, walls propagate in jerks and avalanches. Typical depinning is observed for very small forces in single ferroelastic needle domain. It is shown that jerks occur in elastically driven system both for planar walls (D=2) and for needle tips (which represents a line in the three dimensional crystal, D=1). The experimental power law exponents are ~ -2 for the energy exponent for collective avalanches, -1.3 for the elastic response function and -1.8 for an advancing needle domain in LaAlO3.

Structure of the bacteriophage T4 long tail fiber receptor-binding tip

Bacteriophages are the most numerous organisms in the biosphere. In spite of their biological significance and the spectrum of potential applications, little high-resolution structural detail is available on their receptor-binding fibers. Here we present the crystal structure of the receptor-binding tip of the bacteriophage T4 long tail fiber, which is highly homologous to the tip of the bacteriophage lambda side tail fibers. This structure reveals an unusual elongated six-stranded antiparallel beta-strand needle domain containing seven iron ions coordinated by histidine residues arranged colinearly along the core of the biological unit. At the end of the tip, the three chains intertwine forming a broader head domain, which contains the putative receptor interaction site. The structure reveals a previously unknown beta-structured fibrous fold, provides insights into the remarkable stability of the fiber, and suggests a framework for mutations to expand or modulate receptor-binding specificity.

The noise of the needle: Avalanches of a single progressing needle domain in LaAlO3

The propagation of a single ferroelastic needle domain under weak elastic stress consists of two parts: a continuous front propagation and jerky avalanches. Optical observation and themodynamic analysis show that the continuous behavior is thermally activated. The avalanches follow power law behavior with an energy exponent ε=−1.8±0.2 in agreement with self-similar avalanches close to the depinning threshold. Our experiments on ferroelastic LaAlO3 exclude nucleation of secondary domains, so that the observed behavior is related exclusively to the statistical behavior of one single needle domain.

Formation of needle shaped twin domains in cordierite: A computer simulation study

The formation of needle shaped domains in cordierite is simulated using a simplified two-dimensional computer model with hexagonal symmetry and nonlocal (strain-induced) atomic interactions. Domain walls form along elastically soft directions as expected and sometimes needle domains appear during annealing. During annealing needles are then consumed by the coarsening process or retract into the domains to which they are attached. Needles have rounded, parabolic tips symptomatic of cordierite’s comparatively low anisotropy energy. Needle splitting is not observed but a novel wetting mechanism by which auxiliary domains form at the needle tip is observed. These domains form such as to make a section of the needle tip a strain allowed domain wall and so reduce the bending energies of the domain walls in this region. At higher temperatures, needle domain walls become only poorly orientated along soft directions and needle domains become patchy with blunt tips and increased “wetting” at the needle tips.

Ferroelastic phase transitions and mesoscopic structures

Progress in the analytical description of domain walls, their simulation by computer modelling and their experimental observation using 7 circle diffractomers is summarised and some relevant references are listed. The formation and retraction of needle twins is identified as principal annealing mechanism of complex twin patterns. The shape of the needle domain has been analysed in a local approximation. The role of chemical mixing and external pressure on the phase stability of the ferroic phase is briefly discussed.

Transformation behaviour of a Ti50Ni47Fe3alloy II. Subsequent premartensitic behaviour and the commensurate phase

Abstract A second ‘premartenaitic’ effect in a Ti50Ni47Fe3 alloy was found to occur approximately 12°C below the onset of the initial ‘normal-to-incommensurate’ transition described in the previous paper. This subsequent phase change involves a structural transition from a ‘distorted’ CsCl parent to a rhombohedral product, during which the ‘1/3’ superlattice reflections are shifted to precise 1/3 positions. The rhombohedral distortion is effected by a homogeneous expansion along 〈111〉 directions, allowing the lattice and CDWs to lock in and become commensurate. Microstructural changes associated with this structural transition involve the formation of four crystallographic variants of ‘needle’-like domains (three variants and the ‘matrix’). Each such domain has its unique rhombohedral axis, reflecting the rhombohedral distortion along one of the four 〈111〉 body diagonals of the cubic unit cell. The ‘needle’ domains and the matrix are twin-related with respect to a {110} twinning plane. Small antiphase-like microdomains are found within both the ‘needles’ and the ‘matrix’. Their size is independent of temperature. Electron diffraction patterns show that within a single needle domain 1/3(111) superlattice reflections lie along only one 〈111〉∗ direction, and the 1/3(110) super-lattice reflections lie only along those 〈110〉∗ directions which are normal to 〈111〉∗. The disappearance of the needle domains on heating shows some thermal hysteresis, indicative of a first-order phase change. The above phenomena are interpreted in terms of a first-order incommensurate-to-commensurate structural change, with the formation of twins leading to a reduction in long-range strain distortion.