Crystal Theory Research Articles

Metro Monolithic Track Bed Vibration Characterization

With the rapid development of cities, metro transportation has also developed rapidly to solve the congestion problems caused by urban development. However, with the continuous development of metro transportation, the vibration problems caused by it have become increasingly obvious. Based on the phonon crystal theory, this paper investigates the vibration characteristics of the metro track structure. It analyzes the influence of the track structure parameters on the band gap characteristics to regulate the metro vibration band gap range. To study the band gap characteristics of metro monolithic bed track structure, establish the double-layer Euler beam model and use the plane wave expansion method (PWE) to calculate its energy band structure; use the finite element method (FEM) to calculate to get its band structure, frequency response function, and time domain analysis. The calculation of PWE shows that there is a band gap in the range of 0–300[Formula: see text]Hz for the metro monolithic track bed, which is 0–194.5[Formula: see text]Hz; the calculation of FEM shows that the range of band gap is 0–193.7[Formula: see text]Hz. Fastening spacing, stiffness, and sub-slab support stiffness will have an impact on the band gap, so appropriate fastening and spacing need to be selected for effective vibration damping of the track structure. The results show that the band gap characteristics of the metro monolithic track bed can be calculated effectively and accurately by using the phononic crystal theory.

Probabilistic notch fatigue assessment under size effect using micromechanics-based critical distance theory

Geometrical discontinuities are inevitable in engineering structures due to various functional requirements, which often yield complex stress–strain state and thereby significantly impact their fatigue performances. In this study, crystal plasticity theory is coupled with traditional critical distance theory for notch effect modelling considering microstructural heterogeneity. Specifically, microstructural and geometrical size effects on critical distance and fatigue performance are studied based on Sub-modelling approach. In addition, critical distance theory is coupled with Weibull distribution for probabilistic fatigue life evaluation of notched components. The developed method is verified and compared by using experimental data of GH4169 alloy. The findings demonstrate that the evaluated P-S-N curves exhibit strong agreement with tested data and geometrical size effect poses larger influence than the grain size effect on critical distance and fatigue life.

Stress redistribution and stress triaxiality effect on the fatigue life of notched Ni-based single crystal superalloy at 760℃

The multiaxial stress state caused by geometric discontinuities will result in significant differences in the fatigue performance compared to the uniaxial stress state. It is crucial importance to research the notch fatigue behaviors of nickel-based single crystal (Ni-SX) superalloys at high temperature. This study investigated the impact of stress redistribution and stress triaxiality on the fatigue life of notched Ni-based single crystal superalloy at 760℃. The high temperature fatigue tests were carried out on the specimens under different stress ratios and the stress amplitudes under the same life conditions were obtained. A novel anisotropic damage model, incorporating the influence of stress triaxiality is proposed coupled with crystal plasticity theory. Based on experimental findings, an evaluation of the test parameters was conducted.The results showed that Mises stress, maximum principal stress, normal stress of principal stress along the loading direction, maximum principal strain, and strain along the loading direction were inadequate in reflecting the significant variations of samples observed among different stress ratios. However, the stress triaxiality at the unloading valley exhibited a high sensitivity to changes in fatigue life. To evaluate the fatigue life of notched specimens under different stress ratios, an improved Basquin’s type life prediction model was proposed, utilizing the stress triaxiality at the unloading valley. The proposed model demonstrates a favorable normalization trend for the fatigue life of notched specimens subjected to various stress concentration factor (SCF) conditions.

The melt memory effects in polymer crystallization

AbstractThis paper presents a systematic review of the literature on the melt memory effects observed in polymers, an area that has engendered considerable debate for over 50 years. Recent advances in experimental techniques have provided fresh insights into how a polymer's thermal history influences its recrystallization behavior. It has been observed that given other conditions unchanged, the crystallization temperature during recrystallization decreases with an increase in the melt temperature Ts above the melting point Tm until a critical melt temperature is attained. This phenomenon also extends to the half‐time of crystallization and the secondary structures, such as lamellar thickness, of semi‐crystalline polymers. Despite these findings, a comprehensive constitutive model that encapsulates polymer melt memory effects remains elusive. Cutting‐edge instrumentation, including in situ small and wide‐angle X‐ray scattering, temperature‐controlled Fourier transform infrared spectroscopy, and flash differential scanning calorimetry, have posed significant challenges to the traditional nucleation and growth models established in the 1970s. These models are foundational to our understanding of polymer crystallization, which is an integral part of polymer processing and production. In this review, the historical contours of this discourse are traced, with an examination of both the recent experimental breakthroughs and theoretical advancements pertinent to polymer melt memory effects. This paper delves into the prevailing theories of polymer nucleation and crystallization and engages with theoretical discussions and numerical simulations that attempt to elucidate and rationalize these melt memory phenomena.

Bridging the gap between theory and implementation: National language policy and documentation of mother tongue

Language is an essential aspect of identity and culture, playing a significant role in shaping a nation's socio-political landscape. This is why nations are continuously making effort to preserve their indigenous languages. This paper investigates the grey area of theory and implementation of the national language policy in the preservation, revitalization, documentation of mother tongue. It discusses the challenges such as lack of adequate instructional materials and qualified teachers in indigenous language, facing indigenous languages in Nigeria and how the implementation of language national language policy can promote mother tongue revitalization beyond the classroom. The paper adopts Language ecology model and David Crystal's theory of language revitalization to investigate the study. The paper adopts descriptive analysis methodology, which will use current and historical data to identify gaps in the study. The paper concludes that bridging the gap between theory and implementation of national language policy in Nigeria is a complex but a necessary and essential national task that involves the government allocating resources to produce adequate instructional materials and training teachers to be qualified in teaching indigenous languages. Also government and stakeholders should intensify efforts outside the classroom, preserving mother tongue and revitalizing endangered languages requires a multifaceted approach that extends well beyond the classroom, which involves fostering a cultural environment where the language is valued and used in daily life, creating intergenerational connections, leveraging technology and documenting linguistic resources.

Retraction: “Modeling of plasma wave propagation and crystal lattice theory based on computational simulations” [AIP Adv. 13, 045223 (2023)

Retraction: “Modeling of plasma wave propagation and crystal lattice theory based on computational simulations” [AIP Adv. 13, 045223 (2023)

From quartz (qtz) to diamond (dia) carbon topologies: Stepwise rationale from crystal chemistry and DFT investigations

From crystal chemistry and density functional theory DFT calculations, a stepwise rationale is proposed for the transformation from standalone distorted tetrahedron α-C5favored over standalone regular tetrahedron β-C5to high density – ultra hard orthorhombic α-C6and β-C6withqtz(quartz-based) topology characterized by 3D arrangements of distorted tetrahedra to lower densitydia-C topology (diamond-like, with regular C4 tetrahedra). Progressive C insertions into orthorhombic α-C5, α-C6, and lastly into C7were operated leading to ultimate C8stoichiometry identified as diamond-like. C7was also used as template to devise C3N4carbonitride with exceptional mechanical properties. The induced structural and physical changes are supported with elastic properties pointing to ultra-hardness, larger forqtzα,β-C6thandiaC8and inferred dynamic stability for all stoichiometries from the phonons band structures. The thermodynamic quantities as the specific heat were compared with diamond experimental CV. The electronic band structures reveal semi-conducting C6, metallic C7characterized by diamond-defect structure, and insulating C8. The results are meant to help further systemic understanding of tetrahedral carbon allotropes.

Research on incremental forming simulation based on an improved constitutive model

The incremental sheet metal forming process, characterized by the step-by-step deformation of sheet metal using a simple die, is classified as a type of plastic deformation technology. This method allows for the formation of complex-shaped parts even without the use of a specialized die. Its notable characteristic lies in its low forming load and high flexibility. To accurately forecast finite element simulation outcomes for the incremental sheet forming of 2024-O aluminum alloy sheets, constructing a precise constitutive model is essential. Typically, the uniform strain range in traditional unidirectional tensile tests does not surpass 0.3, primarily due to the necking phenomenon. This limitation hampers the accurate prediction of the actual large plastic deformation process. To address this issue, a theoretical model describing the stress-strain relationship in metal plastic deformation processes is developed using crystal plasticity theory. The constitutive model for the forming of 2024-O aluminum alloy is then constructed by adjusting the hardening coefficient and hardening index. Utilizing the improved constitutive model, the incremental sheet forming process is simulated using ABAQUS software. Upon comparison with experimental results, it is observed that the Thickness Average Absolute Relative Errors (TAARE) of the adjusted constitutive model at forming angles of 60°, 55°, and 50° are 0.414%, 0.467%, and 0.256%, and The Thickness Root Mean Square Errors (TRMSE) are determined as 0.0121, 0.0116, and 0.0094, respectively. These results indicate that the constitutive model and parameters established in this study can adequately capture the mechanical behavior of 2024-O aluminum alloy during the incremental sheet forming process.

Dynamic processes in the liquid crystal-water emulsion under shear flow and electric field

We present the results of experimental investigation of dynamical processes arising in liquid crystal-water emulsion under action of a decay shear flow and ac electric field. The 10 : 1 emulsion, consisting of the well-studied nematic mixture E7 and ionized water was prepared by usage of ultrasonic (29 kHz) mixer. It made possible to get a number of water droplets with the distribution of diameters in the range 2… 20μm. So, the slow decreasing of sizes of these instabilities resulted in corresponding slow motion of the attracted water droplets. The strong electric filled, which stabilized the initial homeotropic orientation of LC suppressed the flow induced instabilities and the slow motion of water droplets mentioned above. It also induced the aggregation of droplets in the vicinity of boundary between regions with strong field and free of field. So, combined action of shear flow and electric field can be effectively used for manipulation of the motion and interaction of water droplets. The obtained results are discussed within the existing theory of liquid crystals.

The role of different electromagnetic fields in magnesium alloys direct-chill casting: Numerical simulation and experimental investigation

Based on the magnetic-fluid-thermal multiphysics transient coupling numerical simulation results of the magnesium alloy direct-chill (DC) casting, the effects of conventional vibration electromagnetic field (VMF), differential phase vibration electromagnetic field (DP-VMF), conventional low-frequency electromagnetic field (LFMF), and differential phase low-frequency electromagnetic field (DP-LFMF) on melt flow were systematically investigated from the perspective of impulse. Based on thermal behavior and crystal growth theory, the relationships between the velocity field, temperature field, and the morphology of the solidification structure were discussed, and the effect and mechanism of different electromagnetic fields in improving the solidification structure were revealed. Simultaneously, the effects of different electromagnetic fields on AZ31B and AZ80 alloys were investigated. The DC casting experiment verified the theoretical results. Results show that applying low-frequency electromagnetic fields (LFMF and DP-LFMF) can effectively inhibit the formation of columnar grain, but the effect of microstructure refinement is weak; the impact of vibration electromagnetic fields (VMF and DP-VMF) is precisely the opposite. The structure refinement effect of DP-VMF and the inhibition effect of DP-LFMF on columnar grains are better than those of their conventional electromagnetic fields. In the presence of DP-VMF, the average grain size of the center, 1/2 radius, and the edge of the ingot decrease by about 42%, 49%, and 77%, respectively, compared with no electromagnetic field.

Solving the Fornberg–Whitham Model Derived from Gilson–Pickering Equations by Analytical Methods

This paper focuses on obtaining traveling wave solutions of the Fornberg–Whitham model derived from Gilson–Pickering equations, which describe the prorogation of waves in crystal lattice theory and plasma physics by some analytical techniques, i.e., the exp-function method (EFM), the multi-exp function method (MEFM) and the multi hyperbolic tangent method (MHTM). We analyze and compare them to show that MEFM is the optimum method.

The Dynamic Model of the Active-Inactive Cell Interface

To explore the morphodynamics of the active-inactive cell monolayer interfaces by using the active liquid crystal model. A continuum mechanical model was established based on the active liquid crystal theory and the active-inactive cell monolayer interfaces were established by setting the activity difference of cell monolayers. The theoretical equations were solved numerically by the finite difference and the lattice Boltzmann method. The active-inactive cell interfaces displayed three typical morphologies, namely, flat interface, wavy interface, and finger-like interface. On the flat interfaces, the cells were oriented perpendicular to the interface, the -1/2 topological defects were clustered in the interfaces, and the interfaces were negatively charged. On the wavy interfaces, cells showed no obvious preference for orientation at the interfaces and the interfaces were neutrally charged. On the finger-like interfaces, cells were tangentially oriented at the interfaces, the +1/2 topological defects were collected at the interfaces, driving the growth of the finger-like structures, and the interfaces were positively charged. The orientation of the cell alignment at the interface can significantly affect the morphologies of the active-inactive cell monolayer interfaces, which is closely associated with the dynamics of topological defects at the interfaces.

Reprogramming the Transition States to Enhance C-N Cleavage Efficiency of Rhodococcus opacusl-Amino Acid Oxidase.

l-Amino acid oxidase (LAAO) is an important biocatalyst used for synthesizing α-keto acids. LAAO from Rhodococcus opacus (RoLAAO) has a broad substrate spectrum; however, its low total turnover number limits its industrial use. To overcome this, we aimed to employ crystal structure-guided density functional theory calculations and molecular dynamic simulations to investigate the catalytic mechanism. Two key steps were identified: S → [TS1] in step 1 and Int1 → [TS2] in step 2. We reprogrammed the transition states [TS1] and [TS2] to reduce the identified energy barrier and obtain a RoLAAO variant capable of catalyzing 19 kinds of l-amino acids to the corresponding high-value α-keto acids with a high total turnover number, yield (≥95.1 g/L), conversion rate (≥95%), and space-time yields ≥142.7 g/L/d in 12-24 h, in a 5 L reactor. Our results indicated the promising potential of the developed RoLAAO variant for use in the industrial production of α-keto acids while providing a potential catalytic-mechanism-guided protein design strategy to achieve the desired physical and catalytic properties of enzymes.

Control over the aggregated structure of donor–acceptor conjugated polymer films for high‐mobility organic field‐effect transistors

AbstractDonor–acceptor (D‐A) conjugated polymers have demonstrated great potential in organic field‐effect transistors application, and their aggregated structure is a crucial factor for high charge mobility. However, the aggregated structure of D‐A conjugated polymer films is complex and the structure–property relationship is difficult to understand. This review provides an overview of recent progress in controlling the aggregated structure of D‐A conjugated polymer films for higher mobility, including the mechanisms, methods, and properties. We first discuss the multilevel microstructures of D‐A conjugated polymer films, and then summarize the current understanding of the relationship between film microstructures and charge transport properties. Subsequently, we review the theory of D‐A conjugated polymer crystallization. After that, we summarize the common methods to control the aggregated structure of semi‐crystalline and near‐amorphous D‐A conjugated polymer films, such as crystallites and aggregates, tie chains, film alignment, and attempt to understand them from the basic theory of polymer crystallization. Finally, we provide the current challenges in controlling the aggregated structure of D‐A conjugated polymer films and in understanding the structure–property relationship.

Modelling micropit formation in rolling contact fatigue of bearings with a crystal plasticity damage theory coupled with cohesive finite elements

Modelling micropit formation under rolling contact fatigue (RCF) is a big challenge due to strong dependence on microstructure. A RCF damage model was developed based on combined crystal plasticity theory and cohesive zone to study the crack growth and micropit formation. The results showed the crack growth is driven by shear stress, but affected by crystal orientation. Cracks would rather propagate transgranularly in the shear stress-dominant region as the damage accumulates inside grains faster than at grain boundaries. They changes to intergranular beyond the stress-dominated region becasue there is no enough driving force. The modelling results agree well the experiment.

Hydrodynamics and multiscale order in confluent epithelia.

We formulate a hydrodynamic theory of confluent epithelia: i.e. monolayers of epithelial cells adhering to each other without gaps. Taking advantage of recent progresses toward establishing a general hydrodynamic theory of p-atic liquid crystals, we demonstrate that collectively migrating epithelia feature both nematic (i.e. p = 2) and hexatic (i.e. p = 6) orders, with the former being dominant at large and the latter at small length scales. Such a remarkable multiscale liquid crystal order leaves a distinct signature in the system's structure factor, which exhibits two different power-law scaling regimes, reflecting both the hexagonal geometry of small cells clusters and the uniaxial structure of the global cellular flow. We support these analytical predictions with two different cell-resolved models of epithelia - i.e. the self-propelled Voronoi model and the multiphase field model - and highlight how momentum dissipation and noise influence the range of fluctuations at small length scales, thereby affecting the degree of cooperativity between cells. Our construction provides a theoretical framework to conceptualize the recent observation of multiscale order in layers of Madin-Darby canine kidney cells and pave the way for further theoretical developments.

سورة الضحى وتاريخية القرآن في الأدبيات الاستشراقية

Orientalists’ researches on the history of the Qur’an were based on claims that it was written in separate periods, the multiplicity of its authors, and the influence of Jewish and Christian beliefs and legislation on its development. Because the short and naive Meccan suras were completely excluded from the circle of their studies on the history and development of Prophet characteristics, as a crude primary product, sūraẗ al-ḍuḥa became a fertile ground for Orientalists’ interpretations that do not pay attention to traditional commentaries or occasions for revelation (āsbāb al-nuzūl). Although sūraẗ al-ḍuḥa refers to the unidentified person using the pronoun of the addressee, the orientalist translators of the Qur’an - such as Rodwell, Richard Bell, and Arthur Arberry – were compelled to link this pronoun to the Prophet peace be upon Him, based on classical exegesis. inadvertently uniting their peers interested in the development of the Messenger and the message, who ruled out that the pronoun belongs to the Messenger. From this hidden confrontation, contradictions arose about the adoption of the causes of revelation by some orientalists concerned with history, such as David Samuel Margolioth, Montgomery Watt, and other authors of controversial philosophical theories on the historicity of the Qur’an, such as John Edward Wansbrough, the author of the theory of historical crystallisation of the Qur’an. This paper is concerned with explaining the dependence of the reasons for the revelation by some orientalists, after which they considered it a natural entrance to the interpretation of the verses, the difference between the interpreters themselves about the reason for the approved revelation, and the interpretation of Surat Al-Duha between the interpreters of the Qur’an and the orientalists, and the approaches they adopted in interpretation. The approach adopted in this paper is the descriptive and analytical approach by going back to the Orientalist sources and books of interpretation to reach a clear presentation of the Orientalist vision criticize it scientifically and uncover the fallacies and contradictions that surrounded their viewpoints.

Orientational Order Parameter Undecyloxy-Cyanobiphenyl (11OCB) and DodecyloxyCyanobiphenyl (12OCB) by using Optical Birefringence Method

High resolution optical birefringence studies throughout the nematic and smectic A phases of undecyloxy-cyanobiphenyl (11OCB) and dodecyloxy-cyanobiphenyl (12OCB) have been performed to evaluate orientational order parameter (<P2>) as a function of temperature at wavelength λ=632.8 nm. The temperature dependence of the birefringence (n) data have been exploited to assess <P2> using a well-known Haller’s extrapolation method. Effectively, in the nematic and smectic A phases the values of <P2> have been fitted with the estimated values from Maier-Saupe mean field theory for nematic liquid crystals and McMillan mean field theory for smectic liquid crystals. Experimentally obtained <P2> values have been compared with those achieved from Maier-Saupe mean field theory and McMillan mean field theory. The agreement between experimental and calculated <P2> values at nematic-isotropic (N-I) is much higher than experimental <P2> values.

Releasing a bound molecular spring with light: a visible light-triggered photosalient effect tied to polymorphism.

Here we present a study on the solid state properties of trans tetra-ortho-bromo azobenzene (4Br-Azo). Two distinct crystal polymorphs were identified: the α-phase and β-phase. Notably, only the β-phase exhibited an extraordinary photosalient effect (jumping/breaking) upon exposure to a wide range of visible light. Powder X-ray diffraction and Raman spectroscopy revealed that the β-phase is metastable and can transition to the α-phase when subjected to specific stimuli like heat and light. Furthermore, single crystal X-ray diffraction and density functional theory calculations highlighted the significance of a highly strained conformer in the β-phase, showing that the metastability of the phase potentially arises from relieving this strain. This metastability leads to a light induced phase transition, which appears to be the cause of the photosalient effect in these crystals. Interestingly the polymorphism at the core of 4Br-Azo's dynamic behavior is based on different arrangements of halogen based intermolecular interactions. It is possible that continued study on combining visible light capturing chromophores with halogen interaction-based polymorphism will lead to the discovery of even more visible light controlled dynamic crystal materials.

Phase field crystal models with applications to laser deposition: A review.

In this article, we address the application of phase field crystal (PFC) theory, a hybrid atomistic-continuum approach, for modeling nanostructure kinetics encountered in laser deposition. We first provide an overview of the PFC methodology, highlighting recent advances to incorporate phononic and heat transport mechanisms. To simulate laser heating, energy is deposited onto a number of polycrystalline, two-dimensional samples through the application of initial stochastic fluctuations. We first demonstrate the ability of the model to simulate plasticity and recrystallization events that follow laser heating in the isothermal limit. Importantly, we also show that sufficient kinetic energy can cause voiding, which serves to suppress shock propagation. We subsequently employ a newly developed thermo-density PFC theory, coined thermal field crystal (TFC), to investigate laser heating of polycrystalline samples under non-isothermal conditions. We observe that the latent heat of transition associated with ordering can lead to long lasting metastable structures and defects, with a healing rate linked to the thermal diffusion. Finally, we illustrate that the lattice temperature simulated by the TFC model is in qualitative agreement with predictions of conventional electron-phonon two-temperature models. We expect that our new TFC formalism can be useful for predicting transient structures that result from rapid laser heating and re-solidification processes.