Effect of defects and surface anchoring on the phase behavior of chiral smectic liquid crystals

The influence of defects and surface effects on the stability of phenomena accompanying phase transitions, mainly coexistence phenomenon, has been studied. Experimental measurements were carried out by varying the cell thickness and using simple experimental on chiral smectic liquid crystal product. The analysis of the results with different cell thickness leads us to interpret the anomaly shown by our product related to impact of defects and surface effects. Moreover, the phase transition is affected by the trace of defects for thick cell and by the surface effect for thin cell. These effects have the same role as an electric local field which can induce phase transition.     

Characterization of size effect of natural convection in melting process of phase change material in square cavity

The accelerating effect of natural convection on the melting of phase change material(PCM) has been extensively demonstrated. However, such an influence is directly dependent on the size and shape of domain in which phase change happens, and how to quantitatively describe such an influence is still challenging. On the other hand, the simulation of natural convection process is considerably difficult, involving complex fluid flow in a region changing with time, and is typically not operable in practice. To overcome these obstacles, the present study aims to quantitatively investigate the size effect of natural convection in the melting process of PCM paraffin filled in a square latent heat storage system through experiment and simulation, and ultimately a correlation equation to represent its contribution is proposed. Firstly, the paraffin melting experiment is conducted to validate the two-dimensional finite element model based on the enthalpy method.Subsequently, a comprehensive investigation is performed numerically for various domain sizes. The results show that the melting behavior of paraffin is dominated by the thermal convection. When the melting time exceeds 50 s, a whirlpoor flow caused by natural convection appears in the upper liquid phase region close to the heating wall, and then its influencing range gradually increases to accelerate the melting of paraffin. However, its intensity gradually decreases as the distance between the melting front and the heating wall increases. Besides, it is found that the correlation between the total melting time and the domain size approximately exhibits a power law. When the domain size is less than 2 mm, the accelerating effect of natural convection becomes very weak and can be ignored in practice. Moreover, in order to simplify the complex calculation of natural convection, the equivalent thermal conductivity concept is proposed to include the contribution of natural convection to the total melting time, and an empirical correlation is given for engineering applications.     

Epitaxy surface effect on the first-order phase transition properties in a ferroelectric thin film

By modifying the interchange interactions and the transverse fields on the epitaxy surface layer,this paper studies the phase transition properties of an n-layer ferroelectric thin film by the Fermi-type Green’s function technique based on the transverse Ising model with a four-spin interaction.The special attention is given to the effect of the epitaxy surface layer on the first-order phase transition properties in the parameter space constructed by the ratios of the bulk transverse field and the bulk four-spin interaction to the bulk two-spin interaction with the framework of the higher-order decoupling approximation to the Fermi-type Green’s function.The results show that the first-order phase transition properties will be changed significantly due to the modification of interchange interaction and transverse field parameters on the epitaxy surface layer.The dependence of the first-order phase transition properties on the thickness of ferroelectric thin films is also discussed.     

外延铁电薄膜相变温度的尺寸效应

考虑外延钙钛矿型铁电薄膜内的等效应力、表面晶格变化和表面电荷引起的退极化效应等机电耦合边界条件,利用铁电薄膜系统的动态金茨堡-朗道方程(DGL),系统分析和讨论了外延铁电薄膜相变温度与临界相变厚度的尺寸效应.结果表明,铁电薄膜相变温度与临界相变厚度完全依赖于各种与薄膜厚度相关的力电耦合边界条件.也给出了BaTiO₃外延铁电薄膜相变温度在各种边界条件下随厚度的变化,从结果看出,本文的分析与结论更符合实验数据. 关键词： 尺寸效应 外延铁电薄膜 相变温度 力电耦合边界     

Electro-optical Kerr effect in the isotropic phase of the two antiferroelectric liquid crystal mixtures

We have experimentally studied for the first time the electro-optical Kerr effect and the pre-transitional behavior in the isotropic phase of two antiferroelectric liquid crystal mixtures, W-232 and W-204D, composed of rod-like ester molecules exhibiting the direct smectic-A to isotropic (SmA-I) phase transition. The Kerr law has been confirmed for the two compounds and the variation of inverse Kerr constant with temperature above the smectic–isotropic transition temperatures were determined. Both the mixtures with very broad antiferroelectric phase around room temperature have similar sequence of the phases (i.e., Cr-SmC*A-SmC*-SmA-I). Although, the pre-transitional behavior is usually complex in the isotropic phase of the chiral smectic liquid crystal compounds, the investigated compounds showed a similar behavior compared to that of nematic–isotropic behavior.     

应力作用下EuTiO3铁电薄膜电热效应的唯象理论研究

基于Laudau-Devonshire的热动力学模型, 计算了EuTiO₃铁电薄膜材料的电热效应. 结果显示在外加应力的调控下, 电极化、电热系数以及绝热温差都会随之变化. 外加垂直于表面的张应力加大, 薄膜的相变温度升高, 绝热温差增加, 最大绝热温差所对应的工作温度向高温区移动. 对于二维平面失配应变u_m =-0.005的薄膜, 当外加张应力σ₃ = 5 GPa时, 其最大电热系数为1.75×10^-3 C/m²·K, 电场变化200 MV/m 时室温下绝热温差ΔT 的最大值可达到14 K 以上, 绝热温差ΔT ≥13 K 的工作温区超过120 K, 表明可以通过调控外部应力来获取室温时较大的绝热温差. 此结果预示着铁电EuTiO₃ 薄膜在室温固态制冷方面可能具有较好的应用前景.     

The influence of the chiral terphenylate on the tilt angle in pyrimidine ferroelectric mixtures

Pyrimidine multicomponent mixture used as a base for the preparation of ferroelectric liquid crystalline mixtures after doping with chiral dopants was tested in the aim of establishing the tilt angle dependence on the concentration of chiral dopant. The compounds being components of this mixture were doped with the same chiral dopant to check the influence of their structure on the tilt angle of ferroelectric mixtures.     

Kerr effect and Kerr constant enhancement in vertically aligned deformed helix ferroelectric liquid crystals

In this article,we review recently achieved Kerr effect progress in novel liquid crystal(LC) material:vertically aligned deformed helix ferroelectric liquid crystal(VADHFLC).With an increasing applied electric field,the induced inplane birefringence of LCs shows quadratic nonlinearity.The theoretical calculations and experimental details are illustrated.With an enhanced Kerr constant to 130 nm/V2,this VADHFLC cell can achieve a 2π modulation by a small efficient electric field with a fast response around 100 μs and thus can be employed in both display and photonics devices.     

Characterization of a planar NID chiral interface under negative and/or positive phase velocity conditions

Using positive and/or negative phase velocity conditions, characteristics of a planar non-integer dimensional (NID) chiral interface are explored for specific values of NID parameter. For this purpose, discussion is divided into four cases. It is noted how characteristics of the interface changes when the situation is changed from one case to another. Impact of variation of NID parameter on the reflected power is also noted for each case.     

Anomeric effect plays a major role in the conformational isomerism of fluorinated pnictogen compounds

According to our theoretical studies, the anomeric effect, an stereoelectronic interaction between lone pair and a vicinal antibonding orbital, has shown to contribute decisively for the conformational isomerism of 1‐fluoro‐N,N‐dimethylmethanamine ( 1 ) and of its corresponding P, As and Sb analogues ( 2 – 4 ). C? X bonds in 2 – 4 are larger than in the parent compound 1 , thus providing a LP_X/C? F^* interaction progressively weaker on going from 1 to 4 . However, such hyperconjugation contributed by more than 1.3 kcal mol^?1 for the stabilization of anti conformer in 4 (θ_{LP? X? C? F} = 180°), increasing to 24.1 kcal mol^?1 in 1 . An isodesmic reaction model supported these findings. Copyright © 2008 John Wiley & Sons, Ltd.     

HfO2基铁电场效应晶体管读写电路的单粒子翻转效应模拟

使用器件-电路仿真方法搭建了氧化铪基铁电场效应晶体管读写电路,研究了单粒子入射铁电场效应晶体管存储单元和外围灵敏放大器敏感节点后读写数据的变化情况,分析了读写数据波动的内在机制.结果表明:高能粒子入射该读写电路中的铁电存储单元漏极时,处于"0"状态的存储单元产生的电子空穴对在器件内部堆积,使得栅极的电场强度和铁电极化增大,而处于"1"状态的存储单元由于源极的电荷注入作用使得输出的瞬态脉冲电压信号有较大波动;高能粒子入射放大器灵敏节点时,产生的收集电流使处于读"0"状态的放大器开启,导致输出数据波动,但是其波动时间仅为0.4 ns,数据没有发生单粒子翻转能正常读出.两束高能粒子时间间隔0.5 ns先后作用铁电存储单元漏极,比单束高能粒子产生更大的输出数据信号波动,读写"1"状态的最终输出电压差变小.     

Orientational order parameters of a binary mixture showing both induced smectic and re-entrant nematic phases

The phase diagram of a new binary system of two polar nematic compounds, 4-cyanophenyl [4′ (4″-n-heptylphenyl)] benzoate(7CPB) and 4-cyanophenyl 4-nonylbenzoate (9.CN), shows the presence of both the induced smectic and re-entrant nematic phases in a certain concentration range 0.4 < x _9.CN < 0.87. The results of X-ray diffraction and density measurements are reported here. Orientational order parameters have been determined in the induced smectic, normal nematic and re-entrant nematic phases from X-ray diffraction measurements. The order parameters have been fitted to those calculated from modified McMillan's theory as proposed by Luckhurst and Timimi. The agreement is found to be closer to the modified model. The experimental variation of the layer thickness with mole fraction of 9.CN has also been explained fairly well by assuming the presence of two types of homo dimers (7CPB + 7CPB, 9.CN + 9.CN) and one type of hetero dimer (7CPB + 9.CN).     

Single event effect in a ferroelectric-gate field-effect transistor under heavy-ion irradiation

The single event effect in ferroelectric-gate field-effect transistor （FeFET） under heavy ion irradiation is investigated in this paper. The simulation results show that the transient responses are much lower in a FeFET than in a conventional metal-oxide-semiconductor field-effect transistor （MOSFET） when the ion strikes the channel. The main reason is that the polarization-induced charges （the polarization direction here is away from the silicon surface） bring a negative surface po- tential which will affect the distribution of carders and charge collection in different electrodes significantly. The simulation results are expected to explain that the FeFET has a relatively good immunity to single event effect.     

Status of the chiral magnetic effect and collisions of isobars

In this review, we examine the current theoretical and experimental status of the chiral magnetic effect.We discuss possible future strategies for resolving uncertainties in interpretation including recommendations for theoretical work, recommendations for measurements based on data collected in the past five years, and recommendations for beam use in the coming years of RHIC. We specifically investigate the case for colliding nuclear isobars(nuclei with the same mass but different charge) and find the case compelling. We recommend that a program of nuclear isobar collisions to isolate the chiral magnetic effect from background sources be placed as a high priority item in the strategy for completing the RHIC mission.     

Electrophysical properties of a system with induced antiferroelectric phase comprising cyano compound

The DSC, electrooptic and X-ray results for the system composed of two synclinic compounds CNCH₂COO(CH₂)₆OphPhCOOPhCOOC*H(CH₃)C₆H₁₃ and C₅H₁₁COO(CH₂)₃OPhCOOPhPhCOOC*H(CH₃)C₆H₁₃ are presented. The antiferroelectric SmC*_A phase induces in this system and it was confirmed by physical measurements. It was found out that the mechanism of SmC*_A phase induction is different than in systems comprising compound with perfluoroalkyl chain.     

Combined effect of the transition layer and interfacial coupling on the properties of ferroelectric bilayer film

Within the framework of modified Ginzburg--Landau--Devonshire phenomenological theory, a ferroelectric bilayer film with a transition layer within each constituent film and an interfacial coupling between two materials has been studied. Properties including the Curie temperature and the spontaneous polarization of a bilayer film composed of two equally thick ferroelectric constituent films are discussed. The results show that the combined effect of the transition layer and the interfacial coupling plays an important role in explaining the interesting behaviour of ferroelectric multilayer structures consisting of two ferroelectric materials.     

Evaluation of the effect of a phase-change material on the thermal response of a bizone building under the climatic conditions of Tunisia

This paper extends the thermoelectric analogy method to study the thermal behavior of a concrete envelope of a dual-zone building containing microencapsulated phase-change material (PCM) and subjected to realistic climatic conditions based on weather data for a typical summer day in Tunisia. This work deals with a numerical study based on the nodal method to predict the effect of phase change on the thermal response as well as the energy flux reduction associated with the composite-envelope building.     

Phase diagram and magnetocaloric effect of alloys

We propose the phase diagram of a new pseudo-ternary compound, CoMnGe_1-xSn_x, in the range x0.1. Our phase diagram is a result of magnetic and calorimetric measurements. We find that the separate magnetic and structural transitions in CoMnGe are tuned together as the level of Sn substitution is increased. We demonstrate the appearance of a hysteretic magnetostructural phase transition in the range x=0.04–0.055, similar to that observed in CoMnGe under hydrostatic pressure. From magnetisation measurements, we show that the isothermal entropy change associated with the magnetostructural transition can be as high as in a field of 1 T. However, the large thermal hysteresis in this transition () will limit its straightforward use in a magnetocaloric device.