Influence of Polarization-Induced Electric Fields on Optical Properties of Intersubband Transitions in Al_xGa_(1-x)N/GaN Double Quantum Wells

The influence of polarization-induced electric fields on the electron distribution and the optical properties of intersubband transitions （ISBT） in AlxGa（1-x）N/GaN coupled double quantum wells （DQWs） is investigated by self-consistent calculation. It is found that the polarization-induced potential drop leads to an asymmetric potential profile of AlxGa（1-x）N/GaN DQWs even though the two wells have the same width and depth. The polarization effects result in a very large Stark shift between the odd and even order subbands,thus shortening the wavelength of the ISBT between the first odd order and the second even order （1odd-2 ） subbands. Meanwhile, the electron distribution becomes asymmetric due to the polarization effects, and the absorption coefficient of the 1odd-2 ISBT decreases with increasing polarization field discontinuity.

Floquet-Engineering Topological Phase Transition in Graphene Nanoribbons by Light

Quasi-one-dimensional(1D)graphene nanoribbons(GNRs)play a crucial role in advancement of nextgeneration devices.Recent studies have suggested their potential to exhibit unique symmetry-protected topological phases defined by a Z_(2) invariant.By employing both the tight-binding model and the Floquet theory,our investigation demonstrates the effective control of the topological phase within quasi-1D armchair GNRs(AGNRs)using elliptically polarized light,unveiling rich topological phase diagrams.Specifically,we observe that varying the amplitude of the light can induce transitions in the band gap(E_(g))of AGNRs,leading to multiple changes in the system’s Z_(2) invariant.Furthermore,for heterojunctions composed of different AGNR segments,the junction state can be either created or eliminated by the application of elliptically polarized light.

Effects of polarization on intersubband transitions of Al_xGa_(1-x)N/GaN multi-quantum wells

The effects of polarization and related structural parameters on the intersubband transitions of A1GaN/GaN multi- quantum wells （MQWs） have been investigated by solving the Schr6dinger and the Poisson equations self-consistently. The results show that the intersubband absorption coefficient increases with increasing polarization while the transition wavelength decreases, which is not identical to the case of the interband transitions. Moreover, it suggests that the well width has a greater effect on the intersubband transitions than the barrier thickness, and the intersubband transition wavelength of the structure when doped in the barrier is shorter than that when doped in the well. It is found that the influences of the structural parameters differ for different electron subbands. The mechanisms responsible for these effects have been investigated in detail.

Valley polarization in transition metal dichalcogenide layered semiconductors:Generation,relaxation,manipulation and transport

In recent years,valleytronics researches based on 2D semiconducting transition metal dichalcogenides have attracted considerable attention.On the one hand,strong spin–orbit interaction allows the presence of spin–valley coupling in this system,which provides spin addressable valley degrees of freedom for information storage and processing.On the other hand,large exciton binding energy up to hundreds of me V enables excitons to be stable carriers of valley information.Valley polarization,marked by an imbalanced exciton population in two inequivalent valleys(+K and-K),is the core of valleytronics as it can be utilized to store binary information.Motivated by the potential applications,we present a thorough overview of the recent advancements in the generation,relaxation,manipulation,and transport of the valley polarization in nonmagnetic transition metal dichalcogenide layered semiconductors.We also discuss the development of valleytronic devices and future challenges in this field.

Relationship measurement between ac-Stark shift of^40Ca^+clock transition and laser polarization direction

Ac-Stark shift of atom levels is caused by an ac-electromagnetic field. As an electromagnetic wave, laser light does induce ac-Stark shift. It is proved experimentally that if the light is linearly polarized, the dynamic polarizability changes with polarization direction. The polarization direction of the linearly-polarized laser is tuned by 720°, and the ac-Stark shifts of the 4S1/2,m=±1/2→3D5/2,m=±1/2 clock transitions in ^40Ca^＋ are measured in steps of 10°. The frequency shifts change with laser polarization in a periodical manner and have values opposite to each other.

Influence of Polar Pressure Transmission Medium on the Pressure Coefficient of Excitonic Interband Transitions in Monolayer WSe_2

The influence of the pressure transmission medium（PTM）on the excitonic interband transitions in monolayer tungsten diselenide（WSe2）is investigated using photoluminescence（PL）spectra under hydrostatic pressure up to 5GPa.Three kinds of PTMs,condensed argon（Ar）,1：1 n-pentane and isopentane mixture（PM）,and4：1 methanol and ethanol mixture（MEM,a PTM with polarity）,are used.It is found that when either Ar or PM is used as the PTM,the PL peak of exciton related to the direct K-K interband transition shows a pressure-induced blue-shift at a rate of 32±4 or 32±1 meV/GPa,while it turns to be 50±9meV/GPa when MEM is used as the PTM.The indirect A-K interband transition presents almost no shift with increasing pressure up to approximatel.y 5 GPa when Ar and PM are used as the PTM,while it shows a red-shift at the rate of-17±7meV/GPa by using MEM as the PTM.These results reveal that the optical interband transitions of monolayer WSe2 are very sensitive to the polarity of the PTM.The anomalous pressure coefficient obtained using the polar PTM of MEM is ascribed to the existence of hydrogen-like bonds between hydroxyl in MEM and Se atoms under hydrostatic pressure.

Subseasonal predictability of the transition of the stratospheric polar vortex:A case study in winter 1987/88

平流层极涡作为冬季次季节尺度上一个重要的可预测性来源,其强度在1987/88年冬季表现为1979-2019年最显著的转折,即在前(后)冬极端偏弱(强),因此在本文中选取这一个例研究了该年冬季平流层极涡在次季节尺度上的可预测性,结果表明弱极涡和强极涡事件的预测与模式能否准确预测上传行星波的强度紧密相关,同时,发现前期对流层欧亚遥相关波列可能是弱极涡事件发生的关键预兆信号.此外,模式对平流层极涡强度和北大西洋涛动预测误差之间存在显著正相关关系,表明模式减少平流层极涡的预测误差可能可以提高北大西洋涛动及相关对流层气候预测.

Theoretical Study of Antiferrodistortive Phase Transition in Strontium Titanate

At 105 K, strontium titanate is known to undergo an antiferrodistortive transition transform-ing from cubic to tetragonal structure as a result of the rotation of the oxygen octahedral around a cubic axe. Based on the Curie principle, the order parameter is determined to be a third-order complete symmetry polarization tensor. To take into account of quantum effects,the dielectric permittivity is measured from Landau free energy, and the Curie Weiss-type behavior is analyzed. From crystallization chemistry viewpoint, the dielectric behavior at low temperature is connected to small radius of Sr^2＋, which is much easier to move around the oxygen octahedral than Ba^2＋ in BaTiO3 or Pb^2＋ in PbTiO3.

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 interracial coupling plays an important role in explaining the interesting behaviour of ferroelectric multilayer structures consisting of two ferroelectrie materials.

Transition state to mode locking in a passively mode-locked erbium-doped fibre ring laser

The transition state between the continuous wave region and the mode-locked region in a passively mode-locked erbium-doped fibre ring laser has been experimentally observed by utilizing the nonlinear polarization rotation technique. When the pump power reaches the mode-locked threshold, the metastable pulse train with a tunable repetition rate is obtained in the transition from the continuous wave state to the passive mode-locked state via proper adjustment of the polarization controller. A simpie model has been established to explain the experimental observation.

STUDIES ON THE MORPHOLOGY OF THERMOTROPIC POLYESTER DURING TRANSITIONS BETWEEN ISOTROPIC AND ANISOTROPIC MELTS

The morphology of a thermotropic aromatic polyester during the transitions between isotropic and anisotropic melts was studied by means of polarizing microscopy and small angle light scattering techniques. Both transition processes were found to be composed of the initiation of a new phase at local places of the old phase matrix and the growth of the new phase domains. A change of Hv scattering patterns was observed in the transition temperature ranges and was explained as the result of heterogeneity of the mesophase system, but not the change in ordering of a homogeneous mesophase.

MORPHOLOGICAL AND KINETIC STUDIES OF PHASE TRANSITIONS OF A SIDE-CHAIN LIQUID CRYSTALLINE POLYMER

The morphological changes of a side-chain liquid-crystalline polymethacrylate during isotropization and liquid-crystallization transitions were studied by means of polarizing microscopy. These transitions were found to be composed of the initiation of a new phase at local places of the old phase matrix and the growth of the new phase: domains. The kinetics of the liquid-crystallization of the polymer from an isotropic melt to a smectic mesophase was also investigated. The isothermal process of the transition can be described by the Avrami equation. The values of the Avrami exponent were found to be around 2.6. which is lower than the value usually obtained for crystallization transition of polymers, but larger than that reported for liquid-crystallization transition of main-chain polymers. These results may indicate the difference in growth geometry of new phase during transition between crystallization and liquid-crystallization in general and between liquid-crystallization of main-chain and side-chain polymers. It was found that the liquid-crystallization of the used side-chain polymethacrylate may occur at small undercoolings with high transformation rate similar to that of main-chain polymers and small-molecule liquid crystals, while the crystallization of polymers can only proceed at large undercoolings. These phenomena can be explained by the idea that the surface free energy of nucleus during liquid-crystallization transition is less than that for crystallization, and evidence was obtained from analysis of the temperature dependence of the transformation rate.

MORPHOLOGICAL STUDIES OF A THERMOTROPIC SIDE-CHAIN LIQUID CRYSTALLINE POLYMER DURING MESOPHASE TRANSITIONS

The morphological features of a side-chain liquid crystalline polymer during the mesophase transitions were investigated by using the DSC technique. The polymer used was polyacrylate with mesogens of three benzene rings attached to the main chain through a flexible spacer. A special two-phase texture was observed in the transition temperature range. Similar to main-chain liquid crystalline polymers the transition process of the side-chain liquid crystalline polymer was composed of an initiation of the new phase at local places of the old phase matrix and a growth process of the new phase domains.

Differential Expression of Genes Involved in Cell Polarity, EMT and Cell-Fate in Breast Cancer and Corresponding Normal Tissue

Objectives: Cell polarity and epithelial morphology are peculiar features of cells forming the terminal ductal lobular unit, and they are early lost during neoplastic transformation because of an epithelial-mesenchymal transition (EMT). To understand these early events we analyzed a set of 125 genes related to cell polarity, EMT and cell-fate decision in 26 breast cancer specimens and corresponding patient-matched normal tissue. Methods: The difference of gene expression was explored by t-paired test. In addition, to evidence latent variables accounting for genes correlations, a Factor Analysis was applied as exploratory technique. Results: Among the 90 differentially expressed genes, those coding for cell polarity complexes, apical-junctional components and luminal cytokeratins were overexpressed in tumor samples (suggesting a terminally differentiated phenotype) whereas those coding for stemness-associated features or related with EMT were expressed in normal tissues but not in tumor samples, suggesting the persistence of stem/progenitor cells. Factor analysis confirmed these findings and indicated that the difference between tumors and normal tissues can be synthesized in three main features representative of specific molecular/morphological alterations. Conclusions: The a priori definition of a selected panel of genes and the application of an exploratory statistical approach, greatly contribute to reduce the intrinsic biological complexity of tumor specimens and to describe the difference between tumor specimens and corresponding histologically normal tissues.

Metal-Insulator Transition of Peierls Type in Quasi-One-Dimensional Crystals of TTT₂I₃

We investigate the metal-insulator transition in quasi-one-dimensional organic crystals of tetrathiotetracene-iodide, TTT2I3, in the 2D model. A crystal physical model is applied which takes into account two the most important hole-phonon interaction mechanisms. One is similar to that of deformation potential and the other is of polaron type. The scattering on defects is also considered and it is crucial for the explanation of the transition. The phonon polarization operator and the renormalized phonon spectrum are calculated in the random phase approximation for different temperatures applying the method of Green functions. We show that the transition is of Peierls type. The effect of lattice distortion on the dispersion of renormalized acoustic phonons is analyzed.

《电化学基础》课程开放性实验设计教改探索

面向国家能源战略及新能源产业的需求,教育部近年设立了一批新能源相关专业,电化学在新能源领域发挥着越来越重要的作用,因此《电化学基础》是本专业的教学重点内容。但是在教学过程中发现,仅通过课堂教学让学生理解一些概念十分困难。基于此,本文以电解水制氢反应为模型,进行《电化学基础》课程开放性实验设计,让本科生进入实验室,完成制氢反应NiCoP纳米电催化剂的制备、物相组成和微观结构分析,并测试催化剂的电解水制氢极化曲线研究其催化性能,通过分析不同测试条件下催化剂的极化曲线特征加深对电化学重要知识点-极化作用的认识,同时培养学生的科研兴趣,提升学生的实践能力和创新思维。

Surface Polarization Effects on Collapse Transition of Polyelectrolyte Brushes

Polyelectrolyte brushes(PEBs)are commonly used to modify surface that have attracted great research interest.The dielectric permittivity of the grafted surface is typically significantly different from that of solution,which results in surface polarization(SP)effect with a jump of electric field.It is thus important to study how SP alters the PEB’s structure and properties.In this work,the SP effects on PEB structure was studied using a statistical thermodynamic theory.The free energy functional to describe SP effect was constructed by using the image-charge method.Meanwhile,the electrostatic potential was solved from a modified Poisson-Boltzmann equation taking the ion solvation effect into consideration.In the absence of SP,the thickness of PEB exhibited a continuous collapse transition when decreasing the solvent quality.In the presence of SP,the collapse became a jump-like transition.Free energy analysis showed that the long-range Coulombic interaction dominated the transition because of the enhanced counterion condensation in the presence of SP.The theory provides an effective tool to study SP effect on PEBs,and the results explain the underlying physics in PEB collapse transition.

Polarization-dependent photoinduced metal–insulator transitions in manganites

In correlated oxides,collaborative manipulation on light intensity,wavelength,pulse duration and polarization has yielded many exotic discoveries,such as phase transitions and novel quantum states.In view of potential optoelectronic applications,tailoring long-lived static properties by light-induced effects is highly desirable.So far,the polarization state of light has rarely been reported as a control parameter for this purpose.Here,we report polarization-dependent metal-to-insulator transition(MIT)in phaseseparated manganite thin films,introducing a new degree of freedom to control static MIT.Specifically,we observed giant photoinduced resistance jumps with striking features:(1)a single resistance jump occurs upon a linearly polarized light incident with a chosen polarization angle,and a second resistance jump occurs when the polarization angle changes;(2)the amplitude of the second resistance jump depends sensitively on the actual change of the polarization angles.Linear transmittance measurements reveal that the origin of the above phenomena is closely related to the coexistence of anisotropic micro-domains.Our results represent a first step to utilize light polarization as an active knob to manipulate static phase transitions,pointing towards new pathways for nonvolatile optoelectronic devices and sensors.

Xihuang Pill(西黄丸) Induces Mesenchymal-Epithelial Transition and Inhibits Loss of Apical-Basal Polarity in Colorectal Cancer Cell through Regulating ZEB1-SCRIB Loop

Objective：To investigate the antiproliferative and anti-metastasis effect of Xihuang Pill（西黄丸,XP） on human colorectal cancer cell and to explore the molecular mechanism by which it produces the effects.Methods：Highly metastatic human colorectal cancer cell line LoVo was treated with low-,medium-,and highdose XP-containing serum（XP-L,XP-M,XP-H） groups for 48 h,cells intervened with no drug rat serum and PD98059[extracellular signal-regulated kinase（ERK） inhibitor]as negative and positive controls（NC and PC）groups.Cell proliferation assay was made using cell counting kit-8（CCK8）.The 8 μm pore-size transwell chamber and 4＇,6-diamidino-2-phenylindole（DAPI） staining were applied to examine the ability of invasion and migration of the cells.The protein expression of ERK1/2,zinc finger E-box-binding homeobox 1（ZEB1）,Scrib and lethal giant larvae homolog 2（Lgl2） was detected by Western blotting while the relative mRNA quantity of E-cadherin,N-cadherin,Occludin and junctional adhesion molecule-1（JAM1） was measured by realtime fluorescent quantitative polymerase chain reaction（RT-qPCR）.Results：XP induced a dose-dependent suppression on the proliferation of LoVo cells（P〈0.05 or P〈0.01）,with the inhibition rates varied from 27.30%to31.08%.Transwell assay showed that when preprocessed with PD98059 and XP-containing serum,the number of cells that passed the filter decreased significantly compared with that of NC group（P〈0.05 or P〈0.01）.Moreover,XP inhibited the protein expression of ERK1/2 and ZEB1（P〈0.05）;and up-regulated the protein expression of Scrib and Lgl2（P〈0.05）.The mRNA levels of E-cadherin,Occludin and JAM1 of the XP intervened groups and PC group markedly ascended（P〈0.05） while that of N-cadherin showed a descending tendency（P〉0.05）.Conclusion：XP intervention suppressed the ability of proliferation,invasion and migration of the LoVo cells.Regulating ZEB1-SCRIB Loop so as to recover epithelial phenotype and apical junctional complex might be one of the mechanisms by which XP produces the anti-metastasis effect.

Pedogenesis affecting the Matuyama-Brunhes polarity transition recorded in Chinese loess?

A detailed record of the Matuyama-Brunhes (M-B) transition has been obtained from the loess unit 8 (L8) at Duanjiapo (34.2° N, 109.2° E), Shannxi Province of China. An investigation of the rock magnetic properties using hysteresis loops, thermomagnetic analyses identifies pseudo-single domain magnetite as the main carrier of the rema-nence, with a small contribution from maghemite and hema-tite. The paleo-direction records obtained reveal: ( i ) The M-B transition was recorded in the middle and lower part of L8, and comprises of five fast reversals. (ii) The duration of the M-B polarity transition related to the directional change is about 4800 a. (iii) The virtual geomagnetic pole (VGP) path during the transition is confined over Africa, peaked 90° away from the sampling site, in contrast with the results obtained from the Weinan loess section. The different VGPs are probably attributed to the pedogenesis.