Inhomogeneous mode-coupling theory and growing dynamic length in supercooled liquids

We extend mode-coupling theory (MCT) to inhomogeneous situations, relevant for supercooled liquid in an external field. We compute the response of the dynamical structure factor to a static inhomogeneous external potential and provide the first direct evidence that the standard formulation of MCT is associated with a diverging length scale. We find that the so-called cages are, in fact, extended objects. Although close to the transition the dynamic length grows as |T-T(c)|(-1/4) in both the beta and alpha regimes, our results suggest that the fractal dimension of correlated clusters is larger in the alpha regime. We derive inhomogeneous MCT equations valid to second order in gradients.     

Assessment of the serotonin pathway as a therapeutic target for pulmonary hypertension

Blockade of the serotonin reuptake transporter (5‐HTT), using fluoxetine, has been identified as a potential therapeutic target for preventing and, importantly, reversing pulmonary hypertension (PH). This study utilized synchrotron radiation microangiography to determine whether fluoxetine could prevent or reverse endothelial dysfunction and vessel rarefaction, which underpin PH. PH was induced by a single injection of monocrotaline (MCT; 60 mg kg^?1). Following MCT administration, rats received daily injections of either saline or fluoxetine (MCT+Fluox; 10 mg kg^?1) for three weeks. A third group of rats also received the fluoxetine regime, but only three weeks after MCT (MCT+Fluox_Delay). Control rats received daily injections of saline. Pulmonary microangiography was performed to assess vessel branching density and visualize dynamic changes in vessel diameter following (i) acute fluoxetine or (ii) acetylcholine, sodium nitroprusside, BQ‐123 (ET‐1_A receptor blocker) and L‐NAME (NOS inhibitor). Monocrotaline induced PH that was inevitably terminal. `Delayed' treatment of fluoxetine (MCT+Fluox_Delay) was unable to reverse the progression of PH. Early fluoxetine treatment pre‐PH (i.e. MCT+Fluox) attenuated but did not completely prevent vascular remodeling, vessel rarefaction and an increase in pulmonary pressure, and it did not prevent pulmonary endothelial dysfunction. Interestingly, fluoxetine treatment did counter‐intuitively prevent the onset of right ventricular hypertrophy. Using synchrotron radiation microangiography, selective blockade of the serotonin reuptake transporter alone is highlighted as not being sufficient to prevent pulmonary endothelial dysfunction, which is the primary instigator for the inevitable onset of vascular remodeling and vessel rarefaction. Accordingly, potential therapeutic strategies should aim to target multiple pathways to ensure an optimal outcome.     

Experimental observation of a nearly logarithmic decay of the orientational correlation function in supercooled liquids on the picosecond-to-nanosecond time scales

Dynamics of five supercooled molecular liquids have been studied using optical heterodyne detected optical Kerr effect experiments. "Intermediate" time scale power law decays (approximately 2 ps to 1-10 ns) with temperature independent exponents close to -1 have been observed in all five samples from high temperature to approximately T(c), the mode-coupling theory (MCT) critical temperature. The amplitude of the intermediate power law increases with temperature as [(T-T(c))/T(c)](1/2). The results cannot be explained by standard MCT, and one possible explanation within MCT would require the higher order singularity scenario, thought to be highly improbable, to be virtually universal.     

Evolution of vibrational excitations in glassy systems

The equations of the mode-coupling theory (MCT) for ideal liquid-glass transitions are used for a discussion of the evolution of the density-fluctuation spectra of glass-forming systems for frequencies within the dynamical window between the band of high-frequency motion and the band of low-frequency-structural-relaxation processes. It is shown that the strong interaction between density fluctuations with microscopic wavelength and the arrested glass structure causes an anomalous-oscillation peak, which exhibits the properties of the so-called boson peak. It produces an elastic modulus which governs the hybridization of density fluctuations of mesoscopic wavelength with the boson-peak oscillations. This leads to the existence of high-frequency sound with properties as found by x-ray-scattering spectroscopy of glasses and glassy liquids. The results of the theory are demonstrated for a model of the hard-sphere system. It is also derived that certain schematic MCT models, whose spectra for the stiff-glass states can be expressed by elementary formulas, provide reasonable approximations for the solutions of the general MCT equations.     

Harmonic measure and winding of conformally invariant curves

The exact joint multifractal distribution for the scaling and winding of the electrostatic potential lines near any conformally invariant scaling curve is derived in two dimensions. Its spectrum f(alpha,lambda) gives the Hausdorff dimension of the points where the potential scales with distance r as H approximately r(alpha) while the curve logarithmically spirals with a rotation angle phi=lambdalnr. It obeys the scaling law f(alpha,lambda)=(1+lambda(2))f(alpha)-blambda(2) with alpha=alpha/(1+lambda(2)) and b=(25-c)/12, and where f(alpha) identical with f(alpha,0) is the pure harmonic measure spectrum, and c the conformal central charge. The results apply to O(N) and Potts models, as well as to stochastic L?wner evolution.     

A statistical-mechanical theory of slow dynamics near the glass transition

A statistical-mechanical theory of slow dynamics near the glass transition in two kinds of glass-forming systems, (M) molecular systems and (S) suspensions of colloids, is presented from a unified point of view based on the Tokuyama-Mori projection operator method. The exact diffusion equations for the coherent- and the incoherent-intermediate scattering functions are first derived, whose memory functions are convolutionless in time and contain the correlation effects due to the hydrodynamic interactions in (S). The analytic expressions of the memory functions are then calculated within the mode-coupling theory (MCT) approximation and are shown to coincide with the conventional ones obtained by MCT. Alternative mode-coupling equations are thus obtained in (M) and (S) separately. Self-diffusion is also discussed. Alternative equations for the mean-square displacement and the non-Gaussian parameter are also derived within MCT approximation. All results in both the systems are compared with those obtained by MCT.     

Dry deposition of pollutant and marker particles onto live mouse airway surfaces enhances monitoring of individual particle mucociliary transit behaviour

Particles suspended in the air are inhaled during normal respiration and unless cleared by airway defences, such as the mucociliary transit (MCT) system, they can remain and affect lung and airway health. Synchrotron phase‐contrast X‐ray imaging (PCXI) methods have been developed to non‐invasively monitor the behaviour of individual particles in live mouse airways and in previous studies the MCT behaviour of particles and fibres in the airways of live mice after deposition in a saline carrier fluid have been examined. In this study a range of common respirable pollutant particles (lead dust, quarry dust and fibreglass fibres) as well as marker particles (hollow glass micro‐spheres) were delivered into the trachea of live mice using a dry powder insufflator to more accurately mimic normal environmental particulate exposure and deposition via inhalation. The behaviour of the particles once delivered onto the airway surface was tracked over a five minute period via PCXI. All particles were visible after deposition. Fibreglass fibres remained stationary throughout while all other particle types transited the tracheal surface throughout the imaging period. In all cases the majority of the particle deposition and any airway surface activity was located close to the dorsal tracheal wall. Both the individual and bulk motions of the glass bead marker particles were visible and their behaviour enabled otherwise hidden MCT patterns to be revealed. This study verified the value of PCXI for examining the post‐deposition particulate MCT behaviour in the mouse trachea and highlighted that MCT is not a uniform process as suggested by radiolabel studies. It also directly revealed the advantages of dry particle delivery for establishing adequate particulate presence for visualizing MCT behaviour. The MCT behaviour and rate seen after dry particle delivery was different from that in previous carrier‐fluid studies. It is proposed that dry particle delivery is essential for producing environmentally realistic particle deposition and studying how living airway surfaces handle different types of inhaled particles by MCT processes.     

Saddles in the energy landscape probed by supercooled liquids

We numerically investigate the supercooled dynamics of two simple model liquids exploiting the partition of the multidimensional configuration space in basins of attraction of the stationary points (inherent saddles) of the potential energy surface. We find that the inherent saddle order and potential energy are well-defined functions of the temperature T. Moreover, by decreasing T, the saddle order vanishes at the same temperature (T(MCT)) where the inverse diffusivity appears to diverge as a power law. This allows a topological interpretation of T(MCT): it marks the transition from a dynamics between basins of saddles (T > T(MCT)) to a dynamics between basins of minima (T < T(MCT)).     

Laser induced damage studies in mercury cadmium telluride

We have investigated laser induced damage at laser wavelength in diamond paste polished (mirror finish) and carborundum polished Hg_0.8Cd_0.2Te (MCT) samples with increasing fluence as well as number of pulses. Evolution of damage morphology in two types of samples is quite different. In case of diamond paste polished samples, evolution of damage morphological features is consistent with Hg evaporation with transport of Cd/Te globules towards the periphery of the molten region. Cd/Te globules get accumulated with successive laser pulses at the periphery indicating an accumulation effect. Real time reflectivity (RTR) measurement has been done to understand melt pool dynamics. RTR measurements along with the thermal profile of the melt pool are in good agreement with thermal melting model of laser irradiated MCT samples. In case of carborundum polished samples, laser damage threshold is significantly reduced. Damage morphological features are significantly influenced by surface microstructural condition. From comparison of the morphological features in the two cases, it can be inferred that laser processing of MCT for device applications depends significantly on surface preparation conditions.     

Power-law Decay and the Ergodic–Nonergodic Transition in Simple Fluids

It is well known that mode coupling theory (MCT) leads to a two-step power-law time decay in dense simple fluids. We show that much of the mathematical machinery used in the MCT analysis can be taken over to the analysis of the systematic theory developed in the Fundamental Theory of Statistical Particle Dynamics (Mazenko in Phys Rev E 81(6):061102, 2010). We show how the power-law exponents can be computed in the second-order approximation where we treat hard-sphere fluids with statics described by the Percus–Yevick solution.     

Cluster mode-coupling approach to weak gelation in attractive colloids

Mode-coupling theory (MCT) predicts the arrest of colloids in terms of their volume fraction, and the range and depth of the interparticle attraction. We discuss how the effective values of these parameters evolve under cluster aggregation. We argue that weak gelation in colloids can be idealized as a two-stage ergodicity breaking: first at short scales (approximated by the bare MCT) and then at larger scales (governed by MCT applied to clusters). The competition between the arrest and phase separation is considered in relation to recent experiments. We predict a long-lived "semiergodic" phase of mobile clusters, showing logarithmic relaxation close to the gel line.     

锦屏深地核天体物理实验(JUNA)地面实验进展

锦屏深地核天体物理(JUNA)实验项目将利用中国锦屏深地实验室(CJPL)的良好条件,在天体物理伽莫夫能量窗口开展核天体关键反应$^{25}{\rm{Mg}}({\rm{p}},{\rm{\gamma}})^{26}{\rm{Al}}$、$^{19}{\rm{F}}({\rm{p}},\alpha)^{16}{\rm{O}}$、$^{13}{\rm{C}}(\alpha, {\rm{n}})^{16}{\rm{O}}$和$^{12}{\rm{C}}(\alpha,{\rm{\gamma}})^{16}{\rm{O}}$的直接测量,为理解恒星演化和元素起源提供新的数据。目前,已经在地面上对加速器装置、束流稳定性、靶、探测器以及电子学进行了系统的测试。地面实验内容包括高纯锗探测器效率刻度,$^{25}{\rm{Mg}}({\rm{p}}, {\rm{\gamma}})^{26}{\rm{Al}}$在304 keV的共振强度测量,$^{19}{\rm{F}}({\rm{p}}, \alpha)^{16}{\rm{O}}$的截面测量,聚乙烯作为慢化体的中子探测器的设计、加工和效率刻度,靶的设计和稳定性检测等。JUNA项目整体进展顺利,地面实验已取得一系列关键进展和初步成果。在不远的将来,JUNA项目将有序开展地下实验,完成设定目标,也将促进更广泛的国际合作,助力于天体演化中的若干重大科学问题的解决。     

A new mixed subgrid-scale model for large eddy simulation of turbulent drag-reducing flows of viscoelastic fluids

A mixed subgrid-scale(SGS) model based on coherent structures and temporal approximate deconvolution(MCT) is proposed for turbulent drag-reducing flows of viscoelastic fluids. The main idea of the MCT SGS model is to perform spatial filtering for the momentum equation and temporal filtering for the conformation tensor transport equation of turbulent flow of viscoelastic fluid, respectively. The MCT model is suitable for large eddy simulation(LES) of turbulent dragreducing flows of viscoelastic fluids in engineering applications since the model parameters can be easily obtained. The LES of forced homogeneous isotropic turbulence(FHIT) with polymer additives and turbulent channel flow with surfactant additives based on MCT SGS model shows excellent agreements with direct numerical simulation(DNS) results. Compared with the LES results using the temporal approximate deconvolution model(TADM) for FHIT with polymer additives, this mixed SGS model MCT behaves better, regarding the enhancement of calculating parameters such as the Reynolds number.For scientific and engineering research, turbulent flows at high Reynolds numbers are expected, so the MCT model can be a more suitable model for the LES of turbulent drag-reducing flows of viscoelastic fluid with polymer or surfactant additives.     

Cooperativity beyond caging: Generalized mode-coupling theory

The validity of mode-coupling theory (MCT) is restricted by an uncontrolled factorization approximation of density correlations. The factorization can be delayed and ultimately avoided, however, by explicitly including higher order correlations. We explore this approach within a microscopically motivated schematic model. Analytic tractability allows us to discuss in great detail the impact of factorization at arbitrary order, including the limit of avoided factorization. Our results indicate a coherent picture for the capabilities as well as limitations of MCT. Moreover, including higher order correlations systematically defers the transition and ultimately restores ergodicity. Power-law divergence of the relaxation time is then replaced by continuous but exponential growth.     

Evidence of early stage precursors of polymer crystals by dielectric spectroscopy

Dielectric spectra of the polyester poly(propylene succinate) were measured upon crystallization. For this model aliphatic polyester the alpha and beta relaxations appear simultaneously and are well resolved in the experimental frequency window. During isothermal crystallization, this fact allows one to use the beta relaxation to characterize the crystalline structural development while the alpha relaxation provides information about the evolution of the amorphous phase dynamics. In this way structure development and dynamics evolution can be characterized by a single experiment during the crystallization process. The unambiguous analysis of the dielectric loss clearly supports the existence of precursors of crystallization in the induction period.     

Interplay between the glass and the gel transition

By changing the control parameters, many physical systems reach a slow dynamics regime followed by an arrested or a quasiarrested state. Examples, among others, are gels and glasses. In this paper, we discuss some experimental and theoretical results in polymer and colloidal systems, where gel and glass transitions interfere, and use models from Mode Coupling Theory(MCT)to illustrate the rich phenomenology observed. The continuous and the discontinuous transition lines, found in the MCT models,are considered suitable to describe respectively the gel and the glass transitions, so we suggest that the interplay between gel and glass may be interpreted in terms of the F_(13) MCT model, clarifying also the origin of logarithmic decays often observed in such systems. In particular, the theoretical predictions of the MCT in the F_(13) model are compared with Molecular Dynamics simulations in model systems for chemical gels and charged colloids.     

B在Hg0.75Cd0.25Te中掺杂效应的第一性原理研究

基于密度泛函理论的第一性原理方法,通过形成能和束缚能的计算研究了B在Hg_0.75Cd_0.25Te 中的掺杂效应.结果表明B在Hg_0.75Cd_0.25Te中存在着两种主要形态:第一种是在完整的 Hg_0.75Cd_0.25Te材料中B稳定存在于六角间隙位置而非替位.此时,B形成容易激活的三级施主使材料表现为n型.另一种是在有Hg空位存在的Hg_0.75Cd_0.25Te中B更容易与Hg空位结合形成缺陷复合体,其束缚能达到了0.96 eV.这种复合体在Hg_0.75Cd_0.25Te材料中形成单施主也使材料表现为n型.考虑到辐照损伤形成的Hg空位受主,这种B与Hg空位的复合体是制约B离子在MCT中注入激活的一个重要因素.     

Slow dynamics of supercooled hydration water in contact with lysozyme: examining the cage effect at different length scales

ABSTRACT

We study by computer simulation the dynamics of hydration water in solution with lysozyme upon approaching the glassy state of water. We calculate the self-density correlation function at different wavelengths to test the Mode Coupling Theory (MCT) of glassy dynamics at different length scales. The results show a strict and clear relation of the behaviour of the structural relaxation with the cage effect. We find a good agreement with the predictions of the MCT in the short and medium scale range, while at increasing length scales the interaction of water molecules with the protein's substrate induces deviations from the MCT behaviour, as found in previous studies. Besides at low temperatures the slow dynamics deviates from MCT due to hopping processes, similar to the bulk, as witnessed by a crossover from a fragile behaviour to a strong behaviour. We show that this deviation is evident at all length scales. Interestingly, we find that in the fragile region the confining cage decreases in radius with temperature while in the strong region it appears stable.     

The empirical construction of mathematical models of measuring and optimal computing transducers

It follows from the theory of measuring-computing systems [1] that the requirements for a measuring transducer (MT) that converts an external influence into an electric signal in order to obtain the maximal interpretation accuracy are significantly different depending on how it is going to function: by itself or as a part of a measuring-computing transducer (MCT) as its component. In the first case, the maximal accuracy has to be provided by the MT and it is bounded by physical laws. In the second case, it has to be provided by the MCT, which is considered to be a measuring device for the same or a different purpose, in particular, that of the “perfect” device for a researcher. The accuracy of an MCT is determined by both the mathematical properties of its model and the “quality” of the algorithm that converts MT output into a form determined by the measurement objective that is achieved by a computing transducer (CT) as a component of the MCT. For any specific mathematical model of the MCT this algorithm has to provide the maximal quality of the MCT. An MT that is optimal for that purpose can often be different from an MT that is optimal by itself. As a rule, the exact mathematical model of the MT and, hence, the algorithm of the CT that is optimal for it, are not known to the researcher, but he can perform test measurements of known input signals that simulate the interaction of the MT and the measured object using the MT. The aim of this article is to use test measurements to synthesize both the response of an MT with an unknown model and the optimal interpretation of the measurement result, i.е., the output signal of the MCT. It is shown that even without knowing the exact MT model, but with the ability to perform test measurements on the same MT a researcher is able to synthesize both the MT response and the results of the interpretation of measurement results, both in an optimal way.     

On the applicability of mode coupling theory to a ϕ 4-model with first order phase transition

A ? ⁴-model with symmetric double-well-like on-site potential and anharmonic, infinite range interactions is investigated. This model exhibits a first order phase transition at a temperature T _c. The time-dependent displacement correlation function is studied in the framework of the mode coupling theory (MCT). Depending on the choice of slow modes, MCT makes qualitatively different predictions which are compared with MD-results. These numerical results suggest that only the order parameter mode {ie1-1} should be considered as slow. In that case it is shown that MCT yields a dynamical transition in the supercooled high-temperature phase {ie1-2} at a temperature T* which coincides with the spinodal temperature T _s (T _s = 0 for our model) where the metastable supercooled phase becomes instable.