Precursor Film in Dynamic Wetting, Electrowetting, and Electro-Elasto-Capillarity

Dynamic wetting and electrowetting are explored using molecular dynamics simulations. The propagation of the precursor film (PF) is fast and obeys the power law with respect to time. Against the former studies, we find the PF is no slip and solidlike. As an important application of the PF, the electro-elasto-capillarity, which is a good candidate for drug delivery at the micro- or nanoscale, is simulated and realized for the first time. Our findings may be one of the answers to the Huh-Scriven paradox and expand our knowledge of dynamic wetting and electrowetting.

Strain gradient theory based on a new framework of non-local model

A new framework of non-local model for the strain energy density is proposed in this paper. The global strain energy density of the representative volume element is treated as a non-local variable and can be obtained through a special integral of the local strain energy density. The local strain energy density is assumed to be dependent on both the strain and the rotation-gradient. As a result of the non-local model, a new strain gradient theory is derived directly, in which the first and second strain gradients, as well as the triadic and tetradic stress, are introduced in the context of work conjugate. For power law hardening materials, size effects in thin metallic wire torsion and ultra-thin cantilever beam bend are investigated. It is found that the result predicted by the theoretical model is well consistent with the experimental data for the thin wire torsion. On the other hand, the calculation result for the micro-cantilever beam bend clearly shows the size effect.

30MeV/u~(40)Ar引起反应中的碎片发射机制

本论文中重点研究了30MeV/u 40Ar+58Ni，64Ni和115In反应中中等质量碎片（IMF）的发射机制。实验中，测量了实验室系5°～140°角度范围内出射碎片的能谱和角分布。对前角区出射的IMF（3≤Z≤13）实现了同位素鉴别，对中后角区出射的碎片在低探测阈（<2MeV/u ）的前提下实现了直到Z～30的元素鉴别。 用运动源模型对不同角度下出射的碎片能谱进行了分析和讨论，并结合角分布特征定性地研究了碎片的三个发射源。通过对各源的贡献随角度以及出射碎片电荷数Z的演化，观察到：类弹源主要发射的是那些前角区出射的、接近束流速度的高能碎片；中等速度源的发射是中角度区出射碎片和前角区低能碎片的主要来源；后角区出射的碎片则主要来自于类熔合源的发射。并观察到相对于类熔合源非平衡源更容易发射较轻的碎片。 通过对前角区出射IMF（3≤Z≤13）的能谱和同位素分布的分析，确定了那些基本保持束流速度的碎片主要来自于弹核碎裂过程。用各种模型对实验同位素分布进行了拟合，发现Sümmerer等人给出的经验公式和abrasion-ablation模型均能比较满意地拟合实验同位素分布的宽度和峰位。同时也观察到abrasion-ablation模型计算对奇Z元素的同位素分布能给出较好的拟合，但对偶Z元素的同位素分布，计算结果与实验值相比出现向丰中子方向的系统性偏移（～lamu）。另外，还着重研究了这些产物的靶核相关性问题。通过系统性分析以及同位旋相关的量子分子动力学（IQMD）模型计算，得出了弹核碎裂产物的靶核相关性是源于靶核表面中子与质子分布的不同和平均场及核子核子相互作用的同位旋效应相关。并且，通过计算还指出了靶核中子皮的厚度对于用弹核碎裂方法产生丰中子同位素的重要性。 通过用统计模型拟合后角区出射碎片的电荷分布，指出了这些碎片主要来自于非完全熔合过程中形成的复合系统的统计发射。 实验中观察到30MeV/u 40Ar轰击Ni和In靶在中角区出射的碎片的电荷分布有不同的特征。相对来说，前者更服从power-law，后者则倾向于服从指数规律。结合核态方程和QMD模型计算分析得出，在30MeV/u 的40Ar引起的反应中，对于弾靶质量接近对称的碰撞对所形成的系统，在一定的碰撞条件下可能已进入spinodal区，而非对称碰撞对的碰撞中压缩能还难以使得系统在膨胀时进入力学不稳定区。从而对观察到的实验现象进行了说明，并认为30MeV/u 40Ar轰击与其质量接近的靶核的反应中出射的碎片中已有相当数量的动力学发射成分的贡献。 利用实验中在前角区出射的接近束流速度的碎片的同位素产额提取了类弹源的温度参数。观察到直接由实验同位素产额比得到的表观核温度与所选择的同位素组合有较强烈的依赖关系，而与靶核和实验室探测角基本无关。利用M.B.Tsang等人给出的修正方法，提取了经边馈效应修正后的发射源温度。得到该温度值与反应靶、探测角以及用于提出温度的同位素组合没有明显的依赖关系，均为～4MeV。并用abrasion-ablation模型计算进行了讨论，得到在假定能级密度参数的倒数k=10MeV时，该温度值与abrasion-ablation模型计算是一致的。

Study on the Cell Structure and Compressive Behavior of Biodegradable Poly(epsilon-caprolactone) Foam

Biodegradable poly(e-caprolactone) (PCL) foams with a series of controlled structures were prepared by using chemical foaming method. The cell morphology was detected by scanning electron microscope (SEM). The compressive behavior of the foams was investigated by uniaxial compression test. The effect of density and structural parameters on the foam compressive behavior was analyzed. It was found that the relative compressive modulus has a power law relationship with relative density. Increasing of both the cell wall thickness and the cell density lead to higher compressive modulus of the foam; however, the cell size has no distinct effect on compressive behavior.

Kinetics and Statistical Distributions of Single-Molecule Conformational Dynamics

We developed a coarse-grained yet microscopic detailed model to study the statistical fluctuations of single-molecule protein conformational dynamics of adenylate kinase. We explored the underlying conformational energy landscape and found that the system has two basins of attractions, open and closed conformations connected by two separate pathways. The kinetics is found to be nonexponential, consistent with single-molecule conformational dynamics experiments. Furthermore, we found that the statistical distribution of the kinetic times for the conformational transition has a long power law tail, reflecting the exponential density of state of the underlying landscape. We also studied the joint distribution of the two pathways and found memory effects.

The complex kinetics of protein folding in wide temperature ranges

The complex protein folding kinetics in wide temperature ranges is studied through diffusive dynamics on the underlying energy landscape. The well-known kinetic chevron rollover behavior is recovered from the mean first passage time, with the U-shape dependence on temperature. The fastest folding temperature T-0 is found to be smaller than the folding transition temperature T-f. We found that the fluctuations of the kinetics through the distribution of first passage time show rather universal behavior, from high-temperature exponential Poissonian kinetics to the relatively low-temperature highly nonexponential kinetics. The transition temperature is at T-k and T-0, T-k, T-f. In certain low-temperature regimes, a power law behavior at long time emerges. At very low temperatures ( lower than trapping transition temperature T< T-0/(4&SIM;6)), the kinetics is an exponential Poissonian process again.

Electrical conductivity of a single Au/polyaniline microfiber

We report the measurements of conductivity, I-V curve, and magnetoresistance of a single Au/polyaniline microfiber with a core-shell structure, on which a pair of platinum microleads was attached by focused ion beam. The Au/polyaniline microfiber shows a much higher conductivity (similar to 110 S/cm at 300 K) and a much weaker temperature dependence of resistance [R(4 K)/R(300 K)=5.1] as compared with those of a single polyaniline microtube [sigma(RT)=30-40 S/cm and R(4 K)/R(300 K)=16.2]. The power-law dependence of R(T)proportional to T-beta, with beta=0.38, indicates that the measured Au/polyaniline microfiber is lying in the critical regime of the metal-insulator transition. In addition, the microfiber shows a H-2 dependent positive magnetoresistance at 2, 4, and 6 K.

First-passage time distribution and non-Markovian diffusion dynamics of protein folding

We study the kinetics of protein folding via statistical energy landscape theory. We concentrate on the local-connectivity case, where the configurational changes can only occur among neighboring states, with the folding progress described in terms of an order parameter given by the fraction of native conformations. The non-Markovian diffusion dynamics is analyzed in detail and an expression for the mean first-passage time (MFPT) from non-native unfolded states to native folded state is obtained. It was found that the MFPT has a V-shaped dependence on the temperature. We also find that the MFPT is shortened as one increases the gap between the energy of the native and average non-native folded states relative to the fluctuations of the energy landscape. The second- and higher-order moments are studied to infer the first-passage time distribution. At high temperature, the distribution becomes close to a Poisson distribution, while at low temperatures the distribution becomes a Levy-type distribution with power-law tails, indicating a nonself-averaging intermittent behavior of folding dynamics. We note the likely relevance of this result to single-molecule dynamics experiments, where a power law (Levy) distribution of the relaxation time of the underlined protein energy landscape is observed.

Diffusion dynamics, moments, and distribution of first-passage time on the protein-folding energy landscape, with applications to single molecules

We study the dynamics of protein folding via statistical energy-landscape theory. In particular, we concentrate on the local-connectivity case with the folding progress described by the fraction of native conformations. We found that the first passage-time (FPT) distribution undergoes a dynamic transition at a temperature below which the FPT distribution develops a power-law tail, a signature of the intermittent nonexponential kinetic phenomena for the folding dynamics. Possible applications to single-molecule dynamics experiments are discussed.

Temperature dependence of the distribution of the first passage time: Results from discontinuous molecular dynamics simulations of an all-atom model of the second beta-hairpin fragment of protein G

More than 22 000 folding kinetic simulations were performed to study the temperature dependence of the distribution of first passage time (FPT) for the folding of an all-atom Go-like model of the second beta-hairpin fragment of protein G. We find that the mean FPT (MFPT) for folding has a U (or V)-shaped dependence on the temperature with a minimum at a characteristic optimal folding temperature T-opt*. The optimal folding temperature T-opt* is located between the thermodynamic folding transition temperature and the solidification temperature based on the Lindemann criterion for the solid. Both the T-opt* and the MFPT decrease when the energy bias gap against nonnative contacts increases. The high-order moments are nearly constant when the temperature is higher than T-opt* and start to diverge when the temperature is lower than T-opt*. The distribution of FPT is close to a log-normal-like distribution at T* greater than or equal to T-opt*. At even lower temperatures, the distribution starts to develop long power-law-like tails, indicating the non-self-averaging intermittent behavior of the folding dynamics. It is demonstrated that the distribution of FPT can also be calculated reliably from the derivative of the fraction not folded (or fraction folded), a measurable quantity by routine ensemble-averaged experimental techniques at dilute protein concentrations.

SURFACE FRACTALS IN BLOCK-COPOLYMERS

A surface fractal model was presented to describe the interface in block copolymers. It gives a simple power-law relationship between the scattering intensity I(q) and the wave vector q in a relatively wide range as qxi >> 1, I(q) is-proportional-to q(D-6

DETERMINATION OF INITIATION VALUE OF MODE-I INTERLAMINAR FRACTURE-TOUGHNESS OF UNIDIRECTIONAL POLYMER COMPOSITES

The use of interlaminar fracture tests to measure the delamination resistance of unidirectional composite laminates is now widespread. However, because of the frequent occurrence of fiber bridging and multiple cracking during the tests, it leads to artificially high values of delamination resistance, which will not represent the behavior of the laminates. Initiation fracture from the crack starter, on the other hand, does not involve bridging, and should be more representative of the delamination resistance of the composite laminates. Since there is some uncertainty involved in determining the initiation value of delamination resistance in mode I tests in the literature, a power law of the form G(IC) = A.DELTA alpha(b) (where G(IC) is mode I interlaminar fracture toughness and DELTA alpha is delamination growth) is presented in this paper to determine initiation value of mode I interlaminar fracture toughness. It is found that initiation values of the mode I interlaminar fracture toughness, G(IC)(ini), can be defined as the G(IC) value at which 1 mm of delamination from the crack starter has occurred. Examples of initiation values determined by this method are given for both carbon fiber reinforced thermoplastic and thermosetting polymers.

Self-organized Criticality Model for Ocean Internal Waves

In this paper, we present a simple spring-block model for ocean internal waves based on the self-organized criticality (SOC). The oscillations of the water blocks in the model display power-law behavior with an exponent of -2 in the frequency domain, which is similar to the current and sea water temperature spectra in the actual ocean and the universal Garrett and Munk deep ocean internal wave model [Geophysical Fluid Dynamics 2(1972) 225; J. Geophys. REs. 80 (1975) 291]. The influence of the ratio of the driving force to the spring coefficient to SOC behaviors in the model is also discussed.

Dielectric responses of graded cylindrical composites

The effective dielectric responses of linear composites with graded cylindrical particles are investigated under an external uniform electric field. As an example, with the Kummer function, we have obtained the analytical solutions of electric potentials of graded composites with a cylindrical inclusion particle of dielectric function profile epsilon(i) = cr(k)e(betar), where r is the inside distance of a point in cylindrical particle from the original point of cylindrical coordinates. In the dilute limit, the effective dielectric response is derived by means of the mean field method. For larger volume fraction, we have estimated the dielectric response of the graded composites with an effective medium approximation. Furthermore, from our results, we have discussed the effective responses of graded composites for power-law and exponential dielectric function profiles, respectively. (C) 2004 Elsevier B.V. All rights reserved.

The nonlinear effective dielectric response of graded composites

The perturbation method is developed to deal with the effective nonlinear dielectric responses of weakly nonlinear graded composites, which consist of the graded inclusion with a linear dielectric function of spatial variables of inclusion material. For Kerr-like nonlinear graded composites, as an example in two dimensions, we have used the perturbation method to solve the boundary value problems of potentials, and studied the effective responses of nonlinear graded composites, where a cylindrical inclusion with linear dielectric function and nonlinear dielectric constant is randomly embedded in a homogeneous host with linear and nonlinear dielectric constants. For the exponential function and the power-law dielectric profiles of cylindrical inclusions, in the dilute limit, we have derived the formulae of effective nonlinear responses of both graded nonlinear composites.