Important aspects when modelling the interaction between surface structures and tunnelling in sand

Tunnelling in urban areas continues to increase and has highlighted the need for a better understanding of the impact of tunnel excavations on existing buildings. This paper considers the influence of surface structures on ground displacements caused by tunnelling in sand through finite element modelling and centrifuge testing. First, the importance of modelling assumptions is evaluated by comparing centrifuge modelling results to finite element modelling results for various soil constitutive models: both a Young's modulus that linearly increases with depth and a power law relation between the soil stiffness and stresses are considered. Second, the most effective soil constitutive model was used to perform a sensitivity study on the effect of different factors governing the structural response. In particular, the effect of the building stiffness and weight on the modification of soil displacements is investigated by introducing a simple surface structure. The use of a no-tension interface between the building and the soil was found to be essential to investigate the effect of weight on gap formation between the soil and the structure, as observed during the experimental tests. Results show the importance of considering the relation between the building weight and the relative stiffness between the building and the soil when assessing the structural response. © 2014 Korean Geotechnical Society.

Band-tail shape and transport near the metal-insulator transition in Si-doped

In the present work, an infrared light-emitting diode is used to photodope molecular-beam-epitaxy-grown Si: Al0.3Ga0.7As, a well-known persistent photoconductor, to vary the effective electron concentration of samples in situ. Using this technique, we examine the transport properties of two samples containing different nominal doping concentrations of Si [1 x 10(19) cm(-3) for sample 1 (S1) and 9 x 10(17) cm(-3) for sample 2 (S2)] and vary the effective electron density between 10(14) and 10(18) cm(-3). The metal-insulator transition for S1 is found to occur at a critical carrier concentration of 5.7 x 10(16) cm(-3) at 350 mK. The mobilities in both samples are found to be limited by ionized impurity scattering in the temperature range probed, and are adequately described by the Brooks-Herring screening theory for higher carrier densities. The shape of the band tail of the density of states in Al0.3Ga0.7As is found electrically through transport measurements. It is determined to have a power-law dependence, with an exponent of -1.25 for S1 and -1.38 for S2.

Antibunching and blinking from a single colloidal CdSe quantum dot

We have investigated the optical properties of single CdSe/ZnS nanocrystals by conducting combinations of experiments on antibunching and photoluminescence intermittence under different experimental conditions. Based on photoluminescence in an antibunching experiment, we analyzed the emission lifetime of QDs by using stretched exponentials. The difference between the parameters obtained from average lifetimes and stretched exponents were analyzed by considering the effect of nonradiative emission. An Auger-assisted tunneling model was used to explain the power law exponents of off time distribution. The power law exponent under high excitation power was correlated with a higher Auger ionization rate. Using the parameters obtained from stretched exponential function and power law, the antibunching phenomena at different time and under different excitation intensity were analyzed.

Electron spin relaxation by nuclei and holes in single InAs quantum dots

Electron spin relaxation of charged excitons X+ and X2+ are investigated by time-resolved and polarization-resolved photoluminescence spectroscopy. For X+ configuration, the electron spin relaxation shows a typical decay curve induced by hyperfine interaction with nuclei, whereas for X2+ state the electron spin relaxation is affected not only by nuclei but also by electron-hole exchange interaction, leading to a power-law time dependence.

Correlations between antibunching and blinking of photoluminescence from a single CdSe quantum dot

The antibunching and blinking from a single CdSe/ZnS nanocrystal with an emission wavelength of 655 nm were investigated under different excitation powers. The decay process of the photoluminescence from nanocrystal was fitted into a stretched exponential, and the small lifetime and the small stretching exponent under a high excitation power were explained by using nonradiative multi-channel model. The probability of distributions for off-times from photoluminescence intermittence was fitted into the power law, and the power exponents were explained by using a tunneling model. For higher excitation power, the Auger-assisted tunneling model takes effect, where the tunneling rate increases and the observed lifetime decreases. For weak excitation power, the electron directly tunnels between the nanocrystal and trapping state without Auger assistance. The correlation between antibunching and blinking from the same nanocrystal was analyzed.

Effect of the growth mode on the two- to three-dimensional transition of InAs grown on vicinal GaAs(001) substrates

Some differences were observed between conventional molecular-beam epitaxy (MBE) and mobility enhanced epitaxy (MEE) of InAs on a vicinal GaAs(001) substrate in the variation of the number density N of the InAs islands, with additional InAs coverage (theta - theta(c)) after the critical InAs coverage theta(c) during the two- to three-dimensional (2D-3D) transition. For MBE the variation was consistent with the power law N(theta) (theta similar to theta(c))(alpha); while for MEE, the linear relation N(theta) proportional to (theta - theta(c)) was observed. The difference is discussed in terms of the randomness in the nucleation of the InAs islands.

A NOVEL ODOR SENSOR COATED WITH A LIPID-MEMBRANE

In this paper, an interdigital electrode lipid film odour sensor (ILOS) is designed, fabricated and tested. It is made from a microfabricated chemiresistor coated with a synthetic multibilayer film. Nine odorants in gas phase at room temperature have been detected using the odour sensor. For most of the odorants, the relation between the response of the ILOS and odorant concentration obeys Stevens' power law, and there is a good correlation between the minimum odorant concentrations that give rise to a change of the sensor's conductance and human olfactory thresholds.

Theoretical analysis of the relationships between hardness, elastic modulus, and the work of indentation for work-hardening materials

In our previous paper, the expanding cavity model (ECM) and Lame solution were used to obtain an analytical expression for the scale ratio between hardness (H) to reduced modulus (E-r) and unloading work (W-u) to total work (W-t) of indentation for elastic-perfectly plastic materials. In this paper, the more general work-hardening (linear and power-law) materials are studied. Our previous conclusions that this ratio depends mainly on the conical angle of indenter, holds not only for elastic perfectly-plastic materials, but also for work-hardening materials. These results were also verified by numerical simulations.

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.