Microtubule dynamics depart from wormlike chain model

Thermal shape fluctuations of grafted microtubules were studied using high resolution particle tracking of attached fluorescent beads. First mode relaxation times were extracted from the mean square displacement in the transverse coordinate. For microtubules shorter than 10 um, the relaxation times were found to follow an L^2 dependence instead of L^4 as expected from the standard wormlike chain model. This length dependence is shown to result from a complex length dependence of the bending stiffness which can be understood as a result of the molecular architecture of microtubules. For microtubules shorter than 5 um, high drag coefficients indicate contributions from internal friction to the fluctuation dynamics.Comment: 4 pages, 4 figures. Updated content, added reference, corrected typo

Liquid-like behaviour of gold nanowire bridges

A combination of Focused Ion Beam (FIB) and Reactive Ion Etch (RIE) was used to fabricate free standing gold nanowire bridges with radii of 30 nm and below. These were subjected to point loading to failure at their mid-points using an Atomic Force Microscope (AFM), providing strength and deformation data. The results demonstrate a dimensionally dependent transition from conventional solid metallic properties to liquid-like behaviour including the unexpected reformation of a fractured bridge. The work reveals mechanical and materials properties of nanowires which could have significant impact on nanofabrication processes and nanotechnology devices such as Nano Electro Mechanical Systems (NEMS)

IPO Earnings Forecast, Corporate Governance and Earnings Management——Empirical study based on the IPO of A-share Mainboard companies

IPO盈利预测披露的问题一直以来都获得了众多学者的重视，因为它对于资本市场有着十分重大的意义。对投资者来说，IPO盈利预测代表着公司对于未来经营业绩的一种预期和描述，向广大投资者提供了支撑决策的信息，提升了市场对于公司的信心，降低了上市公司内部管理者与外部利益相关者之间的信息不对称，帮助投资者进行股票估值和投资决策。因此IPO盈利预测可以提高整个市场的信息效率。但是IPO盈利预测也会带来一个负面的问题，那就是管理层为了迎合预测而进行的盈余管理。 随着我国IPO盈利预测披露制度由强制性转变成了自愿性披露，IPO公司可以自愿选择是否披露盈利预测，这就可能导致披露预测的公司为了降低预测误差而有更强...The disclosure of IPO earnings forecast has always been a focus of study because it is significant for the capital market. For investors, IPO earnings forecast represents the expextation and description for the company’s performance in the future, which provides information for the investors for decision-making, enhances the confidence the market has for the company, reduces information asymmetry...学位：管理学硕士院系专业：管理学院_会计学学号：1752012115111

Statics and Dynamics of the Wormlike Bundle Model

Bundles of filamentous polymers are primary structural components of a broad range of cytoskeletal structures, and their mechanical properties play key roles in cellular functions ranging from locomotion to mechanotransduction and fertilization. We give a detailed derivation of a wormlike bundle model as a generic description for the statics and dynamics of polymer bundles consisting of semiflexible polymers interconnected by crosslinking agents. The elastic degrees of freedom include bending as well as twist deformations of the filaments and shear deformation of the crosslinks. We show that a competition between the elastic properties of the filaments and those of the crosslinks leads to renormalized effective bend and twist rigidities that become mode-number dependent. The strength and character of this dependence is found to vary with bundle architecture, such as the arrangement of filaments in the cross section and pretwist. We discuss two paradigmatic cases of bundle architecture, a uniform arrangement of filaments as found in F-actin bundles and a shell-like architecture as characteristic for microtubules. Each architecture is found to have its own universal ratio of maximal to minimal bending rigidity, independent of the specific type of crosslink induced filament coupling; our predictions are in reasonable agreement with available experimental data for microtubules. Moreover, we analyze the predictions of the wormlike bundle model for experimental observables such as the tangent-tangent correlation function and dynamic response and correlation functions. Finally, we analyze the effect of pretwist (helicity) on the mechanical properties of bundles. We predict that microtubules with different number of protofilaments should have distinct variations in their effective bending rigidity

Statistical Mechanics of Semiflexible Bundles of Wormlike Polymer Chains

We demonstrate that a semiflexible bundle of wormlike chains exhibits a state-dependent bending stiffness that alters fundamentally its scaling behavior with respect to the standard wormlike chain. We explore the equilibrium conformational and mechanical behavior of wormlike bundles in isolation, in crosslinked networks, and in solution.Comment: 4 pages, 3 figures, final version as publishe

Effect of leaning angle of gecko-inspired slanted polymer nanohairs on dry adhesion

We present analysis of adhesion properties of angled polymer nanohairs with a wide range of leaning angles from 0?? to 45?? and ultraviolet (UV)-curable polyurethane acrylate (PUA) materials of two different elastic moduli (19.8 and 320 MPa). It is demonstrated that shear adhesion and adhesion hysteresis can be greatly enhanced by increasing the leaning angle of nanohairs both for soft and hard materials due to increased contact area and reduced structural stiffness.open211

Atomistic Modeling of F-Actin Mechanical Responses and Determination of Mechanical Properties

A molecular structural mechanics (MSM) model was developed for F-actins in cells, where the force constants describing the monomer interaction were achieved using molecular dynamics simulations. The MSM was then employed to predict the mechanical properties of F-actin. The obtained Young’s modulus (1.92 GPa), torsional rigidity (2.36 × 10–26 Nm2), and flexural rigidity (10.84 × 10–26 Nm2) were found to be in good agreement with existing experimental data. Subsequently, the tension-induced bending was studied for F-actins as a result of their helical structure. Mechanical instability was also investigated for the actin filaments in filopodial protrusion by considering the reinforcing effect of the actin-binding proteins. The predicted buckling load agreed well with the experimentally obtained stall force, showing a pivotal role of the actin-binding protein in regulating the stiffness of F-actin bundles during the formation of filopodia protrusion. Herein, it is expected that the MSM model can be extended to the mechanics of more complex filamentous systems such as stress fibers and actin meshwork

Investigation of guided wave propagation in pipes fully- and partially-embedded in concrete

The application of long-range guided-wave testing to pipes embedded in concrete results in unpredictable test-ranges. The influence of the circumferential extent of the embedding-concrete around a steel pipe on the guided wave propagation is investigated. An analytical model is used to study the axisymmetric fully embedded pipe case, while explicit finite-element and semi-analytical finite-element simulations are utilised to investigate a partially embedded pipe. Model predictions and simulations are compared with full-scale guided-wave tests. The transmission-loss of the T(0,1)-mode in an 8 in. steel pipe fully embedded over an axial length of 0.4 m is found to be in the range of 32–36 dB while it reduces by a factor of 5 when only 50% of the circumference is embedded. The transmission-loss in a fully embedded pipe is mainly due to attenuation in the embedded section while in a partially embedded pipe it depend strongly on the extent of mode-conversion at entry to the embedded-section; low loss modes with energy concentrated in the region of the circumference not-covered with concrete have been identified. The results show that in a fully embedded pipe, inspection beyond a short distance will not be possible, whereas when the concrete is debonded over a fraction of the pipe circumference, inspection of substantially longer lengths may be possible

Hydrostatic and uniaxial pressure tuning of iron-based superconductors: Insights into superconductivity, magnetism, nematicity and collapsed tetragonal transitions

Iron-based superconductors are well-known for their intriguing phase diagrams, which manifest a complex interplay of electronic, magnetic and structural degrees of freedom. Among the phase transitions observed are superconducting, magnetic, and several types of structural transitions, including a tetragonal-to-orthorhombic and a collapsed-tetragonal transition. In particular, the widely-observed tetragonal-to-orthorhombic transition is believed to be a result of an electronic order that is coupled to the crystalline lattice and is, thus, referred to as nematic transition. Nematicity is therefore a prominent feature of these materials, which signals the importance of the coupling of electronic and lattice properties. Correspondingly, these systems are particularly susceptible to tuning via pressure (hydrostatic, uniaxial, or some combination). We review efforts to probe the phase diagrams of pressure-tuned iron-based superconductors, with a strong focus on our own recent insights into the phase diagrams of several members of this material class under hydrostatic pressure. These studies on FeSe, Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, Ca(Fe$_{1-x}$Co$_x$)$_2$As$_2$ and CaK(Fe$_{1-x}$Ni$_x$)$_4$As$_4$ were, to a significant extent, made possible by advances of what measurements can be adapted to the use under differing pressure environments. We point out the potential impact of these tools for the study of the wider class of strongly correlated electron systems.Comment: 31 pages, 17 figures, submitted to Annalen der Physi

Nanomechanics of microtubules

We have determined the mechanical anisotropy of a single microtubule by simultaneously measuring the Young's and the shear moduli in vitro. This was achieved by elastically deforming the microtubule deposited on a substrate tailored by electron-beam lithography with a tip of an atomic force microscope. The shear modulus is 2 orders of magnitude lower than the Young's, giving rise to a length-dependent flexural rigidity of microtubules. The temperature dependence of the microtubule's bending stiffness in the (5-40) degreesC range shows a strong variation upon cooling coming from the increasing interaction between the protofilaments