Optical pulling force on nanoparticle clusters with gain due to Fano-like resonance

We demonstrate that,in a simple linearly-polarized plane wave,the optical pulling forces on nanoparticle clusters with gain can be induced by the Fano-like resonance.The numerical results based on the full-wave calculation show that the optical pulling forces can be attributed to the recoil forces for the nanoparticle clusters composed of dipolar nanoparticles with three different configurations.Interestingly,the recoil forces giving rise to optical pulling forces are exactly dominated by the coupling term between the electric and magnetic dipoles excited in the nanoparticle clusters,while other higherorder terms have a negligible contribution.In addition,the optical pulling force can be tailored by modulating the Fano-like resonance via either the particle size or the gain magnitude,offering an alternative freedom degree for optical manipulations of particle clusters.

Pulling force of acoustic-vortex beams on centered elastic spheres based on the annular transducer model

To solve the difficulty of generating an ideal Bessel beam,an simplified annular transducer model is proposed to study the axial acoustic radiation force(ARF)and the corresponding negative ARF(pulling force)exerted on centered elastic spheres for acoustic-vortex(AV)beams of arbitrary orders.Based on the theory of acoustic scattering,the axial distributions of the velocity potential and the ARF for AV beams of different orders generated by the annular transducers with different physical sizes are simulated.It is proved that the pulling force can be generated by AV beams of arbitrary orders with multiple axial regions.The pulling force is more likely to exert on the sphere with a smaller k0a(product of the wave number and the radius)for the AV beam with a bigger topological charge due to the strengthened off-axis acoustic scattering.The pulling force decreases with the increase of the axial distance for the sphere with a bigger k0a.More pulling force areas with wider axial regions can be formed by AV beams using a bigger-sized annular transducer.The theoretical results demonstrate the feasibility of generating the pulling force along the axes of AV beams using the experimentally applicable circular array of planar transducers,and suggest application potentials for multi-position stable object manipulations in biomedical engineering.

Graphene-tuned threshold gain to achieve optical pulling force on microparticle

We investigate optical force on a graphene-coated gain microparticle by adopting the Maxwell's stress tensor method.It is found that there exists a threshold gain in obtaining the Fano-profile optical force which indicates the reversal of optical pushing and pulling force. And giant pushing/pulling force can be achieved if the gain value of the material is in the proximity of the threshold gain. Our results show that the threshold gain is more sensitive to the relaxation time than to the Fermi energy of the graphene. We further study the optical force on larger microparticle to demonstrate the pulling force occurring at octupole resonance with small gain value and then it will appear at quadrupole resonance by increasing gain value. Our work provides an in-depth insight into the interaction between light and gain material and gives the additional degree of freedom to optical manipulation of microparticle.

Effect of micro-dimple patterns on capillary pull-off force and friction force of silicon surface

A microtribometer is used to measure and compare pull-off forces and friction forces exerted on （a） micro-dimpled silicon surfaces, （b） bare silicon surfaces, and （c） octadecyltrichlorosilane （OTS） treated silicon surfaces at different relative humidity （RH） levels separately. It is found that above a critical RH level, the capillary pull-off force increases abruptly and that the micro-dimple textured surface has a lower critical RH value as well as a higher pull-off force value than the other two surfaces. A micro topography parameter, namely sidewall area ratio, is found to play a major role in controlling the capillary pull-off force. Furthermore, micro-dimpled silicon surface is also proved to be not sensitive to variation in RH level, and can realize a stable and decreased friction coefficient compared with un-textured silicon surfaces. The reservoir-like function of micro dimples is considered to weaken or avoid the breakage effect of liquid bridges at different RH levels, thereby maintaining a stable frictional behaviour.

Study on Ultimate Pullout Force of Grouting Anchors of the Anchor-Pull Retaining Wall

Determination of the grouting anchor pullout force is a key step during the design of anchor-pull retaining wall, but it is mostly determined relied on empirical formula at present, and the rationality and the safety cannot be effectively guaranteed. Based on the engineering case of the gravity retaining wall of Qinglin Freeway, the model test was designed, and combined with the results of the ABAQUS finite element numerical analysis, it was analyzed that how the anchor axial pulling force distributes. The results showed that the force of the anchor near the wall bolt was large and which far from the wall was small and the ultimate pullout force was proportional to the length, diameter and shear strength. When the end tension of the anchor was small, the top load played a leading role on the anchor tension. This conclusion confirmed the calculation formula of ultimate pullout force was and provided a theoretical basis for anchor-pull retaining wall design and calculation.

Theoretical and experimental study of the pulling force of jet bits in radial drilling technology

Radial drilling technology, of which the jet bit is the key device, is a research focus in the field of oil drilling and production. This paper establishes mechanical equations for jet bits and analyzes the hydroseal of backward jets in bottom holes. Meanwhile this paper establishes a mechanical equation for a high pressure hose and analyzes the axial force distribution. Laboratory experiments indicate that the flow rate, the angle between the backward nozzle axis and the jet bit axis, and the hole diameter are the major influencing factors; the generation of the pulling force is mainly due to the inlet pressure of the jet bit; the backward jets can significantly increase not only the pulling force but also the stability of jet bits. The pulling force would reach 8,376 N under experimental conditions, which can steadily pull the high-pressure hose forward.

Pressure Gradient Force,Saffman Lift,and Magnus Lift on the Fiber-like Particle in Fluid

Flher-like particle suspensions are common in both na-ture and industry, but there is little work reported on it.The forces acting on the fiber - like particle in fluid arestudied in this paper, and the Magnus lift, Saffman lift,pressure gradient force, and then the dynamics modelhave been received. The numerical study of the simpleshear flow past the cylinders shows that the particles ’motion is controlled by the vortex.

Reducing force transmissibility in multiple degrees of freedom structures through anti-symmetric nonlinear viscous damping

In the present study, the Volterra series theory is adopted to theoretically investigate the force transmissibility of multiple degrees of freedom （MDOF） structures, in which an isolator with nonlinear anti-symmetric viscous damping is assembled. The results reveal that the anti-symmetric nonlinear viscous damping can significantly reduce the force trans- missibility over all resonance regions for MDOF structures with little effect on the transmissibility over non-resonant and isolation regions. The results indicate that the vibration isolators with an anti-symmetric damping characteristic have great potential to solve the dilemma occurring in the design of linear viscously damped vibration isolators where an increase of the damping level reduces the force transmissibility over resonant frequencies but increases the transmissibility over non-resonant frequency regions. This work is an extension of a previous study in which MDOF structures installed on the mount through an isolator with cubic nonlinear damping are considered. The theoretical analysis results are also verified by simulation studies.

Numerical Analysis of the Adhesive Forces in Nano-Scale Structure

Nanohairs, which can be found on the epidermis of Tokay gecko＇s toes, contribute to the adhesion by means of van der Waals force, capillary force, etc. This structure has inspired many researchers to fabricate the attachable nano-scale structures. However, the efficiency of artificial nano-scale structures is not reliable sufficiently. Moreover, the mechanical parameters related to the nano-hair attachment are not yet revealed qualitatively. The mechanical parameters which have influence on the ability of adhesive nano-hairs were investigated through numerical simulation in which only van der Waals force was considered. For the numerical analysis, finite element method was utilized and van der Waals force, assumed as 12-6 Lennard-Jones potential, was implemented as the body force term in the finite element formulation.

An integrated approach for the optimization of wheel-rail contact force measurement systems

A comprehension of railway dynamic behavior implies the measure of wheel-rail contact forces which are affected by disturbances and errors that are often difficult to be quantified. In this study, a benchmark test case is proposed, and a bogie with a layout used on some European locomotives such as SIEMENS El90 is studied. In this layout, an additional shaft on which brake disks are installed is used to transmit the braking torque to the wheelset through a single-stage gearbox. Using a mixed approach based on finite element techniques and statistical considerations, it is possible to evaluate an optimal layout for strain gauge positioning and to optimize the measurement system to diminish the effects of noise and disturbance. We also conducted preliminary evaluations on the precision and frequency response of the proposed system.

Steady vortex force theory and slender-wing flow diagnosis

The concept vortex force in aerodynamics is sys- tematically examined based on a new steady vortex-force theory （Wu et al., Vorticity and vortex dynamics, Springer, 2006） which expresses the aerodynamic force （and moment） by the volume and boundary integrals of the Lamb vector. In this paper, the underlying physics of this theory is explored, including the general role of the Lamb vector in non- linear aerodynamics, its initial formation, and its relevance to the total-pressure non-uniformity. As a typical example, the theory is applied to the flow over a slender delta wing at a large angle of attack. The highly localized flow structures with high Lamb-vector peaks are identified in terms of their net contribution to various constituents of the total aerody-namic force. This vortex-force diagnosis sheds new light on the flow control and configuration optimization.

紫穗槐根-土界面拉拔摩阻特性

[目的]探究不同影响因素下紫穗槐根—土界面拉拔摩阻特性的变化规律,为研究区栽培植物种的选择提供理论依据。[方法]通过室内拉拔试验研究有无须根、根径、拉拔速率对紫穗槐根—土复合体最大拉拔力、拉拔摩阻强度、根土界面摩擦系数的影响。[结果]紫穗槐直根带须根—土复合体和直根—土复合体拉拔过程中的拉拔力—时间曲线以及拉拔力—位移曲线基本一致,但同径级紫穗槐直根带须根—土复合体的最大拉拔力、根土界面摩擦系数、拉拔摩阻强度较直根—土复合体均提高了1.3倍,须根明显提高了根段的固土性能。随根径增大,紫穗槐直根—土复合体的最大拉拔力、拉拔摩阻强度、根土界面摩擦系数呈指数正相关;随拉拔速率增大,紫穗槐直根—土复合体的根土界面摩擦系数、拉拔摩阻强度均呈增大趋势,即500 mm/min(0.74,40.11 kPa)>10 mm/min(0.65,35.58 kPa)。冗余分析表明根径、有无须根、拉拔速率与紫穗槐根—土界面拉拔摩阻特性指标均呈显著相关关系,其中贡献率最高的是根径(55.4%),其次是有无须根(23.7%),第三是拉拔速率(20.9%)。[结论]紫穗槐具有较强的固土性能,在承受大风拉拔、径流冲刷等荷载时能发挥其固土作用。

Monitoring film coalescence from aqueous polymeric dispersions using atomic force microscopy: Surface topographic and nano-adhesion studies

The aim of the investigation was to develop the use of topographic and nano-adhesion atomic force microscopy(AFM) studies as a means of monitoring the coalescence of latex particles within films produced from a pharmaceutically relevant aqueous dispersion(Eudragit~?NE30 D). Films were prepared via spin coating and analysed using AFM, initially via tapping mode for topographic assessment followed by force-distance measurements which allowed assessment of site-specific adhesion. The results showed that colloidal particles were clearly observed topographically in freshly prepared samples, with coalescence detected on curing via the disappearance of discernible surface features and a decrease in roughness indices. The effects of temperature and humidity on film curing were also studied, with the former having the most pronounced effect. AFM force measurements showed that the variation in adhesive force reduced with increasing curing time, suggesting a novel method of quantifying the rate of film formation upon curing. It was concluded that the AFM methods outlined in this study may be used as a means of qualitatively and quantitatively monitoring the curing of pharmaceutical films as a function of time and other variables, thereby facilitating rational design of curing protocols.

Quantization of the 1-D Forced Harmonic Oscillator in the Space (<i>x</i>, <i>v</i>)

The quantization of the forced harmonic oscillator is studied with the quantum variable (x, v∧), with the commutation relation , and using a Schrödinger’s like equation on these variable, and associating a linear operator to a constant of motion K (x, v, t) of the classical system, The comparison with the quantization in the space (x, p) is done with the usual Schrödinger’s equation for the Hamiltonian H(x, p, t), and with the commutation relation . It is found that for the non-resonant case, both forms of quantization bring about the same result. However, for the resonant case, both forms of quantization are different, and the probability for the system to be in the exited state for the (x, v∧) quantization has fewer oscillations than the (x, p∧) quantization, the average energy of the system is higher in (x, p∧) quantization than on the (x, v∧) quantization, and the Boltzmann-Shannon entropy on the (x, p∧) quantization is higher than on the (x, v∧) quantization.

滑条式静磁微执行器的pull-in现象分析

从滑条式静磁微执行器的模型出发,应用静磁微执行器的pull-in方程,分析了滑条式静磁微执行器的pull-in现象,用磁动势控制模型和力学平衡两种方式得出了执行器的吸合位置及吸合时的磁动势.对于特定的滑条式磁微执行器结构,pull-in位置为初始气隙宽度的1/3处.算例计算结果表明,该静磁微执行器的pull-in磁动势仅为3.84A.

中间层液体的表面能对粘着行为中Pull-off力影响的实验研究

中间层液体膜存在的情况下,弯月面力(Cap illary Force)的作用使Pull-off力增加。中间层液体的表面能是影响弯月面力作用强度的重要因素之一。利用表面张力仪测量了1,2二氯丙烷、1,2乙二醇等5种液体的表面能,利用表面力仪测量了这5种液体作为中间层时Pull-off力的值。结果表明,在一定范围内,粘度相近液体量相同时,Pull-off力随表面能增加而增加;表面能相等时,Pull-off力随液体量增加而增加。

多尺度评价相对湿度对沥青-集料黏附性的影响

本工作分别在四种具有代表性的相对湿度条件下,对沥青-集料进行了宏观拉拔试验和微观表面能试验,以研究相对湿度对其黏附性的影响规律。研究结果表明:在宏观上,拉拔力随相对湿度的增加逐渐减小,同时沥青-集料界面由内聚开裂向混合开裂过渡;在微观上,沥青内聚能随相对湿度变化不明显,而沥青-集料界面结合能随着相对湿度的增加而降低。因此,沥青-集料的黏附性随着相对湿度的增加而逐渐减小,水气分子浓度的增大能够加剧水分子对沥青的置换,使得沥青更容易从集料表面剥落。通过沥青的宏观剥落率和微观表面能参数,建立了界面能指标,该指标多尺度地评价了沥青与集料的黏附性,评价结果与宏、微观试验一致,表明界面能指标的有效性。

竹筋-夯土界面的拉拔试验研究

为了研究竹筋-夯土界面性能,设置4种不同类别影响参数——轴向压力(40、80、120、160 kPa)、竹筋构造形式(无竹节、单竹节和单竹节且端部弯起构造形式)、竹筋宽度(1、2、3 cm)、埋置长度(210、290、370、450 mm)进行拉拔试验.结果表明:轴向压力从40 kPa增加到160 kPa时,拉拔力峰值增加了4.37 kN,增幅达47.7%;竹节和端部弯起构造都能提高竹筋与土体间的端阻力,从无竹节到单竹节且端部弯起构造,拉拔力峰值增加4.76 kN,增幅达42.6%;竹筋宽度与埋置长度增大时,竹筋与土体的摩阻力和侧阻力增大,竹筋宽度从1 cm增加到3 cm时拉拔力峰值增加了5.49 kN,增幅达65.4%;埋置长度从210 mm增加到450 mm,拉拔力峰值增加了5.67 kN,增幅达72.4%.竹筋与夯土界面的作用力主要由化学黏结力、摩阻力和端阻力组成;4种影响因素均可以显著提高拉拔力峰值,而增加埋置长度效果最显著.