Optical trapping in micro- and nanoconfinement systems: Role of thermo-fluid dynamics and applications

In this mini-review, recent advances on the role of a focused laser in micro- and nanofluidic systems is widely introduced with special interest in thermo-fluid dynamical aspects and their importance in optical manipulation. As a brief introduction to microfluidic systems, we describe the advantages and challenges of the use of micro- and nanoscale confinement in optical trapping, as well as standard fabrication techniques for micro- and nanofluidic systems. From thermo-fluid dynamical viewpoints, various phenomena that accompany a laser irradiation to fluidic devices, are explained in detail. These phenomena can affect the optical trapping of target materials significantly, and are classified into two categories: one that induces the fluid flow around the target and another that directly acts on it as an external force. These classes are reviewed by shedding light on some recent cutting-edge researches for optical manipulation. Some applications using thermo-fluid dynamics in microfluidic systems for the measurement of optical forces and for the separation, measurement, and detection of target materials are also introduced

Separation of long DNA chains using non-uniform electric field: a numerical study

We study migration of DNA molecules through a microchannel with a series of electric traps controlled by an ac electric field. We describe the motion of DNA based on Brownian dynamics simulations of a beads-spring chain. Our simulation demonstrates that the chain captured by an electrode escapes from the binding electric field due to thermal fluctuation. We find that the mobility of chain would depend on the chain length; the mobility sharply increases when the length of a chain exceeds a critical value, which is strongly affected by the amplitude of the applied ac field. Thus we can adjust the length regime, in which this microchannel well separates DNA molecules, without changing the structure of the channel. We also present a theoretical insight into the relation between the critical chain length and the field amplitude.Comment: 12 pages, 9 figure

Electrochemical response of biased nanoelectrodes in solution

Novel approaches to DNA sequencing and detection require the measurement of electrical currents between metal probes immersed in ionic solution. Here, we experimentally demonstrate that these systems maintain large background currents with a transient response that decays very slowly in time and noise that increases with ionic concentration. Using a non-equilibrium stochastic model, we obtain an analytical expression for the ionic current that shows these results are due to a fast electrochemical reaction at the electrode surface followed by the slow formation of a diffusion layer. During the latter, ions translocate in the weak electric field generated after the initial rapid screening of the strong fields near the electrode surfaces. Our theoretical results are in very good agreement with experimental findings

Area of Compaction to Prevent Uplift by Liquefaction

In this study, shaking table tests, upper seepage flow tests and numerical analyses were conducted to determine the condition of improvement by the compaction method, including the extent of area and the density, to prevent uplift of underground pipes by liquefaction. Based on the results of these investigations, a procedure to determine the improvement conditions was proposed

A computational approach based on ordinary state-based peridynamics with new transition bond for dynamic fracture analysis

The recently developed ordinary state-based peridynamics (OSPD) is further enhanced to study elastodynamic propagating crack based on the dynamic stress intensity factors (DSIFs). The displacement discontinuity such as a crack surface is represented by a bond-failure. Variations of the mixed-mode DSIFs with time are evaluated by the interaction integral method for the dynamic crack propagation. In terms of OSPD fracture modeling, numerical oscillation of DSIFs becomes a critical issue during the evolution of a crack. To overcome this numerical oscillation problem, we introduce a new model of bond-failure, the transition bond. The enhanced OSPD approach using the new transition bond model offers accurate and acceptable results, suppressing the numerical oscillation of responses and reflecting an effective approach. The effects of different types of transition bond are numerically analyzed. Accuracy of the DSIFs is examined employing the various damping parameters and effectiveness of the new PD fracture model is verified. The Kalthoff-Winkler impact test is considered for evaluating the mixed-mode DSIFs and the crack paths

Fracture parameter analysis of flat shells under out-of-plane loading using ordinary state-based peridynamics

The present paper is devoted to numerical investigation on fracture parameters of cracked shells subjected to out-of-plane loading using ordinary state-based peridynamics (PD). The nonlocal deformation gradient and equivalent domain integral are introduced to evaluate fracture parameters. To reduce the surface effect and obtain more accurate results, the energy method and volume correction algorithm are considered. Meanwhile, the adaptive dynamic relaxation technique is employed to obtain steady-state solutions. From comparisons between PD results and reference solutions, the proposed PD shell model successfully evaluates fracture parameters in both single- and mixed-mode loading conditions

Dynamic crack arrest analysis by ordinary state-based peridynamics

Dynamic fracture analysis for the crack arrest phenomenon is performed by ordinary state-based peridynamics formulation and discretization employing transition bond concept. Double cantilever beam specimen is chosen for our numerical evidence purpose. The analysis consists of two main phases namely, generation and application (prediction) phases. In the generation phase, the dynamic stress intensity factors of propagating and arrested cracks are estimated by the present formulation for given crack path histories, and good agreement is achieved. As for the application phase, dynamic stress intensity factors well as total crack lengths after crack arrests are in good agræment with the experiments. Moreover, the influence of transition bond concept on the crack arrest behavior is investigated and it is found that the transition bond is very efficient in the simulation of the crack arrest problem such that premature arrests of cracks are observed without transition bond cases

Characterisation of the static offset in the travelling wave in the cochlear basal turn

The version of record of this article, first published in Pflugers Archiv European Journal of Physiology, is available online at Publisher’s website: https://doi.org/10.1007/s00424-020-02373-6.In mammals, audition is triggered by travelling waves that are evoked by acoustic stimuli in the cochlear partition, a structure containing sensory hair cells and a basilar membrane. When the cochlea is stimulated by a pure tone of low frequency, a static offset occurs in the vibration in the apical turn. In the high-frequency region at the cochlear base, multi-tone stimuli induce a quadratic distortion product in the vibrations that suggests the presence of an offset. However, vibrations below 100 Hz, including a static offset, have not been directly measured there. We therefore constructed an interferometer for detecting motion at low frequencies including 0 Hz. We applied the interferometer to record vibrations from the cochlear base of guinea pigs in response to pure tones. When the animals were exposed to sound at an intensity of 70 dB or higher, we recorded a static offset of the sinusoidally vibrating cochlear partition by more than 1 nm towards the scala vestibuli. The offset’s magnitude grew monotonically as the stimuli intensified. When stimulus frequency was varied, the response peaked around the best frequency, the frequency that maximised the vibration amplitude at threshold sound pressure. These characteristics are consistent with those found in the low-frequency region and are therefore likely common across the cochlea. The offset diminished markedly when the somatic motility of mechanosensitive outer hair cells, the force-generating machinery that amplifies the sinusoidal vibrations, was pharmacologically blocked. Therefore, the partition offset appears to be linked to the electromotile contraction of outer hair cells

Dynamic fracture analysis of functionally graded materials using ordinary state-based peridynamics

Functionally graded materials are regarded as a special kind of composites capable of eliminating material interfaces and the delamination problems. Stress discontinuity can be avoided owing to smooth composition of the functionally graded ingredients. In this study, a recently emerged effective non-local continuum theory for solving fracture problems in solids and structures, peridynamics, is employed to simulate dynamic wave propagation as well as crack propagation in functionally graded materials. Specifically, the ordinary state-based formulation is adopted. The ordinary state-based formulation is slightly modified for the modelling of functionally graded materials. The averaging technique is employed to determine peridynamic parameters associated with the material properties. Firstly, a benchmark problem is considered to validate the present implementation of ordinary state-based peridynamics for brittle fracture of homogeneous materials. Then, the wave propagation in the functionally graded materials under impact loading is simulated. Finally, dynamic crack propagation in the functionally graded materials is studied. The evaluated crack paths and the displacement waves are compared with reference works including numerical and experimental results. Good agreement between the reference and present results is achieved. It is shown that a simple modification of ordinary state-based formulation has led to simulate dynamic fracture of functionally graded materials