Microscopic Motion Research Articles

What do we know about the microscopic motion in simple liquid metals and what can we learn from inelastic scattering experiments?

A short survey on recent inelastic scattering work on liquid alkali metals is given. The classification of liquid alkalis as “simple liquids” is questioned from analysing experimental data measured within the full liquid range from melting point cond

Tunable Fröhlich polarons in organic single-crystal transistors

In organic field-effect transistors (FETs), charges move near the surface of an organic semiconductor, at the interface with a dielectric. In the past, the nature of the microscopic motion of charge carriers--which determines the device performance--has been related to the quality of the organic semiconductor. Recently, it was discovered that the nearby dielectric also has an unexpectedly strong influence. The mechanisms responsible for this influence are not understood. To investigate these mechanisms, we have studied transport through organic single-crystal FETs with different gate insulators. We find that the temperature dependence of the mobility evolves from metallic-like to insulating-like with increasing dielectric constant of the insulator. The phenomenon is accounted for by a two-dimensional Fröhlich polaron model that quantitatively describes our observations and shows that increasing the dielectric polarizability results in a crossover from the weak to the strong polaronic coupling regime. This represents a considerable step forward in our understanding of transport through organic transistors, and identifies a microscopic physical process with a large influence on device performance.

Stability and Asymptotic Analysis of a Fluid-Particle Interaction Model

We are interested in coupled microscopic/macroscopic models describing the evolution of particles dispersed in a fluid. The system consists in a Vlasov–Fokker–Planck equation to describe the microscopic motion of the particles coupled to the Euler equations for a compressible fluid. We investigate dissipative quantities, equilibria and their stability properties and the role of external forces. We also study some asymptotic problems, their equilibria and stability and the derivation of macroscopic two-phase models.

Monotonic and Cyclic Tests of Interface between Structure and Gravelly Soil

Monotonic and cyclic behavior of the interface between a structure and gravelly soil was investigated using systematical tests. A series of monotonic and cyclic tests of the interface between a steel plate and gravel were conducted using a large-scale test apparatus through varying gravel types, surface roughnesses of steel plates, normal boundary conditions, magnitudes of normal stress and displacement amplitudes. Microscopic movements and crushing process of soil particles were measured coupled with macroscopic stress-displacement relationship response. Based on the results, it is concluded that monotonic and cyclic behavior of the interface between a structure and gravelly soil is significantly different from that of gravelly soil itself. Main behaviors of the interface includes: (1) shear strength is proportional to normal stress; (2) the interface between a steel plate and gravel exhibits insignificant strain softening; (3) normal displacement accumulates and the accumulation rate decreases with increasing shear cycles, but varies in well-regulated manner within a single shear cycle; (4) shear deformation is composed of indispensable slippage component on the contact surface and soil deformation component constrained by the structure nearby while the latter mainly contributes to volumetric change due to dilatancy; (5) mechanical response is dependent on shear direction due to cyclic shear application after an initial shear application; (6) evolution of stress-displacement relationship response are governed by the evolution of physical state including particle crushing and soil compression due to shear application; (7) main factors influencing on behavior include surface roughness of the structure, characteristics of the soil and magnitude of normal stress.

Hydrogen Storage: Modeling and Analytical Results

We present a thermomechanical model describing hydrogen storage by use of metal hydrides. The problem is considered as a phase transition phenomenon. The model is recovered by continuum mechanics laws, using a generalization of the principle of virtual power accounting for microscopic movements related to the phase transition. The resulting nonlinear PDE system is investigated from the point of view of existence, uniqueness, and regularity of solutions.

Potential of diffusion imaging in brain tumors: a review

Diffusion magnetic resonance imaging (MRI) is a method for quantifying the microscopic random motion of water molecules in tissues. Diffusion imaging provides indirect structural information of a kind not available on basic MRI sequences of many pathological conditions. Lately, especially brain tumors have been under active investigation, with numerous papers already published, and their number continues to increase. This review summarizes the heterogeneous and complex research data on diffusion imaging of brain tumors.

Contact Area Measurements Reveal Loading-History Dependence of Static Friction

We perform quantitative measurements of the actual area of contact, A, formed by two rough solids that are subjected to different normal loading protocols. We show that microscopic motion, induced by Poisson contraction or expansion, produces a strong memory dependence of on the loading history with a large corresponding influence on the system's frictional strength. These effects, together with accompanying transient dynamics, are independent of humidity, loading rates, and material contrast across the interface.

Shear-Induced Crystallization in Blends of Model Linear and Long-Chain Branched Hydrogenated Polybutadienes

Quiescent and shear-induced crystallizations were performed on several well-defined linear monodisperse hydrogenated polybutadiene blends with a high-molecular-weight long-chain branched (LCB) comb-shaped additive. The connection between microscopic molecular motion and crystallization kinetics has been quantitatively studied with respect to the formation of either isotropic or oriented shish kebab crystal morphology using time-resolved X-ray scattering techniques. Using a constant preshear rate, the addition of small amounts of LCB combs to the sample blends, at concentrations below and just above the overlap concentration c*, has significantly increased the crystallization rates compared to quiescent conditions. However, only one blend showed the formation of an oriented shish kebab morphology. Also, for these model blends, the transition between isotropic and oriented crystals occurs quite sharply between 5 and 10%, which is around c*. We explain these data by using a shish formation mechanism in which...

A physical model for galvanotaxis of Paramecium cell

We propose a qualitative physical model of galvanotaxis of Paramecium cells using a bottom-up approach to link the microscopic ciliary motion and the macroscopic behavior of the cells. From the characteristic pattern of ciliary motion called the Ludloff phenomenon, the torque that orients the cell toward the cathode is derived mathematically. Dynamical equations of motion are derived and their stability is discussed. In numerical simulations using our model, cells exhibit realistic behavior, such as U-turns, like real cells.

Signatures of Glass Formation in a Fluidized Bed of Hard Spheres

We demonstrate that a fluidized bed of hard spheres during defluidization displays properties associated with formation of a glass. The final state is rate dependent, and as this state is approached, the bed exhibits heterogeneity with increasing time and length scales. The formation of a glass results in the arrest of macroscopic particle motion and thus the loss of fluidization. Microscopic motion persists in this state, but the bed can be jammed by application of a small increase in flow rate. Thus a fluidized bed can serve as a test system for studies of glass formation and jamming.

Multi‐photon excitation microscopy in intact animals

Two-photon excitation fluorescence microscopy and backscattered-second harmonic generation microscopy permit the investigation of the subcellular events within living animals but numerous aspects of these experiments need to be optimized to overcome the traditional microscope geometry, motion and optical coupling to the subject. This report describes a stable system for supporting a living instrumented mouse or rabbit during endogenous reduced nicotinamide adenine dinucleotide and exogenous dye two-photon excitation fluorescence microscopy measurements, and backscattered-second harmonic generation microscopy measurements. The system was a modified inverted LSM510 microscope (Carl Zeiss, Inc., Thornwood, NY, U.S.A.) with a rotating periscope that converted the inverted scope to an upright format, with the objective located approximately, 15 cm from the centre of the microscope base, allowing easy placement of an instrumented animal. An Olympus 20x water immersion objective was optically coupled to the tissue, without a cover glass, via a saline bath or custom hydrated transparent gel. The instrumented animals were held on a specially designed holder that poised the animal under the objective as well as permitted different ventilation schemes to minimize motion. Using this approach, quality images were routinely collected in living animals from both the peripheral and body cavity organs. The remaining most significant issue for physiological studies using this approach is motion on the micrometre scale. Several strategies for motion compensation are described and discussed.

WELL-POSEDNESS OF A PHASE TRANSITION MODEL WITH THE POSSIBILITY OF VOIDS

The paper deals with a phase transition model applied to a two-phase system. There is a wide literature on the study of phase transition processes in case that no voids nor overlapping can occur between the two phases. The main novelty of our approach is the possibility of having voids during the phase change. This aspect is described in the model by the mass balance equation whose effects are included by means of the pressure of the system in the dynamical relations. The state variables are the absolute temperature (whose evolution is ruled by the entropy balance equation), the strain tensor (satisfying a quasi-static macroscopic equation of motion), and the volume fractions of the two phases (whose evolutions are described by a vectorial equation coming from the principle of virtual power and related to the microscopic motions). Well-posedness of the initial-boundary value problem associated to the PDEs system resulting from this model is proved.

How Do Muscles Function?

Skeletal muscle is an exquisite example of a structure-function relationship. This presentation will provide a brief review of the microscopic features that enable force generation, with an emphasis on myofilament arrangements, sarcomeres and the muscle cell membrane system. The remainder of the presentation will focus on the structural features that allow transduction of microscopic movement into gross movement. Although skeletal muscle may attach to bone, cartilage, the skin, mucous membranes or an organ, this presentation will focus on the attachment through tendons to bone. The discussion will examine muscle architecture and how fiber arrangement facilitates force production versus excursion. A muscle's ability to generate joint motion or to stabilize a joint may be deduced from its attachments and the relationship of the muscle to the joint. Muscles that act as synergists across a joint frequently have very different architecture to provide both joint range of motion and significant muscle force. The length-tension concept will be discussed in a brief review of muscle mechanics, joint moments and torque. The concepts of muscle tone, and eccentric, concentric, isotonic and isometric contraction will be defined. Lastly, the discussion will expand to the importance of muscle connective tissues, including the effects of muscle contraction within a fascial compartment, and the concepts of tendon flexibility and energy storage.

Assembling of Dense Fluorescent Supramolecular Webs via Self-Propelled Star-Shaped Aggregates

We report a novel mechanism of assembly of dendronized rod molecules into a dense supramolecular fluorescencent web featuring self-propelled mechanistic inward motion of star-shaped aggregates within a solution droplet. We suggest that such a motion (observed in real time) is caused by the self-repulsion of the growing star-shaped nuclei from the liquid-solid-air interface in the course of one-dimensional growth of the anchored arms. An intriguing mechanism discovered here involves microscopic (hundred micrometers) directional motion of the microscopic aggregates driven by one-dimensional molecular assembly, which opens a new venue for guided assembly of dense mesoscopic supramolecular webs. Such assemblies can serve as interesting microfluidic networks, a web of optical switches, and model systems for studying intercellular communication.

Individual foraging behaviors and population distributions of a planktonic predator aggregating to phytoplankton thin layers

Resource distributions in the ocean are heterogeneous in time and space. Theory predicts planktonic predators may exploit these resource patches by modifying their movements in response to mechanical or chemical stimuli. In the laboratory, we used the protistan predator Oxyrrhis marina to simultaneously quantify changes in predator population distributions on scales of centimeters and hours and predators' individual three-dimensional swimming behaviors on scales of micrometers and seconds. Movements of O. marina in a 0.3-m column were monitored for several hours before and after introducing a 5-mm layer of either Isochrysis galbana prey cells or cell-free I. galbana filtrate. Within both types of layers, significant increases in turning rates and decreases in vertical velocities were observed. O. marina swimming speed increased significantly in response to intact I. galbana cells, but not in response to I. galbana exudates. Changes in predators' microscopic movements were concurrent with rapid (minutes) and sustained (hours) increases in relative predator abundance within layers. After 4 h, predator abundance inside the thin layers was up to 20 times higher than before introduction of prey. Estimates of realized growth rates for predator populations with aggregate behaviors were an order of magnitude faster than estimates for hypothetical, nonaggregating predators. The observed foraging behaviors of O. marina, and by implication other planktonic predators, increase effective prey availability to the predators. Modulation of individual-level behaviors can result in significant changes in community-level characteristics, including population distributions, growth, and ingestion rates.

1P1-D34 非線形ばね特性を持つ送り駆動系の動的挙動

This paper concerns dynamic characteristics of a feed drive system with the nonlinear spring behavior. The dynamic characteristics during the microscopic motion can be represented with a mixed term by combining Coulomb friction and the nonlinear spring behavior. Comparing experiment results with simulation results, it can be found that the dynamic characteristics are dominated by the Coulomb friction term in the range of 1OOμm and over, and described by the mixed term in the range of 5〜100μm. It is clarified that the effect of Coulomb friction on the mixed term is excessively strengthened when the Coulomb frictional coefficient is used in the range of 1OOμm and over.

Global solution to a phase transition model with microscopic movements and accelerations in one space dimension

This note deals with a nonlinear system of PDEs accounting for phase transition phenomena. The existence of solutions of a related Cauchy-Neumann problem is established in the one-dimensional setting. A fixed point procedure guarantees the existence of solutions locally in time. Next, an argument based on <em>a priori</em> estimates allows to extend such solutions in the whole time interval. Hence, the uniqueness of the solution is proved by proper contracting estimates.

Analysis of a variable time-step discretization for a phase transition model with micro-movements

This note deals with a semi-implicit time discretization with variable time-step of a phase transition model taking into account the microscopic movements of molecules. In particular, we focus on the study of an unconditionally stable and convergent approximation. Moreover, an a priori estimate for the discretization error is established.

The foundations of diffusion revisited

Diffusion is essentially the macroscopic manifestation of random (Brownian) microscopic motion. This idea has been generalized in the continuous time random walk formalism, which under quite general conditions leads to a generalized master equation (GME) that provides a useful modelling framework for transport. Here we review some of the basic ideas underlying this formalism from the perspective of transport in (magnetic confinement) plasmas.Under some specific conditions, the fluid limit of the GME corresponds to the Fokker–Planck (FP) diffusion equation in inhomogeneous systems, which reduces to Fick's law when the system is homogeneous. It is suggested that the FP equation may be preferable in fusion plasmas due to the inhomogeneity of the system, which would imply that part of the observed inward convection (‘pinch’) can be ascribed to this inhomogeneity.The GME also permits a mathematically sound approach to more complex transport issues, such as the incorporation of critical gradients and non-local transport mechanisms. A toy model incorporating these ingredients was shown to possess behaviour that bears a striking similarity to certain unusual phenomena observed in fusion plasmas.

Stick-Slip-Slap Interface Response Simulation: Formulation and Application of a General Joint/Interface Element

A general interface element is developed for dynamic response analysis of structures with jointed in- terfaces, which can account for damping due to both im- pact and friction. Contact effects are included through a segment-to-segment contact model which considers the stick-slip-slap behavior at every point along the joint in- terface. A nonlinear friction law is adopted at the inter- face to describe microscopic relative motion due to the deformation of the asperities on the interface. Numeri- cal examples demonstrate that the general joint interface element is capable of accounting for both friction and impact damping in jointed interfaces, as well as captur- ing the transfer of vibrational energy from low frequency to high during impact. The development of an interface slip zone is a combined result of the actual friction trac- tion and pressure distribution along the interfaces. It is shown that the general joint interface element is able to address this effectively, and the segment-to-segment con- tact model adopted here allows the general interface el- ement to capture very detailed stick-slip behavior along the interfaces even with a coarse mesh. keyword: Joint, Friction, Interface, Finite element, Contact model.