Direction motion

Electric currents in electrolyte solutions are the directed motions of ions under the influence of an applied electric field. Ions in solution are in a state of continuous kinetic molecular (thermal) motion. This motion is chaotic when an electrostatic field is not present (i.e., the ions do not move preferentially in any particular direction, and there is no current flow). 

Surface switching coupled with geometric and potential asymmetry was used to cause directional motion of a droplet. Sophisticated design and active control of surface properties are important technology for motion control on the micro/nano-scales. 

The first and second integrals have their coordinate systems centered on the catalytic C and noncatalytic N spheres, respectively. The local nonequilibrium average microscopic density field for species a is pa(r) = [Y = 5(r - ( )) The solution of the diffusion equation can be used to estimate this nonequilibrium density, and thus the velocity of the nanodimer can be computed. The simple model yields results in qualitative accord with the MPC dynamics simulations and shows how the nonequilibrium density field produced by reaction, in combination with the different interactions of the B particles with the noncatalytic sphere, leads to directed motion [117],... 

Kinetic energy (associated with directed motion of masses)... 

The two examples of adsorbed side chain substituted macromolecules, i.e., the poly(n-butyl acrylate) brush and the tris(p-undecyloxybenzyloxo) benzoate jacketed polystyrene, demonstrate two rather complementary aspects of the interaction of such molecules with a planar surface. In the first case the two-dimension to three-dimension transition results in a cooperative collapse of an extended coil conformation to a globule. The second case shows a rather high degree ordering with a distinct orientation of the backbone in the substrate plane. Combination of both effects and partial desorption can lead to a repta-tion-hke directed motion as depicted schematically in Fig. 36. 

Fig. 36. Directed motion of cylinders with broken symmetry on a solid surface...

Fig. 38. Persistent and directed motion of a small cluster of five 14ABG-4EO-PMA molecules along the terrace of HOPG...

Kinbara, K. Aida, T. Toward Intelhgent Molecular Machines Directed Motions of Biological and Artificial Molecules and Assemblies. Chem. Rev. 2005,105, 1377-1400. 

In natural systems there are two types of transport phenomena (1) transport by random motion, and (2) transport by directed motion. Both types occur at a wide range of scales from molecular to global distances, from microseconds to geological times. Well-known examples of these types are molecular diffusion (random transport) and advection in water currents (directed transport). There are many other manifestations such as dispersion as a random process (see Chapters 24 and 25) or settling of suspended particles due to gravitation as a directed transport. For simplicity we will subdivide such transport processes into those we will call diffusive for ones caused by random motions and those called advective for ones resulting from directed motions. 

Molecular diffusion deals with the relative motion of one kind of atom or molecule against a set of reference molecules. As explained in the introduction to this chapter (remember the trip in the dining car through the Swiss Alps), the reference system itself may move relative to some chosen coordinates. We called such directed motion advection. If one really looks very closely and wants to use crystal-clear definitions, it turns out that there is more than one way to choose the reference system. Each choice leads to a different separation between diffusion and advection, resulting in different diffusion coefficients. 

As mentioned earlier, turbulent motion is usually more intensive along the horizontal than the vertical axis. Turbulent structures (eddies) can be horizontally very large. For instance, the eddies or gyres produced by the Gulf Stream are more than 100 km wide. Thus, for horizontal transport the separation between random and directed motion plays a more crucial role than for the case of vertical diffusion. 

Free cw-azobenzene, excited at 480 nm displays a biexponential decay of the excited state Si with time constants of 0.1 ps and 0.9 ps. Here the ultrafast kinetic component dominates the absorption change (it contains 90 % of the whole amplitude). A direct interpretation would relate the fast component to a free isomerizational motion, where the most direct reaction path on the Si and So potential energy surface is used without disturbance. The slower process may be assigned to a less direct motion due to hindrance by the surrounding solvent molecules. This interpretation is supported by the observation of the absorption changes in the APB and AMPB peptides. Here both reaction parts are slowed down by a factor of 2 - 3 and both show similar amplitudes The peptide molecules hinder the motion of the azobenzene switch and slow down considerably the initial kinetics. However, in all samples the transition to the ground state is finished within a few picoseconds. 

However, this idealized limiting case material distribution is distinguished from an ordinary material distribution in the sense that the individual particles of which it is composed are each in a state of arbitrarily directed motion, but with equal-magnitude velocities for all particles—and in this sense is more like a quasiphoton gas distribution. For this reason, we interpret the distribution as a rudimentary representation of an inertial material vacuum, and present it as the appropriate physical background within which gravitational processes (as conventionally understood) can be described as point-source perturbations of an inertial spatiotemporal-material background. We briefly discuss how such processes can arise. 

Fig. 2 Positional detection and mean-square displacement (MSD). (a) The x, y-coordinates of a particle at a certain time point are derived from its diffraction limited spot by fitting a 2D-Gaussian function to its intensity profile. In this way, a positional accuracy far below the optical resolution is obtained, (b) The figure depicts a simplified scheme for the analysis of a trajectory and the corresponding plot of the time dependency of the MSD. The average of all steps within the trajectory for each time-lag At, with At = z, At = 2z,... (where z = acquisition time interval from frame to frame) gives a point in the plot of MSD = f(t). (c) The time dependence of the MSD allows the classification of several modes of motion by evaluating the best fit of the MSD plot to one of the four formulas. A linear plot indicates normal diffusion and can be described by = ADAt (D = diffusion coefficient). A quadratic dependence of on At indicates directed motion and can be fitted by = v2At2 + ADAt (v = mean velocity). An asymptotic behavior for larger At with = [1 - exp (—AA2DAt/)] indicates confined diffusion. Anomalous diffusion is indicated by a best fit with = ADAf and a < 1 (sub-diffusive)...

These observations show that there are striking similarities between myosin and kinesin motors, suggesting that both use a similar if not the same mechanism for transforming ATP s free energy into directed motion. There are, however, also notable differences, both in structure and kinetics, which may reflect the diverse functions of the motors. 

In this experiment you are changing work to heat. Work is the energy of directed motion. Riding a bicycle, pushing a weight,and... 

However, because traditional mechanics are based on non-chiral concepts—like the Newtonian center of mass—the effects of chirality on molecular level motion have largely been overlooked [6]. This review is concerned with the relationship between mechanical motion and chirality at the molecular level we will discuss how chirality—or its expression—can be altered through molecular motion, and how a fixed chiral configuration can help to direct motion. But first it is important to briefly describe the physics that governs motion at the molecular level since it is fundamentally different to that which governs movement in the macroscopic world and, in many respects, the differences are somewhat counterintuitive [7]. 

All of these devices show a certain degree of restriction in the movement of their molecular components, but rotation occurs randomly with no control over directionality. In an attempt to achieve directional motion Kelly investigated the dynamic behavior of a so-called molecular ratchet , 6 [21,22],... 

The relationship between chirality and molecular-level motion is a complex one. Chirality is not an inherent requirement for generating directional motion and yet in some cases it is precisely what causes molecular level motion to proceed in one direction only. New generations of molecular machines will undoubtedly shed more light on this matter for instance in establishing the processes for which chirality is an absolute requirement in their design. Conversely, some molecular machines have the ability to dramatically influence the expression of chirality through controlled submolecular motion. This feature has potential application in data storage, displays and switchable catalysis. 

The oscillations of the piston assembly are damped out because the viscous nature of the gas gradually converts gross directed motion of the molecules into chaotic molecular motion. This dissipative process transforms some of the work initially done by the gas in accelerating the piston back into internal energy of the gas. Once the process is initiated, no infinitesimal change in external conditions can reverse its direction the process is irreversible. 

Kinbara K, Aida T (2005) Toward intelligent molecular machines directed motions of biological and artificial molecules and assemblies. Chem Rev 105 1377-1400... 

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