Solidification of a supercooled liquid in a narrow channel

We simulate solidification in a narrow channel through the use of a phase-field model with an adaptive grid. In different regimes, we find that the solid can grow in fingerlike steady-state shapes, or become unstable, exhibiting unsteady growth. At low melt undercoolings, we find good agreement between our results, theoretical predictions, and experiment. For high undercoolings, we report evidence for a new stable steady-state finger shape which exists in experimentally accessible ranges for typical materials.     

Buildup of a narrow plasma channel by microwaves

The paper deals with the effect of the buildup of a narrow plasma channel by a hf right-hand circularly polarized (RHCP) wave propagating through radially inhomogeneous plasma in the direction of the static magnetic field. The plasma channel occurs under conditions when the linear transformation of the RHCP wave takes place. The experiments were carried out in a homogeneous static magnetic field _ce /2.3;, _ce are the frequency of the RHCP wave and the electron cyclotron frequency, respectively.Nademlýnská 600, Praha 9, Czechoslovakia.     

Characteristics of combustion in a narrow channel with a temperature gradient

Characteristics of premixed combustion in a heated channel with an inner diameter smaller than the conventional quenching distance of the employed mixture were investigated experimentally, analytically, and numerically. A cylindrical quartz tube with an inner diameter of 2 mm was used as a model channel. The downstream part of the tube was heated by an external heat source, and hence the temperature gradient in the axial direction was formed in the middle of the tube. Flat and stationary conventional premixed flames were stabilized at a point in this temperature gradient. In addition to these flames, various other flames that exhibit dynamic behaviors such as cyclic oscillatory motions, and repetitive ignition and extinction were also observed experimentally. These flames with large amplitude oscillatory motion might be utilized as a heat source with high speed temporal temperature variations in microsystems for future application. Another stable flame region in extremely low speed criteria at a mixture velocity of 2–3 cm/s was also experimentally confirmed. This flame was inferred to be an example of mild combustion, and it might also be used as a mild heat source for microdevices. The overall stability criteria of these flame regimes were analytically examined, and the detailed structure of each flame on the stable solution branches was numerically examined by employing 1D computation with detailed chemistry. The two results qualitatively agreed with each other and clarified the mechanism of the present various flames and their dynamic characteristics.     

Two-dimensional numerical simulation on galloping detonation in a narrow channel

The numerical simulations of the two-dimensional galloping detonation performed by using two-dimensional full Navier–Stokes simulations with a detailed chemistry model are presented. The detonation in a narrow channel with d = 5 mm, which is approximately twice the half-reaction length of hydrogen, shows a feature of galloping detonation with two initiations during its propagation under the laminar flow assumption. The distance between these two initiations is approximately 1300 mm, which causes the induction time behind the leading shock wave. As the channel width increases, the galloping feature diminishes. The detonation propagates approximately 4% lower than D_CJ for d = 10 and 15 mm. By increasing the channel width, the strength of the detonation increases, as shown in the maximum pressure histories. The effects of turbulence behind the detonation show that the galloping feature disappears, although its propagation velocity becomes 0.9 D_CJ. The strength of the detonation becomes significantly weak compared with the detonation propagating in the wide channel widths, and this feature is similar to the laminar assumption. The trend of the velocity deficits in the NS simulations agrees fairly well with the trend of the modified ZND calculations with η = 0.25.     

Like-charge attraction and hydrodynamic interaction

We demonstrate that the attractive interaction measured between like-charged colloidal spheres near a wall can be accounted for by a nonequilibrium hydrodynamic effect. We present both analytical results and Brownian dynamics simulations which quantitatively capture the one-wall experiments of Larsen and Grier [Nature (London) 385, 230 (1997)], using a single unmeasured parameter.     

Light emitted from a liquid that flows in a narrow channel as triboluminescence

The flow of a liquid through a narrow channel under a high pressure (on the order of tens of atmospheres) can be accompanied by emission of light, which has been termed hydroluminescence. We have shown that this light emission takes place both from the gas and from the liquid phase, with each type of emission being characterized by its own radiation spectrum. The spectra of hydroluminescence are similar to the spectra of photoluminescence obtained upon UV irradiation of a liquid under study. Therefore, the hydroluminescence of a liquid is not a light emission of a specific type; the flow through the narrow channel is only one of the ways of excitation of the light emission, which, in this case, is caused by friction. In other words, hydrodynamic luminescence can be referred to a wider class of phenomena—triboluminescence.     

Capacitance spectroscopy of compressible and incompressible stripes in a narrow electron channel

We study the capacitance of single electron wires in high quantizing magnetic fields. The capacitance spectra obtained on 300 nm wide electron channels are interpreted with a simple model considering the geometry of the incompressible stripes in the electron channel as function of filling factor. The capacitance spectra directly reflect the potential form of the wire edge. This is experimentally demonstrated by the dependence on the confinement potential as well as by a clear asymmetry of the capacitance minimum at filling factor v=2 that can be well explained with the model. For comparison we present capacitance spectra obtained on very narrow, but otherwise similar quantum wires, in which quantization into one-dimensional subbands dominates the behavior.     

Mode interaction in two-stream systems of hydrodynamic type

The nonlinear dynamics of nonequilibrium two-stream hydrodynamic systems is described within the framework of Hamiltonian formalism. A procedure is proposed for diagonalization of the quadratic part of the Hamiltonian based on diagonalization of the dynamic equations by going over to normal variables with subsequent construction of the Hamiltonian as a motion integral. Matrix mode interaction elements are found.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 72–76, December, 1990.     

Formation of a narrow sound beam in the underwater sound channel by a vertical array

The possibility of using a vertical array for the generation of a narrow wave beam that propagates in the underwater sound channel along a given reference ray is discussed. The variational problem of choosing the initial field at the array aperture to provide the minimal possible average beam width along the propagation path of a fixed length is solved.     

S-wave nucleon-antinucleon interaction in a model with confined channel

A model of the low energyN¯N interaction based on an idea of a quark channel acting as a doorway state is proposed. The salient features of the experimental data are well reproduced.     

Dynamics of tandem bubble interaction in a microfluidic channel

The dynamics of tandem bubble interaction in a microfluidic channel (800 × 21 μm, W?×?H) have been investigated using high-speed photography, with resultant fluid motion characterized by particle imaging velocimetry. A single or tandem bubble is produced reliably via laser absorption by micron-sized gold dots (6 μm in diameter with 40 μm in separation distance) coated on a glass surface of the microfluidic channel. Using two pulsed Nd:YAG lasers at λ?=?1064 nm and ～10 μJ/pulse, the dynamics of tandem bubble interaction (individual maximum bubble diameter of 50 μm with a corresponding collapse time of 5.7 μs) are examined at different phase delays. In close proximity (i.e., interbubble distance?=?40 μm or γ?=?0.8), the tandem bubbles interact strongly with each other, leading to asymmetric deformation of the bubble walls and jet formation, as well as the production of two pairs of vortices in the surrounding fluid rotating in opposite directions. The direction and speed of the jet (up to 95 m/s), as well as the orientation and strength of the vortices can be varied by adjusting the phase delay.     

Water transportation across narrow channel of nanometer dimension

Since the discovery of the carbon nanotube and aquaporin, the study of the transportation of water across nanochannels has become one of the hot subjects. When the radius of a nanochannel is only about one nanometer or a little larger, water confined in those nanoscale channels usually exhibits dynamics different from those in bulk system, such as the wet–dry transition due to the confinement, concerted hydrogen-bond orientations and flipping, concerted motion of water molecules, and strong interactions with external charges. Those dynamics correlate with the unique behavior of the water transportation across the channels, such as the extra-high permeability, excellent on–off gating behavior with response to the external mechanical and electrical signals and noises, enhancement by structure outside the channel, directional transportation driven by charges close to a channel or electric field. In this article, we review some of the recent progress on the study of the water molecules inside those narrow nanochannels.