Slit Height Research Articles

Packing Confined Hard Spheres Denser with Adaptive Prism Phases

We show that hard spheres confined between two parallel hard plates pack denser with periodic adaptive prismatic structures which are composed of alternating prisms of spheres. The internal structure of the prisms adapts to the slit height which results in close packings for a range of plate separations, just above the distance where three intersecting square layers fit exactly between the plates. The adaptive prism phases are also observed in real-space experiments on confined sterically stabilized colloids and in Monte Carlo simulations at finite pressure.

Space-resolved extreme ultraviolet spectrometer system for impurity behavior research on experimental advanced superconducting Tokamak

A flat-field extreme ultraviolet (EUV) spectrometer, which covers a wavelength range of 5–50nm, has been developed for the experimental advanced superconducting tokamak (EAST). The spectrometer mainly consists of an entrance slit, a varied line spacing groove grating (1200 grooves/mm at the grating center), and a charge coupled device (CCD). The spectral resolution of the spectrometer is Δλ=0.015nm at 20nm when the width of entrance slit is set at 0.03mm. The spectrometer is capable of surveying impurity line emissions, for both intrinsic low-Z impurities and highly ionized medium- and high-Z impurities. The obtained best time resolution is 25ms and with entrance slit height at 1mm the spatial resolution has reached 45mm. Preliminary experimental results from the recent EAST campaign were presented. The system was shown to be able to measure the spectral lines of C, O, He, Li and metal impurities under various auxiliary heating conditions. By translating the CCD with a step motor, spectral lines from a full wavelength of 5–50nm can be covered. In particular the wavelength interval of 15–20.5nm showed strong line emissions of metal impurities. Time evolutions of second order spectral line of C VI (6.674nm) and Ni XVI (19.219nm) lines are presented and detailed analysis is done while taking into account electron density, electron temperature, auxiliary heating power, C III (464.7nm) and XUV intensities. The profile of Ni XVI is presented to show its good spatial resolution. The EUV spectrometer will be an important addition to the current EAST diagnostic systems in the area of impurity survey and transport research.

Effect of Nanoslit Confinement on the Knotting Probability of Circular DNA.

Monte Carlo simulations are used to study the knotting probability of circular DNA confined in a slit. We systematically vary the slit height, the width, and the contour length of the DNA molecule. We find that the trend in knotting probability with respect to slit height can be monotonic or nonmonotonic, depending on the width and contour length. The nonmonotonic trend is caused by two competing factors: the increase of the effective persistence length and the increase of segment density by slit confinement. These factors are antagonistic, in the sense that the increase in effective persistence length disfavors knot formation, whereas the increase in segment density favors the knotting probability. Our simulation results bring to light the importance of both chain length and width for slit-confined circular DNA and can be used to guide future experiments which aim to produce populations of knotted DNA through cyclization or catalyzed double-strand passage reactions in confinement.

Effects of Topology and Ionic Strength on Double-Stranded DNA Confined in Nanoslits

We investigate experimentally the effects of electrostatic interactions and topological constraints on DNA dynamics in nanoslit confinement by studying the equilibrium shape and dynamics of single linear and circular λ-DNA confined in a silicon/glass nanoslit. Having examined the dependence of chain radius of gyration R∥, shape asphericity A, and relaxation time τ on chain topology, slit height h (20–782 nm), and solvent ionic strength I (8.2–268.8 mM), it is found that the chain shape becomes more aspherical as h and I decrease. Moreover, in strong sub-Kuhn length confinement, the DNA relaxation time increases with decreasing h in a smooth and broad transition. Our results provide experimental evidence to confirm that the scaling exponents of radius of gyration and of relaxation time are the same for linear and circular DNA and help resolve conflicting observations of the qualitative dependencies of chain radius of gyration and relaxation time in sub-Kuhn length slits.

A systematic study of DNA conformation in slitlike confinement

DNA conformation in slitlike confinement is studied using Monte Carlo simulation and scaling theory. We focus on analysing the in-plane DNA extension as a function of slit height and DNA properties, such as contour length, persistence length and width. Similar to tube confinement, we identify an extended de Gennes regime which is prevalent in many experimental studies. However, unlike previous studies in tubes, we find two highly confined regimes (so called Odijk regimes) that depend on chain crossing. Our results support the majority of experiments which display a gradual transition into the Odijk regime and give new insight into the importance of chain width for DNA in nanoslits.

Wang-Landau Simulations of Adsorbed and Confined Lattice Polymers

We demonstrate how Wang-Landau simulations may be used in an effcient manner to investigate the statistical mechanics of lattice polymers adsorbed at a planar surface, and confined in slit geometry between two parallel surfaces. For nearest neighbour interactions, we show that one or two Wang-Landau simulations, recording the density of states as a function of numbers of internal contacts and of surface beads, are suffcient to give a full description of both of these situations. Moreover, the effciency of the simulations is improved by never having to reject moves due to overlap with the surface, and the limit of infinite slit height may be handled easily. The proposed “wall-free” methods have already been applied to homopolymers and heteropolymers (lattice peptides using the HP model) on a uniform surface, as well as regularly patterned surfaces, and could easily be generalized to surfaces with structure.

Modeling and Simulation of an Integrated Micro Packed Bed Reactor-Heat Exchanger Configuration for Direct Dimethyl Ether Synthesis

The application of an integrated micro packed bed reactor-heat exchanger for highly exothermic syngas conversion to dimethyl ether was investigated by numerical simulation. A three-dimensional pseudo-homogeneous model was developed to describe concentration and temperature distributions inside a single reaction slit. The model was adopted at low Reynolds numbers (small catalyst particles and long residence times). The simulation results reveal that the micro packed reaction slit is close to isothermal, and a negligible temperature gradient is predicted also for a doubling of the critical reaction slit dimension, i.e. the reaction slit height. The flow in the reaction slit was modelled by Brinkman’s equation and it was found that the pressure drop in wide range of gas velocity was not significant. The reactor simulation showed good agreement with experimental results and could be further developed to assess the potential of microstructured packed bed reactors to intensify large-scale industrial processes.

Shear viscosity measurements of polymer melts using injection molding machine with adjustable slit die

Rheological properties of polymer melts were studied using a slit die attached to an injection molding machine. The die has three exchangeable inserts to set the slit height to 0.75, 1.0, or 1.5 mm. The modular design eases the die cleaning, and measurements with variable slit heights enable the detection of possible wall slip. Two grades of polypropylene and two grades of polystyrene were studied using the slit die and the results were compared to those obtained using a capillary rheometer and a rotational rheometer in steady and dynamic modes. The examination of the selected polymers with different slits gave essentially the same results at each slit height, verifying the absence of wall slip. The agreement with the conventional off-line rheometer results was very good for all polymers studied. This suggests that a simple slit die construction can be used as an inexpensive rheometer to measure rheological properties of polymer melts for processing purposes. The thermo-mechanical history of the investigated melt in the in-line slit die experiments resembles that in actual melt processing and, therefore, determination of rheological properties under true processing conditions is possible.

Coulomb Forces on DNA Polymers in Charged Fluidic Nanoslits

We investigate the repulsive electrostatic interactions between a DNA polyelectrolyte and the charged walls of a fluidic nanoslit. The scaling of the DNA coil size with the physical slit height revealed electrostatic depletion regions that reduced the effective slit height. These regions exceeded the Debye screening length of the buffer, λ(D)(buffer), and saturated at ≈ 50 nm when λ(D)(buffer) reached 10 nm. We explain these results by modeling a semiflexible charged rod near a charged wall and the electrostatic screening by the polyelectrolyte. These results demonstrate the surprisingly long range over which a nanofluidic device can exert field-effect control over confined molecules.

Analysis of Flowing Characteristics of Abrasive Flow Machining in Slit

Based on the equations of motion and rheological theory of abrasive flow in the slit, effect between wall slip and grinding has been analyzed and grinding flow model of abrasive flow has been built in this paper. Wall pressure, wall shear stress, wall slip and the grinding force equation of abrasive flow were derived using the model. What is important, the effects of relevant factors were analyzed. The results show that wall slip is one of the necessary conditions that in abrasive flow machining, and show that main factors influencing wall slip are viscosity coefficient , grinding coefficient of abrasive flow, and the first normal stress difference. In the meantime, the results also show that grinding force in slit wall is proportional to the entrance pressure of slit. That is to say that the grinding force of per unit length in flow direction increasing dramatically with decreasing slit height.

Simulations of polyelectrolyte dynamics in an externally applied electric field in confined geometry

We consider the dynamics of charged polymers in free solution in a slit geometry under the influence of an electrical field, applied at an angle to the plane parallel walls of the confinement. The simulations are carried out using the Brownian dynamics method with explicit counterions and implicit hydrodynamics. The hydrodynamic interactions between all the particles and the plane parallel walls are taken into account using a diffusion matrix which depends on slit geometry and the actual polyelectrolyte-solute conformations. We observe a selective transport of the charged polymers, as a function of the degree of polymerization and slit height.

Revisiting the Conformation and Dynamics of DNA in Slitlike Confinement

We experimentally investigated the equilibrium conformation and dynamics of single DNA molecules in slitlike nanochannels. We measured the in-plane radius of gyration (R ) diffusivity (D), and longest relaxation time (τ)ofλ-DNA (48.5 kbp) as functions of the slit height using fluorescence microscopy. Our results show that the in-plane radius of gyration increases monotonically with decreasing slit height, in contrast to results from Bonthuis et al. 15 but in agreement with our simulations and those of other groups. In strongconfinement (slit height <100nm), thescaling ofD, τ, andR )with slitheight does notshow anevident change, suggesting that the transition from the de Gennes regime to the Odijk regime is gradual and broad.

Plasmon-Assisted Optical Curtains

We predict an optical curtain effect, i.e., formation of a spatially invariant light field as light emerges from a set of periodic metallic nano-objects. The underlying physical mechanism of generation of this unique optical curtain can be explained in both the spatial domain and the wave-vector domain. In particular, in each period, we use one metallic nanostrip to equate the amplitudes of lights impinging on the openings of two metallic nanoslits and also shift their phases by π difference. We elaborate the influence on the output effect from some geometrical parameters like the periodicity, the slit height, and so on. By controlling the light illuminated on metallic subwavelength apertures, it is practical to generate optical curtains of arbitrary forms, which may open new routes of plasmonic nanolithography.

반구형 도화새우통발에 있어서 적정 탈출구의 설계

In order to design the optimal escape vent for the coon strip shrimp pot, the tank experiments were conducted with the model pot of five different slit height and slit width, respectively. The optimal height and width of escape vent were determined to 20mm and 40mm by tank experiments, respectively. These were determined by the 50% selection carapace length which was denoted to 25mm in selectivity curve. The escape experiments were conducted to determine a number of escape vent with the original shrimp pot to be set the designed escape vent from 2 vents to 10 vents increasing at intervals of 2 vents in tank. The optimal number of escape vents denoted 8 vents. Therefore, to apply the escape vent in commercial shrimp pot will be efficient to reduce small size shrimps to catch.

Microflow hydrodynamics in slits: Effects of the walls relative roughness and spacer inter-filaments distance

A slit designed with very tight dimension tolerances was manufactured to perform pressure drop measurements in fully developed laminar flows, viewing the isolation of the effects of the walls roughness from those of the entrance developing flow and from uncertainties in the channel height. For that, five different values of the slit height, 0.7, 1.0, 1.2, 1.5 and 2.0 mm, were used together with five differently finished surfaces for the channel bottom wall, possessing average roughness values of 31.4, 11.4, 4.1, 1.3 and below 1 μm, which is the sensor detection limit of the contact profilometer used for the measurements. The slit allows also for flow visualization and can accommodate cylindrical-type spacers, positioned transversally to the flow and in direct contact with the bottom wall, with diverse inter-filament distances to study the critical Reynolds numbers marking the departure from the steady-state laminar flow regime. Results with deionised water and 5.4–13.9% of uncertainty for the pressure drop in the open channel showed that surface phenomena due to roughness, irrelevant at macroscale flows, are present in flows like those studied herein. Flow visualization for the same fluid and pressure drop measurements in the channel filled with ladder-type spacers showed that its height is crucial in the set up of the flow instabilities marking the departure from steady laminar flow.

Dynamics of confined suspensions of swimming particles

Low Reynolds number direct simulations of large populations of hydrodynamicallyinteracting swimming particles confined between planar walls are performed. The results ofsimulations are compared with a theory that describes dilute suspensions of swimmers. Thetheory yields scalings with concentration for diffusivities and velocity fluctuations as well asa prediction of the fluid velocity spatial autocorrelation function. Even for uncorrelatedswimmers, the theory predicts anticorrelations between nearby fluid elements thatcorrespond to vortex-like swirling motions in the fluid with length scale set by the size of aswimmer and the slit height. Very similar results arise from the full simulationsindicating either that correlated motion of the swimmers is not significant at theconcentrations considered or that the fluid phase autocorrelation is not a sensitivemeasure of the correlated motion. This result is in stark contrast with resultsfrom unconfined systems, for which the fluid autocorrelation captures large-scalecollective fluid structures. The additional length scale (screening length) introducedby the confinement seems to prevent these large-scale structures from forming.

Monte Carlo simulation of n-alkane adsorption isotherms in carbon slit pores

The single component adsorption of alkanes in carbon slit pores was studied using configurational-biased grand canonical Monte Carlo simulations. Wide ranges of temperature, pressure, alkane chain length, and slit height were studied to evaluate their effects on adsorption. Adsorption isotherms and density and orientation profiles were calculated. The behavior of long alkanes at high temperatures was found to be similar to short alkanes at lower temperatures. This suggests that the isotherms may be related through the Polanyi potential theory.

Impact of fluid path geometry and operating parameters on l/l-dispersion in interdigital micromixers

The dispersion of two immiscible fluids in interdigital micromixers was investigated using silicon oil/water and n -heptane/water as test systems. The experiments revealed the dependence of the average droplet size and size distribution on geometrical parameters of the micromixer and operating conditions. The mean droplet size was found to be correlated with total volume flow, volume flow ratio and corresponding pressure drop of the two liquids for a given micromixer geometry, which could be explained in light of the energy input. As a major focus, the effect of mixing chamber geometry and feeding system geometry was investigated with regard to droplet size distribution by systematically varying decisive dimensions in the mixer and by changing the feeding structure. It was shown that reducing the slit height and the number of feeding channels had a significant effect on droplet size distribution, leading to a smaller mean droplet size. Furthermore, the dispersion efficiency was also investigated by an extraction process.

CFD simulation of effect of baffle on mass transfer in a slit-type pervaporation module

A pervaporation simulation was conducted to describe mass transfer in a slit membrane module that contained mixing-promoting baffles for efficient removal of volatile organic compounds. Commercial computational fluid dynamics (CFD) package was employed to solve hydrodynamics and mass transfer equations. The effects of baffle on enhancing mass transfer in the module were examined. Numerical simulation results indicated 14, 24, and 34% improvements of the average mass transfer coefficient within the flow channel with baffle height of 10, 30, and 50% of the slit height of the module, reaching 1.25 × 10 −5 m/s, 1.35 × 10 −5 m/s, 1.44 × 10 −5 m/s, respectively, as compared with 1.08 × 10 −5 m/s where there was no baffle. In all cases, a second peak of the local flux was observed due to the disruption of the developed boundary layer around the baffle. Separation of the boundary layers was observed for baffles with 30 and 50% of the slit height. The pressure drops over the channel length were compared. An increase in 2, 4, and 27% in pressure drop corresponding to the aforementioned three different baffle heights were observed. The effect of multiple baffles on mass transfer depends on the locations of the second baffle. The effect of multiple baffles in the module is insignificant. Pervaporation (PV) experiments were conducted using polydimethylsiloxane membrane with baffle attached and compared with the simulation results. The experimental result showed good agreement with the simulation results at low Reynolds numbers (<1000).

Generation of Focused Electric Field Patterns at Dielectric Surfaces

We here report on a concept for creating well-defined electric field gradients between the boundaries of capillary electrode (a capillary of a nonconducting material equipped with an interior metal electrode) outlets, and dielectric surfaces. By keeping a capillary electrode opening close to a boundary between a conducting solution and a nonconducting medium, a high electric field can be created close to the interface by field focusing effects. By varying the inner and outer diameters of the capillary, the span of electric field strengths and the field gradient obtained can be controlled, and by varying the slit height between the capillary rim and the surface, or the applied current, the average field strength and gradient can be varied. Field focusing effects and generation of electric field patterns were analyzed using finite element method simulations. We experimentally verified the method by electroporation of a fluorescent dye (fluorescein diphosphate) into adherent, monolayered cells (PC-12 and WSS-1) and obtained a pattern of fluorescent cells corresponding to the focused electric field.