Low Mobility Regions Research Articles

Foam Propagation with Flow Reversal

With a view towards modelling the foam improved oil recovery process, fractional flow theory is used to study the dynamics of a foam as it propagates in a porous medium that is initially filled with liquid. In particular, a case is studied whereby, at a certain time, the net pressure driving the foam is decreased below the hydrostatic pressure at depth, leading to a local change in the flow direction. This is known as flow reversal. In both forward and reverse flow, the boundary between foamed gas and liquid is found as a discontinuous jump in liquid saturation. Over a certain thickness in the neighbourhood of this discontinuity, foam is finely textured, and the mobility of foamed gas drops by orders of magnitude relative to either pure gas or pure liquid. In reverse flow, however, the foam mobility itself and also the thickness over which low mobilities apply might differ from the forward flow case. Fractional flow theory reveals that the thickness of the low mobility region, and hence the resistance to motion that it presents, increases directly proportional to the distance travelled. Previous studies recognised this, but assumed the thickness of this region to be just a small fraction of the distance travelled by the discontinuity. Here, however, we demonstrate that the extent of the low mobility region, in both forward and reverse flow, accounts for a considerable fraction of the distance travelled by the foam, despite what was assumed in previous works.

Intrinsic Mechanism of Mobility Collapse in Short MOSFETs

The mobility degradation with channel length is examined from the viewpoint of electrostatic effects that alter not only the threshold voltage but also the transport properties. Even operated at low drain voltage, short MOSFETs are subject to a strong lateral electric field present over a significant portion of the channel. The lateral field, responsible for threshold voltage roll-off, causes a local degradation in the velocity and mobility of electrons and holes. The low-mobility regions located near the source and drain tend to merge in short devices, giving rise to an ineluctable mobility collapse that compromises the benefit of downscaling. This mechanism is fundamental and universal as it applies to all kinds of MOSFETs. A model of mobility collapse, totally different from existing theories, is proposed together with supportive numerical simulations.

Chemokinesis-driven accumulation of active colloids in low-mobility regions of fuel gradients

Many motile cells exhibit migratory behaviors, such as chemotaxis (motion up or down a chemical gradient) or chemokinesis (dependence of speed on chemical concentration), which enable them to carry out vital functions including immune response, egg fertilization, and predator evasion. These have inspired researchers to develop self-propelled colloidal analogues to biological microswimmers, known as active colloids, that perform similar feats. Here, we study the behavior of half-platinum half-gold (Pt/Au) self-propelled rods in antiparallel gradients of hydrogen peroxide fuel and salt, which tend to increase and decrease the rods’ speed, respectively. Brownian Dynamics simulations, a Fokker–Planck theoretical model, and experiments demonstrate that, at steady state, the rods accumulate in low-speed (salt-rich, peroxide-poor) regions not because of chemotaxis, but because of chemokinesis. Chemokinesis is distinct from chemotaxis in that no directional sensing or reorientation capabilities are required. The agreement between simulations, model, and experiments bolsters the role of chemokinesis in this system. This work suggests a novel strategy of exploiting chemokinesis to effect accumulation of motile colloids in desired areas.

Influence of high and low dielectric constant plasticizers on the ion transport properties of PEO: NH4HF2 polymer electrolytes

Different composition ratio of polymer electrolytes based on poly(ethylene oxide) (PEO) as host polymer, ammonium bifluoride (NH4HF2) as salt, and propylene carbonate (PC), dimethyl acetamide (DMA), dimethyl chloride (DMC), and diethyl carbonate (DEC) as plasticizers has been prepared by solution casting technique. The influence of high dielectric constant plasticizers (PC and DMA) and low dielectric constant plasticizers (DMC and DEC) on the ion transport properties of PEO-NH4HF2 polymer electrolytes has been studied. The increase in ionic conductivity of polymer electrolytes containing PC and DMA is observed to be more as compared to those electrolytes containing DMC and DEC, which is due to an increase in both the amorphous phase and dielectric constant of PEO. X-ray diffraction study reveals the amorphous nature in case of plasticized polymer electrolyte. In the Fourier transform infrared study, the changes and shifting of the different characteristic peaks confirm the polymer–salt complex formation and the dissociation of ion aggregates present at higher concentration of salt with the addition of PC. Maximum ionic conductivity of 1.40 × 10−4 S cm−1 at room temperature has observed in case of plasticized polymer electrolytes containing optimum concentration of PC so that mechanical stability and flexibility be maintained. The variation of linewidth with temperature has also been studied by 1H and 19F nuclear magnetic resonance (NMR), which confirms that both cations and anions are mobile in these polymer electrolytes. Line narrowing associated with the glass transition temperature ( T g; low mobility region) and melting temperature ( T m; high mobility region) of PEO has also been observed for plasticized polymer electrolytes containing PC having optimum conductivity value. Conductivity versus temperature variation study reveals curved nature of plot in case of plasticized polymer electrolytes containing high dielectric constant plasticizers, which is significant for their amorphous nature. Smooth morphology observed in case of plasticized polymer electrolytes having optimum conductivity value is essential key factor for polymer electrolytes to be suitable for practical applications.

Ice is born in low-mobility regions of supercooled liquid water

When an ice crystal is born from liquid water, two key changes occur: (i) The molecules order and (ii) the mobility of the molecules drops as they adopt their lattice positions. Most research on ice nucleation (and crystallization in general) has focused on understanding the former with less attention paid to the latter. However, supercooled water exhibits fascinating and complex dynamical behavior, most notably dynamical heterogeneity (DH), a phenomenon where spatially separated domains of relatively mobile and immobile particles coexist. Strikingly, the microscopic connection between the DH of water and the nucleation of ice has yet to be unraveled directly at the molecular level. Here we tackle this issue via computer simulations which reveal that (i) ice nucleation occurs in low-mobility regions of the liquid, (ii) there is a dynamical incubation period in which the mobility of the molecules drops before any ice-like ordering, and (iii) ice-like clusters cause arrested dynamics in surrounding water molecules. With this we establish a clear connection between dynamics and nucleation. We anticipate that our findings will pave the way for the examination of the role of dynamical heterogeneities in heterogeneous and solution-based nucleation.

Pore-scale simulations of concentration tails in heterogeneous porous media

The retention of contaminants in the finest and less-conductive regions of natural aquifer is known to strongly affect the decontamination of polluted aquifers. In fact, contaminant transfer from low to high mobility regions at the back end of a contaminant plume (i.e. back diffusion) is responsible for the long-term release of contaminants during remediation operation. In this paper, we perform pore-scale calculations for the transport of contaminant through heterogeneous porous media composed of low and high mobility regions with two objectives: (i) study the effect of permeability contrast and solute transport conditions on the exchange of solutes between mobile and immobile regions and (ii) estimate the mass of contaminants sequestered in low mobility regions based on concentration breakthrough curves.

Anatomical consideration of percutaneous transvenous mitral annulo-plasty: A novel procedure for treatment of functional mitral regurgitation

This research paper analyzes, finite element based two dimensional device simulations for top and bottom contact organic field effect transistors (OFETs) by considering uniform and non-consistent mobility regions. To model the morphological disorder in bottom contact structure, some calibrated standards for simulation is developed viz. by considering variable low mobility regions near the contacts. An analytical model is developed, by considering contact resistance and field dependent mobility. The effect of channel length variation (5–40 μm) on performance parameters is highlighted for both the structures. Subsequently, results shows only 1% change in current for bottom contact with 0.5 μm and 1 μm low mobility region near the contacts, due to dominant contact resistance, whereas, linear dependency is observed for other simulated structures. The top contact device shows 0.43 cm2/V s saturation mobility at 5 μm and 13% decrease up to 20 μm and afterwards constant behavior is noticed, whereas low mobility is extracted in bottom contact devices and shows 10–20% increase in both the mobilities for increasing channel length from 5 to 40 μm. For top and bottom devices, total 65% and 62% decrease in contact resistance is observed for increasing gate voltage from −1.8 V to −3 V and this percentage reduces for increasing the length of low mobility region. Further, we have evaluated 13%, 40% and 78% increase in the trap density, while proceeding for 0.25 μm, 0.5 μm and 1 μm low mobility region in the bottom contact structure.

A depth analysis for different structures of organic thin film transistors: Modeling of performance limiting issues

This research paper is focused on finding reasons for performance diversity between top contact (TC) and bottom contact (BC) structures of organic thin film transistors (OTFTs). The electrical characteristics, device physics, performance parameters and conduction mechanism are deeply analyzed using Atlas–Silvaco numerical device simulator. The simulation methodology consists of different approaches based on mapping of crucial issues for OTFTs. Few calibration are common for both TC and BC structures like material parameters along with Poole–Frenkel mobility model, defects in bulk OSC, dipoles at OSC–dielectric interface, correction for drain offset current and elimination of contacts voltage drop. After mapping of these issues, the results for TC structure are found close to the reported experimental results. However, performance of BC structure is reasonably matched only after incorporating some additional fabrication based issues such as unfilled corners and low mobility region around the S/D contacts. The drive current and the mobility are obtained higher by four and three times, respectively for TC than that of BC structure. Also, the sub-threshold slope is improved by 50%. On the contrary, the threshold voltage is lower by 8% for BC structure due to closer proximity of contacts to the dielectric interface.

Nuclear dynamical deformation induced hetero- and euchromatin positioning.

We studied the role of active deformation dynamics in cell nuclei in chromatin positioning. Model chains containing two types of regions, with high (euchromatic) or low (heterochromatic) mobility, were confined in a pulsating container simulating a nucleus showing dynamic deformations. Brownian dynamic simulations show that the positioning of low mobility regions changes from sites near the periphery to the center if the affinity between these regions and the container periphery disappears. The former and latter positionings are similar to the "conventional" and "inverted" chromatin positionings in nuclei of normal differentiated cells and cells lacking Lamin-related proteins. Additionally, nuclear dynamical deformation played essential roles in "inverted" chromatin positioning.

Mapping of performance limiting issues to analyze top and bottom contact organic thin film transistors

This research paper acutely analyzes an assortment of issues to model the behaviour of top contact (TC) and bottom contact (BC) organic thin film transistors (OTFTs) using organic module of Atlas numerical device simulator. Additionally, device performance parameters, such as current $$(I_{D})$$(ID), mobility $$(\mu )$$(μ), threshold voltage $$(V_{T})$$(VT) and sub-threshold slope (SS) are analyzed. Moreover, the contact behaviour is investigated from device physics point of view. Different simulation strategies are incorporated for mapping of various performance issues in analyzing practical TC and BC OTFTs. The complete analysis comprises of five different approaches for both TC and BC structures: (1) material parameters along with Poole---Frankle mobility model, (2) defects in bulk OSC, (3) dipoles at OSC-dielectric interface, (4) correction for leakage current and (5) elimination of contacts voltage drop. After applying these calibration standards, the TC device reasonably matched to the reported results, whereas; some additional issues like unfilled corners and low mobility regions near the source/drain contacts are further accounted to validate the response of BC structure. Additionally, both structures are analyzed at different contact thickness $$(t_{S/D})$$(tS/D). Consequently, on increasing $$t_{S/D}$$tS/D from infinitesimal to 50 nm, the BC parameters are improved by 57, 46, 17, 28 and 23 % in terms of $$I_{D}, \mu , V_{T}$$ID,μ,VT, SS and $$R_{S}$$RS, respectively due to injection of sufficient charge carriers. However, very small change is obtained for TC structure. This study simplifies number of issues associated to design and fabrication of organic material based devices and circuits.

Fluctuating mobility generation and transport in glasses

In the context of the random first order transition theory we use an extended mode coupling theory of the glass transition that includes activated events to account for spatiotemporal structures in rejuvenating glasses. We numerically solve fluctuating dynamical equations for mobility and fictive temperature fields which capture both mobility generation through activated events and facilitation effects. Upon rejuvenating, a source of high mobility at a glass surface initiates a growth front of mobility which propagates into the unstable low mobility region. The speed of the front quantitatively agrees with experiments on the rejuvenation of ultrastable glasses, which "melt" from their surface.

Freeze Core Sampling to Validate Time‐Lapse Resistivity Monitoring of the Hyporheic Zone

A freeze core sampler was used to characterize hyporheic zone storage during a stream tracer test. The pore water from the frozen core showed tracer lingered in the hyporheic zone after the tracer had returned to background concentration in collocated well samples. These results confirmed evidence of lingering subsurface tracer seen in time-lapse electrical resistivity tomographs. The pore water exhibited brine exclusion (ion concentrations in ice lower than source water) in a sediment matrix, despite the fast freezing time. Although freeze core sampling provided qualitative evidence of lingering tracer, it proved difficult to quantify tracer concentration because the amount of brine exclusion during freezing could not be accurately determined. Nonetheless, the additional evidence for lingering tracer supports using time-lapse resistivity to detect regions of low fluid mobility within the hyporheic zone that can act as chemically reactive zones of importance in stream health.

Channel length variation effect on performance parameters of organic field effect transistors

This research paper analyzes, finite element based two dimensional device simulations for top and bottom contact organic field effect transistors (OFETs) by considering uniform and non-consistent mobility regions. To model the morphological disorder in bottom contact structure, some calibrated standards for simulation is developed viz. by considering variable low mobility regions near the contacts. An analytical model is developed, by considering contact resistance and field dependent mobility. The effect of channel length variation (5–40μm) on performance parameters is highlighted for both the structures. Subsequently, results shows only 1% change in current for bottom contact with 0.5μm and 1μm low mobility region near the contacts, due to dominant contact resistance, whereas, linear dependency is observed for other simulated structures. The top contact device shows 0.43cm2/Vs saturation mobility at 5μm and 13% decrease up to 20μm and afterwards constant behavior is noticed, whereas low mobility is extracted in bottom contact devices and shows 10–20% increase in both the mobilities for increasing channel length from 5 to 40μm. For top and bottom devices, total 65% and 62% decrease in contact resistance is observed for increasing gate voltage from −1.8V to −3V and this percentage reduces for increasing the length of low mobility region. Further, we have evaluated 13%, 40% and 78% increase in the trap density, while proceeding for 0.25μm, 0.5μm and 1μm low mobility region in the bottom contact structure.

Continuous polo-like kinase 1 activity regulates diffusion to maintain centrosome self-organization during mitosis

Whether mitotic structures like the centrosome can self-organize from the regulated mobility of their dynamic protein components remains unclear. Here, we combine fluorescence spectroscopy and chemical genetics to study in living cells the diffusion of polo-like kinase 1 (PLK1), an enzyme critical for centrosome maturation at the onset of mitosis. The cytoplasmic diffusion of a functional EGFP-PLK1 fusion correlates inversely with known changes in its enzymatic activity during the cell cycle. Specific EGFP-PLK1 inhibition using chemical genetics enhances mobility, as do point mutations inactivating the polo-box or kinase domains responsible for substrate recognition and catalysis. Spatial mapping of EGFP-PLK1 diffusion across living cells, using raster image correlation spectroscopy and line scanning, detects regions of low mobility in centrosomes. These regions exhibit characteristics of increased transient recursive EGFP-PLK1 binding, distinct from the diffusion of stable EGFP-PLK1-containing complexes in the cytoplasm. Chemical genetic suppression of mitotic EGFP-PLK1 activity, even after centrosome maturation, causes defects in centrosome structure, which recover when activity is restored. Our findings imply that continuous PLK1 activity during mitosis maintains centrosome self-organization by a mechanism dependent on its reaction and diffusion, suggesting a model for the formation of stable mitotic structures using dynamic protein kinases.

Doping Level Dependence of Transport Properties in InAsSb Quantum Wells

We investigated the transport properties of the Al0.1In0.9Sb/InAs0.1Sb0.9 quantum wells (QWs). Intentional doping of donors to the QW is effective to decrease the sheet resistance and suppress its temperature dependence because the carrier density is maintained to be relatively high in low temperature. Additionally, although there exists a low mobility region near the heterointerface of the QW and a high mobility region far from the interface in this system, the doped electrons contribute to keep high mobility in low temperature because the increase of electrons prevents the accumulation of all electrons in the low mobility region.

Electrical conduction in cubic GaN films grown on GaAs(001) by RF‐MBE

AbstractThe electrical conduction property of c‐GaN films grown on GaAs(001) by RF‐MBE has been studied in relation with the amount of the hexagonal phase inclusion, or cubic phase purity. In a high‐phase‐purity (93%) film, the electron concentration and mobility at 300 K are typically 8×1017 cm–3 and 110 cm2/V‐s, respectively. It is known that a parallel conduction is occurring in which the high mobility region somewhat away from the hetero‐interface dominates the conduction at higher currents. In a lower‐phase‐purity (75%) film, it is indicated that the low mobility region extends over the larger region of the film. Above the cubic phase purity of about 90%, the electron concentration rapidly decreases and the mobility rapidly increases by one or two orders of magnitudes, suggesting that the stacking faults are the major source of the carrier electrons and causing the scattering centers responsible for the low mobility region. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The effects of wheat sourdough on glutenin patterns, dough rheology and bread properties

Sourdough was prepared with cellular suspension containing 109 cfu of each strain mL−1 and incubated at 28 °C for 24 h and at 37 °C for 4 h. Two different sourdough levels (20 and 40%) were used in bread dough preparation. The bread doughs were proofed at 30 °C and 85% relative humidity for 60/120/180 min. When glutenin changes that occurred in samples 17, 18, 19, and 20 (40% SD 28) are compared with those that appeared in controls, it is obvious that, the relative intensities of some of the protein bands slightly decreased and a few fainter protein bands appeared (which did not exist in controls). A few fainter protein bands corresponding to the MM ≈ 25 kDa (high-mobility region) and the MM ≈ 66 kDa (low-mobility region) were appeared in the same samples. In the samples prepared with 20% sourdoughs incubated at 28 or 37 °C, the bands were still evident after 180 min of proof. This can be explained that glutenin fractions were not hydrolysed in these applications due to the delay in pH drop. The use of 40% sourdough incubated at 28 °C for 24 h resulted in sticky doughs and breads with lower volume, harder texture, unsatisfactory crumb grain and unpleasant flavour than the rest of the samples. The use of sourdoughs incubated at 37 °C for 4 h caused positive effect on loaf volumes, specific loaf volumes and crumb structure.

Spectral Response and Effective Viscoelastic Properties of Mwnt-Reinforced Polycarbonate

The impact of embedded carbon nanotubes on the effective viscoelastic response of a nanotube-reinforced polycarbonate system is characterized by studying the temperature- and frequency-dependent behaviour of the material. Macroscale experimental results demonstrate that the effective relaxation spectra of the samples is consistent with non-bulk polymer regions of restricted molecular mobility. Such low mobility regions are attributed to localized nanoscale interactions between the nanotubes and individual polymer chains.

Supramolecular aspects of polymer science: a challenge for solid state NMR

AbstractRecent developments in structural elucidation of supramolecular systems by advanced solid state NMR are described. Special emphasis is placed on hydrogen‐bonded sytems and columnar stacks of aromatic moieties. In imidazole‐based proton conductores spatially separated regions of high and low mobility are identified. In stacks of alkyl‐substituted hexabenzocoronenes maximum charge carrier mobility is observed for crystal‐like stacking of the discs.

Experimental study of the immiscible displacement of shear-thinning fluids in pore networks

The pore scale mechanisms and network scale transient pattern of the immiscible displacement of a shear-thinning nonwetting oil phase (NWP) by a Newtonian wetting aqueous phase (WP) are investigated. Visualization imbibition experiments are performed on transparent glass-etched pore networks at a constant unfavorable viscosity ratio and varying values of the capillary number ( Ca), and equilibrium contact angle ( θ e ). Dispersions of ozokerite in paraffin oil are used as the shear-thinning NWP, and aqueous solutions of PEG colored with methylene blue are used as the Newtonian WP. At high Ca values, the tip splitting and lateral spreading of WP viscous fingers are suppressed; at intermediate Ca values, the primary viscous fingers expand laterally with the growth of smaller capillary fingers; at low Ca values, network spanning clusters of capillary fingers separated by hydraulically conductive noninvaded zones of NWP arise. The spatial distribution of the mobility of shear-thinning NWP over the pore network is very broad. Pore network regions of low NWP mobility are invaded through a precursor advancement/swelling mechanism even at relatively high Ca and θ e values; this mechanism leads to irregular interfacial configurations and retention of a substantial amount of NWP along pore walls; it becomes the dominant mechanism in displacements performed at low Ca and θ e values. The residual NWP saturation increases and the end WP relative permeability decreases as Ca increases and both become more sensitive to this parameter as the shear-thinning behavior strengthens. The shear-thinning NWP is primarily entrapped in individual pores of the network rather than in clusters of pores bypassed by the WP. At relatively high flow rates, the amplitude of the variations of pressure drop, caused by fluid redistribution in the pore network, increase with shear-thinning strengthening, whereas at low flow rates, the motion of stable and unstable menisci in pores is reflected in strong pressure drop fluctuations.