Reverse Regime Research Articles

Microscopic Theory of Two-Step Yielding in Attractive Colloids.

Attractive colloids display two distinct amorphous solid phases: the attractive glass due to particle bonding and the repulsive glass due to the hard-core repulsion. By means of a microscopic mean field approach, we analyze their response to a quasistatic shear strain. We find that the presence of two distinct interaction length scales may result in a sharp two-step yielding process, which can be associated with a hysteretic stress response or with a reversible but nonmonotonic stress-strain curve. We derive a generic phase diagram characterized by two distinct yielding lines, an inverse yielding and a critical point separating the hysteretic and reversible regimes. Our results should be applicable to a large class of glassy materials characterized by two distinct interaction length scales.

Direct measurement of microscale flow structures induced by inertial focusing of single particle and particle trains in a confined microchannel

Understanding the flow structures induced by inertial focusing of particles is essential in microfluidics-based applications. In spite of numerous studies described in the literature, such microscale flows have, until today, not been subject to quantitative experimental study. This paper describes the construction and validation of a micro-particle image velocimetry-based experimental setup to investigate particle-induced flows in a confined microchannel. The flow structures around a single inertially focused particle are first visualized and quantitatively measured at Reynolds numbers Re from 21 to 525. A ring-like vortex flow is observed to form in front of the particle at Re = 63 owing to an increased particle lag effect, and finally the reverse flow regime is replaced by a vortex flow regime (at Re ≥ 105). This vortex flow produces a strong wall repulsive force and pushes the equilibrium position of the particle toward the channel center. Then, flows induced by both in-line and staggered particle trains are investigated (for 21 ≤ Re ≤ 105). For in-line particle trains, single-vortex flows are present between two neighboring particles on both sides of the channel. For staggered particle trains, two vortices rather than one are present between two neighboring particles at small Re (Re = 21), but this double-vortex flow develops into a single-vortex flow at relatively high Re (Re = 105). The present investigation helps in understanding particle dynamics and the mechanisms of interaction among particles, fluid, and channel walls. The experimental results presented here also provide validation data for further numerical and analytical studies.

In-situ stress distribution and its influence on the coal reservoir permeability in the Hancheng area, eastern margin of the Ordos Basin, China

During the coalbed methane (CBM) exploration and development, in-situ stress and permeability are two vital reservoir evaluation parameters. In this work, with the injection/falloff well test and in-situ stress data of 11 CBM wells in the Hancheng area, eastern margin of the Ordos Basin, China, the distribution of in-situ stress and its influence on the coal reservoir permeability were investigated. Results show that the maximum (SH, 10.80–53.84 MPa) and minimum horizontal (Sh, 9.96–31.88 MPa), and vertical principal stresses (Sv, 14.37–36.46 MPa) increase with the increasing burial depth. However, the coal reservoir permeability (0.01–0.54 mD) shows a decreasing tendency accompanied by increasing stresses. Three stress fields (I, II, and III) between 532.28 and 1350.55 m could be divided: I is in a compression zone (〈700 m, SH〉Sh ≈ Sv, reverse or strike-slip stress regimes); II is in a tension zone (700–850 m, Sv > SH > Sh, normal stress regime); III is in a compression zone again (>850 m, SH > Sv > Sh, strike-slip stress regime). The top-down in-situ stress regimes result in a “decreasing - increasing - decreasing” permeability variation. Meanwhile, the lateral stress coefficient, stress ratios decreased slowly while the reservoir pressures and temperatures show a positive correlation with increasing burial depth.

Regime shifts caused by adaptive dynamics in prey–predator models and their relationship with intraspecific competition

The paper concerns with regime shifts between multiple attractors in ecological predator–prey models and hysteresis phenomena caused by evolution. We present a survey of eco-evolutionary models with an adaptive trait affecting the prey defence or activity that influence predator functional response and give overview of typical consequences of the trait evolution to the predator–prey dynamics together with important references to related adaptive dynamics research. The selection and mutation process is modelled by a resident-mutant model (possible mutant invasion into a monomorphic resident population). Model derivations are given in detail for all of the common functional responses (Holling’s type I, II, III and generalized). Different types of adaptive trait value dependences with respect to transient dynamics are distinguished according to the effect to the eco-system: we prove that if the prey adaptive trait evolution influence only the functional response of the predator, stable dynamics and irreversible abrupt regime changes are typical, whereas reversible regime shifts or more complex dynamics caused by adaptivity of the prey trait occur for trait adaptations that bring an advantage against predator together with intraspecific competition asymmetry. We confirm possibility of hysteresis eco-evolutionary cycle, persistent oscillations between different attractors of the ecological subsystem driven by adaptive trait dynamics.

In situ stress field in the FZ Block of Qinshui Basin,China: Implications for the permeability and coalbed methane production

In situ stress affects reservoir permeability and stimulation, and thus coalbed methane (CBM) recovery. In this study, the in situ stress field measured from 238 CBM wells in the FZ Block of Qinshui Basin, China, was investigated. The vertical stress, horizontal maximum and minimum principal stress are 5.92–20.08 MPa, 8.03–41.75 MPa, and 5.38–21.24 MPa, respectively. The in situ stress magnitudes increase with burial depth of the coal seams. The FZ Block is dominated by reverse and strike-slip faulting stress regimes. Most of reverse fault stress regimes appear within burial depth less than 500 m, whereas normal and strike faulting stress regimes are deeper than 500 m. The relation between the coefficient of lateral stress and burial depth shows that shallow strata are characterized by horizontal stresses, whereas deep strata are generally hydrostatic pressures that approximately equal to the principal stresses. Low gas and high water production are associated with vertical hydraulic fractures, wherein the horizontal minimum principal stress is the minimum stress. High gas and low water production are associated with horizontal hydraulic fractures, wherein the vertical stress is the minimum stress. This results are attributed to the enhanced permeability of the coal seam and the communication with overlying or underlying aquifers because the minimum stress varies between vertical and horizontal minimum stress. The orientation of the horizontal maximum principal stress is ∼NEE–NE and is locally distorted by faults, which can be used to optimize the drilling, completion, and stimulation of CBM wells in the study area.

3D Current Collectors for Lithium‐Ion Batteries: A Topical Review

AbstractCurrent collectors play important roles in enhancing the electrochemical performance of lithium‐ion batteries. Currently used collectors are mostly made of aluminum or copper foils through slurry casting with binders that have not reached optimal capacity. Furthermore, extended cycles of charge and discharge induce detachment of the cast layer, resulting in damage to the structural integrity. In order to better understand the principles of the performance of and thus optimize current collectors, a critical review is conducted focusing on their structures. Through analysis of data collected from more than 50 publications, the capacity and retention as a function of current density and charge cycle, respectively, are identified. Two new terms, which are characteristic of 3D current collectors, are defined as Regime I and Regime II in the corresponding plots. Regime I refers to the maximum reversible capacity and Regime II to the maximum capacitor retention. The greater the values of those values, the greater the enhancement of capacity and retention. Using these concepts, it is predicted that carbonaceous and fibrous 3D hierarchical current collectors would be beneficial as battery collectors. The results and approach provide perspective for future design and advancement of electrochemical energy‐storage devices.

Dynamics of phenotypic switching of bacterial cells with temporal fluctuations in pressure

Phenotypic switching is one of the mechanisms by which bacteria thrive in ever changing environmental conditions around them. Earlier studies have shown that the application of steady high hydrostatic pressure leads to stochastic switching of mesophilic bacteria from a cellular phenotype having a normal cell cycle to another phenotype lacking cell division. Here, we have studied the dynamics of this phenotypic switching with fluctuating periodic pressure using a set of experiments and a theoretical model. Our results suggest that the phenotypic switching rate from high-pressure phenotype to low-pressure phenotype in the reversible regime is larger as compared to the switching rate from low-pressure phenotype to high-pressure phenotype. Furthermore, we find that even though the cell division and elongation are presumably regulated by a large number of genes the underlying physics of the dynamics of stochastic switching at high pressure is captured reasonably well by a simple two-state model.

Efficient sampling of reversible cross-linking polymers: Self-assembly of single-chain polymeric nanoparticles.

We present a new simulation technique to study systems of polymers functionalized by reactive sites that bind/unbind forming reversible linkages. Functionalized polymers feature self-assembly and responsive properties that are unmatched by the systems lacking selective interactions. The scales at which the functional properties of these materials emerge are difficult to model, especially in the reversible regime where such properties result from many binding/unbinding events. This difficulty is related to large entropic barriers associated with the formation of intra-molecular loops. In this work, we present a simulation scheme that sidesteps configurational costs by dedicated Monte Carlo moves capable of binding/unbinding reactive sites in a single step. Cross-linking reactions are implemented by trial moves that reconstruct chain sections attempting, at the same time, a dimerization reaction between pairs of reactive sites. The model is parametrized by the reaction equilibrium constant of the reactive species free in solution. This quantity can be obtained by means of experiments or atomistic/quantum simulations. We use the proposed methodology to study the self-assembly of single-chain polymeric nanoparticles, starting from flexible precursors carrying regularly or randomly distributed reactive sites. We focus on understanding differences in the morphology of chain nanoparticles when linkages are reversible as compared to the well-studied case of irreversible reactions. Intriguingly, we find that the size of regularly functionalized chains, in good solvent conditions, is non-monotonous as a function of the degree of functionalization. We clarify how this result follows from excluded volume interactions and is peculiar of reversible linkages and regular functionalizations.

Carbon dioxide dissociation in a microwave plasma reactor operating in a wide pressure range and different gas inlet configurations

Microwave (MW) plasmas represent a promising solution for efficient CO2 dissociation. MW discharges are also very versatile and can be sustained at various pressure and gas flow regimes. To identify the most favorable conditions for the further scale-up of the CO2 decomposition reaction, a MW plasma reactor operating in pure CO2 in a wide pressure range (200 mbar–1 bar) is studied. Three different gas flow configurations are explored: a direct, reverse and a vortex regime. The CO2 conversion and energy efficiency drop almost linearly with increasing pressure, regardless of the gas flow regime. The results obtained in the direct flow configuration underline the importance of post-discharge cooling, as the exhaust of the MW plasma reactor in this regime expanded into the vacuum chamber without additional quenching. As a result, this system yields exhaust temperatures of up to 1000 K, which explains the lowest conversion (∼3.5% at 200 mbar and 2% at 1 bar). A post-discharge cooling step is introduced for the reverse gas inlet regime and allows the highest conversion to be achieved (∼38% at 200 mbar and 6.2% at 1 bar, with energy efficiencies of 23% and 3.7%). Finally, a tangential gas inlet is utilized in the vortex configuration to generate a swirl flow pattern. This results in the generation of a stable discharge in a broader range of CO2 flows (15–30 SLM) and the highest energy efficiencies obtained in this study (∼25% at 300 mbar and ∼13% at 1 bar, at conversions of 21% and 12%). The experimental results are complemented with computational fluid dynamics simulations and with the analysis of the latest literature to identify the further research directions.

Applying Petroleum the Pressure Buildup Well Test Procedure on Thermal Response Test—A Novel Method for Analyzing Temperature Recovery Period

The theory of Thermal Response Testing (TRT) is a well-known part of the sizing process of the geothermal exchange system. Multiple parameters influence the accuracy of effective ground thermal conductivity measurement; like testing time, variable power, climate interferences, groundwater effect, etc. To improve the accuracy of the TRT, we introduced a procedure to additionally analyze falloff temperature decline after the power test. The method is based on a premise of analogy between TRT and petroleum well testing, since the origin of both procedures lies in the diffusivity equation with solutions for heat conduction or pressure analysis during radial flow. Applying pressure build-up test interpretation techniques to borehole heat exchanger testing, greater accuracy could be achieved since ground conductivity could be obtained from this period. Analysis was conducted on a coaxial exchanger with five different power steps, and with both direct and reverse flow regimes. Each test was set with 96 h of classical TRT, followed by 96 h of temperature decline, making for almost 2000 h of cumulative borehole testing. Results showed that the ground conductivity value could vary by as much as 25%, depending on test time, seasonal period and power fluctuations, while the thermal conductivity obtained from the falloff period provided more stable values, with only a 10% value variation.

Paleointensity Behavior and Intervals Between Geomagnetic Reversals in the Last 167 Ma

The results of comparative analysis of the behavior of paleointensity and polarity (intervals between reversals) of the geomagnetic field for the last 167 Ma are presented. Similarities and differences in the behavior of these characteristics of the geomagnetic field are discussed. It is shown that bursts of paleointensity and long intervals between reversals occurred at high mean values of paleointensity in the Cretaceous and Paleogene. However, there are differences between the paleointensity behavior and the reversal regime: (1) the characteristic times of paleointensity variations are less than the characteristic times of the frequency of geomagnetic reversals, (2) the achievement of maximum values of paleointensity at the Cretaceous–Paleogene boundary and the termination of paleointensity bursts after the boundary of 45–40 Ma are not marked by explicit features in the geomagnetic polarity behavior.

Microscopic reversal magnetization mechanisms in CoCrPt thin films with perpendicular magnetic anisotropy: Fractal structure versus labyrinth stripe domains

The magnetization reversal of CoCrPt thin films has been examined as a function of thickness using magneto-optical Kerr effect (MOKE) microscopy and first-order reversal curves (FORC) techniques. MOKE images show differentiated magnetization reversal regimes for different film thicknesses: while the magnetic domains in 10-nm-thick CoCrPt film resemble a fractal structure, a labyrinth stripe domain configuration is observed for 20-nm-thick films. Although FORC distributions for both cases show two main features related to irreversible processes (propagation and annihilation fields) separated by a mostly flat region, this method can nonetheless distinguish which magnetization reversal process is active according to the horizontal profile of the first FORC peak, or propagation field. A single-peak FORC profile corresponds to the fractal magnetization reversal, whereas a flat-peak FORC profile corresponds to the labyrinth magnetization reversal.

Flexible electrically resistive-type strain sensors based on reduced graphene oxide-decorated electrospun polymer fibrous mats for human motion monitoring

In this work, a novel flexible electrically resistive-type strain sensor with special three-dimensional conductive network was developed based on reduced graphene oxide (RGO)-decorated flexible thermoplastic polyurethane (TPU) electrospun fibrous mats. Scanning electron microscopy results indicated that RGO was localized on surfaces of the TPU fibers uniformly and formed conductive paths. The interaction between electrospun TPU fibers and RGO was investigated by using Fourier transform infrared spectra and X-ray diffraction. These fibers conductive paths connected with each other and constructed an excellent three-dimensional conductive network. The special hierarchical conductive network endowed our RGO/TPU strain sensors with a desirable integration of good stretchability and high sensitivity (gage factor (GF) of 11 in strain of 10% and 79 in strain of 100% in reversible strain regime), good durability and stability (stretch/release test of 6000 cycles) and a fast response speed. The mechanism of the evolution of residual resistance and residual strain of RGO/TPU strain sensors under cyclic loading were investigated in detail. RGO/TPU strain sensors were attached on skin or clothes to monitor various human motions. The results demonstrate that our flexible strain sensors have wide application prospects in smart wearable device.

Toward Reversible, High Li-Content Insertion into Composite Electrode Enabled By ALD Solid Electrolyte– Revealing the Mechanisms for Superior Performance

To meet the demand for higher capacity, longer life batteries in a “next-generation batteries” technology, advanced electrodes with substantially higher energy density than current electrodes are needed. We have demonstrated the development of ALD solid electrolyte (LiPON) and the benefits of applying a controlled thin ALD layer and solid electrolyte (LiPON) as protective layers for Li and Na anodes as well as on precision-nanostructured conversion materials. [Ref:1-3] Here in this work, we demonstrate a turn to composite electrodes formed from micro/nano size particles typical of today’s battery electrodes. We use atomic layer deposition (ALD) to create highly controlled, thin protective layers on composite FeOF conversion electrodes, testing their efficacy by cycling in batteries. ALD protection layers, the solid-electrolyte LiPON (lithium-phosphous oxynitride), were directly deposited on the electrodes in controlled inert ambient conditions. The porous structure of composite materials allows vapor-phase ALD techniques to penetrate into electrodes to form effective protection layer. We observed that the ALD protected composite conversion electrode exhibits superior cyclability (capacity retention) and high energy (round-trip) efficiency, with decreased overpotentials. Detailed investigation was further performed to understand the mechanisms of superior reversibility for ALD protected composite electrodes, and surprisingly, based on solid-state NMR electron energy loss spectroscopy (EELS) and electrochemical data, we observed that the ALD protection layer allows extra Li insertion to form an extended insertion-like phase for Li storage, which largely increases the capacity for highly reversible insertion regime before it turns into conversion phase transformation. This observation provides a new insight on protection layer altering the phase diagram during Li insertion, and provides technological impact on utilizing high capacity conversion electrode. This interfacial engineering approach can be applied to many commercial electrode systems (e.g. LTO, LMO, V2O5…., etc.) to show beneficial effects to the battery performance that we will briefly discuss in this talk. Ref: A. C. Kozen, C.-F. Lin, A. J. Pearse, M. A. Schroeder, X. Han, L. Hu, S. B. Lee, G. W. Rubloff, and M. Noked, “Next-Generation Lithium Metal Anode Engineering via Atomic Layer Deposition,” ACS Nano , vol. 9, no. 6, pp. 5884–5892, Jun. 2015. DOI: 10.1021/acsnano.5b02166.W. Luo, C-F Lin, O. Zhao, M. Noked, Y. Zhang, G.W. Rubloff, L. Hu, “Ultrathin Surface Coating Enables Stable Sodium Metal Anode”, Adv. Energy Mater .C-F Lin, M. Noked, A.C. Kozen, C. Liu, O. Zhao, K. Gregorczyk, L. Hu, S.B. Lee, G.W. Rubloff, “Solid Electrolyte Lithium Phosphorous Oxynitride as a Protective Nanocladding Layer for 3D High-Capacity Conversion Electrodes”, ACS Nano , vol. 10, no. 2, pp 2693-2701 (2016). DOI:10.1021/acsnano.5b07757

Organic doped/undoped interface based diode structure: Distinct mechanisms underlying forward and reverse bias

Abstract Organic semiconductor diodes fabricated using doped/undoped (high-low) homojunction has the potential of providing controlled and high quality current density-voltage (J-V) characteristics based on majority carrier transport. We study mechanisms of transport underlying such characteristics both in forward and reverse bias regimes of typical doped/undoped homojunction organic diodes fabricated using 4,4′,4″-tris( N -3-methylphenyl- N -phenyl-amino) triphenylamine ( m -MTDATA). We study the J-V characteristics over a wide temperature range (200–300 K), and by varying the intrinsic layer thickness between 10 and 100 nm. The forward bias current, before entering into the space charge limited regime, is exponential over several orders of magnitude with the slope being temperature independent for all intrinsic layer thickness down to 10 nm. The reverse bias characteristics, on the other hand, are highly sensitive to the thickness of the intrinsic layer. While the forward bias is controlled by tunneling at the homojunction interface, the reverse bias is controlled by the interface of cathode (aluminum in this case) and the intrinsic layer. We show that the reverse current is due to Fowler-Nordheim tunneling across a barrier height, which is temperature independent but is sensitive to the layer thickness of the intrinsic layer. The origin of the thickness dependence of barrier height (0.45–0.72 eV for 10–20 nm) is attributed to the change in background carrier concentration in the intrinsic layer due to diffusion of carriers from the highly doped side. The results clearly show that the diffusion length of the majority carriers is approximately 1 nm and is comparable to the nearest neighbor jump distance.

Effects of different stress regimes on hydraulic fracture geometry: a particle flow code approach

Hydraulic fracturing decisions are closely tied to quantitative description of rock mechanical properties and in situ stresses in the subsurface. Geomechanics plays a critical role in successfully optimizing hydraulic fracturing, especially in different stress regimes. For those stress regimes that are not normal, the hydraulic fracture geometry is usually more complex and more difficult to predict and investigate. In this study, a particle flow code (PFC) has been developed to investigate and compare the hydraulic fracture geometry in different stress regimes. The results have demonstrated that hydraulic fracture geometry is closely tied to in situ stress conditions, whereas any change in a predominant stress regime from normal to reverse affects the hydraulic fracture geometry. Based on the developed PFC3D model, in a given fracturing pressure, the width and height of the induced hydraulic fracture in a normal stress regime is higher than a reverse stress regime, while the length of the hydraulic fracture in a reverse stress regime is greater than the normal stress regime. The results from this study can be applied in both planning and real-time decisions during hydraulic fracturing jobs to optimize the operation and prevent any job failure which will in turn affect the ultimate productivity.

Understanding the degradation processes of GaN based LEDs submitted to extremely high current density

This work presents the first analysis of the degradation mechanisms induced by extremely high current densities on green InGaN-based LEDs. To this aim, bare-chip LEDs were submitted to current step-stress, until catastrophic failure. We identified a current density threshold, around 260A/cm2, beyond which the devices start degrading, showing an increase in leakage current both in reverse and forward bias regimes. Moreover, a current crowding effect was detected on the degraded samples by electroluminescence measurements. A lumped element model was developed to describe the effects of stress. Results suggest that localized power dissipation, due to high current density flow under the anode pad, induces the formation of shunt paths and, eventually, leads to the catastrophic failure of the LEDs.

Mössbauer forward scattering in the regime of RF hyperfine field reversals (FeBO3): Temperature dependence of the spectra

A model of frequency and time-domain Mossbauer forward scattering (FS) spectra on a magnetic target in the regime of RF hyperfine field reversals is proposed. The model allows us to describe the temperature dependence of RF effects in the FS frequency spectra of FeBO3 measured at temperatures below the Neel point (~348 K). In the proposed model, temporal (with internal mark) Mossbauer FS spectra on a magnetic target are calculated to study the dependence of the structure of these spectra on the target’s optical thickness, the degree of phase correlation of the RF hyperfine field reversals, and the value of the phase of the RF field used as an external parameter.

Pure ultraviolet emission from ZnO quantum dots-based/GaN heterojunction diodes by MgO interlayer

We demonstrate the fabrication and characterization of ZnO/GaN-based heterojunction light-emitting diodes (LEDs) by using air-stable and solution-processable ZnO quantum dots (QDs) with a thin MgO interlayer acting as an electron blocking layer (EBL). The ZnO QDs/MgO/p-GaN heterojunction can only display electroluminescence (EL) characteristic in reverse bias regime. Under sufficient reverse bias, a fairly pure ultraviolet EL emission located at 370 nm deriving from near band edge of ZnO with a full width at half maximum (FWHM) of 8.3 nm had been obtained, while the deep-level emission had been almost totally suppressed. The EL origination and corresponding carrier transport mechanisms were investigated qualitatively in terms of photoluminescence (PL) results and energy band diagram. Open image in new window

Regional tectonic state and poro-thermo-elasticity analysis of near wellbore zone in field development plan: Utilization of an uncoupled approach

The main aim of this work is to investigate the effects of temperature and pore pressure on stability of wellbore wall, considering the wellbore spatial orientation and regional tectonic state of the field in which the well is drilled. An uncoupled approach was proposed in this research study. Although the combination of fluid and temperature diffusion can be intensely alter the pore pressure and temperature of the near wellbore zone, the uncoupled approach can be considered as a primary, fast and simple method for optimization purposes at the earliest stages of field development when the technical data/information to conduct a coupled simulation is limited. The data used for this study were collected from real, literature and simulation cases. The real data are from geological and geophysical studies of gas reservoirs in Siberia, Russia. The results show that the problem of wellbore breakout (shear failure) happens in the final stages of field development however, the hydraulic fracturing and fluid loss (tensile failure) are the most common problems at the early stages of field development. Increasing wellbore temperature increases the shear failure risk for any wellbore orientation and regional tectonic state however it decreases the risk of tensile failure by increasing the tensile strength of rock. Effect of zenith angle on shear and tensile failure of wellbore depends on the regional fault regime. At the regions with normal fault regime, vertical wellbores are more stable than horizontal and vice-versa for strike-slip cases. For reverse fault regime, there is an optimum wellbore zenith angle where the shear failure is minimum and tensile failure is maximum. The results are further considered not only from drilling point of view but also for hydraulic fracturing job and hot fluid injection in field production life. Real well data from gas condensate reservoir in normal fault regime was provided for comparison and model validation purposes, showing a good agreement.