Steady-state Density Research Articles

Long-Range Coherence and Multiple Steady States in a Lossy Qubit Array.

We show that a simple experimental setting of a locally pumped and lossy array of two-level quantum systems can stabilize states with strong long-range coherence. Indeed, by explicit analytic construction, we show there is an extensive set of steady-state density operators, from minimally to maximally entangled, despite this being an interacting open many-body problem. Such nonequilibrium steady states arise from a hidden symmetry that stabilizes Bell pairs over arbitrarily long distances, with unique experimental signatures. We demonstrate a protocol by which one can selectively prepare these states using dissipation. Our findings are accessible in present-day experiments.

Ion-Enhanced Conversion of CO2 to Formate on Porous Dendrite Bismuth Electrodes with High Efficiency and Durability

Facile synthesis of efficient electrocatalysts that can selectively convert CO2 into value-added chemicals remains a challenge. This study presents the electrochemical synthesis of porous Bi dendrite electrodes and details on their activity toward CO2 conversion to formate in aqueous bicarbonate solutions. The as-synthesized multi-layered porous dendrite Bi electrodes exhibit the faradaic efficiency (FE) of ~100% of formate production. The added halides and cations significantly influence the steady-state partial current density for formate production (J FM) (Cl- > Br- ~ I-; Cs+ > K+ > Li+). Density functional theory calculations have revealed that the reaction pathway involving the species *OCOH occurs predominantly, while co-existence of Cs+ and Cl- changes the overall reactions more spontaneously. A photovoltaic cell-assisted electrocatalysis produces formate with FEs of ~95% (J FM ~10 mA cm-2) at an overall solar conversion efficiency of ~8.5%. The Bi electrodes maintain their activity over 360 h without a change in the surface states. Figure 1

Amperometric Monitoring of Glucose Level for Non-Invasive Cell-Based Assays Based on Glucose Dehydrogenase-Modified SWCNT

INTRODUCTION Glucose sensing is widely used as one of the evaluation methods for cellular activities and functions, since glucose plays an important role in principal source of biological energy. A cellular glucose uptake rate is frequently determined from culture media collected at specific times by conventional analytical instruments. However, due to the low time resolution, dynamic cellular responses are not evaluated in detail. Meanwhile, most of glucose sensors in the conventional analytical instruments often utilize glucose oxidase (GOx) as a biological recognition element for the analysis of glucose. From the amount of H2O2 generated via the GOx-catalyzed oxidation of glucose by oxygen, glucose concentration is indirectly determined. However, even if such GOx-based glucose sensor was used for cell culture systems, the accurate concentration of glucose would not be determined due to the cellular oxygen consumption based on respiratory metabolism. Additionally, H2O2 is well-known to induce apoptotic or necrotic cell death. In the present work, we prepared an oxygen-independent glucose dehydrogenase (GDH)-modified single-walled carbon nanotube (SWCNT) electrode, at the surface of which a cellulose dialysis membrane was modified to improve the stability of the electrochemical signal, and demonstrated its performance of direct glucose monitoring in the cell culture system. EXPERIMENTAL An electrode for monitoring of glucose levels based on GDH-adsorbed SWCNTs (GDH/SWCNT electrode) was prepared as follows. SWCNT dispersion was cast onto the surface of a glassy carbon electrode. After physically adsorption of 1,4-naphthoquinone (NQ), which promotes direct electron transfer between GDH and SWCNT, at the surface of SWCNTs, an aliquot of a mixture of aqueous solution containing GDH and hexamethylenediamine was cast onto the NQ-adsorbed SWCNT electrode surface, subsequently followed by casting of a glutaraldehyde solution to conjugate GDH with NQ-adsorbed SWCNTs rigidly. The obtained electrode surface was covered with Nafion, further followed by covering cellulose dialysis membrane (CDM). Monitoring changes in glucose levels during hepatic glucose metabolism was performed by means of amperometry at +0.4 V vs. Ag|AgCl in a Dulbecco’s Modified Eagle Medium (DMEM)-based culture medium containing 5 mM glucose and 10% fetal bovine serum (FBS). The working electrode was located several handled micrometers from human hepatoma cell line Hep G2. RESULTS AND DISCUSSION We first examined the glucose concentration dependence of the steady-state anodic current densities for GDH/SWCNT electrodes with and without CDM in the phosphate buffered saline (pH 7.4). The responses at the both electrodes linearly increased with increasing glucose concentration up to 30 mM and then leveled off. However, the slope for the GDH/SWCNT electrode with CDM was slightly smaller than that without CDM. This indicates that CDM might restrictsupplying glucose to the GDH/SWCNT surface. We next confirmed the feasibility of the GDH/SWCNT electrode to amperometric monitoring of glucose level for real-time cell-based assays. We examined long-term stability of the GDH/SWCNT electrode in the DMEM-based culture medium containing 5 mM glucose and 10% FBS. In the absence of CDM, the anodic current rapidly decreased less than 40% after 23 h, but in the presence of CDM, the anodic current was observed 70% or larger even after 24 h. We therefore employed the GDH/SWCNT electrode with CDM for a real sample. Figure 1 shows anodic current responses observed at the CDM-covered GDH/SWCNT electrode located near the bottom surface of a culture dish in the presence and absence of Hep G2 cells in the DMEM-based culture medium with and without cisplatin, which is well-known as one of the anti-cancer drugs. In the absence of Hep G2, an anodic current in the presence of cisplatin showed the similar behavior for that in the absence of cisplatin, so that cisplatin unaffected to the current responses. Meanwhile, in the presence of Hep G2 cells without cisplatin, anodic current rapidly decreased because of their glucose metabolism. In contrast, a current response first rapidly, and then, slightly decreased in the presence of both Hep G2 and cisplatin. The former current change rate was the similar case to the presence of Hep G2 cells without cisplatin, indicating cellular glucose metabolism because cisplatin hardly worked soon after its exposure to Hep G2 cells. The latter current change rate was almost the same as that in the absence of Hep G2 cells with cisplatin, indicating the inhibition of their glucose metabolism due to damage of Hep G2 cells by cisplatin. Thus, the CDM-covered GDH/SWCNT electrode would be applicable to non-invasive cell-based safety assays as an index of changes in cellular glucose metabolism. Figure 1

Mott Metal-Insulator Transition from Steady-State Density Functional Theory.

We present a computationally efficient method to obtain the spectral function of bulk systems in the framework of steady-state density functional theory (i-DFT) using an idealized scanning tunneling microscope (STM) setup. We calculate the current through the STM tip and then extract the spectral function from the finite-bias differential conductance. The fictitious noninteracting system of i-DFT features an exchange-correlation (XC) contribution to the bias which guarantees the same current as in the true interacting system. Exact properties of the XC bias are established using Fermi-liquid theory and subsequently implemented to construct approximations for the Hubbard model. We show for two different lattice structures that the Mott metal-insulator transition is captured by i-DFT.

In Vivo Polymerization ("Hard-Wiring") of Bioanodes Enables Rapid Start-Up and Order-of-Magnitude Higher Power Density in a Microbial Battery.

For microbial electrochemical technologies to be successful in the decentralized treatment of wastewater, steady-state power density must be improved and cost must be decreased. Here, we demonstrate in vivo polymerization ("hard-wiring") of a microbial community to a growing layer of conductive polypyrrole on a sponge bioanode of a microbial battery, showing rapid biocatalytic current development (∼10 times higher than a sponge control after 4 h). Moreover, bioanodes with the polymerized inoculant maintain higher steady-state power density (∼2 times greater than the control after 28 days). We then evaluate the same hard-wired bioanodes in both a two-chamber microbial fuel cell and microbial battery with a solid-state NaFeIIFeIII(CN)6 (Prussian Blue) cathode, showing approximately an order-of-magnitude greater volumetric power density with the microbial battery. The result is a rapid start-up, low-cost (no membrane or platinum catalyst), and high volumetric power density system (independent of atmospheric oxygen) for harvesting energy and carbon from dilute organics in wastewater.

The distinct roles of initial transmission and retransmission in the persistence of knowledge in complex networks

The rate of successfully acquiring knowledge depends on whether the individual has previously held that knowledge. In an earlier work, we represented this phenomenon by dividing the dynamical process of knowledge transmission into initial and retransmission stages, and applied mean field theory to identify an approximate condition for knowledge survival on homogeneous networks. In this work we move beyond our earlier, approximate results for homogeneous networks to provide rigorous results applicable to complex networks of arbitrary topology - including heterogeneous real world social networks. Specifically, we extend the Intertwined Continuous Markov Chain (ICMC) and Probabilistic Discrete Markov Chain (PDMC) models to address the Naive-Evangelical-Agnostic-Evangelical (VEAE) knowledge transmission process in complex networks. We identify the corresponding basic reproduction number R0, the quantity which dictates whether or not knowledge survives, and deduce simple upper and lower bounds for this measure. Moreover, simulations are performed to verify both the theoretical results, and the mutual consistency of the ICMC, PDMC and Monte Carlo methods. The simulations demonstrate that the initial transmission process directly affects the initial rate of change of the number of evangelical individuals, but has no effect on evangelical density in the steady state. However, the retransmission process has a direct effect on the steady state density of evangelical individuals.

Filling of smoke due to fire in a room with roof ventilation

Displacement ventilation is one of the ventilation techniques employed in maintaining the interior thermal environment of low-energy buildings. Warm air rising from occupants in a room is removed through a vent in the ceiling, while cool fresh air flows in through the floor level openings. The entire flow is driven by buoyancy forces due to temperature difference of air. In the event of fire in such a room, the smoke from the fire rises to the ceiling and begins filling it from the top, while also draining through the ceiling vent. In this article we investigate filling of smoke due to fire and examine how it is affected by heat loss through walls and ceilings, along with other parameters such as the room's geometry, ceiling vent area, and fire's power. We validate our model using experimental results of Harrak et al., 2019, International Journal of Thermal Sciences. We show that heat loss reduces smoke-layer's steady state depth, and the said depth is unique in the limit of large heat losses. For small aspect-ratio rooms, steady state properties of the smoke-layer can be significantly different for the insulated and conducting wall cases, even for small conductivity in the latter case. We derive formulas for bounds on the smoke-layer's steady state depth and density (and hence temperature), as well as obtain a useful estimate for the time taken for the smoke-layer to reach its steady state depth.

Steady-State Dynamical Response of a Strongly Nonlinear System with Impact and Coulomb Friction Subjected to Gaussian White Noise Excitation

The paper is devoted to the steady-state dynamical response analysis of a strongly nonlinear system with impact and Coulomb friction subjected to Gaussian white noise excitation. The Zhuravlev nonsmooth transformation of the state variables combined with the Dirac delta function is utilized to simplify the original system to one without velocity jump. Then, the steady-state probability density functions of the transformed system are derived in terms of the stochastic averaging method of energy envelope. The effectiveness of the presented analytical procedure is verified by those from the Monte Carlo simulation based on the original system. Effects of different restitution coefficients, amplitudes of friction, and noise intensities on the steady-state dynamical responses are investigated in detail. Results show different intensities of Gaussian white noise can affect the peaks value of the probability density functions, whereas the variations of restitution coefficients and amplitudes of friction can induce the occurrence of stochastic P-bifurcation.

Passive behavior of nickel-based superalloys prepared by high-deposition-rate laser solid forming additive manufacturing

We report the crystallographic texture and passive behavior of nickel-based superalloys prepared by high-deposition-rate laser solid forming (HDR-LSF) additive manufacturing in deaerated 10 wt.% NaNO3. The HDR-LSF Alloy 718, mainly composed of columnar grains, is detected to be weakly fiber textured due to the direction changed structure. However, passive current densities on horizontal and vertical sections have no difference and both increase linearly with the electrode potential. Furthermore, the identical steady-state passive current density on both sections is attributed to the same film/solution interface energy. Amorphous structure of the bi-layer film induces the electrochemical activity isotropy regardless of matrix texture.

Dynamic Analysis of a Tumor-Immune System under Allee Effect

In this paper, we develop a definite tumor-immune model considering Allee effect. The deterministic model is studied qualitatively by mathematical analysis method, including the positivity, boundness, and local stability of the solution. In addition, we explore the effect of random factors on the transition of the tumor-immune system from a stable coexistence equilibrium point to a stable tumor-free equilibrium point. Based on the method of stochastic averaging, we obtain the expressions of the steady-state probability density and the mean first-passage time. And we find that the Allee effect has the greatest impact on the number of cells in the system when the Allee threshold value is within a certain range; the intensity of random factors could affect the likelihood of the system crossing from the coexistence equilibrium to the tumor-free equilibrium.

Diffusion to a cube: A 3D implicit finite difference method

We report the diffusional mass-transport to an isolated cube and numerically determine both the steady-state and the chronoamperometric flux, the latter at both short and long timescales. It is found that across a wide range of timescales the total flux is well approximated (to within 5% error) by the response expected for a sphere of equivalent surface area where the equivalent radius is equal to 1.38 times the half side length of the cube. Under steady-state conditions the size of the equivalent sphere is marginally smaller (equivalent radius 1.34). However, the prime difference between the flux to a cube and a sphere is that in the case of a cube the steady-state flux density across the particle is non-uniform. Towards the cubic particle edges the flux density increases asymptotically. This numerical study was undertaken using a graphics processor unit solving the diffusion equation using a 3D finite difference fully backward implicit scheme. The results are of interest to current-time responses seen in single nanoparticle experiments where non spherical shapes are frequently encountered.

A Bayesian approach to evaluation of soil biogeochemical models

Abstract. To make predictions about the carbon cycling consequences of rising global surface temperatures, Earth system scientists rely on mathematical soil biogeochemical models (SBMs). However, it is not clear which models have better predictive accuracy, and a rigorous quantitative approach for comparing and validating the predictions has yet to be established. In this study, we present a Bayesian approach to SBM comparison that can be incorporated into a statistical model selection framework. We compared the fits of linear and nonlinear SBMs to soil respiration data compiled in a recent meta-analysis of soil warming field experiments. Fit quality was quantified using Bayesian goodness-of-fit metrics, including the widely applicable information criterion (WAIC) and leave-one-out cross validation (LOO). We found that the linear model generally outperformed the nonlinear model at fitting the meta-analysis data set. Both WAIC and LOO computed higher overfitting risk and effective numbers of parameters for the nonlinear model compared to the linear model, conditional on the data set. Goodness of fit for both models generally improved when they were initialized with lower and more realistic steady-state soil organic carbon densities. Still, testing whether linear models offer definitively superior predictive performance over nonlinear models on a global scale will require comparisons with additional site-specific data sets of suitable size and dimensionality. Such comparisons can build upon the approach defined in this study to make more rigorous statistical determinations about model accuracy while leveraging emerging data sets, such as those from long-term ecological research experiments.

FEATURES OF SiO2 REACTIVE-ION ETCHING KINETICS IN CF4 + Ar + O2 AND C4F8 + Ar + O2 GAS MIXTURES

The effect of Ar/O2 mixing ratio on gas-phase characteristics and SiO2 etching kinetics in CF4 + Ar + O2 and C4F8 + Ar + O2 plasmas was studied under conditions of 13.56 MHz inductive RF discharge. The constant processing parameters were fraction of fluorocarbon component in a feed gas (50%) total gas pressure (6 mTorr), input power (700 W) and bias power (200 W). It was found that the full substitution of Ar for O2 in both gas systems results in non-monotonic (with a maximum at ~ 25% Ar + 25% O2) SiO2 etching rates as well as in monotonically increasing photoresist etching rate with higher absolute values for CF4-containing mixture. The steady-state densities of active species were determined using a combination of plasma diagnostics by Langmuir probes and 0-dimensional (global) plasma modeling. Corresponding results indicated that both gas systems are characterized by quite close parameters of electron and ion components while exhibit sufficient differences in the kinetics of neutral species, especially in the presence of O2. The latter produces opposite changes in F atom density as well as in effective probability of ion-assisted chemical reaction vs. Ar/O2 mixing ratio. Relationships between type of fluorocarbon component and heterogeneous process kinetics were analyzed through the set of gas-phase-related parameters (fluxes, flux-to-flux ratios) characterizing chemical etching pathways for SiO2 and formation/destruction balance for the fluorocarbon polymer film. It was suggested that the transition toward O2-rich plasma in the low-polymerizing CF4 + Ar + O2 plasma suppresses the effective probability for SiO2 + F reaction through decreasing efficiency for oxide bond breaking and desorption of etching products due to decreasing ion energy flux. Oppositely, an increase in O2 content in the high-polymerizing C4F8 + Ar + O2 mixture lifts up the effective reaction probability by decreasing fluorocarbon film thickness and providing better access of F atoms to the etched surface.

Grand canonical description of equilibrium and non-equilibrium systems using spin formalism

We consider an open system in contact with a reservoir, where particles as well as energies can be exchanged between them, and present a description of the dynamics in terms of mixed (pseudo)spin and state variables. Specifically, a master equation is constructed out of the exchange rates for particles and for energies, which allows us to probe the system in the grand canonical description. In particular, employing the state resummation analysis, we obtain coupled time evolution equations for the probability distributions of the system as well as the environment. This is exemplified by a standard growth model, where the steady-state density function exhibits power-law behavior with the exponent depending on the microscopic parameters of the rate equations.

Theory of wave-packet transport under narrow gaps and spatial textures: Nonadiabaticity and semiclassicality

We generalise the celebrated semiclassical wavepacket approach from the adiabatic to the non-adiabatic regime. A unified description covering both of these regimes is particularly desired for systems with spatially varying band structures where band gaps of various sizes are simultaneously present, e.g. in moir\'{e} patterns. For a single wavepacket, alternative to the previous derivation by Lagrangian variational approach, we show that the same semiclassical equations of motion can be obtained by introducing a spatial-texture-induced force operator similar to the Ehrenfest theorem. For semiclassically computing the current, the ensemble of wavepackets based on adiabatic dynamics is shown to well correspond to a phase-space fluid for which the fluid's mass and velocity are two distinguishable properties. This distinction is not inherited to the ensemble of wavepackets with the non-adiabatic dynamics. We extend the adiabatic kinetic theory to the non-adiabatic regime by taking into account decoherence, whose joint action with electric field favours certain form of inter-band coherence. The steady-state density matrix as a function of the phase-space variables is then phenomenologically obtained for calculating the transport current. The result, applicable with a finite electric field, expectedly reproduces the known adiabatic limit by taking the electric field to be infinitesimal, and therefore attains a unified description from the adiabatic to the non-adiabatic situations.

Study of VUV Emission From Xe–Ne Microhollow Cathode Discharge in the Self-Pulsing Regime

This article by employing a zero-dimensional model investigates vacuum ultraviolet (VUV) emission from a xenon–neon microdischarge. The effects of the pressure, the input voltage, and the neon fraction are carefully studied. For specific input voltages, the microdischarge operates in an oscillatory regime which is called the self-pulsing regime. The self-pulsing frequency is mainly affected by the input voltage as well as the pressure. Increasing the input voltage enhances the average densities but has no effects on the peak densities. However, the pressure has significant effects on both densities. The main peaks of the VUV emission spectrum are seen at $\lambda =173$ nm and $\lambda =147$ nm which are attributed to xenon triplet-excited dimers and resonance-level excited atoms, respectively. Adding the neon gas enhances the emission at 147 nm through reducing the power loss in elastic collisions, but attenuates the emission at 173 nm. The results also show that steady-state densities of the major VUV emitters in the stationary regime are higher than the time average densities in the self-pulsing regime. Although, the lower power consumption of the self-pulsing regime has a more decisive effect such that the VUV emission efficiency in the self-pulsing regime is greater than that of the stationary regime.

Transport and thermodynamics in quantum junctions: A scattering approach.

We present a scattering approach for the study of the transport and thermodynamics of quantum systems strongly coupled to their thermal environment(s). This formalism recovers the standard non-equilibrium Green's function expressions for quantum transport and reproduces recently obtained results for the quantum thermodynamics of slowly driven systems. Using this approach, new results have been obtained. First, we derived a general explicit expression for the non-equilibrium steady-state density matrix of a system composed of multiple infinite baths coupled through a general interaction. Then, we obtained a general expression for the dissipated power for the driven non-interacting resonant level to the first order in the driving speeds, where both the dot energy level and its couplings are changing, without invoking the wide-band approximation. In addition, we also showed that the symmetric splitting of the system bath interaction, employed for the case of a system coupled to one bath to determine the effective system Hamiltonian [A. Bruch et al., Phys. Rev. B 93, 115318 (2016)], is valid for the multiple bath case as well. Finally, we demonstrated an equivalence of our method to the Landauer-Buttiker formalism and its extension to slowly driven systems developed by Bruch, Lewenkopf, and von Oppen [Phys. Rev. Lett. 120, 107701 (2018)]. To demonstrate the use of this formalism, we analyze the operation of a device in which the dot is driven cyclically between two leads under strong coupling conditions. We also generalize the previously obtained expression for entropy production in such driven processes to the many-bath case.

Plasma Parameters and Silicon Etching Kinetics in C4F8 + O2 + Ar Gas Mixture: Effect of Component Mixing Ratios

In this work, we investigated the possibidlxlity to control both gas-phase chemistry and silicon etching kinetics in C4F8 + O2 + Ar inductively coupled plasma by changes in O2/Ar, C4F8/O2 and C4F8/Ar mixing ratios at the constant fraction of the rest component (50%), gas pressure (10 mTorr), input power (700 W) and bias power (200 W). The combination of plasma diagnostics and modeling tools allowed one: (a) to compare the effects of gas mixing ratios on both steady-state plasma parameters and densities of active species; (b) to figure out key processes which determine the fluorine atom formation/decay balance in each gas system; and (c) to analyze the differences in Si etching kinetics in terms of process-condition-dependent effective reaction probability. It was shown that the maximum changes in gas-phase chemistry take place in O2-rich plasmas due to CFx + O/O(1D) → CFx−1O + F, CFxO + e → CFx−1O + F + e and CFO + O/O(1D) → CO2 + F stepwise dissociation pathways. It was suggested also that the effective probability for Si + xF → SiFx reaction may be controlled by either fluorocarbon film thickness (in C4F8—rich plasmas) or O atom flux (in Ar and O2—rich plasmas) through the balance of adsorption sites on the etched surface.

Stochastic analysis of a nonlinear electromagnetic energy harvesting system with fractional damping under additive and multiplicative stochastic excitation

Electromagnetic energy harvester has been widely concerned in recent years due to its advantages of small size and high sensing frequency. In this paper, the stochastic behaviors of a nonlinear electromagnetic energy harvesting system (NEEH) with fractional damping are investigated under the additive and multiplicative stochastic excitation. Firstly, by applying the stochastic average method to the NEEH system, the mean square of the output current, and the steady-state probability density of vibration amplitude, displacement and velocity are obtained. Meanwhile, the validity of the theoretical results is verified by comparing with the numerical results given by the Monte Carlo method. Secondly, by investigating the theoretical and numerical results, the influences of noise intensity and fractional order on the NEEH system are explored. It is obvious that a higher output voltage can be obtained by the larger intensity of the stochastic excitation, and the smaller coefficient and fractional order of the fractional damping.

Observations of Shoaling Density Current Regime Changes in Internal Wave Interactions

AbstractWe present in situ and remote observations of a Mississippi plume front in the Louisiana Bight. The plume propagated freely across the bight, rather than as a coastal current. The observed cross-front circulation pattern is typical of density currents, as are the small width (≈100 m) of the plume front and the presence of surface frontal convergence. A comparison of observations with stratified density current theory is conducted. Additionally, subcritical to supercritical transitions of frontal propagation speed relative to internal gravity wave (IGW) speed are demonstrated to occur. That is in part due to IGW speed reduction with decrease in seabed depth during the frontal propagation toward the shore. Theoretical steady-state density current propagation speed is in good agreement with the observations in the critical and supercritical regimes but not in the inherently unsteady subcritical regime. The latter may be due to interaction of IGW with the front, an effect previously demonstrated only in laboratory and numerical experiments. In the critical regime, finite-amplitude IGWs form and remain locked to the front. A critical to supercritical transition eventually occurs as the ambient conditions change during frontal propagation, after which IGWs are not supported at the front. The subcritical (critical) to critical (supercritical) transition is related to Froude number ahead (under) the front, consistently with theory. Finally, we find that the front-locked IGW (critical) regime is itself dependent on significant nonlinear speed enhancement of the IGW by their growth to finite amplitude at the front.