Terminal Steady State Research Articles

Optimizing Operations Sequencing and Demulsifier Injection in Offshore Oil Production Platforms

Short-term production optimization of oil assets concerns routing decisions and equipment control settings that induce optimal steady-state operations. Typically, the decisions are made on the scale of hours to days with the aim of maximizing short-term economic and oil gains. Still an evolving field, this paper contributes by presenting a model and solution strategy for sequencing operations over time to drive the system towards an optimal state, while accounting for constraints that ensure smooth transitions until settling at the terminal steady-state. The constraints include the maximum number of wells that undergo a change in the control settings, maximum number and variation on the input signals for each well, and maximum number of changes in each time period, among others. Additionally, the proposed strategy can optimize the rate of injection of demulsifiers into wells considering the limits and impacts on fluid processing capacity. The paper reports simulated results for a real-world offshore production platform, demonstrating the effectiveness of the optimization strategy to cope with the failure and recovery of compression capacity, and manage the injection of demulsifiers.

Eco-Physiological Screening of Different Tomato Genotypes in Response to High Temperatures: A Combined Field-to-Laboratory Approach.

High temperatures represent a limitation for growth and development of many crop species. Several studies have demonstrated that the yield reduction of tomato under high temperatures and drought is mainly due to a photosynthetic decline. In this paper, a set of 15 tomato genotypes were screened for tolerance to elevated temperatures by cultivating plants under plastic walk-in tunnels. To assess the potential tolerance of tomato genotypes to high temperatures, measurements of chlorophyll fluorescence, pigments content and leaf functional traits have been carried out together with the evaluation of the final yields. Based on the greenhouse trials, a group of eight putative heat-sensitive and heat-tolerant tomato genotypes was selected for laboratory experiments aimed at investigating the effects of short-term high temperatures treatments in controlled conditions. The chlorophyll fluorescence induction kinetics were recorded on detached leaves treated for 60 min at 35 °C or at 45 °C. The last treatment significantly affected the photosystem II (PSII) photochemical efficiency (namely maximum PSII quantum efficiency, Fv/Fm, and quantum yield of PSII electron transport, ΦPSII) and the non-photochemical quenching (NPQ) in the majority of genotypes. The short-term heat shock treatments also led to significant differences in the shape of the slow Kautsky kinetics and its significant time points (chlorophyll fluorescence levels minimum O, peak P, semi-steady state S, maximum M, terminal steady state T) compared to the control, demonstrating heat shock-induced changes in PSII functionality. Genotypes potentially tolerant to high temperatures have been identified. Our findings support the idea that chlorophyll fluorescence parameters (i.e., ΦPSII or NPQ) and some leaf functional traits may be used as a tool to detect high temperatures-tolerant tomato cultivars.

Receptor-Ligand Rebinding Kinetics in Confinement

Rebinding kinetics of molecular ligands plays a key role in the operation of biomachinery, from regulatory networks to protein transcription, and is also a key factor in design of drugs and high-precision biosensors. In this study, we investigate initial release and rebinding of ligands to their binding sites grafted on a planar surface, a situation commonly observed in single-molecule experiments and that occurs in vivo, e.g., during exocytosis. Via scaling arguments and molecular dynamic simulations, we analyze the dependence of nonequilibrium rebinding kinetics on two intrinsic length scales: the average separation distance between the binding sites and the total diffusible volume (i.e., height of the experimental reservoir in which diffusion takes place or average distance between receptor-bearing surfaces). We obtain time-dependent scaling laws for on rates and for the cumulative number of rebinding events. For diffusion-limited binding, the (rebinding) on rate decreases with time via multiple power-law regimes before the terminal steady-state (constant on-rate) regime. At intermediate times, when particle density has not yet become uniform throughout the diffusible volume, the cumulative number of rebindings exhibits a novel, to our knowledge, plateau behavior because of the three-dimensional escape process of ligands from binding sites. The duration of the plateau regime depends on the average separation distance between binding sites. After the three-dimensional diffusive escape process, a one-dimensional diffusive regime describes on rates. In the reaction-limited scenario, ligands with higher affinity to their binding sites (e.g., longer residence times) delay entry to the power-law regimes. Our results will be useful for extracting hidden timescales in experiments such as kinetic rate measurements for ligand-receptor interactions in microchannels, as well as for cell signaling via diffusing molecules.

Low temperature induced modulation of photosynthetic induction in non-acclimated and cold-acclimated Arabidopsis thaliana: chlorophyll a fluorescence and gas-exchange measurements.

Cold acclimation modifies the photosynthetic machinery and enables plants to survive at sub-zero temperatures, whereas in warm habitats, many species suffer even at non-freezing temperatures. We have measured chlorophyll a fluorescence (ChlF) and CO2 assimilation to investigate the effects of cold acclimation, and of low temperatures, on a cold-sensitive Arabidopsis thaliana accession C24. Upon excitation with low intensity (40µmol photons m- 2 s- 1) ~ 620nm light, slow (minute range) ChlF transients, at ~ 22°C, showed two waves in the SMT phase (S, semisteady-state; M, maximum; T, terminal steady-state), whereas CO2 assimilation showed a linear increase with time. Low-temperature treatment (down to - 1.5°C) strongly modulated the SMT phase and stimulated a peak in the CO2 assimilation induction curve. We show that the SMT phase, at ~ 22°C, was abolished when measured under high actinic irradiance, or when 3-(3, 4-dichlorophenyl)-1, 1- dimethylurea (DCMU, an inhibitor of electron flow) or methyl viologen (MV, a Photosystem I (PSI) electron acceptor) was added to the system. Our data suggest that stimulation of the SMT wave, at low temperatures, has multiple reasons, which may include changes in both photochemical and biochemical reactions leading to modulations in non-photochemical quenching (NPQ) of the excited state of Chl, "state transitions," as well as changes in the rate of cyclic electron flow through PSI. Further, we suggest that cold acclimation, in accession C24, promotes "state transition" and protects photosystems by preventing high excitation pressure during low-temperature exposure.

Accelerated Degradation of Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layers

In this work, as-received pristine GDLs were degraded (aged) through an accelerated ageing process by immersion into a 35% wt. solution of H2O2 at 90°C for 12 hours. Pristine and degraded GDLs were assembled in custom-built fuel cells for in operando synchrotron X-ray visualization. Electrochemical impedance spectroscopy (EIS) measurements were obtained, while synchrotron X-ray radiography was performed to investigate the effect of ageing on liquid water transport behavior. In both pristine and aged GDLs, the liquid water profile converged to an upper (terminal) threshold in the saturation pattern as the current density increased. The terminal steady state liquid water profile was established at a lower current density for the aged GDLs compared to that of the pristine GDLs. Higher water quantities of liquid water accumulated at the GDL/flow field channel and MPL/carbon fiber substrate interfaces of the fuel cell with an aged GDL compared to the fuel cell with a pristine GDL. The aged GDLs exhibited more liquid water accumulation at lower current densities. Increases in liquid water accumulation and reduced performance were attributed to the reduction in hydrophobicity of the GDL.

Role of the active viscosity and self-propelling speed in channel flows of active polar liquid crystals.

We study channel flows of active polar liquid crystals (APLCs) focusing on the role played by the active viscosity (β) and the self-propelling speed (ω) on the formation and long time evolution of spontaneous flows using a continuum model. First, we study the onset of spontaneous flows by carrying out a linear stability analysis on two special steady states subject to various physical boundary conditions. We identify a single parameter b1, proportional to a linear combination of the active viscosity and the self-propelling speed, and inversely proportional to a Frank elastic constant, the solvent viscosity, and the liquid crystal relaxation time. We show that the active viscosity and the self-propelling speed influence the onset of spontaneous flows through b1 in that for any fixed value of the bulk activity parameter ζ, large enough |b1| can suppress the spontaneous flow. We then follow spontaneous flows in long time to further investigate the role of β and ω on spatial-temporal structures in the nonlinear regime numerically. The numerical study demonstrates a strong correlation between the most unstable eigenfunction obtained from the linear analysis and the terminal steady state or the persistent, traveling wave structure, revealing the genesis of flow and orientational structures in the active matter system. In the nonlinear regime, a nonzero b1 facilitates the formation of traveling waves in the case of boundary anchoring (the Dirichlet boundary condition) so long as the linear stability analysis predicts an onset of spontaneous flows; in the case of the free boundary condition (the Neumann boundary condition), a stable, spatially homogeneous tilted state always emerges in the presence of two active effects. Finally, we note that various fully out-of-plane spatio-temporal structures can emerge in long time dynamics depending on the boundary condition as well as the initial state of the polarity vector field.

Extensional rheometry of cellulose ether solutions: flow instability

Capillary breakup extensional rheometry of semi-dilute hydroxyethyl cellulose (HEC) solutions was performed under several step-stretch conditions. The resulting parameters, i.e. terminal steady state extensional viscosity (η E ) and the timescale for viscoelastic stress growth, commonly referred to as the extensional relaxation time (λ E ) were found to be sensitive to the step-stretch conditions. The λ E decreased with increasing step-strain as opposed to the η E . Prior to the filament break-up, a ‘bead-on-string’ instability was observed close to the mid-plane. It is believed that this instability originated from the accumulation of viscoelastic stresses near the filament neck leading to the ‘elastic recoil’ of the extended polymer chains. The reasons for this belief are discussed in detail with the perspective of the past literature. Such type of flow instability has been reported for the first time for a cellulosic system. Various dimensionless numbers were plotted for the HEC solutions and compared with those obtained from past studies for various biopolymers as well as synthetic polymers.

Strontium source and depth of uptake shifts with substrate age in semiarid ecosystems

AbstractWithout exogenous rock‐derived nutrient sources, terrestrial ecosystems may eventually regress or reach a terminal steady state, but the degree to which exogenous nutrient sources buffer or slow to a theoretical terminal steady state remains unclear. We used strontium isotope ratios (87Sr/86Sr) as a tracer and measured 87Sr/86Sr values in aeolian dust, soils, and vegetation across a well‐constrained 3 Myr semiarid substrate age gradient to determine (1) whether the contribution of atmospheric sources of rock‐derived nutrients to soil and vegetation pools varied with substrate age and (2) to determine if the depth of uptake varied with substrate age. We found that aeolian‐derived nutrients became increasingly important, contributing as much as 71% to plant‐available soil pools and tree (Pinus edulis) growth during the latter stages of ecosystem development in a semiarid climate. The depth of nutrient uptake increased on older substrates, demonstrating that trees in arid regions can acquire nutrients from greater depths as ecosystem development progresses presumably in response to nutrient depletion in the more weathered surface soils. Our results demonstrate that global and regional aeolian transport of nutrients to local ecosystems is a vital process for ecosystem development in arid regions. Furthermore, these aeolian nutrient inputs contribute to deep soil nutrient pools, which become increasingly important for maintaining plant productivity over long time scales.

Modeling chlorophyll a fluorescence transient: relation to photosynthesis.

To honor Academician Alexander Abramovitch Krasnovsky, we present here an educational review on the relation of chlorophyll a fluorescence transient to various processes in photosynthesis. The initial event in oxygenic photosynthesis is light absorption by chlorophylls (Chls), carotenoids, and, in some cases, phycobilins; these pigments form the antenna. Most of the energy is transferred to reaction centers where it is used for charge separation. The small part of energy that is not used in photochemistry is dissipated as heat or re-emitted as fluorescence. When a photosynthetic sample is transferred from dark to light, Chl a fluorescence (ChlF) intensity shows characteristic changes in time called fluorescence transient, the OJIPSMT transient, where O (the origin) is for the first measured minimum fluorescence level; J and I for intermediate inflections; P for peak; S for semi-steady state level; M for maximum; and T for terminal steady state level. This transient is a real signature of photosynthesis, since diverse events can be related to it, such as: changes in redox states of components of the linear electron transport flow, involvement of alternative electron routes, the build-up of a transmembrane pH gradient and membrane potential, activation of different nonphotochemical quenching processes, activation of the Calvin-Benson cycle, and other processes. In this review, we present our views on how different segments of the OJIPSMT transient are influenced by various photosynthetic processes, and discuss a number of studies involving mathematical modeling and simulation of the ChlF transient. A special emphasis is given to the slower PSMT phase, for which many studies have been recently published, but they are less known than on the faster OJIP phase.

Nonlinear signatures of entangled polymer solutions in active microbead rheology.

We present experimental data and numerical modeling of a nonlinear phenomenon in active magnetic microbead rheology that appears to be common to entangled polymer solutions (EPS). Dynamic experiments in a modest range of magnetic forces show: 1. a short-lived high viscosity plateau, followed by 2. a bead acceleration phase with a sharp drop in apparent viscosity, and 3. a terminal steady state that we show resides on the shear-thinning slope of the steady-state flow curve from cone and plate data. This latter feature implies a new protocol to access the nonlinear steady-state flow curve for many biological EPS only available in microliter-scale volumes. We solve the moment-closure form of the Rolie-Poly kinetic model for EPS hydrodynamics, together with a decoupling approximation that obviates the need for a full 3D flow solver, and show that the model qualitatively reproduces the dynamic experimental sequence above. In this way, we explain the phenomenon in terms of entangled polymer physics, and show how the nonlinear event (acceleration and termination on the shear-thinning response curve) is tunable by the interplay between molecular-scale mechanisms (relaxation via reptation and chain retraction) and magnetic force controls. The experimental conditions mimic movement of cilia tips, bacteria, and sperm in mucus barriers, implying a physiological relevance of the phenomenon, and compelling further development of the fully coupled, 3D flow-microstructure model to achieve quantitative accuracy.

A leaky model of long‐term soil phosphorus dynamics

Soil phosphorus (P) leaks rapidly from newly formed land surfaces to upland rivers and lakes, surface water P concentrations peaking early before declining as soil apatite (Ca5(PO4)3(OH)) becomes depleted. We present lake sediment P profiles that record this leakage through the early Holocene. The results are entirely consistent with our re‐analysis of published soil chronosequence data, but conflict with more recent quantitative interpretations of global soil P dynamics that identify far slower loss rates. P inherited from the bedrock on soil formation, long regarded as the major source for terrestrial ecosystems, only lasts ~104 years rather than the previously suggested 106 years, and thus is, globally, much less important in the long term than atmospheric supply. This changes the conceptualization of terrestrial P dynamics, with the “terminal steady state” of Walker and Syers (1976) being the norm not the exception, and with soil P export being little if at all controlled by biotic retention mechanisms. High early export of P from newly formed soil causes a peak in the productivity of terrestrial surface waters, before a decline as the soil P pool depletes. Globally, the 18 × 106 km2 of terrain exposed since the Last Glacial Maximum potentially produced a substantial surge in runoff P, with greatest impacts likely in high‐latitude, restricted basin seas and maximal area of deglaciated terrain.

Rolling/sliding of a particle on a flat wall in a linear shear flow at finite Re

Recently Lee and Balachandar proposed analytically-based expressions for drag and lift coefficients for a spherical particle moving on a flat wall in a linear shear flow at finite Reynolds number. In order to evaluate the accuracy of these expressions, we have conducted direct numerical simulations of a rolling particle for shear Reynolds number up to 100. We assume that the particle rolls on a horizontal flat wall with a small gap separating the particle from the wall ( L = 0.505) and thus avoiding the logarithmic singularity. The influence of the shear Reynolds number and the translational velocity of the particle on the hydrodynamic forces of the particle was investigated under both transient and the final drag-free and torque-free steady state. It is observed that the quasi-steady drag and lift expressions of Lee and Balachandar provide good approximation for the terminal state of the particle motion ranging from perfect sliding to perfect rolling. With regards to transient particle motion in a wall-bounded shear flow it is observed that the above validated quasi-steady drag and lift forces must be supplemented with appropriate wall-corrected added-mass and history forces in order to accurately predict the time-dependent approach to the terminal steady state. Quantitative comparison with the actual particle motion computed in the numerical simulations shows that the theoretical models quite effective in predicting rolling/sliding motion of a particle in a wall-bounded shear flow at moderate Re.

Terrestrial phosphorus limitation: mechanisms, implications, and nitrogen–phosphorus interactions

Nutrient limitation to primary productivity and other biological processes is widespread in terrestrial ecosystems, and nitrogen (N) and phosphorus (P) are the most common limiting elements, both individually and in combination. Mechanisms that drive P limitation, and their interactions with the N cycle, have received less attention than mechanisms causing N limitation. We identify and discuss six mechanisms that could drive P limitation in terrestrial ecosystems. The best known of these is depletion-driven limitation, in which accumulated P losses during long-term soil and ecosystem development contribute to what Walker and Syers termed a "terminal steady state" of profound P depletion and limitation. The other mechanisms are soil barriers that prevent access to P; transactional limitation, in which weathering of P-containing minerals does not keep pace with the supply of other resources; low-P parent materials; P sinks; and anthropogenic changes that increase the supply of other resources (often N) relative to P. We distinguish proximate nutrient limitation (which occurs where additions of a nutrient stimulate biological processes, especially productivity) from ultimate nutrient limitation (where additions of a nutrient can transform ecosystems). Of the mechanisms that drive P limitation, we suggest that depletion, soil barriers, and low-P parent material often cause ultimate limitation because they control the ecosystem mass balance of P. Similarly, demand-independent losses and constraints to N fixation can control the ecosystem-level mass balance of N and cause it to be an ultimate limiting nutrient.

NUMERICAL ANALYSIS OF BUBBLE MOTION BY LEVEL-SET METHOD

Air bubble rising in water is analyzed numerically by Navier-Stokes equation. To capture liquid-gas interface as well as to smooth large gap in density/viscosity, Level-Set method is applied. For typical bubbles of spherical, ellipsoidal and spherical-cap shape, rising velocities with their shapes are calculated, from the start of motion to the terminal steady state. And, their transitions of velocity and corresponding alterations in shape, are examined in detail. In one ellipsoidal case, cyclic alteration in shape, deviating over ellipsoidal regime, is confirmed. Terminal velocities and shapes, for the bubble of equivalent diameter from 1.2mm to 24.5mm, are compared with the existing experiments in distilled water. Good agreement was obtained in shapes, while terminal velocities of our two-dimensional analysis underestimated the corresponding experimental values by about 20 percent.

Genesis and Native Phosphorus Distribution in some Palexeralfs of Southern Spain

AbstractAlthough deeply weathered soils are common on stable landscapes in Mediterranean regions, little information exists regarding the quantities and depth‐distributions of native P forms in such soils. The objective of this investigation was to gather such information to determine the P status of Palexeralfs representative of southern Spain and to evaluate the applicability of current models and paradigms for describing pedogenic P transformations in such soils. Base saturation, clay distribution, absence of primary carbonates, distribution of secondary carbonates, extent of rubification, and properties of Fe (hydr) oxides all indicate that the Palexeralfs are polygenetic. Yellowishred lower sola are considered relicts attributable to deep leaching and weathering during Pleistocene pluvial periods, whereas pedogenesis is active in upper yellowish‐brown B horizons. Low total and labile P contents and the dominance of reductant‐soluble and organic P fractions throughout entire >3‐m sola indicate that soil P distribution attained a terminal steady state during the paleo‐climatic regime and has been little affected during the current semiarid climate. Although organic P (Po) is a major component of total P, stabilization of Po by Fe (hydr) oxides restricts Po mineralization and fosters the labile P deficient state of these soils.

TRANSITION WAVES THAT LEAVE BEHIND REGULAR OR IRREGULAR SPATIOTEMPORAL OSCILLATIONS IN A SYSTEM OF THREE REACTION–DIFFUSION EQUATIONS

Transition waves are widespread in the biological and chemical sciences, and have often been successfully modelled using reaction–diffusion systems. I consider a particular system of three reaction–diffusion equations, and I show that transition waves can destabilise as the kinetic ordinary differential equations pass through a Hopf bifurcation, giving rise to either regular or irregular spatiotemporal oscillations behind the advancing transition wave front. In the case of regular oscillations, I show that these are periodic plane waves that are induced by the way in which the transition wave front approaches its terminal steady state. Further, I show that irregular oscillations arise when these periodic plane waves are unstable as reaction–diffusion solutions. The resulting behavior is not related to any chaos in the kinetic ordinary differential equations.

Soil Development and Nitrogen Turnover in Montane Rainforest Soils on Hawai'i

Soil Development and Nitrogen Turnover in Montane Rainforest Soils on Hawai'i

Chlorophyll a fluorescence of Gonyaulax polyedra grown on a light-dark cycle and after transfer to constant light.

Abstract— The chlorophyll a fluorescence properties of Gonyaulax polyedra cells before and after transfer from a lightdark cycle (LD) to constant dim light (LL) were investigated. The latter display a faster fluorescence transient from the level ‘I’ (intermediary peak) to ‘D’ (dip) to ‘P’ (peak) than the former (3 s as compared to 10 s), and a different pattern of decline in fluorescence from ‘I’ to ‘D’ and from ‘P’ to the steady state level with no clearly separable second wave of slow fluorescence change, referred to as ‘s' (quasi steady state)→‘M’ (maximum) →‘T’ (terminal steady state). The above differences are constant features of cells in LD and LL, and are not dependent on the time of day. They are interpreted as evidence for a greater ratio of photosystem II/photosystem I activity in cells in LL.After an initial photoadaptive response following transfer from LD to LL, the cell absorbance at room temperature and fluorescence emission spectra at 77 K for cells in LL and LD are comparable. The major emission peak is at 685–688 nm (from an antenna Chl a 680, perhaps Chl a‐c complex), but, unlike higher plants and other algae, the emission bands at 696–698 nm (from Chl aII complex, Chl a 685, close to reaction center II) and 710–720 nm (from Chl a1, complexes, Chl a 695, close to reaction center I) are very minor and could be observed only in the fluorescence emission difference spectra of LL minus LD cells and in the ratio spectra of DCMU‐treated to non‐treated cells.Comparison of emission spectra of cells in LL and LD suggested that, in LL, there is a slightly greater net excitation energy transfer from the light‐harvesting peridinin‐Chl a (Chl a 670) complex, fluorescing at 675 nm, to the other antenna chlorophyll a complex fluorescing at 685–688 nm, and from the Chl a., complex to the reaction center II. Comparison of excitation spectra of fluorescence of LL and LD cells, in the presence of DCMU, confirmed that cells in LL transfer energy more extensively from the peridinin‐Chl a complex to other Chl a complexes than do cells in LD.

The control of rapid limb movement in the cat. II. Scaling of isometric force adjustments.

In the previous study it was shown that cats were capable of making rapid and accurate adjustments in the force they applied to a lever in accord with information provided by a compensatory display. In the present study, isometric responses were examined in greater detail to determine 1. if a general control policy (or model) governing responses of different magnitudes could be inferred from the relations among output parameters and 2. if the earliest output measures were scaled to the preceding sensory events. The force adjustments elicited by the sudden motion of the display showed a linera relation between the peak force and the peak of its first derivative, dF/dt. Similarly, the peak d2F/dt2 was a linear function of dF/dt. By contrast, the times required to achieve the peak force and the peak dF/dt were largely independent of their magnitudes. These adjustments were produced by a burst of EMG activity in agonist muscles which coincided with the rising phase of dF/dt. The observations suggest that such motor outputs are determined by a pulse-step control policy. The amplitude of the pulse would control the rate of rise of dF/dt (and therefore also the peak force since the rising phase of dF/dt was of constant duration), and the step would control the level of the terminal steady state force. Both the peak force and the preceding peak dF/dt were highly correlated with the amplitude of the perturbation. Changes in display gain, which altered the required relation between input and output magnitudes, resulted in a gradual readjustment of the output parameters. It was concluded that the motor outputs were scaled from their inception to requirements dictated by the initial sensory information. The selection by the cat of the appropriate scaling function was contingent upon its previous experience with the device.