Outward Flux Research Articles

Potential of proton-pumping rhodopsins: engineering photosystems into microorganisms

A wide range of proton-pumping rhodopsins (PPRs) have been discovered in recent years. Using a synthetic biology approach, PPR photosystems with different features can be easily introduced in nonphotosynthetic microbial hosts. PPRs can provide hosts with the ability to harvest light and drive the sustainable production of biochemicals or biofuels. PPRs use light energy to generate an outward proton flux, and the resulting proton motive force can subsequently power cellular processes. Recently, the introduction of PPRs in microbial production hosts has successfully led to light-driven biotechnological conversions. In this review, we discuss relevant features of natural PPRs, evaluate reported biotechnological applications of microbial production hosts equipped with PPRs, and provide an outlook on future developments.

Temporal and spatial responses of temperature, density and rotation to electron cyclotron heating in JT-60U

The temporal and spatial responses of electron channels (the electron density, ne, and the electron temperature, Te) and ion channels (the ion temperature, Ti, and the toroidal rotation velocity, Vφ) to central electron cyclotron heating (ECH) have been investigated in positive shear H-mode plasmas with a relatively peaked Ti profile and internal transport barrier (ITB) plasmas on JT-60U. Ion temperature decreases with ECH after the increase in the electron temperature in the core region. The time scale of the change in Ti is ≈30–60 ms in H-mode plasmas and almost constant in radius. In ITB plasmas, the time scale is shorter around the ITB foot and becomes longer inside the ITB foot. The experimentally measured causality indicates that the decrease in Ti is consistent with the ion temperature gradient critical gradient reduction. This is also verified through a comparison with linear gyrokinetic stability analyses. The electron heat diffusivity increases with ECH in both H-mode and ITB plasmas, correlating to the increase in the ion heat diffusivity. Electron density with a relatively flat ne profile does not decrease with ECH. On the other hand, the electron density with a peaked ne profile decreases with ECH. The flattening of the ne profile is observed after the increase in the electron temperature in the core region. The time scale of the change in ne is about 200–350 ms. Linear gyrokinetic stability analyses imply that the growth rate of the trapped electron modes, which increase outward particle flux, becomes more pronounced during ECH. The counter intrinsic rotation with ECH is identified on H-mode plasmas with a small torque input (BAL-NBI). The counter intrinsic rotation is generated after the increase in the electron temperature and correlates to the change in the electron temperature with ECH around the EC deposition. The radial region where the counter intrinsic rotation is observed is wider than the radial region where the electron temperature varies with ECH. The time scale of the change in the toroidal rotation velocity is about 90–200 ms around the ECH deposition and longer than the time scale of the change in Te and Ti.

One-Dimensional Transient Analytical Solution for Gas Pressure in Municipal Solid Waste Landfills

Landfill gas (LFG) is generated in municipal solid waste (MSW) landfills because of the decomposition of degradable components. Gas pressure within the landfilled MSWs is of importance as cover or landfill stability may be affected by gas pressure. This paper presents a one-dimensional transient analytical solution for gas pressure profiles in a MSW layer. This solution considers the variation of the LFG generation rate with respect to depth and decay of the LFG generation rate with time. The authors used the specified outward gas flux bottom boundary condition to simulate horizontal LFG collection systems and basal leachate collection systems serving dually as LFG collection systems. The presented solution also gives the outward gas flux from the MSW layer surface, which may be used to assist in the prediction of air quality near landfills. An application of the presented solution shows that averaging the LFG generation rate throughout the MSW layer results in a remarkable overestimation of gas pressure.

Combustion performance of eccentrically rotated flames

Experimental/computational work highlighted the combustion performance with eccentric blockage rotation in the reactive flow passage to augment the turbulence production rates in the flame for acquiring high power to weight ratios and effective heat transfer in industrial applications. The temporal/spatial velocity gradients stimulated around the reactive stream boundaries enhanced the turbulence development in both premixed and non-premixed flames. The eccentric shapes included circular, elliptical, squared and triangular shafts as well as a triple/straight blade rotor. The design was further developed to incorporate simultaneous rotation of the eccentric blockage around its axis via a planetary gear assembly to duplicate the vortical structure. While the premixed flames responded to such cyclic action by having a mixture velocity of 16.8 m/s, the non-premixed flames acquired an increase of 341% in the largest eddy size and a flame length reduction by 42%. Increasing the Strouhal number to 0.94 and the swirl ratio to 0.78 increased the turbulent kinetic energy to 9.1 m2/s2. By controlling the drag coefficient and wake vorticity for the solid shapes, the triangular rotor enhanced the combustor outward heat flux to exhibit a heater efficiency of 36.8% in the premixed flame mode and reduced the HC and CO emissions, respectively, to 0.1% and 513 ppm for non-premixed flames. Decreasing the reactive stream cross-section favorably increased the flow shearing effects, while the elliptical shape showed the highest sensitivity to axes’ orientation with respect to the direction of rotation. Due to the reduction in peak temperatures via increasing the turbulence intensity and heat transfer rate from the flame, the NO x exhaust concentrations decreased to a minimum value around 10 ppm. The combustion efficiency of diffusion flames was optimized with the fuel port central positioning in the burner, where the planetary gear design provided a turbulence intensity of 13.7% by the triple blade rotor.

Vibrio effector protein, VopQ, forms a lysosomal gated channel that disrupts host ion homeostasis and autophagic flux

Defects in normal autophagic pathways are implicated in numerous human diseases--such as neurodegenerative diseases, cancer, and cardiomyopathy--highlighting the importance of autophagy and its proper regulation. Herein we show that Vibrio parahaemolyticus uses the type III effector VopQ (Vibrio outer protein Q) to alter autophagic flux by manipulating the partitioning of small molecules and ions in the lysosome. This effector binds to the conserved Vo domain of the vacuolar-type H(+)-ATPase and causes deacidification of the lysosomes within minutes of entering the host cell. VopQ forms a gated channel ∼18 Å in diameter that facilitates outward flux of ions across lipid bilayers. The electrostatic interactions of this type 3 secretion system effector with target membranes dictate its preference for host vacuolar-type H(+)-ATPase-containing membranes, indicating that its pore-forming activity is specific and not promiscuous. As seen with other effectors, VopQ is exploiting a eukaryotic mechanism, in this case manipulating lysosomal homeostasis and autophagic flux through transmembrane permeation.

A Label-Free Potentiometric Sensor Principle for the Detection of Antibody–Antigen Interactions

We report here on a new potentiometric biosensing principle for the detection of antibody-antigen interactions at the sensing membrane surface without the need to add a label or a reporter ion to the sample solution. This is accomplished by establishing a steady-state outward flux of a marker ion from the membrane into the contacting solution. The immunobinding event at the sensing surface retards the marker ion, which results in its accumulation at the membrane surface and hence in a potential response. The ion-selective membranes were surface-modified with an antibody against respiratory syncytial virus using click chemistry between biotin molecules functionalized with a triple bond and an azide group on the modified poly (vinyl chloride) group of the membrane. The bioassay sensor was then built up with streptavidin and subsequent biotinylated antibody. A quaternary ammonium ion served as the marker ion. The observed potential was found to be modulated by the presence of respiratory syncytial virus bound on the membrane surface. The sensing architecture was confirmed with quartz crystal microbalance studies, and stir effects confirmed the kinetic nature of the marker release from the membrane. The sensitivity of the model sensor was compared to that of a commercially available point-of-care test, with promising results.

Combined effect of global warming and increased CO2-concentration on vegetation growth in water-limited conditions

The most severe impact of climate change on vegetation growth and agriculture is likely to occur under water-limited conditions. Under such conditions the plants optimize the inward flux of CO2 and the outward flux of water vapor (the transpiration) by regulating the size of the stomatal openings. Higher temperature increases water loss through transpiration, forcing the plants to diminish the stomatal openings, which decreases photosynthesis. This is counteracted by higher CO2 concentration, which allows plants to maintain the inward flux of CO2 through the smaller openings. These two counteracting effects, combined with the change in precipitation, determine the net change of biological productivity. Here, a vegetation sensitivity approximation (VSA) is introduced, in order to understand and estimate the combined effect of changed temperature, CO2 and precipitation to first order. The VSA is based on the physical laws of gas flux through the stomatal openings, and is only valid under water-limited conditions. It assumes that the temperature depends logarithmically on the CO2 concentration with a given climate sensitivity. Precipitation is included by assuming that it is proportional to the transpiration. This is reasonable under water-limited conditions, when transpiration is often a large fraction of the precipitation. The VSA is compared to simulations with the dynamic vegetation model LPJ. The agreement is reasonable, and the deviations can be understood by comparison with Köppen's definition of arid climate: in an arid climate growth increases more according to LPJ than according to the VSA, and in non-arid conditions the reverse is true. Both the VSA and the LPJ simulations generally show increased growth with increasing CO2 levels and the resulting temperature increase, assuming precipitation to be unchanged. Thus, in this case the negative temperature effect is more than compensated by the positive effect of CO2.

Analysis of lithium driven electron density peaking in FTU liquid lithium limiter experiments

The impact of lithium impurities on the microstability and turbulent transport characteristics in the core of a typical FTU liquid lithium limiter (LLL) (Mazzitelli et al 2011 Nucl. Fusion 51 073006) discharge during the density ramp-up phase is studied. A non-linear gyrokinetic analysis performed with GKW (Peeters et al 2009 Comput. Phys. Commun. 180 2650) accompanied by a quasi-linear fluid analysis is presented. We show that a centrally peaked, high concentration lithium profile contributes to the electron peaking by reducing the outward electron flux, and that it leads to inward turbulent deuterium transport through ion flux separation.

Semiclassical collapse with tachyon field and barotropic fluid

The purpose of this paper is to extend the analysis presented in Goswami et al. [Phys. Rev. Lett. 96, 031302 (2006)] by means of investigating how a specific type of loop (quantum) effect can alter the outcome of gravitational collapse. To be more concrete, a particular class of spherically symmetric spacetime is considered with a tachyon field $\ensuremath{\phi}$ and a barotropic fluid constituting the matter content; the tachyon potential $V(\ensuremath{\phi})$ is assumed to be of the form ${\ensuremath{\phi}}^{\ensuremath{-}2}$. Within inverse triad corrections, we then obtain, for a semiclassical description, several classes of analytical as well as numerical solutions. Moreover, we identify a subset whose behavior corresponds to an outward flux of energy, thus avoiding either a naked singularity or a black hole formation.

Large-scale solar magnetic field mapping: I.

This article focuses on mapping the Sun’s large-scale magnetic fields. In particular, the model considers how photospheric fields evolve in time. Our solar field mapping method uses Netlogo’s cellular automata software via algorithms to carry out the movement of magnetic field on the Sun via agents. This model's entities consist of two breeds: blue and red agents. The former carry a fixed amount of radially outward magnetic flux: 1023 Mx, and the latter, the identical amount of inward directed flux. The individual agents are distinguished, for clarity, by various shades of blue and red arrows whose orientation indicates the direction the agents are moving, relative to the near-steady bulk fluid motions. The fluid motions generally advect the field with the well known meridional circulation and differential rotation. Our model predominantly focuses on spatial and temporal variations from the bulk fluid motions owing to magnetic interactions. There are but a few effects that agents have on each other: i) while at the poles, field agents are connected via the Babcock - Leighton (B - L) subsurface field to other latitudes. This allows them to undertake two duties there: A) the B - L subsurface field spawns the next generation of new magnetic field via new agents, and B) the B - L subsurface field attracts lower-latitude fields via the “long-range” magnetic stress tension; ii) nearby agents affect each other’s motion by short-range interactions; and iii) through annihilation: when opposite field agents get too close to each other, they disappear in pairs. The behavior of the agents’ long- and short-range magnetic forces is discussed within this paper as well as the model's use of internal boundary conditions. The workings of the model may be seen in the accompanying movies and/or by using the software available via SpringerPlus’ website, or on the NetlogoTM community website, where help is readable available, and should all these fail, some help from the author.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-2-21) contains supplementary material, which is available to authorized users.

Local and Fast Density Pump-out by ECRH in the LHD

A decrease in the electron density is observed during high-power heating, particularly in electron cyclotron resonance heating (ECRH). One possible mechanism is the increase in the number of trapped particles, which can enhance the radial particle flux, because ECRH accelerates electrons in a direction perpendicular to the magnetic field lines. To observe the effects of the production of trapped particles, high-power (1MW) ECRH was applied at the ripple bottom of the magnetic field strength, where trapped particles are readily produced. A rapid local outward flux of electrons was first observed near the heating position shortly after ECRH injection. The outward flux is proportional to the electron density in the density range of 0.4 × 1019 to 0.8 × 1019 m−3. The inward electron flux was subsequently enhanced in the core region.

Effect of plasma shaping and resonance location on minority ion temperature anisotropy in tokamak plasmas heated with ICRH

Poloidal asymmetries of the impurity distribution, which are observed in tokamaks, may influence the impurity cross-field transport. Low field side ion cyclotron resonance heating (ICRH) often results in an inboard accumulation of impurities, which may in turn lead to an outward convective impurity flux. The temperature anisotropy of the ICRH-heated minority ions is identified to be one of the main parameters governing the impurity asymmetry strength. In the present work we analyze the effect of plasma shaping and the ICRH resonance location on the minority temperature anisotropy by means of the TORIC-SSFPQL modelling. We find that ellipticity reduces the anisotropy level due to the wave defocussing and broader absorption regions for the elongated plasmas. The temperature anisotropy decrease in case of the resonance layers located closer to the edge is caused by the significant reduction in heating power densities due to geometrical reasons.

Mesophyll conductance: constraint on carbon acquisition by C3 plants

Mesophyll conductance: constraint on carbon acquisition by C₃ plants

Effect of environment on the scale formed on oxide dispersion strengthened FeCrAl at 1050°C and 1100°C

The surface scale formed on specimens of a commercial oxide dispersion strengthened (ODS) FeCrAl alloy (PM2000) exposed for 1 and 500 h at 1050°C in dry O2, Air+10%H2O and Ar+10%H2O consisted of a two-layer α-Al2O3 structure with a columnar grain inner layer and a finer grain outer layer. The alumina scales formed in Air+10%H2O and Ar+10%H2O were slightly more than half of the thickness of the scale formed in dry O2. The same two-layer structure was also observed after exposure for 500 h at 1100°C in dry O2 and 50%CO2+50%H2O. The alumina scales formed in both atmospheres were similar in thickness. Oxides rich in Y and Ti at the gas – scale interface grew in size and number with time in each case. Using analytical transmission electron microscopy, alumina grain boundary segregation of both Y and Ti was evident near the gas interface but only Y segregation was detected near the metal interface. This difference was attributed to Ti depletion in the adjacent metal and the rapid outward flux of the smaller Ti ion through the scale.

Reactive Solid Surface Morphology Variation via Ionic Diffusion

In gas-solid reactions, one of the most important factors that determine the overall reaction rate is the solid morphology, which can be characterized by a combination of smooth, convex and concave structures. Generally, the solid surface structure varies in the course of reactions, which is classically noted as being attributed to one or more of the following three mechanisms: mechanical interaction, molar volume change, and sintering. Here we show that if a gas-solid reaction involves the outward ionic diffusion of a solid-phase reactant then this outward ionic diffusion could eventually smooth the surface with an initial concave and/or convex structure. Specifically, the concave surface is filled via a larger outward diffusing surface pointing to the concave valley, whereas the height of the convex surface decreases via a lower outward diffusion flux in the vertical direction. A quantitative 2-D continuum diffusion model is established to analyze these two morphological variation processes, which shows consistent results with the experiments. This surface morphology variation by solid-phase ionic diffusion serves to provide a fourth mechanism that supplements the traditionally acknowledged solid morphology variation or, in general, porosity variation mechanisms in gas-solid reactions.

Warburg Revisited: Regulation of Mitochondrial Metabolism by Voltage-Dependent Anion Channels in Cancer Cells

The bioenergetics of cancer cells is characterized by a high rate of aerobic glycolysis and suppression of mitochondrial metabolism (Warburg phenomenon). Mitochondrial metabolism requires inward and outward flux of hydrophilic metabolites, including ATP, ADP and respiratory substrates, through voltage-dependent anion channels (VDACs) in the mitochondrial outer membrane. Although VDACs were once considered to be constitutively open, closure of the VDAC is emerging as an adjustable limiter (governator) of mitochondrial metabolism. Studies of VDACs reconstituted into planar lipid bilayers show that tubulin at nanomolar concentrations decreases VDAC conductance. In tumor cell lines, microtubule-destabilizing agents increase cytoplasmic free tubulin and decrease mitochondrial membrane potential (ΔΨ(m)), whereas microtubule stabilization increases ΔΨ(m). Tubulin-dependent suppression of ΔΨ(m) is further potentiated by protein kinase A activation and glycogen synthase kinase-3β inhibition. Knockdown of different VDAC isoforms, especially of the least abundant isoform, VDAC3, also decreases ΔΨ(m), cellular ATP, and NADH/NAD+, suggesting that VDAC1 and VDAC2 are most inhibited by free tubulin. The brake on mitochondrial metabolism imposed by the VDAC governator probably is released when spindles form and free tubulin decreases as cells enter mitosis, which better provides for the high ATP demands of chromosome separation and cytokinesis. In conclusion, tubulin-dependent closure of VDACs represents a new mechanism contributing to the suppression of mitochondrial metabolism in the Warburg phenomenon.

Loop quantum effect and the fate of tachyon field collapse

We study the fate of gravitational collapse of a tachyon field matter. In presence of an inverse square potential a black hole forms. Loop quantum corrections lead to the avoidance of classical singularities, which is followed by an outward flux of energy.

Physics of intrinsic rotation in flux-driven ITG turbulence

Global, heat flux-driven ITG gyrokinetic simulations which manifest the formation of macroscopic, mean toroidal flow profiles with peak thermal Mach number 0.05, are reported. Both a particle-in-cell (XGC1p) and a semi-Lagrangian (GYSELA) approach are utilized without a priori assumptions of scale separation between turbulence and mean fields. Flux-driven ITG simulations with different edge flow boundary conditions show in both approaches the development of net unidirectional intrinsic rotation in the co-current direction. Intrinsic torque is shown to scale approximately linearly with the inverse scale length of the ion temperature gradient. External momentum input is shown to effectively cancel the intrinsic rotation profile, thus confirming the existence of a local residual stress and intrinsic torque. Fluctuation intensity, intrinsic torque and mean flow are demonstrated to develop inwards from the boundary. The measured correlations between residual stress and two fluctuation spectrum symmetry breakers, namely E × B shear and intensity gradient, are similar. Avalanches of (positive) heat flux, which propagate either outwards or inwards, are correlated with avalanches of (negative) parallel momentum flux, so that outward transport of heat and inward transport of parallel momentum are correlated and mediated by avalanches. The probability distribution functions of the outward heat flux and the inward momentum flux show strong structural similarity.

REPRODUCTION OF THE OBSERVED TWO-COMPONENT MAGNETIC HELICITY IN SOLAR WIND TURBULENCE BY A SUPERPOSITION OF PARALLEL AND OBLIQUE ALFVÉN WAVES

The angular distribution of the normalized reduced magnetic helicity density (sigma(r)(m)) in solar wind turbulence reveals two components of distinct polarity in different angle ranges. This kind of two-component sigma(r)(m) m may indicate the possible wave modes and power spectral densities (PSDs) of the turbulent fluctuations. Here we model the measured angular distribution of sigma(r)(m) m by assuming a PSD distribution for Alfven fluctuations in wavevector space, and then fit the model results to the observations by adjusting the pattern of the PSD distribution. It is found that the two-component form of the PSD, which has a major and minor component close to k(perpendicular to) and k(parallel to), respectively, seems to be responsible for the observed two-component sigma(r)(m). On the other hand, both an isotropic PSD and a PSD with only a single component bending toward k(perpendicular to) fail to reproduce the observations. Moreover, it is shown that the effect of gradual balance between outward and inward wave-energy fluxes with decreasing spatial scale needs to be considered in order to reproduce the observed diminishing of vertical bar sigma(r)(m)vertical bar at shorter scales. Therefore, we suggest that the observed two-component sigma(r)(m) in the solar wind turbulence may be due to a superposition of Alfven waves with quasi-perpendicular (major part) and quasi-parallel (minor part) propagation. The waves seem to become gradually balanced toward shorter scales.

Regulation of Monocarboxylate Transporter MCT1 Expression by p53 Mediates Inward and Outward Lactate Fluxes in Tumors

The monocarboxylate transporter (MCT) family member MCT1 can transport lactate into and out of tumor cells. Whereas most oxidative cancer cells import lactate through MCT1 to fuel mitochondrial respiration, the role of MCT1 in glycolysis-derived lactate efflux remains less clear. In this study, we identified a direct link between p53 function and MCT1 expression. Under hypoxic conditions, p53 loss promoted MCT1 expression and lactate export produced by elevated glycolytic flux, both in vitro and in vivo. p53 interacted directly with the MCT1 gene promoter and altered MCT1 mRNA stabilization. In hypoxic p53(-/-) tumor cells, NF-κB further supported expression of MCT1 to elevate its levels. Following glucose deprivation, upregulated MCT1 in p53(-/-) cells promoted lactate import and favored cell proliferation by fuelling mitochondrial respiration. We also found that MCT1 expression was increased in human breast tumors harboring p53 mutations and coincident features of hypoxia, with higher MCT1 levels associated with poorer clinical outcomes. Together, our findings identify MCT1 as a target for p53 repression and they suggest that MCT1 elevation in p53-deficient tumors allows them to adapt to metabolic needs by facilitating lactate export or import depending on the glucose availability.