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1
de Rouffignac, C. "Quelques pas en direction du site de reconnaissance de l'ion sodium au sein des protéines de transports couplés." médecine/sciences 12, n. 10 (1996): 1136. http://dx.doi.org/10.4267/10608/636.
2
Bellot, J. P., A. Jardy e D. Ablitzer. "Simulation numérique des transports couplés au sein du puits liquide d'un lingot de titane refondu par bombardement électronique". Revue de Métallurgie 92, n. 12 (dicembre 1995): 1399–410. http://dx.doi.org/10.1051/metal/199592121399.
3
Grogan, Dustin F. P., e Terrence R. Nathan. "Passive versus Active Transport of Saharan Dust Aerosols by African Easterly Waves". Atmosphere 12, n. 11 (16 novembre 2021): 1509. http://dx.doi.org/10.3390/atmos12111509.
Abstract (sommario):
Theory and modeling are combined to reveal the physical and dynamical processes that control Saharan dust transport by amplifying African easterly waves (AEWs). Two cases are examined: active transport, in which the dust is radiatively coupled to the circulation; passive transport, in which the dust is radiatively decoupled from the circulation. The theory is built around a dust conservation equation for dust-coupled AEWs in zonal-mean African easterly jets. The theory predicts that, for both the passive and active cases, the dust transports will be largest where the zonal-mean dust gradients are maximized on an AEW critical surface. Whether the dust transports are largest for the radiatively passive or radiatively active case depends on the growth rate of the AEWs, which is modulated by the dust heating. The theoretical predictions are confirmed via experiments carried out with the Weather Research and Forecasting model, which is coupled to a dust conservation equation. The experiments show that the meridional dust transports dominate in the passive case, while the vertical dust transports dominate in the active case.
4
Li, Shuang, Yihu Yang e Weikai Li. "Human ferroportin mediates proton-coupled active transport of iron". Blood Advances 4, n. 19 (2 ottobre 2020): 4758–68. http://dx.doi.org/10.1182/bloodadvances.2020001864.
Abstract (sommario):
Abstract As the sole iron exporter in humans, ferroportin controls systemic iron homeostasis through exporting iron into the blood plasma. The molecular mechanism of how ferroportin exports iron under various physiological settings remains unclear. Here we found that purified ferroportin incorporated into liposomes preferentially transports Fe2+ and exhibits lower affinities of transporting other divalent metal ions. The iron transport by ferroportin is facilitated by downhill proton gradients at the same direction. Human ferroportin is also capable of transporting protons, and this activity is tightly coupled to the iron transport. Remarkably, ferroportin can conduct active transport uphill against the iron gradient, with favorable charge potential providing the driving force. Targeted mutagenesis suggests that the iron translocation site is located at the pore region of human ferroportin. Together, our studies enhance the mechanistic understanding by which human ferroportin transports iron and suggest that a combination of electrochemical gradients regulates iron export.
5
Nathan, Terrence R., Dustin F. P. Grogan e Shu-Hua Chen. "Saharan Dust Transport during the Incipient Growth Phase of African Easterly Waves". Geosciences 9, n. 9 (5 settembre 2019): 388. http://dx.doi.org/10.3390/geosciences9090388.
Abstract (sommario):
An analytical analysis is combined with numerical modeling simulations in order to expose the physical and dynamical processes that control the zonal-mean transport of Saharan mineral dust aerosols during the incipient growth phase of African easterly waves. The analytical analysis provides the theoretical basis for understanding and predicting how the waves and background flow combine to affect the zonal-mean eddy transports of dust. The analytically derived transport equations―which are valid for any wave field, irrespective of its spatial or temporal scale―predict that the eddy transports of dust are largest where the maximum in the background dust gradients coincide with a critical surface, i.e., where the Doppler-shifted frequency of the wave field vanishes. Linear simulations of the eddy dust transports are conducted using a mechanistic version of the Weather Research and Forecasting (WRF) model coupled to an interactive dust model. The simulations show that the eddy dust transports are directed down the background dust gradients and that the meridional transports of dust dominate over the vertical transports. The numerical simulations confirm the theoretical predictions. The predictions are used to explain recent statistical analyses of reanalysis data for dust-coupled African easterly waves.
6
Vellinga, Michael, e Peili Wu. "Relations between Northward Ocean and Atmosphere Energy Transports in a Coupled Climate Model". Journal of Climate 21, n. 3 (1 febbraio 2008): 561–75. http://dx.doi.org/10.1175/2007jcli1754.1.
Abstract (sommario):
Abstract The Third Hadley Centre Coupled Ocean–Atmosphere General Circulation Model (HadCM3) is used to analyze the relation between northward energy transports in the ocean and atmosphere at centennial time scales. In a transient water-hosing experiment, where suppressing the Atlantic meridional overturning circulation (MOC) causes a reduction in northward ocean heat transport of up to 0.75 PW (i.e., 75%), the atmosphere compensates by increasing its northward transport of moist static energy. This compensation is very efficient at low latitudes and near complete at the equator throughout the experiment, but is incomplete farther north across the northern midlatitude storm tracks. The change in atmosphere energy transport enables the model to find a new global-mean radiative equilibrium after 240 yr. In a perturbed physics ensemble of HadCM3 it was found that time-averaged meridional energy transports in ocean and atmosphere can act opposingly. Where model formulation causes an unbalanced mean climate state, for example, an excessive top-of-the-atmosphere radiative surplus at low latitudes, the atmosphere increases its poleward energy transport to disperse this excess. MOC and ocean poleward heat transport tend to be reduced in such model versions, and this offsets the increased poleward atmospheric transport of the low-latitude energy surplus. Model versions that are close to net radiative equilibrium also have ocean heat transport and MOC close to observed values.
7
Beneš, Libor, Rudolf Kaloč e Luboš Minář. "NEW APPROACH TO THE ANALYSIS OF THE CONTACT SURFACES OF ROLLING KINEMATIC COUPLE". TRANSPORT 25, n. 4 (31 dicembre 2010): 382–86. http://dx.doi.org/10.3846/transport.2010.47.
Abstract (sommario):
All physical processes of contact phenomenon especially a slip mechanism occur in the superficial layers related to changes in the micro/macro‐geometry of the surface. It is also the area where thermo‐mechanical processes of non‐isothermal nature arise. The persistent problems of damage to contact surfaces when being dynamically strained may only be gradually resolved using up‐to‐date metallographic methods, i.e. an experimental analysis of samples taken from the contact‐stressed areas. This paper deals with a new theoretical approach to the loading analysis of contact surfaces during rolling and gives basic information about the study on the influence of dynamical loading in the contact area with the possible occurrence of wave effects in contact with the adhesion drive of a rail vehicle (as an example). The experimental part is based on laboratory testing applying a new‐type designed device.
8
Guo, Lirong, Kaiyun Wang, Zaigang Chen, Zhiyong Shi, Kaikai Lv e Rui Zhang. "EFFECT OF LATERAL STIFFNESS OF SECONDARY SUSPENSIONS ON HEAVY-HAUL LOCOMOTIVES STABILITY DURING BRAKING BASED ON SIMULATION AND EXPERIMENT". Transport 34, n. 5 (21 novembre 2019): 548–58. http://dx.doi.org/10.3846/transport.2019.11509.
Abstract (sommario):
This paper aimed to investigate the effect of the lateral stiffness of secondary suspensions on the stability capacity and running safety of heavy-haul locomotives during braking based on the dynamic model and the field braking tests. The dynamic model of heavy-haul locomotives included two double-unit locomotives and five coupler systems. Simulation results indicate that the increasing of the lateral stiffness of secondary suspensions can improve the stability capacity and running safety of heavy-haul locomotives. Then, the field braking experiments were conducted to validate the dynamic model. Comparing the experiment results of different locomotives, the coupler and carbody yaw angles are respectively decreased by 31.8 and 29.5%, which is consistent with the simulation results. It is worthy to be noted that lateral vibration behaviour of the carbody increases with the increasing of the lateral stiffness of secondary suspensions. For the improved locomotive, the main frequency of lateral acceleration is 1…2 Hz. However, the main frequency of lateral acceleration is 0.5…1 Hz in the original locomotive tests. Moreover, the high-frequency vibration is increased, especially in 10…12.5 Hz. According to the simulation and experiment results, the reasonable lateral stiffness of secondary suspensions is 400 kN/m for the test locomotive.
9
Li, Li, Dong Zhang, Xiao-Yun Cheng, Ping Wang e Gui-Ping Wang. "A COMPOSITIONAL APPROACH FOR TRAFFIC DISTRIBUTION EVALUATION OF TRIPLE LEFT-TURN LANES FROM AN INDIVIDUAL PERSPECTIVE". Transport 36, n. 2 (4 maggio 2021): 110–22. http://dx.doi.org/10.3846/transport.2021.14676.
Abstract (sommario):
This study analysed unbalanced traffic distribution on Triple Left-Turn Lanes (TLTLs) at signalized intersections that is caused by left-turn drivers’ unequal lane preferences. To develop statistical bonding between the multilane traffic flow and individual lane choices, the lane volumes are formatted as compositional data to subject the sum-constant constraint. One-way and two-way Compositional ANalysis Of VAriance (CANOVA) models were formulated respectively to estimate the independent effect of one factor and its joint effects with other factors on the multilane traffic distribution. TLTL volume composition was the dependent variable of the models, while the factors of geometric design and traffic control that could affect left-turn drivers’ lane choice were the independent variables. Results indicate that variance of vehicle turning curve, length of the upstream segment, the location of triple left-turn sign, signal phase / cycle length, could affect the traffic distribution, and its balance could be achieved at specific levels of a factor. The joint effects of some factor couples could improve the unbalanced traffic distribution while others could not work.
10
Merryfield, William J., e George J. Boer. "Variability of Upper Pacific Ocean Overturning in a Coupled Climate Model". Journal of Climate 18, n. 5 (1 marzo 2005): 666–83. http://dx.doi.org/10.1175/jcli-3282.1.
Abstract (sommario):
Abstract Variability of subtropical cell (STC) overturning in the upper Pacific Ocean is examined in a coupled climate model in light of large observed changes in STC transport. In a 1000-yr control run, modeled STC variations are smaller than observed, but correlate in a similar way with low-frequency ENSO-like variability. In model runs that include anthropogenically forced climate change, STC pycnocline transports decrease progressively under the influence of global warming, attaining reductions of 8% by 2000 and 46% by 2100. Although the former reduction is insufficient to fully account for the apparent observed decline in STC transport over recent decades, it does suggest that global warming may have contributed to the observed changes. Analysis of coupled model results shows that STC transports play a significant role in modulating tropical Pacific Ocean heat content, and that such changes are dominated by anomalous currents advecting mean temperature, rather than by advection of temperature anomalies by mean currents.
11
Shi, Jin, Shujing Ren e Mengran Zhang. "MODEL-BASED ASSESSMENT OF LONGITUDINAL DYNAMIC PERFORMANCE AND ENERGY CONSUMPTION OF HEAVY HAUL TRAIN ON LONG-STEEP DOWNGRADES". Transport 34, n. 3 (21 marzo 2019): 250–59. http://dx.doi.org/10.3846/transport.2019.9043.
Abstract (sommario):
Longitudinal dynamics performance and energy consumption of heavy haul train should be considered in the design of heavy haul railway profile of long-steep downgrades. A quantitative analytical tool is developed to assess the longitudinal dynamic performance and energy consumption of heavy haul trains with large axle loads on grades with different longitudinal profiles, including a longitudinal dynamic model of the train and a method of calculating the energy consumption during the operation of heavy haul train. The model is then preliminarily validated by the data of coupler force collected in two comprehensive tests. Finally, the proposed analytical tool is used to assess the designed longitudinal track profile of a long-deep downgrade segment of the central south heavy haul railway of Shanxi (China).
12
Ahmmed, Bulbul, Maruti Kumar Mudunuru, Satish Karra, Scott C. James, Hari Viswanathan e John A. Dunbar. "PFLOTRAN-SIP: A PFLOTRAN Module for Simulating Spectral-Induced Polarization of Electrical Impedance Data". Energies 13, n. 24 (11 dicembre 2020): 6552. http://dx.doi.org/10.3390/en13246552.
Abstract (sommario):
Spectral induced polarization (SIP) is a non-intrusive geophysical method that collects chargeability information (the ability of a material to retain charge) in the time domain or its phase shift in the frequency domain. Although SIP is a temporal method, it cannot measure the dynamics of flow and solute/species transport in the subsurface over long times (i.e., 10–100 s of years). Data collected with the SIP technique need to be coupled with fluid flow and reactive-transport models in order to capture long-term dynamics. To address this challenge, PFLOTRAN-SIP was built to couple SIP data to fluid flow and solute transport processes. Specifically, this framework couples the subsurface flow and transport simulator PFLOTRAN and geoelectrical simulator E4D without sacrificing computational performance. PFLOTRAN solves the coupled flow and solute-transport process models in order to estimate solute concentrations, which were used in Archie’s model to compute bulk electrical conductivities at near-zero frequency. These bulk electrical conductivities were modified while using the Cole–Cole model to account for frequency dependence. Using the estimated frequency-dependent bulk conductivities, E4D simulated the real and complex electrical potential signals for selected frequencies for SIP. These frequency-dependent bulk conductivities contain information that is relevant to geochemical changes in the system. This study demonstrated that the PFLOTRAN-SIP framework is able to detect the presence of a tracer in the subsurface. SIP offers a significant benefit over ERT in the form of greater information content. It provided multiple datasets at different frequencies that better constrained the tracer distribution in the subsurface. Consequently, this framework allows for practitioners of environmental hydrogeophysics and biogeophysics to monitor the subsurface with improved resolution.
13
Chen, Zaigang, Jie Zhang, Kaiyun Wang e Pengfei Liu. "NONLINEAR DYNAMIC RESPONSES OF LOCOMOTIVE EXCITED BY RAIL CORRUGATION AND GEAR TIME-VARYING MESH STIFFNESS". Transport 37, n. 6 (31 dicembre 2022): 383–97. http://dx.doi.org/10.3846/transport.2022.17065.
Abstract (sommario):
Rail corrugation is usually generated in modern railway transportations, such as high-speed railway, urban railway, and heavy-haul railway. It is one of the major excitations to the wheel–rail dynamic interaction, which will cause extra vibration and noise, failures, or even risk of derailment to the vehicle and its components. A dynamics model of a heavy-haul locomotive considering the traction power from the electric motor to the wheelset through gear transmission is employed to investigate the nonlinear dynamic responses of the locomotive. This dynamics model couples the motions of the vehicle, the track, and the gear transmission together. In this dynamics model, excitations from the rail corrugation, the nonlinear wheel–rail contact, the time-varying mesh stiffness, and the nonlinear gear backlash are considered. Then, numerical simulations are performed to reveal the dynamic responses of the locomotive. The calculated results indicate that different nonlinear phenomenon can be observed under the excitation of the rail corrugation with different amplitude and wavelength. The high frequency vibrations excited by the time-varying mesh stiffness are usually modulated by the low frequency vibrations caused by the rail corrugation. However, this is likely to vanish under the chaotic conditions with some corrugation wavelength. The vibration level of the vehicle and the gear transmission increases generally with the corrugation amplitude. However, some corrugation lengths have been found to be more responsible for the vibration of the dynamics system, which should be concerned greatly during the locomotive operation. Meanwhile, involvement of gear transmission systems will cause different dynamic responses between the wheelsets under rail corrugation and gear mesh excitations.
14
Graffino, Giorgio, Riccardo Farneti e Fred Kucharski. "Low-frequency variability of the Pacific Subtropical Cells as reproduced by coupled models and ocean reanalyses". Climate Dynamics 56, n. 9-10 (26 gennaio 2021): 3231–54. http://dx.doi.org/10.1007/s00382-021-05639-6.
Abstract (sommario):
AbstractLow-frequency variability of the Pacific Subtropical Cells (STCs) is investigated using outputs from several models included in the two latest phases of Coupled Model Intercomparison Project (CMIP), CMIP5 and CMIP6, as well as ocean reanalysis products. Our analysis focuses on historical simulations and an idealised future scenario integration. Mass and heat transport diagnostics are employed to assess how coupled models and ocean reanalyses reproduce Pacific STCs total and interior transport convergence at the equator and their relationship with equatorial Pacific sea surface temperature (SST). Trends of mass and heat transport are also evaluated, in order to study how the STCs are expected to change in a warming climate. A large spread is obtained across models in simulated mass transports, confirming that coupled models do not agree on reproducing observed Pacific STCs dynamics, with very limited improvement by CMIP6 models. Compared to ocean reanalysis products, coupled models tend to underestimate the STCs interior transport convergence, and are less efficient on propagating the signal generated by the subtropical wind stress towards the equator. Also, mass transport obtained from ocean reanalyses exhibit larger variability, and these products also better reproduce the STCs-SST relationship. Future scenario simulations suggest a weakening (strengthening) of the heat transport by the North (South) Pacific cell under warmer conditions, with a general agreement across models. Equatorward mass transport trends do not confirm this for total and interior components, but they do for the western boundary component.
15
de Saint-Jean, Maud, Vanessa Delfosse, Dominique Douguet, Gaëtan Chicanne, Bernard Payrastre, William Bourguet, Bruno Antonny e Guillaume Drin. "Osh4p exchanges sterols for phosphatidylinositol 4-phosphate between lipid bilayers". Journal of Cell Biology 195, n. 6 (12 dicembre 2011): 965–78. http://dx.doi.org/10.1083/jcb.201104062.
Abstract (sommario):
Osh/Orp proteins transport sterols between organelles and are involved in phosphoinositide metabolism. The link between these two aspects remains elusive. Using novel assays, we address the influence of membrane composition on the ability of Osh4p/Kes1p to extract, deliver, or transport dehydroergosterol (DHE). Surprisingly, phosphatidylinositol 4-phosphate (PI(4)P) specifically inhibited DHE extraction because PI(4)P was itself efficiently extracted by Osh4p. We solve the structure of the Osh4p–PI(4)P complex and reveal how Osh4p selectively substitutes PI(4)P for sterol. Last, we show that Osh4p quickly exchanges DHE for PI(4)P and, thereby, can transport these two lipids between membranes along opposite routes. These results suggest a model in which Osh4p transports sterol from the ER to late compartments pinpointed by PI(4)P and, in turn, transports PI(4)P backward. Coupled to PI(4)P metabolism, this transport cycle would create sterol gradients. Because the residues that recognize PI(4)P are conserved in Osh4p homologues, other Osh/Orp are potential sterol/phosphoinositol phosphate exchangers.
16
Treguier, Anne Marie, Pierre Mathiot, Tim Graham, Dan Copsey, Camille Lique e Jean Sterlin. "Heat Balance in the Nordic Seas in a Global 1/12° Coupled Model". Journal of Climate 34, n. 1 (gennaio 2021): 89–106. http://dx.doi.org/10.1175/jcli-d-20-0063.1.
Abstract (sommario):
AbstractThe Nordic seas are a gateway to the Arctic Ocean, where Atlantic water undergoes a strong cooling during its transit. Here we investigate the heat balance of these regions in the high-resolution Met Office Global Coupled Model GC3 with a 1/12° grid. The GC3 model reproduces the contrasted ice conditions and ocean heat loss between the eastern and western regions of the Nordic seas. In the west (Greenland and Iceland seas), the heat loss experienced by the ocean is stronger than the atmospheric heat gain, because of the cooling by ice melt. The latter is a major contribution to the heat loss over the path of the East Greenland Current and west of Svalbard. In the model, surface fluxes balance the convergence of heat in each of the eastern and western regions. The net east–west heat exchange, integrated from Fram Strait to Iceland, is relatively small: the westward heat transport of the Return Atlantic Current over Knipovich Ridge balances the eastward heat transport by the East Icelandic Current. Time fluctuations, including eddies, are a significant contribution to the net heat transports. The eddy flux represents about 20% of the total heat transport in Denmark Strait and across Knipovich Ridge. The coupled ocean–atmosphere–ice model may overestimate the heat imported from the Atlantic and exported to the Arctic by 10% or 15%. This confirms the tendency toward higher northward heat transports as model resolution is refined, which will impact scenarios of future climate.
17
Harrington, Gregory N., Katherine E. Dibley, Raymond J. Ritchie, Christina E. Offler e John W. Patrick. "Hexose uptake by developing cotyledons of Vicia faba: physiological evidence for transporters of differing affinities and specificities". Functional Plant Biology 32, n. 11 (2005): 987. http://dx.doi.org/10.1071/fp05081.
Abstract (sommario):
Cotyledons of broad bean (Vicia faba L.) develop in an apoplasmic environment that shifts in composition from one dominated by hexoses to one dominated by sucrose. During the latter phase of development, sucrose / H+ symporter activity and expression is restricted to cotyledon epidermal transfer cell complexes that support sucrose fluxes that are 8.5-fold higher than those exhibited by the storage parenchyma. In contrast, the flux difference between these cotyledon tissues is only 1.7-fold for hexoses. Glucose and fructose uptake was shown to be sensitive to PCMBS and phloridzin, both of which slow H+-sugar transport. A low Km (or high affinity transporter, HAT) mechanism transports glucose and glucose-analogues exclusively. No HAT system for fructose could be found. A high Km (low affinity transporter, LAT) mechanism transports a broader range of hexoses, including glucose and fructose. Consistent with glucose and fructose transport being H+-coupled, their uptake was inhibited by dissipating the proton motive force (pmf) by treating cotyledons with carbonyl cyanide m-chlorophenol hydrazone, propionic acid or tetraphenylphosphonium ion. Erythrosin B inhibited hexose uptake, indicating a role for the P-type H+-ATPase in establishing the pmf. It is concluded that H+-coupled glucose and fructose transport mechanisms occur at plasma membranes of dermal transfer cell complexes and storage parenchyma cells. These transport mechanisms are active during pre- and storage phases of cotyledon development. However, hexose symport only makes a quantitative contribution to cotyledon biomass gain during the pre-storage stage of development.
18
Liu, Zhengyu, Chengfei He e Feiyu Lu. "Local and Remote Responses of Atmospheric and Oceanic Heat Transports to Climate Forcing: Compensation versus Collaboration". Journal of Climate 31, n. 16 (agosto 2018): 6445–60. http://dx.doi.org/10.1175/jcli-d-17-0675.1.
Abstract (sommario):
We present a theoretical study on local and remote responses of atmosphere and ocean meridional heat transports (AHT and OHT, respectively) to climate forcing in a coupled energy balance model. We show that, in general, a surface heat flux forces opposite AHT and OHT responses in the so-called compensation response, while a net heat flux into the coupled system forces AHT and OHT responses of the same direction in the so-called collaboration response. Furthermore, unless the oceanic thermohaline circulation is significantly changed, a remote climate response far away from the forcing region tends to be dominated by the collaboration response, because of the effective propagation of a coupled ocean–atmosphere energy transport mode of collaboration structure. The relevance of our theory to previous CGCM experiments is also discussed. Our theoretical result provides a guideline for understanding of the response of heat transports and the associated climate changes.
19
Thomas, Matthew D., Agatha M. De Boer, Helen L. Johnson e David P. Stevens. "Spatial and Temporal Scales of Sverdrup Balance*". Journal of Physical Oceanography 44, n. 10 (1 ottobre 2014): 2644–60. http://dx.doi.org/10.1175/jpo-d-13-0192.1.
Abstract (sommario):
Abstract Sverdrup balance underlies much of the theory of ocean circulation and provides a potential tool for describing the interior ocean transport from only the wind stress. Using both a model state estimate and an eddy-permitting coupled climate model, this study assesses to what extent and over what spatial and temporal scales Sverdrup balance describes the meridional transport. The authors find that Sverdrup balance holds to first order in the interior subtropical ocean when considered at spatial scales greater than approximately 5°. Outside the subtropics, in western boundary currents and at short spatial scales, significant departures occur due to failures in both the assumptions that there is a level of no motion at some depth and that the vorticity equation is linear. Despite the ocean transport adjustment occurring on time scales consistent with the basin-crossing times for Rossby waves, as predicted by theory, Sverdrup balance gives a useful measure of the subtropical circulation after only a few years. This is because the interannual transport variability is small compared to the mean transports. The vorticity input to the deep ocean by the interaction between deep currents and topography is found to be very large in both models. These deep transports, however, are separated from upper-layer transports that are in Sverdrup balance when considered over large scales.
20
Vinson, Valda. "Coupled transport". Science 366, n. 6464 (24 ottobre 2019): 440.16–442. http://dx.doi.org/10.1126/science.366.6464.440-p.
21
Bossuyt, X., e N. Blanckaert. "Mechanism of stimulation of microsomal UDP-glucuronosyltransferase by UDP-N-acetylglucosamine". Biochemical Journal 305, n. 1 (1 gennaio 1995): 321–28. http://dx.doi.org/10.1042/bj3050321.
Abstract (sommario):
We propose the existence in rat liver endoplasmic reticulum (ER) of two asymmetric carrier systems. One system couples UDP-N-acetylglucosamine (UDPGlcNAc) transport to UDP-glucuronic acid (UDPGlcA) transport. When UDPGlcNAc was presented at the cytosolic side of the ER, it then acted as a weak inhibitor of UDPGlcA uptake. By contrast, UDPGlcNAc produced a forceful trans-stimulation of microsomal UDPGlcA uptake when it was present within the lumen of the ER. Likewise, cytosolic UDPGlcA strongly trans-stimulated efflux of intravesicular UDPGlcNAc, whereas cytosolic UDPGlcNAc was ineffective in trans-stimulating efflux of UDPGlcA. A second asymmetric carrier system couples UDPGlcNAc transport to UMP transport. Microsomal UDPGlcNAc influx was markedly stimulated by UMP present inside the microsomes. Such stimulation was only apparent when microsomes had been preincubated and thereby preloaded with UMP, indicating that UMP exerted its effect on UDPGlcNAc uptake by trans-stimulation from the lumenal side of the ER membrane. Contrariwise, extravesicular UMP only minimally trans-stimulated efflux of intramicrosomal UDPGlcNAc. It is widely accepted that UDPGlcNAc acts as a physiological activator of hepatic glucuronidation, but the mechanism of this effect has remained elusive. Based on our findings, we propose a model in which the interaction of two asymmetric transport pathways, i.e. UDPGlcA influx coupled to UDPGlcNAc efflux and UDPGlcNAc influx coupled to UMP efflux, combined with intravesicular metabolism of UDPGlcA, forms a mechanism that leads to stimulation of glucuronidation by UDPGlcNAc.
22
Nikolaeva, O. V. "Surface albedo retrieval based on high spatial resolution data". Computer Optics 46, n. 3 (giugno 2022): 406–14. http://dx.doi.org/10.18287/2412-6179-co-1046.
Abstract (sommario):
The paper aims to compare the accuracy of three methods of solving the atmospheric correction problem for a Lambertian surface using high spatial resolution remotely sensed data. Three couples of formulas are presented. Each couple contains a formula for expressing the reflectance in a target pixel at the upper boundary of the atmosphere via albedo in target and adjacent pixels of the surface and a formula for the surface albedo in a target pixel via reflectances. The derivation of each couple of formulas is given. Derivation conditions are presented. Formulas of only one couple are found by solving the radiation transport equation in 1D geometry. Formulas of two other couples include values obtained by solving the transport equation in 3D geometry. Results of testing the accuracy of all formulas when solving an atmospheric correction problem on data of high (30 m) spatial resolution are given. Problems with aerosol optical depths from 0.2 to 2 for a wavelength of (lambda)=0.55(mu)m for all possible albedo values (from 0.1 to 0.9) in target and adjacent pixels are considered. It is shown that only one couple of formulas out of the three gives high accuracy under any condition. Formulas of the two other couples give sufficient accuracy (with less than 10 % error) only for a small value of the aerosol optical depth and a small difference of the albedo of the target and adjacent pixels.
23
Macara, Ian G. "Nuclear transport: Randy couples". Current Biology 9, n. 12 (giugno 1999): R436—R439. http://dx.doi.org/10.1016/s0960-9822(99)80275-9.
24
Wang, Hong, You-Jun Fei, Vadivel Ganapathy e Frederick H. Leibach. "Electrophysiological characteristics of the proton-coupled peptide transporter PEPT2 cloned from rat brain". American Journal of Physiology-Cell Physiology 275, n. 4 (1 ottobre 1998): C967—C975. http://dx.doi.org/10.1152/ajpcell.1998.275.4.c967.
Abstract (sommario):
We have cloned a peptide transporter from rat brain and found it to be identical to rat kidney PEPT2. In the present study we characterize the transport function of the rat brain PEPT2, with special emphasis on electrophysiological properties and interaction with N-acetyl-l-aspartyl-l-glutamate (NAAG). When heterologously expressed in HeLa cells and in SK-N-SH cells, PEPT2 transports several dipeptides but not free amino acids in the presence of a proton gradient. NAAG competes with other peptides for the PEPT2-mediated transport process. When PEPT2 is expressed in Xenopus laevis oocytes, substrate-induced inward currents are detectable with dipeptides of differing charge in the presence of a proton gradient. Proton activation kinetics are similar for differently charged peptides. NAAG is a transportable substrate for PEPT2, as evidenced by NAAG-induced currents. The Hill coefficient for protons for the activation of the transport of differently charged peptides, including NAAG, is 1. Although the peptide-to-proton stoichiometry for negatively charged peptides is 1, the transport nonetheless is associated with transfer of positive charge into the oocyte, as indicated by peptide-induced inward currents.
25
Farneti, Riccardo, e Geoffrey K. Vallis. "Meridional Energy Transport in the Coupled Atmosphere–Ocean System: Compensation and Partitioning". Journal of Climate 26, n. 18 (9 settembre 2013): 7151–66. http://dx.doi.org/10.1175/jcli-d-12-00133.1.
Abstract (sommario):
Abstract The variability and compensation of the meridional energy transport in the atmosphere and ocean are examined with the state-of-the-art GFDL Climate Model, version 2.1 (CM2.1), and the GFDL Intermediate Complexity Coupled Model (ICCM). On decadal time scales, a high degree of compensation between the energy transport in the atmosphere (AHT) and ocean (OHT) is found in the North Atlantic. The variability of the total or planetary heat transport (PHT) is much smaller than the variability in either AHT or OHT alone, a feature referred to as “Bjerknes compensation.” Natural decadal variability stems from the Atlantic meridional overturning circulation (AMOC), which leads OHT variability. The PHT is positively correlated with the OHT, implying that the atmosphere is compensating, but imperfectly, for variations in ocean transport. Because of the fundamental role of the AMOC in generating the decadal OHT anomalies, Bjerknes compensation is expected to be active only in coupled models with a low-frequency AMOC spectral peak. The AHT and the transport in the oceanic gyres are positively correlated because the gyre transport responds to the atmospheric winds, thereby militating against long-term variability involving the wind-driven flow. Moisture and sensible heat transports in the atmosphere are also positively correlated at decadal time scales. The authors further explore the mechanisms and degree of compensation with a simple, diffusive, two-layer energy balance model. Taken together, these results suggest that compensation can be interpreted as arising from the highly efficient nature of the meridional energy transport in the atmosphere responding to ocean variability rather than any a priori need for the top-of-atmosphere radiation budget to be fixed.
26
Baehr, J., S. Cunnningham, H. Haak, P. Heimbach, T. Kanzow e J. Marotzke. "Observed and simulated estimates of the meridional overturning circulation at 26.5° N in the Atlantic". Ocean Science 5, n. 4 (16 novembre 2009): 575–89. http://dx.doi.org/10.5194/os-5-575-2009.
Abstract (sommario):
Abstract. Daily timeseries of the meridional overturning circulation (MOC) estimated from the UK/US RAPID/MOCHA array at 26.5° N in the Atlantic are used to evaluate the MOC as simulated in two global circulation models: (I) an 8-member ensemble of the coupled climate model ECHAM5/MPI-OM, and (II) the ECCO-GODAE state estimate. In ECHAM5/MPI-OM, we find that the observed and simulated MOC have a similar variability and time-mean within the 99% confidence interval. In ECCO-GODAE, we find that the observed and simulated MOC show a significant correlation within the 99% confidence interval. To investigate the contribution of the different transport components, the MOC is decomposed into Florida Current, Ekman and mid-ocean transports. In both models, the mid-ocean transport is closely approximated by the residual of the MOC minus Florida Current and Ekman transports. As the models conserve volume by definition, future comparisons of the RAPID/MOCHA mid-ocean transport should be done against the residual transport in the models. The similarity in the variance and the correlation between the RAPID/MOCHA, and respectively ECHAM5/MPI-OM and ECCO-GODAE MOC estimates at 26.5° N is encouraging in the context of estimating (natural) variability in climate simulations and its use in climate change signal-to-noise detection analyses. Enhanced confidence in simulated hydrographic and transport variability will require longer observational time series.
27
Zhou, Hui, Dongliang Yuan, Lina Yang, Xiang Li e William Dewar. "Decadal Variability of the Meridional Geostrophic Transport in the Upper Tropical North Pacific Ocean". Journal of Climate 31, n. 15 (agosto 2018): 5891–910. http://dx.doi.org/10.1175/jcli-d-17-0639.1.
Abstract (sommario):
The meridional geostrophic transport (MGT) in the interior tropical North Pacific Ocean is estimated based on global ocean heat and salt content data. The decadal variations of the zonally and vertically integrated MGT in the tropical North Pacific Ocean are found to precede the Pacific decadal oscillation (PDO) by 1–3 years. The dynamics of the MGT are analyzed based on Sverdrup theory. It is found that the total meridional transport variability (MGT plus Ekman) is dominated by the MGT variability having positive correlations with the PDO index. The Sverdrup transports differ from the total meridional transport significantly and have insignificant correlations with PDO index, suggesting that the MGT variability is not controlled by the Sverdrup dynamics. In comparison, the simulated meridional transport variability in the models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) and the Ocean General Circulation Model for the Earth Simulator are dominated by the Sverdrup transports, having insignificant correlations with the simulated PDO indices. The comparison suggests that the non-Sverdrup component in the MGT is important for the predictability of PDO and that significant deficiencies exist in these models in simulating a realistic structure of the tropical ocean gyre variability and predicting the decadal climate variations associated with it.
28
Yang, Qianzi, Yingying Zhao, Qin Wen, Jie Yao e Haijun Yang. "Understanding Bjerknes Compensation in Meridional Heat Transports and the Role of Freshwater in a Warming Climate". Journal of Climate 31, n. 12 (giugno 2018): 4791–806. http://dx.doi.org/10.1175/jcli-d-17-0587.1.
Abstract (sommario):
The Bjerknes compensation (BJC) under global warming is studied using a simple box model and a coupled Earth system model. The BJC states the out-of-phase changes in the meridional atmosphere and ocean heat transports. Results suggest that the BJC can occur during the transient period of global warming. During the transient period, the sea ice melting in the high latitudes can cause a significant weakening of the Atlantic meridional overturning circulation (AMOC), resulting in a cooling in the North Atlantic. The meridional contrast of sea surface temperature would be enhanced, and this can eventually enhance the Hadley cell and storm-track activities in the Northern Hemisphere. Accompanied by changes in both ocean and atmosphere circulations, the northward ocean heat transport in the Atlantic is decreased while the northward atmosphere heat transport is increased, and the BJC occurs in the Northern Hemisphere. Once the freshwater influx into the North Atlantic Ocean stops, or the ocean even loses freshwater because of strong heating in the high latitudes, the AMOC would recover. Both the atmosphere and ocean heat transports would be enhanced, and they can eventually recover to the state of the control run, leading to the BJC to become invalid. The above processes are clearly demonstrated in the coupled model CO2 experiment. Since it is difficult to separate the freshwater effect from the heating effect in the coupled model, a simple box model is used to understand the BJC mechanism and freshwater’s role under global warming. In a warming climate, the freshwater flux into the ocean can cool the global surface temperature, mitigating the temperature rise. Box model experiments indicate clearly that it is the freshwater flux into the North Atlantic that causes out-of-phase changes in the atmosphere and ocean heat transports, which eventually plays a stabilizing role in global climate change.
29
Shaffrey, Len, e Rowan Sutton. "Bjerknes Compensation and the Decadal Variability of the Energy Transports in a Coupled Climate Model". Journal of Climate 19, n. 7 (1 aprile 2006): 1167–81. http://dx.doi.org/10.1175/jcli3652.1.
Abstract (sommario):
Abstract In the 1960s, Jacob Bjerknes suggested that if the top-of-the-atmosphere (TOA) fluxes and the oceanic heat storage did not vary too much, then the total energy transport by the climate system would not vary too much either. This implies that any large anomalies of oceanic and atmospheric energy transport should be equal and opposite. This simple scenario has become known as Bjerknes compensation. A long control run of the Third Hadley Centre Coupled Ocean–Atmosphere General Circulation Model (HadCM3) has been investigated. It was found that northern extratropical decadal anomalies of atmospheric and oceanic energy transports are significantly anticorrelated and have similar magnitudes, which is consistent with the predictions of Bjerknes compensation. The degree of compensation in the northern extratropics was found to increase with increasing time scale. Bjerknes compensation did not occur in the Tropics, primarily as large changes in the surface fluxes were associated with large changes in the TOA fluxes. In the ocean, the decadal variability of the energy transport is associated with fluctuations in the meridional overturning circulation in the Atlantic Ocean. A stronger Atlantic Ocean energy transport leads to strong warming of surface temperatures in the Greenland–Iceland–Norwegian (GIN) Seas, which results in a reduced equator-to-pole surface temperature gradient and reduced atmospheric baroclinicity. It is argued that a stronger Atlantic Ocean energy transport leads to a weakened atmospheric transient energy transport.
30
Zhang, Fengying, Zijun Zhang, Yali Zhao, Chao Du, Yong Li, Jiaqi Gao, Xiaobo Ren, Teng Ma, Boqiong Li e Yuxiang Bu. "Redox-Regulated Magnetic Conversions between Ferro- and Antiferromagnetism in Organic Nitroxide Diradicals". Molecules 28, n. 17 (24 agosto 2023): 6232. http://dx.doi.org/10.3390/molecules28176232.
Abstract (sommario):
Redox-induced magnetic transformation in organic diradicals is an appealing phenomenon. In this study, we theoretically designed twelve couples of diradicals in which two nitroxide (NO) radical groups are connected to the redox-active couplers including p-benzoquinonyl, 1,4-naphthoquinyl, 9,10-anthraquinonyl, naphthacene-5,12-dione, pentacene-6,13-dione, hexacene-6,15-dione, pyrazinyl, quinoxalinyl, phenazinyl, 5,12-diazanaphthacene, 6,13-diazapentacene, and 6,15-diazahexacene. As evidenced at both the B3LYP and M06-2X levels of theory, the calculations reveal that the magnetic reversal can take place from ferromagnetism to antiferromagnetism, or vice versa, by means of redox method in these designed organic magnetic molecules. It was observed that p-benzoquinonyl, 1,4-naphthoquinyl, 9,10-anthraquinonyl, naphthacene-5,12-dione, pentacene-6,13-dione, and hexacene-6,15-dione-bridged NO diradicals produce antiferromagnetism while their dihydrogenated counterparts exhibit ferromagnetism. Similarly, pyrazinyl, quinoxalinyl, phenazinyl, 5,12-diazanaphthacene, 6,13-diazapentacene, and 6,15-diazahexacene-bridged NO diradicals present ferromagnetism while their dihydrogenated counterparts show antiferromagnetism. The differences in the magnetic behaviors and magnetic magnitudes of each of the twelve couples of diradicals could be attributed to their distinctly different spin-interacting pathways. It was found that the nature of the coupler and the length of the coupling path are important factors in controlling the magnitude of the magnetic exchange coupling constant J. Specifically, smaller HOMO-LUMO (HOMO: highest occupied molecular orbital, LUMO: lowest unoccupied molecular orbital) gaps of the couplers and shorter coupler lengths, as well as shorter linking bond lengths, can attain stronger magnetic interactions. In addition, a diradical with an extensively π-conjugated structure is beneficial to spin transport and can effectively promote magnetic coupling, yielding a large |J| accordingly. That is, a larger spin polarization can give rise to a stronger magnetic interaction. The sign of J for these studied diradicals can be predicted from the spin alternation rule, the shape of the singly occupied molecular orbitals (SOMOs), and the SOMO-SOMO energy gaps of the triplet state. This study paves the way for the rational design of magnetic molecular switches.
31
Bucci, Mirella. "Uncoupling coupled transport". Nature Chemical Biology 13, n. 4 (aprile 2017): 343. http://dx.doi.org/10.1038/nchembio.2351.
32
Baehr, J., S. Cunnningham, H. Haak, P. Heimbach, T. Kanzow e J. Marotzke. "Observed and simulated estimates of the meridional overturning circulation at 26.5° N in the Atlantic". Ocean Science Discussions 6, n. 2 (1 luglio 2009): 1333–67. http://dx.doi.org/10.5194/osd-6-1333-2009.
Abstract (sommario):
Abstract. Daily timeseries of the meridional overturning circulation (MOC) estimated from the UK/US RAPID/MOCHA array at 26.5° N in the Atlantic are used to evaluate the MOC as simulated in two global circulation models: (i) an 8-member ensemble of the coupled climate model ECHAM5/MPI-OM, and (ii) the ECCO-GODAE state estimate. In ECHAM5/MPI-OM, we find that the observed and simulated MOC have a similar variability and time-mean within the 99 percent confidence interval. In ECCO-GODAE, we find that the observed and simulated MOC show a significant correlation within the 99 percent confidence interval. To investigate the contribution of the different transport components, the MOC is decomposed into Florida Current, Ekman and upper mid-ocean geostrophic transports. In both models, the mid-ocean transport is closely approximated by the residual of the MOC minus Florida Current and Ekman transports. As the models conserve volume by definition, future comparisons of the RAPID/MOCHA mid-ocean transport should be done against the residual transport in the models. The similarity in the variance and the correlation between the RAPID/MOCHA, and respectively ECHAM5/MPI-OM and ECCO-GODAE MOC estimates at 26.5° N is encouraging in the context of estimating (natural) variability in climate simulations and its use in climate change signal-to-noise detection analyses. Enhanced confidence in simulated hydrographic and transport variability will require longer observational time series.
33
Taghikhani, Kasra, Alexis Dubois, John R. Berger, Sandrine Ricote, Huayang Zhu e Robert J. Kee. "Modeling Electro-Chemo-Mechanical Behaviors within the Dense BaZr0.8Y0.2O3−δ Protonic-Ceramic Membrane in a Long Tubular Electrochemical Cell". Membranes 11, n. 6 (22 maggio 2021): 378. http://dx.doi.org/10.3390/membranes11060378.
Abstract (sommario):
This paper reports an extended Nernst–Planck computational model that couples charged-defect transport and stress in tubular electrochemical cell with a ceramic proton-conducting membrane. The model is particularly concerned with coupled chemo-mechanical behaviors, including how electrochemical phenomena affect internal stresses and vice versa. The computational model predicts transient and steady-state defect concentrations, fluxes, stresses within a thin BaZr0.8Y0.2O3−δ (BZY20) membrane. Depending on the polarization (i.e., imposed current density), the model predicts performance as a fuel cell or an electrolyzer. A sensitivity analysis reveals the importance of thermodynamic and transport properties, which are often not readily available.
34
Linton, S. M., e M. J. O'Donnell. "Novel aspects of the transport of organic anions by the malpighian tubules of Drosophila melanogaster". Journal of Experimental Biology 203, n. 23 (1 dicembre 2000): 3575–84. http://dx.doi.org/10.1242/jeb.203.23.3575.
Abstract (sommario):
Para-aminohippuric acid (PAH) is a negatively charged organic ion that can pass across the epithelium of Malpighian tubules. Its mode of transport was studied in Malpighian tubules of Drosophila melanogaster. PAH transport was an active process, with a K(m) of 2. 74 mmol l(−)(1) and a V(max) of 88.8 pmol min(−)(1). Tubules had a low passive permeability to PAH, but PAH transport rates (832 nmol min(−)(1)mm(2)) and concentrative ability ([PAH](secreted fluid):[PAH](bath)=81.2) were the highest measured to date for insects. Competition experiments indicated that there were two organic anion transporters, one that transports carboxylate compounds, such as PAH and fluorescein, and another that transports sulphonates, such as amaranth and Indigo Carmine. PAH transport appears to be maximal in vivo because the rate of transport by isolated tubules is not increased when these are challenged with cyclic AMP, cyclic GMP, leucokinin I or staurosporine. Basolateral PAH transport was inhibited by ouabain and dependent on the Na(+) gradient. The Malpighian tubules appeared not to possess an organic acid/ α -keto acid exchanger because PAH accumulation was not affected by low concentrations (100 μmol l(−)(1)) of α -keto acids (α -ketoglutarate, glutarate, citrate and succinate) or the activity of phosphokinase C. PAH transport may be directly coupled to the Na(+) gradient, perhaps via Na(+)/organic acid cotransport. Fluorescence microscopy showed that transport of the carboxylate fluorescein was confined to the principal cells of the main (secretory) segment and all the cells of the lower (reabsorptive) segment. Organic anions were transported across the cytoplasm of the principal cells both by diffusion and in vesicles. The accumulation of punctate fluorescence in the lumen is consistent with exocytosis of the cytoplasmic vesicles. Apical PAH transport was independent of the apical membrane potential and may not occur by an electrodiffusive mechanism.
35
Saumon, G., e G. Basset. "Electrolyte and fluid transport across the mature alveolar epithelium". Journal of Applied Physiology 74, n. 1 (1 gennaio 1993): 1–15. http://dx.doi.org/10.1152/jappl.1993.74.1.1.
Abstract (sommario):
The lungs must be kept "dry" for efficient gas exchange. The mechanisms that contribute to clear alveoli from fetal lung fluid at birth are still present during adult life and allow recovery from alveolar flooding. It has recently been shown with the use of different approaches in vitro, as well as in vivo, that alveolar epithelium performs solute-coupled fluid transport. Fluid absorption from alveoli occurs chiefly as a result of active transepithelial Na+ transport. The mechanisms of Na+ transport have been partly elucidated; Na+ enters alveolar cells through apical Na+ channels and Na(+)-coupled solute transporters and is pumped out at the basolateral membrane by a Na(+)-K(+)-adenosinetriphosphatase (ATPase). Transepithelial Na+ transport and fluid absorption are stimulated by beta-adrenergic agonists, with adenosine 3',5'-cyclic monophosphate being the likely intracellular second messenger. K+ is probably secreted into alveoli because its concentration in the epithelial lining fluid is larger than expected for passive distribution. K+ channels have been described that, in conjunction with Na(+)-K(+)-ATP-ase, might provide pathways for active transport. Active proton secretion or bicarbonate absorption have been reported, which may explain the low pH of the alveolar epithelial lining fluid. It is probable that active solute transports are the main determinants of epithelial lining fluid depth and composition. A challenge for the future is to understand how this homeostasis is achieved.
36
Kehres, David G., Anuradha Janakiraman, James M. Slauch e Michael E. Maguire. "SitABCD Is the Alkaline Mn2+ Transporter of Salmonella enterica Serovar Typhimurium". Journal of Bacteriology 184, n. 12 (15 giugno 2002): 3159–66. http://dx.doi.org/10.1128/jb.184.12.3159-3166.2002.
Abstract (sommario):
ABSTRACT MntH, a bacterial homolog of the mammalian natural resistance-associated macrophage protein 1 (Nramp1), is a primary Mn2+ transporter of Salmonella enterica serovar Typhimurium and Escherichia coli. S. enterica serovar Typhimurium MntH expression is important for full virulence; however, strains carrying an mntH deletion are only partially attenuated and display no obvious signs of Mn2+ deficiency. We noted that promoter sequences for mntH and for the putative Fe2+ transporter sitABCD appeared to have the same regulatory element responsive to Mn2+ and so hypothesized that sitABCD could transport Mn2+ with high affinity. We have now characterized transport by SitABCD in S. enterica serovar Typhimurium using 54Mn2+ and 55Fe2+ and compared its properties to those of MntH. SitABCD mediates the influx of Mn2+ with an apparent affinity (Ka ) identical to that of MntH, 0.1 μM. It also transports Fe2+ but with a Ka 30 to 100 times lower, 3 to 10 μM. Inhibition of 54Mn2+ transport by Fe2+ and of 55Fe2+ transport by Mn2+ gave inhibition constants comparable to each cation's Ka for influx. Since micromolar concentrations of free Fe2+ are improbable in a biological system, we conclude that SitABCD functions physiologically as a Mn2+ transporter. The cation inhibition profiles of SitABCD and MntH are surprisingly similar for two structurally and energetically unrelated transporters, with a Cd2+ Ki of ≈1 μM and a Co2+ Ki of ≈20 μM and with Ni2+, Cu2+, and Fe3+ inhibiting both transporters only at concentrations of >0.1 mM. The one difference is that Zn2+ exhibits potent inhibition of SitABCD (Ki = 1 to 3 μM) but inhibits MntH weakly (Ki > 50 μM). We have previously shown that MntH transports Mn2+ most effectively under acidic conditions. In sharp contrast, SitABCD has almost no transport capacity at acid pHs and optimally transports Mn2+ at slightly alkaline pHs. Overall, coupled with evidence that each transporter is multiply but distinctly regulated at the transcriptional level, the distinct transport properties of MntH versus SitABCD suggest that each transporter may be specialized for Mn2+ uptake in different physiological environments.
37
Amir, Laila, e Michel Kern. "Jacobian Free Methods for Coupling Transport with Chemistry in Heterogenous Porous Media". Water 13, n. 3 (31 gennaio 2021): 370. http://dx.doi.org/10.3390/w13030370.
Abstract (sommario):
Reactive transport plays an important role in various subsurface applications, including carbon dioxide sequestration, nuclear waste storage, biogeochemistry and the simulation of hydro–thermal reservoirs. The model couples a set of partial differential equations, describing the transport of chemical species, to nonlinear algebraic or differential equations, describing the chemical reactions. Solution methods for the resulting large nonlinear system can be either fully coupled or can iterate between transport and chemistry. This paper extends previous work by the authors where an approach based on the Newton–Krylov method applied to a reduced system has been developed. The main feature of the approach is to solve the nonlinear system in a fully coupled manner while keeping transport and chemistry modules separate. Here we extend the method in two directions. First, we take into account mineral precipitation and dissolution reactions by using an interior point Newton method, so as to avoid the usual combinatorial approach. Second, we study two-dimensional heterogeneous geometries. We show how the method can make use of an existing transport solver, used as a black box. We detail the methods and algorithms for the individual modules, and for the coupling step. We show the performance of the method on synthetic examples.
38
Yan, Y. Y., J. T. Lin, Y. Kuang, D. Yang e L. Zhang. "Tropospheric carbon monoxide over the Pacific during HIPPO: two-way coupled simulation of GEOS-Chem and its multiple nested models". Atmospheric Chemistry and Physics 14, n. 23 (2 dicembre 2014): 12649–63. http://dx.doi.org/10.5194/acp-14-12649-2014.
Abstract (sommario):
Abstract. Global chemical transport models (CTMs) are used extensively to study air pollution and transport at a global scale. These models are limited by coarse horizontal resolutions that do not allow for a detailed representation of small-scale nonlinear processes over the pollutant source regions. Here we couple the global GEOS-Chem CTM and its three high-resolution nested models to simulate the tropospheric carbon monoxide (CO) over the Pacific Ocean during five High-performance Instrumented Airborne Platform for Environmental Research (HIAPER) Pole-to-Pole Observations (HIPPO) campaigns between 2009 and 2011. We develop a two-way coupler, the PeKing University CouPLer (PKUCPL), allowing for the exchange and interaction of chemical constituents between the global model (at 2.5° long. × 2° lat.) and the three nested models (at 0.667° long. × 0.5° lat.) covering Asia, North America, and Europe. The coupler obtains nested model results to modify the global model simulation within the respective nested domains, and simultaneously acquires global model results to provide lateral boundary conditions (LBCs) for the nested models. Compared to the global model alone, the two-way coupled simulation results in enhanced CO concentrations in the nested domains. Sensitivity tests suggest the enhancement to be a result of improved representation of the spatial distributions of CO, nitrogen oxides, and non-methane volatile organic compounds, the meteorological dependence of natural emissions, and other resolution-dependent processes. The relatively long lifetime of CO allows for the enhancement to be accumulated and carried across the globe. We found that the two-way coupled simulation increased the global tropospheric mean CO concentrations in 2009 by 10.4%, with a greater enhancement at 13.3% in the Northern Hemisphere. Coincidently, the global tropospheric mean hydroxyl radical (OH) was reduced by 4.2%, resulting in a 4.2% enhancement in the methyl chloroform lifetime (MCF; via reaction with tropospheric OH). The resulting CO and OH contents and MCF lifetime are closer to observation-based estimates. Both the global and the two-way coupled models capture the general spatiotemporal patterns of HIPPO CO over the Pacific. The two-way coupled simulation is much closer to HIPPO CO, with a mean bias of 1.1 ppb (1.4%) below 9 km compared to the bias at −7.2 ppb (−9.2%) for the global model alone. The improvement is most apparent over the North Pacific. Our test simulations show that the global model alone could resemble the two-way coupled simulation (especially below 4 km) by increasing its global CO emissions by 15% for HIPPO-1 and HIPPO-3, by 25% for HIPPO-2 and HIPPO-4, and by 35% for HIPPO-5. This has important implications for using the global model alone to constrain CO emissions. Thus, the two-way coupled simulation is a significantly improved model tool for studying the global impacts of air pollutants from major anthropogenic source regions.
39
Robinson, Anne E., Nathan E. Thomas, Emma A. Morrison, Bryan M. Balthazor e Katherine A. Henzler-Wildman. "New free-exchange model of EmrE transport". Proceedings of the National Academy of Sciences 114, n. 47 (7 novembre 2017): E10083—E10091. http://dx.doi.org/10.1073/pnas.1708671114.
Abstract (sommario):
EmrE is a small multidrug resistance transporter found in Escherichia coli that confers resistance to toxic polyaromatic cations due to its proton-coupled antiport of these substrates. Here we show that EmrE breaks the rules generally deemed essential for coupled antiport. NMR spectra reveal that EmrE can simultaneously bind and cotransport proton and drug. The functional consequence of this finding is an exceptionally promiscuous transporter: not only can EmrE export diverse drug substrates, it can couple antiport of a drug to either one or two protons, performing both electrogenic and electroneutral transport of a single substrate. We present a free-exchange model for EmrE antiport that is consistent with these results and recapitulates ∆pH-driven concentrative drug uptake. Kinetic modeling suggests that free exchange by EmrE sacrifices coupling efficiency but boosts initial transport speed and drug release rate, which may facilitate efficient multidrug efflux.
40
Beadling, R. L., J. L. Russell, R. J. Stouffer e P. J. Goodman. "Evaluation of Subtropical North Atlantic Ocean Circulation in CMIP5 Models against the Observational Array at 26.5°N and Its Changes under Continued Warming". Journal of Climate 31, n. 23 (dicembre 2018): 9697–718. http://dx.doi.org/10.1175/jcli-d-17-0845.1.
Abstract (sommario):
Observationally based metrics derived from the Rapid Climate Change (RAPID) array are used to assess the large-scale ocean circulation in the subtropical North Atlantic simulated in a suite of fully coupled climate models that contributed to phase 5 of the Coupled Model Intercomparison Project (CMIP5). The modeled circulation at 26.5°N is decomposed into four components similar to those RAPID observes to estimate the Atlantic meridional overturning circulation (AMOC): the northward-flowing western boundary current (WBC), the southward transport in the upper midocean, the near-surface Ekman transport, and the southward deep ocean transport. The decadal-mean AMOC and the transports associated with its flow are captured well by CMIP5 models at the start of the twenty-first century. By the end of the century, under representative concentration pathway 8.5 (RCP8.5), averaged across models, the northward transport of waters in the upper WBC is projected to weaken by 7.6 Sv (1 Sv ≡ 106 m3 s−1; −21%). This reduced northward flow is a combined result of a reduction in the subtropical gyre return flow in the upper ocean (−2.9 Sv; −12%) and a weakened net southward transport in the deep ocean (−4.4 Sv; −28%) corresponding to the weakened AMOC. No consistent long-term changes of the Ekman transport are found across models. The reduced southward transport in the upper ocean is associated with a reduction in wind stress curl (WSC) across the North Atlantic subtropical gyre, largely through Sverdrup balance. This reduced WSC and the resulting decrease in the horizontal gyre transport is a robust feature found across the CMIP5 models under increased CO2 forcing.
41
Wu, Xiaodong, Falk Feddersen, Sarah N. Giddings, Nirnimesh Kumar e Ganesh Gopalakrishnan. "Mechanisms of Mid- to Outer-Shelf Transport of Shoreline-Released Tracers". Journal of Physical Oceanography 50, n. 7 (1 luglio 2020): 1813–37. http://dx.doi.org/10.1175/jpo-d-19-0225.1.
Abstract (sommario):
AbstractTransport of shoreline-released tracer from the surfzone across the shelf can be affected by a variety of physical processes from wind-driven to submesoscale, with implications for shoreline contaminant dilution and larval dispersion. Here, a high-resolution wave–current coupled model that resolves the surfzone and receives realistic oceanic and atmospheric forcing is used to simulate dye representing shoreline-released untreated wastewater in the San Diego–Tijuana region. Surfzone and shelf alongshore dye transports are primarily driven by obliquely incident wave breaking and alongshore pressure gradients, respectively. At the midshelf to outer-shelf (MS–OS) boundary (25-m depth), defined as a mean streamline, along-boundary density gradients are persistent, dye is surface enhanced and time and alongshelf patchy. Using baroclinic and along-boundary perturbation dye transports, two cross-shore dye exchange velocities are estimated and related to physical processes. Barotropic and baroclinic tides cannot explain the modeled cross-shore transport. The baroclinic exchange velocity is consistent with the wind-driven Ekman transport. The perturbation exchange velocity is elevated for alongshore dye and cross-shore velocity length scales < 1 km (within the submesoscale) and stronger alongshore density gradient ∂ρ/∂y variability, indicating that alongfront geostrophic flows induce offshore transport. This elevated ∂ρ/∂y is linked to convergent northward surface along-shelf currents (likely due to regional bathymetry), suggesting deformation frontogenesis. Both surfzone and shelf processes influence offshore transport of shoreline-released tracers with key parameters of surfzone and shelf alongcoast currents and alongshelf winds.
42
Born, A., T. F. Stocker e A. B. Sandø. "Coupling of eastern and western subpolar North Atlantic: salt transport in the Irminger Current". Ocean Science Discussions 10, n. 2 (15 marzo 2013): 555–79. http://dx.doi.org/10.5194/osd-10-555-2013.
Abstract (sommario):
Abstract. Salt transport in the Irminger Current and thus the coupling between eastern and western subpolar North Atlantic plays an important role for climate variability across a wide range of time scales. High-resolution ocean modeling and observations indicate that salinities in the eastern subpolar North Atlantic decrease with enhanced circulation of the North Atlantic subpolar gyre (SPG). This has led to the perception that a stronger SPG also transports less salt westward. In this study, we analyze a regional ocean model and a comprehensive global coupled climate model, and show that a stronger SPG transports more salt in the Irminger Current irrespective of lower salinities in its source region. The additional salt converges in the Labrador Sea and the Irminger Basin by eddy transports, increases surface salinity in the western SPG, and favors more intense deep convection. This is part of a positive feedback mechanism with potentially large implications for climate variability and predictability.
43
Nathan, Terrence R., e Dustin F. P. Grogan. "Scale-Dependent Transport of Saharan Dust by African Easterly Waves". Geosciences 12, n. 9 (11 settembre 2022): 337. http://dx.doi.org/10.3390/geosciences12090337.
Abstract (sommario):
The scale-dependent transport of Saharan dust aerosols by African easterly waves (AEWs) is examined analytically and numerically. The analytical analysis shows that the meridional and vertical wave transports of dust are modulated by the Doppler-shifted frequency, ωd, and the wave growth rate, ωi, both of which are functions of the zonal wave scale. The analytical analysis predicts that the AEW dust transports, which are driven by the Reynolds stresses acting on the mean dust gradients, are largest for the twin limits: ωd→0, which corresponds to flow near a critical surface, a local effect; and ωi→0, which corresponds to the slowest growing waves, a global effect. The numerical analysis is carried out with the Weather Research and Forecasting (WRF) model, which is radiatively coupled to the dust field. The model simulations are based on an AEW spectrum consistent with observations. The simulations agree with the theoretical predictions: the slowest growing waves have the strongest transports, which are as much as ~40% larger than the transports of the fastest growing wave. Although the transports are highly scale-dependent, largely due to the scale dependence of ωi, the location of the critical surface and thus the location of the maximum dust transports are not.
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Majda, Andrew J., e Samuel N. Stechmann. "Stochastic models for convective momentum transport". Proceedings of the National Academy of Sciences 105, n. 46 (17 novembre 2008): 17614–19. http://dx.doi.org/10.1073/pnas.0806838105.
Abstract (sommario):
The improved parameterization of unresolved features of tropical convection is a central challenge in current computer models for long-range ensemble forecasting of weather and short-term climate change. Observations, theory, and detailed smaller-scale numerical simulations suggest that convective momentum transport (CMT) from the unresolved scales to the resolved scales is one of the major deficiencies in contemporary computer models. Here, a combination of mathematical and physical reasoning is utilized to build simple stochastic models that capture the significant intermittent upscale transports of CMT on the large scales due to organized unresolved convection from squall lines. Properties of the stochastic model for CMT are developed below in a test column model environment for the large-scale variables. The effects of CMT from the stochastic model on a large-scale convectively coupled wave in an idealized setting are presented below as a nontrivial test problem. Here, the upscale transports from stochastic effects are significant and even generate a large-scale mean flow which can interact with the convectively coupled wave.
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Erhun, M., e S. G. Advani. "Heat Transfer Effects During Solidification of Semicrystalline Polymers". Journal of Engineering Materials and Technology 115, n. 1 (1 gennaio 1993): 30–36. http://dx.doi.org/10.1115/1.2902154.
Abstract (sommario):
The build-up of the residual stresses in the plastic parts are directly affected by the transient temperature distribution during the solidification stage of the semicrystalline polymers. Hence for crystallizable polymers, it is important to couple the crystallization kinetics with the transport of heat flow to determine the thermal history during solidification. In this paper, an experimental study of solidification of two semi-crystalline polymers under quiescent conditions is carried out to examine the influence of crystallization kinetics on the thermal history. The selected model materials are Nylon-66 and Poly Ethylene Terephalate (PET). The temperature profiles and the location of the solidification front are recorded during the cooling process. The experimental results are compared with the classical heat diffusion model and also with a numerical approach which couples the crystallization kinetics to the heat diffusion equation by modifying the phase change temperature based on the overall cooling rate in the crystalline domain. The front movement and the solidification temperature predictions of the coupled model are in good agreement with the experimental observations.
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Parker, Joanne L., Chenghan Li, Allete Brinth, Zhi Wang, Lutz Vogeley, Nicolae Solcan, Gregory Ledderboge-Vucinic et al. "Proton movement and coupling in the POT family of peptide transporters". Proceedings of the National Academy of Sciences 114, n. 50 (27 novembre 2017): 13182–87. http://dx.doi.org/10.1073/pnas.1710727114.
Abstract (sommario):
POT transporters represent an evolutionarily well-conserved family of proton-coupled transport systems in biology. An unusual feature of the family is their ability to couple the transport of chemically diverse ligands to an inwardly directed proton electrochemical gradient. For example, in mammals, fungi, and bacteria they are predominantly peptide transporters, whereas in plants the family has diverged to recognize nitrate, plant defense compounds, and hormones. Although recent structural and biochemical studies have identified conserved sites of proton binding, the mechanism through which transport is coupled to proton movement remains enigmatic. Here we show that different POT transporters operate through distinct proton-coupled mechanisms through changes in the extracellular gate. A high-resolution crystal structure reveals the presence of ordered water molecules within the peptide binding site. Multiscale molecular dynamics simulations confirm proton transport occurs through these waters via Grotthuss shuttling and reveal that proton binding to the extracellular side of the transporter facilitates a reorientation from an inward- to outward-facing state. Together these results demonstrate that within the POT family multiple mechanisms of proton coupling have likely evolved in conjunction with variation of the extracellular gate.
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Starn, Timothy K., e Gary M. Hieftje. "Acoustically Driven Device for Introducing Solid Samples into an Inductively Coupled Plasma". Applied Spectroscopy 46, n. 10 (ottobre 1992): 1454–59. http://dx.doi.org/10.1366/000370292789619359.
Abstract (sommario):
A device is described that couples acoustic energy into powdered solid samples to facilitate their transport into an inductively coupled plasma. The system, entitled a sonic suspension device, is inexpensive and simple to build. In an experiment to illustrate its performance, calcium carbonate in a graphite matrix was introduced into an ICP; it offered moderate precision (relative standard deviation of 5% without the use of an internal standard) and acceptable sample-introduction efficiency.
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Liu, Ye, H. E. Markus Meier e Kari Eilola. "Nutrient transports in the Baltic Sea – results from a 30-year physical–biogeochemical reanalysis". Biogeosciences 14, n. 8 (25 aprile 2017): 2113–31. http://dx.doi.org/10.5194/bg-14-2113-2017.
Abstract (sommario):
Abstract. Long-term oxygen and nutrient transports in the Baltic Sea are reconstructed using the Swedish Coastal and Ocean Biogeochemical model (SCOBI) coupled to the Rossby Centre Ocean model (RCO). Two simulations with and without data assimilation covering the period 1970–1999 are carried out. Here, the weakly coupled scheme with the Ensemble Optimal Interpolation (EnOI) method is adopted to assimilate observed profiles in the reanalysis system. The reanalysis shows considerable improvement in the simulation of both oxygen and nutrient concentrations relative to the free run. Further, the results suggest that the assimilation of biogeochemical observations has a significant effect on the simulation of the oxygen-dependent dynamics of biogeochemical cycles. From the reanalysis, nutrient transports between sub-basins, between the coastal zone and the open sea, and across latitudinal and longitudinal cross sections are calculated. Further, the spatial distributions of regions with nutrient import or export are examined. Our results emphasize the important role of the Baltic proper for the entire Baltic Sea, with large net transport (export minus import) of nutrients from the Baltic proper into the surrounding sub-basins (except the net phosphorus import from the Gulf of Riga and the net nitrogen import from the Gulf of Riga and Danish Straits). In agreement with previous studies, we found that the Bothnian Sea imports large amounts of phosphorus from the Baltic proper that are retained in this sub-basin. For the calculation of sub-basin budgets, the location of the lateral borders of the sub-basins is crucial, because net transports may change sign with the location of the border. Although the overall transport patterns resemble the results of previous studies, our calculated estimates differ in detail considerably.
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Paulsen, Bryan D., Simone Fabiano e Jonathan Rivnay. "Mixed Ionic-Electronic Transport in Polymers". Annual Review of Materials Research 51, n. 1 (26 luglio 2021): 73–99. http://dx.doi.org/10.1146/annurev-matsci-080619-101319.
Abstract (sommario):
Polymeric mixed ionic-electronic conductors (MIECs) combine aspects of conjugated polymers, polymer electrolytes, and polyelectrolytes to simultaneously transport and couple ionic and electronic charges, opening exciting new applications in energy storage and conversion, bioelectronics, and display technologies. The many applications of polymeric MIECs lead to a wide range of transport conditions. Ionic and electronic transport are directly coupled through electrochemical doping, while the mechanisms of ionic and electronic transport depend on distinctly different chemical functionality, (macro)molecular structure, and morphology. Despite this, ionic and electronic transport are surprisingly tunable, independent of one another. We review the various types of polymeric MIECs, the mechanisms of ionic and electronic charge transport across conditions, and the interrelations between the two, with special emphasis on the unique aspects of polymeric MIEC transport phenomena.
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Marino, S., M. Shapiro e P. M. Adler. "Coupled Transports in Heterogeneous Media". Journal of Colloid and Interface Science 243, n. 2 (novembre 2001): 391–419. http://dx.doi.org/10.1006/jcis.2001.7826.