Primary Transport Pathways Research Articles

Enhanced Energy Storage Properties and DFT Investigation of a Zn-Co-Mo Heterojunction Rich in Oxygen Vacancies with Dual Electron Transport Pathways.

Petal-like heterojunction materials ZnCo2O4/CoMoO4 with abundant oxygen vacancies are prepared on nickel foam (NF) using modified ionic hybrid thermal calcination technology. Nanoscale ion intermixing between Zn and Mo ions induces oxygen vacancies in the annealing process, thus creating additional electrochemical active sites and enhancing the electrical conductivity. The ZnCo2O4/CoMoO4 conductive network skeleton forms the primary transport pathway for electrons, while the internal electric field of the heterojunction serves as the secondary pathway. ZnCo2O4/CoMoO4 exhibits excellent rate performance and high capacity attributable to its unique double electron transport mode and the effect of oxygen vacancies. The initial discharge capacity at a current of 0.1 A g-1 is approximately 1774 mAh g-1, and the reversible capacity remains at 1100 mAh g-1 after 200 cycles. After a high current of 1 A g-1, the reversible capacity is observed to remain at approximately 1240 mAh g-1. The electronic structure, crystal structure, and work function of the heterojunction interface model are then analyzed by density functional theory (DFT). The analysis results indicate that the charge at the ZnCo2O4/CoMoO4 interface is unevenly distributed, which leads to an enhanced degree of electrochemical reaction. The presence of an internal electric field improves the transport efficiency of the carriers. Experimental and theoretical calculations demonstrate that the ZnCo2O4/CoMoO4 anode material designed in this work provides a reference for fabricating transition metal oxide-based lithium-ion batteries.

Effects of Shallow Surface Drainage Ditches With Controlled Subsurface Drainage Management on Crop Yields in North Carolina

Highlights Shallow surface ditches with controlled subsurface drainage (SD) increased corn and soybean yields in eight of nine growing seasons compared to conventional drainage. The SD system increased corn yields on average by 0.4 Mg/ha, or 4% (0.7 Mg/ha, or 6.6%, excluding 2016). The SD system increased soybean yields on average by 0.5 Mg/ha, or 14.3%. Abstract. Agricultural drainage in the coastal areas of North Carolina (NC) is commonly achieved through large trapezoidal-shaped ditches. The coastal region of NC has limited topographic relief (slopes < 1%) with poorly drained soils that can cause substantial issues with surface water ponding during high-intensity or long-duration precipitation events without some form of surface drainage. Installation of large free flowing surface ditches (FD) with field crowning improves the drainage intensity but can create negative consequences such as over drainage and side slope scouring within the ditch. Large open ditches remove tillable land from production and serve as a primary transport pathway for pollutants. An alternative drainage design (SD) has been implemented that decreases the size of the surface ditches, limiting their drainage effect to only surface water and potentially improving equipment trafficability. The smaller ditches, installed with precision grade equipment, are placed on a grade sufficient to direct surface flow while keeping soil movement to a minimum. Lateral subsurface drainage tiles are installed to provide subsurface drainage and are connected to a main tile line operated with an outlet control structure for controlled drainage (CD). This study evaluates the crop yield and water table effects of the SD system compared to FD over nine crop seasons from 2014-2022. The SD treatment increased yield in eight of the nine crop seasons overall, four of five corn (Zea mays L.) crops, and all four soybean (Glycine max L.) crops. Overall, SD increased corn yields by 0.4 Mg/ha or 4% (0.7 Mg/ha or 6.6% with the exclusion of 2016) and soybean yields by 0.5 Mg/ha (14.3%). The effects of SD on crop yield and water table show that the system can be utilized to improve crop health and provide better management of cropland for producers. Keywords: Corn Yield, Drainage Water Management, Soybean Yield, Surface Drainage, Water Table.

Assimilation of Nitrate into Asparagine for Transport in Soybeans

In this study, the systematic analysis of nitrate assimilation and transport in soybean roots was further improved by analyzing the concentrations of nitrate assimilates, asparagine and glutamine, in soybean roots and the related enzyme activities. This provided a theoretical basis for the efficient utilization of nitrogen fertilizer in soybean farming. A dual-root soybean system with both sides being nodulated was used to provide nitrate withdrawal and resupply in three phases on one side, while the other side received nutrients without nitrogen under sand culture conditions. Measurements were taken of the root’s nitrate reductase and glutamine synthetase activities, as well as the concentrations of asparagine. Measurements were also taken of the asparagine concentration in the basal root peeled skin (where the primary transport pathway is the phloem) and the woody parts (where the primary transport pathway is the xylem). Furthermore, the concentration of glutamine in the roots was also assessed. The findings indicated a positive correlation between the nitrate concentration in the roots and the activity of glutamine synthetase in the roots on both sides. The levels of asparagine in the roots, specifically those in the basal root peeled skin and woody part on both sides, rose when nitrate was added and declined when nitrate was removed. There was no significant change in glutamine concentration within the roots of soybeans. Hence, we deduced that the local provision of nitrate to the dual-root soybeans might enhance the absorption of nitrate into the roots on both sides. Additionally, the assimilated substances were predominantly carried as asparagine through the peeled skin and woody sections of the basal root, facilitating transportation in both directions within the soybean plants (from shoot to root and from root to shoot).

Atmospheric Latent Energy Transport Pathways into the Arctic and Their Connections to Sea Ice Loss during Winter over the Observational Period

Abstract To investigate patterns of horizontal atmospheric latent energy (LE) transport toward the Arctic, we applied the self-organizing maps (SOM) method to the daily vertically integrated horizontal LE flux from ERA5 in winter (January–March) during 1979–2021. A clear picture depicting the LE transport to the Arctic at a synoptic scale then emerged, with four primary transport pathways identified: the northern Europe, the Davis Strait, the Greenland Sea, and the Bering Strait pathways. The four primary pathways occurred at a comparable frequency, and noticeable interannual variability was observed in their time series of frequency during 1979–2021. Further analysis suggested that the northward LE transport through all these pathways is significantly modulated by cyclones, with the northern Europe and the Greenland Sea pathways being mostly affected. Generally, more frequent and stronger cyclones were observed near the entry regions of LE transport compared to other regions. Moreover, this study provides a comprehensive picture of how atmospheric LE transport is related to air temperature, moisture, surface heat flux, and sea ice anomalies over the Arctic Ocean in winter. Through a thermodynamic perspective, we argue that the deleterious impacts of poleward LE transport on Arctic sea ice are to a large extent attributable to the enhanced local atmosphere–ice interactions, which increase downward longwave radiation (DLR) plus turbulent fluxes, consequently warming the surface and promoting the loss of sea ice. According to the quantitative results, among the four primary pathways, LE transport through the Davis Strait and the Greenland Sea could cause the loss of Arctic sea ice most efficiently.

Identification of pollutant delivery processes during different storm events and hydrological years in a semi-arid mountainous reservoir basin

A comprehensive understanding of pollutant delivery processes during storm events is essential for developing strategies to minimize adverse impacts on receiving water bodies. In this paper, hysteresis analysis and principal component analysis were coupled with identified nutrient dynamics to determine different pollutant export forms and transport pathways and analyze the impact of precipitation characteristics and hydrological conditions on pollutant transport processes through continuous sampling between different storm events (4 events) and hydrological years (2018-wet, 2019-dry) in a semi-arid mountainous reservoir watershed. Results showed pollutant dominant forms and primary transport pathways were inconsistent between different storm events and hydrological years. Nitrogen (N) was mainly exported in the form of nitrate-N(NO3-N). Particle phosphorous (PP) was the dominant P form in wet years, but total dissolved P (TDP) in dry year. Ammonia-N (NH4-N), total P (TP), total dissolved P(TDP) and PP had prominent flushing responses to storm events and were delivered mainly from overland sources by surface runoff; while the concentrations of total N(TN) and nitrate-N(NO3-N) were mainly diluted during storm events. Rainfall intensity and amount had significant control over P dynamics and extreme events played a key role in TP exports, accounting for >90 % of the total TP load exports. However, the cumulative rainfall and runoff regime during rainy season exerted significant control over N exports than individual rainfall features. In the dry year, NO3-N and TN were delivered primarily through soil water flow paths during storm events; nevertheless, wet year registered complex control on TN exports via soil water release, followed by surface runoff transport. Relative to dry year, wet year registered higher N concentration and more N load exports. These findings could provide scientific basis for determining effective pollution mitigation strategies in Miyun Reservoir basin and provide important references for other semi-arid mountain watersheds.

Bacterial signal peptides: structure, optimization, and applications

Bacterial signal peptides are N-terminal tags that direct proteins for export through one of various transport pathways. These signal peptides are highly important as they are the key determinants of transport, ensuring that the correct protein ends up at the correct pathway. While these peptides consist of three domains with well conserved biochemical properties, there still remains a large amount of diversity between the signal sequences for different proteins, transport pathways, and bacterial species. Recent advancements have allowed us to predict signal sequences and manipulate them in an attempt to optimize export efficiency. This knowledge can then be exploited in the field of recombinant protein production wherein bacterial species can be used to produce and secrete proteins of interest. By fusing the protein with an optimized signal peptide, the yield or rate of export can be improved. This review focuses on signal peptides for two primary transport pathways (Sec and Tat) in E. coli specifically, with an emphasis on applications and the production of recombinant proteins.

Heavy metals transport pathways: The importance of atmospheric pollution contributing to stormwater pollution

Pollution has become a serious issue in the urban water environment as stormwater runoff transports a range of pollutants to receiving water bodies, undermining water quality and posing human and ecosystem health risks. Commonly, the primary focus of stormwater quality research is on the role of pollutants directly accumulating at the ground phase. However, atmospheric phase can also exert a significant impact on stormwater quality through atmospheric deposition. Unfortunately, only limited research has focused on the linkage between atmospheric and ground phases in relation to urban stormwater quality. The study discussed in this paper characterised the four primary transport pathways, atmospheric build-up (AB), atmospheric deposition (AD) and road surface build-up (BU) and wash-off (WO) in relation to heavy metals, which is a key urban stormwater pollutant. The research outcomes confirmed the direct linkage between atmospheric phase and ground phase and in turn the significance of atmospheric heavy metals as a contributing source to stormwater runoff pollution. Zn was the most dominant heavy metal in all four pathways. For the AB pathway, atmospheric heavy metal pollution on weekdays is more serious than weekends. For the AD pathway, dry atmospheric deposition of heavy metals is positively correlated to dry days, whilst wet (bulk) deposition is related to rainfall depth. For the BU pathway, heavy-duty vehicle traffic volume was found to be the most important source. For the WO pathway, industrial and commercial areas tend to produce higher heavy metal concentrations in stormwater runoff than residential areas. The study results will contribute to the creation of effective urban stormwater pollution mitigation strategies and thereby enhancing the quality of the urban water environment.

Characteristics of intercontinental transport of tropospheric ozone from Africa to Asia

Abstract. In this study, we characterize the transport of ozone from Africa to Asia through the analysis of the simulations of a global chemical transport model, GEOS-Chem, from 1987 to 2006. The receptor region Asia is defined within 5–60∘ N and 60–145∘ E, while the source region Africa is within 35∘ S–15∘ N and 20∘ W–55∘ E and within 15–35∘ N and 20∘ W–30∘ E. The ozone generated in the African troposphere from both natural and anthropogenic sources is tracked through tagged ozone simulation. Combining this with analysis of trajectory simulations using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, we find that the upper branch of the Hadley cell connects with the subtropical westerlies in the Northern Hemisphere (NH) to form a primary transport pathway from Africa to Asia in the middle and upper troposphere throughout the year. The Somali jet that runs from eastern Africa near the equator to the Indian subcontinent in the lower troposphere is the second pathway that appears only in NH summer. The influence of African ozone mainly appears over Asia south of 40∘ N. The influence shows strong seasonality, varying with latitude, longitude, and altitude. In the Asian upper troposphere, imported African ozone is largest from March to May around 30∘ N (12–16 ppbv) and lowest during July–October around 10∘ N (∼ 2 ppbv). In the Asian middle and lower troposphere, imported African ozone peaks in NH winter between 20 and 25∘ N. Over 5–40∘ N, the mean fractional contribution of imported African ozone to the overall ozone concentrations in Asia is largest during NH winter in the middle troposphere (∼ 18 %) and lowest in NH summer throughout the tropospheric column (∼ 6 %). This seasonality mainly results from the collective effects of the ozone precursor emissions in Africa and meteorology and chemistry in Africa, in Asia and along the transport pathways. The seasonal swing of the Hadley circulation and subtropical westerlies along the primary transport pathway plays a dominant role in modulating the seasonality. There is more imported African ozone in the Asian upper troposphere in NH spring than in winter. This is likely due to more ozone in the NH African upper troposphere generated from biogenic and lightning NOx emissions in NH spring. The influence of African ozone on Asia appears larger in NH spring than in autumn. This can be attributed to both higher altitudes of the elevated ozone in Africa and stronger subtropical westerlies in NH spring. In NH summer, African ozone hardly reaches Asia because of the blocking by the Saharan High, Arabian High, and Tibetan High on the transport pathway in the middle and upper troposphere, in addition to the northward swing of the subtropical westerlies. The seasonal swings of the intertropical convergence zone (ITCZ) in Africa, coinciding with the geographic variations of the ozone precursor emissions, can further modulate the seasonality of the transport of African ozone, owing to the functions of the ITCZ in enhancing lightning NOx generation and uplifting ozone and ozone precursors to upper layers. The strength of the ITCZ in Africa is also found to be positively correlated with the interannual variation of the transport of African ozone to Asia in NH winter. Ozone from NH Africa makes up over 80 % of the total imported African ozone over Asia in most altitudes and seasons. The interhemispheric transport of ozone from southern hemispheric Africa (SHAF) is most evident in NH winter over the Asian upper troposphere and in NH summer over the Asian lower troposphere. The former case is associated with the primary transport pathway in NH winter, while the latter case is associated with the second transport pathway. The intensities of the ITCZ in Africa and the Somali jet can each explain ∼ 30 % of the interannual variations in the transport of ozone from SHAF to Asia in the two cases.

Characterization of rapid intervascular transport of cadmium in rice stem by radioisotope imaging.

Participation of the intervascular transport system within the rice stem during cadmium (Cd) partitioning was investigated by characterizing 109Cd behaviour in the shoot. In addition, 45Ca, 32P, and 35S partitioning patterns were analysed for comparison with that of 109Cd. Each tracer was applied to the seedling roots for 15min, and the shoots were harvested either at 15min (i.e. immediately after tracer application) or at 48h. Distribution patterns of each element at 15min were studied to identify the primary transport pathway before remobilization was initiated. 32P was preferentially transported to completely expanded leaf blades having the highest transpiration rate. The newest leaf received minimal amounts of 32P. In contrast, the amount of 35S transported to the newest leaf was similar to that transported to the other mature leaf blades. Preferential movement towards the newest leaf was evident for 109Cd and 45Ca. These results directly indicate that elemental transport is differentially regulated in the vegetative stem as early as 15min before the elements are transported to leaves. Cd behaviour in the stem was investigated in detail by obtaining serial section images from the bottom part of shoots after 109Cd was applied to a single crown root. At 30min, the maximum amount of 109Cd was distributed in the peripheral cylinder of the longitudinal vascular bundles (PV) and, interestingly, some amount of 109Cd was transported downwards along the PV. This transport manner of 109Cd provides evidence that Cd can be loaded on the phloem at the stem immediately after Cd is transported from the root.

Simulating the formation of overdeepenings with coupled ice, water, and sediment models

Eyles identified Kvı́árjökull, an outlet of the icecap Öræfajökull, southeast Iceland, as an exemplar of the glaciated valley landsystem, emphasising rockfall debris supply, passive transport and reworking of a thick cover of supraglacial morainic till. In this paper, we take a fresh look at the sediments and landforms of Kvı́árjökull, focusing on clast form analysis to reconstruct primary transport pathways. New data demonstrate the importance of active transport of debris derived from the glacier bed. Substantial portions of the supraglacial debris cover can be traced back to englacial channel fill deposits or anomalously thick exposures of basal ice. These two types of sediments also make up much of Kvı́árjökull's large Neoglacial moraine rampart. We attribute the abundance of these non-rockfall sediments to the presence of a terminal overdeepening, and the switch from predominantly subglacial to predominantly englacial drainage that this induces. This hydrological switch enhances retention of debris within ice transport, preventing it from being washed away and making it available to feed ice-marginal moraine formation. The complexity of sediment transport processes observed at Kvı́árjökull and the contrast between it and alpine glaciers undermines any single concept of the glaciated valley landsystem; accordingly, we propose Kvı́árjökull as the type example of a distinct subclass, defined by its moderate relief, high-debris turnover, and drainage behaviour characteristic of an overdeepened basin.

Reassessment of Models of Facilitated Transport and Cotransport

Most membrane transport models are determinate, requiring the transported ligand(s) to bind initially to a vacant site, which undergoes translation and releases ligand to the alternate side. The carrier reverts to its initial position to complete the net transport cycle. Ligand affinity may change during translation, but this must be compensated by an equivalent energy change(s) within the transport cycle. However, any asymmetric cyclic equilibrium deduced on this basis is thermodynamically fallacious. Determinate cotransport models imply lossless stoichiometric relationships between the complexed cotransported ligands. Independent ligand leakage apart from the mobile cotransport complex must occur outside the canonical cotransport pathway. In contrast, stochastic transport models assume independent ligand diffusion through a variably occluded channel(s) containing binding sites where ligands may undergo bimolecular exchanges. Energy dissipation is intrinsic to all stochastic transport models and occurs within the primary transport pathway. Frictional interactions within a shared path generate flow coupling between ligands. The primary driving forces causing transmembrane ligand flows are their electrochemical potential differences between the external solutions. Demonstrations that ligand exchanges in CLC and neurotransmitter transporters can be multimodal, encompassing both "channel"-like high and "transporter"-like lower conductance states and have independently regulated import and export exchange fluxes are major challenges to determinate models but are explicable by transient widening of a close-encounter region within the channel, leading to decreased coupling and enhanced efflux.

Water Management Aspects of the Britannia Mine Remediation Project, British Columbia, Canada

The Province of British Columbia, Canada, is undertaking environmental remediation at Britannia Mine, located approximately 45 km north of Vancouver. Britannia Mine operated for 70 years and produced mainly copper and zinc concentrates. During its operating life, and since its closure in 1974, the mine has discharged large volumes of acidic water with elevated concentrations of potentially toxic metals, including copper, zinc, and cadmium. Prior to the recent remedial efforts, metal loadings to Howe Sound averaged 300 kg/day each of copper and zinc. In addition to the acid rock drainage, mine infrastructure and mineral processing activities provide secondary sources of metal contamination of soils, sediments, ground water, and surface water. Effective water management is key to the remedial plan for the mine: ground water and surface water are the primary transport pathways for the metal contamination reaching the local receptors of Britannia and Furry creeks, and Howe Sound. The remedial concept includes diversion of clean water from entering the mine, use of the mine workings as a storage reservoir to balance seasonal flows to a water treatment plant, prior to discharging to Howe Sound via a deep outfall, and the interception of a metal-contaminated ground water plume.

Marine palynology: potentials for onshore—offshore correlation of Pleistocene—Holocene records

A review of marine pollen-spore distributions reveals regional variations in primary transport pathways. Fluvial transport prevails on the mountainous margins of the eastern Pacific and off major river deltas, including Arctic estuaries. Elsewhere, wind and sea ice are the main transport agents, and pollen concentration corresponds to dust influx. Redeposition of Quaternary palynomorphs is also important near emergent continental ice sheet centres where fine-grained sediment is being eroded. Pre-Quaternary palynomorphs can indicate sources of ice-rafted debris. Preservation and transport of pollen in marine sediments is not well understood. Laboratory processing with acetolysis shows damage of bisaccate grains, and copepod feeding experiments show some pollen damage of grains within the faecal pellet membranes. A multi-box model shows the relative importance of rivers, wind and ocean currents in pollen transport to shelves of Atlantic Canada: most pollen is wind-transported, but large storms may indirectly increase influx. In the Arctic, sea ice scouring and sediment transport are important in addition to northeasterly winds. These glacial processes would impact a third of the planet during glaciations. Pleistocene cores from NW Atlantic and Pacific Oceans show that glacial stage transport differed from that during Holocene and other interglacials because glacioeustatic lowstands exposed the continental shelves, and wind strength and direction changed following ice sheet growth. Pollen influxes and ice-volume records show variable leads and lags of palaeometerological events at glacial/interglacial boundaries, with a major decline in terrigenous organics after ∼0.4 Ma (MIS 13-11).

Modeling conservative tracer transport in fracture networks with a hybrid approach based on the Boltzmann transport equation

Fractures often represent the primary transport pathways within low‐permeability rock. Continuum models based on the advective‐dispersion equation have difficulty representing the complex transport phenomenology observed in field studies. Discrete fracture network models can represent a greater range of transport behavior at the price of being computationally intensive, which restricts their application to small rock volumes. The linear Boltzmann transport equation from the kinetic theory of gases includes additional dependencies on the particle speed and direction of travel and can thus represent a greater range of transport behavior compared with the advective‐dispersion equation. The capability of the Boltzmann equation for modeling more complex transport behaviors of conservative tracers was evaluated. Parameters appearing in the Boltzmann equation were calibrated using small‐scale discrete fracture networks. The calibrated Boltzmann model can simulate at spatial/temporal scales that would be prohibitively expensive with a discrete fracture network. This hybrid approach successfully reproduced the results of discrete fracture network simulations in two dimensions.

Sediments and landforms at Kvı́árjökull, southeast Iceland: a reappraisal of the glaciated valley landsystem

Abstract Eyles identified Kviarjokull, an outlet of the icecap Oraefajokull, southeast Iceland, as an exemplar of the glaciated valley landsystem, emphasising rockfall debris supply, passive transport and reworking of a thick cover of supraglacial morainic till. In this paper, we take a fresh look at the sediments and landforms of Kviarjokull, focusing on clast form analysis to reconstruct primary transport pathways. New data demonstrate the importance of active transport of debris derived from the glacier bed. Substantial portions of the supraglacial debris cover can be traced back to englacial channel fill deposits or anomalously thick exposures of basal ice. These two types of sediments also make up much of Kviarjokull's large Neoglacial moraine rampart. We attribute the abundance of these non-rockfall sediments to the presence of a terminal overdeepening, and the switch from predominantly subglacial to predominantly englacial drainage that this induces. This hydrological switch enhances retention of debris within ice transport, preventing it from being washed away and making it available to feed ice-marginal moraine formation. The complexity of sediment transport processes observed at Kviarjokull and the contrast between it and alpine glaciers undermines any single concept of the glaciated valley landsystem; accordingly, we propose Kviarjokull as the type example of a distinct subclass, defined by its moderate relief, high-debris turnover, and drainage behaviour characteristic of an overdeepened basin.