Channel Gradient Research Articles

(Invited) Enabling Scalable CO/CO2 Reduction

Along with mitigation, the effective utilization of waste CO and CO2 from point sources in combination with renewable electrons has the potential to address climate challenges and change the manufacturing paradigm. Numerous funding offices and governments have set device level goals and reduction targets for CO2 emissions putting momentum behind and a focus on electrochemical CO/CO2 reduction. To enable this vision, the identification of limiting phenomena,[1,2] scalable integration and fabrication methods, and corresponding critical breakthroughs to improve stability (constant operation) and/or durability (dynamic operation), combined with selective as well as efficient operation are necessary.The implementation of gas diffusion electrodes over the last several years has enabled higher current densities and lower cell voltages for electrochemical CO/CO2 reduction.[3,4] Here, we pull from our experience in the fuel cell space and aim to serve as a node for the development of cell and electrode architectures that would help the community integrate novel materials (electrocatalysts, membranes, and ionomers), test devices as scales commensurate with the standards in the fuel cell and electrolysis community (>25 cm2), and subsequently characterize and model limiting phenomena. To this end, we will present limiting phenomena for CO2 to formate, CO2 to CO, and CO to various products, focusing on the effects of catholyte composition, ionomer binder chemistry, and the stability/durability of anode and cathode materials.[1] R. Kas, A.G. Star, K. Yang, T. Van Cleve, K.C. Neyerlin, W.A. Smith, Along the Channel Gradients Impact on the Spatioactivity of Gas Diffusion Electrodes at High Conversions during CO 2 Electroreduction, ACS Sustainable Chemistry & Engineering. 9 (2021) 1286–1296. https://doi.org/10.1021/acssuschemeng.0c07694.[2] S. Verma, X. Lu, S. Ma, R. I. Masel, P.J. A. Kenis, The effect of electrolyte composition on the electroreduction of CO 2 to CO on Ag based gas diffusion electrodes, Physical Chemistry Chemical Physics. 18 (2016) 7075–7084. https://doi.org/10.1039/C5CP05665A.[3] Y. Chen, A. Vise, W.E. Klein, F.C. Cetinbas, D.J. Myers, W.A. Smith, T.G. Deutsch, K.C. Neyerlin, A Robust, Scalable Platform for the Electrochemical Conversion of CO 2 to Formate: Identifying Pathways to Higher Energy Efficiencies, ACS Energy Letters. 5 (2020) 1825–1833. https://doi.org/10.1021/acsenergylett.0c00860.[4] D. Higgins, C. Hahn, C. Xiang, T.F. Jaramillo, A.Z. Weber, Gas-Diffusion Electrodes for Carbon Dioxide Reduction: A New Paradigm, ACS Energy Letters. 4 (2019) 317–324. https://doi.org/10.1021/acsenergylett.8b02035.

Biocrusts and catchment asymmetry in Tabernas Desert (Almeria, Spain)

Catchment asymmetry is a fairly frequent phenomenon on a global scale but the main causes leading to its formation are still not well understood. Where the intervention of structural or tectonic causes is not relevant, asymmetry seems to result from differential erosion between opposite slopes that flow into the same channel, which is frequently associated with contrasted biocrust and/or vegetation covers. Biocrusts are known to be important surface stabilizing agents. However, their geomorphological consequences at the landscape scale are little known. In this study we combined field measurements with digital elevation models and image analysis to determine whether catchment asymmetry in the Tabernas Desert (semi-arid SE of Spain) is a local or general phenomenon, and to explore the main factors determining asymmetry occurrence, magnitude and direction. We pay special attention to the role of biocrusts. We found that catchment asymmetry is a very common phenomenon in the area; only 25% of the catchments are symmetrical, while approximately 40% present asymmetry with the relatively shady hillslope having a lower gradient, and 35% with that hillslope being the steeper. Solar radiation reaching the soil, surface area and channel gradient in the considered catchment stretch, as well as the total catchment area upstream from the lower point of the considered stretch were the main abiotic factors controlling the formation of the asymmetry. Microclimatic differentiation due to differences in radiation input caused by the uneven topography favoured the relative stabilization of the shadier hillslope and its colonization by biocrusts and later by plants. The effect of the biocrusts and vegetation protection against water erosion on shadier hillslopes is often stronger than that of the set of abiotic factors and gives rise to asymmetries with lower gradients in the shady hillslope by promoting lateral displacement of the channel. We hypothesised that the opposite pattern, with the sunnier hillslope having a lower gradient, occurs when abiotic factors control the development of asymmetry formation. In these conditions, the effect of biocrusts and plants would act in the opposite direction. We propose a conceptual model of feedbacks generating catchment asymmetry, with biocrust playing a crucial role.

Impact of Changing Concavity Indices on Channel Steepness and Divide Migration Metrics

AbstractThe concavity index, , describes how quickly river channel gradient declines downstream. It is used in calculations of normalized channel steepness index, , a metric for comparing the relative steepness of channels with different drainage area. It is also used in calculating a transformed longitudinal coordinate, , which has been employed to search for migrating drainage divides. A value of 0.45 is typically assumed in studies. Here we quantify the variability in across multiple landscapes distributed across the globe. We describe the degree to which both the spatial distribution and magnitude of and can be distorted if is assumed rather than constrained. Differences between constrained and assumed of 0.1 or less are unlikely to affect the spatial distribution and relative magnitude of values, but larger differences can change the spatial distribution of and in extreme cases invert differences in relative steepness: relatively steep reaches can appear relatively gentle as quantified by . These inversions are function of the range of drainage area in the considered watersheds. We also demonstrate that the coordinate, and therefore the detection of migrating drainage divides, is sensitive to varying values of . The median of most likely across a wide range of mountainous and upland environments is 0.425. This wide range of variability suggests workers should not assume any value for , but should instead calculate a representative for the landscape of interest, and exclude basins for which this value is a poor fit.

Original

Basin morphometry is a crucial method of analysis to understand the geology, lithological structure, infiltration rate of rainwater, runoff, eroded load carrying capacity and flooding potential of a drainage basin. The quantitative techniques applied for linear, aerial and relief aspects of the drainage basin elucidate the rate of erosion, the intensity of denudation and subsequently the potential of the Nandakini river basin to flooding. The morphometric analysis of the Nandakini river basin in the Garwhal Himalayan region of Uttarakhand reveals that the Rf value of the Nandakini river basin is 0.28, indicating an elongated basin shape leading to quick flooding and poor draining out of floodwaters. Similarly, an elevation difference between the highest and lowest elevation is 5380 metres aids quick runoff and deposition of eroded debris in the drainage channels, another cause of channel overflow. The Rh value is high (0.12), indicating a high channel gradient with intense erosional processes operating due to steep gradient and this has a considerable impact on the rate of erosive geomorphic processes operating. The higher elevation on the Eastern part of the basin due to the Vaikrita Thrust, the Munsiyari Thrust (ie. the southern tilting Main Central Thrust) and the Baijnath Klippe has resulted in metamorphism in Miocene and Pliocene explaining the low rate of infiltration and rapid runoff.

Palaeoflood hydrology of the fluvial continental records of western India: A synthesis

Palaeoflood hydrology has emerged as an important tool to infer quantitative and qualitative aspects of ungauged floods based on their physical evidence. Palaeoflood studies in India have largely been undertaken in the rivers of Peninsular India, western India, Ganga plains and the Himalayas to determine the magnitude and age of extreme floods and their connection to variations in the monsoon intensity. Usually, the alluvial domains are unfavourable for the occurrence and preservation of flood deposits and related discharge estimation. However, the alluvial rivers of western India owing to their semi–confined banks comprising late Pleistocene sediments provide an opportunity for investigating both, the high magnitude flood events as well as average flow conditions. In this synthesis we concisely review the recent palaeohydrological studies in western India in terms of flood magnitude, occurrence of extreme events and its relation to the southwest monsoon variability over various time scales. Based on palaeo–fluvial reconstructions, the sedimentation pattern during late Pleistocene appears to be related to changes in channel gradient and the water surface width rather than to discharge variability. On the other hand, the aggradation in channels during early Holocene was largely controlled by the huge sediment influx and the incision that followed was in response to the increase in the discharge and competence of the river flow. The slackwater records from the bedrock channels have revealed that the large magnitude flood events occurred during wet climate phases during the last two millennia. A clustering of high magnitude events at climatic transitions and arid periods during mid–late Holocene has been surmised. Further the flood associated deposits delimited within Quaternary fluvial landforms and channel morphology are vital as these allow quantification of past flood discharges, velocities and stage levels and thus improve the future flood predictions.

Tectonically dominant surface denudation and topography in the Himalaya: Evidence from coupling between bedrock channel and valley hillslope topographies

AbstractThe Himalaya, a leading example of active mountains, is jointly shaped by intense tectonics, extreme climate and surface denudation. However, the causal relationship among these agents remains controversial. In this work, by an integrated analysis of bedrock channels and valley hillslopes using process‐based models, we discover 3D‐linear correlations in logarithmic space among precipitation‐estimated stream discharge, channel gradients and valley hillslope gradients. This finding indicates that channel incision and hillslope denudation are dynamically coupled in sculpting the erosional topography in tectonically active domains of the Himalaya. The channel‐hillslope coupling provides an independent approach to quantify key parameters of erosional models. Surface denudation indices simulated along streams and in drainage basins present a regular arrangement of high‐ and low‐denudation zones across the Himalaya, which coincides well with available thermochronological and structural data and thereby supports a tectonic dominance on surface denudation rates and topography over medium‐long timescale.

Synergistic improvement of device performance and bias stress stability of IGZO TFT via back-channel graded nitrogen doping

The electrical instability of a-IGZO TFTs limits its application in future display. Here, we investigate the effects of nitrogen doping on the electrical properties and bias stability of a-IGZO TFTs, and the IGZO films were obtained by magnetron sputtering using ceramic targets (In:Ga:Zn = 4:2:2). The performance and bias stability of a-IGZO TFTs are improved synergistically. The optimized device has a high mobility of 38.36 cm2/vs, threshold voltage of 1.11 V, subthreshold swing of 101.2 mV/dec, and the performance and stability are effectively improved, which may be mainly due to the back channel gradient nitrogen doping avoiding the formation of heterojunction interface and reducing the defect of bulk channel layer.

RUSLE and SDR model for erosional risk assessment and sediment yield estimation of Achara basin, western coast, India

The phenomenon of accelerated soil erosion, the resulting of irresponsible land use practices and human interference bring considerable changes within the Achara basin. The high rate of soil erosion deteriorates the fertility of the soil and consequently reduces crop productivity. Accumulation of transported soil at the lower part of the basin creates a severe problem of sedimentation within the channel and affects the hydraulic characteristics. The estimated potential sediment yield has been derived by using an integrated RUSLE model accompanied remote sensing database in geospatial environment. The result reveals the estimated average annual soil loss for the watershed as 18.81 t ha-1 year-1 . Sediment Delivery Ratio (SDR) fluctuates from 0.01 to 0.627. It has shown remarkably low for almost all parts of the basin, except steep slope and lower part of the watershed depending on the channel gradient of the major river. The junctions of the main channels are more susceptible to accumulate the sediment (> 4 t ha-1 year-1 ) within the basin. The lowermost portion of the basin receives a massive amount of sediment which ranges between 0.01 to 127 t ha-1 year-1 causing sedimentation within the estuary. The attempted work focuses on assessment of the erosional risk and sedimentation issue of Achara basin. The applied model will be helpful in the disaster management planning of such kind of coastal basins in Maharashtra.

Spatial correlation of macroinvertebrate assemblages in streams and the implications for bioassessment programs.

Stream bioassessment using benthic macroinvertebrate assemblages is widely implemented by regulatory agencies, yet a critical question regarding spatial autocorrelation and sample independence remains: How much of a stream network does a point sample represent? Macroinvertebrate assemblages vary along a longitudinal gradient, likely due to a combination of natural and anthropogenic factors that alter water physiochemistry and habitat. A better understanding of how these gradients affect macroinvertebrate assemblage variance could prevent spatial over- and under-sampling within bioassessment efforts. This project investigated longitudinal patterns (10s of km) of macroinvertebrate assemblages in 14 Wisconsin streams. Spatial autocorrelation was assessed using Moran's I and other multivariate methods with an emphasis on estimating the distance at which assemblages no longer display spatial correlation. Within most streams, there was a linear, direct relationship between assemblage dissimilarity and longitudinal distance, with distance to independence (DTI) ranging from 1.7-13.5km. DTI was most strongly affected by conductivity, which is often a surrogate for a suite of anthropogenic effects. With increasing conductivity, DTI increases, suggesting more homogenous assemblages in disturbed streams. Natural factors like watershed size, channel gradient, and riparian slope also affected DTI. Considering spatial correlation in monitoring designs could improve the efficiency and application of regulatory bioassessment programs.

Case Study: Influence of Three Gorges Reservoir Impoundment on Hydrological Regime of the Acipenser sinensis Spawning Ground, Yangtze River, China

After the construction of the Three Gorges Dam (TGD) in China, the downstream has been affected by the reduction in sediment discharge and regulation of flow processes, which have resulted in severe scouring and changes hydrological regime. Consequently, the spawning ground of Chinese sturgeon distributed along the downstream Yichang reach could be affected. This study examined the effects of TGD on the streamflow, sediment load and channel morphology downstream based on in situ measured data. Results showed that, after the impoundment of the TGD, sediment load at the downstream Yichang hydrological station decreased significantly, and the Yichang reach continued to be scoured. The distribution of erosion was uneven, and the scouring mainly occurred in the branching channels. The channel gradient and riverbed roughness increased with the erosion of the river cross section. After more than 10 years of erosion, the riverbed scouring and armouring in the Yichang reach was basically completed, thus we expected that the spawning grounds of Chinese sturgeon could be retain as the riverbed tends to be stable. The findings in this work have implications in the protection of the critically endangered Chinese sturgeon.

Nitrate removal processes in the riverbed during a single‐peak flood event

AbstractThe effect of the interplay between unsteady flow and bedform in a flood event on nitrogen cycling in the hyporheic zone (HZ) remains poorly understood. In this study, a reactive transport groundwater model with different flood hydrographs was proposed to investigate the effect of modified hyporheic flow on nitrate dynamics in the HZ, including nitrate source‐sink function, response to the single‐peak flood event and removal efficiency. The results demonstrate that there exists an optimal range of river channel gradients that could enhance the biogeochemical reactions (respiration, nitrification and denitrification) in a flood event. The HZ acts as a nitrate sink especially after the flood event, and its source‐sink function is independent of the unsteady discharge/stage conditions. The nitrate in the HZ has a hysteretic response to peak stage/discharge, and its removal efficiency is decreased by up to 70% compared to steady flow conditions. These findings not only provide a better understanding of nitrogen dynamics under the effect of unsteady channel flow, but also can be applied for river restoration to efficiently remove nitrate in the HZ by modifying river channel gradients.

Spatial Variations of Tectonic Uplift - Subducting Plate Effects on the Guerrero Forearc, Mexico

Uplift is the predominant factor controlling fluvial systems in tectonically deforming regions. Mountains along subduction zones force incision, aggradation, or sinuosity modifications, showing differential uplift and variations in erosion rates, in river incision, and in channel gradient produced by ongoing tectonic deformation. Thus, landscape can provide information on the tectonic activity of a defined region. Here, field studies, analysis of geomorphic indices using a digital elevation model, and dating of river terraces were undertaken to extract the following: (1) determine rates of ongoing tectonic deformation, (2) identify evidence of active faulting, and (3) explain the possible relation of ongoing differential uplift in the topography of the overriding plate with the geometry and roughness effects of subducting slab along the Mexican subduction within the Guerrero sector. Landscape analysis using geomorphic indices suggests segmentation along stream of the studied Tecpan River basin. Rates of tectonic uplift were derived from river incision rates computed with the combination of strath terrace heights and associated dating. Tectonic uplift rates vary from ∼1 ± 0.3 mm/yr up to ∼5 ± 0.6 mm/yr during the Holocene, consistent with inferred high tectonic activity in this zone. These results vary significantly spatially, i.e., increasing upstream. Possible explanations for spatial variations of tectonic uplift rates are most likely related to an effect of the geometry and the rugged seafloor of the oceanic Cocos plate subduction beneath a faulted continental lithosphere.

Along the Channel Gradients Impact on the Spatioactivity of Gas Diffusion Electrodes at High Conversions during CO2 Electroreduction

Results of a 2-D transport model for a gas diffusion electrode performing CO₂ reduction to CO with a flowing catholyte are presented, including the concentration gradients along the flow cell, spatial distribution of the current density and local pH in the catalyst layer. The model predicts that both the concentration of CO₂ and the buffer electrolyte gradually diminish along the channels for a parallel flow of gas and electrolyte as a result of electrochemical conversion and nonelectrochemical consumption. At high single-pass conversions, significant concentration gradients exist along the flow channels leading to large local variations in the current density (>150 mA/cm²), which becomes prominent when compared to ohmic losses. In addition, concentration overpotentials change dramatically with CO₂ flow rate, which results in significant differences in outlet concentrations at high conversions. The outlet concentration of CO attains a maximum of 80% along with 5% CO₂ and 15% H₂, although the maximum single-pass conversion is limited to below 60% due to homogeneous consumption by the electrolyte. Fundamental and practical implications of our findings on electrochemical CO₂ reduction are discussed with a focus on the trade-off between high current density operation and high single-pass conversion efficiency.

A tectono-geomorphological perspective of micro-earthquake swarm activity prone areas around Bhavnagar and Jamnagar in Saurashtra, western India

Areas around Bhavnagar and Jamnagar in eastern and northern parts of Saurashtra respectively, are identified previously as prone to recurrent earthquake swarm activity. Sparse seismotectonic studies so far have not revealed any linkage with known faults in Bhavnagar area while no structures are known to occur in the area around Jamnagar. We carried out detailed tectono-geomorphic studies with contrasting geomorphic settings with a view to provide an insight into the swarm activity from a geomorphological perspective. The study is based on extensive field studies and quantitative geomorphic analysis of landscape and drainage. The area around Bhavnagar is divisible into two tectono-geomorphic domains – the E-W trending Sihor Fault zone located to the west of Bhavnagar (domain-I) and the terrain to its south which shows undulating landscape controlled by N–S trending structural trends (domain-II). The quadrant in the SW between these two domains consists of southward titled trappean hills which form source area for drainages flowing northward through Sihor Fault zone and those flowing eastward through domain-II. Late Quaternary, possibly Holocene tectonic activity along the Sihor Fault is indicated by the northward tilt of alluvial plain surface, knickpoint in rivers and small scale minor faults along the fault zone, prominent decrease in depth of fluvial incision away from the fault zone and youthful landscape indicated by drainage basin analysis. Domain-II comprises the largely erosional pediplain developed over trappean and Tertiary rocks to the south of Bhavnagar. The drainages show an early stage of landscape development due to ongoing tectonic activity. The area around Jamnagar is dominantly a peneplain formed over subhorizontal trappean lava flows. The peneplain is a manifestation of the prolonged period of non-erosion and deposition during the Cenozoic. The rivers show youthful landscape in the central part of the peneplain which includes, large knickpoints, rapids, anomalous river bends, steepening of channel gradient and large potholes. This ENE-WSW trending zone of anomalous fluvial geomorphic anomalies points to the existence of a fault or fold in the subsurface. The structure appears to be active as indicated by the denser cluster of earthquake swarm along this zone. We infer that the generation of earthquake swarm activity comprising low to moderate magnitude shocks is caused by the sheared rocks along the Sihor Fault near Bhavnagar and the ENE-WSW trending subsurface structure near Lalpur which provide avenues for downward percolation of rainwater to deeper levels causing loss of frictional resistance along weak planes.

Effects of subsidies from small anadromous Pacific salmon populations on stream and riparian food webs are mediated by channel gradient

AbstractEcological effects of migratory animal populations on ecosystems can be significant, but these impacts may be modified by other environmental factors, especially when migratory populations ...

Influence of water temperature and biotic interactions on the distribution of westslope cutthroat trout (Oncorhynchus clarkii lewisi) in a population stronghold under climate change

Climate warming is expected to have substantial impacts on native trout across the Rocky Mountains, but there is little understanding of how these changes affect future distributions of co-occurring native fishes within population strongholds. We used mixed-effects logistic regression to investigate the role of abiotic (e.g., temperature) and biotic factors (bull trout presence, Salvelinus confluentus) on distributions of westslope cutthroat trout (Oncorhynchus clarkii lewisi; WCT) in the North Fork Flathead River, USA and Canada. The probability of WCT presence increased with stream temperature and decreased with channel gradient and bull trout presence, yet the effect of bull trout was reduced with increasing pool densities. Combining this model with spatially explicit stream temperature projections, we predict a 29% increase in suitable habitat under high emissions through 2075, with gains at mid-elevation sites predicted to exceed bull trout thermal tolerances and high-elevation sites expected to become more thermally suitable for WCT. Our study illustrates the importance of considering abiotic and biotic drivers to assess species response to climate change, helping to guide local-scale climate adaptation and management.

A New Runoff Routing Scheme for Xin’anjiang Model and Its Routing Parameters Estimation Based on Geographical Information

The Xin’anjiang model is a conceptual hydrological model, which has an essential application in humid and semi-humid regions. In the model, the parameters estimation of runoff routing has always been a significant problem in hydrology. The quantitative relationship between parameters of the lag-and-route method and catchment characteristics has not been well studied. In addition, channels in Muskingum method of the Xin’anjiang model are assumed to be virtual channels. Therefore, its parameters need to be estimated by observed flow data. In this paper, a new routing scheme for the Xin’anjiang model is proposed, adopting isochrones method for overland flow and the grid-to-grid Muskingum–Cunge–Todini (MCT) method for channel routing, so that the routing parameters can be estimated according to the geographic information. For the new routing scheme the average overland flow velocity can be determined through the land cover and overland slope, and the channel routing parameters can be determined through channel geometric characteristic, stream order and channel gradient. The improved model was applied at a 90 m grid scale to a nested watershed located in Anhui province, China. The parent Tunxi watershed, with a drainage area of 2692 km2, contains four internal points with available observed streamflow data, allowing us to evaluate the model’s ability to simulate the hydrologic processes within the watershed. Calibration and verification of the improved model were carried out for hourly time scales using hourly streamflow data from 1982 to 2005. Model performance was assessed by comparing simulated and observed flows at the watershed outlet and interior gauging stations. The performance of both original and new runoff routing schemes were tested and compared at hourly scale. Similar and satisfactory performances were achieved at the outlet both in the new runoff routing scheme using the estimated routing parameters and in the original runoff routing scheme using the calibrated routing parameters, with averaged Nash-Sutcliffe efficiency (NSE) of 0.92 and 0.93, respectively. Moreover, the new runoff routing scheme is also able to reproduce promising hydrographs at internal gauges in study catchment with the mean NSE ranging from 0.84 to 0.88. These results indicate that the parameter estimation approach is efficient and the developed model can satisfactorily simulate not only the streamflow at the parent watershed outlet, but also the flood hydrograph at the interior gauging points without model recalibration. This study can provide some guidance for the application of the Xin’anjiang model in ungauged areas.

A hybrid machine-learning model to estimate potential debris-flow volumes

Empirical-statistical models of debris-flow are challenging to implement in environments where sedimentary and hydrologic triggering processes change through time, such as after a large earthquake. The flexible and adaptive statistical methods provided by machine learning algorithms may improve the quality of debris flow predictions where triggering conditions and the nature of sediment that can bulk flows varies with time. We developed a hybrid machine-learning model of future debris-flow volumes using a dataset of measured debris-flow volumes from 60 catchments that generated post-Wenchuan Earthquake (Mw 7.9) debris flows. We input topographic variables (catchment area, topographic relief, channel length, distance from seismic fault, and average channel gradient) and the total volume of co-seismic landslide debris into the PSO-ELM_AdaBoost machine-learning model, created by combining Extreme learning machine (ELM), particle swarm optimization (PSO) and adaptive boosting machine learning algorithm (AdaBoost). The model was trained and tested using post-2008 Mw 7.9 Wenchuan Earthquake debris flows, then applied to understand potential volumes of post-earthquake debris flows associated with other regional earthquakes (2013 Mw 6.6 Lushan Earthquake, 2010 Mw 6.9 Yushu Earthquake). We compared the PSO-ELM_Adaboost method with different machine learning methods, including back-propagation neural network (BPNN), support vector machine (SVM), ELM, PSO-ELM. The Comparative analysis demonstrated that the PSO-ELM_Adaboost method has a higher statistical validity and prediction accuracy with a mean absolute percentage error (MAPE) less than 0.10. The prediction accuracy of debris-flow volumes trigged by other earthquakes decreases to 0.11–0.16 (absolute percentage error), suggesting that once calibrated for a region this method can be applied to other regional earthquakes. This model may be useful for engineering design to mitigate the risk of large post-earthquake debris flows.

Producing synthetic maps of dust polarization using a velocity channel gradient technique

ABSTRACT In modern cosmology, many efforts have been made to detect the primordial B-mode of cosmic microwave background polarization from gravitational waves generated during inflation. Considering the foreground dust contamination of microwave polarization maps, it is essential to obtain a precise prediction for polarization in dust emission. In this work, we show a new method to produce synthetic maps of dust polarization in the magnetized turbulent interstellar medium from more abundant high-resolution H i data. By using the velocity channel gradient technique, we are able to predict both the direction and degree of dust polarization by investigating spectroscopic H i information in position–position–velocity space. We apply our approach to the Galactic Arecibo L-band Feed Array H i data, and find a good correspondence between synthesized maps and Planck’s polarization measurements at 353 GHz.

Morphologic and hydraulic variability of small bedrock and alluvial channels in relation to lithological controls, Upper Ogun River Basin, Southwestern Nigeria

ABSTRACT The influence of lithology on morphological variability across space presents a unique approach to understand how morphological variables and domain units respond to lithological variations. This study examines variation existing in channel morphological variables across domain units within a basement complex. Eighty-three reaches were surveyed across six third-order basins within the Upper Ogun River basin, Nigeria. Each of the six third-order basins is heterogeneously underlain by various lithological formations. Fourteen morphological variables (bankfull; depth, width, cross-sectional area, width-depth ratio, wetted perimeter, hydraulic radius, discharge, total stream power, specific stream power, shear stress, velocity, dimensionless stream power, Darcy-Weisbach friction factor and channel gradient) were measured and estimated across the 83 reaches. Analysis of Variance revealed that significant variation occurs in channel morphological properties between schist and granite and between granite and migmatite. Also, bankfull width showed exponent values of wbf ~ Qbf 0.21 for migmatite; wbf ~ Qbf 0.11 for granites; and wbf ~ Qbf 0.34 for schists. Channel unit sequence using Markov chain presents two transitions identified as bedrock to plane-bed and step-pools to plane-bed. The absence of transitions as observed is closely tied to the occurrence of non-cyclic patterns.