Residual Conductivity Research Articles

Preparation of phosphotungstic acid hybrid proton exchange membranes by constructing proton transport channels for direct methanol fuel cells

For direct methanol fuel cells (DMFCs), a unique hybrid proton exchange membrane (PEM) made of polyvinyl alcohol (PVA) and quaternized polyethyleneimine (QPEI) is presented. Employing QPEI as an anchoring agent is advantageous for enhancing the compatibility of the organic-inorganic interface when phosphotungstic acid (PWA) is used as the proton conductor on the assumption that the leakage of PWA is successfully reduced. Utilizing polymers as a substrate reduces the high solubility of PWA in water owing to hydrogen bonding and electrostatic interactions. Additionally, PWA performs the function of successive proton transport channels in the optimized PVA-QPEI-2 PEM, resulting in a maximum proton conductivity of 194.5 mS cm−1 and residual proton conductivity of more than 80% after 30 days of soaking in deionized water at 80 °C. Furthermore, the fuel cell assembled with PVA-QPEI-2 PEM delivers a peak power density of 147.2 mW cm−2 at 60 °C and 40% relative humidity. Noteworthily, this organic-inorganic hybrid PEM containing PWA as a proton carrier is fabricated by a remarkably simple method, which has a methanol permeability that is an order of magnitude less than the Nafion® used in commercial applications, demonstrating its competitive potential for application in DMFCs.

High-density mapping improves detection of conduction gaps after pulmonary vein isolation ablation with a circular mapping catheter.

High-density (HD) mapping of the pulmonary vein (PVs) has been hypothesized to improve the detection of conduction gaps in the radiofrequency ablation lesions set after pulmonary vein isolation (PVI) for the treatment of atrial fibrillation (AF). We aimed to compare the incidence of gaps after PVI with a standard 20-pole circumferential mapping catheter (CMC-20) and an HD mapping catheter (HD Grid). This prospective study included patients scheduled for high-power short-duration PVI. Acute PVI was defined as an entrance and exit block using the CMC-20 after ≥ 20min waiting period. The left atrium was then remapped using the HD Grid high-density mapping catheter to identify residual conduction gaps in the PVI lines by voltage and activation criteria. The primary endpoint was the number of gaps identified per patient by the HD Grid catheter. A total of 20 patients were included (mean age 59.9 ± 10.8years, 15% female, 70% paroxysmal AF). The new map with the HD Grid identified 6 gaps in 4 patients (20%) or 0.3 ± 0.7 gaps per patient (p = 0.055 when compared to CMC-20). Five gaps (83%) were located at the right PVs. There was no difference in mapping time (CMC-20 12.2 ± 2.6min vs HD Grid 11.7 ± 3.4min, p = 0.452); however, the number of points was significantly higher in the HD Grid map (1662.7 ± 366.1 vs 1171.6 ± 313.6, p < 0.001). HD mapping during AF ablation identified PVI gaps in 1 out of 5 patients. Therefore, HD mapping may have the potential to improve AF ablation success rates in the long term. ClinicalTrials.gov NCT04850508 on April 20, 2021.

Molecular Identification of Free-living Amoebae Isolated from Hospital Water Systems in Southwest Iran.

Free-living amoebae are opportunistic amoebae that usually live freely in various environmental conditions, including warm water and even in water supply network pipes and reservoirs connected to water. In addition to living freely, these protozoa are able to attack the host's body when they enter a human or animal body. Therefore, it is necessary to identify their presence in water resources. So, this study aimed to identify free-living amoebae isolated from water reservoirs of hospitals in southwest Iran. A total of 80 water samples were isolated from the hospitals of Ahvaz city, southwest Iran, and their physical and chemical parameters were measured. The samples were then put into non-food agar culture medium and stained using the Wright-Giemsa staining. Finally, the samples were identified by the PCR molecular method. The mean pH and turbidity values were 7.57 ± 0.03 and 3.31 ± 0.26 nephelometric turbidity unit (NTU), respectively. The mean residual chlorine and electrical conductivity were 0.91 ± 0.02 and 1122.39 ± 24.31, respectively. In addition, 9 (11.25%) and 3 (3.75%) samples were contaminated with Acanthamoeba spp. and Naegleria spp., respectively. However, no positive cases of Balamuthia spp. infection were observed. Moreover, two samples were co-infected with Acanthamoeba spp. and Naegleria spp. Due to the existence of free-living amoebae in water storage tanks at hospitals, it is necessary to prevent possible contamination with these amoebae and infectious agents by using new methods of disinfection and purification of water resources.

Effects of starting powder on microstructure and thermal conductivity of pressureless-sintered fully ceramic microencapsulated fuels

The effects of the starting SiC powder (α or β) with the addition of 5.67 wt% AlN–Y2O3–CeO2–MgO additives on the residual porosity and thermal conductivity of fully ceramic microencapsulated (FCM) fuels were investigated. FCM fuels containing ∼41 vol% and ∼37 vol% tristructural isotropic (TRISO) particles could be sintered at 1870 °C using α-SiC and β-SiC powders, respectively, via a pressureless sintering route. The residual porosities of the SiC matrices in the FCM fuels prepared using the α-SiC and β-SiC powders were 1.1% and 2.3%, respectively. The thermal conductivities of FCM pellets with ∼41 vol% and ∼37 vol% TRISO particles (prepared using the α-SiC and β-SiC powders, respectively) were 59 and 41 Wm−1K−1, respectively. The lower porosity and higher thermal conductivity of FCM fuels prepared using the α-SiC powder were attributed to the higher sinterability of the α-SiC powder than that of the β-SiC powder.

An active convective [formula omitted]He heat switch

The design and experimental demonstration are reported of an active convective heat switch suitable for use at cryogenic temperatures. The switch is mechanically simple, relatively inexpensive, and requires no moving parts, instead being operated entirely using heaters. The working gas used is 4He in a closed cycle and, as such, the switch requires no external gas connections. Closed conductances on the order of 50 mW/K have been demonstrated with residual open conductances on the order of 0.4 mW/K. Novel modelling is presented which shows excellent agreement with the experimental data and significant improvement over existing models.

Stepwise development of atmospheric pressure plasma jet driven by bursts of high-voltage nanosecond pulses at multi-tens MHz

This study employs the bursts of high-voltage nanosecond pulses at multi-tens MHz to drive the helium atmospheric pressure plasma jet. Such bursts are obtained by modulating a high-voltage nanosecond pulse based on the wave reflections in a coaxial cable. The development processes and mechanisms of the plasma jet are analyzed in detail based on the discharge waveforms, discharge images, gas temperature, electron density, and axial electric field. Because the time interval between adjacent pulses is much shorter than the characteristic plasma decay time, the discharge channel driven by the first pulse still has high residual electron density and conductivity when the second pulse arrives. The first discharge channel serves as an extension of the high-voltage electrode. In this case, the second discharge starts at the end of the first discharge channel and continues to propagate forward. Driven by the bursts of high-voltage nanosecond pulses, the stepwise propagation of a guided streamer along the plasma jet is observed. The characteristic of the stepwise development of the guided streamer is stable and repeatable under the same condition and does not change at different helium flow rates if the flow is laminar. Reducing the cable length results in a higher equivalent pulse frequency in the bursts and significantly increases the plasma jet length. However, an excessively high frequency will cause a rise in gas temperature and pressure fluctuation in helium flow, resulting in a reduction in the length of the laminar region and an unstable discharge.

Residual Strength and Thermal Conductivity of Self-Compacting Concrete with Recycled Expanded Polystyrene Subjected to High Temperatures

One of the most important processes of physical deterioration in concrete is the exposure to high temperatures that influences their durability and stability during life service. In addition, if self-compacting concrete is formed by lightweight aggregates, such as EPS, it is necessary to analyze its behaviour after it has been exposed to high temperature conditions. This research shows research that evaluates the effect EPS on the mechanical properties of self-compacting concrete at high temperatures. This study evaluated physical-mechanical properties, including residual compressive strength and thermal conductivity after exposure at 22oC, 150oC, 350oC, 500oC and ISO834. Experimental results showed that the loss of residual compressive strength of the specimens up to 350oC is almost insignificance, but it will be reduced by 49% and 70% when temperatures increase up to 500oC and 700oC respectively. EPS contributes to lightness, thermal insulation, and commitment to the environment in lightweight SCC.

Strong and Flexible High-Performance Anion Exchange Membranes with Long-Distance Interconnected Ion Transport Channels for Alkaline Fuel Cells.

Anion exchange membrane fuel cells (AEMFCs), which operate on a variety of green fuels, can achieve high power without emitting greenhouse gases. However, the lack of high ionic conductivity and long-term durability of anion-exchange membranes (AEMs) as their key components is a major obstacle hindering the commercial application of AEMFCs. Here, a series of homogeneous semi-interpenetrating network (semi-IPN) AEMs formed by cross-linking a copolymer of styrene (St) and 4-vinylbenzyl chloride (VBC) with branched polyethylenimine (BPEI) were designed. The pure carbon copolymer skeleton without sulfone/ether bonds accompanied by the semi-IPN endows the AEMs with excellent chemical stability. Moreover, the cross-linking effect of flexible BPEI chains is supposed to promote the "strong-flexible" mechanical properties, while the presence of multiquaternary ammonium groups can boost the formation of microphase separation, thereby enhancing the ionic conductivity of these AEMs. Consequently, the optimized (S1V1)3Q AEM exhibits an excellent hydroxide conductivity of 106 mS cm-1 at 80 °C, as well as more than 81% residual conductivity after soaking in 1 M NaOH at 60 °C for 720 h. Furthermore, the H2/O2 fuel cell assembled with (S1V1)3Q AEM delivers a peak power density of 150.2 mW cm-2 at 60 °C and 40% relative humidity. All results indicate that the approach of combining a pure carbon backbone polymer with a semi-IPN structure may be a viable strategy for fabricating AEMs that can be used in AEMFCs for long-term applications.

Analyzing Relationships of Conductivity and Alkalinity Using Historical Datasets from Streams in Northern Alberta, Canada

Many measurements, tools, and approaches are used to identify and track the influence of human activities on the physicochemical status of streams. Commonly, chemical concentrations are utilized, but in some areas, such as downstream of coal mines, capacity indices such as specific conductivity have also been used to estimate exposure and risk. However, straightforward tools such as conductivity may not identify human influences in areas with saline groundwater inputs, diffuse exposure pathways, and few discharges of industrial wastewater. Researchers have further suggested in conductivity relative to alkalinity may also reveal human influences, but little has been done to evaluate the utility and necessity of this approach. Using data from 16 example sites in the Peace, Athabasca, and Slave Rivers in northern Alberta (but focusing on tributaries in Canada’s oil sands region) available from multiple regional, provincial, and national monitoring programs, we calculated residual conductivity and determined if it could identify the potential influence of human activity on streams in northern Alberta. To account for unequal sampling intervals within the compiled datasets, but also to include multiple covariates, we calculated residual conductivity using the Generalized Estimating Equation (GEE). The Pearson residuals of the GEEs were then plotted over time along with three smoothers (two locally weighted regressions and one General Additive Model) and a linear model to estimate temporal patterns remaining relative to known changes in human activity in the region or adjacent to the study locations. Although there are some inconsistencies in the results and large gaps in the data at some sites, many increases in residual conductivity correspond with known events in northern Alberta, including the potential influence of site preparation at oil sands mines, reductions in particulate emissions, mining, spills, petroleum coke combustion at one oil sands plant, and hydroelectric development in the Peace basin. Some differences in raw conductivity measurements over time were also indicated. Overall, these analyses suggest residual conductivity may identify broad influences of human activity and be a suitable tool for augmenting broad surveillance monitoring of water bodies alongside current approaches. However, some anomalous increases without apparent explanations were also observed suggesting changes in residual conductivity may also be well-suited for prompting additional and more detailed studies or analyses of existing data.

Low electronic conductivity of Li7La3Zr2O12 solid electrolytes from first principles

The formation of lithium dendrites in solid-state lithium-ion batteries leads to short-circuiting and cell failure. One proposed mechanism for dendrite growth is the direct reduction of lithium ions, due to residual electronic conductivity in the nominally insulating solid electrolyte. This article presents a fully first-principles scheme for modeling the electronic conductivity of nominally insulating materials, such as solid electrolytes, as a function of synthesis protocol, and applies this to the prototypical lithium-ion solid electrolyte Li${}_{7}$La${}_{3}$Zr${}_{2}$O${}_{2}$ (LLZO). LLZO is predicted to have low bulk electronic carrier mobilities and negligible carrier concentrations. This suggests that the bulk electronic conductivity of LLZO is not sufficiently high to enable lithium-dendrite growth, implicating extended defects and surface contributions in any non-negligible electronic conductivity in lithium garnet solid electrolytes.

Validation of Models for Simulating the Soil Moisture Characteristics

Background: The determination of the soil moisture characteristic is a tedious, lengthy and costly laboratory methods. However, for the specific soil texture, once it is known, the soil moisture at various tension can be simulated through modelling approach which eliminates the requirements of performing the experiments every time. Therefore, the attempt was made for the determinations of the soil moisture characteristics during the year-2019 and validating the various models’ using these empirical data. Methods: The present research covers the experimentation during the year 2019 for determination of the soil moisture characteristics and fitting the obtained empirical data to mathematical frames of the various models. The moisture characteristics was obtained by measuring different moisture content values at different suction values through two experiments viz. wetting cycle (Absorption phase) and drying cycle (Desorption phase). The desorption curve was obtained by using the pressure plate apparatus and the wetting curve was measured through the capillary rise open tube method. Result: The saturation, field capacity, permanent wilting, residual moisture content, void ratio and saturated hydraulic conductivity were found as 43.5%v/v, 25.88%v/v, 12.05%v/v, 8.1%v/v. 0.77 and 0.2808 m/day respectively. Among the fitted models, the van Genuchten model was found best fit to observe data to simulate the desorption and sorption phase of the soil moisture retention characteristics. The soil moisture retention characteristics of the sorption and desorption phases indicated a hysteresis of approximately two log cycles.

Low Temperature Specific Heat and Thermal Conductivity in Superconducting UTe2

The measurements [Phys. Rev. B 100, 220504(R) (2019)] do not detect noticeable thermal conductivity in superconducting UTe2 in the T = 0 limit. At the same time the same crystals exhibit a large residual density of states comparable with its normal state value. The improvement of samples quality leads to the augmentation of critical temperature of transition to the superconducting state accompanied by the decreasing of residual specific heat ratio C(T)/T at T → 0. There is presented an analytic derivation of this inverse correlation property in concrete cases of triplet superconducting states with node-less and point-nodes order parameters allowed by symmetry in UTe2. The obtained explicit formulas for the residual thermal conductivity are in reasonable correspondence with observations.

Quality of rainwater drained by a green roof in the metropolitan region of Recife, Brazil

The objective of this study was to evaluate the potential non-potable uses that can be given to the water flowing from a green roof through the characterization of its quality using the parameters and reference values contained in the Brazilian Standard ABNT NBR 15527:2007. The research was carried out in the Garage Building of the Charles Darwin Business, for a period of five months. Fifteen samples were collected from three collection points (rainwater, irrigation, and drainage from the green roof) and evaluated. For the qualitative characterization of the waters, the physicochemical parameters hydrogen potential (pH), turbidity (TBD), apparent color (AC), free residual chlorine (FRC) and electrical conductivity (EC), in addition to the microbiological parameters total coliforms, Escherichia coli and number of heterotrophic bacteria (HB), were determined. Data were subjected to descriptive and multivariate statistical analysis. The results obtained show that the green roof contributed to the reduction of rainwater pH. The green roof drainage water had higher levels of AC and TBD due to the concentrations of suspended particles, which acted as a source of EC. The FRC values complied with the legislation in all treatments. Likewise, the microbiological parameters partially complied with the standards established by the legislation. Cluster analysis formed two distinct groups, G1 comprising HB and TBD, and G2 containing the variables pH, AC, EC, and FRC. Although the quality of the drainage water does not meet all the standards required by law, this water has the potential for reuse for non-potable purposes.

Mechanical and thermo-chemical degradation of concrete exposed to simulated airfield conditions

Surface degradation at parking aprons of military airfields concerns jet aircraft safety. It is caused by the disintegration of coarse aggregates in concrete. This study aims to understand the effects of repeated exposure to various aviation oils and high-temperature on concrete constituent materials. An airfield exposure condition was created to expose samples made with different water to cement ratios (w/c). Samples were tested for residual mechanical properties, thermal conductivity, specific heat, thermogravimetric and microstructural analysis. Results show that the w/c ratio of concrete significantly influences the residual strength of the exposed samples. Moreover, aviation oils react with ordinary concrete at higher temperatures and produce harmful salts. Besides, thermal incompatibility between the aggregates and cement paste triggers microcracks in cement paste and thermal cracks in the coarse aggregate. Due to the simultaneous thermal and chemical attack, concrete suffers the disintegration of aggregates and flake-like concrete pieces on the top surface.

Validation of the peak frequency of bipolar electrograms for detection of residual conduction in atrial scar tissue

Abstract Funding Acknowledgements Type of funding sources: Private company. Main funding source(s): Abbott Background Activation and voltage (Bi-V) maps (Panel A) based on conventional bipolar electrograms (EGMs) are influenced by both near-field (NF) and far-field (FF) EGM components. This represents a limitation in the accurate detection of residual conduction within regions of scar. Peak frequency (PF) EGM analysis may better distinguish NF from FF activation vs conventional detection methods. (Panels B &amp; C) Purpose 1. To validate the use of PF to detect residual conduction in a well-defined model of narrow isthmus of conduction such as subacute pulmonary vein (PV) reconnection following atrial fibrillation ablation. 2. To compare discrimination value of PF and conventional Bi-V to detect such isthmuses. Methods Bi-V and activation maps were acquired during redo PV isolation (PVI) procedures using a rectangular 16-pole catheter (HD-Grid). LA-PV conduction was assessed during coronary sinus (CS) pacing (500ms cycle length). Any conduction gap (GAP) site at which PVI was established using ≤3 focal radiofrequency applications was analyzed. (Panel A) EGMʼs ≤1cm from the site of PVI were classified as GAP (vs EGMʼs ≥1cm - No-Gap). (Panel B) Results 28 GAPs were found in 12 of 14 consecutive patients in the study. 3,976 EGMʼs (1,547 GAP vs 2,429 No-GAP) were analyzed. GAP regions showed significantly higher PF than No-GAP regions (345 ±135 vs 181±116 Hz, P&amp;lt;0.0001) (Panel E). GAP regions also showed significantly higher BiV than No-GAP regions (1.86±2.11 mV vs 0.62±1.22 mV, P&amp;lt;0.0001) (Panel D). ROC curves for GAP vs No-GAP discrimination were better for PF (AUC 0.84) than for Bi-V (AUC 0.74) with optimal cutoffs of 240 Hz and 0.2 mV, respectively. (Panel F) Conclusion PF better detects residual conduction within an atrial scar region than conventional Bi-V. The PF cutoff value for gap discrimination in the PV antra is 240 Hz.

Quantifying the variability of bipolar voltage amplitude with sensing angle in residual conduction isthmuses in atrial scar

Abstract Funding Acknowledgements Type of funding sources: Private company. Main funding source(s): Abbott Background The angle between the activation wavefront and bipole may conceal the conduction isthmus in conventional bipolar voltage mapping, but the extent of variability of electrogram (EGM) voltage amplitude with directional changes has not been quantified. Purpose Using a well-defined model of discrete atrial conduction, we sought to use Omnipolar Technology (OT) to assess variability of voltage amplitude as a function of sensing angle, in sites of residual conduction and scar tissue. Methods During redo pulmonary vein isolation (PVI) procedures, baseline voltage maps were acquired during coronary sinus pacing (500 ms) using a rectangular 16-pole catheter (HD Grid). During retrospective analysis with OT research software, all EGM’s ≤1 cm radius from the site of PVI were classified as GAP (vs No-GAP; Panel A) The variability of voltage amplitude (OT-ΔV) with sensing angle (θ) was computed as the difference between the maximum and minimum voltages (OT-Vmax - OT-Vmin), in both GAP and No-GAP subregions (Panels A &amp; B). Results 23 GAP sites were identified in 12 of 15 consecutive patients studied. 3464 EGM’s (1386 GAP vs 2078 No-GAP) were analyzed. Global mean OT-ΔV was 0.46±0.80 mV. GAP regions showed significantly (P&amp;lt;0.0001) higher OT-ΔV as compared with No-GAP regions (0.80±1.03 mV vs 0.24±0.47 mV respectively; Panel C) The mean Δθ angle for OT-ΔV was similar in both GAP and No-GAP regions (88.6±11.3° vs 88.0±13.6°, P=0.1; Panel D). Conclusion The variability of voltage amplitude as a function of bipole orientation can be significant, especially in GAP regions (0.80±1.03 mV). (2) OT-ΔV holds promise for identification of residual conduction within atrial scar tissue.

Influence of atrial cycle length and site of origin on the peak frequency of bipolar electrograms to discriminate isthmus conduction in atrial scar

Abstract Funding Acknowledgements Type of funding sources: Private company. Main funding source(s): Abbott Background Peak frequency (PF) of conventional bipolar electrograms is a novel parameter which may distinguish between near-field (NF) and far-field (FF) signals. However, the influence of activation rate and the direction of the activation front on it is unknown. Purpose 1. To study the influence of atrial cycle length and wavefront origin on PF to detect residual conduction in a well-defined model of narrow isthmus of conduction such as subacute pulmonary vein (PV) reconnection following atrial fibrillation ablation. 2. To compare this influence with that found for Bipolar voltage (BiV). Methods Baseline maps were acquired in redo PV isolation (PVI) procedures with a 16-pole grid catheter (HD-Grid) during low rate sinus rhythm (SR), low rate coronary sinus pacing at 500 ms cycle length (CSLR) and high rate coronary sinus pacing at 300 ms cycle length (CSHR). PFs were retrospectively computed. PVI sites requiring ≤3 radiofrequency applications were included, with EGMʼs ≤1cm from the PVI site classified as GAP (vs &amp;gt;1cm, No-GAP). Results 28 GAPs were found in 12 of 14 consecutive patients in the study. 3976 EGMʼs (1547 GAP vs 2429 No-GAP) were analyzed. In both GAP and No-GAP, PF was similar in SR vs CSLR (GAP: 363±132 Hz -SR vs 345±135 Hz -CSLR, P=NS ; No-GAP: 196±110 Hz -SR vs 181±116 Hz -CSLR, P=NS). PF was slightly higher for CSLR vs CSHR. (GAP: 345±135 Hz -CSLR vs 317±154 Hz -CSHR, P&amp;lt;0.001; No-GAP 181±116 mV -CSLR vs 162±129 mV -CSHR, P&amp;lt;0.01). (Panel A). BiV was significantly higher in SR vs CS pacing but similar between CSLR and CSHR (GAP: 1.86±2.11 mV -SR vs 0.87±1.19 mV -CSLR vs 0.74±0.92 mV -CSHR, P= NS, No-GAP: 0.62±1.22 mV -SR vs 0.33±0.68 mV - CSLR vs 0.27±0.48 mV - CSHR, P=NS. (Panel B). ROC GAP discrimination for PF was similar between SR and CSLR (AUCʼs: 0.86-SR, 0.84-CSLR) and slightly lower for CSHR (AUC: 0.81) with optimal cutoffs of 260, 240 and 220 Hz, respectively. ROC GAP discrimination for BiV was lower vs PF in all rhythm modes (AUCʼs: 0.77-SR, 0.74-CSLR, 0.75-CSHR), with optimal cutoffs of 0.3, 0.2 and 0.15 mV, respectively. Conclusion ROC gap discrimination was significantly higher for all rhythm modes with PF vs BiV. PF showed slightly decreasing cutoff values for SR, CSLR and CSHR respectively, whereas BiV showed a greater relative decrease in cutoffs for SR, CSLR and CSHR.

Variations in bark structural properties affect both water loss and carbon economics in neotropical savanna trees in the Cerrado region of Brazil

Abstract Even after complete stomatal closure, plants lose water through the leaf cuticles and bark. This residual water conductance of leaves (gleaf‐res) and stems (gbark) can negatively impact plant water balance and affect plant survival in seasonally dry environments. However, little is known about the costs and benefits associated with such water leaks, especially on stem level. Here, we characterized the structural and functional determinants of the variability in gbark across tropical savanna species to elucidate how variations in this trait are related to contrasting growth strategies. The high variability in gbark across species was associated with morphoantomical properties of the outer bark (thickness, density and lenticel investment), and such characteristics influenced both stem transpiration and respiration, suggesting the existence of a trade‐off between water conservation and oxygen permeability, which reflected contrasting growth and dehydration tolerance strategies. For instance, species with higher gbark and gleaf‐res presented a fast resource acquisition strategy but were more prone to drought‐induced mortality by hydraulic failure. However, model simulations revealed that the relative contribution of gleaf‐res and gbark to overall water balance depended on whether leaves were less or more resistant to cavitation than the stems. Synthesis. By combining correlative studies, experimental results and a modelling exercise, we provide a new understanding of the costs and benefits associated with the variability in gbark across tropical savanna species and a new perspective for studies of water relations and carbon economics in species from a hyperdiverse savanna.

EVALUATION OF GROUNDWATER SUITABILITY FOR IRRIGATION PURPOSE USING GIS AND IRRIGATION WATER QUALITY INDICES

As a major source of water for irrigation, the evaluation and assessment of groundwater to ensure it meets the quality for sustainable agriculture is key. This research presents the findings of the quality of groundwater and its suitability for irrigation purposes. This was carried out using the irrigation water quality indices and the Geographic Information System (GIS). The Inverse Distance Weighted (IDW) method of the GIS was used to study the spatial distribution of these indices. Indices considered include Sodium Absorption Ratio (SAR), Percentage Sodium (%Na), Permeability Index (PI), Kelly Ratio (KR), Magnesium Hazard (MH), Total Hardness (TH), Residual Sodium Bicarbonate (RSBC) and Potential Salinity (PS). The values obtained were SAR (0.00 to 10.99, mean of 3.43), Percentage Sodium (26.00% to 94.42%, mean of 70.33%), Permeability Index (94.14% to 379.47%, mean of 161.45%), Kelly Ratio (0.00 to 8.62, mean of 3.19) and Magnesium Hazard (0.00% to 80.33 %, mean of 39.21%). Total Hardness (12.49 mg/L to 77.50 mg/L, mean of 31.35 mg/L), Residual Sodium Bicarbonate (-0.55 meq/L to 5.46 meq/L, mean of 1.41 meq/L), Potential Salinity (0.88 meq/L to 2.53 meq/L, mean of 1.69 meq/L) and Electrical Conductivity (110µS/cm to 910µS/cm, mean of 277.14µS/cm). The computed water indices when compared with known standards show that the groundwater from the study area is generally fit and can be applied for irrigation purposes.

Numerical analysis of electro-convection in dielectric liquids with residual conductivity

Injection-induced electro-convection (EC) of dielectric liquids is a fundamental problem in electrohydrodynamics. However, most previous studies with this type of EC assume that the liquid is perfectly insulating. By perfectly insulating, we mean an ideal liquid with zero conductivity, and in this situation, the free charges in the bulk liquid originate entirely from the injection of ions. In this study, we perform a numerical analysis with the EC of dielectric liquids with a certain residual conductivity based on a dissociation–injection model. The spatiotemporal distributions of the flow field, electric field, and positive/negative charge density in the parallel plate configuration are solved utilizing the finite volume method. It is found that the residual conductivity inhibits the onset of EC flow, as well as the strength of the flow field. The flow features and bifurcations are studied in various scenarios with three different injection strengths in the strong, medium, and weak regimes. Three distinct bifurcation sequences with abundant features are observed by continually increasing or decreasing the electric Reynolds number. The present study shows that the residual conductivity significantly affects the bifurcation process and the corresponding critical point of EC flows.