Kh Values Research Articles

Computational evaluation of phosphonium ILs as CO2 absorbents for electrochemistry

Since phosphonium-based ionic liquids (ILs) are suitable electrolytes for electrochemical reduction, a computationally informed analysis of these ILs was conducted to assess their ability to absorb CO2. In this work, theoretical and experimental approaches were mixed with a focus on gas solubility, transport properties, and structural characterization. The calculations included free energy of solvation (ΔG), the Henry constant (Kh), and short-range energies (Coulomb plus Lennard–Jones). Two ILs, [P1444][TFSI] and [P1444][FSI], were selected for further evaluation because of their lower Kh values. The enthalpy and entropy of the solvation process for these selected ILs were computationally determined; both ILs were found to have a favourable enthalpy of solvation for gas dissolution, and [P1444][TFSI] had a lower penalty for solvation (less negative entropy). Moreover, the analysis revealed competition among the ions interacting with the gas. The structural characterization of the [P1444][TFSI] and [P1444][FSI] with the CO2 systems involved radial and spatial distribution functions. The gas was likely enveloped by an anion cage, and oxygen and fluorine exhibited greater interactions with the carbon atom of CO2 than nitrogen. The viscosity and density were also calculated for the two systems, and the addition of CO2 only caused a slight change on these values. Experiments on viscosity and density confirmed the computational results; here, compared with those of neat ionic liquids, an approximate 4 % decrease in the viscosity of CO2-saturated systems was observed. Finally, the actual CO2 solubility in [P1444][TFSI] was experimentally determined to be 120 mM; this value was nearly four times greater than those of typical aqueous bicarbonate solutions.

Embolism propagation does not rely on pressure only: time-based shifts in xylem vulnerability curves of angiosperms determine the accuracy of the flow-centrifuge method.

Centrifuges provide a fast approach to quantify embolism resistance of xylem in vulnerability curves (VCs). Since embolism formation is assumingly driven by pressure only, spin time is not standardised for flow centrifuge experiments. Here, we explore to what extent embolism resistance could be spin-time dependent, and hypothesise that changes in hydraulic conductivity (Kh) would shift VCs towards higher water potential (Ψ) values over time. We quantified time-based shifts in flow-centrifuge VCs and their parameter estimations for six angiosperm species by measuring Kh over 15minutes of spinning at a particular speed, before a higher speed was applied to the same sample. We compared various VCs per sample based on cumulative spin time, and modelled the relationship between Kh, Ψ, and spin-time. Time-based changes of Kh showed considerable increases and decreases at low and high centrifuge speeds, respectively, which generally shifted VCs towards more positive Ψ values. Values corresponding to 50% loss of hydraulic conductivity (P50) became less negative by up to 0.72MPa in Acer pseudoplatanus, and on average by 8.5% for all six species compared to VCs that did not consider spin-time. By employing an asymptotic exponential model, we estimated time-stable Kh, which improved the statistical significance of VCs in 5 of the 6 species studied. This model also revealed the instability of VCs at short spin times with embolism formation in flow-centrifuges following a saturating exponential growth curve. Although pressure remains the major determinant of embolism formation, spin-time should be considered in flow-centrifuge VCs because not considering the time-dependent stability of Kh overestimates embolism resistance. This spin-time artefact is species-specific, and likely based on relatively slow gas diffusion that is associated with embolism propagation. The accuracy of VCs is improved by determining time-stable Kh values for each centrifuge speed, without considerably extending the experimental time to construct VCs.

Estimating fracture characteristics and hydraulic conductivity from slug tests in epikarst of southwest China

Study regionGuizhou Province, Southwest China Study focusThis study aims to estimate the hydraulic conductivity (Kh) of the weathered rock fractures (epikarst) based on the best fitting of observed water head in 105 slug tests in the study sites. Specifically, comparisons of the estimated results from the analytical and numerical methods reveal the effects of changes in fracture flow conditions (e.g., steady and non-steady) on Kh for various fracture apertures and soil fillings. New hydrological insights for the regionThe results comparatively show that Kh from the analytical solution of steady flow was significantly underestimated, and the numerical modeling of the non-linear and unsteady flow can improve the water head fitting when the Reynolds number (Re) > 17.27. The optimized Kh ranges 0.014–2673 m/d and the mean value of Kh is about 100 times the median value, suggesting that epikarst flow might be controlled by a limited number of larger fractures. Moreover, the soil filling in large fractures (>10 mm) creates a turning point of the exponential increase of Kh with d. Comparatively, the naturally full-filling fractures resemble the soil matrix with a low Kh, and the partial-filling fractures can create preferential flow around the soil-rock interfaces with a high Kh. These results fundamentally improve our understanding of water infiltration, retention, and availability for plant uses in the karst areas of southwest China.

Mechanical and Optical Characterization of Single-shade Resin Composites Used in Posterior Teeth.

This study aimed to evaluate the optical and mechanical performance of two single-shade resin-based composites (RBCs) compared to those of a conventional RBC for restoring posterior teeth. Two single-shade RBCs, Omnichroma (Tukoyama) and Vittra Unique APS (FGM), and a conventional RBC, Filtek Z350XT shade A2 (3M Oral Care), were evaluated in this study. The optical shade-matching performance was measured using a spectrophotometer. The light emitted by VALO Grand (Ultradent) and transmitted through the 2.0-mm RBC specimens was evaluated using beam profiling. Knoop hardness (KH, N/mm2), degree of conversion (DC, %) at the top and bottom, flexural strength (FS, MPa), elastic modulus (E, GPa), postgel shrinkage (Shr, %), and shrinkage stress (MPa) were evaluated. Scanning electron microscopy (SEM) was used to characterize the filler. Data for FS, E, and Shr were analyzed by one-way analysis of variance (ANOVA) and KH and DC by repeated one-way ANOVA measurement followed by Tukey test (α=0.05). The modified von Mises stress values, light transmission, and SEM images were analyzed qualitatively. All single-shade RBCs exhibited higher chromatic adaptation than the Filtek Z350XT (p<0.001). Omnichroma exhibited less color difference than Vittra Unique APS, irrespective of the shade. The light transmitted through Omnichroma and Vittra Unique APS increased during polymerization. KH and DC values were significantly reduced from the top to the bottom of the specimens for all RBCs (p<0.001); however, the ratio values were always higher than 80%. In general, all RBCs demonstrated similar mechanical properties. All RBCs exhibited a similar FS (p=0.083) and Shr value (p=0.144). Filtek Z350XT exhibited significantly higher E (p<0.001) than both single-shade RBCs. All RBCs exhibited similar shrinkage stress during restoration and similar residual stress during occlusal loading. Single-shade Omnichroma and Vittra Unique APS increased light transmission during light-activation, demonstrating better chromatic adaptation than conventional Filtek Z350XT. In general, Omnichroma and Vittra Unique APS exhibited similar mechanical properties and shrinkage stress distributions as Filtek Z350XT during light-activation and occlusal loading.

Enhancing wave energy harvesting: Performance analysis of a dual chamber oscillating water column

This study investigates the hydrodynamic characteristics of a dual chamber oscillating water column (OWC) setup through a series of experiments, aiming to assess its potential for harvesting wave energy. The investigation involves varying frontwall drafts, power take-off (PTO) dampings, and incident wave conditions, while quantitatively evaluating the OWC system's performance using the capture width ratio (CWR) as the key metric. The findings indicate that the dual chamber configuration consistently exhibits enhanced performance for all combinations of orifice ratios, opening heights, and incident wave frequencies studied. As expected, increasing the opening height of the second chamber leads to improved performance of the OWC. Interestingly, the effect of varying applied PTO damping on improvement of CWR values is found to be relatively insensitive. The most significant improvements in CWR are observed for larger incident wave frequency values. For instance, for dimensionless wave frequency (Kh) values of 1.43 and 1.68, the CWR increases from 0.47 and 0.26 to 0.72 and 0.52, respectively, with the orifice ratio combination of τ1, 0.015, and τ2, 0.018. It is worth noting that the single chamber OWC operates most efficiently within the resonant frequency range of 0.94–1.23, while the dual chamber design extends this frequency range, enabling efficient wave energy capture over a wider spectrum of wave conditions. The dual chamber configuration offers considerable advantages for wave energy conversion applications by increasing the effective frequency bandwidth for optimal energy capture. The research findings suggest that this innovative design has the potential to significantly enhance the efficiency and adaptability of wave energy converters, contributing to the advancement of sustainable and renewable energy technologies.

A source-to-surface model of heat and fluid transport in the Taupō Rift, New Zealand

We construct 2-D numerical models of bulk heat and water transport from the mid-crust (10 km depth) to the surface in a 20 km-wide continental rift, based on observations from the Taupō Rift in the central Taupō Volcanic Zone (TVZ) of New Zealand.The model represents a simplified geological setting with two low-permeability basement-like rock-types, the first defining the margins of the rift and the second a distinct ‘rifted basement’. The rift is overlain with a 2 km-thick, 20 km-wide layer of shallow volcanic infill. At the base of model there is a 10 km-deep heat source (the ‘hotplate’) with a specified TVZ-like heat flux of 0.77 Wm−2 and a ‘target’ average hotplate temperature of 700o to 900 °C, required to maintain the low melt fractions at ∼10 km depth inferred from geophysics.Parameterising the permeability of the rifted basement is a key part of the paper as it enables both the heat flux boundary condition and a temperature constraint to be satisfied at the hotplate. More generally, it allows the flexibility to control the depth of temperature contours which represent proxies for geophysical measurements. It is described as a power-law for log10(horizontal component of permeability, kh) with specified values of kh at two depths and a power law exponent as free parameters. Viable models which satisfy all constraints for the hydrothermal system beneath the TVZ rift have a power-law exponent less than ∼0.4, shallow (2 km deep) kh's of 10–14.0 to 10–13.0 m2, and deep (10 km) kh‘s <10–16.5 m2. The vertical component of the rifted basement permeability, kv, is ten times higher than kh.A generic feature of the models is that irregular, unsteady convection occurs in the upper ∼5 km of the rift. This results in temporal and spatial fluctuations in heat and fluid flow which are interpreted as high-temperature TVZ-like geothermal systems which have temperatures of ca. 300 °C at 2 km depth. Over the nominal simulation time of 3 Myr, approximately 40% of the geothermal systems are clustered within ∼2 km of the rift margins, with the remainder distributed roughly uniformly across the rift. Between the geothermal systems cool recharge from the surface occurs, with temperatures as low as 50 °C occurring at 5 km depth. The models successfully match temperature proxies for the depths of maximum seismicity (450 °C) and shallowest partial melt (> 700 °C) inferred from geophysical observations.Heat transport within the rift is dominated by convection. This is true even at 10 km depth, at the base of the geothermal systems, where kh in the rifted basement approaches 10−17 m2. In this situation, the relatively large value of vertical permeability kv, ∼ 10−16 m2, allows convection to occur. Conductive heat transport dominates in regions ∼1 km in vertical extent immediately above the hotplate and between the geothermal systems.The vigour of the hydrothermal systems is controlled by the permeability of the shallow volcanics, through which all cold surface recharge and hot outflows of fluid occur. Models with low permeability for the shallow volcanics produce longer lasting and higher temperature geothermal systems, and those with high permeability produce fewer and cooler geothermal systems.

Cyclic voltammetry studies of malonamide hydrazone derivative and its electrochemical effect on CdCl2

The purpose of this study is to detect the electrochemical reduction of a novel N-(benzo[d]thiazol-2-yl)-3-oxo-3-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)propenamide ligand (o-H2BMP) at varying pH by using a gold electrode in the presence of tetra butyl ammonium bromide as a supporting electrolyte at room temperature. The outcomes results showed that the effective reduction mechanism of the o-H2BMP ligand consumes 8 electrons and 8 hydrogen ions at pH 5, which belong to the reduction of azomethine and two carbonyl groups at (0.0518 V – 0.678 V), respectively. Also, the electrochemical behavior of Cd(II) ions in a cell containing 0.1 M KCl in 50 % (DMSO-water) mixed solvent by using glassy carbon electrode was proceeded with two electrons transfer as Cd+2/Cd0 in reversible mechanism. This work presents a novel structural analysis of the complexes that can be formed in solution and which exhibit stochiometric ratios of (M:L, 1:1, 2:3, 1:2). Moreover, the degree of reversibility of Cd(II) ions redox behavior was evaluated in the absence/presence of the o-H2BMP ligand which indicated that the redox behavior of Cd(II) ions more reversible in the case of free Cd(II) according to the ∆Ep, α, and kh values. While, in the presence of the o-H2BMP ligand, the degree of reversibility was decreased and the number of electrons transferred in the rate-determining step increased which confirming the complexation reaction of Cd(II) with the ligand.

Effect of Ligand Aromaticity on Cyclohexane and Benzene Sorption in IRMOFs: A Computational Study.

A series of four isoreticular MOFs (IRMOF-1, -10, -14, and -16) were selected for a computational investigation of the effect of ligand aromaticity on the adsorption capacity of an aromatic VOC (benzene) compared to its nonaromatic analog (cyclohexane). The affinity of the adsorbates was evaluated by calculating Henry's constants and adsorption enthalpies. It has been evidenced that while KH values decrease with ligand elongation (IRMOF-10 and -16), inserting a pyrene core into the MOF structure (IRMOF-14) increases both the cyclohexane and benzene adsorption efficiency by ∼290 and 54%, respectively. To elucidate host-guest interactions, we sought to locate preferential adsorption sites in MOF structures for the two VOCs studied by using the GCMC method. It appears that benzene interacts with the metal center (Zn4O clusters) and most of the ligand while cyclohexane tends to localize preferentially only near the Zn4O clusters. Coadsorption isotherms (equimolar mixture of benzene and cyclohexane) demonstrated the preferential adsorption of cyclohexane due to the stronger affinity for the MOF structure. On the other hand, for other isoreticular structures, the ligand elongation leads to a shift of the adsorption curve of cyclohexane caused by pore size increase and therefore less interactions with the walls. This phenomenon is counterbalanced in the case of IRMOF-14 due to stronger interactions between the cyclohexane and pyrene groups. The present results thus open perspectives in the design of promising MOF candidates for high-performing separation and sorption/detection of hydrocarbon VOCs.

Kinetics of H· Transfer from CpCr(CO)3H to Various Enamides: Application to Construction of Pyrrolidines.

The rate constants kH (kD) have been determined at 27 °C for H· (D·) transfer from CpCr(CO)3H(D) to the C=C bonds of various enamides. This process leads to the formation of α-amino radicals. Vinyl enamides with N-alkyl and N-phenyl substituents have proven to be good H· acceptors, with rate constants close to those of styrene and methyl methacrylate. A methyl substituent on the incipient radical site decreases kH by a factor of 4; a methyl substituent on the carbon that will receive the H· decreases kH by a factor of 380. The measured kH values indicate that these α-amino radicals can be used for the cyclization of enamides to pyrrolidines. A vanadium hydride, HV(CO)4(dppe), has proven more effective at the cyclization of enamides than Cr or Co hydrides-presumably because the weakness of the V-H bond leads to faster H· transfer. The use of the vanadium hydride is operationally simple, employs mild reaction conditions, and has a broad substrate scope. Calculations have confirmed that H· transfer is the slowest step in these cyclization reactions.

Influence of Mono- and Multiwave Light-curing Units on the Microhardness and Degree of Conversion of Light-cured Resin Cements.

This study evaluated the Knoop hardness (KH, N/mm2) and degree of conversion (DC, %) on the margins of light-cured resin cements with different photoinitiators using a single light-curing unit (LCU) with two heads (mono- and multiwave). Three types of resin cements were used with different photoinitiators: Megalink Esthetic (Odontomega, São Paulo, Brazil) with a camphorquinone photoinitiator; Allcem Veneer (FGM, Joinville, Brazil) with the Advanced Polymerization system (APS), and Variolink Esthetic LC (Ivoclar Vivadent, Schaan, Liechtenstein). Thirty samples were collected and divided into six groups (n=5 each). The resin cement samples were made into the shape of a maxillary right central incisor and photoactivated under a 0.5-mm-thick ceramic sheet. A single LCU (Radii Xpert, SDI) with two heads (mono- and multiwave) was used. The tip of the LCU was positioned at the center of the sample in a standardized manner. Raman spectroscopy was performed to evaluate the DC, and KH was evaluated through the Knoop microhardness test. Five regions were evaluated: cervical, mesial, buccal (center), distal, and incisal. There was a significant difference in the DC only for the type of cement (p<0.001), indicating that the cement with the APS photoinitiator presented excellent results. There were significant differences in the type of cement (p<0.001), type of light (p<0.001), region (p<0.001), and the interaction between the type of cement and type of light (p<0.001). The resin cement with the APS photoinitiator cured with monowave light showed the highest KH values. The beam profiles of all groups, with and without the interposition of ceramic and resin cement, were examined by light transmission. The cement with the APS photoinitiator presented the best results with respect to the DC and KH. In comparison with mono- and multiwaves, the LCU may not be a determining factor for the properties of light-cured resin cements. The buccal region showed the best results for DC and KH, indicating the need for a greater amount of light-curing at the cementation margins.

Effect of four different mono and multi-wave light-curing units on the Knoop hardness of veneer resin composites

ObjectivesTo evaluate the effect of mono and multi-wave light-curing units (LCUs) on the Knoop hardness of resin-based composites (RBC) that use different photoinitiators. MethodsCentral incisor-shaped specimens 12 mm long, 9 mm wide, and 1.5 mm thick were made from 2 RBCs that use different photoinitiators: Tetric N-Ceram (Ivoclar Vivadent) - and Vittra APS (FGM), both A2E shade. They were light-cured with 4 different LCUs: two claimed to be multi-wave - VALO Grand (Ultradent) and Emitter Now Duo (Schuster); and two were monowave - Radii Xpert (SDI) and Elipar DeepCure-L (3 M Oral Care) using 2 different light exposure protocols: one 40 s exposure centered over the specimen; and two 20 s light exposures that delivered light from two positions to better cover the entire tooth. 16 groups with 10 specimens in each group were made. The Knoop hardness (KH, kg/mm2) was measured at the top and bottom of the specimen in the center and at the cervical, incisal, mesial, and distal peripheral regions. The active tip diameters (mm) and spectral radiant powers (mW/nm) of the LCUs were measured with and without the interposition of the RBC, as well as the radiant exposure beam profiles (J/cm²) delivered to the top of the RBCs. The data was analyzed using Three-way ANOVA and Tukey's tests (α = 0.05). ResultsThe VALO Grand (1029 mW) emitted twice the power of the Radii Xpert (500 mW). The KH values of VI and TN resin composite specimens were significantly affected by the LCU used (p < .001), the measurement location (p < .001), and the surface of the specimen (p < .001). LCUs with wider tip diameters produced greater Knoop hardness values at the peripheries of the 12 mm of long, 9 mm wide specimens. In general, the VALO Grand produced the highest KH values, followed by Elipar DeepCure-L, then by Radii Xpert. The Emitter Now Duo LCU produced the lowest values. Exposing the veneers from two locations reduced the differences between the LCUs and the effect of the measurement location. Only the VALO Grand could fully cover the composite veneer with light when the two locations were used. SignificanceThe light tip must cover the entire restoration to photocure the RBC beneath the light tip.

DRIVING OF STRUGGLE VALUES AS MORAL PRESSURE TO CONSTRUCT THE KHAYRA UMMAH SYSTEM

The drive of struggle values and moral pressure in social systems and organizations are interdependent. A good social system is strongly influenced by the values of struggle and moral pressure, so that everything contained in struggle and morality is reflected in social life. Thus, an ideal social order can be constructed through a patented moral approach in a blueprint. In this article, the blueprint of moral pressure refers to the struggle values of KH. Mahmud Zubaidi as a transformative figure in Indonesia in his struggle to construct a civil society, namely a community of the best society (khayra ummah). The study of khayra ummah is specific to the contextualization of KH. Mahmud Zubaidi's concept of prophetic da'wah as moral pressure. This research uses an ethnographic qualitative approach involving 14 key interfaith informants in Indonesia. The results of this study indicate that KH Mahmud Zubaidi's prophetic da'wah carries three pillars of khayra ummah that are constructed as strugle values and moral pressure, including: amar ma'ruf (humanization), nahi munkar (liberation), and iman billah (transcendence). The construction of these three pillars is coordinated by a university as a product of its struggle, which is then translated into various academic and non-academic activity programs. The contextualization of prophetic da'wah and its difference are also discussed.

Rock core VOC profiles diagnostic of aquitard occurrence and integrity in a multi-layered sedimentary rock aquifer flow system

Aquitard assessment poses a challenge for practitioners and researchers managing dense non-aqueous phase liquid (DNAPL) contaminants in sedimentary rock aquifer systems. Within these systems, DNAPL migration and bulk hydraulic properties are controlled by fracture networks which are difficult to characterize at relevant scales with conventional methods. A previous study at a DNAPL contaminated site used contrasts in high-resolution vertical gradients to delineate four aquitards and two surfaces with poor vertical connectivity within a thick (>200 m) sedimentary rock aquifer system primarily composed of layered sandstones. In this study, we corroborate that method by using the existing DNAPL contamination as a tracer to identify and characterize the aquitards in the sequence and assess aquitard integrity. Closely spaced samples of rock from four continuous cores were collected and analyzed for volatile organic compounds (VOCs). The cores were collected along a transect perpendicular to groundwater flow and 75 m downgradient of the DNAPL source zone. Dissolved phase contaminant concentrations were collected using high-resolution multilevel systems placed along the plume centerline, downgradient from the source. The rock core and groundwater VOC concentration profiles suggest a primary aquitard limits vertical migration of both DNAPL and the associated dissolved phase contaminants, despite relatively large, downward gradients across its lower boundary. A calibrated, three-dimensional numerical groundwater flow model indicates an anisotropy factor of 1,000 for this aquitard. The Kv values for all four aquitards are only slightly lower than the values for the aquifers. However, the aquitard Kv values are 1–3 orders of magnitude less than their Kh values, and the aquitard Kh values are often similar to or even greater than the Kh values for the aquifers. Therefore, large anisotropy, rather than exceptionally low Kv values, distinguish the aquitards from the aquifers in this system. Fracture network characterization of nearby outcrops showed the anisotropy of the aquitards can be attributed to laterally extensive, bedding parallel partings coupled with short, frequently terminating, and poorly connected vertical fractures. In addition, the rock VOC profiles combined with fracture network data show that fracture termination surfaces can be powerful inhibitors of downward DNAPL migration providing additional evidence for the importance of these features in sedimentary rock flow systems. Ultimately, this study reveals the important influence of anisotropic aquitards on DNAPL migration, accumulation, and persistence, as well as associated plume migration. Furthermore, it demonstrates that subtle contrasts critical to aquitard integrity may be easily missed with long screened wells and other conventional, low resolution site characterization methods.

Evaluation of tribological interactions and machinability of Ti6Al4V alloy during finish turning under different cooling conditions

The titanium alloy Ti6Al4V has several applications and is considered as a difficult-to-machine material. This study evaluates some tribological interactions in finish turning of Ti6Al4V titanium alloy, including the tool wear, and coefficient of friction in tool-chip interface. Subsequently, the machinability of Ti6Al4V titanium alloy has been investigated, considering the chip geometry, chip thickness ratio, as well as changes in the total cutting force components. The turning process was carried out over a wide range of the feed rate (f) and depths of cut (ap) using hard carbide, GC1115 grade, inserts with double-layer PVD coating. The finish turning tests were conducted under the dry, flood, and MQL (minimum quantity lubrication) cutting conditions. It was found that favorable chip shapes (arc loose) were obtained in the range ap = 0.9–1.2 mm and f = 0.25–0.4 mm/rev. Increasing the f clearly affects the formation of a serrated chip. In addition, the intensity of tool wear, as well as the variations of cutting forces and chip thickness ratios were strongly affected by the applied cooling/lubricating condition. Compared to wet conditions, the Kh values decrease by ∼22 % with dry machining and by ∼12 % with MQL. Compared to wet conditions, for dry machining the cutting forces decrease to 70 % and with MQL to 8 %. The cumulative wear rate under dry machining increases by 18 % compared to wet conditions, and with MQL reduces by 19 %.

ON THE PROBABILITY OF UNIDIRECTIONAL NONLINEAR EXTREME WAVES IN THE PRESENCE OF WAVE REFLECTION

Extreme waves are known to appear in different water depth regimes, and their focusing mechanisms have been intensively studied over the last decades. This experimental study aims to improve understanding of rogue wave statistics when wave reflections are at play. A series of unidirectional JONSWAP wave trains have been generated in a wave flume while varying the water depth and beach inclination slope. The data collected near the beach installation suggests a general decrease in extreme wave probability with the increase of the beach inclination, thus, with the increase of wave reflection. In deep-water, the numerical simulations based on the coupled nonlinear Schrodinger equation, which accounts for the presence of reflective waves, show a very good agreement with the experimental data. The irregular wave measurements in the presence of wave reflection indicate that the decrease in probability of exceedance, which correlates with the decrease in the value of kurtosis, is due to the weakening of third-order effects. When the water depth is decreased to a finite depth regime, we can observe an increase of extreme events, which we attribute to the change of the wave breaking threshold. However, no substantial rogue waves have been observed below the dimensionless depth kh value of 1.36. Then again, nonlinear effects always remain relevant and at play in all cases considered.

Activation and Deactivation of Benzylic C−H Bonds Guided by Stereoelectronic Effects in Hydrogen Atom Transfer from Amides and Amines to Alkoxyl Radicals

AbstractKinetic and product studies on the reactions of tert‐alkoxyl radicals with secondary and tertiary alkanamides bearing benzylic α‐C−H bonds, isoindoline, tetrahydroisoquinoline and the corresponding N‐acetyl derivatives were carried out. Product studies on the reactions with the tert‐butoxyl radical (tBuO⋅) point toward exclusive HAT from the benzylic α‐C−H bonds. Comparison of the kH values measured for reaction with the cumyloxyl radical (CumO⋅) with those obtained previously for the corresponding reactions of N‐alkyl‐ and N,N‐dialkylalkanamides, are indicative of a lack of benzylic activation and the operation of steric and stereoelectronic effects. Compared to N‐methyl and N‐ethyl groups, the presence of N‐benzyl groups increases the barrier required to reach the optimal conformation for HAT, where the α‐C−H bond to be cleaved is perpendicular to the plane of the amide, precluding concurrent overlap with the phenyl π‐system. When the benzylic α‐C−H bonds are in a conformation that allows for optimal overlap with both the phenyl π‐system and the amide π‐system or amine nitrogen lone pair, as in the isoindoline and tetrahydroisoquinoline derivatives, increases in kH that exceed 2‐orders of magnitude were observed, highlighting the strong contribution provided by stereoelectronic activation to these HAT processes.

Understanding the exchange process between ground and surface water using mini drive point piezometer and mathematical models to identify suitable managed aquifer recharge sites.

In the current study, subsurface characteristics within the complex formation of the Shilabati basin system of West Bengal, India, extending over an area of 3888 km2, have been estimated using a cost-effective piezometer and MIKE FEFLOW package based on a steady-state numerical model. Pore size and fine particle content of streambeds are affected by two opposing flow contraptions. Such opposite flow conditions are likely to affect the hydraulic conductivity of the streambed. However, analogies of the hydraulic conductivity (Kh) of streambeds for losing and gaining streams have not been well documented in the recent past. The Kh value from the piezometer has been highest at the Dakshin Pairachali site (6.765 m/day), with the stream gaining water from the discharge of the local aquifer. Analysis of the stream-aquifer interaction using the FEFLOW model has allowed us to understand the groundwater water head of the basin ranging from 160.33 to 0.32 m.a.s.l (meters above sea level). The present study also constitutes the first attempt for the identification of suitable sites for the implementation of managed aquifer recharge (MAR) technology in West Bengal, India, to manage extreme drought events. The suitable sites have been identified by means of three fuzzy multi-criteria decision analysis based on nine criteria: river discharge, moisture content, porosity, drainage type, rainfall, land use type, geology, aquifer material, and hydraulic conductivity. To design a radial collector well and infiltration gallery for the selected site in an anisotropic, homogeneous, unconfined, and semi-infinite aquifer near a fully penetrating stream, a pumping test has been conducted to optimize a safe yield of 12.096 MLD (megaliters per day).

Cylindrical frontwall entrance geometry optimization of an oscillating water column for utmost hydrodynamic performance

The present research focuses on optimizing the diameter of the cylindrical frontwall entrance shape of an Oscillating Water Column (OWC). In particular, 240 experimental runs are performed for five diameter values, various PTO dampings, dimensionless wave frequencies (Kh) and wave heights. The cylindrical front wall entrance geometry is found to improve the Capture Width Ratio (CWR) of the Oscillating Water Column (OWC) under all conditions. The maximum and average CWR improvement are calculated as 45% and 25%, respectively. The simplicity of the front wall entrance modification makes this achievement even more remarkable. A negative correlation is identified between the diameter size and Kh. In particular, for relatively low, intermediate and large Kh values, optimum diameter sizes are found as 12 cm, 7 cm and 5 cm, respectively. In a specific frequency band, diameter that makes CWR maximum is also found as a function of wave height and orifice ratio. Free decay experimental tests are performed to verify the superiority of the cylindrical geometry. Experimental results indicate that cylindrical frontwall entrance geometry prevents or at least diminishes the flow separation that occurs due to sharp frontwall underlip. Consequently, the reduction in diameter size helps to alleviate the shear stresses on both sides of the front wall, thereby improving the structural integrity of the Oscillating Water Column (OWC) chamber.

Efficient degradation of aqueous dichloromethane by an enhanced microbial electrolysis cell: Degradation kinetics, microbial community and metabolic mechanisms

Dichloromethane (DCM) has been listed as a toxic and harmful water pollutant, and its removal needs attention. Microbial electrolysis cells (MECs) are viewed as a promising alternative for pollutant removal, which can be strengthened from two aspects: microbial inoculation and acclimation. In this study, the MEC for DCM degradation was inoculated with the active sludge enhanced by Methylobacterium rhodesianum H13 (strain H13) and then acclimated in the form of a microbial fuel cell (MFC). Both the introduction of strain H13 and the initiation in MFC form significantly promoted DCM degradation. The degradation kinetics were fitted by the Haldane model, with Vmax, Kh, Ki and vmax values of 103.2 mg/L/hr, 97.8 mg/L, 268.3 mg/L and 44.7 mg/L/hr/cm2, respectively. The cyclic voltammogram implies that DCM redox reactions became easier with the setup of MEC, and the electrochemical impedance spectrogram shows that the acclimated and enriched microbes reduced the charge transfer resistance from the electrode to the electrolyte. In the biofilm, the dominant genera shifted from Geobacter to Hyphomicrobium in acclimation stages. Moreover, Methylobacterium played an increasingly important role. DCM metabolism mainly occurred through the hydrolytic glutathione S-transferase pathway, given that the gene dcmA was identified rather than the dhlA and P450/MO. The exogenous electrons facilitated the reduction of GSSG, directly or indirectly accelerating the GSH-catalyzed dehalogenation. This study provides support for the construction of an efficient and stable MEC for DCM removal in water environment.

Effect of polymer architecture on the adsorption behaviour of amphiphilic copolymers: A theoretical study

HypothesisPolymer architecture is known to have significant impact on its adsorption behaviour. Most studies have been concerned with the more concentrated, “close to surface saturation” regime of the isotherm, where complications such as lateral interactions and crowding also additionally affect the adsorption. We compare a variety of amphiphilic polymer architectures by determining their Henry’s adsorption constant (kH), which, as with other surface active molecules, is the proportionality constant between surface coverage and bulk polymer concentration in a sufficiently dilute regime. It is speculated that not only the number of arms or branches, but also the position of adsorbing hydrophobes influence the adsorption, and that by controlling the latter the two can counteract each other. MethodologyThe Self-consistent field calculation of Scheutjens and Fleer was implemented to calculate the adsorbed amount of polymer for many different polymer architectures including linear, star and dendritic. Using the adsorption isotherms at very low bulk concentrations, we determined the value of kH for these. FindingsIt is found that the branched structures (star polymers and dendrimers) can be viewed as analogues of linear block polymers based on the location of their adsorbing units. Polymers containing consecutive trains of adsorbing hydrophobes in all cases showed higher level of adsorption compared to their counterparts, where the hydrophobes were more uniformly distributed on the chains. While increasing the number of branches (or arms for star polymers) also confirmed the known result that the adsorption decreased with the number of arms, this trend can be partially offset by the appropriate choice of the location of anchoring groups.