Half Unit Research Articles

All in One Ionic Liquid. Acts As Catalyst, Electrolyte, and Solvent in Electrochemical Hydrogen Generation

A redox active ionic liquid (RIL), 1-ethyl-4-(methoxycarbonyl)pyridinium bis(fluorosulfonyl)amide with a half unit of methyl viologen, was synthesized from its iodide form by anion exchange reaction and were characterized by NMR, UV-VIS, IR and elemental analysis. The compound exhibited redox waves in CH3CN with or without n-Bu4NPF6 electrolyte at -0.76 and -1.55 V vs. Ag/AgCl attributed to RIL to its radical form (RIL •) and RIL • to its anion form (RIL- ), respectively. The redox behavior indicates the dual role of the ionic liquid as a solvent and electrolyte. The redox wave RILs was also observed in neat condition without any additional solvent and electrolyte using micro-electrode. The cyclic voltammogram (CV) of RILs changed dramatically in the presence of acetic acid to show proton-coupled electron transfer (PCET) process for proton reduction at -1.33 V vs. Ag/AgCl in CH3CN. The change in CV indicates that RIL could act as a catalyst for hydrogen (H2) production via RIL-H as shown in Scheme 1. The bulk electrolysis of acetic acid with RILproduced H2 with 13.4 turnover number based on RIL and current yield of 37.8 %. In addition, the electrolysis for H2generation proceeded in complete ionic liquid system of RIL. The RIL could work as catalyst, electrolyte, and solvent for H2 production. Figure 1

Use of half red blood cell units in oncology patients during severe shortages to extend hospital supply.

The COVID-19 pandemic exerted an unprecedented impact on the blood supply from 2020 through 2022. As a result, throughout 2021 there were months our hospital had less than one-day supply of type O RBCs. To meet transfusion needs, whole RBC units were split into half units and issued to stable, non-bleeding patients. This single-institution, retrospective study examines time intervals to subsequent transfusion and total numbers of RBC units subsequently transfused after the first half or whole RBC unit. Patients who were transfused RBC between May 21, 2021 and November 1, 2021 were divided into in- and outpatient groups, then based on whether they received at least 1 half RBC unit or only whole RBC units during the study period. The time interval between this first half unit transfusion, or first whole unit transfusion in those who did not receive half units, and the subsequent RBC transfusion within 90 days was calculated and compared, as well as the total number of RBC units transfused 30 days after the first unit. In general, patients transfused with half units received a subsequent transfusion significantly earlier than those transfused with whole units. Additionally, receiving an index half unit was associated with more RBC transfusions in the following 30 days (p = .001). Transfusion of half RBC units during a severe RBC blood shortage can temporarily decrease RBC usage but will result in a shorter interval to the next transfusion and greater total number of RBC units transfused in subsequent days.

Optimising subjective grading of corneal staining in Sjögren's syndrome dry eye disease

AimTo assess whether smaller increment and regionalised subjective grading improves the repeatability of corneal fluorescein staining assessment, and to determine the neurological approach adopted for subjective grading by practitioners. MethodsExperienced eye-care practitioners (n = 28, aged 45 ± 12 years), graded 20 full corneal staining images of patients with mild to severe Sjögren's syndrome with the Oxford grading scheme (both in 0.5 and 1.0 increments, globally and in 5 regions), expanded National Eye Institute (NEI) and SICCA Ocular Staining Score (OSS) grading scales in randomised order. This was repeated after 7–10 days. The digital images were also analysed objectively to determine staining dots, area, intensity and location (using ImageJ) for comparison. ResultsThe Oxford grading scheme was similar with whole and half unit grading (2.77vs2.81,p = 0.145), but the variability was reduced (0.14vs0.12,p < 0.001). Regional grade was lower (p < 0.001) and more variable (p < 0.001) than global image grading (1.86 ± 0.44 for whole increment grading and 1.90 ± 0.39 for half unit increments). The correlation with global grading was high for both whole (r = 0.928,p < 0.001) and half increment (r = 0.934,p < 0.001) grading. Average grading across participants was associated with particle number and vertical position, with 74.4–80.4% of the linear variance accounted for by the digital image analysis. ConclusionsUsing half unit increments with the Oxford grading scheme improve its sensitivity and repeatability in recording corneal staining. Regional grading doesn't give a comparable score and increased variability. The key neurally extracted features in assigning a subjective staining grade by clinicians were identified as the number of discrete staining locations (particles) and how close to the vertical centre was their spread, across all three scales.

Two-component Supramolecular Adduct based on Hydroxyl Substituted Triptycene with 4,4’-bipyridine: Crystal Structure Analysis

A new cocrystal solvate possessing 2,7,14-trihydroxytriptycene (THT) and 4,4′-bipyridine (bpy) was grown from a MeOH solution by solvent evaporation to form THT·0.5bpy·MeOH·H2O (1).The crystal structure of 1 was determined by single-crystal X-ray diffraction in the monoclinic space group C2/c. In the new cocrystal solvate (1), the asymmetric unit consists of one unit of THT, a half unit of disordered bpy, one unit of a water molecule and one MeOH molecule. A 2D supramolecular architecture is observed in (1) linking THT, bpy and solvent water molecules via classical O-H···N and O-H···O hydrogen bonds. The MeOH and water molecules entrapped in (1) form stabilizing hydrogen bondswith the surrounding “trimeric cocrystals.” Furthermore, we investigated whether these hydrogen bonds stabilize the crystal packing. The calculations were carried out using Hydrogen Bond Statistics and Full Interaction Maps packages, and the results exhibit common bonding behaviour in terms of bond distances and strength.

Interface atomic structures in a cadmium arsenide/III–V semiconductor heterostructure

The interface atomic structure between an epitaxial thin film of the prototype topological semimetal cadmium arsenide (Cd3As2) and a III–V semiconductor layer is investigated using high-angle annular dark-field imaging in an aberration-corrected scanning transmission electron microscope. We find that the interface unit cell adopts a defined stoichiometry that is CdSb-like, which is achieved through the insertion of periodically arranged Cd vacancies in the terminating Cd-plane of Cd3As2. This interface stoichiometry is consistent with the Sb-termination of the III–V layer and the fact that CdSb is the thermodynamically stable phase in the Cd–Sb binary system. We find at least two distinct alignments of the film with respect to the buffer layer, which are characterized by a 14100Cd3As2 shift parallel to the interface. We show that steps of half unit cell height in the III–V layer can produce these distinct interface structures.

The Hurwitz-Hopf map and harmonic wave functions for integer and half-integer angular momentum

Harmonic wave functions for integer and half-integer angular momentum are given in terms of the Euler angles (θ, ϕ, ψ) that define a rotation in SO(3), and the Euclidean norm r in , keeping the usual meaning of the spherical coordinates (r, θ, ϕ). They form a Hilbert (super)-space decomposed in the form . Following a classical work by Schwinger, 2-dimensional harmonic oscillators are used to produce raising and lowering operators that change the total angular momentum eigenvalue of the wave functions in half units. The nature of the representation space is approached from the double covering group homomorphism SU(2) → SO(3) and the topology involved is taken care of by using the Hurwitz-Hopf map . It is shown how to reconsider H as a 2-to-1 group map, , translating it into an assignment (z 1, z 2) ↦ (r, θ, ϕ, ψ) whose domain consists of pairs (z 1, z 2) of complex variables, under the appropriate identification of with . It is shown how the Lie algebra of G 0 is coupled with two Heisenberg Lie algebras of 2-dimensional (Schwinger’s) harmonic oscillators generated by the operators and their adjoints. The whole set of operators gets algebraically closed either into a 13-dimensional Lie algebra or into a (4∣8)-dimensional Lie superalgebra. The wave functions in can be written in terms of polynomials in the complex coordinates (z 1, z 2) and their complex conjugates and the representations are explicitly constructed via the various highest weight (or lowest weight) vector representations of G 0. Finally, a new nonrelativistic quantum (Schrödinger-like) equation for the hydrogen atom that takes into account the electron spin is introduced and expressed in terms of (r, θ, ϕ, ψ) and the time t. The equation is succeptible to be solved exactly in terms of the harmonic wave functions hereby introduced.

Effects of acidifiers on soil greenhouse gas emissions in calcareous soils in a semi-arid area

In most agricultural fields, when soil pH is high, elemental sulfur or sulfuric acid are used to reduce soil pH and increase the availability of macro and micronutrients for optimum crop yield. However, how these inputs impact soil greenhouse gas emissions is unknown. This study aimed to measure the amount of greenhouse gas emissions and pH after the application of various doses of elemental sulfur (ES) and sulfuric acid (SA). Using static chambers, this study quantifies soil greenhouse gas emissions (CO2, N2O, and CH4) for 12 months after the application of ES (200, 400, 600, 800, and 1000 kg ha−1) and SA (20, 40, 60, 80 and 100 kg ha−1) to a calcareous soil (pH 8.1) in Zanjan, Iran. Also, in order to simulate rainfed and dryland farming which are common practices in this area, this study was conducted with and without sprinkler irrigation. Application of ES slowly decreased soil pH (more than half a unit) over the year whereas application of SA temporarily reduced the pH (less than a half unit) for a few weeks. CO2 and N2O emissions and CH4 uptake were maximum during summer and lowest in winter. Cumulative CO2 fluxes ranged from 1859.2 kg−1 CO2-C ha−1 year−1 in the control treatment to 2269.6 kg CO2-C ha−1 year−1 in the 1000 kg ha−1 ES treatment. Cumulative fluxes for N2O-N were 2.5 and 3.7 kg N2O-N ha−1 year−1 and cumulative CH4 uptakes were 0.2 and 2.3 kg CH4-C ha−1 year−1 in the same treatments. Irrigation significantly increased CO2 and N2O emissions and, depending on the amount of ES applied, decreased or increased CH4 uptake. SA application had a negligible effect on GHGs emissions in this experiment and only the highest amount of SA altered GHGs emissions.

Malignant hyperthermia in Poland: A survey study.

Malignant hyperthermia (MH) is a life-threatening syndrome caused by sudden, uncontrolled skeletal muscle hypermetabolism in response to inhalation anesthetics and depolarizing relaxants. The estimated incidence of MH is between 1:10,000 and 1:250,000 anesthetic procedures. In Poland, due to lack of reporting, the incidence of MH is unknown. Dantrolene is imported as a life-saving drug (target import) and temporally authorized for sale. The aim of the study was to evaluate the prevalence of malignant hyperthermia in Poland and to assess the accessibility to dantrolene in Poland. A questionnaire was conducted among the chiefs of anesthesia and intensive care units in Poland. During the years 2014 to 2019, 10 episodes of MH have been reported in 238 surveyed polish anesthesia departments. The estimated prevalence is 1:350,000. Eight patients survived the MH crisis. Dantrolene is stocked in 48 (20%) anesthesiology departments. Among the surveyed hospitals, only in 38 (16%) it is possible to administer dantrolene within 5 minutes of suspecting a MH reaction. Less than half units (44%) have an algorithm for the management of MH episode in the operating theaters. The results of the study revealed, that the prevalence of MH in Poland is lower than the prevalence reported in other countries. Access to dantrolene in Poland is limited.

Road safety and sustainability performance: A cross-country analysis

In this paper, we study the impact of road safety on sustainability performance in the OECD area. Road safety is proxied by the severity of road accidents, whereas the sustainability performance of each country is captured by its sustainability score. Our dataset covers the period 2000-2021 and consists of 35 OECD countries. The employed panel data analysis unveils a statistically significant negative relationship between the number of severe road crashes and sustainability score. In particular, a unit decrease in the number of deaths per one million inhabitants due to road crashes leads to a half unit increase in the overall sustainability score of a country. Therefore, policy makers should undertake measures that improve the efficiency of the transport system since this translates in higher sustainability performance. Indeed, less severe road crashes do have a positive impact on the economy, the society and the environment, thus contributing to all pillars of sustainable development.

Molecular Modeling to Predict the Optimal Mineralogy of Smectites as Binders of Aflatoxin

AbstractNumerous experiments have verified that smectites can adsorb aflatoxin B1 (AfB1) effectively and the efficiency of this process depends heavily on the chemical, physical, and mineralogical characteristics of the smectite. Several relationships between these characteristics and AfB1 sorption have been determined experimentally, but the molecular mechanisms underlying these were not investigated. In the current study the effects of charge density, type of exchange cation, and charge origin (octahedral vs. tetrahedral) on AfB1 sorption on smectites were analyzed by a series of molecular simulations. The calculations confirmed the formation of water bridges between carbonyl groups of AfB1 molecules and interlayer cations. Flat orientation of AfB1 molecules on smectite surfaces was also confirmed. For larger amounts of AfB1 molecules in the intercalates, self-association of two AfB1 molecules bound by π–π interaction was shown. The thermodynamics of AfB1 sorption depends heavily on the water content in the structure, being optimal for basal distances corresponding to two layers of water. A clear preference for sorption of AfB1 on smectites with bivalent cations (Ba2+, Ca2+) and an octahedral origin of its layer charge was confirmed and this was explained as steric hindrance between hydrated ions and AfB1 molecules, which tend to lie flat on smectite surfaces devoid of ions. Ba-montmorillonite with a charge of 0.4 per half unit cell was shown to have the smallest and thus the best potential energy of adsorption compared to the other layer charges.

34371 Differences in half day outpatient dermatology clinic total work relative value units by patient race, sex, and age

Dermatology encounters for racial minority, female, and younger patients generate fewer work relative value units (wRVU) per encounter. Longer encounters for older white males may explain differences in wRVU. We aimed to determine whether differences in wRVU by patient sociodemographics persisted after adjusting for encounter length. Adult outpatient dermatology encounters from 9/1/2016-3/31/2020 within an academic center were grouped into 4-hour clinic half days (HD). To examine associations between patient demographics and wRVUs generated per HD, we used mixed linear models adjusted for fixed effects of mean age, proportion of patients who were white, proportion male, and number of encounters and random effect of individual dermatology providers. Overall, 4341 HD were included. Encounters were with predominantly white (70.3%) and female (58.6%) patients. Half days generated a mean 12.9 wRVUs (standard deviation, 4.4) and contained a mean 8.5 (2.5) encounters. HD with all white patients were associated with 3.1 (95% CI 2.7-3.6) more wRVUs than HD with no white patients. HD with all male patients were associated with 0.83 (95% CI 0.4-1.3) more wRVUs than HD with no male patients. A 10-year increase in mean age was associated with a 0.36 (0.25-0.47) increase in wRVU. HD clinics with higher proportions of white, male, and older patients generated more wRVUs. Assuming all HD sessions were of equivalent length, encounter length did not explain why older white males generate more wRVUs per encounter. Further studies should determine if differences in wRVUs stem from undervaluation of conditions that affect racial minority, female, and younger patients.

Engineering the stoichiometry of a TiO2-rich SrTiO3(001) surface

We investigate the stoichiometry of a TiO2-rich SrTiO3(001) surface by depositing less than one monolayer of SrO under typical epitaxy conditions. We find that this deposition yields atomically flat islands on the step-and-terrace surface. All these islands have a height of exactly one full SrTiO3 unit cell, instead of the expected half unit cell. Reflection high-energy electron diffraction indicates that a reconstruction occurs on the bare surface, which disappears with SrO deposition. To explain these results, we propose a simple model with two key elements: (i) a TiO2 double layer must intrinsically be present on the as-prepared SrTiO3(001) surface, and (ii) with deposited SrO, this top layer rearranges itself to form islands with a height of one unit cell.

Synthesis, Structure and Properties of Donor-acceptor-type [4]Dendralenes

[4]Dendralene and its analogs possessing both strongly electron-donating 1,3-dithiol-2-ylidenes and electron-accepting dicyanomethylidenes (2b–4b) were successfully synthesized. X-ray structure analysis revealed that 2b adopts a nonplanar structure, in which half units of 2b are significantly inclined to each other. Cyclic voltammograms of 2b–4b consisted of one pair of two-electron oxidation waves and one pair of one-electron reduction waves.

Non-extraction orthodontic treatment in a patient with severe anterior crowding

A 12 years 6 months old Indian male presented with a chief complaint of irregular upper and lower front teeth. Patient exhibited a mild convex profile on Class l skeletal base with slightly decreased vertical proportions. This was complicated by severe upper and lower labial segment crowding. Also the molar relationship was half unit class ll bilaterally. Since the patient did not want to go for extraction of premolars, treatment involved use of Pendulum appliance along with upper and lower pre-adjusted edgewise appliance (0.022x0.028” slot) with MBT prescription. Various elastics and overlay wires were used along with proximal stripping for the correction of severe crowding in upper and lower anterior teeth.: Clinically Angle’s Class I occlusion was achieved bilaterally with good intercuspal relationship. Vertical growth continued throughout the treatment.

Measurement of local contact potential difference of atomic scale Au/Si(111)-(7×7) delocalized adsorption state in room-temperature and ultra-high vacuum environment

The structural properties and local contact potential difference of Au on Si(111)-(7×7) surface are studied by the homemade ultra-high vacuum non-contact Kelvin probe force microscope. Although scanning tunneling microscopy has been widely used to study the metal- adsorbed semiconductor surfaces on an atomic scale, the tunnel current measured by scanning tunneling microscopy is easy to lead the charge states to accidentally switch in the measurement process, and it is limited only to the observation of metal and semiconductor surfaces. Kelvin probe force microscope allows us to directly measure the charges at different positions of various flat surfaces by local contact potential difference on an atomic scale, which has become a more convenient and accurate means of charge characterization. In this paper, the topography and local contact potential difference of Au adsorbed Si(111)-(7×7) surface are measured on an atomic scale by Kelvin probe force microscope at room temperature, and the corresponding adsorption model and first principle calculation are established. The differential charge density distribution of the stable adsorption position of Au/Si(111)-(7×7) is obtained, and the local contact potential energy difference relationship of the stable adsorption position of Au on Si surface is given, The mechanism of charge transfer between Au atom and Si(111)-(7×7) surface during adsorption is analyzed. The experimental results show that at room temperature, single Au atom will form triangular delocalized adsorption state in the half unit cell of Si(111)-(7×7). The delocalized adsorption state is due to the fact that the moving speed of a single Au atom in the HUC is faster than the scanning speed of Kelvin probe force microscope, and the local contact potential difference measurement of Au/Si(111)-(7×7) adsorbed surface can effectively identify Au and Si atoms. Obviously, this research is of great significance in promoting the development of surface charge precision measurement, and is expected to provide some insights into the charge properties of metal adsorbed semiconductor surfaces.

Flowpath influence on stream acid events in tropical urban streams in Singapore

AbstractWe investigated processes contributing to periodic acidification events in headwater streams of Nee Soon Forest Catchment (NSFC) in Singapore by monitoring hydrochemical changes in response to rainfall inputs. Stream chemistry response to most rainfall events was characterized by decreases in pH from means ranging from 5.1 to 5.3 to below 4.8–5.0 and corresponding increases in specific electrical conductivity from baseflow values of 15–30 to 50–80 μS cm−1, indicative of low‐total dissolved solids in stormflow. The decreases in pH in the streams, which are typically acidic year‐round, were related to occasional highly acidic rainfall inputs (pH ~4.05) and likely the flushing of organic acids into the stream by shallow subsurface flow interacting with surface litter and/or organic‐rich soil horizons. The interaction of rainwater runoff with organic matter in the soil matrix possibly alters the chemical composition of stormflow, influencing pH. Decomposition of instream organic matter also reduces stream water pH. Leaching experiments revealed that the overland flow passing through organic matter and A horizon material has the potential to lower stream water pH by approximately a half unit or more, in part, by flushing nitrates that were produced by microbial decomposition of organic matter and/or precipitated sulphur that enterred the forest by wet or dry atmospheric deposition. The observed periodic acid events are a natural phenomenon in the stream system in this urban environment because of naturally acidic rainfall and granitic soils with low buffering potential. However, acid events are likely amplified in frequency and magnitude by anthropogenic pollution emissions of sulphur and nitrogen species (e.g., SO2and NOx) from local and regional sources that lower rainfall pH. Although, acid runoff events are typically short‐lived (&lt;12–24 h), further longitudinal monitoring and experimental studies are needed to investigate the long‐term implications on sensitive taxa in the NSFC streams. Finally, understanding the flow pathways of stormflow water in the nested system was critical for deciphering the mechanisms driving stream acid events at the site.

Organic molecule intercalation sites in Sr2CaCu2Oy superconductor

AbstractThe organic molecule adsorption sites in a Sr2CaCu2Oy (0(Sr)212) half unit cell upon water molecule intercalation were estimated by simulation using Molecular Orbital PACkage (MOPAC) program. For water molecules, the unit cell was elongated with increasing the number of molecules. Upon four water molecules intercalated between the two SrO layers, the upper Sr atom moved along the c‐axis by 1.49 Å. This value was smaller than but comparable to the experimentally obtained elongation of half of the c‐parameter. The primary reason of the elongation is the repulsive force between Sr–H atoms in the two SrO layers. For ethanol and acetone molecules, stable intercalation sites were not found in the 0(Sr)212 crystal. These results coincided to the experimental results, which did not show intercalations. It was concluded that MOPAC can reproduce the organic molecule intercalation phenomena in oxide crystals.

Effect of Montmorillonite Layer Charge on the Thermal Stability of Bentonite

AbstractThe thermal stability of bentonite is vitally important for its application in the casting field and the layer charge of montmorillonite (Qm) is one of its central crystal-chemical parameters. As the main component of bentonite, the influence of Qm on montmorillonite properties and behavior needs to be considered if bentonite is to be used in high-temperature environments. The objective of the current study was to investigate the relationship between Qm and the thermal stability of Chinese bentonite samples collected from Wuhu, Anhui Province (marked as WH); Xinyang, Henan Province (marked as XY); and Santai, Sichuan Province (marked as ST) below. The values of Qm were obtained using the O (11) method, and the structural properties of the bentonite samples were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetry-differential scanning calorimetry (TG-DSC), and field emission scanning electron microscopy (FESEM). The results showed that, in the samples investigated, Qm was inversely related to the thermal stability of bentonite. The Qm value (electrons per half unit cell, e/huc) was greatest for sample ST (0.725 e/huc), followed by sample XY (0.470 e/huc), and by sample WH (0.354 e/huc). The dehydroxylation temperature changed related to Qm; the sample with the largest Qm value was WH (701°C), followed by sample XY (684°C), and sample ST (630°C). After the samples were calcined at 600°C, sample WH had the best montmorillonite structural integrity with the greatest degree of reusability (78.21%); while the montmorillonite structures of samples XY and ST were destroyed, and their reusabilities were only 9.48 and 6.01%, respectively.

On fiscal and monetary policy-induced macroeconomic volatility dynamics

This paper studies macroeconomic volatility dynamics induced by government spending and monetary policy changes. The policy level and volatility shocks, which are identified through sign restrictions from a time-varying SVAR model, are used to derive explicit functions of macroeconomic volatility impulse responses and decompositions. The SVAR model is specified with time-varying coefficients and stochastic volatility that is included in the mean equation. The empirical results show that the impact of a shock to uncertainty about monetary policy explains about 40% and 25% of output and inflation historical volatility dynamics, respectively, more than other policy shocks since the mid-1980s. The impact of a one-unit government spending level shock on output and inflation uncertainties is equivalent to the impact of about a half unit of a monetary policy volatility shock in the long run, or of about a quarter unit of a monetary policy level shock in the short run.

Structure of glycerol-Mg2+-smectites/vermiculites complex based on molecular dynamics and implementation of the model for X-ray diffraction modeling

Smectites and vermiculites can be distinguished from each other after Mg2+-saturation and solvation with glycerol (GLY). Smectites generally expand to c.a. 18 Å, forming a two-layer complex, while vermiculites to c.a. 14.5 Å, forming a one-layer complex. Additionally, the distribution of layer charges within one population of crystallites can lead to mixed-layered one−/two-GLY layer complexes. Thus far, the model of the GLY intercalate has not been implemented in programs used for XRD modeling of clay minerals. The aim of this study was to obtain a model of the structure of Mg2+-GLY-smectite/vermiculite with the help of molecular dynamic (MD) simulations.A wide range of GLY and H2O contents, in the simulated structures of montmorillonites with charges: 0.3, 0.5, and 0.75 per half unit cell (phuc), and beidellite with a charge of 0.75 phuc, were considered.The average atomic density profiles along the z-direction were calculated for all of the simulations. Subsets corresponding to certain basal spacings (plateaus) were chosen as representative for one- and two-layer intercalates. The electronic density profiles of GLY, H2O, and Mg2+ ions were fitted with Gaussian functions. The purpose of the work was to minimize the number of functions in order to achieve a maximally simple, yet flexible model of the interlayer structures.It was possible to determine relationships between positions of the atomic distributions and the basal spacings. All the relationships were implemented in Sybilla and BGMN computer programs. The new model of the complex was used for fitting of diffractograms of Mg2+-montmorillonites and Mg2+-vermiculite with different layer charges.