Coverage Dependence Research Articles

Theoretical Investigation of the Adsorbate and Potential-Induced Stability of Cu Facets during Electrochemical CO2 and CO Reduction

The activity and product selectivity of electrocatalysts for reactions like the carbon dioxide and carbon monoxide reduction reactions (CO2RR and CORR) are intimately dependent on the catalyst’s structure and composition. While engineering catalytic surfaces can improve performance, discovering the key sets of rational design principles remains challenging due to limitations in modeling catalyst stability under operating conditions. Herein, we perform first-principles density functional calculations adopting implicit solvation methods with potential control to study the influence of adsorbates and applied potential on the stability of different facets of model Cu electrocatalysts. Using coverage dependencies extracted from microkinetic models, we describe an approach for calculating potential and adsorbate-dependent contributions to surface energies under reaction conditions, where Wulff constructions are used to understand the morphological evolution of Cu electrocatalysts under CO2RR and CORR conditions. We identify that CO*, a key reaction intermediate, exhibits higher kinetically and thermodynamically accessible coverages on (100) relative to (111) facets, which can translate into an increased relative stabilization of the (100) facet during CO2RR. Our results support the known tendency for increased (111) faceting of Cu nanoparticles under more reducing conditions and that the relative increase in (100) faceting observed under CO2RR conditions is likely attributed to differences in CO* coverage between these facets.This work was partially performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344 and partially supported by the U.S. DOE, Office of Energy Efficiency and Renewable Energy, Advanced Materials & Manufacturing Office.

Cannabis and Craniotomy for Glioblastoma: Impact on Complications and Health Care Utilization

Despite advances in treatment of glioblastomas (GBMs), the median survival remains 14-16 months. In the United States, 52.5 million people ≥12 years of age used cannabis in 2021. We aim to elucidate differences in complications after craniotomy for resection of GBM between users and nonusers of cannabis. Merative MarketScan Research Data (2008-2019) (includes >265 million patients) were used to extract adults (≥18 years of age) with GBM diagnosis (International Classification of Diseases-9 code 191.x and International Classification of Diseases-10 code C71.x) who had a craniotomy (Current Procedure Terminology code 61510) from inpatient admission data. The inverse probability treatment weighted analysis balanced the groups of cannabis abuse disorder (CAD) and no CAD in terms of age, gender, insurance coverage, comorbidities, and prior 12-month opioid dependence. Individuals with CAD were younger (median, 37 vs. 51 years; P < 0.0001). There was a lower percentage of women (19% vs. 45%; P < 0.0001). In the CAD group, opioid abuse pattern for ≥12 months was higher (16% vs. 5%; P=0.001) and the rate of complications was higher (32% vs. 15%; P= 0.001) during index hospital stay. At 6 months postdischarge, neurologic complications were higher among the CAD group (27% vs. 8%; P < 0.001). At 1 year postdischarge, patients with CAD sought feweroutpatient services (P= 0.012). More neurologic complications were seen in the CAD group (31% vs. 12%; P< 0.001). This retrospective population-based study sounds a higher rate of neurologic complications among patients using cannabis who also had a newly diagnosed GBM. This suggests the lack of a protective effect from use of cannabis in patients with primary malignant brain tumors.

Coverage Dependence upon Early Oxidation Stages of Hafnium-Adsorbed Si(111)-7 × 7

Coverage Dependence upon Early Oxidation Stages of Hafnium-Adsorbed Si(111)-7 × 7

Adsorption mechanisms of heavy metal atoms As, Pb, and Zn on thermally activated palygorskite Si–O/Mg–O (200) surfaces: A first-principles calculations

Heavy metal pollution on air, water, and soil is an issue of increasing global concern. Adsorption is widely recognized as one of the most effective methods for removing heavy metal pollution. The adsorption mechanisms of As (Arsenic), Pb (Lead), and Zn (Zinc) atoms on thermally activated palygorskite Si–O (200) and Mg–O (200) surfaces were investigated using first-principles calculations based on DFT. The coverage dependence of the adsorption configurations and energies on the most stable adsorption sites was also analyzed. The bridge site was found to be the most stable adsorption site for As and Pb on the Si–O (200) surface, while the adsorption energy of Zn was ＜ 0.1 eV on the surface. The adsorption capacity order of the surface was As > Pb ≫ Zn. On the Mg–O (200) surface, the hollow site was the most stable site for three heavy metal atoms. The adsorption energies of them gradually decreased with increasing coverage, thus indicating the lower stability of surface adsorption due to the repulsion of neighboring heavy metal atoms. The adsorption capacity of the Mg–O (200) surface followed the order of As > Pb > Zn. Further exploration was performed on the changes in structure and electronic properties within the adsorption process by studying the lattice relaxation, Bader charge, and electronic density of states (DOS) of the thermally activated palygorskite (200)/heavy metal atoms system.

Investigation of coverage dependence of the stretching frequency of CO adsorbed on Pd surfaces at low coverage limits

The stretching frequency of the CO bond is a sensitive probe of the local environment of a surface-bound CO molecule, including the adorption site and density, i.e. surface coverage. In this work, we extend our analysis beyond the frequency shift due to differences in adsorption configurations. Using density functional theory (DFT) calculations, we directly explore the correlations between surface coverage and the stretching frequency of adsorbed CO on Pd surfaces. We also perform constant pressure infrared reflection absorption measurements of CO on Pd(111) and use existing relations between pressure and coverage to derive coverage dependency. Both results are compared to previously reported experimental data. Our derived correlations of peak frequency and area with surface coverage can help interpret experimental IR spectra in real time and extract time-dependent concentration data from transient kinetic experiments.

Theoretical Investigation of the Adsorbate and Potential-Induced Stability of Cu Facets During Electrochemical CO2 and CO Reduction.

The activity and product selectivity of electrocatalysts for reactions like the carbon dioxide reduction reaction (CO2RR) are intimately dependent on the catalyst's structure and composition. While engineering catalytic surfaces can improve performance, discovering the key sets of rational design principles remains challenging due to limitations in modeling catalyst stability under operating conditions. Herein, we perform first-principles density functional calculations adopting implicit solvation methods with potential control to study the influence of adsorbates and applied potential on the stability of different facets of model Cu electrocatalysts. Using coverage dependencies extracted from microkinetic models, we describe an approach for calculating potential and adsorbate-dependent contributions to surface energies under reaction conditions, where Wulff constructions are used to understand the morphological evolution of Cu electrocatalysts under CO2RR conditions. We identify that CO*, a key reaction intermediate, exhibits higher kinetically and thermodynamically accessible coverages on (100) relative to (111) facets, which can translate into an increased relative stabilization of the (100) facet during CO2RR. Our results support the known tendency for increased (111) faceting of Cu nanoparticles under more reducing conditions and that the relative increase in (100) faceting observed under CO2RR conditions is likely attributed to differences in CO* coverage between these facets.

Multicoverage Study of Femtosecond Laser-Induced Desorption of CO from Pd(111).

We study the strong coverage dependence of the femtosecond laser-induced desorption of CO from Pd(111) using molecular dynamics simulations that consistently include the effect of the laser-induced hot electrons on both the adsorbates and surface atoms. Adiabatic forces are obtained from a multicoverage neural network potential energy surface that we construct using data from density functional theory calculations for 0.33 and 0.75 monolayer (ML). Our molecular dynamics simulations performed for these two trained coverages and an additional intermediate coverage of 0.60 ML reproduce well the peculiarities of the experimental findings. The performed simulations also permit us to disentangle the relative role played by the excited electrons and phonons on the desorption process and discover interesting properties of the reaction dynamics as the relevance that the precursor physisorption well acquires during the dynamics as coverage increases.

Capturing the Coverage Dependence of Aromatics' Adsorption through Mean-Field Models.

To capture the dominant interactions (surface-mediated and through-space) in catalytic hydrodeoxygenation systems, coverage-dependent mean-field models of aromatic adsorption are developed on Pt(111) and Ru(0001). We derive three key insights from this work: (1) we can universally apply mean-field models to capture the coverage-dependent behavior of oxygenated aromatics on transition-metal surfaces, (2) we can deconvolute surface-mediated and through-space interactions from the mean-field model, and (3) we can develop relatively accurate models that predict the adsorption energy of aromatics on transition-metal surfaces for the full coverage range using the work function at the lowest modeled coverage. Our approach enables the rapid prediction of the coverage-dependent behavior of oxygenated aromatics on transition-metal surfaces, reducing the computational cost associated with these studies by an order of magnitude.

Energetics of silicon in the bulk and near surfaces of tungsten: a first-principles study

Siliconization of the tokamak walls is a candidate method to improve plasma confinement in fusion tokamaks containing tungsten plasma facing components (W PFCs). To understand the interactions of silicon (Si) with W, the Si behavior in bulk W, and near three low-index W surfaces ((100), (110) and (111)) has been investigated using first-principles density functional theory. In bulk W, Si interstitial atoms have a low solution ability and high mobility, and Si atoms can be strongly trapped by W vacancies. The interaction between two Si adatoms is responsible for the stability of adatom superstructures on W surfaces, consistent with previous experimental observation (Tsong and Casanova 1981 Phys. Rev. Lett. 47 113). Although the coverage dependence of Si adsorption and diffusion energetics on surfaces is related to surface orientation, the W(110) surface has lower Si adsorption affinity and higher Si diffusivity than either the W(111) or W(100) surfaces. The most stable Si adatom superstructure on W surfaces is: square c(2 × 2) pattern on W(100) covered with 0.5 ML Si; rectangular c(4 × 2) pattern on W(110) with 0.25 ML Si; and rhombus p(1 × 1) pattern on W(111) with 1 ML Si. The coverage dependence of Si mobility on/toward W surfaces is generally related to the stability of the Si superstructures as a function of coverage on each surface. Interestingly, Si adatoms prefer to transport below the surface and into W subsurface by an exchange mechanism with W atoms, indicating the likelihood of epitaxial growth of W silicide layers on W surfaces during the operation of W PFCs.

When China strikes: Quantifying Australian companies' stock price responses to China's trade restrictions

AbstractIn early 2020, China, Australia's top export market, unilaterally imposed trade restrictions on Australian barley, beef, coal, cotton, timber, copper and wine. However, convincing evidence regarding the effects of such trade restrictions on firms is scarce. Leveraging data on daily stock returns from 20 listed Australian and 32 listed Chinese firms that produce the restricted commodities, we provide the first systematic analysis of the firm‐level economic impacts of China's trade restrictions on Australian and Chinese firms. We find significant adverse effects on Australian firms' stock returns, leading to almost 20% loss within 10 trading days; however, most firms' stock returns immediately rebounded. In contrast, Chinese firms usually saw significant positive stock returns, leading to almost 30% gains, and the positive abnormal returns continuously increased within 10 trading days. Media coverage and trade dependence substantially impact Australian and Chinese firms' stock returns—industries with stronger trade dependence on China saw greater losses in Australian firms' stock returns. Our results suggest that trade reallocation and deflection are two effective mitigation mechanisms for Australian exporters facing China's trade restrictions.

Holistic Resilience and Reliability Measures for Cellular Telecommunication Networks

Nowadays, our lives have become increasingly inseparable from the services facilitated by telecommunication networks. Disruption of this service may result in a significant detrimental effect, especially in smart manufacturing, remote surgery, and harbor logistic. With the development and deployment of the new generation of telecommunication, i.e., 5G mobile networks, reliability has been repeatedly emphasized as a critical issue. Contemporary telecommunication networks often have a large scale. Evaluating network reliability is a challenging issue related to the spatiotemporal characteristics of the network and of the connection principles. In this paper, we bring together concepts from computational geometry and reliability engineering to forge a new approach to address the challenging issue. We first formulate a Voronoi-based Graphic network (VGN) model with a novel built-in dependence, coverage dependence, that manifests the resilience of the network. Based on the VGN model, we propose two new measures for holistically assessing the resilience and reliability of telecommunication networks in a large region. Ultimately, we employ the designed approach to telecommunication networks. The result indicates that coverage dependence and resilience are important factors for delivering ultra-reliable service to users promised by the 5G.

Mean field model parameterization to recover coverage-dependent kinetics

Lateral interactions between adsorbates introduce coverage dependence into adsorption energies and activation barriers of surface reactions. Lattice-based kinetic Monte Carlo (kMC) simulations can capture these interactions quantitatively but are laborious to parameterize and solve. Mean field models are more tractable, but protocols to construct and parameterize them are unclear. Here we explore the ability of a coverage-aware mean-field model to map to a lattice-kMC model of a generic two-step reaction network, including quasi-equilibrated adsorption and rate-limiting dissociation steps. We derive expressions for mean-field and coverage-dependent adsorption energies and dissociation barriers and parameterize against lattice-kMC predictions. We show that the parameterized mean-field rates correlate with ground truth lattice-kMC results across a wide range of reaction conditions and identify regions where the mean field fails. The mean field model similarly captures kMC-derived rate-order, Arrhenius and Sabatier plots at a greatly reduced computational cost. The results provide guidance for parameterizing mean-field models, benchmarked against explicit lattice-based approaches for incorporating the influence of coverage effects.

First principles investigation on adsorption mechanism of As(OH)3 on the kaolinite (001) surface

The environmental fate of arsenic (As) and arsenic-containing compounds are garnering more attention as a result of the global As contamination. Arsenous acid (As(OH)3) exists as a common arsenic-containing compound in the aqueous phase. Natural clay minerals like kaolinite have the potential to be adsorbents. First-principles calculations based on DFT were used to investigate the adsorption mechanism between As(OH)3 molecules and the kaolinite (001) surface. The two-fold bridge sites of the kaolinite (001) surface were found to be most stable for As(OH)3 adsorption. Three representative stable adsorption configurations, B2, H6, and T3, were selected to analyze. Strong hydrogen bonds formed between As(OH)3 molecules and the kaolinite (001) surfaces made the main contribution to the adsorption. The coverage (Θ) dependence to the adsorption stability was methodically investigated with a wide coverage range of 0 < Θ ≤ 1.0 monolayers (ML). The adsorption energy of As(OH)3 increased in the coverage range of 0 < Θ ≤ 0.5 ML and then decreased in the coverage range of 0.5 < Θ ≤ 1.0 ML. Other properties of the As(OH)3/kaolinite (001) system, including the bonding interaction, atom population/charge, electronic density of states, and lattice relaxation were also discussed and analyzed in detail.

Landsat-8 Observations of Foam Coverage under Fetch-Limited Wave Development

In this paper, we aimed to clarify the problem of foam coverage dependence on wave fetch, which is of interest in satellite microwave radiometry, but for which controversial results were reported previously. The classical approach to investigating developing waves was applied. That is, the waves are considered as coming from the coast under approximately constant wind velocity. The study includes two scenes of intensive katabatic winds in the Gulf of Lion and the Gulf of Tehuantepec. We used two Bands of Landsat OLI images to extract the wave spectral peak frequency and the sea fraction covered by foam simultaneously along the wave fetch. The distributions of the spectral peak frequency along the fetch obeying the classical wave growth law clearly showed that we observed the developing waves. Along the fetch, the sea surface covered with foam grows about three times with the power law. This development of foam coverage occurred at the range of dimensionless fetches from 50 up to 7000 if the fetch is scaled using wind velocity and gravity acceleration. A simple model of the foam coverage growth with wave fetch is suggested. We modeled wave energy dissipation rate using the JONSWAP wave spectrum for developing seas. The model explains the observations at the quantitative level. Reported results can be applied to investigations of tropical cyclones using satellite microwave radiometry.

Periodic DFT study on heavy metals Cu(II) and Pb(II) atoms adsorption on Na-montmorillonite (010) edge surface

Heavy metal (HM) pollution is of great concern currently because it has been recognized as a potential threat to air, water,and soil. Adsorption is one of the most effective strategies for removing heavy metals. Montmorillonite as the adsorbent with a low cost and high thermal stability has received much attention. The adsorption of heavy metal Copper [Cu(II)] and Plumbum [Pb(II)] atoms on Na-montmorillonite hydroxylated (010) edge surface was analyzed using the generalized gradient approximation and density functional theory in the supercell technique. The coverage dependence of the adsorption structure and energetics was systematically investigated for a wide range of coverage from 0 to 1.0 monolayer (ML). Among all the possible adsorption sites, the most stable adsorption site for Cu(II) atom was a three-fold hollow site while the most favorable adsorption site for Pb(II) atom was a three-fold hollow site and followed by a two-fold bridge site. The adsorption energy increased with increasing coverage of Pb(II) atoms, indicating higher stability of surface adsorption and a tendency for the formation of adsorbate island clusters with increasing coverage. However, the adsorption energy of Cu(II) atoms decreased with increasing coverage. In the coverage range of 0 < Θ ≤ 0.5 ML the recovery capacity of the Na-montmorillonite for the heavy metal atoms was in the order of Cu(II)>Pb(II), while the recovery capacity of the Na-montmorillonite in the coverage range of 0.5 < Θ ≤ 1 ML was in the order of Pb(II)>Cu(II). The other aspects of the Cu(II) and Pb(II)/Na-montmorillonite (010) systems, including adsorption geometry, differential charge distribution, and electronic density of states were also studied and discussed in detail.

Adjuvant Radiation Treatment of Breast Cancer After Mastectomy: Advanced Algorithms and Partial Bolus Improve the Dose Calculation Accuracy in the Case of Thin-Chest-Wall Irradiation

The aim of this study was to examine measured and calculated dose distributions in a thin-chest-wall phantom and estimate the variations in the dose-volume histogram (DVH) parameters used in plan evaluation for patient geometries with chest-wall thicknesses <15 mm with and without bolus implementation. Measurements were made using thermoluminescent dosimeters in a chest-wall phantom. The Monte Carlo method, anisotropic analytical algorithm, and Acuros XB Eclipse algorithms were used to calculate dose distributions for clinical plans. DVH parameters for clinical target volume tumor (CTVT) and planning target volume (PTV) and mean doses were evaluated for 15 patients with a chest-wall thickness of 8 to 15 mm with and without partial bolus and for 10 patients with a chest-wall thickness of 20 to 25 mm without bolus. Measurements showed that the dose at a depth of 2 to 12 mm at the beam entrance and laterally was within 90% of the dose at 8 mm depth. Monte Carlo and Acuros XB calculations were well aligned with the experimental data, whereas the anisotropic analytical algorithm underestimated the beam entrance and lateral doses. The DVH parameters for the patients with a thin chest wall were sensitive to calculation algorithm, resolution, body structure definition, and patient geometry. The parameters CTVTV95%, CTVTD98%, and PTVD98% were much lower than the tolerance criteria. Partial bolus improved the values for all algorithms and decreased the variations due to patient geometry. Dose calculations for patients with a chest-wall thickness of 20 to 25 mm resulted in sufficient target coverage and low dependence on patient geometry and calculation algorithm without the use of bolus. Dose calculations using advanced algorithms and resolution <2 mm are recommended for patients with a thin chest wall. Specific DVH criteria or the implementation of partial bolus was needed to facilitate plan development and evaluation for this patient group.

Adsorption dynamics of O2 on Cu(111): a supersonic molecular beam study.

We have studied the adsorption of O2 on Cu(111) using supersonic molecular beam techniques. For incident energies ranging between 100 and 400 meV, we have determined the sticking probability as a function of angle of incidence, surface temperature, and coverage. Initial sticking probabilities range from near 0 to 0.85 with an onset near 100 meV, making Cu(111) considerably less reactive than Cu(110) and Cu(100). Normal energy scaling applies and reactivity increases appreciably over the entire range of surface temperatures from 90 to 670 K. A strictly linearly decreasing coverage dependence on sticking precludes adsorption and dissociation via an extrinsic or long-lived mobile precursor state. We cannot exclude that sticking also occurs molecularly at the lowest surface temperatures. However, all tell tales from our experiments suggest that sticking is predominantly direct and dissociative. Comparison to earlier data shows implications for the relative reactivity of Cu(111) vs. Cu/Ru(0001) overlayers.

Analysis of Temperature-Programmed Desorption via Equilibrium Thermodynamics.

Temperature-programmed desorption (TPD) experiments in surface science are usually analyzed using the Polanyi-Wigner equation and/or transition-state theory. These methods are far from straightforward, and the determination of the pre-exponential factor is often problematic. We present a different method based on equilibrium thermodynamics, which builds on an approach previously used for TPD by Kreuzer et al. (Surf. Sci. 1988). Equations for the desorption rate are presented for three different types of surface-adsorbate interactions: (i) a 2D ideal hard-sphere gas with a negligible diffusion barrier, (ii) an ideal lattice gas, that is, fixed adsorption sites without interaction between the adsorbates, and (iii) a lattice gas with a distribution of (site-dependent) adsorption energies. We show that the coverage dependence of the sticking coefficient for adsorption at the desorption temperature determines whether the desorption process can be described by first- or second-order kinetics. The sticking coefficient at the desorption temperature must also be known for a quantitative determination of the adsorption energy, but it has a rather weak influence (like the pre-exponential factor in a traditional TPD analysis). Quantitative analysis is also influenced by the vibrational contributions to the energy and entropy. For the case of a single adsorption energy, we provide equations to directly convert peak temperatures into adsorption energies. These equations also provide an approximation of the desorption energy in cases that cannot be described by a fixed pre-exponential factor. For the case of a distribution of adsorption energies, the desorption spectra cannot be considered a superposition of desorption spectra corresponding to the different energies. Nevertheless, we present a method to extract the distribution of adsorption energies from TPD spectra, and we rationalize the energy resolution of TPD experiments. The analytical results are complemented by a program for simulation and analysis of TPD data.

Osteocalcin active center models: Electrochemical adsorption on platinum and quantum chemical analysis

An attempt was made to simulate the electrochemical behavior of the osteocalcin active site simple models on the platinum component of a bimetallic Ti/Pt implant. Dicarboxylic glutamic acid and dicarboxylic aspartic acid, and ethylmalonic acid as the third model successfully complementing the model range. The surface coverage of the platinum electrode during adsorption of model dicarboxylic acids was estimated using cyclic voltammetry and electrochemical impedance spectroscopy. All three compounds demonstrate similar trends in the surface coverage dependencies on the adsorption potential, acids' adsorption onto platinum surface is weak, and in none of cases studied amino group participates in adsorption on the platinum electrode surface. Using quantum chemical calculations, the most stable conformations of model compounds and the values of voids between adsorbed dicarboxylic acid molecules were obtained. Since all three models have a relatively low surface coverage and are participants in the outer sphere process of nonspecific adsorption on platinum, the residues of γ-carboxyglutamic acid present in osteocalcin will not be specifically adsorbed on the platinum component of the bimetallic implant, and the absence of interactions between it and the platinum electrode should have a positive effect on the dynamics of osteoregeneration.

Coverage Probability Analysis of Passive Reflectors in Indoor Environments

Since millimeter wave (mmWave) and sub-terahertz bands are highly vulnerable to blockage and penetration loss effects, wireless coverage enhancement is one of the critical challenges in indoor mmWave deployments. In particular, when the line-of-sight (LoS) link is blocked, a strong non-LoS (NLoS) path can provide a stable link quality. One of the efficient ways to improve the NLoS link is the use of strategically placed passive reflectors. In this letter, we study the indoor coverage improvement by using a transparent passive reflector attached on a wall. We consider an indoor open-door scenario, where the LoS link is blocked by the walls for receivers inside the room, and the coverage can only be achieved via an NLoS link through a passive reflector. We analytically derive closed-form equations of the reflection visibility probability and the coverage probability. By simulation and analytical results, we show the coverage dependency on the location and size of the reflector.