Silica Polymerization Driving Opposite Effects of pH on Aqueous Carbonation Using Crystalline and Amorphous Calcium Silicates.

The aqueous carbonation of calcium silicate (CS), a representative alkaline-earth silicate, has been widely explored in studies of carbon dioxide (CO2) mineralization. In this context, we conducted a specific comparison of the carbonation behaviors between the crystalline calcium silicate (CCS) and amorphous calcium silicate (ACS) across a pH range from 9.0 to 12.0. Interestingly, we observed opposite pH dependencies in the carbonation efficiencies (i.e., CaO conversion into CaCO3 in 1 M Na2CO3/NaHCO3 solution under ambient conditions) of CCS and ACS─the carbonation efficiency of CCS decreased with increasing the solution basicity, while that of ACS showed an inverse trend. In-depth insights were gained through in situ Raman characterizations, indicating that these differing trends appeared to originate from the polymerization/depolymerization behaviors of silicates released from minerals. More specifically, higher pH conditions seemed to favor the carbonation of minerals containing polymerized silica networks. These findings may contribute to a better understanding of the fundamental factors influencing the carbonation behaviors of alkaline earth silicates through interfacial coupled dissolution and precipitation processes. Moreover, they offer valuable insights for selecting optimal carbonation conditions for alkaline-earth silicate minerals.

How close are the classical two-body potentials to ab initio calculations? Insights from linear machine learning based force matching.

In this work, we propose a linear machine learning force matching approach that can directly extract pair atomic interactions from ab initio calculations in amorphous structures. The local feature representation is specifically chosen to make the linear weights a force field as a force/potential function of the atom pair distance. Consequently, this set of functions is the closest representation of the ab initio forces, given the two-body approximation and finite scanning in the configurational space. We validate this approach in amorphous silica. Potentials in the new force field (consisting of tabulated Si-Si, Si-O, and O-O potentials) are significantly different than existing potentials that are commonly used for silica, even though all of them produce the tetrahedral network structure and roughly similar glass properties. This suggests that the commonly used classical force fields do not offer fundamentally accurate representations of the atomic interaction in silica. The new force field furthermore produces a lower glass transition temperature (Tg ∼ 1800 K) and a positive liquid thermal expansion coefficient, suggesting the extraordinarily high Tg and negative liquid thermal expansion of simulated silica could be artifacts of previously developed classical potentials. Overall, the proposed approach provides a fundamental yet intuitive way to evaluate two-body potentials against ab initio calculations, thereby offering an efficient way to guide the development of classical force fields.

Comparison of Over-the-Scope Clips to Standard Endoscopic Treatment as the Initial Treatment in Patients With Bleeding From a Nonvariceal Upper Gastrointestinal Cause : A Randomized Controlled Trial.

BACKGROUND: Current endoscopic methods in the control of acute nonvariceal bleeding have a small but clinically significant failure rate. The role of over-the-scope clips (OTSCs) as the first treatment has not been defined. OBJECTIVE: To compare OTSCs with standard endoscopic hemostatic treatments in the control of bleeding from nonvariceal upper gastrointestinal causes. DESIGN: A multicenter, randomized controlled trial. (ClinicalTrials.gov: NCT03216395). SETTING: University teaching hospitals in Hong Kong, China, and Australia. PATIENTS: 190 adult patients with active bleeding or a nonbleeding visible vessel from a nonvariceal cause on upper gastrointestinal endoscopy. INTERVENTION: Standard hemostatic treatment (n = 97) or OTSC (n = 93). MEASUREMENTS: The primary outcome was 30-day probability of further bleeds. Other outcomes included failure to control bleeding after assigned endoscopic treatment, recurrent bleeding after initial hemostasis, further intervention, blood transfusion, and hospitalization. RESULTS: The 30-day probability of further bleeding in the standard treatment and OTSC groups was 14.6% (14 of 97) and 3.2% (3 of 93), respectively (risk difference, 11.4 percentage points [95% CI, 3.3 to 20.0 percentage points]; P = 0.006). Failure to control bleeding after assigned endoscopic treatment in the standard treatment and OTSC groups was 6 versus 1 (risk difference, 5.1 percentage points [CI, 0.7 to 11.8 percentage points]), respectively, and 30-day recurrent bleeding was 8 versus 2 (risk difference, 6.6 percentage points [CI, -0.3 to 14.4 percentage points]), respectively. The need for further interventions was 8 versus 2, respectively. Thirty-day mortality was 4 versus 2, respectively. In a post hoc analysis with a composite end point of failure to successfully apply assigned treatment and further bleeds, the event rate was 15 of 97 (15.6%) and 6 of 93 (6.5%) in the standard and OTSC groups, respectively (risk difference, 9.1 percentage points [CI, 0.004 to 18.3 percentage points]). LIMITATION: Clinicians were not blinded to treatment and the option of crossover treatment. CONCLUSION: Over-the-scope clips, as an initial treatment, may be better than standard treatment in reducing the risk for further bleeding from nonvariceal upper gastrointestinal causes that are amenable to OTSC placement. PRIMARY FUNDING SOURCE: General Research Fund to the University Grant Committee, Hong Kong SAR Government.

Enhancing Aqueous Carbonation of Calcium Silicate through Acid and Base Pretreatments with Implications for Efficient Carbon Mineralization.

Carbon dioxide (CO2) mineralization based on aqueous carbonation of alkaline earth silicate minerals is a promising route toward large-scale carbon removal. Traditional aqueous carbonation methods largely adopt acidification-based approaches, e.g., using concentrated/pressurized CO2 or acidic media, to accelerate mineral dissolution and carbonation. In this study, we designed and tested three distinctive routes to evaluate the effect of pretreatments under different pH conditions on aqueous carbonation, using amorphous calcium silicate (CS) as an example system. Pretreating CS with high concentrations (100 mM) of HCl (Route I) or NaOH (Route II and III) enhanced their carbonation degrees. However, NaOH pretreatment overall yielded higher carbonation degrees than the HCl pretreatment, with the highest carbonation degree achieved through Route III, where an extra step is taken after the NaOH pretreatment to remove the solution containing dissolved silica prior to carbonation. The HCl and NaOH pretreatments formed different intermediate silica products on the CS surface. Silica precipitated from the HCl pretreatment had a minimal effect on the carbonation degree. The high Ca/Si ratio intermediate phases formed from the NaOH, on the other hand, can be readily carbonated. In contrast to commonly utilized acidification-based approaches, basification offers a more promising route to accelerate aqueous carbonation as it can mitigate the need for costly pH swing and high-concentration/pressurized CO2. The key to aqueous carbonation under basic conditions, as suggested by this study, is the control of aqueous silica species that have a suppressing effect on carbonation. Overall, this study highlights the critical needs for investigations of aqueous mineral carbonation in a broader pH region.

Sodium tanshinone IIA sulphate inhibits angiogenesis in lung adenocarcinoma via mediation of miR-874/eEF-2K/TG2 axis.

CONTEXT: Sodium tanshinone IIA sulphate (STS) is a product originated from Salvia miltiorrhiza Bunge [Lamiaceae], which exerts an antitumour effect. However, the role of STS on lung adenocarcinoma (LUAD) remains unexplored. OBJECTIVE: Our study explores the effect and mechanism of STS against LUAD. MATERIALS AND METHODS: LUAD cells were treated with 100 µM STS for 24 h and control group cells were cultured under normal medium conditions. Functionally, the viability, migration, invasion and angiogenesis of LUAD cells were examined by MTT, wound healing, transwell and tube formation assay, respectively. Moreover, cells were transvected with different transfection plasmids. Dual luciferase reporter and RNA immunoprecipitation (RIP) assays were used to verify the relationship between miR-874 and eEF-2K. RESULTS: STS significantly decreased the viability (40-50% reduction), migration (migration rate of A549 cells from 0.67 to 0.28, H1299 cells from 0.71 to 0.41), invasion (invasion numbers of A549 cells from 172 to 55, H1299 cells from 188 to 35) and angiogenesis (80-90% reduction) of LUAD cells. Downregulation of miR-874 partially abolished the antitumour effect of STS. EEF-2K was identified to be the target of miR-874, and its downregulation markedly abolished the effects of miR-874 downregulation on tumourigenesis of LUAD. Moreover, silencing of TG2 abrogated eEF-2K-induced progression of LUAD. DISCUSSION AND CONCLUSIONS: STS attenuated the tumourigenesis of LUAD through the mediation of the miR-874/eEF-2K/TG2 axis. STS is a promising drug to fight against lung cancer, which might effectively reverse drug resistance when combined with classical anticancer drugs.

Anisotropic Molecular Organization at a Liquid/Vapor Interface Promotes Crystal Nucleation with Polymorph Selection.

The molecules at the surface of a liquid have different organization and dynamics from those in the bulk, potentially altering the rate of crystal nucleation and polymorphic selection, but this effect remains poorly understood. Here we demonstrate that nucleation at the surface of a pure liquid, d-arabitol, is vastly enhanced, by 12 orders of magnitude, and selects a different polymorph. The surface effect intensifies with cooling and can be inhibited by a dilute, surface-active second component. This phenomenon arises from the anisotropic molecular packing at the interface and its similarity to the surface-nucleating polymorph. Our finding is relevant for controlling the crystallization and polymorphism in any system with a significant interface such as nanodroplets and atmospheric water.

Understanding the Fragile-to-Strong Transition in Silica from Microscopic Dynamics.

In this work, we revisit the fragile-to-strong transition (FTS) in the simulated BKS silica from the perspective of microscopic dynamics in an effort to elucidate the dynamical behaviors of fragile and strong glass-forming liquids. Softness, which is a machine-learned feature from local atomic structures, is used to predict the microscopic activation energetics and long-term dynamics. The FTS is found to originate from a change in the temperature dependence of the microscopic activation energetics. Furthermore, results suggest there are two diffusion channels with different energy barriers in BKS silica. The fast dynamics at high temperatures is dominated by the channel with small energy barriers (<∼1 eV), which is controlled by the short-range order. The rapid closing of this diffusion channel when lowering temperature leads to the fragile behavior. On the other hand, the slow dynamics at low temperatures is dominated by the channel with large energy barriers controlled by the medium-range order. This slow diffusion channel changes only subtly with temperature, leading to the strong behavior. The distributions of barriers in the two channels show different temperature dependences, causing a crossover at ∼3100 K. This transition temperature in microscopic dynamics is consistent with the inflection point in the configurational entropy, suggesting there is a fundamental correlation between microscopic dynamics and thermodynamics.

Surface Diffusion Is Controlled by Bulk Fragility across All Glass Types.

Surface diffusion is vastly faster than bulk diffusion in some glasses, but only moderately enhanced in others. We show that this variation is closely linked to bulk fragility, a common measure of how quickly dynamics is excited when a glass is heated to become a liquid. In fragile molecular glasses, surface diffusion can be a factor of 10^{8} faster than bulk diffusion at the glass transition temperature, while in the strong system SiO_{2}, the enhancement is a factor of 10. Between these two extremes lie systems of intermediate fragility, including metallic glasses and amorphous selenium and silicon. This indicates that stronger liquids have greater resistance to dynamic excitation from bulk to surface and enables prediction of surface diffusion, surface crystallization, and formation of stable glasses by vapor deposition.

eEF-2K knockdown synergizes with STS treatment to inhibit cell proliferation, migration, and invasion via the TG2/ERK pathway in A549 cells.

Emerging research has suggested the anticancer potential of tanshinone IIA, the bioactive ingredient isolated from the traditional Chinese herb Salvia miltiorrhiza. However, the molecular mechanism of sodium tanshinone IIA sulfonate (STS) antilung cancer effect is not very clear. In this study, our purpose is to investigate the roles of STS and elongation factor-2 kinase (eEF-2K) in regulating the proliferation, migration, and invasion of A549 cells and explore the implicated pathways. We found that STS suppressed A549 cell survival and proliferation in a time- and xdose-dependent manner. Knockdown of eEF-2K and treatment with STS synergistically exerted antiproliferative, -migratory, and -invasive effects on A549 cells. These effects were caused by attenuation of the extracellular signal-regulated kinase (ERK) pathway via inhibition of tissue transglutaminase (TG2). In summary, the inhibition of eEF-2K synergizes with STS treatment, exerting anticancer effects on lung adenocarcinoma cells through the TG2/ERK signaling pathway, which provides a potential therapeutic target for treating lung adenocarcinoma.

Safety, tolerability, and immunogenicity of a recombinant adenovirus type-5 vectored COVID-19 vaccine: a dose-escalation, open-label, non-randomised, first-in-human trial.

BACKGROUND: A vaccine to protect against COVID-19 is urgently needed. We aimed to assess the safety, tolerability, and immunogenicity of a recombinant adenovirus type-5 (Ad5) vectored COVID-19 vaccine expressing the spike glycoprotein of a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) strain. METHODS: We did a dose-escalation, single-centre, open-label, non-randomised, phase 1 trial of an Ad5 vectored COVID-19 vaccine in Wuhan, China. Healthy adults aged between 18 and 60 years were sequentially enrolled and allocated to one of three dose groups (5 × 1010, 1 × 1011, and 1·5 × 1011 viral particles) to receive an intramuscular injection of vaccine. The primary outcome was adverse events in the 7 days post-vaccination. Safety was assessed over 28 days post-vaccination. Specific antibodies were measured with ELISA, and the neutralising antibody responses induced by vaccination were detected with SARS-CoV-2 virus neutralisation and pseudovirus neutralisation tests. T-cell responses were assessed by enzyme-linked immunospot and flow-cytometry assays. This study is registered with ClinicalTrials.gov, NCT04313127. FINDINGS: Between March 16 and March 27, 2020, we screened 195 individuals for eligibility. Of them, 108 participants (51% male, 49% female; mean age 36·3 years) were recruited and received the low dose (n=36), middle dose (n=36), or high dose (n=36) of the vaccine. All enrolled participants were included in the analysis. At least one adverse reaction within the first 7 days after the vaccination was reported in 30 (83%) participants in the low dose group, 30 (83%) participants in the middle dose group, and 27 (75%) participants in the high dose group. The most common injection site adverse reaction was pain, which was reported in 58 (54%) vaccine recipients, and the most commonly reported systematic adverse reactions were fever (50 [46%]), fatigue (47 [44%]), headache (42 [39%]), and muscle pain (18 [17%]. Most adverse reactions that were reported in all dose groups were mild or moderate in severity. No serious adverse event was noted within 28 days post-vaccination. ELISA antibodies and neutralising antibodies increased significantly at day 14, and peaked 28 days post-vaccination. Specific T-cell response peaked at day 14 post-vaccination. INTERPRETATION: The Ad5 vectored COVID-19 vaccine is tolerable and immunogenic at 28 days post-vaccination. Humoral responses against SARS-CoV-2 peaked at day 28 post-vaccination in healthy adults, and rapid specific T-cell responses were noted from day 14 post-vaccination. Our findings suggest that the Ad5 vectored COVID-19 vaccine warrants further investigation. FUNDING: National Key R&D Program of China, National Science and Technology Major Project, and CanSino Biologics.

Immunogenicity and safety of a recombinant adenovirus type-5-vectored COVID-19 vaccine in healthy adults aged 18 years or older: a randomised, double-blind, placebo-controlled, phase 2 trial.

BACKGROUND: This is the first randomised controlled trial for assessment of the immunogenicity and safety of a candidate non-replicating adenovirus type-5 (Ad5)-vectored COVID-19 vaccine, aiming to determine an appropriate dose of the candidate vaccine for an efficacy study. METHODS: This randomised, double-blind, placebo-controlled, phase 2 trial of the Ad5-vectored COVID-19 vaccine was done in a single centre in Wuhan, China. Healthy adults aged 18 years or older, who were HIV-negative and previous severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection-free, were eligible to participate and were randomly assigned to receive the vaccine at a dose of 1 × 1011 viral particles per mL or 5 × 1010 viral particles per mL, or placebo. Investigators allocated participants at a ratio of 2:1:1 to receive a single injection intramuscularly in the arm. The randomisation list (block size 4) was generated by an independent statistician. Participants, investigators, and staff undertaking laboratory analyses were masked to group allocation. The primary endpoints for immunogenicity were the geometric mean titres (GMTs) of specific ELISA antibody responses to the receptor binding domain (RBD) and neutralising antibody responses at day 28. The primary endpoint for safety evaluation was the incidence of adverse reactions within 14 days. All recruited participants who received at least one dose were included in the primary and safety analyses. This study is registered with ClinicalTrials.gov, NCT04341389. FINDINGS: 603 volunteers were recruited and screened for eligibility between April 11 and 16, 2020. 508 eligible participants (50% male; mean age 39·7 years, SD 12·5) consented to participate in the trial and were randomly assigned to receive the vaccine (1 × 1011 viral particles n=253; 5 × 1010 viral particles n=129) or placebo (n=126). In the 1 × 1011 and 5 × 1010 viral particles dose groups, the RBD-specific ELISA antibodies peaked at 656·5 (95% CI 575·2-749·2) and 571·0 (467·6-697·3), with seroconversion rates at 96% (95% CI 93-98) and 97% (92-99), respectively, at day 28. Both doses of the vaccine induced significant neutralising antibody responses to live SARS-CoV-2, with GMTs of 19·5 (95% CI 16·8-22·7) and 18·3 (14·4-23·3) in participants receiving 1 × 1011 and 5 × 1010 viral particles, respectively. Specific interferon γ enzyme-linked immunospot assay responses post vaccination were observed in 227 (90%, 95% CI 85-93) of 253 and 113 (88%, 81-92) of 129 participants in the 1 × 1011 and 5 × 1010 viral particles dose groups, respectively. Solicited adverse reactions were reported by 183 (72%) of 253 and 96 (74%) of 129 participants in the 1 × 1011 and 5 × 1010 viral particles dose groups, respectively. Severe adverse reactions were reported by 24 (9%) participants in the 1 × 1011 viral particles dose group and one (1%) participant in the 5 × 1010 viral particles dose group. No serious adverse reactions were documented. INTERPRETATION: The Ad5-vectored COVID-19 vaccine at 5 × 1010 viral particles is safe, and induced significant immune responses in the majority of recipients after a single immunisation. FUNDING: National Key R&D Programme of China, National Science and Technology Major Project, and CanSino Biologics.

Investigating the microstructure of high-calcium fly ash-based alkali-activated material for aqueous Zn sorption.

The performance of adsorbents prepared by alkali activation of high calcium fly ash was investigated for removing aqueous Zn. Two formulations involving the use of NaOH and Na2SiO3 activating solutions were used to prepare the adsorbents that feature different microstructural characteristics. The Zn sorption data indicates a sorption process that is controlled by both chemisorption and intra-particle diffusion. The Na2SiO3-activated material displayed higher sorption rates compared to the NaOH-activated material. The sorption kinetics show strong dependence on the microstructures of the adsorbents, wherein the Na2SiO3-activated material featuring higher contents of amorphous phases (96 %mass) in the hydrated phase assemblage, with attendant improved porosity and surface area, performed better than the NaOH-activated material (86 %mass amorphous phases) which showed higher degree of crystallinity and coarse morphology. The Na2SiO3-activated material exhibited 100% Zn removal efficiency within the first 5 min in all studied initial adsorbate concentrations(corresponding to sorption capacity of up to 200 mg/g), while the NaOH-activated analogue tends to lag, reaching 99.99% Zn removal efficiency after about 240 min in most cases. The two formulations were also examined with thermodynamic modeling and the results agree with experimental data in indicating that the use of alkali-silicate activating solution is most suitable for converting high calcium fly ash into efficient adsorbent for removing aqueous heavy metals.

Kras mutant genetically engineered mouse models of human cancers are genomically heterogeneous.

KRAS mutant tumors are largely recalcitrant to targeted therapies. Genetically engineered mouse models (GEMMs) of Kras mutant cancer recapitulate critical aspects of this disease and are widely used for preclinical validation of targets and therapies. Through comprehensive profiling of exomes and matched transcriptomes of >200 KrasG12D-initiated GEMM tumors from one lung and two pancreatic cancer models, we discover that significant intratumoral and intertumoral genomic heterogeneity evolves during tumorigenesis. Known oncogenes and tumor suppressor genes, beyond those engineered, are mutated, amplified, and deleted. Unlike human tumors, the GEMM genomic landscapes are dominated by copy number alterations, while protein-altering mutations are rare. However, interspecies comparative analyses of the genomic landscapes demonstrate fidelity between genes altered in KRAS mutant human and murine tumors. Genes that are spontaneously altered during murine tumorigenesis are also among the most prevalent found in human indications. Using targeted therapies, we also demonstrate that this inherent tumor heterogeneity can be exploited preclinically to discover cancer-specific and genotype-specific therapeutic vulnerabilities. Focusing on Kras allelic imbalance, a feature shared by all three models, we discover that MAPK pathway inhibition impinges uniquely on this event, indicating distinct susceptibility and fitness advantage of Kras-mutant cells. These data reveal previously unknown genomic diversity among KrasG12D-initiated GEMM tumors, places them in context of human patients, and demonstrates how to exploit this inherent tumor heterogeneity to discover therapeutic vulnerabilities.

Gefitinib versus vinorelbine plus cisplatin as adjuvant treatment for stage II-IIIA (N1-N2) EGFR-mutant NSCLC (ADJUVANT/CTONG1104): a randomised, open-label, phase 3 study.

BACKGROUND: Cisplatin-based adjuvant chemotherapy is the standard of care for patients with resected stage II-IIIA non-small-cell lung cancer (NSCLC). RADIANT and SELECT trial data suggest patients with EGFR-mutant stage IB-IIIA resected NSCLC could benefit from adjuvant EGFR tyrosine kinase inhibitor treatment. We aimed to compare the efficacy of adjuvant gefitinib versus vinorelbine plus cisplatin in patients with completely resected EGFR-mutant stage II-IIIA (N1-N2) NSCLC. METHODS: We did a randomised, open-label, phase 3 trial at 27 centres in China. We enrolled patients aged 18-75 years with completely resected (R0), stage II-IIIA (N1-N2), EGFR-mutant (exon 19 deletion or exon 21 Leu858Arg) NSCLC. Patients were stratified by N stage and EGFR mutation status and randomised (1:1) by Pocock and Simon minimisation with a random element to either gefitinib (250 mg once daily) for 24 months or intravenous vinorelbine (25 mg/m2 on days 1 and 8) plus intravenous cisplatin (75 mg/m2 on day 1) every 3 weeks for four cycles. The primary endpoint was disease-free survival in the intention-to-treat population, which comprised all randomised patients; the safety population included all randomised patients who received at least one dose of study medication. Enrolment to the study is closed but survival follow-up is ongoing. The study is registered with ClinicalTrials.gov, number NCT01405079. FINDINGS: Between Sept 19, 2011, and April 24, 2014, 483 patients were screened and 222 patients were randomised, 111 to gefitinib and 111 to vinorelbine plus cisplatin. Median follow-up was 36·5 months (IQR 23·8-44·8). Median disease-free survival was significantly longer with gefitinib (28·7 months [95% CI 24·9-32·5]) than with vinorelbine plus cisplatin (18·0 months [13·6-22·3]; hazard ratio [HR] 0·60, 95% CI 0·42-0·87; p=0·0054). In the safety population, the most commonly reported grade 3 or worse adverse events in the gefitinib group (n=106) were raised alanine aminotransferase and asparate aminotransferase (two [2%] patients with each event vs none with vinorelbine plus cisplatin). In the vinorelbine plus cisplatin group (n=87), the most frequently reported grade 3 or worse adverse events were neutropenia (30 [34%] patients vs none with gefitinib), leucopenia (14 [16%] vs none), and vomiting (eight [9%] vs none). Serious adverse events were reported for seven (7%) patients who received gefitinib and 20 (23%) patients who received vinorelbine plus cisplatin. No interstitial lung disease was noted with gefitinib. No deaths were treatment related. INTERPRETATION: Adjuvant gefitinib led to significantly longer disease-free survival compared with that for vinorelbine plus cisplatin in patients with completely resected stage II-IIIA (N1-N2) EGFR-mutant NSCLC. Based on the superior disease-free survival, reduced toxicity, and improved quality of life, adjuvant gefitinib could be a potential treatment option compared with adjuvant chemotherapy in these patients. However, the duration of benefit with gefitinib after 24 months might be limited and overall survival data are not yet mature. FUNDING: Guangdong Provincial Key Laboratory of Lung Cancer Translational Medicine; National Health and Family Planning Commission of People's Republic of China; Guangzhou Science and Technology Bureau; AstraZeneca China.

New insights into the atomic structure of amorphous TiO2 using tight-binding molecular dynamics.

Amorphous TiO2 (a-TiO2) could offer an attractive alternative to conventional crystalline TiO2 phases for photocatalytic applications. However, the atomic structure of a-TiO2 remains poorly understood with respect to that of its crystalline counterparts. Here, we conduct some classical molecular dynamics simulations of a-TiO2 based on a selection of empirical potentials. We show that, on account of its ability to dynamically assign the charge of each atom based on its local environment, the second-moment tight-binding charge equilibration potential yields an unprecedented agreement with available experimental data. Based on these simulations, we investigate the degree of order and disorder in a-TiO2. Overall, the results suggest that a-TiO2 features a large flexibility in its local topology, which may explain the high sensitivity of its structure to the synthesis method being used.

Topological Control on the Structural Relaxation of Atomic Networks under Stress.

Upon loading, atomic networks can feature delayed irreversible relaxation. However, the effect of composition and structure on relaxation remains poorly understood. Herein, relying on accelerated molecular dynamics simulations and topological constraint theory, we investigate the relationship between atomic topology and stress-induced structural relaxation, by taking the example of creep deformations in calcium silicate hydrates (C─S─H), the binding phase of concrete. Under constant shear stress, C─S─H is found to feature delayed logarithmic shear deformations. We demonstrate that the propensity for relaxation is minimum for isostatic atomic networks, which are characterized by the simultaneous absence of floppy internal modes of relaxation and eigenstress. This suggests that topological nanoengineering could lead to the discovery of nonaging materials.

Irradiation- vs. vitrification-induced disordering: The case of 𝜶-quartz and glassy silica.

Irradiation and vitrification can both result in the disordering of minerals. However, it remains unclear whether these effects are comparable or if the glassy state represents an upper limit for irradiation-induced disordering. By reactive molecular dynamics simulations, we compare the structure of irradiated quartz to that of glassy silica. We show that although they share some degree of similarity, the structure of irradiated quartz and glassy silica differs from each other, both at the short- (<3 Å) and the medium-range (>3 Å and <10 Å). In particular, the atomic network of irradiated quartz is found to comprise coordination defects, edge-sharing units, and large rings, which are absent from glassy silica. These results highlight the different nature of irradiation- and vitrification-induced disordering.

Cooling rate effects in sodium silicate glasses: Bridging the gap between molecular dynamics simulations and experiments.

Although molecular dynamics (MD) simulations are commonly used to predict the structure and properties of glasses, they are intrinsically limited to short time scales, necessitating the use of fast cooling rates. It is therefore challenging to compare results from MD simulations to experimental results for glasses cooled on typical laboratory time scales. Based on MD simulations of a sodium silicate glass with varying cooling rate (from 0.01 to 100 K/ps), here we show that thermal history primarily affects the medium-range order structure, while the short-range order is largely unaffected over the range of cooling rates simulated. This results in a decoupling between the enthalpy and volume relaxation functions, where the enthalpy quickly plateaus as the cooling rate decreases, whereas density exhibits a slower relaxation. Finally, we show that, using the proper extrapolation method, the outcomes of MD simulations can be meaningfully compared to experimental values when extrapolated to slower cooling rates.

Enhancement of binding kinetics on affinity substrates by laser point heating induced transport.

Enhancing the time response and detection limit of affinity-binding based biosensors is an area of active research. For diffusion limited reactions, introducing active mass transport is an effective strategy to reduce the equilibration time and improve surface binding. Here, a laser is focused on the ceiling of a microchamber to generate point heating, which introduces natural advection and thermophoresis to promote mass transport to the reactive floor. We first used the COMSOL simulation to study how the kinetics of ligand binding is influenced by the optothermal effect. Afterwards, binding of biotinylated nanoparticles to NeutrAvidin-treated substrates is quantitatively measured with and without laser heating. It is discovered that laser induced point heating reduces the reaction half-life locally, and the reduction improves with the natural advection velocity. In addition, non-uniform ligand binding on the substrate is induced by the laser with predictable binding patterns. This optothermal strategy holds promise to improve the time-response and sensitivity of biosensors and microarrays.

Luminescence of delafossite-type CuAlO2 fibers with Eu substitution for Al cations.

CuAlO2 has been examined as a potential luminescent material by substituting Eu for Al cations in the delafossite structure. CuAlO2:Eu3+ nanofibers have been prepared via electrospinning for the ease of mitigating synthesis requirements and for future optoelectronics and emerging applications. Single-phase CuAlO2 fibers could be obtained at a temperature of 1100 °C in air. The Eu was successfully doped in the delafossite structure and two strong emission bands at ~405 and 610 nm were observed in the photoluminescence spectra. These bands are due to the intrinsic near-band-edge transition of CuAlO2 and the f-f transition of the Eu3+ activator, respectively. Further electrical characterization indicated that these fibers exhibit semiconducting behavior and the introduction of Eu could act as band-edge modifiers, thus changing the thermal activation energies. In light of this study, CuAlO2:Eu3+ fibers with both strong photoluminescence and p-type conductivity could be produced by tailoring the rare earth doping concentrations.