Search

Nonadiabatic quantum molecular dynamics is used to investigate the evolution of GeTe photoexcited states. Results reveal a photoexcitation-induced picosecond nonthermal path for the loss of long-range order. A valence electron excitation threshold of 4% is found to trigger local disorder by switching Ge atoms from octahedral to tetrahedral sites and promoting Ge-Ge bonding. The resulting loss of long-range order for a higher valence electron excitation fraction is achieved without fulfilling the Lindemann criterion for melting, therefore utilizing a nonthermal path. The photoexcitation-induced structural disorder is accompanied by charge transfer from Te to Ge, Ge-Te bonding-to-antibonding, and Ge-Ge antibonding-to-bonding change, triggering Ge-Te bond breaking and promoting the formation of Ge-Ge wrong bonds. These results provide an electronic-structure basis to understand the photoexcitation-induced ultrafast changes in the structure and properties of GeTe and other phase-change materials.

Background: Little is known about the long-term risks of stroke and ischemic heart disease (IHD) in women who had a hysterectomy alone (HA) or with bilateral oophorectomy (HBO) for benign diseases, particularly in China where the burden of cardiovascular diseases (CVD) is high. We assessed mean levels of cardiovascular risk factors and relative risks of stroke and IHD in Chinese women who had a HA or HBO. Methods: A total of 302 510 women, aged 30 to 79 years were enrolled in the China Kadoorie Biobank from 2004 to 2008 and followed up for a mean of 9.8 years. The analysis involved premenopausal women without prior cardiovascular disease or cancer at enrollment. We calculated adjusted hazard ratios for incident cases of CVD and their pathological types (ischemic stroke, hemorrhagic stroke, and IHD) after HA and HBO. Analyses were stratified by age and region and adjusted for levels of education, household income, smoking status, alcohol consumption, physical activity, body mass index, systolic blood pressure, diabetes, self-reported health, and number of pregnancies. Results: Among 282 722 eligible women, 8478 had HA, and 1360 had HBO. Women who had HA had 9% higher risk of CVD after HA (hazard ratio, 1.09 [95% CI, 1.06–1.12]) and 19% higher risk of CVD after HBO (1.19 [95% CI, 1.12–1.26]) compared with women who did not. Both HA and HBO were associated with higher risks of ischemic stroke and IHD but not with hemorrhagic stroke. The relative risks of CVD associated with HA and HBO were more extreme at younger age of surgery. Conclusions: Women who had either HA or HBO have higher risks of ischemic stroke and IHD, and these risks should be evaluated when discussing these interventions. Additional screening for risk factors for CVD should be considered in women following HA and HBO operations, especially if such operations are performed at younger age.

Background: Little research has been done on the mental health of western Chinese university students during the Coronavirus disease (COVID-19) pandemic. This work aims to fill the gap by gaining insight into the positive psychological capital and its influencing factors among university students in western China during the COVID-19 pandemic. Methods: An online cross-sectional study was conducted in college students from a medical school. Participants were surveyed anonymously using a general information questionnaire and the Positive Psychological Capital Scale. The key factors and models affecting the psychological capital were obtained by using the gradual regression method. If P < 0.05, the difference would be considered statistically significant. Results: The total score of positive psychological capital among university students in western China was 118.51±16.91, Taking the psychological capital as the dependent variable, gender and grade as the independent variables, the key factors and models affecting the psychological capital were obtained by using the gradual regression method.The results showed that the P-value of each influencing factor was

Despite the growing success of machine learning for predicting structure-property relationships in molecules and materials, such as predicting the dielectric properties of polymers, it is still in its infancy. We report on the effectiveness of solving structure-property relationships for a computer-generated database of dielectric polymers using recurrent neural network (RNN) models. The implementation of a series of optimization strategies was crucial to achieving high learning speeds and sufficient accuracy: (1) binary and nonbinary representations of SMILES (Simplified Molecular Input Line System) fingerprints and (2) backpropagation with affine transformation of the input sequence (ATransformedBP) and resilient backpropagation with initial weight update parameter optimizations (iRPROP- optimized). For the investigated database of polymers, the binary SMILES representation was found to be superior to the decimal representation with respect to the training and prediction performance. All developed and optimized Elman-type RNN algorithms outperformed nonoptimized RNN models in the efficient prediction of nonlinear structure-activity relationships. The average relative standard deviation (RSD) remained well below 5%, and the maximum RSD did not exceed 30%. Moreover, we provide a C++ codebase as a testbed for a new generation of open programming languages that target increasingly diverse computer architectures.

Abstract Transition metal dichalcogenides have shown great potential for next-generation electronic and optoelectronic devices. However, native oxidation remains a major issue in achieving their long-term stability, especially for Zr-containing materials such as ZrS2. Here, we develop a first principles-informed reactive forcefield for Zr/O/S to study oxidation dynamics of ZrS2. Simulation results reveal anisotropic oxidation rates between (210) and (001) surfaces. The oxidation rate is highly dependent on the initial adsorption of oxygen molecules on the surface. Simulation results also provide reaction mechanism for native oxide formation with atomistic details. Graphic Abstract

A thorough understanding of native oxides is essential for designing semiconductor devices. Here we report a study of the rate and mechanisms of spontaneous oxidation of bulk single crystals of ZrS$_x$Se$_{2-x}$ alloys and MoS$_2$. ZrS$_x$Se$_{2-x}$ alloys oxidize rapidly, and the oxidation rate increases with Se content. Oxidation of basal surfaces is initiated by favorable O$_2$ adsorption and proceeds by a mechanism of Zr-O bond switching, that collapses the van der Waals gaps, and is facilitated by progressive redox transitions of the chalcogen. The rate-limiting process is the formation and out-diffusion of SO$_2$. In contrast, MoS$_2$ basal surfaces are stable due to unfavorable oxygen adsorption. Our results provide insight and quantitative guidance for designing and processing semiconductor devices based on ZrS$_x$Se$_{2-x}$ and MoS$_2$, and identify the atomistic-scale mechanisms of bonding and phase transformations in layered materials with competing anions.

Dual-phase membranes, consisting of molten alkali metal carbonates infiltrated into an oxygen ion or mixed-conducting substrate, are a promising technology for high-temperature CO2 separations and other energy conversion applications, such as membrane reactors. In this paper, we report a new fabrication technique for triple-phase membranes capable of high-temperature CO2 transport using an oxygen ion-conducting ceramic combined with an electronic-conducting metal layer. An oxygen ion-conducting, 4YSZ porous substrate tube was coated with a thin layer of metal (Pd/Ag or Ni) using electroless plating to prepare a mixed-conducting (oxygen ion and electronic) support for the triple-phase membranes. The porous section was then filled with a molten carbonate (MC) salt consisting of a eutectic mixture of Li/K or Na/K carbonates. This enabled both the mixed oxygen and carbonate ion conductor (MOCC) and mixed electron and carbonate ion conductor (MECC) CO2 transport mechanisms. The highest CO2 permeance (flux/driving force) of 1.07 × 10–7 mol m–2 s–1 Pa–1 (a flux of 0.8 cm3(STP) cm–2 min–1) was measured on a 4YSZ support coated with a Pd/Ag layer and infiltrated with the eutectic Li/K carbonate salt; it was measured at 725 °C with a 50/50 CO2/O2 feed gas mixture at a transmembrane pressure of 110 kPa. The apparent activation energy for CO2 transport was calculated to be 57 kJ mol–1 between 450 and 600 °C, suggesting that the rate-limiting step was the diffusion of the carbonate ion in the molten carbonate; however, the activation energy was observed to increase to 74 kJ mol–1 (650–750 °C), which was attributed to the influence of oxygen anion transport at higher temperatures.

Background Menstrual migraine is a particular form of migraine with a significant impact on the quality of life for women afflicted. Presently, no study has reported the quality of life in menstrual migraine patients. This work aims to assess the health-related quality of life and identify its associated factors among Chinese menstrual migraine patients. Methods The cross-sectional study group consisted of 109 patients with menstrual migraine, and the control group consisted of 397 female patients with non-menstrual migraine. In total, 506 patients completed questionnaires for demographic and clinical information, the Self-rating Idea of Suicide Scale, the Hamilton Depression Scale, the Hamilton Anxiety Scale, the Headache Impact Test-6, the Perceived Social Support Scale, the Pittsburgh Sleep Quality Index. Health-related quality of life was measured using the 36-Item Short Form Survey. Results Compared with non-menstrual migraine patients, five dimensions of health-related quality of life were all found to be significantly impaired in menstrual migraine patients. Headache frequency (ß = − 0.218, P = 0.014), the impact of headache on daily life (ß = − 0.270, P = 0.002), depression symptoms (ß = − 0.345, P P P P Conclusion Menstrual migraine patients had a significantly poorer health-related quality of life in many domains than non-menstrual migraine patients. Headache frequency, the impact of headache on daily life, depression symptoms, social support, and suicidal ideation were significantly associated with health-related quality of life in menstrual migraine patients. Trial registration: ChiCTR1800014343. This study was registered prospectively on 7 January 2018 at Chinese Clinical Trial registry. http://www.chictr.org.cn/showproj.aspx?proj=24526

Background Menstrual migraine is a special form of migraine with significant impact on quality of life for those women afflicted. Presently, there is no study reported on quality of life in menstrual migraine patients. The study reported here aimed to assess the health-related quality of life and identify its associated factors among Chinese menstrual migraine patients. Methods The cross-sectional study group consisted of 109 patients with menstrual migraine and the control group consisted of 397 female patients with non-menstrual migraine. In total, 506 patients completed questionnaires for demographic and clinical information, Self-rating Idea of Suicide Scale, Hamilton Depression Scale, Hamilton Anxiety Scale, Headache Impact Test-6, Perceived Social Support Scale, Pittsburgh Sleep Quality Index. Health-related quality of life was measured using the 36-Item Short Form Survey. Results Compared with non-menstrual migraine patients, five dimensions of health-related quality of life were all found to be significantly impaired in menstrual migraine patients. Headache frequency (ß=-0.218, P=0.014), the impact of headache on daily life (ß=-0.270, P=0.002), depression symptoms (ß=-0.345, P

Background and aims Observational studies have associated resting heart rate with incident diabetes. Whether the associations are causal remains unclear. We aimed to examine the shape and strength of the associations and assessed the causal relevance of such associations in Chinese adults. Methods and results The China Kadoorie Biobank enrolled 512,891 adults in China. Cox proportional hazard regression models was conducted to estimate hazard ratios (HRs) for the associations of resting heart rate with type 2 diabetes and total diabetes. Among 92,724 participants, 36 single-nucleotide polymorphisms (SNPs) related to resting heart rate were used to construct genetic risk score. We used Mendelian randomization analyses to make the causal inferences. During a median follow-up of 9 years, 7872 incident type 2 diabetes and 13,349 incident total diabetes were documented. After regression dilution bias adjustment, each 10 bpm higher heart rate was associated with about a 26% higher risk of type 2 diabetes (HR, 1.26 [95% CI, 1.23, 1.29]) and 23% higher risk of total diabetes (HR, 1.23 [95% CI, 1.20, 1.26]). Instrumental variable analyses showed participants at top quintile compared with those at bottom quintile had 30% higher risk for type 2 diabetes (HR, 1.30 [95% CI, 1.17, 1.43]), and 10% higher risk for total diabetes (HR, 1.10 [95% CI, 1.02, 1.20]). Conclusions This study provides evidence that resting heart rate is an important risk factor for diabetes risk. The results suggest that novel treatment approaches targeting reduction of high heart rate for incidence of diabetes may be worth further investigation.

A thorough understanding of native oxides is essential for designing semiconductor devices. Here, we report a study of the rate and mechanisms of spontaneous oxidation of bulk single crystals of ZrS

The deoxygenation of palmitic and lauric acids over 0.5 wt % Pt/ZIF-67 membrane/zeolite 5A bead catalysts is demonstrated. Almost complete conversion (% deoxygenation of ≥95%) of these two fatty acids was observed over both fresh and recycled catalyst after a 2 h reaction time. The catalysts displayed high selectivity to pentadecane and undecane via decarboxylation reaction pathway even at low 0.5 wt % Pt loading. Selectivity to pentadecane and undecane as high as ∼92% and ∼94% was observed under CO2 atmosphere when palmitic and lauric acids were used respectively as reactants. Depending on the reaction gas atmosphere, two distinctive reaction pathways were observed: decarboxylation and hydrodeoxygenation. Specifically, it was found that decarboxylation reaction pathway was more favorable in the presence of helium and CO2, while hydrodeoxygenation pathway strongly competed against the decarboxylation pathway when hydrogen was employed during the deoxygenation reactions. Esters were identified as the key r...

Background Lean body mass has been identified as a key determinant of left ventricular mass and wall thickness. However, the importance of lean body mass or other body‐size measures as normative determinants of carotid intima‐media thickness ( cIMT ), a widely used early indicator of atherosclerosis, has not been well established. Methods and Results Carotid artery ultrasound measurements of cIMT and carotid artery plaque burden (derived from plaque number and maximum size) and measurements of body size, including height, body mass index, weight, body fat proportion, and lean body mass ([1−body fat proportion]×weight), were recorded in 25 020 participants from 10 regions of China. Analyses were restricted to a healthy younger subset (n=6617) defined as never or long‐term ex‐regular smokers aged cIMT , but was not associated with plaque burden: overall, each 10 kg higher lean body mass was associated with a 0.03 (95% CI , 0.03–0.04) mm higher cIMT ( P =5×10 −33 ). Fat mass, height, and other body‐size measures were more weakly associated with cIMT . Conclusions The strong association of lean body mass with cIMT, but not with plaque burden, in healthy adults suggests a normative relationship rather than reflecting atherosclerotic pathology. Common mechanisms may underlie the associations of lean body mass with cIMT and with nonatherosclerotic vascular traits.

Removing oxygen from fatty acids leads to the formation of paraffinic hydrocarbons that can potentially serve as or be converted to direct replacements for traditional petroleum-derived liquid transportation fuels and paraffinic petrochemical feedstocks. Herein we review recent research progress that has been done in the development of metal-organic framework (MOF) as catalysts and catalytic supports for the conversion of fatty acids into liquid transport fuels. In particular, some of these MOFs as catalytic supports display enhanced performance for the decarboxylation and deoxygenation of fatty acids to liquid fuels as compared to benchmark catalyst-support systems. Important aspects that require attention from the scientific community to envision these porous crystals as effective catalysts to convert liquid biomass into valuable liquid fuels are discussed.

The heat transfer in fluid flow through static assemblies of randomly distributed spheroids, including spheres, prolates, and oblates, is investigated using direct numerical simulation (DNS). Constant heat fluxes are imposed at individual particle surface by the Neumann boundary condition for temperature. The superficial Reynolds number (Re) and the solid volume fraction (φ) range from 2.5 to 200, and from 0.1 to 0.3, respectively. The simulation results for spheres and prolates agree well with the DNS data and correlations in literature and new correlations for prolates and oblates are proposed. With these results, the particle shape effect on the average Nusselt number (Nuavg) is described more comprehensively: At low φ (e.g., 0.1), the Nuavg for prolates and oblates are higher than that of spheres, and as Re increases, the Nuavg of oblates gradually catches up that of prolates and becomes comparable at Re≈200. Moreover, oblates attenuate and intensify the heat transfer at low and high Re at high φ, respectively.

BACKGROUND Carboxylic acids obtained from biomass raw materials are attractive starting chemicals in the conversion to linear, paraffinic hydrocarbons. The resultant hydrocarbon products can be used as platform chemicals for the production of fuels, lubricants and other valuable chemicals. RESULTS The effects of reaction parameters on the decarboxylation of oleic acid to paraffins, and hydrocarbons over Pt supported on zeolite 5A beads coated with ZIF-67 membrane (Pt/ZIF-67 membrane/zeolite 5A) were investigated. Almost complete conversion of oleic acid was observed for all reaction conditions studied here. The catalysts displayed high selectivity to heptadecane even with as low as 0.5 wt% Pt loading. Moderate reaction temperature and pressure were favorable to obtain high yield of heptadecane. The catalysts displayed a slight decrease in catalytic activity after recycling. Interestingly, of all explored reaction conditions, the catalysts exhibited the highest selectivity to heptadecane (~91%) in the presence of CO2. CONCLUSION The results from this work, demonstrate that the studied reaction parameters greatly affected the overall catalytic performance (mainly product distribution) for the decarboxylation of oleic acid into heptadecane over Pt/ZIF-67 membrane/zeolite 5A catalysts.

Rationale Little evidence from large-scale cohort studies exists about the relationship of solid fuel use with hospitalization and mortality from major respiratory diseases. Objectives To examine the associations of solid fuel use and risks of acute and chronic respiratory diseases. Methods A cohort study of 277,838 Chinese never-smokers with no prior major chronic diseases at baseline. During 9 years of follow-up, 19,823 first hospitalization episodes or deaths from major respiratory diseases, including 10,553 chronic lower respiratory disease (CLRD), 4,398 chronic obstructive pulmonary disease (COPD), and 7,324 acute lower respiratory infection (ALRI), were recorded. Cox regression yielded adjusted hazard ratios (HRs) for disease risks associated with self-reported primary cooking fuel use. Measurements and Main Results Overall, 91% of participants reported regular cooking, with 52% using solid fuels. Compared with clean fuel users, solid fuel users had an adjusted HR of 1.36 (95% confidence interval, 1.32–1.40) for major respiratory diseases, whereas those who switched from solid to clean fuels had a weaker HR (1.14, 1.10–1.17). The HRs were higher in wood (1.37, 1.33–1.41) than coal users (1.22, 1.15–1.29) and in those with prolonged use (≥40 yr, 1.54, 1.48–1.60; Conclusions Among Chinese adults, solid fuel use for cooking was associated with higher risks of major respiratory disease admissions and death, and switching to clean fuels or use of ventilated cookstoves had lower risk than not switching.

The synthesis of Pt supported on zeolite 5A beads for the decarboxylation of oleic acid to heptadecane is demonstrated. The use of a microporous ZIF-67 crystalline layer on zeolite 5A beads not only improved the heptadecane selectivity but also, most importantly, improved the stability of the resultant catalyst. Heptadecane yields as high as ∼81% were observed for the fresh catalysts. The catalysts displayed only low to moderate loss of catalytic activity after two rounds of recycle. To our best knowledge, the catalytic performance of these catalysts is superior to those of the state-of-the-art catalysts at mild reaction conditions. In addition, as compared to powders, beads are much easier to recycle, can be fully recovered, and are more amenable for potential scale-up. The resultant catalysts are promising for the catalytic conversion of fatty acid molecules into gasoline/diesel-range hydrocarbons.

Herein we demonstrate the catalytic decarboxylation and conversion of oleic acid to paraffins and hydrocarbons over bare and Pt supported Cu, Al and Ga based metal organic frameworks. Moderate degrees of decarboxylation were observed for all metal organic framework catalysts. The incorporation of Pt with the porous frameworks resulted in high degrees of decarboxylation. All MOF catalysts showed high thermal stability, resulting in recyclable catalysts displaying low catalytic activity loss. Of all studied catalysts, Ga-MOF catalysts were the most effective catalysts, displaying moderate to high degrees of decarboxylation. In addition, the Pt–Ga-MOF catalyst displayed selectivity to heptadecane, an important industrial chemical. Octadecane, heptadecane, dodecane, undecane, decane, nonane, octane, and heptane were observed as the main side products. To our best knowledge, the catalytic ability of a metal organic framework both as catalyst and support for the decarboxylation of a model fatty acid molecule is reported for the first time.

Background Self‐rated health ( SRH ) is a strong predictor of mortality in different populations. However, the associations between SRH measures and risk of ischemic heart disease ( IHD ) have not been extensively explored, especially in a Chinese population. Methods and Results More than 500 000 adults from 10 cities in China were followed from baseline (2004–2008) through December 31, 2013. Global and age‐comparative SRH were reported from baseline questionnaires. Incident IHD cases were identified through links to well‐established disease registry systems and the national health insurance system. During 3 423 542 person‐years of follow‐up, we identified 24 705 incident cases of IHD . In multivariable‐adjusted models, both global and age‐comparative SRH was significantly associated with incident IHD . Compared with excellent SRH , the hazard ratios for good, fair, and poor SRH were 1.02 (95% confidence interval [CI], 0.98–1.07), 1.32 (95% CI, 1.27–1.37), and 1.76 (95% CI, 1.68–1.85), respectively. Compared with better age‐comparative SRH , the hazard ratios for same and worse age‐comparative SRH were 1.23 (95% CI, 1.19–1.27) and 1.78 (95% CI, 1.70–1.86), respectively. The associations persisted in all subgroup analyses, although they were slightly modified by study location, education, and income levels. Conclusions A simple questionnaire for self‐assessment of health status was significantly associated with incident IHD in Chinese adults. Individuals and healthcare providers can use SRH measures as a convenient tool for assessing future IHD risk.

BACKGROUND: Adherence to a combination of healthy lifestyle factors has been related to a considerable reduction of cardiovascular risk in white populations; however, little is known whether such associations persist in nonwhite populations like the Asian population. OBJECTIVES: This study aimed to examine the associations of a combination of modifiable, healthy lifestyle factors with the risks of ischemic cardiovascular diseases and estimate the proportion of diseases that could potentially be prevented by adherence to these healthy lifestyle patterns. METHODS: This study examined the associations of 6 lifestyle factors with ischemic heart disease and ischemic stroke (IS) in the China Kadoorie Biobank of 461,211 participants 30 to 79 years of age who did not have cardiovascular diseases, cancer, or diabetes at baseline. Low-risk lifestyle factors were defined as nonsmoking status or having stopped smoking for reasons other than illness, alcohol consumption of

Background Increasing evidence has suggested that major depression ( MD ) is associated with an increased risk of ischemic heart disease ( IHD ). We examined this association in Chinese adults using data from the China Kadoorie Biobank study. Methods and Results Over 0.5 million adults aged 30 to 79 years were followed from baseline interview (2004–2008) until December 31, 2013. Past year MD was measured with the modified Chinese version of Composite International Diagnostic Interview‐Short Form at baseline. Incident IHD cases were identified through linkage to related medical databases, and defined as having International Statistical Classification of Diseases and Related Health Problems 10th Revision codes of I20 to I25. Cox proportional hazards regression models were used to estimate hazard ratios and 95% CI s for the MD ‐ IHD association with adjustment for sociodemographic variables and established cardiovascular risk factors. During 3 423 542 person‐years of follow‐up, 24 705 incident IHD cases were documented. Higher IHD incidence was observed in participants with MD compared with those without (8.76 versus 7.21 per 1000 person‐years), and the multivariable‐adjusted hazard ratio was 1.32 (95% CI 1.15–1.53). Geographic location modified the association ( P for interaction=0.005), and a positive association was observed in urban residents (hazard ratio 1.72; 95% CI 1.39–2.14) but not rural residents (1.13; 0.93–1.37). Compared with participants without depressive symptoms, the hazard ratio (95% CI ) of IHD was 1.13 (1.04–1.23) for those with depressive symptoms only and 1.33 (1.15–1.53) for those with MD . Conclusions Past year major depression was associated with an increased risk of IHD in Chinese adults, independent of other major cardiovascular risk factors.

The extraction performance in a T-junction microchannel was investigated experimentally. CuSO4/H2SO4/AD-100/260# solvent oil was chosen as the working system. The velocities of the aqueous and oil phases were varied from 0.0016 to 0.45 ms-1, with ReM varying between 9 and 200. The experimental results show that the extraction process of copper in the microchannel is controlled by both reaction intrinsic kinetics and mass transfer, depending on the characteristics of the reaction and the fluid hydrodynamics. The maximum extraction efficiency is about 0.96, and the apparent overall volumetric mass transfer coefficient (kappa) is in the range of 0.02-0.2s-1. In addition, the effects of the Cu2+ concentration and the pH in the aqueous phase, the volumetric fraction of AD-100 in the oil phase, and the temperature on the extraction performance were investigated in detail.

OBJECTIVES: Mean blood pressure varies moderately with outdoor air temperature in many western populations. Substantial uncertainty exists, however, about the strength of the relationship in other populations and its relevance to age, adiposity, medical treatment, climate and housing conditions. METHODS: To investigate the relationship of blood pressure with season and outdoor temperature, we analysed cross-sectional data from the China Kadoorie Biobank study of 506,673 adults aged 30-79 years recruited from 10 diverse urban and rural regions in China. Analyses related mean blood pressure - overall and in various subgroups - to mean local outdoor temperature. RESULTS: The mean difference in SBP between summer (June-August) and winter (December-February) was 10 mmHg overall, and was more extreme, on average, in rural than in urban areas (12 vs. 8 mmHg; P for interaction

Here, a facial and scalable method for efficient exfoliation of bulk transition metal dichalcogenides (TMD) and graphite in aqueous solution with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to prepare single- and few-layer nanosheets is demonstrated. Importantly, these TMD nanosheets retain the single crystalline characteristic, which is essential for application in organic solar cells (OSCs). The hybrid PEDOT:PSS/WS2 ink prepared by a simple centrifugation is directly integrated as a hole extraction layer for high-performance OSCs. Compared with PEDOT:PSS, the PEDOT:PSS/WS2-based devices provide a remarkable power conversion efficiency due to the “island” morphology and benzoid–quinoid transition. This study not only demonstrates a novel method for preparing single- and few-layer TMD and graphene nanosheets but also paves a way for their applications without further complicated processing.

This work presents atomic-level simulations that study the surface segregation profiles in Cu–Pd catalysts at various concentrations of Cu. It is found that Cu normally enriches on the surface of 201-atom Cu–Pd cluster but depletes from the surface at very low Cu concentrations. This phenomenon was observed in experiments previously and can be reproduced by the molecular dynamics/Monte Carlo-corrected effective medium theory if the latest modifications, to fit the alloy heats of mixing, are included in the interaction potential. This study also reveals different surface segregation behaviours for clusters having different shapes. It appears that most of the thermally accessible shapes of the cluster exhibit reverse surface segregation. However, these shapes are metastable. The lowest-energy configuration tested, having the cubo-octahedral shape, does not show reverse surface segregation; instead, it shows normal surface segregation with Cu enrichment on the surface at all concentrations. Thus, th...

The electrostatic potential and component dielectric constants from molecular dynamics (MD) trajectories of tuftsin, a tetrapeptide with the amino acid sequence Thr-Lys-Pro-Arg in water and in saline solution are presented. The results obtained from the analysis of the MD trajectories for the total electrostatic potential at points on a grid using the Ewald technique are compared with the solution to the Poisson-Boltzmann (PB) equation. The latter was solved using several sets of dielectric constant parameters. The effects of structural averaging on the PB results were also considered. Solute conformational mobility in simulations gives rise to an electrostatic potential map around the solute dominated by the solute monopole (or lowest order multipole). The detailed spatial variation of the electrostatic potential on the molecular surface brought about by the compounded effects of the distribution of water and ions close to the peptide, solvent mobility, and solute conformational mobility are not qualitatively reproducible from a reparametrization of the input solute and solvent dielectric constants to the PB equation for a single structure or for structurally averaged PB calculations. Nevertheless, by fitting the PB to the MD electrostatic potential surfaces with the dielectric constants as fitting parameters, we found that the values that give the best fit are the values calculated from the MD trajectories. Implications of using such field calculations on the design of tuftsin peptide analogues are discussed.

We present a simple method to improve the accuracy of the calculated heat of mixing for the Cu-Pd alloy within the formalism of the molecular dynamics/ Monte Carlo-corrected effective medium (MD/MC-CEM) theory by adding a fitted Morse potential to the pair interaction between Cu and Pd atoms. This leads to a much better agreement between the theoretical and experimental values of heats of mixing for five different compositions of the Cu-Pd alloy in the bulk phases. Using this newly fitted model, we have performed simulations on CuPd clusters consisting of 50–10000 atoms with fee and bcc structures. Our calculations show that in the range of cluster sizes of several thousand atoms, the fee structure is energetically favoured over the bcc structure. We estimate an approximate size for the fee to bcc (CsCl, known bulk structure for CuPd) transition in these clusters to be around 10000 atoms. Additionally, we have also performed calculations of the X-ray diffraction patterns of a variety of cluster g...

We have analyzed a 1.2-ns molecular dynamics simulation of 51 mM d(CG.G)7 with 21 Na+ counter-ions and 1 M NaCl in water. Via the dipole fluctuations, the dielectric constant for the DNA is found to be around 16, whereas that for the bases and sugars combined is only 3. The dielectric constant for water in this system is 41, which is much smaller than 71 for pure SPC/E water, because of the strong restriction imposed on the motion of water molecules by the DNA and the ions. Also addressed in the present work are several technical issues related to the calculation of the dipole moment of an ionic solution from molecular dynamics simulations using periodic boundary conditions.

The general structure of small fcc metal clusters was investigated through the use of site energies, i.e., interaction energy per atom as a function of coordination. The authors used only experimental data on the dimer binding energy, the surface energy, and the bulk cohesive energy to determine these energies for all 15 fcc metals. These showed that real fcc metal systems exhibit a slight bond weakening as the number of bonds increases. It is also demonstrated that experimental data are much closer to the limit of constant bond energy than to that of constant interaction energy per atom. The constant bond energy model leads to compact structures which maximize the number of bonds, and thus the authors predicted that real small cluster systems would also be compact. Using molecular dynamics/Monte Carlo corrected effective medium theory, which nearly duplicates the experimental site energy curves, the authors studied the structures of 13-atom clusters of fcc metals via repeated melting and quenching in computer simulations. The lowest-energy structure was found to be a compact icosahedron with very high symmetry in every case. Simulations in the presence of a SiO{sub 2} support indicate that the 13-atom Pt cluster maintained its nearly icosahedral shape. 31more » refs., 3 figs., 1 tab.« less

A five-state statistical-mechanical model is employed in the present study of surface segregation in 201-atom bimetallic clusters having truncated cubo-octahedral shape. The model uses ideal entropy of mixing and assumes zero heat of mixing. Surface segregation is studied via direct minimization of the free energy without performing Monte Carlo simulations. The effects of size mismatch between atoms of different type are included via a new empirical formula, based upon dimensional scaling arguments, leading to an increase in the surface fraction of larger atoms. We used the corrected effective medium potentials to generate the site energies (interaction energy per atom) used in the model. A complete list of site energies for nine fcc metals is presented for 201-, 586-, 1289-atom clusters and semi-infinite surfaces. In particular, the corner and edge site energies are found to be independent of cluster size. The model reproduced qualitatively the surface and edge-comer segregation results for 11 50%-50% bimetallic clusters generated by atomistic simulations at 600 K that we reported earlier. The remaining difference in results between the model and the simulations is attributed to the effect of nonzero heats of mixing. For systems with very large (> 12%) lattice-size mismatch such as Ni-Ag and Cu-Ag, the distortion from the perfect lattice structure is significant according to the simulations; thus, simple modeling involving a few well-defined states is problematic.

Two similar semiempirical interatomic potentials were used to study 13‐atom Pt clusters. One predicts very compact icosahedral structure with high symmetry while the other predicts open and fluxional structures with low symmetries. This can be understood in terms of the low‐coordination atomic binding energies produced by the potentials.

Computer simulations were performed to study the surface composition of Rh x Pd 1 − x , Rh x Ni 1 − x and Ni x Pd 1 − x clusters where 0.1 ⩽ x ⩽ 0.9. Clusters containing 201 and 1289 atoms were simulated at 200, 600 and 1000 K. The simulation consists of the Monte Carlo (MC) exchange of the positions of unlike atoms and the molecular-dynamics (MD) evolution of all atoms between exchanges. A corrected effective medium (CEM) theory based interatomic potential, with acronym MD/MC-CEM, was used to generate the forces. Our simulations indicate that the metal with lower surface energy segregates first to the catalytically very important edge-corner sites, then to other surface sites. Increasing the temperature decreases the degree of segregation at edge-corner sites more strongly than on the entire surface. Interestingly, NiPd exhibits stronger surface segregation but weaker edge-corner segregation than RhNi. Results for other 201- and 1289-atom 50%-50% bimetallic clusters at 600 K, selected from Rh, Ni, Pd, Cu and Ag, are also presented. In particular, the large lattice-size mismatch in NiAg and CuAg invalidates the simple geometrical constraints on surface segregation that hold for other bimetallic clusters.

We report a temperature-dependent study of the vibrations and the structure of Cu(110) using molecular-dynamics codes based on potentials obtained from the embedded-atom method. The calculated linewidths and frequencies of the surface phonons and resonances and the mean-square vibrational amplitudes of the atoms indicate a sharp rise in surface anharmonic vibrations at about 600 K. Additionally, vacancies and adatoms begin to appear in the simulations of Cu(110) around 900 K. Comparison is made with experimental data and simulations of Cu(100)

We present lattice-dynamical calculations of the mean-square displacements of the adsorbate and first-layer substrate atoms for c(2\ifmmode\times\else\texttimes\fi{}2) S and O overlayers on Ni(100). To be consistent with available structural information and to reproduce the observed surface-phonon dispersion data on these systems, surface force constants between Ni atoms are chosen to be different from the value in the bulk. It is found that for sulfur atoms the mean-square displacement in the plane parallel to the surface is larger than that along the surface normal. The opposite is the case for the oxygen atoms. The underlying Ni atoms in the two systems also display dissimilar anisotropies in the three orthogonal directions. We have examined the relative strengths of the mean-square relative displacements between the adsorbate and the first- and second-layer substrate atoms for both systems and explored the effect of the variation of the surface force constants on these quantities. These results have been brought in contact with available surface extended x-ray-absorption fine-structure data on these systems.

A 3.5-ns atomic-level computer simulation of a DNA solution was performed. We found that a dodecamer of DNA, which contains the recognition site for Eco RI endonuclease, transforms from B-form to A-form in 0.45 M salt water. This supports an earlier proposal on the A-DNA binding site for transcription factor IIIA.