196746 research outputs found
Sort by
Benchmarking water adsorption on metal surfaces with ab initio molecular dynamics
No full textSolid-water interfaces are ubiquitous in nature and technology. In particular, technologies evolving in the green transition, such as electrocatalysis, heavily rely on the junction of an electrolyte and an electrode as a central part of the device. For the understanding of atomic-scale processes taking place at the electrolyte-electrode interface, density functional theory (DFT) has become the de facto standard. The validation of DFT’s ability to simulate the interfacial solid/water interaction is crucial, and ideal simulation setups need to be identified in order to prevent avoidable systematic errors. Here, we develop a rigorous sampling protocol for benchmarking the adsorption/desorption energetics of water on metallic surfaces against experimental temperature programmed desorption, single crystal adsorption calorimetry, and thermal energy atom scattering. We screened DFT’s quality on a series of transition metal surfaces, applying three of the most common exchange-correlation approximations: PBE-D3, RPBE-D3, and BEEF-vdW. We find that all three xc-functionals reflect the pseudo-zeroth order desorption of water rooted in the combination of attractive adsorbate-adsorbate interactions and their saturation at low and intermediate coverages, respectively. However, both RPBE-D3 and BEEF-vdW lead to more accurate water adsorption strengths, while PBE-D3 clearly overbinds near-surface water. We relate the variations in binding strength to specific variations in water-metal and water-water interactions, highlighting the structural consequences inherent in an uninformed choice of simulation parameters. Our study gives atomistic insight into water’s complex adsorption equilibrium. Furthermore, it represents a guideline for future DFT-based simulations of solvated solid interfaces by providing an assessment of systematic errors in specific setups.</p
Can planned control measures for private passenger vehicles achieve China's carbon peak goal and mitigate the environmental impact?
No full textThere is a lack of consensus as to whether planned control measures for vehicular emissions can achieve China's carbon peak goal and mitigate the environmental impact of private passenger vehicles. This paper studies the environmental benefits of China's planned control measures by using a dynamic fleet-based life cycle assessment (LCA) method and “what-if” scenario analysis at a full national scale in a life-cycle systematic perspective. The results showed that burden-shifting may occur for electric vehicle (EV) deployment and demand-side interventions. China cannot achieve carbon peak goal before 2030 with the current planned control measures, unless the internal combustion engine vehicle (ICEV) fleet or the power grid is improved significantly. Large-scale deployment of EVs in the short term, with much improved ICEVs and a less clean power grid, is not conducive to peak fleet carbon emissions. Therefore, improving the ICEV fleet should be a priority for policy-making in the short term
Development of a novel real-time RT-PCR method using peptide nucleic acid (PNA) probes for detecting and genotyping of viral haemorrhagic septicaemia virus (VHSV)
No full textViral haemorrhagic septicaemia (VHS) is one of the most serious viral diseases in salmonid and olive flounder farms. The causative agent of VHS is the VHS virus (VHSV), which has been classified into four genotypes (I–IV), based on sequence analysis of the genes encoding for nucleoprotein, glycoprotein, and non-structural viral protein. Among the various diagnostic methods, real-time reverse transcription PCR method based on TaqMan-probe (RT-qPCR) is a stable, rapid, specific, and highly sensitive method for viral gene detection. However, the currently accepted diagnostic method based on RT-qPCR can only detect viral presence and load, and does not provide information about viral genotype. Peptide nucleic acids (PNAs) are artificially synthesized DNA analogues with an uncharged peptide backbone. PNA probes can effectively detect a target gene by amplification and a specific melting temperature signal. It was reported that PNA probes can effectively distinguish between mismatched sequences based on their different melting temperatures in amplified PCR products. The present study reports a novel real-time RT-PCR method for simultaneous detection and genotyping of VHSV using PNA probes. The newly-developed method showed a sensitivity similar to that of the infectious titre by fish cell cultures inoculated with the virus, except for genotype IVa, where viral inoculation in cell culture showed a 10-fold higher sensitivity than the novel method. The melting point analysis to distinguish the four genotypes was performed on 80 VHSV isolates representing all known genotypes, showing that this novel real-time RT-PCR can distinguish between all VHSV genotypes without the need of further sequencing
Comparing airborne infectious aerosol exposures in sparsely occupied large spaces utilizing large-diameter ceiling fans
No full textIn sparsely occupied large industrial and commercial buildings, large-diameter ceiling fans (LDCFs) are commonly utilized for comfort cooling and destratification; however, a limited number of studies were conducted to guide the operation of these devices during the COVID-19 pandemic. This study conducted 223 parametrical computational-fluid-dynamics (CFD) simulations of LDCFs in the U.S. Department of Energy warehouse reference building to compare the impacts of fan operations, index-person, and worker-packing-line locations on airborne exposures to infectious aerosols under both summer and winter conditions. The steady-state airflow fields were modeled while transient exposures to particles of varying sizes (0.5–10 μm) were evaluated over an eight-hour period. Both the airflow and aerosol models were validated by measurement data from the literature. It was found that it is preferable to create a breeze from LDCFs for increased airborne dilution into a sparsely occupied large warehouse, which is more similar to an outdoor scenario than a typical indoor scenario. Operation of fans at the highest feasible speed while maintaining thermal-comfort requirements consistently outperformed the other options in terms of airborne exposures. There is no substantial evidence that fan reversal is beneficial in the current large space of interest. Reversal flow direction to create upward flows at higher fan speeds generally reduced performance compared with downward flows, as there was less airflow through the fan blades at the same rotational speed. Reversing flow at lower fan speeds decreased airflow speeds and dilution in the space and, thus, increased whole-warehouse concentrations
Ship grounding model tests in a water tank: An experimental study
No full textShip grounding experiments are important benchmarks used to validate numerical analysis, analytical and empirical formulation. They are key to the understanding of damage mechanism. A set of small-scale ship model grounding tests over a sharp rock are conducted in a water tank considering the influence of surrounding water. Two damage modes are observed in the grounding tests, Mode I for discontinuous fracture/tear and Mode II for continuous fracture/tear. The horizontal grounding resistance forces, damage extents of ship bottom plates, and ship motions are recorded and discussed in detail. Moreover, the energy dissipation process of ship model during grounding process is analyzed based on the test results. The influence of the initial velocity, the initial relative height between the upper surface of the horizontal ship bottom plate and the rock tip, and the rock eccentricity on the ship motion response and structural damage are studied
Deciphering anaerobic ethanol metabolic pathways shaped by operational modes
No full textEfficient anaerobic digestion requires the syntrophic cooperation among diverse microorganisms with various metabolic pathways. In this study, two operational modes, i.e., the sequencing batch reactor (SBR) and the continuous-flow reactor (CFR), were adopted in ethanol-fed systems with or without the supplement of powdered activated carbon (PAC) to examine their effects on ethanol metabolic pathways. Notably, the operational mode of SBR and the presence of CO2 facilitated ethanol metabolism towards propionate production. This was further evidenced by the dominance of Desulfobulbus, and the increased relative abundances of enzymes (EC: 1.2.7.1 and 1.2.7.11) involved in CO2 metabolism in SBRs. Moreover, SBRs exhibited superior biomass-based rates of ethanol degradation and methanogenesis, surpassing those in CFRs by 53.1% and 22.3%, respectively. Remarkably, CFRs with the extended solids retention time enriched high relative abundances of Geobacter of 71.7% and 70.4% under conditions with and without the addition of PAC, respectively. Although both long-term and short-term PAC additions led to the increased sludge conductivity and a reduced methanogenic lag phase, only the long-term PAC addition resulted in enhanced rates of ethanol degradation and propionate production/degradation. The strategies by adjusting operational mode and PAC addition could be adopted for modulating the anaerobic ethanol metabolic pathway and enriching Geobacter
Synthesis of bioactive hemoglobin-based oxygen carrier nanoparticles via metal-phenolic complexation
No full textThe transfusion of donor red blood cells (RBCs) is seriously hampered by important drawbacks that include limited availability and portability, the requirement of being stored in refrigerated conditions, a short shelf life or the need for RBC group typing and crossmatching. Thus, hemoglobin (Hb)-based oxygen (O2) carriers (HBOCs) which make use of the main component of RBCs and the responsible protein for O2 transport, hold a lot of promise in modern transfusion and emergency medicine. Despite the great progress achieved, it is still difficult to create HBOCs with a high Hb content to attain the high O2 demands of our body. Herein a metal–phenolic self-assembly approach that can be conducted in water and in one step to prepare nanoparticles (NPs) fully made of Hb (Hb-NPs) is presented. In particular, by combining Hb with polyethylene glycol, tannic acid (TA) and manganese ions, spherical Hb-NPs with a uniform size around 350–525 nm are obtained. The functionality of the Hb-NPs is preserved as shown by their ability to bind and release O2 over multiple rounds. The binding mechanism of TA and Hb is thoroughly investigated by UV–vis absorption and fluorescence spectroscopy. The binding site number, apparent binding constant at two different temperatures and the corresponding thermodynamic parameters are identified. The results demonstrate that the TA-Hb interaction takes place through a static mechanism in a spontaneous process as shown by the decrease in Gibbs free energy. The associated increase in entropy suggests that the TA-Hb binding is dominated by hydrophobic interactions.</p
Microscopic heterogeneity of low cyclic fatigue damage in Ni-based single crystal superalloy DD413
No full textThe heterogeneous low cyclic fatigue damage level in the Ni-based single crystal superalloy DD413 was quantitatively assessed under the strain control of ±0.8% and ± 1.1%. The specimens subjected to ±0.8% strain amplitude exhibited an almost pure elastic deformation response throughout the entire cyclic loading period. In contrast, the ±1.1% strain-controlled deformed specimen exhibited a gradual increase in plastic strain, rising from 0.046% in the 1st cycle to 0.072% by the 268th cycle. The brittle carbides caused a significant mechanical incompatibility with the matrix. This was observed through the orientation dispersal over 16° in the {001} pole figure of the ±1.1% specimen, which was substantially broader than the ±0.8% specimen where the dispersion was only 1.2°. The large orientation gradient in the interdendrite (IR) triggered the dispersion of the microstructure-averaged orientation of the ±1.1% specimen, as evidenced by a mean grain reference orientation deviation (GROD) angle three times higher in the IR compared to the dendrite (DR). While the DR and IR of ±0.8% specimen showed similar mean GROD angles. This substantial orientation gradient was sustained by the high density of geometrically necessary dislocations (GNDs) in the IR, which was double that of the DR. Differently, the DR and IR in the ±0.8% specimen exhibited similar mean densities of GNDs. The study suggests that minimizing microstructural heterogeneity at the dendritic scale may enhance the durability of DD413 alloy components when exposed to cyclical stress with greater strain amplitudes
Large Bandgap Photovoltaic Devices and Tandem Integration with Silicon Solar Cells
No full textIn this thesis, I present the main results of my PhD project, which focuses on the study of selenium as a photovoltaic material. Selenium, the world’s oldest photovoltaic material, is experiencing a research renaissance due to its irresistible monoatomic simplicity, as well as its wide bandgap, making it a potential candidate for the top cell absorber in tandem devices. However, achieving high-efficiency selenium thin-film solar cells remains a challenge, and despite being the key driver of this renewed attention, a tandem device featuring selenium has yet to been demonstrated. Addressing these issues constitutes the core of my work. Here, I list what I consider to be the main highlights.First, we developed and optimized a process flow to fabricate tunnel oxide passivated contact (TOPCon) silicon solar cells, which serve as the bottom cells in our tandem devices. While silicon technologies are well-established in industry, our inhouse processing allows us to modify the device structure to accommodate the top cell processing. The optimized silicon solar cells demonstrate implied open-circuit voltages greater than 0.72 V and implied fill-factors exceeding 83%, all while remaining resilient to the backend processing.Second, we reproduced the state-of-the-art selenium solar cell device architecture presented in a recent publication by IBM. From this baseline, we replaced the gold electrode with a transparent conductive oxide to fabricate the first bifacial selenium solar cells, and discovered that our selenium solar cells are strongly polarity dependent. To address this polarity dependence, we investigated potential device inversion strategies and the band alignment in our devices. This study lead us to the conclusion that our ZnMgO/poly-Se heterostructure forms an ideal pn-heterojunction. However, due to the optimal elemental composition of ZnMgO, the FTO/ZnMgO heterointerface is prone to form charge carrier transport barriers. To resolve this issue, we explored the potential of multilayered buffers and native doping strategies, guided by SCAPS-1D device simulations. Additionally, to improve reproducibility, we developed a closed-space annealing strategy, which significantly enhances the collection efficiency in our devices.Third, we demonstrated a record open-circuit voltage of 0.99 V, providing an ideal startingpoint for investigating the origin of the still significant opencircuit voltage deficit. In this study, we found that trigonal selenium possesses a quasi-indirect bandgap, the thin-films exhibit no detectable photoluminescence at room temperature, the absorption onset is quite broad, and the photoconductance decay features two characteristic lifetimes. Following the associated publication, I will present new, unpublished results, where the mobility-lifetime product is interpreted differently. This new interpretation leads to our device simulations quantitatively matching our experimental data. Fourth, we studied the defect physics in selenium. After concluding an ideal band alignment in our pn-heterojunction, no detectable photoluminescence at room temperature, and that the effective carrier lifetime is likely to fall within the picosecond range, I have no doubt that the most significant losses in our devices originate from non-radiative recombination within the absorber. However, as point defects and their properties may be challenging to probe experimentally, we used first-principles methods based on density functional theory to support and guide our experimental investigation. We examined the effects of both intrinsic and extrinsic defects, and detected halogen impurities in our absorber layer originating from the tellurium source material. We suspect that the halogen species could potentially form killer defects in selenium, but this has yet to be proven.Fifth, we explored the potential of laser-annealing as a defectengineering tool. Unlike thermal annealing, the charge carriers in selenium are not in thermal equilibrium with their surroundings during laser-annealing. This non-equilibrium state has implications for the formation energies of both extrinsic and intrinsic defects, and hence their concentrations. To prevent sublimation of selenium from the surface of the film, the laser is guided through the semitransparent substrate, resulting in the formation of a selenium crystallites in the vicinity of the carrier-separating junction. This seed layer served as a growth template for solid-phase epitaxy, facilitating the formation of larger, more preferentially oriented crystal grains with negligible surface roughness.Finally, although the efficiencies of our selenium thin-film solar cells are still too low for tandem integration to be viable, we have successfully fabricated and demonstrated the first monolithically integrated selenium/silicon tandem solar cell. The tandem device consolidates all the individual conclusions drawn throughout this project: polarity dependence, device inversion, the ideal band alignment of the ZnMgO/poly-Se pnheterojunction, the formation of charge transport barriers, the low-energy photon collection efficiency issues, and the optoelectronic quality of our selenium thin-films limiting the overall device performance. Additionally, during the crystallization process in this study, we observed the formation of large craterlike holes in the selenium thin-films, a phenomenon that has been elaborated on in greater detail following the presentation of the tandem paper