Probing the Structure of Water on Surfaces: From Water Absorption to Ice Nucleation

Water, essential for all life forms, is the most abundant, simple, yet mysterious molecule in the world. This molecule, consisting of only three atoms, behaves in unexpectedly different ways with the change of environment. In the past, studies of water under different conditions (temperature, pressure, on the surfaces, with confinement) have been conducted using experimental and computational methods. However, the influence of a given environment on water properties is yet to be fully understood. This dissertation studies water at complex interfaces (surfaces with various chemistry and physics properties) in both the liquid and crystalline states. Various heterogeneous systems used to study the water adsorption, surface ion adsorption in the aqueous phase, and ice nucleating ability of different substrates is covered in this work. We apply molecular dynamics (MD) and density functional theory (DFT) to study the interplay of surface properties on water behavior. In addition, we extend the knowledge of the influence of liquid water properties on nucleating abilities without simulating nucleation. We investigated the effects of the ions’ charge, type, and displacements on the mica surface on interfacial water behavior at both room temperature and freezing conditions. We found that the mica surfaces substituted with multivalent charged cations are better nucleating agents due to their ability to promote the formation of large, stable water clusters in the regions where no ions are adsorbed. Moreover, to uncover the role of bare mica (areas with no ions adsorbed), we have applied a novel seeding method developed by our group to study the ice nucleation on mica surfaces with multiple ion displacements. The ions orient the surrounding water in a form different from the ice-like structure, restraining their ability to re-orient, thus reducing the nucleating propensity. Surfaces that promote nucleation must be able to localize water molecules to create hydrogen-bonded water clusters while also orienting them in a manner that allows flexibility to reorient and form an ice-like structure, thus minimizing the entropy penalty

Water Structure and Its Correlation to Heterogeneous Ice Nucleation

Clouds, a mixture of water vapor, condensed liquid droplets, solid crystals and aerosol particles, exert an importance on weather and climate via controlling the amount of precipitation and transportation of radiative fluxes. One of the major processes involved in clouds is heterogeneous ice nucleation, which is nucleation facilitated by the presence of mineral substrates. Understanding the role played by solid surfaces in influencing the structure and dynamics of water and thus regulating ice nucleation paves the road for forecasting long-term climate change and designing surfaces with customer-specified ice nucleation properties. The goal of our research is to be able to predict the nucleating ability of a surface based on the interfacial water structure and dynamics. To investigate this problem, we focus on mica, which has a molecularly smooth nature to begin with, thus eases out the complexity of dealing with surface defects. By combining molecular dynamics (MD) simulations with Fourier-transform infrared spectroscopy (FTIR), we probe the change in interfacial water arrangement, spatial correlation and dynamics on mica surface. The interplay of ion-water, ion-surface, and surface-water interactions affect the interfacial water arrangement along with the hydrogen bond network, which is found to be the crucial part in altering surface nucleating ability

High Genetic Diversity of HIV-1 and Active Transmission Clusters among Male-to-Male Sexual Contacts (MMSCs) in Zhuhai, China

Monitoring genetic diversity and recent HIV infections (RHIs) is critical for understanding HIV epidemiology. Here, we report HIV-1 genetic diversity and RHIs in blood samples from 190 HIV-positive MMSCs in Zhuhai, China. MMSCs with newly reported HIV were enrolled from January 2020 to June 2022. A nested PCR was performed to amplify the HIV polymerase gene fragments at HXB2 positions 2604–3606. We constructed genetic transmission network at both 0.5% and 1.5% distance thresholds using the Tamura-Nei93 model. RHIs were identified using a recent infection testing algorithm (RITA) combining limiting antigen avidity enzyme immunoassay (LAg-EIA) assay with clinical data. The results revealed that 19.5% (37/190) were RHIs and 48.4% (92/190) were CRF07_BC. Two clusters were identified at a 0.5% distance threshold. Among them, one was infected with CRF07_BC for the long term, and the other was infected with CRF55_01B recently. We identified a total of 15 clusters at a 1.5% distance threshold. Among them, nine were infected with CRF07_BC subtype, and RHIs were found in 38.8% (19/49) distributed in eight genetic clusters. We identified a large active transmission cluster (n = 10) infected with a genetic variant, CRF79_0107. The multivariable logistic regression model showed that clusters were more likely to be RHIs (adjusted OR: 3.64, 95% CI: 1.51~9.01). The RHI algorithm can help to identify recent or ongoing transmission clusters where the prevention tools are mostly needed. Prompt public health measures are needed to contain the further spread of active transmission clusters

Comparison between HIV self-testing and facility-based HIV testing approach on HIV early detection among men who have sex with men: A cross-sectional study

Background To assess whether HIV self-testing (HIVST) has a better performance in identifying HIV-infected cases than the facility-based HIV testing (HIVFBT) approach. Methods A cross-sectional study was conducted among men who have sex with men (MSM) by using an online questionnaire (including information on sociodemographic, sexual biography, and HIV testing history) and blood samples (for limiting antigen avidity enzyme immunoassay, gene subtype testing, and taking confirmed HIV test). MSM who were firstly identified as HIV positive through HIVST and HIVFBT were compared. Chi-square or Fisher’s exact test was used to explore any association between both groups and their subgroups. Results In total, 124 MSM HIV cases were identified from 2017 to 2021 in Zhuhai, China, including 60 identified through HIVST and 64 through HIVFBT. Participants in the HIVST group were younger (≤30 years, 76.7% vs. 46.9%), were better educated (>high school, 61.7% vs. 39.1%), and had higher viral load (≥1,000 copies/ml, 71.7% vs. 50.0%) than MSM cases identified through HIVFBT. The proportion of early HIV infection in the HIVST group was higher than in the HIVFBT group, identified using four recent infection testing algorithms (RITAs) (RITA 1, 46.7% vs. 25.0%; RITA 2, 43.3% vs. 20.3%; RITA 3, 30.0% vs. 14.1%; RITA 4, 26.7% vs. 10.9%; all p < 0.05). Conclusions The study showed that HIVST has better HIV early detection among MSM and that recent HIV infection cases mainly occur in younger and better-educated MSM. Compared with HIVFBT, HIVST is more accessible to the most at-risk population on time and tends to identify the case early. Further implementation studies are needed to fill the knowledge gap on this medical service model among MSM and other target populations

Dietary Methionine Requirements of Pacific White Shrimp Litopenaeus vannamei, of Three Different Sizes

Three feeding trials were conducted to determine the dietary methionine requirements for Litopenaeus vannamei of three different sizes, small (0.55±0.01g), medium (4.18±0.05g), and large (9.77±0.08g). Seven diets were formulated with seven different levels of methionine (0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or 0.6%). The greatest weight gain (WG) and specific growth rate (SGR) of small and large shrimp were observed when dietary methionine levels were 0.8%, and 0.71%, respectively (P<0.05). The highest survival rate of small and large shrimp was observed when dietary methionine levels were 0.97%, and 1.07%, respectively (P<0.05). For small and medium shrimp, the optimal dietary methionine level for maximum weight gain estimated by quadratic regression analysis was 0.91% and 0.67% of dry diet, respectively. For large shrimp, the optimal dietary methionine requirement estimated by broken-line model based on weight gain was 0.66% of dry diet

Evaporation Effect on Thickness Distribution for Spin-Coated Films on Rectangular and Circular Substrates

Spin-coating is widely applied in the field of thin-film fabrication due to its simplicity and high film uniformity. To prepare thin films on rectangular substrates by spin-coating, the simulation and experimental methods were used to study the characteristics of the film thickness in this work. The two-phase flow simulations of spin-coating on a rectangular substrate and circular substrate were carried out with the volume of fluid (VOF) method. The simulation results showed that the airflow field and the substrate geometry had little effect on the evolution of spin-coated film thickness. However, in the experimental results, there was a significant difference in the thickness of the spin-coated film on the rectangular substrate and the circular substrate. According to further study, the solvent evaporation that was neglected in the simulation was the dominant factor of the differences. In addition, it was concluded that the non-uniform evaporation caused by the surface tension and edge accumulation in the later spin-coating stage was the main reason for the film accumulation of the windward area on the rectangular substrate. This work is useful to obtain a deeper understanding of the thin-film formation mechanism of spin-coating

Water Structure on Mica Surfaces: Investigating the Effect of Cations

We studied thin films of water at the mica-air interface using infrared spectroscopy and molecular dynamics simulations. We investigate the influence of ions on interfacial water by exchanging the naturally occurring K+ ion with H+/Na+, Ca2+, and Mg2+. The experiments do not show a difference in the bulk structure (i. e. in the infrared spectra), but indicate that water is more strongly attracted to the Mg2+ mica. The simulations reveal that the cation-water interactions significantly influence the microscopic arrangement of water on mica. Our results indicate that the divalent cations result in strong water-mica interactions, which leads to longer hydrogen bond lifetimes and larger hydrogen bonded clusters of interfacial water molecules. These results have implications for surface-mediated processes such as heterogeneous ice nucleation, protein assembly and catalysis

Research Progress <i>in situ</i> Hf Isotopic Analysis of Oxide-type U-bearing Accessory Minerals

BACKGROUND: In recent years, the in situ Hf isotopic determination method of zircon has been widely used in isotopic geochemistry, and has become an important method to explore the genesis of rocks, the source of ore-forming materials and the evolution of crust and mantle. However, for some rocks, the lack of zircon seriously hinders the restriction of formation and evolution. The development of Hf isotopic determination methods for oxide-type U-bearing accessory minerals, such as rutile, cassiterite and columbite is urgently needed.OBJECTIVES: In order to accelerate the studies of in situ Hf isotopic determination of oxide-type U-bearing minerals and their application to the geological research.METHODS: In situ Hf isotopic analysis of oxide-type U-bearing accessory minerals was reviewed with NEPTUNE multiple-collector inductively coupled plasma-mass spectrometry (MC-ICPMS) and a 193nm excimer laser ablation system.RESULTS: Combined with relevant research work in recent years, the development history of Lu-Hf isotope analysis technology for accessory minerals was briefly described, and the latest progress and existing problems in in-situ Hf isotope determination methods for oxide-type uranium-bearing minerals such as rutile, cassiterite and niobite were systematically reviewed. The current technical difficulties such as the correction strategy for isobaric interference, the lack of quality control standard samples, the lower Hf content, and the improvement of analytical sensitivity were discussed in detail.CONCLUSIONS: The low Hf content of oxide-type U-bearing accessory minerals requires a larger spot diameter. The femtosecond laser has the characteristics of fine and uniform grain size of the ablation samples. The combination of femtosecond laser and MC-ICPMS (fs-LA-MC-ICPMS) can reduce the spot diameter and improve the spatial resolution, which is the development direction of in situ Hf isotope analysis of oxide-type U-bearing accessory minerals in the future

Identification of TiO₂ Polymorphs of the Bauxite Deposit in Central Guangxi by Laser Raman Spectroscopy

BACKGROUND: Rutile, anatase and brookite are TiO2 polymorphs. In the rutile in-situ U-Pb dating, rutile was determined primarily on electron microprobe data and cathodoluminescence images, while these methods sometimes could not effectively distinguish rutile, anatase and brookite. If there are a small number of the TiO2 polymorphs in the sample, the obtained age may be a mixed age with no significant geological significance. Therefore, the identification of TiO2 polymorphs is very important.OBJECTIVES: To identify TiO2 polymorphs from the bauxite deposit in central Guangxi.METHODS: TiO2 minerals in bauxite from central Guangxi were used as the research object, and laser Raman spectroscopy was applied to the identification of TiO2 isomorphic minerals.RESULTS: Four groups of laser Raman spectral lines with different characteristics were identified. The first three groups have laser Raman spectral peaks of anatase, rutile and brookite, respectively. The fourth group has two kinds of laser Raman spectral characteristic lines, one has both anatase characteristic peaks of 144, 198, 397, 513, 636cm-1 and rutile characteristic peaks of 442, 607cm-1, the other has both anatase characteristic peak of 144cm-1 and brookite characteristic peak of 153, 247, 325, 636cm-1.CONCLUSIONS:The TiO2 polymorphs of the bauxite deposit includs rutile, anatase, brookite and intermediate minerals that undergo phase transformation. The study indicates that the bauxite deposit in central Guangxi may have undergone a later regional metamorphism, leading to the transformation of TiO2 polymorphs. The laser Raman spectroscopy provides a new method for the identification of TiO2 polymorphs andrutile for in-situ U-Pb dating