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

Enhancing Representation in Medical Vision-Language Foundation Models via Multi-Scale Information Extraction Techniques

The development of medical vision-language foundation models has attracted significant attention in the field of medicine and healthcare due to their promising prospect in various clinical applications. While previous studies have commonly focused on feature learning at a single learning scale, investigation on integrating multi-scale information is lacking, which may hinder the potential for mutual reinforcement among these features. This paper aims to bridge this gap by proposing a method that effectively exploits multi-scale information to enhance the performance of medical foundation models. The proposed method simultaneously exploits features at the local, instance, modality and global aspects, facilitating comprehensive representation learning within the models. We evaluate the effectiveness of the proposed method on six open-source datasets across different clinical tasks, demonstrating its ability to enhance the performance of medical foundation models

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

Incidence and spontaneous clearance of gonorrhea and chlamydia infections among men who have sex with men: a prospective cohort study in Zhuhai, China

BackgroundMen who have sex with men (MSM) face significant risks of Chlamydia trachomatis (CT) and/or Neisseria gonorrhoeae (NG) infection. Nevertheless, only limited studies have looked into the site-specific infection and clearance of CT/NG. In order to prevent transmission, it is essential to understand the underlying factors that drive infection and spontaneous clearance.MethodsA 12-week cohort study examined the association between CT/NG infection, self-clearance, and sexual behaviors among MSM. The Willingness Service recruited participants who completed weekly questionnaires and provided urine, throat, and rectal swab samples.ResultsThe study involved 151 men, in which 51 (33.8%) were diagnosed with CT/NG infection during the study period. HIV (OR = 11.31), kissing (OR = 1.59), receptive oral sex (OR = 36.64), and insertive anal sex (OR = 19.73) constituted significant risk factors. 100% condom use (OR = 5.78) and antibiotic (OR = 7.53) were more likely to cause spontaneous clearance.DiscussionMSM may engage in riskier sexual behaviors due to insufficient knowledge and awareness of STI prevention, leading to increased susceptibility to NG/CT. It is crucial to concentrate on enhancing health education for MSM.ConclusionThis study found that the rectum was the most prevalent site of CT/NG and sexual behavior can influence the infection. Additionally, the appropriate use of antibiotics and consistent condom use may contribute to clear spontaneously

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