Nanomechanical properties of polymer samples were calculated using an adhesive contact model appropriate for AFM indentation problems. A series of Polydimethylsiloxane (PDMS) samples were indented by ...the sharp indenter in the air by using an AFM, and dozens of the force-displacement curves of each sample were obtained. An adhesive contact model suitable for sharp indentation with adhesion was established based on the same assumptions of the JKR model which is only suitable for spherical indentation at small penetration depth. Differences between sharp indentation problems with and without adhesion were discussed, and the limitations of the traditional adhesion model were given. The elastic modulus was obtained by fitting experimental force-displacement curves with theoretical ones, and results were compared to those macroscopic values in literature. The adhesion energy between the indenter and the sample surface was accurately calculated using the adhesion model based on the calculated elastic modulus. The influence of the indenter tip angle on the calculation results of the elastic modulus was also discussed theoretically. In this study, the mechanical properties of polymer samples were calculated at the nanoscale considering the adhesion effect.
The Bohai Sea is a large, semi-enclosed bay of China with a transport timescale of more than 1 year. Residence time (RT) is an important indicator used to determine the water exchange rate of coastal ...oceans, and it has a significant influence on coastal ecosystems and the environment. In this study, the RT and its seasonal variability within the Bohai Sea were investigated using a 3-D hydrodynamic model and the adjoint method of the RT. The model results show that the annual mean RT in the Bohai Sea is 3.43 years, and the RT increases from the Bohai Strait to the northwestern coast. The seasonal variability of the RT averaged over the entire Bohai Sea is not obvious; however, the regional RT has a significant seasonal variation, which could be more than 290% on average. When the monsoon winds were removed from the model, the sensitivity experiment showed an annual mean RT increase of ~ 90% with negligible seasonal variations in most areas of the Bohai Sea. The wind-induced residual current controls the seasonal variation in ocean circulation and induces the seasonal variability in RT; thus, monsoon winds play a dominant role in the seasonal variations of the water exchange rate in the Bohai Sea. Sensitivity experiments also suggest that tides can slow the water exchange rate, whereas the baroclinic processes and river runoff can accelerate the water exchange rate in the region near the Yellow River estuary. This study highlights the critical role of monsoon winds in affecting seasonal variabilities in the coastal transport timescale and exchange rate.
Climate variability over the Tropical and North Pacific Ocean (TPO and NPO, respectively) modulates marginal sea variability. The South China Sea (SCS), the largest marginal sea in the western NPO, ...is an outstanding example of a region that responds quickly to climate change. However, there is considerable uncertainty regarding the response of the deep SCS to large‐scale climate variability. Multivariate empirical orthogonal function analysis revealed three prominent modes of interconnected temperature anomaly fluctuations within the TPO and NPO. These coherent modes highlight the interactive dynamics among climate variations and reveal their modulation mechanisms for previously less explored potential temperature variabilities in the deep SCS. On the atmospheric bridge, external forces modify the upper‐layer Luzon Strait Transport (LST) by adjusting the Ekman transport and Kuroshio intrusion. For the oceanic pathway, climate variations disturb the deep‐layer LST by adjusting the barotropic flows in the upper layer.
Plain Language Summary
This study utilizes multivariate empirical orthogonal function analysis to examine long‐term hydrographic observations and identify coherent variations in surface temperature anomalies in the Tropical and North Pacific Ocean. The leading mode displays in‐phase combinations of the East Pacific El Niño and warm Pacific Decadal Oscillation. The second mode displays a Central Pacific El Niño and North Pacific Meridional Mode‐like mode. The third mode resembles a Central Pacific El Niño and Victoria Mode‐like mode. The objective is to comprehend the synergies between the climatic variabilities in the Tropical and North Pacific Ocean, as well as the processes by which the predominant climate variabilities regulate the undocumented potential temperature variabilities in the deep South China Sea. Extrinsic forcings in the Tropical and North Pacific Ocean regulate the interannual–decadal temperature variabilities by modulating the Luzon Strait Transport. On the atmospheric bridge, these extrinsic forcings affect the upper‐layer Luzon Strait Transport by altering the local Ekman transport and Kuroshio intrusion associated with the bifurcation of the North Equatorial Current. On the oceanic pathway, climate variabilities disturb the deep‐layer Luzon Strait Transport by changing the ocean bottom pressure between the two sides of the Luzon Strait.
Key Points
Coherent climate variabilities in the Tropical and North Pacific Ocean are obtained through MVEOF analysis
Potential temperature observations from the deep South China Sea indicate interannual–decadal variability
Climate variabilities affect deep temperature variability through the changing atmospheric bridge and oceanic pathway
Saline lakes are sensitive to climatic changes, however, it is challenging to reconstruct paleoclimate based on terrestrial evaporite records using conventional elemental and isotopic proxies. ...Magnesium is a major element in saline lakes, and the Mg isotope composition of brine is responsive to climate-driven processes such as carbonate precipitation and freshwater input. However, little has been explored on the application of Mg isotopes to studies of saline lakes. In this study, the Middle Pleistocene halite deposit from the Xiaoliangshan (XLS) evaporite section in the Qaidam Basin, Northwest China, was selected as a case to evaluate the response of Mg isotopes in the saline lake to environmental events. The Mg isotope data of the halite are complemented by geochemical analyses major elements and Sr-Cl isotopes of the halite component, and C-O isotopes of the associated carbonates. The 87Sr/86Sr ratios of the halite remained homogeneous (0.7111 to 0.7112) throughout the section, suggesting that the material source did not change significantly during the precipitation of the halite beds. By contrast, element ratios (Mg/Na and K/Na) and stable isotope ratios of C, O, Cl, and Mg show remarkable fluctuations along with the sediment profile. Based on the C-O-Cl isotope data, we identified events of freshwater recharging and desalination in an overall dry climatic background that were recorded in the halite. Notably, halite δ26Mg values vary by up to 2‰ in the section (from −1.63‰ to 0.46‰), and the low δ26Mg signature of halite was interpreted to reflect the input of light Mg isotopes into the saline lake in a freshwater recharging event, while the high δ26Mg values were produced by the precipitation of carbonate minerals under arid climatic conditions. Collectively, we suggest that Mg isotopes in terrestrial halite could be a sensitive tracer of basin hydrology. This study for the first time demonstrates the potential of Mg isotopes in terrestrial evaporites to unravel paleoclimatic events.
•The first report of δ26Mg values of halite samples from terrestrial saline lakes.•The δ26Mg values of terrestrial halite show stratigraphic variation of >2‰.•The δ26Mg values of brine are controlled by the balance of river input and carbonate precipitation.•δ26Mg values of halite deposits in terrestrial saline lakes are sensitive to basin hydrology.
Evaporites are important sedimentary records of seawater history, and their Mg and K isotopic signatures could be used to constrain the evolution of surficial cycles of Mg and K on Earth. However, ...the lack of detailed understanding of the Mg and K isotopic behaviors during the precipitation of key evaporite minerals has impeded the applications of Mg and K isotopes in evaporites. In this study, we systematically investigated Mg and K isotope fractionation factors between carnallite (KCl·MgCl2·6H2O) and saturated brine through mineral synthesis experiments, laboratory simulation of brine evaporation, and analysis of field samples. Carnallite synthesis experiments were performed at three different temperatures, and the results show that carnallite preferentially incorporates heavy Mg isotopes and light K isotopes over brines. Specifically, the Mg isotope fractionation factors (Δ26Mgcar-sol) at 5, 25, and 50 °C are 0.83 ± 0.09 ‰, 0.84 ± 0.09 ‰, and 0.57 ± 0.08 ‰, respectively, whereas the measured K isotope fractionation factors (Δ41Kcar-sol) at 5, 25, and 50 °C are −0.49 ± 0.08 ‰, −0.43 ± 0.11 ‰, and −0.41 ± 0.08 ‰, respectively. The Mg and K isotope fractionation factors calibrated by the synthesis experiment were verified by brine evaporation experiments and field samples. Based on a set of laboratory brine evaporation experiment, the instantaneous isotope fractionation factors for carnallite are 0.82 ‰ ∼ 0.83 ‰ (Δ26Mgcar-sol) and −0.38 ‰ ∼ −0.43 ‰ (Δ41Kcar-sol) after correction based on Li contents and a Rayleigh fractionation model. Additionally, based on analyses of brine and carnallite samples from the salt pan in the Qarhan Salt Lake region, Δ26Mgcar-sol and Δ41Kcar-sol are determined to be 0.85 ± 0.05 ‰ and −0.45 ± 0.09 ‰, respectively.
Using the obtained Mg and K fractionation factors for evaporite minerals and thermodynamic calculations, we predicted how the Mg and K isotopes of brine would change in response to the evaporation of seawater with varying chemistries. The modeling results show that different initial seawater/brine chemistry (e.g., Ca-rich, sulfate-rich, and “Ca-SO4 crossover”) would result in different evolutionary trends of δ41K and δ26Mg in the brines during evaporation, primarily driven by carnallite precipitation. Therefore, Mg and K isotope signatures in evaporites or brines can provide key constraints for brine evolution in enclosed basins and ancient seawater chemistry.
In this paper, the relationship between motion artifacts and magnetoencephalogram (MEG) source localization errors was established for the MEG system based on array optically pumped magnetometers ...(OPM). The influences of bias fields on OPM's performances were first evaluated through theoretical and experimental analysis, whose results proved that the bias magnetic fields along the sensitive axis affect the gain and sensitivity of OPM, while the pumping axis bias magnetic fields affect the direction of the sensitive axis. The OPM with a large linewidth has better anti-interference ability but worse sensitivity. Then, MEG simulations were carried out on the basis of OPM performance testing. The relative error of the forward model proved that the rotated sensitive axis would affect the forward model, while the gain error and sensitivity directly affect the signal-to-noise ratio of the MEG signal. The experiment and simulation also proved that it is recommended to use biaxial mode for OPM-MEG experiments and the motion artifact detected by OPMs should be reduced to less than 1nT at least. Moreover, the linewidth of the OPM's cell is positively correlated with the anti-interference capability of OPM. Therefore, sensitivity and anti-interference capability must be simultaneously considered in the design of OPM by optimizing the cell's linewidth to adapt to more scenarios.
In this study, nutrient and heavy metal contamination in surface sediments of the Xiashan stream were investigated. Determining pollution degree of nutrient and heavy metal were the main objectives ...of this investigation. For this reason, the concentrations of total nitrogen (TN), total phosphorus (TP), seven heavy metals (Cu, Zn, Pb, Cd, Cr, Ni, Hg), and metalloid (As) were analyzed at 55 sampling sites. The mean TN concentration in surface sediments was 5.007 g/kg, while the mean TP concentration was 0.385 g/kg. Based on the sediment quality guideline (SQG
s
) and background values of Chinese soil and sediment, the majority of the mean TN concentrations in surface sediments were higher than their background values, while the TP concentrations were different from those observed for TN. For heavy metal concentrations in surface sediments, most of sampling stations were higher than their background values. The mean geo-accumulation (I
geo
) indices for heavy metals were ranked as follows: Cd > Hg > Cu > Zn > Pb > Ni > Cr > As. The potential ecological risk index (RI) indicated heavy metal contamination level in Xiashan stream was very high ecological risk. According to I
geo
and RI values, heavy metals especially Cd and Hg are influenced significantly by anthropogenic activities. Cd and Hg are not only as pollutant but also considerable contributor to ecological risk. Multivariate statistical investigations showed that there is a significant and positive correlation between Pb, As, and Cd. Cu, Ni, and Cr have similar characteristic and therefore probably originated from the same sources. Suggested by the results, it is necessary to control nitrogen and heavy metal contamination caused by human activities in the study area.
In the present work, the effects of oxidation treatment on the structures and properties of a novel TiZrHfNbFe0.5 refractory multi-principal element alloy (MPEA) were reported. It is found that the ...TiZrHfNbFe0.5 MPEA exhibits a sluggish oxidation rate at 1,000 °C, which is attributed to the formation of a compact and stable oxide layer consisting of complex metallic oxides like Ti2ZrO6 and Fe2O3. In comparison with the as-cast MPEA, the microhardness of the 1,000 °C oxidized MPEA significantly increases by 1.6 times, resulting in a two orders of magnitude higher wear resistance. Furthermore, the bio-corrosion resistance, hydrophilicity, and bioactivity of the MPEA are remarkably enhanced by the 1,000 °C oxidation. In short, the formation of a highly protective oxide layer with enhanced wear and corrosion resistance by heating the TiZrHfNbFe0.5 MPEA at 1,000 °C, which shows promising prospects for biomedical applications.
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•Shear behaviors of sulfate-exposed shotcrete specimens were investigated.•The normal stress and sulfate-exposure time were considered.•A shear model of shotcrete specimens considering sulfate damage ...was proposed.
Direct shear tests were carried out on sulfate-exposed and non-exposed shotcrete specimens to study the shear mechanical behaviors, taking into account the effects of normal stress and exposure time. The shotcrete mixtures with different water-to-binder ratio (w/b) were in-situ prepared using dry-spray method. Sulfate attack tests were performed by placing the shotcrete specimens in 5% w/w solutions of sulfate sodium subjected to natural dry-wet cycle condition. Results show that the mechanical behaviors of shotcrete specimens under direct shearing were significantly influenced by sulfate attack. For example, peak shear stresses of shotcrete specimens under the same normal stress condition decreased over exposure period, while peak shear stresses of specimens under different normal stress conditions were accorded with the Mohr-Coulomb (M-C) criterion. The nominal cohesion and nominal internal friction angle calculated from linear M-C criterion showed a distinct degeneration over exposure time. Based on these experimental data and a statistical model, a shear model of shotcrete specimens considering the effects of normal stress and sulfate-exposure time was proposed. By a series of parameter learning and model validations, this sulfate-damage shear model was proved to have good performance on the prediction of shear mechanical behaviors of sulfate-exposed and non-exposed shotcrete specimens.
Gain-of-function mutations in the TRPV3 gene can cause Olmsted syndrome characterized by palmoplantar and periorificial keratoderma, itch, and hair loss. The mechanism underlying the hair loss ...remains unclear. In this study, we engineered an Olmsted syndrome mouse model by introducing the point mutation G568V to the corresponding Trpv3 locus in the mice. These mice developed fully penetrant hair loss. The hair loss was associated with premature differentiation of follicular keratinocytes characterized by precocious degeneration of trichohyalin and keratins, increased production of deiminated proteins, elevated apoptosis, and attenuation of transcription regulators (Foxn1, Msx2, Dlx3, and Gata3) known to regulate hair follicle differentiation. These abnormalities occurred in the medial‒proximal region of the inner root sheath and the hair shaft, where Trpv3 is highly expressed, and correlated with an impaired formation of the hair canal and the hair shaft. The mutant Trpv3 mice also exhibited increased proliferation in the outer root sheath, accelerated hair cycle, reduction of hair follicle stem cells, and miniaturization of regenerated hair follicles. Findings from this study suggest that precocious maturation of postmitotic follicular keratinocytes drives hair loss in patients with Olmsted syndrome.
