Vegetation grows more luxuriantly in Arctic permafrost drained lake basins.

As Arctic warming, permafrost thawing, and thermokarst development intensify, increasing evidence suggests that the frequency and magnitude of thermokarst lake drainage events are increasing. Presently, we lack a quantitative understanding of vegetation dynamics in drained lake basins, which is necessary to assess the extent to which plant growth in thawing ecosystems will offset the carbon released from permafrost. In this study, continuous satellite observations were used to detect thermokarst lake drainage events in northern Alaska over the past 20 years, and an advanced temporal segmentation and change detection algorithm allowed us to determine the year of drainage for each lake. Quantitative analysis showed that the greenness (normalized difference vegetation index [NDVI]) of tundra vegetation growing on wet and nutrient-rich lake sediments increased approximately 10 times faster than that of the peripheral vegetation. It takes approximately 5 years (4-6 years for the 25%-75% range) for the drainage lake area to reach the greenness level of the peripheral vegetation. Eventually, the NDVI values of the drained lake basins were 0.15 (or 25%) higher than those of the surrounding areas. In addition, we found less lush vegetation in the floodplain drained lake basins, possibly due to water logging. We further explored the key environmental drivers affecting vegetation dynamics in and around the drained lake basins. The results showed that our multivariate regression model well simulated the growth dynamics of the drainage lake ecosystem ( Radj2=.73 , p < .001) and peripheral vegetation ( Radj2=.68 , p < .001). Among climate variables, moisture variables were more influential than temperature variables, indicating that vegetation growth in this area is susceptible to water stress. Our study provides valuable information for better modeling of vegetation dynamics in thermokarst lake areas and provides new insights into Arctic greening and carbon balance studies as thermokarst lake drainage intensifies.

Additively Manufactured Zn-2Mg Alloy Porous Scaffolds with Customizable Biodegradable Performance and Enhanced Osteogenic Ability.

The combination of bioactive Zn-2Mg alloy and additively manufactured porous scaffold is expected to achieve customizable biodegradable performance and enhanced bone regeneration. Herein, Zn-2Mg alloy scaffolds with different porosities, including 40% (G-40-2), 60% (G-60-2), and 80% (G-80-2), and different unit sizes, including 1.5 mm (G-60-1.5), 2 mm (G-60-2), and 2.5 mm (G-60-2.5), are manufactured by a triply periodic minimal surface design and a reliable laser powder bed fusion process. With the same unit size, compressive strength (CS) and elastic modulus (EM) of scaffolds substantially decrease with increasing porosities. With the same porosity, CS and EM just slightly decrease with increasing unit sizes. The weight loss after degradation increases with increasing porosities and decreasing unit sizes. In vivo tests indicate that Zn-2Mg alloy scaffolds exhibit satisfactory biocompatibility and osteogenic ability. The osteogenic ability of scaffolds is mainly determined by their physical and chemical characteristics. Scaffolds with lower porosities and smaller unit sizes show better osteogenesis due to their suitable pore size and larger surface area. The results indicate that the biodegradable performance of scaffolds can be accurately regulated on a large scale by structure design and the additively manufactured Zn-2Mg alloy scaffolds have improved osteogenic ability for treating bone defects.

In vitro and in vivo studies on biodegradable Zn porous scaffolds with a drug-loaded coating for the treatment of infected bone defect.

Additively manufactured biodegradable zinc (Zn) scaffolds have great potential to repair infected bone defects due to their osteogenic and antibacterial properties. However, the enhancement of antibacterial properties depends on a high concentration of dissolved Zn2+, which in return deteriorates osteogenic activity. In this study, a vancomycin (Van)-loaded polydopamine (PDA) coating was prepared on pure Zn porous scaffolds to solve the above dilemma. Compared with pure Zn scaffolds according to comprehensive in vitro tests, the PDA coating resulted in a slow degradation and inhibited the excessive release of Zn2+ at the early stage, thus improving cytocompatibility and osteogenic activity. Meanwhile, the addition of Van drug substantially suppressed the attachment and proliferation of S. aureus and E. coli bacterial. Furthermore, in vivo implantation confirmed the simultaneously improved osteogenic and antibacterial functions by using the pure Zn scaffolds with Van-loaded PDA coating. Therefore, it is promising to employ biodegradable Zn porous scaffolds with the proposed drug-loaded coating for the treatment of infected bone defects.

An adaptive biodegradable zinc alloy with bidirectional regulation of bone homeostasis for treating fractures and aged bone defects.

Healing of fractures or bone defects is significantly hindered by overactivated osteoclasts and inhibited osteogenesis in patients with abnormal bone metabolism. Current clinical approaches using titanium alloys or stainless steel provide mechanical support but have no biological effects on bone regeneration. Therefore, designing and fabricating degradable metal materials with sufficient mechanical strength and bidirectional regulation of both osteoblasts and osteoclasts is a substantial challenge. Here, this study first reported an adaptive biodegradable Zn-0.8 Mg alloy with bidirectional regulation of bone homeostasis, which promotes osteogenic differentiation by activating the Pi3k/Akt pathway and inhibits osteoclast differentiation by inhibiting the GRB2/ERK pathway. The anti-osteolytic ability of the Zn-0.8 Mg alloy was verified in a mouse calvarial osteolysis model and its suitability for internal fracture fixation with high-strength screws was confirmed in the rabbit femoral condyle fracture model. Furthermore, in an aged postmenopausal rat femoral condyle defect model, 3D printed Zn-0.8 Mg scaffolds promoted excellent bone regeneration through adaptive structures with good mechanical properties and bidirectionally regulated bone metabolism, enabling personalized bone defect repair. These findings demonstrate the substantial potential of the Zn-0.8 Mg alloy for treating fractures or bone defects in patients with aberrant bone metabolism.

Multiscale architecture design of 3D printed biodegradable Zn-based porous scaffolds for immunomodulatory osteogenesis.

Reconciling the dilemma between rapid degradation and overdose toxicity is challenging in biodegradable materials when shifting from bulk to porous materials. Here, we achieve significant bone ingrowth into Zn-based porous scaffolds with 90% porosity via osteoinmunomodulation. At microscale, an alloy incorporating 0.8 wt% Li is employed to create a eutectoid lamellar structure featuring the LiZn4 and Zn phases. This microstructure optimally balances high strength with immunomodulation effects. At mesoscale, surface pattern with nanoscale roughness facilitates filopodia formation and macrophage spreading. At macroscale, the isotropic minimal surface G unit exhibits a proper degradation rate with more uniform feature compared to the anisotropic BCC unit. In vivo, the G scaffold demonstrates a heightened efficiency in promoting macrophage polarization toward an anti-inflammatory phenotype, subsequently leading to significantly elevated osteogenic markers, increased collagen deposition, and enhanced new bone formation. In vitro, transcriptomic analysis reveals the activation of JAK/STAT pathways in macrophages via up regulating the expression of Il-4, Il-10, subsequently promoting osteogenesis.

The relationships between self-esteem, self-efficacy, and test anxiety: A cross-lagged study.

The aim of the present study was to illuminate the causal relationships between self-esteem and test anxiety, as well as between general self-efficacy and test anxiety using two-wave longitudinal research design with a sample of 252 Chinese college students. After controlling for gender, grade and autoregressive effects, the results revealed that (1) self-esteem at T1 did not significantly predict test anxiety at T2; (2) general self-efficacy at T1 did not significantly predict test anxiety at T2; (3) test anxiety at T1 significantly and negatively predicted self-esteem at T2; and (4) test anxiety at T1 marginally significantly and negatively predicted general self-efficacy at T2. These results suggest that test anxiety is more likely to affect self-esteem and general self-efficacy rather than vice versa, and that the causal relationship between self-esteem and test anxiety are clearer than the causal relationship between general self-efficacy and test anxiety. However, given the limitation of the longitudinal research using cross-lagged analysis for revealing causality, these results should be viewed with caution.

Mechanical properties, in vitro biodegradable behavior, biocompatibility and osteogenic ability of additively manufactured Zn-0.8Li-0.1Mg alloy scaffolds.

Alloying and structural design provide flexibility to modulate performance of biodegradable porous implants manufactured by laser powder bed fusion (L-PBF). Herein, bulk Zn-0.8Li-0.1Mg was first fabricated to indicate the influence of the ternary alloy system on strengthening effect. Porous scaffolds with different porosities, including 60 % (P60), 70 % (P70) and 80 % (P80), were designed and fabricated to study the influence of porosity on mechanical properties, in vitro degradation behavior, biocompatibility and osteogenic ability. Pure Zn (Zn-P70) scaffolds with a porosity of 70 % were utilized for the comparison. The results showed Zn-0.8Li-0.1Mg bulks had an ultimate tensile strength of 460.78 ± 5.79 MPa, which was more than 3 times that of pure Zn ones and was the highest value ever reported for Zn alloys fabricated by L-PBF. The compressive strength (CS) and elastic modulus (E) of scaffolds decreased with increasing porosities. The CS of P70 scaffolds was 24.59 MPa, more than 2 times that of Zn-P70. The weight loss of scaffolds during in vitro immersion increased with increasing porosities. Compared with Zn-P70, a lower weight loss, better biocompatibility and improved osteogenic ability were observed for P70 scaffolds. P70 scaffolds also exhibited the best biocompatibility and osteogenic ability among all the used porosities. Influence mechanism of alloying elements and structural porosities on mechanical behaviors, in vitro biodegradation behavior, biocompatibility and osteogenic ability of scaffolds were discussed using finite element analysis and the characterization of degradation products. The results indicated that the proper design of alloying and porosity made Zn-0.8Li-0.1Mg scaffolds promising for biodegradable applications.

Tracking lake drainage events and drained lake basin vegetation dynamics across the Arctic.

Widespread lake drainage can lead to large-scale drying in Arctic lake-rich areas, affecting hydrology, ecosystems and permafrost carbon dynamics. To date, the spatio-temporal distribution, driving factors, and post-drainage dynamics of lake drainage events across the Arctic remain unclear. Using satellite remote sensing and surface water products, we identify over 35,000 (~0.6% of all lakes) lake drainage events in the northern permafrost zone between 1984 and 2020, with approximately half being relatively understudied non-thermokarst lakes. Smaller, thermokarst, and discontinuous permafrost area lakes are more susceptible to drainage compared to their larger, non-thermokarst, and continuous permafrost area counterparts. Over time, discontinuous permafrost areas contribute more drained lakes annually than continuous permafrost areas. Following drainage, vegetation rapidly colonizes drained lake basins, with thermokarst drained lake basins showing significantly higher vegetation growth rates and greenness levels than their non-thermokarst counterparts. Under warming, drained lake basins are likely to become more prevalent and serve as greening hotspots, playing an important role in shaping Arctic ecosystems.

Machine learning-enabled constrained multi-objective design of architected materials.

Architected materials that consist of multiple subelements arranged in particular orders can demonstrate a much broader range of properties than their constituent materials. However, the rational design of these materials generally relies on experts' prior knowledge and requires painstaking effort. Here, we present a data-efficient method for the high-dimensional multi-property optimization of 3D-printed architected materials utilizing a machine learning (ML) cycle consisting of the finite element method (FEM) and 3D neural networks. Specifically, we apply our method to orthopedic implant design. Compared to uniform designs, our experience-free method designs microscale heterogeneous architectures with a biocompatible elastic modulus and higher strength. Furthermore, inspired by the knowledge learned from the neural networks, we develop machine-human synergy, adapting the ML-designed architecture to fix a macroscale, irregularly shaped animal bone defect. Such adaptation exhibits 20% higher experimental load-bearing capacity than the uniform design. Thus, our method provides a data-efficient paradigm for the fast and intelligent design of architected materials with tailored mechanical, physical, and chemical properties.

A drug-loaded composite coating to improve osteogenic and antibacterial properties of Zn-1Mg porous scaffolds as biodegradable bone implants.

Zinc (Zn) alloy porous scaffolds produced by additive manufacturing own customizable structures and biodegradable functions, having a great application potential for repairing bone defect. In this work, a hydroxyapatite (HA)/polydopamine (PDA) composite coating was constructed on the surface of Zn-1Mg porous scaffolds fabricated by laser powder bed fusion, and was loaded with a bioactive factor BMP2 and an antibacterial drug vancomycin. The microstructure, degradation behavior, biocompatibility, antibacterial performance and osteogenic activities were systematically investigated. Compared with as-built Zn-1Mg scaffolds, the rapid increase of Zn2+, which resulted to the deteriorated cell viability and osteogenic differentiation, was inhibited due to the physical barrier of the composite coating. In vitro cellular and bacterial assay indicated that the loaded BMP2 and vancomycin considerably enhanced the cytocompatibility and antibacterial performance. Significantly improved osteogenic and antibacterial functions were also observed according to in vivo implantation in the lateral femoral condyle of rats. The design, influence and mechanism of the composite coating were discussed accordingly. It was concluded that the additively manufactured Zn-1Mg porous scaffolds together with the composite coating could modulate biodegradable performance and contribute to effective promotion of bone recovery and antibacterial function.

Detection of thermokarst lake drainage events in the northern Alaska permafrost region.

The rapidly warming Arctic climate is reducing the stability of near-surface permafrost, and the thawing of ice-rich permafrost causes landscape changes known as thermokarst processes. Growing evidence suggests an increasing trend in the frequency and magnitude of thermokarst lake drainage events, which would significantly alter topography and hydrology, affecting ecosystem stability and carbon cycling. Dynamic monitoring of thermokarst lakes through satellite imagery remains a challenging task, as current temporal trend analysis methods have difficulty in accurately detecting when thermokarst lake drainage events occur. In this study, to improve the detection of time series breakpoints, an advanced temporal segmentation and change detection algorithm developed for forest change detection was, for the first time, transposed to monitor thermokarst lake dynamics. Moreover, to filter out spurious signals caused by fluctuations in lake area, we developed a hybrid algorithm to validate the detected thermokarst lake drainage events at the pixel-level and lake object-level, respectively. The method developed in this study demonstrates its effectiveness in detecting thermokarst lake drainage events in Arctic permafrost ecosystems and the potential to monitor the evolution of thermokarst landscapes using Landsat archive. A time-series analysis of changes in the thermokarst lake region of northern Alaska since 2000 using all available Landsat continuous data was performed on the Google Earth Engine platform. In total, 90 drainage lakes larger than 5 ha in size were detected in our study area, nearly a third of which were almost completely drained. As thermokarst lakes drainage represent hotspots of permafrost degradation, we publicly share information on these drained lakes to help select more targeted sites for costly fieldwork and validation activities. This study provides a basis for understanding and quantifying thermokarst lake dynamics in the Arctic permafrost region, which will contribute to the goal of integrating thermokarst processes into earth system models.

Additive manufacturing of Zn-Mg alloy porous scaffolds with enhanced osseointegration: In vitro and in vivo studies.

Biodegradable metals (BM) and additive manufacturing (AM) are regarded revolutionary biomaterials and biofabrication technologies for bone repairing metal implants, the combination of both, namely AM of BM, is thus expected to solve the dual technical difficulties including "conventional medical metals are biologically inert and exist in the human body permanently" and "conventional manufacturing processes are inadequate to fabricate personalized implants of complicated structure". This work additively manufactured biodegradable Zn-Mg alloy porous scaffolds by laser powder bed fusion (L-PBF). By using the pre-alloyed Zn-xMg (x = 1, 2 and 5 wt.%) powder and the optimized processing conditions, high fusion quality with the relative density greater than 99.5% was confirmed for the L-PBF parts. The influence of Mg content on microstructure, mechanical properties, in vitro corrosion, cytocompatibility, in vivo degradation, biocompatibility and osteogenic effect was investigated. Fine α-Zn grains and precipitation phases including Mg2Zn11 and MgZn2 were observed in the Zn-xMg L-PBF parts. The hardness increased, and the strength increases firstly and then decreased with increasing the Mg content. The compressive strength and elastic modulus of Zn-1Mg porous scaffolds reached the highest as 40.9 ± 0.4 MPa and 1.17 ± 0.11 GPa, respectively, equivalent to those of cancellous bone. The corrosion rate and cell viability slightly rose with increasing the Mg content. Histological analysis after 6-week and 12-week implantation in rabbit femurs showed enhanced bone formation around the Zn-1Mg porous scaffolds compared with pure Zn counterparts. In summary, Zn-1Mg porous scaffolds produced by L-PBF presented promising results to fulfill customized requirements of biodegradable bone implants. STATEMENT OF SIGNIFICANCE: Additive manufacturing of biodegradable metal porous scaffolds is expected to solve the dual challenges from customized structures and bioactive function required for bone implants. It was the first to present a systematic in vitro and in vivo investigation into the compositions, microstructure, mechanical properties, biodegradation, biocompatibility and osteogenic effect of additively manufactured Zn-Mg alloy porous scaffolds. Reliable formation quality and performance evaluation was achieved by using the pre-alloyed Zn-xMg (x = 1, 2 and 5 wt.%) powder and the optimized laser powder bed fusion process. Although the Zn-1Mg scaffolds exhibited promising mechanical strength, biocompatibility, and osteogenic effect, their degradation rate needs to be further accelerated compared with the term of bone reconstruction.

Processing optimization, mechanical properties, corrosion behavior and cytocompatibility of additively manufactured Zn-0.7Li biodegradable metals.

Biodegradable Zn-Li alloys exhibit superior mechanical performance and favorable osteogenic capability for load-bearing bone devices. Additive manufacturing (AM) endows freedom for the fabrication of bone implants of personalized structure to satisfy patient-specific needs. In this paper, AM of Zn-Li alloys was attempted for the first-time using laser powder bed fusion (LPBF), and the fabricated samples exhibited good fusion quality and high dimensional accuracy. The processing optimization, mechanical properties, in vitro corrosion behavior and cytocompatibility were investigated by using Zn-0.7Li bulk and porous samples. The ultimate tensile strength and elastic modulus of bulk samples respectively reached 416.5 MPa and 83.3 GPa, and both were the highest among various additively manufactured Zn alloys reported so far. Porous samples achieved compressive strength (18.2 MPa) and elastic modulus (298.0 MPa), which were comparable to those of cancellous bone. Porous samples exhibited a higher corrosion rate and alleviated the problem of slow degradation of Zn-Li alloys. Nevertheless, osteoblastic cells showed a more spreading and healthier morphology when adhering to the porous samples compared to the bulk samples, thus a better cytocompatibility was confirmed. This work shows tremendous potential to precisely design and modulate biodegradable Zn alloys to fulfill clinical needs by using AM technology. STATEMENT OF SIGNIFICANCE: This paper firstly studied processing optimization during laser powder bed fusion of Zn-Li alloy. Bulk and porous Zn-0.7Li samples in customized design were obtained with high formation quality. The tensile strength of bulk samples reached 416.5 MPa, while the compressive strength and modulus of porous samples reduced to 18.2 MPa and 298.0 MPa, comparable to those of bone. The weight loss of porous samples was roughly 5 times that of bulk samples; osteoblastic cells showed a more spreading and healthier morphology at porous samples, indicating improved biodegradation rate and cytocompatibility. This work shows tremendous potential to precisely design and modulate biodegradable Zn alloy porous scaffolds to fulfill clinical needs by using additive manufacturing technology.

Using the Google Earth Engine to estimate a 10 m resolution monthly inventory of soil fugitive dust emissions in Beijing, China.

Soil fugitive dust (SFD) is an important contributor to ambient particulate matter (PM), but most current SFD emission inventories are updated slowly or have low resolution. In areas where vegetation coverage and climatic conditions undergo significant seasonal changes, the classic wind erosion equation (WEQ) tends to underestimate SFD emissions, increasing the need for higher spatiotemporal data resolution. Continuous acquisition of precise bare soil maps is the key barrier to compiling monthly high-resolution SFD emission inventories. In this study, we proposed taking advantage of the massive Landsat and Sentinel-2 imagery data sets stored in the Google Earth Engine (GEE) cloud platform to enable the rapid production of bare soil maps with spatial resolutions of up to 10 m. The resulting improved spatiotemporal resolution of wind erosion parameters allowed us to estimate SFD emissions in Beijing as being ~5-7 times the level calculated by the WEQ. Spring and winter accounted for >85% of SFD emissions, while April was the dustiest month with SFD emissions of PM10 exceeding 11,000 t. Our results highlighted the role of SFD in air pollution during winter and spring in northern China, and suggested that GEE should be further used for image acquisition, data processing, and compilation of gridded SFD inventories. These inventories can help identify the location and intensity of SFD sources while providing supporting information for local authorities working to develop targeted mitigation measures.

Mitigation of Arctic permafrost carbon loss through stratospheric aerosol geoengineering.

The Arctic is warming far faster than the global average, threatening the release of large amounts of carbon presently stored in frozen permafrost soils. Increasing Earth's albedo by the injection of sulfate aerosols into the stratosphere has been proposed as a way of offsetting some of the adverse effects of climate change. We examine this hypothesis in respect of permafrost carbon-climate feedbacks using the PInc-PanTher process model driven by seven earth system models running the Geoengineering Model Intercomparison Project (GeoMIP) G4 stratospheric aerosol injection scheme to reduce radiative forcing under the Representative Concentration Pathway (RCP) 4.5 scenario. Permafrost carbon released as CO2 is halved and as CH4 by 40% under G4 compared with RCP4.5. Economic losses avoided solely by the roughly 14 Pg carbon kept in permafrost soils amount to about US$ 8.4 trillion by 2070 compared with RCP4.5, and indigenous habits and lifestyles would be better conserved.

Quantifying economic impacts of climate change under nine future emission scenarios within CMIP6.

The concept of "environmental determinism" suggests that climate conditions played a substantial role in shaping modern society. To minimize the social costs of future climate change and to promote economic development through identification of cost-effective adaptation strategies and mitigation policies, quantitative assessments are needed for obtaining a better understanding of the causal impacts of climate change on human society. In this work, we estimate the economic impacts of climate change during the 21st century under nine CMIP6 scenarios, using the PAGE-ICE integrated assessment model driven by the latest anthropogenic emission and socio-economic projections. Our results show that the largest climate change damages occur under the SSP3-7.0 scenario (involving regional rivalry and high anthropogenic emissions), followed by the SSP3-LowNTCF scenario (which considers significantly reduced NTCF emissions), and that climate change damage costs are expected to grow much faster than global GDP (reaching ~47% of global GDP in 2100). Gaps in adaptation resulting from regional inequalities would lead to higher climate change damages in poorer and warmer regions such as Africa and the Middle East. The outcomes obtained under the SSP1-1.9 and SSP1-2.6 scenarios, in which the warming limit targets of 1.5 °C and 2 °C set forth in the Paris Agreement are considered, respectively, reveal that aggressive mitigation strategies pass a cost-benefit analysis and could significantly reduce the economic impacts of climate change.

Economic losses of carbon emissions from circum-Arctic permafrost regions under RCP-SSP scenarios.

Under rapid Arctic warming, the vast amount of labile organic carbon stored in Arctic permafrost soils poses a potentially huge threat. Thawing permafrost will release hundreds of billion tons of soil carbon into the atmosphere in the form of CO2 and CH4 that would further intensify global warming and bring more challenges to human society. In this study, we use the PInc-PanTher model to estimate carbon emissions from thawing permafrost in the circum-Arctic during 2010-2100 followed by the PAGE09 integrated assessment model to evaluate the net economic losses caused by these permafrost carbon emissions. Our results show that in terms of net present value (NPV), the release of CO2 and CH4 from circum-Arctic permafrost will generate estimated net economic losses of US$2.5 trillion (5-95% range: 0.3-11.2 US$ trillion) under the RCP4.5-SPP1 scenario and US$12.7 trillion (5-95% range: 1.6-41.8 US$ trillion) under the RCP8.5-SPP3 scenario between 2010 and 2100, which contribute ~4.9% and ~6.4% respectively of net economic losses of global carbon emissions.