Unstable Areas Research Articles

Tectonically Stable Parts in Iraq Are Not Stable

Iraq is located in the extreme northeastern part of the Arabian Plate, which is in collision with the Iranian (Eurasian) Plate. The collision, which is still ongoing has created tens of folds some of which exhibit different types of faults. The exerted compressional forces are believed to be decreasing southwestwards as being far from the collision area (Suture Zone). Accordingly, all the existing tectonic and geological maps compiled by different authors and all the existing published articles, reports and books have considered two main tectonic domains in Iraq. The Stable Shelf and Unstable Shelf or Inner Platform and Outer Platform. The contact between these two main divisions follows almost the Euphrates River; towards the west of the river is the tectonically Stable area and towards the east and north is the tectonically Unstable area, which means the presence of different structural forms. In the current study, we have recognized tens of different Neotectonic evidence in the Stable part indicating that the area is tectonically not stable. Among those indications are abandoned valleys, development of sinkholes along certain lineaments, bending of valleys in right angles, and development of nick-points in valleys along certain lineaments.

Remote volcano monitoring using crowd-sourced imagery and Structure-from-Motion photogrammetry: A case study of Oldoinyo Lengai's active pit crater since the 2007–08 paroxysm

Active volcanic craters are highly dynamic geological features that undergo morphological changes on a broad range of spatial and temporal scales. Such changes have implications for the stability of the edifice, the eruptive style and the associated hazards. However, monitoring the morphological evolution of active craters at high spatial resolution and over long periods of time can be challenging, especially at remote volcanoes. In this study, we demonstrate the potential of Structure-from-Motion Multi-View Stereo photogrammetry technique based on crowd-sourced data, applied to the case study of Oldoinyo Lengai (OL) volcano in northern Tanzania. Following the 2007–08 paroxysm, OL volcano resumed its characteristic effusive activity and started to fill in with lava the newly-formed 300 m wide and 130 m deep pit crater. Monitoring capability is limited at OL due to its location in a remote non-urbanized area, therefore, the eruptive and morphological evolution is poorly constrained (e.g., lava emission rates, number of vents, location of unstable areas), with hazard implications for tourists visiting the summit area. Here we use crowd-sourced images, including Unoccupied Aircraft System (UAS) images, ground-based videos and pictures collected between October 2014 and June 2022, to reconstruct high-resolution topographic time-series of OL's summit crater. With these data, we have generated 7 Digital Elevation Models (DEMs) of OL's pit crater spanning the past 8 years, and estimated the emitted volume of lava and the corresponding time averaged discharge rates (TADR). From this we characterize the geomorphological evolution of OL pit crater since the 2007–08 paroxysm and perform a preliminary hazard assessment of the crater area. InSAR COSMO-SkyMed and Sentinel-1 data covering the periods 2013–2014 and 2018–2019 were also used in this study to complement our observations. Our results indicate that the main location of lava emission within the crater floor has repeatedly shifted over the years and that the 2008 cone has experienced a subsidence over time. OL's TADR has increased over the years, reaching values one order of magnitude higher in the period 2021–2022 compared to 2014–2018. Assuming similar TADR in the coming years, the crater could be filled in by lava within the next decade, leading to new lava overflows on the flanks of the volcano.

Assessing Geotourism Aspects of Ungaran Geothermal Areas for Promoting Sustainable Energy through Volcano-Geothermal Tourist Destination

The indigenous nature of the Ungaran volcano-geothermal area allows us to bring the benefit to its nearest community. Geotourism can be an opportunity to introduce geological knowledge and foster the socio-cultural acceptance of society towards geothermal. This study aims to assess the potential of the study area as tourist destination. The research method is collecting data on geothermal manifestations and volcanic feature sites, quantitative assessment of geosites and geomorphosites, and preliminary hazard risk analysis. Study results identify six geosites: Gedong Songo area, Nglimut hot spring, Diwak-Derekan-Kaliulo warm spring, and Mawar camping area which features a volcanic landscape. Five of six geosites have high geotourism value of more than 0.5 in average, except for Kaliulo site. The recommendation of activities to do are leisure activities in nature, hiking, camping, thermal bathing, horseback riding, and geological excursion.Ttourists should be cautious of potential hazards risk from volcanic gases, hot and acid waters, slippery and unstable areas, landslides, rugged terrain, and extreme weather. A geotourism model is constructed to highlight each site and their attributes to Ungaran volcano-geothermal setting, tourism activities, and possible risks. By exploring the natural and geological richness offered by this destination, tourists will discover the uniqueness of volcano-geothermal tourism experience.

Activation of a new landslide process on Bureya according to interferometric measurements by the PALSAR-2 radar

Based on the results of processing an interferometric pair of radar images with synthesized aperture (SAR) L-band PALSAR-2 taken over the territory of the Bureya landslide in May 2019 and May 2020 from the ALOS-2 satellite, a new unstable surface area was discovered. Rated the average monthly rate of soil displacement is up to 1 cm/month along the surface of the slope at the site of the formation of a new separation wall. It was noted that interferometric processing of archival data had not previously revealed any movements of the slope surface in this place. The most possible reason for the activation of the landslide process in the new area has been identified: a violation of stability as a result of the collapse of the underlying landslide body in December 2018.

Widespread slowdown in thinning rates of West Antarctic ice shelves

Abstract. Antarctica's floating ice shelves modulate discharge of grounded ice into the ocean by providing a backstress. Ice shelf thinning and grounding line retreat have reduced this backstress, driving rapid drawdown of key unstable areas of the Antarctic Ice Sheet, leading to sea-level rise. If ice shelf loss continues, it may initiate irreversible glacier retreat through the marine ice sheet instability. Identification of areas undergoing significant change requires knowledge of spatial and temporal patterns in recent ice shelf loss. We used 26 years (1992–2017) of satellite-derived Antarctic ice shelf thickness, flow, and basal melt rates to construct a time-dependent dataset of ice shelf thickness and basal melt on a 3 km grid every 3 months. We used a novel data fusion approach, state-of-the-art satellite-derived velocities, and a new surface mass balance model. Our data revealed an overall pattern of thinning all around Antarctica, with a thinning slowdown starting around 2008 widespread across the Amundsen, Bellingshausen, and Wilkes sectors. We attribute this slowdown partly to modulation in external ocean forcing, altered in West Antarctica by negative feedbacks between ice shelf thinning rates and grounded ice flow, and sub-ice-shelf cavity geometry and basal melting. In agreement with earlier studies, the highest rates of ice shelf thinning are found for those ice shelves located in the Amundsen and Bellingshausen sectors. Our study reveals that over the 1992–2017 observational period the Amundsen and Bellingshausen ice shelves experienced a slight reduction in rates of basal melting, suggesting that high rates of thinning are largely a response to changes in ocean conditions that predate our satellite altimetry record, with shorter-term variability only resulting in small deviations from the long-term trend. Our work demonstrates that causal inference drawn from ice shelf thinning and basal melt rates must take into account complex feedbacks between thinning and ice advection and between ice shelf draft and basal melt rates.

A new mining method for reopening the opencast mine of Kef Essennoun

Purpose. To treat the stability problem of the phosphate Kef Essennoun quarry in the mining field of Jebel Onk located in the Northeastern part of Algeria. Methodology. To achieve these objectives, we started by monitoring the unstable area, using two monitoring systems: control stations and inclinometer. We then carried out a digital assessment of the Northwestern edge stability of the quarry under the current operating conditions of exploitation. After that, we proposed a new operating plan for the reopening of the depot under the required security conditions. At the end, we carried out an assessment of the edge stability, as the work to reopen and develop the Kef Essennoun quarry progressed. Findings. The results show that, under the current operating conditions of exploitation, the Northwestern edge of the Kef Essennoun quarry is unstable (FS < 1). The backfilling of the pilot pit of the mine, lead to the assurance of the mine walls stability, by increasing the values of safety factors with a rate of more than 30 %. Originality. The backfilling of the pilot pit of the mine and the resumption of top-down mining exploitation will ensure the stability of the quarry during and after the operating exploitation mining. Practical value. The study of the stability of the embankments bleachers, the edges of the quarries and the facings of the slag heaps during the open pit mining of useful ores deposits is an essential step that must be done gradually according to the development of mining works to guarantee the safety of personnel, materials, reserves and the environment.

Analysis of the Complex Three-Dimensional Flow Structure in the Circulation Pump of the Flow-Making System Based on Delayed Detached Eddy Simulation

As the core component of the flow-making system, the circulating pump has differences in its internal flow structure under different operating conditions, which affects the flow quality of the environmental simulation test area and the authenticity of marine environmental simulation. To explore the internal flow characteristics and outlet evolution characteristics of the circulating pump, this paper uses the DDES (delayed detached eddy simulation) method for numerical simulation. This paper combines BVF (boundary vorticity flow) diagnosis and the limit streamline method to analyze the evolution characteristics of the unstable flow area on the blade surface; it uses the Q criterion to identify the vortex structure inside the pump and analyze its evolution and development laws. Additionally, a quantitative analysis of the flow state of the circulating pump using flow uniformity indexes is performed. The results show that the surface of impeller blades is uniform under 1.0 QN. At 0.7 QN, the evolution process of the blade suction surface BVF is periodic, with a corresponding period of about 2/9 T (0.02 s). At 1.0 QN, the strength and scale of the separated vortices inside the guide vanes are minimized compared to other flow rates, and the scale and strength of the vortices show a decreasing trend along the outer normal direction. The evolution period of the separation vortex on the pressure surface of the guide vane is about 1/3 T (0.033 s) under 1.1 QN and the evolution period of the suction surface of the guide vane is about 2/3 T (0.067 s) under 0.7 QN. The flow uniformity indexes value downstream of the pump outlet under 1.0 QN are very close to the ideal value; with a corresponding value of Ϛi = 0.023, θ¯ = 89.94°, γ = 0.95, λ = 97.9%, the outflow can be approximately regarded as axial uniform flow. The research results can provide theoretical support for the further optimization design of circulating pumps and lay the foundation for the implementation of real systems.

Shimmy Suppression of an Aircraft Nose Landing Gear Using Torsional Nonlinear Energy Sink

Abstract Shimmy motion may occur for an aircraft nose landing gear (NLG) during its takeoff, landing, and taxiing procedure, which is an undesirable motion and should be suppressed. Here, a novel torsional nonlinear energy sink (NES) based on the cam-roller mechanism is proposed and applied in the NLG to improve its shimmy performance. The torsional NES is connected with the upper and lower struts of the NLG and its mechanical characteristic is studied. A seven-dimensional dynamic model of the NLG coupled with NES is built, which considers the NLG torsional and lateral motions, and the nonlinear tire model. The numerical continuation method is applied to analyze its shimmy performance, the stable area and limit cycle oscillation (LCO) amplitude are acquired, further compared with those of the original NLG without using the NES. The results show that as the NES is used in the NLG, the torsional shimmy dominated unstable area reduces significantly and the lateral shimmy dominated unstable area decreases slightly, which results in the increase of the stable area of the NLG; the maximum LCO amplitudes for the NLG torsional and lateral shimmy become smaller, the forward speed ranges as the torsional and lateral shimmy occur become narrower, which indicates that the stable forward speed ranges of the NLG become wider; the NLG shimmy performance improves as the NES has larger torsional inertia and damping, and smaller torsional linear stiffness. Thus, the NES can suppress the NLG shimmy motion and enhance its shimmy performance effectively.

Influence of non-urban reference delineation on trend estimate of surface urban heat island intensity: A comparison of seven methods

Increasing concern over urban heat mitigation creates an emerging necessity to track the evolution of urban heat island intensity (UHII) to assess the effectiveness of existing plans in combating urban heat. However, complex human-environment interactions make it difficult to accurately isolate urban effects in UHII evolutions due to unstable non-urban references. This study provided the first test on the sensitivity of surface UHII (SUHII) trend estimate to seven methods of non-urban reference delineation across 281 Chinese cities. The corresponding seven non-urban references include administrative non-urban areas, administrative non-urban areas excluding extreme elevations, administrative low plant areas, suburb, outer suburb, outer suburbs progressively excluding unstable areas interfered by evident greening/desertification trends and the SUHI footprint of neighboring cities, respectively. Results revealed that the selection of different non-urban references significantly altered SUHII and the nature of observed surface thermal island (heat or cold) in 74% and 8% of cities, respectively. Besides, due to diverse and inconsistent land use and land cover changes across and nearby non-urban areas, the way of non-urban reference delineation also affected the amplitude and even direction of statistically significant SUHII trends in 41% and 21% of cities, respectively. Among the seven methods, the use of suburb which was collectively interfered by urban and non-urban changing factors, produced a large number of misestimated significant downtrends (2.7-4.5 times more cities than other methods) and was therefore in general not recommended. Administrative non-urban areas were not suitable to cities with evident greening/desertification trends, yet the applicability can be largely enhanced by removing areas with extreme elevations. Low plant areas were in general feasible, except for the cities with suburban low plants additionally warmed up by urban areas. Outer suburb was relatively the optimal, particularly the areas with all concerned interferences excluded. Overall, this study provided empirical evidence supporting the need to use stable non-urban references for reliable trend estimate of urban-induced SUHII variations. The results may benefit more accurate assessments of the causes, progress, and consequences of SUHI evolution, thereby minimizing the chances of policy failure in SUHI mitigation.

Effect of negative stiffness nonlinearity on the vibration control effectiveness of tuned negative stiffness inerter damper

Recently, tuned negative stiffness inerter damper (TNSID) integrating the advantages of both negative stiffness and inerter elements has been proposed and verified to be effective for structural vibration control. In previous studies, the stiffness of the negative stiffness element was normally regarded as a constant for simplicity. However, it is well-known that negative stiffness is generally accompanied by nonlinearity, which may lead to undesirable nonlinear vibrations and unstable responses. Therefore, in this paper, the influence of the nonlinearity of negative stiffness, including weakening and strengthening nonlinear negative stiffness, on the performances of two representative TNSIDs with different configurations is investigated. The working mechanisms and optimal parameters of the TNSIDs with simplified linear negative stiffness are introduced firstly. Following that, based on the harmonic balance method, the dynamic responses of the two TNSIDs with different nonlinear negative stiffness are attained. The unstable problems and performance degradation caused by the nonlinearity of negative stiffness are analysed. Parametric studies are further carried out to evaluate the effects of the nonlinear coefficient, excitation amplitude, internal frequency ratio, and damping ratio on the performances of the two nonlinear TNSIDs. Moreover, to eliminate the impact of the negative stiffness nonlinearity, a new structural parameter optimization is conducted by minimizing the maximum displacement amplitude-frequency response of the TNSIDs. The results indicate that the nonlinearity of negative stiffness could lead to the bend and jump of the displacement amplitude-frequency response curves of TNSIDs, as well as superharmonic resonances, especially when the performance of TNSIDs is sensitive to the variation of negative stiffness. Besides, the unstable areas and the maximum displacement amplitude-frequency responses of TNSIDs are dependent on the excitation amplitude and nonlinear coefficient. To avoid the unstable vibration phenomenon and maintain effective vibration control performance, TNSID-P2 is recommended to be equipped with a weakening negative stiffness under both moderate and strong excitations, while TNSID-P1 should be designed with a weakening negative stiffness and work under a moderate excitation due to its performance being highly sensitive to the variation of negative stiffness.

Constitutive Equation and Processing Map of CoCrFeNiMo0.3 High Entropy Alloy Based on The Thermoplastic Deformation

The unique characteristics of high entropy alloys are challenging the field of traditional materials science and are expected to apply innovations in fields such as aerospace and defense, making them one of the strong candidates. The thermoplastic deformation mechanisms and processing maps of CoCrFNiMo0.3 alloy were studied at a temperature (T) ranging from 950 - 1250 °C and a strain rate () ranging from 0.001 - 0.1 s−1. A sharp rise is observed in the flow curve in the early stage, as the strain increases, slowly increasing flow stress due to the presence of dynamic softening, then turns to decrease, finally reaches a steady state. The optimal processing area was at 1050 - 1250 °C and 0.001 - 0.1 s−1, and there is an unstable area appearing at 950 - 1050 °C and 0.01 - 0.1 s−1. The η in the hot processing region are high, and they are not in the instability region.

IPSO-ELM intelligent prediction of landslide displacement in complex and unstable area of karst landform

In southern China, the karst landform areas possess a complex geological and topographic environment, a fragile ecosystem, poor surface stability, and frequent occurrences of landslides and other geological disasters. To effectively monitor and predict such events, it is crucial to process landslide monitoring data and establish reliable prediction models. This paper presents an IPSO-ELM displacement prediction model that integrates the improved particle swarm optimization algorithm (IPSO) and extreme learning machine (ELM). The proposed coupling model predicts decomposed displacement subsequences individually, which are then reconstructed to obtain the total displacement prediction value. In this study, displacement monitoring data from a typical landslide in the karst landform area between 2007 and 2012 were selected. Various prediction and verification scenarios were established to validate the accuracy and stability of the prediction model. The MAPE of the IPSO-ELM model is 0.18%, which outperforms the ELM and BPNN models with MAPEs of 0.56% and 0.65%, respectively, in predicting landslide displacement in karst landform areas. This study provides a solid theoretical foundation and practical value for landslide displacement prediction.

Deep learning powered long-term warning systems for reservoir landslides

The reservoir landslides are characterized by repeated phases of acceleration and isokinetic deformation under long-term periodic external forces. The state-of-the-art research lacks reliable prediction methods and judgment of their evolution stages. This work promotes the application of the deep learning algorithm and landslide evolution model in long-term warning systems. The test site is the Sifangbei landslide in the Three Gorges reservoir area of China. The main innovative features are: (i) the displacement of the landslide is considered as the prediction target, and the optimal model (i.e., conditioning factors and hyper-parameters combination) driven by the deep learning framework is used for spatial prediction; (ii) different warning methods (from both literature and current practice) are compared to single out the one that can best describe the evolution stage of the reservoir landslide; and (iii) deep learning model and adaptive evolution model are combined to analyze the temporal-spatial kinematic characteristics and evolution trend of the landslide under extreme scenarios related to rainfall and reservoir water levels. The results show that the predicted displacements of the lower and central part of the landslide are respectively controlled by reservoir water level and rainfall; the five-stage evolution model can capture the long-term evolution trend of the Sifangbei landslide; under extreme scenarios, landslide deformation exhibits step-like characteristics and is more likely to start from the middle of the lower portion of the unstable area. These models represent the up-to-date steps of a long-term research plan. The gathered knowledge can be used to analyze the spatial evolution characteristics of landslides and promote the setup of long-term warning systems. Furthermore, the results show that combining the proposed deep learning and evolution methods provides forecast information that could help adjusting short-term warning strategies in such a complex risk area as the Three Gorges Reservoir.

IMPLEMENTATION OF THE DBSCAN METHOD FOR CLUSTER MAPPING OF EARTHQUAKE SPREAD LOCATION

West Java area is located on the Pacific Circum and Mediterranean Circum routes, this causes West Java area to be an unstable area that is characterized by many active working volcanoes and frequent earthquakes. An analysis of the grouping of earthquake data in West Java Province area is urgently needed. The purpose of this study was to classify areas based on the density of earthquake occurrence areas in West Java using Density-Based Spatial Clustering of Application with Noise (DBSCAN). The population in this study are all earthquake events occurred in 2021. While the sample used in this study is data on the location of the distribution of earthquakes in West Java Province in 2021 taken from the BMKG online data website at dataonline.bmkg.go.id. This research began with nearest-neighbor analysis to see patterns of data distribution. If the data distribution pattern is grouped, then DBSCAN analysis can be continued. The DBSCAN algorithm uses a combination of parameters, namely minimum points (MinPts) and epsilon (Eps). Cluster results are evaluated using the silhouette coefficient. Then, in this study, deeper data exploration was carried out in three ways, namely: (1) Clustering based on the highest silhouette value, (2) clustering by lowering the MinPts value, and (3) clustering based on the smallest upper limit (supremum) value of the silhouette coefficient. The data exploration here aimed to form more clusters while still considering the silhouette coefficient value limits so that there are more areas prone to earthquakes but also maintaining the validity of the results obtained. Next, determine the best cluster results by comparing the cluster results obtained. The best cluster results were obtained at Eps=10000 and MinPts=3 which formed 12 clusters with a silhouette coefficient value of 0.713, which means that the clusters have a strong structure. It is hoped that the information regarding the grouping of areas where earthquakes frequently occur can be used as a form of earthquake disaster mitigation and minimize the impact of losses due to the earthquake.

Spatiotemporal dynamics of periodic waves in SIR model with driving factors

The world faces Covid-19 waves, and the overall pattern of confirmed cases shows periodic oscillations. In this paper, we investigate the spatiotemporal spread of Covid-19 in the network-organized SIR model with an extrinsic incubation period of the driving factors. Firstly, Our analysis shows the occurrences of Hopf bifurcation and periodic outbreaks consistent with the actual spread of Covid-19. And we investigate periodic waves on spatial scales using Turing instability, and the spread of infected individuals increases the localized hot spots. We study the effect of the incubation period, and more incubation periods generate Turing instability resulting in periodic outbreaks. There is an occurrence of bursting states at peaks of periodic waves due to small diffusion of infected and susceptible, which means stable and unstable areas try to convert each other due to high competition among nodes. Also, We note the disappearance of these bursts when infected and susceptible individuals’ movements are easier; thus, the dominance of infected individuals prevails everywhere. Effective policy interventions and seasonality can cause periodic perturbations in the model, and therefore we study the impact of these perturbations on the spread of Covid-19. Periodic perturbations on the driving factors, infected individuals show co-existing spatial patterns. Chaotic outbreak becomes periodic outbreaks through alternating periodic or period-2 outbreaks as we regulate the amplitude and frequency of infected individuals. In short, regulations can erase period-2 and chaotic spread through policy interventions.

Alexandre Kostov, ed. Contemporary Balkans. The Challenges of the 21st Century

Alexandre Kostov, ed. <i>Contemporary Balkans. The Challenges of the 21st Century</i>

Ship rolling equation: Comparison of the different damping models

In the paper, a comparison of the ship rolling numerical simulations results for four roll damping models is presented. In the first two models, constant damping coefficients are used, in linear and nonlinear notation. These damping models are commonly used, however have a significant disadvantage - the damping coefficients are independent of the roll amplitude and frequency. In the next two models, the damping coefficients are dependent on rolling amplitude and frequency and are implemented in roll equation with linear and nonlinear notation. The overall goal of the study is to test the effect of value and notation of damping on the results of the ship rolling numerical simulations. However, the main goal is to test if the damping dependent on roll amplitude and frequency will have an effect on ship rolling numerical simulations results. Comparison of roll damping models comprises three tests. The first two tests refer to the frequency response curve while the third test concerns the rolling equation unstable solution area. Research shows that the rolling equation is sensitive to the applied damping model and that the damping dependent on roll amplitude and frequency can have a significant impact on the results of ship rolling numerical simulations.

Improving landslide inventories by combining satellite interferometry and landscape analysis: the case of Sierra Nevada (Southern Spain)

An updated and complete landslide inventory is the starting point for an appropriate hazard assessment. This paper presents an improvement for landslide mapping by integrating data from two well-consolidated techniques: Differential Synthetic Aperture Radar (DInSAR) and Landscape Analysis through the normalised channel steepness index (ksn). The southwestern sector of the Sierra Nevada mountain range (Southern Spain) was selected as the case study. We first propose the double normalised steepness (ksnn) index, derived from the ksn index, to remove the active tectonics signal. The obtained ksnn anomalies (or knickzones) along rivers and the unstable ground areas from the DInSAR analysis rapidly highlighted the slopes of interest. Thus, we provided a new inventory of 28 landslides that implies an increase in the area affected by landslides compared with the previous mapping: 33.5% in the present study vs. 14.5% in the Spanish Land Movements Database. The two main typologies of identified landslides are Deep-Seated Gravitational Slope Deformations (DGSDs) and rockslides, with the prevalence of large DGSDs in Sierra Nevada being first revealed in this work. We also demonstrate that the combination of DInSAR and Landscape Analysis could overcome the limitations of each method for landslide detection. They also supported us in dealing with difficulties in recognising this type of landslides due to their poorly defined boundaries, a homogeneous lithology and the imprint of glacial and periglacial processes. Finally, a preliminary hazard perspective of these landslides was outlined.

Feasibility, Uptake, and Results of COVID-19 Antigen Rapid Diagnostic Tests among Refugees and Migrants in a Pilot Project in North-West Syria.

North-west Syria (NWS) is a conflict-affected and unstable area. Due to its limited health infrastructure, accessing advanced COVID-19 testing services is challenging. COVID-19 antigen rapid diagnostic tests (Ag-RDTs) have the potential to overcome this barrier. A pilot project was implemented to introduce Ag-RDTs in NWS, aiming to determine the feasibility, uptake, and results of Ag-RDTs and identify facilitators and barriers to testing with Ag-RDTs. A cross-sectional study design involving secondary analysis of data collected during the project was employed. A local non-governmental organization implemented 25,000 Ag-RDTs that were conducted cross-border by trained community health workers. In total, 27,888 eligible individuals were enrolled, 24,956 (89.5%) consented to test, and 121 (0.5%) were COVID-19-positive. The highest positivity was observed among those with severe COVID-19 symptoms (12.7%), with respiratory illnesses (2.5%), enrolled at hospitals in Afrin (2.5%), and healthcare workers (1.9%). A non-random sample of 236 individuals underwent confirmatory RT-PCR testing. Observed sensitivity, specificity, and positive and negative predictive values were 80.0%, 96.1%, 91.4%, and 90.3%, respectively. Challenges included obtaining informed consent and conducting confirmatory testing. Ag-RDTs represent a feasible screening/diagnostic tool for COVID-19 infections in NWS, with nearly 90% uptake. Embedding Ag-RDTs into COVID-19 testing and screening strategies would be highly beneficial.

Stress prediction of heated crude oil pipeline in permafrost region via fully coupled heat-moisture-stress numerical simulation and SVM algorithm

Large diameter crude oil transmission pipelines in unstable permafrost areas have been put into operation in China in recent dozen years. The perennial positive temperature operation of buried heating transmission pipelines leads to freeze–thaw of the soil around pipelines, and the axial stresses generated by thawing settlement of permafrost may induce fracture failure of weld crack. However, there are many shortcomings in existing frozen soil thawing settlement analysis and pipeline stress assessment methods, which makes it difficult to accurately analyze and predict the axial additional stress of pipelines induced by thawing settlement. Based on heat conduction and permafrost thawing consolidation settlement theory, numerical inversion analysis of centrifuge test was conducted to verify the accuracy of the finite element method. The key influencing factors such as wall thickness, insulation layer thickness, buried depth of pipe, and length of thawing settlement zone on the axial stress and strain state of buried pipeline under the condition of double pipe operation of Mo-da line were investigated. The results show that: Pipeline with an insulation layer, larger wall thickness and smaller buried depth is beneficial to improve the bearing capacity of buried pipeline under thawing settlement of permafrost. The axial stress varies nonlinearly with the increase of the thawing settlement zone length. Based on support vector regression (SVR) model, the axial stress prediction model of pipe crown and invert at different positions in the thaw settlement area was proposed and verified by field monitoring data of buried pipeline. The relative error between the prediction results and the field monitoring results is less than 15 %. This study can provide some theoretical support for the structural design of pipelines in thaw settlement area.