Low Gradient Research Articles

From Pre‐Darcy Flow to Darcy Flow in Porous Media: A Simple Unified Model

AbstractExtensive experiments have demonstrated that fluid flow in low‐permeability media deviates from Darcy's law at low pressure gradients, which is called pre‐Darcy flow. Although numerous pre‐Darcy flow models have been proposed, these models generally contain one or more empirical parameters with no clear physical meaning. In this paper, we present a simple unified model to describe pre‐Darcy flow in porous media by introducing the concept of loss permeability. The physical meaning of the loss permeability parameter and its relationship to permeability are analyzed. Based on the statistics of the loss permeability parameter results of 24 core samples, we found that there is a good positive correlation between the loss permeability parameter and the absolute permeability. A smaller loss permeability indicates a stronger fluid‐solid interaction and a stronger nonlinearity between the flow velocity and the pressure gradient. Taking a one‐dimensional linear unsteady flow of a slightly compressible fluid in a homogeneous porous medium as an example, we solve the pressure diffusion equation based on the proposed model using a finite difference method. Our results demonstrate that the rate of pressure propagation for pre‐Darcy flow is slower than that for Darcy flow for the entire observation period, which corrects previous conclusions. This study is highly important for improving the understanding of fluid flow in low‐permeability media.

Statistical Interdependence between Daily Precipitation and Extreme Daily Temperature in Regions of Mexico and Colombia.

We study the statistical interdependence between daily precipitation and daily extreme temperature for regions of Mexico (14 climatic stations, period 1960-2020) and Colombia (7 climatic stations, period 1973-2020) using linear (cross-correlation and coherence) and nonlinear (global phase synchronization index, mutual information, and cross-sample entropy) synchronization metrics. The information shared between these variables is relevant and exhibits changes when comparing regions with different climatic conditions. We show that precipitation and temperature records from La Mojana are characterized by high persistence, while data from Mexico City exhibit lower persistence (less memory). We find that the information exchange and the level of coupling between the precipitation and temperature are higher for the case of the La Mojana region (Colombia) compared to Mexico City (Mexico), revealing that regions where seasonal changes are almost null and with low temperature gradients (less local variability) tend to display higher synchrony compared to regions where seasonal changes are very pronounced. The interdependence characterization between precipitation and temperature represents a robust option to characterize and analyze the collective dynamics of the system, applicable in climate change studies, as well as in changes not easily identifiable in future scenarios.

Screening, Synthesis, and Characterization of a More Rapidly Dissolving Celecoxib Crystal Form.

The prevalence of poor solubility in active pharmaceutical ingredients (APIs) such as celecoxib (CEL) is a major bottleneck in the pharmaceutical industry, leading to a low concentration gradient, poor passive diffusion, and in vivo failure. This study presents the synthesis and characterization of a new cocrystal of the API CEL. CEL is a nonsteroidal anti-inflammatory drug used for the treatment of osteoarthritis and rheumatoid arthritis. Computational screening was completed for CEL against a large library of generally recognized as safe (GRAS) coformers, based on molecular complementarity and hydrogen bond propensity (HBP). The generated list of 17 coformers with a likelihood for cocrystallization with CEL were experimentally screened using four techniques: liquid-assisted grinding (LAG), solvent evaporation (SE), gas antisolvent crystallization (GAS), and supercritical enhanced atomization (SEA). One new crystalline form was isolated, employing the liquid coformer N-ethylacetamide (NEA). This novel form, celecoxib-di-N-ethylacetamide (CEL·2NEA), was characterized by a variety of different techniques. The crystal structure was determined through single-crystal X-ray diffraction. Both NEA molecules are evolved from the crystal structure at a desolvation temperature of approximately 65 °C. The CEL·2NEA cocrystal exhibited a dissolution rate, with more than a twofold improvement in comparison to as-received CEL after only 15 min.

Kryteria projektowania sieci dróg rowerowych z wykorzystaniem GIS, niwelacji topograficznej i analizy przestrzennej

The current need for the creation of cycleways in traditional cities often presents problems. Converting existing roads into cycleways frequently creates serious traffic issues without leading to the expected increase in bicycle use. In order to overcome some of these problems, this paper presents a composite methodology using GIS, topographic levelling and spatial analysis. Upon application of this methodology in a case study in the city of Patras, Greece, problems with the city’s existing, recently-constructed cycleway are identified. After applying topographical, qualitative and population criteria, an alternative network of cycleways is proposed. This proposed new network does not create traffic congestion, as the basic criterion for selecting roads is their low traffic load. At the same time, topographic leveling is employed to select routes with a very low gradient (<2%), which is a determining factor in making the network attractive to users. Using spatial analysis, the network is spread in order to serve all areas of the city, making it available to the vast majority of residents. Finally, the findings of a social research poll (through the use of a questionnaire) indicate that the creation of such a network could increase bicycle use by a factor of up to18, which would make bicycles the main mode of transport for 22% of residents.

Dual-channel end-to-end network with prior knowledge embedding for improving spatial resolution of magnetic particle imaging

Magnetic particle imaging (MPI) is an emerging non-invasive medical imaging tomography technology based on magnetic particles, with excellent imaging depth penetration, high sensitivity and contrast. Spatial resolution and signal-to-noise ratio (SNR) are key performance metrics for evaluating MPI, which are directly influenced by the gradient of the selection field (SF). Increasing the SF gradient can improve the spatial resolution of MPI, but will lead to a decrease in SNR. Deep learning (DL) methods may enable obtaining high-resolution images from low-resolution images to improve the MPI resolution under low gradient conditions. However, existing DL methods overlook the physical procedures contributing to the blurring of MPI images, resulting in low interpretability and hindering breakthroughs in resolution. To address this issue, we propose a dual-channel end-to-end network with prior knowledge embedding for MPI (DENPK-MPI) to effectively establish a latent mapping between low-gradient and high-gradient images, thus improving MPI resolution without compromising SNR. By seamlessly integrating MPI PSF with DL paradigm, DENPK-MPI leads to a significant improvement in spatial resolution performance. Simulation, phantom, and in vivo MPI experiments have collectively confirmed that our method can improve the resolution of low-gradient MPI images without sacrificing SNR, resulting in a decrease in full width at half maximum by 14.8%–23.8 %, and the accuracy of image reconstruction is 18.2 %–27.3 % higher than other DL methods. In conclusion, we propose a DL method that incorporates MPI prior knowledge, which can improve the spatial resolution of MPI without compromising SNR and possess improved biomedical application.

Landscape Ecological Risk and Drivers of Land-Use Transition under the Perspective of Differences in Topographic Gradient

Human activities have caused different degrees of land-use change on different topographic gradients, with impacts on the landscape and ecosystem. Effectively preventing and addressing ecological risk (ER) and achieving harmonious coexistence between humans and nature are important aspects of sustainable development. In this study, we used Gansu Province as an example, adopted five periods of land-use data in 1980, 1990, 2000, 2010 and 2020, and used the geoinformatic Tupu method and the terrain distribution index to study land-use changes under different topographic gradients, and then constructed the landscape ecological risk assessment (LERA) model based on the landscape pattern index to analyze landscape ecological risk (LER) spatiotemporal changes under different topographic gradients, and finally explored the LER driving factors using the geodetector model. The results showed that (1) the dominant land-use types were unused land and grassland, accounting for approximately 74% of the land. The situation of transferring and changing each type was more drastic. The distribution and changes in cropland and built-up land were easily found in low topographic gradient areas with low elevations and small slopes; the distribution and changes in woodland, grassland and water areas were easily found in high topographic gradient areas with high elevations and large slopes. (2) The landscape ecological risk index (LERI) was 0.018, 0.019, 0.019, 0.019 and 0.020, respectively, with spatial expressions of high in the northwest and low in the southeast. Low LER was concentrated in high topographic gradient ecological reserves; high LER was concentrated in low topographic gradient human interference areas and high topographic gradient natural environmental complex areas. (3) Natural factors mainly acted on the LER on moderate and high topographic position gradients; socioeconomic factors mainly acted on the LER on low topographic position gradients. Human interference interacted with natural factors more than human interference alone on LER. This study can provide a scientific basis for ensuring ecological security and sustainable development in areas with complex topography and geomorphology.

Cerenkov free micro-dosimetry in small-field radiation therapy technique

Objective. Optical fiber-based scintillating dosimetry is a recent promising technique owing to the miniature size dosimeter and quality measurement in modern radiation therapy treatment. Despite several advantages, the major issue of using scintillating dosimeters is the Cerenkov effect and predominantly requires extra measurement corrections. Therefore, this work highlighted a novel micro-dosimetry technique to ensure Cerenkov-free measurement in radiation therapy treatment protocol by investigating several dosimetric characteristics. Approach. A micro-dosimetry technique was proposed with the performance evaluation of a novel infrared inorganic scintillator detector (IR-ISD). The detector essentially consists of a micro-scintillating head based on IR-emitting micro-clusters with a sensitive volume of 1.5 × 10−6 mm3. The proposed system was evaluated under the 6 MV LINAC beam used in patient treatment. Overall measurements were performed using IBATM water tank phantoms by following TRS-398 protocol for radiotherapy. Cerenkov measurements were performed for different small fields from 0.5 × 0.5 cm2 to 10 × 10 cm2 under LINAC. In addition, several dosimetric parameters such as percentage depth dose (PDD), high lateral resolution beam profiling, dose linearity, dose rate linearity, repeatability, reproducibility, and field output factor were investigated to realize the performance of the novel detector. Main results. This study highlighted a complete removal of the Cerenkov effect using a point-like miniature detector, especially for small field radiation therapy treatment. Measurements demonstrated that IR-ISD has acceptable behavior with dose rate variability (maximum standard deviation ∼0.18%) for the dose rate of 20–1000 cGy s−1. An entire linear response (R 2 = 1) was obtained for the dose delivered within the range of 4–1000 cGy, using a selected field size of 1 × 1 cm2. Perfect repeatability (max 0.06% variation from average) with day-to-day reproducibility (0.10% average variation) was observed. PDD profiles obtained in the water tank present almost identical behavior to the reference dosimeter with a build-up maximum depth dose at 1.5 cm. The small field of 0.5 × 0.5 cm2 profiles have been characterized with a high lateral resolution of 100 µm. Significance. Unlike recent plastic scintillation detector systems, the proposed micro-dosimetry system in this study requires no Cerenkov corrections and showed efficient performance for several dosimetric parameters. Therefore, it is expected that considering the detector correction factors, the IR-ISD system can be a suitable dose measurement tool, such as in small-field dose measurements, high and low gradient dose verification, and, by extension, in microbeam radiation and FLASH radiation therapy.

The Hydraulic Evolution of Groundwater-Fed Pit Lakes After Mine Closure.

Open pit mining frequently requires regional water tables to be lowered to access ore deposits. When mines close, dewatering ceases allowing the water table to recover. In arid and semi-arid mining regions, the developing pit lakes are predominantly fed by groundwater during this recovery phase and pit lakes develop first into "terminal sinks" for the surrounding groundwater system. With time, the re-establishment of regional hydraulic gradients can cause pit lakes to develop into throughflow systems, in which pit lake water outflows into adjacent aquifers. In this study, we use numerical groundwater modeling to aid process understanding of how regional hydraulic gradients, aquifer properties, net evaporation rates, and pit geometry determine the hydraulic evolution of groundwater-fed pit lakes. We find that before the recovery of the regional water table to its new equilibrium, pit lakes frequently transition to throughflow systems. Throughflow from pit lakes to downstream aquifers can develop within two decades following cessation of dewatering even under low hydraulic gradients (e.g., 5 × 10-4) or high net evaporation rates (e.g., 2.5 m/year). Pit lakes remain terminal sinks only under suitable combinations of high evaporation rates, low hydraulic gradients, and low hydraulic conductivities. In addition, we develop an approximate analytical solution for a rapid assessment of the hydraulic status of pit lakes under steady-state conditions. Understanding whether pit lakes remain terminal sinks or transition into throughflow systems largely determines the long-term water quality of pit lakes and downstream aquifers. This knowledge is fundamental for mine closure and planning post-mining land use.

Snowpack variations and their hazardous effects under climate warming in the central Tianshan Mountains

Climate change alters snowpack evolution, which in turn influences the likelihood of snow avalanches and flood risks. The lack of systemic observational data on key snow characteristics in high mountains remains a scientific challenge in terms of systematically elucidating the dynamic chain of variations in climate–snowpack–snow disasters. This restricts our understanding and poses challenges in the prediction of snow-related disaster risks. As such, this study analysed the variations of temperature and snowfall and the physical characteristics of snowpacks based on ground-based observations from the Kunse River Valley situated in the Tianshan Mountains from 1967 to 2021. The results reveal that the temperature increased significantly by 0.32 °C per decade (p < 0.01) during the snow season, along with more extreme snowfall events. The snow-cover duration was observed to have been shortened by 4.77 d per decade (p < 0.01) from 1967 to 2021, which is characterised by later snow-cover onset and earlier snowmelt. Concurrently, average and maximum snow depths increased along with an increase in peak snow water equivalent, thus indicating a higher frequency of extremely scarce or abundant snow years. The low snowpack temperature gradient and earlier snowmelt dates in spring lead to earlier occurrences of snowmelt floods and wet avalanches. As the risks of these events increase, they pose greater threats to farmlands, road transportation, water–electricity infrastructure and several other human activities. Therefore, these insights are critical for providing vital information that can deepen our understanding of the impact of climate change on snowpack characteristics and improve management strategies for snow-related disaster prevention and mitigation.

Stroke volume index (SVI) predicts all-cause mortality following transcatheter aortic valve replacement (TAVR)

BackgroundLeft ventricular systolic dysfunction in patients with severe aortic stenosis (AS) may result in low transvalvular gradients and underestimation of AS severity. A low-flow state may occur with reduced LVEF. Little is known about the implications of low compared to normal flow in patients with reduced LVEF undergoing transcatheter aortic valve replacement (TAVR). ObjectivesWe compared survival rates with degree of flow across stenosed aortic valves and left ventricular dysfunction. We hypothesized that the stroke volume index (SVI) offers essential information regarding survival following TAVR. MethodsWe retrospectively reviewed patients with LVEF <50 % undergoing TAVR at the Gates Vascular Institute in Buffalo, New York, from 2012 to 2017. We performed Receiver Operator Characteristics to examine the value of SVI in predicting the postoperative outcome of patients. Kaplan-Meier and Cox regression analyses were used to investigate the effect of a low-flow state on five-year survival in patients with systolic dysfunction undergoing TAVR. ResultsFive-year survival following TAVR was decreased in patients with low-flow AS (SVI <35 mL/m2) compared to patients with normal flow. Seventy-four percent (n = 50) of patients with low-flow compared to 43 % (n = 22) of patients with normal flow were deceased five years post-TAVR (p ≤0.001). ROC curve indicated SVI to be a clinical predictor of five year survival (AUC 0.732, 95 % CI: 0.641–0.823, p < 0.001). ConclusionPatients with systolic dysfunction and low transvalvular flow AS had increased mortality five years following TAVR. These findings highlight a better prognosis in patients with normal flow and LV systolic dysfunction. Condensed abstractLow-flow aortic stenosis can occur with reduced left ventricular function. We compared survival rates of patients with known reduced left ventricular function in low-flow and normal flow aortic stenosis. This retrospective single-center study examined mortality rates following transcatheter aortic valve replacement. The mean gradient was not a predictor of mortality. This study shows patients with low-flow aortic stenosis have decreased five-year survival following valve replacement.

Insights into the development of small-volume long lava flows: A case study of the Coalstoun Lakes Volcanic Field, southeast Queensland, Australia

Long lava flows exceeding 50 km in length are usually produced during large-volume flood basalt eruptions (>100 to 10,000 km3) but can also occur from small to moderate-volume (<30 km3) basaltic eruptions in continental intraplate monogenetic volcanic fields. Eruptive volume, therefore, is not an a priori barrier to producing long lava flows. Key factors that promote long lava flows include efficient lava transport systems that minimise heat loss, long-lived and sustained effusion rates to maintain flow advancement, and lava flow across low topographic gradients (<1°-10°) with minimal topographic barriers.Here, we focus on an anomalously young and poorly studied basaltic monogenetic volcanic field in southeast Queensland, Australia, that formed part of the broader intraplate volcanism in eastern Australia since the Late Cretaceous. The Coalstoun Lakes Volcanic Field (CLVF) comprises three lava fields: the Barambah Basalt Flow Field, the Deep Creek Flow Field and the Hunters Hill Flow Field. Basalt from the Barambah Basalt Flow Field has been redated here by Ar40/Ar39 analysis of groundmass material, yielding a weighted mean age of 0.520 ± 0.016 Ma. The Barambah Basalt Flow Field contains most of the eruptive volume and has advanced up to 165 km from the vent. The Hunters Hill and the Deep Creek flow fields are comparatively smaller in volume and have advanced ∼30 and ∼ 20 km from the vent, respectively. Lava tubes are only known from proximal regions and do not appear to be a significant factor in promoting long run-out in the CLVF. Flow confinement and utilisation of existing drainage networks are features of both lava flow fields, and advancement down the sand-based and ephemeral Burnett River significantly promoted long run-out despite low topographic gradients.New whole-rock geochemical data on our CLVF samples indicates that all lavas are hawaiites, a common feature of other Quaternary long lava flows globally. Overall, there is some compositional variation, but a cryptic zonation is readily apparent in trace element abundances, which helps to further distinguish the flow fields as the products of separate but closely spaced eruptions. The combination of field and geochemical data indicates that the long lava flow of the Barambah Basalt Flow Field resulted from a sustained and relatively low effusion eruption, creating a pāhoehoe flow field that continuously advanced across the landscape, utilising a drainage system that guided lava flow and helped to circumvent any topographic barriers.

Impact of Elevated Gradients After Transcatheter Aortic Valve Implantation for Degenerated Surgical Aortic Valve Bioprostheses.

Elevated aortic valve gradients are common after transcatheter aortic valve implantation for degenerated surgical aortic valve replacement bioprostheses, but their clinical impact is uncertain. A total of 12 122 patients who underwent transcatheter aortic valve implantation-in-surgical aortic valve replacement from November 2011 to December 2019 in the Society of Thoracic Surgery/American College of Cardiology Transvalvular Therapeutics Registry were included. The primary outcome was a composite of 1-year all-cause mortality, stroke, myocardial infarction, or valve reintervention. Secondary outcomes included 1-year all-cause mortality, readmission, and change from baseline 12-question self-administered Kansas City Cardiomyopathy Questionnaire-Overall Summary Score. Due to nonlinearity observed with restricted cubic splines analysis, a Cox regression analysis with aortic valve mean gradient modeled as a spline-continuous variable (with 20 mm Hg as a cutoff) was used to study the 1-year composite outcome and mortality. The composite outcome occurred most frequently in patients with aortic valve mean gradient ≥30 and <10 mm Hg, as compared with those with 10 to 20 and 20 to 30 mm Hg ranges (unadjusted rates, 13.9%, 12.1%, 7.5%, and 6.5%, respectively; P=0.002). When the mean aortic valve gradient was ≥20 mm Hg, higher gradients were associated with greater risk of the 1-year composite outcome (adjusted hazard ratio, 1.02 [1.02-1.03] per mm Hg; P<0.001) and 1-year mortality (adjusted hazard ratio, 1.02 [1.00-1.03] per mm Hg; P=0.007). Whereas when the mean aortic valve gradient was <20 mm Hg, higher gradients were not significantly associated with the composite outcome (adjusted hazard ratio, 0.99 [0.98-1.003] per mm Hg; P=0.12) but were associated with lower 1-year mortality (adjusted hazard ratio, 0.98 [0.97-0.99] per mm Hg; P=0.007). The relationship between postprocedural aortic valve mean gradient after transcatheter aortic valve implantation-in-surgical aortic valve replacement and clinical outcomes is complex and nonlinear, with relatively greater adverse events occurring at low and high gradient extremes. Further study of factors mediating the relationship between postprocedural gradients and clinical outcomes, including low-flow states, is necessary.

Diagnostic Challenges in Aortic Stenosis.

Aortic stenosis (AS) is the most prevalent degenerative valvular disease in western countries. Transthoracic echocardiography (TTE) is considered, nowadays, to be the main imaging technique for the work-up of AS due to high availability, safety, low cost, and excellent capacity to evaluate aortic valve (AV) morphology and function. Despite the diagnosis of AS being considered straightforward for a very long time, based on high gradients and reduced aortic valve area (AVA), many patients with AS represent a real dilemma for cardiologist. On the one hand, the acoustic window may be inadequate and the TTE limited in some cases. On the other hand, a growing body of evidence shows that patients with low gradients (due to systolic dysfunction, concentric hypertrophy or coexistence of another valve disease such as mitral stenosis or regurgitation) may develop severe AS (low-flow low-gradient severe AS) with a similar or even worse prognosis. The use of complementary imaging techniques such as transesophageal echocardiography (TEE), multidetector computed tomography (MDTC), or cardiac magnetic resonance (CMR) plays a key role in such scenarios. The aim of this review is to summarize the diagnostic challenges associated with patients with AS and the advantages of a comprehensive multimodality cardiac imaging (MCI) approach to reach a precise grading of the disease, a crucial factor to warrant an adequate management of patients.

Quaternary tectonic and climatic forcing on the spatio-temporal evolution of the Meuse fluvial terrace staircase

The Quaternary is characterized by pronounced alterations between cold and warm climatic states, with the Mid-Pleistocene Transition marking a strong increase in the intensity of cold-climate conditions. River systems are sensitive to environmental perturbation (e.g., climate, tectonics, base level) and are expected to respond to such profound changes. This study uses a combination of terrace mapping and analysis of a dense borehole database to investigate the Meuse terrace staircase (and its deposits), and gain insight on how it reflects climatic and tectonic perturbations during the Quaternary. The lower reaches of the Meuse river, which has both its main water and sediment source in the Ardennes displays a well-developed terrace staircase that was sculpted mainly throughout the Quaternary. The staircase is located near the cities of Maastricht (southern Netherlands) and Liège (northwestern Belgium). About 30 terrace levels reflect signals of environmental perturbations in the lithological composition, gradients, thicknesses, and spatial distribution. The terraces are organized in groups, based on their morphological position, from old to young; these are the East Meuse terrace group and West Meuse High-, Middle- and Low terrace groups. Our findings show a consistent increase in the gravel content from older to younger terraces. The sandier composition of the deposits of the oldest terraces (Early Pleistocene) is closely related to the supply of the Miocene-Pliocene weathered material from the Ardennes. Younger terraces (Middle and Late Pleistocene) are much richer in gravel, evidencing sediment input from fresh or partially weathered bedrock. These changes point to a downstream migration of the gravel front throughout the Quaternary. The mean thickness of the terrace groups shows a slight increase, even though the same trend is not clear when each terrace is analyzed on an individual basis. The anomalous thickness of the Caberg 1 terrace suggests increased sediment input during the cold climatic conditions of the Elsterian (MIS 12), the first Quaternary glacial during which an ice sheet extended into the northern Netherlands. Reconstruction of terrace gradients reveals that older East Meuse terraces show a (reversed) gradient opposite to reconstructed palaeo flow directions, which is attributed to a combination of low gradients during terrace formation and footwall back-tilting of the Feldbiss Fault Zone. In our analysis we do not see clear evidence for the imprint of the Mid-Pleistocene Transition, which suggests that due to its gradual nature, its signal is either buffered or assimilated by the overall climatic signal of the Quaternary. This study offers a first complete temporal analysis of the Meuse terrace staircase, providing an important basis for better understanding the effects of Quaternary climatic change and tectonics, and their resulting effects in other river systems worldwide.

Effect of Altitude Gradients on the Spatial Distribution Mechanism of Soil Bacteria in Temperate Deciduous Broad-Leaved Forests.

Soil bacteria are an important part of the forest ecosystem, and they play a crucial role in driving energy flow and material circulation. Currently, many uncertainties remain about how the composition and distribution patterns of bacterial communities change along altitude gradients, especially in forest ecosystems with strong altitude gradients in climate, vegetation, and soil properties. Based on dynamic site monitoring of the Baiyun Mountain Forest National Park (33°38'-33°42' N, 111°47'-111°51' E), this study used Illumina technology to sequence 120 soil samples at the site and explored the spatial distribution mechanisms and ecological processes of soil bacteria under different altitude gradients. Our results showed that the composition of soil bacterial communities varied significantly between different altitude gradients, affecting soil bacterial community building by influencing the balance between deterministic and stochastic processes; in addition, bacterial communities exhibited broader ecological niche widths and a greater degree of stochasticity under low-altitude conditions, implying that, at lower altitudes, community assembly is predominantly influenced by stochastic processes. Light was the dominant environmental factor that influenced variation in the entire bacterial community as well as other taxa across different altitude gradients. Moreover, changes in the altitude gradient could cause significant differences in the diversity and community composition of bacterial taxa. Our study revealed significant differences in bacterial community composition in the soil under different altitude gradients. The bacterial communities at low elevation gradients were mainly controlled by stochasticity processes, and bacterial community assembly was strongly influenced by deterministic processes at middle altitudes. Furthermore, light was an important environmental factor that affects differences. This study revealed that the change of altitude gradient had an important effect on the development of the soil bacterial community and provided a theoretical basis for the sustainable development and management of soil bacteria.

CARDIOGENIC SHOCK IN A PATIENT WITH SEVERE AORTIC VALVE STENOSIS AND MULTIVESSEL CORONARY DISEASE: ADVANCED THERAPEUTIC STRATEGIES

Abstract We describe a case of a 58 years old man. He was referred to emergency room for episodes of vomiting and epigastric pain for about a week. Upon admission he was confused with systolic–diastolic blood pressure values ​​70/40 mmHg, heart rate 120 bpm, sinus rhythm. pO2 was 80 mmHg and SO2 in air 97%. Lactate values 10, blood sugar &amp;gt; 300 mg/dl. The electrocardiogram showed sinus tachycardia with the results of antero–septal necrosis and incomplete left bundle branch block. The fast echocardiogram showed a dilated left ventricle with severe depression of the ejection fraction (EF about 10–15%), severe low flow–low gradient aortic valve stenosis (AVA bidimensional was approximately 0.9 cm²), severe mitral valve insufficiency due to a dual mechanism. The dimension of Inferior vena cava was 1.5 cm, collapsible. There was thrombotic stratification in the apex of the left ventricle and VA coupling was 2. The patient was admitted to the ICU with stage C cardiogenic shock according to SCAI classification. We found a value of PVC 3 mmHg. After fluide challenge there was an increase in blood pressure values to 100/60 mmHg. Noradrenaline vasopressor was started and subsequently a low dose of adrenaline. Blood pressure values maintained around 90/60 mmHg and undergo a sudden drop after increasing the dosage of the vasopressor. Diuresis was approximately 50 ml/h, lactates clear completely after approximately 4 hours. After 6 hours, due to a new sudden reduction in blood pressure, the patient was referred for IABP and coronary angiography control. In the context of multivessel coronary artery disease and cardiogenic shock he was therefore a candidate for urgent cardiac surgery of aortic valve replacement, by–pass and mitral anulovalvuloplasty. This case gave us the opportunity to analyze how to proceed in such a critical conditions with the below conclusions: a) the choice of vasopressors and inotropes is limited in case of severe aortic valve stenosis b) the presence of left ventricular intracavitary thrombosis limits the choice of ventricular assistance system c) in case of cardiogenic shock and severe aortic valve stenosis the patient must be a candidate for valve replacement surgery as soon as possible.

Analysis of time-dependent bearing capacity of pile foundation in marine soft soil region considering non-Darcy flow

Due to the deviation of pore water seepage in marine soft soils from Darcy flow under low hydraulic gradients, existing methods face challenges in accurately calculating the time-dependent bearing capacity of piles in such areas. This paper adopts the secondary development of Python to ABAQUS and employs a continuous coupling analysis method to establish a numerical model capable of simultaneously solving the large deformation of pile driving and non-Darcy flow. The model addresses issues such as mesh distortion during pile driving and the numerical implementation of three-dimensional non-Darcy flow. The accuracy of the model was verified through comparison with two experimental cases. Subsequently, the study analyzed how non-Darcy flow affects soil consolidation around the pile and the time-dependent bearing capacity of pile. Results indicate that when the permeability coefficient of the soil around the pile is less than 1 × 10−7 m/s, non-Darcy flow significantly delays the consolidation of soil within three times the pile diameter around the pile, thereby reducing the time-dependent bearing capacity of pile, with a greater impact observed for lower permeability coefficients of the soil. Once the soil around the pile reaches 90% consolidation, subsequent construction can proceed to shorten the project duration while maintaining safety.

Plane and vertical design research on end-around taxiways at high plateau airports

The end-around taxiways have been proven to effectively reduce the risk of runway incursions caused by frequent aircraft crossings on closely spaced parallel runways, thus enhancing airport capacity. This practice has gained popularity in recent years, especially in large airports. However, there is currently limited experience in designing and operating end-around taxiways, particularly in high plateau airports facing challenging conditions such as a high water table and low obstacle clearance gradient. In this paper, we present a case study of the second runway project at a specific airport and propose various operational schemes for end-around taxiway construction, including straight, oblique, and controlled designs. We calculate aircraft payload under different obstacle clearance gradients using flight performance analysis. Taking into account both operational and groundwater levels, we determine the appropriate plane and vertical design of end-around taxiways. The findings of this research provide valuable references for the design of end-around taxiways.

High- versus low-gradient aortic stenosis: Is our evaluation limited by aorto-mitral angle on cardiovascular CT?

BackgroundAccurate assessment of aortic valve (AV) stenosis (AS) on transthoracic echocardiogram is crucial for appropriate clinical management. However, discordance between aortic valve area (AVA) and Doppler can complicate the diagnosis of severe AS in low-gradient (LG) AS phenotypes. MethodsWe reviewed 220 consecutive patients with suspected severe AS and AVA ≤1.0 cm2 on transthoracic echocardiogram who were evaluated for transcatheter AV replacement (TAVR) within a large health system from 2015 to 2019. We compared AV calcium score and aorto-mitral angle (AMA) on 3-chamber views from ECG-gated cardiovascular CT among patients with high-gradient (HG) AS (N = 19), paradoxical low-flow low-gradient (PLFLG) AS (N = 24) and normal-flow low-gradient (NFLG) AS (N = 14). ResultsAll groups had comparable age, comorbidities, and AV calcium scores. Compared to patients with HG AS (mean AMA 120 ± 10°), those with PLFLG AS (104 ± 12°; p < 0.001) and NFLG AS (106 ± 13°; p = 0.008) had narrower mean AMA values on cardiovascular CT. ConclusionLG AS patients have significantly narrower AMA than HG AS patients on cardiovascular CT. Due to difficulty obtaining parallel Doppler alignment, narrower AMA may contribute to AVA-Doppler discordance on echocardiogram. These findings emphasize the need for additional information in the setting of LG AS.

Manipulation and diagnosis of femtosecond relativistic electron bunch using terahertz-driven resonators

Using strong electromagnetic fields generated by lasers to interact with electrons for precise diagnosis and manipulation of electron beams represents a recent focal point in accelerator technology. This approach surpasses the limitations of conventional RF technology, such as low electric field gradients and timing jitters, effectively enhancing the accuracy of ultrafast electron beam diagnostics and manipulations. As demands for precision continue to rise, the precise diagnosis of crucial parameters of ultrafast electron beams remains challenging. This study delves into the electromagnetic behavior of THz-driven devices and proposes an all-optical method utilizing single-cycle THz radiation to compress and characterize a 3 MeV electron beam. Particle tracking simulations demonstrate an astonishing compression effect, reducing the bunch length from 54.0 fs to 4.3 fs, and achieving sub-femtosecond bunch length measurement resolution. Moreover, when combined with an orthogonal THz streak camera, this method shows even greater potential in multi-bunch scenarios.