Abstract
Face stability is a critical issue in the stability analysis of tunnels, especially in soft soils and crushed rock masses. In this paper, considering two three-dimensional collapse ...mechanisms, upper-bound solutions are presented for determining the face pressure of deep and shallow tunnels excavated in rock masses. The Hoek–Brown failure criterion was considered for the rock mass surrounding the tunnel. The proposed upper-bound formulations were compared with three-dimensional finite-element simulations and also with centrifuge test results available in the literature. The obtained results showed that the face pressure decreases with increasing σci, mi, and geological strength index. Besides, increasing the tunnel diameter and the rock mass density led to an increase in the face pressure, where for larger tunnels, the effect of the density became more pronounced. Finally, some charts were presented to specify the range of applicability of the concepts of deep and shallow tunnels. The results obtained from these charts demonstrated that the reduction in the Hoek–Brown parameters of the rock mass results in spreading the collapse mechanism from the tunnel face to the ground surface.
Different sensing methods provide valuable information for comprehensive monitoring strategies, which are crucial for the ecological management of lakes and watersheds. Subsequently, the resulting ...spatio-temporal information can be considered the fundamental knowledge for the water resources management of watersheds. Lake Urmia is deemed one of the most important aquatic habitats in Iran. It has been experiencing significant changes during recent years due to climate change, anthropogenic activities, and a lack of coherent management approaches. Hence, awareness of the hydro-ecological factors during the last few decades is critical for identifying the problems. In this research, the impacts of changes in key parameters such as precipitation, evapotranspiration, water surface temperatures, suspended sediment concentration, saline features, and vegetation are explored using satellite imagery. The primary purpose of this study is to evaluate the Lake Urmia crisis concerning human-involved and climate factors such as the agriculture sector and construction of the causeway. In this regard, a limbic-based Emotional Artificial Neural Network (EANN) is developed as a non-linear universal mapping and implemented for the first time to demonstrate the interactions between the considered hydro-ecological factors and the sensitivity of the two indicators the lake health. Providing a comprehensive spatio-temporal analysis is another objective of this study to detect the onset of deterioration in the parameters. The values of the efficiency criteria were measured to evaluate the sensitivity of the EANN models to the related inputs. The results of the model in scenario 4 with evapotranspiration, precipitation, runoff and vegetation as input variables led to higher performance with the best efficiency criteria, including DC = 0.868 and RMSE = 0.096. The quantitative results confirm that the combination of both climate and anthropogenic factors, including the agricultural sector's overdraft, leads to the most efficient EANN model and, consequently, is considered the leading cause of the crisis.
Objective
To evaluate the diagnostic accuracy of split-bolus single-scan computed tomography angiography (CTA) protocol for evaluation of acute mesenteric ischemia and alternate diagnoses.
Materials ...and methods
In this IRB-approved, HIPAA-compliant retrospective study, consecutive patients from 21 October 2016 to 6 May 2018 evaluated for mesenteric ischemia with split-bolus CTA (a single scan in concurrent arterial and portal venous phase) in a single tertiary academic institution were included. Intravenous contrast was administered on weight-based basis. Quantitative and qualitative assessments of superior mesenteric artery (SMA) and superior mesenteric vein (SMV) attenuation and patency were performed by two independent reviewers. CT imaging findings were correlated with clinical reference outcomes.
Results
One hundred fifty-four patients (age 66.3 ± 14.1 years, BMI 27.3 ± 6, 86 (56%) female) were included. CTA studies were performed with a volumetric CT dose index of 15.9 ± 5.5 mSv and dose length product of 1042.9 ± 389.4 mGy cm. Average intravenous contrast volume administered was 164.3 ± 12.1 cc. SMA attenuation was 263.6 ± 92.4HU, SMV was 190 ± 50.2HU. Qualitative assessment of SMA and SMV showed good opacification in all patients. 17/154 (11%) patients were diagnosed on CT with mesenteric ischemia; in 6/154 (4%), CTA studies were indeterminate; in 131/154 (85%), CTA confidently ruled out mesenteric ischemia. Alternate diagnoses were made in 38/154 (25%) patients. Using composite clinical outcomes as a reference standard, sensitivity of split-bolus CTA protocol for diagnosis of mesenteric ischemia is 100% (95% CI 79–100%), and specificity is 99% (95% CI 96–100%).
Conclusions
Split-bolus CTA has high sensitivity and specificity for diagnosis of acute mesenteric ischemia.
Key Points
• Split-bolus CTA protocol for mesenteric ischemia has great diagnostic accuracy with lower radiation exposure and fewer images to interpret compared with standard multiphasic CTA.
Due to the importance of surface and subsurface settlements to prevent damages to building foundations and sensitive structures in the urban cities, in this study, the ABAQUS finite element software ...has used to conduct a series of numerical modeling analysis on ground surface settlement caused from the asynchronous excavation of twin-tunnel. The effects of tunnel diameter, center-to-center tunnel spacing, and tunnel depth are discussed in detail and the shape of the surface settlement curves is also plotted. The numerical modeling has been verified by the results of three sequential twin-tunneling centrifuge tests conducted by the City University of London with 94.22%, 98.71% and 99.56% accuracy, respectively. Based on the results of this study, reducing the tunnel diameter decreases the amount of the maximum ground surface settlements and reducing the depth of tunnels and the distance between twin-tunnel to less than 2D (D is the diameter of the tunnels) increase the maximum surface settlements. Installation of 30 cm of tunnel lining can decrease the maximum ground surface settlement up to almost 79%.
Earthquakes of large magnitudes cause fault ruptures propagation in soil layers and lead to interactions with subsurface and surface structures. The emergence of fault ruptures on or adjacent to the ...position of existing tunnels cause significant damage to the tunnels. The objective of this paper is to study the interaction of an embedded tunnel within a soil layer and the soil deformations imposed upon by normal faulting. A centrifuge modeling under 80-g acceleration was conducted to investigate the rupture propagation pattern for different relative tunnel positions. Compared with the free field condition, due to tunnel and normal fault rupture interactions, focused on soil relative density and tunnel rigidity in this research, found that they can dramatically modify the rupture path depending on the tunnel position relative to the fault tip. The tunnel diverts the rupture path to its sides. This study presents the normal fault-tunnel interaction with the tunnel axis parallel to the normal fault line, to examine the changes that take place in fault rupture plane locations, the vertical displacement of the ground surface with tunnel presence and the effect of tunnel rigidity and soil density on fault tunnel interaction.
This research proposes a novel nature-based design of a new concrete armour unit for the cover layer of a rubble-mound breakwater. Armour units are versatile with respect to shape, orientation, ...surface condition details, and porosity. Therefore, a detailed analysis is required to investigate the exact state of their hydraulic interactions and structural responses. In this regard, the performance results of several traditional armour units, including the Antifer cube, Tetrapod, X-block and natural stone, are considered for the first step of this study. Then, the related observed results are compared with those obtained for a newly designed (artificial coral) armour unit. The research methodology utilizes the common wave flume test procedure. Furthermore, several verified numerical models in OpenFOAM code are used to gain the extra required data. The proposed armour is configured to provide an effective shore protection as an environmental-friendly coastal structure. Thus it is designed with a main trunk including deep grooves to imitate the typical geometry of a coral type configuration, so as to attain desirable performance. The observed results and an analytic hierarchy process (AHP) concept are used to compare the hydraulic performance of the studied traditional and newly proposed (artificial coral) armour units. The results indicate that the artificial coral armour unit demonstrates acceptable performance. The widely used traditional armour units might be replaced by newer designs for better wave energy dissipation, and more importantly, for fewer adverse effects on the marine environment.
Conventional design of pier structures is based on the assumption of fully rigid joints. In practice, the real connections are semi-rigid that cause changes in dynamic characteristics. In this study, ...quality of the joints is investigated by considering changes in natural frequencies. For this purpose, numerical and experimental modal analyses are carried out on related physical model of a pier type structure. When numerical results are evaluated, natural frequencies generally do not match the expected experimental results. Uncertainties in different aspects of engineering problems are always a challenge for researchers. The numerical models which are constructed on the basis of highly idealized scheme may not be able to represent all of the physical aspects of the physical one. For this study, determination of percentage of semi-rigid joints is considered as an optimization problem based on the numerical and experimental frequencies. Probabilistic sensitivity analysis is also used to determine the search space. A new technique of optimization problem is solved by a combination of smart particle swarm optimization (PSO) and genetic algorithms, and a complicated and efficient system for model updating process is introduced. It is observed that the hybrid PSO-Genetic algorithm is applicable and appropriate in model updating process. It performs better than PSO algorithm, considering the good agreement between theoretical frequencies and experimental ones, before and after model updating.
In previous work, concrete mixes incorporated with different types of acetates (inorganic and organic) were formulated, cured for 28 days in water, and then tested for compressive strength. The ...effect of the water-to-cement ratio and the acetate content was optimized using a central composited design based on the response surface methodology approach. The results confirmed that the optimum compressive strength was achieved for the mixes incorporated with calcium acetate (CaA) using of 0.48 water-to-cement ratio. In the current work, the effect of curing age on compressive strength and density was studied for the optimum mixes. Also, the water absorption of the mixes carried out by immersion test was assessed at different temperatures (25-55 °C). Microscopic observations were also noted. The results obtained confirmed that the compressive strength and density of the CaA-concrete mix increase with increasing the curing age. The thermodynamic study of water absorption assured the dependence of water absorption on temperature. The activation energies depicted from the Arrhenius relation and the decrease in the water absorption rate for the concrete incorporated with CaA are considered as an indicator of decreasing the porosity of the concrete mixes compared to the control mixes without CaA. The findings assured that the modified mixes with CaA are promising construction materials owing to their outstanding strength and lower water absorption rates compared to conventional concrete.
Carcinosarcomas of the biliary tract are an extremely rare type of malignancy and may be low on a differential when presenting as multiple metastatic masses. In this case report, we report a case of ...a female who presented with an aggressive late-stage disease whose initial workup did not indicate a malignant process. Further complicating her care, biopsy samples taken from extra-hepatic masses were culture-positive for
. Given the late stage of the patient's disease, hospice care was initiated. The patient passed away four months after the initial presentation.
A new fault classification/diagnosis method based on artificial immune system(AIS) algorithms for the structural systems is proposed. In order to improve the accuracy of the proposed method, i.e., ...higher success rate, Gaussian and non-Gaussian noise generating models are applied to simulate environmental noise. The identification of noise model, known as training process, is based on the estimation of the noise model parameters by genetic algorithms(GA) utilizing real experimental features. The proposed fault classification/diagnosis algorithm is applied to the noise contaminated features. Then, the results are compared to that obtained without noise modeling. The performance of the proposed method is examined using three laboratory case studies in two healthy and damaged conditions. Finally three different types of noise models are studied and it is shown experimentally that the proposed algorithm with non-Gaussian noise modeling leads to more accurate clustering of memory cells as the major part of the fault classification procedure.
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