Random walks on complex networks under time-dependent stochastic resetting

We study discrete-time random walks on networks subject to a time-dependent stochastic resetting, where the walker either hops randomly between neighboring nodes with a probability $1-\phi(a)$, or is reset to a given node with a complementary probability $\phi(a)$. The resetting probability $\phi(a)$ depends on the time $a$ since the last reset event (also called $a$ the age of the walker). Using the renewal approach and spectral decomposition of transition matrix, we formulize the stationary occupation probability of the walker at each node and the mean first passage time between arbitrary two nodes. Concretely, we consider that two different time-dependent resetting protocols that are both exactly solvable. One is that $\phi(a)$ is a step-shaped function of $a$ and the other one is that $\phi(a)$ is a rational function of $a$. We demonstrate the theoretical results on two different networks, also validated by numerical simulations, and find that the time-modulated resetting protocols can be more advantageous than the constant-probability resetting in accelerating the completion of a target search process.Comment: 10 pages, 3 figures. arXiv admin note: text overlap with arXiv:2105.0832

Microstructured Thin Film Nitinol for a Neurovascular Flow-Diverter

A cerebral aneurysm occurs as a result of a weakened blood vessel, which allows blood to flow into a sac or a ballooned section. Recent advancement shows that a new device, ‘flow-diverter’, can divert blood flow away from the aneurysm sac. People found that a flow-diverter based on thin film nitinol (TFN), works very effectively, however there are no studies proving the mechanical safety in irregular, curved blood vessels. Here, we study the mechanical behaviors and structural safety of a novel microstructured TFN membrane through the computational and experimental studies, which establish the fundamental aspects of stretching and bending mechanics of the structure. The result shows a hyper-elastic behavior of the TFN with a negligible strain change up to 180° in bending and over 500% in radial stretching, which is ideal in the use in neurovascular curved arteries. The simulation determines the optimal joint locations between the TFN and stent frame. In vitro experimental test qualitatively demonstrates the mechanical flexibility of the flow-diverter with multi-modal bending. In vivo micro X-ray and histopathology study demonstrate that the TFN can be conformally deployed in the curved blood vessel of a swine model without any significant complications or abnormalities

Design, Parameter Optimization and In Vitro Evaluation of Implantable Medical Devices

The number of implantable medical devices ranging from dental implants to cardiovascular implants has been exponentially increased in the last decades and various materials including metallic materials and polymeric materials are used in medical device manufacturing. In metallic materials, nitinol is widely used due to its superelasticity and well-known biocompatibility. Finite element modeling (FEM) along with in vitro and in vivo is being adopted to evaluate the medical device performance in patients and optimize medical designs. In this dissertation, four innovative implantable medical devices were developed and their performances were evaluated using finite element modeling and in vitro testing: 1) ventriculoamniotic shunt for aqueductal stenosis treatment. It has the conduit to drain excessive cerebrospinal fluid (CSF) to lower intracranial pressure in fetal brains and the anchors to prevent the device dislocation during the treatment. The shunt tube design was optimized using computational fluid dynamics calculations. The anchor design was determined with ANSYS Static Structural and the prototype was manufactured based on modeling results. In vitro pressure and flow rate measurement within shunt device demonstrate that the pressure in fetal brain can be reduced by 95.2% while the pressure elevation in amniotic sac is negligible. 2) TFN flow-diverter integrated with flow sensing system for cerebral aneurysm post-treatment monitoring. The flexibility of TFN membrane was investigated using both computational modeling and stretching experiment. As the TFN was wrapped on a flow-diverter backbone with junction points, we evaluated the attachment patterns between a TFN and stent backbone. Finally, micro-scale flow sensor was designed and fabricated based on the computational modeling. 3) compartmentalized stent to isolate the perfusion of the abdominal organs. The fluid dynamics inside the arterial and venous organ perfusion stent (OPS) was analyzed in terms of velocity distribution and wall shear stress (WSS). In vitro pressure difference both in arterial and venous OPS showed that the stent deployment with perfusion flow to the abdominal organs will not generate a significant load on the donor's heart. 4) retrievable stent graft for noncompressible hemorrhage control. The mechanical and biological properties of ePTFE membrane were investigated and the nitinol framed backbone was evaluated in terms of radial force

Reform Exploration for Safety Course System of Oil and Gas Storage and Transportation Facilities

In recent years, the safety of oil and gas storage and transportation facilities has been paid more attention by the state and enterprises due to frequent accidents. The oil and gas storage and transportation facilities safety courses in China University of Petroleum (Beijing) includes “Engineering mechanics”, “Strength design of pipelines and tanks” and “Safety and integrity management of oil and gas storage and transportation facilities”. The three courses lack relevance and the teaching mode is too rigid, resulting in students losing their initiative in learning. If students can’t use the knowledge flexibly, it will affect the achievement of the objectives of the training program. Therefore, oil and gas storage and transportation facilities safety courses are reformed, training plans are adjusted and teaching methods are improved. The practice shows that the reform enriches the teaching content, improves the teaching quality, stimulates classroom activity and gets a good evaluation of students. The reform of safety courses has a certain significance for cultivating compound talents who have the ability to solve practical problems in engineering

Risk Assessment of Nautical Navigational Environment Based on Grey Fixed Weight Cluster

In order to set up a mathematical model suitable for nautical navigational environment risk evaluation and systematically master the navigational environment risk characteristics of the Qiongzhou Strait in a quantitative way, a risk assessment model with approach steps is set up based on the grey fixed weight cluster (GFWC). The evaluation index system is structured scientifically through both literature review and expert investigation. The relative weight of each index is designed to be obtained via fuzzy analytic hierarchy process (FAHP); Index membership degree of every grey class is proposed to be achieved by fuzzy statistics (FS) to avoid the difficulty of building whiten weight functions. By using the model, nautical navigational environment risk of the Qiongzhou Strait is determined at a “moderate” level according to the principle of maximum membership degree. The comprehensive risk evaluation of the Qiongzhou Strait nautical navigational environment can provide theoretical reference for implementing targeted risk control measures. It shows that the constructed GFWC risk assessment model as well as the presented steps are workable in case of incomplete information. The proposed strategy can excavate the collected experts’ knowledge mathematically, quantify the weight of each index and risk level, and finally lead to a comprehensive risk evaluation result. Besides, the adoptions of probability and statistic theory, fuzzy theory, aiming at solving the bottlenecks in case of uncertainty, will give the model a better adaptability and executability.</p

Reform of Elastic-Plastic Mechanics and Strength Design of Pipelines Based on Ideological and Political Education

Oil and gas storage and transportation safety courses are very important in oil and gas storage and transportation engineering. With the ideological and political construction of the course in the new period, the mode of professional knowledge teaching cannot meet the teaching requirements. The teaching team has been practicing in the course for many years. By inserting typical characters, typical projects, national policies and industry trends into the course, students' patriotism, academic confidence and environmental protection awareness have been cultivated, and remarkable results have been achieved. At the same time, it can provide some reference for the ideological and political education of engineering majors