The force and dynamic response of low-velocity projectile impact into 3D dense wet granular media

The presence of liquid bridges between particles in a wet granular media gives rise to capillary forces at the microscopic scale that dramatically alters the material's microstructure and macroscopic responses. Previous experimental studies show significant differences in the penetration depth of the projectile into assemblies of dry or wet particles. Still, there is a lack of fundamental understanding of the difference induced by the presence of liquid bridges in dynamic regimes. In this study, the contact model parameters of wet glass beads are calibrated employing the angle of repose tests and cylinder lifting tests, and a series of three-dimensional discrete element method simulations of spheres impact into wet granular packings are conducted. The dynamic characteristics of the projectile are obtained numerically and found to be in good agreement with the experimental data. The analyses indicate that the final penetration depth in the wet granular media is linearly related to the initial velocity and has a power function relationship with the impact energy. The generalized Poncelet law is suitable for wet granular materials, but the presence of liquid significantly affects the values of the parameters. There is a velocity “stagnation zone” at the initial stage of the wet granular impact, and the final penetration depth and the duration interaction time are smaller than that of the dry case. The difference can be attributed to the resistance evolution of the projectile exerted by particles and gives the parameter scaling law of the peak impact force. Further, a macro-micro transition technique is employed to characterize the velocity field, pressure field, and stress field inside the wet granular media and the spatial distribution is quantified based on stress theory.</p

Interactive Physically-Based Simulation of Roadheader Robot

Roadheader is an engineering robot widely used in underground engineering and mining industry. Interactive dynamics simulation of roadheader is a fundamental problem in unmanned excavation and virtual reality training. However, current research is only based on traditional animation techniques or commercial game engines. There are few studies that apply real-time physical simulation of computer graphics to the field of roadheader robot. This paper aims to present an interactive physically-based simulation system of roadheader robot. To this end, an improved multibody simulation method based on generalized coordinates is proposed. First, our simulation method describes robot dynamics based on generalized coordinates. Compared to state-of-the-art methods, our method is more stable and accurate. Numerical simulation results showed that our method has significantly less error than the game engine in the same number of iterations. Second, we adopt the symplectic Euler integrator instead of the conventional fourth-order Runge-Kutta (RK4) method for dynamics iteration. Compared with other integrators, our method is more stable in energy drift during long-term simulation. The test results showed that our system achieved real-time interaction performance of 60 frames per second (fps). Furthermore, we propose a model format for geometric and robotics modeling of roadheaders to implement the system. Our interactive simulation system of roadheader meets the requirements of interactivity, accuracy and stability

Effect of Strain on Thermal Conductivity of Si Thin Films

Nonequilibrium molecular dynamics (NEMD) simulations are employed to gain an understanding of the effect of strain on the thermal conductivity of Si thin films. The analysis shows that the strain has an appreciable influence on the thermal conductivity of Si thin films. The thermal conductivity decreases as the tensile strain increases and increases as the compressive strain increases. The decrease of the phonon velocities and surface reconstructions generated under strain could explain well the effects of strain on the thermal conductivity of Si thin films

A comparison between the effectiveness of PBL and LBL on improving problem-solving abilities of medical students using questioning

In daily patient-history taking and diagnosis practice, doctors ask questions to gather information from patients and narrow down diagnostic hypotheses. Training medical students to be efficient problem solvers through the use of questioning is therefore important. In this study, the effectiveness of problem-based learning (PBL) and lecture-based learning in improving the questioning abilities of medical students (N=104) was assessed by a modified 20-question task. In this task, the participants were asked to identify target pictures by asking questions, the problem-solving process of which resembles that of the diagnosis scenario. Moreover, this task requires no medical knowledge, and therefore allows knowledge-irrelevant questioning abilities to be assessed independently. The results show that PBL students generally ask more efficient questions and use fewer questions to complete the task. This finding suggests that PBL curricula may help improve the questioning strategies of medical students and help them diagnose more efficiently in future diagnosis practice.</p

Clinical characteristics and long term post-operative outcome of cardiac myxoma

Background and aim: Myxoma is the most common type of primary cardiac neoplasm, but the clinical characteristics and long term outcome are less known in the elderly in China. Methods: We analyzed medical records of 112 consecutive patients who underwent operative resection of cardiac myxoma between December 1988 and December 2010 in our hospital. Their data were retrospectively analyzed and the difference between two age groups (< 60 years, n = 87 and ≥ 60 years, n = 25) was compared. Results: The mean age of 112 patients was 48.8 ± 12.5 (range 13 ~ 75) years, and 66 patients (58.9 %) were female. The interval from onset of symptoms to diagnosis was 12 months and the most common presenting symptoms were chest distress (66 patients 58.9 %), followed by palpitations (55 patients, 49.1 %) and dyspnea (47 patients, 42.0 %). Mitral valve diastolic murmur was heard in 67 (59.1 %) patients. The tumor was located in the left atrium in 96 (85.8 %) patients. There were no in-hospital death. During follow-up ranged between one and twenty-one (7.3 ± 5.3) years, there was no malignancy. Myxoma recurred in 3 (2.7 %) patients and deaths occurred in 5 (4.5 %) patients. The 5 and 15 years survival was 97.8 % and 89.5 %, respectively. To compare with the younger patients, the elderly have higher ratios of concomitant hypertension, fewer complaints of dyspnea and chest distress (p < 0.05). Conclusion: The elderly have lower complaints of dyspnea and chest distress, surgical treatment is associated with low long-term mortality and recurrence rate even in the elder patients

Effect and Action Mechanism of Magnetic Field Treatment on the Fermentation Characteristics of Dough

Magnetic fields can improve the quality of foods by influencing the arrangement of water molecules, thus altering the distribution of water in foods. In this study, dough was fermented at magnetic field strengths of 0, 0.5, 1.0, 1.5, and 2.0 mT for 1 h. The effect of magnetic field treatment on the fermentation characteristics, moisture distribution, and protein molecular structure of dough was investigated by low-field nuclear magnetic resonance (NMR) and in situ Raman spectroscopy, with a view to providing a theoretical basis for the development of high-quality Chinese dough-based foods. The results showed that the fermentability of dough tended to increase first and then decrease as the magnetic field strength increased, and the most significant effect on the fermentability was observed at a magnetic field strength of 1.5 mT. The specific volume of steamed bread initially increased and then decreased. When the magnetic field strength was 1.0 mT, the specific volume was 2.24 mL/g. The hardness, stickiness, and chewiness showed a trend of initially decreasing and then increasing, but there was no obvious change in the elasticity, cohesiveness or resilience. The contents of strongly bound water and free water initially decreased and then increased, whereas the opposite trend was observed for weakly bound water. The effect of 1.0 mT magnetic field strength on the water distribution was most significant. The relative content of α-helix increased first and then declined, while the reverse trend was observed for random coil. At a magnetic field strength of 0.5 mT, the relative content of α-helix was the highest (54%) and the relative content of random coil was lowest (21%). Proper magnetic field treatment could increase the fermentability of dough, the specific volume and textural properties of steamed bread, accelerate the water distribution in dough and improve the stability of the gluten network. In conclusion, magnetic field treatment could improve the fermentability of dough and the textural properties of steamed bread by improving the distribution of water, increasing the moisture uniformity, and changing the molecular structure of gluten proteins in dough

Factors associated with psychological insulin resistance among patients with type 2 diabetes in China

ObjectiveThe aim of this study was to understand the psychological insulin resistance status among Chinese patients with type 2 diabetes and investigate its associated factors in these patients.MethodsA multi-stage stratified random sampling was performed to randomly select patients with type 2 diabetes from the eastern, central, and western regions in Shandong Province, China, and 660 valid questionnaires were collected. Psychological insulin resistance was assessed by the scale of My Opinion on Insulin (MOI). Factors associated with psychological insulin resistance were examined in a binary logistic model.ResultsFour-fifths of the patients with type 2 diabetes (82.1%) had psychological insulin resistance. Being female (OR = 1.770, 95% CI: 1.063–2.950, p &lt; 0.05), having a monthly income of greater than 4,000 Renminbi (approximately $1,540) (OR = 0.444, 95% CI: 0.216–0.915, p &lt; 0.05), living with type 2 diabetes for 11 years or more (OR = 0.387, 95% CI: 0.238–0.630, p &lt; 0.05), self-rated poor health (OR = 1.706, 95% CI: 1.092–2.664, p &lt; 0.05), and moderate discrimination against type 2 diabetes (OR = 1.924, 95% CI: 1.166–3.175, p &lt; 0.05) were associated with psychological insulin resistance.ConclusionsThe prevalence of psychological insulin resistance among Chinese patients with type 2 diabetes is relatively high. Approaches are needed to address the issue of psychological insulin resistance of type 2 diabetes

Research on the Influence of Moisture State, Microscopic Morphology and Physical Properties of the Resting Dough

To study the effect of resting on the quality of frozen dough, the changes in the moisture state of the dough during the resting process (0, 30, 60, 90, 120 min), the moisture distribution of dough and their effects on ice crystal distribution, microstructure, and creep recovery characteristics after dough freezing were investigated. The results showed that the freezable water content in the dough was decreased by 0.96% with the extension of the resting time. The pores and number of ice crystals formed in the dough during the freezing process gradually decreased and the distribution of ice crystals became more and more uniform. The average pore area decreased from 22.65 to 11.80 with the extension of the resting time from 0 min to 120 min, and the number of pores decreased from 22.65 to 11.80 with the extension of the resting time. The maximum creep flexibility Jmax increased significantly (P<0.05) and the zero shear viscosity η0 decreased significantly (P<0.05) during the creep phase as the resting time was extended. After resting for 120 mins, the maximum creep flexibility Jmax of frozen dough decreased by 0.50×10−4 Pa−1, and the zero shear viscosity η0 decreased by 0.43×105 Pa−1. This indicated that the hardness of frozen dough decreases and the shape of the dough was easier to maintain. During the recovery process, the instantaneous flexibility J0 and viscoelastic flexibility Jm increased by 1.26×10−4 and 2.88×10−4 Pa−1, respectively, and the recovery force of the frozen dough increased. In summary, resting process of dough would reduce the content of freezeable water, improve the water holding capacity, and reduce the damage of ice crystals to the dough network structure in the freezing process to improve the quality of the frozen dough