DEM simulation of the mechanical properties of SiC ceramic under pre-stressing

In this paper, the method of discrete element model (DEM) simulation was used to investigate the mechanical properties of SiC ceramic materials under the action of pre-stress. Using the bonded particle model (BPM), several different numerical tests (such as UCT, TPB, SENB tests) of SiC ceramic were established. Different pre-stress values were applied on the lateral surface of the ceramic specimen during the numerical simulation process, all tests were carried out at least 5 times with different random number, and the average mechanical properties results were calculated. It was showed that the existence of pre-stress has a significant effect on the mechanical properties of materials. It can enhance the strength of materials, while the force action on material in machining process force or action force the crack’s initiation and propagation was limited

SU(4) Spin-Orbital Two-Leg Ladder, Square and Triangle Lattices

Based on the generalized valence bond picture, a Schwinger boson mean field theory is applied to the symmetric SU(4) spin-orbital systems. For a two-leg SU(4) ladder, the ground state is a spin-orbital liquid with a finite energy gap, in good agreement with recent numerical calculations. In two-dimensional square and triangle lattices, the SU(4) Schwinger bosons condense at (\pi/2,\pi/2) and (\pi/3,\pi/3), respectively. Spin, orbital, and coupled spin-orbital static susceptibilities become singular at the wave vectors, twice of which the bose condensation arises at. It is also demonstrated that there are spin, orbital, and coupled spin-orbital long-range orderings in the ground state.Comment: 5 page

Multiple sources of infection and potential endemic characteristics of the large outbreak of dengue in Guangdong in 2014

A large outbreak of dengue, with the most documented cases, occurred in Guangdong China in 2014. Epidemiological studies and phylogenetic analysis of the isolated dengue virus (DENV) showed this outbreak was attributed to multiple sources and caused by at least two genotypes of DENV-1 (Genotypes I and III) and two genotypes of DENV-2 (Cosmopolitan and Asian I Genotypes). A retrospective review and phylogenetic analysis of DENV isolated in Guangdong showed that DENV-1 Genotype I strains were reported continuously during 2004-2014, Genotype III strains were reported during 2009-2014 ; DENV-2 Cosmopolitan and Asian I Genotype strains were reported continuously during 2012-2014. At least 45,171 cases were reported in this outbreak, with 65.9% of the patients in the 21-55-year-old group. A trend toward a decrease in the daily newly emerged cases lagged by approximately 20 days compared with the mosquito density curve. Several epidemiological characteristics of this outbreak and the stably sustained serotypes and genotypes of DENV isolated in Guangdong suggest that Guangdong has been facing a threat of transforming from a dengue epidemic area to an endemic area. The high temperature, drenching rain, rapid urbanization, and pandemic of dengue in Southeast Asia may have contributed to this large outbreak of dengue

Spike Timing-Dependent Plasticity in CA1 Pyramidal Neuron-Controlling Hippocampal Circuits: a Model Study

Spike timing-dependent plasticity (STDP) plays an important role in sculpting neural circuits to store information in the hippocampus, since motor learning and memory are thought to be closely linked with this type of synaptic plasticity. We built a computational model to study the potential learning rule by linearly changing the synaptic weight and number of the synapses involved. The main findings are the following: (i) changes in the synaptic weight and number of synapses can lead to different long-term changes in the synaptic efficacy; (ii) the first spike pair of two neurons exerts a great influence on the subsequent spike pair; a pre-post spiking pair reinforces the subsequent paired spiking, while a post-pre spiking pair depresses this paired spiking; (iii) when the synaptic weight and synaptic number change, the interval in the first spiking pair is reduced, which directly influences the first spiking pair, and (iv) when a stellate neuron is stimulated weakly or the capacitance of a CA1 pyramidal neuron is decreased, LTP is produced more easily than LTD; in the opposite case, LTD is produced more readily; an increase of the synaptic number can promote activation of CA1 pyramidal neurons.Пластичність, залежна від часу генерації імпульсів (spike timing-dependent plasticity – STDP), відіграє важливу роль у функціонуванні нейронних мереж гіпокампа, що накопичують інформацію; вважають, що моторне навчання та пам’ять тісно пов’язані зі синаптичною пластичністю саме цього типу. Ми створили комп’ютерну модель, щоб вивчити можливі закономірності в процесі навчання, залежні від лінійних змін синаптичної ваги та кількості залучених синапсів у таких мережах. Основні експериментальні знахідки були наступними: 1) варіювання синаптичної ваги та числа синапсів можуть призводити до різних тривалих змін ефективності синаптичної передачі; 2) перша пара імпульсів, генерована двома синаптично пов’язаними нейронами, здійснює потужний вплив на наступну пару імпульсів; пара імпульсів у послідовності “пре–пост” полегшує генерацію наступної пари імпульсів, тоді як пара імпульсів у послідовності “пост–пре” пригнічує таку парну генерацію; 3) коли змінюються синаптична вага та кількість залучених синапсів, міжімпульсний інтервал у першій парі скорочується, тобто реалізується прямий вплив на характеристики такої пари; 4) коли інтенсивність стимуляції зірчастого нейрона є низькою або ємність мембрани пірамідного нейрона зони CA1 є зменшеною, тривала потенціація синаптичної передачі індукується легше, ніж тривала депресія; в іншому випадку легше виникає тривала депресія; збільшення кількості синапсів сприяє активації пірамідних нейронів у зоні CA1

Strength Prediction Model of a Particle-Reinforced Shellproof Ceramic Composite

On the basis of the microstructure of particle-reinforced shellproof ceramic composite, and the intergranular fracture feature, a dislocation pile-up fracture model of the small-particle ceramic composite is developed, the mechanism of formation, growth and coalescence of microcracks. The complex effect of the small particle pull-out and large particle cracking is concerned, when constructing the crack extension fracture model. Thereafter, the influence of particles’ volume fraction and matrix grain diameter on fracture strength is studied. The experimental data shows that the proposed strength prediction model is successful and can be generally applied.На основе микроструктуры пуленепробиваемого керамического композиционного материала, упрочненного мелкими частицами, и характера его внутрикристаллического разрушения разработана модель разрушения при скоплении дислокаций, т.е. исследован механизм образования, роста и слияния трещин. При разработке модели разрушения при распространении трещины учитывали совместное влияние процессов выкрашивания мелких частиц и растрескивания крупных частиц. Изучено влияние относительного объема частиц и диаметра матричного зерна на сопротивление разрушению. Экспериментальные результаты показали, что данная модель прогнозирования прочности является эффективной и общеприменимой.На основі мікроструктури куленепробивного керамічного композиційного матеріалу, зміцненого дрібними частинками, і характеру внутрішньокристалічного руйнування розроблено модель руйнування при скупченні дислокацій, тобто досліджено механізм виникнення, росту і злиття тріщин. При розробці моделі руйнування при розповсюдженні тріщини враховували спільний вплив процесів викришування дрібних частинок і розтріскування великих. Вивчено вплив відносного об’єму частинок і діаметра матричного зерна на опір руйнуванню. Експериментальні дані показали, що запропонована модель прогнозування міцності є ефективною і загальновживаною

Cycle-Consistent Generative Adversarial Network: Effect on Radiation Dose Reduction and Image Quality Improvement in Ultralow-Dose CT for Evaluation of Pulmonary Tuberculosis

OBJECTIVE: To investigate the image quality of ultralow-dose CT (ULDCT) of the chest reconstructed using a cycle-consistent generative adversarial network (CycleGAN)-based deep learning method in the evaluation of pulmonary tuberculosis. MATERIALS AND METHODS: Between June 2019 and November 2019, 103 patients (mean age, 40.8 ± 13.6 years; 61 men and 42 women) with pulmonary tuberculosis were prospectively enrolled to undergo standard-dose CT (120 kVp with automated exposure control), followed immediately by ULDCT (80 kVp and 10 mAs). The images of the two successive scans were used to train the CycleGAN framework for image-to-image translation. The denoising efficacy of the CycleGAN algorithm was compared with that of hybrid and model-based iterative reconstruction. Repeated-measures analysis of variance and Wilcoxon signed-rank test were performed to compare the objective measurements and the subjective image quality scores, respectively. RESULTS: With the optimized CycleGAN denoising model, using the ULDCT images as input, the peak signal-to-noise ratio and structural similarity index improved by 2.0 dB and 0.21, respectively. The CycleGAN-generated denoised ULDCT images typically provided satisfactory image quality for optimal visibility of anatomic structures and pathological findings, with a lower level of image noise (mean ± standard deviation [SD], 19.5 ± 3.0 Hounsfield unit [HU]) than that of the hybrid (66.3 ± 10.5 HU, p 0.908). The CycleGAN-generated images showed the highest contrast-to-noise ratios for the pulmonary lesions, followed by the model-based and hybrid iterative reconstruction. The mean effective radiation dose of ULDCT was 0.12 mSv with a mean 93.9% reduction compared to standard-dose CT. CONCLUSION: The optimized CycleGAN technique may allow the synthesis of diagnostically acceptable images from ULDCT of the chest for the evaluation of pulmonary tuberculosis

SSVEP-based Brain-Computer Interface Controlled Robotic Platform with Velocity Modulation

Steady-state visual evoked potential (SSVEP)-based brain-computer interfaces (BCIs) have been extensively studied due to many benefits, such as non-invasiveness, high information transfer rate, and ease of use. SSVEP-based BCI has been investigated in various applications by projecting brain signals to robot control commands. However, the movement direction and speed are generally fixed and prescribed, neglecting the user’s requirement for velocity changes during practical implementations. In this study, we proposed a velocity modulation method based on stimulus brightness for controlling the robotic arm in the SSVEP-based BCI system. A stimulation interface was designed, incorporating flickers, target and a cursor workspace. The synchronization of the cursor and robotic arm does not require the subject’s eye switch between the stimuli and the robot. The feature vector consists of the characteristics of the signal and the classification result. Subsequently, the Gaussian mixture model (GMM) and Bayesian inference were used to calculate the posterior probabilities that the signal came from a high or low brightness flicker. A brain-actuated speed function was designed by incorporating the posterior probability difference. Finally, the historical velocity was considered to determine the final velocity. To demonstrate the effectiveness of the proposed method, online experiments, including single- and multi-target reaching tasks, were conducted. The extensive experimental results validated the feasibility of the proposed method in reducing reaching time and achieving proximity to the target

Chirality in odd-AA nucleus 135^{135}Nd in particle rotor model

A particle rotor model is developed which couples several valence protons and neutrons to a rigid triaxial rotor core. It is applied to investigating the chirality in odd-$A$ nucleus $^{135}$Nd with $\pi h_{11/2}^2\otimes\nu h^{-1}_{11/2}$ configuration for the first time in a fully quantal approach. For the two chiral sister bands, the observed energies and the $B(M1)$ and $B(E2)$ values for the in-band as well as interband transitions are reproduced excellently. Root mean square values of the angular momentum components and their probability distributions are used for discussing in detail the chiral geometry of the aplanar rotation and its evolution with angular momentum. Chirality is found to change from a soft chiral vibration to nearly static chirality at spin $I=39/2$ and back to another type of chiral vibration at higher spin.Comment: 16 pages, 5 figure

Quantitative Upper Limb Impairment Assessment for Stroke Rehabilitation: A Review

With the number of people surviving a stroke soaring, automated upper limb impairment assessment has been extensively investigated in the past decades since it lays the foundation for personalised precision rehabilitation. The recent advancement of sensor systems, such as high-precision and real-time data transmission, have made it possible to quantify the kinematic and physiological parameters of stroke patients. In this paper, we review the development of sensor-based upper limb quantitative impairment assessment, concentrating on the capable of comprehensively and accurately detecting motion parameters and measuring physiological indicators to achieve the objective and rapid quantification of the stroke severity. The paper discusses various features used by different sensors, detectable actions, their utilization techniques, and effects of sensor placement on system accuracy and stability. In addition, both the advantages and disadvantages of the model-based and model-free algorithms are also reviewed. Furthermore, challenges encompassing comprehensive assessment of medical scales, neurological deficits assessment, random movement detection, the effect of the sensor placement, and the effect of the number of sensors are also discussed