90 research outputs found
Nonlinear dynamic simulation and parametric analysis of a rotor-AMB-TDB system experiencing strong base shock excitations
The introduction of active magnetic bearings (AMBs) has enabled turbomachinery to increase power density, controllability, and general resilience to external disturbances. However, because of the limited load capacity of AMBs, the base shock condition that "on-board" machines often encounter may result in contact between the rotor and the touchdown bearings (TDBs), which can seriously damage the machine. A challenge in AMB applications is to alleviate this problem. This study presents a dynamic analysis of a rotor-AMB-TDB system under strong base shocks while the AMBs are operating. Detailed TDB and contact models are presented using Hertzian contact theory. A PD controller was then designed considering system saturation and friction, based on the Coulomb model and the effect of lubrication. The dynamic equations were solved for the dynamic trajectory and FFT spectra, STFT spectra, Poincaré maps and bifurcation diagrams were used for the parametric analysis. The results show that the rotor had three motion modes. System parameters, including unbalance eccentricity, magnetic gap clearance and equivalent stiffness and damping ratio, may lead to complex nonlinear dynamic behavior including periodic, KT-periodic, and quasi-periodic responses and jump phenomenon. Suitable designs that consider these parameters may avoid undesirable rotor dynamic behavior. This study reveals the mechanism for nonlinear response, providing a method for its prediction, and core controller parameter designs for rotor re-levitation
Improving the Brain-Computer Interface Learning Process with Gamification in Motor Imagery: A Review
Brain-computer-interface-based motor imagery (MI-BCI), a control method for transferring the imagination of motor behavior to computer-based commands, could positively impact neural functions. With the safety guaranteed by non-invasive BCI devices, this method has the potential to enhance rehabilitation and physical outcomes. Therefore, this MI-BCI control strategy has been highly researched. However, applying a non-invasive MI-BCI to real life is still not ideal. One of the main reasons is the monotonous training procedure. Although researchers have reviewed optimized signal processing methods, no suggestion is found in training feedback design. The authors believe that enhancing the engagement interface via gamification presents a potential method that could increase the MI-BCI outcome. After analyzing 2524 articles (from 2001 to 2020), 28 pieces of research are finally used to evaluate the feasibility of using gamified MI-BCI system for training. This paper claims that gamification is feasible for MI-BCI training with an average accuracy of 74.35% among 111 individuals and positive reports from 26 out of 28 studies. Furthermore, this literature review suggests more emphasis should be on immersive and humanoid design for a gaming system, which could support relieving distraction, stimulate correct MI and improve learning outcomes. Interruptive training issues such as disturbing graphical interface design and potential solutions have also been presented for further research
Manufacturing with light – micro-assembly of opto-electronic microstructures
Optical micromanipulation allows the movement and patterning of discrete micro-particles within a liquid environment. However, for manufacturing applications it is desirable to remove the liquid, leaving the patterned particles in place. In this work, we have demonstrated the use of optoelectronic tweezers (OET) to manipulate and accurately assemble Sn62Pb36Ag2 solder microspheres into tailored patterns. A technique based on freeze-drying technology was then developed that allows the assembled patterns to be well preserved and fixed in place after the liquid medium in the OET device is removed. After removing the liquid from the OET device and subsequently heating the assembled pattern and melting the solder microspheres, electrical connections between the microspheres were formed, creating a permanent conductive bridge between two isolated metal electrodes. Although this method is demonstrated with 40 µm diameter solder beads arranged with OET, it could be applied to a great range of discrete components from nanowires to optoelectronic devices, thus overcoming one of the basic hurdles in using optical micromanipulation techniques in a manufacturing micro-assembly setting
Potential of Core-Collapse Supernova Neutrino Detection at JUNO
JUNO is an underground neutrino observatory under construction in Jiangmen, China. It uses 20kton liquid scintillator as target, which enables it to detect supernova burst neutrinos of a large statistics for the next galactic core-collapse supernova (CCSN) and also pre-supernova neutrinos from the nearby CCSN progenitors. All flavors of supernova burst neutrinos can be detected by JUNO via several interaction channels, including inverse beta decay, elastic scattering on electron and proton, interactions on C12 nuclei, etc. This retains the possibility for JUNO to reconstruct the energy spectra of supernova burst neutrinos of all flavors. The real time monitoring systems based on FPGA and DAQ are under development in JUNO, which allow prompt alert and trigger-less data acquisition of CCSN events. The alert performances of both monitoring systems have been thoroughly studied using simulations. Moreover, once a CCSN is tagged, the system can give fast characterizations, such as directionality and light curve
Detection of the Diffuse Supernova Neutrino Background with JUNO
As an underground multi-purpose neutrino detector with 20 kton liquid scintillator, Jiangmen Underground Neutrino Observatory (JUNO) is competitive with and complementary to the water-Cherenkov detectors on the search for the diffuse supernova neutrino background (DSNB). Typical supernova models predict 2-4 events per year within the optimal observation window in the JUNO detector. The dominant background is from the neutral-current (NC) interaction of atmospheric neutrinos with 12C nuclei, which surpasses the DSNB by more than one order of magnitude. We evaluated the systematic uncertainty of NC background from the spread of a variety of data-driven models and further developed a method to determine NC background within 15\% with {\it{in}} {\it{situ}} measurements after ten years of running. Besides, the NC-like backgrounds can be effectively suppressed by the intrinsic pulse-shape discrimination (PSD) capabilities of liquid scintillators. In this talk, I will present in detail the improvements on NC background uncertainty evaluation, PSD discriminator development, and finally, the potential of DSNB sensitivity in JUNO
Real-time Monitoring for the Next Core-Collapse Supernova in JUNO
Core-collapse supernova (CCSN) is one of the most energetic astrophysical
events in the Universe. The early and prompt detection of neutrinos before
(pre-SN) and during the SN burst is a unique opportunity to realize the
multi-messenger observation of the CCSN events. In this work, we describe the
monitoring concept and present the sensitivity of the system to the pre-SN and
SN neutrinos at the Jiangmen Underground Neutrino Observatory (JUNO), which is
a 20 kton liquid scintillator detector under construction in South China. The
real-time monitoring system is designed with both the prompt monitors on the
electronic board and online monitors at the data acquisition stage, in order to
ensure both the alert speed and alert coverage of progenitor stars. By assuming
a false alert rate of 1 per year, this monitoring system can be sensitive to
the pre-SN neutrinos up to the distance of about 1.6 (0.9) kpc and SN neutrinos
up to about 370 (360) kpc for a progenitor mass of 30 for the case
of normal (inverted) mass ordering. The pointing ability of the CCSN is
evaluated by using the accumulated event anisotropy of the inverse beta decay
interactions from pre-SN or SN neutrinos, which, along with the early alert,
can play important roles for the followup multi-messenger observations of the
next Galactic or nearby extragalactic CCSN.Comment: 24 pages, 9 figure
Shock-induced persistent contact and synchronous re-levitation control in an AMB-rotor system
Active magnetic bearings (AMBs) have limited dynamic load capacity due to magnetic saturation. Hence, large external disturbances (such as shock loads) may cause contact between the rotor and touchdown bearings (TDBs), which may evolve into complex dynamic behaviour and damage the machine. This paper considers the shock responses of a rotor and viable re-levitation control options when the AMB is still functional. Bi-stable responses and shock-induced persistent forward rubbing were observed in an experimental AMB-flexible rotor facility and its numerical model. The analytical solution for steady synchronous motions with rubbing of a general AMB-flexible rotor system was proposed. The standard control action for a contact-free rotor state would not be appropriate due to phase changes and the displacement amplitude differences in the frequency responses. To destabilise the persistent contact responses and restore contact-free levitation, open-loop phase search based synchronous compensation (PSSC) control and synchronous motion compensation (SMC) control are designed, which are activated when a persistent contact is detected. Stability of the control system and the effectiveness of these two re-levitation control methods are verified by simulation and experimental results. It is also found by comparison that the efficiency of PSSC depends on the phase difference (incorrect phases may degrade rotor response), while the SMC consumes more computing effort.</p
Shock-induced persistent contact and synchronous re-levitation control in an AMB-rotor system
Combination Therapy of Wuweizi (Schisandrae Chinensis Fructus) and Dexamethasone Alleviated Dexamethasone-Induced Glucocorticoid Osteoporosis in Rats with Idiopathic Pulmonary Fibrosis
Objective. To investigate the therapeutic effect of combined application of Wuweizi (Schisandrae Chinensis Fructus) and dexamethasone in rats with idiopathic pulmonary fibrosis (IPF) and the possible protective effect of Wuweizi against dexamethasone-induced glucocorticoid osteoporosis (GIOP). Methods. There were five groups in this study, including the sham operation group, model group, Wuweizi group, dexamethasone group, and the combination group. A rat IPF model was made by the endotracheal injection of bleomycin. After modeling, rats were given drug interventions for 7 and 28 days. Rats were sacrificed for pathological morphology examination of the bone and lung and quantitative determination of biochemical markers of bone metabolism and angiogenesis-related cytokine to observe therapeutic efficacy on the 7th and 28th day. ELISA was used for the quantitative determination of tartrate-resistant acid phosphatase (TRACP), bone alkaline phosphatase (BALP), hypoxia-inducible factor (HIF-1α), platelet-derived growth factor (PDGF), pigment epithelium-derived factor (PEDF), and endostatin in serum. The concentrations of calcium (Ca) and phosphorus (P) were detected with the automatic biochemical analyzer. Results. After drug interventions for 7 and 28 days, alveolitis and pulmonary fibrosis in treatment groups showed significant improvement compared with those in the model group (P<0.05). Bone histopathological figures showed severely damaged trabecular bone and bone marrow cavity in the dexamethasone group, but it was significantly alleviated in the combination group. The concentrations of BALP and Ca in the combination group were significantly higher than those in the dexamethasone group after treatment, while the concentrations of TRACP and P were lower than those in the dexamethasone group (P<0.05). The concentrations of HIF-1α and PDGF in treatment groups were significantly lower (P<0.05) compared with those in the model group, while PEDF and endostatin were increased (P<0.01). However, the concentration of HIF-1α in the combination group was higher than that in the dexamethasone group, and the concentration of PEDF was lower than that in the dexamethasone group. Conclusions. The combination therapy of Wuweizi and dexamethasone effectively treated IPF rats by regulating angiogenesis, meanwhile distinctly alleviating dexamethasone-induced GIOP
Influence of tumor size on oncological outcomes of pathological T3aN0M0 renal cell carcinoma treated by radical nephrectomy
<div><p>Objective</p><p>To evaluate the prognostic significance of tumor size in pathological T3aN0M0 renal cell carcinoma (RCC) treated by radical nephrectomy.</p><p>Materials and methods</p><p>Patients who underwent radical nephrectomy for sporadic RCC with pathological T3aN0M0 RCC at our institution between January 2006 and June 2015 were identified. The entire cohort was divided into two groups according to the cutoff of tumor size obtained from receiver operating characteristic (ROC) curve. Clinicopathological variables were retrospectively collected and compared. Kaplan-Meier analysis and multivariate Cox regression were conducted to evaluate the effect of tumor size on survival outcomes.</p><p>Results</p><p>163 pT3aN0M0 RCC patients were included with a median follow-up period of 31 months. The optimal cutoff for tumor size was 7 cm according to the ROC curve. 90 cases (55.2%) presented tumors which measured 7 cm or less, and 73 cases (44.8%) showed tumor size greater than 7 cm. Patients with larger tumors tended to exhibit higher rates of symptoms and higher Fuhrman grades; they also indicated more necrosis features, and were more likely to invade the collecting system and renal vein. Compared with patients who exhibited tumor size of≤7 cm, those with tumor size>7 cm were associated with shorter estimated five-year cancer-specific survival (CSS, 46.6% versus 75.0%, <i>P</i> = 0.003) and five-year recurrence-free survival (RFS, 35.6% versus 62.7%, <i>P</i> = 0.011). Multivariate Cox analysis revealed that tumor size was retained as an independent factor for CSS (HR = 2.506, 95% CI 1.169–5.373, <i>P</i> = 0.018).</p><p>Conclusions</p><p>The tumor size significantly affected the survival outcomes of pT3aN0M0 RCC treated by radical nephrectomy, and a cutoff size of 7 cm can help enhance the prognostic discrimination. Thus, the tumor size may be considered in the future TNM classification of stage pT3a.</p></div
- …