Francis turbines operating at part-load experience the development of a precessing cavitation vortex rope at the runner outlet, which acts as an excitation source for the hydraulic system. In case of ...resonance, the resulting pressure pulsations seriously compromise the stability of the machine and of the electrical grid to which it is connected. As such off-design conditions are increasingly required for the integration of unsteady renewable energy sources into the existing power system, an accurate assessment of the hydropower plant stability is crucial. However, the physical mechanisms driving this excitation source remain largely unclear. It is for instance essential to establish the link between the draft tube flow characteristics and the intensity of the excitation source. In this study, a two-component particle image velocimetry system is used to investigate the flow field at the runner outlet of a reduced-scale physical model of a Francis turbine. The discharge value is varied from 55 to 81 % of the value at the best efficiency point. A particular set-up is designed to guarantee a proper optical access across the complex geometry of the draft tube elbow. Based on phase-averaged velocity fields, the evolution of the vortex parameters with the discharge, such as the trajectory and the circulation, is determined for the first time. It is shown that the rise in the excitation source intensity is induced by an enlargement of the vortex trajectory and a simultaneous increase in the precession frequency, as well as the vortex circulation. Below a certain value of discharge, the structure of the vortex abruptly changes and loses its coherence, leading to a drastic reduction in the intensity of the induced excitation source.
This paper introduces the Method of Microwave Rainfall Normalization (MMN) for the Global Satellite Mapping of Precipitation (GSMaP) algorithm in its latest version (V05, algorithm version 8), ...released in December 2021. The method aims to mitigate the discrepancy of GSMaP rainfall estimates among passive microwave (PMW) imagers/sounders (MWIs/MWSs) due to differences in sensor specifications and retrieval algorithms. The basic idea of the MMN module is to calibrate target PMW sensors with reference sensors (the Global Precipitation Measurement (GPM) Microwave Imager (GMI) and the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI)) using the cumulative distribution function (CDF) of the rain rate. Differences between the CDF and normalization table for MWSs are greater than MWIs due to different rain retrieval algorithms. More (less) MWS rainfall is detected over the ocean (land) than GMI rainfall. Matchup rainfall data between GMI and a target PMW sensor are compared to evaluate MMN performance. The monthly mean rainfall and mean bias error were improved for almost all PMW sensors. This study leaves open the possibility for further inter-calibration and improvement of rain detection and heavy rainfall retrievals.
Effect of Mg content on age-hardening response, tensile properties, and microstructures of a T5-treated thixo-cast Al–7wt.%Si–0.01wt.%Sr alloy has been investigated. The strengths of the T5-treated ...alloy increase with increasing the Mg content due to the dispersion of high density of needle-like precipitates (β” phases). Also, the addition of 1.0wt.% Mg results in the formation of evenly distributed fine Mg2Si phases and Fe-rich compounds in the eutectic Si regions, and therefore, the Al–7wt.%Si–1.0wt.%Mg–0.01wt.%Sr alloy exhibits high 0.2% proof stress of 241 MPa and moderate elongation to failure of 5.1%, which are comparable to those of T6-treated gravity-cast Al–7wt.%Si–0.3wt.%Mg (ASTM A356) alloys. Although the addition of 1.5wt.% Mg or more further improves the strengths, the excess additions of Mg lead to the formation of coarse Mg2Si phases. This causes significant loss of ductility, and the alloys show poor elongation to failure of ~2%.
Up to now, there has been less results from on-site pilot-scale anaerobic co-digestion system, especially for high-rise building application. The objective of this study was to develop an on-site ...prototype two-stage anaerobic digester for co-digestion of food waste and sewage sludge from high-rise building for biogas production. The optimal mixing ratio of food waste to sewage sludge, obtained from laboratory-scale, was found to be 7:1. Then, the prototype two-stage anaerobic digester was further designed and constructed. The results showed that COD and total volatile solid (TVS) reduction could be achieved up to 89 and 74%, respectively with the applied hydraulic retention time (HRT) of 24 days. The methane content of biogas was 64 percent. Up to now, the biogas from on-site production has been utilized for cooking at Chulalongkorn University as a model case study for high-rise building application.
•A prototype two-stage anaerobic digester for co-digestion of food waste and sewage sludge was newly designed and built.•Effects of hydraulic retention time and mixing ratio of food waste and sewage sludge on biogas production were investigated.•Anaerobic co-digestion can achieve the highest methane yield by mixing food waste with sewage sludge at the ratio of 7:1.•The methane content of biogas significantly decreased with a decrease in HRT in operating the two-stage co-digestion system.•At present, the biogas has been utilized for cooking as a model case study for high-rise building application.
We used a model of chronic unloading followed by reloading to examine the apoptotic responses associated with soleus muscle atrophy and subsequent recovery. Male Wistar rats were subjected to ...hindlimb unloading (HU) for 2 weeks and subsequent reloading for 0, 3, 7 and 14 days. One-half of the HU-reloaded rats were administered cyclosporine A (CsA), a calcineurin (CaN) inhibitor. There was fibre atrophy (73%) and a decrease in slow type I fibre/myosin heavy chain (MyHC) composition in the soleus muscle after 2 weeks of HU. Fibre size and type I MyHC composition recovered to near the age-matched control levels by recovery day 14 in non-treated, but not in CsA-treated, rats. Myonuclear number was lower and the number of apoptotic nuclei higher in 2-week HU than control rats. These values returned to control levels after 7 and 14 days of recovery, respectively, in both HU-recovery groups. After 2 weeks of HU, the levels of heat shock proteins (Hsp) 60 and 72, mitochondrial cytochrome c oxidase subunit IV (Cox IV), and peroxisome proliferator-activated receptor gamma coactivator 1 (PGC-1) proteins were lower than control. The levels of all of these proteins gradually increased to or above the control levels during cage recovery in both groups. Our results indicate that apoptotic mechanisms are involved in the modulation of myonuclear number during chronic unloading and subsequent reloading. Furthermore, it appears that CaN is related to fibre size and phenotype adaptations, but not to apoptotic responses.
To compare the diagnostic performance of diffusion-weighted (DW) magnetic resonance (MR) imaging with that of dynamic contrast material-enhanced (DCE) MR imaging in evaluating the depth of myometrial ...invasion and overall stage in patients with endometrial cancer.
The institutional review board approved this retrospective study; patient consent was not required. From May 2008 to February 2010, 48 women with endometrial cancer underwent preoperative MR imaging, including T1- and T2-weighted imaging, DW MR imaging (b=0 and 800 sec/mm2) and DCE MR imaging. Two radiologists independently interpreted the depth of myometrial invasion, overall stage, and presence of pitfalls associated with inaccurate assessment of myometrial invasion at T1- and T2-weighted imaging, DW MR imaging, and DCE MR imaging. Myometrial invasion and overall stage were compared by using the McNemar test, and κ statistics were used for reader agreement.
For assessing the depth of myometrial invasion, diagnostic accuracy, sensitivity, and specificity, respectively, were as follows: DW MR imaging-reader 1, 90%, 84%, and 100%; reader 2, 85%, 84%, and 88%; DCE MR imaging-reader 1, 71%, 61%, and 88%; reader 2, 79%, 77%, and 82%. The improvement in diagnostic accuracy for reader 1 was significant (P=.035). For myometrial invasion, κ values were 0.75 with DW MR imaging and 0.26 with DCE MR imaging. There was no association between inaccurate assessment of myometrial invasion and standard pitfalls with DW MR imaging. Readers 1 and 2 correctly staged more patients by using DW MR imaging (39 and 38 patients, respectively) than by using DCE MR imaging (29 and 30 patients, respectively) (P<.05). For overall stage, κ values were 0.74 with DW MR imaging and 0.22 with DCE MR imaging.
DW MR imaging has superior diagnostic accuracy in the assessment of myometrial invasion and significantly higher staging accuracy compared with DCE MR imaging.
Oscillatory shear stress could not be directly measured in consideration of direction, although cerebrospinal fluid has repetitive movements synchronized with heartbeat. Our aim was to evaluate the ...important of oscillatory shear stress in the cerebral aqueduct and foramen magnum in idiopathic normal pressure hydrocephalus by comparing it with wall shear stress and the oscillatory shear index in patients with idiopathic normal pressure hydrocephalus.
By means of the 4D flow application, oscillatory shear stress, wall shear stress, and the oscillatory shear index were measured in 41 patients with idiopathic normal pressure hydrocephalus, 23 with co-occurrence of idiopathic normal pressure hydrocephalus and Alzheimer-type dementia, and 9 age-matched controls. These shear stress parameters at the cerebral aqueduct were compared with apertures and stroke volumes at the foramen of Magendie and cerebral aqueduct.
Two wall shear stress magnitude peaks during a heartbeat were changed to periodic oscillation by converting oscillatory shear stress. The mean oscillatory shear stress amplitude and time-averaged wall shear stress values at the dorsal and ventral regions of the cerebral aqueduct in the idiopathic normal pressure hydrocephalus groups were significantly higher than those in controls. Furthermore, those at the ventral region of the cerebral aqueduct in the idiopathic normal pressure hydrocephalus group were also significantly higher than those in the co-occurrence of idiopathic normal pressure hydrocephalus with Alzheimer-type dementia group. The oscillatory shear stress amplitude at the dorsal region of the cerebral aqueduct was significantly associated with foramen of Magendie diameters, whereas it was strongly associated with the stroke volume at the upper end of the cerebral aqueduct rather than that at the foramen of Magendie.
Oscillatory shear stress, which reflects wall shear stress vector changes better than the conventional wall shear stress magnitude and the oscillatory shear index, can be directly measured on 4D flow MR imaging. Oscillatory shear stress at the cerebral aqueduct was considerably higher in patients with idiopathic normal pressure hydrocephalus.
Two types of storm‐time Pc5 waves are excited in the magnetosphere–ionosphere coupled model. We conduct magnetosphere–ionosphere (M–I) coupling between geospace environment modeling system for ...integrated studies‐ring current (GEMSIS‐RC) and GEMSIS‐POTential solver (GEMSIS‐POT) models in order to investigate the excitation of storm‐time Pc5 waves under more realistic conditions. The coupled model enables us to simulate ion transport from the plasma sheet by the convection electric field. First, we find the excitation of fundamental mode Pc5 waves on the dayside. These waves are generated by the drift resonance and driven by positive energy gradient of ion phase space density (PSD). The wave excitation is similar with the case without M–I coupling. Second, we detect second harmonic mode Pc5 waves with high azimuthal wave number in the dusk and premidnight region. The PSD oscillates associated with the waves, and the drift‐bounce resonance occurs at 50–80 keV ions. We find that these ions drift around the Earth and reach the nightside again at t ∼ 4,500 s, whose time scale is comparable to the drift period of these ions. At that time, inward gradient of the PSD is created, which contributes to the wave growth. This effect does not happen in the case without dawn‐to‐dusk convection electric field driven by Region 1 field aligned current (FAC). We find that the shielding by Region 2 FAC suppresses the flux of newly injected ions at the nightside, inward gradient of the PSD, and power spectra of second harmonic mode waves.
Key Points
Two types of poloidal Pc5 waves are reproduced in a magnetosphere–ionosphere coupled model, where the growth rate is positive
Fundamental mode Pc5 waves are excited by the drift resonance in the dayside, where ions have positive energy gradient of the PSD
Second harmonic Pc5 waves are excited by the drift‐bounce resonance in the duskside, where ions have inward gradient of the PSD
In order to assess the characteristics with respect to surface strength of thin hard coatings of the Micro Slurry-jet Erosion (MSE) test which we have developed, the erosion behaviors of PVD TiN ...coating were studied. The MSE tests were conducted impacting a slurry-jet consisting of angular alumina particles with an average size of 1.2 μm or 41 μm, and spherical alumina particles with an average diameter of 3 μm, perpendicular to the specimen surface. The variations of the eroded surface profiles and the erosion depths were measured, and the eroded surfaces were observed using SEM, AFM and TEM. The erosion rates and the morphology of the eroded surface depend strongly on the size and shape of the erodent particles. For tiny angular particles, the main erosion mechanism is impact fatigue and sub-micro-cutting, while plastic deformation and micro-crack propagation due to fatigue are the main erosion mechanism for tiny spherical particles. On the contrary, in the case of large angular particles, brittle fracture followed by cutting due to large impact forces is the main characteristic. The depth to which the impacts of particles have an influence depends on the size and shape of the particles; the range of influence is from several tens of nanometers for tiny particles to several hundreds of nanometers for large angular particles. From these findings, it is concluded that the MSE test can be used to evaluate the properties related to various strengths by selection of the appropriate erodent particles.
•PD is characterized by dopaminergic neurodegeneration and iron overload in the SNpc.•QSM can quantify iron deposition.•Neuromelanin imaging can quantify loss of dopaminergic neurons.•A novel ...automatic volumetric SNpc region of interest selection method was developed.•QSM and neuromelanin imaging are useful for quantifying the SNpc alterations in PD.
To quantify dopaminergic neurodegeneration and iron overload in the substantia nigra pars compacta (SNpc) to evaluate Parkinson’s disease (PD) using both quantitative susceptibility mapping (QSM) and neuromelanin imaging.
We studied 39 PD patients (PD group) and 25 healthy controls (HC group) who underwent brain MRI with QSM and neuromelanin imaging. QSM and neuromelanin values of the SNpc were obtained using a voxel-based automated region segmentation system. The signal-to-noise ratio (SNR) of the SNpc in the neuromelanin images was calculated based on the mean value for the background region. The neuromelanin value was defined as the neuromelanin volume with an SNR higher than that of the background. The significance of the intergroup differences, and according to the severity stages in the PD group was tested for each QSM and neuromelanin value. Receiver-operating characteristic (ROC) analysis for diagnosing PD was performed for QSM and neuromelanin values.
The QSM value was significantly higher in the PD group than in the HC group (P < 0.05). The neuromelanin value was significantly smaller in the PD group than in the HC group (P < 0.05). The areas under the ROC curve were 0.68 and 0.86 for QSM and neuromelanin values, respectively. Using QSM and neuromelanin imaging to classify the PD stage was difficult.
Quantifying the SNpc alterations with our region-based approach is useful for the diagnosis of PD.
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