Neutrons produced by cosmic ray muons are an important background for underground experiments studying neutrino oscillations, neutrinoless double beta decay, dark matter, and other rare-event ...signals. A measurement of the neutron yield in the three different experimental halls of the Daya Bay Reactor Neutrino Experiment at varying depth is reported. The neutron yield in Daya Bay’s liquid scintillator is measured to be Yn=(10.26±0.86)×10−5, (10.22±0.87)×10−5, and (17.03±1.22)×10−5 μ−1 g−1 cm2 at depths of 250, 265, and 860 meters-water-equivalent. These results are compared to other measurements and the simulated neutron yield in Fluka and Geant4. A global fit including the Daya Bay measurements yields a power law coefficient of 0.77±0.03 for the dependence of the neutron yield on muon energy.
Mitigation of Edge localized mode(ELM) has been achieved with different external actuators such as lower hybrid wave (LHW), mixture supersonic molecular beam injection(SMBI), and laser blow-off(LBO) ...impurity seeding on HL-2A. During these experiments, the pedestal turbulence enhancement is commonly observed, which is found closely related to ELM mitigation. The turbulence enhancement is caused by the externally driven the velocity shear rate without change of the turbulence correlation length, but correlated to its radial wavenumber spectral shift. A common plausible mechanism for the ELM mitigation with different external source input seems to be involved. A modified theoretical model based on the turbulence radial wavenumber spectral shift is used and successfully interprets the experimental observations. The simulation suggests that a critical growth rate of the most unstable mode, also identified by the experimental results, survives in the competition of the velocity shear rate, enhancing the turbulence intensity. An example of the LHW case is used and good agreements have been found between the experimental results and simulation results.
According to the variation law of stress induced by hydraulic fractures during the initial fracturing of shale gas wells, the temporary plugging refracturing technology was studied. Based on the ...research on the mechanism of fracture reorientation from temporary plugging, the process parameters (such as the particle size combination of the temporary plugging agent, the temporary plugging timing, and the amount of temporary plugging agent) were optimized, and the key material for temporary plugging were evaluated. Temporary plugging refracturing technology suitable for shale gas horizontal well was initially formed. Excellent results of trial test were achieved and the production rate after refracturing was increased by 5 times compared with that before stimulation. This study can provide some reference for temporary plugging refracturing of shale gas wells.
For the first time supersonic molecular beam injection (SMBI) and cluster jet injection (CJI) were applied to mitigate edge-localized modes (ELMs) in HL-2A successfully. The ELM frequency increased ...by a factor of 2-3 and the heat flux on the divertor target plates decreased by 50% on average after SMBI or CJI. Energetic particle induced modes were observed in different frequency ranges with high-power electron cyclotron resonance heating (ECRH). The high frequency (200-350 kHz) of the modes with a relatively small amplitude was close to the gap frequency of the toroidicity-induced Alfvén eigenmode. The coexistent multi-mode magnetic structures in the high-temperature and low-collision plasma could affect the plasma transport dramatically. Long-lived saturated ideal magnetohydrodynamic instabilities during strong neutral beam injection heating could be suppressed by high-power ECRH. The absolute rate of nonlinear energy transfer between turbulence and zonal flows was measured and the secondary mode competition between low-frequency (LF) zonal flows (ZFs) and geodesic acoustic modes (GAMs) was identified, which demonstrated that ZFs played an important role in the L-H transition. The spontaneously generated E × B shear flow was identified to be responsible for the generation of a large-scale coherent structure (LSCS), which provided unambiguous experimental evidence for the LSCS generation mechanism. New meso-scale electric potential fluctuations (MSEFs) at frequency f ∼ 10.5 kHz with two components of n = 0 and m/n = 6/2 were also identified in the edge plasmas for the first time. The MSEFs coexisted and interacted with magnetic islands of m/n = 6/2, turbulence and LF ZFs.
To construct a preoperative evaluation system for partial nephrectomy using CT three-dimensional visualization technology and to explore its practical value.
The clinical data of the patients who ...underwent partial nephrectomy for renal tumors in Department of Urology, Peking University First Hospital were collected retrospectively. At the same time, the homogenized standard data of patients who underwent partial nephrectomy for renal tumors were collected in 16 clinical centers in China. The CT three-dimensional visualization system was applied (IPS system, Yorktal) to evaluate tumor anatomy, blood supply, perirenal fat and other information. The parameters were summarized to build a three-dimensional nephrometry system, on the basis of which virtual surgery design and intraoperative navigation were completed.
A three-dimensional visualization image was established based on the enhanced CT urography. The nephrometry system included the longest diameter and volume of the tumor, proportion volume of tumor invad
To improve the firing dispersion of the tank, the influences of random factors on firing dispersion are analyzed quantitatively. Based on the six-degree-of-freedom rigid-body ballistic equation, ...considering the influences of processing and assembly errors, initial disturbances and the wind on flight, using the Sobol' global sensitivity analysis method, the weights of affecting factor are obtained. The analysis results show that, under the current manufacturing and measuring conditions, the initial disturbance of projectile is the premier factor that takes effect on the firing dispersion of the straight shooting weapon (such as a tank) with small elevation angle.
Experiments to study inward heat transport phenomena have been performed in the Tore Supra tokamak with off-axis electron cyclotron resonance heating (ECRH). Both power balance and perturbation ...transport analysis have been done for low-frequency (1 Hz) ECRH modulation experiments. Heat diffusivity and heat pinch have been separately determined by fitting the experimental data of the amplitude and phase of the Fourier transform of the modulated temperature with a linear transport model including convection term. Comparison with the critical gradient model has shown that the heat pinch previously obtained could include a pseudo-pinch due to the non-linearity of the diffusivity and an additional non-diffusive heat pinch. The pinch effect is reduced for higher densities.
This paper presents a numeric study of the dynamic stabilization of the ablative Rayleigh-Taylor instability (ARTI) in the presence of a temporally modulated laser pulse. The results show that the ...specially modulated laser produces a dynamically stabilized configuration near the ablation front. The physical features of the relevant laser-driven parameters in the unperturbed ablative flows have been analyzed to reveal the inherent stability mechanism underlying the dynamically stabilized configuration. A single-mode ARTI for the modulated laser pulse is first compared with that of the unmodulated laser pulse. The results show that the modulated laser stabilizes the surface perturbations and reduces the linear growth rate and enhancement of the cutoff wavelength. For multimode perturbations, the dynamic stabilization effect of the modulated laser pulse contributes to suppress the small-scale structure and reduce the width of the mixing layer. Moreover, the results show that the stabilization effect of the modulated laser pulse decreases as the maximum wavelength increases.
In this work, a series of Ti1 - xAlxN (0 < = x < = 0.7) coatings were deposited on high speed steel (HSS) substrates by a vacuum arc reactive evaporation process from two lateral rotating elemental ...titanium and aluminium cathodes in a pure nitrogen atmosphere. The composition, crystalline structure and hardness of the as-deposited coatings were analyzed by energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and nanoindentation experiments. The abrasion wear resistance of the TiAlN coatings was measured by a micro-abrasion tester with the presence of SiC water-based slurry with a concentration of 0.35 g/cm3. It was found that with increasing the Al/Ti atomic ratio the hardness of the as-deposited TiAlN coatings initially increased up to a maximum value of about 40 GPa at around Al/Ti = 1.22, and then the coating hardness decreased rapidly with increasing aluminium content further. The abrasion wear resistance of the TiAlN coatings is evidently better, with one order of magnitude lower in the wear rate, than the bare HSS substrate. With increasing Al/Ti atomic ratio, the variation trend of the abrasion wear rate of the TiAlN coatings is generally opposite to that of coating hardness. This means the abrasion wear resistance of the TiAlN PVD hard coatings is predominately determined by the hardness of the coating materials. It was also noted that, besides the coating hardness, the composition of the TiAlN coatings also plays an important role in determining their abrasive wear resistance. The coatings in the higher Al content range (Al/Ti > = 1.60) exhibited an evident better abrasive wear resistance than those in the lower aluminium content range (Al/Ti < = 0.32) when their hardness is similar. This fact could be related to the finer microstructure of the coatings incorporated with higher aluminium content.
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