We present measurements of spin relaxation times (T1, T1ρ, T2) on very shallow (≲5 nm) nitrogen-vacancy centers in high-purity diamond single crystals. We find a reduction of spin relaxation times ...up to 30 times compared to bulk values, indicating the presence of ubiquitous magnetic impurities associated with the surface. Our measurements yield a density of 0.01-0.1μB/nm2 and a characteristic correlation time of 0.28(3) ns of surface states, with little variation between samples and chemical surface terminations. A low temperature measurement further confirms that fluctuations are thermally activated. The data support the atomistic picture where impurities are associated with the top carbon layers, and not with terminating surface atoms or adsorbate molecules. The low spin density implies that the presence of a single surface impurity is sufficient to cause spin relaxation of a shallow nitrogen-vacancy center.
Abstract We investigate the effect of the electron temperature gradient (ETG) driven turbulence on the energy transport in JT-60U L-mode plasma by means of the multi-scale gyrokinetic simulation. In ...the core region at r / a = 0.5 , the instability in the ion scale is driven by the ion temperature gradient (ITG), meanwhile strong unstable ETG modes are found in the electron scale. The nonlinear multi-scale gyrokinetic simulation shows that ETG modes are stabilized in the nonlinear phase and the energy transport in the multi-scale simulation is similar to that obtained in the ion scale ITG simulation. In an outer region at r / a = 0.6 , the ion scale instability changes to be the trapped electron mode (TEM). The multi-scale simulation shows that both the ion and the electron energy flux are reduced by ∼ 30 % compared to those obtained in the single scale TEM simulation. Interestingly, the electron energy flux is close to the experimental value after this reduction. From the data analyses, we find that ETG turbulence damps the energy of TEM modes through the ion scale/electron scale coupling and the electron scale/electron scale coupling, and can be modeled as a turbulent diffusion of TEM modes. These results suggest that the single ion scale simulation seems to be still valid in the inner region with r / a < 0.5 . However, in the outer region it is necessary to include the ETG modes in the gyrokinetic simulations to explain the energy transport in this L-mode plasma. This is the first result showing that ETG turbulence can reduce the electron energy loss via the cross-scale interaction in a real tokamak equilibrium profile.
We have developed a noninvasive pneumatics-based system by which to measure heartbeat, respiration, snoring, and body movements of a subject in bed. A thin, air-sealed cushion is placed under the bed ...mattress of the subject and the small movements attributable to human automatic vital functions are measured as changes in pressure using a pressure sensor having an almost flat frequency response from 0.1 to 5 kHz and a sensitivity of 56 mV/Pa. Using the newly developed system, heartbeat, respiration, apnea, snoring and body movements are clearly measured. In addition, the optimal signal-to-noise (S/N) ratio by which to evaluate the reliability of the heart rate measurement is presented. Heart rates were measured for four different body postures, 13 different subjects, four different bed mattresses, and three different sensor positions. For these measurements, the S/N ratios ranged from 15.9 to 23.5 dB, and so were determined to be reliable.
The KamLAND-Zen experiment has provided stringent constraints on the neutrinoless double-beta (0νββ) decay half-life in ^{136}Xe using a xenon-loaded liquid scintillator. We report an improved search ...using an upgraded detector with almost double the amount of xenon and an ultralow radioactivity container, corresponding to an exposure of 970 kg yr of ^{136}Xe. These new data provide valuable insight into backgrounds, especially from cosmic muon spallation of xenon, and have required the use of novel background rejection techniques. We obtain a lower limit for the 0νββ decay half-life of T_{1/2}^{0ν}>2.3×10^{26} yr at 90% C.L., corresponding to upper limits on the effective Majorana neutrino mass of 36-156 meV using commonly adopted nuclear matrix element calculations.
For understanding of film cooling flow fields on gas turbine blades, this paper reports on a series of large-eddy simulations of an inclined round jet issuing into a crossflow. Simulations were ...performed at four blowing ratios, BR=0.1, 0.5, 0.7 and 1.0, and the Reynolds number, Re=15,300, based on the crossflow velocity and film cooling hole diameter. Results showed that the cooling jet flow structure drastically changed with the blowing ratio. A pair of rear vortices and hairpin vortices were observed for BR=0.1. A horseshoe vortex periodically ejected, a pair of hanging vortices, a pair of rear vortices and hairpin vortices were observed for BR=0.5. Similar vortical structures to BR=0.5 were observed for BR=0.7 although horseshoe vortex was not ejected periodically and stayed at a leading edge of the hole exit. For BR=1.0, in addition to the former mentioned vortices, shear layer vortices and vertical streaks were observed on an upstream edge of the jet. It was consequently understood that the ubiquitous counter-rotating vortex pair which can be observed in the time-averaged flow field was actually originated in the different vortical structures with varying BR conditions. Temperature fields were also investigated to clarify how these different vortical structures affect the film cooling effectiveness.
Abstract
Multi-scale gyrokinetic theory and simulations of a toroidal magnetized plasma have revealed the existence of cross-scale interactions of the trapped electron mode (TEM) and the electron ...temperature gradient (ETG) turbulence. Reduction of the TEM instability growth rate in the ETG turbulence is clearly identified, and is well represented in the form of effective diffusion. A theoretical model based on the stochastic forcing by the ETG turbulence well describes the turbulent diffusion coefficient observed in multi-scale turbulence simulations.
Robust entanglement at room temperature is a necessary requirement for practical applications in quantum technology. We demonstrate the creation of bipartite- and tripartite-entangled quantum states ...in a small quantum register consisting of individual ¹³C nuclei in a diamond lattice. Individual nuclear spins are controlled via their hyperfine coupling to a single electron at a nitrogen-vacancy defect center. Quantum correlations are of high quality and persist on a millisecond time scale even at room temperature, which is adequate for sophisticated quantum operations.
A unified physical model of auroral arc growth and electron acceleration is constructed from the gyrokinetic and two‐fluid equations for the magnetosphere‐ionosphere (M‐I) coupling system. The ...present theory describes destabilization of kinetic Alfvén waves (KAWs) in the M‐I coupling, where development of upward and downward field‐aligned currents carried by the KAWs leads to ionospheric density enhancement and depletion, respectively. The feedback M‐I coupling through KAWs elucidates growth of auroral arcs and field‐aligned acceleration of electrons self‐consistently and provides a possible explanation to the Alfvénic auroras observed by the FAST spacecraft.
Key PointsA kinetic model of magnetosphere‐ionosphere coupling is constructedAuroral growth, KAW excitation, and electron acceleration are unified by theoryThe feedback coupling via KAWs possibly explains the Alfvén aurora
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