Beta-induced Alfvén eigenmodes and geodesic acoustic modes in presence of strong tearing activity during the current ramp-down on JET

The analysis of the current ramp-down phase of JET plasmas has revealed the occurrence of additional magnetic oscillations in pulses characterized by large magnetic islands. The frequencies of these oscillations range from 5 kHz to 20 kHz, being well below the toroidal gap in the Alfven continuum and of the same order of the low-frequency gap opened by plasma compressibility. The additional oscillations only appear when the magnetic island width exceeds a critical threshold, suggesting that the oscillations could tap their energy from the tearing mode (TM) by a non-linear coupling mechanism. A possible role of fast ions in the excitation process can be excluded, being the pulse phase considered characterized by very low additional heating. The calculation of the coupled Alfven-acoustic continuum in toroidal geometry suggests the possibility of beta-induced Alfven eigenmodes (BAE) rather than beta-induced Alfven acoustic eigenmodes (BAAE). As a main novelty compared to previous works, the analysis of the electron temperature profiles from electron cyclotron emission has shown the simultaneous presence of magnetic islands on different rational surfaces in pulses with multiple magnetic oscillations in the low-frequency gap of the Alfven continuum. This observation supports the hypothesis of different BAE with toroidal mode number n = 1 associated with different magnetic islands. As another novelty, the observation of magnetic oscillations with n = 2 in the BAE range is reported for the first time in this work. Some pulses, characterized by slowly rotating tearing modes, exhibit additional oscillations with n = 0, likely associated with geodesic acoustic modes (GAM), and a cross-spectral bicoherence analysis has confirmed a non-linear interaction among TM, BAE and GAM, with the novelty of the observation of multiple triplets (twin BAEs plus GAM), due to the simultaneous presence of several magnetic islands in the plasma.

Zonal flow generation and toroidal Alfvén eigenmode excitation due to tearing mode induced energetic particle redistribution

Generation of the n = 0 zonal flow and excitation of the n = 1 toroidal Alfvén eigenmode (TAE) due to the redistribution of energetic particles (EPs) by the m/n = 2/1 tearing mode (TM) are systematically studied with the hybrid drift-kinetic magnetohydrodynamic (MHD) simulations (m and n represent the poloidal and toroidal mode number, respectively). In the presence of the m/n = 2/1 TM, the amplitude of the n = 1 TAE shows a slower decay after its first saturation due to the wave-particle nonlinearity and the nonlinear generation of the n = 0 & higher-n (n ≥ 2) sidebands. Meanwhile, a strong n = 0 zonal flow component is nonlinearly generated when both TAE and TM grow to large amplitudes. The redistribution of EPs by the m/n = 2/1 magnetic island results in a continuous drive on the background plasma, and finally produces the zonal flow through the MHD nonlinearity. In addition, the large m/n = 2/1 magnetic island is found to be responsible for the formation of the strong spatial gradient of the EP distribution through the resonance between EPs and TM, which can lead to burst of unstable TAE and destabilization of originally stable TAE.

Hybrid Cognitive-Radio NOMA with Blind Transmission Mode Identification and BER Constraints

<div>The synergy of nonorthogonal multiple access (NOMA) and cognitive radio (CR) can provide efficient spectrum utilization for future wireless networks and enable supporting heterogeneous quality of service (QoS) requirements. In this context, this article aims at evaluating the throughput of a downlink CR-NOMA network where the secondary user (SU) data is opportunistically multiplexed with the primary user (PU) data using power-domain NOMA. The data multiplexing process is constrained by the PU QoS requirements. The multiplexing process can be considered seamless with respect to the PU because its receiver design will generally remain unchanged. Moreover, we consider the case where the SU detects its own data by blindly identifying the adopted transmission mode (TM) at the base station, which can be PU orthogonal multiple access PU-OMA, SU-OMA, PU/SU-NOMA, and no transmission. Consequently, the network can be classified as a hybrid underlay-interweave. The detection process is considered blind because the SU does not receive side information about the adopted TM. The obtained analytical results corroborated by Monte Carlo simulation results show that the proposed CR-NOMA network can provide substantial throughput improvement over conventional NOMA networks, particularly at low signal-to-noise ratios (SNRs) because the unutilized PU spectrum can be used by the SU. Moreover, in good channel conditions the PU can tolerate some interference from the SU, which may improve the channel utilization significantly. </div><div><br></div>

Hybrid Cognitive-Radio NOMA with Blind Transmission Mode Identification and BER Constraints

<div>The synergy of nonorthogonal multiple access (NOMA) and cognitive radio (CR) can provide efficient spectrum utilization for future wireless networks and enable supporting heterogeneous quality of service (QoS) requirements. In this context, this article aims at evaluating the throughput of a downlink CR-NOMA network where the secondary user (SU) data is opportunistically multiplexed with the primary user (PU) data using power-domain NOMA. The data multiplexing process is constrained by the PU QoS requirements. The multiplexing process can be considered seamless with respect to the PU because its receiver design will generally remain unchanged. Moreover, we consider the case where the SU detects its own data by blindly identifying the adopted transmission mode (TM) at the base station, which can be PU orthogonal multiple access PU-OMA, SU-OMA, PU/SU-NOMA, and no transmission. Consequently, the network can be classified as a hybrid underlay-interweave. The detection process is considered blind because the SU does not receive side information about the adopted TM. The obtained analytical results corroborated by Monte Carlo simulation results show that the proposed CR-NOMA network can provide substantial throughput improvement over conventional NOMA networks, particularly at low signal-to-noise ratios (SNRs) because the unutilized PU spectrum can be used by the SU. Moreover, in good channel conditions the PU can tolerate some interference from the SU, which may improve the channel utilization significantly. </div><div><br></div>

Characteristics of inherent coupling structure of model climates

This work proposes a framework to examine interactions of climate modes that are identified as leading EOF modes; their coupling structure is unveiled through correlation analysis and helps constructing a regression model, whose performance is compared across GCMs, thereby providing a quantitative overview of model performances in simulating mode-interaction. As demonstration surface temperature is analyzed for five CMIP5 PiControl simulations. Along with the seasonal land and ocean modes, four interannual modes are identified: Tropical Mode (TM) associated with the Hadley circulation, Tropical Pacific Mode (TPM) characterizing a zonal temperature contrast between the eastern tropical Pacific and the Atlantic-Indian ocean, and two annular modes: Arctic Mode (AM) and Ant-arctic Mode (AAM). All GCMs converge on the following: 1) TM strongly couples with seasonal signals of the previous year; 2) TPM leads TM by 1 year, thus a weaker zonal temperature contrast in the tropics contributes to warming in the entire tropical band one year later; 3) AM weakly couples to TM at a one-year lead, suggesting a colder north pole may contribute to colder tropics. In addition, all GCMs do not support a linear coupling between AAM and TM. The above-learned coupling structure is incorporated to construct an optimum regression model that demonstrates considerable predictive power. The proposed approach may both serve as a useful tool for dynamical analysis and lend insight into GCM differences. Its merit is demonstrated by the finding that different representations of the mean seasonal cycle in GCMs may account for the GCM-dependence of relative contributions of seasonal and inter-annual modes to TM variability.

Compact and Hexaband Rectangular Microstrip Patch Antenna for Wireless Applications

A Compact Corner Split Ring with Split C Slot Rectangular Microstrip patch Antenna (CCSR-SCS) fed by a 50 Ω microstripline is discussed. A Corner split ring with C shaped slot has been etched in rectangular microstrip antenna. The slot increases the length of the surface current for the dominant mode TM 10 leading to the decrease in resonance frequency. The size reduction along with proposed antenna Hexaband is obtained with the antenna and it is best suited for wireless communication. The proposed work is simulated using 3DEM of Mentorgraphics. The results show that Hexaband with compactness is achieved.

Single-Longitudinal-Mode Laser at 1123 nm Based on a Twisted-Mode Cavity

A single-longitudinal-mode (SLM) Neodymiun-doped Yttrium Aluminium Garnet (Nd:YAG) laser at 1123 nm was first demonstrated with a twisted-mode (TM) cavity. By eliminating the spatial hole burning phenomenon, a stable SLM 1123 nm laser output was obtained. An efficient TM cavity was designed based on the Brewster plate with high reflection under s-polarization radiation. At an incident pump power of 7.65 W, the maximum output power of 689 mW was obtained. The corresponding optical conversion efficiency was about 9%. The center wavelength was 1122.58 nm and the line-width was <140 MHz.

Diaphragm Paralysis After Cardiac Surgery: A Frequent Cause of Post-Operative Respiratory Failure

BackgroundDiaphragmatic dysfunction (DD) is found in 1.2-60% of patients after cardiac surgery. The aim of this study was to reinvestigate the incidence, risk factors and outcomes of DD with actual cardiac surgery procedures.MethodsThis is an observational study based on a prospectively collected database in one cardiac surgery centre. The DD group included patients with clinically perceptible diaphragmatic paralysis, which was confirmed by chest ultrasound (amplitude of the diaphragm movement in time-motion mode [TM] at rest, after a sniff test). The primary endpoint was the incidence of DD. ResultsA total of 3577 patients were included between January 2016 and September 2019. We found 272 cases of DD (7.6%). Individuals with DD had more arterial hypertension (64.3% vs. 52.6%; p<0.0001), higher body mass index (BMI) (28[25–30] kg/m2 vs. 26[24-29] kg/m2; p<0.0002) and higher incidence of coronary bypass grafting (58.8% vs. 46.6%; p=0.0001). DD was associated with more postoperative pneumonia (23.9% vs. 8.7%; p<0.0001), reintubation (8.8% vs. 2.9%; p<0.0001), tracheotomy (3.3% vs. 0.3%; p<0.0001), non-invasive ventilation (45.6% vs. 5.4%; p<0.0001), duration of mechanical ventilation (5[4-11] h vs. 4[3-6] h; p<0.0001), and ICU and hospital stays (14[11-17] days vs. 13[11–16] days; p<0.0001). In multivariate analysis, DD was associated with coronary artery bypass grafting (OR=1.9[1.5-2.6]; p=0.0001), arterial hypertension (OR=1.4[1.1- 1.9]; p=0.008), and BMI (OR per point =1.04[1.01-1.07] kg/m2; p=0.003).ConclusionThe incidence of symptomatic DD after cardiac surgery was 7.6%, leading to respiratory complications and increased ICU stay. Coronary bypass grafting was the principal factor associated with DD.

The Conformal Finite-Difference Time-Domain Simulation of GPR Wave Propagation in Complex Geoelectric Structures

The finite-difference time-domain (FDTD) method adopts the most popular numerical model simulating ground penetrating radar (GPR) wave propagation in an underground structure. However, a staircase approximation method is usually adopted to simulate the curved boundary of an irregular object in the FDTD and symplectic partitioned Runge-Kutta (SPRK) methods. The approximate processing of rectangular mesh parameters will result in calculation errors and virtual surface waves for irregular targets of an underground structure. In this paper, we examine transverse mode (TM) electromagnetic waves with numerical models of electromagnetic wave propagation in geoelectric structures with conformal finite-difference time-domain (CFDTD) method technology in which the effective dielectric parameters are used to accurately simulate the dielectric surface and to absorb waves at the edges of the grid. The third orders of the transmission boundary are used in this paper. Additionally, three complex geocentric models of inclined layered media, spherical media, and three-layered pavement model with structural damages are set up for simulation calculations, then we carry out the actual radar wave detection in a laboratory as the fourth numerical example. Comparison of simulated reflectance waveform of FDTD, symplectic partitioned Runge-Kutta (SPRK), and CFDTD methods shows that at least 50% of the virtual waves can be reduced by using the proposed algorithm. Wiggle diagrams of FDTD and CFDTD methods show that much of the virtual waves have been reduced, and the radar image is clearer than before. This provides a method for the detection of complex geoelectric and layered structures in actual engineering.

Fixed off Time Based Power-Factor Correction for AC-DC Converter

The conversion of A.C to D.C determines the distortion of the mains current A.C., which degrades the input power factor. The main reason for a poor power factor is the non-linear nature of the circuit. In this paper power factor is improved by using a basic boost converter and a control technique based on the fixed off time(FOT) approach .The traditional approach to the correction of the power factor in the boost converter is the continuous conduction mode with fixed frequency (FF-CCM) and the transition mode (TM) PWM (fixed connection time, variable frequency). In the first mode, the inductor operates in continuous conduction mode (CCM) and uses the average current-mode control mode; a complex technique involves a considerable number of components. The second method uses the more complex control technique of the peak current mode that makes the inductor work between continuous and discontinuous mode, which uses fewer components, unstable greater than 50% duty cycle and is more cost efficient. A third approach, the fixed off time (FOT) is gaining popularity which is conditionally stable for a duty cycle of over 50% and does not need compensation. The paper work carried out to use the power factor correction (PFC) based on DC-DC Flyback converter. To verify the design and operation of the circuit, the simulation is performed in PSIM .A prototype is developed and results are presented.