Performance enhancement of armchair graphene nanoribbon resonant tunneling diode using V-shaped potential well

We study the electron transport in armchair graphene nanoribbon (AGNR) resonant tunneling diode (RTD) using square and V-shaped potential well profiles. We use non-equilibrium Green’s function formalism to analyze the transmission and I-V characteristics. Results show that an enhancement in the peak current (Ip ) can be obtained by reducing the well width (Ww ) or barrier width (Wb ). As Ww decreases, Ip shifts to a higher peak voltage (Vp ), while there is almost no change in Vp with decreasing Wb . It is gratifying to note that there is an enhancement in Ip by about 1.6 times for a V-shaped well over a square well. Furthermore, in the case of a V-shaped well, the negative differential resistance occurs in a shorter voltage range, which may beneficial for ultra-fast switching and high-frequency signal generation. Our work anticipates the suitability of graphene, having better design flexibility, to develop ideally 2D RTDs for use in ultra-dense nano-electronic circuits and systems.

Kilometer-scale structure on the core-mantle boundary at the source of the Hawaiian mantle plume

The lowermost mantle right above the core-mantle boundary is highly heterogeneous containing multiple poorly understood seismic features visible across a wide range of length scales. The smallest but most extreme heterogeneities yet observed are 'Ultra-Low Velocity Zones' (ULVZ), several of which have recently been linked to the base of mantle plumes. We exploit seismic shear waves that diffract along the core-mantle boundary to provide new insight into these enigmatic structures. We demonstrate that these waves have a strong frequency-dependent sensitivity to structure at different length scales above the core-mantle boundary. We measure a rare core-diffracted signal refracted by a ULVZ at the base of the Hawaiian mantle plume at unprecedentedly high frequencies. This signal shows remarkably longer time delays at higher compared to lower frequencies, indicating extreme internal variability within the Hawaiian ULVZ. Utilizing the latest computational advances in 3D synthetic waveform modeling, we are able to model this high frequency signal and constrain high-resolution structure on the scale of kilometers at the core-mantle boundary, for the first time. Results reveal that the lowermost part of the Hawaiian ULVZ is extremely reduced in shear wave velocity, by up to -40%. This new observation suggests a chemically distinct ULVZ with increasing iron content towards the core-mantle boundary, which has implications for Earth’s early evolutionary history and core-mantle interaction.

Sensorless Predictive Current Control of a Permanent Magnet Synchronous Motor Powered by a Three-Level Inverter

Permanent magnet synchronous motors and their relevant control techniques have become more and more prevalent in electric vehicle driving applications because of their outstanding performance. This paper studies a simple and effective sensorless scheme based on a current observer for a permanent magnet synchronous motor powered by a three-level inverter, which avoids the injection of a high-frequency signal and the observation of back-electromotive force. In this way, a current observer is constructed to observe d–q-axes currents by relying on an extended-current model. Thereafter, the position and speed of the machine can be extracted from two PI controllers associated with the d–q-axes current-tracking errors. Meanwhile, it takes into account the model predictive current control with neutral-point voltage balance to maintain the stability of the three-level inverter system. In general, this scheme realizes sensorless operation in a full-speed domain and is no longer limited by the types of inverter and method used.

Re-Design of Machine Tool Joint Components Based on Polymer Fillings for High-Speed Performance

In this paper, we report the results of an experimental study of a re-design approach using filling polymers and particulate composites with a polymer matrix, thus creating a macroscopic hybrid structure. The re-design is focused on the joint of a textile machine. It is a re-design of already existing machine parts of a joint in order to increase the damping of components, reduce the amplitudes of high-frequency vibrations and acoustic emission for high-speed operation of textile rotors, and to compare individual structural modifications of the rotor housing body and absorber of high-speed textile rotor in a spinning unit with respect to dynamic properties of that measured mechanical system. The experiments included a bump test, determination of logarithmic decrement, measurement of vibration acceleration, a wavelet analysis, and measurement of acoustic emission. When excited by high frequency signal amplitudes up to 5 g, the benefits of polymer filling were manifested by an approximately 50% reduction in amplitude vibrations, a 66% reduction in acoustic emission amplitude, and an 85% reduction of the maximum peak in the acoustic emission FFT spectrum. In the area above 10 g, the stiffness of the component dominated to reduce the magnitude of vibrations.

Relevance of Frequency-Domain Analyses to Relate Shoe Cushioning, Ground Impact Forces and Running Injury Risk: A Secondary Analysis of a Randomized Trial With 800+ Recreational Runners

Cushioning systems in running shoes are used assuming that ground impact forces relate to injury risk and that cushioning materials reduce these impact forces. In our recent trial, the more cushioned shoe version was associated with lower injury risk. However, vertical impact peak force was higher in participants with the Soft shoe version. The primary objective of this study was to investigate the effect of shoe cushioning on the time, magnitude and frequency characteristics of peak forces using frequency-domain analysis by comparing the two study groups from our recent trial (Hard and Soft shoe group, respectively). The secondary objective was to investigate if force characteristics are prospectively associated with the risk of running-related injury. This is a secondary analysis of a double-blinded randomized trial on shoe cushioning with a biomechanical running analysis at baseline and a 6-month follow-up on running exposure and injury. Participants (n = 848) were tested on an instrumented treadmill at their preferred running speed in their randomly allocated shoe condition. The vertical ground reaction force signal for each stance phase was decomposed into the frequency domain using the discrete Fourier transform. Both components were recomposed into the time domain using the inverse Fourier transform. An analysis of variance was used to compare force characteristics between the two study groups. Cox regression analysis was used to investigate the association between force characteristics and injury risk. Participants using the Soft shoes displayed lower impact peak force (p < 0.001, d = 0.23), longer time to peak force (p < 0.001, d = 0.25), and lower average loading rate (p < 0.001, d = 0.18) of the high frequency signal compared to those using the Hard shoes. Participants with low average and instantaneous loading rate of the high frequency signal had lower injury risk [Sub hazard rate ratio (SHR) = 0.49 and 0.55; 95% Confidence Interval (CI) = 0.25–0.97 and 0.30–0.99, respectively], and those with early occurrence of impact peak force (high frequency signal) had greater injury risk (SHR = 1.60; 95% CI = 1.05–2.53). Our findings may explain the protective effect of the Soft shoe version previously observed. The present study also demonstrates that frequency-domain analyses may provide clinically relevant impact force characteristics.Clinical Trial Registration:https://clinicaltrials.gov/, identifier: 9NCT03115437.

Coherent Random-Modulated Continuous-Wave LiDAR Based on Phase-Coded Subcarrier Modulation

A coherent random-modulated continuous-wave (RMCW) LiDAR transmits a lightwave modulated by a pseudo-random binary sequence (PRBS). The lightwave backscattered from targets is received and used to reconstruct the PRBS. Then, the time-of-flight is extracted by correlating the reconstructed PRBS and the original PRBS. We propose a coherent RMCW LiDAR based on phase-coded subcarrier modulation, in which the impacts of internal reflection and optical Doppler frequency shift (DFS) are mitigated. A continuous lightwave is amplitude-modulated by an RF signal which is phase-coded with a PRBS. Coherent detection is used in the receiver. A beat signal that consisted of a low-frequency signal and a high-frequency signal is obtained by a single balanced photodetector (BPD). The optical DFS can be directly extracted from the low-frequency signal. It is used to compensate for the frequency offset of PRBS, which is extracted from the high-frequency signal. In addition, the background noise caused by internal reflection is suppressed by averaging over successive measurement spots. In this paper, the performance of a coherent RMCW LiDAR is firstly analyzed by numeric simulations and demonstration experiments. Then, line-scanning measurements for moving targets are implemented to demonstrate the 3D imaging capability of the proposed coherent RMCW LiDAR.

ALGORITHMS FOR THE FORMATION OF NARROW-BAND SPECTRAL-EFFICIENT RADIO SIGNALS OUTSIDE THE RING OF PULSE-PHASE AUTOMATIC FREQUENCY TUNING OF THE FREQUENCY SYNTHESIZER

Рассмотрен процесс формирования радиосигнала с помощью квадратурного модулятора. Точность осуществления переноса на несущую является критически важным фактором. При передаче информационного сообщения значения сигнала несущей частоты должны принимать соответствующие дискретные значения, согласно закону изменения информационной последовательности, таким образом, формирование неискажённого радиосигнала является одним из основных требований, предъявляемых к работе квадратурного модулятора. При реализации сигналов с угловой модуляцией, как правило, используют генератор, управляемый напряжением. Проанализирована работа квадратурного модулятора и квадратурного фазового модулятора, основанного на формирователях функциональных составляющих модулирующего сигнала. Предложен метод компенсации искажений, возникающих в балансных смесителях и фазовращателе за счет быстроизменяющихся помех, приходящих с выхода высокочастотного генератора или с выхода усилителя мощности по цепи обратной связи, а также медленных отклонений фазы и амплитуды сигнала. Проведено моделирование работы схемы, осуществляющей компенсацию амплитудно-фазовых искажений квадратурного модулятора сигналов угловой модуляции за счёт генерирования компенсационных сигналов. Предложена структурная схема синтеза неискаженного сигнала амплитудно-фазовой модуляции с компенсацией амплитудно-фазовой нестабильности квадратурного формирователя, позволяющая осуществлять нелинейное усиление радиосигнала The paper considers the process of data transmission over a radio channel by modulating the parameters of the carrier wave with an information signal. When transmitting an information signal, the carrier frequency values must take discrete values in one-to-one correspondence with the information sequence, thus the formation of an undistorted radio signal is one of the main requirements for the operation of a quadrature modulator. The article analyzes the operation of a quadrature modulator and a quadrature phase modulator based on the shapers of the functional components of the modulating signal. We propose a distortion compensation method using synthesized compensation signals, which makes it possible to effectively compensate, firstly, rapidly changing noise inside balanced modulators and phase shifters, and secondly, noise coming along with an input high-frequency signal, for example, from the output of a power amplifier through circuits feedback and, third, slow deviations of amplitudes and phases. We carried out the modeling of the distortion compensation method using synthesized compensation signals