duty cycles
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2022 ◽  
Vol 22 (2) ◽  
pp. 1-26
Author(s):  
Nikumani Choudhury ◽  
Rakesh Matam ◽  
Mithun Mukherjee ◽  
Jaime Lloret

The IEEE 802.15.4 standard is one of the widely adopted specifications for realizing different applications of the Internet of Things. It defines several physical layer options and Medium Access Control (MAC) sub-layer for devices with low-power operating at low data rates. As devices implementing this standard are primarily battery-powered, minimizing their power consumption is a significant concern. Duty-cycling is one such power conserving mechanism that allows a device to schedule its active and inactive radio periods effectively, thus preventing energy drain due to idle listening. The standard specifies two parameters, beacon order and superframe order, which define the active and inactive period of a device. However, it does not specify a duty-cycling scheme to adapt these parameters for varying network conditions. Existing works in this direction are either based on superframe occupation ratio or buffer/queue length of devices. In this article, the particular limitations of both the approaches mentioned above are presented. Later, a novel duty-cycling mechanism based on MAC parameters is proposed. Also, we analyze the role of synchronization schemes in achieving efficient duty-cycles in synchronized cluster-tree network topologies. A Markov model has also been developed for the MAC protocol to estimate the delay and energy consumption during frame transmission.


2022 ◽  
Vol 13 (1) ◽  
Author(s):  
Cecilia Clivati ◽  
Alice Meda ◽  
Simone Donadello ◽  
Salvatore Virzì ◽  
Marco Genovese ◽  
...  

AbstractQuantum mechanics allows distribution of intrinsically secure encryption keys by optical means. Twin-field quantum key distribution is one of the most promising techniques for its implementation on long-distance fiber networks, but requires stabilizing the optical length of the communication channels between parties. In proof-of-principle experiments based on spooled fibers, this was achieved by interleaving the quantum communication with periodical stabilization frames. In this approach, longer duty cycles for the key streaming come at the cost of a looser control of channel length, and a successful key-transfer using this technique in real world remains a significant challenge. Using interferometry techniques derived from frequency metrology, we develop a solution for the simultaneous key streaming and channel length control, and demonstrate it on a 206 km field-deployed fiber with 65 dB loss. Our technique reduces the quantum-bit-error-rate contributed by channel length variations to <1%, representing an effective solution for real-world quantum communications.


2021 ◽  
Vol 60 (1) ◽  
Author(s):  
Eunbi Ye ◽  
Jung Lee ◽  
Young-Soo Lim ◽  
Seung Yang ◽  
Sung-Min Park

Author(s):  
Gaopan Lei ◽  
Dong Zhu ◽  
Di Zhu

In the aerospace field, difficult-to-machine materials are used widely to improve engine performance. As a nickel-based material that performs well in all aspects, Inconel 625 is used for the blisks of aircraft engines, and electrochemical trepanning (ECTr) is used widely to fabricate such blisks because of its unique advantages regarding ruled surface parts. In this study, to investigate the performance of Inconel 625 in ECTr, measurements were made of the electrochemical characteristics firstly, specifically the anodic polarization curve and the actual volumetric electrochemical equivalent curve. Then, via dynamic electric-field simulations, the processes for forming Inconel 625 blades using ECTr were examined under direct voltage (DV) and pulsed voltage. The contours and current density distributions of formed blades at different times were obtained under different duty cycles. With decreasing duty cycle, the forming accuracy improved gradually and the stray current was reduced. To verify the simulation results, ECTr experiments with Inconel 625 were performed under different voltage conditions. With DV and 90% and 80% duty cycle, the taper angles of the machined blades were 7.784°, 6.278°, and 5.191°, respectively, and the surface roughness ( Ra) values were 0.95, 0.81, and 0.72 μm, respectively. With DV, there were obvious flow marks and gullies on the microscopic surface. With decreasing duty cycle, stray corrosion was reduced effectively and the state of the flow field was improved. Overall, the simulation results were verified effectively.


2021 ◽  
Vol 9 ◽  
Author(s):  
Woohyeon Jo ◽  
Dasol Jeong ◽  
Jaebum Jeong ◽  
Taegeon Kim ◽  
Seungyeon Han ◽  
...  

Nickel phosphide (Ni-P) films as a catalytic cathode for the hydrogen evolution reaction (HER) of a water splitting were fabricated by a pulse-reverse electrodeposition technique. The electrochemical behaviors for the electrodeposition of Ni-P were investigated by the characterization of peaks in a cyclic voltammogram. The composition of the electrodeposited Ni-P alloys was controlled by adjusting duty cycles of the pulse-reverse electrodeposition. The HER electrocatalytic properties of the Ni-P electrodeposits with an amorphous phase as a function of phosphorous contents existing in Ni-P were electrochemically characterized by the analysis of overpotentials, Tafel slopes, and electrochemical impedance spectrometry. Additionally, the elemental Ni-embedded crystalline Ni3P was prepared by an annealing process with the amorphous Ni69P31 electrodeposit with high contents of phosphorus. The crystalline structure with Ni inclusions in the matrix of Ni3P was formed by the precipitation of excess Ni. The electrocatalytic properties of crystalline Ni3P with elemental Ni inclusions were also investigated by electrochemical characterization.


2021 ◽  
Author(s):  
Walid Issa ◽  
Jose Ortiz-Gonzalez ◽  
Yihua Hu

<p>Low-gain buck converters will enable low voltage loads to access high voltage DC sources by a single stage converter at very low duty cycles. SiC MOSFETs are still limited to 1.7kV commercially and by seriesing them with adequate gate driving strategy, high voltages can be switched. This paper proposes a driving circuit for series SiC MOSFETs to block higher voltages. The driving circuit provides negative off-state voltage and turn on/off transitions in less than 100ns. The low-gain buck converter performance is assessed when using a single IGBT switch and series SiC MOSFETs. A simulation is implemented and shows the superiority of the proposed driven series SiC MOSFETs with distributed voltage and thermal stresses.</p>


2021 ◽  
Author(s):  
Walid Issa ◽  
Jose Ortiz-Gonzalez ◽  
Yihua Hu

<p>Low-gain buck converters will enable low voltage loads to access high voltage DC sources by a single stage converter at very low duty cycles. SiC MOSFETs are still limited to 1.7kV commercially and by seriesing them with adequate gate driving strategy, high voltages can be switched. This paper proposes a driving circuit for series SiC MOSFETs to block higher voltages. The driving circuit provides negative off-state voltage and turn on/off transitions in less than 100ns. The low-gain buck converter performance is assessed when using a single IGBT switch and series SiC MOSFETs. A simulation is implemented and shows the superiority of the proposed driven series SiC MOSFETs with distributed voltage and thermal stresses.</p>


2021 ◽  
Vol 11 (22) ◽  
pp. 10883
Author(s):  
Qinwen Liu ◽  
Ezaz Ahmed ◽  
K. M. Mohibul Kabir ◽  
Xiaojing Huang ◽  
Dan Xiao ◽  
...  

Electrospray ionisation (ESI) is renowned for its ability to ionise intact proteins for sensitive detection by mass spectrometry (MS). However, the use of a conventional direct current ESI voltage can result in the formation of relatively large initial droplet sizes, which can limit efficient ion desolvation and sensitivity. Here, pulsed nanoESI (nESI) MS using nanoscale emitters with inner diameters of ~250 nm is reported. In this approach, the nESI voltage is rapidly pulsed from 0 to ~1.5 kV with sub-nanosecond rise times, duty cycles from 10 to 90%, and repetition rates of 10 to 350 kHz. Using pulsed nESI, the performance of MS for the detection of intact proteins can be improved in terms of increased ion abundances and decreased noise. The absolute ion abundances and signal-to-noise levels of protonated ubiquitin, cytochrome C, myoglobin, and carbonic anhydrase II formed from standard denaturing solutions can be increased by up to 82% and 154% using an optimal repetition rate of ~200 kHz compared to conventional nESI-MS. Applying pulsed nESI-MS to a mixture of four proteins resulted in the signal for each protein increasing by up to 184% compared to the more conventional nESI-MS. For smaller ions (≤1032 m/z), the signal can also be increased by the use of high repetition rates (200–250 kHz), which is consistent with the enhanced performance depending more on general factors associated with the ESI process (e.g., smaller initial droplet sizes and reduced Coulombic repulsion in the spray plume) rather than analyte-specific effects (e.g., electrophoretic mobility). The enhanced sensitivity of pulsed nESI is anticipated to be beneficial for many different types of tandem mass spectrometry measurements.


Author(s):  
Adamu Murtala Zungeru ◽  
Dauda Duncan ◽  
Bakary Diarra ◽  
Joseph Chuma ◽  
Modisa Mosalaosi ◽  
...  

Global concerns over the inappropriate utilization of abundant renewable energy sources, the damages due to instability of fuel prices, and fossil fuels' effect on the environment have led to an increased interest in green energy (natural power generation) from renewable sources. In renewable energy, photovoltaic is relatively the dominant technique and exhibits non-linearities, leading to inefficiencies. Maximum Power Point is required to be tracked rapidly and improve the power output levels. The target is to use a Neural network controller by training historical data of ambient irradiance and temperature levels as inputs and voltage levels as output for the photovoltaic module to predict duty cycles across the DC-DC converter. The DC-DC converter is the electrical power conditioner at the Botswana International University of Science and Technology, Palapye Off-Grid photovoltaic system. Perturb and Observe algorithm on PSIM environment is only implemented to acquire the historical data for the training and Matlab for the modeling of the network. Relatively long period ambient irradiance and temperature data of Palapye were acquired from the Southern African Science Service Centre for Climate Change and Adaptive Land Management (SASSCAL) WeatherNet in Botswana. Matlab environment was used for the simulation of the backpropagation algorithm for training. The Neural network's feedforward to optimize the non-linear nature of the PV module input and output relationship with relatively fewer processes is required. The results show promising, and the Mean Errors appear to be typically about 0.1 V, and the best performance is 193.5812 at Epoch 13, while the regression delivered a relatively low measured error. The maximum power delivered by the duty cycles from the model with 90 % prediction accuracy. The article demonstrates Neural Network controller is more efficient than the conventional Perturb and Observe Maximum Power Point algorithm.


2021 ◽  
Vol 54 (5) ◽  
pp. 769-776
Author(s):  
Karima Benamrane ◽  
Thameur Abdelkrim ◽  
Benlahbib Benlahbib ◽  
Noureddine Bouarroudj ◽  
Abdelhalim Borni ◽  
...  

This paper proposes a new optimized control of photovoltaic two stages conversion cascade composed by Three Levels Boost (TLB) and Three Levels Neutral Point Clamped (TLNPC) inverter. In order to extract the maximum power from photovoltaic generator and get a balanced DC bus voltage, the duty cycles of the two TLB switches are determinate from a Fuzzy Logic Controller (FLC) for the first switch and by adding to the first duty cycle an additional duty cycle obtained by integration of the error between the two capacitors voltages of DC bus. Balancing the bus voltages by the TLB using a single regulator avoid us to use a complex balancing algorithm by the redundant vectors of TLNPC inverter. For the control of the inverter, we used a Proportional Integral (PI) regulator optimized by PSO. This command allows us to have on one side a constant DC bus voltage and a current injection in phase with the grid voltage. To have an efficient follow-up of the TLNPC inverter reference voltages, the Space Vector Pulse Width Modulation (SVPWM) is applied. The simulation is carried out in MATLAB/SIMULINK platform. The results obtained from the application of the FLC command associated with PI PSO are better compared to the simulation without optimization in terms of sum of the absolute values of the errors at the inputs of the three PI regulators.


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