20,634 research outputs found
Joint Trajectory and Power Optimization for Energy-Efficient UAV Redeployment Against an Eavesdropper Under Consistent Fairness Constraint
No full textWe consider a scenario where a UAV transmits data to ground users under consistent fairness constraint, which requires stable data transmission to every user at each moment. It is assumed that a ground eavesdropper is detected during the transmission. Due to the consistent fairness constraint, the UAV transmits at an optimal hovering point maximizing the minimum rate (secrecy rate) before (after) detecting the eavesdropper, and the UAV moves the two hovering points before and after the detection while considering the minimum secrecy rate at each moment. We solve these problems of optimizing UAV hovering points and power allocation before and after the detection, and optimizing UAV trajectory and power allocation for moving between the two hovering points. In particular, we impose an energy constraint for moving between the two hovering points. It is shown that a large amount of energy can be saved, with a relatively small sacrifice of the secrecy rate.
Fully Automated Valet Parking System Based on Infrastructure Sensing
No full textIn this paper, we propose a novel automated valet parking system exploiting infrastructure hardware for a more applicable, safe and efficient solution. The infrastructure equipped with camera and computing device-detect automobiles on IPM (Inverse Perspective Mapping) image, generate a path to the empty parking space and control the vehicle to track the path. In order to recognize empty parking spaces and vehicles, a deep learning-based recognition model was used to have a robust recognition rate in various lighting conditions and environments. In addition, a more efficient route was created by creating a parking path considering the vehicle model. Our system was tested in a 1/4-sized experimental environment; it showed a high parking success rate and confirmed that our system works well in various environments. Therefore, from our system proposed in this paper, we can see the possibility of the development of an efficient and highly intelligent free autonomous parking system based on infrastructure sensing. Our source code is publicly available at https://github.com/FVCD2019. © 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd
Fabrication of Micro-Patterned Chip with Controlled Thickness for High-Throughput Cryogenic Electron Microscopy
No full text© 2022 JoVE Journal of Visualized Experiments.A major limitation for the efficient and high-throughput structure analysis of biomolecules using cryogenic electron microscopy (cryo-EM) is the difficulty of preparing cryo-EM samples with controlled ice thickness at the nanoscale. The silicon (Si)-based chip, which has a regular array of micro-holes with graphene oxide (GO) window patterned on a thickness-controlled silicon nitride (SixNy) film, has been developed by applying microelectromechanical system (MEMS) techniques. UV photolithography, chemical vapor deposition, wet and dry etching of the thin film, and drop-casting of 2D nanosheet materials were used for mass-production of the micro-patterned chips with GO windows. The depth of the micro-holes is regulated to control the ice thickness on-demand, depending on the size of the specimen for cryo-EM analysis. The favorable affinity of GO toward biomolecules concentrates the biomolecules of interest within the micro-hole during cryo-EM sample preparation. The micro-patterned chip with GO windows enables high-throughput cryo-EM imaging of various biological molecules, as well as inorganic nanomaterials.11Nsciescopu
Analysis of the relationships between the hospitality workforce and job- satisfaction factors according to age, gender, native language, and racial- ethnicity / Chang Lee and Jungwon Lee
No full textThe purpose of this study is to investigate the relationships between the hospitality workforce and certain job satisfaction factors. It also addresses what aspects of a position an employee believes to be valued and important. A total of 17 attributes were collected and used from each member of 24 properties. Factor analyses were used to determine the subsets of employee job satisfaction and satisfaction with workforce diversity. MANOVA was performed to determine the differences between job-satisfaction factors, overall job satisfaction, and retention according to workers’ age, gender, native language, and racial-ethnicity. A relationship between satisfaction with workforce diversity and overall satisfaction was investigated using simple regression analysis. The findings revealed that women are more attached to their work than men are. Tenured workers consider their employment important in terms of belonging to the society and the community. Workforce diversity plays a more important role among those in management positions than it does for subordinate employees. Employees who are a part of the major racial-ethnic group in the workplace tend to have a more sensitive attitude toward workforce diversity
All-fiber-photonic sub-10(-14)-level comb-line stabilization
No full textWe demonstrate a fiber delay line-based direct comb-line stabilization with 6x10(-15) frequency instability within 1 s. Two combs could be simultaneously stabilized to a single fiber delay-line with similar to 1-Hz relative linewidth and similar to 20-Hz absolute linewidth. (C) 2020 The Author(s
Simple-structured, subfemtosecond-resolution optical-microwave phase detector
No full textWe demonstrate a simple all-fiber photonic phase detector that can measure the phase (timing) difference between an optical pulse train and a microwave signal with subfemto-second resolution and -60 dB-level amplitude-to-phase conversion coefficient. It is based on passive phase biasing of a Sagnac loop by the intrinsic phase shift of a symmetric 3 x 3 fiber coupler. By eliminating the necessity of magneto-optic components or complex radio frequency (RF) electronics for phase biasing of the Sagnac loop, this phase detector has potential to be implemented as an integrated photonic device as well. When using this device for synchronization between a 250 MHz mode-locked Er-fiber laser and an 8 GHz microwave oscillator, the minimum residual phase noise floor reaches < - 154 dBc/Hz (at 8 GHz carrier) with integrated root mean square (rms) timing jitter of 0.97 fs [1 Hz-1 MHz]. The long-term rms timing drift and frequency instability are 0.92 fs (over 5000 s) and 4 x 10(-19) (at 10,000 s averaging time), respectively. (C) 2018 Optical Society of America
FPGA-Driven Soliton Locking for Reduced Manual Intervention in Microcombs
No full textIn this article, we propose and demonstrate a soliton locking structure based on FPGA control. The FPGA integrates all necessary control modules for power-kicking control and incorporates additional techniques to simplify the locking process and reduce the need for manual intervention. These techniques include decoupling the PZT driving voltage from the laser frequency through pre-distortion, using reinforcement learning to elongate the soliton, and implementing automatic soliton tracking to cancel the relative frequency drift between the pump laser and the microresonator. In our experiment, each locking attempt requires only 8.24 ms. On average, approximately 10 attempts are sufficient to re-lock single soliton after an abrupt vibration induced by beating the optical table, resulting in an average locking time of 82 ms. The FPGA-based system automatically detects and re-locks without manual intervention, ensuring reliable soliton locking. The results show that this structure effectively locks single solitons in silica microcombs for both 17 GHz and 22 GHz microresonators with a Q factor above 10(8), showing a state-of-the-art stability and robustness.
Easy access to highly crystalline mesoporous transition-metal oxides with controllable uniform large pores by using block copolymers synthesized via atom transfer radical polymerization
No full textWe report the synthesis of highly crystalline and thermally stable mesoporous titanium oxide and niobium oxide with uniform and controllable pores by employing laboratory-made polystyrene-b-poly(ethylene oxide)s (PS-b-PEOs) as structure-directing agents for combined assembly of soft and hard chemistries (CASH). The structure-directing agent PS-b-PEO has been simply synthesized via atom transfer radical polymerization (ATRP) method. With the increase of molecular weight of PS-b-PEO, the pore size of TiO(2) has been tuned in the range of 14.9-20.7 nm. The highly crystalline CASH-PS-TiO(2) exhibited promising photocatalytic activity in both hydrogen evolution and methylene blue (MB) degradation compared to conventional TiO(2) templated by Pluronic P123. Notably, the approach used in this research combines the advantages of CASH and ATRP and can hence be easily adopted by researchers without any prior experience in polymer synthesis. (C) 2011 Elsevier Inc. All rights reserved.
Plane-Selective Coating of Li2SnO3 on Li[NixCo1x]O2 for High Power Li ion Batteries
No full textInterphase engineering is becoming increasingly important in improving the electrochemical performance of cathode materials for rechargeable batteries, including Li ion, Li metal, and all-solid-state batteries, because irreversible surface reactions, such as electrolyte decomposition, and transition metal dissolution, constitute one of these batteries' failure modes. In this connection, various surface-engineered cathode materials have been investigated to improve interfacial properties. No synthesis methods, however, have considered a plane-selective surface modification of cathode materials. Herein, we introduce the basal-plane-selective coating of Li2SnO3 on layered Li[NixCo1-x]O-2 (x = 0 and 0.5) using the concept of the thermal phase segregation of Sn-doped Li[NixCo1-x]O-2 due to the solubility variation of Sn in Li[NixCo1-x]O-2 with respect to temperature. The plane-selective surface modification enables the formation of Li2SnO3 nanolayers on only the Li[NixCo1-x]O-2 basal plane without hindering the charge transfer of Li+ ions. As a result, the vertical heterostructure of Li[NixCo1-x]O-2-Li2SnO3 core-shells show promising electrochemical performance.N
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