8,518 research outputs found
Adaptive Maximum Power Transfer for Movable device in Wireless Power Transfer system
More and more applications are adopting the charging topology of wireless
power transmission. However, most wireless charging systems can not charge
mobile devices which are moving in position while charging. Currently, many
commercialized wireless charging systems adopt an inductive coupling method,
which has very short charging distances. In addition, the frequency of the two
coupled coils that produce maximum power transfer keeps varying, depending on
the coupling coefficient that relies on the separation between coils, and this
tendency becomes more severe when the coupling is strengthened at a close
charging distance by the phenomenon called frequency splitting. Therefore, the
existing wireless power transmission system using a fixed operating frequency
can not optimize power transmission for a fluctuating charging environment as
the coupling between coils changes, and charging efficiency is greatly reduced
by frequency splitting when charging at a very short distance. To solve this
problem, we proposed the method of estimating the RX side power and mutual
inductance using the information from the TX side such as input impedance
rather than using a direct communication link which adds more cost and
complexity. Also, we derived a mathematical model for the above estimation
method. To prove this mathematical model, the proposed wireless power
transmission system was implemented in a SIMULINK environment, and the system
model was validated through simulation. Also comparison between the adaptive
frequency tracking method and static impedance matching circuit is made by
analyzing simulation results.Comment: 10pages, 10 figures, 3 table
The dark side of corporate social responsibility
The interests of employees take a back seat when firms mobilise resources for CSR, write Heung-Jun Jung and Dong-One Ki
Towards Secure Blockchain-enabled Internet of Vehicles: Optimizing Consensus Management Using Reputation and Contract Theory
In Internet of Vehicles (IoV), data sharing among vehicles is essential to
improve driving safety and enhance vehicular services. To ensure data sharing
security and traceability, highefficiency Delegated Proof-of-Stake consensus
scheme as a hard security solution is utilized to establish blockchain-enabled
IoV (BIoV). However, as miners are selected from miner candidates by
stake-based voting, it is difficult to defend against voting collusion between
the candidates and compromised high-stake vehicles, which introduces serious
security challenges to the BIoV. To address such challenges, we propose a soft
security enhancement solution including two stages: (i) miner selection and
(ii) block verification. In the first stage, a reputation-based voting scheme
for the blockchain is proposed to ensure secure miner selection. This scheme
evaluates candidates' reputation by using both historical interactions and
recommended opinions from other vehicles. The candidates with high reputation
are selected to be active miners and standby miners. In the second stage, to
prevent internal collusion among the active miners, a newly generated block is
further verified and audited by the standby miners. To incentivize the standby
miners to participate in block verification, we formulate interactions between
the active miners and the standby miners by using contract theory, which takes
block verification security and delay into consideration. Numerical results
based on a real-world dataset indicate that our schemes are secure and
efficient for data sharing in BIoV.Comment: 12 pages, submitted for possible journal publicatio
Effect of laser-dimpled titanium surfaces on attachment of epithelial-like cells and fibroblasts.
PurposeThe objective of this study was to conduct an in vitro comparative evaluation of polished and laserdimpled titanium (Ti) surfaces to determine whether either surface has an advantage in promoting the attachment of epithelial-like cells and fibroblast to Ti.Materials and methodsForty-eight coin-shaped samples of commercially pure, grade 4 Ti plates were used in this study. These discs were cleaned to a surface roughness (Ra: roughness centerline average) of 180 nm by polishing and were divided into three groups: SM (n=16) had no dimples and served as the control, SM15 (n=16) had 5-µm dimples at 10-µm intervals, and SM30 (n=16) had 5-µm dimples at 25-µm intervals in a 2 × 4 mm(2) area at the center of the disc. Human gingival squamous cell carcinoma cells (YD-38) and human lung fibroblasts (MRC-5) were cultured and used in cell proliferation assays, adhesion assays, immunofluorescent staining of adhesion proteins, and morphological analysis by SEM. The data were analyzed statistically to determine the significance of differences.ResultsThe adhesion strength of epithelial cells was higher on Ti surfaces with 5-µm laser dimples than on polished Ti surfaces, while the adhesion of fibroblasts was not significantly changed by laser treatment of implant surfaces. However, epithelial cells and fibroblasts around the laser dimples appeared larger and showed increased expression of adhesion proteins.ConclusionThese findings demonstrate that laser dimpling may contribute to improving the periimplant soft tissue barrier. This study provided helpful information for developing the transmucosal surface of the abutment
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