4,087 research outputs found
Development of EB-PVD TBC'S : the role of deposition temperature and plasma assistance
No full textGas turbine manufacturers have achieved continuingly improved engine
efficiency and thrust-to-weight ratio by designing with increased Turbine
Entry Temperature (TET). The protection of High Pressure Turbine (HPT)
aerofoils with thin insulating ceramic coatings, referred to as Thermal Barrier
Coatings (TBC's), has emerged as the next key technology to allow for further
increases in TET. Electron Beam Physical Vapour Deposition (EB-PVD) is
today's most promising processing route for the manufacture of TBC's applied
on aerofoils.
The purpose of this work was to generate a sound understanding of the
relationship between the EB-PVD process and the structure of Zr02-
8wt%Y2O3 ceramic deposits, which could be exploited to achieve improved
TBC performance. In particular, the role of deposition temperature and the
potential benefits in using RF and DC plasma assistance of the EB-PVD
process were investigated, together with their influence on the erosion
performance of EB-PVD TBC's. The significance of particulate erosion as a
degradation mode is assessed under conditions representative of the HPT
environment. New explorable routes to achieve reduced thermal conductivity
of EB-PVD TBC's are identified.
It is shown that EB-PVD TBC's deposited at low temperature contain a
massive content of microscopic voidage (-50%) which is responsible for their
lack of thermal stability. The growth of EB-PVD TBC's at elevated deposition
temperatures is explained in terms of dynamic sintering, whereby diffusion
processes compete against the high rate arrival of vapour atoms to overcome
the spontaneous defectiveness of the atomic build up. Modelling of the gas
discharge physics has highlighted scope for improving the effectiveness of
plasma assistance in causing ceramic structural damage, capable of modifying
the coating thermal properties.
The erosion rate of EB-PVD TBC's is shown to be controlled by their degree
of plastic deformation upon particle impacts, which in turn depends on the
ceramic column diameter and inherent porosity
Differential gene expression analysis comparing the temporal responses to EB-induced transcription in the AVPV+ and ARH+, by comparing expression levels at baseline with 6 hrs post-EB and 24 hrs post-EB within each brain region.
No full text(A-F) Volcano Plots illustrating fold-change (log base 2) plotted against FDR-adjusted p value (- log base 10) of genes differentially expressed between EB treatment conditions. Note that in the baseline ARH vs. AVPV plot, -log10(adjusted p value) of Pmch was set to 145 so all points could be plotted within the 0–150 range. Horizontal bar at y = 1 represents a significance level of FDR |1.3| (grey dots did not reach our threshold of significance). (G) Overall (i.e., regardless of time post-EB), EB causes greater up-regulation of genes in the AVPV+ and the ARH+ (chi square df = 7.614, 1; z = 2.759, p <0.0058). EB causes higher differential expression of genes in the AVPV+ compared with the ARH+. (H) In the AVPV+ the highest number of genes differentially expressed by EB is observed 24 hours post-EB. In the ARH, the highest number of genes differentially expressed by EB occurs between 6 and 24 hours post-EB. (I) Venn diagram depicting the overlap of genes differentially expressed by estradiol relative to baseline 6 hrs post-EB, 24 hrs post-EB in both the AVPV+ and ARH+. (J) Venn diagram depicting the overlap of genes differentially expressed between 6 and 24 hrs post-EB in both the AVPV+ and ARH+.</p
Luby Transform Coding Aided Iterative Detection for Downlink SDMA Systems
Get PDFA Luby Transform (LT) coded downlink Spatial Division Multiple Access (SDMA) system using iterative detection is proposed, which invokes a low-complexity near-Maximum-Likelihood (ML) Sphere Decoder (SD). The Ethernet-based Internet section of the transmission chain inflicts random packet erasures, which is modelled by the Binary Erasure Channel (BEC), which the wireless downlink imposes both fading and noise. A novel log-Likelihood Ratio based packet reliability metric is used for identifying the channel-decoded packets, which are likely to be error-infested. Packets having residual errors must not be passed on to the KT decoder for the sake of avoiding LT-decoding –induced error propagation. The proposed scheme is capable of maintaining an infinitesimally low packet error ratio in the downlink of the wireless Internet for Eb/n0 values in excess of about 3dB
Combined Prediction Method of Short-Term Distance Headway Based on EB-GRA-TCN
No full textAs an essential parameter to represent vehicle following characteristics, distance headway (DHW) plays an essential role in microtraffic flow simulation, traffic control, and traffic safety alarm. However, due to the randomness, nonlinearity, and correlation of DHW data, constructing DHW prediction models is difficult. Moreover, few studies have considered the time correlation between the historical DHW and the target DHW. To solve the above problems, a DHW prediction model is proposed in this paper by integrating entropy-based grey relation analysis (EB-GRA) and temporal convolutional network (TCN), named as EB-GRA-TCN model. In the model, the EB-GRA is adopted to calculate the correlation between the target DHW and historical DHW sequences, and the DHW data with high correlation are dynamically selected as the optimal input of the DHW prediction model. Then, the TCN algorithm is used to train the DHW prediction model. The TCN architecture integrates the advantages of recurrent neural network (RNN) and convolutional neural network (CNN), which could fully use the previous DHW information. In the experiment, the DHW data from Hefei Expressway are utilized for training the EB-GRA-TCN model. The prediction results showed that the average root mean square error (RMSE) and mean absolute error (MAE) of the proposed model were 0.115 and 0.090, respectively, in the 5, 10, and 15 predicted steps. Compared with the autoregressive integrated moving average (ARIMA), TCN, RNN, and long short-term memory (LSTM) models, the EB-GRA-TCN model achieved the best prediction accuracy. The results indicated that the EB-GRA-TCN model obtained good predictive performance and could provide support for road traffic control and traffic safety warming
The Effect of Bond Coat Roughness on the CMAS Hot Corrosion Resistance of EB-PVD Thermal Barrier Coatings
No full textIn a high-temperature, high-flame-velocity, and high-pressure gas corrosion environment, the intercolumnar pores and gaps of electron beam–physical vapor deposition (EB-PVD) thermal barrier coatings (TBCs) may serve as infiltration channels for molten calcium–magnesium–alumino–silicate (CMAS), leading to the severe degradation of TBCs. In order to clarify the relationship between the roughness of the bond coat and the CMAS corrosion resistance of the EB-PVD TBCs, 7 wt.% yttria-stabilized zirconia (7YSZ) TBCs were prepared on the surfaces of four different roughness-treated bond coats. The effect of the bond coat roughness on the columnar microstructure of the EB-PVD YSZ was investigated. The effect of the change of the bond coat’s microstructure on the CMAS corrosion resistance of the EB-PVD YSZ was studied in detail. The results showed that the reduction in the roughness of the bond coat contributes to the improved formation of the EB-PVD YSZ columns. The small and dense columns are similar to a lotus leaf-like structure, which could reduce the wettability of CMAS and minimize the spread area between the coating and the CMAS melt. Thus, the CMAS corrosion resistance of the coating can be greatly improved. This preparation process also provides a reference for the preparation of other TBC materials, improving the resistance to CMAS hot corrosion
Precoded Sphere Packing Aided Bit-Interleaved Differential Spa ce-Time Coded Modulation Using Iterative Decoding
Get PDFAbstract—In this treatise, we investigate a precoded and sphere packing (SP)-aided bit-interleaved differential space-time coded modulation scheme using iterative decoding. The amalgamated design and interworking of the SP, differential encoding, and iteratively detected bit-interleaved schemes are investigated. A rate-1 precoder is integrated into the system, where iterative decoding is carried out between the precoder and an outer channel code. We identify the optimal SP mapping and investigate the convergence behavior of this concatenated scheme with the aid of EXtrinsic Information Transfer (EXIT) charts. Furthermore, we consider various rate-1 precoders having different memory sizes and demonstrate that the memory-1 precoder performs best when an RSC(2,1,5) is employed as the outer code, creating an open EXIT chart convergence tunnel at Eb/N0 = 6 dB. On the other hand, the memory-3 precoder is more suitable for the proposed system employing irregular convolutional codes, resulting in an infinitesimally low bit error rate at Eb/N0 = 5.5 dB. Index Terms—Differential space-time block code (STBC), EXtrinsic Information Transfer (EXIT) charts, iterative detection, sphere packing
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