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排序方式: 共有658条查询结果,搜索用时 15 毫秒
11.
12.
A series of soluble novel polyesterimides was synthesized from diamines [a mixture of 2,2‐bis(4‐(4‐aminophenoxy)phenyl)propane (BAPP) with amine‐terminated polysiloxane (ATPS) in various mole ratios] and the ester‐group‐containing dianhydrides. The ester group containing dianhydrides in turn was synthesized by the transesterification reaction of trimellitic anhydride (TMA) with diacetate ester of hydroquinone (HQ), 4,4′‐dihydrophenyl (BP), 1,6‐hexanediol, or ethylene glycol. The resulted polyesterimides were characterized by using Fourier‐transform infrared spectroscopy, inherent viscosity, solubility, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The polyesterimides of BP and HQ had relatively high glass transition temperatures in the range of 214.7–227.2 and 195.7–210.5°C, respectively. The glass transitions decreased rather slowly with the increase in polysiloxane content. Thermal stability and the weight‐loss behavior of polyesterimides were studied by TGA. All polyesterimides of BP and HQ (BPI and HQI) showed no significant weight loss below 500°C in a N2 environment, and the decomposition temperatures (Td5%) of BPI and HQI were >520°C. Most polyesterimides were soluble in polar aprotic solvents and m‐cresol. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 730–738, 2004 相似文献
13.
A high-performance trifunctional epoxy resin based on the triglycidyl ether of tris (4-hydroxyphenyl)-methane (TETM) was synthesized by the condensation of 4-hydroxybenzaldehyde with phenol followed by epoxidation with epichlorohydrin. The structure of TETM was confirmed by mass spectra, infrared and nuclear magnetic resonance spectroscopy. Amino-terminated poly(dimethylsiloxane)s were used to reduce the stress of the trifunctional epoxy resin cured with phenolic novolac resin for electronic encapsulation application. The dispersed silicone rubbers effectively reduce the stress of cured epoxy resins by reducing the coefficient of thermal expansion and flexural modulus while the glass transition temperature was hardly depressed. 相似文献
14.
Kung-Chin Chang Chih-Wei Peng Jen-Chyuan Shieh Jen-Chang Yang 《Electrochimica acta》2007,52(16):5191-5200
In this paper, DBSA-doped polyaniline (PANI)/Na+-montmorillonite (MMT) clay nanocomposite (PCN) materials have been successfully prepared with dodecylbenzenesulfonic acid (DBSA) as emulsifier and dopant for the emulsion polymerization of aniline. The as-prepared DBSA-doped samples were subsequently characterized by FTIR spectroscopy, WAXRD patterns and TEM. It should be noted that the nanocomposite coating containing 1 wt.% of clay loading was found to exhibit an observable enhanced corrosion protection on cold-rolled steel (CRS) electrode at higher operational temperature of 50 °C, which was even better than that of uncoated and electrode-coated with PANI alone at room temperature of 30 °C based on the electrochemical parameter evaluations (e.g., Ecorr, Rp, Icorr, Rcorr and impedance). In this work, all electrochemical measurements were performed at a double-wall jacketed cell, covered with a glass plate, through which water was circulated from a thermostat to maintain a constant operational temperature of 30, 40 and 50 ± 0.5 °C. Moreover, a series of electrochemical parameters shown in Tafel, Nyquist and Bode plots were all used to evaluate PCN coatings at three different operational temperatures in 5 wt.% aqueous NaCl electrolyte. Effect of material composition on the molecular weight and optical properties of neat PANI and PCN materials, in the form of solution, were studied by gel permeation chromatography (GPC) and UV-vis spectra, respectively. Finally, electrical conductivity at three different operational temperatures of PANI and PCN powder-pressed pellets doped with different inorganic acids such as HCl, HNO3 and H2SO4 was also investigated through the measurements of standard four-point-probe technique. 相似文献
15.
Current research in indexing and mining time series data has produced many interesting algorithms and representations. However,
the algorithms and the size of data considered have generally not been representative of the increasingly massive datasets
encountered in science, engineering, and business domains. In this work, we introduce a novel multi-resolution symbolic representation
which can be used to index datasets which are several orders of magnitude larger than anything else considered in the literature.
To demonstrate the utility of this representation, we constructed a simple tree-based index structure which facilitates fast
exact search and orders of magnitude faster, approximate search. For example, with a database of one-hundred million time
series, the approximate search can retrieve high quality nearest neighbors in slightly over a second, whereas a sequential
scan would take tens of minutes. Our experimental evaluation demonstrates that our representation allows index performance
to scale well with increasing dataset sizes. Additionally, we provide analysis concerning parameter sensitivity, approximate
search effectiveness, and lower bound comparisons between time series representations in a bit constrained environment. We
further show how to exploit the combination of both exact and approximate search as sub-routines in data mining algorithms,
allowing for the exact mining of truly massive real world datasets, containing tens of millions of time series. 相似文献
16.
GW Gao SH Lin YF Lin LK Diang KC Lu FC Yu SD Shieh 《Canadian Metallurgical Quarterly》1996,57(6):438-442
Despite a general national decline in criminal activities in the 1990s, juvenile criminal offenses continue to increase, (including violent, property, and delinquency acts). In addition increased numbers of children are being held in juvenile jails. It is all but impossible for pediatric health providers to think that "their patients" and "their practices" are immune from the epidemic of crime that affects and is caused by "just kids." 相似文献
17.
In this paper, a new digital redesign composed of pulse width modulator (PWM) is proposed. The proposed PWM combines fuzzy logic with genetic algorithm (GA) to tune the parameter of the proposed controller such that the output response of hybrid system closely matches the one of original continuous system. Finally, an illustrated example is proposed to show the proposed method is superior to the existing one. 相似文献
18.
Byte level Forward Error Correction (B-FEC) is efficient for recovery from uniform bit errors, but not suitable to handle recovery from burst bit errors. Conversely, Sub-Packet level Forward Error Correction (SP-FEC) can alleviate the problem of large encoding/decoding delay jitter in Packet level Forward Error Correction (P-FEC) to efficiently handle recovery from burst bit errors, but has large error recovery overhead as P-FEC for recovery from uniform bit errors. This paper proposes a dynamic combination of byte level and Sub-Packet level Forward Error Correction (BSP-FEC) in the Hybrid Automatic Repeat reQuest (HARQ) mechanism to reduce the error recovery overhead. BSP-FEC not only can solve the problems appearing in B-FEC and SP-FEC, but also can get the advantages of B-FEC and SP-FEC in the HARQ mechanism. BSP-FEC replaces the SP-FEC checksum with B-FEC and uses Automatic Repeat reQuest (ARQ) when the network condition deteriorates. BSP-FEC not only utilizes an overhead cost model to dynamically decide the SP-FEC parameter and the B-FEC bit rate according to network conditions, but also utilizes a time constraint model to decide the ARQ retry limit. BSP-FEC dynamically adjusts the FEC redundancy to save bandwidth and improves the Decodable Frame Rate (DFR) and the Peak Signal to Noise Ratio (PSNR) of the delivered video streaming. Accordingly, BSP-FEC can improve multimedia communication performance to both avoid network congestion and shorten end-to-end delay by decreasing effective packet loss rate and packet recovery overhead. Because of the low packet recovery overhead, furthermore, BSP-FEC allows applications to transmit more application data in networks with limited bandwidth. Considering the compatibility, BSP-FEC is implemented in the application layer as the end-to-end protection method to protect packets from errors in wired/wireless networks. Numerical and simulation experimental results show that BSP-FEC obtains better recovery efficiency with the minimum error recovery overhead. 相似文献
19.
Ming-Fong Tsai Ce-Kuen Shieh Chih-Heng Ke Der-Jiunn Deng 《Multimedia Tools and Applications》2010,47(1):49-69
Traditional Forward Error Correction (FEC) mechanisms can be divided into Packet level FEC (PFEC) mechanisms and Byte level
FEC (BFEC) mechanisms. The PFEC mechanism of recovering from errors in a source packet requires an entire FEC redundant packet
even though the error involves a few bit errors. The recovery capability of the BFEC mechanism is only half of the FEC redundancy.
Accordingly, an adaptive Sub-Packet FEC (SPFEC) mechanism is proposed in this paper to improve the quality of video streaming
data over wireless networks, simultaneously enhancing the recovery performance and reducing the end-to-end delay jitter. The
SPFEC mechanism divides a packet into n sub-packets by means of the concept of a virtual packet. The SPFEC mechanism uses a checksum in each sub-packet to identify
the position of the error sub-packet. Simulation experiments show the adaptive SPFEC mechanism achieves high recovery performance
and low end-to-end delay jitter. The SPFEC mechanism outperforms traditional FEC mechanism in terms of packet loss rate and
video Peak Signal-to-Noise Ratio (PSNR). SPFEC offers an alternative for improved efficiency video streaming that will be
of interest to the designers of the next generation environments. 相似文献
20.
Ming-Fong Tsai Tzu-Chi Huang Chih-Heng Ke Ce-Kuen Shieh Wen-Shyang Hwang 《Multimedia Systems》2011,17(4):327-340
The Hybrid ARQ (HARQ) mechanism is the well-known error packet recovery solution composed of the Automation Repeat reQuest
(ARQ) mechanism and the Forward Error Correction (FEC) mechanism. However, the HARQ mechanism neither retransmits the packet
to the receiver in time when the packet cannot be recovered by the FEC scheme nor dynamically adjusts the number of FEC redundant
packets according to network conditions. In this paper, the Adaptive Hybrid Error Correction Model (AHECM) is proposed to
improve the HARQ mechanism. The AHECM can limit the packet retransmission delay to the most tolerable end-to-end delay. Besides,
the AHECM can find the appropriate FEC parameter to avoid network congestion and reduce the number of FEC redundant packets
by predicting the effective packet loss rate. Meanwhile, when the end-to-end delay requirement can be met, the AHECM will
only retransmit the necessary number of redundant FEC packets to receiver in comparison with legacy HARQ mechanisms. Furthermore,
the AHECM can use an Unequal Error Protection to protect important multimedia frames against channel errors of wireless networks.
Besides, the AHECM uses the Markov model to estimate the burst bit error condition over wireless networks. The AHECM is evaluated
by several metrics such as the effective packet loss rate, the error recovery efficiency, the decodable frame rate, and the
peak signal to noise ratio to verify the efficiency in delivering video streaming over wireless networks. 相似文献