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101.
The stability of five major phenolics, namely (−)-epicatechin (EC), procyanidin B2 (PC-B2), chlorogenic acid (ChA), hyperoside (HP) and isoquercitrin (IQ), in hawthorn fruits and a canned hawthorn drink were evaluated during 6 months of storage in the dark at three different temperatures (4, 23 and 40 °C). HPLC with a diode-array detector was used to determine the contents of the individual compounds. The results showed that the studied phenolics in the hawthorn fruits and the drink were both stable at 4 °C and relatively unstable at 23 and 40 °C with varied extents of degradation. At room temperature (23 °C), marked degradations of EC and PC-B2 were observed in both the fruits and the drink with around 50% and 30% decrease after a 6-month storage, respectively. A more significant decrease of the phenolics was observed at 40 °C, especially for EC and PC-B2, which were almost completely degraded after a 6-month storage. HP, IQ and ChA were relatively stable at 23 °C, but unstable at 40 °C. Therefore, low-temperature storage is recommended for maintaining the quality and efficacy of hawthorn fruits and its preparations. 相似文献
102.
The current-voltage (I-V) characteristics of metal-oxide-semiconductor (MOS) structures with hafnium oxide as the gate dielectric film were studied. Sharp shifts from a low-voltage ohmic regime to a tunneling conduction were observed in the high-voltage range. The paper demonstrates that this behavior can be described very well with a double-layer dielectric model. Excellent fittings of the experimental curves were obtained and the related key structural and physical parameters were obtained. The model fitting further suggests the optimal annealing conditions for preparing the hafnium oxide films. 相似文献
103.
《Journal of power sources》2006,153(2):413-418
Three types of electrically conducting polymers (ECPs), i.e. polyaniline (PANI), polypyrrole (PPy) and poly-(3,4-ethylenedioxythiophene) (PEDOT) have been tested as supercapacitor electrode materials in the form of composites with multiwalled carbon nanotubes (CNTs). The energy storage in such a type of composite combines an electrostatic attraction as well as quick faradaic processes called pseudo-capacitance. It has been shown that carbon nanotubes play the role of a perfect backbone for a homogenous distribution of ECP in the composite. It is well known that pure conducting polymers are mechanically weak, hence, the carbon nanotubes preserve the ECP active material from mechanical changes (shrinkage and breaking) during long cycling. Apart of excellent conducting and mechanical properties, the presence of nanotubes improves also the charge transfer that enables a high charge/discharge rate. For an optimal use of ECPs in electrochemical capacitors, a special electrode composition with ca. 20 wt.% of CNTs and a careful selection of the potential range is necessary. The capacitance values ranging from 100 to 330 F g−1 could be reached for different asymmetric configurations with a capacitor voltage from 0.6 to 1.8 V. It is also noteworthy that such a type of ECP/CNTs composite does not need any binding substance that is an important practical advantage. 相似文献
104.
Distributed Denial-of-Service (DDoS) attacks pose a serious threat to Internet security. Most current research focuses on
detection and prevention methods on the victim server or source side. To date, there has been no work on defenses using valuable
information from the innocent client whose IP has been used in attacking packets. In this paper, we propose a novel cooperative
system for producing warning of a DDoS attack. The system consists of a client detector and a server detector. The client
detector is placed on the innocent client side and uses a Bloom filter-based detection scheme to generate accurate detection
results yet consumes minimal storage and computational resources. The server detector can actively assist the warning process
by sending requests to innocent hosts. Simulation results show that the cooperative technique presented in this paper can
yield accurate DDoS alarms at an early stage. We theoretically show the false alarm probability of the detection scheme, which
is insensitive to false alarms when using specially designed evaluation functions.
This work is partially supported by HK Polyu ICRG A-PF86 and CERG Polyu 5196/04E, and by the National Natural Science Foundation
of China under Grant No. 90104005. 相似文献
105.
《Composites Part B》2007,38(5-6):598-613
This study presents a computational model to simulate the behavior of confined concrete in column plastic hinge zones. The model describes the distribution of confining stresses within a circular column cross-section and the hysteretic behavior of concrete under passive confinement. Of particular interest is the ability of the model to predict the maximum circumferential strains and thus estimate the limit state of the confining medium rather than relying on empirical limits such as concrete compressive strain or drift ratio. This is performed with fiber-discretized beam column analysis without the computational expenses of a continuum finite element (FE) model. The confined section and material model are implemented in an object-oriented computational platform for structural analysis. New classes are developed and presented for a confined fiber section, a confined concrete material, and associated hysteretic behavior rules. Finally, the results from two experimental programs on columns strengthened using fiber reinforced polymer (FRP) lamina are reproduced using the developed computational model. Comparison of simulation and experiment shows that the computational model can closely match the observed response characteristics and can adequately predict the deformation level leading to FRP rupture. 相似文献
106.
《Materials Letters》2007,61(11-12):2295-2298
The water absorption behavior of bone-cements of PMMA reinforced with 1.5 wt.%, 2.5 wt.%, and 3.5 wt.% silane-treated powders of hydroxyapatite (synthetic, or derived from bovine bones, or teeth enamel), β-tricalcium phosphate (TCP), bioactive glass (45S5), and zirconia, was investigated. The experimental results showed that addition of calcium phosphate in the polymeric matrix favors water absorption except in the case of enamel hydroxyapatite. Water uptake is also suppressed when 45S5-bioglass or zirconia is added. The solubility is not affected by addition of hydroxyapatite or 45S5-bioglass but it increases when β-TCP or zirconia is added. A superior behavior of bone-cements reinforced with bioglass-45S5 and enamel hydroxyapatite can be suggested. 相似文献
107.
《Soils and Foundations》2006,46(4):415-425
This paper proposes a procedure to investigate the effect of construction control on the safety of driven piles, and provides a theoretical basis to verify and support existing empirical factors of safety (FS) and resistance factors used to account for the effect of construction control. The procedure is formalized in the Bayesian framework. In particular, how the FS and resistance factor can be determined in a rational manner based on on-site dynamic pile tests is explored. Five design methods for driven piles are investigated to illustrate the proposed procedure and parametric studies are performed to evaluate the effect of number of tests or analyses on the updated FS. The results indicate that the required FS can be reduced and resistance factor can be increased considerably through careful construction control, which depends on design methods, on-site test methods, and the level of control implemented. The required FSs and resistance factors after construction control obtained from this study are consistent with the existing empirical values. After sufficient control tests, the required FSs and resistance factors for different design methods are not sensitive to the accuracy of the individual design methods. 相似文献
108.
S.Y.Y. Leung J.K.C. Leung 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2007,263(1):306-310
Solid-state nuclear track detectors (SSNTDs), such as LR 115, have been commonly used in diffusion chambers for long-term measurements of radon gas concentrations. For the LR 115 SSNTD, it has been found that the active layer removed during chemical etching is significantly affected by the presence and amount of stirring, and thus cannot be controlled easily. However, the sensitivity of the LR 115 detector inside a diffusion chamber to the radon and/or thoron gas concentration is dependent on the actual removed active layer thickness. This relationship is dependant on the geometry of the diffusion chamber and the deposition fraction of 218Po in the diffusion chamber, as well as the V function for the LR 115 detector (V is the ratio between the track etch velocity Vt to the bulk etch velocity Vb). This paper presents the experimentally determined relationships between the sensitivity of the LR 115 detector inside a Karlsruhe diffusion chamber and the removed active layer thickness, for both radon and thoron. A V function was adjusted to simulate the relationships. In particular, for the case of 222Rn, we have found f ∼ 0.5, where f is the fraction of 218Po which decays inside the diffusion chamber before deposition onto available inner surfaces of the chamber. In conclusion, we have found that the sensitivities critically depend on the actual removed active layer thickness, so this should be monitored and used in determining the sensitivities. 相似文献
109.
V. Geros M. Santamouris S. Amourgis S. Medved E. Milford G. Robinson K. Steemers S. Karatasou 《Renewable Energy》2006,31(15):2447-2459
The present paper aims to present a distant-learning training module that concerns the environmental design of urban buildings. The whole approach attempts to integrate topics that concern the design of urban buildings from various points of views, e.g. active and passive systems, automation systems, indoor air quality, economic aspects, energy and resources management. The package offers both printed and electronic material that gives the possibility to the students to study the various topics by using different educational methods. Additionally, the present package contains software tools that permit the students to examine real or hypothetical situations and to study further the influence of various parameters that concern the environmental building design. 相似文献
110.
Confidence measures are computed to estimate the certainty that target acoustic units are spoken in specific speech segments. They are applied in tasks such as keyword verification or utterance verification. Because many of the confidence measures use the same set of models and features as in recognition, the resulting scores may not provide an independent measure of reliability. In this paper, we propose two articulatory feature (AF) based phoneme confidence measures that estimate the acoustic reliability based on the match in AF properties. While acoustic-based features, such as Mel-frequency cepstral coefficients (MFCC), are widely used in speech processing, some recent works have focus on linguistically based features, such as the articulatory features that relate directly to the human articulatory process which may better capture speech characteristics. The articulatory features can either replace or complement the acoustic-based features in speech processing. The proposed AF-based measures in this paper were evaluated, in comparison and in combination, with the HMM-based scores on phoneme and keyword verification tasks using children’s speech collected for a computer-based English pronunciation learning project. To fully evaluate their usefulness, the proposed measures and combinations were evaluated on both native and non-native data; and under field test conditions that mis-matches with the training condition. The experimental results show that under the different environments, combinations of the AF scores with the HMM-based scores outperforms HMM-based scores alone on phoneme and keyword verification. 相似文献