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ABSTRACT: The oxidation behavior of reaction-bonded porous silicon carbide (RPSC) ceramics in dry oxygen between 1100° and 1500°C was investigated based on four specimens with different porosities. RPSC ceramics exhibited a rapid mass increase in the initial stage of oxidation but a slow mass increase in the following oxidation, which was considerably different from the oxidation behavior of dense SiC. The oxidation kinetics for RPSC can be better represented by an asymptotic law rather than the parabolic law for dense SiC. We suppose that, although oxidation occurred in the entire pore channels at the beginning, the pores were rapidly blocked by the oxide as their growth rate near the pore mouth was very fast due to sufficient oxygen. As the result, the oxidation of the pore interior was stopped in the absence of further oxygen supply.
Journal of the American Ceramic Society 03/2010; 93(7):2062 - 2067. · 2.27 Impact Factor
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ABSTRACT: In this paper, the effective thermal conductivity k
eff of three-dimensional (3D) reticulated SiC foams were investigated through experimental and numerical methods. The results
showed that the k
eff of SiC foams increases as the volume fraction f increases from 30% to 50%. However, there are no systematic changes detected in k
eff when the cell size of the foam varies at a fixed volume fraction. The k
eff of SiC foams as a function of f was obtained. Compared the experimental results with the calculated ones, it indicated that the outcome can be widely applied
in estimating the effective thermal conductivity of other foam materials.
Journal of Porous Materials 01/2009; 16(1):65-71. · 1.24 Impact Factor
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ABSTRACT: In delay-based TCP congestion avoidance mechanisms, a source adjusts its window size to adapt to changes in network conditions as measured through changing queueing delays. Although network calculus (NC) has been used to study window flow control and determine performance bounds, there is a lack of a bridge between NC theory and the practical issues of delay-based TCP congestion avoidance. In this paper, we use an NC-based approach to derive ideal congestion controllers for representative delay-based window flow control models with time-variant feedback delays. We show that the basic delay-based TCP congestion avoidance mechanisms in TCP Vegas, Enhanced TCP Vegas, and FAST TCP can be viewed as different approaches to approximating a certain NC controller. Moreover, we derive another NC controller that is explicitly constructed to address the throughput degradation of the current delay-based methods due to delayed acknowledgement (ACK) packets caused by network traffic in the reverse path (ACK packet) direction. The approximation of this F-model NC-based controller is shown to provide better throughput and fairness over the existing delay-based methods for a variety of network topologies in ns-2 simulations.
Computer Networks. 01/2009;
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ABSTRACT: Modeling and prediction of electromagnetic wave absorbing properties of SiC foams as novel stealth materials in the X-band range of 8.2–12.4 GHz are presented. Appropriate material parameters, including the conductivity, volume fraction, cell size, thickness, and surface modified foam structure, are determined through optimization calculations, where the impedance difference between the SiC foam and free space is minimized. The minimum reflection coefficient, reaching −8 dB, is obtained when the SiC conductivity is about 2.27 S m −1 , the volume fraction is 28%, and the thickness is 20 mm in the case of SiC foam. For surface modified foam, the reflection can be less than −10 dB throughout the entire band investigated.
Smart Mater. Struct. 01/2006; 15:759-766.
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ABSTRACT: Osmotic-response element-binding protein (OREBP), also known as TonEBP or NFAT5, is thought to be responsible for the induction of osmolyte-accumulating genes when cells are under hypertonic stress. Recent studies suggest that OREBP also plays a role in water reabsorption in the kidney, T-cell proliferation, and embryonic development. We developed transgenic mice that express the dominant-negative OREBP (OREBPdn) specifically in the lens because our earlier studies showed that it is particularly sensitive to osmotic stress. The transgenic mice developed nuclear cataract soon after birth, suggesting defects in lens development. The developing transgenic lenses showed incomplete elongation of fiber cells and formation of vacuoles. This is accompanied by evidence of DNA strand breaks, activation of p53, and induction of checkpoint kinase, suggesting that the developing fiber cells lacking OREBP are in a similar physiological state as cells experiencing hypertonic stress. These results indicate that OREBP-mediated accumulation of osmolytes is essential during elongation of the lens fiber cells.
Journal of Biological Chemistry 06/2005; 280(20):19986-91. · 4.77 Impact Factor
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ABSTRACT: This paper describes the latest version of the Chinese-Japanese-English handheld speech-to-speech translation system developed by NICT/ATR, which is now ready to be deployed for travelers. With the entire speech-to-speech translation function being implemented into one terminal, it realizes real-time, location-free speech-to-speech translation. A new noise-suppression technique notably improves the speech recognition performance. Corpus-based approaches of speech recognition, machine translation, and speech synthesis enable coverage of a wide variety of topics and portability to other languages. Test results show that the character accuracy of speech recognition is 82%-94% for Chinese speech, with a bilingual evaluation understudy score of machine translation is 0.55–0.74 for Chinese-Japanese and Chinese-English.
Tsinghua Science & Technology.
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ABSTRACT: This paper presents a new scheme to deal with variations in fundamental frequency (F0) contours for lexical tone recognition in continuous Chinese speech. We divide F0 contour of a syllable into tone nucleus and adjacent articulatory transitions. We only use acoustic features of the tone nucleus for tone recognition. Tone nucleus of a syllable is assumed to be the target F0 of the associated lexical tone, and usually conforms more likely to the standard tone pattern than the articulatory transitions. A tone nucleus can be detected from a syllable F0 contour by a two-step algorithm. First, the syllable F0 contour is segmented into several linear F0 loci that serve as candidates for the tone-nucleus using segmental K-means segmentation algorithm. Then, tone nucleus is chosen from a set of candidates by a predictor based on linear discriminant analysis. Speaker dependent tone recognition experiments using tonal HMMs showed our new approach achieved an improvement of up to 6% for tone recognition rate compared with a conventional one. This indicates not only that tone-nucleus keeps important discriminant information for the lexical tones, but also that our tone-nucleus based tone recognition algorithm works properly.
Speech Communication.
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ABSTRACT: This paper introduces several important features of the Chinese large vocabulary continuous speech recognition system in the NICT/ATR multi-lingual speech-to-speech translation system. The features include: (1) a flexible way to derive an information rich phoneme set based on mutual information between a text corpus and its phoneme set; (2) a hidden Markov network acoustic model and a successive state splitting algorithm to generate its model topology based on a minimum description length criterion; and (3) advanced language modeling using multi-class composite N-grams. These features allow a recognition performance of 90% character accuracy in tourism related dialogue with a real time response speed.
Tsinghua Science & Technology.
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ABSTRACT: Theanine, an amino acid contained in green tea, is known to possess many pharmacological functions. In this paper, we investigated the absorption of theanine in the human intestinal epithelium, using a Caco-2 monolayer model. Different concentrations of either pure theanine or green tea extracts were administered to Caco-2 cells. The theanine content in the samples was analysed by high-performance liquid chromatography, coupled with fluorescence detection. Cell permeation was also measured. The data revealed that the transport of pure theanine occurred in a manner consistent with passive diffusion. Surprisingly, pure theanine showed good absorption, whereas theanine in the green tea extract was poorly absorbed in the Caco-2 cell model. Furthermore, the transport of theanine in green tea extract in the basolateral (BL) to apical (AP) direction was much greater than that in the AP–BL direction, suggesting that green tea components profoundly affect the trans-epithelial transport of theanine in this Caco-2 cell model.
Food Chemistry.
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Xinyi Yin,
Ming He,
Kejun Dong,
Shaoyong Wu, Jinsong Zhang,
Jilong Zhang,
Tongxin Wang,
Anzhi Cui,
Yinggen Ouyang,
Zhiyong Zhang,
Jian Yuan,
Shan Jiang
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ABSTRACT: 151Sm is an interesting nuclide in many research fields. Measurement methods of the long-lived 151Sm with accelerator mass spectrometry have been developed at China Institute of Atomic Energy. The chemical form of samples was Sm2O3 and the extracted ion was SmO−. To date, the sensitivity, that is, the isotopic ratio, of 151Sm measured using accelerator mass spectrometry is about 10−8. This method was also used to measure the concentration of tracer 151Sm in biological samples for clarifying whether the rare earth elements can enter into the brain. It is not possible at present to determine whether the tracer has penetrated the blood–brain barrier into the brain.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms.
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ABSTRACT: Design and simulation of a new type of stealthy material are presented, including theory, methodology, and results/discussion. This material consists of a three-dimensional periodic lattice of SiC ceramic dielectric rods with SiO2 as matrix. Transmission, reflection and absorption coefficients of the material are calculated. Proper parameters which meet the stealthy requirements are obtained from the numerical calculation. It's found that when conductivity is equal to 1 × 100.4 Sm−1, the maximum absorption loss is got at 6 GHz. The main advantages of this material are light-weight, high temperature stability, and high impedance matching the free space.
Materials Research Bulletin.
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ABSTRACT: In the present paper we investigate the precise large deviations for heavy-tailed random sums. First, we obtain a result which improves the relative result in Klüppelberg and Mikosch (J. Appl. Probab. 34 (1997) 293). Then we introduce a more realistic risk model than classical ones, named the compound renewal model, and establish the precise large deviations in this model.
Statistics & Probability Letters.
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ABSTRACT: Three different pore size carbon foams with variable electric conductivities were prepared by a polymer sponge replication method. The electromagnetic parameters of these carbon foams and their corresponding pulverized powders were measured by a resonant cavity perturbation technique at a frequency of 2450 MHz. The results show that carbon foams have smaller dielectric constants but several times larger dielectric loss compared with their corresponding pulverized powders. Moreover, carbon foams show magnetic loss while no magnetic loss can be observed from their corresponding pulverized powders. The magnetic loss of carbon foams is apparently a kind of extrinsically magnetic loss and believed to be able to maintain at high temperatures. The electromagnetic characteristics of carbon foams demonstrate that macrostructure modification is an effective way to modulate electromagnetic properties of such materials.
Carbon.
