298 research outputs found
Watt-level fluoroindate based glass fibre laser operating around 3 μm
No full textWatt-level ∼2.9 μm laser emission in Ho3+/Pr3+ co-doped InF3–ZnF2–BaF2-GaF3-SrF2-PbF2-LiF-YF3-LaF3-NaF fluoroindate glass fibre is demonstrated for the first time. The glass composition is refined to obtain glasses with suitable thermal properties to be drawn into a fibre. Refractive indices are adjusted to operate as core and cladding materials. The maximum output power of 1.35 W with a slope efficiency of 21.14% is achieved at the wavelength of 2864 nm by using a 27 cm length fluoroindate fibre under a 1150 nm Raman laser pumping. The fibre has an attenuation of ∼1 dB/m at 1570 nm, and the effect of fibre length on the slope efficiency is used to optimize the fibre length. The experimental results indicate that fluoroindate glass is a very promising glass material for lasing applications operating within the mid-infrared wavelength range
Cheng Li, Evaluation of LED Sources Based on Colour Appearance Data ABSTRACT Evaluation of LED Sources Based on Colour Appearance Data
No full textThe current CIE colour rendering index (CRI) has been widely used to test the quality of light sources over 30 years. However, this method is outdated and problematic, especially for evaluating white light emitting diode (LED) sources. A psychophysical experiment was conducted to evaluate the quality of three D65 simulators. The results were also compared with the CRI and the other method, known as CQS. Furthermore, both indices were modified based on CAM02-UCS, and some improvements were found
Accelerated Discovery of Strong and Thermally Stable Nanostructured High-Entropy Alloys
No full textNanostructured metals and alloys typically exhibit higher strength and hardness compared to their bulk-state counterparts. However, grain coarsening in such nanostructured materials at elevated temperatures sacrifices their mechanical performance and limits their wide engineering applications. Thus, the discovery of strong and thermally stable nanostructured materials is needed. High-entropy alloys (HEAs) comprise multi-principal elements (typically more than four) and exhibit both enhanced thermal stability and mechanical strength. So far, only a few HEAs have been empirically identified from a vast compositional space. This thesis focuses on discovering strong and thermally stable nanostructured HEAs based on emerging combinatorial high-throughput techniques over a wide temperature range, as well as providing a fundamental understanding of phase formability and transition mechanisms.The materials studied in this thesis are a group of refractory high-entropy alloys (RHEAs) - TiZrHfNbTa system. This work performed the magnetron co-sputtering technique to deposit (TiZrHf)x(NbTa)1-x alloy libraries on silicon wafers. The synchrotron X-ray mapping method enabled the characterization of the composition and structure distributions, showing uniform composition gradient and phase transition from fully crystalline bcc to nanocomposite structures. The phase formability was discussed based on the critical cooling rate. The nanoindentation mapping method determined the distributions of elastic modulus and hardness. High-throughput annealing allowed for adding a temperature dimension into composition-structure-property relationships. Increasing the TiZrHf component enhanced thermal stability upon annealing, exhibiting a crystallization process different from conventional mechanisms. CALPHAD calculation also demonstrated the phase transition tendency over the composition space.
Similar high-throughput strategies were performed in TiZrNb, TiZrTa, and TiZrNbTa systems. TiZrNb underwent grain growth in a single bcc phase; TiZrNbTa showed no significant change; TiZrTa transformed from fcc to bcc phases as the TiZr content increased. Accordingly, the effects of individual elements in TiZrHfNbTa systems were evaluated. This thesis also explored the addition of Mo or W in the TiZrHfNbTa system (i.e., TiZrHfNbTaMo and TiZrHfNbTaW), leading to the formation of amorphous structure and the improvement of hardness and thermal stability.
The thesis demonstrates that high-throughput methodologies are effective ways for the accelerated discovery of nanostructured HEAs with improved thermal stability and hardness. The combinatorial methodology in this thesis exhibits versatility in the selection of composition and temperature spaces for other compositionally complex alloys.Ph.D
P A TAIL BEHAVIOR OF THE SUPREMUM OF A RANDOM WALK WITH HEAVY-TAILED INCREMENTS AND PERTURBATIONS
No full textAbstract: Let {ξ n , n ≥ 1} be a sequence of independent and identically distributed random variables with a common distribution F and {η n , n ≥ 1} a sequence of independent normal random variables with zero means and different variances. Set T n = n i=1 X i , n ≥ 1 and T 0 = 0, where Under conditions that the two sequences of random variables are independent to each other and the integrated tail distribution of F belongs to the subexponential distribution class, we derive the asymptotic tail behavior of the supremum of the partial sums T n , n ≥ 0
Joint Channel Assignment and Transmission Scheduling for Throughput Optimization in Wireless Mesh Networks - Further Study on a Partitioning Approach
No full text1.55μm Fabry-Perot Thermo-Optical Tunable Filter with amorphous-Si as Cavity
No full textA 1.55μm Fabry-Perot (F-P) thermo-optical tunable filter is fabricated. The cavity is made of amorphous silicon (a-Si) layer grown by electron-beam evaporation technique. Due to the excellent thermo-optical property of a-Si, the refractive index of the F-P cavity will be changed by heating; the transmittance resonant peak will therefore shift substantially. The measured tuning range is 12nm, FWHM (full-width-at-half-maximum) of the transmission peak is 9nm, and heating efficiency is 0.1K/mW. The large FWHM is mainly due to the non-ideal coating deposition and mirror undulation. Possible improvements to increase the efficiency of heating are suggested
The revision and phylogenetic position of Hippasa bifasciata Buchar, 1997 (Araneae, Lycosidae)
No full textHogna Simon, 1885 is the second-largest genus in the family Lycosidae after Pardosa C. L. Koch, 1847 (517 species), including 232 species so far. This genus has a cosmopolitan distribution spanning multiple continents. However, only four species (Hogna rubetra (Schenkel, 1963), Hogna trunca Yin, Bao & Zhang, 1996, Hogna jiafui Peng, Yin, Zhang & Kim, 1997 and Hogna arborea Lo, Wei & Cheng, 2023) have been recorded in China.A new combination, Hogna bifasciata (Buchar, 1997), comb. nov. (from Yunnan and Sichuan Provinces in south-western China), is proposed with both morphological and molecular evidence. Detailed morphological descriptions, photographs, scanning electron micrographs and a distribution map are provided. This species is distinguished from congeners by the unique structure of the female epigyne and its somatic pattern. Molecular phylogenetic analyses suggest H. bifasciata (Buchar, 1997) and all analysed Hogna species cluster together within the subfamily Lycosinae and the species is sister to the group, including Hogna frondicola Emerton, 1885, Hogna carolinensis Walckenaer, 1805 and Hogna crispipes L. Koch, 1877
Expansion and equality in Chinese higher education
No full textWhat is the relationship between the fast expansion of higher education and the equality of college enrollment opportunity in China? Based on the data from four large-scale surveys on college graduates in China, this paper explores this question by conducting empirical analysis on the family occupational, educational, regional, and economic status through descriptive and regression analyses. The result shows: Firstly, quantitatively speaking, enrollment opportunities have equalized in some aspects as well as unequalized in some others. The percentage of students from medium and inferior occupational families and the percentage of female students have increased, while the percentage of students from families with low academic qualification has not changed much more; but the percentage of students from county and below has obviously decreased. Secondly, qualitatively speaking, enrollment opportunity inequality has deepened continuously. Students with better family occupational, educational, regional, and economic status and male students have more chances to enter elite universities, and those groups have become more and more advantaged with the passing of time. (C) 2014 Elsevier Ltd. All rights reserved.Education & Educational [email protected]
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