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排序方式: 共有279条查询结果,搜索用时 15 毫秒
71.
G. Roshan Deen Vivien Chua Usman Ilyas 《Journal of polymer science. Part A, Polymer chemistry》2012,50(16):3363-3372
Poly(N‐acryloyl‐N′‐ethyl piperazine‐co‐N‐isopropylacrylamide) hydrogels were prepared by thermal free‐radical copolymerization of N‐acryloyl‐N′‐ethyl piperazine (AcrNEP) and N‐isopropylacrylamide (NIPAM) in solution using N, N′‐methylene bisacrylamide as the crosslinking agent. The gels were responsive to changes in external stimuli such as pH and temperature. The pH and temperature responsive character of the gels was greatly dependent on the monomer content, namely AcrNEP and NIPAM, respectively. The gels swelled in acidic (pH 2) and de‐swelled in basic (pH 10) solutions with a response time of 60 min. With increase in temperature from 23 to 80 °C the swelling of the gels decreased continuously and this effect was different in acidic and basic solutions. The temperature dependence of equilibrium water content of the gels was evaluated by the Gibbs–Helmholtz equation. Detailed analysis of the swelling properties of these new gels in relation to molecular heterogeneity in acidic (pH 2) and basic (pH 10) solutions were performed. Water transport property of the gels was studied gravimetrically. In acidic solution, the diffusion process was non‐Fickian (anomalous) while in basic solution, the diffusion was quasi‐Fickian. The effect was more evident in solution of pH 2 than in pH 10. Various structural parameters of the gels such as number‐average molar mass between crosslink (Mc), the crosslink density (ρc), and the mesh size (ξ) were evaluated. The mesh sizes of the hydrogels were between 64 and 783 Å in the swollen state in acidic solution and 20 and 195 Å in the collapsed state in basic solution. The mesh size increased between three to four times during the pH‐dependent swelling process. The amount of unbound water (free water) and bound water of the gels was also evaluated using differential scanning calorimetry. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
72.
C.B. Soh C.B. Tay S.J. Chua H.Q. Le N.S.S. Ang J.H. Teng 《Journal of Crystal Growth》2010,312(11):1848-1854
In this study, we report on the enhancement in the light extraction efficiency of GaN blue LEDs topped with ZnO nanorods. The ZnO nanorods were grown by a two-step hydrothermal synthesis with pre-coated ZnO nanoparticles under optimized condition to give the appropriate size and quality, giving an increase in the light output efficiency of 66%. This improvement is attributed to the optimal rod size and spacing with improved thermal dissipation as compared to light extraction from plain GaN surface. During the ZnO growth on the LEDs, 0.55 M of NH3 was added and the ZnO sample was later annealed at 475 °C in N2 ambient, to drive out interstitial oxygen atoms from the tetrahedral unstable site. As a result, a high ratio of UV to orange defect band emission was achieved. The two-step growth of ZnO nanorods on GaN LEDs was effective in generating array of ZnO nanorods which serve as reflector to enhance light extraction from LEDs. 相似文献
73.
M. Tang M. H. Hong Y. S. Choo Z. Tang Daniel H. C. Chua 《Applied Physics A: Materials Science & Processing》2010,101(3):503-508
In this work, super-hydrophobic surfaces were fabricated by femtosecond laser micro-machining and chemical vapor deposition
to constitute hybrid scale micro/nano-structures formed by carbon nanotube (CNT) clusters. Nickel thin-film microstructures,
functioning as CNT growth catalyst, precisely control the distribution of the CNT clusters. To obtain minimal heat-affected
zones, femtosecond laser was used to trim the nickel thin-film coating. Plasma treatment was subsequently carried out to enhance
the lotus-leaf effect. The wetting property of the CNT surface is improved from hydrophilicity to super-hydrophobicity at
an advancing contact angle of 161 degrees. The dynamic water drop impacting test further confirms its enhanced water-repellent
property. Meanwhile, this super-hydrophobic surface exhibits excellent transparency with quartz as the substrate. This hybrid
fabrication technique can achieve super-hydrophobic surfaces over a large area, which has potential applications as self-cleaning
windows for vehicles, solar cells and high-rise buildings. 相似文献
74.
Wang Y Zang K Chua S Sander MS Tripathy S Fonstad CG 《The journal of physical chemistry. B》2006,110(23):11081-11087
Dense, crystalline arrays of InGaN nanorings, nanodots, and nanoarrows have been fabricated on GaN substrates by template-assisted nano-area selective growth. To create the nanostructures, we have used nanoporous anodic alumina films as templates to pattern nanopores in an SiO2 transfer layer, and then used this patterned SiO2 layer as a template for nitride growth by metalorganic chemical vapor deposition. We have varied the diameter of the deposited nitride nanostructures from 35 to 250 nm by changing the initial anodic alumina template structure. In addition, by controlling the nitride growth time we have created various types of nanostructures, from nanorings to nanoarrows. This structural evolution begins with the nucleation and formation of a nanoring structure, followed by coalescence and growth to form faceted nanodots, and finally lateral overgrowth to form faceted nanoarrows. 相似文献
75.
76.
A novel organocatalytic asymmetric tandem Michael-Henry reaction catalyzed by 9-amino-9-deoxyepiquinine (VI) has been developed. The reaction was efficiently catalyzed by catalyst VI to give highly functionalized cyclohexanes with four stereogenic carbons including two quaternary stereocenters in excellent enantioselectivities (97 to >99% ee) and high diastereoselectivities (93:7-99:1 dr). Thus, the first organocatalytic asymmetric Henry reaction of common ketones as acceptors is shown. 相似文献
77.
Identification of a serine protease inhibitor homologue in Bird's Nest by an integrated proteomics approach. 总被引:4,自引:0,他引:4
For centuries, the edible nests of Collocalia spp. ("Bird's Nests") have been used as a Chinese delicacy that had been claimed to be an effective health-giving tonic. However, clinical studies indicated that in Singapore, Bird's Nest is the most common cause of food-induced anaphylaxis in children, which could lead to potentially life-threatening allergenic reactions. The purpose of this study was to characterize the major allergens in Bird's Nest by using the combined technologies of two-dimensional gel electrophoresis (2-DE), immunochemistry, N-terminal protein sequencing, and mass spectrometry. Results from the immunostaining of the Western blots of the Bird's Nest 2-DE separated proteins with the sera from allergic patients indicated the presence of a major allergen of 66 kDa. Initial searches of the matrix assisted laser desorption/ionization--time of flight--mass spectrometry (MALDI-TOF-MS) tryptic peptide masses of the allergen in the SWISS-PROT and NCBI nonredundant databases revealed that this protein was novel. Based on the partial protein sequence information obtained from N-terminal microsequencing and nanoelectrospray-tandem MS, the 66 kDa immunoreactive allergen was found to be homologous to ovoinhibitor, a Kazal-type serine protease inhibitor, which is one of the dominant allergens found in chicken egg white. 相似文献
78.
79.
S.K.?Donthu D.Z.?ChiEmail author S.?Tripathy A.S.W.?Wong S.J.?Chua 《Applied Physics A: Materials Science & Processing》2004,79(3):637-642
The micro-Raman spectroscopic technique was used to investigate vibrational properties of NiSi thin films formed on three different (100)Si substrates: non-implanted, 20 keV BF2+-implanted, and 20 keV B+-implanted. Raman measurements were also performed on NiSi powder to identify various phonon modes associated with different selection rules of group theory. It was found that the Raman peaks for NiSi thin films formed on the BF2+-implanted substrate were broader and shifted to lower frequencies compared to those for films formed on the other substrates. The broadening of the Raman peaks for these films, which also exhibit much improved thermal stability, is attributed to the small grains that probably result from the segregation of fluorine to grain boundaries and interfaces. It is further proposed that grain boundary segregation influences the stress in the silicide film, resulting in shifts in phonon peak positions. PACS 78.30.Am; 74.25.Kc; 68.35.Dv; 68.55.Ln; 66.30.Jt 相似文献
80.
Kok Seng Chua 《Archiv der Mathematik》2003,81(1):11-21
Let p(n)
denote the number of unrestricted partitions of the positive integer
n, and let
m be a prime $\geq 13$. We prove, for
k = 1, explicit congruences of the form
where $r_{m,k}, \delta_{m,k}$ are integers depending on m and
k and $\phi_{m,k}(z)$ are explicitly computable level one
holomorphic modular forms of small weight. We also give theoretical and numerical support
that the congruences also hold for k > 1.
Our main idea is a level reduction result for the modular forms which originated
from Atkin-Lehner. From our result, we deduce periodicity properties for the
partition function with short periods which improve upon recent results
of K. Ono.
Received: 24 January 2002 相似文献