Showing papers by "Wuhan University published in 2008"

Magnetic Iron Oxide Nanoparticles: Synthesis and Surface Functionalization Strategies

Abstract: Surface functionalized magnetic iron oxide nanoparticles (NPs) are a kind of novel functional materials, which have been widely used in the biotechnology and catalysis. This review focuses on the recent development and various strategies in preparation, structure, and magnetic properties of naked and surface functionalized iron oxide NPs and their corresponding application briefly. In order to implement the practical application, the particles must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of iron oxide NPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The problems and major challenges, along with the directions for the synthesis and surface functionalization of iron oxide NPs, are considered. Finally, some future trends and prospective in these research areas are also discussed.

Remote sensing imagery in vegetation mapping: a review

Abstract: Aims Mapping vegetation through remotely sensed images involves various considerations, processes and techniques. Increasing availability of remotely sensed images due to the rapid advancement of remote sensing technology expands the horizon of our choices of imagery sources. Various sources of imagery are known for their differences in spectral, spatial, radioactive and temporal characteristics and thus are suitable for different purposes of vegetation mapping. Generally, it needs to develop a vegetation classification at first for classifying and mapping vegetation cover from remote sensed images either at a community level or species level. Then, correlations of the vegetation types (communities or species) within this classification system with discernible spectral characteristics of remote sensed imagery have to be identified. These spectral classes of the imagery are finally translated into the vegetation types in the image interpretation process, which is also called image processing. This paper presents an overview of how to use remote sensing imagery to classify and map vegetation cover. Methods Specifically, this paper focuses on the comparisons of popular remote sensing sensors, commonly adopted image processing methods and prevailing classification accuracy assessments. Important findings The basic concepts, available imagery sources and classification techniques of remote sensing imagery related to vegetation mapping were introduced, analyzed and compared. The advantages and limitations of using remote sensing imagery for vegetation cover mapping were provided to iterate the importance of thorough understanding of the related concepts and careful design of the technical procedures, which can be utilized to study vegetation cover from remote sensed images.

Resolution of GPS carrier-phase ambiguities in Precise Point Positioning (PPP) with daily observations

Abstract: Precise Point Positioning (PPP) has been demonstrated to be a powerful tool in geodetic and geodynamic applications. Although its accuracy is almost comparable with network solutions, the east component of the PPP results is still to be improved by integer ambiguity fixing, which is, up to now, prevented by the presence of the uncalibrated phase delays (UPD) originating in the receivers and satellites. In this paper, it is shown that UPDs are rather stable in time and space, and can be estimated with high accuracy and reliability through a statistical analysis of the ambiguities estimated from a reference network. An approach is implemented to estimate the fractional parts of the single-difference (SD) UPDs between satellites in wide- and narrow-lane from a global reference network. By applying the obtained SD-UPDs as corrections to the SD-ambiguities at a single station, the corrected SD-ambiguities have a naturally integer feature and can therefore be fixed to integer values as usually done for the double-difference ones in the network mode. With data collected at 450 stations of the International GNSS Service (IGS) through days 106 to 119 in 2006, the efficiency of the presented ambiguity-fixing strategy is validated using IGS Final products. On average, more than 80% of the independent ambiguities could be fixed reliably, which leads to an improvement of about 27% in the repeatability and 30% in the agreement with the IGS weekly solutions for the east component of station coordinates, compared with the real-valued solutions.

Alkaline polymer electrolyte fuel cells completely free from noble metal catalysts

Abstract: In recent decades, fuel cell technology has been undergoing revolutionary developments, with fundamental progress being the replacement of electrolyte solutions with polymer electrolytes, making the device more compact in size and higher in power density. Nowadays, acidic polymer electrolytes, typically Nafion, are widely used. Despite great success, fuel cells based on acidic polyelectrolyte still depend heavily on noble metal catalysts, predominantly platinum (Pt), thus increasing the cost and hampering the widespread application of fuel cells. Here, we report a type of polymer electrolyte fuel cells (PEFC) employing a hydroxide ion-conductive polymer, quaternary ammonium polysulphone, as alkaline electrolyte and nonprecious metals, chromium-decorated nickel and silver, as the catalyst for the negative and positive electrodes, respectively. In addition to the development of a high-performance alkaline polymer electrolyte particularly suitable for fuel cells, key progress has been achieved in catalyst tailoring: The surface electronic structure of nickel has been tuned to suppress selectively the surface oxidative passivation with retained activity toward hydrogen oxidation. This report of a H2–O2 PEFC completely free from noble metal catalysts in both the positive and negative electrodes represents an important advancement in the research and development of fuel cells.

A Simple Carbazole/Oxadiazole Hybrid Molecule: An Excellent Bipolar Host for Green and Red Phosphorescent OLEDs

Abstract: Phosphorescent organic light-emitting diodes (PHOLEDs) continue to attract intense interest because they can, in theory, approach a 100% internal quantum efficiency by utilizing both singlet and triplet excitons. To achieve highly efficient electrophosphorescence by reducing competitive factors such as concentration quenching and triplet–triplet annihilation, phosphorescent emitters of heavy-metal complexes are usually doped into a suitable host material. Thus the synthesis of host materials and dopants are equally important for the formation of efficient PHOLEDs. It is desirable that the host materials have a large enough bandgap for effective energy transfer to the guest, good carrier transport properties for a balanced recombination of carriers in the emitting layer, and energy-level matching with neighboring layers for effective charge injection. Recently, bipolar hosts have aroused considerable interests in the area of organic light-emitting diodes (OLEDs) because they can provide more balance in electron and hole fluxes and simplify device structure. However, a compromise is required between the bipolar transporting property and band gap of the material, because the electron-donating and electron-withdrawing moieties in bipolar molecules unavoidably lower the band gap of the material by intramolecular charge transfer, while the low triplet energy of the host can cause reverse energy transfer from the guest back to the host, which consequently decreases the efficiency of PHOLEDs. To address this issue, most recent molecular designs focus on the interruption of the p conjugation between electron-donating and electron-withdrawing moieties by the incorporation of steric groups and/or meta linkages between the two moieties. Efficient blue (46 lmW , 24%), green (27.3 cdA ) and orange (22 cdA , 7.8%) electrophosphorescence from such small bipolar host molecules has been reported. Carbazole derivatives can be used as host materials because of their high triplet energy and good hole-transporting ability. For example, 4,4’-N,N’-dicarbazolbiphenyl (CBP) is a popular host for triplet emitters. PHOLEDs that use CBP as a host material for various dopants have been reported to have peak efficiencies as high as 28 cdA 1 for green (fac-tris(2-phenylpyridinato-N,C)iridium, [Ir(ppy)3]), [1a] 52 cdA 1 for green (tris[3,6-bis(phenyl)-pyridazinato-N,C]iridium [Ir(BPPya)3]) [7] and 5.82 cdA 1 for deep red (a dendritic iridium complex). Unfortunately, the CBP host is prone to crystallization, especially when the dopant concentration is too low. Furthermore, red PHOLEDs containing a CBP host usually need high driving voltages because the poor energy match between CBP and adjacent holeand electron-transporting layers can result in insufficient and/or unbalanced injection of holes and electrons. It is a worthwhile target to develop host materials with good thermal stability and matching energy levels to replace CBP. Oxadiazole derivatives have been proven to be very effective in improving the injection and transport of electrons. For example, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) and 1,3-bis[4-tert-butylphenyl)-1,3,4-oxadiazolyl]phenylene (OXD7) are usually incorporated in OLEDs as electron-transport materials. Herein we report a novel carbazole/oxadiazole hybrid molecule o-CzOXD linked through the 9-position of carbazole with the ortho position of 2,5-diphenyl-1,3,4-oxadiazole. The bipolar molecule o-CzOXD was easily prepared by an aromatic nucleophilic substitution reaction between carbazole and the fluoroarene, which was activated by the electron-withdrawing oxadiazole, with good yields of over 80% (Scheme 1). The reaction proceeded in the absence of any catalyst, and the product was easily purified by recrystallization from CHCl3/C2H5OH rather than column chromatography. Thus, this simple method has obvious advantages over common palladium-catalyzed coupling reactions. oCzOXD was characterized by H NMR and C NMR spectroscopy, mass spectrometry, and elemental analysis; its molecular structure was further confirmed by X-ray crystallography (Figure 1). The dihedral angle between the carbazole unit and the phenyl ring is 51.48 ; this twist in the

Fluorescence Study on the Interaction of Bovine Serum Albumin with P-Aminoazobenzene

Abstract: In this paper, the interaction between p-aminoazobenzene (PAAB) and BSA was investigated mainly by fluorescence quenching spectra, circular dichroism (CD) and three-dimensional fluorescence spectra under simulative physiological conditions. It was proved that the fluorescence quenching of BSA by PAAB was mainly a result of the formation of a PAAB-BSA complex. The modified Stern-Volmer quenching constant Ka and the corresponding thermodynamic parameters ΔH, ΔG and ΔS at different temperatures were calculated. The results indicated that van der Waals interactions and hydrogen bonds were the predominant intermolecular forces in stabilizing the complex. The distance r = 4.33 nm between the donor (BSA) and acceptor (PAAB) was obtained according to Forster’s non-radioactive energy transfer theory. The synchronous fluorescence, CD and three-dimensional fluorescence spectral results showed that the hydrophobicity of amino acid residues increased and the losing of α-helix content (from 63.57 to 51.83%) in the presence of PAAB. These revealed that the microenvironment and conformation of BSA were changed in the binding reaction.

Market orientation, job satisfaction, product quality, and firm performance: Evidence from China

Abstract: This article examines the processes by which market orientation (MO) affects performance using a cross-level approach. The results of a survey of 2,754 employees from 180 firms in China show that organization-level MO culture leads to unit-level MO behavior, which improves employee-level job satisfaction and then product quality, which in turn fosters organizational performance. In particular, MO behavior fully mediates the effects of MO culture on employee satisfaction, product quality, and organizational performance. Leadership quality strengthens the effect of MO culture on unit-level MO behavior. Moreover, MO behavior enhances firm performance indirectly through employee job satisfaction and product quality. Copyright © 2008 John Wiley & Sons, Ltd.

Cellulose Aerogels from Aqueous Alkali Hydroxide–Urea Solution

Abstract: Highly porous and strong cellulose aerogels were prepared by gelation of cellulose from aqueous alkali hydroxide/urea solution, followed by drying with supercritical CO2. Their morphology, pore structure, and physical properties were characterized by scanning and transmission electron microscopy, X-ray diffraction, nitrogen adsorption measurements, UV/Vis spectrometry, and tensile tests. The cellulose hydrogel was composed of interconnected about 20 nm wide. By using supercritical CO2 drying, the network structure in the hydrogel was well preserved in the aerogel. The results are preliminary but demonstrate the ability of this method to give cellulose aerogels of large surface areas (400-500 m2 g(-1)) which may be useful as adsorbents, heat/sound insulators, filters, catalyst supports, or carbon aerogel precursors.

A New Evolutionary Algorithm for Solving Many-Objective Optimization Problems

Abstract: In this paper, we focus on the study of evolutionary algorithms for solving multiobjective optimization problems with a large number of objectives. First, a comparative study of a newly developed dynamical multiobjective evolutionary algorithm (DMOEA) and some modern algorithms, such as the indicator-based evolutionary algorithm, multiple single objective Pareto sampling, and nondominated sorting genetic algorithm II, is presented by employing the convergence metric and relative hypervolume metric. For three scalable test problems (namely, DTLZ1, DTLZ2, and DTLZ6), which represent some of the most difficult problems studied in the literature, the DMOEA shows good performance in both converging to the true Pareto-optimal front and maintaining a widely distributed set of solutions. Second, a new definition of optimality (namely, L-optimality) is proposed in this paper, which not only takes into account the number of improved objective values but also considers the values of improved objective functions if all objectives have the same importance. We prove that L-optimal solutions are subsets of Pareto-optimal solutions. Finally, the new algorithm based on L-optimality (namely, MDMOEA) is developed, and simulation and comparative results indicate that well-distributed L-optimal solutions can be obtained by utilizing the MDMOEA but cannot be achieved by applying L-optimality to make a posteriori selection within the huge Pareto nondominated solutions. We can conclude that our new algorithm is suitable to tackle many-objective problems.

Negative refraction and focusing of ultrasound in two-dimensional phononic crystals

Abstract: We present experimental demonstrations of negative refraction and focusing of ultrasonic waves in two-dimensional phononic crystals made of stainless steel rods assembled in a triangular lattice and immersed in a liquid. Negative refraction is achieved for the range of frequencies in the second band, where the directions of the wave vector and group velocity are antiparallel to each other due to circular equifrequency contours. Negative refraction is unambiguously observed using a prism-shaped crystal. By exploiting the circular equifrequency contours in the second band, focusing of the ultrasonic field emitted by a pointlike source was demonstrated using a flat phononic crystal filled with and immersed in water. During these experiments, the importance of imaging in the regime of all angle negative refraction (AANR) was established for obtaining high-quality images. The regime of AANR was achieved in a similar flat crystal, in which the liquid inside the crystal (methanol) was different from the outside medium (water). This design resulted in matching circular equifrequency contours at the frequency of $0.55\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$, implying that a flat ultrasonic lens with an effective refractive index of $\ensuremath{-}1$ was realized. By imaging a subwavelength line source with this crystal, a resolution of $0.55\ensuremath{\lambda}$ was observed, which is just above the diffraction limit.

A triallelic system of S5 is a major regulator of the reproductive barrier and compatibility of indica-japonica hybrids in rice

Abstract: Hybrid sterility is a major form of postzygotic reproductive isolation. Although reproductive isolation has been a key issue in evolutionary biology for many decades in a wide range of organisms, only very recently a few genes for reproductive isolation were identified. The Asian cultivated rice (Oryza sativa L.) is divided into two subspecies, indica and japonica. Hybrids between indica and japonica varieties are usually highly sterile. A special group of rice germplasm, referred to as wide-compatibility varieties, is able to produce highly fertile hybrids when crossed to both indica and japonica. In this study, we cloned S5, a major locus for indica-japonica hybrid sterility and wide compatibility, using a map-based cloning approach. We show that S5 encodes an aspartic protease conditioning embryo-sac fertility. The indica (S5-i) and japonica (S5-j) alleles differ by two nucleotides. The wide compatibility gene (S5-n) has a large deletion in the N terminus of the predicted S5 protein, causing subcellular mislocalization of the protein, and thus is presumably nonfunctional. This triallelic system has a profound implication in the evolution and artificial breeding of cultivated rice. Genetic differentiation between indica and japonica would have been enforced because of the reproductive barrier caused by S5-i and S5-j, and species coherence would have been maintained by gene flow enabled by the wide compatibility gene.

Highly effective colorimetric and visual detection of nucleic acids using an asymmetrically split peroxidase DNAzyme.

Abstract: G-quadruplex containing peroxidase DNAzyme is a complex of hemin and a single-stranded guanine-rich DNA (hemin-binding DNA aptamer), which is used as an attractive catalytic label for biosensing recently. Therein, the hemin-binding DNA aptamer contains four GGG repeats and can fold into a G-quadruplex structure. In this paper, we have developed a new split mode to divide the hemin-binding DNA aptamer into two parts: one possesses three GGG repeats, and another part possesses one GGG repeat, namely, the 3:1 split mode. The combination of G-quadruplex and hemin binding could be used as a sensitive probe for the identification of single nucleotide polymorphisms by giving a color signal, visible to the naked eye at room temperature. The G-quadruplex containing peroxidase DNAzyme utilizes the 3:1 split mode and can be directly used for the identification of SNPs with a detection limit in the nM range when the matching length of the probe is short enough. When the matching length of the probe is relatively long...

Herbivore-Induced Callose Deposition on the Sieve Plates of Rice: An Important Mechanism for Host Resistance

Abstract: The brown planthopper (Nilaparvata lugens Stal; BPH) is a specialist herbivore on rice (Oryza sativa) that ingests phloem sap from the plant through its stylet mouthparts. Electronic penetration graphs revealed that BPH insects spent more time wandering over plants carrying the resistance genes Bph14 and Bph15, but less time ingesting phloem than they did on susceptible plants. They also showed that their feeding was frequently interrupted. Tests with [(14)C]sucrose showed that insects ingested much less phloem sap from the resistant than the susceptible plants. BPH feeding up-regulated callose synthase genes and induced callose deposition in the sieve tubes at the point where the stylet was inserted. The compact callose remained intact in the resistant plants, but genes encoding beta-1,3-glucanases were activated, causing unplugging of the sieve tube occlusions in susceptible plants. Continuing ingestion led to a remarkable reduction in the susceptible plants' sucrose content and activation of the RAmy3D gene, leading to starch hydrolysis and ultimately carbohydrate deprivation in the plants. Our results demonstrate that BPH feeding induces the deposition of callose on sieve plates in rice and that this is an important defense mechanism that prevents insects from ingesting phloem sap. In response, however, the BPH can unplug sieve tube occlusions by activating beta-1,3-glucanase genes in rice plants.

Human mesenchymal stem cells license adult CD34+ hemopoietic progenitor cells to differentiate into regulatory dendritic cells through activation of the Notch pathway.

Abstract: The mechanisms underlying the immunomodulatory functions of mesenchymal stem cells (MSC) on dendritic cells (DC) have been shown to involve soluble factors, such as IL-6 or TGF-β, or cell-cell contact, or both depending on the report referenced. In this study, we intend to clarify these mechanisms by examining the immunosuppressive effect of human adult MSC on adult DC differentiated from CD34 + hemopoietic progenitor cells (HPC). MSC have been shown to inhibit interstitial DC differentiation from monocytes and umbilical CD34 + HPC. In this study, we confirm that MSC not only halt interstitial DC but also Langerhans cell differentiation from adult CD34 + HPC, as assessed by the decreased expression of CD1a, CD14, CD86, CD80, and CD83 Ags on their cell surface. Accordingly, the functional capacity of CD34 + HPC-derived DC (CD34-DC) to stimulate alloreactive T cells was impaired. Furthermore, we showed that 1) MSC inhibited commitment of CD34 + HPC into immature DC, but not maturation of CD34-DC, 2) this inhibitory effect was reversible, and 3) DC generated in coculture with MSC (MSC-DC) induced the generation of alloantigen-specific regulatory T cells following secondary allostimulation. Conditioned medium from MSC cultures showed some inhibitory effect independent of IL-6, M-CSF, and TGF-β. In comparison, direct coculture of MSC with CD34 + HPC resulted in much stronger immunosuppressive effect and led to an activation of the Notch pathway as assessed by the overexpression of Hes1 in MSC-DC. Finally, DAPT, a γ-secretase inhibitor that inhibits Notch signaling, was able to overcome MSC-DC defects. In conclusion, our data suggest that MSC license adult CD34 + HPC to differentiate into regulatory DC through activation of the Notch pathway.

An Adaptive Mean-Shift Analysis Approach for Object Extraction and Classification From Urban Hyperspectral Imagery

Abstract: In this paper, an adaptive mean-shift (MS) analysis framework is proposed for object extraction and classification of hyperspectral imagery over urban areas. The basic idea is to apply an MS to obtain an object-oriented representation of hyperspectral data and then use support vector machine to interpret the feature set. In order to employ MS for hyperspectral data effectively, a feature-extraction algorithm, nonnegative matrix factorization, is utilized to reduce the high-dimensional feature space. Furthermore, two bandwidth-selection algorithms are proposed for the MS procedure. One is based on the local structures, and the other exploits separability analysis. Experiments are conducted on two hyperspectral data sets, the DC Mall hyperspectral digital-imagery collection experiment and the Purdue campus hyperspectral mapper images. We evaluate and compare the proposed approach with the well-known commercial software eCognition (object-based analysis approach) and an effective spectral/spatial classifier for hyperspectral data, namely, the derivative of the morphological profile. Experimental results show that the proposed MS-based analysis system is robust and obviously outperforms the other methods.

Physicochemical characterization and antioxidant activity of quercetin-loaded chitosan nanoparticles

Abstract: Quercetin is an abundant flavonoid in food plants with numerous biological activities and widely used as a potent antioxidant. Being sparingly soluble in water and subject to degradation in aqueous intestinal fluids, the absorption of quercetin is limited upon oral administration. In the present study, chitosan nanoparticles and quercetin-loaded nanoparticles were prepared based on the ionic gelation of chitosan with tripolyphosphate anions. The encapsulation of quercetin in the chitosan nanoparticles were confirmed by differential scanning calorimetry, X-ray powder diffractometry, Fourier transformed infrared spectroscopy, ultraviolet-visible spectrum, and fluorescence spectrum. The morphology of the nanoparticles was characterized by atomic force microscopy. The antioxidant activity of the quercetin-nanoparticles was also evaluated in vitro by two different methods (free radical scavenging activity test and reducing power test), which indicates that inclusion of quercetin in chitosan nanopaticles may be useful in improving the bioavailabilty of quercetin. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008