Creat membership Creat membership
Sign in

Forgot password?

  • Forgot password?
    Sign Up
  • Confirm
    Sign In
home > search

Now showing items 193 - 208 of 446


    Xu, Hai   Lou, Yue  

    This article focuses on the treatment of the spatial preposition to in English learners' dictionaries. Few in-depth studies have been undertaken on the preposition to though it has a high frequency and a rich meaning, and both its sense differentiation and definition in dictionaries are sometimes not satisfactory. Adopting a cognitive approach, we classified the spatial uses of the preposition to into six primary groups. Evidence suggests that the dynamic 'Unspecified Source - Path - Goal' schema on the horizontal plane is the proto-schema of to, around which a semantic network can be organised. We then analysed some of its abstract senses, which are metaphorically connected with its spatial uses. Finally, we proposed a 'four-tier' model to arrange the senses of the preposition to. This study not only aims to optimize the preposition entry to for learners' dictionaries, but to explore a new perspective from which spatial preposition entries can be made more reasonable and streamlined.
    Download Collect
  • Contribution of susceptibility- and diffusion-weighted magnetic resonance imaging for grading gliomas

    Xu, Jianxing   Xu, Hai   Zhang, Wei   Zheng, Jiangang  

    The aim of the present study was to assess the value of susceptibility-weighted imaging (SWI) and diffusion-weighted imaging (DWI) in the grading of gliomas and to evaluate the correlation between these quantitative parameters derived from SWI and DWI. A total of 49 patients with glioma were assessed by DWI and SWI. The evaluation included the ratio of apparent diffuse coefficient values between the solid portion of tumors and contralateral normal white matter (rADC) and the degree of intratumoral susceptibility signal intensity (ITSS) within tumors. Receiver operating characteristic curve (ROC) analyses were performed and the area under the ROC curve was calculated to compare the diagnostic performance, determine optimum thresholds for tumor grading, and calculate the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for identifying high-grade gliomas. The correlation between DWI- and SWI-derived parameters was also evaluated. The rADC and the degrees of ITSS within tumors were significantly higher in high-grade gliomas than those in low-grade gliomas. ROC curve analysis indicated that the rADC was a better index for grading gliomas than the ITSS degree. Statistical analysis demonstrated a threshold value of 1.497 for rADC to provide a sensitivity, specificity, PPV and NPV of 86.2, 85.0, 89.3 and 81.0%, respectively, for determining high-grade gliomas. A degree of ITSS of 1.5 was defined as the threshold to identify high-grade gliomas and sensitivity, specificity, PPV and NPV of 82.8, 75.0, 82.8 and 75.0% were obtained, respectively. Furthermore, a moderate inverse correlation between rADC and the ITSS degree was revealed. Combination of SWI with DWI may provide valuable information for glioma grading.
    Download Collect
  • Pre-vascularization in fibrin Gel/PLGA microsphere scaffolds designed for bone regeneration

    Liu, Jun   Chen, Gang   Xu, Hai   Hu, Ke   Sun, Jianfei   Liu, Mei   Zhang, Feimin   Gu, Ning  

    Blood supply plays a central role in alveolar bone regeneration within a large bone defect filled with a cell-laden scaffold material, as it provides sufficient oxygen and nutrition to cells inside the scaffold. To address the issue of insufficient vascularization within scaffolds designed to promote bone regeneration, we developed a pre-vascularized scaffold to enable the repair of large alveolar bone defects. Peripheral blood-derived mesenchymal stem cells (PBMSCs) and endothelial colony-forming cells (ECFCs) were collected from peripheral blood and incorporated into fibrin gel, which was then mixed with poly(lactic-co-glycolic acid) (PLGA) microspheres to form a fibrin gel/PLGA microsphere (FP) scaffold. The induction of osteogenic differentiation of PBMSCs and the pre-vascularization in the FP scaffold were achieved separately under different conditions. PBMSCs seeded into the FP scaffolds with fibrin gel tended to migrate to the surface of PLGA microspheres and express high levels of osteogenic markers. ECFCs co-cultured with PBMSCs in FP scaffolds were inclined to form a capillary-like structure in the gel substrate. These capillary-like structures penetrated the space among the microspheres and are supposed to anastomosis with blood capillaries in vivo. Together these results indicate that the pre-vascularized FP scaffold may overcome the shortages of oxygen and nutrition inside conventional scaffolds, leading to a better clinical effect.
    Download Collect
  • Bilateral internal carotid arteries ligation temporary impairs brain vasculaturev in young rats

    Gong, Hui   Shu, Liang   Xu, Hai   Chen, Ben   Mao, Renling   Zhang, Fayong   Wang, Yun  

    Bilateral internal carotid artery ligation (BICL) rat model is one of the chronic cerebral hypoperfusion animal models used for investigating brain dysfunction related diseases. Cerebral blood flow decreases in different cerebral regions in a time-dependent manner after the BICL However little is known about the cerebral vasculature change in the brain after the BICL. In the current study, the bilateral internal carotid arteries of the juvenile rats were permanently ligated and the change of the cerebral vasculature was studied 7, 14 and 21 days after the BICL. In the juvenile rats, 7 days after the BICL, the functional vascular area was decreased significantly in the anterior half of the cerebral cortex, but it had only little decrease in the posterior half of the cerebral cortex and hippocampus. However, at the time points of 14 and 21 days after the surgery, the functional vascular area throughout the whole cerebral cortex and hippocampus was almost similar to those in the sham control rats. In conclusion, the results from our current study showed that in the BICL hypoperfusion model in young rats, the brain functional vascular area was impaired initially in certain brain regions after the artery ligation, but likely to be quickly self-recovered late after. The results suggest that the brain vasculature in young rats has plasticity to external insult caused by cerebral hypoperfusion. (C) 2012 Elsevier B.V. All rights reserved.
    Download Collect
  • Surface properties of nucleolipids and photo-controlled release of hydrophobic guest molecules from their micellar aggregates.

    Sun, Yawei   Yu, Haiyan   Yan, Yongfeng   Chen, Cuixia   Xu, Wenwen   Lu, Jian R   Xu, Hai  

    Two series of nucleolipids have been designed and synthesized, one with a varying chain length (the dT-Cn series) and the other incorporating an aromatic photo-responsive moiety at the molecular hydrophobic and hydrophilic interface (the P-dT-Cn series). Surface tension measurements revealed the variations of critical micelle concentrations (CMCs) with the alkyl chain length and the incorporation of the photo-responsive segment. The P-dT-Cn series showed broadly lower CMCs and the minimum area per molecule (Amin) values because the pi-pi stacking between the additional aromatic rings favours more tight packing in the micelle formation. Both series showed similar surface tensions at the CMCs to conventional surfactants with equivalent molecular structures. Their micellar aggregates were used for encapsulation of hydrophobic Nile Red (NR). For the P-dT-Cn series, the encapsulated NR was released upon light irradiation and the controlled release was readily realized by controlling irradiation intensities or switching on and off irradiation. The integration of biocompatibility, complementary base recognition and photo-responsiveness makes the amphiphilic nucleolipids promising in biomedical and biotechnological applications. =20
    Download Collect
  • Controlling the Diameters of Nanotubes Self-Assembled from Designed Peptide Bolaphiles

    Zhao, Yurong   Yang, Wei   Wang, Dong   Wang, Jiqian   Li, Zongyi   Hu, Xuzhi   King, Stephen   Rogers, Sarah   Lu, Jian R.   Xu, Hai  

    Controlling the diameters of nanotubes represents a major challenge in nanostructures self-assembled from templating molecules. Here, two series of bolaform hexapeptides are designed, with Set I consisting of Ac-KI4K-NH2, Ac-KI(3)NleK-NH2, Ac-KI3LK-NH2 and Ac-KI(3)TleK-NH2, and Set II consisting of Ac-KI3VK-NH2, Ac-KI2V2K-NH2, Ac-KIV3K-NH2 and Ac-KV4K-NH2. In Set I, substitution for Ile in the C-terminal alters its side-chain branching, but the hydrophobicity is retained. In Set II, the substitution of Val for Ile leads to thedecrease of hydrophobicity, but the side-chain -branching is retained. The peptide bolaphiles tend to form long nanotubes, with the tube shell being composed of a peptide monolayer. Variation in core side-chain branching and hydrophobicity causes a steady shift of peptide nanotube diameters from more than one hundred to several nanometers, thereby achieving a reliable control over the underlying molecular self-assembling processes. Given the structural and functional roles of peptide tubes with varying dimensions in nature and in technological applications, this study exemplifies the predictive templating of nanostructures from short peptide self-assembly.
    Download Collect
  • Visual discrimination of citrus HLB based on image features

    Liu, YanDe   Xiao, Huaichun   Xu, Hai   Rao, Yu   Jiang, Xiaogang   Sun, Xudong  

    Citrus greening (Huanglongbing, HLB) has seriously threatened the healthy development of citrus industry in recent years, and it is great significance to diagnose citrus HLB timely and accurately. Hyperspectral technology has the characteristics of spectral analysis and image processing, which has shown great advantages in plant disease detection. The visual discrimination methods of citrus HLB based on features of images combined with hyperspectral imaging technology were discussed. Five types of citrus leaves, including the mild HLB, moderate HLB, serious HLB, malnourished and normal were studied and polymerase chain reaction (PCR) test was used to verify visual division. Effective spectral variables were selected by successive projections algorithm (SPA) and features of images were extracted by principal component analysis (PCA). Texture features of images based on grayscale co-occurrence matrix (GLCM) were used to develop the partial least squares discriminant analysis (PLS-DA) models. The influence of the number of textures on the models was discussed, and the effect of discrimination model was the best when a total of 36 variables which were obtained from 4 independent texture features were as input, which resulted in greater misjudgment rate of 3.12%, higher correlation coefficient for prediction (RP) of 0.98, lower root mean square error for prediction (RMSEP) of 0.32, and the number of principal component factors (PCs) of 16. The results highlighted that the image texture features based on GLCM combined with the PLS-DA models could realize the identification of citrus HLB, and provide the important reference value for the visual discrimination research of HLB.
    Download Collect
  • Demonstration of an active quantum key distribution network - art. no. 630506 RID A-7285-2010 RID B-5877-2009

    Tang, Xiao   Ma, Lijun   Mink, Alan   Nakassis, Anastase   Xu, Hai   Hershman, Barry   Bienfang, Joshua   Su, David   Boisvert, Ronald F.   Clark, Charles   Williams, Carl  

    We previously demonstrated a high speed, point to point, quantum key distribution (QKD) system with polarization coding over a fiber link, in which the resulting cryptographic keys were used for one-time pad encryption of real time video signals. In this work, we extend the technology to a three-node active QKD network - one Alice and two Bobs. A QKD network allows multiple users to generate and share secure quantum keys. In comparison with a passive QKD network, nodes in an active network can actively select a destination as a communication partner and therefore, its sifted-key rate can remain at a speed almost as high as that in the point-to-point QKD. We demonstrate our three-node QKD network in the context of a QKD secured real-time video surveillance system. In principle, the technologies for the three-node network are extendable to multi-node networks easily. In this paper, we report our experiments, including the techniques for timing alignment and polarization recovery during switching, and discuss the network architecture and its expandability to multi-node networks.
    Download Collect
  • Chopper Sugarcane Combine Harvester with Middle-Mounted Primary Extractor

    Wu, Tao   Liang, Xiao-Ling   Liu, Qing-Ting   Zhang, Zeng-Xue   Xu, Hai   Huang, Ji-Bai   Li, Jin-Xin   Zou, Xiao-Ping  

    Conventional chopper sugarcane combine harvesters had numerous drawbacks, including high center of gravity, easy clogging, and high trash rate. In order to resolve these problems, a chopper sugarcane combine harvester with shorter roller train and primary extractor installed in the middle was designed in the present study. The proposed harvester was equipped with the roller train and billet transporters. Moreover, the structure of the primary extractor was improved, and its position was selected to address the issues of chopper harvesters. Performing the field experiment shows that the average traveling speed of the proposed machine was 2 km/h, while the average feed capacity was 5.5 kg/s. Furthermore, it was found that the qualified rate of the cutting height, rate of the broken perennial ratoon, total loss, trash rate, and the qualified rate of cane billets were 90.1%, 9.6%, 3.1%, 4.4%, and 92.1%, respectively. Field experiment showed that the proposed machine harvested 2 x 10(4) kg of sugarcane per hour, where the average harvesting cost was about 45 RMB per 1000 kg of the cane. It was found that the operating efficiency was approximately 200 times higher than that of the manual harvesting, while the corresponding costs were reduced by 55%-70%. Moreover, it was concluded that the proposed machine was superior over AS60 and 4GZQ-260 in terms of the harvesting performance and almost reached the level of them in regard to the economic performance.
    Download Collect
  • Temperature variations at Lake Qinghai on decadal scales and the possible relation to solar activities

    Xu, Hai   Liu, Xiaoyan   Hou, Zhaohua  

    Temperature variations at Lake Qinghai, northeastern Qinghai-Tibet plateau, were reconstructed based on four high resolution temperature indicators of the delta O-18 and the delta C-13 of the bulk carbonate, total carbonate content, and the detrended delta N-15 of the organic matter. There are four obvious cold intervals during the past 600 years at Lake Qinghai, namely 1430-1470, 1650-1715 1770-1820, and 1920-1940, synchronous with those recorded in tree rings at the northeast Qinghai-Tibet plateau. The intervals of 1430-1470, 1650-1715, and 1770-1820 are consistent with the three coldest intervals of the Little Ice Age. These obvious cold intervals are also synchronous with the minimums of the sunspot numbers during the past 600 years, suggesting that solar activities may dominate temperature variations on decadal scales at the northeastern Qinghai-Tibet plateau. (c) 2007 Elsevier Ltd. All rights reserved.
    Download Collect
  • Preparation of sub-micron porous yttria-stabilized ceramics with ultra-low density by a TBA-based gel-casting method

    Xu, Hai   Du, Haiyan   Liu, Jiachen   Guo, Anran  

    Sub-micron porous yttria-stabilized zirconia (ZrO(2)-5 mol% Y(2)O(3), YSZ) ceramics with ultra low density were successfully fabricated by a novel tert-butyl alcohol (TBA)-based gel-casting method. In this work, polymerization of acrylamide was realized in tert-butyl alcohol (TBA)/ZrO(2) slurries with solid loading ranging from 10 to 30 wt.%. Green bodies with ultra-low density (from 1.18 to 1.65 g/cm(3)) could be dried with very small shrinkage (from 0.36% to 0.10%), and relatively high bending strengths (from 26.26 to 112.92 MPa) were achieved. By choosing different initial solid loadings, the green bodies were sintered at different temperatures and subsequently characterized in terms of both microstructure and properties to study effects of solid loading and sintering temperature. Both microstructure and properties exhibited obvious dependence on solid loading. By setting the solid loading (20 wt.%) and changing the sintering temperature from 1350 to 1500 degrees C, the porosity of the sintered samples varied within the range of 69.9% and 54.1%, as the linear shrinkage varied from 15.8% to 25.2% and pore sizes from 0.58 to 0.44 mu m. Due to the neck formation between particles, there were also some smaller pores around 1.7 and 3.0 nm. But the most important characteristics of the porous structure were the uniformity and the interconnection of pores with sizes about 0.5 mu m. (C) 2011 Elsevier B.V. All rights reserved.
    Download Collect
  • A review of toxicity and mechanisms of individual and mixtures of heavy metals in the environment

    Wu, Xiangyang   Cobbina, Samuel J.   Mao, Guanghua   Xu, Hai   Zhang, Zhen   Yang, Liuqing  

    The rational for the study was to review the literature on the toxicity and corresponding mechanisms associated with lead (Pb), mercury (Hg), cadmium (Cd), and arsenic (As), individually and as mixtures, in the environment. Heavy metals are ubiquitous and generally persist in the environment, enabling them to biomagnify in the food chain. Living systems most often interact with a cocktail of heavy metals in the environment. Heavy metal exposure to biological systems may lead to oxidation stress which may induce DNA damage, protein modification, lipid peroxidation, and others. In this review, the major mechanism associated with toxicities of individual metals was the generation of reactive oxygen species (ROS). Additionally, toxicities were expressed through depletion of glutathione and bonding to sulfhydryl groups of proteins. Interestingly, a metal like Pb becomes toxic to organisms through the depletion of antioxidants while Cd indirectly generates ROS by its ability to replace iron and copper. ROS generated through exposure to arsenic were associated with many modes of action, and heavy metal mixtures were found to have varied effects on organisms. Many models based on concentration addition (CA) and independent action (IA) have been introduced to help predict toxicities and mechanisms associated with metal mixtures. An integrated model which combines CA and IA was further proposed for evaluating toxicities of non-interactive mixtures. In cases where there are molecular interactions, the toxicogenomic approach was used to predict toxicities. The high-throughput toxicogenomics combines studies in genetics, genome-scale expression, cell and tissue expression, metabolite profiling, and bioinformatics.
    Download Collect
  • Molecular basis of the inhibitor selectivity and insights into the feedback inhibition mechanism of citramalate synthase from Leptospira interrogans

    Zhang, Peng   Ma, Jun   Zhang, Zilong   Zha, Manwu   Xu, Hai  

    LiCMS (Leptospira interrogans citramalate synthase) catalyses the first reaction of the isoleucine biosynthesis pathway in L. interrogans, the pathogen of leptospirosis. The catalytic reaction is regulated through feedback inhibition by its end product isoleucine. To understand the molecular basis of the high selectivity of the inhibitor and the mechanism of feedback inhibition, we determined the crystal structure of LiCMSC (C-terminal regulatory domain of LiCMS) in complex with isoleucine, and performed a biochemical study of the inhibition of LiCMS using mutagenesis and kinetic methods. LiCMSC forms a dimer of dimers in both the crystal structure and solution and the dimeric LiCMSC is the basic functional unit. LiCMSC consists of six-strands forming two anti-parallel beta-sheets and two alpha-helices and assumes a beta alpha beta three-layer sandwich structure. The inhibitor isoleucine is bound in a pocket at the dimer interface and has both hydrophobic and hydrogen-bonding interactions with several conserved residues of both subunits. The high selectivity of LiCMS for isoleucine over leucine is primarily dictated by the residues, Tyr(430), Leu(451), Tyr(454), Ile(458) and Val(468), that form a hydrophobic pocket to accommodate the side chain of the inhibitor. The binding of isoleucine has inhibitory effects on the binding of both the substrate, pyruvate, and coenzyme, acetylCoA, in a typical pattern of K-type inhibition. The structural and biochemical data from the present study together suggest that the binding of isoleucine affects the binding of the substrate and coenzyme at the active site, possibly via conformational change of the dimer interface of the regulatory domain, leading to inhibition of the catalytic reaction.
    Download Collect
  • Virus-like supramolecular assemblies formed by cooperation of base pairing interaction and peptidic association

    Cao, Meiwen   Wang, Ningning   Zhou, Peng   Sun, Yawei   Wang, Jiqian   Wang, Shengjie   Xu, Hai  

    A peptide nucleic acid (PNA)-peptide conjugated molecule, T'(3)(AKAE)(2), was designed to have both a PNA segment for oligonucleotide binding and an ionic self-complementary peptide sequence for self-association. T'(3)(AKAE)(2) could co-assemble with oligoadenines (d(A) (x) ) to form virus-like supramolecular structures whose morphology showed dependence on the chain length and rigidity of the d(A) (x) molecules. Smaller nanospheres with diameters of 13.0 +/- 2.0 nm were produced in the case of d(A)(6). Wormlike aggregates with lengths of 20-50 nm and diameters of 15.0 +/- 2.5 nm were found in the cases of d(A)(12), d(A)(18), d(A)(24) and d(A)(30). And larger spherical aggregates with diameters of 18 +/- 5 nm came into presence in the cases of d(A)(36) and d(A)(42). These nanostructures were suggested to be formed under a cooperative effect of base pair recognition and peptidic association. The study provides insights into the programmed assembly of a multi-components system as well as control of the size and shape of the co-assembled structures, which is of great significance in developing gene/drug delivery systems.
    Download Collect
  • Peptide-templated synthesis of branched MnO2 nanowires with improved electrochemical performances

    Du, Mingxuan   Bu, Yong   Zhou, Yan   Zhao, Yurong   Wang, Shengjie   Xu, Hai  

    Although many nanomaterials have been prepared in vitro by mimicking biomineralization, the biomimetic synthesis of hybrids with both well-ordered nanostructures and specific functions is still in its infancy. A short designed peptide amphiphile I3K can form uniform and stable nanofibers in aqueous solution, with a surface enriched in cationic lysine residue. In the present study, we have demonstrated that the peptide nanofibers could direct the synthesis of MnO2 nanowires under mild conditions. By varying the concentration of manganese precursors (KMnO4 and Mn(NO3)(2)), uniform branched MnO2/peptide hybrid nanowires with high porosity and a large specific surface area were obtained. The well-defined MnO2 hybrid nanowires showed significantly improved electrochemical supercapacitive properties relative to compact MnO2 nanowires and urchin-like MnO2 spheres. Their specific capacitance could attain a higher value of 421 F g(-1) and retained about 93% of the initial capacitance after 2500 cycles at a scan rate of 5 mV s(-1), and remained little changed during the process of progressively varying the current density. Furthermore, the electrode prepared from the uniform MnO2 hybrid nanowires showed an excellent reversibility and a reasonably high-rate capability during the charge/discharge process. Such a study provides a new methodology to prepare functional MnO2 nanostructures under mild conditions that can be used in electrochemical energy storage.
    Download Collect
  • The in vivo action of chronic bisphenol F showing potential immune disturbance in juvenile common carp (Cyprinus carpio)

    Qiu, Wenhui   Zhan, Hongyan   Tian, Yiqun   Zhang, Ting   He, Xin   Luo, Shusheng   Xu, Hai   Zheng, Chunmiao  

    Bisphenol F (BPF) has been increasingly introduced into industrial applications as a replacement for bisphenol A (BPA), and has emerged as a ubiquitous environmental contaminant worldwide. Few studies have assessed the in vivo toxicities of BPF, particularly long-term exposure toxicities. In the present study, we examined whether long-term BPF exposure in vivo would evoke oxidative stress in the immune system of juvenile common carp. The results suggested that BPF exposure increased ROS content, oxidative stress indices, complement component 3, and immunoglobulin M contents, as well as the expression of inflammatory cytokine genes. Moreover, higher levels of nf-?b p65 gene expression were correlated with the induced ROS content and NF-?B pathway-associated genes, a strong indication that the mode of action of BPF is related to the NF-?B signaling pathway. We also provide evidence that the effects of BPF are comparable to those of BPA with regards to regulation of the immune response in teleosts, and therefore suggest that such chemical analogs should be thoroughly evaluated for their potential toxicity before they can be considered as "safer" replacements. (C) 2018 Elsevier Ltd. All rights reserved.
    Download Collect
8 9 10 11 12 13 14 15 16 17


If you have any feedback, Please follow the official account to submit feedback.

Turn on your phone and scan

Submit Feedback