Showing papers by "Nankai University published in 2006"

Electromagnetic Interference (EMI) Shielding of Single-Walled Carbon Nanotube Epoxy Composites

Abstract: Single-walled carbon nanotube (SWNT)−polymer composites have been fabricated to evaluate the electromagnetic interference (EMI) shielding effectiveness (SE) of SWNTs. Our results indicate that SWNTs can be used as effective lightweight EMI shielding materials. Composites with greater than 20 dB shielding efficiency were obtained easily. EMI SE was tested in the frequency range of 10 MHz to 1.5 GHz, and the highest EMI shielding efficiency (SE) was obtained for 15 wt % SWNT, reaching 49 dB at 10 MHz and exhibiting 15−20 dB in the 500 MHz to 1.5 GHz range. The EMI SE was found to correlate with the dc conductivity, and this frequency range is found to be dominated by reflection. The effects of SWNT wall defects and aspect ratio on the EMI SE were also studied.

Adapting ranking SVM to document retrieval

Abstract: The paper is concerned with applying learning to rank to document retrieval. Ranking SVM is a typical method of learning to rank. We point out that there are two factors one must consider when applying Ranking SVM, in general a "learning to rank" method, to document retrieval. First, correctly ranking documents on the top of the result list is crucial for an Information Retrieval system. One must conduct training in a way that such ranked results are accurate. Second, the number of relevant documents can vary from query to query. One must avoid training a model biased toward queries with a large number of relevant documents. Previously, when existing methods that include Ranking SVM were applied to document retrieval, none of the two factors was taken into consideration. We show it is possible to make modifications in conventional Ranking SVM, so it can be better used for document retrieval. Specifically, we modify the "Hinge Loss" function in Ranking SVM to deal with the problems described above. We employ two methods to conduct optimization on the loss function: gradient descent and quadratic programming. Experimental results show that our method, referred to as Ranking SVM for IR, can outperform the conventional Ranking SVM and other existing methods for document retrieval on two datasets.

Decay of Loschmidt echo enhanced by quantum criticality.

Abstract: We study the transition of a quantum system S from a pure state to a mixed one, which is induced by the quantum criticality of the surrounding system E coupled to it. To characterize this transition quantitatively, we carefully examine the behavior of the Loschmidt echo (LE) of E modeled as an Ising model in a transverse field, which behaves as a measuring apparatus in quantum measurement. It is found that the quantum critical behavior of E strongly affects its capability of enhancing the decay of LE: near the critical value of the transverse field entailing the happening of quantum phase transition, the off-diagonal elements of the reduced density matrix describing S vanish sharply.

Facile controlled synthesis of MnO2 nanostructures of novel shapes and their application in batteries.

Abstract: In this paper, MnO2 nanomaterials of different crystallographic types and crystal morphologies have been selectively synthesized via a facile hydrothermal route and electrochemically investigated as the cathode active materials of primary and rechargeable batteries. β-MnO2 nano/microstructures, including one-dimensional (1-D) nanowires, nanorods, and nanoneedles, as well as 2-D hexagramlike and dendritelike hierarchical forms, were obtained by simple hydrothermal decomposition of an Mn(NO3)2 solution under controlled reaction conditions. α- and γ-MnO2 nanowires and nanorods were also prepared on the basis of previous literature. The as-synthesized samples were characterized by instrumental analyses such as XRD, SEM, TEM, and HRTEM. Furthermore, the obtained 1-D α- and γ-MnO2 nanostructures were found to exhibit favorable discharge performance in both primary alkaline Zn−MnO2 cells and rechargeable Li−MnO2 cells, showing their potential applications in high-energy batteries.

Shape-Controlled Synthesis of Ternary Chalcogenide ZnIn2S4 and CuIn(S,Se)2 Nano-/Microstructures via Facile Solution Route

Abstract: We demonstrated in this paper the shape-controlled synthesis of ZnIn2S4, CuInS2, and CuInSe2 nano- and microstructures through a facile solution-based route. One-dimensional ZnIn2S4 nanotubes and nanoribbons were synthesized by a solvothermal method with pyridine as the solvent, while ZnIn2S4 solid or hollow microspheres were hydrothermally prepared in the presence of a surfactant such as cetyltrimethylammonium bromide (CTAB) or poly(ethylene glycol) (PEG). The mechanisms related to the phase formation and morphology control of ZnIn2S4 are proposed and discussed. The UV−vis absorption spectra show that the as-prepared nano- and micromaterials have strong absorption in a wide range from UV to visible light and that their band gaps are somewhat relevant to the size and morphology. The photoluminescence measurements of the ZnIn2S4 microspheres at room temperature reveal intense excitation at ∼575 nm and red emission at ∼784 nm. Furthermore, CuInS2 and CuInSe2 with different morphologies such as spheres, plat...

CD80 in immune suppression by mouse ovarian carcinoma-associated Gr-1+CD11b+ myeloid cells.

Abstract: An elevated number of Gr-1+CD11b+ myeloid cells has been described in mice bearing transplantable tumors, and has been associated with immune suppression. We examined the role of such myeloid suppressor cells in mice bearing the spontaneously transformed syngeneic mouse ovarian surface epithelial cell line, 1D8. We observed high levels of CD80 expression by Gr-1+CD11b+ cells from spleen, ascites, and tumor tissue of mice bearing 1D8 ovarian carcinoma, whereas CD40 and CD86 were absent. CD80 expression was not detected on Gr-1+CD11b+ cells from naive mice. However, the expression of CD80 by Gr-1+CD11b+ cells from naive mice was promoted by coculture with 1D8 cells. Because irradiated 1D8 cells, but not 1D8-conditioned medium, up-regulate CD80 expression by Gr-1+CD11b+ cells, this phenomenon likely requires direct interaction. Gr-1+CD11b+ cells derived from 1D8 tumor–bearing mice provided significant suppression of antigen-specific immune responses, but Gr-1+CD11b+ cells from naive mice did not. Both short interfering RNA–mediated knockdown and genetic knockout of CD80 expression by Gr-1+CD11b+ cells of 1D8 tumor–bearing mice alleviated the suppression of antigen-specific immune responses. Suppression via CD80 on Gr-1+ CD11b+ myeloid cells was mediated by CD4+CD25+ T regulatory cells and required CD152. CD80 knockout or antibody blockade of either CD80 or CD152 retarded the growth of 1D8 tumor in mice, suggesting that expression of CD80 on Gr-1+CD11b+ myeloid cells triggered by 1D8 ovarian carcinoma suppresses antigen-specific immunity via CD152 signaling and CD4+CD25+ T regulatory cells. Thus, CD80-dependent responses to myeloid suppressor cells may contribute to tumor tolerance and the progression of ovarian carcinoma.(Cancer Res 2006; 66(13): 6807-15)

Delivery of Telomerase Reverse Transcriptase Small Interfering RNA in Complex with Positively Charged Single-Walled Carbon Nanotubes Suppresses Tumor Growth

Abstract: Purpose: To determine whether -CONH-(CH 2 ) 6 -NH 3 + Cl − functionalized single-walled carbon nanotubes (SWNT) carrying complexed small interfering RNA (siRNA) can enter into tumor cells, wherein they release the siRNA to silence the targeted gene. Experimental Design: -CONH-(CH 2 ) 6 -NH 3 + Cl − was used to mediate the conjugation of telomerase reverse transcriptase (TERT) siRNA to SWNTs. The ability of TERT siRNA delivered via SWNT complexes to silence the expression of TERT was assessed by their effects on the proliferation and growth of tumor cells both in vitro and in mouse models. Results: The functionalized SWNTs -CONH-(CH 2 ) 6 -NH 3 + Cl − could facilitate the coupling of siRNAs that specifically target murine TERT expression to form the mTERT siRNA:SWNT+ complex. These functionalized SWNTs rapidly entered three cultured murine tumor cell lines, suppressed mTERT expression, and produced growth arrest. Injection of mTERT siRNA:SWNT+ complexes into s.c. Lewis lung tumors reduced tumor growth. Furthermore, human TERT siRNA:SWNT+ complexes also suppressed the growth of human HeLa cells both in vitro and when injected into tumors in nude mice. Conclusions: -CONH-(CH 2 ) 6 -NH 3 + Cl − functionalized SWNTs carry complexed siRNA into tumor cells, wherein they release the siRNA from the nanotube sidewalls to silence the targeted gene. The -CONH-(CH 2 ) 6 -NH 3 + Cl − functionalized SWNTs may represent a new class of molecular transporters applicable for siRNA therapeutics.

Cooperative Binding and Multiple Recognition by Bridged Bis(β-cyclodextrin)s with Functional Linkers

Abstract: Possessing two β-cyclodextrin cavities in close vicinity and a functional linker with good structural variety in a single molecule, bridged bis(β-cyclodextrin)s can significantly enhance the original binding ability and molecular selectivity of native β-cyclodextrin and thus be successfully utilized in drug carriers, solubilizers, catalysis, photochemical materials, etc. This Account describes recent developments in the intramolecular cooperative binding and multiple recognition of bridged bis(β-cyclodextrin)s with functional linkers in solution, as well as their molecular assembly behaviors through the intermolecular cooperative binding. It also gives a description of unique properties and wide applications of bis(β-cyclodextrin)s and their assemblies.

A Promising MgII‐Ion‐Selective Luminescent Probe: Structures and Properties of Dy–Mn Polymers with High Symmetry

Abstract: Two Dy-Mn polymers, {[Dy(L1)3Mn(1.5)(H2O)3]3.125H2O}n (1, L1 = pyridine-2,6-dicarboxylic acid) and {[Dy(L2)3Mn(1.5)(H2O)6]8.25H2O}n (2, L2 = 4-hydroxylpyridine-2,6-dicarboxylic acid), with high symmetry (S6) have been prepared. Polymer 1 has a nanoporous 3D framework with channel of about 17.6 A diameter, while 2 has a honeycomb-type 2D structure with the cavity of approximately 14.4 A diameter. In the construction of multidimensional porous polymers with 3d-4f mixed metals, it is the first observation that a ligand substituent effect leads to dramatic differences in the structures formed. Luminescent studies reveal that the emission intensities of 1 and 2 increase significantly upon the addition of Mg2+, whereas the introduction of other metal ions leaves the intensity unchanged or even weakens it; hence, both of them may serve as good candidates of Mg2+ luminescent probes. To our knowledge, complex 1 is also the first example of a 3d-4f metal-based nanoporous polymer to exhibit luminescent selectivity for Mg2+. Magnetic susceptibility measurements reveal a rather rare ferromagnetic interaction in 2. Thermal gravimetric analyses and powder X-ray diffraction investigations have also been performed, suggestive of high thermal stability of 1.

Confinement-induced novel morphologies of block copolymers.

Abstract: Self-assembly of block copolymers confined in cylindrical nanopores is studied systematically using a simulated annealing technique. For diblock copolymers which form two-dimensional hexagonally packed cylinders with period L0 in the bulk, novel structures such as helices and stacked toroids spontaneously form inside the cylindrical pores. These confinement-induced morphologies have no counterpart in the bulk system and they depend on the pore diameter (D) and the surface-polymer interactions, reflecting the importance of structural frustration and interfacial interactions. On tightening the degree of confinement, transitions from helices to toroids to spheres are observed. Mechanisms of the morphological transitions can be understood based on the degree of structural frustration parametrized by the ratio D/L0.

Oxygen-defect-induced magnetism to 880 K in semiconducting anatase TiO2−δ films

Abstract: We demonstrate a semiconducting material, TiO2??, with ferromagnetism up to 880?K, without the introduction of magnetic ions. The magnetism in these films stems from the controlled introduction of anion defects from both the film?substrate interface as well as processing under an oxygen-deficient atmosphere. The room-temperature carriers are n-type with n~3 ? 1017?cm?3. The density of spins is ~1021?cm?3. Magnetism scales with conductivity, suggesting that a double exchange interaction is active. This represents a new approach in the design and refinement of magnetic semiconductor materials for spintronics device applications.

Crossings and nestings of matchings and partitions

Abstract: We present results on the enumeration of crossings and nestings for matchings and set partitions. Using a bijection between partitions and vacillating tableaux, we show that if we fix the sets of minimal block elements and maximal block elements, the crossing number and the nesting number of partitions have a symmetric joint distribution. It follows that the crossing numbers and the nesting numbers are distributed symmetrically over all partitions of [n], as well as over all matchings on [2n]. As a corollary, the number of k-noncrossing partitions is equal to the number of k-nonnesting partitions. The same is also true for matchings. An application is given to the enumeration of matchings with no k-crossing (or with no k-nesting). Mathematics Subject Classification. Primary 05A18, secondary 05E10, 05A15.

Synthesis and characterization of metal-organic frameworks based on 4-hydroxypyridine-2,6-dicarboxylic acid and pyridine-2,6-dicarboxylic acid ligands.

Abstract: The self-assembly of 4-hydroxypyridine-2,6-dicarboxylic acid (H(3)CAM) and pyridine-2,6-dicarboxylic acid (H2PDA) with Zn(II) salts under hydrothermal conditions gave two novel coordination polymers {[Zn(HCAM)].H2O}n (1) and {[Zn(PDA)(H2O)(1.5)]}n (1a). 1 and 1a comprise of a 2D (4,4) net and a 1D zigzag chain, respectively, in which a new coordination mode of PDA is found. The reactions of H(3)CAM and H2PDA with Nd2O3 in the M/L ratio 2:3 gave {[Nd2(HCAM)3(H2O)4].2H2O}n (2) and {[Nd(2)(PDA)3(H2O)(3)].0.5H2O}n (2a). In 2, a square motif as a building block constructed by four Nd(III) ions was further assembled into a highly ordered 2D (4,4) grid. 2a is a 3D microporous coordination polymer. It is interesting to note that, when Ln(III) salts rather than oxides were employed, the reaction produced {[Ln(CAM)(H2O)3].H2O}n (Ln = Gd, 3; Dy, 4; Er, 5) for H(3)CAM and {[Gd2(PDA)3(H2O)3].H2O}n (3a) for H2PDA. 3-5 are 2D coordination polymers with a 3(3)4(2) uniform net, where hydroxyl groups of H3CAM coordinate with metal ions. The reaction of H3CAM and Er2O3 instead of Er(ClO4)3 produced {[Er2(HCAM)3(H2O)4].2H2O}n (6). The compounds 2a and 3a, 2 and 6 are isomorphous. The stereochemical and supramolecular effects of hydroxyl groups result in the dramatic structural changes from 1D (1a) to 2D (1) and from 2D (2) to 3D (2a). When Ln(III) salts instead of Ln2O3 were employed in the hydrothermal reactions with H(3)CAM, different self-assembly processes gave the products of different metal/ligand ratio with reactants (3-5).

Control chart based on change-point model for monitoring linear profiles

Abstract: A control chart based on the change-point model is proposed that is able to monitor linear profiles whose parameters are unknown but can be estimated from historical data. This chart can detect a shift in either the intercept, slope or standard deviation. Simulation results show that the proposed approach performs well across a range of possible shifts, and that it can be used during the start-up stages of a process. Simple diagnostic aids are also given to estimate the location of the change and to determine which of the parameters has changed.

Synthesis of cyclic carbonates from epoxides and carbon dioxide over silica-supported quaternary ammonium salts under supercritical conditions

Abstract: A silica-supported quaternary ammonium salt is reported for the first time as a recyclable and efficient catalyst for the synthesis of propylene carbonate from propylene oxide and carbon dioxide under supercritical conditions, which requires no additional organic solvents either for the reaction or for the separation of product. Moreover, the catalyst can be easily recovered by a simple filtration and reused over four times without obvious loss of its catalytic activity. The effects of the types of cation and anion of quaternary ammonium salts, and other reaction parameters on the reaction are investigated. This organic solvent-free process presented here could show much potential application in industry due to its simplicity, easy product separation from reaction medium and catalyst recycling. It could be profitably applied to the development of fix-bed continuous flow reactors, avoiding the use of solvent to isolate the products.

Understanding information inequality: Making sense of the literature of the information and digital divides

Abstract: This paper reviews related research since the early 1990s on the information and digital divides. It shows that, despite their shared concerns with illustrating social inequality through the lens of information resource distribution, the two areas in effect represent two overlapping research communities. The research focus and discourse of the former were primarily shaped by three different theoretical perspectives and were inspired by a fairly strong sense of ethical principles; those of the latter, on the other hand, were shaped primarily by four different political standpoints and were imbued with a fairly strong concern for political and economical interests. The co-existence of multifarious perspectives and standpoints has produced divergent, and sometimes contradictory, research findings and policy recommendations, which inevitably perplex researchers and policy makers. The paper concludes with some suggestions for future research and policy making.

Vapor-transportation preparation and reversible lithium intercalation/deintercalation of alpha-MoO3 microrods.

Abstract: We report on the preparation and electrochemical application of rechargeable lithium-ion batteries of alpha-MoO3 microrods. A simple and efficient vapor-transportation approach was developed to yield large-scale alpha-MoO3 microrods. The as-prepared products were present in long, uniform, rodlike structures with a diameter of approximately 2 approximately 6 microm, and the proportion of the rod morphology was about 95% according to the analysis of scanning electron microscopy (SEM). The electrochemical lithium intercalation/deintercalation characteristic of the as-prepared microrods was investigated by cyclic voltammetry and a galvanostatic charge-discharge method. The results showed that the alpha-MoO3 microrods exhibited high capacity (225 mAh g(-1)) and excellent cycling reversibility, and are thus promising cathode candidates in advanced rechargeable lithium-ion batteries. The correlation between the specific structural features of the microrods and their superior electrode performance is discussed in detail, revealing that the unique rodlike structure plays an important role in optimizing the electrochemical performance of the electrode.

Covalently porphyrin-functionalized single-walled carbon nanotubes: a novel photoactive and optical limiting donor–acceptor nanohybrid

Abstract: Novel covalently porphyrin-functionalized single-walled carbon nanotubes (SWNTs) have been synthesized by the reaction of SWNTs with in situ generated porphyrin diazonium compounds. The resulting nanohybrid was characterized by spectroscopic (UV-Vis-NIR, FTIR and Raman) and microscopic (TEM and AFM) methods. The Raman and absorption spectroscopy data showed that the electronic properties of the modified tubes were mostly retained, without damaging their one-dimensional electronic properties. The fluorescence from the porphyrin moiety was almost completely quenched by SWNTs, indicating that the unique direct linkage mode facilitated the effective energy and electron transfer between the excited porphyrin moiety and the extended π-system of SWNTs. This novel nanohybrid material also exhibited excellent optical limiting properties.

Well-defined chiral spiro iridium/phosphine-oxazoline cationic complexes for highly enantioselective hydrogenation of imines at ambient pressure.

Abstract: New chiral phosphine-oxazoline ligands (7, SIPHOX) with a rigid and bulky spirobiindane scaffold were synthesized, starting with optically pure 7-diphenylphosphino-7'-trifluoromethanesulfonyloxyl-1,1'-spirobiindane, in four steps in 40-64% overall yield. Iridium complexes of 7, the chiral analogues of the Crabtree catalyst, were generated by coordination of ligands 7 and [Ir(COD)Cl](2) in the presence of sodium tetrakis-3,5-bis(trifluoromethyl)phenylborate. The complexes were characterized by NMR, ESI-MS, and X-ray diffraction analysis. The Ir-SIPHOX complexes can catalyze the hydrogenation of acyclic N-aryl ketimines under ambient pressure with excellent enantioselectivities (up to 97% ee) and full conversions. This result represents the highest enantioselectivity and the first example of the hydrogenation of imines catalyzed by chiral analogues of the Crabtree catalyst at ambient pressure. Studies on the stability of the catalysts revealed that the catalysts Ir-SIPHOX are very stable and resistant to the formation of inactive trimers under hydrogenation conditions. On the basis of the X-ray diffraction analysis of the structures of catalysts and amine products, a rational explanation for the enantiocontrol of the chiral catalysts in the hydrogenation of imines is proposed.