96 research outputs found

    Through-Bond Energy Transfer Cassettes for Multicolor Encoding

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    Through-bond energy transfer (TBET) has been proposed as a versatile strategy to develop encoded microspheres. Together with the donor molecule, two TBET cassettes with high intramolecular TBET efficiencies (98% and 99%) and pseudo-Stokes shifts about 70 and 160 nm have been codoped into PS microspheres. Upon exclusive excitation at 480 nm, these microspheres emit simultaneously triple peaks at 512, 570, and 656 nm. Further confocal imaging and flow cytometric analysis demonstrates satisfactory performances of the new encoded microspheres

    Unique Configuration of a Nitrogen-Doped Graphene Nanoribbon: Potential Applications to Semiconductor and Hydrogen Fuel Cell

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    Systematic studies on a recently synthesized nitrogen-doped tetragonal-shaped single crystal graphene (NTSG) recover an orderly growth mechanism, which lead to an undiscovered novel structure of this new kind of nitrogen-doped graphene nanoribbon. The nitrogen atoms, bringing in high spin state depending on the length of the single crystal, endue the NTSG array with special electromagnetic property and possible application in the field of semiconductor. Further examination on oxygen adsorption at NTSG reveals high electrocatalytic activity of NTSG in oxygen reduction reaction, indicating that this nitrogen-doped graphene material could be used as a potential catalyst for hydrogen fuel cells. This work may be helpful for the further research on nitrogen-doped graphene nanoribbon and promoting the development of a new functional device

    Characteristics of the sample (N = 2264).

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    <p>Characteristics of the sample (N = 2264).</p

    Catalytic Asymmetric Difunctionalization of Stable Tertiary Enamides with Salicylaldehydes: Highly Efficient, Enantioselective, and Diastereoselective Synthesis of Diverse 4‑Chromanol Derivatives

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    Catalyzed by a chiral BINOL–Ti­(O<i>i</i>Pr)<sub>4</sub> complex, various stable tertiary enamides reacted with salicylaldehydes to afford diverse <i>cis,trans</i>-configured 4-chromanols that contain three continuous stereogenic centers in good yields with excellent diastereoselectivity and enantioselectivity. The reaction proceeded through the addition of enamide to aldehyde followed by the intramolecular interception of the resulting iminium by the hydroxy group. Oxidation of the resulting 4-chromanols yielded almost quantitatively chroman-4-one derivatives which underwent diastereospecific reduction with NaBH<sub>4</sub> to produce <i>cis,cis</i>-configured 4-chromanols

    Catalytic Asymmetric Difunctionalization of Stable Tertiary Enamides with Salicylaldehydes: Highly Efficient, Enantioselective, and Diastereoselective Synthesis of Diverse 4‑Chromanol Derivatives

    No full text
    Catalyzed by a chiral BINOL–Ti­(O<i>i</i>Pr)<sub>4</sub> complex, various stable tertiary enamides reacted with salicylaldehydes to afford diverse <i>cis,trans</i>-configured 4-chromanols that contain three continuous stereogenic centers in good yields with excellent diastereoselectivity and enantioselectivity. The reaction proceeded through the addition of enamide to aldehyde followed by the intramolecular interception of the resulting iminium by the hydroxy group. Oxidation of the resulting 4-chromanols yielded almost quantitatively chroman-4-one derivatives which underwent diastereospecific reduction with NaBH<sub>4</sub> to produce <i>cis,cis</i>-configured 4-chromanols

    Percentage distribution of respondents’ preferred living arrangements by their characteristics.

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    <p>Percentage distribution of respondents’ preferred living arrangements by their characteristics.</p

    Epoxy and Oxidoannulene Oxidation Mechanisms of Fused-Pentagon Chlorofullerenes: Oxides Linked by a Pirouette-Type Transition State

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    Recently, the oxidative functionalization of double-fused-pentagon (DFP)-containing chlorofullerenes <sup>#271</sup>C<sub>50</sub>Cl<sub>10</sub> and <sup>#913</sup>C<sub>56</sub>Cl<sub>10</sub> was carried out, resulting in two monoepoxides with the oxygen atom added at the ortho site of pentalene on the DFP moiety. To uncover the reactivity of isolated-pentagon-rule violating fullerenes upon oxidation, two possible formation processes (ozone molecule and oxygen radical served as oxidation reagents) of these two oxides were systematically investigated through density functional theory calculations. For the ozone oxidation, two possible pathways were explored, and the results indicate that the biradical mechanism Path<sub>os</sub>-RACDP is kinetically more favorable than Path<sub>os</sub>-RABP, where R, A, and P represent reactants, ozonide intermediates, and oxidation products and B, C, and D represent another three oxygen-containing intermediates. The products obtained by ozone oxidation ([6,6]-55-closed epoxides P–C<sub>3</sub>–C<sub>29</sub> for <sup>#271</sup>C<sub>50</sub>Cl<sub>10</sub> and P–C<sub>42</sub>–C<sub>43</sub> for <sup>#913</sup>C<sub>56</sub>Cl<sub>10</sub> with oxygen atom added at the shortest and highest HOMO-contribution bonds) are consistent with experimental observations. However, the oxygen radical additions on these two chlorofullerenes favor generation of the [5,6]-66-open oxidoannulene adducts P–C<sub>3</sub>–C<sub>2</sub> and P–C<sub>42</sub>–C<sub>54</sub>, respectively. Subsequent analyses of their geometrical features and structural stabilities suggest that these two oxidoannulene adducts are energetically unfavorable and could be converted to more stable epoxides mentioned above by undergoing a pirouette-type transition state. In these two diverse oxidation procedures, the favorable C–C bonds for ozone attacking and C atoms for oxygen-adsorption are rationalized in terms of their bond lengths and HOMO contributions as well as pyramidalization angles

    Multiple logistic regression analysis of respondents’ characteristics and living arrangement preferences.

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    <p>Multiple logistic regression analysis of respondents’ characteristics and living arrangement preferences.</p

    Quantum Chemical Determination of Novel C<sub>82</sub> Monometallofullerenes Involving a Heterogeneous Group

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    By means of density functional theory methods together with statistical thermodynamic analysis, the C<sub>82</sub> monometallofullerenes including special heterogeneous triangular clusters were theoretically probed for the first time. Despite having analogous structures, the YCN@C<sub>82</sub> and TbCN@C<sub>82</sub> series exhibit dissimilar thermodynamic stabilities, which lead to different components of experimental products. Significant relationship between the thermodynamic stabilities and geometry structures of C<sub>82</sub> metallofullerenes is disclosed. Studies of the electronic configurations of MCN@C<sub>82</sub> species not only explain their redox potentials but also recover complicated interaction mechanisms within them. In addition, predictions of the optical spectra of observed MCN@C<sub>82</sub> species coincide with experimental detections well, indicating that simulations for other structures will be helpful for future characterization of these cyanoclusterfullerenes

    Automatic initial and final segmentation in cleft palate speech of Mandarin speakers

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    <div><p>The speech unit segmentation is an important pre-processing step in the analysis of cleft palate speech. In Mandarin, one syllable is composed of two parts: initial and final. In cleft palate speech, the resonance disorders occur at the finals and the voiced initials, while the articulation disorders occur at the unvoiced initials. Thus, the initials and finals are the minimum speech units, which could reflect the characteristics of cleft palate speech disorders. In this work, an automatic initial/final segmentation method is proposed. It is an important preprocessing step in cleft palate speech signal processing. The tested cleft palate speech utterances are collected from the Cleft Palate Speech Treatment Center in the Hospital of Stomatology, Sichuan University, which has the largest cleft palate patients in China. The cleft palate speech data includes 824 speech segments, and the control samples contain 228 speech segments. The syllables are extracted from the speech utterances firstly. The proposed syllable extraction method avoids the training stage, and achieves a good performance for both voiced and unvoiced speech. Then, the syllables are classified into with “quasi-unvoiced” or with “quasi-voiced” initials. Respective initial/final segmentation methods are proposed to these two types of syllables. Moreover, a two-step segmentation method is proposed. The rough locations of syllable and initial/final boundaries are refined in the second segmentation step, in order to improve the robustness of segmentation accuracy. The experiments show that the initial/final segmentation accuracies for syllables with quasi-unvoiced initials are higher than quasi-voiced initials. For the cleft palate speech, the mean time error is 4.4ms for syllables with quasi-unvoiced initials, and 25.7ms for syllables with quasi-voiced initials, and the correct segmentation accuracy P<sub>30</sub> for all the syllables is 91.69%. For the control samples, P<sub>30</sub> for all the syllables is 91.24%.</p></div
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