217 research outputs found

    Multi-wavelength Stellar Polarimetry of the Filamentary Cloud IC5146: I. Dust Properties

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    We present optical and near-infrared stellar polarization observations toward the dark filamentary clouds associated with IC5146. The data allow us to investigate the dust properties (this paper) and the magnetic field structure (Paper II). A total of 2022 background stars were detected in RcR_{c}-, ii'-, HH-, and/or KK-bands to AV25A_V \lesssim 25 mag. The ratio of the polarization percentage at different wavelengths provides an estimate of λmax\lambda_{max}, the wavelength of peak polarization, which is an indicator of the small-size cutoff of the grain size distribution. The grain size distribution seems to significantly change at AVA_V \sim 3 mag, where both the average and dispersion of PRc/PHP_{R_c}/P_{H} decrease. In addition, we found λmax\lambda_{max} \sim 0.6-0.9 μ\mum for AV>2.5A_V>2.5 mag, which is larger than the \sim 0.55 μ\mum in the general ISM, suggesting that grain growth has already started in low AVA_V regions. Our data also reveal that polarization efficiency (PE Pλ/AV\equiv P_{\lambda}/A_V) decreases with AVA_V as a power-law in RcR_c-, ii'-, and KK-bands with indices of -0.71±\pm0.10, -1.23±\pm0.10 and -0.53±\pm0.09. However, HH-band data show a power index change; the PE varies with AVA_V steeply (index of -0.95±\pm0.30) when AV<2.88±0.67A_V < 2.88\pm0.67 mag but softly (index of -0.25±\pm0.06) for greater AVA_V values. The soft decay of PE in high AVA_V regions is consistent with the Radiative Aligned Torque model, suggesting that our data trace the magnetic field to AV20A_V \sim 20 mag. Furthermore, the breakpoint found in HH-band is similar to the AVA_V where we found the PRc/PHP_{R_c}/P_{H} dispersion significantly decreased. Therefore, the flat PE-AVA_V in high AVA_V regions implies that the power index changes result from additional grain growth.Comment: 31 pages, 17 figures, and 3 tables; accepted for publication in Ap

    A simple way to fine tune the redox potentials of cobalt ions encapsulated in nitrogen doped graphene molecular catalysts for the oxygen evolution reaction

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    Co2+ ions encapsulated in nitrogen doped graphene were applied as an oxygen evolution catalyst. Their redox potentials were tuned using different counter anions as liable ligands, and the redox potential related catalytic rates were explored. It was proposed that the electron density of Co2+ ions was a general descriptor for activity

    بررسی حیطه‌های موجود در فرم‌های ارزشیابی از دیدگاه دانشجویان در دانشگاه علوم پزشکی زنجان در سال تحصیلی 86- 87

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    زمینه و هدف: ارزشیابی استادان متداول‌ترین روش جهت سنجش کیفیت آموزش می‌باشد. دانشجویان بیش از دست‌اندرکاران در جریان روند آموزش قرار‌دارند بنابراین با نظرخواهی از آنان دیدگاه کاملی برای مسئولین در مورد نقاط قوت و ضعف استادان به‌دست می‌آید. هدف از این پژوهش بررسی حیطه‌های موجود در فرم‌های ارزشیابی از دیدگاه دانشجویان در دانشکده‌های پزشکی، پیراپزشکی و پرستاری و مامایی می‌باشد. روش بررسی: این تحقیق به صورت توصیفی انجام گرفت. 1683 برگ ارزشیابی دانشجویان از استادان هیأت علمی (73 نفر) مربوط به دانشکده‌های پزشکی، پیراپزشکی و پرستاری- مامایی بررسی شد. پرسش‌نامه‌ی دانشجویان پزشکی حاوی 15 سؤوال و دانشجویان پیراپزشکی و پرستاری مامایی 21 سؤوال بود که بر اساس مقیاس لیکرات از حیطه‌های مختلف مقرراتی، علمی و آموزشی، نظارتی و نگرشی تشکیل شده بود. نمرات سؤوالات از نمره‌ی 100 محاسبه شد، نمرات بالاتر بیانگر عملکرد مطلوب‌تراستادان می‌باشد. تجزیه و تحلیل داده‌ها به‌صورت آمار توصیفی با نرم‌افزار SPSS انجام شد. یافته‌ها: نتایج نشان داد مقایسه در سطوح کلی بین دانشکده‌ها، دانشکده‌ی پیراپزشکی با میانگین کل و انحراف معیار 61/3 ±50/85 نسبت به سایر دانشکده‌ها برتری دارد. دانشکده‌ی پیراپزشکی در حیطه‌ی مقرراتی با میانگین و انحراف معیار 89/3±01/91، دانشکده‌ی پزشکی در حیطه‌ی نگرشی با میانگین و انحراف معیار 45/5±48/90 و دانشکده‌ی پرستاری مامایی در حیطه‌ی مقرراتی با میانگین و انحراف معیار 25/4±34/88 بیشترین امتیاز را داشتند. نتیجه‌نهایی نشان می‌دهد، حیطه‌ی علمی و آموزشی نسبت به سایر حیطه‌ها در سطح پایین‌تر می‌باشد. نتایج حیطه‌ها (علمی و آموزشی، نظارتی و نگرشی) بین دانشکده‌ها معنی‌دار می‌باشد (0001/0=P). نتیجه‌گیری: به نظر می‌رسد با برنامه‌ریزی جهت برگزاری کارگاه‌های آموزشی، روش تدریس و تحقیق جهت ارتقای آموزش استادان، اعطا‌ی فرصت مطالعاتی و تشویق انجام کارهای تحقیقاتی و پژوهشی گام مؤثری جهت ارتقای سطح علمی و بالاخره عملکرد بالای استادان خواهد بود

    Development of Transition-Metal-Catalyzed Transformations of Triazoles

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    This thesis defense presentation describes the development of transition-metal-catalyzed transformations of fused pyridotriazoles, as well as monocyclic N-sulfonyl-1,2,3-triazoles, which allows efficient synthesis of various valuable nitrogen-containing compounds. One major focus of Part I lies in subsequent section describing the development of a general and efficient rhodium-catalyzed reaction of pyridotriazoles with amides and amines, allowing facile synthesis of valuable picolylamine derivatives, providing expeditious access to various disubstituted imidazopyridines in a one-pot manner via the subsequent cyclization. With this method, we broke the structural limitation of pyridotriazoles (activating group at C7-position, EWG at C3-position). Moreover, the imidazopyridines obtained with this protocol are not accessible by previously reported transannulation reaction of pyridotriazoles with nitriles. Another focus of Part I is the discovery of copper-catalyzed intramolecular transannulation reaction of pyridotriazoles with internal alkynes, offering efficient construction of various tri-, tetra-, and pentacyclic fused indolizines. It is not only the first intramolecular transannulation reaction of pyridotriazoles, but also for the first time it is shown that this reaction could also be triggered by Lewis acids. In Part II, we developed a method for expeditious access to various 5,5-fused pyrroles from easily available N-sulfonyl-1,2,3-triazoles. Moreover, it can also be used to efficiently construct spiro systems, as well as fused tetrahydropyrrolo-pyrrole cores. In contrast to previously reported methods where ylides are key intermediates, preliminary mechanistic study reveals that a Rh-carbene-alkyne metathesis step is involved in this transformation

    Intramolecular Transannulation of Alkynyl Triazoles via Alkyne–Carbene Metathesis Step: Access to Fused Pyrroles

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    An intramolecular Rh-catalyzed transannulation reaction of alkynyl triazoles has been developed. This method allows efficient construction of various 5,5-fused pyrroles, including tetrahydropyrrolo and spiro systems. The method demonstrates excellent functional group compatibility. A rhodium carbene–alkyne metathesis mechanism is proposed for this transformation

    Effect of Tacticity Sequence of the Poly(<i>N</i>‑isopropylacrylamide) Oligomer on Phase Transition Behavior in Aqueous Solution

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    The tacticity of poly(N-isopropylacrylamide) (PNIPAM) has a strong impact on the lower critical solution temperature (LCST) in aqueous solution. The sequence of meso diads (m) and racemo diads (r) further contributes to such an effect. In this work, the phase transition behaviors of poly(N-isopropylacrylamide) pentamers with four kinds of sequences, i.e., rrmm, rmmr, mrrm, and rmrm, in water were studied applying replica exchange molecular dynamics with a modified OPLS/AA force field. The difference in local component concentration in the system was used as an order parameter to quantitatively describe the phase separation extent. It was found that the phase separation degree of rrmm and rmmr is higher than that of mrrm and rmrm at the same temperature. The LCSTs of rrmm and rmmr are lower than those of mrrm and rmrm. The radial distribution function and hydrogen bond analysis revealed that the average values of hydrogen bonds between pentamers for rrmm and rmmr are greater than those of mrrm and rmrm, whereas the average values of hydrogen bonds between pentamers and water for rrmm and rmmr are less than those of mrrm and rmrm. It was demonstrated that the isotactic triad (mm) plays an important role in the thermosensitive behaviors of the PNIPAM pentamer. The increase of isotactic triad (mm) content in the PNIPAM chain promotes the formation of intermolecular hydrogen bonds between amide and amide and leads to a higher aggregation of the pentamer with the sequence of rrmm or rmmr. Finally, the effect of the isotactic triad was qualitatively explained with the mean-field theory

    The influence of cell membrane and SNAP25 linker loop on the dynamics and unzipping of SNARE complex

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    <div><p>The soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex is composed of three neuronal proteins VAMP2, Syntaxin and SNAP25, which plays a core role during the process of membrane fusion. The zipping assembly of the SNARE complex releases energies and drives the vesicle and cell membrane into close proximity. In this study, we use all-atom molecular dynamics simulations to probe the dynamics of SNARE and its unzipping process in the context of membrane at the atomistic details. Our results indicated that the NTD of SNARE core domain is relatively more stable than CTD, which is in agreement with previous experiments. More importantly, possible interactions between the linker loop (LL) region of SNAP25 and VAMP2 are observed, suggests that the LL region may facilitate VAMP2 binding and SNARE initiation. The forced unzipping of SNARE in the presence of membrane and LL of SNAP25 reveals the possible pathway for energy generation of SNARE zipping, provides information to understand how force may regulate the cooperativity between the membrane and the SNARE complex.</p></div

    Analysis of SMD simulations.

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    <p>(A)Force-extension curves of SMD simulations FU1, FU2 and FU4. The yellow, shaded area represents zero layer position. (B)The change of the SNARE orientation with the membrane during the simulations.</p

    The free molecular dynamics simulations.

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    <p>(A)The RMSD of three different simulations, resutls for SNARE core domain and LL region are shown. (B)The change of the angle between SNARE core domain and the membrane. (C)Change of the angle between the transmembrane domain of Syntaxin and the membrane.</p

    Synthesis of Cylindrical Polymer Brushes with Umbrella-Like Side Chains via a Combination of Grafting-from and Grafting-onto Methods

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    Cylindrical polymer brushes with umbrella-like side chains have been synthesized by a combination of grafting-from and grafting-onto methods. First, the polymer brushes with azido end-functionalized poly­(<i>tert</i>-butyl acrylate) (P<i>t</i>BA-N<sub>3</sub>) side chains, PBIEM-<i>g</i>-(P<i>t</i>BA-N<sub>3</sub>), were prepared by atom transfer radical polymerization (ATRP) of <i>t</i>BA monomers using polyinitiator PBIEM followed by a substitution of bromo-side terminals with sodium azide. Subsequently, polyamidoamino dendrons of three generations with a propargyl focal point (G<i>n</i>) were introduced onto the brush-shaped P<i>t</i>BA-N<sub>3</sub> by copper-catalyzed azide–alkyne cycloaddition (CuAAC) coupling reaction. The efficiency of CuAAC between P<i>t</i>BA-N<sub>3</sub> side chains and G<i>n</i> has showed a dependence on generation number <i>n</i> of the dendrons. At the feed ratio of [G<i>n</i>]:[N<sub>3</sub>] = 1:1, the grafting efficiency of the first generation dendron (G1) reached above 95%, whereas that of G2 and G3 was at least 84% and 73%, respectively. AFM images indicated that diameter of the brushes hybridized with G3 increased obviously than that of the brushes without dendrons
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