A selenium-doped carbon anode of high performance for lithium ion batteries

Journal of Solid State Electrochemistry - The strong demand on high-performance lithium ion batteries has brought up an attention upsurge in the research society and the commercial market. Carbon...     

Microstructure elucidation of historic silk (Bombyx mori) by nuclear magnetic resonance

¹H NMR cryoporometry and solid-state ¹³C cross-polarization (CP) magic-angle spinning (MAS) NMR spectroscopy were used to characterize the microstructure of historic and fresh silk samples. Silk is a polymeric bicomponent material composed of fibroin and water located in micropores. According to the ¹H NMR cryoporometry method, the intensity of the water resonance as a function of the temperature was used to obtain the pore size distribution, which was strongly asymmetric with a well-defined maximum at 1.1 nm. Compared with the fresh silk samples, the volume of pores around 1.1 nm decreased distinctly in the historic silk, and more pores larger than 2 nm emerged accordingly. In addition, these results correlated well with solid-state ¹³C CP/MAS NMR spectroscopy as the percentage of random coil in the historic silk sample was much less than that in the fresh silk samples. Therefore, it is suggested that the water-filled microvoids grow larger as the random coil conformation fades away in the degradation process.

Unambiguous Diagnosis of Photoinduced Charge Carrier Signatures in a Stoichiometrically Controlled Semiconducting Polymer‐Wrapped Carbon Nanotube Assembly

Single‐walled carbon nanotube (SWNT)‐based nanohybrid compositions based on (6,5) chirality‐enriched SWNTs ([(6,5) SWNTs]) and a chiral n‐type polymer (S‐PBN(b)‐Ph₄PDI) that exploits a perylenediimide (PDI)‐containing repeat unit are reported; S‐PBN(b)‐Ph₄PDI‐[(6,5) SWNT] superstructures feature a PDI electron acceptor unit positioned at 3 nm intervals along the nanotube surface, thus controlling rigorously SWNT–electron acceptor stoichiometry and organization. Potentiometric studies and redox‐titration experiments determine driving forces for photoinduced charge separation (CS) and thermal charge recombination (CR) reactions, as well as spectroscopic signatures of SWNT hole polaron and PDI radical anion (PDI^?.) states. Time‐resolved pump–probe spectroscopic studies demonstrate that S‐PBN(b)‐Ph₄PDI‐[(6,5) SWNT] electronic excitation generates PDI^?. via a photoinduced CS reaction (τ_CS≈0.4 ps, Φ_CS≈0.97). These experiments highlight the concomitant rise and decay of transient absorption spectroscopic signatures characteristic of the SWNT hole polaron and PDI^?. states. Multiwavelength global analysis of these data provide two charge‐recombination time constants (τ_CR≈31.8 and 250 ps) that likely reflect CR dynamics involving both an intimately associated SWNT hole polaron and PDI^?. charge‐separated state, and a related charge‐separated state involving PDI^?. and a hole polaron site produced via hole migration along the SWNT backbone that occurs over this timescale.     

Effect of interaction between loop bases and ions on stability of G-quadruplex DNA

G-quadruplexes(GQs) are guanine-rich, non-canonical nucleic acid structures that play fundamental roles in biological processes. The topology of GQs is associated with the sequences and lengths of DNA, the types of linking loops, and the associated metal cations. However, our understanding on the basic physical properties of the formation process and the stability of GQs is rather limited. In this work, we employed ab initio, molecular dynamics(MD), and steered MD(SMD)simulations to study the interaction between loop bases and ions, and the effect on the stability of G-quadruplex DNA, the Drude oscillator model was used in MD and SMD simulations as a computationally efficient manner method for modeling electronic polarization in DNA ion solutions. We observed that the binding energy between DNA bases and ions(K⁺/Na⁺)is about the base stacking free energies indicates that there will be a competition among the binding of M⁺-base, H-bonds between bases, and the base-stacking while ions were bound in loop of GQs. Our SMD simulations indicated that the side loop inclined to form the base stacking while the loop sequence was Thy or Ade, and the cross-link loop upon the G-tetrads was not easy to form the base stacking. The base stacking side loop complex K+was found to have a good stabilization synergy. Although a stronger interaction was observed to exist between Cyt and K+, such an interaction was unable to promote the stability of the loop with the sequence Cyt.     

Circular dichroism induced by the helical conformations of acylated chitosan derivatives bearing cinnamate chromophores

Through regioselective modifications, some acylated chitosan derivatives, O‐cinnamoyl chitosans with degree of substitution (DS) varying from 0.8 to 2.0 and N‐fatty acyl‐O‐dicinnamoyl chitosans with different fatty acyl chain lengths (C₂–C₁₂), were prepared, and their chiroptical properties in dilute solutions were investigated by circular dichroism (CD). Exciton coupling between two vicinal cinnamoyl chromophores appended to the helical mainchains gave rise to bisignate Cotton effects (CEs), which were used to deduce the absolute sense of the twisting structures in solution phase. It was found that the absolute helicities vary with DS, length of the fatty chain, and solvent property, but are nearly independent of thermal stimulus. The molecular interactions (hydrogen bonding and hydrophobic interaction) involved possibly in the self‐assembled ordered structures were discussed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1354–1364, 2005     

Spherulite morphology studies of N‐alkyl chitosan films cast from formic acid solutions

The films of N‐ethyl chitosan were prepared via the solution‐casting technique with formic acid as a solvent. The solutions with different concentrations (35 and 40 wt %) were prepared previously from dilute solution (1 wt %) via evaporating process. The crystalline morphology of these films was investigated by means of polarized optical microscopy and scanning electron microscopy. Normal spherulites with a low growth rate formed in the casting films. The different morphologies of spherulite appeared in the films cast from the solutions with different concentrations. After further crystallizing for a few days, the spherulites were decorated by thousands of needlelike extended‐chain crystals, which had a typical size of ～50 μm (length) × 2～5 μm (width) × 1～2 μm (height) in the central part of the spherulite, but a typical size of ～5 μm (lenght)× 1～2 μm (width) × 1～2 μm (height) in the fringe part of the spherulite. The real concentration for crystallization was determined to be 65–82 wt%. Thus, the crystallization actually appeared in supersaturated solution. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2033–2038, 2003     

一类特殊的分式规划问题的ε-近似算法

本文针对一类特殊的分式规划问题基于网格搜索提出了一个求其全局最优解的算法,且从理论上证明了算法的收敛性与计算复杂性,通过算例验证了算法的可行性与有效性.     

Silica nanoparticle assisted DNA assays for optical signal amplification of conjugated polymer based fluorescent sensors

A cationic conjugated polymer provided over 110-fold signal amplification for silica nanoparticle based assays, which allow detection of target DNAs at a concentration of 10 pM with a standard fluorometer.     

Precise Asymptotic in the Complete Moment Convergence of NA Sequence

We achieves some results of precise asymptotic in the complete moment convergence of NA random variables.     

OPTIMAL REINSURANCE UNDER EXPECTED VALUE PRINCIPLE

The paper concerns the problem how to purchase the reinsurance in order to make the insurer and the reinsurance company＇s total risk to be least under the expected value principle. When the insurer and reinsurance company take arbitrary risk measures, sufficient con- ditions for optimality of reinsurance contract are given within the restricted class of admissible contracts. Further, the explicit forms of optimal reinsurance contract under several special risk measures are given, and the method to decide parameters as well.