Ab initio studies on n-type and p-type Li4Ti5O12

This paper studies the structure and electronic properties of Li4Ti5O12, as anode material for lithium ion batteries, from first principles calculations. The results suggest that there are two kinds of unit cell of Li4Ti5O12: n-type and p-type. The two unit cells have different structures and electronic properties:the n-type with two 16d site Li ions is metallic by electron, while the p-type with three 16d Li ions is metallic by hole. However, the Li4Ti5O12 is an insulator. It is very interesting that one n-type cell and two p-type cells constitute one Li4Ti5O12 supercell which is insulating. The results show that the intercalation potential obtained with a p-type unit cell with one additional electron is quite close to the experimental value of 1.5 V.     

Luminescence spectra of stilbene-3 doped lead-tin-fluorophosphate glass excited by VUV-UV synchrotron radiation

The stilbene-3 doped lead-tin-fluorophosphate glasses were successfully prepared and the luminescence spectra obtained from VUV-UV synchrotron radiation were investigated. The emission peaked about 440 nm from the undoped glass is observed at low temperature but quenches at room temperature. The doped glass exhibits strong characteristic emission of stilbenen-3 with 467 and 436 nm Gaussian bands under ultraviolet 250-330 nm excitation (characteristic excitation of stilbene-3) but weak emission under vacuum ultraviolet 190 nm excitation (host excitation). It is suggested that the energy transfer from host to the stilbene-3 dye can occur but the efficiency is still fairly low.     

Solid-phase microextraction under controlled agitation conditions for rapid on-site sampling of organic pollutants in water

An electric drill coupled with a solid-phase microextraction (SPME) polydimethylsiloxane (PDMS) fiber or a PDMS thin film was used for rapid sampling of polycyclic aromatic hydrocarbons (PAHs) in aqueous samples. Laboratory experiments demonstrated that the sampling rates of SPME fiber and thin film can be predicted theoretically. Compared with the SPME fiber, the PDMS thin film active sampler exhibited a higher sampling rate and much better sensitivity due to its higher surface-to-volume ratio and its larger extraction phase volume. The amount of the analytes extracted by the thin film was around 100 times higher than those obtained by fiber, for both 5 min rapid sampling and equilibrium extraction. A new thin film active sampler was then developed for rapid on-site water sampling. The sampling kit included a portable electric drill, a copper mesh pocket, a piece of thin film, and a liner. Laboratory experiments indicated that the sampling remained in the linear uptake phase with this sampler to 8 min for the PAHs. Field test illustrated that this novel sampler was excellent for rapid on-site water sampling due to its short sampling period, high sampling efficiency and durability The thin film sampling kit facilitates on-site sampling, sample preparation, storage and transport. This new sampler is more user-friendly and easier to commercialize than previous samplers.     

One-step extraction and derivatization liquid-phase microextraction for the determination of chlorophenols by gas chromatography–mass spectrometry

A sample pretreatment method for the determination of 18 chlorophenols (CPs) in aqueous samples by derivatization liquid-phase microextraction (LPME) was investigated using gas chromatography–mass spectrometry. Derivatization reagent was spiked into the extraction solvent to combine derivatization and extraction into one step. High sensitivity of 18 CPs derivatives could be achieved after optimization of several parameters such as extraction solvent, percentage of derivatization reagent, extraction time, pH, and ionic strength. The results from the optimal method showed that calibration ranging from 0.5 to 500 μg L⁻¹ could be achieved with the RSDs between 1.75% and 9.39%, and the limits of detection (LOD) are ranging from 0.01 to 0.12 μg L⁻¹ for the CPs. Moreover, the proposed LPME method was compared with solid-phase microextraction (SPME) coupled with on-fiber derivatization technique. The results suggested that using both methods are quite agreeable. Furthermore, the recoveries of LPME evaluated by spiked environmental samples ranged from 87.9% (3,5-DCP) to 114.7% (2,3,5,6-TeCP), and environmental water samples collected from the Pearl River were analyzed with the optimized LPME method, the concentrations of 18 CPs ranged from 0.0237 μg L⁻¹ (3,5-DCP) to 0.3623 μg L⁻¹ (2,3,6-TCP).     

Upper Embeddability,Girth and the Degree-Sum of Nonadjacent Vertices

Let G be a 2-edge-connected simple graph with girth g, independence number α(G), and if one of the following two conditions holds

Essential normality of linear fractional composition operators in the unit ball of ℂ<Superscript><Emphasis Type="Italic">N</Emphasis></Superscript>

Let φ be a linear fractional self-map of the ball B _N with a boundary fixed point e ₁, we show that

Isolation and Difference in Anti-Staphylococcus aureus Bioactivity of Curvularin Derivates from Fungus Eupenicillium sp.

With the anti-microbial and anti-tumor composite screening model, bioassay-guided fractionation led to the isolation of two structurally related bioactive compounds, curvularin and αβ-dehydrocurvularin, from ethyl acetate extract of Eupenicillium sp. associated with marine sponge Axinella sp. Further study on the structure–activity relationship demonstrated that both compounds exhibited differences in bioactive profiles which are highly associated with their minor structural differences. Both curvularin and αβ-dehydrocurvularin have similar level of anti-fungal and anti-tumorous activity, while αβ-dehydrocurvularin is active against Staphylococcus aureus with a minimal inhibitory concentration of 375 μg/ml but curvularin does not. No detectable activity against Gram-negative bacteria such as Escherichia coli and Pseudomonas aeruginosa exists for both compounds. It is suggested that the partial planar backbone structure, due to the conjugation of π electrons in the presence of a 3,4-double bond and the carbonyl group at position C-2 in αβ-dehydrocurvularin, acts as a key factor for the inhibition of S. aureus, a Gram-positive low G + C bacteria that are often the hospital-acquired and/or community-acquired pathogen.     

An image encryption scheme combining chaos with cycle operation for DNA sequences

An image encryption scheme is proposed using high-dimensional chaotic systems and cycle operation for DNA sequences. In the scheme, the pixels of the original image are encoded randomly with the DNA coding rule controlled by a key stream produced from Chen’s hyper-chaos. In addition to confusion on the DNA sequence matrix with Lorenz system, a cycle operation for DNA sequences is projected to diffuse the pixel values of the image. In order to enhance the diffusion effect, a bitwise exclusive-OR operation is carried out for the decoded matrices with a binary key stream, and then the cipher-image is obtained. Simulation results demonstrate that the proposed image encryption scheme with acceptable robustness is secure against exhaustive attack, statistical attack and differential attack.     

天然产物Echinoclathrines A的全合成

Echinoclathrines A是海洋天然产物.首次完成了Echinoclathrines A的全合成,反应总共4步,总收率为12%.该全合成的关键步骤是钯催化的芳基氯与2-甲基-4-吡啶硼酸的Suzuki偶联反应.     

An arithmetic-geometric mean inequality approach for determining the optimal production lot size with backlogging and imperfect rework process

Some classical studies on economic production quantity (EPQ) models with imperfect production processes have focused on determining the optimal production lot size. However, these models neglect the fact that the total production-inventory costs can be reduced by reworking imperfect items for a relatively small repair and holding cost. To account for the above phenomenon, we take the out of stock and rework into account and establish an EPQ model with imperfect production processes, failure in repair and complete backlogging. Furthermore, we assume that the holding cost of imperfect items is distinguished from that of perfect ones, as well as, the costs of repair, disposal, and shortage are all included in the proposed model. In addition, without taking complex differential calculus to determine the optimal production lot size and backorder level, we employ an arithmetic-geometric mean inequality method to determine the optimal solutions. Finally, numerical examples and sensitivity analysis are analyzed to illustrate the validity of the proposed model. Some managerial insights are obtained from the numerical examples.