Mixed matrix membrane comprising polyimide with crystalline porous imide‐linked covalent organic framework for N2/O2 separation

An imide‐linked covalent organic framework (COF) was successfully synthesized by directly heating a mixture of melamine and biphenyltetracarboxylic dianhydride (BPDA) in a tubular oven at 335°C. The crystalline and nanostructure of this COF was characterized by X‐ray diffraction (XRD) and Brunauer‐Emmett‐Teller (BET). A mixed matrix membrane (MMM) was prepared by blending the COF into the commercial P84 polyimide in solution. It is found that the COF particles not only act as gas channels for N₂ and O₂ permeation but also provided an inverse permselective property with higher permeability of N₂. The effect of COF nanostructure and its loading amount on N₂ and O₂ permeability and selectivity has been investigated.     

Ultrasensitive fluorescent probe for copper ion based on cadmium selenide/cadmium sulfide quantum dots capped with dimercaprol

A new ultrasensitive copper ion fluorescent probe based on cadmium selenide/cadmium sulfide quantum dots capped with dimercaprol is described. Dimercaprol was bonded to the quantum dots through a surface ligand exchange to form dimercaprol-capped quantum dots whose fluorescence could be quenched by the coordination of dimercaprol on quantum dots’ surface with copper ion. The fluorescent probe based on dimercaprol-capped quantum dots showed a very good linear response range to copper ion from 0.1 to 50?µg?L^?1 with the detection limit of 0.087?µg?L^?1. The proposed method exhibited excellent sensitivity and selectivity due to the specific and strong affinity of dimercaprol with copper ion and the unique photoluminescence properties of quantum dots. The possible quenching mechanism was discussed and the probe was successfully applied to the determination of ultratrace copper in real samples.     

A repeated yielding model under periodic perturbation

The Ananthakrishna model, seeking to explain the phenomenon of repeated yielding of materials, is studied with or without periodic perturbation. For the unforced model, Hopf bifurcation, degenerate Hopf bifurcation and saddle-node bifurcation are detected. For the periodically forced model, two elementary periodic mechanisms are analyzed corresponding to five bifurcation cases of the unforced one. Rich dynamical behaviors arise, including stable and unstable periodic solutions of different periods, quasi-periodic solutions, chaos through torus destruction or cascade of period doublings. Moreover, even small change of a parameter can lead to bifurcation of different periodic solutions. Finally, according to the forced Ananthakrishna model, four types of stress–time curves are simulated, which can well interpret various experimental phenomena of repeated yielding.     

Slotted Photonic Crystal Microring Resonators

We propose using a slotted photonic crystal nanobeam to construct a microring resonator. The transmission characteristics of the slotted photonic crystal nanobeam and the microring resonator are demonstrated by two-dimensional finite-difference time-domain simulation, and the mechanism of these characteristics is analyzed considering the introduction of the slot. The refractive index sensitivity of the slotted photonic crystal microring resonator is evaluated to be larger than those of a slot waveguide microring resonator and a nonslotted photonic crystal microring resonator.     

Magnetic molecularly imprinted polymers for selective extraction and determination of naphthols

Microchimica Acta - The authors describe a magnetic molecular imprinted polymer (MMIP) for the extraction and detection of naphthols synthesized by surface imprinting technology using 1-naphthol as...     

Mechanistic Insight into the Intramolecular Benzylic C−H Nitrene Insertion Catalyzed by Bimetallic Paddlewheel Complexes: Influence of the Metal Centers

The intramolecular benzylic C?H amination catalyzed by bimetallic paddlewheel complexes was investigated by using density functional theory calculations. The metal–metal bonding characters were investigated and the structures featuring either a small HOMO–LUMO gap or a compact SOMO energy scope were estimated to facilitate an easier one‐electron oxidation of the bimetallic center. The hydrogen‐abstraction step was found to occur through three manners, that is, hydride transfer, hydrogen migration, and proton transfer. The imido N species are more preferred in the Ru–Ru and Pd–Mn cases whereas coexisting N species, namely, singlet/triplet nitrene and imido, were observed in the Rh–Rh and Pd–Co cases. On the other hand, the triplet nitrene N species were found to be predominant in the Pd–Ni and Pd–Zn systems. A concerted asynchronous mechanism was found to be modestly favorable in the Rh–Rh‐catalyzed reactions whereas the Pd–Co‐catalyzed reactions demonstrated a slight preference for a stepwise pathway. Favored stepwise pathways were seen in each Ru–Ru‐ and Pd–Mn‐catalyzed reactions and in the triplet nitrene involved Pd–Ni and Pd–Zn reactions. The calculations suggest the feasibility of the Pd–Mn, Pd–Co, and Pd–Ni paddlewheel complexes as being economical alternatives for the expensive dirhodium/diruthenium complexes in C?H amination catalysis.     

TIME-DELAY AND SPECTRAL DENSITY FOR STARK HAMILTONIANS(Ⅱ)——ASYMPTOTICS OF TRACE FORMULAE

This paper studies the Schrodinger operator with a homogeneous electric field of the form -△+x_1+V(x), where x= (x_1,…, x_n)∈R~n. It is proved that in the specctral representation of the free Stark Hamiltonian, the time-delay operator in scattering theory can be expressed in trems of scattering matrix and under reasonable assumptions on the decay of the potential V, the on-shell time-delay operator is of trace class and its trace is related to the local spectral density via an explicit integral formula. Some asymptotics for the trace are estabhshed when the energy tends to infinity.     

铕(Ⅲ)离子光谱探针Eu(DBM)32AP络合物中Eu(Ⅲ)格位

在77K测得的激发光谱说明Eu(DBM)32AP(DBM:二苯甲酸甲烷根,AP:安替吡啉)络合物中Eu3+离子仅有一种晶格格位.5DO→7FJ(J=0-4)跃迁光谱说明中心Eu3+离子具有C2v格位对称性.实验测得的配位体总电荷为-2.75,与理论计算值-3.00吻合较好.     

Bounds on widths of resonances for stark hamiltonians

Resonances of Schrödinger operators are closely related to the poles of certain meromorphic extension of the resolvent. In this paper, we study the resonances in Stark effect, generated by negative eigenvalues. We give precise location for the resonances and prove in particular that the widths of resonances are exponentially small and can be measured by some Agmon's distance.     

小白鼠组织和骨中铜锌铁钙镁的测定

本实验利用原子吸收光谱法对小白鼠组织及骨中Ｃｕ，Ｚｎ，Ｆｅ，Ｃａ，Ｍｇ含量进行了测定。样品采用浓ＨＮＯ２和ＨＣｌＯ４湿法消化，并用国家计量局的猪肝（ＧＢＷ０８５５１）作为标准物对测定方法进行了考核，测定值与标准值吻合。方法加收率：Ｃｕ９９－１００％，Ｚｎ１０２－１０３％，Ｆｅ９９－１００％，Ｃａ９９－１０４％，Ｍｇ１０１－１０３％，ＣＶ值为１．７－３．９％。方法简便，快速，准确度高，需样量少，符合