Theoretical investigations on the spin Hamiltonian parameters for Er3+ ion in LiYF4

The spin Hamiltonian parameters g_∥, g_⊥, A_∥ and A_⊥ for Er³⁺ ion in LiYF₄ are investigated by using the perturbation formulas of these parameters for a 4f¹¹ ion in tetragonal symmetry. In these formulas, the contributions to the spin Hamiltonian parameters from the second-order perturbation terms and the admixtures of different states are considered. The relevant crystal field parameters are calculated from the superposition model and the local structural parameters of the Y³⁺ site occupied by impurity Er³⁺. The theoretical optical spectra within ⁴I_15/2 and ⁴I_13/2 states and the spin Hamiltonian parameters obtained in this work are consistent with the observed values.     

Bridging stresses in sintered reaction-bonded Si3N4 from COD measurements

Crack opening displacement measurements on a sintered reaction-bonded Si₃N₄ ceramic obtained in bending tests with edge-V-notched specimens were evaluated. A procedure is proposed which allows a straight-forward evaluation of the experimental results in order to obtain the bridging stresses as a function of crack opening displacements. Bridging stresses up to 160 MPa were found acting over a distance of about 0.4 μm. In addition crack profile measurements were performed for Vickers indentation cracks which could approximately be described by use of the bridging relation obtained.     

The combustion of kerosene: Experimental results and kinetic modelling using 1- to 3-component surrogate model fuels

The oxidation of kerosene Jet-A1 and that of n-decane have been studied experimentally in a jet-stirred reactor at atmospheric pressure and constant residence time, over the high temperature range 900–1300 K, and for variable equivalence ratio (0.5≤ϕ≤2). Concentration profiles of the reactants, stable intermediates, and final products have been obtained by probe sampling followed by on-line and off-line GC analyses. The oxidation of neat n-decane and of kerosene in these conditions was modeled using a detailed kinetic reaction mechanism (209 species and 1673 reactions, most of them reversible). The present model was successfully used to simulate the structure of a fuel-rich premixed n-decane–oxygen–nitrogen flame. In the modelling, kerosene was represented by four surrogate model fuels: 100% n-decane, n-decane-n-propylbenzene (74%/26% mol), n-decane-n-propylcyclohexane (74%/26% mol), and n-decane-n-propylbenzene-n-propylcyclohexane (74%/15%/11% mol). The 3-component model fuel was the most appropriate for simulating the JSR experiments. It was also successfully used to simulate the structure of a fuel-rich premixed kerosene–oxygen–nitrogen flame.     

Red Emissive Carbon Dots Prepared from Polymers as an Efficient Nanocarrier for Coptisine Delivery in vivo and in vitro

Negatively charged fluorescent carbon dots (CDs, E_m=608 nm) were hydrothermally prepared from thiophene phenylpropionic acid polymers and then successfully loaded with the positively charged anticancer cargo coptisine, which suffers from poor bioavailability. The formed CD-coptisine complexes were thoroughly characterized by particle size, morphology, drug loading efficiency, drug release, cellular uptake and cellular toxicity in vitro and antitumor activities in vivo. In this nano-carrier system, red emissive CDs possess multiple advantages as follows: 1) high drug loading efficiency (>96 %); 2) sustained drug release; 3) enhanced drug efficacy towards cancer cells; 4) EPR effect; 5) drug release tracing with near-infrared imaging. These properties indicated that red emissive CDs prepared from polymers could be used as a novel drug delivery system with integrated therapeutic and imaging functions in cancer therapy, which are expected to have great potential in future clinical applications.     

An unusual 3D three-fold parallel interpenetrating network self-assembled from the grid-containing 2D layer motifs

The new complex {[Cu(dde)(bpe)] · H₂O}_n (1) (dde = 4,4′-dicarboxydiphenyl ether, bpe = 1,2-bis(4-pyridyl)ethene) has been synthesized and characterized. It exhibits a novel (2D → 3D) three-fold parallel interpenetrating architecture that is obtained for the first time from the self-assembly of grid-containing 2D (4, 4) layer motifs. The fluorescent property of 1 is discussed.     

Caking property and active components of coal based on group component separation

The content and the caking index of the heavy,the dense medium and the loose medium components of coal,obtained by extraction and stripping with CS_2/N-methyl-2-pyrrolidinone mixed solvent(1:1 by volume),were studied and correlated with the caking property of raw coals.Images of the three group components after heat treatment were analyzed.The results show that both caking index(G) and maximum thickness of plastic layer(Y) of coals have a good linear relationship with the content of the medium component;the dense medium and the loose medium components are the two key factors to determine the caking property of raw coals-they are the source materials of fluidity and swelling of coal,respectively;the heavy component without the swelling and fluidity was cohered by the other components;two new indexes,which can extend current understanding of the caking properties,were introduced.     

An Efficient One-Arrow-Two-Hawks Strategy Achieves High Efficiency and Stable Batch Variance for Benzodifuran-based Polymer Solar Cells

With the development of organic solar cells (OSCs), the high-performance and stable batch variance are becoming a new challenge for designing polymer donors. To obtain high photovoltaic performance, adopting polymers with high molecular weight as donors is an ordinary strategy. However, the high molecular weight need to subtly control the reaction time and state, inevitably caused batch-to-batch variations. Herein, a strategy of steric effect is applied to benzodifuran (BDF)-based polymer by introducing different positions of Cl atom, producing two polymers PBDFCl-1 and PBDFCl-2. The more twisted side chains conformation not only achieve the control of moderate molecular weight for PBDFCl-2, but also easily form molecular stacking through adopting BDF unit and maintain sufficient polymeric crystallinity. Due to the optimized stacking mode and good blend miscibility, PBDFCl-2-based device exhibitsa more elegant power conversion efficiency (PCE) of 17.00% compared to PBDFCl-1-based device. This is the highest efficiency record for BDF-based binary OSCs. Meanwhile, the PCE device variation of the different molecular weights for PBDFCl-2 is little, indicating the reduction of the batch variation. Therefore, smartly using steric effect of Cl atom in strong crystalline BDF unit can form efficient molecular stacking regulations and realize the coordination of high-performance and stable batch variance.     

Photo-Driven Hydrogen Production from Methanol and Water using Plasmonic Cu Nanoparticles Derived from Layered Double Hydroxides

Methanol steam reforming (MSR) is viewed as an important technology in the growth of a future hydrogen economy, with methanol serving as an easily transportable and storable liquid hydrogen carrier. However, the thermocatalytic MSR reaction is energy intensive as it requires high temperatures. Herein, a novel L-Cu catalyst is successfully fabricated for photo-driven MSR through reduction of CuAl layered double hydroxide (CuAl-LDH) nanosheets. L-Cu offers outstanding activity for the photothermal conversion of methanol and water to hydrogen (160.5 µmol g_cat⁻¹ s⁻¹) under ultraviolet-visible irradiation, with this rate being much higher than that achieved for L-Cu at the same temperature in the dark. Characterization studies using X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and high-resolution transmission electron microscopy determine that L-Cu catalyst comprise Cu nanoparticles on an amorphous alumina support. Computational calculations reveale that Cu localized surface plasmon resonance effects promote the activation of H₂O, thereby underpinning the remarkable hydrogen production rates achieved during photo-driven MSR. This study introduces a novel photothermal strategy for hydrogen generation from methanol, demonstrating the enormous potential of photothermal catalysis in the chemical and energy sectors.     

Experimental study of the influence of cold heat exchanger geometry on the performance of a co-axial pulse tube cooler

Improving the performance of the pulse tube cooler is one of the important objectives of the current studies. Besides the phase shifters and regenerators, heat exchangers also play an important role in determining the system efficiency and cooling capacity. A series of experiments on a 10 W @ 77 K class co-axial type pulse tube cooler with different cold heat exchanger geometries are presented in this paper. The cold heat exchangers are made from a copper block with radial slots, cut through using electrical discharge machining. Different slot widths varying from 0.12 mm to 0.4 mm and different slot numbers varying from around 20–60 are investigated, while the length of cold heat exchangers are kept the same. The cold heat exchanger geometry is classified into three groups, namely, constant heat transfer area, constant porosity and constant slot width. The study reveals that a large channel width of 0.4 mm (about ten times the thermal penetration depth of helium gas at 77 K, 100 Hz and 3.5 MPa) shows poor performance, the other results show complicated interaction effects between slot width and slot number. These systematic comparison experiments provide a useful reference for selecting a cold heat exchanger geometry in a practical cooler.     

1-D transient numerical model of a regenerator in a novel sub Kelvin Active Magnetic Regenerative Refrigerator

A sub Kelvin Active Magnetic Regenerative Refrigerator (AMRR) is being developed at the University of Wisconsin – Madison. This AMRR consists of two circulators, two regenerators, one superleak, one cold heat exchanger, and two warm heat exchangers. The circulators are novel non-moving part pumps that reciprocate a superfluid mixture of ⁴He–³He in the system. Heat from the mixture is removed within the two regenerators of this tandem system. An accurate model of the regenerators in this AMRR is necessary in order to predict the performance of these components, which in turn helps predicting the overall performance of the AMRR system. This work presents modeling methodology along with results from a 1-D transient numerical model of the regenerators of an AMRR capable of removing 2.5 mW at 850 mK at cyclic steady state.