Engineering topics
Chen, Jun
Publications and source records attributed to Chen, Jun.
Discovering Large Isotropic Negative Thermal Expansion in Framework Compound AgB(CN)[subscript 4] vi
Explore the source record for details and available documents.
Nuclear Data Sheets for A=98
Experimental spectroscopic data on nuclear structure and decay are evaluated for known nuclides of mass 98 (Br, Kr, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In). Detailed evaluation results of individual reactions and decays are presented together with the Adopted values that are recommended for level properties, γ and β radiations, and other spectroscopic information. 98 Mo remains as the most extensively studied nuclide via various reactions and decays. Level schemes of Sr, Y, Zr, Tc, and Pd nuclides in this mass chain are also well established to date; while Kr, Rb, Nb, Ag and Cd are amongst the least-studied ones for excited states, with only limited data available for each. On the neutron-rich side, 98 Br has been identified in the 9 Be(238U,F) reaction, but no spectroscopic data are yet available, while for 98 In on the proton-rich side, only the ground state and an isomer are known with half-lives measured but their spin-parities and the absolute level energy of the isomer yet to be determined. While 98 Ru and 98 Rh have also been extensively studied, large discrepancies exist between the high-spin sections of the proposed level schemes in different measurements, and these need to be clarified and resolved with further experimental investigations to improve the currently-adopted ones, which have been selected from the measurements with higher statistics, considering no other criteria of preference. Furthermore, this work supersedes all the earlier evaluations of A=98 (2003Si07, 1998Si18, 1992Si21, 1983Mu21, 1974Me34).
Broadband Tunable Mid-infrared Plasmon Resonances in Cadmium Oxide Nanocrystals Induced by Size-Dependent Nonstoichiometry
A central theme of nanocrystal (NC) research involves synthesis of dimension-controlled NCs and study of size-dependent scaling laws governing their optical, electrical, magnetic, and thermodynamic properties. In this paper, we describe the synthesis of monodisperse CdO NCs that exhibit high quality-factor (up to 5.5) mid-infrared (MIR) localized surface plasmon resonances (LSPR) and elucidate the inverse scaling relationship between carrier concentration and NC size. The LSPR wavelength is readily tunable between 2.4 and similar to 6.0 μm by controlling the size of CdO NCs. Structural and spectroscopic characterization provide strong evidence that free electrons primarily originate from self-doping due to NC surface-induced nonstoichiometry. The ability to probe and to control NC stoichiometry and intrinsic defects will pave the way toward predictive synthesis of doped NCs with desirable LSPR characteristics.
Transforming Thermal Expansion from Positive to Negative: The Case of Cubic Magnetic Compounds of (Zr,Nb)Fe 2
Negative thermal expansion (NTE) is an intriguing property for not only fundamental studies but also technological applications. However, few NTE materials are available compared with the huge amount of positive thermal expansion materials. The discovery of new NTE materials remains challenging. In this paper, we report a chemical modification strategy to transform thermal expansion from positive to negative in cubic magnetic compounds of (Zr,Nb)Fe 2 by tuning the magnetic exchange interaction. Furthermore, an isotropic zero thermal expansion can be established in Zr 0.8 Nb 0.2 Fe 2 (α 1 = 1.4 x 10 -6 K -1 , 3-470 K) over a broad temperature range that is even wider than that of the prototype Invar alloy of Fe 0.64 Ni 0.36 . The NTE of (Zr,Nb)Fe 2 is originated from the weakened magnetic exchange interaction and the increased d electrons of Fe by the Nb chemical substitution, so that the magnetovolume effect overwhelms the contribution of anharmonic lattice vibration.
Strong Negative Thermal Expansion in a Low-Cost and Facile Oxide of Cu 2 P 2 O 7
Negative thermal expansion (NTE) behaviors have been observed in various types of compounds. The achievement in the merits of promising low-cost and facile NTE oxides remains challenging. In the present work, a simple and low-cost Cu 2 P 2 O 7 has been found to exhibit the strongest NTE among the oxides (alpha(v) similar to -27.69 X 10 -6 K -1 , 5-375 K). The complex NTE mechanism has been investigated by the combined methods of high-resolution synchrotron X-ray diffraction, neutron powder diffraction, X-ray pair distribution function, extended X-ray absorption fine structure spectroscopy, and density functional theory calculations. Interesting, the direct experimental evidence reveals that the coupling twist and rotation of PO 4 and CuO 5 polyhedra are the inherent factors for the NTE nature of Cu 2 P 2 O 7 , which is triggered by the transverse vibrations of oxygen atoms. The present new NTE material of Cu 2 P 2 O 7 also has been verified for the practical application.
A Novel NASICON‐Type Na 4 MnCr(PO 4 ) 3 Demonstrating the Energy Density Record of Phosphate Cathodes for Sodium‐Ion Batteries
Abstract Sodium‐ion batteries (SIBs) have attracted incremental attention as a promising candidate for grid‐scale energy‐storage applications. To meet practical requirements, searching for new cathode materials with high energy density is of great importance. Herein, a novel Na superionic conductor (NASICON)‐type Na 4 MnCr(PO 4 ) 3 is developed as a high‐energy cathode for SIBs. The Na 4 MnCr(PO 4 ) 3 nanoparticles homogeneously embedded in a carbon matrix can present an extraordinary reversible capacity of 160.5 mA h g −1 with three‐electron reaction at ≈3.53 V during the Na + extraction/insertion process, realizing an unprecedentedly high energy density of 566.5 Wh kg −1 in the phosphate cathodes for SIBs. It is intriguing to reveal the underlying mechanism of the unique Mn 2+ /Mn 3+ , Mn 3+ /Mn 4+ , and Cr 3+ /Cr 4+ redox couples via X‐ray absorption near‐edge structure spectroscopy. The whole electrochemical reaction undergoes highly reversible single‐phase and biphasic transitions with a moderate volume change of 7.7% through in situ X‐ray diffraction and ex situ high‐energy synchrotron X‐ray diffraction. Combining density functional theory (DFT) calculations with the galvanostatic intermittent titration technique, the superior performance is ascribed to the low ionic‐migration energy barrier and desirable Na‐ion diffusion kinetics. The present work can offer a new insight into the design of multielectron‐reaction cathode materials for SIBs.
Negative thermal expansion and the role of hybridization in perovskite-type PbTiO 3 -Bi(Cu 0.5 Ti 0.5) O 3
PbTiO 3 -BiMeO 3 ferroelectrics have attracted much attention due to not only their extremely large polarization and piezoelectricity but also their controllable thermal expansion. In this study, we present a new binary system of (1 - x)PbTiO 3 -xBi(Cu 0.5 Ti 0.5 )O 3 possessing large tetragonality and enhanced spontaneous polarization. Interestingly, a combination of near zero thermal expansion and negative thermal expansion over a temperature range of RT to T C (~550 °C) has been observed in tetragonal 0.85PbTiO 3 -0.15Bi(Cu 0.5 Ti 0.5 )O 3 . The comprehensive structure analysis addressed that the abnormal thermal expansion is coupled to the spontaneous volume ferroelectrostriction. Moreover, the chemical bonding investigation by a maximum entropy method further attests that the covalent hybridization of Pb/Bi–O bonds plays a vital role in the improved ferroelectricity and interacts with thermal vibration to dominate the crossover from positive to negative thermal expansion. fINALLY, The present studies would give direct evidence to verify the theoretical calculations and could be extended to reveal the nature of thermal expansion in ferroelectrics.
An essential role for Arabidopsis Trs33 in cell growth and organization in plant apical meristems
TRAPP complexes, composed of multimeric subunits, are guanine–nucleotide exchange factors for certain Rab GTPases and are believed to be involved in the regulation of membrane trafficking, but the cases in Arabidopsis are largely unknown. Trs33, recently proposed to be a component of TRAPP IV, is non-essential in yeast cells. A single copy of Trs33 gene, AtTrs33, was identified in Arabidopsis. GUS activity assay indicated that AtTrs33 was ubiquitously expressed. Based on a T-DNA insertion line, we found that loss-of-function of AtTrs33 is lethal for apical growth. Knock-down or knock-in of AtTrs33 affects apical meristematic growth and fertility, which indicates that AtTrs33 plays an important role in keeping apical meristematic activity and dominance in Arabidopsis. Analysis of auxin responses and PIN1/2 localization indicate that impaired apical meristematic activity and dominance were caused by altered auxin responses through non-polarized PIN1 localization. The present study reported that AtTrs33 plays an essential role in Arabidopsis cell growth and organization, which is different with its homologue in yeast. These findings provide new insights into the functional divergence of TRAPP subunits.
Electric-field-induced structure and domain texture evolution in PbZrO 3 -based antiferroelectric by in-situ high-energy synchrotron X-ray diffraction
Antiferroelectrics (AFEs) have a great potential for modern electronic devices by virtue of the large strain during the antiferroelectric-to-ferroelectric (AFE-FE) phase transition under external electric fields. Although the fascinating macroscopic properties of AFE materials have been extensively studied, it is still unclear how the underlying structure evolution engenders their defining properties. Here we employ an electric biasing in-situ high-energy synchrotron X-ray diffraction technique to reveal the phase, domain texture, and lattice evolution in a high performance PbZrO 3 -based AFE material. During the reversible AFE-FE transition triggered by electric fields, the evolution of the superstructure for AFE pseudo-tetragonal and FE rhombohedral phase is found to display strong dependence on the angle with respect to the field direction. In contrast to previous prediction, it is found that there is no obvious domain reorientation in the AFE phase, when the system is far away from the AFE-FE transitions. The electric-field-induced FE rhombohedral phase exhibits an unusual microscopic behavior, distinguished from the normal one, presenting small changes in domain texture and lattice strain with electric field, and leading to a small piezoelectric response. The longitudinal, transverse, and volume strains estimated from the XRD peak profiles are well consistent with the macroscopic strain measurements. It is demonstrated that the large strain arises from the structural change associated with anisotropic lattice strain and highly preferential domain reorientation during the AFE-FE transitions. Finally, the AFE-FE switching sequence is constructed based on the present study, which provides a further understating of AFE materials.
Slow expansion in the scalar-tensor theory of gravity
In this paper, we analyze the slow expansion scenario in the scalar-tensor theory of gravity. After considering the slow expansion solution H≃0, we discuss the slow expansion in the scalar-tensor theory by terms of the nearly scale-invariant primordial power spectrum and find that the primordial power spectrum can be determined by the coupling function f(φ). After the slow expansion phase ends, general relativity can be recovered under certain conditions, and then the universe evolves in accordance with the standard cosmology. In the scalar-tensor theory, the slow expansion scenario provides a possible way to avoid the big bang singularity.
Controllable thermal expansion and magnetic structure in Er 2 (Fe,Co) 14 B intermetallic compounds
The control of thermal expansion is attractive but remains challenging for the studies of negative thermal expansion materials. Here, we report a continuously controllable thermal expansion from negative to positive by means of adjusting the magnetic moment of Fe in Er 2 (Fe,Co) 14 B intermetallic compounds. Interestingly, a zero thermal expansion (ZTE) has been achieved in a wide temperature range (ΔT = 355 K), which is larger than most existing ZTE alloys. The spontaneous magnetostriction (ω S ) reveals a negative contribution arising from the magneto-volume effect to the controllable thermal expansion. The present study could be suitable for the design of controllable thermal expansion of other alloys related to the magneto-volume effect.
Large and Reconfigurable Infrared Photothermoelectric Effect at Oxide Interfaces
Not provided.