Construction of a Graphene/Au‐Nanoparticles/Cucurbit[7]uril‐Based Sensor for Pb2+ Sensing

The development of highly sensitive and selective methods for the detection of lead ion (Pb²⁺) is of great scientific importance. In this work, we develop a new surface‐enhanced Raman scattering (SERS)‐based sensor for the selective trace measurement of Pb²⁺. The SERS‐based sensor is assembled from gold nanoparticles (AuNPs) and graphene using cucurbit[7]uril (CB[7]) as a precise molecular glue and a local SERS reporter. Upon the addition of Pb²⁺, CB[7] forms stronger complexes with Pb²⁺ and desorbs from AuNPs, resulting in a sensitive “turn‐off” of SERS signals. This SERS‐based assay shows a limit of detection (LOD) of 0.3 nm and a linear detection range from 1 nm to 0.3 μm for Pb²⁺. The feasibility of the assay is further demonstrated by probing Pb²⁺ in real water samples. This SERS‐based analytical method is highly sensitive and selective, and therefore holds promising applications in environmental analysis.     

Estimation of partially specified spatial panel data models with random-effects

In this article, we study estimation of a partially specified spatial panel data linear regression with random-effects. Under the conditions of exogenous spatial weighting matrix and exogenous regressors, we give an instrumental variable estimation. Under certain sufficient assumptions, we show that the proposed estimator for the finite dimensional parameter is root-N consistent and asymptotically normally distributed and the proposed estimator for the unknown function is consistent and asymptotically distributed. Consistent estimators for the asymptotic variance-covariance matrices of both the parametric and unknown components are provided. The Monte Carlo simulation results verify our theory and suggest that the approach has some practical value.     

Oxidation of aromatic sulfides with molecular oxygen: Controllable synthesis of sulfoxides or sulfones

The recent development of selective oxidation of aromatic sulfides with molecular oxygen was highlighted. The sulfoxides and sulfones could be obtained by simply switching the reaction media, i.e., bis(2-butoxyethyl)ether (BBE) or poly(ethylene glycol)dimethyl ether (PEGDME). The application of the high-boiling-point polyether as an initiator and green media can eliminate the need of large quantities of additives and volatile solvents. This strategy represents an economic and eco-friendly method that could find potential applications.     

Tuning the electronic properties of hydrogen passivated C3N nanoribbons through van der Waals stacking

The two-dimensional (2D) C₃N has emerged as a material with promising applications in high performance device owing to its intrinsic bandgap and tunable electronic properties. Although there are several reports about the bandgap tuning of C₃N via stacking or forming nanoribbon, bandgap modulation of bilayer C₃N nanoribbons (C₃NNRs) with various edge structures is still far from well understood. Here, based on extensive first-principles calculations, we demonstrated the effective bandgap engineering of C₃N by cutting it into hydrogen passivated C₃NNRs and stacking them into bilayer heterostructures. It was found that armchair (AC) C₃NNRs with three types of edge structures are all semiconductors, while only zigzag (ZZ) C₃NNRs with edges composed of both C and N atoms (ZZCN/ CN) are semiconductors. The bandgaps of all semiconducting C₃NNRs are larger than that of C₃N nanosheet. More interestingly, AC-C₃NNRs with CN/CN edges (AC-CN/CN) possess direct bandgap while ZZ-CN/CN have indirect bandgap. Compared with the monolayer C₃NNR, the bandgaps of bilayer C₃NNRs can be greatly modulated via different stacking orders and edge structures, varying from 0.43 eV for ZZ-CN/CN with AB′-stacking to 0.04 eV for AC-CN/CN with AA-stacking. Particularly, transition from direct to indirect bandgap was observed in the bilayer AC-CN/CN heterostructure with AA′-stacking, and the indirect-to-direct transition was found in the bilayer ZZ-CN/CN with ABstacking. This work provides insights into the effective bandgap engineering of C₃N and offers a new opportunity for its applications in nano-electronics and optoelectronic devices.     

基于四波混频过程和线性分束器产生四组份纠缠

多组份纠缠是量子信息处理的重要资源,它的产生通常涉及到许多复杂的线性和非线性过程.本文从理论上提出了一种利用两个独立的四波混频过程和线性分束器产生真正的四组份纠缠的方案,其中,线性分束器的作用是将两个独立的四波混频过程联系起来.首先应用部分转置正定判据研究了强度增益对四组份纠缠的影响,结果表明,在整个增益区域内都存在真正的四组份纠缠,并且随着强度增益的增加,纠缠也在增强.然后研究了线性分束器的透射率对四组份纠缠的影响,发现只要线性分束器的透射率不为0或1,该系统也可以产生真正的四组份纠缠.最后,通过研究该系统可能存在的三组份纠缠和两组份纠缠来揭示该系统的纠缠结构.本文理论结果为实验上利用原子系综四波混频过程产生真正的四组份纠缠提供了可靠的方案.     

利用相位步进脉冲消除探头13C NMR背景信号

由静态探头线圈外有机材料产生的¹³C NMR背景信号强度大，化学位移范围广（δ_C 20~250），此背景信号在交叉极化实验中还可被增强，并随着样品信号的累积而累积，严重影响谱图分析.将相位步进脉冲引入交叉极化实验（称为PIPCP）中可以有效去除经交叉极化增强的¹³C NMR背景信号，但样品信号不受影响.这是由于经过相位步进脉冲后，线圈外相位严重畸变，而且线圈外锁定场强度急剧降低，来自探头材料的¹³C NMR背景信号无法有效地进行交叉极化.而对于被测样品甘氨酸来说，由于I核和S核之间强烈的偶极耦合作用，所加相位步进脉冲对锁定场强度的影响只有1.4%.     

Charged anisotropic collapsing stars with heat flux in f(R) gravity

In the present article, we have studied the effects of electromagnetic field on the conformally flat collapsing stars with anisotropic heat conducting fluid in the framework of modified f(R) theory of gravity. For this purpose, we have formulated the junction conditions between the Vaidya spacetime and interior manifold at the junction interface for the extraction of an exact collapsing solution and the continuity of scalar curvature. Thereafter the physical parameters such as pressures P_r and P_t, energy density and heat flux are elucidated in the presence of electric charge through graphical representation. Also, we have investigated the different energy conditions for the physical viability of the system. It is found that the presence of charge, divergence of a non-zero acceleration and heat flux diminishes the rate of collapse and settle down the system in a zero volume.     

Testing the energy diffusion approximation for the escape of a Brownian particle from a potential pocket

For the first time, the energy diffusion approximation is confronted at the percent level with the exact numerical modeling of thermal decay of a metastable state. This model is useful in many branches of natural sciences: e.g. in biology, nuclear physics, chemistry, etc. The exact (within the statistical errors about 2%) quasistationary decay rates result from the Langevin equations for the coordinate and conjugated momentum. For the energy (or action) diffusion approach, a Langevin-type equation for the action is constructed, validated, and solved numerically. The comparison of these two approaches is performed for four potentials (two of which are anharmonic) in a wide range of two dimensionless scaling parameters: i) the governing parameter G reflecting how high is the barrier with respect to the temperature and ii) the damping parameter φ expressing the friction strength. It turns out that the energy diffusion approach produces the rate which comes into 50%-agreement with the exact one only at φ < 0.02. Thus, we quantify, for the first time by our knowledge, the condition φ ≪ 1 known in the literature.     

MRI phase offset correction method impacts quantitative susceptibility mapping

Individual channel ultra-high field (7T) phase images have to be phase offset corrected prior to the mapping of magnetic susceptibility of tissue. Whilst numerous methods have been proposed for gradient recalled echo MRI phase offset correction, it remains unclear how they affect quantitative magnetic susceptibility values derived from phase images. Methods already proposed either employ a single or multiple echo time MRI data. In terms of the latter, offsets can be derived using an ultra-short echo time acquisition, or by estimating the offset based on two echo points with the assumption of linear phase evolution with echo time. Our evaluation involved 32 channel multi-echo time 7T GRE (Gradient Recalled Echo) and ultra-short echo time PETRA (Pointwise Encoding Time Reduction with Radial Acquisition) MRI data collected for a susceptibility phantom and three human brains. The combined phase images generated using four established offset correction methods (two single and two multiple echo time) were analysed, followed by an assessment of quantitative susceptibility values obtained for a phantom and human brains. The effectiveness of each method in removing the offsets was shown to reduce with increased echo time, decreased signal intensity and reduced overlap in coil sensitivity profiles. Quantitative susceptibility values and how they change with echo time were found to be method specific. Phase offset correction methods based on single echo time data have a tendency to produce more accurate and less noisy quantitative susceptibility maps in comparison with methods employing multiple echo time data.