Lepton-portal dark matter in hidden valley model and the DAMPE recent results

We study the recent e±cosmic ray excess reported by DAMPE in a Hidden Valley Model with lepton-portal dark matter. We find the electron-portal can account for the excess well and satisfy the DM relic density and direct detection bounds, while electron+muon/electron+muon+tau-portal suffers from strong constraints from lepton flavor violating observables, such as μ→3 e. We also discuss possible collider signatures of our model, both at the LHC and a future 100 Te V hadron collider.     

Electron paramagnetic resonance studies on manganite Pr0.5Sr0.5Mn1−x Ga x O3 (x=0 and 0.05)

In this paper, we present the investigations of electron paramagnetic resonance on perovskite manganite Pr_0.5Sr_0.5MnO₃ and Ga-doped Pr_0.5Sr_0.5Mn_0.95Ga_0.05O₃. The temperature dependent paramagnetic resonance spectra parameters (effective g-factor, peak-to-peak linewidth ΔH _pp and double integrated intensities) have been used to study the paramagnetic spin correlations and spin dynamics. The gradual increase of effective g-factor is attributed to the presence of orbital ordering above T _C. The model fittings of temperature dependent double integrated intensities reveal Arrhenius law is appropriate for describing Pr_0.5Sr_0.5Mn_0.95Ga_0.05O₃ instead of Pr_0.5Sr_0.5MnO₃ system. As for Pr_0.5Sr_0.5MnO₃, the broadening of linewidth with the temperature increase origins from the contribution of small polaron hopping in the PM regime. However, as for Pr_0.5Sr_0.5Mn_0.95Ga_0.05O₃, the broadening of EPR linewidth can be understood with the spin-lattice relaxation mechanism.     

Seed-mediated synthesis of acanthosphere-like gold microstructures with tunable LSPR in the NIR region using gemini surfactants as directing agents for SERS applications

Acanthosphere-like gold microstructures (AGMs) were synthesized using a facile, two-step, seed-mediated method and butanediyl-1,4-bis(dimethylhexadecylammonium bromide) (16-4-16) as a structure-directing agent. The morphologies and sizes of the products were controlled during the synthesis process by adjusting the concentrations of 16-4-16, the AgNO₃ feed, HAuCl₄, ascorbic acid, the amount of Ag seeds and the types of gemini surfactants used through systematic inquiry; particle sizes ranging from 130 to 800 nm were well prepared. Correspondingly, the morphology of the products changed between regular and irregular AGMs, and the products presented a number of new morphologies, such as open-mouthed submicrostructures and ribbon nanowires. In particular, with the increase in the 16-4-16 concentration, the structural morphology of the thorns clearly changed from a tip to a lamellar structure. A UV-vis spectroscopic analysis indicated that the localized surface plasmon resonance (LSPR) peak of the AGMs could be adjusted by changing the above factors, which extended from 500 to 1350 nm in the near-infrared (NIR) region, enabling a tremendous potential for using the AGMs as platforms for various biomedical applications. Based on the intermediate products, we propose a two-stage growth mechanism for the AGMs in which their solid cores and tips are generated successively. Surface-enhanced Raman scattering (SERS) measurements indicate that the AGMs can serve as sensitive SERS substrates; a SERS detection limit of 5 × 10^?7 M is presented for rhodamine B molecules.

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Graphical abstract

     

Numerical Simulation of Mixing Characteristics and Energy Consumption in Vane Extruders with Different Structure Parameters

Numerical simulation was performed with the Computational Fluid Dynamics (CFD) analysis software POLYFLOW (ANSYS, Inc., USA) to investigate the melt transportation energy consumption and mixing characteristics of vane extruders. By modifying related parameters in the numerical simulation models, the effects of vane arrangement and eccentricity between rotor and stator were studied. The results showed that for different vane arrangements, the vane unit with four vanes distributed uniformly had the lowest energy consumption per unit melt transported in one cycle and the best mixing characteristics. With the increase of eccentricity, the average rotational power transmitted by the vanes to the melt increased, and the rate of increase increased. The same tendency occurred for the maximum shear rate and stretching rate experienced by the particles in the vane extruder. This suggested that the mixing performance of the vane unit increased significantly with the increase of eccentricity.     

Observation of ZnO nanoparticles outside pores of nano Zn4O(C8H4O4)3 metal-organic framework

It was recognized that ZnO can be formed during synthesizing nano Zn₄O(C₈H₄O₄)₃ metal-organic framework (nano MOF-5). Furthermore, it is generally accepted that the ZnO is dispersed inside the pores of MOF-5. However, herein, the measurements of X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) showed that the crystal particle sizes of ZnO in MOF-5 are in the range of 5-18 nm, which are larger than the pore size of MOF-5 (1.3 nm). This clearly demonstrates that those ZnO nanoparticles are located outside the pores of MOF-5.     

Control the revisit time of the electron wave packet

Ionization of molecules by strong laser fields launches an electron wave packet. This electron wave packet, which can be driven back by the field to recollide with the parent ion, has been widely explored to probe the ultrafast nuclear dynamics. We numerically demonstrate the precise control of the temporal characteristic of the recolliding electron wave packet (REWP) by orthogonally polarized two-color fields. Through changing the relative phase of the two fields, the revisit time of REWP can be manipulated with a resolution of less than 200 attos, thus significantly improving the resolution of the well known molecular clock. This provides an efficient method for real-time observation of the ultrafast molecular dynamics with attosecond resolution.     

空间高层大气遥感远紫外成像光谱仪的光学系统

空间高层大气遥感远紫外成像光谱仪主要用于观测高层大气中的远紫外辐射和实现对其内部中尺度现象成像的功能。目前我国该类的相关仪器研究基础还比较薄弱,针对这种情况,在光学系统设计的角度上给出了一种适用于130～180nm波段探测的光学系统方案。该成像光谱仪光学系统以离轴抛物镜为物镜,串联Wadsworth结构为成像光谱系统;这种串联Wadsworth成像光谱系统采用离轴抛物镜做准直镜,分光器件为平面光栅和球面光栅串联,实现二次色散,同时球面光栅起到聚焦成像作用;在像差理论的基础上,对该结构的光程函数和各像差进行了分析,获得了改进结构的宽波段完善成像条件。针对低轨空间探测应用要求设计了相关改进型Wadsworth结构成像光谱仪光学系统,设计结果证明系统像差得到了充分校正,在奈奎斯特频率(20lp/mm)下全视场全波段调制传递函数值在0.6以上。该优化结构同时具备高空间分辨率和高光谱分辨率,性能优越。     

温度测量综述——现代计量科学专题之十

1温度与热 温度是国际单位制中七个基本量之一,是人类接触最早,与人类生存关系最为密切,而又难于理解和不易测准的物理量.在科学地定义温度之前,人们把温度的变化与物体所含的热量混为一谈.直到近两个世纪,随着工业和科学技术的发展,逐渐建立起热力学和统计学理论,温度的本质才逐渐被揭示.     

1,2,4,6—四苯基—2—羟基—8—氮杂双环[3、2、1]辛烷的核磁共振研究

用多种核磁共振实验方法并结合其它结构信息,确定1,2,4,6-四苯基-2-羟基8-氮杂双环[3、2、1]辛烷的化学结构,并指定该化合物的核磁共振归属。     

Assessment of dispersion corrections in DFT calculations on large biological systems

The performance of empirical dispersion corrections in DFT calculations has been assessed for several large, genuine biological systems that include MbAB, H64L(AB), and V68N(AB) (AB?=?CO, O₂), where Mb stands for a wild-type myoglobin, H64L is the (histidine64?→?leucine) mutated myoglobin, and V68N is the (valine68?→?asparagine) mutated myoglobin. The effects of the local protein environment are accounted for by including the five nearest surrounding residues in the calculated systems and they are examined by comparing the binding energies of AB to the myoglobin and to the porphyrin (Por) without residues. Three versions of Grimme's dispersion correction methods, labeled as DFT-D1, DFT-D2, and DFT-D3, were all tested. In the first version (-D1), the dispersion correction (E_disp) is calculated only for noncovalent interactions between molecular fragments and E_disp within a covalent molecule is not calculated. For the DFT functionals, for which the calculated Por–AB binding energies are already too large, only further overestimation occurs when a dispersion correction is made. The geometry optimizations show that the DFT-D2 and DFT-D3 approaches give too short distances between the residues and the heme moiety in the myoglobins and their calculated relative binding energies ΔE_bind(myoglobin-AB/Por–AB) are in poor agreement with experiment in most cases. DFT-D1 performs very well, ensuring structural and energetic features in close agreement with experiment.