从“刘玉秀案”看误纳金退还期限

目前,我国《税收征管法》中关于纳税人溢缴税款的退还期限规定较为粗糙,其中第51条仅规定了“纳税人超过应纳税额缴纳的税款”情形下的退税期限。以“刘玉秀案”为例,在实践中,由于交易性质的逆转,导致税务机关不再具有课税依据的情形屡见不鲜,纳税人与税务机关就该情形下的退税期限存在较大争议。应当在《税收征管法》中完善误纳金退税期限的规定,从其诉讼时效的性质出发,通过规定最长诉讼期间和最短诉讼期间两种模式,填补《税收征管法》中关于退税期限的法律漏洞,切实保障纳税人退税请求权。

Microscopic mechanical characteristics analysis of ultranano-crystalline diamond films

The microscopic mechanical characteristics of ultranano-crystalline diamond films which were prepared in four different atmospheres were investigated for the applications in microelectron-mechanical system（MEMS）.The loading-unloading curves and the change of modulus and hardness of samples along with depth were achieved through nanoindenter.The results show that the films which are made in atmosphere without Ar have the highest recovery of elasticity,hardness（72.9 GPa） and elastic modulus（693.7 GPa） among the samples.Meanwhile,samples fabricated at a low Ar content have higher hardness and modulus.All the results above demonstrate that atmosphere without Ar or low Ar content leads to better mechanical properties of nanodiamond films that are the candidates for applications in MEMS.

Superelastic behavior of nanostructured Ti_(50)Ni_(48)Co_2 shape memory alloy with cold rolling processing

Effects of cold rolling followed by annealing on microstructural evolution and superelastic properties of the Ti50Ni48Co2 shape memory alloy were investigated. Results showed that during cold rolling, the alloy microstructure evolved through six basic stages including stress-induced martensite transformation and plastic deformation of martensite, deformation twinning, accumulation of dislocations along twin and variant boundaries in martensite, nanocrystallization, amorphization and reverse transformation of martensite to austenite. After annealing at 400 ℃ for 1 h, the amorphous phase formed in the cold-rolled specimens was completely crystallized and an entirely nanocrystalline structure was achieved. The value of stress level of the upper plateau in this nanocrystalline alloy was measured as high as 730 MPa which was significantly higher than that of the coarse-grained Ni50Ti50 and Ti50Ni48Co2 alloys. Moreover, the nanocrystalline Ti50Ni48Co2 alloy had a high damping capacity and considerable efficiency for energy storage.

Fabrication of carbon nanotubes reinforced AZ91D composites by ultrasonic processing

Magnesium matrix nanocomposite reinforced with carbon nanotubes(CNTs/AZ91D) was fabricated by mechanical stirring and high intensity ultrasonic dispersion processing.The microstructures and mechanical properties of the nanocomposite were investigated.The results show that CNTs are well dispersed in the matrix and combined with the matrix very well.As compared with AZ91D magnesium alloy matrix,the tensile strength,yield strength and elongation of the 1.5%CNTs/AZ91D nanocomposite are improved by 22%,21%and 42%respectively in permanent mold casting.The strength and ductility of the nanocomposite are improved simultaneously.The tensile fracture analysis shows that the damage mechanism of nanocomposite is still brittle fracture.But the CNTs can prevent the local crack propagation to some extent.

Emerging two-dimensional metallenes:Recent advances in structural regulations and electrocatalytic applications

Benefiting from the ultrahigh specific surface areas,highly accessible surface atoms,and highly tunable microscopic structures,the two-dimensional metallenes as nanocatalysts have displayed promising performance for various electrocatalytic reactions.Herein,we reviewed recent advances on metallenes in structural regulations including defect,phase,strain,interface,doping,and alloying engineering strategies and their applications in energy electrocatalytic reactions involving oxygen reduction reaction,carbon dioxide reduction reaction,hydrogen evolution reaction,and small molecules oxidation reaction.Finally,we proposed the future challenges and directions in this emerging area.

Oxygen Electroreduction Performance of Ultrasmall Gold Nanoclusters

Ultrasmall gold nanoclusters consisting of 2-4 Au atoms were synthesized and their per- formance in electrocatalytic oxygen reduction reactions （ORR） was examined. These clus- ters were synthesized by exposing AuPPh3Cl to the aqueous ammonia medium for one week. Electrospray ionization mass spectrometry （ESI-MS）, X-ray absorption fihe struc- ture （XAFS）, and X-ray photoelectron spectroscopy （XPS） analyses indicate that the as- synthesized gold clusters （abbreviated as Aux） consist of 2-4 Au atoms coordinated by the triphenylphosphine, hydroxyl, and adsorbed oxygen ligands. A glassy carbon disk electrode loaded with the Aux clusters （Aux/GC） was characterized by the cyclic and linear-sweep voltammetry for ORR. The cyclic voltammogram vs. RHE shows the onset potential of 0.87 V, and the kinetic parameters of JK at 0.47 V and the electron-transfer mmlber per oxygen molecule were calculated to be 14.28 mA/cm2 and 3.96 via the Koutecky-Levich equations, respectively.

Negative supracrystals inducing a FCC-BCC transition in gold nanocrystal superlattices

The growth of nanocrystal superlattices of 5 nm single domain Au nanocrystals at an air-toluene interface induces formation of well-defined thin films （300--400 nm） with large coherence lengths. High-resolution electron microscopy showed that polyhedral holes （negative supracrystal） were formed on the nanocrystal superlattice surface. Formation of negative supracrystals is attributed to inclusion in the superlattice of organic molecules （dodecanethiol）, which are present in concentrated zones at the air-toluene interface. The coexistence of two supracrystalline structures （bcc/fcc） is attributed to diffusion of dodecanethiol molecules resulting in a Bain deformation of the nanocrystal array.

Role of plastic deformation in tailoring ultrafine microstructure in nanotwinned diamond for enhanced hardness

Nanotwinned diamond（nt-diamond）,which demonstrates unprecedented hardness and stability,is synthesized through the martensitic transformation of onion carbons at high pressure and high temperature（HPHT）.Its hardness and stability increase with decreasing twin thickness at the nanoscale.However,the formation mechanism of nanotwinning substructures within diamond nanograins is not well established.Here,we characterize the nanotwins in nt-diamonds synthesized under different HPHT conditions.Our observation shows that the nanotwin thickness reaches a minimum at ~20 GPa,below which phase-transformation twins and deformation twins coexist.Then,we use the density-functional-based tight-binding method and kinetic dislocation theory to investigate the subsequent plastic deformation mechanism in these pre-existing phase-transformation diamond twins.Our results suggest that pressure-dependent conversion of the plastic deformation mechanism occurs at a critical synthetic pressure for nt-diamond,which explains the existence of the minimum twin thickness.Our findings provide guidance on optimizing the synthetic conditions for fabricating nt-diamond with higher hardness and stability.

Size-dependent transition of the deformation behavior of Au nanowires

Inspired by the controversy over tensile deformation modes of single-crystalline 〈110〉/{111} Au nanowires, we investigated the dependency of the deformation mode on diameters of nanowires using the molecular dynamics technique. A new criterion for assessing the preferred deformation mode-slip or twin propagation--of nanowires as a function of nanowire diameter is presented. The results demonstrate the size-dependent transition, from superplastic deformation mediated by twin propagation to the rupture by localized slips in deformed region as the nanowire diameter decreases. Moreover, the criterion was successfully applied to explain the superplastic deformation of Cu nanowires.

Surface Dislocation Nucleation Mediated Deformation and Ultrahigh Strength in Sub-10-nm Gold Nanowires

The plastic deformation and the ultrahigh strength of metals at the nanoscale have been predicted to be controlled by surface dislocation nucleation. In situ quantitative tensile tests on individual 〈111〉 single crystalline ultrathin gold nanowires have been performed and significant load drops observed in stress-strain curves suggest the occurrence of such dislocation nucleation. High-resolution transmission electron microscopy （HRTEM） imaging and molecular dynamics simulations demonstrated that plastic deformation was indeed initiated and dominated by surface dislocation nucleation, mediating ultrahigh yield and fracture strength in sub-lO-nm gold nanowires.

Metal-film-assisted ultra-clean transfer of single-walled carbon nanotubes

Transfer printing of nanomaterials onto target substrates has been widely used in the fabrication of nanodevices, but it remains a challenge to fully avoid contamination introduced in the transfer process. Here we report a metal-film- assisted method to realize an ultra-clean transfer of single-walled carbon nanotubes （SWCNTs） mediated by poly（methyl methacrylate） （PMMA）. The amount of PMMA residue can be greatly reduced due to its strong physical adhesion to the metal film, leading to ultra-clean surfaces of both the SWCNTs and the substrates. This metal-film-assisted transfer method is efficient, nondestructive, and scalable. It is also suitable for the transfer of graphene and other nanostructures. Furthermore, the relatively low temperature employed allows this technique to be compatible with nanomaterial-based flexible electronics.

Bio-inspired multifunctional metallic glass

As a novel class of metallic materials, bulk metallic glasses(BMGs) have attracted a great deal of attention owing to their technological promise for practical engineering applications. In nature, biological materials exhibit inherent multifunctional integration, which provides some inspiration for scientists and engineers to construct multifunctional artificial materials. In this contribution, inspired by superhydrophobic self-cleaning lotus leaves, multifunctional bulk metallic glasses(BMG) materials have been fabricated through the thermoplastic forming-based process followed by the SiO_2/soot deposition. To mimic the microscale papillae of the lotus leaf, the BMG micropillar with a hemispherical top was first fabricated using micro-patterned silicon templates based on thermoplastic forming. The deposited randomly distributed SiO_2/soot nanostructures covered on BMG micropillars are similar to the branch-like nanostructures on papillae of the lotus leaf. Micro-nanoscale hierarchical structures endow BMG replica with superhydrophobicity, a low adhesion towards water, and self-cleaning, similar to the natural lotus leaf. Furthermore, on the basis of the observation of the morphology of BMG replica in the Si mould, the formation mechanism of BMG replica was proposed in this work. The BMG materials with multifunction integration would extend their practical engineering applications and we expect this method could be widely adopted for the fabrication of other multifunctional BMG surfaces.