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摘要： 为获得径向水平喷射钻井（RHJD）的实时钻井轨迹，提出了一种基于磁梯度张量（MGT）的磁化喷嘴定位方法。MGT 系统由五个三轴磁力计、一个三轴加速度计和一个三轴陀螺仪组成并安装在外壳中。磁化喷嘴由强磁性永磁体制成，其位置可以通过测量自身在测量点产生的MGT来获得。对该定位方法进行了仿真和实验，结果表明该方法具有较高的精度。检测距离为40m时，误差仅为0.07m，满足工程实践要求。磁力计的精度、基线距离和喷嘴的磁化强度是影响定位误差的主要因素。这种定位方法能够满足实际工程中对定位精度的要求，极大地避免了RHJD的钻孔失败，具有广泛的应用前景。

关键词： Fused filament fabrication   Extruder temperature   Raster orientation   Mechanical properties   Polylactic acid  

摘要： Purpose The purpose of this study is to investigate the influences of extruder temperatures and raster orientations on the mechanical properties of polylactic-acid (PLA) material processed by using fused filament fabrication (FFF). Design/methodology/approach In this research, the PLA specimens were first printed with nozzle or extruder temperatures of 205 degrees C, 215 degrees C and 225 degrees C and then evaluated in terms of their physical, chemical and mechanical properties. An appropriate extruder temperature was then selected based on this experiment and used for the printing of the other PLA specimens having various raster orientations. A series of tensile tests were carried out again to investigate the influence of raster orientations on the tensile strength, tensile strain and elastic modulus of those FFF-processed PLA materials. In the end, the one-way ANOVA was applied for the statistical analysis and the Mohr's circle was established to aid in the analysis of the data obtained in this experiment. Findings The result of this study shows that the chemistry, porosity, degree of crystallinity and mechanical properties (tensile strength, strain and elastic modulus) of the PLA material printed with a raster angle of 0 degrees were all insensitive to the increasing extruder temperature from 205 degrees C to 225 degrees C. Meanwhile, the mechanical properties of such printed PLA material were obviously influenced by its raster orientation. In this case, a PLA material with a raster orientation parallel to its loading axis, i.e. those with a raster angle of theta = 0 degrees, was found as the strongest material. Meanwhile, the raster configuration-oriented perpendicular to its loading axis or theta = 90 degrees yielded the weakest PLA material. The results of the tensile tests for the PLA material printed with bidirectional raster orientations, i.e. theta = 0 degrees/90 degrees and 45 degrees/-45 degrees demonstrated their strengths with values falling between t

关键词： Molecules  

摘要： Photochemical reactions that produce a detectable change in the spectroscopic properties of organic chromophores can be exploited to harness the principles of Boolean algebra and design molecule-based logic circuits. Moreover, the logic processing capabilities of these photoactive molecules can be directed to protect, encode, and conceal information at the molecular level. We have designed a photochemical strategy to read, write and encrypt data in the form of optical signals. We have synthesized a supramolecular system based on the known dye resazurin, and investigated a series of photochemical transformations that can be used to regulate its absorption and emission properties upon illumination with ultraviolet or visible light. We have then examined the logic behaviour of the photochemistry involved, and illustrated its potential application in data encryption.

关键词： nanocatalysts   nanoclusters   size-selected clusters   machine learning   deep learning   XANES  

摘要： Size-selected clusters are important model catalysts because of their narrow size and compositional distributions, as well as enhanced activity and selectivity in many reactions. Still, their structure-activity relationships are, in general, elusive. The main reason is the difficulty in identifying and quantitatively characterizing the catalytic active site in the clusters when it is confined within subnanometric dimensions and under the continuous structural changes the clusters can undergo in reaction conditions. Using machine learning approaches for analysis of the operando X-ray absorption near-edge structure spectra, we obtained accurate speciation of the CuxPdy cluster types during the propane oxidation reaction and the structural information about each type. As a result, we elucidated the information about active species and relative roles of Cu and Pd in the clusters.

关键词： Z-scan   TPA saturation   double perovskite   nonlinear optics   nonlinear refractive index  

摘要： Lead halide perovskites have been widely explored in the field of photovoltaics, light-emitting diodes, and lasers due to their outstanding linear and nonlinear optical (NLO) properties. But, the presence of lead toxicity and low chemical stability remain serious concerns. Lead-free double perovskite with excellent optical properties and chemical stability could be an alternative. However, proper examination of the NLO properties of such a material is crucial to identify their utility for future nonlinear device applications. Herein, we have made use of femtosecond (fs) Z-scan technique to explore the NLO properties of Cs2AgIn0.9Bi0.1Cl6 nanocrystals (NCs). Our measurements suggest that under nonresonant fs excitation, perovskite NCs exhibit strong twophoton absorption (TPA). The observed saturation of TPA at high light intensities has been explained by a customized model. Furthermore, we have demonstrated a change in the nonlinear refractive index of the NCs under varying input intensities. The strong TPA absorption of lead-free double perovskite NCs could be used for Kerr nonlinearity-based nonlinear applications such as optical shutters for picosecond lasers.

关键词： metamaterials   wideband absorber   microwave   luminescence   LED array  

摘要： Traditional microwave absorbers can hide target objects from the detection of radar waves without tackling optical waves. However, in actual scenarios, the objects might still be observed by a hyperspectral remote sensor or an imaging system from comparison with environmental optical features, in particular for variable backgrounds. For this aspect, a comprehensive stealthing technique able to deal with microwaves and optical features simultaneously adapting to the variable environment is highly desired. In this work, an ultrathin flexible metamaterial that can simultaneously realize wideband microwave absorption and controllable visible and near-infrared luminescence spectra is proposed. The designed artificial coat can absorb more than 80% of the incident energy in the X-band (8-12 GHz) within a large incidence angle range up to 54 degrees at low polarization sensitivity, while its real-time visible and near-infrared luminescence spectrum can be electrically adjusted through an integrated emission system. The method proposed here can be extended to broader wave bands and find important applications in multifunctional stealthing technologies.

关键词： Mars   Shergottite   Impact glass   Sulfate mineral   XANES   Surface oxidation  

摘要： The surface of Mars has experienced progressive oxidation, resulting in the formation of sulfate minerals as evidenced from surface exploration missions. However, no clear evidence for the presence of sulfate minerals has been reported within Martian meteorites. This study examined sulfur speciation in impact glasses of three basaltic shergottites, Elephant Moraine (EETA) 79001, Larkman Nunatak (LAR) 06319, and Dhofar 019, using X-ray absorption near-edge structure (XANES) spectroscopy. The measured XANES spectra were classified into four types: (1) sulfide, (2) highly reduced sulfide glass (similar to IW+1), (3) mixture of sulfide and sulfate, and (4) sulfate. The sulfate spectra observed from EETA79001 and LAR 06319 were mixed with sulfide from the reduced igneous host rock as impact glasses were formed by shock on the surface of Mars, both sulfide and sulfate would have possibly originated on Mars. Besides, highly reduced sulfide present in the same impact glasses is inconsistent with secondary alteration on the oxic Earth's environment. In contrast to EETA79001 and LAR 06319, all of the XANES spectra from Dhofar 019 showed the only sulfate, whose origin is most likely from terrestrial alteration. Combining with the geochemical signatures of volatile elements (e.g., D/H, C, and halogens) in impact glasses of EETA79001 and LAR 06319, we propose two possible scenarios for the formation of sulfate species to the shergottite host-rocks: (i) oxidation of sulfide minerals by subsurface oxic water in Mars, or (ii) precipitation of sulfate mineral derived from Martian subsurface water. The difference between the two models is the source of S(VI) species, whether it originated from (i) magmatic sulfide in shergottite or (ii) sulfate ion in the subsurface water/ice. Both models indicate that the ancient (similar to 4 Ga) water reservoir might have already been oxic, and it requires post-magmatic water-rock interaction that formed sulfate minerals whose oxidized signatures

关键词： Transient absorption spectroscopy  

摘要： Excited states of nickel complexes undergo a variety of photochemical processes, such as charge transfer, ligation/deligation, and redox reactions, relevant to solar energy conversion and photocatalysis. The efficiencies of the aforementioned processes are closely coupled to the molecular structures in the ground and excited states. The conventional optical transient absorption spectroscopy has revealed important excited-state pathways and kinetics, but information regarding the metal center, in particular transient structural and electronic properties, remains limited. These deficiencies are addressed by X-ray transient absorption (XTA) spectroscopy, a detailed probe of 3d orbital occupancy, oxidation state and coordination geometry. The examples of excited-state structural dynamics of nickel porphyrin and nickel phthalocyanine have been described from our previous studies with highlights on the unique structural information obtained by XTA spectroscopy. We close by surveying prospective applications of XTA spectroscopy to active areas of Ni-based photocatalysis based on the knowledge gained from our previous studies.

关键词： nonlinear plasma   general function photonic crystals   optical nonreciprocity   transfer matrix method  

摘要： In this paper, a one-dimensional asymmetric layered structure combining general-function photonic crystals and nonlinear plasmas is proposed. The novel structure is theoretically investigated using the conventional transfer matrix method. Using these two special nonlinear materials, the optical nonreciprocity of the bistable absorption caused by forward and backward propagation is comprehensively studied. It is found that due to the asymmetry of the spatial distribution and the nonlinear properties of the nonlinear materials, the absorption, reflection, and transmission of light in two different directions, forward and backward, have apparent optical nonreciprocity. It is notable that when the light is traveling in the forward direction, the position of the working interval of the bistable absorption is significantly higher than that of the backward direction, and that the magnitudes of the absorptances corresponding to the forward and backward directions are also evidently different. Meanwhile, the sensitivity properties of the incident frequency and the angle under this optical nonreciprocity are further analyzed, and the reason for this extraordinary nonreciprocity phenomenon is explicated by the electric and magnetic field distributions of the proposed structure.

关键词： Monolayers  

摘要： Two-dimensional (2D) materials with a moderate bandgap and high carrier mobility are useful for applications in optoelectronics. In this work, we present a systematic investigation of the mechanical, electronic and optical properties of a B2P6 monolayer using first-principles calculations. Monolayer B2P6 was estimated to be an anisotropic material from direction-dependent in-plane Young's moduli and Poisson's ratios. Also, B2P6 exhibits an ultrahigh electron mobility of similar to 5888 cm(2) V-1 s(-1), showing advantages for application in high-speed optoelectronic devices. More importantly, for the B2P6 monolayer, a desirable transformation from an indirect to direct band gap was observed at a biaxial tensile strain of similar to 4%. Increasing the biaxial strain reduces the gap and preserves the suitable band edge positions for photocatalytic water splitting in the observed strain range of 1-8%. The decreased gap also enhances the visible light absorption of the B2P6 monolayer. These findings indicate that the B2P6 monolayer has promising applications in photocatalytic and photovoltaic devices.