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Long carrier diffusion length is important for optoelectronic devices that require large electrode spacing or thick active layers. Formamidinium lead triiodide (FAPbI3) perovskite is a promising candidate with ultra-long carrier diffusion length, but the existence of internal tensile strain and formation of ion vacancies make its photoactive black phase thermodynamically unstable. Herein, phase-stable FAPbI3-based single crystals with negligible absorption loss are achieved by synergy of iodide immobilization and compressive strain. Incorporation of guanidinium (GA+) cations strengthens the interaction with the inorganic framework and suppresses the formation of iodide ion vacancies. Besides, the interface compressive strain introduced from the indium tin oxide (ITO) substrate counteracts the lattice tensile strain. The as-grown GA0.015FA0.985PbI3single crystals exhibit no phase transition after storage in air for 2,000 h. Moreover, the GA0.015FA0.985PbI3single crystals exhibit ultra-long electron carrier diffusion length of about 600 μm, which is a record value for perovskite materials and only half of silicon single crystals.

Evaluating velocity-porosity relationships of hydrate-bearing marine sediments is essential for characterizing natural gas hydrates below seafloor as either a potential energy resource or geohazards risks. Four sites had cored using pressure and non-pressure methods during the gas hydrates drilling project (GMGS4) expedition at Shenhu Area, north slope of the South China Sea. Sediments were cored above, below, and through the gas-hydrate-bearing zone guided with logging-while-drilling analysis results. Gamma density and P-wave velocity were measured in each pressure core before subsampling. Methane hydrates volumes in total 62 samples were calculated from the moles of excess methane collected during depressurization experiments. The concentration of methane hydrates ranged from 0.3% to 32.3%. The concentrations of pore fluid (25.44% to 68.82%) and sediments (23.63% to 54.28%) were calculated from the gamma density. The regression models of P-wave velocity were derived and compared with a global empirical equation derived from shallow, unconsolidated sediments data. The results were close to the global trend when the fluid concentration is larger than the critical porosity. It is concluded that the dominant factor of P-wave velocity in hydrate-bearing marine sediments is the presence of the hydrate. Methane hydrates can reduce the fluid concentration by discharging the pore fluid and occupying the original pore space of sediments after its formation.

In this work, a new series of monocyclic compounds based on 1,2,4-oxadiazol-5(4H)-one was synthesized. The molecular structure, thermal stability and sensitivity to external stimuli for these compounds were characterized by X-ray diffraction analysis, NMR (1H and 13C) spectroscopy, IR spectroscopy, differential scanning calorimetry (DSC) and the standard BAM method. Compound 3-((2,2,2-trinitroethyl) amino)-1,2,4-oxadiazol (3) with trinitromethyl exhibits a higher decomposition temperature (Td = 143°C) than that of 3-(dinitromethyl)-1,2,4-oxadiazol-5-one (4) (Td = 76°C) reported in the literature. In addition, compound 3exhibits lower impact sensitivities (IS) (IS = 10 J) than 4, N3-(2,2,2-Trinitroethyl)-1,2,4-oxadiazole-3,5-diamine (5) and RDX(4: 6 J; 5: 6 J; RDX: 7.4 J). Charge distribution and Hirshfeld surface were calculated to make further research on the intermolecular interaction of 3with trinitromethyl. The difference in stability of these compounds is mainly due to the existence of intermolecular hydrogen bonds. These results indicate that compound 3has promising application prospects as the energetic material.

We report a switchable and spacing tunable dual-wavelength spatiotemporal mode-locked (STML) laser based on the multimode interference filtering effect in an all-fiber linear cavity. The dual-wavelength STML operations combined with different pulse patterns are achieved. By adjusting the polarization controllers, the dual-wavelength STML pulses can be switched to single wavelength operation, which is tunable up to 35 nm under certain pump powers. Moreover, the dual-wavelength spacing can also be tuned from 8 nm to 22 nm. The obtained results contribute to understanding and exploring the spatiotemporal characteristics operating in the multi-wavelength regime of STML fiber lasers. All-fiber STML lasers with lasing wavelength tunability and flexibility may have applications in the fields of optical communications and optical measurements.

Insulating polymer PVP is combined with CdTe nanocrystals (NCs) for fabricating the hybrid solar cells. The voids among spherical CdTe NCs are effectively blocked and the interfacial contact area between CdTe and MoO3is reduced. As a result, a photovoltaic device with suppressed leakage current and interfacial recombination is obtained and the power conversion efficiency enhanced by 37%.

We present PYATB, a Python package designed for computing band structures and related properties of materials using the ab initio tight-binding Hamiltonian. The Hamiltonian is directly obtained after conducting self-consistent calculations with first-principles packages using numerical atomic orbital bases, such as ABACUS. The package comprises three modules: Bands, Geometric, and Optical. In the Bands module, one can calculate essential properties of band structures, including the partial density of states, fat bands, Fermi surfaces, and Weyl/Dirac points. The band unfolding method is utilized to obtain the energy band spectra of a supercell by projecting the electronic structure of the supercell onto the Brillouin zone of the primitive cell. With the Geometric module, one can compute the Berry phase and Berry curvature-related quantities, such as electric polarization, Wilson loops, Chern numbers, and anomalous Hall conductivities. The Optical module offers a range of optical property calculations, including optical conductivity and nonlinear optical responses, such as shift current and Berry curvature dipole. Program title: PYATB CPC Library link to program files: https://doi.org/10.17632/fsfpdy9t5r.1 Developer's repository link: https://github.com/pyatb/pyatb Code Ocean capsule: https://codeocean.com/capsule/9408682 Licensing provisions: GPLv3 Programming language: C++, Python Nature of problem: This program is to study the electronic structure, electronic polarization, band topological properties, topological classification, linear and nonlinear optical response of solid crystal systems. Solution method: Based on the tight binding method to solve the band structure, the Wilson loop is used to classify the topological phases, and the optical response is calculated by Berry curvature and Berry connection. [ABSTRACT FROM AUTHOR]

As a route to improving the energy conversion of organic-inorganic hybrid-solar cells, we have tested the performance of poly (phenylene vinylene) (PPV), poly(2,5-thienylene vinylene) (PWTV) polymers and CdTe nanocrystal devices produced via aqueous-processing. It is found that small differences in the conformation of the sensitizer lead to dramatic effects on the solar cell efficiency. Using a combination of UV-Vis absorption spectroscopy and first-principles non-adiabatic molecular dynamics (NAMD) based on time-dependent density-functional theory (TDDFT), PPV is found to have a longer electron injection and recombination time despite seeming to have a better energy alignment with the substrate, which leads to a higher devices performance than PWTV. The present results shed new light on the understanding of organic-inorganic hybrid-solar cells and will trigger further experimental and theoretical investigations.

Aqueous-processed nanocrystal solar cells have attracted increasing attention due to the advantage of its environmentally friendly nature, which provides a promising approach for large-scale production. The urgent affair is boosting the power conversion efficiency (PCE) for further commercial applications. The low PCE is mainly attributed to the imperfect device structure, which leads to abundant nonradiative recombination at the interfaces. In this work, an environmentally friendly and efficient method is developed to improve the performance of aqueous-processed CdTe nanocrystal solar cells. Polymer/CdTe planar heterojunction solar cells (PHSCs) with optimized band alignment are constructed, which results in reduced interfacial charge recombination, enhanced carrier collection efficiency and built-in field. Finally, a champion PCE of 5.9%, which is a record for aqueous-processed solar cells based on CdTe nanocrystals, is achieved after optimizing the photovoltaic device.

Due to their environmentally friendly ideology, aqueous-processed hybrid solar cells (HSCs) are favored for industrial production. However, relatively low device performance urges the progress in power conversion efficiency (PCE) for their further applications. In this work, the function of polymer and nanocrystal (NC) is studied by investigating three different device structures. The polymer (low hole mobility), which plays an important role even if the content is extremely low, is mainly responsible for enhancing the Vocand FF, while the NC (high hole mobility) is the principle part in light absorbing, carrier generating, and transporting. The intensive study of polymer and NC makes it possible to achieve high performance through adjusting the thickness of different active layers by using device structures of the cathode/electron transport layer (ETL)/NC/polymer:NC/hole transport layer (HTL)/anode. An efficient aqueous-processed HSC with PCE of 5.64% is obtained which presents the highest performance among polymer/NC HSCs to date.

To investigate the abnormal ground pressures and roof control problem in fully mechanized repeated mining of residual coal after room and pillar mining, the roof fracture structural model and mechanical model were developed using numerical simulation and theoretical analysis. The roof fracture characteristics of a repeated mining face were revealed and the ground pressure law and roof supporting conditions of the repeated mining face were obtained. The results indicate that when the repeated mining face passes the residual pillars, the sudden instability causes fracturing in the main roof above the old goaf and forms an extra-large rock block above the mining face. A relatively stable “Voussoir beam” structure is formed after the advance fracturing of the main roof. When the repeated mining face passes the old goaf, as the large rock block revolves and touches gangue, the rock block will break secondarily under overburden rock loads. An example calculation was performed involving an integrated mine in Shanxi province, results showed that minimum working resistance values of support determined to be reasonable were respectively 11,412kN and 10,743kN when repeated mining face passed through residual pillar and goaf. On-site ground pressure monitoring results indicated that the mechanical model and support resistance calculation were reasonable.

A novel kind of hybrid solar cell (HSC) was developed by introducing water-soluble insulating polymer poly(vinyl alcohol) (PVA) into nanocrystals (NCs), which revealed that the most frequently used conjugated polymer could be replaced by an insulating one. It was realized by strategically taking advantage of the characteristic of decomposition for the polymer at annealing temperature, and it was interesting to discover that partial decomposition of PVA left behind plenty of pits on the surfaces of CdTe NC films, enlarging surface contact area between CdTe NCs and subsequently evaporated MoO3. Moreover, the residual annealed PVA filled in the voids among spherical CdTe NCs, which led to the decrease of leakage current. An improved shunt resistance (increased by ∼80%) was achieved, indicating the charge-carrier recombination was effectively overcome. As a result, the new HSCs were endowed with increased Voc, fill factor, and power conversion efficiency compared with the pure NC device. This approach can be applied to other insulating polymers (e.g., PVP) with advantages in synthesis, type, economy, stability, and so on, providing a novel universal cost-effective way to achieve higher photovoltaic performance.

In this work, improved solar cells from aqueous CdTe NCs is achieved by replacing evaporated MoOxwith spiro-OMeTAD as a hole transfer layer. The increased Vocand Jsccan be attributed to interfacial dipole effect and reduced back recombination loss, respectively. A high PCE of 6.56% for solar cells from aqueous NCs is obtained by optimizing the microstructure further.

Aqueous processed nanocrystal (NC) solar cells are attractive due to their environmental friendliness and cost effectiveness. Controlling the bandgap of absorbing layers is critical for achieving high efficiency for single and multijunction solar cells. Herein, we tune the bandgap of CdTe through the incorporation of Se via aqueous process. The photovoltaic performance of aqueous CdSexTe1–xNCs is systematically investigated, and the impacts of charge generation, transport, and injection on device performance for different compositions are deeply discussed. We discover that the performance degrades with the increasing Se content from CdTe to CdSe. This is mainly ascribed to the lower conduction band (CB) of CdSexTe1–xwith higher Se content, which reduces the driving force for electron injection into TiO2. Finally, the performance is improved by mixing CdSexTe1–xNCs with conjugated polymer poly(p-phenylenevinylene) (PPV), and power conversion efficiency (PCE) of 3.35% is achieved based on ternary NCs. This work may provide some information to further optimize the aqueous-processed NC and hybrid solar cells.

In the context of a room-and-pillar mining gob in Shanxi province in China, this paper numerically investigates the stress distribution and deformation rules of roadway surrounding rocks at various locations of residual coal pillars in room-and-pillar mining gobs using software FLAC3D. It is found that the concentrated stress beneath coal pillars distributes in a shape of ellipse. A reasonable roadway layout is then proposed. In this design, it is indicated that roadways should be designed to avoid the supporting zones of pillars with increasing compression and take into account the roof falling and crushing in the upper gob. According to the surrounding rock deformation characteristics and mining roadway locations as well as the supporting principles of timely support, rock reinforcing, piecewise management and suiting local conditions, a new asymmetric shield supporting plan is proposed. The field surveying results show that this supporting plan can effectively control the roadway rock deformation, thus guarantee the safe and smooth construction of roadways.

Without using any environmentally hazardous organic solution, we fabricated hybrid solar cells (HSCs) based on the aqueous-solution-processed poly(3-hexylthiophene) (P3HT) dots and CdTe nanocrystals (NCs). As a novel aqueous donor material, the P3HT dots are prepared through a reprecipitation method and present an average diameter of 2.09 nm. When the P3HT dots are mixed with the aqueous CdTe NCs, the dependence of the device performance on the donor–acceptor ratio shows that the optimized ratio is 1:24. Specifically, the dependence of the device performance on the active-layer thermal annealing conditions is investigated. As a result, the optimized annealing temperature is 265 °C, and the incorporation of P3HT dots as donor materials successfully reduced the annealing time from 1 h to 10 min. In addition, the transmission electron microscopy and atomic force microscopy measurements demonstrate that the size of the CdTe NCs increased as the annealing time increased, and the annealing process facilitates the formation of a smoother interpenetrating network in the active layer. Therefore, charge separation and transport in the P3HT dots:CdTe NCs layer are more efficient. Eventually, the P3HT dots:CdTe NCs solar cells achieved 4.32% power conversion efficiency. The polymer dots and CdTe NCs based aqueous-solution-processed HSCs provide an effective way to avoid a long-time thermal annealing process of the P3HT dots:CdTe NCs layer and largely broaden the donor materials for aqueous HSCs.

The UEs at the edge of the cell in TD-LTE-Advanced system suffer from a poor communication quality invariably. In this paper, a novel relay mechanism, called Device-to-Device mobile relay (D2DMR), is proposed. In the D2DMR mechanism, the UE at the edge of the cell or in a poor coverage area can communicate with eNodeB via another UE’s relay. The link between these two UEs is established in the Device-to-Device (D2D) communication mode. The D2DMR mechanism can expand the cell coverage and improve the system capacity of TD-LTE-Advanced system with little interference. Numerical analysis and simulation results show that the D2DMR mechanism can improve the throughput of the TD-LTE-Advanced system greatly.

Aqueous-processed solar cells have evolved into a new generation of promising and renewable energy materials due to their excellent optical, electrical, and low-cost properties. In this work, Cd0.75Hg0.25Te colloid quantum dots (CQDs) were incorporated into a water-soluble conjugated polymer with broad absorption and high charge-carrier-mobility (5 × 10–4cm2V–1s–1) to obtain a composite with an absorption spectrum ranging from 300 to 1200 nm. The matched energy level between polymer and CQDs ensured the effective electron transfer, while the interpenetrating network structure formed via heat treatment guaranteed the quick electron transport. Moreover, the formation process of the interpenetrating network was systematically monitored by using AFM and TEM instruments and further confirmed through the measurement of charge-carrier-mobility of the active layers. In combination with the surface modification of a single Cd0.75Hg0.25Te layer, this aqueous-processed solar cell showed excellent photovoltaic response and the power conversion efficiency (PCE) reached 2.7% under AM 1.5 G illumination (100 mW cm–2). Especially, the contribution of the Herschel infrared region (780–1100 nm) to the photocurrent was as high as 15.04%. This device showed the highest PCE among organic-inorganic hybrid solar cells (HSCs) based on CdxHg1–xTe CQDs and the highest near infrared (NIR) contribution among aqueous-processed HSCs, indicating the enormous potential of taking advantage of NIR energy in a solar spectrum and a promising application in solar cells especially used in cloudy weather.

Chinas offshore oil and gas has been developed from shallow water to deep water. Subsea production facilities play more and more role in deepwater oil and gas fields, in which Christmas tree is the key equipment to control and regulate the oil well production of deepwater production systems, but it has great installation costs and risk. For complex underwater environment, it is necessary to find a best way to install the Christmas tree securely and rapidly. ROV (Remotely Operated Vehicle) is wildly used in the field of offshore oil, especially in deep water for its large working depth, safe, efficient and other characteristics, and it has become an indispensable tool for development of deep-sea oil and gas. In one Christmas tree installation at Liwan3-1 deepwater oilfield, the ROV succeeded in assisting the installation of Christmas tree. The solutions for winding and wrong operation risk in installation process are given in the end.

Because both of the volume and the weight of the photoelectric platform are small, the structure of two frames and two axes is used in the photoelectric platform. As the key component of the photoelectric platform, the main frame should have sufficient strength and rigidity. In order to achieve this object, three-dimensional entity model of the main frame is established using CATIA software. Then the finite-element analysis of the model is finished with ANSYS Workbench. Based on the analysis results, the weak links of the main frame is found. Then these links are improved and the main frame is analyzed again. After improving the structure, the results of the finite-element analysis show that the main frame meets the requirements of design and has perfect overall performance.

In order to accurately emulate the operation conditions of high-speed motorized spindle in the reliability experiment, a dynamic loading system is proposed. This system allows simultaneously loading torque, radial and axial force against the spindle. The torque load is carried out by the electric dynamometer; the non-contact vibration exciter completes the radial load; the axial load is carried out by a self-made electromagnet. Moreover, this system also can detect out the basic features and failure data of the motorized spindle during the loading. And these sampling data provide a quantitative elevation for its reliability analysis. This paper presents a simple solution to the high-speed motorized spindle reliability research where the loading experiment is designed with the spindle whose maximum rotational speed is 18000rpm.

The S-N curves of medium carbon steel(MCS) are determined by the ultrasonic symmetric bending fatigue system (20 KHz). The results show that two S-N curves of MCS display the characteristic of “continually decreasing type” up to 109 cycles and exhibit no traditional horizontal plateau beyond 106 cycles. When the fatigue cycles are over 109, fatigue failure do occurs. By comparison of the two curves of 2mm thick and 5mm thick MCS, the results show that in the high-cycle stage(107cycles), size effect has no significant impact on fatigue Properties. This can also be explained by the theory of crack initiation, in high cycle stage, fatigue crack initiation exists in the sample surface, and in ultra-high-cycle stage, fatigue crack initiation exists in internal initiation.

We report Q-switched mode-locked (QML) pulses generation in an Yb-doped multimode fiber (MMF) laser by using a graphene-deposited multimode microfiber (GMM) for the first time, to the best of our knowledge. The single-wavelength QML operation with the central wavelength tunable from 1028.81 nm to 1039.20 nm and the dual-wavelength QML operation with the wavelength spacing tunable from 0.93 nm to 5.79 nm are achieved due to the multimode interference filtering effect induced by the few-mode fiber and MMF structure and the GMM in the cavity. Particularly, in the single-wavelength QML operation, the fifth harmonic is also realized owing to the high nonlinear effect of the GMM. The obtained results indicate that the QML pulses can be generated in the MMF laser, and such a flexible tunable laser has promising applications in optical sensing, measuring, and laser processing.