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Aircraft icing has long been a plague to aviation for its serious threat to flight safety. Recently, researches about a newly proposed deicing method based on Plasma Synthetic Jet Actuator (PSJA) have just started. To meet the requirements of in-flight deicing, structure of PSJA needs to be adjusted. This paper completed the detailed design and experimental validation of a novel plasma striker, which was a modified version of PSJA. Influences of mass of the moving part and rod shapes on the ice-breaking performances were also studied. Besides, a “conical-nosed rod configuration” was proposed. Its purpose was to ensure a good ice-breaking performance of the plasma striker on long ice, by generating a splitting failure. Results show that, though mass of the moving part was just several grams, ice-breaking performance was better when the mass was lighter. The rectangular rod could generate an elliptical circumferential crack, whose major axis was parallel to the direction of the long side of the rectangular rod. And the “conical-nosed rod” concept was verified to be able to generate a splitting crack which can spread completely to the far end of long ice, and the crack direction was parallel to edge line of the cone. In general, the plasma striker has the advantages of simple structure, low energy consumption, little harm to the flow field and the aircraft skin. Simulations will be carried out in future works to study in detail the working process of the plasma striker.

To study the influence of fillings on rock failure. By turning to the Drucker-Prager strength model and cumulative damage criteria, investigations are made, with the nonlinear AUTODYN software, into crack propagation behaviors in crack-filled and unfilled specimens under uniaxial dynamic loading. Under investigations are crack initiation position, sequence and angle, and coalescence mode. According to the mode of propagation and coalescence, cracks are divided into three types, i.e., the tensile wing, the antiwing, and the horsetail. The simulation results show that under uniaxial dynamic loading, differences are found in initiation position, angle, and coalescence mode for specimens with cracks filled or otherwise. However, filling does not affect crack initiation sequence. Under the same loading, the damage to filled specimen is less severe than that to the unfilled specimen.

Shock wave/boundary layer interaction (SWBLI) is still one of the unresolved bottlenecks that restrict the development of more advanced flight vehicles. Supersonic forward-facing step (FFS), an extreme case of compression ramp, often occurs severe SWBLIs with a large separation bubble. In this paper, experimental investigations on vortical structures and density fluctuations characteristics of supersonic FFS controlled by self-sustaining dual synthetic jets (SDSJ) are carried out in a Mach number 2.95 wind tunnel. High spatial–temporal resolution flowfield images of FFS without/with active flow control are captured by adopting nano-particle-based planar laser scattering technique. The control effects of the distance between the actuator and the step are mainly compared. The paper finds that the SDSJ can effectively change the feature of flowfield, eliminate the separation shock and the reattachment shock, compel the original shock induced by the step leading edge to distort and reduce its intensity finally. Density fluctuations analysis demonstrates that the whole flows seem to move upstream with the increase of distance (dS-J). Discrete Fourier transformation spectrums results reveal that the fluctuations are mainly located in the low-frequency region at first. High-frequency components and frequency bandwidth increase slightly after the SDSJ are applied.

A simple estimation method of momentum coefficient of synthetic jet actuator has been proposed. Flow separation over an airfoil can be suppressed sufficiently with the estimated momentum coefficient. At a certain angle of attack (AOA), momentum deficit of boundary layer at front of separation point can be quantified based on Bernoulli's theorem. The function of synthetic jet actuator is deemed to be momentum addition and two stages of the addition corresponding to blowing and suction phases are considered respectively. The required momentum coefficient as well as the associated injection angle is determined preliminarily with the assumption of synthetic jet actuator at front of separation point. Since synthetic jet actuator is usually installed near the leading edge, a modification is introduced to consider the influence of excitation location. Using this method, flow separation over a NACA0015 airfoil is suppressed nearly completely with AOA = 15° and synthetic jet actuator at x/ c = 10%. Different angle of attacks corresponding to pre-stall angle, post-stall angle, and deep stall angle have been examined, respectively. Results indicate that the method is effective at pre-stall angle and post-stall angle. However, momentum coefficient will be underestimated when the separation point is upstream to the location of the airfoil's maximum thickness. At deep stall angle, the method is invalid. The estimation method is useful for practices of flow separation control with synthetic jet actuator.

The interaction between self-sustaining dual jets and supersonic laminar boundary layer is experimentally studied using the nanoparticle-based planar laser scattering in a Ma 2.95 supersonic low-turbulence wind tunnel for the first time. The typical fine flow structures, such as separation shock, “W” bow shock, barrel shock, horseshoe vortex, large-scale vortex structures and counter-rotating vortex pairs, are clearly identified by streamwise and spanwise flowfield images. The curves of jet penetration depth are fitted at the momentum ratio of 0.55 between self-sustaining dual jets and supersonic crossflow. The results play a significant role in further and comprehensive exploration of the active flow control for a supersonic flow.

We present TexelBlocks, modular blocks that dynamically change their surfaces to support rich physical interactions. The core component of each block is a motorized crawler belt with a set of material patches attached to it, allowing each of the TexelBlocks to change their surface independently and be concatenated into flat surfaces of various sizes. We implemented a working system that controls 24 TexelBlocks to form 6 × 4 dynamic surfaces. With the working prototype, we developed five applications such as context-aware surface adaptation, real-time tactile feedback, immersive storytelling with dynamic background, real-time embodied platform game, and a surface-changing board game to demonstrate rich physical interactions of dynamic surfaces.

We present Impossible Staircase, a real-walking virtual reality system that allows users to climb an infinite virtual tower. Our set-up consists of an one-level scaffold and a lifter. A user climbs up the scaffold by real walking on a stairway while wearing a head-mounted display, and gets reset to the ground level by a lifter imperceptibly. By repeating this process, the user perceives an illusion of climbing an infinite number of levels. Our system achieves the illusion by (1) controlling the movement of the lifter to generate reverse and imperceptible motion, (2) guiding the user through the scaffold with delay mechanisms to reset the lifter in time, and (3) procedural generating overlapping structures to enlarge perceived height of each level. We built a working system and demonstrated it with a 15-min experience. With the working system, we conducted user studies to gain deeper insights into vertical motion simulation and vertical real walking in virtual reality.

Grouting prevents groundwater leakage into tunnels, based on the exponent model that expresses the nonlinear variation of the hydraulic conductivity of the surrounding rock, the formulas for predicting the magnitude of water inflow and outer water pressure of the lining after grouting are deduced. The parameter analysis shows how the water inflow decreases as the hydraulic conductivity of the grouting circle diminishes and the thickness of the grouting circle increases. When the parameter α (attenuation coefficient), which expresses the decreasing amplitude of the permeability coefficient of the surrounding rock with depth, is greater than 0, the water inflow increases until it reaches a maximum at a certain depth, and then the inflow decreases to 0 if deep enough. After considering the variation in the hydraulic conductivity of the surrounding rock, the thickness and hydraulic conductivity of the grouting circle may be designed to be too large to reduce the magnitude of the water inflow. Meanwhile, to reach the limited drainage criterion of the tunnel groundwater, the grouting circle thickness decreases gradually as α increases after the nonlinear variation of the hydraulic conductivity of the surrounding rock, which can reduce the cost for plugging the groundwater. Thus, it is critical to consider hydraulic conductivity variation during water inflow predicting and grouting when designing tunnels.

Geometrically nonlinear dynamic analysis of functionally graded carbon nanotube reinforced composite (FG-CNTRC) rectangular plates subjected to blast loads is conducted based on Reddy’s higher-order shear deformation theory using the weak form quadrature element method. The von-Karman strain terms are introduced to consider the geometrically nonlinear effects . The polymer composite plate is reinforced by single-walled carbon nanotubes (SWCNTs) with the uniform and functionally graded distribution in the plate thickness direction. The effective material properties of the FG-CNTRC plates are estimated with the extended rule of mixture. The Newmark- β time integration scheme and the Newton–Raphson iteration technique are adopted to solve the nonlinear incremental dynamic equilibrium equation in temporal domain. Comparative and convergence studies are carried out to validate the accuracy, efficiency and numerical stability of the presented weak form quadrature element formulation. The effects of the carbon nanotube distribution and volume fraction, plate width-to-thickness ratio, plate aspect ratio, load type and boundary condition on the dynamic response of the FG-CNTRC plates under blast loads are systematically investigated through the parametric studies .

Water seepage from a tunnel may induce the drawdown of the groundwater table and destroy vegetation and the ecological environment in the tunnel area. One of the primary objectives in tunnel engineering is to develop effective methods to estimate the amount of the limiting drainage of a mountain tunnel. Based on the area-well theory, a groundwater seepage model of a tunnel is established. Due to the model and groundwater dynamics, the equation describing the relationship between the amount of water inflow and drawdown of the groundwater table for a tunnel is derived under unsteady flow conditions. After the ecological groundwater table for vegetation is introduced, a method of calculating the amount of the limiting drainage for a mountain tunnel is proposed to prevent the drawdown of groundwater table from exceeding the ecological groundwater table required to support vegetation. According to the proposed method, the three-dimensional form of the groundwater drawdown funnels and the influence scope of tunnel water inflow are determined. The rainfall recharge amount Wt within the influence scope is obtained based on the rainfall infiltration coefficient method, and the value is compared to the total groundwater discharge Q. These values Wt and Q are then equated through adjusting the unit groundwater inflow q0. The values less than or equal to q0 can be determined as the limiting drainage value of groundwater for the tunnel, and the groundwater table will not drop and balances the groundwater and the vegetation ecological environment. The results and case study show that the proposed method exhibits good agreement with actual conditions and is suitable for use in tunnel construction.

Strength training improves overall health, well-being, physical appearance, and sports performance, with training programs specifying variables such as sets, repetitions, rest time, weight, and tempo. The repetitive nature of strength training, typically performed at fixed tempo, has made it challenging to develop entertaining exergames for common strength training exercises. We present StrengthGaming, which uses scaling and shuffling technique to provide tempo variations to strength training while preserving the training volume and training goals. It affords game designers more flexibility in designing strength training-based exergames. We developed a prototype game, inspired by FlappyBird, that uses a wearable orientation sensor to track the repetition tempo to control a flying character, using both fixed tempo design and dynamic tempo design. Results from our 24-person user study showed that dynamic tempo was significantly more entertaining than fixed tempo (p

By March 31, 2020, COVID-19 had spread to more than 200 countries. Over 750,000 confirmed cases were reported, leading to more than 36,000 deaths. In this study, we analysed the efficiency of various intervention strategies to prevent infection by the virus, SARS-CoV-2, using an agent-based SEIIR model, in the fully urbanised city of Shenzhen, Guangdong Province, China. Shortening the duration from symptom onset to hospital admission, quarantining recent arrivals from Hubei Province, and letting symptomatic individuals stay at home were found to be the three most important interventions to reduce the risk of infection in Shenzhen. The ideal time window for a mandatory quarantine of arrivals from Hubei Province was between 10 January and January 17, 2020, while the ideal time window for local intervention strategies was between 15 and 22 January. The risk of infection could have been reduced by 50% if all symptomatic individuals had immediately gone to hospital for isolation, and by 35% if a 14-day quarantine for arrivals from Hubei Province had been introduced one week earlier. Intervention strategies implemented in Shenzhen were effective, and the spread of infection would be controlled even if the initial basic reproduction number had doubled. Our results may be useful for other cities when choosing their intervention strategies to prevent outbreaks of COVID-19., Highlights • Shortening the delay to hospital is the most effective intervention in Shenzhen. • 10 to 17 January is the best time for a mandatory quarantine of Hubei's arrivals. • 15 to 22 January is the best time for local intervention strategy in Shenzhen. • Work/school closure and mask wearing are effective interventions in other countries. • Airport screening is not very effective.

Strength training improves overall health, well-being, and sports performance. However, the training process is often repetitive, making the experiences boring and tiring after going through the long-term session. This paper proposes FitBird, which uses wearable sensors to map existing strength training motion to game designs to enhance entertainment level during exercising. We chose 1:1:1 as the time intervals proportion of three distinct phases during exercises repetition: 1) Eccentric: muscle lengthening, 2) Isometric: same muscle length, and 3) Concentric: muscle shortening, and integrated this tempo for the well-known game - FlappyBird as the training guidance. We evaluated the proof-of-concept prototype with 12-person study that participants conducted strength training while using our system. The results showed that FitBird significantly improve user's entertainment level during strength training and was preferred by most of the users.

Pr3+/Er3+ co-doped tellurite glass with composition 80TeO2-10Na2O-5WO3-5Nb2O5 was synthesized by the conventional melt-quenching technique, and the obtained glass was characterized by the UV/Vis/NIR absorption spectrum, near-infrared fluorescence spectrum, differential scanning calorimeter (DSC) curve, X-Ray diffraction (XRD) pattern and Raman spectrum. Under the 488 nm excitation, it was found that Pr3+/Er3+ co-doped tellurite glass could emit an ultra-broadband near-infrared fluorescence which extended from 1200 to 1650 nm with full-width at half-maximum (FWHM) of about 236 nm, and this ultra-broadband fluorescence was contributed by the multichannel emissions of Pr3+ and 1.53 µm band emission of Er3+. The luminescent mechanism and energy transfer processes between Pr3+ and Er3+ ions which are responsible for the observed ultra-broadband fluorescence were analyzed. Meanwhile, optical absorption bands that are assigned with corresponding electronic transitions with respect to Pr3+ and Er3+ ions were identified from the measured absorption spectrum, and based on the optical absorption data, the gain coefficient and important spectroscopic parameters like Judd-Ofelt intensity parameter, spontaneous radiative transition probability, radiative lifetime and branching ratio were calculated to elucidate the radiative properties of doped rare-earth ions. In addition, the DSC curve exhibited the good thermal stability of glass host with Δ T >150 °C, Raman spectral study displayed the presence of different vibrational groups and XRD pattern confirmed the amorphous structural nature of the prepared glass. The present results indicate that Pr3+/Er3+ co-doped tellurite glass is promising for the ultra-broadband near-infrared band fiber amplifiers covering the expanded low-loss communication window.

Improving the lasing emission property of rare-earth doped vitreous material is a research topic. In this paper, Er3+/Yb3+/Tm3+ tri-doped tellurite glasses with and without WO3 component were synthesized using melt-quenching technique and the effect of WO3 addition on the 1.80 μm band fluorescence of Tm3+ was investigated. The obtained samples were characterized by X-ray diffraction (XRD) pattern, differential scanning calorimeter (DSC) curve, Raman spectrum, UV/Vis/NIR absorption spectrum, near-infrared emission spectrum and fluorescence decay curve. The XRD pattern confirmed amorphous structural nature of synthesized tellurite glass, the DSC curve revealed good thermal stability with Δ T >100 °C and the Raman spectrum displayed a stretching vibration band around 920 cm−1 for glass host with WO3. Under the excitation of 980 nm laser diode (LD), the intense 1.80 μm band fluorescence of Tm3+ originated from the 3F4→3H6 transition was observed in the Er3+/Yb3+/Tm3+ tri-doped tellurite glass and the intensity increases further with the addition of a certain amount of WO3, which is attributed to the enhanced energy transfers from Yb3+ (Er3+) to Tm3+ ions due to the increased phonon energy of glass host. The energy transfer mechanism between them was elucidated by analyzing fluorescence decay behavior of Tm3+ and quantitatively calculating energy transfer coefficient as well as phonon contribution ratio. Meanwhile, based on the absorption spectrum, some important spectroscopic parameters such as Judd-Ofelt parameter, spontaneous radiative transition probability, fluorescence branching ratio, absorption and emission cross-sections, and gain coefficient spectrum were calculated to reveal spectroscopic properties of doped Tm3+ ions. The obtained results indicate that Er3+/Yb3+/Tm3+ tri-doped tellurite glass with an appropriate amount of WO3 is a promising gain medium applied for the 1.80 μm band solid-state lasers.

In this work, the near-infrared photoluminescence properties in Tm3 +/Ho3 + co-doped tellurite glass was investigated. The tellurite glass with composition TeO2-ZnO-Na2O-La2O3 was synthesized using conventional melt-quenching technique and characterized by UV/Vis/NIR absorption and near-infrared emission spectroscopies, fluorescence decay measurement and differential scanning calorimeter (DSC) analysis. Under the excitation of 808 nm laser diode (LD), a broadband 2.0 μm band luminescence ranging from 1600 to 2200 nm with a full width at half maximum (FWHM) of 362 nm was observed, which was contributed by 1.85 μm fluorescence from Tm3 +: 3F4 → 3H6 and 2.05 μm fluorescence from Ho3 +: 5I7 → 5I8. The fluorescence emission of Ho3 + was originated from the energy transfer from Tm3 + to Ho3 + ions, and the energy transfer mechanism was elucidated by analyzing fluorescence decay behavior of Tm3 + and quantitative calculation of phonon contribution joined in the energy transfer process. Meanwhile, based on the absorption spectrum, some important spectroscopic parameters such as Judd-Ofelt intensity parameter, spontaneous radiative transition probability, fluorescence branching ratio, absorption and emission cross-sections, and gain coefficient spectrum were calculated to reveal the spectroscopic properties of doped tellurite glass. Furthermore, from the DSC curve it can be derived that the investigated glass possesses a good thermal stability with ΔT(= Tx − Tg) larger than 152 °C. These results indicate that Tm3 +/Ho3 + co-doped tellurite glass could be a promising gain medium applied for 2.0 μm near-infrared band broad fiber amplifiers and tunable fiber lasers.

Pr3+-doped tellurite glasses containing metallic silver NPs were synthesized by the conventional melt-quenching technique. Structural, thermal and optical properties of the synthesized glass samples were characterized by X-Ray diffraction (XRD) curves, Raman spectra, differential scanning calorimeter (DSC) curves, transmission electron microscopy (TEM) images, UV/Vis/NIR absorption and near-infrared fluorescence emission spectra. The XRD curves confirmed the amorphous structural nature of the synthesized glasses, the Raman spectra identified the presence of different vibrational groups, the DSC curves verified the good thermal stability, and the TEM images revealed the nucleated silver NPs with average diameter about 10 nm dispersed in the glass matrix and its surface Plasmon resonance (SPR) absorption band was located at around 510 nm. Besides, Judd-Ofelt intensity parameters Ω t (t = 2, 4, 6) and other important spectroscopic parameters like transition probability, radiative lifetime, branching ratio were calculated to evaluate the radiative properties of Pr3+ levels from the measured optical absorption spectra. It was found that Pr3+-doped tellurite glasses could emit an ultra-broadband fluorescence extending from 1250 to 1650 nm under the 488 nm excitation, and this fluorescence emission increased further with the introduction of silver NPs. The enhanced fluorescence was mainly attributed to the increased local electric field around Pr3+ induced by silver NPs. The present results demonstrate that Pr3+-Ag codoped tellurite glass is a promising candidate for the near-infrared band ultra-broadband fiber amplifiers covering the expanded low-loss communication window.

This paper reports an enhanced and broadband near-infrared fluorescence emission in the Pr3+/Nd3+ co-doped tellurite glass, which was prepared using melt-quenching technique. Under the excitation of 488 nm laser diode (LD), three near-infrared emission bands at around 0.9, 1.04 and 1.30 μm from 3P1,0 → 1G4, 1G4→3H4 and 1G4→3H5 radiative transitions respectively were observed in the Pr3+ single-doped glass, and the fluorescence intensities increased further with the introduction of Nd3+ ions, which is mainly attributed to the energy transfers from Nd3+ to Pr3+ emissions. Meanwhile, the spectral overlapping of Pr3+:1G4→3H4 and Nd3+:4F3/2 → 4I11/2 radiative transitions resulted in a broadband emission ranging from 1000 to 1100 nm, whose full-width at half-maximum (FWHM) reached about 66 nm. Additionally, the spectroscopic properties of Nd3+ and Pr3+ ions were analyzed using Judd-Ofelt theory and the thermal stability property of prepared glass was characterized by the differential scanning calorimeter (DSC) measurement, and larger than 134 °C for the difference Δ T ( = T x − T g ) was observed, which indicates its feasibility for later fiber drawing. The enhanced fluorescence and broadband emission indicate that Pr3+/Nd3+ co-doped tellurite glass can be applied in the near-infrared band tunable lasers and broadband optical amplifiers.

The B 2 O 3 oxide in different concentration was introduced into Er 3+ /Ho 3+ codoped tellurite glass with conventional composition TeO 2 ZnO Na 2 O to investigate its effect on the near-infrared band luminescence of doped rare-earth ions under the excitation of 980 nm LD. The UV/Vis/NIR absorption spectrum, Vis/NIR fluorescence emission spectrum, fluorescence decay curve, DSC curve and Raman spectrum of the prepared glass samples were measured and investigated. With the introduction of B 2 O 3 in a certain concentration range, the 1.55 μm band fluorescence of Er 3+ improved greatly, whereas the 2.03 μm band one of Ho 3+ decreased first and then increased slightly. The Judd-Ofelt intensity parameter, radiative transition probability, quantum efficiency, multi-phonon relaxation rate and energy transfer micro-parameter were calculated to explain the obtained experimental results. The present works indicate that the enhanced multi-phonon relaxation of excited state ions and energy transfer between Er 3+ and Ho 3+ ions due to the increased phonon energy of glass host with the introduction of B 2 O 3 are responsible for the observed luminescent phenomena, and Er 3+ /Ho 3+ codoped tellurite glass with an appropriate amount of high phonon energy B 2 O 3 is a promising candidate applied for the near-infrared band solid-state lasers and fiber amplifiers.

Although airborne transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been recognized, the condition of ventilation for its occurrence is still being debated. We analyzed a coronavirus disease 2019 (COVID-19) outbreak involving three families in a restaurant in Guangzhou, China, assessed the possibility of airborne transmission, and characterized the associated environmental conditions. We collected epidemiological data, obtained a full video recording and seating records from the restaurant, and measured the dispersion of a warm tracer gas as a surrogate for exhaled droplets from the index case. Computer simulations were performed to simulate the spread of fine exhaled droplets. We compared the in-room location of subsequently infected cases and spread of the simulated virus-laden aerosol tracer. The ventilation rate was measured using the tracer gas concentration decay method. This outbreak involved ten infected persons in three families (A, B, C). All ten persons ate lunch at three neighboring tables at the same restaurant on January 24, 2020. None of the restaurant staff or the 68 patrons at the other 15 tables became infected. During this occasion, the measured ventilation rate was 0.9 L/s per person. No close contact or fomite contact was identified, aside from back-to-back sitting in some cases. Analysis of the airflow dynamics indicates that the infection distribution is consistent with a spread pattern representative of long-range transmission of exhaled virus-laden aerosols. Airborne transmission of the SARS-CoV-2 virus is possible in crowded space with a ventilation rate of 1 L/s per person., Graphical abstract Image 1

Tellurite glasses with different concentrations of Nd3 + ions and WO3 oxide were prepared using melt-quenching technique. The prepared glasses were characterized by the absorption spectrum, emission spectrum, Raman spectrum, fluorescence decay curve and DSC curve measurements, together with Judd-Ofelt intensity parameter, radiative transition probability and fluorescence branching ratio calculations to reveal the effects of Nd3 + and WO3 concentration on the structure, photo-luminescence and thermal stability. Under the excitation of 808 nm LD, three near-infrared band fluorescence emissions at around 0.9, 1.06 and 1.34 μm, corresponding to the transitions from the 4F3/2 → 4I9/2, 4I11/2 and 4I13/2 levels respectively, are observed, and the fluorescence intensities increase with the increase of doped Nd3 + concentration up to 0.6 mol%. Furthermore, the fluorescence intensities continue to increase greatly with the introduction of WO3 oxide. Compared with 0.6 mol% Nd3 +-doped glass without WO3 oxide, the luminescent intensity of 1.06 μm band increases by about 95% in the glass with 9 mol% amount of WO3, which is mainly attributed to the rapid population of Nd3 + ions in the excited level 4F3/2 due to the enhanced multi-phonon relaxation process with the increased phonon energy of glass host. Therefore, the enhanced luminescent intensity as well as the good thermal stability demonstrated by DSC curve indicate that the prepared 0.6 mol% Nd3 +-doped tellurite glass with 9 mol% amount of WO3 oxide is a potential gain medium applied for near-infrared band solid-state lasers and fiber amplifiers.

Metallic silver nanoparticles (Ag NPs) with various concentrations were embedded into Er3+/Tm3+/Yb3+ tri-doped tellurite glasses prepared using melt-quenching and heat-treated techniques. Heat-treatment at temperature above the glass transition temperature induced the nucleation and growth of near-spherical shape silver NPs confirmed by the transmission electron microscopy (TEM) images, and the average diameter of silver NPs was about 10 nm. The thermal stability, structural and optical properties of the prepared glasses were characterized by the differential scanning calorimeter (DSC) curves, X-ray diffraction (XRD) patterns, absorption spectra, luminescence spectra and fluorescence decay curves. The DSC curves displayed that the prepared glasses possess good thermal stability with ∆ T larger than 138 °C while the XRD patterns indicated the amorphous structural nature. Under the excitation of 980 nm LD, the luminescence spectra exhibited two intense near-infrared band fluorescence at 1.81 and 1.53 μm in the wavelength range of 1400–2200 nm, which are originated from the Tm3+:3F4 → 3H6 and Er3+:4I13/2 → 4I15/2 transitions respectively. With the embedding of 0.5 mol % amount of silver NPs, the 1.81 μm band fluorescence of Tm3+ increased significantly by about 70%, mainly due to the local electric field enhanced effect induced by silver NPs on the basis of energy transfers from Er3+ to Tm3+ ions, and the energy transfer efficiency, micro-coefficient and critical radius were calculated to elucidate the interaction mechanism between Er3+ and Tm3+ ions. Additionally, the intensity parameters Ω t (t = 2, 4, 6) and radiative properties of Tm3+ such as the transition probabilities, radiative lifetimes and branching ratios were calculated from the measured absorption spectra based on Judd-Ofelt theory. The present results indicate that the Er3+/Tm3+/Yb3+ tri-doped tellurite glass with an appropriate amount of silver NPs is a promising luminescent material applied for the near-infrared band solid-state lasers and fiber amplifiers.

To assess the water inflow which is more suitable to the actual conditions of tunnel, an empirical correlation about the permeability coefficient changing with depth is introduced. Supposing that the surrounding rock is heterogeneous isotropy, the formula for calculating water inflow of tunnel with the nonlinear variation of permeability coefficient is deduced. By the contrast analysis with the existing formulas, the presented method has the similar value to them; moreover, the presented method has more simple form and easy to use. Due to parameter analysis, the water inflow decreases after considering the nonlinear variation of permeability coefficient. When the attenuation coefficient a>0, the water inflow increases first till reaches the maximum at a certain depth, then decreases and is close to 0 finally if deep enough. Thus, it is better to keep away from the certain depth where it is with the maximum water inflow for safe operation and economical construction, and reduce the water damage. Based on the analysis, the radius of tunnel has less impact on the amount of water inflow, and the water inflow just increases by 6.7% when the radius of tunnel increases by 1 m.

WO3 oxides with relatively high phonon energy and different concentrations were introduced into the Nd3+-doped tellurite-based glasses of TeO2-ZnO-Na2O to improve the 1.32 μm band fluorescence emission. The absorption spectra, Raman spectra, 1.32 μm band fluorescence spectra and differential scanning calorimeter (DSC) curves were measured, together with the Judd-Ofelt intensity parameters, stimulated emission and gain parameters were calculated to evaluate the effects of WO3 amount on the glass structure and spectroscopic properties of 1.32 μm band fluorescence. It is shown that the introduction of an appropriate amount of WO3 oxide can effectively improve the 1.32 μm band fluorescence intensity through the enhanced multi-phonon relaxation (MPR) processes between the excited levels of Nd3+. The results indicate that the prepared Nd3+-doped tellurite glass with an appropriate amount of WO3 oxide is a potential gain medium applied for the O-band broad and high-gain fiber amplifier.

The Er 3+ /Tm 3+ co-doped tellurite glasses with and without silver nanoparticles (Ag NPs) have been synthesized by the conventional melt-quenching technique and characterized by the UV/Vis/NIR absorption spectra, 1.85 μm band fluorescence emission spectra, differential scanning calorimeter (DSC) curves, X-ray diffraction (XRD) curves and transmission electron microscopy (TEM) images to investigate the effects of Ag NPs on the 1.85 μm band spectroscopic properties of Tm 3+ ions, thermal stability and structural nature of glass hosts. The TEM image reveals the presence of Ag NPs with average diameter of ∼14 nm in the prepared Er 3+ /Tm 3+ co-doped tellurite glasses, and the presence of Ag NPs significantly enhance the 1.85 μm band fluorescence emission of Tm 3+ ions under the excitation of 808 nm LD, which is mainly attributed to the intensified local electric field induced by Ag NPs scattered around the doped rare-earth ions, together with the energy transfer between Er 3+ and Tm 3+ ions. The energy transfer mechanisms between Er 3+ and Tm 3+ ions were further investigated by calculating energy transfer micro-parameters and phonon contribution ratios. Meanwhile, the Judd-Ofelt intensity parameters Ω t ( t = 2,4,6), spontaneous radiative transition probabilities, fluorescence branching ratios and radiative lifetimes of relevant excited levels of Tm 3+ ions were calculated based on the Judd-Ofelt theory to reveal the improved effects of Ag NPs on the 1.85 μm band spectroscopic properties. An improvement by about 75% of fluorescence intensity is found in the studied Er 3+ /Tm 3+ co-doped tellurite glass containing 1.0 mol% amount of Ag NPs, and the thermal stability of glass host increases slightly with the Ag NPs while the glass structure maintains the amorphous nature. The above results indicate that the prepared Er 3+ /Tm 3+ co-doped tellurite glass with an appropriate amount of Ag NPs is a promising host material applied for 1.85 μm band solid-state lasers and amplifiers.

Tm3+/Yb3+ co-doped tellurite glasses with different silver nanoparticles (Ag NPs) concentrations were prepared using the conventional melt-quenching technique and characterized by the UV/Vis/NIR absorption spectra, 1.85 μm band fluorescence emission spectra, transmission electron microscopy (TEM) images, differential scanning calorimeter (DSC) curves and X-ray diffraction (XRD) patterns to investigate the effects of Ag NPs on the 1.85 μm band spectroscopic properties of Tm3+ ions, thermal stability and structural nature of glass hosts. Under the excitation of 980 nm laser diode (LD), the 1.85 μm band fluorescence emission of Tm3+ ions enhances significantly in the presence of Ag NPs with average diameter of ∼8 nm and local surface Plasmon resonance (LSPR) band of ∼590 nm, which is mainly attributed to the increased local electric field induced by Ag NPs at the proximity of doped rare-earth ions on the basis of energy transfer from Yb3+ to Tm3+ ions. An improvement by about 110% of fluorescence intensity is observed in the Tm3+/Yb3+ co-doped tellurite glass containing 0.5 mol% amount of AgNO3 while the prepared glass samples possess good thermal stability and amorphous structural nature. Meanwhile, the Judd-Ofelt intensity parameters Ω t (t = 2,4,6), spontaneous radiative transition probabilities, fluorescence branching ratios and radiative lifetimes of relevant excited levels of Tm3+ ions were determined based on the Judd-Ofelt theory to reveal the enhanced effects of Ag NPs on the 1.85 μm band spectroscopic properties, and the energy transfer micro-parameters and phonon contribution ratios were calculated based on the non-resonant energy transfer theory to elucidate the energy transfer mechanism between Yb3+ and Tm3+ ions. The present results indicate that the prepared Tm3+/Yb3+ co-doped tellurite glass with an appropriate amount of Ag NPs is a promising lasing media applied for 1.85 μm band solid-state lasers and amplifiers.

For enhancing the 2.0 μm band fluorescence of Ho3+, a certain amount of WO3 oxide was introduced into Ho3+/Tm3+/Yb3+ tri-doped tellurite glass prepared using melt-quenching technique. The prepared tri-doped tellurite glass was characterized by the absorption spectra, fluorescence emission and Raman scattering spectra, together with the stimulated absorption, emission cross-sections and gain coefficient. The research results show that the introduction of WO3 oxide can further improve the 2.0 μm band fluorescence emission through the enhanced phonon-assisted energy transfers between Ho3+/Tm3+/Yb3+ ions under the excitation of 980 nm laser diode (LD). Meanwhile, the maximum gain coefficient of Ho3+ at 2.0 μm band reaches about 2.36 cm-1. An intense 2.0 μm fluorescence emission can be realized.

The significant criterion for evaluating the merits of a new type of high molecular polymer lies in its engineering properties and eco-friendliness. The focus of this study was to determine the effects of preparation conditions on the viscosity of the polyvinyl acetate (PVAc) emulsion, including reaction temperature (Tr), initiator concentration (CAPS), monomer concentration (CVA), pH value, and degree of dilution (Ddi). Based on the results of a series of laboratory tests, the range of viscosity value of PVAc was obtained under different conditions, and one set of viscosity values out of these was applied to soil reinforcement tests. Meanwhile, based on the test results, the engineering properties of PVAc solution were evaluated using strength and moisture retention tests, and the reinforcement mechanism was analyzed using scanning electron microscopy (SEM). In addition, it was proven through a vegetation growth test that the PVAc was eco-friendly.

Procedural generation in virtual reality (VR) has been used to adapt the virtual world to various indoor environments, fitting different geometries and interiors with virtual environments. However, such applications require that the physical environment be known or pre-scanned prior to use to then generate the corresponding virtual scene, thus restricting the virtual experience to a controlled space. In this paper, we present VRoamer, which enables users to walk unseen physical spaces for which VRoamer procedurally generates a virtual scene on-the-fly. Scaling to the size of office buildings, VRoamer extracts walkable areas and detects physical obstacles in real time, instantiates pre-authored virtual rooms if their sizes fit physically walkable areas or otherwise generates virtual corridors and doors that lead to undiscovered physical areas. The use of these virtual structures allows VRoamer to (1) temporarily block users' passage, thus slowing them down while increasing VRoamer's insight into newly discovered physical areas, (2) prevent users from seeing changes beyond the current virtual scene, and (3) obfuscate the appearance of physical environments. VRoamer animates virtual objects to reflect dynamically discovered changes of the physical environment, such as people walking by or obstacles that become apparent. In our proof-of-concept study, participants were able to walk long distances through a procedurally generated dungeon experience and reported high levels of immersion.

Short-term load prediction is important for demand side management at a distribution system. Accurate Load prediction for the distribution system operation is challenging due to the complicated load characteristics and numerous influence factors. In this paper a new hybrid load predicting strategy with input selection is introduced to improve the forecasting performance. The hybrid forecasting method contains a seasonal autoregressive integrated moving average function and a neural network (SARIMA-NN). The input selection aims to find the history days which has similar load curve as the forecasted day based on a heat index criteria (HI-SD), and the input variables are chosen by the factor affecting degree on different forecasted days. This novel strategy captures distinct load characteristics at different climate level, considering the effectively similarities between load days, choosing accurately input variables, and shows a great forecasting performance as demonstrated by a practical substation datasets.

We present a method of inspecting surface defects of ring magnets by using deep learning technology, and the inspection system developed utilizing this method has achieved much better accuracy and speed than human inspectors in actual production environment, while such accuracy and speed are essential for such systems. The proposed method can also be used for the surface defect inspection of many other industrial products and systems.

Improving the spectroscopic properties of rare earth (RE) doped glass materials is a challenging task. In the present work the metallic silver nanoparticles (Ag NPs) were embedded into Er 3+ /Yb 3+ codoped tellurite glasses with composition TeO 2 –Bi 2 O 3 –TiO 2 , prepared using melt-quenching and subsequent heat-treated techniques, and the improved effect of Ag NPs on the 1.53 μm band fluorescence of Er 3+ ions was investigated. About 24 h heat-treatment of Er 3+ /Yb 3+ codoped tellurite glass containing 1 mol % amount of AgNO 3 at the temperature 370 °C yielded the well-dispersed and near-spherical Ag NPs with ∼11.4 nm average diameter as evidenced by transmission electron microscopy (TEM) image. The intense 1.53 μm band fluorescence was observed in the prepared Er 3+ /Yb 3+ codoped tellurite glasses under the excitation of 980 nm and was further improved with the presence of Ag NPs in the glass matrix, which is attributed to the enhanced local electric field around doped RE ions induced by Ag NPs and the possible energy transfer from Ag NPs to Er 3+ ions. The enhanced local electric field was well demonstrated by comparing the variation of emission spectra of hypersensitive probe Eu 3+ ions in tellurite glasses with and without Ag NPs. From the Judd-Ofelt analysis, it was also found that the value of Ω 6 intensity parameter increased slightly with the increase of Ag NPs concentration in a certain range, also confirming the possibility of realizing strong fluorescence emission. In addition, the amorphous structural nature was demonstrated by the measured X-ray diffraction (XRD) patterns with no sharp diffraction peak. The enhanced 1.53 μm band fluorescence indicates that the Er 3+ /Yb 3+ codoped tellurite glass with an appropriate amount of Ag NPs is a promising candidate for the development of Er 3+ -doped fiber amplifiers (EDFAs) applied in the WDM systems.

The soil ground with low moisture content has the mechanical properties of low viscosity and high friction, which have a great influence on the traveling of a tracked vehicle. In this paper, a movement model of the rigid track on low moisture soil is established based on the discrete element method (DEM) simulation. The soil simulation model was verified by the triaxial compression test. The traction simulation of the track under different vertical stress was carried out, and the traction performance of the track was analyzed by combining with the results of the soil bin test. The analysis shows that the tractive effort increases with the increase in vertical stress. The tractive effort distribution of the track is basically the same as the shape of the bottom of the track, and the tractive effort on both sides of the track cannot be ignored. The average error of tractive effort in simulation is 3.94%. DEM simulation can reproduce the mechanical properties and the discontinuous nature of low moisture soil particles under dynamic load, which is suitable for the numerical study of the interaction between the track and soil.

Although virtual reality hardware is now widely available, the uptake of real walking is hindered by the fact that it requires often impractically large amounts of physical space. To address this, we present VirtualSpace, a novel system that allows overloading multiple users immersed in different VR experiences into the same physical space. VirtualSpace accomplishes this by containing each user in a subset of the physical space at all times, which we call tiles; app-invoked maneuvers then shuffle tiles and users across the entire physical space. This allows apps to move their users to where their narrative requires them to be while hiding from users that they are confined to a tile. We show how this enables VirtualSpace to pack four users into 16m2. In our study we found that VirtualSpace allowed participants to use more space and to feel less confined than in a control condition with static, pre-allocated space.

We present a system that complements virtual reality experiences with passive props, yet still allows modifying the virtual world at runtime. The main contribution of our system is that it does not require any actuators; instead, our system employs the user to reconfigure and actuate otherwise passive props. We demonstrate a foldable prop that users reconfigure to represent a suitcase, a fuse cabinet, a railing, and a seat. A second prop, suspended from a long pendulum, not only stands in for inanimate objects, but also for objects that move and demonstrate proactive behavior, such as a group of flying droids that physically attack the user. Our approach conveys a sense of a living, animate world, when in reality the user is the only animate entity present in the system, complemented with only one or two physical props. In our study, participants rated their experience as more enjoyable and realistic than a corresponding no-haptics condition.

Human actuation is the idea of using people to provide large-scale force feedback to users. The Haptic Turk system, for example, used four human actuators to lift and push a virtual reality user; TurkDeck used ten human actuators to place and animate props for a single user. While the experience of human actuators was decent, it was still inferior to the experience these people could have had, had they participated as a user. In this paper, we address this issue by making everyone a user. We introduce mutual human actuation, a version of human actuation that works without dedicated human actuators. The key idea is to run pairs of users at the same time and have them provide human actuation to each other. Our system, Mutual Turk, achieves this by (1) offering shared props through which users can exchange forces while obscuring the fact that there is a human on the other side, and (2) synchronizing the two users' timelines such that their way of manipulating the shared props is consistent across both virtual worlds. We demonstrate mutual human actuation with an example experience in which users pilot kites though storms, tug fish out of ponds, are pummeled by hail, battle monsters, hop across chasms, push loaded carts, and ride in moving vehicles.

We explore how to add haptics to walls and other heavy objects in virtual reality. When a user tries to push such an object, our system actuates the user's shoulder, arm, and wrist muscles by means of electrical muscle stimulation, creating a counter force that pulls the user's arm backwards. Our device accomplishes this in a wearable form factor. In our first user study, participants wearing a head-mounted display interacted with objects provided with different types of EMS effects. The repulsion design (visualized as an electrical field) and the soft design (visualized as a magnetic field) received high scores on "prevented me from passing through" as well as "realistic". In a second study, we demonstrate the effectiveness of our approach by letting participants explore a virtual world in which all objects provide haptic EMS effects, including walls, gates, sliders, boxes, and projectiles.

We propose a class of passive haptics that we call Sparse Haptic Proxy: a set of geometric primitives that simulate touch feedback in elaborate virtual reality scenes. Unlike previous passive haptics that replicate the virtual environment in physical space, a Sparse Haptic Proxy simulates a scene's detailed geometry by redirecting the user's hand to a matching primitive of the proxy. To bridge the divergence of the scene from the proxy, we augment an existing Haptic Retargeting technique with an on-the-fly target remapping: We predict users' intentions during interaction in the virtual space by analyzing their gaze and hand motions, and consequently redirect their hand to a matching part of the proxy. We conducted three user studies on haptic retargeting technique and implemented a system from three main results: 1) The maximum angle participants found acceptable for retargeting their hand is 40°, with an average rating of 4.6 out of 5. 2) Tracking participants' eye gaze reliably predicts their touch intentions (97.5%), even while simultaneously manipulating the user's hand-eye coordination for retargeting. 3) Participants preferred minimized retargeting distances over better-matching surfaces of our Sparse Haptic Proxy when receiving haptic feedback for single-finger touch input. We demonstrate our system with two virtual scenes: a flight cockpit and a room quest game. While their scene geometries differ substantially, both use the same sparse haptic proxy to provide haptic feedback to the user during task completion.