Effect of sintering temperature on luminescence properties of borosilicate matrix blue–green emitting color conversion glass ceramics

The color conversion glass ceramics which were made of borosilicate matrix co-doped(SrBaSm)Si2O2N2:(Eu^3+Ce^3+) blue-green phosphors were prepared by two-step method in co-sintering. The change in luminescence properties and the drift of chromaticity coordinates(CIE) of the(SrBaSm)Si2O2N2:(Eu^3+Ce^3+) blue-green phosphors and the color conversion glass ceramics were studied in the sintering temperature range from 600℃ to 800℃. The luminous intensity and internal quantum yield(QY) of the blue-green phosphors and glass ceramics decreased with the sintering temperature increasing. When the sintering temperature increased beyond 750℃, the phosphors and the color conversion glass ceramics almost had no peak in photoluminescence(PL) and excitation(PLE) spectra. The results showed that the blue-green phosphors had poor thermal stability at higher temperature. The lattice structure of the phosphors was destroyed by the glass matrix and the Ce^3+ in the phosphors was oxidized to Ce^4+, which further caused a decrease in luminescent properties of the color conversion glass ceramics.

Asymptotic solutions of the flow of a Johnson-Segalman fluid through a slowly varying pipe using double perturbation strategy

A double perturbation strategy is presented to solve the asymptotic solutions of a Johnson-Segalman （J-S） fluid through a slowly varying pipe. First, a small parameter of the slowly varying angle is taken as the small perturbation parameter, and then the second-order asymptotic solution of the flow of a Newtonian fluid through a slowly varying pipe is obtained in the first perturbation strategy. Second, the viscoelastic parameter is selected as the small perturbation parameter in the second perturbation strategy to solve the asymptotic solution of the flow of a J-S fluid through a slowly varying pipe. Finally, the parameter effects, including the axial distance, the slowly varying angle, and the Reynolds number, on the velocity distributions are analyzed. The results show that the increases in both the axial distance and the slowly varying angle make the axial velocity slow down. However, the radial velocity increases with the slowly varying angle, and decreases with the axial distance. There are two special positions in the distribution curves of the axial velocity and the radial velocity with different Reynolds numbers, and there are different trends on both sides of the special positions. The double perturbation strategy is applicable to such problems with the flow of a non-Newtonian fluid through a slowly varying pipe.

Active control of flow past an elliptic cylinder using an artificial neural network trained by deep reinforcement learning

The active control of flow past an elliptical cylinder using the deep reinforcement learning(DRL)method is conducted.The axis ratio of the elliptical cylinderΓvaries from 1.2 to 2.0,and four angles of attackα=0°,15°,30°,and 45°are taken into consideration for a fixed Reynolds number Re=100.The mass flow rates of two synthetic jets imposed on different positions of the cylinderθ1andθ2are trained to control the flow.The optimal jet placement that achieves the highest drag reduction is determined for each case.For a low axis ratio ellipse,i.e.,Γ=1.2,the controlled results atα=0°are similar to those for a circular cylinder with control jets applied atθ1=90°andθ2=270°.It is found that either applying the jets asymmetrically or increasing the angle of attack can achieve a higher drag reduction rate,which,however,is accompanied by increased fluctuation.The control jets elongate the vortex shedding,and reduce the pressure drop.Meanwhile,the flow topology is modified at a high angle of attack.For an ellipse with a relatively higher axis ratio,i.e.,Γ1.6,the drag reduction is achieved for all the angles of attack studied.The larger the angle of attack is,the higher the drag reduction ratio is.The increased fluctuation in the drag coefficient under control is encountered,regardless of the position of the control jets.The control jets modify the flow topology by inducing an external vortex near the wall,causing the drag reduction.The results suggest that the DRL can learn an active control strategy for the present configuration.

Dynamic study of compressed electron layer driven by linearly polarized laser

The dynamics of the compressed electron layer（CEL） are investigated when a linearly polarized（LP） laser pulse irradiates a plasma target. The turbulent motion of the CEL is investigated by a simple model, which is verified by particlein-cell（PIC） simulations. It is found that the compressed layer disperses in a few cycles of the laser duration, because the CEL comes back with a large velocity in the opposite direction of the laser incident. A larger wavelength laser can be used to tailor the proton beam by reducing the turbulence of the CEL in the region of the LP laser acceleration.

Effect of different bending shapes on thermal properties of flexible light-emitting diode filament

Heat dissipation is an important part of light-emitting diode(LED)filament research and has aroused constant concern.In this paper,we studied the thermal performance of flexible LED filament by numerical simulation and through experiment.The heat dissipation characteristics of spring-like structure flexible LED filament were computed by finite volume method,and it was found that the chip junction temperature was closely related to the pitch and the bending radius.The effect of inclination angle of lighting LED filament was discussed because it is relevant to the spring-like structure flexible LED filament in geometry.The results demonstrated that the temperature of the filament increases as the inclination angle improves.

Scale properties of turbulent transport and coherent structure in stably stratified flows

The empirical mode decomposition （EMD） is used to study the scale properties of turbulent transport and coherent structures based on velocity and temperature time series in stably stratified turbulence. The analysis is focused on the scale properties of intermittency and coherent structures in different modes and the contributions of energy-contained coherent structures to turbulent scalar counter-gradient transport （CGT）. It is inferred that the velocity intermittency is scattered to more modes with the development of the stratified flow, and the intermittency is enhanced by the vertical stratification, especially in small scales. The anisotropy of the field is presented due to different time scales of coherent structures of streamwise and vertical velocities. There is global counter-gradient heat transport close to the turbulence-generated grid, and there is local counter-gradient heat transport at certain modes in different positions. Coherent structures play a principal role in the turbulent vertical transport of temperature.

Polarization manipulation of bright-dark vector bisolitons

We simulate the polarization manipulation of bright-dark vector bisolitons at 1-µm wavelength regime.Through changing the pulse parameters,different kinds of pulse shapes and optical spectra are generated in output orthogonal polarization directions.When the input vector bisoliton is polarization-locked with 1064 nm central wavelength,“1+1”fundamental dark-dark and“2+1”pseudo-high-order bright-dark group-velocity-locked vector solitons can be achieved through changing the projection angle.When the input vector bisoliton is group-velocity-locked with 1063 nm and 1065 nm central wavelengths,“2+1”and“2+2”pseudo-high-order bright-dark group-velocity-locked vector solitons,bright-dark group-velocity-locked vector solitons with chirp-like temporal oscillations are generated.Our simulation results can provide beneficial conduct for polarization manipulation of vector multi-solitons,and have promising applications in quantum information register,optical communications,nanophotonics,and all-optical switching.

Multidimensional Stability of Subsonic Phase Transitions in a Non-Isothermal Van Der Waals Fluid

We show the multidimensional stability of subsonic phase transitions in a non-isothermal van der Waals fluid. Based on the existence result of planar waves in our previous work [1], a jump condition is posed on non-isothermal phase boundaries which makes the argument possible. Stability of planar waves both in one dimensional and multidi-mensional spaces are proved.

Pulse shaping of bright-dark vector soliton pair

We simulate pulse shaping of bright-dark vector soliton pair in an optical fiber system.Through changing input pulse parameters(amplitude ratio,projection angle,time delay,and phase difference),different kinds of pulse shapes and spectra can be generated.For input bright-dark vector soliton pair with the same central wavelength,“2+1”-and“2+2”-type pseudo-high-order bright-dark vector soliton pairs are achieved.While for the case of different central wavelengths,bright-dark vector soliton pairs with multiple pulse peaks/dips are demonstrated with appropriate pulse parameter setting.

Optical properties of wavelength-tunable green-emitting color conversion glass ceramics

Color conversion glass ceramics are prepared by cosintering borosilicate glass frits and green 0.06Ce：Y2.94（Al1-xGax）5O12 phosphors. The crystal structures, the influence of Ga concentration on the photoluminescence （PL）, and reliability properties of the color conversion glass ceramics are investigated. The PL emission wavelengths of 0.06Ce：Y2.94（Al1-xGax）5O12 glass ceramics show blue shift from 545 nm to 525 nm with increasing Ga content （x value） under excited at 460 nm. Reliability test results show that the quantum yield （QY） of 0.06Ce：Y2.94（Al1-xGax）5O12 glass ceramics decreases from 70.60% to 59.06% with x value increasing from 0.15 to 0.35 under the ambient condition of 85℃/RH85% for the exposure time of 168 h. And the quantum yield （QY） of 0.06Ce：Y2.94（Al1-xGax）5O12 glass ceramics decreases from 65.13% to 52.23% after being soaked into boiled water for 4 h. The finding reveals that the addition of Ga can deteriorate the reliability of the color conversion glass ceramics.

Behavioral Decision-Making of Key Stakeholders in Public-Private Partnerships:A Hybrid Method and Benefit Distribution Study

Public-private partnerships(PPPs)have been used by governments around the world to procure and construct infrastructural amenities.It relies on private sector expertise and funding to achieve this lofty objective.However,given the uncertainties of project management,transparency,accountability,and expropriation,this phenomenon has gained tremendous attention in recent years due to the important role it plays in curbing infrastructural deficits globally.Interestingly,the reasonable benefit distribution scheme in a PPP project is related to the behavior decisionmaking of the government and social capital,aswell as the performance of the project.In this paper,the government and social capital which are the key stakeholders of PPP projects were selected as the research objects.Based on the fuzzy expected value model and game theory,a hybrid method was adopted in this research taking into account the different risk preferences of both public entities and private parties under the fuzzy demand environment.To alleviate the problem of insufficient utilization of social capital in a PPP project,this paper seeks to grasp the relationship that exists between the benefit distribution of stakeholders,their behavioral decision-making,and project performance,given that they impact the performance of both public entities and private parties,as well as assist in maximizing the overall utility of the project.Furthermore,four game models were constructed in this study,while the expected value and opportunity-constrained programming model for optimal decision-making were derived using alternate perspectives of both centralized decision-making and decentralized decision-making.Afterward,the optimal behavioral decision-making of public entities and private parties in four scenarios was discussed and thereafter compared,which led to an ensuing discussion on the benefit distribution system under centralized decision-making.Lastly,based on an example case,the influence of different confidence levels,price,and fuzzy uncertainties of PPP projects on the equilibrium strategy results of both parties were discussed,giving credence to the effectiveness of the hybrid method.The results indicate that adjusting different confidence levels yields different equilibriumpoints,and therefore signposts that social capital has a fair perception of opportunities,as well as identifies reciprocal preferences.Nevertheless,we find that an increase in the cost coefficient of the government and social capital does not inhibit the effort of both parties.Our results also indicate that a reasonable benefit distribution of PPP projects can assist them in realizing optimum Pareto improvements over time.The results provide us with very useful strategies and recommendations to improve the overall performance of PPP projects in China.

Effects of density profile and multi-species target on laser-heated thermal-pressure-driven shock wave acceleration

The shock wave acceleration of ions driven by laser-heated thermal pressure is studied through one-dimensional particle-in-cell simulation and analysis. The generation of high-energy mono-energetic protons in recent experiments （D. Haberberger et al., 2012 Nat. Phys. 8 95） is attributed to the use of exponentially decaying density profile of the plasma target. It does not only keep the shock velocity stable but also suppresses the normal target normal sheath acceleration. The effects of target composition are also examined, where a similar collective velocity of all ion species is demonstrated. The results also give some reference to future experiments of producing energetic heavy ions.

Composition and structure design of three-layered composite phosphors for high color rendering chip-on-board light-emitting diode devices

A three-layered phosphor structure was designed and prepared by the spin coating of BaSi_(2)N_(2)O_(2):Eu(cyan-emitting)and(Sr,Ca)AlSiN_(3):Eu(red-emitting)phosphor films on the yellowemitting Y_(3)Al_(5)O_(12):Ce(YAG:Ce)phosphor ceramic synthesized by the solid-state reaction under vacuum sintering.In order to achieve high color rendering lighting,the influence of the composition and structure of the three-layered phosphors on the optical,thermal,and electrical properties of the chip-on-board(COB)packaged white-light-emitting diodes(WLEDs)was studied systematically.The WLED with the structure of“red+cyan+yellow”(R+C+Y)three-layered phosphor generated neutral white light and had a luminous efficacy of 75 lm/W,the fidelity index(R_(f))of 93,the gamut index(R_(g))of 97,and the correlated color temperature(CCT)of 3852 K.Under the excitation of laser diode(LD),the layer-structured phosphor yielded the white light with a luminous efficacy of 120 lm/W,color rendering index(CRI)of 90,and CCT of 5988 K.The result indicates that the three-layered phosphor structure is a promising candidate to achieve high color rendering and high luminous efficacy lighting.

Development of optical-thermal coupled model for phosphor-converted LEDs

In this review, first, we discussed the effect of phosphor features on optical properties by the software simulation in detail. A combination of these parameters: phosphor material, phosphor particle size and particle distribution, phosphor layer concentration, phosphor layer thickness, geometry, and location of the phosphor layer, will result in the final optical performance of the phosphor layer. Secondly, we introduced how to improve light extraction efficiency with various proposed methods. Thirdly, we summarized the thermal models to predict the phosphor temperature and the junction temperature. To stabilize the optical performance of phosphor-converted light emitting diodes (PC-LEDs), much effort has been made to reduce the junction temperature of the LED chips. The phosphor temperature, a critical reliability concern for PC-LEDs, should be attracted academic interest. Finally, we summed up optical-thermal coupled model for phosphors and summarized future optical- thermal issues exploring the light quality for LEDs. We foresee that optical-thermal coupled model for PC-LEDs should be paid more attention in the future.

Analysis of temperature time series based on Hilbert-Huang Transform

In this paper, with consideration of the nonlinear and non-stationary properties of the temperature time series, we employ the Hilbert-Huang Transform, based on the empirical mode decomposition（EMD）, to analyze the temperature time series from 1959 to 2012 in the Fengxian district of Shanghai, obtained from a certain monitoring station. The oscillating mode is drawn from the data, and its characteristics of the time series are investigated. The results show that the intrinsic modes of 1, 2 and 6 represent the periodic properties of 1 year, 2.5 years, and 27 years. The mean temperature shows periodic variations, but the main trend of this fluctuation is the rising of the temperature in the recent 50 years. The analysis of the reconstructed modes with the wave pattern shows that the variations are quite large from 1963 to 1964, from 1977 to 1982 and from 2003 to 2006, which indicates that the temperature rises and falls dramatically in these periods. The volatility from 1993 to 1994 is far more dramatic than in other periods. And the volatility is the most remarkable in recent 50 years. The log-linear plots of the mean time scales T and M show that each mode associated with a time scale almost twice as large as the time scale of the preceding mode. The Hilbert spectrum shows that the energy is concentrated in the range of low frequency from 0.05 to 0.1 Hz, and a very small amount of energy is distributed in the range of higher frequency over 0.1 Hz. In conclusion, the HHT is better than other traditional signal analysis methods in processing the nonlinear signals to obtain the periodic variation and volatility＇s properties of different time scales.

EFFECT OF SWEEP AND EJECTION EVENTS ON PARTICLE DISPERSION IN WALL BOUNDED TURBULENT FLOWS

This paper studies the sweep and ejection events in a channel flow with Reτ = 80 by using Direct Numerical Simulation （DNS）. The effects of ejection and sweep events on the transport of fluid particles are analyzed separately through a quadrant technique. By analyzing trajectories of the particles released at different wall-normal locations, it is found that the particles from the ejection events mainly move upward while the particles from the sweep events move downward of the flow during short and intermediate diffusion time durations. Numerical results show that the effects of the ejection and sweep events on the mean displacement and the mean square dispersion remain for a long time, one-order of magnitude larger than the streamwise Lagrangian integral ~cales.

Continuity of functors with respect to generalized inductive limits

Let(Ai,φi,i+1) be a generalized indue Live system of a sequeiiee (Ai) of unital separable C^*-algebras,with A =limi→∞(Ai,φi,i+1). Set φj,i=φi-1,i^0…0φj+1,j+2^0 φj,j+1 for all i>j. We prove that if φj,i are order zero completely positive contractions for all j and i>j, And L:=inf{λ|λ∈σ(φj,i(1Aj)) for all j uud i>j}>0, where σ(φj,i(1Aj)) is the speetrum of φj,i(1Aj),than limi→∞(Cu(Ai),Cu((φi,i+1))=Cu(A), where Cu(A) is a stable version of the Cuntz semigroup of C^*-algebra A. Let (An,φm,n) be a generalized inductive syfitem of C^*-algahrafl, with the ipmkn order zero completely positive contractions. We also prove that if the decomposition rank (nuclear dimension) of ,4n is no more t han some integer k for each n, then the decompostition rank (nuclear dimension) of A is also no more than k.

Scale analysis of turbulent channel flow with varying pressure gradient

In this paper orthogonal wavelet transformations are applied to decompose experimental velocity signals in fully develo-ped channel flows with varying pressure gradient into scales. We analyze the time series from turbulent data, to obtain the statistical characteristics, correlations between the adjacent scales and the principal scale of coherent structures in different scales by wavelet transformations. The results show that, in the counter gradient transport （CGT） region, skewness factors and flatness factors deviate strongly from the corresponding values of Gaussian distribution on certain scales. PDFs on each scale confirm this observation. Scale-scale correlations show further that the fluctuations on some certain special scales are more intermittent than nearby. Principal scale of coherent structure is coincident with the scales on which the statistical properties depart from Gaussian distribution. These features are the same for different families of wavelets, and it also shows some different features in the region between favorable pressure gradient and adverse pressure gradient.

Evolution of vortex structure around a wall-mounted rough hemisphere

In this paper,the large eddy simulation(LES)method is used to calculate Reynolds numbers the range in the range of 3000–30000(based on the diameter of the hemisphere D),and then the statistical analysis method is used to study the influence of Re on the characteristics of the flow field around the rough hemisphere and the evolution law of the tail vortex.The effect of the Reynolds number on the structure of the rough hemisphere flow field and the evolution of vortex structure is studied by vorticity distribution,POD method,and correlation analysis.It can be observed that with the increase of Reynolds number,the shear in the recirculating region of the rough hemisphere is enhanced,the large-scale structure is reduced,the small-scale structure is increased,and the angle between the hairpin vortex and the wall is reduced.λ_(ci)vortex identification and the Q-criterion are used to capture the evolution of a periodic vortex structure.Q-criterion gives the three-dimensional vortex structure behind the hemispherical flow.It is found that the horseshoe vortex and arch vortex generated by the incoming flow after passing through the hemisphere will interact with the wall surface to form a hairpin vortex,and the hairpin vortex structure will continue to evolve downstream to form a new vortex structure.

Scaling of maximum probability density function of velocity increments in turbulent Rayleigh-Bénard convection

In this paper, we apply a scaling analysis of the maximum of the probability density function（pdf） of velocity increments, i.e., max（） = max（）up p u, for a velocity field of turbulent Rayleigh-Bénard convection obtained at the Taylor-microscale Reynolds number Re60. The scaling exponent is comparable with that of the first-order velocity structure function, （1）, in which the large-scale effect might be constrained, showing the background fluctuations of the velocity field. It is found that the integral time T（x/ D） scales as T（x/ D）（x/ D）, with a scaling exponent =0.25 0.01, suggesting the large-scale inhomogeneity of the flow. Moreover, the pdf scaling exponent （x, z） is strongly inhomogeneous in the x（horizontal） direction. The vertical-direction-averaged pdf scaling exponent （x） obeys a logarithm law with respect to x, the distance from the cell sidewall, with a scaling exponent 0.22 within the velocity boundary layer and 0.28 near the cell sidewall. In the cell＇s central region, （x, z） fluctuates around 0.37, which agrees well with （1） obtained in high-Reynolds-number turbulent flows, implying the same intermittent correction. Moreover, the length of the inertial range represented in decade（）IT x is found to be linearly increasing with the wall distance x with an exponent 0.65 0.05.