Self-aerated free-surface flow studies have a more recent history compared to classical fluid dynamics. Traditional velocimetry techniques are adversely affected by the presence of gas–liquid interfaces. In the present study, detailed air-water flow measurements were performed in a highly turbulent free-surface flow, and three velocimetry approaches were applied: (a) centreline dual-tip phase-detection needle probe measurements at all step edges downstream of the inception location of free-surface aeration; (b) Optical Flow (OF) data based upon ultra-high-speed video movies through the left sidewall; and (c) Optical Flow (OF) data based upon ultra-high-speed video movies overlooking the self-aerated flow, in a direction normal to the pseudo-bottom formed by the staircase profile. The study was conducted in a steep channel and three stepped invert geometries were tested. The results highlighted both advantages and limitations of the three complementary metrologies in free-surface flows with strong turbulence. The dual-tip phase-detection probe delivered reliable interfacial velocity data, but in the form of point measurements. The sideview OF technique provided a great level of details of the cavity recirculation and shear zone between mainstream and cavity, but the data were unreliable for void fractions>0.30 and only limited to the sidewall region. The top view OF technique characterised the surface velocity field across the entire chute width, highlighting the occurrence of three-dimensional air-water surface patterns. One observed limitation of the OF was the requirements of a high frame rate (i.e. 10,000 fps or more) and high-quality light source. Overall, these measurement techniques provided complementary results for a better understanding of the physical behaviour of highly turbulent multiphase flows on stepped channels.

Highly turbulent free-surface flows are characterised by complex and rapidly varying air-water surface features, leading to enhanced surface roughness, breakup and disintegration processes. Such a strong free-surface turbulence has an impact on a number of environmental flows, and a deeper understanding of its physical nature is fundamental. Unsteady breaking bores are of particular interest because of their recirculating motion, with large air entrainment and splashes, resulting in highly fluctuating and rapidly varying free-surface flows. Herein, new methodologies and innovative approaches are used in support of a deeper understanding of the physical processes within a breaking roller, inclusive of a comprehensive assessment of its free-surface dynamics. Because of the unsteadiness of the flow, multiple repetitions were necessary and all results were based upon an ensemble statistical analysis. Ultra-high-speed videos recorded from both top and side views allowed for a detailed characterisation of the roller's free surface, providing a description and classification of the most recurring air-water surface features. A quantification of their main properties in terms of geometry, duration and frequency of appearance revealed an evolution of these features during their lifespans. In parallel, the use of optical flow techniques provided a characterisation of the surface velocity fields, yielding information on the free-surface kinematic properties and revealing a strong link between air-water surface features, energy dissipation and time/length scales.

Obtaining a tiny focal spot is desired for super resolution. We do a vectorial numerical analysis of the linearly, circularly, and radidally polarized electromagnetic fields being focused through a dielectric micro/nanoparticle of size comparable to the wavelength. We find tiny focal spots (up to ∼ 0.05 λ²) can be obtained behind micro/nanoparticles of various shapes, e.g. spherical, disk-shaped, and cuboid micro/nanoparticles. Furthermore, we also investigate the influence of the misalignment of a real lens system on the tiny focal spots. We find that tiny focal spots can still be generated even though they are distorted due to the misalignment.

A detailed investigation on photoluminescence properties and energy transfer (ET) dynamics of Ce³⁺, Pr³⁺-doped BaY₂Si₃O₁₀ is provided along with the potential X-ray excited luminescence application. The luminescence properties of Pr³⁺ are studied in VUV-UV-vis spectral range at low temperature, and the spectral profiles of Pr^{3+ 3}P₀ and ¹D₂ emission lines are determined using time-resolved emission spectra. Upon 230 nm excitation, the electron population from Pr³⁺ 4f5d state to its 4f² excited state is discussed in detail. As Pr³⁺ concentration rises, Pr^{3+ 3}P₀ and ¹D₂ luminescence possess different concentration-related properties. The incorporation of Ce³⁺ in the codoped sample produces the strong Ce³⁺ luminescence under 230 nm excitation, which is the combined result of Pr³⁺ 4f5d → Ce³⁺ 5d ET and Ce³⁺ intrinsic excitation. On the other hand, the increasingly strong ET of Ce³⁺ 5d → Pr³⁺ 4f² results in the decrease of Ce³⁺ emission intensity and the gradual deviation of Ce³⁺ luminescence decay from the single exponential in the system. By employing the Inokuti-Hirayama model, the dipole-dipole interaction is confirmed as the predominant multipolar effect in controlling this ET process, and the value of C_DA is determined to be 9.97 × 10^-47 m⁶·s^-1. Finally, the relatively low scintillation light yield of Ce³⁺-doped BaY₂Si₃O₁₀ material impedes its application potential in the scintillator field, and the cosubstitution of Pr³⁺ results in the observable decline of scintillation performance.

A series of Ce³⁺-doped (Ca,Sr)₂Al₂SiO₇ phosphors with different Ce³⁺ and Ca²⁺/Sr²⁺ concentrations were prepared by a high temperature solid-state reaction technique. To get insight into the structure-luminescence relationship, the impact of incorporation of Sr²⁺ on structure of (Ca,Sr)₂Al₂SiO₇ was first investigated via Rietveld refinement of high quality X-ray diffraction (XRD) data, and then the VUV-UV excitation and UV-vis emission spectra of (Ca,Sr)₂Al₂SiO₇:Ce³⁺ were collected at low temperature. The results reveal that the crystal structure evolution of (Ca,Sr)₂Al₂SiO₇:Ce³⁺ has influences on band gaps and Ce³⁺ luminescence properties including 4f-5d_i (i = 1-5) transition energies, radiative lifetime, emission intensity, quantum efficiency, and thermal stability. Moreover, the influence of Sr²⁺ content on the energy of Eu³⁺-O^2- charge-transfer states (CTS) in (Ca,Sr)₂Al₂SiO₇:Eu³⁺ was studied in order to construct vacuum referred binding energy (VRBE) schemes with the aim to further understand the luminescence properties of (Ca,Sr)₂Al₂SiO₇:Ce³⁺. Finally, X-ray excited luminescence (XEL) spectra were measured to evaluate the possibility of (Ca,Sr)₂Al₂SiO₇:Ce³⁺ as a scintillation material.

In this work, we demonstrate a potential thermometric material after systematic studies on the concentration/temperature-dependent spectroscopic properties of Pr³⁺ excited multiplets and of the Pr³⁺-Ti⁴⁺ intervalence charge transfer (IVCT) state in (La_1-xPr_x)₂MgTiO₆. The experimental results indicate that the electron population efficiency between the involved Pr³⁺ 4f multiplets is directly governed by multi-phonon relaxation (MPR) and cross relaxation (CR), and the IVCT state provides an additional contribution to the ¹D₂ luminescence. A schematic energy level diagram is proposed to illustrate the electron population pathway in Pr³⁺ doped La₂MgTiO₆. The observations clarify that the dramatic thermal-quenching of ³P₀ luminescence is mainly induced by the electronic configuration crossover between the ³P₀ multiplet and the IVCT state. On the other hand, the ¹D₂ luminescence possesses an excellent thermal stability in a large temperature region. These temperature sensing features of the Pr³⁺ doped La₂MgTiO₆ material indicate its potential application in optical thermometric techniques.