Hydrodynamic instability of the axisymmetric flow of an ideal fluid with an interphase

We study the instability under simultaneous rotational and translational flow of a fluid and ambient medium in the cases of a cylindrical annular jet, capillary jet, and cylindrical fluid layers on the inner and outer surfaces of a cylinder.     

论矿石产品二氧化硅的检测方法

随着科技的不断发展和进步,检测矿石产品二氧化硅的方法也在不断的更新和完善。下面就矿石产品二氧化硅的两种检测方法进行了详细介绍,并对检测过程中需要注意的有关问题进行了分析和探讨。     

Time-resolved luminescence from annealed quartz

The influence of annealing on the lifetime and luminescence intensity has been studied in quartz annealed at 873, 1073, 1173, and 1273 K and in unannealed quartz. Luminescence was stimulated by pulsed green (525 nm) light. Luminescence intensity increased as a function of temperature from 293 K to a peak at 373 K, and decreased thereafter to 473 K, the maximum temperature in the investigations. Luminescence lifetimes from both unannealed quartz and samples annealed at 873 K for up to 5 min were constant at about 40 micros below 373 K. Lifetimes decreased strictly monotonically with temperature in samples annealed above 873 K. Values of the activation energy for thermal assistance accounting for the increase in luminescence intensity, and of thermal quenching describing the decrease of luminescence intensity and luminescence lifetimes are presented.     

Alkali-silica reaction products: Comparison between samples from concrete structures and laboratory test specimens

Alkali-silica gels (ASG) were investigated in concrete from bridge structures (constructed from the 1920s to 2000), as well as in experimental specimens; employing optical microscopy, petrographic image analysis, and scanning electron microscopy combined with energy dispersive spectroscopy (SEM/EDS). The main differences were found in the chemical composition and morphology of the ASGs. ASGs which had formed in older concrete samples (50–80 years old) show a partly crystalline structure and higher Ca²⁺ content, indicating their aging and maturation. Younger concrete samples and experimental test specimens exhibit the presence of amorphous ASG. The chemistry of ASG from experimental specimens reflects the chemical composition of accelerating solutions.     

Time resolved luminescence of quartz from Nigeria

Characteristics of luminescence lifetimes and luminescence intensity obtained from time resolved spectra of quartz from Nigeria are presented. The luminescence was pulse-stimulated at 11 μs width at 470 nm. Samples used consisted of unannealed quartz as well as samples annealed at 500 °C, 600 °C, 700 °C, 800 °C and 900 °C. The luminescence lifetimes and luminescence intensities were studied as a function of annealing temperature, irradiation dose and measurement temperature. It was found that there is a decrease, although non-monotonic, in the luminescence lifetime with change in annealing temperature from 20 to 900 °C. In addition, lifetimes extracted from time resolved spectra of unannealed samples as well as ones annealed at 500 °C and 600 °C are initially independent of irradiation dose but do later decrease with further irradiation. Regarding the luminescence intensity it was observed that in general, the intensity passes through a peak as the measurement temperature is increased from 20 to 200 °C with slight differences in the detailed pattern dependent on preheating. Activation energies for thermal quenching and thermal assistance evaluated from temperature-dependent changes of luminescence lifetime and luminescence intensity are given. The results are discussed in terms of a model consisting of three luminescence centres with probability of hole trapping during irradiation being highest for the luminescence centre associated with the least lifetime.     

Convective instability in a two-layer system with an interfacial reaction

Linear analysis of convective stability was carried out for a system with two liquid layers of finite thickness in the presence of the concentration-capillary effect and a second-order interfacial reaction. It was assumed that the surface tension at the liquid-liquid interface depends on the concentrations of the reaction components.Translated from InzhenernoFizicheskii, Zhurnal, Vol. 58, No. 6, pp. 972–979, June, 1990.     

A charged-particle spectrometer for measuring neutron-induced reaction products

We describe a spectrometer consisting of plastic scintillators and multiwire proportional counters which is suitable to measure light charged particles from neutron-induced reactions at forward angles. The performance of the spectrometer is demonstrated in the case of a measurement of the n-p capture cross section at E_n = 25 MeV.     

不同温度下硒化镉(CdSe)量子点的生长及荧光性研究

研究了以氧化镉（CdO）和硒（Se）粉为前驱体,在三辛基膦（TOP）和油酸中合成无机半导体量子点（quantum dots, QDs）CdSe.研究了在不同的反应温度下粒子的生长,通过紫外吸收光谱（UV-Vis）、荧光发射光谱（PL）、透射电子显微镜（TEM）等手段跟踪反应过程并对样品性能进行了表征.实验结果表明,反应温度和反应时间对量子点的生长和荧光性能有很大的影响.     

Highly efficient multiphoton-absorption-induced luminescence from gold nanoparticles

We demonstrate that highly efficient photoluminescence is generated from gold nanoparticles as small as a few nanometers in diameter upon irradiation with sub-100-fs pulses of 790-nm light. Strong emission is observed at excitation intensities comparable to or less than those typically used for multiphoton imaging of fluorescently labeled biological samples. The particles have polarized emission, can radiate more efficiently than single molecules, do not exhibit significant blinking, and are photostable under hours of continuous excitation. These observations suggest that metal nanoparticles are a viable alternative to fluorophores or semiconductor nanoparticles for biological labeling and imaging.     

Blue luminescence from carbon modified ZnO nanoparticles

In this work, a novel method was used to prepare carbon modified ZnO nanoparticles. The nanoparticles were coated with a layer of poly(methyl methacrylate) by γ radiation firstly, and then the coated nanoparticles were annealed in air. The polymer was burned and carbon was left on the surface of ZnO nanoparticles. A stable blue luminescence peak (~420 nm) can be observed for the carbon modified ZnO nanoparticles. The carbon modified ZnO nanoparticles were also investigated by X-ray photoelectron spectroscopy. The origin of the blue emission was discussed. The blue PL is related to the left carbon. This novel method also can be used to prepare other carbon modified nanoparticles.     

Substrate effect of STM-induced luminescence from porphyrin molecules

We investigated scanning tunneling microscope (STM)-induced luminescence from Meso-tetrakis (3,5-di-tertiarybutyl-phenyl) porphyrin (H₂TBPP) thin films on various metal substrates (copper, platinum and silver) under ambient conditions. Molecular fluorescence similar to the corresponding photoluminescence was observed from the H₂TBPP/Ag and H₂TBPP/Pt, but not H₂TBPP/Cu, depending on the spectra of the surface plasmons of the substrates. The results support the mechanism that intense molecular fluorescence from porphyrin film on the noble metals is a result of enhancement of molecular excitation by substrate surface plasmons.     

Optical recognition of local reaction products in ceramic combinatorial syntheses

Optical responses (luminescence and second harmonic generation) were measured to demonstrate local product formation on the μm scale in combinatorial ceramic samples made by reacting simultaneously 16 or 30 different M_xO_y oxides or carbonates. Observation of distinct hot spots on the surface of reacted pellets, micrometer thin cuts and desaggregated particles confirm local property formation by the single sample concept (SSC). Statistical calculations applied to 2D cuts of SSC samples demonstrate, that by reacting micrometer sized starting materials, compounds existing in the large phase space are likely to be formed, because the SSC is providing the starting compositions many times (tents to hundreds) depending on the total number of starting components.     

Detection of aneuploidy with digital polymerase chain reaction

The widespread use of genetic testing in high-risk pregnancies has created strong interest in rapid and accurate molecular diagnostics for common chromosomal aneuploidies. We show here that digital polymerase chain reaction (dPCR) can be used for accurate measurement of trisomy 21 (Down syndrome), the most common human aneuploidy. dPCR is generally applicable to any aneuploidy, does not depend on allelic distribution or gender, and is able to detect signals in the presence of mosaics or contaminating maternal DNA.     

High-temperature edge luminescence from cubic cadmium selenide layers

High-temperature electrical and luminescent properties of β-CdSe layers synthesized by the solid-state substitution reaction were studied. In the temperature interval from 290 to 450 K, the edge emission band related to the annihilation of free excitons inelastically scattered from free charge carriers dominates in the photoluminescence spectrum. The binding energies of the excitons and optical phonons were measured. The bandgap width and the temperature coefficient of its variation were determined.     

Bright room-temperature green luminescence from YSZ:Tb

The room temperature spectroscopic properties of terbium doped zirconia fibres grown by Laser Floating Zone method are reported. The fibres were found to be stabilised in the tetragonal crystalline phase as measured by X-ray diffraction and Raman spectroscopy techniques. The doping with terbium ions was performed during the growth process and their incorporation on the wide band gap oxide host assumes an important role on the stabilisation of the high temperature tetragonal crystalline phase. Under ultraviolet optical pumping a bright green luminescence was observed by naked eye at room temperature, corresponding to the 4f → 4f transitions between the crystal-field split energy levels of the ⁵D₄ and ⁷F₅ manifolds of the 4f⁸ electronic configuration of the Tb³⁺ ions. These results suggest that YSZ:Tb³⁺ could be considered as a promising candidate for applications in green electroluminescent devices.