Over the last decade, demand has increased for developing the hot-galvanized quenching and partitioning (Q&P) steel to overcome the disadvantages associated with vehicle safety, fuel consumption and ...corrosion resistant. The present work aims to elucidate the effects of quenching temperature on phase transformation kinetics, microstructure evolutions and mechanical properties of a hot-galvanized Q&P steel (0.225C-0.85Si-2.02Mn-0.91Al, in wt.%) by combining modeling and experimental research. Using dilatometry, SEM, EBSD, EPMA, TEM, PED, XRD and Image-Pro Plus (IPP) software, we quantitatively investigated the microstructure evolution at different quenching temperatures. Results indicated that a larger fraction of primary martensite at lower quenching temperature could strongly promote subsequent bainite transformation kinetics, which is attributed to more martensite-austenite interfaces and defect density. By fitting the dilatometer curves and establishing the equation of transformation rate vs. quenching temperature, a Kolmogorov-Johnson-Mehl-Avram (KJMA) equation was established to describe insufficient bainite formation kinetics during high-temperature short-time overaging. Furthermore, a modified CCE model taking into account intercritical ferrite and short-time bainite transformation was proposed and the predicted RA fractions are more consistent with the experimental values. As the quenching temperature decreases, small-sized blocky RA along martensite boundaries and filmy RA between martensite laths increase, while coarse lath/blocky RA inside bainite structures or at bainite boundaries decreases gradually. In addition, the YS decreases from 763 MPa to 431 MPa with the increase of quenching temperature, while the UTS varies in a narrow range between 967 MPa and 1036 MPa. A stable TEL of 22.6–25.7% can be obtained at a wide range quenching temperature (150–275 °C), which is attributed to the joint effects of TRIP effect and multiphase structure. This research would be of guiding significance for the industrial practice.
•A review of DNA-templated gold, silver and copper nanoclusters.•Summary of synthesis, characterization, and analytical applications of nanoclusters.•Biosensor development reviewed based on the ...reactions unique to the nanoclusters.•Future development trends discussed from fundamental and application perspectives.
Fluorescent silver, gold and copper nanoclusters (NCs) have emerged for biosensor development. Compared to semiconductor quantum dots, there is less concern about the toxicity of metal NCs, which can be more easily conjugated to biopolymers. These NCs need a stabilizing ligand. Many polymers, proteins and nucleic acids stabilize NCs, and many DNA sequences produce highly-fluorescent NCs. Coupling these DNA stabilizers with other sequences, such as aptamers, has generated a large number of biosensors.
We summarize the synthesis of DNA and nucleotide-templated NCs; and, we discuss their chemical interactions. We briefly review properties of NCs, such as fluorescence quantum yield, emission wavelength and lifetime, structure and photostability.
We categorize sensor-design strategies using these NCs into:(1)fluorescence de-quenching;(2)generation of templating DNA sequences to produce NCs;(3)change of nearby environment; and,(4)reacting with heavy metal ions or other quenchers.
Finally, we discuss future trends.
Here, we report features of YVO4:Sm3+ nanocrystalline powders prepared via modified Pechini technique. Doping concentration effect on structural and luminescence properties has been studied in ...detail. XRD and Raman spectroscopy confirmed synthesis of single phase nanoparticles with no additional phase. SEM images showed that prepared nanophosphors have average size of 60 nm. Emission and excitation spectra of Sm3+-doped YVO4 nanocrystalline powders consisted of the characteristic lines corresponding to the intra-configurational f-f transitions dominated by electric dipole 4G5/2–6H9/2 transition. The optimal Sm3+ doping concentration was found to be dependent on excitation mechanism. Concentration quenching in YVO4:Sm3+ nanophosphors occurred via dipole–dipole interaction regardless of the excitation. Temperature effect on emission spectrum was investigated in terms of luminescence intensity and chromaticity coordinates. YVO4:Sm3+ nanoparticles have potential application in ratiometric luminescence thermometry. 4G5/2 lifetime gradually declined along with increase of Sm3+ ions amount.
Display omitted
•Sm3+-doped YVO4 concentration series was prepared using modified Pechini method.•Sm3+ optimal doping concentration depends on excitation mechanism.•Concentration quenching in YVO4:Sm3+ phosphors occurred due to dipole–dipole interaction.•Temperature effect was studied through luminescence intensity and chromaticity coordinates.•YVO4:Sm3+ nanoparticles were successfully used as ratiometric luminescence thermometer.
Most present-day galaxies with stellar masses ≥1011 solar masses show no ongoing star formation and are dense spheroids. Ten billion years ago, similarly massive galaxies were typically forming stars ...at rates of hundreds solar masses per year. It is debated how star formation ceased, on which time scales, and how this "quenching" relates to the emergence of dense spheroids. We measured stellar mass and star-formation rate surface density distributions in star-forming galaxies at redshift 2.2 with ∼1-kiloparsec resolution. We find that, in the most massive galaxies, star formation is quenched from the inside out, on time scales less than 1 billion years in the inner regions, up to a few billion years in the outer disks. These galaxies sustain high star-formation activity at large radii, while hosting fully grown and already quenched bulges in their cores.
The fluorescence quenching effect of unfolded-fullerene nanoparticles (UFNPs) in the presence of Cu2+ ions in water solution has been investigated for a broad range of fluorophore/quencher ...concentrations. The experimental Stern-Volmer plot exhibited a nonlinear behaviour with an initial upward curvature even though carbon nanoparticles are known to form stable complexes with metal ions and thus a dominant static quenching with a linear plot is expected according to the classical Stern-Volmer equation. A generalized model for static quenching, applicable to any value of fluorophore/quencher concentrations, provided a very good fit with the experimental data without the need to introduce any second-order effect, such as in the sphere of action model or diffusion-limited processes. Moreover, by changing the dilution of the UFNP solution, we could study how the quenching ratio depended on the fluorophore concentration, whereas it is predicted to be constant by the standard model. In addition to providing a significant test of the nonlinear model for static quenching, we believe this study could help find the best parameters for the optimization of sensitivity and signal-to-noise ratio in applications such as fluorescence sensing.
•Exit quenching on SMR rod bundle CHF has been introduced.•Proposed that the potential of a reflood quenching effect is highly plausible under low pressure, low flow and high-quality conditions as ...the location of the CHF event will be much closer to the exit plenum, especially in the case of exit power peaking.•The On-line, Real-time Liquid Level Monitoring System (OR_LLMS) and On-line, Real-time dynamic Quenching Front Tracking Systems (OR_QFTS), which allow accurate measurements of rod bundle CHF as a function of both liquid level and degree of downward quenching under various test conditions are presented.•SMR rod bundle CHF tests with liquid level monitoring and quenching front tracking system are proposed.
In most Light Water Reactor (LWR) based Small Modular Reactors (SMRs), one of the critical factors that might affect Critical Heat Flux (CHF) and other thermal–hydraulic phenomena under low flow, low pressure, high-quality conditions is the existence of high water column over a relatively short fuel core in the majority of the integral design SMR reactor vessels. With the existence of this water column over the relatively short and high-power peaking fuel bundle, the potential of a reflood quenching effect is highly plausible under low pressure, low flow and high-quality conditions as the location of the CHF event will be much closer to the exit plenum, especially in the case of exit power peaking. The results from CFD modeling and flow visualization tests presented in this paper demonstrate the importance of liquid level as well as its impacts on rod bundle CHF. Such a critical factor has often been overlooked by the prevailing SMR designs as many of the rod bundle CHF tests performed for SMR, including those with the licensing data, have either neglected the effects of the exit quenching effect, or were performed with non- prototypical heater rod designs or surrogate fluid that may not include such exit quenching phenomena.
In this paper, the phenomenon of exit quenching on SMR rod bundle CHF has been introduced with the development of the proprietary On-line, Real-time Liquid Level Monitoring System (OR_LLMS) and On-line, Real-time dynamic Quenching Front Tracking Systems (OR_QFTS), which allow accurate measurements of rod bundle CHF as a function of both liquid level and degree of downward quenching under various test conditions. The future application is also presented, which will aid in the development of rod bundle CHF correlations that account for and take advantage of different water levels over the reactor core.
The quenching and partitioning (Q&P) processing of advanced high strength steels has been shown to result in a distinct improvement of their strength and ductility. The selection of the quench ...temperature during Q&P processing makes it possible to obtain a wide range of mechanical properties for the final martensite-austenite microstructures. In the present study, a physically-based model describing the relationship between the microstructure and the mechanical properties of Q&P processed steels is developed. The model is applied to the mechanical properties of a Q&P processed medium Mn steel.
Display omitted
In this paper, a comprehensive analytical approach is presented for modeling the counting statistics of active quenching and passive quenching single-photon avalanche diode (SPAD) detectors. It is ...shown that, unlike ideal photon counting receiver for which the detection process is described by a Poisson arrival process, photon counts in practical SPAD receivers do not follow a Poisson distribution and are highly affected by the dead time caused by the quenching circuit. Using the concepts of renewal theory, the exact expressions for the probability distribution and moments (mean and variance) of photocounts in the presence of dead time are derived for both active quenching and passive quenching SPADs. The derived probability distributions are validated through Monte Carlo simulations and it is demonstrated that the moments match with the existing empirical models for the moments of SPAD photocounts. Furthermore, an optical communication system with on-off keying and binary pulse position modulation is considered and the bit error performance of the system for different dead time values and background count levels is evaluated.
PDF
