可聚合型非离子乳化剂合成及其在苯乙烯辐射细乳液聚合中的应用

为深入探讨细乳液稳定机理,本文设计合成了一种可聚合型的非离子乳化剂丙烯酸羟乙酯-2,4-甲苯二异氰酸酯-单甲基聚乙二醇(HEA-TDI-PEO),该乳化剂的亲水性和溶解度可通过改变PEO链分子量和总分子量进行调节。通过在苯乙烯辐射细乳液聚合中的应用研究发现,HEA-TDI-PEO在作为乳化剂的同时也能起到助稳定剂的作用,其聚合动力学符合细乳液液滴成核的特征,但聚合速率慢,转化率低。当PEO分子量为2000时,用HEA-TDI-PEO乳化剂配制的细乳液体系最为稳定,粒子形貌均一。这种可聚合的乳化剂可以减少环境污染,在工业生产中具有潜在的应用前景。     

238U and 232Th concentrations measured in different medical drugs by using solid-state nuclear track detectors and resulting radiation doses to the skin of patients

Urban populations in Morocco receive free medical drugs as prescribed by doctors in district health centres.To explore the exposure pathway of ~(238)U and~(232)Th and their decay products on the skin of patients,these radionuclides were measured in various medical drugs by using solid-state nuclear track detectors(SSNTDs).The measured concentrations range of ~(238)U and ~(232)Th in the medical drug samples of interest vary from(4.3±0.3) to(11.1±0.7) mBq 1~(-1) and(0.49±0.03) to(1.3±0.1)mBq 1~(-1),respectively.A new dosimetric model,based on the concept of specific alpha-dose and alpha-particle residual energy,was developed for evaluating radiation doses to skin following the application of different medical drugs by patients.The maximum total equivalent effective dose to skin due to the ~(238)U and ~(232)Th series from cutaneous application of different medical drugs by patients was found to be 2.8 mSv year~(-1) cm~(-2).     

Modeling operation amplifier based on VHDL-AMS for TID effect

A model of the operational amplifier based on VHDL-AMS is proposed. According to needs of simulating the total ionizing dose(TID) radiation effect, parameters of operational amplifier are taken into account when the performance is specified. The operational amplifier model used for the TID radiation effect simulation is completed after verifying each modeled parameter. And a parameter for describing the external environment is introduced to make the model combined with TID. Finally, an example is used to illustrate the TID effect on the operational amplifier of MC14573, proving the validity of the model.     

Structure and Reactions of Aliphatic Bridged Bifunctional Radical Ions: Exploring Fine-Tuning in Radiation Chemistry

Bridged bifunctional molecules of general structure X (CH₂)_n Y are useful models for investigations into the effects of intra- and intermolecular interactions in primary radiation-induced processes, with a number of implications for radiation chemistry, radiobiology, and molecular electronics. This short Review presents an outline of recent studies on the structure and reactivity of aliphatic bifunctional radical ions in low-temperature matrices using EPR spectroscopy and quantum-chemical calculations. Both EPR data and DFT calculations for radical cations show that the delocalization of charge and spin density occurs if XY or X and Y have close electronic properties. If the difference in the ionization potentials between X and Y is large, localized radical cations are observed with ground-state properties close to those of the corresponding monofunctional species. Nevertheless, the remote second functional group may affect the photochemistry of such radical cations at a specific bridge length, probably due to intramolecular interactions in a certain conformation. The stabilization of bridged bifunctional radical anions containing two carbonyl groups was found to be very sensitive to the local environment, which may be described in terms of a microsolvation model at the MP2 level of theory. Two independent reactions pathways with excess electrons, yielding different types of localized radical anions, were demonstrated for asymmetrical bifunctional molecules. The obtained results and their implications are discussed in terms of fine-tuning effects in radiation-induced chemical processes in condensed phases.     

Cryogenic thermal absorptance measurements on small-diameter stainless steel tubing

The Mid Infrared Instrument (MIRI) on the James Webb Space Telescope includes a mechanical cryocooler which cools its detectors to their 6 K operating temperature. The coolant gas flows through several meters of small-diameter stainless steel tubing, which is exposed to thermal radiation from its environment. Over much of its length this tubing is gold-plated to minimize the absorption of this radiant heat. In order to confirm that the cryocooler will meet MIRI’s requirements, the thermal absorptance of this tubing was measured as a function of its environment temperature. We describe the measurement technique and present the results.     

Turbulent non-premixed hydrogen-air flame structure in the pressure range of 1-10 atm

A numerical study of hydrogen turbulent diffusion flame structure is carried out in the pressure range of 1-10 atm with a special emphasis on mixing. The investigation is conducted under constant volumetric fuel and air flows. Mixing is characterized by mixture fraction, its variance and the scalar dissipation rate. The flow field and the chemistry are coupled by the flamelet assumption. Mixture fraction and its variance are transported by computational fluid dynamic (CFD). Computational predictions are analysed at two radial stations (the first one represent the near-field region and the second one the far-field region). The computational results indicate a deterioration of mixing with pressure rise. As a result, flame reaction zone becomes thicker. In addition, mixing and flame structure sensitivity to pressure are found to be high in the first location. Further analysis revealed that the gas becomes increasingly heavy with pressure rise, which hampered its ability to mix.     

Spectral and kinetic peculiarities of the radiation trapping effect in doped materials

The results of detailed study of the radiation trapping effect in doped materials are presented. A special excitation and detection scheme is developed that allows in fluorescent signals significantly distinguish the contributions from the regions of the crystal excited directly by the laser radiation and excited by radiation transfer of the excitation in the non-irradiated part of the sample. This technique was used to investigate the radiation trapping phenomenon in infrared spectral region around 1.6 μm for YAG:Er³⁺ crystal excited by continuous and pulsed laser radiations at 970 nm wavelength. Spectral redistributions in fluorescent bands of the crystal under study were registered due to presence of the radiation trapping effect. The strong dependence of the luminescence decay times on geometry of both excitation and registration is revealed for the material under study. Within the framework of existing models of radiation trapping effect in doped solids, an analysis of the obtained results is carried out.     

PDF model for NO calculations with radiation and consistent NO–NO2 chemistry in non-premixed turbulent flames

A consistent method to derive the parameterized NO source term from a given flamelet library is presented. The approach was tested by conducting PDF simulations and comparing computed solutions of the Sandia D flame with measurements. The parameterization is based on laminar flamelets with additional parameters for NO formation and radiation. To obtain feedback of the NO concentration on the NO source term, evolution to equilibrium is calculated with a complex chemical mechanism (including nitrogen chemistry), whereas the concentration of all non-nitrogen species are parameters obtained from flamelet profiles. With this method, which requires an appropriate initialization of the nitrogen containing species, unrealistically large NO source terms are avoided, which is a shortcoming of previously devised methods.In addition, to properly account for radiative heat losses, an additional progress variable was introduced. Simulation results obtained with our PDF method are in excellent agreement with experimental data. While the NO concentration values appear too high (by approximately 30% at the exit of the burner), if radiation effects are ignored, their match is very good, if radiation effects are taken into account.     

Modeling of an isolated liquid hydrogen droplet evaporation and combustion

In this model, diffusive governing equations of Liquid Hydrogen (LH) evaporation and combustion were solved. The simulation reveals that, there exists a critical radius (a_cri) where radiation heat is equal to conduction heat (Q_rad = Q_cond) and a_cri is a function of ambient temperature during LH droplet evaporation process. Under pure evaporation condition, for large liquid hydrogen droplets (a > a_cri) radiation heat is dominant at a given environment temperature, but as liquid droplet size decreases, radiation heat becomes insignificant and thermal conduction will be dominant for liquid evaporation. When LH droplet is burned in a cold environment (T_∞ = 300 K), there are two films above the LH surface, Film I is from LH surface to flame front within which a dense hydrogen gas cloud is formed; Film II is from flame front to the free stream where oxygen is diffused inward to react with hydrogen. The flame front is located about 95 times of the droplet radius (r_f = 95a) and the flame temperature could rise up to 2077 K. When an LH droplet is immersed in a hot environment (T_∞ = 2050 K), the flame front is located at a similar distance to the LH droplet (r_f/a = 114) and flame temperature could go up to 3769 K.     

Radiation effects in new materials for nano-devices

Exposure to radiation poses significant challenges for electronic devices, including parametric degradation, loss of data, or catastrophic failure. The challenges and solutions change significantly as new materials are introduced and feature sizes become smaller. This paper reviews the effects of radiation on electronics, with emphasis on the impact of new materials.