The high hydrostatic pressure effect on shallow donor binding energies in GaAs-(Ga, Al)As cylindrical quantum well wires at selected temperatures

We have presented the behavior of a shallow donor impurity with binding energy in cylindrical-shaped GaAs/Ga_0.7Al_0.3As quantum well wires under high hydrostatic pressure values. Our results are obtained in the effective mass approximation using the variational procedures. In our calculations, we have not considered the pressure related Γ−X crossover effects. The hydrostatic pressure dependence on the expectation value of ground state binding energy is calculated as a function of wire radius at selected temperatures. We have also discussed the effects of high hydrostatic pressure and temperature on some physical parameters such as effective mass, dielectric constant, and barrier height. A detailed analysis of these calculations has proved that the effective mass is the most important parameter, which explains the dependency of donor impurity binding energies on the high hydrostatic pressure values.     

Heavy particle modes and signature of the I-Regime

The recently discovered properties of the I-confinement Regime are explained as resulting from the excitation of a heavy particle mode. The theoretically predicted mode phase velocity in the direction of the electron diamagnetic velocity and the induced confinement of impurities at the edge of the plasma column have been confirmed by the experiments. The direction of the mode phase velocity is consistent with that (opposite) of the spontaneous rotation in the plasma core. The mode is of the “ion-mixing” type, in that it does not produce any electron transport across the fields and it involves significant poloidal magnetic field fluctuations.     

Iron-related luminescence centers in ZnWO 4 :Fe

A systematic spectroscopic study of single ZnWO 4 :Fe crystals with different iron concentrations has been performed under excitation by ultraviolet light, by synchrotron radiation or under photostimulation by near-infrared light. The luminescence of Fe 3+ -related centres has been studied. It is shown that iron centres of different types efficiently promote the formation of crystal defects at low temperatures. Electrons and holes can be trapped near Fe 2+ or Fe 3+ ions, which is further revealed in phosphorescence, thermostimulated or photostimulated luminescence. At room temperature the main effect of iron impurity is to reduce the light yield of a ZnWO 4 scintillator.     

Observation of inverse sawtooth activity on central soft X-ray emission during impurity injection in the J-TEXT tokamak

Short- and long-time lasting inverse sawtooth activities during neon (Ne) gas injection, not during helium (He) or argon (Ar) though, have been clearly observed on soft X-ray emissions from chords viewing the central plasma region of the Joint Texas Experimental Tokamak (J-TEXT). A self-consistent interpretation of the inverse sawtooth activity depending on the impurity radiation characteristics is proposed. It is evidenced that the radiation loss caused by the injection of noble gas not only depends on the amount of the noble gas itself, but also depends on the temperature region where the noble gas can reach.     

On the effective field and optical constants of alkali halides containingF colour centres

Summary The Onsager and Lorentz local fields ofF colour centres are compared and their change as a function of angular frequency and temperature is also considered. The change of these fields is proportional to the change of the refractive index produced byF centres. Some approximations about the explicit temperature dependence of the refractive-index change are also presented.

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Riassunto I campi locali di Onsager e Lorentz diF centri di colore sono confrontati e si considera il loro cambiamento in funzione della frequenza angolare e della temperatura. Il cambiamento di questi campi è proporzionale al cambiamento dell'indice di rifrazione prodotto daF centri. Si presentano anche alcune approssimazioni riguardo alla esplicita dipendenza dalla temperatura del cambiamento dell'indice di rifrazione.

     

Ab initio theory of transport in FeRh-based natural magnetic multilayers

The electronic structure and the residual resistivity of random FeRh-based alloys in the CsCl structure are calculated for different spin configurations using the tight-binding linear muffin–tin orbital method. The effect of substitutional impurities (Pd, Rh) is described by means of the coherent potential approximation. It is shown that impurity scattering leads to giant magnetoresistance effects in qualitative agreement with experiment.     

原子模型势理论中径向微分算符矩阵元的计算

本文推广［７，８］的工作，导出了多电子原子模型势理论中含径向微分算符的矩阵元通式，可直接用于以“速度”及“加速度”形式跃迁振子强度计算。     

The limitimg behaviour of the well width of a quantum two-dimensional metal–insulator transition

Metal–Insulator transition using an exact two-dimensional (2D) dielectric function is investigated for a shallow donor in an isolated well of a GaAs/Ga_1−xAl_sAs superlattice system within the effective mass approximation. Vanishing of the donor ionization energy as a function of well width and the donor concentration suggests that a phase transition is not possible even below a well width of 10 Å, supporting the scaling theory of localization. The effects of Anderson localization, exchange and correlation in the Hubbard model are included in a simple way. The relationship between the present model and the Mott criterion in terms of Hubbard model is also brought out. The critical concentration appears to be enhanced when a random distribution of impurities is considered. The limiting behaviour of the well width for a quantum 2D well is brought out. A simple expression is derived for a Mott constant in 2D, a*N_c^1/2 exp (9.86 exp (−L/a*))=0.123, where N_c is the critical concentration per area. Results are compared with the existing data available and discussed in the light of existing literature.     

Reversed‐phase liquid chromatography with electrospray mass detection and 1H and 13C NMR characterization of new process‐related impurities,including forced degradants of Efavirenz: Related substances correlated to the synthetic pathway

In this study, a stability‐indicating reversed‐phase liquid chromatographic electrospray mass spectrometric method was developed and validated for the determination of process‐related impurities and forced degradants of Efavirenz in bulk drugs. Efavirenz was subjected to acid, alkaline hydrolysis, H₂O₂ oxidation, photolysis, and thermal stress. Significant degradation was observed during alkaline hydrolysis, and the degradants were isolated on a mass‐based purification system and characterized by high‐resolution mass spectrometry, positive electrospray ionization tandem mass spectrometry, and ¹H and ¹³C NMR spectroscopy. Accurate mass measurement and NMR spectroscopy revealed the possible structure of process‐related impurities and degradant under stress conditions. The acceptable separation was accomplished on Waters bondapak C₁₈ column (250 mm × 4.6 mm; 5 μm), using 5 mM ammonium acetate and acetonitrile as a mobile phase in a gradient elution mode at a flow rate of 1.0 mL/min. The eluents were monitored by diode array detector at 247 nm and quantitation limits were obtained in the range of 0.1–2.5 μg/mL for Efavirenz, degradants, and process‐related impurities. The liquid chromatography method was validated with respect to accuracy, precision, linearity, robustness, and limits of detection and quantification as per International Conference on Harmonization guidelines.     

An improved and practical route for the synthesis of enzalutamide and potential impurities study

An improved and practical synthesis of enzalutamide was accomplished in five steps. Starting from 4-bromo-2-fluoro-benzonic acid, a methyl esterification, Ullmann ligation, methyl esterification, ring closing reaction and final methyl amidation provided the target in 35% total yield with 99.8% purity. Five identified impurities were also synthesized. This efficient and economical procedure avoids the use of highly toxic reagents and multiple recrystallization operations, which is suitable for further industrialization.