Modeling of supersonic plasma flow in the scrape-off layer

The substantial drop of the plasma temperature along magnetic field lines with increasing plasma density is one of the main features in tokamak divertors. As a result the temperature gradient at the divertor plates becomes very steep and the boundary condition normally applied for the parallel Mach number M at the target, M_t = 1, cannot be satisfied. In this case the value of M_t based on the general form of the Bohm criterion, M_t  1, has to be determined from the continuity of plasma parameters.In the present paper a new approach to resolve the Mach number at the target for such a situation is proposed. This method avoids the singularity problem that arises by treating the particle balance and parallel motion equations in a differential form. Instead, the integral representation of the equations is formulated for an arbitrary form of particle and momentum sources. The approach can also take into account transport perpendicular to the magnetic field lines.The proposed method is demonstrated on the example of a one-dimensional stationary model for the scrape-off layer (SOL) plasma and includes the continuity-, parallel momentum- and heat transfer equations. The recycled neutrals are described in the diffusion approximation. In the case of low density the normal condition M_t = 1 is satisfied and the results are in agreement with the two-point model. At high enough plasma density solutions with the supersonic flow at the divertor plates, M_t > 1, are found. These states correspond to a partially detached plasma with a temperature of a few eV.     

Time dependence of isothermal magnetization in single-phase B1 MoCy encapsulated in multiwall carbon nanocages

Isothermal magnetization M(t) in nanocrystalline single-phase B1 MoC_y encapsulated in multiwall carbon nanocages is studied within the time window of 100 < t < 5000 s. The current density J exhibits a linear logarithmic time decay. The effective activation energy U_eff increases linearly with increasing temperature T, and decreases linearly with increasing J. The behaviors of J(t), U_eff(T), and U_eff(J) can be described by the Anderson–Kim flux-creep model for thermally activated motion of uncorrelated vortices or vortex bundles over a net potential barrier U_eff. The slower relaxation of current density above the broad peak field in the isothermal magnetization curves suggests that the peak is a result of vortex dynamics.     

Structure and conductivity investigations of alkaline earth substituted uranium oxide,U1 − xMxO2 ± δ (M = Mg,Ca, Sr) for solid oxide fuel cell applications

Alkaline earth substituted UO₂ (U_1 − xM_xO_2 ± δ; M = Mg, Ca, Sr; 0.1 ≤ x ≤ 0.525) with fluorite structure was synthesized in reducing atmosphere. Structure and conductivity properties of U_1 − xM_xO_2 ± δ fluorites were investigated for possible application in solid oxide fuel cells (SOFC). At room temperature and ambient atmosphere the materials are stable; however they decompose at an oxygen partial pressure p_O2 > 10^− 4 atm and temperatures higher than 600 °C. The total conductivity measured for the best conducting U_1 − xM_xO_2 ± δ material with M = Ca and x = 0.177 is as high as 3 S/cm at p_O2 < 10^− 4 atm at 600 °C. The relatively low ionic transference number (t_i∼0.02) is disadvantageous for potential use as electrolyte material for SOFC applications. The high conductivity and possible depolarization effects suggest potential use as anode materials in SOFC.     

Radiation stability of M1 − xPrxF2 + x (M = Ca,Sr, Ba) crystals

The radiation stability of the mixed crystals M_1 ? xR_xF_2 + x (M = Ca, Sr, Ba) depends on types of the alkaline-earth and rare-earth ions. Different to Eu- and Ce-containing systems, M_1 ? xPr_xF_2 + x solid solutions have a low radiation resistance, which may be associated with hole trapping on praseodymium ion according to the reaction Pr³⁺ → Pr⁴⁺ which is typical for praseodymium. The coloration efficiency of M_1 ? xPr_xF_2 + x crystals grows in the row Ca → Sr → Ba, which is explained satisfactorily within the model of rare-earth clusters, the structure of which is determined by the ratio of the base alkaline-earth cation to the praseodymium ion radii.     

Ultrasonic effects on the degradation kinetics,preliminary characterization and antioxidant activities of polysaccharides from Phellinus linteus mycelia

In this study, a high-molecular-weight polysaccharide PL-N isolated from the alkaline extract of Phellinus linteus mycelia was degraded by ultrasound. Results showed that ultrasound treatment at different ultrasonic intensities decreased the intrinsic viscosity and molecular weight of PL-N, as well as narrowed the molecular weight distribution. A larger reduction in intrinsic viscosity and molecular weight was caused by a higher ultrasonic intensity. The degradation kinetics model was fitted to (1/M_t − 1/M₀) = k·t, and the reaction rate constant (k) increased with increasing ultrasonic intensity. Ultrasound degradation did not change the primary structure of PL-N, and scanning electron microscopy analysis indicated that the morphology of the original PL-N was different from that of degraded PL-N fractions. Antioxidant activity assays in vitro indicated that the degraded PL-N fraction with low molecular weight had stronger hydroxyl radical scavenging capacity and higher TEAC and FRAP values.     

Magnetic properties and magnetocaloric effects in Gd1−xHoxNiIn intermetallic compounds

Magnetic properties and magnetocaloric effects (MCEs) of the intermetallic Gd_1?xHo_xNiIn (x=0?1) compounds have been evaluated by magnetization and heat capacity measurements. The Curie temperature T_C can be tuned from near 100 K to 20 K by substituting Ho for Gd atoms. In addition, all the compounds with Ho atoms undergo two successive magnetic transitions with the decrease of temperature: a paramagnetic (PM) to ferromagnetic (FM) transition around T_C and a spin-reorientation (SR) transition around 7?9 K. It is found that both transitions contribute to the magnetic entropy change (ΔS_M). For a field change of 5 T, the maximum values of ?ΔS_M for Gd_0.4Ho_0.6NiIn are 6 J/kg K at T_t=9 K and 10 J/kg K at T_C=52 K, respectively. These two ?ΔS_M peaks overlap partly and result in a wide working temperature range of MCE, and thus leading to the largest RC value of 443 J/kg in the Gd_1?xHo_xNiIn system.     

Insulation room for aero-acoustic experiments at moderate Reynolds and low Mach numbers

A non-expensive insulation box for aero-acoustic experiments at moderate Reynolds numbers Re < 2 × 10⁴ and low Mach numbers M < 0.2 is presented. Its performance is evaluated with particular attention to unwanted noise sources inherent to the flow facility. Objective acoustic parameters of the insulation box are assessed.     

CUDA accelerated method for motion correction in MR PROPELLER imaging

In PROPELLER, raw data are collected in N strips, each locating at the center of k-space and consisting of M_x sampling points in frequency encoding direction and L lines in phase encoding direction. Phase correction, rotation correction, and translation correction are used to remove artifacts caused by physiological motion and physical movement, but their time complexities reach O(M_x × M_x × L × N), O(N × R_A × M_x × L × (M_x × L + R_N × R_N)), and O(N × (R_N × R_N + M_x × L)) where R_N × R_N is the coordinate space each strip gridded onto and R_A denotes the rotation range. A CUDA accelerated method is proposed in this paper to improve their performances. Although our method is implemented on a general PC with Geforce 8800GT and Intel Core(TM)2 E6550 2.33 GHz, it can directly run on more modern GPUs and achieve a greater speedup ratio without being changed. Experiments demonstrate that (1) our CUDA accelerated phase correction achieves exactly the same result with the non-accelerated implementation, (2) the results of our CUDA accelerated rotation correction and translation correction have only slight differences with those of their non-accelerated implementation, (3) images reconstructed from the motion correction results of CUDA accelerated methods proposed in this paper satisfy the clinical requirements, and (4) the speed up ratio is close to 6.5.     

Influence of a magnetic field on the electronic Raman response in high-Tc cuprates

The effect of a magnetic field parallel to the CuO₂ plane on the Raman spectra is investigated based on the Slave–Boson approach to the t − t′ − J model with a Zeeman field and the random-phase approximation. We find that the Raman spectra intensities in the superconducting (SC) state are suppressed for both the B_1g and the B_2g channels with a slight shift of the peaks position toward lower frequency in the B_1g channel and a negligible shift in the B_2g channel due to the Zeeman splitting. There is a field-induced peak and dip structure at low energy response in the B_2g channel at very low temperature. While rising temperature has a similar effect in reducing the Raman response peak in the superconducting (SC) state, it smears out the field-induced peak and dip structure in the B_2g channel. We compare these results with experiments and give explanations based on the field-induced changes of the density of the superconducting condensate, the momentum distribution of the quasiparticle energy and the scattering rate.     

Ultrasonic degradation of N-di and trihydroxy benzoyl chitosans and its effects on antioxidant activity

Modified chitosans with 3,4-dihydroxy benzoyl groups (CS-DHBA) and 3,4,5-trihydroxy benzoyl groups (CS-THBA) were synthesized and their chemical structures were determined by Fourier transform infrared (FT-IR) and ¹H nuclear magnetic resonance (¹H NMR) spectroscopy. Then, ultrasonic degradation of CS, CS-DHBA and CS-THBA in 1% acetic acid solution was investigated. The kinetics studies of degradation were followed by gel permeation chromatography (GPC). The results indicated that the weight-average molecular weight of chitosan decreased obviously after ultrasound treatment, but molecular weights of CS-DHBA and CS-THBA decreased slowly with increasing sonication time. Degradation kinetics model based on 1/M_t−1/M₀ = kt was used to estimate the degradation rate constant. It was found that the rates of degradation of CS-DHBA and CS-THBA are lower than CS, and follow the order: CS₄ > CS₈ > CS₁₂ > CS-THBA₄ > CS-THBA₈ ≈ CS-DHBA₄ > CS-THBA₁₂ > CS-DHBA₈ > CS-DHBA₁₂. The antioxidant activity of the CS, CS-DHBA and CS-THBA before and after sonication was investigated by the radical scavenging activity method using 1,1-diphenyl-2-picrylhydrazyl (DPPH). The DPPH scavenging free radical capacity of CS-THBA and CS-DHBA increased up to 89% and 74% respectively, when the concentration reached 6 μg/ml. The ultrasonic treatment of CS-DHBA and CS-THBA after 30 min decreased the DPPH free radical scavenging activity but ultrasonic treatment of CS increased the DPPH free radical scavenging activity.     

A new method for estimating the critical current density of a superconductor from its hysteresis loop

The critical current density J_c of some of the superconducting samples, calculated on the basis of the Bean’s model, shows negative curvature for low magnetic field with a downward bending near H = 0. To avoid this problem Kim’s expression of the critical current density, J_c = k/(H₀ + H), where J_c has positive curvature for all H, has been employed by connecting the positive constants k and H₀ with the features of the hysteresis loop of a superconductor. A relation between the full penetration field H_p and the magnetic field H_min, at which the magnetization is minimum, is obtained from the Kim’s theory. Taking the value of J_c at H = H_p according to the actual loop width, as in the Bean’s theory, and at H = 0 according to an enhanced loop width due to the local internal field, values of k and H₀ are obtained in terms of the magnetization values M⁺(?H_min), M^?(H_min), M⁺(H_p) and M^?(H_p). The resulting method of estimating J_c from the hysteresis loop turns out to be as simple as the Bean’s method.     

Use of film thickness and Cu additive to improve (0 0 1) texture in MgO/FePtCu(C) bilayers

A multilayer structure has been proposed that demonstrates improved (0 0 1) texture for FePt-based L1₀ perpendicular media. Achieving a strong perpendicular magnetic anisotropy requires aligning the L1₀ crystallographic c-axis along the film normal. The ordered L1₀ FePt structure is tetragonal with a c/a ratio close to 0.965. This makes discriminating between the three crystallographic variants ([1 0 0], [0 1 0], and the desired [0 0 1]) difficult. Alloying FePt with Cu to reduce the c/a ratio and using a multilayer approach to keep the magnetic layers thin results in a structure with an adjustable M_rt and a strong (0 0 1) texture (rocking curve widths around 2°). This is a remarkable improvement in texture from pure FePt multilayered films or monolithic FePt(X) films. The proposed [MgO(2 nm)/Fe_50−xPt₅₀Cu_x(5 nm)]_×n structure limits grain size in the vertical (perpendicular) direction albeit not in the plane of the film. Carbon can be added to the FePtCu layer to reduce the grain size with minimal degradation of the (0 0 1) orientation.     

The experimental study of Ba 6pjnk |M| = 0, 1 autoionizing series

The spectra of the Ba 6pnk autoionizing Stark states with |M| = 0, 1, converging to the 6p_1/2⁺ and 6p_3/2⁺ ionization thresholds, are measured as a function of the electric field strength F. Several 6p_jnk Stark manifolds with n = 13–15 have been systematically studied in order to explore their characteristics of configuration interaction. Experimental results are analyzed by fitting them to the Lorentzian profile, from which the positions and widths are determined. Different spectroscopic properties between the Ba 6p_1/2nk and 6p_3/2nk autoionizing Stark states are investigated. Comparison between the Ba 6p_jnk autoionizing Stark states with |M| = 0 and those with |M| = 1 are made.     

Synthesis of ammonia at atmospheric pressure with Ce0.8M0.2O2−δ (M = La,Y, Gd,Sm) and their proton conduction at intermediate temperature

Ionic conduction in fluorite-type structure oxide ceramics Ce_0.8M_0.2O_2−δ (M = La, Y, Gd, Sm) at temperature 400–800 °C was systematically studied under wet hydrogen/dry nitrogen atmosphere. On the sintered complex oxides as solid electrolyte, ammonia was synthesized from nitrogen and hydrogen at atmospheric pressure in the solid states proton conducting cell reactor by electrochemical methods, which directly evidenced the protonic conduction in those oxides at intermediate temperature. The rate of evolution of ammonia in Ce_0.8M_0.2O_2−δ (M = La, Y, Gd, Sm) is up to 7.2 × 10^− 9, 7.5 × 10^− 9, 7.7 × 10^− 9, 8.2 × 10^− 9 mol s^− 1 cm^− 2, respectively.     

Structural and magnetic properties of HCP-CoCrPt–SiO2 granular media

Granular HCP-(CoCrPt)_100−x(SiO₂)_x thin films with Cr underlayers have been fabricated by sputtering multilayers followed by post-deposition annealing. Magnetic and structural properties of the films for potential applications in magnetic recording media have been investigated in detail. In as-deposited films coercivities exceeding 2.5 kOe have been obtained with SiO₂ varying from 8 to 16 vol%; high coercivity of 5.6 kOe and anisotropy of 4.6×10⁶ erg/cm³ have been achieved at low M_rt value (about 0.4 memu/cm²) in the post-annealed films. VSM measurements showed that the magnetic moment lies well in the film plane under proper preparation conditions. Grain isolation in the magnetic layer was improved by segregating SiO₂ into grain boundaries and further enhanced by post-deposition annealing. The rapid increase of the coercivity upon annealing is most likely due to the significant decrease in intergranular exchange coupling, as shown by the δM measurement in which the peak value of δM curves changed from a positive value to a negative value upon annealing. Magnetic reversal properties of the films have also been systematically studied. These results show that the HCP-CoCrPt–SiO₂ granular film is a promising candidate for ultra-high-density recording media up to 100 Gbit/in² or beyond because of its low Pt content and desirable properties.     

Adsorption of γ-mercaptopropyltrimethoxysilane on zinc: A study of the competition between thiol and silanol functions related to the age of the siloxane solution,its pH and the oxidation state of the surface

We describe the adsorption of γ–mercaptopropyltrimethoxysilane (γ-MPS) on zinc under various experimental conditions, including the age of the siloxane solution (t_ag), its pH (7 or 4), and the mode of preparation of the surface (RCA treatment or in situ polishing). It is shown by XPS studies that the structure of the adsorbed monolayer varies dramatically with the pH of the solution. At the natural pH of the siloxane solution (pH 7) where no hydrolysis of the SiOCH₃ group occurs, adsorption proceeds through the SH moiety and not through SiOCH₃ groups. This preferential attachment through SH is found whatever the age of the solution and the treatment of the zinc. It is confirmed by the fact that n-propyltrimethoxysilane (PSi) does not interact with the surface in the case of very old solutions (adsorption is not observed when Zn is polished in situ and only occurs with RCA zinc treatment for t_ag > 40 min). With siloxane solutions at pH 4, adsorption of γ-MPS is more complex and the structure of the adsorbed layer depends mainly on the age of the solution. With a fresh solution, hydrolysis is not very advanced and, as mentioned previously, adsorption occurs through the SH group. With older solutions and as a consequence of the progressive hydrolysis of the SiOCH₃ group to SiOH, the density of the grafted siloxane monolayer increases (6 min < t_ag < 10 min), followed by a mixed adsorption through SH and SiOH (10 min < t_ag < 40–50 min) revealed by the decrease in the normalised (Si2p/S2p)* intensity ratio. Finally, adsorption of dimers and oligomers is observed with still older siloxane solutions. In contrast to PSi whose adsorption on zinc is favoured by the RCA treatment, neither treatment of the surface changes the results significantly in the case of γ-MPS. Comparison with alkanethiols confirms the transition from monomer to dimer adsorption and IRRAS studies clearly indicate a condensation reaction between OH and SH groups.     

Ultrasound effects on the degradation kinetics,structure and rheological properties of apple pectin

The effects of ultrasound on the molecular weight of apple pectin were investigated. The structure and rheological properties of the degradation products were also tentatively identified by High Performance Liquid Chromatography–Photodiode Array Detector (HPLC–PAD), Infrared spectroscopy (IR), Nuclear Magnetic Resonance spectroscopy (NMR) and Rheometer. The results indicated that the weight-average molecular weight of apple pectin decreased obviously after ultrasound treatment. The molecular weight of degradation products had a uniform and narrow distribution. Ultrasound intensity and temperature play an important role in the degradation reaction. Degradation kinetics model of apple pectin fitted to 1/M_t ? 1/M₀ = kt from 5 to 45 °C. The degree of methylation of apple pectin reduced according to IR analysis when ultrasound was applied. Ultrasound treatment could not alter the primary structure of apple pectin according to the results determined by HPLC, IR and NMR. Meanwhile, the viscosity of apple pectin was 10³ times as large as that of ultrasound-treated apple pectin. The ultrasound-treated apple pectin showed predominantly viscous responses (G′ < G″) over the same frequency range. The results suggested that ultrasound provided a viable alternative method for the modification of pectin.     

Magnetic fluid thermochemotherapy of murine tumors

Four series of water-based dextran-ferrite (DF) magnetic fluids (MFs) containing Melphalan (MP) were prepared. Their saturation magnetization (M_s) was from 0.8 to 7.8 kA/m; specific power absorption rates were 240 W/g Fe. After nine courses of magnetic fluid thermochemotherapy with MP containing DF MF (M_s 7.5 kA/m, pH 6.6, ζ+15 mV) at 44–46 °C for 30 min in an AC magnetic field (0.88 MHz, 9.3 kA/m, 0.3 kW), complete P388 tumor regression was seen in 30% of BDF₁ mice. Furthermore, a life span increase of 180% was achieved.     

Defect interactions in La0.3Sr0.7Fe(M′)O3−δ (M′ = Al,Ga) perovskites: Atomistic simulations and analysis of p(O2)-T-δ diagrams

Atomistic modelling showed that a key factor affecting the p(O₂) dependencies of point defect chemical potentials in perovskite-type La_0.3Sr_0.7Fe_1−xM′_xO_3−δ (M′ = Ga, Al; x = 0–0.4) under oxidizing conditions, relates to the coulombic repulsion between oxygen vacancies and/or electron holes. The configurations of A- and B-site cations with stable oxidation states have no essential influence on energetics of the mobile charge carriers, whereas the electrons formed due to iron disproportionation are expected to form defect pair clusters with oxygen vacancies. These results were used to develop thermodynamic models, adequately describing the p(O₂)-T-δ diagrams of La_0.3Sr_0.7Fe(M′)O_3−δ determined by the coulometric titration technique at 923–1223 K in the oxygen partial pressure range from 1 × 10^− 5 to 0.5 atm. The thermodynamic functions governing the oxygen intercalation process were found independent of the defect concentration. Doping with aluminum and gallium leads to increasing oxygen deficiency and induces substantial changes in the behavior of iron cations, increasing the tendencies to disproportionation and hole localization. Despite similar oxygen nonstoichiometry in the Al- and Ga-substituted ferrites at a given dopant content, the latter tendency is more pronounced in the case of aluminum-containing perovskites.     

Derivation and solution of multifrequency radiation diffusion equations for homogeneous refractive lossy media

Starting from the radiation transport equation for homogeneous, refractive lossy media, we derive the corresponding time-dependent multifrequency diffusion equations. Zeroth and first moments of the transport equation couple the energy density, flux and pressure tensor. The system is closed by neglecting the temporal derivative of the flux and replacing the pressure tensor by its diagonal analogue. The radiation equations are coupled to a diffusion equation for the matter temperature. We are interested in modeling heating and cooling of silica (SiO₂), at possibly rapid rates. Hence, in contrast to related work, we retain the temporal derivative of the radiation field. We derive boundary conditions at a planar air–silica interface taking account of reflectivities obtained from the Fresnel relations that include absorption. The spectral dimension is discretized into a finite number of intervals leading to a system of multigroup diffusion equations. Three simulations are presented. One models cooling of a silica slab, initially at 2500 K, for 10 s. The other two are 1D and 2D simulations of irradiating silica with a CO₂ laser, λ = 10.59 μm. In 2D, a laser beam (Gaussian profile, r₀ = 0.5 mm for 1/e decay) shines on a disk (radius = 0.4, thickness = 0.4 cm).