Boron Density Research Articles

Superconductivity in laser-annealed monocrystalline silicon films: The role of boron implant

33 nm thick silicon on insulator films were implanted with boron at high dose (1.5 × 1016 or 2.5 × 1016 at/cm2) and low energy (3 or 4 keV), then further annealed with 160 ns laser pulses. When the laser energy is set such as to lead to the near complete melt of silicon, superconductivity is found in 4 keV-implanted films only, with a critical temperature that increases with dose from 270 to 390 mK. This latter temperature is 200 mK higher than the one recently reported in polycrystalline films of same thickness. Transmission electron microscopy images demonstrate that the films annealed at this particular laser energy are monocrystalline, with a lower density of boron precipitates in superconducting ones at a given dose. A simple model shows that the appearance of superconductivity in 4 keV-implanted films is due to the broader shape of the as-implanted boron distribution.

How positioning of a hard ceramic TiB2 layer in Al/CuO multilayers can regulate the overall energy release behavior

This study reports on a new ternary thermite comprising of Al-TiB2/CuO multilayers, designed to take the advantage of high ignitability of titanium (Ti), high volumetric density of boron (B), and low melting point of aluminum (Al). Results demonstrate synergetic effects leading to an energetic layer outperforming its single fuel counterparts, Al/CuO or TiB2/CuO, while being safe to handle. The additive TiB2 not only lowers the ignition energy by 100%, but also enhances the burn rate by more than a factor of two compared to the single fuel samples (Al/CuO and TiB2/CuO). The thermite reaction sequences and synergy of Ti, B and Al oxidation, examined by thermo-analytical analyses coupled with X-ray spectroscopy and high-resolution electron energy loss spectroscopy, demonstrate the strong affinity of TiB2 to oxygen that catalyzes CuO decomposition at temperatures as low as 380 °C; followed by a dual-step TiB2 oxidation: first to TiO, and then to TiO2 led by a reaction limiting step of oxidizer availability. Finally, Al undergoes oxidation via liquid boron oxide as well as gaseous oxygen. This study also underlines the crucial effect of the nanolayer morphology in the thin-film technology: when Al is sputter-deposited onto the TiB2 layer, Al ions penetrate into the grain boundaries penalizing TiB2 reactivity. The results demonstrate the advantages of using TiB2 fuel to improve the ignitability and the combustion performance of Al based thermite and offer some means to finely tune the energetic properties.

A quantitative calculation method for fracture density using the neutron self-shielding modification and neutron-induced gamma logging

As the critical parameter of hydraulic fracture evaluation, fracture density is significant for fracturing model optimization and production prediction. To compensate for the low response sensitivity of fracture density and the saturation of fracture evaluation in nonradioactive technology (NRT), we have developed a method based on modifying the neutron self-shielding effect to quantitatively calculate fracture density. The gamma counts of elements with content that did not change before and after fracturing are used to calculate the self-shielding correction factor. We establish the mathematical relationship between the corrected gamma counts of boron and fracture density to achieve a quantitative calculation of fracture density. Compared to NRT, the new method uses measured energy spectral information to eliminate the effect of neutron self-shielding on fracture density and improve calculation accuracy. Meanwhile, the scope or range of accurate fracture density estimation extends from the original 4% to more than 10%. Moreover, we further examine fracture response under different formations and borehole conditions using the Monte Carlo N-particle transport code. The salinity of formation water and borehole water has the most significant impact on fracture density calculation, shale content and porosity, lithology, and fluid type of formation; in contrast, borehole parameters are the least significant. Finally, in this paper, we illustrate the feasibility of the method through a continuous-depth numerical calculation.

Structure–compressibility correlation among MoBx

Molybdenum forms a large number of borides with various stoichiometries. In this paper the trends in the compressibility behaviour among MoBx (x: 0.5, 1, 2 and 3) were investigated. High-pressure structural stability studies on MoB3 were carried out up to a pressure of 40 GPa using a Mao–Bell-type diamond anvil cell. The hexagonal structure remained stable up to 40 GPa. High-pressure X-ray diffraction data yielded a bulk modulus of 254 GPa and were in good agreement with computed bulk moduli of 258–295 GPa with various potentials. First-principles calculations were carried out to investigate the structural, elastic and mechanical properties of molybdenum borides based on generalized gradient approximation proposed by Perdew–Burke–Ernzerhof. The compressibility behaviour of MoBx (x = 0.5, 1, 2 and 3) showed parabolic trend and was explained in terms of electronic structure and mainly arose due to the partial charge density of boron.

Evaluation of Alpha Particle Emission Rate Due to the p-11B Fusion Reaction in the Large Helical Device

A numerical study of the alpha particle emission rate due to the p-11B fusion reaction based on the respectively obtained Large Helical Device (LHD) plasma parameters in an experiment is performed. First, the total alpha particle emission rate is estimated by employing the beam ion distribution calculation code FIT3D and the fusion reaction rate calculation code FBURN based on the classic confinement of beam ions. Then, the calculation is performed using hydrogen-beam-heated hydrogen plasma parameters and the radial boron density profile obtained from boron drop discharge. The result shows that the total alpha particle emission rate reaches approximately 1014 s−1. Then, based on the radial profile of the alpha particle emission calculated by the FBURN code, the distribution of the first orbit loss of5.78-MeV alpha particles created by the p-11B reaction on the vacuum vessel and the divertor plate is calculated by the collisionless Lorentz orbit code LORBIT. Although most of the alpha particles are lost to the divertor plate, some of the alpha particles are lost on the vacuum vessel. Finally, a feasibility study of alpha particle detection by the existing manipulators and fast ion loss detector position is performed. The number of particles as a function of position shows that a substantial number of alpha particles can be detected. Alpha particles with a pitch angle of ~130 deg can reach manipulator positions. In contrast, particles with pitch angles of ~50 and ~110 deg can reach the fast ion loss detector position. The calculation shows that measurement of alpha particles due to p-11B is thought to be possible using charged particle detectors.

Tailoring Electron‐Riched Boron Sites in BCN for Nitrogen Fixation via Alternate Mechanism

AbstractThe electrochemical nitrogen reduction reaction (eNRR) is promising for achieving sustainable ammonia (NH3) production under mild conditions. However, it is still challenged by nitrogen activation and strong competition with the hydrogen evolution reaction. Here, it is revealed that fine‐tuning the local electron density of boron (B) sites at the boron carbon nitride (BCN) solid catalysts has significant effects on the eNRR activity and selectivity. The concentration of electron‐rich B sites at BCN catalysts are mediated by solid‐state reaction, where their electronic structures are confirmed by electron energy‐loss spectroscopy (EELS) and electron paramagnetic resonance (EPR). Over the density functional theory (DFT) calculations, the nitrogen (N2) activation and reduction at an electron‐riched B site is through an alternate pathway with the determining‐step energy of only 0.92 eV. The optimized BCN5 catalyst with the highest ratio of electron‐riched B sites achieves an outstanding NH3 production rate of 29.3 µg h−1 mg−1cat and the highest Faradaic efficiency of 39%.

Validation of low-Z impurity transport theory using boron perturbation experiments at ASDEX upgrade

An experimental technique has been developed at ASDEX upgrade (AUG) to separately identify the diffusive and convective components of the boron particle flux. Using this technique a database of B transport coefficients has been assembled that shows that the normalized ion temperature gradient () is the strongest organizing parameter for both the B diffusion and convection and large is a necessary ingredient to obtain hollow B density profiles in AUG. This database also shows that large changes in the applied neutral beam injection (NBI) have a relatively small impact on impurity transport compared to similar changes in electron cyclotron resonance heating (ECRH). Even low levels of ECRH power dramatically increase both the diffusive and convective fluxes and lead to peaking of the impurity density profile. Comparisons to a combination of neoclassical and quasi-linear gyrokinetic simulations show good agreement in the measured and predicted diffusion coefficients. The outward convection measured in NBI dominated plasmas, however, is not well captured by the simulations, despite the inclusion of fast ions. In contrast, the convection is reasonably well reproduced for plasmas with flat or peaked boron density profiles. This dataset provides an excellent experimental validation of the non-monotonic, predicted, convective-particle-flux created by the combination of pure-pinch, thermo-diffusion, and roto-diffusion. In addition, this dataset demonstrates a non-monotonic dependence of the experimental particle diffusivity to ion heat conductivity (D/χ i) in qualitative agreement with theoretical predictions.

Interactions of Urea-Based Inhibitors with Prostate-Specific Membrane Antigen for Boron Neutron Capture Therapy.

In this study, molecular interactions of prostate-specific membrane antigen (PSMA) with five chemically distinct urea-based boron-containing inhibitors have been investigated at the atomic level using molecular docking and molecular dynamics simulations. The PSMA–inhibitor complexations have been analyzed by comparing their binding modes, secondary structures, root-mean-square deviations, noncovalent interactions, principal components, and binding free energies. PSMA is a cell surface glycoprotein upregulated in cancerous cells and can be targeted by boron-labeled inhibitors for boron neutron capture therapy (BNCT). The effective BNCT requires the selective boron delivery to the tumor area and highly specific PSMA-mediated cellular uptake by tumor. Thus, a potent inhibitor must exhibit both high binding affinity and high boron density. The computational results suggest that the chemical nature of inhibitors affects the binding mode and their association with PSMA is primarily dominated by hydrogen bonding, salt bridge, electrostatic, and π–π interactions. The binding free energies (−28.0, −15.2, −43.9, −23.2, and −38.2 kcal/mol) calculated using λ-dynamics for all inhibitors (In1–5) predict preferential binding that is in accordance with experimental data. Among all inhibitors, In5 was found to be the best candidate for BNCT. The binding of this inhibitor to PSMA preserved its overall secondary structure. These results provide computational insights into the coordination flexibility of PSMA and its interaction with various inhibitors. They can be used for the design and synthesis of efficient BNCT agents with improved drug selectivity and high boron percentage.

Thermal conductivity of densified borosilicate glasses

In this work, we study the thermal conductivity of densified soda lime borosilicate glasses with varying B2O3/SiO2 ratio. Densification is induced by hot compression up to 2 GPa at the glass transition temperature. We find that the structural and mechanical properties of the glasses exhibit a similar response to hot compression as other oxide glasses, including increasing density, elastic moduli, and fraction of four-coordinated boron across the full compositional range. Generally, we find that thermal conductivity increases upon densification, but with a pronounced composition dependence, as silica-rich glasses exhibit only a minor increase (~8-10%) while borate-rich glasses exhibit a significant increase (>50%). We rationalize these variations in terms of topological constraint theory by showing a connection between the contribution of propagative vibrational modes to heat transfer and the volumetric constraint density across both as-made and densified samples. These findings thus provide insights into the linkages between structure and thermal conductivity.

Assessment of neutronic safety parameters of VVER-1000 core under accident conditions

The major issue in designing safety and control systems for power reactors is preventing accidents or reducing the hazard imposed. Any change in reactor power causes a change in temperature and material densities of the system that will affect the reactivity, which in turn, causes transients/accident conditions. The analysis of main safety parameters is essential for any change to ensure the safe operation of the reactor in both steady and transient situations. In this paper, the impact of temperature, moderator density, boron concentration and control rods position changes on the safety parameters is studied to assess the behavior of the reactor under accident conditions. The main safety parameters as temperature reactivity coefficients, power peaking factor, effective delayed neutron fraction and generation time are evaluated under accident conditions for VVER-1000 core using MCNP6 code and ENDF/B-VII.1library. The results evidenced that the reactivity coefficients are still negative, under accident conditions, which guarantee the safe operation of the reactor. The effective delayed neutron fraction increased as a result of increased temperature, decreased moderator density and addition of the soluble boron. The worth of the control rods is sufficient to make the reactor into a subcritical state either in emergency situations or with regular shutdown.

Fertilidad y producción de caña de azúcar en Hueyapan De Ocampo, Veracruz, México

Se analizaron las principales características químicas para determinar el estado de fertilidad de los suelos tipo Andosol, Vertisol y Gleysol, donde se establece el sistema productivo caña de azúcar en Zapoapan de Amapan perteneciente al municipio de Hueyapan de Ocampo del estado de Veracruz. La importancia de este trabajo radica en ubicar la situación que origina rendimientos muy por debajo de lo que se específica para México. El objetivo del presente trabajo fue evaluar los parámetros pH, materia orgánica, conductividad eléctrica, nitrógeno inorgánico, fósforo, contenidos de potasio, calcio, magnesio, fierro, cobre, manganeso, boro y densidad aparente, siguiendo los métodos establecidos en la NOM-021-RECNAT-2000, para ubicar el estado de fertilidad de los suelos y los posibles impactos ambientales ejercidos sobre este recurso natural. Los resultados mostraron que los suelos andosoles tuvieron las mejores condiciones de fertilidad para el cultivo de caña de azúcar; en tanto que los suelos tipo vertisol mostraron problemas leves de contaminación por los contenidos de boro obtenidos. La materia orgánica y el nitrógeno inorgánico son las variables que se deben atender para mejorar la fertilidad de los suelos. La producción de caña de azúcar en la comunidad de Zapoapan de Amapan, es baja (de 25 a 50 ton hectárea), por lo que se recomienda mejorar las prácticas agrícolas con el fin de incrementar los contenidos de nutrimentos en los tres tipos de suelo.

Light impurity transport in tokamaks: on the impact of neutral beam fast ions

Previous studies (e.g. (Kappatou 2019 Nucl. Fusion 59 056014)) have shown that discrepancies exist between experimental and modelled light impurity peaking in specific regimes. In particular, in NBI heated plasmas, the strong hollowness of boron profiles are not captured by the modelling. In this context, a dedicated ASDEX Upgrade discharge, including boron and helium density measurements, is studied where such discrepancies appear. Emphasis is given to the impact of fast ions on the turbulent and neoclassical impurity transport computed with the codes GKW and NEO, respectively. It is shown that fast ions increase the turbulent outward impurity convection via an increase of both thermo- and roto-diffusion. This increase is correlated with the stabilisation of the ion temperature gradient driven mode (ITG). Additionally, the ratio of the turbulent impurity diffusion over the ion heat diffusion is reduced with fast ions, which in turn, increases the neoclassical contributions to the impurity peaking. Finally, neoclassical convection is also enhanced through changes in the ion density gradient due to the modification of the quasi-neutrality condition in the presence of peaked fast ion profiles. The combination of these three mechanisms induced by the fast ion population has a significant impact on the development of hollow boron profiles, up to experimental levels.

Preparation and Properties of Boron Nitride Fiber Reinforced SiBON Composites

In this paper, BNf/SiBON composites were prepared by adding short boron nitride fibers and in-situ inorganic solid state reaction. The relationships among hot-pressing sintering temperature, boron nitride fiber content, density and flexural strength of the composites were studied. The phase composition and microstructure of the composites were also analyzed and characterized. The results show that the bending strength of BNf/SiBON increases with the increase of sintering temperature when the fiber content is constant, and decreases with the increase of fiber content when the sintering temperature is constant. XRD diffraction patterns also showed that BN had higher crystallinity and larger grain size when the sintering temperature was 1700°C and the content of BN fiber was 40%. Therefore, the best content of boron nitride fibers is in the range of 20% to 40%, and the hot pressing sintering temperature is about 1700°C.

Understanding helium transport: experimental and theoretical investigations of low-Z impurity transport at ASDEX Upgrade

The presence of helium is fundamentally connected to the performance of a fusion reactor, as fusion-produced helium is expected to heat the plasma bulk, while He ‘ash’ accumulation dilutes the fusion fuel. An understanding of helium transport via experimentally validated theoretical models of the low-Z impurity turbulent transport is indispensable to predict the helium density profile in future fusion devices. At ASDEX Upgrade, detailed, multi-species investigations of low-Z impurity transport have been undertaken in dedicated experiments, resulting in an extensive database of helium and boron density profiles over a wide range of parameters relevant for turbulent transport (normalised gradients of the electron density, the ion temperature, and the toroidal rotation profiles, the collisionality and the electron to ion temperature ratio). Helium is not found to accumulate in the parameter space investigated, as the shape of the helium density profile follows largely that of the electron density. Helium is observed to be as peaked as the electron density at high electron cyclotron resonance heating fraction, and less peaked than the electron density at high neutral beam heating fraction. The boron density profile is found to be consistently less peaked than the electron density profile. Detailed comparisons of the experimental density gradients of both impurities with quasilinear gyrokinetic simulations have shown that a qualitative agreement between experiment and theory cannot always be obtained, with strong discrepancies observed in some cases.

Study of interface induced anisotropic exchange coupling in amorphous FeCoB/MgO bilayer

In this work, we present a detailed magneto-optical Kerr effect (MOKE) study of amorphous FeCoB (FCB)/MgO bilayer grown on Si (100) substrate. Two regions with different boron density has been identified in single FCB layer in the as-deposited bilayer due to boron diffusion from FCB to MgO layer at the interface: (i) a boron-deficient layer near FCB/MgO interface (FCBi) and (ii) bulk FeCoB layer (FCBb) located farther away from FCB/MgO interface and having comparatively high boron concentration. As a result, a stress-induced uniaxial magnetic anisotropy is observed in the boron deficient FCBi layer, which is found to be superimposed with the magnetization of FCBb layer. Depending on the angle between the applied magnetic field and the uniaxial easy axis of the FCBi layer, magnetization reversal with single step or double step are observed. Role of interlayer exchange coupling between FCBi and FCBb layer is determined by separating out their magnetic contributions by fitting hysteresis loops with a mathematical function. The disappearance of double step behavior after in-situ annealing up to 473 K, suggests that the observed magnetic anisotropy mainly originates from the strain in the film.

A novel method of studying the core boron transport at ASDEX Upgrade

A new ion cyclotron resonance frequency (ICRF) modulation technique has been developed and exploited at ASDEX Upgrade for obtaining time perturbed boron density signals. Square wave modulation of the ICRF heating power results in a periodic modulation of the boron density in the edge, which propagates inward. From this time perturbed boron density signal, the boron diffusivity and convection in the radial transport equation are individually determined. This task is done by solving an inverse problem by a quasi-Newton method. This implemented framework has been verified with the Method of Manufactured Solutions and benchmarked with the transport code STRAHL. The experimental transport coefficients are compared with neoclassical calculations with the code NEO and gyrokinetic simulations with the code GKW. The neoclassical diffusivity is well below the experimental one. The comparison to gyrokinetic theory shows a good agreement in the diffusivity, but the theoretical convection predicts a more peaked boron density profile than measured in the experiment.

Development of Albumin‐closo‐Dodecaborate Conjugates as Boron Carriers for Neutron‐Capture Therapy by Ru(bpy)3‐Photocatalyzed Modification of Tyrosine

Serum albumin has attracted significant attention as a drug‐delivery carrier to tumor tissue. We previously reported boron neutron capture therapy (BNCT), an effective method that uses maleimide‐functionalized closo‐dodecaborate albumin conjugates (MID‐ACs). MID can form covalent bonds with the free thiol group of Cys34 and with lysine residues in albumin. In this study, we synthesized tyrosyl‐radical‐trapping‐moiety‐functionalized closo‐dodecaborates (TRT‐DBs), which were expected to form covalent bonds with tyrosine residues. N′‐Acetyl‐N,N‐dimethylphenylenediamine was chosen as the TRT moiety to bind to closo‐dodecaborate through an amide linker (TRT‐DB 1) and an ammonium linker (TRT‐DB 2). TRT‐DB 1 more efficiently conjugated to bovine serum albumin (BSA) than 2: approximately 2.4 molecules of 1 were bound to each BSA if BSA (10 µm) was treated with 1 (1 mm) in the presence of Ru(bpy)3 (1 mm; bpy = 2,2′‐bipyridyl) and ammonium persulfate (1 mm) under light irradiation for 1 min. Furthermore, double modification of BSA with 1 and MID increased the boron density in BSA for efficient boron delivery to tumors. Western blot analysis using the anti‐B12 cluster antibody revealed that closo‐dodecaborate‐conjugated BSAs were taken up by colon 26 cells.

Complementary photogating effect in microcrystalline silicon n-i-p structures

Spectral responses above the unity at short wavelengths have not been yet reported in μc-Si:H based n-i-p devices illuminated with a red bias light. In solar cells this effect is known as the Complementary Photo-Gating Effect. After calibrating the input parameters of our computer code by matching experimental output device characteristics, the necessary conditions to predict these anomalous responses at short wavelengths were explored. In order to obtain SR higher than unity at short wavelengths in μc-Si:H n-i-p devices under red bias illumination a highly defective buffer layer must be present at the p/i interface. The short wavelength a.c. probe beam modulates the carrier concentration trapped at the gap states of the defective interface strengthen the electrical field in the intrinsic layer and weaken the electrical field inside the p-doped and p/i buffer layers. The short wavelength a.c. probe beam reduces the total recombination loss inside the intrinsic layer with respect to its counterpart under only red bias light illumination generating a net gain and spectral responses over unity. This phenomenon is predicted in devices with either high or low mobility (p)-layers, such as (p)-a-SiC:H and (p)-μc-Si:H respectively, that are not very efficiently doped with boron. Spectral responses higher than one are very sensitive to the electrical parameters of the p/i defective buffer such as mobility gap, thickness, density of defects, mobilities, capture cross sections of donor traps, and to the Boron density present in the p-layer and to the spectral content of the red bias light.

Electro-oxidation and characterization of nickel foam electrode for removing boron

The electrocoagulation (EC) using metallic Ni foam as electrodes was studied for the removal of boron from solution. The electrolytic parameters were pH (4–12), current density (0.6–2.5 mA cm−2), and initial concentration of boron (10–100 mg L−1). Experimental results revealed that removal efficiency was maximized at pH 8–9, and decreased as the pH increased beyond that range. At particular onset potentials (0.5–0.8 V vs. Hg/HgO), the micro-granular nickel oxide that was created on the surface of the nickel metal substrate depended on pH, as determined by cyclic voltammetry. Most of the crystallites of the precipitates comprised a mixed phase of β-Ni(OH)2, a theophrastite phase, and NiOOH, as revealed by XRD and SEM analyses. A current density of 1.25 mA cm−2 was effective in the EC of boron, and increasing the concentration of boric acid from 10 to 100 mg L−1 did not greatly impair removal efficiency. A kinetic investigation revealed that the reaction followed a pseudo-second order rate model. The optimal conditions under which 99.2% of boron was removed from treated wastewater with 10 mg L−1-B, leaving less than 0.1 mg L−1-B in the electrolyte, were pH 8 and 1.25 mA cm−2 for 120 min.

Effect of 10-year continuous saffron cultivation on physical and chemical properties of soil

The effect of 10-year continuous saffron cultivation on physical and chemical properties of a silty clay loam soil was investigated in a research farm of College of Agriculture, Shiraz University, Shiraz (52 o 33ʹ E Longitude and 29o 36ʹ N latitude), Iran. This farm was irrigated with different regimes (100% of saffron's potential evapotranspiration (ETp), 75%ETp, 50%ETp) including rain fed treatment under two irrigation methods (basin and furrow irrigation). The results showed that the values of electrical conductivity, sodium adsorption ratio, Arsenic, Boron and soil bulk density of soil in the root zone increased significantly, but the final infiltration rate decreased significantly compared to the original soil. The value of pH in 100%ETp and 75%ETp treatments decreased and in 50%ETp and rain fed treatments increased compared to the original soil. Corms under high irrigation treatment had more weight up to a 6-year cultivation. However, after that, the corm weight declined to levels equal to or less than the low irrigation treatment cases. The number of total corms increased up to 6 years of cultivation and decreased after that. So, the continuous saffron cultivation causes some undesirable change in soil chemical and physical properties, which become pronounced after 6 years of cultivation.