On the Determination of Elastic Properties of Single-Walled Boron Nitride Nanotubes by Numerical Simulation

The elastic properties of chiral and non-chiral single-walled boron nitride nanotubes in a wide range of their chiral indices and diameters were studied. With this aim, a three-dimensional finite element model was used to assess their rigidities and, subsequently, elastic moduli and Poisson’s ratio. An extensive study was performed to understand the impact of the input parameters on the results obtained by numerical simulation. For comparison, the elastic properties of single-walled boron nitride nanotubes are shown together with those obtained for single-walled carbon nanotubes.     

Characteristics of Cr-B Coatings Produced on Vanadis® 6 Tool Steel Using Laser Processing

The paper presents the results of a study of the microstructure, chemical composition, microhardness and corrosion resistance of Cr-B coatings produced on Vanadis 6 tool steel. In this study, chromium and boron were added to the steel surface using a laser alloying process. The main purpose of the study was to determine the impact of those chemical elements on surface properties. Chromium and boron as well as their mixtures were prepared in various proportions and then were applied on steel substrate in the form of precoat of 100 µm thickness. Depending on the type of precoat used and laser processing parameters, changes in microstructure and properties were observed. Coatings produced using precoat containing chromium and boron mixture were characterized by high microhardness (900 HV0.05–1300 HV0.005) while maintaining good corrosion resistance. It was also found that too low laser beam power contributed to the formation of cracks and porosity.     

Low Recombination Firing-Through Al Paste for N-Type Solar Cell with Boron Emitter

A kind of low recombination firing-through screen-printing aluminum (Al) paste is proposed in this work to be used for a boron-diffused N-type solar cell front side metallization. A front side fire-through contact (FTC) approach has been carried out for the formation of local contacts for a front surface passivated solar cell. With a low contact resistivity (ρ_c) of 1.0 mΩ·cm², good ohmic contact between the boron-doped front surface of the silicon sample and the Al paste was realized. To obtain a good energy conversion efficiency, a balance can be achieved between the open circuit voltage (V_oc) and contact resistivity (ρ_c) of the cell by combining suitable Al powders and appropriate additives. The detailed micro-contact difference in Si/metallization between the firing-through Al paste and silver-aluminum (Ag-Al) paste was analyzed. The dark saturation current density beneath the metal contact (J_{0, metal}) of the Si/metallization region using our firing-through Al paste was discussed, which was proven to be 61% lower than using Ag-Al paste. The pseudo energy conversion efficiency of the cell using Al paste measured by Suns-V_OC was also higher than using Ag-Al paste. The role of Al paste in low surface metal recombination is discussed. The utilization of this new kind of Al paste was much cheaper and more convenient, compared to the traditional process using Ag or Ag-Al paste.     

Effects of Boron Carbide on Coking Behavior and Chemical Structure of High Volatile Coking Coal during Carbonization

Modified cokes with improved resistance to CO₂ reaction were produced from a high volatile coking coal (HVC) and different concentrations of boron carbide (B₄C) in a laboratory scale coking furnace. This paper focuses on modification mechanism about the influence of B₄C on coking behavior and chemical structure during HVC carbonization. The former was studied by using a thermo-gravimetric analyzer. For the latter, four semi-cokes prepared from carbonization tests for HVC with or without B₄C at 450 °C and 750 °C, respectively, were analyzed by using Fourier transform infrared spectrum and high-resolution transmission electron microscopy technologies. It was found that B₄C will retard extensive condensation and crosslinking reactions by reducing the amount of active oxygen obtained from thermally produced free radicals and increase secondary cracking reactions, resulting in increasing size of aromatic layer and anisotropic degree in coke structure, which eventually improves the coke quality.     

饮食加硼治疗维甲酸诱导骨质疏松模型大鼠的效果观察

目的观察饮食加硼治疗维甲酸诱导的骨质疏松模型大鼠的效果,为硼临床治疗骨质疏松症提供实验依据。方法SD大鼠32只,随机分为正常组(n=8)和骨质疏松模型组(n=24)。以维甲酸80mg.kg-1.d-1灌胃15d,诱导骨质疏松模型。模型复制成功后,骨质疏松模型组又随机分为无措施对照组(n=8)、饮食加硼治疗组(n=8)和雌二醇治疗组(n=8)。治疗30d后,测定大鼠血清钙、磷、硼含量,及碱性磷酸酶(AKP)和酸性磷酸酶(TRAP)活性,测量大鼠全身、腰椎和胫骨骨密度,并观察大鼠股骨形态计量学变化。结果四组大鼠血清Ca和P含量无显著性差异,而硼含量硼治疗组明显高于其它三组。对照组大鼠血清AKP和TRAP活性增加,股骨松质骨和皮质骨骨量减少,破骨细胞数量增加,腰椎、胫骨骨密度下降,呈现骨质疏松变化。饮食加硼和雌激素治疗组大鼠血清TRAP活性显著下降,股骨平均骨小梁数、平均骨小梁宽度、骨小梁面积百分比、皮质骨面积百分比和全身、腰椎、胫骨骨密度等显著增加,松质骨区破骨细胞数明显减少,与正常组大鼠骨质无明显差异。硼治疗组大鼠血清AKP活性及松质骨区活跃成骨细胞数显著增加。结论饮食加硼可提高大鼠血清硼含量,增加骨形成,减少骨吸收,对骨质疏松有明显的治疗作用。     

Residual Stress Induced by Addition of Nanosized TiC in Titanium Matrix Composite

A hot pressing process was employed to produce titanium-based composites. Nanosized TiC particles were incorporated in order to improve mechanical properties of the base material. The amount of nanosized additions in the composites was 0.5, 1.0, and 2.0 wt %, respectively. Moreover, a TiB phase was produced by in situ method during sintering process. The microstructure of the Ti–TiB–TiC composites was characterized by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) techniques. Due to the hot pressing process the morphology of primary TiC particles was changed. Observed changes in the size and shape of the reinforcing phase suggest the transformation of primary carbides into secondary carbides. Moreover, an in situ formation of TiB phase was observed in the material. Additionally, residual stress measurements were performed and revealed a mostly compressive nature with the fine contribution of shear. With an increase in TiC content, linear stress decreased, which was also related with the presence of the TiB phase.     

Study of Nano h-BN Impact on Lubricating Properties of Selected Oil Mixtures

Our experiments aimed to study the influence of layered materials with nanometric-scale particles, which are part of lubricant oils, on their tribological properties. The object of this study was a lubricant oil made using base oil PAO4, which contained nanoparticle hexagonal boron nitride (nano h-BN) and a dispersant based on succinic acid imide. Comparative tests for engine oil (CB30) were also performed. The paper presents the method of preparing the test material and the tribological test results, including wear spot diameter (wear mark), limit wear load, and seizure load. The test results obtained demonstrate that nano-hexagonal boron nitride improves the tribological properties of lubricant oils. However, oil preparation and the quantitative selection of components markedly influence the results.     

Environmental boron exposure and activity of delta-aminolevulinic acid dehydratase (ALA-D) in a newborn population.

Following boron intake, multiple effects have been observed in animal experiments. However, human data is lacking, and no data is available on the ability of boron to accumulate in fetal tissues. Positive responses in animal species suggest that developmental toxicity may be an area of concern in humans, following exposure to boron. Two hypotheses have seemed to account for the multiple effects described in scientific findings. One hypothesis is that boron is a negative regulator that influences a number of metabolic pathways by competitively inhibiting some key enzyme reactions. The other hypothesis is that boron has a role in ionic membrane transport regulations. To better understand boron potential toxicity, the present study examined the relationship between boron exposure and some key enzymes, well-known for their affinity for mineral elements, such as delta-aminolevulinic acid dehydratase (ALA-D), and two fundamental enzymes having a role in ionic membrane transport regulations (Ca-pump and Na(+)K(+)-ATPase). We investigated the potential effects of an environmental boron exposure on the activity of these enzymes in an urban population of 197 "normal" newborns. Environmental boron exposure was assessed in placental tissue. Because of the well-known inhibiting effect of lead on these enzymes, cord blood and placental lead were also analyzed. After adjustment for potential confounders, including lead, placental boron levels were negatively significantly correlated to ALA-D activity while Ca-pump and Na(+)K(+)-ATPase activities did not seem to be affected by the level of boron exposure. Given boron's ability, as a Lewis acid, to complex with hydroxyl groups, we suggest that such a mechanism would explain the inhibiting effect of boron on ALA-D.     

Pharamacokinetic modeling for boronophenylalanine-fructose mediated neutron capture therapy: 10B concentration predictions and dosimetric consequences

Summary A two-compartment open model has been developed for predicting¹⁰B concentrations in blood following intravenous infusion of thel-p-boronophenylalanine-fructose complex in humans and derived from pharmacokinetic studies of 24 patients in Phase I clinical trials of boron neutron capture therapy. The¹⁰B concentration profile in blood exhibits a characteristic rise during the infusion to a peak of ∼32 μg/g (for infusion of 350 mg/kg over 90 min) followed by a biexponential disposition profile with harmonic mean half-lives of 0.32±0.08 and 8.2±2.7 h, most likely due to redistribution and primarily renal elimination, respectively. The mean model rate constantsk ₁₂,k ₂₁, andk ₁₀ are (mean ±SD) 0.0227±0.0064 min⁻¹, 0.0099±0.0027 min⁻¹, 0.0052±0.0016 min⁻¹, respectively, and the central compartment volume of distributionV ₁ is 0.235 ± 0.042 L/kg. In anticipation of the initiation of clinical trials using an intense neutron beam with concomitantly short irradiations, the ability of this model to predict, in advance, the average blood¹⁰B concentration during brief irradiations was simulated in a retrospective analysis of the pharmacokinetic data from these patients. The prediction error for blood boron concentration and its effect on simulated dose delivered for each irradiation field are reported for three different prediction strategies. In this simulation, error in delivered dose (or, equivalently, neutron fluence) for a given single irradiation field resulting from error in predicted blood¹⁰B concentration was limited to less than 10%. In practice, lower dose errors can be achieved by delivering each field in two fractions (on two separate days) and by adjusting the second fraction’s dose to offset error in the first.     

Boron Neutron Capture Therapy of Brain Tumors: Clinical Trials at the Finnish Facility Using Boronophenylalanine

Two clinical trials are currently running at the Finnish dedicated boron neutron capture therapy (BNCT) facility. Between May 1999 and December 2001, 18 patients with supratentorial glioblastoma were treated with boronophenylalanine (BPA)-based BNCT within a context of a prospective clinical trial (protocol P-01). All patients underwent prior surgery, but none had received conventional radiotherapy or cancer chemotherapy before BNCT. BPA-fructose was given as 2-h infusion at BPA-dosages ranging from 290 to 400mg/kg prior to neutron beam irradiation, which was given as a single fraction from two fields. The average planning target volume dose ranged from 30 to 61Gy (W), and the average normal brain dose from 3 to 6Gy (W). The treatment was generally well tolerated, and none of the patients have died during the first months following BNCT. The estimated 1-year overall survival is 61%. In another trial (protocol P-03), three patients with recurring or progressing glioblastoma following surgery and conventional cranial radiotherapy to 50–60Gy, were treated with BPA-based BNCT using the BPA dosage of 290mg/kg. The average planning target dose in these patients was 25–29Gy (W), and the average whole brain dose 2–3Gy (W). All three patients tolerated brain reirradiation with BNCT, and none died during the first three months following BNCT. We conclude that BPA-based BNCT has been relatively well tolerated both in previously irradiated and unirradiated glioblastoma patients. Efficacy comparisons with conventional photon radiation are difficult due to patient selection and confounding factors such as other treatments given, but the results support continuation of clinical research on BPA-based BNCT.