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[en] High purity boron nitride, without Si and a low carbon content, is prepared by pyrolysis, under an ammoniac atmosphere, of the reaction product between a B-trihalogenoborazole and a primary amine RNH2 when R is a hydrocarbon radical eventually substituted containing from 1 to 6 carbon atoms inclusively
[fr]Du nitrure de bore de haute purete, exempt de silicium et a faible teneur en carbone, est prepare par pyrolyse sous une atmosphere d'ammoniac du produit de reaction entre un B-trihalogenoborazole et une amine primaire: H2 N - R ou R est un radical hydrocarbone, eventuellement substitue, contenant inclusivement entre 1 et 6 atomes de carbone
[en] Highlights: • Investigated keff of PBT composites contain spherical and platelet-shaped hBN. • PMC filled with spherical hBN of relatively small size possessed the highest keff. • Hybrid hBN fillers showed synergistic effect on PMC's keff. • Platelet-shaped hBN of significant size difference exhibited most increase in keff.
[en] Inferring causality has long been a challenging task in environmental impact studies and monitoring programs, mostly because of the problem of confounding bias, i.e. the difficulty of separating impact from natural variation. Traditional approaches for dealing with confounding, despite improvements in study design and statistical analysis, are inadequate. Using aquatic biota as a case study, this review explains the limitations of traditional methods used to separate the impact of human-made pollution from natural variation in the environment. Advantages and disadvantages of the traditional and novel techniques are enumerated. Bayesian networks (BNs) and structural equation modelling (SEM) as causal modelling techniques are introduced as approaches to improve environmental impact monitoring.
[en] The writings of the text on the last line, left column on the 4th page and the text on lines 8th, 10th, 11th and 16th in the 4th paragraph, left column and on lines from 1st to 8th in the 1st paragraph, right column on the 5th page, and the text on line 4th in the 1st paragraph, left column on the 9th page, and Figure 3 and its caption on the 5th page in the original version of this article were unfortunately incorrect.
[en] We study thermoelectric properties of zigzag graphene nanoribbon (ZGNR)–boron nitride (BN) junctions coupled to square electrodes using nonequilibrium Green function formalism in the linear response regime. The embedding of hexagonal BN cells into the ZGNR results in the change of the thermoelectric properties with the length and position of BN cells. The influence of the width variation on the electrical conductance and the Seebeck coefficient of the ZGNR–BN junctions is examined. Also, the coupling of asymmetric electrodes to the ZGNR–BN junctions and the pristine ZGNR is considered. It is observed that the asymmetric electrodes lead to the increase of the Seebeck coefficients of both structures, while the phonon thermal conductance is decreased because of the reduction of the phonon transport in inhomogeneous structures. Our results predict that the thermoelectric efficiency of the system is increased by embedding the hexagonal BN cells, as well as coupling to the asymmetric electrodes. (paper)
[en] Highlights: • Piezopotential of boron nitride honeycombs (BNHCs) is studied by FE-MD simulations. • BNHCs possess a combination of tensile and shear piezoelectricity. • Piezopotential properties of BNHCs can be tailored by adjusting their cell length. • BNHCs possess extremely high specific piezopotential coefficients. Exploring new piezoelectric nanomaterials (PNMs) with unique piezoelectric and piezopotential properties plays a crucial role in designing novel piezotronics nanodevices. In this paper, using hybrid finite element-molecular dynamics simulations, we find a remarkable piezopotential property in the recently proposed boron nitride honeycomb (BNHC) structures. Our results show that, due to their unique polarization distribution BNHCs possess a tensile piezoelectricity in the armchair direction and a shear piezoelectricity in the zigzag direction. It is expected that such a combination of tensile and shear piezoelectricity in BNHCs render them have the ability to harvest almost all types of mechanical energies in the ambient environment. Moreover, the elastic constant, the piezoelectric coefficient and the dielectric constant of BNHCs are found to decrease when their cell length increases, which makes the piezopotential coefficients of BNHCs significantly increase in this process. This observation indicates that the piezopotential properties of BNHCs can be efficiently tailored by adjusting their cell length. As for BNHCs with a proper cell length, we find that their specific piezopotential coefficients can become much larger than those of most existing PNMs. In addition to the remarkable piezopotential properties, a large failure strain is also observed in BNHCs. Such high specific piezopotential coefficients and failure strain in BNHCs render them appealing in the design of novel piezotronics nanodevices with ultralight weight and ultrahigh stretchability.
[en] High temperature BN-insulated heaters for use as fuel pin simulators in reactor thermal hydraulic test facility studies comprise a cylindrical housing and a concentric heating element disposed within the housing and spaced apart from the housing to define an annular region therebetween. The annular region contains BN for providing electrical resistance and thermal conductivity between the housing and the heating element. The fabrication method of this invention comprises the steps of cold pressing BN powder at a pressure of 20 to 80,000 psig and a dwell time of at least 0.1 to 3 seconds to provide hollow cylindrical preforms of suitable dimensions for insertion into the annular region, the BN powder having a tap density of about 0.6 to 1.1 g/cm3 and an orientation ratio of at least about 100/3.5. The preforms are inserted into the annular region and crushed in place