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991.
The assessment of the toxicity of airborne nanofibers is an important task. It relies on toxicological inhalation studies and validated exposure measurement techniques. Both require nanofiber-containing aerosols of known morphological composition and controlled fraction of individual fibers. Here, a dry powder dispersion method is presented that operates with mixtures of nanofibers and microscale beads. Aerosolization experiments of mixtures of multi-walled carbon nanotubes (MWCNTs) and glass beads that were continuously fed into a Venturi nozzle enabled high generation rates of aerosols composed of individual and agglomerate nanofiber structures. The aerosol process achieved good stability over more than 2 h with respect to concentration and aerodynamic size distribution. Its operation duration is limited only by the reservoir volume of the cyclone used to separate the beads from the aerosol. The aerosol concentration can be controlled by changing the mass ratio of MWCNTs and glass beads or by adapting the mass feed rate to the nozzle. For two agglomerated MWCNT materials, aerosol concentrations ranged from 1700 to 64,000 nano-objects per cm3. Comprehensive scanning electron microscope analysis of filter samples was performed to categorize and determine the morphological composition of the aerosol, its fiber content as well as fiber length and diameter distributions. High fractions of individual fibers of up to 34% were obtained, which shows the setup to be capable of dispersing also highly tangled MWCNT agglomerates effectively.  相似文献   
992.
Mixed Cu–Ag alloys with different compositions have been produced and subjected to an accelerated sulphidation process which causes the development of a mixed sulphide‐rich corroded film on their surface. It was called tarnishing, that is, the formation of a blue‐brownish patina when Cu–Ag alloys are exposed in a sulfur‐containing atmosphere. The structures of the pristine alloys have been determined by the combined analytical techniques as scanning electron microscopy energy dispersive X‐ray microanalysis and X‐ray diffraction. The experimental conclusions confirmed the occurrence of micro phase separation with the formation of different dendritic domains of about 10 µm in width. The sulphidized samples were firstly investigated by optical microscopy and X‐ray diffraction in order to verify the homogeneity of the patina and to identify the different AgCuS phases appearing on the alloy surfaces. It was observed that, despite the inherent micro‐heterogeneity of the alloys, the sulphide layer was throughout uniform in composition at the micro‐scale. The complex scenario of the relative stability of all the various mixed sulphides involved was then explored by micro‐Raman spectroscopy (μ‐RS), pointing out that the Cu‐for‐Ag substitution in the crystal lattice of the mixed Ag–Cu sulphides caused a monotonous blue shift of the vibrational wavenumbers in Raman spectra. This study has unveiled microscopic details of the tarnishing process, furnishing an innovative, cheap and non‐destructive methodology based on μ‐Raman spectroscopy for the evaluation of the silver‐copper artefacts via the compositions of their corroded products. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
993.
Abstract

We present the excitation spectra of KI:T1 measured in the region of the B and C absorption bands at several emission wavelengths and at 20 K, 80 K and 300 K. An accurate analysis of these spectra shows new properties of the excitation spectra, that we relate to the non radiative relaxation of the excited electrons towards the luminescent states.  相似文献   
994.
Photonic band gap (PBG) crystals have been used as a perfectly reflecting substrate for many millimeter wave applications. In this work the fin line directional coupler with substrate PBG was analyzed using the TTL - Transverse Transmission Line - method. Compared to other full wave methods the TTL is an efficient tool to determine the coupler characteristics, making possible a significant algebraic simplification of the equations involved in the process. In order to analyze this structure the effective dielectric constant, the attenuation constant and the coupling were determined. The results obtained for this application and the conclusions are presented. This work was partially financed by CNPQ.  相似文献   
995.
We have imagined a numerical experiment to explore the onset of turbulent intermittency associated with a spatial perturbation of the correlation length. We place two isotropic regions, with different integral scales, inside a volume where the turbulent kinetic energy is initially uniform and leave them to interact and evolve in time. The different length scales produce different decay rates in the two regions. Since the smaller-scale region decays faster, a transient turbulent energy gradient is generated at the interface between the two regions. The transient is characterized by three phases in which the kinetic energy gradient across the interface grows, peaks and then slowly decays. The transient lifetime is almost proportional to the initial ratio of the correlation lengths. The direct numerical simulations also show that the interface width grows in time. The velocity moments inside this interaction zone are seen to depart from their initial isotropic values and, with a certain lag, the anisotropy is seen to spread to small scales. The longitudinal derivative moments also become anisotropic after a few eddy turnover times. This anisotropic behaviour is different from that observed in sheared homogeneous turbulent flows, where high transverse derivative moments are generated, but longitudinal moments almost maintain the isotropic turbulence values. Apart from the behaviour of the energy gradient transients, the results also show the timescaling of the interface diffusion width, and data on the anisotropy of the large and small scales, observed through one-point statistics determined inside the intermittency sublayer, which is associated with the interaction zone.  相似文献   
996.
Different silver nanostructures have been rapidly synthesized under microwave irradiation from a solution of silver nitrate (AgNO3) and ββ-D glucose; neither additional reducing nor capping agent were required in this soft green solution approach. Not only spherical nanoparticles, but also necklace and wires have been synthesized. The plasmon resonances of the synthesized silver nanostructures were tuned by varying the irradiation time and hence by changing size and morphology of nanostructures. The obtained nanostructures were characterized by X-Ray diffraction (XRD), Uv–Vis spectroscopy (Uv–Vis), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The change of peak position and the shape of the absorption spectra were clearly observed during the whole reaction process; in fact, it was evidenced that initially Ag nanoparticles were formed, which, as reaction time elapsed, self-assembled and fused with each other to yield nanowires.  相似文献   
997.
First order phase transitions involve nucleation, formation of nanoscale regions of a new phase within a metastable parent phase. Using the heterogeneous nucleation theorem we show how clusters formed by nucleation on single molecules evolve from the gas phase and determine the critical size beyond which condensation starts to form aerosol particles. Our experiments reveal the activation of molecules into droplets to happen via formation of critical clusters substantially larger than the seed molecule. The nanosized critical clusters were found to be well predicted by the Kelvin-Thomson relation pointing directly to the key step in the phase transition.  相似文献   
998.
The synthesis procedure represents a key aspect in designing the physical and chemical properties of gold nanoparticles. The current study proposes a simple approach for gold nanoparticles synthesis using non-thermal plasma. The novelty of the setup consists in producing an in-liquid plasma discharge in argon bubbles that are externally generated in the solution exposed to treatment. Because plasma is the source of active species which are directly involved in gold reduction, no additional reducing agent was necessary. Collagen protein was used as capping agent. A plasma treatment of 10 min is sufficient for obtaining stable colloidal solutions with UV-Vis absorption maximum at 530 nm. Transmission electron microscopy images revealed preponderant spherical nanoparticles with dimensions in the range of 6–20 nm. The method of synthesis distinguishes by its good reproducibility, facility, efficiency, and ability to generate stable colloidal nanoparticles after several minutes of plasma exposure.  相似文献   
999.
Molecular Diversity - SARS-CoV-2 Mpro, also known as the main protease or 3C-like protease, is a key enzyme involved in the replication process of the virus that is causing the COVID-19 pandemic....  相似文献   
1000.
We report the realization of the continuous wave laser emission in the orange at 607 nm from a Pr:BaY(2)F(8) (Pr:BYF) crystal pumped by a blue GaN laser diode. A maximal output power of 78 mW is obtained in a quasi-single transverse mode beam. The effect of reabsorption losses at the laser wavelength is also evidenced.  相似文献   
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