177,017 research outputs found
Direct surface modification of ligand-free silicon quantum dots prepared by femtosecond laser ablation in deionized water
No full textAmine-terminated, ultra-small silicon nanoparticles (Si-NPs) were prepared in one step avoiding the conventional chemical or thermal treatment of Si surface, by introducing organosilane in Si-NPs colloidal solution freshly prepared by ultra-fast laser ablation of silicon target in deionized water. Surface chemistry studies of Si-NPs conducted by Raman and Fourier infrared spectroscopy demonstrated the hydroxyl-terminated surface of Si-NPs. The reactivity of hydroxyl-terminated surface with aminopropyltriethoxysilane in aqueous solution was investigated. Electron microscopy, dynamic light scattering, infrared spectroscopy and stability studies confirmed the successful functionalization of Si-NPs leading to 5 nm Si dots covered by aminopropyltriethoxysilane thick layer. Detailed infrared spectroscopy analysis of the Si-O-Si region as a function of immersion time revealed the formation of interfacial Si-O bonds between the organosilane and hydroxyl groups of the nanoparticles. The biocompatible Si nanostructure containing amine functional group prepared using a one-step green protocol opens the route for biomedical applications and successful translation into clinical setting, as bio-labels, contrast agents and vector delivery
Extensive Characterization of Oxide-Coated Colloidal Gold Nanoparticles Synthesized by Laser Ablation in Liquid
No full textLaser-Fabricated Fluorescent, Ligand-Free Silicon Nanoparticles: Scale-up, Biosafety, and 3D Live Imaging of Zebrafish under Development
No full textThis work rationalizes the scalable synthesis of ultrasmall, ligand-free silicon nanomaterials via liquid-phase pulsed laser ablation process using picosecond pulses at ultraviolet wavelengths. Results showed that the irradiation time drives hydrodynamic NP size. Isolated, monodisperse Si-NPs are obtained at high yield (72%) using post-treatment process. The obtained Si-NPs have an average size of 10 nm (not aggregated) and display photoemission in the green spectral range. We directly characterized the ligand-free Si-NPs in a vertebrate animal (zebrafish) and assessed their toxicity during the development. In vivo assay revealed that Si-NPs are found inside in all the early life stages of embryos and larvae growth, showing that the biosafety of Si-NPs and malformation types are independent of the Si-NP dose. Si-NPs were directly imaged inside developing embryos by spinning disk-imaging technique with optical sectioning capability. We showed that Si-NPs can passively enter inside embryos by the pore canals of chorion, can diffuse in the circulatory system, i.e., blood vessel, and accumulate inside larvae midgut and yolk sac, and in the eye lens, indicating the crossing of the blood barrier
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Luminescent silicon nanoparticles prepared by ultra short pulsed laser ablation in liquid for imaging applications
No full textOptical properties of femtosecond laser-synthesized Silicon nanoparticles in deionized water
No full textSilicon nanoparticles were prepared by ultrafast laser ablation of a silicon target in deionized water. The nanoparticles were characterized by using optical absorption, Raman spectroscopy, and transmission electron microscopy. The mean size is found to vary from 60 to 2.5 nm in the absence of any reducing chemical reagents, decreasing the pulse energy value. High-resolution transmission electron microscopy together with Raman spectroscopy confirms the crystalline structure of the generated silicon nanoparticles. The energy confinement of carriers which is evaluated from optical experiments varies from 90 to 550 meV when the mean nanoparticles size decreases from 60 to 2.5 nm. In particular, the evaluated nanoparticle sizes from optical analysis and the LCAO theoretical model are found in agreement with transmission electron microscopy and Raman measurements for the silicon nanoparticles with a size less than 6 nm. Finally, we present stability studies which show that the smallest nanoparticles aggregate over time
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Optical characterization of silicon nanoparticle obtained via femtosecond laser ablation in deionized water
No full textWe reported the synthesis of silicon nanoparticles with mean size varying from 60 nm to 3 nm, by ultrafast laser ablation of a silicon target in deionized water. Optical absorption, Raman spectroscopy and Electron microscopy were performed to characterize the nanoparticles. The crystalline structure of the obtained silicon nanoparticles was confirmed with Raman spectroscopy combined with High resolution transmission electronic microscopy. The energy confinement of carriers which is evaluated from optical experiments varies from 90 meV to 440 meV when the mean nanoparticles size decreases from 60 nm to 3 nm. In particular, the evaluated nanoparticles size from optical analysis and LCAO theoretical model are found in agreement with Transmission Electron Microscopy and Raman measurements for the silicon nanoparticles with a size less than 6 nm. Finally, we studied the stability of silicon nanoparticles with time which demonstrates that the smallest nanoparticle aggregates over time
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Facile fabrication of bioactive ultra-small protein-hydroxyapatite nanoconjugates via liquid-phase laser ablation and their enhanced osteogenic differentiation activity.
No full textHydroxyapatite bioactive complexes are being increasingly recognized as effective available means in regenerative medicine. Conventional technologies for their synthesis have drawbacks from a synthetic standpoint, mainly requiring high temperatures and multi-step processes. Here, we show that ultra-small hydroxyapatite conjugated-nanoparticles (Ha-CNPs) can be obtained at room temperature by Pulsed Laser Ablation (PLA) directly in protein solution using picosecond pulses at near infrared wavelengths. The results showed that the nanoparticle size was driven by the concentration of the protein. Using this approach, we obtained aqueous soluble and ultra-small crystalline nanoparticles of ≈3 nm diameter coated with protein molecules (surface coverage ≈ 5.5 pmol cm−2; zeta potential ≈−33.5 mV). These nanoparticles showed low cytotoxicity in vitro compared to chemically synthesized nanoparticles, and revealed proliferative and osteoinductive effects on human bone marrow mesenchymal stem cells (hMSCs). The resulting enhanced cell osteogenic differentiation suggested that our PLA-based synthetic approach might be exploited in novel applications of regenerative medicine
- …
