1,721,007 research outputs found
Plasmon Enhanced Luminescence : Interaction of Silver and Gold Nanoparticles with Perovskite Nanocomposites
No full textviii, 28 p.All inorganic CsPbX3 (X = Cl, Br, I) perovskites have shown fabulous optical properties and tunable ability by different halide composition which covers the whole visible spectrum of 410 nm to 700 nm. This interesting property gathered researchers’ attention on promising application to solar cells and LEDs. One of the crucial aspects of these applications is energy efficiency. To generate a good quantum yield, this research focused on how to enhance photoluminescence of CsPbX3 perovskites by Plasmon resonance effect of metallic nanoparticles. Six different halide composition CsPbX3 were synthesized and interacted with gold and silver nanoparticles to observe the change or enhancement in an optical property of CsPbX3 perovskites. UV-visible spectra, emission scan, fluorescence lifetime measurement, and TEM were used to study the interaction between CsPbX3 perovskites with metallic nanoparticles. Photoluminescence enhancement of CsPbCl3 perovskite with both gold and silver nanoparticles was observed. In addition, CsPbBr3 and CsPbI3 perovskites also shown photoluminescence enhancement with gold nanoparticles. CsPbX3 perovskites with chloride composition performed photoluminescence enhancement with silver nanoparticles. Other combinations CsPbX3 perovskites and metallic nanoparticles resulted in quenching of fluorescence, but by observing quenching rate of fluorescence and fluorescence lifetime, the research was able to understand the interaction between CsPbX3 perovskites with metallic nanoparticles
Analyzing the Stability and Interactions of GQuadruplex and G-Triplex DNA in Drug Systems by Using Novel Optical Spectroscopy Techniques
No full textix, 76 p.There have been studies that demonstrate the existence of non-canonical DNA such as G-Quadruplex and G-Triplex within the human body. These structures tend to serve biological roles within telomeres and other DNA systems. G-Quadruplex and Triplex structure in the telomeres have shown to be anticancerous by preventing the rapid replication of cancer cells. However, one needs to stabilize the G-quadruplex and G-triplex DNA structures to stop replication, which is the main motivation of the present work. In our approach, we analyzed the stability of the G-Quadruplex and G-Triplex with different drug systems in order to understand which drugs made these non-canonical DNA systems more stable and how they bind to the DNA backbone. In this process, we propose to establish new spectroscopic technique based on relative twophoton absorption that can monitor drug-DNA binding interactions. For these studies, temperature-dependent UV-Vis, 1-photon and 2-photon fluorescence, circular dichroism, and relative 2-photon cross-sections were carried out. Most important among them is the utilization of the relative 2-photon cross-section in monitoring the binding orientation of the drug relative to the DNA backbone. Interesting stability trends were obtained that can be correlated with the structure of the drug and DNA binding modes. More experiments are needed to establish more inroads into 2PA cross-section techniques such as fluorescence anisotropy to see another perspective of drug binding
Chromophore Synthesis and Functionalization of Au25 Nanoclusters
No full textx, 43 p.Gold nanoclusters (<2nm in size) exhibit interesting optical properties due to the role of quantum confinement in their electronic energy levels. Functionalization of these clusters with chromophores has already found application in the biomedical fields among others and thus synthesis of novel clusters with new properties is desirable. This project aimed to create several novel functionalizations of [Au25(PPh3)10(SC6)5Cl2 ]2+ nanorods and [Au25(SC6)18]− nanospheres with N-(2-mercaptoethyl)pyrene-1-carboxamide, N-(2-mercaptoethyl)anthracene-1- carboxamide, and mercaptoethylcoumarin343 carboxamide. Ligands were synthesized by a twostep synthetic route, with an acyl chloride serving as the intermediate between the carboxylic acid starting materials and the final thiolated amines. Pure products were not produced and therefore no pure, functionalized clusters were produced. Instead, UV-Visible and fluorescence analysis of different concentrations of prepared ligands with the nanoclusters was conducted in order to investigate possible formation of functionalized clusters and their optical properties. This investigation revealed that when the ligands and nanoclusters were combined, shifts in fluorescence and absorbance were observed with nanocluster-N-(2-mercaptoethyl)pyrene-1- carboxamide and nanocluster-N-(2-mercaptoethyl)anthracene-1-carboxamide systems. Such shifts were not observed in nanocluster-anthracene carboxylic acid and nanocluster-pyrene carboxylic acid systems
Two-Photon Spectroscopy To Differentiate Molecule-DNA Binding Interactions
No full textviii, 46 p.The objective of this study is to search for novel spectroscopic techniques to monitor molecule-DNA interactions using the 2PA cross-sections of molecules as markers. The hypothesis is that the 2PA cross-section is very sensitive to electric fields, and the DNA backbone possesses an inherent electric field that can alter the 2PA cross-sections of DNA chromophores. Molecules can interact with DNA through intercalation or minor-groove binding, altering the specified electric field. The method of molecules binding to DNA was studied using five dyes; Hoe33258, AcrO, ThT, DTI, and DTDCI. The 2PA cross-section was determined and 2PA enhancements were obtained and used as markers for DNA-molecule interactions. In addition, CD and absorption spectral changes were used to follow the binding of the molecules with DNA. The results of the 2PA cross-sections have shown that ThT, AcrO, and DTI dyes bind to DNA through intercalation, shown by a decrease or no change in the 2PA cross-section, while Hoe33258 and DTDCI dyes are minor-groove binders, shown by an enhancement of the cross-sections. These results confirm the electric field hypothesis where the electric field is parallel to the molecular dipole for minor-grove binding and perpendicular to the molecular dipole for intercalation. Monitoring the electric field of the samples could also be an efficient and cost-effective way to determine which molecule is a reliable indicator for specific DNA. Measurements were performed to understand the role of single, double and quadruple stranded DNA on molecule-DNA interactions. The research was mainly focused on obtaining better markers to study molecule-G-quadruplex DNA interactions that were implied in apoptosis. Hoe33258 was unable to differentiate between duplex and quadruplex DNA. Hoe33258 and AcrO were able to differentiate between single and quadruplex DNA. ThT was able to successfully indicate each strand, single, duplex, and quadruplex DNA.Department of Chemistry. Western Michigan University. Kalamazoo, Michigan
Synthesis and Temperature-Dependent Optical Properties of CsPbX3 (X=C1, Br, I) Nanoctystals: Towards Water Soluble Perovskite Nanocrystals
No full textvii, 32 p.Lead-halide based perovskites and perovskite nanocomposites have witnessed exponential growth in research attention largely because of their promising applications in solar cells, light emitting diodes and biological imaging. All inorganic CsPbX3nanocrystals show luminescence in the visible region ranging from 420-700 nm, based on the composition and temperature of the synthesis of the halide. To develop robust perovskite nanocomposites for applications in optoelectronic processes, several fundamental questions must be understood, such as the influence of temperature and passivation on the optical properties. This study is aimed at understanding the influence of temperature and photo-passivation on the optical properties of perovskite nanocrystals, as well as to develop strategies to synthesize perovskite nanocrystals that maintain their optical properties and are soluble in water. To achieve the objectives, CsPbX3 (X = Cb, CbBr, ClBr2,Bn, Bnh Brh, I3) were synthesized using a hot injection method. Optical absorption and steady-state PL measurements were used to identify perovskite nanocomposites. Temperature dependent studies shows that inhomegeneities in nanocrystals are more pronounced at higher temperatures. Photo-passivation experiments suggest that the initial photopassivation reduced the non-radiative deactivation. While the PL intensity of CsPbBn NC decreased with increased time when they are in the presence of block copolymers. In addition, synthesis of CsPbBr3 nanocrystals were carried out while adding block copolymers during the synthesis that yielded CsPbBr3 nanocrystals that are soluble in polar solvents without significant changes in PL properties
Electron – Phonon Interactions In Atomically Precise Silver Nanoclusters And Metal Doped Silver Nanoclusters
No full text21 p.Temperature dependent absorption measurements were run for Ag25(SPhMe2)18 -, Ag24Au(SPhMe2)18 -, Ag24Pt(SPhMe2)18 -, Ag24Pd(SPhMe2)18 -, and Ag24Hg(SPhMe2)18 to further investigate and understand the properties of the “Golden” silver nanoparticle. Ag25 was doped with transitional metals to see the effect each atom has on the overall optical properties of the cluster. It was seen that the optical properties are temperature dependent, which agrees with previous research done by Dr. Bakr4. Electron-phonon coupling constants were calculated from each absorption spectrum using a modified Bose-Einstein equation developed by O’Donnel and Chen7. It was observed that Pd and Au had the largest effect on the coupling constant, with values of 16.228 and 17.422 respectively compared to 12.956 for Ag25. This differs from Hg and Pt with coupling constants of 12.956 and 12.959 respectively. This result provides an interesting route for further research to find a more efficient method to increase the electron-phonon interaction within Ag25 nanoclusters
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
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