1,721,000 research outputs found
Computational and Spectroscopic Characterization of the Photocycle of an Artificial Rhodopsin
Get PDFThe photocycle of a reversible photoisomerizing rhodopsin mimic (M2) is investigated. This system, based on the cellular retinoic acid binding protein, is structurally different from natural rhodopsin systems, but exhibits a similar isomerization upon light irradiation. More specifically, M2 displays a 15-cis to all-trans conversion of retinal protonated Schiff base (rPSB) and all-trans to 15-cis isomerization of unprotonated Schiff base (rUSB). Here we use hybrid quantum mechanics/molecular mechanics (QM/MM) tools coupled with transient absorption and cryokinetic UV-vis spectroscopies to investigate these isomerization processes. The results suggest that primary rPSB photoisomerization of M2 occurs around the C13═C14 double bond within 2 ps following an aborted-bicycle pedal (ABP) isomerization mechanism similar to natural microbial rhodopsins. The rUSB isomerization is much slower and occurs within 48 ps around the C15═N double bond. Our findings reveal the possibility to engineer naturally occurring mechanistic features into artificial rhodopsins and also constitute a step toward understanding the photoisomerization of UV pigments. We conclude by reinforcing the idea that the presence of the retinal chromophore inside a tight protein cavity is not mandatory to exhibit ABP mechanism
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
Recommended from our members
Exploration of Oxidative Etching of Plasmonic Gold Nanostructures
Get PDFThe utilization of plasmonic nanomaterials has inspired scientists for decades due to their unique optical phenomenon, known as localized surface plasmon resonance (LSPR). This phenomenon is one of the driving forces behind the creation of new nanostructures due to their material, size-, and shape-dependent properties. Significant research, in the field of nanoplasmonics, has been done to create nanomaterials used for various applications in catalysis, surface enhanced Raman scattering (SERS), and LSPR-based sensors. Gold nanorod (AuNRs) are of exceptional interest due to their shape dependent properties which allow the longitudinal mode of the LSPR to be tuned from the visible to the near infrared region. Chapter 1 reviews the common synthetic methods for gold nanorods and the importance of surface modification.Chapter 2 provides an in-depth analysis of the theoretical simulations of the LSPR for gold nanostructures for both analytical and numerical methods. Insights on the shape, size, and refractive index dependence for the LSPR is addressed. Furthermore, in the subsequent chapters, the extinction efficiencies are calculated for all the synthesized nanomaterials presented in this dissertation using discrete dipole approximation (DDA) method, introduced in this chapter.
The focus of Chapter 3 is on the controlled etching of silica coated gold nanorods into twelve different gold nanostructures. This chapter highlights how shape control is crucial to fine tune the optical properties of a nanostructure. Investigation into the mechanisms to synthesize each of these nanostructures was done via UV-Vis-NIR spectroscopy, NMR spectroscopy, and optical microscopy imaging.
Chapter 4 introduces a unique nanomaterial called Agu, which has less than 2 nm layer of silver coating on spherical gold nanoparticles. For 100 nm gold nanoparticle with a silver coating between 0.5 and 2 nm, the shift in the surface plasmonic resonance (SPR) peak follows a sigmoidal function as a function of silver thickness on gold. This nanomaterial was used to detect X-ray irradiation etching of silver.
The final chapter offers concluding remarks on the various nanostructures which have been synthesized throughout this dissertation. Description of the future work and applications are given
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
Recommended from our members
Investigations of Enhancing X-ray Effects by Nanomaterials and Development of Nanostructures for Potential Application
Get PDFX-ray is widely used in medical areas, typically for cancer treatment. Studies seek to enhance the X-ray effect using nanomaterials to increase energy deposition efficiency and a new discipline called X-ray nanochemistry was established based on these studies. While nanoparticles with high Z materials are proven to be able to deposit more X-ray energy to a system, nanoparticles are also found to be involved in the chemical reactions triggered by X-ray or biological response under radiation. These findings lead to discussions about other types of dose enhancement factors like chemical enhancement and biological enhancement are discussed. More studies were still needed to study the mechanisms and deconvolute these dose enhancement factors. The dissertation presents continuous work in the field of X-ray nanochemistry, focusing on type 2 physical enhancement and chemical enhancement. Direct quantification of type 2 physical enhancement (T2PE) was done by conjugating a 12-mer single-strand DNA onto surfaces of silica-coated gold nanoparticles (Au@SiO2). T2PE comes from energy deposited by secondary electrons emitted from nanoparticles in radiation which are low-energy electrons and will disappear a few nanometers from the surface of the nanoparticles. 3 reporters were linked to DNA strands respectively and the magnitude of T2PE was determined by comparing the number of reporters released from Au@SiO2 versus the same size of SiO2 when DNA strand breaks occurred. More than 9 times more reporters were released in the presence of 1wt% Au@SiO2. T2PE showed a much higher dose enhancement factor than T1PE and can help to develop X-ray-triggered releasing nanosystems by using single-strand DNA as linkers on the nanoparticle surface.
An EPR study was performed using spin trap BMPO(5-tert-Butoxycarbonyl-5-methyl-1-pyrroline-N-oxide) to detect •OH produced by X-ray radiation in the presence of 3-nm THPC (Tetrakis(hydroxymethyl)phosphonium chloride) AuNPs. Similar amounts of •BMPO-OH, the intermediate, were detected compared to the solution irradiated without the presence of AuNPs. More •BMPO-H adduct was detected when AuNPs were in the solution during radiation. Such a result indicated that for low concentration of small AuNPs didn’t increase the production of •OH but catalyzed the conversion of a hydroxylation intermediate to another product. A triple jumps mechanism was then proposed based on this finding.
The possible existence of catalyzed breakage of single-strand DNA on small AuNPs surfaces was explored. DNA strands with fluorophores and quenchers at each end were loaded on Au surfaces then irradiated. The FRET (Förster resonance energy transfer) effect on the DNA strand was interrupted when the strand is broken. Amounts of SSBs (single-strand breaks) were determined using increased fluorescence intensity after X-ray irradiation. Mass spectrometry was used to quantify DNA damage after irradiation using an internal standard in the samples. Nearly 9 times more SSBs with correction when DNA strands were on 5-nm citrate AuNPs. A higher SSBs to total DNA damage ratio was also found, indicating possible catalytic base damage conversion to strand breaks on Au surfaces.
A nanoreactor for X-ray application was synthesized and tested. A •OH probe, 3CCA (coumarin-3-carboxylic acid) was encapsulated in hollow mesoporous silica shells. The shells were sealed with another layer of solid silica to prevent probes from escaping. A dose-dependent response was measured with fluorometry. A linear dose response was observed when the nanoreactors were in dry form or suspended in solutions with scavengers or with small AuNPs. Results showed that the synthesized structure can be used as a nanoreactor for X-ray application. The silica layer was not interacting with probes trapped inside and successfully isolated internal molecules
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
- …
