1,720,977 research outputs found
Parameter-Aware I/O Management for Solid State Disks (SSDs)
No full textSolid state disks (SSDs) have many advantages over hard disk drives, including better reliability, performance, durability, and power efficiency. However, the characteristics of SSDs are completely different from those of hard disk drives with rotating disks. To achieve the full potential performance improvement with SSDs, operating systems or applications must understand the critical performance parameters of SSDs to fine-tune their accesses. However, the internal hardware and software organizations vary significantly among SSDs and, thus, each SSD exhibits different parameters which influence the overall performance. In this paper, we propose a methodology which can extract several essential parameters affecting the performance of SSDs, and apply the extracted parameters to SSD systems for performance improvement. The target parameters of SSDs considered in this paper are 1) the size of read/write unit, 2) the size of erase unit, 3) the size of read buffer, and 4) the size of write buffer. We modify two operating system components to optimize their operations with the SSD parameters. The experimental results show that such parameter-aware management leads to significant performance improvements for large file accesses by performing SSD-specific optimizations
Post-functionalization of polyethers by photoinduced C–H amidation via polar-radical relay
No full textAbstract The C–H functionalization of polymers enables the direct incorporation of new functional groups into polymer backbones, presenting significant opportunities for the upcycling of commodity polymers. However, developing reactions that achieve selective functionalization while preserving the intrinsic features of polymers and avoiding undesirable structure deformation remains a considerable challenge. In this study, we present a transition metal-free post-functionalization approach for polyethers via a photoinduced α-C–H amidation reaction. This strategy provides a route to previously unattainable α-amino polyethers, which exhibit distinct physical properties from those of the parent polymer. By leveraging a polar-radical relay mechanism, we effectively incorporate C–N bonds into the polyether backbone while suppressing degradation and cross-linking. Conducted under mild and convenient conditions, this approach demonstrates significant site selectivity at the ethereal α-position, even in the presence of other types of C–H bonds, achieving tailed post-functionalization of macromolecules. Furthermore, the present strategy holds promise for broader applications, including the amidative degradation of commodity polymers and transformation of polyethylene glycol (PEG) network
Merging NiH Catalysis and Inner-Sphere Metal-Nitrenoid Transfer for Hydroamidation of Alkynes
No full textThe formal hydroamination/hydroamidation utilizing metal hydride is an appealing synthetic tool for the construction of valuable nitrogen-containing compounds from unsaturated hydrocarbons. While significant advances have been made for the functionalizations of alkenes in this realm, the direct hydroamidation of alkynes remains rather limited due to the high feasibility of the key metal-alkenyl intermediate to choose other reaction pathways. Herein, we report a NiH-catalyzed strategy for the hydroamidation of alkynes with dioxazolones, which allows convenient access to synthetically useful secondary enamides in (E)-anti-Markovnikov or Markovnikov selectivity. The reaction is viable for both terminal and internal alkynes and is also tolerant with a range of subtle functional groups. With H2O found as an essential component for high catalyst turnovers, the involvement of inner-sphere nitrenoid transfer is proposed that outcompetes an undesired semireduction process, thus representing the first example to show the competence of Ni catalysis for metal-nitrenoid formation from dioxazolones.11Nsciescopu
Endo-Selective Intramolecular Alkyne Hydroamidation Enabled by NiH Catalysis Incorporating Alkenylnickel Isomerization
No full text© Intramolecular alkyne hydroamidation represents a straightforward approach for the access to synthetically valuable cyclic enamides. Despite some advances made in this realm, the ability to attain a precise regiocontrol still remains challenging, especially for endo cyclization that leads to six-membered and larger azacyclic rings. Herein, we report a NiH-catalyzed intramolecular hydroamidation of alkynyl dioxazolones that allows for an excellent endo selectivity, thus affording a range of six- to eight-membered endocyclic enamides with a broad scope. Mechanistic investigations revealed that Ni(I) catalysis is operative in the current system, proceeding via regioselective syn-hydronickelation, alkenylnickel E/Z isomerization, and Ni-centered inner-sphere nitrenoid transfer. In particular, the key alkenylnickel isomerization step, which previously lacked mechanistic understandings, was found to take place through the η2-vinyl transition state. The synthetic value of this protocol was demonstrated by diastereoselective modifications of the obtained endocyclic enamides to highly functionalized δ-lactam scaffolds.11Nsciescopu
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
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