1,721,163 research outputs found
기능적 근적외선 분광법을 이용한 2차 판별분석 기반 운동 상상 상태 분류에 관한 연구
No full text뇌-컴퓨터 인터페이스; 근적외선 분광기; 신호처리; 선형 판별 분석; 부분공간방법Abstract i
List of contents ii
List of figures iii
Ⅰ. Introduction 1
Ⅱ. Background · 3
1. Modified Beer-Lambert Law (MBLL) 3
2. Temporal derivative distribution repair (TDDR) · 4
3. Mutual Subspace method (MSM) · 5
4. Linear discriminant analysis (LDA) · 6
Ⅲ. Method 8
1. Data acquisition 8
2. Data pre-processing 9
3. Conventional methods · 10
3.1 Statistical feature extraction for LDA 10
3.2 Mutual Subspace Method (MSM) · 11
4. Proposed Method · 11
5. Performance evaluation 13
Ⅳ. Result 14
Ⅴ. Conclusion 16
Ⅵ. Reference · 17MasterdCollectio
High utilization of methanol in toluene methylation using MFI zeolite nanosponge catalyst
No full textA highly mesoporous MFI zeolite nanosponge, which was composed of a disordered assembly of 2.5-nm thick zeolite frameworks, was synthesized using a meso- and micropore dual structure-directing surfactant. The zeolite nanosponge was investigated as a catalyst for toluene methylation by methanol. The results showed remarkably high toluene conversion and xylene yield, in comparison with the bulk zeolite counterparts. The high catalytic performance was attributed to the suppression of side reactions that could convert methanol to linear hydrocarbons. This suppression can be attributed to the fact that the dealkylation of polymethylbenzenes, which must take place before linear hydrocarbon formation, did not occur significantly in the zeolite nanosponge as compared to the case of bulk zeolites. In addition to the aforementioned high performance, the MFI zeolite nanosponge was also superior to the bulk MFI in terms of catalytic longevity. © 2017 Elsevier B.V
Facile synthesis of mesoporous zeolite Y using seed gel and amphiphilic organosilane
No full text© 2019 Elsevier Inc.Zeolite Y is widely used as an industrial catalyst for catalytic cracking of heavy feedstocks to lighter olefins. However, incorporation of uniform mesoporosity in zeolite Y without compromising the microporous characteristics is required to improve the catalyst efficiency and minimize catalyst deactivation. Here, we report a facile synthesis method for mesoporous zeolite Y (MPYsg) using seed gel and amphiphilic organosilane, that results in mesoporous zeolite showing a narrow mesopore size distribution (3–4 nm) with high external surface area (110 m2g-1) and high micropore surface area (654 m2g-1). During the crystallization of MPYsg, the organosilane acted as a mesopore-generating agent, and the seed gel provided secondary nuclei that created a uniform mesoporous structure in the zeolite Y nanocrystals. Analysis of aluminosilicate precursors collected during the crystallization revealed that the crystallization process starts with a long nucleation period, followed by rapid crystal growth. Due to the highly accessible strong acid sites present on its external surface, MPYsg shows catalytic activity in the decalin cracking reaction higher than that of conventional microporous zeolite Y11sciescopu
Bulk crystal seeding on the generation of mesopores by organosilane surfactants in zeolite synthesis
No full textZeolites of MOR, CHA, and FAU-X topologies were conventionally synthesized using Na+ or an organic structure-directing agent, except that organosilane surfactants were added as a mesopore-generating agent. The organosilanes were represented by the structural formula (CH3O)(3)Si-C3H6-N+(CH3)(2)CnH2n+1, where n was varied from 12 to 16 and 18. Each zeolite synthesis was seeded with a small amount of bulk zeolites of the same structure type. The synthesis result indicated that the bulk zeolite seeds disappeared completely from the zeolite products, indicating their disintegration into tiny fragments that were undetectable by high-resolution transmission electron microscopy. Nevertheless, the zeolite seeding caused a dramatic decrease in synthesis time. More importantly, crystal seeding, in comparison to unseeded synthesis, was highly effective in extending the organosilane-directed mesopore-generating strategy to a wide range of mesoporous and zeolite structures.117191sciescopu
Mesopore-selective incorporation of strong Brønsted acid catalytic sites via aluminium grafting on hierarchically porous siliceous MFI zeolite
No full text© 2020 Elsevier Inc. Post-synthetic Al grafting onto the surface silanols in mesoporous MFI zeolite has been investigated in an attempt to obtain a model catalytic material that possesses strong Brønsted acid sites at mesopore surfaces of the zeolite, but not inside the microporous framework. To this end, a siliceous MFI zeolite with a mesopore/micropore hierarchy was synthesized using a meso-micro dual structure-directing diammonium surfactant. The hierarchically porous zeolite was treated with anhydrous AlCl3 for the formation of Si–O–Al bonding with silanols on the mesopore surfaces. According to solid-state 31P NMR spectroscopy of the surface-adsorbed phosphine oxides and catalytic activity for decalin cracking, the Al-grafting treatment performed in the conventional manner resulted in the formation of weak Brønsted acid sites, similar to Al grafting on SBA-15 mesoporous silica. To obtain strong Brønsted acid sites, we have developed a method of heating the AlCl3-grafted zeolite in a controlled-humidity chamber before calcination. The resultant zeolite was catalytically active for cracking of hydrocarbons requiring strong acid sites, but not for methanol-to-hydrocarbon conversion. The results support that the moisture treatment caused a local reconstruction of the initially grafted Al–O–Si framework portion to a strong Brønsted acid site. In addition, our model catalytic zeolite material unveiled the catalytic activity of Brønsted acid sites at the mesopore surfaces in hierarchically porous zeolite in n-octane cracking. Furthermore, we confirmed that this method was effective for other mesoporous MFI zeolites obtained through a post-synthetic desilication route11sciescopu
Electrochemical Reduction of CO2 to CO by N,S Dual-Doped Carbon Nanoweb Catalysts
No full textConverting CO2 into useful chemicals through an electrocatalytic process is an attractive solution to reduce CO2 in the atmosphere. However, the process suffers from high overpotential, low activity, or poor product selectivity. In this study, N,S dual-doped carbon nanoweb (NSCNW) materials were proposed as an efficient nonmetallic electrocatalyst for CO2 reduction. The NSCNW catalysts preferentially and rapidly converted CO2 into CO with a high Faradaic efficiency of 93.4 % and a partial current density of -5.93 mA cm(-2) at a low overpotential of 490 mV. A small Tafel slope value (93 mV dec(-1)) was obtained, demonstrating a high rate for CO2 reduction. Moreover, the catalysts also exhibited a quite stable current-density profile during 20 h with a high CO Faradaic efficiency above 90 % throughout the electrolysis reaction. The high catalytic performance of the catalysts for CO2 reduction could be attributed to synergistic effects associated with the structural advantages of 3 D carbon nanoweb structures and effective S doping of the carbon materials with the highest ratio of thiophene-like S to oxidized S species.11Nsciescopu
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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