Página 1 dos resultados de 4272 itens digitais encontrados em 0.046 segundos

A Study on Physical and Chemical Properties of Cellulose Paper Immersed in Various Solvent Mixtures

Sahin, Halil Turgut; Arslan, Mustafa Burak
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 25/01/2008 EN
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550.18164%
The cellulose paper treated in proportional mixture systems showed higher liquid absorption compare to only EtOH and MeOH treatments. It was approximately 40–70% and 50–91% higher for EtOH-NaOH and MeOH-NaOH treated papers, respectively. All conditions apparently bring about an effect of decreased strength for papers. The lowest tensile strength of 13.0 N/mm was found with EtOH and NaOH treated samples after 5th repeating wetting-drying stage. But, some conditions gave approximately 21–59.5% higher stretch than untreated samples. The pore size distributions of papers were evaluated with Simons stain procedure and experimental results usually consisted with sorption data. The less intense CH2–CH2- vibrations (1450–1700 cm−1) and C-C and C-O-C peak areas in FTIR spectra indicates lowering H-bonds in solvent treated and dried paper network structure.

Tip-enhanced Raman spectroscopic imaging of patterned thiol monolayers

Stadler, Johannes; Schmid, Thomas; Opilik, Lothar; Kuhn, Phillip; Dittrich, Petra S; Zenobi, Renato
Fonte: Beilstein-Institut Publicador: Beilstein-Institut
Tipo: Artigo de Revista Científica
Publicado em 30/08/2011 EN
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452.07746%
Full spectroscopic imaging by means of tip-enhanced Raman spectroscopy (TERS) was used to measure the distribution of two isomeric thiols (2-mercaptopyridine (2-PySH) and 4-mercaptopyridine (4-PySH)) in a self-assembled monolayer (SAM) on a gold surface. From a patterned sample created by microcontact printing, an image with full spectral information in every pixel was acquired. The spectroscopic data is in good agreement with the expected molecular distribution on the sample surface due to the microcontact printing process. Using specific marker bands at 1000 cm−1 for 2-PySH and 1100 cm−1 for 4-PySH, both isomers could be localized on the surface and semi-quantitative information was deduced from the band intensities. Even though nanometer size resolution information was not required, the large signal enhancement of TERS was employed here to detect a monolayer coverage of weakly scattering analytes that were not detectable with normal Raman spectroscopy, emphasizing the usefulness of TERS.

Paper modified with ZnO nanorods – antimicrobial studies

Jaisai, Mayuree; Baruah, Sunandan; Dutta, Joydeep
Fonte: Beilstein-Institut Publicador: Beilstein-Institut
Tipo: Artigo de Revista Científica
Publicado em 11/10/2012 EN
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553.80355%
Paper with antimicrobial properties was developed through in situ growth of ZnO nanorods. The targeted application for this type of paper is in health centers as wallpaper, writing paper, facemasks, tissue paper, etc. The paper was tested on three model microbes, Gram-positive bacteria Staphylococcus aureus, Gram-negative bacteria Escherichia coli and common airborne fungus Aspergillus niger. No viable bacterial colonies or fungal spores could be detected in the areas surrounding test samples of the antimicrobial paper. Gram-negative bacteria Escherichia coli were found to be inhibited in an area that is 239% and 163% the area of the paper sample under different room lighting conditions, i.e., halogen and fluorescent lamp illumination, respectively. For Gram-positive bacteria Staphylococcus aureus the zones of inhibition surrounding the paper samples are 102% and 70%, and for Aspergillus niger, 224% and 183% of the sample area, under similar lighting conditions.

A New PC and LabVIEW Package Based System for Electrochemical Investigations

Stević, Zoran; Andjelković, Zoran; Antić, Dejan
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 15/03/2008 EN
Relevância na Pesquisa
450.638%
The paper describes a new PC and LabVIEW software package based system for electrochemical research. An overview of well known electrochemical methods, such as potential measurements, galvanostatic and potentiostatic method, cyclic voltammetry and EIS is given. Electrochemical impedance spectroscopy has been adapted for systems containing large capacitances. For signal generation and recording of the response of investigated electrochemical cell, a measurement and control system was developed, based on a PC P4. The rest of the hardware consists of a commercially available AD-DA converter and an external interface for analog signal processing. The interface is a result of authors own research. The software platform for desired measurement methods is LabVIEW 8.2 package, which is regarded as a high standard in the area of modern virtual instruments. The developed system was adjusted, tested and compared with commercially available system and ORCAD simulation.

Changes in Spectral Properties, Chlorophyll Content and Internal Mesophyll Structure of Senescing Populus balsamifera and Populus tremuloides Leaves

Castro, Karen L.; Sanchez-Azofeifa, G. Arturo
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 09/01/2008 EN
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456.323%
In this paper we compare leaf traits and spectral reflectance for sunlit and shafded leaves of Populus tremuloides and Populus balsamifera during autumn senescence using information derived from an Analytical Spectral Devise (ASD) Full Range spectrometer. The modified simple ratio (mSR705) and modified normalized difference index (mND705) were effective in describing changes in chlorophyll content over this period. Highly significant (P<0.01) correlation coefficients were found between the chlorophyll indices (mSR705, mND705)) and chlorophyll a, b, total chlorophyll and chlorophyll a/b. Changes in mesophyll structure were better described by the plant senescence reflectance index (PSRI) than by near-infrared wavebands. Overall, P. balsamifera exhibited lower total chlorophyll and earlier senescence than P. tremuloides. Leaves of P. balsamifera were also thicker, had a higher proportion of intercellular space in the spongy mesophyll, and higher reflectance at 800 nm. Further research, using larger sample sizes over a broader range of sites will extend our understanding of the spectral and temporal dynamics of senescence in P. tremuloides and P. balsamifera and will be particularly useful if species differences are detectable at the crown level using remotely sensed imagery.

Sensitivity of PZT Impedance Sensors for Damage Detection of Concrete Structures

Yang, Yaowen; Hu, Yuhang; Lu, Yong
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 21/01/2008 EN
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451.6444%
Piezoelectric ceramic Lead Zirconate Titanate (PZT) based electro-mechanical impedance (EMI) technique for structural health monitoring (SHM) has been successfully applied to various engineering systems. However, fundamental research work on the sensitivity of the PZT impedance sensors for damage detection is still in need. In the traditional EMI method, the PZT electro-mechanical (EM) admittance (inverse of the impedance) is used as damage indicator, which is difficult to specify the effect of damage on structural properties. This paper uses the structural mechanical impedance (SMI) extracted from the PZT EM admittance signature as the damage indicator. A comparison study on the sensitivity of the EM admittance and the structural mechanical impedance to the damages in a concrete structure is conducted. Results show that the SMI is more sensitive to the damage than the EM admittance thus a better indicator for damage detection. Furthermore, this paper proposes a dynamic system consisting of a number of single-degree-of-freedom elements with mass, spring and damper components to model the SMI. A genetic algorithm is employed to search for the optimal value of the unknown parameters in the dynamic system. An experiment is carried out on a two-storey concrete frame subjected to base vibrations that simulate earthquake. A number of PZT sensors are regularly arrayed and bonded to the frame structure to acquire PZT EM admittance signatures. The relationship between the damage index and the distance of the PZT sensor from the damage is studied. Consequently...

Ferromagnetic behaviour of Fe-doped ZnO nanograined films

Straumal, Boris B; Protasova, Svetlana G; Mazilkin, Andrei A; Tietze, Thomas; Goering, Eberhard; Schütz, Gisela; Straumal, Petr B; Baretzky, Brigitte
Fonte: Beilstein-Institut Publicador: Beilstein-Institut
Tipo: Artigo de Revista Científica
Publicado em 13/06/2013 EN
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451.3291%
The influence of the grain boundary (GB) specific area s GB on the appearance of ferromagnetism in Fe-doped ZnO has been analysed. A review of numerous research contributions from the literature on the origin of the ferromagnetic behaviour of Fe-doped ZnO is given. An empirical correlation has been found that the value of the specific grain boundary area s GB is the main factor controlling such behaviour. The Fe-doped ZnO becomes ferromagnetic only if it contains enough GBs, i.e., if s GB is higher than a certain threshold value s th = 5 × 104 m2/m3. It corresponds to the effective grain size of about 40 μm assuming a full, dense material and equiaxial grains. Magnetic properties of ZnO dense nanograined thin films doped with iron (0 to 40 atom %) have been investigated. The films were deposited by using the wet chemistry “liquid ceramics” method. The samples demonstrate ferromagnetic behaviour with J s up to 0.10 emu/g (0.025 μB/f.u.ZnO) and coercivity H c ≈ 0.03 T. Saturation magnetisation depends nonmonotonically on the Fe concentration. The dependence on Fe content can be explained by the changes in the structure and contiguity of a ferromagnetic “grain boundary foam” responsible for the magnetic properties of pure and doped ZnO.

A Compact Laboratory Spectro-Goniometer (CLabSpeG) to Assess the BRDF of Materials. Presentation, Calibration and Implementation on Fagus sylvatica L. Leaves

Biliouris, Dimitrios; Verstraeten, Willem W.; Dutré, Phillip; van Aardt, Jan A.N.; Muys, Bart; Coppin, Pol
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 07/09/2007 EN
Relevância na Pesquisa
452.07746%
The design and calibration of a new hyperspectral Compact Laboratory Spectro-Goniometer (CLabSpeG) is presented. CLabSpeG effectively measures the bidirectional reflectance Factor (BRF) of a sample, using a halogen light source and an Analytical Spectral Devices (ASD) spectroradiometer. The apparatus collects 4356 reflectance data readings covering the spectrum from 350 nm to 2500 nm by independent positioning of the sensor, sample holder, and light source. It has an azimuth and zenith resolution of 30 and 15 degrees, respectively. CLabSpeG is used to collect BRF data and extract Bidirectional Reflectance Distribution Function (BRDF) data of non-isotropic vegetation elements such as bark, soil, and leaves. Accurate calibration has ensured robust geometric accuracy of the apparatus, correction for the conicality of the light source, while sufficient radiometric stability and repeatability between measurements are obtained. The bidirectional reflectance data collection is automated and remotely controlled and takes approximately two and half hours for a BRF measurement cycle over a full hemisphere with 125 cm radius and 2.4 minutes for a single BRF acquisition. A specific protocol for vegetative leaf collection and measurement was established in order to investigate the possibility to extract BRDF values from Fagus sylvatica L. leaves under laboratory conditions. Drying leaf effects induce a reflectance change during the BRF measurements due to the laboratory illumination source. Therefore...

Non-Destructive Evaluation of Historical Paper Based on pH Estimation from VOC Emissions

Strlič, Matija; Cigić, Irena Kralj; Kolar, Jana; de Bruin, Gerrit; Pihlar, Boris
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 05/12/2007 EN
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551.2721%
Volatile organic compounds (VOCs) emitted from materials during degradation can be a valuable source of information. In this work, the emissions of furfural and acetic acid from cellulose were studied using solid-phase micro-extraction (SPME) in combination with gas chromatography-mass spectrometry. Two sampling techniques were employed: static headspace sampling using SPME for 1 h at 40 °C after 18-h sample preparation at 80 °C in a closed glass vial, and contact SPME in a stack of paper (or a book). While a number of VOCs are emitted from paper under conditions of natural or accelerated degradation, two compounds were confirmed to be of particular diagnostic value: acetic acid and furfural. The emissions of furfural are shown to correlate with pH of the cellulosic environment. Since pH is one of the most important parameters regarding durability of this material, the developed method could be used for non-destructive evaluation of historical paper.

A Novel Pulse Measurement System by Using Laser Triangulation and a CMOS Image Sensor

Wu, Jih-Huah; Chang, Rong-Seng; Jiang, Joe-Air
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 19/12/2007 EN
Relevância na Pesquisa
449.0286%
This paper presents a novel, non-invasive, non-contact system to measure pulse waveforms of artery via applying laser triangulation method to detect skin surface vibration. The proposed arterial pulsation measurement (APM) system chiefly consists of a laser diode and a low cost complementary metal-oxide semiconductor (CMOS) image sensor. Laser triangulation and centroid method are combined with the Fast Fourier Transform (FFT) in this study. The shape and frequency of the arterial pulsation can be detected rapidly by using our APM system. The relative variation of the pulse at different measurement points near wrist joint is used as a prognostic guide in traditional Chinese medicine (TCM). An extensive series of experiments was conducted to evaluate the performance of the designed APM system. From experimental results, the pulse amplitude and frequency at the Chun point (related to the small intestine) of left hand showed an obvious increase after having food. In these cases, the peak to peak amplitudes and the frequencies of arterial pulsations range from 38 to 48 μm and from 1.27 to 1.35 Hz, respectively. The height of arterial pulsations on the area near wrist joint can be estimated with a resolution of better than 4 μm. This research demonstrates that applying a CMOS image sensor in designing a non-contact...

High-Rise Buildings versus Outdoor Thermal Environment in Chongqing

Lu, Jun; Chen, Jin-hua; Tang, Ying; Feng, Yuan; Wang, Jin-sha
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 11/10/2007 EN
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450.18164%
This paper gives a brief description of the over quick urbanization since Chongqing, one of the biggest cities in China, has been a municipality directly under the Central Government in 1997, excessive development and exceeding increase of high-rise buildings because of its special geographical position which finally leads to the worsening of the urban outdoor thermal environment. Then, this paper makes a bright balance to the field measurement and simulated results of the wind speed field, temperature field of one multifunctional high-rise building in Chongqing university located in the city center, and the contrasted results validate the correctness of CFD in the outdoor thermal environmental simulation, expose the disadvantages of high-rise buildings on the aspects of blocking the wind field, decreasing wind speed which results in accumulation of the air-conditioning heat revolving around and periscian region where sunshine can not rip into. Finally, in order to improve the urban outdoor thermal environment near the high-rise buildings especially for the angle of natural ventilation, this paper simulates the wind environment in different architectural compositions and architectural layouts by CFD, and the simulated results show that freestyle and tower buildings which can guarantee the wind speed and take the air-conditioning heat away are much suitable and reasonable for the special Chongqing geography. These conclusions can also be used as a reference in other mountain cities...

Structural Characteristics and Reactivity Relationships of Nitroaromatic and Nitramine Explosives – A Review of Our Computational Chemistry and Spectroscopic Research

Qasim, Mohammad M.; Moore, Brett; Taylor, Lyssa; Honea, Patricia; Gorb, Leonid; Leszczynski, Jerzy
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 13/12/2007 EN
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545.64414%
Although much has been discovered, discussed and written as to problems of contamination by various military unique compounds, particularly by the nitrogen based energetics (NOCs), remaining problems dictate further evaluation of actual and potential risk to the environment by these energetics and their derivatives and metabolites through determination of their environmental impact—transport, fate and toxicity. This work comprises an effort to understand structural relationships and degradation mechanisms of current and emerging explosives, including nitroaromatic; cyclic and cage cyclic nitramine; and a nitrocubane. This review of our computational chemistry and spectroscopic research describes and compares competitive degradation mechanisms by free radical oxidative, reductive and alkali hydrolysis, relating them, when possible, to environmental risk.

Some reflections on the understanding of the oxygen reduction reaction at Pt(111)

Gómez-Marín, Ana M; Rizo, Ruben; Feliu, Juan M
Fonte: Beilstein-Institut Publicador: Beilstein-Institut
Tipo: Artigo de Revista Científica
Publicado em 27/12/2013 EN
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449.0286%
The oxygen reduction reaction (ORR) is a pivotal process in electrochemistry. Unfortunately, after decades of intensive research, a fundamental knowledge about its reaction mechanism is still lacking. In this paper, a global and critical view on the most important experimental and theoretical results regarding the ORR on Pt(111) and its vicinal surfaces, in both acidic and alkaline media, is taken. Phenomena such as the ORR surface structure sensitivity and the lack of a reduction current at high potentials are discussed in the light of the surface oxidation and disordering processes and the possible relevance of the hydrogen peroxide reduction and oxidation reactions in the ORR mechanism. The necessity to build precise and realistic reaction models, which are deducted from reliable experimental results that need to be carefully taken under strict working conditions is shown. Therefore, progress in the understanding of this important reaction on a molecular level, and the choice of the right approach for the design of the electrocatalysts for fuel-cell cathodes is only possible through a cooperative approach between theory and experiments.

Rationale for full-season dosing for passive antibody prophylaxis of respiratory syncytial virus

Makari, Doris; Checchia, Paul A; DeVincenzo, John
Fonte: Landes Bioscience Publicador: Landes Bioscience
Tipo: Artigo de Revista Científica
EN
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452.07746%
Palivizumab monthly injections throughout the RSV season prevent severe respiratory syncytial virus (RSV) disease in preterm infants ≤ 35 wGA. However, some RSV guidelines currently recommend stopping palivizumab after 3 months of age in the midst of the RSV season. This article evaluates the need for full-season dosing by reviewing the pharmacokinetic properties of palivizumab and RSV hospitalization (RSVH) risk as a function of chronologic age. Precise human palivizumab protective levels are not established. Clinical trials show significant interpatient variability in palivizumab serum trough concentrations. Partial season dosing is associated with increased risk of RSVH. For late-preterm infants, data suggest that the risk of RSVH remains elevated through at least 6 months of age. Monthly, full-season palivizumab dosing provides the only empirically proven protection from RSVH. In conclusion, late-preterm infants are at significant risk for RSVH through at least 6 months of age and would benefit from dosing throughout the RSV season.

Copolymerization and terpolymerization of carbon dioxide/propylene oxide/phthalic anhydride using a (salen)Co(III) complex tethering four quaternary ammonium salts

Jeon, Jong Yeob; Eo, Seong Chan; Varghese, Jobi Kodiyan; Lee, Bun Yeoul
Fonte: Beilstein-Institut Publicador: Beilstein-Institut
Tipo: Artigo de Revista Científica
Publicado em 05/08/2014 EN
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452.07746%
The (salen)Co(III) complex 1 tethering four quaternary ammonium salts, which is a highly active catalyst in CO2/epoxide copolymerizations, shows high activity for propylene oxide/phthalic anhydride (PO/PA) copolymerizations and PO/CO2/PA terpolymerizations. In the PO/PA copolymerizations, full conversion of PA was achieved within 5 h, and strictly alternating copolymers of poly(1,2-propylene phthalate)s were afforded without any formation of ether linkages. In the PO/CO2/PA terpolymerizations, full conversion of PA was also achieved within 4 h. The resulting polymers were gradient poly(1,2-propylene carbonate-co-phthalate)s because of the drift in the PA concentration during the terpolymerization. Both polymerizations showed immortal polymerization character; therefore, the molecular weights were determined by the activity (g/mol-1) and the number of chain-growing sites per 1 [anions in 1 (5) + water (present as impurity) + ethanol (deliberately fed)], and the molecular weight distributions were narrow (M w/M n, 1.05–1.5). Because of the extremely high activity of 1, high-molecular-weight polymers were generated (M n up to 170,000 and 350,000 for the PO/PA copolymerization and PO/CO2/PA terpolymerization, respectively). The terpolymers bearing a substantial number of PA units (f PA...

Back-to-front Down-under? Estimating the Part-time/Full-time Wage Differential over the Period 2001-2003

Booth, Alison L; Wood, Margi
Fonte: Centre for Economic Policy Research, RSSS, ANU Publicador: Centre for Economic Policy Research, RSSS, ANU
Tipo: Working/Technical Paper
EN
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452.07746%
In 2003, part-time employment in Australia accounted for over 42% of the Australian female workforce, nearly 17% of the male workforce, and represented 28% of total employment. Of the OECD countries, only the Netherlands has a higher proportion of working women employed part-time and Australia tops the OECD league in terms of its proportion of working men who are part-time. In this paper we investigate part-time full-time hourly wage gaps using important new panel data from the first four waves of the new Household, Income and Labour Dynamics in Australia Survey. We find that, once unobserved individual heterogeneity has been taken into account, part-time men and women typically earn an hourly pay premium. This premium varies with casual employment status, but is always positive, a result that survives our robustness checks. We advance some hypotheses as to why there is a part-time pay advantage in Australia.; yes

From Curtin to Keating : the 1945 and 1994 White Papers on Employment: a better environment for human and economic diversity?

Coombs, HC
Fonte: North Australia Research Unit, Australian National University Publicador: North Australia Research Unit, Australian National University
Tipo: Livro
EN
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461.63906%
This short paper provides a brief background to the 1945 White Paper and evaluate its assumptions, shortcomings and successes (The White paper itself is included as there are so few copies available). Nugget also questions many of today’s political and industrial strategies that form the basis of the recent Keating Government’s paper on employment. In particular he questions the assumptions that economic growth and the ‘market’ will lead to growth in employment and a decent livelihood or most Australians.; no

Land and Urban Policies for Poverty Reduction : Proceedings of the Third International Urban Research Symposium Held in Brasilia, April 2005, Volume 1

Freire, Mila; Lima, Ricardo; Cira, Dean; Ferguson, Bruce; Kessides, Christine; Mota, Jose Aroudo; Motta, Diana
Fonte: World Bank, Washington, DC and Institute for Applied Economic Research, Brasilia Publicador: World Bank, Washington, DC and Institute for Applied Economic Research, Brasilia
Tipo: Publications & Research :: Working Paper; Publications & Research
ENGLISH; EN_US
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464.03605%
The first paper of this section (Durand-Laserve) documents how increasing pressures on urban land and the 'commodification' of shelter and settlement has increased 'market evictions' of families holding intermediate tide to property, although international declarations and pressures have contributed to reducing 'forced evictions.' The second paper (Mooya and Cloete) uses the tools of the New Institutional Economics to analyze the argument in Hernando DeSoto's path-breaking book, The Mystery of Capital, that full legal tide is the key to turning 'dead capital' in the form of informal property held by many low-income families into an economic asset and to detonating broad-based economic growth. The paper concludes that intermediate forms of tenure can have the virtues of full legal tide if properly constructed, and then examines the case of Namibia in this context. The third paper (Fernandes) documents and assesses the recent efforts of the Brazilian federal Ministry of Cities to develop a comprehensive approach for regularizing title throughout that country. In the fourth paper...

Framework for automatic information extraction from research papers on nanocrystal devices

Dieb, Thaer M; Yoshioka, Masaharu; Hara, Shinjiro; Newton, Marcus C
Fonte: Beilstein-Institut Publicador: Beilstein-Institut
Tipo: Artigo de Revista Científica
Publicado em 07/09/2015 EN
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556.52496%
To support nanocrystal device development, we have been working on a computational framework to utilize information in research papers on nanocrystal devices. We developed an annotated corpus called “ NaDev” (Nanocrystal Device Development) for this purpose. We also proposed an automatic information extraction system called “NaDevEx” (Nanocrystal Device Automatic Information Extraction Framework). NaDevEx aims at extracting information from research papers on nanocrystal devices using the NaDev corpus and machine-learning techniques. However, the characteristics of NaDevEx were not examined in detail. In this paper, we conduct system evaluation experiments for NaDevEx using the NaDev corpus. We discuss three main issues: system performance, compared with human annotators; the effect of paper type (synthesis or characterization) on system performance; and the effects of domain knowledge features (e.g., a chemical named entity recognition system and list of names of physical quantities) on system performance. We found that overall system performance was 89% in precision and 69% in recall. If we consider identification of terms that intersect with correct terms for the same information category as the correct identification, i.e....

Effective ascorbate-free and photolatent click reactions in water using a photoreducible copper(II)-ethylenediamine precatalyst

Beniazza, Redouane; Bayo, Natalia; Molton, Florian; Duboc, Carole; Massip, Stéphane; McClenaghan, Nathan; Lastécouères, Dominique; Vincent, Jean-Marc
Fonte: Beilstein-Institut Publicador: Beilstein-Institut
Tipo: Artigo de Revista Científica
Publicado em 21/10/2015 EN
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451.3291%
The search for copper catalysts able to perform effectively click reactions in water in the absence of sodium ascorbate is an active area of current research with strong potential for applications in bioconjugation. The water-soluble and photoreducible copper(II)–EDA (EDA = ethylenediamine) complex 1, which has two 4-benzoylbenzoates acting as both counterion and photosensitizer, has been synthesized and characterized by different techniques including single crystal X-ray diffraction. Highly efficient photoreduction was demonstrated when solutions of 1 in hydrogen atom donating solvents, such as THF or MeOH, were exposed to UVA radiation (350–400 nm) provided by a low pressure mercury lamp (type TLC = thin-layer chromatography, 365 nm), or by a 23 W fluorescent bulb, or by ambient/sunlight. In water, a much poorer hydrogen atom donating solvent, the photoreduction of 1 proved inefficient. Interestingly, EPR studies revealed that complex 1 could nonetheless be effectively photoreduced in water when alkynes were present in solution. The catalytic activity of 1 for click reactions involving a range of water-soluble alkynes and azides, in particular saccharides, was tested under various illumination conditions. Complex 1 was found to exhibit a photolatent character...