1,721,121 research outputs found
On the Environmentally Friendly Synthesis of 2‐Hydroxyethyl Furan‐5‐Carboxylic Acid (MHEF) and bis(2‐Hydroxyethyl) Furan‐2,5‐Dicarboxylate (BHEF)
Full text linkTo better understand how the biocatalyzed depolymerization of polyesters works, model molecules are needed to develop activity assays and determine enzymatic kinetic parameters. In this communication the chemical synthesis and characterization of 2-hydroxyethyl furan-5-carboxylic acid and bis(2-hydroxyethyl) furan-2,5-dicarboxylates as potential model molecules to further study the enzymatic depolymerization of poly(ethylene furanoate) was investigated
The quest for the new CaLB:Potential of three thermostable polyester hydrolases for esterification reactions
Full text linkThe potential of three thermophilic enzymes from the α,β-hydrolases superfamily, that have recently been described for polyester hydrolysis, was investigated for polyester synthesis, esterification and transesterification reactions. The hydrolases (LCC, leaf-branch compost cutinase; its variant LCCICCG, Thb from Thermoanaerobacterales bacterium) were recombinantly expressed, purified and immobilized onto polypropylene beads. A design of experiments (DoE) assisted study was performed to investigate their synthetic potential to produce short flavor esters by analyzing their thermostability and selectivity towards alcohols and acids with different chain lengths. The factors considered in the DoE (i.e., temperature, alcohol chain length, acid chain length and reaction time) were optimized using MODDE® software to generate a predictive model defining the optimal synthetic conditions for the three enzymes. In each experiment, the monitored response was the acid conversion rate, quantified with GC-FID analysis. For synthesis, the temperature optima of LCC, LCCICCG and Thb were 60 °C, 55 °C, and 80 °C, respectively, corresponding to the maximum percentage of monomers conversion for long-chain alcohols and acids as substrates. Polymerization of dimethyl adipate and 1,8-octanediol as building blocks was carried out to confirm the applicability of the obtained model for the synthesis of larger macromolecules via polycondensation reactions. The proposed approach highlights the innovative application of these novel thermophilic enzymes, traditionally associated with hydrolytic functions, as effective biocatalysts in synthetic processes, enabling the production of a well-known class of polyesters through an alternative and sustainable enzymatic route. Conversion of monomers, as determined by nuclear magnetic resonance (NMR) analysis, was ∼90 % for all enzymes while the average molecular weights (Mn) of the polyesters, analyzed by gel permeation chromatography, were between 3600 Da, for LCC and its variant LCCICCG, and 3800 Da for Thb
Efficient Depolymerization of Poly(ethylene 2,5-furanoate) Using Polyester Hydrolases
Full text linkPoly(ethylene 2,5-furanoate) (PEF) is considered to be the next-generation green polyester and is hailed as a rising star among novel plastics. It is biobased, is nontoxic, and has comparable or improved properties compared to polyethylene terephthalate (PET). Biobased PEF offers lower life-cycle greenhouse gas emissions than PET. However, with its industrial production starting soon, relatively little is known about its actual recyclability. This work reports on the near complete depolymerization of PEF using two efficient PET hydrolases, FastPETase and leaf compost-cutinase (LCC), at loadings 4.5–17 times lower than previously reported. FastPETase and LCC exhibited maximum depolymerization of PEF, measured by weight loss and 2,5-furandicarboxylic acid (FDCA) production, using potassium phosphate–NaOH buffer at 50 and 65 °C, respectively. The 98% depolymerization of 13 g L–1 PEF film was achieved by three additions of the LCC in 72 h, while 78% weight loss was obtained using FastPETase in controlled conditions. Nonetheless, 92% weight loss was obtained with FastPETase when using only 6 g L–1 PEF. The main reaction products were identified as FDCA, ethylene glycol, and mono(2-hydroxyethyl)-furanoate. LCC performed better than FastPETase, in terms of both FDCA release and weight loss. The effect of crystallinity was evident on the enzymes’ performance, as only 4% to 7% weight loss of crystalline PEF (32%) was recorded. Microscopy studies of the treated PEF films provided information on the surface erosion processes and revealed higher resistance of the crystalline phase, explaining the low level of depolymerization. The study presents important insights into the enzymatic hydrolysis of biobased PEF material and paves the path toward more viable applications within biopolymer waste recycling
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
Modelling and Analysis of TCSC Application to Transmission System
No full textM.E. (PSED)The need for more efficient electricity systems management has given rise to
innovative technologies in power generation and transmission. Flexible AC
Transmission Systems (FACTS) is one of such technologies that respond to these
needs. It significantly alters the way transmission systems are developed and
controlled together with improvement in asset utilization, system flexibility and
system performance. Different types of FACTS devices are being used now-a-days.
Thyristor Controlled Series Compensator is one of the series compensating FACTS
devices.
Thyristor Controlled Series Compensator (TCSC) consists of a series
compensating capacitor shunted by a Thyristor Controlled Reactor (TCR). The basic
idea behind the TCSC scheme is to provide continuously variable impedance by
means of partially canceling the effective compensating capacitance by the TCR.
Transmission lines compensation by means of TCSC can be used to increase the
power transfer capability, improve transient stability, reduce transmission losses and
dampen power system oscillations.
In this thesis work device modelling of TCSC has been carried out along with
development of transmission system using MATLAB7.5/Simulink. Then this device
has been applied to the transmission network using Power System blockset. The
response of transmission systems has been studied for various types of faults with and
without TCSC, thus analyzing the impact of TCSC on the performance of
transmission line in terms of various parameters, under consideration. Impact of
variation of degree of compensation on power flow has also been studied which
shows that for a fixed angular difference, with the increase in degree of compensation
power flow increases.EC
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
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