1,720,962 research outputs found
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
Production and Assessment of Cellulose Nanofibril Films
No full textThesis (Master's)--University of Washington, 2024This research was a study on the production and characterization of novel, high (i.e. above 80 wt.%) nanocellulose (CNF) content. These films were successfully created after an established CNF production process (Pascoli, Dichiara, Roumeli, Gustafson, & Bura, 2022) using alkaline pulping and a peracetic acid (PAA) pretreatment was scaled to a kilogram scale. The resulting CNF pulping yield was 68 %, and both chemical and morphological composition of the CNF was maintained from the translation from gram to kilogram scale production. The average CNF fiber diameter was 21.0 nm and the average length weighted was 0.89 mm; high levels of cellulose (100 %) and hemicellulose (92 %) were maintained, contributing to the optical and mechanical properties of the CNF. This CNF was then used in combination with polyvinyl alcohol (PVA) to create film composites at high CNF (i.e. above 80 wt.%) and low PVA (i.e. below 20 wt.%) ratios. These films had unexpectedly impressive optical properties with a maximum haze of 94.7 % in 100 % CNF films and a maximum light transmittance at 660 nm of 85.7 % at 660 nm in 85 % CNF films. This unique combination of high haze and high light transmittance lends the films to a variety of exciting applications. The composite films were also evaluated for mechanical properties, and 100 % CNF were found to have a high tensile strength of 86.3 MPa with a peak elongation of 4.2 %. These results indicated that the films retain flexibility associated with traditional plastic while benefiting from enhanced mechanical properties associated with CNF. Furthermore, the films were evaluated for mass retention when submerged in moist soil for eleven weeks and for susceptibility to water via contact angle analysis. It was found that the films did not immediately undergo decomposition and remained relatively stable in soil, and they exhibited a decreased susceptibility to water when compared to 100 % PVA control films. The outstanding properties of the film suggest potential applications in solar energy conversion devices, single-use food packaging, or agricultural mulch coverings
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
Life Cycle Assessment of Drop-in Bio-jet Fuel and Acetic Acid from the Bioconversion of Poplar Biomass
No full textThesis (Ph.D.)--University of Washington, 2021In this dissertation, research to evaluate the environmental impacts resulting fromthe commercial scale production of bio-jet fuel and bio-acetic acid produced from short
rotation coppice harvest poplar tree feedstock is presented. The poplar feedstock is
chipped during harvest and transported to a biorefinery where enzymatic hydrolysis and
fermentation steps are used to convert the lignocellulosic biomass to acetic acid. The
acetic-acid can be pulled out through a distillation recovery process and sold as a
standalone commodity. Or, the acetic acid can go through additional chemical
conversion steps, including hydrogenation, to produce a hydrocarbon jet fuel. In either
case, the bio-jet fuel and bio-acetic acid are identical to the petroleum based versions of
the products they are intended to replace. Life cycle assessment is used to analyze the
potential environmental impacts of producing bio-jet fuel and bio-acetic acid at
commercial scale. The research in this dissertation consists of three separate, but
related studies. The first study is an LCA of bio-jet fuel production. It looks at the
system as a whole, without defining a location for the poplar bioenergy farm or the
biorefinery, and focuses on the ‘cradle to wake’ global warming potential and fossil fuel
use of bio-jet fuel production and use. The second study is a regional poplar feedstock
‘cradle to farm gate’ assessment that uses spatial analysis to locate lands in the
western U.S. that could be used to grow poplar trees for regionally located biorefineries.
The final study is a LCA ‘cradle to biorefinery exit gate’ analysis of bio-acetic acid
production and assesses the global warming potential and fossil fuel use of two different
acetic acid recovery methods. Below follows abstracts for the three studies:
Hydrocarbon bio-jet fuel from bioconversion of poplar biomass: life cycle
assessment
Bio-jet fuels compatible with current aviation infrastructure are needed as an
alternative to petroleum based jet fuel to lower greenhouse gas emissions and reduce
dependence on fossil fuels. Cradle to grave life cycle analysis is used to investigate the
global warming potential and fossil fuel use of converting poplar biomass to drop-in
bio-jet fuel via a novel bioconversion platform. Unique to the biorefinery designs in this
research is an acetogen fermentation step. Following dilute acid pretreatment and
enzymatic hydrolysis, poplar biomass is fermented to acetic acid and then distilled,
hydroprocessed, and oligomerized to jet fuel. Natural gas steam reforming and lignin
gasification are proposed to meet hydrogen demands at the biorefineries. Separate
well to wake simulations are performed using the hydrogen production processes to
obtain life cycle data. Both biorefinery designs are assessed using natural gas and hog
fuel to meet excess heat demands.
Global warming potential of the natural gas steam reforming and lignin
gasification bio-jet fuel scenarios range from CO2 equivalences of 60 g MJ-1 to 66 g MJ-1
and 32 g MJ-1 to 73 g MJ-1, respectively. Fossil fuel usage of the natural gas steam
reforming and lignin gasification bio-jet fuel scenarios range from 0.78 MJ MJ-1 to 0.84
MJ MJ-1 and 0.71 MJ MJ-1 to 1.0 MJ MJ-1, respectively. Lower values for each impact
category result from using hog fuel to meet excess heat/steam demands. Higher values
result from using natural gas to meet the excess heat demands.
Bio-jet fuels produced from the bioconversion of poplar biomass reduce the
global warming potential and fossil fuel use compared to petroleum based jet fuel.
Production of hydrogen is identified as a major source of greenhouse gas emissions
and fossil fuel use in both the natural gas steam reforming and lignin gasification bio-jet
simulations. Using hog fuel instead of natural gas to meet heat demands can help
lower the global warming potential and fossil fuel use at the biorefineries.
Hydrocarbon bio-jet fuel from bioconversion of poplar biomass: life cycle
assessment of site specific impacts
Hydrocarbon drop-in bio-jet fuels could help to reduce greenhouse gas emissions
within the aviation sector. The commercial scale production of these bio-jet fuels will
require investments into new bioconversion facilities to convert biomass to hydrocarbon
drop-in jet fuel. These conversion facilities will need dependable year-round supply of
biomass feedstock. Large tracts of land will be required to grow this feedstock and the
change in management of these lands could have significant environmental impacts.
This research investigates potential environmental impacts associated with converting
land to grow poplar trees for conversion to drop-in bio-jet fuel. Spatial analysis and life
cycle methodologies are used to evaluate changes to land use and management in 4
different regions within the western United States. The four regions are based around
biorefineries proposed to be located near Pilchuck WA, Hayden ID, Jefferson OR, and
Clarksburg CA. Each of the four regions would annually supply 125 million tonnes of
poplar biomass to a biorefinery producing 380 million liters of bio-jet fuel. The amount
of land converted is based off of predicted poplar yields for each region. The type of
land converted to growing poplar, as well as the impacts associated with land use
change will depend on regionally specific factors.
The Clarksburg region is predicted to have the highest poplar yield and least
amount of land converted. Of the land converted in the Clarksburg region, the majority
of the land would come from croplands. Relative to the other regions, the conversion of
intensively managed cropland to less intensively managed poplar production results in a
decrease of fertilizer use and small increase in chemical inputs and fuel use. This
translates to the lowest annual Global Warming Potential (GWP) for the Clarksburg
region relative to the GWPs of Pilchuck, Jefferson, and Hayden. Conversely, the land in
the Jefferson region would primarily come from unmanaged rangelands. Bringing this
rangeland into managed production results in a regional increase of nitrogen fertilizer
use, chemical inputs, and fuel use, as well as the largest increase in GWP, relative to
the other regions. The type of land converted isn’t the only predictor for changes in
agricultural inputs and GWP; total land converted also plays a significant role as
demonstrated by the Hayden region. Poplar yields are predicted to be lower in the
Hayden region and more land must be converted to meet the biorefinery feedstock
needs. The increased use of land leads to higher fuel use and greater greenhouse gas
emissions in the Hayden region.
Combining life cycle assessment methodology with spatial analysis can help
provide a more detailed view of the shifts in land use and resulting impacts. Feedstock
growth and harvesting is a necessary and important process in the production for
biofuels. The total contribution of feedstock production to the overall global warming
potential likely will not be as significant as downstream conversion and processing of
biomass into biofuel, but changes to land use and management could result in changes
at the local level that could result in unintended negative environmental consequences.
It is important that these impacts to land use, along with greenhouse gas emissions, are
modelled and evaluated to better understand the regional and local implications of
building a biofuels industry.
Production routes to bio-acetic acid: Life cycle assessment
Similar to biofuels, numerous chemicals produced from petroleum resources can
also be made from biomass. In this research we investigate cradle to biorefinery exit
gate life cycle impacts of producing acetic acid from poplar biomass using a
bioconversion process. A key step in developing acetic acid for commercial markets is
producing a product with 99.8 % purity. This process has been shown to be potentially
energy intensive and in this work two distillation and liquid-liquid extraction methods are
evaluated to produce glacial bio-acetic acid. Method one uses ethyl acetate for
extraction. Method two uses alamine and diisobutyl ketone. Additionally two different
options for meeting energy demands at the biorefinery are modeled. Option one
involves burning lignin and natural gas onsite to meet heat/steam and electricity
demands. Option two uses only natural gas onsite to meet heat/steam demands,
purchases electricity from the grid to meet biorefinery needs, and sells lignin from the
poplar biomass as a co-product to a coal burning power plant to be co-fired with coal.
System expansion is used to account for byproducts and co-products for the main life
cycle assessment. Allocation assessments are also performed to compare the life cycle
tradeoffs of using system expansion, mass allocation, or economic allocation for
bio-acetic acid production. Finally, a sensitivity analysis is conducted to determine
potential effects of a decrease in the fermentation of glucose to acetic acid.
Global warming potential (GWP) and fossil fuel use (FFU) for ethyl acetate
extraction range from 1000 - 2500 kg CO2eq. and 32 - 56 GJ per tonne of acetic acid,
respectively. Alamine and diisobutyl ketone extraction method GWP and FFU ranges
from -370 - 180 kg CO2eq. and 15 - 25 GJ per tonne of acetic acid, respectively.
Overall the alamine/diisobutyl ketone extraction method results in lower GWP
and FFU values compared to the ethyl acetate extraction method. Only the
alamine/diisobutyl extraction method finds GWP and FFU values lower than those of
petroleum based acetic acid. For both extraction methods, exporting lignin as a
co-product produced larger GWPs and FFU values compared to burning the lignin at
the biorefinery
Life Cycle Assessment of Biofuels Produced from Short Rotation Woody Crops
No full textThesis (Master's)--University of Washington, 2013In an effort to find a substitute for petroleum based liquid transportation fuels many countries are turning to biofuels. The newest form of these biofuels, also known as the second generation or cellulosic biofuels, have received considerable attention. Short rotation woody crops (SRWC) such as willow and poplar have been proposed as possible sources of biomass to produce these biofuels via biochemical conversion. Before moving to commercial scale, the impacts these biofuels could place on environment must be investigated. In this thesis two research projects to assess environmental performance of SRWC biofuels using Life Cycle Assessment (LCA) are presented. In the first project an LCA of ethanol production via bioconversion of willow biomass crop feedstock is investigated. Willow crop data are used to assess feedstock production impacts. The bioconversion process is modeled with an Aspen simulation that predicts an overall conversion yield of 310 liters of ethanol per tonne of feedstock (74 gal per US short ton). Vehicle combustion impacts are assessed using greenhouse gases, regulated emissions, and energy use in transportation (GREET) model. The impacts of bioconversion produced ethanol are compared with those of gasoline on an equivalent energy basis. Results of the LCA show that the life-cycle global warming potential of ethanol is slightly negative. Carbon emissions from ethanol production and use are balanced by carbon absorption in the growing willow feedstock and the displacement of fossil fuel produced electricity with renewable electricity produced in the bioconversion process. The fossil fuel input required for producing 1 MJ of energy from ethanol is 141 percent less than that from gasoline. More water is needed, however, to produce 1 MJ of ethanol fuel than 1 MJ of gasoline. The life-cycle water use for ethanol is 169 percent greater than that for gasoline. The largest contributors to water use are the conversion process itself and the production of chemicals and materials used in the process, such as enzymes and sulfuric acid. In the second project, LCA for two lignocellulosic bioethanol production pathways are simulated using hybrid poplar as a feedstock are developed and compared. Both processes use a dilute acid pretreatment followed by enzymatic hydrolysis. The processes differ in the fermentation process. In the first pathway an ethanologen is used to produce ethanol. The second pathway is fermented with an acetogen to produce acetic acid. Acetic acid undergoes hydrogenation to produce ethanol. Both bioconversion pathways are modeled in ASPEN-plus simulations. In both processes lignin is recovered and burned onsite to produce electricity. The critical difference between the two processes is that the acetic acid pathway has a higher product yield but requires hydrogen for the process. Steam methane reforming is assumed to be the source of hydrogen. Greenhouse gases, regulated emissions, and energy use in transportation (GREET) is used to model combustion of ethanol from each scenario in a flex fuel vehicle. All necessary chemicals, transportation, and processes required by each production pathway are included within the LCAs. Each pathway is assessed to determine the global warming potential (GWP), fossil fuel use, and freshwater use. Compared to gasoline the ethanologen pathway has a GWP that is 97 percent lower, uses 97 percent less fossil fuels, and 180 percent more water. The acetogen pathway has a GWP 53 percent lower than gasoline, reduces fossil fuel use by 55 percent, and increases water use by 81 percent. In regards to the GWP and fossil fuel use the ethanologen pathway achieves larger reductions compared to gasoline. However, the acetogen pathway will produce more ethanol per unit of land and this may play a crucial role in choosing a lignocellulosic ethanol production method if land is a limited resource
Mechanisms and kinetics of ethylene oligomerization over nickel-based heterogeneous catalysts
No full textThesis (Ph.D.)--University of Washington, 2021The present research describes the kinetics and mechanisms of the ethylene oligomerization over nickel-based solid catalysts at subcritical and supercritical ethylene conditions. The Ni-H-Beta catalyst was used due to its high activity for the conversion of ethylene into higher alkenes. Initially, the role of nickel and Brønsted sites on the ethylene oligomerization over Ni-H-Beta catalysts is investigated. According to the catalyst characterization results, nickel is present on the catalyst surface as Ni2+, from the free NiO phase and highly dispersed Ni2+ interacting with the catalyst’s lattice oxygen. Ethylene sorption results indicate that ethylene dissociates over two active sites upon adsorption over the Ni-H-Beta. Further characterization via pyridine sorption suggests that the presence of non-coordinated Ni2+ or Brønsted sites decreases the probability for the formation of the active sites on the catalyst surface. Then, the kinetics of ethylene oligomerization over the Ni-H-Beta are discussed. A kinetic model was developed for temperatures varying between 50 and 100oC and pressures varying between 5 and 28 atm. The results indicate the butene and hexene are formed via a series of ethylene coordination-insertion steps and the formation of octene follows the co-oligomerization of ethylene and desorbed butene. In the present study, we refer to the pathway involving co-oligomerization of butene and hexene as “cascade co-oligomerization”. A detailed reaction network is proposed and modeled based on the Langmuir-Hinshelwood-Hougen-Watson kinetics. After studying the mechanisms and kinetics of the ethylene oligomerization under subcritical conditions, the solubility of coke in supercritical ethylene is discussed. The solubility of coke in ethylene was investigated at 30, 50, and 75oC and pressures ranging from 1 to 68 bar; conditions previously screened by our research group for ethylene oligomerization. The approach uses n-decane as a model compound to simulate coke formed during the catalytic process. A detailed thermodynamic model is developed for the solubility of n-decane in subcritical and supercritical ethylene. Beyond the ethylene critical point (P = 50.3 bar and T = 9.4oC) the solubility of n-decane in ethylene at 30oC reaches a maximum value of 3.0%; close to the value observed at 50 and 75oC, under the same pressure. Comparison of kinetic and solubility data show that the transport of products from the catalyst to the bulk of the supercritical fluid is a function of the reaction temperature. At low temperatures (30oC), coke dissolution rates are higher than apparent coke production rates. However, at high temperatures (60 and 90oC), coke dissolution rates are not able to outcompete the high rates of coke formation. The last step of the study with the Ni-H-Beta catalyst involves a kinetic model under supercritical ethylene conditions. The kinetic data under supercritical conditions are modeled based on the Langmuir-Hinshelwood-Hougen-Watson kinetics. Three different reaction limiting steps are compared: adsorption, chain-growth, and desorption. The model that assumes desorption of products as the reaction limiting step provides the best fitting of the kinetic data among the models proposed in the present work. Therefore, the slow desorption of products from the catalyst surface to the bulk of supercritical ethylene limits the reaction. This result is consistent with the result obtained in the solubility study.Based on the previous solubility and kinetic studies, a novel catalyst is designed for the oligomerization of supercritical ethylene. This catalyst is composed of nickel supported on mesoporous SIRAL support. We report the production of liquid products at 50, 100, and 200oC and 40 and 65 bar operating at both single and dual reactor configurations. The novel Ni-SIRAL catalyst is able to oligomerize ethylene at supercritical conditions without experiencing deactivation. The liquid product is composed of linear alkenes and a substantial fraction of cycloalkanes (8.5 wt. %). A high yield for liquid hydrocarbons of 60.8 wt. % is reported at 200oC and 65 bar
Nanocellulose design; characterizing ammonium persulfate oxidation of wood and a non-wood agricultural residual, Humulus lupulus, bine from the Yakima valley.
No full textThesis (Ph.D.)--University of Washington, 2022Low-density biomass resources such as Humulus lupulus are handicapped by high transportation costs due to widely distributed – low-density acreage and the need for densification of the biomass. Life Cycle Assessment aims to assess the impact of segregating the residual woody waste (co-product) of an agricultural crop, hops (Humulus lupulus) on the greenhouse gas (GHG) emissions and on soil carbon sequestration. The growth in the Humulus lupulus L. or hops industry, a perennial species, driven by demand from brewers has had annual revenue growth of 11.3% since 2015 making it one of the fastest-growing agricultural commodities in the Pacific Northwest(PNW). The high carbohydrate content, 58%, is similar to other lignocellulosic materials suitable for bioenergy feedstocks. The fiber has morphological characteristics similar to hardwood with length and width centered around 0.85 mm and 16.5 μm, respectively. This fiber presents a sustainable multi-use commodity with excellent application in biobased products and paper-making. We demonstrate that the environmentally friendly ammonium persulfate is effective at producing similar surface chemistry in lignin-containing wood and non-wood fibers, hop bine, without pretreatment or adjustment of experimental conditions. As-prepared materials exhibited surface charge and crystallinity index ranging from 0.6 mmol/g to 1.4 mmol/g carboxylic acid and 72 to 88%, respectively. The morphological characteristics varied from 48 to 80 for the aspect ratio, from 2.7 to 4.5 nm for the diameter, and from 146 to 247 nm for the length. The response surface model developed in this research allows for designing nano cellulose with targeted surface charge, crystallinity and aspect ratio.
Nanocellulose fibers (NFCs) were designed using this response surface model to evaluate NFC retention, as well as barrier and strength properties of NFC-reinforced paper. The results demonstrate that low-surface charge nanofiber reinforced paper exhibit reduced air permeability, high fiber retention, and higher tensile strength. We demonstrate that nano fibrillated cellulose, engineered with specific surface charge and aspect ratio, produced via green chemistry, is as effective at improving the physical properties and performance of paper, comparable to nanofibers produced through TEMPO-mediated oxidation
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
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
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