815 research outputs found
Improving small-scale agriculture and countering deforestation: the case of biochar and biochar producing stoves in Embu County, Kenya
This research examines the introduction and diffusion of biochar as a soil amendment and biochar producing stoves in Embu County, Kenya, together with its related socio-economic potentials and challenges. The area has seen rapid rates of deforestation together with declining soil fertility during the last couple of decades. Biochar as a soil amendment and biochar producing stoves offers a viable solution to these problems, at the same time as it may improve the productivity in the small-scale agriculture, the main income-generating activity in the area. In order to do so, it is of utmost importance that these innovations are well adapted to local socio-economic, geographical and cultural pre-conditions. Through a case study in Embu County, I have investigated the perceptions and pre-conditions of small-scale farmers in relation to local socio-economic geographical or cultural challenges and the related potential solutions. The findings suggest that these new innovations have a high potential in the area and that they could play a vital part of a sustainable agricultural intensification process
The black bar mitzvah : Representations of Jews in US hip-hop lyrics
References to Jews and to matters included in Jewish discourse are commonplace in US popular culture in general and in US-produced hip-hop lyrics in particular. This article deals with the latter, and aims to analyse how Jews are represented there. It is suggested here that 1. these representations are rendered comprehensible by analysing them in the light of the term coined by Zygmunt Bauman: allosemitism, which denotes that Jews are âotherâ. This article further suggests that 2. the representations of Jews featured in the lyrics cannot be made comprehensible without looking into the historical relations between American Jews and African Americans. According to Jeffrey Melnick, this relation is characterised by ârobust ambivalencesâ. This article arrives at the conclusion that the representations of Jews draw on classical conspiratorial and economic antisemitic ideas that situate Jews within the realms of shadowy (economic and instrumental) power, but which at times can be understood as philosemitic, as Jews are represented as wealthy and influential role models. Hence the usage of the term allosemitism to analyse the empirics
Scale-up Analysis of Continuous Cross-flow Atomic Layer Deposition Reactor Designs
This paper presents the development of a non-dimensional model of a continuous cross-flow atomic layer deposition (ALD) reactor with temporally separated precursor pulsing and a structured model-based methodology for scaling up the substrate dimensions. The model incorporates an ALD gasâsurface reaction kinetic mechanism for the deposition of thin ZnO films from Zn(C2H5)2 and H2O precursors that was experimentally validated in our previous work (Holmqvist et al., 2012, 2013a). In order to maintain dynamic similarity, a scaling analysis was applied based on the dimensionless numbers, appearing in non-dimensionalized momentum and species mass conservation equations, that describe the convective laminar flow, mass transfer and heterogeneous reaction. The impact on these dimensionless numbers and, more importantly, the impact on the limit-cycle deposition rate and its relative uniformity was thoroughly investigated when linearly scaling up the substrate dimensions. In the scale-up procedure, the limit-cycle precursor utilization was maximized by means of dynamic optimization, while ensuring that identical deposition profiles were obtained in the scaled-up system. The results presented here demonstrated that the maximum precursor yields were promoted at higher substrate dimensions. Limit-cycle dynamic solutions to the non-dimensionalized model, computed with a collocation discretization in time, revealed that it is a combination of the degree of precursor depletion in the flow direction and the magnitude of the pressure drop across the reactor chamber that governs the extent of the deposition profile non-uniformity. A key finding of this study is the identification of optimal scaling rules for maximizing precursor utilization in the scaled-up system while maintaining fixed absolute growth rate and its relative uniformity
Ekonomisk vÀrdering av anvÀndandet av underbett pÄ timmerbilar
Holmen Skog has in some places in their operation area access to timber trucks with centre mounted scrapers. They make transportation more flexible and reduce reliance on contractors for road maintenance. The trucks with centre mounted scrapers have a higher tare weight, making them less productive and therefore they receive compensation with a 0.75 % increase on transportation price.
The purpose of this study was to investigate what actions a timber truck with centre mounted scraper can perform with acceptable quality in winter, and to examine if it is an economically profitable solution for the truck operator and charterer.
The study was done in three stages; interviews, performance analysis of the transportations carried out and an economic analysis with the help of Sven Erik Gilles spreadsheet tool. The study included the districts Delsbo and Hudiksvall. Data for the study included three years to reduce the seasonal effect.
In the study it was concluded that trucks with centre mounted scrapers primarily were used for clearing ice from roads, they also replace some sanding when the road is roughened and gravel material is brought to the surface. Among the advantages, the short time between identifying a need to performing an action was mentioned. The main disadvantage was considered to be the increase in tare weight. The performance analysis of transportations carried out showed that the trucks with a centre mounted scraper had served a larger number of unique timber orders than a conventional self loading timber truck. The economic analysis showed that current reimbursement does not fully cover the revenue loss incurred by having a centre mounted scraper.
The way the study was carried out it was not possible to economically evaluate the benefits of having a timber truck with a centre mounted scraper. Because of that it could not give an unequivocal answer to the question if there is an economically profitable concept for the charterer and the truck operator
Inhysningssystem för tjurar
ItŽs important when you are about to build a new stable or just increasing your production that you choose the right housing system and that it fits your own farm. In this study I have put together facts about different housing system for fattening bulls in order to get a clearer picture of witch system is the most suitable for my own farm depending on the conditions I have. The background of this work is my own interest for breeding bulls and I will hopefully increase my own production. Due to this I wanted to learn more and increase my knowledge about different housing systems. Through a literature study I have found out the facts about the housing systems I find suitable for housing bulls. There are of course more alternatives and combinations between different systems but these are the most common in Sweden and I find them suitable for housing bulls. The systems I have looked closer at are: pens with slatted floor, straw bed, deep straw bed, straw bed with manure scraper, sliding straw bed, straw bed with outside pen and finally loose housing with cubicles. I have also interviewed two farmers who have newly built stables with some of the systems I have gone through. They have given their reflections about things to consider and how to get the systems to work properly and what they would like to change. To be able to compare the different systems and reach some result I have compared the systems advantages and disadvantages to the needs and conditions for my own farm. A deep straw bed demands a lot of straw but if you have an alley with a manure scraper in the front of the pen or a sliding straw bed it drastically reduces the need of straw. Cubicles often demands a larger investment and a more expensive stable building then a stable with straw bed, but the need of straw is smaller. The work effort for littering and taking out the manure can be hold on a low level in a well planned and functional stable with cubicles, thanks to the fact that the manure can be taken out mechanically and the consumption of bedding material is low. What system you should choose depends on the conditions of your own farm, access to straw, work force and what system you want to have for dealing with the manure. It also depends on if you have available structures that you would like to use or if you are about to build a new stable. For my part the access of straw is an important issue, because in the case of great consumption of litter I have to buy it from a great distance and that can be rather expensive. This means that a system of low consumption of litter for example loose housing with cubicles is a suitable choice for me. In the end it is important that you carefully calculate the systems that you like and think is suitable for you. To combine an inexpensive building with a low operating cost and a low work effort is not an easy task.Det Àr viktigt vid en nybyggnation eller utökande av djurbesÀttningen att man vÀljer det inhysningssystem som passar den egna gÄrden bÀst. I detta arbete har jag sammanstÀllt fakta om olika inhysningssystem för tjurar för att i slutÀnden fÄ en klarare bild om vilket system som kan passa min gÄrd bÀst med tanke pÄ de förutsÀttningar jag har. Grunden till arbetet kommer frÄn mitt eget intresse av tjuruppfödning och att jag förhoppningsvis kommer att utöka den egna produktionen. PÄ grund av det ville jag fördjupa mina kunskaper om de olika inhysningssystemen och vilket som skulle passa mig och min gÄrd bÀst. Genom en litteraturstudie har jag tagit reda pÄ fakta om de system som jag tycker passar till tjuruppfödning. Det finns sjÀlvklart fler alternativ eller kombinationer mellan de olika systemen men det Àr dessa som Àr de vanligaste för tillfÀllet och som jag tycker passar till tjurar. De system jag har tittat nÀrmare pÄ Àr: boxar med gödseldrÀnerande golv, ströbÀdd, djupströbÀdd, djupströbÀdd med skrapad gÄng, glidande ströbÀdd, ströbÀdd med rastfÄlla samt liggbÄs. Jag har ocksÄ intervjuat tvÄ lantbrukare som har nybyggda ladugÄrdar med nÄgra av systemen som jag har gÄtt igenom. De har fÄtt ge sina reflektioner om vad man ska tÀnka pÄ för att fÄ systemen att fungera tillfredstÀllande och vad de skulle vilja Àndra pÄ i efterhand. För att kunna jÀmföra de olika systemen och komma fram till ett resultat har jag jÀmfört de olika systemens fördelar och nackdelar mot behovet och förutsÀttningarna pÄ min gÄrd. DjupströbÀddar krÀver mycket strömedel men att lÀgga till en skrapgÄng nÀrmast foderbordet eller att ha en glidande ströbÀdd minskar strömedelsbehovet vÀsentligt. LiggbÄs krÀver en större byggnadsinvestering och dyrare stallar Àn system med djupströbÀdd medan ströÄtgÄngen Àr betydligt mindre. Arbetsinsatsen för att strö och gödsla ut kan hÄllas lÄg i ett vÀl fungerande stall med liggbÄs, tack vare att utgödslingen kan vara automatisk och ströÄtgÄngen Àr lÄg. Vad man ska vÀlja för system beror mycket pÄ gÄrdens förutsÀttningar, tillgÄng pÄ strömedel, arbetskraft och vilket utgödslingssystem man vill ha. Det beror ocksÄ pÄ om man har befintliga byggnader som man vill anvÀnda eller om det handlar om nybyggnation. För min del blir ströÄtgÄngen en viktig faktor eftersom jag vid stor ÄtgÄng mÄste köpa in strömedel lÄngt hemifrÄn vilket kan bli en stor kostnad. Detta medför att ett system med liten ströÄtgÄng som lösdrift med liggbÄs skulle vara ett bra alternativ. Det krÀvs i slutÀnden att man rÀknar pÄ de förslag man tycker passar. Att bÄde bygga en billig byggnad, ha en lÄg driftskostnad och en lÄg arbetsinsats Àr ingen lÀtt uppgift
Kartering av skogsskador hos bok och ek i södra Sverige med hjÀlp av satellitdata
PopulĂ€rvetenskaplig sammanfattning: Kan satellitbilder anvĂ€ndas för att studera skador pĂ„ bok och ek? Sedan mitten av 1970-talet har man sett ökande skador pĂ„ skogen i stora delar av Europa. Olika storlek pĂ„ skadorna och att storleken pĂ„ skadorna skiljer sig Ă„t beroende pĂ„ var man befinner sig har gjort det svĂ„rt att förklara orsaken. För att undersöka ifall skadorna Ă€ven ökat i Sverige har Skogsstyrelsen utfört inventeringar pĂ„ bok- och ekbestĂ„nd i södra Sverige under tre tillfĂ€llen; 1988, 1993 och 1999. Resultatet frĂ„n undersökningen visar att konditionen hos bok och ek i södra Sverige har försĂ€mrats sedan den första inventeringen 1988. Som ett mĂ„tt pĂ„ hur trĂ€den mĂ„r, har kronutglesning anvĂ€nts och resultatet visar att det har skett en kraftig ökning i kronutglesning mellan Ă„ren 1988 till 1999. Undersökningen visade ocksĂ„ att det fanns ett samband mellan fattiga jordar med t.ex. lĂ„gt nĂ€ringsĂ€mnesinnehĂ„ll och ökad kronutglesning pĂ„ trĂ€den. Syftet med denna studie Ă€r att undersöka möjligheten att studera skogsskador hos bok och ek i södra Sverige med hjĂ€lp av satellitensensorn Landsat enhanced thematic mapper plus (ETM+), utifrĂ„n befintlig inventeringsdata i form av bok- och ekdatabasen. Samband mellan kronutglesning och reflektans som satellitsensorn registrerar har undersökts, och ett försök gjordes att dela in kronutglesningen i klasser. Resultatet frĂ„n studien visar att det finns ett samband mellan kronutglesning och Landsat ETM+ reflektanser. Sambanden visar att reflektanserna minskar nĂ€r kronutglesningen ökar. Sambanden Ă€r dock inte sĂ€rskilt starka och kan dĂ€rför inte anvĂ€ndas för att studera skador pĂ„ bok och ek. En orsak till det svaga sambandet mellan kronutglesning och reflektans samt svĂ„righeten att klassificera bok- och ekbestĂ„nd kan vara hur inventeringsdata som anvĂ€nts Ă€r insamlad. Data Ă€r insamlad i heterogena bestĂ„nd, dĂ€r enskilda trĂ€d har bedömts i olika riktningar och avstĂ„nd frĂ„n de kĂ€nda punkterna.Ăkande skador pĂ„ skogen har observerats i stora delar av Europa sedan mitten av 1970-talet. Samma indikationer pĂ„ skador sĂ„gs ganska snart Ă€ven i Sverige. Skadorna observerades först pĂ„ barrtrĂ€dsbestĂ„nd, men under 1980-talet observerades Ă€ven skador pĂ„ lövtrĂ€d, framförallt hos bok och ek. Skogsstyrelsen lĂ€t till följd av detta genomföra skogsskadeinventeringar 1988, 1993 och 1999 av bok (Fagus sylvatica) och ek (Quercus robur och Quercus petraea) i Sydsverige, vilket inkluderade SkĂ„ne, Halland och Blekinge. Vid inventeringen 1999 inkluderades Ă€ven vissa delar av SmĂ„land. Resultatet frĂ„n fĂ€ltinventeringarna visar att konditionen hos bok och ek i södra Sverige har försĂ€mrats kraftigt mellan Ă„ren 1988 till 1999. Under optimala förhĂ„llanden har satellitbaserad fjĂ€rranalys visat sig vara ett kvalitativt acceptabelt och ekonomiskt fördelaktigt alternativ till fĂ€ltbaserade skogsskadeinventeringar. Syftet med denna studie Ă€r att undersöka möjligheten att kartera skogsskador hos bok och ek i södra Sverige med hjĂ€lp av Landsat enhanced thematic mapper plus (ETM+), utifrĂ„n befintlig inventerings-data i form av bok och ekdatabasen. Kronutglesning representerade skadegraden vid fĂ€ltinventeringen och dess relation till reflektans observerad av satelliten ifrĂ„n inventeringsytorna har undersökts. Samband mellan kronutglesning och reflektans frĂ„n ett flertal spektrala band och index undersöktes, samt utfördes en klassificering av kronutglesning. Resultatet visar att det finns en signifikant negativ korrelation mellan kronutglesning och Landsat ETM+ reflektanser hos flera band och kombinationer av band. Sambanden Ă€r dock inte sĂ€rskilt starka och klusterna har en stor spridning och kan dĂ€rför inte anvĂ€ndas vid skadekartering. Det bĂ€sta enskilda bandet för kronutglesningsestimering Ă€r det nĂ€ra infraröda bandet (ETM+ 4) och bland indexen Ă€r SR (ETM+ 4/ETM+ 3) bĂ€st. De spektrala signaturerna för bok och ek samt klasserna 25 % kronutglesning överlappar varandra, vilket gör det svĂ„rt att skilja dom Ă„t. En orsak till den lĂ„ga korrelationen mellan kronutglesning och reflektans samt svĂ„righeten att klassificera bok- och ekbestĂ„nd kan vara hur inventeringsdata som anvĂ€nts Ă€r insamlad. Data Ă€r insamlad i heterogena bestĂ„nd, dĂ€r enskilda trĂ€d har bedömts i olika riktningar och avstĂ„nd frĂ„n de kĂ€nda koordinatsatta punkterna. Detta har inneburit att Landsat ETM+ med en upplösning pĂ„ 30 x 30 meter har registrerat ett flertal olika skadeklasser inom en pixel.Since the middle of the 1970ÂŽs damage to forest have been observed in large areas of central Europe. The same indications on forest damage were soon found in Sweden as well. Forest damage was first observed in coniferous forest stands, but during the 1980ÂŽs damage indication were also observed on deciduous forest stand, particularly on beech and oak. To investigate this further the National Board of Forestry has in 1988, 1993 and 1999 carried out field surveys on forest condition in beech (Fagus sylvatica) and oak (Quercus robur and Quercus petraea) forests in southern Sweden. Results showed that the condition of beech and oak has deteriorated between 1988 and 1999. Remote sensing has a potential role in forest damage mapping because it can provide spatially explicit data on vegetation change due to disturbance. The study aims at investigating the use of Landsat enhanced thematic mapper plus (ETM+) for mapping defoliation in beech and oak stands in southern Sweden. The relationship between defoliation and reflectance of a number of single spectral bands and several vegetation indices was investigated. A classification of stands into defoliation classes was also carried out. The results indicate negative significant relationships between Landsat ETM+ reflectance and defoliation, but the relationship is not very strong. The best single band on defoliation estimate is the near infrared (ETM+ 4) and the best vegetation index is the simple ratio (ETM+ 4/ETM+ 3). To discriminate beech from oak stands and the two defoliation classes 25 % from each other is very hard due to overlapping in spectral signatures. The weak correlations found between defoliation and Landsat ETM+ reflectance and the low capability to classify defoliation in beech and oak stands is probably due to the field data collection method. Defoliation estimates were carried out on single trees, in several directions and distance from a known grid point. This means that the Landsat ETM+ with its 30 x 30 meter resolution may cover vastly different damage classes in a single pixel
Geo-mapping of time trends in childhood caries risk - a method for assessment of preventive care
Background: Dental caries is unevenly distributed within populations with a higher burden in low socio-economy groups. Several attempts have been made to allocate resources to those that need them the most; there is a need for convenient approaches to population-based monitoring of caries risk over time. The aim of this study was to develop the geo-map concept, addressing time trends in caries risk, and demonstrate the novel approach by analyzing epidemiological data from preschool residents in the region of Halland, Sweden. Methods: The study population consisted of 9,973 (2006) and 10,927 (2010) children between 3 to 6 years of age (similar to 77% of the eligible population) from whom caries data were obtained. Reported dmfs >0 for a child was considered as the primary caries outcome. Each study individual was geo-coded with respect to his/her residence parish (66 parishes in the region). Smoothed caries risk geo-maps, along with corresponding statistical certainty geo-maps, were produced by using the free software Rapid Inquiry Facility and the ESRI (R) ArcGIS system. Parish-level socioeconomic data were available. Results: The overall proportion of caries-free (dmfs = 0) children improved from 84.0% in 2006 to 88.6% in 2010. The ratio of maximum and minimum (parish-level) smoothed relative risks (SmRRs) increased from 1.76/0.44 = 4.0 in 2006 to 2.37/0.33 = 7.2 in 2010, which indicated an increased geographical polarization of early childhood caries in the population. Eight parishes showed evidential, positional changes in caries risk between 2006 and 2010; their corresponding SmRRs and statistical certainty ranks changed markedly. No considerable parallel changes in parish-level socioeconomic characteristics were seen during the same time period. Conclusion: Geo-maps based on caries risk can be used to monitor changes in caries risk over time. Thus, geo-mapping offers a convenient tool for evaluating the effectiveness of tailored health promotion and preventive care in child populations
Blood alcohol concentration at 0.06 and 0.10% causes a complex multifaceted deterioration of body movement control.
Alcohol-related falls are recognized as a major contributor to the occurrence of traumatic brain injury. The control of upright standing balance is complex and composes of contributions from several partly independent mechanisms such as appropriate information from multiple sensory systems and correct feedback and feed forward movement control. Analysis of multisegmented body movement offers a rarely used option for detecting the fine motor problems associated with alcohol intoxication. The study aims were to investigate whether (1) alcohol intoxication at 0.06 and 0.10% blood alcohol concentration (BAC) affected the body movements under unperturbed and perturbed standing; and (2) alcohol affected the ability for sensorimotor adaptation. Body movements were recorded in 25 participants (13 women and 12 men, mean age 25.1 years) at five locations (ankle, knee, hip, shoulder, and head) during quiet standing and during balance perturbations from pseudorandom pulses of calf muscle vibration over 200s with eyes closed or open. Tests were performed at 0.00, 0.06, and 0.10% BAC. The study revealed several significant findings: (1) an alcohol dose-specific effect; (2) a direction-specific stability decrease from alcohol intoxication; (3) a movement pattern change related to the level of alcohol intoxication during unperturbed standing and perturbed standing; (4) a sensorimotor adaptation deterioration with increased alcohol intoxication; and (5) that vision provided a weaker contribution to postural control during alcohol intoxication. Hence, alcohol intoxication at 0.06 and 0.10% BAC causes a complex multifaceted deterioration of human postural control
Thermal and electron stimulated chemistry of complex adsorbates on metal surfaces
Due to intrinsic limitations of conventional silicon based devices the trend of miniaturisation cannot continue indefinitely, thus molecular devices are being used to develop smaller, faster and higher storage density memory devices. We present a thermally activated, switchable hetero-polyoxometalate (HPOM) cluster immobilised on a highly polarisable gold surface which has potential as such a device. This cluster consists of a nanometre sized Mo(IV) oxide âshellâ which encapsulates two electronically active pyramidal sulfite (SIVO32-) groups, and has the ability to reversibly interconvert between two electronic states. In the passive state, at cryogenic temperatures (77 K), the two SO32- groups are non-bonding with respect to the sulfur centres, however upon thermal activation, i.e. when the temperature is increased to room (298 K), two electrons are ejected from the active sulfite anions and delocalised over the metal oxide cluster cage. This has the effect of switching it from a fully oxidised to a two-electron reduced state, along with the concomitant formation of an S-S bonding interaction between the two sulfur centres inside the cluster shell. This process does not occur in the crystalline state and to proceed requires the stabilising effects provided by an image charge, generated as a consequence of being adsorbed onto a metal surface. The prototypical enantio-selective heterogeneously catalysed reaction involves the hydrogenation of the α-ketoester, methyl pyruvate on Pt. Using TPD, XPS and UPS we have investigated this compoundâs behaviour on a model Cu(111) single crystal surface. Monolayers of methyl pyruvate at 180 K consist predominately (ca. 66%) of a chemisorbed methyl pyruvate moiety, with its keto-carbonyl bonded to the surface in a η2configuration, this moiety desorbs intact at 364 K. The rest of the monolayer contains weakly adsorbed methyl pyruvate, which desorbs at 234 K, and interacts with the surface through the lone pair electrons of the oxygen atoms of the C=O groups, adopting a η1 configuration. The observation of a strongly chemisorbed moiety in the present study is attributed to the activation of the keto-carbonyl by the electron withdrawing ester group, and is consistent with the homogeneous inorganic chemistry of ketones. It is widely assumed that the α-ketoester needs to be Ï-bonded to the surface for the enantio-selective hydrogenation to proceed, consequently, given both the formation of a η2 bonded methyl pyruvate moiety on Cu(l11) and the known activity of Cu as a selective hydrogenation catalyst, it is suggested that it is maybe worthwhile considering the possibility of testing the effectiveness of chirally modified supported Cu as an enantio-selective catalyst. The thermal and electron induced chemistry of (S)- and (R)-methyl lactate (MLac) on Cu(111) was investigated; both enantiomers exhibited similar behaviour. MLac adopts one of two adsorption modes on the terraces of a Cu(111) crystal, which desorb molecularly at 209 K and 220 K. Concerning the molecules adsorbed at defect sites, as the temperature is increased over the range 250 â 300 K, a fraction desorb intact, while the majority lose a hydrogen atom to form the more strongly bound alkoxy species on the surface. Of these, some recombine with the hydrogen and proceed to desorb as MLac at 360 K, while a larger proportion are dehydrogenated further and methyl pyruvate and hydrogen are ejected from the surface at 380 K. When a monolayer of MLac is irradiated with a low energy electron beam, the molecules at the terrace sites are electronically excited and desorb as intact molecules, while those at the defect sites undergo electron induced hydroxyl O-H bond cleavage. Subsequent to electron bombardment there is consequently a decrease in molecularly adsorbed MLac and an increase in the number of strongly bound alkoxy species on the surface, entities which are not susceptible to ESD. We believe the ESD excitation mechanism is dissociative electron attachment. Low energy electrons of <1 eV are prevalent in the secondary electron background and can excite the hydroxyl O-H stretch, facilitating its cleavage at a threshold of 1.4 + 0.7 eV. The cross sections for the electron induced processes are high, 3.0 + 0.4 x 10-16 cm2 for 50 eV electrons, thus MLac is extremely susceptible to electron stimulated desorption. The enantio-specific adsorption of both the (S)- and (R)- enantiomers of methyl lactate on the chiral Cu(643)R surface has been investigated. The results from the (111) surface enabled us to assign the features in the TPD profiles. The peaks arising from molecular desorption at terrace and step sites occurred at the same temperature for both enantiomers, however, those attributed to desorption from the kink sites differed by 13 K, representing an enantio-specific difference in desorption energies of 0.94 kcal mol-1. This value is significantly larger than those observed in previous experimental work, although it is consistent with theoretical studies. Furthermore, we also observed enantio-specific surface reactions. It was found that there was a greater tendency for the (R)- enantiomer to undergo both the alkoxide recombination reaction and further dehydrogenation to methyl pyruvate, while the (S)-enantiomer had a greater proclivity to undergo total decomposition. We have discovered, to the best of our knowledge, the first example of enantio-specific surface chemistry initiated by a beam of non-chiral low energy electrons. When (S)- and (R)-methyl lactate molecularly adsorbed at the chiral kink sites of a Cu(643)R substrate is irradiated with 50 eV electrons, it has been found that (R)-methyl lactate is more receptive to both electron induced desorption of the parent molecule and electron induced cleavage of the hydroxyl O-H bond. This behaviour has been attributed to the (S)-enantiomer forming a more intimate bond with the kink site than the (R)-enantiomer, as evidenced by its higher desorption temperature. Consequently the substrate is more effective at providing relaxation channels to the electronically excited adsorbate, which reduces the probability of ESD occurring. Starting with a racemic mixture, we have demonstrated a 20% enantiomeric enrichment in the molecular adsorbates at the chiral kink sites, after only 30% depletion of the initial population. As a control, the initial rates of desorption from terrace and step sites were found to be unaffected by enantiomeric identity, which was to be expected because these sites are achiral, and as such both enantiomers interact to a similar degree with each. When the monolayer is considered as a whole, it was found that electron irradiation drives desorption more completely with an (R)-MLac covered surface than with (S). It has been suggested that this property of the system could be exploited in the laboratory as a method for separating racemic mixtures, and that in an astrochemical context, it could provide insight into the origins of biohomochirality.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Dynamic parameter estimation of atomic layer deposition kinetics applied to in situ quartz crystal microbalance diagnostics
This paper presents the elaboration of an experimentally validated model of a continuous cross-flow atomic layer deposition (ALD) reactor with temporally separated precursor pulsing encoded in the Modelica language. For the experimental validation of the model, in situ quartz crystal microbalance (QCM) diagnostics was used to yield submonolayer resolution of mass deposition resulting from thin film growth of ZnO from Zn(C2H5)2 and H2O precursors. The ZnO ALD reaction intrinsic kinetic mechanism that was developed accounted for the temporal evolution of the equilibrium fractional surface concentrations of precursor adducts and their transition states for each half-reaction. This mechanism was incorporated into a rigorous model of reactor transport, which comprises isothermal compressible equations for the conservation of mass, momentum and gas-phase species. The physically based model in this way relates the local partial pressures of precursors to the dynamic composition of the growth surface, and ultimately governs the accumulated mass trajectory at the QCM sensor. Quantitative rate information can then be extracted by means of dynamic parameter estimation. The continuous operation of the reactor is described by limit-cycle dynamic solutions and numerically computed using Radau collocation schemes and solved using CasADi's interface to IPOPT. Model predictions of the transient mass gain per unit area of exposed surface QCM sensor, resolved at a single pulse sequence, were in good agreement with experimental data under a wide range of operating conditions. An important property of the limit-cycle solution procedure is that it enables the systematic approach to analyze the dynamic nature of the growth surface composition as a function of process operating parameters. Especially, the dependency of the film growth rate per limit-cycle on the half-cycle precursor exposure dose and the process temperature was thoroughly assessed and the difference between ALD in saturating and in non-saturating film growth conditions distinguished
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