1,128 research outputs found
Modeling and analysis of the dynamic behavior of the XlnR regulon in Aspergillus niger
Full text linkBackground: In this paper the dynamics of the transcription-translation system for XlnR regulon in Aspergillus niger is modeled. The model is based on Hill regulation functions and uses ordinary differential equations. The network response to a trigger of D-xylose is considered and stability analysis is performed. The activating, repressive feedback, and the combined effect of the two feedbacks on the network behavior are analyzed. Results: Simulation and systems analysis showed significant influence of activating and repressing feedback on metabolite expression profiles. The dynamics of the D-xylose input function has an important effect on the profiles of the individual metabolite concentrations. Variation of the time delay in the feedback loop has no significant effect on the pattern of the response. The stability and existence of oscillatory behavior depends on which proteins are involved in the feedback loop. Conclusions: The dynamics in the regulation properties of the network are dictated mainly by the transcription and translation degradation rate parameters, and by the D-xylose consumption profile. This holds true with and without feedback in the network. Feedback was found to significantly influence the expression dynamics of genes and proteins. Feedback increases the metabolite abundance, changes the steady state values, alters the time trajectories and affects the response oscillatory behavior and stability conditions. The modeling approach provides insight into network behavioral dynamics particularly for small-sized networks. The analysis of the network dynamics has provided useful information for experimental design for future in vitro experimental wor
People on the Move: Barriers of Culture, Networks and Language
Full text linkNijkamp, P. [Promotor]Chiswick, B.R. [Copromotor]Graaff, T. de [Copromotor
Gerador de Van de Graaff: conceitos de eletrostática baseado na experimentação
Full text linkFaced with the limitations and difficulties that the teacher finds in the teaching of Physics and in the execution of experimental activities, the present research aims to propose the use of the Van de Graaff generator. The generator components will be presented, highlighting its operation and application, in addition to showing the assembly process of a model made from easily obtainable and loxw cost reusable materials. Based on the contents of electrostatics, especially electrification by friction, proposals for activities and possible approaches to them with the generator were prepared. More than evaluating the effectiveness of the resource, this research aims to provide an alternative to the Physics teacher in the classroom and in the laboratories of IFAM/CMDI.Diante das limitações e dificuldades que o professor encontra no ensino de Física e na execução de atividades experimentais, a presente pesquisa tem como objetivo propor o uso do gerador de Van de Graaff. Serão apresentados os componentes do gerador, destacando o seu funcionamento e aplicação, além de mostrar o processo de montagem de um modelo confeccionado a partir de materiais reaproveitáveis de fácil obtenção e baixo custo. Com base nos conteúdos de eletrostática, em especial a eletrização por atrito, foram elaboradas propostas de atividades e as possíveis abordagens das mesmas com o gerador. Mais do que avaliar a eficácia do recurso, esta pesquisa tem como intenção maior possibilitar uma alternativa ao professor de Física em sala de aula e nos laboratórios do IFAM/CMDI.
Palavras-chave: Ensino de Física; Atividade Experimental; Gerador de Van de Graaf
[Uitslaande kaart van den Maleischen Archipel, de Noord- en West-kusten van Australië, 1690-1714] [cartographic material] = [Folding chart of the Malay Archipelago, the North- and West-coast of Australia] /
No full textFacsimile of the composite map of Dutch discoveries made up to ca. 1700 on the western and northern coast of Hollandia Nova [i.e. Australia]. De Graaf was appointed as chief mapmaker of the VOC in 1705 following Joan Blaeu. The map notes the discoveries of Dirk Hartog in 1616 in his ship Eendracht - from 1619 that part of the West Australian coast was known as Eendrachtsland or Land van de Eendracht and referred to on this map as Zuydland of t' Land van de Eendracht. It also includes the discoveries by Willem De Vlamingh's expedition of 1696-7 such as Vlaming Head [i.e. Northwest Cape] on the Exmouth Gulf and expanding discoveries further along the south coast. This map is considered as a general record of the Dutch discoveries on the north and western coasts of Australia during the 17th century.; Title from contents page of source item.; Map 14 from: Het aandeel der Nederlanders in de ontdekking vman Australie 1606-1765 = The part borne by the Dutch in the discovery of Australia 1606-1765 / by J.E. Heeres. London : Luzac, 1899.; Also available in electronic version via the Internet: http://mnla.gov.au/nla.map-gmod90; Facsimile reproduction. [Leiden : E.J. Brill ; London : Luzac & Co., 1899 (Den Haag : Lith. J. Smulders & Co.) 1 folded map : col. ; 49 x 72 cm. folded to 33 x 21 cm.Folding chart of the Malay Archipelago, the North- and West-coast of AustraliaPart borne by the Dutch in the discovery of Australia 1606-1765
A typology of farm households for the Umutara Province in Rwanda
Full text linkRwanda, Farm household, Farm typology, Technology adoption, Multivariate analysis,
Sub-100 keV ion beam generation with a Van De Graaff accelerator using an external DC voltage supply
No full textKeywords: Van de Graaff Medium energy ion beam Ion beam irradiation a b s t r a c t We present a method to produce stable proton and helium ion beams with energies of 10-100 keV from a 30-year-old Van De Graaff accelerator using an external stabilized DC voltage supply instead of the belt charging system. Requiring no other modifications, this makes an ideal system for ion irradiation with fluences up to 10 15 ions/cm 2 . Such ion energies and fluences are required in the emerging fields such as silicon micromachining using ion irradiation and we give examples of structures created with sizes as small as 200 nm
Proteomic analysis of the secretory response of Aspergillus niger to D-maltose and D-xylose
No full textFungi utilize polysaccharide substrates through extracellular digestion catalyzed by secreted enzymes. Thus far, protein secretion by the filamentous fungus Aspergillus niger has mainly been studied at the level of individual proteins and by genome and transcriptome analyses. To extend these studies, a complementary proteomics approach was applied with the aim to investigate the changes in secretome and microsomal protein composition resulting from a shift to a high level secretion condition. During growth of A. niger on D-sorbitol, small amounts of D-maltose or D-xylose were used as inducers of the extracellular amylolytic and xylanolytic enzymes. Upon induction, protein compositions in the extracellular broth as well as in enriched secretory organelle (microsomal) fractions were analyzed using a shotgun proteomics approach. In total 102 secreted proteins and 1,126 microsomal proteins were identified in this study. Induction by D-maltose or D-xylose resulted in the increase in specific extracellular enzymes, such as glucoamylase A on D-maltose and ß-xylosidase D on D-xylose, as well as of microsomal proteins. This reflects the differential expression of selected genes coding for dedicated extracellular enzymes. As expected, the addition of extra D-sorbitol had no effect on the expression of carbohydrate-active enzymes, compared to addition of D-xylose or D-maltose. Furthermore, D-maltose induction caused an increase in microsomal proteins related to translation (e.g., Rpl15) and vesicular transport (e.g., the endosomal-cargo receptor Erv14). Millimolar amounts of the inducers D-maltose and D-xylose are sufficient to cause a direct response in specific protein expression levels. Also, after induction by D-maltose or D-xylose, the induced enzymes were found in microsomes and extracellular. In agreement with our previous findings for D-xylose induction, D-maltose induction leads to recruitment of proteins involved in proteasome-mediated degradatio
An European cross-country comparison of the impact of housing market institutions on labour mobility
No full textDe Graaff T. and van Leuvensteijn M. A European cross-country comparison of the impact of homeownership and transaction costs on job tenure, Regional Studies. This paper looks at the impacts across European countries of homeownership and transaction costs on job tenure. The analysis is based on a representative household sample of fourteen European countries covering the period 1994-2001. These data are merged with country-specific transaction tax data and aggregate homeownership rates. Similar to previous microeconomic studies, the results indicate that homeownership reduces job mobility as well as the probability of becoming unemployed or economically inactive. It is found, however, that this effect is severely mitigated by two factors. First, it decreases when aggregate homeownership rates are higher. Thus, homeowners have larger job tenures, but more so in countries with low homeownership rates. Second, transaction costs on the housing market are positively associated with the probability of becoming unemployed. © 2013 © 2013 Regional Studies Association
Bio-economic farm modelling to analyse agricultural land productivity in Rwanda
No full text Keywords: Rwanda; farm household typology; sustainable technology adoption; multivariate analysis; land degradation; food security; bioeconomic model; crop simulation models; organic fertiliser; inorganic fertiliser; policy incentives In Rwanda, land degradation contributes to the low and declining agricultural productivity and consequently to food insecurity. As a result of land degradation and increasing population pressure, there is urgent need to simultaneously enhance food security and agro-ecological sustainability. The main objective of this PhD thesis was to make an assessment of technology options and policy incentives that can enhance sustainable farming in Rwanda. A multivariate analysis approach was used to clearly identify five types of farm households and their socio-economic characteristics. The main differences between the five farm types relate to gender, age, education, risk perception, risk attitude, labour availability, land tenure and income. A bio-economic model capable of analysing the impacts of soil erosion, family planning and land consolidation policies on food security in Rwanda was developed, and applied for one typical farm household. Calculations with the bio-economic model showed that a higher availability of good farm land would increase the farm income. Additionally, preserving soils against erosion and reducing risk would allow for using more marginal land which would increase food production for home consumption and for the market. Increasing the opportunities for off-farm employment can also increase farm household income. The simulation of crop yields under sustainable land management showed that predicted crop yields were distinctly higher than the actual yields for the current small-scale farming practices that are common in the region. Using the developed bio-economic model, model results showed that these sustainable agricultural technologies will clearly enhance food production (after a learning period) and income for all farm household types except the household with the largest farm for which cash at the beginning of the season is too restricted to switch to the new technologies. Provision of credit and availability off-farm activities have emerged as the most serious policies likely to affect the adoption of alternative technologies in all the farm households. The bio-economic farm model and its applications developed in this study give more insights into the possibilities of transforming the current farming system towards more sustainable farming. . </p
Numeriek model voor de berekening van kustlijnveranderinen t.g.v. golven en getij
No full textIn samenwerking tussen Rijkswaterstaat afdeling Kustonderzoek van de Directie Waterhuishouding en Waterbeweging en de vakgroep Kustvlaterbouwkunde van de Technische Hogeschool in Delft is een serie rekenprogrammma's tot stand gekomen met het doel de veranderingen van kustvormen onder invloed van golfaanval te voorspellen. In 1975 heeft Casteleyn [8J deze programma's gebundeld in een tweetal standaard programma's. Het eerste deel (KC) berekent de zandtransporten in het geschematiseerde kustvak met de zandtransportformule van het CERC. Het tweede deel (KL) berekent de kustlijn veranderingen volgens de eenlijn theorie van Bakker [lJ . In deze aanpak is het echter niet mogelijk de invloed van het getij in rekening te brengen, aangezien bij de formule van het CERC wordt aangenomen dat het zandtransport evenwijdig aan de kust recht evenredig is met een component van de golfenergieflux. De door golven opgewekte langsstroom wordt dan oak niet in de berekening opgenomen. Er is daarom behoefte aan een soortgel ijk rekenprogramma dat de morfologische veranderingen in een kustgebied berekent t.g.v. door golven en getij opgewekte langsstromen. Hierbij wordt dan tevens rekening gehouden met de continuiteitsvergelijking voor water, zodat er een dwarstransport ontstaat t.g.v. een debiet loodrecht op de kust. Dit dwarstransport komt uiteraard niet tot uiting in de aanpak van het KC en KL programma. Momenteel kan op aannemelijke wijze de door onregelmatige golven opgewekte langstroomsnelheidsverdeling binnen en juist buiten de brandingszone worden berekend. Hierin is de invloed van het getij op eenvoudige wijze te verwerken. In 1977 is door Van de Graaff en de schrijver [9J een vergelijking gemaakt tussen enkele moderne zandtransportformules en de CERC-formule. Uit deze vergelijking blijkt dat de zandtransportformule van Bijker [7] , die gebaseerd is op de formules van Kalinske-Frijlink en Einstein-Rouse, verrev/eg de voorkeur verdient boven de voor golven en stt'oom aangepaste formules van White-Ackers en Engelund-Hansen. In dit rapport zal een beschrijving worden gegeven van de eerste aanzet van het computerprogramma NL (n-lijn). Dit programma dient uiteindelijk de veranderingen te berekenen in een kustgebi ed, da t geschematiseerd is . door n-dieptelijnen. In deze eerste aanzet wordt het effect van het getij nog niet in rekening gebracht. De snelheidsverdeling wordt berekend uit de formule voor de aandrijvende kracht van onregelmatige golven volgens Battjes [SJ en de formule voor de bodemschuifspanning volgens Bijker [7J . Uit deze snelheidsverdeling wordt een twee-dimensionaal snelheidsbeeld afgeleid, waarbij de zandtransporten worden berekend met de formule van Bijker. Het dwarstransport t.g.v. afwijkingen van het profiel t.o.v. het evenwichtsprofiel worden berekend met de dwarstransportformule van SVlart [17J . In hoofdstuk 2 wordt een overzicht gegeven van enkele bestaande rekenprogramma's voor de berekening van kustlijn veranderingen, waarna in hoofdstuk 3 een beschrijving wordt gegeven van de in het NL-programma toegepaste schematisaties en formules. In hoofdstuk 4 wordt een eenvoudig voorbeeld uitgewerkt met zowel het NL-programma als het KC en KL (eenlijn) programma. In hoofdstuk 5 wordt een overzicht gegeven van de beperk-ingen van het huidige programma en warden aanbevelingen gegeven voor verdere uitbreiding, waarna het rapport wordt afgesloten met een samenvatting en conclusies.Hydraulic EngineeringCivil Engineering and Geoscience
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