Scaling up the effects of inbreeding depression from individuals to metapopulations

Abstract Inbreeding is common in nature, and many laboratory studies have documented that inbreeding depression can reduce the fitness of individuals. Demonstrating the consequences of inbreeding depression on the growth and persistence of populations is more challenging because populations are often regulated by density- or frequency-dependent selection and influenced by demographic and environmental stochasticity. A few empirical studies have shown that inbreeding depression can increase extinction risk of local populations. The importance of inbreeding depression at the metapopulation level has been conjectured based on population-level studies but has not been evaluated. We quantified the impact of inbreeding depression affecting the fitness of individuals on metapopulation persistence in heterogeneous habitat networks of different sizes and habitat configuration in a context of natural butterfly metapopulations. We developed a spatial individual-based simulation model of metapopulations with explicit genetics. We used Approximate Bayesian Computation to fit the model to extensive demographic, genetic, and life-history data available for the well-studied Glanville fritillary butterfly (Melitaea cinxia) metapopulations in the Åland islands in SW Finland. We compared 18 semi-independent habitat networks differing in size and fragmentation. The results show that inbreeding is more frequent in small habitat networks, and consequently, inbreeding depression elevates extinction risks in small metapopulations. Metapopulation persistence and neutral genetic diversity maintained in the metapopulations increase with the total habitat amount in and mean patch size of habitat networks. Dispersal and mating behavior interact with landscape structure to determine how likely it is to encounter kin while looking for mates. Inbreeding depression can decrease the viability of small metapopulations even when they are strongly influenced by stochastic extinction-colonization dynamics and density-dependent selection. The findings from this study support that genetic factors, in addition to demographic factors, can contribute to extinctions of small local populations and also of metapopulations. This article is protected by copyright. All rights reserved.Peer reviewe

INVESTIGATING THE REGULATION OF GROWTH MECHANISMS IN TWO DISTINCT BRANCHES OF PHOTOSYNTHETIC LIFE

Photosynthetic organisms often have limited mobility and rely on a variety of environmental, physiological, and chemical signals to regulate aspects of growth and development. In this thesis, I investigated how two such organisms, one a flowering plant and the other a heterokont alga, incorporate external signaling cues to make decisions regarding reproduction. My dissertation research is focused on 1) investigating molecular mechanisms of crosstalk between photoperiod and shade in regulating asexual reproduction in the wild strawberry Fragaria vesca, and 2) elucidating the mechanism of a bacterium-derived agent in the stimulation of cell division in the marine diatom Phaeodactylum tricornutum. First, strawberry, including woodland strawberry Fragaria vesca, is capable of a form of asexual reproduction by producing horizontal stems with daughter plants at the nodes. These horizontal stems, referred to as stolon, are derived from axillary meristems at the base of the leaves. Depending on the signals the axillary meristem receives, it will give rise to either a branch crown (a flowering shoot) or a stolon. Stolon allows for asexual reproduction to maintain the superior hybrid genotype and hence is of great significance agriculturally. Daughter plants derived from stolon are sold and propagated in strawberry farming. In this work, I have shown that a key regulatory protein FveRGA1 in GA signaling pathway functions as a repressor of stolon development. I further expanded this work by showing that the light quality (shade) signaling pathway interacts with the GA signaling to regulate stolon development. I identified and demonstrated FvePIF3 as a key transcription factor that positively regulates stolon initiation under far-red light (shade). Understanding the mechanisms underlying axillary meristem cell fate determination could advance biotechnology to increase strawberry production. Second, I have discovered and characterized a bacterium-based growth stimulation of the diatom Phaeodactylum tricornutum. Specifically, I noticed that a culture of P. tricornutum that had been accidentally contaminated with bacteria exhibited faster growth. I subsequently identified the responsible bacterium as Bacillus sp, which stimulated rapid Phaeodactylum cell division when added to the Phaeodactylum culture. I experimentally determined that the growth stimulating agent was heat labile and proteinase K-resistant. Further, I showed that the mother cell lysate of Bacillus sp. under sporulation was just as effective in promoting Phaeodactylum. In collaboration with Dr. Jon Clardy lab, we identified the growth-stimulating compounds as two distinct peptide-signaling molecules. The work revealed that the peptides may be previously under-reported signaling molecules for cross-kingdom communications. In addition to the fundamental discovery of novel signaling mechanisms between bacterium and algae, this work may facilitate large-scale diatom culture in biomass production for biofuel and biopharma

Inside-pipe heat transfer coefficient characterisation of a one third height scale model of a natural circulation loop suitable for a reactor cavity cooling system of the Pebble Bed Modular Reactor

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011.ENGLISH ABSTRACT: The feasibility of a closed loop thermosyphon for the Reactor Cavity Cooling System of the Pebble Bed Modular Reactor has been the subject of many research projects. Difficulties identified by previous studies include the hypothetical inaccuracies of heat transfer coefficient correlations available in literature. The aim of the research presented here is to develop inside-pipe heat transfer correlations that are specific to the current design of the RCCS. In order to achieve this, a literature review is performed which identifies reactors which employ closed loop thermosyphons and natural circulation. The literature review also explains the general one-dimensional two-fluid conservation equations that form the basis for numerical modelling of natural circulation loops. The literature review lastly discusses available heat transfer coefficient correlations with the aim of identifying over which ranges and under which circumstances these correlations are considered accurate. The review includes correlations commonly used in natural circulation modelling in the nuclear industry in aims of identifying correlations applicable to the modelling of the proposed RCCS. One of the objectives of this project is to design and build a one-third-height-scale model of the RCCS. Shortcomings of previous experimental models were assessed and, as far as possible, compensated for in the design of the model. Copper piping is used, eliminating material and surface property uncertainties. Several sight glasses are incorporated in the model, allowing for the visual identification of two-phase flow regimes. An orifice plate is used allowing for bidirectional flow measurement. The orifice plate, thermocouples and pipe-in-pipe heat exchangers are calibrated in-situ to minimize experimental error and aid repeatability. Twelve experiments are performed with data logging occurring every ten seconds. The results presented here are limited to selected single and two-phase flow operating mode results. Error analyses and repeatability of experimental measurements for single and two-phase operating modes as well as cooling water mass flow rates are performed, to show repeatability of experimental results. These results are used to mathematically determine the experimental inside-pipe heat transfer coefficients for both the evaporator and condenser sections. Trends in the heat transfer coefficient profiles are identified and the general behaviour of the profiles is thoroughly explained. The RCCS is modelled as a one-dimensional system. Correlations for the friction factor, heat transfer coefficient, void fraction and two-phase frictional multiplier are identified. The theoretical heat transfer coefficients are calculated using the mathematical model and correlations identified in the literature review. Fluid parameters are evaluated using experimentally determined temperatures and mass flow rates. The resulting heat transfer coefficient profiles are compared to experimentally determined profiles, to confirm the hypothesis that existing correlations do not accurately predict the inside-pipe heat transfer coefficients. The experimentally determined coefficients are correlated to 99% confidence intervals. These generated correlations, along with identified and established twophase heat transfer coefficient correlations, are used in a mathematical model to generate theoretical coefficient profiles. These are compared to the experimentally determined coefficients to show prediction accuracy.AFRIKAANSE OPSOMMING: Die haalbaarheid van ‘n natuurlike sirkulasie geslote lus vir die Reaktor Holte Verkoeling Stelsel (RHVS) van die Korrelbed Modulêre Kern-Reaktor (KMKR) is die onderwerp van talle navorsings projekte. Probleme geïdentifiseer in vorige studies sluit in die hipotetiese onakkuraatheid van hitte-oordrag koëffisiënt korrelasies beskikbaar in literatuur. Die doel van die navorsing aangebied is om binne-pyp hitte-oordrag koëffisiënt korrelasies te ontwikkel spesifiek vir die huidige ontwerp van die RHVS. Ten einde dit te bereik, word ‘n literatuurstudie uitgevoer wat kern-reaktors identifiseer wat gebruik maak van natuurlike sirkulasie lusse. Die literatuurstudie verduidelik ook die algemene een-dimensionele twee-vloeistof behoud vergelykings wat die basis vorm vir numeriese modellering van natuurlike sirkulasie lusse. Die literatuurstudie bespreek laastens beskikbare hitte-oordrag koëffisiënt korrelasies met die doel om te identifiseer vir welke massavloei tempo waardes en onder watter omstandighede hierdie korrelasies as korrek beskou is. Die ontleding sluit korrelasies in wat algemeen gebruik word in die modellering van natuurlike sirkulasie in die kern industrie met die hoop om korrelasies vir gebruik in die modellering van die voorgestelde RHVS te identifiseer. Een van die doelwitte van die projek is om ‘n een-derde-hoogte-skaal model van die RHVS te ontwerp en te bou. Tekortkominge van vorige eksperimentele modelle is geidentifiseer en, so ver as moonlik, voor vergoed in die ontwerp van die model. Koper pype word gebruik wat die onsekerhede van materiaal en opperkvlak eindomme voorkom. Verkseie deursigtige polikarbonaat segmente is ingesluit wat visuele identifikasie van twee-fase vloei regimes toelaat. ‘n Opening plaat word gebruik om voorwaartse en terugwaartse vloeimeting toe te laat. Die opening plaat, termokoppels en hitte uitruilers is gekalibreer in plek om eksperimentele foute te verminder en om herhaalbaarheid te verseker. Twaalf eksperimente word uitgevoer en data word elke tien sekondes aangeteken. Die resultate wat hier aangebied word, is beperk tot geselekteerde enkel- en tweefase vloei meganismes van werking. Fout ontleding en herhaalbaarheid van eksperimentele metings, om die herhaalbaarheid van eksperimentele resultate te toon. Hierdie is gebruik om wiskundig te bepaal wat die eksperimentele binne-pyp hitte-oordrag koëffisiënte is vir beide die verdamper en kondenseerder afdelings. Tendense in die hitte-oordrag koëffisiënt profiele word geïdentifiseer en die algemene gedrag van die profiles is deeglik verduidelik. Die RHVS is gemodelleer as 'n een-dimensionele stelsel. Korrelasies vir die wrywing faktor, hitte-oordrag koëffisiënte, leegte-breuk en twee-fase wrywings vermenigvuldiger word geïdentifiseer. Die teoretiese hitte-oordrag koëffisiënte word bereken deur middle van die wiskundige model en korrelasies wat in literatuur geidentifiseer is. Vloeistof parameters is geëvalueer met eksperimenteel bepaalde temperature en massa-vloei tempos. Die gevolglike hitte-oordrag koëffisiënt profiles is vergelyk met eksperimentele profiele om die hipotese dat die bestaande korrelasies nie die binne-pyp hitte-oordrag koëffisiënte akkuraat voorspel nie, te bevestig. Die eksperimenteel bepaalde koëffisiënte is gekorreleer en die gegenereerde korrelasies, saam met geïdentifiseerde twee-fase hitte-oordrag koëffisiënt korrelasies, word gebruik in 'n wiskundige model om teoretiese koëffisiënt profiele te genereer. Dit word dan vergelyk met die eksperimenteel bepaalde hitteoordrag koëffisiënte om die akkuraatheid van voorspelling te toon. Tekortkominge in die teoretiese en eksperimentele model word geïdentifiseer en aanbevelings gemaak om hulle aan te spreek in die toekoms

Mutation analysis of the promoter region of CYBRD1, HFE, LTF, HAMP and SLC40A1 in a Tuberculosis cohort

Thesis (MSc)--Stellenbosch University, 2014.ENGLISH ABSTRACT: Tuberculosis (TB) is an epidemic disease characterised by wet, persistent coughing, weight loss, fever, fatigue, and blood in the sputum. It has been reported that one in every three individuals is currently infected with Mycobacterium tuberculosis, the causative agent of TB, and that 10% of them will develop the active disease. The high prevalence and low penetrance of this disease has resulted in increased research performed to ascertain what factors play a role in susceptibility to M. tuberculosis infection. Some factors known to play a role in a minority of cases may include: HIV infection, diabetes, alcohol abuse and old age, but racial differences in susceptibility have also been observed. However, the influence of genetic factors is gaining popularity in current research. M. tuberculosis requires iron to proliferate, which it must appropriate from its host. For this reason the genes involved in the metabolism of iron in the human host are of particular interest when considering susceptibility to M. tuberculosis infection. In order to determine whether the expression of these genes may influence disease susceptibility, the promoter region of the CYBRD1, HAMP, HFE, LTF and SLC40A1 genes have been targeted for investigation. The aim of this study was to determine whether DNA variation in the promoter region of these genes involved in iron metabolism is associated with M. tuberculosis susceptibility. The study cohort consisted of 49 TB patients and 51 healthy, unrelated, population-matched controls, all of whom were Black, Xhosa-speaking individuals. Initially, 15 patient samples were randomly selected for exploratory screening, utilising semi-automated bi-directional sequencing analysis. In this manner, 40 variants were identified of which 30 were previously described. The novel variants included CYBRD1: -849 C/G, -492 A/G, -454 C/T, -397 A/C; HAMP: -323 C/T; HFE: -561 A/G, -331 A/C; and LTF: -1377 T/G, -457 T/C, -437 C/G. A number of loci demonstrated a statistically significant difference in allele and genotype frequencies, and in iron parameter levels when comparing the patient and control groups and for each variant separately. In silico analyses revealed the creation and/or abolishment of several transcription factor binding sites (TFBSs) due to the presence or absence of certain identified variants. The change in the composition of TFBSs in the promoter region may lead to differential expression of the gene. This study served as a pilot investigation to identify promoter region variants in the candidate genes involved in iron metabolism, in TB patients. The results presented here indicate that the identified variants (-1813 C/T, -1459 T/C, -238 A/G, -166 C/G [CYBRD1]; -561 A/G [HFE]; -1470 C/T, -1355 G/C and -1098 G/A [SLC40A1]) could possibly contribute to the increased absorption of iron in the TB patient group, which could subsequently increase the occurrence of pathogenic infection. The findings of this study could further aid in the elucidation of the exact mechanism(s) by which iron, its metabolism, and the genes involved affect disease susceptibility, more specifically, M. tuberculosis susceptibility.AFRIKAANSE OPSOMMING: Tuberkulose (TB) is „n epidemiese siekte gekarakteriseer deur nat, aanhoudende hoes, gewigsverlies, moegheid, en bloed in die speeksel. Dit is gerapporteer dat een in elke drie individue tans geïnfekteer is met Mycobacterium tuberculosis, die veroorsakende agent van TB, en dat 10% van dié individue die aktiewe vorm van die siekte sal ontwikkel. Die hoë voorkoms en lae effek van hierdie siekte het daartoe gelei dat meer navorsing mettertyd gedoen is om die faktore wat „n rol mag speel in M. tuberculosis infeksie, te bepaal. Sommige faktore bekend vir hul rol in „n minderheid van gevalle sluit in: MIV infeksie, diabetes, alkoholmisbruik en bejaardheid, maar etniese verskille in vatbaarheid vir die siekte is ook al waargeneem. Die waarskynlikheid van genetiese invloed op die ontwikkeling van TB word ook meer deur navorsers ondersoek. M. tuberculosis benodig yster om te vermeerder, wat dit moet bekom vanaf die gasheer. Vir hierdie rede is die gene betrokke by yster metabolisme in die menslike gasheer veral van belang vir die oorweging van vatbaarheid vir M. tuberculosis. Om te bepaal of die uitdrukking van hierdie gene moontlik „n invloed het op vatbaarheid vir die siekte, was die promoter areas van die CYBRD1, HAMP, HFE, LTF en SLC40A1 gene geteiken. Die doel van hierdie studie was om te bepaal of DNS variasie in die promoter area van hierdie gene betrokke in yster metabolisme moontlik verband kan hou met vatbaarheid vir M. tuberculosis. Die studie kohort het uit 49 TB pasiënte en 51 gesonde, onverwante, populasie-gepaarde kontroles, waarvan almal Swart, Xhosa-sprekende individue was, bestaan. Aanvanklik was 15 pasiënt monsters lukraak gekies vir ondersoekende sifting, deur die gebruik van semi-outomatiese twee-rigting volgordebepalings. Op hierdie manier is 40 variante geïdentifiseer waarvan 30 voorheen beskryf is. Die nuwe variante sluit in CYBRD1: -849 C/G, -492 A/G, -454 C/T, -397 A/C; HAMP: -323 C/T; HFE: -561 A/G, -331 A/C; en LTF: -1377 T/G, -457 T/C, -437 C/G. „n Aantal loci het statisties betekenisvolle verskille getoon in alleel en genotipe frekwensies, en in yster parameter vlakke met die vergelyking van die pasiënt groep met die kontrole groep. In silico analise het verder die skepping en/of afskaffing van verskeie transkripsiefaktor bindingsetels (TFBSs), as gevolg van die teenwoordigheid of afwesigheid van sekere variante, getoon. Die verandering in die samestelling van TFBSs in die promoter area kan lei tot differensiële uitdrukking van die geen. Dié studie het gedien as „n voorlopige ondersoek om te bepaal of promoter area variante, geïdentifiseer in kandidaat gene betrokke by yster metabolisme, „n invloed het in die ontwikkeling van TB. Die resultate wat hier gewys word dui aan dat die geïdentifiseerde variante (-1813 C/T, -1459 T/C, -238 A/G, -166 C/G [CYBRD1]; -561 A/G [HFE]; -1470 C/T, -1355 G/C and -1098 G/A [SLC40A1]) moontlik die verhoogde opname van yster kan veroorsaak, wat later die toename van die patogeniese infeksie kan veroorsaak. Die bevindinge van hierdie studie kan moontlik bydra tot die toeligting van die presiese meganisme(s) waardeur yster, yster metabolisme, en die betrokke gene vatbaarheid vir siekte, meer spesifiek M. tuberculosis vatbaarheid, beïnvloed

Die Auswirkung einer mangelbedingten Rückabwicklung des Liefervertrags auf den Finanzierungsleasingvertrag

Der mangelbedingte Rücktritt eines Leasingnehmers lässt wegen der Drittverweisungsklausel den Finanzierungsleasingvertrag unberührt und führt »nur« zur Rückabwicklung des Liefervertrags nach §§ 346 ff. BGB.Stephanie Sittmann-Haury verwirft die sich daran anschließende »Geschäftsgrundlagenrechtsprechung« und die Gegenvorschläge aus der Literatur, die gleichwohl eine Auswirkung auf den Leasingvertrag zu begründen versuchen, und entwickelt eine eigene Lösung, die die zuvor herausgearbeitete Risikoverteilung im Verhältnis Leasinggeber/Leasingnehmer konsequent beachtet: Dem Leasinggeber wird die Überlassung der Sache an den Leasingnehmer durch die Rückgewähr an den Lieferanten unmöglich, gleichwohl schuldet der Leasingnehmer nach § 326 Abs. 2 S. 1 Var. 1 BGB weiterhin Leasingraten. Jedoch kann er vom Leasinggeber die Herausgabe des diesem vom Lieferanten zurückgezahlten Kaufpreises nach § 285 Abs. 1 BGB verlangen und beim Lieferanten darüber hinausgehende Belastungen (höhere Zinsen und Gewinnanteile in den Leasingraten) als Schaden geltend machen, §§ 398, 437 Nr. 3, 280 Abs. 1, 3, 281 BGB

Use of passive cooling systems in generation IV nuclear reactors for core decay heat removal and containment cooling

ENGLISH ABSTRACT: The Pebble Bed Modular Reactor (PBMR) concept evolved from a German high temperature helium-cooled reactor design with ceramic spherical fuel pebbles. The removal of parasitic heat between the reactor core and concrete citadel is facilitated through the Reactor Cavity Cooling System (RCCS). The RCCS primary function is to passively maintain the cavity temperature within a required range. This is in order to provide protection to the concrete structures surrounding the reactor and also, during loss of coolant accident operating conditions, to transport parasitic heat from the reactor to the environment. Several Generation IV reactor designs incorporate passive safety systems. The main objective of this study is to familiarise the reader with specific “innovative” nuclear reactor designs and discuss the different passive safety systems employed in these designs for core decay heat removal and containment cooling systems. A table is given comparing the type, thermal efficiency, fuel, coolant and passive safety systems employed by each reactor to those of the PBMR.Pre-prin

Exercitatio Tertia De ordine decretorum divinorum in salute humani generis constituenda, & primo quidem De Voluntate Dei Benevolentissima Et Misericordissima Erga Totum Genus Humanum ...

In Incluta Wittebergensium Academia ad disputandum publice proposita, Praeside Johanne Scharfio ... Respondente M. Hartwico Sittmann/ Otterndorpio-Hadelensi ... Ad diem XVII. Februarii ..

Inside-pipe heat transfer coefficient characterization of a thermosyphon-type heat pipe suitable for the reactor cavity cooling system of the Pebble Bed Modular Reactor

ENGLISH ABSTRACT: The feasibility of a closed loop thermosyphon for the Reactor Cavity Cooling System of the Pebble Bed Modular Reactor has been the subject of many research projects. One of the difficulties identified by previous studies is the hypothetical inaccuracies of heat transfer coefficient correlations available in literature. This article presents the development of an inside-pipe heat transfer correlation, for both the evaporator and condenser sections, that is specific to the current design of the RCCS. A one-third-height-scale model of the RCCS was designed and manufactured using copper piping and incorporating several strategically placed sight glasses, allowing for the visual identification of two-phase flow regimes and an orifice plate to allow for forward and reverse flow measurement. Twelve experiments, lasting at least 5 hours each, were performed with data logging occurring every ten seconds. The experimental results are used to mathematically determine the experimental inside-pipe heat transfer coefficients for both the evaporator and condenser sections. The experimentally determined heat transfer coefficients are correlated by assuming that the average heat flux can be described by a functional dependence on certain fluid properties, the average heat flux is directly proportional to the heat transfer coefficient and that the heat transfer coefficient is a function of the Nusselt number. The single-phase inside-pipe heat transfer coefficients were correlated to 99% confidence intervals and with less than 30% standard deviation from experimental results. The generated correlations, along with identified and established two-phase heat transfer coefficient correlations, are used in a mathematical model, with experimental mass flow rates and temperatures used as input variables, to generate theoretical heat transfer coefficient profiles. These are compared to the experimentally determined heat transfer coefficients to show that the generated correlations accurately predict the experimentally determined inside-pipe heat transfer coefficients.Pre-prin