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Im, Hsung J. "Metal Contacts to Silicon Carbide and Gallium Nitride Studied with Ballistic Electron Emission Microscopy." The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1000844302.
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Obernhuber, Sandra. "Ballistische Elektronen-Emissions-Mikroskopie (BEEM) an Ferromagnet-Halbleitergrenzflächen." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=984769412.
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Che, Yulu. "Ambipolar Ballistic Electron Emission Microscopy Studies of Gate-field Modified Schottky Barriers." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1282070943.
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Caud, Francois. "Microscopie tunnel à électrons balistiques: vers le Magnétisme." Phd thesis, Université Paris Sud - Paris XI, 2006. http://tel.archives-ouvertes.fr/tel-00080846.
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Ce travail a consisté à développer une microscopie tunnel à électrons balistiques (BEEM) dont l'application finale est l'obtention d'un dispositif d'étude d'objets magnétiques, à l'échelle du nanomètre (imagerie de domaines et de nanostructures magnétiques). Nous présentons ici une formulation poussée de calculs de spectres macroscopiques I(V) et de spectres BEEM Ib(V) qui se révèle très efficace pour l'analyse des données expérimentales. L'étude des I(V) macroscopiques permet, avant toute mesure microscopique, de connaître les caractéristiques importantes d'un échantillon BEEM: hauteur de barrière Schottky, facteur d'idéalité et résistance à tension nulle de la jonction Schottky. Les fonctions d'ajustement des spectres BEEM ont été calculées à partir d'un modèle publié par les pionniers de la technique, que nous décrivons ici dans ses différents stades de raffinement. La mise au point d'un processus chimique adapté à la préparation de surface des substrats de silicium et le travail de salle blanche pour mener à bien les étapes technologiques sont ensuite exposés. Les échantillons fabriqués par évaporation ultra-vide ont révélé de meilleures caractéristiques que ceux faits par pulvérisation cathodique: hauteur de barrière plus élevée, transmission plus grande, bruit réduit. Les mesures BEEM ont montré l'obtention de différents contrastes sur le signal des électrons balistiques. Certains sont nettement liés à une atténuation des électrons chauds par effet d'épaisseur de la couche métallique alors que d'autres contrastes, à la nature clairement différente, ne sont pas totalement compris. La préparation et la caractérisation d'échantillons magnétiques est aussi abordée.
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Tivarus, Cristian Alexandru. "Schottky barrier formation at metal-quantum well interfaces studied with ballistic electron emission microscopy." The Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=osu1134419471.
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Guézo, Sophie. "Microscopie à Emission d'ELectrons Balistiques (BEEM): étude des propriétés électroniques locales d'hétérostructures." Phd thesis, Université Rennes 1, 2009. http://tel.archives-ouvertes.fr/tel-00429319/en/.
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Nous avons développé un microscope à émission d'électrons balistiques (BEEM) sous ultra-vide, dédié à l'étude des propriétés électroniques d'interfaces d'hétérostructures à base de semiconducteurs III-V pertinentes pour des applications potentielles en électronique de spin. Dans un premier temps, nous avons étudié les contacts Schottky épitaxiés Au(110)/GaAs(001) et Fe(001)/GaAs(001). Nous montrons d'un point de vue théorique que le transport cohérent d'électrons chauds à travers le métal et la conservation de la composante transverse du vecteur d'onde électronique à l'interface métal/GaAs sont à l'origine des signatures spectroscopiques BEEM contrastées observées expérimentalement sur ces deux systèmes. Ensuite, l'étude du contact tunnel MgO/GaAs(001) a révélé la présence de canaux de conduction situés dans la bande interdite de MgO. Ces canaux sont associés à la présence de lacunes d'oxygène localisées dans l'oxyde, qui diminuent fortement la hauteur de barrière tunnel. Finalement, le phénomène de magnétorésistance d'électrons chauds dans la vanne de spin Fe/Au/Fe/GaAs(001) permet d'observer par BEEM des domaines et des parois de domaines magnétiques avec une résolution latérale nanométrique.
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Guézo, Sophie. "Microscopie à Emission d’Electrons Balistiques (BEEM) : étude des propriétés électroniques locales d’hétérostructures." Rennes 1, 2009. https://tel.archives-ouvertes.fr/tel-00429321.
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Ce travail de thèse s’est développé autour de la microscopie à émission d’électrons balistiques (BEEM) sous ultra-vide, dédiée à l’étude des propriétés électroniques d’interfaces d’hétérostructures pertinentes pour des applications potentielles en électronique de spin. Dans un premier temps, l’étude de la jonction Schottky Au/GaAs(001) a permis de mettre en évidence l’influence des propriétés structurales sur le transport d’électrons chauds. Une étude similaire sur Fe/GaAs(001) a confirmé la sensibilité du BEEM aux effets de structures électroniques. Ensuite, l’étude BEEM sur les propriétés électroniques locales de la barrière MgO/GaAs(001) a révélé la présence de canaux de conduction situés dans la bande interdite de MgO. Ces canaux sont associés à la présence de lacunes d’oxygène localisées dans l’oxyde, qui diminuent fortement la hauteur de barrière tunnel. Enfin, des études préliminaires de transport d’électrons chauds dépendants du spin sur Fe/Au/Fe/GaAs(001) sont présentéesThis thesis work has been developed on ballistic electron emission microscopy (BEEM) under ultra-high vacuum, dedicated to the study of interface electronic properties of heterostructures based on III-V semiconductors, essentially for further potential applications in spintronics. First, the study of Au/GaAs Schottky junction has shown, by comparison between experimental measurements and theorical calculations, the effect of structural properties on hot-electron transport. A similar study realized on Fe/GaAs(001) has confirmed the BEEM sensitivity to electronic structure effects. Then, BEEM measurements on the barrier MgO/GaAs(001) have revealed new conduction channels localized in the band gap of MgO. They are related to oxygen vacancies in the oxide layer, which strongly reduce the tunnel barrier height. Finally, first measurements of spin-polarized hot-electron transport realized on Fe/Au/Fe/GaAs(001) spin-valve are presented
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Beardsley, Jonas T. "Charge-Spin Transport Correlation in Local Electrical Spin Injection in Silicon." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1417777678.
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Wennerberg, Fåhraeus Maja. "How to succeed with energy efficient refurbishment measures : A study of the CONCERTO initiative, BEEM-UP project and EPC model." Thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-267908.
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Buildings consume 40 % of Europe’s total energy consumption and causes 33 % of the CO2 emissions. (Pol and Lippert, 2010) Existing old buildings, especially those constructed with limited energy standards before 1960, are in need of refurbishment and energy efficiency. (Economidou, 2011) The thesis is a part of the EU project GrowSmarter, where smart solutions for sustainable cities are to be implemented in the lighthouse cities Stockholm, Cologne and Barcelona. (European Commission, 2014) The purpose of this thesis is to look into the experiences, success factors and barriers from the CONCERTO initiative, BEEM-UP project and EPC model, focusing on energy efficient refurbishment. The intent is that e.g. authorities, municipalities, companies and building owners, who are planning on performing energy efficient refurbishment measures, can access identified success factors and barriers in previous projects of different scale and methods. The conclusions of this study are that the communication and cooperation between stakeholders in a project, knowledge transfer and training of installers are important factors for successful projects. Information and involvement of tenants facilitates work execution, improves results after refurbishment and increases energy knowledge and awareness. The data quantity and quality is another influencing factor on building performance and the difference between calculated and measured energy savings. Stakeholder approach, energy performance regulations, ownership structure and financial status/possibilities for the building owner can affect project results.GrowSmarter
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Junay, Alexandra. "Étude des propriétés électroniques et de transport multi-échelle de jonctions tunnel Au/Alcanethiols/n-GaAs(001)." Thesis, Rennes 1, 2015. http://www.theses.fr/2015REN1S024/document.
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Les hétérostructures hybrides organique-inorganique présentent des propriétés intéressantes, notamment pour des applications dans le domaine de l’électronique et de la spintronique. Notre intérêt s’est porté particulièrement sur la réalisation d’hétérostructures de type Métal/Monocouche organique/Semiconducteur, dont l’étape de reprise de top-contact métallique reste actuellement un verrou majeur à la réalisation de telles jonctions. L’expérience de l’équipe sur des hétérostructures de type MOS (Métal/Oxyde/Semiconducteur), ainsi que les différentes techniques de surface et de transport disponibles au laboratoire, sont appliquées ici à l’étude de ces hétérostructures hybrides. En particulier, la Microscopie à Emission d’Electrons Balistiques (BEEM) permet d’étudier localement les propriétés électroniques des hétérostructures, avec une résolution spatiale nanométrique. A partir du système Au/GaAs(001) bien connu au laboratoire, nous avons intercalé une monocouche d’alcanethiols à l’interface, pour former des hétérostructures de type Au/Alcanethiols/GaAs(001), entièrement préparées sous ultra-vide. Lors du dépôt d’or à température ambiante, les images BEEM ont révélé des interfaces hétérogènes, avec des zones où le peigne moléculaire est court-circuité ou non par le métal. Une analyse quantitative en spectroscopie BEEM des zones non court-circuitées a mis en évidence des signatures particulières, avec une première contribution associée au passage tunnel des électrons à travers le peigne moléculaire, et une seconde contribution, à plus haute énergie, révélant l’existence de nouveaux canaux de conduction associés à l’existence d’états inoccupés dans la monocouche organique. Les effets de l’épaisseur du métal déposé, de la longueur de chaîne des molécules organiques, ainsi que du groupe terminal de la chaîne organique, ont été discutés. Afin d’améliorer le dépôt du contact métallique, un dispositif expérimental original a permis de déposer l’or sur le substrat refroidi, sur lequel une couche tampon de Xénon est condensée (méthode BLAG : Buffer Layer Assisted Growth). L’analyse BEEM de ces hétérostructures a révélé ici des interfaces homogènes, sans pénétration du métal. Des signatures spectroscopiques similaires aux zones non court-circuitées précédentes ont été mises en évidence. Une étude complète de ces hétérostructures préparées par la méthode BLAG a été réalisée via des mesures de transport à l’échelle macroscopique (J(V) et C(V)), ainsi que des mesures de photoémission par rayonnement synchrotron. Ces mesures ont confirmé le caractère reproductible des jonctions formées, avec des hauteurs de barrière en accord avec celles déterminées par BEEMIn molecular electronics and spintronics, top-contact metal electrode deposition on organic molecular monolayer (OML)/semiconductor hybrid heterostructures is still a critical issue, leading to metal penetration through the molecules and monolayer’s damage. The experimental set-ups available in the lab and the team’s experience in inorganic-inorganic heterostructures are here applied to hybrid organic-inorganic heterostructures. In particular, the Ballistic Electron Emission Microscopy (BEEM), a technique derived from Scanning Tunneling Microscopy (STM), allows to study electronic properties of such heterostructures, at a nanometer scale. Starting from the well-known Au/GaAs(001) Schottky contact, we here intercalate an alkanethiols monolayer, in order to obtain Au/Alkanethiols/GaAs(001) heterostructures, fully grown in ultra-high vacuum environment. In the case of room-temperature metal deposition, BEEM imaging reveals domains which are short-circuited or not by the metal. A quantitative analysis of non-short-circuited interfaces is realized by BEEM in spectroscopy mode. Particular fingerprints are obtained, with a first component related to electron tunnel transport through the monolayer, and a second component, at higher energy, related to first unoccupied states of the molecular layer reachable for electrons. The effects of metal thickness, molecular chain length and terminal group are discussed. In order to minimize the degree of gold penetration, an alternative top-contact deposition method is used, based on buffer-layer assisted growth (BLAG). BEEM studies on these heterostructures reveal homogeneous interfaces without metal penetration, and similar spectroscopic fingerprints. Complementary studies at macroscopic scale (J(V) and C(V) transport measurements and photoemission by synchrotron radiation) confirm the reproducible character of the junctions with barrier height values similar to the ones obtained by BEEM
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Heller, Eric. "Ultra low signals in ballistic electron emission microscopy." Columbus, Ohio : Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1060979803.
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Thesis (Ph. D.)--Ohio State University, 2003.Title from first page of PDF file. Document formatted into pages; contains xvii, 237 p.; also includes graphics. Includes abstract and vita. Advisor: Jonathan P. Pelz, Dept. of Physics. Includes bibliographical references (p. 232-237).
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Claveau, Yann. "Modeling of ballistic electron emission microscopy." Thesis, Rennes 1, 2014. http://www.theses.fr/2014REN1S074/document.
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Après la découverte de la magnéto-résistance géante (GMR) par Albert Fert et Peter Grünberg, l'électronique a connu une véritable avancée avec la naissance d'une nouvelle branche appelée spintronique. Cette discipline, encore jeune, consiste à exploiter le spin des électrons dans le but notamment de stocker de l'information numérique. La plupart des dispositifs exploitant cette propriété quantique des électrons consistent en une alternance de fines couches magnétiques et non magnétiques sur un substrat semi-conducteur. L'un des outils de choix pour la caractérisation de ces structures, inventé en 1988 par Kaiser et Bell, est le microscope à émission d'électrons balistiques (BEEM). A l'origine, ce microscope, dérivé du microscope à effet tunnel (STM), était dédié à l'imagerie d'objets (nanométriques) enterrés ainsi qu'à l'étude de la barrière de potentiel (barrière Schottky) qui se forme à l'interface d'un métal et d'un semi-conducteur lors de leur mise en contact. Avec l'essor de la spintronique, le BEEM est devenu une technique de spectroscopie essentielle mais encore fondamentalement incomprise. C'est en 1996 que le premier modèle réaliste, basé sur le formalisme hors équilibre de Keldysh, a été proposé pour décrire le transport des électrons dans cette microscopie. Il permettait notamment d'expliquer certains résultats expérimentaux jusqu'alors incompris. Cependant, malgré son succès, son usage a été limité à l'étude de structures semi-infinies via un méthode de calcul appelée décimation de fonctions de Green. Dans ce contexte, nous avons étendu ce modèle au cas des films minces et des hétéro-structures du type vanne de spin : partant du même postulat que les électrons suivent la structure de bandes du matériaux dans lesquels ils se propagent, nous avons établi une formule itérative permettant le calcul des fonctions de Green du système fini par la méthode des liaisons fortes. Ce calcul des fonctions de Green a été encodé dans un programme Fortran 90, BEEM v3, afin de calculer le courant BEEM ainsi que la densité d'états de surface. En parallèle, nous avons développé une autre méthode, plus simple, qui permet de s'affranchir du formalisme hors équilibre de Keldysh. En dépit de sa naïveté, nous avons montré que cette approche permettait l'interprétation et la prédiction de certains résultats expérimentaux de manière intuitive. Cependant, pour une étude plus fine, le recours à l'approche “hors équilibre” reste inévitable, notamment pour la mise en évidence d'effets d'épaisseur, lés aux interfaces inter-plans. Nous espérons que ces deux outils puissent se révéler utiles aux expérimentateurs, et notamment pour l'équipe Surfaces et Interfaces de notre départementAfter the discovery of Giant Magneto-Resistance (GMR) by Albert Fert and Peter Grünberg, electronics had a breakthrough with the birth of a new branch called spintronics. This discipline, while still young, exploit the spin of electrons, for instance to store digital information. Most quantum devices exploiting this property of electrons consist of alternating magnetic and nonmagnetic thin layers on a semiconductor substrate. One of the best tools used for characterizing these structures, invented in 1988 by Kaiser and Bell, is the so-called Ballistic Electron Emission Microscope (BEEM). Originally, this microscope, derived from the scanning tunneling microscope (STM), was dedicated to the imaging of buried (nanometer-scale) objects and to the study of the potential barrier (Schottky barrier) formed at the interface of a metal and a semiconductor when placed in contact. With the development of spintronics, the BEEM became an essential spectroscopy technique but still fundamentally misunderstood. It was in 1996 that the first realistic model, based on the non-equilibrium Keldysh formalism, was proposed to describe the transport of electrons during BEEM experiments. In particular, this model allowed to explain some experimental results previously misunderstood. However, despite its success, its use was limited to the study of semi-infinite structures through a calculation method called decimation of Green functions. In this context, we have extended this model to the case of thin films and hetero-structures like spin valves: starting from the same postulate that electrons follow the band structure of materials in which they propagate, we have established an iterative formula allowing calculation of the Green functions of the finite system by tight-binding method. This calculation of Green’s functions has been encoded in a FORTRAN 90 program, BEEM v3, in order to calculate the BEEM current and the surface density of states. In parallel, we have developed a simpler method which allows to avoid passing through the non-equilibrium Keldysh formalism. Despite its simplicity, we have shown that this intuitive approach gives some physical interpretation qualitatively similar to the non-equilibrium approach. However, for a more detailed study, the use of “non-equilibrium approach” is inevitable, especially for the detection of thickness effects linked to layer interfaces. We hope these both tools should be useful to experimentalists, especially for the Surfaces and Interfaces team of our department
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Šuta, Václav. "Automatický posuv pro digitální zapisovač dat." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2011. http://www.nusl.cz/ntk/nusl-219187.
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Master theses of Automatic Shift Control of the Digital Data Recorder is primarily concerned to design and construction of equipment used for measuring the half-width of the laser beam. The introductory part is devoted to the related theoretical basics and serves for better orientation in the following chapters. The second part is devoted to construction, completion and basic setting of product.
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Ashley, Michael John Siew Leung, and ashley@gravity psu edu. "Singularity theorems and the abstract boundary construction." The Australian National University. Faculty of Science, 2002. http://thesis.anu.edu.au./public/adt-ANU20050209.165310.
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The abstract boundary construction of Scott and Szekeres has proven a practical
classification scheme for boundary points of pseudo-Riemannian manifolds. It
has also proved its utility in problems associated with the re-embedding of exact
solutions containing directional singularities in space-time. Moreover it provides
a model for singularities in space-time - essential singularities. However the literature
has been devoid of abstract boundary results which have results of direct
physical applicability.¶
This thesis presents several theorems on the existence of essential singularities
in space-time and on how the abstract boundary allows definition of optimal em-
beddings for depicting space-time. Firstly, a review of other boundary constructions
for space-time is made with particular emphasis on the deficiencies they possess for
describing singularities. The abstract boundary construction is then pedagogically
defined and an overview of previous research provided.¶
We prove that strongly causal, maximally extended space-times possess essential
singularities if and only if they possess incomplete causal geodesics. This result
creates a link between the Hawking-Penrose incompleteness theorems and the existence of essential singularities. Using this result again together with the work of
Beem on the stability of geodesic incompleteness it is possible to prove the stability
of existence for essential singularities.¶
Invariant topological contact properties of abstract boundary points are presented
for the first time and used to define partial cross sections, which are an
generalization of the notion of embedding for boundary points. Partial cross sections
are then used to define a model for an optimal embedding of space-time.¶
Finally we end with a presentation of the current research into the relationship
between curvature singularities and the abstract boundary. This work proposes
that the abstract boundary may provide the correct framework to prove curvature
singularity theorems for General Relativity. This exciting development would culminate over 30 years of research into the physical conditions required for curvature singularities in space-time.
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Wagner, Jennie Faith. "Can Beef Be Bee-Friendly? Using Native Warm-Season Grasses and Wildflowers in Pastures to Conserve Bees." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/98621.
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Over the past several decades, native and managed bee populations have decreased in the United States and worldwide. Although bee decline is attributable to several factors, habitat loss is the primary driver. Simultaneously, cattle producers in the eastern U.S. rely primarily on cool-season forages that peak in biomass production in late spring, leading to a lack of forage in the summer months and increasing the costs of cattle production. Seeding pastures with a mix of native warm-season grasses and native wildflowers could increase forage availability while also increasing available resources for bees. In this study, a mix of three native warm-season grasses (NWSGs) and 15 wildflower species was planted at the Virginia Tech Shenandoah Valley Agricultural Research and Extension Center (SVAREC). The objectives of this project were to document the establishment and species composition of NWSG + wildflower pasture mixtures, compare the attractiveness of wildflowers and weedy species to bees, and compare the bee community between NWSG + wildflower pastures and more typical cool-season grass pastures. The wildflowers in the NWSG + wildflower pastures dominated over grasses. All wildflower species that established were attractive to bees, as were some weedy species. The NWSG + wildflower treatments had the highest abundance of bees collected, with an average of 14.8 bees collected per pasture per sampling date in 2018, and an average of 12.4 bees collected per pasture per sampling date in 2019. These results indicate that with modification of establishment methods so that more grasses are present, this pasture system could be beneficial from both a cattle production and bee conservation standpoint.Master of Science in Life Sciences
Over the past several decades, there has been a decline in bee populations in the U.S. and around the world. Bees play an important role in pollinating many food crops, including most fruits and vegetables. Habitat loss is the biggest contributor to their decline. There are also issues with cattle production in the eastern U.S. Most farmers rely on grasses that are the most productive in the late spring and early summer, meaning that by mid- and late summer, there is little grass available for cattle. Planting pastures with native grasses designed to be the most productive in the late summer and native wildflowers could increase food available for cattle as well as provide more pollen and nectar for bees. In this experiment, we planted a mix of three grasses and 15 wildflowers. We documented how well the grasses and wildflowers established. We also examined how attractive wildflowers and weeds were to bees and compared the number and types of bees collected between the new pastures and traditional pastures. We found that the wildflowers, instead of the grasses, dominated the pastures. All wildflowers that established, as well as some weeds, attracted bees and provided resources. Higher numbers of bees were collected in the pastures with wildflowers than standard grass pastures, but there were not necessarily more bee species present. These results suggest that, with some modifications, planting native grasses and wildflowers in pastures could help conserve bees as well as benefit cattle farmers.
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Kaidatzis, Andreas. "Transport dépendant du spin d'électrons chauds et imagerie magnétique à l'échelle nanométrique de structures métal/silicium." Phd thesis, Université Paris Sud - Paris XI, 2008. http://tel.archives-ouvertes.fr/tel-00354769.
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Nous étudions expérimentalement le transport dépendant du spin d'électrons chauds dans des multicouches (MC) magnétiques, qui contiennent des couches uniques magnétiques, ou des tricouches de type "vannes de spin" (VS). Pour cela, nous avons mis en oeuvre la microscopie à émission d'électrons balistiques (BEEM), une extension à trois contacts de la microscopie à effet tunnel sur des structures métal/semiconducteur. La méthode mise au point pour satisfaire les nombreuses contraintes imposées par le BEEM sur les échantillons est décrite en détail. La transmission des électrons chauds dans des MC a été systématiquement mesurée dans la gamme d'énergie 1-2 eV au dessus du niveau de Fermi. De l'étude en fonction des épaisseurs des couches magnétiques nous avons déduit les longueurs d'atténuation des électrons chauds en fonction du spin et de l'énergie. Ces mesures, sur le cobalt et l'alliage doux NiFe, sont comparées à des calculs et résultats expérimentaux de la littérature. Pour des épaisseurs inférieures à la monocouche atomique, une organisation spatialement hétérogene a été observée, avec un effet très important sur la transmission BEEM, variant sur une échelle subnanométrique. En mode imagerie, nous avons étudié les configurations magnétiques de VS, en particulier des parois à 360° dans des couches de cobalt. Les effets de l'intensité et la direction du champ appliqué sur la structure de ces parois ont été observés. Ces résultats ont été comparés quantitativement à des calculs micromagnétiques, avec un accord excellent. Ceci a permis de montrer que la résolution magnétique du BEEM est meilleure que 50 nm.
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Squire, Ursula A. "BEE CAUSE: Is Legislative Action Protecting Bees from Neonicotinoids Justified?" PDXScholar, 2016. http://pdxscholar.library.pdx.edu/open_access_etds/2988.
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The potential harm caused to bees and other pollinators by the widespread use of neonicotinoids has the capacity to pose a real and immediate threat to both the environment and humans. The benefits that bees and other pollinators provide, combined with the potential of harm they may face, are important enough to warrant a more comprehensive testing apparatus by which to evaluate threats to their population. Environmentally, bees and other pollinators are an important piece of ecosystemic balance--from pest management to pollination of plants that are a part of many species' diet. Anthropologically speaking, the way of life humans have been accustomed to and even need in order to survive is also largely dependent on a healthy population of bees and other pollinators; up to 70% of plants and vegetables we eat are directly a result of pollinators, and one third of every mouthful humans consume is attributed to pollinators. Without a healthy population of pollinators, the agricultural variety and nutritional availability would drastically decrease. Moreover, these agricultural products pollinators are responsible for also affect billions of dollars on both a national and global level. In many ways, the economic stability of the United States is at an equal risk as the pollinators. For example, an inability to produce many of our own agricultural staples would leave local and regional livelihoods disrupted and change the United States' import/export position. Moreover, this is not just a national problem. Pollinators are responsible for over 150 billion dollars globally in agriculture. Many of the nutrients humans need to be healthy would be in short supply.
While scientists continue to study the possible effects of neonicotinoids on pollinators, how should policy makers respond? In this thesis, I argue that the various and drastic ways in which pollinators impact our environment and every day life, combined with the potential of the harsh threats their collapse would entail, warrant a more stringent approach to the evaluation of potential harms like neonicotinoids. An ethical risk assessment, as I define one, would be an appropriate tool to apply to this situation to guide policy makers in drafting regulations even in the absence of scientific certainty. Ethical risk assessments are a tool by which to evaluate the moral and ethical responsibilities in a whole host of different scenarios, one of which is neonics and pollinators. In other words, this ethical risk assessment will be used as an instrument by which to determine whether or not there is a sufficient risk to the population of pollinators, thus determining whether regulation is appropriate. Through application of this risk assessment, I will show that in this particular case regulation is appropriate due to the risks neonics pose to pollinators in light of the evidence that we do have.
I develop a set of criteria for an ethical risk assessment. The criteria are a result of a combination of existing literature and some novel connections I draw here. This list, I argue, is what constitutes an ethical risk assessment. Ethical risk assessment, grounded in Utility Theory, is appropriate here because of its calculative apparatus and sociopolitical applicability.
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Wenczel, Rita. "Untersuchungen zur Messung der Körperzusammensetzung und Knochenmineraldichte beim Schwein und beim Schaf mittels "Pencil-" und "Fan-Beam"-Dualenergie Röntgenabsorptiometrie." Diss., Ludwig-Maximilians-Universität München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-162738.
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Ziel dieser Arbeit war es die Beziehung zwischen den Messergebnissen der Geräte Lunar DPX-IQ und Lunar iDXA der Firma General Electrics zu überprüfen. Um die Vergleichbarkeit bei "in vivo" Messungen zu gewährleisten, wurden 218 lebende Schweine, 21 Eberschlachtkörperhälften und 20 lebende Schafe sowie 17 Schaf-Schlachtkörper jeweils mit beiden Geräten gescannt. Die Genauigkeit und die Präzision des iDXA wurde mit einem “Variable Composition Phantom” in Kombination mit einer “Aluminium-Wirbelsäule” getestet. Diese Ergebnisse wurden mit denen aus der Dissertation von [ruge2006a] verglichen, da die Autorin bereits mit dem selben Phantom die Genauigkeit des DPX-IQ überprüfte. Zusätzlich wurde mit Hilfe der verschiedenen Versuchstierarten die Beziehung zwischen den Messergebnissen der iDXA-Modi “Dick” und “Standard” untersucht.
Bedingt durch die unterschiedliche Anatomie der Schweine im Vergleich zu kleinen Wiederkäuern wurden die Ergebnisse getrennt analysiert. Bei den Schweinen erreichen die Geräte die engste Beziehung für das errechnete Gesamtgewebe (R²=0,99) gefolgt vom Magerweichgewebe (R² = 0,93) und Fettgewebe (R² = 0,82-0,90). Die Messergebnisse des Knochenmineralgehaltes und der Knochenmineraldichte zeigen mit R² = 0,75 - 0,85 und R² = 0,67 - 0,69 die vergleichsweise niedrigsten Bestimmtheitsmaße. Bei der Untersuchung der unterschiedlichen Gewichtsklassen entfernen sich die Messergebnisse in den höheren Gewichtsbereichen (> 100 kg) deutlich weiter von der Identitätslinie. Somit ist die Übereinstimmung zwischen den Messergebnissen beider Geräte bei Tieren > 100 kg am niedrigsten.
Die Untersuchung der Schafe bringt ähnliche Resultate, wobei vermutet wird, dass wegen des Pansens und dessen Inhalts die Geräte für das Fettgewebe verminderte Übereinstimmungen zwischen den Messergebnissen zeigen (R² = 0,65 - 0,66). Die engste Beziehung weisen die Geräte erneut bei der Bestimmung des Gesamtgewebes (R² = 0,99) und des Magerweichgewebes (R² = 0,93 - 0,94) auf. Die Beziehungen der Messergebnisse des Knochenmineralgehaltes und der Knochenmineraldichte (R² = 0,88 und R² = 0,59 - 0,68) sind wie bei den Schweinen vergleichsweise am niedrigsten.
Die Ergebnisse der Schaf-Schlachtkörper zeigen engere Übereinstimmungen als die der lebenden Schafe, da das Eingeweide inklusive Magen-Darm-Trakt entfernt wurde. Die höchsten Bestimmtheitsmaße erreichen die Geräte wiederholt bei der Messung des Gesamtgewebes (R² = 0,96 - 0,97) und des Magerweichgewebes (R² = 0,89 - 0,93). Diesen folgt die Analyse des Fettgewebes mit R² = 0,75 - 0,91. Knochenmineralgehalt und Knochenmineraldichte liegen bei den Messungen der Schaf-Schlachtkörper enger beieinander. Die Geräte erreichen diesbezüglich Bestimmtheitsmaße von R² = 0,82 - 0,84 und R² = 0,68 - 0,81.
Bei der Überprüfung der Genauigkeit und der Präzision des iDXA und dem Vergleich der Daten mit den Messergebnissen von [ruge2006a] wurden mit dem iDXA insgesamt die genaueren und präziseren Werte erreicht als mit dem DPX-IQ.
Anhand der Ergebnisse dieser Dissertation kann der Lunar iDXA der Firma General Electrics empfohlen werden. Allerdings müssen bei geräteübergreifenden Studien Regressionsgleichungen für die Anpassung der Messergebnisse verwendet werden. Da sich die absoluten Messwerte modi-abhängig unterscheiden, sind für jedes Tiermodell und jeden Modus eigene Regressionsgleichungen zu verwenden. Die Gleichungen aus dieser Arbeit können für Studien des Lehr- und Versuchsgutes mit dem Lunar DPX-IQ und dem Lunar iDXA herangezogen werden. Bei Langzeitstudien wird allerdings zum Einsatz nur eines DXA-Gerätes geraten.
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Larsson, Magnus. "To Bee or Not to Be : Critical Floral Resources of Wild-Bees." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Universitetsbiblioteket [distributör], 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7108.
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Cai, Wei. "Ballistic Electron Emission Microscopy and Internal Photoemission Study on Metal Bi-layer/Oxide/Si, High-k Oxide/Si, and “End-on” Metal Contacts to Vertical Si Nanowires." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1269521615.
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Marrè, Badalló Roser. "Implementation and Testing of Two Bee-Based Algorithms in Finite Element Model Updating." Thesis, KTH, Bro- och stålbyggnad, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-140846.
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Finite Element Model Updating has recently arisen as an issue of vast importance on the design, construction and maintenance of structures in civil engineering. Many algorithms have been proposed, developed and enhanced in order to accomplish the demands of the updating process, mainly to achieve computationally efficient programs and greater results.The present Master Thesis proposes two new algorithms to be used in Finite Element Model Updating: the Bees Algorithms (BA) and the Artificial Bee Colony algorithm (ABC). Both were first proposed in 2005, are based on the foraging behaviour of bees and have been proved to be efficient algorithms in other fields. The objective of this Master Thesis is, thus, to implement and to test these two newalgorithms in Finite Element Model Updating for a cantilever beam. The Finite Element Model and the algorithms are programmed, followed by the extraction of the experimental frequencies and the updating process. Results, comparison of these two methods and conclusions are given at the end of this report, as well as suggestions for further work.
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Crous, Kendall Lauren. "Brood cycles in queenless colonies of Apis mellifera capensis." Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1005335.
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In a honeybee colony, the loss of a queen is considered to be a serious occurrence and, if a new queen is not produced, ultimately doomed. However, in colonies of Apis mellifera capensis (Cape honeybees), numerous pathways are available for a colony which unexpectedly losses a queen. At the onset of this experiment, four colonies of A. m. capensis were dequeened. Following this photographs of all brood frames in each colony were taken and the contents of the cells analysed. Cells were chosen at random but once selected were repeatedly analysed for the duration of the experiment. The contents of a total of 44 888 individual cells were analysed. Any queen cells constructed during the sampling period were removed, maintaining a queenless state. In each colony, as predicted, the removal of the queen evoked a variety of responses in an attempt to rectify the sudden loss. However, ultimately three of the four colonies absconded, leaving little by way of stores. Three of the four colonies initially attempted to rear a new queen while one colony was immediately invaded by a presumed foreign queen and hence any attempt at queen cell construction ceased. An increased number of queen cells in the swarm position were recorded in all colonies. The invasion of a colony by a foreign queen was considered to be a new pathway available for queenless colonies of A.m capensis. Worker policing and suspected brood cannibalism was prevalent in all sampled colonies yet in addition, the transfer of eggs and larvae from cell to cell was also observed which may have increased the suspected cases of policing and cannibalism. It was unclear whether an egg or larva had been consumed or simply moved to another cell on the brood frame. All colonies contained eggs from laying workers to varying degrees, based on the length of each individual sampling period which varied between colonies due to differences in absconding dates. A steady breakdown in the effectiveness of the division of labour amongst the worker bees was observed in each of the colonies highlighting the vital role of a queen. This breakdown was clearly seen in the reduction in general housekeeping within a colony. An increase in stores indicated a possible increase in the number of forager bees, thereby reducing the number of worker bees available for other duties. Pathways available to broodright colonies and strategies used following sudden queen loss are discussed.
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Macpherson, Erin. "An examination of the competitiveness of the methods by which beer has been distributed in the UK focusing on the beer tie agreement." Thesis, University of Glasgow, 2015. http://theses.gla.ac.uk/6678/.
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The thesis seeks to examine the competitiveness of the methods by which beer has been distributed in the UK, particularly the beer tying agreement, with the objective of setting out recommendations for the future. In order to fulfil this objective, the thesis aims firstly to engage in a scholarly exercise of clarifying the role and purpose of the beer tie; the application of the EU competition law provisions to the brewing industry; and the UK Government’s approach to regulating it. Secondly, the thesis engages in comparative research and will consider how other non-UK markets have dealt with the distribution of beer, and more specifically the issue of the beer tie. In doing so, the thesis seeks to ascertain how competitive the UK market is in the context of these other geographical markets. The thesis will also compare the UK beer market with another UK market in which the use of tying agreements is prevalent in order to ascertain whether the same issues have been faced in this market as in the beer market. The intention of the comparative research in the thesis is to provide assistance to legal policy makers on the future regulation of beer distribution in the UK. The thesis does not however undertake to propose measures to achieve a state of perfect competition. Rather, it undertakes, as the third aim of the thesis, to propose informed recommendations that address better the ongoing anti-competitive concerns associated with the operation of the beer tie today and ensure a socially acceptable level of workable competition.
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Paini, Dean. "The impact of the European honey bee (Apis mellifera) on Australian native bees." University of Western Australia. School of Animal Biology, 2004. http://theses.library.uwa.edu.au/adt-WU2004.0022.
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The European honey bee (Apis mellifera) has been present in Australia for approximately 150 years. For the majority of that time it was assumed this species could only be of benefit to Australia‘s natural ecosystems. More recently however, researchers and conservationists have questioned this assumption. Honey bees are an introduced species and may be affecting native fauna and flora. In particular, native bees have been highlighted as an animal that may be experiencing competition from honey bees as they are of similar sizes and both species require nectar and pollen for their progeny. Most research to date has focused on indirect measures of competition between honey bees and native bees (resource overlap, visitation rates and resource harvesting). The first chapter of this thesis reviews previous research explaining that many experiments lack significant replication and indirect measures of competition cannot evaluate the impact of honey bees on native bee fecundity or survival. Chapters two and four present descriptions of nesting biology of the two native bee species studied (Hylaeus alcyoneus and an undescribed Megachile sp.). Data collected focused on native bee fecundity and included nesting season, progeny mass, number of progeny per nest, sex ratio and parasitoids. This information provided a picture of the nesting biology of these two species and assisted in determining the design of an appropriate experiment. Chapters three and five present the results of two experiments investigating the impact of honey bees on these two species of native bees in the Northern Beekeepers Nature Reserve in Western Australia. Both experiments focused on the fecundity of these native bee species in response to honey bees and also had more replication than any other previous experiment in Australia of similar design. The first experiment (Chapter three), over two seasons, investigated the impact of commercial honey bees on Hylaeus alcyoneus, a native solitary bee. The experiment was monitored every 3-4 weeks (measurement interval). However, beekeepers did not agist hives on sites simultaneously so measurement intervals were initially treated separately using ANOVA. Results showed no impact of honey bees at any measurement interval and in some cases, poor power. Data from both seasons was combined in a Wilcoxon‘s sign test and showed that honey bees had a negative impact on the number of nests completed by H. alcyoneus. The second experiment (Chapter 5) investigated the impact of feral honey bees on an undescribed Megachile species. Hive honey bees were used to simulate feral levels of honey bees in a BACI (Before/After, Control/Impact) design experiment. There was no impact detected on any fecundity variables. The sensitivity of the experiment was calculated and in three fecundity variables (male and female progeny mass and the number of progeny per nest) the experiment was sensitive enough to detect 15-30% difference between control and impact sites. The final chapter (Chapter six) makes a number of research and management recommendations in light of the research findings.
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Tiwari, Astha. "A Deep Learning Approach to Recognizing Bees in Video Analysis of Bee Traffic." DigitalCommons@USU, 2018. https://digitalcommons.usu.edu/etd/7076.
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Colony Collapse Disorder (CCD) has been a major threat to bee colonies around the world which affects vital human food crop pollination. The decline in bee population can have tragic consequences, for humans as well as the bees and the ecosystem. Bee health has been a cause of urgent concern for farmers and scientists around the world for at least a decade but a specific cause for the phenomenon has yet to be conclusively identified.
This work uses Artificial Intelligence and Computer Vision approaches to develop and analyze techniques to help in continuous monitoring of bee traffic which will further help in monitoring forager traffic. Bee traffic is the number of bees moving in a given area in front of the hive over a given period of time. And, forager traffic is the number of bees entering and/or exiting the hive over a given period of time. Forager traffic is an important variable to monitor food availability, food demand, colony age structure, impact of pesticides, etc. on bee hives. This will lead to improved remote monitoring and general hive status and improved real time detection of the impact of pests, diseases, pesticide exposure and other hive management problems.
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Beer, Ragnar. "Merkmale von Partnerschaftszielen als Veränderungs-Mediatoren in der verhaltenstherapeutischen Kurzzeit-Paartherapie." [S.l. : s.n.], 2001. http://webdoc.sub.gwdg.de/diss/2001/beer/beer.pdf.
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Wenczel, Rita [Verfasser], and Armin [Akademischer Betreuer] Scholz. "Untersuchungen zur Messung der Körperzusammensetzung und Knochenmineraldichte beim Schwein und beim Schaf mittels "Pencil-" und "Fan-Beam"-Dualenergie Röntgenabsorptiometrie / Rita Wenczel. Betreuer: Armin Scholz." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2013. http://d-nb.info/1045152889/34.
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Baušienė, Inga. "Bičių kūno masės priklausomybė nuo korio." Master's thesis, Lithuanian Academic Libraries Network (LABT), 2007. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2007~D_20070419_165731-23870.
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Bees interested people because of honey and wax from ancient times. They were called God’s beetles, God’s workers. Bee products were used for food and medicine. It is advisable for people to eat about 1,8 kg of honey a year. Lately bee farms have been growing stronger. The owners of some apiaries are increasing and modernizing their farms. At the moment 83 thousand families are bred in Lithuania. AIM OF RESEARCH. To establish the dependence of bee mass on the springs of comb, comparing the used discs of the springs of the bee family natural wax combs an artificial combs. METHODS AND CONDITIONS OF RESEARCH. The data for research were collected during the summer of 2006 from bee families bred in Kaunas. In individual variants hives were expanded by discs of springs of natural wax comb and plastic discs of springs of combs. After 8 days after making of cells they were put into well warmed hives or a thermostat for breeding. After 24-36 hours after breeding of bees they were weighed. This experiment will negate the widely spread groundless statements that plastic combs influence the mass of bees. Apirians may safely use plastic wax discs for making combs for bee families. CONCLUSIONS: 1. Artificial discs are more accurate that natural wax discs in all directions of the cells of the comb. 2. Wax discs and artificial comb discs do not influence the mass of bees, as bees bred on such discs during the research showed no significant differences.
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Palubinskytė, Sigita. "Bičių (Apis mellifera) kolonijų produkcinių ir reprodukcinių savybių tyrimas." Bachelor's thesis, Lithuanian Academic Libraries Network (LABT), 2012. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2012~D_20120831_091258-33661.
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Darbo tikslas – ištirti bičių kolonijų produkcines ir reprodukcines savybes, laikant įvairaus dydţio aviliuose. Siekiant šio tikslo bus iškelti sekantys uţdaviniai: 1. Įtakoti bičių kolonijų pavasarinio apsiskraidymo laiką; 2. Įvertinti bičių svorį po pavasarinio apsiskraidymo; 3. Nustatyti avilio tipo įtaką bičių šeimų ţiemojimui bei jų fiziologinei būklei; 4. Nustatyti traninių perų pasirodymo laiką bičių kolonijoje; 5. Nustatyti Varroa destructor erkių įtaką tranų lervučių masei; 6. Nustatyti avilio talpumo įtaką motinių lopšelių skaičiui bei bičių produkcijai. Buvo stebimas bičių kolonijų pavasarinis apsiskraidymas, sveriamos bitės po pavasarinio apsiskraidymo, stebimas aptūptų bitėmis korių skaičius 2010–2011 metais. Apţiūrimi pirmieji traniniai perai bičių kolonijoje, sveriant tranų lervas nustatinėjama erkių Varroa destructor įtaka jų masei, įvertinama bičių kolonijų fiziologinė būklė. Taip pat registruojami motininiai lopšeliai bičių šeimose ir medaus kopimo metu atliekama išsukto medaus apskaita.
Bičių apsiskraidymas vyko dviem etapais, pirmą kartą apsiskraidė 4 bičių šeimos, o antra likusios 12 šeimų. Ištyrus bičių svorį po pavasarinio apsiskraidymo paaiškėjo, kad iš 60 % tirtų bičių svoris yra 0,11 g, o likusių bičių svoris maţesnis. Nustatant avilio įtaką bičių šeimų ţiemojimui 2010–2011 metais, buvo nustatyta, kad 27 korių aviliuose bičių šeimos yra stipriausios. Apţiūrint bičių kolonijas, iš 16 bičių šeimų, 4 šeimos buvo su pirmaisiais traniniais perais... [toliau žr. visą tekstą]The aim – to investigate bee colony productive and reproductive characteristics. To achieve this objective will be to raise the following goals: 1. Influence first fly colonies in spring time; 2. To evaluate the weight of the bees in the spring after first fly; 3. Identify type of impact on the hive of bees and their families in winter physiological condition; 4. Set the time of the appearance of peers traninių bee colony; 5. Determine the impact of Varroa destructor mites in drone larvae masses; 6. Set the capacity of the hive mother influence the number of nursery and bee products. Colonies were observed in spring first flight, weighed after spring first flight bees, bees, combs sits observed number 2010–2011 years. Also examined the first drones peers bee colony, weighing the drone larvae of identical mite Varroa destructor influence their weight, assess the physiological state of bee colonies. The nursery also recorded maternal families of honey bees climbing in done unfolded honey accounting. First flight bees gone through two phases, the first flight four colonies, and the second the remaining 12 families. Examination of the weight of the bee first fly spring showed that 60% of tested bees weighing 0.1138 g and the weight of the remaining bees. In determining the impact of the hive bee families influence winter 2010–2011, has been found that 27 hives of bees honeycomb is the strongest of the family. Survey of bee colonies in 16 hives, four families were the first drone... [to full text]
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Yang, Ming-Xian. "Studies on mixed-species colonies of honeybees, Apis cerana and Apis mellifera." Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1005467.
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The honeybees Apis cerana and Apis mellifera are derived from the same ancestral base about two million years ago. With speciation and evolution, they have acquired many advanced living skills in common, but have also evolved very different living strategies due to different distributions. This thesis is an intensive study of the biology of the mixed-species colonies of these species, the aims of which were to investigate their behavioural relationships and uncover the evolutionary conserved features of their behaviours subsequent to speciation. The results show that the two species can form a stable society to perform normal tasks. First, workers of both species in the mixed-colonies could form the typical retinue behaviour to hetero-species queens, thus indicating that queen pheromones could be spread to and by both species. Secondly, both species did not show significantly different ovarian activation under hetero-species queens, suggesting that the queen pheromones more likely play a role of "honest signal" rather than a "repression" substance in the honeybee colonies. Thirdly, both species could mutually decode each other‘s waggle dances, with unexpectedly low misunderstanding; revealing that the dance language in a dark environment is quite adaptive for cavity-nesting honeybees. Fourthly, workers of both species could cooperate with each other in comb construction, although the combs they built contain many irregular cells. Interestingly, A. cerana workers could be stimulated by A. mellifera workers to perform this task, thus confirming self-organization theory in the colony. Fifthly, A. mellifera workers behaved more "defectively" in thermoregulation, but perhaps because A. cerana workers are more sensitive to changes in hive temperature. Given these differences in strategy, A. mellifera workers‘ performance might in fact reduce conflicts. Lastly, when faced with threats of predatory wasps, both species engaged in aggressive defence. Although they did not learn from each other‘s responses, species-specific strategies were adopted by each of them so that the defence of the mixed-colonies is very effective. I conclude that the two species can adapt to each other‘s efforts and task allocation is reasonably organized allowing mixed-species colonies to reach stability. These results suggest that all of the social behaviours discussed here were highly conserved following speciation. This thesis could provide some clues for the study of honeybee evolution from open-nesting to the transition of cavity-nesting.
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Krupinski, Tabea [Verfasser], and Meinrad [Akademischer Betreuer] Beer. "Nachweis von morphologischen Veränderungen beim Nierenscreening von Frühgeborenen und deren klinische Relevanz / Tabea Krupinski. Betreuer: Meinrad Beer." Würzburg : Universitätsbibliothek der Universität Würzburg, 2012. http://d-nb.info/1028490410/34.
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Foy, Andrew Scott. "A GIS-Based Landscape Scale Model for Native Bee Habitat." Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/35169.
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Through pollination, bees are responsible for the persistence of many biological systems on our planet. Bees have also been used for thousands of years in agriculture to improve crop quality and yield. Recently, there have been declines in honeybees worldwide. This decline is concerning because it threatens food supplies and global biodiversity. An alternative to alleviating the effect of a honey bee shortage could be to use native bees. Problems with adoption of native bees in agriculture occur because of a lack of large scale analysis methods for native bees, regional species lists and management knowledge.
This research explores the use of GIS in modeling native bee habitat to provide a landscape scale analysis method for native bees and develop a systematic sampling method for regional species list development. Raster GIS modeling, incorporating decision support and Poisson statistical methods were used to develop a native bee habitat model. The results show landscape composition is important to bee abundance and diversity. In addition, habitat fragmentation may not be as detrimental to bees as previously thought. Bees are most sensitive to landscape composition at a scale of 250 m, but require large patches of floral resources. GIS proved to be very useful in modeling bee habitat and provides an opportunity to conduct landscape scale bee population analysis.Master of Science
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Haas, Stephanie. "The Mite-y Bee: Factors Affecting the Mite Community of Bumble Bees (Bombus spp., Hymenoptera: Apidae)." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/35759.
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Parasites and other associates can play an important role in shaping the communities of their hosts; and their hosts, in turn, shape the community of host-associated organisms. This makes the study of associates vital to understanding the communities of their hosts. Mites associated with bees have a range of lifestyles on their hosts, acting as anything from parasitic disease vectors to harmless scavengers to mutualistic hive cleaners. For instance, in Apis mellifera (the European honey bee) the parasitic mite Varroa destructor has had a dramatic impact as one of the causes of colony-collapse disorder. However, little is known about mites associated with bees outside the genus Apis or about factors influencing the makeup of bee-associated mite communities. In this thesis, I explore the mite community of bees of the genus Bombus and how it is shaped by extrinsic and intrinsic aspects of the bees' environment at the individual bee, bee species, and bee community levels. Bombus were collected from 15 sites in the Ottawa area along a land-use gradient and examined for mites. The number of individual mites and number of mite species hosted by particular bee species increased significantly with bee species abundance. In addition, several bee species differed in terms of mite abundance, mite species richness, mite prevalence, and mite diversity at the level of individual bees and at the species level. In particular, individuals of rare bee species tended to have particularly high mite abundance in comparison to other bees. However, geography, site quality, and bee diversity were never significant predictors of mite community attributes at any level of analysis. Overall, the best predictor of bee-mite community attributes is the bee species themselves. Thus, these mite communities were not shaped by the factors that are known to shape the parasite communities of other species (i.e., geographic distance, host diversity), perhaps because of the commensalistic nature of most of the mite species investigated here. These findings have implications for conservation of bumble bees, given that commensals may become cleptoparasitic at high densities and may act as disease vectors.
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Bask, Tanmay. "A Model For Heat Transfer In A Honey Bee Swarm." Thesis, Indian Institute of Science, 1994. http://hdl.handle.net/2005/131.
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During spring, it has been observed that several thousand bees leave their hive, and settle on some object such as a tree branch. Some of the scout bees search for a suitable place where a new hive can be set up, while the rest collect together to form a swarm.
Heinrich (J. of Exp. Biology 91 (1981) 25; Science 212 (1981) 565; Scientific American 244:6 (1981) 147) has done some experiments with free and captive swarms. His observations are as follows.
(1)The core (centre) temperature is around 35°C irrespective of the ambient
temperature.
(2)The mantle (outer surface) temperature exceeds the ambient temperature by 2- 3°C, provided the ambient temperature is greater than 20°C. Otherwise the mantle temperature is maintained around 17°C.
(3) The temperature gradient vanishes just before take-off of the swarm.
The present work attempts to predict temperature profiles in swarms and compare them with the data of Heinrich. A continuum model involving unsteady heat conduction and heat generation within the swarm is used. Heat loss from the outer surface of the swarm by free convection and radiation is accounted for approximately. To simplify the analysis, internal convection within the swarm is neglected. The energy balance equation is solved using the finite element method.
The effective thermal conductivity (k) is determined by comparing model predictions with data for a swarm of dead bees. The estimated value of k is 0.20 W/m-K. Both spherical and a non-spherical axisymmetric shapes are considered.
Considering axisymmetric swarms of live bees, temperature profiles are obtained using various heat generation functions which are available in literature. The effective thermal conductivity is assumed to be the same as that for the swarm of dead bees. Results based on a modified version of Southwick's heat generation function (The Behavior and Physiology of Bees, pp. 28-47, 1991) are qualitatively in accord with the data. The predicted maximum temperature within the swarm and the temperature at the lower surface of the swarm at the ambient temperature of 5°C are 34°C and 17-20°C, respectively. These are comparable to the measured values of 36°C and 19°C. The predicted maximum temperature within the swarm and the temperature at the lower surface of the swarm at the ambient temperature of 9°C are 36.5°C and 17-22°C, respectively. These are comparable to the measured values of 35°C and 19°C. The predicted oxygen consumption rates are 2.55 ml/g/hr for a swarm of 5284 bees at an ambient temperature Ta = 5°C and 1.15 ml/g/hr for 16,600 bees at Ta = 9°C. These are of the same order as the measured values (2 ml/g/hr for 5284 bees at Ta = 4.4DC and 0.45-0.55 ml/g/hr for 5284 bees at Ta = 10°C).
Omholt and Lanvik (J. of Theoretical Biology, 120 (1986) 447) assumed a non-uniform steady state profile and used it to estimate the heat generation function. Using this function in the transient energy balance, it is found that their steady state profile is unstable.
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Pérez, Brenda Rubi Bautista. "Eficiência de três métodos : alternativo, biológico e químico, no controle do ácaro Varroa destructor Anderson e Trueman (2000) em Apis mellifera Linnaeus (1758)." Universidade Federal de São Carlos, 2016. https://repositorio.ufscar.br/handle/ufscar/8011.
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Consejo Nacional de Ciencia y Tecnología (CONACYT)
Bees are the most important pollinators of agricultural ecosystems by carrying out pollination of up to 90% of native plants and more than one third of cultivated plants. Studies conducted around the world have been demonstrating a phenomenon called CCD (Colony Collapse Disorder), whose causal agent several factors including diseases that affect this group. Among them, the varroa resulting from the Varroa destructor mite attack, is reported as pathogen major impact factor on the Apis mellifera. In view of this, the objective of this study was to test the efficiency of three methods to control V. destructor: alternative, obtained from the distillation of oregano (Origanum vulgare Linnaeus, 1753), thyme (Thymus vulgaris Linnaeus, 1753) and sugar beet (Beta vulgaris Linnaeus, 1753); biological, run base drones and larvae chemical, carried out with the application of active flumethrin principle. The results were evaluated by statistical analysis in R program to determine the differences between treatments and proposed mergers and select the best method of control. In the analysis, it was observed that the alternative method showed a significant difference by highlighting thyme distillation as more efficient because there is no significant killing of bees and cause the death of all the mites in a shorter time compared to the other distillates. The biological method hornets larvae base is also preferably effective due to mite in these individuals. In chemical control the use of the active ingredient flumethrin caused poisoning in bees, with diarrhea in the first 6 hours after application, and after 48 hours caused a mortality of 100%, which demonstrates be impractical to control the mite.
As abelhas são os agentes polinizadores mais importantes dos agroecossistemas por realizarem a polinização de até 90% das plantas nativas e de mais de 1/3 das plantas cultivadas. Estudos desenvolvidos ao redor do mundo vêm demostrando um fenômeno chamado CCD (Colony Collapse Disorder), que tem como agente causal vários fatores incluindo as doenças que afetam este grupo. Dentre elas, a varroose, resultante do ataque do ácaro Varroa destructor, é o patógeno relatado como fator de grande impacto sobre a espécie Apis mellifera. Diante disto, o objetivo deste trabalho foi testar a eficiência de três métodos para o controle de V. destructor: o alternativo, obtido a partir da destilação de orégano (Origanum vulgare Lineus, 1753), tomilho (Thymus vulgaris Lineus, 1753) e beterraba (Beta vulgaris Lineus, 1753); o biológico, executado a base de larvas de zangões e o químico, realizado com a aplicação do princípio ativo flumetrina. Os resultados foram avaliados por meio de análise estatística no programa R para determinar as diferenças entre os tratamentos e as concentrações propostas e selecionar o melhor método para controle. Nas análises, foi observado que o método alternativo apresentou diferença significativa, destacando as destilações de tomilho como mais eficientes por não haver morte significativa das abelhas, além de causar a morte de todos os ácaros em menor tempo comparado, aos outros destilados. O método biológico a base de larvas de zangões também é eficiente devido a preferência do ácaro por estes indivíduos. No controle químico o uso do ingrediente ativo flumetrina, causou intoxicação nas abelhas, com diarreia nas primeiras 6 horas após aplicação, e depois de 48 horas causou uma mortalidade de 100%, o que demostra ser inviável para o controle do ácaro.
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Hollinghurst, Joe. "Enabling software defined networking in high criticality networks." Thesis, University of Bristol, 2018. http://hdl.handle.net/1983/8ac68df0-62ba-4cf8-beee-b69ee807f43e.
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High-criticality networking solutions are often dedicated, highly specialised, even bespoke in case of hard real-time guarantees. This is required to ensure (quasi) deterministic behaviour of the network services as seen by critical applications. However, dedicated networks incur significant expense, along with the inability to update the system efficiently and effectively. Software-Defined Networking (SDN) uses controllers to allow dynamic, user-controlled, on-demand configuration of the network. This provokes interesting questions on the applicability of SDN concepts and architectures in high-criticality networks. Although SDN offers flexibility and programmability to the network infrastructure through the introduction of a controller, the controller introduces extra delay into the system. This is due to new flows querying the controller for instructions of how to route traffic. This becomes an increasing problem for large scale and delay sensitive networks such as those found in high-criticality infrastructure. The delay introduced can be minimised by optimal placement of the controller or decreased further by introducing additional controllers. Although the problem of optimal placement for multiple controllers is known to be NP hard, approximations can be used. The analysis of three different methods has been conducted and investigates the scalability, and how the accuracy of the methods varies with the complexity. In the latter stage of the thesis the use of redundancy and coding is analysed with the aim to reduce latency and increase reliability within the network. The objective is to provide an analysis of the gains achievable through the use of redundant messages and coding. Both redundancy and coding increase the network load and hence the delay of each packet, but can reduce overall delay by exploiting independent randomness across multiple paths. Both the average delay minimisation and probabilistic guarantees on delay exceeding some tolerance threshold are considered.
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Mertz, Jeffrey Barclay. "A visionary among the radicals : William Blake and the circle of Joseph Johnson, 1790-95." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:c1816fad-c35f-4587-bee6-0c4c67d96a36.
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Blake’s critics have never attempted to illustrate in a systematic manner how Blake used information he learned from writings published by members of the circle of Joseph Johnson in his own works during the period 1790-95. Although Blake was a peripheral figure in the Johnson circle – known to them through his profession of engraving and marginalized on account of his social position and lack of university education – his works reveal a continuing engagement with topics addressed in the writings of authors associated with Johnson, perhaps signifying Blake’s desire to be recognized as an author participating, like them, in the literary deliberations of the public sphere. Chapter 1, ‘Blake, Priestley and Swedenborg’, examines Blake’s treatment in The Marriage of Heaven and Hell of body and soul, the natures of God and Jesus Christ, and Swedenborgianism in relation to Joseph Priestley’s History of the Corruptions of Christianity (1782) and Letters to the Members of The New Jerusalem Church (1791). Chapter 2, ‘The Voice of a Devil and the Printing House in Hell’, considers The Marriage as an attempt to join the Revolution controversy and compares this work with writings by Richard Price, Mary Wollstonecraft and Thomas Paine. Chapter 2 also assesses the relationship between The Marriage and radical diabolism and Blake’s engagement with ‘energy’ as a distinctively radical concept in the work of Erasmus Darwin, Henry Fuseli, William Godwin, Priestley and Mary Wollstonecraft. Chapter 3, ‘Topical Representations in The French Revolution’, considers Blake’s engagement with Edmund Burke’s Reflections on the Revolution in France (1790) and the Bastille in relation to responses to Reflections by Wollstonecraft, Paine and other authors published by Johnson. Chapter 3 concludes with an analysis of the response The French Revolution might have elicited from the Analytical Review. Chapter 4, ‘The French Revolution and Three Contemporary Discourses’, approaches this poem in terms of the discourses of ancient liberty, nature and the sublime, once again in comparison with responses to Reflections by members of the Johnson circle. My discussion of the sublime considers the possible influence on The French Revolution of Burke’s Philosophical Enquiry into the Origin of our Ideas of the Sublime and Beautiful (1757) and Bishop Robert Lowth’s Lectures on the Sacred Poetry of the Hebrews (1787). Chapter 5, ‘The Continental Prophecies: Prophetic Form and Contemporary Prophecy’, examines America, Europe and The Song of Los in relation to writings concerning prophecy published by Johnson (with special emphasis on Lowth’s Lectures and Priestley’s 1793 and 1794 Fast Day sermons). The second part of Chapter 5 compares aspects of the works of Blake and Richard Brothers with Priestley’s Fast Day sermons, suggesting that Priestley and Blake’s works of 1793 and 1794 are rather less dissimilar than traditionally assumed. Chapter 6, ‘Blake’s “Bible of Hell” and Contemporary Critics of the Bible’, discusses Urizen, The Book of Ahania and The Book of Los in light of biblical criticism from the 1780s and 1790s (with particular reference to the Analytical and the writings of Alexander Geddes, Priestley and Paine). The final section of Chapter 6 reads Ahania in terms of the contemporary debate regarding the doctrine of the Atonement. The Conclusion, ‘ “melting apparent surfaces away”: Continuities in the Thought of Priestley and Blake’, revisits my discussion in Chapter 5 of similarities between Priestley and Blake and proposes that they are not so far apart in ideas and the content of their works as modern scholars usually argue.
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Gallagher, Alexis. "Evolvability : a formal approach." Thesis, University of Oxford, 2009. http://ora.ox.ac.uk/objects/uuid:d3b0511e-bee5-4778-8822-703c514c1c1d.
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This dissertation clarifies the concept of evolvability, the increased capacity of some organisms or systems to support evolution, especially the evolution of life-like complexity. I survey the literature, which is spread over the fields of population genetics, developmental biology, artificial life, and microbial and molecular evolution. Finding that researchers have often used the term vaguely and incompatibly I identify five distinct kinds or senses of evolvability. I also identify five key constituent ideas, which I discuss in the context of organismic evolvability, a sense of evolvability with deep roots in the traditional fields of animal development and macroevolution. In these fields research into evolvability has historically been hampered by an insufficiently detailed knowledge of development. Research in molecular evolution has produced a thorough knowledge of the folding of RNA into secondary structure, which can be regarded as a model of development. This has motivated new approaches to evolvability based on representing development via a single genotype-phenotype mapping function. I build on these approaches to invent new mathematical methods to formalise the traditional ideas. I create an exact model illustrating a classic example of evolvability, the capacity for repeated segmentation and simple modularity. I analyse this with two new formal approaches. First is the genospace algebra, a propositional calculus based on graph theory. It is a formal language for describing genotype-phenotype maps. It provides a system for making calculations, proofs, and diagrams about mutational structures in genotype space, and it is flexible enough to allow description at arbitrary degrees of resolution. Second is a pair of concepts, the genetic leverage and the genetic fulcrum. The leverage provides a crude numerical measure of evolvability, and the fulcrum provides a heuristic for identifying the genomic and developmental causes of evolvability. Besides its specific relevance to diversification and development, evolvability is also crucial to the fundamental question of how evolution produces ordinary biological life. Simulation systems that implement only a conventional textbook model of evolution -– systems possessing only variation, inheritance, and selection –- fail to evolve anything resembling the complexity of the biological world. Research into evolvability is our best bet to illuminate the "missing ingredient" for life-like evolution.
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van, Taack William. "Socioeconomic risk and the class-basis of reasoning during market transitions." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:bf708266-82bc-4dce-bee3-b8c6234a412f.
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This dissertation investigates the nature by which social class membership and identity figure in judgements of transition institutions for the citizens of post-communist Central and Eastern Europe. Using a unique dataset and a series of novel conceptual frameworks, it argues that social class is, in effect, an operationalisation of socioeconomic risk and vulnerability-a premise from which several important implications derive. Drawing on social identity theory, it presents and tests a model of self-conceptualisation, grounded in the belief that individuals variously identify with their social classes, depending on their perceptions of shared socioeconomic risk. From this, it follows that strong identifiers should derive more relevant information about the emerging market system from class-level economic experiences, and therefore accord these cues greater weight in judgements about transition institutions. Beyond testing this theory of interpersonal variation, it invokes signal detection theory from cognitive psychology to determine whether cross-group differences in economic vulnerability are responsible for observed class differentials in reliance on class-based economic cues. It then takes a wider view of class-based economic cognition by considering how the process of transition, itself, influenced the evaluative calculus of post-communist citizens. Building on cognitive mobilisation theory in political science, it is posited that on-going exposure to the prevailing economic system endows these citizens with the ability to link their class-level economic experiences to the effects of the market mechanism. The analysis largely supports the constituent hypotheses, as well as the larger notion that perceptions of shared socioeconomic risk led social class experiences to figure prominently in the minds of post-communist citizens.
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Lange, Priscila Kienteca. "Putting marine microbes on the map : determining the global distribution of marine picophytoplankton using a combination of satellite and field data." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:ae64c955-336e-46b2-bee1-db41fb4be1c9.
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Picophytoplanktonic cells (0.2-2 μm) are the dominant phytoplankters in the largest marine biomes on Earth: the subtropical gyres. The overaching aim of this thesis is to develop algorithms that use remote-sensing observables to map the distribution of the smallest and most abundant member of picophytoplankton, Prochlorococcus, and assess its contribution to the marine carbon cycle. To understand how the photoacclimatory status and growth of Prochlorococcus and its sister genera Synechococcus are influenced by light and nutrients, experiments were conducted in the South Atlantic Gyre (SAG). Results from the manipulation experiments show that, in the central region of the SAG, nutrient addition can induce marked changes in the optical properties of Prochlorococcus cells when subjected to saturating light levels, leading to a decrease in cell abundance, whereas at the gyre periphery no substantive changes in cell growth or optical characteristics were observed. Since light plays a central role in shaping the distribution of cyanobacteria, an empirical algorithm based on relationships between Prochlorococcus abundance and remotely-sensed observables was developed. The outputs were then used in a modified primary production model to predict the vertical distribution of carbon fixation by Prochlorococcus. The models estimate that ∼ 3.4 x 1027 Prochlorococcus cells in the global ocean fix 4.7 Gt C year-1. Most of the cell biomass and primary productivity is concentrated in the subtropical gyres and areas near the Equatorial Convergence, and 61% of the carbon fixation occurs in the upper water column (0-45 metres), where only 43% of the cells reside. However, in the gyres, carbon fixation is highest (62%) in deeper layers (45-200m), and both cell abundance and carbon fixation show marked seasonal patterns. The models developed in this study provide an unprecedented view of the vertical distribution of Prochlorococcus cells and their corresponding rates of carbon fixation in the global ocean.
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Lee, Joanna. "MFS transporter superfamily : modelling and dynamics." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:c1b28272-c35f-46a3-beee-92bb560933d8.
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The aims for this thesis were threefold. First, is it possible to develop a numbering protocol to aid homology modelling, despite the diversity of MFS sequences? Given these methods, apply these to improve the homology model of a putative MFS protein, SV2A. Finally, can Molecular Dynamics (MD) simulations be used to elucidate the transport mechanism in an MFS protein? There are several solved X-ray crystal structures of secondary active transporter MFS proteins, all of which have a core 12 transmembrane (TM) helix fold. Despite this highly conserved fold, the sequence identity between the transporters is low (15-25 % identity between structures) and so this provides difficulties when exploring homology modelling of target proteins based on known structures of MFS transporters. To overcome this, exploration of both conservation of amino acid type in multiple sequence alignments (MSAs) and conservation of contacts between helices elucidate 'anchor points' in the structure. This analysis can be used to aid alignment between template and target in homology modelling, such as for SV2A, which is the binding site for an anti-epileptic drug, levetiracetam. The binding site was thought to be in the central cavity of the TM region of the MFS protein and so drug-protein interactions were explored using MD simulations. Finally, MD simulations were conducted on FucP, the X-ray crystal structure of which is solved in an outward open conformation (open to the perplasmic cavity). The aim for this work was to investigate the movement from the outward open state to the occluded state and determine whether there is any effect on placing static hydrogen atoms on two key titrable residues in the central TM cavity, D46 and E135.
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O'Brien, Stephen Gerard Michael. "The impact of New Labour's educational vision : a case study of secondary teachers' perceptions of the 'raising standards' agenda." Thesis, University of Bristol, 2001. http://hdl.handle.net/1983/51956dc3-6c42-4ae5-bee4-0f094417bef2.
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Allison, P. A. "The taphonomy of soft-bodied fossil biotas." Thesis, University of Bristol, 1987. http://hdl.handle.net/1983/0ae5c2b2-cfb9-473b-beef-7b5034401d4f.
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Crompton, Matthew John. "The thin aerofoil leading edge separation bubble." Thesis, University of Bristol, 2001. http://hdl.handle.net/1983/25312c88-4d89-4149-bee9-d56cf80d9735.
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Vimont, Michael. "The anthropological construction of Czech identity : academic and popular discourses of identity in 20th century Bohemia." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:bb316968-60a1-472c-bee4-b8de3af5ebbd.
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Through close textual analysis of 20th century Czech anthropological texts from the Revivalist and Socialist periods and contemporary social research conducted after the Velvet Revolution, I demonstrate certain prominent discourses of identity developed in early Bohemian anthropology and their continuities in present day popular discourses. In each period, identity is deeply intertwined with teleological theories of history with Czech populations at the apex of cultural evolutionary development. In the Revivalist period this apex was believed to be the democratic nation state, transitioning to a Marxist nation state in the Socialist period, and in the contemporary period is conceived of as a neoliberal nation state. A major function of anthropology in the Revivalist and Socialist periods was to legitimate either period’s respective teleological theory and Czech possession of relevant values as 'objective' and 'natural' fact, a general mode of discourse which continued in the contemporary period in numerous editorials in the 1990s on the advantages of capitalism. The contemporary manifestation has particularly noteworthy consequences for the Roma minority, which I argue has provided Czech discourses with an ethnic category 'anti-thetical' to their own identity, providing a 'repository' for negative Czech self-stereotypes emerging from collaboration in the Socialist period.
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Meakin, James A. "Velocity selective preparations in Magnetic Resonance Imaging." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:a4247c64-d113-42e6-beee-5795e78a4cdc.
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Arterial Spin Labeling (ASL) is a Magnetic Resonance Imaging (MRI) technique that is able to non-invasively quantify the rate of delivery of arterial blood to tissue, known as perfusion. In this thesis a method that uses Velocity Selective (VS) preparations to generate contrast between blood and tissue spins is investigated. The systematic errors associated with performing a VSASL experiment on imperfect hardware is first investigated. It is shown through simulations and experiments that some VS preparations will underestimate perfusion due to static and transmit magnetic field errors, and that eddy currents caused by switching of magnetic gradients lead to an overestimation of perfusion with VSASL by up to a factor 2. A novel VS preparation, BIR-8, is presented which is shown to be the most robust to these imperfections. The BIR-8 VSASL technique is then applied in brain tumours where it is found that significant VSASL signal can be detected in less than 5 minutes. However, in a comparison with a spatially selective ASL technique it is found that VSASL overestimates perfusion in these tumours, despite agreeing in Grey Matter. The systematic errors due to physiology are then modelled, and it is shown that both diffusion and bulk motion will systematically bias the VSASL measurement. A diffusion insensitive VSASL technique, VS-TILT, is then developed and it is found that a significant proportion of the VSASL signal originates from diffusion effects. Theoretical models for the shape of the bolus in vascular networks are also derived, and it is shown that an isotropic network of laminar vessels produces the most efficient saturation, but saturation is also achieved with plug flow. The diffusion insensitive VS preparation is then applied in an attempt to isolate the venous compartment in order to measure Oxygen Extraction Fraction. A kinetic model is derived in order to optimise the acquisition. However, it is found that accurate measurements of OEF would not be produced by this sequence in a clinically realistic time.
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McNamara, Denise. "Endocrine associations with beef carcass quality and yield." Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/5954.
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Thesis (Ph. D.)--University of Missouri-Columbia, 2007.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on March 7, 2008) Includes bibliographical references.
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Lindqvist, Camilla. "Tambins inverkan på naturligt förekommande pollinatörer." Thesis, Högskolan i Gävle, Avdelningen för elektronik, matematik och naturvetenskap, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-18543.
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Det här arbetet handlar om tambins inverkan på naturligt förekommande pollinatörer. Min frågeställning berör: tillgången på näring, hälsotillståndet och populationsnivån hos naturligt förekommande pollinatörer i förhållande till tambins närvaro. Det som framkommit av den här litteraturstudien är att introducerade tambin leder till att naturligt förekommande pollinatörer minskar i antal kring bikuporna, en del arter söker föda på andra blommor eller senare på dygnet än tidigare. Den minskade tillgången på föda som denna konkurrens innebär har en negativ inverkan på humlors kroppsstorlek och därmed deras överlevnad. Samt att tambin kan föra över patogener så som varroakvalster, nosemasjuka och deformed wing virus till humlor vilket leder till minskad livslängd och sämre fortplantning.This study is about the impact of honeybees on native pollinators. My questions concerns: availability of food, the health and population level of native pollinators in relation to the presence of honeybees. What has emerged from this literature review is that the introduction of honeybees lead to a decline in numbers of bee and bumblebee pollinators in proximity of the hives and also alters their behaviour, some species choose to forage on other flowers, or later in the day than before honeybees where introduced. The reduced availability of food that this competition induces has a negative impact on the size of bumblebees body’s and thus their survival. What was also discovered was that honeybees can transfer pathogens such as varroa mites, the microsporidium Nosema ceranae and deformed wing virus to bumblebees, leading to reduced life expectancy and poor propagation.
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Motamedian, Hamid Reza. "Robust Formulations for Beam-to-Beam Contact." Licentiate thesis, KTH, Hållfasthetslära (Avd.), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-183980.
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Contact between beam elements is a specific category of contact problems which was introduced by Wriggers and Zavarise in 1997 for normal contact and later extended by Zavarise and Wriggers to include tangential and frictional contact. In these works, beam elements are assumed to have rigid circular cross-sections and each pair of elements cannot have more than one contact point. The method proposed in the early papers is based on introducing a gap function and calculating the incremental change of that gap function and its variation in terms of incremental change of the nodal displacement vector and its variation. Due to complexity of derivations, specially for tangential contact, it is assumed that beam elements have linear shape functions. Furthermore, moments at the contact point are ignored. In the work presented in this licentiate thesis, we mostly adress the questions of simplicity and robustness of implementations, which become critical once the number of contact is large. In the first paper, we have proposed a robust formulation for normal and tangential contact of beams in 3D space to be used with a penalty stiffness method. This formulation is based on the assumption that contact normal, tangents, and location are constant (independent of displacements) in each iteration, while they are updated between iterations. On the other hand, we have no restrictions on the shape functions of the underlying beam elements. This leads to a mathematically simpler derivation and equations, as the linearization of the variation of the gap function vanishes. The results from this formulation are verified and benchmarked through comparison with the results from the previous algorithms. The proposed method shows better convergence rates allowing for selecting larger loadsteps or broader ranges for penalty stiffness. The performance and robustness of the formulation is demonstrated through numerical examples. In the second paper, we have suggested two alternative methods to handle in-plane rotational contact between beam elements. The first method follows the method of linearizing the variation of gap function, originally proposed by Wriggers and Zavarise. To be able to do the calculations, we have assumed a linear shape function for the underlying beam elements. This method can be used with both penalty stiffness and Lagrange multiplier methods. In the second method, we have followed the same method that we used in our first paper, that is, using the assumption that the contact normal is independent of nodal displacements at each iteration, while it is updated between iterations. This method yields simpler equations and it has no limitations on the shape functions to be used for the beam elements, however, it is limited to penalty stiffness methods. Both methods show comparable convergence rates, performance and stability which is demonstrated through numerical examples.Kontakt mellan balkelement är en speciell typ av kontaktproblem som först analyserades 1997 av Wriggers och Zavarise med avseende på kontakt i normalriktningen. Teorin utvecklades senare av Zavarise och Wriggers och inkluderade då även kontakt i tangentiella riktningar. I dessa arbeten antas balkelementen ha ett styvt cirkulärt tvärsnitt och varje elementpar kan inte ha mer än en kontaktpunkt. Metodiken i dessa artiklar bygger på att en glipfunktion införs och därefter beräknas den inkrementella förändringen av glipfunktionen, och också dess variation, som funktion av den inkrementella förändringen av förskjutningsvektorn och dess variation. På grund av de komplicerade härledningar som resulterar, speciellt för den tangentiella kontakten, antas det att balkelementen har linjära formfunktioner. Dessutom tas ingen hänsyn till de moment som uppstår vid kontaktpunkten. I de arbeten som presenteras i denna licentiatavhandling har vi valt att inrikta oss mot frågeställningar kring enkla och robusta implementeringar, något som blir viktigt först när problemet innefattar ett stort antal kontakter. I den första artikeln i avhandlingen föreslår vi en robust formulering för normal och tangentiell kontakt mellan balkar i en 3D-rymd.Formuleringen bygger på en kostnadsmetod och på antagandet att kontaktens normal- och tangentriktning samt dess läge förblir detsamma (oberoende av förskjutning) under varje iteration. Dock uppdateras dessa storheter mellan varje iteration. Å andra sidan har inga begränsningar införts för formfunktionerna hos de underliggande balkelementen. Detta leder till en matematiskt enklare härledning samt enklare ekvationer, eftersom variationen hos glipfunktionen försvinner. Resultat framtagna med hjälp av denna formulering har verifierats och jämförts med motsvarande resultat givna av andra metoder. Den föreslagna metoden ger snabbare konvergens vilket ger möjlighet att använda större laststeg eller större omfång hos styvheten i kontaktpunkten (s.k. kostnadsstyrhet). Genom att lösa numeriska exempel påvisas prestanda och robusthet hos den föreslagna formuleringen. I den andra artikeln föreslår vi två alternativa metoder för att hantera rotationer i kontaktplanet hos balkelementen. I den första metoden linjäriseras glipfunktionen. Denna metod presenterades först av Wriggers och Zavarise. För att kunna genomföra beräkningarna ansattes linjära formfunktioner för balkelementen. Den här metoden kan användas både med kostnadsmetoder och metoder baserade på Lagrangemultiplikatorer. I den andra föreslagna metoden har vi valt att följa samma tillvägagångsätt som i vår första artikel. Detta betyder att vi antar att kontaktens normalriktning är oberoende av förskjutningarna under en iteration men uppdateras sedan mellan iterationerna. Detta tillvägagångsätt ger enklare ekvationer och har inga begränsningar vad gäller de formfunktioner som används i balkelementen. Dock är metoden begränsad till att utnyttja kostnadsmetoder. Båda de föreslagna metoderna i denna artikel ger jämförbar konvergens, prestanda och stabilitet vilket påvisas genom att lösningar till olika numeriska exempel presenteras.
QC 20160408
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Adamson, Nancy Lee. "An Assessment of Non-Apis Bees as Fruit and Vegetable Crop Pollinators in Southwest Virginia." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/26313.
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Declines in pollinators around the globe, notably the loss of honey bees (Apis mellifera L.) to Colony Collapse Disorder, coupled with a dearth of quantitative data on non-Apis bee pollinators, led to this dissertation research, which documents the role of non-Apis bees in crop pollination in southwest Virginia. Major findings of this first study of its kind in the region were that non-Apis bees provided the majority of pollination—measured by visitation—for several economically important entomophilous crops (apple, blueberry, caneberry, and cucurbits); diverse bee populations may be helping to stabilize pollination service (105 species on crop flowers); landscape factors were better predictors of non-Apis crop pollination service than farm management factors or overall bee diversity; and non-Apis bees in the genera Andrena, Bombus, and Osmia were as constant as honey bees when foraging on apple.
Non-Apis, primarily native, bees made up between 68% (in caneberries) and 83% (in cucurbits) of bees observed visiting crop flowers. While 37–59 species visited crop flowers, there was low correspondence between bee communities across or within crop systems ("within crop" Jaccard similarity indices for richness ranged from 0.12–0.28). Bee community diversity on crop flowers may help stabilize pollination service if one or more species declines temporally or spatially. A few species were especially important in each crop: Andrena barbara in apple; Andrena carlini and A. vicina in blueberry; Lasioglossum leucozonium in caneberry; and Peponapis pruinosa and Bombus impatiens in cucurbits. Eight species collected were Virginia state records.
In models testing effects of farm management and landscape on non-Apis crop pollination service, percent deciduous forest was positively correlated in apple, blueberry, and squash, but at different scales. For apple and blueberry, pollination service declined with an increase in utilized alternative forage but was positively related to habitat heterogeneity. For squash, percent native plants also related positively, possibly due to increased presence of bumble bees in late summer.
Species collected from both bowl traps and flowers was as low as 22% and overall site bee diversity had no effect on crop pollination service, highlighting the value in pollination research of monitoring bees on flowers.Ph. D.