1,439 research outputs found
Probing the SU(N) Fermi-Hubbard model with ytterbium atoms in an optical lattice
This thesis reports on the experimental realization of the 3D SU(N) Fermi-Hubbard model and the direct probing of the equation of state with an ultracold quantum gas of fermionic ytterbium in an optical lattice. Ultracold atoms in optical lattices constitute a flexible and highly tunable system to investigate Hamiltonians of condensed matter physics such as the Hubbard model. In particular, ytterbium atoms are ideal candidates for the realization of the Fermi-Hubbard model with SU(N)-symmetry due to a high decoupling of the nuclear spin from the electronic configuration. As a consequence of this enlarged symmetry, thermodynamic properties of the atomic sample depend on N, the number of spin components in the quantum gas, and novel, exotic phases are predicted to emerge at low temperatures.
By locally probing a quantum gas of 173Yb in a 3D optical lattice, we determine the equation of state of the SU(6) and SU(3) Fermi-Hubbard model. The measurement of the equation of state allows us to obtain direct, model-independent access to the thermodynamic quantities of the lattice gas. In this way, we can characterize the crossover from a Fermi liquid to an SU(N) Mott insulator when tuning the interaction strength, and can probe the compressibility of the quantum gas in different interaction regimes. Moreover, we find a low specific entropy of the SU(6) gas below that of
uncorrelated spins, indicating the presence of partial spin correlations in the atomic sample. The ability to access the equation of state of such high spin systems, as well as the low obtained entropy, represent an important step towards the realization of SU(N) spin Hamiltonians and the characterization of novel SU(N) phases.Diese Doktorarbeit beschreibt die experimentelle Umsetzung des 3D SU(N) Fermi-Hubbard Modells und die direkte Messung der Zustandsgleichung mit Hilfe eines ultrakalten Quantengases von fermionischen Ytterbium-Atomen in einem optischen Gitter. Ultrakalte, neutrale Atome in optischen Gittern stellen ein gut kontrollierbares und hochflexibles System dar um Modelle aus der Festkörperphysik, wie z.B. das Hubbard Modell, zu untersuchen. Insbesondere erlauben Ytterbium-Atome, diese Modelle mit SU(N) Symmetrie zu realisieren, da bei ihnen der Kernspin nahezu vollständig von der elektronischen Konfiguration der Atome entkoppelt ist. Als Folge dieser erweiterten Symmetrie hängen die thermodynamischen Größen von N – der Anzahl der Spinkomponenten im Quantengas – ab, und man erwartet neuartige Phasenzustände dieser Systeme bei niedrigen Temperaturen.
Durch Messen der lokalen Eigenschaften eines 173Yb Quantengases, erhalten wir die Zustandsgleichung des SU(6) und SU(3) Fermi-Hubbard Modells. Die Zustandsgleichung erlaubt es uns, direkten, modellunabhängigen Zugang zu den thermodynamischen Größen des Gases im Gitter zu erlangen. Hiermit ist es möglich, durch Ändern der Wechselwirkungsstärke den Übergang von einer Fermi-Flüssigkeit zu einem SU(N) Mott-Isolator zu beobachten, sowie die Kompressibilität des Gases für unterschiedlich starke Wechselwirkungen zu ermitteln. In dem Experiment beobachten wir eine niedrige spezifische Entropie des SU(6) Gases, niedriger als die von unkorrelierten Spins, was auf partielle Spinkorrelationen im Quantengas hinweist. Die Möglichkeit, die Zustandsgleichung solcher Systeme mit hohem Spin direkt zu bestimmen, sowie die niedrige Entropie die erzielt wurde, stellen einen wichtigen Schritt für die Realisierung von SU(N) Spin-Hamiltonoperatoren dar, sowie für die Charakterisierung von neuartigen SU(N) Phasenzuständen
In-company project: An integrated communication plan to increase the usage of the e-floater sharing service in Lisbon
This Master’s project is an in-company project about the micro mobility company Floatility
that offers an electric micro scooter sharing service with its three-wheeled e-floater. The
company figured out that most its e-floater trips were conducted by users who did three or
more trips. In order to address these regular users and trigger more trips by them, it needs an
effective integrated communication plan. As Floatility does not yet have a clear and structured
communication plan for these regular users, the objective of this Master’s project is to
develop an effective communication plan for the regular users of the e-floater sharing service
in Lisbon. The users with the most trips during the three-month pilot project in Lisbon
Carnide served as the target audience who were interviewed and surveyed in order to develop
an integrated communication plan. Firstly, a situation analysis has been done incorporating
the shared mobility market in Lisbon, Floatility’s competitors in Lisbon and the company’s efloater
including its plans for the Lisbon market. Next, the integrated communication plan has
been developed based on six steps proposed by Kotler and Armstrong (2012). They consist of
identifying the target audience, determining the communication objectives, designing a
message, choosing the right media, selecting the message source and collecting feedback from
the users. Having analysed the results of the primary research with the regular users of the
pilot project, eventually an implementation plan is recommended for Floatility’s operations in
the entire city of Lisbon.Este projeto de mestrado é um projeto in company sobre a empresa de micro mobilidade
Floatility que oferece um serviço de partilha de micro scooter elétrico com o seu e-floater de
três rodas. A empresa descobriu que a maioria das suas viagens de e-floater foram realizadas
por utilizadores que fizeram três ou mais viagens. Para atender a esses usuários regulares e
desencadear mais viagens por eles, é necessário um plano de comunicação integrado e eficaz.
Como a Floatility ainda não tem um plano de comunicação claro e estruturado para estes
utilizadores regulares, o objectivo deste projecto de mestrado é desenvolver um plano de
comunicação eficaz para os utilizadores regulares do serviço e-floater sharing em Lisboa. Os
utilizadores que fizeram mais viagens durante os três meses de projeto piloto no Polo de
Carnide, em Lisboa, serviram de público alvo e foram entrevistados de forma a desenvolver
um plano de comunicação integrado. Em primeiro lugar, foi feita uma análise da situação
incorporando o mercado de mobilidade partilhada em Lisboa, os concorrentes da Floatility em
Lisboa e o e-floater da empresa incluindo os seus planos para o mercado de Lisboa. Em
seguida, o plano de comunicação integrada foi desenvolvido com base em seis etapas
propostas por Kotler e Armstrong (2012). Consistem em identificar o público-alvo,
determinar os objetivos de comunicação, desenhar uma mensagem, escolher o meio de
comunicação adequado, selecionar a fonte da mensagem e recolher o feedback dos
utilizadores. Tendo analisado os resultados da investigação primária com os utilizadores
regulares do projecto-piloto, recomenda-se eventualmente um plano de implementação para
as operações da Floatility em toda a cidade de Lisboa
InP microdisks for optical signal processing and data transmission
The performance increase in telecommunication and computing systems demands an ever increasing input-output (IO) bandwidth and IO density, which can be met by integrated photonics. Using photonic integration, much higher densities of optical components can be achieved allowing for short-range optical communication systems in, e.g., high performance computers. The key functionalities required for these optical communication systems are light generation, light modulation and light detection. In addition to this other functionalities are also desirable, such as wavelength conversion. This thesis highlights the design and fabrication of indium phosphide (InP) microdisks heterogeneously integrated on silicon-on-insulator substrates. The fabrication of the microdisks in a laboratory clean-room environment is described. These devices can fulfil the above-mentioned functions required in optical communication. Experiments are then performed on the fabricated devices dealing with these various functionalities that are required for optical communication. The lasing properties of the devices are shown and simulated with a spatiallydependent rate equation model accurately predicting the device behaviour. A detailed speed analysis is given, including a parameter extraction of the devices. The operation of the devices as detectors is highlighted. Furthermore the PhD thesis provides a deep analysis of the use of InP microdisks as modulators. Besides the forward-biased operation principle using the free-carrier plasma-dispersion effect, also a high-speed reversely biased operation mode is proposed and demonstrated experimentally. The thesis also describes various approaches on how to improve the performance of the devices, in particular when using them as lasers. Ways how to increase the output power and how to enhance the operation speed are discussed. Because the device is strongly dependent on the coupling between the resonant InP cavity and the silicon waveguide, an extensive analysis of the coupling and the influence of certain process steps on the device performance are given. The PhD thesis concludes the work carried out on InP microdisks and gives an outlook about improving the device performance with respect to specific applications and how to further improve the manufacturability of the devices. Finally, for the InP microdisk-based devices an outlook is given about suitable applications, such as on-chip optical links for instance
Chapel of Rest in Graz
Material of interest: Reinforced Concrete
The chapel of rest for the Steinfeld cemetery is designed in the form of two curving formwork elements made of reinforced concrete and appearing as two carefully receptive hands.https://openscholarship.wustl.edu/bcs/1219/thumbnail.jp
The Transitivity of Trust Problem in the Interaction of Android Applications
Mobile phones have developed into complex platforms with large numbers of
installed applications and a wide range of sensitive data. Application security
policies limit the permissions of each installed application. As applications
may interact, restricting single applications may create a false sense of
security for the end users while data may still leave the mobile phone through
other applications. Instead, the information flow needs to be policed for the
composite system of applications in a transparent and usable manner. In this
paper, we propose to employ static analysis based on the software architecture
and focused data flow analysis to scalably detect information flows between
components. Specifically, we aim to reveal transitivity of trust problems in
multi-component mobile platforms. We demonstrate the feasibility of our
approach with Android applications, although the generalization of the analysis
to similar composition-based architectures, such as Service-oriented
Architecture, can also be explored in the future
Pflanzen- und ackerbauliche Maßnahmen zur Ampferbekämpfung auf Acker- und Grünlandflächen unter den Produktionsbedingungen des Ökologischen Landbaus
In Ökologisch wirtschaftenden Betrieben stellen Ampferarten, vor allen Dingen Rumex crispus und R. obtusifolius, weit verbreitete und hartnäckige Unkräuter sowohl im Acker als auch im Grünland dar. In diesem Beitrag werden Ergebnisse zur vegetativen und generativen Vermehrung von Ampfer vorgestellt, die auf der Versuchsstation für Ökologischen Landbau Kleinhohenheim der Universität Hohenheim im Jahr 2000 erhoben wurden. In Keimtests wurde die Keimbereitschaft von Ampfersamen unterschiedlichen Alters (Zeiternten in wöchentlichen Abständen von Mitte Mai bis Ende Juni) untersucht, um so einen Anhaltspunkt über den Einfluß des Schnittzeitpunkts von Grünland auf die generative Verbreitung von Ampfer zu erhalten. Die Ergebnisse zeigten, daß die Keimbereitschaft der Samen zur Heureife nur gering war. Mit zunehmender Reife der Pflanzen stieg jedoch die Keimbereitschaft auf Werte über 80 % an (Prüfung bei Dauerlicht und Wechseltemperatur). In einem zweiten Versuch wurden auf einer Ackerfläche etablierte Ampferpflanzen durch teilweises Entfernen von Sproß- und Wurzelmasse beschädigt und nach sechs Wochen Sproß- und Wurzelmasse erhoben. Hierbei zeigte sich, daß eine nachhaltige Bekämpfung um so eher möglich war, je mehr Biomasse von den Pflanzen entfernt wurde. Die Beschädigung der Pflanzen mit dem Ampferstecher erwies sich hierbei als eine besonders effektive Methode.
Die Ergebnisse der beiden Versuche zeigen somit, daß es wirkungsvolle nicht chemische Kontrollmaßnahmen gibt, um die Verbreitung von Ampfer einzuschränken. In dem Beitrag wird die Frage diskutiert, warum Ampferarten im Ökologischen Landbau dennoch ein weit verbreitetes Problem darstellen.
Pekrun, Carola und Jund, Dorothea und Hofrichter, Veit und Wagner, Susanne und Thumm, Ulrich und Claupein, Wilhelm (2002) Pflanzen- und ackerbauliche Maßnahmen zur Ampferbekämpfung auf Acker- und Grünlandflächen unter den Produktionsbedingungen des Ökologischen Landbaus [Indirect means of weed control against Rumex spec. on arable fields and grassland in organic farming]. Zeitschrift Pflanzenkrankheiten Pflanzenschutz, Sonderheft XVIII:533-540
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