61 research outputs found
High-order time-splitting Hermite and Fourier spectral methods
No full textIn this paper, we are concerned with the numerical solution of the time-dependent Gross-Pitaevskii Equation (GPE) involving a quasi-harmonic potential. Primarily, we consider discretisations that are based on spectral methods in space and higher-order exponential operator splitting methods in time. The resulting methods are favourable in view of accuracy and efficiency; moreover, geometric properties of the equation such as particle number and energy conservation are well captured. Regarding the spatial discretisation of the GPE, we consider two approaches. In the unbounded domain, we employ a spectral decomposition of the solution into Hermite basis functions: on the other hand. restricting the equation to a sufficiently large bounded domain, Fourier techniques are applicable. For the time integration of the GPE, we study various exponential operator splitting methods of convergence orders two, four, and six. Our main objective is to provide accuracy and efficiency comparisons of exponential operator splitting Fourier and Hermite pseudospectral methods for the time evolution of the GPE. Furthermore, we illustrate the effectiveness of higher-order time-splitting methods compared to standard integrators in a long-term integration
Polynomization of the Chern–Fu–Tang conjecture
No full textBessenrodt and Ono’s work on additive and multiplicative properties of the partition function and DeSalvo and Pak’s paper on the log-concavity of the partition function have generated many beautiful theorems and conjectures. In January 2020, the first author gave a lecture at the MPIM in Bonn on a conjecture of Chern–Fu–Tang, and presented an extension (joint work with Neuhauser) involving polynomials. Partial results have been announced. Bringmann, Kane, Rolen, and Tripp provided complete proof of the Chern–Fu–Tang conjecture, following advice from Ono to utilize a recently provided exact formula for the fractional partition functions. They also proved a large proportion of Heim–Neuhauser’s conjecture, which is the polynomization of Chern–Fu–Tang’s conjecture. We prove several cases, not covered by Bringmann et. al. Finally, we lay out a general approach for proving the conjecture
Ranks, Cranks, and Automorphic Forms
No full textThe results of this thesis cover the author’s work on partitions, on statistics related to the rank and crank, and on analytic number theory. The connection between t-cores and sums of squares was initiated by Ono and Sze for 4-cores and further studied by Bringmann, Kane, and Males for self-conjugate 7-cores. Males and the author investigate this phenomenon for all t-cores and self-conjugated t-cores, and the details of this paper and of an alternate proof of a q-series identity of Garvan, Kim, and Stanton are provided in Chapter II. Recently, Stanton conjectured that certain polynomials defined in terms of the rank and crank have divisibility properties that may give an insight into how to define a map between the equinumerous classes provided by the rank and crank. Bringmann, Gomez, Rolen, and the author prove part of Stanton’s conjecture and provide cranks for k-colored partitions (similar to those of Rolen, Wagner, and the author) that appear to satisfy a conjecture similar to Stanton’s. Full proofs of these results are given in Chapter III. The log-concavity of p(n) for n > 25 is a well-known result that was independently proven by Nicolas and by DeSalvo and Pak. Many other inequalities combining multiplicative and additive properties of the partition function and related functions have been shown. Chern, Fu, and Tang and Heim and Neuhauser have conjectured such an inequality for k-colored partitions and fractional partitions respectively, and work of Bringmann, Kane, Rolen, and the author has provided partial progress towards the conjecture of Heim–Neuhauser and proved the conjecture of Chern–Fu–Tang. In particular, it follows that the k-colored partition function is log-concave for integral k ≥ 3. Details of the analytic proof of this fact are given in Chapter IV. In the final two chapters, a summary of the author’s work with Griffin, Ono, Rolen, Thorner, and Wagner concerning effective results towards an alternative criterion for the Riemann Hypothesis and of forthcoming work of Alsharif, Gibson, de Laat, Milinovich, Rolen, Wagner, and the author concerning the proportions of distinct zeros of the Dedekind zeta function are given
3D-TSV: The 3D Trajectory-based Stress Visualizer
No full textWe present the 3D Trajectory-based Stress Visualizer (3D-TSV), a visual
analysis tool for the exploration of the principal stress directions in 3D
solids under load. 3D-TSV provides a modular and generic implementation of key
algorithms required for a trajectory-based visual analysis of principal stress
directions, including the automatic seeding of space-filling stress lines,
their extraction using numerical schemes, their mapping to an effective
renderable representation, and rendering options to convey structures with
special mechanical properties. In the design of 3D-TSV, several perceptual
challenges have been addressed when simultaneously visualizing three mutually
orthogonal stress directions via lines. We present a novel algorithm for
generating a space-filling and evenly spaced set of mutually orthogonal lines.
The algorithm further considers the locations of lines to obtain a more regular
appearance, and enables the extraction of a level-of-detail representation with
adjustable sparseness of the trajectories along a certain stress direction. To
convey ambiguities in the orientation of the principal stress directions, the
user can select a combined visualization of two principal directions via
oriented ribbons. Additional depth cues improve the perception of the spatial
relationships between trajectories. 3D-TSV is accessible to end users via a
C++- and OpenGL-based rendering frontend that is seamlessly connected to a
MatLab-based extraction backend. The code (BSD license) of 3D-TSV as well as
scripts to make ANSYS and ABAQUS simulation results accessible to the 3D-TSV
backend are publicly available.Comment: 13 page
Existentially closed models of fields with a distinguished submodule
No full textThis paper deals with the class of existentially closed models of fields with
a distinguished submodule (over a fixed subring). In the positive
characteristic case, this class is elementary and was investigated by the
first-named author. Here we study this class in Robinson's logic, meaning the
category of existentially closed models with embeddings following Haykazyan and
Kirby, and prove that in this context this class is NSOP and TP
A bijection for tuples of commuting permutations and a log-concavity conjecture
No full textLet denote the number of -tuples of commuting
permutations of elements whose permutation action results in exactly
orbits or connected components. We provide a new proof of an explicit formula
for which is essentially due to Bryan and Fulman, in their work
on orbifold higher equivariant Euler characteristics. Our proof is
self-contained, elementary, and relies on the construction of an explicit
bijection, in order to perform the reduction. We also
investigate a conjecture by the first author, regarding the log-concavity of
with respect to . The conjecture generalizes a previous one by
Heim and Neuhauser related to the Nekrasov-Okounkov formula.Comment: 11 page
Diffusion or cogeneration of knowledge in Agroecology? Reflections based on three case studies of the Metropolitan Region of Buenos Aires, Argentina. (Period 2000-2018)
No full textA partir de su tesis doctoral, la autora desarrolla este artículo a fin de analizar más a fondo las respuestas encontradas a una de las preguntas centrales de dicho trabajo: a partir de los resultados del trabajo de campo llevado a cabo en tres experiencias de sistemas en transición de la Región Metropolitana de Buenos Aires, ¿qué modalidades de circulación de conocimiento en técnicas agroecológicas fueron puestas en juego y parecen haber prevalecido?
Para ese fin, cita autores y presenta definiciones de estos conceptos de modo sucinto, los cuales derivan de dos corrientes distintas en la Extensión Rural, que se han presentado muchas veces como contrapuestas: la “visión transferencista” versus las modalidades que apuestan a un conocimiento generado de modo conjunto por los diversos actores intervinientes en los procesos de transición agroecológica (paradigma constructivista).
El artículo presenta una reflexión acerca de la necesidad de analizar con cuidado la diferenciación de ambas modalidades, tomando en consideración que ha habido una tendencia entre los extensionistas a considerar que la mayoría de las experiencias realizadas recientemente – en especial en experiencias agroecológicas- ocurrieron según una modalidad de circulación de conocimiento cogenerado entre productores y extensionistas.
Además, ha habido una tendencia a sobrevalorar las posibilidades de los enfoques de tipo “agricultor a agricultor”, que han sido ampliamente utilizados en las experiencias de transición agroecológica. La autora analiza, de modo crítico, esas modalidades y da argumentos para debatir acerca de esos supuestos, a fin de contribuir a la reflexión sobre estas prácticas de la Extensión Rural recientemente.Based on her doctoral thesis, the author develops this article in order to further analyze the answers found to one of the central questions of said work: based on the results of the fieldwork carried out in three experiences of systems in transition of the AMBA, what modalities of circulation of knowledge in agroecological techniques were put into play and seem to have prevailed?
To that end, it cites authors and presents definitions of these concepts succinctly, which derive from two different currents in Rural Extension, which have often been presented as opposed: the «transfer vision» versus the modalities that bet on knowledge generated jointly by the various actors involved in the agroecological transition processes. Discussion that has been very much in vogue in the last 20 years in the Rural Extension.
The article presents a reflection on the need to carefully analyze the differentiation of both modalities, taking into consideration that there has been a tendency among extension agents to consider that most of the experiences carried out recently –especially in agroecological experiences– occurred according to a modality of circulation of knowledge cogenerated between producers and extensionists.
Alternatively, there has been a tendency to overestimate the scope and possibilities of «farmer-to-farmer» approaches, which have been widely used in agroecological transition experiences in recent decades. The author critically analyzes these modalities and gives arguments to debate about these assumptions, in order to contribute to the reflection on these extension practices in recent years.Facultad de Ciencias Agrarias y Forestale
Experimental and numerical study of cavitating flow around a surface mounted semi-circular cylinder
No full textIn this paper, the cavitating flow around a bluff body is studied both experimentally and numerically. The bluff body has a finite length with semi-circular cross section and is mounted on a surface in the throat of a converging-diverging channel. This set-up creates various 3D flow structures around the body, from cavitation inception to super cavities, at high Reynolds numbers (Re=5.6×104−2.2×105) and low cavitation numbers (σ=0.56−1.69). Earlier studies have shown this flow to be erosive and the erosion pattern varies by changing the flow rate and w/o the cylinder; hence, this study is an attempt to understand different features of the cavitating flow due to the cylinder effect. In the experiments, high-speed imaging is used. Two of the test cases are investigated in more detail through numerical simulations using a homogeneous mixture model. Non-cavitating simulations have also been performed to study the effect of cavitation on the flow field. Based on the observed results, vortex shedding can have different patterns in cavitating flows. While at higher cavitation numbers the vortices are shed in a cyclic pattern, at very low cavitation numbers large fixed cavities are formed in the wake area. For mid-range cavitation numbers a transitional regime is seen in the shedding process. In addition, the vapour structures have a small effect on the flow behaviour for high cavitation numbers, while at lower cavitation numbers they have significant influence on the exerted forces on the bluff body as well as vortical structures and shedding mechanisms. Besides, at very low cavitation numbers, a reverse flow is observed that moves upstream and causes the detachment of the whole cavity from the cylinder. Such a disturbance is not seen in non-cavitating flows.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Fluid MechanicsMulti Phase System
Diffusion or cogeneration of knowledge in Agroecology? Reflections based on three case studies of the Metropolitan Region of Buenos Aires, Argentina. (Period 2000-2018)
No full textA partir de su tesis doctoral, la autora desarrolla este artículo a fin de analizar más a fondo las respuestas encontradas a una de las preguntas centrales de dicho trabajo: a partir de los resultados del trabajo de campo llevado a cabo en tres experiencias de sistemas en transición de la Región Metropolitana de Buenos Aires, ¿qué modalidades de circulación de conocimiento en técnicas agroecológicas fueron puestas en juego y parecen haber prevalecido?
Para ese fin, cita autores y presenta definiciones de estos conceptos de modo sucinto, los cuales derivan de dos corrientes distintas en la Extensión Rural, que se han presentado muchas veces como contrapuestas: la “visión transferencista” versus las modalidades que apuestan a un conocimiento generado de modo conjunto por los diversos actores intervinientes en los procesos de transición agroecológica (paradigma constructivista).
El artículo presenta una reflexión acerca de la necesidad de analizar con cuidado la diferenciación de ambas modalidades, tomando en consideración que ha habido una tendencia entre los extensionistas a considerar que la mayoría de las experiencias realizadas recientemente – en especial en experiencias agroecológicas- ocurrieron según una modalidad de circulación de conocimiento cogenerado entre productores y extensionistas.
Además, ha habido una tendencia a sobrevalorar las posibilidades de los enfoques de tipo “agricultor a agricultor”, que han sido ampliamente utilizados en las experiencias de transición agroecológica. La autora analiza, de modo crítico, esas modalidades y da argumentos para debatir acerca de esos supuestos, a fin de contribuir a la reflexión sobre estas prácticas de la Extensión Rural recientemente.Based on her doctoral thesis, the author develops this article in order to further analyze the answers found to one of the central questions of said work: based on the results of the fieldwork carried out in three experiences of systems in transition of the AMBA, what modalities of circulation of knowledge in agroecological techniques were put into play and seem to have prevailed?
To that end, it cites authors and presents definitions of these concepts succinctly, which derive from two different currents in Rural Extension, which have often been presented as opposed: the «transfer vision» versus the modalities that bet on knowledge generated jointly by the various actors involved in the agroecological transition processes. Discussion that has been very much in vogue in the last 20 years in the Rural Extension.
The article presents a reflection on the need to carefully analyze the differentiation of both modalities, taking into consideration that there has been a tendency among extension agents to consider that most of the experiences carried out recently –especially in agroecological experiences– occurred according to a modality of circulation of knowledge cogenerated between producers and extensionists.
Alternatively, there has been a tendency to overestimate the scope and possibilities of «farmer-to-farmer» approaches, which have been widely used in agroecological transition experiences in recent decades. The author critically analyzes these modalities and gives arguments to debate about these assumptions, in order to contribute to the reflection on these extension practices in recent years.Facultad de Ciencias Agrarias y Forestale
Leveraging ADL Archetypes by transforming them to AML Archetypes
No full textUniversity of Minnesota M.S. thesis. August 2015. Major: Biomedical Informatics and Computational Biology. Advisors: Christopher Chute, Claudia Neuhauser. 1 computer file (PDF); ix, 37 pages.The Clinical Information Modeling Initiative (CIMI) has developed the Archetype Modeling Language (AML) specifications, which is now an Object Management Group (OMG) standard. The AML is for modeling archetypes using the Unified Modeling Language (UML). The development of the AML specifications is part of one of the goals for CIMI - to deliver a shared repository of clinical models that is open and free to use. The AML is an attractive option to create, reuse and extend archetypes and the ability to share these archetypes greatly improves interoperability. AML is new standard with lot of promises and benefits, but lacks support of any tooling to get started with creating AML archetypes easily. The ADL archetypes are built using a proprietary format and hence lack an easy gateway to Model-Driven Architecture. The author has created maps for transforming existing archetypes in the OpenEHR's Archetype Definition Language (ADL) to AML workspace. These proven mappings bridge the gap between ADL and AML by providing seamless transition and leverage the ADL archetypes to the AML modeling workspace. This thesis is about these mappings and their implementation.Sharma, Deepak. (2015). Leveraging ADL Archetypes by transforming them to AML Archetypes. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/174713
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