14,434 research outputs found
Meso-scale FDM material layout design strategies under manufacturability constraints and fracture conditions
In the manufacturability-driven design (MDD) perspective, manufacturability of the product or system is the most important of the design requirements. In addition to being able to ensure that complex designs (e.g., topology optimization) are manufacturable with a given process or process family, MDD also helps mechanical designers to take advantage of unique process-material effects generated during manufacturing. One of the most recognizable examples of this comes from the scanning-type family of additive manufacturing (AM) processes; the most notable and familiar member of this family is the fused deposition modeling (FDM) or fused filament fabrication (FFF) process. This process works by selectively depositing uniform, approximately isotropic beads or elements of molten thermoplastic material (typically structural engineering plastics) in a series of pre-specified traces to build each layer of the part. There are many interesting 2-D and 3-D mechanical design problems that can be explored by designing the layout of these elements. The resulting structured, hierarchical material (which is both manufacturable and customized layer-by-layer within the limits of the process and material) can be defined as a manufacturing process-driven structured material (MPDSM). This dissertation explores several practical methods for designing these element layouts for 2-D and 3-D meso-scale mechanical problems, focusing ultimately on design-for-fracture. Three different fracture conditions are explored: (1) cases where a crack must be prevented or stopped, (2) cases where the crack must be encouraged or accelerated, and (3) cases where cracks must grow in a simple pre-determined pattern. Several new design tools, including a mapping method for the FDM manufacturability constraints, three major literature reviews, the collection, organization, and analysis of several large (qualitative and quantitative) multi-scale datasets on the fracture behavior of FDM-processed materials, some new experimental equipment, and the refinement of a fast and simple g-code generator based on commercially-available software, were developed and refined to support the design of MPDSMs under fracture conditions. The refined design method and rules were experimentally validated using a series of case studies (involving both design and physical testing of the designs) at the end of the dissertation. Finally, a simple design guide for practicing engineers who are not experts in advanced solid mechanics nor process-tailored materials was developed from the results of this project.U of I OnlyAuthor's request
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Ensuring Access to Safe and Nutritious Food for All Through the Transformation of Food Systems
OpenContrails: Benchmarking Contrail Detection on GOES-16 ABI
Contrails (condensation trails) are line-shaped ice clouds caused by aircraft
and are likely the largest contributor of aviation-induced climate change.
Contrail avoidance is potentially an inexpensive way to significantly reduce
the climate impact of aviation. An automated contrail detection system is an
essential tool to develop and evaluate contrail avoidance systems. In this
paper, we present a human-labeled dataset named OpenContrails to train and
evaluate contrail detection models based on GOES-16 Advanced Baseline Imager
(ABI) data. We propose and evaluate a contrail detection model that
incorporates temporal context for improved detection accuracy. The human
labeled dataset and the contrail detection outputs are publicly available on
Google Cloud Storage at gs://goes_contrails_dataset
A scalable solution for the extended multi-channel facility location problem
We study the extended version of the non-uniform, capacitated facility
location problem with multiple fulfilment channels between the facilities and
clients, each with their own channel capacities and service cost. Though the
problem has been extensively studied in the literature, all the prior works
assume a single channel of fulfilment, and the existing methods based on linear
programming, primal-dual relationships, local search heuristics etc. do not
scale for a large supply chain system involving millions of decision variables.
Using the concepts of sub-modularity and optimal transport theory, we present a
scalable algorithm for determining the set of facilities to be opened under a
cardinality constraint. By introducing various schemes such as: (i) iterative
facility selection using incremental gain, (ii) approximation of the linear
program using novel multi-stage Sinkhorn iterations, (iii) creation of
facilities one for each fulfilment channel etc., we develop a fast but a tight
approximate solution, requiring
instances of optimal transport problems to select k facilities from m options,
each solvable in linear time. Our algorithm is implicitly endowed with all the
theoretical guarantees enjoyed by submodular maximisation problems and the
Sinkhorn distances. When compared against the state-of-the-art commercial MILP
solvers, we obtain a 100-fold speedup in computation, while the difference in
objective values lies within a narrow range of 3%
Modelling uncertainties for measurements of the H → γγ Channel with the ATLAS Detector at the LHC
The Higgs boson to diphoton (H → γγ) branching ratio is only 0.227 %, but this
final state has yielded some of the most precise measurements of the particle. As
measurements of the Higgs boson become increasingly precise, greater import is
placed on the factors that constitute the uncertainty. Reducing the effects of these
uncertainties requires an understanding of their causes. The research presented
in this thesis aims to illuminate how uncertainties on simulation modelling are
determined and proffers novel techniques in deriving them.
The upgrade of the FastCaloSim tool is described, used for simulating events in
the ATLAS calorimeter at a rate far exceeding the nominal detector simulation,
Geant4. The integration of a method that allows the toolbox to emulate the
accordion geometry of the liquid argon calorimeters is detailed. This tool allows
for the production of larger samples while using significantly fewer computing
resources.
A measurement of the total Higgs boson production cross-section multiplied
by the diphoton branching ratio (σ × Bγγ) is presented, where this value was
determined to be (σ × Bγγ)obs = 127 ± 7 (stat.) ± 7 (syst.) fb, within agreement
with the Standard Model prediction. The signal and background shape modelling
is described, and the contribution of the background modelling uncertainty to the
total uncertainty ranges from 18–2.4 %, depending on the Higgs boson production
mechanism.
A method for estimating the number of events in a Monte Carlo background
sample required to model the shape is detailed. It was found that the size of
the nominal γγ background events sample required a multiplicative increase by
a factor of 3.60 to adequately model the background with a confidence level of
68 %, or a factor of 7.20 for a confidence level of 95 %. Based on this estimate,
0.5 billion additional simulated events were produced, substantially reducing the
background modelling uncertainty.
A technique is detailed for emulating the effects of Monte Carlo event generator
differences using multivariate reweighting. The technique is used to estimate the
event generator uncertainty on the signal modelling of tHqb events, improving the
reliability of estimating the tHqb production cross-section. Then this multivariate
reweighting technique is used to estimate the generator modelling uncertainties
on background V γγ samples for the first time. The estimated uncertainties were
found to be covered by the currently assumed background modelling uncertainty
Annals [...].
Pedometrics: innovation in tropics; Legacy data: how turn it useful?; Advances in soil sensing; Pedometric guidelines to systematic soil surveys.Evento online. Coordenado por: Waldir de Carvalho Junior, Helena Saraiva Koenow Pinheiro, Ricardo Simão Diniz Dalmolin
Aspects of the topological dynamics of sparse graph automorphism groups
We examine sparse graph automorphism groups from the perspective
of the Kechris-Pestov-Todorčević (KPT) correspondence. The sparse
graphs that we discuss are Hrushovski constructions: we consider the
'ab initio’ Hrushovski construction M_0, the Fraïssé limit of the class of 2-sparse graphs with self-sufficient closure; M_1, a simplified version
of M_0; and the ω-categorical Hrushovski construction M_F. We prove
a series of results that show that the automorphism groups of these
Hrushovski constructions demonstrate very different behaviour to previous classes studied in the KPT context. Extending results of Evans,
Hubička and Nešetřil, we show that Aut(M_0) has no coprecompact
amenable subgroup. We investigate the fixed points on type spaces
property, a weakening of extreme amenability, and show that for a
particular choice of control function F, Aut(M_F) does not have any
closed oligomorphic subgroup with this property. Next we consider the
Aut(M_1)-flow of linear orders on M_1, and show that minimal subflows
of this have all Aut(M_1)-orbits meagre. We give partial analogous results for the Aut(M_0)-flow of linear orders on M_0, and find the universal
minimal flow of the automorphism group of the “dimension 0” part of
M_0.Open Acces
Contemporary, decadal, and millennial-scale permafrost- and vegetation dynamics and carbon release in an alpine region of Jotunheimen, Norway
Climatic warming in northern alpine regions facilitates the thawing of permafrost, the associated release of soil carbon into the atmosphere, and the altitudinal shifts in vegetation patterns. Here, a multi-disciplinary approach is adopted to investigate the response of an alpine permafrost landscape (Jotunheimen, Norway, with focus on Galdhøpiggen) to climatic changes over long- to medium timescales. First, a gas analyser is used to explore how ecosystem respiration is affected by ecosystem (soil and vegetation) and geomorphological (cryogenic disturbance) factors during the peak growing season. A palaeoecological record is then analysed to infer the past dynamics of the alpine tree lines and the lower limit of permafrost on Galdhøpiggen over the millennial- and centennial scales. Finally, remotely sensed satellite imagery is combined with observed air temperatures to create a model that provides an estimation of land surface temperatures over the past six decades. The model is then used to predict surface ‘greenness’ over the same period. Palynological evidence from Galdhøpiggen indicates that the altitudinal limits of alpine tree lines have shifted by hundreds of metres in response to climatic changes over the millennial scale. Since 1957, the model predictions indicate substantial increases in land surface temperatures and growing season surface ‘greenness’ (i.e., vegetation abundance) in Jotunheimen, but the change has not been spatially uniform. The highest increases were recorded over the low- and mid-alpine heaths above the tree line (1050-1500 m a.s.l.), which was attributed to increased shrub cover. This trend could facilitate carbon release from the ground, as peak growing season ecosystem respiration was found to be most strongly controlled by soil microclimate and plant growth forms. The likely future scenario in response to warming in Jotunheimen will be continued permafrost degradation, with higher altitudes (≥1500 m a.s.l.) experiencing decreased cryoturbation, increased shrub encroachment and higher surface CO2 emissions
Contribution of non-canonical DNA G-quadruplex structures to premature ageing
Previous studies have identified Cockayne Syndrome B (CSB) as a helicase that can resolve non-canonical DNA structures, called G-quadruplexes (G4s). The aim of this study is to investigate the properties of CSB as a G4-binder and -resolvase, and examine the correlation between the G4-helicase activity of CSB and premature ageing phenotype observed in CSB-deficient cells. Accordingly, the recombinant CSB full-length protein (FL) and its helicase- “like" domain (HD) were respectively expressed from insect and bacterial cells, and their resolvase and binding activities were tested over a large panel of DNA substrates. Native gel analysis and biophysical characterisations revealed that ribosomal DNA (rDNA) sequences, that typically act as CSB substrate, can form intermolecular G4s. We discovered that intermolecular G4s were strongly bound by CSB with picomolar affinity, whilst negligible binding to intramolecular G4s was observed. In vitro and cellular data demonstrated that G4-ligands can compete with CSB for binding to intermolecular rDNA G4, which results in CSB being displaced off the nucleoli of cells upon treatment with G4-ligands. Immunostaining with the selective G4-antibody BG4 revealed a lack of BG4-staining in the nucleoli of CSB-deficient cells after exogenous expression of recombinant CSB, further corroborating the hypothesis that CSB can bind intermolecular rDNA G4s in the nucleoli and compete with BG4 for the binding of such DNA-substrate. The work presented in this thesis allowed us to observe that (I) intermolecular G4s are likely to form from long-range distant rDNA sequences within the nucleoli of cells, and (II) CSB specifically binds and resolves these structures. Our results provide the first evidence of an endogenous protein that specifically interacts with intermolecular G4s, suggesting potential biological significance of these structures. The biological relevance of intermolecular rDNA G4s could be key in rare genetic disorders like Cockayne Syndrome, where senescence and premature ageing is observed when CSB is functionally mutated.Open Acces
The mechanisms of antibody generation in the llama
The llama is able to generate a unique class of antibody. The heavy chain immunoglobulins consist only of two heavy chain polypeptides and bind antigen specifically through single protein domains. Although the mechanisms by which such an antibody interacts with antigen has been studied at some length the manner in which the heavy chain antibody is generated within the llama is unknown. In this study a number of components of the llama immune system have been characterised. The isolation of genes encoding the variable domain of the heavy chain antibody indicates that specific genetic elements within the llama genome are responsible for the generation of the heavy chain antibody. The discovery of constant region genes that encode the heavy chain antibody provides an explanation for the absence of a major immunoglobulin domain from the final, secreted gene product. The lack of this domain within the expressed antibody is believed to be the result of a single nucleotide splice site mutation. In order to investigate the process of llama antibody generation further additional components of the llama immune system, the recombination activating genes (rag) were isolated. One such llama rag gene (rag-i) was cloned, expressed and utilised in an in vitro assay system to investigate recombination events taking place during antibody generation. This assay involved the use of specific signal sequences derived from variable domain gene sequence data and represents, to our knowledge, the first examination of non-murine RAG activity. Through the use of this system distinct differences between llama and mouse recombination signal sequences (RSSs) were uncovered. These differences, located within a specific region of the RSS known as the coding flank, may play an important role in llama antibody generation. These results have led to the proposal of a number of models for the mechanisms involved in llama antibody generation
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