405 research outputs found
Aortoarteritis with tuberculosis
No full textAortoarteritis is an inflammatory condition of the aorta, which has been rarely reported due to tuberculous infection. We report two cases of children who had aortoarteritis along with tuberculosis (TB), of which one had collapse consolidation and the other had latent TB. Both patients were treated with anti-TB therapy and steroids
Dynamics of Network Formation Processes in the Co-Author Model
No full textThis article studies the dynamics in the formation processes of a mutual consent network in game theory setting: the Co-Author Model. In this article, a limited observation is applied and analytical results are derived. Then, 2 parameters are varied: the number of individuals in the network and the initial probability of the links in the network in its initial state. A simulation result shows a finding that is consistent with an analytical result for a state of equilibrium while it also shows different possible equilibria.Dynamics, Network, Game Theory, Model,Simulation, Equilibrium, Complexity
Isolated propeller aeroacoustics at positive and negative thrust Author links open overlay panel
No full textUsing propellers in negative thrust conditions can potentially result in many benefits, such as a steeper descent, a reduced landing run, reduced community noise, energy regeneration, etc. However, the aerodynamics and aeroacoustics of propellers in this regime are not well understood. This paper presents an aeroacoustic analysis of an isolated propeller operating in both positive and negative thrust conditions, using scale-resolved lattice-Boltzmann very large eddy simulations and the Ffowcs Williams & Hawkings analogy. The propeller was operated at a constant tip Mach number so that any differences in tonal noise between positive and negative thrust conditions were due to changes in blade loading. Results showed that the flow separation around the blades in the negative thrust case led to a 2 to 6 times higher standard deviation in integrated thrust compared to the positive thrust case. The blade loading in the negative thrust case shows the amplitude of fluctuations up to 18% for inboard sections and up to 30% near the blade tip compared to the time-averaged loads. The noise in the propeller plane is 10 dB higher in the positive thrust regime than in the negative thrust regime at a given absolute thrust level of
. The lower noise at negative thrust is caused by two factors: the lower magnitude of the negative torque compared to the positive torque at a given thrust level and the shift of the blade loading inboard in the negative thrust condition due to the stall of the blade tip. Along the propeller axis, the negative thrust regime has 13-15 dB higher noise because of the increased broadband noise generated by the flow separation. In the negative thrust case, the noise along the propeller axis (89 dB) and propeller plane (92 dB) are comparable. However, this is not the case for the propulsive case. The comparison of noise in the vicinity of the propeller plane showed that using the propellers in negative thrust conditions allows for a steeper and quieter descent compared to a conventional descent; as long as the magnitude of the negative torque produced is equal to or less than the torque required to operate the propeller in a conventional landing
Inferring object states and articulation modes from egocentric videos
No full textWe develop algorithms for understanding objects from the point of view of interacting with them. There are two key aspects to obtaining such an understanding. First, objects can occur in different states and we need features that are sensitive to such states. Second, different objects can be articulated in different ways and we need to understand how to correctly infer their modes of articulation. We propose self and weakly supervised techniques to obtain such an understanding of objects purely through observation of how humans interact with the world around them through their hands. Our experiments on the challenging EPIC- KITCHENS dataset show the merits of using human hands as a probe for understanding objects.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2023-05-01The student, Rishabh Goyal, accepted the attached license on 2021-04-27 at 12:26.The student, Rishabh Goyal, submitted this Thesis for approval on 2021-04-27 at 13:39.This Thesis was approved for publication on 2021-04-28 at 09:43.DSpace SAF Submission Ingestion Package generated from Vireo submission #16585 on 2021-09-16 at 17:06:08Made available in DSpace on 2021-09-17T02:34:49Z (GMT). No. of bitstreams: 2
GOYAL-THESIS-2021.pdf: 26378428 bytes, checksum: 5fb34e7c3f1a83a84f3c5ba07fefd80f (MD5)
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Previous issue date: 2021-04-28Embargo set by: Seth Robbins for item 118591
Lift date: 2023-09-17T02:34:57Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Onl
Isogeometric Shell Discretizations for Flexible Multibody Dynamics
No full textThis work aims at including nonlinear elastic shell models in a multibody framework. We focus our attention to Kirchhoff-Love shells and explore the benefits of an isogeometric approach, the latest development in finite element methods, within a multibody system. Isogeometric analysis extends isoparametric finite elements to more general functions such as B-Splines and Non-Uniform Rational B-Splines (NURBS) and works on exact geometry representations even at the coarsest level of discretizations. Using NURBS as basis functions, high regularity requirements of the shell model, which are difficult to achieve with standard finite elements, are easily fulfilled. A particular advantage is the promise of simplifying the mesh generation step, and mesh refinement is easily performed by eliminating the need for communication with the geometry representation in a Computer-Aided Design (CAD) tool.
Quite often the domain consists of several patches where each patch is parametrized by means of NURBS, and these patches are then glued together by means of continuity conditions. Although the techniques known from domain decomposition can be carried over to this situation, the analysis of shell structures is substantially more involved as additional angle preservation constraints between the patches might arise. In this work, we address this issue in the stationary and transient case and make use of the analogy to constrained mechanical systems with joints and springs as interconnection elements. Starting point of our work is the bending strip method which is a penalty approach that adds extra stiffness to the interface between adjacent patches and which is found to lead to a so-called stiff mechanical system that might suffer from ill-conditioning and severe stepsize restrictions during time integration. As a remedy, an alternative formulation is developed that improves the condition number of the system and removes the penalty parameter dependence. Moreover, we study another alternative formulation with continuity constraints applied to triples of control points at the interface. The approach presented here to tackle stiff systems is quite general and can be applied to all penalty problems fulfilling some regularity requirements.
The numerical examples demonstrate an impressive convergence behavior of the isogeometric approach even for a coarse mesh, while offering substantial savings with respect to the number of degrees of freedom. We show a comparison between the different multipatch approaches and observe that the alternative formulations are well conditioned, independent of any penalty parameter and give the correct results. We also present a technique to couple the isogeometric shells with multibody systems using a pointwise interaction.Diese Arbeit zielt darauf ab, nicht-lineare elastische Schalenmodelle in ein Mehrkörpersystem zu integrieren. Wir konzentrieren unsere Aufmerksamkeit auf Kirchhoff-Love Schalen und untersuchen die Vorteile eines isogeometrischen Ansatzes, der die neueste Entwicklung unter den Finite-Elemente-Methoden darstellt, angewandt auf ein Mehrkörpersystem. Isogeometrische Analyse erweitert isoparametrische finite Elemente auf allgemeinere Funktionen wie B-Splines und Non-Uniform Rational B-Splines (NURBS) und arbeitet auf einer exakten Darstellung der Geometrie - sogar auf der gröbsten Diskretisierung. Wenn man NURBS als Basisfunktionen verwendet, werden die hohen Anforderungen an die Regularität des Schalenmodells, die bei Finiten Elementen schwer zu garantieren sind, einfach erfüllt. Ein besonderer Vorteil ist hierbei das Versprechen, dass die Netzgenerierung vereinfacht wird. Die Netzverfeinerung wird leicht dadurch ermöglicht, dass eine Kommunikation mit der Geometrie-Schnittstelle eines Computer-Aided Design (CAD)-Werkzeuges entfällt.
Häufig besteht das Gebiet aus mehreren Abschnitten, wobei jeder Abschnitt mit Hilfe von NURBS parametrisiert ist. Diese Flächenstücke werden dann durch Stetigkeitsbedingungen verklebt. Obwohl die Techniken, die aus der Gebietszerlegung bekannt sind, auch hier angewandt werden könnten, ist die Analyse von Schalenstrukturen wesentlich komplizierter, da zusätzliche Bedingungen zur Erhaltung der Winkel zwischen den Flächen auftreten können. In dieser Arbeit beschäftigen wir uns mit dieser Frage im stationären und transienten Fall und nutzen die Analogie zu mechanischen Systemen, die Gelenke und Federn als Verbindungselemente besitzen. Ausgangspunkt ist der bending strip-Ansatz, der künstlich als Strafterm eine steife Feder an der Grenzfläche zwischen zwei benachbarten Flächen einfügt und zu einem so genannten steifen mechanischen System führt. Solche Systeme führen im Allgemeinen zu schlechter Kondition und starken Schrittweitenbeschränkungen für das Zeitintegrationsverfahren. Als Abhilfe wird eine modifizierte Formulierung entwickelt, die die Konditionszahl des Systems verbessert und die Abhängigkeit von der Größe des Strafterms entfernt. Darüber hinaus untersuchen wir einen weiteren Ansatz, der mit Stetigkeitsbedingungen zwischen Kontrollpunkt-Tripeln an der Schnittstelle arbeitet. Das hier vorgestellte Vorgehen steife Systeme zu lösen ist sehr allgemein und kann auf alle Probleme mit Straftermen angewandt werden, die gewisse Anforderungen an ihre Regularität erfüllen.
Die numerischen Beispiele zeigen ein eindrucksvolles Konvergenzverhalten des Isogeometrische Ansatzes auch für grobe Gitter und bieten erhebliche Einsparungen in Bezug auf die Anzahl der Freiheitsgrade. Wir zeigen einen Vergleich zwischen den verschiedenen Mehr-Flächen-Ansätzen und beobachten, dass die alternativen Formulierungen gut konditioniert und unabhängig von der Größe des Strafterms sind und die korrekten Ergebnisse erzielen. Ebenfalls stellen wir ein Vorgehen vor, die Isogeometrischen Schalen durch punktweise Interaktion mit Mehrkörpersystemen zu koppeln
Aerodynamics and Far-field Noise Emissions of a Propeller in Positive and Negative Thrust Regimes at Non-zero Angles of Attack
No full textThis paper studies the effect of operation at non-zero angles of attack on the aerodynamic performance and far-field noise emissions of an isolated propeller operating at positive and negative thrust conditions. To achieve this, scale-resolved lattice-Boltzmann very large eddy simulations coupled with the Ffowcs Williams & Hawkings analogy have been used. The results show that when the propeller operates with a 10◦ angle of attack at the positive thrust condition, the blade loading increases on the advancing side and decreases on the retreating side, leading to a 9.6% increase in integrated thrust (when computed along the propeller axis) and a negligible increase (0.1%) in propeller efficiency. Conversely, at the negative thrust condition, the operation at 10 deg angle of attack results in a 7.9% decrease in thrust magnitude and an 11.1% reduction in energy-harvesting efficiency. In this condition, the positively cambered blade sections exhibit dynamic stall at the 10◦ angle of attack, resulting in broadband fluctuations of up to 10% of the mean loading. As a result of the opposite change in absolute blade loading in the negative thrust condition compared to the positive thrust condition at the 10◦ angle of attack, the change in the noise directivity is also the opposite. Whereas in the positive thrust case, the noise increases in the region from which the propeller is tilted away (i.e., below the propeller at a positive angle of attack), in the negative thrust case, it is the other way around. This study highlights the need to account for non-zero angles of attack in propeller design and optimization analyses
Small world: Narrow, wide, and long replication of Goyal, van der Leij and Moraga‐Gonzélez (JPE 2006) and a comparison of EconLit and Scopus
No full textI undertake a narrow, wide, and long replication of Goyal, van der Leij and Moraga‐Gonzélez (2006, https://doi.org/10.1086/500990). Using social network analysis, they show that the Economics profession gradually evolved into a small world. Small worlds (or small world networks) have unique information transmission capabilities. The trend is explained by the emergence of frequently publishing researchers with many distinct co‐authors. In a social network, they resemble stars. The original results are robust to the usage of (I) another software, (II) a recent version of the originally used data, and (III) another database and a more sophisticated author disambiguation
Small World: Narrow, Wide and Long replication of Goyal, van der Leij and Moraga-González (JPE 2006) and a Comparison of EconLit and Scopus
No full textI undertake a narrow, wide and long replication of Goyal, van der Leij and Moraga-González (Journal of Political Economy 2006; 114(2): 403–412). Using social network analysis they show that the Economics profession gradually evolved into a small world. Small worlds (or small world networks) have unique information transmission capabilities. The trend is explained by the emergence of frequently publishing researchers with many distinct co-authors. In a social network they resemble stars. The original results are robust to the usage of (I) another software, (II) a recent version of the originally used data, and (III) another database and a more sophisticated author disambiguation
Small is the new big: An overview of newer supraglottic airways for children
No full textAlmost all supraglottic airways (SGAs) are now available in pediatric sizes. The availability of these smaller sizes, especially in the last five years has brought a marked change in the whole approach to airway management in children. SGAs are now used for laparoscopic surgeries, head and neck surgeries, remote anesthesia; and for ventilation during resuscitation. A large number of reports have described the use of SGAs in difficult airway situations, either as a primary or a rescue airway. Despite this expanded usage, there remains little evidence to support its usage in prolonged surgeries and in the intensive care unit. This article presents an overview of the current options available, suitability of one over the other and reviews the published data relating to each device. In this review, the author also addresses some of the general concerns regarding the use of SGAs and explores newer roles of their use in children
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