61 research outputs found
Slow Manifolds, Canard Orbits and the Organization of Mixed-Mode Oscillations
No full textA mixed-mode oscillation is a complex waveform with a pattern of alternating smallamplitude oscillations (SAOs) and large-amplitude oscillations (LAOs). MMOs have been observed in many applications, including semiconductor lasers, neuron models and chemical reactions. In this thesis, we aim to understand and elucidate the phenomenological behavior of MMOs inherited in slow-fast systems, which take the form of ordinary differential equations with a group of fast variables and a group of slow variables, with a time-scale separation parameter ". Geometric singular perturbation theory predicts the existence of locally invariant slow manifolds that organize the slow dynamics. The fast dynamics are typically organized by stable and unstable (fast) manifolds of slow manifolds. Interactions of slow manifolds give rise to so-called canard orbits, which create a mechanism for generating SAOs. On the other hand, LAOs require a global return mechanism. In this thesis, we present a framework for studying two-dimensional slow manifolds, canard orbits and their roles in organizing MMOs in parameter regimes where " is too large for applying classical results from the theory. This is achieved by employing advanced numerical methods based on a two-point boundary value problem setup. We first consider an autocatalytic chemical reaction model with one fast and two slow variables. In this system, we find that canard orbits, which occur along intersections of two-dimensional attracting and repelling slow manifolds, are organized in pairs that we call twin canard orbits. Consequently, the extended attracting slow manifold is divided into subsurfaces called ribbons. Ribbons and associated twin canard orbits organize MMOs when " is relatively large. A continuation analysis illustrates how twin canard orbits arise due to generic quadratic tangencies of slow manifolds. In systems with two fast and two slow variables, two-dimensional slow manifolds of saddle type play a key role in organizing MMOs. One goal of this thesis is to introduce a general approach for computing two-dimensional saddle slow manifolds and their threedimensional stable and unstable manifolds, as well as associated canard orbits in R4. We first test and demonstrate our methods for an extended normal form of a folded node. These methods are then reliably implemented for the full four-dimensional Hodgkin- Huxley neuron model, where " is again relatively large. Our results show that MMOs of this model are also organized by ribbons of the attracting slow manifold and bounding twin canard orbits. Overall, we conclude that our approach is suitable for computing two-dimensional slow manifolds in R3 as well as in R4, and in parameter regimes that are beyond what is known from established theory. In particular, we show that it is practical to study fourdimensional slow-fast vector fields without the need for applying any reduction technique
The transition between square-wave and pseudo-plateau bursting
No full textFull text is available to authenticated members of The University of Auckland only.Electrically excitable cells such as neurons may exhibit different types of bursting activities due to a difference in timescales between changes in electrical potential across the cell membrane and changes in concentration of ions inside the cells. Some of these bursting activities can be observed in mathematical models with multiple timescales. We focus on two types of bursting patterns that appear to be very similar in the observed experimental data but are different in terms of the mathematical mechanism by which they are generated; these are so-called squarewave and pseudo-plateau bursting. In this thesis, we study the mathematical structure of square-wave and pseudo-plateau bursting patterns in a polynomial system of ordinary differential equations with one slow and two fast variables. We use the technique of freezing the single slow variable and relating the resulting bifurcation diagram of the fast subsystem to the dynamics of the full system. This polynomial system can exhibit both types of bursting, depending on the choice of parameters. We are interested in a continuous deformation from square-wave to pseudo-plateau bursting, which we study by numerical continuation. We find that a direct transition between the two bursting patterns through a single connected family can be obtained via a variation of a single bifurcation parameter. As the pseudo-plateau bursting pattern transforms into the square-wave bursting pattern, a transitional bursting pattern arises. This transitional bursting pattern can be viewed as a mix between square-wave and pseudo-plateau bursting. Based on our understanding gained from studying the polynomial model, we propose precise definitions for square-wave, pseudo-plateau and transitional bursting patterns in generic systems with one slow and two fast variables. Our classifications of the different bursting patterns depend mainly on the underlying bifurcation diagram of the fast subsystem, the location of the nullcline of the slow variable and the timescale ratio between the variables
Synthesis of insightful algorithms
No full text"A methodology is developed for the synthesis of Insightful Algorithms. We define ""Insightful Algorithm"" as an analog of a biological system which is capable of fusing environmental observations with multiple predictive models of its process and/or its relationship to its environment, in the form of a Generalized Body of Evidence, which it then uses to respond to contingencies. These combine probability density functions arising from the environmental observations and the sensors measurements, to membership functions representing the expectations of the system's models. This couples Probability Theory to Fuzzy Set Theory, and uses Zadeh's concept of the probability of a Fuzzy event. Estimation of the future performance level uses a methodology based on the Algebra of Logic and Measure Theory where exact analytical representations of the fuzzy logical operations are derived."The implementation of the constructed system is achieved by using the Blackboard Paradigm. In this context, it acts as a synchronization scheme over a distributed processing configuration, a global database, and a job control language. The multiple processors are used for distributing the tasks over the network among different processors with the job control file on a higher hierarchy. A symbolic model based on the Emergency Operating Procedures (EOPs) is used in the form of production rules describing logically the system's operational mode. The system's models chosen are based on the statistical forecasting and time series analysis methods.The developed methodology is applied to the task of monitoring a nuclear power plant with the objective of maximizing its future performance and anticipating any undesirable future conditions so as to steer the system away from them rather than just react to them. The synthesis of the modeling approach is illustrated for the construction of an insightful nuclear plant monitoring system for a Boiling Water Reactor. The insightful ability of the proposed approach is compared to results of actual nuclear power plant transients, to transients generated by numerical thermal hydraulic codes, and to transients generated on plant simulators. It appears that the proposed methodology offers a promising approach to the task of the predictive monitoring a nuclear power plant.Made available in DSpace on 2011-05-07T13:44:53Z (GMT). No. of bitstreams: 2
license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5)
9215845.pdf: 7185291 bytes, checksum: ecf8994fcfda078545e2e2cf1651ec59 (MD5)
Previous issue date: 1992Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:58:40Z
Item is restricted indefinitely.Restriction data tranferred 2014-07-01T11:27:37-05:00
Original Data
Group with Access UIUC Users [automated]
Release Date: none
Reason: ETDs are only available to UIUC Users without author permissionETDs are only available to UIUC Users without author permissionU of I Onl
margin of appreciation applying in the light of legal schools and European Court of Human Rights case law
No full textCodification, interpretation, enforcement, interpretation and modification, all are mainly affected by governments will. Margin of appreciation doctrine isn’t an exception in this respect. This doctrine provides certain flexibilities for implementation of the obligations of states under some circumstances. One would pose a question that in case the matter in question is one dealing with human rights how much and to what extent Margin of appreciation doctrine play its role under international human rights norms. This descriptive-analytical study examines the dimensions of the marginal doctrine and its effectiveness in the context of the principles of sovereignty and human rights and freedoms. In this regard, the said doctrine is analyzed in light of both the natural positivism schools to see its manifestation in the practice and view of the European Court of Human Rights. The results of the research show that, by determination of certain Criteria and restrictions for margin of appreciation doctrine as a product of legal positivism (voluntarism), European court of Human Rights attempts that considerations of the natural law school is being considered by states
Aortic Valve Fibroelastoma Masquerading as Transient Ischaemic Attack
No full textThe following paper is on a 49-year-old man who presented to accident and emergency department having experienced five hours of left-sided chest pain, tightness in the chest, and shortness of breath. He also reported paresthesia and an ache in the left arm. Further investigations revealed an aortic valve papillary fibroelastoma. Although histologically papillary fibroelastomas are described as benign, they carry with them considerable risk of morbidity and mortality. This patient experienced recurrent transient ischemic attacks (TIAs’). He was taken to theatre on urgent basis to remove the papillary fibroelastoma. His aortic valve was preserved during the operation. The patient had an uneventful recovery following the surgery. His neurologic symptoms resolved following the operation. The operation was curative and no further symptoms were reported at followup
Fail-safe source-driven fission and fusion-fission hybrid reactor configurations
No full textA source-driven nuclear reactor configuration with a unity infinite medium multiplication factor fission core (1k), is investigated for both fission and fusion-fission hybrid systems. Suchaconfiguration is thought to offer adesirable fail-safe reactor alternative in that the loss of the fission or the fusion neutron sourceswould automatically lead to a shut-down of the system into a stable subcritical statewith an effective multiplication factor of less than unity (1effk). This is sosincethe fission core cannot sustain a chain reactionwithout the presence of the neutron source. A circulating liquid molten salt using the Th-233Ufuel cycle,where the fission products are continuously extracted,further contributes to the fail-safe characteristic by avoiding the cooling neededfor the decay heat or afterheat after reactor shut-down. Through the extraction of the 233Parelatively long-lived12( 27 )T daysprecursorisotope,and allowing it sufficient time to decay intoits 233Udaughter, breeding in either thermal orfast neutron spectrais a distinct possibility.The presence of trace amounts of 232Uand thestrong gamma-emitting 208Tldaughter isotope offers a desirable non-proliferation characteristicfor the cycle.As a proof of principle, a simplifiedanalytical one-group neutronics analysis isfirstattemptedfor the pure fission core system. This is then supplemented withnumerical one-group criticality calculationsusing an iterative finite-difference methodology. Further, amore detailed continuous energyMonte Carlo neutronics analysis of the fission core reactor driven by a 233Ufissionneutron source, Deuterium-Tritium(DT) and Deuterium-Deuterium (DD) fusion neutron sourceswas conducted usingthe MCNP5computer code.The first system studiedwas a spherical reactor core with a unity infinite medium multiplication factor (1k)and surrounded by a reflector. A 232Th and 233U FLiBe molten salt wasused as the fuel in the core. The reactor is made criticalwith the addition of a thin region of FLiBe salt with a spike of fissile material (233U). With a kin the core and total system effkof unity, the flux profile for the system becomes flat, resulting in uniform fuel burnup andpower profile. Such a configuration was found to have a conversion ratio of 1.4 in the core. However, 233U production in the core would not be able to replace the 233U consumed in the fissile source
iiiregionwithout exceeding a 3-5 percent concentration. This maybe possibly achievedusing other stockpiled fissile materials such as 235Uor Pu239at higher enrichment levels.Alternatively, the fissile source region can be replaced by a fusion neutron source such as from DT or DD fusion. The systemstudiedconsisted of a cylindrical core surroundedby a fusion source. It is envisioned that the source could be provided by several cylindrical electrodynamic inertial fusion generators. A small 318 MWthsystem can be driven by a 22.3 MWDT source or a 9 MW DD source. A DT system would be able to achieve fissile breeding at the expenseof requiring an outside source of tritium. Alternatively, a DD system can use a sodium-based moltensalt and breed 233U witha doubling time of 9.2 years.The results of the investigationsuggestthat source-driven systemsassociated with a molten-saltcan be contemplatedwith substantialfail-safe benefits. Running a subcritical reactor eliminates the need for excessive reactivity control systems and providessafety in a loss of power transient situation. Furthermore, utilizing a fissile neutron source yieldsbeneficial power and flux profiles. Lastly, such systems can breed fissile material and support afuture alternative Th-233Uthorium fuel cycle.Item withdrawn by Mark Zulauf ([email protected]) on 2013-07-08T15:13:55Z
Item was in collections:
University of Illinois Theses & Dissertations (ID: 1)
No. of bitstreams: 2
SINGH_MONISH.docx: 4397896 bytes, checksum: 92835462d73dcea263b905b99b2a6884 (MD5)
SINGH_MONISH.pdf: 2776083 bytes, checksum: 2cb8d004a685b5c6b85e5277d142234d (MD5)Made available in DSpace on 2013-08-22T16:48:35Z (GMT). No. of bitstreams: 3
Monish_Singh.pdf: 2775481 bytes, checksum: 61bac28932827e2dae2a5cbbe5c6b253 (MD5)
SINGH_MONISH.docx: 4390088 bytes, checksum: 2d10b421abc87266ffd0d2d255b9f14a (MD5)
license.txt: 4062 bytes, checksum: e89fb7a224e86f25c60a91aa98d1472a (MD5)Restriction data tranferred 2014-07-01T11:21:16-05:00
Original Data
Group with Access UIUC Users [automated]
Release Date: 2015-08-22 11:49:27 UTC
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemItem marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Seth Robbins ([email protected]) on 2013-08-22T16:49:42Z
Item is restricted until 2015-08-22T16:49:27ZU of I Only Restriction Lifted for Item 45565 on 2015-08-22T10:00:54Z
The Achilles heel of composite arterial grafting: Early occlusion of the distal right coronary limb
No full textAbstractJ Thorac Cardiovasc Surg 2002;124:186-
First record of Pteroplatytrygon violacea (Bonaparte, 1832) with annotation of cartilaginous fishes by-catch by gill nets (Egyptian Mediterranean)
No full textFive cartilaginous fish species were recognized and identified as by-catch species during studying the catch of gill nets operated in the coastal area of Alexandria City from the Egyptian Mediterranean Waters during the study periods from Feb. 2018 to June 2018 and from Dec. 2019 to Nov. 2020. The by-catch included the first record of Pteroplatytrygon violacea, the closely related species Dasyatis pastinaca and Dasyatis tortonesei, the rarely found species Rhinoptera marginata, and the blackchin guitarfish Glaucostegus cemiculus. Among these five species, four species are listed in the IUCN Red List; as least concern for P. violacea, data deficient for D. pastinaca in the Mediterranean Sea, near threatened for R. marginata, and critically endangered for G. cemiculus. Morphological characters and morphometric measurements were studied to provide identification of these species. The species have been dissected for more biological information
- …
