Electronic Theses and Dissertations (ETDs)
https://yorkspace.library.yorku.ca/xmlui/handle/10315/26310
Mon, 06 Apr 2020 11:04:37 GMT2020-04-06T11:04:37ZComparative study on the detection of early dental caries using thermo-photonic lock-in imaging and optical coherence tomography
https://yorkspace.library.yorku.ca/xmlui/handle/10315/37119
Comparative study on the detection of early dental caries using thermo-photonic lock-in imaging and optical coherence tomography
Shokouhi, Elnaz B.; Razani, Marjan; Gupta, Ashish; Tabatabaei, Nima
Early detection of dental caries is known to be the key to the effectiveness of therapeutic and preventive approaches in dentistry. However, existing clinical detection techniques, such as radiographs, are not sufficiently sensitive to detect and monitor the progression of caries at early stages. As such, in recent years, several optics-based imaging modalities have been proposed for the early detection of caries. The majority of these techniques rely on the enhancement of light scattering in early carious lesions, while a few of them are based on the enhancement of light absorption at early caries sites. In this paper, we report on a systemic comparative study on the detection performances of optical coherence tomography (OCT) and thermophotonic lock-in imaging (TPLI) as representative early caries detection modalities based on light scattering and absorption, respectively. Through controlled demineralization studies on extracted human teeth and µCT validation experiments, several detection performance parameters of the two modalities such as detection threshold, sensitivity and specificity have been qualitatively analyzed and discussed. Our experiment results suggests that both modalities have sufficient sensitivity for the detection of well-developed early caries on occlusal and smooth surfaces; however, TPLI provides better sensitivity and detection threshold for detecting very early stages of caries formation, which is deemed to be critical for the effectiveness of therapeutic and preventive approaches in dentistry. Moreover, due to the more specific nature of the light absorption contrast mechanism over light scattering, TPLI exhibits better detection specificity, which results in less false positive readings and thus allows for the proper differentiation of early caries regions from the surrounding intact areas. The major shortcoming of TPLI is its inherent depth-integrated nature, prohibiting the production of depth-resolved/B-mode like images. The outcomes of this research justify the need for a light-absorption based imaging modality with the ability to produce tomographic and depth-resolved images, combining the key advantages of OCT and TPLI.
Sat, 01 Sep 2018 00:00:00 GMThttps://yorkspace.library.yorku.ca/xmlui/handle/10315/371192018-09-01T00:00:00ZThermoelectric Nanocomposite Foams Using Non-Conducting Polymers with Hybrid 1D and 2D Nanofillers
https://yorkspace.library.yorku.ca/xmlui/handle/10315/37095
Thermoelectric Nanocomposite Foams Using Non-Conducting Polymers with Hybrid 1D and 2D Nanofillers
Aghelinejad, Mohammadmehdi; Leung, Siu Ning
A facile processing strategy to fabricate thermoelectric (TE) polymer nanocomposite foams with non-conducting polymers is reported in this study. Multilayered networks of graphene nanoplatelets (GnPs) and multi-walled carbon nanotubes (MWCNTs) are deposited on macroporous polyvinylidene fluoride (PVDF) foam templates using a layer-by-layer (LBL) assembly technique. The open cellular structures of foam templates provide a platform to form segregated 3D networks consisting of one-dimensional (1D) and/or two-dimensional (2D) carbon nanoparticles. Hybrid nanostructures of GnP and MWCNT networks synergistically enhance the material system’s electrical conductivity. Furthermore, the polymer foam substrates possess high porosity to provide ultra-low thermal conductivity without compromising the electrical conductivity of the TE nanocomposites. With an extremely low GnP loading (i.e., ~1.5 vol.%), the macroporous PVDF nanocomposites exhibit a thermoelectric figure-of-merit of ~10−3. To the best of our knowledge, this ZT value is the highest value reported for organic TE materials using non-conducting polymers and MWCNT/GnP nanofillers. The proposed technique represents an industrially viable approach to fabricate organic TE materials with enhanced energy conversion efficiencies. The current study demonstrates the potential to develop light-weight, low-cost, and flexible TE materials for green energy generation.
Tue, 18 Sep 2018 00:00:00 GMThttps://yorkspace.library.yorku.ca/xmlui/handle/10315/370952018-09-18T00:00:00ZA Hybrid Approach for Large-Scale Product Categorization Based on Weighted KNN and LSTM-BPV
https://yorkspace.library.yorku.ca/xmlui/handle/10315/36836
A Hybrid Approach for Large-Scale Product Categorization Based on Weighted KNN and LSTM-BPV
Hu, Haohao
In modern e-commerce systems, large volumes of new items are being added to the product list everyday, which calls for automatic product categorization. In this thesis we propose a weighted K-Nearest Neighbour (KNN) based classification system for solving large-scale e-commerce product taxonomy classification problem. We use information retrieval (IR) model as similarity function in our weighted KNN algorithm. Among all IR models used in this study, we achieved highest classification performance through using information-based (IB) model as similarity function in the KNN algorithm. Moreover, our proposed method can improve the overall performance when combining prediction results with those from advanced neural network based method, namely Long Short-Term Memory with Balanced Pooling Views (LSTM-BPV). The hybrid system could achieve results comparable to the state of the art (SotA). We also get good results by fine-tuning pre-trained Bidirectional Encoder Representations from Transformers (BERT) model.
Wed, 04 Dec 2019 00:00:00 GMThttps://yorkspace.library.yorku.ca/xmlui/handle/10315/368362019-12-04T00:00:00ZC+ - Algebras and the Uncountable: A Systematic Study of the Combinatorics of the Uncountable in the Noncommutative Framework
https://yorkspace.library.yorku.ca/xmlui/handle/10315/36807
C+ - Algebras and the Uncountable: A Systematic Study of the Combinatorics of the Uncountable in the Noncommutative Framework
Vaccaro, Andrea
In this dissertation we investigate nonseparable C-algebras using methods coming from logic, specifically from set theory. The material is divided into three main parts.
In the first part we study algebras known as counterexamples to Naimarks problem, namely C-algebras that are not isomorphic to the algebra of compact operators on some Hilbert space, yet still have only one irreducible representation up to unitary equivalence.
Such algebras have to be simple, nonseparable and non-type I, and they are known to exist if the diamond principle (a strengthening of the continuum hypothesis) is assumed. With the motivation of finding further characterizations for these counterexamples, we undertake the study of their trace spaces, led by some elementary observations about the unitary action on the state space of these algebras, which seem to suggest that a counterexample to Naimarks problem could have at most one trace. We show that this is not the case and, assuming diamond, we prove that every Choquet simplex with countably many extreme points occurs as the trace space of a counterexample to Naimarks problem and that, moreover, there exists a counterexample whose tracial simplex is nonseparable. The second part of this dissertation revolves around the Calkin algebra (H) and the
general problem of what nonseparable C-algebras embed into it. We prove that, under Martins axiom, all C-algebras of density character less than 20 embed into the Calkin algebra. Moving to larger C-algebras, we show that (within ZFC alone) Cred(F20 ) and Cm ax(F20 ), where F20 is the free group on 20 generators, and every nonseparable UHF algebra with density character at most 20 , embed into the Calkin algebra. On the other hand, we prove that it is consistent with ZFC + 20 , for every ordinal 2, that the abelian C-algebra generated by an increasing chain of 2 projections does not embed into Q(H). Hence, the statement Every C-algebra of density character strictly less than 20 embeds into the Calkin algebra is independent from ZFC+ 20 , for every ordinal > 2. Finally, we show that the proof of Voiculescus noncommutative version of the Weyl-
von Neumann theorem consists, when looked from the right perspective, of a sequence of applications of the Baire category theorem to certain ccc posets. This allows us, assuming
Martins axiom, to generalize Voiculescus results to nonseparable C-algebras of density character less than 20 .
The last part of this manuscript concerns lifting of abelian subalgebras of coronas of non-unital C-algebras. Given a subset of commuting elements in a corona algebra, we study what could prevent the existence of a commutative lifting of such subset to the
multiplier algebra. While for finite and countable families the only issues arising are of K-theoretic nature, for larger families the size itself becomes an obstruction. We prove in fact, for a primitive, non-unital, -unital C-algebra A, that there exists a set of 1
orthogonal positive elements in the corona of A which cannot be lifted to a collection of
commuting elements in the multiplier algebra of A.
Fri, 22 Nov 2019 00:00:00 GMThttps://yorkspace.library.yorku.ca/xmlui/handle/10315/368072019-11-22T00:00:00Z