Electronic Theses and Dissertations (ETDs)
https://yorkspace.library.yorku.ca/xmlui/handle/10315/26310
Thu, 23 Jan 2020 01:30:54 GMT2020-01-23T01:30:54ZA 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/10315/368072019-11-22T00:00:00ZAbstracting Cubesat Operations: A Path to Real Cubesat Interoperability
https://yorkspace.library.yorku.ca/xmlui/handle/10315/36806
Abstracting Cubesat Operations: A Path to Real Cubesat Interoperability
Jain, Vidushi
Introduction of the CubeSat form factor brought a paradigm shift in the industry. With the size becoming a standard, cost and development time were able to be reduced significantly. However, the industry has not yet fully realized the potential of this new paradigm. Many other simplifications or standardizations can be made, whilst still meeting CubeSat mission requirements.
One area that can be addressed without significant change is CubeSat mission operations. Many operations activities for CubeSat busses are common, or the differences between missions are close enough to benefit from common streamlining.
This thesis proposes abstracted operations sequence for CubeSats. The sequence is demonstrated by applying it to an upcoming CubeSat mission - DESCENT. Simplifications made as a result of this abstraction are demonstrated. The thesis also points to some of the other improvements that could be made longer-term for CubeSat mission designers and operators through further industry standardization.
Fri, 22 Nov 2019 00:00:00 GMThttps://yorkspace.library.yorku.ca/xmlui/handle/10315/368062019-11-22T00:00:00ZDroplet Impact onto a Spherical Particle in Mid-Air
https://yorkspace.library.yorku.ca/xmlui/handle/10315/36805
Droplet Impact onto a Spherical Particle in Mid-Air
Banitabaei, Sayed Abdolhossein
Collision between a droplet and a particle has a wide range of applications in chemical and petrochemical industries, polyethylene synthesis, and particle coating. Various studies in the literature indicate that the collision products are very different depending on the size and velocity of the particle and droplet, particle wettability and roughness, and physical properties of the liquid and the surrounding gas. The collision outcome is a liquid film (i.e. lamella) and the objective of this thesis is to identify various impact products in different conditions and to study how each category of the above mentioned parameters or a combination of them affect the lamella formation. Investigation of the droplet impact was divided into two parts: drop impact onto a still particle, and droplet impact onto a moving particle in mid-air. Contribution of this thesis to the field can be summarized as following. First, studying the impact phenomenon in a wider range of both Weber number (0.1<We<1146) and droplet-to-particle diameter ratio (1.4<Dr<5.0) compared to what already exists in the literature. Both experimental and numerical tools were developed and used to study the head-on impact between a droplet and a particle. Second, studying the effect of impact velocity, particle wettability, and the amount that each of these parameter contributes on collision outcomes. The required conditions for a lamella to be formed was also studied, and how the lamella geometry changes in case the impact velocity is changed, or hydrophilic/hydrophobic types of particles are used. Third, investigation of the effect of liquid viscosity on lamella formation; what the dynamics of the liquid is inside the film, and how the fluid field inside the lamella is affected by the viscosity changes. Fourth, identifying the role of ambient gas in lamella formation and how each of the drag and lift forces contribute in creating the liquid film. Fifth, developing a pneumatic droplet generator capable of producing single drops with various droplet sizes. The breakup phenomenon in the nozzle and droplet velocity upon pinch-off were also investigated in detail.
Fri, 22 Nov 2019 00:00:00 GMThttps://yorkspace.library.yorku.ca/xmlui/handle/10315/368052019-11-22T00:00:00Z