Christina Zamfirescu - Profile on Academia.edu (original) (raw)

Papers by Christina Zamfirescu

Model for quantification and analysis of pulmonary emphysema from low-dose radiation ct scans

This thesis presents techniques for the automated analysis of low-dose helical CT scans used in t... more This thesis presents techniques for the automated analysis of low-dose helical CT scans used in the detection of pulmonary emphysema. Our work focused on solving the following problems: (1) Determine if existing quantification methods can be successfully used in the detection and quantification of pulmonary emphysema from helical low-radiation CT scans. (2) Develop better models for quantifying emphysema based on additional spatial and densitometric information. The primary contributions of this work are: The development of an automated segmentation algorithm for low-dose lung CT scans. The algorithm is modular, allowing for the removal of surrounding body tissue, vessels, and airways. The development of the sliding window method for quantifying emphysema. The development of a graphical display method of the emphysema index based on slice location. The graphical display will allow radiologists to not only quantify emphysema for the entire lung, but also to understand what regions of...

Quantum cellular neural networks: a theoretical model

Journal of Combinatorial Theory, Series B, 1984

This paper extends previous results of the authors. In particular, non-treerealizable metrics are... more This paper extends previous results of the authors. In particular, non-treerealizable metrics are investigated and it is shown that every finite metric has an optimal realization by a graph.

Transformations of Digraphs Viewed as Intersection Digraphs

The intersection number of a digraph D is the minimum size of a set U, such that D is the interse... more The intersection number of a digraph D is the minimum size of a set U, such that D is the intersection digraph of ordered pairs of subsets of U. The paper describes much of the work done in the area of intersection graphs and digraphs, and proves two main results: Theorem 1 The intersection number of the line digraph of D equals the number of vertices of D that are neither sources nor sinks. Theorem 2 If D contains no loops, the intersection numbers of total digraph, middle digraph and subdivision digraph of D are all equal to the number of vertices of D that are not sources, added to the number of vertices of D that are not sinks.

Hamiltonicity of Topological Grid Graphs

In this paper we study connectivity and hamiltonicity properties of the topological grid graphs, ... more In this paper we study connectivity and hamiltonicity properties of the topological grid graphs, which are a natural type of planar graphs associated with finite subgraphs of the usual square lattice graph of the plane. The main results are as follows. The shortness coefficient of the family of all topological grid graphs is at most 16/17. Every 3-connected topological grid graph is hamiltonian.

On nonhamiltonian homgeneously traceable graphs

Lokale und globale Untersuchungen der Line-, Middle- und Total-Digraphen /

Thesis (doctoral)--Rheinisch-Westfälische Technische Hochschule Aachen, 1977.

An algorithmic characterization of total digraphs

Journal of Algorithms, 1986

ABSTRACT We consider total digraphs of digraphs and present: (i) a structural characterization, (... more ABSTRACT We consider total digraphs of digraphs and present: (i) a structural characterization, (ii) an algorithmic characterization based on a labeling procedure, and (iii) an efficient recognition algorithm. The computational complexity of the algorithm is dominated by the complexity of finding the square of a Boolean (adjacency) matrix of a digraph.

Cyclic and cliquewise connectedness of line graphs

ABSTRACT The connectivity and the line connectivity numbers of a graph and of its line graph are ... more ABSTRACT The connectivity and the line connectivity numbers of a graph and of its line graph are dependent on each other. Another important related notion is the cyclic connectedness, and we establish here a strong relationship between the cyclic connectivity number and the cyclic line connectivity number of a graph and of its line graph. Moreover, we introduce a related new notion involving cliques instead of cycles and undertake a similar investigation.

An algorithmic characterization of total digraphs

Journal of Algorithms, 1986

ABSTRACT We consider total digraphs of digraphs and present: (i) a structural characterization, (... more ABSTRACT We consider total digraphs of digraphs and present: (i) a structural characterization, (ii) an algorithmic characterization based on a labeling procedure, and (iii) an efficient recognition algorithm. The computational complexity of the algorithm is dominated by the complexity of finding the square of a Boolean (adjacency) matrix of a digraph.

Connection digraphs and second-order line digraphs

Discrete Mathematics, 1982

ABSTRACT

Hamiltonicity of Topological Grid Graphs

J Ucs, 2007

ABSTRACT In this paper we study connectivity and hamiltonicity properties of the topological grid... more ABSTRACT In this paper we study connectivity and hamiltonicity properties of the topological grid graphs, which are a natural type of planar graphs associated with finite subgraphs of the usual square lattice graph of the plane. The main results are as follows. The shortness coefficient of the family of all topological grid graphs is at most 16/17. Every 3-connected topological grid graph is hamiltonian.

Survey questionnaires and graphs

Electronic Journal of Statistics, 2015

Establishing Frenet's formulae (Roumanian)

Submatrices of non-tree-realizable distance matrices

Complexity and Diversity of Digraphs

Unifying Themes in Complex Systems, 2011

ABSTRACT There has been a great deal of ferment in `Complexity Science' in recent years, ... more ABSTRACT There has been a great deal of ferment in `Complexity Science' in recent years, as chronicled in the proceedings of the New England Complex Systems Institute's International Conference on Complex Systems [Minai & Bar-Yam 2006, 2008] and those of the Santa Fe Institute [Nadel & Stein 1995, Cowan 1994]. We have been primarily focused on developing metrics of complexity relevant to chemistry, especially synthetic chemistry [Bertz 2003a-c]. Our approach involves abstracting a molecule or a plan for its synthesis as a graph and then using the tools of graph theory to characterize its complexity and diversity.

Submatrices of non-tree-realizable distance matrices

Linear Algebra and its Applications, 1982

Intersections of longest cycles in grid graphs

Journal of Graph Theory, 1997

ABSTRACT It is well-known that the largest cycles of a graph may have empty intersection. This is... more ABSTRACT It is well-known that the largest cycles of a graph may have empty intersection. This is the case, for example, for any hypohamiltonian graph. In the literature, several important classes of graphs have been shown to contain examples with the above property. This paper investigates a (nontrivial) class of graphs which, on the contrary, admits no such example. © 1997 John Wiley & Sons, Inc. J Graph Theory 25: 37–52, 1997

Hamiltonian properties of Toeplitz graphs

Discrete Mathematics, 1996

... Cornu6jols et al. [-3, 4-] gave a poly-nomial-time algorithm for the TSP restricted to Halin ... more ... Cornu6jols et al. [-3, 4-] gave a poly-nomial-time algorithm for the TSP restricted to Halin graphs and Ratliff and Rosen-thal [12 ... Discrete Mathematics 159 (1996) 69-81 v+t, v+2t~ ~-~ v+t2 V+tt+t2 v+2t~ +t2 ! ! ... [] Another interesting situation occurs when n is a multiple of tl + t2. ...

Approximate Inclusion-Exclusion

Combinatorica, 1990

The Inclusion-Exclusion formula expresses the size of a union of a family of sets in terms of the... more The Inclusion-Exclusion formula expresses the size of a union of a family of sets in terms of the sizes of intersections of all subfamilies. This paper considers approximating the size of the union when intersection sizes are known for only some of the subfamilies, or when these quantities are given to within some error, or both.

Model for quantification and analysis of pulmonary emphysema from low-dose radiation ct scans

This thesis presents techniques for the automated analysis of low-dose helical CT scans used in t... more This thesis presents techniques for the automated analysis of low-dose helical CT scans used in the detection of pulmonary emphysema. Our work focused on solving the following problems: (1) Determine if existing quantification methods can be successfully used in the detection and quantification of pulmonary emphysema from helical low-radiation CT scans. (2) Develop better models for quantifying emphysema based on additional spatial and densitometric information. The primary contributions of this work are: The development of an automated segmentation algorithm for low-dose lung CT scans. The algorithm is modular, allowing for the removal of surrounding body tissue, vessels, and airways. The development of the sliding window method for quantifying emphysema. The development of a graphical display method of the emphysema index based on slice location. The graphical display will allow radiologists to not only quantify emphysema for the entire lung, but also to understand what regions of...

Quantum cellular neural networks: a theoretical model

Journal of Combinatorial Theory, Series B, 1984

This paper extends previous results of the authors. In particular, non-treerealizable metrics are... more This paper extends previous results of the authors. In particular, non-treerealizable metrics are investigated and it is shown that every finite metric has an optimal realization by a graph.

Transformations of Digraphs Viewed as Intersection Digraphs

The intersection number of a digraph D is the minimum size of a set U, such that D is the interse... more The intersection number of a digraph D is the minimum size of a set U, such that D is the intersection digraph of ordered pairs of subsets of U. The paper describes much of the work done in the area of intersection graphs and digraphs, and proves two main results: Theorem 1 The intersection number of the line digraph of D equals the number of vertices of D that are neither sources nor sinks. Theorem 2 If D contains no loops, the intersection numbers of total digraph, middle digraph and subdivision digraph of D are all equal to the number of vertices of D that are not sources, added to the number of vertices of D that are not sinks.

Hamiltonicity of Topological Grid Graphs

In this paper we study connectivity and hamiltonicity properties of the topological grid graphs, ... more In this paper we study connectivity and hamiltonicity properties of the topological grid graphs, which are a natural type of planar graphs associated with finite subgraphs of the usual square lattice graph of the plane. The main results are as follows. The shortness coefficient of the family of all topological grid graphs is at most 16/17. Every 3-connected topological grid graph is hamiltonian.

On nonhamiltonian homgeneously traceable graphs

Lokale und globale Untersuchungen der Line-, Middle- und Total-Digraphen /

Thesis (doctoral)--Rheinisch-Westfälische Technische Hochschule Aachen, 1977.

An algorithmic characterization of total digraphs

Journal of Algorithms, 1986

ABSTRACT We consider total digraphs of digraphs and present: (i) a structural characterization, (... more ABSTRACT We consider total digraphs of digraphs and present: (i) a structural characterization, (ii) an algorithmic characterization based on a labeling procedure, and (iii) an efficient recognition algorithm. The computational complexity of the algorithm is dominated by the complexity of finding the square of a Boolean (adjacency) matrix of a digraph.

Cyclic and cliquewise connectedness of line graphs

ABSTRACT The connectivity and the line connectivity numbers of a graph and of its line graph are ... more ABSTRACT The connectivity and the line connectivity numbers of a graph and of its line graph are dependent on each other. Another important related notion is the cyclic connectedness, and we establish here a strong relationship between the cyclic connectivity number and the cyclic line connectivity number of a graph and of its line graph. Moreover, we introduce a related new notion involving cliques instead of cycles and undertake a similar investigation.

An algorithmic characterization of total digraphs

Journal of Algorithms, 1986

ABSTRACT We consider total digraphs of digraphs and present: (i) a structural characterization, (... more ABSTRACT We consider total digraphs of digraphs and present: (i) a structural characterization, (ii) an algorithmic characterization based on a labeling procedure, and (iii) an efficient recognition algorithm. The computational complexity of the algorithm is dominated by the complexity of finding the square of a Boolean (adjacency) matrix of a digraph.

Connection digraphs and second-order line digraphs

Discrete Mathematics, 1982

ABSTRACT

Hamiltonicity of Topological Grid Graphs

J Ucs, 2007

ABSTRACT In this paper we study connectivity and hamiltonicity properties of the topological grid... more ABSTRACT In this paper we study connectivity and hamiltonicity properties of the topological grid graphs, which are a natural type of planar graphs associated with finite subgraphs of the usual square lattice graph of the plane. The main results are as follows. The shortness coefficient of the family of all topological grid graphs is at most 16/17. Every 3-connected topological grid graph is hamiltonian.

Survey questionnaires and graphs

Electronic Journal of Statistics, 2015

Establishing Frenet's formulae (Roumanian)

Submatrices of non-tree-realizable distance matrices

Complexity and Diversity of Digraphs

Unifying Themes in Complex Systems, 2011

ABSTRACT There has been a great deal of ferment in `Complexity Science' in recent years, ... more ABSTRACT There has been a great deal of ferment in `Complexity Science' in recent years, as chronicled in the proceedings of the New England Complex Systems Institute's International Conference on Complex Systems [Minai & Bar-Yam 2006, 2008] and those of the Santa Fe Institute [Nadel & Stein 1995, Cowan 1994]. We have been primarily focused on developing metrics of complexity relevant to chemistry, especially synthetic chemistry [Bertz 2003a-c]. Our approach involves abstracting a molecule or a plan for its synthesis as a graph and then using the tools of graph theory to characterize its complexity and diversity.

Submatrices of non-tree-realizable distance matrices

Linear Algebra and its Applications, 1982

Intersections of longest cycles in grid graphs

Journal of Graph Theory, 1997

ABSTRACT It is well-known that the largest cycles of a graph may have empty intersection. This is... more ABSTRACT It is well-known that the largest cycles of a graph may have empty intersection. This is the case, for example, for any hypohamiltonian graph. In the literature, several important classes of graphs have been shown to contain examples with the above property. This paper investigates a (nontrivial) class of graphs which, on the contrary, admits no such example. © 1997 John Wiley & Sons, Inc. J Graph Theory 25: 37–52, 1997

Hamiltonian properties of Toeplitz graphs

Discrete Mathematics, 1996

... Cornu6jols et al. [-3, 4-] gave a poly-nomial-time algorithm for the TSP restricted to Halin ... more ... Cornu6jols et al. [-3, 4-] gave a poly-nomial-time algorithm for the TSP restricted to Halin graphs and Ratliff and Rosen-thal [12 ... Discrete Mathematics 159 (1996) 69-81 v+t, v+2t~ ~-~ v+t2 V+tt+t2 v+2t~ +t2 ! ! ... [] Another interesting situation occurs when n is a multiple of tl + t2. ...

Approximate Inclusion-Exclusion

Combinatorica, 1990

The Inclusion-Exclusion formula expresses the size of a union of a family of sets in terms of the... more The Inclusion-Exclusion formula expresses the size of a union of a family of sets in terms of the sizes of intersections of all subfamilies. This paper considers approximating the size of the union when intersection sizes are known for only some of the subfamilies, or when these quantities are given to within some error, or both.