Tue, 3 Feb 2009 13:41:24
 CombinaTexas Registration Form is submitted by Mr.  Jonathan Gamez

From: Mr.  Jonathan Gamez
E-Mail: j_g12soccer@yahoo.com

From Position and Institution: Student at University of Houston - Downtown
Address Line 1: One Main Street
Address Line 2: Houston, TX 77002
Address Line 3:

Contribute Talk: No
Talk Title:
Abstract:

Wed, 4 Feb 2009 21:24:28
 CombinaTexas Registration Form is submitted by Dr.  Colton Magnant

 From: Dr.  Colton Magnant
 E-Mail: com208@lehigh.edu

 From Position and Institution: Post-Doc at Lehigh University
 Address Line 1: Christmas-Saucon Hall
 Address Line 2: 14 E. Packer Ave.
 Address Line 3: Bethlehem, PA 18015


 Contribute Talk: Yes
 Talk Title: Rainbow Ramsey Theory
 Abstract:
This talk will provide a brief survey of recent rainbow ramsey results and how
they relate to the literature.  Classical ramsey theory involves finding monochromatic structures in colored graphs.  Similarly, rainbow ramsey theory involves finding either a monochromatic copy of a graph or a rainbow (totally multicolored) copy of another graph.  For some rainbow graphs, for example the triangle, this question has been reasonably well studied.  For most others, the problem is wide open.

Mon, 16 Feb 2009 14:15:33 -0600
CombinaTexas Registration Form is submitted by Dr.  Geir Helleloid

 From: Dr.  Geir Helleloid
 E-Mail: geir@math.utexas.edu

 From Position and Institution: Bing Instructor (post-doc), U. of Texas at Austin
 Address Line 1: Dept. of Mathematics, UT-Austin
 Address Line 2: 1 University Station C1200
 Address Line 3: Austin, TX 78712


 Contribute Talk: Yes
 Talk Title: Recognition and Reconstruction of Vertex-Edge Incidence Graphs
 Abstract:
In order to study the strong chromatic index of multigraphs, Brualdi and Massey introduced the incidence coloring number, which can be defined as the chromatic number of the vertex-edge incidence graph (VEIG) of a graph. VEIGs are reminiscent of line graphs, and much work has been done on structural characterizations and recognition algorithms for line graphs.  I will discuss an  analogous linear-time recognition algorithm for VEIGs that also permits the reconstruction of a graph from its VEIG.  I will also mention work on a forbidden subgraph characterization of the hereditary family of VEIGs of digraphs.  This is joint work with Stephen Hartke.

Sat, 21 Feb 2009 21:22:57
CombinaTexas Registration Form is submitted by Dr.  Mahir Bilen Can

 From: Dr.  Mahir Bilen Can
 E-Mail: mcan@tulane.edu

 From Position and Institution: faculty at Tulane University
 Address Line 1: 1823 Audubon Street, New Orleans, 70118, LA.
 Address Line 2:
 Address Line 3:


 Contribute Talk: Yes
 Talk Title: Symmetric functions and reducutive monoids
 Abstract:
A J-irreducible reductive monoid is the (Zariski) closure of an irreducible representation
of a reductive group $G$. In this talk, we will construct a family of symmetric functions for these
monoids following Bergeron - Sottile construction of the (quasi)symmetric functions for a labeled
graded poset.

Wed, 11 Feb 2009 16:31:27
CombinaTexas Registration Form is submitted by   Abraham Martin del Campo

 From:   Abraham Martin del Campo
 E-Mail: asanchez@math.tamu.edu

 From Position and Institution: Graduate Student at Texas A&M University
 Address Line 1: Department of Mathematics
 Address Line 2: Texas A&M University - 3368
 Address Line 3: College Station, TX 77843-3368


 Contribute Talk: No
 Talk Title:
 Abstract:

Tue, 24 Feb 2009 13:13:37
CombinaTexas Registration Form is submitted by Dr.  Ken W. Smith

 From: Dr.  Ken W. Smith
 E-Mail: kenwsmith@shsu.edu

 From Position and Institution: Faculty, Sam Houston State University
 Address Line 1: Department of Mathematics and Statistics, PO Box 2206
 Address Line 2: Sam Houston State University
 Address Line 3: Huntsville, TX 77341-2206

 Request for Support: No
 Comment on support:

 Contribute Talk: Yes
 Talk Title: Rational Idempotents in the Integral Group Ring and Their Applications
 Abstract:
Given a finite abelian group G, we construct a variety of combinatorial objects in G (such as difference sets and partial difference sets) using the rational idempotents of the group ring  Q[G].  Since combinatorial objects typically live in Z[G], these techniques provide divisibility conditions which dramatically narrow the search space for the combinatorial object.  In some cases, these techniques allow a full enumeration of the combinatorial objects or provide the means for an exhaustive search. 

We give an introduction to this "idempotent" approach and provide a number of examples of objects constructed by this method.

Sat, 28 Feb 2009 09:41:25
 CombinaTexas Registration Form is submitted by Ms.  Svetlana Poznanovik

 From: Ms.  Svetlana Poznanovik
 E-Mail: spoznan@math.tamu.edu

 From Position and Institution: graduate student at Texas A&M University
 Address Line 1: Department of Mathematics
 Address Line 2: Texas A&M University
 Address Line 3: College Station, TX 77843-3368


 Contribute Talk: Yes
 Talk Title: Major Index for 01-Fillings of Moon Polyominoes
 Abstract:
In my talk I will present a definition for major index on 01-fillings of moon polyominoes. When specialized to certain shapes, this statistic reduces to the major index for permutations and set partitions. We consider the set $\mathbf{F}(\mathcal{M}, \textbf{s}; A)$ of all 01-fillings of a moon polyomino $\mathcal{M}$ with given column sum $\textbf{s}$ whose empty rows are $A$ and prove that this major index has the same distribution as the number of north-east chains,  which are a natural extension of inversions (resp. crossings) for permutations (resp. set partitions). Hence our result generalizes the classical equidistribution result for the permutation statistics inv and maj. I will present two proofs: an algebraic one using generating functions and a bijective one in the spirit of Foata's second fundamental transformation on words and permutations (this is joint work with William Chen, Catherine Yan, and Arthur Yang).

Tue, 3 Mar 2009 23:17:17
 CombinaTexas Registration Form is submitted by Mr.  Fred Galvin

 From: Mr.  Fred Galvin
 E-Mail: galvin@math.ku.edu

 From Position and Institution: faculty at the University of Kansas
 Address Line 1: 3004 Oxford Road
 Address Line 2: Lawrence, KS 66049
 Address Line 3:


 Contribute Talk: Yes
 Talk Title: TBA
 Abstract:

 Thu, 5 Mar 2009 11:38:49

CombinaTexas Registration Form is submitted by Dr.  Catherine Yan

From: Dr.  Catherine Yan
E-Mail: cyan@math.tamu.edu

From Position and Institution: Professor at Texas A&M University
Address Line 1: Department of Mathematics
Address Line 2: Texas A&M University
Address Line 3: College Station, TX 77843-3368


Contribute Talk: No
Talk Title:
Abstract:

 Sun, 8 Mar 2009 16:04:22

CombinaTexas Registration Form is submitted by Mr.  Stanley Parkerson

 From: Mr.  Stanley Parkerson
 E-Mail: andy_parkerson@yahoo.com

 From Position and Institution: Instructor at University of Louisiana at Lafayette
 Address Line 1: 1123 1/2 W Main St
 Address Line 2: New Iberia, LA
 Address Line 3: 70560


 Contribute Talk: Yes
 Talk Title: Antiautomorphisms on Directed Triple Systems
 Abstract:
A transitive triple $(a,b,c)$ is defined to be the set $\{(a,b),(b,c),(a,c)\}$ of ordered pairs. A directed triple system of order $v$, $DTS(v)$, is a pair $(V,\B)$, where $V$ is a set of $v$ points and $\B$ is a collection of transitive triples of pairwise distinct points of $V$ such that any ordered pair of distinct points of $V$ is contained in precisely one element of $\B$. A permutation of $V$ that maps $\B$ to itself is called an automorphism of $(V,\B)$. An antiautomorphism of $(V,\B)$ is a permutation of $V$ that maps $\B$ to $\B^{-1}$, where $\B^{-1}=\{(c,b,a)\mid(a,b,c)\in\B\}$. A permutation on a $DTS(v)$ is called $1$-bicyclic if the permutation consists of two cycles and one fixed point. Considered in this talk are necessary and sufficient conditions for the existence of a $DTS(v)$ admitting a $1$-bicyclic antiautomorphism with cycles of lengths $M$ and $N$.

Tue, 10 Mar 2009 17:07:53

CombinaTexas Registration Form is submitted by Dr.  Ernst L. Leiss

 From: Dr.  Ernst L. Leiss
 E-Mail: coscel@cs.uh.edu

 From Position and Institution: Professor of Computer Science, University of Houston
 Address Line 1: Department of Computer Science
 Address Line 2: University of Houston
 Address Line 3: Houston Texas 77204-3010


 Contribute Talk: Yes
 Talk Title: Some Comments on the Towers of Hanoi Problem
 Abstract:
A number of years ago (a quarter of a century…), I took an interest in the Towers of Hanoi game. This is a problem that is frequently (ab)used in data structures and algorithms classes to illustrate the power of recursion. I subsequently generalized the game to be played on graphs; specifically, I assume a finite directed graph G=(V,E) with two distinguished nodes S and D, there are n disks of different sizes on node S such that no larger disk may lie on top of a smaller disk, and the objective is to move the n disks from S to D subject to the following rules:
1. Only one disk may be moved at a time and only along an edge in G.
2. A disk is always placed on top of all the disks on the node where it is moved and no larger disk may ever be placed on top of a smaller disk.
If the problem can be solved for a given graph for all n≥1, I call this Hanoi problem solvable. It turned out that there is a rather elegant characterization of all those graphs with solvable Hanoi problems (Leiss). If for a given graph the associated Hanoi problem is not solvable, I call it a finite Hanoi problem. It is an interesting question how many disks can be moved in finite Hanoi problems. It turns out that there are graphs where sub-exponentially many disks can be moved (Leiss; Azriel and Berend). A related question is how many moves are required. While the original Hanoi problem (the complete graph on three nodes) requires 2n-1 moves, recent work (Azriel, Solomon and Solomon) indicates that significantly fewer moves may be required for some graphs with solvable Hanoi problems.

Tue, 17 Mar 2009 13:35:31

CombinaTexas Registration Form is submitted by Mr.  Eric Swartz

 From: Mr.  Eric Swartz
 E-Mail: eswartz@math.ohio-state.edu

 From Position and Institution: graduate student at The Ohio State University
 Address Line 1: Department of Mathematics, The Ohio State University
 Address Line 2: 231 West 18th Avenue
 Address Line 3: Columbus, OH 43202


 Contribute Talk: Yes
 Talk Title: 2-ARC TRANSITIVE POLYGONAL GRAPHS OF LARGE GIRTH AND VALENCY
 Abstract:
A near-polygonal graph is a graph $\Gamma$ which has a set $\mathcal{C}$ of $m$-cycles for some positive integer $m$ such that each 2-path of $\Gamma$ is contained in exactly one cycle in $\mathcal{C}.$  If $m$ is the girth of $\Gamma$ then the graph is called polygonal.  Up until now, the only examples of 2-arc transitive polygonal graphs with arbitrarily large valency had girth no larger than seven, and the 2-arc transitive polygonal graph with largest girth had valency five and girth twenty-three (in fact, even with no restrictions on the automorphism group, there were no examples of polygonal graphs with odd girth greater than twenty-three).   We provide a construction of an infinite family of polygonal graphs of arbitrary girth $m$ with 2-arc transitive automorphism groups, showing that there are 2-arc transitive polygonal graphs of arbitrarily large valency for each girth $m$.

Thu, 19 Mar 2009 10:14:26

CombinaTexas Registration Form is submitted by Mr.  Doug Ray

 From: Mr.  Doug Ray
 E-Mail: dr36@txstate.edu

 From Position and Institution: lecturer at Texas State University
 Address Line 1: Department of Mathematics
 Address Line 2: 601 University Drive
 Address Line 3: San Marcos, Texas  78666


 Contribute Talk: Yes
 Talk Title: Cubic Cages
 Abstract:
Cages are graphs of specified regular degree and girth with the smallest possible order.
A review of the current cubic cages will be given along with an algorithm for producing cages with a relatively small amount of information.

Thu, 19 Mar 2009 10:14:26

CombinaTexas Registration Form is submitted by Dr.  Lenore J. Cowen

 From: Dr.  Lenore J. Cowen
 E-Mail: cowen@cs.tufts.edu

 From Position and Institution: faculty at Tufts University
 Address Line 1: Department of Computer Science, Halligan Hall
 Address Line 2: Tufts University
 Address Line 3: Medford, MA 02155


 Contribute Talk:
 Talk Title: Fault Tolerance in Protein Interaction Networks: Stable Bipartite Subgraphs and Redundant Pathways
 Abstract:

As increasing amounts of high-throughput data for the yeast interactome becomes available, more system-wide properties are uncovered. One interesting question concerns the fault tolerance of protein interaction networks: whether there exist alternative pathways that can perform some required function if a gene essential to the main mechanism is defective, absent or suppressed. One signature pattern for redundant pathways is the BPM (between-pathway model) motif, first suggested by Kelley and Ideker. Past methods proposed to search for BPM motifs have had several important limitations. First, they have been driven heuristically by local greedy searches, which can lead to the inclusion of extra genes that may not belong in the motif; second, they have been validated solely by functional coherence of the putative pathways using GO enrichment, making it difficult to evaluate putative BPMs in the absence of already known biological annotation.

We show how a simple "folk" theorem in graph theory (probably due to Erdos) can help us identify possible BPMs in such a way that not only do we get better coherence of biological function, but we also have a direct way to validate our results based directly on the structure of the network. We uncover some interesting biological examples of previously unknown putative redundant pathways in such areas as vesicle-mediated transport and DNA repair.

Sun, 22 Mar 2009 22:02:56

CombinaTexas Registration Form is submitted by Dr.  Li

 From: Dr.  Li
 E-Mail: liliangpan@yahoo.com.cn

 From Position and Institution: Postdoctoral research associate at Texas State University
 Address Line 1: Mathematics Department, Texas State University
 Address Line 2: 601 University Drive
 Address Line 3: San Marcos, TX 78666


 Contribute Talk: Yes
 Talk Title: On the Chung-Erdos inequality and the Borel-Cantelli lemma
 Abstract:
The Chung-Erdos inequality gives a lower bound on the amount of the union of finitely many finite sets if we know the amounts of all individual sets and all pairwise intersections. The Kochen-Stone inequality gives a lower bound on the probability of the upper limit of infinitely many events if we know the probabilities of all individual events and all pairwise intersections. In this talk, we generalize these two inequalities into weighted versions.

Thu, 19 Mar 2009 10:14:26

CombinaTexas Registration Form is submitted by Dr.  Daniela Ferrero

 From: Dr.  Daniela Ferrero
 E-Mail: dferrero@txstate.edu

 From Position and Institution: Faculty, Texas State University
 Address Line 1: Department of Mathematics
 Address Line 2: Texas State University
 Address Line 3: San Marcos, TX 78666

 Contribute Talk: Yes
 Talk Title: Balance and Connectivity in Signed Graphs
 Abstract:
The sign of a cycle in a sign graph is defined as the product of the signs of its edges. A signed graph is locally balanced at a given vertex if all the cycles that contain it, are positive. A signed graph is balanced if it is balanced at every vertex, or equivalently, if all of its cycles have positive sign.  In this work we establish conditions for a signed graph to be balanced in terms of the connectivity of its underlying graph. Particularly, we prove that if the underlying graph is highly connected, local balance implies balance of the signed graph. These results are applied to some families of signed graphs whose underlying graphs are line graphs.

Mon, 23 Mar 2009 12:56:08

 CombinaTexas Registration Form is submitted by Mr.  Roberto Barrera

 From: Mr.  Roberto Barrera
 E-Mail: rb1222@txstate.edu

 From Position and Institution: student at Texas State University - San Marcos
 Address Line 1: 7906 Lowdes Dr.
 Address Line 2: Austin, TX 78745
 Address Line 3:

 
 Contribute Talk: Yes
 Talk Title: Power Domination in Cylinders and Tori
 Abstract:
A crucial task for electric power companies consists of the continuous monitoring of their power
network. This monitoring can be efficiently accomplished by placing phase measurement units
(PMUs) at selected network locations. However, due to the high cost of the PMUs, their number
must be minimized. The power domination problem consists of finding the minimum number of
PMUs needed to monitor a given power network, as well as to determine the locations where
they should be placed. In terms of graphs, the problem consists of finding minimal sets of
vertices that dominate the entire graph according to some given propagation rules imposed by
the nature of the power network. The power dominating problem is NP-complete. However,
closed formulas for the power domination number of certain families of graphs, such as
rectangular grids have been found. We extend the results for grids to other families of graph
products: the cylinders Pn ×Cm for integers n > 1, m >2, and the tori Cn ×Cm for integers n,m
>2. Joint work with D. Ferrero.

Thu, 12 Mar 2009 11:29:53

CombinaTexas Registration Form is submitted by Dr.  Brian K. Miceli

 From: Dr.  Brian K. Miceli
 E-Mail: bmiceli@trinity.edu

 From Position and Institution: Assistant Professor
 Address Line 1: Mathematics Department
 Address Line 2: One Trinity Place
 Address Line 3: San Antonio, TX 78212


 Contribute Talk: No
 Talk Title:
 Abstract:

Sun, 22 Mar 2009 14:27:15

CombinaTexas Registration Form is submitted by Mr.  Thomas Zaslavsky

 From: Mr.  Thomas Zaslavsky
 E-Mail: zaslav@math.binghamton.edu

 From Position and Institution: Professor at Binghamton University (SUNY)
 Address Line 1: Dept. of Mathematical Sciences
 Address Line 2: Binghamton University (SUNY)
 Address Line 3: Binghamton, NY 13902-6000


 Contribute Talk:
 Talk Title:
 Abstract:

Mon, 23 Mar 2009 17:19:45

 CombinaTexas Registration Form is submitted by Dr.  Neil Robertson

 From: Dr.  Neil Robertson
 E-Mail: robertso@math.ohio-state.edu

 From Position and Institution: Emeritus Professor
 Address Line 1: 6520 Wesley Way
 Address Line 2: Westerville, Ohio 43082
 Address Line 3:


 Contribute Talk:
 Talk Title:
 Abstract:

Mon, 23 Mar 2009 22:23:18

 CombinaTexas Registration Form is submitted by Dr.  Kiran B. Chilakamarri

 From: Dr.  Kiran B. Chilakamarri
 E-Mail: Kchilakamarri@yahoo.com

 From Position and Institution: Faculty at Teaxs Southern University
 Address Line 1: 11022 Silkwood Drive, Houston, TX 77031
 Address Line 2:
 Address Line 3:

 Contribute Talk: No
 Talk Title:
 Abstract:

Mon, 23 Mar 2009 22:57:44

CombinaTexas Registration Form is submitted by Dr.  Mahmud Akelbek

 From: Dr.  Mahmud Akelbek
 E-Mail: am44@txstate.edu

 From Position and Institution: post-doc/lecturer at Texas State University 
 Address Line 1: Department of Mathematics
 Address Line 2: Texas State University, 601 University Drive
 Address Line 3: San Marcos, TX 78666, USA


 Contribute Talk: Yes
 Talk Title: A bound on the scrambling index of primitive digraph in terms of boolean rank
 Abstract:
The scrambling index of a primitive digraph $D$ is the smallest positive integer $k$ such that for every pair of vertices $u$ and $v$, there is a  vertex $w$ such that we can get to $w$ from $u$ and $v$ in $D$ by directed walks of length $k$; it is denoted  by $k(D)$. %The scrambling index of a primitive matrix $A$ can also defined as the smallest positive integer $k$ such that $A^k(A^t)^k=J$,   

For an $m\times n$ boolean matrix $M$, its {\it boolean rank} $b(M)$ is the smallest positive integer $b$ such that for some $m \times b$ boolean matrix $A$ and $b\times n$ boolean matrix $B$, $M=AB$. The boolean rank of the zero matrix is defined to be zero. $M=AB$ is called a {\it boolean rank factorization} of $M$. 

In this talk, we present an upper bound on the scrambling index of primitive digraph $D$ in terms of boolean rank $b(A)$ of its adjacency matrix $A(D)$.

Tue, 24 Mar 2009 07:25:10

CombinaTexas Registration Form is submitted by Mr.  Shanzhen Gao

 From: Mr.  Shanzhen Gao
 E-Mail: sgao2@fau.edu

 From Position and Institution: Ph.D. Student at Florida Atlantic Univeristy
 Address Line 1: 260 nw 19th street, apt 5
 Address Line 2: Boca Raton
 Address Line 3: Florida 33432


 Contribute Talk: Yes
 Talk Title: Some results and problems on self-avoiding walks
 Abstract:
Some results and problems on self-avoiding walks
Shanzhen Gao,  Shaun Sullivan,  Heinrich Niederhausen
Florida Atlantic University

A self-avoiding walk (SAW) is a sequence of moves on a lattice which does not visit the same point more than once. It was given as one of the two classical combinatorial problems in the Encylopaedia Britannica. A SAW is interesting for simulations because its properties cannot be calculated analytically. Calculating the number of self-avoiding walks in any given lattice is a common computational problem. We will present some interesting problems on SAWs and show you how to solve one problem.

Tue, 24 Mar 2009 12:29:08

CombinaTexas Registration Form is submitted by Mr.  Shaun Sullivan

From: Mr.  Shaun Sullivan
E-Mail: ssulli21@fau.edu

From Position and Institution: graduate student at Florida Atlantic University
Address Line 1: 777 Glades Rd.
Address Line 2: Boca Raton, FL 33431
Address Line 3:


Contribute Talk: Yes
Talk Title: Counting Strings in Ballot Paths
Abstract:
A ballot path stays weakly above the diagonal $y=x$, starts at the origin,
and takes steps from the set $\{\uparrow ,\rightarrow \}=\{u,r\}$. A pattern is a finite
string made from the same step set; it is also a path. We consider $b_{n,k}(m)$, the number of ballot paths containing a given pattern $k$ times reaching $(n,m)$. Certain types of patterns give sequences of polynomials that can be solved using multivariate Finite Operator Calculus. We only consider patterns $p$ such that its reverse pattern $\tilde{p}$ is a ballot path. We require this restriction so that the recurrence relation contains only values of the polynomial sequence that correspond to ballot paths and not the extensions of the polynomial sequence. For example, the pattern $p=uuurr$ would give the recurrence $b_{n,k}(m)=b_{n-1,k}(m)+b_{n,k}(m-1)-b_{n-2,k}(m-3)+b_{n-2,k-1}(m-3)$ when $m>n$ and $b_{n,k}(n)=b_{n-1,k}(n)$, so if we used the first recurrence to define the polynomials, we would be using values below the diagonal that do not correspond to ballot paths. Notice that $\tilde{p}=uurrr$ is not a ballot path. The patterns we consider here are called depth zero. To develop the recursions, we need to investigate the properties of the pattern we wish to avoid. Ballot paths reaching the diagonal can be viewed as Dyck paths, thus we are also counting strings in Dyck paths as a special case.

Keywords: Pattern enumeration, ballot path, Dyck path, Finite Operator
Calculus, Umbral Calculus

Tue, 24 Mar 2009 22:25:35

 CombinaTexas Registration Form is submitted by Mr.  Adrian Heinz

 From: Mr.  Adrian Heinz
 E-Mail: hadriann@yahoo.com

 From Position and Institution: Graduate student at Ball State University
 Address Line 1: 2000 N Oakwood Ave. Apt 204
 Address Line 2: Muncie, IN 47304
 Address Line 3:


 Contribute Talk: Yes
 Talk Title:
 Abstract:

Tue, 24 Mar 2009 22:39:15

CombinaTexas Registration Form is submitted by Mr.  Anthony Harrison

 From: Mr.  Anthony Harrison
 E-Mail: ah1411@txstate.edu

 From Position and Institution: student at Texas State University
 Address Line 1: 350 North St. #1218, San Marcos, TX 78666
 Address Line 2:
 Address Line 3:


 Contribute Talk: Yes
 Talk Title: L(2,1)-labeling of hypercubes
 Abstract:
The channel assignment problem consists of assigning frequencies to transmitters so that the spectrum of frequencies used is minimized, while the communications do not interfere. Two transmitters are considered to interfere with each other if they share similar frequencies and are at a prescribed distance from one another.

The channel assignment problem translates into the following graph problem: find the minimum d such that the vertices of a given graph can be labeled with integers 0,1,…,d so that labels of vertices at a prescribed distance differ in a fixed amount. In particular, an L(2,1)-labeling of a graph prescribes that labels at adjacent vertices must differ by at least 2 and that labels for vertices at distance 2 must differ by at least 1. This problem was found to be NP-complete. We find L(2,1)-labelings for
hypercubes that improve known upper bounds and show them to be minimal. Joint work with R. Barrera and D. Ferrero.

Wed, 25 Mar 2009 10:01:46

CombinaTexas Registration Form is submitted by Ms.  Kirsti Wash

 From: Ms.  Kirsti Wash
 E-Mail: kw1308@txstate.edu

 From Position and Institution: graduate student Texas State University
 Address Line 1: 601 University Dr.
 Address Line 2: San Marcos, TX 78666
 Address Line 3:


 Contribute Talk: Yes
 Talk Title: On The Bounds of The Domination Number of Permutation Graphs
 Abstract:
To follow

Wed, 25 Mar 2009 11:37:52

CombinaTexas Registration Form is submitted by Ms.  Valerie Hajdik

 From: Ms.  Valerie Hajdik
 E-Mail: valerie.hajdik@gmail.com

 From Position and Institution: incoming (fall) graduate student at University of Houston
 Address Line 1: 3100 W 38th Ave
 Address Line 2: Apt 8
 Address Line 3: Denver, CO 80211

 Contribute Talk: Yes
 Talk Title: Experiences with "undergraduate" version of Graffiti.
 Abstract:
Graffiti is a computer program that makes conjectures in various sub-fields of mathematics and chemistry. Initial versions of Graffiti invented many conjectures that led to research publications - many by well-known mathematicians - and subsequent version of this program were used by students to learn graph theory "Texas style". I will discuss working on selected conjectures of Graffiti suitable for undergraduate students.

Wed, 25 Mar 2009 14:06:07

 CombinaTexas Registration Form is submitted by Ms.  Jill Cochran

 From: Ms.  Jill Cochran
 E-Mail: jc1781@txstate.edu

 From Position and Institution: doctoral student at Texas State University at San Marcos
 Address Line 1: 117 Lake Washington Dr.
 Address Line 2:
 Address Line 3:


 Contribute Talk: Yes
 Talk Title: Finding and Visualizing Networks of Terrorism Buried in Large Data Sets
 Abstract:
        The increasing availability of large amounts of information regarding terrorist activities and security of shipments amplifies the need for improved methods of analyzing and visualizing large data sets. We focus on the need to create accurate models to represent multidimensional data visually. These models are graphs, which represent networks of information derived from properties of the data or specifically related to geography or chronological sequences. Better visualization tools aid in preliminary data analysis. Then exploratory data analysis techniques such as clustering methods and graph theory techniques lead to better understandings of the data so that more informed decisions can be made in a timely manner. Tools have been developed to explore subnetworks or communities of interest by using clustering techniques related to minimum spanning trees and multidimensional scaling.

Wed, 25 Mar 2009 14:06:07

 CombinaTexas Registration Form is submitted by Dr.  Ji Li

 From: Dr.  Ji Li
 E-Mail: jli@math.arizona.edu

 From Position and Institution: postdoc at the University of Arizona
 Address Line 1: 3033 E 6th Street
 Address Line 2: G14
 Address Line 3: Tucson, AZ85716

 Contribute Talk: Yes
 Talk Title: Fibonacci Compositions
 Abstract:
In Richard Stanley’s Enumerative Combinatorics, Vol. 1, Exercise 14, page 46, we find several formulas expressing Fibonacci numbers in terms of sums over compositions. These formulas are easily proved using generating functions. Our goal is to study identities of this form systematically, and in particular, to answer the following questions: How can we find such identities? How can we prove them combinatorially?

In this talk, I will provide some (probably incomplete) answers to the above questions. The work is mainly done by Professor Ira Gessel. This talk will be accessible to anybody who maintains a basic knowledge of generating functions.

Thu, 26 Mar 2009 22:52:05

 CombinaTexas Registration Form is submitted by Dr.  Jian Shen

 From: Dr.  Jian Shen
 E-Mail: js48@txstate.edu

 From Position and Institution: faculty at Texas State University
 Address Line 1: 601 University Drive
 Address Line 2: Department of Mathematics
 Address Line 3: San Marcos, TX 78666


 Contribute Talk: No
 Talk Title:
 Abstract:

Sun, 29 Mar 2009 14:33:31

CombinaTexas Registration Form is submitted by Mr.  Vikram Kamat

 From: Mr.  Vikram Kamat
 E-Mail: vikram.kamat@asu.edu

 From Position and Institution: Graduate Student at Arizona State University
 Address Line 1: Department of Mathematics & Statistics
 Address Line 2: Box 1804 Arizona State University
 Address Line 3:  Tempe, AZ 85287

 
 Contribute Talk: Yes
 Talk Title: Erd\"os-Ko-Rado theorems for chordal graphs and trees
 Abstract:
One of the more recent generalizations of the Erd\"os-Ko-Rado theorem, formulated by Holroyd, Spencer and Talbot, defines the Erd\"os-Ko-Rado property for graphs in the following manner: for a graph G and a positive integer r, G is said to be r-EKR if no intersecting subfamily of the family of all independent vertex sets of size r is larger than the largest star, where a star centered at a vertex v is the family of all independent sets of size r containing v. In this talk, we present theorems which prove Erd\"os-Ko-Rado results for chordal graphs. We also consider the problem of finding maximum sized stars in trees. We conjecture that for any tree $T$, there is a maximum sized star centered at a leaf and prove this conjecture for $r\leq 4$. This is joint work with G. Hurlbert, Arizona State University.

Sun, 29 Mar 2009 23:23:00

 CombinaTexas Registration Form is submitted by Dr.  Shelly Harvey

 From: Dr.  Shelly Harvey
 E-Mail: shelly@rice.edu

 From Position and Institution: Assistant Professor at Rice University
 Address Line 1: Department of Mathematics, MS 136
 Address Line 2: Rice University, P.O. Box 1892
 Address Line 3: Houston, TX 77251-1892


 Contribute Talk: No
 Talk Title:
 Abstract:

Mon, 6 Apr 2009 08:19:11

CombinaTexas Registration Form is submitted by   Siemion Fajtlowicz

 From:   Siemion Fajtlowicz
 E-Mail: math0@bayou.uh.edu

 From Position and Institution: University of Houston, Professor
 Address Line 1:
 Address Line 2:
 Address Line 3:

 Contribute Talk: No
 Talk Title:
 Abstract:

Wed, 8 Apr 2009 15:50:12

 CombinaTexas Registration Form is submitted by Dr.  Vladimir R. Rosenfeld

 From: Dr.  Vladimir R. Rosenfeld
 E-Mail: rosenfev@tamug.edu

 From Position and Institution: postdoc at the A&M University at Galveston
 Address Line 1:
 Address Line 2:
 Address Line 3:


 Contribute Talk: Yes <=== CANCEL TALK
 Talk Title: Monoids of Endomorphisms and Strong Endomorphisms of Graphs
 Abstract:
Let G be a finite graph with or without self-loops. A mapping of G to G is a graph
endomorphism if it preserves adjacency (edges), and a strong graph endomorphism if, in addition, it also preserves nonedges. The monoids of all endomorphisms and of all strong endomorphisms of a graph G are denoted by EndG and SEndG, respectively. It is known that SEndG is always regular. Ulrich Knauer posed the following three questions:
1. Which regular monoids appear as SEndG for some graph G?
2. For which graphs G is EndG regular?
3. For which graphs is EndG = SEndG valid?
We answer each of these questions.

Thu, 9 Apr 2009 09:23:22

CombinaTexas Registration Form is submitted by Dr.  Sosina Martirosyan Peterson

 From: Dr.  Sosina Martirosyan Peterson
 E-Mail: martsosi@yahoo.com

 From Position and Institution: University of Houston -Clear Lake faculty
 Address Line 1:
 Address Line 2:
 Address Line 3:



 Contribute Talk: Yes
 Talk Title: Perfect Hash Families
 Abstract:


A perfect hash family, PHF(N;k,v,t) is an N x k array with entries from a set of v symbols such that every Nxt  sub-array contains at least one row having distinct symbols. Perfect hash families have been studied intensively in the last two decades as they find numerous applications in computer sciences and cryptography. They are also useful tools in constructions of covering arrays and other designs. Combinatorial methods are used to provide explicit constructions of perfect hash families with improved parameters.  Several recursive constructions of perfect hash families are presented.

Thu, 9 Apr 2009 11:52:01

CombinaTexas Registration Form is submitted by Dr.  Art Duval

 From: Dr.  Art Duval
 E-Mail: artduval@math.utep.edu

 From Position and Institution: faculty at University of Texas at El Paso
 Address Line 1: University of Texas at El Paso
 Address Line 2: Department of Mathematical Sciences
 Address Line 3: El Paso, TX  79968-0514


 Contribute Talk: Yes
 Talk Title: Spanning trees and Laplacians of cubical complexes
 Abstract:
In previous work, we had extended the concept of a spanning tree from graphs to simplicial complexes; now we extend this idea further to CW-complexes, focusing especially on cubical complexes.  Once again, if a complex satsifies a mild technical condition, then its spanning trees can enumerated using its Laplacian matrices, generalizing the matrix-tree theorem.  We apply this to enumerate the spanning trees of cubes and of their complete skeleta, by first computing their Laplacian eigenvalues, which turn out to be integral.  We also define shifted cubical complexes, analogous to shifted simplicial complexes, and show that their Laplacian eigenvalues are integral as well.

This is joint work with Croline Klivans and Jeremy Martin.

Mon, 13 Apr 2009 08:50:55

CombinaTexas Registration Form is submitted by Ms.  Ingeborg Matthews

 From: Ms.  Ingeborg Matthews
 E-Mail: Mingeborg@aol.com

 From Position and Institution:
 Address Line 1: 21311 Hannover Pines Dr.
 Address Line 2: Spring, TX 77388
 Address Line 3:


 Contribute Talk: No
 Talk Title:
 Abstract:

Tue, 14 Apr 2009 09:23:22

CombinaTexas Registration Form is submitted by Dr.  Ermelinda DeLaVina

From: Dr.  Ermelinda DeLaVina
E-Mail: delavinae@uhd.edu

From Position and Institution: faculty at the University of Houston - Downtown
Address Line 1: CMS department S705
Address Line 2: University of Houston - Downtown
Address Line 3: Houston, TX 77002


Contribute Talk: No
Talk Title:
Abstract:

Tue, 14 Apr 2009 10:39:32

CombinaTexas Registration Form is submitted by Dr.  Bill Waller

From: Dr.  Bill Waller
E-Mail: wallerw@uhd.edu

From Position and Institution: faculty at University of Houston-Downtown
Address Line 1: CMS Department
Address Line 2: 1 Main St.
Address Line 3: Houston TX 77002

Contribute Talk: No
Talk Title:
Abstract:

Tue, 14 Apr 2009 11:18:39

CombinaTexas Registration Form is submitted by Dr.  Ryan Pepper

From: Dr.  Ryan Pepper
E-Mail: pepperr@uhd.edu

From Position and Institution: Faculty at UH-D
Address Line 1: University of Houston -- Downtown
Address Line 2: One Main Street
Address Line 3: Houston, TX 77002

Contribute Talk: No
Talk Title:
Abstract:

Wed, 15 Apr 2009 14:04:10

CombinaTexas Registration Form is submitted by Dr.  Jay Bagga

 From: Dr.  Jay Bagga
 E-Mail: jbagga@bsu.edu

 From Position and Institution: Professor, Ball State University
 Address Line 1:
 Address Line 2:
 Address Line 3:

 Contribute Talk: Yes
 Talk Title:
 Abstract:

Wed, 15 Apr 2009 11:58:23

CombinaTexas Registration Form is submitted by Dr.  Martin Malandro

 From: Dr.  Martin Malandro
 E-Mail: malandro@shsu.edu

 From Position and Institution: Assistant Professor at Sam Houston State University
 Address Line 1:
 Address Line 2:
 Address Line 3:
:

 Contribute Talk: No
 Talk Title:
 Abstract:

Wed, 15 Apr 2009 17:02:47

CombinaTexas Registration Form is submitted by Dr.  Xingde Jia

 From: Dr.  Xingde Jia
 E-Mail: jia@txstate.edu

 From Position and Institution: Professor at Texas State University
 Address Line 1: 601 University Drive
 Address Line 2: San Marcos, Texas 78666
 Address Line 3:


 Contribute Talk: No
 Talk Title:
 Abstract:

Thu, 16 Apr 2009 00:12:57

CombinaTexas Registration Form is submitted by Dr.  Laura Felicia Matusevich

 From: Dr.  Laura Felicia Matusevich
 E-Mail: laura@math.tamu.edu

 From Position and Institution: faculty at Texas A&M
 Address Line 1: Dept. of Mathematics, Texas A&M University
 Address Line 2: Mailstop 3368
 Address Line 3: College Station, TX 77843-3368

 Contribute Talk:
 Talk Title:
 Abstract:

Fri, 17 Apr 2009 14:53:11

CombinaTexas Registration Form is submitted by Dr.  Frank Sottile

 From: Dr.  Frank Sottile
 E-Mail: sottile@math.tamu.edu

 From Position and Institution: Professor at Texas A&M University
 Address Line 1:
 Address Line 2:
 Address Line 3:

 Contribute Talk: No
 Talk Title:
 Abstract:

Fri, 17 Apr 2009 20:28:32

CombinaTexas Registration Form is submitted by Dr.  Nathaniel Dean

 From: Dr.  Nathaniel Dean
 E-Mail: nd17@txstate.edu

 From Position and Institution: Professor at Texas State University
 Address Line 1: Department of Mathematics
 Address Line 2: 601 University Drive
 Address Line 3: San Marcos, TX 78666

 Contribute Talk: No
 Talk Title:
 Abstract:

Fri, 17 Apr 2009 21:10:24

CombinaTexas Registration Form is submitted by Dr.  Aaron Lauve

 From: Dr.  Aaron Lauve
 E-Mail: lauve@math.tamu.edu

 From Position and Institution: Visiting Professor at Texas A&M University
 Address Line 1: 1525 E 29th ST, #610
 Address Line 2: Bryan, TX  77802
 Address Line 3:

 Contribute Talk: No
 Talk Title:
 Abstract:

Fri, 24 Apr 2009 23:47:22

CombinaTexas Registration Form is submitted by Ms.  Jing Ma

 From: Ms.  Jing Ma
 E-Mail: jm11.rice@gmail.com

 From Position and Institution: PH.D student of Rice University
 Address Line 1: 1515 Bissonnet St. Unit 208
 Address Line 2: Houston, Texas, 77005
 Address Line 3:

 Request for Support: No
 Comment on support:

 Contribute Talk: No
 Talk Title:
 Abstract: