Hwee Kim

Alignment with Non-overlapping Inversions on Two Strings

The inversion is one of the important operations in bio sequence analysis and the sequence alignment problem is well-studied for efficient bio sequence comparisons. Based on inversion operations, we introduce the alignment with non-overlapping inversion problem: Given two strings x and y, does there exist an alignment with non-overlapping inversions for x and y. We, in particular, consider the alignment problem when non-overlapping inversions are allowed for both x and y. We design an efficient algorithm that determines the existence of non-overlapping inversions and present another efficient algorithm that retrieves such an alignment, if exists.

Pseudo-inversion on Formal Languages

We consider the pseudo-inversion operation inspired by a biological event as a result of the partial inversion. We define the pseudo-inversion of a string w = uxv to consist of all strings v R xu R , where uv ≠ λ and consider the operation from a formal language theoretic viewpoint. We show that regular languages are closed under the pseudo-inversion operation whereas context-free languages are not. Furthermore, we consider the iterated pseudo-inversion operation and establish the basic properties. Finally, we introduce the pseudo-inversion-freeness and examine closure properties and decidability problems for regular and context-free languages. We establish that pseudo-inversion-freeness is decidable in polynomial time for regular languages and undecidable for context-free languages.

Alignment with non-overlapping inversions and translocations on two strings

An inversion and a translocation are important in bio sequence analysis and motivate researchers to consider the sequence alignment problem using these operations. Based on inversion and translocation, we introduce a new alignment problem with non-overlapping inversions and translocations-given two strings x and y, find an alignment with non-overlapping inversions and translocations for x and y. This problem has interesting application for finding a common sequence from two mutated sequences. We, in particular, consider the alignment problem when non-overlapping inversions and translocations are allowed for both x and y. We design an efficient algorithm that determines the existence of such an alignment and retrieves an alignment, if exists.

Ruleset Optimization on Isomorphic Oritatami Systems

RNA cotranscriptional folding refers to the phenomenon in which an RNA transcript folds upon itself while being synthesized out of a gene. The oritatami system (OS) is a computation model of this phenomenon, which lets its sequence of beads (abstract molecules) fold cotranscriptionally by the interactions between beads according to its ruleset. We study the problem of reducing the ruleset size while maintaining the terminal conformations geometrically same. We first prove the hardness of finding the smallest ruleset, and suggest two approaches that reduce the ruleset size efficiently.

Self-attraction Removal from Oritatami Systems

RNA cotranscriptional folding refers to the phenomenon in which an RNA transcript folds upon itself while being synthesized (transcribed). Oritatami is a computational model of this phenomenon, which lets its transcript, a sequence of beads (abstract molecules) fold cotranscriptionally via interactions between beads according to its ruleset. In this paper, we study the problem of removing self-attractions, which lets a bead interact with another bead of the same kind, from a given oritatami system without changing its behavior. We provide an algorithm for that with overhead linear in the delay parameter, which should be considerably smaller than the length of its transcript. We also show that this overhead is tight.

Nondeterministic Seedless Oritatami Systems and Hardness of Testing Their Equivalence

The oritatami system (OS) is a model of computation by cotranscriptional folding, being inspired by the recent experimental succeess of RNA origami to self-assemble an RNA tile cotranscriptionally. The OSs implemented so far, including binary counter and Turing machine simulator, are deterministic, that is, uniquely fold into one conformation, while nondeterminism is intrinsic in biomolecular folding. We introduce nondeterminism to OS (NOS) and propose an NOS that chooses an assignment of Boolean values nondeterministically and evaluates a logical formula on the assignment. This NOS is seedless in the sense that it does not require any initial conformation to begin with like the RNA origami. The NOS allows to prove the co-NP hardness of deciding, given two NOSs, if there exists no conformation that one of them folds into but the other does not.

Nondeterministic seedless oritatami systems and hardness of testing their equivalence

The oritatami system (OS) is a model of computation by cotranscriptional folding, being inspired by the recent experimental success of RNA origami to self-assemble an RNA tile cotranscriptionally. The OSs implemented so far, including the binary counter and Turing machine simulator, are deterministic, that is, uniquely fold into one conformation, while nondeterminism is intrinsic in biomolecular folding. We introduce nondeterminism to the OS and propose a nondeterministic OS (NOS) that chooses an assignment of Boolean values nondeterministically and evaluates a logical formula on the assignment. This NOS is seedless in the sense that it does not require any initial conformation like the RNA origami. The NOS enables proving the coNP-hardness of deciding, given two NOSs, if there exists no conformation that one of them folds but the other does not.

A CA model for target tracking in distributed mobile wireless sensor network

We present a cellular automaton model that efficiently tracks a target in distributed mobile wireless sensor network. We focus on simulating the mobile wireless sensor networks for tracking a moving target considering energy-efficiency. Using the mobility of sensors, we first disperse sensors as far as possible for the better coverage while preserving connectivity. Furthermore, we introduce a tri-level alert system for activating sensors selectively. We conduct experiments for evaluating the performance of the proposed model. The performance of our model is measured in terms of lifetime, coverage and tracking quality, and compared with other models.

Construction of Geometric Structure by Oritatami System

Self-assembly is the process where smaller components autonomously assemble to form a larger and more complex structure. One of the application areas of self-assembly is engineering and production of complicated nanostructures. Recently, researchers proposed a new folding model called the oritatami model (OM) that simulates the cotranscriptional self-assembly, based on the kinetics on the final shape of folded molecules. Nanostructures in oritatami system (OS) are represented by a sequence of beads and interactions on the lattice. We propose a method to design a general OS, which we call GEOS, that constructs a given geometric structure. The main idea is to design small modular OSs, which we call hinges, for every possible pair of adjacent points in the target structure. Once a shape filling curve for the target structure is ready, we construct an appropriate primary structure that follows the curve by a sequence of hinges. We establish generalized guidelines on designing a GEOS, and propose two GEOSs.

Frequent Pattern Mining with Non-overlapping Inversions

Frequent pattern mining is widely used in bioinformatics since frequent patterns in bio sequences often correspond to residues conserved during evolution. In bio sequence analysis, non-overlapping inversions are well-studied because of their practical properties for local sequence comparisons. We consider the problem of finding frequent patterns in a bio sequence with respect to non-overlapping inversions, and design efficient algorithms.