Jong Kwan Lee

Oriented connectivity-based method for segmenting solar loops

A method based on oriented connectivity that can automatically segment arc-like structures (solar loops) from intensity images of the Suns corona is introduced. The method is a constructive approach that uses model-guided processing to enable extraction of credible loop structures. Since the solar loops are vestiges of the solar magnetic field, the model-guided processing exploits external estimates of this fields local orientations that are derived from a physical magnetic field model. Empirical studies of the methods effectiveness are also presented. The oriented connectivity-based method is the first automatic method for the segmentation of solar loops.

Cloudlet Scheduling with Particle Swarm Optimization

Cloud computing is a particularly interesting and truly complex concept of providing services over networks on demand. Many tools have previously been created to simulate the work of the clouds, such as CloudSim. The main use of these tools is evaluation and testing of architectures and services before deployment on network centers and hosts in order to avoid any potential failures or inconveniences. The benefits of using the pay-per-use clouds may be affected by underutilization of the already reserved resources, so the maximization of system utilization while simultaneously minimizing makespan is of great interest to cloud providers wishing to reduce costs. To minimize makespan and increase resource utilization, a hybrid of particle swarm optimization and simulated annealing is implemented inside of CloudSim to advance the work of the already implemented simple broker. The new method maximizes the resource utilization and minimizes the makespan.

Very fast ellipse detection using GPU-based RHT

An approach to very rapid computation of one class of randomized Hough transform (RHT) using parallel processing capabilities of a programmable graphics processing unit is described. The method is able to detect ellipses in real-time, even in large images. It uses fragment processing in recovering ellipse shape parameters. Its effectiveness is evaluated through experiments on synthetic and real images.

Automated detection of solar loops by the oriented connectivity method

An automated technique to segment solar coronal loops from intensity images of the suns corona is introduced. It exploits physical characteristics of the solar magnetic field to enable robust extraction from noisy images. The technique is a constructive curve detection approach, constrained by collections of estimates of the magnetic fields orientation. Its effectiveness is evaluated through experiments on synthetic and real coronal images.

Acceleration of opacity correction mechanisms for over-sampled volume ray casting

Techniques for accelerated opacity correction for over-sampled volume ray casting on commodity hardware are described. The techniques exploit processing capabilities of programmable GPUs and cluster computers. The GPU-based technique follows a fine-grained parallel approach that exposes to the GPU the inherent parallelism in the opacity correction process. The cluster computation techniques follow less finely-granular data parallel approaches that allow exploitation of computational resources with minimal inter-CPU communication. The performance improvements offered by the accelerated approaches over opacity correction on a single CPU are also exhibited for real volumetric datasets.

On accuracy of marching isosurfacing methods

Representational accuracy of the isosurface meshes produced by well-known marching isosurfacing methods is considered. Accuracy is determined versus the isosurface given by trilinear interpolation and quantified using a new measure of volumetric divergence. The new measure is an accurate estimate of spatial discrepancy between a produced mesh and the isosurface of trilinear interpolation. Through experimental testing using the measure, suitability of the considered methods to well-model the isosurface of trilinear interpolations behavior on grid cell interiors is also established.

Dynamic Aperture-based Solar Loop Segmentation

A new method to automatically segment arc-like loop structures from intensity images of the Suns corona is introduced. The method constructively segments credible loop structures by exploiting the Gaussian-like shape of loop cross-sectional intensity profiles. The experimental results show that the method reasonably segments most of the well-defined loops in coronal images. The method is only the second published automated solar loop segmentation method. Its advantage over the other published method is that it operates independently of supplemental time specific data

An Improved Algorithm for Querying Encrypted Data in the Cloud

Organizations have begun outsourcing management of their data to third party cloud service providers after the introduction of Database as a Service (DAS) model. A cloud database is a database that typically runs on a cloud computing platform, such as Amazon EC2, GoGrid, Salesforce and Rackspace. But outsourcing the data raises concerns over privacy. A typical solution is to store databases in encrypted form on the remote server. Queried records are downloaded from the server and decrypted for further processing. Bucketization is one technique for executing queries over encrypted data on a DAS server. This paper is an extension to work done by other researchers [1-4]. Query Optimal Bucketization (QOB) algorithm [1-2] divides the server data into buckets subject to an optimality constraint. In an earlier paper [3], the authors proposed Binary Query Bucketization (BQB) to improve the search time for bucketized datasets and reduce the number of records that are processed by QOB. In this paper, we propose a Parallel Binary Query Bucketization (PBQB) algorithm to query records located in the DAS. It integrates parallel search [4] and BQB. Parallel search divides the search workload into chunks with each thread/processor working on a chunk. Simulation is used to assess the numerical performance of PBQB. It is shown that the proposed algorithm outperforms BQB.

On Privacy Preserving Encrypted Data Stores

Bucketization techniques allow for effective organization of encrypted data at untrusted servers and for querying by clients. This paper presents a new metric for estimating the risk of data exposure over a set of bucketized data. The metric accounts for the importance of bucket distinctness relative to bucket access. Additionally, we review a method of controlled diffusion which improves bucket security by maximizing entropy and variance. In conjunction with our metric we use this method to show that the advantages of bucketization may be offset due to a loss of bucket security.

Coronal Loop Mapping to Infer the Best Magnetic Field Models for Active Region Prominences

This article comments on the results of a new, rapid, and flexible manual method to map on-disk individual coronal loops of a two-dimensional EUV image into a three-dimensional coronal loop. The method by Gary, Hu, and Lee (2013) employs cubic Bezier splines to map coronal loops using only four free parameters per loop. A set of 2D splines for coronal loops is transformed to the best 3D magnetic fields for a particular coronal model. The results restrict the magnetic field models derived from extrapolations of magnetograms to those admissible and inadmissible via a fitness parameter. This method uses the minimization of the misalignment angles between the magnetic field model and the best set of 3D field lines that match a set of closed coronal loops. We comment on the implication of the fitness parameter in connection with the magnetic free energy and comment on extensions of our earlier work by considering the issues of employing open coronal loops or employing partial coronal loop. .