Browsing by Author "Kaya, K."

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Open Access
Efficient broadcast encryption with user profiles
(Elsevier Inc., 2010-03-15) Ak, M.; Kaya, K.; Onarlıoglu, K.; Selçuk, A. A.
Broadcast encryption (BE) deals with secure transmission of a message to a group Of users such that only an authorized subset of users can decrypt the message. Some of the most effective BE schemes in the literature are the tree-based schemes of complete subtree (CS) and subset difference (SD). The key distribution trees in these schemes are traditionally constructed without considering user preferences In fact these schemes can be made significantly more efficient when user profiles are taken into account In tills paper, we consider this problem and study how to construct the CS and SD trees more efficiently according to user profiles. We first analyze the relationship between the transmission cost and the user profile distribution and prove a number of key results in this aspect. Then we propose several optimization algorithms which can reduce the bandwidth requirement of the CS and SD schemes significantly. This reduction becomes even more significant when a number of free riders can be allowed in the system. (C) 2009 Elsevier Inc All rights reserved.
Open Access
Endovenous laser ablation of great saphenous vein for the treatment of lower extremity: Two years experience
(Turkiye Klinikleri, 2014) Zaim, C.; Kahraman, D.; Koujan, A.; Kaya, K.; Yiğit, L.; Özyurda, Ü.
Objective: Chronic venous insufficiency and varicose veins are very common in the society, and in some clinical cases can lead to serious complications. Especially in the lower extremity superficial venous insufficiency depends more frequently on vena saphena magna, less frequently depending on the vena saphena parva. In the treatment of venous insufficiency, surgical methods was applied previously but nowadays endovenous laser (EVLA) and radiofrequency (RFA) methods are used. Material and Methods: In our study, a total of 207 patients with 220 extremity saphenous veins treated with EVLA [Radial-Emitting Fiber (REF) Advanced Fiber Tools, Germany)] procedure. The entire procedure was performed under doppler ultrasound (General Electric Logiq 500 pro, USA) guided with combination of spinal anestesia and tumescent local anesthesia (Nouvag Dispenser DP20, Switzerland). Before the procedure, all patients the clinical severity, etiology, anatomy, pathophysiology (CEAP) were classified according to the classification. Results: EVLA application of the 220 extremities, all (100%) pathophysiology, was determined depending on reflux. The preoperative diameter of the VSM at the knee level was between 3.8 mm and 6.2 mm (mean 4.6±1.8), while in saphenofemoral junction was found to be between 5.2 mm and 12.4 mm (mean 8.6±2.2). Postoperative diameter of the VSM, especially in the 3rd month of the knee level diameter was 1.7 mm to 3.9 mm (mean 2.2±0.8 p<0.05), in saphenofemoral junction between 2.3 mm to 4.8 mm (mean 3.9±1.8 p<0.05) was changed. As a result of the six-month follow-up of 216 patients (98.6%) showed complete occlusion. There were no major complications was detected but minor complications as cellulite in 6 patients, thrombophlebitis in 8 patients, hematoma in 4 patients and 10 patients paresthesia at knee level demonstrated. Conclusion: EVLA treatment can be performed safely with early mobilization, less pain and lower morbidity rates. Copyright © 2014 by Türkiye Klinikleri.
Open Access
Heuristics for scheduling file-sharing tasks on heterogeneous systems with distributed repositories
(Academic Press, 2007) Kaya, K.; Uçar, B.; Aykanat, Cevdet
We consider the problem of scheduling an application on a computing system consisting of heterogeneous processors and data repositories. The application consists of a large number of file-sharing otherwise independent tasks. The files initially reside on the repositories. The processors and the repositories are connected through a heterogeneous interconnection network. Our aim is to assign the tasks to the processors, to schedule the file transfers from the repositories, and to schedule the executions of tasks on each processor in such a way that the turnaround time is minimized. We propose a heuristic composed of three phases: initial task assignment, task assignment refinement, and execution ordering. We experimentally compare the proposed heuristics with three well-known heuristics on a large number of problem instances. The proposed heuristic runs considerably faster than the existing heuristics and obtains 10-14% better turnaround times than the best of the three existing heuristics. © 2006 Elsevier Inc. All rights reserved.
Open Access
HPC4BD 2015 workshop foreword
(Institute of Electrical and Electronics Engineers Inc., 2015) Kaya, K.; Gedik, B.; Çatalyürek, Ü. V.
Open Access
HPC4BD 2016 workshop foreword and program committee
(Institute of Electrical and Electronics Engineers Inc., 2016) Kaya, K.; Gedik, B.; Çatalyürek, U. V.
Open Access
HPC4BD 2017 workshop foreword and program committee
(Institute of Electrical and Electronics Engineers Inc., 2017) Kaya, K.; Gedik, B.; Çatalyürek, U. V.
Open Access
Iterative-improvement-based heuristics for adaptive scheduling of tasks sharing files on heterogeneous master-slave environments
(Institute of Electrical and Electronics Engineers, 2006) Kaya, K.; Aykanat, Cevdet
The scheduling of independent but file-sharing tasks on heterogeneous master-slave platforms has recently found important applications in Grid environments. The scheduling heuristics recently proposed for this problem are all constructive in nature and based on a common greedy criterion which depends on the momentary completion time values of the tasks. We show that this greedy decision criterion has shortcomings in exploiting the file-sharing interaction among tasks since completion time values are inadequate to extract the global view of this interaction. We propose a three-phase scheduling approach which involves initial task assignment, refinement, and execution ordering phases. For the refinement phase, we model the target application as a hypergraph and, with an elegant hypergraph-partitioning-like formulation, we propose using iterative-improvement-based heuristics for refining the task assignments according to two novel objective functions. Unlike the turnaround time, which is the actual schedule cost, the smoothness of proposed objective functions enables the use of iterative-improvement-based heuristics successfully since their effectiveness and efficiency depend on the smoothness of the objective function. Experimental results on a wide range of synthetically generated heterogeneous master-slave frameworks show that the proposed three-phase scheduling approach performs much better than the greedy constructive approach. © 2006 IEEE.
Open Access
Optimal subset-difference broadcast encryption with free riders
(Elsevier Inc., 2009-09-29) Ak, M.; Kaya, K.; Selçuk, A. A.
Broadcast encryption (BE) deals with secure transmission of a message to a group of receivers such that only an authorized subset of receivers can decrypt the message. The transmission cost of a BE system can be reduced considerably if a limited number of free riders can be tolerated in the system. In this paper, we study the problem of how to optimally place a given number of free riders in a subset-difference (SD)-based BE system, which is currently the most efficient BE scheme in use and has also been incorporated in standards, and we propose a polynomial-time optimal placement algorithm and three more efficient heuristics for this problem. Simulation experiments show that SD-based BE schemes can benefit significantly from the proposed algorithms. © 2009 Elsevier Inc. All rights reserved.
Open Access
Sharing DSS by the Chinese remainder theorem
(2012) Kaya, K.; Selçuk, Ali Aydın
Open Access
Task assignment in heterogeneous computing systems
(Academic Press, 2006-01) Ucar, B.; Aykanat, Cevdet; Kaya, K.; Ikinci, M.
The problem of task assignment in heterogeneous computing systems has been studied for many years with many variations. We consider the version in which communicating tasks are to be assigned to heterogeneous processors with identical communication links to minimize the sum of the total execution and communication costs. Our contributions are three fold: a task clustering method which takes the execution times of the tasks into account; two metrics to determine the order in which tasks are assigned to the processors; a refinement heuristic which improves a given assignment. We use these three methods to obtain a family of task assignment algorithms including multilevel ones that apply clustering and refinement heuristics repeatedly. We have implemented eight existing algorithms to test the proposed methods. Our refinement algorithm improves the solutions of the existing algorithms by up to 15% and the proposed algorithms obtain better solutions than these refined solutions. © 2005 Elsevier Inc. All righs reserved.
Open Access
Threshold cryptography based on Asmuth–Bloom secret sharing
(Elsevier Inc., 2007-10-01) Kaya, K.; Selçuk, A. A.
In this paper, we investigate how threshold cryptography can be conducted with the Asmuth-Bloom secret sharing scheme and present three novel function sharing schemes for RSA, ElGamal and Paillier cryptosysterns. To the best of our knowledge, these are the first provably secure threshold cryptosystems realized using the Asmuth-Bloom secret sharing. Proposed schemes are comparable in performance to earlier proposals in threshold cryptography. (c) 2007 Elsevier Inc. All rights reserved.