Browsing by Subject "Integrated circuits"

Now showing 1 - 7 of 7

Open Access
Access pattern-based code compression for memory-constrained systems
(Association for Computing Machinery, 2008-09) Ozturk, O.; Kandemir, M.; Chen, G.
As compared to a large spectrum of performance optimizations, relatively less effort has been dedicated to optimize other aspects of embedded applications such as memory space requirements, power, real-time predictability, and reliability. In particular, many modern embedded systems operate under tight memory space constraints. One way of addressing this constraint is to compress executable code and data as much as possible. While researchers on code compression have studied efficient hardware and software based code compression strategies, many of these techniques do not take application behavior into account; that is, the same compression/decompression strategy is used irrespective of the application being optimized. This article presents an application-sensitive code compression strategy based on control flow graph (CFG) representation of the embedded program. The idea is to start with a memory image wherein all basic blocks of the application are compressed, and decompress only the blocks that are predicted to be needed in the near future. When the current access to a basic block is over, our approach also decides the point at which the block could be compressed. We propose and evaluate several compression and decompression strategies that try to reduce memory requirements without excessively increasing the original instruction cycle counts. Some of our strategies make use of profile data, whereas others are fully automatic. Our experimental evaluation using seven applications from the MediaBench suite and three large embedded applications reveals that the proposed code compression strategy is very successful in practice. Our results also indicate that working at a basic block granularity, as opposed to a procedure granularity, is important for maximizing memory space savings. © 2008 ACM.
Open Access
Band Structure and Optical Properties of Kesterite Type Compounds: First principle calculations
(Institute of Physics Publishing, 2017) Palaz S.; Unver H.; Ugur G.; Mamedov, Amirullah; Özbay, Ekmel
In present work, our research is mainly focused on the electronic structures, optical and magnetic properties of Cu2FeSnZ4 (Z = S, Se) compounds by using ab initio calculations within the generalized gradient approximation (GGA). The calculations are performed by using the Vienna ab-initio simulation package (VASP) based on the density functional theory. The band structure of the Cu2FeSnZ4 ( Z = S, Se) compounds for majority spin (spin-up) and minority spin (spin-down) were calculated. It is seen that for these compounds, the majority spin states cross the Fermi level and thus have the metallic character, while the minority spin states open the band gaps around the Fermi level and thus have the narrow-band semiconducting nature. For better understanding of the electronic states, the total and partial density of states were calculated, too. The real and imaginary parts of dielectric functions and hence the optical functions such as energy-loss function, the effective number of valance electrons and the effective optical dielectric constant for Cu2FeSnZ4 (Z = S, Se) compounds were also calculated. © Published under licence by IOP Publishing Ltd.
Open Access
Electro-optic modulation of InAs quantum dot waveguides
(Technische Universiteit Eindhoven, 2008) Akça, İmran. B.; Dâna, Aykutlu; Aydınlı, Atilla; Rossetti, M.; Li, L.; Fiore, A.; Dağlı, N.
The linear electro-optic properties in waveguides containing self-organized In As quantum dots were studied experimentally. Fabry-Perot measurements at 1515 nm on InAs/GaAs quantum dot structures yield a significantly enhanced linear electro-optic efficiency compared to bulk GaAs.
Open Access
Inductorless realisation of Chua oscillator
(IET, 1995) Morgül, Ö.
An inductorless realisation of a Chua oscillator, which exhibits chaotic behaviour is presented. This new realisation consists of the Wien bridge oscillator, coupled in parallel with the same nonlinear resistor used in the standard realisation of a Chua oscillator. This new circuit is shown experimentally to also exhibit similar chaotic behaviour.
Open Access
Integrated microfluidic systems for droplet detection and sorting
(2015-09) İşgör, Pelin Kübra
Microdroplet based microfluidic systems have gained a lot of attention during the last decades due to enhanced analytical performance, low cost and high-throughput. One of the fundamental requirements of a droplet based system is detection of droplets. Capacitive sensing of droplets have been used for droplet detection, however they lack the required sensitivity for droplet content detection. Here a portable, low cost, scalable and highly sensitive droplet content detection system is demonstrated using coplanar electrodes. The designed microfluidic system enables droplet content modification on the run. While changing droplet content, i.e., dielectric content, capacitive signal amplitude is measured. The system resolves 3 unit of dielectric permittivity. 5% material change in droplet is detected. Following droplet content detection, sorting of laden droplets enables further experimentation with material of interest in the droplet. Dielectrophoresis is a commonly used method for droplet sorting. Dielectrophoretic sorting of droplets is demonstrated using two dimensional and there dimensional electrodes. Low cost and portable electronic components are integrated with microfluidic devices for droplet content detection and sorting using microfabricated electrodes. The cost and signal to noise ratio of the system are aimed to be decreased by implementing detection and sorting system on a printed circuit board. Sensing and sorting electrodes are fabricated and all of the electronic components are placed on a printed circuit board. Microchannels are reversibly placed over electrodes, therefore the platform becomes reusable. This feature of the system enables various experimentation using microdroplets on the same base platform. This approach will lead to microfluidic systems that are programmable and easy-to-use by means of off-the-shelf and low cost electronic components.
Open Access
SPM management using markov chain based data access prediction
(IEEE, 2008-11) Yemliha, T.; Srikantaiah, S.; Kandemir, M.; Öztürk, Özcan
Leveraging the power of scratchpad memories (SPMs) available in most embedded systems today is crucial to extract maximum performance from application programs. While regular accesses like scalar values and array expressions with affine subscript functions have been tractable for compiler analysis (to be prefetched into SPM), irregular accesses like pointer accesses and indexed array accesses have not been easily amenable for compiler analysis. This paper presents an SPM management technique using Markov chain based data access prediction for such irregular accesses. Our approach takes advantage of inherent, but hidden reuse in data accesses made by irregular references. We have implemented our proposed approach using an optimizing compiler. In this paper, we also present a thorough comparison of our different dynamic prediction schemes with other SPM management schemes. SPM management using our approaches produces 12.7% to 28.5% improvements in performance across a range of applications with both regular and irregular access patterns, with an average improvement of 20.8%.
Open Access
Topological Insulators: Electronic Band Structure and Spectroscopy
(Institute of Physics Publishing, 2017) Palaz S.; Koc, H.; Mamedov, Aamirullah M.; Özbay, Ekmel
In this study, we present the results of our ab initio calculation of the elastic constants, density of states, charge density, and Born effective charge tensors for ferroelectric (rhombohedral) and paraelectric phases (cubic) of the narrow band ferroelectrics (GeTe, SnTe) pseudopotentials. The related quantities such as bulk modulus and shear modulus using obtained elastic constants have also been estimated in the present work. The total and partial densities of states corresponding to the band structure of Sn(Ge)Te(S,Se) were calculated. We also calculated the Born effective charge tensor of an atom (for instance, Ge, Sn, Te, etc.), which is defined as the induced polarization of the solid along the main direction by a unit displacement in the perpendicular direction of the sublattice of an atom at the vanishing electric field. © Published under licence by IOP Publishing Ltd.