Self-powered piezoelectric energy harvester for bicycle

Dejan Vasic,Yu-Yin Chen,François Costa 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.7

Various electronic accessories, such as on-board computers, communication devices, and wireless sensor nodes, have been installed onbicycles for several years. A powering scheme from ambient energy could avoid the use of batteries and improve the availability of thesedevices even when the bicycle is unused for a long time. This paper reports on vibration resources detected in a bicycle as a potentialenergy source for supplying these on-board devices. Measurements showed that the bandwidth of energy vibration is reduced with speedand that the vibrations at any location in the bicycle are nevertheless sufficient for useful vibration harvesting. For this application, a piezoelectricvibration harvester was designed and equipped with a voltage switching interface circuit. Sufficient energy is harvested duringthe field test.

Dielectric relaxation in nanopillar NiFe-silicon structures in high magnetic fields

R. Vasic,J.S. Brooks,E. Jobiliong,S. Aravamudhan,K. Luongo,S. Bhansali 한국물리학회 2007 Current Applied Physics Vol.7 No.1

We explore the dielectric relaxation properties of NiFe nanowires in a nanoporous silicon template. Dielectric data of the NiFesil-icon structure show a strong relaxation resonance near 30 K. This system shows Arrhenius type of behavior in the temperature depen-in the dielectric spectrum related to multiple relaxation rates. A magnetic eld aects both the exponential prefactor in the Arrheniusformula and the activation energy. From this eld dependence we derive a simple exponential eld dependence for the prefactor andlinear eld approximation for the activation energy which describes the data. We nd a signicant angular dependence of the dielectricrelaxation spectrum for regular silicon and nanostructured silicon vs. magnetic eld direction, and describe a simple sum rule thatNiFesilicon shows a more complex, magnetic eld dependent relaxation spectrum.

Lightweight and adaptable solution for security agility

( Valter Vasic ),( Miljenko Mikuc ),( Marin Vukovic ) 한국인터넷정보학회 2016 KSII Transactions on Internet and Information Syst Vol.10 No.3

Secure communication is an important aspect of today`s interconnected environments and it can be achieved by the use of cryptographic algorithms and protocols. However, many existing cryptographic mechanisms are tightly integrated into communication protocols. Issues emerge when security vulnerabilities are discovered in cryptographic mechanisms because their replacement would eventually require replacing deployed protocols. The concept of cryptographic agility is the solution to these issues because it allows dynamic switching of cryptographic algorithms and keys prior to and during the communication. Most of today`s secure protocols implement cryptographic agility (IPsec, SSL/TLS, SSH), but cryptographic agility mechanisms cannot be used in a standalone manner. In order to deal with the aforementioned limitations, we propose a lightweight cryptographically agile agreement model, which is formally verified. We also present a solution in the Agile Cryptographic Agreement Protocol (ACAP) that can be adapted on various network layers, architectures and devices. The proposed solution is able to provide existing and new communication protocols with secure communication prerequisites in a straightforward way without adding substantial communication overhead. Furthermore, it can be used between previously unknown parties in an opportunistic environment. The proposed model is formally verified, followed by a comprehensive discussion about security considerations. A prototype implementation of the proposed model is demonstrated and evaluated.

Semi-passive piezoelectric structural damping based on a pulse-width modulation switching circuit

Yuan-Ping Liu,Dejan Vasic 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.12

Studies in the past focused on the implementation of semi-passive damping techniques that could significantly reduce structural vibration. Recently, the performances of these damping techniques have been enhanced by artificially increasing the voltage amplitude delivered by the piezoelectric patches with an external voltage source. To maintain the stability of this damping method, an adaptive voltage source must be used. To satisfy this requirement, this study proposes an enhanced semi-passive damping technique based on pulse-width modulation. The proposed method allows the waveform of the piezoelectric voltage to adapt to the vibration velocity. Thus, this method can maintain its stability with a constant voltage source and simultaneously exhibit superior performance. This study consists of a theoretical part and an experimental proof-of-concept demonstration of the proposed damping technique.

Transport and melt processing in functionalized pentacene with "organic wire" connections

J.S.Brooks,R.Vasic,T.Tokumoto,D.Graf,O.H.Chung,J.E.Anthony,S.A.Odom 한국물리학회 2004 Current Applied Physics Vol.4 No.5

We explore melt processing of functionalized pentacene for use in electronic and photonic devices. In parallel, the use of carbonbers to make electrical contact to the melt-lms is described. We discuss the morphology of the melted lms which includes theappearance of dendritic growth, carbon ber contacts to the lms, and the temperature dependence of the carbon, PEDOT, andpentacene components of the various structures.

Coexistence of Internal Carotid Artery Stenosis in Patients with Abdominal Aortic Aneurysm

Milica Vranes,Lazer Davidovic,Dragan Vasic,Oliver Radmili 대한심장학회 2013 Korean Circulation Journal Vol.43 No.8

Background and Objectives: Abdominal Aortic Aneurysm (AAA) and carotid disease have medical and social significance, considering their morbidity, disability, and economic consequences. The study objectives were to determine the prevalence of asymptomatic internal carotid artery (ICA) lesions ≥70% in patients with AAA, the correlation of AAA diameter with the degree of ICA stenosis and symptoms,and the importance of preventive ultrasound checkups. Subjects and Methods: A prospective non-randomized controlled study including 740 patients, aged from 18-85 years, who were suit-able for the inclusion and exclusion criteria and reported at the vascular laboratory of the Institute for Vascular and Endovascular Surgery,Clinical Center of Serbia from 1st of December 2011 to the 1st of November 2012. Results: The prevalence of asymptomatic ICA stenosis ≥70% in patients with AAA is 10.8%. Male representatives have more symptomat-ic ICA stenosis ≥70%. Patients with small aneurysms more often have asymptomatic ICA stenosis ≥70%. The occurrence of symptoms of carotid disease was more prevalent among patients with ICA stenosis ≥70% compared to the group with stenosis <70%. There was no correlation found between the grade of ICA stenosis with the size of AAA. Conclusion: The prevalence of asymptomatic ICA stenosis ≥70% in patients with AAA is found to be 10.8%. Male patients with ICA steno-sis ≥70% more often had symptoms of carotid disease. In the smaller aneurysms, ICA stenosis ≥70% occurs frequently, but without the symptoms of carotid disease, and there was no correlation between the size of AAA and the grade of ICA stenosis. Clinical implications of ICA imaging in patients with previously diagnosed AAA is necessary.

The investigation of transport properties of mesoscopic graphite in high magnetic field

E. Jobiliong,J.G. Park,J.S. Brooks,R. Vasic 한국물리학회 2007 Current Applied Physics Vol.7 No.4

structures made from Kish graphite exhibit Shubnikov-de Haas (SdH) oscillations in magnetic elds up to 33 T, with a strong gate volt-age dependence. A two band model can be used to explain the linear dependence of the SdH frequency on the gate voltage. The tem-perature dependence of the SdH oscillation amplitude allows the determination of the eective masses of the carriers, which remaincomparable between mesoscopic and bulk graphite samples. However, mesoscopic graphite thinner than 130 nm does not exhibit the field induced charge density wave transition seen in bulk samples above 25 T at low temperatures.

Growth of small organic molecules on 2D materials

Christian TEICHERT,Markus KRATZER,Benjamin KAUFMANN,Jakob GENSER,Aleksandar MATKOVIC,J. Marcelo J. LOPES,Henning RIECHERT,Bernhard BAYER,Boris VASIC,Rados GAJIC 한국진공학회 2016 한국진공학회 학술발표회초록집 Vol.2016 No.8

Three-Dimensional Microstructural Modelling of Wear, Crack Initiation and Growth in Rail Steel

Fletcher, D.I.,Franklin, F.J.,Garnham, J.E.,Muyupa, E.,Papaelias, M.,Davis, C.L.,Kapoor, A.,Widiyarta, M.,Vasic, G. The Korean Society for Railway 2008 International Journal of Railway Vol.1 No.3

Rolling-sliding, cyclic contact of wheel and rail progressively alters the microstructure of the contacting steels, eventually leading to micro-scale crack initiation, wear and macro-scale crack growth in the railhead. Relating the microstructural changes to subsequent wear and cracking is being accomplished through modelling at three spatial scales: (i) bulk material (ii) multi-grain and (iii) sub-grain. The models incorporate detailed information from metallurgical examinations of used rails and tested rail material. The initial 2-dimensional models representing the rail material are being further developed into 3-dimensional models. Modelling is taking account of thermal effects, and traffic patterns to which the rails are exposed.