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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only Chaos in rotating triatomic clusters(Editions Physique, 1997) Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129Lyapunov exponent distributions of rotating triatomic Lennard-Jones clusters are calculated to analyze the effects of the vibrational and rotational motion on the extent of chaotic behavior. Initial momentum components are assigned to atoms either to rotate the clusters around symmetry axes or to generate random angular momenta. In both cases, it is seen that the initial kinetic energy assigned to vibrational modes is the dominant factor which determines the degree of chaos.Publication Metadata only Efficient continuous-wave radiatively cooled Cr4+: forsterite lasers at room temperature(Optical Soc Amer, 1998) Department of Physics; Sennaroğlu, Alphan; Faculty Member; Department of Physics; College of Sciences; 23851Results of a detailed experimental investigation aimed at reducing the thermal loading problem in a cw Cr4+:forsterite laser at elevated temperatures are presented. From a Cr4+:forsterite crystal with a differential absorption coefficient of 0.57 cm(-1), as much as 900 mW of cw output power has been obtained at 1.26 mu m and at a crystal boundary temperature of 15 degrees C with an absorbed pump power of only 4.5 W at 1.06 mu m. No chopping of the the pump beam was necessary. An efficient radiative cooling technique was further employed to cool the laser and no subsequent power fading was observed. To the author's knowledge, the measured absorbed power slope efficiency of 29.5% represents the highest cw power performance reported to date: from a Cr4+:forsterite laser pumped by a Nd:YAG laser around room temperature. The role of the low differential absorption coefficient in the reduction of thermal loading is further elucidated by presenting comparative cw power performance data with a second Cr4+:forsterite crystal having a differential absorption coefficient of 1.78 cm(-1) in the temperature range between 12 and 35 degrees C. Finally, some interesting multipulse effects of the laser observed in the millisecond regime during quasi-cw operation at 50% duty cycle are described.Publication Metadata only Interior energy focusing within an elasto-plastic material(Pergamon-Elsevier Science Ltd, 1996) Tadi, M; Rabitz, H; Kim, YS; Prevost, JH; McManus, JB; Department of Mathematics; Aşkar, Attila; Faculty Member; Department of Mathematics; College of Sciences; 178822In this paper we consider the problem of focusing acoustic energy within a subsurface volume in a solid by means of a designed surface pattern, and ask how that focusing is affected by plastic yield of the material. Surface force patterns that yield efficient subsurface acoustic focusing have been designed using optimal control theory, based on a linear elastic model of a solid. The acoustic waves generated by these forces then are propagated, via numerical algorithms, in a model solid that exhibits plastic yield. Numerical results indicate that as the amplitude of the force increases, yield begins to develop at the focus, with the formation of an expanding region of permanent plastic deformation. Despite the occurrence of yield near the focus, acoustic energy still can be delivered to the focal volume with good efficiency.Publication Metadata only Overtime scheduling: an application in finite-capacity real-time scheduling(Taylor & Francis, 1996) Department of Business Administration; Akkan, Can; Faculty Member; Department of Business Administration; College of Administrative Sciences and Economics; N/ANegotiating and meeting due-times for work-orders is often the most important concern of managers of manufacturing systems. We propose a new approach called overtime scheduling that determines on which work-centres, when and how much overtime is required to meet a requested due-time with minimum overtime cost. This method would be used as a part of a finite-capacity real-time scheduling and planning system. We propose a work-order insertion based approach, where a new work-order is scheduled without substantially changing the schedule of previously scheduled work-orders. Based on this approach, we characterise the solution space and present experimental results on the performances of several heuristics.Publication Metadata only Efficient continuous-wave operation of a diode-pumped Nd:YVO4 laser at 1342 nm(Elsevier Science Bv, 1999) Department of Physics; Sennaroğlu, Alphan; Faculty Member; Department of Physics; College of Sciences; 23851The experimental study described in this paper investigates the continuous-wave power performance of an efficient diode-pumped Nd:YVO4 laser at 1342 nm by employing four different end pumping configurations. When pumped by a high-power fiber-coupled diode array at 806 nm, the compact resonator consisting of a 9.25-mm long Nd:YVO4 crystal and a 3.6% transmitting output coupler produced as high as 3550 mW of output power. The absorbed power slope efficiency was measured to be 28.1%. By using the experimentally measured threshold data, the stimulated emission cross-section of the gain medium was determined to be 13 X 10(-19) cm(2) at 1342 nm. Above absorbed pump powers of 11 W, strong thermal loading caused saturation of the output power and the focal length of the induced thermal lens was measured as a function of the pump power. Results further showed that the laser output was insensitive to variations in the crystal boundary temperature between 20 degrees C and 40 degrees C.Publication Metadata only Regionalism, nationalism and realpolitik in Central Asia(Carfax Publ Co, 1997) N/A; Department of International Relations; Kubicek, Paul J.; Faculty Member; Department of International Relations; College of Administrative Sciences and Economics; N/AN/APublication Metadata only The political economy of structural adjustment in Tunisia and Algeria(Taylor and Francis, 1998) Department of International Relations; Dillman, Bradford L.; Faculty Member; Department of International Relations; College of Administrative Sciences and EconomicsThis analysis of the economic reform programmes launched in Tunisia and Algeria from the late 1980s seeks to account for their divergent outcomes, namely that the Tunisian exercise has met with a large measure of success, whereas Algerian efforts have not. Attention is focused on international factors, economic institutions and domestic political dynamics. Briefly stated, four factors appear to have had a major influence on the relative success of economic reform: (1) the nature of ties to international financial markets; (2) the timing and sequence of economic reforms; (3) the nature of the state reform coalition; and (4) the nature of organised political opposition.Publication Metadata only Agile manufacturing and management of variability(Wiley-Blackwell, 1998) Department of Business Administration; Tan, Barış; Faculty Member; Department of Business Administration; College of Administrative Sciences and Economics; 28600In this study, the relationship between agile manufacturing and management of variability is discussed. First, the key concepts of agility and agile manufacturing are introduced. These key concepts are then related to the management of variability. Previous studies on the modeling of variability of manufacturing systems are reviewed. Then the effects of variability of the structure of the production system, and also the processing time variability on the performance of a manufacturing system are studied by utilizing a simple model of a synchronous production line with identical stations and random processing times. Numerical results that examine the effects of the coefficient of variation of service time and the number of stations on the variability of the cycle time are also given.Publication Metadata only Time-series properties, adjustment processes, and forecasting of financial ratios(Sage, 1996) Eckstein, Claire; Greene, William H.; Ronen, Joshua; Department of Economics; Aksu, Celal; Faculty Member; Department of Economics; College of Administrative Sciences and Economics; N/AN/APublication Metadata only A theoretical study of structural defects in conjugated polymers(Elsevier Science Sa, 1999) Yurtsever, Mine; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129Accurate ab-initio calculations are performed for pyrrole and thiophene oligomers bonded through alpha and beta carbons. The thermodynamical stabilitiy of all possible binding types including the branched forms of tetramers and pentamers are compared. Employing the probabilities obtained from these calculations, a Monte Carlo type growth scheme is applied to predict branching as functions of the chain length and temperature. A high degree of branching for polypyrrole is reported whereas the linear chains dominate the structure of polythiophene.