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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only Thalamic neuronal activity correlated with essential tremor(British Med Journal Publ Group, 1998) Hua, S.E.; Lenz, F.A.; Reich, S.G.; Dougherty, P.M.; N/A; Zırh, Tahsin Ali; Doctor; N/A; N/AAnimal studies suggest that an olivocerebello-bulbospinal pathway mediates harmaline induced tremor, which resembles essential tremor in humans. However, recent evidence suggests that thalamocortical pathways participate in essential tremor. Thalamic single neuron activity has been analysed during thalamotomy for essential tremor. It has been shown by spectral cross correlation analysis that thalamic activity has a significant, linear relation to forearm EMG activity during tremor. The presence of this tremor related activity at the site where a lesion abolishes essential tremor suggests that the thalamus has an important role in the mechanism of essential tremor.Publication Metadata only Stratified partial likelihood estimation(Elsevier, 1999) Ridder, Gert; Department of Economics; Tunalı, Fehmi İnsan; Faculty Member; Department of Economics; College of Administrative Sciences and Economics; 105635When multiple durations are generated by a single unit, they may be related in a way that is not fully captured by the regressors. The omitted unit-specific variables might vary over the durations, They might also be correlated with the variables in the regression component. We propose an estimator that responds to these concerns and develop a specification test for detecting unobserved unit-specific effects, Data from Malaysia reveal that concentration of child mortality in some families is imperfectly explained by observed explanatory variables, and that failure to control for unobserved heterogeneity seriously biases the parameter estimates.Publication Metadata only Efficient continuous-wave operation of a radiatively cooled CR4+: forsterite laser at room temperature(Optical Society of America, 1997) Department of Physics; Department of Physics; Sennaroğlu, Alphan; Kurt, Adnan; Faculty Member; Teaching Faculty; Department of Physics; College of Sciences; College of Sciences; 23851; 194455Results of a detailed experimental investigation aimed at reducing the thermal loading problem in a cw Cr(4+):forsterite laser at elevated temperatures are presented. From a Cr(4+):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 mum and at a crystal boundary temperature of 15 degrees C with an absorbed pump power of only 4.5 W at 1.06 mum. No chopping of 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 Cr(4+):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 Cr(4+):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 Femtosecond optical parametric oscillator based on periodically poled KTiOPO(4)(1998) Kartaloğlu, Tolga; Köprülü, Kahraman G; Aytur, Orhan; Risk, William; Department of Physics; Sundheimer, Michael; Faculty Member; Department of Physics; College of Sciences; N/AWe report a femtosecond optical parametric oscillator based on a periodically poled KTiOPO4 crystal for which quasi-phase matching is achieved with a 24−µm poling period. The singly resonant parametric oscillator, synchronously pumped by a Ti:sapphire laser at a wavelength of 758 nm, generates a signal at 1200 nm and an idler at 2060 nm. The maximum signal power conversion efficiency of the device is 22% with a pump depletion of 69%. We tune the signal wavelength over a 200-nm band by changing the cavity length. In addition, pump wavelength tuning provides output tunability in the 1000–1235-nm range.Publication Metadata only The sensitivity of conformational free energies of the alanine dipeptide to atomic site charges(Wiley, 1997) Maye, Peter V.; Mezei, Mihaly; Department of Physics; Reşat, Haluk; Faculty Member; Department of Physics; College of Sciences; N/ADifferent atomic point charge sets are obtained for the are and C7,eq conformations of the alanine dipeptide by fitting the charges of each conformation to the respective ab initio electrostatic potential surfaces both individually and simultaneously, in both the united atom and the all-atom representations. Using these charge sets, the sensitivity of the relative conformational aqueous free energies to the atomic site charges is investigated. For this particular system, we find that the solute-water contributions to the conformational free energy differences have a rather weak dependence on site charges; the calculated intramolecular contributions, however, show a rather strong dependence on the atomic site charges. It is suggested that the calculated results for the alanine dipeptide using a single, simultaneously fit set of charges for both conformations are in better agreement with experiments than the calculations carried out with charges determined individually for each conformation. © 1997 John Wiley & Sons, Inc.Publication Metadata only Experimental determination of fractional thermal loading in an operating diode-pumped nd:yvo4 minilaser at 1064 nm(Optica Publishing Group, 1999) Department of Physics; Sennaroğlu, Alphan; Faculty Member; Department of Physics; College of Sciences; 23851A practical in, situ method is described and used for determination of the fractional thermal-loading parameter eta(h) in an operating diode-pumped Nd:YVO4 minilaser at 1064 nm. Readily applicable to the thermal characterization of other solid-state media, the method is based on the fact that thermally induced lensing will cause the laser oscillation to be quenched at a critical pump power whose magnitude depends on the cavity configuration, thermo-optical properties of the gain medium, and, in particular, on the value of eta(h). In the experiments described here, a 0.5-mm-long coated Nd:YVO4 crystal with 3-at. % Nd concentration was used to construct the diode-pumped laser with a flat highly reflecting end mirror and an intracavity lens. For the method to be effective, the resonator was set up close to the edge of the stability range. Above the oscillation threshold, the pump power at which lasing was quenched because of the onset of the thermally induced resonator instability was measured as a function of the intracavity lens position. A numerical model that accounted for absorption saturation and pump-induced thermal lensing was then used to analyze the experimentally measured data with eta(h) as an adjustable parameter. The average best-fit value of eta(h) was determined to be 0.40 with an estimated statistical variation of 8%.Publication Metadata only Determination of the optimum absorption coefficient in Cr4+: forsterite lasers under thermal loading(Optical Soc Amer, 1998) Department of Physics; Department of Physics; Sennaroğlu, Alphan; Pekerten, Barış; Faculty Member; Undergraduated Student; Department of Physics; College of Sciences; College of Sciences; 23851; N/AWe present the results of a novel experimental and numerical investigation aimed at minimizing thermal loading effects in room-temperature Cr4+:forsterite lasers. In the model we numerically calculated the incident primp power required for oscillation threshold to be attained by taking into account pump absorption saturation, pump-induced thermal gradients inside the crystal, and the temperature dependence of the upper-state fluorescence lifetime. Excellent agreement was obtained between model predictions and experimental threshold data. We then used the model to calculate the optimum absorption coefficient that minimizes the incident threshold pump power. At a crystal boundary temperature of 15 degrees C the optimum value of the absorption coefficient was numerically determined to be 0.64 cm(-1). Such optimization studies, which are readily applicable to other laser systems, should make a significant contribution to the improvement of the power performance of Cr4+:forsterite lasers at room temperature.Publication Metadata only Enzyme-inhibitor association thermodynamics: explicit and continuum solvent studies(Cell Press, 1997) Marrone, Tami; McCammon, James Andrew; Department of Physics; Reşat, Haluk; Faculty Member; Department of Physics; College of Sciences; N/APublication Metadata only Continuous-wave power transmission and thermal lensing of a saturable absorber subject to excited-state absorption(Optical Soc Amer, 1999) Department of Physics; Sennaroğlu, Alphan; Faculty Member; Department of Physics; College of Sciences; 23851Rate-equation analysis has been used in an investigation of the role of saturation and excited-state absorption in the power transmission characteristics and thermal lensing of an absorber. Use of an iterative approach gives explicit analytical results for power transmission and thermal focal length in the presence of excited-state absorption. Sample calculations indicate that pump absorption can increase or decrease with increasing incident pump power, depending on the relative strength of the excited-state absorption cross section with respect to the ground-state absorption cross section. In the case of thermal lensing, results further indicate that saturation and excited-state absorption act as two competing effects, the former reducing the strength of the thermal lens and the latter causing the opposite effect. The analytical was derived in this analysis should prove useful to experimentalists in determination of ground-state and excited-state absorption cross sections from experimental power transmission and lensing data.Publication Metadata only Determination of the optimum absorption coefficient in Cr4+: forsterite lasers under thermal loading: errata(Optical Soc Amer, 1999) Department of Physics; Department of Physics; Sennaroğlu, Alphan; Pekerten, Barış; Faculty Member; Undergraduated Student; Department of Physics; College of Sciences; College of Sciences; 23851; N/AIn our recent Letter,[1] in which we analyzed the effects of thermal loading in room-temperature Cr4+:forsterite lasers, a scaling error was made in the best-fit and optimization calculations. In the comparison of theory with experiment (Fig. 2), the correct best-fit value of the stimulated-emission cross section 𝜎𝑒 should have been 0.98×10−19 cm2. In addition, the correct optimum value of the small-signal absorption coefficient that minimizes the incident threshold pump power (see Fig. 3) should have been 0.34 cm−1, corresponding to a net unsaturated pump absorption of 49% for a 2-cm-long crystal. The corrections did not affect any of the trends predicted by the theory.