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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 7486-7493 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Raman noncoincidence effect and line width of the symmetric C(large-closed-square)O stretching band have been measured in liquid propylene carbonate (PC), chloroethylene carbonate (CC), and dichloroethylene carbonate (DC) as a function of pressure up to 3 kbar and over the temperature range from −20 °C to 40 °C. The transition dipole moments of the C(large-closed-square)O mode for these liquids have also been determined by means of infrared spectroscopy at ambient conditions. The temperature, density, and transition dipole moment dependences of the experimental noncoincidence effect for these liquids are quantitatively interpreted in terms of Logan theory. An excellent agreement between the experimental results and theoretical predictions indicates that the observed noncoincidence effect is due to the transition dipole moment coupling and permanent dipole moment coupling. For the study of isotropic bandwidths, the band narrowing with increasing density is found for liquid CC and DC and quantitatively explained by means of intermolecular interactions, whereas band broadening is observed for PC. The latter broadening is unexpected since PC possesses the largest permanent dipole moment of these three liquids. A probable reason for difficulty in the interpretation of this result is given.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 9324-9334 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The production of acoustic waves by the absorption of radiation, known as the photoacoustic effect, is described by two coupled differential equations for pressure and temperature. Here, solutions to the coupled equations are given for sinusoidal deposition of heat in space as is typically generated using two picosecond laser beams to form a transient grating. The solutions to the coupled equations, along with the equation of state of the fluid, gives the pressure, temperature, and density of the fluid following rapid deposition of heat. The time dependence of the grating diffraction efficiency is readily calculated from the modulation of the density and temperature. For small values of the viscosity and heat conduction parameters, closed form expressions for the state variables are given which describe thermal and acoustic modes of wave motion in the fluid. The method is applied for computation of the state variables using a frequency-dependent viscosity. Experiments with ethylene glycol are reported where the viscosity and sound speed are measured as functions of temperature.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 4017-4022 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Erbium/ytterbium co-doped fibers have been investigated in this work for the first time to determine their potential in thermometry applications based on the use of fluorescence decay. Several samples have been used and their performance characteristics determined. These have included studies of fiber annealing as well as thermal cycling tests and it was found that unlike other rare-earth ion doped fibers previously studied, such as Nd3+, Er3+, or Tm3+ doped fibers, the Er/Yb co-doped samples used here have shown a much smaller degree of thermal annealing when their thermal characteristics have been evaluated and compared. The response of the thermometer and the error in the measurement was found to be, at 〈±5 °C, within the stability of the oven used in the tests over a wide temperature range from 0 to 850 °C. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 146-151 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The use of multiple material fluorescence-based sensors, where each is optimized to a particular temperature range yet is pumped by the same light source, emitting over the same spectral region, makes for a very simple, convenient and promising optical arrangement which can be applied in real-time, quasidistributed temperature sensor systems. The fluorescence lifetime approach, which is an important technique to enable fluorescence emission to be exploited for thermometry, is adopted in the system discussed. An analysis scheme using Prony's method has been reported which enables exponential decays from either single-material or two material and quasidistributed sensors to be deconvolved and thus data and associated measurand information encoded in each individual signal to be recovered. In this work, in the development of quasidistributed temperature sensor algorithms based on Prony's method are used for the estimation of exponential time constants of a convolved triple exponential fluorescence decay, each corresponding to a different-point temperature. Experimental results obtained are presented to justify their use in practical multiexponential fluorescence decay analysis and show a comparison of the Prony method to the Marquardt nonlinear least-squares approximation algorithm to achieve the deconvolution. The computational time for Prony's approach is approximately one-thousandth that of the Marquardt technique while the accuracy achieved using Prony's method is still high enough for practical use. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 3447-3451 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An analysis of the fluorescence decay behavior of Pr 3+ in ZBLAN glass, at different concentrations, has been undertaken, for applications of the material to fiber optic thermometry. The study has shown that with the temperature increase, the measured lifetimes of the fluorescence emission from the Pr 3+ doped glass are also seen to increase slowly. The results obtained are found not to support a simple two-level model based on the thermalization of the states involved but a new three-level model that has been introduced can explain the observed results in a very satisfactory way. The application of the work in optical thermometry is discussed and comparisons with other systems are made. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 3442-3446 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An analysis of the fluorescence decay behavior of alexandrite emission, at higher dopant concentrations, has been undertaken for optical sensor application purposes. A double exponential decay behavior of the fluorescence emission has been observed, which differs from the single exponential behavior of alexandrite at lower concentrations of the active Cr 3+ ion. The origin of the phenomenon has been investigated both experimentally and theoretically and found to be produced by the joint contribution from the Cr3+ dopant in both the mirror, as well as in the inversion sites of that ion. The two lifetimes resulting, each having a different temperature dependence, both can be represented through the use of the configurational coordinate model which considers the effect of thermal quenching. The intensity ratio of these two aspects is seen to change regularly with the temperature within the important region for sensing of 273–773 K, and thus provides an alternative means to produce a calibrated fluorescence-based sensor. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 2924-2929 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The use of rare-earth-doped fibers for high temperature measurement has shown considerable promise. In this work, studies of the key characteristics of the performance of Er-doped fiber-based thermometer probes using the fluorescence decay time technique were carried out. Results showed the effects of fluorescence intensity as a function of doped fiber length and temporal and dopant concentration features of the probes. Annealing effects were seen to occur, and a satisfactory stable performance at up to 1100 °C was reported from this material, yielding improvement on results obtained with Nd-based systems. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 2930-2934 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A fluorescence-based intrinsic doped fiber temperature sensing system for determining local extremes of high temperatures has been demonstrated in this work. Data on this temperature rise are analyzed using a mathematical relationship, based on a correlation coefficient ratio scheme, to relate to the reduced fluorescence decay time information thus associated with the hot part of the fiber. In schemes incorporating this mathematical analysis, two separate sensor configurations have been demonstrated, one of which is to use short, single lengths of fiber spliced into a network and the other a long single length of doped fiber, using both Nd and Er doped fiber materials. The results show that the correlation coefficient ratio, R, will deviate from and be smaller than unity with the increase of the temperature of the localized region where the heat is applied, providing the mechanism for a simple high temperature excursion detection system. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 1716-1723 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Average, rather than point specific temperature measurement is important in a number of industrial situations. In this work, a method to improve this type of measurement using the fluorescence lifetime-related mathematical parameter, the singular value (SV), is discussed in detail. The analysis reported shows that with rare-earth doped fibers used as temperature sensor probe elements, for average temperature measurement, such a system works well especially when the lifetimes obtained from different sensing probes are very close to each other. The SV scheme, based on matrix theory, is important because the average temperature-dependent singular value possesses the characteristics of both high speed and high precision. Using the method, an average temperature sensing scheme is demonstrated in experiments carried out over the region from 20 to 100 °C, in which Nd3+ doped fibers are employed as the intrinsic temperature sensor elements. When two temperature sensing probes are used in the measuring region, the precision determined for the average temperature estimation is ±3.6 °C. When three sensors are employed instead of two, the precision is similar at ±3.4 °C. Results obtained indicate that with more sensor elements used in the sensing region, the accuracy achieved is not diminished due to the averaging effect in the measurement. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 4179-4185 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A series of different Yb-doped fibers has been investigated to determine their potential for use as the active elements in fluorescence–lifetime based thermometry, over a wide range from room temperature to 700 °C. Heat treatment ("annealing") has been shown to be necessary in practical applications to achieve consistent and reproducible calibration curves, each of which is consistent with the results of a simple two level model. Each sample studied was found to possess unique sensitivity characteristics, enabling an optimized selection for specific applications. The response of the thermometer and the error in the measurement was found to be, at 〈±5 °C, consistent with the stability of the calibrated oven used. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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