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Advances in understanding the photophysics and photochemistry of transition metal complexes offer opportunities to utilize these materials as luminescence sensors and probes. However, heterogeneity has an enormous effect on luminescence, quenching, and photochemistry. An intimate understanding of the detailed interactions between the complexes and their environment will be necessary before the rational design of new high performance sensors and probes can be achieved. Such understanding is fairly well established for homogeneous media, but it is still in its infancy in solid supports (surfaces and polymers). We present case studies involving luminescent metal complexes bound to a variety of polymer systems. Both their potential and the difficulties inherent in these composite systems are presented. We discuss tools that have proved useful or are likely to be valuable in unraveling these complex systems. 相似文献
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The emission spectra of four mercury vapor lamps are used to obtain wavelength calibration curves for the double-grating emission monochromator of a spectrofluorimeter. The use of second- and third-order diffraction lines and emission lines from the argon carrier gas provides a rich spectrum, which extends well into the near-infrared spectral region and produces an improved calibration curve. More than 60 emission lines are listed between 250 and 900 nm, which is sufficient to produce an extremely accurate monochromator calibration. Additional second- and third-order lines can be used to even longer wavelengths (>1200 nm). The effectiveness of three scattering surfaces is compared. 相似文献
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Nathan H. Mack William D. Bare Wenying Xu J. N. Demas B. A. DeGraff 《Journal of fluorescence》2001,11(2):113-118
An apparatus is described for the automated collection of luminescence emission decay curves over a wide range of analyte concentrations. The decay curves allow for determination of the excited-state lifetime or calculated steady-state intensity of a luminophore as a function of the analyte concentration. The data presented here demonstrate the use of the apparatus for pH titrations. 相似文献
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To improve the wear resistance of polytetrafluoroethylene (PTFE), a crosslinked aromatic thermosetting polyester (ATSP) has been blended directly with PTFE. Cured ATSP powder which was directly synthesized as a cured powder form was used for this application. Because of the similar processing temperature range of cured ATSP and PTFE, composites within the entire composition range were successfully prepared by blending these two powders using a hot press. Tribological pin‐on‐disk tests (composite pins sliding against gray cast iron disks) showed improvement on friction coefficient of all composites and much less wear than pure PTFE. The composites survived at contact pressures of 7 MPa, which is higher than either pure PTFE or pure ATSP could sustain. With an increase in the amount of ATSP in the composites, storage modulus, and glass transition temperature were higher, and the wear resistance was enhanced. SEM images helped provide explanations for the unusually low mean wear rates that were observed for these composite samples. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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Nathan Kelso Seung-Kyun Lee Louis-S. Bouchard Vasiliki Demas Michael Mück Alexander Pines John Clarke 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2009,200(2):285-290
MRI is a powerful technique for clinical diagnosis and materials characterization. Images are acquired in a homogeneous static magnetic field much higher than the fields generated across the field of view by the spatially encoding field gradients. Without such a high field, the concomitant components of the field gradient dictated by Maxwell’s equations lead to severe distortions that make imaging impossible with conventional MRI encoding. In this paper, we present a distortion-free image of a phantom acquired with a fundamentally different methodology in which the applied static field approaches zero. Our technique involves encoding with pulses of uniform and gradient field, and acquiring the magnetic field signals with a SQUID. The method can be extended to weak ambient fields, potentially enabling imaging in the Earth’s field without cancellation coils or shielding. Other potential applications include quantum information processing and fundamental studies of long-range ferromagnetic interactions. 相似文献
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Polubarinova-Kochina's analytical differential equation methodis used to determine the pseudo-steady-state solution to problemsinvolving the freezing (solidification) of wedges of liquidwhich are initially at their fusion temperature. In particular,we consider four distinct problems for wedges which are: freezingwith the same constant boundary temperature, freezing with thesame constant boundary heat fluxes, freezing with distinct constantboundary temperatures and freezing with distinct constant fluxesat the boundaries. For the last two problems, a Heun's differentialequation with an unknown singularity is derived, which in bothcases admits a particularly elegant simple solution for thespecial case when the wedge angle is . The moving boundariesobtained are shown pictorially. 相似文献
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