Constant-current mode instrumentation

The power supply to the electrolyser was a Model 710 from The Electrosynthesis Company, Inc. of Lancaster NY. It was operated in constant current mode rather than in constant voltage mode. The maximum current and maximum voltage available was 50 amperes and 20 volts, respectively. In addition to current measurement provided by the power supply, a calibrated shunt was connected to the output to allow for independent measurement of current. Voltage taps independently connected to the cell electrodes were connected to the data acquisition system (DAS). The instrument signals from thermocouples, pressure gages, and flowmeters were connected to the DAS, which was comprised of a Dell computer with special acquisition boards and Labview software. Observations and some data were manually recorded in a laboratory notebook. 

For STM studies, 10 pi solution of the catalyst (containing 1 mg catalyst/ml methylene chloride) was deposited onto freshly cleaved highly oriented pyrolytic graphite (Union Carbide) and dried in vacuum. The STM was operated in air at atmospheric pressure with a tipto-substrate bias of 150 mV and a tunnelling current of 1 nA. Etched tips of Pt/Ir (80 20) wires (0.5 mm in diameter. Digital Instruments, Santa Barbara, CA) were used in constant current mode. 

Electrically active regions of nanocrystalline silicon (nc-Si) films have been investigated by using a SEM/STM combined instrument. STM constant current images reveal a cell structure in the nc-Si which is also observed in the remote electron beam induced mode of the STM. The STM-REBIC contrast indicates the existence of space charge regions at the cell boundaries. 

Material functions must however be considered with respect to the mode of deformation and whether the applied strain is constant or not in time. Two simple modes of deformation can be considered simple shear and uniaxial extension. When the applied strain (or strain rate) is constant, then one considers steady material functions, e.g. q(y,T) or ri (e,T), respectively the shear and extensional viscosity functions. When the strain (purposely) varies with time, the only material functions that can realistically be considered from an experimental point of view are the so-called dynamic functions, e.g. G ((D,y,T) and ri (a), y,T) or E (o),y,T) and qg(o),y, T) where the complex modulus G (and its associated complex viscosity T] ) specifically refers to shear deformation, whilst E and stand for tensile deformation. It is worth noting here that shear and tensile dynamic deformations can be applied to solid systems with currently available instruments, whUst in the case of molten or fluid systems, only shear dynamic deformation can practically be experimented. There are indeed experimental and instrumental contingencies that severely limit the study of polymer materials in the conditions of nonlinear viscoelasticity, relevant to processing. 

Measurements. Absorption spectra measurements on the film and solutions of the metal complexes were measured on a modified Cary 14 spectrometer. Luminescence spectra were recorded with a custom photon counting spectrometer or a PTI (Deer Park Drive, South Brunswick, NJ 08852) luminescence spectrometer system. The FT-IR spectra were recorded with a PE-1600 spectrometer or a Bio-Rad FTS-40 spectrometer (Professor R. Crooks, Chemistry Department, University of New Mexico). RA spectra for LB films were measured on the FTS-40 with a Hanick gra2dng angle attachment and MCT detection system. Typically 256 scans were requir to obtain adequate intensity for the monolayer films. The scanning tunneling microscopy measurements employed a Nanoscope II system (Digital Instruments, Inc.). Etched Pt-Ir tips were used with the standard, 0.6 micron head. The system can be operated in either the constant current or constant height mode but the film contours were similar for either. 

Fig. 8 Schematic of a tandem quadrupole MS/MS instrument. A tandem quadrupole MS/MS instrument consists of two quad-rupole MS filters, MSI and MS2, separated by a collision cell. Each quadrupole MS filter consists of four cylindrical or hyperbolic shaped rods. A unique combination of direct current (dc) potential and radiofrequency (rf) potential is applied to each pair of rods (one pair 180° out of phase with the other). A mass spectrum results by varying the voltages at a constant rf/dc ratio. A variety of scan modes (e.g., full scan, product ion, precursor ion, neutral loss) provide unique capabilities for quantitative and qualitative structure analysis. (Courtesy of Micromass, Manchester, UK.)...

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