Nernst source

Natural bandwidth, 256 Natural width, 278 Nephelometry, 208 Nemst coefficient, 4 Nernst source, 175 Nessler tube, 207 Neutral marker, 116 Nier-Johnson, 296 NPD, 36... 

In the mid-IR several type of sources are used. They are either a lamp filament (Figure 10.13), or a hollow rod, 1-3 mm in diameter and 2 to 4 cm long, made of fused mixtures of zirconium oxide or rare earth oxides (Nernst source) heated by Joule effect by the means of an internal resistor (for example Globar ). These sources are heated to 1500 °C, without a protective shield. They dissipate power of the order of a hundred watts by emitting radiation over a large domain ranging from visible to thermal IR. A maximum is observed for A = 3000/T (A in... 

The main sources of infrared radiation used in spectrophotometers are (1) a nichrome wire wound on a ceramic support, (2) the Nernst glower, which is a filament containing zirconium, thorium and cerium oxides held together by a binder, (3) the Globar, a bonded silicon carbide rod. These are heated electrically to temperatures within the range 1200- 2000 °C when they will glow and produce the infrared radiation approximating to that of a black body. 

Erwin N. Hiebert. Walther Nernst and the Application of Physics to Chemistry. In Springs of Scientific Creativity Essays on Founders of Modem Science, Rutherford Aris et al., eds. Minneapolis University of Minnesota Press, 1983, pp. 203-231. Source for Nernst s fight with Haber. 

Jeffrey Allan Johnson. The Kaiser s Chemists Science and Modernization in Imperial Germany. Chapel Hill, NC The University of North Carolina Press, 1990. Source for German professorate cold war atmosphere Boer war fight with Nernst and Jewish participation in Kaiser Wilhelm institutes. 

IR spectrometers have the same components as UY/visible, except the materials need to be specially selected for their transmission properties in the IR (e.g., NaCl prisms for the monochromators). The radiation source is simply an inert substance heated to about 1500 °C (e.g., the Nernst glower, which uses a cylinder composed of rare earth oxides). Detection is usually by a thermal detector, such as a simple thermocouple, or some similar device. Two-beam system instruments often work on the null principle, in which the power of the reference beam is mechanically attenuated by the gradual insertion of a wedge-shaped absorber inserted into the beam, until it matches the power in the sample beam. In a simple ( flatbed ) system with a chart recorder, the movement of the mechanical attenuator is directly linked to the chart recorder. The output spectrum is essentially a record of the degree of... 

The approach just used for fractional crystallization can be transposed immediately to fractional melting, a process by which each packet of melt is withdrawn from the source thereby prevented from equilibration with the solid. Again, these equations will be developed in Chapter 9, but the present section emphasizes a representation which does not require constant Berthelot-Nernst partition coefficients, and therefore is more useful for major elements. 

The potential of oxygen over platinum responded nicely to changes in oxygen pressure according to the Nernst expression (5). The reference electrode was silver immersed in 0 1M silver nitrate in the fused alkali nitrates, the mixture being contained in a thin glass envelope. To test the effect of changes in oxide ion concentration on the potential, a source of pure alkali oxide was needed. It is also ulti-... 

The amount of radiation used is also important. A Nernst glower is used in ordinary infrared spectroscopy. This light source emits a relatively low amount of radiation, and no destruction of the analyzed material occurs. However, Raman infrared spectroscopy employs a radiation source of much greater energy. This radiation is sufficiently energetic to cause bond disruption and some destruction of the analyzed material. 

The superscript o refers to concentrations in the external bathing solution, and the superscript i refers to the cytosol. The Nernst potentials (ENj) were calculated from Equation 3.6 using concentration ratios and a numerical factor of 58.2 mV because the temperature was 20°C The potential across the plasma membrane (EM) was —138 mV. The fluxes indicated for the dark refer to values soon after cessation of illumination. (Sources MacRobbie, 1962 Spanswick and Williams, 1964.)... 

Infrared radiation is usually detected by means of a bolometer or a thermocouple. Since emission spectra are often too weak to be detected, we are here primarily interested in absorption spectra. These are obtained by interposing the substance between the prism and a source of infrared emission, such as a Nernst glower or any other suitable incandescent solid body at temperatures of 1000 to 1500°C. Several discussions on this subject are available. ... 

The first and third half-reactions have half-cell potentials (AgCl CH Ag) and (Hg2Cl2 cr Hg)that can be combined and called A ef because they make a constant contribution to the cell voltage. The second reaction is the source of a variable potential in the cell, corresponding to the free energy of dilution of H30 from a concentration of 1.0 M to an unknown and variable concentration, and its potential exists across the thin glass membrane of the glass electrode. The Nernst equation for the cell can therefore be written as... 

We will use standard electrode potentials throughout the rest of this text to calculate cell potentials and equilibrium constants for redox reactions as well as to calculate data for redox titration curves. You should be aware that such calculations sometimes lead to results that are significantly different from those you would obtain in the laboratory. There are two main sources of these differences (1) the necessity of using concentrations in place of activities in the Nernst equation and (2) failure to take into account other equilibria such as dissociation, association, complex formation, and solvolysis. Measurement of electrode potentials can allow us to investigate these equilibria and determine their equilibrium constants, however. 

A Nernst glower is a cylinder of zirconium and yttrium oxides that emits IR radiation when heated to a high temperature by an electric current. Electrically heated spirals of nichrome wire also serve as Inexpensive IR sources. 

The infrared light source generates wideband radiation by heating solid materials to incandescence using electric power. There are two commonly used IR sources the Nernst glower, which is composed of mainly oxides of rare-earth elements and the Globar, which is... 

Fig. 6. (A) Redox titration of the primary electron acceptor in Rb. sphaeroides chromatophores at pH 11. The amplitude of absorption changes Induced by short flashes is plotted as a function of the redox potential solid dots and empty circles represent reductive and oxidative titrations, respectively. The solid line is the theoretical Nernst curve. (B) Equilibrium midpoint potentials of the primary acceptor as determined in (A) plotted as a function of pH. Figure source Prince and Dutton (1978) Protonation and the reducing potential of the primary electron acceptor. In RK Clayton and WR Sistrom (eds) The Photosynthetic Bacteria, p 443, 444. Plenum.

Fig. 5. Redox titration of Chl-a fluorescence yield in isolated chloroplasts containing redox mediators that excludes (top) and includes (bottom) neutral red. Round and square dots are for reductive and oxidative titrations, respectively. Dashed line represents Nernst plots for n=l at both -247 and -45 mV (top) and for n=1 at -85 and -40 mV and n=2 at -375 mV (bottom). See text for discussion. Figure source Horton and Croze (1979) Characterization of two quenchers of chlorophyit fiuorescence with different midpoint oxidation-reduction potentiais in chloroplasts. Biochim Biophys Acta 545 191,192.

Fig. 6. (A) Plot of amplitude of light-induced pheophytin-reduction signal vs. ambient potential of the medium. (B) Effed of ambient redox potential on the extent of light-induced PS-II reaction-center triplet signal in pea chloroplast particles. (C) Plot of the extent of the light-induced triplet EPR signal in (B) vs. redox potential. Open and closed circles are for reductive and oxidative titrations, respedively. The solid curve is a computer fit of the Nernst equation with n=1 and E , was estimated to be -604 mV. Figure source (A) Klimov. Allakhverdiev. Demeter and Krasnovsky (1979) Photoreduction ofpheophytin in photosystem 2 ofchloroplasts with respect to the redox potential of the medium. DokI Akad NaukSSSR 249 229 (B and C) Rutherford, Mullet and Crofts (1981) Measurement of the midpoint potential of the pheophytin acceptor of photosystem II. FEBS Lett 123 236,237...

Fig. 6. Direct redox titration of FeS-X by monitoring the amplitude of light-induced EPR signal at 9 K as a function of redox potential. (A) EPR spectra of PS-1 particles titrated to -680 and -749 mV recorded in the dark (solid lines) and under illumination (dashed lines). (B) Plot of EPR signal at g=1.76 vs. potential. The solid-line plot was calculated from the Nernst equation for n=1 and E = -705 mV. Figure source Chamorovsky and Cammack (1982) Direct determination of the midpoint potential of the acceptor X in chloroplast photosystem I by electrochemical reduction and ESR spectroscopy. Photobiochem Photobiophys 4 198, 199,...

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