Temperature, excitation

Time-resolved IR spectra of similar peptides following a laser-excited temperature jump showed two relaxation times, unfolding 160 ns and faster components <10 ns (Williams et al., 1996). These times are very sensitive to the length, sequence, and environment of these peptides, but do show that the fundamental helix unfolding process is quite fast. These fast IR data have been contrasted with Raman and fluorescence-based T-jump experiments (Thompson et al., 1997). Raman experiments at various temperatures have suggested a folding in 1 /xs, based on an equilibrium analysis (Lednev et al., 2001). But all agree that the mechanism of helix formation is very fast. 

Fig. 1. Oxygen abundances as a function of the activity index, Rx, derived from X-ray data (left-hand panels) and the excitation temperature Texc (right-hand panels). The bottom panels show the difference between [O/Fe] yielded by the OI triplet at about 7774 A and the [OI] A6300 line. Filled circles RS CVn binaries ([2] and [3]), filled squares field subgiants [3], filled triangles Pleiades stars, open triangles Hyades stars, open circles, squares and hexagons disk dwarfs. The source of the literature data for the open cluster and Galactic disk stars can be found in [4].

Consider continuous radiation with specific intensity I incident normally on a uniform slab with a source function 5 = Bv(Tex) unit volume per unit solid angle to the volume absorption coefficient Kp and is equal to the Planck function Bv of an excitation temperature Tcx obtained by force-fitting the ratio of upper to lower state atomic level populations to the Boltzmann formula, Eq. (3.4). For the interstellar medium at optical and UV wavelengths, effectively S = 0. 

Borisov SM, Klimant I (2008) Blue LED excitable temperature sensors based on a new europium(III) chelate. J Fluoresc 18 581-589... 

Example The intensity of atomic absorption lines for the alkali metals, such as potassium (K) rubidium (Rb) and caesium (Cs), is found to be affected by temperature in a complex way. Under certain experimental parameters a noticeable decrease in absorption may be observed in hotter flames. Hence, lower excitation temperatures are invariably recommended for the analysis of alkali metals. 

It is uncertain to what extent thermal equilibria are achieved in different parts of the flames. — A number of procedures are (in principle) available to determine flame temperatures The immediate measurement, for example by thermocouples, the thermochemical calculation, line reversal methods for electronic excitation temperatures, determination of vibrational or rotational temperatures. In addition more recent methods like advanced Raman techniques may be applied. 

On pp 289-310 (Ref 21), A.G. Gaydon, Shock-Tube Studies of Processes of Electronic Excitation in Gases reported that the spectrum-line reversal temperature in shock-heated gases can be used to obtain information about efficiencies and processes of electronic excitation of metal atoms at high temperatures. For excitation by molecules, the electronic excitation temperature tends to follow the effective vibrational temperature of the molecules, and reversal temperatures may be low near the shock front if. the vibrational relaxation time is appreciable. Although excitation of metal atoms by cold inert gases has a very small effective cross-section, it is shown that at 2500°K the cross-sections of excitation of Cr or Na by Ar or Ne are around 1/20 of the gas-kinetic cross-sections... 

ICP-AES is characterized by low detection limits of the order of 1-100 ng mT as shown in Fig. 4.17, because of its high excitation temperature compared with the flame. It has a large linear dynamic range... 

The capacitatively coupled microwave plasma is formed by coupling a 2450 MHz magnetron, via a coaxial waveguide, to metal plates or a torch where the plasma is formed. Considerable problems have been encountered with this low-cost plasma, particularly from easily ionizable elements which cause dramatic changes in the excitation temperature in the plasma. 

Direct current plasma (DCP) this is produced by a dc discharge between electrodes. DCPs allow the analysis of solutions. Experiments have shown that although excitation temperatures can reach 6000 K, sample volatilisation is not complete because residence times in the plasma are relatively short (this can be troublesome with samples containing materials that are difficult to volatilise). A major drawback is the contamination introduced by the electrodes. 

M. Grotti, C. Lagomarsino and J. M. Mermet, Effect of operating conditions on excitation temperature and electron number density in axially-viewed ICP-OES with introduction of vapors or aerosols, J. Anal. At. Spectrom., 21(9), 2006, 963-969. 

First,one important result of the infrared molecular spectroscopy is a discovery of stationary CO layer in Mira type variable star x Gyg, in which CO lines that stay stationary have been clearly separated from the photospheric CO lines that show cyclic Doppler-shifts by the large amplitude pulsation of the photosphere in time series spectra( Hinkle, Hall, Ridgway, 1982). It was suggested that the stationary CO layer may be located at several stellar radii above the stellar surface, since excitation temperature of the stationary CO layer of x Cyg was found to be 800K. 

Excess CO absorption can be seen not only in 2-0 band but also in 3-1 band, and excitation temperatures of the CO absorption layer are between 1000 and 2000K. 

FIG. 1— The logarithmic abundances of H, Sc, Sr, and Ba with respect to Fe in SN 1987A relative to their solar system values, as a function of the envelope excitation temperature Texc. The abundances are derived from the absorption lines in May 1987, and the vertical arrow shows the appropriate temperature at that time. 

The influence of excitation temperature on the the a-value parameter for tunnelling luminescence kinetics is described in [94],... 

ORM assumes that the atmosphere is in local thermodynamic equilibrium this means that the temperature of the Boltzmann distribution is equal to the kinetic temperature and that the source function in Eq. (4) is equal to the Planck function at the local kinetic temperature. This LTE model is expected to be valid at the lower altitudes where kinetic collisions are frequent. In the stratosphere and mesosphere excitation mechanisms such as photochemical processes and solar pumping, combined with the lower collision relaxation rates make possible that many of the vibrational levels of atmospheric constituents responsible for infrared emissions have excitation temperatures which differ from the local kinetic temperature. It has been found [18] that many C02 bands are strongly affected by non-LTE. However, since the handling of Non-LTE would severely increase the retrieval computing time, it was decided to select only microwindows that are in thermodynamic equilibrium to avoid Non-LTE calculations in the forward model. 

The Cosmic Microwave Background (CMB) was first seen via its effect on the interstellar CN radical (Adams, 1941) but the significance of the this datum was not realized until after 1965 (Thaddeus, 1972 Kaiser and Wright, 1990). In fact, Herzberg, 1950 calculated a 2.3 K excitation temperature for the CN transition and said it had of course only a very restricted meaning. Later work by Roth et al., 1993 obtained a value for T0 = 2.729iJj Jjif i K at the CN 1-0 wavelength of 2.64 mm which is still remarkably accurate. 

However, if there is no thermodynamic equilibrium, as is common for interstellar cases, it is convenient to define between two energy levels an excitation temperature Tex which is determined by fitting the observed molecular distribution to the Boltzmann formula, Eq. (13). 

Excitation temperatures in interstellar molecular clouds are typically 3 °K < Tex < 50 °K, and thus the approximation (14b) looses its validity in the shorter mm-wavelength region. 

Typical kinetic gas temperatures in dense interstellar clouds are 7k < 30 °K but may in some cases reach values of v 80 °K (e. g. the Orion molecular cloud). The relation between excitation temperature Tex and kinetic gas temperature 7k is further discussed in Sections III. E and III. F. 

Strong H2 lines have been reported in 11 reddened stars (E (B - V) > 0.10). Considerably less or no H2 absorption was detected in unreddened stars. Large column densities have been reported in higher rotational levels (up to J = 6) which correspond to an excitation temperature between 150° and 200 °K. The ratio of ortho-hydrogen (J = odd) to para-hydrogen (J = even) correspond to about 80 °K. Absorption of two lines of the Lyman bands of HD were also reported in nine stars, indicating a ratio of HD/H2 10 6. However, in the star (3 Cen a deuterium to hydrogen ratio of N(D)/N(H) = 1.047 (0.125,... 

If tv 1 it follows from Eq. (25c) that TL = Tex, i.e. in this case the observation yields directly the excitation temperature of the line. For optically thin clouds (r 1) seen in emission one obtains... 

Furthermore, one can generally use approximation (14b) for the correction factor for stimulated emission. Hence according to Eqs. (16 and 20) the optical depth of radio molecular lines is inversely proportional to the excitation temperature... 

Here, nx is the number of molecules per cm3 in the lower level, ju the electric dipole transition matrix element, Tex the excitation temperature of the molecule and f(y) the line shape function normalized to... 

Fig. 15. Plots of the peak absorption coefficients of the K = 0 lines of different J transitions for methylcyanide. The variation of intensity for the different K components is shown for the 7=6-5 transition. The inset gives the wavelength region in which the strongest rotational lines occur for various symmetric top molecules. The excitation temperature is assumed to be 150 °K...

---