Excitation mechanism

Electromagnetic earthquake forerunners show themselves like the electromagnetic phenomena, including electromagnetic emission (EME) in a radio frequency range. This emission caused by collective exiting of the set of local mechano-electrical transformers (MET). The excitation mechanism inside the crust is determined by the fact that elastic tension ranges up to the threshold level within the source area. 

Shen T-C, Wang C, Abein G C, Tucker J R, Lyding J W, Avouris P and Walkup R E 1995 Atomic-scale desorption through electronic and vibrational excitation mechanisms Science 268 1590... 

The second excitation mechanism, impact scattering, involves a short range interaction between the electron and the molecule (put simply, a collision) which scatters the electrons over a wide range of angles. The usefiil feature of impact scattering is that all vibrations may be excited and not only the dipole active ones. As in Raman spectroscopy, the electron may also take an amount of energy hv away from excited molecules and leave the surface with an energy equal to Eq + hv. 

Figure Bl.25.12. Excitation mechanisms in electron energy loss spectroscopy for a simple adsorbate system Dipole scattering excites only the vibration perpendicular to the surface (v ) in which a dipole moment nonnal to the surface changes the electron wave is reflected by the surface into the specular direction. Impact scattering excites also the bending mode v- in which the atom moves parallel to the surface electrons are scattered over a wide range of angles. The EELS spectra show the higlily intense elastic peak and the relatively weak loss peaks. Off-specular loss peaks are in general one to two orders of magnitude weaker than specular loss peaks.

Lee, J. (1993). Lumazine protein and the excitation mechanism in bacterial bioluminescence. Biophys. Chem. 48 149-158. 

They also discussed the excitation mechanism of alkali-metal atoms as follows. The addition of a metal species from a liquid solution into cavitating bubbles is through the ablation of the bubble-liquid interface, the ablation of liquid jet or the evaporation of droplets, since the evaporation of salt is negligible. The salt molecules are released and decomposed into atoms via homolysis, analogous with the projection into a flame of metal species from salt solutions. The metal atoms are... 

We have now to go one step further and to build stellar evolution models where the transport of angular momentum will be followed self-consistently under the action of meridional circulation, shear turbulence, and internal gravity waves. In this path some important aspects still need to be clarified Can we better describe the excitation mechanisms and evaluate in a more reliable way the quantitative properties of the wave spectra What is the direct contribution of 1GW to the transport of chemicals, especially in the dynamical shear layer produced just below the convective envelope by the wave-mean flow interaction What is the influence of the Coriolis force on IGW How do 1GW interact with a magnetic field Work is in progress in this direction. 

The zincblende (ZB), or sphalerite, structure is named after the mineral (Zn,Fe) S, and is related to the diamond structure in consisting entirely of tetrahedrally-bonded atoms. The sole difference is that, unlike diamond, the atoms each bond to four unlike atoms, with the result that the structure lacks an inversion center. This lack of an inversion center, also characteristic of the wurtzite structure (see below), means that the material may be piezoelectric, which can lead to spurious ringing in the free-induction decay (FID) when the electric fields from the rf coil excite mechanical resonances in the sample. (Such false signals can be identified by their strong temperature dependence due to thermal expansion effects, and by their lack of dependence on magnetic field strength). 

Figure 6 Proposed formation of an alternative C204 structure in the excitation mechanism for peroxyoxalate chemiluminescence.

Lastly, we mention one more excitation mechanism that has been observed in molecules. It is well-established that following strong field ionization in atoms and molecules, under certain conditions, the ionized electron can be driven back to the ion core where it can recombine to produce high-harmonic radiation, induce further ionization, or experience inelastic scattering. However, there is also the possibility of collisional excitation. Such excitation was observed in [43] in N2 and O2. In both molecules, one electron is tunnel ionized by the strong laser field. When the electron rescatters with the ion core, it can collisionally ionize and excite the molecular ion, creating either N + or Ol+ in an excited state. When the double ion dissociates, its initial state can... 

Where infrared and Raman spectroscopy are limited to vibrations in which a dipole moment or the molecular polarizability changes, EELS detects all vibrations. Two excitation mechanisms play a role in EELS dipole and impact scattering. 

Luminescence is, in some ways, the inverse process to absorption. We have seen in the previous section how a simple two-level atomic system shifts to the excited state after photons of appropriate frequency are absorbed. This atomic system can return to the ground state by spontaneous emission of photons. This de-excitation process is called luminescence. However, the absorption of light is only one of the multiple mechanisms by which a system can be excited. In a general sense, luminescence is the emission of light from a system that is excited by some form of energy. Table 1.2 lists the most important types of luminescence according to the excitation mechanism. 

Figure 3.11 Photo-excitation mechanisms in (a) intrinsic and (b) extrinsic photoelectric detectors.

CONTENTS Preface, Joseph Sneddon. Analyte Excitation Mechanisms in the Inductively Coupled Plasma, Kuang-Pang Li and J.D. Winefordner. Laser-Induced Ionization Spectrometry, Robert B. Green and Michael D. Seltzer. Sample Introduction in Atomic Spectroscopy, Joseph Sneddon. Background Correction Techniques in Atomic Absorption Spectrometry, G. Delude. Flow Injection Techniques for Atomic Spectrometry, Julian F. Tyson. 

Some sensory neurons of the VNO express two gene superfamilies, termed Vlr and V2r, that encode over 240 proteins of the seven-transmembrane type (Matsunami and Buck, 1997). These G-protein-linked putative pheromone receptors are distantly related to the main olfactory system s receptors. Receptors of the VNO are linked to different G-proteins, and their extracellular N-terminal domains are longer than those of the receptors in the main olfactory system. (Vi receptors are linked to Gi-proteins and V2 receptors to Go-proteins). The intracellular excitation mechanism in VNO sensory neurons also differs from that in the main olfactory systems instead of linking to adenylyl cyclase, the VNO receptors activate the phosphoinositol second messenger system. This has been demonstrated in several mammalian species. In hamsters, aphrodisin increases inositol 1,4,5-trisphosphate (IP3) levels in VNO membranes. Boar seminal fluid and urine stimulate increases of IP3 in the VNO of the female pig. (However, in the pig, the VNO is not necessarily essential for responses to pheromones [Dorries etal., 1997]). 

A further striking finding by Stelmakh and Tsvirko is the S2 fluorescence following excitation to the S state by a low-energy photon. They also proposed possible excitation mechanisms to explain their results (24-26). Pumping can be achieved by two different ways of unimolecular successive two-photon absorption ... 

Nevertheless, there are two highly efficient CL systems which are believed to involve the CIEEL mechanism in the chemiexcitation step, i.e. the peroxyoxalate reaction and the electron transfer initiated decomposition of properly substituted 1,2-dioxetanes (Table 1)17,26 We have recently confirmed the high quantum yields of the peroxyoxalate system and obtained experimental evidence for the validity of the CIEEL hypothesis as the excitation mechanism in this reaction. The catalyzed decomposition of protected phenoxyl-substituted 1,2-dioxetanes is believed to be initiated by an intramolecular electron transfer, analogously to the intermolecular CIEEL mechanism. Therefore, these two highly efficient systems demonstrate the feasibility of efficient excited-state formation by subsequent electron transfer, chemical transformation (cleavage) and back-electron transfer steps, as proposed in the CIEEL hypothesis. 

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