Electromagnetic effect

The metal substrate evidently affords a huge ( 10 and even as high as 10 [84, 85]) increase in the cross-section for Raman scattering of the adsorbate. There are two broad classes of mechanisms which are said to contribute to this enhancenient [, and Ml- The first is based on electromagnetic effects and the second on cheniicaT effects. Of these two classes the fomier is better understood and, for the most part, the specific mechanisms are agreed upon the latter is more complicated and is less well understood. SERS enhancenient can take place in either physisorbed or chemisorbed situations, with the chemisorbed case typically characterized by larger Raman frequency shifts from the bulk phase. 

There are do2ens of flow meters available for the measurement of fluid flow (30). The primary measurements used to determine flow include differential pressure, variable area, Hquid level, electromagnetic effects, thermal effects, and light scattering. Most of the devices discussed herein are those used commonly in the process industries a few for the measurement of turbulence are also described. 

Measurement by Electromagnetic Effects. The magnetic flow meter is a device that measures the potential developed when an electrically conductive flow moves through an imposed magnetic field. The voltage developed is proportional to the volumetric flow rate of the fluid and the magnetic field strength. The process fluid sees only an empty pipe so that the device has a very low pressure drop. The device is useful for the measurement of slurries and other fluid systems where an accumulation of another phase could interfere with flow measurement by other devices. The meter must be installed in a section of pipe that is much less conductive than the fluid. This limits its appHcabiHty in many industrial situations. 

Measurement based on electromagnetic effect Experimental investigation has been done to examine the use of an electromagnetic flow meter to measure the continu-... 

The problem relates directly to the constancy of c, which implies that the velocity of light is independent of both the motion of its source and the direction of propagation, a condition that cannot hold in more than one Newtonian inertial frame if the Galilean principle of relativity applies. Since there is no evidence that the laws of physics are not identical in all inertial frames of reference the only conclusion is that the prescription for Galilean transformations needs modification to be consistent, not only with simple mechanics, but also with electromagnetic effects. 

Quantum theory started as an explanation of electromagnetic effects (black-body radiation) in terms of corpuscular properties of light, expressed... 

In the plane-wave approximation, all electromagnetic effects are derived from the structured time-like potential difference... 

Since Covalon is a spin-paired boson (not fermion) conventional electromagnetic effect from electron-current flow will not be expected and must be studied and explored separately. 

The electromagnetic effect enhances by some orders of magnitude the local electric field nearby the metallic surface. The chemical effect, instead, derives from polarizability changes when molecules are bound to active sites of the metal substrates. Both mechanisms are related to metal surface irregularities or defects, on nanometric or atomic scale, as shown in Scheme 20.1. 

Muniz-Miranda M, Cardini G, Schettino V (2004) Surface-enhanced Raman spectra of pyridine and pyrazolide on silver colloids chemical and electromagnetic effects. Theor Chem Acc 111 264-269... 

Electromagnetic Effects Under Isothermal-Isochoric Conditions... 

The performance of a membrane process is a function of the intrinsic properties of the membrane, the imposed operating and hydrodynamic conditions, and the namre of the feed. This chapter describes methods available to enhance performance by various techniques, mainly hydrodynamic but also chemical and physical. The focus is on the liquid-based membrane processes where performance is characterized by attainable flux, fouling control, and separation capabilities. The techniques discussed include secondary flows, flow channel spacers, pulsed flow, two-phase flow, high shear devices, electromagnetic effects, and ultrasound. 

To recall, the Ag modes are enhanced via the long range electromagnetic effect, while the activation of modes is characteristic for the molecules in intimate contact with the metal. Therefore the intensity of modes relative to that of Ag modes will be considered in the following to extract the metal diffusion depth into the organic films. 

Evidence for an electromagnetic effect comes from several types of experiment which have been summarized helpfully by Chang [10]. The ingenious "spacer experiments of Murray et al. [11] demonstrated the importance of... 

The surface enhancement is ascribed to the occurrence of two separate effects, electromagnetic and chemical (70). The electromagnetic effect arises from small surface structures arising in the ORC that cause strong local increases of the electric fields of the excitation and scattered radiation via surface plasmon waves. The chemical effect is attributed to interactions between the adsorbed molecule and the metal surface which lead to electronic (charge-transfer) transitions between molecule and metal. The result is a res-onance-Raman-like effect. Since both effects operate only over very small distances, SERS is specific for molecules at the electrode surface. 

---