Ultra narrow band

Keywords tomography moving targets spatial diversity ultra narrow band (UNB) monostatic radar multistatic radar. 

The narrow absorption and emission bands of rare-earth 0-diketonates in the visible, near ultra-violet and near infra-red is attributed to 4f-4f transitions. These transitions are electric dipole forbidden to first order, but are allowed by the electric quadrupole, vibronic, magnetic dipole and forced electric dipole mechanisms. The magnetic dipole character of the Dq F transition of the Eu + ion was demonstrated in 1939 by... 

Neither La nor Lu show absorption bands in the ultra-violet, visible or near infrared, but the rest do. The bands are narrow compared with those of the normal transition ions. The energy changes involved are probably due to excitations within the 4f shell, since complexing agents, which alter the absorption spectra of normal transition ions by modifying their outer structure, have little effect on the lanthanide ions. An ion with n... 

Low-dispersion HPLC systems are necessitated by the increasing trend of using shorter and narrower HPLC columns, which are more susceptible to the deleterious effects of extra-column band-broadening. HPLC manufacturers are designing newer analytical HPLC systems with improved instrumental bandwidths compatible with 2-mm i.d. columns by using micro injectors, smaller i.d. connection tubing, and detector flow cells. A new generation of ultra-low dispersion systems dedicated for micro and nano LC is also available. 

Fusion of a benzene ring to a heterocyclic nucleus causes a bathochromic shift and increases the intensity of absorption. Thus, quinoline, isoquinoline, indole and quinolium and isoqumolium ions fluoresce in the ultra-violet. Acridine, acridone and carbazole exhibit visible fluorescence. Porphyrin18 and some of its derivatives are characterized by narrow well-defined vibrational bands and their fluorescence bands are in the red region of the spectrum. 

This difference in behaviour of the shift of ultra-violet absorption on melting is borne out by other characteristics of the ultraviolet absorption bands. For melts that appear to contain association complexes, these bands tend to be narrower and may have absorption maxima of intensity comparable with that in the crystals. This contrasts with melts of ions with inert gas structures, but conforms with expectations for association complexes in which the packing, though of lower symmetry, is somewhat tighter than in the crystals. 

Spectral properties The spectra of tripositive lanthanides show very sharp line like bands in the ultra-violet, visible or near infrared regions. The bands become more and more narrow and sharp as the temperature is lowered. These bands arise due to electronic transitions within the Af orbitals. The spectra of tri positive lanthanide ions and their complexes is similar because the environmental changes affecting the outermost orbitals do not much alter the wavelengths of the bands. These bands are very useful for characterising the lanthanides for their quantitative estimations. 

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