159 elements only between states which differ in one of the single-electron wave functions, in short, HeR induces only one-electron transitions. The matrix elements 1mn and Pmn reduce to matrix elements between the single-electron wave functions. We are interested primarily in crystalline solids for which the band model is a good approximation. The Bloch single-electron wave function in this model has the form: N'I ili-';; U. r.;;) ( (1.14) "nk r, =e nh , where n is the band index and U (r) has the periodicity of the lattice. The form of the Bloch function follows from the translational...

The dynamical properties of solids have recently attracted renewed interest in connection with the increasing understanding of phase transitions and re lated phenomena. In particular, soft modes or, more generally, phonon 'anom alies' seem to play an important role in structural and electronic phase tran sitions, such as ferroelectric or superconducting transitions. The understanding of the mechanisms responsible for the occurrence of unusually low frequencies in phonon spectra requires a detailed analysis of the microscopic forces governing the lattice vibrations. Of particular importance is...

69 Eine typische Aufgabe ist die: Ein bestimmter, kreisfOrmiger Objekt-Ebenen- Ausschnitt (F eld genannt) soIl mit weiBem Licht durch ein System aus brechenden Kugel- oder Plan-Flachen abgebildet werden auf eine Bild-Ebene, in einem be- 1 stimmten MaBstab und (meistens) unter Beachtung weiterer Bedingungen . Dabei sollen die Linsenfassungen und die Blende des Systems solche Durchmesser haben, daB mindestens die Punkte der Feld-Mitte durch Strahlenbiindel bestimmter GroBe (Offnung genannt) abgebildet werden. SchlieBlich sollen die unvermeid- lichen Abweichungen von der idealen punktformigen...

Sect. 23. 325 transitions have been drawn for which L1 =0 (n-components). Moreover it is assumed that the hfs splitting of the 3 s 2 Pal, level is negligibly small compared with that of the 3 s 25, /, level. BACK and GOUDSMIT succeeded in resolving the structure of the components of the Bi I line A 4722 A. In each transition they found 10 components, so that in this case 21 ] 1 = 10, and the nuclear spin of 209 Bi becomes 1 = 9/, Later on their results for a group of components were 2 reproduced and published by ZEEMAN, BACK and GOUDSMITI. There are only a few examples where the influence of...