AliSTUACTS OF TKCIIMCAL AIITICLKS 1253 



(^Uiilily l"]k'cti'()iii(' CDUipoiKMits. l*i-()cco(liii<2;s, \\'u.sli., I). ('., May 5-7, 

 1952. Wash., D. C, R. T. M. A., 1052. 



Energy of a Block Wall on the Band Picture. II. Perlurbation. Approach. 

 ('. Herring'. Phys. Rev., 87, pp. 00-70, July 1, 1952. 



The "oxchanjre stiffness" constant, which ajipears in the theory of tlie Bloch 

 intenloniain wall in ferroniagnetics, can be calculated by coniputin};' the response 

 of a saturated sjiecinien to a small si)atially varyinji perturbinji field. This calcu- 

 lation is carried out here in the self-consistent field appioxiniation, using ruiniing 

 wa\'es for the one-electron states, and the result is intcr])reted phj'sicall.v in 

 terms of precession of tlie spins of moving electrons. Combination of the present 

 theoiy with the Stoner-Wohlfarth model of the ferromagnetic electrons in nickel 

 does not give satisfactory results, pi'obably because the latter model does not 

 approximate the actual self-consistent field solution very well. However, appUca- 

 tion of the theoi-y (o the free electron gas is of interest as a confirmation of the 

 validity of the ])erturbati()n approach. It is shown that there exist, even in a 

 ferromagnetic metal, (juantum states oi-thogonal to all the low-lying states of the 

 conventional band picture and ha\-ing the proi)erties of spin waves. The pre- 

 sumably univei'sal relation between the exchange stiffness constant and the 

 energies of spin waves of long wavelength is \-erified in the present approximation. 

 It is shown that spin waves carry a current in a metal, though not in an insulator. 

 For spin waves of long wavelength the present theorj^ can be shown to include 

 Slater's theory of spin waves in a ferromagnetic insulator, and a fortiori to include 

 all previous theories based on the atomic model. 



Nonsynchronous Pulse Multiplex System. A. L. Hopper^ Electronics, 

 25, pp. 116-120, August, 1952. 



A'oice transmitters use one frequency simultaneous!}" but no sj'nchronizing 

 pulse is necessary, although time-division multiplexing is used. Random samples 

 from each transmitter are tagged for identification at proper receiver. S3'Stem 

 is applicable to rural telephony and moving-vehicle communication. 



Design of Modulation lujuipincnt for Modern Single-Sideband Trans- 

 witters. A. E. Kerwikx'. /. R. E., Proe., 40, pp. 797-80,3, .Tuly, 1952. 

 (.Monograph 2012). 



This paper deals with considerations that go into the design of modulation 

 equipment for a single-sideband radiotelephone transmitter in which filters are 

 used for sideband suppression. Balance requirements, frequency- stability, the 

 choice of intermediate frequencies, and methods of avoiding transmission of 

 spurious frequencies are among the factors which are discussed. 



,4 Multichannel Single-Sideband Radio Transmitter. Ij. M. Klenk\ A. 

 J. Munn\ and J. Nedelka\ /. R. E. Proe., 40, pp. 797-803, July, 1952. 

 (Monograph 2012). 



This paper describes a new single-sideband radio transmitter for transoceanic 



* Bell Telephone Laboratories 



