Asymptotic directional structure of radiation for fields of algebraic type D

The directional behavior of dominant components of algebraically special spin-s fields near a spacelike, timelike or null conformal infinity is studied. By extending our previous general investigations, we concentrate on fields which admit a pair of equivalent algebraically special null directions, such as the Petrov type-D gravitational fields or algebraically general electromagnetic fields. We introduce and discuss a canonical choice of the reference tetrad near infinity in all possible situations, and we present the corresponding asymptotic directional structures using the most natural parametrizations.Dedicated to Prof. Jií Horáek on the occasion of his 60th birthday     

Supersymmetric SO10 seesaw mechanism with low B-L scale

We propose a new seesaw mechanism for neutrino masses within a class of supersymmetric SO(10) models with broken D parity. It is shown that in such scenarios the B-L scale can be as low as TeV without generating inconsistencies with gauge coupling unification nor with the required magnitude of the light neutrino masses. This leads to a possibly light new neutral gauge boson as well as relatively light quasi-Dirac heavy leptons. These particles could be at the TeV scale and mediate lepton flavor and CP violating processes at appreciable levels.     

Anisotropic exchange and magnetic excitations in KCoF3

A superexchange mechanism is used for the determination of the form of the exchange Hamiltonian in KCoF₃ introducing only two independent parameters. The Co²⁺ ions are orbitally degenerate and this leads to the anisotropic exchange in KCoF₃. The collective excitations are introduced being based on the space of selfconsistently determined states of Co²⁺ ions in the low temperature approximation. The effective exchange field is introduced in this many-level system so that the one-ion eigenvalue problem can be solved. The agreement with two lowest branches of magnetic excitation spectra is satisfactory. It is emphasized that the appropriate general form of the exchange Hamiltonian which includes the orbital operators should be used for the interpretation of experimental data instead of the simple isotropic form. In the case of KCoF₃, however, it appears that the dispersion relation for magnetic excitations is rather insensitive on the form of the model Hamiltonian.     

The use of the kramers-kronig relations in determining optical constants

The paper discusses some of the ways in which to avoid difficulties in applying dispersion relations to experimental data of the optical constants of solids, particularly with regard to measurements in a narrow frequency range.

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Double cascade transitions of gamma rays from radiative capture on Co59

Pairs of gamma quanta, giving a sum equal to the binding energy of the last neutron in a Co⁶⁰ isotope, were studied during radiation capture on a Co⁵⁹ nucleus. The energies of the gamma quanta giving such cascades were determined and an attempt was made to determine the relative intensities of the different cascades.

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Co⁵⁹ -, Co⁶⁰. -, , .

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In conclusion the authors thank J. Vávra for cooperation in the measurements.     

The influence of the divergence of X-rays on the determination of volume of diffracting particles

The relation was investigated of the number of diffraction spots from unit volume of a polycrystal to the mean instrumental divergence _m of X-ray beam. Experimental evidence proves this dependence to be decreasing, in contradiction to the generally accepted theoretical basis of the method. These experimental results mean an increasing effective volume of diffracting particles with increasing instrumental divergence. Thus the application of the quantity _m itself distorts the true dependence of number of spots on instrumental divergence. We shall prove this statement and shall apply the previous experimental results to infer more detailed ideas on the mentioned dependence, while using the instrumental divergence instead of the mean value _m .This detailed analysis of experimental results contributes to better understanding of the method and suggests the precautions to be taken in the interpretation of results when determining the volume of diffracting particles from spotty diffraction lines.The author is indebted to Dr. J.ermák C.Sc. for encouraging discussions and for steady interest during the work.     

Morphology and crystallography of martensite in Fe-23% Ni-0·38% C alloy induced by plastic deformation of austenite

A tensile deformation at the temperatures between Ms and Md induces in Fe-23% Ni-0·38% C alloy the so-called butterfly martensite, whose morphology is different from that of thermally transformed martensite. The amount of these butterflies increases gradually with deformation and contributes to the transformation — induced plasticity. The difference in morphology corresponds with a different structure, substructure and crystallography and it is caused by the change of transformation mechanism.The author would like to express his thanks to Ing. P.Michalika for his help with metallographic preparation of specimens.     

On the numerical solution of the evolution equation in QCD

We discuss in some detail the algorithm for the numerical solution of QCD evolution equations in the next-to-leading order. Relative merits and shortcomings of this method are presented and compared with those of other available approaches. Effective control of the accuracy of obtained results is stressed.     

Sums of prime powers

It is shown that iff is a suitable polynomial then every sufficiently large positive integer is a sum of distinct summands taken from the sequence {f(p)}, wherep runs through rational primes.