Confinement of chiral magnetic modulations in the precursor region of FeGe.

We report on magnetic susceptibility and specific heat measurements of the cubic helimagnet FeGe in external magnetic fields and temperatures near the onset of long-range magnetic order at TC = 278.2(3) K. Pronounced anomalies in the field-dependent χac(H) data as well as in the corresponding imaginary part χ''ac(H) reveal a precursor region around TC in the magnetic phase diagram. The occurrence of a maximum at T0 = 279.6 K in the zero-field specific heat data indicates a second-order transition into a magnetically ordered state. A shoulder evolves above this maximum as a magnetic field is applied. The field dependence of both features coincides with crossover lines from the field-polarized to the paramagnetic state deduced from χac(T) at constant magnetic fields. The experimental findings are analyzed within the standard Dzyaloshinskii theory for cubic helimagnets. The remarkable multiplicity of modulated precursor states and the complexity of the magnetic phase diagram near the magnetic ordering are explained by the change of the character of solitonic inter-core interactions and the onset of specific confined chiral modulations in this area.

Precursor phenomena at the magnetic ordering of the cubic helimagnet FeGe.

We report on detailed magnetic measurements on the cubic helimagnet FeGe in external magnetic fields and temperatures near the onset of long-range magnetic order at T(C)=278.2(3) K. Precursor phenomena display a complex succession of temperature-driven crossovers and phase transitions in the vicinity of T(C). The A-phase region, present below T(C) and fields H<0.5 kOe, is split in several pockets. The complexity of the magnetic phase diagram is theoretically explained by the confinement of solitonic kinklike or Skyrmionic units that develop an attractive and oscillatory intersoliton coupling owing to the longitudinal inhomogeneity of the magnetization.

[Interaction of 23S ribosomal RNA helices 89 and 91 of Escherichia coli contributes to the activity of IF2 but is insignificant for elongation factors functioning].

The non-canonical base-pair C2475/G2529 joins helices 89 and 91 of the 23S rRNA in the large subunit of E. coli ribosomes. These nucleotides are located at the "crossroads" between the peptidyl transferase center, the sarcin-ricin loop and the GTPase-associated center. We probed the functional role of nucleotides C2475/G2529 by the mutations C2475G, C2475G/G2529C and deltaA2471/U2479 of 23S rRNA. All these mutations had no influence on the elongation factors activity but had different effects on the cell growth, 23S rRNA conformation and translation initiation. C2475G/G2529C and C2475G mutations led to more or less substantial decrease in IF2.GDPNP binding to the ribosomes, and IF2-assisted initiation complex formation. Ribosome-dependent GTPase activity of IF2 was enhanced by both C2475G/G2529C and C2475G mutations. Mutation deltaA2471/U2479 has no influence on IF2.GDPNP binding to the ribosome, but reduces IF2-dependent formation of initiation complex and the ribosome-dependent GTPase activity. Thus, the contact between helices 89 and 91 is important for efficient IF2 functioning in translation initiation.

Apollo-Soyuz Test Project on biorhythm of zone-forming fungi: preliminary work.

The purpose of the experiment was to study general and local effects of space flight factors on the rhythm of cellular activity and on the morphological and genetic properties of biological objects. The Pushchino strain, Actinomyces levoris Kras 17-225A-IBFM, isolated at the Institute of Biological Physics, Moscow, was chosen as the main biological object. Under appropriate conditions it gives distinct and continuous rings of spore formation reflecting its intrinsic high degree of synchronism in changing its reproduction forms seen with the unaided eye as transparent rings (vegetative growth) alternate with convex white rings (spore-formation growth). As an additional test object, a film culture of bacteriophage T4Br+ developed at the institute was used. The strains were placed together in one bioblock together with plastic detectors for detecting nuclear particles. The film culture of bacteriophage enabled us to amplify the area of registration of local radiation effects by studying the genetic effects of these: frequency of mutations, induced radiation, their spectrum, subsequent revertability under the action of chemical mutagens with known mechanisms of action on DNA molecules.