Triazine chloro derivatives: atrazine, simazine manifest no mutagenic and recombinogenic properties in yeasts; triazine methylthio derivatives: prometryne, semeron (desmetryne) generate both genetic ...events with low concentrations of 0.5 and 5 mg/l. It is found that prometryne is more able to generate point mutations, while semeron--to generate mitotic recombinations. In this case frequency of experimental prototrophs is twice higher than the control level.
Changes in yeast cells induced by the fungicide zineb were studied using biochemical, genetic techniques and electron microscopy. The primary changes involved anabolic processes since RNA and protein ...content increased in the cells. The data were consistent with a larger size of mitochondria. The oxidative-reductive activity of cell extracts did not change under the action of the fungicide. Zineb at a concentration of 0.5 to 50 mg/litre exerted a genetic activity towards indicator microorganisms. The changes in the morphophysiological characteristics of yeast growth under the action of zineb are presumed to be of a protective nature. Zineb traces in soil must be controlled in terms of the microbiological index.
Following the early prediction of the skyrmion lattice (SkL)--a periodic array of spin vortices--it has been observed recently in various magnetic crystals mostly with chiral structure. Although ...non-chiral but polar crystals with Cnv symmetry were identified as ideal SkL hosts in pioneering theoretical studies, this archetype of SkL has remained experimentally unexplored. Here, we report the discovery of a SkL in the polar magnetic semiconductor GaV4S8 with rhombohedral (C3v) symmetry and easy axis anisotropy. The SkL exists over an unusually broad temperature range compared with other bulk crystals and the orientation of the vortices is not controlled by the external magnetic field, but instead confined to the magnetic easy axis. Supporting theory attributes these unique features to a new Néel-type of SkL describable as a superposition of spin cycloids in contrast to the Bloch-type SkL in chiral magnets described in terms of spin helices.
Controlling and sensing spin polarization of electrons forms the basis of spintronics. Here, we report a study of the effect of helium on the spin polarization of the tunneling current and magnetic ...contrast in spin-polarized scanning tunneling microscopy (SP STM). We show that the magnetic contrast in SP STM images recorded in the presence of helium depends sensitively on the tunneling conditions. From tunneling spectra and their variation across the atomic lattice we establish that the helium can be reversibly ejected from the tunneling junction by the tunneling electrons. The energy of the tunneling electrons required to eject the helium depends on the relative spin polarization of the tip and sample, making the microscope sensitive to the magnetic exchange interactions. We show that the time-averaged spin polarization of the tunneling current is suppressed in the presence of helium and thereby demonstrate voltage control of the spin polarization of the tunneling current across the tip-sample junction.
We report the observation of an antipolar phase in cubic GaNb_{4}S_{8} driven by an unconventional microscopic mechanism, the cooperative Jahn-Teller effect of Nb_{4}S_{4} molecular clusters. The ...assignment of the antipolar nature is based on sudden changes in the crystal structure and a strong drop of the dielectric constant at T_{JT}=31 K, also indicating the first-order nature of the transition. In addition, we found that local symmetry lowering precedes long-range orbital ordering, implying the presence of a dynamic Jahn-Teller effect in the cubic phase above T_{JT}. Based on the variety of structural polymorphs reported in lacunar spinels, also including ferroelectric phases, we argue that GaNb_{4}S_{8} may be transformable to a ferroelectric state, which would further classify the observed antipolar phase as antiferroelectric.
Abstract
Magnetoelectric phenomena are intimately linked to relativistic effects and also require the material to break spatial inversion symmetry and time-reversal invariance. Magnetoelectric ...coupling can substantially affect light–matter interaction and lead to non-reciprocal light propagation. Here, we confirm on a fully experimental basis, without invoking either symmetry-based or material-specific assumptions, that the optical magnetoelectric effect in materials with non-parallel magnetization (
M
) and electric polarization (
P
) generates a trilinear term in the refractive index,
δ
n
∝
k
⋅ (
P
×
M
), where
k
is the propagation vector of light. Its sharp magnetoelectric resonances in the terahertz regime, which are simultaneously electric and magnetic dipole active excitations, make Co
2
Mo
3
O
8
an ideal compound to demonstrate this fundamental relation via independent variation of
M
,
P
, and
k
. Remarkably, the material shows almost perfect one-way transparency in moderate magnetic fields for one of these magnetoelectric resonances.
Sponges are probably the earliest branching animals, and their fossil record dates back to the Precambrian. Identifying their skeletal structure and composition is thus a crucial step in improving ...our understanding of the early evolution of metazoans. Here, we present the discovery of 505-million-year-old chitin, found in exceptionally well preserved Vauxia gracilenta sponges from the Middle Cambrian Burgess Shale. Our new findings indicate that, given the right fossilization conditions, chitin is stable for much longer than previously suspected. The preservation of chitin in these fossils opens new avenues for research into other ancient fossil groups.
The recent discovery of chitin within skeletons of numerous marine and freshwater sponges (Porifera) stimulates further experiments to identify this structural aminopolysaccharide in new species of ...these aquatical animals. Aplysina fistularis (Verongida: Demospongiae: Porifera) is well known to produce biologically active bromotyrosines. Here, we present a detailed study of the structural and physico-chemical properties of the three-dimensional skeletal scaffolds of this sponge. Calcofluor white staining, Raman and IR spectroscopy, ESI-MS as well as chitinase digestion test were applied in order to unequivocally prove the first discovery of α-chitin in skeleton of A. fistularis.
Excitations in a spin ice behave as magnetic monopoles, and their population and mobility control the dynamics of a spin ice at low temperature. CdEr2Se4 is reported to have the Pauling entropy ...characteristic of a spin ice, but its dynamics are three orders of magnitude faster than the canonical spin ice Dy2Ti2O7. In this Letter we use diffuse neutron scattering to show that both CdEr2Se4 and CdEr2S4 support a dipolar spin ice state-the host phase for a Coulomb gas of emergent magnetic monopoles. These Coulomb gases have similar parameters to those in Dy2Ti2O7, i.e., dilute and uncorrelated, and so cannot provide three orders faster dynamics through a larger monopole population alone. We investigate the monopole dynamics using ac susceptometry and neutron spin echo spectroscopy, and verify the crystal electric field Hamiltonian of the Er3+ ions using inelastic neutron scattering. A quantitative calculation of the monopole hopping rate using our Coulomb gas and crystal electric field parameters shows that the fast dynamics in CdEr2X4 (X=Se, S) are primarily due to much faster monopole hopping. Our work suggests that CdEr2X4 offer the possibility to study alternative spin ice ground states and dynamics, with equilibration possible at much lower temperatures than the rare earth pyrochlore examples.
The roots of Salvia miltiorrhiza (“Danshen”) are used in traditional Chinese medicine for the treatment of numerous ailments including cardiovascular disease, hypertension, and ischemic stroke. ...Extracts of S. miltiorrhiza roots in the formulation “Compound Danshen Dripping Pill” are undergoing clinical trials in the United States. To date, the active components of this material have not been conclusively identified. We have determined that S. miltiorrhiza roots contain potent human carboxylesterase (CE) inhibitors, due to the presence of tanshinones. K i values in the nM range were determined for inhibition of both the liver and intestinal CEs. As CEs hydrolyze clinically used drugs, the ability of tanshinones and S. miltiorrhiza root extracts to modulate the metabolism of the anticancer prodrug irinotecan (CPT-11) was assessed. Our results indicate that marked inhibition of human CEs occurs following incubation with both pure compounds and crude material and that drug hydrolysis is significantly reduced. Consequently, a reduction in the cytotoxicity of irinotecan is observed following dosing with either purified tanshinones or S. miltiorrhiza root extracts. It is concluded that remedies containing tanshinones should be avoided when individuals are taking esterified agents and that patients should be warned of the potential drug–drug interaction that may occur with this material.
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