174 research outputs found
Magnetic and spectral properties of multi-sublattice oxides SrY2O4:Er3+ and SrEr2O4
SrEr2O4 is a geometrically frustrated magnet which demonstrates rather
unusual properties at low temperatures including a coexistence of long- and
short-range magnetic order, characterized by two different propagation vectors.
In the present work, the effects of crystal fields (CF) in this compound
containing four magnetically inequivalent erbium sublattices are investigated
experimentally and theoretically. We combine the measurements of the CF levels
of the Er3+ ions made on a powder sample of SrEr2O4 using neutron spectroscopy
with site-selective optical and electron paramagnetic resonance measurements
performed on single crystal samples of the lightly Er-doped nonmagnetic
analogue, SrY2O4. Two sets of CF parameters corresponding to the Er3+ ions at
the crystallographically inequivalent lattice sites are derived which fit all
the available experimental data well, including the magnetization and dc
susceptibility data for both lightly doped and concentrated samples.Comment: 14 pages, 9 figure
Diagnostics of artificial ionospheric irregularities using short sounding radio paths
In this work, we consider the possibilities of diagnostics of artificial ionospheric irregularities with the transverse size l⊥ ≈ 50-200 m, which are excited in the Earth's ionosphere by highpower short-wave radio-frequency radiation from the "Sura" facility using the method of vertical sounding of the ionosphere by the ionosonde located near the heating facility. Some results of the performed studies showing the features of such a diagnostics are presented. © 2012 Springer Science+Business Media, Inc
Alternative route to charge density wave formation in multiband systems
Charge and spin density waves, periodic modulations of the electron and
magnetization densities, respectively, are among the most abundant and
non-trivial low-temperature ordered phases in condensed matter. The ordering
direction is widely believed to result from the Fermi surface topology.
However, several recent studies indicate that this common view needs to be
supplemented. Here, we show how an enhanced electron-lattice interaction can
contribute to or even determine the selection of the ordering vector in the
model charge density wave system ErTe3. Our joint experimental and theoretical
study allows us to establish a relation between the selection rules of the
electronic light scattering spectra and the enhanced electron-phonon coupling
in the vicinity of band degeneracy points. This alternative proposal for charge
density wave formation may be of general relevance for driving phase
transitions into other broken-symmetry ground states, particularly in multiband
systems such as the iron based superconductors
Laser Printing of Gel Microdrops with Living Cells and Microorganisms
We report the results of experiments on laser printing (wavelength λ=1064 nm) with gel microdrops acting as carriers of living microbial and cellular objects. The dynamics of transport processes with the help of high-speed optical video was studied, which allows to determine characteristics of the formed gel jets and to optimize the operating mode of the laser. It is shown that laser pulses of 4 to 20 ns duration and energy E ≤ 20 μJ should be used to minimize the negative effect on living systems. The results can be used to optimize the technologies of cellular printing and laser engineering of microbial systems (LEMS). LEMS technology is used to isolate hard-cultivated and non-cultivated by classical methods of microorganisms that can act as producers of new biologically active substances and antibiotics.
Keywords: laser printing, gel, microdrop, living cell, microbia
Novel base-pairing interactions at the tRNA wobble position crucial for accurate reading of the genetic code
Posttranscriptional modifications at the wobble position of transfer RNAs play a substantial role in deciphering the degenerate genetic code on the ribosome. The number and variety of modifications suggest different mechanisms of action during messenger RNA decoding, of which only a few were described so far. Here, on the basis of several 70S ribosome complex X-ray structures, we demonstrate how Escherichia coli tRNA Lys UUU with hypermodified 5-methylaminomethyl-2-thiouridine (mnm 5 s 2 U) at the wobble position discriminates between cognate codons AAA and AAG, and near-cognate stop codon UAA or isoleucine codon AUA, with which it forms pyrimidine-pyrimidine mismatches. We show that mnm 5 s 2 U forms an unusual pair with guanosine at the wobble position that expands general knowledge on the degeneracy of the genetic code and specifies a powerful role of tRNA modifications in translation. Our models consolidate the translational fidelity mechanism proposed previously where the steric complementarity and shape acceptance dominate the decoding mechanism
EPR Study of the Vanadium Ions in Mg2SiO4 Crystal
Vanadium-doped forsterite crystal has been studied with X-band electron paramagnetic resonance (EPR) spectroscopy. The sample was grown by the Czochralski technique in an argon atmosphere with 2 vol% of hydrogen. The EPR spectrum of the sample at T = 15 K is predominantly represented by the V4+ ion signals that possess a characteristic eight-line hyperfine structure and are observed close to g = 2. The observation of the two magnetically nonequivalent centers in the angular dependence in the (ab) crystal plane and one center in the (ac) and (bc) planes, combined with the published optical spectroscopy data, unambiguously show that the V4+ ions are located at the silicon lattice site. Principal values of the hyperfine A and g-tensor and magnetic axes orientations of the V4+ centers have been determined. The orientation disorder of the V4+ centers has been found around the crystalline c axis but not in the (ab) crystal plane. The angular variation of the hyperfine component linewidth is described best with a disorder range of ±3. 0°. © 2012 Springer-Verlag Wien
Quantum Transport in Ladder-Type Networks: Role of nonlinearity, topology and spin
We investigate quantum transport of electrons, phase solitons, etc. through
mesoscopic networks of zero-dimensional quantum dots. Straight and circular
ladders are chosen as networks with each coupled with three semi-infinite leads
(with one incoming and the other two outgoing). Two transmission probabilities
(TPs) as a function of the incident energy show a transition from
anti-phase aperiodic to degenerate periodic spectra at the critical energy
which is determined by a bifurcation point of the bulk energy
dispersions. TPs of the circular ladder depend only on the parity of the
winding number. Introduction of a single missing bond (MB) or missing step
doubles the period of the periodic spectra at . Shift of
the MB by lattice constant results in a striking switching effect at
. In the presence of the electric-field induced spin-orbit
interaction (SOI), an obvious spin filtering occurs against the
spin-unpolarized injection. Against the spin-polarized injection, on the other
hand, the spin transport shows spin-flip (magnetization reversal) oscillations
with respect to SOI. We also show a role of soliton in the context of its
transport through the ladder networks.Comment: 10 pages, 16 figure
Ultrafast changes in lattice symmetry probed by coherent phonons
The electronic and structural properties of a material are strongly
determined by its symmetry. Changing the symmetry via a photoinduced phase
transition offers new ways to manipulate material properties on ultrafast
timescales. However, in order to identify when and how fast these phase
transitions occur, methods that can probe the symmetry change in the time
domain are required. We show that a time-dependent change in the coherent
phonon spectrum can probe a change in symmetry of the lattice potential, thus
providing an all-optical probe of structural transitions. We examine the
photoinduced structural phase transition in VO2 and show that, above the phase
transition threshold, photoexcitation completely changes the lattice potential
on an ultrafast timescale. The loss of the equilibrium-phase phonon modes
occurs promptly, indicating a non-thermal pathway for the photoinduced phase
transition, where a strong perturbation to the lattice potential changes its
symmetry before ionic rearrangement has occurred.Comment: 14 pages 4 figure
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