Ferroelectricity induced by spin-dependent metal-ligand hybridization in Ba₂CoGe₂O₇

We have investigated the variation of induced ferroelectric polarization under a magnetic field with various directions and magnitudes in a staggered antiferromagnet Ba?CoGe?O?. While the ferroelectric polarization cannot be explained by the well-accepted spin current model nor the exchange striction mechanism, we have shown that it is induced by the spin-dependent p-d hybridization between the transition metal (Co) and ligand (O) via the spin-orbit interaction. On the basis of the correspondence between the direction of electric polarization and the magnetic state, we have also demonstrated the electrical control of the magnetization direction.     

Structural and valence changes of europium hydride induced by application of high-pressure H₂

Europium hydride EuH(x), when exposed to high-pressure H?, has been found to exhibit the following structural and valence changes: Pnma(x = 2, divalent) → P6?/mmc(x = 2, 7.2-8.7 GPa) → I4/m(x > 2, 8.7-9.7 GPa) → I4/mmm(x > 2, 9.7 GPa-,trivalent). With a trivalent character and a distorted cubic fcc structure, the I4/mmm structure is the β phase commonly observed for other rare-earth metal hydrides. Our study clearly demonstrates that EuH(x) is no longer an irregular member of the rare-earth metal hydrides.     

Selective detection of ¹³CHD₂ signals from a mixture of ¹³CH₃/¹³CH₂D/¹³CHD₂ methyl isotopomers in proteins

In NMR spectra of partially deuterated proteins methyl correlations are commonly observed as a combination of signals from 13CH?, 13CH?D and 13CHD? isotopomers. In a number of NMR applications, methyl groups of the 13CHD? variety are targeted because of their AX-like character and concomitant simplification of the involved relaxation mechanisms. Although complete elimination of signals from 13CH?D methyl groups can be easily achieved in such applications, if the magnetization is not transferred through deuterium nuclei, efficient suppression of usually stronger 13CH? peaks is more problematic. A pair of simple pulse-scheme elements are presented that achieve almost complete suppression of 13CH? signals in the mixtures of 13CH?/13CH?D/13CHD? methyl isotopomers of small proteins at the expense of a moderate (～20-to-40%) reduction in intensities of the targeted 13CHD? groups. The approaches described are based purely on scalar coupling (1J(CH)) evolution properties of different 13C and 1H transitions within 13CH? spin-systems and are superior to magnetization transfer through deuterons with respect to sensitivity of the detected 13CHD? methyl signals.     

The infra-red L.M.R. spectrum of SeH in the X 2Π state

Magnetic dipole transitions between the ²Π_1/2 and ²Π_3/2 components of the ground state of SeH have been observed at about 1780 cm^-1 in a L.M.R. experiment using a CO laser. Transitions have been detected for the four most abundant natural isotopes of Se. The transition frequencies depend primarily on the magnitude of the spin-orbit coupling constant and have been analysed in conjunction with data from the E.P.R. spectrum to yield

The admixture of other electronic states by spin-orbit coupling has been investigated to third order in perturbation theory and found to produce significant effects.     

Ultrafast hopping dynamics of 5f electrons in the Mott insulator UO₂ studied by femtosecond pump-probe spectroscopy

We describe a femtosecond pump-probe study of ultrafast hopping dynamics of 5f electrons in the Mott insulator UO? following Mott-gap excitation at temperatures of 5-300 K. Hopping-induced response of the lattice and electrons is probed by transient reflectivity at mid- and above-gap photon energies, respectively. These measurements show an instantaneous hop, subsequent picosecond lattice deformation, followed by acoustic phonon emission and microsecond relaxation. Temperature-dependent studies indicate that the slow relaxation results from Hubbard excitons formed by U3?-U?? pairs.     

Dynamic modelling and simulation of ¹⁵N separation by chemical exchange in NO, NO₂-HNO₃ system

The dynamic behaviour of a 1?N separation process by chemical exchange in a NO, NO?-HNO? system has been analysed based on an accurate mathematical model. A nonlinear system of first-order partial differential equations was determined by considering the multiple exchange reactions between the components of the gaseous mixture and the liquid phase constituents. The mathematical model of the process describes the space-time variation of the 1?N mole fraction in gas and liquid phases and provides a better understanding of operating limits and decision support in process design and optimisation.     

Measurement of magnetic excitations in the two-dimensional antiferromagnetic Sr₂CuO₂Cl₂ insulator using resonant x-ray scattering: evidence for extended interactions

We measured the momentum dependence of magnetic excitations in the model spin-1/2 2D antiferromagnetic insulator Sr2CuO2Cl2 (SCOC). We identify a single-spin-wave feature and a multimagnon continuum, with different polarization dependences. The spin waves display a large (70 meV) dispersion between the zone-boundary points (π, 0) and (π/2, π/2). Employing an extended t-t'-t'-U one-band Hubbard model, we find significant electronic hopping beyond nearest-neighbor Cu ions, indicative of extended magnetic interactions. The spectral line shape at (π, 0) indicates sizable quantum effects in SCOC and probably more generally in the cuprates.     

Ionization of Hafnium L—Shell by Electron Impact

A lower-energy electron beam has been directed on to a hafnium thin target with thick backing to investigate the process of L-shell ionization.By using a Si(Li) detector to count the x-rays from the L-subshell,the partial and total production cross sections and mean ionization cross sections versus electron energies have been deduced simultaneously (from threshold to 36keV),The influence of the electron reflected from the backing on measurements has been corrected.The path of the electron multi-scattered in the target itself has also been calculated by using the Monte Carlo programme(EGS4).A comparison with both theoretical predictions is given.     

Comment on “Role of the velocity frame of reference in thermodiffusion in liquid mixtures” by M. Eslamian,C.G. Jiang and M.Z. Saghir

We analyze the material transport equations (MTE) derived by Eslamian and co-authors and address the criticism expressed regarding the approach formulated in our previous work. In doing so, we show that the MTE formulated by Eslamian and co-authors are valid only in closed stationary non-isothermal systems in combination with the restrictions on the Onsager coefficients formulated in our work which is criticized, and that for non-stationary systems the approach we took can be used.     

Cascaded Raman shifting of high-peak-power nanosecond pulses in As₂S₃ and As₂Se₃ optical fibers

We report efficient cascaded Raman scattering of near-IR nanosecond pulses in large-core (65 μm diameter) As?S? and As?Se? optical fibers. Raman scattering dominates other spectral broadening mechanisms, such as four-wave mixing, modulation instability, and soliton dynamics, because the fibers have large normal group-velocity dispersion in the spectral range of interest. With ~2 ns pump pulses at a wavelength of 1.9 μm, four Stokes peaks, all with peak powers greater than 1 kW, have been measured.     

Comment on “Evaluation of concentration-depth profiles by sputtering in SIMS and AES” by S. Hofmann

The statistics of the sputtering process, which has been used to explain sputterbroadening effect due to surface roughness, has been treated with conditional probabilities. This results in the relationship, , instead of derived by S. Hofmann [Appl. Phys.9, 59 (1976)], where δz,z, and are the depth resolution, sputtered depth and sputtering yield, respectively.     

Evaluation of the oral ¹³C-bicarbonate tracer technique for the estimation of CO₂ production and energy expenditure in dogs during rest and physical activity

For feeding of working dogs during their daily life, illness, routine jobs or sporting activities, an accurate determination of their nutritional requirements is essential to ensure their optimal health and performance. To predict the appropriate guidelines about how to feed dogs, it appears essential to determine the energy expenditure (EE) in a reliable and feasible way. In the present experiment, the non-invasive oral 13C-bicarbonate tracer technique (o13CT), i.e. collection of breath samples after oral administration of NaH13CO?, was used for the estimation of CO? production and EE in dogs. Measurements were conducted during two days of rest, and during three days with 3 h of exercise per day. Average EE was 483 and 876 kJ kg??·?? d?1 during rest and exercise, respectively. The o13CT seems appropriate to use as a minimal restrictive and non-invasive method to obtain reliable estimates of EE in dogs at different activity levels under near natural conditions.     

V.L. Ginzburg’s elliptic screw polarization modes in an optical medium with linear birefringence and twist: Determination of their parameters by the method of Jones matrices

The effect of electromagnetically induced transparency (EIT) has been experimentally implemented for the first time for the (4S _1/2–4P _1/2–4S _1/2) Λ-system of potassium atom levels in a nanocell with a 770-nm-thick column of atomic vapor. It is shown that, at such a small thickness of the vapor column, the EIT resonance can be observed only when the coupling-laser frequency is in exact resonance with the frequency of the corresponding atomic transition. The EIT resonance disappears even if the coupling-laser frequency differs slightly (by ~50 MHz) from that of the corresponding atomic transition, which is due to the high thermal velocity of K atoms. The EIT resonance and related velocity selective optical pumping resonances caused by optical pumping (formed by the coupling) can be simultaneously recorded because of the small (~462 MHz) hyperfine splitting of the lower 4S _1/2 level.     

Gate-voltage control of chemical potential and weak antilocalization in Bi₂Se₃

We report that Bi?Se? thin films can be epitaxially grown on SrTiO? substrates, which allow for very large tunablity in carrier density with a back gate. The observed low field magnetoconductivity due to weak antilocalization (WAL) has a very weak gate-voltage dependence unless the electron density is reduced to very low values. Such a transition in WAL is correlated with unusual changes in longitudinal and Hall resistivities. Our results suggest a much suppressed bulk conductivity at large negative gate voltages and a possible role of surface states in the WAL phenomena.     

High-Order Harmonic Generation by Two Non-Collinear Femtosecond Laser Pulses in CO

We have experimentally studied the high order harmonic generation (HHG) in CO molecules by two femtosecond laser pulses using a pump-probe technique. The delay time between two pulses is longer than the pulse duration, and the pump intensity is about 6.2 x 10^14 W/cm^2. It is found that the HHG signal is independent of the time delay in the picosecond region, but it is dependent on the distance between the centres of focuses of the two beams. The phase modulation induced by the pump pulse is regarded to be responsible for this.