Crystal truncation rods in kinematical and dynamical x-ray diffraction theories

Crystal truncation rods calculated in the kinematical approximation are shown to quantitatively agree with the sum of the diffracted waves obtained in the two-beam dynamical calculations for different reflections along the rod. The choice and the number of these reflections are specified. The agreement extends down to at least $\sim 10^{-7}$ of the peak intensity. For lower intensities, the accuracy of dynamical calculations is limited by truncation of the electron density at a mathematically planar surface, arising from the Fourier series expansion of the crystal polarizability

High-pressure versus isoelectronic doping effect on the honeycomb iridate Na2_2IrO3_3

We study the effect of isoelectronic doping and external pressure in tuning the ground state of the honeycomb iridate Na$_2$IrO$_3$ by combining optical spectroscopy with synchrotron x-ray diffraction measurements on single crystals. The obtained optical conductivity of Na$_2$IrO$_3$ is discussed in terms of a Mott insulating picture versus the formation of quasimolecular orbitals and in terms of Kitaev-interactions. With increasing Li content $x$, (Na$_{1-x}$Li$_x$)$_2$IrO$_3$ moves deeper into the Mott insulating regime and there are indications that up to a doping level of 24\% the compound comes closer to the Kitaev-limit. The optical conductivity spectrum of single crystalline $\alpha$-Li$_2$IrO$_3$ does not follow the trends observed for the series up to $x=0.24$. There are strong indications that $\alpha$-Li$_2$IrO$_3$ is less close to the Kitaev-limit compared to Na$_2$IrO$_3$ and closer to the quasimolecular orbital picture. Except for the pressure-induced hardening of the phonon modes, the optical properties of Na$_2$IrO$_3$ seem to be robust against external pressure. Possible explanations of the unexpected evolution of the optical conductivity with isolectronic doping and the drastic change between $x=0.24$ and $x=1$ are given by comparing the pressure-induced changes of lattice parameters and the optical conductivity with the corresponding changes induced by doping.Comment: 12 pages, 6 figures, accepted for publication in Phys. Rev.

Ferromagnetism or slow paramagnetic relaxation in Fe-doped Li3_3N?

We report on isothermal magnetization, M\"ossbauer spectroscopy, and magnetostriction as well as temperature-dependent alternating-current (ac) susceptibility, specific heat, and thermal expansion of single crystalline and polycrstalline Li$_2$(Li$_{1-x}$Fe$_x$)N with $x = 0$ and $x \approx 0.30$. Magnetic hysteresis emerges at temperatures below $T \approx 50\,$K with coercivity fields of up to $\mu_0H = 11.6\,$T at $T = 2\,$K and magnetic anisotropy energies of $310\,$K ($27\,$meV). The ac susceptibility is strongly frequency dependent ($f\,=\,10$--$10,000\,$Hz) and reveals an effective energy barrier for spin reversal of $\Delta E \approx 1100\,$K. The relaxation times follow Arrhenius behavior for $T > 25\,$K. For $T < 10\,$K, however, the relaxation times of $\tau \approx 10^{10}\,$s are only weakly temperature-dependent indicating the relevance of a quantum tunneling process instead of thermal excitations. The magnetic entropy amounts to more than $25\,$J mol$^{-1}_{\rm Fe}\,$K$^{-1}$ which significantly exceeds $R$ln2, the value expected for the entropy of a ground state doublet. Thermal expansion and magnetostriction indicate a weak magneto-elastic coupling in accordance with slow relaxation of the magnetization. The classification of Li$_2$(Li$_{1-x}$Fe$_x$)N as ferromagnet is stressed and contrasted with highly anisotropic and slowly relaxing paramagnetic behavior.Comment: 12 pages, 10 figure

Starburst in the Intragroup Medium of Stephan's Quintet

Based on new ISO mid-infrared observations and ground based $H_\alpha$ and near-infrared observations, we report the detection of a bright starburst in the intragroup medium (IGM) of the famous compact group of galaxies Stephan's Quintet (Source A in Fig.1). We demonstrate that this starburst is caused by a collision between a high velocity ($\delta$V$\sim$ 1000 km/sec) intruder galaxy (NGC7318b) and the IGM of the group. While this is the only starburst known today that is induced by a galaxy/cold-intergalactic-medium collision, it provides new constraints to the theory for interaction-induced starbursts, and may hint at a new mechanism for the star formation excess seen in more distant clusters.Comment: 17 pages, 2 PS figures. Accepted by Ap

Persistent detwinning of iron pnictides by small magnetic fields

Our comprehensive study on EuFe$_2$As$_2$ reveals a dramatic reduction of magnetic detwinning fields compared to other AFe$_2$As$_2$ (A = Ba, Sr, Ca) iron pnictides by indirect magneto-elastic coupling of the Eu$^{2+}$ ions. We find that only 0.1T are sufficient for persistent detwinning below the local Eu$^{2+}$ ordering; above $T_\text{Eu}$ = 19K, higher fields are necessary. Even after the field is switched off, a significant imbalance of twin domains remains constant up to the structural and electronic phase transition (190K). This persistent detwinning provides the unique possibility to study the low temperature electronic in-plane anisotropy of iron pnictides without applying any symmetrybreaking external force.Comment: accepted by Physical Review Letter

Анализ методов повышения эффективности эксплуатации газлифтных скважин на месторождениях Вьетнама

Объектами исследования являются нефтяные месторождения Белый Тигр и Дракон (Вьетнам). Цель работы – проанализировать исследования скважин на режимах сниженных расходов газлифтного газа с целью определения оптимального режима работы на месторождениях "Белый Тигр" и "Дракон". Задачи работы: изучить основные геологические характеристики месторождений "Белый Тигр" и "Дракон"; оценить состояние разработки месторождений "Белый Тигр" и "Дракон"; проанализировать применение газлифтной технологии на данных месторождениях; выбрать и обосновать оптимальный режим работы газлифтных скважин; проводить расчет затрат на замену НКТ большего диаметра; изучить информацию по технике безопасности при эксплуатации газлифтных скважин.The objects of the study are “White Tiger” and “Dragon” (Vietnam) oil fields. The purpose of the research is to analyze well survey at reduced rate regimes of gaslift gas in order to determine the optimum regime on “White Tiger” and “Dragon” oil fields. The tasks of the study: to examine the main geological characteristic of “White Tiger” and “Dragon” oil fields; to value the development state of “White Tiger” and “Dragon” oil fields; to analyze the application of gaslift technology on these oil fields; to choose and give proof of an optimal regime of gaslift gaslift well; to calculate the cost estimating of replacement to bigger diameter oil-well tubing; to find information of safety techniques of gas-lift well operation

A 100ks XMM-Newton view of the Seyfert 1.8 ESO113-G010. I. Discovery of large X-ray variability and study of the FeKalpha line complex

(Abridged) We present here a long (100ks) XMM-Newton follow-up of the Seyfert 1.8 galaxy ESO113-G010 performed in November 2005, in order to study over a longer time-scale its main X-ray properties. The source was found in a higher/softer time-averaged flux state, and timing analysis of this source reveals strong, rapid variability. The Power Spectral Density (PSD) analysis indicates (at 95% c.l.) a break at 3.7 x 10^-4 Hz. This cut-off frequency is comparable to those measured in some other rapidly-variable Seyferts, such as MCG-6-30-15 and NGC4051. From the mass-luminosity-time-scale, we infer that M_BH ranges from 4 x 10^6 - 10^7 M_odot and the source is accreting at or close to the Eddington rate (or even higher). The existing data cannot distinguish between spectral pivoting of the continuum and a two-component origin for the spectral softening, primarily because the data do not span a broad enough flux range. In the case of the two-component model, the fractional offsets measured in the flux-flux plots increase significantly toward higher energies (similar to what is observed in MCG-6-30-15) as expected if there exists a constant reflection component. Contrary to May 2001, no significant highly redshifted emission line is observed (which might be related to the source flux level), while two narrow emission lines at about 6.5keV and 7keV are observed. The S/N is not high enough to establish if the lines are variable or constant. As already suggested by the 2001 observation, no significant constant narrow 6.4keV FeK line (EW~32eV) is observed, hence excluding any dominant emission from distant cold matter such as a torus in this Seyfert type 1.8 galaxy.Comment: Accepted for publication in A&A, 10 pages, 11 figures, 2 table