2,115 research outputs found
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 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 NaIrO
We study the effect of isoelectronic doping and external pressure in tuning
the ground state of the honeycomb iridate NaIrO by combining optical
spectroscopy with synchrotron x-ray diffraction measurements on single
crystals. The obtained optical conductivity of NaIrO 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 ,
(NaLi)IrO 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 -LiIrO does not follow the trends observed for the
series up to . There are strong indications that -LiIrO
is less close to the Kitaev-limit compared to NaIrO and closer to the
quasimolecular orbital picture. Except for the pressure-induced hardening of
the phonon modes, the optical properties of NaIrO 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 and 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 LiN?
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(LiFe)N with and .
Magnetic hysteresis emerges at temperatures below K with
coercivity fields of up to T at K and magnetic
anisotropy energies of K (meV). The ac susceptibility is strongly
frequency dependent (--Hz) and reveals an effective energy
barrier for spin reversal of K. The relaxation times
follow Arrhenius behavior for K. For K, however, the
relaxation times of 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
J molK which significantly exceeds 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(LiFe)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 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 (V 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 EuFeAs reveals a dramatic reduction of
magnetic detwinning fields compared to other AFeAs (A = Ba, Sr, Ca)
iron pnictides by indirect magneto-elastic coupling of the Eu ions. We
find that only 0.1T are sufficient for persistent detwinning below the local
Eu ordering; above = 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
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