1,944 research outputs found
Planar Resonators for Metamaterials
This paper presents the results of an investigation into a combination of electric and magnetic planar resonators in order to design the building element of a volumetric metamaterial showing simultaneously negative electric and magnetic polarizabilities under irradiation by an electromagnetic wave. Two combinations of particular planar resonators are taken into consideration. These planar resonators are an electric dipole, a split ring resonator and a double H-shaped resonator. The response of the single resonant particle composed of a resonator with an electric response and a resonator with a magnetic response is strongly anisotropic. Proper spatial arrangement of these particles can make the response isotropic. This is obtained by proper placement of six planar resonators on the surface of a cube that now represents a metamaterial unit cell. The cells are distributed in space with 3D periodicity
Analysis of dynamic inlet distortion applied to a parallel compressor model
An investigation of surge was conducted by using a parallel compressor model of the J85-13 compressor implement on an analog computer. Surges were initiated by various types of dynamic disturbances in inlet pressure. The compressor model was less sensitive to disturbances of short duration, high frequency, and long duration where the compressor discharge pressure could react. Adding steady distortion to dynamic disturbances reduced the amount of dynamic disturbance required to effect surge. Steady and unsteady distortions combined linearly to reduce surge margin
Cooperative Effect of Electron Correlation and Spin-Orbit Coupling on the Electronic and Magnetic Properties of Ba2NaOsO6
The electronic and magnetic properties of the cubic double perovskite
Ba2NaOsO6 were examined by performing first-principles density functional
theory calculations and analyzing spin-orbit coupled states of an Os7+ (d1) ion
at an octahedral crystal field. The insulating behavior of Ba2NaOsO6 was shown
to originate from a cooperative effect of electron correlation and spin-orbit
coupling. This cooperative effect is responsible not only for the absence of
orbital ordering in Ba2 NaOsO6 but also for a small magnetic moment and a weak
magnetic anisotropy in Ba2NaOsO6
Ferromagnetic insulating state in tensile-strained LaCoO thin films
With local density approximation + Hubbard (LDA+) calculations, we
show that the ferromagnetic (FM) insulating state observed in tensile-strained
LaCoO epitaxial thin films is most likely a mixture of low-spin (LS) and
high-spin (HS) Co, namely, a HS/LS mixture state. Compared with other FM
states, including the intermediate-spin (IS) state (\textit{metallic} within
LDA+), which consists of IS Co only, and the insulating IS/LS mixture state,
the HS/LS state is the most favorable one. The FM order in HS/LS state is
stabilized via the superexchange interactions between adjacent LS and HS Co. We
also show that Co spin state can be identified by measuring the electric field
gradient (EFG) at Co nucleus via nuclear magnetic resonance (NMR) spectroscopy
Magnetic structure and orbital ordering in BaCoO3 from first-principles calculations
Ab initio calculations using the APW+lo method as implemented in the WIEN2k
code have been used to describe the electronic structure of the
quasi-one-dimensional system BaCoO3. Both, GGA and LDA+U approximations were
employed to study different orbital and magnetic orderings. GGA predicts a
metallic ground state whereas LDA+U calculations yield an insulating and
ferromagnetic ground state (in a low-spin state) with an alternating orbital
ordering along the Co-Co chains, consistent with the available experimental
data.Comment: 8 pages, 9 figure
Are the renormalized band widths in TTF-TCNQ of structural or electronic origin? - An angular dependent NEXAFS study
We have performed angle-dependent near-edge x-ray absorption fine structure
measurements in the Auger electron yield mode on the correlated
quasi-one-dimensional organic conductor TTF-TCNQ in order to determine the
orientation of the molecules in the topmost surface layer. We find that the
tilt angles of the molecules with respect to the one-dimensional axis are
essentially the same as in the bulk. Thus we can rule out surface relaxation as
the origin of the renormalized band widths which were inferred from the
analysis of photoemission data within the one-dimensional Hubbard model.
Thereby recent theoretical results are corroborated which invoke long-range
Coulomb repulsion as alternative explanation to understand the spectral
dispersions of TTF-TCNQ quantitatively within an extended Hubbard model.Comment: 6 pages, 5 figure
Extracorporeal Immunoglobulin Elimination for the Treatment of Severe Myasthenia Gravis
Myasthenia gravis (MG) is a neuromuscular disorder leading to fluctuating muscle weakness and fatigue. Rarely, long-term stabilization is not possible through the use of thymectomy or any known drug therapy. We present our experience with extracorporeal immunoglobulin (Ig) elimination by immunoadsorption (adsorbers with human Ig antibodies). Acetylcholine receptor antibodies (AChRAs) were measured during long-term monitoring (4.7 ± 2.9 years; range 1.1â8.0). A total of 474 samples (232 pairs) were analyzed, and a drop in AChRA levels was observed (P = .025). The clinical status of patients improved and stabilized. Roughly 6.8% of patients experienced clinically irrelevant side effects. The method of Ig elimination by extracorporeal immunoadsorption (IA) is a clinical application of the recent biotechnological advances. It offers an effective and safe therapy for severe MG even when the disease is resistant to standard therapy
Stabilization of the high-spin state of Co in LaCoRhO
The rhodium doping in the LaCoRhO perovskite series
() has been studied by X-ray diffraction, electric transport and
magnetization measurements, complemented by electronic structure GGA+U
calculations in supercell for different concentration regimes. No charge
transfer between Co and Rh is evidenced. The diamagnetic ground
state of LaCoO, based on Co in low-spin (LS) state, is disturbed
even by a small doping of Rh. The driving force is the elastic energy connected
with incorporation of a large Rh cation into the matrix of small LS
Co cations, which is relaxed by formation of large Co in
high-spin (HS) state in the next-nearest sites to the inserted Rh atom. With
increasing temperature, the population of Co in HS state increases
through thermal excitation, and a saturated phase is obtained close to room
temperature, consisting of a nearest-neighbor correlation of small (LS
Co) and large (HS Co and LS Rh) cations in a kind of
double perovskite structure. The stabilizing role of elastic and electronic
energy contributions is demonstrated in supercell calculations for dilute Rh
concentration compared to other dopants with various trivalent ionic radius.Comment: 8 pages, 8 figure
Systematic investigation of a family of gradient-dependent functionals for solids
Eleven density functionals are compared with regard to their performance for
the lattice constants of solids. We consider standard functionals, such as the
local-density approximation and the Perdew-Burke-Ernzerhof (PBE)
generalized-gradient approximation (GGA), as well as variations of PBE GGA,
such as PBEsol and similar functionals, PBE-type functionals employing a
tighter Lieb-Oxford bound, and combinations thereof. Several of these
variations are proposed here for the first time. On a test set of 60 solids we
perform a system-by-system analysis for selected functionals and a full
statistical analysis for all of them. The impact of restoring the gradient
expansion and of tightening the Lieb-Oxford bound is discussed, and confronted
with previous results obtained from other codes, functionals or test sets. No
functional is uniformly good for all investigated systems, but surprisingly,
and pleasingly, the simplest possible modifications to PBE turn out to have the
most beneficial effect on its performance. The atomization energy of molecules
was also considered and on a testing set of six molecules, we found that the
PBE functional is clearly the best, the others leading to strong overbinding
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