Magnetic excitations in infinite-layer nickelates Lu, H.; Rossi, M.; Nag, A. ...
Science (American Association for the Advancement of Science),
07/2021, Letnik:
373, Številka:
6551
Journal Article
Recenzirano
Odprti dostop
Looking for magnetic clues
Thin films of the neodymium nickelate NdNiO
2
doped with strontium have recently been found to be superconducting. This materials class bears structural and electronic ...similarities to the famed cuprate superconductors, but how far the analogy goes remains unclear. Lu
et al.
used resonant inelastic x-ray scattering to look for magnetism, which exists in the cuprates, in Nd
1-x
Sr
x
NiO
2
films (see the Perspective by Benckiser). The authors observed magnetic modes in the undoped compound that had a doping evolution consistent with the behavior of a doped Mott insulator.
Science
, abd7726, this issue p.
213
; see also abi6855, p.
157
Resonant inelastic x-ray scattering is used to probe the magnetic excitations in Nd
1−
x
Sr
x
NiO
2
films.
The discovery of superconductivity in infinite-layer nickelates brings us tantalizingly close to a material class that mirrors the cuprate superconductors. We measured the magnetic excitations in these nickelates using resonant inelastic x-ray scattering at the Ni
L
3
-edge. Undoped NdNiO
2
possesses a branch of dispersive excitations with a bandwidth of approximately 200 milli–electron volts, which is reminiscent of the spin wave of strongly coupled, antiferromagnetically aligned spins on a square lattice. The substantial damping of these modes indicates the importance of coupling to rare-earth itinerant electrons. Upon doping, the spectral weight and energy decrease slightly, whereas the modes become overdamped. Our results highlight the role of Mottness in infinite-layer nickelates.
Free vibration of non-uniform functionally graded beams is analyzed via the Timoshenko beam theory. Bending stiffness and distributed mass density are assumed to obey a unified exponential law. For ...various boundary conditions, exact frequency equations are derived in closed form. These frequency equations can reduce to those for classical Timoshenko beams if the gradient index disappears. Moreover, the frequency equations of exponentially graded Rayleigh, shear, and Euler–Bernoulli beams can be obtained as special cases of the present. The gradient index has a strong influence on the natural frequencies. For Timoshenko beams, there exist two critical frequencies depending on the gradient index. Harmonic vibration cannot be excited for frequencies less than the lower critical frequency. The obtained results can serve as a benchmark for examining the accuracy of numerical frequencies based on other approaches for analyzing transverse vibration of non-uniform axially graded Timoshenko beams. The results also apply to bending vibration of rectangular Timoshenko beams with constant thickness and exponentially decaying/amplifying width.
•Free vibration of functionally graded Timoshenko beams is analyzed.•Exact frequency equations of exponentially graded Timoshenko beams are obtained.•Effect of end constraints of functionally graded Timoshenko beams is examined.•Natural frequencies depend on the gradient index and admit jump property.•Natural frequencies for graded beams using Euler–Bernoulli, shear, Rayleigh, and Timoshenko theories are compared.
Shear transformation is the elementary process for plastic deformation of metallic glasses, the prediction of the occurrence of the shear transformation events is therefore of vital importance to ...understand the mechanical behavior of metallic glasses. In this Letter, from the view of the potential energy landscape, we find that the protocol-dependent behavior of shear transformation is governed by the stress gradient along its minimum energy path and we propose a framework as well as an atomistic approach to predict the triggering strains, locations, and structural transformations of the shear transformation events under different shear protocols in metallic glasses. Verification with a model Cu_{64}Zr_{36} metallic glass reveals that the prediction agrees well with athermal quasistatic shear simulations. The proposed framework is believed to provide an important tool for developing a quantitative understanding of the deformation processes that control mechanical behavior of metallic glasses.
Abstract The aerodynamic drag of a cyclist in time trial (TT) position is strongly influenced by the torso angle. While decreasing the torso angle reduces the drag, it limits the physiological ...functioning of the cyclist. Therefore the aims of this study were to predict the optimal TT cycling position as function of the cycling speed and to determine at which speed the aerodynamic power losses start to dominate. Two models were developed to determine the optimal torso angle: a ‘Metabolic Energy Model’ and a ‘Power Output Model’. The Metabolic Energy Model minimised the required cycling energy expenditure, while the Power Output Model maximised the cyclists׳ power output. The input parameters were experimentally collected from 19 TT cyclists at different torso angle positions (0–24°). The results showed that for both models, the optimal torso angle depends strongly on the cycling speed, with decreasing torso angles at increasing speeds. The aerodynamic losses outweigh the power losses at cycling speeds above 46 km/h. However, a fully horizontal torso is not optimal. For speeds below 30 km/h, it is beneficial to ride in a more upright TT position. The two model outputs were not completely similar, due to the different model approaches. The Metabolic Energy Model could be applied for endurance events, while the Power Output Model is more suitable in sprinting or in variable conditions (wind, undulating course, etc.). It is suggested that despite some limitations, the models give valuable information about improving the cycling performance by optimising the TT cycling position.
Global satellite observations of temperature and geopotential height (GPH) from the Microwave Limb Sounder (MLS) on the EOS Aura spacecraft are discussed. The precision, resolution, and accuracy of ...the data produced by the MLS version 2.2 processing algorithms are quantified, and recommendations for data screening are made. Temperature precision is 1 K or better from 316 hPa to 3.16 hPa, degrading to ∼3 K at 0.001 hPa. The vertical resolution is 3 km at 31.6 hPa, degrading to 6 km at 316 hPa and to ∼13 km at 0.001 hPa. Comparisons with analyses (Goddard Earth Observing System version 5.0.1 (GEOS‐5), European Centre for Medium‐range Weather Forecasts (ECMWF), Met Office (MetO)) and other observations (CHAllenging Minisatellite Payload (CHAMP), Atmospheric Infrared Sounder/Advanced Microwave Sounder Unit (AIRS/AMSU), Sounding of the Atmosphere using Broadband Radiometry (SABER), Halogen Occultation Experiment (HALOE), Atmospheric Chemistry Experiment (ACE), radiosondes) indicate that MLS temperature has persistent, pressure‐dependent biases which are between −2.5 K and +1 K between 316 hPa and 10 hPa. The 100‐hPa MLS v2.2 GPH surface has a bias of ∼150 m relative to the GEOS‐5 values. These biases are compared to modeled systematic uncertainties. GPH biases relative to correlative measurements generally increase with height owing to an overall cold bias in MLS temperature relative to correlative temperature measurements in the upper stratosphere and mesosphere.
This study was conducted to evaluate the effect of linseed oil (LO) replacing different levels of fish oil (FO) on growth, muscle fatty acid composition and metabolism of gift tilapia (Oreochromis ...niloticus) (mean initial weight 22 ± 0.5 g) in indoor recycle aquarium tanks for 8 weeks. Fish fed the diet with 50% of the oil as LO had higher final body weight (FWG), specific growth rate (SGR) and protein efficiency ratio (PER) than the other groups (P < 0.05). Hepatopancreas lipid content of fish fed 50% LO was lower than the other groups. Total n‐3 and n‐6 PUFA contents in the dorsal muscle and superoxide dismutase (SOD) activity in serum increased with increasing dietary LO level. Fish fed 50% LO had higher alanine transaminase (ALT), aspartate transaminase (AST) and lipoprotein lipase (LPL) activities in hepatopancreas and total antioxidant capacity (T‐AOC) and alkaline phosphatase (AKP) activities in serum than the other groups (P < 0.05). However, malate dehydrogenase (MDH) activities and malondialdehyde (MDA) contents in hepatopancreas were lower than other groups (P < 0.05) with a 50% substitution level. Results of this study indicated that LO could substitute <50% FO without influencing the growth of tilapia. The higher substitution levels of LO induced negative influences on growth, feed utilization and antioxidant ability of tilapia, but could promote DHA synthesis in tilapia muscle.
Perovskite SrIrO3 has long been proposed as an exotic semimetal induced by the interplay between the spin-orbit coupling and electron correlations. However, its low-lying electronic structure is ...still lacking. We synthesize high-quality perovskite SrIrO3 (100) films by means of oxide molecular beam epitaxy, and then systemically investigate their low energy electronic structure using in-situ angle-resolved photoemission spectroscopy. We find that the hole-like bands around R and the electron-like bands around U(T) intersect the Fermi level simultaneously, providing the direct evidence of the semimetallic ground state in this compound. Comparing with the density functional theory, we discover that the bandwidth of states near Fermi level is extremely small, and there exists a pronounced mixing between the Jeff = 1/2 and Jeff = 3/2 states. Moreover, our data reveal that the predicted Dirac degeneracy protected by the mirror-symmetry, which was theoretically suggested to be the key to realize the non-trivial topological properties, is actually lifted in perovskite SrIrO3 thin films. Our findings pose strong constraints on the current theoretical models for the 5d iridates.
Autoimmune encephalitis is a heterogeneous group of newly identified disorders that are being diagnosed with increasing frequency. Early recognition and treatment of autoimmune encephalitis are ...crucial for patients, but diagnosis remains challenging and time-consuming. In this retrospective case series, we describe the findings of conventional MR imaging and 3D pseudocontinuous arterial spin-labeling in patients with autoimmune encephalitis confirmed by antibody testing. All patients with autoimmune encephalitis showed increased CBF in the affected area, even when some of them presented with normal or slightly abnormal findings on conventional MR imaging. Additionally, serial 3D pseudocontinuous arterial spin-labeling showed perfusion reduction in 1 patient after therapy. For patients with highly suspected autoimmune encephalitis, 3D pseudocontinuous arterial spin-labeling may be added to the clinical work-up. Further studies and longitudinal data are needed to corroborate whether and to what extent 3D pseudocontinuous arterial spin-labeling improves the diagnostic work-up in patients with autoimmune encephalitis compared with conventional MR imaging.
In this study, the characteristics of the Arctic mixed‐phase cloud (AMC) have been investigated using data collected at the Atmospheric Radiation Measurement North Slope Alaska site from October 2006 ...to September 2009. AMC has an annual occurrence frequency of 42.3%, which includes 18.7% of single‐layered AMCs and 23.6% for multiple layers. Two cloud base heights (CBHs) are defined from ceilometer and micropulse lidar (MPL) measurements. For single‐layered AMC, the ceilometer‐derived CBH represents the base of the liquid‐dominant layer near the cloud top, while MPL‐derived CBH represents base of the lower ice‐dominant layer. The annual mean CBHs from ceilometer and MPL measurements are 1.0 km and 0.6 km, respectively, with the largest difference (~1.0 km) occurring from December to March and the smallest difference in September. The humidity inversion occurrence decreases with increasing humidity inversion intensity (stronger in summer than in winter). During the winter months, AMC occurrences increase from 15% to 35% when the inversion intensity increases from 0.1 to 0.9 g/kg. On the contrary, despite a higher frequency of strong humidity inversion in summer, AMC occurrences are nearly invariant for different inversion intensities. On average, humidity and temperature inversion frequencies of occurrence above an AMC are 5 and 8 times, respectively, as high as those below an AMC. The strong inversion occurrences for both humidity and temperature above an AMC provide the moisture sources from above for the formation and maintenance of AMCs. This result helps to reconcile the persistency of AMCs even when the Arctic surface is covered by snow and ice.
Key Points
Both ceilometer and MPL define the cloud bases for the Arctic mixed‐phase cloud
The stronger the humidity inversion, the more Arctic mixed‐phase cloud in winter
When humidity inversion >0.9 g/kg, the mixed‐phase cloud occurrence is ~40%
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