Ideal Spin Hydrodynamics from the Wigner Function Approach

Based on the Wigner function in local equilibrium, we derive hydrodynamical quantities for a system of polarized spin-1/2 particles: the particle number current density, the energy-momentum tensor, the spin tensor, and the dipole moment tensor. Compared with ideal hydrodynamics without spin, additional terms at the first and second orders in the Knudsen number Kn and the average spin polarization χs have been derived. The Wigner function can be expressed in terms of matrix-valued distributions, whose equilibrium forms are characterized by thermodynamical parameters in quantum statistics. The equations of motion for these parameters are derived by conservation laws at the leading and next-to-leading order Kn and χs .

Unidirectional propagation of the Bloch surface wave excited by the spinning magnetic dipole in two-dimensional photonic crystal slab

The photonic spin Hall effect (PSHE) can be realized in a photonic crystal (PC) slab, that is, the unidirectional Bloch surface wave can propagate along the surface of the PC slab under the excitation of elliptical polarized magnetic dipole. It is further proved that PSHE is caused by the interference of the component surface waves excited by the different components of the incident light, which is the so called component wave interference (CWI) theory. In addition, we also find that the spin of the surface wave oscillates periodically in space, and the oscillation period is a unit cell. In a unit cell, the average spin keeps the spin orbit locked. The results show that the spin separation can also be modulated by the position and the polarization state of the magnetic dipole.

Adsorption mechanisms and electronic and magnetic properties of oxygen on iron tetranitride

The oxide layer on iron nitrides restricts the conductivity of electrode materials. The adsorption and dissociation processes of O2 on the Fe4N have been analyzed by using first-principles. Comparing all the O2Fe4N isomers, we find that O atom prefers to locate at the center site of Fe–Fe–Fe plane which stays away from N atom. It means that O2 molecule is dissociated on the surface of Fe4N molecule. Endothermic and exothermic processes occur with the adsorption and decomposition of O2 on the surface of Fe4N. All the O2Fe4N clusters still present higher kinetic activity. For the O2Fe4N clusters, the internal electrons transfer from 4[Formula: see text] to 3[Formula: see text] and 4[Formula: see text] orbitals which are obviously more than those transfer to the other atoms. O atoms acquire less electron from nearby Fe atoms which confirms that the adsorption of O2 on Fe4N is a physical adsorption process. The average spin of the ground-state O2Fe4N clusters is 1.805 [Formula: see text]/atom.

An X-ray and optical study of the outbursting behaviour of the SMC Be X-ray binary SXP 91.1

ABSTRACT In this paper we report on the optical and X-ray behaviour of the Be X-ray binary, SXP 91.1, during a recent type I outburst. We monitored the outburst using the Neil Gehrels Swift Observatory. These data were supported by optical data from the Southern African Large Telescope and the Optical Gravitational Lensing Experiment (OGLE) to show the circumstellar disc activity. Matter from this disc accretes on to the neutron star, giving rise to the X-ray outburst as seen in the synchronous evolution of the optical and X-ray light curves. Using data taken with OGLE we show that the circumstellar disc has exhibited stable behaviour over two decades. A positive correlation is seen between the colour and magnitude from the OGLE and massive compact halo object observations, which indicates that the disc is orientated at relatively low-inclination angles. From the OGLE and Swift data, we demonstrate that the system has shown relative phase offsets that have persisted for many years. The spin period derivative is seen to be at maximum spin-up at phases when the mass accretion rate is at maximum. We show that the neutron star in SXP 91.1 is an unusual member of its class in the sense that it has had a consistent spin period derivative over many years, with the average spin-up rate being one of the highest for known Small Magellanic Cloud pulsars. The most recent measurements of the spin-up rate reveal higher values than the global trend, which is attributed to the recent mass accretion event leading to the current outburst.

Structures, electronic properties and adsorption mechanisms of the O2Fe3N clusters

The structures, adsorption mechanisms and electronic attributes of the O2Fe3N clusters are calculated at Perdew, Burke and Ernzerhof (PBE) functional. The results show that two O atoms prefer to be located at the Fe–Fe bridge site of Fe–N molecule which form the ground-state O2Fe3N cluster, respectively. It means that O2 molecule is dissociated by Fe3N molecule. Compared to the isomer (3)–(6), it indicates that an O2 molecule is preferentially adsorbed on the top site of Fe atom which is close to N atom of the Fe3N molecule in the vertical direction. The adsorptions of Fe3N with O2 are the exothermic before endothermic reaction. All the O2Fe3N clusters possess higher kinetic activity. The average spin magnetic moments of the O2Fe3N clusters are as follows: isomer (6) [Formula: see text] isomer (1) [Formula: see text] isomer (3) [Formula: see text] isomer (5) [Formula: see text] ground-state [Formula: see text] isomer (2) [Formula: see text] isomer (4). Compared to the external charge transfer of the O2Fe3N clusters, the transfer of electrons between 4s and 3d, 4p orbitals in the same atom is significantly higher.

Relativistic Fe Kα line in the composite X-ray spectra of radio-loud active galactic nuclei

ABSTRACT While a broad Fe Kα emission line is generally found in the X-ray spectra of radio quiet (RQ) active galactic nuclei (AGNs), this feature, commonly thought to be broadened by the relativistic effects near the central black hole, appears to be rare in their radio loud (RL) counterparts. In this paper, we carry out a detailed study of the ensemble property of the X-ray spectra, focusing on the Fe line, of 97 RL AGNs by applying the spectral stacking method to the spectra obtained with XMM–Newton. For comparison, the same analysis is also performed for 193 RQ AGNs. Both a narrow and a broad component of the Fe Kα line are detected at high significance in the stacked spectra of both samples. The broad lines can be well fitted with relativistically broadened line profiles. Our results suggest that, as in their RQ counterparts, a relativistic Fe line component is commonly present in RL AGNs, though it may not be detected unambiguously in individual objects with spectra of relatively low signal to noise. We try to constrain the average spin of the black holes for both the RL and RQ AGN samples by modelling their composite Fe line spectral profiles with relativistic disc line models. For the RL sample, the average spin is loosely constrained and a wide range is allowed except for very fast spins (<0.78, 90 per cent confidence), while for the RQ sample, it is constrained to be low or moderate (<0.24). We conclude that the more precise measurement of the black hole spins in RL AGNs has to await for the advent of future high-throughput X-ray telescopes.

Impurity-Induced Spin-State Crossover in La0.8Sr0.2Co1−xAlxO3

We have prepared a set of polycrystalline samples of La 0.8 Sr 0.2 Co 1 − x Al x O 3 ( 0 ≤ x ≤ 0.2 ), and have measured the magnetization as functions of temperature and magnetic field. We find that the average spin number per Co ion ( S Co ) evaluated from the room-temperature susceptibility is around 1.2–1.3 and independent of x. However, we further find that S Co evaluated from the saturation magnetization at 2 K is around 0.3–0.7, and decreases dramatically with x. This naturally indicates that a significant fraction of the Co 3 + ions experience a spin-state crossover from the intermediate- to low-spin state with decreasing temperature in the Al-substituted samples. This spin-state crossover also explains the resistivity and the thermopower consistently. In particular, we find that the thermopower is anomalously enhanced by the Al substitution, which can be consistently explained in terms of an extended Heikes formula.

Technical Note: An efficient method for accelerating the spin-up process for process-based biogeochemistry models

To better understand the role of terrestrial ecosystems in the global carbon cycle and their feedbacks to the global climate system, process-based biogeochemistry models need to be improved with respect to model parameterization and model structure. To achieve these improvements, the spin-up time for those differential equation-based models needs to be shortened. Here, an algorithm for a fast spin-up was developed by finding the exact solution of a linearized system representing the cyclo-stationary state of a model and implemented in a biogeochemistry model, the Terrestrial Ecosystem Model (TEM). With the new spin-up algorithm, we showed that the model reached a steady state in less than 10 years of computing time, while the original method requires more than 200 years on average of model run. For the test sites with five different plant functional types, the new method saves over 90 % of the original spin-up time in site-level simulations. In North American simulations, average spin-up time savings for all grid cells is 85 % for either the daily or monthly version of TEM. The developed spin-up method shall be used for future quantification of carbon dynamics at fine spatial and temporal scales.

Learning quantum annealing

We propose and develop a new procedure, whereby a quantum system can learn to anneal to a desired ground state. We demonstrate successful learning to produce an entangled state for a two-qubit system, then demonstrate generalizability to larger systems. The amount of additional learning necessary decreases as the size of the system increases. Because current technologies limit measurement of the states of quantum annealing machines to determination of the average spin at each site, we then construct a “broken pathway” between the initial and desired states, at each step of which the average spins are nonzero, and show successful learning of that pathway. Using this technique we show we can direct annealing to multiqubit GHZ and W states, and verify that we have done so. Because quantum neural networks are robust to noise and decoherence we expect our method to be readily implemented experimentally; we show some preliminary results which support this.