Spontaneous spin-polarized current in a nonuniform Rashba interaction system

We investigate the electron transport through a two-dimensional semiconductor with a nonuniform Rashba spin-orbit interaction. Due to the combination of the coherence effect and the Rashba interaction, a spontaneous spin-polarized current emerges in the absence of any magnetic material and magnetic field. For a two-terminal device, only the local current contains polarization; however, with a four-terminal setup, a polarized total current is produced. This phenomenon may offer a novel way for generating a spin-polarized current, replacing the traditional spin-injection method.Comment: 4 pages, 4 figure

Viscous diffusion and photoevaporation of stellar disks

The evolution of a stellar disk under the influence of viscous evolution, photoevaporation from the central source, and photoevaporation by external stars is studied. We take the typical parameters of TTSs and the Trapezium Cluster conditions. The photoionizing flux from the central source is assumed to arise both from the quiescent star and accretion shocks at the base of stellar magnetospheric columns, along which material from the disk accretes. The accretion flux is calculated self-consistently from the accretion mass loss rate. We find that the disk cannot be entirely removed using only viscous evolution and photoionization from the disk-star accretion shock. However, when FUV photoevaporation by external massive stars is included the disk is removed in 10^6 -10^7yr; and when EUV photoevaporation by external massive stars is included the disk is removed in 10^5 - 10^6yr. An intriguing feature of photoevaporation by the central star is the formation of a gap in the disk at late stages of the disk evolution. As the gap starts forming, viscous spreading and photoevaporation work in resonance. There is no gap formation for disks nearby external massive stars because the outer annuli are quickly removed by the dominant EUV flux. On the other hand, at larger, more typical distances (d>>0.03pc) from the external stars the flux is FUV dominated. As a consequence, the disk is efficiently evaporated at two different locations; forming a gap during the last stages of the disk evolution.Comment: 27 pages, 11 figures, accepted for publication in Ap

A Highly Antibacterial Achievement of Hollow Fiber Polyethersulfone (PES) Membrane Loaded with Silver Nanoparticles

A highly antibacterial of hollow fiber polyethersulfone (PES) membrane was prepared by loading silver nanoparticles within the PES graft acrylamide (AAm)-membrane. The grafted layers of AAm were provided the matrix for silver nanoparticles (AgNPs) entrapment. The characterization of the prepared hollowfiber (HF) PES membrane loaded with silver nanoparticles were examined by using transmission electron microscopy (TEM). To examine the antibacterial property of the prepared AgNPs-AAm-PES membrane, the halo zone and the shaking flask test were carried out. In these tests, both of unmodified PES membrane and AgNPs-AAm-PES membrane were exposed to pure culture suspension of Escherichia coli (E. Coli) bacteria with the concentration of 107 CFU/ml. The viable bacteria formed within the membrane surfaces and themembrane circumferences were observed by the halo zone formation, while the percentage of bacteria killing ratio was determined by shaking flask test method. The TEM results showed that the silver nanoparticles were formed within grafted layers of AAm-PES membrane and the size of silver nanoparticleswere about 10 nm. The AgNPs-AAm-PES membrane were highly effective to prevent the membrane biofouling as shown by the clearly halo zone formation compared with the unmodified PES membrane. The shake flask test were also revealed that almost 99.9 percent of the E. coli bacteria were killed when theyhaving exposed to the AgNPs-AAm-PES membrane. This was due to the silver ions are allowed to release from its membrane surfac

Halting planet migration by photoevaporation from the central source

The recent discovery of Jupiter-mass planets orbiting at a few AU from their stars compliments earlier detections of massive planets on very small orbits. The short period orbits strongly suggest that planet migration has occurred, with the likely mechanism being tidal interactions between the planets and the gas disks out of which they formed. The newly discovered long period planets, together with the gas giant planets in our solar system, show that migration is either absent or rapidly halted in at least some systems. We propose a mechanism for halting type-II migration at several AU in a gas disk. Photoevaporation of the disk by irradiation from the central star can produce a gap in the disk at a few AU, preventing planets outside the gap from migrating down to the star. This would result in an excess of systems with planets at or just outside the photoevaporation radius.Comment: 12 pages, 3 figures, accepted for publication by ApJ Letter

Quantum transport theory for nanostructures with Rashba spin-orbital interaction

We report on a general theory for analyzing quantum transport through devices in the Metal-QD-Metal configuration where QD is a quantum dot or the device scattering region which contains Rashba spin-orbital and electron-electron interactions. The metal leads may or may not be ferromagnetic, they are assumed to weakly couple to the QD region. Our theory is formulated by second quantizing the Rashba spin-orbital interaction in spectral space (instead of real space), and quantum transport is then analyzed within the Keldysh nonequilibrium Green's function formalism. The Rashba interaction causes two main effects to the Hamiltonian: (i) it gives rise to an extra spin-dependent phase factor in the coupling matrix elements between the leads and the QD; (ii) it gives rise to an inter-level spin-flip term but forbids any intra-level spin-flips. Our formalism provides a starting point for analyzing many quantum transport issues where spin-orbital effects are important. As an example, we investigate transport properties of a Aharnov-Bohm ring in which a QD having Rashba spin-orbital and e-e interactions is located in one arm of the ring. A substantial spin-polarized conductance or current emerges in this device due to a combined effect of a magnetic flux and the Rashba interaction. The direction and strength of the spin-polarization are shown to be controllable by both the magnetic flux and a gate voltage.Comment: 12 pages, 8 figure

Coherent current transport in wide ballistic Josephson junctions

We present an experimental and theoretical investigation of coherent current transport in wide ballistic superconductor-two dimensional electron gas-superconductor junctions. It is found experimentally that upon increasing the junction length, the subharmonic gap structure in the current-voltage characteristics is shifted to lower voltages, and the excess current at voltages much larger than the superconducting gap decreases. Applying a theory of coherent multiple Andreev reflection, we show that these observations can be explained in terms of transport through Andreev resonances.Comment: 4 pages, 4 figure

Time-dependent rotational stability of dynamic planets with elastic lithospheres

True polar wander (TPW), a reorientation of the rotation axis relative to the solid body, is driven by mass redistribution on the surface or within the planet and is stabilized by two aspects of the planet's viscoelastic response: the delayed viscous readjustment of the rotational bulge and the elastic stresses in the lithosphere. The latter, following Willemann (1984), is known as remnant bulge stabilization. In the absence of a remnant bulge, the rotation of a terrestrial planet is said to be inherently unstable. Theoretical treatments have been developed to treat the final (equilibrium) state in this case and the time-dependent TPW toward this state, including nonlinear approaches that assume slow changes in the inertia tensor. Moreover, remnant bulge stabilization has been incorporated into both equilibrium and linearized, time-dependent treatments of rotational stability. We extend the work of Ricard et al. (1993) to derive a nonlinear, time-dependent theory of TPW that incorporates stabilization by both the remnant bulge and viscous readjustment of the rotational bulge. We illustrate the theory using idealized surface loading scenarios applied to models of both Earth and Mars. We demonstrate that the inclusion of remnant bulge stabilization reduces both the amplitude and timescale of TPW relative to calculations in which this stabilization is omitted. Furthermore, given current estimates of mantle viscosity for both planets, our calculations indicate that departures from the equilibrium orientation of the rotation axis in response to forcings with timescale of 1 Myr or greater are significant for Earth but negligible for Mars

Brain2Music: Reconstructing Music from Human Brain Activity

The process of reconstructing experiences from human brain activity offers a unique lens into how the brain interprets and represents the world. In this paper, we introduce a method for reconstructing music from brain activity, captured using functional magnetic resonance imaging (fMRI). Our approach uses either music retrieval or the MusicLM music generation model conditioned on embeddings derived from fMRI data. The generated music resembles the musical stimuli that human subjects experienced, with respect to semantic properties like genre, instrumentation, and mood. We investigate the relationship between different components of MusicLM and brain activity through a voxel-wise encoding modeling analysis. Furthermore, we discuss which brain regions represent information derived from purely textual descriptions of music stimuli. We provide supplementary material including examples of the reconstructed music at https://google-research.github.io/seanet/brain2musicComment: Preprint; 21 pages; supplementary material: https://google-research.github.io/seanet/brain2musi