Presence Of Moderate Magnetic Fields Research Articles

Numerical simulation of electrically conducting jet flow in a straight duct under longitudinal homogeneous magnetic field

Spatial evolution of electrically conducting jet flow at a supercritical Reynolds number, entering a duct filled with the liquid of the same physical properties, is studied by direct numerical simulations for the case of a streamwise uniform magnetic field. In contrast to the case of a transverse field, here the jet mean velocity does not interact with the streamwise field, and only the turbulent fluctuations of the flow are influenced and suppressed by the field. In this case, the jet saves its energy and has a tendency to spread at much larger distances. Therefore, one interesting and important property of this setup is the flow stabilization, i.e., transition to turbulence can be largely delayed due to the stabilizing effect of the magnetic field. This occurs in the presence of moderate magnetic fields. At strong magnetic fields, the second instability evolves—the jet profile becomes unsteady due to the traveling waves, which propagate along the jet while not interacting with the field. These traveling waves are generated by the interaction of secondary radial flows and magnetic field.

Quantum decoherence dynamics of divacancy spins in silicon carbide.

Long coherence times are key to the performance of quantum bits (qubits). Here, we experimentally and theoretically show that the Hahn-echo coherence time of electron spins associated with divacancy defects in 4H–SiC reaches 1.3 ms, one of the longest Hahn-echo coherence times of an electron spin in a naturally isotopic crystal. Using a first-principles microscopic quantum-bath model, we find that two factors determine the unusually robust coherence. First, in the presence of moderate magnetic fields (30 mT and above), the 29Si and 13C paramagnetic nuclear spin baths are decoupled. In addition, because SiC is a binary crystal, homo-nuclear spin pairs are both diluted and forbidden from forming strongly coupled, nearest-neighbour spin pairs. Longer neighbour distances result in fewer nuclear spin flip-flops, a less fluctuating intra-crystalline magnetic environment, and thus a longer coherence time. Our results point to polyatomic crystals as promising hosts for coherent qubits in the solid state.

Magneto-optical reflectance and absorbance of PbS quantum dots

Reflectance and absorbance of colloidal 2.5 nm PbS quantum dots were coincidentally measured under the presence of moderate magnetic fields below one Tesla. The work provides further insight to the optical and magneto-optical properties of quantum dots by revealing disconnect of band gap data collected in different experimental geometries and by the demonstration of reflective magneto-optical devices addressable with weak magnetic fields.

Constructing spin interference devices from nanometric rings

The study of nanospintronic devices utilizing coherent transport through molecular scale multiply connected geometries in the presence of moderate magnetic fields is presented. It is shown how two types of simple devices, spin filters and spin splitters, may be constructed from molecular nanometric rings utilizing the Aharonov-Bohm effect. The current is calculated within a single-electron approximation and within a many-body master equation approach where charging effects are accounted for in the Coulomb blockade regime. We provide rules and tools to develop and analyze efficient spintronic devices based on nanometric interferometers.

Optical supernova remnant observations from Skinakas Observatory

High energy studies of supernova remnants provide direct insight into major properties of these objects. Morphological and spectral studies of remnants in X-rays allow us to estimate parameters like the age of the remnant, the explosion energy and the ambient interstellar density. Optical studies of supernova remnants focus on the interaction of the primary blast wave with dense “clouds” found in the interstellar medium. Optical observations of individual remnants performed at Skinakas Observatory in Crete, Greece consist of flux calibrated wide field CCD images taken with the 0.3 m telescope and absolute flux calibrated long-slit spectra obtained with the 1.3 m telescope. The site conditions and the unique capabilities of a small telescope equipped with a CCD camera allowed us to perform high quality deep observations leading to the discovery of optical emission from several remnants for the first time. We present results on the known supernova remnants G73.9+0.9, G82.2+5.3 as well as current results on previously unknown filamentary structures. Typical densities of the interstellar “clouds” are of the order of a few atoms per cm 3, and the shock velocities are found in the range of 90–140 km s −1. The optical spectra further suggest the presence of moderate magnetic fields.

A Pulsed NMR Study of Molecular Motions and Ordering Ethyl-[p-(p-methoxybenzylidene)-amino]-cinnamate

Abstract Pulsed nuclear magnetic resonance techniques were used to study the phase transitions in ethyl-[p-(p-methoxybenzylidene)-amino]-cinnamate from the room temperature solid phase through the isotropic liquid. Both the proton spin-lattice relaxation time an second moment were observed to change near each of the phase transitions. These quantities exhibited anisotropies in the semectic B phase similar to those observed for a typical nematic ordered in an electric field. The molecular order was stable in the smectic B phase, while molecular reordering was observed in the smectic A phase in the presence of moderate magnetic fields.