32,737 research outputs found
Dynamical stability of entanglement between spin ensembles
We study the dynamical stability of the entanglement between the two spin
ensembles in the presence of an environment. For a comparative study, we
consider the two cases: a single spin ensemble, and two ensembles linearly
coupled to a bath, respectively. In both circumstances, we assume the validity
of the Markovian approximation for the bath. We examine the robustness of the
state by means of the growth of the linear entropy which gives a measure of the
purity of the system. We find out macroscopic entangled states of two spin
ensembles can stably exist in a common bath. This result may be very useful to
generate and detect macroscopic entanglement in a common noisy environment and
even a stable macroscopic memory.Comment: 4 pages, 1 figur
Compensation of Effective Field in the Field-Induced Superconductor k-(BETS)2FeBr4 Observed by 77Se NMR
We report results of 77Se NMR frequency shift in the normal state of the
organic charge-transfer-salt k-(BETS)2FeBr4 which shows magnetic field-induced
superconductivity (FISC). From a simple mean field analysis, we determined the
field and the temperature dependences of the magnetization m_{pi} of the \pi
conduction electrons on BETS molecules. We found that the Fe spins are
antiferromagnetically coupled to the pi electrons and determined the exchange
field to be J = -2.3T/mu_B. The exchange field from the fully saturated Fe
moments (5 mu_B) is compensated by an external field of 12T. This is close to
the central field of the FISC phase, consistent with the Jaccarino-Peter local
field-compensation mechanism for FISC (Phys. Rev. Lett. 9, 290 (1962))
A Wedge-DCB Test Methodology to Characterise High Rate Mode-I Interlaminar Fracture Properties of Fibre Composites
A combined numerical-experimental methodology is presented to measure dynamic Mode-I fracture properties of fiber reinforced composites. A modified wedge-DCB test using a Split-Hopkinson Bar technique along with cohesive zone modelling is utilised for this purpose. Three different comparison metrics, namely, strain-displacement response, crack propagation history and crack opening history are employed in order to extract unique values for the cohesive fracture properties of the delaminating interface. More importantly, the complexity of dealing with the frictional effects between the wedge and the DCB specimen is effectively circumvented by utilising right acquisition techniques combined with an inverse numerical modelling procedure. The proposed methodology is applied to extract the high rate interlaminar fracture properties of carbon fiber reinforced epoxy composites and it is further shown that a high level of confidence in the calibrated data can be established by adopting the proposed methodology
Berry's phase with quantized field driving: effects of inter-subsystem coupling
The effect of inter-subsystem couplings on the Berry phase of a composite
system as well as that of its subsystem is investigated in this paper. We
analyze two coupled spin- particles with one driven by a quantized
field as an example, the pure state geometric phase of the composite system as
well as the mixed state geometric phase for the subsystem is calculated and
discussed.Comment: 4 pages, 1 figur
Modelling Velocity Profiles of Aerated Flows Down Grassed Spillways
The ecological and environmental benefits of grassed spillways present a green solution to the construction of low head conveyance structures. On a grassed spillway, the aggregate of the grass canopy and root structure may alter flow resistance, velocity distribution and other flow properties. While subcritical flows in vegetated open channels have been extensively researched, only little is known about flow properties in supercritical high-velocity flows, which are typically characterized by self-aeration. The current study explores the application of a velocity superposition to supercritical aerated flows on a spillway with artificial grass. Velocity measurements were conducted with a Pitot tube and a phase-detection conductivity probe, allowing for the extraction of shear velocities at the canopy top which revealed an additional free-stream velocity layer. A comparison of the mixing layer length scale with the shear length scale (of the mixing layer) demonstrated a good correlation. Overall, this study provided new insights into the flow resistance of supercritical flows on grassed spillways
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