1,067 research outputs found
Single spin-torque vortex oscillator using combined bottom-up approach and e-beam lithography
A combined bottom-up assembly of electrodeposited nanowires and electron beam
lithography technique has been developed to investigate the spin transfer
torque and microwave emission on specially designed nanowires containing a
single Co/Cu/Co pseudo spin valve. Microwave signals have been obtained even at
zero magnetic field. Interestingly, high frequency vs. magnetic field
tunability was demonstrated, in the range 0.4 - 2 MHz/Oe, depending on the
orientation of the applied magnetic field relative to the magnetic layers of
the pseudo spin valve. The frequency values and the emitted signal frequency as
a function of the external magnetic field are in good quantitative agreement
with the analytical vortex model as well as with micromagnetic simulations.Comment: 9 pages, 4 figure
Optimization of laser-plasma injector via beam loading effects using ionization-induced injection
Simulations of ionization induced injection in a laser driven plasma
wakefield show that high-quality electron injectors in the 50-200 MeV range can
be achieved in a gas cell with a tailored density profile. Using the PIC code
Warp with parameters close to existing experimental conditions, we show that
the concentration of in a hydrogen plasma with a tailored
density profile is an efficient parameter to tune electron beam properties
through the control of the interplay between beam loading effects and varying
accelerating field in the density profile. For a given laser plasma
configuration, with moderate normalized laser amplitude, and maximum
electron plasma density, , the
optimum concentration results in a robust configuration to generate electrons
at 150~MeV with a rms energy spread of 4\% and a spectral charge density of
1.8~pC/MeV.Comment: 13 pages, 10 figure
Effects of wall compliance on the laminar–turbulent transition of torsional Couette flow
Torsional Couette flow between a rotating disk and a stationary wall is studied experimentally. The surface of the disk is either rigid or covered with a compliant coating. The influence of wall compliance on characteristic flow instabilities and on the laminar–turbulent flow transition is investigated. Data obtained from analysing flow visualizations are discussed. It is found that wall compliance favours two of the three characteristic wave patterns associated with the transition process and broadens the parameter regime in which these patterns are observed. The results for the effects of wall compliance on the third pattern are inconclusive. However, the experiments indicate that the third pattern is not a primary constituent of the laminar–turbulent transition process of torsional Couette flow
Formal Total Synthesis of the Algal Toxin (−)-Polycavernoside A
A concise and largely catalysis-based approach to the potent algal toxin polycavernoside A (1) is described that intercepts a late-stage intermediate of a previous total synthesis; from there on, this challenging target can be reached in a small number of steps. Key to success was a sequence of a molybdenum-catalyzed ring-closing alkyne metathesis (RCAM) reaction to forge the macrocyclic frame, followed by a gold-catalyzed and strictly regioselective transannular hydroalkoxylation of the resulting cycloalkyne that allows the intricate oxygenation pattern of the macrolactone ring of 1 to be properly set. The required cyclization precursor 5 was assembled by the arguably most advanced fragment coupling process based on an Evans–Tishchenko redox esterification known to date, which was optimized to the extent that the precious coupling partners could be used in an almost equimolar ratio (6/7 1:1.3). The preparation of these building blocks features, inter alia, the power of the Sc(OTf)3-catalyzed Leighton crotylation as well as the superb selectivities of alkene cross metathesis, asymmetric keto-ester hydrogenation, and the Jacobsen epoxidation/epoxide resolution technologies
Syracosphaera azureaplaneta sp. nov. and revision of Syracosphaera corolla Lecal, 1966
Here we show that the extant coccolithophore Syracosphaera corolla Lecal, 1966 comprises two consistently
different non-intergrading morphotypes characterised respectively by exothecal coccoliths with wide and
narrow central-areas. These are interpreted as separate species and so a new species is described, S. azureaplaneta,
and a revised description is given for S. corolla
Regulatory Dynamics on Random Networks: Asymptotic Periodicity and Modularity
We study the dynamics of discrete-time regulatory networks on random
digraphs. For this we define ensembles of deterministic orbits of random
regulatory networks, and introduce some statistical indicators related to the
long-term dynamics of the system. We prove that, in a random regulatory
network, initial conditions converge almost surely to a periodic attractor. We
study the subnetworks, which we call modules, where the periodic asymptotic
oscillations are concentrated. We proof that those modules are dynamically
equivalent to independent regulatory networks.Comment: 23 pages, 3 figure
- …