Search results for "Helium-4"

showing 4 items of 44 documents

Time-domain analysis of electronic spectra in superfluid 4He

2004

Abstract Electronic absorption spectra of impurities in superfluid helium is developed in time domain, using time-dependent density functional theory to describe liquid 4 He and time-dependent perturbation theory to describe the electronic degrees of freedom of the impurity. Angularly isotropic potentials are used to describe the molecule–helium interactions in the ground and excited electronic states. The calculations rationalize experimentally observed phonon side-bands in 4 He droplets and in bulk helium, and allow assignments of spectral features to specific motions of the liquid.

SuperfluiditychemistryPhononDegrees of freedom (physics and chemistry)General Physics and Astronomychemistry.chemical_elementDensity functional theoryPhysical and Theoretical ChemistryPerturbation theoryAtomic physicsHeliumSpectral lineSuperfluid helium-4Chemical Physics Letters
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Refrigeration of an array of cylindrical nanosystems by superfluid helium counterflow

2017

Abstract Motivated by the challenge of computer refrigeration, we study the limits set by the transition to quantum turbulence on the cooling of an array of heat-producing cylindrical nanosystems by means of superfluid-helium counterflow. The effective thermal conductivity in laminar counterflow superfluid helium is obtained in channels with rectangular cross section, through arrays of mutually parallel cylinders and in the combined situation of arrays of orthogonal cylinders inside the rectangular channel. The maximum cooling capacity is analyzed on the condition that turbulence is avoided and that the highest temperature does not exceed the lambda temperature.

Thermal conductivity Liquid helium Quantum turbulence Micropores Quantized vortices Computer refrigerationQuantum turbulenceCooling capacity01 natural sciences010305 fluids & plasmaslaw.inventionPhysics::Fluid DynamicsThermal conductivitylaw0103 physical sciencesthermal conductivity010306 general physicsSettore MAT/07 - Fisica Matematicathermal conductivity; liquid helium; quantum turbulence; micropores; quantized vortices; computer refrigerationquantized vorticesCondensed Matter::Quantum GasesFluid Flow and Transfer ProcessesPhysicsCondensed matter physicsliquid heliumTurbulenceLiquid heliumMechanical Engineeringcomputer refrigerationRefrigerationquantum turbulenceLaminar flowMechanicsCondensed Matter PhysicsmicroporesSuperfluid helium-4
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Vortex dynamics in rotating counterflow and plane Couette and Poiseuille turbulence in superfluid Helium

2008

An equation previously proposed to describe the evolution of vortex line density in rotating counterflow turbulent tangles in superfluid helium is generalized to incorporate nonvanishing barycentric velocity and velocity gradients. Our generalization is compared with an analogous approach proposed by Lipniacki, and with experimental results by Swanson et al. in rotating counterflow, and it is used to evaluate the vortex density in plane Couette and Poiseuille flows of superfluid helium.

quantum vorticePhysicsCondensed Matter::Quantum GasesTurbulencePlane (geometry)Condensed Matter::OtherFOS: Physical sciencesLaminar flowVorticityCondensed Matter PhysicsHagen–Poiseuille equationNonlinear Sciences::Cellular Automata and Lattice Gasessuperfluid turbulenceElectronic Optical and Magnetic MaterialsVortexCondensed Matter - Other Condensed MatterPhysics::Fluid Dynamicscoflow and counterflowClassical mechanicsSettore MAT/07 - Fisica MatematicaCouette flowSuperfluid helium-4Other Condensed Matter (cond-mat.other)
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Transport and extraction of radioactive ions stopped in superfluid helium

2003

A new approach to convert a high energy beam to a low energy one, which is essential for the next generation radioactive ion beam facilities, has been proposed and tested at Jyvaskyla, Finland. An open Ra-223 alpha-decay-recoil source has been used to produce radioactive ions in superfluid helium. The alpha spectra demonstrate that the recoiling Rn-219 ions have been extracted out of liquid helium. This first observation of the extraction of heavy positive ions across the superfluid helium surface was possible thanks to the high sensitivity of radioactivity detection. An efficiency of 36% was obtained for the ion extraction out of liquid helium. (C) 2003 Elsevier Science B.V. All rights res…

radioactive ion beamNuclear and High Energy PhysicssnowballIon beamChemistryLiquid heliumExtraction (chemistry)superfluid heliumIGISOL TECHNIQUENUCLEAR-SPIN POLARIZATIONSpectral linelaw.inventionIonHelium-4lawPhysics::Accelerator PhysicsPhysics::Atomic PhysicsAtomic physicsNuclear ExperimentInstrumentationBeam (structure)Superfluid helium-4
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