ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    4He atom reflection from rough liquid4He surfaces (1995)
    Springer
    Journal of low temperature physics 101 (1995), S. 531-536 
    Details
    ISSN: 1573-7357
    Keywords: 67.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract When an atom is evaporated from or added to a free liquid surface there is a density perturbation of the surface. We have detected this surface spoiling using a4He atomic beam at glancing angles to the surface. With a perfect free liquid surface some of the atoms reflect specularly and some condense. We find that the specular reflection coefficient decreases as the surface is spoiled by another beam of4He atoms. The degree of spoiling as measured by the decrease in reflectivity, is initially proportional to the spoiling beam flux, but at higher fluxes the spoiling saturates. A phenomenological model is developed to describe this behaviour.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00753349
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Lifetimes of Fast R+ Rotons due to Scattering by Thermal Phonons in Superfluid 4He (1998)
    Springer
    Journal of low temperature physics 110 (1998), S. 425-430 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have injected R + rotons into superfluid 4 He at low temperatures (0.05K〈T〈0.25K), and measured the attenuation of roton → atom quantum evaporation signals with increasing liquid temperature. The most important cause of this attenuation is the interaction of the rotons with thermal phonons via the R + p → R′ + p′ process. As the liquid temperature is increased, we find that the fastest rotons are attenuated more than the slower rotons. This corresponds to a scattering rate which increases with roton velocity due to the increasing density of final states. We have modelled the attenuation using Landau and Khalatnikov's expression for the interaction between rotons and phonons. This yields the observed behaviour of the roton mean free path as a function of velocity. The mean free paths and lifetimes of the fastest rotons are ≍ two orders of magnitude shorter than those of the slowest rotons observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022521824905
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    A Fast Pulsed Source of Ballistic R− Rotons in Superfluid 4He (1998)
    Springer
    Journal of low temperature physics 110 (1998), S. 455-460 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Superfluid 4 He is unique in having well-defined excitations (R − rotons) with momentum oppositely directed to their velocity. If a beam of R − rotons can be produced, it could be unambiguously detected by quantum evaporation because the atoms will emerge in the opposite quadrant to that for atoms evaporated by R + rotons and phonons. Previous work shows that a heated metal film which is immersed in superfluid 4 He only creates phonons and R + rotons. A sponge-like heater does appear to produce R − rotons but, because it has a long time constant, it cannot be used in time of flight studies. We have developed a source that produces fast pulses of R − rotons suitable for time of flight measurements. The method uses interactions between R + rotons to create R − rotons, so a transient high density of R + rotons in a small confined volume is needed. The source appears to operate as we expect from a model of the evolution of the R + and R − roton populations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022582010793
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    The Energy Dependence of Roton Quantum Evaporation from Superfluid 4He (2000)
    Springer
    Journal of low temperature physics 121 (2000), S. 333-338 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have measured the energy dependence of roton quantum evaporation. A transiently heated cavity filled with superfluid 4 He generates R+ and R− rotons. The emitted rotons are collimated and arrive at the free liquid surface with a narrow range of incident angles. We detect two beams of evaporated atoms, one due to R+ rotons and the other due to R− rotons. Our numerical simulation of roton and atom trajectories, using an evaporation probability of 1, yields two angular distributions of atom flux which are similar to our experimental results, but do have systematic differences which we attribute to the evaporation probability. The ratio of the observed signal to the computed value at each bolometer position gives the relative roton quantum evaporation probability as a function of roton energy. We find that this probability increases with roton energy, except perhaps for low energy R− rotons. We compare these results with theoretical predictions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1017581125621
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Evaporation Probability of R− Rotons Relative to R+ Rotons in Superfluid 4He (1998)
    Springer
    Journal of low temperature physics 113 (1998), S. 615-620 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The evaporation of superfluid 4 He by rotons is investigated using a recently developed pulsed source of both positive (R + ) and negative (R − ) group velocity rotons. The R + and R − rotons have very different momenta parallel to the free liquid surface and this causes angular dispersion of the two beams of evaporated atoms in the vacuum. On moving a bolometer horizontally through these beams, we find that the maximum flux of atoms from R − rotons occurs at an angle corresponding to an average R − roton energy of ħω/k B ≃ 10.5 K. The signal at this angle is compared with the evaporation signal at the maximum flux caused by R + rotons. These R + rotons have an average energy of ≃ 10.7K. The relative sizes of these two signals enables an estimate to be made of the probability of evaporation by R − rotons relative to that for R + rotons. We find that «P −a »/«P +a » ≃ 4 × 10−3 where the brackets signify averages over the angles and energies allowed by the geometry of the experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022501623126
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Spatial Evolution of High Frequency Phonons in Superfluid 4He from a Pulse-Heated Metal Film (1998)
    Springer
    Journal of low temperature physics 113 (1998), S. 621-626 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An almost monochromatic spectrum of high frequency (ħω/k B ∼ 10 K) phonons in superfluid 4 He is created by a short (∼ 0.1μs) pulse of Joule-heating in a metal film submerged in the liquid at saturated vapour pressure (svp). These phonons have lifetimes that tend to infinity as T → 0, and are the ones effective in quantum evaporation experiments. Most of these high frequency (hf) phonons are not injected into the liquid 4 He across the metal—liquid interface, but are created in the liquid by energy-increasing interactions which begin with the injected phonons of much lower energy (ħω/k B ∼ 1 K). These hf phonons are created up to ∼ 5 millimetres in front of the heater, hence the time of flight from a heater to a detector only gives an approximate value (lower bound) of their energies. Here we present measurements at svp of phonon energy fluxes in liquid 4 He at various distances from a pulse-heated metal film. Analysis of these signals gives an improved determination of the hf phonon spectrum (peaked at 10.20 ± 0.05 K with HWHM ≃ 0.2 K on the high energy side).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022553607196
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Elastic reflection of4He atoms from the surface of liquid4He (1995)
    Springer
    Journal of low temperature physics 100 (1995), S. 105-120 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The reflection of incident4He atoms from the surface of liquid4He can yield information on the microscopic features of the liquid at the surface. Edwards et al. have measured this reflectivity and have developed a theoretical model which successfully described the measurements. However, the density profile of the liquid4He surface has recently been determined experimentally, and this can now be used to model the reflectivity without any freely adjustable parameters. We use this density profile and the experimentally-determined interatomic pair potential to derive an effective potential for the incoming atom, and then solve the single-particle Schroedinger equation to find the reflectivity as a function of wavevector perpendicular to the surface. Within the uncertainty in the density profile and interatomic potential, we have chosen values that give good agreement between the measured and calculated reflectivities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00753838
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    facet.materialart.
    Unknown
    Reflectivity of4He Atoms from Liquid4He: Direct Observation of the Effect of Phonons and Rotons (1995)
    American Physical Society
    Details
    Publication Date: 1995-06-26
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 9
    facet.materialart.
    Unknown
    Predicting Cotton Lint Yield Maps from Aerial Photographs (2004)
    Springer
    Details
    Publication Date: 2004-12-01
    Print ISSN: 1385-2256
    Electronic ISSN: 1573-1618
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Springer
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 10
    facet.materialart.
    Unknown
    High-energy phonon creation from cold phonons in pulses of different length in He II (2000)
    American Physical Society
    Details
    Publication Date: 2000-10-01
    Print ISSN: 0163-1829
    Electronic ISSN: 1095-3795
    Topics: Physics
    Published by American Physical Society
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...