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221.
Gary A. Williams 《Journal of Low Temperature Physics》2008,150(3-4):649-653
The Kosterlitz-Thouless (KT) transition in two-dimensional BEC systems is calculated taking into account the fact that in
experiments these are finite-size systems. The outer boundaries of the condensate effectively act as hard walls, and this
has a polarizing effect on the vortex pairs of the KT transition, causing the superfluid fraction to become strongly anisotropic.
The decreased pair energy near the walls results in a strongly enhanced vortex density near the boundaries. Since the pair
density can now be directly measured, we extend here our previous calculations to include the vortex density as a function
of the distance from the boundaries. Possible experiments using sound propagation in the gases are proposed to probe the anisotropic
properties of the superfluid density, including an unusual sharp dip in the superfluid density that is predicted to occur
down the middle of a long superfluid strip.
相似文献
222.
A. T. Fiory D. R. Harshman J. Jung I. -Y. Isaac W. J. Kossler A. J. Greer D. R. Noakes C. E. Stronach E. Koster John D. Dow 《Journal of Electronic Materials》2005,34(5):474-483
Positive-muon spin rotation (μ+SR) spectroscopy and magnetic moment measurements were used to probe fluxon (or vortex) formation
in the superconducting mixed state of a high-purity YBa2Cu3O7 crystal. Random potentials caused by crystal-lattice defects pin fluxons. A fluxon lattice forms in an external magnetic
field, and changes of thermal activation lead to fluxon pinning and depinning. The root second moment of the local magnetic
field distribution (σ) determined by μ+SR contains information on the magnetic penetration depth and the pinning. Fluxon pinning
leads to temperature-dependent transverse displacements of the fluxons that decrease σ and also fluctuations in the separation
between fluxons that tend to increase σ. By accounting for the field-dependent and temperature-activated fluxon disorder,
it is found that the experimental results for the penetration depth are consistent with a supercon-ducting order parameter
of a strong-coupling two-fluid model, confirming that the superconductivity is nodeless with s-wave superconducting pairing.
Quantitative results for fluxon displacements are discussed within the context of the fluxon field-temperature phase diagram. 相似文献
223.
224.
Amir Shamloo Seyedamirhosein Abdorahimzadeh Rohollah Nasiri 《American Institute of Chemical Engineers》2019,65(11):e16741
Separation of particles or cells has various applications in biotechnology, pharmaceutical and chemical industry. Inertial cell separation, in particular, has been gaining a great attention in the recent years since it has exhibited a label-free, high-throughput and efficient performance. In this work, first, an inertial contraction–expansion array microchannel device, capable of passively separating two particles with diameters of 4 and 10 μm, was numerically studied. Then, the validated model was combined with curved geometries in order to investigate the effect of curve features on the separation process. The overall purpose was to investigate the interaction between the two different separation methods (separation with curved channels and with contraction–expansion arrays) to find an ideal model that can enjoy the merits of both contraction–expansion and curved channel based methods. Moreover, the relation between separation strength and the aspect ratio in the contraction and expansion zones of the simulated model as well as its height were examined. Then, a new model that combines the curved and the contraction–expansion geometries was tested for its efficiency. This new geometry showed that separation could be achieved with shorter lengths compared with straight contraction–expansion geometries. 相似文献
225.
226.
Malte Wagenfeld 《Architectural Design》2008,78(3):20-25
Malte Wagenfeld tackles the difficult problem of visualising air, and in his physical experiments reveals a world of eddies, swirls and wafting particles circulating around moving bodies. Here he offers a literal and conceptual glimpse at the invisible nature of atmosphere. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
227.
228.
Mike Silver 《Architectural Design》2006,76(4):5-11
In his introduction to this issue of AD, guest-editor Mike Silver celebrates ‘the flexible language of commands and logical procedures’ of computers whose creative potential has until now been undervalued in architecture. He explains how the ‘happy accident’ of late 1990s blob architecture is now giving way to a focus on programming and composing new code, which promises ‘to generate new and unprecedented modes of expression’. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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230.
Shi Feng Cunliang Pan Hongfei Ye Wendong Liu Wenbo Yang Yingdi Lv Shengyang Tao 《Small (Weinheim an der Bergstrasse, Germany)》2023,19(19):2207383
Mixing in microfluidic channels is dominated by diffusion owing to the absence of chaotic flow. However, high-efficiency microscale mixing over short distances is desired for the development of lab-on-chip systems. Here, enhanced mixing in microchannels achieved using magnetic nonspherical particles (MNSPs), is reported. Benefiting from the nonspherical shape of the MNSPs, secondary vortices exhibiting cyclical characteristics appear in microchannels when the MNSPs rotate under an external magnetic field. Increasing the rotation rate enlarges the secondary vortices, expanding the mixing zone and enhancing the mixing, resulting in a mixing efficiency exceeding 0.9 at Re of 0.069–0.69. Complementary micro-particle image velocimetry (µPIV) for flow field analysis clarifies the mixing mechanism. In addition, a chaotic vortex area is generated in the presence of two MNSPs, which shortens the distance required for achieving an appropriate mixing efficiency. This study demonstrates the potential of employing MNSPs as efficient mixers in lab-on-chip devices. 相似文献