Dynamics, properties and spectrum of reconnecting vortex loops in superfluid helium (Review article)

2021 ◽  
Vol 47 (9) ◽  
pp. 740-753
Author(s):  
L. P. Kondaurova ◽  
V. A. Andryushchenko
Keyword(s):  
Superfluid Helium ◽  
Review Article ◽  
Vortex Loops

The nucleation of vorticity by ions in superfluid 4 He I. Basic theory

1984 ◽  
Vol 311 (1518) ◽  
pp. 433-467 ◽  
Keyword(s):  
High Pressure ◽  
Potential Barrier ◽  
Superfluid Helium ◽  
Recent Observation ◽  
Critical Value ◽  
Vortex Loop ◽  
Quantum Tunnelling ◽  
Vortex Loops ◽  
Very High ◽  
Vortex Nucleation

A theory is developed of vortex nucleation by an ion moving in superfluid helium at a low temperature. It is shown that production of a vortex loop attached to the side of the ion becomes energetically possible when the velocity of the ion exceeds a critical value, but that nucleation is impeded by the presence of a small potential barrier. The predicted critical velocity is close to that observed experimentally, at least at high pressure. Nucleation of an encircling vortex ring, considered some years ago by Schwarz & Jang (Phys.Rev. A8,3199 (1973)), probably becomes possible only at a higher velocity, and it is impeded by a large potential barrier. It is shown that for vortex loops the potential barrier can probably be overcome at a rate consistent with experiment either by quantum tunnelling at the lowest temperatures or thermally, by absorption of a single roton, at higher temperatures. Possible explanations of the recent observation by Bowley et al . {Phil. Trans. R. Soc. Lond. A307, 201 (1982)) that at high pressure the rate of vortex nucleation falls off at very high velocities are discussed.

Dynamics of vortex loops after reconnection in superfluid helium at different temperatures

2018 ◽  
Vol 44 (10) ◽  
pp. 1020-1024 ◽  
Author(s):  
V. A. Andryushchenko ◽  
L. P. Kondaurova
Keyword(s):  
Superfluid Helium ◽  
Vortex Loops ◽  
Different Temperatures

Desiderata in connection by the calibration of the MK-system

1966 ◽  
Vol 24 ◽  
pp. 348-349
Author(s):  
Th. Schmidt-Kaler
Keyword(s):  
Absolute Magnitude ◽  
Review Article ◽  
Stellar Systems ◽  
Astronomical Data ◽  
Intrinsic Colour

This is only an informal remark about some difficulties I am worrying about.I have tried to recalibrate the MK system in terms of intrinsic colour (B–V)0and absolute magnitudeMv. The procedures used have been described in a review article by Voigt (Mitt. Astr. Ges.1963, p. 25–35), and the results for stars of the luminosity classes Ia-O,I and II have been given also in Blaauw's article on the calibration of luminosity criteria in vol. III (Basic Astronomical Data, p. 401) ofStars and Stellar Systems.

High-Resolution Cryo-Electron Microscopy of Biological Macromolecules

1990 ◽  
Vol 48 (1) ◽  
pp. 126-127
Author(s):  
Yoshinori Fujiyoshi
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Diffraction Pattern ◽  
Superfluid Helium ◽  
Copper Phthalocyanine ◽  
Optical Diffraction ◽  
Irradiation Damage ◽  
Biological Macromolecules ◽  
Cross Sectional ◽  
Instrumental Resolution

The resolution of direct images of biological macromolecules is normally restricted to far less than 0.3 nm. This is not due instrumental resolution, but irradiation damage. The damage to biological macromolecules may expect to be reduced when they are cooled to a very low temperature. We started to develop a new cryo-stage for a high resolution electron microscopy in 1983, and successfully constructed a superfluid helium stage for a 400 kV microscope by 1986, whereby chlorinated copper-phthalocyanine could be photographed to a resolution of 0.26 nm at a stage temperature of 1.5 K. We are continuing to develop the cryo-microscope and have developed a cryo-microscope equipped with a superfluid helium stage and new cryo-transfer device.The New cryo-microscope achieves not only improved resolution but also increased operational ease. The construction of the new super-fluid helium stage is shown in Fig. 1, where the cross sectional structure is shown parallel to an electron beam path. The capacities of LN2 tank, LHe tank and the pot are 1400 ml, 1200 ml and 3 ml, respectively. Their surfaces are placed with gold to minimize thermal radiation. Consumption rates of liquid nitrogen and liquid helium are 170 ml/hour and 140 ml/hour, respectively. The working time of this stage is more than 7 hours starting from full LN2 and LHe tanks. Instrumental resolution of our cryo-stage cooled to 4.2 K was confirmed to be 0.20 nm by an optical diffraction pattern from the image of a chlorinated copper-phthalocyanine crystal. The image and the optical diffraction pattern are shown in Fig. 2 a, b, respectively.

Electron-deficient boron-based catalysts for C–H bond functionalisation

2021 ◽  
Author(s):  
Yuanhong Ma ◽  
Shao-Jie Lou ◽  
Zhaomin Hou
Keyword(s):  
Review Article ◽  
Current Status ◽  
Comprehensive Overview

This review article provides a comprehensive overview to recognise the current status of electron-deficient boron-based catalysis in C–H functionalisations.

Amino-functional polyethers: versatile, stimuli-responsive polymers

2020 ◽  
Vol 11 (24) ◽  
pp. 3940-3950 ◽  
Author(s):  
Patrick Verkoyen ◽  
Holger Frey
Keyword(s):  
Ring Opening ◽  
Review Article ◽  
Stimuli Responsive ◽  
New Class ◽  
Stimuli Responsive Polymers ◽  
Responsive Polymers

Amino-functional polyethers have emerged as a new class of “smart”, i.e. pH- and thermoresponsive materials. This review article summarizes the synthesis and applications of these materials, obtained from ring-opening of suitable epoxide monomers.

Developing Evidence-Based Assessment to Prevent Over- or Underidentification of Disorders for New Language Learners

2020 ◽  
Vol 5 (4) ◽  
pp. 1026-1038
Author(s):  
Sandra Levey ◽  
Li-Rong Lilly Cheng ◽  
Diana Almodovar
Keyword(s):  
Language Learners ◽  
Grade Level ◽  
Reading Skills ◽  
Language Disorder ◽  
Academic Development ◽  
Review Article ◽  
Evidence Based ◽  
Clinical Knowledge ◽  
Language And Literacy ◽  
Support Evidence

Purpose The purpose of this review article is to present certain linguistic domains to consider in the assessment of children learning a new language. Speech-language pathologists frequently face difficulty when determining if a bilingual or multilingual child possesses a true speech or language disorder. Given the increased number of new language learners across the world, clinicians must understand differences versus disorders to prevent underidentification or overidentification of a disorder. Conclusions Early identification of a true disorder has been shown to prevent language and literacy difficulties, given that children are able to achieve grade-level reading skills when given intervention. Clinical knowledge and skills are strongly required so that children receive evidence-based assessment to support their academic development. Learning Goal Readers will gain an understanding of the factors that support evidence-based assessment of bilingual and multilingual language learners.

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