111 research outputs found
Angular momentum in rotating superfluid droplets
The angular momentum of rotating superfluid droplets originates from quantized vortices and capillary waves, the interplay between which remains to be uncovered. Here, the rotation of isolated submicrometer superfluid 4He droplets is studied by ultrafast x-ray diffraction using a free electron laser. The diffraction patterns provide simultaneous access to the morphology of the droplets and the vortex arrays they host. In capsule-shaped droplets, vortices form a distorted triangular lattice, whereas they arrange along elliptical contours in ellipsoidal droplets. The combined action of vortices and capillary waves results in droplet shapes close to those of classical droplets rotating with the same angular velocity. The findings are corroborated by density functional theory calculations describing the velocity fields and shape deformations of a rotating superfluid cylinder
Shapes of rotating normal fluid 3He versus superfluid 4He droplets in molecular beams
Previous single-pulse extreme ultraviolet and X-ray coherent diffraction
studies revealed that superfluid 4He droplets obtained in free jet expansion
acquire sizable angular momentum, resulting in significant centrifugal
distortion. Similar experiments with normal fluid 3He droplets may help
elucidating the origin of the of the large degree of rotational excitation and
highlight similarities and differences of dynamics in normal and superfluid
droplets. Here, we present the first comparison of the shapes of isolated 3He
and 4He droplets following expansion of the corresponding fluids in vacuum at
temperatures as low as ~ 2 K. Large 3He and 4He droplets with average radii of
~160 nm and ~350 nm, respectively, were produced. We find that the majority of
the 3He droplets in the beam correspond to rotating oblate spheroids with
reduced average angular momentum () and reduced angular velocities
() similar to that of 4He droplets. Given the different physical nature
of 3He and 4He, this similarity in and may be surprising and
suggest that similar mechanisms induce rotation regardless of the isotope. We
hypothesized that the observed distribution of droplet sizes and angular
momenta stem from processes in the dense region close to the nozzle. In this
region, the significant velocity spread and collisions between the droplets
induce excessive rotation followed by droplet fission. The process may repeat
itself several times before the droplets enter the collision-fee high vacuum
region further downstream.Comment: 29 pages, 6 figure
Surface Deposition and Imaging of Large Ag Clusters Formed in He Droplets
The utility of a continuous beam of He droplets for the assembly and surface
deposition of Ag clusters, ~ 300 - 6 000, is studied with transmission
electron microscopy. Images of the clusters on amorphous carbon substrates
obtained at short deposition times have provided for a measure of the size
distribution of the metal clusters. The average sizes of the deposited clusters
are in good agreement with an energy balance based estimate of Ag cluster
growth in He droplets. Measurements of the deposition rate indicate that upon
impact with the surface the He-embedded cluster is attached with high
probability. The stability of the deposited clusters on the substrate is
discussed.Comment: 24 pages, 5 figure
ПРИМЕНЕНИЕ ХИРУРГИЧЕСКИХ МЕТОДИК В ПРОЦЕССЕ ЛЕЧЕНИЯ ВОСПАЛИТЕЛЬНЫХ ЗАБОЛЕВАНИЙ ПАРОДОНТА
The inflammatory periodontal diseases (IPD) take the second place after caries of teeth therefore the questions of treatment and prevention of IPD are especially actual. In the IPD treatment are the most effective, it is possible to allocate the surgical methods. In the present article questions of improvement of traditional techniques of surgical treatment, and also development and deployment of the new are considered.Воспалительные заболевания пародонта (ВЗП) по своей распространенности занимают 2-е место после кариеса зубов, поэтому вопросы лечения и профилактики ВЗП являются особенно актуальными. В лечении ВЗП как наиболее эффективные можно выделить хирургические методы. Рассматриваются вопросы совершенствования традиционных методик хирургического лечения, а также разработка и внедрение новых методик
Runoff variations in Lake Balkhash Basin, Central Asia, 1779-2015, inferred from tree rings
Long highly-resolved proxies for runoff are in high demand for hydrological forecasts and water management in arid Central Asia. An accurate (R2 = 0.53) reconstruction of October-September discharge of the Ili River in Kazakhstan, 1779–2015, is developed from moisture-sensitive tree rings of spruce sampled in the Tian Shan Mountains. The fivefold extension of the gauged discharge record represents the variability of runoff in the Lake Balkhash Basin for the last 235 years. The reconstruction shows a 40 year long interval of low discharge preceded a recent high peak in the first decade of the 2000s followed by a decline to more recent levels of discharge not seen since the start of the gauged record. Most reconstructed flow extremes (± 2σ) occur outside the instrumental record (1936–2015) and predate the start of large dam construction (1969). Decadal variability of the Ili discharge corresponds well with hydrological records of other Eurasian internal drainages modeled with tree rings. Spectral analysis identifies variance peaks (highest near 42 year) consistent with main hemispheric oscillations of the Eurasian climatic system. Seasonal comparison of the Ili discharge with sea-level-pressure and geopotential height data suggests periods of high flow likely result from the increased contribution of snow to runoff associated with the interaction of Arctic air circulation with the Siberian High-Pressure System and North Atlantic Oscillation
Suprafluide Heliumtröpfchen: außergewöhnlich kalte Nanomatrices für Moleküle und molekulare Komplexe
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