Малоугловое рассеяние нейтронов в нормальном и сверхтекучем жидком гелии

Представлены результаты экспериментов по малоугловому рассеянию нейтронов в жидком гелии в диапазоне температур 1,0–5 К, проведенных на импульсном источнике нейтронов ISIS (Англия). Подробные измерения углового распределения рассеянных нейтронов позволили обнаружить существенное изменение в температурной зависимости второго момента парной корреляционной функции (первой производной углового распределения при малых углах рассеяния). При высоких температурах угловое распределение рассеянных нейтронов следует классическому описанию малоуглового рассеяния, а при температурах ниже -точки наблюдается квантовое поведение — рассеяние нейтронов на квантовых флуктуациях. Экспериментально подтверждено, что во всей области температур сечение рассеяния ней-тронов под нулевым углом определяется классическими термодинамическими флуктуациями плотности.Представлено результати експериментів по малокутовому розсіянню нейтронів в рідкому гелії в діапазоні температур 1,0–5 К, які проведено на імпульсному джерелі нейтронів ISIS (Англія). Докладні виміри кутового розподілу розсіяних нейтронів дозволили виявити істотну зміну в температурній залежності другого моменту парної кореляційної функції (першій похідній кутового розподілу при малих кутах розсіяння). При високих температурах кутовий розподіл розсіяних нейтронів відповідає класичному опису малокутового розсіяння, а при температурах нижче -точки спостерігається квантова поведінка — розсіяння нейтронів на квантових флуктуаціях. Експериментально підтверджено, що в усій області температур переріз розсіяння нейтронів під нульовим кутом визначається класичними термодинамічними флуктуаціями.The results of experiments on small-angle neutron scattering in liquid helium in the range of temperatures of 1–5 K, performed on a neutron pulse source ISIS (England), are presented. The detailed measurements of angular distribution of scattered neutrons allowed one to observe an essential change in temperature de-pendence of the second moment of pair correlation function (the first derivative of angular distribution at small angles of scattering). At high temperatures the angular distribution of scattered neutrons follows the classical description of small-angle scattering, but at temperatures below the -point a quantum behavior is observed neutron-scattering by quantum fluctuations. It is experimentally confirmed that in the whole tem-perature range the cross-section of neutron scattering at a zero angle is determined by the classical thermo-dynamic fluctuations of density

Segregated water observed in a putative fish embryo cryopreservative

Development of new cryopreservation strategies has major potential in medicine and agriculture and is critical to the conservation of endangered species that currently cannot be preserved. A critical property of any potential cryopreservative solution is its ability to prevent cell-damaging ice formation during cooling and subsequent heating. This study focuses on the freezing behaviour of promising model cryoprotective solutions. We perform neutron scattering analysis, combined with computer modelling, of the water structure after quench cooling these solutions. It is found that water in this solution forms nano-clusters encapsulated by the surrounding matrix of cryoprotectant solute molecules. We posit that these small volumes inhibit ice formation, because water does not have space for the structural relaxation required to crystallize on the timescale of the cooling process

Observation of inter-edge magnetoplasmon mode in a degenerate two-dimensional electron gas

We study the propagation of edge magnetoplasmons by time-resolved current measurements in a sample which allows for selective detection of edge states in the quantum Hall regime. We observe two decoupled modes of edge and inter-edge magnetoplasmons at filling factors close to 3. From the analysis of the propagation velocities of each mode the internal spatial parameters of the edge structure are derived.Comment: 4 pages, 4 figures, submitte

Estimation of the preservation effectiveness of the removed tooth duct using PRP and PRF technique according to laser-correlation spectrometry

The purpose of this work was to evaluate the effectiveness of some modern methods of preservation of the hole, aimed at preserving the tissues of the alveolar process of the jaws immediately after tooth extraction. Clinical studies were conducted in 69 patients with planned indications for tooth extraction, after which the tooth well was either not subjected to additional interventions, or was filled with a composition of PRP and Kollapan or a clot of PRF. The effectiveness of the effects was evaluated according to laser correlation spectrometry, which showed the best regeneration in the PRF well of the clot

Influence of the liquid helium meniscus on neutron reflectometry data

Neutron reflectometry offers a unique opportunity for the direct observation of nanostratification in ³He–⁴He mixtures in the ultra-low temperature limit. Unfortunately the results of recent experiments could not be wellmodelled on account of a seemingly anomalous variation of reflectivity with momentum transfer. We now hypothesize that this effect is attributable to an optical distortion caused by the liquid’s meniscus near the container wall. The validity of this idea is tested and confirmed through a subsidiary experiment on a D₂O sample, showing that the meniscus can significantly distort results if the beam size in the horizontal plane is comparable with, or bigger than, the diameter of the container. The meniscus problem can be eliminated if the beam size is substantially smaller than the diameter of the container, such that reflection takes place only from the flat region of the liquid surface thus excluding the meniscus tails. Practical measures for minimizing the meniscus distortion effect are discussed