On charged impurity structures in liquid helium

The thermoluminescence spectra of impurity-helium condensates (IHC) submerged in superfluid helium have been observed for the first time. Thermoluminescence of impurity-helium condensates submerged in superfluid helium is explained by neutralization reactions occurring in impurity nanoclusters. Optical spectra of excited products of neutralization reactions between nitrogen cations and thermoactivated electrons were rather different from the spectra observed at higher temperatures, when the luminescence due to nitrogen atom recombination dominates. New results on current detection during the IHC destruction are presented. Two different mechanisms of nanocluster charging are proposed to describe the phenomena observed during preparation and warmup of IHC samples in bulk superfluid helium, and destruction of IHC samples out of liquid helium

Oxygen atoms and nitrogen molecules as spectroscopic probes for the temperature determination in non-equilibrium cryogenic helium plasma jets

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Optical spectroscopy and current detection during warm-up and destruction of impurity–helium condensates

New experimental results on detection of optical spectra and ion currents during destruction of impurity–helium condensates (IHCs) have been obtained. It is shown that emission during IHC sample destruction is accompanied by current pulses, pressure peaks and temperature changes. The molecular bands of excimer molecules XeO* are assigned to molecules stabilized in films of molecular nitrogen covering the heavier cores of impurity clusters which form impurity–helium condensates

THERMOLUMINESCENCE OF IMPURITY-HELIUM SOLIDS IMMERSED IN LIQUID HELIUM

Acknowledgement: The work was carried out with support from Russian Foundation for Basic Research (Grant 99-03-33261). $^{a}$E.B. Gordon V. V. Khmelenko, A. A. Pelmenev, E.A. Popov, O.F. Pugachev, A.F. Shestakov, Chem. Phys. 170, 411(1993). $^{b}$R.E. Boltnev, E.B. Gordon, V.V. Khmelenko, I.N. Krushinskaya, M.V. Martyneko, A.A.Pelmenev, E.A. Popov, A.F. Shestakov, Chem. Phy., 189,367 (1994)Author Institution: Institute of Energy Problems of Chemical Physics; Institute of Problems of Chemical PhysicsA solidification of liquid helium around impurity particles injected in its volume results in IHSP (impurity-Helium Solid Phase) $formation ^{a}$, so the particles can be stabilized with inert environment during long time. Particular interest is stabilization of metastable particles. The capture of $N(^{2}D)$ atoms from discharge allows to save ones at T = 1.5 K during $10^{4}$ s -time comparable with their lifetime, $4.4 \times 10^{4}$ s. Nevertheless, even small temperature increase ($< 0.1$ K) causes the luminescence on the $^{2}D- ^{4}S$ transition. It was explained as thermoactivated association of neighbouring centers of IHSP. $N+N_{2}$ or $N + R_{g}$, which partially removes the prohibition because of ``heavy particle $effect""^{b}$. The main part of stabilized nitrogen atoms is in the ground state $^{4}S$, so thermoactivated mobility leads to the pair recombination N + N or $N+O(O_{2}$ presents as trace in condensed gas mixture). The results presented in report confirm that heating of IHSP sample causes a blue emission which can be assigned to excited states of $N_{2}$ or NO

Memory and Brain in Food-Storing Birds: Space Oddities or Adaptive Specializations?

Scatterhoarding birds that cache food items have become an important model system for the study of spatial memory and its correlates in the brain. In particular, it has been suggested that through adaptive specialization, species that cache food have better spatial memory and a relatively larger hippocampus than their non-caching relatives. Critics of this approach, dubbed neuroecology, maintain that neither of these hypotheses has been confirmed. Here, we review the evidence pertaining to a correlation between food-storing capability and the relative volume of the hippocampus. Hippocampal volume has been related to food-storing behaviour in comparisons between species, within species, or within individuals, but the evidence is not consistent. There are several possible reasons for this inconsistency, including: (1) food-hoarding birds may not always use memory for retrieval, (2) there may be systematic differences between data from North American and Eurasian species that affect the analysis, and (3) sample sizes have in many cases been too small. In addition, both the independent variable (degree of food-hoarding specialization) and the dependent variable (relative volume of the hippocampus) are not clearly and consistently defined. Alternatively, it is possible that the neuroecological hypothesis is false. Systematic empirical research is necessary to determine whether or not food-storing birds have evolved adaptive specializations in brain and cognition