712 research outputs found
Quantum reflection of antihydrogen from a liquid helium film
We study the quantum reflection of ultracold antihydrogen atoms bouncing on
the surface of a liquid helium film. The Casimir-Polder potential and quantum
reflection are calculated for different thicknesses of the film supported by
different substrates. Antihydrogen can be protected from anni- hilation for as
long as 1.3s on a bulk of liquid 4He, and 1.7s for liquid 3He. These large
lifetimes open interesting perspectives for spectroscopic measurements of the
free fall acceleration of antihydrogen. Variation of the scattering length with
the thickness of a film of helium shows interferences which we interpret
through a Liouville transformation of the quantum reflection problem
A spectroscopy approach to measure the gravitational mass of antihydrogen
We study a method to induce resonant transitions between antihydrogen
() quantum states above a material surface in the gravitational field
of the Earth. The method consists of applying a gradient of magnetic field,
which is temporally oscillating with the frequency equal to a frequency of
transition between gravitational states of antihydrogen. A corresponding
resonant change in the spatial density of antihydrogen atoms could be measured
as a function of the frequency of applied field. We estimate an accuracy of
measuring antihydrogen gravitational states spacing and show how a value of the
gravitational mass of the atom could be deduced from such a
measurement. We also demonstrate that a method of induced transitions could be
combined with a free-fall-time measurement in order to further improve the
precision
Evidence of entropically driven C₆₀ fullerene aggregation in aqueous solution
In the present work, we report the first experimental evidence of entropically driven C₆₀ fullerene aggregation in aqueous solution, occurring with nearly zero enthalpy chang
Complexation of aromatic drugs with single-walled carbon nanotubes
We report a detailed study of the complexation of aromatic molecules and drugs with the surface of single-walled carbon nanotubes (SWCNTs, the diameter and the length ranges are 0.5-2 nm and 1-5 μm, respectively) in terms of equilibrium binding constants, K. It is found that the binding constants have magnitudes of the order of 104-105 M-1 and that there is some ligand specificity to the SWCNT surface depending on the structure of the aromatic molecul
Spectroscopic study of proflavine adsorption on the carbon nanotube surface
The present paper sheds light on one of the possible mechanisms of interaction between the typical aromatic dye proflavine and the carbon nanotube surface, namely, π-stacking between aromatic rings of these compounds. To investigate such a complexation, a qualitative analysis was performed by means of ultraviolet visible, infrared, and nuclear magnetic resonance spectroscopy. The data obtained suggest that π-stacking brings the major contribution to the stabilization of the complex between proflavine and the carbon nanotub
A magneto-gravitational trap for precision studies of gravitational quantum states
Observation time is the key parameter for improving the precision of
measurements of gravitational quantum states of particles levitating above a
reflecting surface. We propose a new method of long confinement in such states
of atoms, anti-atoms, neutrons and other particles possessing a magnetic
moment. The Earth gravitational field and a reflecting mirror confine particles
in the vertical direction. The magnetic field originating from electric current
passing through a vertical wire confines particles in the radial direction.
Under appropriate conditions, motions along these two directions are decoupled
to a high degree. We estimate characteristic parameters of the problem, and
list possible systematic effects that limit storage times due to the coupling
of the two motions. In the limit of low particle velocities and magnetic
fields, precise control of the particle motion and long storage times in the
trap can provide ideal conditions for both gravitational, optical and hyperfine
spectroscopy: for the sensitive verification of the equivalence principle for
antihydrogen atoms; for increasing the accuracy of optical and hyperfine
spectroscopy of atoms and antiatoms; for improving constraints on extra
fundamental interactions from experiments with neutrons, atoms and antiatoms
Variational calculations for the hydrogen-antihydrogen system with a mass-scaled Born-Oppenheimer potential
The problem of proton-antiproton motion in the --
system is investigated by means of the variational method. We introduce a
modified nuclear interaction through mass-scaling of the Born-Oppenheimer
potential. This improved treatment of the interaction includes the nondivergent
part of the otherwise divergent adiabatic correction and shows the correct
threshold behavior.
Using this potential we calculate the vibrational energy levels with angular
momentum 0 and 1 and the corresponding nuclear wave functions, as well as the
S-wave scattering length. We obtain a full set of all bound states together
with a large number of discretized continuum states that might be utilized in
variational four-body calculations. The results of our calculations gives an
indication of resonance states in the hydrogen-antihydrogen system
Development of a PbWO4 Detector for Single-Shot Positron Annihilation Lifetime Spectroscopy at the GBAR Experiment
We have developed a PbWO4 (PWO) detector with a large dynamic range to measure the intensity of a positron beam and the absolute density of the ortho-positronium (o-Ps) cloud it creates. A simulation study shows that a setup based on such detectors may be used to determine the angular distribution of the emission and reflection of o-Ps to reduce part of the uncertainties of the measurement. These will allow to improve the precision in the measurement of the cross-section for the (anti)hydrogen formation by (anti)proton-positronium charge exchange and to optimize the yield of antihydrogen ion which is an essential parameter in the GBAR experiment
Increased distractibility in schizotypy: Independent of individual differences in working memory capacity?
Individuals with schizophrenia typically show increased levels of distractibility. This has been attributed to impaired working memory capacity (WMC), since lower WMC is typically associated with higher distractibility, and schizophrenia is typically associated with impoverished WMC. Here, participants performed verbal and spatial serial recall tasks that were accompanied by to-be-ignored speech tokens. For the few trials wherein one speech token was replaced with a different token, impairment was produced to task scores (a deviation effect). Participants subsequently completed a schizotypy questionnaire and a WMC measure. Higher schizotypy scores were associated with lower WMC (as measured with operation span, OSPAN), but WMC and schizotypy scores explained unique variance in relation to the mean magnitude of the deviation effect. These results suggest that schizotypy is associated with heightened domain-general distractibility, but that this is independent of its relationship with WMC
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