1,784 research outputs found
Precise laser spectroscopy of the antiprotonic helium atom and CPT test on antiproton mass and charge
We have measured twelve transition frequencies of the antiprotonic helium
atom (pbar-He+) with precisions of 0.1--0.2 ppm using a laser spectroscopic
method. The agreement between the experiment and theories was so good that we
can put a limit on the proton-antiproton mass (or charge) difference. The new
limit is expected to be much smaller than the already published value, 60 ppb.Comment: proceeding of the conference, "PANIC02
Anharmonicity and asymmetry of Landau levels for a two-dimensional electron gas
We calculate the density of states of a two dimensional electron gas located
at the interface of a GaAlAs/GaAs heterojunction. The disorder potential which
is generally created by a single doping layer behind a spacer, is here enhanced
by the presence of a second delta doped layer of scatterers which can be
repulsive or attractive impurities. We have calculated the density of states by
means of the Klauder's approximation, in the presence of a magnetic field of
arbitrary strength. At low field either band tails or impurity bands are
observed for attractive potentials, depending on the impurity concentration. At
higher field, impurity bands are observed for both repulsive and attractive
potentials. We discuss the effect of such an asymmetrical density of states on
the transport properties in the quantum Hall effect regime.Comment: 22 pages, 12 figures. submitted to Phys. Rev.
Systematic study of the decay rates of antiprotonic helium states
A systematic study of the decay rates of antiprotonic helium (\pbhef and
\pbhet) at CERN AD (Antiproton Decelerator) has been made by a laser
spectroscopic method. The decay rates of some of its short-lived states, namely
those for which the Auger rates are much larger than
their radiative decay rates ( s),
were determined from the time distributions of the antiproton annihilation
signals induced by laser beams, and the widths of the atomic resonance lines.
The magnitude of the decay rates, especially their relation with the transition
multipolarity, is discussed and compared with theoretical calculations.Comment: 6 pages, 5 figures, and 1 tabl
Hyperfine structure of antiprotonic helium revealed by a laser-microwave-laser resonance method
Using a newly developed laser-microwave-laser resonance method, we observed a
pair of microwave transitions between hyperfine levels of the
state of antiprotonic helium. This experiment confirms the quadruplet hyperfine
structure due to the interaction of the antiproton orbital angular momentum,
the electron spin and the antiproton spin as predicted by Bakalov and Korobov.
The measured frequencies of GHz and
GHz agree with recent theoretical
calculations on a level of .Comment: 4 pages, 4 figures, 1 tabl
The antimicrobial peptide TAT-RasGAP<sub>317-326</sub> inhibits the formation and expansion of bacterial biofilms in vitro.
Biofilms are structured aggregates of bacteria embedded in a self-produced matrix that develop in diverse ecological niches. Pathogenic bacteria can form biofilms on surfaces and in tissues, causing nosocomial and chronic infections that are difficult to treat. While antibiotics are largely inefficient in limiting biofilm formation and expansion, antimicrobial peptides (AMPs) are emerging as alternative antibiofilm treatments. In this study, we explore the effect of the newly described AMP TAT-RasGAP <sub>317-326</sub> on Acinetobacter baumannii, Pseudomonas aeruginosa and Staphylococcus aureus biofilms.
Efficiency of TAT-RasGAP <sub>317-326</sub> on biofilms was tested in vitro. Both viability of bacteria contained in the biofilm as well as biomass of the biofilm were quantified using resazurin and crystal violet staining, respectively. The antibiofilm effect of TAT-RasGAP <sub>317-326</sub> was compared with a selection of classical antibiotics and AMPs.
We observe that TAT-RasGAP <sub>317-326</sub> inhibits biofilm formation at concentrations equivalent or two times greater than the minimum inhibitory concentration (MIC) of planktonic bacteria. Moreover, TAT-RasGAP <sub>317-326</sub> limits the expansion of A. baumannii and P. aeruginosa established biofilms at twice the concentration inhibiting biofilm formation.
These results underscore the potential use of TAT-RasGAP <sub>317-326</sub> against biofilms and encourage further studies in the development of AMPs to treat biofilm-related infections
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Preliminary Results from Recent Measurements of the Antiprotonic Helium Hyperfine Structure
We report on preliminary results from a systematic study of the hyperfine
(HF) structure of antiprotonic helium. This precise measurement which was
commenced in 2006, has now been completed. Our initial analysis shows no
apparent density or power dependence and therefore the results can be averaged.
The statistical error of the observable M1 transitions is a factor of 60
smaller than that of three body quantum electrodynamic (QED) calculations,
while their difference has been resolved to a precision comparable to theory (a
factor of 10 better than our first measurement). This difference is sensitive
to the antiproton magnetic moment and agreement between theory and experiment
would lead to an increased precision of this parameter, thus providing a test
of CPT invariance.Comment: 6 pages, 4 figure
Search for long-lived states in antiprotonic lithium
The spectrum of the (L_i^3 + p-bar + 2e) four-body system was calculated in
an adiabatic approach. The two-electron energies were approximated by a sum of
two single-electron effective charge two-center energies as suggested in [6].
While the structure of the spectrum does not exclude the existence of
long-lived states, their experimental observability is still to be clarified
First observation of two hyperfine transitions in antiprotonic He-3
We report on the first experimental results for microwave spectroscopy of the
hyperfine structure of antiprotonic He-3. Due to the helium nuclear spin,
antiprotonic He-3 has a more complex hyperfine structure than antiprotonic He-4
which has already been studied before. Thus a comparison between theoretical
calculations and the experimental results will provide a more stringent test of
the three-body quantum electrodynamics (QED) theory. Two out of four
super-super-hyperfine (SSHF) transition lines of the (n,L)=(36,34) state were
observed. The measured frequencies of the individual transitions are
11.12559(14) GHz and 11.15839(18) GHz, less than 1 MHz higher than the current
theoretical values, but still within their estimated errors. Although the
experimental uncertainty for the difference of these frequencies is still very
large as compared to that of theory, its measured value agrees with theoretical
calculations. This difference is crucial to be determined because it is
proportional to the magnetic moment of the antiproton.Comment: 8 pages, 6 figures, just published (online so far) in Physics Letters
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