529 research outputs found
Frequency Metrology on single trapped ions in the weak binding limit: The 3s1/2-3p3/2 transition in 24-Mg+
We demonstrate a method for precision spectroscopy on trapped ions in the
limit of unresolved motional sidebands. By sympathetic cooling of a chain of
crystallized ions we suppress adverse temperature variations induced by the
spectroscopy laser that usually lead to a distorted line profle and obtain a
Voigt profile with negligible distortions. We applied the method to measure the
absolute frequency of the astrophysically relevant D2 transition in single
24-Mg+ ions and find 1072082934.33(16)MHz, a nearly 400fold improvement over
previous results. Further, we find the excited state lifetime to be 3.84(10)
ns.Comment: 4 pages, 5 figure
Injection Locking of a Trapped-Ion Phonon Laser
We report on injection locking of optically excited mechanical oscillations of a single, trapped ion. The injection locking dynamics are studied by analyzing the oscillator spectrum with a spatially selective Fourier transform technique and the oscillator phase with stroboscopic imaging. In both cases we find excellent agreement with theory inside and outside the locking range. We attain injection locking with forces as low as 5(1)×10^(-24)  N so this system appears promising for the detection of ultraweak oscillating forces
Sub-milliKelvin spatial thermometry of a single Doppler cooled ion in a Paul trap
We report on observations of thermal motion of a single, Doppler-cooled ion
along the axis of a linear radio-frequency quadrupole trap. We show that for a
harmonic potential the thermal occupation of energy levels leads to Gaussian
distribution of the ion's axial position. The dependence of the spatial thermal
spread on the trap potential is used for precise calibration of our imaging
system's point spread function and sub-milliKelvin thermometry. We employ this
technique to investigate the laser detuning dependence of the Doppler
temperature.Comment: 5 pages, 4 figure
New cloud chamber experiments on the heterogeneous ice nucleation ability of oxalic acid in the immersion mode
The heterogeneous ice nucleation ability of oxalic acid in the immersion
mode has been investigated by controlled expansion cooling runs with
airborne, ternary solution droplets composed of, (i), sodium chloride,
oxalic acid, and water (NaCl/OA/H<sub>2</sub>O) and, (ii), sulphuric acid, oxalic
acid, and water (H<sub>2</sub>SO<sub>4</sub>/OA/H<sub>2</sub>O). Polydisperse aerosol
populations with median diameters ranging from 0.5–0.7 μm and
varying solute concentrations were prepared. The expansion experiments were
conducted in the AIDA aerosol and cloud chamber of the Karlsruhe Institute
of Technology at initial temperatures of 244 and 235 K. In the ternary
NaCl/OA/H<sub>2</sub>O system, solid inclusions of oxalic acid, presumably
nucleated as oxalic acid dihydrate, were formed by temporarily exposing the
ternary solution droplets to a relative humidity below the efflorescence
point of NaCl. The matrix of the crystallised NaCl particulates triggered
the precipitation of the organic crystals which later remained as solid
inclusions in the solution droplets when the relative humidity was
subsequently raised above the deliquescence point of NaCl. The embedded
oxalic acid crystals reduced the critical ice saturation ratio required for
the homogeneous freezing of pure NaCl/H<sub>2</sub>O solution droplets at a
temperature of around 231 K from 1.38 to about 1.32. Aqueous solution
droplets with OA inclusions larger than about 0.27 μm in diameter
efficiently nucleated ice by condensation freezing when they were activated
to micron-sized cloud droplets at 241 K, i.e., they froze well above the
homogeneous freezing temperature of pure water droplets of about 237 K. Our
results on the immersion freezing potential of oxalic acid corroborate the
findings from a recent study with emulsified aqueous solutions containing
crystalline oxalic acid. In those experiments, the crystallisation of oxalic
acid diyhdrate was triggered by a preceding homogeneous freezing cycle with
the emulsion samples. The expansion cooling cycles with ternary
H<sub>2</sub>SO<sub>4</sub>/OA/H<sub>2</sub>O solution droplets were aimed to analyse whether
those findings can be transferred to ice nucleation experiments with
airborne oxalic acid containing aerosol particles. Under our experimental
conditions, the efficiency by which the surface of homogeneously nucleated
ice crystals triggered the precipitation of oxalic acid dihydrate was very
low, i.e., less than one out of a hundred ice crystals that were formed by
homogeneous freezing in a first expansion cooling cycle left behind an
ice-active organic crystal that acted as immersion freezing nucleus in a
second expansion cooling cycle
Precision spectroscopy of the 3s-3p fine structure doublet in Mg+
We apply a recently demonstrated method for precision spectroscopy on strong
transitions in trapped ions to measure both fine structure components of the
3s-3p transition in 24-Mg+ and 26-Mg+. We deduce absolute frequency reference
data for transition frequencies, isotope shifts and fine structure splittings
that are in particular useful for comparison with quasar absorption spectra,
which test possible space-time variations of the fine structure constant. The
measurement accuracy improves previous literature values, when existing, by
more than two orders of magnitude
Missing Transverse-Doppler Effect in Time-Dilation Experiments with High-Speed Ions
Recent experiments with high-speed ions have investigated potential
deviations from the time-dilation predicted by special relativity (SR). The
main contribution of this article is to show that the SR predictions are
matched by the experimental results only when the transverse Doppler effect in
the observed emissions from the ions are neglected in the analysis. However,
the Doppler effect in the emission cannot be neglected because it is similar to
the time dilation effect. Thus, the article highlights the need to consider
Doppler emission effects when validating SR time dilation using high-speed ion
experiments.Comment: 3 pages, 3 figure
Downregulation of Cinnamyl-Alcohol Dehydrogenase in Switchgrass by RNA Silencing Results in Enhanced Glucose Release after Cellulase Treatment
Cinnamyl alcohol dehydrogenase (CAD) catalyzes the last step in monolignol biosynthesis and genetic evidence indicates CAD deficiency in grasses both decreases overall lignin, alters lignin structure and increases enzymatic recovery of sugars. To ascertain the effect of CAD downregulation in switchgrass, RNA mediated silencing of CAD was induced through Agrobacterium mediated transformation of cv. ‘‘Alamo’’ with an inverted repeat construct containing a fragment derived from the coding sequence of PviCAD2. The resulting primary transformants accumulated less CAD RNA transcript and protein than control transformants and were demonstrated to be stably transformed with between 1 and 5 copies of the TDNA. CAD activity against coniferaldehyde, and sinapaldehyde in stems of silenced lines was significantly reduced as was overall lignin and cutin. Glucose release from ground samples pretreated with ammonium hydroxide and digested with cellulases was greater than in control transformants. When stained with the lignin and cutin specific stain phloroglucinol- HCl the staining intensity of one line indicated greater incorporation of hydroxycinnamyl aldehydes in the lignin
Enhanced dielectronic recombination of lithium-like Ti19+ ions in external ExB fields
Dielectronic recombination(DR) of lithium-like Ti19+(1s2 2s) ions via 2s->2p
core excitations has been measured at the Heidelberg heavy ion storage ring
TSR. We find that not only external electric fields (0 <= Ey <= 280 V/cm) but
also crossed magnetic fields (30 mT <= Bz <= 80 mT) influence the DR via high-n
(2p_j nl)-Rydberg resonances. This result confirms our previous finding for
isoelectronic Cl14+ ions [Bartsch T et al, PRL 82, 3779 (1999)] that
experimentally established the sensitivity of DR to ExB fields. In the present
investigation the larger 2p_{1/2}-2p_{3/2} fine structure splitting of Ti19+
allowed us to study separately the influence of external fields via the two
series of Rydberg DR resonances attached to the 2s -> 2p_{1/2} and 2s ->
2p_{3/2} excitations of the Li-like core, extracting initial slopes and
saturation fields of the enhancement. We find that for Ey > 80 V/cm the field
induced enhancement is about 1.8 times stronger for the 2p_{3/2} series than
for the 2p_{1/2} series.Comment: 10 pages, 3 figures, to be published in Journal of Physics B, see
also http://www.strz.uni-giessen.de/~k
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