771 research outputs found
To grate a liquid into tiny droplets by its impact on a hydrophobic micro-grid
We report on experiments of drop impacting a hydrophobic micro-grid, of
typical spacing a few tens of m. Above a threshold in impact speed, liquid
emerges to the other side, forming micro-droplets of size about that of the
grid holes. We propose a method to produce either a mono-disperse spray or a
single tiny droplet of volume as small as a few picoliters corresponding to a
volume division of the liquid drop by a factor of up to 10. We also discuss
the discrepancy of the measured thresholds with that predicted by a balance
between inertia and capillarity.Comment: 3 pages, 5 figures, Accepted for publication in Applied Physics
Letter
Trajectory Synthesis for Fisher Information Maximization
Estimation of model parameters in a dynamic system can be significantly
improved with the choice of experimental trajectory. For general, nonlinear
dynamic systems, finding globally "best" trajectories is typically not
feasible; however, given an initial estimate of the model parameters and an
initial trajectory, we present a continuous-time optimization method that
produces a locally optimal trajectory for parameter estimation in the presence
of measurement noise. The optimization algorithm is formulated to find system
trajectories that improve a norm on the Fisher information matrix. A
double-pendulum cart apparatus is used to numerically and experimentally
validate this technique. In simulation, the optimized trajectory increases the
minimum eigenvalue of the Fisher information matrix by three orders of
magnitude compared to the initial trajectory. Experimental results show that
this optimized trajectory translates to an order of magnitude improvement in
the parameter estimate error in practice.Comment: 12 page
Magnetic-dipole transition probabilities in B-like and Be-like ions
The magnetic-dipole transition probabilities between the fine-structure
levels (1s^2 2s^2 2p) ^2P_1/2 - ^2P_3/2 for B-like ions and (1s^2 2s 2p) ^3P_1
- ^3P_2 for Be-like ions are calculated. The configuration-interaction method
in the Dirac-Fock-Sturm basis is employed for the evaluation of the
interelectronic-interaction correction with negative-continuum spectrum being
taken into account. The 1/Z interelectronic-interaction contribution is derived
within a rigorous QED approach employing the two-time Green function method.
The one-electron QED correction is evaluated within framework of the anomalous
magnetic-moment approximation. A comparison with the theoretical results of
other authors and with available experimental data is presented
Variation of the Fine-Structure Constant and Laser Cooling of Atomic Dysprosium
Radio-frequency electric-dipole transitions between nearly degenerate,
opposite parity levels of atomic dysprosium (Dy) were monitored over an
eight-month period to search for a variation in the fine-structure constant,
. The data provide a rate of fractional temporal variation of
of yr or a value of for , the variation coefficient for in a changing
gravitational potential. All results indicate the absence of significant
variation at the present level of sensitivity. We also present initial results
on laser cooling of an atomic beam of dysprosium.Comment: 10 pages, 6 figures, fixed typos in section 5, updated result
Investigation of the Gravitational Potential Dependence of the Fine-Structure Constant Using Atomic Dysprosium
Radio-frequency E1 transitions between nearly degenerate, opposite parity
levels of atomic dysprosium were monitored over an eight month period to search
for a variation in the fine-structure constant. During this time period, data
were taken at different points in the gravitational potential of the Sun. The
data are fitted to the variation in the gravitational potential yielding a
value of for the fit parameter . This
value gives the current best laboratory limit. In addition, our value of
combined with other experimental constraints is used to extract
the first limits on k_e and k_q. These coefficients characterize the variation
of m_e/m_p and m_q/m_p in a changing gravitational potential, where m_e, m_p,
and m_q are electron, proton, and quark masses. The results are and .Comment: 6 pages, 3 figure
First direct mass-measurement of the two-neutron halo nucleus 6He and improved mass for the four-neutron halo 8He
The first direct mass-measurement of He has been performed with the
TITAN Penning trap mass spectrometer at the ISAC facility. In addition, the
mass of He was determined with improved precision over our previous
measurement. The obtained masses are (He) = 6.018 885 883(57) u and
(He) = 8.033 934 44(11) u. The He value shows a deviation from
the literature of 4. With these new mass values and the previously
measured atomic isotope shifts we obtain charge radii of 2.060(8) fm and
1.959(16) fm for He and He respectively. We present a detailed
comparison to nuclear theory for He, including new hyperspherical harmonics
results. A correlation plot of the point-proton radius with the two-neutron
separation energy demonstrates clearly the importance of three-nucleon forces.Comment: 4 pages, 2 figure
First Penning-trap mass measurement in the millisecond half-life range: the exotic halo nucleus 11Li
In this letter, we report a new mass for Li using the trapping
experiment TITAN at TRIUMF's ISAC facility. This is by far the shortest-lived
nuclide, , for which a mass measurement has ever been
performed with a Penning trap. Combined with our mass measurements of
Li we derive a new two-neutron separation energy of 369.15(65) keV: a
factor of seven more precise than the best previous value. This new value is a
critical ingredient for the determination of the halo charge radius from
isotope-shift measurements. We also report results from state-of-the-art
atomic-physics calculations using the new mass and extract a new charge radius
for Li. This result is a remarkable confluence of nuclear and atomic
physics.Comment: Formatted for submission to PR
Trapped-ion decay spectroscopy towards the determination of ground-state components of double-beta decay matrix elements
A new technique has been developed at TRIUMF's TITAN facility to perform
in-trap decay spectroscopy. The aim of this technique is to eventually measure
weak electron capture branching ratios (ECBRs) and by this to consequently
determine GT matrix elements of decaying nuclei. These branching
ratios provide important input to the theoretical description of these decays.
The feasibility and power of the technique is demonstrated by measuring the
ECBR of Cs.Comment: 9 pages, 9 figure
Collisional perturbation of radio-frequency E1 transitions in an atomic beam of dysprosium
We have studied collisional perturbations of radio-frequency (rf)
electric-dipole (E1) transitions between the nearly degenerate opposite-parity
levels in atomic dysprosium (Dy) in the presence of 10 to 80 Torr of
H, N, He, Ar, Ne, Kr, and Xe. Collisional broadening and
shift of the resonance, as well as the attenuation of the signal amplitude are
observed to be proportional to the foreign-gas density with the exception of
H and Ne, for which no shifts were observed. Corresponding rates and cross
sections are presented. In addition, rates and cross sections for O are
extracted from measurements using air as foreign gas. The primary motivation
for this study is the need for accurate determination of the shift rates, which
are needed in a laboratory search for the temporal variation of the
fine-structure constant [A. T. Nguyen, D. Budker, S. K. Lamoreaux, and J. R.
Torgerson, Phys. Rev. A \textbf{69}, 22105 (2004)].Comment: 11 pages, 8 figure
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