918 research outputs found
High-fidelity imaging of a band insulator in a three-dimensional optical lattice clock
We report on the observation of a high-density, band insulating state in a
three-dimensional optical lattice clock. Filled with a nuclear-spin polarized
degenerate Fermi gas of 87Sr, the 3D lattice has one atom per site in the
ground motional state, thus guarding against frequency shifts due to contact
interactions. At this high density where the average distance between atoms is
comparable to the probe wavelength, standard imaging techniques suffer from
large systematic errors. To spatially probe frequency shifts in the clock and
measure thermodynamic properties of this system, accurate imaging techniques at
high optical depths are required. Using a combination of highly saturated
fluorescence and absorption imaging, we confirm the density distribution in our
3D optical lattice in agreement with a single spin band insulating state.
Combining our clock platform with this high filling fraction opens the door to
studying new classes of long-lived, many-body states arising from dipolar
interactions.Comment: 10 pages, 8 figure
Observation of mHz-level cooperative Lamb shifts in an optical atomic clock
We report on the direct observation of resonant electric dipole-dipole
interactions in a cubic array of atoms in the many-excitation limit. The
interactions, mediated by single-atom couplings to the shared electromagnetic
vacuum, are shown to produce spatially-dependent cooperative Lamb shifts when
spectroscopically interrogating the mHz-wide optical clock transition in
strontium-87. We show that the ensemble-averaged shifts can be suppressed below
the level of evaluated systematic uncertainties for state-of-the-art optical
atomic clocks. Additionally, we demonstrate that excitation of the atomic
dipoles near a Bragg angle can enhance these effects by nearly an order of
magnitude compared to non-resonant geometries. Given the remarkable precision
of frequency measurements and the high accuracy of the modeled response, our
work demonstrates that such a clock is a novel platform for studies of the
quantum many-body physics of spins with long-range interactions mediated by
propagating photons
Dynamical Instability of a Doubly Quantized Vortex in a Bose-Einstein condensate
Doubly quantized vortices were topologically imprinted in Na
condensates, and their time evolution was observed using a tomographic imaging
technique. The decay into two singly quantized vortices was characterized and
attributed to dynamical instability. The time scale of the splitting process
was found to be longer at higher atom density.Comment: 5 pages, 4 figure
Psychological Safety and Norm Clarity in Software Engineering Teams
In the software engineering industry today, companies primarily conduct their
work in teams. To increase organizational productivity, it is thus crucial to
know the factors that affect team effectiveness. Two team-related concepts that
have gained prominence lately are psychological safety and team norms. Still,
few studies exist that explore these in a software engineering context.
Therefore, with the aim of extending the knowledge of these concepts, we
examined if psychological safety and team norm clarity associate positively
with software developers' self-assessed team performance and job satisfaction,
two important elements of effectiveness.
We collected industry survey data from practitioners (N = 217) in 38
development teams working for five different organizations. The result of
multiple linear regression analyses indicates that both psychological safety
and team norm clarity predict team members' self-assessed performance and job
satisfaction. The findings also suggest that clarity of norms is a stronger
(30\% and 71\% stronger, respectively) predictor than psychological safety.
This research highlights the need to examine, in more detail, the
relationship between social norms and software development. The findings of
this study could serve as an empirical baseline for such, future work.Comment: Submitted to CHASE'201
Quasi-chemical study of Be(aq) speciation
Be(aq) hydrolysis can to lead to the formation of multi-beryllium
clusters, but the thermodynamics of this process has not been resolved
theoretically. We study the hydration state of an isolated Be ion using
both the quasi-chemical theory of solutions and ab initio molecular dynamics.
These studies confirm that Be(aq) is tetra-hydrated. The quasi-chemical
approach is then applied to then the deprotonation of Be(H_2O)_4^{2+}} to
give BeOH(H_2O)_3{}^{+}}. The calculated pK of 3.8 is in good agreement
with the experimentally suggested value around 3.5. The calculated energetics
for the formation of BeOHBe are then obtained in fair agreement with
experiments.Comment: 11 pages, 3 figure
Recommended from our members
The Observations Of The X-Ray Source Hz Herculis-Hercules X-1
NASAESASRCAstronom
High LET, passive space radiation dosimetry and spectrometry
The development of high linear energy transfer (LET), passive radiation dosimetry and spectrometry is needed for the purpose of accurate determination of equivalent doses and assessment of health risks to astronauts on long duration missions. Progress in the following research areas is summerized: intercomparisons of cosmic ray equivalent dose and LET spectra measurements between STS missions and between astronauts; increases LET spectra measurement accuracy with ATAS; space radiation measurements for intercomparisons of passive (PNTD, TLD, TRND, Emulsion) and active (TEPC, RME-111) dosimeters; interaction of cosmic ray particles with nuclei in matter; radiation measurements after long duration space exposures; ground based dosimeter calibrations; neutron detector calibrations; radiation measurements on Soviet/Russian spacecraft; space radiation measurements under thin shielding; and space radiation
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