862 research outputs found
Dynamic acoustic field activated cell separation (DAFACS)
Advances in diagnostics, cell and stem cell technologies drive the development of application-specific tools
for cell and particle separation. Acoustic micro-particle separation offers a promising avenue for highthroughput,
label-free, high recovery, cell and particle separation and isolation in regenerative medicine.
Here, we demonstrate a novel approach utilizing a dynamic acoustic field that is capable of separating an
arbitrary size range of cells. We first demonstrate the method for the separation of particles with different
diameters between 6 and 45 μm and secondly particles of different densities in a heterogeneous medium.
The dynamic acoustic field is then used to separate dorsal root ganglion cells. The shearless, label-free and
low damage characteristics make this method of manipulation particularly suited for biological applications.
Advantages of using a dynamic acoustic field for the separation of cells include its inherent safety and
biocompatibility, the possibility to operate over large distances (centimetres), high purity (ratio of particle
population, up to 100%), and high efficiency (ratio of separated particles over total number of particles to
separate, up to 100%)
Extreme non-linear response of ultra-narrow optical transitions in cavity QED for laser stabilization
We explore the potential of direct spectroscopy of ultra-narrow optical
transitions of atoms localized in an optical cavity. In contrast to
stabilization against a reference cavity, which is the approach currently used
for the most highly stabilized lasers, stabilization against an atomic
transition does not suffer from Brownian thermal noise. Spectroscopy of
ultra-narrow optical transitions in a cavity operates in a very highly
saturated regime in which non-linear effects such as bistability play an
important role. From the universal behavior of the Jaynes-Cummings model with
dissipation, we derive the fundamental limits for laser stabilization using
direct spectroscopy of ultra-narrow atomic lines. We find that with current
lattice clock experiments, laser linewidths of about 1 mHz can be achieved in
principle, and the ultimate limitations of this technique are at the 1 Hz
level.Comment: 5 pages, 4 figure
Magneto-Optical Trap for Thulium Atoms
Thulium atoms are trapped in a magneto-optical trap using a strong transition
at 410 nm with a small branching ratio. We trap up to atoms at
a temperature of 0.8(2) mK after deceleration in a 40 cm long Zeeman slower.
Optical leaks from the cooling cycle influence the lifetime of atoms in the MOT
which varies between 0.3 -1.5 s in our experiments. The lower limit for the
leaking rate from the upper cooling level is measured to be 22(6) s. The
repumping laser transferring the atomic population out of the F=3 hyperfine
ground-state sublevel gives a 30% increase for the lifetime and the number of
atoms in the trap.Comment: 4 pages, 6 figure
Transverse laser cooling of a thermal atomic beam of dysprosium
A thermal atomic beam of dysprosium (Dy) atoms is cooled using the
transition at 421 nm. The cooling is
done via a standing light wave orthogonal to the atomic beam. Efficient
transverse cooling to the Doppler limit is demonstrated for all observable
isotopes of dysprosium. Branching ratios to metastable states are demonstrated
to be . A scheme for enhancement of the
nonzero-nuclear-spin-isotope cooling, as well as a method for direct
identification of possible trap states, is proposed.Comment: 5 pages, 4 figures v2: 7 pages, 7 figure
Sympathetic Cooling of Mixed Species Two-Ion Crystals for Precision Spectroscopy
Sympathetic cooling of trapped ions has become an indispensable tool for
quantum information processing and precision spectroscopy. In the simplest
situation a single Doppler-cooled ion sympathetically cools another ion which
typically has a different mass. We analytically investigate the effect of the
mass ratio of such an ion crystal on the achievable temperature limit in the
presence of external heating. As an example, we show that cooling of a single
Al+ with Be+, Mg+ and Ca+ ions provides similar results for heating rates
typically observed in ion traps, whereas cooling ions with a larger mass
perform worse. Furthermore, we present numerical simulation results of the
rethermalisation dynamics after a background gas collision for the Al+/Ca+
crystal for different cooling laser configurations.Comment: Made Graphics black & white print compatible, clarified abstract and
summar
Hyper-Ramsey Spectroscopy of Optical Clock Transitions
We present non-standard optical Ramsey schemes that use pulses individually
tailored in duration, phase, and frequency to cancel spurious frequency shifts
related to the excitation itself. In particular, the field shifts and their
uncertainties of Ramsey fringes can be radically suppressed (by 2-4 orders of
magnitude) in comparison with the usual Ramsey method (using two equal pulses)
as well as with single-pulse Rabi spectroscopy. Atom interferometers and
optical clocks based on two-photon transitions, heavily forbidden transitions,
or magnetically induced spectroscopy could significantly benefit from this
method. In the latter case these frequency shifts can be suppressed
considerably below a fractional level of 10^{-17}. Moreover, our approach opens
the door for the high-precision optical clocks based on direct frequency comb
spectroscopy.Comment: 5 pages, 4 figure
Coopetition of software firms in Open source software ecosystems
Software firms participate in an ecosystem as a part of their innovation
strategy to extend value creation beyond the firms boundary. Participation in
an open and independent environment also implies the competition among firms
with similar business models and targeted markets. Hence, firms need to
consider potential opportunities and challenges upfront. This study explores
how software firms interact with others in OSS ecosystems from a coopetition
perspective. We performed a quantitative and qualitative analysis of three OSS
projects. Finding shows that software firms emphasize the co-creation of common
value and partly react to the potential competitiveness on OSS ecosystems. Six
themes about coopetition were identified, including spanning gatekeepers,
securing communication, open-core sourcing and filtering shared code. Our work
contributes to software engineering research with a rich description of
coopetition in OSS ecosystems. Moreover, we also come up with several
implications for software firms in pursing a harmony participation in OSS
ecosystems.Comment: This is the author's version of the work. Copyright owner's version
can be accessed at
https://link.springer.com/chapter/10.1007/978-3-319-69191-6_10, Coopetition
of software firms in Open source software ecosystems, 8th ICSOB 2017, Essen,
Germany (2017
Influence of optical aberrations in an atomic gyroscope
In atom interferometry based on light-induced diffraction, the optical
aberrations of the laser beam splitters are a dominant source of noise and
systematic effect. In an atomic gyroscope, this effect is dramatically reduced
by the use of two atomic sources. But it remains critical while coupled to
fluctuations of atomic trajectories, and appears as a main source of noise to
the long term stability. Therefore we measure these contributions in our setup,
using cold Cesium atoms and stimulated Raman transitions
Doppler cooling and trapping on forbidden transitions
Ultracold atoms at temperatures close to the recoil limit have been achieved
by extending Doppler cooling to forbidden transitions. A cloud of ^40Ca atoms
has been cooled and trapped to a temperature as low as 6 \mu K by operating a
magneto-optical trap on the spin-forbidden intercombination transition.
Quenching the long-lived excited state with an additional laser enhanced the
scattering rate by a factor of 15, while a high selectivity in velocity was
preserved. With this method more than 10% of pre-cooled atoms from a standard
magneto-optical trap have been transferred to the ultracold trap. Monte-Carlo
simulations of the cooling process are in good agreement with the experiments
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