336 research outputs found
Alkali vapor pressure modulation on the 100ms scale in a single-cell vacuum system for cold atom experiments
We describe and characterize a device for alkali vapor pressure modulation on
the 100ms timescale in a single-cell cold atom experiment. Its mechanism is
based on optimized heat conduction between a current-modulated alkali dispenser
and a heat sink at room temperature. We have studied both the short-term
behavior during individual pulses and the long-term pressure evolution in the
cell. The device combines fast trap loading and relatively long trap lifetime,
enabling high repetition rates in a very simple setup. These features make it
particularly suitable for portable atomic sensors.Comment: One reference added, one correcte
Stability of a trapped atom clock on a chip
We present a compact atomic clock interrogating ultracold 87Rb magnetically
trapped on an atom chip. Very long coherence times sustained by spin
self-rephasing allow us to interrogate the atomic transition with 85% contrast
at 5 s Ramsey time. The clock exhibits a fractional frequency stability of
at 1 s and is likely to integrate into the
range in less than a day. A detailed analysis of 7 noise
sources explains the measured frequency stability. Fluctuations in the atom
temperature (0.4 nK shot-to-shot) and in the offset magnetic field
( relative fluctuations shot-to-shot) are the main noise
sources together with the local oscillator, which is degraded by the 30% duty
cycle. The analysis suggests technical improvements to be implemented in a
future second generation set-up. The results demonstrate the remarkable degree
of technical control that can be reached in an atom chip experiment.Comment: 12 pages, 11 figure
Spin waves and Collisional Frequency Shifts of a Trapped-Atom Clock
We excite spin-waves with spatially inhomogeneous pulses and study the
resulting frequency shifts of a chip-scale atomic clock of trapped Rb.
The density-dependent frequency shifts of the hyperfine transition simulate the
s-wave collisional frequency shifts of fermions, including those of optical
lattice clocks. As the spin polarizations oscillate in the trap, the frequency
shift reverses and it depends on the area of the second Ramsey pulse,
exhibiting a predicted beyond mean-field frequency shift. Numerical and
analytic models illustrate the observed behaviors.Comment: Will appear soon in Physical Review Letters - Typos correcte
Millimeter-long Fiber Fabry-Perot cavities
We demonstrate fiber Fabry-Perot (FFP) cavities with concave mirrors that can
be operated at cavity lengths as large as 1.5mm without significant
deterioration of the finesse. This is achieved by using a laser dot machining
technique to shape spherical mirrors with ultralow roughness and employing
single-mode fibers with large mode area for good mode matching to the cavity.
Additionally, in contrast to previous FFPs, these cavities can be used over an
octave-spanning frequency range with adequate coatings. We also show directly
that shape deviations caused by the fiber's index profile lead to a finesse
decrease as observed in earlier attempts to build long FFP cavities, and show a
way to overcome this problem
Pitfalls in efficacy testing â how important is the validation of neutralization of chlorhexidine digluconate?
<p>Abstract</p> <p>Background</p> <p>Effective neutralization of active agents is essential to obtain valid efficacy results, especially when non-volatile active agents like chlorhexidine digluconate (CHG) are tested. The aim of this study was to determine an effective and non-toxic neutralizing mixture for a propan-1-ol solution containing 2% CHG.</p> <p>Methods</p> <p>Experiments were carried out according to ASTM E 1054-02. The neutralization capacity was tested separately with five challenge microorganisms in suspension, and with a rayon swab carrier. Either 0.5 mL of the antiseptic solution (suspension test) or a saturated swab with the antiseptic solution (carrier test) was added to tryptic soy broth containing neutralizing agents. After the samples were mixed, aliquots were spread immediately and after 3 h of storage at 2 â 8°C onto tryptic soy agar containing a neutralizing mixture.</p> <p>Results</p> <p>The neutralizer was, however, not consistently effective in the suspension test. Immediate spread yielded a valid neutralization with <it>Staphylococcus aureus, Staphylococcus epidermidis </it>and <it>Corynebacterium jeikeium </it>but not with <it>Micrococcus luteus </it>(p < 0.001) and <it>Candida albicans </it>(p < 0.001). A 3-h storage period of the neutralized active agents in suspension resulted in significant carry-over activity of CHG in addition against <it>Staphylococcus epidermidis </it>(p < 0.001) and <it>Corynebacterium jeikeium </it>(p = 0.044). In the carrier test, the neutralizing mixture was found to be effective and non toxic to all challenge microorganisms when spread immediately. However, after 3 h storage of the neutralized active agents significant carry-over activity of CHG against <it>Micrococcus luteus </it>(p = 0.004; Tukey HSD) was observed.</p> <p>Conclusion</p> <p>Without effective neutralization in the sampling fluid, non-volatile active ingredients will continue to reduce the number of surviving microorganisms after antiseptic treatment even if the sampling fluid is kept cold straight after testing. This can result in false-positive antiseptic efficacy data. Attention should be paid during the neutralization validation process to the amount of antiseptic solution, the storage time and to the choice of appropriate and sensitive microorganisms.</p
Ccl2 and Ccl3 Mediate Neutrophil Recruitment via Induction of Protein Synthesis and Generation of Lipid Mediators
Objective: Although the chemokines monocyte chemoattractant protein-1 (Ccl2/JE/MCP-1) and macrophage inflammatory protein-1α (Ccl3/MIP-1α) have recently been implicated in neutrophil migration, the underlying mechanisms remain largely unclear.
Methods and Results: Stimulation of the mouse cremaster muscle with Ccl2/JE/MCP-1 or Ccl3/MIP-1α induced a significant increase in numbers of firmly adherent and transmigrated leukocytes (>70% neutrophils) as observed by in vivo microscopy. This increase was significantly attenuated in mice receiving an inhibitor of RNA transcription (actinomycin D) or antagonists of platelet activating factor (PAF; BN 52021) and leukotrienes (MK-886; AA-861). In contrast, leukocyte responses elicited by PAF and leukotriene-B4 (LTB4) themselves were not affected by actinomycin D, BN 52021, MK-886, or AA-861. Conversely, PAF and LTB4, but not Ccl2/JE/MCP-1 and Ccl3/MIP-1α, directly activated neutrophils as indicated by shedding of CD62L and marked upregulation of CD11b. Moreover, Ccl2/JE/
MCP-1- and Ccl3/MIP-1α-elicited leakage of fluorescein isothiocyanate dextran as well as collagen IV remodeling within the venular basement membrane were completely absent in neutrophil-depleted mice.
Conclusions: Ccl2/JE/MCP-1 and Ccl3/MIP-1α mediate firm adherence and (subsequent) transmigration of neutrophils via protein synthesis and secondary generation of leukotrienes and PAF, which in turn directly activate neutrophils. Thereby, neutrophils facilitate basement membrane remodeling and promote microvascular leakage
Coherence in Microchip Traps
We report the coherent manipulation of internal states of neutral atoms in a
magnetic microchip trap. Coherence lifetimes exceeding 1 s are observed with
atoms at distances of m from the microchip surface. The coherence
lifetime in the chip trap is independent of atom-surface distance within our
measurement accuracy, and agrees well with the results of similar measurements
in macroscopic magnetic traps. Due to the absence of surface-induced
decoherence, a miniaturized atomic clock with a relative stability in the
range can be realized. For applications in quantum information
processing, we propose to use microwave near-fields in the proximity of chip
wires to create potentials that depend on the internal state of the atoms.Comment: Revised version, accepted for publication in Phys. Rev. Lett., 4
pages, 4 figure
Valorization of organic carbon in primary sludge via semi-continuous dark fermentation: First step to establish a wastewater biorefinery
In this study, lab-scale, bench-scale, and pilot-scale experiments were carried out to optimize short-chain fatty acids production from primary sludge. Batch tests showed the requirement of short retention times and semi-continuous operation mode showed a plateau of maximum daily productivity at 36-hours hydraulic retention time with minimal methanation. Optimization from pH 5 to pH 10 at 36 h-hydraulic retention time under long-term semi-continuous operating mode revealed that production of short-chain fatty acids was pH dependent and highest yields could be achieved at pH 7 by establishing optimum redox conditions for fermentation. Pilot-scale experiments at 32 °C showed that daily productivity (3.1 gâLâd) and yields (150 mgâg; OLR = 21 gâLâd; pH 7) of short-chain fatty acids could be significantly improved, specifically for acetic and propionic acids. From these results, a robust dark fermentation step for recovery of valuable products from the solids treatment step in a biorefinery can be achieved
A waveguide atom beamsplitter for laser-cooled neutral atoms
A laser-cooled neutral-atom beam from a low-velocity intense source is split
into two beams while guided by a magnetic-field potential. We generate our
multimode-beamsplitter potential with two current-carrying wires on a glass
substrate combined with an external transverse bias field. The atoms bend
around several curves over a -cm distance. A maximum integrated flux of
is achieved with a current density of
in the 100- diameter
wires. The initial beam can be split into two beams with a 50/50 splitting
ratio
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