6,401 research outputs found
3D printing of gas jet nozzles for laser-plasma accelerators
Recent results on laser wakefield acceleration in tailored plasma channels
have underlined the importance of controlling the density profile of the gas
target. In particular it was reported that appropriate density tailoring can
result in improved injection, acceleration and collimation of laser-accelerated
electron beams. To achieve such profiles innovative target designs are
required. For this purpose we have reviewed the usage of additive layer
manufacturing, commonly known as 3D printing, in order to produce gas jet
nozzles. Notably we have compared the performance of two industry standard
techniques, namely selective laser sintering (SLS) and stereolithography (SLA).
Furthermore we have used the common fused deposition modeling (FDM) to
reproduce basic gas jet designs and used SLA and SLS for more sophisticated
nozzle designs. The nozzles are characterized interferometrically and used for
electron acceleration experiments with the Salle Jaune terawatt laser at
Laboratoire d'Optique Appliqu\'ee
Hierarchical functionalisation of single-wall carbon nanotubes with DNA through positively charged pyrene
A simple and efficient method to link reversibly DNA to SWNTs via electrostatic interaction is reported. The DNA/nanotube hybrids are characterised by a combination of gel electrophoresis and AFM
Low temperature transition to a superconducting phase in boron-doped silicon films grown on (001)-oriented silicon wafers
We report on a detailed analysis of the superconducting properties of
boron-doped silicon films grown along the 001 direction by Gas Immersion Laser
Doping. The doping concentration cB has been varied up to approx. 10 at.% by
increasing the number of laser shots to 500. No superconductivity could be
observed down to 40mK for doping level below 2.5 at.%. The critical temperature
Tc then increased steeply to reach 0.6K for cB = 8 at%. No hysteresis was found
for the transitions in magnetic field, which is characteristic of a type II
superconductor. The corresponding upper critical field Hc2(0) was on the order
of 1000 G, much smaller than the value previously reported by Bustarret et al.
in Nature (London) 444, 465 (2006).Comment: 4 pages including 4 figures, submitted to PRB-Rapid Communicatio
IRS Spectra of Solar-Type Stars: \break A Search for Asteroid Belt Analogs
We report the results of a spectroscopic search for debris disks surrounding
41 nearby solar type stars, including 8 planet-bearing stars, using the {\it
Spitzer Space Telescope}. With accurate relative photometry using the Infrared
Spectrometer (IRS) between 7-34 \micron we are able to look for excesses as
small as 2% of photospheric levels with particular sensitivity to weak
spectral features. For stars with no excess, the upper limit in a
band at 30-34 m corresponds to 75 times the brightness of our
zodiacal dust cloud. Comparable limits at 8.5-13 m correspond to
1,400 times the brightness of our zodiacal dust cloud. These limits correspond
to material located within the 1 to 5 AU region that, in our solar
system, originates from debris associated with the asteroid belt. We find
excess emission longward of 25 m from five stars of which four also
show excess emission at 70 m. This emitting dust must be located around
5-10 AU. One star has 70 micron emission but no IRS excess. In this case, the
emitting region must begin outside 10 AU; this star has a known radial velocity
planet. Only two stars of the five show emission shortward of 25 \micron
where spectral features reveal the presence of a population of small, hot dust
grains emitting in the 7-20 m band. The data presented here strengthen the
results of previous studies to show that excesses at 25 \micron and shorter
are rare: only 1 star out of 40 stars older than 1 Gyr or % shows an
excess. Asteroid belts 10-30 times more massive than our own appear are rare
among mature, solar-type stars
Induction in a von Karman flow driven by ferromagnetic impellers
We study magnetohydrodynamics in a von K\'arm\'an flow driven by the rotation
of impellers made of material with varying electrical conductivity and magnetic
permeability. Gallium is the working fluid and magnetic Reynolds numbers of
order unity are achieved. We find that specific induction effects arise when
the impeller's electric and magnetic characteristics differ from that of the
fluid. Implications in regards to the VKS dynamo are discussed.Comment: 14 pages, 7 figure
Nutrients
Vitamin K participates in brain physiology. This study aimed to determine whether using vitamin K antagonists (VKAs), which interfere with the vitamin K cycle, were (i) cross-sectionally associated with altered cognitive performance, and (ii) independent predictors of cognitive changes in older adults over 24 months. Information was collected on the use of VKAs (i.e., warfarin, acenocoumarol, and fluindione) among 378 geriatric outpatients (mean, 82.3 +/- 5.6 years; 60.1% female). Global cognitive performance and executive functions were assessed with Mini-Mental State Examination (MMSE) and Frontal Assessment Battery (FAB) scores, respectively, at baseline and after 12 and 24 months of follow-up. Age, gender, body mass index, mean arterial pressure, disability, gait speed, comorbidities, atrial fibrillation, stroke, carotid artery stenosis, leukoaraiosis grade on computed tomography (CT) scan, psychoactive drugs, antidementia drugs, blood-thinning drugs (i.e., anticoagulants other than VKAs, antiplatelet medications), serum creatinine levels, and vitamin B12 concentrations were considered as potential confounders. Using VKAs was associated with lower (i.e., worse) FAB score at baseline (adjusted beta = -2.1, p = 0.026), and with a decrease in FAB score after 24 months (adjusted beta = -203.6%, p = 0.010), but not after 12 months (p = 0.659). Using VKAs was not associated with any change in MMSE score at baseline (p = 0.655), after 12 months (p = 0.603), or after 24 months (p = 0.201). In conclusion, we found more severe executive dysfunction at baseline and incident executive decline over 24 months among geriatric patients using VKAs, when compared with their counterparts
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