3,551 research outputs found
Diffraction limited optics for single atom manipulation
We present an optical system designed to capture and observe a single neutral
atom in an optical dipole trap, created by focussing a laser beam using a large
numerical aperture N.A.=0.5 aspheric lens. We experimentally evaluate the
performance of the optical system and show that it is diffraction limited over
a broad spectral range (~ 200 nm) with a large transverse field (+/- 25
microns). The optical tweezer created at the focal point of the lens is able to
trap single atoms of 87Rb and to detect them individually with a large
collection efficiency. We measure the oscillation frequency of the atom in the
dipole trap, and use this value as an independent determination of the waist of
the optical tweezer. Finally, we produce with the same lens two dipole traps
separated by 2.2 microns and show that the imaging system can resolve the two
atoms.Comment: 8 pages, 9 figures; typos corrected and references adde
3D Porous Architecture of Stacks of β-TCP Granules Compared with That of Trabecular Bone: A microCT, Vector Analysis, and Compression Study
The 3D arrangement of porous granular biomaterials usable to fill bone defects has received little study. Granular biomaterials occupy 3D space when packed together in a manner that creates a porosity suitable for the invasion of vascular and bone cells. Granules of beta-tricalcium phosphate (β-TCP) were prepared with either 12.5 or 25 g of β-TCP powder in the same volume of slurry. When the granules were placed in a test tube, this produced 3D stacks with a high (HP) or low porosity (LP), respectively. Stacks of granules mimic the filling of a bone defect by a surgeon. The aim of this study was to compare the porosity of stacks of β-TCP granules with that of cores of trabecular bone. Biomechanical compression tests were done on the granules stacks. Bone cylinders were prepared from calf tibia plateau, constituted high-density (HD) blocks. Low-density (LD) blocks were harvested from aged cadaver tibias. Microcomputed tomography was used on the β-TCP granule stacks and the trabecular bone cores to determine porosity and specific surface. A vector-projection algorithm was used to image porosity employing a frontal plane image, which was constructed line by line from all images of a microCT stack. Stacks of HP granules had porosity (75.3 ± 0.4%) and fractal lacunarity (0.043 ± 0.007) intermediate between that of HD (respectively 69.1 ± 6.4%, p < 0.05 and 0.087 ± 0.045, p < 0.05) and LD bones (respectively 88.8 ± 1.57% and 0.037 ± 0.014), but exhibited a higher surface density (5.56 ± 0.11 mm(2)/mm(3) vs. 2.06 ± 0.26 for LD, p < 0.05). LP granular arrangements created large pores coexisting with dense areas of material. Frontal plane analysis evidenced a more regular arrangement of β-TCP granules than bone trabecule. Stacks of HP granules represent a scaffold that resembles trabecular bone in its porous microarchitecture
Cholesterol-Independent Effects of Methyl-β-Cyclodextrin on Chemical Synapses
The cholesterol chelating agent, methyl-β-cyclodextrin (MβCD), alters synaptic function in many systems. At crayfish neuromuscular junctions, MβCD is reported to reduce excitatory junctional potentials (EJPs) by impairing impulse propagation to synaptic terminals, and to have no postsynaptic effects. We examined the degree to which physiological effects of MβCD correlate with its ability to reduce cholesterol, and used thermal acclimatization as an alternative method to modify cholesterol levels. MβCD impaired impulse propagation and decreased EJP amplitude by 40% (P<0.05) in preparations from crayfish acclimatized to 14°C but not from those acclimatized to 21°C. The reduction in EJP amplitude in the cold-acclimatized group was associated with a 49% reduction in quantal content (P<0.05). MβCD had no effect on input resistance in muscle fibers but decreased sensitivity to the neurotransmitter L-glutamate in both warm- and cold-acclimatized groups. This effect was less pronounced and reversible in the warm-acclimatized group (90% reduction in cold, P<0.05; 50% reduction in warm, P<0.05). MβCD reduced cholesterol in isolated nerve and muscle from cold- and warm-acclimatized groups by comparable amounts (nerve: 29% cold, 25% warm; muscle: 20% cold, 18% warm; P<0.05). This effect was reversed by cholesterol loading, but only in the warm-acclimatized group. Thus, effects of MβCD on glutamate-sensitivity correlated with its ability to reduce cholesterol, but effects on impulse propagation and resulting EJP amplitude did not. Our results indicate that MβCD can affect both presynaptic and postsynaptic properties, and that some effects of MβCD are unrelated to cholesterol chelation
The Microchannel X-ray Telescope on Board the SVOM Satellite
We present the Micro-channel X-ray Telescope (MXT), a new narrow-field (about
1{\deg}) telescope that will be flying on the Sino-French SVOM mission
dedicated to Gamma-Ray Burst science, scheduled for launch in 2021. MXT is
based on square micro pore optics (MPOs), coupled with a low noise CCD. The
optics are based on a "Lobster Eye" design, while the CCD is a focal plane
detector similar to the type developed for the seven eROSITA telescopes. MXT is
a compact and light (<35 kg) telescope with a 1 m focal length, and it will
provide an effective area of about 45 cmsq on axis at 1 keV. The MXT PSF is
expected to be better than 4.2 arc min (FWHM) ensuring a localization accuracy
of the afterglows of the SVOM GRBs to better than 1 arc min (90\% c.l. with no
systematics) provided MXT data are collected within 5 minutes after the
trigger. The MXT sensitivity will be adequate to detect the afterglows for
almost all the SVOM GRBs as well as to perform observations of non-GRB
astrophysical objects. These performances are fully adapted to the SVOM science
goals, and prove that small and light telescopes can be used for future small
X-ray missions.Comment: 6 pages, 6 figures, proceedings of the conference "Swift: 10 years of
Discovery", Rome, December 2-5, 2014. To be published by Po
LHCb Preshower Front-End Electronics Board
This note describes the digital part of the fully synchronous solution developped for the lhcb preshower detector Front-End electronics. The general design and the main features of this board are given including trigger part
LHCb Preshower Front-End Electronics Board. Qualification of the final prototype
This note describes the tests performed on the final prototypes of the SPD/Preshower Front-End electronics boards
The prominent role of the heaviest fragment in multifragmentation and phase transition for hot nuclei
The role played by the heaviest fragment in partitions of multifragmenting
hot nuclei is emphasized. Its size/charge distribution (mean value,
fluctuations and shape) gives information on properties of fragmenting nuclei
and on the associated phase transition.Comment: 11 pages, Proceedings of IWND09, August 23-25, Shanghai (China
Asymmetry Function of Interstellar Scintillations of Pulsars
A new method for separating intensity variations of a source's radio emission
having various physical natures is proposed. The method is based on a joint
analysis of the structure function of the intensity variations and the
asymmetry function, which is a generalization of the asymmetry coefficient and
characterizes the asymmetry of the distribution function of the intensity
fluctuations on various scales for the inhomogeneities in the diffractive
scintillation pattern. Relationships for the asymmetry function in the cases of
a logarithmic normal distribution of the intensity fluctuations and a normal
distribution of the field fluctuations are derived. Theoretical relationships
and observational data on interstellar scintillations of pulsars (refractive,
diffractive, and weak scintillations) are compared. Pulsar scintillations match
the behavior expected for a normal distribution of the field fluctuations
(diffractive scintillation) or logarithmic normal distribution of the intensity
fluctuations (refractive and weak scintillation). Analysis of the asymmetry
function is a good test for distinguishing scintillations against the
background of variations that have different origins
Evaluating Arguments From the Reaction of the Audience
In studying how lay people evaluate arguments, psychologists have typically focused on logical form and content. This emphasis has masked an important yet underappreciated aspect of everyday argument evaluation: social cues to argument strength. Here we focus on the ways in which observers evaluate arguments by the reaction they evoke in an audience. This type of evaluation is likely to occur either when people are not privy to the content of the arguments or when they are not expert enough to appropriately evaluate it. Four experiments explore cues that participants might take into account in evaluating arguments from the reaction of the audience. They demonstrate that participants can use audience motivation, expertise, and size as clues to argument quality. By contrast we find no evidence that participants take audience diversity into account
- …