814 research outputs found
Sol-Gel Processing of Nanostructured Inorganic Scintillating
The development of scintillating materials is believed to reach a new step by controlling their preparation on a nanometric level. Sol-Gel chemistry offers very unique tools for nanoscale mastering of the materials preparation. In particular, shaping of the materials as thin films or nanoparticles offers new application in medical imaging. The control of doping ions dispersion thanks to soft chemistry is also a great advantage of such synthetic routes. In this paper, we will review recent work devoted to the sol-gel preparation of inorganic scintillating materials. We will focus on the new possibilities and advantages offered by sol-gel chemistry for the preparation of new scintillators and improvement of existing ones
The monoclinic phase of PZT ceramics: Raman and phenomenological theory studies
This work reports on the first Raman detection of the tetragonal to
monoclinic phase transition in PZT ceramics near morphotropic phase boundary at
low temperatures. The transition is characterized by changes in the frequency
of lattice modes with the temperature. The results presented here confirm the
previous one recently reported by Noheda et al. using high-resolution
synchrotron X-ray powder diffraction technique and dielectric measurements. The
stability of the new phase is discussed within the framework of
phenomenological Landau-Devonshire Theory.Comment: 6 pages including 4 figures, Latex, submitted to Applied Physics
Letter
Analysis of segregated boundary-domain integral equations for mixed variable-coefficient BVPs in exterior domains
This is the post-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2011 Birkhäuser Boston.Some direct segregated systems of boundary–domain integral equations (LBDIEs) associated with the mixed boundary value problems for scalar PDEs with variable coefficients in exterior domains are formulated and analyzed in the paper. The LBDIE equivalence to the original boundary value problems and the invertibility of the corresponding boundary–domain integral operators are proved in weighted Sobolev spaces suitable for exterior domains. This extends the results obtained by the authors for interior domains in non-weighted Sobolev spaces.The work was supported by the grant EP/H020497/1 ”Mathematical analysis of localised boundary-domain integral equations for BVPs with variable coefficients” of the EPSRC, UK
Correction: Preferential site substitution of Eu3+ ions in Ca10(PO4)6Cl2 nanoparticles obtained usinga microwave stimulated wet chemistry technique
International audience“In accordance with the rule of 2J + 1 at Cs symmetry a maximum of five sublevels should be present for the 5D0 → 7F1 andeight in the case of the 5D0 → 7F2 transitions whereas at C3 symmetry the 5D0 → 7F1 splits into two and the 5D0 → 7F2 into threeStark components.”Should have read:In accordance with the rule of 2J + 1 at Cs symmetry a maximum of three sublevels should be present for the 5D0 → 7F1 andfive in the case of the 5D0 → 7F2 transitions whereas at C3 symmetry the 5D0 → 7F1 splits into two and the 5D0 → 7F2 into threeStark components.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.2780
Biological activity of a SiO2-CaO-P2O5 sol-gel glass highlighted by PIXE-RBS methods
It is proposed in this study to observe the influence of P2O5 on the
formation of the apatite-like layer in a bioactive glass via a complete PIXE
characterization. A glass in the SiO2-CaO-P2O5 ternary system was elaborated by
sol-gel processing. Glass samples were soaked in biological fluids for periods
up to 10 days. The surface changes were characterized using Particle Induced
X-ray Emission (PIXE) associated to Rutherford Backscattering Spectroscopy
(RBS), which are efficient methods for multielemental analysis. Elemental maps
of major and trace elements were obtained at a micrometer scale and revealed
the bone bonding ability of the material. The formation of a calcium
phosphate-rich layer containing magnesium occurs after a few days of
interaction. We demonstrate that the presence of phosphorus in the material has
an impact on the development and the formation rate of the bone-like apatite
layer. Indeed, the Ca/P atomic ratio at the glass/biological fluids interface
is closer to the nominal value of pure apatite compared to P2O5 free glasses.
It would permit, in vivo, an improved chemical bond between the biomaterials
and bone.Comment: presented at CAARI 2006:19th International Conference on the
Application of Accelerators in Research and Industry, Forth Worth, Etats
Unis, 20-25 Aug 2006, 11 pp, 4 figures, submitted to NIM
Proposing a Pedigree Risk Measurement Strategy: Capturing the Intergenerational Transmission of Antisocial Behavior in a Nationally Representative Sample of Adults
An impressive literature has revealed that variation in virtually every measurable phenotype is the result of a combination of genetic and environmental influences. Based on these findings, studies that fail to use genetically informed modeling strategies risk model misspecification and biased parameter estimates. Twin- and adoption-based research designs have frequently been used to overcome this limitation. Despite the many advantages of such approaches, many available datasets do not contain samples of twins, siblings or adoptees, making it impossible to utilize these modeling strategies. The current study proposes a measurement strategy for estimating the intergenerational transmission of antisocial behavior (ASB) within a nationally representative sample of singletons using an extended pedigree risk approach that relies on information from first- and second-degree relatives. An evaluation of this approach revealed a pattern of findings that directly aligned with studies examining ASB using more traditional twin- and adoption-based research designs. While the proposed pedigree risk approach is not capable of effectively isolating genetic and environmental influences, this overall alignment in results provides tentative evidence suggesting that the proposed pedigree risk measure effectively captures genetic influences. Future replication studies are necessary as this observation remains preliminary. Whenever possible, more traditional quantitative genetic methodologies should be favored, but the presented strategy remains a viable alternative for more limited samples
Validation of Aura Microwave Limb Sounder O-3 and CO observations in the upper troposphere and lower stratosphere
International audienceGlobal satellite observations of ozone and carbon monoxide from the Microwave Limb Sounder (MLS) on the EOS Aura spacecraft are discussed with emphasis on those observations in the 215–100 hPa region (the upper troposphere and lower stratosphere). The precision, resolution and accuracy of the data produced by the MLS “version 2.2” processing algorithms are discussed and quantified. O3 accuracy is estimated at ~40 ppbv +5% (~20 ppbv +20% at 215 hPa) while the CO accuracy is estimated at ~30 ppbv +30% for pressures of 147 hPa and less. Comparisons with expectations and other observations show good agreements for the O3 product, generally consistent with the systematic errors quoted above. In the case of CO, a persistent factor of ~2 high bias is seen at 215 hPa. However, the morphology is shown to be realistic, consistent with raw MLS radiance data, and useful for scientific study. The MLS CO data at higher altitudes are shown to be consistent with other observations
Enhanced reaction kinetics in biological cells
The cell cytoskeleton is a striking example of "active" medium driven
out-of-equilibrium by ATP hydrolysis. Such activity has been shown recently to
have a spectacular impact on the mechanical and rheological properties of the
cellular medium, as well as on its transport properties : a generic tracer
particle freely diffuses as in a standard equilibrium medium, but also
intermittently binds with random interaction times to motor proteins, which
perform active ballistic excursions along cytoskeletal filaments. Here, we
propose for the first time an analytical model of transport limited reactions
in active media, and show quantitatively how active transport can enhance
reactivity for large enough tracers like vesicles. We derive analytically the
average interaction time with motor proteins which optimizes the reaction rate,
and reveal remarkable universal features of the optimal configuration. We
discuss why active transport may be beneficial in various biological examples:
cell cytoskeleton, membranes and lamellipodia, and tubular structures like
axons.Comment: 10 pages, 2 figure
Dynamic concentration of motors in microtubule arrays
We present experimental and theoretical studies of the dynamics of molecular
motors in microtubule arrays and asters. By solving a convection-diffusion
equation we find that the density profile of motors in a two-dimensional aster
is characterized by continuously varying exponents. Simulations are used to
verify the assumptions of the continuum model. We observe the concentration
profiles of kinesin moving in quasi two-dimensional artificial asters by
fluorescent microscopy and compare with our theoretical results.Comment: 4pages, 4 figures revte
Anomalous fluctuations of active polar filaments
Using a simple model, we study the fluctuating dynamics of inextensible,
semiflexible polar filaments interacting with active and directed force
generating centres such as molecular motors. Taking into account the fact that
the activity occurs on time-scales comparable to the filament relaxation time,
we obtain some unexpected differences between both the steady-state and
dynamical behaviour of active as compared to passive filaments. For the
statics, the filaments have a {novel} length-scale dependent rigidity.
Dynamically, we find strongly enhanced anomalous diffusion.Comment: 5 pages, 3 figure
- …