97 research outputs found
Etudes préliminaires du Synchrotron rapidement pulsé du projet Beta-Beam
National audienceCet article expose les premiÚres études de dynamique faisceau sur le Synchrotron rapidement pulsé du projet Beta-Beam, projet européen de source de neutrino
Mouvement de particules autour de l'orbite fermée chromatique dans un synchrotron
ACCCette note a pour but d'établir les expressions analytiques utilisées dans le code BETA[1] pour caratériser le mouvement des particules autour de l'orbite fermée chromatique dans un cyclotron. Elle détaille des calculs effectués depuis dix ans. Le formalisme utilisé est celui des aberrations au second ordre développé pour le code TRANSPORT[2]. Il conduit aux expressions de la fonction dispersion au second ordre. Des chromaticités au premier ordre et du "momentum compaction" au second ordre en fonction des termes de la matrice de transfert de la maille au second ordre
Magnetic anisotropy determination and magnetic hyperthermia properties of small Fe nanoparticles in the superparamagnetic regime
We report on the magnetic and hyperthermia properties of iron nanoparticles
synthesized by organometallic chemistry. They are 5.5 nm in diameter and
display a saturation magnetization close to the bulk one. Magnetic properties
are dominated by the contribution of aggregates of nanoparticles with respect
to individual isolated nanoparticles. Alternative susceptibility measurements
are been performed on a low interacting system obtained after eliminating the
aggregates by centrifugation. A quantitative analysis using the Gittleman s
model allow a determination of the effective anisotropy Keff = 1.3 * 10^5
J.m^{-3}, more than two times the magnetocristalline value of bulk iron.
Hyperthermia measurements are performed on agglomerates of nanoparticles at a
magnetic field up to 66 mT and at frequencies in the range 5-300 kHz. Maximum
measured SAR is 280 W/g at 300 kHz and 66 mT. Specific absorption rate (SAR)
displays a square dependence with the magnetic field below 30 mT but deviates
from this power law at higher value. SAR is linear with the applied frequency
for mu_0H=19 mT. The deviations from the linear response theory are discussed.
A refined estimation of the optimal size of iron nanoparticles for hyperthermia
applications is provided using the determined effective anisotropy value
Ortho-Fluoro Effect on the CâC Bond Activation of Benzonitrile Using Zerovalent Nickel
The effect of fluoro substitution on the CâC bond activation of aromatic nitriles has been studied by reacting a variety of fluorinated benzonitriles with the nickel(0) fragment [Ni(dippe)] and by locating the reaction intermediates and transition-state structures on the potential energy surface by using density functional theory calculations with the [Ni(dmpe)] fragment (dippe = 1,2-bis(diisopropylphosphino)ethane, dmpe = 1,2-bis(dimethylphosphino)ethane). As in the previous reports, the reaction of fluorinated benzonitriles with the [Ni(dippe)] fragment initially formed an η2-nitrile complex, which then converted to the CâCN bond activation product. Thermodynamic parameters for the equilibrium between these complexes have been determined experimentally in both a polar (tetrahydrofuran) and a nonpolar (toluene) solvent for 3-fluoro- and 4-fluorobenzonitrile. The stability of the CâC bond activation products is shown to be strongly dependent on the number of ortho-F substituents (â6.6 kcal/mol per o-F) and only slightly dependent on the number of meta-F substituents (â1.8 kcal/mol per m-F)
The 20 years of PROSITE
PROSITE consists of documentation entries describing protein domains, families and functional sites, as well as associated patterns and profiles to identify them. It is complemented by ProRule, a collection of rules based on profiles and patterns, which increases the discriminatory power of profiles and patterns by providing additional information about functionally and/or structurally critical amino acids. In this article, we describe the implementation of a new method to assign a status to pattern matches, the new PROSITE web page and a new approach to improve the specificity and sensitivity of PROSITE methods. The latest version of PROSITE (release 20.19 of 11 September 2007) contains 1319 patterns, 745 profiles and 764 ProRules. Over the past 2 years, about 200 domains have been added, and now 53% of UniProtKB/Swiss-Prot entries (release 54.2 of 11 September 2007) have a PROSITE match. PROSITE is available on the web at: http://www.expasy.org/prosit
The 20 years of PROSITE
PROSITE consists of documentation entries describing protein domains, families and functional sites, as well as associated patterns and profiles to identify them. It is complemented by ProRule, a collection of rules based on profiles and patterns, which increases the discriminatory power of profiles and patterns by providing additional information about functionally and/or structurally critical amino acids. In this article, we describe the implementation of a new method to assign a status to pattern matches, the new PROSITE web page and a new approach to improve the specificity and sensitivity of PROSITE methods. The latest version of PROSITE (release 20.19 of 11 September 2007) contains 1319 patterns, 745 profiles and 764 ProRules. Over the past 2 years, about 200 domains have been added, and now 53% of UniProtKB/Swiss-Prot entries (release 54.2 of 11 September 2007) have a PROSITE match. PROSITE is available on the web at: http://www.expasy.org/prosite/
Fragmentation branching ratios of highly excited hydrocarbon molecules CnH and their cations CnH+ (n<4)
We have measured fragmentation branching ratios of neutral CnH and CnH+
cations produced in high velocity (4.5 a.u) collisions between incident CnH+
cations and helium atoms. Electron capture gives rise to excited neutral
species CnH and electronic excitation to excited cations CnH+. Thanks to a
dedicated set-up, based on coincident detection of all fragments, the
dissociation of the neutral and cationic parents were recorded separately and
in a complete way. For the fragmentation of CnH, the H-loss channel is found to
be dominant, as already observed by other authors. By contrast, the H-loss and
C-loss channels equally dominate the two-fragment break up of CnH+ species. For
these cations, we provide the first fragmentation data (n > 2). Results are
also discussed in the context of astrochemistry
Large specific absorption rates in the magnetic hyperthermia properties of metallic iron nanocubes
We report on the magnetic hyperthermia properties of chemically synthesized
ferromagnetic 11 and 16 nm Fe(0) nanoparticles of cubic shape displaying the
saturation magnetization of bulk iron. The specific absorption rate measured on
16 nm nanocubes is 1690+-160 W/g at 300 kHz and 66 mT. This corresponds to
specific losses-per-cycle of 5.6 mJ/g, largely exceeding the ones reported in
other systems. A way to quantify the degree of optimization of any system with
respect to hyperthermia applications is proposed. Applied here, this method
shows that our nanoparticles are not fully optimized, probably due to the
strong influence of magnetic interactions on their magnetic response. Once
protected from oxidation and further optimized, such nano-objects could
constitute efficient magnetic cores for biomedical applications requiring very
large heating power
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