514 research outputs found
Magnetic properties of HO2 thin films
We report on the magnetic and transport studies of hafnium oxide thin films
grown by pulsed-laser deposition on sapphire substrates under different oxygen
pressures, ranging from 10-7 to 10-1 mbar. Some physical properties of these
thin films appear to depend on the oxygen pressure during growth: the film
grown at low oxygen pressure (P ~= 10-7 mbar) has a metallic aspect and is
conducting, with a positive Hall signal, while those grown under higher oxygen
pressures (7 x 10-5 <= P <= 0.4 mbar) are insulating. However, no intrinsic
ferromagnetic signal could be attributed to the HfO2 films, irrespective of the
oxygen pressure during the deposition.Comment: 1
Assessing the accuracy of energy turbulent diffusion dispersion correlation in a porous two-fluid model dedicated to PWR core simulations
International audienceCATHARE is a 2-fluid thermal-hydraulic code, capable of simulating thermal and mechanical phenomena occurring in the primary and secondary circuits of Pressurized Water Reactor under a wide variety of accidental situations. One of the medium-term objectives of system code CATHARE-3 is modeling a PWR core at assembly scale to simulate various accidental situations such as the loss of coolant accident (LOCA) and steam line break accident. This requires the monophasic and two-phase models that adapted to the assembly scale. However, there exists 3D models for the whole core and sub-channel scale models, which have a certain degree of validation. For more macroscopic three-dimensional models, we only have global validations without local measurements, which is necessary for the validations of each closure law's separate effects. The objective of my PhD project is improving the sub-channel scale models and developing the assembly scale models in CATHARE-3 system code with the sub-channel scale simulations and experiments results
Ferromagnetism in the Strong Hybridization Regime of the Periodic Anderson Model
We determine exactly the ground state of the one-dimensional periodic
Anderson model (PAM) in the strong hybridization regime. In this regime, the
low energy sector of the PAM maps into an effective Hamiltonian that has a
ferromagnetic ground state for any electron density between half and three
quarters filling. This rigorous result proves the existence of a new magnetic
state that was excluded in the previous analysis of the mixed valence systems.Comment: Accepted in Phys. Rev.
Spectrally-resolved UV photodesorption of CH4 in pure and layered ices
Context. Methane is among the main components of the ice mantles of
insterstellar dust grains, where it is at the start of a rich solid-phase
chemical network. Quantification of the photon-induced desorption yield of
these frozen molecules and understanding of the underlying processes is
necessary to accurately model the observations and the chemical evolution of
various regions of the interstellar medium. Aims. This study aims at
experimentally determining absolute photodesorption yields for the CH4 molecule
as a function of photon energy. The influence of the ice composition is also
investigated. By studying the methane desorption from layered CH4:CO ice,
indirect desorption processes triggered by the excitation of the CO molecules
is monitored and quantified. Methods. Tunable monochromatic VUV light from the
DESIRS beamline of the SOLEIL synchrotron is used in the 7 - 13.6 eV (177 - 91
nm) range to irradiate pure CH4 or layers of CH4 deposited on top of CO ice
samples. The release of species in the gas phase is monitored by quadrupole
mass spectrometry and absolute photodesorption yields of intact CH4 are
deduced. Results. CH4 photodesorbs for photon energies higher than ~9.1 eV
(~136 nm). The photodesorption spectrum follows the absorption spectrum of CH4,
which confirms a desorption mechanism mediated by electronic transitions in the
ice. When it is deposited on top of CO, CH4 desorbs between 8 and 9 eV with a
pattern characteristic of CO absorption, indicating desorption induced by
energy transfer from CO molecules. Conclusions. The photodesorption of CH4 from
the pure ice in various interstellar environments is around 2.0 x 10^-3
molecules per incident photon. Results on CO-induced indirect desorption of CH4
provide useful insights for the generalization of this process to other
molecules co-existing with CO in ice mantles
X-ray photodesorption of complex organic molecules in protoplanetary disks -- I. Acetonitrile CH3CN
X-rays emitted from pre-main-sequence stars at the center of protoplanetary
disks can induce nonthermal desorption from interstellar ices populating the
cold regions. This X-ray photodesorption needs to be quantified for complex
organic molecules (COMs), including acetonitrile CH3CN, which has been detected
in several disks. We experimentally estimate the X-ray photodesorption yields
of neutral species from pure CH3CN ices and from interstellar ice analogs for
which CH3CN is mixed either in a CO- or H2O-dominated ice. The ices were
irradiated at 15 K by soft X-rays (400-600 eV) from synchrotron light (SOLEIL
synchrotron). X-ray photodesorption was probed in the gas phase via quadrupole
mass spectrometry. X-ray photodesorption yields were derived from the mass
signals and were extrapolated to higher X-ray energies for astrochemical
models. X-ray photodesorption of the intact CH3CN is detected from pure CH3CN
ices and from mixed 13CO:CH3CN ices, with a yield of about 5x10^(-4)
molecules/photon at 560 eV. When mixed in H2O-dominated ices, X-ray
photodesorption of the intact CH3CN at 560 eV is below its detection limit,
which is 10^(-4) molecules/photon. Yields associated with the desorption of
HCN, CH4 , and CH3 are also provided. The derived astrophysical yields
significantly depend on the local conditions expected in protoplanetary disks.
They vary from 10^(-4) to 10(-6) molecules/photon for the X-ray photodesorption
of intact CH3CN from CO-dominated ices. Only upper limits varying from
5x10^(-5) to 5x10^(-7) molecules/photon could be derived for the X-ray
photodesorption of intact CH3CN from H2O-dominated ices. X-ray photodesorption
of intact CH3CN from interstellar ices might in part explain the abundances of
CH3CN observed in protoplanetary disks. The desorption efficiency is expected
to vary with the local physical conditions, hence with the disk region
Wavelength-Dependent UV Photodesorption of Pure and Ices
Context: Ultraviolet photodesorption of molecules from icy interstellar grains can explain observations of cold gas in regions where thermal desorption is negligible. This non-thermal desorption mechanism should be especially important where UV fluxes are high. Aims: and are expected to play key roles in astrochemical reaction networks, both in the solid state and in the gas phase. Measurements of the wavelength-dependent photodesorption rates of these two infrared-inactive molecules provide astronomical and physical-chemical insights into the conditions required for their photodesorption.
Methods: Tunable radiation from the DESIRS beamline at the SOLEIL synchrotron in the astrophysically relevant 7 to 13.6 eV range is used to irradiate pure and thin ice films. Photodesorption of molecules is monitored through quadrupole mass spectrometry. Absolute rates are calculated by using the well-calibrated CO photodesorption rates. Strategic and isotopolog mixtures are used to investigate the importance of dissociation upon irradiation. Results: photodesorption mainly occurs through excitation of the state and subsequent desorption of surface molecules. The observed vibronic structure in the photodesorption spectrum, together with the absence of formation, supports that the photodesorption mechanism of is similar to CO, i.e., an indirect DIET (Desorption Induced by Electronic Transition) process without dissociation of the desorbing molecule. In contrast, photodesorption in the 7â13.6 eV range occurs through dissociation and presents no vibrational structure. Conclusions: Photodesorption rates of and integrated over the far-UV field from various star-forming environments are lower than for CO. Rates vary between and photodesorbed molecules per incoming photon.Astronom
Critical flow prediction by system codes â Recent analyses made within the FONESYS network
A benchmark activity on Two-Phase Critical Flow (TPCF) prediction was conducted in the framework of the
Forum & Network of System Thermal-Hydraulics Nuclear Reactor Thermal-Hydraulics (FONESYS). FONESYS is a
network among code developers who share the common objective to strengthen current technology. The aim of
the FONESYS Network is to highlight the capabilities and the robustness as well as the limitations of current SYSTH
codes to predict the main phenomena during transient scenarios in nuclear reactors for safety issues.
Six separate effect test facilities, more than 90 tests, both in steady and transient conditions, were considered
for the activity. Moreover, two ideal tests were designed for code to code comparison in clearly defined conditions.
Overall eight System Thermal-Hydraulic (SYS-TH) codes were adopted, mostly by the developers
themselves, ensuring the minimization of the user effect. Results from selected tests were also compared against
Delayed Equilibrium Model, not yet implemented in industrial version of SYS-TH codes.
Generally, the results of the benchmark show an improvement of the capability of SYS-TH codes to predict
TPCF in the last three decades. However, predicting break flowrate remains a major source of uncertainty in
accidental transient simulations of Water-Cooled Nuclear Reactors (WCNR). A set of possible actions is proposed
to go beyond the current limitations of choked flow models. More detailed guidelines for using 0-D choked flow
models is possible by using the experience gained by the benchmark results as well as all available validation
results. Progress in understanding and 1-D modelling of flashing and choked flow might be achieved by a deeper
physical analysis leading to more mechanistic models based on specific flow regime maps for high speed flow.
Also the use of advanced 3-D numerical tools may help to understand and predict the complex 3-D geometrical
effect
Electronic sculpting of ligand-GPCR subtype selectivity:the case of angiotensin II
GPCR subtypes possess distinct functional
and pharmacological profiles,
and thus development of subtype-selective ligands has immense therapeutic
potential. This is especially the case for the angiotensin receptor
subtypes AT1R and AT2R, where a functional negative control has been
described and AT2R activation highlighted as an important cancer drug
target. We describe a strategy to fine-tune ligand selectivity for
the AT2R/AT1R subtypes through electronic control of ligand aromatic-prolyl
interactions. Through this strategy an AT2R high affinity (<i>K</i><sub>i</sub> = 3 nM) agonist analogue that exerted 18,000-fold
higher selectivity for AT2R versus AT1R was obtained. We show that
this compound is a negative regulator of AT1R signaling since it is
able to inhibit MCF-7 breast carcinoma cellular proliferation in the
low nanomolar range
Comparative analysis of slot dimension in lingual bracket systems
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