189 research outputs found
Annealing of defects in Fe after MeV Heavy ion irradiation
We report study of recovery dynamics, followed by in-situ resistivity
measurement after 100 MeV oxygen ion irradiation, in cold rolled Fe at 300K.
Scaling behavior with microstructural density and temperature of sample have
been used to establish stress induced defects formed during irradiation as a
new type of sink. The dynamics after irradiation has been shown to be due to
migration of defects to two types of sinks i.e. stress induced defect as
variable sinks and internal surfaces as fixed sinks. Experimental data obtained
under various experimental conditions have been fitted to theoretical curves.
Parameters thus obtained from fitting are employed to establish effect of
electronic energy loss and temperature on recovery dynamics and stress
associated with variable sinks.Comment: 12 pages, 7 figures. Europhysics Letter (in press
Thermal annealing study of swift heavy-ion irradiated zirconia
Sintered samples of monoclinic zirconia (alpha-ZrO2) have been irradiated at
room temperature with 6.0-GeV Pb ions in the electronic slowing down regime.
X-ray diffraction (XRD) and micro-Raman spectroscopy measurements showed
unambiguously that a transition to the 'metastable' tetragonal phase
(beta-ZrO2) occurred at a fluence of 6.5x10^12 cm-2 for a large electronic
stopping power value (approx 32.5 MeV m-1). At a lower fluence of
1.0x10^12 cm-2, no such phase transformation was detected. The
back-transformation from beta- to alpha-ZrO2 induced by isothermal or
isochronal thermal annealing was followed by XRD analysis. The
back-transformation started at an onset temperature around 500 K and was
completed by 973 K. Plots of the residual tetragonal phase fraction deduced
from XRD measurements versus annealing temperature or time are analyzed with
first- or second-order kinetic models. An activation energy close to 1 eV for
the back-transformation process is derived either from isothermal annealing
curves, using the so-called "cross-cut" method, or from the isochronal
annealing curve, using a second-order kinetic law. Correlation with the thermal
recovery of ion-induced paramagnetic centers monitored by EPR spectroscopy is
discussed. Effects of crystallite size evolution and oxygen migration upon
annealing are also addressed
Thermal recovery of colour centres induced in cubic yttria-stabilized zirconia by charged particle irradiations
We have used electron paramagnetic resonance to study the thermal annealing
of colour centres induced in cubic yttria-stabilized zirconia by swift electron
and heavy ion-irradiations. Single crystals were irradiated with 1 or 2-MeV
electrons, and 200-MeV 127I, or 200-MeV 197Au ions. Electron and ion beams
produce the same colour centres: namely i) an F+-like centre, ii) the so-called
T-centre (Zr3+ in a trigonal oxygen local environment), and iii) a hole center.
Isochronal annealing was performed up to 973 K. Isothermal annealing was
performed at various temperatures on samples irradiated with 2-MeV electrons.
The stability of paramagnetic centres increases with fluence and with a TCR
treatment at 1373 K under vacuum prior to the irradiations. Two distinct
recovery processes are observed depending on fluence and/or thermal treatment.
The single-stage type I process occurs for F+-like centres at low fluences in
as-received samples, and is probably linked to electron-hole recombination.
T-centres are also annealed according to a single-stage process regardless of
fluence. The annealing curves allow one to obtain activation energies for
recovery. The two-stage type II process is observed only for the F+-like
centres in as-received samples, at higher fluences, or in reduced samples.
These centres are first annealed in a first stage below 550 K, like in type I,
then transform into new paramagnetic centres in a second stage above 550 K. A
simple kinetics model is proposed for this process. Complete colour centre
bleaching is achieved at about 1000 K
Superconducting and Normal State Properties of Neutron Irradiated MgB2
We have performed a systematic study of the evolution of the superconducting
and normal state properties of neutron irradiated MgB wire segments as a
function of fluence and post exposure annealing temperature and time. All
fluences used suppressed the transition temperature, Tc, below 5 K and expanded
the unit cell. For each annealing temperature Tc recovers with annealing time
and the upper critical field, Hc2(T=0), approximately scales with Tc. By
judicious choice of fluence, annealing temperature and time, the Tc of damaged
MgB2 can be tuned to virtually any value between 5 and 39 K. For higher
annealing temperatures and longer annealing times the recovery of Tc tends to
coincide with a decrease in the normal state resistivity and a systematic
recovery of the lattice parameters.Comment: Updated version, to appear in Phys. Rev.
Effects of Neutron Irradiation on Carbon Doped MgB2 Wire Segments
We have studied the evolution of superconducting and normal state properties
of neutron irradiated Mg(BC) wire segments as a function
of post exposure annealing time and temperature. The initial fluence fully
suppressed superconductivity and resulted in an anisotropic expansion of the
unit cell. Superconductivity was restored by post-exposure annealing. The upper
critical field, H(T=0), approximately scales with T starting with an
undamaged T near 37 K and H(T=0) near 32 T. Up to an annealing
temperature of 400 C the recovery of T tends to coincide with a
decrease in the normal state resistivity and a systematic recovery of the
lattice parameters. Above 400 C a decrease in order along the c- direction
coincides with an increase in resistivity, but no apparent change in the
evolution of T and H. To first order, it appears that carbon doping
and neutron damaging effect the superconducting properties of MgB
independently
International consensus statement on allergy and rhinology: Allergic rhinitis – 2023
Background
In the 5 years that have passed since the publication of the 2018 International Consensus Statement on Allergy and Rhinology: Allergic Rhinitis (ICAR-Allergic Rhinitis 2018), the literature has expanded substantially. The ICAR-Allergic Rhinitis 2023 update presents 144 individual topics on allergic rhinitis (AR), expanded by over 40 topics from the 2018 document. Originally presented topics from 2018 have also been reviewed and updated. The executive summary highlights key evidence-based findings and recommendation from the full document. Methods
ICAR-Allergic Rhinitis 2023 employed established evidence-based review with recommendation (EBRR) methodology to individually evaluate each topic. Stepwise iterative peer review and consensus was performed for each topic. The final document was then collated and includes the results of this work. Results
ICAR-Allergic Rhinitis 2023 includes 10 major content areas and 144 individual topics related to AR. For a substantial proportion of topics included, an aggregate grade of evidence is presented, which is determined by collating the levels of evidence for each available study identified in the literature. For topics in which a diagnostic or therapeutic intervention is considered, a recommendation summary is presented, which considers the aggregate grade of evidence, benefit, harm, and cost. Conclusion
The ICAR-Allergic Rhinitis 2023 update provides a comprehensive evaluation of AR and the currently available evidence. It is this evidence that contributes to our current knowledge base and recommendations for patient evaluation and treatment
Basic principles of postgrowth annealing of CdTe:Cl ingot to obtain semi-insulating crystals
The process of annealing of a CdTe:Cl ingot during its cooling after growth
was studied. The annealing was performed in two stages: a high-temperature
stage, with an approximate equality of chlorine and cadmium vacancy
concentrations established at the thermodynamic equilibrium between the crystal
and vapors of volatile components, and a low-temperature stage, with charged
defects interacting to form neutral associations. The chlorine concentrations
necessary to obtain semi-insulating crystals were determined for various ingot
cooling rates in the high temperature stage. The dependence of the chlorine
concentration [Cl+Te] in the ingot on the temperature of annealing in the
high-temperature stage was found. The carrier lifetimes and drift mobilities
were obtained in relation to the temperature and cadmium vapor pressure in the
postgrowth annealing of the ingot.Comment: 6 pages, 6 figure
Melting Point and Lattice Parameter Shifts in Supported Metal Nanoclusters
The dependencies of the melting point and the lattice parameter of supported
metal nanoclusters as functions of clusters height are theoretically
investigated in the framework of the uniform approach. The vacancy mechanism
describing the melting point and the lattice parameter shifts in nanoclusters
with decrease of their size is proposed. It is shown that under the high vacuum
conditions (p<10^-7 torr) the essential role in clusters melting point and
lattice parameter shifts is played by the van der Waals forces of
cluster-substrate interation. The proposed model satisfactorily accounts for
the experimental data.Comment: 6 pages, 3 figures, 1 tabl
Chemical Beam Epitaxy of Compound Semiconductors
Contains reports on three research projects and a list of publications.3M Company Faculty Development GrantAT&T Research Foundation Special Purpose GrantCharles S. Draper Laboratories Contract DL-H-418484Defense Advanced Research Projects Agency Subcontract 216-25013Defense Advanced Research Projects Agency Subcontract 542383Joint Services Electronics Program Contract DAAL03-89-C-0001Joint Services Electronics Program Contract DAAL03-92-C-0001National Science Foundation Grant ECS 88-46919National Science Foundation Grant ECS 89-05909Defense Advanced Research Projects Agency Subcontract 5300716-07U.S. Navy - Office of Naval Research Contract N00014-88-K-0564Defense Advanced Research Projects Agency Subcontract 530-0716-07National Science Foundation Subcontract DMR 90-0789
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