3,753 research outputs found
Dark Interactions and Cosmological Fine-Tuning
Cosmological models involving an interaction between dark matter and dark
energy have been proposed in order to solve the so-called coincidence problem.
Different forms of coupling have been studied, but there have been claims that
observational data seem to narrow (some of) them down to something annoyingly
close to the CDM model, thus greatly reducing their ability to deal
with the problem in the first place. The smallness problem of the initial
energy density of dark energy has also been a target of cosmological models in
recent years. Making use of a moderately general coupling scheme, this paper
aims to unite these different approaches and shed some light as to whether this
class of models has any true perspective in suppressing the aforementioned
issues that plague our current understanding of the universe, in a quantitative
and unambiguous way.Comment: 13 pages, 9 figures, accepted for publication in JCAP. Minor
corrections, one figure replaced, references adde
Growth of GaInTlAs layers on InP by molecular beam epitaxy
International audienceGrowth of GaInTlAs alloys on InP001 has been attempted by solid source molecular beam epitaxy. Thallium incorporation into Ga 1x In x As matrices was studied as a function of substrate temperature, arsenic overpressure, matrix composition, and growth rate. At high temperatures 350 °C thallium evaporates, whereas at intermediary temperatures 270-350 °C thallium segregates into droplets on the surface. Only in the low temperature range 180-260 °C can thallium be incorporated in some conditions, leading to mirror-like surfaces. Up to 18% Tl content was incorporated into a Ga 0.70 In 0.30 As matrix and up to 40% Tl into a GaAs matrix. For these high Tl concentrations, Tl droplets are avoided and Tl incorporation is achieved only when using high arsenic pressures. However, this limits surface adatom diffusion and leads to amorphous, polycrystalline, or twinned materials. Finally, a narrow window for single-crystal growth has been found for low Tl contents 4% using optimized growth conditions with low V/III pressure ratios and high growth rates
Improving Mechanical Properties and Reaction to Fire of EVA/LLDPE Blends for Cable Applications with Melamine Triazine and Bentonite Clay
The high flame-retardant loading required for ethylene-vinyl acetate copolymer blends with polyethylene (EVA-PE) employed for insulation and sheathing of electric cables represents a significant limitation in processability and final mechanical properties. In this work, melamine triazine (TRZ) and modified bentonite clay have been investigated in combination with aluminum trihydroxide (ATH) for the production of EVA-PE composites with excellent fire safety and improved mechanical properties. Optimized formulations with only 120 parts per hundred resin (phr) of ATH can achieve self-extinguishing behavior according to the UL94 classification (V0 rating), as well as reduced combustion kinetics and smoke production. Mechanical property evaluation shows reduced stiffness and improved elongation at break with respect to commonly employed EVA-PE/ATH composites. The reduction in filler content also provides improved processability and cost reductions. The results presented here allow for a viable and halogen-free strategy for the preparation of high performing EVA-PE composites
Bayesian estimation of one-parameter qubit gates
We address estimation of one-parameter unitary gates for qubit systems and
seek for optimal probes and measurements. Single- and two-qubit probes are
analyzed in details focusing on precision and stability of the estimation
procedure. Bayesian inference is employed and compared with the ultimate
quantum limits to precision, taking into account the biased nature of Bayes
estimator in the non asymptotic regime. Besides, through the evaluation of the
asymptotic a posteriori distribution for the gate parameter and the comparison
with the results of Monte Carlo simulated experiments, we show that asymptotic
optimality of Bayes estimator is actually achieved after a limited number of
runs. The robustness of the estimation procedure against fluctuations of the
measurement settings is investigated and the use of entanglement to improve the
overall stability of the estimation scheme is also analyzed in some details.Comment: 10 pages, 5 figure
Binary optical communication in single-mode and entangled quantum noisy channels
We address binary optical communication in single-mode and entangled quantum
noisy channels. For single-mode we present a systematic comparison between
direct photodetection and homodyne detection in realistic conditions, i.e.
taking into account the noise that occurs both during the propagation and the
detection of the signals. We then consider entangled channels based on
twin-beam state of radiation, and show that with realistic heterodyne detection
the error probability at fixed channel energy is reduced in comparison to the
single-mode cases for a large range of values of quantum efficiency and noise
parameters
Process design for the manufacturing of soft X-ray gratings in single-crystal diamond by high-energy heavy-ion irradiation
This paper describes in detail a novel manufacturing process for optical gratings suitable for use in the UV and soft X-ray regimes in a single-crystal diamond substrate based on highly focused swift heavy-ion irradiation. This type of grating is extensively used in light source facilities such as synchrotrons or free electron lasers, with ever-increasing demands in terms of thermal loads, depending on beamline operational parameters and architecture. The process proposed in this paper may be a future alternative to current manufacturing techniques, providing the advantage of being applicable to single-crystal diamond substrates, with their unique properties in terms of heat conductivity and radiation hardness. The paper summarizes the physical principle used for the grating patterns produced by swift heavy-ion irradiation and provides full details for the manufacturing process for a specific grating configuration, inspired in one of the beamlines at the ALBA synchrotron light source, while stressing the most challenging points for a potential implementation. Preliminary proof-of-concept experimental results are presented, showing the practical implementation of the methodology proposed herein
Process design for the manufacturing of soft X-ray gratings in single-crystal diamond by high-energy heavy-ion irradiation
Artículo con 9 figurasThis paper describes in detail a novel manufacturing process for optical gratings suitable for use in the UV and soft X-ray regimes in a single-crystal diamond substrate based on highly focused swift heavy-ion irradiation. This type of grating is extensively used in light source facilities such as synchrotrons or free electron lasers, with ever-increasing demands in terms of thermal loads, depending on beamline operational parameters and architecture. The process proposed in this paper may be a future alternative to current manufacturing techniques, providing the advantage of being applicable to single-crystal diamond substrates, with their unique properties in terms of heat conductivity and radiation hardness. The paper summarizes the physical principle used for the grating patterns produced by swift heavy-ion irradiation and provides full details for the manufacturing process for a specific grating configuration, inspired in one of the beamlines at the ALBA synchrotron light source, while stressing the most challenging points for a potential implementation. Preliminary proof-of-concept experimental results are presented, showing the practical implementation of the methodology proposed herein.The authors acknowledge funding support by the following projects: PID2020-112770RB-C22 from the Spanish Ministry of Science
and Innovation, TechnoFusión (III)-CM (S2018/EMT-4437) from Comunidad de Madrid (cofinanced by ERDF and ESF), agreement between Community
of Madrid and Universidad Autónoma de Madrid (item “Excellence of University Professorate”). M.L.C. acknowledges financial support from the research
project “Captacion de Talento UAM” Ref: #541D300 supervised by the Vice-Chancellor of Research of Universidad Autónoma de Madrid (UAM). LOREA
beamline at ALBA is a project co-funded by the European Regional Development Fund (ERDF) within the Framework of the Smart Growth Operative
Programme 2014-2020. The authors acknowledge the support from The Centro de Microanálisis de Materiales (CMAM)—Universidad Autónoma de Madrid,
for the beam time proposal (demonstration of a grating profile for soft X-rays in diamond via ion lithography) with code IuB-005/21, and its technical staff
for their contribution to the operation of the accelerator. We also acknowledge P. Olivero for very useful comments on the manuscript draf
Second international congress on immunopharmacology : delivery systems and current strategies for drug design
The 2nd International Congress on Immunopharmacology was held in June of 2011 at the Conference Center of Plaza America in Varadero, Cuba. The main goal of this meeting was to provide state-of-the-art communications for scientists, manufacturers, regulators and healthcare workers, to accelerate progress in the development of biological and biotechnological products and to promote exchange/scientific cooperation between researchers. 300 delegates from 22 countries attended the conference. The wide-ranging programme commenced with a plenary session and then split into a series of parallel workshops and symposia, covering “Advances in Immunopharmacology”, “Neuroimmunology”, “Therapeutic Biological Products”, “Prophylaxis and Treatment of Helicobacter pylori”, “Pharmacology of Cytochrome P450”, “Hereditary Ataxias” and “Delivery Systems and Current Strategies for Drug Design”. In this last Symposium, a substantial body of data was presented relating to the development of delivery systems with adjuvant and vaccine potential and also to strategies focused in therapeutic and prophylactic approaches against tuberculosis. This issue is dedicated to some of the results presented in this area
Recrystallization of amorphous nano-tracks and uniform layers generated by swift-ion-beam irradiation in lithium niobate.
The thermal annealing of amorphous tracks of nanometer-size diameter generated in lithium niobate (LiNbO3) by Bromine ions at 45 MeV, i.e., in the electronic stopping regime, has been investigated by RBS/C spectrometry in the temperature range from 250°C to 350°C. Relatively low fluences have been used (<1012 cm−2) to produce isolated tracks. However, the possible effect of track overlapping has been investigated by varying the fluence between 3×1011 cm−2 and 1012 cm−2. The annealing process follows a two-step kinetics. In a first stage (I) the track radius decreases linearly with the annealing time. It obeys an Arrhenius-type dependence on annealing temperature with activation energy around 1.5 eV. The second stage (II) operates after the track radius has decreased down to around 2.5 nm and shows a much lower radial velocity. The data for stage I appear consistent with a solid-phase epitaxial process that yields a constant recrystallization rate at the amorphous-crystalline boundary. HRTEM has been used to monitor the existence and the size of the annealed isolated tracks in the second stage. On the other hand, the thermal annealing of homogeneous (buried) amorphous layers has been investigated within the same temperature range, on samples irradiated with Fluorine at 20 MeV and fluences of ∼1014 cm−2. Optical techniques are very suitable for this case and have been used to monitor the recrystallization of the layers. The annealing process induces a displacement of the crystalline-amorphous boundary that is also linear with annealing time, and the recrystallization rates are consistent with those measured for tracks. The comparison of these data with those previously obtained for the heavily damaged (amorphous) layers produced by elastic nuclear collisions is summarily discussed
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