Radiative capture reaction for 17^{17}Ne formation within a full three-body model

Background: The breakout from the hot Carbon-Nitrogen-Oxigen (CNO) cycles can trigger the rp-process in type I x-ray bursts. In this environment, a competition between $^{15}\text{O}(\alpha,\gamma){^{19}\text{Ne}}$ and the two-proton capture reaction $^{15}\text{O}(2p,\gamma){^{17}\text{Ne}}$ is expected. Purpose: Determine the three-body radiative capture reaction rate for ${^{17}\text{Ne}}$ formation including sequential and direct, resonant and non-resonant contributions on an equal footing. Method: Two different discretization methods have been applied to generate $^{17}$Ne states in a full three-body model: the analytical transformed harmonic oscillator method and the hyperspherical adiabatic expansion method. The binary $p$--$^{15}$O interaction has been adjusted to reproduce the known spectrum of the unbound $^{16}$F nucleus. The dominant $E1$ contributions to the $^{15}\text{O}(2p,\gamma){^{17}\text{Ne}}$ reaction rate have been calculated from the inverse photodissociation process. Results: Three-body calculations provide a reliable description of $^{17}$Ne states. The agreement with the available experimental data on $^{17}$Ne is discussed. It is shown that the $^{15}\text{O}(2p,\gamma){^{17}\text{Ne}}$ reaction rates computed within the two methods agree in a broad range of temperatures. The present calculations are compared with a previous theoretical estimation of the reaction rate. Conclusions: It is found that the full three-body model provides a reaction rate several orders of magnitude larger than the only previous estimation. The implications for the rp-process in type I x-ray bursts should be investigated.Comment: 10 pages, 10 figures. Corrected versio

Luminescence Dynamics of Silica-Encapsulated Quantum Dots During Optical Trapping

"This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/10.1021/acs.jpcc.6b11867."[EN] The trade-off between photobrightening and photobleaching controls the emission stability of colloidal quantum dots. This balance is critical in optical trapping configurations, where irradiances that confine and simultaneously excite the nanocrystals in the focal region cannot be indefinitely lowered. In this work, we studied the photobrightening and bleaching behaviors of two types of silica-encapsulated quantum dots excited upon two-photon absorption in an optical trap. The first type consists of alloyed CdSeZnS quantum dots covered with a silica shell. We found that the dynamics of these as-prepared architectures are similar to those previously reported for bare surface-deposited quantum dots, where thousands of times smaller irradiances were used. We then analyzed the same quantum dot systems treated with an extra intermediate sulfur passivating shell for the better understanding of the surface traps influence in the temporal evolution of their emission in the optical trap. We found that these latter systems exhibit better homogeneity in their photodynamic behavior compared to the untreated ones. These features strengthen the value of quantum dot preparations in optical manipulation as well as for applications where both long and maximal emission stability in physiological and other polar media are required.The authors thank A. Blanco and D. Granados for fruitful discussion and S. de Lorenzo for technical help. H.R-R. is supported by an FPI-UAM fellowship and M. A. by a contract from Fundacion IMDEA Nanociencia. The research leading to these results has received funding from the Spanish Ministry of Economy and Competitiveness (grant numbers MAT2015-71806-R and FIS2015-67367-C2-1-P), from Comunidad de Madrid (S2013/MIT-2740) and from UAM-Banco Santander (CEAL-AL/2015-15).Rodríguez-Rodríguez, H.; Acebrón, M.; Juárez, B.; Arias-Gonzalez, JR. (2017). Luminescence Dynamics of Silica-Encapsulated Quantum Dots During Optical Trapping. The Journal of Physical Chemistry C. 121(18):10124-10130. https://doi.org/10.1021/acs.jpcc.6b11867S10124101301211

Optical Trapping of Single Nanostructures in a Weakly Focused Beam. Application to Magnetic Nanoparticles

"This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see [insert ACS Articles on Request author-directed link to Published Work, see https://pubs.acs.org/doi/10.1021/acs.jpcc.8b04676."[EN] Optical trapping of individual particles is believed to be only effective under highly focused beams because these conditions strengthen the gradient forces. This is especially critical in the beam propagating direction, where the scattering and absorption forces must be counterbalanced. Here, we demonstrate that optical trapping of nanostructures is also possible in a weakly focused beam. We study the theoretical conditions for effective three-dimensional optical confinement and verify them experimentally on iron-oxide-based nanoparticles with and without a silica coating, for which scattering, absorption, and gradient forces exist. This chemical approach to their all-optical control is, in turn, convenient for making magnetic nanostructures biocompatible. Weakly focused beams reduce the irradiance in the focal region and therefore the photon damage to the samples, which is further important to delay quantum dot quenching in the trap or to prevent artifacts in the study of biomolecular motor dynamics.We are grateful to Dr. Maria Acebron and Dr. Beatriz H. Juarez for their support in the silica encapsulation of the nano particles. This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO, Grant MAT2015-71806-R). IMDEA Nanociencia acknowledges support from the "Severo Ochoa" Programme for Centers of Excellence in R&D (MINECO, Grant SEV-2016-0686). H.R.-R. is supported by an FPI-UAM fellowship.Rodríguez-Rodríguez, H.; De Lorenzo, S.; De La Cueva, L.; Salas, G.; Arias-Gonzalez, JR. (2018). Optical Trapping of Single Nanostructures in a Weakly Focused Beam. Application to Magnetic Nanoparticles. The Journal of Physical Chemistry C. 122(31):18094-18101. https://doi.org/10.1021/acs.jpcc.8b04676S18094181011223

Influence of MWCNT/surfactant dispersions on the mechanical properties of Portland cement pastes

This work studies the reinforcing effect of Multi Walled Carbon Nanotubes (MWCNT) on cement pastes. A 0.35% solid concentration of MWCNT in powder was dispersed in deionized water with sodium dodecyl sulfate (cationic surfactant), cetylpyridinium chloride (anionic surfactant) and triton X-100 (amphoteric surfactant) using an ultrasonic tip processor. Three concentrations of each surfactant (1mM, 10mM and 100mM) were tested, and all samples were sonicated until an adequate dispersion degree was obtained. Cement pastes with additions of carbon nanotubes of 0.15% by mass of cement were produced in two steps; first the dispersions of MWCNT were combined with the mixing water using an ultrasonic tip processor to guarantee homogeneity, and then cement was added and mixed until a homogeneous paste was obtained. Direct tensile strength, apparent density and open porosity of the pastes were measured after 7 days of curing. It was found that the MWCNT/surfactants dispersions decrease the mechanical properties of the cement based matrix due to an increased porosity caused by the presence of surfactants. © Published under licence by IOP Publishing Ltd

Temperature measurements on ES steel sheets subjected to perforation by hemispherical projectiles

In this paper is reported a study on the behaviour of ES mild steel sheets subjected to perforation by hemispherical projectiles. Experiments have been conducted using a pneumatic cannon within the range of impact velocities 5m/s<=V0<=60m/s. The experimental setup allowed evaluating initial velocity, failure mode and post-mortem deflection of the plates. The tests have been recorded using high speed infrared camera. It made possible to obtain temperature contours of the specimen during impact. Thus, special attention is focussed on the thermal softening of the material which is responsible for instabilities and failure. Assuming adiabatic conditions of deformation, the increase of temperature may be related to the plastic deformation. The critical strain leading to target-failure is evaluated coupling temperature measurements with numerical simulations and with analytical predictions obtained by means of the Rusinek-Klepaczko constitutive relation [Rusinek, A., Klepaczko, J.R. Shear testing of sheet steel at wide range of strain rates and a constitutive relation with strain rate and temperature dependence of the flow stress. Int J Plasticity. 2001; 17, 87-115]. It has been estimated that the process of localization of plastic deformation which leads to target-failure involves local values close to for the boundary value problem approached. Subsequently, this failure strain level has been applied to simulate the perforation process and the numerical results obtained show satisfactory agreement with the experiments in terms of ballistic limit, temperature increase and failure mode of the target.The researchers of the University Carlos III of Madrid are indebted to the Comunidad Autónoma de Madrid (Project CCG08 UC3M/MAT 4464) and to the Ministerio de Ciencia e Innovación de España (Project DPI/2008 06408)Publicad

Four-body continuum-discretized coupled-channels calculations using a transformed harmonic oscillator basis

The scattering of a weakly bound three-body system by a target is discussed. A transformed harmonic oscillator basis is used to provide an appropriate discrete and finite basis for treating the continuum part of the spectrum of the projectile. The continuum-discretized coupled channels framework is used for the scattering calculations. The formalism is applied to different reactions, 6He+12C at 229.8 MeV, 6He+64Zn at 10 and 13.6 MeV, and 6He+208Pb at 22 MeV, induced by the Borromean nucleus 6He. Both the Coulomb and nuclear interactions with a target are taken into account.Comment: Published in Phys. Rev.

Ab initio study of the influence of nanoscale doping inhomogeneities in the phase separated state of La1−x_{1-x}Cax_{x}MnO3_3

The chemical influence in the phase separation phenomenon that occurs in perovskite manganites is discussed by means of ab initio calculations. Supercells have been used to simulate a phase separated state, that occurs at Ca concentrations close to the localized to itinerant crossover. We have first considered a model with two types of magnetic ordering coexisting within the same compound. This is not stable. However, a non-isotropic distribution of chemical dopants is found to be the ground state. This leads to regions in the system with different effective concentrations, that would always accompany the magnetic phase separation at the same nanometric scale, with hole-rich regions being more ferromagnetic in character and hole-poor regions being in the antiferromagnetic region of the phase diagram, as long as the system is close to a phase crossover.Comment: 8 pages, 7 figures, 1 tabl

Layer-by-layer assembly of chitosan and recombinant biopolymers into biomimetic coatings with multiple stimuli-responsive properties

In this work, biomimetic smart thin coatings using chitosan and a recombinant elastin-like recombinamer (ELR) containing the cell attachment sequence arginine–glycine–(aspartic acid) (RGD) are fabricated through a layer-by-layer approach. The synthetic polymer is characterized for its molecular mass and composition using mass spectroscopy and peptide sequencing. The adsorption of each polymeric layer is followed in situ at room temperature and pH 5.5 using a quartz-crystal microbalance with dissipation monitoring, showing that both polymers can be successfully combined to conceive nanostructured, multilayered coatings. The smart properties of the coatings are tested for their wettability by contact angle (CA) measurements as a function of external stimuli, namely temperature, pH, and ionic strength. Wettability transitions are observed from a moderate hydrophobic surface (CAs approximately from 62° to 71°) to an extremely wettable one (CA considered as 0°) as the temperature, pH, and ionic strength are raised above 50 °C, 11, and 1.25 m, respectively. Atomic force microscopy is performed at pH 7.4 and pH 11 to assess the coating topography. In the latter, the results reveal the formation of large and compact structures upon the aggregation of ELRs at the surface, which increase water affinity. Cell adhesion tests are conducted using a SaOs-2 cell line. Enhanced cell adhesion is observed in the coatings, as compared to a coating with a chitosan-ending film and a scrambled arginine–(aspartic acid)–glycine (RDG) biopolymer. The results suggest that such films could be used in the future as smart biomimetic coatings of biomaterials for different biomedical applications, including those in tissue engineering or in controlled delivery systems.EUJCyL - VA034A09, VA030A08Fundação para a Ciência e Tecnologia (FCT) - SFRH/BD/61126/2009, SFRH/BD/61390/2009MICINN - MAT 2007-66275-C02-01, MAT 2007-61604, MAT 2009-14195-C03-03, PSE-300100-2006-1European regional development fund (ERDF)Junta de Castilla y LeonNetwork Center of Regenerative Medicine and Cellular Therapy of Castilla and LeónCIBER-BBN (project CB06-01-0003