Neutron Scattering and magnetization studies of Ba2_2Cu2.95_{2.95}Co0.05_{0.05}O4_4Cl2_2: A decorated two-dimensional antiferromagnet

Ba$_2$Cu$_3$O$_4$Cl$_2$ has two inter-penetrating square Cu sublattices, one with square root 2 times the in-plane spacing of the other. Isotropic magnetic interactions between the two sublattices are completely frustrated. Quantum fluctuations resolve the intrinsic degeneracy in the ordering direction of the more weakly coupled sublattice in favor of collinear ordering. We present neutron scattering and magnetization studies of the magnetic structure when the Cu ions are substituted with Co. The Co spins create new magnetic interactions between the two sublattices. The ordering behavior of both Cu sublattices is retained largely unmodified. Between the phase transitions of the two sublattices spin-glass behavior is observed. Magnetization results show a strong enhancement to the ferromagnetic aspect of the magnetic structure. The combination of glassy behavior and large moments strongly suggest that the Co moments induce the formation of local canted states.Comment: 4 figure

Three-Dimensional Simulations of Mixing Instabilities in Supernova Explosions

We present the first three-dimensional (3D) simulations of the large-scale mixing that takes place in the shock-heated stellar layers ejected in the explosion of a 15.5 solar-mass blue supergiant star. The outgoing supernova shock is followed from its launch by neutrino heating until it breaks out from the stellar surface more than two hours after the core collapse. Violent convective overturn in the post-shock layer causes the explosion to start with significant asphericity, which triggers the growth of Rayleigh-Taylor (RT) instabilities at the composition interfaces of the exploding star. Deep inward mixing of hydrogen (H) is found as well as fast-moving, metal-rich clumps penetrating with high velocities far into the H-envelope of the star as observed, e.g., in the case of SN 1987A. Also individual clumps containing a sizeable fraction of the ejected iron-group elements (up to several 0.001 solar masses) are obtained in some models. The metal core of the progenitor is partially turned over with Ni-dominated fingers overtaking oxygen-rich bullets and both Ni and O moving well ahead of the material from the carbon layer. Comparing with corresponding 2D (axially symmetric) calculations, we determine the growth of the RT fingers to be faster, the deceleration of the dense metal-carrying clumps in the He and H layers to be reduced, the asymptotic clump velocities in the H-shell to be higher (up to ~4500 km/s for the considered progenitor and an explosion energy of 10^{51} ergs, instead of <2000 km/s in 2D), and the outward radial mixing of heavy elements and inward mixing of hydrogen to be more efficient in 3D than in 2D. We present a simple argument that explains these results as a consequence of the different action of drag forces on moving objects in the two geometries. (abridged)Comment: 15 pages, 8 figures, 30 eps files; significantly extended and more figures added after referee comments; accepted by The Astrophysical Journa

Study of nuclear correlation effects via 12C(p,n)12N(g.s.,1+) at 296 MeV

We report measurements of the cross section and a complete set of polarization observables for the Gamow--Teller ${}^{12}{\rm C}(\vec{p},\vec{n}){}^{12}{\rm N}({\rm g.s.},1^+)$ reaction at a bombarding energy of 296 MeV. The data are compared with distorted wave impulse approximation calculations employing transition form factors normalized to reproduce the observed beta-decay $ft$ value. The cross section is significantly under-predicted by the calculations at momentum transfers $q \gtrsim$ 0.5 ${\rm fm^{-1}}$. The discrepancy is partly resolved by considering the non-locality of the nuclear mean field. However, the calculations still under-predict the cross section at large momentum transfers of $q$ $\simeq$ 1.6 ${\rm fm^{-1}}$. We also performed calculations employing random phase approximation response functions and found that the observed enhancement can be attributed in part to pionic correlations in nuclei.Comment: 5 figures, submitted to Phys. Lett.

Complete set of polarization transfer coefficients for the 3He(p,n){}^{3}{\rm He}(p,n) reaction at 346 MeV and 0 degrees

We report measurements of the cross-section and a complete set of polarization transfer coefficients for the ${}^{3}{\rm He}(p,n)$ reaction at a bombarding energy $T_p$ = 346 MeV and a reaction angle $\theta_{\rm lab}$ = $0^{\circ}$. The data are compared with the corresponding free nucleon-nucleon values on the basis of the predominance of quasi-elastic scattering processes. Significant discrepancies have been observed in the polarization transfer $D_{LL}(0^{\circ})$, which are presumably the result of the three-proton $T$ = 3/2 resonance. The spin--parity of the resonance is estimated to be $1/2^-$, and the distribution is consistent with previous results obtained for the same reaction at $T_p$ = 48.8 MeV.Comment: 4 figures, Accepted for publication in Physical Review

Tight-binding parameters and exchange integrals of Ba_2Cu_3O_4Cl_2

Band structure calculations for Ba_2Cu_3O_4Cl_2 within the local density approximation (LDA) are presented. The investigated compound is similar to the antiferromagnetic parent compounds of cuprate superconductors but contains additional Cu_B atoms in the planes. Within the LDA, metallic behavior is found with two bands crossing the Fermi surface (FS). These bands are built mainly from Cu 3d_{x^2-y^2} and O 2p_{x,y} orbitals, and a corresponding tight-binding (TB) model has been parameterized. All orbitals can be subdivided in two sets corresponding to the A- and B-subsystems, respectively, the coupling between which is found to be small. To describe the experimentally observed antiferromagnetic insulating state, we propose an extended Hubbard model with the derived TB parameters and local correlation terms characteristic for cuprates. Using the derived parameter set we calculate the exchange integrals for the Cu_3O_4 plane. The results are in quite reasonable agreement with the experimental values for the isostructural compound Sr_2Cu_3O_4Cl_2.Comment: 5 pages (2 tables included), 4 ps-figure

Thin Ice Target for 16^{16}O(p,p') experiment

A windowless and self-supporting ice target is described. An ice sheet with a thickness of 29.7 mg/cm$^2$ cooled by liquid nitrogen was placed at the target position of a magnetic spectrometer and worked stably in the $^{16}$O$(p,p')$ experiment at $E_{p}=392$ MeV. Background-free spectra were obtained.Comment: 14 pages, 4 figures, Nucl. Instr. & Meth. A (in press

Confirmation of Anomalous Dynamical Arrest in attractive colloids: a molecular dynamics study

Previous theoretical, along with early simulation and experimental, studies have indicated that particles with a short-ranged attraction exhibit a range of new dynamical arrest phenomena. These include very pronounced reentrance in the dynamical arrest curve, a logarithmic singularity in the density correlation functions, and the existence of `attractive' and `repulsive' glasses. Here we carry out extensive molecular dynamics calculations on dense systems interacting via a square-well potential. This is one of the simplest systems with the required properties, and may be regarded as canonical for interpreting the phase diagram, and now also the dynamical arrest. We confirm the theoretical predictions for re-entrance, logarithmic singularity, and give the first direct evidence of the coexistence, independent of theory, of the two coexisting glasses. We now regard the previous predictions of these phenomena as having been established.Comment: 15 pages,15 figures; submitted to Phys. Rev.

Internalization of methotrexate conjugates by folate receptor-α

The folate antagonist methotrexate is a cytotoxic drug used in the treatment of several cancer types. Methotrexate entry into the cell is mediated by two main transport systems: the reduced folate carrier and membrane-associated folate receptors. These transporters differ considerably in their mechanism of (anti)folate uptake, substrate specificity and tissue specificity. Although the mechanism of action of the reduced folate carrier is fairly well-established, that of the folate receptor has remained doubtful. The development of specific folate receptor-targeted antifolates would be accelerated if additional mechanistic data becomes available. In this work, we used two fluorescent-labeled conjugates of methotrexate, differently linked at the terminal groups, to clarify the uptake mechanism by the folate receptor-α. The results demonstrate the importance of methotrexate amino groups in the interaction with the folate receptor-α.E.A. (SFRH/BD/122952/2016) and J.N. (SFRH/BD/121673/ 2016) hold scholarships from the Portuguese Foundation for Science and Technology (FCT). This study was supported by the FCT under the scope of the strategic funding of the UID/ BIO/04469/2013 unit and the COMPETE 2020 (POCI-010145-FEDER-006684) and BioTecNorte operation (NORTE01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020Programa Operacional Regional do Norte. This work has also received funding from the European Union 7th Framework Programme (FP7/2007−2013), under Grant Agreement NMP4-LA-2009228827 NANOFOL, and the Horizon 2020 research and innovation program under Grant Agreement NMP-06-2015683356 FOLSMART.info:eu-repo/semantics/publishedVersio

Production process aiming at the implementation of Cleaner Production in an industrial metalworking

Considering that companies are concerned with sustainable management in their production processes, it ir of importance to check the production processes in a metalworking industry, with an emphasis on the cleaner production process as a tool in business decision making. In this paper we propose the suggestion of a system of contínuos improvement using the cleaner production in the machinery departamento in a metalworking industry that produces agricultural implements in the north of Rio Grande do Sul. The participant observation method for the description of production processes with semi-structured interviews, with contente analysis as results. The use of this tool was satisfactory, since there was decrease of componentes in the production as raw material, and improvement in the productive processes. It should be noted that cleaner production generates savings in manufacturing processes, eliminating waste such as raw materials, waste, water and energy, generating financial and sustainable returns to companies