603 research outputs found
Neutron Scattering and magnetization studies of BaCuCoOCl: A decorated two-dimensional antiferromagnet
BaCuOCl 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 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 value.
The cross section is significantly under-predicted by the calculations at
momentum transfers 0.5 .
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 1.6 .
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 reaction at 346 MeV and 0 degrees
We report measurements of the cross-section and a complete set of
polarization transfer coefficients for the reaction at a
bombarding energy = 346 MeV and a reaction angle =
.
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
, which are presumably the result of the three-proton =
3/2 resonance.
The spin--parity of the resonance is estimated to be , and the
distribution is consistent with previous results obtained for the same reaction
at = 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 O(p,p') experiment
A windowless and self-supporting ice target is described. An ice sheet with a
thickness of 29.7 mg/cm cooled by liquid nitrogen was placed at the target
position of a magnetic spectrometer and worked stably in the O
experiment at 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 contÃnuos 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
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