Spin-orbit induced mixed-spin ground state in RRNiO3_3 perovskites probed by XAS: new insight into the metal to insulator transition

We report on a Ni L$_{2,3}$ edges x-ray absorption spectroscopy (XAS) study in $R$NiO$_3$ perovskites. These compounds exhibit a metal to insulator ($MI$) transition as temperature decreases. The L$_{3}$ edge presents a clear splitting in the insulating state, associated to a less hybridized ground state. Using charge transfer multiplet calculations, we establish the importance of the crystal field and 3d spin-orbit coupling to create a mixed-spin ground state. We explain the $MI$ transition in $R$NiO$_3$ perovskites in terms of modifications in the Ni$^{3+}$ crystal field splitting that induces a spin transition from an essentially low-spin (LS) to a mixed-spin state.Comment: 4 pages, 4 figures, accepted as PRB - Rapid Comm. Dez. 200

Effective Potential and Thermodynamics for a Coupled Two-Field Bose Gas Model

We study the thermodynamics of a two-species homogeneous and dilute Bose gas that is self-interacting and quadratically coupled to each other. We make use of field theoretical functional integral techniques and evaluate the one-loop finite temperature effective potential for this system considering the resummation of the leading order temperature dependent as well as infrared contributions. The symmetry breaking pattern associated to the model is then studied by considering different values of self and inter-species couplings. We pay special attention to the eventual appearance of reentrant phases and/or shifts in the observed critical temperatures as compared to the monoatomic (one-field Bose) case.Comment: 21 pages, 4 eps figure

Sound and light from fractures in scintillators

Prompted by intriguing events observed in certain particle-physics searches for rare events, we study light and acoustic emission simultaneously in some inorganic scintillators subject to mechanical stress. We observe mechanoluminescence in ${Bi}_4{Ge}_{3}{O}_{12}$, ${CdWO}_{4}$ and ${ZnWO}_{4}$, in various mechanical configurations at room temperature and ambient pressure. We analyze how the light emission is correlated to acoustic emission during fracture. For ${Bi}_4{Ge}_{3}{O}_{12}$, we set a lower bound on the energy of the emitted light, and deduce that the fraction of elastic energy converted to light is at least $3 \times 10^{-5}$

Análise da folga de produtividade na produção de grãos no Brasil em nível estadual.

O trabalho tem como objetivos: descrever e aplicar um método alternativo de estimação da produtividade potencial, originalmente proposto para o nível nacional (Ramos; Garagorry, 2018); estimar anualmente a magnitude da folga de produtividade dos grãos (como agregado) em nível estadual, bem como as distribuições das contribuições mesorregionais para sua formação; examinar a dinâmica dessas distribuições espaciais como indicativa da velocidade de mudanças intraestaduais na composição das folgas estimadas; e, no conjunto do País, detectar mesorregiões que, apresentando situações extremas, mereceriam estudos mais detalhados ou ações específicas. Espera-se, assim, ilustrar a utilidade da análise de folga de produtividade, segundo a abordagem aplicada, para o planejamento e avaliação territorial de intervenções na agricultura.bitstream/item/214755/1/DOCUMENTOS-Analise-folga-produtividade2020.pd

Low X-Ray Luminosity Galaxy Clusters: Main goals, sample selection, photometric and spectroscopic observations

We present the study of nineteen low X-ray luminosity galaxy clusters (L$_X \sim$ 0.5--45 $\times$ $10^{43}$ erg s$^{-1}$), selected from the ROSAT Position Sensitive Proportional Counters (PSPC) Pointed Observations (Vikhlinin et al. 1998) and the revised version of Mullis et al. (2003) in the redshift range of 0.16 to 0.7. This is the introductory paper of a series presenting the sample selection, photometric and spectroscopic observations and data reduction. Photometric data in different passbands were taken for eight galaxy clusters at Las Campanas Observatory; three clusters at Cerro Tololo Interamerican Observatory; and eight clusters at the Gemini Observatory. Spectroscopic data were collected for only four galaxy clusters using Gemini telescopes. With the photometry, the galaxies were defined based on the star-galaxy separation taking into account photometric parameters. For each galaxy cluster, the catalogues contain the PSF and aperture magnitudes of galaxies within the 90\% completeness limit. They are used together with structural parameters to study the galaxy morphology and to estimate photometric redshifts. With the spectroscopy, the derived galaxy velocity dispersion of our clusters ranged from 507 km~s$^{-1}$ for [VMF98]022 to 775 km~s$^{-1}$ for [VMF98]097 with signs of substructure. Cluster membership has been extensively discussed taking into account spectroscopic and photometric redshift estimates. In this sense, members are the galaxies within a projected radius of 0.75 Mpc from the X-ray mission peak and with cluster centric velocities smaller than the cluster velocity dispersion or 6000 km~s$^{-1}$, respectively. These results will be used in forthcoming papers to study, among the main topics, the red cluster sequence, blue cloud and green populations; the galaxy luminosity function and cluster dynamics.Comment: 13 pages, 6 tables, 9 figures. Uses emulateapj. Accepted for publication in The Astronomical Journal. Some formatting errors fixe

Decoherence in a Josephson junction qubit

The zero-voltage state of a Josephson junction biased with constant current consists of a set of metastable quantum energy levels. We probe the spacings of these levels by using microwave spectroscopy to enhance the escape rate to the voltage state. The widths of the resonances give a measurement of the coherence time of the two states involved in the transitions. We observe a decoherence time shorter than that expected from dissipation alone in resonantly isolated 20 um x 5 um Al/AlOx/Al junctions at 60 mK. The data is well fit by a model including dephasing effects of both low-frequency current noise and the escape rate to the continuum voltage states. We discuss implications for quantum computation using current-biased Josephson junction qubits, including the minimum number of levels needed in the well to obtain an acceptable error limit per gate.Comment: 4 pages, 6 figure

Fermionic R-Operator and Algebraic Structure of 1D Hubbard Model: Its application to quantum transfer matrix

The algebraic structure of the 1D Hubbard model is studied by means of the fermionic R-operator approach. This approach treats the fermion models directly in the framework of the quantum inverse scattering method. Compared with the graded approach, this approach has several advantages. First, the global properties of the Hamiltonian are naturally reflected in the algebraic properties of the fermionic R-operator. We want to note that this operator is a local operator acting on fermion Fock spaces. In particular, SO(4) symmetry and the invariance under the partial particle hole transformation are discussed. Second, we can construct a genuinely fermionic quantum transfer transfer matrix (QTM) in terms of the fermionic R-operator. Using the algebraic Bethe Ansatz for the Hubbard model, we diagonalize the fermionic QTM and discuss its properties.Comment: 22 pages, no figure

Abrigos para criação do Acari Zebra, Hypancistrus zebra, em cativeiro.

Os Loricarídeos, conhecidos como cascudos ou acaris, destacam-se pela grande variedade de formas e padrões, o que têm atraído grande interesse do mercado aquarista nacional e internacional (CAMARGO; GHILARDI, 2009). Isto tem estimulado sua captura em ambiente de ocorrência, com prejuízos às populações exploradas por levar àredução dos estoques naturais.bitstream/item/127601/1/COT149.pd

A One-Parameter Family of Hamiltonian Structures for the KP Hierarchy and a Continuous Deformation of the Nonlinear \W_{\rm KP} Algebra

The KP hierarchy is hamiltonian relative to a one-parameter family of Poisson structures obtained from a generalized Adler map in the space of formal pseudodifferential symbols with noninteger powers. The resulting \W-algebra is a one-parameter deformation of \W_{\rm KP} admitting a central extension for generic values of the parameter, reducing naturally to \W_n for special values of the parameter, and contracting to the centrally extended \W_{1+\infty}, \W_\infty and further truncations. In the classical limit, all algebras in the one-parameter family are equivalent and isomorphic to \w_{\rm KP}. The reduction induced by setting the spin-one field to zero yields a one-parameter deformation of \widehat{\W}_\infty which contracts to a new nonlinear algebra of the \W_\infty-type.Comment: 31 pages, compressed uuencoded .dvi file, BONN-HE-92/20, US-FT-7/92, KUL-TF-92/20. [version just replaced was truncated by some mailer