52 research outputs found
Feiras livres como alternativa de comercialização de produtos da agrofloresta.
Com a busca por alternativas comerciais socialmente justas como maneira de otimizar a comercialização de produtos provenientes de agricultura familiar, destaca se a venda direta através de feiras, livres, que permite acesso direto ao consumidor sem necessidade de intermediadores. O Grupo de Produtores Agroflorestais Gralha Azul, de Morretes-PR, iniciou plantios de agroflorestas agroecológicas em 2009, sendo formado, atualmente, por 12 famílias de agricultores. Há um ano, o Gralha Azul iniciou sua participação na Matinfeira, feira semanal de produtos da agricultura familiar em Matinhos, PR. Com o objetivo de caracterização dos produtos, produtores e do processo de comercialização, foram acompanhados e sistematizados em planilha a comercialização destes produtos em 22 feiras semanais, entre maio e dezembro de 2012. Onze produtores participaram da Matinfeira, comercializando entre 13 e 29 variedades de alimentos, e proporcionando uma renda que variou de R 386,50, por semana. Mensalmente, as feiras permitiram uma receita bruta de R$ 141,17 por produtor familiar agroflorestal. Apesar desse baixo valor, há que se considerar que o mesmo reflete os primeiros seis meses de atuação do Grupo no processo de comercialização na feira (Matinfeira). A venda direta através desta feira livre mostra potencial como alternativa comercial socialmente justa para os produtores em transição agroecológica do Grupo Gralha Azul
Diamagnetism above Tc in underdoped Bi2.2Sr1.8Ca2Cu3O10+d
Single crystals of (Bi2223) with were grown by a traveling solvent floating
zone method in order to investigate the superconducting properties of highly
underdoped Bi2223.Grown crystals were characterized by X-ray diffraction, DC
susceptibility and resistivity measurements, confirming Bi2223 to be the main
phase.The crystals were annealed under various oxygen partial pressures to
adjust their carrier densities from optimally doped to highly underdoped.The
fluctuation diamagnetic component above the superconducting transition
temperature extracted from the anisotropic normal state
susceptibilities () and ()
was found to increase with underdoping, suggesting a decrease in the
superconducting dimensionality and/or increase in the fluctuating vortex liquid
region.Comment: 6 pages, 7 figures, corrected fig.4 and references, published in J.
Phys. Soc. Jpn. 79, 114711 (2010
Dependence of carrier doping on the impurity potential in transition-metal-substituted FeAs-based superconductors
In order to examine to what extent the rigid-band-like electron doping
scenario is applicable to the transition metal-substituted Fe-based
superconductors, we have performed angle-resolved photoemission spectroscopy
studies of Ba(FeNi)As (Ni-122) and
Ba(FeCu)As (Cu-122), and compared the results with
Ba(FeCo)As (Co-122). We find that Ni 3-derived
features are formed below the Fe 3 band and that Cu 3-derived
ones further below it. The electron and hole Fermi surface (FS) volumes are
found to increase and decrease with substitution, respectively, qualitatively
consistent with the rigid-band model. However, the total extra electron number
estimated from the FS volumes (the total electron FS volume minus the total
hole FS volume) is found to decrease in going from Co-, Ni-, to Cu-122 for a
fixed nominal extra electron number, that is, the number of electrons that
participate in the formation of FS decreases with increasing impurity
potential. We find that the Nel temperature and
the critical temperature maximum are determined by the FS volumes
rather than the nominal extra electron concentration nor the substituted atom
concentration.Comment: Total: 9 pages, 10 figure
Pseudogap, Superconducting Gap, and Fermi Arc in High-Tc Cuprates Revealed by Angle-Resolved Photoemission Spectroscopy
We present an overview of angle-resolved photoemission spectroscopy (ARPES)
studies of high-temperature cuprate superconductors aiming at elucidating the
relationship between the superconductivity, the pseudogap, and the Fermi arc.
ARPES studies of underdoped samples show a momentum dependence of the energy
gap below Tc which deviates from a simple d-wave form, suggesting the
coexistence of multiple energy scales in the superconducting state. Hence, two
distinct energy scales have been introduced, namely, the gap near the node
(characterized by Delta_0) and in the anti-nodal region (characterized by
Delta^*). Dichotomy between them has been demonstrated from the material,
doping, and temperature dependence of the energy gap. While Delta^* at the same
doping level is approximately material independent, Delta_0 shows a strong
material dependence tracking the magnitude of Tc,max. The anti-nodal gap does
not close at Tc in contrast to the gap near the node which follows something
closer to a BCS-like temperature dependence. An effective superconducting gap
Delta_sc defined at the end point of the Fermi arc is found to be proportional
to Tc's in various materials.Comment: 20 pages, 10 figures, (SPECIAL TOPICS: Recent Developments in
Superconductivity, in Journal of the Physical Society of Japan
High-Tc Superconductivity and Antiferromagnetism in Multilayered Copper Oxides - A New Paradigm of Superconducting Mechanism -
High-temperature superconductivity (HTSC) in copper oxides emerges on a
layered CuO2 plane when an antiferromagnetic Mott insulator is doped with
mobile hole carriers. We review extensive studies of multilayered copper oxides
by site-selective nuclear magnetic resonance (NMR), which have uncovered the
intrinsic phase diagram of antiferromagnetism (AFM) and HTSC for a
disorder-free CuO2 plane with hole carriers. We present our experimental
findings such as the existence of the AFM metallic state in doped Mott
insulators, the uniformly mixed phase of AFM and HTSC, and the emergence of
d-wave SC with a maximum Tc just outside a critical carrier density, at which
the AFM moment on a CuO2 plane disappears. These results can be accounted for
by the Mott physics based on the t-J model. The superexchange interaction J_in
among spins plays a vital role as a glue for Cooper pairs or mobile
spin-singlet pairs, in contrast to the phonon-mediated attractive interaction
among electrons established in the Bardeen-Cooper-Schrieffer (BCS) theory. We
remark that the attractive interaction for raising the of HTSC up to
temperatures as high as 160 K is the large J_in (~0.12 eV), which binds
electrons of opposite spins to be on neighboring sites, and that there are no
bosonic glues. It is the Coulomb repulsive interaction U(> 6 eV) among Cu-3d
electrons that plays a central role in the physics behind high-Tc phenomena. A
new paradigm of the SC mechanism opens to strongly correlated electron matter.Comment: 20 pages, 25 figures, Special topics "Recent Developments in
Superconductivity" in J. Phys. Soc. Jpn., Published December 26, 201
A Complete Spectroscopic Survey of the Milky Way Satellite Segue 1: The Darkest Galaxy
We present the results of a comprehensive Keck/DEIMOS spectroscopic survey of
the ultra-faint Milky Way satellite galaxy Segue 1. We have obtained velocity
measurements for 98.2% of the stars within 67 pc (10 arcmin, or 2.3 half-light
radii) of the center of Segue 1 that have colors and magnitudes consistent with
membership, down to a magnitude limit of r=21.7. Based on photometric,
kinematic, and metallicity information, we identify 71 stars as probable Segue
1 members, including some as far out as 87 pc. After correcting for the
influence of binary stars using repeated velocity measurements, we determine a
velocity dispersion of 3.7^{+1.4}_{-1.1} km/s, with a corresponding mass within
the half-light radius of 5.8^{+8.2}_{-3.1} x 10^5 Msun. The stellar kinematics
of Segue 1 require very high mass-to-light ratios unless the system is far from
dynamical equilibrium, even if the period distribution of unresolved binary
stars is skewed toward implausibly short periods. With a total luminosity less
than that of a single bright red giant and a V-band mass-to-light ratio of 3400
Msun/Lsun, Segue 1 is the darkest galaxy currently known. We critically
re-examine recent claims that Segue 1 is a tidally disrupting star cluster and
that kinematic samples are contaminated by the Sagittarius stream. The
extremely low metallicities ([Fe/H] < -3) of two Segue 1 stars and the large
metallicity spread among the members demonstrate conclusively that Segue 1 is a
dwarf galaxy, and we find no evidence in favor of tidal effects. We also show
that contamination by the Sagittarius stream has been overestimated. Segue 1
has the highest measured dark matter density of any known galaxy and will
therefore be a prime testing ground for dark matter physics and galaxy
formation on small scales.Comment: 24 pages, 4 tables, 11 figures (10 in color). Submitted for
publication in ApJ. V3 revised according to comments from the refere
Common Variants in the COL4A4 Gene Confer Susceptibility to Lattice Degeneration of the Retina
Lattice degeneration of the retina is a vitreoretinal disorder characterized by a visible fundus lesion predisposing the patient to retinal tears and detachment. The etiology of this degeneration is still uncertain, but it is likely that both genetic and environmental factors play important roles in its development. To identify genetic susceptibility regions for lattice degeneration of the retina, we performed a genome-wide association study (GWAS) using a dense panel of 23,465 microsatellite markers covering the entire human genome. This GWAS in a Japanese cohort (294 patients with lattice degeneration and 294 controls) led to the identification of one microsatellite locus, D2S0276i, in the collagen type IV alpha 4 (COL4A4) gene on chromosome 2q36.3. To validate the significance of this observation, we evaluated the D2S0276i region in the GWAS cohort and in an independent Japanese cohort (280 patients and 314 controls) using D2S0276i and 47 single nucleotide polymorphisms covering the region. The strong associations were observed in D2S0276i and rs7558081 in the COL4A4 gene (Pc = 5.8×10−6, OR = 0.63 and Pc = 1.0×10−5, OR = 0.69 in a total of 574 patients and 608 controls, respectively). Our findings suggest that variants in the COL4A4 gene may contribute to the development of lattice degeneration of the retina
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