3,369 research outputs found
Irradiation-induced confinement in a quasi-one-dimensional metal
The anisotropic resistivity of PrBaCuO has been measured as a
function of electron irradiation fluence. Localization effects are observed for
extremely small amounts of disorder corresponding to electron mean-free-paths
of order 100 unit cells. Estimates of the localization corrections suggest that
this anomalous localization threshold heralds a crossover to a ground state
with pronounced one-dimensional character in which conduction electrons become
confined to a small cluster of chains.Comment: 4 pages, 4 figure
Fragile three-dimensionality in the quasi-one-dimensional cuprate PrBa_2Cu_4O_8
In this article we report on the experimental realization of dimensional
crossover phenomena in the chain compound PrBaCuO using
temperature, high magnetic fields and disorder as independent tuning
parameters. In purer crystals of PrBaCuO, a highly anisotropic
three-dimensional Fermi-liquid state develops at low temperatures. This
metallic state is extremely susceptible to disorder however and localization
rapidly sets in. We show, through quantitative comparison of the relevant
energy scales, that this metal/insulator crossover occurs precisely when the
scattering rate within the chain exceeds the interchain hopping rate(s), i.e.
once carriers become confined to a single conducting element.Comment: 12 pages, 5 figures, published at
http://www.iop.org/EJ/article/1367-2630/8/9/172/njp6_9_172.htm
Spin dynamics and antiferromagnetic order in PrBa2Cu4O8 studied by Cu nuclear respnance
Results of the nuclear resonance experiments for the planar Cu sites in
PrBa2Cu4O8 are presented. The NMR spectrum at 1.5 K in zero magnetic field
revealed an internal field of 6.1 T, providing evidence for an
antiferromagnetic order of the planar Cu spins. This confirms that the CuO2
planes are insulating, therefore, the metallic conduction in this material is
entirely due to the one-dimensional zigzag Cu2O2 chains. The results of the
spin-lattice relaxation rates measured by zero field NQR above 245 K in the
paramagnetic state are explained by the theory for a Heisenberg model on a
square lattice.Comment: 4 pages, 2 figure
Possible high temperature superconductivity in Ti-doped A-Sc-Fe-As-O (A= Ca, Sr) system
We report a systematic study on the effect of partial substitution of
Sc by Ti in SrScFeAsO, CaScFeAsO and
SrScFeAsO on their electrical properties. High
level of doping results in an increased carrier concentration and leads to the
appearance of superconductivity with the onset of T up to 45 K.Comment: 8 pages, 4 figures, 2 new figure
Angle-resolved photoemission study of insulating and metallic Cu-O chains in PrBaCuO and PrBaCuO
We compare the angle-resolved photoemission spectra of the hole-doped Cu-O
chains in PrBaCuO (Pr123) and in PrBaCuO (Pr124).
While, in Pr123, a dispersive feature from the chain takes a band maximum at
(momentum along the chain) and loses its spectral weight
around the Fermi level, it reaches the Fermi level at in
Pr124. Although the chains in Pr123 and Pr124 are approximately 1/4-filled,
they show contrasting behaviors: While the chains in Pr123 have an instability
to charge ordering, those in Pr124 avoid it and show an interesting spectral
feature of a metallic coupled-chain system.Comment: 4 pages, 5 figures, to be published in PR
Performance de novilhas holandesas alimentadas com silagens de cana-de-açúcar tratadas com uréia, benzoato de sódio ou Lactobacillus Buchneri.
A fermentação alcoólica influencia negativamente a qualidade de silagens de cana-de-açúcar e pode prejudicar a performance dos animais. Alguns aditivos podem reduzir a produção de etanol e as perdas nessas silagens. Este experimento objetivou avaliar a performance de novilhas alimentadas com rações contendo silagens de cana-de-açúcar aditivadas ou sem tratamento. Trinta e duas novilhas Holandesas foram aleatoriamente distribuídas em um delineamento em blocos, para avaliar rações (46% silagem; 54% concentrado; 12% proteína bruta) contendo silagem sem aditivo (controle) ou silagens tratadas com (base matéria verde) uréia (0,5%), benzoato de sódio (0,1 %) ou "Lactobacillus buchneri" (3,64 x 10"5" ufc g"-1"). A inoculação com "Lactobacillus buchneri" melhorou (P < 0,01) o ganho diário (1,24 vs 0,94 kg/dia) e com o benzoato melhorou a conversão alimentar (7.6 vs 9,4 kg de matéria seca/kg de peso vivo). Os tratamentos não afetaram o consumo de matéria seca (2,19% do peso vivo, em média. O tratamento com uréia não tenha melhorou o desempenho dos animais. Concluiu-se que o tratamento com aditivos pode ser um método eficiente para obtenção de silagens de cana-de-açúcar de melhor valor nutritivo
Marine nitrogen fixation as a possible source of atmospheric water-soluble organic nitrogen aerosols in the subtropical North Pacific
Water-soluble organic nitrogen (WSON) in marine
atmospheric aerosols affect the water solubility, acidity, and
light-absorbing properties of aerosol particles, which are important
parameters in assessing both the climate impact and the biogeochemical
cycling of bioelements. Size-segregated aerosol and surface seawater (SSW)
samples were simultaneously collected over the subtropical North Pacific to
investigate the origin of WSON in the marine atmosphere. The fine-mode WSON
concentration (7.5 ± 6.6 ngN m−3) at 200–240∘ E
along 23∘ N, defined as the eastern North Pacific (ENP), was
significantly higher than that (2.4 ± 1.9 ngN m−3) at
135–200∘ E, defined as the western North Pacific (WNP).
Analysis of the stable carbon isotope ratio of water-soluble organic carbon
(WSOC; δ13CWSOC) together with backward trajectory
indicated that most of the observed WSON in the fine particles in the ENP
originated from the ocean surface. We found positive relations among
nitrogen-fixation rate, dissolved organic nitrogen (DON) in SSW, and the
WSON concentrations. The result suggests that reactive nitrogen (DON and
ammonium), produced and exuded by nitrogen-fixing microorganisms in SSW,
contributed to the formation of WSON aerosols. This study provides new
insights into the role of ocean-derived reactive nitrogen aerosols
associated with marine microbial activity.</p
Measurement of the cross-section and charge asymmetry of bosons produced in proton-proton collisions at TeV with the ATLAS detector
This paper presents measurements of the and cross-sections and the associated charge asymmetry as a
function of the absolute pseudorapidity of the decay muon. The data were
collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with
the ATLAS experiment at the LHC and correspond to a total integrated luminosity
of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements
varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the
1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured
with an uncertainty between 0.002 and 0.003. The results are compared with
predictions based on next-to-next-to-leading-order calculations with various
parton distribution functions and have the sensitivity to discriminate between
them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables,
submitted to EPJC. All figures including auxiliary figures are available at
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13
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