8,210 research outputs found
Antiferromagnetism at T > 500 K in the Layered Hexagonal Ruthenate SrRu2O6
We report an experimental and computational study of magnetic and electronic
properties of the layered Ru(V) oxide SrRu2O6 (hexagonal, P-3 1m), which shows
antiferromagnetic order with a N\'eel temperature of 563(2) K, among the
highest for 4d oxides. Magnetic order occurs both within edge-shared octahedral
sheets and between layers and is accompanied by anisotropic thermal expansivity
that implies strong magnetoelastic coupling of Ru(V) centers. Electrical
transport measurements using focused ion beam induced deposited contacts on a
micron-scale crystallite as a function of temperature show p-type
semiconductivity. The calculated electronic structure using hybrid density
functional theory successfully accounts for the experimentally observed
magnetic and electronic structure and Monte Carlo simulations reveals how
strong intralayer as well as weaker interlayer interactions are a defining
feature of the high temperature magnetic order in the material.Comment: Physical Review B 2015 accepted for publicatio
Contracepção e doenças sexualmente transmissíveis: crenças de estudantes do ensino superior da área da saúde
O elevado número de concepções não planeadas e o aumento da prevalência de doenças sexualmente transmissíveis, especialmente em populações jovens, vem sublinhar a importância de uma intervenção a nível da promoção da saúde sexual e reprodutiva, que potencie a adopção de práticas saudáveis e a diminuição de comportamentos de risco. Dos factores modificáveis através desta
intervenção destacam-se as crenças de saúde, elemento fundamental na predisposição para a mudança de comportamentos. Objectivo do estudo: identificar e caracterizar as crenças de estudantes do ensino superior da área da saúde, relativas à contracepção e doenças sexualmente transmissíveis
Superconducting density of states at the border of an amorphous thin film grown by focused-ion-beam
We present very low temperature Scanning Tunneling Microscopy and
Spectroscopy (STM/S) measurements of a W based amorphous thin film grown with
focused-ion-beam. In particular, we address the superconducting properties
close to the border, where the thickness of the superconducting film decreases,
and the Au substrate emerges. When approaching the Au substrate, the
superconducting tunneling conductance strongly increases around the Fermi
level, and the quasiparticle peaks do not significantly change its position.
Under magnetic fields, the vortex lattice is observed, with vortices positioned
very close to the Au substrate.Comment: To appear in Journal of Physics: Conference serie
Depth-varying rupture properties of subduction zone megathrust faults
Subduction zone plate boundary megathrust faults accommodate relative plate motions with spatially varying sliding behavior. The 2004 Sumatra-Andaman (M_w 9.2), 2010 Chile (Mw 8.8), and 2011 Tohoku (M_w 9.0) great earthquakes had similar depth variations in seismic wave radiation across their wide rupture zones – coherent teleseismic short-period radiation preferentially emanated from the deeper portion of the megathrusts whereas the largest fault displacements occurred at shallower depths but produced relatively little coherent short-period radiation. We represent these and other depth-varying seismic characteristics with four distinct failure domains extending along the megathrust from the trench to the downdip edge of the seismogenic zone. We designate the portion of the megathrust less than 15 km below the ocean surface as domain A, the region of tsunami earthquakes. From 15 to ∼35 km deep, large earthquake displacements occur over large-scale regions with only modest coherent short-period radiation, in what we designate as domain B. Rupture of smaller isolated megathrust patches dominate in domain C, which extends from ∼35 to 55 km deep. These isolated patches produce bursts of coherent short-period energy both in great ruptures and in smaller, sometimes repeating, moderate-size events. For the 2011 Tohoku earthquake, the sites of coherent teleseismic short-period radiation are close to areas where local strong ground motions originated. Domain D, found at depths of 30–45 km in subduction zones where relatively young oceanic lithosphere is being underthrust with shallow plate dip, is represented by the occurrence of low-frequency earthquakes, seismic tremor, and slow slip events in a transition zone to stable sliding or ductile flow below the seismogenic zone
Formation of finite antiferromagnetic clusters and the effect of electronic phase separation in Pr{_0.5}Ca{_0.5}Mn{_0.975}Al{_0.025}O{_3}
We report the first experimental evidence of a magnetic phase arising due to
the thermal blocking of antiferromagnetic clusters in the weakened charge and
orbital ordered system Pr{_0.5}Ca{_0.5}Mn{_0.975}Al{_0.025}O{_3}. The third
order susceptibility (\chi_3) is used to differentiate this transition from a
spin or cluster glass like freezing mechanism. These clusters are found to be
mesoscopic and robust to electronic phase separation which only enriches the
antiphase domain walls with holes at the cost of the bulk, without changing the
size of these clusters. This implies that Al substitution provides sufficient
disorder to quench the length scales of the striped phases.Comment: 4 Post Script Figure
The Chemical Composition of the Small Magellanic Cloud H II Region NGC 346 and the Primordial Helium Abundance
Spectrophotometry in the 3400-7400 range is presented for 13 areas of the
brightest H II region in the SMC: NGC 346. The observations were obtained at
CTIO with the 4-m telescope. Based on these observations its chemical
composition is derived. The helium and oxygen abundances by mass are given by:
Y(SMC)=0.2405+-0.0018 and O(SMC)=0.00171+-0.00025. From models and observations
of irregular and blue compact galaxies it is found that dY/dO=3.5+-0.9 and
consequently that the primordial helium abundance by mass is given by:
Yp=0.2345+-0.0026 (1-sigma). This result is compared with values derived from
Big Bang nucleosynthesis, and with other determinations of Yp.Comment: 32 pages + 5 figures Referee Revised Versio
Science-based restoration monitoring of coastal habitats, Volume One: A framework for monitoring plans under the Estuaries and Clean Waters Act of 2000 (Public Law 160-457)
Executive Summary:
The Estuary Restoration Act of 2000 (ERA), Title I of the Estuaries and Clean Waters Act of 2000, was created to promote the restoration of habitats along the coast of the United States (including the US protectorates and the Great Lakes). The NOAA National Centers for Coastal Ocean Science was charged with the development of a guidance manual for monitoring plans under this Act.
This guidance manual, titled Science-Based Restoration Monitoring of Coastal Habitats, is written in two volumes. It provides technical assistance, outlines necessary steps, and provides useful tools for the development and implementation of sound scientific monitoring of coastal restoration efforts. In addition, this manual offers a means to detect early warnings that the restoration is on track or not, to gauge how well a restoration site is functioning, to coordinate projects and efforts for consistent and successful restoration, and to evaluate the ecological health of specific coastal habitats both before and after project completion (Galatowitsch et al. 1998).
The following habitats have been selected for discussion in this manual: water column, rock bottom, coral reefs, oyster reefs, soft bottom, kelp and other macroalgae, rocky shoreline, soft shoreline, submerged aquatic vegetation, marshes, mangrove swamps, deepwater swamps, and riverine forests. The classification of habitats used in this document is generally based on that of Cowardin et al. (1979) in their Classification of Wetlands and Deepwater Habitats of the United States, as called for in the ERA Estuary Habitat Restoration Strategy.
This manual is not intended to be a restoration monitoring “cookbook” that provides templates of monitoring plans for specific habitats. The interdependence of a large number of site-specific factors causes habitat types to vary in physical and biological structure within and between regions and geographic locations (Kusler and Kentula 1990). Monitoring approaches used should be tailored to these differences. However, even with the diversity of habitats that may need to be restored and the extreme geographic range across which these habitats occur, there are consistent principles and approaches that form a common basis for effective monitoring.
Volume One, titled A Framework for Monitoring Plans under the Estuaries and Clean Waters Act of 2000, begins with definitions and background information. Topics such as restoration, restoration monitoring, estuaries, and the role of socioeconomics in restoration are discussed. In addition, the habitats selected for discussion in this manual are briefly described. (PDF contains 116 pages
Phase separation in double exchange systems
Ferromagnetic systems described by the double exchange model are
investigated. At temperatures close to the Curie temperature, and for a wide
range of doping levels, the system is unstable toward phase separation. The
chemical potential decreases upon increasing doping, due to the significant
dependence of the bandwidth on the number of carriers. The reduction of the
electronic bandwidth by spin disorder leads to an enormously enhanced
thermopower which peaks near T_c, with a sign opposite that predicted by a
rigid band model.Comment: 4 pages, 2 encapsulated PostScript figure
Magnetic Anisotropy Variations and Non-Equilibrium Tunneling in a Cobalt Nanoparticle
We present detailed measurements of the discrete electron-tunneling level
spectrum within nanometer-scale cobalt particles as a function of magnetic
field and gate voltage, in this way probing individual quantum many-body
eigenstates inside ferromagnetic samples. Variations among the observed levels
indicate that different quantum states within one particle are subject to
different magnetic anisotropy energies. Gate-voltage studies demonstrate that
the low-energy tunneling spectrum is affected dramatically by the presence of
non-equilibrium spin excitations
Quantum critical behavior in disordered itinerant ferromagnets: Logarithmic corrections to scaling
The quantum critical behavior of disordered itinerant ferromagnets is
determined exactly by solving a recently developed effective field theory. It
is shown that there are logarithmic corrections to a previous calculation of
the critical behavior, and that the exact critical behavior coincides with that
found earlier for a phase transition of undetermined nature in disordered
interacting electron systems. This confirms a previous suggestion that the
unspecified transition should be identified with the ferromagnetic transition.
The behavior of the conductivity, the tunneling density of states, and the
phase and quasiparticle relaxation rates across the ferromagnetic transition is
also calculated.Comment: 15pp., REVTeX, 8 eps figs, final version as publishe
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