410 research outputs found
Spin-polarized tunneling spectroscopy in tunnel junctions with half-metallic electrodes
We have studied the magnetoresistance (TMR) of tunnel junctions with
electrodes of La2/3Sr1/3MnO3 and we show how the variation of the conductance
and TMR with the bias voltage can be exploited to obtain a precise information
on the spin and energy dependence of the density of states. Our analysis leads
to a quantitative description of the band structure of La2/3Sr1/3MnO3 and
allows the determination of the gap delta between the Fermi level and the
bottom of the t2g minority spin band, in good agreement with data from
spin-polarized inverse photoemission experiments. This shows the potential of
magnetic tunnel junctions with half-metallic electrodes for spin-resolved
spectroscopic studies.Comment: To appear in Physical Review Letter
Optical spin injection and spin lifetime in Ge heterostructures
We demonstrate optical orientation in Ge/SiGe quantum wells and study their
spin properties. The ultrafast electron transfer from the center of the
Brillouin zone to its edge allows us to achieve high spin-polarization
efficiencies and to resolve the spin dynamics of holes and electrons. The
circular polarization degree of the direct-gap photoluminescence exceeds the
theoretical bulk limit, yielding ~37% and ~85% for transitions with heavy and
light holes states, respectively. The spin lifetime of holes at the top of the
valence band is found to be ~0.5 ps and it is governed by transitions between
heavy and light hole states. Electrons at the bottom of the conduction band, on
the other hand, have a spin lifetime that exceeds 5 ns below 150 K. Theoretical
analysis of the electrons spin relaxation indicates that phonon-induced
intervalley scattering dictates the spin lifetime.Comment: 5 pages, 3 figure
Bulk Cr tips for scanning tunneling microscopy and spin-polarized scanning tunneling microscopy
A simple, reliable method for preparation of bulk Cr tips for Scanning
Tunneling Microscopy (STM) is proposed and its potentialities in performing
high-quality and high-resolution STM and Spin Polarized-STM (SP-STM) are
investigated. Cr tips show atomic resolution on ordered surfaces. Contrary to
what happens with conventional W tips, rest atoms of the Si(111)-7x7
reconstruction can be routinely observed, probably due to a different
electronic structure of the tip apex. SP-STM measurements of the Cr(001)
surface showing magnetic contrast are reported. Our results reveal that the
peculiar properties of these tips can be suited in a number of STM experimental
situations
Porphyrin central metal ion driven self-assembling in heterogeneous ZnTPP – CoTPP films grown on Fe(0 0 1)-p(1 × 1)O
Surfactant-like Effect and Dissolution of Ultrathin Fe Films on Ag(001)
The phase immiscibility and the excellent matching between Ag(001) and
Fe(001) unit cells (mismatch 0.8 %) make Fe/Ag growth attractive in the field
of low dimensionality magnetic systems. Intermixing could be drastically
limited at deposition temperatures as low as 140-150 K. The film structural
evolution induced by post-growth annealing presents many interesting aspects
involving activated atomic exchange processes and affecting magnetic
properties. Previous experiments, of He and low energy ion scattering on films
deposited at 150 K, indicated the formation of a segregated Ag layer upon
annealing at 550 K. Higher temperatures led to the embedding of Fe into the Ag
matrix. In those experiments, information on sub-surface layers was attained by
techniques mainly sensitive to the topmost layer. Here, systematic PED
measurements, providing chemical selectivity and structural information for a
depth of several layers, have been accompanied with a few XRD rod scans,
yielding a better sensitivity to the buried interface and to the film long
range order. The results of this paper allow a comparison with recent models
enlightening the dissolution paths of an ultra thin metal film into a different
metal, when both subsurface migration of the deposit and phase separation
between substrate and deposit are favoured. The occurrence of a surfactant-like
stage, in which a single layer of Ag covers the Fe film is demonstrated for
films of 4-6 ML heated at 500-550 K. Evidence of a stage characterized by the
formation of two Ag capping layers is also reported. As the annealing
temperature was increased beyond 700 K, the surface layers closely resembled
the structure of bare Ag(001) with the residual presence of subsurface Fe
aggregates.Comment: 4 pages, 3 figure
ESPACIOS, TRADICIONES Y CAMBIOS EN CONCHUCOS. Ecos desde la Escuela de etnografía del Proyecto “Antonio Raimondi”, Ancash Perú
Este volumen nace con dos finalidades precisas. La primera, dar a conocer los trabajos de investigación etnográfica que un grupo de nueve estudiantes de la Universidad de Bologna (Italia) y otro de la Pontificia Universidad Católica del Perú han desarrollado en la provincia de Huari, Ancash, Perú, durante seis años, entre 2003 y 2008 en el marco del Proyecto Arqueológico y Antropológico “Antonio Raimondi”. La segunda finalidad es realizar la difusión de las únicas miradas etnográficas que hasta hoy se han producido sobre la región Conchucos.
Otro objetivo, más teórico y más implícito, es desplegar a lo largo del camino de la lectura de los casos etnográficos, una visión processual y dinamista de la escritura etnográfica y de la especulación antropológica, procedente de una manera precisa de hacer trabajo de campo. Los artículos aquí propuestos presentan, mediante varios estilos y diferentes acercamientos, una realidad sociocultural en movimiento, en constante cambio. Construyendo cuadros de varios aspectos sociales, políticos y culturales de la provincia de Huari, los autores delinean un escenario en proceso en el cual diferentes actores, ámbitos y dinámicas socioculturales se interrelacionan, participando de maneras diferents en la transformación
Early detection of poor glycemic control in patients with diabetes mellitus in sub-Saharan Africa: a cohort study in Mozambique
Introduction: WHO estimates 422 million cases of diabetes mellitus worldwide. Mozambique has the second-highest mortality related to DM in the African region. Objectives of the present study are to provide data about a DM care service in Mozambique and to evaluate early outcomes of treatment. Methods: The new patients diagnosed with DM in a two-years period in a health centre in Maputo (Mozambique) were included in a retrospective cohort study. Fasting blood glucose (FBG), waist circumference (WC) and BMI were collected at baseline and after three months. Results: 188 patients were enrolled. Median BMI, WC and FBG at baseline were respectively 28 kg/m2(Inter Quartile Range [IQR]23.4-31.8), 98cm (IQR 87-105) and 209mg/dL (IQR 143-295). A non-pharmacological intervention was prescribed for six patients, while 182 patients received metformin 500 mg b.i.d. FBG was significantly reduced at control (226[±103.7]mg/dL vs 186[±93.2]mg/dL, p<0.000); however, glycemic control was reached in 74 patients (39.4%); not controlled patients changed regimen. Elderly patients had a higher glycemic control (adjusted Odds Ratio 2.50, 95% CI 1.11-5.06, p=0.002). Conclusion: Strategies for early detection of scarce glycemic control are feasible in Mozambique and could lead to prompt regimen switch; an invasive therapeutic approach could be preferable in selected cases to achieve control
- …