769 research outputs found
Scanning Gate Spectroscopy on Nanoclusters
A gated probe for scanning tunnelling microscopy (STM) has been developed.
The probe extends normal STM operations by means of an additional electrode
fabricated next to the tunnelling tip. The extra electrode does not make
contact with the sample and can be used as a gate. We report on the recipe used
for fabricating the tunnelling tip and the gate electrode on a silicon nitride
cantilever. We demonstrate the functioning of the scanning gate probes by
performing single-electron tunnelling spectroscopy on 20-nm gold clusters for
different gate voltages.Comment: 3 pages, 4 figure
Effects of long term application of compost and poultry manure on soil quality of citrus orchards in Southern Italy.
A six-year study was carried out in an organically managed orange orchard located in Sicily (Southern Italy) to assess the effect of compost and organic fertilizers utilisation on soil quality. Adopting a randomized-block experimental design with three replicates, four treatments were carried out. In treatments 1 and 2, two different composts (C1 from distillery by products and C2 from livestock wastes) were applied. The plots of treatment 3 were fertilized using dried poultry manure. The control treatment was fertilized with mineral/synthetic fertilizers. In order to verify the hypothesis that composts and organic fertilizers improve soil fertility, soil quality was evaluated by selecting dynamic soil parameters, as indicators linked to C and N cycles. Total organic C, total N, C/N ratio, humified fraction, isoelectric focusing (IEF) of extracted organic matter, microbial biomass C, potentially mineralisable N under anaerobic conditions, potenzially mineralizable C, C mineralization quotient and metabolic quotient were determined for each sample. Furthermore, the Comunity level Physiological Profile (by Biolog tecnique) was defined, calculating derived functional biodiversity and versatility indexes. Parameters related to IEF and potentially mineralizable C showed significant differences among the treatments. Moreover, total C, total N and humification parameters tended to increase, while no differences were observed in biodiversity indexes. On these findings, it was concluded that composts and poultry manure only weakly affected soil properties, though they increased soil nutritive elements potentially available to crops
Welfare Quality® project: from scientific research to on farm assessment of animal welfare
Welfare Quality® is the acronym of the European research project "Integration of ani- mal welfare in the food quality chain: from public concern to improved welfare and transparent quality". This European project is focused on the integration of animal welfare in the food quality chain. Italian researchers from University of Milan, Naples, Padua, Parma and Pisa are involved in different tasks of this project. The second sub-project of Welfare Quality® aims to develop assessment systems to evaluate and monitor the quality of animal welfare on farms or at slaughter in 7 livestock species. Researchersof Researchers of the Department of Animal Science of the University of Milan worked together other European partners to find and develop the most suitable animal-based measures for dairy and beef cattle
Large Magnetoresistance in Co/Ni/Co Ferromagnetic Single Electron Transistors
We report on magnetotransport investigations of nano-scaled ferromagnetic
Co/Ni/Co single electron transistors. As a result of reduced size, the devices
exhibit single electron transistor characteristics at 4.2K. Magnetotransport
measurements carried out at 1.8K reveal tunneling magnetoresistance (TMR)
traces with negative coercive fields, which we interpret in terms of a
switching mechanism driven by the shape anisotropy of the central wire-like Ni
island. A large TMR of about 18% is observed within a finite source-drain bias
regime. The TMR decreases rapidly with increasing bias, which we tentatively
attribute to excitation of magnons in the central island.Comment: 12 pages (including 4 figures). Accepted for publishing on AP
Electron-magnon coupling and nonlinear tunneling transport in magnetic nanoparticles
We present a theory of single-electron tunneling transport through a
ferromagnetic nanoparticle in which particle-hole excitations are coupled to
spin collective modes. The model employed to describe the interaction between
quasiparticles and collective excitations captures the salient features of a
recent microscopic study. Our analysis of nonlinear quantum transport in the
regime of weak coupling to the external electrodes is based on a rate-equation
formalism for the nonequilibrium occupation probability of the nanoparticle
many-body states. For strong electron-boson coupling, we find that the
tunneling conductance as a function of bias voltage is characterized by a large
and dense set of resonances. Their magnetic field dependence in the large-field
regime is linear, with slopes of the same sign. Both features are in agreement
with recent tunneling experiments.Comment: 4 pages, 2 figure
Gamma–ray spectroscopy with single–carrier collection in high–resistivity semiconductors
With the standard plane–parallel configuration of semiconductor detectors, good γ–ray spectra can only be obtained when both electrons and holes are completely collected. We show by calculations (and experiments) that with contacts of hemispherical configuration one can obtain γ–ray spectra of adequate resolution and with signal heights of nearly full amplitude even when only one type of carrier is collected. Experiments with CdTe detectors for which the µτ product for electrons is about 10^(3) times that of the holes confirm these calculations. The adoption of hemispherical contacts thus widens the range of high–resistivity semiconductors potentially acceptable for γ–ray detection at room temperature
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Hemojuvelin and bone morphogenetic protein (BMP) signaling in iron homeostasis
Mutations in hemojuvelin (HJV) are the most common cause of the juvenile-onset form of the iron overload disorder hereditary hemochromatosis. The discovery that HJV functions as a co-receptor for the bone morphogenetic protein (BMP) family of signaling molecules helped to identify this signaling pathway as a central regulator of the key iron hormone hepcidin in the control of systemic iron homeostasis. This review highlights recent work uncovering the mechanism of action of HJV and the BMP-SMAD signaling pathway in regulating hepcidin expression in the liver, as well as additional studies investigating possible extra-hepatic functions of HJV. This review also explores the interaction between HJV, the BMP-SMAD signaling pathway and other regulators of hepcidin expression in systemic iron balance
New Class of Random Matrix Ensembles with Multifractal Eigenvectors
Three recently suggested random matrix ensembles (RME) are linked together by
an exact mapping and plausible conjections. Since it is known that in one of
these ensembles the eigenvector statistics is multifractal, we argue that all
three ensembles belong to a new class of critical RME with multifractal
eigenfunction statistics and a universal critical spectral statitics. The
generic form of the two-level correlation function for weak and extremely
strong multifractality is suggested. Applications to the spectral statistics at
the Anderson transition and for certain systems on the border of chaos and
integrability is discussed.Comment: 4 pages RevTeX, resubmitte
Probing Spin Accumulation in Ni/Au/Ni Single-Electron Transistors with Efficient Spin Injection and Detection Electrodes
We have investigated spin accumulation in Ni/Au/Ni single-electron
transistors assembled by atomic force microscopy. The fabrication technique is
unique in that unconventional hybrid devices can be realized with unprecedented
control, including real-time tunable tunnel resistances. A grid of Au discs, 30
nm in diameter and 30 nm thick, is prepared on a SiO2 surface by conventional
e-beam writing. Subsequently, 30 nm thick ferromagnetic Ni source, drain and
side-gate electrodes are formed in similar process steps. The width and length
of the source and drain electrodes were different to exhibit different coercive
switching fields. Tunnel barriers of NiO are realized by sequential Ar and O2
plasma treatment. Using an atomic force microscope with specially designed
software, a single non-magnetic Au nanodisc is positioned into the 25 nm gap
between the source and drain electrodes. The resistance of the device is
monitored in real-time while the Au disc is manipulated step-by-step with
Angstrom-level precision. Transport measurements in magnetic field at 1.7 K
reveal no clear spin accumulation in the device, which can be attributed to
fast spin relaxation in the Au disc. From numerical simulations using the
rate-equation approach of orthodox Coulomb blockade theory, we can put an upper
bound of a few ns on the spin-relaxation time for electrons in the Au disc. To
confirm the magnetic switching characteristics and spin injection efficiency of
the Ni electrodes, we fabricated a test structure consisting of a Ni/NiO/Ni
magnetic tunnel junction with asymmetric dimensions of the electrodes similar
to those of the SETs. Magnetoresistance measurements on the test device
exhibited clear signs of magnetic reversal and a maximum TMR of 10%, from which
we deduced a spin-polarization of about 22% in the Ni electrodes.Comment: 10 pages, 5 figure
Theory of tunneling spectroscopy in a Mn_12 single-electron transistor by density-functional theory methods
We consider tunneling transport through a Mn12 molecular magnet using spin density functional theory. A tractable methodology for constructing many-body wave functions from Kohn-Sham orbitals allows for the determination of spin-ependent matrix elements for use in transport calculations. The tunneling
conductance at finite bias is characterized by peaks representing transitions between spin multiplets, separated by an energy on the order of the magnetic anisotropy. The energy splitting of the spin multiplets and the spatial part of their many-body wave functions, describing the orbital degrees of freedom of the
excess charge, strongly affect the electronic transport, and can lead to negative differential conductance
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