324 research outputs found
Charging of highly resistive granular metal films
We have used the Scanning Kelvin probe microscopy technique to monitor the
charging process of highly resistive granular thin films. The sample is
connected to two leads and is separated by an insulator layer from a gate
electrode. When a gate voltage is applied, charges enter from the leads and
rearrange across the sample. We find very slow processes with characteristic
charging times exponentially distributed over a wide range of values, resulting
in a logarithmic relaxation to equilibrium. After the gate voltage has been
switched off, the system again relaxes logarithmically slowly to the new
equilibrium. The results cannot be explained with diffusion models, but most of
them can be understood with a hopping percolation model, in which the
localization length is shorter than the typical site separation. The technique
is very promising for the study of slow phenomena in highly resistive systems
and will be able to estimate the conductance of these systems when direct
macroscopic measurement techniques are not sensitive enough.Comment: 8 pages, 7 figure
New approaches on the study of the psychometric properties of the STAI
The main purpose of this study was to analyze the psychometric properties of the State-Trait Anxiety Inventory (STAI1). Previous studies have indicated different factor solutions. Nevertheless, there is still a lack of consensus about the best dimensional model of STAI scores.The sample consisted of 417 participants, composed of 387 (29.71% male) healthy participants (comparison group: M=35.5 years; SD=8.40), and 30 (36.66% male) patient (clinical group M=35.8 years; SD=12.94).The internal consistency evaluated through Ordinal Alpha was good, 0.98 and 0.94 in the non-clinical and the clinical samples, respectively. Test-retest reliability (two weeks) for Total Score was 0.81 for the non-clinical subsample, and 0.93 for the clinical subsample. Confirmatory factor analyses supported both a four factor model and bifactor model. Also, STAI scores showed statistically significant correlations with Burns Anxiety Inventory (Burns-A) scores. Furthermore, results showed statistically significant differences in the mean scores of the STAI between the clinical and the non-clinical subsamples.The psychometric properties of the STAI were adequate. The present study contributes to better understand the STAI structure through the comparison of new approaches in the study of the STAI internal structure. The results found may contribute in the efforts to improve the evaluation and identification of anxiety symptoms and disorders
Organic production of native potato landrace "pintaboca" (Solanum stenotomum Juz. & Bukasov) in Bolivia:experimenting planting times and cultivation strategies
Acclimation to short-term low temperatures in two Eucalyptus globulus clones with contrasting drought resistance
We tested the hypothesis that Eucalyptus
globulus Labill. genotypes that are more resistant to dry
environments might also exhibit higher cold tolerances
than drought-sensitive plants. The effect of low temperatures
was evaluated in acclimated and unacclimated
ramets of a drought-resistant clone (CN5) and a
drought-sensitive clone (ST51) of E. globulus. We
studied the plants’ response via leaf gas exchanges, leaf
water and osmotic potentials, concentrations of soluble
sugars, several antioxidant enzymes and leaf electrolyte
leakage. Progressively lowering air temperatures (from
24/16 to 10/ 2 C, day/night) led to acclimation of both
clones. Acclimated ramets exhibited higher photosynthetic
rates, stomatal conductances and lower membrane
relative injuries when compared to unacclimated ramets.
Moreover, low temperatures led to significant increases
of soluble sugars and antioxidant enzymes activity
(glutathione reductase, ascorbate peroxidase and superoxide
dismutases) of both clones in comparison to plants
grown at control temperature (24/16 C). On the other
hand, none of the clones, either acclimated or not,
exhibited signs of photoinhibition under low temperatures
and moderate light. The main differences in the
responses to low temperatures between the two clones
resulted mainly from differences in carbon metabolism,
including a higher accumulation of soluble sugars in the
drought-resistant clone CN5 as well as a higher capacity
for osmotic regulation, as compared to the droughtsensitive
clone ST51. Although membrane injury data
suggested that both clones had the same inherent
freezing tolerance before and after cold acclimation,
the results also support the hypothesis that the droughtresistant
clone had a greater cold tolerance at intermediate
levels of acclimation than the drought-sensitive
clone. A higher capacity to acclimate in a short period
can allow a clone to maintain an undamaged leaf surface
area along sudden frost events, increasing growt
First full-beam PET acquisitions in proton therapy with a modular dual-head dedicated system
During particle therapy irradiation, positron emitters with half-lives ranging from 2 to 20 min are generated from nuclear processes. The half-lives are such that it is possible either to detect the positron signal in the treatment room using an in-beam positron emission tomography (PET) system, right after the irradiation, or to quickly transfer the patient to a close PET/CT scanner. Since the activity distribution is spatially correlated with the dose, it is possible to use PET imaging as an indirect method to assure the quality of the dose delivery. In this work, we present a new dedicated PET system able to operate in-beam. The PET apparatus consists in two 10 cm × 10 cm detector heads. Each detector is composed of four scintillating matrices of 23 × 23 LYSO crystals. The crystal size is 1.9 mm × 1.9 mm × 16 mm. Each scintillation matrix is read out independently with a modularized acquisition system. The distance between the two opposing detector heads was set to 20 cm. The system has very low dead time per detector area and a 3 ns coincidence window, which is capable to sustain high single count rates and to keep the random counts relatively low. This allows a new full-beam monitoring modality that includes data acquisition also while the beam is on. The PET system was tested during the irradiation at the CATANA (INFN, Catania, Italy) cyclotron-based proton therapy facility. Four acquisitions with different doses and dose rates were analysed. In all cases the random to total coincidences ratio was equal or less than 25%. For each measurement we estimated the accuracy and precision of the activity range on a set of voxel lines within an irradiated PMMA phantom. Results show that the inclusion of data acquired during the irradiation, referred to as beam-on data, improves both the precision and accuracy of the range measurement with respect to data acquired only after irradiation. Beam-on data alone are enough to give precisions better than 1 mm when at least 5 Gy are delivered
Quantum and classical localisation, the spin quantum Hall effect and generalisations
We consider network models for localisation problems belonging to symmetry
class C. This symmetry class arises in a description of the dynamics of
quasiparticles for disordered spin-singlet superconductors which have a
Bogoliubov - de Gennes Hamiltonian that is invariant under spin rotations but
not under time-reversal. Our models include but also generalise the one studied
previously in the context of the spin quantum Hall effect. For these systems we
express the disorder-averaged conductance and density of states in terms of
sums over certain classical random walks, which are self-avoiding and have
attractive interactions. A transition between localised and extended phases of
the quantum system maps in this way to a similar transition for the classical
walks. In the case of the spin quantum Hall effect, the classical walks are the
hulls of percolation clusters, and our approach provides an alternative
derivation of a mapping first established by Gruzberg, Read and Ludwig, Phys.
Rev. Lett. 82, 4254 (1999).Comment: 11 pages, 5 figure
Safety and efficacy of a feed additive consisting of a dry grape extract (Nor-Grape® α) for all avian species (Nor-Feed S.A.S.)
Following a request from the European Commission, EFSA was asked to deliver a scientific opinion on the safety and efficacy of a feed additive consisting of a dry grape extract (Nor-Grape® α) as a zootechnical feed additive, functional group physiological condition stabilisers - increase antioxidant defences, for all avian species. The additive is already authorised for use as a feed flavouring for all animal species, except dogs. The FEEDAP Panel concluded that the additive is safe for all avian species. The use of the additive in animal nutrition is of no concern for consumer safety. Based on the data submitted, the FEEDAP Panel could not conclude on the potential of the additive to be a skin or eye irritant or a dermal or respiratory sensitiser. However, the Panel considered that exposure through inhalation is likely. The use of the feed additive is considered safe for the environment. The Panel was unable to conclude on the potential of the additive to be efficacious under the proposed conditions of use
Efficacy and safety of tacrolimus compared with ciclosporin A in renal transplantation: three-year observational results
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