Interactions among plant layers in shrub-encroached Iberian dehesas and consequences for their persistance

PosterWe analyze the effect of shrub understory on the functioning and persistence of Iberian dehesas (grazed open woodlands). We study the effect of two contrasting, in terms of morphological traits and reproductive strategy, shrub species: Retama sphaerocarpa (a deep rooted shrub) and Citus ladanifer (a shallow rooted shrub), in order to account for specie-specific effects, on neighboring vegetation (tree and pasture). Pasture and tree rooting profile, soil resources availability (water and nutrients), tree and pasture production, tree physiological status and tree regeneration were assessed with and without the presence of shrubs. The results showed that the presence of shrubs deeply modify tree and pasture root systems. Trees growing either with Cistus or Retama exhibited a significantly deeper rooting profile than growing without competition, whereas herbaceous species showed the opposite trend, shifting most of their roots upwards to shallower soil horizons. Cistus appeared to be a great competitor for soil resources, what led to significantly lower tree leaf water potential, leaf gas exchange parameters, acorn production and growth. Cistus encroachment also reduced pasture yield by 68 to 98 %. Retama ameliorated top soil fertility and showed positive effect on soil moisture. Retama increased significantly pasture yield by 11 to 157 % and tree growth by 6 to 13 %, but had a neutral to negative effect on acorn yield. Both shrubs showed a similar positive effect on tree seedling emergence in spring and survivorship after summer. However, as seedling aged, this positive association strengthened with Retama and weakened over time with Cistus. To sum up, shrubs have the potential to modify the functioning and persistence of Mediterranean open oak woodlands. Thus, future management practices must bear in mind this specificity of effects and try to optimize the positive effect of shrubs without jeopardizing the productivity or functioning of the system

Evidence for the evolutionary steps leading to mecA-mediated ß-lactam resistance in staphylococci

The epidemiologically most important mechanism of antibiotic resistance in Staphylococcus aureus is associated with mecA–an acquired gene encoding an extra penicillin-binding protein (PBP2a) with low affinity to virtually all β-lactams. The introduction of mecA into the S. aureus chromosome has led to the emergence of methicillin-resistant S. aureus (MRSA) pandemics, responsible for high rates of mortality worldwide. Nonetheless, little is known regarding the origin and evolution of mecA. Different mecA homologues have been identified in species belonging to the Staphylococcus sciuri group representing the most primitive staphylococci. In this study we aimed to identify evolutionary steps linking these mecA precursors to the β-lactam resistance gene mecA and the resistance phenotype. We sequenced genomes of 106 S. sciuri, S. vitulinus and S. fleurettii strains and determined their oxacillin susceptibility profiles. Single-nucleotide polymorphism (SNP) analysis of the core genome was performed to assess the genetic relatedness of the isolates. Phylogenetic analysis of the mecA gene homologues and promoters was achieved through nucleotide/amino acid sequence alignments and mutation rates were estimated using a Bayesian analysis. Furthermore, the predicted structure of mecA homologue-encoded PBPs of oxacillin-susceptible and -resistant strains were compared. We showed for the first time that oxacillin resistance in the S. sciuri group has emerged multiple times and by a variety of different mechanisms. Development of resistance occurred through several steps including structural diversification of the non-binding domain of native PBPs; changes in the promoters of mecA homologues; acquisition of SCCmec and adaptation of the bacterial genetic background. Moreover, our results suggest that it was exposure to β-lactams in human-created environments that has driven evolution of native PBPs towards a resistance determinant. The evolution of β-lactam resistance in staphylococci highlights the numerous resources available to bacteria to adapt to the selective pressure of antibiotics

A low-noise CMOS front-end for TOF-PET

An analogue CMOS front-end for triggering and amplification of signals produced by a silicon photomultiplier (SiPM) coupled to a LYSO scintillator is proposed. The solution is intended for time-of-flight measurement in compact Positron Emission Tomography (TOF-PET) medical imaging equipments where excellent timing resolution is required (approximate to 100 ps). A CMOS 0.13 mu m technology was used to implement such front end, and the design includes preamplification, shaping, baseline holder and biasing circuitry, for a total silicon area of 500x90 mu m. Waveform sampling and time-over-threshold (ToT) techniques are under study and the front-end provides fast and shaped outputs for time and energy measurements. Post layout simulation results show that, for the trigger of a single photoelectron, the time jitter due to the pre-amplifier noise can be as low as 15 ps (FWHM), for a photodetector with a total capacitance of 70 pF. The very low input impedance of the pre-amplifier (approximate to 5 Omega) allows 1.8 ns of peaking time, at the cost of 10 mW of power consumption

Multi-contrast computed laminography at ANKA light source

X-ray computed laminography has been developed as a non-destructive imaging technique for inspecting laterally extended objects. Benefiting from a parallel-beam geometry, high photon flux of synchrotron sources and modern high-resolution detector systems, synchrotron radiation computed laminography (SRCL) results in a powerful three-dimensional microscopy technique. SRCL can be combined with different contrast modes, such as absorption, phase and dark-field contrasts, in order to provide complementary information for the same specimen. Here we show the development of SRCL at the TopoTomo beamline of the ANKA light source. A novel instrumentation design is reported and compared to the existing one. For this design, experimental results from different contrast modalities are shown

A low-noise CMOS front-end for TOF-PET

An analogue CMOS front-end for triggering and amplification of signals produced by a silicon photomultiplier (SiPM) coupled to a LYSO scintillator is proposed. The solution is intended for time-of-flight measurement in compact Positron Emission Tomography (TOF-PET) medical imaging equipments where excellent timing resolution is required (approximate to 100 ps). A CMOS 0.13 mu m technology was used to implement such front end, and the design includes preamplification, shaping, baseline holder and biasing circuitry, for a total silicon area of 500x90 mu m. Waveform sampling and time-over-threshold (ToT) techniques are under study and the front-end provides fast and shaped outputs for time and energy measurements. Post layout simulation results show that, for the trigger of a single photoelectron, the time jitter due to the pre-amplifier noise can be as low as 15 ps (FWHM), for a photodetector with a total capacitance of 70 pF. The very low input impedance of the pre-amplifier (approximate to 5 Omega) allows 1.8 ns of peaking time, at the cost of 10 mW of power consumption

A low-noise CMOS front-end for TOF-PET

An analogue CMOS front-end for triggering and amplification of signals produced by a silicon photomultiplier (SiPM) coupled to a LYSO scintillator is proposed. The solution is intended for time-of-flight measurement in compact Positron Emission Tomography (TOF-PET) medical imaging equipments where excellent timing resolution is required (approximate to 100 ps). A CMOS 0.13 mu m technology was used to implement such front end, and the design includes preamplification, shaping, baseline holder and biasing circuitry, for a total silicon area of 500x90 mu m. Waveform sampling and time-over-threshold (ToT) techniques are under study and the front-end provides fast and shaped outputs for time and energy measurements. Post layout simulation results show that, for the trigger of a single photoelectron, the time jitter due to the pre-amplifier noise can be as low as 15 ps (FWHM), for a photodetector with a total capacitance of 70 pF. The very low input impedance of the pre-amplifier (approximate to 5 Omega) allows 1.8 ns of peaking time, at the cost of 10 mW of power consumption

Three-dimensional imaging of vortex structure in a ferroelectric nanoparticle driven by an electric field

AbstractTopological defects of spontaneous polarization are extensively studied as templates for unique physical phenomena and in the design of reconfigurable electronic devices. Experimental investigations of the complex topologies of polarization have been limited to surface phenomena, which has restricted the probing of the dynamic volumetric domain morphology in operando. Here, we utilize Bragg coherent diffractive imaging of a single BaTiO3 nanoparticle in a composite polymer/ferroelectric capacitor to study the behavior of a three-dimensional vortex formed due to competing interactions involving ferroelectric domains. Our investigation of the structural phase transitions under the influence of an external electric field shows a mobile vortex core exhibiting a reversible hysteretic transformation path. We also study the toroidal moment of the vortex under the action of the field. Our results open avenues for the study of the structure and evolution of polar vortices and other topological structures in operando in functional materials under cross field configurations.</jats:p

Ferroelectric characterization of aligned barium titanate nanofibres

We report the synthesis, structural and ferroelectric characterization of continuous well-aligned nanofibres of barium titanate produced by the electrospinning technique. The fibres with average diameter of 150–400 nm consist of connected nanoparticles of BaTiO 3 stacked together to form the shape of a long filament. The tetragonal phase in the obtained nanofibres was revealed by the x-ray diffraction and Raman spectroscopy and has been also confirmed by the second harmonic generation (SHG) and piezoresponse force microscopy (PFM). The temperature dependence of the SHG in the vicinity of the paraelectric–ferroelectric phase transition suggests that barium titanate nanofibres are indeed ferroelectric with an apparent glass-like state caused by metastable polar nanoregions. The existence of domain structure and local switching studied by PFM present clear evidence of the polar phase at room temperature.Fundação para a Ciência e a Tecnologia (FCT