594 research outputs found
Strain stiffening of peripheral nerves subjected to longitudinal extensions in vitro
The mechanical response of peripheral nerves is crucial to understand their physiological and pathological conditions. However, their response to external mechanical solicitations is still partially unclear, since peripheral nerves could behave in a quite complex way. In particular, nerves react to longitudinal strains increasing their stiffness to keep axons integrity and to preserve endoneural structures from overstretch. In this work, the strain stiffening of peripheral nerves was investigated in vitro through a recently introduced computational framework, which is able to theoretically reproduce the experimental behaviour of excised tibial and sciatic nerves. The evolution and the variation of the tangent modulus of tibial and sciatic nerve specimens were quantitatively investigated and compared to explore how stretched peripheral nerves change their instantaneous stiffness
The free-electron laser harmonic cascade
Free-electron laser (FEL) devices based on a sequence of amplifiers with a harmonic relation between the resonant frequencies of each section have been proposed to extend to shorter wavelengths the FEL operating range. Because of the practical limit on the tunability of undulator magnets, the e-beam energy still represents the main constraint on the shortest reachable wavelength of the cascade. In this paper, we propose a scheme where the undulators of the cascade are tuned at different, not-harmonic, fundamental frequencies having instead one of the higher order harmonics at a common frequency. A short and intense seed pulse in such a system creates a superradiant pulse which harmonically seeds the following undulator at the common multiple frequency. The microbunching at the higher harmonic in the second undulator is enhanced by the modulation of the previous undulator so that lasing at shorter wavelengths may be obtained with a relatively low-energy electron beam
Seeded x-ray free-electron laser generating radiation with laser statistical properties
The invention of optical lasers led to a revolution in the field of optics
and even to the creation of completely new fields of research such as quantum
optics. The reason was their unique statistical and coherence properties. The
newly emerging, short-wavelength free-electron lasers (FELs) are sources of
very bright coherent extreme-ultraviolet (XUV) and x-ray radiation with pulse
durations on the order of femtoseconds, and are presently considered to be
laser sources at these energies. Most existing FELs are highly spatially
coherent but in spite of their name, they behave statistically as chaotic
sources. Here, we demonstrate experimentally, by combining Hanbury Brown and
Twiss (HBT) interferometry with spectral measurements that the seeded XUV FERMI
FEL-2 source does indeed behave statistically as a laser. The first steps have
been taken towards exploiting the first-order coherence of FELs, and the
present work opens the way to quantum optics experiments that strongly rely on
high-order statistical properties of the radiation.Comment: 24 pages, 10 figures, 37 reference
Observation and Control of Laser-Enabled Auger Decay
Single photon laser enabled Auger decay (spLEAD) has been redicted
theoretically [Phys. Rev. Lett. 111, 083004 (2013)] and here we report its
first experimental observation in neon. Using coherent, bichromatic
free-electron laser pulses, we have detected the process and coherently
controlled the angular distribution of the emitted electrons by varying the
phase difference between the two laser fields. Since spLEAD is highly sensitive
to electron correlation, this is a promising method for probing both
correlation and ultrafast hole migration in more complex systems.Comment: 5 pages, 3 figure
Effects of systemic glucocorticosteroids on peripheral neutrophil functions in asthmatic subjects: an ex vivo study
In 21 asthmatic subjects, several functions of isolated peripheral neutrophils (chemokinesis and chemotaxis toward 10% E. coli; superoxide anion generation after PMA; leukotriene B4 (LTB4) release from whole blood and isolated neutrophtls, before and after different stimuli) were evaluated during an acute exacerbation of asthma, and after 14 – 54 days of treatment with systemic glucocorticosteroids (GCS). During acute exacerbation, superoxide anion generation was higher in asthmatics than in eleven normal subjects (39.2 ± 14.1 vs. 25.2 ± 7.3 nmol, p < 0.05); there was a significant correlation between FEV1 (% of predicted) and neutrophil chemotaxis (r = −0.52, p = 0.04). After treatment, there was no significant change in all neutrophil functions, except for a decrease in neutrophil chemotaxis in subjects who showed an FEV1 increase > 20% after GCS treatment (from 131 ± 18 to 117 ± 21 μm, p = 0.005). Chemokinesis sicantly decreased in all subjects, and the changes significantly correlated with an arbitrary score of the total administered dose of GCS (r = 0.57, p < 0.05). These data suggest that neutrophil activation plays a minor role in asthma, and that treatment with GCS is not able to modify most functions of peripheral neutrophils in asthmatic subjects; chemotaxis seems to be related only to the severity of the asthma and it could reflect the improvement of the disease
{\AA}ngstr\"om-resolved Interfacial Structure in Organic-Inorganic Junctions
Charge transport processes at interfaces which are governed by complex
interfacial electronic structure play a crucial role in catalytic reactions,
energy storage, photovoltaics, and many biological processes. Here, the first
soft X-ray second harmonic generation (SXR-SHG) interfacial spectrum of a
buried interface (boron/Parylene-N) is reported. SXR-SHG shows distinct
spectral features that are not observed in X-ray absorption spectra,
demonstrating its extraordinary interfacial sensitivity. Comparison to
electronic structure calculations indicates a boron-organic separation distance
of 1.9 {\AA}, wherein changes as small as 0.1 {\AA} result in easily detectable
SXR-SHG spectral shifts (ca. 100s of meV). As SXR-SHG is inherently ultrafast
and sensitive to individual atomic layers, it creates the possibility to study
a variety of interfacial processes, e.g. catalysis, with ultrafast time
resolution and bond specificity.Comment: 19 page
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