282 research outputs found
Structural and electrical characterization of hybrid metal-polypyrrole nanowires
We present here the synthesis and structural characterization of hybrid
Au-polypyrrole-Au and Pt- polypyrrole-Au nanowires together with a study of
their electrical properties from room-temperature down to very low temperature.
A careful characterization of the metal-polymer interfaces by trans- mission
electron microscopy revealed that the structure and mechanical strength of
bottom and upper interfaces are very different. Variable temperature electrical
transport measurements were performed on both multiple nanowires - contained
within the polycarbonate template - and single nanowires. Our data show that
the three-dimensional Mott variable-range-hopping model provides a complete
framework for the understanding of transport in PPy nanowires, including
non-linear current-voltage characteristics and magnetotransport at low
temperatures.Comment: Phys. Rev. B Vol. 76 Issue 11 (2007
Maximizing rehabilitation outcomes in geriatric hip fracture patients: the impact of surgical variables
Background and aim: Hip fracture is a major traumatic event with high mortality and disability rate. Its management in the acute setting and in the rehabilitation process is highly debated. This study evaluates the possible determinants of hip fracture rehabilitation outcome, among which surgical intervention type, weight-bearing status and hospitalization length Methods: The data of 738 hip fracture patients, who completed rehabilitation process in our centre, were collected and patients' functional abilities at the time of admission and discharge were analysed. Results: It has been observed that functional recovery depends on several factors: the type of surgery, the post-operative course and related complications, the hospitalisation time, the surgeon's techniques and expertise and the Orthopaedics centre where the operation is performed. Conclusions: In conclusion, data integration in perspective of an individualised rehabilitation program appears crucial for the functional recovery of the hip fracture patient
Collective Autoionization in Multiply-Excited Systems: A novel ionization process observed in Helium Nanodroplets
Free electron lasers (FELs) offer the unprecedented capability to study
reaction dynamics and image the structure of complex systems. When multiple
photons are absorbed in complex systems, a plasma-like state is formed where
many atoms are ionized on a femtosecond timescale. If multiphoton absorption is
resonantly-enhanced, the system becomes electronically-excited prior to plasma
formation, with subsequent decay paths which have been scarcely investigated to
date. Here, we show using helium nanodroplets as an example that these systems
can decay by a new type of process, named collective autoionization. In
addition, we show that this process is surprisingly efficient, leading to ion
abundances much greater than that of direct single-photon ionization. This
novel collective ionization process is expected to be important in many other
complex systems, e.g. macromolecules and nanoparticles, exposed to high
intensity radiation fields
Pinning of quantized vortices in helium drop by dopant atoms and molecules
Using a density functional method, we investigate the properties of liquid
4He droplets doped with atoms (Ne and Xe) and molecules (SF_6 and HCN). We
consider the case of droplets having a quantized vortex pinned to the dopant. A
liquid drop formula is proposed that accurately describes the total energy of
the complex and allows one to extrapolate the density functional results to
large N. For a given impurity, we find that the formation of a
dopant+vortex+4He_N complex is energetically favored below a critical size
N_cr. Our result support the possibility to observe quantized vortices in
helium droplets by means of spectroscopic techniques.Comment: Typeset using Revtex, 3 pages and 5 figures (4 Postscript, 1 jpeg
Real-time dynamics of the formation of hydrated electrons upon irradiation of water clusters with extreme ultraviolet light
Free electrons in a polar liquid can form a bound state via interaction with the molecular environment. This so-called hydrated electron state in water is of fundamental importance e.g.~in cellular biology or radiation chemistry. Hydrated electrons are highly reactive radicals that can either directly interact with DNA or enzymes, or form highly excited hydrogen (H∗) after being captured by protons. Here, we investigate the formation of the hydrated electron in real-time employing XUV femtosecond pulses from a free electron laser, in this way observing the initial steps of the hydration process. Using time-resolved photoelectron spectroscopy we find formation timescales in the low picosecond range and resolve the prominent dynamics of forming excited hydrogen states
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
Evolution and ion kinetics of a XUV-induced nanoplasma in ammonia clusters
High-intensity extreme ultraviolet (XUV) pulses from a free-electron laser
can be used to create a nanoplasma in clusters. In Ref. [Michiels et al. PCCP,
2020; 22: 7828-7834] we investigated the formation of excited states in an
XUV-induced nanoplasma in ammonia clusters. In the present article we expand
our previous study with a detailed analysis of the nanoplasma evolution and ion
kinetics. We use a time-delayed UV laser as probe to ionize excited states of H
and H in the XUV-induced plasma. Employing covariance mapping techniques,
we show that the correlated emission of protons plays an important role in the
plasma dynamics. The time-dependent kinetic energy of the ions created by the
probe laser is measured, revealing the charge neutralization of the cluster
happens on a sub-picosecond timescale. Furthermore, we observe ro-vibrationally
excited molecular hydrogen ions H being ejected from the clusters. We
rationalize our data through a qualitative model of a finite-size non-thermal
plasma
Two-photon resonant excitation of interatomic coulombic decay in neon dimers
The recent availability of intense and ultrashort extreme ultraviolet sources opens up the possibility of investigating ultrafast electronic relaxation processes in matter in an unprecedented regime. In this work we report on the observation of two-photon excitation of interatomic Coulombic decay (ICD) in neon dimers using the tunable intense pulses delivered by the free electron laser FERMI. The unique characteristics of FERMI (narrow bandwidth, spectral stability, and tunability) allow one to resonantly excite specific ionization pathways and to observe a clear signature of the ICD mechanism in the ratio of the ion yield created by Coulomb explosion. The present experimental results are explained by ab initio electronic structure and nuclear dynamics calculations
Stability of Terrestrial Planets in the Habitable Zone of Gl 777 A, HD 72659, Gl 614, 47 Uma and HD 4208
We have undertaken a thorough dynamical investigation of five extrasolar
planetary systems using extensive numerical experiments. The systems Gl 777 A,
HD 72659, Gl 614, 47 Uma and HD 4208 were examined concerning the question of
whether they could host terrestrial like planets in their habitable zones
(=HZ). First we investigated the mean motion resonances between fictitious
terrestrial planets and the existing gas giants in these five extrasolar
systems. Then a fine grid of initial conditions for a potential terrestrial
planet within the HZ was chosen for each system, from which the stability of
orbits was then assessed by direct integrations over a time interval of 1
million years. The computations were carried out using a Lie-series integration
method with an adaptive step size control. This integration method achieves
machine precision accuracy in a highly efficient and robust way, requiring no
special adjustments when the orbits have large eccentricities. The stability of
orbits was examined with a determination of the Renyi entropy, estimated from
recurrence plots, and with a more straight forward method based on the maximum
eccentricity achieved by the planet over the 1 million year integration.
Additionally, the eccentricity is an indication of the habitability of a
terrestrial planet in the HZ; any value of e>0.2 produces a significant
temperature difference on a planet's surface between apoapse and periapse. The
results for possible stable orbits for terrestrial planets in habitable zones
for the five systems are summarized as follows: for Gl 777 A nearly the entire
HZ is stable, for 47 Uma, HD 72659 and HD 4208 terrestrial planets can survive
for a sufficiently long time, while for Gl 614 our results exclude terrestrial
planets moving in stable orbits within the HZ.Comment: 14 pages, 18 figures submitted to A&
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