132 research outputs found
Self-Assembled Ruthenium(II)Porphyrin-Aluminium(III)Porphyrin-Fullerene Triad for Long-Lived Photoinduced Charge Separation
A very efficient metal-mediated strategy led, in a single step, to a quantitative construction of a new three-component
multichromophoric system containing one fullerene monoadduct, one aluminium(III) monopyridylporphyrin, and one
ruthenium(II) tetraphenylporphyrin. The Al(III) monopyridylporphyrin component plays the pivotal role in directing the correct
self-assembly process and behaves as the antenna unit for the photoinduced processes of interest. A detailed study of the
photophysical behavior of the triad was carried out in different solvents (CH2Cl2, THF, and toluene) by stationary and timeresolved
emission and absorption spectroscopy in the pico- and nanosecond time domains. Following excitation of the Alporphyrin,
the strong fluorescence typical of this unit was strongly quenched. The time-resolved absorption experiments
provided evidence for the occurrence of stepwise photoinduced electron and hole transfer processes, leading to a chargeseparated
state with reduced fullerene acceptor and oxidized ruthenium porphyrin donor. The time constant values
measured in CH2Cl2 for the formation of charge-separated state Ru-Al+-C60 - (10 ps), the charge shift process (Ru-Al+-C60
- \u2192 Ru+-Al-C60 -), where a hole is transferred from Al-based to Ru-based unit (75 ps), and the charge recombination
process to ground state (>5 ns), can be rationalized within the Marcus theory. Although the charge-separating
performance of this triad is not outstanding, this study demonstrates that, using the self-assembling strategy, improvements
can be obtained by appropriate chemical modifications of the individual molecular components
Radiation Problem in Transplanckian Scattering
We investigate hard radiation emission in small-angle transplanckian
scattering. We show how to reduce this problem to a quantum field theory
computation in a classical background (gravitational shock wave). In momentum
space, the formalism is similar to the flat-space light cone perturbation
theory, with shock wave crossing vertices added. In the impact parameter
representation, the radiating particle splits into a multi-particle virtual
state, whose wavefunction is then multiplied by individual eikonal factors. As
a phenomenological application, we study QCD radiation in transplanckian
collisions of TeV-scale gravity models. We derive the distribution of initial
state radiation gluons, and find a suppression at large transverse momenta with
respect to the standard QCD result. This is due to rescattering events, in
which the quark and the emitted gluon scatter coherently. Interestingly, the
suppression factor depends on the number of extra dimensions and provides a new
experimental handle to measure this number. We evaluate the leading-log
corrections to partonic cross-sections due to the initial state radiation, and
prove that they can be absorbed into the hadronic PDF. The factorization scale
should then be chosen in agreement with an earlier proposal of Emparan, Masip,
and Rattazzi. In the future, our methods can be applied to the gravitational
radiation in transplanckian scattering, where they can go beyond the existing
approaches limited to the soft radiation case.Comment: 41 pp, v2: minor changes and added refs, conforms with published
versio
sp hybridization in free carbon nanoparticles-presence and stability observed by near edge X-ray absorption fine structure spectroscopy
The presence and stability of sp hybridized atoms in free carbon nanoparticles was investigated by NEXAFS spectroscopy. The experiments show that a predominant fraction of carbon atoms is found in linear sp-chains and that conversion into sp(2) structures proceeds already at low temperature and in the gas phase
Microscopic unitary description of tidal excitations in high-energy string-brane collisions
The eikonal operator was originally introduced to describe the effect of
tidal excitations on higher-genus elastic string amplitudes at high energy. In
this paper we provide a precise interpretation for this operator through the
explicit tree-level calculation of generic inelastic transitions between closed
strings as they scatter off a stack of parallel Dp-branes. We perform this
analysis both in the light-cone gauge, using the Green-Schwarz vertex, and in
the covariant formalism, using the Reggeon vertex operator. We also present a
detailed discussion of the high energy behaviour of the covariant string
amplitudes, showing how to take into account the energy factors that enhance
the contribution of the longitudinally polarized massive states in a simple
way.Comment: 58 page
Regge behavior saves string theory from causality violations
Higher-derivative corrections to the Einstein-Hilbert action are present in bosonic string theory leading to the potential causality violations recently pointed out by Camanho et al. [1]. We analyze in detail this question by considering high-energy string-brane collisions at impact parameters b †l s (the string-length parameter) with l s â« R p (the characteristic scale of the D p -brane geometry). If we keep only the contribution of the massless states causality is violated for a set of initial states whose polarization is suitably chosen with respect to the impact parameter vector. Such violations are instead neatly avoided when the full structure of string theory â and in particular its Regge behavior â is taken into account
Electroweak Bloch-Nordsieck violation at the TeV scale: "strong" weak interactions ?
Hard processes at the TeV scale exhibit enhanced (double log) EW corrections
even for inclusive observables, leading to violation of the Bloch-Nordsieck
theorem. This effect, previously related to the non abelian nature of free EW
charges in the initial state (e- e+, e- p, p p ...), is here investigated for
fermion initiated hard processes and to all orders in EW couplings. We find
that the effect is important, especially for lepton initiated processes,
producing weak effects that in some cases compete in magnitude with the strong
ones. We show that this (double log) BN violating effect has a universal energy
dependence, related to the Sudakov form factor in the adjoint representation.
The role of this form factor is to suppress cross section differences within a
weak isospin doublet, so that at very large energy the cross sections for
left-handed electron-positron and neutrino-positron scattering become equal.
Finally, we briefly discuss the phenomenological relevance of our results for
future colliders.Comment: 18 pages, 6 figures, uses epsfig.sty and subequation.st
Towards Collinear Evolution Equations in Electroweak Theory
We consider electroweak radiative corrections to hard inclusive processes at
the TeV scale, and we investigate how collinear logarithms factorize in a
spontaneously broken gauge theory, similarly to the DGLAP analysis in QCD.
Due to the uncancelled double logs noticed previously, we find a
factorization pattern which is qualitatively different from the analogous one
in QCD. New types of splitting functions emerge which are needed to describe
the initial beam charges and are infrared-sensitive, that is dependent on an
infrared cutoff provided, ultimately, by the symmetry breaking scale. We derive
such splitting functions at one-loop level in the example of SU(2) gauge
theory, and we also discuss the structure functions' evolution equations, under
the assumption that isospin breaking terms present in the Ward identities of
the theory are sufficiently subleading at higher orders.Comment: 5 pages, 3 figure
Tuning electrical properties of hierarchically assembled Al-doped ZnO nanoforests by room temperature Pulsed Laser Deposition
Large surface area, 3D structured transparent electrodes with effective light management capability may represent a key component in the development of new generation optoelectronic and energy harvesting devices. We present an approach to obtain forest-like nanoporous/hierarchical Al-doped ZnO conducting layers with tunable transparency and light scattering properties, by means of room temperature Pulsed Laser Deposition in a mixed Ar:O2 atmosphere. The composition of the background atmosphere during deposition can be varied to modify stoichiometry-related defects, and therefore achieve control of electrical and optical properties, while the total background
pressure controls the material morphology at the nano- and mesoscale and thus the light scattering properties. This approach allows to tune electrical resistivity over a very wide range (10^-1 - 10^6 Ohm*cm), both in the in-plane and cross-plane directions. Optical transparency and haze can also be tuned by varying the stoichiometry and thickness of the nano-forests
The Highly Energetic Expansion of SN2010bh Associated with GRB 100316D
We present the spectroscopic and photometric evolution of the nearby (z =
0.059) spectroscopically confirmed type Ic supernova, SN 2010bh, associated
with the soft, long-duration gamma-ray burst (X-ray flash) GRB 100316D.
Intensive follow-up observations of SN 2010bh were performed at the ESO Very
Large Telescope (VLT) using the X-shooter and FORS2 instruments. Owing to the
detailed temporal coverage and the extended wavelength range (3000--24800 A),
we obtained an unprecedentedly rich spectral sequence among the hypernovae,
making SN 2010bh one of the best studied representatives of this SN class. We
find that SN 2010bh has a more rapid rise to maximum brightness (8.0 +/- 1.0
rest-frame days) and a fainter absolute peak luminosity (L_bol~3e42 erg/s) than
previously observed SN events associated with GRBs. Our estimate of the ejected
(56)Ni mass is 0.12 +/- 0.02 Msun. From the broad spectral features we measure
expansion velocities up to 47,000 km/s, higher than those of SNe 1998bw (GRB
980425) and 2006aj (GRB 060218). Helium absorption lines He I lambda5876 and He
I 1.083 microm, blueshifted by ~20,000--30,000 km/s and ~28,000--38,000 km/s,
respectively, may be present in the optical spectra. However, the lack of
coverage of the He I 2.058 microm line prevents us from confirming such
identifications. The nebular spectrum, taken at ~186 days after the explosion,
shows a broad but faint [O I] emission at 6340 A. The light-curve shape and
photospheric expansion velocities of SN 2010bh suggest that we witnessed a
highly energetic explosion with a small ejected mass (E_k ~ 1e52 erg and M_ej ~
3 Msun). The observed properties of SN 2010bh further extend the heterogeneity
of the class of GRB supernovae.Comment: 37 pages and 12 figures (one-column pre-print format), accepted for
publication in Ap
Neutrophil elastase in bronchiectasis
The role of neutrophil elastase (NE) is poorly understood in bronchiectasis because of the lack of preclinical data and so most of the assumptions made about NE inhibitor potential benefit is based on data from CF. In this context, NE seems to be a predictor of long-term clinical outcomes and a possible target of treatment. In order to better evaluate the role of NE in bronchiectasis, a systematic search of scientific evidence was performed.Two investigators independently performed the search on PubMed and included studies published up to May 15, 2017 according to predefined criteria. A final pool of 31 studies was included in the systematic review, with a total of 2679 patients. For each paper data of interest were extracted and reported in table.In this review sputum NE has proved useful as an inflammatory marker both in stable state bronchiectasis and during exacerbations and local or systemic antibiotic treatment. NE has also been associated with risk of exacerbation, time to next exacerbation and all-cause mortality. This study reviews also the role of NE as a specific target of treatment in bronchiectasis. Inhibition of NE is at a very early stage and future interventional studies should evaluate safety and efficacy for new molecules and formulations
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