218 research outputs found
Dynamical-charge neutrality at a crystal surface
For both molecules and periodic solids, the ionic dynamical charge tensors
which govern the infrared activity are known to obey a dynamical neutrality
condition. This condition enforces their sum to vanish (over the whole finite
system, or over the crystal cell, respectively). We extend this sum rule to the
non trivial case of the surface of a semiinfinite solid and show that, in the
case of a polar surface of an insulator, the surface ions cannot have the same
dynamical charges as in the bulk. The sum rule is demonstrated through
calculations for the Si-terminated SiC(001) surface.Comment: 4 pages, latex file, 1 postscript figure automatically include
An alternative nonlinear collimation system for the LHC
The optics design of an alternative nonlinear collimation system for the LHC is presented. We discuss an optics scheme based on a single spoiler located in between a pair of skew sextupoles for betatron collimation. The nonlinear system allows opening up the collimator gaps, thereby, reduces the collimator impedance, which presently limits the LHC intensity. After placing secondary collimators at locations behind the spoiler, we analyze the beam losses and calculate the cleaning efficiency from tracking studies. The results are compared with those of the conventional linear collimation system
Exhaled Interleukine-6 and 8-isoprostane in chronic obstructive pulmonary disease: effect of carbocysteine lysine salt monohydrate (SCMC-Lys).
Chronic obstructive pulmonary disease (COPD) is characterized by an airways inflammation and by an enhanced generation of reactive oxygen species. The aim of our study was to assess the inflammation and the oxidative stress in airways of COPD patients with acute exacerbation of disease and in stability. Furthermore, we investigated the anti-inflammatory and antioxidant effects of 6 months treatment with carbocysteine lysine salt monohydrate (SCMC-Lys) in COPD. We studied 30 mild acute COPD, 10 mild stable COPD and 15 healthy subjects. 8-isoprostane and Interleukine-6 were measured in their breath condensate through immunoassay. Significantly higher concentrations of exhaled 8-isoprostane and Interleukine-6 were found in acute COPD patients compared to stable COPD and healthy controls (21.8+/-5.1 vs. 13.2+/-2.0 vs. 4.7+/-1.8 pg/ml and 7.4+/-0.9 vs. 5.8+/-0.2 vs. 2.7+/-0.6 pg/ml, p<0.0001). COPD patients treated with SCMC-Lys showed a marked reduction of exhaled 8-isoprostane and Interleukine-6 (8.9+/-1.5 and 4.6+/-0.8 pg/ml, p<0.0001). These findings suggest that there is an increase of 8-isoprostane and Interleukine-6 concentrations in the breath condensate of COPD patients compared to healthy controls especially during acute exacerbations of the disease. Moreover, we showed an anti-inflammatory and antioxidant effect of short-term administration of SCMC-Lys in COPD, suggesting the importance of a further placebo-controlled study that should evaluate the effects of this drug
Role of defects in the electronic properties of amorphous/crystalline Si interface
The mechanism determining the band alignment of the amorphous/crystalline
Si heterostructures is addressed with direct atomistic simulations of the
interface performed using a hierarchical combination of various computational
schemes ranging from classical model-potential molecular dynamics to ab-initio
methods. We found that in coordination defect-free samples the band alignment
is almost vanishing and independent on interface details. In defect-rich
samples, instead, the band alignment is sizeably different with respect to the
defect-free case, but, remarkably, almost independent on the concentration of
defects. We rationalize these findings within the theory of semiconductor
interfaces.Comment: 4 pages in two-column format, 2 postscript figures include
Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
Quantum ESPRESSO is an integrated suite of computer codes for
electronic-structure calculations and materials modeling, based on
density-functional theory, plane waves, and pseudopotentials (norm-conserving,
ultrasoft, and projector-augmented wave). Quantum ESPRESSO stands for "opEn
Source Package for Research in Electronic Structure, Simulation, and
Optimization". It is freely available to researchers around the world under the
terms of the GNU General Public License. Quantum ESPRESSO builds upon
newly-restructured electronic-structure codes that have been developed and
tested by some of the original authors of novel electronic-structure algorithms
and applied in the last twenty years by some of the leading materials modeling
groups worldwide. Innovation and efficiency are still its main focus, with
special attention paid to massively-parallel architectures, and a great effort
being devoted to user friendliness. Quantum ESPRESSO is evolving towards a
distribution of independent and inter-operable codes in the spirit of an
open-source project, where researchers active in the field of
electronic-structure calculations are encouraged to participate in the project
by contributing their own codes or by implementing their own ideas into
existing codes.Comment: 36 pages, 5 figures, resubmitted to J.Phys.: Condens. Matte
Phonons and related properties of extended systems from density-functional perturbation theory
This article reviews the current status of lattice-dynamical calculations in
crystals, using density-functional perturbation theory, with emphasis on the
plane-wave pseudo-potential method. Several specialized topics are treated,
including the implementation for metals, the calculation of the response to
macroscopic electric fields and their relevance to long wave-length vibrations
in polar materials, the response to strain deformations, and higher-order
responses. The success of this methodology is demonstrated with a number of
applications existing in the literature.Comment: 52 pages, 14 figures, submitted to Review of Modern Physic
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