3,377 research outputs found
Interaction of a CO molecule with a Pt monatomic wire: electronic structure and ballistic conductance
We carry out a first-principles density functional study of the interaction
between a monatomic Pt wire and a CO molecule, comparing the energy of
different adsorption configurations (bridge, on top, substitutional, and tilted
bridge) and discussing the effects of spin-orbit (SO) coupling on the
electronic structure and on the ballistic conductance of two of these systems
(bridge and substitutional). We find that, when the wire is unstrained, the
bridge configuration is energetically favored, while the substitutional
geometry becomes possible only after the breaking of the Pt-Pt bond next to CO.
The interaction can be described by a donation/back-donation process similar to
that occurring when CO adsorbs on transition-metal surfaces, a picture which
remains valid also in presence of SO coupling. The ballistic conductance of the
(tipless) nanowire is not much reduced by the adsorption of the molecule on the
bridge and on-top sites, but shows a significant drop in the substitutional
case. The differences in the electronic structure due to the SO coupling
influence the transmission only at energies far away from the Fermi level so
that fully- and scalar-relativistic conductances do not differ significantly.Comment: 12 pages, 12 figures; figure misplacement and minor syntax issues
fixed, some references updated and correcte
First-principles study of lattice instabilities in the ferromagnetic martensite NiMnGa
The phonon dispersion relations and elastic constants for ferromagnetic
NiMnGa in the cubic and tetragonally distorted Heusler structures are
computed using density-functional and density-functional perturbation theory
within the spin-polarized generalized-gradient approximation. For
, the TA tranverse acoustic branch along and
symmetry-related directions displays a dynamical instability at a wavevector
that depends on . Through examination of the Fermi-surface nesting and
electron-phonon coupling, this is identified as a Kohn anomaly. In the parent
cubic phase the computed tetragonal shear elastic constant,
C=(CC)/2, is close to zero, indicating a marginal
elastic instability towards a uniform tetragonal distortion. We conclude that
the cubic Heusler structure is unstable against a family of energy-lowering
distortions produced by the coupling between a uniform tetragonal distortion
and the corresponding modulation. The computed relation between the
ratio and the modulation wavevector is in excellent agreement with
structural data on the premartensitic ( = 1) and martensitic ( =
0.94) phases of NiMnGa.Comment: submitted to Phys. Rev.
Total thyroidectomy versus hemithyroidectomy for patients with follicular neoplasm. A cost-utility analysis
AbstractIntroductionThyroid nodules are a common condition. Overall, 20% of the nodules assessed with FNAB correspond to the follicular pattern. A partial thyroidectomy is the minimal procedure that should be performed to determine the nature of these nodules. Some authors have suggested performing a total thyroidectomy based on the elimination of reoperation and ultrasound follow-up. The aim of this study was to evaluate the most cost-useful surgical strategy in a patient with an undetermined nodule, assessing complications, reoperation, recurrence and costs.Material and methodsA cost-utility study was designed to compare hemithyroidectomy and total thyroidectomy. The outcomes were complications (definitive RLN palsy, permanent hypoparathyroidism, reoperation for cancer, and recurrence of the disease), direct costs and utility. We used the payer perspective at 5 years. A deterministic and probabilistic sensitivity analysis was completed.ResultsIn a deterministic analysis, the cost, utility and cost-utility ratio was COP 291.310 for total thyroidectomy and COP 340.044 for partial thyroidectomy, respectively. The incremental cost-utility ratio was −$535.302 favoring total thyroidectomy. Partial thyroidectomy was more cost-effective when the risks of RLN injury and definitive hypoparathyroidism were greater than 8% and 9% in total thyroidectomy, respectively. In total, 46.8% of the simulations for partial thyroidectomy were located in the quadrant of more costly and less effective.ConclusionUnder a common range of complications, and considering the patient's preference and costs, total thyroidectomy should be selected as the most cost-effective treatment for patients with thyroid nodules and follicular patterns
Spontaneous polarization and piezoelectric constants of III-V nitrides
The spontaneous polarization, dynamical Born charges, and piezoelectric
constants of the III-V nitrides AlN, GaN, and InN are studied ab initio using
the Berry phase approach to polarization in solids. The piezoelectric constants
are found to be up 10 times larger than in conventional III-V's and II-VI's,
and comparable to those of ZnO. Further properties at variance with those of
conventional III-V compounds are the sign of the piezoelectric constants
(positive as in II-VI's) and the very large spontaneous polarization.Comment: RevTeX 4 pages, improved upon revie
Pathways of 4-hydroxy-2-nonenal detoxification in a human astrocytoma cell line
One of the consequences of the increased level of oxidative stress that often characterizes the cancer cell environment is the abnormal generation of lipid peroxidation products, above all 4-hydroxynonenal. The contribution of this aldehyde to the pathogenesis of several diseases is well known. In this study, we characterized the ADF astrocytoma cell line both in terms of its pattern of enzymatic activities devoted to 4-hydroxynonenal removal and its resistance to oxidative stress induced by exposure to hydrogen peroxide. A comparison with lens cell lines, which, due to the ocular function, are normally exposed to oxidative conditions is reported. Our results show that, overall, ADF cells counteract oxidative stress conditions better than normal cells, thus confirming the redox adaptation demonstrated for several cancer cells. In addition, the markedly high level of NADP+-dependent dehydrogenase activity acting on the glutahionyl-hydroxynonanal adduct detected in ADF cells may promote, at the same time, the detoxification and recovery of cell-reducing power in these cells
Salivary cytokines and airways disease severity in patients with cystic fibrosis
About 50% of patients with cystic fibrosis (CF) have sinonasal complications, which include inferior turbinate hypertrophy (NTH) and/or nasal polyposis (NP), and different degrees of lung disease, which represents the main cause of mortality. Monitoring of sinonasal disease requires complex instrumental procedures, while monitoring of lung inflammation requires invasive collection of bronchoalveolar lavage fluid. The aim of this study was to investigate the associations between salivary cytokines levels and CF-related airway diseases. Salivary biochemical parameters and cytokines, i.e., interleukin-6 (IL-6), IL-8, and tumor necrosis factor alpha (TNF-α), were analyzed in resting saliva from healthy subjects and patients with CF. Patients with CF showed significantly higher levels of salivary chloride, IL-6, IL-8, and TNF-α and lower calcium levels than healthy subjects. Among patients with CF, IL-6 and IL-8 were significantly higher in patients with NTH, while TNF-α was significantly lower in patients with NP. A decreasing trend of TNF-α in patients with severe lung disease was also observed. On the other hand, we did not find significant correlation between cytokine levels and Pseudomonas aeruginosa or Stenotrophomonas maltophilia colonization. These preliminary results suggest that salivary IL-6 and IL-8 levels increase during the acute phase of sinonasal disease (i.e., NTH), while the end stages of pulmonary disease and sinonasal disease (i.e., NP) show decreased TNF-α level
Polar and non-polar organic binder characterization in Pompeian wall paintings: comparison to a simulated painting mimicking an a secco technique.
The use of Fourier transform infrared spectromicroscopy and mass spectrometry (MS) allowed us to characterize the composition of polar and non-polar binders present in sporadic wall paint fragments taken from Pompeii's archaeological excavation. The analyses of the polar and non-polar binder components extracted from paint powder layer showed the presence of amino acids, sugars, and fatty acids but the absence of proteinaceous material. These results are consistent with a water tempera painting mixture composed of pigments, flours, gums, and oils and are in agreement with those obtained from a simulated wall paint sample made for mimicking an ancient "a secco" technique. Notably, for the first time, we report the capability to discriminate by tandem MS the presence of free amino acids in the paint layer
Mirrors for space telescopes: degradation issues
Mirrors are a subset of optical components essential for the success of
current and future space missions. Most of the telescopes for space programs
ranging from Earth Observation to Astrophysics and covering all the
electromagnetic spectrum from X-rays to Far-Infrared are based on reflective
optics. Mirrors operate in diverse and harsh environments that range from
Low-Earth Orbit, to interplanetary orbits and the deep space. The operational
life of space observatories spans from minutes (sounding rockets) to decades
(large observatories), and the performance of the mirrors within the optical
system is susceptible to degrade, which results in a transient optical
efficiency of the instrument. The degradation that occurs in space environments
depends on the operational life on the orbital properties of the space mission,
and it reduces the total system throughput and hence compromises the science
return. Therefore, the knowledge of potential degradation physical mechanisms,
how they affect mirror performance, and how to prevent it, is of paramount
importance to ensure the long-term success of space telescopes. In this review
we report an overview on current mirror technology for space missions with a
particular focus on the importance of degradation and radiation resistance of
the coating materials. Particular detail will be given to degradation effects
on mirrors for the far and extreme UV as in these ranges the degradation is
enhanced by the strong absorption of most contaminants
Short-term physiological effects of a very low-calorie ketogenic diet: Effects on adiponectin levels and inflammatory states
Adipose tissue is a multifunctional organ involved in many physiological and metabolic processes through the production of adipokines and, in particular, adiponectin. Caloric restriction is one of the most important strategies against obesity today. The very low-calorie ketogenic diet (VLCKD) represents a type of caloric restriction with very or extremely low daily food energy consumption. This study aimed to investigate the physiological effects of a VLCKD on anthropometric and biochemical parameters such as adiponectin levels, as well as analyzing oligomeric profiles and cytokine serum levels in obese subjects before and after a VLCKD. Twenty obese subjects were enrolled. At baseline and after eight weeks of intervention, anthropometric and biochemical parameters, such as adiponectin levels, were recorded. Our findings showed a significant change in the anthropometric and biochemical parameters of these obese subjects before and after a VLCKD. We found a negative correlation between adiponectin and lipid profile, visceral adipose tissue (VAT), C-reactive protein (CRP), and pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α), which confirmed the important involvement of adiponectin in metabolic and inflammatory diseases. We demonstrated the beneficial short-term effects of a VLCKD not only in the treatment of obesity but also in the establishment of obesity-correlated diseases
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