3,280 research outputs found
On-surface and Subsurface Adsorption of Oxygen on Stepped Ag(210) and Ag(410) Surfaces
The adsorption of atomic oxygen and its inclusion into subsurface sites on
Ag(210) and Ag(410) surfaces have been investigated using density functional
theory. We find that--in the absence of adatoms on the first metal
layer--subsurface adsorption results in strong lattice distortion which makes
it energetically unfavoured. However subsurface sites are significantly
stabilised when a sufficient amount of O adatoms is present on the surface. At
high enough O coverage on the Ag(210) surface the mixed on-surface + subsurface
O adsorption is energetically favoured with respect to the on-surface only
adsorption. Instead, on the Ag(410) surface, at the coverage we have considered
(3/8 ML), the existence of stable terrace sites makes the subsurface O
incorporation less favourable. These findings are compatible with the results
of recent HREEL experiments which have actually motivated this work.Comment: 8 pages, 4 figures and 1 tabl
Nonintegrable Interaction of Ion-Acoustic and Electromagnetic Waves in a Plasma
In this paper we re-examine the one-dimensional interaction of
electromagnetic and ion acoustic waves in a plasma. Our model is similar to one
solved by Rao et al. (Phys. Fluids, vol. 26, 2488 (1983)) under a number of
analytical approximations. Here we perform a numerical investigation to examine
the stability of the model. We find that for slightly over dense plasmas, the
propagation of stable solitary modes can occur in an adiabatic regime where the
ion acoustic electric field potential is enslaved to the electromagnetic field
of a laser. But if the laser intensity or plasma density increases or the laser
frequency decreases, the adiabatic regime loses stability via a transition to
chaos. New asymptotic states are attained when the adiabatic regime no longer
exists. In these new states, the plasma becomes rarefied, and the laser field
tends to behave like a vacuum field.Comment: 19 pages, REVTeX, 6 ps figures, accepted for publication in Phys.
Rev.
Long-term subjective outcomes of barbed reposition pharyngoplasty for obstructive sleep apnea syndrome treatment
Background: The purpose of this study was to evaluate long-term subjective outcomes of barbed reposition pharyngoplasty for obstructive sleep apnea syndrome (OSAS) treatment using a specific questionnaire, the Palate Postoperative Problem Score (PPOPS). Methods: 140 patients who underwent barbed reposition pharyngoplasty (BRP) surgery in the Morgagni Pierantoni Hospital of Forlì, Italy were enrolled in the study. Postoperative outcomes were evaluated in a short- and long-term follow-up using the PPOPS questionnaire. The average period of follow-up was 26 months. All patients received the PPOPS questionnaire by telephone in a period between April and August 2019. Results: 51% of patients complained of swallowing problems after surgery. In 91% of cases, the problem cleared up spontaneously. At the time of the interview, only 9% of patients had a residual swallowing difficult. At the time of PPOPS evaluation, rhinolalia was observed in 8% of patients, whereas nose regurgitation was present in 2% of patients. In 20% of patients, the foreign body sensation was present during follow-up. The value of apnea-hypopnea index (AHI) reduced from the preoperative value of 31.5 to the postoperative value of 11.4. Conclusions: BRP surgery proved to be an effective technique, appreciated by the majority of patients. Use of the PPOPS questionnaire has demonstrated that the BRP technique seems to ensure efficacy and lower morbidity, with few complications after surgery
Exogenous sex hormones, menstrual and reproductive history, and risk of non-melanoma skin cancer among women: a systematic literature review and meta-analysis
Non-melanoma skin cancers (NMSC) are more frequent among men, but women (especially those aged < 40 years) have experienced steeper growth in their incidence rates in recent years. Hormonal factors were hypothesized to be playing a role in modulating NMSC risk, but the studies published to date provided conflicting results. We systematically reviewed and meta-analysed the studies focusing on the association between hormone-related characteristics (use of exogenous sex hormones, and aspects of menstrual and reproductive history) and the risk of NMSC among women. We included observational and experimental studies published in PubMed and EMBASE until February 2020. We calculated summary relative risk (SRR) and 95% confidence intervals (CI) by applying random effects models with maximum likelihood estimation, and used the I2 statistics to quantify the degree of heterogeneity of risk estimates across studies. Eleven independent studies encompassing a total of over 30,000 NMSC cases were included in quantitative analyses. No evidence of an increased NMSC risk emerged among ever vs. never users of oral contraceptives (SRR 1.13, 95% CI 0.88–1.45) or hormones for menopause (SRR 1.09, 95% CI 0.87–1.37). Likewise, age at menarche or at menopause and parity were not associated with NMSC risk. Heterogeneity across studies was low, and pooled results were comparable between NMSC subtypes. We found no evidence that hormonal factors play a role in the pathogenesis of NMSC among women
Is workaholism associated with inflammatory response? The moderating role of work engagement
The aim of this study was to investigate the association between two different forms of heavy work investment, namely workaholism and work engagement, and serum levels of the proinflammatory cytokine interleukin-17 (IL-17), a possible biomarker of stress. Given the different motivational underpinnings and outcomes of workaholism and work engagement and drawing on the allostatic load and the effort-recovery models, we hypothesized that workaholism is positively associated with IL-17, and that work engagement buffers this association. Workers in an Italian healthcare organization (88 females and 31 males) completed a self-report questionnaire, and then underwent blood sample collection. Data were analysed using moderated multiple regression. Results showed that workaholism was positively associated with IL-17, controlling for the effect of gender, age, and body mass index. Work engagement buffered this association, which was nonsignificant when work engagement was high. To reduce the risk of future health complaints, interventions should be aimed at preventing workaholism and promoting work engagement
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
Design of a low band gap oxide ferroelectric: BiTiO
A strategy for obtaining low band gap oxide ferroelectrics based on charge
imbalance is described and illustrated by first principles studies of the
hypothetical compound BiTiO, which is an alternate stacking of
the ferroelectric BiTiO. We find that this compound is
ferroelectric, similar to BiTiO although with a reduced
polarization. Importantly, calculations of the electronic structure with the
recently developed functional of Tran and Blaha yield a much reduced band gap
of 1.83 eV for this material compared to BiTiO. Therefore,
BiTiO is predicted to be a low band gap ferroelectric material
Electric fields and valence band offsets at strained [111] heterojunctions
[111] ordered common atom strained layer superlattices (in particular the
common anion GaSb/InSb system and the common cation InAs/InSb system) are
investigated using the ab initio full potential linearized augmented plane wave
(FLAPW) method. We have focused our attention on the potential line-up at the
two sides of the homopolar isovalent heterojunctions considered, and in
particular on its dependence on the strain conditions and on the strain induced
electric fields. We propose a procedure to locate the interface plane where the
band alignment could be evaluated; furthermore, we suggest that the
polarization charges, due to piezoelectric effects, are approximately confined
to a narrow region close to the interface and do not affect the potential
discontinuity. We find that the interface contribution to the valence band
offset is substantially unaffected by strain conditions, whereas the total band
line-up is highly tunable, as a function of the strain conditions. Finally, we
compare our results with those obtained for [001] heterojunctions.Comment: 18 pages, Latex-file, to appear in Phys.Rev.
Enhancement of piezoelectricity in a mixed ferroelectric
We use first-principles density-functional total energy and polarization
calculations to calculate the piezoelectric tensor at zero temperature for both
cubic and simple tetragonal ordered supercells of Pb_3GeTe_4. The largest
piezoelectric coefficient for the tetragonal configuration is enhanced by a
factor of about three with respect to that of the cubic configuration. This can
be attributed to both the larger strain-induced motion of cations relative to
anions and higher Born effective charges in the tetragonal case. A normal mode
decomposition shows that both cation ordering and local relaxation weaken the
ferroelectric instability, enhancing piezoelectricity.Comment: 5 pages, revtex, 2 eps figure
- …