Ab-initio theory of metal-insulator interfaces in a finite electric field

We present a novel technique for calculating the dielectric response of metal/insulator heterostructures. This scheme allows, for the first time, the fully first-principles calculation of the microscopic properties of thin-film capacitors at finite bias potential. The method can be readily applied to pure insulators, where it provides an interesting alternative to conventional finite-field techniques based on the Berry-phase formalism. We demonstrate the effectiveness of our method by performing comprehensive numerical tests on a model Ag/MgO/Ag heterostructure.Comment: 10 pages, 5 figures, major revisio

Band Offsets at the Si/SiO2_2 Interface from Many-Body Perturbation Theory

We use many-body perturbation theory, the state-of-the-art method for band gap calculations, to compute the band offsets at the Si/SiO$_2$ interface. We examine the adequacy of the usual approximations in this context. We show that (i) the separate treatment of band-structure and potential lineup contributions, the latter being evaluated within density-functional theory, is justified, (ii) most plasmon-pole models lead to inaccuracies in the absolute quasiparticle corrections, (iii) vertex corrections can be neglected, (iv) eigenenergy self-consistency is adequate. Our theoretical offsets agree with the experimental ones within 0.3 eV

First-principles study on dielectric properties of NaCl crystal and ultrathin NaCl films under finite external electric field

We present a first-principles study on the dielectric properties of an NaCl crystal and ultrathin NaCl films under a finite external electric field. Our results show that the high-frequency dielectric constant of the films is not affected by the finite size effect from crystal surfaces and is close to that of the crystal, whereas the static one is sensitive to the thickness of the film due to the difference in the atomic configurations between the surface and inside of the film.Comment: 11 pages and 4 figure

Dielectric screening in extended systems using the self-consistent Sternheimer equation and localized basis sets

We develop a first-principles computational method for investigating the dielectric screening in extended systems using the self-consistent Sternheimer equation and localized non-orthogonal basis sets. Our approach does not require the explicit calculation of unoccupied electronic states, only uses two-center integrals, and has a theoretical scaling of order O(N^3). We demonstrate this method by comparing our calculations for silicon, germanium, diamond, and LiCl with reference planewaves calculations. We show that accuracy comparable to planewaves calculations can be achieved via a systematic optimization of the basis set.Comment: 6 pages, 3 figure

GW method with the self-consistent Sternheimer equation

We propose a novel approach to quasiparticle GW calculations which does not require the computation of unoccupied electronic states. In our approach the screened Coulomb interaction is evaluated by solving self-consistent linear-response Sternheimer equations, and the noninteracting Green's function is evaluated by solving inhomogeneous linear systems. The frequency-dependence of the screened Coulomb interaction is explicitly taken into account. In order to avoid the singularities of the screened Coulomb interaction the calculations are performed along the imaginary axis, and the results are analytically continued to the real axis through Pade' approximants. As a proof of concept we implemented the proposed methodology within the empirical pseudopotential formalism and we validated our implementation using silicon as a test case. We examine the advantages and limitations of our method and describe promising future directions.Comment: 18 pages, 6 figure

Physical activity levels and related energy expenditure during COVID-19 quarantine among the sicilian active population: A cross-sectional online survey study

Background: During the coronavirus disease 2019 (COVID-19) pandemic, the Italian government has adopted containment measures to control the virus's spread, including limitations to the practice of physical activity (PA). The aim of this study was to estimate the levels of PA, expressed as energy expenditure (MET-minute/week), among the physically active Sicilian population before and during the last seven days of the COVID-19 quarantine. Furthermore, the relation between this parameter and specific demographic and anthropometric variables was analyzed. Methods: 802 Sicilian physically active participants (mean age: 32.27 ± 12.81 years; BMI: 23.44 ± 3.33 kg/m2) were included in the study and grouped based on gender, age and BMI. An adapted version of the International Physical Activity Questionnaire-short form (IPAQ-SF) was administered to the participants through an online survey. The Wilcoxon signed-rank test and the Kruskal-Wallis rank-sum test were used for statistical analyses. Results: As expected, we observed a significant decrease of the total weekly energy expenditure during the COVID-19 quarantine (p < 0.001). A significant variation in the MET-min/wk in the before quarantine condition (p = 0.046) and in the difference between before and during quarantine (p = 0.009) was found for males and females. The male group decreased the PA level more than the female one. Moreover, a significant difference in the MET-min/wk was found among groups distributions of BMI (p < 0.001, during quarantine) and of age (p < 0.001, both before and during quarantine). In particular, the highest and the lowest levels of PA were reported by the young and the elderly, respectively, both before and during quarantine. Finally, the overweight group showed the lowest level of PA during quarantine. Conclusion: Based on our outcomes, we can determine that the current quarantine has negatively affected the practice of PA, with greater impacts among males and overweight subjects. In regards to different age groups, the young, young adults and adults were more affected than senior adults and the elderly

Application of T-Thesys Therapy in post-operative recovery in knee-surgical interventions: A case study

T-Thesys therapy is an innovative treatment that can be used even in the presence of recent injuries. For this reason, we studied the T-Thesys use in the post-operative phase of the anterior cruciate ligament (ACL) reconstruction of the knee. For our study, we selected 51 patients for ACL surgery, and we divided participants in two groups: the Experimental Group (EG) and the Control Group (CG). The EG consisted of 34 patients (age: 26.9 ± 7.65 years) who underwent T-Thesys therapy after surgery, while the CG included 17 patients (age: 26.7 ± 6.8 years) who was not subjected to T-Thesys therapy after surgery. T-Thesys therapy was performed on a daily basis and participants' parameters were monitored throughout the treatment. For the EG, we did not find any significant differences, however, subjective disorders seemed to disappear, almost entirely, at the seventh application. The CG showed no significant differences, even in the subjective disorders investigated. Therefore, the therapeutic treatment associated with T-Thesys therapy seems to not show any efficacy compared to the surgical treatment alone. However, from our findings emerged differences which tend to highlight a better clinical response, a faster recovery time, an improvement on the quality of life in patients, and, moreover, a better use of the National Health System resources

Saddle Pressures Factors in Road and Off-Road Cyclists of Both Genders: A Narrative Review

: The contact point of the pelvis with the saddle of the bicycle could generate abnormal pressure, which could lead to injuries to the perineum in cyclists. The aim of this review was to summarize in a narrative way the current literature on the saddle pressures and to present the factors that influence saddle pressures in order to prevent injury risk in road and off-road cyclists of both genders. We searched the PubMed database to identify English-language sources, using the following terms: "saddle pressures", "pressure mapping", "saddle design" AND "cycling". We also searched the bibliographies of the retrieved articles. Saddle pressures are influenced by factors such as sitting time on the bike, pedaling intensity, pedaling frequency, trunk and hand position, handlebars position, saddle design, saddle height, padded shorts, and gender. The jolts of the perineum on the saddle, especially on mountain bikes, generate intermittent pressures, which represent a risk factor for various pathologies of the urogenital system. This review highlights the importance of considering these factors that influence saddle pressures in order to prevent urogenital system injuries in cyclists

Apogeotropic posterior semicircular canal benign paroxysmal positional vertigo: some clinical and therapeutic considerations

We lately reported the cases of patients complaining positional vertigo whose nystagmic pattern was that of a peripheral torsional vertical positional down beating nystagmus originating from a lithiasis of the non-ampullary arm of the posterior semicircular canal (PSC). We considered this particular pathological picture the apogeotropic variant of PSC benign paroxysmal positional vertigo (BPPV). Since the description of the pilot cases we observed more than 150 patients showing the same clinical sign and course of symptoms. In this paper we describe, in detail, both nystagmus of apogeotropic PSC BPPV (A-PSC BPPV) and symptoms reported by patients trying to give a reasonable explanation for these clinical features. Moreover we developed two specific physical therapies directed to cure A-PSC BPPV. Preliminary results of these techniques are related