291 research outputs found
About the screening of the charge of a proton migrating in a metal
The amount of screening of a proton in a metal, migrating under the influence
of an applied electric field, is calculated using different theoretical
formulations. First the lowest order screening expression derived by Sham
(1975) is evaluated. In addition 'exact' expressions are evaluated which were
derived according to different approaches. For a proton in a metal modeled as a
jellium the screening appears to be 15 +/- 10 %, which is neither negligible
not reconcilable with the controversial full-screening point of view of
Bosvieux and Friedel (1962). In reconsidering the theory of electromigration, a
new simplified linear-response expression for the driving force is shown to
lead to essentially the same result as found by Sorbello (1985), who has used a
rather complicated technique. The expressions allow for a reduction such that
only the scattering phase shifts of the migrating impurity are required.
Finally it is shown that the starting formula for the driving force of Bosvieux
and Friedel leads exactly to the zero-temperature limit of well-established
linear response descriptions, by which the sting of the controversy has been
removed.Comment: 14 pages, 5 figure
Are current-induced forces conservative?
The expression for the force on an ion in the presence of current can be
derived from first principles without any assumption about its conservative
character. However, energy functionals have been constructed that indicate that
this force can be written as the derivative of a potential function. On the
other hand, there exist compelling specific arguments that strongly suggest the
contrary. We propose physical mechanisms that invalidate such arguments and
demonstrate their existence with first-principles calculations. While our
results do not constitute a formal resolution to the fundamental question of
whether current-induced forces are conservative, they represent a substantial
step forward in this direction.Comment: 4 pages, 4 Figures, submitted to PR
The role of Joule heating in the formation of nanogaps by electromigration
We investigate the formation of nanogaps in gold wires due to
electromigration. We show that the breaking process will not start until a
local temperature of typically 400 K is reached by Joule heating. This value is
rather independent of the temperature of the sample environment (4.2-295 K).
Furthermore, we demonstrate that the breaking dynamics can be controlled by
minimizing the total series resistance of the system. In this way, the local
temperature rise just before break down is limited and melting effects are
prevented. Hence, electrodes with gaps < 2 nm are easily made, without the need
of active feedback. For optimized samples, we observe quantized conductance
steps prior the gap formation.Comment: including 7 figure
Spin-Hall interface resistance in terms of Landauer type spin dipoles
We considered the nonequlibrium spin dipoles induced around spin independent
elastic scatterers by the intrinsic spin-Hall effect associated with the Rashba
spin-orbit coupling. The normal to 2DEG spin polarization has been calculated
in the diffusion range around the scatterer. We found that although around each
impurity this polarization is finite, the corresponding macroscopic spin
density, obtained via averaging of individual spin dipole distributions over
impurity positions is zero in the bulk. At the same time, the spin density is
finite near the boundary of 2DEG, except for a special case of a hard wall
boundary. The boundary value of the spin polarization can be associated with
the interface spin-Hall resistance determining the additional energy
dissipation due to spin accumulation.Comment: 7 page
Scaling of 1/f noise in tunable break-junctions
We have studied the voltage noise of gold nano-contacts in
electromigrated and mechanically controlled break-junctions having resistance
values that can be tuned from 10 (many channels) to 10 k
(single atom contact). The noise is caused by resistance fluctuations as
evidenced by the dependence of the power spectral density
on the applied DC voltage . As a function of the normalized noise
shows a pronounced cross-over from for low-ohmic
junctions to for high-ohmic ones. The measured powers of 3
and 1.5 are in agreement with -noise generated in the bulk and reflect the
transition from diffusive to ballistic transport
Impact of COVID-19 Outbreak on Healthcare Workers in Italy: Results from a National E-Survey
Italy has been the first-hit European country to face the outbreak of coronavirus disease 2019 (COVID-19). Aim of this survey was to assess in depth the impact of the outbreak on healthcare workers (HCW). A 40-item online survey was disseminated via social media inviting Italian HCW, with questions exploring demographics, health status and work environment of respondents. A total of 527 were invited to take part in March 2020, of whom 74% (n = 388) responded to the survey. Of these, 235 (61%) were women. HCW were mostly physicians (74%), from high-prevalence regions (52%). 25% experienced typical symptoms during the last 14 days prior to survey completion, with only 45% of them being tested for COVID-19. Among the tested population, 18 (18%) resulted positive for COVID-19, with 33% being asymptomatic. Only 22% of HCW considered personal protective equipment adequate for quality and quantity. Females and respondents working in high-risk sectors were more likely to rate psychological support as useful (OR, 1.78 [CI 95% 1.14–2.78] P = 0.012, and 2.02 [1.12–3.65] P = 0.020, respectively) and workload as increased (mean increase, 0.38 [0.06–0.69] P = 0.018; and 0.54 [0.16–0.92] P = 0.005, respectively). The insights from this survey may help authorities in countries where COVID-19 epidemic has not yet broken out. Management strategies should be promptly undertaken in order to enhance safety and optimise resource allocation
Telenoid android robot as an embodied perceptual social regulation medium engaging natural human–humanoid interaction
The present paper aims to validate our research on human–humanoid interaction (HHI) using the
minimalist humanoid robot Telenoid. We conducted the human–robot interaction test with 142 young people who had no prior interaction experience with this robot. The main goal is the analysis of the two social dimensions (‘‘Perception’’ and ‘‘Believability’’) useful for increasing the natural behaviour between users and Telenoid.Weadministered our custom questionnaire to human subjects in association with a well defined experimental setting (‘‘ordinary and goal-guided task’’). A thorough analysis of the questionnaires has been carried out and reliability and internal consistency in correlation between the multiple items has been calculated. Our experimental results show that the perceptual behaviour and believability, as implicit social competences, could improve the meaningfulness and the natural-like sense of human–humanoid interaction in everyday life task-driven activities. Telenoid is perceived as an autonomous cooperative agent for a shared environment by human beings
An android architecture for bio-inspired honest signalling in Human-Humanoid Interaction
This paper outlines an augmented robotic architecture to study the conditions of successful Human-Humanoid Interaction (HHI). The architecture is designed as a testable model generator for interaction centred on the ability to emit, display and detect honest signals. First we overview the biological theory in which the concept of honest signals has been put forward in order to assess its explanatory power. We reconstruct the application of the concept of honest signalling in accounting for interaction in strategic contexts and in laying bare the foundation for an automated social metrics. We describe the modules of the architecture, which is intended to implement the concept of honest signalling in connection with a refinement provided by delivering the sense of co-presence in a shared environment. Finally, an analysis of Honest Signals, in term of body postures, exhibited by participants during the preliminary experiment with the Geminoid Hi-1 is provided
Risk factors for difficult Laryngeal Mask Airway LMA-Supreme™ (LMAS) placement in adults: A multicentric prospective observational study in an Italian population
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