220 research outputs found
Direct correlation between strengthening mechanisms and electrical noise in strained copper wires
We have measured the resistance noise of copper metallic wires during a
tensile stress. The time variation of the main resistance is continuous up to
the wire breakdown, but its fluctuations reveal the intermittent and
heterogeneous character of plastic flow. We show in particular direct
correlations between strengthening mechanisms and noise spectra
characteristics.Comment: accepted in Phys Rev
Effects of deposition dynamics on epitaxial growth
The dynamic effects, such as the steering and the screening effects during
deposition, on an epitaxial growth (Cu/Cu(001)), is studied by kinetic Monte
Carlo simulation that incorporates molecular dynamic simulation to rigorously
take the interaction of the deposited atom with the substrate atoms into
account.
We find three characteristic features of the surface morphology developed by
grazing angle deposition:
(1) enhanced surface roughness, (2) asymmetric mound, and (3) asymmetric
slopes of mound sides.
Regarding their dependence on both deposition angle and substrate
temperature, a reasonable agreement of the simulated results with the previous
experimental ones is found.
The characteristic growth features by grazing angle deposition are mainly
caused by the inhomogeneous deposition flux due to the steering and screening
effects, where the steering effects play the major role rather than the
screening effects.
Newly observed in the present simulation is that the side of mound in each
direction is composed of various facets instead of all being in one selected
mound angle even if the slope selection is attained, and that the slope
selection does not necessarily mean the facet selection.Comment: 9 pages, 10 figure
The formation of a Sn monolayer on Ge(1 0 0) studied at the atomic scale
The growth of multi-layer germanium-tin (GeSn) quantum wells offers an intriguing pathway towards the integration of lasers in a CMOS platform. An important step in growing high quality quantum well interfaces is the formation of an initial wetting layer. However, key atomic-scale details of this process have not previously been discussed. We use scanning tunneling microscopy combined with density functional theory to study the deposition of Sn on Ge(1 0 0) at room temperature over a coverage range of 0.01 to 1.24 monolayers. We demonstrate the formation of a sub-2% Ge content GeSn wetting layer from three atomic-scale characteristic ad-dimer structural components, and show that small quantities of Sn incorporate into the Ge surface forming two atomic configurations. The ratio of the ad-dimer structures changes with increasing Sn coverage, indicating a change in growth kinetics. At sub-monolayer coverage, the least densely packing ad-dimer structure is most abundant. As the layer closes, forming a two-dimensional wetting layer, the more densely packing ad-dimer structure become dominant. These results demonstrate the capability to form an atomically smooth wetting layer at room temperature, and provide critical atomic-scale insights for the optimization of growth processes of GeSn multi-quantum-wells to meet the quality requirements of optical GeSn-based devices
Monolithic growth of ultra-thin Ge nanowires on Si(001)
Self-assembled Ge wires with a height of only 3 unit cells and a length of up
to 2 micrometers were grown on Si(001) by means of a catalyst-free method based
on molecular beam epitaxy. The wires grow horizontally along either the [100]
or the [010] direction. On atomically flat surfaces, they exhibit a highly
uniform, triangular cross section. A simple thermodynamic model accounts for
the existence of a preferential base width for longitudinal expansion, in
quantitative agreement with the experimental findings. Despite the absence of
intentional doping, first transistor-type devices made from single wires show
low-resistive electrical contacts and single hole transport at sub-Kelvin
temperatures. In view of their exceptionally small and self-defined cross
section, these Ge wires hold promise for the realization of hole systems with
exotic properties and provide a new development route for silicon-based
nanoelectronics.Comment: 23 pages, 5 figure
Domain wall dynamics and Barkhausen effect in metallic ferromagnetic materials. II. Experiments
Barkhausen effect (BE) phenomenology in iron‐based ferromagnetic alloys is investigated by a proper experimental method, in which BE experiments are restricted to the central part of the hysteresis loop, and the amplitude probability distribution, P0(Φ), and power spectrum, F(ω), of the B flux rate Φ are measured under controlled values of the magnetization rate and differential permeability μ. It is found that all of the experimental data are approximately consistent with the law P0(Φ)∝Φ−1 exp(−Φ/〈Φ〉), where all dependencies on and μ are described by the single dimensionless parameter >0. Also the parameters describing the shape of F(ω) are found to obey remarkably simple and general laws of dependence on and μ. The experimental results are interpreted by means of the Langevin theory of domain‐wall dynamics proposed in a companion paper. The theory is in good agreement with experiments, and permits one to reduce the basic aspects of BE phenomenology to the behavior of two parameters describing the stochastic fluctuations of the local coercive field experienced by a moving domain wall
Modelling radiation-induced cell cycle delays
Ionizing radiation is known to delay the cell cycle progression. In
particular after particle exposure significant delays have been observed and it
has been shown that the extent of delay affects the expression of damage such
as chromosome aberrations. Thus, to predict how cells respond to ionizing
radiation and to derive reliable estimates of radiation risks, information
about radiation-induced cell cycle perturbations is required. In the present
study we describe and apply a method for retrieval of information about the
time-course of all cell cycle phases from experimental data on the mitotic
index only. We study the progression of mammalian cells through the cell cycle
after exposure. The analysis reveals a prolonged block of damaged cells in the
G2 phase. Furthermore, by performing an error analysis on simulated data
valuable information for the design of experimental studies has been obtained.
The analysis showed that the number of cells analyzed in an experimental sample
should be at least 100 to obtain a relative error less than 20%.Comment: 19 pages, 11 figures, accepted for publication in Radiation and
Environmental Biophysic
Hydrostatic strain enhancement in laterally confined SiGe nanostripes
Strain-engineering in SiGe nanostructures is fundamental for the design of
optoelectronic devices at the nanoscale. Here we explore a new strategy, where
SiGe structures are laterally confined by the Si substrate, to obtain high
tensile strain avoiding the use of external stressors, and thus improving the
scalability. Spectro-microscopy techniques, finite element method simulations
and ab initio calculations are used to investigate the strain state of
laterally confined Ge-rich SiGe nano-stripes. Strain information is obtained by
tip enhanced Raman spectroscopy with an unprecedented lateral resolution of ~
30 nm. The nano-stripes exhibit a large tensile hydrostatic strain component,
which is maximum at the center of the top free surface, and becomes very small
at the edges. The maximum lattice deformation is larger than the typical values
of thermally relaxed Ge/Si(001) layers. This strain enhancement originates from
a frustrated relaxation in the out-of-plane direction, resulting from the
combination of the lateral confinement induced by the substrate side walls and
the plastic relaxation of the misfit strain in the (001) plane at the SiGe/Si
interface. The effect of this tensile lattice deformation at the stripe surface
is probed by work function mapping, performed with a spatial resolution better
than 100 nm using X-ray photoelectron emission microscopy. The nano-stripes
exhibit a positive work function shift with respect to a bulk SiGe alloy,
quantitatively confirmed by electronic structure calculations of tensile
strained configurations. The present results have a potential impact on the
design of optoelectronic devices at a nanometer length scale.Comment: 40 pages, 11 figures, submitted to Physical Review
A novel epilepsy mutation in the sodium channel SCN1A identifies a cytoplasmic domain for {beta} subunit interaction
A mutation in the sodium channel SCN1A was identified in a small Italian family with dominantly inherited generalized epilepsy with febrile seizures plus (GEFS+). The mutation, D1866Y, alters an evolutionarily conserved aspartate residue in the C-terminal cytoplasmic domain of the sodium channel {alpha} subunit. The mutation decreased modulation of the {alpha} subunit by {beta}1, which normally causes a negative shift in the voltage dependence of inactivation in oocytes. There was less of a shift with the mutant channel, resulting in a 10 mV difference between the wild-type and mutant channels in the presence of {beta}1. This shift increased the magnitude of the window current, which resulted in more persistent current during a voltage ramp. Computational analysis suggests that neurons expressing the mutant channels will fire an action potential with a shorter onset delay in response to a threshold current injection, and that they will fire multiple action potentials with a shorter interspike interval at a higher input stimulus. These results suggest a causal relationship between a positive shift in the voltage dependence of sodium channel inactivation and spontaneous seizure activity. Direct interaction between the cytoplasmic C-terminal domain of the wild-type{alpha} subunit with the {beta}1or {beta}3 subunit was first demonstrated by yeast two-hybrid analysis. The SCN1A peptide K1846-R1886 is sufficient for {beta} subunit interaction. Coimmunoprecipitation from transfected mammalian cells confirmed the interaction between the C-terminal domains of the {alpha} and {beta}1 subunits. The D1866Y mutation weakens this interaction, demonstrating a novel molecular mechanism leading to seizure susceptibility
Adjunctive Brivaracetam in Focal Epilepsy: Real-World Evidence from the BRIVAracetam add-on First Italian netwoRk STudy (BRIVAFIRST)
Background: In randomized controlled trials, add-on brivaracetam (BRV) reduced seizure frequency in patients with drug-resistant focal epilepsy. Studies performed in a naturalistic setting are a useful complement to characterize the drug profile. Objective: This multicentre study assessed the effectiveness and tolerability of adjunctive BRV in a large population of patients with focal epilepsy in the context of real-world clinical practice. Methods: The BRIVAFIRST (BRIVAracetam add-on First Italian netwoRk STudy) was a retrospective, multicentre study including adult patients prescribed adjunctive BRV. Patients with focal epilepsy and 12-month follow-up were considered. Main outcomes included the rates of seizure\u2010freedom, seizure response ( 65 50% reduction in baseline seizure frequency), and treatment discontinuation. The incidence of adverse events (AEs) was also considered. Analyses by levetiracetam (LEV) status and concomitant use of strong enzyme-inducing antiseizure medications (EiASMs) and sodium channel blockers (SCBs) were performed. Results: A total of 1029 patients with a median age of 45 years (33\u201356) was included. At 12 months, 169 (16.4%) patients were seizure-free and 383 (37.2%) were seizure responders. The rate of seizure freedom was 22.3% in LEV-naive patients, 7.1% in patients with prior LEV use and discontinuation due to insufficient efficacy, and 31.2% in patients with prior LEV use and discontinuation due to AEs (p < 0.001); the corresponding values for 65 50% seizure frequency reduction were 47.9%, 29.7%, and 42.8% (p < 0.001). There were no statistically significant differences in seizure freedom and seizure response rates by use of strong EiASMs. The rates of seizure freedom (20.0% vs. 16.6%; p = 0.341) and seizure response (39.7% vs. 26.9%; p = 0.006) were higher in patients receiving SCBs than those not receiving SCBs; 265 (25.8%) patients discontinued BRV. AEs were reported by 30.1% of patients, and were less common in patients treated with BRV and concomitant SCBs than those not treated with SCBs (28.9% vs. 39.8%; p = 0.017). Conclusion: The BRIVAFIRST provided real-world evidence on the effectiveness of BRV in patients with focal epilepsy irrespective of LEV history and concomitant ASMs, and suggested favourable therapeutic combinations
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