354 research outputs found
Extended Huckel theory for bandstructure, chemistry, and transport. II. Silicon
In this second paper, we develop transferable semi-empirical parameters for
the technologically important material, silicon, using Extended Huckel Theory
(EHT) to calculate its electronic structure. The EHT-parameters areoptimized to
experimental target values of the band dispersion of bulk-silicon. We obtain a
very good quantitative match to the bandstructure characteristics such as
bandedges and effective masses, which are competitive with the values obtained
within an orthogonal-tight binding model for silicon. The
transferability of the parameters is investigated applying them to different
physical and chemical environments by calculating the bandstructure of two
reconstructed surfaces with different orientations: Si(100) (2x1) and Si(111)
(2x1). The reproduced - and -surface bands agree in part
quantitatively with DFT-GW calculations and PES/IPES experiments demonstrating
their robustness to environmental changes. We further apply the silicon
parameters to describe the 1D band dispersion of a unrelaxed rectangular
silicon nanowire (SiNW) and demonstrate the EHT-approach of surface passivation
using hydrogen. Our EHT-parameters thus provide a quantitative model of
bulk-silicon and silicon-based materials such as contacts and surfaces, which
are essential ingredients towards a quantitative quantum transport simulation
through silicon-based heterostructures.Comment: 9 pages, 9 figure
First-principles modelling of molecular single-electron transistors
We present a first-principles method for calculating the charging energy of a
molecular single-electron transistor operating in the Coulomb blockade regime.
The properties of the molecule are modeled using density-functional theory, the
environment is described by a continuum model, and the interaction between the
molecule and the environment are included through the Poisson equation. The
model is used to calculate the charge stability diagrams of a benzene and
C molecular single-electron transistor
From Fully Strained to Relaxed: Epitaxial Ferroelectric Al<sub>1-x</sub>Sc<sub>x</sub>N for III-N Technology
The recent emergence of wurtzite-type nitride ferroelectrics such as Al1-xScxN has paved the way for the introduction of all-epitaxial, all-wurtzite-type ferroelectric III-N semiconductor heterostructures. This paper presents the first in-depth structural and electrical characterization of such an epitaxial heterostructure by investigating sputter deposited Al1-xScxN solid solutions with x between 0.19 and 0.28 grown over doped n-GaN. The results of detailed structural investigations on the strain state and the initial unit-cell polarity with the peculiarities observed in the ferroelectric response are correlated. Among these, a Sc-content dependent splitting of the ferroelectric displacement current into separate peaks, which can be correlated with the presence of multiple strain states in the Al1-xScxN films is discussed. Unlike in previously reported studies on ferroelectric Al1-xScxN, all films thicker than 30 nm grown on the metal (M)-polar GaN template feature an initial multidomain state. The results support that regions with opposed polarities in as-grown films do not result as a direct consequence of the in-plane strain distribution, but are rather mediated by the competition between M-polar epitaxial growth on an M-polar template and a deposition process that favors nitrogen (N)-polar growth
Totally laparoscopic versus conventional ileoanal pouch procedure – design of a single-centre, expertise based randomised controlled trial to compare the laparoscopic and conventional surgical approach in patients undergoing primary elective restorative proctocolectomy- LapConPouch-Trial
BACKGROUND: Restorative proctocolectomy is increasingly being performed minimal invasively but a totally laparoscopic technique has not yet been compared to the standard open technique in a randomized study. METHODS/DESIGN: This is a two armed, single centre, expertise based, preoperatively randomized, patient blinded study. It is designed as a two-group parallel superiority study. Power calculation revealed 80 patients per group in order to recruit the 65 patients to be analysed for the primary endpoint. The primary objective is to investigate intra-operative blood loss and the need for blood transfusions. We hypothesise that intra-operative blood loss and the need for peri-operative blood transfusions are significantly higher in the conventional group. Additionally a set of surgical and non-surgical parameters related to the operation will be analysed as secondary objectives. These will include operative time, complications, postoperative pain, lung function, postoperative length of hospital stay, a cosmetic score and pre-and postoperative quality of life. DISCUSSION: The trial will answer the question whether there is indeed an advantage in the laparoscopic group in regard to blood loss and the need for blood transfusions. Moreover, it will generate data on the safety and potential advantages and disadvantages of the minimally invasive approach
Observation of Non-Exponential Orbital Electron Capture Decays of Hydrogen-Like Pr and Pm Ions
We report on time-modulated two-body weak decays observed in the orbital
electron capture of hydrogen-like Pr and Pm
ions coasting in an ion storage ring. Using non-destructive single ion,
time-resolved Schottky mass spectrometry we found that the expected exponential
decay is modulated in time with a modulation period of about 7 seconds for both
systems. Tentatively this observation is attributed to the coherent
superposition of finite mass eigenstates of the electron neutrinos from the
weak decay into a two-body final state.Comment: 12 pages, 5 figure
High-resolution measurement of the time-modulated orbital electron capture and of the decay of hydrogen-like Pm ions
The periodic time modulations, found recently in the two-body orbital
electron-capture (EC) decay of both, hydrogen-like Pr and
Pm ions, with periods near to 7s and amplitudes of about 20%,
were re-investigated for the case of Pm by using a 245 MHz
resonator cavity with a much improved sensitivity and time resolution. We
observed that the exponential EC decay is modulated with a period s, in accordance with a modulation period s as obtained
from simultaneous observations with a capacitive pick-up, employed also in the
previous experiments. The modulation amplitudes amount to and
for the 245 MHz resonator and the capacitive pick-up,
respectively. These new results corroborate for both detectors {\it exactly}
our previous findings of modulation periods near to 7s, though with {\it
distinctly smaller} amplitudes. Also the three-body decays have been
analyzed. For a supposed modulation period near to 7s we found an amplitude , compatible with and in agreement with the preliminary
result of our previous experiment. These observations could
point at weak interaction as origin of the observed 7s-modulation of the EC
decay. Furthermore, the data suggest that interference terms occur in the
two-body EC decay, although the neutrinos are not directly observed.Comment: In memoriam of Prof. Paul Kienle, 9 pages, 1 table, 5 figures Phys.
Lett. B (2013) onlin
Present and Future Experiments with Stored Exotic Nuclei at Relativistic Energies
Recent progress is presented from experiments on masses and lifetimes of bare
and few-electron exotic nuclei at GSI.Comment: Proceedings of International Conference on "Frontiers in Nuclear
Structure, Astrophysics and Reactions", Kos, Greece, September 12-17, 200
eta-Nucleus interactions and in-medium properties of N*(1535) in chiral models
The properties of eta-nucleus interaction and their experimental consequences
are investigated with eta-nucleus optical potentials obtained by postulating
the N*(1535) dominance for eta-N system. The N*(1535) properties in nuclear
medium are evaluated by two kinds of chiral effective models based on distinct
pictures of N*(1535). We find that these two models provide qualitatively
different optical potentials of the eta meson, reflecting the in-medium
properties of N*(1535) in these models. In order to compare these models in
physical observables, we calculate spectra of (d,3He) reactions for the eta
mesic nucleus formation with various kinds of target nuclei. We show that the
(d,3He) spectra obtained in these models are significantly different and are
expected to be distinguishable in experiments.Comment: 24 pages, 8 figure
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