1,051 research outputs found
Efficient Charge Separation in 2D Janus van der Waals Structures with Build-in Electric Fields and Intrinsic p-n Doping
Janus MoSSe monolayers were recently synthesised by replacing S by Se on one
side of MoS (or vice versa for MoSe). Due to the different
electronegativity of S and Se these structures carry a finite out-of-plane
dipole moment. As we show here by means of density functional theory (DFT)
calculations, this intrinsic dipole leads to the formation of built-in electric
fields when the monolayers are stacked to form -layer structures. For
sufficiently thin structures () the dipoles add up and shift the vacuum
level on the two sides of the film by eV. However, for
thicker films charge transfer occurs between the outermost layers forming
atomically thin n- and p-doped electron gasses at the two surfaces. The doping
concentration can be tuned between about e/cm and
e/cm by varying the film thickness. The surface charges
counteract the static dipoles leading to saturation of the vacuum level shift
at around 2.2 eV for . Based on band structure calculations and the
Mott-Wannier exciton model, we compute the energies of intra- and interlayer
excitons as a function of film thickness suggesting that the Janus multilayer
films are ideally suited for achieving ultrafast charge separation over atomic
length scales without chemical doping or applied electric fields. Finally, we
explore a number of other potentially synthesisable 2D Janus structures with
different band gaps and internal dipole moments. Our results open new
opportunities for ultrathin opto-electronic components such as tunnel diodes,
photo-detectors, or solar cells
A large magnetic storage ring for Bose-Einstein condensates
Cold atomic clouds and Bose-Einstein condensates have been stored in a 10cm
diameter vertically-oriented magnetic ring. An azimuthal magnetic field enables
low-loss propagation of atomic clouds over a total distance of 2m, with a
heating rate of less than 50nK/s. The vertical geometry was used to split an
atomic cloud into two counter-rotating clouds which were recombined after one
revolution. The system will be ideal for studying condensate collisions and
ultimately Sagnac interferometry.Comment: 4 pages, 5 figure
NOSTROMO - D5.1 - ATM Performance Metamodels - Preliminary Release
This deliverable presents the results obtained with the meta-modelling process presented in D3.1 and D3.2 applied to the two micromodels (or simulators), Mercury and FLITAN, themselves implementing concepts from four SESAR solutions, PJ01.01, PJ07.02, PJ08-01, and PJ02.08.
The objective of the meta-modelling process is explained briefly again in the introduction, in particular with respect to performance assessment. The rationale for the selection of the SESAR solutions implemented in the simulators are briefly explained too.
The simulators are presented in two distinct chapters. First, a general presentation of each simulator is given, with past challenges and development, before explaining the development steps carried out to implement the concepts from the chosen solutions. Domain research questions that could be answered by these implementations are highlighted along the way.
The meta-modelling process is then briefly explained again, followed by the results obtained with the two simulators, in distinct sections. The results highlight the performance of the meta-model with respect to approximating the output of the micromodels, but not the performance of the models themselves with respect to the research questions, which will be explored in WP7 instead.
The deliverable closes with some considerations on the meta-modelling performance and next steps for this line of work
The Briard Problem
The Briard breed has stimulated some ophthalmic interest in Canada, Europe, and the United States. Ophthalmoscopic changes similar to central progressive retinal atrophy have been diagnosed. This report adds further insight into the type of retinal degeneration and questions the associated physical findings as they may relate to the retinal disease
Detecting sterile neutrinos with KATRIN like experiments
A sterile neutrino with mass in the eV range, mixing with the electron
antineutrino, is allowed and possibly even preferred by cosmology and
oscillation experiments. If such eV-mass neutrinos exist they provide a much
better target for direct detection in beta decay experiments than the active
neutrinos which are expected to have sub-eV masses. Their relatively high mass
would allow for an easy separation from the primary decay signal in experiments
such as KATRIN.Comment: 23 pages, 7 figures. References & Figures updated. Text reviewed and
revised. Accepted for publication JCA
Learning and Generalizing Polynomials in Simulation Metamodeling
The ability to learn polynomials and generalize out-of-distribution is
essential for simulation metamodels in many disciplines of engineering, where
the time step updates are described by polynomials. While feed forward neural
networks can fit any function, they cannot generalize out-of-distribution for
higher-order polynomials. Therefore, this paper collects and proposes
multiplicative neural network (MNN) architectures that are used as recursive
building blocks for approximating higher-order polynomials. Our experiments
show that MNNs are better than baseline models at generalizing, and their
performance in validation is true to their performance in out-of-distribution
tests. In addition to MNN architectures, a simulation metamodeling approach is
proposed for simulations with polynomial time step updates. For these
simulations, simulating a time interval can be performed in fewer steps by
increasing the step size, which entails approximating higher-order polynomials.
While our approach is compatible with any simulation with polynomial time step
updates, a demonstration is shown for an epidemiology simulation model, which
also shows the inductive bias in MNNs for learning and generalizing
higher-order polynomials
Explainable Metamodels for ATM Performance Assessment
Fast-time simulation constitutes a well-known and
long-established technique within the Air Traffic Management
(ATM) community. However, it is often the case that simulation input and output spaces are underutilized, limiting the full understandability, transparency, and interpretability of the obtained results.
In this paper, we propose a methodology that combines simulation metamodeling and SHapley Additive exPlanations (SHAP) values, aimed at uncovering the intricate hidden relationships among the input and output variables of a simulated ATM system in a rather practical way. Whereas metamodeling provides explicit functional approximations mimicking the behavior of the simulators, the SHAP-based analysis delivers a systematic framework for improving their explainability. We illustrate our approach using a state-of-the-art ATM simulator across two case studies in which two delay-centered performance metrics are analyzed. The results show that the proposed methodology can effectively make simulation and its results more explainable, facilitating the interpretation of the obtained emergent behavior, and additionally opening new opportunities towards novel performance assessment processes within the ATM research field
Laser frequency stabilization to a single ion
A fundamental limit to the stability of a single-ion optical frequency
standard is set by quantum noise in the measurement of the internal state of
the ion. We discuss how the interrogation sequence and the processing of the
atomic resonance signal can be optimized in order to obtain the highest
possible stability under realistic experimental conditions. A servo algorithm
is presented that stabilizes a laser frequency to the single-ion signal and
that eliminates errors due to laser frequency drift. Numerical simulations of
the servo characteristics are compared to experimental data from a frequency
comparison of two single-ion standards based on a transition at 688 THz in
171Yb+. Experimentally, an instability sigma_y(100 s)=9*10^{-16} is obtained in
the frequency difference between both standards.Comment: 15 pages, 5 figures, submitted to J. Phys.
Control Flow Analysis for BioAmbients
AbstractThis paper presents a static analysis for investigating properties of biological systems specified in BioAmbients. We exploit the control flow analysis to decode the bindings of variables induced by communications and to build a relation of the ambients that can interact with each other. We eventually apply our analysis to an example of gene regulation by positive feedback taken from the literature
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