173 research outputs found
Simulation of the elementary evolution operator with the motional states of an ion in an anharmonic trap
Following a recent proposal of L. Wang and D. Babikov, J. Chem. Phys. 137,
064301 (2012), we theoretically illustrate the possibility of using the
motional states of a ion trapped in a slightly anharmonic potential to
simulate the single-particle time-dependent Schr\"odinger equation. The
simulated wave packet is discretized on a spatial grid and the grid points are
mapped on the ion motional states which define the qubit network. The
localization probability at each grid point is obtained from the population in
the corresponding motional state. The quantum gate is the elementary evolution
operator corresponding to the time-dependent Schr\"odinger equation of the
simulated system. The corresponding matrix can be estimated by any numerical
algorithm. The radio-frequency field able to drive this unitary transformation
among the qubit states of the ion is obtained by multi-target optimal control
theory. The ion is assumed to be cooled in the ground motional state and the
preliminary step consists in initializing the qubits with the amplitudes of the
initial simulated wave packet. The time evolution of the localization
probability at the grids points is then obtained by successive applications of
the gate and reading out the motional state population. The gate field is
always identical for a given simulated potential, only the field preparing the
initial wave packet has to be optimized for different simulations. We check the
stability of the simulation against decoherence due to fluctuating electric
fields in the trap electrodes by applying dissipative Lindblad dynamics.Comment: 31 pages, 8 figures. Revised version. New title, new figure and new
reference
Movement generation using dynamical systems : a humanoid robot performing a drumming task
The online generation of trajectories in humanoid
robots remains a difficult problem. In this contribution, we present a system that allows the superposition, and the switch between, discrete and rhythmic movements. Our approach uses
nonlinear dynamical systems for generating trajectories online and in real time. Our goal is to make use of attractor properties of dynamical systems in order to provide robustness against small perturbations and to enable online modulation of the trajectories. The system is demonstrated on a humanoid robot performing a drumming task.This work was made possible thanks to the support of the Swiss National Science Foundation (A.I.) and of the European Commissions Cognition Unit, project no. IST-2004-004370 : RobotCub (S.D.
Nano-scale hydrogen-bond network improves the durability of greener cements
More than ever before, the world's increasing need for new infrastructure demands the construction of efficient, sustainable and durable buildings, requiring minimal climate-changing gas-generation in their production. Maintenance-free “greener” building materials made from blended cements have advantages over ordinary Portland cements, as they are cheaper, generate less carbon dioxide and are more durable. The key for the improved performance of blends (which substitute fine amorphous silicates for cement) is related to their resistance to water penetration. The mechanism of this water resistance is of great environmental and economical impact but is not yet understood due to the complexity of the cement's hydration reactions. Using neutron spectroscopy, we studied a blend where cement was replaced by ash from sugar cane residuals originating from agricultural waste. Our findings demonstrate that the development of a distinctive hydrogen bond network at the nano-scale is the key to the performance of these greener materials
Fluctuation-dissipation relations in the non-equilibrium critical dynamics of Ising models
We investigate the relation between two-time, multi-spin, correlation and
response functions in the non-equilibrium critical dynamics of Ising models in
d=1 and d=2 spatial dimensions. In these non-equilibrium situations, the
fluctuation-dissipation theorem (FDT) is not satisfied. We find FDT
`violations' qualitatively similar to those reported in various glassy
materials, but quantitatively dependent on the chosen observable, in contrast
to the results obtained in infinite-range glass models. Nevertheless, all FDT
violations can be understood by considering separately the contributions from
large wavevectors, which are at quasi-equilibrium and obey FDT, and from small
wavevectors where a generalized FDT holds with a non-trivial limit
fluctuation-dissipation ratio X. In d=1, we get X = 1/2 for spin observables,
which measure the orientation of domains, while X = 0 for observables that are
sensitive to the domain-wall motion. Numerical simulations in d=2 reveal a
unique X = 0.34 for all observables. Measurement protocols for X are discussed
in detail. Our results suggest that the definition of an effective temperature
Teff = T / X for large length scales is generically possible in non-equilibrium
critical dynamics.Comment: 26 pages, 10 figure
The XMM-LSS survey. Survey design and first results
We have designed a medium deep large area X-ray survey with XMM - the XMM
Large Scale Structure survey, XMM-LSS - with the scope of extending the
cosmological tests attempted using ROSAT cluster samples to two redshift bins
between 0<z<1 while maintaining the precision of earlier studies. Two main
goals have constrained the survey design: the evolutionary study of the
cluster-cluster correlation function and of the cluster number density. The
results are promising and, so far, in accordance with our predictions as to the
survey sensitivity and cluster number density. The feasibility of the programme
is demonstrated and further X-ray coverage is awaited in order to proceed with
a truly significant statistical analysis. (Abridged)Comment: Published in Journal of Cosmology and Astroparticle Physic
Human Ageing Genomic Resources:updates on key databases in ageing research
Ageing is a complex and multifactorial process. For two decades, the Human Ageing Genomic Resources (HAGR) have aided researchers in the study of various aspects of ageing and its manipulation. Here, we present the key features and recent enhancements of these resources, focusing on its six main databases. One database, GenAge, focuses on genes related to ageing, featuring 307 genes linked to human ageing and 2205 genes associated with longevity and ageing in model organisms. AnAge focuses on ageing, longevity, and life-history across animal species, containing data on 4645 species. DrugAge includes information about 1097 longevity drugs and compounds in model organisms such as mice, rats, flies, worms and yeast. GenDR provides a list of 214 genes associated with the life-extending benefits of dietary restriction in model organisms. CellAge contains a catalogue of 866 genes associated with cellular senescence. The LongevityMap serves as a repository for genetic variants associated with human longevity, encompassing 3144 variants pertaining to 884 genes. Additionally, HAGR provides various tools as well as gene expression signatures of ageing, dietary restriction, and replicative senescence based on meta-analyses. Our databases are integrated, regularly updated, and manually curated by experts. HAGR is freely available online (https://genomics.senescence.info/).</p
Human Ageing Genomic Resources:updates on key databases in ageing research
Ageing is a complex and multifactorial process. For two decades, the Human Ageing Genomic Resources (HAGR) have aided researchers in the study of various aspects of ageing and its manipulation. Here, we present the key features and recent enhancements of these resources, focusing on its six main databases. One database, GenAge, focuses on genes related to ageing, featuring 307 genes linked to human ageing and 2205 genes associated with longevity and ageing in model organisms. AnAge focuses on ageing, longevity, and life-history across animal species, containing data on 4645 species. DrugAge includes information about 1097 longevity drugs and compounds in model organisms such as mice, rats, flies, worms and yeast. GenDR provides a list of 214 genes associated with the life-extending benefits of dietary restriction in model organisms. CellAge contains a catalogue of 866 genes associated with cellular senescence. The LongevityMap serves as a repository for genetic variants associated with human longevity, encompassing 3144 variants pertaining to 884 genes. Additionally, HAGR provides various tools as well as gene expression signatures of ageing, dietary restriction, and replicative senescence based on meta-analyses. Our databases are integrated, regularly updated, and manually curated by experts. HAGR is freely available online (https://genomics.senescence.info/).</p
Multichromophoric Cyclodextrins. 3. Investigation of Dynamics of Energy Hopping by Frequency-Domain Fluorometry
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