226 research outputs found
A quantum spin transducer based on nano electro-mechancial resonator arrays
Implementation of quantum information processing faces the contradicting
requirements of combining excellent isolation to avoid decoherence with the
ability to control coherent interactions in a many-body quantum system. For
example, spin degrees of freedom of electrons and nuclei provide a good quantum
memory due to their weak magnetic interactions with the environment. However,
for the same reason it is difficult to achieve controlled entanglement of spins
over distances larger than tens of nanometers. Here we propose a universal
realization of a quantum data bus for electronic spin qubits where spins are
coupled to the motion of magnetized mechanical resonators via magnetic field
gradients. Provided that the mechanical system is charged, the magnetic moments
associated with spin qubits can be effectively amplified to enable a coherent
spin-spin coupling over long distances via Coulomb forces. Our approach is
applicable to a wide class of electronic spin qubits which can be localized
near the magnetized tips and can be used for the implementation of hybrid
quantum computing architectures
Resonance and frequency-locking phenomena in spatially extended phytoplankton-zooplankton system with additive noise and periodic forces
In this paper, we present a spatial version of phytoplankton-zooplankton
model that includes some important factors such as external periodic forces,
noise, and diffusion processes. The spatially extended
phytoplankton-zooplankton system is from the original study by Scheffer [M
Scheffer, Fish and nutrients interplay determines algal biomass: a minimal
model, Oikos \textbf{62} (1991) 271-282]. Our results show that the spatially
extended system exhibit a resonant patterns and frequency-locking phenomena.
The system also shows that the noise and the external periodic forces play a
constructive role in the Scheffer's model: first, the noise can enhance the
oscillation of phytoplankton species' density and format a large clusters in
the space when the noise intensity is within certain interval. Second, the
external periodic forces can induce 4:1 and 1:1 frequency-locking and spatially
homogeneous oscillation phenomena to appear. Finally, the resonant patterns are
observed in the system when the spatial noises and external periodic forces are
both turned on. Moreover, we found that the 4:1 frequency-locking transform
into 1:1 frequency-locking when the noise intensity increased. In addition to
elucidating our results outside the domain of Turing instability, we provide
further analysis of Turing linear stability with the help of the numerical
calculation by using the Maple software. Significantly, oscillations are
enhanced in the system when the noise term presents. These results indicate
that the oceanic plankton bloom may partly due to interplay between the
stochastic factors and external forces instead of deterministic factors. These
results also may help us to understand the effects arising from undeniable
subject to random fluctuations in oceanic plankton bloom.Comment: Some typos errors are proof, and some strong relate references are
adde
An exact expression to calculate the derivatives of position-dependent observables in molecular simulations with flexible constraints
In this work, we introduce an algorithm to compute the derivatives of
physical observables along the constrained subspace when flexible constraints
are imposed on the system (i.e., constraints in which the hard coordinates are
fixed to configuration-dependent values). The presented scheme is exact, it
does not contain any tunable parameter, and it only requires the calculation
and inversion of a sub-block of the Hessian matrix of second derivatives of the
function through which the constraints are defined. We also present a practical
application to the case in which the sought observables are the Euclidean
coordinates of complex molecular systems, and the function whose minimization
defines the constraints is the potential energy. Finally, and in order to
validate the method, which, as far as we are aware, is the first of its kind in
the literature, we compare it to the natural and straightforward
finite-differences approach in three molecules of biological relevance:
methanol, N-methyl-acetamide and a tri-glycine peptideComment: 13 pages, 8 figures, published versio
Dzyaloshinskii-Moriya Interaction and Spiral Order in Spin-orbit Coupled Optical Lattices
We show that the recent experimental realization of spin-orbit coupling in
ultracold atomic gases can be used to study different types of spin spiral
order and resulting multiferroic effects. Spin-orbit coupling in optical
lattices can give rise to the Dzyaloshinskii-Moriya (DM) spin interaction which
is essential for spin spiral order. By taking into account spin-orbit coupling
and an external Zeeman field, we derive an effective spin model in the Mott
insulator regime at half filling and demonstrate that the DM interaction in
optical lattices can be made extremely strong with realistic experimental
parameters. The rich finite temperature phase diagrams of the effective spin
models for fermions and bosons are obtained via classical Monte Carlo
simulations.Comment: 7 pages, 5 figure
Equivalence of three-dimensional spacetimes
A solution to the equivalence problem in three-dimensional gravity is given
and a practically useful method to obtain a coordinate invariant description of
local geometry is presented. The method is a nontrivial adaptation of Karlhede
invariant classification of spacetimes of general relativity. The local
geometry is completely determined by the curvature tensor and a finite number
of its covariant derivatives in a frame where the components of the metric are
constants. The results are presented in the framework of real two-component
spinors in three-dimensional spacetimes, where the algebraic classifications of
the Ricci and Cotton-York spinors are given and their isotropy groups and
canonical forms are determined. As an application we discuss Goedel-type
spacetimes in three-dimensional General Relativity. The conditions for local
space and time homogeneity are derived and the equivalence of three-dimensional
Goedel-type spacetimes is studied and the results are compared with previous
works on four-dimensional Goedel-type spacetimes.Comment: 13 pages - content changes and corrected typo
Analyzing derived metallicities and ionization parameters from model-based determinations in ionized gaseous nebulae
We analyze the reliability of oxygen abundances and ionization parameters
obtained from different diagnostic diagrams. For this, we compiled from the
literature observational emission line intensities and oxygen abundance of 446
star-forming regions whose O/H abundance was determined by direct estimation of
electron temperature. The abundances compiled were compared with the values
calculated in this work using different diagnostic diagrams in combination with
results from a grid of photoionization models. We found that the
[\ion{O}{iii}]/[\ion{O}{ii}] vs. [\ion{N}{ii}]/[\ion{O}{ii}],
[\ion{O}{iii}]/H vs. [\ion{N}{ii}]/[\ion{O}{ii}], and
([\ion{O}{iii}]/H)/([\ion{N}{ii}]/H) vs.
[\ion{S}{ii}]/[\ion{S}{iii}] diagnostic diagrams give O/H values close to the
-method, with differences of about 0.04 dex and dispersion of about
0.3 dex. Similar results were obtained by detailed models but with a dispersion
of 0.08 dex. The origin of the dispersion found in the use of diagnostic
diagrams is probably due to differences between the real N/O-O/H relation of
the sample and the one assumed in the models. This is confirmed by the use of
detailed models that do not have a fixed N/O-O/H relation. We found no
correlation between ionization parameter and the metallicity for the objects of
our sample. We conclude that the combination of two line ratio predicted by
photoionization models, one sensitive to the metallicity and another sensitive
to the ionization parameter, which takes into account the physical conditions
of star-forming regions, gives O/H estimates close to the values derived using
direct detections of electron temperatures.Comment: 12 pages, 9 figures, accepted by MNRA
Cross section measurements of 155,157Gd(n, Îł) induced by thermal and epithermal neutrons
© SIF, Springer-Verlag GmbH Germany, part of Springer Nature 2019Neutron capture cross section measurements on 155Gd and 157Gd were performed using the time-of-flight technique at the n_TOF facility at CERN on isotopically enriched samples. The measurements were carried out in the n_TOF experimental area EAR1, at 185 m from the neutron source, with an array of 4 C6D6 liquid scintillation detectors. At a neutron kinetic energy of 0.0253 eV, capture cross sections of 62.2(2.2) and 239.8(8.4) kilobarn have been derived for 155Gd and 157Gd, respectively, with up to 6% deviation relative to values presently reported in nuclear data libraries, but consistent with those values within 1.6 standard deviations. A resonance shape analysis has been performed in the resolved resonance region up to 181 eV and 307 eV, respectively for 155Gd and 157Gd, where on average, resonance parameters have been found in good agreement with evaluations. Above these energies and up to 1 keV, the observed resonance-like structure of the cross section has been analysed and characterised. From a statistical analysis of the observed neutron resonances we deduced: neutron strength function of 2. 01 (28) à 10 - 4 and 2. 17 (41) à 10 - 4; average total radiative width of 106.8(14) meV and 101.1(20) meV and s-wave resonance spacing 1.6(2) eV and 4.8(5) eV for n + 155Gd and n + 157Gd systems, respectively.Peer reviewedFinal Accepted Versio
Molecular excitation in the Interstellar Medium: recent advances in collisional, radiative and chemical processes
We review the different excitation processes in the interstellar mediumComment: Accepted in Chem. Re
Search for pair-produced long-lived neutral particles decaying to jets in the ATLAS hadronic calorimeter in ppcollisions at âs=8TeV
The ATLAS detector at the Large Hadron Collider at CERN is used to search for the decay of a scalar boson to a pair of long-lived particles, neutral under the Standard Model gauge group, in 20.3fbâ1of data collected in protonâproton collisions at âs=8TeV. This search is sensitive to long-lived particles that decay to Standard Model particles producing jets at the outer edge of the ATLAS electromagnetic calorimeter or inside the hadronic calorimeter. No significant excess of events is observed. Limits are reported on the product of the scalar boson production cross section times branching ratio into long-lived neutral particles as a function of the proper lifetime of the particles. Limits are reported for boson masses from 100 GeVto 900 GeV, and a long-lived neutral particle mass from 10 GeVto 150 GeV
Cost-effective external interference for promoting the evolution of cooperation.
The problem of promoting the evolution of cooperative behaviour within populations of self-regarding individuals has been intensively investigated across diverse fields of behavioural, social and computational sciences. In most studies, cooperation is assumed to emerge from the combined actions of participating individuals within the populations, without taking into account the possibility of external interference and how it can be performed in a cost-efficient way. Here, we bridge this gap by studying a cost-efficient interference model based on evolutionary game theory, where an exogenous decision-maker aims to ensure high levels of cooperation from a population of individuals playing the one-shot Prisoner's Dilemma, at a minimal cost. We derive analytical conditions for which an interference scheme or strategy can guarantee a given level of cooperation while at the same time minimising the total cost of investment (for rewarding cooperative behaviours), and show that the results are highly sensitive to the intensity of selection by interference. Interestingly, we show that a simple class of interference that makes investment decisions based on the population composition can lead to significantly more cost-efficient outcomes than standard institutional incentive strategies, especially in the case of weak selection.</p
- âŠ