4,712 research outputs found
CULTURAL ISSUES IN SUSTAINABLE SUPPLY CHAIN MANAGEMENT
This paper aims at contributing to literature debate on sustainable supply chain management by including the cultural factors as a strategic element. The focus in is on the role role of culture in the relationships of sustanible supply chain. The analysis sheds light on the CSR practices followed by MNC and provide a first contribute to identify the consideration of cultural issues as central theme to Sustainable supply chain management
From perfect to fractal transmission in spin chains
Perfect state transfer is possible in modulated spin chains, imperfections
however are likely to corrupt the state transfer. We study the robustness of
this quantum communication protocol in the presence of disorder both in the
exchange couplings between the spins and in the local magnetic field. The
degradation of the fidelity can be suitably expressed, as a function of the
level of imperfection and the length of the chain, in a scaling form. In
addition the time signal of fidelity becomes fractal. We further characterize
the state transfer by analyzing the spectral properties of the Hamiltonian of
the spin chain.Comment: 8 pages, 10 figures, published versio
Evolutionary importance of intraspecific variation in sex pheromones
Sex pheromones in many insect species are important species-recognition signals that attract conspecifics and inhibit attraction between heterospecifics; therefore, sex pheromones have predominantly been considered to evolve due to interactions between species. Recent research, however, is uncovering roles for these signals in mate choice, and that variation within and between populations can be drivers of species evolution. Variation in pheromone communication channels arises from a combination of context-dependent, condition-dependent, or genetic mechanisms in both signalers and receivers. Variation can affect mate choice and thus gene flow between individuals and populations, affecting species' evolution. The complex interactions between intraspecific and interspecific selection forces calls for more integrative studies to understand the evolution of sex pheromone communication.Peer reviewe
Entanglement at the quantum phase transition in a harmonic lattice
The entanglement properties of the phase transition in a two dimensional
harmonic lattice, similar to the one observed in recent ion trap experiments,
are discussed both, for finite number of particles and thermodynamical limit.
We show that for the ground state at the critical value of the trapping
potential two entanglement measures, the negativity between two neighbouring
sites and the block entropy for blocks of size 1, 2 and 3, change abruptly.
Entanglement thus indicates quantum phase transitions in general; not only in
the finite dimensional case considered in [Phys. Rev. Lett. {\bf 93}, 250404
(2004)]. Finally, we consider the thermal state and compare its exact
entanglement with a temperature entanglement witness introduced in [Phys. Rev.
A {\bf 77} 062102 (2008)].Comment: extended published versio
Inhomogeneous Kibble-Zurek mechanism: vortex nucleation during Bose-Einstein condensation
The Kibble-Zurek mechanism is applied to the spontaneous formation of
vortices in a harmonically trapped thermal gas following a temperature quench
through the critical value for Bose-Einstein condensation. While in the
homogeneous scenario vortex nucleation is always expected, we show that it can
be completely suppressed in the presence of the confinement potential, whenever
the speed of the spatial front undergoing condensation is lower than a
threshold velocity. Otherwise, the interplay between the geometry and causality
leads to different scaling laws for the density of vortices as a function of
the quench rate, as we also illustrate for the case of a toroidal trapping
potential.Comment: 11 pages, 3 figure
Entanglement evolution after connecting finite to infinite quantum chains
We study zero-temperature XX chains and transverse Ising chains and join an
initially separate finite piece on one or on both sides to an infinite
remainder. In both critical and non-critical systems we find a typical increase
of the entanglement entropy after the quench, followed by a slow decay towards
the value of the homogeneous chain. In the critical case, the predictions of
conformal field theory are verified for the first phase of the evolution, while
at late times a step structure can be observed.Comment: 15 pages, 11 figure
recommendations to optimise reporting of epidemiological studies on antimicrobial resistance and informing improvement in antimicrobial stewardship
Objectives To explore the accuracy of application of the Strengthening the
Reporting of Observational Studies in Epidemiology (STROBE) tool in
epidemiological studies focused on the evaluation of the role of antibiotics
in selecting resistance, and to derive and test an extension of STROBE to
improve the suitability of the tool in evaluating the quality of reporting in
these area. Methods A three-step study was performed. First, a systematic
review of the literature analysing the association between antimicrobial
exposure and acquisition of methicillin-resistant Staphylococcus aureus and/or
multidrug-resistant Acinetobacter baumannii was performed. Second, articles
were reviewed according to the STROBE checklist for epidemiological studies.
Third, a set of potential new items focused on antimicrobial-resistance
quality indicators was derived through an expert two-round RAND-modified
Delphi procedure and tested on the articles selected through the literature
review. Results The literature search identified 78 studies. Overall, the
quality of reporting appeared to be poor in most areas. Five STROBE items,
comprising statistical analysis and study objectives, were satisfactory in
<25% of the studies. Informative abstract, reporting of bias, control of
confounding, generalisability and description of study size were missing in
more than half the articles. A set of 21 new items was developed and tested.
The new items focused particularly on the study setting, antimicrobial usage
indicators, and patients epidemiological and clinical characteristics. The
performance of the new items in included studies was very low (<25%).
Conclusions Our paper reveals that reporting in epidemiological papers
analysing the association between antimicrobial usage and development of
resistance is poor. The implementation of the newly developed STROBE for
antimicrobial stewardship (AMS) tool should enhance appropriate study design
and reporting, and therefore contribute to the improvement of evidence to be
used for AMS programme development and assessment
Optimal control of atom transport for quantum gates in optical lattices
By means of optimal control techniques we model and optimize the manipulation
of the external quantum state (center-of-mass motion) of atoms trapped in
adjustable optical potentials. We consider in detail the cases of both non
interacting and interacting atoms moving between neighboring sites in a lattice
of a double-well optical potentials. Such a lattice can perform
interaction-mediated entanglement of atom pairs and can realize two-qubit
quantum gates. The optimized control sequences for the optical potential allow
transport faster and with significantly larger fidelity than is possible with
processes based on adiabatic transport.Comment: revised version: minor changes, 2 references added, published versio
Adiabatic dynamics of an inhomogeneous quantum phase transition: the case of z > 1 dynamical exponent
We consider an inhomogeneous quantum phase transition across a multicritical
point of the XY quantum spin chain. This is an example of a Lifshitz transition
with a dynamical exponent z = 2. Just like in the case z = 1 considered in New
J. Phys. 12, 055007 (2010) when a critical front propagates much faster than
the maximal group velocity of quasiparticles vq, then the transition is
effectively homogeneous: density of excitations obeys a generalized
Kibble-Zurek mechanism and scales with the sixth root of the transition rate.
However, unlike for z = 1, the inhomogeneous transition becomes adiabatic not
below vq but a lower threshold velocity v', proportional to inhomogeneity of
the transition, where the excitations are suppressed exponentially.
Interestingly, the adiabatic threshold v' is nonzero despite vanishing minimal
group velocity of low energy quasiparticles. In the adiabatic regime below v'
the inhomogeneous transition can be used for efficient adiabatic quantum state
preparation in a quantum simulator: the time required for the critical front to
sweep across a chain of N spins adiabatically is merely linear in N, while the
corresponding time for a homogeneous transition across the multicritical point
scales with the sixth power of N. What is more, excitations after the adiabatic
inhomogeneous transition, if any, are brushed away by the critical front to the
end of the spin chain.Comment: 10 pages, 6 figures, improved version accepted in NJ
Excitations in two-component Bose-gases
In this paper, we study a strongly correlated quantum system that has become
amenable to experiment by the advent of ultracold bosonic atoms in optical
lattices, a chain of two different bosonic constituents. Excitations in this
system are first considered within the framework of bosonization and Luttinger
liquid theory which are applicable if the Luttinger liquid parameters are
determined numerically. The occurrence of a bosonic counterpart of fermionic
spin-charge separation is signalled by a characteristic two-peak structure in
the spectral functions found by dynamical DMRG in good agreement with
analytical predictions. Experimentally, single-particle excitations as probed
by spectral functions are currently not accessible in cold atoms. We therefore
consider the modifications needed for current experiments, namely the
investigation of the real-time evolution of density perturbations instead of
single particle excitations, a slight inequivalence between the two
intraspecies interactions in actual experiments, and the presence of a
confining trap potential. Using time-dependent DMRG we show that only
quantitative modifications occur. With an eye to the simulation of strongly
correlated quantum systems far from equilibrium we detect a strong dependence
of the time-evolution of entanglement entropy on the initial perturbation,
signalling limitations to current reasonings on entanglement growth in
many-body systems
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