3,806 research outputs found
Dark solitons, modulation instability and breathers in a chain of weakly non-linear oscillators with cyclic symmetry
In the aerospace industry the trend for light-weight structures and the
resulting complex dynamic behaviours currently challenge vibration engineers.
In many cases, these light-weight structures deviate from linear behaviour, and
complex nonlinear phenomena can be expected. We consider a cyclically symmetric
system of coupled weakly nonlinear undamped oscillators that could be
considered a minimal model for different cyclic and symmetric aerospace
structures experiencing large deformations. The focus is on localised
vibrations that arise from wave envelope modulation of travelling waves. For
the defocussing parameter range of the approximative nonlinear evolution
equation, we show the possible existence of dark solitons and discuss their
characteristics. For the focussing parameter range, we characterise modulation
instability and illustrate corresponding nonlinear breather dynamics.
Furthermore, we show that for stronger nonlinearity or randomness in initial
conditions, transient breather-type dynamics and decay into bright solitons
appear. The findings suggest that significant vibration localisation may arise
due to mechanisms of nonlinear modulation dynamics
Production of optical phase space vortices with non-locally distributed mode converters
Optical vortices have been observed in a wide variety of optical systems.
They can be observed directly in the wavefront of optical beams, or in the
correlations between pairs of entangled photons. We present a novel optical
vortex which appears in a non-local plane of the two-photon phase space,
composed of a single degree of freedom of each photon of an entangled pair. The
preparation of this vortex can be viewed as a "non-local" or distributed mode
converter. We show how these novel optical vortices of arbitrary order can be
prepared in the spatial degrees of freedom of entangled photons.Comment: To appear in upcoming special issue "Orbital Angular Momentum" of the
Journal of Optic
Single observable concurrence measurement without simultaneous copies
We present a protocol that allows us to obtain the concurrence of any two
qubit pure state by performing a minimal and optimal tomography of one of the
subsystems through measuring a single observable of an ancillary four
dimensional qudit. An implementation for a system of trapped ions is also
proposed, which can be achieved with present day experimental techniques.Comment: 4 pages, 1 figur
Does a new research-funding model ask for a new evaluation framework? The case of Serrapilheira in Brazil
The purpose of this manuscript is to present an on-going experience of impact evaluation applied to a recently created S&T funding agency. The Institute Serrapilheira (ISP) is a private nonprofit organization created to fund new and challenging themes of research. Serrapilheira brings innovation to the Brazilian scenario of science funding in at least three directions. First, ISP is the first family-philanthropically funded organization totally dedicated to support science in Brazil. Secondly, as a private institution, it can provide researchers with greater flexibility in terms of resource allocation comparing to public funding agencies. The 2018 estimated budget is US$ 4,5 million. Thirdly, in its first call for proposals launched in mid-2017, ISP asked young researchers to present proposals out of the “Normal Science”. The definition of the impact evaluation model of the first call of Serrapilheira was based on both the institutional model proposed by the organization – and its main purposes – as well as on the particular goals of the first call. As a first step, these objectives were discussed with Serrapilheira’s staff. The second step consisted of detecting evaluation hypotheses, themes and indicators based on the discussion of the model’s objectives. As a result, six evaluation themes were defined – one oriented to characterizing the grantees both in terms of diversity and academic training and the other five oriented to measure impacts: (i) professional trajectory, (ii) scientific and technology production, (iii) night science, (iv) insertion and prominence and (v) research culture. Traditional and widely accepted indicators of scientific and technological impact were used, even for dialogue with communities and scientific institutions and terms of comparison. Nevertheless, the main challenge was to identify indicators that allow the measurement of variables that directly or indirectly approach the particularities of the research-funding model. As a first remark, we understand that the particularities of the new research-funding model proposed by ISP asks for a new evaluation framework, more oriented to alternative indicators and to a broad perspective about outputs, outcomes and impacts in a more diverse and multifaceted research system. In this current hands-on impact-study a methodology is being built and simultaneously applied to a concrete case. This experience may contribute to the field of impact evaluation to the extent it proposes not only alternative indicators to be mixed with traditional ones, but also because it has a longitudinal perspective of following grantees since the inception (with the advantage of starting with a baseline) till two years after projects end, performing a 5-year long evaluation. Another possible contribution refers to the understanding about the ways funding agencies are evaluating the outcomes and impacts of their initiatives
Experimental Observation of Environment-induced Sudden Death of Entanglement
We demonstrate the difference between local, single-particle dynamics and
global dynamics of entangled quantum systems coupled to independent
environments. Using an all-optical experimental setup, we show that, while the
environment-induced decay of each system is asymptotic, quantum entanglement
may suddenly disappear. This "sudden death" constitutes yet another distinct
and counter-intuitive trait of entanglement.Comment: 4 pages, 4 figure
Entropic Entanglement Criteria for Continuous Variables
We derive several entanglement criteria for bipartite continuous variable
quantum systems based on the Shannon entropy. These criteria are more sensitive
than those involving only second-order moments, and are equivalent to
well-known variance product tests in the case of Gaussian states. Furthermore,
they involve only a pair of quadrature measurements, and will thus should prove
extremely useful the experimental identification of entanglement.Comment: 4 pages, 2 figure
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