1,721,079 research outputs found
Array-enhanced synchronization and coherence resonance in coupled excitable semiconductor lasers
No full textWe present a numerical study of the nonlinear dynamics of a population of coupled semiconductor lasers with saturable absorber operating in the excitable regime [1] and described by a set of coupled Yamada models [2]. In particular we have investigated the self-organized synchronization process taking place spontaneously among the lasers, showing significant correlations between the spike-like pulses emitted by different lasers. Our findings demonstrate that synchronization in time and also in intensity occurs in a large region of the parameter space and for different population sizes and furthermore it is robust with respect to random distribution of the lasers' pump parameter which is linked to the excitability threshold
Collective dynamics of evanescently coupled excitable lasers with saturable absorber
No full textWe present a numerical study of the collective dynamics in a population of coupled excitable lasers with saturable absorber. At variance with previous studies where real-valued (lossy) coupling was considered, we focus here on the purely imaginary coupling (evanescent wave coupling). We show that evanescently coupled excitable lasers exhibit synchronization like the lossy coupled ones. Furthermore, we show that out-of-diagonal disorder-induced localization of excitability takes place for imaginary coupling too, but it can be frustrated by nonvanishing linewidth enhancement factor
Collective excitability, synchronization, and array-enhanced coherence resonance in a population of lasers with a saturable absorber
No full textIn this article we present a numerical study of the collective dynamics in a population of coupled semiconductor lasers with a saturable absorber, operating in the excitable regime under the action of additive noise. We demonstrate that temporal and intensity synchronization takes place in a broad region of the parameter space and for various array sizes. The synchronization is robust and occurs even for a set of nonidentical coupled lasers. The cooperative nature of the system results in a self-organization process which enhances the coherence of the single element of the population too and can have broad impact for detection purposes, for building all-optical simulators of neural networks and in the field of photonics-based computation
Disorder-induced localization of excitability in an array of coupled lasers
No full textWe report on the localization of excitability induced by disorder in an array of coupled semiconductor lasers with a saturable absorber. Through numerical simulations we show that the exponential localization of excitable waves occurs if a certain critical amount of randomness is present in the coupling coefficients among the lasers. The results presented in this Rapid Communication demonstrate that disorder can induce localization in lattices of excitable nonlinear oscillators, and can be of interest in the study of photonics-based random networks, neuromorphic systems, and, by analogy, in biology, in particular, in the investigation of the collective dynamics of neuronal cell populations
Optical black hole lasers
Full text linkUsing numerical simulations we show how to realize an optical black hole laser, i.e. an amplifier formed by travelling refractive index perturbations arranged so as to trap light between a white and a black hole horizons. The simulations highlight the main features of these lasers: the growth inside the cavity of positive and negative frequency modes accompanied by a weaker emission of modes that occurs in periodic bursts corresponding to the cavity round trips of the trapped modes. We then highlight a new regime in which the trapped mode spectra broaden until the zero-frequency points on the dispersion curve are reached. Amplification at the horizon is highest for zero-frequencies, therefore leading to a strong modification of the structure of the trapped light. For sufficiently long propagation times, lasing ensues only at the zero-frequency modes
Role of Dexmedetomidine for Sedation in Neurocritical Care Patients: A Qualitative Systematic Review and Meta-analysis of Current Evidence
No full textIntroduction: This systematic review appraises the clinical evidence on
efficacy and safety of dexmedetomidine (DEX), as a sole sedative or as
sedative adjunct in adult neurocritical care (NCC) patients.
Materials and Methods: A database search was conducted to identify
randomized clinical trials and observational studies reporting the use of
DEX alone or as adjunct for sedation in NCC setting. The primary outcome
was the occurrence of hemodynamic changes, whereas the secondary out comes were sedative and analgesic efficacy, quality and time to awakening,
and development of adverse events.
Results: Eight trials including 3 randomized controlled trials and 5 obser vational studies, enrolling 650 patients, were selected. All the retrieved
studies had a high risk of bias and a low to moderate quality. Dexmedetomi dine provided a better sedation score and reduced analgesic requirements
when compared to propofol or midazolam sedation. No statistically signif icant difference in the combined hemodynamic effect (hypotension or bra dycardia) between DEX and controls (risk ratio, 1.50; 95% confidence
interval, 0.65–3.48; P = 0.34; I
2 = 56%) was identified. Adverse events
were not consistently reported.
Conclusions: Available clinical literature supporting the efficacy and
safety of DEX use in adult NCC setting is of limited quantity and quality.
However, from the current evidence on the use of DEX in NCC, as sole
sedative agent or as an adjunct, seems to be both efficient and safe
Superiorities of time-correlated single-photon counting against standard fluorimetry in exploiting the potential of fluorochromized oligonucleotide probes for biomedical investigation
No full textSite-specific fluorescence-resonance-energy-transfer donor-Acceptor dual-labelled oligonucleotide probes are widely used in state-of-Art biotechnological applications. Such applications include their usage as primers in polymerase chain reaction. However, the steady-state fluorescence intensity signal emitted by these molecular tools strongly depends from the specificities of the probe conformation. For this reason, the information which can be reliably inferred by steady-state fluorimetry performed on such samples is forcedly confined to a semi-qualitative level. Namely, fluorescent emission is frequently used as ON/OFF indicator of the probe hybridization state, i.e. detection of fluorescence signals indicates either hybridization to or detachment from the template DNA of the probe. Nonetheless, a fully quantitative analysis of their fluorescence emission properties would disclose other exciting applications of dual-labelled probes in biosensing. Here we show how time-correlated single-photon counting can be applied to get rid of the technical limitations and interpretational ambiguities plaguing the intensity analysis, and to derive information on the template DNA reaching single-base
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
On the use of superthermal light for imaging applications
No full textGhost imaging and differential ghost imaging are well-known imaging techniques based on the use of both classical and quantum correlated states of light. The existence of correlations within bipartite states has been shown to be the main resource to implement ghost imaging and differential ghost imaging protocols. Here we analyze the advantages and disadvantages of using two different kinds of superthermal states of light, which are more fluctuating than the typically employed thermal states, and thus originate correlations when divided at a beam splitter. To make a fair comparison, we calculate the contrast (C) and the signal-to-noise ratio (SNR) of the reconstructed image. While the larger values of C suggest the usefulness of these superthermal states, the values of SNR do not improve at increasing the intensity light fluctuations, but remain the same as those exhibited by thermal light
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