Slowdown and splitting of gap solitons in apodized Bragg gratings

We study the motion of gap solitons in two models of apodized nonlinear fiber Bragg gratings (BGs), with the local reflectivity (LR) varying along the fiber. A single step of LR, and a periodic array of alternating steps with opposite signs (a "Bragg superstructure") are considered. A challenging possibility is to slow down and eventually halt the soliton by passing it through the step of increasing reflectivity, thus capturing a pulse of standing light. First, we develop an analytical approach, assuming adiabatic evolution of the soliton, and making use of the energy conservation and balance equation for the momentum. Comparison with simulations shows that the analytical approximation is quite accurate (unless the inhomogeneity is too steep): the soliton is either transmitted across the step or bounces back. If the step is narrow, systematic simulations demontrate that the soliton splits into transmitted and reflected pulses (splitting of a BG soliton which hits a chirped grating was observed in experiments). Moving through the periodic "superstructure", the soliton accummulates distortion and suffers radiation loss if the structure is composed of narrow steps. The soliton moves without any loss or irreversible deformation through the array of sufficiently broad steps.Comment: to appear in a special issue on Wave-Optical Engineering, Journal of Modern Optic

All-optical switching in a two-channel waveguide with cubic-quintic nonlinearity

We consider dynamics of spatial beams in a dual-channel waveguide with competing cubic and quintic (CQ) nonlinearities. Gradually increasing the power in the input channel, we identify four different regimes of the pulses coupling into the cross channel, which alternate three times between full pass and full stop, thus suggesting three realizations of switching between the channels. As in the case of the Kerr (solely cubic) nonlinearity, the first two regimes are the linear one, and one dominated by the self-focusing nonlinearity, with the beam which, respectively, periodically couples between the channels, or stays in the input channel. Further increase of the power reveals two novel transmission regimes, one characterized by balance between the competing nonlinearities, which again allows full coupling between the channels, and a final regime dominated by the self-defocusing quintic nonlinearity. In the latter case, the situation resembles that known for a self-repulsive Bose-Einstein condensate trapped in a double-well potential, which is characterized by strong symmetry breaking; accordingly, the beam again abides in the input channel, contrary to an intuitive expectation that the self-defocusing nonlinearity would push it into the cross channel. The numerical results are qualitatively explained by a simple analytical model based on the variational approximation.Comment: Journal of Physics B (in press

Controle de arritmias atriais com período refratário atrial controlado por sensor e mudança automática de modo em pacientes portadores de marcapasso dupla-câmara com sensor de ventilaçao por minuto

Apesar de um longo período refratário atrial pós evento ventricular (PVARP) poder prevenir a ocorrência de taquicardias mediadas pelo marca passo e também o sincronismo inapropriado com arritmias atriais na estimulaçao dupla-câmara (DDD) a limitaçao da freqüência máxima será necessariamente comprometida. Testamos a possibilidade de utilizar um marca passo dupla-câmara com sensor de ventilaçao por minuto (DDDR) e com capacidade de encurtar o PVARP durante o exercício em 13 pacientes com bradicardia (PVARP em repouso = 463 ± 29 ms) a fim de prevenir a limitaçao prematura da freqüência máxima. O teste de esforço em esteira nos modos DDD e DDDR com este PVARP resultou em freqüências máximas de 98 bpm ± 8 bpm e 142 bpm ± 3 bpm respectivamente (P < 0,DDD1). Estes resultados foram obtidos graças à incompetência cronotrópica e à limitaçao da freqüência máxima no modo DDD, ambas contornadas pelo uso do sensor. Com a finalidade de simular arritmias atriais, foi aplicada estimulaçao na parede torácica por 30 segundos, a uma freqüência de 250 bpm e com uma sensibilidade atrial uni polar média de 0,82 mV. No modo DDD, ocorreu uma resposta ventricular irregular (as freqüências com um PVARP de 280 ms e 463 ms ± 29 ms foram respectivamente 92 bpm ± 5 bpm e 66 bpm ± 3 bpm (P < 0,DDD1). No modo DDDR, com um PVARP de 463 ms ± 29 ms, ocorreu uma estimulaçao ventricular regular a 53 bpm ± 2 bpm, devida à mudança de mDDD para VVIR, na presença de eventos repetitivos captados dentro do PVARP. Um paciente desenvolveu fibrilaçao atrial espontânea durante o seguimento, que foi corretamente identificada pelo algoritmo do marcapasso, resultando na mudança de modo de DDDR para WIR e na preservaçao da resposta em freqüência. Em conclusao, o PVARP controlado pelo sensor permite a utilizaçao de um PVARP mais longo durante o repouso, sem comprometer a freqüência máxima durante o exercício. Adicionalmente, ao oferecer em proteçao contra conduçao retrógrada, o PVARP longo e a mudança automática de mDDD também limitam a freqüência durante as arritmias atriais, permitindo uma resposta ventricular de acordo com a demanda fisiológica

Pan-viral serology implicates enteroviruses in acute flaccid myelitis.

Since 2012, the United States of America has experienced a biennial spike in pediatric acute flaccid myelitis (AFM)1-6. Epidemiologic evidence suggests non-polio enteroviruses (EVs) are a potential etiology, yet EV RNA is rarely detected in cerebrospinal fluid (CSF)2. CSF from children with AFM (n = 42) and other pediatric neurologic disease controls (n = 58) were investigated for intrathecal antiviral antibodies, using a phage display library expressing 481,966 overlapping peptides derived from all known vertebrate and arboviruses (VirScan). Metagenomic next-generation sequencing (mNGS) of AFM CSF RNA (n = 20 cases) was also performed, both unbiased sequencing and with targeted enrichment for EVs. Using VirScan, the viral family significantly enriched by the CSF of AFM cases relative to controls was Picornaviridae, with the most enriched Picornaviridae peptides belonging to the genus Enterovirus (n = 29/42 cases versus 4/58 controls). EV VP1 ELISA confirmed this finding (n = 22/26 cases versus 7/50 controls). mNGS did not detect additional EV RNA. Despite rare detection of EV RNA, pan-viral serology frequently identified high levels of CSF EV-specific antibodies in AFM compared with controls, providing further evidence for a causal role of non-polio EVs in AFM

A Switch from a Gradient to a Threshold Mode in the Regulation of a Transcriptional Cascade Promotes Robust Execution of Meiosis in Budding Yeast

Tight regulation of developmental pathways is of critical importance to all organisms, and is achieved by a transcriptional cascade ensuring the coordinated expression of sets of genes. We aimed to explore whether a strong signal is required to enter and complete a developmental pathway, by using meiosis in budding yeast as a model. We demonstrate that meiosis in budding yeast is insensitive to drastic changes in the levels of its consecutive positive regulators (Ime1, Ime2, and Ndt80). Entry into DNA replication is not correlated with the time of transcription of the early genes that regulate this event. Entry into nuclear division is directly regulated by the time of transcription of the middle genes, as premature transcription of their activator NDT80, leads to a premature entry into the first meiotic division, and loss of coordination between DNA replication and nuclear division. We demonstrate that Cdk1/Cln3 functions as a negative regulator of Ime2, and that ectopic expression of Cln3 delays entry into nuclear division as well as NDT80 transcription. Because Ime2 functions as a positive regulator for premeiotic DNA replication and NDT80 transcription, as well as a negative regulator of Cdk/Cln, we suggest that a double negative feedback loop between Ime2 and Cdk1/Cln3 promotes a bistable switch from the cell cycle to meiosis. Moreover, our results suggest a regulatory mode switch that ensures robust meiosis as the transcription of the early meiosis-specific genes responds in a graded mode to Ime1 levels, whereas that of the middle and late genes as well as initiation of DNA replication, are regulated in a threshold mode

Au+Au Reactions at the AGS: Experiments E866 and E917

Particle production and correlation functions from Au+Au reactions have been measured as a function of both beam energy (2-10.7AGeV) and impact parameter. These results are used to probe the dynamics of heavy-ion reactions, confront hadronic models over a wide range of conditions and to search for the onset of new phenomena.Comment: 12 pages, 14 figures, Talk presented at Quark Matter '9

Device-detected subclinical atrial tachyarrhythmias: Definition, implications and management - An European Heart Rhythm Association (EHRA) consensus document, endorsed by Heart Rhythm Society (HRS), Asia Pacific Heart Rhythm Society (APHRS) and Sociedad Latinoamericana de Estimulaci\uf3n Card\uedaca y Electrofisiolog\ueda (SOLEACE)

Among atrial tachyarrhythmias (AT), atrial fibrillation (AF) is the most common sustained arrhythmia. Many patients with AT have no symptoms during brief or even extended periods of the arrhythmia, making detection in patients at risk for stroke challenging. Subclinical atrial tachyarrhythmia and asymptomatic or silent atrial tachyarrhythmia often precede the development of clinical AF. Clinical AF and subclinical atrial fibrillation (SCAF) are associated with an increased risk of thromboembolism. Indeed, in many cases, SCAF is discovered only after complications such as ischaemic stroke or congestive heart failure have occurred