Temporal dissipative Kerr solitons in optical microresonators enable the generation of ultrashort pulses and low-noise frequency combs at microwave repetition rates. They have been demonstrated in a ...growing number of microresonator platforms, enabling chip-scale frequency combs, optical synthesis of low-noise microwaves and multichannel coherent communications. In all these applications, accessing and maintaining a single-soliton state is a key requirementone that remains an outstanding challenge. Here, we study the dynamics of multiple-soliton states and report the discovery of a simple mechanism that deterministically switches the soliton state by reducing the number of solitons one by one. We demonstrate this control in Si3N4 and MgF2 resonators and, moreover, we observe a secondary peak to emerge in the response of the system to a pump modulation, an eect uniquely associated with the soliton regime. Exploiting this feature, we map the multi-stability diagram of a microresonator experimentally. Our measurements show the physical mechanism of the soliton switching and provide insight into soliton dynamics in microresonators. The technique provides a method to sequentially reduce, monitor and stabilize an arbitrary state with solitons, in particular allowing for feedback stabilization of single-soliton states, which is necessary for practical applications.
Supermassive black holes (SMBH) are essential for the production of jets in radio-loud active galactic nuclei (AGN). Theoretical models based on (Blandford & Znajek 1977, MNRAS, 179, 433) extract the ...rotational energy from a Kerr black hole, which could be the case for NGC 1052, to launch these jets. This requires magnetic fields on the order of 103G to 104G. We imaged the vicinity of the SMBH of the AGN NGC 1052 with the Global Millimetre VLBI Array and found a bright and compact central feature that is smaller than 1.9 light days (100 Schwarzschild radii) in radius. Interpreting this as a blend of the unresolved jet bases, we derive the magnetic field at 1 Schwarzschild radius to lie between 200 G and ~ 8.3 × 104 G consistent with Blandford & Znajek models.
We have examined the compact structure in 250 flat-spectrum extragalactic radio sources using interferometric fringe visibilities obtained with the Very Long Baseline Array (VLBA) at 15 GHz. With ...projected baselines out to 440 Ml, we are able to investigate source structure on typical angular scales as small as 0.05 mas. This scale is similar to the resolution of the VLBI Space Observatory Programme data obtained on longer baselines at a lower frequency and with somewhat poorer accuracy. For 171 sources in our sample, more than half of the total flux density seen by the VLBA remains unresolved on the longest baselines. There are 163 sources in our list with a median correlated flux density at 15 GHz in excess of 0.5 Jy on the longest baselines; these will be useful as fringe finders for short-wavelength VLBA observations. The total flux densities recovered in the VLBA images at 15 GHz are generally close to the values measured around the same epoch at the same frequency with the RATAN-600 and University of Michigan Radio Astronomy Observatory telescopes.
The core shift effect in the blazar 3C 454.3 Kutkin, A. M; Sokolovsky, K. V; Lisakov, M. M ...
Monthly notices of the Royal Astronomical Society,
02/2014, Volume:
437, Issue:
4
Journal Article
Peer reviewed
Open access
Opacity-driven shifts of the apparent very long baseline interferometry (VLBI) core position with frequency (the 'core shift' effect) probe physical conditions in the innermost parts of jets in ...active galactic nuclei. We present the first detailed investigation of this effect in the brightest γ-ray blazar 3C 454.3 using direct measurements from simultaneous 4.6-43 GHz very long baseline array observations, and a time lag analysis of 4.8-37 GHz light curves from the University of Michigan Radio Observatory, Crimean Astrophysical Observatory and Metsähovi observations in 2007-2009. The results support the standard Königl model of jet physics in the VLBI core region. The distance of the core from the jet origin r
c(ν), the core size W(ν) and the light curve time lag ΔT(ν) all depend on the observing frequency ν as r
c(ν) ∝ W(ν) ∝ ΔT(ν) ∝ ν−1/k
. The obtained range of k = 0.6-0.8 is consistent with the synchrotron self-absorption being the dominating opacity mechanism in the jet. The similar frequency dependence of r
c(ν) and W(ν) suggests that the external pressure gradient does not dictate the jet geometry in the cm-band core region. Assuming equipartition, the magnetic field strength scales with distance r as B = 0.4(r/1 pc)−0.8 G. The total kinetic power of electron/positron jet is about 1044 ergs s−1.
We predict the existence of a novel type of the flat-top dissipative solitonic pulses, "platicons", in microresonators with normal group velocity dispersion (GVD). We propose methods to generate ...these platicons from cw pump. Their duration may be altered significantly by tuning the pump frequency. The transformation of a discrete energy spectrum of dark solitons of the Lugiato-Lefever equation into a quasicontinuous spectrum of platicons is demonstrated. Generation of similar structures is also possible with bi-harmonic, phase/amplitude modulated pump or via laser injection locking.
We present Space-VLBI RadioAstron observations at 1.6 GHz and 4.8 GHz of the flat spectrum radio quasar 3C 273, with detections on baselines up to 4.5 and 3.3 Earth Diameters, respectively. Achieving ...the best angular resolution at 1.6 GHz to date, we have imaged limb-brightening in the jet, not previously detected in this source. In contrast, at 4.8 GHz, we detected emission from a central stream of plasma, with a spatial distribution complementary to the limb-brightened emission, indicating an origin in the spine of the jet. While a stratification across the jet width in the flow density, internal energy, magnetic field, or bulk flow velocity are usually invoked to explain the limb-brightening, the different jet structure detected at the two frequencies probably requires a stratification in the emitting electron energy distribution. Future dedicated numerical simulations will allow the determination of which combination of physical parameters are needed to reproduce the spine-sheath structure observed by Space-VLBI with RadioAstron in 3C 273.
Jet ejection by accreting black holes is a mass invariant mechanism unifying stellar and supermassive black holes (SMBHs) that should also apply for intermediate-mass black holes (IMBHs), which are ...thought to be the seeds from which SMBHs form. We present the detection of an off-nuclear IMBH of ∼5 × 104 M⊙ located in an unusual spiral arm of the galaxy NGC 2276 based on quasi-simultaneous Chandra X-ray observations and European VLBI Network (EVN) radio observations. The IMBH, NGC2276-3c, possesses a 1.8 pc radio jet that is oriented in the same direction as large-scale (∼650 pc) radio lobes and whose emission is consistent with flat to optically thin synchrotron emission between 1.6 and 5 GHz. Its jet kinetic power (4 × 1040 erg s−1) is comparable to its radiative output and its jet efficiency (≥46 per cent) is as large as that of SMBHs. A region of ∼300 pc along the jet devoid of young stars could provide observational evidence of jet feedback from an IMBH. The discovery confirms that the accretion physics is mass invariant and that seed IMBHs in the early Universe possibly had powerful jets that were an important source of feedback.
This study analyzes the impact of research and development (R&D) expenditures on CO2 emissions in 16 Organisation for Economic Co-operation and Development (OECD) countries for the period between ...1981 and 2014. The estimates of long-run regression models show that the expected average effect of R&D expenditures on CO2 emissions is negative. Growth of R&D investments by 1% reduces CO2 emissions by 0.09%–0.15% on average. However, estimated country-specific regressions indicate that the long-run effect of R&D expenditures on CO2 emissions can be both positive and negative, and they vary from −0.79% in Denmark to 0.52% in Belgium. In other words, in most cases, viewed from a long-term perspective, higher R&D expenditures reduce CO2 emissions, but this does not apply to about 40% of countries. In addition, the estimation of the short-run time-varying coefficient panel data models indicated that R&D impact can be positive, negative, but also neutral (insignificant) for many years. Such findings suggest a conclusion that the effect of R&D investments on CO2 emissions cannot be characterized as negative in advance, as pointed out by numerous analysis, but must be empirically estimated. The practical significance of this study is reflected in the fact that it directs decision-makers to concentrate their efforts on promoting R&D programs, such as those in the US and Germany, which are directly focused on reducing CO2 emissions and increasing the use thereof.
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•Average long-run effect of R&D expenditures on CO2 emissions is negative.•Individual long-run effect of R&D on CO2 emissions is positive for about 40% of countries.•Short-run R&D impact on CO2 emissions can be positive, negative, but also insignificant.•The actual R&D influence on CO2 emissions should be empirically estimated.•R&D programs focused on reducing CO2 emissions and increasing its use are necessary.
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