Flare Mode Research Articles

Ignition of water-coal fuel droplets during radiative-convective- conductive heating in relation to boilers operating on the technology of circulating fluidized bed

• Inert material significantly accelerates the ignition of a drop of coal-water fuel. • The effect of an inert material is most pronounced at moderate temperatures (Tg = 873 K). • At high oxidizer temperatures, the inert material does not affect the ignition process. • Inert material leads to dispersion of the near-surface layer of the fuel. One of the most promising options for reducing anthropogenic heating of coal-fired power plants on the environment is the use of not homogeneous coal as the main fuel, but coal-water suspensions. But the combustion of coal-water fuels is associated with the solution of the problem of large values of the ignition delay times for such fuels. Therefore, an important task of great practical importance is the selection (or development) of technologies for combustion of coal-water suspensions in the furnaces of steam and coal-water boilers. The article presents the results of experimental studies of the coal-water fuel drops ignition processes. They were carried out in order to establish the temporal characteristics and conditions of ignition under conditions of a flare mode and combustion in a circulating fluidized bed of an inert material. According to the results of experiments, it was found that at moderate temperatures of the environment (T g ≤ 873 K), particles of inert material (sand) accelerate the ignition of coal-water fuel drops. With high-temperature heating, the ignition delay times for these two fuel combustion technologies are identical in relation to the combustion of coal-water fuels prepared from typical (for energy purposes) semi-anthracite and high-volatile A bituminous coal. Colloquium. The energy crisis in autumn 2021 showed the problem of the rapid transition of the world community from traditional thermal energy to the energy of non-traditional renewable energy generators (wind, sun, biomass). It became obvious that in the next few decades, developed countries will be forced to use coal as their main energy source. Therefore, at present, an urgent task is to reduce the concentration of anthropogenic oxides in the flue gases of coal-fired power plants. One of the most promising technological solutions to this problem is the combustion of coal in the composition of coal-water fuel (CWF). But the technologies of combustion of coal-water fuels in the furnaces of steam and hot water boilers have not yet been developed, mainly due to the problem of large values of the ignition delay times for droplets of such fuels. Therefore, furnace devices of the traditional design of the chamber type with flare combustion of CWF have not yet been developed. One of the promising technologies for the combustion of coal-water fuel can be the technology of a circulating fluidized bed of inert material. But the results of studies of the coal-water fuels drops ignition processes under conditions corresponding to combustion devices operating on the technology of a circulating fluidized bed have not yet been published.

Multiwavelength Evidence for a New Flare-mode Transitional Millisecond Pulsar

Abstract We report the discovery of a new low-mass X-ray binary near the center of the unassociated Fermi GeV γ-ray source 4FGL J0540.0–7552. The source shows the persistent presence of an optical accretion disk and exhibits extreme X-ray and optical variability. It also has an X-ray spectrum well-fit by a hard power law with Γ = 1.8 and a high ratio of X-ray to γ-ray flux. Together, these properties are consistent with the classification of the binary as a transitional millisecond pulsar (tMSP) in the subluminous disk state. Uniquely among the candidate tMSPs, 4FGL J0540.0–7552 shows consistent optical, X-ray, and γ-ray evidence for having undergone a state change, becoming substantially brighter in the optical and X-rays and fainter in GeV γ-rays sometime in mid-2013. In its current subluminous disk state, and like one other candidate tMSP in the Galactic field, 4FGL J0540.0–7552 appears to always be in an X-ray “flare mode,” indicating that this could be common phenomenology for tMSPs.

The Flare-dominated Accretion Mode of a Radio-bright Candidate Transitional Millisecond Pulsar

Abstract We report new simultaneous X-ray and radio continuum observations of 3FGL J0427.9−6704, a candidate member of the enigmatic class of transitional millisecond pulsars. These XMM-Newton and Australia Telescope Compact Array observations of this nearly edge-on, eclipsing low-mass X-ray binary were taken in the sub-luminous disk state at an X-ray luminosity of erg s−1. Unlike the few well-studied transitional millisecond pulsars, which spend most of their disk state in a characteristic high or low accretion mode with occasional flares, 3FGL J0427.9−6704 stayed in the flare mode for the entire X-ray observation of ∼20 hr, with the brightest flares reaching ∼2 × 1034 erg s−1. The source continuously exhibited flaring activity on timescales of ∼10–100 s in both the X-ray and optical/ultraviolet (UV). No measurable time delay between the X-ray and optical/UV flares is observed, but the optical/UV flares last longer, and the relative amplitudes of the X-ray and optical/UV flares show a large scatter. The X-ray spectrum can be well-fit with a partially absorbed power law (Γ ∼ 1.4–1.5), perhaps due to the edge-on viewing angle. Modestly variable radio continuum emission is present at all epochs, and is not eclipsed by the secondary, consistent with the presence of a steady radio outflow or jet. The simultaneous radio/X-ray luminosity ratio of 3FGL J0427.9−6704 is higher than any known transitional millisecond pulsars and comparable to that of stellar-mass black holes of the same X-ray luminosity, providing additional evidence that some neutron stars can be as radio-loud as black holes.

X-ray study of high-and-low luminosity modes and peculiar low-soft-and-hard activity in the transitional pulsar XSS J12270−4859

XSS J12270−4859 (henceforth J12270) is the first low-mass X-ray binary to exhibit a transition, taking place at the end of 2012, from an X-ray active state to a radio pulsar state. The X-ray emission based on archival XMM-Newton observations is highly variable, showing rapid variations (∼10 s) from a high X-ray luminosity mode to a low mode and back. A flaring mode has also been observed. X-ray pulsations have been detected during the high mode only. In this work we present two possible interpretations for the rapid swings between the high and low modes. In the first scenario, this phenomenon can be explained by a rapid oscillation between a propeller state and a radio-ejection pulsar state, during which the pulsar wind prevents matter from falling onto the neutron star surface. In the second scenario, a radio pulsar is always active, the intra-binary shock is located just outside the light cylinder in the high mode, while it expands during the low mode. At variance with other transitional pulsars, J12270 shows two instances of the low mode: a low-soft and low-hard mode. Performing an X-ray spectral analysis, we show that the harder component, present in the low-hard spectra, is probably related to the tail of the flare emission. This supports the understanding that the flare mechanism is independent of the high-to-low mode transitions.

Ten-antenna prototype of a radio heliograph based on the Siberian Solar Radio Telescope

An upgrade of the Siberian Solar Radio Telescope (SSRT) [Smolkov et al., 1986; Grechnev et al., 2003] to a multiwave radio heliograph has been started. The radio heliograph being created will be designed mainly to measure coronal magnetic fields, to determine the locations of solar-flare energy release, and to investigate coronal mass ejections. These tasks define the parameters of next-generation radio heliographs. A high spatial resolution, a high image acquisition rate, and a high sensitivity are required simultaneously. All these parameters should be realized in the widest possible frequency range—from fractions to tens of GHz). The expected parameters of the future SSRT-based radio heliograph are listed below: spatial resolution 12″–24″, temporal resolution 0.02–1.0 s, frequency range 4–8 GHz, sensitivity up to 100 K, left-hand and right-hand circular polarizations, data rate 0.5–20 Mb s−1 (normal and flare modes). In this paper, we describe the broadband antennas, analog optical data transmission lines, and correlator used in the 10-antenna radio heliograph prototype.

X-ray spectral evolution of the extragalactic Z source LMC X-2

We present the results obtained by a detailed study of the extragalactic Z source, LMC X-2, using broad band Suzaku data and a large ($ \sim 750$ ksec) data set obtained with the proportional counter array (PCA) onboard RXTE. The PCA data allows for studying the complete spectral evolution along the horizontal, normal and flaring branches of the Z-track. Comparison with previous study show that the details of spectral evolution (like variation of Comptonizing electron temperature), is similar to that of GX 17+2 but unlike that of Cyg X-2 and GX 349+2. This suggests that Z sources are heterogeneous group with perhaps LMC X-2 and GX 17+2 being member of a subclass. However non monotonic evolution of the Compton y-parameter seems to be generic to all sources. The broad band {\it Suzaku} data reveals that the additional soft component of the source modelled as a disk blackbody emission is strongly preferred over one where it is taken to be a blackbody spectrum. This component as well as the temperature of seed photons do not vary when source goes into a flaring mode and the entire variation can be ascribed to the Comptonizing cloud. The bolometric unabsorbed luminosity of the source is well constrained to be $ \sim 2.23 \times 10^{38}$ ergs/sec which if the source is Eddington limited implies a neutron star mass of 1.6 M$_\odot$. We discuss the implications of these results.

Possibility of Excitation of Low-ℓ P-Modes by Energetic Solar Transients

We examine the temporal variation of power in low-l modes using GONG data for the period of May 1995–October 2005 and compare this with disk-integrated flare and CME indices. A poor correlation between the running means of Flare Index and mode power is found. A similar result is found for CME Index also. Variations in the running mean mode power corresponding to l = 0 modes with different radial orders are generally stochastic in nature. This behaviour is also reflected in the distribution of mode power.

Radio-loud flares from microquasars and radio-loudness of quasars

The low-frequency power spectra of the X-ray and radio emission from four microquasars suggest that two distinct modes of energy output are at work: (i) the ‘coupled’ mode in which the X-ray and radio luminosities are closely coupled and vary only weakly, and (ii) the ‘flaring’ mode, which dramatically boosts the radio luminosity but makes no impact on the X-ray luminosity. The systems are in the flaring mode only a few per cent of the time. However, flares completely dominate the power spectrum of radio emission, with the consequence that sources in which the flaring mode occurs, such as GRS 1915+105 and Cyg X-3, have radio power spectra that lie more than an order of magnitude above the corresponding X-ray power spectra. Of the four microquasars for which we have examined data, in only one, Cyg X-1, is the flaring mode seemingly inactive. While Cyg X-1 is a black hole candidate, one of the three flaring sources, Sco X-1, is a neutron star. Consequently, it is likely that both modes are driven by the accretion disc rather than black hole spin. Radio imaging strongly suggests that the flaring mode involves relativistic jets. A typical microquasar is in the flaring mode a few per cent of the time, which is similar to the fraction of quasars that are radio-loud. Thus there may be no essential difference between radio-loud and radio-quiet quasars; radio-loudness may simply be a function of the epoch at which the source is observed.

YOHKOH/HXT Evidence for a Hyperhot Loop-Top Source in The Pre-Impulsive Phase of a Loop Flare

A loop flare that occurred on 22 April 1993 near the disk center is examined using the Yohkoh Hard X-ray Telescope (HXT). We specifically looked into the faint early phase of the flare prior to the start of the strong impulsive phase. The pre-impulsive phase, though weak in intensity, is expected to contain essential clues to the mechanism of loop flares according to the causality principle, but it has not received attention previously, probably due to the insufficient dynamic range and cadence of observations by the instruments on earlier satellites. Observations with Yohkoh/HXT can clarify what occurs in this phase. This flare, like many other flares of this type, shows a relatively weak emission with a smooth and gradual increase during this pre-impulsive phase, followed by impulsive bursts, and then turns into a smooth decay phase without impulsive bursts. First, we found that the spectrum for the initial smooth rise part is consistent with a thin-thermal source at a temperature around 80 MK. Imaging of this phase in the HXT/L and M bands shows a single source between the footpoint sources that will come up in the impulsive phase following this phase, suggesting that this hyperhot source is located at a high part of the loop between the footpoints, since this flare takes a form of a loop. Furthermore, as we go up to the earliest times of the flare before this `hyperhot' source phase, two fainter sources are found near the footpoint sources that will appear later in the impulsive phase. The spectra of these sources at this earliest time of the flare, in contrast to the `hyperhot' source, cannot be determined from the HXT because the instrument was not in flare mode, and HXT/M1, M2, and H-band data are, unfortunately, not available at this very initial time. We can guess, however, that they are also of thermal character because the time profile is smooth without any spikes just as in the following `hyperhot' thermal phase, and in the post-impulsive `superhot' thermal phase coming up much later. These findings suggest that there is an important, and probably dynamic, early phase in loop flares that has been unnoticed in the still dark pre-impulsive phase, because the very early footpoint sources change into the loop top source in a matter of 20–30 s, comparable to the dynamic Alfven time scale. Some implications of our new findings are discussed.

Hard X-ray observations of transient X-ray source GS 1843+00

The transient X-ray source GS 1843+00 was observed in the hard X-ray region from 20 to 200 keV, during its flare mode in 1997 March. Spectral measurements were made during a balloon flight experiment using a newly designed large-area scintillation counter telescope. The present observations correspond to the mid-point of the transient phase. The X-ray spectrum, observed for the first time beyond 40 keV, is quite hard and the estimated intensity of the source corresponds to ∼ 100 mCrab in the 20--180 keV region. The time-averaged spectrum can be represented by a photon power-law index α∼ 1.7 ± 0.2. A complex function consisting of a power law with exponential term is necessary to produce the best fit to the data. We discuss the new data in terms of the source geometry and the X-ray emission mechanism.

Subclinical inflammation after laser in situ keratomileusis

Purpose: To determine whether laser in situ keratomileusis (LASIK) for the correction of myopia induces an anterior chamber inflammatory response measurable with laser flare-cell photometry.Setting: Instituto Oftalmolãgico de Alicante, University of Alicante, Alicante, Spain.Methods: Twenty eyes in 20 patients had LASIK to correct myopia ranging from 2.50 to 15.00 diopters (D) (mean -8.94 ± 3.25 [SD]). Anterior chamber inflammation was measured preoperatively and 1, 3, 7, and 15 days and 1 and 3 months postoperatively using the flare mode of a laser flare-cell meter. All eyes received topical fluorometholone 0.1% drops for 2 weeks postoperatively.Results: Anterior chamber flare values at 1 and 3 days and 1 week postoperatively were not significantly different from those found preoperatively. However, a significant decrease was found at 2 weeks and 1 month (P < .01 and P < .05, respectively). Flare values returned to their preoperative levels at 3 months. No significant correlations between postoperative flare values and depth of ablation were found.Conclusion: In this study, LASIK did not induce an inflammatory response in the anterior chamber in the myopic eye.

Deconvolution of Directly Precipitating and Trap‐Precipitating Electrons in Solar Flare Hard X‐Rays. II.Compton Gamma Ray ObservatoryData Analysis

Based on the deconvolution method developed in the first paper of this series, we present here the data analysis of 20-200 keV hard X-ray (HXR) data from the Burst and Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory (CGRO) recorded during 103 solar flares in 1991-1995. These are all of the flares simultaneously observed by CGRO with high time resolution (64 ms) and by Yohkoh in flare mode. The deconvolution method takes the measured HXR count rates as function of energy and time, I(ε, t), and computes the following self-consistently: the electron injection function n(E, t), the directly precipitating electron flux nprec(E, t), the trapped-precipitating flux ntrap(E, t), the fraction of directly precipitating electrons (qprec), the electron time-of-flight distance (lTOF), and the electron density at the loss cone site of the trap (ne). We find that the electron time-of-flight distances (lTOF = 20.0 ± 7.3 Mm) inferred with the deconvolution method are fully consistent with those obtained earlier using a Fourier filter method. The trap electron densities (ne = 1010.96±0.57 cm-3) obtained from deconvolving the e-folding decay times of HXR pulses (according to the trap model of Melrose & Brown) are found to be statistically a factor of 1.5 lower than those inferred from cross-correlation delays. The fraction qprec of directly precipitating electrons, measured for the first time here, is found to have a mean (and standard deviation) of qprec = 0.42 ± 0.16. Based on this precipitation fraction, we infer loss cone angles of α0 ≈ 20°-70° and magnetic mirror ratios of R = Bloss/Binj ≈ 1.2 - 3 (with a median value of Rmedian = 1.6) between the loss cone site and injection/acceleration site, assuming an isotropic pitch angle distribution at the injection site. The TOF distances and mirror ratios constrain magnetic scale heights in flare loops to λB = 10-150 Mm. The fact that this two-component model (with free-streaming and trapped electrons) satisfactorily fits the energy-dependent time delays in virtually all flares provides strong evidence that electron time-of-flight differences and collisional scattering times dominate the observed HXR timing, while the injection of electrons appears to be synchronized (independent of energy) and does not reveal the timing of the acceleration process.

Detection of Hα Intensity Oscillations in Solar Flares

We report here the first direct evidence for detection of Hα intensity oscillations in two extended flares of 15 November 1989 and 20 April 1991. The relative intensity variations measured with time at 18 different flare and chromospheric locations were analysed to obtain the oscillation modes. The analysis shows prominent 5- and 3-min modes in flares in addition to their existence in the chromosphere. However, there exists a frequency difference between the flare and chromospheric modes. This frequency deviation of about 300 µHz is proposed as an influence of higher magnetic field, location of the measurements (height) in chromosphere, and high temperature in the flare.

Surgical correction of high myopia in phakic eyes with Worst-Fechner myopia intraocular lenses.

Implanting an anterior chamber intraocular lens in a phakic eye is an effective surgical procedure for the correction of high myopia. However, the potential risks on the anterior segment structures are not well-known. We conducted a prospective study to evaluate the effectiveness, predictability, and safety after Worst-Fechner lenses were implanted to correct high myopia. We studied 32 eyes with preoperative myopia from -9.50 to -27.00 diopters (D) (-16.60 +/- 6.29 D). All 32 eyes were studied by clinical specular microscopy, and the endothelium was analyzed for cell density. Twenty eyes were additionally examined by fluorophotometry for lens transmittance changes. Thirty eyes were additionally examined using the flare mode of a laser flare cell photometer for anterior chamber inflammation; the patients were divided into three subgroups of ten eyes each according to when the postoperative flare measurements were done: 12 months, 18 months, and 24 months. Thirteen phakic eyes with myopia greater than -6.00 D were used as a control group for the flare study. The mean follow-up was 18.3 +/- 8 months (range 6 to 24 mo). Fifty-seven per cent of eyes (16 of 28) had an uncorrected visual acuity of 20/40 or better 12 months after surgery, and 58% (10 of 17 eyes) at 24 months. Spectacle-corrected visual acuity improved: 0.15 at 12 months and 0.16 at 24 months (0.1 = one line) from preoperative values. Visual acuity was stable after 3 months. Eighty per cent of eyes (25 of 31) at 6 months, 75% (21 of 28) at 12 months, and 76.5% (13 of 17) at 24 months had been correctly planned to within +/-1.00 D of emmetropia. The refractive results were stable 3 months after surgery. The mean endothelial cell loss was 7.2% at 3 months, 10.6% at 6 months, 13% at 12 months, and 17.6% at 24 months after surgery. The mean lens transmittance loss was 0.62% at 3 months, 0.72% at 6 months, 0.82% at 12 months, and 1.03% at 18 months after surgery. Flare values were significantly higher for eyes implanted with Worst-Fechner lenses than were those of the control group in all periods under consideration (Mann-Whitney test, p < 0.05). A decentration greater than 0.5 mm was present in 43% of eyes (14 of 32), and halos in 56% (18 of 32). In three eyes (9.3%), fixation of the lens to the iris was not stable. Our results for the Worst-Fechner myopia lens confirm earlier findings on the effectiveness of the refractive results. However, our study showed a continual decrease in endothelial cell density, a decrease in lens transmittance, and a chronic subclinical inflammation after the implantation of these lenses. Moreover, decentration was common, and the fixation of the IOL to the iris was not stable in some eyes.

Chronic subclinical inflammation in phakic eyes with intraocular lenses to correct myopia

Purpose: To evaluate whether either of two anterior chamber intraccular lenses (IOLs) implanted in myopic, phakic eyes induced an inflammatory response that was measurable with a laser flare-cell meter but that could not be measured by other methods.Setting: Jiménez-Díaz Foundation and San Carlos University Hospital, Madrid, Spain.Methods: Thirty eyes with a Worst-Fechner IOL and 30 eyes with a Baikoff ZB5M IOL were evaluated using the flare mode of a laser flare-cell meter. Patients in each group were divided into three subgroups of 10 eyes each according to when the postoperative flare measurements were done: 12 months, 18 months, and 24 months. Thirteen phakic eyes with myopia greater than −6.00 diopters were used as controls.Results: Postoperative flare in the Worst-Fechner group was 27.05 ± 19 photons per millisecond (photons/ms) (mean ± SD) at 12 months, 18.09 ± 17.38 photons/ms at 18 months, and 31.03 ± 28.8 photons/ms at 24 months. Postoperative flare in the Baikoff group was 21.1 ± 5.9 photons/ms at 12 months, 16.13 ± 8.3 photons/ms at 18 months, and 21.05 ± 23.5 photons/ms at 24 months. Flare in the control group was 4.24 ± 2.8 photons/ms. Postoperative flare values were significantly higher in both IOL groups than in the control group at all follow-ups (Mann-Whitney test, P < .05). Postoperative flare values in the Worst-Fechner group were higher than in the Baikoff group at 12, 18, and 24 months, although the difference was not significant (Mann-Whitney test, P > .05).Conclusions: Our study shows chronic subdinical inflammation between 1 and 2 years after implantation of both IOL types.