New mysteries and challenges from the Toothbrush relic: wideband observations from 550 MHz to 8 GHz

Context. Radio relics are diffuse extended synchrotron sources that originate from shock fronts induced by galaxy cluster mergers. The particle acceleration mechanism at the shock fronts is still under debate. The galaxy cluster 1RXS J0603.3+4214 hosts one of the most intriguing examples of radio relics, known as the Toothbrush. Aims. In order to understand the mechanism(s) that accelerate(s) relativistic particles in the intracluster medium, we investigated the spectral properties of large-scale diffuse extended sources in the merging galaxy cluster 1RXS J0603.3+4214. Methods. We present new wideband radio continuum observations made with uGMRT and VLA. Our new observations, in combination with previously published data, allowed us to carry out a detailed high-spatial-resolution spectral and curvature analysis over a wide range of frequencies. Results. The integrated spectrum of the Toothbrush closely follows a power law over almost two orders of magnitude in frequency, with a spectral index of −1.16 ± 0.02. We do not find any evidence of spectral steepening below 8 GHz. The subregions of the Toothbrush also exhibit near-perfect power laws and identical spectral slopes, suggesting that the observed spectral index is rather set by the distribution of Mach numbers which may have a similar shape at different parts of the shock front. Indeed, numerical simulations show an intriguing similar spectral index, indicating that the radio spectrum is dominated by the average over the inhomogeneities within the shock, with most of the emission coming from the tail of the Mach number distribution. In contrast to the Toothbrush, the spectra of the fainter relics show a high-frequency steepening. Moreover, the integrated spectrum of the halo also follows a power law from 150 MHz to 3 GHz with a spectral index of −1.16 ± 0.04. We do not find any evidence for spectral curvature, not even in subareas of the halo. This suggest a homogeneous acceleration throughout the cluster volume. Between the “brush” region of the Toothbrush and the halo, the color-color analysis reveals emission that was consistent with an overlap between the two different spectral regions. Conclusions. None of the relic structures, that is, the Toothbrush as a whole or its subregions or the other two fainter relics, show spectral shapes consistent with a single injection of relativistic electrons, such as at a shock, followed by synchrotron aging in a relatively homogeneous environment. Inhomogeneities in some combination of Mach number, magnetic field strength, and projection effects dominate the observed spectral shapes.

Download Full-text

The GLEAM 200-MHz local radio luminosity function for AGN and star-forming galaxies

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2021.36 ◽

2021 ◽

Vol 38 ◽

Author(s):

T. M. O. Franzen ◽

N. Seymour ◽

E. M. Sadler ◽

T. Mauch ◽

S. V. White ◽

...

Keyword(s):

Spectral Index ◽

Luminosity Function ◽

Radio Continuum ◽

Radio Luminosity ◽

Low Frequencies ◽

Star Forming ◽

Wide Range ◽

Murchison Widefield Array ◽

Radio Luminosity Function ◽

Local Radio

Abstract The GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) is a radio continuum survey at 76–227 MHz of the entire southern sky (Declination $<\!{+}30^{\circ}$ ) with an angular resolution of ${\approx}2$ arcmin. In this paper, we combine GLEAM data with optical spectroscopy from the 6dF Galaxy Survey to construct a sample of 1 590 local (median $z \approx 0.064$ ) radio sources with $S_{200\,\mathrm{MHz}} > 55$ mJy across an area of ${\approx}16\,700\,\mathrm{deg}^{2}$ . From the optical spectra, we identify the dominant physical process responsible for the radio emission from each galaxy: 73% are fuelled by an active galactic nucleus (AGN) and 27% by star formation. We present the local radio luminosity function for AGN and star-forming (SF) galaxies at 200 MHz and characterise the typical radio spectra of these two populations between 76 MHz and ${\sim}1$ GHz. For the AGN, the median spectral index between 200 MHz and ${\sim}1$ GHz, $\alpha_{\mathrm{high}}$ , is $-0.600 \pm 0.010$ (where $S \propto \nu^{\alpha}$ ) and the median spectral index within the GLEAM band, $\alpha_{\mathrm{low}}$ , is $-0.704 \pm 0.011$ . For the SF galaxies, the median value of $\alpha_{\mathrm{high}}$ is $-0.650 \pm 0.010$ and the median value of $\alpha_{\mathrm{low}}$ is $-0.596 \pm 0.015$ . Among the AGN population, flat-spectrum sources are more common at lower radio luminosity, suggesting the existence of a significant population of weak radio AGN that remain core-dominated even at low frequencies. However, around 4% of local radio AGN have ultra-steep radio spectra at low frequencies ( $\alpha_{\mathrm{low}} < -1.2$ ). These ultra-steep-spectrum sources span a wide range in radio luminosity, and further work is needed to clarify their nature.

Download Full-text

A Method for Correlating the Influence of External Crossflow on the Discharge Coefficients of Film Cooling Holes

Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/2000-gt-0294 ◽

2000 ◽

Author(s):

D. A. Rowbury ◽

M. L. G. Oldfield ◽

G. D. Lock

Keyword(s):

Reynolds Number ◽

Mach Number ◽

Film Cooling ◽

Guide Vane ◽

Density Ratio ◽

External Flow ◽

Published Data ◽

Discharge Coefficients ◽

Wide Range ◽

Film Cooling Holes

An empirical means of predicting the discharge coefficients of film cooling holes in an operating engine has been developed. The method quantifies the influence of the major dimensionless parameters, namely hole geometry, pressure ratio across the hole, coolant Reynolds number, and the freestream Mach number. The method utilises discharge coefficient data measured on both a first-stage high-pressure nozzle guide vane from a modern aero-engine and a scale (1.4 times) replica of the vane. The vane has over 300 film cooling holes, arranged in 14 rows. Data was collected for both vanes in the absence of external flow. These non-crossflow experiments were conducted in a pressurised vessel in order to cover the wide range of pressure ratios and coolant Reynolds numbers found in the engine. Regrettably, the proprietary nature of the data collected on the engine vane prevents its publication, although its input to the derived correlation is discussed. Experiments were also conducted using the replica vanes in an annular blowdown cascade which models the external flow patterns found in the engine. The coolant system used a heavy foreign gas (SF6/Ar mixture) at ambient temperatures which allowed the coolant-to-mainstream density ratio and blowing parameters to be matched to engine values. These experiments matched the mainstream Reynolds and Mach numbers and the coolant Mach number to engine values, but the coolant Reynolds number was not engine representative (Rowbury et al., 1997 and 1998). A correlation for discharge coefficients in the absence of external crossflow has been derived from this data and other published data. An additive loss coefficient method is subsequently applied to the cascade data in order to assess the effect of the external crossflow. The correlation is used successfully to reconstruct the experimental data. It is further validated by successfully predicting data published by other researchers. The work presented is of considerable value to gas turbine design engineers as it provides an improved means of predicting the discharge coefficients of engine film cooling holes.

Download Full-text

Chandra and XMM–Newton observations of A2256: cold fronts, merger shocks, and constraint on the IC emission

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2320 ◽

2020 ◽

Vol 497 (4) ◽

pp. 4704-4717

Author(s):

Chong Ge ◽

Ruo-Yu Liu ◽

Ming Sun ◽

Heng Yu ◽

Lawrence Rudnick ◽

...

Keyword(s):

Power Law ◽

Electron Spectrum ◽

Galaxy Cluster ◽

X Ray ◽

Cold Fronts ◽

Inverse Compton ◽

Galaxy Kinematics ◽

The Magnetic Field ◽

Primary Cluster ◽

Shock Fronts

ABSTRACT We present the results of deep Chandra and XMM–Newton observations of a complex merging galaxy cluster Abell 2256 (A2256) that hosts a spectacular radio relic (RR). The temperature and metallicity maps show clear evidence of a merger between the western subcluster (SC) and the primary cluster (PC). We detect five X-ray surface brightness edges. Three of them near the cluster centre are cold fronts (CFs): CF1 is associated with the infalling SC; CF2 is located in the east of the PC; and CF3 is located to the west of the PC core. The other two edges at cluster outskirts are shock fronts (SFs): SF1 near the RR in the NW has Mach numbers derived from the temperature and the density jumps, respectively, of MT = 1.62 ± 0.12 and Mρ = 1.23 ± 0.06; SF2 in the SE has MT = 1.54 ± 0.05 and Mρ = 1.16 ± 0.13. In the region of the RR, there is no evidence for the correlation between X-ray and radio substructures, from which we estimate an upper limit for the inverse-Compton emission, and therefore set a lower limit on the magnetic field (∼ 450 kpc from PC centre) of B > 1.0 μG for a single power-law electron spectrum or B > 0.4 μG for a broken power-law electron spectrum. We propose a merger scenario including a PC, an SC, and a group. Our merger scenario accounts for the X-ray edges, diffuse radio features, and galaxy kinematics, as well as projection effects.

Download Full-text

YIELD STRESS OF FRACTAL AGGREGATES

Fractals ◽

10.1142/s0218348x15500280 ◽

2015 ◽

Vol 23 (03) ◽

pp. 1550028 ◽

Cited By ~ 3

Author(s):

YUE XI ◽

JINJIAN CHEN ◽

YONGFU XU ◽

FEIFEI CHU ◽

CHUANXIN LIU

Keyword(s):

Fractal Dimension ◽

Yield Stress ◽

Power Law ◽

Volume Fraction ◽

Solid Volume Fraction ◽

Published Data ◽

Proposed Model ◽

Wide Range ◽

The Relationship ◽

Theory And Experiments

A model for the yield stress of aggregates is presented that incorporates fractal dimension taking into account the solid volume fraction and the aggregate diameter. The model shows the yield stress (σy) of aggregates increases with the solid volume fraction (ϕs) as a power law, and is given by [Formula: see text], where the exponent (m) is related to fractal dimension (D), and σy0 is a referenced parameter. The relationship between exponent (m) and fractal dimension is validated by published data of aggregates and represents the measured data very well, over a wide range of the solid volume fractions. The referenced parameter (σy0) is calibrated from experiments of yield stress using power law fittings. The agreement between theory and experiments supports the idea that yielding is ultimately caused by the rupture of a few interparticle bonds within aggregates. In addition, the proposed model for the yield stress of aggregates is found to match better with experiments by comparing with all models in literature.

Download Full-text

Observations by GMRT at 323 MHz of radio-loud quasars at z > 5

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038469 ◽

2020 ◽

Vol 641 ◽

pp. A85

Author(s):

Yali Shao ◽

Jeff Wagg ◽

Ran Wang ◽

Chris L. Carilli ◽

Dominik A. Riechers ◽

...

Keyword(s):

Power Law ◽

Rest Frame ◽

Low Frequency ◽

Point Sources ◽

Radio Continuum ◽

Spectral Energy ◽

Synchrotron Emission ◽

Energy Distributions ◽

Radio Range ◽

Wide Range

We present Giant Metrewave Radio Telescope (GMRT) 323 MHz radio continuum observations toward 13 radio-loud quasars at z > 5, sampling the low-frequency synchrotron emission from these objects. Among the 12 targets successfully observed, we detected 10 above 4σ significance, while 2 remain undetected. All of the detected sources appear as point sources. Combined with previous radio continuum detections from the literature, 9 quasars have power-law spectral energy distributions throughout the radio range; for some the flux density drops with increasing frequency while it increases for others. Two of these sources appear to have spectral turnover. For the power-law-like sources, the power-law indices have a positive range between 0.18 and 0.67 and a negative values between −0.90 and −0.27. For the turnover sources, the radio peaks around ∼1 and ∼10 GHz in the rest frame, the optically thin indices are −0.58 and −0.90, and the optically thick indices are 0.50 and 1.20. A magnetic field and spectral age analysis of SDSS J114657.59+403708.6 at z = 5.01 may indicate that the turnover is not caused by synchrotron self-absorption, but rather by free-free absorption by the high-density medium in the nuclear region. Alternatively, the apparent turnover may be an artifact of source variability. Finally, we calculated the radio loudness R2500 Å for our sample, which spans a very wide range from 12−13+13 to 4982−254+279.

Download Full-text

It is better an approximate answer to the right question than the exact answer to the wrong question : the case of the psychometric analysis of the ASQ:SE

10.31234/osf.io/a5tdf ◽

2020 ◽

Author(s):

Luis Anunciacao ◽

janet squires ◽

J. Landeira-Fernandez

Keyword(s):

Internal Structure ◽

Statistical Methods ◽

Principal Component ◽

Psychological Theory ◽

Published Data ◽

Multivariate Statistical ◽

Exact Answer ◽

Wide Range ◽

Ages And Stages Questionnaire ◽

The Right

One of the main activities in psychometrics is to analyze the internal structure of a test. Multivariate statistical methods, including Exploratory Factor analysis (EFA) and Principal Component Analysis (PCA) are frequently used to do this, but the growth of Network Analysis (NA) places this method as a promising candidate. The results obtained by these methods are of valuable interest, as they not only produce evidence to explore if the test is measuring its intended construct, but also to deal with the substantive theory that motivated the test development. However, these different statistical methods come up with different answers, providing the basis for different analytical and theoretical strategies when one needs to choose a solution. In this study, we took advantage of a large volume of published data (n = 22,331) obtained by the Ages and Stages Questionnaire Social-Emotional (ASQ:SE), and formed a subset of 500 children to present and discuss alternative psychometric solutions to its internal structure, and also to its subjacent theory. The analyses were based on a polychoric matrix, the number of factors to retain followed several well-known rules of thumb, and a wide range of exploratory methods was fitted to the data, including EFA, PCA, and NA. The statistical outcomes were divergent, varying from 1 to 6 domains, allowing a flexible interpretation of the results. We argue that the use of statistical methods in the absence of a well-grounded psychological theory has limited applications, despite its appeal. All data and codes are available at https://osf.io/z6gwv/.

Download Full-text

Regulation of Cytochrome c Oxidase by Natural Compounds Resveratrol, (–)-Epicatechin, and Betaine

Cells ◽

10.3390/cells10061346 ◽

2021 ◽

Vol 10 (6) ◽

pp. 1346

Author(s):

Icksoo Lee

Keyword(s):

Cytochrome C ◽

Cytochrome C Oxidase ◽

Model Systems ◽

Health Improvement ◽

Published Data ◽

Mitochondrial Electron Transport Chain ◽

Naturally Occurring ◽

Transport Chain ◽

Wide Range ◽

Experimental Model Systems

Numerous naturally occurring molecules have been studied for their beneficial health effects. Many compounds have received considerable attention for their potential medical uses. Among them, several substances have been found to improve mitochondrial function. This review focuses on resveratrol, (–)-epicatechin, and betaine and summarizes the published data pertaining to their effects on cytochrome c oxidase (COX) which is the terminal enzyme of the mitochondrial electron transport chain and is considered to play an important role in the regulation of mitochondrial respiration. In a variety of experimental model systems, these compounds have been shown to improve mitochondrial biogenesis in addition to increased COX amount and/or its enzymatic activity. Given that they are inexpensive, safe in a wide range of concentrations, and effectively improve mitochondrial and COX function, these compounds could be attractive enough for possible therapeutic or health improvement strategies.

Download Full-text

Bipolar outflow of gas in the spiral galaxy NGC 3079

Canadian Journal of Physics ◽

10.1139/p86-100 ◽

1986 ◽

Vol 64 (4) ◽

pp. 531-535 ◽

Cited By ~ 1

Author(s):

Nebojsa Duric ◽

E. R. Seaquist

Keyword(s):

Spectral Index ◽

Spiral Galaxy ◽

Central Region ◽

Qualitative Description ◽

Radio Continuum ◽

Large Array ◽

Very Large Array ◽

Bipolar Outflow ◽

The Galaxy

Very large array, radio-continuum observations of the edge-on spiral galaxy NGC 3079 are presented. The observations reveal that the nucleus has windlike properties and that the central region of the galaxy exhibits an unusual figure-eight morphology that shows evidence of severe depolarization and a flattening spectral index away from the nucleus. A qualitative description of a model is presented to account for the observed radio properties. It is shown that a wind-driven shock propagating away from the nucleus and focused by the ambient disk gas can give rise to the observed morphology.

Download Full-text

The Effect of Pulsed Blowing on the Boundary Layer of a Highly Loaded Low Pressure Turbine Blade

Volume 6A: Turbomachinery ◽

10.1115/gt2013-94566 ◽

2013 ◽

Cited By ~ 3

Author(s):

Marion Mack ◽

Roland Brachmanski ◽

Reinhard Niehuis

Keyword(s):

Boundary Layer ◽

Reynolds Number ◽

Mach Number ◽

Suction Side ◽

Reynolds Numbers ◽

Low Pressure ◽

Trailing Edge ◽

Low Pressure Turbine ◽

Wide Range ◽

Highly Loaded

The performance of the low pressure turbine (LPT) can vary appreciably, because this component operates under a wide range of Reynolds numbers. At higher Reynolds numbers, mid and aft loaded profiles have the advantage that transition of suction side boundary layer happens further downstream than at front loaded profiles, resulting in lower profile loss. At lower Reynolds numbers, aft loading of the blade can mean that if a suction side separation exists, it may remain open up to the trailing edge. This is especially the case when blade lift is increased via increased pitch to chord ratio. There is a trend in research towards exploring the effect of coupling boundary layer control with highly loaded turbine blades, in order to maximize performance over the full relevant Reynolds number range. In an earlier work, pulsed blowing with fluidic oscillators was shown to be effective in reducing the extent of the separated flow region and to significantly decrease the profile losses caused by separation over a wide range of Reynolds numbers. These experiments were carried out in the High-Speed Cascade Wind Tunnel of the German Federal Armed Forces University Munich, Germany, which allows to capture the effects of pulsed blowing at engine relevant conditions. The assumed control mechanism was the triggering of boundary layer transition by excitation of the Tollmien-Schlichting waves. The current work aims to gain further insight into the effects of pulsed blowing. It investigates the effect of a highly efficient configuration of pulsed blowing at a frequency of 9.5 kHz on the boundary layer at a Reynolds number of 70000 and exit Mach number of 0.6. The boundary layer profiles were measured at five positions between peak Mach number and the trailing edge with hot wire anemometry and pneumatic probes. Experiments were conducted with and without actuation under steady as well as periodically unsteady inflow conditions. The results show the development of the boundary layer and its interaction with incoming wakes. It is shown that pulsed blowing accelerates transition over the separation bubble and drastically reduces the boundary layer thickness.

Download Full-text

Lateral skull base surgery: a complicated pursuit?

The Journal of Laryngology & Otology ◽

10.1017/s0022215107000436 ◽

2007 ◽

Vol 122 (3) ◽

pp. 221-229

Author(s):

V C Cousins

Keyword(s):

Skull Base ◽

Skull Base Surgery ◽

Treatment Modalities ◽

Published Data ◽

Know How ◽

Team Assessment ◽

Pathological Conditions ◽

Lateral Skull Base ◽

Wide Range ◽

Multi Disciplinary Team

AbstractThe management of lesions of the lateral skull base is a highly sophisticated branch of surgery generally performed by otolaryngology–head and neck surgeons as part of a multi-disciplinary team. Assessment of patients with diseases affecting the lateral skull base can be complex, as can the application of the various treatment modalities and the management of the expected and unexpected side effects of that treatment.A wide range of pathological conditions occur in the lateral skull base. Many operations and procedures have been described for dealing with them. There is not necessarily one correct solution to the management of any particular problem in the skull base, with multiple factors to be considered in planning and intervention.As surgeons, we need to know how our own results and outcomes compare with pooled, published data concerning the implications and complications occurring as a result of intervention, in order to better advise our patients on their management.

Download Full-text