Unification Scheme Research Articles

Low-frequency radio observations of Seyfert galaxies: A test of the unification scheme

Aims. We present low-frequency radio imaging and spectral properties of a well defined sample of Seyfert galaxies using GMRT 240/610 MHz dual frequency observations. Radio spectra of Seyfert galaxies over 240 MHz to 5.0 GHz are investigated using 240 MHz, 610 MHz flux densities derived from GMRT, and 1.4 GHz and 5.0 GHz flux densities mainly from published VLA data. We test the predictions of Seyfert unification scheme by comparing the radio properties of Seyfert type 1s and type 2s. Methods. We choose a sample such that the two Seyfert subtypes have matched distributions in parameters that are independent to the orientation of AGN, obscuring torus and the host galaxy. Our sample selection criteria allow us to assume that the two Seyfert subtypes are intrinsically similar within the framework of the unification scheme. Results. The new observations at 240/610 MHz, together with archival observations at 1.4 GHz, 5.0 GHz show that type 1s and type 2s have statistically similar radio luminosity distributions at 240 MHz, 610 MHz, 1.4 GHz and 5.0 GHz. The spectral indices at selected frequency intervals as well as index measured over 240 MHz to 5.0 GHz for the two Seyfert subtypes have similar distributions with median spectral index $/sim$ -0.7, consistent with the synchrotron emission from optically thin plasma. In our snap-shot 240/610 MHz GMRT observations, most of the Seyfert galaxies show primarily an unresolved central radio component, except a few sources in which faint kpc-scale extended emission is apparent at 610 MHz. Our results on the statistical comparison of the multifrequency radio properties of our sample Seyfert galaxies are in agreement with the predictions of the Seyfert unification scheme.

Black hole binaries and microquasars

This is a general review on the observations and physics of black hole X-ray binaries and microquasars, with the emphasize on recent developments in the high energy regime. The focus is put on understanding the accretion flows and measuring the parameters of black holes in them. It includes mainly two parts: i) Brief review of several recent review article on this subject; ii) Further development on several topics, including black hole spin measurements, hot accretion flows, corona formation, state transitions and thermal stability of standard think disk. This is thus not a regular bottom-up approach, which I feel not necessary at this stage. Major effort is made in making and incorporating from many sources useful plots and illustrations, in order to make this article more comprehensible to non-expert readers. In the end I attempt to make a unification scheme on the accretion-outflow (wind/jet) connections of all types of accreting BHs of all accretion rates and all BH mass scales, and finally provide a brief outlook.

A simplified view of blazars: the γ-ray case

We have recently proposed a new simplified scenario where blazars are classified as flat-spectrum radio quasars (FSRQs) or BL Lacs according to the prescriptions of unified schemes, and to a varying combination of Doppler boosted radiation from the jet, emission from the accretion disk, the broad line region, and light from the host galaxy. Here we extend our approach, previously applied to radio and X-ray surveys, to the gamma-ray band and, through detailed Monte Carlo simulations, compare our predictions to Fermi-LAT survey data. Our simulations are in remarkable agreement with the overall observational results, including the percentages of BL Lacs and FSRQs, the fraction of redshift-less objects, and the redshift, synchrotron peak, and gamma-ray spectral index distributions. The strength and large scatter of the oft-debated observed Gamma-ray -- radio flux density correlation is also reproduced. In addition, we predict that almost 3/4 of Fermi-LAT BL Lacs, and basically all of those without redshift determination, are actually FSRQs with their emission lines swamped by the non-thermal continuum and as such should be considered. Finally, several of the currently unassociated high Galactic latitude Fermi sources are expected to be radio-faint blazars displaying a pure elliptical galaxy optical spectrum.

Implementation of infection control best practice in intensive care units throughout Europe: a mixed-method evaluation study

BackgroundThe implementation of evidence-based infection control practices is essential, yet challenging for healthcare institutions worldwide. Although acknowledged that implementation success varies with contextual factors, little is known regarding the most critical specific conditions within the complex cultural milieu of varying economic, political, and healthcare systems. Given the increasing reliance on unified global schemes to improve patient safety and healthcare effectiveness, research on this topic is needed and timely. The ‘InDepth’ work package of the European FP7 Prevention of Hospital Infections by Intervention and Training (PROHIBIT) consortium aims to assess barriers and facilitators to the successful implementation of catheter-related bloodstream infection (CRBSI) prevention in intensive care units (ICU) across several European countries.MethodsWe use a qualitative case study approach in the ICUs of six purposefully selected acute care hospitals among the 15 participants in the PROHIBIT CRBSI intervention study. For sensitizing schemes we apply the theory of diffusion of innovation, published implementation frameworks, sensemaking, and new institutionalism. We conduct interviews with hospital health providers/agents at different organizational levels and ethnographic observations, and conduct rich artifact collection, and photography during two rounds of on-site visits, once before and once one year into the intervention. Data analysis is based on grounded theory. Given the challenge of different languages and cultures, we enlist the help of local interpreters, allot two days for site visits, and perform triangulation across multiple data sources.Qualitative measures of implementation success will consider the longitudinal interaction between the initiative and the institutional context. Quantitative outcomes on catheter-related bloodstream infections and performance indicators from another work package of the consortium will produce a final mixed-methods report.ConclusionA mixed-methods study of this scale with longitudinal follow-up is unique in the field of infection control. It highlights the ‘Why’ and ‘How’ of best practice implementation, revealing key factors that determine success of a uniform intervention in the context of several varying cultural, economic, political, and medical systems across Europe. These new insights will guide future implementation of more tailored and hence more successful infection control programs.Trial registrationTrial number: PROHIBIT-241928 (FP7 reference number)

DISCOVERY OF GIANT RELIC RADIO LOBES STRADDLING THE CLASSICAL DOUBLE RADIO GALAXY 3C452

We report the discovery of a pair of megaparsec size radio lobes of extremely steep spectrum straddling the well-known classical double radio source 3C452. The existence of such fossil lobes was unexpected since for the past several decades this powerful radio galaxy has been regarded as a textbook example of an edge-brightened double radio source of Fanaroff-Riley type II (FR II), which we now show to be a bona fide double-double radio galaxy (DDRG). Thus, 3C452 presents a uniquely robust example of recurrent nuclear activity in which the restarted jets are expanding non-relativistically within the relic synchrotron plasma from an earlier active phase and hence the inner double fed by them has evolved into a perfectly normal FR II radio source. This situation contrasts markedly with the strikingly narrow inner doubles observed in a few other DDRGs that have been interpreted in terms of compression of the synchrotron plasma of the relic outer lobes at the relativistic bow-shocks driven by the near ballistic propagation of the two inner jets through the relic plasma. A key ramification of this finding is that it cautions against the currently widespread use of FR II classical double radio sources for testing cosmological models and unification schemes for active galactic nuclei.

Unification Scheme in Double Radio Sources: Bend Angle versus Arm Length Ratio Relations

From radio source unification scheme, asymmetries are more pronounced in quasars than in radio galaxies. Using a sample of 625 double radio sources (316 radio galaxies and 309 quasars), we investigated the variations between bend angle, arm-length ratio and redshift. We find no significant correlation (0.045) between bend angle and redshift for the entire sample and at low z for radio galaxies while a weak correlation (0.121) between bend angle and redshift for quasars for the entire sampleis observed. A weak correlation (radio galaxies, r = 0.173 and quasars, r = 0.102) between the bend angle and arm-length ratio for the double radio sources used in this study is observed. Kharbet al. (2008) in their study of powerful classical double radio galaxies noted that this correlation could suggest that the environmental asymmetries that give rise to the arm- length ratio could be contributory to the misalignment angles in these sources. Quasars appear much more bent and misaligned. This is consistent with quasars being radio galaxies viewed at small angles.

Quasar emission lines, radio structures and radio unification

Unified schemes of radio sources, which account for different types of radio AGN in terms of anisotropic radio and optical emission, together with different orientations of the ejection axis to the line of sight, have been invoked for many years. Recently, large samples of optical quasars, mainly from the Sloan Digital Sky Survey, together with large radio samples, such as FIRST, have become available. These hold the promise of providing more stringent tests of unified schemes but, compared to previous samples, lack high resolution radio maps. Nevertheless they have been used to investigate unified schemes, in some cases yielding results which appear inconsistent with such theories. Here we investigate using simulations how the selection effects to which such investigations are subject can influence the conclusions drawn. In particular, we find that the effects of limited resolution do not allow core-dominated radio sources to be fully represented in the samples, that the effects of limited sensitivity systematically exclude some classes of sources and the lack of deep radio data make it difficult to decide to what extent closely separated radio sources are associated. Nevertheless, we conclude that relativistic unified schemes are entirely compatible with the current observational data. For a sample selected from SDSS and FIRST which includes weak-cored triples we find that the equivalent width of the [OIII] emission line decreases as core-dominance increases, as expected, and also that core-dominated quasars are optically brighter than weak-cored quasars.

Active Galactic Nuclei under the scrutiny of CTA

Active Galactic Nuclei (hereafter AGN) produce powerful outflows which offer excellent conditions for efficient particle acceleration in internal and external shocks, turbulence, and magnetic reconnection events. The jets as well as particle accelerating regions close to the supermassive black holes (hereafter SMBH) at the intersection of plasma inflows and outflows, can produce readily detectable very high energy gamma-ray emission. As of now, more than 45 AGN including 41 blazars and 4 radiogalaxies have been detected by the present ground-based gamma-ray telescopes, which represents more than one third of the cosmic sources detected so far in the VHE gamma-ray regime. The future Cherenkov Telescope Array (CTA) should boost the sample of AGN detected in the VHE range by about one order of magnitude, shedding new light on AGN population studies, and AGN classification and unification schemes. CTA will be a unique tool to scrutinize the extreme high-energy tail of accelerated particles in SMBH environments, to revisit the central engines and their associated relativistic jets, and to study the particle acceleration and emission mechanisms, particularly exploring the missing link between accretion physics, SMBH magnetospheres and jet formation. Monitoring of distant AGN will be an extremely rewarding observing program which will inform us about the inner workings and evolution of AGN. Furthermore these AGN are bright beacons of gamma-rays which will allow us to constrain the extragalactic infrared and optical backgrounds as well as the intergalactic magnetic field, and will enable tests of quantum gravity and other “exotic” phenomena.

Unified Control for a Wind Turbine-Superconducting Magnetic Energy Storage Hybrid System Based on Current Source Converters

This paper proposes the unified control for a novel wind turbine-superconducting magnetic energy storage (SMES) hybrid system, where the SMES coil is integrated with the DC link of the current source converter (CSC) fed wind energy conversion system. The unified power and current control schemes are proposed for general grid conditions by designing the proper active damping, the closed-loop grid current regulation, and the decoupled double synchronous frame phase locked loop (DDSRF-PLL). Furthermore, the system operation schemes are proposed and designed for both the normal SMES current condition and the low SMES current condition. The performance of the proposed control schemes are verified by computer simulation.

Unified iterative learning control schemes for nonlinear dynamic systems with nonlinear input uncertainties

In many ILC algorithms, nonlinear input uncertainties such as saturation, dead-zone and hysteresis, which do exist due to practical implementations, are always ignored. Although various ILC algorithms have been proposed to compensate various nonlinear input uncertainties, a systematic design framework is still missing. This note presents a unified design framework to deal with very general nonlinear input uncertainties. The concept of a dual-loop ILC is introduced. One ILC loop (ILC Loop 1) is designed for the nominal model without nonlinear input uncertainties. The other ILC loop (ILC Loop 2) uses some iterative algorithms to handle nonlinear input uncertainties. Two ILC loops can be designed independently and are connected by a proper time-scale separation. Our first result shows that by using time-scale separation, the overall system semi-globally practically converges to the desired trajectory if ILC Loop 2 uniformly converges. Furthermore, if ILC Loop 2 converges “almost” monotonically, ILC Loop 1 and ILC Loop 2 can update simultaneously to achieve uniform convergence of the overall system.

TheINTEGRAL/IBIS AGN catalogue - I. X-ray absorption properties versus optical classification

In this work we present the most comprehensive INTEGRAL AGN sample which lists 272 objects. Here we mainly use this sample to study the absorption properties of active galaxies, to probe new AGN classes and to test the AGN unification scheme. We find that half (48%) of the sample is absorbed while the fraction of Compton thick AGN is small (~7%). In line with our previous analysis, we have however shown that when the bias towards heavily absorbed objects which are lost if weak and at large distance is removed, as it is possible in the local Universe, the above fractions increase to become 80% and 17%. We also find that absorption is a function of source luminosity, which implies some evolution in the obscuration properties of AGN. Few peculiar classes, so far poorly studied in the hard X-ray band, have been detected and studied for the first time such as 5 XBONG, 5 type 2 QSOs and 11 LINERs. In terms of optical classification, our sample contains 57% of type 1 and 43% of type 2 AGN; this subdivision is similar to that found in X-rays if unabsorbed versus absorbed objects are considered, suggesting that the match between optical and X-ray classification is overall good. Only a small percentage of sources (12%) does not fulfill the expectation of the unified theory as we find 22 type 1 AGN which are absorbed and 10 type 2 AGN which are unabsorbed. Studying in depth these outliers we found that most of the absorbed type 1 AGN have X-ray spectra characterized by either complex or warm/ionized absorption more likely due to ionized gas located in an accretion disk wind or in the biconical structure associated to the central nucleus, therefore unrelated to the toroidal structure. Among 10 type 2 AGN which resulted to be unabsorbed, at most 3-4% is still eligible to be classified as a "true" type 2 AGN.

Testing the AGN Unification Model in the Infrared

We present near-to-mid-infrared spectral energy distributions (SEDs) for 21 Seyfert galaxies, using subarcsecond resolution imaging data. Our aim is to compare the properties Seyfert 1 (Sy1) and Seyfert 2 (Sy2) tori using clumpy torus models and a Bayesian approach to fit the infrared (IR) nuclear SEDs. These dusty tori have physical sizes smaller than 6 pc radius, as derived from our fits. Active galactic nuclei (AGN) unification schemes account for a variety of observational differences in terms of viewing geometry. However, we find evidence that strong unification may not hold, and that the immediate dusty surroundings of Sy1 and Sy2 nuclei are intrinsically different. The Type 2 tori studied here are broader, have more clumps, and these clumps have lower optical depths than those of Type 1 tori. The larger the covering factor of the torus, the smaller the probability of having direct view of the AGN, and vice-versa. In our sample, Sy2 tori have larger covering factors (CT = 0.95±0.02) and smaller escape probabilities than those of Sy1 (CT = 0.5±0.1). Thus, on the basis of the results presented here, the classification of a Seyfert galaxy may depend more on the intrinsic properties of the torus rather than on its mere inclination, in contradiction with the simplest unification model.

NEW CONSTRAINTS ON YUKAWA-TYPE INTERACTIONS FROM THE CASIMIR EFFECT

Measurements of the Casimir force are used to obtain stronger constraints on the parameters of hypothetical interactions predicted in different unification schemes beyond the Standard Model. We review new strong constraints on the Yukawa-type interactions derived during the last two years from recent experiments on measuring the lateral Casimir force, Casimir force in configurations with corrugated boundaries and the Casimir–Polder force. Specifically, from measurements of the lateral Casimir force compared with the exact theory the strengthening of constraints up to a factor of 24 millions was achieved. We also discuss further possibilities to strengthen constraints on the Yukawa interactions from the Casimir effect.

Adaptive pseudo-continuous conduction mode operation schemes and circuit designs for single-inductor multiple-output switching converters

As single-inductor multiple-output (SIMO) switching converters proliferate in integrated power management designs, pseudo-continuous conduction mode (PCCM) operation with freewheel switching has been well adopted owing to its effectiveness on cross-regulation, voltage ripple and switching noise issues, especially in heavy load scenarios. However, the technique faces a direct challenge in unbalanced loading conditions. Potential lengthy freewheel switching periods and high I dc current levels could lead to conduction and switching power losses, degrading the efficiency of the converters. To alleviate this problem, this paper presents adaptive PCCM operation schemes with the respective distributed and unified freewheel switching schemes. The optimal freewheel switching durations are achieved in various load conditions by adaptively adjusting the phase durations and freewheel switching I dc current level, thereby reducing the conduction and switching losses effectively. The switching power loss is further reduced by turning on/off the freewheel switch less frequently, without compromising the performance of operation. The proposed schemes have been implemented and verified in digital and analog-based SIMO power converters designed with 130 nm CMOS process.

VLTI/AMBER observations of the Seyfert nucleus of NGC 3783

Context. The putative tori surrounding the accretion disks of active galactic nuclei (AGNs) play a fundamental role in the unification scheme of AGNs. Infrared long-baseline interferometry allows us to study the inner dust distribution in AGNs with unprecedented spatial resolution over a wide infrared wavelength range. Aims. Near- and mid-infrared interferometry is used to investigate the milli-arcsecond-scale dust distribution in the type 1.5 Seyfert nucleus of NGC 3783. Methods. We observed NGC 3783 with the VLTI/AMBER instrument in the K-band and compared our observations with models. Results. From the K-band observations, we derive a ring-fit torus radius of 0.74 +/- 0.23 mas or 0.16 +/- 0.05 pc. We compare this size with infrared interferometric observations of other AGNs and UV/optical-infrared reverberation measurements. For the interpretation of our observations, we simultaneously model our near- and mid-infrared visibilities and the SED with a temperature/density-gradient model including an additional inner hot 1400 K ring component.

Bolometric luminosities and brightness temperatures of BL Lac Objects and FR I radio galaxies

To understand the connection among the subclasses of BL Lac Objects, FR I radio galaxies and Flat spectrum radio quasars (FSRQs), here the correlations of the bolometric luminosities with redshifts and brightness temperatures of these objects are studied. The bolometric luminosities vary linearly with redshifts, but few objects are scattered at high redshift. The bolometric luminosity versus brightness temperature distribution shows a correlation between these two components, except a few scattered objects, mostly RBLs. The bolometric luminosities and brightness temperatures of FR I radio galaxies with low redshift (<0.1) and low spectral index (αrx<0.75) are comparable to those of XBLs and those characteristics of FR I radio galaxies, with relatively high redshift (>0.2) and high spectral index, can be comparable with RBLs with low redshift (z<0.5) and low bolometric luminosity. Those scattered RBLs with high redshifts (z>0.5) are believed to be in complex environment with companion galaxies, most of these RBLs are still unresolved. The bolometric luminosity and brightness temperature of these scattered RBLs are comparable to those of quasars. The FSRQs are at high redshifts and bolometric luminosities and the brightness temperatures are also high relative to BL Lac Objects. These results support the FRI/BL Lac unification scheme. It suggests that, the FR I radio galaxies may be the parent populations of the BL Lac Objects, but it needs more investigation to confirm the unification of FR I radio galaxies, XBLs and RBLs.

Unified Authentication Scheme Based on IBE in Trusted Network

The existing unified authentication schemes are based on Public Key Infrastructure (PKI)/Privilege Management Infrastructure (PMI), WS-Security, Kerberos etc. But they can't support the developing Trusted Network Connect (TNC) environment. To solve the problem, a unified authentication scheme supporting multi-authentication modes based on Identity-Based Encryption (IBE) in trusted network named IEUAS is proposed. IEUAS authenticates the identity of a user by loading different authentication plugins to communicate with the related authentication servers. According to the legal identity of the user, a lightweight IBE system enforces four management mechanisms. They are the identity management, the key management, the application management and the domain management. Single Sign-On (SSO) and cross-domain SSO are implemented. The experiment results show that IEUAS can effectively solve the unified authentication problem in the TNC environment, and provide better security, efficiency and availability.

Accounting and networks of corruption

This study examines the nature and role of accounting practices in a network of corruption in an influence-market setting. The study focuses on the Canadian government’s Sponsorship Program (1994–2003), a national unification scheme that saw approximately $50 million diverted into the bank accounts of political parties, program administrators, and their families, friends and business colleagues. Relying on the institutional sociology of Bourdieu, the study demonstrates the precise role of accounting practices in the organization of a corrupt network imbued with a specific telos and certain accounting tasks. The study illustrates how accounting is accomplished and by whom, and it shows how the ‘skillful use’ of accounting practices and social interactions around these practices together enable corruption. In so doing, the study builds on a growing body of work examining criminogenic networks and the contextual, collaborative and systemic uses of accounting in such networks.

A simplified view of blazars: clearing the fog around long-standing selection effects

We propose a scenario where blazars are classified as flat-spectrum radio quasars (FSRQs), BL Lacs, low synchrotron, or high synchrotron peaked objects according to a varying mix of the Doppler boosted radiation from the jet, the emission from the accretion disk, the broad line region, and the light from the host galaxy. In this framework the peak energy of the synchrotron power (nu_peak) in blazars is independent of source type and of radio luminosity. We test this new approach, which builds upon unified schemes, using extensive Monte Carlo simulations and show that it can provide simple answers to a number of long-standing issues including, amongst others, the different cosmological evolution of BL Lacs selected in the radio and X-ray bands, the larger nu_peak values observed in BL Lacs, the fact that high synchrotron peaked blazars are always of the BL Lac type, and the existence of FSRQ/BL Lac transition objects. Objects so far classified as BL Lacs on the basis of their observed weak, or undetectable, emission lines are of two physically different classes: intrinsically weak lined objects, more common in X-ray selected samples, and heavily diluted broad lined sources, more frequent in radio selected samples, which explains some of the confusion in the literature. We also show that strong selection effects are the main cause of the diversity observed in radio and X-ray samples, and that the correlation between luminosity and nu_peak, that led to the proposal of the "blazar sequence", is also a selection effect arising from the comparison of shallow radio and X-ray surveys, and to the fact that high nu_peak-high radio power objects have never been considered because their redshift is not measurable.

Hybrid Unified Kalman Tracking Algorithms for Heterogeneous Wireless Location Systems

Location estimation and tracking for mobile stations have attracted a significant amount of attention in recent years. Different types of signal sources are considered available to provide measurement inputs for location estimation and tracking in heterogeneous wireless networks. Various techniques have been studied and combined for location tracking, e.g., the least square methods for location estimation associated with the Kalman filters for location tracking. In this paper, the hybrid unified Kalman tracking (HUKT) technique is proposed to provide an integrated algorithm for precise location tracking based on both time of arrival (TOA) and time difference of arrival (TDOA) measurements. A new variable is incorporated as an additional state within the Kalman filtering formulation to consider the nonlinear behavior in the measurement update process. The relationship between this new variable and the desired location estimate is applied in the state update process of the Kalman filter. Three different designs of hybrid factor are proposed to adaptively adjust the weighting value between the TOA and TDOA measurements. Moreover, similar concepts are also utilized in the design of unified Kalman tracking schemes for pure TOA and TDOA measurement inputs in this paper. Compared with existing schemes, numerical results illustrate that the proposed HUKT algorithm can achieve enhanced accuracy for mobile location tracking, particularly under environments with an insufficient number of measurements in one of the signal paths.