GPS Sources Research Articles

Performance evaluation student result using k-means clustering

The performance of students is a vital and significant element of institutions of higher learning, for both the student and the academic community as a whole. As a result, higher education institutions must be more flexible in terms of performance metrics and ideas. However, when the student population grows owing to sessional admission, obtaining accurate information on students' performance becomes more difficult due to the huge amount of data in educational databases (for about 1-100years). Clustering is one of the data mining techniques used to examine large amounts of data. It organizes data into clusters so that items are placed together in the same cluster if they are comparable based on certain criteria. Several methods for improving the performance of the K-means clustering algorithm used in big data analysis have been proposed in the literature, but the proposed modified K-means clustering algorithm is less time-consuming, more efficient, has less complexity, and, most importantly, produces better clustering. To categorize numerical data, the modified K mean method is employed. However, the data in each cluster may be susceptible to outliers and noisy data, which may decrease the accuracy rate of data matching, since pattern matching will not readily enable prediction of the cluster center and therefore cannot characterize the data in the cluster. The modified k-means clustering method, which is suitable for large data from social media, sensors, search engines, GPS, transaction/financial records, satellites, e-commerce sites, and other sources, is suggested to address the issue and assess the results produced.

The gaseous natal environments of GPS and CSS sources with ASKAP–FLASH

AbstractGHz‐Peaked Spectrum (GPS) and compact steep spectrum (CSS) sources are thought to represent a young and/or confined sub‐population of radio‐loud active galactic nuclei (AGN) that are yet to evacuate their surrounding ambient interstellar gas. By studying the gaseous environments of these objects, we can gain an insight into the inter‐dependent relationship between galaxies and their supermassive black holes (SMBHs). The First Large Absorption Survey in Hi (FLASH) will build a census of the neutral atomic hydrogen (Hi) gas in galaxies at intermediate cosmological redshifts. FLASH is expected to detect at least several hundred Hi absorbers associated with GPS and CSS sources. These absorbers provide an important probe of the abundance and kinematics of line‐of‐sight neutral gas toward radio AGN, in some cases revealing gas associated with infalling clouds and outflows. Observations are now complete for the first phase of the FLASH Pilot Survey and early analysis has already yielded several detections, including the GPS source PKS 2311‐477. Optical imaging of this galaxy reveals an interacting system that could have supplied the neutral gas seen in absorption and triggered the radio‐loud AGN. FLASH will provide a statistically significant sample with which the prevalence of such gas‐rich interactions among compact radio galaxies can be investigated.

Young radio sources: From newly born to short‐lived objects

AbstractThe evolutionary stage of a powerful radio source originated by an active galactic nucleus is related to its linear size. Following the evolution models, intrinsically compact objects would evolve into the population of classical radio galaxies. However, the fraction of young radio sources in flux density‐limited samples is much larger than what is expected from the number counts of large radio sources, suggesting the existence of short‐lived objects. We present results of multi‐epoch very large array and very long baseline array observations of a sub‐sample of extreme GPS sources that should be at the very beginning of their radio evolution. We also briefly introduce a new project aiming at determining the incidence of short‐lived objects among a statistically complete sample of young radio sources.

High-resolution VLA Imaging of Obscured Quasars: Young Radio Jets Caught in a Dense ISM

Abstract We present new subarcsecond-resolution Karl G. Jansky Very Large Array (VLA) imaging at 10 GHz of 155 ultraluminous (L bol ∼ 1011.7–1014.2 L ⊙) and heavily obscured quasars with redshifts z ∼ 0.4–3. The sample was selected to have extremely red mid-infrared–optical color ratios based on data from the Wide-Field Infrared Survey Explorer (WISE) along with a detection of bright, unresolved radio emission from the NRAO VLA Sky Survey (NVSS) or Faint Images of the Radio Sky at Twenty cm Survey. Our high-resolution VLA observations have revealed that the majority of the sources in our sample (93 out of 155) are compact on angular scales <0.″2 (≤1.7 kpc at z ∼ 2). The radio luminosities, linear extents, and lobe pressures of our sources are similar to young radio active galactic nuclei (e.g., gigahertz-peaked spectrum [GPS] and compact steep-spectrum [CSS] sources), but their space density is considerably lower. Application of a simple adiabatic lobe expansion model suggests relatively young dynamical ages (∼104–7 yr), relatively high ambient ISM densities (∼1–104 cm−3), and modest lobe expansion speeds (∼30–10,000 km s−1). Thus, we find our sources to be consistent with a population of newly triggered, young jets caught in a unique evolutionary stage in which they still reside within the dense gas reservoirs of their hosts. Based on their radio luminosity function and dynamical ages, we estimate that only ∼20% of classical large-scale FR I/II radio galaxies could have evolved directly from these objects. We speculate that the WISE-NVSS sources might first become GPS or CSS sources, of which some might ultimately evolve into larger radio galaxies.

A Highly Reliable and Cost-Efficient Multi-Sensor System for Land Vehicle Positioning.

In this paper, we propose a novel positioning solution for land vehicles which is highly reliable and cost-efficient. The proposed positioning system fuses information from the MEMS-based reduced inertial sensor system (RISS) which consists of one vertical gyroscope and two horizontal accelerometers, low-cost GPS, and supplementary sensors and sources. First, pitch and roll angle are accurately estimated based on a vehicle kinematic model. Meanwhile, the negative effect of the uncertain nonlinear drift of MEMS inertial sensors is eliminated by an H∞ filter. Further, a distributed-dual-H∞ filtering (DDHF) mechanism is adopted to address the uncertain nonlinear drift of the MEMS-RISS and make full use of the supplementary sensors and sources. The DDHF is composed of a main H∞ filter (MHF) and an auxiliary H∞ filter (AHF). Finally, a generalized regression neural network (GRNN) module with good approximation capability is specially designed for the MEMS-RISS. A hybrid methodology which combines the GRNN module and the AHF is utilized to compensate for RISS position errors during GPS outages. To verify the effectiveness of the proposed solution, road-test experiments with various scenarios were performed. The experimental results illustrate that the proposed system can achieve accurate and reliable positioning for land vehicles.

Numerical calculations of spectral turnover and synchrotron self-absorption in CSS and GPS radio sources

The dependence of the turnover frequency on the linear size is presented for a sample of GPS and CSS radio sources derived from complete samples. The dependence of the luminosity of the emission at the peak frequency with the linear size and the peak frequency is also presented for the galaxies in the sample. The luminosity of the smaller sources evolve strongly with the linear size. Optical depth effects have been included to the 3D model for the radio source of Kaiser (2000) to study the spectral turnover. Using this model, the observed trend can be explained by synchrotron self absorption. The observed trend in the peak-frequency -- linear-size plane is not affected by the luminosity evolution of the sources.

The Lockman Hole with LOFAR: Searching for GPS and CSS sources at low frequencies

AbstractThe Lockman Hole Project is a wide international collaboration aimed at exploiting the multi‐band extensive and deep information available for the Lockman Hole region, with the aim of better characterizing the physical and evolutionary properties of the various source populations detected in deep radio fields. Recent observations with the LOw‐Frequency ARray (LOFAR) extends the multi‐frequency radio information currently available for the Lockman Hole (from 350 MHz up to 15 GHz) down to 150 MHz, allowing us to explore a new radio spectral window for the faint radio source population. These LOFAR observations allow us to study the population of sources with spectral peaks at lower radio frequencies, providing insight into the evolution of GPS and CSS sources. In this general framework, I present preliminary results from 150 MHz LOFAR observations of the Lockman Hole field. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Tracing the neutral gas environments of young radio AGN with ASKAP

AbstractAt present neutral atomic hydrogen (H I) gas in galaxies at redshifts above z ∼ 0.3 (the extent of 21 cm emission surveys in individual galaxies) and below z ∼ 1.7 (where the Lyman‐α line is not observable with ground‐based telescopes) has remained largely unexplored. The advent of precursor telescopes to the Square Kilometre Array will allow us to conduct the first systematic radio‐selected 21 cm absorption surveys for H I over these redshifts. While H I absorption is a tracer of the reservoir of cold neutral gas in galaxies available for star formation, it can also be used to reveal the extreme kinematics associated with jet‐driven neutral outflows in radio‐loud active galactic nuclei. Using the six‐antenna Boolardy Engineering Test Array of the Australian Square Kilometre Array Pathfinder, we have demonstrated that in a single frequency tuning we can detect H I absorption over a broad range of redshifts between z = 0.4 and 1.0. As part of our early science and commissioning program, we are now carrying out a search for absorption towards a sample of the brightest GPS and CSS sources in the southern sky. These intrinsically compact sources present us with an opportunity to study the circumnuclear region of recently re‐started radio galaxies, in some cases showing direct evidence of mechanical feedback through jetdriven outflows. With the sensitivity of the full ASKAP array we will be able to study the kinematics of atomic gas in a few thousand radio galaxies, testing models of radio jet feedback well beyond the nearby Universe. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A possible link between high rotation measure and CSS‐GPS sources

AbstractWe report here the study, in the radio band, of a sample of candidates of high rotation measure (RM). The point‐like objects (at kpc scale) were selected by choosing unpolarized sources from the NVSS which show significant linear polarization at 10.45 GHz. Assuming in‐band depolarization, this feature suggests the presence of a very dense medium surrounding them in a combination of a strong magnetic field. Further single‐dish observations were performed with the 100‐m Effelsberg telescope to characterise the SEDs of the sample and to well determine their RM in the 11 to 2 cm wavelength range. Besides, a wideband (L, S, C and X band) full polarisation observational campaign was performed at the JVLA facility. It allows us to analyse the in‐band RM for the most extreme objects. Some Effelsberg results and analysis, and preliminary JVLA results are presented. The observations reveal that sources with young, newly growing, radio components at high frequency (i.e. GPS and HFP sources) are characterised by a really dense and/or a magnetised medium that strongly rotates the polarisation angle at the different frequencies, leading to a high RM. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Small jets in radio‐loud hot DOGs

AbstractWe address the impact of young radio jets on the ISM and star formation in a sample of radiatively efficient, highly obscured, radio AGN with look back times that place them near the peak of the galaxy and BH building era, z ∼ 1–3. By selecting systems with a high mid‐infrared (MIR) luminosity we aim to identify radiatively efficient (“quasar‐mode” or “radiative‐mode”) AGN in a peak fueling phase, and by selecting compact radio sources we favor young or re‐generated radio jets which are confined within the hosts. By selecting AGN which are very red through the optical‐MIR we favor highly obscured systems likely to have been recently merger‐triggered and still in the pre‐blow‐out phase of AGN feedback into the surrounding ISM. ALMA imaging at 345 GHz of 49 sources has revealed that they are accretion dominated, relative to star formation, with luminosities reaching 1014 L⊙. Extensive VLA imaging at 8–10 GHz in both A‐array and B‐array for 155 sources reveals that the majority of these powerful radio systems are compact on <2–5 kpc scales while some have resolved structures on 3–25 kpc scales, and a small number have giant radio lobes on hundreds of kpc scales. The majority of the GHz range radio SEDs are typical of optically thin synchrotron, however for the 34 sources with data at more than 2 frequencies, 40% are likely to be CSS, GPS, or HFP sources. VLBA imaging of 62 sources reveals varied morphologies, from unresolved sources to complex multicomponent 1–10 mas scale structures. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A LOFAR view on the duty cycle of young radio sources

AbstractCompact Steep Spectrum, Gigahertz Peaked Spectrum, and High Frequency Peak (CSS, GPS, HFP) sources are considered to be young radio sources, but the details of their duty cycle are not well understood. In some cases they are thought to develop in FRI/FRII radio galaxies while in other cases their jets may remain confined within the host galaxy, and some may experience intermittent activity or die prematurely, never reaching the size of large classical double radio galaxies. Studying in a systematic way the presence and the properties of any extended emission surrounding these compact sources can provide firmer constraints on their evolutionary history and on the timescales of activity of the radio source. Remnant emission from previous outbursts is supposed to have very low surface brightness and to be brighter at low frequency. Taking advantage of the unprecedented sensitivity and resolution provided by the Low Frequency Array (LOFAR) we have started a systematic search of new CSS, GPS, and HFP sources with extended emission, as well as a more detailed study of some well‐known of these sources. Here we present the key points of our search in the LOFAR fields and a more in‐depth analysis on the source B2 0258+35, a CSS source surrounded by a pair of large, diffuse radio lobes. In this way, we aim to provide a better census of restarted sources and a better knowledge of the variety of their duty cycle. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The Parsec-Scale Morphology of Southern GPS Sources

AbstractMulti-frequency, multi-epoch ATCA observations of a sample of AGN resulted in the identification of nine new candidate Giga-hertz Peaked Spectrum sources. Here, we present Long Baseline Array observations at 4.8 GHz of the four candidates with no previously published VLBI image, and consider these together with previously published VLBI images of the other five sources. We find core-jet or compact double morphologies dominate, with further observations required to distinguish between these two possibilities for some sources. One of the nine candidates, PKS 1831–711, displays appreciable variability, suggesting its GPS spectrum is more ephemeral in nature. We focus in particular on the apparent relationship between a narrow spectral width and ‘compact double’ parsec-scale morphology, finding further examples, but also exceptions to this trend. An examination of the VLBI morphologies high-redshift (z > 3) sub-class of GPS sources suggests that core-jet morphologies predominate in this class.

Sensor data fusion for an indoor and outdoor localization

Geolocation systems are constantly evolving to enhance the integrity, accuracy and availability. Today, the applications are emerging and multiplying which are parts of an overall context of mobility. In outdoor environments, GNSS systems used, such as GPS and Galileo, provide a good accuracy, but in the indoor environments, GNSS signal is deteriorated due to the signal degradation by different obstacles. Many techniques are used to locate users in the indoor environments such as Infrared, Ultrasound or Radiofrequency techniques. The use of these techniques facilitates the exchange and dissemination of information. This paper presents a new design of Indoor-Outdoor positioning system based on the combination of data from UWB and GPS sources.

Information Abstraction for Heterogeneous Real World Internet Data

Everyday around 2.5 quintillion bytes of data are created. There is also a growing trend toward integrating real world data into the Internet, which is provided by sensory devices, smart phones, GPS, and many other sources that capture and communicate real world data. The term Internet of Things (IoT) refers to billions of devices that produce and exchange data related to real world objects (i.e., Things). This paper focuses on how to optimize the data exchange between the sensory devices and applications in IoT and Cyber-Physical systems. In particular, a method to construct higher-level abstractions of data at local gateways is proposed. This will reduce the traffic load imposed on the communication networks that provide the real world data. The proposed method is based on an information processing algorithm where gateways analyze the data collected from the sensors and create higher level abstractions. We enhance the symbolic aggregate approximation (SAX) algorithm that is used as a building block of the abstraction creation framework, into an optimized version for sensor data, called sensor SAX. We extend the parsimonious covering theory that is usually used for medical purposes with a probabilistic parsimonious criterion in the temporal domain to infer abstractions based on time-dependent sensor data. The proposed method is analyzed and evaluated over a real world data set and the results are discussed in terms of the data size reduction, accuracy, and latency needed to create the abstractions.

Hazard Analysis Methodology and Derivation of Performance Criteria for ADS-B and Alternate Surveillance Means

Recent standards work has derived minimum performance criteria for ADS-B surveillance using radar-like separation standards and operational methods in en route and terminal airspace. This paper introduces an alternative methodology for deriving ADS-B, radar and other surveillance system performance requirements based on generic hazard analysis methodology summarized by the FAA in recent Safety Management System (SMS) documents. The methodology is illustrated by first principles derivation of ADS-B performance criteria such as containment integrity (NIC, SIL) and position accuracy (NACp) for specified separation standards using GPS and alternate position sources. The level of the analysis is consistent with preliminary hazard analysis (PHA), to identify candidate surveillance sensors and initial performance criteria to meet desired target level of safety (TLS) criteria for specified separation minima. A simplified separation error probability (SEP) methodology is introduced that enables direct derivation of accuracy and integrity criteria for ADS-B systems, and provides a generic methodology for other positioning sensors, such as radar. The SEP methodology is extendable for end-to-end analysis, i.e., from generation of aircraft position and velocity reports to display of aircraft traffic for air traffic control and separation management.

Candidate GPS sources near the North Celestial Pole

Results of observations of the five candidate GPS sources J0626+8202, J0726+7911, J1044+8054, J1823+7938, and J1935+8130 are presented. GPS sources are extragalactic sources whose spectral peaks are near several GHz. These objects were observed on the RATAN-600 radio telescope from 1999 through 2010 at 1.1, 2.3, 4.8, 7.7, 11.2, and 21.7 GHz. These radio sources were selected from a complete sample (Sv ≥ 200 mJy at 1.4 GHz) in the vicinity of the North Celestial Pole (+75° ≤ δ ≤ +88°); four are considered as GPS candidates for the first time here. Their spectral properties, variability and morphology are analyzed, and confirms that these can be classified as GPS sources. These four to five GPS sources probably comprise a complete sample of this class of object in this region of the celestial sphere.

Observations and properties of candidate high-frequency GPS radio sources in the AT20G survey

We used the Australia Telescope Compact Array (ATCA) to obtain 40 GHz and 95 GHz observations of a number of sources that were selected from the Australia Telescope Compact Array 20 GHz (AT20G) survey . The aim of the observations was to improve the spectral coverage for sources with spectral peaks near 20 GHz or inverted (rising) radio spectra between 8.6 GHz and 20 GHz. We present the radio observations of a sample of 21 such sources along with optical spectra taken from the ANU Siding Spring Observatory 2.3m telescope and the ESO-New Technology Telescope (NTT). We find that as a group the sources show the same level of variability as typical GPS sources, and that of the 21 candidate GPS sources roughly 60% appear to be genuinely young radio galaxies. Three of the 21 sources studied show evidence of being restarted radio galaxies. If these numbers are indicative of the larger population of AT20G radio sources then as many as 400 genuine GPS sources could be contained within the AT20G with up to 25% of them being restarted radio galaxies.

The follow-up European VLBI Network observations of twelve GPS radio sources at 5 GHz

We defined a sub-sample of twelve GPS sources which have not been observed with the VLBI before, from the Parkes half-Jansky sample, and carried out VLBI observations at 1.6 GHz and 5 GHz with the European VLBI Network (EVN) in 2006 and 2008, respectively, to classify the source structure and to find compact symmetric objects (CSOs). Additionally, we carried out the 4.85 GHz flux density observations for these sources with the Urumqi 25-m telescope between the years 2007 and 2009 to study whether there is any variability in the total flux density of the GPS sources. The results of the 5 GHz VLBI observations and total flux densities of these sources are presented in this paper. From the VLBI morphologies, the spectral indices of components and the total flux variability of the twelve targets, we firmly classify three sources J0210+0419, J1135$-$0021, and J2058+0540 as CSOs, and classify J1057+0012, J1203+0414, and J1600$-$0037 as core-jet sources. The others J0323+0534, J0433$-$0229, J0913+1454, J1109+1043, and J1352+0232 are labelled CSO candidates, and J1352+1107 is a complex feature. Apart from core-jet sources, the total flux densities of the CSOs and candidates are quite stable at 5 GHz both during a long-term of $\sim$20 years relative to the PKS90 data and in a period between 2007 and 2009. The total flux densities are resolved-out by more than 20\% in the 5 GHz VLBI images for 6 sources, probably because of diffuse emission. In addition, we estimated the jet viewing angles $\Theta$ for the confirmed CSOs by using the double-lobe flux ratio of the sources, the result being indicative of relatively large $\Theta$ for the CSOs.

H I 21 cm ABSORPTION AND UNIFIED SCHEMES OF ACTIVE GALACTIC NUCLEI

In this paper we further explore the implications that this has for the currently popular consensus that it is the orientation of the circumnuclear obscuring torus which determines whether absorption is present along our sight-line. The fact that at logL > 23 W/Hz, both type-1 and type-2 objects exhibit a 50% probability of detection, suggests that this is not the case and that the bias against detection of HI absorption in type-1 objects is due purely to the inclusion of the logL > 23 W/Hz sources. Similarly, the ultra-violet luminosities can also explain why the presence of 21-cm absorption shows a preference for radio galaxies over quasars and the higher detection rate in compact sources, such as CSS or GPS sources, may also be biased by the inclusion of high-luminosity sources. Being comprised of all 21-cm searched sources at z>0.1, this is a necessarily heterogeneous sample, the constituents of which have been observed by various instruments. By this same token, however, the dependence on the UV luminosity may be an all encompassing effect, superseding the unified schemes model, although there is the possibility that the exclusive 21-cm non-detections at high UV luminosities could be caused by a bias towards gas-poor ellipticals. Additionally, the high UV fluxes could be sufficiently exciting/ionising the HI above 21-cm detection thresholds, although the extent to which this is related to the neutral gas deficit in ellipticals is currently unclear.

GPS and CSS radio sources

The spectral and kinematic properties of GPS and CSS radio sources and methods for determining theirages are discussed. The data presented here do not support a mechanism of accretion of dust or moleculargas on massive black holes located in the central regions of radio galaxies of these classes as the sourceof their activity. The nature of GPS and CSS objects has not been fully clarified. Further detailed studiesin the optical, radio, and other spectral ranges will be required in order to establish the true nature ofthis class of source.