bluuebunny/crossref_metadata_2025_split huggingface dataset:
Arbitrary amplitude dust-acoustic solitons in a weakly non-ideal plasma with non-thermal ions
Authors: MAHARAJ S. K. , BHARUTHRAM R. , PILLAY S. R. 
Published: May 2007

AbstractThe nonlinear propagation of the dust-acoustic wave is investigated in a weakly non-ideal plasma comprising Boltzmann electrons, non-thermal ions characterized by a non-thermal parameter α and a negatively charged dust fluid. The non-ideal dust fluid is represented by the van der Waals equation of state. Arbitrary amplitude soliton solutions are found to occur for both supersonic and subsonic values of the Mach number. Upper and lower limits of the range of values of α for which solitons exist are examined as a function of the non-ideal parameters associated with the effects of volume reduction and the cohesive forces, for both the supersonic and subsonic cases.
Fugitive women: Slavery and social change in early modern Southeast Asia
Authors: Jones Eric A. 
Published: May 2007

AbstractFemale slaves in VOC-controlled Southeast Asia did not fare well under a legal code which erected a firm partition between free and slave status. This codification imposed a rigid dichotomy for what had been fluid, abstract conceptions of social hierarchy, in effect silting up the flow of underclass mobility. At the same time, conventional relationships between master and slave shifted in the context of a changing economic climate. This article closely narrates the lives of several eighteenth-century female slaves who, left with increasingly fewer options in this new order, resorted to running away.
On agent technology for e-commerce: trust, security and legal issues
Authors: FASLI MARIA 
Published: May 2007

AbstractThe vision of future electronic marketplaces (e-markets) is that of markets being populated by autonomous intelligent entities—software, trading, e-agents—representing their users or owners and conducting business on their behalf. For this vision to materialize, one fundamental issue that needs to be addressed is that of trust. First, users need to be able to trust that the agents will do what they say they do. Second, they need to be confident that their privacy is protected and that the security risks involved in entrusting agents to perform transactions on their behalf are minimized. Finally, users need to be assured that any legal issues relating to agents trading electronically are fully covered as they are in traditional trading practices. In this paper we consider the barriers for the adoption of agent technology in electronic commerce (e-commerce) which pertain to trust, security and legal issues. We discuss the perceived risks of the use of agents in e-commerce and the fundamental issue of trust in this context. Issues regarding security, and how some of these can be addressed through the use of cryptography, are described. The impact of the use of agent technology on the users' privacy and how it can be both protected as well as hindered by it is also examined. Finally, we discuss the legal issues that arise in agent-mediated e-commerce and discuss the idea of attributing to software agents the status of legal persons or e-persons and the various implications.
A review of associative classification mining
Authors: THABTAH FADI 
Published: May 2007

AbstractAssociative classification mining is a promising approach in data mining that utilizes the association rule discovery techniques to construct classification systems, also known as associative classifiers. In the last few years, a number of associative classification algorithms have been proposed, i.e. CPAR, CMAR, MCAR, MMAC and others. These algorithms employ several different rule discovery, rule ranking, rule pruning, rule prediction and rule evaluation methods. This paper focuses on surveying and comparing the state-of-the-art associative classification techniques with regards to the above criteria. Finally, future directions in associative classification, such as incremental learning and mining low-quality data sets, are also highlighted in this paper.
Ontologies for probabilistic networks: a case study in the oesophageal-cancer domain
Authors: HELSPER EVELINE M. , VAN DER GAAG LINDA C. 
Published: May 2007

AbstractBuilding a probabilistic network for a real-life domain of application is a hard and time-consuming process, which is generally performed with the help of domain experts. As the scope and, hence, the size and complexity of networks are increasing, the need for proper management of the elicited domain knowledge becomes apparent. To study the usefulness of ontologies for this purpose, we constructed an ontology for the domain of oesophageal cancer, based on a real-life probabilistic network for the staging of cancer of the oesophagus and the knowledge elicited for its construction. In this paper, we describe the various components of our ontology and outline the benefits of using ontologies in engineering probabilistic networks.
Automated Verification of Weak Equivalence within thesmodelsSystem
Authors: JANHUNEN TOMI , OIKARINEN EMILIA 
Published: May 2007

AbstractIn answer set programming (ASP), a problem at hand is solved by (i) writing a logic program whose answer sets correspond to the solutions of the problem, and by (ii) computing the answer sets of the program using ananswer set solveras a search engine. Typically, a programmer creates a series of gradually improving logic programs for a particular problem when optimizing program length and execution time on a particular solver. This leads the programmer to a meta-level problem of ensuring that the programs are equivalent, i.e., they give rise to the same answer sets. To ease answer set programming at methodological level, we propose a translation-based method for verifying the equivalence of logic programs. The basic idea is to translate logic programsPandQunder consideration into a single logic program EQT(P,Q) whose answer sets (if such exist) yield counter-examples to the equivalence ofPandQ. The method is developed here in a slightly more general setting by taking thevisibilityof atoms properly into account when comparing answer sets. The translation-based approach presented in the paper has been implemented as a translator calledlpeqthat enables the verification of weak equivalence within thesmodelssystem using the same search engine as for the search of models. Our experiments withlpeqandsmodelssuggest that establishing the equivalence of logic programs in this way is in certain cases much faster than naive cross-checking of answer sets.
Energy spectra of X-ray quasi-periodic oscillations in accreting black hole binaries
Authors: Życki P. T. , Sobolewska M. A. , Niedźwiecki A. 
Published: May 2007

AbstractWe investigate the energy dependencies of X-ray quasi-periodic oscillations in black hole X-ray binaries. We analyze RXTE data on both the low- and high-frequency QPO. We construct the low-f QPO energy spectra, and demonstrate that they do not contain the thermal disk component, even though the latter is present in the time averaged spectra. The disk thus does not seem to participate in the oscillations. Moreover the QPO spectra are harder than the time averaged spectra when the latter are soft, which can be modeled as a result of modulations occurring in the hot plasma. The QPO spectra are softer than the time averaged spectra when the latter are hard. The absence of the disk component in the QPO spectra is true also for the high-frequency (hecto-Hz) QPO observed in black hole binaries. We compute the QPO spectra expected from the model of disk resonances.
Microquasars: disk–jet coupling in stellar-mass black holes
Authors: Mirabel I. Félix 
Published: May 2007

AbstractMicroquasars provide new insights into: 1) the physics of relativistic jets from black holes, 2) the connection between accretion and ejection, and 3) the physical mechanisms in the formation of stellar-mass black holes. Furthermore, the studies of microquasars in our Galaxy can provide in the future new insights on: 1) a large fraction of the ultraluminous X-ray sources in nearby galaxies, 2) gamma-ray bursts (GRBs) of long duration in distant galaxies, and 3) the physics in the jets of blazars. If jets in GRBs, microquasars and Active Galactic Nuclei (AGN) are due to a unique universal magnetohydrodynamic mechanism, synergy of the research on these three different classes of cosmic objects will lead to further progress in black hole physics and astrophysics.
Quasar evolution: black hole mass and accretion rate determination
Authors: Dultzin-Hacyan Deborah , Marziani Paola , Negrete C. Alenka , Sulentic Jack W. 
Published: May 2007

AbstractAccurate measurements of emission line properties are crucial to understand the physics of the broad line region in quasars. This region consists of warm gas that is closest to the quasar central engine and has not been spatially resolved for almost all sources. We present here an analysis of optical and IR data for a large sample of quasars, covering the Hi Hβ spectral region in the redshift range 0 ≲ z ≲ 2.5. Spectra were interpreted within the framework of the the so-called “eigenvector 1” parameter space, which can be viewed as a tentative H-R diagram for quasars. We stress the lack of spectral evolution in the low ionization lines of quasars, with prominent Fe ii emission also at z ≳ 2. We also show how selection effects influence the ability to find quasars radiating at low Eddington ratio in flux-limited surveys. The quasar similarity at different redshift is probably due to the absence of super-Eddington radiators (at least within the caveats of black hole mass and Eddington ratio determination discussed in this paper) as well as to the limited Eddington ratio range within which quasars seem to radiate.
Local active black hole mass functions
Authors: Greene Jenny E. , Ho Luis C. 
Published: May 2007

AbstractWhile black holes (BHs) are apparently a ubiquitous component of the nuclei of local spheroids, their role in galaxy evolution remains largely unknown. The tight correlations between galaxy spheroid properties and BH mass provide an important boundary condition for models of the coevolution of BHs and galaxies. Here we consider another important boundary condition: the local mass function of broad-line active galaxies. We use standard virial mass estimation techniques to examine the distribution of BH masses and accretion rates for active galaxies in the local universe, and we also compare the distribution of BH masses in local broad and narrow-line objects, and find that both populations have a characteristic mass of ∼107M⊙. Most importantly, this is the first BH mass function to consider BH with masses ∼106M⊙. The space density of this important population allows us to place constraints on potential mechanisms for the creation of seed BHs in the early Universe.
Mapping the circumnuclear dust in nearby AGN with MIDI
Authors: Tristram Konrad R. W. , Meisenheimer Klaus , Jaffe Walter , Cotton William D. 
Published: May 2007

AbstractWe observed four nearby AGN with MIDI at the VLTI to investigate the mid-infrared emission from these sources. With our measurements we resolve the dusty structure around the nucleus of the Circinus galaxy. We find two dust components: a hot, small elongated structure with a size of 0.4 pc and a cooler, almost round component with a size of 1.9 pc. We interpret the emission to be originating in a geometrically thick dusty torus oriented perpendicular to the ionisation cone. Hence our finding nicely confirms the unified picture. We also observed the nucleus of Centaurus A and find that 70% of the mid infrared flux originates from an unresolved source with a size of less than 0.2 pc. In this case, the majority of the emission comes from a synchrotron source at the base of the radio jet. Two further galaxies, Mrk 1239 (Seyfert 1) and MCG -05-23-016 (Seyfert 2), also show unresolved mid infrared sources limiting the size of the dust distribution to less than 5 and 2 pc respectively.
The soft X-ray spectrum of PG1211+143
Authors: Pounds K. A. , Page K. L. , Reeves J. N. 
Published: May 2007

AbstractThe narrow line QSO PG1211+143 has been a focus of recent attempts to understand the soft excess in AGN, while the 2001 XMM-Newton observation of this luminous AGN also provided evidence for a massive and energetic outflow. Here we consider a physical link between the energetic outflow and the variable soft excess.
Warped discs and the Unified Scheme
Authors: Lawrence Andrew 
Published: May 2007

AbstractThe standard torus picture for explaining the difference between Type I and Type II AGN is physically unlikely and provides no natural explanation for a number of simple facts - the average covering factor, the broad range of covering factors, and the characteristic reprocessing distance. Parsec scale warped discs are a strong alternative. A very simple “misaligned disc” model produces good agreement with covering factor statistics, but predicts too many off-axis emission line cones. I discuss possible ways to improve such a model.
Search for the event horizon by means of optical observations with high temporal resolution
Authors: Beskin G. , Debur V. , Karpov S. , Plokhotnichenko V. , Biryukov A. 
Published: May 2007

AbstractThe critical property of the black hole is the presence of the event horizon. It may be detected only by means of the detailed study of the emission features of its surroundings. The temporal resolution of such observations has to be better than ∼ rg/c, and it lies in the 10−6–10s range depending on the black hole mass. In SAO RAS we have developed the MANIA hardware and software complex based on the panoramic photon counter and use it in observations on 6m telescope for the search and investigation of the optical variability on the time scales of 106–103 s of various astronomical objects. We present the hardware and methods used for these photometrical, spectroscopic and polarimetrical observations, the principles and criteria of the object selection. The list of the latter includes objects with featureless optical spectra (DC white dwarfs, blazars) and long microlensing events.We present the results of the observations of two objects-candidates – long MACHO event MACHO-1999-BLG-22 and radio-loud x-ray source with featureless optical spectrum J1942+10 – on the 6-m telescope in June-July 2006.
SS433 and the nature of ultra-luminous X-ray sources
Authors: Charles P. A. , Barnes A. D. , Casares J. , Clark J. S. , Cornelisse R. , Knigge C. , Steeghs D. 
Published: May 2007

AbstractThe prototypical micro-quasar, SS433, one of the most bizarre objects in the Galaxy, is a weak X-ray source, yet the kinetic energy of its relativistic, precessing jets is vastly greater. In spite of its importance as the nearest example of directly observable relativistic phenomena, we know remarkably little about the nature of this binary system. There are ongoing arguments not only about the mass of the compact object, but even as to whether it is a black hole or a neutron star, an argument that recent high resolution optical spectroscopy has contributed to.Combined with the INTEGRAL discovery of a new class of highly obscured galactic high-mass X-ray binaries, one of which has been found to precess on a similar timescale to SS433, we suggest that these would indeed be seen by external observers as ULXs, once additional effects such as beaming (either relativistic or geometrical) are included.
The inner workings of early-type galaxies: cores, nuclei and supermassive black holes
Authors: Ferrarese Laura , Côté Patrick 
Published: May 2007

AbstractRecent years have seen dramatic progress in the study of the core and nuclear properties of galaxies. The structure of the cores has been shown to vary methodically with global and nuclear properties, as cores respond to the mechanisms by which galaxies form/evolve. The dynamical centers of galaxies have been found capable of hosting two seemingly disparate objects: supermassive black holes (SBHs) and compact stellar nuclei. In a drastic departure from previous beliefs, it has been discovered that both structures are common: galaxies lacking SBHs and/or stellar nuclei are the exception, rather than the norm. This review explores the connection between cores, SBHs and stellar nuclei in early-type galaxies, as revealed by the ACS Virgo Cluster Survey.
Radiatively inefficient accretion disks in low-luminosity AGN†
Authors: Macchetto Ferdinando D. , Chiaberge Marco 
Published: May 2007

AbstractWe study a complete and distance-limited sample of 25 LINERs, 21 of which have been imaged with the Hubble Space Telescope to study their physical properties and to compare their radio and optical properties with those of other samples of local AGNs, namely Seyfert galaxies and low-luminosity radio galaxies (LLRG). Our results show that the LINERs population is not homogeneous, as there are two subclasses: i) the first class is similar to LLRG, as it extends the population of radio-loud nuclei to lower luminosities; ii) the second is similar to Seyferts, and extends the properties of radio-quiet nuclei towards the lowest luminosities. The different nature of the various classes of local AGN are best understood when the fraction of the Eddington luminosity they irradiate, Lo/LEdd, is plotted against the nuclear radio-loudness parameter: Seyferts are associated with relatively high radiative efficiencies Lo/LEdd ≳ 104 (and high accretion rates onto low mass black holes); LLRG are associated with low radiative efficiencies (and low accretion rates onto high black hole masses); all LINERs have low radiative efficiency (and accretion rates), and can be radio-loud or radio quiet depending on their black hole mass.
A survey of AGN and supermassive black holes in the COSMOS Survey
Authors: Impey Chris D. , Trump Jon R. , McCarthy Pat J. , Elvis Martin , Huchra John P. , Scoville Nick Z. , Lilly Simon J. , Brusa Marcella , Hasinger Günther , Schinnerer Eva , Capak Peter , Gabor Jared 
Published: May 2007

AbstractThe Cosmic Evolution Survey (COSMOS) is an HST/ACS imaging survey of 2 square degrees centered on RA = 10:00:28.6, Dec = + 02:12:21 (J2000). While the primary goal of the survey is to study evolution of galaxy morphology and large scale structure, an extensive multi-wavelength data set allows for a sensitive survey of AGN. Spectroscopy of optical counterparts to faint X-ray and radio sources is being carried out with the Magallen (Baade) Telescope and the ESO VLT. By achieving ∼80 redshift completeness down to I AB = 3, the eventual yield of AGN will be ∼1100 over the whole field.Early results on supermassive black holes are described. The goals of the survey include a bolometric census of AGN down to moderate luminosities, the cosmic evolution and fueling history of the central engines, and a study of AGN environments on scales ranging from the host galaxy to clusters and superclusters.
Cosmic evolution of black holes and galaxies to z=0.4
Authors: Woo J.-H. , Treu T. , Malkan M. A. , Blanford R. D. 
Published: May 2007

AbstractWe test the evolution of the correlation between black hole mass and bulge properties, using a carefully selected sample of 20 Seyfert 1 galaxies at z=0.36 ±0.01. We estimate black hole mass from the Hβ line width and the optical luminosity at 5100 Å, based on the empirically calibrated photo-ionization method. Velocity dispersion are measured from stellar absorption lines around Mgb (5175 Å) and Fe (5270 Å) using high S/N Keck spectra, and bulge properties (luminosity and effective radius) are measured from HST images by fitting surface brightness. We find a significant offset from the local relations, in the sense that bulge sizes were smaller for given black hole masses at z=0.36 than locally. The measured offset is Δ M•=0.62 ± 0.10, 0.45 ±0.13, 0.59 ±0.19, respectively for M•–σ, M•–Lbulge, and M•–Mbulge relations. At face value, this result implies a substantial growth of bulges in the last 4 Gyr, assuming that the local M•–bulge property relation is the universal evolutionary end-point. This result is consistent with the growth of black holes predating the final growth of bulges at these mass scales (〈σ〉=170 km s−1).
Monte Carlo simulations of dusty gas discs around supermassive black holes
Authors: Baes Maarten , Piasecki Sławomir 
Published: May 2007

AbstractUsing detailed Monte Carlo radiative transfer simulations in realistic models for galactic nuclei, we critically investigate the influence of interstellar dust in ionised gas discs on the rotation curves and the resulting black hole mass measurements. We find that absorption and scattering by interstellar dust leaves the shape of the rotation curves basically unaltered, but slightly decreases the central slope of the rotation curves. As a result, the “observed” black hole masses are systematically underestimated by some 10 to 20% for realistic optical depths.
Black hole masses in type II AGNs from the Sloan Digital Sky Survey
Authors: Bian W. , Gu Q. , Zhao Y. 
Published: May 2007

AbstractThe stellar population synthesis method is used to model the stellar contribution for a sample of 209 type II AGNs at 0.3>z>0.83 from the Sloan Digital Sky Survey. The reliable stellar velocity dispersions are obtained for 33 type II AGNs with significant stellar absorption features. We use the formula of Greene & Ho to obtain the corrected stellar velocity dispersions (σ*c). 20 of which can be classified as type II quasars. The SMBHs masses and the Eddington ratios are calculated. We measure the gas velocity dispersion (σg) from NLRs, and find that the relation between σg and σ*c becomes much weaker at higher redshifts than at smaller redshifts. We find that the deviation of σg from σ*c is correlated with the Eddington ratio.
Accretion in the broad line region of active galactic nuclei
Authors: Bon E. , Popović L. Č. , Ilić D. 
Published: May 2007

AbstractWe modeled the single-peaked Broad Emission Lines (BELs) with two-component model (accretion disk, with surrounding spherical region), comparing it with observational line profiles for a number of Active Galactic Nuclei (AGN). We find that the accretion in the Broad Line Region (BLR) can be present even if the profiles of BELs are single-peaked.
Triaxial orbit-based model of NGC 4365
Authors: van den Bosch Remco C. E. , van de Ven Glenn , Cappellari Michele , de Zeeuw P. Tim 
Published: May 2007

AbstractWe have developed an orbit-based method for constructing triaxial models of elliptical galaxies, which fit their observed surface brightness and kinematics (van den Bosch et al). We have tested this extended Schwarzschild method (1979) against analytical models with general distribution functions (DF) and find that we can recover the DF (van de Ven et al). Here, we present a model of NGC 4365.
Evolution of black-hole intermediate-mass X-ray binaries
Authors: Chen Wen-Cong , Li Xiang-Dong 
Published: May 2007

AbstractWe propose a plausible mechanism for orbital angular momentum loss in black-hole intermediate-mass X-ray binaries, assuming that a small fraction of the transferred mass form a circumbinary disc. The disc can effectively drain orbital angular momentum from the binary, leading to the formation of compact black-hole low-mass X-ray binaries. This scenario also suggests the possible existence of luminous, persistent black hole low-mass X-ray binaries.
Upper limits on the mass of supermassive black holes from HST/STIS archival data
Authors: Corsini E. M. , Beifiori A. , Bontà E. Dalla , Pizzella A. , Coccato L. , Sarzi M. , Bertola F. 
Published: May 2007

AbstractThe growth of supermassive black holes (SBHs) appears to be closely linked with the formation of spheroids. There is a pressing need to acquire better statistics on SBH masses, since the existing samples are preferentially weighted toward early-type galaxies with very massive SBHs. With this motivation we started a project aimed at measuring upper limits on the mass of the SBHs in the center of all the nearby galaxies (D < 100 Mpc) for which STIS/G750M spectra are available in the HST archive. These upper limits will be derived by modeling the central emission-line widths observed in the Hα region over an aperture of ∼0.1″. Here we present our results for a subsample of 22 S0-Sb galaxies within 20 Mpc.