551 research outputs found
Providing contexts for classification of transients in a wide-area sky survey: An application of noise-induced cluster ensemble
With new sensor systems that capture sky survey at high quality level, analyzing the resulting data within a limited time frame appears to be the next challenge. Specific to the GOTO project, this task proves to be crucial to discover new transients from a pool of large candidates. Initial works based on the feature-based approach design this detection as imbalance classification, where a data-level method can be used to resolve the difference in cardinality between classes. This paper presents a context generation framework to complement the previously proposed model. In particular, samples are clustered to form data contexts to which different learning strategies may be applied. To ensure the quality of data clustering, a noise-induced cluster ensemble technique that has been recently introduced in the literature is employed here. The results with simulated data and algorithms of NB, C4.5 and KNN have shown that the proposed framework can filter out some negative samples quickly, while making classification of the rest more effective. In particular, it enhances predictive performance of basic classifiers by lifting F1 scores from less than 0.1 to around 0.3â0.5. Besides, parameter analysis is also given as a guideline for its application
Are the black hole masses in Narrow Line Seyfert 1 galaxies actually small?
Narrow Line Seyfert 1 galaxies (NLS1s) are generally considered peculiar
objects among the broad class of Type 1 active galactic nuclei, due to the
relatively small width of the broad lines, strong X-ray variability, soft X-ray
continua, weak [OIII], and strong FeII line intensities. The mass M_BH of the
central massive black hole (MBH) is claimed to be lighter than expected from
known MBH-host galaxy scaling relations, while the accretion rate onto the MBH
larger than the average value appropriate to Seyfert 1 galaxies. In this
Letter, we show that NLS1 peculiar M_BH and L/L_Edd turn out to be fairly
standard, provided that the broad line region is allowed to have a disc-like,
rather than isotropic, geometry. Assuming that NLS1s are rather ``normal''
Seyfert 1 objects seen along the disc axis, we could estimate the typical
inclination angles from the fraction of Seyfert 1 classified as NLS1s, and
compute the geometrical factor relating the observed FWHM of broad lines to the
virial mass of the MBH. We show that the geometrical factor can fully account
for the "black hole mass deficit" observed in NLS1s, and that L/L_Edd is (on
average) comparable to the value of the more common broad line Seyfert 1
galaxies.Comment: 5 pages, 3 figures. Accepted for publication in MNRAS Letters. Wrong
version was uploaded! Check for the correct one in the replacemen
Electrochemical Characterization of Self-Assembled Monolayers on Gold Substrates Derived from Thermal Decomposition of Monolayer-Protected Cluster Films
Networked films of monolayer-protected clusters (MPCs), alkanethiolate-stabilized gold nanoparticles, can be thermally decomposed to form stable gold on glass substrates that are subsequently modified with self-assembled monolayers (SAMs) for use as modified electrodes. Electrochemical assessment of these SAM-modified gold substrates, including double-layer capacitance measurements, linear sweep desorption of the alkanethiolates, and diffusional redox probing, all show that SAMs formed on gold supports formed from thermolysis of MPC films possess substantially higher defect density compared to SAMs formed on traditional evaporated gold. The density of defects in the SAMs on thermolyzed gold is directly related to the strategies used to assemble the MPC film prior to thermolysis. Specifically, gold substrates formed from thermally decomposing MPC films formed with electrostatic bridges between carboxylic acid-modified MPCs and metal ion linkers are particularly sensitive to the degree of metal exposure during the assembly process. While specific metal dependence was observed, metal concentration within the MPC precursor film was determined to be a more significant factor. Specific MPC film linking strategies and pretreatment methods that emphasized lower metal exposure resulted in gold films that supported SAMs of lower defect density. The defect density of a SAM-modified electrode is shown to be critical in certain electrochemical experiments such as protein monolayer electrochemistry of adsorbed cytochrome c. While the thermal decomposition of nanoparticle film assemblies remains a viable and interesting technique for coating both flat and irregular shaped substrates, this study provides electrochemical assessment tools and tactics for determining and controlling SAM defect density on this type of gold structure, a property critical to their effective use in subsequent electrochemical applications
Determining patterns of student graduation using a bi-level learning framework
The practice of data science, artificial intelligence (AI) in general, has expanded greatly in terms of both theoretical and application domains. Many existing and new problems have been tackled using different reasoning and learning methods. These include the research subject, generally referred to as education data mining (or EDM). Among many issues that have been studied in this EMD community, student performance and achievement provide an interesting, yet useful result to shaping effective learning style and academic consultation. Specific to this work at Mae Fah Luang University, the pattern of studentsâ graduation is determined based on their profile of performance in different categories of courses. This course-group approach is picked up to generalize the framework for various undergraduation programmes. In that, a bi-level learning method is proposed in order to predict the length of study before graduation. At the first tier, clustering is applied to derive major types of performance profiles, for which classification models can be developed to refine the prediction further. With the experiments on a real data collection, this framework usually provides accurate predictive outcomes, using several conventional classification techniques
Morphological alterations of small intestinal epithelium of calves caused by feeding soybean protein.
The objective of this experiment was to detect alterations of small intestinal mucosa due to incorporation of large amounts of soybean protein in milk replacers and to relate these alterations to calf performance
The X-Ray Star Formation Story as Told by Lyman Break Galaxies in the 4 Ms CDF-S
We present results from deep X-ray stacking of {gt}4000 high-redshift galaxies from z {ap} 1 to 8 using the 4 Ms Chandra Deep Field-South data, the deepest X-ray survey of the extragalactic sky to date. The galaxy samples were selected using the Lyman break technique based primarily on recent Hubble Space Telescope ACS and WFC3 observations. Based on such high specific star formation rates (sSFRs): log SFR/M {gt} -8.7, we expect that the observed properties of these Lyman break galaxies (LBGs) are dominated by young stellar populations. The X-ray emission in LBGs, eliminating individually detected X-ray sources (potential active galactic nucleus), is expected to be powered by X-ray binaries and hot gas. We find, for the first time, evidence of evolution in the X-ray/SFR relation. Based on X-ray stacking analyses for z {lt} 4 LBGs (covering ~{}90% of the universe's history), we find that the 2-10 keV X-ray luminosity evolves weakly with redshift (z) and SFR as log L = 0.93log (1 + z) + 0.65log SFR + 39.80. By comparing our observations with sophisticated X-ray binary population synthesis models, we interpret that the redshift evolution of L /SFR is driven by metallicity evolution in high mass X-ray binaries, likely the dominant population in these high sSFR galaxies. We also compare these models with our observations of X-ray luminosity density (total 2-10 keV luminosity per Mpc) and find excellent agreement. While there are no significant stacked detections at z {gt}~{} 5, we use our upper limits from 5 {lt}~{} z {lt}~{} 8 LBGs to constrain the supermassive black hole accretion history of the universe around the epoch of reionization
Black Holes in the Early Universe
The existence of massive black holes was postulated in the sixties, when the
first quasars were discovered. In the late nineties their reality was proven
beyond doubt, in the Milky way and a handful nearby galaxies. Since then,
enormous theoretical and observational efforts have been made to understand the
astrophysics of massive black holes. We have discovered that some of the most
massive black holes known, weighing billions of solar masses, powered luminous
quasars within the first billion years of the Universe. The first massive black
holes must therefore have formed around the time the first stars and galaxies
formed. Dynamical evidence also indicates that black holes with masses of
millions to billions of solar masses ordinarily dwell in the centers of today's
galaxies. Massive black holes populate galaxy centers today, and shone as
quasars in the past; the quiescent black holes that we detect now in nearby
bulges are the dormant remnants of this fiery past. In this review we report on
basic, but critical, questions regarding the cosmological significance of
massive black holes. What physical mechanisms lead to the formation of the
first massive black holes? How massive were the initial massive black hole
seeds? When and where did they form? How is the growth of black holes linked to
that of their host galaxy? Answers to most of these questions are work in
progress, in the spirit of these Reports on Progress in Physics.Comment: Reports on Progress in Physics, in pres
The transcriptional response of Caenorhabditis elegans to ivermectin exposure identifies novel genes involved in the response to reduced food intake
We have examined the transcriptional response of Caenorhabditis elegans following exposure to the anthelmintic drug ivermectin (IVM) using whole genome microarrays and real-time QPCR. Our original aim was to identify candidate molecules involved in IVM metabolism and/or excretion. For this reason the IVM tolerant strain, DA1316, was used to minimise transcriptomic changes related to the phenotype of drug exposure. However, unlike equivalent work with benzimidazole drugs, very few of the induced genes were members of xenobiotic metabolising enzyme families. Instead, the transcriptional response was dominated by genes associated with fat mobilization and fatty acid metabolism including catalase, esterase, and fatty acid CoA synthetase genes. This is consistent with the reduction in pharyngeal pumping, and consequential reduction in food intake, upon exposure of DA1316 worms to IVM. Genes with the highest fold change in response to IVM exposure, cyp-37B1, mtl-1 and scl-2, were comparably up-regulated in response to shortâterm food withdrawal (4 hr) independent of IVM exposure, and GFP reporter constructs confirm their expression in tissues associated with fat storage (intestine and hypodermis). These experiments have serendipitously identified novel genes involved in an early response of C. elegans to reduced food intake and may provide insight into similar processes in higher organisms
Herschel FIR counterparts of selected Ly-alpha emitters at z~2.2. Fast evolution since z~3 or missed obscured AGNs?
Ly-alpha emitters (LAEs) are seen everywhere in the redshift domain from
local to z~7. Far-infrared (FIR) counterparts of LAEs at different epochs could
provide direct clues on dust content, extinction, and spectral energy
distribution (SED) for these galaxies. We search for FIR counterparts of LAEs
that are optically detected in the GOODS-North field at redshift z~2.2 using
data from the Herschel Space Telescope with the Photodetector Array Camera and
Spectrometer (PACS). The LAE candidates were isolated via color-magnitude
diagram using the medium-band photometry from the ALHAMBRA Survey, ancillary
data on GOODS-North, and stellar population models. According to the fitting of
these spectral synthesis models and FIR/optical diagnostics, most of them seem
to be obscured galaxies whose spectra are AGN-dominated. From the analysis of
the optical data, we have observed a fraction of AGN or composite over source
total number of ~0.75 in the LAE population at z~2.2, which is marginally
consistent with the fraction previously observed at z=2.25 and even at low
redshift (0.2<z<0.45), but significantly different from the one observed at
redshift ~3, which could be compatible either with a scenario of rapid change
in the AGN fraction between the epochs involved or with a non detection of
obscured AGN in other z=2-3 LAE samples due to lack of deep FIR observations.
We found three robust FIR (PACS) counterparts at z~2.2 in GOODS-North. This
demonstrates the possibility of finding dust emission in LAEs even at higher
redshifts.Comment: 11 pages (including Appendices), 6 figures. Accepted for publication
in Astronomy & Astrophysics Letters (two references added
The Quasar Feedback Survey: characterising CO excitation in quasar host galaxies
We present a comprehensive study of the molecular gas properties of 17 Type 2
quasars at 10^{42.1}\rm ergs^{-1}_{up}r_{21}_{21}_{CO(2-1)}_{CO(1-0)}r_{21}r_{21}\sim_{21}\simr_{21} values, for the 7
targets with the required data we find low excitation in CO(6-5) & CO(7-6)
(r_{61}r_{62}$ < 0.6 in all but one target), unlike high redshift
quasars in the literature, which are far more luminous and show higher line
ratios. The ionised gas traced by [OIII] exhibit systematically higher
velocities than the molecular gas traced by CO. We conclude that any effects of
quasar feedback (e.g. via outflows and radio jets) do not have a significant
instantaneous impact on the global molecular gas content and excitation and we
suggest that it only occurs on more localised scales.Comment: 32 pages (20 in the main body of the paper and 12 in the appendix),
28 figures (10 in main body of paper and 18 in appendix) Accepted for
publication in MNRAS. Data available at
https://doi.org/10.25405/data.ncl.2431250
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