57,228 research outputs found
A simple disc wind model for broad absorption line quasars
No full textApproximately 20 per cent of quasi-stellar objects (QSOs) exhibit broad, blue-shifted absorption lines in their ultraviolet spectra. Such features provide clear evidence for significant outflows from these systems, most likely in the form of accretion disc winds. These winds may represent the ‘quasar’ mode of feedback that is often invoked in galaxy formation/evolution models, and they are also key to unification scenarios for active galactic nuclei (AGN) and QSOs. To test these ideas, we construct a simple benchmark model of an equatorial, biconical accretion disc wind in a QSO and use a Monte Carlo ionization/radiative transfer code to calculate the ultraviolet spectra as a function of viewing angle. We find that for plausible outflow parameters, sightlines looking directly into the wind cone do produce broad, blue-shifted absorption features in the transitions typically seen in broad absorption line (BAL) QSOs. However, our benchmark model is intrinsically X-ray weak in order to prevent overionization of the outflow, and the wind does not yet produce collisionally excited line emission at the level observed in non-BAL QSOs. As a first step towards addressing these shortcomings, we discuss the sensitivity of our results to changes in the assumed X-ray luminosity and mass-loss rate, Ṁwind. In the context of our adopted geometry, Ṁwind ∼ Ṁacc is required in order to produce significant BAL features. The kinetic luminosity and momentum carried by such outflows would be sufficient to provide significant feedback
The sim gene of Escherichia coli phage P1: nucleotide sequence and purification of the processed protein
Get PDFMaillou J, Dreiseikelmann B. The sim gene of Escherichia coli phage P1: nucleotide sequence and purification of the processed protein. Virology. 1990;175(2):500-507.The sim gene of bacteriophage P1 causes exclusion of a superinfecting P1 phage. We determined the nucleotide sequence of a 1.9-kb DNA fragment that, in plasmids, causes Sim phenotype. There are two open reading frames within this region for proteins of 82 and 259 amino acids. A 1.3-kb fragment containing the larger open reading frame was inserted into an expression vector. Induced cells carrying the hybrid plasmid, termed pBD5, were not infected by phage P1 and produced a 24-kDa protein and, to a smaller extent, a 25-kDa protein. The 24-kDa protein was purified. Comparison of its amino-terminal amino acid sequence with the nucleotide sequence indicated that it is processed from a precursor protein by removal of a hydrophobic leader peptide of 20 amino acids. In vivo processing depends on secA gene function and is necessary for Sim interference with P1 infection. The data are discussed with respect to the function of the sim gene in superinfection exclusion
A Quadrature RC Oscillator With Noise Reduction by Voltage Swing Control
No full textThis paper presents a low power and low noise quadrature RC oscillator based on a frequency locked loop. Voltage swing control of each of the two sub-oscillators reduces the effect of 1/f noise on the accumulated jitter. In addition, the use of quadrature phases greatly relieves timing constraints of sampling operations and helps the reduction of power consumption. With a discrete-time modeling of the quadrature oscillator, noise analysis is also provided for quantitative estimation of the circuit-driven effects on the phase noise. The proposed oscillator is fabricated using 180-nm CMOS process in an active area of 0.058mm(2). The measurement shows a period jitter of 0.047% and a standard deviation of 0.94% in untrimmed frequency (444.9kHz) in a wafer. The oscillator achieves a figure-of-merit of 155 dBc/Hz at 100 Hz offset frequency.11Nsciescopu
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
Agent-based Cloud service composition
Get PDFService composition in multi-Cloud environments
must coordinate self-interested participants, automate
service selection, (re)configure distributed services, and deal
with incomplete information about Cloud providers and
their services. This work proposes an agent-based approach
to compose services in multi-Cloud environments for different
types of Cloud services: one-time virtualized services,
e.g., processing a rendering job, persistent virtualized services,
e.g., infrastructure-as-a-service scenarios, vertical services,
e.g., integrating homogenous services, and horizontal
services, e.g., integrating heterogeneous services. Agents
are endowed with a semi-recursive contract net protocol and
service capability tables (information catalogs about Cloud
participants) to compose services based on consumer requirements.
Empirical results obtained from an agent-based
testbed show that agents in this work can: successfully compose
services to satisfy service requirements, autonomously
select services based on dynamic fees, effectively cope with
constantly changing consumers’ service needs that trigger
updates, and compose services in multiple Clouds even with
incomplete information about Cloud participants
Evolving Fuzzy Rules for Relaxed-Criteria Negotiation
Get PDFIn the literature on automated negotiation, very few negotiation agents are designed with the flexibility to slightly relax their negotiation criteria to reach a consensus more rapidly and with more certainty. Furthermore, these relaxed-criteria negotiation agents were not equipped with the ability to enhance their performance by learning and evolving their relaxed-criteria negotiation rules. The impetus of this work is designing market-driven negotiation agents (MDAs) that not only have the flexibility of relaxing bargaining criteria using fuzzy rules, but can also evolve their structures by learning new relaxed-criteria fuzzy rules to improve their negotiation outcomes as they participate in negotiations in more e-markets. To this end, an evolutionary algorithm for adapting and evolving relaxed-criteria fuzzy rules was developed. Implementing the idea in a testbed, two kinds of experiments for evaluating and comparing EvEMDAs (MDAs with relaxed-criteria rules that are evolved using the evolutionary algorithm) and EMDAs (MDAs with relaxed-criteria rules that are manually constructed) were carried out through stochastic simulations. Empirical results show that: 1) EvEMDAs generally outperformed EMDAs in different types of e-markets and 2) the negotiation outcomes of EvEMDAs generally improved as they negotiated in more e-markets
An ultrasonic scanner to probe 3-D finger skin structures for biometric recognition
No full textTo use the three-dimensional (3-D) structure of finger skin for personal identification, a 3-D ultrasonic finger skin scanner is implemented by combining a commercial 25 MHz ultrasound transducer, a three-axis motor system, an analog-to-digital converter a field-programmable gate array, a Universal Serial Bus 3.0 interface, and a PC. The scanner was successfully applied to monitoring the deep-layer pattern 1500 μm below the surface of an artificial finger module, as well as the surface fingerprint pattern, with an axial resolution of 123 μm. The Hilbert transform and 50x interpolation were performed on the received ultrasound data to enhance the axial and lateral resolutions, respectively. B-mode and C-mode imaging and a contour plot were presented for the surface fingerprint and the deep-layer pattern. © 2019 Institute of Electronics and Information Engineers. All rights reserved.11Nscopuskc
Functional characterization of the ribosome biogenesis factors PES, BOP1, and WDR12 (PeBoW), and mechanisms of defective cell growth and proliferation caused by PeBoW deficiency in Arabidopsis
No full textThe nucleolar protein pescadillo (PES) controls biogenesis of the 60S ribosomal subunit through functional interactions with Block of Proliferation 1 (BOP1) and WD Repeat Domain 12 (WDR12) in plants. In this study, we determined protein characteristics and in planta functions of BOP1 and WDR12, and characterized defects in plant cell growth and proliferation caused by a deficiency of PeBoW (PES-BOP1-WDR12) proteins. Dexamethasone-inducible RNAi of BOP1 and WDR12 caused developmental arrest and premature senescence in Arabidopsis, similar to the phenotype of PES RNAi. Both the N-terminal domain and WD40 repeats of BOP1 and WDR12 were critical for specific associations with 60S/80S ribosomes. In response to nucleolar stress or DNA damage, PeBoW proteins moved from the nucleolus to the nucleoplasm. Kinematic analyses of leaf growth revealed that depletion of PeBoW proteins led to dramatically suppressed cell proliferation, cell expansion, and epidermal pavement cell differentiation. A deficiency in PeBoW proteins resulted in reduced cyclin-dependent kinase Type A activity, causing reduced phosphorylation of histone H1 and retinoblastoma-related (RBR) protein. PeBoW silencing caused rapid transcriptional modulation of cell-cycle genes, including reduction of E2Fa and Cyclin D family genes, and induction of several KRP genes, accompanied by down-regulation of auxin-related genes and up-regulation of jasmonic acid-related genes. Taken together, these results suggest that the PeBoW proteins involved in ribosome biogenesis play a critical role in plant cell growth and survival, and their depletion leads to inhibition of cell-cycle progression, possibly modulated by phytohormone signaling. © 2016 The Author 2016. Published by Oxford University Press on behalf of the Society for Experimental Biology6
Grid Resource Negotiation: Survey and New Directions
Get PDFSince Grid computing systems involve large-scale resource sharing, resource management is central to their operations. Whereas there are more Grid resource management systems adopting auction, commodity market, and contract-net (tendering) models, this survey supplements and complements existing surveys by reviewing, comparing, and highlighting existing research initiatives on applying bargaining (negotiation) as a mechanism to Grid resource management. The contributions of this paper are: 1) discussing the motivations for considering bargaining models for Grid resource allocation; 2) discussing essential design considerations such as modeling devaluation of Grid resources, considering market dynamics, relaxing bargaining terms, and co-allocation of resources when building Grid negotiation mechanisms; 3) reviewing the strategies and protocols of state-of-the-art Grid negotiation mechanisms; 4) providing detailed comparisons and analyses on how state-of-the-art Grid negotiation mechanisms address the design considerations mentioned in 3); and 5) suggesting possible new directions
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