5,305 research outputs found
Development of high energy density primary batteries Fourth quarterly report, 22 Mar. - 21 Jun. 1966
High energy density primary batteries for space flight applications - electrolyte systems, cell systems, and positive electrode constructio
Near Infrared Spectroscopy of High Redshift Active Galactic Nuclei. II. Disappearing Narrow Line Regions and the Role of Accretion
We present new near infrared spectroscopic measurements for 29 luminous
high-z quasars and use the data to discuss the size and other properties of the
NLRs in those sources. The high resolution spectra have been used to carefully
model the Fe II blends and to provide reliable [O III], Fe II and Hb
measurements. We find that about 2/3 of all high luminosity sources show strong
[O III] lines while the remaining objects show no or very weak such line. While
weak [O III] emitters are also found among lower luminosity AGN, we argue that
the implications for very high luminosity objects are different. In particular,
we suggest that the averaging of these two populations in other works gave rise
to claims of a Baldwin relationship in [O III] which is not confirmed by our
data. We also argue that earlier proposed relations of the type R_NLR \propto
L_[O III]^{1/2}, where R_NLR is the NLR radius, are theoretically sound yet
they must break down for R_NLR exceeding a few kpc. This suggests that the NLR
properties in luminous sources are different from those observed in nearby AGN.
In particular, we suggest that some sources lost their very large, dynamically
unbound NLR while others are in a phase of violent star-forming events that
produce a large quantity of high density gas in the central kpc. This gas is
ionized and excited by the central radiation source and its spectroscopic
properties may be different from those observed in nearby, lower luminosity
NLRs. We also discuss the dependence of EW(Hb) and Fe II/Hb on L, M_BH, and
accretion rate for a large sample of AGNs. The strongest dependence of the two
quantities is on the accretion rate and the Fe II/Hb correlation is probably
due to the EW(Hb) dependence on accretion rate. We show the most extreme values
measured so far of Fe II/Hb and address its correlation with EW([O III]).Comment: 10 pages (emulateapj), 9 figures. Accepted by Ap
Does Every Quasar Harbor A Blazar?
Assuming there is a blazar type continuum in every radio-loud quasar, we find
that the free-free heating due to the beamed infrared continuum can greatly
enhance collisionally excited lines, and thus explain the stronger CIV
1549 line emission observed in radio loud quasars. We further predict
that the CIV line should show variability {\it not} associated with observed
continuum or Ly variability.Comment: 15 pages, 3 figures; to appear in Astrophys. J. Let
TechMiner: Extracting Technologies from Academic Publications
In recent years we have seen the emergence of a variety of scholarly datasets. Typically these capture âstandardâ scholarly entities and their connections, such as authors, affiliations, venues, publications, citations, and others. However, as the repositories grow and the technology improves, researchers are adding new entities to these repositories to develop a richer model of the scholarly domain. In this paper, we introduce TechMiner, a new approach, which combines NLP, machine learning and semantic technologies, for mining technologies from research publications and generating an OWL ontology describing their relationships with other research entities. The resulting knowledge base can support a number of tasks, such as: richer semantic search, which can exploit the technology dimension to support better retrieval of publications; richer expert search; monitoring the emergence and impact of new technologies, both within and across scientific fields; studying the scholarly dynamics associated with the emergence of new technologies; and others. TechMiner was evaluated on a manually annotated gold standard and the results indicate that it significantly outperforms alternative NLP approaches and that its semantic features improve performance significantly with respect to both recall and precision
Moving from a Product-Based Economy to a Service-Based Economy for a More Sustainable Future
Traditionally, economic growth and prosperity have been linked with the availability, production and distribution of tangible goods as well as the ability of consumers to acquire such goods. Early evidence regarding this connection dates back to Adam Smith's Wealth of Nations (1776), in which any activity not resulting in the production of a tangible good is characterized as unproductive of any value." Since then, this coupling of economic value and material production has been prevalent in both developed and developing economies throughout the world. One unintended consequence of this coupling has been the exponential increase in the amount of solid waste being generated. The reason is that any production and consumption of material goods eventually generates the equivalent amount of (or even more) waste. Exacerbating this problem is the fact that, with today's manufacturing and supply chain management technologies, it has become cheaper to dispose and replace most products rather than to repair and reuse them. This has given rise to what some call a disposable society." To put things in perspective: In 2012 households in the U.K. generated approximately 22 thousand tons of waste, which amounted to 411 kg of waste generated per person (Department for Environment, Food & Rural Affairs, 2015). During the same time period, households in the U.S. generated 251 million tons of waste, which is equivalent to a person generating approximately 2 kg of waste every day (U.S. Environmental Protection Agency, 2012). Out of these 251 million tons of total waste generated, approximately 20% of the discarded items were categorized as durable goods. The disposal of durable goods is particularly worrisome because they are typically produced using material from non- renewable resources such as iron, minerals, and petroleum-based raw materials
Proton Cyclotron Features in Thermal Spectra of Ultra-magnetized Neutron Stars
A great deal of interest has been recently raised in connection with the
possibility that soft -ray repeaters (SGRs) and anomalous X-ray pulsars
(AXPs) contain {\em magnetars}, young neutron stars endowed with magnetic
fields G. In this paper we calculate thermal spectra from
ultra-magnetized neutron stars for values of the luminosity and magnetic field
believed to be relevant to SGRs and AXPs. Emergent spectra are found to be very
close to a blackbody at the star effective temperature and exhibit a
distinctive absorption feature at the proton cyclotron energy keV. The proton cyclotron features (PCFs) are
conspicuous (equivalent width of up to many hundreds eV) and relatively broad
(). The detection of the PCFs is well within the
capabilities of present X-ray spectrometers, like the HETGS and METGS on board
Chandra. Their observation might provide decisive evidence in favor of the
existence of magnetars.Comment: 7 pages, 4 figures, minor changes included, typos corrected. Accepted
for publication in Ap
Speedy Transactions in Multicore In-Memory Databases
Silo is a new in-memory database that achieves excellent performance and scalability on modern multicore machines. Silo was designed from the ground up to use system memory and caches efficiently. For instance, it avoids all centralized contention points, including that of centralized transaction ID assignment. Silo's key contribution is a commit protocol based on optimistic concurrency control that provides serializability while avoiding all shared-memory writes for records that were only read. Though this might seem to complicate the enforcement of a serial order, correct logging and recovery is provided by linking periodically-updated epochs with the commit protocol. Silo provides the same guarantees as any serializable database without unnecessary scalability bottlenecks or much additional latency. Silo achieves almost 700,000 transactions per second on a standard TPC-C workload mix on a 32-core machine, as well as near-linear scalability. Considered per core, this is several times higher than previously reported results.Engineering and Applied Science
Markarian 421's Unusual Satellite Galaxy
We present Hubble Space Telescope (HST) imagery and photometry of the active
galaxy Markarian 421 and its companion galaxy 14 arcsec to the ENE. The HST
images indicate that the companion is a morphological spiral rather than
elliptical as previous ground--based imaging has concluded. The companion has a
bright, compact nucleus, appearing unresolved in the HST images. This is
suggestive of Seyfert activity, or possibly a highly luminous compact star
cluster. We also report the results of high dynamic range long-slit
spectroscopy with the slit placed to extend across both galaxies and nuclei. We
detect no emission lines in the companion nucleus, though there is evidence for
recent star formation. Velocities derived from a number of absorption lines
visible in both galaxies indicate that the two systems are probably tidally
bound and thus in close physical proximity. Using the measured relative
velocities, we derive a lower limit on the MKN 421 mass within the companion
orbit (R \sim 10 kpc) of 5.9 \times 10^{11} solar masses, and a mass-to-light
ratio of >= 17. Our spectroscopy also shows for the first time the presence of
H\alpha and [NII] emission lines from the nucleus of MKN 421, providing another
example of the appearance of new emission features in the previously
featureless spectrum of a classical BL Lac object. We see both broad and narrow
line emission, with a velocity dispersion of several thousand km s^{-1} evident
in the broad lines.Comment: LaTeX (aaspp4 style), 28 pages, 8 figures, to appear in AJ. Revised
text from ref. comments; new & modified figures; new photometry included;
minor corrections of typos. Color version of Fig. 1 to appear in Feb. 2000
Sky & Telescop
Nursing and community rates of Mycobacterium tuberculosis infection among students in Harare, Zimbabwe.
BACKGROUND: African hospitals have experienced major increases in admissions for tuberculosis, but they are ill-equipped to prevent institutional transmission. We compared institutional rates and community rates of tuberculin skin test (TST) conversion in Harare, Zimbabwe. METHODS: We conducted a cohort study of TST conversion 6, 12, and 18 months into training among 159 nursing and 195 polytechnic school students in Harare. Students had negative TST results (induration diameter, or =10 mm) per 100 person-years (95% confidence interval [CI], 14.2-26.2 conversions per 100 person-years), and polytechnic school students experienced 6.0 (95% CI, 3.5-10.4) conversions per 100 person-years. The rate of difference was 13.2 conversions (95% CI, 6.5-20.0) per 100 person-years. With a more stringent definition of conversion (increase in the induration diameter of > or =10 mm to at least 15 mm), which is likely to increase specificity but decrease sensitivity, conversion rates were 12.5 and 2.8 conversions per 100 person-years in nursing and polytechnic school students, respectively (rate difference, 9.7 conversions per 100 person-years; 95% CI, 4.5-14.8 conversions per 100 person-years). Nursing students reportedly nursed 20,868 inpatients with tuberculosis during 315 person-years of training. CONCLUSIONS: Both groups had high TST conversion rates, but the extremely high rates among nursing students imply high occupational exposure to Mycobacterium tuberculosis. Intense exposure to inpatients with tuberculosis was reported during training. Better prevention, surveillance, and management of institutional M. tuberculosis transmission need to be supported as part of the international response to the severe human immunodeficiency virus infection epidemic and health care worker crisis in Africa
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