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In our attempt to investigate the basic active galactic nucleus (AGN) paradigm requiring a centrally located supermassive black hole (SMBH), a close to Keplerian accretion disk and a jet perpendicular to its plane, we have searched for radio continuum in galaxies with H2O megamasers in their disks. We observed 18 such galaxies with the Very Large Baseline Array in C band (5 GHz, ~2 mas resolution) and we detected 5 galaxies at 8 σ or higher levels. For those sources for which the maser data is available, the positions of masers and those of the 5 GHz radio continuum sources coincide within the uncertainties, and the radio continuum is perpendicular to the maser disk’s orientation within the position angle uncertainties.
Fossiliferous Ediacaran successions of South China, the Doushantuo and Dengying formations and their equivalents, are key to understanding bio- and geological evolution at the Neoproterozoic–Cambrian transition. However, their absolute ages, especially the upper Ediacaran successions, are poorly constrained. SIMS zircon U–Pb dating results in this study suggest that ash beds at the basal and middle parts of the Jiucheng Member (middle Dengying Formation) in eastern Yunnan Province were deposited at 553.6 ± 2.7/(3.8) Ma and 546.3 ± 2.7/(3.8) Ma, respectively. These new dates indicate that the age for the base of Dengying Formation in eastern Yunnan Province is similar to the 550.55 ± 0.75 Ma date, which is from an ash bed at the top of the Miaohe Member and has been regarded as the age for the base of Dengying Formation in Yangtze Gorges area. These dates do not permit a clear test of the two correlation models for the chronostratigraphic position of the Miaohe Member (uppermost Doushantuo Formation vs. middle Dengying Formation), implying that further integrated intra-basinal stratigraphic correlations and more high-resolution chronological data from the upper Ediacaran deposits of South China are required. New dates of the Jiucheng Member constrain the age of the fossil biotas in the middle Dengying Formation and extend the stratigraphic range of Rangea, Hiemalora and Charniodiscus to 546.3 ± 2.7/(3.8) Ma. The geochronology of the Dengying Formation implies that Ediacaran-type fossils preserved in this formation are younger than the White Sea Assemblage and temporally overlapping with the Nama Assemblage.
We made dynamical black hole mass measurements from nineteen Seyfert 2 galaxies which host sub-parsec H2O maser disks using the H2O megamaser technique. The nearly perfect Keplerian rotation curves in many of these maser systems guarantee the high accuracy and precision of the black hole mass measurements. With the stellar velocity dispersion (σ∗) of the galaxy bulges measured with the Dupont 2.5 m telescope at Las Campanas Observatory in the South and the Apache Point Observatory (APO) 3.5m telescope in the North, we found that H2O maser galaxies, most of which host pseudo bulges rather than classical bulges, do not all follow the MBH–σ∗ relation shown in the literature. This result is well consistent with the latest findings by Kormendy & Ho (2013) that only early type galaxies and galaxies with classical bulges follow a tight MBH–σ∗ relation. Such a tight correlation may not exist in pseudo bulge galaxies.
This review addresses Creutzfeldt–Jakob disease in the context of ENT, and aims to summarise the relevant history, pathophysiology and implications for contemporary practice.
Creutzfeldt–Jakob disease is a rare, fatal, neurodegenerative disorder. It is a prion disease with four different subtypes that can only be definitively diagnosed post-mortem. The main implications for the ENT surgeon lie in the risk of iatrogenic transmission. The three facets of assessing individual patient risk are: patient history; tissue infectivity; and procedure infectivity.
This is a controversial area in medicine, and ENT in particular. This review highlights a clinically applicable approach for everyday use.
I have combined data from sky surveys in the UV to the mid-IR, along with radio and X-ray data, to identify the most luminous QSOs in the Universe. The primary sky surveys were the Sloan Digital Sky Survey (SDSS) 7th Data Release QSO Catalog, which provides unambiguous broad-line QSO classification and robust redshifts, and the Wide-field Infrared Survey Explorer (WISE) mid-IR catalog, because a large percentage of QSO bolometric luminous emerges in the IR. Out of the 100,000 SDSS/WISE QSOs, we find 140 (< 0.2%) with bolometric luminosity greater than 2×1014Lo, with redshifts ranging from about 1.7 to 5. The most luminous QSO found has Lbol ≈7×1014Lo. Merger-based galaxy evolution models predict that the host galaxies of such sources at peak QSO luminosity are undergoing a short-lived phase of extreme AGN feedback and massive star-formation activity after a major merger. Upcoming sub-mm observations with the new Atacama Large Millimeter/Sub-millimeter Array (ALMA), for a subset of the sample, will soon reveal crucial host galaxy properties of this unique sample.
Zircons from a bentonite near the base of the Purley Shale Formation in the Nuneaton area, Warwickshire, yield a 206Pb/238U age of 517.22 ± 0.31 Ma. Based on the fauna of small shelly fossils and the brachiopod Micromitra phillipsii in the underlying Home Farm Member of the Hartshill Sandstone Formation, trilobite fragments that are questionably referred to Callavia from the basal Purley Shale Formation, and the presence of trilobites diagnostic of the sabulosa Biozone 66 m above the base of the Purley Shale Formation, the bentonite likely dates an horizon within Cambrian Stage 3, at about the level of the Fallotaspis or basal Callavia Biozone. This is consistent with bentonite ages from other localities in southern Britain, which constrain the age of the lower and uppermost parts of Cambrian Stage 3. The new date provides additional chronological control on the earliest occurrence of trilobites in the Midland Microcraton, a date for the marine transgression at the base of the Purley Shale Formation, and is the first radiometric age from the Cambrian succession of Warwickshire.
In the lead-up to the Square Kilometre Array (SKA) project, several next-generation radio telescopes and upgrades are already being built around the world. These include APERTIF (The Netherlands), ASKAP (Australia), e-MERLIN (UK), VLA (USA), e-EVN (based in Europe), LOFAR (The Netherlands), MeerKAT (South Africa), and the Murchison Widefield Array. Each of these new instruments has different strengths, and coordination of surveys between them can help maximise the science from each of them. A radio continuum survey is being planned on each of them with the primary science objective of understanding the formation and evolution of galaxies over cosmic time, and the cosmological parameters and large-scale structures which drive it. In pursuit of this objective, the different teams are developing a variety of new techniques, and refining existing ones. To achieve these exciting scientific goals, many technical challenges must be addressed by the survey instruments. Given the limited resources of the global radio-astronomical community, it is essential that we pool our skills and knowledge. We do not have sufficient resources to enjoy the luxury of re-inventing wheels. We face significant challenges in calibration, imaging, source extraction and measurement, classification and cross-identification, redshift determination, stacking, and data-intensive research. As these instruments extend the observational parameters, we will face further unexpected challenges in calibration, imaging, and interpretation. If we are to realise the full scientific potential of these expensive instruments, it is essential that we devote enough resources and careful study to understanding the instrumental effects and how they will affect the data. We have established an SKA Radio Continuum Survey working group, whose prime role is to maximise science from these instruments by ensuring we share resources and expertise across the projects. Here we describe these projects, their science goals, and the technical challenges which are being addressed to maximise the science return.
EMU is a wide-field radio continuum survey planned for the new Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The primary goal of EMU is to make a deep (rms ∼ 10 μJy/beam) radio continuum survey of the entire Southern sky at 1.3 GHz, extending as far North as +30° declination, with a resolution of 10 arcsec. EMU is expected to detect and catalogue about 70 million galaxies, including typical star-forming galaxies up to z ∼ 1, powerful starbursts to even greater redshifts, and active galactic nuclei to the edge of the visible Universe. It will undoubtedly discover new classes of object. This paper defines the science goals and parameters of the survey, and describes the development of techniques necessary to maximise the science return from EMU.
Water vapor megamasers from the center of active galaxies provide a powerful tool to trace accretion disks at sub-parsec resolution and, through an entirely geometrical method, measure direct distances to galaxies up to 200 Mpc. The Megamaser Cosmology Project (MCP) is formed by a team of astronomers with the aim of identifying new maser systems, and mapping their emission at high angular resolution to determine their distance. Two types of observations are necessary to measure a distance: single-dish monitoring to measure the acceleration of gas in the disk, and sensitive VLBI imaging to measure the angular size of the disk, measure the rotation curve, and model radial displacement of the maser feature. The ultimate goal of the MCP is to make a precise measurement of H0 by measuring such distances to at least 10 maser galaxies in the Hubble flow. We present here the preliminary results from a new maser system, Mrk 1419. Through a model of the rotation from the systemic masers assuming a narrow ring, and combining these results with the acceleration measurement from the Green Bank Telescope, we determine a distance to Mrk 1419 of 81 ± 10 Mpc. Given that the disk shows a significant warp that may not be entirely traced by our current observations, more sensitive observations and more sophisticated disk modeling will be essential to improve our distance estimation to this galaxy.
The Hubble constant H0 describes not only the expansion of local space at redshift z ~ 0, but is also a fundamental parameter determining the evolution of the universe. Recent measurements of H0 anchored on Cepheid observations have reached a precision of several percent. However, this problem is so important that confirmation from several methods is needed to better constrain H0 and, with it, dark energy and the curvature of space. A particularly direct method involves the determination of distances to local galaxies far enough to be part of the Hubble flow through water vapor (H2O) masers orbiting nuclear supermassive black holes. The goal of this article is to describe the relevance of H0 with respect to fundamental cosmological questions and to summarize recent progress of the ‘Megamaser Cosmology Project’ (MCP) related to the Hubble constant.
Assessments of infectious disease spread in hospitals seldom account for interfacility patient sharing. This is particularly important for pathogens with prolonged incubation periods or carrier states.
We quantified patient sharing among all 32 hospitals in Orange County (OC), California, using hospital discharge data. Same-day transfers between hospitals were considered “direct” transfers, and events in which patients were shared between hospitals after an intervening stay at home or elsewhere were considered “indirect” patient-sharing events. We assessed the frequency of readmissions to another OC hospital within various time points from discharge and examined interhospital sharing of patients with Clostridium difficile infection.
In 2005, OC hospitals had 319,918 admissions. Twenty-nine percent of patients were admitted at least twice, with a median interval between discharge and readmission of 53 days. Of the patients with 2 or more admissions, 75% were admitted to more than 1 hospital. Ninety-four percent of interhospital patient sharing occurred indirectly. When we used 10 shared patients as a measure of potential interhospital exposure, 6 (19%) of 32 hospitals “exposed” more than 50% of all OC hospitals within 6 months, and 17 (53%) exposed more than 50% within 12 months. Hospitals shared 1 or more patient with a median of 28 other hospitals. When we evaluated patients with C. difficile infection, 25% were readmitted within 12 weeks; 41% were readmitted to different hospitals, and less than 30% of these readmissions were direct transfers.
In a large metropolitan county, interhospital patient sharing was a potential avenue for transmission of infectious agents. Indirect sharing with an intervening stay at home or elsewhere composed the bulk of potential exposures and occurred unbeknownst to hospitals.
Relations between Europe and Mexico have been dramatic ever since Hernán Cortez conquered the Aztec empire and established New Spain in the early sixteenth century. Along with many other Latin American countries, Mexico gained its independence from Spain in 1810 in a war of independence, after almost three centuries of Mexican gold and silver financing Spanish wars in Europe. Half a century later, Napoleon installed Maximilian von Hapsburg and his wife, Carlotta, as Emperor and Empress of Mexico in a dispute over debts owed to France. The Mexicans later shot Maximilian by firing squad in Querétero, while Carlotta went mad and died a ward of the Vatican (only to be resurrected decades later by Bette Davis in the black-and-white Hollywood movie, Juárez).
Trade liberalization and foreign investment were welcomed for three decades under Mexican dictator, Porfirio Díaz. That cycle of economic opening ended with the Mexican Revolution in 1910. The twentieth century witnessed the nationalization of the oil industry under President Lázaro Cárdenas in 1938 and of the banking industry under President José López Portillo in 1982, before swinging back to trade liberalization and a reopening to foreign investment under President Carlos Salinas de Gortari in the 1990s. On 1 July 2000, the new century marked the entry into force of the Mexico–European Union Free Trade Agreement (MEUFTA or Global Agreement), the most comprehensive trade agreement between Europe and Mexico since the Spanish conquistadores first established transatlantic trade relations almost half a millennium earlier.
An observational study was carried out, using data collected from four areas in the Irish midlands, between 1989 and 2004, to critically evaluate the long-term effects of proactive badger culling and to provide insights into reactive badger culling tuberculosis (TB) prevalence in cattle. Confirmed cattle herd TB incidence is the outcome measure used throughout. Relative to reactive culling, proactive badger culling was associated with a decrease in incidence in each of the 16 years of observation, which encompassed periods of both intensive and less-intensive badger removal. By 2004, we observed a decrease of 22% [95% confidence interval (CI) 15–29, P<0·001] in the entire proactive and 37% (95% CI 25–47, P<0·001), in the inner proactive removal areas. The size of the decrease increased with time (P=0·055). There was a decrease (constant over time) of at least 14% (95% CI 76–97, P=0·013) in incidence in the inner compared to the outer control area (herds ⩽2 km, >2 km, from proactive removal area boundaries, respectively). Incidence in the outer proactive removal area (herds <1·6 km from the proactive removal boundary) was similar to the inner control area (P=0·890). Incidence in the outer control area and total control area, compared to a neighbouring area some distance away, increased over the course of the study. Differences with the total control area were not statistically significant but the outer control area was 11% higher than the neighbouring area by 2004 (borderline significance P=0·057).
Physiological research has shown that measurements on small plots of stomatal conductance, canopy temperature depression (CTD) or carbon isotope discrimination may be useful for screening breeding populations for yield potential, prior to the execution of expensive replicated yield trials. Such indirect selection criteria may be very effective as lower cost alternatives for estimating genetic gain for complex characteristics such as yield that are relatively expensive to measure accurately in the field. In the present paper, economic analysis is undertaken of the results of trials conducted at the International Maize and Wheat Improvement Center (CIMMYT) over three seasons to determine the value of the physiological traits being assessed. The results indicate that the economic value of incorporating these measurements into CIMMYT's breeding programme is potentially important. CTD and stomatal conductance are relatively cheap to measure and could be used to discard lines prior to extensive yield testing, whereas carbon isotope discrimination is relatively expensive and would not be economic for this purpose. The analysis indicates that the incorporation of physiological measurements is likely to provide important economic benefits to the programme. Indications are that other breeding programmes with similar breeding goals and comparable costing structures might also consider using such indirect selection traits.
A determination of the Hubble Constant (H0) to better than 3% would be the best complement to cosmic microwave background (CMB) data to constrain the equation of state of Dark Energy. Water vapor megamasers provide perhaps the best opportunity for measuring direct distances to galaxies out to about 200 Mpc. We have formed a team of astronomers in the Megamaser Cosmology Project to pursue the ambitious goal of making a precise measurement of H0 by measuring such distances using the techniques pioneered on the disk maser in NGC 4258 by Herrnstein et al (1999). In recent surveys we have made significant progress identifying new maser systems analogous to that in NGC 4258, but more distant. Once the appropriate candidates are identified, two types of observations are necessary to ultimately measure a distance: single-dish monitoring to measure the acceleration of gas in the disk, and sensitive VLBI imaging in order to measure the angular size of the disk, measure the rotation curve, and model radial displacement of the systemic maser features. We have recently obtained preliminary VLBI maps of the masers in two systems, NGC 6323 and UGC 3789. The maser disks in both galaxies were discovered and monitored with the Green Bank Telescope (GBT) and subsequently imaged with the High Sensitivity Array (VLBA + GBT + Effelsberg). In this contribution we present a map of the maser distribution in one of those systems, NGC 6323. The map demonstrates that pc-scale maser disks as distant as ~ 100 Mpc can be imaged with existing telescopes. Results on UGC 3789 will be presented in a later publication.
We present an atlas of extragalactic water vapor masers. As of 2007, one hundred galaxies have been detected as sources of water vapor maser emission, two thirds of them discovered since 2003. Extragalactic water masers fall in at least three categories: those associated with nuclear jets or winds, those in starbursts or star-forming regions, and those in AGN accretion disks. While all maser systems offer the possibility of unique investigations into their physical environments, it is the disk masers that have been most aggressively sought because of their potential for use as precision distance indicators. Type 2 Seyfert and LINER galaxies are hosts to such disk masers. Insingle-dish spectra, disk masers are often revealed by the presence of high-velocity emission features (defined roughly by having anomalous velocities in excess of 200 km s−1). About one third of the extragalactic water masers detected to date show evidence of disk origin. Only a few galaxies are currently identified as jet-type or star-forming type. The remaining systems show only a few narrow doppler components, usually near the systemic velocity, and are difficult to categorize. These unclassified systems are detected toward AGNs and are also possibly associated with disks or winds near the nucleus. Detection rates in large maser surveys are typically 5% or less, but the observing efficiency and sensitivity of the Green Bank Telescope (GBT) allow for short integration times (typically 10 minutes to detect a narrow 30 mJy line) so many galaxies can be searched. Recently, GBT surveys targeting type 2 Seyfert galaxies identified by the SDSS have been the most productive, identifying 17 systems in surveys observed during 2006.
High-precision geochronological techniques have improved in the past decade to the point where volcanic ash beds interstratified with fossil-bearing rocks can be dated to a precision of 0.1% or better. The integration of high-precision U-Pb zircon geochronology with bio/chemo-stratigraphic data brings about new opportunities and challenges toward constructing a fully calibrated time scale for the geologic record, which is necessary for a thorough understanding of the distribution of time and life in Earth history. Successful implementation of geochronology as an integral tool for the paleontologist relies on a basic knowledge of its technical aspects, as well as an ability to properly evaluate and compare geochronologic results from different methods. This paper summarizes the methodology and new improvements in U-Pb zircon geochronology by isotope dilution thermal ionization mass spectrometry, specifically focused on its application to the stratigraphic record.
Far-infrared (FIR), ultraviolet (UV), and soft X-ray observations are easily degraded by dust and gas between the source and the telescope. They must be made from space, where they are still affected by the interstellar medium (ISM) of our Galaxy. Fortunately the ISM is quite patchy, with several “cosmic windows” covering ∼ 100 deg2 of sky having exceptionally low interstellar extinction and cirrus emission. Since the universe is nearly isotropic, these windows contain representative samples of cosmologically distant sources and will be the targets of deep multiwavelength studies including SWIRE, GALEX/DIS, and XMM-LSS. Overlapping optical and radio surveys provide essential source identifications, redshifts, morphologies, and continuum spectra. The prototype VLA survey (see http://www.cv.nrao.edu/sirtf_fls/) covers the 5 deg2 SIRTF First-Look Survey (FLS) and is being used to identify the expected FIR sources in advance. Most will be star-forming galaxies obeying the very tight far-infrared/radio correlation and thus continuum radio sources stronger than S ≈ 100 μJy at 1.4 GHz. Proposed VLA surveys covering the remaining “cosmic windows” will be useful for studying the evolution of obscured AGNs, clusters, and other uncommon objects.
Nearly all discrete radio sources are extragalactic and lie at
cosmological distances. Most sources stronger than ~1 mJy at
1.4 GHz are powered by active galactic nuclei (AGNs), while the
majority of fainter sources are in starburst galaxies. Recent all-sky
surveys have detected most of this AGN population, and smaller surveys
are now sensitive enough to probe the evolution of star formation in
selected areas. Sensitive new radio surveys will complement
far-infrared, ultraviolet, and X-ray surveys now being made in “cosmic
windows” having exptionally low interstellar extinction. They will
help define the evolution of star-formation and dust-shrouded AGNs
over cosmological timescales.
The primary goal of radio source surveys is to generate flux-limited samples. Sources selected at very low frequencies are dominated by unbeamed emission and give the only unbiased view of the parent populations used by “unification” models to account for the diversity of sources seen at high frequencies. Low-frequency surveys favor sources with exceptionally steep spectra. They include radio galaxies at high redshifts, radio halos of nearby galaxies, relic radio sources, diffuse cluster emission, pulsars that may be missed by traditional pulse searches, and a new class of unidentified compact sources. Flux densities from low-frequency surveys extend the spectra of known source populations to frequencies at which free-free and synchrotron absorption become significant and constrain basic source parameters. Finally, telescope fields-of-view scale ∝ λ2, so gridded surveys can be more efficient than directed observations of individual targets. This review covers recent and proposed low-frequency source surveys and their astronomical uses.