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During 2016 February, CSIRO Astronomy and Space Science and the Max-Planck-Institute for Radio Astronomy installed, commissioned, and carried out science observations with a phased array feed receiver system on the 64-m diameter Parkes radio telescope. Here, we demonstrate that the phased array feed can be used for pulsar observations and we highlight some unique capabilities. We demonstrate that the pulse profiles obtained using the phased array feed can be calibrated and that multiple pulsars can be simultaneously observed. Significantly, we find that an intrinsic polarisation leakage of −31 dB can be achieved with a phased array feed beam offset from the centre of the field of view. We discuss the possibilities for using a phased array feed for future pulsar observations and for searching for fast radio bursts with the Parkes and Effelsberg telescopes.
Salmonella is a leading cause of bacterial foodborne illness. We report the collaborative investigative efforts of US and Canadian public health officials during the 2013–2014 international outbreak of multiple Salmonella serotype infections linked to sprouted chia seed powder. The investigation included open-ended interviews of ill persons, traceback, product testing, facility inspections, and trace forward. Ninety-four persons infected with outbreak strains from 16 states and four provinces were identified; 21% were hospitalized and none died. Fifty-four (96%) of 56 persons who consumed chia seed powder, reported 13 different brands that traced back to a single Canadian firm, distributed by four US and eight Canadian companies. Laboratory testing yielded outbreak strains from leftover and intact product. Contaminated product was recalled. Although chia seed powder is a novel outbreak vehicle, sprouted seeds are recognized as an important cause of foodborne illness; firms should follow available guidance to reduce the risk of bacterial contamination during sprouting.
We have observed 23 halo stars with space velocities and metallicities [Fe/H] ≤ −0.6. Twelve of these 23 show the more extreme properties and [Fe/H] ≤ −1.4 and should therefore constitute an especially old, homogeneous subgroup. The principal results for these 12 extreme halo stars and 5 similar stars observed in previous studies are that (1) a single, well defined relation, previously discovered and discussed by Spite and Spite, exists without exception between the atmospheric Li/H ratio and Te, and (2) at Te ≥ 5600 K the average lithium abundance is <Li/H> = 1.2 ± 0.3 × 10−10. The latter value constitutes a lower limit on the 7Li fraction produced in primordial nucleosynthesis and thereby significantly constrains the cosmic ratio of baryons to photons.
We discuss the relative gas-phase abundances found for the predominantly neutral interstellar clouds — located in the Galactic disk and halo, in the LMC or SMC, and (perhaps) in between — along the lines of sight to Sk 108 in the SMC and to SN 1987A in the LMC.
The extraordinary DIBs observed toward Herschel 36 (Dahlstrom et al. 2013) have been analyzed (Oka et al. 2013). The analysis led us to a new way to classify the carriers of DIBs depending on whether the molecules are polar or non-polar. The pronounced Extended Tails toward Red (ETR) observed for DIBs λ5780.5, λ5797.1, and λ6613.6 are explained as due to radiative excitation of high rotational levels of polar carrier molecules in an environment with high radiative temperature ~90 K. Other DIBs (e.g., λ5849.8, λ6196.0, and λ6379.3) which do not show ETR are likely due to non-polar molecules. Model calculations taking into account the interplay of radiative and collisional effects reproduce the observed ETR using realistic molecular parameters if the radiative temperature is sufficiently high (~90 K). The calculation suggests that the carriers of DIBs with ETR are likely medium size molecules with 3 - 6 heavy atoms unless the radiative temperature is much higher.
We present the first results of a dedicated search for Diffuse Interstellar Bands that have profiles with FWHM > 6 Å. Broad DIBs have been noticed in past surveys using averages of multiple sight lines (e.g. Jenniskens & Désert, 1994), but careful detection, measurement, and cataloguing for individual sight lines has not been done since the pioneering work of Herbig (1995). We have initiated an observing campaign using the Apache Point Observatory in order to obtain low-resolution spectra to search for such broad DIBs and monitor their behaviour from star to star. A first sample of 21 stars with 0.3 < E(B-V) < 3.3 mag, along with 15 matched low-reddening stars, were observed with the APO/DIS B400 (R ~ 450) and R300 (R ~ 1000) gratings to obtain spectra having S/N > 500.
Anomalously broad diffuse interstellar bands (DIBs) at 5780.5, 5797.1, 6196.0, and 6613.6 Å are found in absorption along the line of sight to Herschel 36, an O star system next to the bright Hourglass nebula of the Hii region Messier 8. Excited lines of CH and CH+ are seen as well. We show that the region is very compact and itemize other anomalies of the gas. An infrared-bright star within 400 AU is noted. The combination of these effects produces anomalous DIBs, interpreted by Oka et al. (2013, see also this volume) as being caused predominantly by infrared pumping of rotational levels of relatively small molecules.
The PULSE@Parkes project has been designed to monitor the rotation of radio pulsars over time spans of days to years. The observations are obtained using the Parkes 64-m and 12-m radio telescopes by Australian and international high school students. These students learn the basis of radio astronomy and undertake small projects with their observations. The data are fully calibrated and obtained with the state-of-the-art pulsar hardware available at Parkes. The final data sets are archived and are currently being used to carry out studies of 1) pulsar glitches, 2) timing noise, 3) pulse profile stability over long time scales and 4) the extreme nulling phenomenon. The data are also included in other projects such as gamma-ray observatory support and for the Parkes Pulsar Timing Array project. In this paper we describe the current status of the project and present the first scientific results from the Parkes 12-m radio telescope. We emphasise that this project offers a straightforward means to enthuse high school students and the general public about radio astronomy while obtaining scientifically valuable data sets.
The first direct detection of gravitational waves may be made through observations of pulsars. The principal aim of pulsar timing-array projects being carried out worldwide is to detect ultra-low frequency gravitational waves (f ∼ 10−9–10−8 Hz). Such waves are expected to be caused by coalescing supermassive binary black holes in the cores of merged galaxies. It is also possible that a detectable signal could have been produced in the inflationary era or by cosmic strings. In this paper, we review the current status of the Parkes Pulsar Timing Array project (the only such project in the Southern hemisphere) and compare the pulsar timing technique with other forms of gravitational-wave detection such as ground- and space-based interferometer systems.
The future of centimetre and metre-wave astronomy lies with the Square Kilometre Array (SKA), a telescope under development by a consortium of 17 countries that will be 50 times more sensitive than any existing radio facility. Most of the key science for the SKA will be addressed through large-area imaging of the Universe at frequencies from a few hundred MHz to a few GHz. The Australian SKA Pathfinder (ASKAP) is a technology demonstrator aimed in the mid-frequency range, and achieves instantaneous wide-area imaging through the development and deployment of phased-array feed systems on parabolic reflectors. The large field-of-view makes ASKAP an unprecedented synoptic telescope that will make substantial advances in SKA key science. ASKAP will be located at the Murchison Radio Observatory in inland Western Australia, one of the most radio-quiet locations on the Earth and one of two sites selected by the international community as a potential location for the SKA. In this paper, we outline an ambitious science program for ASKAP, examining key science such as understanding the evolution, formation and population of galaxies including our own, understanding the magnetic Universe, revealing the transient radio sky and searching for gravitational waves.
A ‘pulsar timing array’ (PTA), in which observations of a large sample of pulsars spread across the celestial sphere are combined, allows investigation of ‘global’ phenomena such as a background of gravitational waves or instabilities in atomic timescales that produce correlated timing residuals in the pulsars of the array. The Parkes Pulsar Timing Array (PPTA) is an implementation of the PTA concept based on observations with the Parkes 64-m radio telescope. A sample of 20 ms pulsars is being observed at three radio-frequency bands, 50 cm (~700 MHz), 20 cm (~1400 MHz), and 10 cm (~3100 MHz), with observations at intervals of two to three weeks. Regular observations commenced in early 2005. This paper describes the systems used for the PPTA observations and data processing, including calibration and timing analysis. The strategy behind the choice of pulsars, observing parameters, and analysis methods is discussed. Results are presented for PPTA data in the three bands taken between 2005 March and 2011 March. For 10 of the 20 pulsars, rms timing residuals are less than 1 μs for the best band after fitting for pulse frequency and its first time derivative. Significant ‘red’ timing noise is detected in about half of the sample. We discuss the implications of these results on future projects including the International Pulsar Timing Array and a PTA based on the Square Kilometre Array. We also present an ‘extended PPTA’ data set that combines PPTA data with earlier Parkes timing data for these pulsars.
The Parkes pulsar data archive currently provides access to 144044 data files obtained from observations carried out at the Parkes observatory since the year 1991. Around 105 files are from surveys of the sky, the remainder are observations of 775 individual pulsars and their corresponding calibration signals. Survey observations are included from the Parkes 70 cm and the Swinburne Intermediate Latitude surveys. Individual pulsar observations are included from young pulsar timing projects, the Parkes Pulsar Timing Array and from the PULSE@Parkes outreach program. The data files and access methods are compatible with Virtual Observatory protocols. This paper describes the data currently stored in the archive and presents ways in which these data can be searched and downloaded.
Psychotic-like experiences (PLEs) in the general population are common, particularly in childhood, and may constitute part of a spectrum of normative development. Nevertheless, these experiences confer increased risk for later psychotic disorder, and are associated with poorer health and quality of life.
This study used factor analytic methods to determine the latent structure underlying PLEs, problem behaviours and personal competencies in the general child population, and used item response theory (IRT) to assess the psychometric properties of nine PLE items to determine which items best represented a latent psychotic-like construct (PSY). A total of 7966 children aged 9–11 years, constituting 95% of eligible children, completed self-report questionnaires.
Almost two-thirds of the children endorsed at least one PLE item. Structural analyses identified a unidimensional construct representing psychotic-like severity in the population, the full range of which was well sampled by the nine items. This construct was discriminable from (though correlated with) latent dimensions representing internalizing and externalizing problems. Items assessing visual and auditory hallucination-like experiences provided the most information about PSY; delusion-like experiences identified children at more severe levels of the construct.
Assessing PLEs during middle childhood is feasible and supplements information concerning internalizing and externalizing problems presented by children. The hallucination-like experiences constitute appropriate items to screen the population to identify children who may require further clinical assessment or monitoring. Longitudinal follow-up of the children is required to determine sensitivity and specificity of the PLE items for later psychotic illness.
Current high permittivity material deposition techniques produce a low permittivity oxide interfacial layer consequently increasing the equivalent oxide thickness. This interfacial oxide layer can be prevented by initially growing a thin nitride layer to act as a diffusion barrier. The interfacial nitride layer must also have low interface state densities comparable to state-of-the-art SiO2 insulators in order to be suitable for MOSFETs. The nitride layer used in this study was formed by thermal nitridation in a UHV system, with the subsequent high permittivity deposition done in an adjoining system. After forming capacitors from these films, capacitance vs. voltage (C-V) techniques were used to determine the interface state density and equivalent oxide thickness of the films. Gate stack films were produced on Si(100) and Si(111) and the results are compared. Gate stacks on Si(100) show a slight increase in stretchout in the high frequency C-V curves for both n-type and p-type samples. Initial data suggests that Si(111) has a lower interface state density than the Si(100) gate stacks. This may be attributed to the Si3N4layer on Si(111) being epitaxial nitride.
In this paper, we have reported an attempt to decrease equivalent oxide thickness (EOT) of TiO2gate insulator by thinning the amorphous layer formed at the TiO2/Si interface. We have decreased the thickness of the TiO2/Si interfacial layer to as little as 1.6 nm by suppressing the oxygen flow rate during the TiO2 sputtering. It was confirmed that the dielectric constant of the interfacial layer revealed higher value than that of SiO2, depending on the sputtering condition. Titanium in the interfacial layer, which was responsible for the polarization enhancement, was explicitly identified by high spatial resolution TEM-EELS. As a result, EOT of 1.3 nm was realized by TiO2/Ti-Si-O stacked gate insulator without any degradation in the electrical characteristics.
Tungsten silicide (WSix) films, deposited by chemical vapour deposition are normally amorphous in nature, and need to be annealed at high temperature to obtain low resistivity required for interconnections and metallization layers in VLSI circuits. In this paper, we focus on this annealing process for films deposited on Si and SiO2 substrate, and having Si/W ratio of 2.4. The characterization methods used were time-resolved X-ray diffraction, Resistivity measurement, and Rutherford backscattering spectroscopy analysis. We observe that 30 minutes is not sufficient for complete transformation of the WSi2.4 films on Si substrate. We also report on the dependence of annealing behaviour of nonstoichiometric WSixfilm on the substrate type.
Laser annealed arsenic implanted silicon specimens with doses ranging from 6×1015 to 7×1016 As/cm 2 have been investigated by transmission electron microscopy (TEM) and double crystal xray diffractometry (DCD). For the highest implant dose, laser powers ranging from 1.1 to 2.2 J/cm 2 have been used. Experimental observations show two new features for this kind of specimen. First, in some cases, TEM micrographs evidence small (˜50Å diameter) precipitate-like defects and/or dislocation loops confined within the heavily doped region. Second, in some cases, DCD shows a positive strain in addition to the negative strain attributed to 90% As in substitutional sites. X-ray rocking-curve simulations reveal that the negative strain drops to zero around 1000Å before the end of the As distribution. This might be related to the presence of Si interstitials in the deepest region of the As distribution.
Modern methods of sample preparation have made it possible to analyze complete, packaged integrated circuits by transmission electron microscopy. TEM has two unique capabilities that cannot be matched by other characterization methods: 1) it is a direct crystallographic probe and 2) it has excellent spatial resolution, 0.2 nm. Small personal computers can be used to translate the micrographic data into statistical information that can be analyzed by non-TEM trained engineers. The data can also be stored in a MICROSTRUCTURAL DATABANK. The experimental data is automatically compared by the computer with previously established criteria. This methodology generates additional information that is used for quality and reliability assurance testing of integrated circuits. The method is applicable to devices that are removed from electronic systems after field operation, as well as to devices that have been lifetime tested. Two examples are described and discussed: aluminum grain size distribution analysis and silicide layer thickness measurement.
Convergent-beam diffraction in the transmission electron microscope is a powerful technique for the characterization of crystalline materials. Examples are presented to show the way in which convergent-beam zone-axis patterns can be used to determine: the unit cell; the symmetry; the strain of a crystal. The patterns are also recognizable and so can be used, like fingerprints, to identify phases.