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The streamwise inclination angle of large wall-attached structures, in the log region of a canonical turbulent boundary layer, is estimated via spectral coherence analysis, and is found to be approximately
. This is consistent with assumptions used in prior attached eddy model-based simulations. Given that the inclination angle obtained via standard two-point correlations is influenced by the range of scales in the turbulent flow (Marusic, Phys. Fluids, vol. 13 (3), 2001, pp. 735–743), the present result is obtained by isolating the large wall-attached structures from the rest of the turbulence. This is achieved by introducing a spanwise offset between two hot-wire probes, synchronously measuring the streamwise velocity at a near-wall and log-region reference location, to assess the wall coherence. The methodology is shown to be effective by applying it to data sets across Reynolds numbers,
Sorghum (Sorghum bicolor (L.) Moench) is an important resource to the national economy and it is essential to assess the genetic diversity in existing sorghum germplasm for better conservation, utilization and crop improvement. The aim of this study was to evaluate the level of genetic diversity within and among sorghum germplasms collected from diverse institutes in Nigeria and Mali using Single Nucleotide Polymorphic markers. Genetic diversity among the germplasm was low with an average polymorphism information content value of 0.24. Analysis of Molecular Variation revealed 6% variation among germplasm and 94% within germplasms. Dendrogram revealed three groups of clustering which indicate variations within the germplasms. Private alleles identified in the sorghum accessions from National Center for Genetic Resources and Biotechnology, Ibadan, Nigeria and International Crop Research Institute for the Semi-Arid Tropics, Kano, Nigeria shows their prospect for sorghum improvement and discovery of new agronomic traits. The presence of private alleles and genetic variation within the germplasms indicates that the accessions are valuable resources for future breeding programs.
The difference in the defect structures produced by different ion masses in a tungsten lattice is investigated using 80 MeV Au7+ ions and 10 MeV B3+ ions. The details of the defects produced by ions in recrystallized tungsten foil samples are studied using transmission electron microscopy. Dislocations of type b = 1/2 and  were observed in the analysis. While highly energetic gold ion produced small clusters of defects with very few dislocation lines, boron has produced large and sparse clusters with numerous dislocation lines. The difference in the defect structures could be due to the difference in separation between primary knock-on atoms produced by gold and boron ions.
We observed single pulses from PSR J0034-0721 (B0031-07) simultaneously at the MWA (185 MHz) and the GMRT (610 MHz). Correlation analyses reveal that the phase difference of the average profiles at the two frequencies differs from the phase difference observed between individual subpulses, indicating that the individual emission columns above the pulsar’s rotating carousel of sparks do not evolve in frequency in the same way that the global magnetosphere does. This hints at a possible departure from the dipolar field geometry in this pulsar’s emission region. Moreover, the discrepancy depends on the drift mode, suggestive of a way to constrain the emission heights associated with each drift mode.
Polarization of radiation in the UBVRI spectral bands of the stars in the vicinity of four Bok Globules/dark clouds is observed with 1.5 and 1m telescopes. Moderate to high degree of polarization and alignment of polarization vectors indicate the possibility of frozen magnetic fields. Other possibilities for retarding the cloud collapse have also been pointed out.
Polarization measurement of the background stars in the region of dark globules is important to study the magnetic field geometry and grants characteristics in the globule. These parameters are important for the formation and evolution of dark globules. We made Polarimetric observations of stars in three nearby dark clouds - B5, L134 and Heiles Cloud 2. Polarization measurements of stars in the region of B5 were made with ‘MINIPOL’ (Frecker and Serkowski, 1976) on 61″ telescope of University of Arizona. Observations for the stars in the region of L134 and Heiles Cloud 2 were made using PRL Polarimeter (Deshpande et al. 1985) on 1 meter telescope of Indian Institute of Astrophysics, Bangalore. Results are presented and discussed here. Figure 1 shows the polarization vectors projected on the sky plane for the above globules.
We have measured 14C, 210Pb and 137Cs profiles in two representative cores from Manasbal Lake, Kashmir, India. The sedimentation rate derived from 210Pb and 137Cs in the upper part of the core is in the range of 3.4 to 5.5 mm yr−1. In contrast, 14C ages show an inversion at depths >20 cm. These results are attributed to the erosion of the ubiquitous 10–20-m-thick loess mantle, based on the similarity of 14C ages of the inversion layer in the sediments and the paleosols present in the catchment area. Frequency-dependent mineral magnetic susceptibility (χfd), carbon to nitrogen ratios and pigment concentrations in the profile show a significant amount of allochthonous component in the lake deposits and support the conclusion that the 14C dates do not reflect the chronology of the in-situ lake sedimentation but episodic deposition of the surrounding loess. Thus, 14C serves as a useful tracer to understand source components of the sediments.
Sedimentological, mineral magnetic and carbon isotopic studies on cores from Mansar Lake in the Jammu area provide paleomonsoonal history dating back to 580 bc. From ca. 580 bc to ad 300, the region experienced precipitation similar to the present, whereas from ad 300 to 1400, the monsoon was relatively subdued. A small excursion ca. ad 1100 suggests an effect of medieval warming. Studies in the Kumaon region did not provide a proper precipitation record, as anthropogenic activity interfered with sedimentation. Manasbal Lake in Kashmir gave an inversion of 14C chronology due to younger paleosols in the drainage basin. Further, the episodic nature of sedimentation in Manasbal Lake hampered the reconstruction of precipitation history in the area.
We have compiled a catalogue of H ii regions detected with the Murchison Widefield Array between 72 and 231 MHz. The multiple frequency bands provided by the Murchison Widefield Array allow us identify the characteristic spectrum generated by the thermal Bremsstrahlung process in H ii regions. We detect 306 H ii regions between 260° < l < 340° and report on the positions, sizes, peak, integrated flux density, and spectral indices of these H ii regions. By identifying the point at which H ii regions transition from the optically thin to thick regime, we derive the physical properties including the electron density, ionised gas mass, and ionising photon flux, towards 61 H ii regions. This catalogue of H ii regions represents the most extensive and uniform low frequency survey of H ii regions in the Galaxy to date.
Interplanetary Scintillation (IPS) is a diffraction phenomenon in which coherent electro-magnetic radiation, from a distant radio source, passes through the solar wind, which is a turbulent refracting medium, and suffers scattering. This results in random temporal variations of the signal intensity (scintillation) at the Earth. IPS observations to monitor the interplanetary medium (IPM), to measure solar wind velocities in the directions of a number of compact extra-galactic radio sources and to estimate the angular diameters of their compact components have been carried out for many years at 103 MHz using the IPS facility (Alurkar et al. 1989) of the Physical Research Laboratory (PRL), Ahmedabad, India. Over a period of approximately 10 years of such observations, it has been seen that PSR 0950+08 has always remained well within the noise level. We observed a sudden enhancement in its flux (Deshpande et al. 1994) on 29 July, 1992. The ionospheric observations which are being carried out on a regular basis at PRL using an ionosonde also recorded a steep increase in the absorption index Fmin, which is an indicator of the excess ionization produced due to X-rays. During this period, the Sun was exceptionally quiet, thereby raising the question about the origin of the X-ray flux responsible for the observed steep rise in Fmin during the transit of PSR 0950+08.
“Solar X-ray Spectrometer (SOXS)” mission on-board GSAT-2 Indian spacecraft was launched on 08 May 2003 by GSLV-D2 and deployed in geostationery orbit to study the X-ray emission from solar flares with high spectral and temporal resolution. The SOXS consists of two independent payloads viz. SOXS Low Energy Detector (SLD) payload, and SOXS High Energy Detector (SHD) payload. The SLD consists of two solid state detectors Si PIN and CZT, which cover the energy range from 4-60 keV, while the SHD has NaI(Tl)/CsI(Na) sandwiched phoswich detector that covers energy range from 20 keV to 10 MeV. We present very briefly the science objectives and instrumentation of SLD payload. After the successful In-orbit Tests (IOT), the first light was fed into SLD payload on 08 June 2003 when the solar flare was already in progress. We briefly present the first results from the SLD payload.
We compare first-order (refractive) ionospheric effects seen by the MWA with the ionosphere as inferred from GPS data. The first-order ionosphere manifests itself as a bulk position shift of the observed sources across an MWA field of view. These effects can be computed from global ionosphere maps provided by GPS analysis centres, namely the CODE. However, for precision radio astronomy applications, data from local GPS networks needs to be incorporated into ionospheric modelling. For GPS observations, the ionospheric parameters are biased by GPS receiver instrument delays, among other effects, also known as receiver DCBs. The receiver DCBs need to be estimated for any non-CODE GPS station used for ionosphere modelling. In this work, single GPS station-based ionospheric modelling is performed at a time resolution of 10 min. Also the receiver DCBs are estimated for selected Geoscience Australia GPS receivers, located at Murchison Radio Observatory, Yarragadee, Mount Magnet and Wiluna. The ionospheric gradients estimated from GPS are compared with that inferred from MWA. The ionospheric gradients at all the GPS stations show a correlation with the gradients observed with the MWA. The ionosphere estimates obtained using GPS measurements show promise in terms of providing calibration information for the MWA.
GLEAM, the GaLactic and Extragalactic All-sky MWA survey, is a survey of the entire radio sky south of declination + 25° at frequencies between 72 and 231 MHz, made with the MWA using a drift scan method that makes efficient use of the MWA’s very large field-of-view. We present the observation details, imaging strategies, and theoretical sensitivity for GLEAM. The survey ran for two years, the first year using 40-kHz frequency resolution and 0.5-s time resolution; the second year using 10-kHz frequency resolution and 2 s time resolution. The resulting image resolution and sensitivity depends on observing frequency, sky pointing, and image weighting scheme. At 154 MHz, the image resolution is approximately 2.5 × 2.2/cos (δ + 26.7°) arcmin with sensitivity to structures up to ~ 10° in angular size. We provide tables to calculate the expected thermal noise for GLEAM mosaics depending on pointing and frequency and discuss limitations to achieving theoretical noise in Stokes I images. We discuss challenges, and their solutions, that arise for GLEAM including ionospheric effects on source positions and linearly polarised emission, and the instrumental polarisation effects inherent to the MWA’s primary beam.
The Murchison Widefield Array is a Square Kilometre Array Precursor. The telescope is located at the Murchison Radio–astronomy Observatory in Western Australia. The MWA consists of 4 096 dipoles arranged into 128 dual polarisation aperture arrays forming a connected element interferometer that cross-correlates signals from all 256 inputs. A hybrid approach to the correlation task is employed, with some processing stages being performed by bespoke hardware, based on Field Programmable Gate Arrays, and others by Graphics Processing Units housed in general purpose rack mounted servers. The correlation capability required is approximately 8 tera floating point operations per second. The MWA has commenced operations and the correlator is generating 8.3 TB day−1 of correlation products, that are subsequently transferred 700 km from the MRO to Perth (WA) in real-time for storage and offline processing. In this paper, we outline the correlator design, signal path, and processing elements and present the data format for the internal and external interfaces.
The Murchison Widefield Array is a new low-frequency interferometric radio telescope built in Western Australia at one of the locations of the future Square Kilometre Array. We describe the automated radio-frequency interference detection strategy implemented for the Murchison Widefield Array, which is based on the aoflagger platform, and present 72–231 MHz radio-frequency interference statistics from 10 observing nights. Radio-frequency interference detection removes 1.1% of the data. Radio-frequency interference from digital TV is observed 3% of the time due to occasional ionospheric or atmospheric propagation. After radio-frequency interference detection and excision, almost all data can be calibrated and imaged without further radio-frequency interference mitigation efforts, including observations within the FM and digital TV bands. The results are compared to a previously published Low-Frequency Array radio-frequency interference survey. The remote location of the Murchison Widefield Array results in a substantially cleaner radio-frequency interference environment compared to Low-Frequency Array’s radio environment, but adequate detection of radio-frequency interference is still required before data can be analysed. We include specific recommendations designed to make the Square Kilometre Array more robust to radio-frequency interference, including: the availability of sufficient computing power for radio-frequency interference detection; accounting for radio-frequency interference in the receiver design; a smooth band-pass response; and the capability of radio-frequency interference detection at high time and frequency resolution (second and kHz-scale respectively).
Cryptosporidium parvum (C. parvum) is one of the most prevalent protozoan pathogens responsible for inducing human and animal disease worldwide. In this study, the glycoprotein-60 (gp60) subtyping tool was employed to assess the molecular diversity of C. parvum from human feces throughout Scotland during potential outbreaks. Over a 24-month period, microscopy analysis revealed 1139 positive feces containing Cryptosporidium species with 256 identified by molecular methods specifically as C. parvum. Cryptosporidium parvum was shown to be more prevalent in rural areas of Scotland and subtyping of 87 isolates demonstrated the predominant family as IIa, which occurred in 94% (n = 82) of isolates. The IIaA15G1R1 subtype was most common, being isolated from 47% (n = 41) of Scottish human cases. Non-IIa strains constituted a total of 5 isolates and included subtypes from the IIc, IId and IIg families. This information contributes significantly to existing knowledge and understanding of C. parvum subtypes in Scotland which is vital in assisting with the management of future local and national outbreaks.
The Murchison Widefield Array (MWA) is one of three Square Kilometre Array Precursor telescopes and is located at the Murchison Radio-astronomy Observatory in the Murchison Shire of the mid-west of Western Australia, a location chosen for its extremely low levels of radio frequency interference. The MWA operates at low radio frequencies, 80–300 MHz, with a processed bandwidth of 30.72 MHz for both linear polarisations, and consists of 128 aperture arrays (known as tiles) distributed over a ~3-km diameter area. Novel hybrid hardware/software correlation and a real-time imaging and calibration systems comprise the MWA signal processing backend. In this paper, the as-built MWA is described both at a system and sub-system level, the expected performance of the array is presented, and the science goals of the instrument are summarised.
Human genomic structural variation (SV) is significant factor in genome complexity, and thus has substantial implications to the cause, development and progression of genetic diseases. These SVs, ranging in size of 1kbp-1Mbp, are challenging to assess with current technologies. As such, we have developed a commercial system (nanoAnalyzer® 1000) for the rapid linear analysis of genomes at single-molecule level.
The core of our system is a nanofluidic chip consisting of an array of channels with a diameter less than 100 nm, nanofabricated on the surface of a silicon substrate. Thousands of unamplified genomic DNA molecules of 100’s kbps to several Mbps can be isolated and linearly streamed into the array for analysis in a parallel fashion. Fluorescently labeled sequence-specific signatures can then be identified and aligned to reference patterns at high resolution with custom software. This automated, multi-color imaging platform will enable a wide range of applications, such as accurate sequencing assembly, discovering genome structural variations, and uncovering epigenomic content. Nanochannel arrays promise to substantially lower the barriers of entry for single-molecule DNA analysis for scientists and clinicians, greatly impacting the advancement of molecular diagnostics, personalized medicine, and biomedical research.
This paper reports on some of the recent advances in the development and testing of molecular-scale electronic devices, devices that may ultimately be the basis of a molecular-based computer. These advances include: the synthesis of molecules which will perform specific electronic functions, self-assembled monolayer formation of rigid-rod conjugated oligomers, novel methodologies for the design and testing of molecular electronic devices, and the observance of negative differential resistance (NDR) through a molecule.