The non-coplanar baselines effect in radio interferometry: The W-Projection algorithm

We consider a troublesome form of non-isoplanatism in synthesis radio telescopes: non-coplanar baselines. We present a novel interpretation of the non-coplanar baselines effect as being due to differential Fresnel diffraction in the neighborhood of the array antennas. We have developed a new algorithm to deal with this effect. Our new algorithm, which we call "W-projection", has markedly superior performance compared to existing algorithms. At roughly equivalent levels of accuracy, W-projection can be up to an order of magnitude faster than the corresponding facet-based algorithms. Furthermore, the precision of result is not tightly coupled to computing time. W-projection has important consequences for the design and operation of the new generation of radio telescopes operating at centimeter and longer wavelengths.Comment: Accepted for publication in "IEEE Journal of Selected Topics in Signal Processing

Fundamentals of Chemical Vapor Deposited Graphene and Emerging Applications

Graphene, the atomically thin sheet of sp2 hybridized carbon atoms arranged in honeycomb structure, is becoming the forefront of material research. The chemical vapor deposition (CVD) process has been explored significantly to synthesis large size single crystals and uniform films of monolayer and bilayer graphene. In this prospect, the nucleation and growth mechanism of graphene on a catalytic substrate play the fundamental role on the control growth of layers and large domain. The transition metals and their alloys have been recognized as the active catalyst for growth of monolayer and bilayer graphene, where the surface composition of such catalysts also plays critical role on graphene growth. CVD-synthesized graphene has been integrated with bulk semiconductors such as Si and GaN for the fabrication of solar cells, photodetectors, and light-emitting diodes. Furthermore, CVD graphene has been integrated with hexagonal boron nitride (hBN) and transition metal dichalcogenides (TMDCs) for the fabrication of van der Waals heterostructure for nanoelectronic, optoelectronic, energy devices, and other emerging technologies. The fundamental of the graphene growth process by a CVD technique and various emerging applications in heterostructure devices is discussed in detail

Eksistensi Fungsi Dewan Perwakilan Daerah (DPD) Dalam Sistem Ketatanegaraan Indonesia Menurut Undang-Undang Dasar Negara Republik Indonesia 1945

Penelitian ini bertujuan untuk menganalisis peraturan perundang-undangan yang mengatur tentang peranan DPD dalam sistem parlemen di Indonesia pada saat ini dalam perspektif sistem bikameral efektif dan untuk menganalisis konstruksi hukum yang ideal dalam mengatur peranan DPD dalam sistem parlemen di Indonesia dalam rangka revitalisasi pemberdayaan DPD dalam sistem kelembagaan negara. Jenis penelitian yang digunakan yuridis normatif dan tipe penelitian dengan pendekatan perundang-undangan (statuteapproach), pendekatan perbandingan (comparationapproach) dan pendekatan konseptual (conceptual approach). Hasil penelitian menunjukan bahwa Peraturan perundang-undangan yang ada baik di dalam UUD NRI Tahun 1945, UU No 22 Tahun 2003 dan UU No 27 Tahun 2009 yangmengatur tentang DPD, masih kurang dari dari harapan awal pembentukanDPD. Hal ini dikarenakan Pasal-pasal yang terkait membatasi kewenangan DPD di bidang fungsi legislasi, fungsi anggaran dan fungsi pengawasan, Terjadi ketimpangan kewenangan yang berat sebelah antara DPD dan DPR, Pasal-pasal yang membatasi kewenangan DPD membuat tidakadanya suatu “double check” dan “check and balances”. Dengan adanya peraturan perundang-undangan baik di dalam UUD NRI Tahun 1945, UU Nomor 22 Tahun 2003 serta UU Nomor 27 Tahun 2009 yang mengatur tentang DPD, perlu adanya suatu konstruksi hukum dalam rangka revitalisasi peranan DPD dalam sistem parlemen di Indonesia.

Two-dimensional homography-based correction of positional errors in widefield MRT images

A steradian of the southern sky has been imaged at 151.5 MHz using the Mauritius Radio Telescope (MRT). These images show systematics in positional errors of sources when compared to source positions in the Molonglo Reference Catalogue (MRC). We have applied two-dimensional homography to correct for systematic positional errors in the image domain and thereby avoid re-processing the visibility data. Positions of bright (above 15-{\sigma}) point sources, common to MRT catalogue and MRC, are used to set up an over-determined system to solve for the homography matrix. After correction the errors are found to be within 10% of the beamwidth for these bright sources and the systematics are eliminated from the images. This technique will be of relevance to the new generation radio telescopes where, owing to huge data rates, only images after a certain integration would be recorded as opposed to raw visibilities. It is also interesting to note how our investigations cued to possible errors in the array geometry. The analysis of positional errors of sources showed that MRT images are stretched in declination by ~1 part in 1000. This translates to a compression of the baseline scale in the visibility domain. The array geometry was re-estimated using the astrometry principle. The estimates show an error of ~1 mm/m, which results in an error of about half a wavelength at 150 MHz for a 1 km north-south baseline. The estimates also indicate that the east-west arm is inclined by an angle of ~40 arcsec to the true east-west direction.Comment: 9 pages, 8 figures, accepted for publication in MNRA

On the association of G343.1-2.3 and PSR 1706-44

The association of G343.1-2.3 and PSR 1706-44 has been controversial from its first proposal. In this paper we address the difficulties, and argue that the association is still likely. New evidence comes from images of G343.1-2.3 obtained using the Australia Telescope Compact Array (ATCA), and the pulsar obtained using the CHANDRA X-ray observatory. Mosaicing was required to cover the full extent of G343.1-2.3, and we present the polarisation images from this experiment. Also an X-ray pulsar wind nebula has been found in the archived CHANDRA observations, with the correct morphology to support the association. The ATCA observations confirm the much larger extent of the SNR, which now encompasses the pulsar. The X-ray morphology points back toward the centre of the SNR, indicating the direction of the proper motion, and that the PSR and SNR are associated.Comment: 11 pages, 5 figures, submitted to MNRA

G343.1-2.3 and PSR 1706-44

The association of G343.1-2.3 and PSR 1706-44 has been controversial from its first proposal. In this paper we present new evidence from images made by with the Australia Telescope Compact Array (ATCA), MRT and Mt. Pleasant. To cover the full extent of G343.1-2.3 with ATCA mosaicing was required, and we present the polarisation images from this experiment. The ATCA observations confirms the much larger extent of the SNR, which now encompasses the pulsar

A low frequency radio telescope at Mauritius for a Southern sky survey

A new, meter-wave radio telescope has been built in the North-East of Mauritius, an island in the Indian ocean, at a latitude of -20.14 deg. The Mauritius Radio Telescope (MRT) is a Fourier Synthesis T-shaped array, consisting of a 2048 m long East-West arm and a 880 m long South arm. In the East-West arm 1024 fixed helices are arranged in 32 groups and in the South arm 16 trolleys, with four helices on each, which move on a rail are used. A 512 channel digital complex correlation receiver is used to measure the visibility function. At least 60 days of observing are required for obtaining the visibilities up to 880 m spacing. The Fourier transform of the calibrated visibilities produces a map of the area of the sky under observation with a synthesized beam width 4'X 4.6'sec(dec+20.14) at 151.5 MHz. The primary objective of the telescope is to produce a sky survey in the declination range -70 deg to -10 deg with a point source sensitivity of about 200 mJy (3-sigma level). This will be the southern sky equivalent of the Cambridge 6C survey. In this paper we describe the telescope, discuss the array design and the calibration techniques used, and present a map made using the telescope

Microwave wide band absorption by carbon from Corn cob-1

Corn cob, an agricultural waste, is paralyzed at different temperatures (700oC, 800oC and 900oC). Microwave absorption of carbon in the frequency range of 2 GHz to 8 GHz is reported. Carbon activated with 5% nickel nitrate showed more than 90% absorption of microwave in the frequency range from 6 GHz to 8 GHz, while carbon activated with 10% Nickel nitrate treated corn cob showed 90% absorption in the frequency range of 2.5 GHz to 5 GHz. Carbon showing the best absorption are characterized by XRD, Raman spectra and SEM . It is suggested that corn cob treatment alone with KOH did not improve the microwave absorption, whereas treatment along with nickel nitrate improved the absorption property much better. It is proposed that treatment with nickel nitrate helps in creating suitable pores in carbon  which improved the absorption behavior because while treating carbon with 1N HCl helps to leach out nickel creating equivalent amount of pores in the carbon