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Crab Pulsar (PSR B0531+21) is known to emit pulsed emission in all bands of the electromagnetic spectrum. It also emits giant radio pulses (GRPs) frequently, which are roughly a hundred to million times brighter than the normal pulses. We aim to study whether there is a significant X-ray enhancement correlated with the occurrence of GRPs, using simultaneous observations with the ASTROSAT, the Giant Meterwave Radio telescope (1300 MHz) and the Ooty Radio telescope (325 MHz). This required determination of fixed pipeline offsets between different instruments. We find the offset between ASTROSAT and GMRT to be −30.181 ± 0.095 ms and that between ASTROSAT and ORT to be −18.4 ± 0.2 ms. Our preliminary results with 1300 MHz data also show a break in pulse intensity distribution at ~ 33 Jy in the main pulse and ~ 28 Jy in the inter-pulse.
Monitoring the glacier mass balance of summer-accumulation-type Himalayan glaciers is critical to not only assess the impact of climate change on the volume of such glaciers but also predict the downstream water availability and the global sea-level change in future. To better understand the change in meteorological parameters related to glacier mass balance and runoff in a glacierized basin and to assess the highly heterogeneous glacier responses to climate change in the Nepal Himalaya and nearby ranges, the Cryosphere Monitoring Project (CMP) carries out meteorological observations in Langtang Valley and mass-balance measurements on Yala Glacier, a debris-free glacier in the same valley. A negative annual mass balance of –0.89m w.e. and the rising equilibrium-line altitude of Yala Glacier indicate a continuation of a secular trend toward more negative mass balances. Lower temperature lapse rate during the monsoon, the effect of convective precipitation associated with mesoscale thermal circulation in the local precipitation and the occurrence of distinct diurnal cycles of temperature and precipitation at different stations in the valley are other conclusions of this comprehensive scientific study initiated by CMP which aims to yield multi-year glaciological, hydrological and meteorological observations in the glacierized Langtang River basin.
Deriving glacier outlines from satellite data has become increasingly popular in the past decade. In particular when glacier outlines are used as a base for change assessment, it is important to know how accurate they are. Calculating the accuracy correctly is challenging, as appropriate reference data (e.g. from higher-resolution sensors) are seldom available. Moreover, after the required manual correction of the raw outlines (e.g. for debris cover), such a comparison would only reveal the accuracy of the analyst rather than of the algorithm applied. Here we compare outlines for clean and debris-covered glaciers, as derived from single and multiple digitizing by different or the same analysts on very high- (1 m) and medium-resolution (30 m) remote-sensing data, against each other and to glacier outlines derived from automated classification of Landsat Thematic Mapper data. Results show a high variability in the interpretation of debris-covered glacier parts, largely independent of the spatial resolution (area differences were up to 30%), and an overall good agreement for clean ice with sufficient contrast to the surrounding terrain (differences ∼5%). The differences of the automatically derived outlines from a reference value are as small as the standard deviation of the manual digitizations from several analysts. Based on these results, we conclude that automated mapping of clean ice is preferable to manual digitization and recommend using the latter method only for required corrections of incorrectly mapped glacier parts (e.g. debris cover, shadow).
Giant pulses (GPs), occasional individual pulses with an intensity 100 times the average intensity, have been detected in four pulsars to date. Their origin is not well understood, but studies suggest a connection between the strength of magnetic field at the light cylinder Blc and the existence of GPs. Here, we report on detection of significant Large Amplitude Pulses (LAPs) in two more pulsars with high values of Blc, PSRs J0218+4232 and B1957+20, observed using Giant Meterwave Radio Telescope (GMRT).
High sensitivity data were obtained on PSR B0031-07 using Ooty Radio Telescope (ORT), which has a single polarization. As this pulsar lies outside the range of other sensitive instruments, such observations are possible only with ORT. Some earlier results, such as the different drift modes, were verified. Our analysis suggests competition between the energies of pairs of drifting sub-pulses and a phase memory across short nulls. The constraints these results put on the theories of pulse emission are enumerated.
A regional, multistate investigation into a June–August 2013 cyclosporiasis outbreak was conducted in Nebraska, Iowa, and neighbouring states. Cases were confirmed on the basis of laboratory and clinical findings. Of 227 cases in Iowa (n = 140) and Nebraska (n = 87) residents, 162 (71%) reported dining at chain A/B restaurants – 96% reported house salad consumption. A case-control study identified chain A/B house salad as the most likely vehicle. Traceback was conducted to ascertain production lot codes of bagged salad mix (iceberg and romaine lettuce, red cabbage, and carrots) served as house salad in implicated restaurants. A single production lot code of salad mix supplied by both a common producer and distributor was linked to the majority of confirmed cases in persons reporting regional chain A/B exposure. The salad mix linked to illnesses contained imported romaine lettuce from two separate single-grower fields-of-origin and ⩾1 additional field from another grower.
We report here on the first dedicated simultaneous imaging and pulsar observations towards the supernova remnant (SNR) G15.4+0.1, the possible counterpart of the very high energy (VHE) source HESS J1818–154. The observations were carried out using the Giant Metrewave Radio Telescope (GMRT) at 610 and 1400 MHz. Preliminary analysis of data suggests absence of pulsations towards the centroid of HESS J1818–154, with upper limits of 0.6 and 0.3 mJy at 610 and 1400 MHz, respectively. Analysis of data with a larger beam is in progress, which may confirm the presence of a putative pulsar and its wind nebula if it is offset from the centroid of HESS J1818–154.
Observation of pulsar glitches remains a powerful tool for studying the interior of neutron stars. Many of the observed glitch properties are shown to result from the evolution of glitches in the different manifestations of neutron stars. Specifically, the type of glitches associated with the Crab and Vela pulsars are explained by this model. We are, also, able to adequately account for the absence, or very low rate, of glitches among the youngest and the very old pulsars.
The generation of 1–5 MeV protons from the interaction of a 3 ps TW CO2 laser pulse with a gas target with a peak density around the critical plasma density has been studied by 2D particle-in-cell simulations. The proton acceleration in the preformed plasma with a symmetric, linearly ramped density distribution occurs via formation of sheath of the hot electrons on the back surface of the target. The maximum energy of the hot electrons and, hence, net acceleration of protons is mainly defined by Forward Raman scattering instability in the underdense part of the plasma. Forward directed ion beams from a debris free gaseous target can find an application as a high-brightness ion source-injector to a conventional accelerator operating up to kHz pulse repetition frequency.
The dielectric constant of a material is strongly dependent on both the polarizability and the density of the material through the Clausius Mossotti equation. While the atomic polarizability depends on the stoichiometry of the constituent atoms, the molecular polarizability is a function of the atoms’ short range bonding structure and hence can be strongly dependent on processing conditions. Since the density of the material also depends on the thermally activated diffusivity of atoms during processing, varying the processing temperatures has an effect on both the molecular polarizability and the density. The dielectric constant of Zr0.2Sn0.2Ti0.6O2 is shown to be a strong function of the substrate temperature during sputter deposition with the highest value ∼55 at 200 °C and lower values at both higher and lower process temperatures. We have investigated the bonding structure and density of the oxide dielectric deposited at a variety of substrate temperatures in order to elucidate the relative effects of each.
This paper gives physical and chemical properties of some Canadian fly ashes. Specific surface area, magnetic fraction, water soluble fraction and fraction finer than 45 μm were determined as part of the physical tests. Thermo-gravimetric analyses (TGA) in oxygen and nitrogen were conducted on raw ash samples. The change of pH with time in suspensions of the different ashes in water was also determined. Pozzolanic activity of the ashes with lime for all the ashes was evaluated to measure ash reactivity.
The ash activity seems to be related to fineness of the ash measured by the Blaine air permeability method, but not to the fineness measured by nitrogen sorption. Generally the greater the specific surface area, the higher the reactivity of the ash. The correlation was, however, not strong and no other physical or chemical parameter measured in this investigation seems to be related to pozzolanic activity.
The results of pH and TGA tests indicated that the ashes differ in many respects from each other. The TGA data suggest that loss on-ignition in many of the ashes is not entirely due to the presence of unburned carbon. Specific surface area determined by various methods seems to provide different values. No characterization parameter was found that was uniquely related to coal type.
Pore structures of portland and blended cement mortars prepared with sea water were assessed by mercury intrusion porosimetry. Comparison is made with similar mortars made with fresh water. Mortars were made using cement containing 0%, 25% or 50% (by volume) of one of two Alberta fly ashes. They were tested after 90 days of continuous immersion in sea water at 5°C or 20° C. Results show that the mortars made with sea water generally contained a much higher volume of fine pores although the porosity was, in some cases, greater than that of mortars made with fresh water. Nevertheless, the volume of larger pores was lower in the mortars made with sea water. The pore structure of the various mortars is discussed in relation to potential durability.
In this paper, a detailed reliability investigation is presented for ultra-thin tunneling (∼50 Å) oxides grown in N2O ambient using rapid thermal processing (RTP). These N2Oss-oxides are compared with oxides of identical thickness grown in O2 ambient by RTP. The reliability investigations include time-dependent dielectric breakdown as well as stress-induced leakage current in MOS capacitors with these gate dielectrics. Results show that ultra-thin N2O-oxides show much improved reliability as compared to oxide grown in O2 ambient.
Thin films of layered-structure solid-solution material, (1−x)SrBi2Ta2O9−xBi3Ti(TayNb1−y)O9, have shown much improved ferroelectric properties compared to SrBi2Ta2O9, a leading candidate material for ferroelectric random access memory applications. The higher Pr, higher Tc, and lower crystallization temperature of the thin films of solid solution material promise to solve many problems with the present materials of interest. The films were fabricated by metalorganic solution deposition technique using room temperature processed alkoxide-carboxylate precursor solution and characterized in terms of structural, dielectric, and ferroelectric properties. It was possible to obtain a pyrochlore free crystalline phase at an annealing temperature of 600 °C. The effects of annealing temperature and excess Bi content on the film microstructure and properties were analyzed. The electrical measurements were conducted on metal-ferroelectric-metal (MFM) capacitors using Pt as the top and bottom electrode. It was possible to obtain good ferroelectric properties on films annealed at 650 °C. For example, thin films with 0.7SrBi2Ta2O9-0.3Bi3TiTaO9 composition, which were annealed at 650 °C, exhibited typical 2Pr and Ec values of 12.4 μC/cm2 and 80 kV/cm, respectively. The films exhibited low leakage current density, good fatigue characteristics under bipolar stressing at least up to 1010 switching cycles, and good memory retention characteristics after about 106 s of memory retention indicating a favorable behavior for memory applications.
This research investigates the potential of pulsed laser deposition to create reliable high current ohmic contacts of Ni2Si on single crystal 4H-SiC. Since this stoichiometry is the stable interphase in the nickel-silicon carbide diffusion couple, direct deposition eliminates the detrimental excess carbon normally formed by direct sintering Ni on SiC, the surface roughening that results from this sintering as well as the need for post-deposition high-temperature (900°C) anneals that are required in complex multi-component contacts. This study examines the processing parameters that must be used during deposition to obtain the desired microstructural characteristics for the contact. Pulsed laser deposition of nickel silicide produces smooth films with an amorphous or nanocrystalline structure interspersed with macroparticles. Macroparticle formation on the resulting films appear in the form of solidified droplets of the eutectic composition nickel silicide (3:1) that form during the long term target processing. The dependence of the number and size distributions of these droplets on laser fluence sample temperature is examined.