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In this paper, a wideband circularly polarized corrugated G-shaped grounded ring slot antenna is presented. The proposed antenna structure is excited using a coplanar waveguide-fed monopole antenna, which is placed inside a corrugated G-shaped grounded ring. Due to the asymmetry in the ground plane, two orthogonal modes, having equal magnitude and out of phase by 90° are excited, resulting in circular polarization (CP). The generation of the CP in the proposed antenna structure is explained using thin dipole current element approximation. A prototype of the proposed antenna is fabricated and tested. The measured results exhibit a 3 dB axial ratio bandwidth of 37.6% (2.22–3.25 GHz), and reflection coefficient bandwidth (|S11| ≤ −10 dB) of 47.91% (2.13–3.47 GHz). Additionally, the design guidelines are also presented for G-shaped grounded ring slot antennas.
Glaciological ablation is computed from point-scale data at a few ablation stakes that are usually regressed as a function of elevation and averaged over the area-elevation distribution of a glacier. This method is contingent on a tight control of elevation on local ablation. However, in debris-covered glaciers, systematic and random spatial variations of debris thickness modify the ablation rates. We propose and test a method to compute sub-debris ablation where stake data are interpolated as a function of debris-thickness alone and averaged over the debris-thickness distribution at different parts of the glacier. We apply this method on Satopanth Glacier located in Central Himalaya utilising ~1000 ablation measurements obtained from a network of up to 56 stakes during 2015–2017. The estimated mean sub-debris ablation ranges between 1.5±0.2 to 1.7±0.3 cm d−1. We show that the debris-thickness-dependent regression describes the spatial variability of the sub-debris ablation better than the elevation dependent regression. The uncertainties in ablation estimates due to the corresponding uncertainties in the measurement of ablation and debris-thickness distribution, and those due to interpolation procedures are estimated using Monte Carlo methods. Possible biases due to a finite number of stakes used are also investigated.
A polarization and band reconfigurable cross-slot antenna for multiband applications is presented in this paper. The antenna consists of four p–i–n diodes embedded in the cross-shaped slot in a ground plane and excited by a microstrip feed line. The p–i–n diodes are placed in such a way that they produce multiple bands, with linearly and circularly polarized (CP) radiation. By switching the states of the p–i–n diodes, the sense of rotation of the electric field in CP radiation can be reconfigured. The proposed structure can be configured to produce two bands that radiate linearly polarized waves or three bands, where, two are linearly polarized and one is CP. The proposed design concepts are validated bythe CST studio suite as well as measurementsare carried out on fabricated prototypes.
In this paper, a compact wideband tightly-coupled dipole antenna array has been developed. Dipole elements are placed in the triangular lattice to reduce the side lobe level in the radiation pattern of one of the planes. To obtain the initial dimensions, 1-D infinite array analysis of the proposed array is carried out. The infinite array is designed to operate in 5–14.3 GHz (96.3% impedance bandwidth) frequency band. The antenna array can be used in C and X band applications. Inter-element coupling is utilized to achieve ultra-wideband performance in the proposed array. A 2 × 8 elements finite array is designed with the feed network. An ultra-wideband parallel strip to microstrip transition is used to feed the array elements. A metallic shielding for the feed network helps in reducing the back lobes. The overall size of the array with the reflector and the feed network is 148 mm × 224 mm × 54.5 mm. To validate the proposed concept, the antenna array is fabricated and tested. Impedance bandwidth of 2.8:1 along with broadside radiation pattern throughout the band of interest is observed.
Avalanching is a prominent source of accumulation on glaciers that have high and steep valley-walls surrounding their accumulation zones. These glaciers are typically characterised by an extensive supraglacial debris cover and a low accumulation area ratio. Despite an abundance of such glaciers in the rugged landscapes of the High Himalaya, attempts to quantify the net avalanche contribution to mass balance and its long-term variation are almost missing. We first discuss diagnostic criteria to identify strongly avalanche-fed glaciers. Second, we develop an approximate method to quantify the magnitude of the avalanche accumulation exploiting its expected control on the dynamics of these glaciers. The procedure is based on a simplified flowline model description of the glacier concerned and utilises the known glaciological mass-balance, velocity and surface-elevation profiles of the glacier. We apply the method to three Himalayan glaciers and show that the data on the recent dynamics of these glaciers are consistent with a dominant contribution of avalanches to the total accumulation. As a control experiment, we also simulate another Himalayan glacier where no significant avalanche contribution is expected, and reproduce the recent changes in that glacier without any additional avalanche contribution.
The propagation of intense few-cycle laser beams in plasma media is considered when the quiver velocity of the electron approaches the velocity of light c. The modifications in the spatio-temporal profile of the initial Gaussian beam are found to depend on the combined effect of relativistic plasma frequency and diffraction. The results of the variation of the temporal profile of the envelope at points on the axis as well away from the axis are presented. The results so obtained are compared with those of vacuum propagation. Pulses get broadened and frequency gets chirped as a result of diffraction, phase dispersion and relativistic mass correction. The effect of the plasma on the group velocity dispersion including curvatures of pulse and phase fronts in pulsed Gaussian beam is numerically investigated.
Hafnium oxide ultra thin films on Si (100) are being developed to replace thermally grown SiO2 gates in CMOS devices. In this work, a specially designed Attenuated Total Reflectance - Fourier Transform Infra Red Spectroscopy (ATR-FTIR) reaction cell has been developed to observe chemisorption of hafnium (IV) t-butoxide onto a Si and Ge ATR crystal heated up to 250°C and under 1 torr of vacuum to observe the initial reaction pathways and species on the substrate surface in real time and under typical process conditions. Chemisorption spectra were compared to spectra of the liquid precursor and to spectra generated by density functional theory (DFT) calculations of liquid, monodentate and bidentate absorbed precursor. An asymmetric stretching mode located at ~1017 cm-1 present in the chemisorbed spectra but not in the liquid spectra indicates that the adsorbed hafnium containing group is prevalent as a bidentate ligand according to calculations. Surface concentration of the chemisorbed species was dependant on the substrate temperature and precursor partial pressure allowing for determination of heats of adsorption which was 26.5 kJ/mol on Si.
Size dependence of the low frequency vibrational spectra of ZnO nanocrystals prepared using chemical method has been investigated. Optical transmission spectra of the ZnO colloid solution exhibit a shift in the onset of the absorption band edge from 332 to 350 nm due to particle growth. X-ray diffraction analysis of the prepared ZnO nanocrystals exhibit peaks corresponding to the hexagonal wurtzite structure. Two peaks with unusually very high intensity were observed in the low frequency (∼ 10- 25 cm-1) Raman spectra of these nanocrystals. The peak position of these phonon modes shifted towards lower frequencies as the size of the nanocrystals increases and assigned to the confinement of acoustic phonons in ZnO nanocrystals.
Hafnium oxide (HfO2) and silicon containing hafnium oxide (HfSixOy) thin films were deposited by thermal and plasma enhanced chemical vapor deposition (PECVD) using Hf (IV) t-butoxide and either O2, N2O, H2O, O2 plasma or N2O plasma as an oxygen source. Silane, 2% in He, was added to the reactant gas mixture to incorporate Si. Deposition rate and composition dependence on substrate temperature was studied and the deposited films were annealed in air for 30 min at 1100°C to observe changes in crystallinity and composition. Silicon incorporation was higher for H2O deposited HfSixOy films (5 at.%) than O2 and N2O deposited films (2 at.%) and had a lower deposition rate. Arrhenius plots reveal a non-simplistic reaction scheme since higher temperatures result in lower deposition rates due to precursor desorption. XRD indicate that as-deposited films using H2O are amorphous while O2 and N2O deposited films are microcrystalline with a monoclinic phase.
A tracheo-innominate artery fistula is an uncommon but frequently fatal complication of tracheostomy. Rarely, it can also occur in laryngectomized patients. We report a post-laryngectomy, post-radiotherapy patient using a metal tracheostomy tube, who developed a tracheo-innominate artery fistula about two months after radiotherapy. To our knowledge this is only the second reported case in a laryngectomized patient. The computed tomography (CT) angiography findings helped confirm the diagnosis and the patient was successfully managed by surgical exploration and ligation of the innominate artery. Coagulase negative Staphylococcus aureus was cultured from a tracheal swab. The clinical features, CT angiography findings, management protocols and possible aetiological factors are discussed.
A case of subglottic narrowing caused by an extranodal deposit of sinus histiocytosis in a 29-year-old man is reported. The characteristic features of Rosai-Dorfman disease, such as massive painless cervical lymphadenopathy, fever, raised erythrocyte sedimentation rate and raised white cell count, were all found to be absent. However, typical histological features, such as diffuse lymphoplasmacytic infiltrate, Russel bodies, foamy histiocytes and histiocytes with emperipoiesis, confirmed the diagnosis. Rosai-Dorfman disease is an uncommon disorder and its presentation with progressive subglottic narrowing is extremely rare. Our experience in the management of this condition is reported and the review of literature is discussed.
In this paper we report the fabrication and characterization of Ag/(Ba,Sr)TiO3 /LaNiO3/LaAlO3 capacitors. All the films, including the top (silver) and bottom (LaNiO3) electrodes, were deposited using a pulsed laser deposition technique. The electrical and dielectric properties of (Ba,Sr)TiO3 capacitors were found to improve significantly by means of silver doping. For example, the leakage current density of a Ag/Ag-doped-(Ba,Sr)TiO3 /LaNiO3/ capacitor was about an order of magnitude lower and dielectric constant was ∼40 % higher than that of a Ag/(Ba,Sr)TiO3 /LaNiO3/capacitor over a range of biases. The improvement in the electrical properties of (Ba,Sr)TiO3 films is believed to be caused by a double role of silver. The first one is associated with the reduced oxygen vacancies due to improved oxygenation of BST films in presence of silver and the second one is associated unpinning effect of domain walls again in presence of silver.
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