Resonant frequencies of whispering gallery modes of dielectric resonator

The modal spectrum of the whispering gallery modes of dielectric resonator depends mainly on its physical dimensions, dielectric constant, and to a lesser extent, on the environment. This paper carries investigation of the resonant frequencies in dielectric disc utilising the ring resonator model. Results of the structural design parameters are used to generate a nume!ical expression for describing the operational frequencies useful for computer-aided design applications. Theoretical and experimental results are given for resonators of various sizes

Dielectric relaxation studies of acetonitrile/propylene glycol and their binary mixtures

Dielectric relaxation spectra in the frequency range 0.02 < ν/GHz < 20 have been collected for propylene glycol (PG), acetonitrile (AN) and their binary mixtures between 303 K-323 K. The average relaxation times have been calculated by the Cole-Davidson and Cole-Cole relaxation models. The experimental determined values of static dielectric permittivity (ε0), relaxation time (τ), excess permittivity (εE) and excess inverse relaxation time (1/τ)E show smooth temperature dependence. The larger relaxation time values of propylene glycol when compared to acetonitrile are due to the co-operative process of multimers with O-H-O linkage and also the steric hindrance behavior phenomena. The activation entropy (ΔS*), activation enthalpy (ΔH*), Kirkwood correlation factor (gf), Helmholtz energy (ΔFE) parameters have also been determined for propylene glycol and acetonitrile and the results have been correlated

Microwave Hall mobility and electrical properties of electrospun polymer nanofibers

10.1063/1.3556456Journal of Applied Physics1097-JAPI

Pyroelectric Ferroelectric and Resistivity Studies on Samarium Modified Barium Strontium Sodium Niobate Ceramics

Barium Strontium Sodium Niobate (Ba1-xSrx)2NaNb5O15 (BSNN) belongs to tungsten bronze ferroelectric morphotrophic phase boundary (MPB) system at x = 0.6, having large spontaneous polarisation, pyroelectric coefficient and low dielectic constant and is expected to be applicable for piezoceramic filter and pyroelectic devices. Present communication illustrates preparative conditions and the influence of Sm2O3 on structure, ferroelectric, dielectric, pyroelectric and resistivity properties at and around MPB. Substitution of Sm2O3 decreased the cell volume and Curie temperature and enhance the room temperature dielectric constant. The pyroelectric coefficient at room temperature has been observed to be in the order of 10-9 C/cm2 0C. The figure of merits FMRV, FMRN and FMRIhave been observed to be higher values of the order 10-14 CM/J, 10-12 CM/J, 10-11 CM/J, respectively on both pure and Sm: BSNN compositions. Resistivity studies indicated a PTCR response in the compositions. (Botswana Journal of Technology: 2003 12(2): 1-7

Indigenous Rain Forecasting in Andhra Pradesh

Not AvailableNot AvailableICAR-CRID

Primary leptomeningeal primitive neuroectodermal tumor: A difficult entity to diagnose

A 25-year-old male presented with difficulty in walking, loss of vision, and seizures. A clinical possibility of craniospinal meningeal pathology was considered. On computed tomography (CT) scan and magnetic resonance imaging, there was an enhancement of leptomeninges with few ring-enhancing lesions in both frontal lobes and right frontoparietal region. He was evaluated for low backache and occipital headache 2½ years earlier and was found to have communicating hydrocephalus on CT scan. He underwent ventriculoperitoneal shunt and was followed up with CT scans. Meningeal biopsy was done in the present admission, and there was a diffusely infiltrating small round cell tumor. Immunohistochemistry was done, and the tumor cells were found to be negative for glial, mesenchymal, melanotic, and lymphoid markers. The cells were positive for neuron-specific enolase, chromogranin, and vimentin. A diagnosis of primitive neuroectodermal tumor involving the meninges was made. A possibility of primary leptomeningeal tumor extending to parenchyma was considered based on the clinical progression. Patient was treated with chemotherapy and radiotherapy. He improved partially and was stable at 3-year follow-up

Long range B-site cation ordering and Briet–Wigner–Fano line shape of A_1g-like Raman mode in Nd_1−xSm_xMg_0.5Ti_0.5O₃ microwave dielectric ceramics

Nd1−xSmxMg0.5Ti0.5O3 (x = 0.0–1.0) samples were prepared by solid-state reaction method. Rietveld refinement of X-ray diffraction data was done using P2 1/n space group with monoclinic symmetry, which supports 1:1 B-site cation ordering. Long Range Ordering (LRO) parameter decreased up to x = 0.5 and then found to increase with further increase in Sm concentration. The A1g-like mode in Raman spectra was observed to possess Briet–Wigner–Fano line shape. The variation in obtained line width of the A1g-like mode supported LRO. Microwave dielectric characteristics such as dielectric constant (εr), quality factor (Q) and temperature coefficient of resonant frequency (τf) were measured in the range of 7–9 GHz. εr decreased from 26.5 to 24.9 and τf become less negative from −58 ppm/°C to −36 ppm/°C with increase in Sm concentration. Q × f decreased from 47,500 GHz (for x = 0) to 39,800 GHz (for x = 0.5) and then increased to 44,600 GHz (for x = 1)