Nonlinear Response of HTSC Thin Film Microwave Resonators in an Applied DC Magnetic Field

The non-linear microwave surface impedance of patterned YBCO thin films, was measured using a suspended line resonator in the presence of a perpendicular DC magnetic field of magnitude comparable to that of the microwave field. Signature of the virgin state was found to be absent even for relatively low microwave power levels. The microwave loss was initially found to decrease for small applied DC field before increasing again. Also, non-linearities inherent in the sample were found to be substantially suppressed at low powers at these applied fields. These two features together can lead to significant improvement in device performance.Comment: 4 pages, LaTeX type, Uses IEEE style files, 600 dpi PostScript file with color figures available at http://sagar.physics.neu.edu/preprints.html Submitted to IEEE Transactions on Applied Superconductivit

Supplementing an AD-HOC Wireless Network Routing Protocol with Radio Frequency Identification (RFID) Tags

Wireless sensor networks (WSNs) have a broad and varied range of applications, yet all of these are limited by the resources available to the sensor nodes that make up the WSN. The most significant resource is energy. A WSN may be deployed to an inhospitable or unreachable area, leaving it with a non-replenishable power source. This research examines a way of reducing energy consumption by augmenting the nodes with radio frequency identification (RFID) tags that contain routing information. It was expected that RFID tags would reduce the network throughput, the ad hoc on-demand distance vector (AODV) routing traffic sent, and the amount of energy consumed. However, the results show that RFID tags have little effect on the network throughput or the AODV routing traffic sent. They also increase ETE delays in sparse networks as well as the amount of energy consumed in both sparse and dense networks. Furthermore, there was no statistical difference in the amount of user data throughput received. The density of the network is shown to have an effect on the variation of the data but the trends are the same for both sparse and dense networks. This counter-intuitive result is explained, and conditions for such a scheme to be effective are discussed

Comments on "Vortex Glass and Lattice Melting Transitions in a YNi_2B_2C Single Crystal"

Recently, Mun et.al. (Phys. Rev. Lett., 76, 2790 (1996)) have published their results on single crystal YNi_2B_2C, claiming that their experimental observations can be explained in terms of formation of Vortex Glass and Lattice melting. Our experiments, carried out on samples obtained from the SAME source, reveal a much richer phase diagram and span wider regions of experimental parameter space than Mun et. al. that encompasses most of their observations. We speculate that this material has anomalous intrinsic properties and the results cannot be explained by simple models about the flux lattice.Comment: 1 page, LaTeX type, 1 PostScript figure, Uses PRABIB.STY file, 600 dpi PS file available at http://sagar.physics.neu.edu/preprints.html To appear in Physical Review Letter

The Dynamic Grid: Time-Varying Parameters for Musical Instrument Simulations Based on Finite-Difference Time-Domain Schemes

Several well-established approaches to physical modeling synthesis for musical instruments exist. Finite-difference time-domain methods are known for their generality and flexibility in terms of the systems one can model but are less flexible with regard to smooth parameter variations due to their reliance on a static grid. This paper presents the dynamic grid, a method to smoothly change grid configurations of finite-difference time-domain schemes based on sub-audio–rate time variation of parameters. This allows for extensions of the behavior of physical models beyond the physically possible, broadening the range of expressive possibilities for the musician. The method is applied to the 1D wave equation, the stiff string, and 2D systems, including the 2D wave equation and thin plate. Results show that the method does not introduce noticeable artefacts when changing between grid configurations for systems, including loss.Several well-established approaches to physical modeling synthesis for musical instruments exist. Finite-difference time-domain methods are known for their generality and flexibility in terms of the systems one can model but are less flexible with regard to smooth parameter variations due to their reliance on a static grid. This paper presents the dynamic grid, a method to smoothly change grid configurations of finite-difference time-domain schemes based on sub- audio–rate time variation of parameters. This allows for extensions of the behavior of physical models beyond the physically possible, broadening the range of expressive possibilities for the musician. The method is applied to the 1D wave equation, the stiff string, and 2D systems, including the 2D wave equation and thin plate. Results show that the method does not introduce noticeable artefacts when changing between grid configurations for systems, including loss

Creativity in (Digital) Journalism Studies: Broadening our Perspective on Journalism Practice

Creativity in journalism studies includes the use of arts-based research, artistic methods, and other ways of theorising, researching, analysing and presenting data on journalism. Its purpose is to recognise and capture the many forms of journalism that are currently practiced, to develop new approaches to research (digital) journalism, and to enable the telling of the widest possible variety of stories about (digital) journalism. Creativity has a triple implication: as a concept that informs what we are looking for when studying journalism, a guide for the range of available research methods, and an inspiration for the stories we tell about our research

Critical State Flux Penetration and Linear Microwave Vortex Response in YBa_2Cu_3O_{7-x} Films

The vortex contribution to the dc field (H) dependent microwave surface impedance Z_s = R_s+iX_s of YBa_2Cu_3O_{7-x} thin films was measured using suspended patterned resonators. Z_s(H) is shown to be a direct measure of the flux density B(H) enabling a very precise test of models of flux penetration. Three regimes of field-dependent behavior were observed: (1) Initial flux penetration occurs on very low field scales H_i(4.2K) 100Oe, (2) At moderate fields the flux penetration into the virgin state is in excellent agreement with calculations based upon the field-induced Bean critical state for thin film geometry, parametrized by a field scale H_s(4.2K) J_c*d 0.5T, (3) for very high fields H >>H_s, the flux density is uniform and the measurements enable direct determination of vortex parameters such as pinning force constants \alpha_p and vortex viscosity \eta. However hysteresis loops are in disagreement with the thin film Bean model, and instead are governed by the low field scale H_i, rather than by H_s. Geometric barriers are insufficient to account for the observed results.Comment: 20 pages, LaTeX type, Uses REVTeX style files, Submitted to Physical Review B, 600 dpi PostScript file with high resolution figures available at http://sagar.physics.neu.edu/preprints.htm

Direct in situ GDD measurement in optical coating process

In the presented work a fast frequency domain measurement system to determine group delay (GD) and group delay dispersion (GDD) of optical coatings is proposed. The measurements are performed in situ directly on moving substrates during the thin film coating process. The method is based on a Michelson interferometer, which is equipped with a high power broad band light source and a fast spectrometer. Especially for the production of chirped mirrors it is advantageous to obtain group delay and group delay dispersion data of the last layers. This additional information allows for online corrections of coating errors to enhance the precision of complex interference filters for short pulse applications. © 2015 SPIE

Automated Determination of Stellar Parameters from Simulated Dispersed Images for DIVA

We have assessed how well stellar parameters (T_eff, logg and [Fe/H]) can be retrieved from low-resolution dispersed images to be obtained by the DIVA satellite. Although DIVA is primarily an all-sky astrometric mission, it will also obtain spectrophotometric information for about 13 million stars (operational limiting magnitude V ~ 13.5 mag). Constructional studies foresee a grating system yielding a dispersion of ~200nm/mm on the focal plane (first spectral order). For astrometric reasons there will be no cross dispersion which results in the overlapping of the first to third diffraction orders. The one-dimensional, position related intensity function is called a DISPI (DISPersed Intensity). We simulated DISPIS from synthetic spectra (...) for a limited range of metallicites i.e. our results are for [Fe/H] in the range -0.3 to 1 dex. We show that there is no need to deconvolve these low resolution signals in order to obtain basic stellar parameters. Using neural network methods and by including simulated data of DIVA's UV telescope, we can determine T_eff to an average accuracy of about 2% for DISPIS from stars with 2000 K < T_eff < 20000 K and visual magnitudes of V=13 mag (end of mission data). logg can be determined for all temperatures with an accuracy better than 0.25 dex for magnitudes brighter than V=12 mag. For low temperature stars with 2000 K < T_eff < 5000 K and for metallicities in the range -0.3 to +1 dex a determination of [Fe/H] is possible (to better than 0.2 dex) for these magnitudes. Additionally we examined the effects of extinction E(B-V) on DISPIS and found that it can be determined to better than 0.07 mag for magnitudes brighter than V=14 mag if the UV information is included.Comment: 12 pages, 8 figures, Accepted for publication in A&