Broad band antennas and feed methods

DOE Office of Scientific and Technical Information (OSTI.GOV)

Benzel, David M.; Twogood, Richard E.

Two or more Vivaldi antennas, consisting of two plates each, each with the antenna's natural impedance of approximately 100 ohms, are placed in parallel to achieve a 50 ohm impedance in the case of two antennas or other impedances (100/n ohms) for more than two antennas. A single Vivaldi antenna plate (half Vivaldi antenna) over a ground plane can also be used to achieve a 50 ohm impedance, or two or more single plates over a ground plane to achieve other impedances. Unbalanced 50 ohm transmission lines, e.g. coaxial cables, can be used to directly feed, the dual Vivaldi (fourmore » plate) antenna in a center fed angled center departure, or more desirably, a center fed offset departure configuration.« less

Dielectric monitoring of carbon nanotube network formation in curing thermosetting nanocomposites

NASA Astrophysics Data System (ADS)

Battisti, A.; Skordos, A. A.; Partridge, I. K.

2009-08-01

This paper focuses on monitoring of carbon nanotube (CNT) network development during the cure of unsaturated polyester nanocomposites by means of electrical impedance spectroscopy. A phenomenological model of the dielectric response is developed using equivalent circuit analysis. The model comprises two parallel RC elements connected in series, each of them giving rise to a semicircular arc in impedance complex plane plots. An established inverse modelling methodology is utilized for the estimation of the parameters of the corresponding equivalent circuit. This allows a quantification of the evolution of two separate processes corresponding to the two parallel RC elements. The high frequency process, which is attributed to CNT aggregates, shows a monotonic decrease in characteristic time during the cure. In contrast, the low frequency process, which corresponds to inter-aggregate phenomena, shows a more complex behaviour explained by the interplay between conductive network development and the cross-linking of the polymer.

Impedance and electric modulus approaches to investigate four origins of giant dielectric constant in CaCu3Ti4O12 ceramics

NASA Astrophysics Data System (ADS)

Yuan, Wen-Xiang

2012-03-01

The frequency dependence of electric modulus of polycrystalline CaCu3Ti4O12 (CCTO) ceramics has been investigated. The experimental data have also been analyzed in the complex plane of impedance and electric modulus, and a suitable equivalent circuit has been proposed to explain the dielectric response. Four dielectric responses are first distinguished in the impedance and modulus spectroscopies. The results are well interpreted in terms of a triple insulating barrier capacitor model. Using this model, these four dielectric relaxations are attributed to the domain, domain-boundary, grain-boundary, and surface layer effects with three Maxwell-Wagner relaxations. Moreover, the values of the resistance and capacitance of bulk CCTO phase, domain-boundary, grain-boundary and surface layer contributions have been calculated directly from the peak characteristics of spectroscopic plots.

Frequency dispersions of human skin dielectrics.

PubMed Central

Poon, C S; Choy, T T

1981-01-01

The electrical properties of many biological materials are known to exhibit frequency dispersions. In the human skin, the impedance measured at various frequencies closely describes a circular locus of the Cole-Cole type in the complex impedance plane. In this report, the formative mechanisms responsible for the anomalous circular-arc behavior of skin impedance were investigated, using data from impedance measurements taken after successive strippings of the skin. The data were analyzed with respect to changes in the parameters of the equivalent Cole-Cole model after each stripping. For an exponential resistivity profile (Tregear, 1966, Physical Functions of Skin; Yamamoto and Yamamoto, 1976, Med. Biol. Eng., 14:151--158), the profile of the dielectric constant was shown to be uniform across the epidermis. Based on these results, a structural model has been formulated in terms of the relaxation theory of Maxwell and Wagner for inhomogeneous dielectric materials. The impedance locus obtained from the model approximates a circular are with phase constant alpha = 0.82, which compares favorably with experimental data. At higher frequencies a constant-phase, frequency-dependent component having the same phase constant alpha is also demonstrated. It is suggested that an approximately rectangular distribution of the relaxation time over the epidermal dielectric sheath is adequate to account for the anomalous frequency characteristics of human skin impedance. PMID:7213928

Multivariable Dynamic Ankle Mechanical Impedance With Relaxed Muscles

PubMed Central

Lee, Hyunglae; Krebs, Hermano Igo; Hogan, Neville

2015-01-01

Neurological or biomechanical disorders may distort ankle mechanical impedance and thereby impair locomotor function. This paper presents a quantitative characterization of multivariable ankle mechanical impedance of young healthy subjects when their muscles were relaxed, to serve as a baseline to compare with pathophysiological ankle properties of biomechanically and/or neurologically impaired patients. Measurements using a highly backdrivable wearable ankle robot combined with multi-input multi-output stochastic system identification methods enabled reliable characterization of ankle mechanical impedance in two degrees-of-freedom (DOFs) simultaneously, the sagittal and frontal planes. The characterization included important ankle properties unavailable from single DOF studies: coupling between DOFs and anisotropy as a function of frequency. Ankle impedance in joint coordinates showed responses largely consistent with a second-order system consisting of inertia, viscosity, and stiffness in both seated (knee flexed) and standing (knee straightened) postures. Stiffness in the sagittal plane was greater than in the frontal plane and furthermore, was greater when standing than when seated, most likely due to the stretch of bi-articular muscles (medial and lateral gastrocnemius). Very low off-diagonal partial coherences implied negligible coupling between dorsiflexion-plantarflexion and inversion-eversion. The directions of principal axes were tilted slightly counterclockwise from the original joint coordinates. The directional variation (anisotropy) of ankle impedance in the 2-D space formed by rotations in the sagittal and frontal planes exhibited a characteristic “peanut” shape, weak in inversion-eversion over a wide range of frequencies from the stiffness dominated region up to the inertia dominated region. Implications for the assessment of neurological and biomechanical impairments are discussed. PMID:24686292

Multivariable dynamic ankle mechanical impedance with relaxed muscles.

PubMed

Lee, Hyunglae; Krebs, Hermano Igo; Hogan, Neville

2014-11-01

Neurological or biomechanical disorders may distort ankle mechanical impedance and thereby impair locomotor function. This paper presents a quantitative characterization of multivariable ankle mechanical impedance of young healthy subjects when their muscles were relaxed, to serve as a baseline to compare with pathophysiological ankle properties of biomechanically and/or neurologically impaired patients. Measurements using a highly backdrivable wearable ankle robot combined with multi-input multi-output stochastic system identification methods enabled reliable characterization of ankle mechanical impedance in two degrees-of-freedom (DOFs) simultaneously, the sagittal and frontal planes. The characterization included important ankle properties unavailable from single DOF studies: coupling between DOFs and anisotropy as a function of frequency. Ankle impedance in joint coordinates showed responses largely consistent with a second-order system consisting of inertia, viscosity, and stiffness in both seated (knee flexed) and standing (knee straightened) postures. Stiffness in the sagittal plane was greater than in the frontal plane and furthermore, was greater when standing than when seated, most likely due to the stretch of bi-articular muscles (medial and lateral gastrocnemius). Very low off-diagonal partial coherences implied negligible coupling between dorsiflexion-plantarflexion and inversion-eversion. The directions of principal axes were tilted slightly counterclockwise from the original joint coordinates. The directional variation (anisotropy) of ankle impedance in the 2-D space formed by rotations in the sagittal and frontal planes exhibited a characteristic "peanut" shape, weak in inversion-eversion over a wide range of frequencies from the stiffness dominated region up to the inertia dominated region. Implications for the assessment of neurological and biomechanical impairments are discussed.

Reproducibility experiments on measuring acoustical properties of rigid-frame porous media (round-robin tests).

PubMed

Horoshenkov, Kirill V; Khan, Amir; Bécot, François-Xavier; Jaouen, Luc; Sgard, Franck; Renault, Amélie; Amirouche, Nesrine; Pompoli, Francesco; Prodi, Nicola; Bonfiglio, Paolo; Pispola, Giulio; Asdrubali, Francesco; Hübelt, Jörn; Atalla, Noureddine; Amédin, Celse K; Lauriks, Walter; Boeckx, Laurens

2007-07-01

This paper reports the results of reproducibility experiments on the interlaboratory characterization of the acoustical properties of three types of consolidated porous media: granulated porous rubber, reticulated foam, and fiberglass. The measurements are conducted in several independent laboratories in Europe and North America. The studied acoustical characteristics are the surface complex acoustic impedance at normal incidence and plane wave absorption coefficient which are determined using the standard impedance tube method. The paper provides detailed procedures related to sample preparation and installation and it discusses the dispersion in the acoustical material property observed between individual material samples and laboratories. The importance of the boundary conditions, homogeneity of the porous material structure, and stability of the adopted signal processing method are highlighted.

A Review of the Scattering-Parameter Extraction Method with Clarification of Ambiguity Issues in Relation to Metamaterial Homogenization

NASA Astrophysics Data System (ADS)

Arslanagic, S.; Hansen, T. V.; Mortensen, N. A.; Gregersen, A. H.; Sigmund, O.; Ziolkowski, R. W.; Breinbjerg, O.

2013-04-01

The scattering parameter extraction method of metamaterial homogenization is reviewed to show that the only ambiguity is the one related to the choice of the branch of the complex logarithmic function (or the complex inverse cosine function), whereas it has no ambiguity for the sign of the wave number and intrinsic impedance. While the method indeed yields two signs of the intrinsic impedance, and thus the wave number, the signs are dependent, and moreover, both sign combinations lead to the same permittivity and permeability, and are thus permissible. This observation is in distinct contrast to a number of statements in the literature where the correct sign of the intrinsic impedance and wave number, resulting from the scattering parameter method, is chosen by imposing additional physical requirements such as passivity. The scattering parameter method is reviewed through an investigation of a uniform plane wave normally incident on a planar slab in free-space, and the severity of the branch ambiguity is illustrated through simulations of a known metamaterial realization. Several approaches for proper branch selection are reviewed and their suitability to metamaterial samples is discussed.

Impedance Eduction in Ducts with Higher-Order Modes and Flow

NASA Technical Reports Server (NTRS)

Watson, Willie R.; Jones, Michael G.

2009-01-01

An impedance eduction technique, previously validated for ducts with plane waves at the source and duct termination planes, has been extended to support higher-order modes at these locations. Inputs for this method are the acoustic pressures along the source and duct termination planes, and along a microphone array located in a wall either adjacent or opposite to the test liner. A second impedance eduction technique is then presented that eliminates the need for the microphone array. The integrity of both methods is tested using three sound sources, six Mach numbers, and six selected frequencies. Results are presented for both a hardwall and a test liner (with known impedance) consisting of a perforated plate bonded to a honeycomb core. The primary conclusion of the study is that the second method performs well in the presence of higher-order modes and flow. However, the first method performs poorly when most of the microphones are located near acoustic pressure nulls. The negative effects of the acoustic pressure nulls can be mitigated by a judicious choice of the mode structure in the sound source. The paper closes by using the first impedance eduction method to design a rectangular array of 32 microphones for accurate impedance eduction in the NASA LaRC Curved Duct Test Rig in the presence of expected measurement uncertainties, higher order modes, and mean flow.

In-Plane Impedance Spectroscopy measurements in Vanadium Dioxide thin films

NASA Astrophysics Data System (ADS)

Ramirez, Juan; Patino, Edgar; Schmidt, Rainer; Sharoni, Amos; Gomez, Maria; Schuller, Ivan

2012-02-01

In plane Impedance Spectroscopy measurements have been done in Vanadium Dioxide thin films in the range of 100 Hz to 1 MHz. Our measurements allows distinguishing between the resistive and capacitive response of the Vanadium Dioxide films across the metal-insulator transition. A non ideal RC behavior was found in our thin films from room temperature up to 334 K. Around the MIT, an increase of the total capacitance is observed. A capacitor-network model is able to reproduce the capacitance changes across the MIT. Above the MIT, the system behaves like a metal as expected, and a modified equivalent circuit is necessary to describe the impedance data adequately.

Conduction in In 2O 3/YSZ heterostructures: Complex interplay between electrons and ions, mediated by interfaces

DOE PAGES

Veal, B. W.; Eastman, J. A.

2017-03-01

Thin film In 2O 3/YSZ heterostructures exhibit significant increases in electrical conductance with time when small in-plane electric fields are applied. Contact resistances between the current electrodes and film, and between current electrodes and substrate are responsible for the behavior. With an in-plane electric field, different field profiles are established in the two materials, with the result that oxygen ions can be driven across the heterointerface, altering the doping of the n-type In 2O 3. Furthermore, a low frequency inductive feature observed in AC impedance spectroscopy measurements under DC bias conditions was found to be due to frequency-dependent changes inmore » the contact resistance.« less

The acoustic field of a point source in a uniform boundary layer over an impedance plane

NASA Technical Reports Server (NTRS)

Zorumski, W. E.; Willshire, W. L., Jr.

1986-01-01

The acoustic field of a point source in a boundary layer above an impedance plane is investigated anatytically using Obukhov quasi-potential functions, extending the normal-mode theory of Chunchuzov (1984) to account for the effects of finite ground-plane impedance and source height. The solution is found to be asymptotic to the surface-wave term studies by Wenzel (1974) in the limit of vanishing wind speed, suggesting that normal-mode theory can be used to model the effects of an atmospheric boundary layer on infrasonic sound radiation. Model predictions are derived for noise-generation data obtained by Willshire (1985) at the Medicine Bow wind-turbine facility. Long-range downwind propagation is found to behave as a cylindrical wave, with attention proportional to the wind speed, the boundary-layer displacement thickness, the real part of the ground admittance, and the square of the frequency.

International Conference on Mathematical Methods in Electromagnetic Theory (MMET 2000), Volume 2 Held in Kharkov, Ukraine on September 12-15, 2000

DTIC Science & Technology

2000-09-01

frequencies of the WG-modes of the resonator are determined as the points on the complex frequency plane for which nontrivial solutions of (3) exist...allow to determine a surface impedance of end-walls using the experimentally measured frequencies and basic Q-factors of resonance oscillations of a...Y0 = Y,. The com- plex eigen frequencies K’ = Re< + i. Im< (v is the number of the resonance in the zones

Design and fabrication of a 40-MHz annular array transducer

PubMed Central

Ketterling, Jeffrey A.; Lizzi, Frederic L.; Aristizábal, Orlando; Turnbull, Daniel H.

2006-01-01

This paper investigates the feasibility of fabricating a 5-ring, focused annular array transducer operating at 40 MHz. The active piezoelectric material of the transducer was a 9-μm thick polyvinylidene fluoride (PVDF) film. One side of the PVDF was metallized with gold and forms the ground plane of the transducer. The array pattern of the transducer and electrical traces to each annulus were formed on a copper-clad polyimide film. The PVDF and polyimide were bonded with a thin layer of epoxy, pressed into a spherically curved shape, and then back filled with epoxy. A 5-ring transducer with equal area elements and 100 μm kerfs between annuli was fabricated and tested. The transducer had a total aperture of 6 mm and a geometric focus of 12 mm. The pulse/echo response from a quartz plate located at the geometric focus, two-way insertion loss (IL), complex impedance, electrical cross-talk, and lateral beamwidth were all measured for each annulus. The complex impedance data from each element were used to perform electrical matching and the measurements were repeated. After impedance matching, fc ≈ 36 MHz and BWs ranged from 31 to 39%. The ILs for the matched annuli ranged from −28 to −38 dB. PMID:16060516

Cavity resonance absorption in ultra-high bandwidth CRT deflection structure by a resistive load

DOEpatents

Dunham, M.E.; Hudson, C.L.

1993-05-11

An improved ultra-high bandwidth helical coil deflection structure for a cathode ray tube is described comprising a first metal member having a bore therein, the metal walls of which form a first ground plane; a second metal member coaxially mounted in the bore of the first metal member and forming a second ground plane; a helical deflection coil coaxially mounted within the bore between the two ground planes; and a resistive load disposed in one end of the bore and electrically connected to the first and second ground planes, the resistive load having an impedance substantially equal to the characteristic impedance of the coaxial line formed by the two coaxial ground planes to inhibit cavity resonance in the structure within the ultra-high bandwidth of operation. Preferably, the resistive load comprises a carbon film on a surface of an end plug in one end of the bore.

Cavity resonance absorption in ultra-high bandwidth CRT deflection structure by a resistive load

DOEpatents

Dunham, Mark E.; Hudson, Charles L.

1993-01-01

An improved ultra-high bandwidth helical coil deflection structure for a hode ray tube is described comprising a first metal member having a bore therein, the metal walls of which form a first ground plane; a second metal member coaxially mounted in the bore of the first metal member and forming a second ground plane; a helical deflection coil coaxially mounted within the bore between the two ground planes; and a resistive load disposed in one end of the bore and electrically connected to the first and second ground planes, the resistive load having an impedance substantially equal to the characteristic impedance of the coaxial line formed by the two coaxial ground planes to inhibit cavity resonance in the structure within the ultra-high bandwidth of operation. Preferably, the resistive load comprises a carbon film on a surface of an end plug in one end of the bore.

On the Propagation of Plane Acoustic Waves in a Duct With Flexible and Impedance Walls

NASA Technical Reports Server (NTRS)

Frendi, Abdelkader; Vu, Bruce

2003-01-01

This Technical Memorandum (TM) discusses the harmonic and random plane acoustic waves propagating from inside a duct to its surroundings. Various duct surfaces are considered, such as rigid, flexible, and impedance. In addition, the effects of a mean flow are studied when the duct alone is considered. Results show a significant reduction in overall sound pressure levels downstream of the impedance wall for both mean flow and no mean flow cases and for a narrow duct. When a wider duct is used, the overall sound pressure level (OSPL) reduction downstream of the impedance wall is much smaller. In the far field, the directivity is such that the overall sound pressure level is reduced by about 5 decibels (dB) on the side of the impedance wall. When a flexible surface is used, the far field directivity becomes asymmetric with an increase in the OSPL on the side of the flexible surface of about 7 dB.

On the long range propagation of sound over irregular terrain

NASA Technical Reports Server (NTRS)

Howe, M. S.

1984-01-01

The theory of sound propagation over randomly irregular, nominally plane terrain of finite impedance is discussed. The analysis is an extension of the theory of coherent scatter originally proposed by Biot for an irregular rigid surface. It combines Biot's approach, wherein the surface irregularities are modeled by a homogeneous distribution of hemispherical bosses, with more conventional analyses in which the ground is modeled as a smooth plane of finite impedance. At sufficiently low frequencies the interaction of the surface irregularities with the nearfield of a ground-based source leads to the production of surface waves, which are effective in penetrating the ground shadow zone predicted for a smooth surface of the same impedance.

Interference effects in phased beam tracing using exact half-space solutions.

PubMed

Boucher, Matthew A; Pluymers, Bert; Desmet, Wim

2016-12-01

Geometrical acoustics provides a correct solution to the wave equation for rectangular rooms with rigid boundaries and is an accurate approximation at high frequencies with nearly hard walls. When interference effects are important, phased geometrical acoustics is employed in order to account for phase shifts due to propagation and reflection. Error increases, however, with more absorption, complex impedance values, grazing incidence, smaller volumes and lower frequencies. Replacing the plane wave reflection coefficient with a spherical one reduces the error but results in slower convergence. Frequency-dependent stopping criteria are then applied to avoid calculating higher order reflections for frequencies that have already converged. Exact half-space solutions are used to derive two additional spherical wave reflection coefficients: (i) the Sommerfeld integral, consisting of a plane wave decomposition of a point source and (ii) a line of image sources located at complex coordinates. Phased beam tracing using exact half-space solutions agrees well with the finite element method for rectangular rooms with absorbing boundaries, at low frequencies and for rooms with different aspect ratios. Results are accurate even for long source-to-receiver distances. Finally, the crossover frequency between the plane and spherical wave reflection coefficients is discussed.

Single Mode Theory for Impedance Eduction in Large-Scale Ducts with Grazing Flow

NASA Technical Reports Server (NTRS)

Watson, Willie R.; Gerhold, Carl H.; Jones, Michael G.; June, Jason C.

2014-01-01

An impedance eduction theory for a rigid wall duct containing an acoustic liner with an unknown impedance and uniform grazing flow is presented. The unique features of the theory are: 1) non-planar waves propagate in the hard wall sections of the duct, 2) input data consist solely of complex acoustic pressures acquired on a wall adjacent to the liner, and 3) multiple higher-order modes may exist in the direction perpendicular to the liner and the opposite rigid wall. The approach is to first measure the axial propagation constant of a dominant higher-order mode in the liner sample section. This axial propagation constant is then used in conjunction with a closed-form solution to a reduced form of the convected Helmholtz equation and the wall impedance boundary condition to educe the liner impedance. The theory is validated on a conventional liner whose impedance spectrum is educed in two flow ducts with different cross sections. For the frequencies and Mach numbers of interest, no higher-order modes propagate in the hard wall sections of the smaller duct. A benchmark method is used to educe the impedance spectrum in this duct. A dominant higher-order vertical mode propagates in the larger duct for similar test conditions, and the current theory is applied to educe the impedance spectrum. Results show that when the theory is applied to data acquired in the larger duct with a dominant higher-order vertical mode, the same impedance spectra is educed as that obtained in the small duct where only the plane wave mode is present and the benchmark method is used. This result holds for each higher-order vertical mode that is considered.

Plane wave diffraction by a finite plate with impedance boundary conditions.

PubMed

Nawaz, Rab; Ayub, Muhammad; Javaid, Akmal

2014-01-01

In this study we have examined a plane wave diffraction problem by a finite plate having different impedance boundaries. The Fourier transforms were used to reduce the governing problem into simultaneous Wiener-Hopf equations which are then solved using the standard Wiener-Hopf procedure. Afterwards the separated and interacted fields were developed asymptotically by using inverse Fourier transform and the modified stationary phase method. Detailed graphical analysis was also made for various physical parameters we were interested in.

Perfect absorption of low-frequency sound waves by critically coupled subwavelength resonant system

NASA Astrophysics Data System (ADS)

Long, Houyou; Cheng, Ying; Tao, Jiancheng; Liu, Xiaojun

2017-01-01

The perfect absorption (PA) for low-frequency audible sound waves has been achieved by critically coupling the inherent loss factor to the inherent leakage factor of a system, which is constructed by attaching a deep-subwavelength lossy resonant plate (LRP) to a backed rigid wall closely. We have certified it by using the graphical method in the complex frequency plane. By coupling the LRP to an air cavity in front of the rigid wall, the high efficient (>80%) low-frequency broadband absorption is obtained from 99.1 Hz to 294.8 Hz. Here, the thickness of LRP is only 1/13.5 of the relevant wavelength at 294.8 Hz. The impedance analyses further demonstrate that the impedances are perfectly matched between the system and the surrounding background medium at PA.

Laterally Placed CDRA with Triangular Notches for Ultra Wideband Applications

NASA Astrophysics Data System (ADS)

Sankaranarayanan, Dileep; Venkata Kiran, Duggirala; Mukherjee, Biswajeet

2017-12-01

In this paper, a Coaxial probe-fed Laterally placed Cylindrical Dielectric Resonator Antenna (LCDRA) with symmetrical triangular notches is presented. The lateral surface of the Cylindrical Dielectric Resonator Antenna (CDRA) is kept on the ground plane with its longitudinal axis parallel to the ground plane. LCDRA has a lower resonant frequency than the CDRA and it offers considerably wider impedance bandwidth than CDRA. Finally, two symmetrical triangular notches are introduced on the two edges of LCDRA which is perpendicular to the axis to further improve the impedance bandwidth. The proposed antenna offers a wide impedance bandwidth (S_{11} <-10 dB) of 76.7 % (4.5-10.1 GHz). The radiation pattern of the proposed antenna is stable and broadside throughout the impedance bandwidth of operation. The prototype of the proposed antenna is fabricated and measured results are found to be in good agreement with the simulated one.

Influence of strike object grounding on close lightning electric fields

NASA Astrophysics Data System (ADS)

Baba, Yoshihiro; Rakov, Vladimir A.

2008-06-01

Using the finite difference time domain (FDTD) method, we have calculated vertical electric field Ez, horizontal (radial) electric field Eh, and azimuthal magnetic field Hϕ produced on the ground surface by lightning strikes to 160-m- and a 553-m-high conical strike objects representing the Peissenberg tower (Germany) and the CN Tower (Canada), respectively. The fields were computed for a typical subsequent stroke at distances d' from the bottom of the object ranging from 5 to 100 m for the 160-m tower and from 10 to 300 m for the 553-m tower. Grounding of the 160-m object was assumed to be accomplished by its underground basement represented by a 10-m-radius and 8-m-long perfectly conducting cylinder with or without a reference ground plane located 2 m below. The reference ground plane simulates, to some extent, a higher-conducting ground layer that is expected to exist below the water table. The configuration without reference ground plane actually means that this plane is present, but is located at an infinitely large depth. Grounding of the 553-m object was modeled in a similar manner but in the absence of reference ground plane only. In all cases considered, waveforms of Eh and Hϕ are not much influenced by the presence of strike object, while waveforms of Ez are. Waveforms of Ez are essentially unipolar (as they are in the absence of strike object) when the ground conductivity σ is 10 mS/m (the equivalent transient grounding impedance is several ohms) or greater. Thus, for the CN Tower, for which σ ≥ 10 mS/m, the occurrence of Ez polarity change is highly unlikely. For the 160-m tower and for σ = 1 and 0.1 mS/m, waveforms of Ez become bipolar (exhibit polarity change) at d' ≤ 10 m and d' ≤ 50 m, respectively, regardless of the presence of the reference ground plane. The corresponding equivalent transient grounding impedances are about 30 and 50 Ω in the absence of the reference ground plane and smaller than 10 Ω in the presence of the reference ground plane. The source of opposite polarity Ez is the potential rise at the object base (at the air/ground interface) relative to the reference ground plane. For a given grounding electrode geometry, the strength of this source increases with decreasing σ, provided that the grounding impedance is linear. Potential rises at the strike object base for σ = 1 and 0.1 mS/m are some hundreds of kilovolts, which is sufficient to produce electrical breakdown from relatively sharp edges of the basement over a distance of several meters (or more) along the ground surface. The resultant ground surface arcs will serve to reduce the equivalent grounding impedance and, hence, potential rise. Therefore, the polarity change of Ez near the Peissenberg tower, for which σ is probably about 1 mS/m, should be a rare phenomenon, if it occurs at all. The equivalent transient grounding impedance of the cylindrical basement is similar to that of a hemispherical grounding electrode of the same radius. For the 160-m tower and for hemispherical grounding electrode, the transient grounding impedance is higher than its dc grounding resistance for σ = 10 and 1 mS/m, but lower for σ = 0.1 mS/m. For the 553-m tower, the transient grounding impedance of hemispherical electrode is equal to or larger than its dc resistance for all values of σ considered.

Direct Electrical Probing of Periodic Modulation of Zinc-Dopant Distributions in Planar Gallium Arsenide Nanowires.

PubMed

Choi, Wonsik; Seabron, Eric; Mohseni, Parsian K; Kim, Jeong Dong; Gokus, Tobias; Cernescu, Adrian; Pochet, Pascal; Johnson, Harley T; Wilson, William L; Li, Xiuling

2017-02-28

Selective lateral epitaxial (SLE) semiconductor nanowires (NWs), with their perfect in-plane epitaxial alignment, ability to form lateral complex p-n junctions in situ, and compatibility with planar processing, are a distinctive platform for next-generation device development. However, the incorporation and distribution of impurity dopants in these planar NWs via the vapor-liquid-solid growth mechanism remain relatively unexplored. Here, we present a detailed study of SLE planar GaAs NWs containing multiple alternating axial segments doped with Si and Zn impurities by metalorganic chemical vapor deposition. The dopant profile of the lateral multi-p-n junction GaAs NWs was imaged simultaneously with nanowire topography using scanning microwave impedance microscopy and correlated with infrared scattering-type near-field optical microscopy. Our results provide unambiguous evidence that Zn dopants in the periodically twinned and topologically corrugated p-type segments are preferentially segregated at twin plane boundaries, while Si impurity atoms are uniformly distributed within the n-type segments of the NWs. These results are further supported by microwave impedance modulation microscopy. The density functional theory based modeling shows that the presence of Zn dopant atoms reduces the formation energy of these twin planes, and the effect becomes significantly stronger with a slight increase of Zn concentration. This implies that the twin formation is expected to appear when a threshold planar concentration of Zn is achieved, making the onset and twin periodicity dependent on both Zn concentration and nanowire diameter, in perfect agreement with our experimental observations.

Computer code for scattering from impedance bodies of revolution. Part 3: Surface impedance with s and phi variation. Analytical and numerical results

NASA Technical Reports Server (NTRS)

Uslenghi, Piergiorgio L. E.; Laxpati, Sharad R.; Kawalko, Stephen F.

1993-01-01

The third phase of the development of the computer codes for scattering by coated bodies that has been part of an ongoing effort in the Electromagnetics Laboratory of the Electrical Engineering and Computer Science Department at the University of Illinois at Chicago is described. The work reported discusses the analytical and numerical results for the scattering of an obliquely incident plane wave by impedance bodies of revolution with phi variation of the surface impedance. Integral equation formulation of the problem is considered. All three types of integral equations, electric field, magnetic field, and combined field, are considered. These equations are solved numerically via the method of moments with parametric elements. Both TE and TM polarization of the incident plane wave are considered. The surface impedance is allowed to vary along both the profile of the scatterer and in the phi direction. Computer code developed for this purpose determines the electric surface current as well as the bistatic radar cross section. The results obtained with this code were validated by comparing the results with available results for specific scatterers such as the perfectly conducting sphere. Results for the cone-sphere and cone-cylinder-sphere for the case of an axially incident plane were validated by comparing the results with the results with those obtained in the first phase of this project. Results for body of revolution scatterers with an abrupt change in the surface impedance along both the profile of the scatterer and the phi direction are presented.

Enhancement of Signal-to-noise Ratio in Natural-source Transient Magnetotelluric Data with Wavelet Transform

NASA Astrophysics Data System (ADS)

Zhang, Y.; Paulson, K. V.

For audio-frequency magnetotelluric surveys where the signals are lightning-stroke transients, the conventional Fourier transform method often fails to produce a high quality impedance tensor. An alternative approach is to use the wavelet transform method which is capable of localizing target information simultaneously in both the temporal and frequency domains. Unlike Fourier analysis that yields an average amplitude and phase, the wavelet transform produces an instantaneous estimate of the amplitude and phase of a signal. In this paper a complex well-localized wavelet, the Morlet wavelet, has been used to transform and analyze audio-frequency magnetotelluric data. With the Morlet wavelet, the magnetotelluric impedance tensor can be computed directly in the wavelet transform domain. The lightning-stroke transients are easily identified on the dilation-translation plane. Choosing those wavelet transform values where the signals are located, a higher signal-to-noise ratio estimation of the impedance tensor can be obtained. In a test using real data, the wavelet transform showed a significant improvement in the signal-to-noise ratio over the conventional Fourier transform.

Positioning of electrode plane systematically influences EIT imaging.

PubMed

Krueger-Ziolek, Sabine; Schullcke, Benjamin; Kretschmer, Jörn; Müller-Lisse, Ullrich; Möller, Knut; Zhao, Zhanqi

2015-06-01

Up to now, the impact of electrode positioning on electrical impedance tomography (EIT) had not been systematically analyzed due to the lack of a reference method. The aim of the study was to determine the impact of electrode positioning on EIT imaging in spontaneously breathing subjects at different ventilation levels with our novel lung function measurement setup combining EIT and body plethysmography. EIT measurements were conducted in three transverse planes between the 3rd and 4th intercostal space (ICS), at the 5th ICS and between the 6th and 7th ICS (named as cranial, middle and caudal) on 12 healthy subjects. Pulmonary function tests were performed simultaneously by body plethysmography to determine functional residual capacity (FRC), vital capacity (VC), tidal volume (VT), expiratory reserve volume (ERV), and inspiratory reserve volume (IRV). Ratios of impedance changes and body plethysmographic volumes were calculated for every thorax plane (ΔIERV/ERV, ΔIVT/VT and ΔIIRV/IRV). In all measurements of a subject, FRC values and VC values differed ≤5%, which confirmed that subjects were breathing at comparable end-expiratory levels and with similar efforts. In the cranial thorax plane the normalized ΔIERV/ERV ratio in all subjects was significantly higher than the normalized ΔIIRV/IRV ratio whereas the opposite was found in the caudal chest plane. No significant difference between the two normalized ratios was found in the middle thoracic plane. Depending on electrode positioning, impedance to volume ratios may either increase or decrease in the same lung condition, which may lead to opposite clinical decisions.

Design and implementation of low profile antenna for dual-band applications using rotated e-shaped conductor-backed plane.

PubMed

Jalali, Mahdi; Sedghi, Tohid; Shafei, Shahin

2014-01-01

A novel configuration of a printed monopole antenna with a very compact size for satisfying WLAN operations at the 5.2/5.8 GHz and also for X-band operations at the 10 GHz has been proposed. The antenna includes a simple square-shaped patch as the radiator, the rotated U-shaped conductor back plane element with embedded strip on it, and the partial rectangular ground surface. By using the rotated U-shaped conductor-backed plane with proper values, good impedance matching and improvement in bandwidth can be achieved, at the lower and upper bands. The impedance bandwidth for S11 < -10 dB is about 1.15 GHz for 5 GHz band and 5.3 GHz for X-band. The measured peak gains are about 1.9 dBi at WLAN-band and 4.2 dBi at X-band. The experimental results represent that the realized antenna with good omnidirectional radiation characteristics, enough impedance bandwidth, and reasonable gains can be appropriate for various applications of the future developed technologies and handheld devices.

Impedance measurement using a two-microphone, random-excitation method

NASA Technical Reports Server (NTRS)

Seybert, A. F.; Parrott, T. L.

1978-01-01

The feasibility of using a two-microphone, random-excitation technique for the measurement of acoustic impedance was studied. Equations were developed, including the effect of mean flow, which show that acoustic impedance is related to the pressure ratio and phase difference between two points in a duct carrying plane waves only. The impedances of a honeycomb ceramic specimen and a Helmholtz resonator were measured and compared with impedances obtained using the conventional standing-wave method. Agreement between the two methods was generally good. A sensitivity analysis was performed to pinpoint possible error sources and recommendations were made for future study. The two-microphone approach evaluated in this study appears to have some advantages over other impedance measuring techniques.

Discharge current distribution in stratified soil under impulse discharge

NASA Astrophysics Data System (ADS)

Eniola Fajingbesi, Fawwaz; Shahida Midi, Nur; Elsheikh, Elsheikh M. A.; Hajar Yusoff, Siti

2017-06-01

The mobility of charge particles traversing a material defines its electrical properties. Soil (earth) have long been the universal grounding before and after the inception of active ground systems for electrical appliance purpose due to it semi-conductive properties. The soil can thus be modelled as a single material exhibiting semi-complex inductive-reactive impedance. Under impulse discharge such as lightning strikes to soil this property of soil could result in electric potential level fluctuation ranging from ground potential rise/fall to electromagnetic pulse coupling that could ultimately fail connected electrical appliance. In this work we have experimentally model the soil and lightning discharge using point to plane electrode setup to observe the current distribution characteristics at different soil conductivity [mS/m] range. The result presented from this research indicate above 5% shift in conductivity before and after discharge which is significant for consideration when dealing with grounding designs. The current distribution in soil have also be successfully observed and analysed from experimental result using mean current magnitude in relation to electrode distance and location, current density variation with depth all showing strong correlation with theoretical assumptions of a semi-complex impedance material.

Axolemmal and septal conduction in the impedance of the earthworm medial giant nerve fiber.

PubMed Central

Krause, T L; Fishman, H M; Bittner, G D

1994-01-01

Ionic conduction in the axolemmal and septal membranes of the medial giant fiber (MGF) of the earthworm (EW) Lumbricus terrestris was assessed by impedance spectroscopy in the frequency range 2.5-1000 Hz. Impedance loci in the complex plane were described by two semi-circular arcs, one at a lower characteristic frequency (100 Hz) and the other at a higher frequency (500 Hz). The lower frequency arc had a chord resistance of 53 k omega and was not affected by membrane potential changes or ion channel blockers [tetrodotoxin (TTX), 3,4-diaminopyridine (3,4-DAP), 4-aminopyridine (4-AP), and tetraethylammonium (TEA)]. The higher frequency arc had a chord resistance of 274 k omega at resting potential, was voltage-dependent, and was affected by the addition of TTX, 3,4-DAP, 4-AP, and TEA to the physiological EW salines. When all four blockers were added to the bathing solution, the impedance locus was described by two voltage-independent arcs. Considering the effects of these and other (i.e., Cd and Ni) ion channel blockers, we conclude that: 1) the higher frequency locus reflects conduction by voltage-sensitive ion channels in the axolemmal membrane, which contains at least four ion channels selective for sodium, calcium, and potassium (delayed rectifier and calcium-dependent), and 2) the lower frequency locus reflects voltage-insensitive channels in the septal membrane, which separates adjacent MGFs. PMID:7524713

An improved water-filled impedance tube.

PubMed

Wilson, Preston S; Roy, Ronald A; Carey, William M

2003-06-01

A water-filled impedance tube capable of improved measurement accuracy and precision is reported. The measurement instrument employs a variation of the standardized two-sensor transfer function technique. Performance improvements were achieved through minimization of elastic waveguide effects and through the use of sound-hard wall-mounted acoustic pressure sensors. Acoustic propagation inside the water-filled impedance tube was found to be well described by a plane wave model, which is a necessary condition for the technique. Measurements of the impedance of a pressure-release terminated transmission line, and the reflection coefficient from a water/air interface, were used to verify the system.

Design and Implementation of Low Profile Antenna for Dual-Band Applications Using Rotated E-Shaped Conductor-Backed Plane

PubMed Central

Jalali, Mahdi; Sedghi, Tohid; Shafei, Shahin

2014-01-01

A novel configuration of a printed monopole antenna with a very compact size for satisfying WLAN operations at the 5.2/5.8 GHz and also for X-band operations at the 10 GHz has been proposed. The antenna includes a simple square-shaped patch as the radiator, the rotated U-shaped conductor back plane element with embedded strip on it, and the partial rectangular ground surface. By using the rotated U-shaped conductor-backed plane with proper values, good impedance matching and improvement in bandwidth can be achieved, at the lower and upper bands. The impedance bandwidth for S 11 < −10 dB is about 1.15 GHz for 5 GHz band and 5.3 GHz for X-band. The measured peak gains are about 1.9 dBi at WLAN-band and 4.2 dBi at X-band. The experimental results represent that the realized antenna with good omnidirectional radiation characteristics, enough impedance bandwidth, and reasonable gains can be appropriate for various applications of the future developed technologies and handheld devices. PMID:24711732

Electrical transport properties of LiNiV O ceramics

NASA Astrophysics Data System (ADS)

Ram, Moti

2009-08-01

The LiNiV O 4 fine powder has been synthesized by chemical "pyrophoric reaction process". The formation of LiNiV O 4 is confirmed by X-ray diffraction analysis. X-ray analysis shows that the compound has cubic crystal structure with lattice constant ( a=8.2243(2) Å). Microstructure of the sintered pellet is identified by taking the field emission scanning electron microscopy (FE-SEM) pictures, which reveals the grain size as ˜0.2-2 μm. Electrical properties are measured using complex impedance spectroscopy technique. Bulk contribution to electrical response is identified by the analysis of complex plane diagrams. The activation energy calculated from σ vs 10 3/T graph is ˜0.06 eV (25-225 ∘C) and ˜0.55 eV (225-375 ∘C). Complex modulus study shows non-Debye type (polydispersive) conductivity relaxation in the compound.

On the method of lumens

PubMed Central

Shera, Christopher A.

2014-01-01

Parent and Allen [(2007). J. Acoust. Soc. Am. 122, 918–931] introduced the “method of lumens” to compute the plane-wave reflectance in a duct terminated with a nonuniform impedance. The method involves splitting the duct into multiple, fictitious subducts (lumens), solving for the reflectance in each subduct, and then combining the results. The method of lumens has considerable intuitive appeal and is easily implemented in the time domain. Previously applied only in a complex acoustical setting where proper evaluation is difficult (i.e., in a model of the ear canal and tympanic membrane), the method is tested here by using it to compute the reflectance from an area constriction in an infinite lossless duct considered in the long-wavelength limit. Neither the original formulation of the method—shown here to violate energy conservation except when the termination impedance is uniform—nor a reformulation consistent with basic physical constraints yields the correct solution to this textbook problem in acoustics. The results are generalized and the nature of the errors illuminated. PMID:25480060

Optimal distance of multi-plane sensor in three-dimensional electrical impedance tomography.

PubMed

Hao, Zhenhua; Yue, Shihong; Sun, Benyuan; Wang, Huaxiang

2017-12-01

Electrical impedance tomography (EIT) is a visual imaging technique for obtaining the conductivity and permittivity distributions in the domain of interest. As an advanced technique, EIT has the potential to be a valuable tool for continuously bedside monitoring of pulmonary function. The EIT applications in any three-dimensional (3 D) field are very limited to the 3 D effects, i.e. the distribution of electric field spreads far beyond the electrode plane. The 3 D effects can result in measurement errors and image distortion. An important way to overcome the 3 D effect is to use the multiple groups of sensors. The aim of this paper is to find the best space resolution of EIT image over various electrode planes and select an optimal plane spacing in a 3 D EIT sensor, and provide guidance for 3 D EIT electrodes placement in monitoring lung function. In simulation and experiment, several typical conductivity distribution models, such as one rod (central, midway and edge), two rods and three rods, are set at different plane spacings between the two electrode planes. A Tikhonov regularization algorithm is utilized for reconstructing the images; the relative error and the correlation coefficient are utilized for evaluating the image quality. Based on numerical simulation and experimental results, the image performance at different spacing conditions is evaluated. The results demonstrate that there exists an optimal plane spacing between the two electrode planes for 3 D EIT sensor. And then the selection of the optimal plane spacing between the electrode planes is suggested for the electrodes placement of multi-plane EIT sensor.

Electromagnetic Wave Excitation by a Longitudinal Slot in a Broad Wall of Rectangular Waveguide in the Presence of Passive Impedance Vibrators Outside the Waveguide

NASA Astrophysics Data System (ADS)

Berdnik, S. L.; Katrich, V. A.; Nesterenko, M. V.; Penkin, Yu. M.

2016-09-01

Purpose: A problem of electromagnetic wave diffraction by a longitudinal slot cut in a waveguide wide wall is solved. The slot is cut in a wide wall of a rectangular waveguide and radiates in a half-space above a perfectly conducting plane where two vertical impedance monopoles with arbitrary lengths placed with their bases placed on the plane. The paper is aimed at studying the electrodynamic characteristics of vibratorwaveguide-slot structures which allow to form the emission fields as that in a Clavin element with two identical passive ideally conducting monopoles of a fixed length located on a set distance from a slot center on both sides of a narrow halfwave slot. Design/methodology/approach: The problem is solved by a generalized method of induced electromotive and magnetomotive forces in approximation of electric currents in the vibrators and equivalent magnetic current in the slot by the functions obtained by the asymptotic averaging method. Findings: The influence of geometric parameters of the structure on the directional characteristics of Clavin type element is analyzed on the assumption of simultaneous account for relative level of sidelobes in the E-plane and beamwidth differences at -3 dB level in the main planes. It is shown that the directional characteristics and energy characteristics of the radiators: radiation and reflection coefficients, antenna directivity and gain can be varied within wide limits by changing the electrical length and/or distributed surface impedances of the vibrators, providing at that a low level of radiation within a slot plane. Conclusions: The results obtained can be useful when designing both small-size and multi-element antenna arrays with Clavin elements.

Thin conformal antenna array for microwave power conversions

NASA Technical Reports Server (NTRS)

Dickinson, R. M. (Inventor)

1978-01-01

A structure of a circularly polarized, thin conformal, antenna array which may be mounted integrally with the skin of an aircraft employs microstrip elliptical elements and interconnecting feed lines spaced from a circuit ground plane by a thin dielectric layer. The feed lines are impedance matched to the elliptical antenna elements by selecting a proper feedpoint inside the periphery of the elliptical antenna elements. Diodes connected between the feed lines and the ground plane rectify the microwave power, and microstrip filters (low pass) connected in series with the feed lines provide dc current to a microstrip bus. Low impedance matching strips are included between the elliptical elements and the rectifying and filtering elements.

A Physics-Based Approach for Power Integrity in Multi-Layered PCBs

NASA Astrophysics Data System (ADS)

Zhao, Biyao

Developing a power distribution network (PDN) for ASICs and ICs to achieve the low-voltage ripple specifications for current digital designs is challenging with the high-speed and low-voltage ICs. Present methods are typically guided by best engineering practices for low impedance looking into the PDN from the IC. A pre-layout design methodology for power integrity in multi-layered PCB PDN geometry is proposed in the thesis. The PCB PDN geometry is segmented into four parts and every part is modelled using different methods based on the geometry details of the part. Physics-based circuit models are built for every part and the four parts are re-assembled into one model. The influence of geometry details is clearly revealed in this methodology. Based on the physics-based circuit mode, the procedures of using the pre-layout design methodology as a guideline during the PDN design is illustrated. Some common used geometries are used to build design space, and the design curves with the geometry details are provided to be a look up library for engineering use. The pre-layout methodology is based on the resonant cavity model of parallel planes for the cavity structures, and parallel-plane PEEC (PPP) for the irregular shaped plane inductance, and PEEC for the decoupling capacitor connection above the top most or bottom most power-return planes. PCB PDN is analyzed based on the input impedance looking into the PCB from the IC. The pre-layout design methodology can be used to obtain the best possible PCB PDN design. With the switching current profile, the target impedance can be selected to evaluate the PDN performance, and the frequency domain PDN input impedance can be used to obtain the voltage ripple in the time domain to give intuitive insight of the geometry impact on the voltage ripple.

Validation of a New Procedure for Impedance Eduction in Flow

NASA Technical Reports Server (NTRS)

Watson, W. R.; Jones, M. G.

2010-01-01

A new impedance eduction procedure is validated by comparing the educed impedance spectrum to that of an older but well-tested eduction procedure. The older procedure requires the installation of a microphone array in the liner test section but the new procedure removes this requirement. A 12.7-mm stainless steel plate and a conventional liner consisting of a perforated plate bonded to a honeycomb core are tested. Test data is acquired from a grazing flow, impedance tube facility for a range of source frequencies and mean flow Mach numbers for which only plane waves are cut on. For the stainless steel plate, the educed admittance spectrum using the new procedure shows an improvement over that of the old procedure. This improvement shows up primarily in the educed conductance spectrum. Both eduction procedures show discrepancies in educed admittance in the mid-frequency range. Indications are that this discrepancy is triggered by an inconsistency between the measured eduction data (that contains boundary layer effects) and the two eduction models (for which the boundary layer is neglected). For the conventional liner, both eduction procedures are in very good agreement with each other. Small discrepancies occur for one or two frequencies in the mid-frequency range and for frequencies beyond the cut on frequency of higher-order duct modes. This discrepancy in the midfrequency range occurs because an automated optimizer is used to educe the impedance and the objective function used by the optimizer is extremely flat and therefore sensitive to initial starting values. The discrepancies at frequencies beyond the cut on frequency of higher order duct modes are due to the assumption of only plane waves in the impedance eduction model, although higher order modes are propagating in the impedance tube facility.

Identification of fluids and an interface between fluids by measuring complex impedance

DOEpatents

Lee, David O.; Wayland, Jr., James R.

1989-01-01

Complex impedance measured over a predefined frequency range is used to determine the identity of different oils in a column. The location of an interface between the oils is determined from the percent frequency effects of the complex impedance measured across the interface.

Coupling impedance and wake functions for laminated structures with an application to the Fermilab Booster

DOE PAGES

Macridin, Alexandru; Spentzouris, Panagiotis; Amundson, James; ...

2011-06-28

We calculate the impedance and wake functions for laminated structures with parallel-plane and circular geometries. We critically examine the approximations used in the literature for the coupling impedance in laminated chambers and find that most of them are not justified because the wall surface impedance is large. A comparison between flat and circular geometry impedances is presented. We apply our calculation in a state-of-the-art beam dynamics simulation of the Fermilab Booster which includes nonlinear optics, laminated wakefields, and space charge impedance. The latter can have a significant effect away from the ultrarelativistic limit. Even though the simulations and the comparisonmore » with the experiment are done at the Booster injection energy, where the relativistic factor γ = 1.42, we find good agreement between our calculation of the coherent tune shift and recent experimental measurements.« less

Interlimb Differences in Coordination of Unsupported Reaching Movements

PubMed Central

Schaffer, Jacob E.; Sainburg, Robert L.

2017-01-01

Previous research suggests that interlimb differences in coordination associated with handedness might result from specialized control mechanisms that are subserved by different cerebral hemispheres. Based largely on the results of horizontal plane reaching studies, we have proposed that the hemisphere contralateral to the dominant arm is specialized for predictive control of limb dynamics, while the non-dominant hemisphere is specialized for controlling limb impedance. The current study explores interlimb differences in control of 3-D unsupported reaching movements. While the task was presented in the horizontal plane, participant’s arms were unsupported and free to move within a range of the vertical axis, which was redundant to the task plane. Results indicated significant dominant arm advantages for both initial direction accuracy and final position accuracy. The dominant arm showed greater excursion along a redundant axis that was perpendicular to the task, and parallel to gravitational forces. In contrast, the non-dominant arm better impeded motion out of the task-plane. Nevertheless, left arm task errors varied substantially more with shoulder rotation excursion than did dominant arm task errors. These findings suggest that the dominant arm controller was able to take advantage of the redundant degrees of freedom of the task, while non-dominant task errors appeared enslaved to motion along the redundant axis. These findings are consistent with a dominant controller that is specialized for intersegmental coordination, and a non-dominant controller that is specialized for impedance control. However, the findings are inconsistent with previously documented conclusions from planar tasks, in which non-dominant control leads to greater final position accuracy. PMID:28344068

Identification of fluids and an interface between fluids by measuring complex impedance

DOEpatents

Lee, D.O.; Wayland, J.R. Jr.

1989-12-05

Complex impedance measured over a predefined frequency range is used to determine the identity of different oils in a column. The location of an interface between the oils is determined from the percent frequency effects of the complex impedance measured across the interface. 5 figs.

Superconducting active impedance converter

DOEpatents

Ginley, David S.; Hietala, Vincent M.; Martens, Jon S.

1993-01-01

A transimpedance amplifier for use with high temperature superconducting, other superconducting, and conventional semiconductor allows for appropriate signal amplification and impedance matching to processing electronics. The amplifier incorporates the superconducting flux flow transistor into a differential amplifier configuration which allows for operation over a wide temperature range, and is characterized by high gain, relatively low noise, and response times less than 200 picoseconds over at least a 10-80 K. temperature range. The invention is particularly useful when a signal derived from either far-IR focal plane detectors or from Josephson junctions is to be processed by higher signal/higher impedance electronics, such as conventional semiconductor technology.

Structural and electrical properties of nickel substituted cadmium ferrite

NASA Astrophysics Data System (ADS)

Chethan, B.; Raj Prakash, H. G.; Vijayakumari, S. C.; Ravikiran, Y. T.

2018-05-01

Spinal nano-sized Cadmium ferrite (CD) and Nickel substituted cadmium ferrite (NSCF) were fabricated by sol-gel auto combustion method. The formation of spinal structure of ferrite materials was confirmed by X-ray diffraction (XRD) analysis. The crystallites size of CF and NSCF as determined by Scherrer's formula were found to be 24.73 nm and 17.70 nm respectively. comparative study of Fourier transform infrared spectroscopy (FTIR) of CF and NSCF revealed tetrahedral absorption bands shifted slightly towards higher frequency where as octahedral bands shifted towards lower frequency side confirming interfacial interaction between Ni and CF. The AC conductivity (σ), loss tangent (tan δ) and complex plane impedance plots for both CF and NSCF are determined at various frequencies ranging from 50 kHz to 5 MHz and comparatively analyzed. The increase in AC conductivity of the NSCF nano particles as compared to CF was explained in the light of hopping model. The impedance measurement of NSCF show presence of a semi-circle corresponding to the grain boundary resistance and hence shows that the conductivity takes place largely through grain boundaries.

Characterizing the ear canal acoustic reflectance and impedance by pole-zero fitting

PubMed Central

Robinson, Sarah R.; Nguyen, Cac T.; Allen, Jont B.

2013-01-01

This study characterizes middle ear complex acoustic reflectance (CAR) and impedance by fitting poles and zeros to real-ear measurements. The goal of this work is to establish a quantitative connection between pole-zero locations and the underlying physical properties of CAR data. Most previous studies have analyzed CAR magnitude; while the magnitude accounts for reflected power, it does not encode latency information. Thus, an analysis that studies the real and imaginary parts of the data together could be more powerful. Pole-zero fitting of CAR data is examined using data compiled from various studies, dating back to Voss and Allen (1994). Recent CAR measurements were taken using a middle ear acoustic power analyzer (MEPA) system (HearID, Mimosa Acoustics), which makes complex acoustic impedance and reflectance measurements in the ear canal over the 0.2 to 6.0 kHz frequency range. Pole-zero fits to measurements over this range are achieved with an average RMS relative error of less than 3% using 12 poles. Factoring the reflectance fit into its all-pass and minimum-phase components approximates the effect of the ear canal, allowing for comparison across measurements. It was found that individual CAR magnitude variations for normal middle ears in the 1 to 4 kHz range often give rise to closely-placed pole-zero pairs, and that the locations of the poles and zeros in the s-plane may differ between normal and pathological middle ears. This study establishes a methodology for examining the physical and mathematical properties of CAR using a concise parametric model. Pole-zero modeling shows promise for precise parameterization of CAR data and for identification of middle ear pathologies. PMID:23524141

Correlation between ionic radii of metals and thermal decomposition of supramolecular structure of azodye complexes

NASA Astrophysics Data System (ADS)

El-Sonbati, A. Z.; Diab, M. A.; El-Bindary, A. A.; Eldesoky, A. M.; Morgan, Sh. M.

2015-01-01

An interesting azodye heterocyclic ligand of copper(II), cobalt(II), nickel(II) and uranyl(II) complexes have been synthesized by the reaction of metal salts with 5-(2,3-dimethyl-1-phenylpyrazol-5-one azo)-2-thioxo-4-thiazolidinone (HL) yields 1:1 and 1:2 (M:L) complexes depending on the reaction conditions. The elemental analysis, magnetic moments, spectral (UV-Vis, IR, 1H and 13C NMR and ESR) and thermal studies were used to characterize the isolated complexes. The molecular structures of the ligand tautomers are optimized theoretically and the quantum chemical parameters are calculated. The IR spectra showed that the ligand (HL) act as monobasic tridentate/neutral bidentate through the (sbnd Ndbnd N), enolic (Csbnd O)- and/or oxygen keto moiety groups forming a five/six-membered structures. According to intramolecular hydrogen bond leads to increasing of the complexes stability. The molar conductivities show that all the complexes are non-electrolytes. The ESR spectra indicate that the free electron is in dxy orbital. The calculated bonding parameter indicates that in-plane σ-bonding is more covalent than in-plane π-bonding. The coordination geometry is five/six-coordinated trigonal bipyramidal for complex (1) and octahedral for complexes (2-6). The value of covalency factor β12 and orbital reduction factor K accounts for the covalent nature of the complexes. The activation thermodynamic parameters are calculated using Coats-Redfern and Horowitz-Metzger methods. The synthesized ligand (HL) and its Cu(II) complexes (1, 2 and 4) are screened for their biological activity against bacterial and fungal species. The ligand (HL) showed antimicrobial activities against Escherichia coli. The ligand (HL) and its Cu(II) complexes (2 and 4) have very high antifungal activity against Penicillium italicum. The inhibitive action of ligand (HL), against the corrosion of C-steel in 2 M HCl solution has been investigated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS).

Three-dimensional electrical impedance tomography based on the complete electrode model.

PubMed

Vauhkonen, P J; Vauhkonen, M; Savolainen, T; Kaipio, J P

1999-09-01

In electrical impedance tomography an approximation for the internal resistivity distribution is computed based on the knowledge of the injected currents and measured voltages on the surface of the body. It is often assumed that the injected currents are confined to the two-dimensional (2-D) electrode plane and the reconstruction is based on 2-D assumptions. However, the currents spread out in three dimensions and, therefore, off-plane structures have significant effect on the reconstructed images. In this paper we propose a finite element-based method for the reconstruction of three-dimensional resistivity distributions. The proposed method is based on the so-called complete electrode model that takes into account the presence of the electrodes and the contact impedances. Both the forward and the inverse problems are discussed and results from static and dynamic (difference) reconstructions with real measurement data are given. It is shown that in phantom experiments with accurate finite element computations it is possible to obtain static images that are comparable with difference images that are reconstructed from the same object with the empty (saline filled) tank as a reference.

Complex Impedance of Fast Optical Transition Edge Sensors up to 30 MHz

NASA Astrophysics Data System (ADS)

Hattori, K.; Kobayashi, R.; Numata, T.; Inoue, S.; Fukuda, D.

2018-03-01

Optical transition edge sensors (TESs) are characterized by a very fast response, of the order of μs, which is 10^3 times faster than TESs for X-ray and gamma-ray. To extract important parameters associated with the optical TES, complex impedances at high frequencies (> 1 MHz) need to be measured, where the parasitic impedance in the circuit and reflections of electrical signals due to discontinuities in the characteristic impedance of the readout circuits become significant. This prevents the measurements of the current sensitivity β , which can be extracted from the complex impedance. In usual setups, it is hard to build a circuit model taking into account the parasitic impedances and reflections. In this study, we present an alternative method to estimate a transfer function without investigating the details of the entire circuit. Based on this method, the complex impedance up to 30 MHz was measured. The parameters were extracted from the impedance and were compared with other measurements. Using these parameters, we calculated the theoretical limit on an energy resolution and compared it with the measured energy resolution. In this paper, the reasons for the deviation of the measured value from theoretically predicted values will be discussed.

An anisotropic lens for transitioning plane waves between media of different permittivities

NASA Astrophysics Data System (ADS)

Stone, Alexander P.; Baum, Carl E.

1988-11-01

A particularly simple geometry is considered in which an inhomogeneous and anisotropic lens is specified for the transition of plane waves between media of different permittivities. The permittivities of the regions outside of the lens can be constant, but the permittivity of the lens region depends on position. Results are presented for a plane wave in the second medium propagating normally to the assumed plane boundary of that medium. The results for the case of normal incidence are then generalized to the case of nonnormal incidence. The conditions of transit time conservation and impedance matching are related to the Brewster angle.

Time-varying impedance of the human ankle in the sagittal and frontal planes during straight walk and turning steps.

PubMed

Ficanha, Evandro M; Ribeiro, Guilherme A; Knop, Lauren; Rastgaar, Mo

2017-07-01

This paper describes the methods and experiment protocols for estimation of the human ankle impedance during turning and straight line walking. The ankle impedance of two human subjects during the stance phase of walking in both dorsiflexion plantarflexion (DP) and inversion eversion (IE) were estimated. The impedance was estimated about 8 axes of rotations of the human ankle combining different amounts of DP and IE rotations, and differentiating among positive and negative rotations at 5 instants of the stance length (SL). Specifically, the impedance was estimated at 10%, 30%, 50%, 70% and 90% of the SL. The ankle impedance showed great variability across time, and across the axes of rotation, with consistent larger stiffness and damping in DP than IE. When comparing straight walking and turning, the main differences were in damping at 50%, 70%, and 90% of the SL with an increase in damping at all axes of rotation during turning.

Compact Interconnection Networks Based on Quantum Dots

NASA Technical Reports Server (NTRS)

Fijany, Amir; Toomarian, Nikzad; Modarress, Katayoon; Spotnitz, Matthew

2003-01-01

Architectures that would exploit the distinct characteristics of quantum-dot cellular automata (QCA) have been proposed for digital communication networks that connect advanced digital computing circuits. In comparison with networks of wires in conventional very-large-scale integrated (VLSI) circuitry, the networks according to the proposed architectures would be more compact. The proposed architectures would make it possible to implement complex interconnection schemes that are required for some advanced parallel-computing algorithms and that are difficult (and in many cases impractical) to implement in VLSI circuitry. The difficulty of implementation in VLSI and the major potential advantage afforded by QCA were described previously in Implementing Permutation Matrices by Use of Quantum Dots (NPO-20801), NASA Tech Briefs, Vol. 25, No. 10 (October 2001), page 42. To recapitulate: Wherever two wires in a conventional VLSI circuit cross each other and are required not to be in electrical contact with each other, there must be a layer of electrical insulation between them. This, in turn, makes it necessary to resort to a noncoplanar and possibly a multilayer design, which can be complex, expensive, and even impractical. As a result, much of the cost of designing VLSI circuits is associated with minimization of data routing and assignment of layers to minimize crossing of wires. Heretofore, these considerations have impeded the development of VLSI circuitry to implement complex, advanced interconnection schemes. On the other hand, with suitable design and under suitable operating conditions, QCA-based signal paths can be allowed to cross each other in the same plane without adverse effect. In principle, this characteristic could be exploited to design compact, coplanar, simple (relative to VLSI) QCA-based networks to implement complex, advanced interconnection schemes. The proposed architectures require two advances in QCA-based circuitry beyond basic QCA-based binary-signal wires described in the cited prior article. One of these advances would be the development of QCA-based wires capable of bidirectional transmission of signals. The other advance would be the development of QCA circuits capable of high-impedance state outputs. The high-impedance states would be utilized along with the 0- and 1-state outputs of QCA.

Superconducting active impedance converter

DOEpatents

Ginley, D.S.; Hietala, V.M.; Martens, J.S.

1993-11-16

A transimpedance amplifier for use with high temperature superconducting, other superconducting, and conventional semiconductors allows for appropriate signal amplification and impedance matching to processing electronics. The amplifier incorporates the superconducting flux flow transistor into a differential amplifier configuration which allows for operation over a wide temperature range, and is characterized by high gain, relatively low noise, and response times less than 200 picoseconds over at least a 10-80 K. temperature range. The invention is particularly useful when a signal derived from either far-IR focal plane detectors or from Josephson junctions is to be processed by higher signal/higher impedance electronics, such as conventional semiconductor technology. 12 figures.

Optimal one-dimensional inversion and bounding of magnetotelluric apparent resistivity and phase measurements

NASA Astrophysics Data System (ADS)

Parker, Robert L.; Booker, John R.

1996-12-01

The properties of the log of the admittance in the complex frequency plane lead to an integral representation for one-dimensional magnetotelluric (MT) apparent resistivity and impedance phase similar to that found previously for complex admittance. The inverse problem of finding a one-dimensional model for MT data can then be solved using the same techniques as for complex admittance, with similar results. For instance, the one-dimensional conductivity model that minimizes the χ2 misfit statistic for noisy apparent resistivity and phase is a series of delta functions. One of the most important applications of the delta function solution to the inverse problem for complex admittance has been answering the question of whether or not a given set of measurements is consistent with the modeling assumption of one-dimensionality. The new solution allows this test to be performed directly on standard MT data. Recently, it has been shown that induction data must pass the same one-dimensional consistency test if they correspond to the polarization in which the electric field is perpendicular to the strike of two-dimensional structure. This greatly magnifies the utility of the consistency test. The new solution also allows one to compute the upper and lower bounds permitted on phase or apparent resistivity at any frequency given a collection of MT data. Applications include testing the mutual consistency of apparent resistivity and phase data and placing bounds on missing phase or resistivity data. Examples presented demonstrate detection and correction of equipment and processing problems and verification of compatibility with two-dimensional B-polarization for MT data after impedance tensor decomposition and for continuous electromagnetic profiling data.

Printed wide-slot antenna design with bandwidth and gain enhancement on low-cost substrate.

PubMed

Samsuzzaman, M; Islam, M T; Mandeep, J S; Misran, N

2014-01-01

This paper presents a printed wide-slot antenna design and prototyping on available low-cost polymer resin composite material fed by a microstrip line with a rotated square slot for bandwidth enhancement and defected ground structure for gain enhancement. An I-shaped microstrip line is used to excite the square slot. The rotated square slot is embedded in the middle of the ground plane, and its diagonal points are implanted in the middle of the strip line and ground plane. To increase the gain, four L-shaped slots are etched in the ground plane. The measured results show that the proposed structure retains a wide impedance bandwidth of 88.07%, which is 20% better than the reference antenna. The average gain is also increased, which is about 4.17 dBi with a stable radiation pattern in the entire operating band. Moreover, radiation efficiency, input impedance, current distribution, axial ratio, and parametric studies of S11 for different design parameters are also investigated using the finite element method-based simulation software HFSS.

Printed Wide-Slot Antenna Design with Bandwidth and Gain Enhancement on Low-Cost Substrate

PubMed Central

Samsuzzaman, M.; Islam, M. T.; Mandeep, J. S.; Misran, N.

2014-01-01

This paper presents a printed wide-slot antenna design and prototyping on available low-cost polymer resin composite material fed by a microstrip line with a rotated square slot for bandwidth enhancement and defected ground structure for gain enhancement. An I-shaped microstrip line is used to excite the square slot. The rotated square slot is embedded in the middle of the ground plane, and its diagonal points are implanted in the middle of the strip line and ground plane. To increase the gain, four L-shaped slots are etched in the ground plane. The measured results show that the proposed structure retains a wide impedance bandwidth of 88.07%, which is 20% better than the reference antenna. The average gain is also increased, which is about 4.17 dBi with a stable radiation pattern in the entire operating band. Moreover, radiation efficiency, input impedance, current distribution, axial ratio, and parametric studies of S11 for different design parameters are also investigated using the finite element method-based simulation software HFSS. PMID:24696661

Computer Program for Thin Wire Antenna over a Perfectly Conducting Ground Plane. [using Galerkins method and sinusoidal bases

NASA Technical Reports Server (NTRS)

Richmond, J. H.

1974-01-01

A computer program is presented for a thin-wire antenna over a perfect ground plane. The analysis is performed in the frequency domain, and the exterior medium is free space. The antenna may have finite conductivity and lumped loads. The output data includes the current distribution, impedance, radiation efficiency, and gain. The program uses sinusoidal bases and Galerkin's method.

Transmission-line model to design matching stage for light coupling into two-dimensional photonic crystals.

PubMed

Miri, Mehdi; Khavasi, Amin; Mehrany, Khashayar; Rashidian, Bizhan

2010-01-15

The transmission-line analogy of the planar electromagnetic reflection problem is exploited to obtain a transmission-line model that can be used to design effective, robust, and wideband interference-based matching stages. The proposed model based on a new definition for a scalar impedance is obtained by using the reflection coefficient of the zeroth-order diffracted plane wave outside the photonic crystal. It is shown to be accurate for in-band applications, where the normalized frequency is low enough to ensure that the zeroth-order diffracted plane wave is the most important factor in determining the overall reflection. The frequency limitation of employing the proposed approach is explored, highly dispersive photonic crystals are considered, and wideband matching stages based on binomial impedance transformers are designed to work at the first two photonic bands.

Electrical impedance tomography in 3D using two electrode planes: characterization and evaluation.

PubMed

Wagenaar, Justin; Adler, Andy

2016-06-01

Electrical impedance tomography (EIT) uses body surface electrical stimulation and measurements to create conductivity images; it shows promise as a non-invasive technology to monitor the distribution of lung ventilation. Most applications of EIT have placed electrodes in a 2D ring around the thorax, and thus produced 2D cross-sectional images. These images are unable to distinguish out-of-plane contributions, or to image volumetric effects. Volumetric EIT can be calculated using multiple electrode planes and a 3D reconstruction algorithm. However, while 3D reconstruction algorithms are available, little has been done to understand the performance of 3D EIT in terms of the measurement configurations available. The goal of this paper is to characterize the phantom and in vivo performance of 3D EIT with two electrode planes. First, phantom measurements are used to measure the reconstruction characteristics of seven stimulation and measurement configurations. Measurements were then performed on eight healthy volunteers as a function of body posture, postures, and with various electrode configurations. Phantom results indicate that 3D EIT using two rings of electrodes provides reasonable resolution in the electrode plane but low vertical resolution. For volunteers, functional EIT images are created from inhalation curve features to analyze the effect of posture (standing, sitting, supine and decline) on regional lung behaviour. An ability to detect vertical changes in lung volume distribution was shown for two electrode configurations. Based on tank and volunteer results, we recommend the use of the 'square' stimulation and measurement pattern for two electrode plane EIT.

Effects of finite ground plane on the radiation characteristics of a circular patch antenna

NASA Astrophysics Data System (ADS)

Bhattacharyya, Arun K.

1990-02-01

An analytical technique to determine the effects of finite ground plane on the radiation characteristics of a microstrip antenna is presented. The induced currents on the ground plane and on the upper surface of the patch are determined from the discontinuity of the near field produced by the equivalent magnetic current source on the physical aperture of the patch. The radiated fields contributed by the induced current on the ground plane and the equivalent sources on the physical aperture yield the radiation pattern of the antenna. Radiation patterns of the circular patch with finite ground plane size are computed and compared with the experimental data, and the agreement is found to be good. The radiation pattern, directive gain, and input impedance are found to vary widely with the ground plane size.

An integrated and highly sensitive ultrafast acoustoelectric imaging system for biomedical applications

NASA Astrophysics Data System (ADS)

Berthon, Beatrice; Dansette, Pierre-Marc; Tanter, Mickaël; Pernot, Mathieu; Provost, Jean

2017-07-01

Direct imaging of the electrical activation of the heart is crucial to better understand and diagnose diseases linked to arrhythmias. This work presents an ultrafast acoustoelectric imaging (UAI) system for direct and non-invasive ultrafast mapping of propagating current densities using the acoustoelectric effect. Acoustoelectric imaging is based on the acoustoelectric effect, the modulation of the medium’s electrical impedance by a propagating ultrasonic wave. UAI triggers this effect with plane wave emissions to image current densities. An ultrasound research platform was fitted with electrodes connected to high common-mode rejection ratio amplifiers and sampled by up to 128 independent channels. The sequences developed allow for both real-time display of acoustoelectric maps and long ultrafast acquisition with fast off-line processing. The system was evaluated by injecting controlled currents into a saline pool via copper wire electrodes. Sensitivity to low current and low acoustic pressure were measured independently. Contrast and spatial resolution were measured for varying numbers of plane waves and compared to line per line acoustoelectric imaging with focused beams at equivalent peak pressure. Temporal resolution was assessed by measuring time-varying current densities associated with sinusoidal currents. Complex intensity distributions were also imaged in 3D. Electrical current densities were detected for injected currents as low as 0.56 mA. UAI outperformed conventional focused acoustoelectric imaging in terms of contrast and spatial resolution when using 3 and 13 plane waves or more, respectively. Neighboring sinusoidal currents with opposed phases were accurately imaged and separated. Time-varying currents were mapped and their frequency accurately measured for imaging frame rates up to 500 Hz. Finally, a 3D image of a complex intensity distribution was obtained. The results demonstrated the high sensitivity of the UAI system proposed. The plane wave based approach provides a highly flexible trade-off between frame rate, resolution and contrast. In conclusion, the UAI system shows promise for non-invasive, direct and accurate real-time imaging of electrical activation in vivo.

Optimal one-section and two-section circular sound-absorbing duct liners for plane-wave and monopole sources without flow

NASA Technical Reports Server (NTRS)

Lester, H. C.; Posey, J. W.

1976-01-01

A discrete frequency study is made of the influence of source characteristics on the optimal properties of acoustically lined uniform and two section ducts. Two simplified sources, a plane wave and a monopole, are considered in some detail and over a greater frequency range than has been previously studied. Source and termination impedance effects are given limited examination. An example of a turbomachinery source and three associated source variants is also presented. Optimal liner designs based on modal theory approach the Cremer criterion at low frequencies and the geometric acoustics limit at high frequencies. Over an intermediate frequency range, optimal two section liners produced higher transmission losses than did the uniform configurations. Source distribution effects were found to have a significant effect on optimal liner design, but source and termination impedance effects appear to be relatively unimportant.

Ventilation inhomogeneity in obstructive lung diseases measured by electrical impedance tomography: a simulation study.

PubMed

Schullcke, B; Krueger-Ziolek, S; Gong, B; Jörres, R A; Mueller-Lisse, U; Moeller, K

2017-10-10

Electrical impedance tomography (EIT) has mostly been used in the Intensive Care Unit (ICU) to monitor ventilation distribution but is also promising for the diagnosis in spontaneously breathing patients with obstructive lung diseases. Beside tomographic images, several numerical measures have been proposed to quantitatively assess the lung state. In this study two common measures, the 'Global Inhomogeneity Index' and the 'Coefficient of Variation' were compared regarding their capability to reflect the severity of lung obstruction. A three-dimensional simulation model was used to simulate obstructed lungs, whereby images were reconstructed on a two-dimensional domain. Simulations revealed that minor obstructions are not adequately recognized in the reconstructed images and that obstruction above and below the electrode plane may result in misleading values of inhomogeneity measures. EIT measurements on several electrode planes are necessary to apply these measures in patients with obstructive lung diseases in a promising manner.

Implementation and Validation of an Impedance Eduction Technique

NASA Technical Reports Server (NTRS)

Watson, Willie R.; Jones, Michael G.; Gerhold, Carl H.

2011-01-01

Implementation of a pressure gradient method of impedance eduction in two NASA Langley flow ducts is described. The Grazing Flow Impedance Tube only supports plane-wave sources, while the Curved Duct Test Rig supports sources that contain higher-order modes. Multiple exercises are used to validate this new impedance eduction method. First, synthesized data for a hard wall insert and a conventional liner mounted in the Grazing Flow Impedance Tube are used as input to the two impedance eduction methods, the pressure gradient method and a previously validated wall pressure method. Comparisons between the two results are excellent. Next, data measured in the Grazing Flow Impedance Tube are used as input to both methods. Results from the two methods compare quite favorably for sufficiently low Mach numbers but this comparison degrades at Mach 0.5, especially when the hard wall insert is used. Finally, data measured with a hard wall insert mounted in the Curved Duct Test Rig are used as input to the pressure gradient method. Significant deviation from the known solution is observed, which is believed to be largely due to 3-D effects in this flow duct. Potential solutions to this issue are currently being explored.

Assistive-as-needed strategy for upper-limb robotic systems: A preliminary evaluation of the impedance control architecture

NASA Astrophysics Data System (ADS)

Khairuddin, I. M.; Sidek, S. N.; Yusof, H. Md; Majeed, A. P. P. Abdul; Puzi, A. Ahmad; Mat Rosly, H.

2018-04-01

Rehabilitation is a necessary restoration process of recovering impaired joint motion and muscle strength. Recent trends of rehabilitation have also moved towards providing more participation of the patient in therapy rather than simple passive treatments as it has been demonstrated to be non-trivial in promoting neural plasticity meant to promote motor recovery process. This paper presents an assistive control strategy based on impedance control technique. Dynamic modelling of upper arm is obtained by utilising the Euler-Lagrange formulation. The proportional-derivative (PD), computed torque control (CTC) impedance based framework is applied to examine its effectiveness in performing joint-space control with objectives specified in rehabilitating the elbow joint along the sagittal plane. A feasibility study through simulation was carried out to investigate the efficacy of the proposed controller on acceleration-based impedance model. The results show that impedance controller is more suitable as it allows the cooperative effort of the patient.

Design and Preliminary Evaluation of a Two DOFs Cable-Driven Ankle–Foot Prosthesis with Active Dorsiflexion–Plantarflexion and Inversion–Eversion

PubMed Central

Ficanha, Evandro Maicon; Ribeiro, Guilherme Aramizo; Dallali, Houman; Rastgaar, Mohammad

2016-01-01

This paper describes the design of an ankle–foot robotic prosthesis controllable in the sagittal and frontal planes. The prosthesis was designed to meet the mechanical characteristics of the human ankle including power, range of motion, and weight. To transfer the power from the motors and gearboxes to the ankle–foot mechanism, a Bowden cable system was used. The Bowden cable allows for optimal placement of the motors and gearboxes in order to improve gait biomechanics such as the metabolic energy cost and gait asymmetry during locomotion. Additionally, it allows flexibility in the customization of the device to amputees with different residual limb sizes. To control the prosthesis, impedance controllers in both sagittal and frontal planes were developed. The impedance controllers used torque feedback from strain gages installed on the foot. Preliminary evaluation was performed to verify the capability of the prosthesis to track the kinematics of the human ankle in two degrees of freedom (DOFs), the mechanical efficiency of the Bowden cable transmission, and the ability of the prosthesis to modulate the impedance of the ankle. Moreover, the system was characterized by describing the relationship between the stiffness of the impedance controllers to the actual stiffness of the ankle. Efficiency estimation showed 85.4% efficiency in the Bowden cable transmission. The prosthesis was capable of properly mimicking human ankle kinematics and changing its mechanical impedance in two DOFs in real time with a range of stiffness sufficient for normal human walking. In dorsiflexion–plantarflexion (DP), the stiffness ranged from 0 to 236 Nm/rad and in inversion–eversion (IE), the stiffness ranged from 1 to 33 Nm/rad. PMID:27200342

Novel high-gain, improved-bandwidth, finned-ladder V-band Traveling-Wave Tube slow-wave circuit design

NASA Technical Reports Server (NTRS)

Kory, Carol L.; Wilson, Jeffrey D.

1994-01-01

The V-band frequency range of 59-64 GHz is a region of the millimeter-wave spectrum that has been designated for inter-satellite communications. As a first effort to develop a high-efficiency V-band Traveling-Wave Tube (TWT), variations on a ring-plane slow-wave circuit were computationally investigated to develop an alternative to the more conventional ferruled coupled-cavity circuit. The ring-plane circuit was chosen because of its high interaction impedance, large beam aperture, and excellent thermal dissipation properties. Despite these advantages, however, low bandwidth and high voltage requirements have, until now, prevented its acceptance outside the laboratory. In this paper, the three-dimensional electrodynamic simulation code MAFIA (solution of MAxwell's Equation by the Finite-Integration-Algorithm) is used to investigate methods of increasing the bandwidth and lowering the operating voltage of the ring-plane circuit. Calculations of frequency-phase dispersion, beam on-axis interaction impedance, attenuation and small-signal gain per wavelength were performed for various geometric variations and loading distributions of the ring-plane TWT slow-wave circuit. Based on the results of the variations, a circuit termed the finned-ladder TWT slow-wave circuit was designed and is compared here to the scaled prototype ring-plane and a conventional ferruled coupled-cavity TWT circuit over the V-band frequency range. The simulation results indicate that this circuit has a much higher gain, significantly wider bandwidth, and a much lower voltage requirement than the scaled ring-plane prototype circuit, while retaining its excellent thermal dissipation properties. The finned-ladder circuit has a much larger small-signal gain per wavelength than the ferruled coupled-cavity circuit, but with a moderate sacrifice in bandwidth.

High-Resolution Large-Field-of-View Ultrasound Breast Imager

DTIC Science & Technology

2012-06-01

plane waves all having the same wave vector magnitude 0k but propagating in different directions . This observation forms the mathematical basis of the...origin of the object Fourier space and is oriented opposite the propagation direction of the probing plane wave field. Moreover, the 43 radius of...in water. Each element was electrically tuned to match to the 50-Ohm impedance of an RF Amplifier powered by a 4.0 MHz electrical signal from a

Structural and electrical properties of LiCo3/5Cu2/5VO4 ceramics

NASA Astrophysics Data System (ADS)

Ram, Moti

2010-05-01

The LiCo3/5Cu2/5VO4 compound is prepared by a solution-based chemical method and characterized by the techniques of X-ray diffraction, scanning electron microscopy and complex impedance spectroscopy. The X-ray diffraction study shows an orthorhombic unit cell structure of the material with lattice parameters a=13.8263 (30) Å, b=8.7051 (30) Å and c=3.1127 (30) Å. The nature of scanning electron micrographs of a sintered pellet of the material reveals that grains of unequal sizes (˜0.2-3 μm) present an average grain size with a polydisperse distribution on the surface of the sample. Complex plane diagrams indicate grain interior and grain boundary contributions to the electrical response in the material. The electrical conductivity study reveals that electrical conduction in the material is a thermally activated process. The frequency dependence of the a.c. conductivity obeys Jonscher’s universal law.

Transfer impedance measurements of the space shuttle Solid Rocket Motor (SRM) joints, wire meshes and a carbon graphite motor case

NASA Technical Reports Server (NTRS)

Papazian, Peter B.; Perala, Rodney A.; Curry, John D.; Lankford, Alan B.; Keller, J. David

1988-01-01

Using three different current injection methods and a simple voltage probe, transfer impedances for Solid Rocket Motor (SRM) joints, wire meshes, aluminum foil, Thorstrand and a graphite composite motor case were measured. In all cases, the surface current distribution for the particular current injection device was calculated analytically or by finite difference methods. The results of these calculations were used to generate a geometric factor which was the ratio of total injected current to surface current density. The results were validated in several ways. For wire mesh measurements, results showed good agreement with calculated results for a 14 by 18 Al screen. SRM joint impedances were independently verified. The filiment wound case measurement results were validated only to the extent that their curve shape agrees with the expected form of transfer impedance for a homogeneous slab excited by a plane wave source.

Investigation of an Anomaly Observed in Impedance Eduction Techniques

NASA Technical Reports Server (NTRS)

Watson, W. R.; Jones, M. G.; Parrott, T. L.

2008-01-01

An intensive investigation into the cause of anomalous behavior commonly observed in impedance eduction techniques is performed. The investigation consists of grid refinement studies, detailed evaluation of results at and near anti-resonance frequencies, comparisons of different model results with synthesized and measured data, assessment or optimization techniques, and evaluation or boundary condition effects. Results show that the root cause of the anomalous behavior is the sensitivity of the educed impedance to small errors in the measured termination resistance at frequencies near anti-resonance or cut-on of a higher-order mode. Evidence is presented to show that the common usage of an anechoic, plane wave termination boundary condition in ducts where the "true" termination is reflective may act as a trigger for these anomalies. Replacing the exit impedance boundary condition by an exit pressure condition is shown to reduce the anomalous results.

Antenna Performance Influenced by the Finite Extent and Conductivity of Ground Planes: A Collection of Reprints

DTIC Science & Technology

1990-09-01

FORMULATION OF PROBLEM denoted by AZ and is given by With reference to a cylindrical polar coordinate 17-Z-Zs.- P, 1." * ()d. (4a) system (p,O,Z) the...without limit as a approaches zero. This formulation is not actually valid in this limiting case since one terminal of the generator would then be connected...current. APPE.IXx I Formulation of the input impedance. An expression is here for- mulated for the input impedance at the terminals of an antenna

Control of Electromagnetic Scattering by Antenna Impedance Loading

DTIC Science & Technology

1974-07-01

system and whose profile in a plane perpendicular to the z axis is the closed curve c. Let n be an outward unit vector to c and let t be a unit... vector in the tangential direction, such that t, n and z form a right-hand system. Then, on the surface, the impedance boundary con- dition is...and is given by J Mn x z)H* where n is the unit outward normal vector to the surface. Using the GTD solution for the total magnetic field, the

Transition section for acoustic waveguides

DOEpatents

Karplus, H.H.B.

1975-10-28

A means of facilitating the transmission of acoustic waves with minimal reflection between two regions having different specific acoustic impedances is described comprising a region exhibiting a constant product of cross-sectional area and specific acoustic impedance at each cross-sectional plane along the axis of the transition region. A variety of structures that exhibit this feature is disclosed, the preferred embodiment comprising a nested structure of doubly reentrant cones. This structure is useful for monitoring the operation of nuclear reactors in which random acoustic signals are generated in the course of operation.

Improved Capacitive Liquid Sensor

NASA Technical Reports Server (NTRS)

Waldman, Francis A.

1992-01-01

Improved capacitive sensor used to detect presence and/or measure thickness of layer of liquid. Electrical impedance or admittance of sensor measured at prescribed frequency, and thickness of liquid inferred from predetermined theoretical or experimental relationship between impedance and thickness. Sensor is basically a three-terminal device. Features interdigitated driving and sensing electrodes and peripheral coplanar ground electrode that reduces parasitic effects. Patent-pending because first to utilize ground plane as "shunting" electrode. System less expensive than infrared, microwave, or refractive-index systems. Sensor successfully evaluated in commercial production plants to characterize emulsions, slurries, and solutions.

Performance characteristics of plane-wall venturi-like reverse flow diverters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, G.V.; Counce, R.M.

1984-02-01

The results of an analytical and experimental study of plane-wall venturi-like reverse flow diverters (RFD) are presented. In general, the flow characteristics of the RFD are reasonably well predicted by the mathematical model of the RFD, although a divergence between theory and data is observed for the output characteristics in the reverse flow mode as the output impedance is reduced. Overall, the performance of these devices indicates their usefulness in fluid control and fluid power systems, such as displacement pumping systems.

Performance characteristics of plane-wall venturi-like reverse flow diverters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, G.V.; Counce, R.M.

1982-01-01

The results of an analytical and experimental study of plane-wall venturi-like reverse flow diverters (RFD) are presented. In general, the flow characteristics of the RFD are reasonably well predicted by the mathematical model of the RFD, although a divergence between theory and data is observed for the output characteristics in the reverse flow mode as the output impedance is reduced. Overall, the performance of these devices indicates their usefulness in fluid control and fluid power systems, such as displacement pumping systems.

Impedance Eduction in Large Ducts Containing Higher-Order Modes and Grazing Flow

NASA Technical Reports Server (NTRS)

Watson, Willie R.; Jones, Michael G.

2017-01-01

Impedance eduction test data are acquired in ducts with small and large cross-sectional areas at the NASA Langley Research Center. An improved data acquisition system in the large duct has resulted in increased control of the acoustic energy in source modes and more accurate resolution of higher-order duct modes compared to previous tests. Two impedance eduction methods that take advantage of the improved data acquisition to educe the liner impedance in grazing flow are presented. One method measures the axial propagation constant of a dominant mode in the liner test section (by implementing the Kumarsean and Tufts algorithm) and educes the impedance from an exact analytical expression. The second method solves numerically the convected Helmholtz equation and minimizes an objective function to obtain the liner impedance. The two methods are tested first on data synthesized from an exact mode solution and then on measured data. Results show that when the methods are applied to data acquired in the larger duct with a dominant higher-order mode, the same impedance spectra are educed as that obtained in the small duct where only the plane wave mode propagates. This result holds for each higher-order mode in the large duct provided that the higher-order mode is sufficiently attenuated by the liner.

Liner Optimization Studies Using the Ducted Fan Noise Prediction Code TBIEM3D

NASA Technical Reports Server (NTRS)

Dunn, M. H.; Farassat, F.

1998-01-01

In this paper we demonstrate the usefulness of the ducted fan noise prediction code TBIEM3D as a liner optimization design tool. Boundary conditions on the interior duct wall allow for hard walls or a locally reacting liner with axially segmented, circumferentially uniform impedance. Two liner optimization studies are considered in which farfield noise attenuation due to the presence of a liner is maximized by adjusting the liner impedance. In the first example, the dependence of optimal liner impedance on frequency and liner length is examined. Results show that both the optimal impedance and attenuation levels are significantly influenced by liner length and frequency. In the second example, TBIEM3D is used to compare radiated sound pressure levels between optimal and non-optimal liner cases at conditions designed to simulate take-off. It is shown that significant noise reduction is achieved for most of the sound field by selecting the optimal or near optimal liner impedance. Our results also indicate that there is relatively large region of the impedance plane over which optimal or near optimal liner behavior is attainable. This is an important conclusion for the designer since there are variations in liner characteristics due to manufacturing imprecisions.

Cavity-backed, micro-strip dipole antenna array

NASA Technical Reports Server (NTRS)

Ellis, H., Jr. (Inventor)

1981-01-01

A flush-mounted antenna assembly includes a generally rectangular, conductive, box structure open along one face to form a cavity. Within the cavity a pair of mutually orthogonal dielectric plane surfaces in an "egg crate" arrangement are mounted normal to the plane of the open face, each diagonally within the cavity. Each dielectric plane supports a pair of printed circuit dipoles typically each fed from the opposite side of the dielectric plane by a printed "cone-shaped" feed line trace which also serve as an impedance matching device and functions as a balun connected from an unbalanced strip line external feed. The open face of the conductive cavity can be flush mounted with a randome thereover, the assembly thereby being flush with the skin of a aircraft or space vehicle.

Cavity-backed, micro-strip dipole antenna array

NASA Astrophysics Data System (ADS)

Ellis, H., Jr.

1981-09-01

A flush-mounted antenna assembly includes a generally rectangular, conductive, box structure open along one face to form a cavity. Within the cavity a pair of mutually orthogonal dielectric plane surfaces in an "egg crate" arrangement are mounted normal to the plane of the open face, each diagonally within the cavity. Each dielectric plane supports a pair of printed circuit dipoles typically each fed from the opposite side of the dielectric plane by a printed "cone-shaped" feed line trace which also serve as an impedance matching device and functions as a balun connected from an unbalanced strip line external feed. The open face of the conductive cavity can be flush mounted with a randome thereover, the assembly thereby being flush with the skin of a aircraft or space vehicle.

MWM-Array Characterization of Mechanical Damage and Corrosion

DOT National Transportation Integrated Search

2011-02-09

The MWM-Array is an inductive sensor that operates like a transformer in a plane. The MWMArray is based on the original MWM(R) (Meandering Winding Magnetometer) developed at MIT in the 1980s. A rapid multivariate inverse method converts impedance dat...

Accelerated Time-Domain Modeling of Electromagnetic Pulse Excitation of Finite-Length Dissipative Conductors over a Ground Plane via Function Fitting and Recursive Convolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Campione, Salvatore; Warne, Larry K.; Sainath, Kamalesh

In this report we overview the fundamental concepts for a pair of techniques which together greatly hasten computational predictions of electromagnetic pulse (EMP) excitation of finite-length dissipative conductors over a ground plane. In a time- domain, transmission line (TL) model implementation, predictions are computationally bottlenecked time-wise, either for late-time predictions (about 100ns-10000ns range) or predictions concerning EMP excitation of long TLs (order of kilometers or more ). This is because the method requires a temporal convolution to account for the losses in the ground. Addressing this to facilitate practical simulation of EMP excitation of TLs, we first apply a techniquemore » to extract an (approximate) complex exponential function basis-fit to the ground/Earth's impedance function, followed by incorporating this into a recursion-based convolution acceleration technique. Because the recursion-based method only requires the evaluation of the most recent voltage history data (versus the entire history in a "brute-force" convolution evaluation), we achieve necessary time speed- ups across a variety of TL/Earth geometry/material scenarios. Intentionally Left Blank« less

Distributed Antenna-Coupled TES for FIR Detectors Arrays

NASA Technical Reports Server (NTRS)

Day, Peter K.; Leduc, Henry G.; Dowell, C. Darren; Lee, Richard A.; Zmuidzinas, Jonas

2007-01-01

We describe a new architecture for a superconducting detector for the submillimeter and far-infrared. This detector uses a distributed hot-electron transition edge sensor (TES) to collect the power from a focal-plane-filling slot antenna array. The sensors lay directly across the slots of the antenna and match the antenna impedance of about 30 ohms. Each pixel contains many sensors that are wired in parallel as a single distributed TES, which results in a low impedance that readily matches to a multiplexed SQUID readout These detectors are inherently polarization sensitive, with very low cross-polarization response, but can also be configured to sum both polarizations. The dual-polarization design can have a bandwidth of 50The use of electron-phonon decoupling eliminates the need for micro-machining, making the focal plane much easier to fabricate than with absorber-coupled, mechanically isolated pixels. We discuss applications of these detectors and a hybridization scheme compatible with arrays of tens of thousands of pixels.

Cross-plane coherent acoustic phonons in two-dimensional organic-inorganic hybrid perovskites.

PubMed

Guo, Peijun; Stoumpos, Constantinos C; Mao, Lingling; Sadasivam, Sridhar; Ketterson, John B; Darancet, Pierre; Kanatzidis, Mercouri G; Schaller, Richard D

2018-05-22

Two-dimensional Ruddlesden-Popper organic-inorganic hybrid layered perovskites (2D RPs) are solution-grown semiconductors with prospective applications in next-generation optoelectronics. The heat-carrying, low-energy acoustic phonons, which are important for heat management of 2D RP-based devices, have remained unexplored. Here we report on the generation and propagation of coherent longitudinal acoustic phonons along the cross-plane direction of 2D RPs, following separate characterizations of below-bandgap refractive indices. Through experiments on single crystals of systematically varied perovskite layer thickness, we demonstrate significant reduction in both group velocity and propagation length of acoustic phonons in 2D RPs as compared to the three-dimensional methylammonium lead iodide counterpart. As borne out by a minimal coarse-grained model, these vibrational properties arise from a large acoustic impedance mismatch between the alternating layers of perovskite sheets and bulky organic cations. Our results inform on thermal transport in highly impedance-mismatched crystal sub-lattices and provide insights towards design of materials that exhibit highly anisotropic thermal dissipation properties.

Evaluation of Grounding Impedance of a Complex Lightning Protective System Using Earth Ground Clamp Measurements and ATP Modeling

NASA Technical Reports Server (NTRS)

Mata, Carlos T.; Rakov, V. A.; Mata, Angel G.

2010-01-01

A new Lightning Protection System (LPS) was designed and built at Launch Complex 39B (LC39B), at the Kennedy Space Center (KSC), Florida, which consists of a catenary wire system (at a height of about 181 meters above ground level) supported by three insulators installed atop three towers in a triangular configuration. A total of nine downconductors (each about 250 meters long, on average) are connected to the catenary wire system. Each of the nine downconductors is connected to a 7.62-meter radius circular counterpoise conductor with six equally spaced 6-meter long vertical grounding rods. Grounding requirements at LC39B call for all underground and above ground metallic piping, enclosures, raceways, and cable trays, within 7.62 meters of the counterpoise, to be bounded to the counterpoise, which results in a complex interconnected grounding system, given the many metallic piping, raceways, and cable trays that run in multiple direction around LC39B. The complexity of this grounding system makes the fall of potential method, which uses multiple metallic rods or stakes, unsuitable for measuring the grounding impedances of the downconductors. To calculate the downconductors grounding impedance, an Earth Ground Clamp (a stakeless grounding resistance measuring device) and a LPS Alternative Transient Program (ATP) model are used. The Earth Ground Clamp is used to measure the loop impedance plus the grounding impedance of each downconductor and the ATP model is used to calculate the loop impedance of each downconductor circuit. The grounding impedance of the downconductors is then calculated by subtracting the ATP calculated loop impedances from the Earth Ground Clamp measurements.

Evaluation of Wall Boundary Conditions for Impedance Eduction Using a Dual-Source Method

NASA Technical Reports Server (NTRS)

Watson, W. R.; Jones, M. G.

2012-01-01

The accuracy of the Ingard-Myers boundary condition and a recently proposed modified Ingard-Myers boundary condition is evaluated for use in impedance eduction under the assumption of uniform mean flow. The evaluation is performed at three centerline Mach numbers, using data acquired in a grazing flow impedance tube, using both upstream and downstream propagating sound sources, and on a database of test liners for which the expected behavior of the impedance spectra is known. The test liners are a hard-wall insert consisting of 12.6 mm thick aluminum, a linear liner without a facesheet consisting of a number of small diameter but long cylindrical channels embedded in a ceramic material, and two conventional nonlinear liners consisting of a perforated facesheet bonded to a honeycomb core. The study is restricted to a frequency range for which only plane waves are cut on in the hard-wall sections of the flow impedance tube. The metrics used to evaluate each boundary condition are 1) how well it educes the same impedance for upstream and downstream propagating sources, and 2) how well it predicts the expected behavior of the impedance spectra over the Mach number range. The primary conclusions of the study are that the same impedance is educed for upstream and downstream propagating sources except at the highest Mach number, that an effective impedance based on both the upstream and downstream measurements is more accurate than an impedance based on the upstream or downstream data alone, and that the Ingard-Myers boundary condition with an effective impedance produces results similar to that achieved with the modified Ingard-Myers boundary condition.

Generation and detection of broadband airborne ultrasound with cellular polymer ferroelectrets

NASA Astrophysics Data System (ADS)

Dansachmüller, Mario; Minev, Ivan; Bartu, Petr; Graz, Ingrid; Arnold, Nikita; Bauer, Siegfried

2007-11-01

Cellular polypropylene ferroelectrets are useful for broadband airborne ultrasound generation and detection up to the fundamental thickness extension resonance. The authors show that the coupling of ferroelectrets to air alters the electromechanical resonance of the foam. In an acoustical cavity, Fabry-Perot resonances are obtained, which is in excellent agreement with the plane wave model calculations. For material assessment in airborne ultrasound applications, a figure of merit is used based on the electromechanical coupling factor and acoustical impedance of the material. The good coupling of ferroelectrets to gases results from the small acoustical impedance of the material.

Locating damage using integrated global-local approach with wireless sensing system and single-chip impedance measurement device.

PubMed

Lin, Tzu-Hsuan; Lu, Yung-Chi; Hung, Shih-Lin

2014-01-01

This study developed an integrated global-local approach for locating damage on building structures. A damage detection approach with a novel embedded frequency response function damage index (NEFDI) was proposed and embedded in the Imote2.NET-based wireless structural health monitoring (SHM) system to locate global damage. Local damage is then identified using an electromechanical impedance- (EMI-) based damage detection method. The electromechanical impedance was measured using a single-chip impedance measurement device which has the advantages of small size, low cost, and portability. The feasibility of the proposed damage detection scheme was studied with reference to a numerical example of a six-storey shear plane frame structure and a small-scale experimental steel frame. Numerical and experimental analysis using the integrated global-local SHM approach reveals that, after NEFDI indicates the approximate location of a damaged area, the EMI-based damage detection approach can then identify the detailed damage location in the structure of the building.

Analysis of an infinite array of rectangular microstrip patches with idealized probe feeds

NASA Technical Reports Server (NTRS)

Pozar, D. M.; Schaubert, D. H.

1984-01-01

A solution is presented to the problem of an infinite array of microstrip patches fed by idealized current probes. The input reflection coefficient is calculated versus scan angle in an arbitrary scan plane, and the effects of substrate parameters and grid spacing are considered. It is pointed out that even when a Galerkin method is used the impedance matrix is not symmetric due to phasing through a unit cell, as required for scanning. The mechanism by which scan blindness can occur is discussed. Measurement results are presented for the reflection coefficient magnitude variation with angle for E-plane, H-plane, and D-plane scans, for various substrate parameters. Measured results from waveguide simulators are also presented, and the scan blindness phenomenon is observed and discussed in terms of forced surface waves and a modified grating lobe diagram.

WMSA for wireless communication applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vats, Monika; Agarwal, Alok, E-mail: alokagarwal26@yahoo.com; Kumar, Ravindra

2016-03-09

Modified rectangular compact microstrip patch antenna having finite ground plane is proposed in this paper. Wideband Microstrip Antenna (WMSA) is achieved by corner cut and inserting air gaps inside the edges of the radiating patch having finite ground plane. The obtained impedance bandwidth for 10 dB return loss for the operating frequency f{sub 0} = 2.09 GHz is 28.7 % (600 MHz), which is very high as compared to the bandwidth obtained for the conventional microstrip antenna. Compactness with wide bandwidth of this antenna is practically useful for the wireless communication systems.

Mechanical Impedance of the Non-loaded Lower Leg with Relaxed Muscles in the Transverse Plane

PubMed Central

Ficanha, Evandro Maicon; Ribeiro, Guilherme Aramizo; Rastgaar, Mohammad

2015-01-01

This paper describes the protocols and results of the experiments for the estimation of the mechanical impedance of the humans’ lower leg in the External–Internal direction in the transverse plane under non-load bearing condition and with relaxed muscles. The objectives of the estimation of the lower leg’s mechanical impedance are to facilitate the design of passive and active prostheses with mechanical characteristics similar to the humans’ lower leg, and to define a reference that can be compared to the values from the patients suffering from spasticity. The experiments were performed with 10 unimpaired male subjects using a lower extremity rehabilitation robot (Anklebot, Interactive Motion Technologies, Inc.) capable of applying torque perturbations to the foot. The subjects were in a seated position, and the Anklebot recorded the applied torques and the resulting angular movement of the lower leg. In this configuration, the recorded dynamics are due mainly to the rotations of the ankle’s talocrural and the subtalar joints, and any contribution of the tibiofibular joints and knee joint. The dynamic mechanical impedance of the lower leg was estimated in the frequency domain with an average coherence of 0.92 within the frequency range of 0–30 Hz, showing a linear correlation between the displacement and the torques within this frequency range under the conditions of the experiment. The mean magnitude of the stiffness of the lower leg (the impedance magnitude averaged in the range of 0–1 Hz) was determined as 4.9 ± 0.74 Nm/rad. The direct estimation of the quasi-static stiffness of the lower leg results in the mean value of 5.8 ± 0.81 Nm/rad. An analysis of variance shows that the estimated values for the stiffness from the two experiments are not statistically different. PMID:26697424

Calculating the Lightning Protection System Downconductors' Grounding Resistance at Launch Complex 39B, Kennedy Space Center

NASA Technical Reports Server (NTRS)

Mata, Carlos T.; Mata, Angel G.

2012-01-01

A new Lightning Protection System (LPS) was designed and built at Launch Complex 39B (LC39B), at the Kennedy Space Center (KSC), Florida, which consists of a catenary wire system (at a height of about 181 meters above ground level) supported by three insulators installed atop three towers in a triangular configuration. Nine downconductors (each about 250 meters long) are connected to the catenary wire system. Each downconductor is connected to a 7.62-meter-radius circular counterpoise conductor with six equally spaced, 6-meter-long vertical grounding rods. Grounding requirements at LC39B call for all underground and aboveground metallic piping, enclosures, raceways, and cable trays, within 7.62 meters of the counterpoise, to be bonded to the counterpoise, which results in a complex interconnected grounding system, given the many metallic piping, raceways, and cable trays that run in multiple directions around LC39B. The complexity of this grounding system makes the fall-of-potential method, which uses multiple metallic rods or stakes, unsuitable for measuring the grounding impedances of the downconductors. To calculate the grounding impedance of the downconductors, an Earth Ground Clamp (EGC) (a stakeless device for measuring grounding impedance) and an Alternative Transient Program (ATP) model of the LPS are used. The EGC is used to measure the loop impedance plus the grounding impedance of each downconductor, and the ATP model is used to calculate the loop impedance of each downconductor circuit. The grounding resistance of the downconductors is then calculated by subtracting the ATP calculated loop impedances from the EGC measurements.

Identification of fluids and an interface between fluids

DOEpatents

Lee, D.O.; Wayland, J.R. Jr.

1988-03-10

Complex impedance measured over a predefined frequency range is used to determine the identity of different oils in a column. The location of an interface between the oils is determined from the percent frequency effects of the complex impedance measured across the interface. 4 figs.

Complex numbers in chemometrics: examples from multivariate impedance measurements on lipid monolayers.

PubMed

Geladi, Paul; Nelson, Andrew; Lindholm-Sethson, Britta

2007-07-09

Electrical impedance gives multivariate complex number data as results. Two examples of multivariate electrical impedance data measured on lipid monolayers in different solutions give rise to matrices (16x50 and 38x50) of complex numbers. Multivariate data analysis by principal component analysis (PCA) or singular value decomposition (SVD) can be used for complex data and the necessary equations are given. The scores and loadings obtained are vectors of complex numbers. It is shown that the complex number PCA and SVD are better at concentrating information in a few components than the naïve juxtaposition method and that Argand diagrams can replace score and loading plots. Different concentrations of Magainin and Gramicidin A give different responses and also the role of the electrolyte medium can be studied. An interaction of Gramicidin A in the solution with the monolayer over time can be observed.

Hardware Specific Integration Strategy for Impedance-Based Structural Health Monitoring of Aerospace Systems

NASA Technical Reports Server (NTRS)

Owen, Robert B.; Gyekenyesi, Andrew L.; Inman, Daniel J.; Ha, Dong S.

2011-01-01

The Integrated Vehicle Health Management (IVHM) Project, sponsored by NASA's Aeronautics Research Mission Directorate, is conducting research to advance the state of highly integrated and complex flight-critical health management technologies and systems. An effective IVHM system requires Structural Health Monitoring (SHM). The impedance method is one such SHM technique for detection and monitoring complex structures for damage. This position paper on the impedance method presents the current state of the art, future directions, applications and possible flight test demonstrations.

Construction and Testing of Broadband High Impedance Ground Planes (HIGPS) for Surface Mount Antennas

DTIC Science & Technology

2008-03-01

Conductor PMC: Perfect Magnetic Conductor RF: Radio Frequency RH: Right-handed SNG : Single Negative TACAN: Tactical Air Navigation UAV: Unmanned Aerial...negative ( SNG ) and double-negative (DNG) materials, and their fascinating properties have driven the interest in MTMs (Engheta and Ziolkowski, 2006

Study of electrical properties of Sc doped BaFe12O19 ceramic using dielectric, impedance, modulus spectroscopy and AC conductivity

NASA Astrophysics Data System (ADS)

Gupta, Surbhi; Deshpande, S. K.; Sathe, V. G.; Siruguri, V.

2018-04-01

We present dielectric, complex impedance, modulus spectroscopy and AC conductivity studies of the compound BaFe10Sc2O19 as a function of temperature and frequency to understand the conduction mechanism. The variation in complex dielectric constant with frequency and temperature were analyzed on the basis of Maxwell-Wagner-Koop's theory and charge hopping between ferrous and ferric ions. The complex impedance spectroscopy study shows only grain contribution whereas complex modulus plot shows two semicircular arcs which indicate both grain and grain boundary contributions in conduction mechanism. AC conductivity has also been evaluated which follows the Jonscher's law. The activation energy calculated from temperature dependence of DC conductivity comes out to be Ea˜ 0.31eV.

Practical aspects of NMR signal assignment in larger and challenging proteins

PubMed Central

Frueh, Dominique P.

2014-01-01

NMR has matured into a technique routinely employed for studying proteins in near physiological conditions. However, applications to larger proteins are impeded by the complexity of the various correlation maps necessary to assign NMR signals. This article reviews the data analysis techniques traditionally employed for resonance assignment and describes alternative protocols necessary for overcoming challenges in large protein spectra. In particular, simultaneous analysis of multiple spectra may help overcome ambiguities or may reveal correlations in an indirect manner. Similarly, visualization of orthogonal planes in a multidimensional spectrum can provide alternative assignment procedures. We describe examples of such strategies for assignment of backbone, methyl, and nOe resonances. We describe experimental aspects of data acquisition for the related experiments and provide guidelines for preliminary studies. Focus is placed on large folded monomeric proteins and examples are provided for 37, 48, 53, and 81 kDa proteins. PMID:24534088

Modal Control of a Satellite in Orbit about L3.

DTIC Science & Technology

1980-12-01

the right- half of the complex plane , are removed via the controller moving the unstable roots from the right- half to the left- half of the ...complex plane . Simultaneously, the other system roots remain in their original locations in the complex plane . Since the Poincare exponents of Hamiltonian... half - plane , the conjugate root in the left- half -

Graphical Representation of Complex Solutions of the Quadratic Equation in the "xy" Plane

ERIC Educational Resources Information Center

McDonald, Todd

2006-01-01

This paper presents a visual representation of complex solutions of quadratic equations in the xy plane. Rather than moving to the complex plane, students are able to experience a geometric interpretation of the solutions in the xy plane. I am also working on these types of representations with higher order polynomials with some success.

Argand-plane vorticity singularities in complex scalar optical fields: an experimental study using optical speckle.

PubMed

Rothschild, Freda; Bishop, Alexis I; Kitchen, Marcus J; Paganin, David M

2014-03-24

The Cornu spiral is, in essence, the image resulting from an Argand-plane map associated with monochromatic complex scalar plane waves diffracting from an infinite edge. Argand-plane maps can be useful in the analysis of more general optical fields. We experimentally study particular features of Argand-plane mappings known as "vorticity singularities" that are associated with mapping continuous single-valued complex scalar speckle fields to the Argand plane. Vorticity singularities possess a hierarchy of Argand-plane catastrophes including the fold, cusp and elliptic umbilic. We also confirm their connection to vortices in two-dimensional complex scalar waves. The study of vorticity singularities may also have implications for higher-dimensional fields such as coherence functions and multi-component fields such as vector and spinor fields.

Energy absorption due to spatial resonance of Alfven waves at continuum tip

NASA Astrophysics Data System (ADS)

Chen, Eugene; Berk, Herb; Breizman, Boris; Zheng, Linjin

2011-10-01

We investigate the response of tokamak plasma to an external driving source. An impedance-like function depending on the driving frequency that is growing at a small rate, is calculated and interpreted with different source profiles. Special attention is devoted to the case where driving frequency approaches that of the TAE continuum tip. The calculation can be applied to the estimation of TAE damping rate by analytically continuing the inverse of the impedance function to the lower half plane. The root of the analytic continuation corresponds to the existence of a quasi-mode, from which the damping rate can be found.

Micro-reaction chamber electrodes for neural stimulation and recording.

PubMed

Shanmugasundaram, Balaji; Gluckman, Bruce J

2011-01-01

Biocompatible electrodes with smaller geometric area are preferred to improve the selectivity of the neural recording and stimulation applications. We introduce the concept of a micro-reaction chamber (μRC) in which a volume within the electrode back plane is used to confine and sequester the electrochemical reactions used for charge passage. The URC electrode design helps decrease impedance and improves the charge storage capacity without altering the geometry of the active site. Here we demonstrate that μRC electrodes fabricated from 50 μm diameter microwire have significantly improved charge storage capacity and lowered impedance at physiologically relevant frequencies in phosphate buffered saline solution compared with other designs.

Comparison of a Convected Helmholtz and Euler Model for Impedance Eduction in Flow

NASA Technical Reports Server (NTRS)

Watson, Willie R.; Jones, Michael G.

2006-01-01

Impedances educed from a well-tested convected Helmholtz model are compared to that of a recently developed linearized Euler model using two ceramic test liners under the assumed conditions or uniform flow and a plane wave source. The convected Helmholtz model is restricted to uniform mean flow whereas the linearized Euler model can account for the effect or the shear layer. Test data to educe the impedance is acquired from measurements obtained in the NASA Langley Research Center Grazing Incidence Tube for mean flow Mach numbers ranging from 0.0 to 0.5 and source frequencies ranging from 0.5 kHz to 3.0 kHz. The unknown impedance of the liner b educed by judiciously chooingth e impedance via an optimization method to match the measured acoustic pressure on the wall opposite the test liner. Results are presented on four spatial grids using three different optimization methods (contour deformation, Davidon-Fletcher Powell, and the Genetic Algorithm). All three optimization methods converge to the same impedance when used with the same model and to nearly identical impedances when used on different models. h anomaly was observed only at 0.5 kHz for high mean flow speeds. The anomaly is likely due to the use of measured data in a flow regime where shear layer effects are important but are neglected in the math models. Consistency between the impedances educed using the two models provides confidence that the linearized Euler model is ready For application to more realistic flows, such as those containing shear layers.

Differential InP HEMT MMIC Amplifiers Embedded in Waveguides

NASA Technical Reports Server (NTRS)

Kangaslahti, Pekka; Schlecht, Erich; Samoska, Lorene

2009-01-01

Monolithic microwave integrated-circuit (MMIC) amplifiers of a type now being developed for operation at frequencies of hundreds of gigahertz contain InP high-electron-mobility transistors (HEMTs) in a differential configuration. The differential configuration makes it possible to obtain gains greater than those of amplifiers having the single-ended configuration. To reduce losses associated with packaging, the MMIC chips are designed integrally with, and embedded in, waveguide packages, with the additional benefit that the packages are compact enough to fit into phased transmitting and/or receiving antenna arrays. Differential configurations (which are inherently balanced) have been used to extend the upper limits of operating frequencies of complementary metal oxide/semiconductor (CMOS) amplifiers to the microwave range but, until now, have not been applied in millimeter- wave amplifier circuits. Baluns have traditionally been used to transform from single-ended to balanced configurations, but baluns tend to be lossy. Instead of baluns, finlines are used to effect this transformation in the present line of development. Finlines have been used extensively to drive millimeter- wave mixers in balanced configurations. In the present extension of the finline balancing concept, finline transitions are integrated onto the affected MMICs (see figure). The differential configuration creates a virtual ground within each pair of InP HEMT gate fingers, eliminating the need for inductive vias to ground. Elimination of these vias greatly reduces parasitic components of current and the associated losses within an amplifier, thereby enabling more nearly complete utilization of the full performance of each transistor. The differential configuration offers the additional benefit of multiplying (relative to the single-ended configuration) the input and output impedances of each transistor by a factor of four, so that it is possible to use large transistors that would otherwise have prohibitively low impedances. Yet another advantage afforded by the virtual ground of the differential configuration is elimination of the need for a ground plane and, hence, elimination of the need for back-side metallization of the MMIC chip. In turn, elimination of the back-side metallization simplifies fabrication, reduces parasitic capacitances, and enables mounting of the MMIC in the electric-field plane ("E-plane") of a waveguide. E-plane mounting is consistent with (and essential for the utility of) the finline configuration, in which transmission lines lie on a dielectric sheet in the middle of a broad side of the waveguide. E-plane mounting offers a combination of low loss and ease of assembly because no millimeter-wave wire bonds or transition substrates are required. Moreover, because there is no ground plane behind the MMIC, the impedance for the detrimental even (single-ended) mode is high, suppressing coupling to that mode. Still another advantage of E-plane mounting is that the fundamental waveguide mode is inherently differential, eliminating the need for a balun to excite the differential mode.

Design and investigation of planar technology based ultra-wideband antenna with directional radiation patterns

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meena, M. L., E-mail: madan.meena.ece@gamil.com; Parmar, Girish, E-mail: girish-parmar2002@yahoo.com; Kumar, Mithilesh, E-mail: mith-kr@yahoo.com

A novel design technique based on planar technology for ultra-wideband (UWB) antennas with different ground shape having directional radiation pattern is being presented here. Firstly, the L-shape corner reflector ground plane antenna is designed with microstrip feed line in order to achieve large bandwidth and directivity. Thereafter, for the further improvement in the directivity as well as for better impedance matching the parabolic-shape ground plane has been introduced. The coaxial feed line is given for the proposed directional antenna in order to achieve better impedance matching with 50 ohm transmission line. The simulation analysis of the antenna is done onmore » CST Microwave Studio software using FR-4 substrate having thickness of 1.6 mm and dielectric constant of 4.4. The simulated result shows a good return loss (S11) with respect to -10 dB. The radiation pattern characteristic, angular width, directivity and bandwidth performance of the antenna have also been compared at different resonant frequencies. The designed antennas exhibit low cost, low reflection coefficient and better directivity in the UWB frequency band.« less

Millimeter-wave integrated-horn antennas. I - Theory. II - Experiment

NASA Technical Reports Server (NTRS)

Eleftheriades, George V.; Ali-Ahmad, Walid Y.; Katehi, Linda P. B.; Rebeiz, Gabriel M.

1991-01-01

Full-wave analysis is employed to determine the far-field pattern and input impedance of a dipole-fed horn antenna in a ground plane, and the theoretical results are compared with mm-wave and microwave data. The theoretical work exploits the Green's function corresponding to the horn structure and the method of moments. It is determined that the horn should have 70 sections/wavelength and 50 secondary modes for optimized accuracy, and certain dipole positions can reduce the resonance to zero. The experimentally derived impedance and radiation patterns agree with the constraints developed theoretically. The 70-degree flare-angle horn with selected dipole positions and horn apertures yields good radiation patterns, cross-polarization levels, and resonant dipole impedances. The conclusions are of interest to the development of the horn antennas etched in Si/GaAs for applications to zero-visibility tracking, radio astronomy, plasma diagnostics, and remote sensing.

Enhanced tunability of magneto-impedance and magneto-capacitance in annealed Metglas/PZT magnetoelectric composites

NASA Astrophysics Data System (ADS)

Leung, Chung Ming; Zhuang, Xin; Xu, Junran; Li, Jiefang; Zhang, Jitao; Srinivasan, G.; Viehland, D.

2018-05-01

This report is on a new class of magnetostatically tunable magneto-impedance and magneto-capacitance devices based on a composite of ferromagnetic Metglas and ferroelectric lead zirconate titanate (PZT). Layered magneto-electric (ME) composites with annealed Metglas and PZT were studied in a longitudinal in-plane magnetic field-transverse electric field (L-T) mode. It was found that the degree of tunability was dependent on the annealing temperature of Metglas. An impedance tunability (ΔZ/Z0) of ≥400% was obtained at the electromechanical resonance (EMR) frequency (fr) for a sample with Metglas layers annealed at Ta = 500oC. This tunability is a factor of two higher than for composites with Metglas annealed at 350oC. The tunability of the capacitance, (ΔC/C0), was found to be 290% and -135k% at resonance and antiresonance, respectively, for Ta = 500oC. These results provide clear evidence for improvement in static magnetic field tunability of impedance and capacitance of ME composites with the use of annealed Metglas and are of importance for their potential use in tunable electronic applications.

Microstructure and electrical properties of CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shao, S. F.; Zhang, J. L.; Zheng, P.

2006-04-15

CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) ceramics are prepared by the conventional solid-state reaction method under various sintering temperatures from 1000 to 1120 deg. C at an interval of 10 deg. C. Microstructures and crystalline structures are examined by scanning electronic microscopy and x-ray diffraction, respectively. Dielectric properties and complex impedances are investigated within the frequency range of 40 Hz-110 MHz over the temperature region from room temperature to 350 deg. C. It has been disclosed that the microstructures can be categorized into three different types: type A (with the small but uniform grain sizes), type B (with the bimodal distributionmore » of grain sizes) and type C (with the large and uniform grain sizes), respectively. The largeness of low-frequency dielectric permittivity at room temperature is closely related to the microstructure. Ceramics with different types of microstructures show the diverse temperature-dependent behaviors of electrical properties. However, the existence of some common characteristics is also found among them. For all of the ceramics, a Debye-type relaxation emerges in the frequency range of 100 Hz-100 kHz at high measuring temperatures, which has the larger dielectric dispersion strength than the one known in the frequency range above 100 kHz. Thus, the high-temperature dielectric dispersion exhibits a large low-frequency response and two Debye-type relaxations. Furthermore, all of the ceramics show three semicircles in the complex impedance plane. These semicircles are considered to represent individually different electrical mechanisms, among which the one in the low-frequency range arises most probably from the contribution of the domain boundaries, and the other two are ascribed to the contributions of the domains and the grain boundaries, respectively.« less

Determination of Complex Microcalorimeter Parameters with Impedance Measurements

NASA Technical Reports Server (NTRS)

Saab, T.; Bandler, S. R.; Chervenak, J.; Figueroa-Feliciano, E.; Finkbeiner, F.; Iyomoto, N.; Kelley, R.; Kilbourne, C. A.; Lindeman, M. A.; Porter, F. S.;

Effect of iron doping at Mn-site on complex impedance spectroscopy properties of Nd0.67Ba0.33MnO3 perovskite

NASA Astrophysics Data System (ADS)

Hsini, Mohamed; Hamdaoui, Nejeh; Hcini, Sobhi; Bouazizi, Mohamed Lamjed; Zemni, Sadok; Beji, Lotfi

2018-03-01

The effect of Fe-doping at Mn-site on the structural and electrical properties of Nd0.67Ba0.33Mn1-xFexO3 (0 ≤ x ≤ 0.05) perovskites has been investigated. X-ray diffraction patterns show that the structural parameters change slightly due to the fact that the Fe3+ ions replacing the Mn3+ have similar ionic radius. The electrical properties of these samples have been investigated using complex impedance spectroscopy technique. a function of the frequency at different temperatures. When increasing the Fe-content, a decrease of dc conductivity was observed throughout the whole explored temperature range and the deduced activation energy values are found to increase from 128 meV for x = 0 to 166 meV for x = 0.05. The curves of the imaginary part of impedance (Z″) show the presence of relaxation phenomenon in our samples. The complex impedance spectra show semicircle arcs at different temperatures and an equivalent circuit of the type of Rg + (Rgb//Cgb) has been proposed to explain the impedance results.

Investigation of laser Doppler anemometry in developing a velocity-based measurement technique

NASA Astrophysics Data System (ADS)

Jung, Ki Won

2009-12-01

Acoustic properties, such as the characteristic impedance and the complex propagation constant, of porous materials have been traditionally characterized based on pressure-based measurement techniques using microphones. Although the microphone techniques have evolved since their introduction, the most general form of the microphone technique employs two microphones in characterizing the acoustic field for one continuous medium. The shortcomings of determining the acoustic field based on only two microphones can be overcome by using numerous microphones. However, the use of a number of microphones requires a careful and intricate calibration procedure. This dissertation uses laser Doppler anemometry (LDA) to establish a new measurement technique which can resolve issues that microphone techniques have: First, it is based on a single sensor, thus the calibration is unnecessary when only overall ratio of the acoustic field is required for the characterization of a system. This includes the measurements of the characteristic impedance and the complex propagation constant of a system. Second, it can handle multiple positional measurements without calibrating the signal at each position. Third, it can measure three dimensional components of velocity even in a system with a complex geometry. Fourth, it has a flexible adaptability which is not restricted to a certain type of apparatus only if the apparatus is transparent. LDA is known to possess several disadvantages, such as the requirement of a transparent apparatus, high cost, and necessity of seeding particles. The technique based on LDA combined with a curvefitting algorithm is validated through measurements on three systems. First, the complex propagation constant of the air is measured in a rigidly terminated cylindrical pipe which has very low dissipation. Second, the radiation impedance of an open-ended pipe is measured. These two parameters can be characterized by the ratio of acoustic field measured at multiple locations. Third, the power dissipated in a variable RLC load is measured. The three experiments validate the LDA technique proposed. The utility of the LDA method is then extended to the measurement of the complex propagation constant of the air inside a 100 ppi reticulated vitreous carbon (RVC) sample. Compared to measurements in the available studies, the measurement with the 100 ppi RVC sample supports the LDA technique in that it can achieve a low uncertainty in the determined quantity. This dissertation concludes with using the LDA technique for modal decomposition of the plane wave mode and the (1,1) mode that are driven simultaneously. This modal decomposition suggests that the LDA technique surpasses microphone-based techniques, because they are unable to determine the acoustic field based on an acoustic model with unconfined propagation constants for each modal component.

Impedance spectroscopy and electric modulus behavior of Molybdenum doped Cobalt-Zinc ferrite

NASA Astrophysics Data System (ADS)

Pradhan, A. K.; Nath, T. K.; Saha, S.

2017-07-01

The complex impedance spectroscopy and the electric modulus of Mo doped Cobalt-Zinc inverse spinel ferrite has been investigated in detail. The conventional ceramic technique has been used to prepare the CZMO. The HRXRD technique has been used to study the structural analysis which confirms the inverse spinel structure of the material and also suggest the material have Fd3m space group. The complex impedance spectroscopic data and the electric modulus formalism have been used to understand the dielectric relaxation and conduction process. The contribution of grain and grain boundary in the electrical conduction process of CZMO has been confirmed from the Cole-Cole plot. The activation energy is calculated from both the IS (Impedance Spectroscopy) and electric modulus formalism and found to be nearly same for the materials.

Plane Transformations in a Complex Setting I: Homotheties-Translations

ERIC Educational Resources Information Center

Dana-Picard, T.

2006-01-01

A previous note described how complex numbers can be used for elementary analytic geometry in the plane, describing lines, circles and their intersections using complex Cartesian equations. In the present note, a description of elementary plane transformations, namely homotheties and translations, their group structure and their operations on…

Oscillation mechanics of the respiratory system.

PubMed

Bates, Jason H T; Irvin, Charles G; Farré, Ramon; Hantos, Zoltán

2011-07-01

The mechanical impedance of the respiratory system defines the pressure profile required to drive a unit of oscillatory flow into the lungs. Impedance is a function of oscillation frequency, and is measured using the forced oscillation technique. Digital signal processing methods, most notably the Fourier transform, are used to calculate impedance from measured oscillatory pressures and flows. Impedance is a complex function of frequency, having both real and imaginary parts that vary with frequency in ways that can be used empirically to distinguish normal lung function from a variety of different pathologies. The most useful diagnostic information is gained when anatomically based mathematical models are fit to measurements of impedance. The simplest such model consists of a single flow-resistive conduit connecting to a single elastic compartment. Models of greater complexity may have two or more compartments, and provide more accurate fits to impedance measurements over a variety of different frequency ranges. The model that currently enjoys the widest application in studies of animal models of lung disease consists of a single airway serving an alveolar compartment comprising tissue with a constant-phase impedance. This model has been shown to fit very accurately to a wide range of impedance data, yet contains only four free parameters, and as such is highly parsimonious. The measurement of impedance in human patients is also now rapidly gaining acceptance, and promises to provide a more comprehensible assessment of lung function than parameters derived from conventional spirometry. © 2011 American Physiological Society.

A new hybrid active/passive sound absorber with variable surface impedance

NASA Astrophysics Data System (ADS)

Betgen, Benjamin; Galland, Marie-Annick

2011-07-01

The context of the present paper is the wall treatment of flow ducts, notably aero-engine nacelle intakes and outlets. For this purpose, hybrid active/passive absorbers have been developed at the LMFA for about 15 years. A hybrid cell combines passive absorbent properties of a porous layer and active control at its rear face. Active control is mainly used to increase absorption at low frequencies by cancelling the imaginary part of the surface impedance presented by the absorber. However, the optimal impedance (i.e. the one that produces the highest noise reduction) of an absorber for flow duct applications is generally complex and frequency dependent. A new hybrid absorber intended to realise any of impedance has therefore been developed. The new cell uses one microphone on each side of a resistive cloth. Normal velocity can then be deduced by a simple pressure difference, which allows an estimation of the surface impedance of the absorber. In order to obtain an error signal related to a target impedance, the target impedance has to be reproduced in time domain. The design of a stable and causal filter is a difficult task, considering the kind of frequency response we seek. An alternative way of representing the impedance in time domain is therefore given. The new error signal is integrated into a feedback control structure. Fast convergence and good stability are observed for a wide range of target impedances. Typical optimal impedances with a positive increasing real part and a negative decreasing imaginary part have been successfully realised. Measurements in a grazing-incidence tube show that the new complex impedance absorber clearly outperforms the former active absorber.

Micro-Reaction Chamber Electrodes for Neural Stimulation and Recording

PubMed Central

Shanmugasundaram, Balaji; Gluckman, Bruce J.

2012-01-01

Biocompatible electrodes with smaller geometric area are preferred to improve the selectivity of the neural recording and stimulation applications. We introduce the concept of a micro-reaction chamber (µRC) in which a volume within the electrode back plane is used to confine and sequester the electrochemical reactions used for charge passage. The µRC electrode design helps decrease impedance and improves the charge storage capacity without altering the geometry of the active site. Here we demonstrate that µRC electrodes fabricated from 50 µm diameter microwire have significantly improved charge storage capacity and lowered impedance at physiologically relevant frequencies in phosphate buffered saline solution compared with other designs. PMID:22254394

Reducing the beam impedance of the kicker at the 3-GeV rapid cycling synchrotron of the Japan Proton Accelerator Research Complex

NASA Astrophysics Data System (ADS)

Shobuda, Yoshihiro; Chin, Yong Ho; Hayashi, Naoki; Irie, Yoshiro; Takayanagi, Tomohiro; Togashi, Tomohito; Toyama, Takeshi; Yamamoto, Kazami; Yamamoto, Masanobu

2018-06-01

The present four-terminal kicker at the rapid cycling synchrotron (RCS) at the Japan Proton Accelerator Research Complex has the power-saving benefit that it allows beam extraction by doubling the excitation currents with two shorted ends. In this configuration, two terminals of the kicker are connected to the pulse-forming line while the other two are terminated in a short circuit. On the other hand, beam instabilities are excited in the RCS by the kicker beam impedances, which result from the short-circuit termination of the kicker. In this paper, we describe a scheme to reduce the beam impedance of the kicker using diodes (nonlinear devices), while retaining the benefit of the doubled kicker excitation currents. We employ a simulation technique to determine the beam impedance of the kicker, even when such nonlinear devices and long cables are included. The characteristic of beam impedance measured using the accelerated beams is well explained by that obtained from the simulation.

Electromagnetic on-aircraft antenna radiation in the presence of composite plates

NASA Technical Reports Server (NTRS)

Kan, S. H-T.; Rojas, R. G.

1994-01-01

The UTD-based NEWAIR3 code is modified such that it can model modern aircraft by composite plates. One good model of conductor-backed composites is the impedance boundary condition where the composites are replaced by surfaces with complex impedances. This impedance-plate model is then used to model the composite plates in the NEWAIR3 code. In most applications, the aircraft distorts the desired radiation pattern of the antenna. However, test examples conducted in this report have shown that the undesired scattered fields are minimized if the right impedance values are chosen for the surface impedance plates.

Impedance of Barrier-Type Oxide Layer on Aluminum

NASA Astrophysics Data System (ADS)

Oh, Han-Jun; Kim, Jung-Gu; Jeong, Yong-Soo; Chi, Choong-Soo

2000-12-01

The impedance characteristics of barrier-type oxide layers on aluminum was studied using impedance spectroscopy. Since anodic films on Al have a variable stoichiometry with a gradual reduction of oxygen deficiency towards the oxide-electrolyte interface, the interpretation of impedance spectra for oxide layers is complex and the impedance of surface layers differs from those of ideal capacitors. This frequency response of the layer with conductance gradients cannot be described by a single resistance-capacitance (RC) element. The oxide layers of Al are properly described by the Young model of dielectric constant with a vertical decay of conductivity.

An E-plane analysis of aperture-matched horn antennas using the moment method and the uniform geometrical theory of diffraction

NASA Technical Reports Server (NTRS)

Heedy, D. J.; Burnside, W. D.

1984-01-01

The moment method and the uniform geometrical theory of diffraction are utilized to obtain two separate solutions for the E-plane field pattern of an aperture-matched horn antenna. This particular horn antenna consists of a standard pyramidal horn with the following modifications: a rolled edge section attached to the aperture edges and a curved throat section. The resulting geometry provides significantly better performance in terms of the pattern, impedance, and frequency characteristics than normally obtainable. The moment method is used to calculate the E-plane pattern and BSWR of the antenna. However, at higher frequencies, large amounts of computation time are required. The uniform geometrical theory of diffraction provides a quick and efficient high frequency solution for the E-plane field pattern. In fact, the uniform geometrical theory of diffraction may be used to initially design the antenna; then, the moment method may be applied to fine tune the design. This procedure has been successfully applied to a compact range feed design.

Plane Transformations in a Complex Setting II: Isometries

ERIC Educational Resources Information Center

Dana-Picard, Thierry

2007-01-01

This paper is the second part of a study of plane transformations using a complex setting. The first part was devoted to homotheties and translations, now attention is turned towards plane isometries. The group theoretic properties of plane isometries are easy to derive and images of classical geometrical objects by these transformations are…

An investigation of the diffraction of an acoustic plane wave by a curved surface of finite impedance. Ph.D. Thesis Final Technical Report, 1 Feb. 1985 - 1 Sep. 1989

NASA Technical Reports Server (NTRS)

Kearns, James A.

1989-01-01

Phenomena associated with long range propagation of sound over irregular topography motivated this work, which was to analyze the diffraction effects which would occur near the tops of hills and ridges. The diffraction of a high frequency plane wave due to its grazing of a two-dimensional curved surface of finite impedance was also studied. Laboratory scale models were constructed and measurements were made of the field on, above, and behind either of two curved surfaces possessing distinctly different impedances; that is, one was soft while the other was hard. The experimental technique consisted of simultaneously measuring the pressure at a reference point and at a field point due to a transient pulse generated by an electric spark. The pressure waveforms were digitized and processed. The ratio of the discrete Fourier transforms of the two waveforms provided an estimate of the insertion loss between them. The results of the measurements were compared with the predictions of a theory which was derived by Pierce using the method of Matched Asymptotic Expansions (MAE). The predictions relied upon the experimental evaluation of the impedance of each surface at grazing angles of incidence. This evaluation was achieved by a fairly standard technique involving empirical models of various generic types of surfaces. An example was shown of the important role that the structural intricacies of a surface play in the determination of an appropriate model. The comparison between the measurements and predictions indicated that the theory gives an excellent description of the field anywhere near a curved surface. Further, with a simple modification, the theory was also shown to give nearly as good of a description of the field surrounding a curved surface even at distances far behind the surface yet near the line of sight.

Impedance Spectroscopy Analysis of Mg4Nb2O9 Ceramics with Different Additions of V2O5 for Microwave and Radio Frequency Applications

NASA Astrophysics Data System (ADS)

Filho, J. M. S.; Rodrigues Junior, C. A.; Sousa, D. G.; Oliveira, R. G. M.; Costa, M. M.; Barroso, G. C.; Sombra, A. S. B.

2017-07-01

The complex impedance spectroscopy study of magnesium niobate Mg4Nb2O9 (MN) ceramics with different additions of V2O5 (0%, 2%, 5%) was performed in this present paper. The preparation of MN samples were carried out by using the solid-state reaction method with a high-energy milling machine. Frequency and temperature dependence of the complex impedance, complex modulus analysis, and conductivity were measured and calculated at different temperatures by using a network impedance analyzer. A non-Debye type relaxation was observed showing a decentralization of the semicircles. Cole-Cole formalism was adopted here with the help of a computer program used to fit the experimental data. A typical universal dielectric response in the frequency-dependent conductivity at different temperatures was found. The frequency dependent ac conductivity at different temperatures indicates that the conduction process is thermally activated. The activation energy was obtained from the Arrhenius fitting by using conductivity and electrical modules data. The results would help to understand deeply the relaxation process in these types of materials.

Technique for measurement of characteristic impedance and propagation constant for porous materials

NASA Astrophysics Data System (ADS)

Jung, Ki Won; Atchley, Anthony A.

2005-09-01

Knowledge of acoustic properties such as characteristic impedance and complex propagation constant is useful to characterize the acoustic behaviors of porous materials. Song and Bolton's four-microphone method [J. Acoust. Soc. Am. 107, 1131-1152 (2000)] is one of the most widely employed techniques. In this method two microphones are used to determine the complex pressure amplitudes for each side of a sample. Muehleisen and Beamer [J. Acoust. Soc. Am. 117, 536-544 (2005)] improved upon a four-microphone method by interchanging microphones to reduce errors due to uncertainties in microphone response. In this paper, a multiple microphone technique is investigated to reconstruct the pressure field inside an impedance tube. Measurements of the acoustic properties of a material having square cross-section pores is used to check the validity of the technique. The values of characteristic impedance and complex propagation constant extracted from the reconstruction agree well with predicted values. Furthermore, this technique is used in investigating the acoustic properties of reticulated vitreous carbon (RVC) in the range of 250-1100 Hz.

An analytic model for acoustic scattering from an impedance cylinder placed normal to an impedance plane

NASA Astrophysics Data System (ADS)

Swearingen, Michelle E.

2004-04-01

An analytic model, developed in cylindrical coordinates, is described for the scattering of a spherical wave off a semi-infinite reight cylinder placed normal to a ground surface. The motivation for the research is to have a model with which one can simulate scattering from a single tree and which can be used as a fundamental element in a model for estimating the attenuation in a forest comprised of multiple tree trunks. Comparisons are made to the plane wave case, the transparent cylinder case, and the rigid and soft ground cases as a method of theoretically verifying the model for the contemplated range of model parameters. Agreement is regarded as excellent for these benchmark cases. Model sensitivity to five parameters is also explored. An experiment was performed to study the scattering from a cylinder normal to a ground surface. The data from the experiment is analyzed with a transfer function method to yield frequency and impulse responses, and calculations based on the analytic model are compared to the experimental data. Thesis advisor: David C. Swanson Copies of this thesis written in English can be obtained from

Detection and quantification of intraperitoneal fluid using electrical impedance tomography.

PubMed

Sadleir, R J; Fox, R A

2001-04-01

A prototype electrical impedance tomography system was evaluated prior to its use for the detection of intraperitoneal bleeding, with the assistance of patients undergoing continuous ambulatory peritoneal dialysis (CAPD). The system was sensitive enough to detect small amounts of dialysis fluid appearing in subtractive images over short time periods. Uniform sensitivity to blood appearing anywhere within the abdominal cavity was produced using a post-reconstructive filter that corrected for changes in apparent resistivity of anomalies with their radial position. The image parameter used as an indication of fluid quantity, the resistivity index, varied approximately linearly with the quantity of fluid added. A test of the system's response to the introduction of conductive fluid out of the electrode plane (when a blood-equivalent fluid was added to the stomach) found that the sensitivity of the system was about half that observed in the electrode plane. Breathing artifacts were found to upset quantitative monitoring of intraperitoneal bleeding, but only on time scales short compared with the fluid administration rate. Longer term breathing changes, such as those due to variations in the functional residual capacity of the lungs, should ultimately limit the sensitivity over long time periods.

Biosonar signal propagation in the harbor porpoise's (Phocoena phocoena) head: The role of various structures in the formation of the vertical beam.

PubMed

Wei, Chong; Au, Whitlow W L; Ketten, Darlene R; Song, Zhongchang; Zhang, Yu

2017-06-01

Harbor porpoises (Phocoena phocoena) use narrow band echolocation signals for detecting and locating prey and for spatial orientation. In this study, acoustic impedance values of tissues in the porpoise's head were calculated from computer tomography (CT) scan and the corresponding Hounsfield Units. A two-dimensional finite element model of the acoustic impedance was constructed based on CT scan data to simulate the acoustic propagation through the animal's head. The far field transmission beam pattern in the vertical plane and the waveforms of the receiving points around the forehead were compared with prior measurement results, the simulation results were qualitatively consistent with the measurement results. The role of the main structures in the head such as the air sacs, melon and skull in the acoustic propagation was investigated. The results showed that air sacs and skull are the major components to form the vertical beam. Additionally, both beam patterns and sound pressure of the sound waves through four positions deep inside the melon were demonstrated to show the role of the melon in the biosonar sound propagation processes in the vertical plane.

Electromagnetic and scalar diffraction by a right-angled wedge with a uniform surface impedance

NASA Technical Reports Server (NTRS)

Hwang, Y. M.

1974-01-01

The diffraction of an electromagnetic wave by a perfectly-conducting right-angled wedge with one surface covered by a dielectric slab or absorber is considered. The effect of the coated surface is approximated by a uniform surface impedance. The solution of the normally incident electromagnetic problem is facilitated by introducing two scalar fields which satisfy a mixed boundary condition on one surface of the wedge and a Neumann of Dirichlet boundary condition on the other. A functional transformation is employed to simplify the boundary conditions so that eigenfunction expansions can be obtained for the resulting Green's functions. The eigenfunction expansions are transformed into the integral representations which then are evaluated asymptotically by the modified Pauli-Clemmow method of steepest descent. A far zone approximation is made to obtain the scattered field from which the diffraction coefficient is found for scalar plane, cylindrical or sperical wave incident on the edge. With the introduction of a ray-fixed coordinate system, the dyadic diffraction coefficient for plane or cylindrical EM waves normally indicent on the edge is reduced to the sum of two dyads which can be written alternatively as a 2 X 2 diagonal matrix.

Micromachined 1-3 composites for ultrasonic air transducers

NASA Astrophysics Data System (ADS)

Haller, M. I.; Khuri-Yakub, B. T.

1994-06-01

Airborne ultrasound has many applications, such as robotic sensing, NDE, and gas flow measurements. Coupling of ultrasound into air from plane piston piezoelectric transducers is inefficient because of the large impedance mismatch between the piezoelectric and air, and the lack of appropriate matching materials. Standard design practice requires the use of a matching layer material with an acoustic impedance of approximately 0.02 MRayls and a thickness of a quarter-wavelength. Such materials are not readily available. A method to manufacture low impedance materials using micromachining techniques for matching piezoelectrics into air are presented here. These materials are capped 1-3 composites of air and Kapton(R). The acoustic effect of the cap is significant and necessitates a modified design technique. This technique involves the use of two matching layers with inverted acoustic impedances. Using the new fabrication technology and the new design technique, an 860-kHz transducer was fabricated with a one-way insertion loss of 17 dB and a fractional 3 dB bandwidth of 6%. It is believed that, using this technology, a transducer with a one-way insertion loss of 10 dB and a fractional bandwidth of 10% is possible.

Mechanical Impedance Modeling of Human Arm: A survey

NASA Astrophysics Data System (ADS)

Puzi, A. Ahmad; Sidek, S. N.; Sado, F.

2017-03-01

Human arm mechanical impedance plays a vital role in describing motion ability of the upper limb. One of the impedance parameters is stiffness which is defined as the ratio of an applied force to the measured deformation of the muscle. The arm mechanical impedance modeling is useful in order to develop a better controller for system that interacts with human as such an automated robot-assisted platform for automated rehabilitation training. The aim of the survey is to summarize the existing mechanical impedance models of human upper limb so to justify the need to have an improved version of the arm model in order to facilitate the development of better controller of such systems with ever increase in complexity. In particular, the paper will address the following issue: Human motor control and motor learning, constant and variable impedance models, methods for measuring mechanical impedance and mechanical impedance modeling techniques.

Frequency effects on charge ordering in Y0.5Ca0.5MnO3 by impedance spectroscopy

NASA Astrophysics Data System (ADS)

Sarwar, Tuba; Qamar, Afzaal; Nadeem, Muhammad

2015-02-01

In this work, structural and electrical properties of Y0.5Ca0.5MnO3 are investigated by employing X-ray diffraction and impedance spectroscopy, respectively. Applied ac electric field showed the charge ordering transition temperature around 265 K and below this temperature the heteromorphic behavior of the sample is discussed in the proximity of TCO. With frequency effects the volume of robust charge orbital ordering (COO) domains diminishes due to different competing phases along with Jahn Teller distortions. Comprehensive melting and collapse of charge orbital ordering occurs below TN(125 K), where a colossal drop in the value of impedance is observed. The change in profile of modulus plane plots determines the spreading of relaxation time of intermingled phases. Hopping mechanism is elaborated in terms of strong electron phonon coupling. Variable range hopping model and Arrhenius model are used to discuss the short and long range hopping between Mn3+ and Mn4+ channels assessing the activation energy Ea.

Analysis of the electromagnetic scattering from an inlet geometry with lossy walls

NASA Technical Reports Server (NTRS)

Myung, N. H.; Pathak, P. H.; Chunang, C. D.

1985-01-01

One of the primary goals is to develop an approximate but sufficiently accurate analysis for the problem of electromagnetic (EM) plane wave scattering by an open ended, perfectly-conducting, semi-infinite hollow circular waveguide (or duct) with a thin, uniform layer of lossy or absorbing material on its inner wall, and with a simple termination inside. The less difficult but useful problem of the EM scattering by a two-dimensional (2-D), semi-infinite parallel plate waveguide with an impedance boundary condition on the inner walls was chosen initially for analysis. The impedance boundary condition in this problem serves to model a thin layer of lossy dielectric/ferrite coating on the otherwise perfectly-conducting interior waveguide walls. An approximate but efficient and accurate ray solution was obtained recently. That solution is presently being extended to the case of a moderately thick dielectric/ferrite coating on the walls so as to be valid for situations where the impedance boundary condition may not remain sufficiently accurate.

Measuring impedance in congestive heart failure: Current options and clinical applications

PubMed Central

Tang, W. H. Wilson; Tong, Wilson

2011-01-01

Measurement of impedance is becoming increasingly available in the clinical setting as a tool for assessing hemodynamics and volume status in patients with heart failure. The 2 major categories of impedance assessment are the band electrode method and the implanted device lead method. The exact sources of the impedance signal are complex and can be influenced by physiologic effects such as blood volume, fluid, and positioning. This article provides a critical review of our current understanding and promises of impedance measurements, the techniques that have evolved, as well as the evidence and limitations regarding their clinical applications in the setting of heart failure management. PMID:19249408

Time-Domain Impedance Boundary Conditions for Computational Aeroacoustics

NASA Technical Reports Server (NTRS)

Tam, Christopher K. W.; Auriault, Laurent

1996-01-01

It is an accepted practice in aeroacoustics to characterize the properties of an acoustically treated surface by a quantity known as impedance. Impedance is a complex quantity. As such, it is designed primarily for frequency-domain analysis. Time-domain boundary conditions that are the equivalent of the frequency-domain impedance boundary condition are proposed. Both single frequency and model broadband time-domain impedance boundary conditions are provided. It is shown that the proposed boundary conditions, together with the linearized Euler equations, form well-posed initial boundary value problems. Unlike ill-posed problems, they are free from spurious instabilities that would render time-marching computational solutions impossible.

Evaluation of a cost-effective loads approach. [shock spectra/impedance method for Viking Orbiter

NASA Technical Reports Server (NTRS)

Garba, J. A.; Wada, B. K.; Bamford, R.; Trubert, M. R.

1976-01-01

A shock spectra/impedance method for loads predictions is used to estimate member loads for the Viking Orbiter, a 7800-lb interplanetary spacecraft that has been designed using transient loads analysis techniques. The transient loads analysis approach leads to a lightweight structure but requires complex and costly analyses. To reduce complexity and cost, a shock spectra/impedance method is currently being used to design the Mariner Jupiter Saturn spacecraft. This method has the advantage of using low-cost in-house loads analysis techniques and typically results in more conservative structural loads. The method is evaluated by comparing the increase in Viking member loads to the loads obtained by the transient loads analysis approach. An estimate of the weight penalty incurred by using this method is presented. The paper also compares the calculated flight loads from the transient loads analyses and the shock spectra/impedance method to measured flight data.

On deformation of complex continuum immersed in a plane space

NASA Astrophysics Data System (ADS)

Kovalev, V. A.; Murashkin, E. V.; Radayev, Y. N.

2018-05-01

The present paper is devoted to mathematical modelling of complex continua deformations considered as immersed in an external plane space. The complex continuum is defined as a differential manifold supplied with metrics induced by the external space. A systematic derivation of strain tensors by notion of isometric immersion of the complex continuum into a plane space of a higher dimension is proposed. Problem of establishing complete systems of irreducible objective strain and extrastrain tensors for complex continuum immersed in an external plane space is resolved. The solution to the problem is obtained by methods of the field theory and the theory of rational algebraic invariants. Strain tensors of the complex continuum are derived as irreducible algebraic invariants of contravariant vectors of the external space emerging as functional arguments in the complex continuum action density. Present analysis is restricted to rational algebraic invariants. Completeness of the considered systems of rational algebraic invariants is established for micropolar elastic continua. Rational syzygies for non-quadratic invariants are discussed. Objective strain tensors (indifferent to frame rotations in the external plane space) for micropolar continuum are alternatively obtained by properly combining multipliers of polar decompositions of deformation and extra-deformation gradients. The latter is realized only for continua immersed in a plane space of the equal mathematical dimension.

Novel Implementations of Wideband Tightly Coupled Dipole Arrays for Wide-Angle Scanning

NASA Astrophysics Data System (ADS)

Yetisir, Ersin

Ultra-wideband (UWB) antennas and arrays are essential for high data rate communications and for addressing spectrum congestion. Tightly coupled dipole arrays (TCDAs) are of particular interest due to their low-profile, bandwidth and scanning range. But existing UWB (>3:1 bandwidth) arrays still suffer from limited scanning, particularly at angles beyond 45° from broadside. Almost all previous wideband TCDAs have employed dielectric layers above the antenna aperture to improve scanning while maintaining impedance bandwidth. But even so, these UWB arrays have been limited to no more than 60° away from broadside. In this work, we propose to replace the dielectric superstrate with frequency selective surfaces (FSS). In effect, the FSS is used to create an effective dielectric layer placed over the antenna array. FSS also enables anisotropic responses and more design freedom than conventional isotropic dielectric substrates. Another important aspect of the FSS is its ease of fabrication and low weight, both critical for mobile platforms (e.g. unmanned air vehicles), especially at lower microwave frequencies. Specifically, it can be fabricated using standard printed circuit technology and integrated on a single board with active radiating elements and feed lines. In addition to the FSS superstrate, a modified version of the stripline-based folded Marchand balun is presented. As usual the balun serves to match the 50Ω coaxial cable to the high input impedance ( 200Ω) at the terminals of array elements. Doing so, earlier Wilkinson power dividers, which degrade efficiency during E-plane scanning, are eliminated. To verify the proposed array concept, 12x12 TCDA prototype was fabricated using the modified balun and the new FSS superstrate layer. The design and experimental data showed an impedance bandwidth of 6.1:1 with VSWR<3.2. The latter VSWR was achieved even when scanning down to +/-60° in the H-plane, +/-70° in the D-plane and +/-75° in the E-plane. All array components, including the FSS, radiating dipoles and the feed lines are placed on the same PCB, vertically oriented over the array ground plane, resulting in a low-cost and light-weight structure. The effects of finite aperture sizes in presence of FSS or dielectric superstrates are also considered. Specifically, we compare the performance of finite TCDAs with FSS or dielectric loading. The performance metric is beam pointing accuracy for moderate array sizes ( 30dBi gain) with various edge element terminations. It is shown that even terminating two unit cells at the array edges can provide effective suppression of edge-born waves and achieve excellent beam accuracy. This is the case when both the FSS elements and radiating dipoles are resistively loaded in the unit-cells along the aperture edges.

Evaluation of Spanwise Variable Impedance Liners with Three-Dimensional Aeroacoustics Propagation Codes

NASA Technical Reports Server (NTRS)

Jones, M. G.; Watson, W. R.; Nark, D. M.; Schiller, N. H.

2017-01-01

Three perforate-over-honeycomb liner configurations, one uniform and two with spanwise variable impedance, are evaluated based on tests conducted in the NASA Grazing Flow Impedance Tube (GFIT) with a plane-wave source. Although the GFIT is only 2" wide, spanwise impedance variability clearly affects the measured acoustic pressure field, such that three-dimensional (3D) propagation codes are required to properly predict this acoustic pressure field. Three 3D propagation codes (CHE3D, COMSOL, and CDL) are used to predict the sound pressure level and phase at eighty-seven microphones flush-mounted in the GFIT (distributed along all four walls). The CHE3D and COMSOL codes compare favorably with the measured data, regardless of whether an exit acoustic pressure or anechoic boundary condition is employed. Except for those frequencies where the attenuation is large, the CDL code also provides acceptable estimates of the measured acoustic pressure profile. The CHE3D and COMSOL predictions diverge slightly from the measured data for frequencies away from resonance, where the attenuation is noticeably reduced, particularly when an exit acoustic pressure boundary condition is used. For these conditions, the CDL code actually provides slightly more favorable comparison with the measured data. Overall, the comparisons of predicted and measured data suggest that any of these codes can be used to understand data trends associated with spanwise variable-impedance liners.

[Activities of the Department of Electrical Engineering, Howard University

NASA Technical Reports Server (NTRS)

Yalamanchili, Raj C.

1997-01-01

Theoretical derivations, computer analysis and test data are provided to demonstrate that the cavity model is a feasible one to analyze thin-substrate, rectangular-patch microstrip antennas. Seven separate antennas were tested. Most of the antennas were designed to resonate at L-band frequencies (1-2 GHz). One antenna was designed to resonate at an S-band (2-4 GHz) frequency of 2.025 GHz. All dielectric substrates were made of Duroid, and were of varying thicknesses and relative dielectric constant values. Theoretical derivations to calculate radiated free space electromagnetic fields and antenna input impedance were performed. MATHEMATICA 2.2 software was used to generate Smith Chart input impedance plots, normalized relative power radiation plots and to perform other numerical manipulations. Network Analyzer tests were used to verify the data from the computer programming (such as input impedance and VSWR). Finally, tests were performed in an anechoic chamber to measure receive-mode polar power patterns in the E and H planes. Agreement between computer analysis and test data is presented. The antenna with the thickest substrate (e(sub r) = 2.33,62 mils thick) showed the worst match to theoretical impedance data. This is anticipated due to the fact that the cavity model generally loses accuracy when the dielectric substrate thickness exceeds 5% of the antenna's free space wavelength. A method of reducing computer execution time for impedance calculations is also presented.

Cell Electrical Impedance as a Novel Approach for Studies on Senescence Not Based on Biomarkers

PubMed Central

Cha, Jung-Joon; Park, Yangkyu; Yun, Joho; Kim, Hyeon Woo; Park, Chang-Ju; Kang, Giseok; Jung, Minhyun; Pak, Boryeong; Jin, Suk-Won

2016-01-01

Senescence of cardiac myocytes is frequently associated with heart diseases. To analyze senescence in cardiac myocytes, a number of biomarkers have been isolated. However, due to the complex nature of senescence, multiple markers are required for a single assay to accurately depict complex physiological changes associated with senescence. In single cells, changes in both cytoplasm and cell membrane during senescence can affect the changes in electrical impedance. Based on this phenomenon, we developed MEDoS, a novel microelectrochemical impedance spectroscopy for diagnosis of senescence, which allows us to precisely measure quantitative changes in electrical properties of aging cells. Using cardiac myocytes isolated from 3-, 6-, and 18-month-old isogenic zebrafish, we examined the efficacy of MEDoS and showed that MEDoS can identify discernible changes in electrical impedance. Taken together, our data demonstrated that electrical impedance in cells at different ages is distinct with quantitative values; these results were comparable with previously reported ones. Therefore, we propose that MEDoS be used as a new biomarker-independent methodology to obtain quantitative data on the biological senescence status of individual cells. PMID:27812531

Electrical conductivity and dielectric behavior in sodium zinc divanadates

NASA Astrophysics Data System (ADS)

Sallemi, F.; Louati, B.; Guidara, K.

2014-11-01

The Na2ZnV2O7 compound was obtained by the conventional solid-state reaction. The sample was characterized by X-ray powder diffraction, Raman and impedance spectroscopy. The ac electrical conductivity and dielectric properties have been investigated in the frequency and temperature range of 200 Hz-1 MHz and 513 K-729 K, respectively. The direct current conductivity process is thermally activated. The frequency dependence of the conductivity is interpreted using the power law. The close values of activation energies obtained from the analysis of hopping frequency and dc conductivity implies that the transport is due to Na+ cation displacement parallel to (0 0 1) plane located between ZnO4 and VO4 tetrahedra. The evolution of the complex permittivity as a function of angular frequency was investigated. Several important parameters such as charge carrier concentration, ionic mobility and diffusion coefficient were determined. Thermodynamic parameters such as the free energy of activation ∆F, the enthalpy ∆H, and the change in entropy ∆S have been calculated.

Conformal dual-band textile antenna with metasurface for WBAN application

NASA Astrophysics Data System (ADS)

Giman, Fatin Nabilah; Soh, Ping Jack; Jamlos, Mohd Faizal; Lago, Herwansyah; Al-Hadi, Azremi Abdullah; Abdulmalek, Mohamedfareq; Abdulaziz, Nidhal

2017-01-01

This paper presents the design of a dual-band wearable planar slotted dipole integrated with a metasurface. It operates in the 2.45 GHz (lower) and 5.8 GHz (upper) bands and made fully using textiles to suit wireless body area network applications. The metasurface in the form of an artificial magnetic conductor (AMC) plane is formed using a rectangular patch incorporated with a diamond-shaped slot to generate dual-phase response. This plane is then integrated with the planar slotted dipole antenna prior to its assessment in free space and bent configurations. Simulations and measurements indicated a good agreement, and the antenna featured an impedance bandwidth of 164 and 592 MHz in the lower and upper band, respectively. The presence of the AMC plane also minimized the backward radiation toward the human body and enhanced realized gains by up to 3.01 and 7.04 dB in the lower and upper band.

Bioelectrical Impedance Methods for Noninvasive Health Monitoring: A Review

PubMed Central

Bera, Tushar Kanti

2014-01-01

Under the alternating electrical excitation, biological tissues produce a complex electrical impedance which depends on tissue composition, structures, health status, and applied signal frequency, and hence the bioelectrical impedance methods can be utilized for noninvasive tissue characterization. As the impedance responses of these tissue parameters vary with frequencies of the applied signal, the impedance analysis conducted over a wide frequency band provides more information about the tissue interiors which help us to better understand the biological tissues anatomy, physiology, and pathology. Over past few decades, a number of impedance based noninvasive tissue characterization techniques such as bioelectrical impedance analysis (BIA), electrical impedance spectroscopy (EIS), electrical impedance plethysmography (IPG), impedance cardiography (ICG), and electrical impedance tomography (EIT) have been proposed and a lot of research works have been conducted on these methods for noninvasive tissue characterization and disease diagnosis. In this paper BIA, EIS, IPG, ICG, and EIT techniques and their applications in different fields have been reviewed and technical perspective of these impedance methods has been presented. The working principles, applications, merits, and demerits of these methods has been discussed in detail along with their other technical issues followed by present status and future trends. PMID:27006932

Dielectric supported radio-frequency cavities

DOEpatents

Yu, David U. L.; Lee, Terry G.

2000-01-01

A device which improves the electrical and thermomechanical performance of an RF cavity, for example, in a disk-loaded accelerating structure. A washer made of polycrystalline diamond is brazed in the middle to a copper disk washer and at the outer edge to the plane wave transformer tank wall, thus dissipating heat from the copper disk to the outer tank wall while at the same time providing strong mechanical support to the metal disk. The washer structure eliminates the longitudinal connecting rods and cooling channels used in the currently available cavities, and as a result minimizes problems such as shunt impedance degradation and field distortion in the plane wave transformer, and mechanical deflection and uneven cooling of the disk assembly.

Rectangular microstrip antenna with corrugation like defects at radiating edge: A new approach to reduce cross polarization radiation

NASA Astrophysics Data System (ADS)

Pawar, U. A.; Mondal, D.; Nagaraju, A.; Chakraborty, S.; Singh, L. L. K.; Chattopadhyay, S.

2018-03-01

In this paper, single layer, simple and compact RMA, with corrugation like defects at the radiating edge, is studied thoroughly to reduce XP radiation from the patch. Unlike the earlier works reported on defected ground structure integrated patches and defect patch structures, in this work, corrugation like linear defects have been placed at the radiating edges of the patch to reduce cross polarisation radiation. Around 30-40 dB of CP-XP isolation is observed in H-plane with 7% impedance bandwidth and in E-plane also, more than 55 dB CP-XP isolation is found. The proposed structure is very simple to design and easy to fabricate.

Comparison of Two Acoustic Waveguide Methods for Determining Liner Impedance

NASA Technical Reports Server (NTRS)

Jones, Michael G.; Watson, Willie R.; Tracy, Maureen B.; Parrott, Tony L.

2001-01-01

Acoustic measurements taken in a flow impedance tube are used to assess the relative accuracy of two waveguide methods for impedance eduction in the presence of grazing flow. The aeroacoustic environment is assumed to contain forward and backward-traveling acoustic waves, consisting of multiple modes, and uniform mean flow. Both methods require a measurement of the complex acoustic pressure profile over the length of the test liner. The Single Mode Method assumes that the sound pressure level and phase decay-rates of a single progressive mode can be extracted from this measured complex acoustic pressure profile. No a priori assumptions are made in the Finite Element. Method regarding the modal or reflection content in the measured acoustic pressure profile. The integrity of each method is initially demonstrated by how well their no-flow impedances match those acquired in a normal incidence impedance tube. These tests were conducted using ceramic tubular and conventional perforate liners. Ceramic tubular liners were included because of their impedance insensitivity to mean flow effects. Conversely, the conventional perforate liner was included because its impedance is known to be sensitive to mean flow velocity effects. Excellent comparisons between impedance values educed with the two waveguide methods in the absence of mean flow and the corresponding values educed with the normal incident impedance tube were observed. The two methods are then compared for mean flow Mach numbers up to 0.5, and are shown to give consistent results for both types of test liners. The quality of the results indicates that the Single Mode Method should be used when the measured acoustic pressure profile is clearly dominated by a single progressive mode, and the Finite Element Method should be used for all other cases.

Broadband Impedance Microscopy for Research on Complex Quantum Materials

DTIC Science & Technology

2016-02-08

function in various materials. Figure 2. Sensitivity limit of the broadband impedance microscope (BIM). Figure 3. Preliminary BIM data on YMnO3...2 Statement of the Problem The objective of this DURIP award is to construct a broadband impedance microscope (BIM) for frequency-dependent...platforms and specialized cantilever probes [1] in the PI’s lab, the BIM can now simultaneously obtain microscopic (10 – 100 nm) and quasi- spectroscopic

Not so Complex: Iteration in the Complex Plane

ERIC Educational Resources Information Center

O'Dell, Robin S.

2014-01-01

The simple process of iteration can produce complex and beautiful figures. In this article, Robin O'Dell presents a set of tasks requiring students to use the geometric interpretation of complex number multiplication to construct linear iteration rules. When the outputs are plotted in the complex plane, the graphs trace pleasing designs…

Short wavelength HgCdTe staring focal plane for low background astronomy applications

NASA Technical Reports Server (NTRS)

Hall, D.; Stobie, J.; Hartle, N.; Lacroix, D.; Maschhoff, K.

1989-01-01

The design of a 128x128 staring short wave infrared (SWIR) HgCdTe focal plane incorporating charge integrating transimpedance input preamplifiers is presented. The preamplifiers improve device linearity and uniformity, and provide signal gain ahead of the miltiplexer and readout circuitry. Detector's with cutoff wavelength of 2.5 microns and operated at 80 K have demonstrated impedances in excess of 10(exp 16) ohms with 60 percent quantum efficiency. Focal plane performance using a smaller format device is presented which demonstrates the potential of this approach. Although the design is capable of achieving less than 30 rms electrons with todays technology, initial small format devices demonstrated a read noise of 100 rms electrons and were limited by the atypical high noise performance of the silicon process run. Luminescence from the active silicon circuitry in the multiplexer limits the minimum detector current to a few hundred electrons per second. Approaches to eliminate this excessive source of current is presented which should allow the focal plane to achieve detector background limited performance.

Complex capacitance in the representation of modulus of the lithium niobate crystals

NASA Astrophysics Data System (ADS)

Alim, Mohammad A.; Batra, A. K.; Bhattacharjee, Sudip; Aggarwal, M. D.

2011-03-01

The lithium niobate (LiNbO 3 or LN) single crystal is grown in-house. The ac small-signal electrical characterization is conducted over a temperature range 35 ≤T≤150 °C as a function of measurement frequency (10 ≤f≤10 6 Hz). Meaningful observation is noted only in a narrow temperature range 59 ≤T≤73 °C. These electrical data when analyzed via complex plane formalisms revealed single semicircular relaxation both in the complex capacitance ( C*) and in the modulus ( M*) planes. The physical meaning of this kind of observation is obtained on identifying the relaxation type, and then incorporating respective equivalent circuit model. The simplistic non-blocking nature of the equivalent circuit model obtained via M*-plane is established as the lumped relaxation is identified in the C*-plane. The feature of the eventual equivalent circuit model allows non-blocking aspect for the LN crystal attributing to the presence of the operative dc conduction process. Identification of this leakage dc conduction via C*-plane is portrayed in the M*-plane where the blocking nature is removed. The interacting interpretation between these two complex planes is successfully presented.

Real-time estimation of lesion depth and control of radiofrequency ablation within ex vivo animal tissues using a neural network.

PubMed

Wang, Yearnchee Curtis; Chan, Terence Chee-Hung; Sahakian, Alan Varteres

2018-01-04

Radiofrequency ablation (RFA), a method of inducing thermal ablation (cell death), is often used to destroy tumours or potentially cancerous tissue. Current techniques for RFA estimation (electrical impedance tomography, Nakagami ultrasound, etc.) require long compute times (≥ 2 s) and measurement devices other than the RFA device. This study aims to determine if a neural network (NN) can estimate ablation lesion depth for control of bipolar RFA using complex electrical impedance - since tissue electrical conductivity varies as a function of tissue temperature - in real time using only the RFA therapy device's electrodes. Three-dimensional, cubic models comprised of beef liver, pork loin or pork belly represented target tissue. Temperature and complex electrical impedance from 72 data generation ablations in pork loin and belly were used for training the NN (403 s on Xeon processor). NN inputs were inquiry depth, starting complex impedance and current complex impedance. Training-validation-test splits were 70%-0%-30% and 80%-10%-10% (overfit test). Once the NN-estimated lesion depth for a margin reached the target lesion depth, RFA was stopped for that margin of tissue. The NN trained to 93% accuracy and an NN-integrated control ablated tissue to within 1.0 mm of the target lesion depth on average. Full 15-mm depth maps were calculated in 0.2 s on a single-core ARMv7 processor. The results show that a NN could make lesion depth estimations in real-time using less in situ devices than current techniques. With the NN-based technique, physicians could deliver quicker and more precise ablation therapy.

Fast and sensitive detection of foodborne pathogen using electrochemical impedance analysis, urease catalysis and microfluidics.

PubMed

Chen, Qi; Wang, Dan; Cai, Gaozhe; Xiong, Yonghua; Li, Yuntao; Wang, Maohua; Huo, Huiling; Lin, Jianhan

2016-12-15

Early screening of pathogenic bacteria is a key to prevent and control of foodborne diseases. In this study, we developed a fast and sensitive bacteria detection method integrating electrochemical impedance analysis, urease catalysis with microfluidics and using Listeria as model. The Listeria cells, the anti-Listeria monoclonal antibodies modified magnetic nanoparticles (MNPs), and the anti-Listeria polyclonal antibodies and urease modified gold nanoparticles (AuNPs) were incubated in a fluidic separation chip with active mixing to form the MNP-Listeria-AuNP-urease sandwich complexes. The complexes were captured in the separation chip by applying a high gradient magnetic field, and the urea was injected to resuspend the complexes and hydrolyzed under the catalysis of the urease on the complexes into ammonium ions and carbonate ions, which were transported into a microfluidic detection chip with an interdigitated microelectrode for impedance measurement to determine the amount of the Listeria cells. The capture efficiency of the Listeria cells in the separation chip was ∼93% with a shorter time of 30min due to the faster immuno-reaction using the active magnetic mixing. The changes on both impedance magnitude and phase angle were demonstrated to be able to detect the Listeria cells as low as 1.6×10(2)CFU/mL. The detection time was reduced from original ∼2h to current ∼1h. The recoveries of the spiked lettuce samples ranged from 82.1% to 89.6%, indicating the applicability of this proposed biosensor. This microfluidic impedance biosensor has shown the potential for online, automatic and sensitive bacteria separation and detection. Copyright © 2016 Elsevier B.V. All rights reserved.

Measurements of complex impedance in microwave high power systems with a new bluetooth integrated circuit.

PubMed

Roussy, Georges; Dichtel, Bernard; Chaabane, Haykel

2003-01-01

By using a new integrated circuit, which is marketed for bluetooth applications, it is possible to simplify the method of measuring the complex impedance, complex reflection coefficient and complex transmission coefficient in an industrial microwave setup. The Analog Devices circuit AD 8302, which measures gain and phase up to 2.7 GHz, operates with variable level input signals and is less sensitive to both amplitude and frequency fluctuations of the industrial magnetrons than are mixers and AM crystal detectors. Therefore, accurate gain and phase measurements can be performed with low stability generators. A mechanical setup with an AD 8302 is described; the calibration procedure and its performance are presented.

Intra-Beam Scattering, Impedance, and Instabilities in Ultimate Storage Rings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bane, Karl; /SLAC

We have investigated collective effects in an ultimate storage ring, i.e. one with diffraction limited emittances in both planes, using PEP-X as an example. In an ultimate ring intra-beam scattering (IBS) sets the limit of current that can be stored. In PEP-X, a 4.5 GeV ring running round beams at 200 mA in 3300 bunches, IBS doubles the emittances to 11.5 pm at the design current. The Touschek lifetime is 11 hours. Impedance driven collective effects tend not to be important since the beam current is relatively low. We have investigated collective effects in PEP-X, an ultimate storage ring, i.e.more » one with diffraction limited emittances (at one angstrom wavelength) in both planes. In an ultimate ring intra-beam scattering (IBS) sets the limit of current that can be stored. In PEP-X, IBS doubles the emittances to 11.5 pm at the design current of 200 mA, assuming round beams. The Touschek lifetime is quite large in PEP-X, 11.6 hours, and - near the operating point - increases with decreasing emittance. It is, however, a very sensitive function of momentum acceptance. In an ultimate ring like PEP-X impedance driven collective effects tend not to be important since the beam current is relatively low. Before ultimate PEP-X can be realized, the question of how to run a machine with round beams needs serious study. For example, in this report we assumed that the vertical emittance is coupling dominated. It may turn out that using vertical dispersion is a preferable way to generate round beams. The choice will affect IBS and the Touschek effect.« less

Methodological considerations of task and shoe wear on joint energetics during landing.

PubMed

Shultz, Sandra J; Schmitz, Randy J; Tritsch, Amanda J; Montgomery, Melissa M

2012-02-01

To better understand methodological factors that alter landings strategies, we compared sagittal plane joint energetics during the initial landing phase of drop jumps (DJ) vs. drop landings (DL), and when shod vs. barefoot. Surface electromyography, kinematic and kinetic data were obtained on 10 males and 10 females during five consecutive drop landings and five consecutive drop jumps (0.45m) when shod and when barefoot. Energy absorption was greater in the DJ vs. DL (P=.002), due to increased energy absorption at the hip during the DJ. Joint stiffness/impedance was more affected by shoe condition, where overall stiffness/impedance was greater in shod compared to barefoot conditions (P=.036). Further, hip impedance was greater in shod vs. barefoot for the DL only (via increased peak hip extensor moment in DL), while ankle stiffness was greater in the barefoot vs. shod condition for the DJ only (via decreased joint excursion and increased peak joint moment in DJ vs. DL) (P=.011). DJ and DL place different neuromechanical demands upon the lower extremities, and shoe wear may alter impact forces that modulate stiffness/impedance strategies. The impact of these methodological differences should be considered when comparing landing biomechanics across studies. Copyright © 2011 Elsevier Ltd. All rights reserved.

MOM3D method of moments code theory manual

NASA Technical Reports Server (NTRS)

Shaeffer, John F.

1992-01-01

MOM3D is a FORTRAN algorithm that solves Maxwell's equations as expressed via the electric field integral equation for the electromagnetic response of open or closed three dimensional surfaces modeled with triangle patches. Two joined triangles (couples) form the vector current unknowns for the surface. Boundary conditions are for perfectly conducting or resistive surfaces. The impedance matrix represents the fundamental electromagnetic interaction of the body with itself. A variety of electromagnetic analysis options are possible once the impedance matrix is computed including backscatter radar cross section (RCS), bistatic RCS, antenna pattern prediction for user specified body voltage excitation ports, RCS image projection showing RCS scattering center locations, surface currents excited on the body as induced by specified plane wave excitation, and near field computation for the electric field on or near the body.

Wideband dual frequency modified ellipse shaped patch antenna for WLAN/Wi-MAX/UWB application

NASA Astrophysics Data System (ADS)

Jain, P. K.; Jangid, K. G.; R. Sharma, B.; Saxena, V. K.; Bhatnagar, D.

2018-05-01

This paper communicates the design and performance of microstrip line fed modified ellipses shaped radiating patch with defected ground structure. Wide impedance bandwidth performance is achieved by applying a pentagonal slot and T slot structure in ground plane. By inserting two semi ellipses shaped ring in ground, we obtained axial ratio bandwidth approx 600 MHz. The proposed antenna is simulated by utilizing CST Microwave Studio simulator 2014. This antenna furnishes wide impedance bandwidth approx. 4.23 GHz, which has spread into two bands 2.45 GHz - 5.73 GHz and 7.22 GHz - 8.17 GHz with nearly flat gain in operating frequency range. This antenna may be proved as a practicable structure for modern wireless communication systems including Wi-MAX, WLAN and lower band of UWB.

Time-domain representation of frequency-dependent foundation impedance functions

USGS Publications Warehouse

Safak, E.

2006-01-01

Foundation impedance functions provide a simple means to account for soil-structure interaction (SSI) when studying seismic response of structures. Impedance functions represent the dynamic stiffness of the soil media surrounding the foundation. The fact that impedance functions are frequency dependent makes it difficult to incorporate SSI in standard time-history analysis software. This paper introduces a simple method to convert frequency-dependent impedance functions into time-domain filters. The method is based on the least-squares approximation of impedance functions by ratios of two complex polynomials. Such ratios are equivalent, in the time-domain, to discrete-time recursive filters, which are simple finite-difference equations giving the relationship between foundation forces and displacements. These filters can easily be incorporated into standard time-history analysis programs. Three examples are presented to show the applications of the method.

Wavelet transformation to determine impedance spectra of lithium-ion rechargeable battery

NASA Astrophysics Data System (ADS)

Hoshi, Yoshinao; Yakabe, Natsuki; Isobe, Koichiro; Saito, Toshiki; Shitanda, Isao; Itagaki, Masayuki

2016-05-01

A new analytical method is proposed to determine the electrochemical impedance of lithium-ion rechargeable batteries (LIRB) from time domain data by wavelet transformation (WT). The WT is a waveform analysis method that can transform data in the time domain to the frequency domain while retaining time information. In this transformation, the frequency domain data are obtained by the convolution integral of a mother wavelet and original time domain data. A complex Morlet mother wavelet (CMMW) is used to obtain the complex number data in the frequency domain. The CMMW is expressed by combining a Gaussian function and sinusoidal term. The theory to select a set of suitable conditions for variables and constants related to the CMMW, i.e., band, scale, and time parameters, is established by determining impedance spectra from wavelet coefficients using input voltage to the equivalent circuit and the output current. The impedance spectrum of LIRB determined by WT agrees well with that measured using a frequency response analyzer.

Plane Transformations in a Complex Setting III: Similarities

ERIC Educational Resources Information Center

Dana-Picard, Thierry

2009-01-01

This is the third part of a study of plane transformations described in a complex setting. After the study of homotheties, translations, rotations and reflections, we proceed now to the study of plane similarities, either direct or inverse. Their group theoretical properties are described, and their action on classical geometrical objects is…

An inverter-based capacitive trans-impedance amplifier readout with offset cancellation and temporal noise reduction for IR focal plane array

NASA Astrophysics Data System (ADS)

Chen, Hsin-Han; Hsieh, Chih-Cheng

2013-09-01

This paper presents a readout integrated circuit (ROIC) with inverter-based capacitive trans-impedance amplifier (CTIA) and pseudo-multiple sampling technique for infrared focal plane array (IRFPA). The proposed inverter-based CTIA with a coupling capacitor [1], executing auto-zeroing technique to cancel out the varied offset voltage from process variation, is used to substitute differential amplifier in conventional CTIA. The tunable detector bias is applied from a global external bias before exposure. This scheme not only retains stable detector bias voltage and signal injection efficiency, but also reduces the pixel area as well. Pseudo-multiple sampling technique [2] is adopted to reduce the temporal noise of readout circuit. The noise reduction performance is comparable to the conventional multiple sampling operation without need of longer readout time proportional to the number of samples. A CMOS image sensor chip with 55×65 pixel array has been fabricated in 0.18um CMOS technology. It achieves a 12um×12um pixel size, a frame rate of 72 fps, a power-per-pixel of 0.66uW/pixel, and a readout temporal noise of 1.06mVrms (16 times of pseudo-multiple sampling), respectively.

Forced sound transmission through a finite-sized single leaf panel subject to a point source excitation.

PubMed

Wang, Chong

2018-03-01

In the case of a point source in front of a panel, the wavefront of the incident wave is spherical. This paper discusses spherical sound waves transmitting through a finite sized panel. The forced sound transmission performance that predominates in the frequency range below the coincidence frequency is the focus. Given the point source located along the centerline of the panel, forced sound transmission coefficient is derived through introducing the sound radiation impedance for spherical incident waves. It is found that in addition to the panel mass, forced sound transmission loss also depends on the distance from the source to the panel as determined by the radiation impedance. Unlike the case of plane incident waves, sound transmission performance of a finite sized panel does not necessarily converge to that of an infinite panel, especially when the source is away from the panel. For practical applications, the normal incidence sound transmission loss expression of plane incident waves can be used if the distance between the source and panel d and the panel surface area S satisfy d/S>0.5. When d/S ≈0.1, the diffuse field sound transmission loss expression may be a good approximation. An empirical expression for d/S=0  is also given.

Manipulating Acoustic Wavefront by Inhomogeneous Impedance and Steerable Extraordinary Reflection

PubMed Central

Zhao, Jiajun; Li, Baowen; Chen, Zhining; Qiu, Cheng-Wei

2013-01-01

We unveil the connection between the acoustic impedance along a flat surface and the reflected acoustic wavefront, in order to empower a wide wariety of novel applications in acoustic community. Our designed flat surface can generate double reflections: the ordinary reflection and the extraordinary one whose wavefront is manipulated by the proposed impedance-governed generalized Snell's law of reflection (IGSL). IGSL is based on Green's function and integral equation, instead of Fermat's principle for optical wavefront manipulation. Remarkably, via the adjustment of the designed specific acoustic impedance, extraordinary reflection can be steered for unprecedented acoustic wavefront while that ordinary reflection can be surprisingly switched on or off. The realization of the complex discontinuity of the impedance surface has been proposed using Helmholtz resonators. PMID:23985717

Implementing digital holograms to create and measure complex-plane optical fields

NASA Astrophysics Data System (ADS)

Dudley, Angela; Majola, Nombuso; Chetty, Naven; Forbes, Andrew

2016-02-01

The coherent superposition of a Gaussian beam with an optical vortex can be mathematically described to occupy the complex plane. We provide a simple analogy between the mathematics, in the form of the complex plane, and the visual representation of these two superimposed optical fields. We provide detailed instructions as to how one can experimentally produce, measure, and control these fields with the use of digital holograms encoded on a spatial light modulator.

Elastic-wave propagation and site amplification in the Salt Lake Valley, Utah, from simulated normal faulting earthquakes

USGS Publications Warehouse

Benz, H.M.; Smith, R.B.

1988-01-01

The two-dimensional seismic response of the Salt Lake valley to near- and far-field earthquakes has been investigated from simulations of vertically incident plane waves and from normal-faulting earthquakes generated on the basin-bounding Wasatch fault. The plane-wave simulations were compared with observed site amplifications in the Salt Lake valley, based on seismic recordings from nuclear explosions in southern Nevada, that show 10 times greater amplification with the basin than measured values on hard-rock sites. Synthetic seismograms suggest that in the frequency band 0.3 to 1.5 Hz at least one-half the site amplitication can be attributed to the impedance contrast between the basin sediments and higher velocity basement rocks. -from Authors

A Research Program on the Asymptotic Description of Electromagnetic Pulse Propagation in Spatially Inhomogeneous Temporally Dispersive, Attenuative Media

DTIC Science & Technology

2007-09-01

the right- half of the complex wo- plane . The Sommerfeld precursor then describes the signal front which arrives at 0 = 1 with...resonance Lorentz model dielectric [18], the complex phase function qO(w, 0) is analytic in the w- plane formed by the two branch cuts in the lower half of... the w,- plane symmetrically located about the imaginary axis. In the right half plane , the branch

High Frequency Electromagnetic Impedance Measurements for Characterization, Monitoring and Verification Efforts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Ki Ha; Becker, Alex; Framgos, William

1999-06-01

Non-invasive, high-resolution imaging of the shallow subsurface is needed for delineation of buried waste, detection of unexploded ordinance, verification and monitoring of containment structures, and other environmental applications. Electromagnetic measurements at frequencies between 1 and 100 MHz are important for such applications, because the induction number of many targets is small and the ability to determine the dielectric permittivity in addition to electrical conductivity of the subsurface is possible. Earlier workers were successful in developing systems for detecting anomalous areas, but no quantifiable information was accurately determined. For high-resolution imaging, accurate measurements are necessary so the field data can bemore » mapped into the space of the subsurface parameters. We are developing a non-invasive method for accurately imaging the electrical conductivity and dielectric permittivity of the shallow subsurface using the plane wave impedance approach. Electric and magnetic sensors are being tested in a known area against theoretical predictions, thereby insuring that the data collected with the high-frequency impedance (HFI) system will support high-resolution, multi-dimensional imaging techniques.« less

High-Frequency Electromagnetic Impedance Measurements for Characterization, Monitoring, and Verification Efforts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Ki Ha; Becker, Alex

2000-06-01

Non-invasive, high-resolution imaging of the shallow subsurface is needed for delineation of buried waste, detection of unexploded ordinance, verification and monitoring of containment structures, and other environmental applications. Electromagnetic measurements at frequencies between 1 and 100 MHz are important for such applications, because the induction number of many targets is small and the ability to determine the dielectric permittivity in addition to electrical conductivity of the subsurface is possible. Earlier workers were successful in developing systems for detecting anomalous areas, but no quantifiable information was accurately determined. For high-resolution imaging, accurate measurements are necessary so the field data can bemore » mapped into the space of the subsurface parameters. We are developing a non-invasive method for accurately imaging the electrical conductivity and dielectric permittivity of the shallow subsurface using the plane wave impedance approach (Song et al., 1997). Electric and magnetic sensors are being tested in a known area against theoretical predictions, thereby insuring that the data collected with the high-frequency impedance (HFI) system will support high-resolution, multi-dimensional imaging techniques.« less

Strain effects on oxygen vacancy energetics in KTaO 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xi, Jianqi; Xu, Haixuan; Zhang, Yanwen

Due to lattice mismatch between epitaxial films and substrates, in-plane strain fields are produced in the thin films, with accompanying structural distortions, and ion implantation can be used to controllably engineer the strain throughout the film. Because of the strain profile, local defect energetics are changed. In this study, the effects of in-plane strain fields on the formation and migration of oxygen vacancies in KTaO 3 are investigated using first-principles calculations. In particular, the doubly positive charged oxygen vacancy (V 2+O) is studied, which is considered to be the main charge state of the oxygen vacancy in KTaO 3. Wemore » find that the formation energies for oxygen vacancies are sensitive to in-plane strain and oxygen position. The local atomic configuration is identified, and strong relaxation of local defect structure is mainly responsible for the formation characteristics of these oxygen vacancies. Based on the computational results, formation-dependent site preferences for oxygen vacancies are expected to occur under epitaxial strain, which can result in orders of magnitude differences in equilibrium vacancy concentrations on different oxygen sites. In addition, all possible migration pathways, including intra- and inter-plane diffusions, are considered. In contrast to the strain-enhanced intra-plane diffusion, the diffusion in the direction normal to the strained plane is impeded under the epitaxial strain field. Lastly, these anisotropic diffusion processes can further enhance site preferences.« less

Strain effects on oxygen vacancy energetics in KTaO 3

DOE PAGES

Xi, Jianqi; Xu, Haixuan; Zhang, Yanwen; ...

2017-02-07

Due to lattice mismatch between epitaxial films and substrates, in-plane strain fields are produced in the thin films, with accompanying structural distortions, and ion implantation can be used to controllably engineer the strain throughout the film. Because of the strain profile, local defect energetics are changed. In this study, the effects of in-plane strain fields on the formation and migration of oxygen vacancies in KTaO 3 are investigated using first-principles calculations. In particular, the doubly positive charged oxygen vacancy (V 2+O) is studied, which is considered to be the main charge state of the oxygen vacancy in KTaO 3. Wemore » find that the formation energies for oxygen vacancies are sensitive to in-plane strain and oxygen position. The local atomic configuration is identified, and strong relaxation of local defect structure is mainly responsible for the formation characteristics of these oxygen vacancies. Based on the computational results, formation-dependent site preferences for oxygen vacancies are expected to occur under epitaxial strain, which can result in orders of magnitude differences in equilibrium vacancy concentrations on different oxygen sites. In addition, all possible migration pathways, including intra- and inter-plane diffusions, are considered. In contrast to the strain-enhanced intra-plane diffusion, the diffusion in the direction normal to the strained plane is impeded under the epitaxial strain field. Lastly, these anisotropic diffusion processes can further enhance site preferences.« less

Image Reconstruction Under Contact Impedance Effect in Micro Electrical Impedance Tomography Sensors.

PubMed

Liu, Xiayi; Yao, Jiafeng; Zhao, Tong; Obara, Hiromichi; Cui, Yahui; Takei, Masahiro

2018-06-01

Contact impedance has an important effect on micro electrical impedance tomography (EIT) sensors compared to conventional macro sensors. In the present work, a complex contact impedance effect ratio ξ is defined to quantitatively evaluate the effect of the contact impedance on the accuracy of the reconstructed images by micro EIT. Quality of the reconstructed image under various ξ is estimated by the phantom simulation to find the optimum algorithm. The generalized vector sampled pattern matching (GVSPM) method reveals the best image quality and the best tolerance to ξ. Moreover, the images of yeast cells sedimentary distribution in a multilayered microchannel are reconstructed by the GVSPM method under various mean magnitudes of contact impedance effect ratio |ξ|. The result shows that the best image quality that has the smallest voltage error U E = 0.581 is achieved with measurement frequency f = 1 MHz and mean magnitude |ξ| = 26. In addition, the reconstructed images of cells distribution become improper while f < 10 kHz and mean value of |ξ| > 2400.

A Computer Aided Broad Band Impedance Matching Technique Using a Comparison Reflectometer. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Gordy, R. S.

1972-01-01

An improved broadband impedance matching technique was developed. The technique is capable of resolving points in the waveguide which generate reflected energy. A version of the comparison reflectometer was developed and fabricated to determine the mean amplitude of the reflection coefficient excited at points in the guide as a function of distance, and the complex reflection coefficient of a specific discontinuity in the guide as a function of frequency. An impedance matching computer program was developed which is capable of impedance matching the characteristics of each disturbance independent of other reflections in the guide. The characteristics of four standard matching elements were compiled, and their associated curves of reflection coefficient and shunt susceptance as a function of frequency are presented. It is concluded that an economical, fast, and reliable impedance matching technique has been established which can provide broadband impedance matches.

Acoustic Propagation and Barrier Diffraction Over an Impedance Plane.

DTIC Science & Technology

1982-10-13

Further appreciation is extended to Dr. Eugen"J. Skudrzyk, Dr. Jiri Tichy, Dr. Alan D. Stuart, and Dr. Vernon H. Neubert for actively participating on my...10 More recent theoretical studies have expanded upon the foundations laid by Rudnick, Lawhead, and Ingard. Paul (1957) studied the two-media problem...series for functions occurring in the theory of diffraction of waves by wedges. Journal of Mathematical Physics, 1956, 34, 245-255. Paul , D. I

Various DC-driven point-to-plain discharges as non-thermal plasma sources and their bactericidal effects

NASA Astrophysics Data System (ADS)

Khun, Josef; Scholtz, Vladimír; Hozák, Pavel; Fitl, Přemysl; Julák, Jaroslav

2018-06-01

The appearance of several types of ballast serial impedance-stabilized DC-driven electric corona discharges in the point-to-plane configuration is described. In addition to well-known corona discharges, new ones were observed, namely curved transient spark, interrupted channel and branched transient spark. Their properties are described by volt-ampere characteristics and UV-vis emission spectra. Their bactericidal ability for two bacterial species is also given.

Circularly polarized triple band glass shaped monopole patch antenna with metallic reflector for bluetooth & wireless applications

NASA Astrophysics Data System (ADS)

Jangid, K. G.; Choudhary, N.; Jain, P.; Sharma, B. R.; Saini, J. S.; Kulhar, V. S.; Bhatnagar, D.

2016-03-01

This paper presents the design and performance of strip line fed glass shaped monopole patch antenna having with overall size 30mm × 30 mm × 1.59 mm. In the patch; an eight shaped slot and in the ground plane an eight shaped ring are introduced. A metallic ground plane is also introduced at appropriate location beneath the ground plane. The proposed antenna is simulated by applying CST Microwave Studio simulator. Antenna provides circularly polarized radiations, triple broad impedance bandwidth of 203MHz (2.306GHz to 2.510GHz), 42MHz (2.685GHz to 2.757GHz) & GHz (3.63 GHz to 6.05 GHz), high flat gain (close to 5dBi) and good radiation properties in the desired frequency range. This antenna may be a very useful tool for 2.45GHz Bluetooth communication band as well as for 2.4GHz/5.2 GHz /5.8 GHz WLAN bands & 3.7GHz/5.5 GHz Wi-Max bands.

Analysis of the Impedance Resonance of Piezoelectric Multi-Fiber Composite Stacks

NASA Technical Reports Server (NTRS)

Sherrit, S.; Djrbashian, A.; Bradford, S C

2013-01-01

Multi-Fiber CompositesTM (MFC's) produced by Smart Materials Corp behave essentially like thin planar stacks where each piezoelectric layer is composed of a multitude of fibers. We investigate the suitability of using previously published inversion techniques for the impedance resonances of monolithic co-fired piezoelectric stacks to the MFCTM to determine the complex material constants from the impedance data. The impedance equations examined in this paper are those based on the derivation. The utility of resonance techniques to invert the impedance data to determine the small signal complex material constants are presented for a series of MFC's. The technique was applied to actuators with different geometries and the real coefficients were determined to be similar within changes of the boundary conditions due to change of geometry. The scatter in the imaginary coefficient was found to be larger. The technique was also applied to the same actuator type but manufactured in different batches with some design changes in the non active portion of the actuator and differences in the dielectric and the electromechanical coupling between the two batches were easily measureable. It is interesting to note that strain predicted by small signal impedance analysis is much lower than high field stains. Since the model is based on material properties rather than circuit constants, it could be used for the direct evaluation of specific aging or degradation mechanisms in the actuator as well as batch sorting and adjustment of manufacturing processes.

Impedance spectroscopy measurements as a tool for distinguishing different luminal content during bolus transit studies.

PubMed

Ruiz-Vargas, A; Mohd Rosli, R; Ivorra, A; Arkwright, J W

2018-01-08

Intraluminal electrical impedance is a well-known diagnostic tool used to study bolus movement in the human esophagus. However, it is use in the human colon it is hindered by the fact that the content cannot be controlled and may include liquid, gas, solid, or a mixture of these at any one time. This article investigates the use of complex impedance spectroscopy to study different luminal content (liquid and gas). An excised section of guinea pig proximal colon was placed in an organ bath with Krebs solution at 37°C and a custom built bioimpedance catheter was placed in the lumen. Liquid (Krebs) and gas (air) content was pumped through the lumen and the intraluminal impedance was measured at five different frequencies (1, 5.6, 31.6, 177.18 kHz and 1 MHz) at 10 samples per second. A numerical model was created to model the passage of bolus with different content and compared to the experimental data. Differences in mean impedance magnitude and phase angle were found (from 1 to 177.18 kHz) for different contents. The numerical results qualitatively agreed with those in the experimental study. Conductivities of bolus had an effect on detecting its passage. Complex impedance spectroscopy can distinguish between different luminal content within a range of measuring frequencies. The numerical model showed the importance of bolus conductivities for bolus transit studies in those where the bolus is controlled. © 2018 John Wiley & Sons Ltd.

Flow Duct Data for Validation of Acoustic Liner Codes for Impedance Eduction

NASA Technical Reports Server (NTRS)

Ahuja, K. K.; Munro, Scott; Gaeta, R. J., Jr.

2000-01-01

The objective of the study reported here was to acquire acoustic and flow data with hard and lined duct wall duct sections for validation of a liner prediction code being developed at NASA LaRC. Both the mean flowfield and acoustic flowfields were determined in a cross-plane of the rectangular duct. A flow duct facility with acoustic drivers connected to a rectangular (4.7 x 2.0 inch) source section and a linear acoustic liner mounted downstream of the source section was used in this study. The liner section was designed to allow liner materials to be placed on all 4 walls of the duct. The test liner was of the locally-reacting type and was made from a ceramic material. The material, consisting of a tubular structure, was provided by NASA LaRC. The liner was approximately 8.89 cm (3.5 inches) thick. For the current study, only the two "short" sides of the duct were lined with liner material. The other two sides were hard walls. Two especially built instrumentation sections were attached on either sides of the liner section to allow acoustic and flow measurements to be made upstream and downstream of the liner. The two instrumentation duct sections were built to allow measurement of acoustic and flow properties at planes perpendicular to flow upstream and downstream of the liner section. The instrumentation section was also designed to provide a streamwise gradient in acoustic (complex) pressure from which the acoustic particle velocity, needed for the model validation, can be computed. Flow measurements included pressure, temperature, and velocity profiles upstream of the liner section. The in-flow sound pressure levels and phases were obtained with a microphone probe equipped with a nose cone in two cross planes upstream of the liner and two cross plane downstream of the liner. In addition to the acoustic measurements at the cross planes. axial centerline acoustic data was acquired using an axially traversing microphone probe which was traversed from a location upstream of the liner to some distance downstream of the liner. All probes used here had to be calibrated with respect to a standard microphone equipped with a nose cone to allow for the effects of flow.

The craniofacial complex in 47, XXX females.

PubMed

Krusinskiene, Viktorija; Krusinskie, Viktorija; Alvesalo, Lassi; Sidlauskas, Antanas

2005-08-01

A study of the craniofacial complex in four 47, XXX Finnish females, or females with an extra X chromosome, was carried out using cephalometric analysis comprising linear and angular measurements. The lengths of the anterior and posterior cranial bases, the calvarium, mandibular ramus and posterior and upper anterior face heights were found to be significantly shorter than in female controls, while the angles between the foraminal and clival planes, the mandibular plane and cranial base, the maxillary and occlusal planes, the maxillary and mandibular planes and the foraminal and mandibular planes, and also the gonial angle, were significantly enlarged. The present findings of reduced linear measurements, together with the results of studies on the craniofacial complex of 47, XXY and 47, XYY males, suggest dimensional variation between these groups from the promoting effect of an extra Y chromosome and the retarding effect of an extra X chromosome on craniofacial growth.

Stochastic estimation of human shoulder impedance with robots: an experimental design.

PubMed

Park, Kyungbin; Chang, Pyung Hun

2011-01-01

Previous studies assumed the shoulder as a hinge joint during human arm impedance measurement. This is obviously a vast simplification since the shoulder is a complex of several joints with multiple degrees of freedom. In the present work, a practical methodology for more general and realistic estimation of human shoulder impedance is proposed and validated with a spring array. It includes a gravity compensation scheme, which is developed and used for the experiments with a spatial three degrees of freedom PUMA-type robot. The experimental results were accurate and reliable, and thus it has shown a strong potential of the proposed methodology in the estimation of human shoulder impedance. © 2011 IEEE

Optimal Chebyshev polynomials on ellipses in the complex plane

NASA Technical Reports Server (NTRS)

Fischer, Bernd; Freund, Roland

1989-01-01

The design of iterative schemes for sparse matrix computations often leads to constrained polynomial approximation problems on sets in the complex plane. For the case of ellipses, we introduce a new class of complex polynomials which are in general very good approximations to the best polynomials and even optimal in most cases.

Wideband analytical equivalent circuit for one-dimensional periodic stacked arrays.

PubMed

Molero, Carlos; Rodríguez-Berral, Raúl; Mesa, Francisco; Medina, Francisco; Yakovlev, Alexander B

2016-01-01

A wideband equivalent circuit is proposed for the accurate analysis of scattering from a set of stacked slit gratings illuminated by a plane wave with transverse magnetic or electric polarization that impinges normally or obliquely along one of the principal planes of the structure. The slit gratings are printed on dielectric slabs of arbitrary thickness, including the case of closely spaced gratings that interact by higher-order modes. A Π-circuit topology is obtained for a pair of coupled arrays, with fully analytical expressions for all the circuit elements. This equivalent Π circuit is employed as the basis to derive the equivalent circuit of finite stacks with any given number of gratings. Analytical expressions for the Brillouin diagram and the Bloch impedance are also obtained for infinite periodic stacks.

Stand-off transmission lines and method for making same

DOEpatents

Tuckerman, David B.

1991-01-01

Standoff transmission lines in an integrated circuit structure are formed by etching away or removing the portion of the dielectric layer separating the microstrip metal lines and the ground plane from the regions that are not under the lines. The microstrip lines can be fabricated by a subtractive process of etching a metal layer, an additive process of direct laser writing fine lines followed by plating up the lines or a subtractive/additive process in which a trench is etched over a nucleation layer and the wire is electrolytically deposited. Microstrip lines supported on freestanding posts of dielectric material surrounded by air gaps are produced. The average dielectric constant between the lines and ground plane is reduced, resulting in higher characteristic impedance, less crosstalk between lines, increased signal propagation velocities, and reduced wafer stress.

Modeling the growth processes of polyelectrolyte multilayers using a quartz crystal resonator.

PubMed

Salomäki, Mikko; Kankare, Jouko

2007-07-26

The layer-by-layer buildup of chitosan/hyaluronan (CH/HA) and poly(l-lysine)/hyaluronan (PLL/HA) multilayers was followed on a quartz crystal resonator (QCR) in different ionic strengths and at different temperatures. These polyelectrolytes were chosen to demonstrate the method whereby useful information is retrieved from acoustically thick polymer layers during their buildup. Surface acoustic impedance recorded in these measurements gives a single or double spiral when plotted in the complex plane. The shape of this spiral depends on the viscoelasticity of the layer material and regularity of the growth process. The polymer layer is assumed to consist of one or two zones. A mathematical model was devised to represent the separation of the layer to two zones with different viscoelastic properties. Viscoelastic quantities of the layer material and the mode and parameters of the growth process were acquired by fitting a spiral to the experimental data. In all the cases the growth process was mainly exponential as a function of deposition cycles, the growth exponent being between 0.250 and 0.275.

Tracking of electrochemical impedance of batteries

NASA Astrophysics Data System (ADS)

Piret, H.; Granjon, P.; Guillet, N.; Cattin, V.

2016-04-01

This paper presents an evolutionary battery impedance estimation method, which can be easily embedded in vehicles or nomad devices. The proposed method not only allows an accurate frequency impedance estimation, but also a tracking of its temporal evolution contrary to classical electrochemical impedance spectroscopy methods. Taking into account constraints of cost and complexity, we propose to use the existing electronics of current control to perform a frequency evolutionary estimation of the electrochemical impedance. The developed method uses a simple wideband input signal, and relies on a recursive local average of Fourier transforms. The averaging is controlled by a single parameter, managing a trade-off between tracking and estimation performance. This normalized parameter allows to correctly adapt the behavior of the proposed estimator to the variations of the impedance. The advantage of the proposed method is twofold: the method is easy to embed into a simple electronic circuit, and the battery impedance estimator is evolutionary. The ability of the method to monitor the impedance over time is demonstrated on a simulator, and on a real Lithium ion battery, on which a repeatability study is carried out. The experiments reveal good tracking results, and estimation performance as accurate as the usual laboratory approaches.

Mechanical Impedance of the Human Body in the Horizontal Direction

NASA Astrophysics Data System (ADS)

Holmlund, P.; Lundström, R.

1998-08-01

The mechanical impedance of the seated human body in horizontal directions (fore-and-aft and lateral) was measured during different experimental conditions, such as vibration level (0·25-1·4 m/s2r.m.s.), frequency (1·13-80 Hz), body weight (54-93 kg), upper body posture (relaxed and erect) and gender. The outcome showed that impedance, normalized by the sitting weight, varies with direction, level, posture and gender. Generally the impedance spectra show one peak for the fore-and-aft (X) direction while two peaks are found in the lateral (Y) direction. Males showed a lower normalized impedance than females. Increasing fore-and-aft vibration decreases the frequency at which maximum impedance occurs but also reduces the overall magnitude. For the lateral direction a more complex pattern was found. The frequency of impedance peaks are constant with increasing vibration level. The magnitude of the second peak decreases when changing posture from erect to relaxed. Males showed a higher impedance magnitude than females and a greater dip between the two peaks. The impedance spectra for the two horizontal directions have different shapes. This supports the idea of treating them differently; such as with respect to risk assessments and development of preventative measures.

Microstrip Yagi Antenna with Dual Aperture-Coupled Feed

NASA Technical Reports Server (NTRS)

Pogorzelski, Ronald; Venkatesan, Jaikrishna

2008-01-01

A proposed microstrip Yagi antenna would operate at a frequency of 8.4 GHz (which is in the X band) and would feature a mechanically simpler, more elegant design, relative to a prior L-band microstrip Yagi antenna. In general, the purpose of designing a microstrip Yagi antenna is to combine features of a Yagi antenna with those of a microstrip patch to obtain an antenna that can be manufactured at low cost, has a low profile, and radiates a directive beam that, as plotted on an elevation plane perpendicular to the antenna plane, appears tilted away from the broadside. Such antennas are suitable for flush mounting on surfaces of diverse objects, including spacecraft, aircraft, land vehicles, and computers. Stated somewhat more precisely, what has been proposed is a microstrip antenna comprising an array of three Yagi elements. Each element would include four microstrip-patch Yagi subelements: one reflector patch, one driven patch, and two director patches. To obtain circular polarization, each driven patch would be fed by use of a dual offset aperture-coupled feed featuring bow-tie-shaped apertures. The selection of the dual offset bow-tie aperture geometry is supported by results found in published literature that show that this geometry would enable matching of the impedances of the driven patches to the 50-Omega impedance of the microstrip feedline while maintaining a desirably large front-to-back lobe ratio.

Note: Rapid offset reduction of impedance bridges taking into account instrumental damping and phase shifting.

PubMed

van der Wel, C M; Kortschot, R J; Bakelaar, I A; Erné, B H; Kuipers, B W M

2013-03-01

The sensitivity of an imperfectly balanced impedance bridge is limited by the remaining offset voltage. Here, we present a procedure for offset reduction in impedance measurements using a lock-in amplifier, by applying a complex compensating voltage external to the bridge. This procedure takes into account instrumental damping and phase shifting, which generally occur at the high end of the operational frequency range. Measurements demonstrate that the output of the circuit rapidly converges to the instrumentally limited noise at any frequency.

An efficient method for the calculation of mean extinction. I - The analyticity of the complex extinction efficiency of homogeneous spheres

NASA Astrophysics Data System (ADS)

Xing, Zhang-Fan; Greenberg, J. M.

1992-11-01

Results of an investigation of the analyticity of the complex extinction efficiency Q-tilde(ext) in different parameter domains are presented. In the size parameter domain, x = omega(a/c), numerical Hilbert transforms are used to study the analyticity properties of Q-tilde(ext) for homogeneous spheres. Q-tilde(ext) is found to be analytic in the entire lower complex x-tilde-plane when the refractive index, m, is fixed as a real constant (pure scattering) or infinity (perfect conductor); poles, however, appear in the left side of the lower complex x-tilde-plane as m becomes complex. The computation of the mean extinction produced by an extended size distribution of particles may be conveniently and accurately approximated using only a few values of the complex extinction evaluated in the complex plane.

Frictionless Contact of Multilayered Composite Half Planes Containing Layers With Complex Eigenvalues

NASA Technical Reports Server (NTRS)

Zhang, Wang; Binienda, Wieslaw K.; Pindera, Marek-Jerzy

1997-01-01

A previously developed local-global stiffness matrix methodology for the response of a composite half plane, arbitrarily layered with isotropic, orthotropic or monoclinic plies, to indentation by a rigid parabolic punch is further extended to accommodate the presence of layers with complex eigenvalues (e.g., honeycomb or piezoelectric layers). First, a generalized plane deformation solution for the displacement field in an orthotropic layer or half plane characterized by complex eigenvalues is obtained using Fourier transforms. A local stiffness matrix in the transform domain is subsequently constructed for this class of layers and half planes, which is then assembled into a global stiffness matrix for the entire multilayered half plane by enforcing continuity conditions along the interfaces. Application of the mixed boundary condition on the top surface of the half plane indented by a rigid punch results in an integral equation for the unknown pressure in the contact region. The integral possesses a divergent kernel which is decomposed into Cauchy-type and regular parts using the asymptotic properties of the local stiffness matrix and a relationship between Fourier and finite Hilbert transform of the contact pressure. The solution of the resulting singular integral equation is obtained using a collocation technique based on the properties of orthogonal polynomials developed by Erdogan and Gupta. Examples are presented that illustrate the important influence of low transverse properties of layers with complex eigenvalues, such as those exhibited by honeycomb, on the load versus contact length response and contact pressure distributions for half planes containing typical composite materials.

The Frequency Spectral Properties of Electrode-Skin Contact Impedance on Human Head and Its Frequency-Dependent Effects on Frequency-Difference EIT in Stroke Detection from 10Hz to 1MHz.

PubMed

Yang, Lin; Dai, Meng; Xu, Canhua; Zhang, Ge; Li, Weichen; Fu, Feng; Shi, Xuetao; Dong, Xiuzhen

2017-01-01

Frequency-difference electrical impedance tomography (fdEIT) reconstructs frequency-dependent changes of a complex impedance distribution. It has a potential application in acute stroke detection because there are significant differences in impedance spectra between stroke lesions and normal brain tissues. However, fdEIT suffers from the influences of electrode-skin contact impedance since contact impedance varies greatly with frequency. When using fdEIT to detect stroke, it is critical to know the degree of measurement errors or image artifacts caused by contact impedance. To our knowledge, no study has systematically investigated the frequency spectral properties of electrode-skin contact impedance on human head and its frequency-dependent effects on fdEIT used in stroke detection within a wide frequency band (10 Hz-1 MHz). In this study, we first measured and analyzed the frequency spectral properties of electrode-skin contact impedance on 47 human subjects' heads within 10 Hz-1 MHz. Then, we quantified the frequency-dependent effects of contact impedance on fdEIT in stroke detection in terms of the current distribution beneath the electrodes and the contact impedance imbalance between two measuring electrodes. The results showed that the contact impedance at high frequencies (>100 kHz) significantly changed the current distribution beneath the electrode, leading to nonnegligible errors in boundary voltages and artifacts in reconstructed images. The contact impedance imbalance at low frequencies (<1 kHz) also caused significant measurement errors. We conclude that the contact impedance has critical frequency-dependent influences on fdEIT and further studies on reducing such influences are necessary to improve the application of fdEIT in stroke detection.

The Frequency Spectral Properties of Electrode-Skin Contact Impedance on Human Head and Its Frequency-Dependent Effects on Frequency-Difference EIT in Stroke Detection from 10Hz to 1MHz

PubMed Central

Zhang, Ge; Li, Weichen; Fu, Feng; Shi, Xuetao; Dong, Xiuzhen

2017-01-01

Frequency-difference electrical impedance tomography (fdEIT) reconstructs frequency-dependent changes of a complex impedance distribution. It has a potential application in acute stroke detection because there are significant differences in impedance spectra between stroke lesions and normal brain tissues. However, fdEIT suffers from the influences of electrode-skin contact impedance since contact impedance varies greatly with frequency. When using fdEIT to detect stroke, it is critical to know the degree of measurement errors or image artifacts caused by contact impedance. To our knowledge, no study has systematically investigated the frequency spectral properties of electrode-skin contact impedance on human head and its frequency-dependent effects on fdEIT used in stroke detection within a wide frequency band (10 Hz-1 MHz). In this study, we first measured and analyzed the frequency spectral properties of electrode-skin contact impedance on 47 human subjects’ heads within 10 Hz-1 MHz. Then, we quantified the frequency-dependent effects of contact impedance on fdEIT in stroke detection in terms of the current distribution beneath the electrodes and the contact impedance imbalance between two measuring electrodes. The results showed that the contact impedance at high frequencies (>100 kHz) significantly changed the current distribution beneath the electrode, leading to nonnegligible errors in boundary voltages and artifacts in reconstructed images. The contact impedance imbalance at low frequencies (<1 kHz) also caused significant measurement errors. We conclude that the contact impedance has critical frequency-dependent influences on fdEIT and further studies on reducing such influences are necessary to improve the application of fdEIT in stroke detection. PMID:28107524

Dynamic Primitives of Motor Behavior

PubMed Central

Hogan, Neville; Sternad, Dagmar

2013-01-01

We present in outline a theory of sensorimotor control based on dynamic primitives, which we define as attractors. To account for the broad class of human interactive behaviors—especially tool use—we propose three distinct primitives: submovements, oscillations and mechanical impedances, the latter necessary for interaction with objects. Due to fundamental features of the neuromuscular system, most notably its slow response, we argue that encoding in terms of parameterized primitives may be an essential simplification required for learning, performance, and retention of complex skills. Primitives may simultaneously and sequentially be combined to produce observable forces and motions. This may be achieved by defining a virtual trajectory composed of submovements and/or oscillations interacting with impedances. Identifying primitives requires care: in principle, overlapping submovements would be sufficient to compose all observed movements but biological evidence shows that oscillations are a distinct primitive. Conversely, we suggest that kinematic synergies, frequently discussed as primitives of complex actions, may be an emergent consequence of neuromuscular impedance. To illustrate how these dynamic primitives may account for complex actions, we briefly review three types of interactive behaviors: constrained motion, impact tasks, and manipulation of dynamic objects. PMID:23124919

Dynamic Simulation of the 2011 M9.0 Tohoku Earthquake with Geometric Complexity on a Rate- and State-dependent Subduction Plane

NASA Astrophysics Data System (ADS)

Luo, B.; Duan, B.

2015-12-01

The Mw 9.0 Tohoku megathrust earthquake on 11 March 2011 is a great surprise to the scientific community due to its unexpected occurrence on the subduction zone of Japan Trench where earthquakes of magnitude ~7 to 8 are expected based on historical records. Slip distribution and kinematic slip history inverted from seismic data, GPS and tsunami recordings reveal two major aspects of this big event: a strong asperity near the hypocenter and large slip near the trench. To investigate physical conditions of these two aspects, we perform dynamic rupture simulations on a shallow-dipping rate- and state-dependent subduction plane with topographic relief. Although existence of a subducted seamount just up-dip of the hypocenter is still an open question, high Vp anomalies [Zhao et al., 2011] and low Vp/Vs anomalies [Yamamoto et al., 2014] there strongly suggest some kind of topographic relief exists there. We explicitly incorporate a subducted seamount on the subduction surface into our models. Our preliminary results show that the subducted seamount play a significant role in dynamic rupture propagation due to the alteration of the stress state around it. We find that a subducted seamount can act as a strong barrier to many earthquakes, but its ultimate failure after some earthquake cycles results in giant earthquakes. Its failure gives rise to large stress drop, resulting in a strong asperity in slip distribution as revealed in kinematic inversions. Our preliminary results also suggest that the rate- and state- friction law plays an important role in rupture propagation of geometrically complex faults. Although rate-strengthening behavior near the trench impedes rupture propagation, an energetic rupture can break such a barrier and manage to reach the trench, resulting in significant uplift at seafloor and hence devastating tsunami to human society.

Physiological modules for generating discrete and rhythmic movements: component analysis of EMG signals.

PubMed

Bengoetxea, Ana; Leurs, Françoise; Hoellinger, Thomas; Cebolla, Ana Maria; Dan, Bernard; Cheron, Guy; McIntyre, Joseph

2014-01-01

A central question in Neuroscience is that of how the nervous system generates the spatiotemporal commands needed to realize complex gestures, such as handwriting. A key postulate is that the central nervous system (CNS) builds up complex movements from a set of simpler motor primitives or control modules. In this study we examined the control modules underlying the generation of muscle activations when performing different types of movement: discrete, point-to-point movements in eight different directions and continuous figure-eight movements in both the normal, upright orientation and rotated 90°. To test for the effects of biomechanical constraints, movements were performed in the frontal-parallel or sagittal planes, corresponding to two different nominal flexion/abduction postures of the shoulder. In all cases we measured limb kinematics and surface electromyographic activity (EMG) signals for seven different muscles acting around the shoulder. We first performed principal component analysis (PCA) of the EMG signals on a movement-by-movement basis. We found a surprisingly consistent pattern of muscle groupings across movement types and movement planes, although we could detect systematic differences between the PCs derived from movements performed in each shoulder posture and between the principal components associated with the different orientations of the figure. Unexpectedly we found no systematic differences between the figure eights and the point-to-point movements. The first three principal components could be associated with a general co-contraction of all seven muscles plus two patterns of reciprocal activation. From these results, we surmise that both "discrete-rhythmic movements" such as the figure eight, and discrete point-to-point movement may be constructed from three different fundamental modules, one regulating the impedance of the limb over the time span of the movement and two others operating to generate movement, one aligned with the vertical and the other aligned with the horizontal.

Physiological modules for generating discrete and rhythmic movements: component analysis of EMG signals

PubMed Central

Bengoetxea, Ana; Leurs, Françoise; Hoellinger, Thomas; Cebolla, Ana Maria; Dan, Bernard; Cheron, Guy; McIntyre, Joseph

2015-01-01

A central question in Neuroscience is that of how the nervous system generates the spatiotemporal commands needed to realize complex gestures, such as handwriting. A key postulate is that the central nervous system (CNS) builds up complex movements from a set of simpler motor primitives or control modules. In this study we examined the control modules underlying the generation of muscle activations when performing different types of movement: discrete, point-to-point movements in eight different directions and continuous figure-eight movements in both the normal, upright orientation and rotated 90°. To test for the effects of biomechanical constraints, movements were performed in the frontal-parallel or sagittal planes, corresponding to two different nominal flexion/abduction postures of the shoulder. In all cases we measured limb kinematics and surface electromyographic activity (EMG) signals for seven different muscles acting around the shoulder. We first performed principal component analysis (PCA) of the EMG signals on a movement-by-movement basis. We found a surprisingly consistent pattern of muscle groupings across movement types and movement planes, although we could detect systematic differences between the PCs derived from movements performed in each shoulder posture and between the principal components associated with the different orientations of the figure. Unexpectedly we found no systematic differences between the figure eights and the point-to-point movements. The first three principal components could be associated with a general co-contraction of all seven muscles plus two patterns of reciprocal activation. From these results, we surmise that both “discrete-rhythmic movements” such as the figure eight, and discrete point-to-point movement may be constructed from three different fundamental modules, one regulating the impedance of the limb over the time span of the movement and two others operating to generate movement, one aligned with the vertical and the other aligned with the horizontal. PMID:25620928

Links between quantum physics and thought.

PubMed

Robson, Barry

2009-01-01

Quantum mechanics (QM) provides a variety of ideas that can assist in developing Artificial Intelligence for healthcare, and opens the possibility of developing a unified system of Best Practice for inference that will embrace both QM and classical inference. Of particular interest is inference in the hyperbolic-complex plane, the counterpart of the normal i-complex plane of basic QM. There are two reasons. First, QM appears to rotate from i-complex Hilbert space to hyperbolic-complex descriptions when observations are made on wave functions as particles, yielding classical results, and classical laws of probability manipulation (e.g. the law of composition of probabilities) then hold, whereas in the i-complex plane they do not. Second, i-complex Hilbert space is not the whole story in physics. Hyperbolic complex planes arise in extension from the Dirac-Clifford calculus to particle physics, in relativistic correction thereby, and in regard to spinors and twisters. Generalization of these forms resemble grammatical constructions and promote the idea that probability-weighted algebraic elements can be used to hold dimensions of syntactic and semantic meaning. It is also starting to look as though when a solution is reached by an inference system in the hyperbolic-complex, the hyperbolic-imaginary values disappear, while conversely hyperbolic-imaginary values are associated with the un-queried state of a system and goal seeking behavior.

Evaluation of a cost-effective loads approach. [for Viking Orbiter light weight structural design

NASA Technical Reports Server (NTRS)

Garba, J. A.; Wada, B. K.; Bamford, R.; Trubert, M. R.

1976-01-01

A shock spectra/impedance method for loads prediction is used to estimate member loads for the Viking Orbiter, a 7800-lb interplanetary spacecraft that has been designed using transient loads analysis techniques. The transient loads analysis approach leads to a lightweight structure but requires complex and costly analyses. To reduce complexity and cost a shock spectra/impedance method is currently being used to design the Mariner Jupiter Saturn spacecraft. This method has the advantage of using low-cost in-house loads analysis techniques and typically results in more conservative structural loads. The method is evaluated by comparing the increase in Viking member loads to the loads obtained by the transient loads analysis approach. An estimate of the weight penalty incurred by using this method is presented. The paper also compares the calculated flight loads from the transient loads analyses and the shock spectra/impedance method to measured flight data.

A Reconstruction Algorithm for Breast Cancer Imaging With Electrical Impedance Tomography in Mammography Geometry

PubMed Central

Kao, Tzu-Jen; Isaacson, David; Saulnier, Gary J.; Newell, Jonathan C.

2009-01-01

The conductivity and permittivity of breast tumors are known to differ significantly from those of normal breast tissues, and electrical impedance tomography (EIT) is being studied as a modality for breast cancer imaging to exploit these differences. At present, X-ray mammography is the primary standard imaging modality used for breast cancer screening in clinical practice, so it is desirable to study EIT in the geometry of mammography. This paper presents a forward model of a simplified mammography geometry and a reconstruction algorithm for breast tumor imaging using EIT techniques. The mammography geometry is modeled as a rectangular box with electrode arrays on the top and bottom planes. A forward model for the electrical impedance imaging problem is derived for a homogeneous conductivity distribution and is validated by experiment using a phantom tank. A reconstruction algorithm for breast tumor imaging based on a linearization approach and the proposed forward model is presented. It is found that the proposed reconstruction algorithm performs well in the phantom experiment, and that the locations of a 5-mm-cube metal target and a 6-mm-cube agar target could be recovered at a target depth of 15 mm using a 32 electrode system. PMID:17405377

Complex space monofilar approximation of diffraction currents on a conducting half plane

NASA Technical Reports Server (NTRS)

Lindell, I. V.

1987-01-01

Simple approximation of diffraction surface currents on a conducting half plane, due to an incoming plane wave, is obtained with a line current (monofile) in complex space. When compared to an approximating current at the edge, the diffraction pattern is seen to improve by an order of magnitude for a minimal increase of computation effort. Thus, the inconvient Fresnel integral functions can be avoided for quick calculations of diffracted fields and the accuracy is good in other directions than along the half plane. The method can be applied to general problems involving planar metal edges.

Full extraction methods to retrieve effective refractive index and parameters of a bianisotropic metamaterial based on material dispersion models

NASA Astrophysics Data System (ADS)

Hsieh, Feng-Ju; Wang, Wei-Chih

2012-09-01

This paper discusses two improved methods in retrieving effective refractive indices, impedances, and material properties, such as permittivity (ɛ) and permeability (μ), of metamaterials. The first method modified from Kong's retrieval method allows effective constitutive parameters over all frequencies including the anti-resonant band, where imaginary parts of ɛ or μ are negative, to be solved. The second method is based on genetic algorithms and optimization of properly defined goal functions to retrieve parameters of the Drude and Lorentz dispersion models. Equations of effective refractive index and impedance at any reference planes are derived. Split ring resonator-rod based metamaterials operating in terahertz frequencies are designed and investigated with proposed methods. Retrieved material properties and parameters are used to regenerate S-parameters and compared with simulation results generated by cst microwave studio software.

Improved design and in-situ measurements of new beam position monitors for Indus-2

NASA Astrophysics Data System (ADS)

Kumar, M.; Babbar, L. K.; Holikatti, A. C.; Yadav, S.; Tyagi, Y.; Puntambekar, T. A.; Senecha, V. K.

2018-01-01

Beam position monitors (BPM) are important diagnostic devices used in particle accelerators to monitor position of the beam for various applications. Improved version of button electrode BPM has been designed using CST Studio Suite for Indus-2 ring. The new BPMs are designed to replace old BPMs which were designed and installed more than 12 years back. The improved BPMs have higher transfer impedance, resonance free output signal, equal sensitivity in horizontal and vertical planes and fast decaying wakefield as compared to old BPMs. The new BPMs have been calibrated using coaxial wire method. Measurement of transfer impedance and time domain signals has also been performed in-situ with electron beam during Indus-2 operation. The calibration and beam based measurements results showed close agreement with the design parameters. This paper presents design, electromagnetic simulations, calibration result and in-situ beam based measurements of newly designed BPMs.

Ultrathin and lightweight microwave absorbers made of mu-near-zero metamaterials

PubMed Central

Zhong, Shuomin; He, Sailing

2013-01-01

We present a theory of perfect absorption in a bilayer model composed of a mu-near-zero (MNZ) metamaterial (MM) absorbing layer on a metallic substrate. Our analytical solutions reveal that a MM layer with a large purely imaginary permeability and a moderate permittivity backed by a metallic plane has a zero reflection at normal incidence when the thickness is ultrathin. The impedance-mismatched metamaterial absorber (MA) can be 77.3% thinner than conventional impedance-matched MAs with the same material loss in order to get the same absorption. A microwave absorber using double-layered spiral MMs with a thickness of only about one percent of the operating wavelength is designed and realized. An absorption efficiency above 93% at 1.74 GHz is demonstrated experimentally at illumination angles up to 60 degrees. Our absorber is 98% lighter than traditional microwave absorbers made of natural materials working at the same frequencies. PMID:23803861

Experimental investigation of microwave interaction with magnetoplasma in miniature multipolar configuration using impedance measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dey, Indranuj, E-mail: indranuj@aees.kyushu-u.ac.jp; Toyoda, Yuji; Yamamoto, Naoji

2014-09-15

A miniature microwave plasma source employing both radial and axial magnetic fields for plasma confinement has been developed for micro-propulsion applications. Plasma is initiated by launching microwaves via a short monopole antenna to circumvent geometrical cutoff limitations. The amplitude and phase of the forward and reflected microwave power is measured to obtain the complex reflection coefficient from which the equivalent impedance of the plasma source is determined. Effect of critical plasma density condition is reflected in the measurements and provides insight into the working of the miniature plasma source. A basic impedance calculation model is developed to help in understandingmore » the experimental observations. From experiment and theory, it is seen that the equivalent impedance magnitude is controlled by the coaxial discharge boundary conditions, and the phase is influenced primarily by the plasma immersed antenna impedance.« less

Study of the dopamine effect into cell solutions by impedance analysis

NASA Astrophysics Data System (ADS)

Paivana, G.; Apostolou, T.; Kaltsas, G.; Kintzios, S.

2017-11-01

Electrochemical Impedance Spectroscopy (EIS) has become a technique that is frequently used for biological assays. Impedance is defined as a complex - valued generalization of resistance and varies depending on its use per application field. In health sciences, bioimpedance is widely used as non-invasive and low cost alternative in many medical areas that provides valuable information about health status. This work focuses on assessing the effects of a bioactive substance applied to immobilized cells. Dopamine was used as a stimulant in order to implement impedance analysis with a specific type of cells. Dopamine constitutes one of the most important catecholamine neurotransmitters in both the mammalian central and peripheral nervous systems. The main purpose is to extract calibration curves at different frequencies with known dopamine concentrations in order to describe the behavior of cells applied to dopamine using an impedance measurement device. For comparison purposes, non-immobilized cells were tested for the same dopamine concentrations.

Digital synthetic impedance for application in vibration damping.

PubMed

Nečásek, J; Václavík, J; Marton, P

2016-02-01

In this work we present construction details of a precision, standalone, and compact digital synthetic impedance for application in the field of vibration damping. The presented device is based on an embedded ARM microcontroller with external AD and DA converters and a special analog front-end. The performance of the device is tested by comparing the actually synthesized impedance with several prescribed impedances and shows very good match. Fine-tuning ability of the device, which is crucial for the considered application, is also demonstrated and reaches as small step as 0.1% for the most complicated impedance structure and drops below the level of direct measurability with less complex structures. The real application in vibration damping is demonstrated on a simple and well understood case of a one-dimensional vibrating spring-mass system with piezoelectric actuator embedded as the interface between source of vibrations and vibrating mass.

Digital synthetic impedance for application in vibration damping

NASA Astrophysics Data System (ADS)

Nečásek, J.; Václavík, J.; Marton, P.

2016-02-01

In this work we present construction details of a precision, standalone, and compact digital synthetic impedance for application in the field of vibration damping. The presented device is based on an embedded ARM microcontroller with external AD and DA converters and a special analog front-end. The performance of the device is tested by comparing the actually synthesized impedance with several prescribed impedances and shows very good match. Fine-tuning ability of the device, which is crucial for the considered application, is also demonstrated and reaches as small step as 0.1% for the most complicated impedance structure and drops below the level of direct measurability with less complex structures. The real application in vibration damping is demonstrated on a simple and well understood case of a one-dimensional vibrating spring-mass system with piezoelectric actuator embedded as the interface between source of vibrations and vibrating mass.

ac Modeling and impedance spectrum tests of the superconducting magnetic field coils for the Wendelstein 7-X fusion experiment.

PubMed

Ehmler, Hartmut; Köppen, Matthias

2007-10-01

The impedance spectrum test was employed for detection of short circuits within Wendelstein 7-X (W7-X) superconducting magnetic field coils. This test is based on measuring the complex impedance over several decades of frequency. The results are compared to predictions of appropriate electrical equivalent circuits of coils in different production states or during cold test. When the equivalent circuit is not too complicated the impedance can be represented by an analytic function. A more detailed analysis is performed with a network simulation code. The overall agreement of measured and calculated or simulated spectra is good. Two types of short circuits which appeared are presented and analyzed. The detection limit of the method is discussed. It is concluded that combined high-voltage ac and low-voltage impedance spectrum tests are ideal means to rule out short circuits in the W7-X coils.

The complex dynamics of products and its asymptotic properties

PubMed Central

Cristelli, Matthieu; Zaccaria, Andrea; Pietronero, Luciano

2017-01-01

We analyse global export data within the Economic Complexity framework. We couple the new economic dimension Complexity, which captures how sophisticated products are, with an index called logPRODY, a measure of the income of the respective exporters. Products’ aggregate motion is treated as a 2-dimensional dynamical system in the Complexity-logPRODY plane. We find that this motion can be explained by a quantitative model involving the competition on the markets, that can be mapped as a scalar field on the Complexity-logPRODY plane and acts in a way akin to a potential. This explains the movement of products towards areas of the plane in which the competition is higher. We analyse market composition in more detail, finding that for most products it tends, over time, to a characteristic configuration, which depends on the Complexity of the products. This market configuration, which we called asymptotic, is characterized by higher levels of competition. PMID:28520794

Acoustic radiation from lined, unflanged ducts: Acoustic source distribution program

NASA Technical Reports Server (NTRS)

Beckemeyer, R. J.; Sawdy, D. T.

1971-01-01

An acoustic radiation analysis was developed to predict the far-field characteristics of fan noise radiated from an acoustically lined unflanged duct. This analysis is comprised of three modular digital computer programs which together provide a capability of accounting for the impedance mismatch at the duct exit plane. Admissible duct configurations include circular or annular, with or without an extended centerbody. This variation in duct configurations provides a capability of modeling inlet and fan duct noise radiation. The computer programs are described in detail.

Effects of refraction by means flow velocity gradients on the standing wave pattern in three-dimensional, rectangular waveguides

NASA Technical Reports Server (NTRS)

Hersh, A. S.

1979-01-01

The influence of a mean vortical flow on the connection between the standing wave pattern in a rectangular three dimensional waveguide and the corresponding duct axial impedance was determined analytically. The solution was derived using a perturbation scheme valid for low mean flow Mach numbers and plane wave sound frequencies. The results show that deviations of the standing wave pattern due to refraction by the mean flow gradients are small.

Longitudinal and transverse feedback kickers for the ALS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Corlett, J.N.; Johnson, J.; Lambertson, G.

We describe the development of electromagnetic kickers for coupled-bunch feedback systems at the ALS. Transverse kickers are of a stripline design with one kicker per plane, operating in the baseband, 10 kHz to 250 MHz. Longitudinal lockers are of a coaxial design with electrodes paired in series operating over the band 1.00 to 1.25 GHz. Operating-band measurements and parasitic impedance measurements are presented. Power levels from beam induced signals are presented. Fabrication techniques are discussed.

The acoustic monopole in motion

NASA Technical Reports Server (NTRS)

Norum, T. D.; Liu, C. H.

1976-01-01

The results of an experiment are presented in which a small monochromatic source which behaves like an acoustic monopole when stationary is moved at a constant speed over an asphalt surface past stationary microphones. An analysis of the monopole moving above a finite impedance reflecting plane is given. The theoretical and experimental results are compared for different ground to observer heights, source frequencies, and source velocities. A computation of the effects of source acceleration on the noise radiated by the monopole is also presented.

Aircraft noise propagation. [sound diffraction by wings

NASA Technical Reports Server (NTRS)

Hadden, W. J.; Pierce, A. D.

1978-01-01

Sound diffraction experiments conducted at NASA Langley Research Center to study the acoustical implications of the engine over wing configuration (noise-shielding by wing) and to provide a data base for assessing various theoretical approaches to the problem of aircraft noise reduction are described. Topics explored include the theory of sound diffraction around screens and wedges; the scattering of spherical waves by rectangular patches; plane wave diffraction by a wedge with finite impedence; and the effects of ambient flow and distribution sources.

Damage Diagnosis in Semiconductive Materials Using Electrical Impedance Measurements

NASA Technical Reports Server (NTRS)

Ross, Richard W.; Hinton, Yolanda L.

2008-01-01

Recent aerospace industry trends have resulted in an increased demand for real-time, effective techniques for in-flight structural health monitoring. A promising technique for damage diagnosis uses electrical impedance measurements of semiconductive materials. By applying a small electrical current into a material specimen and measuring the corresponding voltages at various locations on the specimen, changes in the electrical characteristics due to the presence of damage can be assessed. An artificial neural network uses these changes in electrical properties to provide an inverse solution that estimates the location and magnitude of the damage. The advantage of the electrical impedance method over other damage diagnosis techniques is that it uses the material as the sensor. Simple voltage measurements can be used instead of discrete sensors, resulting in a reduction in weight and system complexity. This research effort extends previous work by employing finite element method models to improve accuracy of complex models with anisotropic conductivities and by enhancing the computational efficiency of the inverse techniques. The paper demonstrates a proof of concept of a damage diagnosis approach using electrical impedance methods and a neural network as an effective tool for in-flight diagnosis of structural damage to aircraft components.

Structural and impedance spectroscopy properties of La0.8Ba0.1Ca0.1Mn1-xRuxO3 perovskites

NASA Astrophysics Data System (ADS)

Chebaane, M.; Talbi, N.; Dhahri, A.; Oumezzine, M.; Khirouni, K.

2017-03-01

Polycrystalline samples La0.8Ba0.1Ca0.1Mn1-xRuxO3 (x=0 and 0.075) were prepared by sol-gel-based Pechini method. The X ray diffraction study has shown that all the samples exhibit a single phase with rhombohedral structure (space group R 3 ̅c, no. 167). The complex impedance has been investigated in the temperature range 160-320 K and in the frequency range 40 Hz-1 MHz. The imaginary part of the complex impedance (Z‧‧) frequency dependence revealed one relaxation peak. The Cole-Cole plots of the impedance values exhibited a semi -circular arc that can be described by an R1+(R2//ZCPE) electrical equivalent circuit. The conductance spectra have been investigated by the Jonscher universal power law: G(ω)=GDC+Aωn, where ω is the frequency of the ac field, and n is the exponent. The activation energy obtained both from the conductance and from time relaxation analyses are very similar, and hence the relaxation process may be attributed to the same type of charge carriers.

Impedance analysis of a disk-type SOFC using doped lanthanum gallate under power generation

NASA Astrophysics Data System (ADS)

Kato, Tohru; Nozaki, Ken; Negishi, Akira; Kato, Ken; Monma, Akihiko; Kaga, Yasuo; Nagata, Susumu; Takano, Kiyonami; Inagaki, Toru; Yoshida, Hiroyuki; Hosoi, Kei; Hoshino, Koji; Akbay, Taner; Akikusa, Jun

Impedance measurements were carried out under practical power generation conditions in a disk-type SOFC, which may be utilized as a small-scale power generator. The tested cell was composed of doped lanthanum gallate (La 0.8Sr 0.2Ga 0.8Mg 0.15Co 0.05O 3- δ) as the electrolyte, Sm 0.5Sr 0.5CoO 3 as the cathode electrode and Ni/Ce 0.8Sm 0.2O 2 cermet as the anode electrode. The cell impedance was measured between 10 mHz and 10 kHz by varying the fuel utilization and gas flow rate and plotted in complex impedance diagrams. The observed impedance shows a large semi-circular pattern on the low frequency side. The semi-circular impedance, having a noticeably low characteristic frequency between 0.13 and 0.4 Hz, comes from the change in gas composition, originally caused by the cell reaction. The change in impedance with the fuel utilization (load current) and the gas flow rate agreed qualitatively well with the theoretical predictions from a simulation. This impedance was dominant under high fuel-utilization power-generation conditions. The impedance, which described the activation polarizations in the electrode reactions, was comparatively small and scarcely changed with the change in fuel utilization (load current) and gas flow rate.

Bioelectrical Impedance and The Frequency Dependent Current Conduction Through Biological Tissues: A Short Review

NASA Astrophysics Data System (ADS)

Kanti Bera, Tushar

2018-03-01

Biological tissues are developed with biological cells which exhibit complex electrical impedance called electrical bioimpedance. Under an alternating electrical excitation the bioimpedance varies with the tissue anatomy, composition and the signal frequency. The current penetration and conduction paths vary with frequency of the applied signal. Bioimpedance spectroscopy is used to study the frequency response of the electrical impedance of biological materials noninvasively. In bioimpedance spectroscopy, a low amplitude electrical signal is injected to the tissue sample or body parts to characterization the sample in terms of its bioimpedance. The electrical current conduction phenomena, which is highly influenced by the tissue impedance and the signal frequency, is an important phenomena which should be studied to understand the bioimpedance techniques like bioelectrical impedance analysis (BIA), EIS, or else. In this paper the origin of bioelectrical impedance and current conduction phenomena has been reviewed to present a brief summary of bioelectrical impedance and the frequency dependent current conduction through biological tissues. Simulation studies are conducted with alternation current injection through a two dimensional model of biological tissues containing finite number of biological cells suspended in extracellular fluid. The paper demonstrates the simulation of alternating current conduction through biological tissues conducted by COMSOL Multiphysics. Simulation studies also show the frequency response of the tissue impedance for different tissue compositions.

Microwave switching power divider. [antenna feeds

NASA Technical Reports Server (NTRS)

Stockton, R. J.; Johnson, R. W. (Inventor)

1981-01-01

A pair of parallel, spaced-apart circular ground planes define a microwave cavity with multi-port microwave power distributing switching circuitry formed on opposite sides of a thin circular dielectric substrate disposed between the ground planes. The power distributing circuitry includes a conductive disk located at the center of the substrate and connected to a source of microwave energy. A high speed, low insertion loss switching diode and a dc blocking capacitor are connected in series between the outer end of a transmission line and an output port. A high impedance, microwave blocking dc bias choke is connected between each switching diode and a source of switching current. The switching source forward biases the diodes to couple microwave energy from the conductive disk to selected output ports and, to associated antenna elements connected to the output ports to form a synthesized antenna pattern.

Sound Transmission through a Cylindrical Sandwich Shell with Honeycomb Core

NASA Technical Reports Server (NTRS)

Tang, Yvette Y.; Robinson, Jay H.; Silcox, Richard J.

1996-01-01

Sound transmission through an infinite cylindrical sandwich shell is studied in the context of the transmission of airborne sound into aircraft interiors. The cylindrical shell is immersed in fluid media and excited by an oblique incident plane sound wave. The internal and external fluids are different and there is uniform airflow in the external fluid medium. An explicit expression of transmission loss is derived in terms of modal impedance of the fluids and the shell. The results show the effects of (a) the incident angles of the plane wave; (b) the flight conditions of Mach number and altitude of the aircraft; (c) the ratios between the core thickness and the total thickness of the shell; and (d) the structural loss factors on the transmission loss. Comparisons of the transmission loss are made among different shell constructions and different shell theories.

Stand-off transmission lines and method for making same

DOEpatents

Tuckerman, D.B.

1991-05-21

Standoff transmission lines in an integrated circuit structure are formed by etching away or removing the portion of the dielectric layer separating the microstrip metal lines and the ground plane from the regions that are not under the lines. The microstrip lines can be fabricated by a subtractive process of etching a metal layer, an additive process of direct laser writing fine lines followed by plating up the lines or a subtractive/additive process in which a trench is etched over a nucleation layer and the wire is electrolytically deposited. Microstrip lines supported on freestanding posts of dielectric material surrounded by air gaps are produced. The average dielectric constant between the lines and ground plane is reduced, resulting in higher characteristic impedance, less crosstalk between lines, increased signal propagation velocities, and reduced wafer stress. 16 figures.

Electrochemical Impedance Imaging via the Distribution of Diffusion Times

NASA Astrophysics Data System (ADS)

Song, Juhyun; Bazant, Martin Z.

2018-03-01

We develop a mathematical framework to analyze electrochemical impedance spectra in terms of a distribution of diffusion times (DDT) for a parallel array of random finite-length Warburg (diffusion) or Gerischer (reaction-diffusion) circuit elements. A robust DDT inversion method is presented based on complex nonlinear least squares regression with Tikhonov regularization and illustrated for three cases of nanostructured electrodes for energy conversion: (i) a carbon nanotube supercapacitor, (ii) a silicon nanowire Li-ion battery, and (iii) a porous-carbon vanadium flow battery. The results demonstrate the feasibility of nondestructive "impedance imaging" to infer microstructural statistics of random, heterogeneous materials.

Development and Validation of an Interactive Liner Design and Impedance Modeling Tool

NASA Technical Reports Server (NTRS)

Howerton, Brian M.; Jones, Michael G.; Buckley, James L.

2012-01-01

The Interactive Liner Impedance Analysis and Design (ILIAD) tool is a LabVIEW-based software package used to design the composite surface impedance of a series of small-diameter quarter-wavelength resonators incorporating variable depth and sharp bends. Such structures are useful for packaging broadband acoustic liners into constrained spaces for turbofan engine noise control applications. ILIAD s graphical user interface allows the acoustic channel geometry to be drawn in the liner volume while the surface impedance and absorption coefficient calculations are updated in real-time. A one-dimensional transmission line model serves as the basis for the impedance calculation and can be applied to many liner configurations. Experimentally, tonal and broadband acoustic data were acquired in the NASA Langley Normal Incidence Tube over the frequency range of 500 to 3000 Hz at 120 and 140 dB SPL. Normalized impedance spectra were measured using the Two-Microphone Method for the various combinations of channel configurations. Comparisons between the computed and measured impedances show excellent agreement for broadband liners comprised of multiple, variable-depth channels. The software can be used to design arrays of resonators that can be packaged into complex geometries heretofore unsuitable for effective acoustic treatment.

Clinical implementation of electrical impedance tomography with hyperthermia.

PubMed

Moskowitz, M J; Ryan, T P; Paulsen, K D; Mitchell, S E

1995-01-01

We describe the use of electrical impedance tomography (EIT) for non-invasive thermal imaging in conjunction with a clinical treatment of a superficial scalp lesion utilizing a spiral microstrip antenna. This is our first reported use of EIT with a clinical hyperthermia treatment and perhaps the first world-wide. The thermal measurements recorded during treatment compare favourably with the images reconstructed from impedance data gathered during heating. A linear relation, measured in phantom material, between the change in temperature with the change in reconstructed impedance was assumed. The average discrepancy between the measured temperature changes with the temperatures reconstructed from the impedance changes was 1.4 degrees C, with the maximum being 8.9 degrees C. These preliminary data suggest that impedance changes can be measured during hyperthermia delivery and temperature estimates based on these observed changes are possible in the clinical setting. These findings also point to the complex, yet critical nature of the impedance versus temperature relationship for tissue in vivo. The reconstructed thermal images may provide complementary information about the overall thermal damage imposed during heating. Based on this initial clinical experience we feel that EIT has great potential as a viable clinical aid in imaging the temperature changes imposed during hyperthermia.

On the solution of two-point linear differential eigenvalue problems. [numerical technique with application to Orr-Sommerfeld equation

NASA Technical Reports Server (NTRS)

Antar, B. N.

1976-01-01

A numerical technique is presented for locating the eigenvalues of two point linear differential eigenvalue problems. The technique is designed to search for complex eigenvalues belonging to complex operators. With this method, any domain of the complex eigenvalue plane could be scanned and the eigenvalues within it, if any, located. For an application of the method, the eigenvalues of the Orr-Sommerfeld equation of the plane Poiseuille flow are determined within a specified portion of the c-plane. The eigenvalues for alpha = 1 and R = 10,000 are tabulated and compared for accuracy with existing solutions.

Single-Sided Deafness: Impact of Cochlear Implantation on Speech Perception in Complex Noise and on Auditory Localization Accuracy.

PubMed

Döge, Julia; Baumann, Uwe; Weissgerber, Tobias; Rader, Tobias

2017-12-01

To assess auditory localization accuracy and speech reception threshold (SRT) in complex noise conditions in adult patients with acquired single-sided deafness, after intervention with a cochlear implant (CI) in the deaf ear. Nonrandomized, open, prospective patient series. Tertiary referral university hospital. Eleven patients with late-onset single-sided deafness (SSD) and normal hearing in the unaffected ear, who received a CI. All patients were experienced CI users. Unilateral cochlear implantation. Speech perception was tested in a complex multitalker equivalent noise field consisting of multiple sound sources. Speech reception thresholds in noise were determined in aided (with CI) and unaided conditions. Localization accuracy was assessed in complete darkness. Acoustic stimuli were radiated by multiple loudspeakers distributed in the frontal horizontal plane between -60 and +60 degrees. In the aided condition, results show slightly improved speech reception scores compared with the unaided condition in most of the patients. For 8 of the 11 subjects, SRT was improved between 0.37 and 1.70 dB. Three of the 11 subjects showed deteriorations between 1.22 and 3.24 dB SRT. Median localization error decreased significantly by 12.9 degrees compared with the unaided condition. CI in single-sided deafness is an effective treatment to improve the auditory localization accuracy. Speech reception in complex noise conditions is improved to a lesser extent in 73% of the participating CI SSD patients. However, the absence of true binaural interaction effects (summation, squelch) impedes further improvements. The development of speech processing strategies that respect binaural interaction seems to be mandatory to advance speech perception in demanding listening situations in SSD patients.

Circularly polarized triple band glass shaped monopole patch antenna with metallic reflector for bluetooth & wireless applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jangid, K. G.; Kulhar, V. S.; Choudhary, N.

This paper presents the design and performance of strip line fed glass shaped monopole patch antenna having with overall size 30mm × 30 mm × 1.59 mm. In the patch; an eight shaped slot and in the ground plane an eight shaped ring are introduced. A metallic ground plane is also introduced at appropriate location beneath the ground plane. The proposed antenna is simulated by applying CST Microwave Studio simulator. Antenna provides circularly polarized radiations, triple broad impedance bandwidth of 203MHz (2.306GHz to 2.510GHz), 42MHz (2.685GHz to 2.757GHz) & GHz (3.63 GHz to 6.05 GHz), high flat gain (close to 5dBi) and good radiationmore » properties in the desired frequency range. This antenna may be a very useful tool for 2.45GHz Bluetooth communication band as well as for 2.4GHz/5.2 GHz /5.8 GHz WLAN bands & 3.7GHz/5.5 GHz Wi-Max bands.« less

Effects of Mev Si Ions and Thermal Annealing on Thermoelectric and Optical Properties of SiO2/SiO2+Ge Multi-nanolayer thin Films

NASA Astrophysics Data System (ADS)

Budak, S.; Alim, M. A.; Bhattacharjee, S.; Muntele, C.

Thermoelectric generator devices have been prepared from 200 alternating layers of SiO2/SiO2+Ge superlattice films using DC/RF magnetron sputtering. The 5 MeV Si ionsbombardmenthasbeen performed using the AAMU Pelletron ion beam accelerator to formquantum dots and / or quantum clusters in the multi-layer superlattice thin films to decrease the cross-plane thermal conductivity, increase the cross-plane Seebeck coefficient and increase the cross-plane electrical conductivity to increase the figure of merit, ZT. The fabricated devices have been annealed at the different temperatures to tailor the thermoelectric and optical properties of the superlattice thin film systems. While the temperature increased, the Seebeck coefficient continued to increase and reached the maximum value of -25 μV/K at the fluenceof 5x1013 ions/cm2. The decrease in resistivity has been seen between the fluence of 1x1013 ions/cm2 and 5x1013 ions/cm2. Transport properties like Hall coefficient, density and mobility did not change at all fluences. Impedance spectroscopy has been used to characterize the multi-junction thermoelectric devices. The loci obtained in the C*-plane for these data indicate non-Debye type relaxation displaying the presence of the depression parameter.

Extracting Cross-Sectional Clinical Images Based on Their Principal Axes of Inertia

PubMed Central

Fan, Yuzhou; Djuric, Marija; Li, Zhiyu; Antonijevic, Djordje; Milenkovic, Petar; Sun, Yueyang; Li, Ruining

2017-01-01

Cross-sectional imaging is considered the gold standard in diagnosing a range of diseases. However, despite its widespread use in clinical practice and research, no widely accepted method is available to reliably match cross-sectional planes in several consecutive scans. This deficiency can impede comparison between cross-sectional images and ultimately lead to misdiagnosis. Here, we propose and demonstrate a method for finding the same imaging plane in images obtained during separate scanning sessions. Our method is based on the reconstruction of a “virtual organ” from which arbitrary cross-sectional images can be extracted, independent of the axis orientation in the original scan or cut; the key is to establish unique body coordinates of the organ from its principal axes of inertia. To verify our method a series of tests were performed, and the same cross-sectional plane was successfully extracted. This new approach offers clinicians access, after just a single scanning session, to the morphology and structure of a lesion through cross-sectional images reconstructed along arbitrary axes. It also aids comparable detection of morphological and structural changes in the same imaging plane from scans of the same patient taken at different times—thus potentially reducing the misdiagnosis rate when cross-sectional images are interpreted. PMID:29410714

Frame junction vibration transmission with a modified frame deformation model.

PubMed

Moore, J A

1990-12-01

A previous paper dealt with vibration transmission through junctions of connected frame members where the allowed frame deformations included bending, torsion, and longitudinal motions [J.A. Moore, J. Acoust. Soc. Am. 88, 2766-2776 (1990)]. In helicopter and aircraft structures the skin panels can constitute a high impedance connection along the length of the frames that effectively prohibits in-plane motion at the elevation of the skin panels. This has the effect of coupling in-plane bending and torsional motions within the frame. This paper discusses the transmission behavior through frame junctions that accounts for the in-plane constraint in idealized form by assuming that the attached skin panels completely prohibit inplane motion in the frames. Also, transverse shear deformation is accounted for in describing the relatively deep web frame constructions common in aircraft structures. Longitudinal motion in the frames is not included in the model. Transmission coefficient predictions again show the importance of out-of-plane bending deformation to the transmission of vibratory energy in an aircraft structure. Comparisons are shown with measured vibration transmission data along the framing in the overhead of a helicopter airframe, with good agreement. The frame junction description has been implemented within a general purpose statistical energy analysis (SEA) computer code in modeling the entire airframe structure including skin panels.

Extracting Cross-Sectional Clinical Images Based on Their Principal Axes of Inertia.

PubMed

Fan, Yuzhou; Luo, Liangping; Djuric, Marija; Li, Zhiyu; Antonijevic, Djordje; Milenkovic, Petar; Sun, Yueyang; Li, Ruining; Fan, Yifang

2017-01-01

Cross-sectional imaging is considered the gold standard in diagnosing a range of diseases. However, despite its widespread use in clinical practice and research, no widely accepted method is available to reliably match cross-sectional planes in several consecutive scans. This deficiency can impede comparison between cross-sectional images and ultimately lead to misdiagnosis. Here, we propose and demonstrate a method for finding the same imaging plane in images obtained during separate scanning sessions. Our method is based on the reconstruction of a "virtual organ" from which arbitrary cross-sectional images can be extracted, independent of the axis orientation in the original scan or cut; the key is to establish unique body coordinates of the organ from its principal axes of inertia. To verify our method a series of tests were performed, and the same cross-sectional plane was successfully extracted. This new approach offers clinicians access, after just a single scanning session, to the morphology and structure of a lesion through cross-sectional images reconstructed along arbitrary axes. It also aids comparable detection of morphological and structural changes in the same imaging plane from scans of the same patient taken at different times-thus potentially reducing the misdiagnosis rate when cross-sectional images are interpreted.

A simple formula for the effective complex conductivity of periodic fibrous composites with interfacial impedance and applications to biological tissues

NASA Astrophysics Data System (ADS)

Bisegna, Paolo; Caselli, Federica

2008-06-01

This paper presents a simple analytical expression for the effective complex conductivity of a periodic hexagonal arrangement of conductive circular cylinders embedded in a conductive matrix, with interfaces exhibiting a capacitive impedance. This composite material may be regarded as an idealized model of a biological tissue comprising tubular cells, such as skeletal muscle. The asymptotic homogenization method is adopted, and the corresponding local problem is solved by resorting to Weierstrass elliptic functions. The effectiveness of the present analytical result is proved by convergence analysis and comparison with finite-element solutions and existing models.

Characterizing and Modeling the Noise and Complex Impedance of Feedhorn-Coupled TES Polarimeters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Appel, J. W.; Beall, J. A.; Essinger-Hileman, T.

2009-12-16

We present results from modeling the electrothermal performance of feedhorn-coupled transition edge sensor (TES) polarimeters under development for use in cosmic microwave background (CMB) polarization experiments. Each polarimeter couples radiation from a corrugated feedhorn through a planar orthomode transducer, which transmits power from orthogonal polarization modes to two TES bolometers. We model our TES with two- and three-block thermal architectures. We fit the complex impedance data at multiple points in the TES transition. From the fits, we predict the noise spectra. We present comparisons of these predictions to the data for two TESes on a prototype polarimeter.

Rheoencephalographic (REG) Assessment of Head and Neck Cooling for use with Multiple Sclerosis Patients

NASA Technical Reports Server (NTRS)

Montogomery, Leslie D.; Ku, Yu-Tsuan E.; Webbon, Bruce W. (Technical Monitor)

1995-01-01

We have prepared a computer program (RHEOSYS:RHEOencephalographic impedance trace scanning SyStem) that can be used to automate the analysis of segmental impedance blood flow waveforms. This program was developed to assist in the post test analysis of recorded impedance traces from multiple segments of the body. It incorporates many of the blood flow, segmental volume, and vascular state indices reported in the world literature. As it is currently programmed, seven points are selected from each blood flow pulse and associated ECG waveforrn: 1. peak of the first ECG QRS complex, 2. start of systolic slope on the blood flow trace, 3. maximum amplitude of the impedance pulse, 4. position of the dicrotic notch, 5. maximum amplitude of the postdicrotic segment, 6. peak of the second ECG QRS complex, and 7. start of the next blood flow pulse. These points we used to calculate various geometric, area, and time-related values associated with the impedance pulse morphology. RHEOSYS then calculates a series of 34 impedance and cardiac cycle parameters which include pulse amplitudes; areas; pulse propagation times; cardiac cycle times; and various measures of arterial and various tone, contractility, and pulse volume. We used this program to calculate the scalp and intracranial blood flow responses to head and neck cooling as it may be applied to lower the body temperatures of multiple sclerosis patients. Twelve women and twelve men were tested using a commercially available head and neck cooling system operated at its maximum cooling capacity for a period of 30 minutes. Head and neck cooling produced a transient change in scalp blood flow and a significant, (P<0.05) decrease of approx. 30% in intracranial blood flow. Results of this experiment will illustrate how REG and RHEOSYS can be used in biomedical applications.

A FEM-based method to determine the complex material properties of piezoelectric disks.

PubMed

Pérez, N; Carbonari, R C; Andrade, M A B; Buiochi, F; Adamowski, J C

2014-08-01

Numerical simulations allow modeling piezoelectric devices and ultrasonic transducers. However, the accuracy in the results is limited by the precise knowledge of the elastic, dielectric and piezoelectric properties of the piezoelectric material. To introduce the energy losses, these properties can be represented by complex numbers, where the real part of the model essentially determines the resonance frequencies and the imaginary part determines the amplitude of each resonant mode. In this work, a method based on the Finite Element Method (FEM) is modified to obtain the imaginary material properties of piezoelectric disks. The material properties are determined from the electrical impedance curve of the disk, which is measured by an impedance analyzer. The method consists in obtaining the material properties that minimize the error between experimental and numerical impedance curves over a wide range of frequencies. The proposed methodology starts with a sensitivity analysis of each parameter, determining the influence of each parameter over a set of resonant modes. Sensitivity results are used to implement a preliminary algorithm approaching the solution in order to avoid the search to be trapped into a local minimum. The method is applied to determine the material properties of a Pz27 disk sample from Ferroperm. The obtained properties are used to calculate the electrical impedance curve of the disk with a Finite Element algorithm, which is compared with the experimental electrical impedance curve. Additionally, the results were validated by comparing the numerical displacement profile with the displacements measured by a laser Doppler vibrometer. The comparison between the numerical and experimental results shows excellent agreement for both electrical impedance curve and for the displacement profile over the disk surface. The agreement between numerical and experimental displacement profiles shows that, although only the electrical impedance curve is considered in the adjustment procedure, the obtained material properties allow simulating the displacement amplitude accurately. Copyright © 2014 Elsevier B.V. All rights reserved.

In-plane omnidirectional magnetic field sensor based on Giant Magneto Impedance (GMI)

NASA Astrophysics Data System (ADS)

Díaz-Rubio, Ana; García-Miquel, Héctor; García-Chocano, Víctor Manuel

2017-12-01

In this work the design and characterization of an omnidirectional in-plane magnetic field sensor are presented. The sensor is based on the Giant Magneto Impedance (GMI) effect in glass-coated amorphous microwires of composition (Fe6Co94)72.5Si12.5B15. For the first time, a circular loop made with a microwire is used for giving omnidirectional response. In order to estimate the GMI response of the circular loop we have used a theoretical model of GMI, determining the GMI response as the sum of longitudinal sections with different angles of incidence. As a consequence of the circular loop, the GMI ratio of the sensor is reduced to 15% instead of 100% for the axial GMI response of a microwire. The sensor response has been experimentally verified and the GMI response of the circular loop has been studied as function of the magnetic field, driven current, and frequency. First, we have measured the GMI response of a longitudinal microwire for different angles of incidence, covering the full range between the tangential and perpendicular directions to the microwire axis. Then, using these results, we have experimentally verified the decomposition of a microwire with circular shape as longitudinal segments with different angles of incidence. Finally, we have designed a signal conditioning circuit for the omnidirectional magnetic field sensor. The response of the sensor has been studied as a function of the amplitude of the incident magnetic field.

A More Accurate and Efficient Technique Developed for Using Computational Methods to Obtain Helical Traveling-Wave Tube Interaction Impedance

NASA Technical Reports Server (NTRS)

Kory, Carol L.

1999-01-01

The phenomenal growth of commercial communications has created a great demand for traveling-wave tube (TWT) amplifiers. Although the helix slow-wave circuit remains the mainstay of the TWT industry because of its exceptionally wide bandwidth, until recently it has been impossible to accurately analyze a helical TWT using its exact dimensions because of the complexity of its geometrical structure. For the first time, an accurate three-dimensional helical model was developed that allows accurate prediction of TWT cold-test characteristics including operating frequency, interaction impedance, and attenuation. This computational model, which was developed at the NASA Lewis Research Center, allows TWT designers to obtain a more accurate value of interaction impedance than is possible using experimental methods. Obtaining helical slow-wave circuit interaction impedance is an important part of the design process for a TWT because it is related to the gain and efficiency of the tube. This impedance cannot be measured directly; thus, conventional methods involve perturbing a helical circuit with a cylindrical dielectric rod placed on the central axis of the circuit and obtaining the difference in resonant frequency between the perturbed and unperturbed circuits. A mathematical relationship has been derived between this frequency difference and the interaction impedance (ref. 1). However, because of the complex configuration of the helical circuit, deriving this relationship involves several approximations. In addition, this experimental procedure is time-consuming and expensive, but until recently it was widely accepted as the most accurate means of determining interaction impedance. The advent of an accurate three-dimensional helical circuit model (ref. 2) made it possible for Lewis researchers to fully investigate standard approximations made in deriving the relationship between measured perturbation data and interaction impedance. The most prominent approximations made in the analysis were addressed and fully investigated for their accuracy by using the three-dimensional electromagnetic simulation code MAFIA (Solution of Maxwell's Equations by the Finite Integration Algorithm) (refs. 3 and 4). We found that several approximations introduced significant error (ref. 5).

On high explosive launching of projectiles for shock physics experiments

NASA Astrophysics Data System (ADS)

Swift, Damian C.; Forest, Charles A.; Clark, David A.; Buttler, William T.; Marr-Lyon, Mark; Rightley, Paul

2007-06-01

The hydrodynamic operation of the "Forest Flyer" type of explosive launching system for shock physics projectiles was investigated in detail using one and two dimensional continuum dynamics simulations. The simulations were numerically converged and insensitive to uncertainties in the material properties; they reproduced the speed of the projectile and the shape of its rear surface. The most commonly used variant, with an Al alloy case, was predicted to produce a slightly curved projectile, subjected to some shock heating and likely exhibiting some porosity from tensile damage. The curvature is caused by a shock reflected from the case; tensile damage is caused by the interaction of the Taylor wave pressure profile from the detonation wave with the free surface of the projectile. The simulations gave only an indication of tensile damage in the projectile, as damage is not understood well enough for predictions in this loading regime. The flatness can be improved by using a case of lower shock impedance, such as polymethyl methacrylate. High-impedance cases, including Al alloys but with denser materials improving the launching efficiency, can be used if designed according to the physics of oblique shock reflection, which indicates an appropriate case taper for any combination of explosive and case material. The tensile stress induced in the projectile depends on the relative thickness of the explosive, expansion gap, and projectile. The thinner the projectile with respect to the explosive, the smaller the tensile stress. Thus if the explosive is initiated with a plane wave lens, the tensile stress is lower than that for initiation with multiple detonators over a plane. The previous plane wave lens designs did, however, induce a tensile stress close to the spall strength of the projectile. The tensile stress can be reduced by changes in the component thicknesses. Experiments verifying the operation of explosively launched projectiles should attempt to measure porosity induced in the projectile: arrival time measurements are likely to be insensitive to porous regions caused by damaged or recollected material.

Predicting chroma from luma with frequency domain intra prediction

NASA Astrophysics Data System (ADS)

Egge, Nathan E.; Valin, Jean-Marc

2015-03-01

This paper describes a technique for performing intra prediction of the chroma planes based on the reconstructed luma plane in the frequency domain. This prediction exploits the fact that while RGB to YUV color conversion has the property that it decorrelates the color planes globally across an image, there is still some correlation locally at the block level.1 Previous proposals compute a linear model of the spatial relationship between the luma plane (Y) and the two chroma planes (U and V).2 In codecs that use lapped transforms this is not possible since transform support extends across the block boundaries3 and thus neighboring blocks are unavailable during intra- prediction. We design a frequency domain intra predictor for chroma that exploits the same local correlation with lower complexity than the spatial predictor and which works with lapped transforms. We then describe a low- complexity algorithm that directly uses luma coefficients as a chroma predictor based on gain-shape quantization and band partitioning. An experiment is performed that compares these two techniques inside the experimental Daala video codec and shows the lower complexity algorithm to be a better chroma predictor.

Variable electrical properties in composites: Application to vanadium dioxide pigments in a polyethylene host

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alfred-Duplan, C.; Musso, J.; Gavarri, J.R.

1994-05-01

Composite pellets were prepared from low-density polyethylene (LDPE) and vanadium dioxide powders. The VO[sub 2] pigments are used for their insulating-to-metallic transition at 341 K in order to obtain electrically variable composite materials. The volume fractions of VO[sub 2] powders vary from [phi] = 0 to [phi] = 0.55. The composite samples are characterized by X-ray diffraction and scanning electron microscopy. Complex impedance analysis in the frequency range 10[sup [minus]1] to 10[sup 6]. Hz is carried out at room temperature and at T = 363 K, to observe the insulator-metal transition of VO[sub 2] pigments dispersed in the polymer host.more » The variation of the complex impedance modulus [vert bar]Z[vert bar] with frequency and with VO[sub 2] volume fraction ([phi]) is discussed. A specific (R, C) impedance model permits interpretation of the experimental results in terms of percolation; the observed variations can be accounted for.« less

Evaluation of indirect impedance for measuring microbial growth in complex food matrices.

PubMed

Johnson, N; Chang, Z; Bravo Almeida, C; Michel, M; Iversen, C; Callanan, M

2014-09-01

The suitability of indirect impedance to accurately measure microbial growth in real food matrices was investigated. A variety of semi-solid and liquid food products were inoculated with Bacillus cereus, Listeria monocytogenes, Staphylococcus aureus, Lactobacillus plantarum, Pseudomonas aeruginosa, Escherichia coli, Salmonella enteriditis, Candida tropicalis or Zygosaccharomyces rouxii and CO2 production was monitored using a conductimetric (Don Whitely R.A.B.I.T.) system. The majority (80%) of food and microbe combinations produced a detectable growth signal. The linearity of conductance responses in selected food products was investigated and a good correlation (R(2) ≥ 0.84) was observed between inoculum levels and times to detection. Specific growth rate estimations from the data were sufficiently accurate for predictive modeling in some cases. This initial evaluation of the suitability of indirect impedance to generate microbial growth data in complex food matrices indicates significant potential for the technology as an alternative to plating methods. Copyright © 2014 Elsevier Ltd. All rights reserved.

Staging in polyacetylene-iodine conductors

NASA Astrophysics Data System (ADS)

Baughman, R. H.; Murthy, N. S.; Miller, G. G.; Shacklette, L. W.

1983-07-01

Evidence is presented for the existence of highly conducting polyacetylene complexes with structures related to high-stage graphite, as well as structures related to first-stage graphite. X-ray diffraction measurements on polyacetylene-iodine complexes indicate equatorial lines at 7.7-8.0 and 13.8-14.3 Å. The shorter spacing arises in part from a structure in which iodine-rich planes alternate with planes of polyacetylene chains. The longer spacing, which disappears upon atmospheric exposure, is consistent with a structure analogous to third-stage graphite in which dopant-rich planes are separated by three close-packed planes of polyacetylene chains. The third-stage complex can be viewed as a perturbation of the structure of undoped polyacetylene, with the region between dopant layers consisting essentially of a one unit cell thickness of the parent polymer structure. Packing calculations for this model, in which a linear column of anions (I3- and/or I5-) displaces either every chain or every other chain in the dopant-rich layer, provide an interlayer spacing which is equal to that observed. Evidence consistent with third-stage structures (with both fractional occupation and complete occupation of the dopant plane) is also found by reexamination of published sorption data, which provides slope changes at close to the calculated limiting compositions for these structures [(CHI0.056)x and (CHI0.13)x]. However, a first-stage structure with alternating dopant arrays and polymer chains in the dopant plane [for which (CHI0.13)x is calculated] provides a better explanation for the second slope change, as well as for the composition obtained under dynamic vacuum, (CHI0.14)x. These results for iodine complexes are compared with those derived for the group VA halide complexes of polyacetylene.

Correlation of the impedance and effective electrode area of doped PEDOT modified electrodes for brain-machine interfaces.

PubMed

Harris, Alexander R; Molino, Paul J; Kapsa, Robert M I; Clark, Graeme M; Paolini, Antonio G; Wallace, Gordon G

2015-05-07

Electrode impedance is used to assess the thermal noise and signal-to-noise ratio for brain-machine interfaces. An intermediate frequency of 1 kHz is typically measured, although other frequencies may be better predictors of device performance. PEDOT-PSS, PEDOT-DBSA and PEDOT-pTs conducting polymer modified electrodes have reduced impedance at 1 kHz compared to bare metal electrodes, but have no correlation with the effective electrode area. Analytical solutions to impedance indicate that all low-intermediate frequencies can be used to compare the electrode area at a series RC circuit, typical of an ideal metal electrode in a conductive solution. More complex equivalent circuits can be used for the modified electrodes, with a simplified Randles circuit applied to PEDOT-PSS and PEDOT-pTs and a Randles circuit including a Warburg impedance element for PEDOT-DBSA at 0 V. The impedance and phase angle at low frequencies using both equivalent circuit models is dependent on the electrode area. Low frequencies may therefore provide better predictions of the thermal noise and signal-to-noise ratio at modified electrodes. The coefficient of variation of the PEDOT-pTs impedance at low frequencies was lower than the other conducting polymers, consistent with linear and steady-state electroactive area measurements. There are poor correlations between the impedance and the charge density as they are not ideal metal electrodes.

[The functional assessment of the upper urinary tract by the methods of 2-frequency impedance measurement and multichannel impedance ureterography].

PubMed

Mudraia, I S; Kirpatovskiĭ, V I

1993-01-01

The paper describes impedance methods of investigating upper urinary tracts (UUT) which may serve adjuvants in the diagnosis of the urinary tract wall disturbances due to diseases caused by impaired urine evacuation from the kidney and which may prove helpful in the choice of therapeutic policy, evaluation of the postoperative period and outcomes prognosis. UUT impedance tests can be performed during endoscopic manipulations or under open operative interventions. Two-frequency impedancemetry allows rapid detection of non-functioning UUT parts or sclerosal sites of the UUT wall, relevant criteria being the ratio of basic impedances of the site under low and high scanning current. This value is computed by an urological two-frequency impedancemeter IDU-M. To assess the UUT wall functionally, use should be made of 6-channel urological rheograph REUR-6 providing multichannel registration of immediate impedance ureterograms. In this manner one can obtain qualitative and quantitative assessment of the ureteral peristalsis through its all length, the criteria being the amplitude of impedance ureterographic complexes, their shape, duration, frequency, rhythm, sequence and rate of distribution. Loading tests increase the accuracy of UUT impedance measurements, are able to define compensatory reserves of the wall contractility. The introduction of rheological methods in urological practice makes broader the armory of diagnostic techniques in urology, upgrade pathogenetic validity of surgical and therapeutic measures.

Impedance Measurement Box

ScienceCinema

Christophersen, Jon; Morrison, Bill

2018-02-14

Energy storage devices, primarily batteries, are now more important to consumers, industries and the military. With increasing technical complexity and higher user expectations, there is also a demand for highly accurate state-of-health battery assessment techniques. IMB incorporates patented, proprietary, and tested capabilities using control software and hardware that can be part of an embedded monitoring system. IMB directly measures the wideband impedance spectrum in seconds during battery operation with no significant impact on service life. It also can be applied to batteries prior to installation, confirming health before entering active service, as well as during regular maintenance. For more information about this project, visit http://www.inl.gov/rd100/2011/impedance-measurement-box/

Electrochemical Impedance Imaging via the Distribution of Diffusion Times.

PubMed

Song, Juhyun; Bazant, Martin Z

2018-03-16

We develop a mathematical framework to analyze electrochemical impedance spectra in terms of a distribution of diffusion times (DDT) for a parallel array of random finite-length Warburg (diffusion) or Gerischer (reaction-diffusion) circuit elements. A robust DDT inversion method is presented based on complex nonlinear least squares regression with Tikhonov regularization and illustrated for three cases of nanostructured electrodes for energy conversion: (i) a carbon nanotube supercapacitor, (ii) a silicon nanowire Li-ion battery, and (iii) a porous-carbon vanadium flow battery. The results demonstrate the feasibility of nondestructive "impedance imaging" to infer microstructural statistics of random, heterogeneous materials.

High-resolution 3T Magnetic Resonance Imaging of the Triangular Fibrocartilage Complex in Chinese Wrists: Correlation with Cross-sectional Anatomy.

PubMed

Zhan, Hui-Li; Li, Wen-Ting; Bai, Rong-Jie; Wang, Nai-Li; Qian, Zhan-Hua; Ye, Wei; Yin, Yu-Ming

2017-04-05

The injury of the triangular fibrocartilage complex (TFCC) is a common cause of ulnar-sided wrist pain. The aim of this study was to investigate if the high-resolution 3T magnetic resonance imaging (MRI) could demonstrate the detailed complex anatomy of TFCC in Chinese. Fourteen Chinese cadaveric wrists (from four men and three women; age range at death from 30 to 60 years; mean age at 46 years) and forty healthy Chinese wrists (from 20 healthy volunteers, male/female: 10/10; age range from 21 to 53 years with a mean age of 32 years) in Beijing Jishuitan Hospital from March 2014 to March 2016 were included in this study. All cadavers and volunteers had magnetic resonance (MR) examination of the wrist with coronal T1-weighted and proton density-weighted imaging with fat suppression in three planes, respectively. MR arthrography (MRAr) was performed on one of the cadaveric wrists. Subsequently, all 14 cadaveric wrists were sliced into 2 mm thick slab with band saw (six in coronal plane, four in sagittal plane, and four in axial plane). The MRI features of normal TFCC were analyzed in these specimens and forty healthy wrists. Triangular fibrocartilage, the ulnar collateral ligament, and the meniscal homolog could be best observed on images in coronal plane. The palmar and dorsal radioulnar ligaments were best evaluated in transverse plane. The ulnotriquetral and ulnolunate ligaments were best visualized in sagittal plane. The latter two structures and the volar and dorsal capsules were better demonstrated on MRAr. High-resolution 3T MRI is capable to show the detailed complex anatomy of the TFCC and can provide valuable information for the clinical diagnosis in Chinese.

High-resolution 3T Magnetic Resonance Imaging of the Triangular Fibrocartilage Complex in Chinese Wrists: Correlation with Cross-sectional Anatomy

PubMed Central

Zhan, Hui-Li; Li, Wen-Ting; Bai, Rong-Jie; Wang, Nai-Li; Qian, Zhan-Hua; Ye, Wei; Yin, Yu-Ming

2017-01-01

Background: The injury of the triangular fibrocartilage complex (TFCC) is a common cause of ulnar-sided wrist pain. The aim of this study was to investigate if the high-resolution 3T magnetic resonance imaging (MRI) could demonstrate the detailed complex anatomy of TFCC in Chinese. Methods: Fourteen Chinese cadaveric wrists (from four men and three women; age range at death from 30 to 60 years; mean age at 46 years) and forty healthy Chinese wrists (from 20 healthy volunteers, male/female: 10/10; age range from 21 to 53 years with a mean age of 32 years) in Beijing Jishuitan Hospital from March 2014 to March 2016 were included in this study. All cadavers and volunteers had magnetic resonance (MR) examination of the wrist with coronal T1-weighted and proton density-weighted imaging with fat suppression in three planes, respectively. MR arthrography (MRAr) was performed on one of the cadaveric wrists. Subsequently, all 14 cadaveric wrists were sliced into 2 mm thick slab with band saw (six in coronal plane, four in sagittal plane, and four in axial plane). The MRI features of normal TFCC were analyzed in these specimens and forty healthy wrists. Results: Triangular fibrocartilage, the ulnar collateral ligament, and the meniscal homolog could be best observed on images in coronal plane. The palmar and dorsal radioulnar ligaments were best evaluated in transverse plane. The ulnotriquetral and ulnolunate ligaments were best visualized in sagittal plane. The latter two structures and the volar and dorsal capsules were better demonstrated on MRAr. Conclusion: High-resolution 3T MRI is capable to show the detailed complex anatomy of the TFCC and can provide valuable information for the clinical diagnosis in Chinese. PMID:28345546

A Double-Negative Metamaterial-Inspired Mobile Wireless Antenna for Electromagnetic Absorption Reduction.

PubMed

Alam, Touhidul; Faruque, Mohammad Rashed Iqbal; Islam, Mohammad Tariqul

2015-07-29

A double-negative metamaterial-inspired antenna is presented for mobile wireless applications. The antenna consists of a semi-circular radiating patch and a 3 × 4 hexagonal shaped metamaterial unit cell array in the ground plane. The antenna is fed with a 50 Ω microstrip feed line. The electric dimensions of the proposed antenna are 0.20λ × 0.26λ × 0.004λ, at the low-end frequency. The proposed antenna achieves a -10 dB impedance with a bandwidth of 2.29 GHz at the lower band and 1.28 GHz at the upper band and can operate for most of the mobile applications such as upper GSM bands, WiMAX, Bluetooth, and wireless local area network (WLAN) frequency bands. The focused novelties of the proposed antenna are its small size, multi-standard operating bands, and electromagnetic absorption reduction at all the operating frequencies using the double-negative metamaterial ground plane.

Characteristics of the wire biconical antenna used for EMC measurements

NASA Astrophysics Data System (ADS)

Austin, Brian A.; Fourie, Andre P. C.

1991-08-01

The characteristics of a wire biconical antenna that determine its antenna factor were computed by using the method of moments code NEC-2. A fairly extensive validation exercise was conducted from which a suitable computer model was derived. The input impedance, gain, and radiation patterns of the antenna were computed for special cases where the biconical antenna is used above a conducting ground plane for open-field EMC (electromagnetic compatibility) testing. The effects of height above the ground plane and polarization of the antenna on these parameters were found and the antenna factor was corrected for them. The current distribution along the antenna elements was also examined, and it was found that significant pattern distortion can occur at some frequencies when a horizontal wire biconical antenna is used close to the ground. These results will allow this broadband antenna to be used with confidence in applications where previously only resonant dipoles were specified.

Impedance magnitude optimization of the regenerator in Stirling pulse tube cryocoolers working at liquid-helium temperatures

NASA Astrophysics Data System (ADS)

Cao, Q.; Qiu, L. M.; Zhi, X. Q.; Han, L.; Gan, Z. H.; Zhang, X. B.; Zhang, X. J.; Sun, D. M.

2013-12-01

The impedance magnitude is important for the design and operation of a Stirling pulse tube cryocooler (SPTC). However, the influence of the impedance magnitude on the SPTC working at liquid-helium temperatures is still not clear due to the complexity of refrigeration mechanism at this temperature range. In this study, the influence of the impedance magnitude on the viscous and thermal losses has been investigated, which contributes to the overall refrigeration efficiency. Different from the previous study at liquid nitrogen temperatures, it has been found and verified experimentally that a higher impedance magnitude may result in a larger mass flow rate accompanied with larger losses in the warmer region, hence the refrigeration efficiency is lowered. Numerical simulation is carried out in SPTCs of different geometry dimensions and working parameters, and the experimental study is carried out in a three-stage SPTC. A minimum no-load refrigeration temperature is achieved with an appropriate impedance magnitude that is determined by the combination of frequency and precooling temperature. A lowest temperature of 4.76 K is achieved at 28 Hz and a precooling temperature of 22.6 K, which is the lowest temperature ever achieved with He-4 for SPTCs. Impedance magnitude optimization is clearly an important consideration for the design of a 4 K SPTC.

A low-power CMOS trans-impedance amplifier for FM/cw ladar imaging system

NASA Astrophysics Data System (ADS)

Hu, Kai; Zhao, Yi-qiang; Sheng, Yun; Zhao, Hong-liang; Yu, Hai-xia

2013-09-01

A scannerless ladar imaging system based on a unique frequency modulation/continuous wave (FM/cw) technique is able to entirely capture the target environment, using a focal plane array to construct a 3D picture of the target. This paper presents a low power trans-impedance amplifier (TIA) designed and implemented by 0.18 μm CMOS technology, which is used in the FM/cw imaging ladar with a 64×64 metal-semiconductor-metal(MSM) self-mixing detector array. The input stage of the operational amplifier (op amp) in TIA is realized with folded cascade structure to achieve large open loop gain and low offset. The simulation and test results of TIA with MSM detectors indicate that the single-end trans-impedance gain is beyond 100 kΩ, and the -3 dB bandwidth of Op Amp is beyond 60 MHz. The input common mode voltage ranges from 0.2 V to 1.5 V, and the power dissipation is reduced to 1.8 mW with a supply voltage of 3.3 V. The performance test results show that the TIA is a candidate for preamplifier of the read-out integrated circuit (ROIC) in the FM/cw scannerless ladar imaging system.

Electrical behavior of natural manganese dioxide (NMD)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gorgulho, H.F.; Fernandes, R.Z.D.; Pernaut, J.M.

NMD samples from Brazil have been submitted to magnetic and particle size separations and characterized by X-ray diffraction and fluorescence and thermogravimetric analyses. Results showed that simple physical treatments can lead to more than 60% enriched MnO{sub 2} materials which could satisfy some electrochemical applications. The electrical properties of the samples conditioned as pressed pellets have been investigated by four-points direct current probe and impedance spectroscopy, varying the conditions of preparation and measurement. It is proposed that the higher frequency impedance is equivalent to the intrinsic electronic resistance of the MnO{sub 2} phases while at lower frequencies occurs an interphasemore » charge separation coupled with a possible ionic transport. The corresponding contact resistance depends on the particle size distribution of the material, the compactation pressure of pellets and the iron content of the materials. The interphase dielectric relaxation does not behave ideally; the depression of the impedance semicircles as shown in the Nyquist plane is assumed to be related to the roughness of the bulk interfaces. Recent developments have shown the possibility of using manganese oxides as reversible electrodes for battery or supercapacitor applications for electrical vehicle. In these perspectives it is important to study the electrical and electrochemical properties of NMD in order to estimate its suitability for this kind of applications.« less

Scattering of ultrasonic waves from porous piezoelectric multilayered structures immersed in a fluid

NASA Astrophysics Data System (ADS)

Vashishth, Anil K.; Gupta, Vishakha

2012-12-01

The interest in porous piezoelectric materials is due to the demand for low-frequency hydrophone/actuator devices for use in underwater acoustic systems and other oceanographic applications. Porosity decreases the acoustic impedance, thus improving the transfer of acoustic energy to water or biological tissues. The impedance mismatching problem between the dense piezoelectric materials and the surrounding medium can be solved by inclusion of porosity in dense piezoceramics. The complete description of acoustic propagation in a multilayered system is of great interest in a variety of applications, such as non-destructive evaluation and acoustic design, and there is need for a flexible model that can describe the reflection and transmission of ultrasonic waves in these media. The present paper elaborates a theoretical model, based on the transfer matrix method, for describing reflection and transmission of plane elastic waves through a porous piezoelectric laminated plate, immersed in a fluid. The analytical expressions for the reflection coefficient, transmission coefficient and acoustic impedance are derived. The effects of frequency, angle of incidence, number of layers, layer thickness and porosity are observed numerically for different configurations. The results obtained are deduced for the piezoelectric laminated structure, piezoelectric layer and poro-elastic layer immersed in a fluid, which are in agreement with earlier established results and experimental studies.

Thickness-, Composition-, and Magnetic-Field-Dependent Complex Impedance Spectroscopy of Granular-Type-Barrier Co/Co-Al2O3/Co MTJs

NASA Astrophysics Data System (ADS)

Tuan, Nguyen Anh; Anh, Nguyen Tuan; Nga, Nguyen Tuyet; Tue, Nguyen Anh; Van Cuong, Giap

2016-06-01

The alternating-current (ac) electrical properties of granular-type-barrier magnetic tunnel junctions (GBMTJs) based on Co/Co x (Al2O3)1- x ( t)/Co trilayer structures have been studied using complex impedance spectroscopy (CIS). Their CIS characteristics were investigated in external magnetic fields varying from 0 kOe to 3 kOe as a function of Co composition x at 10 at.%, 25 at.%, and 35 at.%, with barrier layer thickness t of 20 nm to 90 nm. The influence of these factors on the behaviors of the ac impedance response of the GBMTJs was deeply investigated and attributed to the dielectric or conducting nature of the Co-Al2O3 barrier layer. The most remarkable typical phenomena observed in these behaviors, even appearing paradoxical, include lower impedance for thicker t for each given x, a declining trend of Z with increasing x, a clear decrease of Z with H, and especially a partition of Z into zones according to the H value. All these effects are analyzed and discussed to demonstrate that diffusion-type and mass-transfer-type phenomena can be inferred from processes such as spin tunneling and Coulomb or spin blockade in the Co-Al2O3 barrier layer.

Transition operators in electromagnetic-wave diffraction theory - General theory

NASA Technical Reports Server (NTRS)

Hahne, G. E.

1992-01-01

A formal theory is developed for the scattering of time-harmonic electromagnetic waves from impenetrable immobile obstacles with given linear, homogeneous, and generally nonlocal boundary conditions of Leontovich (impedance) type for the wave of the obstacle's surface. The theory is modeled on the complete Green's function and the transition (T) operator in time-independent formal scattering theory of nonrelativistic quantum mechanics. An expression for the differential scattering cross section for plane electromagnetic waves is derived in terms of certain matrix elements of the T operator for the obstacle.

A systematic uncertainty analysis for liner impedance eduction technology

NASA Astrophysics Data System (ADS)

Zhou, Lin; Bodén, Hans

2015-11-01

The so-called impedance eduction technology is widely used for obtaining acoustic properties of liners used in aircraft engines. The measurement uncertainties for this technology are still not well understood though it is essential for data quality assessment and model validation. A systematic framework based on multivariate analysis is presented in this paper to provide 95 percent confidence interval uncertainty estimates in the process of impedance eduction. The analysis is made using a single mode straightforward method based on transmission coefficients involving the classic Ingard-Myers boundary condition. The multivariate technique makes it possible to obtain an uncertainty analysis for the possibly correlated real and imaginary parts of the complex quantities. The results show that the errors in impedance results at low frequency mainly depend on the variability of transmission coefficients, while the mean Mach number accuracy is the most important source of error at high frequencies. The effect of Mach numbers used in the wave dispersion equation and in the Ingard-Myers boundary condition has been separated for comparison of the outcome of impedance eduction. A local Mach number based on friction velocity is suggested as a way to reduce the inconsistencies found when estimating impedance using upstream and downstream acoustic excitation.

Noncommutative reading of the complex plane through Delone sequences

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ali, S. Twareque; Balkova, Lubka; Gazeau, J. P.

2009-04-15

The Berezin-Klauder-Toeplitz ('anti-Wick') quantization or 'noncommutative reading' of the complex plane, viewed as the phase space of a particle moving on the line, is derived from the resolution of the unity provided by the standard (or Gaussian) coherent states. The construction of these states and their attractive properties are essentially based on the energy spectrum of the harmonic oscillator, that is, on the natural numbers. This work is an attempt for following the same path by considering sequences of non-negative numbers which are not 'too far' from the natural numbers. In particular, we examine the consequences of such perturbations onmore » the noncommutative reading of the complex plane in terms of its probabilistic, functional, and localization aspects.« less

A semi-analytical model for the acoustic impedance of finite length circular holes with mean flow

NASA Astrophysics Data System (ADS)

Yang, Dong; Morgans, Aimee S.

2016-12-01

The acoustic response of a circular hole with mean flow passing through it is highly relevant to Helmholtz resonators, fuel injectors, perforated plates, screens, liners and many other engineering applications. A widely used analytical model [M.S. Howe. "Onthe theory of unsteady high Reynolds number flow through a circular aperture", Proc. of the Royal Soc. A. 366, 1725 (1979), 205-223] which assumes an infinitesimally short hole was recently shown to be insufficient for predicting the impedance of holes with a finite length. In the present work, an analytical model based on Green's function method is developed to take the hole length into consideration for "short" holes. The importance of capturing the modified vortex noise accurately is shown. The vortices shed at the hole inlet edge are convected to the hole outlet and further downstream to form a vortex sheet. This couples with the acoustic waves and this coupling has the potential to generate as well as absorb acoustic energy in the low frequency region. The impedance predicted by this model shows the importance of capturing the path of the shed vortex. When the vortex path is captured accurately, the impedance predictions agree well with previous experimental and CFD results, for example predicting the potential for generation of acoustic energy at higher frequencies. For "long" holes, a simplified model which combines Howe's model with plane acoustic waves within the hole is developed. It is shown that the most important effect in this case is the acoustic non-compactness of the hole.

Centre-based restricted nearest feature plane with angle classifier for face recognition

NASA Astrophysics Data System (ADS)

Tang, Linlin; Lu, Huifen; Zhao, Liang; Li, Zuohua

2017-10-01

An improved classifier based on the nearest feature plane (NFP), called the centre-based restricted nearest feature plane with the angle (RNFPA) classifier, is proposed for the face recognition problems here. The famous NFP uses the geometrical information of samples to increase the number of training samples, but it increases the computation complexity and it also has an inaccuracy problem coursed by the extended feature plane. To solve the above problems, RNFPA exploits a centre-based feature plane and utilizes a threshold of angle to restrict extended feature space. By choosing the appropriate angle threshold, RNFPA can improve the performance and decrease computation complexity. Experiments in the AT&T face database, AR face database and FERET face database are used to evaluate the proposed classifier. Compared with the original NFP classifier, the nearest feature line (NFL) classifier, the nearest neighbour (NN) classifier and some other improved NFP classifiers, the proposed one achieves competitive performance.

Variability in EIT Images of Lung Ventilation as a Function of Electrode Planes and Body Positions

PubMed Central

Zhang, Jie; Patterson, Robert

2014-01-01

This study is aimed at investigating the variability in resistivity changes in the lung region as a function of air volume, electrode plane and body position. Six normal subjects (33.8 ± 4.7 years, range from 26 to 37 years) were studied using the Sheffield Electrical Impedance Tomography (EIT) portable system. Three transverse planes at the level of second intercostal space, the level of the xiphisternal joint, and midway between upper and lower locations were chosen for measurements. For each plane, sixteen electrodes were uniformly positioned around the thorax. Data were collected with the breath held at end expiration and after inspiring 0.5, 1.0, or 1.5 liters of air from end expiration, with the subject in both the supine and sitting position. The average resistivity change in five regions, two 8x8 pixel local regions in the right lung, entire right, entire left and total lung regions, were calculated. The results show the resistivity change averaged over electrode positions and subject positions was 7-9% per liter of air, with a slightly larger resistivity change of 10 % per liter air in the lower electrode plane. There was no significant difference (p>0.05) between supine and sitting. The two 8x8 regions show a larger inter individual variability (coefficient of variation, CV, is from 30% to 382%) compared to the entire left, entire right and total lung (CV is from 11% to 51%). The results for the global regions are more consistent. The large inter individual variability appears to be a problem for clinical applications of EIT, such as regional ventilation. The variability may be mitigated by choosing appropriate electrode plane, body position and region of interest for the analysis. PMID:25110529

Variability in EIT Images of Lung Ventilation as a Function of Electrode Planes and Body Positions.

PubMed

Zhang, Jie; Patterson, Robert

2014-01-01

This study is aimed at investigating the variability in resistivity changes in the lung region as a function of air volume, electrode plane and body position. Six normal subjects (33.8 ± 4.7 years, range from 26 to 37 years) were studied using the Sheffield Electrical Impedance Tomography (EIT) portable system. Three transverse planes at the level of second intercostal space, the level of the xiphisternal joint, and midway between upper and lower locations were chosen for measurements. For each plane, sixteen electrodes were uniformly positioned around the thorax. Data were collected with the breath held at end expiration and after inspiring 0.5, 1.0, or 1.5 liters of air from end expiration, with the subject in both the supine and sitting position. The average resistivity change in five regions, two 8x8 pixel local regions in the right lung, entire right, entire left and total lung regions, were calculated. The results show the resistivity change averaged over electrode positions and subject positions was 7-9% per liter of air, with a slightly larger resistivity change of 10 % per liter air in the lower electrode plane. There was no significant difference (p>0.05) between supine and sitting. The two 8x8 regions show a larger inter individual variability (coefficient of variation, CV, is from 30% to 382%) compared to the entire left, entire right and total lung (CV is from 11% to 51%). The results for the global regions are more consistent. The large inter individual variability appears to be a problem for clinical applications of EIT, such as regional ventilation. The variability may be mitigated by choosing appropriate electrode plane, body position and region of interest for the analysis.

Reliability tests and guidelines for B-mode ultrasound assessment of central adiposity.

PubMed

Stoner, Lee; Chinn, Victoria; Cornwall, Jon; Meikle, Grant; Page, Rachel; Lambrick, Danielle; Faulkner, James

2015-11-01

Ultrasound represents a validated and relatively inexpensive diagnostic device for assessing central adiposity; however, widespread adoption has been impeded by the lack of reliable standard operating procedures. To examine the reliability of, and describe guidelines for, ultrasound-derived recording of intra-abdominal fat thickness (IAT) and maximal preperitoneal fat thickness (PFT). Ultrasound scans were obtained from 20 adults (50% female, 26 ± 7 years, 24·5 kg/m(2) ) on three different mornings. IAT was assessed 2 cm above the umbilicus (transverse plane) measuring from linea alba to: (i) anterior aorta, (ii) posterior aorta and (iii) anterior aspect of the vertebral column. PFT was measured from linea alba to visceral peritoneum in (i) sagittal and (ii) transverse planes, immediately over and inferior to the xiphi-sternum, respectively. For IAT, the criterion intraclass correlation coefficient (ICC) of 0·75 was exceeded for measurements to anterior aorta (0·95), posterior aorta (0·94) and vertebra (0·96). The reliability coefficient expressed as a percentage of the mean (RC%) was lowest (better) for measurement to vertebrae (9·8%). For PFT, mean thickness was comparable for sagittal (1·74 cm) and transverse (1·76 cm) planes; ICC values were also comparable for both planes (0·98 vs. 0·98, respectively), as were RC% (7·5% vs. 7·1%, respectively). IAT assessments to the vertebra were marginally more reliable than those to other structures. While PFT assessments were equally reliable for both measurements planes, precise probe placement was easier for the sagittal plane. Based on these findings, guidelines for the reliable measurement of central adiposity using ultrasound are presented. © 2015 Stichting European Society for Clinical Investigation Journal Foundation.

Multifunctional structural lithium ion batteries for electrical energy storage applications

NASA Astrophysics Data System (ADS)

Javaid, Atif; Zeshan Ali, Muhammad

2018-05-01

Multifunctional structural batteries based on carbon fiber-reinforced polymer composites are fabricated that can bear mechanical loads and act as electrochemical energy storage devices simultaneously. Structural batteries, containing woven carbon fabric anode; lithium cobalt oxide/graphene nanoplatelets coated aluminum cathode; filter paper separator and cross-linked polymer electrolyte, were fabricated through resin infusion under flexible tooling (RIFT) technique. Compression tests, dynamic mechanical thermal analysis, thermogravimetric analysis and impedance spectroscopy were done on the cross-linked polymer electrolytes while cyclic voltammetry, impedance spectroscopy, dynamic mechanical thermal analysis and in-plane shear tests were conducted on the fabricated structural batteries. A range of solid polymer electrolytes with increasing concentrations of lithium perchlorate salt in crosslinked polymer epoxies were formulated. Increased concentrations of electrolyte salt in cross-linked epoxy increased the ionic conductivity, although the compressive properties were compromised. A structural battery, exhibiting simultaneously a capacity of 0.16 mAh L‑1, an energy density of 0.32 Wh L‑1 and a shear modulus of 0.75 GPa have been reported.

A Compact Inductive Position Sensor Made by Inkjet Printing Technology on a Flexible Substrate

PubMed Central

Jeranče, Nikola; Vasiljević, Dragana; Samardžić, Nataša; Stojanović, Goran

2012-01-01

This paper describes the design, simulation and fabrication of an inductive angular position sensor on a flexible substrate. The sensor is composed of meandering silver coils printed on a flexible substrate (Kapton film) using inkjet technology. The flexibility enables that after printing in the plane, the coils could be rolled and put inside each other. By changing the angular position of the internal coil (rotor) related to the external one (stator), the mutual inductance is changed and consequently the impedance. It is possible to determine the angular position from the measured real and imaginary part of the impedance, in our case in the frequency range from 1 MHz to 10 MHz. Experimental results were compared with simulation results obtained by in-house developed software tool, and very good agreement has been achieved. Thanks to the simple design and fabrication, smaller package space requirements and weight, the presented sensor represents a cost-effective alternative to the other sensors currently used in series production applications. PMID:22438710

Physically elastic analysis of a cylindrical ring as a unit cell of a complete composite under applied stress in the complex plane using cubic polynomials

NASA Astrophysics Data System (ADS)

Monfared, Vahid

2018-03-01

Elastic analysis is analytically presented to predict the behaviors of the stress and displacement components in the cylindrical ring as a unit cell of a complete composite under applied stress in the complex plane using cubic polynomials. This analysis is based on the complex computation of the stress functions in the complex plane and polar coordinates. Also, suitable boundary conditions are considered and assumed to analyze along with the equilibrium equations and bi-harmonic equation. This method has some important applications in many fields of engineering such as mechanical, civil and material engineering generally. One of the applications of this research work is in composite design and designing the cylindrical devices under various loadings. Finally, it is founded that the convergence and accuracy of the results are suitable and acceptable through comparing the results.

Calibrated complex impedance of CHO cells and E. coli bacteria at GHz frequencies using scanning microwave microscopy

NASA Astrophysics Data System (ADS)

Tuca, Silviu-Sorin; Badino, Giorgio; Gramse, Georg; Brinciotti, Enrico; Kasper, Manuel; Oh, Yoo Jin; Zhu, Rong; Rankl, Christian; Hinterdorfer, Peter; Kienberger, Ferry

2016-04-01

The application of scanning microwave microscopy (SMM) to extract calibrated electrical properties of cells and bacteria in air is presented. From the S 11 images, after calibration, complex impedance and admittance images of Chinese hamster ovary cells and E. coli bacteria deposited on a silicon substrate have been obtained. The broadband capabilities of SMM have been used to characterize the bio-samples between 2 GHz and 20 GHz. The resulting calibrated cell and bacteria admittance at 19 GHz were Y cell = 185 μS + j285 μS and Y bacteria = 3 μS + j20 μS, respectively. A combined circuitry-3D finite element method EMPro model has been developed and used to investigate the frequency response of the complex impedance and admittance of the SMM setup. Based on a proposed parallel resistance-capacitance model, the equivalent conductance and parallel capacitance of the cells and bacteria were obtained from the SMM images. The influence of humidity and frequency on the cell conductance was experimentally studied. To compare the cell conductance with bulk water properties, we measured the imaginary part of the bulk water loss with a dielectric probe kit in the same frequency range resulting in a high level of agreement.

Dielectric relaxation of NdMnO{sub 3} nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saha, Sujoy, E-mail: sahasujoy3@gmail.com; Chanda, Sadhan; Dutta, Alo

2013-11-15

Graphical abstract: (a) TEM image of particle distribution of NMO. (b) HRTEM image of a single NMO particle under 4,000,000× magnification. (c) SAED pattern of a single NMO nanoparticle. - Highlights: • NdMnO{sub 3} nanoparticles are synthesized by sol–gel process. • TEM micrograph shows a granular characteristic with an average particle size of ∼50 nm. • HRTEM is consistent with the spacing between the (2 0 0) planes of the orthorhombic NdMnO{sub 3}. • Band gap is found to be 4.4 eV. • Cole–Cole model has been used to explain the dielectric relaxation in the material. • The activation energymore » of the material is found to be ∼0.43 eV. - Abstract: The neodymium manganate (NdMnO{sub 3}) nanoparticles are synthesized by the sol–gel process. The phase formation and particle size of the sample are determined by X-ray diffraction analysis and transmission electron microscopy. The band gap of the material is obtained by UV–visible absorption spectroscopy using Tauc relation. Dielectric properties of the sample have been investigated in the frequency range from 42 Hz to 1 MHz and in the temperature range from 303 K to 573 K. The dielectric relaxation peaks are observed in the frequency dependent dielectric loss spectra. The Cole–Cole model is used to explain the dielectric relaxation mechanism of the material. The complex impedance plane plot confirms the existence of both the grain and grain-boundary contribution to the relaxation. The temperature dependence of both grain and grain-boundary resistances follow the Arrhenius law with the activation energy of 0.427 and 0.431 eV respectively. The frequency-dependent conductivity spectra follow the power law.« less

Photovoltaic effect in organic polymer-iodine complex

NASA Technical Reports Server (NTRS)

Hermann, A. M.; Rembaum, A.

1967-01-01

Certain charge transfer complexes formed from organic polymers and iodine generate appreciable voltages at relatively low impedances upon exposure to light. These films show promise in applications requiring chemically and electrically stable films as detectors of optical radiation and as energy converters in photovoltaic cells.

Method and apparatus for in-situ characterization of energy storage and energy conversion devices

DOEpatents

Christophersen, Jon P [Idaho Falls, ID; Motloch, Chester G [Idaho Falls, ID; Morrison, John L [Butte, MT; Albrecht, Weston [Layton, UT

2010-03-09

Disclosed are methods and apparatuses for determining an impedance of an energy-output device using a random noise stimulus applied to the energy-output device. A random noise signal is generated and converted to a random noise stimulus as a current source correlated to the random noise signal. A bias-reduced response of the energy-output device to the random noise stimulus is generated by comparing a voltage at the energy-output device terminal to an average voltage signal. The random noise stimulus and bias-reduced response may be periodically sampled to generate a time-varying current stimulus and a time-varying voltage response, which may be correlated to generate an autocorrelated stimulus, an autocorrelated response, and a cross-correlated response. Finally, the autocorrelated stimulus, the autocorrelated response, and the cross-correlated response may be combined to determine at least one of impedance amplitude, impedance phase, and complex impedance.

Waveguide Transition for Submillimeter-Wave MMICs

NASA Technical Reports Server (NTRS)

Leong, Kevin M.; Deal, William R.; Radisic, Vesna; Mei, Xiaobing; Uyeda, Jansen; Lai, Richard; Fung, King Man; Gaier, Todd C.

2009-01-01

An integrated waveguide-to-MMIC (monolithic microwave integrated circuit) chip operating in the 300-GHz range is designed to operate well on high-permittivity semiconductor substrates typical for an MMIC amplifier, and allows a wider MMIC substrate to be used, enabling integration with larger MMICs (power amplifiers). The waveguide-to- CBCPW (conductor-backed coplanar waveguide) transition topology is based on an integrated dipole placed in the E-plane of the waveguide module. It demonstrates low loss and good impedance matching. Measurement and simulation demonstrate that the loss of the transition and waveguide loss is less than 1-dB over a 340-to-380-GHz bandwidth. A transition is inserted along the propagation direction of the waveguide. This transition uses a planar dipole aligned with the maximum E-field of the TE10 waveguide mode as an inter face between the waveguide and the MMIC. Mode conversion between the coplanar striplines (CPS) that feed the dipole and the CBCPW transmission line is accomplished using a simple air-bridge structure. The bottom side ground plane is truncated at the same reference as the top-side ground plane, leaving the end of the MMIC suspended in air.

Coherent states on the m-sheeted complex plane as m-photon states

NASA Technical Reports Server (NTRS)

Vourdas, Apostolos

1994-01-01

Coherent states on the m-sheeted complex plane are introduced and properties like overcompleteness and resolution of the identity are studied. They are eigenstates of the operators a(sub m)(+), a(sub m) which create and annihilate clusters of m-particles. Applications of this formalism in the study of Hamiltonians that describe m-particle clustering are also considered.

Sibling Curves and Complex Roots 2: Looking Ahead

ERIC Educational Resources Information Center

Harding, Ansie; Engelbrecht, Johann

2007-01-01

This paper, the second of a two part article, expands on an idea that appeared in literature in the 1950s to show that by restricting the domain to those complex numbers that map onto real numbers, representations of functions other than the ones in the real plane are obtained. In other words, the well-known curves in the real plane only depict…

Assessment of alterations in the electrical impedance of muscle after experimental nerve injury via finite-element analysis.

PubMed

Wang, Lucy L; Ahad, Mohammad; McEwan, Alistair; Li, Jia; Jafarpoor, Mina; Rutkove, Seward B

2011-06-01

The surface measurement of electrical impedance of muscle, incorporated as the technique of electrical impedance myography (EIM), provides a noninvasive approach for evaluating neuromuscular diseases, including amyotrophic lateral sclerosis. However, the relationship between alterations in surface impedance and the electrical properties of muscle remains uncertain. In order to investigate this further, a group of healthy adult rats, a group of rats two weeks postsciatic crush, and a group of animals six months postcrush underwent EIM of the gastrocnemius-soleus complex. The animals were then killed and the conductivity and permittivity of the extracted muscle measured. Finite-element models based on MRI data were then constructed for each group. The characteristic EIM parameter, 50 kHz phase (±standard error), obtained with surface impedance measurements was 17.3° ± 0.3° for normal animals, 13.8° ± 0.7° for acutely injured animals, and 16.1° ± 0.5° for chronically injured animals. The models predicted parallel changes with phase values of 24.3°, 18.8°, and 21.2° for the normal, acute, and chronic groups, respectively. Other multifrequency impedance parameters showed similar alterations. These results confirm that surface impedance measurements taken in conjunction with anatomical data and finite-element models may offer a noninvasive approach for assessing biophysical alterations in muscle in neuromuscular disease states.

Dielectric, Impedance and Conduction Behavior of Double Perovskite Pr2CuTiO6 Ceramics

NASA Astrophysics Data System (ADS)

Mahato, Dev K.; Sinha, T. P.

2017-01-01

Polycrystalline Pr2CuTiO6 (PCT) ceramics exhibits dielectric, impedance and modulus characteristics as a possible material for microelectronic devices. PCT was synthesized through the standard solid-state reaction method. The dielectric permittivity, impedance and electric modulus of PCT have been studied in a wide frequency (100 Hz-1 MHz) and temperature (303-593 K) range. Structural analysis of the compound revealed a monoclinic phase at room temperature. Complex impedance Cole-Cole plots are used to interpret the relaxation mechanism, and grain boundary contributions towards conductivity have been estimated. From electrical modulus formalism polarization and conductivity relaxation behavior in PCT have been discussed. Normalization of the imaginary part of impedance ( Z″) and the normalized imaginary part of modulus ( M″) indicates contributions from both long-range and localized relaxation effects. The grain boundary resistance along with their relaxation frequencies are plotted in the form of an Arrhenius plot with activation energy 0.45 eV and 0.46 eV, respectively. The ac conductivity mechanism has been discussed.

Organic electrochemical transistors for cell-based impedance sensing

NASA Astrophysics Data System (ADS)

Rivnay, Jonathan; Ramuz, Marc; Leleux, Pierre; Hama, Adel; Huerta, Miriam; Owens, Roisin M.

2015-01-01

Electrical impedance sensing of biological systems, especially cultured epithelial cell layers, is now a common technique to monitor cell motion, morphology, and cell layer/tissue integrity for high throughput toxicology screening. Existing methods to measure electrical impedance most often rely on a two electrode configuration, where low frequency signals are challenging to obtain for small devices and for tissues with high resistance, due to low current. Organic electrochemical transistors (OECTs) are conducting polymer-based devices, which have been shown to efficiently transduce and amplify low-level ionic fluxes in biological systems into electronic output signals. In this work, we combine OECT-based drain current measurements with simultaneous measurement of more traditional impedance sensing using the gate current to produce complex impedance traces, which show low error at both low and high frequencies. We apply this technique in vitro to a model epithelial tissue layer and show that the data can be fit to an equivalent circuit model yielding trans-epithelial resistance and cell layer capacitance values in agreement with literature. Importantly, the combined measurement allows for low biases across the cell layer, while still maintaining good broadband signal.

Electrically Small Microstrip Quarter-Wave Monopole Antennas

NASA Technical Reports Server (NTRS)

Young, W. Robert

2004-01-01

Microstrip-patch-style antennas that generate monopole radiation patterns similar to those of quarter-wave whip antennas can be designed to have dimensions smaller than those needed heretofore for this purpose, by taking advantage of a feed configuration different from the conventional one. The large sizes necessitated by the conventional feed configuration have, until now, made such antennas impractical for frequencies below about 800 MHz: for example, at 200 MHz, the conventional feed configuration necessitates a patch diameter of about 8 ft (.2.4 m) . too large, for example, for mounting on the roof of an automobile or on a small or medium-size aircraft. By making it possible to reduce diameters to between a tenth and a third of that necessitated by the conventional feed configuration, the modified configuration makes it possible to install such antennas in places where they could not previously be installed and thereby helps to realize the potential advantages (concealment and/or reduction of aerodynamic drag) of microstrip versus whip antennas. In both the conventional approach and the innovative approach, a microstrip-patch (or microstrip-patch-style) antenna for generating a monopole radiation pattern includes an electrically conductive patch or plate separated from an electrically conductive ground plane by a layer of electrically insulating material. In the conventional approach, the electrically insulating layer is typically a printed-circuit board about 1/16 in. (.1.6 mm) thick. Ordinarily, a coaxial cable from a transmitter, receiver, or transceiver is attached at the center on the ground-plane side, the shield of the cable being electrically connected to the ground plane. In the conventional approach, the coaxial cable is mated with a connector mounted on the ground plane. The center pin of this connector connects to the center of the coaxial cable and passes through a hole in the ground plane and a small hole in the insulating layer and then connects with the patch above one-third of the radial distance from the center. The modified feed configuration of the innovative approach is an inductive-short-circuit configuration that provides impedance matching and that has been used for many years on other antennas but not on microstrip-style monopole antennas. In this configuration, the pin is connected to both the conductive patch and the ground plane. As before, the shield of the coaxial cable is connected to the ground plane, but now the central conductor is connected to a point on the pin between the ground plane and the conductive plate (see figure). The location of the connection point on the pin is chosen so that together, the inductive short circuit and the conductive plate or patch act as components of a lumped-element resonant circuit that radiates efficiently at the resonance frequency and, at the resonance frequency, has an impedance that matches that of the coaxial cable. It should be noted that the innovative design entails two significant disadvantages. One disadvantage is that the frequency bandwidth for efficient operation is only about 1/20 to 1/15 that of a whip antenna designed for the same nominal frequency. The other disadvantage is that the estimated gain is between 3-1/2 and 4-1/2 dB below that of the whip antenna. However, if an affected radio-communication system used only a few adjacent frequency channels and the design of the components of the system other than the antenna provided adequate power or gain margin, then these disadvantages could be overcome.

Factors promoting or potentially impeding school success: disparities and state variations for children with special health care needs.

PubMed

Bethell, Christina; Forrest, Christopher B; Stumbo, Scott; Gombojav, Narangerel; Carle, Adam; Irwin, Charles E

2012-04-01

School success predicts many pathways for health and well-being across the life span. Factors promoting or potentially impeding school success are critical to understand for all children and for children with special health care needs (CSHCN), whose life course trajectories are already impacted by their chronic health problems. The 2007 National Survey of Children's Health was used (1) to estimate national and state prevalence and within and across states disparities in factors promoting school success (engagement, participation, safety) or potentially impeding success (missing school, grade repetition, school identified problems) for all children and CSHCN and (2) to evaluate associations with CSHCN service need complexity and presence of emotional, behavioral or developmental problems (EBD) as well as with school case management policies in states. Among school age children, 60 % experienced all three factors promoting school success (49.3-73.8 % across states), dropping to 51.3 % for CSHCN (39.4-64.7 % across states) and to 36.2 % for the 40 % of all CSHCN who have both more complex service needs and EBD. CSHCN were more likely to experience factors potentially impeding school success. After accounting for child factors, CSHCN living in states requiring case management in schools for children with disabilities were less likely to experience grade repetition (OR 0.65). Within-state disparities between non-CSHCN and CSHCN varied across states. Threats to school success for US children are pervasive and are especially pronounced for CSHCN with more complex needs and EBD. Findings support broad, non-condition specific efforts to promote school success for CSHCN and consideration of state school policies, such as case management.

A Micro-Grid Simulator Tool (SGridSim) using Effective Node-to-Node Complex Impedance (EN2NCI) Models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Udhay Ravishankar; Milos manic

2013-08-01

This paper presents a micro-grid simulator tool useful for implementing and testing multi-agent controllers (SGridSim). As a common engineering practice it is important to have a tool that simplifies the modeling of the salient features of a desired system. In electric micro-grids, these salient features are the voltage and power distributions within the micro-grid. Current simplified electric power grid simulator tools such as PowerWorld, PowerSim, Gridlab, etc, model only the power distribution features of a desired micro-grid. Other power grid simulators such as Simulink, Modelica, etc, use detailed modeling to accommodate the voltage distribution features. This paper presents a SGridSimmore » micro-grid simulator tool that simplifies the modeling of both the voltage and power distribution features in a desired micro-grid. The SGridSim tool accomplishes this simplified modeling by using Effective Node-to-Node Complex Impedance (EN2NCI) models of components that typically make-up a micro-grid. The term EN2NCI models means that the impedance based components of a micro-grid are modeled as single impedances tied between their respective voltage nodes on the micro-grid. Hence the benefit of the presented SGridSim tool are 1) simulation of a micro-grid is performed strictly in the complex-domain; 2) faster simulation of a micro-grid by avoiding the simulation of detailed transients. An example micro-grid model was built using the SGridSim tool and tested to simulate both the voltage and power distribution features with a total absolute relative error of less than 6%.« less

The effects of non-stationary noise on electromagnetic response estimates

NASA Astrophysics Data System (ADS)

Banks, R. J.

1998-11-01

The noise in natural electromagnetic time series is typically non-stationary. Sections of data with high magnetic noise levels bias impedances and generate unreliable error estimates. Sections containing noise that is coherent between electric and magnetic channels also produce inappropriate impedances and errors. The answer is to compute response values for data sections which are as short as is feasible, i.e. which are compatible both with the chosen bandwidth and with the need to over-determine the least-squares estimation of the impedance and coherence. Only those values that are reliable are selected, and the best single measure of the reliability of Earth impedance estimates is their temporal invariance, which is tested by the coherence between the measured and predicted electric fields. Complex demodulation is the method used here to explore the temporal structure of electromagnetic fields in the period range 20-6000 s. For periods above 300 s, noisy sections are readily identified in time series of impedance values. The corresponding estimates deviate strongly from the normal value, are biased towards low impedance values, and are associated with low coherences. Plots of the impedance against coherence are particularly valuable diagnostic aids. For periods below 300 s, impedance bias increases systematically as the coherence falls, identifying input channel noise as the cause. By selecting sections with high coherence (equivalent to the impedance being invariant over the section) unbiased impedances and realistic errors can be determined. The scatter in impedance values among high-coherence sections is due to noise that is coherent between input and output channels, implying the presence of two or more systems for which a consistent response can be defined. Where the Earth and noise responses are significantly different, it may be possible to improve estimates of the former by rejecting sections that do not generate satisfactory values for all the response elements.

Impedance Spectroscopy and AC Conductivity Studies of Bulk 3-Amino-7-(dimethylamino)-2-methyl-hydrochloride

NASA Astrophysics Data System (ADS)

El-Shabaan, M. M.

2018-02-01

Impedance spectroscopy and alternating-current (AC) conductivity (σ AC) studies of bulk 3-amino-7-(dimethylamino)-2-methyl-hydrochloride (neutral red, NR) have been carried out over the temperature (T) range from 303 K to 383 K and frequency (f) range from 0.5 kHz to 5 MHz. Dielectric data were analyzed using the complex impedance (Z *) and complex electric modulus (M *) for bulk NR at various temperatures. The impedance loss peaks were found to shift towards high frequencies, indicating an increase in the relaxation time (τ 0) and loss in the material, with increasing temperature. For each temperature, a single depressed semicircle was observed at high frequencies, originating from the bulk transport, and a spike in the low-frequency region, resulting from the electrode effect. Fitting of these curves yielded an equivalent circuit containing a parallel combination of a resistance R and constant-phase element (CPE) Q. The carrier transport in bulk NR is governed by the correlated barrier hopping (CBH) mechanism, some parameters of which, such as the maximum barrier height (W M), charge density (N), and hopping distance (r), were determined as functions of both temperature and frequency. The frequency dependence of σ AC at different temperatures indicated that the conduction in bulk NR is a thermally activated process. The σ AC value at different frequencies increased linearly with temperature.

3D modelling of the human thorax for ventilation distribution measured through electrical impedance tomography

NASA Astrophysics Data System (ADS)

Fan, W. R.; Wang, H. X.

2010-11-01

Thoracic electrical impedance tomography (EIT) aims to reconstruct a cross-sectional image of the internal spatial distribution of conductivity from electrical measurements made by injecting small alternating currents via an electrode array placed on the surface of the thorax. It is a non-invasive, radiation-free monitoring technique. In this paper, true 3D thorax models with conductivity distribution or complex conductivity distribution under different ARDS conditions are built up in comparison with the 2.5D ones, and EIT-derived numeric indices are also employed for evaluation of the lung ventilation. The purpose of this paper is to study different effects of different thorax models with either conductivity or complex conductivity on the reconstructed images and ventilation indices.

Building a Culture of Collaboration in Schools

ERIC Educational Resources Information Center

Sutton, Paul S.; Shouse, Andrew W.

2016-01-01

Teaching is complex; teachers and school leaders crave more meaningful collaborative experiences to make sense of that complexity. However, the structural, cultural, and historical factors involved with schooling impede the extent to which teachers can collaborate. Teachers spend five to six periods of the day teaching classes, largely working in…

Propagation characteristics of some novel coplanar waveguide transmission lines on GaAs at MM-wave frequencies

NASA Technical Reports Server (NTRS)

Simons, Rainee N.

1986-01-01

Three new Coplanar Waveguide (CPW) transmission lines, namely, Suspended CPW (SCPW), Stripline-like Suspended CPW (SSCPW) and Inverted CPW (ICPW), are proposed and also analyzed for their propagation characteristics. The substrate thickness, permittivity and dimensions of housing are assumed to be arbitrary. These structures have the following advantages over conventional CPW. Firstly, the ratio of guide wavelength to free space wavelength is closer to unity which results in larger dimensions and hence lower tolerances. Secondly, the effective dielectric constant is lower and hence the electromagnetic field energies are concentrated more in the air regions which should reduce attenuation. Thirdly, for a prescribed impedance level, the above structures have a wider slot width for identical strip width. Thus, low impedance lines can be achieved with reasonable slot dimensions. Fourthly, in an inverted CPW shunt mounting of active devices, such as Gunn and IMPATT diodes, between the strip and the metal trough is possible. This feature further enhances the attractiveness of the above structures. Lastly, an E-plane probe type transition from a rectangular waveguide to suspended CPW can also be easily realized. The computed results for GaAs at Ka-band illustrate the variation of normalized guide wavelength, effective dielectric constant and the characteristic impedance as a function of the: (1) frequency; (2) distance of separation between the trough side walls; (3) normalized strip and slot widths; and (4) normalized air gap.

Step voltage analysis for the catenoid lightning protection system

NASA Technical Reports Server (NTRS)

Chai, J. C.; Briet, R.; Barker, D. L.; Eley, H. E.

1991-01-01

The main objective of the proposed overhead Catenoid Lightning Protection System (CLPS) is personnel safety. To ensure working personnel's safety in lightning situations, it is necessary that the potential difference developed across a distance equal to a person's pace (step voltage) does not exceed a separately established safe voltage in order to avoid electrocution (ventricular fibrillation) of humans. Therefore, the first stage of the analytical effort is to calculate the open circuit step voltage. An impedance model is developed for this purpose. It takes into consideration the earth's complex impedance behavior and the transient nature of the lightning phenomenon. In the low frequency limit, this impedance model is shown to reduce to results similar to those predicted by the conventional resistor model in a DC analysis.

Electrical Characterization of Complex Memories. Part II. Assessment of a Circuit Implementation to Measure EPROM Data Storage Margins.

DTIC Science & Technology

1981-01-01

HIGH DESELECT DON’T CARE +5 V IMPEDANCE IH DON ’T HtIGH PO1WEAR DOWN VI1 +5 CARE IMPEDENCE PULSED PR RXPAM V TO V +25 v DATA NPRGA IL VIH VIl t PRORAM...VERIFY V +25 V DATA OUT IL IL PRARAM INHtIBIT VIL +25 VIH HIGH IMPEDANCE *[HIRESlHOLD MEASUREMENT +25V VARY V DATA OUT OV TO VT IL DFPR0GROVA +25V...VIL.C’E - VIH ) ! [l VCC Active Power Supply Current 57 100 mA 2 (5T C VIL) VPP Current (VPP - 5 25V) 6 mA 2.3 Vi.l Output High Voltage 24 Volts IOH -400

An intermittent control model of flexible human gait using a stable manifold of saddle-type unstable limit cycle dynamics

PubMed Central

Fu, Chunjiang; Suzuki, Yasuyuki; Kiyono, Ken; Morasso, Pietro; Nomura, Taishin

2014-01-01

Stability of human gait is the ability to maintain upright posture during walking against external perturbations. It is a complex process determined by a number of cross-related factors, including gait trajectory, joint impedance and neural control strategies. Here, we consider a control strategy that can achieve stable steady-state periodic gait while maintaining joint flexibility with the lowest possible joint impedance. To this end, we carried out a simulation study of a heel-toe footed biped model with hip, knee and ankle joints and a heavy head-arms-trunk element, working in the sagittal plane. For simplicity, the model assumes a periodic desired joint angle trajectory and joint torques generated by a set of feed-forward and proportional-derivative feedback controllers, whereby the joint impedance is parametrized by the feedback gains. We could show that a desired steady-state gait accompanied by the desired joint angle trajectory can be established as a stable limit cycle (LC) for the feedback controller with an appropriate set of large feedback gains. Moreover, as the feedback gains are decreased for lowering the joint stiffness, stability of the LC is lost only in a few dimensions, while leaving the remaining large number of dimensions quite stable: this means that the LC becomes saddle-type, with a low-dimensional unstable manifold and a high-dimensional stable manifold. Remarkably, the unstable manifold remains of low dimensionality even when the feedback gains are decreased far below the instability point. We then developed an intermittent neural feedback controller that is activated only for short periods of time at an optimal phase of each gait stride. We characterized the robustness of this design by showing that it can better stabilize the unstable LC with small feedback gains, leading to a flexible gait, and in particular we demonstrated that such an intermittent controller performs better if it drives the state point to the stable manifold, rather than directly to the LC. The proposed intermittent control strategy might have a high affinity for the inverted pendulum analogy of biped gait, providing a dynamic view of how the step-to-step transition from one pendular stance to the next can be achieved stably in a robust manner by a well-timed neural intervention that exploits the stable modes embedded in the unstable dynamics. PMID:25339687

An intermittent control model of flexible human gait using a stable manifold of saddle-type unstable limit cycle dynamics.

PubMed

Fu, Chunjiang; Suzuki, Yasuyuki; Kiyono, Ken; Morasso, Pietro; Nomura, Taishin

2014-12-06

Stability of human gait is the ability to maintain upright posture during walking against external perturbations. It is a complex process determined by a number of cross-related factors, including gait trajectory, joint impedance and neural control strategies. Here, we consider a control strategy that can achieve stable steady-state periodic gait while maintaining joint flexibility with the lowest possible joint impedance. To this end, we carried out a simulation study of a heel-toe footed biped model with hip, knee and ankle joints and a heavy head-arms-trunk element, working in the sagittal plane. For simplicity, the model assumes a periodic desired joint angle trajectory and joint torques generated by a set of feed-forward and proportional-derivative feedback controllers, whereby the joint impedance is parametrized by the feedback gains. We could show that a desired steady-state gait accompanied by the desired joint angle trajectory can be established as a stable limit cycle (LC) for the feedback controller with an appropriate set of large feedback gains. Moreover, as the feedback gains are decreased for lowering the joint stiffness, stability of the LC is lost only in a few dimensions, while leaving the remaining large number of dimensions quite stable: this means that the LC becomes saddle-type, with a low-dimensional unstable manifold and a high-dimensional stable manifold. Remarkably, the unstable manifold remains of low dimensionality even when the feedback gains are decreased far below the instability point. We then developed an intermittent neural feedback controller that is activated only for short periods of time at an optimal phase of each gait stride. We characterized the robustness of this design by showing that it can better stabilize the unstable LC with small feedback gains, leading to a flexible gait, and in particular we demonstrated that such an intermittent controller performs better if it drives the state point to the stable manifold, rather than directly to the LC. The proposed intermittent control strategy might have a high affinity for the inverted pendulum analogy of biped gait, providing a dynamic view of how the step-to-step transition from one pendular stance to the next can be achieved stably in a robust manner by a well-timed neural intervention that exploits the stable modes embedded in the unstable dynamics.

Detection of thoracic vascular structures by electrical impedance tomography: a systematic assessment of prominence peak analysis of impedance changes.

PubMed

Wodack, K H; Buehler, S; Nishimoto, S A; Graessler, M F; Behem, C R; Waldmann, A D; Mueller, B; Böhm, S H; Kaniusas, E; Thürk, F; Maerz, A; Trepte, C J C; Reuter, D A

2018-02-28

Electrical impedance tomography (EIT) is a non-invasive and radiation-free bedside monitoring technology, primarily used to monitor lung function. First experimental data shows that the descending aorta can be detected at different thoracic heights and might allow the assessment of central hemodynamics, i.e. stroke volume and pulse transit time. First, the feasibility of localizing small non-conductive objects within a saline phantom model was evaluated. Second, this result was utilized for the detection of the aorta by EIT in ten anesthetized pigs with comparison to thoracic computer tomography (CT). Two EIT belts were placed at different thoracic positions and a bolus of hypertonic saline (10 ml, 20%) was administered into the ascending aorta while EIT data were recorded. EIT images were reconstructed using the GREIT model, based on the individual's thoracic contours. The resulting EIT images were analyzed pixel by pixel to identify the aortic pixel, in which the bolus caused the highest transient impedance peak in time. In the phantom, small objects could be located at each position with a maximal deviation of 0.71 cm. In vivo, no significant differences between the aorta position measured by EIT and the anatomical aorta location were obtained for both measurement planes if the search was restricted to the dorsal thoracic region of interest (ROIs). It is possible to detect the descending aorta at different thoracic levels by EIT using an intra-aortic bolus of hypertonic saline. No significant differences in the position of the descending aorta on EIT images compared to CT images were obtained for both EIT belts.

Preliminary Characterization of Erythrocytes Deformability on the Entropy-Complexity Plane

PubMed Central

Korol, Ana M; D’Arrigo, Mabel; Foresto, Patricia; Pérez, Susana; Martín, Maria T; Rosso, Osualdo A

2010-01-01

We present an application of wavelet-based Information Theory quantifiers (Normalized Total Shannon Entropy, MPR-Statistical Complexity and Entropy-Complexity plane) on red blood cells membrane viscoelasticity characterization. These quantifiers exhibit important localization advantages provided by the Wavelet Theory. The present approach produces a clear characterization of this dynamical system, finding out an evident manifestation of a random process on the red cell samples of healthy individuals, and its sharp reduction of randomness on analyzing a human haematological disease, such as β-thalassaemia minor. PMID:21611139

Resonance behavior of atomic and molecular photoionization amplitudes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cherepkov, N. A.; Kuznetsov, V. V.; Semenov, S. K.

The behavior of the partial photoionization amplitudes with a given orbital angular momentum l in the complex plane in resonances is studied. In the autoionization resonances the trajectory of the amplitude in the complex plane corresponds to a circle. With increasing photoelectron energy the amplitude moves about a circle in the counterclockwise direction. The new expressions for the partial amplitudes in the resonance are proposed which are similar to the Fano form but contain the 'partial' profile parameters which are connected with the Fano parameter q by a simple relation. In the giant dipole resonances the amplitudes in the complexmore » plane also move about a circle in the counterclockwise direction provided the Coulomb phase is excluded from the amplitude. In the correlational resonances created by channel interactions with the giant dipole resonance the trajectories of the amplitudes acquire a loop about which the amplitudes move in the counterclockwise direction. Very similar behavior of partial photoionization amplitudes in the complex plane is demonstrated also for the dipole transitions from the K shells of the N{sub 2} molecule in the {sigma}* shape resonance.« less

Microstrip antenna developments at JPL

NASA Technical Reports Server (NTRS)

Huang, John

1991-01-01

The in-house development of microstrip antennas, initiated in 1981, when a spaceborne lightweight and low-profile planar array was needed for a satellite communication system, is described. The work described covers the prediction of finite-ground-plane effects by the geometric theory of diffraction, higher-order-mode circularly polarized circular patch antennas, circularly polarized microstrip arrays with linearly polarized elements, an impedance-matching teardrop-shaped probe feed, a dual-polarized microstrip array with high isolation and low cross-polarization, a planar microstrip Yagi array, a microstrip reflectarray, a Ka-band MMIC array, and a series-fed linear arrays.

Influence of dielectric substrate on the responsivity of microstrip dipole-antenna-coupled infrared microbolometers.

PubMed

Codreanu, Iulian; Boreman, Glenn D

2002-04-01

We report on the influence of the dielectric substrate on the performance of microstrip dipole-antenna-coupled microbolometers. The location, the width, and the magnitude of the resonance of a printed dipole are altered when the dielectric substrate is backed by a ground plane. A thicker dielectric substrate shifts the antenna resonance toward shorter dipole lengths and leads to a stronger and slower detector response. The incorporation of an air layer into the antenna substrate further increases thermal impedance, leading to an even stronger response and shifting the antenna resonance toward longer dipole lengths.

Metamaterial-based "sabre" antenna

NASA Astrophysics Data System (ADS)

Hafdallah Ouslimani, Habiba; Yuan, Tangjie; Kanane, Houcine; Priou, Alain; Collignon, Gérard; Lacotte, Guillaume

2014-05-01

The "sabre" antenna is an array of two monopole elements, vertically polarized with omnidirectional radiation patterns, and placed on either side of a composite material on the tail of an airplane. As an in-phase reflector plane, the antenna uses a compact dual-layer high-impedance surface (DL-HIS) with offset mushroom-like Sivenpiper square shape unit cells. This topology allows one to control both operational frequency and bandgap width, while reducing the total height of the antenna to under λ0/36. The designed antenna structure has a wide bandwidth higher than 24% around 1.4 GHz. The measurements and numerical simulations agree very well.

Design of electromagnetic refractor and phase transformer using coordinate transformation theory.

PubMed

Lin, Lan; Wang, Wei; Cui, Jianhua; Du, Chunlei; Luo, Xiangang

2008-05-12

We designed an electromagnetic refractor and a phase transformer using form-invariant coordinate transformation of Maxwell's equations. The propagation direction of electromagnetic energy in these devices can be modulated as desired. Unlike the conventional dielectric refractor, electromagnetic fields at our refraction boundary do not conform to the Snell's law in isotropic materials and the impedance at this boundary is matched which makes the reflection extremely low; and the transformation of the wave front from cylindrical to plane can be realized in the phase transformer with a slab structure. Two dimensional finite-element simulations were performed to confirm the theoretical results.

Uranyl ion coordination

USGS Publications Warehouse

Evans, H.T.

1963-01-01

A review of the known crystal structures containing the uranyl ion shows that plane-pentagon coordination is equally as prevalent as plane-square or plane-hexagon. It is suggested that puckered-hexagon configurations of OH - or H2O about the uranyl group will tend to revert to plane-pentagon coordination. The concept of pentagonal coordination is invoked for possible explanations of the complex crystallography of the natural uranyl hydroxides and the unusual behavior of polynuclear ions in hydrolyzed uranyl solutions.

A Double-Negative Metamaterial-Inspired Mobile Wireless Antenna for Electromagnetic Absorption Reduction

PubMed Central

Alam, Touhidul; Faruque, Mohammad Rashed Iqbal; Islam, Mohammad Tariqul

2015-01-01

A double-negative metamaterial-inspired antenna is presented for mobile wireless applications. The antenna consists of a semi-circular radiating patch and a 3 × 4 hexagonal shaped metamaterial unit cell array in the ground plane. The antenna is fed with a 50 Ω microstrip feed line. The electric dimensions of the proposed antenna are 0.20λ × 0.26λ × 0.004λ, at the low-end frequency. The proposed antenna achieves a −10 dB impedance with a bandwidth of 2.29 GHz at the lower band and 1.28 GHz at the upper band and can operate for most of the mobile applications such as upper GSM bands, WiMAX, Bluetooth, and wireless local area network (WLAN) frequency bands. The focused novelties of the proposed antenna are its small size, multi-standard operating bands, and electromagnetic absorption reduction at all the operating frequencies using the double-negative metamaterial ground plane. PMID:28793474

Front-Side Microstrip Line Feeding a Raised Antenna Patch

NASA Technical Reports Server (NTRS)

Hodges, Richard; Hoppe, Daniel

2005-01-01

An improved design concept for a printed-circuit patch antenna and the transmission line that feeds the patch calls for (1) a microstrip transmission line on the front (radiative) side of a printed-circuit board based on a thin, high-permittivity dielectric substrate; (2) using the conductor covering the back side of the circuit board as a common ground plane for both the microstrip line and the antenna patch; (3) supporting the antenna patch in front of the circuit board on a much thicker, lower-permittivity dielectric spacer layer; and (4) connecting the microstrip transmission line to the patch by use of a thin wire or narrow ribbon that extends through the thickness of the spacer and is oriented perpendicularly to the circuit-board plane. The thickness of the substrate is typically chosen so that a microstrip transmission line of practical width has an impedance between 50 and 100 ohms. The advantages of this design concept are best understood in the context of the disadvantages of prior design concepts, as explained

High input impedance amplifier

NASA Technical Reports Server (NTRS)

Kleinberg, Leonard L.

1995-01-01

High input impedance amplifiers are provided which reduce the input impedance solely to a capacitive reactance, or, in a somewhat more complex design, provide an extremely high essentially infinite, capacitive reactance. In one embodiment, where the input impedance is reduced in essence, to solely a capacitive reactance, an operational amplifier in a follower configuration is driven at its non-inverting input and a resistor with a predetermined magnitude is connected between the inverting and non-inverting inputs. A second embodiment eliminates the capacitance from the input by adding a second stage to the first embodiment. The second stage is a second operational amplifier in a non-inverting gain-stage configuration where the output of the first follower stage drives the non-inverting input of the second stage and the output of the second stage is fed back to the non-inverting input of the first stage through a capacitor of a predetermined magnitude. These amplifiers, while generally useful, are very useful as sensor buffer amplifiers that may eliminate significant sources of error.

Modeling electrical double-layer effects for microfluidic impedance spectroscopy from 100 kHz to 110 GHz.

PubMed

Little, Charles A E; Orloff, Nathan D; Hanemann, Isaac E; Long, Christian J; Bright, Victor M; Booth, James C

2017-07-25

Broadband microfluidic-based impedance spectroscopy can be used to characterize complex fluids, with applications in medical diagnostics and in chemical and pharmacological manufacturing. Many relevant fluids are ionic; during impedance measurements ions migrate to the electrodes, forming an electrical double-layer. Effects from the electrical double-layer dominate over, and reduce sensitivity to, the intrinsic impedance of the fluid below a characteristic frequency. Here we use calibrated measurements of saline solution in microfluidic coplanar waveguide devices at frequencies between 100 kHz and 110 GHz to directly measure the double-layer admittance for solutions of varying ionic conductivity. We successfully model the double-layer admittance using a combination of a Cole-Cole response with a constant phase element contribution. Our analysis yields a double-layer relaxation time that decreases linearly with solution conductivity, and allows for double-layer effects to be separated from the intrinsic fluid response and quantified for a wide range of conducting fluids.

How do clarinet players adjust the resonances of their vocal tracts for different playing effects?

NASA Astrophysics Data System (ADS)

Fritz, Claudia; Wolfe, Joe

2005-11-01

In a simple model, the reed of the clarinet is mechanically loaded by the series combination of the acoustical impedances of the instrument itself and of the player's airway. Here we measure the complex impedance spectrum of players' airways using an impedance head adapted to fit inside a clarinet mouthpiece. A direct current shunt with high acoustical resistance allows players to blow normally, so the players can simulate the tract condition under playing conditions. The reproducibility of the results suggest that the players' ``muscle memory'' is reliable for this task. Most players use a single, highly stable vocal tract configuration over most of the playing range, except for the altissimo register. However, this ``normal'' configuration varies substantially among musicians. All musicians change the configuration, often drastically for ``special effects'' such as glissandi and slurs: the tongue is lowered and the impedance magnitude reduced when the player intends to lower the pitch or to slur downwards, and vice versa.

A Review of Electrical Impedance Spectrometry Methods for Parametric Estimation of Physiologic Fluid Volumes

NASA Technical Reports Server (NTRS)

Dewberry, B.

2000-01-01

Electrical impedance spectrometry involves measurement of the complex resistance of a load at multiple frequencies. With this information in the form of impedance magnitude and phase, or resistance and reactance, basic structure or function of the load can be estimated. The "load" targeted for measurement and estimation in this study consisted of the water-bearing tissues of the human calf. It was proposed and verified that by measuring the electrical impedance of the human calf and fitting this data to a model of fluid compartments, the lumped-model volume of intracellular and extracellular spaces could be estimated, By performing this estimation over time, the volume dynamics during application of stimuli which affect the direction of gravity can be viewed. The resulting data can form a basis for further modeling and verification of cardiovascular and compartmental modeling of fluid reactions to microgravity as well as countermeasures to the headward shift of fluid during head-down tilt or spaceflight.

Model development and validation of geometrically complex eddy current coils using finite element methods

NASA Astrophysics Data System (ADS)

Brown, Alexander; Eviston, Connor

2017-02-01

Multiple FEM models of complex eddy current coil geometries were created and validated to calculate the change of impedance due to the presence of a notch. Capable realistic simulations of eddy current inspections are required for model assisted probability of detection (MAPOD) studies, inversion algorithms, experimental verification, and tailored probe design for NDE applications. An FEM solver was chosen to model complex real world situations including varying probe dimensions and orientations along with complex probe geometries. This will also enable creation of a probe model library database with variable parameters. Verification and validation was performed using other commercially available eddy current modeling software as well as experimentally collected benchmark data. Data analysis and comparison showed that the created models were able to correctly model the probe and conductor interactions and accurately calculate the change in impedance of several experimental scenarios with acceptable error. The promising results of the models enabled the start of an eddy current probe model library to give experimenters easy access to powerful parameter based eddy current models for alternate project applications.

Synthesis and properties of the compound: LiNi 3/5Cu 2/5VO 4

NASA Astrophysics Data System (ADS)

Ram, Moti

2009-12-01

The LiNi 3/5Cu 2/5VO 4 is synthesized by solution-based chemical method and its formation has been checked by X-ray diffraction (XRD) study. XRD study shows a tetragonal unit cell structure with lattice parameters of a = 11.6475 (18) Å, c = 2.4855 (18) Å and c/ a = 0.2134 Å. Electrical properties are verified using complex impedance spectroscopy (CIS) technique. Complex impedance analysis reveals following points: (i) the bulk contribution to electrical properties up to 200 °C, (ii) the bulk and grain boundary contribution at T ≥ 225 °C, (iii) the presence of temperature dependent electrical relaxation phenomena in the material. D.c. conductivity study indicates that electrical conduction in the material is a thermally activated process.

Organic electrochemical transistors for cell-based impedance sensing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rivnay, Jonathan, E-mail: rivnay@emse.fr, E-mail: owens@emse.fr; Ramuz, Marc; Hama, Adel

2015-01-26

Electrical impedance sensing of biological systems, especially cultured epithelial cell layers, is now a common technique to monitor cell motion, morphology, and cell layer/tissue integrity for high throughput toxicology screening. Existing methods to measure electrical impedance most often rely on a two electrode configuration, where low frequency signals are challenging to obtain for small devices and for tissues with high resistance, due to low current. Organic electrochemical transistors (OECTs) are conducting polymer-based devices, which have been shown to efficiently transduce and amplify low-level ionic fluxes in biological systems into electronic output signals. In this work, we combine OECT-based drain currentmore » measurements with simultaneous measurement of more traditional impedance sensing using the gate current to produce complex impedance traces, which show low error at both low and high frequencies. We apply this technique in vitro to a model epithelial tissue layer and show that the data can be fit to an equivalent circuit model yielding trans-epithelial resistance and cell layer capacitance values in agreement with literature. Importantly, the combined measurement allows for low biases across the cell layer, while still maintaining good broadband signal.« less

A spectral dynamic stiffness method for free vibration analysis of plane elastodynamic problems

NASA Astrophysics Data System (ADS)

Liu, X.; Banerjee, J. R.

2017-03-01

A highly efficient and accurate analytical spectral dynamic stiffness (SDS) method for modal analysis of plane elastodynamic problems based on both plane stress and plane strain assumptions is presented in this paper. First, the general solution satisfying the governing differential equation exactly is derived by applying two types of one-dimensional modified Fourier series. Then the SDS matrix for an element is formulated symbolically using the general solution. The SDS matrices are assembled directly in a similar way to that of the finite element method, demonstrating the method's capability to model complex structures. Any arbitrary boundary conditions are represented accurately in the form of the modified Fourier series. The Wittrick-Williams algorithm is then used as the solution technique where the mode count problem (J0) of a fully-clamped element is resolved. The proposed method gives highly accurate solutions with remarkable computational efficiency, covering low, medium and high frequency ranges. The method is applied to both plane stress and plane strain problems with simple as well as complex geometries. All results from the theory in this paper are accurate up to the last figures quoted to serve as benchmarks.

Structure and function of cytochrome c2 in electron transfer complexes with the photosynthetic reaction center of Rhodobacter sphaeroides: optical linear dichroism and EPR.

PubMed

Drepper, F; Mathis, P

1997-02-11

The photosynthetic reaction center (RC) and its secondary electron donor the water-soluble cytochrome (cyt) c2 from the purple bacterium Rhodobacter sphaeroides have been used in cross-linked and non-cross-linked complexes, oriented in compressed gels or partially dried multilayers, to study the respective orientation of the primary donor P (BChl dimer) and of cyt c2. Three methods were used: (i) Polarized optical absorption spectra at 295 and 10 K were measured and the linear dichroism of the two individual transitions (Qx, Qy), which are nearly degenerate within the alpha-band of reduced cyt c2, was determined. Attribution of the polarization directions to the molecular axes within the heme plane yielded the average cyt orientation in the complexes. (ii) Time-resolved flash absorption measurements using polarized light allowed determination of the orientation of cyt c2 in complexes which differ in their kinetics of electron transfer. (iii) EPR spectroscopy of ferricyt c2 in cross-linked RC-cyt c2 complexes was used to determine the angle between the heme and the membrane plane. The results suggest the following structural properties for the docking of cyt c2 to the RC: (i) In cross-linked complexes, the two cytochromes displaying half-lives of 0.7 and 60 micros for electron transfer to P+ are similarly oriented (difference < 10 degrees). (ii) For cross-linked cyt c2 the heme plane is parallel to the symmetry axis of the RC (0 degrees +/- 10 degrees). Moreover, the Qy transition, which is assumed to be polarized within the ring III-ring I direction of the heme plane, makes an angle of 56 degrees +/- 1 degree with the symmetry axis. (iii) The dichroism spectrum for the fast phase (0.7 micros) for the non-cross-linked cyt c2-RC complex suggests an orientation similar to that of cross-linked cyt c2, but the heme plane is tilted about 20 degrees closer to the membrane. An alternative model is that two or more bound states of cyt c2 with heme plane tilt angles between 0 degrees and 30 degrees allow the fast electron transfer. Zero-length cross-linking of cyt c2 may take place in one of these bound states. These orientations of cyt c2 are compared to different structural models of RC-cyt c2 complexes proposed previously. The relation of the two kinetic phases observed in cross-linked cyt c2 complexes to biphasic kinetics of the mobile reaction partners is discussed with respect to the dynamic electrostatic interactions during the formation of a docking complex and its dissociation. A mechanism is proposed in which a pre-orientation of cyt c2 relative to the membrane plane occurs by interaction of its strong electrostatic dipole with the negative surface charges of the RC. The optimal matching of the oppositely charged surfaces of the two proteins necessitates further rotation of the cyt around its dipole axis.

A feasibility study of the use of bounded beams resembling the shape of evanescent and inhomogeneous waves.

PubMed

Declercq, Nico F; Leroy, Oswald

2011-08-01

Plane waves are solutions of the visco-elastic wave equation. Their wave vector can be real for homogeneous plane waves or complex for inhomogeneous and evanescent plane waves. Although interesting from a theoretical point of view, complex wave vectors normally only emerge naturally when propagation or scattering is studied of sound under the appearance of damping effects. Because of the particular behavior of inhomogeneous and evanescent waves and their estimated efficiency for surface wave generation, bounded beams, experimentally mimicking their infinite counterparts similar to (wide) Gaussian beams imitating infinite harmonic plane waves, are of special interest in this report. The study describes the behavior of bounded inhomogeneous and bounded evanescent waves in terms of amplitude and phase distribution as well as energy flow direction. The outcome is of importance to the applicability of bounded inhomogeneous ultrasonic waves for nondestructive testing. Copyright © 2011. Published by Elsevier B.V.

Operator dynamics for stability condition in haptic and teleoperation system: A survey.

PubMed

Li, Hongbing; Zhang, Lei; Kawashima, Kenji

2018-04-01

Currently, haptic systems ignore the varying impedance of the human hand with its countless configurations and thus cannot recreate the complex haptic interactions. The literature does not reveal a comprehensive survey on the methods proposed and this study is an attempt to bridge this gap. The paper includes an extensive review of human arm impedance modeling and control deployed to address inherent stability and transparency issues in haptic interaction and teleoperation systems. Detailed classification and comparative study of various contributions in human arm modeling are presented and summarized in tables and diagrams. The main challenges in modeling human arm impedance for haptic robotic applications are identified. The possible future research directions are outlined based on the gaps identified in the survey. Copyright © 2018 John Wiley & Sons, Ltd.

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: High-frequency impedance and spontaneous carrier lifetime in narrow-stripe semiconductor injection lasers

NASA Astrophysics Data System (ADS)

Hoernlein, W.

1988-11-01

Measurements were made of the complex reflection coefficient of hf (10-400 MHz) signals from semiconductor injection lasers supplied with a direct bias current ranging from several milliamperes up to the threshold value or higher. The hf impedance was calculated. The parameters of the equivalent electrical circuit made it possible to predict the modulation characteristics. The impedance corresponding to currents below the lasing threshold was used to find the differential carrier lifetime from the RC constant of the p-n junction of a laser diode. A description of the apparatus is supplemented by an account of the method used in calculation of the electrical parameters and carrier lifetimes. The first results obtained using this apparatus and method are reported.

Non-contact multi-frequency magnetic induction spectroscopy system for industrial-scale bio-impedance measurement

NASA Astrophysics Data System (ADS)

O'Toole, M. D.; Marsh, L. A.; Davidson, J. L.; Tan, Y. M.; Armitage, D. W.; Peyton, A. J.

2015-03-01

Biological tissues have a complex impedance, or bio-impedance, profile which changes with respect to frequency. This is caused by dispersion mechanisms which govern how the electromagnetic field interacts with the tissue at the cellular and molecular level. Measuring the bio-impedance spectra of a biological sample can potentially provide insight into the sample’s properties and its cellular structure. This has obvious applications in the medical, pharmaceutical and food-based industrial domains. However, measuring the bio-impedance spectra non-destructively and in a way which is practical at an industrial scale presents substantial challenges. The low conductivity of the sample requires a highly sensitive instrument, while the demands of industrial-scale operation require a fast high-throughput sensor of rugged design. In this paper, we describe a multi-frequency magnetic induction spectroscopy (MIS) system suitable for industrial-scale, non-contact, spectroscopic bio-impedance measurement over a bandwidth of 156 kHz-2.5 MHz. The system sensitivity and performance are investigated using calibration and known reference samples. It is shown to yield rapid and consistently sensitive results with good long-term stability. The system is then used to obtain conductivity spectra of a number of biological test samples, including yeast suspensions of varying concentration and a range of agricultural produce, such as apples, pears, nectarines, kiwis, potatoes, oranges and tomatoes.

Giant magneto-impedance and magneto-inductive effects in amorphous alloys

NASA Astrophysics Data System (ADS)

Panina, L. V.; Mohri, K.; Bushida, K.; Noda, M.

1994-11-01

Recent experiments have discovered giant and sensitive magneto-impedance and magneto-inductive effects in FeCoSiB amorphous wires. These effects include a sensitive change in an ac wire voltage with the application of a small dc longitudinal magnetic field. At low frequencies (1-10 kHz) the inductive voltage drops by 50% for a field of 2 Oe (25%/Oe) reflecting a strong field dependence of the circumferential permeability. At higher frequencies (0.1-10 MHz) when the skin effect is essential, the amplitude of the total wire voltage decreases by 40%-60% for fields of 3-10 Oe (about 10%/Oe). These effects exhibit no hysteresis for the variation of an applied field and can be obtained even in wires of 1 mm length and a few micrometer diameter. These characteristics are very useful to constitute a highly sensitive microsensor head to detect local fields of the order of 10(exp -5) Oe. In this paper, we review recently obtained experimental results on magneto-inductive and magneto-impedance effects and present a detailed discussion for their mechanism, developing a general approach in terms of ac complex impedance in a magnetic conductor. In the case of a strong skin effect the total wire impedance depends on the circumferential permeability through the penetration depth, resulting in the giant magneto-impedance effect.

A Calculation Method of Electric Distance and Subarea Division Application Based on Transmission Impedance

NASA Astrophysics Data System (ADS)

Fang, G. J.; Bao, H.

2017-12-01

The widely used method of calculating electric distances is sensitivity method. The sensitivity matrix is the result of linearization and based on the hypothesis that the active power and reactive power are decoupled, so it is inaccurate. In addition, it calculates the ratio of two partial derivatives as the relationship of two dependent variables, so there is no physical meaning. This paper presents a new method for calculating electrical distance, namely transmission impedance method. It forms power supply paths based on power flow tracing, then establishes generalized branches to calculate transmission impedances. In this paper, the target of power flow tracing is S instead of Q. Q itself has no direction and the grid delivers complex power so that S contains more electrical information than Q. By describing the power transmission relationship of the branch and drawing block diagrams in both forward and reverse directions, it can be found that the numerators of feedback parts of two block diagrams are all the transmission impedances. To ensure the distance is scalar, the absolute value of transmission impedance is defined as electrical distance. Dividing network according to the electric distances and comparing with the results of sensitivity method, it proves that the transmission impedance method can adapt to the dynamic change of system better and reach a reasonable subarea division scheme.

Electromagnetic scattering from two-dimensional thick material junctions

NASA Technical Reports Server (NTRS)

Ricoy, M. A.; Volakis, John L.

1990-01-01

The problem of the plane wave diffraction is examined by an arbitrary symmetric two dimensional junction, where Generalized Impedance Boundary Conditions (GIBCs) and Generalized Sheet Transition Conditions (GSTCs) are employed to simulate the slabs. GIBCs and GSTCs are constructed for multilayer planar slabs of arbitrary thickness and the resulting GIBC/GSTC reflection coefficients are compared with exact counterparts to evaluate the GIBCs/GSTCs. The plane wave diffraction by a multilayer material slab recessed in a perfectly conducting ground plane is formulated and solved via the Generalized Scattering Matrix Formulation (GDMF) in conjunction with the dual integral equation approach. Various scattering patterns are computed and validated with exact results where possible. The diffraction by a material discontinuity in a thick dielectric/ferrite slab is considered by modelling the constituent slabs with GSTCs. A non-unique solution in terms of unknown constants is obtained, and these constants are evaluated for the recessed slab geometry by comparison with the solution obtained therein. Several other simplified cases are also presented and discussed. An eigenfunction expansion method is introduced to determine the unknown solution constants in the general case. This procedure is applied to the non-unique solution in terms of unknown constants; and scattering patterns are presented for various slab junctions and compared with alternative results where possible.

Optimization of Planar Monopole Wideband Antenna for Wireless Communication System

PubMed Central

Moghavvemi, Mahmoud; Mahadi, Wan Nor Liza

2016-01-01

In this paper, a new compact wideband monopole antenna is presented for wireless communication applications. This antenna comprises of a new radiating patch, a new arc-shaped strip, microstrip feed line, and a notched ground plane. The proposed radiating patch is combined with a rectangular and semi-circular patch and is integrated with a partial ground plane to provide a wide impedance bandwidth. The new arc-shaped strip between the radiating patch and microstrip feed line creates an extra surface on the patch, which helps further widen the bandwidth. Inserting one step notch on the ground plane further enhances the bandwidth. The antenna has a compact size of 16×20×1.6mm3. The measured result indicated that the antenna achieves a 127% bandwidth at VSWR≤2, ranging from 4.9GHz to 22.1GHz. Stable radiation patterns with acceptable gain are achieved. Also, a measured bandwidth of 107.7% at VSWR≤1.5 (5.1-17GHz) is obtained, which is suitable for UWB outdoor propagation. This antenna is compatible with a good number of wireless standards, including UWB band, Wimax 5.4 GHz band, MVDDS (12.2–12.7GHz), and close range radar and satellite communication in the X-band (8-12GHz), and Ku band (12-18GHz). PMID:27992466

Optimization of Planar Monopole Wideband Antenna for Wireless Communication System.

PubMed

Shakib, Mohammed Nazmus; Moghavvemi, Mahmoud; Mahadi, Wan Nor Liza

2016-01-01

In this paper, a new compact wideband monopole antenna is presented for wireless communication applications. This antenna comprises of a new radiating patch, a new arc-shaped strip, microstrip feed line, and a notched ground plane. The proposed radiating patch is combined with a rectangular and semi-circular patch and is integrated with a partial ground plane to provide a wide impedance bandwidth. The new arc-shaped strip between the radiating patch and microstrip feed line creates an extra surface on the patch, which helps further widen the bandwidth. Inserting one step notch on the ground plane further enhances the bandwidth. The antenna has a compact size of 16×20×1.6mm3. The measured result indicated that the antenna achieves a 127% bandwidth at VSWR≤2, ranging from 4.9GHz to 22.1GHz. Stable radiation patterns with acceptable gain are achieved. Also, a measured bandwidth of 107.7% at VSWR≤1.5 (5.1-17GHz) is obtained, which is suitable for UWB outdoor propagation. This antenna is compatible with a good number of wireless standards, including UWB band, Wimax 5.4 GHz band, MVDDS (12.2-12.7GHz), and close range radar and satellite communication in the X-band (8-12GHz), and Ku band (12-18GHz).

Holographic leaky-wave metasurfaces for dual-sensor imaging.

PubMed

Li, Yun Bo; Li, Lian Lin; Cai, Ben Geng; Cheng, Qiang; Cui, Tie Jun

2015-12-10

Metasurfaces have huge potentials to develop new type imaging systems due to their abilities of controlling electromagnetic waves. Here, we propose a new method for dual-sensor imaging based on cross-like holographic leaky-wave metasurfaces which are composed of hybrid isotropic and anisotropic surface impedance textures. The holographic leaky-wave radiations are generated by special impedance modulations of surface waves excited by the sensor ports. For one independent sensor, the main leaky-wave radiation beam can be scanned by frequency in one-dimensional space, while the frequency scanning in the orthogonal spatial dimension is accomplished by the other sensor. Thus, for a probed object, the imaging plane can be illuminated adequately to obtain the two-dimensional backward scattered fields by the dual-sensor for reconstructing the object. The relativity of beams under different frequencies is very low due to the frequency-scanning beam performance rather than the random beam radiations operated by frequency, and the multi-illuminations with low relativity are very appropriate for multi-mode imaging method with high resolution and anti- noise. Good reconstruction results are given to validate the proposed imaging method.

Suppression of Gain Ripples in Superconducting Traveling-Wave Kinetic Inductance Amplifiers

NASA Astrophysics Data System (ADS)

Bal, Mustafa; Erickson, Robert P.; Ku, Hsiang Sheng; Wu, Xian; Pappas, David P.

Superconducting traveling-wave kinetic inductance (KIT) amplifiers demonstrated gain over a wide bandwidth with high dynamic range and low noise. However, the gain curve exhibits ripples. Impedance mismatch at the input and output ports of the KIT amplifier as wells as split ground planes of the coplanar waveguide (CPW) geometry are potential contributors to the ripple in the gain curve. Here we study the origin of these ripples in KIT amplifiers configured in CPW geometry using approximately 20 nm thick NbTiN films grown by reactive co-sputtering of NbN and TiN. Our NbTiN films have non-linear kinetic inductance as a function of current, described by L =L0 (1 +(I /I*) 2) , where I* = 15 . 96 +/- 0 . 11 mA measured by time domain reflectometry. We report the results of implementing an impedance taper that takes into account a significantly reduced phase velocity as it narrows, adding Au onto the CPW split grounds, as well as employing different designs of dispersion engineering. Qubit Measurements using KIT amplifiers will also be reported.

Two-dimensional plasmons in the random impedance network model of disordered thin film nanocomposites

NASA Astrophysics Data System (ADS)

Olekhno, N. A.; Beltukov, Y. M.

2018-05-01

Random impedance networks are widely used as a model to describe plasmon resonances in disordered metal-dielectric nanocomposites. Two-dimensional networks are applied when considering thin films despite the fact that such networks correspond to the two-dimensional electrodynamics [Clerc et al., J. Phys. A 29, 4781 (1996), 10.1088/0305-4470/29/16/006]. In the present work, we propose a model of two-dimensional systems with the three-dimensional Coulomb interaction and show that this model is equivalent to the planar network with long-range capacitive links between distant sites. In the case of a metallic film, we obtain the well-known dispersion of two-dimensional plasmons ω ∝√{k } . We study the evolution of resonances with a decrease in the metal filling factor within the framework of the proposed model. In the subcritical region with the metal filling p lower than the percolation threshold pc, we observe a gap with Lifshitz tails in the spectral density of states (DOS). In the supercritical region p >pc , the DOS demonstrates a crossover between plane-wave two-dimensional plasmons and resonances of finite clusters.

Application of conformal transformation to elliptic geometry for electric impedance tomography.

PubMed

Yilmaz, Atila; Akdoğan, Kurtuluş E; Saka, Birsen

2008-03-01

Electrical impedance tomography (EIT) is a medical imaging modality that is used to compute the conductivity distribution through measurements on the cross-section of a body part. An elliptic geometry model, which defines a more general frame, ensures more accurate results in reconstruction and assessment of inhomogeneities inside. This study provides a link between the analytical solutions defined in circular and elliptical geometries on the basis of the computation of conformal mapping. The results defined as voltage distributions for the homogeneous case in elliptic and circular geometries have been compared with those obtained by the use of conformal transformation between elliptical and well-known circular geometry. The study also includes the results of the finite element method (FEM) as another approach for more complex geometries for the comparison of performance in other complex scenarios for eccentric inhomogeneities. The study emphasizes that for the elliptic case the analytical solution with conformal transformation is a reliable and useful tool for developing insight into more complex forms including eccentric inhomogeneities.

Electrical Conductivity, Relaxation and the Glass Transition: A New Look at a Familiar Phenomenon

NASA Technical Reports Server (NTRS)

Angel, Paul W.; Cooper, Alfred R.; DeGuire, Mark R.

1996-01-01

Annealed samples from a single melt of a 10 mol% K2O-90SiO2 glass were reheated to temperatures ranging from 450 to 800 C, held isothermally for 20 min, and then quenched in either air or a silicon oil bath. The complex impedance of both the annealed and quenched samples was measured as a function of temperature from 120 to 250 C using ac impedance spectroscopy from 1 Hz to 1 MHz. The dc conductivity, sigma(sub dc), was measured from the low frequency intercept of depressed semicircle fits to the complex impedance data. When the sigma(sub dc) at 150 C was plotted against soak temperature, the results fell into three separate regions that are explained in terms of the glass structural relaxation time, tau(sub S). This sigma(sub dc) plot provides a new way to look the glass transition range, Delta T(sub r). In addition, sigma(sub dc) was measured for different soak times at 550 C, from which an average relaxation time of 7.3 min was calculated. It was found that the size and position of the Delta T(sub r) is controlled by both the soak time and cooling rate.

Bimodal electric tissue ablation (BETA) - in-vivo evaluation of the effect of applying direct current before and during radiofrequency ablation of porcine liver.

PubMed

Cockburn, J F; Maddern, G J; Wemyss-Holden, S A

2007-03-01

To examine the effect of applying increasing amounts of direct current (DC) before and during alternating current radiofrequency ablation of porcine liver. Using a Radiotherapeutics RF3000 generator, a 9 V AC/DC transformer and a 16 G plain aluminium tube as an electrode, a control group of 24 porcine hepatic radiofrequency ablation zones was compared with 24 zones created using a bimodal electric tissue ablation (BETA) technique in three pigs. All ablations were terminated when tissue impedance rose to greater than 999 Omega or radiofrequency energy input fell below 5 W on three successive measurements taken at 1 min intervals. BETA ablations were performed in two phases: an initial phase of variable duration DC followed by a second phase during which standard radiofrequency ablation was applied simultaneously with DC. During this second phase, radiofrequency power input was regulated by the feedback circuitry of the RF3000 generator according to changes in tissue impedance. The diameters (mm) of each ablation zone were measured by two observers in two planes perpendicular to the plane of needle insertion. The mean short axis diameter of each ablation zone was subjected to statistical analysis. With increased duration of prior application of DC, there was a progressive increase in the diameter of the ablation zone (p<0.001). This effect increased sharply up to 300 s of pre-treatment after which a further increase in diameter occurred, but at a much lesser rate. A maximum ablation zone diameter of 32 mm was produced (control diameters 10-13 mm). Applying a 9 V DC to porcine liver in vivo, and continuing this DC application during subsequent radiofrequency ablation, results in larger ablation zone diameters compared with radiofrequency ablation alone.

Glassy dielectric response in Tb2NiMnO6 double perovskite with similarities to a Griffiths phase

NASA Astrophysics Data System (ADS)

Nhalil, Hariharan; Nair, Harikrishnan S.; Bhat, H. L.; Elizabeth, Suja

2013-12-01

Results of frequency-dependent and temperature-dependent dielectric measurements performed on the double-perovskite Tb2NiMnO6 are presented. The real (\\epsilon_1 (f,T)) and imaginary (\\epsilon_2 (f,T)) parts of dielectric permittivity show three plateaus suggesting dielectric relaxation originating from the bulk, grain boundaries and the sample-electrode interfaces, respectively. The \\epsilon_1 (f,T) and \\epsilon_2 (f,T) are successfully simulated by a RC circuit model. The complex plane of impedance, Z'\\text{-}Z'' , is simulated using a series network with a resistor R and a constant phase element. Through the analysis of \\epsilon (f,T) using the modified Debye model, two different relaxation time regimes separated by a characteristic temperature, T^* , are identified. The temperature variation of R and C corresponding to the bulk and the parameter α from modified Debye fit lend support to this hypothesis. Interestingly, the T^* compares with the Griffiths temperature for this compound observed in magnetic measurements. Though these results cannot be interpreted as magnetoelectric coupling, the relationship between lattice and magnetism is markedly clear. We assume that the observed features have their origin in the polar nanoregions which originate from the inherent cationic defect structure of double perovskites.

Rotational Analysis of Phase Plane Curves: Complex and Pure Imaginary Eigenvalues

ERIC Educational Resources Information Center

Murray, Russell H.

2005-01-01

Although the phase plane can be plotted and analyzed using an appropriate software package, the author found it worthwhile to engage the students with the theorem and the two proofs. The theorem is a powerful tool that provides insight into the rotational behavior of the phase plane diagram in a simple way: just check the signs of c and [alpha].…

Human-Derived Disturbance Estimation and Compensation (DEC) Method Lends Itself to a Modular Sensorimotor Control in a Humanoid Robot.

PubMed

Lippi, Vittorio; Mergner, Thomas

2017-01-01

The high complexity of the human posture and movement control system represents challenges for diagnosis, therapy, and rehabilitation of neurological patients. We envisage that engineering-inspired, model-based approaches will help to deal with the high complexity of the human posture control system. Since the methods of system identification and parameter estimation are limited to systems with only a few DoF, our laboratory proposes a heuristic approach that step-by-step increases complexity when creating a hypothetical human-derived control systems in humanoid robots. This system is then compared with the human control in the same test bed, a posture control laboratory. The human-derived control builds upon the identified disturbance estimation and compensation (DEC) mechanism, whose main principle is to support execution of commanded poses or movements by compensating for external or self-produced disturbances such as gravity effects. In previous robotic implementation, up to 3 interconnected DEC control modules were used in modular control architectures separately for the sagittal plane or the frontal body plane and successfully passed balancing and movement tests. In this study we hypothesized that conflict-free movement coordination between the robot's sagittal and frontal body planes emerges simply from the physical embodiment, not necessarily requiring a full body control. Experiments were performed in the 14 DoF robot Lucy Posturob (i) demonstrating that the mechanical coupling from the robot's body suffices to coordinate the controls in the two planes when the robot produces movements and balancing responses in the intermediate plane, (ii) providing quantitative characterization of the interaction dynamics between body planes including frequency response functions (FRFs), as they are used in human postural control analysis, and (iii) witnessing postural and control stability when all DoFs are challenged together with the emergence of inter-segmental coordination in squatting movements. These findings represent an important step toward controlling in the robot in future more complex sensorimotor functions such as walking.

Human-Derived Disturbance Estimation and Compensation (DEC) Method Lends Itself to a Modular Sensorimotor Control in a Humanoid Robot

PubMed Central

Lippi, Vittorio; Mergner, Thomas

2017-01-01

The high complexity of the human posture and movement control system represents challenges for diagnosis, therapy, and rehabilitation of neurological patients. We envisage that engineering-inspired, model-based approaches will help to deal with the high complexity of the human posture control system. Since the methods of system identification and parameter estimation are limited to systems with only a few DoF, our laboratory proposes a heuristic approach that step-by-step increases complexity when creating a hypothetical human-derived control systems in humanoid robots. This system is then compared with the human control in the same test bed, a posture control laboratory. The human-derived control builds upon the identified disturbance estimation and compensation (DEC) mechanism, whose main principle is to support execution of commanded poses or movements by compensating for external or self-produced disturbances such as gravity effects. In previous robotic implementation, up to 3 interconnected DEC control modules were used in modular control architectures separately for the sagittal plane or the frontal body plane and successfully passed balancing and movement tests. In this study we hypothesized that conflict-free movement coordination between the robot's sagittal and frontal body planes emerges simply from the physical embodiment, not necessarily requiring a full body control. Experiments were performed in the 14 DoF robot Lucy Posturob (i) demonstrating that the mechanical coupling from the robot's body suffices to coordinate the controls in the two planes when the robot produces movements and balancing responses in the intermediate plane, (ii) providing quantitative characterization of the interaction dynamics between body planes including frequency response functions (FRFs), as they are used in human postural control analysis, and (iii) witnessing postural and control stability when all DoFs are challenged together with the emergence of inter-segmental coordination in squatting movements. These findings represent an important step toward controlling in the robot in future more complex sensorimotor functions such as walking. PMID:28951719

State-plane analysis of parallel resonant converter

NASA Technical Reports Server (NTRS)

Oruganti, R.; Lee, F. C.

1985-01-01

A method for analyzing the complex operation of a parallel resonant converter is developed, utilizing graphical state-plane techniques. The comprehensive mode analysis uncovers, for the first time, the presence of other complex modes besides the continuous conduction mode and the discontinuous conduction mode and determines their theoretical boundaries. Based on the insight gained from the analysis, a novel, high-frequency resonant buck converter is proposed. The voltage conversion ratio of the new converter is almost independent of load.

Bi-material plane with interface crack for the model of semi-linear material

NASA Astrophysics Data System (ADS)

Domanskaya, T. O.; Malkov, V. M.; Malkova, Yu. V.

2018-05-01

The singular plane problems of nonlinear elasticity (plane strain and plane stress) are considered for bi-material infinite plane with interface crack. The plane is formed of two half-planes. Mechanical properties of half-planes are described by the model of semi-linear material. Using model of this harmonic material has allowed to apply the theory of complex functions and to obtain exact analytical global solutions of some nonlinear problems. Among them the problem of bi-material plane with the stresses and strains jumps at an interface is considered. As an application of the problem of jumps, the problem of interface crack is solved. The values of nominal (Piola) and Cauchy stresses and displacements are founded. Based on the global solutions the asymptotic expansions are constructed for stresses and displacements in a vicinity of crack tip. As an example the case of a free crack in bi-material plane subjected to constant stresses at infinity is studied. As a special case, the analytical solution of the problem of a crack in a homogeneous plane is obtained from the problem for bi-material plane with interface crack.

Prediction of lamb carcass composition by impedance spectroscopy.

PubMed

Altmann, M; Pliquett, U; Suess, R; von Borell, E

2004-03-01

The objective of this study was to compare impedance spectroscopy with resistance measurements at a single frequency (50 kHz) for the prediction of lamb carcass composition. The impedance spectrum is usually recorded by measuring the complex impedance at various frequencies (frequency domain); however, in this study, we also applied the faster and simpler measurement in the time domain (application of a current step and measurement of the voltage response). The study was carried out on 24 male, German Black-headed Mutton lambs with an average BW of 45 kg. Frequency- and time domain-based impedance measurements were collected at 20 min and 24 h postmortem with different electrode placements. Real and imaginary parts at various frequencies were calculated from the locus diagram. Left sides were dissected into lean, fat, and bone, and right sides were ground to determine actual carcass composition. Crude fat, crude protein, and moisture were chemically analyzed on ground samples. Frequency- and time domain-based measurements did not provide the same absolute impedance values; however, the high correlations (P < 0.001) between these methods for the "real parts" showed that they ranked individuals in the same order. Most of the time domain data correlated higher to carcass composition than did the frequency domain data. The real parts of impedance showed correlations between -0.37 (P > 0.05) and -0.74 (P < 0.001) to water, crude fat, lean, and fatty tissue, whereas the relations to CP were much lower (from 0.00 to -0.47, P < 0.05). Electrode placements at different locations did not substantially improve the correlations with carcass composition. The "imaginary parts" of impedance were not suitable for the prediction of carcass composition. The highest accuracy (R2 = 0.66) was reached for the estimation of crude fat percentage by a regression equation with the time domain-based impedance measured at 24 h postmortem. Furthermore, there was not a clear superiority of measurements in a wide frequency range over a single frequency measurement at 50 kHz for the prediction of carcass composition. Even though we calculated the impedance at 50 kHz based on the locus diagram, which allowed for a high precision for predicting this impedance trait, single-frequency impedance devices typically used in practice cannot record the locus diagram and, therefore, exhibit a greater amount of uncertainty.

Complex impedance analyses and magnetoelectric effect in ferrite ferroelectric composite ceramics

NASA Astrophysics Data System (ADS)

Patankar, K. K.; Kanade, S. A.; Padalkar, D. S.; Chougule, B. K.

2007-02-01

Magnetoelectric (ME) composites yBa0.8Pb0.2TiO3 (1-y)CuFe2O4 are prepared by ceramic method. The component phases are prepared from two different routes, viz. CuFe2O4 (ferrite phase) is prepared by oxalate precursor route and Ba0.8Pb0.2TiO3 (ferroelectric phase) by solid-state reaction route. No intermediate phases are observed in the composites containing these ferrite and ferroelectric phases. ME conversion factor (measure of ME effect) is found to be enhanced compared to those reported in the composites, in which the component phases were prepared by only one route, i.e. solid-state reaction route. The results on ME conversion are well accounted by measuring the complex impedance and analyzing their Nyquist plots.

Nanostructured gold and platinum electrodes on silicon structures for biosensing

NASA Astrophysics Data System (ADS)

Ogurtsov, V. I.; Sheehan, M. M.

2005-01-01

Gold and platinum metal electrodes on Si/SiO2 having undergone anisotropic potassium hydroxide (KOH) etch treatment are considered. This treatment etches at different rates and directions in the material resulting in creation of numerous pyramid shaped holes in the silicon substrate. This surface is used to make metal electrodes with increased electrode efficiency. The electrodes can serve as the sensors or as the sensor substrates (for surface polymer modification) and because both gold and platinum are inert they have applications for food safety biosensing. Wine, an economically significant food product, was chosen as a matrix, and impedance spectroscopy (EIS) was selected as a method of investigation of electrode behaviour. Based on results of EIS, different complexity equivalent circuits were determined by applying fitting mean square root optimisation of sensor complex impedance measurements.

Monitoring of bacteria growth using a wireless, remote query resonant-circuit sensor: application to environmental sensing

NASA Technical Reports Server (NTRS)

Ong, K. G.; Wang, J.; Singh, R. S.; Bachas, L. G.; Grimes, C. A.; Daunert, S. (Principal Investigator)

2001-01-01

A new technique is presented for in-vivo remote query measurement of the complex permittivity spectra of a biological culture solution. A sensor comprised of a printed inductor-capacitor resonant-circuit is placed within the culture solution of interest, with the impedance spectrum of the sensor measured using a remotely located loop antenna; the complex permittivity spectra of the culture is calculated from the measured impedance spectrum. The remote query nature of the sensor platform enables, for example, the in-vivo real-time monitoring of bacteria or yeast growth from within sealed opaque containers. The wireless monitoring technique does not require a specific alignment between sensor and antenna. Results are presented for studies conducted on laboratory strains of Bacillus subtilis, Escherichia coli JM109, Pseudomonas putida and Saccharomyces cerevisiae.

Permutation entropy and statistical complexity analysis of turbulence in laboratory plasmas and the solar wind.

PubMed

Weck, P J; Schaffner, D A; Brown, M R; Wicks, R T

2015-02-01

The Bandt-Pompe permutation entropy and the Jensen-Shannon statistical complexity are used to analyze fluctuating time series of three different turbulent plasmas: the magnetohydrodynamic (MHD) turbulence in the plasma wind tunnel of the Swarthmore Spheromak Experiment (SSX), drift-wave turbulence of ion saturation current fluctuations in the edge of the Large Plasma Device (LAPD), and fully developed turbulent magnetic fluctuations of the solar wind taken from the Wind spacecraft. The entropy and complexity values are presented as coordinates on the CH plane for comparison among the different plasma environments and other fluctuation models. The solar wind is found to have the highest permutation entropy and lowest statistical complexity of the three data sets analyzed. Both laboratory data sets have larger values of statistical complexity, suggesting that these systems have fewer degrees of freedom in their fluctuations, with SSX magnetic fluctuations having slightly less complexity than the LAPD edge I(sat). The CH plane coordinates are compared to the shape and distribution of a spectral decomposition of the wave forms. These results suggest that fully developed turbulence (solar wind) occupies the lower-right region of the CH plane, and that other plasma systems considered to be turbulent have less permutation entropy and more statistical complexity. This paper presents use of this statistical analysis tool on solar wind plasma, as well as on an MHD turbulent experimental plasma.

CPW fed UWB antenna with enhanced bandwidth & dual band notch characteristics

NASA Astrophysics Data System (ADS)

Jangid, K. G.; Jain, P. K.; Sharma, B. R.; Saxena, V. K.; Kulhar, V. S.; Bhatnagar, D.

2018-05-01

This paper reports the design and performance of CPW fed UWB antenna having two U-shaped slots etched in the radiating structure. UWB performance of proposed structure is obtained through the truncated shape of the patch and L-slits etched in ground plane. By applying two U- shaped slots in a radiating patch, we achieved dual notch band characteristics. The proposed antenna is simulated by applying CST Microwave Studio simulator. This antenna provides wide impedance bandwidth of 12.585 GHz (2.74GHz - 15.325 GHz) with dual notched band characteristics. This antenna may be proved as a useful structure for modern wireless communication systems including UWB band.

Static properties of hydrostatic thrust gas bearings with curved surfaces.

NASA Technical Reports Server (NTRS)

Rehsteiner, F. H.; Cannon, R. H., Jr.

1971-01-01

The classical treatment of circular, hydrostatic, orifice-regulated thrust gas bearings, in which perfectly plane bearing plates are assumed, is extended to include axisymmetric, but otherwise arbitrary, plate profiles. Plate curvature has a strong influence on bearing load capability, static stiffness, tilting stiffness, and side force per unit misalignment angle. By a suitable combination of gas inlet impedance and concave plate profile, the static stiffness can be made almost constant over a wide load range, and to remain positive at the closure load. Extensive measurements performed with convex and concave plates agree with theory to within the experimental error throughout and demonstrate the practical feasibility of using curved plates.

WAVE DELAYING STRUCTURE FOR RECTANGULAR WAVE-GUIDES

DOEpatents

Robertson-Shersby-Harvie, R.B.; Dain, J.

1956-11-13

This patent relates to wave-guides and in particular describes wave delaying structure located within a wave-guide. The disclosed wave-guide has an elongated fiat metal sheet arranged in a central plane of the guide and formed with a series of transverse inductive slots such that each face presents an inductive impedance to the guide. The sheet is thickened in the area between slots to increase the self capacity of the slots. Experimental results indicate that in a wave-guide loaded in accordance with the invention the guided wavelength changes more slowly as the air wavelength is changed than the guided wavelength does in wave-guides loaded by means of corrugations.

1980 Summer Study Program in Geophysical Fluid Dynamics - Coherent Features in Geophysical Flows.

DTIC Science & Technology

1980-11-01

odei un a inplii.ude motions on the beta plane. He extended the analysis to more complex flows in the ocean and the atmosphere and in the process...Technology Maxworthy, Anthony University of Southern California McWilliams, James National Center for Atmospheric Reserch Nelkin, Mark Cornell University...Nortweg-de Vries equation via a model of finite amplitude motions on the beta plane. He extended the analysis to more complex flows in the ocean and the

Techniques to measure complex-plane fields

NASA Astrophysics Data System (ADS)

Dudley, Angela; Majola, Nombuso; Chetty, Naven; Forbes, Andrew

2014-10-01

In this work we construct coherent superpositions of Gaussian and vortex modes which can be described to occupy the complex-plane. We demonstrate how these fields can be experimentally constructed in a digital, controllable manner with a spatial light modulator. Once these fields have been generated we illustrate, with three separate techniques, how the constituent components of these fields can be extracted, namely by measuring the intensity of the field at two adjacent points; performing a modal decomposition and a new digital Stokes measurement.

Local Bifurcation Control,

DTIC Science & Technology

1987-01-01

X, (0) in the open left half complex plane . (S) Eq. (1) has an equilibrium zo(p) when u = 0. Furthermore, the linearization of (1) near z0, p = 0...possesses a simple eigenvalue X(p) with XI(O) = 0, X; (0) 74 0, with the remaining eigenvalues X(0), . . . , X. (0) in the open left half complex plane ...Conference, Lausanne, June 1984. (11) "Chaos In dynamical systems by the Poincare -Melnikov-Arnold method" Proc. ARO Workshop, March 1984. %I 2.I JUAN C

Comparison of different coil positions for ventilation monitoring with contact-less magnetic impedance measurements

NASA Astrophysics Data System (ADS)

Cordes, A.; Pollig, D.; Leonhardt, S.

2010-04-01

For monitoring the health status of individuals, proper monitoring of ventilation is desirable. Therefore, a continuous measurement technique is an advantage for many patients since it allows personal home care scenarios. As an example, monitoring of elderly people at home could enable them to live in their familiar environment on their own with the safety of a continuous monitoring. Therefore, a measurement technique without the restriction of mobility is required. Since it is possible to monitor ventilation with magnetic impedance measurements without conductive contact, this technique is well suited for the mentioned scenario. Integrated in a chair, a person's health state could be monitored in many situations, e.g. during meals, while watching TV or reading a book. In this paper, we compare different positions of coil arrays for a magnetic impedance measurement system integrated in a chair in order to monitor ventilation continuously. For limiting the costs and technical complexity of the magnetic impedance measurement system, we have a focus on coil configurations with one RF channel. To limit the needed space and thickness of the array in the backrest, planar gradiometer coil setups are investigated. All measurements will be performed with a new developed portable magnetic impedance measurement system and a standard office chair.

Efficient Simultaneous Reconstruction of Time-Varying Images and Electrode Contact Impedances in Electrical Impedance Tomography.

PubMed

Boverman, Gregory; Isaacson, David; Newell, Jonathan C; Saulnier, Gary J; Kao, Tzu-Jen; Amm, Bruce C; Wang, Xin; Davenport, David M; Chong, David H; Sahni, Rakesh; Ashe, Jeffrey M

2017-04-01

In electrical impedance tomography (EIT), we apply patterns of currents on a set of electrodes at the external boundary of an object, measure the resulting potentials at the electrodes, and, given the aggregate dataset, reconstruct the complex conductivity and permittivity within the object. It is possible to maximize sensitivity to internal conductivity changes by simultaneously applying currents and measuring potentials on all electrodes but this approach also maximizes sensitivity to changes in impedance at the interface. We have, therefore, developed algorithms to assess contact impedance changes at the interface as well as to efficiently and simultaneously reconstruct internal conductivity/permittivity changes within the body. We use simple linear algebraic manipulations, the generalized singular value decomposition, and a dual-mesh finite-element-based framework to reconstruct images in real time. We are also able to efficiently compute the linearized reconstruction for a wide range of regularization parameters and to compute both the generalized cross-validation parameter as well as the L-curve, objective approaches to determining the optimal regularization parameter, in a similarly efficient manner. Results are shown using data from a normal subject and from a clinical intensive care unit patient, both acquired with the GE GENESIS prototype EIT system, demonstrating significantly reduced boundary artifacts due to electrode drift and motion artifact.

ELECTRIC IMPEDANCE OF NITELLA DURING ACTIVITY

PubMed Central

Cole, Kenneth S.; Curtis, Howard J.

1938-01-01

The changes in the alternating current impedance which occur during activity of cells of the fresh water plant Nitella have been measured with the current flow normal to the cell axis, at eight frequencies from 0.05 to 20 kilocycles per second, and with simultaneous records of the action potential under the impedance electrodes. At each frequency the resting cell was balanced in a Wheatstone bridge with a cathode ray oscillograph, and after electrical stimulation at one end of the cell, the changes in the complex impedance were determined from the bridge unbalance recorded by motion pictures of the oscillograph figure. An extension of the previous technique of interpretation of the transverse impedance shows that the normal membrane capacity of 0.9 µf./cm.2 decreases about 15 per cent without change of phase angle, while the membrane resistance decreases from 105 ohm cm.2 to about 500 ohm cm.2 during the passage of the excitation wave. This membrane change occurs during the latter part of the rising phase of the action potential, and it is shown that the membrane electromotive force remains unchanged until nearly the same time. The part of the action potential preceding these membrane changes is probably a passive fall of potential ahead of a partial short circuit. PMID:19873091

Equivalent complex conductivities representing the effects of T-tubules and folded surface membranes on the electrical admittance and impedance of skeletal muscles measured by external-electrode method

NASA Astrophysics Data System (ADS)

Sekine, Katsuhisa

2017-12-01

In order to represent the effects of T-tubules and folded surface membranes on the electrical admittance and impedance of skeletal muscles measured by the external-electrode method, analytical relations for the equivalent complex conductivities of hypothetical smooth surface membranes were derived. In the relations, the effects of each tubule were represented by the admittance of a straight cable. The effects of the folding of a surface membrane were represented by the increased area of surface membranes. The equivalent complex conductivities were represented as summation of these effects, and the effects of the T-tubules were different between the transversal and longitudinal directions. The validity of the equivalent complex conductivities was supported by the results of finite-difference method (FDM) calculations made using three-dimensional models in which T-tubules and folded surface membranes were represented explicitly. FDM calculations using the equivalent complex conductivities suggested that the electrically inhomogeneous structure due to the existence of muscle cells with T-tubules was sufficient for explaining the experimental results previously obtained using the external-electrode method. Results of FDM calculations in which the structural changes caused by muscle contractions were taken into account were consistent with the reported experimental results.

Equivalent circuit for the characterization of the resonance mode in piezoelectric systems

NASA Astrophysics Data System (ADS)

Fernández-Afonso, Y.; García-Zaldívar, O.; Calderón-Piñar, F.

2015-12-01

The impedance properties in polarized piezoelectric can be described by electric equivalent circuits. The classic circuit used in the literature to describe real systems is formed by one resistor (R), one inductance (L) and one capacitance C connected in series and one capacity (C0) connected in parallel with the formers. Nevertheless, the equation that describe the resonance and anti-resonance frequencies depends on a complex manner of R, L, C and C0. In this work is proposed a simpler model formed by one inductance (L) and one capacity (C) in series; one capacity (C0) in parallel; one resistor (RP) in parallel and one resistor (RS) in series with other components. Unlike the traditional circuit, the equivalent circuit elements in the proposed model can be simply determined by knowing the experimental values of the resonance frequency fr, anti-resonance frequency fa, impedance module at resonance frequency |Zr|, impedance module at anti-resonance frequency |Za| and low frequency capacitance C0, without fitting the impedance experimental data to the obtained equation.

Large improvement of the electrical impedance of imaging and high-intensity focused ultrasound (HIFU) phased arrays using multilayer piezoelectric ceramics coupled in lateral mode.

PubMed

Song, Junho; Lucht, Benjamin; Hynynen, Kullervo

2012-07-01

With a change in phased-array configuration from one dimension to two, the electrical impedance of the array elements is substantially increased because of their decreased width (w)-to-thickness (t) ratio. The most common way to compensate for this impedance increase is to employ electrical matching circuits at a high cost of fabrication complexity and effort. In this paper, we introduce a multilayer lateral-mode coupling method for phased-array construction. The direct comparison showed that the electrical impedance of a single-layer transducer driven in thickness mode is 1/(n²(1/(w/t))²) times that of an n-layer lateral mode transducer. A large reduction of the electrical impedance showed the impact and benefit of the lateral-mode coupling method. A one-dimensional linear 32-element 770-kHz imaging array and a 42-element 1.45-MHz high-intensity focused ultrasound (HIFU) phased array were fabricated. The averaged electrical impedances of each element were measured to be 58 Ω at the maximum phase angle of -1.2° for the imaging array and 105 Ω at 0° for the HIFU array. The imaging array had a center frequency of 770 kHz with an averaged -6-dB bandwidth of approximately 52%. For the HIFU array, the averaged maximum surface acoustic intensity was measured to be 32.8 W/cm² before failure.

Novel Approach on the Optimisation of Mid-Course Corrections Along Interplanetary Trajectories

NASA Astrophysics Data System (ADS)

Iorfida, Elisabetta; Palmer, Phil; Roberts, Mark

The primer vector theory, firstly proposed by Lawden, defines a set of necessary conditions to characterise whether an impulsive thrust trajectory is optimal with respect to propellant usage, within a two-body problem context. If the conditions are not satisfied, one or more potential intermediate impulses are performed along the transfer arc, in order to lower the overall cost. The method is based on the propagation of the state transition matrix and on the solution of a boundary value problem, which leads to a mathematical and computational complexity.In this paper, a different approach is introduced. It is based on a polar coordinates transformation of the primer vector which allows the decoupling between its in-plane and out-of-plane components. The out-of-plane component is solved analytically while for the in-plane ones a Hamiltonian approximation is made.The novel procedure reduces the mathematical complexity and the computational cost of Lawden's problem and gives also a different perspective about the optimisation of a transfer trajectory.

Comparing the basins of attraction for several methods in the circular Sitnikov problem with spheroid primaries

NASA Astrophysics Data System (ADS)

Zotos, Euaggelos E.

2018-06-01

The circular Sitnikov problem, where the two primary bodies are prolate or oblate spheroids, is numerically investigated. In particular, the basins of convergence on the complex plane are revealed by using a large collection of numerical methods of several order. We consider four cases, regarding the value of the oblateness coefficient which determines the nature of the roots (attractors) of the system. For all cases we use the iterative schemes for performing a thorough and systematic classification of the nodes on the complex plane. The distribution of the iterations as well as the probability and their correlations with the corresponding basins of convergence are also discussed. Our numerical computations indicate that most of the iterative schemes provide relatively similar convergence structures on the complex plane. However, there are some numerical methods for which the corresponding basins of attraction are extremely complicated with highly fractal basin boundaries. Moreover, it is proved that the efficiency strongly varies between the numerical methods.

Triboluminescence and crystal structure of the complex [Eu(NО3 )3 (HMPA)3 ]: role of cleavage planes.

PubMed

Bukvetskii, B V; Mirochnik, A G; Zhikhareva, P A

2017-05-01

The atomic structure of crystals of the [Eu(NО 3 ) 3 (HMPA) 3 ] [hexamethylphosphotriamide (HMPA)] complex characterized by an intensive luminescence and triboluminescence was determined using X-ray structural analysis. Noncentrosymmetric crystals have a monoclinic syngony: a = 16.0686 (3), b = 11.0853 (2), c = 20.9655 Å (4), β = 93.232° (1), space group P2 1 , Z = 4, ρ calc  = 1.560 g/cm 3 . The crystal structure is represented by individual С 18 Н 54 EuN 12 O 12 P 3 complexes linked through van der Waals interactions with clearly expressed cleavage planes. The Eu(III) atom coordination polyhedron reflected the state of a distorted square antiprism. Structural aspects of the suggested model, including formation of triboluminescence properties, were considered and the role of the cleavage planes was discussed. Copyright © 2016 John Wiley & Sons, Ltd.

A new method to assess skin treatments for lowering the impedance and noise of individual gelled Ag-AgCl electrodes.

PubMed

Piervirgili, G; Petracca, F; Merletti, R

2014-10-01

A model-based new procedure for measuring the single electrode-gel-skin impedance (ZEGS) is presented. The method is suitable for monitoring the contact impedance of the electrodes of a large array with limited modifications of the hardware and without removing or disconnecting the array from the amplifier. The procedure is based on multiple measurements between electrode pairs and is particularly suitable for electrode arrays. It has been applied to study the effectiveness of three skin treatments, with respect to no treatment, for reducing the electrode-gel-skin impedance (ZEGS) and noise: (i) rubbing with alcohol; (ii) rubbing with abrasive conductive paste; (iii) stripping with adhesive tape. The complex impedances ZEGS of the individual electrodes were measured by applying this procedure to disposable commercial Ag-AgCl gelled electrode arrays (4  ×  1) with a 5 mm(2) contact area. The impedance unbalance ΔZ = ZEGS1 - ZEGS2 and the RMS noise (VRMS) were measured between pairs of electrodes. The tissue impedance ZT was also obtained, as a collateral result. Measurements were repeated at t0 = 0 min and at t30 = 30 min from the electrode application. Mixed linear models and linear regression analysis applied to ZEGS, ΔZ and noise VRMS for the skin treatment factor demonstrated (a) that skin rubbing with abrasive conductive paste is more effective in lowering ZEGS, ΔZ and VRMS (p < 0.01) than the other treatments or no treatment, and (b) a statistically significant decrement (p < 0.01), between t0 and t30, of magnitude and phase of ZEGS.Rubbing with abrasive conductive paste significantly decreased the noise VRMS with respect to other treatments or no treatment.

Coherent field propagation between tilted planes.

PubMed

Stock, Johannes; Worku, Norman Girma; Gross, Herbert

2017-10-01

Propagating electromagnetic light fields between nonparallel planes is of special importance, e.g., within the design of novel computer-generated holograms or the simulation of optical systems. In contrast to the extensively discussed evaluation between parallel planes, the diffraction-based propagation of light onto a tilted plane is more burdensome, since discrete fast Fourier transforms cannot be applied directly. In this work, we propose a quasi-fast algorithm (O(N 3  log N)) that deals with this problem. Based on a proper decomposition into three rotations, the vectorial field distribution is calculated on a tilted plane using the spectrum of plane waves. The algorithm works on equidistant grids, so neither nonuniform Fourier transforms nor an explicit complex interpolation is necessary. The proposed algorithm is discussed in detail and applied to several examples of practical interest.

Ambient and Cryogenic, Decade Bandwidth, Low Noise Receiving System for Radio Astronomy Using Sinuous Antenna

NASA Astrophysics Data System (ADS)

Gawande, Rohit Sudhir

Traditionally, radio astronomy receivers have been limited to bandwidths less than an octave, and as a result multiple feeds and receivers are necessary to observe over a wide bandwidth. Next generation of instruments for radio astronomy will benefit greatly from reflector antenna feeds that demonstrate very wide instantaneous bandwidth, and exhibit low noise behavior. There is an increasing interest in wideband systems from both the cost and science point of view. A wideband feed will allow simultaneous observations or sweeps over a decade or more bandwidth. Instantaneous wide bandwidth is necessary for detection of short duration pulses. Future telescopes like square kilometer array (SKA), consisting of 2000 to 3000 coherently connected antennas and covering a frequency range of 70 MHz to 30 GHz, will need decade bandwidth single pixel feeds (SPFs) along with integrated LNAs to achieve the scientific objectives in a cost effective way. This dissertation focuses on the design and measurement of a novel decade bandwidth sinuous-type, dual linear polarized, fixed phase center, low loss feed with an integrated LNA. A decade bandwidth, low noise amplifier is specially designed for noise match to the higher terminal impedance encountered by this antenna yielding an improved sensitivity over what is possible with conventional 50 O amplifiers. The self-complementary, frequency independent nature of the planar sinuous geometry results in a nearly constant beam pattern and fixed phase center over more than a 10:1 operating frequency range. In order to eliminate the back-lobe response over such a wide frequency range, we have projected the sinuous pattern onto a cone, and a ground plane is placed directly behind the cone's apex. This inverted, conical geometry assures wide bandwidth operation by locating each sinuous resonator a quarter wavelength above the ground plane. The presence of a ground plane near a self complementary antenna destroys the self complementary nature of the composite structure resulting in frequency dependent impedance variations. We demonstrate, using simulations and measurements, how the return loss can be improved by modifying the sinuous geometry. The feed-LNA combination is characterized for important properties such as return loss, system noise, far field beam patterns including cross-polarization over a wide frequency range. The system is developed as a feed for a parabolic reflector. The overall system performance is calculated in terms of the A/Tsys ratio. A cryogenic version would have a direct impact on specialized observing applications requiring large instantaneous bandwidths with high sensitivity. A novel cryogenic implementation of this system is demonstrated using a Stirling cycle, one-stage refrigerator. The cryocooler offers advantages like low cost, light weight, small size, low power consumption, and does not require routine maintenance. The higher antenna input impedance and a balanced feeding method for the sinuous antenna offers a unique set of challenges when developing a cryogenic system.

Use of One Time Pad Algorithm for Bit Plane Security Improvement

NASA Astrophysics Data System (ADS)

Suhardi; Suwilo, Saib; Budhiarti Nababan, Erna

2017-12-01

BPCS (Bit-Plane Complexity Segmentation) which is one of the steganography techniques that utilizes the human vision characteristics that cannot see the change in binary patterns that occur in the image. This technique performs message insertion by making a switch to a high-complexity bit-plane or noise-like regions with bits of secret messages. Bit messages that were previously stored precisely result the message extraction process to be done easily by rearranging a set of previously stored characters in noise-like region in the image. Therefore the secret message becomes easily known by others. In this research, the process of replacing bit plane with message bits is modified by utilizing One Time Pad cryptography technique which aims to increase security in bit plane. In the tests performed, the combination of One Time Pad cryptographic algorithm to the steganography technique of BPCS works well in the insertion of messages into the vessel image, although in insertion into low-dimensional images is poor. The comparison of the original image with the stegoimage looks identical and produces a good quality image with a mean value of PSNR above 30db when using a largedimensional image as the cover messages.

Study of the longitudinal space charge compensation and longitudinal instability of the ferrite inductive inserts in the Los Alamos Proton Storage Ring

NASA Astrophysics Data System (ADS)

Beltran, Chris

Future high intensity synchrotrons will have a large space charge effect. It has been demonstrated in the Proton Storage Ring (PSR) at the Los Alamos National Laboratory (LANL) that ferrite inductive inserts can be used to compensate for the longitudinal space charge effect. However, simply installing ferrite inductors in the PSR led to longitudinal instabilities that were not tolerable. It was proposed that heating the ferrite would change the material properties in such a way as to reduce the instability. This proposal was tested in the PSR, and found to be true. This dissertation investigates and describes the complex permeability of the ferrite at room temperature and at an elevated temperature. The derived complex permeability is then used to obtain an impedance at the two temperatures. The impedance is used to determine the amount of space charge compensation supplied by the inductors and predict the growth time and frequency range of the longitudinal instability. The impedance is verified by comparing the experimental growth time and frequency range of the longitudinal instability to theoretical and computer simulated growth times and frequency ranges of the longitudinal instability. Lastly, an approach to mitigating the longitudinal instability that does not involve heating the ferrite is explored.

Dielectric relaxation behavior and impedance studies of Cu2+ ion doped Mg - Zn spinel nanoferrites

NASA Astrophysics Data System (ADS)

Choudhary, Pankaj; Varshney, Dinesh

2018-03-01

Cu2+ substituted Mg - Zn nanoferrites is synthesized by low temperature fired sol gel auto combustion method. The spinel nature of nanoferrites was confirmed by lab x-ray technique. Williamson - Hall (W-H) analysis estimate the average crystallite size (22.25-29.19 ± 3 nm) and micro strain induced Mg0.5Zn0.5-xCuxFe2O4 (0.0 ≤ x ≤ 0.5). Raman scattering measurements confirm presence of four active phonon modes. Red shift is observed with enhanced Cu concentration. Dielectric parameters exhibit a non - monotonous dispersion with Cu concentration and interpreted with the support of hopping mechanism and Maxwell-Wagner type of interfacial polarization. The ac conductivity of nanoferrites increases with raising the frequency. Complex electrical modulus reveals a non - Debye type of dielectric relaxation present in nanoferrites. Reactive impedance (Z″) detected an anomalous behavior and is related with resonance effect. Complex impedance demonstrates one semicircle corresponding to the intergrain (grain boundary) resistance and also explains conducting nature of nanoferrites. For x = 0.2, a large semicircle is observed revealing the ohmic nature (minimum potential drop at electrode surface). Dielectric properties were improved for nanoferrites with x = 0.2 and is due to high dielectric constant, conductivity and minimum loss value (∼0.009) at 1 MHz.

A critical analysis of single-frequency LCR databridge impedance measurements of human skin.

PubMed

White, Erick A; Orazem, Mark E; Bunge, Annette L

2011-06-01

Testing whether the barrier of skin samples has sufficient integrity for meaningful measurements of in-vitro chemical permeability is usually required when data are generated for regulatory purposes. Recently, skin integrity has been assessed using LCR databridge measurements, which are reported as resistances determined in either series (SER) or parallel (PAR) modes at a single frequency, typically 100 or 1000Hz. Measurements made at different combinations of mode and frequency are known to differ, although the skin literature reveals confusion over the meaning of these differences and the impact on the interpretation of integrity test results. Here, the theoretical meanings of resistance and capacitance measurements in PAR and SER mode are described and confirmed experimentally. SER-mode resistances are equal to the real part of the complex impedance; whereas, PAR-mode resistances are the inverse of the real part of the admittance. Capacitance measurements reported in SER and PAR modes are similar manipulations of the imaginary parts of the complex impedance and admittance. A large body of data from human cadaver skin is used to show that the PAR-mode resistance and SER-mode capacitance measured at 100Hz are sensitive to skin resistivity, which is the electrical measurement most closely related to skin integrity. Copyright © 2011 Elsevier Ltd. All rights reserved.

Structural and Optoelectronic Properties of SnO2 Thin Films Doped by Group-Ia Elements

NASA Astrophysics Data System (ADS)

Benhebal, Hadj; Benrabah, Bedhiaf; Ammari, Aek; Madoune, Yacine; Lambert, Stéphanie D.

This paper presents the results of an experimental work devoted to the synthesis and the characterization of tin dioxide (SnO2) thin layers doped with group-IA elements (Li, Na and K). The materials were synthesized by the sol-gel method and deposited by dip-coating, using tin (II) chloride dihydrate as a source of tin and absolute ethyl alcohol as solvent. Thin films prepared were characterized by several techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), visible and ultraviolet spectroscopy and complex impedance method. The results obtained show that the materials kept their tetragonal rutile structure with preferred orientation of (101), whereas doping leads to a reduction of their energy band gap. The complex impedance analysis suggests that the different processes occurring at the electrode interface are modeled by an electrical circuit not affected by the doping.

A Meier-Gorlin syndrome mutation in a conserved C-terminal helix of Orc6 impedes origin recognition complex formation.

PubMed

Bleichert, Franziska; Balasov, Maxim; Chesnokov, Igor; Nogales, Eva; Botchan, Michael R; Berger, James M

2013-10-08

In eukaryotes, DNA replication requires the origin recognition complex (ORC), a six-subunit assembly that promotes replisome formation on chromosomal origins. Despite extant homology between certain subunits, the degree of structural and organizational overlap between budding yeast and metazoan ORC has been unclear. Using 3D electron microscopy, we determined the subunit organization of metazoan ORC, revealing that it adopts a global architecture very similar to the budding yeast complex. Bioinformatic analysis extends this conservation to Orc6, a subunit of somewhat enigmatic function. Unexpectedly, a mutation in the Orc6 C-terminus linked to Meier-Gorlin syndrome, a dwarfism disorder, impedes proper recruitment of Orc6 into ORC; biochemical studies reveal that this region of Orc6 associates with a previously uncharacterized domain of Orc3 and is required for ORC function and MCM2-7 loading in vivo. Together, our results suggest that Meier-Gorlin syndrome mutations in Orc6 impair the formation of ORC hexamers, interfering with appropriate ORC functions. DOI:http://dx.doi.org/10.7554/eLife.00882.001.

Wideband characterization of the complex wave number and characteristic impedance of sound absorbers.

PubMed

Salissou, Yacoubou; Panneton, Raymond

2010-11-01

Several methods for measuring the complex wave number and the characteristic impedance of sound absorbers have been proposed in the literature. These methods can be classified into single frequency and wideband methods. In this paper, the main existing methods are revisited and discussed. An alternative method which is not well known or discussed in the literature while exhibiting great potential is also discussed. This method is essentially an improvement of the wideband method described by Iwase et al., rewritten so that the setup is more ISO 10534-2 standard-compliant. Glass wool, melamine foam and acoustical/thermal insulator wool are used to compare the main existing wideband non-iterative methods with this alternative method. It is found that, in the middle and high frequency ranges the alternative method yields results that are comparable in accuracy to the classical two-cavity method and the four-microphone transfer-matrix method. However, in the low frequency range, the alternative method appears to be more accurate than the other methods, especially when measuring the complex wave number.

Computed tomography arthrography using a radial plane view for the detection of triangular fibrocartilage complex foveal tears.

PubMed

Moritomo, Hisao; Arimitsu, Sayuri; Kubo, Nobuyuki; Masatomi, Takashi; Yukioka, Masao

2015-02-01

To classify triangular fibrocartilage complex (TFCC) foveal lesions on the basis of computed tomography (CT) arthrography using a radial plane view and to correlate the CT arthrography results with surgical findings. We also tested the interobserver and intra-observer reliability of the radial plane view. A total of 33 patients with a suspected TFCC foveal tear who had undergone wrist CT arthrography and subsequent surgical exploration were enrolled. We classified the configurations of TFCC foveal lesions into 5 types on the basis of CT arthrography with the radial plane view in which the image slices rotate clockwise centered on the ulnar styloid process. Sensitivity, specificity, and positive predictive values were calculated for each type of foveal lesion in CT arthrography to detect foveal tears. We determined interobserver and intra-observer agreements using kappa statistics. We also compared accuracies with the radial plane views with those with the coronal plane views. Among the tear types on CT arthrography, type 3, a roundish defect at the fovea, and type 4, a large defect at the overall ulnar insertion, had high specificity and positive predictive value for the detection of foveal tears. Specificity and positive predictive values were 90% and 89% for type 3 and 100% and 100% for type 4, respectively, whereas sensitivity was 35% for type 3 and 22% for type 4. Interobserver and intra-observer agreement was substantial and almost perfect, respectively. The radial plane view identified foveal lesion of each palmar and dorsal radioulnar ligament separately, but accuracy results with the radial plane views were not statistically different from those with the coronal plane views. Computed tomography arthrography with a radial plane view exhibited enhanced specificity and positive predictive value when a type 3 or 4 lesion was identified in the detection of a TFCC foveal tear compared with historical controls. Diagnostic II. Copyright © 2015 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.

On the maximum-entropy/autoregressive modeling of time series

NASA Technical Reports Server (NTRS)

Chao, B. F.

1984-01-01

The autoregressive (AR) model of a random process is interpreted in the light of the Prony's relation which relates a complex conjugate pair of poles of the AR process in the z-plane (or the z domain) on the one hand, to the complex frequency of one complex harmonic function in the time domain on the other. Thus the AR model of a time series is one that models the time series as a linear combination of complex harmonic functions, which include pure sinusoids and real exponentials as special cases. An AR model is completely determined by its z-domain pole configuration. The maximum-entropy/autogressive (ME/AR) spectrum, defined on the unit circle of the z-plane (or the frequency domain), is nothing but a convenient, but ambiguous visual representation. It is asserted that the position and shape of a spectral peak is determined by the corresponding complex frequency, and the height of the spectral peak contains little information about the complex amplitude of the complex harmonic functions.

Thinking Forbidden Thoughts: The Oedipus Complex as a Complex of Knowing.

PubMed

Schein, Michael

2016-04-01

The Oedipus complex, considered by Freud the "nuclear complex of development," played a central role in the evolution of psychoanalytic thought. This paper returns to the point of transition from the seduction theory, Freud's initial theorem, to the oedipal model, and suggests that the Oedipus complex is first and foremost a text and as such contains a multiplicity of narratives. In particular, the author articulates the close relation between the Oedipus complex and the subject of knowing, postulating that underlying its surface level, the deep-level structure of this complex is one of knowing. As a complex of knowing it is of dual quality, both promoting and impeding the ability to know.

Dynamics of Helium-Loaded Grain Boundaries under Shear Deformation in α-Fe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Fei; Yang, Li; Heinisch, Howard L.

2014-03-30

The defects produced in collision cascades will interact with microstructural features in materials, such as GBs and dislocations. The coupled motion of GBs under stress has been widely observed in simulations and experiments. Two symmetric tilt GBs with a common <110> tilt axis (Σ3 and Σ11) in bcc iron are used to investigate the coupled motion of GBs under shear deformation. Also, we have explored the effect of self-interstitial atoms (SIAs) loading on the GB motion, with different concentrations of interstitials randomly inserted around the GB plane. The simulation results show that the interstitial loading reduces the critical stress ofmore » the GB coupled motion for the Σ3 GB. Furthermore, the interstitials and vacancies are inserted randomly at the GB plane and at a distance of 1 nm away from the GB plane, respectively, to understand the self-healing mechanism of GBs under stress. The behavior of the defect-loaded GBs depends on the GB structure. The loaded interstitials in the Σ3 GB easily form <111> interstitial clusters that do not move along with the GB. The vacancies in the Σ3 GB impede the GB motion. However, the interstitials move along with the Σ11 GB and annihilate with vacancies when the GB moves into the vacancy-rich region, leading to the self-healing and damage recovery of the Σ11 GB.« less

Dielectric and impedance spectral characteristics of bulk ZnIn2Se4

NASA Astrophysics Data System (ADS)

El-Nahass, M. M.; Attia, A. A.; Salem, G. F.; Ali, H. A. M.; Ismail, M. I.

2014-02-01

The frequency and temperature dependence of ac conductivity, dielectric constant and dielectric loss of ZnIn2Se4 in a pellet form were investigated in the frequency range of 102-106 Hz and temperature range of 293-356 K. The behavior of ac conductivity was interpreted by the correlated barrier hopping (CBH) model. Temperature dependence of ac conductivity indicates that ac conduction is a thermally activated process. The density of localized states N(EF) and ac activation energy were estimated for various frequencies. Dielectric constant and dielectric loss showed a decrease with increasing frequency and an increase with increasing in temperature. The frequency dependence of real and imaginary parts of the complex impedance was investigated. The relaxation time decreases with the increase in temperature. The impedance spectrum exhibits the appearance of the single semicircular arc. The radius of semicircular arcs decreases with increasing temperature which suggests a mechanism of temperature-dependent on relaxation.

Development of an Inductively Coupled Thermometer for a Cryogenic Half-Wave Plate

NASA Astrophysics Data System (ADS)

Madurowicz, Alexander; Kusaka, Akito

2017-01-01

The current state of Cosmic Microwave Background (CMB) research has focused much attention on the measurement of polarization. In an effort to modulate the CMB polarization while also minimizing photon noise due to thermal emission, we are developing a sapphire half-wave plate (HWP) cooled to 50 K rotating at 2 Hz on a superconducting magnetic levitating bearing. In order to measure the temperature of the rotor without making physical contact, we designed an inductively coupled cryogenic thermometer. The complex impedance of the circuit has a resonant peak when driven around 1 MHz. The width of this resonance is dependent on the value of the resistor, which varies with temperature and functions as a thermometer once calibrated. In this talk, we will present results from stationary measurements of this impedance and discuss the temperature accuracy of this thermometer, as well as a preliminary circuit design to measure this impedance during the HWP rotation.

High frequency lateral flow affinity assay using superparamagnetic nanoparticles

NASA Astrophysics Data System (ADS)

Lago-Cachón, D.; Rivas, M.; Martínez-García, J. C.; Oliveira-Rodríguez, M.; Blanco-López, M. C.; García, J. A.

2017-02-01

Lateral flow assay is one of the simplest and most extended techniques in medical diagnosis for point-of-care testing. Although it has been traditionally a positive/negative test, some work has been lately done to add quantitative abilities to lateral flow assay. One of the most successful strategies involves magnetic beads and magnetic sensors. Recently, a new technique of superparamagnetic nanoparticle detection has been reported, based on the increase of the impedance induced by the nanoparticles on a RF-current carrying copper conductor. This method requires no external magnetic field, which reduces the system complexity. In this work, nitrocellulose membranes have been installed on the sensor, and impedance measurements have been carried out during the sample diffusion by capillarity along the membrane. The impedance of the sensor changes because of the presence of magnetic nanoparticles. The results prove the potentiality of the method for point-of-care testing of biochemical substances and nanoparticle capillarity flow studies.

High-Tc Superconducting Bolometer Noise Measurement Using Low Noise Transformers - Theory and Optimization

NASA Technical Reports Server (NTRS)

Aslam, Shahid; Jones, Hollis H.

2011-01-01

Care must always be taken when performing noise measurements on high-Tc superconducting materials to ensure that the results are not from the measurement system itself. One situation likely to occur is with low noise transformers. One of the least understood devices, it provides voltage gain for low impedance inputs (< 100 ), e.g., YBaCuO and GdBaCuO thin films, with comparatively lower noise levels than other devices for instance field effect and bipolar junction transistors. An essential point made in this paper is that because of the complex relationships between the transformer ports, input impedance variance alters the transformer s transfer function in particular, the low frequency cutoff shift. The transfer of external and intrinsic transformer noise to the output along with optimization and precautions are treated; all the while, we will cohesively connect the transfer function shift, the load impedance, and the actual noise at the transformer output.

Difference in electrodynamic transduction between speaker and alternator in thermoacoustic applications.

PubMed

Gonen, Eran; Grossman, Gershon

2015-09-01

Conventional reciprocating pistons, normally found in thermoacoustic engines, tend to introduce complex impedance characteristics, including acoustic, mechanical, and electrical portions. System behavior and performance usually rely on proper tuning processes and selection of an optimal point of operation, affected substantially by complementary hardware, typically adjusted for the specific application. The present study proposes an alternative perspective on the alternator behavior, by considering the relative motion between gas and piston during the engine mode of operation. Direct analytical derivation of the velocity distribution inside a tight seal gap and the associated impedance is employed to estimate the electro-acoustic conversion efficiency, thus indicating how to improve the system performance. The influence of acoustic phase, gap dimensions, and working conditions is examined, suggesting the need to develop tighter and longer seal gaps, having increased impedance, to allow optimization for use in upcoming sustainable power generation solutions and smart grids.

The application of dual-electrode through vial impedance spectroscopy for the determination of ice interface temperatures, primary drying rate and vial heat transfer coefficient in lyophilization process development.

PubMed

Smith, Geoff; Jeeraruangrattana, Yowwares; Ermolina, Irina

2018-06-22

Through vial impedance spectroscopy (TVIS) is a product non-invasive process analytical technology which exploits the frequency dependence of the complex impedance spectrum of a composite object (i.e. the freeze-drying vial and its contents) in order to track the progression of the freeze-drying cycle. This work demonstrates the use of a dual electrode system, attached to the external surface of a type I glass tubing vial (nominal capacity 10 mL) in the prediction of (i) the ice interface temperatures at the sublimation front and at the base of the vial, and (ii) the primary drying rate. A value for the heat transfer coefficient (for a chamber pressure of 270 µbar) was then calculated from these parameters and shown to be comparable to that published by Tchessalov[1]. Copyright © 2018. Published by Elsevier B.V.

Adaptive microwave impedance memory effect in a ferromagnetic insulator.

PubMed

Lee, Hanju; Friedman, Barry; Lee, Kiejin

2016-12-14

Adaptive electronics, which are often referred to as memristive systems as they often rely on a memristor (memory resistor), are an emerging technology inspired by adaptive biological systems. Dissipative systems may provide a proper platform to implement an adaptive system due to its inherent adaptive property that parameters describing the system are optimized to maximize the entropy production for a given environment. Here, we report that a non-volatile and reversible adaptive microwave impedance memory device can be realized through the adaptive property of the dissipative structure of the driven ferromagnetic system. Like the memristive device, the microwave impedance of the device is modulated as a function of excitation microwave passing through the device. This kind of new device may not only helpful to implement adaptive information processing technologies, but also may be useful to investigate and understand the underlying mechanism of spontaneous formation of complex and ordered structures.

Real-time electrochemical impedance spectroscopy diagnosis of the solid oxide fuel cell for marine power applications

NASA Astrophysics Data System (ADS)

Nakajima, Hironori; Kitahara, Tatsumi

2017-11-01

We have investigated the behavior of an operating solid oxide fuel cell (SOFC) with supplying a simulated syngas to develop diagnosis method of the SOFC for marine power applications fueled with liquefied natural gas (LNG). We analyze the characteristics of a syngas-fueled intermediate temperature microtubular SOFC at 500 ∘C for accelerated deterioration by carbon deposition as a model case by electrochemical impedance spectroscopy (EIS) to in-situ find parameters useful for the real-time diagnosis. EIS analyses are performed by complex nonlinear least squares (CNLS) curve fitting to measured impedance spectra with an equivalent electric circuit model consisting of several resistances and capacitances attributed to the anode and cathode processes as well as Ohmic resistance of the cell. The characteristic changes of those circuit parameters by internal reforming and anode degradation are extracted, showing that they can be used for the real-time diagnosis of operating SOFCs.

Impedance Measurement of a Gamma-Ray TES Calorimeter with a Bulk Sn Absorber

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akamatsu, H.; Ishisaki, Y.; Hoshino, A.

2009-12-16

We performed complex impedance measurements with a Ti/Au-based gamma-ray TES calorimeter with a bulk Sn absorber. Excellent energy resolution of 38.4{+-}0.9eV at 60 keV was observed. The impedance of the calorimeter can be well explained by a two-body thermal model. We investigated the behavior of the parameters of the calorimeter during the superconducting-to-normal transition. We confirmed that C and G{sub a} are in good agreement with the predicted values. We performed a noise analysis and found several excess noise components, as well as internal thermal fluctuation noise (ITFN) term due to the thermal conductance between the Sn absorber and themore » Ti/Au TES. Dominanting the noise is an excess noise having a similar frequency dependence to the phonon noise and the ITFN noise.« less

Adaptive microwave impedance memory effect in a ferromagnetic insulator

PubMed Central

Lee, Hanju; Friedman, Barry; Lee, Kiejin

2016-01-01

Adaptive electronics, which are often referred to as memristive systems as they often rely on a memristor (memory resistor), are an emerging technology inspired by adaptive biological systems. Dissipative systems may provide a proper platform to implement an adaptive system due to its inherent adaptive property that parameters describing the system are optimized to maximize the entropy production for a given environment. Here, we report that a non-volatile and reversible adaptive microwave impedance memory device can be realized through the adaptive property of the dissipative structure of the driven ferromagnetic system. Like the memristive device, the microwave impedance of the device is modulated as a function of excitation microwave passing through the device. This kind of new device may not only helpful to implement adaptive information processing technologies, but also may be useful to investigate and understand the underlying mechanism of spontaneous formation of complex and ordered structures. PMID:27966536

Development of an Algorithm for Automatic Analysis of the Impedance Spectrum Based on a Measurement Model

NASA Astrophysics Data System (ADS)

Kobayashi, Kiyoshi; Suzuki, Tohru S.

2018-03-01

A new algorithm for the automatic estimation of an equivalent circuit and the subsequent parameter optimization is developed by combining the data-mining concept and complex least-squares method. In this algorithm, the program generates an initial equivalent-circuit model based on the sampling data and then attempts to optimize the parameters. The basic hypothesis is that the measured impedance spectrum can be reproduced by the sum of the partial-impedance spectra presented by the resistor, inductor, resistor connected in parallel to a capacitor, and resistor connected in parallel to an inductor. The adequacy of the model is determined by using a simple artificial-intelligence function, which is applied to the output function of the Levenberg-Marquardt module. From the iteration of model modifications, the program finds an adequate equivalent-circuit model without any user input to the equivalent-circuit model.

Low cost impulse compatible wideband antenna

DOEpatents

Rosenbury, Erwin T.; Burke, Gerald J.; Nelson, Scott D.; Stever, Robert D.; Governo, George K.; Mullenhoff, Donald J.

2002-01-01

An antenna apparatus and method for building the antenna is disclosed. Impulse signals travel through a feed point of the antenna with respect to a ground plane. A geometric fin structure is connected to the feed point, and through a termination resistance to the ground plane. A geometric ridge structure connected to the ground is positioned with respect to the fin in order to receive and radiate electromagnetic energy from the impulse signal at a predetermined impedance and over a predetermined set of frequencies. The fin and ridge can be either a wire or a planar surface. The fin and ridge may be disposed within a radiation cavity such as a horn. The radiation cavity is constructed of stamped and etched metal sheets bent and then soldered together. The fin and ridge are also formed from metal sheets or wires. The fin is attached to the feed point and then to the cavity through a termination resistance. The ridge is attached to the cavity and disposed with respect to the fin in order to achieve a particular set of antenna characteristics.

Unidirectional Magneto-Electric Dipole Antenna for Base Station: A Review

NASA Astrophysics Data System (ADS)

Idayachandran, Govindanarayanan; Nakkeeran, Rangaswamy

2018-04-01

Unidirectional base station antenna design using Magneto-Electric Dipole (MED) has created enormous interest among the researchers due to its excellent radiation characteristics like low back radiation, symmetrical radiation at E-plane and H-plane compared to conventional patch antenna. Generally, dual polarized antennas are used to increase channel capacity and reliability of the communication systems. In order to serve the evolving mobile communication standards like long term evolution LTE and beyond, unidirectional dual polarized MED antenna are required to have broad impedance bandwidth, broad half power beamwidth, high port isolation, low cross polarization level, high front to back ratio and high gain. In this paper, the critical electrical requirements of the base station antenna and frequently used frequency bands for modern mobile communication have been presented. It is followed by brief review on broadband patch antenna and discussion on complementary antenna concepts. Finally, the performance of linearly polarized and dual polarized magneto-electric dipole antennas along with their feeding techniques are discussed and summarized. Also, design and modeling of developed MED antenna is presented.

Efficient reduction of defects in (1120) non-polar and (1122) semi-polar GaN grown on nanorod templates

NASA Astrophysics Data System (ADS)

Bai, J.; Gong, Y.; Xing, K.; Yu, X.; Wang, T.

2013-03-01

(1120) non-polar and (1122) semi-polar GaNs with a low defect density have been achieved by means of an overgrowth on nanorod templates, where a quick coalescence with a thickness even below 1 μm occurs. On-axis and off-axis X-ray rocking curve measurements have shown a massive reduction in the linewidth for our overgrown GaN in comparison with standard GaN films grown on sapphire substrates. Transmission electron microscope observation demonstrates that the overgrowth on the nanorod templates takes advantage of an omni-directional growth around the sidewalls of the nanostructures. The dislocations redirect in basal planes during the overgrowth, leading to their annihilation and termination at voids formed due to a large lateral growth rate. In the non-polar GaN, the priority <0001> lateral growth from vertical sidewalls of nanorods allows basal plane stacking faults (BSFs) to be blocked in the nanorod gaps; while for semi-polar GaN, the propagation of BSFs starts to be impeded when the growth front is changed to be along inclined <0001> direction above the nanorods.

Slip, twinning, and fracture at a grain boundary in the L1/sub 2/ ordered structure: A. sigma. = 9 tilt boundary

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoo, M.H.; King, A.H.

The role of interaction between slip dislocations and a ..sigma.. = 9 tilt boundary in localized microplastic deformation, cleavage, or intergranular fracture in the L1/sub 2/ ordered structure has been analyzed by using the anisotropic elasticity theory of dislocations and fracture. Screw superpartials cross slip easily at the boundary onto the (11-bar1) and the (001) planes at low and high temperatures, respectively. Transmission of primary slip dislocations onto the conjugate slip system occurs with a certain degree of difficulty, which is eased by localized disordering. When the transmission is impeded, cleavage fracture on the (1-bar11) plane is predicted to occur,more » not intergranular fracture, unless a symmetric double pileup occurs simultaneously. Absorption (or emission) of superpartials occurs only when the boundary region is disordered. Slip initiation from pre-existing sources near the boundary can occur under the local stress concentration. Implications of the present result on the inherent brittleness of grain boundaries in Ni/sub 3/ Al and its improvement by boron segregation are discussed.« less

Accuracy and reliability of noninvasive stroke volume monitoring via ECG-gated 3D electrical impedance tomography in healthy volunteers.

PubMed

Braun, Fabian; Proença, Martin; Adler, Andy; Riedel, Thomas; Thiran, Jean-Philippe; Solà, Josep

2018-01-01

Cardiac output (CO) and stroke volume (SV) are parameters of key clinical interest. Many techniques exist to measure CO and SV, but are either invasive or insufficiently accurate in clinical settings. Electrical impedance tomography (EIT) has been suggested as a noninvasive measure of SV, but inconsistent results have been reported. Our goal is to determine the accuracy and reliability of EIT-based SV measurements, and whether advanced image reconstruction approaches can help to improve the estimates. Data were collected on ten healthy volunteers undergoing postural changes and exercise. To overcome the sensitivity to heart displacement and thorax morphology reported in previous work, we used a 3D EIT configuration with 2 planes of 16 electrodes and subject-specific reconstruction models. Various EIT-derived SV estimates were compared to reference measurements derived from the oxygen uptake. Results revealed a dramatic impact of posture on the EIT images. Therefore, the analysis was restricted to measurements in supine position under controlled conditions (low noise and stable heart and lung regions). In these measurements, amplitudes of impedance changes in the heart and lung regions could successfully be derived from EIT using ECG gating. However, despite a subject-specific calibration the heart-related estimates showed an error of 0.0 ± 15.2 mL for absolute SV estimation. For trending of relative SV changes, a concordance rate of 80.9% and an angular error of -1.0 ± 23.0° were obtained. These performances are insufficient for most clinical uses. Similar conclusions were derived from lung-related estimates. Our findings indicate that the key difficulty in EIT-based SV monitoring is that purely amplitude-based features are strongly influenced by other factors (such as posture, electrode contact impedance and lung or heart conductivity). All the data of the present study are made publicly available for further investigations.

Accuracy and reliability of noninvasive stroke volume monitoring via ECG-gated 3D electrical impedance tomography in healthy volunteers

PubMed Central

Proença, Martin; Adler, Andy; Riedel, Thomas; Thiran, Jean-Philippe; Solà, Josep

2018-01-01

Cardiac output (CO) and stroke volume (SV) are parameters of key clinical interest. Many techniques exist to measure CO and SV, but are either invasive or insufficiently accurate in clinical settings. Electrical impedance tomography (EIT) has been suggested as a noninvasive measure of SV, but inconsistent results have been reported. Our goal is to determine the accuracy and reliability of EIT-based SV measurements, and whether advanced image reconstruction approaches can help to improve the estimates. Data were collected on ten healthy volunteers undergoing postural changes and exercise. To overcome the sensitivity to heart displacement and thorax morphology reported in previous work, we used a 3D EIT configuration with 2 planes of 16 electrodes and subject-specific reconstruction models. Various EIT-derived SV estimates were compared to reference measurements derived from the oxygen uptake. Results revealed a dramatic impact of posture on the EIT images. Therefore, the analysis was restricted to measurements in supine position under controlled conditions (low noise and stable heart and lung regions). In these measurements, amplitudes of impedance changes in the heart and lung regions could successfully be derived from EIT using ECG gating. However, despite a subject-specific calibration the heart-related estimates showed an error of 0.0 ± 15.2 mL for absolute SV estimation. For trending of relative SV changes, a concordance rate of 80.9% and an angular error of −1.0 ± 23.0° were obtained. These performances are insufficient for most clinical uses. Similar conclusions were derived from lung-related estimates. Our findings indicate that the key difficulty in EIT-based SV monitoring is that purely amplitude-based features are strongly influenced by other factors (such as posture, electrode contact impedance and lung or heart conductivity). All the data of the present study are made publicly available for further investigations. PMID:29373611

Synthesis, dielectric, conductivity and magnetic studies of LiNi1/3Co1/3Mn(1/3)-xAlxO2 (x = 0.0, 0.02, 0.04 and 0.06) for cathode materials of lithium-ion batteries

NASA Astrophysics Data System (ADS)

Murali, N.; Margarette, S. J.; Veeraiah, V.

Layered structure cathode materials LiNi1/3Co1/3Mn(1/3)-xAlxO2 (x = 0.0, 0.02, 0.04 and 0.06) are prepared by the sol-gel method by adding citric acid as chelating agent. The physical, electrical and magnetic properties of the synthesized materials are systematically discussed using the structural (XRD, FESEM with EDS and FT-IR), impedance (LCR) and electron spin resonance (ESR) measurements. The X-ray diffraction pattern of the synthesized samples possessed the α-NaFeO2 structure of the space group, R 3 bar m , with no evidence of any impurities. The peak intensity ratio I(104)/I(003) increased with Al concentration, which indicated the cation mixing between transition metal layer and lithium layer. The field effect scanning electron microscopy showed the particle size distribution in the range of 230-250 nm and EDS has been analysed for elemental mapping. The local structure is investigated by vibrational spectroscopy in FT-IR study. The impedance studies are characterized by complex impedance spectroscopy (CIS) in the frequency range from 42 Hz to 1 MHz at room temperature (30 °C). The dielectric properties are analyzed in the framework of complex dielectric permittivity and formalism of the complex electric modulus. For these samples, the ESR analysis of magnetic measurements, the degree of cation mixing, is estimated to be Ni2+(3b) = 2.75%.

Wave propagation in media having negative permittivity and permeability.

PubMed

Ziolkowski, R W; Heyman, E

2001-11-01

Wave propagation in a double negative (DNG) medium, i.e., a medium having negative permittivity and negative permeability, is studied both analytically and numerically. The choices of the square root that leads to the index of refraction and the wave impedance in a DNG medium are determined by imposing analyticity in the complex frequency domain, and the corresponding wave properties associated with each choice are presented. These monochromatic concepts are then tested critically via a one-dimensional finite difference time domain (FDTD) simulation of the propagation of a causal, pulsed plane wave in a matched, lossy Drude model DNG medium. The causal responses of different spectral regimes of the medium with positive or negative refractive indices are studied by varying the carrier frequency of narrowband pulse excitations. The smooth transition of the phenomena associated with a DNG medium from its early-time nondispersive behavior to its late-time monochromatic response is explored with wideband pulse excitations. These FDTD results show conclusively that the square root choice leading to a negative index of refraction and positive wave impedance is the correct one, and that this choice is consistent with the overall causality of the response. An analytical, exact frequency domain solution to the scattering of a wave from a DNG slab is also given and is used to characterize several physical effects. This solution is independent of the choice of the square roots for the index of refraction and the wave impedance, and thus avoids any controversy that may arise in connection with the signs of these constituents. The DNG slab solution is used to critically examine the perfect lens concept suggested recently by Pendry. It is shown that the perfect lens effect exists only under the special case of a DNG medium with epsilon(omega)=mu(omega)=-1 that is both lossless and nondispersive. Otherwise, the closed form solutions for the field structure reveal that the DNG slab converts an incident spherical wave into a localized beam field whose parameters depend on the values of epsilon and mu. This beam field is characterized with a paraxial approximation of the exact DNG slab solution. These monochromatic concepts are again explored numerically via a causal two-dimensional FDTD simulation of the scattering of a pulsed cylindrical wave by a matched, lossy Drude model DNG slab. These FDTD results demonstrate conclusively that the monochromatic electromagnetic power flow through the DNG slab is channeled into beams rather then being focused and, hence, the Pendry perfect lens effect is not realizable with any realistic metamaterial.

Line-source excitation of realistic conformal metasurface cloaks

NASA Astrophysics Data System (ADS)

Padooru, Yashwanth R.; Yakovlev, Alexander B.; Chen, Pai-Yen; Alù, Andrea

2012-11-01

Following our recently introduced analytical tools to model and design conformal mantle cloaks based on metasurfaces [Padooru et al., J. Appl. Phys. 112, 034907 (2012)], we investigate their performance and physical properties when excited by an electric line source placed in their close proximity. We consider metasurfaces formed by 2-D arrays of slotted (meshes and Jerusalem cross slots) and printed (patches and Jerusalem crosses) sub-wavelength elements. The electromagnetic scattering analysis is carried out using a rigorous analytical model, which utilizes the two-sided impedance boundary conditions at the interface of the sub-wavelength elements. It is shown that the homogenized grid-impedance expressions, originally derived for planar arrays of sub-wavelength elements and plane-wave excitation, may be successfully used to model and tailor the surface reactance of cylindrical conformal mantle cloaks illuminated by near-field sources. Our closed-form analytical results are in good agreement with full-wave numerical simulations, up to sub-wavelength distances from the metasurface, confirming that mantle cloaks may be very effective to suppress the scattering of moderately sized objects, independent of the type of excitation and point of observation. We also discuss the dual functionality of these metasurfaces to boost radiation efficiency and directivity from confined near-field sources.

Modification of the sagittal split osteotomy of the mandibular ramus: mobilizing vertical osteotomy of the internal ramus segment.

PubMed

Ricard, Daniel; Ferri, Joël

2009-08-01

We describe a new surgical procedure to improve stability when counterclockwise rotation of the maxillomandibular complex and the occlusal plane is intended. This preliminary prospective study evaluated 10 patients (8 female patients and 2 male patients) who each underwent maxillomandibular surgical advancement with counterclockwise rotation of the occlusal plane. A mandibular counterclockwise rotation was done in all cases with bilateral ramus sagittal split osteotomy. After the split of the ramus had been completed, a vertical osteotomy was done distally to the second molar on the internal ramus segment. With the completion of this vertical osteotomy, the internal ramus segment became completely mobile. All osteotomies were stabilized with rigid internal fixation by use of plates with monocortical screws. Ten patients have been treated with the "mobilizing vertical osteotomy of the internal ramus segment." The mean reduction of the occlusal plane angle was 10.1 degrees , showing a substantial counterclockwise rotation of the maxillomandibular complex. All patients had significant improvement of their facial balance. After a 1-year follow-up period, all cases but 1 showed very good stability of their occlusion and occlusal plane angle. An 11.4% relapse of the forward movement of the mandible was noted. On the basis of this prospective study, we conclude that when performing a counterclockwise rotation of the maxillomandibular complex, the mobilizing vertical osteotomy of the internal ramus segment combined with the sagittal split osteotomy of the mandible potentially enhances the occlusal plane angle and occlusal stability after a 1-year period.

Measurement of electrical impedance of a Berea sandstone core during the displacement of saturated brine by oil and CO2 injections

NASA Astrophysics Data System (ADS)

Liu, Yu; Xue, Ziqiu; Park, Hyuck; Kiyama, Tamotsu; Zhang, Yi; Nishizawa, Osamu; Chae, Kwang-seok

2015-12-01

Complex electrical impedance measurements were performed on a brine-saturated Berea sandstone core while oil and CO2 were injected at different pressures and temperatures. The saturations of brine, oil, and CO2 in the core were simultaneously estimated using an X-ray computed tomography scanner. The formation factor of this Berea core and the resistivity indexes versus the brine saturations were calculated using Archie's law. The experimental results found different flow patterns of oil under different pressures and temperatures. Fingers were observed for the first experiment at 10 MPa and 40 °C. The fingers were restrained as the viscosity ratio of oil and water changed in the second (10 MPa and 25 °C) and third (5 MPa and 25 °C) experiments. The resistivity index showed an exponential increase with a decrease in brine saturation. The saturation exponent varied from 1.4 to 4.0 at different pressure and temperature conditions. During the oil injection procedure, the electrical impedance increased with oil saturation and was significantly affected by different oil distributions; therefore, the impedance varied whether the finger was remarkable or not, even if the oil saturation remained constant. During the CO2 injection steps, the impedance showed almost no change with CO2 saturation because the brine in the pores became immobile after the oil injection.

Ferroelectric relaxor behaviour and impedance spectroscopy of Bi2O3-doped barium zirconium titanate ceramics

NASA Astrophysics Data System (ADS)

Mahajan, Sandeep; Thakur, O P; Bhattacharya, D K; Sreenivas, K

2009-03-01

Bi2O3-doped barium zirconate titanate ceramics, Ba1-xBix(Zr0.05Ti0.95)O3, have been prepared by the conventional solid-state reaction method. The ferroelectric relaxor behaviour and dielectric properties have been investigated in detail. By XRD analysis, it is suggested that up to x = 0.04, Bi3+ substitutes A-site ion, and thereafter with higher Bi3+ content, it enters the B-site sub lattice. Substitution of Bi3+ ions induces ferroelectric relaxor behaviour and the degree of relaxation behaviour increases with bismuth concentration. The remanent polarization and strain behaviour show a slight increase with the substitution level. The degree of hysteresis (strain versus electric field) also reduces from 21.4% to 4.6% with bismuth substitution. Impedance measurements were made on the prepared sample over a wide range of temperatures (300-723 K) and frequencies (40 Hz-1 MHz), which show the presence of both bulk and grain boundary effects in the material. The bulk and grain boundary conductivities determined from impedance study indicate the Arrhenius-type thermally activated process. Impedance spectroscopy is shown to be an efficient method capable of detecting the contributions of the resistances of grains and grain boundaries to the complex impedance of a ceramic system, accurately estimating its electrical conductivity as well as its corresponding activation energies and drawing conclusions on its structural properties.

Calculating realistic voltages across the US power grid utilizing measured impedances and magnetic fields

NASA Astrophysics Data System (ADS)

Lucas, G.; Love, J. J.; Kelbert, A.; Bedrosian, P.; Rigler, E. J.

2017-12-01

Space weather induces significant geoelectric fields within Earth's subsurface that can adversely affect electric power grids. The complex interaction between space weather and the solid Earth has traditionally been approached with the use of simple 1-D impedance functions relating the inducing magnetic field to the induced geoelectric field. Ongoing data collection through the NSF EarthScope program has produced measured impedance data across much of the continental US. In this work, impedance data are convolved with magnetic field variations, obtained from USGS magnetic observatories, during a geomagnetic storm. This convolution produces geoelectric fields within the earth. These geoelectric fields are then integrated across power transmission lines to determine the voltage generated within each power line as a function of time during a geomagnetic storm. The voltages generated within the electric power grid will be shown for several historic geomagnetic storms. The estimated voltages calculated from 1-D and 3-D impedances differ by more than 100 V across some transmission lines. In combination with grounding resistance data and network topology, these voltage estimates can be utilized by power companies to estimate geomagnetically-induced currents throughout the network. These voltage estimates can provide information on which power lines are most vulnerable to geomagnetic storms, and assist power grid companies investigating where to install additional protections within their grid.

Monitoring and Characterizing Crop Root Systems Using Electrical Impedance Tomography (EIT)

NASA Astrophysics Data System (ADS)

Weigand, M.; Kemna, A.

2016-12-01

A better understanding of root-soil interactions and associated processes is essential to achieve progress in crop breeding and management, prompting the need for high-resolution and non-destructive characterization methods. Such methods are still lacking, in particular for characterizing root growth and function in the field. A promising technique in this respect is electrical impedance tomography (EIT), which provides images of the low-frequency electrical conduction and polarization properties and thus can be used to investigate polarization processes occurring within and in the direct vicinity of roots under the influence of an external alternating electric field. This approach takes advantage of the well-known polarization properties associated with electrical double layers forming at membranes of cells and cell clusters. However, upscaling these processes to the scale of an impedance, or complex conductivity, spectrum of the whole root system is not trivial given the lack of electrical root models, the complexity of root systems, and the occurrence of additional larger-scale, ion-selective, and therefore polarizable, structures such as the Casparian strip. We here present results from several EIT laboratory studies on rhizotrons with crop root systems in aqueous solutions. Based on optimized experimental and data analysis procedures, enabling the imaging of the weak signals encountered in our studies, we found systematic spatial and temporal changes of both the magnitude and the shape of the spectral polarization signatures during nutrient deprivation and in response to the decapitation of plants. Consistent, but relatively weak, spectral impedance changes were also observed over diurnal cycles. Our results provide evidence for the capability of EIT to non-invasively image and monitor root systems at the rhizotron scale. They further suggest that EIT is a promising tool for imaging, characterizing, and monitoring crop roots at the field scale.

The orbital ground state of the azide-substrate complex of human heme oxygenase is an indicator of distal H-bonding: implications for the enzyme mechanism.

PubMed

Ogura, Hiroshi; Evans, John P; Peng, Dungeng; Satterlee, James D; Ortiz de Montellano, Paul R; La Mar, Gerd N

2009-04-14

The active site electronic structure of the azide complex of substrate-bound human heme oxygenase 1 (hHO) has been investigated by (1)H NMR spectroscopy to shed light on the orbital/spin ground state as an indicator of the unique distal pocket environment of the enzyme. Two-dimensional (1)H NMR assignments of the substrate and substrate-contact residue signals reveal a pattern of substrate methyl contact shifts that places the lone iron pi-spin in the d(xz) orbital, rather than the d(yz) orbital found in the cyanide complex. Comparison of iron spin relaxivity, magnetic anisotropy, and magnetic susceptibilities argues for a low-spin, (d(xy))(2)(d(yz),d(xz))(3), ground state in both azide and cyanide complexes. The switch from singly occupied d(yz) for the cyanide to d(xz) for the azide complex of hHO is shown to be consistent with the orbital hole determined by the azide pi-plane in the latter complex, which is approximately 90 degrees in-plane rotated from that of the imidazole pi-plane. The induction of the altered orbital ground state in the azide relative to the cyanide hHO complex, as well as the mean low-field bias of methyl hyperfine shifts and their paramagnetic relaxivity relative to those in globins, indicates that azide exerts a stronger ligand field in hHO than in the globins, or that the distal H-bonding to azide is weaker in hHO than in globins. The Asp140 --> Ala hHO mutant that abolishes activity retains the unusual WT azide complex spin/orbital ground state. The relevance of our findings for other HO complexes and the HO mechanism is discussed.

The orbital ground state of the azide-substrate complex of human heme oxygenase is an indicator of distal H-bonding: Implications for the enzyme mechanism‡

PubMed Central

Ogura, Hiroshi; Evans, John P.; Peng, Dungeng; Satterlee, James D.; de Montellano, Paul R. Ortiz; Mar, Gerd N. La

2009-01-01

The active site electronic structure of the azide complex of substrate-bound human heme oxygenase-1, (hHO) has been investigated by 1H NMR spectroscopy to shed light on the orbital/spin ground state as an indicator of the unique distal pocket environment of the enzyme. 2D 1H NMR assignments of the substrate and substrate-contact residue signals reveal a pattern of substrate methyl contact shifts, that places the lone iron π-spin in the dxz orbital, rather than the dyz orbital found in the cyanide complex. Comparison of iron spin relaxivity, magnetic anisotropy and magnetic susceptibilities argues for a low-spin, (dxy)2(dyz,dxz)3, ground state in both azide and cyanide complexes. The switch from singly-occupied dyz for the cyanide to dxz for the azide complex of hHO is shown to be consistent with the orbital hole determined by the azide π-plane in the latter complex, which is ∼90° in-plane rotated from that of the imidazole π-plane. The induction of the altered orbital ground state in the azide relative to the cyanide hHO complex, as well as the mean low-field bias of methyl hyperfine shifts and their paramagnetic relaxivity relative to those in globins, indicate that azide exerts a stronger ligand field in hHO than in the globins, or that the distal H-bonding to azide is weaker in hHO than in globins. The Asp140 → Ala hHO mutant that abolishes activity retains the unusual WT azide complex spin/orbital ground state. The relevance of our findings for other HO complexes and the HO mechanism is discussed. PMID:19243105

Atrial septal pacing in small dogs: a pilot study.

PubMed

Jones, Ashley E; Estrada, Amara H; Pariaut, Romain; Sosa-Samper, Ivan; Shih, Andre C; Mincey, Brandy D; Moïse, N Sydney

2014-09-01

To determine the feasibility of atrial septal pacing via a delivery catheter-guided small non-retracting helix pacing lead. Six healthy beagles (8.3-12.9 kg). Using single plane fluoroscopic guidance, Medtronic(®) 3830 SelectSecure leads were connected to the atrial septum via Medtronic® Attain Select® II standard 90 Left Heart delivery catheter. Pacing threshold and lead impedance were measured at implantation. The Wenckebach point was tested via atrial pacing up to 220 paced pulses per minute (ppm). Thoracic radiographs were performed following implantation to identify the lead position, and repeated at 24 h, 1 month, and 3 months post-operatively. Macro-lead dislodgement occurred in two dogs at 24 h and in three dogs at one-month post-implantation. Lead impedance, measured at the time of implantation, ranged from 583 to 1421 Ω. The Wenckebach point was >220 ppm in four of the six dogs. The remaining two dogs had Wenckebach points of 120 and 190 ppm. This pilot study suggests the selected implantation technique and lead system were inadequate for secure placement in the atrial septum of these dogs. The possible reasons for inadequate stability include unsuitable lead design for this location, inadequate lead slack at the time of implantation and inadequate seating of the lead as evidenced by low impedance at the time of implantation. Other implantation techniques and/or pacing leads should be investigated to determine the optimal way of pacing the atria in small breed dogs that are prone to sinus node dysfunction. Copyright © 2014 Elsevier B.V. All rights reserved.

Spacecraft Orbit Design in the Circular Restricted Three-Body Problem Using Higher-Dimensional Poincare Maps

DTIC Science & Technology

2013-12-01

the plane of the primary bodies. That is, motion is possible only in the x and y directions. For example, in the ...Earth-Moon planar CR3BP, the S/C path remains in the same plane as the Moon’s orbit about the Earth—more precisely, the orbit of both the Earth and...travels out of the plane of the massive primaries, in the z direction as well. Importantly, there is added complexity in the spatial

2008 Program of Study: Perspectives and Challenges in GFD (Geophysical Fluid Dynamics)

DTIC Science & Technology

2009-03-01

half of the complex k- plane , and Φ− is similarly well defined in the lower half of 338 PSfrag replacements Im k Re k−i +i Figure 2: Branch cuts in...domains ⊕ and , which include, respectively, the upper and lower half k- planes . The full Fourier transform of φ (and of h, d, etc.) is then well defined in...contour at infinity in the lower half k- plane ; the solution will only contain waves arising from poles located in the

Polarization Utilization in Radar Target Reconstruction: C-Wide (Multi-Frequency) Band Relationship of a Target’s Characteristic Operators with Its Unique Set of Natural Eigenfrequencies.

DTIC Science & Technology

1983-12-14

the left half of the s- plane . These are representation independent. We shall be interested in these poles only. These poles are the complex...on the Left Half Plane Asymptotic Behavior of the SEM Expansion of Surface Currents, Published in Special Issue on the Singularity Expansion Method...precisely, the polarization chart is an orthogonal projection of the Poincare Sphere on a plane , having polar coordinates p= cos (2-) and

Plasmonic diabolo cavity enhanced spin pumping

NASA Astrophysics Data System (ADS)

Qian, Jie; Gou, Peng; Gui, Y. S.; Hu, C. M.; An, Zhenghua

2017-09-01

Low spin-current generation efficiency has impeded further progress in practical spin devices, especially in the form of wireless excitation. To tackle this problem, a unique Plasmonic Diabolo Cavity (PDC) is proposed to enhance the spin pumping (SP) signal. The SP microwave photovoltage is enhanced ˜22-fold by PDC at ferromagnetic resonance (FMR). This improvement owes to the localization of the microwave magnetic field, which drives the spin precession process to more effectively generate photovoltage at the FMR condition. The in-plane anisotropy of spin pumping is found to be suppressed by PDC. Our work suggests that metamaterial resonant structures exhibit rich interactions with spin dynamics and could potentially be applied in future high-frequency spintronics.

WAVE DELAYING STRUCTURE FOR RECTANGULAR WAVE-GUIDES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robertson-Shersby-Harvie, R.B.; Dain, J.

1956-11-13

This patent relates to wave-guides and in particular describes wave delaying structure located within a wave-guide. The disclosed wave-guide has an elongated fiat metal sheet arranged in a central plane of the guide and formed with a series of transverse inductive slots such that each face presents an inductive impedance to the guide. The sheet is thickened in the area between slots to increase the self capacity of the slots. Experimental results indicate that in a wave-guide loaded in accordance with the invention the guided wavelength changes more slowly as the air wavelength is changed than the guided wavelength doesmore » in wave-guides loaded by means of corrugations.« less

Projecting non-diffracting waves with intermediate-plane holography.

PubMed

Mondal, Argha; Yevick, Aaron; Blackburn, Lauren C; Kanellakopoulos, Nikitas; Grier, David G

2018-02-19

We introduce intermediate-plane holography, which substantially improves the ability of holographic trapping systems to project propagation-invariant modes of light using phase-only diffractive optical elements. Translating the mode-forming hologram to an intermediate plane in the optical train can reduce the need to encode amplitude variations in the field, and therefore complements well-established techniques for encoding complex-valued transfer functions into phase-only holograms. Compared to standard holographic trapping implementations, intermediate-plane holograms greatly improve diffraction efficiency and mode purity of propagation-invariant modes, and so increase their useful non-diffracting range. We demonstrate this technique through experimental realizations of accelerating modes and long-range tractor beams.

Acoustic Impedance Inversion of Seismic Data Using Genetic Algorithm

NASA Astrophysics Data System (ADS)

Eladj, Said; Djarfour, Noureddine; Ferahtia, Djalal; Ouadfeul, Sid-Ali

2013-04-01

The inversion of seismic data can be used to constrain estimates of the Earth's acoustic impedance structure. This kind of problem is usually known to be non-linear, high-dimensional, with a complex search space which may be riddled with many local minima, and results in irregular objective functions. We investigate here the performance and the application of a genetic algorithm, in the inversion of seismic data. The proposed algorithm has the advantage of being easily implemented without getting stuck in local minima. The effects of population size, Elitism strategy, uniform cross-over and lower mutation are examined. The optimum solution parameters and performance were decided as a function of the testing error convergence with respect to the generation number. To calculate the fitness function, we used L2 norm of the sample-to-sample difference between the reference and the inverted trace. The cross-over probability is of 0.9-0.95 and mutation has been tested at 0.01 probability. The application of such a genetic algorithm to synthetic data shows that the inverted acoustic impedance section was efficient. Keywords: Seismic, Inversion, acoustic impedance, genetic algorithm, fitness functions, cross-over, mutation.

Self-healing bolted joint employing a shape memory actuator

NASA Astrophysics Data System (ADS)

Muntges, Daniel E.; Park, Gyuhae; Inman, Daniel J.

2001-08-01

This paper is a report of an initial investigation into the active control of preload in the joint using a shape memory actuator around the axis of the bolt shaft. Specifically, the actuator is a cylindrical Nitinol washer that expands axially when heated, according to the shape memory effect. The washer is actuated in response to an artificial decrease in torque. Upon actuation, the stress generated by its axial strain compresses the bolted members and creates a frictional force that has the effect of generating a preload and restoring lost torque. In addition to torque wrenches, the system in question was monitored in all stages of testing using piezoelectric impedance analysis. Impedance analysis drew upon research techniques developed at Center for Intelligent Material Systems and Structures, in which phase changes in the impedance of a self-sensing piezoceramic actuator correspond to changes in joint stiffness. Through experimentation, we have documented a successful actuation of the shape memory element. Due to complexity of constitutive modeling, qualitative analysis by the impedance method is used to illustrate the success. Additional considerations encountered in this initial investigation are made to guide further thorough research required for the successful commercial application of this promising technique.

Phase-field simulations of GaN growth by selective area epitaxy on complex mask geometries

DOE PAGES

Aagesen, Larry K.; Coltrin, Michael Elliott; Han, Jung; ...

2015-05-15

Three-dimensional phase-field simulations of GaN growth by selective area epitaxy were performed. Furthermore, this model includes a crystallographic-orientation-dependent deposition rate and arbitrarily complex mask geometries. The orientation-dependent deposition rate can be determined from experimental measurements of the relative growth rates of low-index crystallographic facets. Growth on various complex mask geometries was simulated on both c-plane and a-plane template layers. Agreement was observed between simulations and experiment, including complex phenomena occurring at the intersections between facets. The sources of the discrepancies between simulated and experimental morphologies were also investigated. We found that the model provides a route to optimize masks andmore » processing conditions during materials synthesis for solar cells, light-emitting diodes, and other electronic and opto-electronic applications.« less

Complexity-entropy causality plane: A useful approach for distinguishing songs

NASA Astrophysics Data System (ADS)

Ribeiro, Haroldo V.; Zunino, Luciano; Mendes, Renio S.; Lenzi, Ervin K.

2012-04-01

Nowadays we are often faced with huge databases resulting from the rapid growth of data storage technologies. This is particularly true when dealing with music databases. In this context, it is essential to have techniques and tools able to discriminate properties from these massive sets. In this work, we report on a statistical analysis of more than ten thousand songs aiming to obtain a complexity hierarchy. Our approach is based on the estimation of the permutation entropy combined with an intensive complexity measure, building up the complexity-entropy causality plane. The results obtained indicate that this representation space is very promising to discriminate songs as well as to allow a relative quantitative comparison among songs. Additionally, we believe that the here-reported method may be applied in practical situations since it is simple, robust and has a fast numerical implementation.

Deformable registration of CT and cone-beam CT with local intensity matching.

PubMed

Park, Seyoun; Plishker, William; Quon, Harry; Wong, John; Shekhar, Raj; Lee, Junghoon

2017-02-07

Cone-beam CT (CBCT) is a widely used intra-operative imaging modality in image-guided radiotherapy and surgery. A short scan followed by a filtered-backprojection is typically used for CBCT reconstruction. While data on the mid-plane (plane of source-detector rotation) is complete, off-mid-planes undergo different information deficiency and the computed reconstructions are approximate. This causes different reconstruction artifacts at off-mid-planes depending on slice locations, and therefore impedes accurate registration between CT and CBCT. In this paper, we propose a method to accurately register CT and CBCT by iteratively matching local CT and CBCT intensities. We correct CBCT intensities by matching local intensity histograms slice by slice in conjunction with intensity-based deformable registration. The correction-registration steps are repeated in an alternating way until the result image converges. We integrate the intensity matching into three different deformable registration methods, B-spline, demons, and optical flow that are widely used for CT-CBCT registration. All three registration methods were implemented on a graphics processing unit for efficient parallel computation. We tested the proposed methods on twenty five head and neck cancer cases and compared the performance with state-of-the-art registration methods. Normalized cross correlation (NCC), structural similarity index (SSIM), and target registration error (TRE) were computed to evaluate the registration performance. Our method produced overall NCC of 0.96, SSIM of 0.94, and TRE of 2.26 → 2.27 mm, outperforming existing methods by 9%, 12%, and 27%, respectively. Experimental results also show that our method performs consistently and is more accurate than existing algorithms, and also computationally efficient.

Deformable registration of CT and cone-beam CT with local intensity matching

NASA Astrophysics Data System (ADS)

Park, Seyoun; Plishker, William; Quon, Harry; Wong, John; Shekhar, Raj; Lee, Junghoon

2017-02-01

Cone-beam CT (CBCT) is a widely used intra-operative imaging modality in image-guided radiotherapy and surgery. A short scan followed by a filtered-backprojection is typically used for CBCT reconstruction. While data on the mid-plane (plane of source-detector rotation) is complete, off-mid-planes undergo different information deficiency and the computed reconstructions are approximate. This causes different reconstruction artifacts at off-mid-planes depending on slice locations, and therefore impedes accurate registration between CT and CBCT. In this paper, we propose a method to accurately register CT and CBCT by iteratively matching local CT and CBCT intensities. We correct CBCT intensities by matching local intensity histograms slice by slice in conjunction with intensity-based deformable registration. The correction-registration steps are repeated in an alternating way until the result image converges. We integrate the intensity matching into three different deformable registration methods, B-spline, demons, and optical flow that are widely used for CT-CBCT registration. All three registration methods were implemented on a graphics processing unit for efficient parallel computation. We tested the proposed methods on twenty five head and neck cancer cases and compared the performance with state-of-the-art registration methods. Normalized cross correlation (NCC), structural similarity index (SSIM), and target registration error (TRE) were computed to evaluate the registration performance. Our method produced overall NCC of 0.96, SSIM of 0.94, and TRE of 2.26 → 2.27 mm, outperforming existing methods by 9%, 12%, and 27%, respectively. Experimental results also show that our method performs consistently and is more accurate than existing algorithms, and also computationally efficient.

Complex plane integration in the modelling of electromagnetic fields in layered media: part 1. Application to a very large loop

NASA Astrophysics Data System (ADS)

Silva, Valdelírio da Silva e.; Régis, Cícero; Howard, Allen Q., Jr.

2014-02-01

This paper analyses the details of a procedure for the numerical integration of Hankel transforms in the calculation of the electromagnetic fields generated by a large horizontal loop over a 1D earth. The method performs the integration by deforming the integration path into the complex plane and applying Cauchy's theorem on a modified version of the integrand. The modification is the replacement of the Bessel functions J0 and J1 by the Hankel functions H_0^{(1)} and H_1^{(1)} respectively. The integration in the complex plane takes advantage of the exponentially decaying behaviour of the Hankel functions, allowing calculation on very small segments, instead of the infinite line of the original improper integrals. A crucial point in this problem is the location of the poles. The companion paper shows two methods to estimate the pole locations. We have used this method to calculate the fields of very large loops. Our results show that this method allows the estimation of the integrals with fewer evaluations of the integrand functions than other methods.

Conduction mechanism, impedance spectroscopic investigation and dielectric behavior of La0.5Ca0.5-xAgxMnO3 manganites with compositions below the concentration limit of silver solubility in perovskites (0 ≤ x ≤ 0.2).

PubMed

Rahmouni, H; Smari, M; Cherif, B; Dhahri, E; Khirouni, K

2015-06-14

This study presents the electrical properties, complex impedance analysis and dielectrical behavior of La0.5Ca0.5-xAgxMnO3 manganites with compositions below the concentration limit of silver solubility in perovskites (0 ≤ x ≤ 0.2). Transport measurements indicate that all the samples have a semiconductor-like behavior. The metal-semiconductor transition is not observed across the whole temperature range explored [80 K-700 K]. At a specific temperature, a saturation region was marked in the σ (T) curves. We obtained a maximum σdc value at ambient temperature with the introduction of 20% Ag content. Two hopping models were applied to study the conduction mechanism. We found that activation energy (Ea) related to ac-conductivity is lower than the Ea implicated in dc-conductivity. Complex impedance analysis confirms the contribution of grain boundary to conductivity and permits the attribution of grain boundary capacitance evolution to the temperature dependence of the barrier layer width. From the temperature dependence of the average normalized change (ANC), we deduce the temperature at which the available density of trapped charge states vanishes. Such a temperature is close to the temperature at which the saturation region appears in σ(T) curves. Moreover, complex impedance analysis (CIA) indicates the presence of electrical relaxation in materials. It is noteworthy that relaxation species such as defects may be responsible for electrical conduction. The dielectric behavior of La0.5Ca0.5-xAgxMnO3 manganites has a Debye-like relaxation with a sharp decrease in the real part of permittivity at a frequency where the imaginary part of permittivity (ε'') and tg δ plots versus frequency demonstrate a relaxation peak. The Debye-like relaxation is explained by Maxwell-Wagner (MW) polarization. Experimental results are found to be in good agreement with the Smit and Wijn theory.

Grain Boundary Plane Orientation Fundamental Zones and Structure-Property Relationships

PubMed Central

Homer, Eric R.; Patala, Srikanth; Priedeman, Jonathan L.

2015-01-01

Grain boundary plane orientation is a profoundly important determinant of character in polycrystalline materials that is not well understood. This work demonstrates how boundary plane orientation fundamental zones, which capture the natural crystallographic symmetries of a grain boundary, can be used to establish structure-property relationships. Using the fundamental zone representation, trends in computed energy, excess volume at the grain boundary, and temperature-dependent mobility naturally emerge and show a strong dependence on the boundary plane orientation. Analysis of common misorientation axes even suggests broader trends of grain boundary energy as a function of misorientation angle and plane orientation. Due to the strong structure-property relationships that naturally emerge from this work, boundary plane fundamental zones are expected to simplify analysis of both computational and experimental data. This standardized representation has the potential to significantly accelerate research in the topologically complex and vast five-dimensional phase space of grain boundaries. PMID:26498715

Grain boundary plane orientation fundamental zones and structure-property relationships

DOE Office of Scientific and Technical Information (OSTI.GOV)

Homer, Eric R.; Patala, Srikanth; Priedeman, Jonathan L.

2015-10-26

Grain boundary plane orientation is a profoundly important determinant of character in polycrystalline materials that is not well understood. This work demonstrates how boundary plane orientation fundamental zones, which capture the natural crystallographic symmetries of a grain boundary, can be used to establish structure-property relationships. Using the fundamental zone representation, trends in computed energy, excess volume at the grain boundary, and temperature-dependent mobility naturally emerge and show a strong dependence on the boundary plane orientation. Analysis of common misorientation axes even suggests broader trends of grain boundary energy as a function of misorientation angle and plane orientation. Due to themore » strong structure-property relationships that naturally emerge from this work, boundary plane fundamental zones are expected to simplify analysis of both computational and experimental data. This standardized representation has the potential to significantly accelerate research in the topologically complex and vast five-dimensional phase space of grain boundaries.« less

Innovative compact focal plane array for wide field vis and ir orbiting telescopes

NASA Astrophysics Data System (ADS)

Hugot, Emmanuel; Vives, Sébastien; Ferrari, Marc; Gaeremynck, Yann; Jahn, Wilfried

2017-11-01

The future generation of high angular resolution space telescopes will require breakthrough technologies to combine large diameters and large focal plane arrays with compactness and lightweight mirrors and structures. Considering the allocated volume medium-size launchers, short focal lengths are mandatory, implying complex optical relays to obtain diffraction limited images on large focal planes. In this paper we present preliminary studies to obtain compact focal plane arrays (FPA) for earth observations on low earth orbits at high angular resolution. Based on the principle of image slicers, we present an optical concept to arrange a 1D FPA into a 2D FPA, allowing the use of 2D detector matrices. This solution is particularly attractive for IR imaging requiring a cryostat, which volume could be considerably reduced as well as the relay optics complexity. Enabling the use of 2D matrices for such an application offers new possibilities. Recent developments on curved FPA allows optimization without concerns on the field curvature. This innovative approach also reduces the complexity of the telescope optical combination, specifically for fast telescopes. This paper will describe the concept and optical design of an F/5 - 1.5m telescope equipped with such a FPA, the performances and the impact on the system with a comparison with an equivalent 1.5m wide field Korsch telescope.

Design of a dual-band radiation system for a complex magnetically insulated line oscillator

NASA Astrophysics Data System (ADS)

Yu, Yuanqiang; Wang, Xiaoyu; Fan, Yuwei; Li, Ankun; Li, Sirui

2018-05-01

In this paper, a dual-band radiation system for a complex magnetically insulated line oscillator (MILO) is designed and investigated numerically. The radiation system comprises a coaxial plate-inserted mode converter, a power combiner and a conical horn antenna. The mode converter converts the coaxial TEM mode microwaves (1.775 GHz and 3.175 GHz) which are generated by the complex MILO into the coaxial TE11 mode microwaves, and then the coaxial TE11 mode microwaves are combined by the power combiner in a circular waveguide. Lastly, the microwaves are radiated by a conical horn antenna into the air. The gains of the dual-band radiation system are calculated to be 17.8 dB at 1.775 GHz and 18.9 dB at 3.175 GHz. The 3 dB beam widths are 20.5° in E-plane, 26.4° in H-plane at 1.775 GHz and 20.8° in E-plane, 15.1° in H-plane at 3.175 GHz. The power transmission efficiencies of the dual-band radiation system are 98.5% at 1.775 GHz and 95.7% at 3.175 GHz respectively. The power handling capacities of the dual-band radiation system are 4.2 GW at 1.775 GHz and 4.7 GW at 3.175 GHz, respectively.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aagesen, Larry K.; Coltrin, Michael Elliott; Han, Jung

Three-dimensional phase-field simulations of GaN growth by selective area epitaxy were performed. Furthermore, this model includes a crystallographic-orientation-dependent deposition rate and arbitrarily complex mask geometries. The orientation-dependent deposition rate can be determined from experimental measurements of the relative growth rates of low-index crystallographic facets. Growth on various complex mask geometries was simulated on both c-plane and a-plane template layers. Agreement was observed between simulations and experiment, including complex phenomena occurring at the intersections between facets. The sources of the discrepancies between simulated and experimental morphologies were also investigated. We found that the model provides a route to optimize masks andmore » processing conditions during materials synthesis for solar cells, light-emitting diodes, and other electronic and opto-electronic applications.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aagesen, Larry K.; Thornton, Katsuyo, E-mail: kthorn@umich.edu; Coltrin, Michael E.

Three-dimensional phase-field simulations of GaN growth by selective area epitaxy were performed. The model includes a crystallographic-orientation-dependent deposition rate and arbitrarily complex mask geometries. The orientation-dependent deposition rate can be determined from experimental measurements of the relative growth rates of low-index crystallographic facets. Growth on various complex mask geometries was simulated on both c-plane and a-plane template layers. Agreement was observed between simulations and experiment, including complex phenomena occurring at the intersections between facets. The sources of the discrepancies between simulated and experimental morphologies were also investigated. The model provides a route to optimize masks and processing conditions during materialsmore » synthesis for solar cells, light-emitting diodes, and other electronic and opto-electronic applications.« less

Modeling State-Space Aeroelastic Systems Using a Simple Matrix Polynomial Approach for the Unsteady Aerodynamics

NASA Technical Reports Server (NTRS)

Pototzky, Anthony S.

2008-01-01

A simple matrix polynomial approach is introduced for approximating unsteady aerodynamics in the s-plane and ultimately, after combining matrix polynomial coefficients with matrices defining the structure, a matrix polynomial of the flutter equations of motion (EOM) is formed. A technique of recasting the matrix-polynomial form of the flutter EOM into a first order form is also presented that can be used to determine the eigenvalues near the origin and everywhere on the complex plane. An aeroservoelastic (ASE) EOM have been generalized to include the gust terms on the right-hand side. The reasons for developing the new matrix polynomial approach are also presented, which are the following: first, the "workhorse" methods such as the NASTRAN flutter analysis lack the capability to consistently find roots near the origin, along the real axis or accurately find roots farther away from the imaginary axis of the complex plane; and, second, the existing s-plane methods, such as the Roger s s-plane approximation method as implemented in ISAC, do not always give suitable fits of some tabular data of the unsteady aerodynamics. A method available in MATLAB is introduced that will accurately fit generalized aerodynamic force (GAF) coefficients in a tabular data form into the coefficients of a matrix polynomial form. The root-locus results from the NASTRAN pknl flutter analysis, the ISAC-Roger's s-plane method and the present matrix polynomial method are presented and compared for accuracy and for the number and locations of roots.

Altered astronaut lower limb and mass center kinematics in downward jumping following space flight

NASA Technical Reports Server (NTRS)

Newman, D. J.; Jackson, D. K.; Bloomberg, J. J.

1997-01-01

Astronauts exposed to the microgravity conditions encountered during space flight exhibit postural and gait instabilities upon return to earth that could impair critical postflight performance. The aim of the present study was to determine the effects of microgravity exposure on astronauts' performance of two-footed jump landings. Nine astronauts from several Space Shuttle missions were tested both preflight and postflight with a series of voluntary, two-footed downward hops from a 30-cm-high step. A video-based, three-dimensional motion-analysis system permitted calculation of body segment positions and joint angular displacements. Phase-plane plots of knee, hip, and ankle angular velocities compared with the corresponding joint angles were used to describe the lower limb kinematics during jump landings. The position of the whole-body center of mass (COM) was also estimated in the sagittal plane using an eight-segment body model. Four of nine subjects exhibited expanded phase-plane portraits postflight, with significant increases in peak joint flexion angles and flexion rates following space flight. In contrast, two subjects showed significant contractions of their phase-plane portraits postflight and three subjects showed insignificant overall changes after space flight. Analysis of the vertical COM motion generally supported the joint angle results. Subjects with expanded joint angle phase-plane portraits postflight exhibited larger downward deviations of the COM and longer times from impact to peak deflection, as well as lower upward recovery velocities. Subjects with postflight joint angle phase-plane contraction demonstrated opposite effects in the COM motion. The joint kinematics results indicated the existence of two contrasting response modes due to microgravity exposure. Most subjects exhibited "compliant" impact absorption postflight, consistent with decreased limb stiffness and damping, and a reduction in the bandwidth of the postural control system. Fewer subjects showed "stiff" behavior after space flight, where contractions in the phase-plane portraits pointed to an increase in control bandwidth. The changes appeared to result from adaptive modifications in the control of lower limb impedance. A simple 2nd-order model of the vertical COM motion indicated that changes in the effective vertical stiffness of the legs can predict key features of the postflight performance. Compliant responses may reflect inflight adaptation due to altered demands on the postural control system in microgravity, while stiff behavior may result from overcompensation postflight for the presumed reduction in limb stiffness inflight.

A six-coordinate ytterbium complex exhibiting easy-plane anisotropy and field-induced single-ion magnet behavior.

PubMed

Liu, Jun-Liang; Yuan, Kang; Leng, Ji-Dong; Ungur, Liviu; Wernsdorfer, Wolfgang; Guo, Fu-Sheng; Chibotaru, Liviu F; Tong, Ming-Liang

2012-08-06

The field-induced blockage of magnetization behavior was first observed in an Yb(III)-based molecule with a trigonally distorted octahedral coordination environment. Ab initio calculations and micro-SQUID measurements were performed to demonstrate the exhibition of easy-plane anisotropy, suggesting the investigated complex is the first pure lanthanide field-induced single-ion magnet (field-induced SIM) of this type. Furthermore, we found the relaxation time obeys a power law instead of an exponential law, indicating that the relaxation process should be involved a direct process rather than an Orbach process.

Two bladders and two vaginas in two planes: one urogenital sinus.

PubMed

Shaw, Matthew B K; Cain, Mark P; Rink, Richard C

2003-07-01

We report 2 cases of persistent urogenital sinus (UGS) with duplication of the bladder and vagina in different planes. Cystoscopy and vaginoscopy were used to diagnose persistent UGS with bladder and vaginal duplication in 2 infants with recurrent urinary tract infection. Surgical repair was done by way of a midline abdominal and perineal approach using tubularized UGS to reconstruct the urethra. Persistent UGS represents a major anomaly; these patients had the added complexity of duplication of the bladder and vagina. In these complex patients, the true anatomy may only become apparent during the surgical reconstruction, necessitating a flexible, individual approach.

Padé approximations for Painlevé I and II transcendents

NASA Astrophysics Data System (ADS)

Novokshenov, V. Yu.

2009-06-01

We use a version of the Fair-Luke algorithm to find the Padé approximate solutions of the Painlevé I and II equations. We find the distributions of poles for the well-known Ablowitz-Segur and Hastings-McLeod solutions of the Painlevé II equation. We show that the Boutroux tritronquée solution of the Painleé I equation has poles only in the critical sector of the complex plane. The algorithm allows checking other analytic properties of the Painlevé transcendents, such as the asymptotic behavior at infinity in the complex plane.

Simulation of the microwave heating of a thin multilayered composite material: A parameter analysis

NASA Astrophysics Data System (ADS)

Tertrais, Hermine; Barasinski, Anaïs; Chinesta, Francisco

2018-05-01

Microwave (MW) technology relies on volumetric heating. Thermal energy is transferred to the material that can absorb it at specific frequencies. The complex physics involved in this process is far from being understood and that is why a simulation tool has been developed in order to solve the electromagnetic and thermal equations in such a complex material as a multilayered composite part. The code is based on the in-plane-out-of-plane separated representation within the Proper Generalized Decomposition framework. To improve the knowledge on the process, a parameter study in carried out in this paper.

METHOD AND MEANS FOR RECOGNIZING COMPLEX PATTERNS

DOEpatents

Hough, P.V.C.

1962-12-18

This patent relates to a method and means for recognizing a complex pattern in a picture. The picture is divided into framelets, each framelet being sized so that any segment of the complex pattern therewithin is essentially a straight line. Each framelet is scanned to produce an electrical pulse for each point scanned on the segment therewithin. Each of the electrical pulses of each segment is then transformed into a separate strnight line to form a plane transform in a pictorial display. Each line in the plane transform of a segment is positioned laterally so that a point on the line midway between the top and the bottom of the pictorial display occurs at a distance from the left edge of the pictorial display equal to the distance of the generating point in the segment from the left edge of the framelet. Each line in the plane transform of a segment is inclined in the pictorial display at an angle to the vertical whose tangent is proportional to the vertical displacement of the generating point in the segment from the center of the framelet. The coordinate position of the point of intersection of the lines in the pictorial display for each segment is determined and recorded. The sum total of said recorded coordinate positions being representative of the complex pattern. (AEC)

2-D magnetotelluric experiment to investigate the Nassugtoqidian orogeny in South-East Greenland

NASA Astrophysics Data System (ADS)

Heincke, Björn; Chen, Jin; Riisager, Peter; Kolb, Jochen; Jørgensen, Asta F.

2015-04-01

The northwest-trending Palaeoproterozoic Nagssugtoqidian orogen extends over 250 km along the east coast of Greenland in the area around the village Tasiilaq. The geological evolution of this area closely compares with the ones of the Lewisian complex of Scotland and the Nagssugtoqidian orogen in western Greenland and, hence, leads to the suggestion that they belong to the same continental-scale orogenic belt. However, an accurate correlation across the inland ice is challenging and still ambiguous and therefore more detailed knowledge about the individual orogens might help to understand their relationship. Details about the large-scale tectonic evolution during the Nagssugtoqidian orogeny in this remote Arctic region are not known due to complex geology, relatively coarse geological mapping and the lack of extensive geophysical investigations. E.g. the vergence of the orogen, subduction-related magmatism and accretion history are matters of ongoing discussion (Kalsbeek et al., 1993; Nutman et al., 2008 and Kolb, 2013). We performed a 2-D magnetotelluric (MT) experiment across the southern part of the orogen along the Sermilik Fjord in order to improve our understanding of the orogenic process in general and to better constrain the location and vergence of the suture zone. However, because of the rough climate and the lack of infrastructure, this study is considered as a first test to investigate how MT surveys can be most efficiently performed in this remote part of the world. The NE-SW trending profile consists of eight MT stations and has a total length of ~70 km using long period LEMI-420 systems. The quality of the data is severely affected by polar electrojets that do not satisfy the plane wave assumptions, which is typical for regions close to the magnetic poles. In order to reduce the distortion from these signals onto the impedance estimates, we tested different advanced processing schemes. In addition to the more conventional robust response function estimator BIRRP from Chave and Thomson (2004), we applied a recent technique that is based on empirical mode decomposition EMD proposed by Chen et al. (2012). This method works rather in the time than in the frequency domain and appears promising to reduce the impact of such time limited noise signals typically associated with electrojets. As first results, we present obtained impedance estimates, induction vectors and dimensionality analysis. Experience from this first feasibility study will be to develop strategies for larger MT surveys for the challenging conditions in Greenland.

Novel Micro Strip-to-Waveguide Feed Employing a Double-Y Junction

NASA Technical Reports Server (NTRS)

Venkatesan, Jaikrishina

2010-01-01

Previous micro strip -to -waveguide transitions either required a hermetically sealed waveguide configuration, or a balun that needed to be tuned according to the frequency band of interest. In this design, the balun is realized using a double -Y junction to transition from microstrip to coplanar strip feeding a quasi-Yagi dipole array (see figure). The length of the feed (Lf) extending into the waveguide is 15.54 mm. The length of the ground plane below the ULTRALAM substrate is 7.75 mm. The lengths L1 , L2, and L3 are 8.50 mm, 4.38 mm, and 2.14 mm, respectively. These lengths were computed via a preliminary optimization aimed at improving the return loss at the band edges. The waveguide feed was designed to excite the TE10 mode in a WR-90 waveguide, and to operate over the recommended frequencies of 8.2 to 12.4 GHz. The feed employs a Rogers 6010 substrate (dielectric constant Er approx. equals 10.2) bonded with a Rogers ULTRALAM substrate (Er approx. equals 2.5). The ULTRALAM substrate serves to provide mechanical strength for 6010 substrate, and to mitigate loses due to parasitic modes (the ground plane is etched on the bottom of this layer due to the topology of the double -Y balun). The double-Y balun transitioning from an unbalanced microstrip line to a balanced coplanar strip (CPS) line does not provide inherent impedance transformation; hence, Klopfenstein impedance tapers were synthesized to transition from 50 to 77 Ohms in the microstrip section and from 77 to 110 Ohms in the CPS section. At the balun junction, the CPS stub lengths were chosen such that the X/ 8 resonance is pushed outside the bandwidth of operation. Also, the smallest allowable conductor width and gap spacing were chosen to meet acceptable manufacturing tolerances.

Design and characterization of thick InxGa1-xAs metamorphic buffer layers grown by hydride vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Schulte, K. L.; Zutter, B. T.; Wood, A. W.; Babcock, S. E.; Kuech, T. F.

2014-03-01

Thick InxGa1-xAs metamorphic buffer layers (MBLs) grown by hydride vapor phase epitaxy (HVPE) were studied. Relationships between MBL properties and growth parameters such as grading rate, cap layer thickness, final xInAs, and deposition temperature (TD) were explored. The MBLs were characterized by measurement of in-plane residual strain (ɛ¦¦), surface etch pit density (EPD), and surface roughness. Capping layer thickness had a strong effect on strain relaxation, with thickly capped samples exhibiting the lowest ɛ¦¦. EPD was higher in samples with thicker caps, reflecting their increased relaxation through dislocation generation. ɛ¦¦ and EPD were weakly affected by the grading rate, making capping layer thickness the primary structural parameter which controls these properties. MBLs graded in discrete steps had similar properties to MBLs with continuous grading. In samples with identical thickness and 10-step grading style, ɛ¦¦ increased almost linearly with final xInAs, while total relaxation stayed relatively constant. Relaxation as a function of xInAs could be described by an equilibrium model in which dislocation nucleation is impeded by the energy of the existing dislocation array. EPD was constant from xInAs = 0 to 0.24 then increased exponentially, which is related to the increased dislocation interaction and blocking seen at higher dislocation densities. RMS roughness increased with xInAs above a certain strain rate (0.15%/µm) samples grown below this level possessed large surface hillocks and high roughness values. The elimination of hillocks at higher values of xInAs is attributed to increased density of surface steps and is related to the out-of-plane component of the burgers vector of the dominant type of 60° dislocation. TD did not affect ɛ¦¦ for samples with a given xInAs. EPD tended to increase with TD, indicating dislocation glide likely is impeded at higher temperatures.

Detection and Tracking of Moving Targets Behind Cluttered Environments Using Compressive Sensing

NASA Astrophysics Data System (ADS)

Dang, Vinh Quang

Detection and tracking of moving targets (target's motion, vibration, etc.) in cluttered environments have been receiving much attention in numerous applications, such as disaster search-and-rescue, law enforcement, urban warfare, etc. One of the popular techniques is the use of stepped frequency continuous wave radar due to its low cost and complexity. However, the stepped frequency radar suffers from long data acquisition time. This dissertation focuses on detection and tracking of moving targets and vibration rates of stationary targets behind cluttered medium such as wall using stepped frequency radar enhanced by compressive sensing. The application of compressive sensing enables the reconstruction of the target space using fewer random frequencies, which decreases the acquisition time. Hardware-accelerated parallelization on GPU is investigated for the Orthogonal Matching Pursuit reconstruction algorithm. For simulation purpose, two hybrid methods have been developed to calculate the scattered fields from the targets through the wall approaching the antenna system, and to convert the incoming fields into voltage signals at terminals of the receive antenna. The first method is developed based on the plane wave spectrum approach for calculating the scattered fields of targets behind the wall. The method uses Fast Multiple Method (FMM) to calculate scattered fields on a particular source plane, decomposes them into plane wave components, and propagates the plane wave spectrum through the wall by integrating wall transmission coefficients before constructing the fields on a desired observation plane. The second method allows one to calculate the complex output voltage at terminals of a receiving antenna which fully takes into account the antenna effects. This method adopts the concept of complex antenna factor in Electromagnetic Compatibility (EMC) community for its calculation.

Aqua­{6,6′-dimeth­oxy-2,2′-[ethane-1,2-diylbis(nitrilo­methyl­idyne)]diphenolato}nickel(II)

PubMed Central

Guo, Zhenghua; Li, Lianzhi; Xu, Tao; Li, Jinghong; Wang, Daqi

2009-01-01

The title complex, [Ni(C18H18N2O4)(H2O)], lies on a mirror plane with the NiII ion coordinated by two N and two O atoms of a tetra­dentate Schiff base ligand and one water O atom in a distorted square-pyramidal enviroment. The –CH2–CH2– group of the ligand is disordered equally over two sites about the mirror plane. The dihedral angle between the mean planes of the two symmetry-related chelate rings is 37.16 (6)°. In the crystal structure, inter­molecular O—H⋯O hydrogen bonds link complex mol­ecules into one-dimensional chains along [100] and these chains are linked, in turn, by very weak inter­molecular C—H⋯O hydrogen bonds into a two-dimensional network. PMID:21577698

Tempest in a glass tube: A helical vortex formation in a complex plasma

NASA Astrophysics Data System (ADS)

Saitou, Yoshifumi; Ishihara, Osamu; Ishihara

2014-12-01

A collective behavior of dust particles in a complex plasma with a magnetic field (up to 4 kG) is investigated. Dust particles form a dust disk which is rotating in a horizontal plane pushed by ions rotating with the E × B drift as a trigger force. The thickness of the disk is determined by controlling the experimental conditions. The disk rotates in a horizontal plane and forms a two-dimensional thin structure when the pressure pAr is relatively high. The dust particles are ejected from near the disk center and form a rotation in the vertical plane and, hence, forms a helical vortex when the disk is thick for relatively low pAr . The reason the dust disk has the different thickness is due to the neutral pressure. Under a higher (lower) neutral gas pressure, the disk becomes two (three) dimensional due to the influence of the neutral drag force.

RTEMIS: Real-time Tumoroid and Environment Monitoring Using Impedance Spectroscopy and pH Sensing

NASA Astrophysics Data System (ADS)

Alexander, Frank A., Jr.

This research utilizes Electrical Impedance Spectroscopy, a technique classically used for electrochemical analysis and material characterization, as the basis for a non-destructive, label-free assay platform for three dimensional (3D) cellular spheroids. In this work, a linear array of microelectrodes is optimized to rapidly respond to changes located within a 3D multicellular model. In addition, this technique is coupled with an on chip micro-pH sensor for monitoring the environment around the cells. Finally, the responses of both impedance and pH are correlated with physical changes within the cellular model. The impedance analysis system realized through this work provides a foundation for the development of high-throughput drug screening systems that utilize multiple parallel sensing modalities including pH and impedance sensing in order to quickly assess the efficacy of specific drug candidates. The slow development of new drugs is mainly attributed to poor predictability of current chemosensitivity and resistivity assays, as well as genetic differences between the animal models used for tests and humans. In addition, monolayer cultures used in early experimentation are fundamentally different from the complex structure of organs in vivo. This requires the study of smaller 3D models (spheroids) that more efficiently replicate the conditions within the body. The main objective of this research was to develop a microfluidic system on a chip that is capable of deducing viability and morphology of 3D tumor spheroids by monitoring both the impedance of the cellular model and the pH of their local environment. This would provide a fast and reliable method for screening pharmaceutical compounds in a high-throughput system.

Real-time ultrasound-guided spinal anesthesia using the SonixGPS ultrasound guidance system: a feasibility study.

PubMed

Niazi, A U; Chin, K J; Jin, R; Chan, V W

2014-08-01

Real-time ultrasound-guided neuraxial blockade remains a largely experimental technique. SonixGPS® is a new needle tracking system that displays needle tip position on the ultrasound screen. We investigated if this novel technology might aid performance of real-time ultrasound-guided spinal anesthesia. Twenty patients with body mass index < 35 kg/m(2) undergoing elective total joint arthroplasty under spinal anesthesia were recruited. Patients with previous back surgery and spinal abnormalities were excluded. Following a pre-procedural ultrasound scan, a 17G proprietary needle-sensor assembly was inserted in-plane to the transducer in four patients and out-of-plane in 16 patients. In both approaches, the trajectory of insertion was adjusted in real-time until the needle tip lay just superficial to the ligamentum flavum-dura mater complex. At this point, a 25G 120 mm Whitacre spinal needle was inserted through the 17G SonixGPS® needle. Successful dural puncture was confirmed by backflow of cerebrospinal fluid from the spinal needle. An overall success rate of 14/20 (70%) was seen with two failures (50%) and four failures (25%) in the in-plane and out-of-plane groups respectively. Dural puncture was successful on the first skin puncture in 71% of patients and in a single needle pass in 57% of patients. The median total procedure time was 16.4 and 11.1 min in the in-plane and out-of-plane groups respectively. The SonixGPS® system simplifies real-time ultrasound-guided spinal anesthesia to a large extent, especially the out-of-plane approach. Nevertheless, it remains a complex multi-step procedure that requires time, specialized equipment, and a working knowledge of spinal sonoanatomy. © 2014 The Acta Anaesthesiologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.

Making the Tent Function Complex

ERIC Educational Resources Information Center

Sprows, David J.

2010-01-01

This note can be used to illustrate to the student such concepts as periodicity in the complex plane. The basic construction makes use of the Tent function which requires only that the student have some working knowledge of binary arithmetic.

PGE(2) activation of apical membrane Cl(-) channels in A6 epithelia: impedance analysis.

PubMed Central

Păunescu, T G; Helman, S I

2001-01-01

Measurements of transepithelial electrical impedance of continuously short-circuited A6 epithelia were made at audio frequencies (0.244 Hz to 10.45 kHz) to investigate the time course and extent to which prostaglandin E(2) (PGE(2)) modulates Cl(-) transport and apical membrane capacitance in this cell-cultured model epithelium. Apical and basolateral membrane resistances were determined by nonlinear curve-fitting of the impedance vectors at relatively low frequencies (<50 Hz) to equations (Păunescu, T. G., and S. I. Helman. 2001. Biophys. J. 81:838--851) where depressed Nyquist impedance semicircles were characteristic of the membrane impedances under control Na(+)-transporting and amiloride-inhibited conditions. In all tissues (control, amiloride-blocked, and amiloride-blocked and furosemide-pretreated), PGE(2) caused relatively small (< approximately 3 microA/cm(2)) and rapid (<60 s) maximal increase of chloride current due to activation of a rather large increase of apical membrane conductance that preceded significant activation of Na(+) transport through amiloride-sensitive epithelial Na(+) channels (ENaCs). Apical membrane capacitance was frequency-dependent with a Cole-Cole dielectric dispersion whose relaxation frequency was near 150 Hz. Analysis of the time-dependent changes of the complex frequency-dependent equivalent capacitance of the cells at frequencies >1.5 kHz revealed that the mean 9.8% increase of capacitance caused by PGE(2) was not correlated in time with activation of chloride conductance, but rather correlated with activation of apical membrane Na(+) transport. PMID:11463630

Factors that Predict Quality Classroom Technology Use

ERIC Educational Resources Information Center

Hastings, Tricia A.

2009-01-01

Despite technological advancements intended to enhance teaching and learning in the 21st century, numerous teacher and school factors continue to impede quality classroom technology use. Determining the effectiveness of educational technology is challenging and requires a detailed understanding of multifaceted, complex, contextual relationships.…

A high resolution radiation hybrid map of wheat chromosome 4A

USDA-ARS?s Scientific Manuscript database

Bread wheat has a large and complex allohexaploid genome with low recombination level at chromosome centromeric and peri-centromeric regions. This significantly hampers ordering of markers, contigs of physical maps and sequence scaffolds and impedes obtaining of high-quality reference genome sequenc...

Influence of temperature on AC conductivity of nanocrystalline CuAlO2

NASA Astrophysics Data System (ADS)

Prakash, T.

2012-07-01

Nanocrystalline CuAlO2 was synthesized by mechanical alloying of Cu2O and α-Al2O3 powders in the molar ratio of 1:1 for 20 h in toluene medium with tungsten carbide balls and vials using planetary ball mill. The ball milling was carried out at 300 rpm with a ball to powder weight ratio of 10:1 and then annealed at 1373 K in a platinum crucible for 20 h to get CuAlO2 phase with average crystallite size 45 nm. Complex impedance spectroscopic measurement in the frequency region 1 Hz to 10 MHz between the temperatures 333 to 473 K was carried out for nanocrystalline CuAlO2 sample. The obtained complex impedance data was analyzed for AC conductivities, DC and AC conductivities correlations and crossover frequencies ( f co ). The BNN (Barton, Nakajima and Namikawa) relation was applied to understand the correlation between DC and AC conductivities. The observed experimental results were discussed in the paper.

Acoustic and electromagnetic wave interaction in the detection and identification of buried objects

NASA Astrophysics Data System (ADS)

Lawrence, Daniel Edward

2002-09-01

In order to facilitate the development of a hybrid acoustic and electromagnetic (EM) system for buried object detection, a number of analytical solutions and a novel numerical technique are developed to analyze the complex interaction between acoustic and EM scattering. The essence of the interaction lies in the fact that identifiable acoustic properties of an object, such as acoustic resonances, can be observed in the scattered EM Doppler spectrum. Using a perturbation approach, analytical solutions are derived for the EM scattering from infinitely long circular cylinders, both metallic and dielectric, under acoustic vibration in a homogeneous background medium. Results indicate that both the shape variation and dielectric constant contribute to the scattered EM Doppler spectrum. To model the effect of a cylinder beneath an acoustically excited half-space, a new analytical solution is presented for EM scattering from a cylinder beneath a slightly rough surface. The solution is achieved by using plane-wave expansion of the fields and an iterative technique to account for the multiple interactions between the cylinder and rough surface. Following a similar procedure, a novel solution for elastic-wave scattering from a solid cylinder embedded in a solid half-space is developed and used to calculate the surface displacement. Simulations indicate that only a finite range of spatial surface frequencies, corresponding to surface roughness on the order of the EM wavelength; affect the EM scattering from buried objects and suggest that object detection can be improved if the acoustic excitation induces surface roughness outside this range. To extend the study to non-canonical scenarios, a novel numerical approach is introduced in which time-varying impedance boundary conditions (IBCs) are used in conjunction with the method of moments (MoM) to model the EM scattering from vibrating metallic objects of arbitrary shape. It is shown that the standard IBC provides a first order solution for TM polarization, but a second order IBC is needed for TE polarization. The crucial factor in the calculation of the potentially small Doppler components is that the time-varying nature of the cylinder boundary, contained within the surface impedance expressions, can be isolated from the unperturbed terms in the scattered field.

Experimental observation and simulation of unusual microwave response for the superconducting microstrip resonator at small dc magnetic field

NASA Astrophysics Data System (ADS)

Ong, C. K.; Rao, X. S.; Jin, B. B.

1999-11-01

An unusual microwave response of the surface impedance Zs of high-Tc thin films at an applied small dc magnetic field (Bdc) at 77 K, namely a decrease of Zs, is observed with the microstrip resonator technique. The resonant frequency is 1.107 GHz. The direction of Bdc is parallel or perpendicular to the a-b plane. Bdc ranges from 0 to 200 G. It is found that the surface resistance (Rs) at Bdc parallel to the a-b plane first decreases with Bdc and then increases above a crossover field. The Rs behaviour for Bdc perpendicular to the a-b plane is the same but with a different crossover field. The two behaviours can be collapsed to one curve by scaling the crossover fields. The changes of surface reactance Xs correlated linearly with the changes of Rs in the ranges of Bdc. The ratios rH of changes of Rs and Xs (rH = icons/Journals/Common/Delta" ALT="Delta" ALIGN="TOP"/> Rs/icons/Journals/Common/Delta" ALT="Delta" ALIGN="TOP"/> Xs) are 0.5 at Bdc less than the crossover field and 0.1 at Bdc greater than the crossover field. The measurements also show that the crossover field is independent of rf input power. A phenomenological model is also proposed to explain this unusual behaviour. By adjusting fitting parameters the computed results agree with the experimental results qualitatively.

Spin-torque diode with tunable sensitivity and bandwidth by out-of-plane magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, X.; Zheng, C.; Pong, Philip W. T.

Spin-torque diodes based on nanosized magnetic tunnel junctions are novel microwave detectors with high sensitivity and wide frequency bandwidth. While previous reports mainly focus on improving the sensitivity, the approaches to extend the bandwidth are limited. This work experimentally demonstrates that through optimizing the orientation of the external magnetic field, wide bandwidth can be achieved while maintaining high sensitivity. The mechanism of the frequency- and sensitivity-tuning is investigated through analyzing the dependence of resonant frequency and DC voltage on the magnitude and the tilt angle of hard-plane magnetic field. The frequency dependence is qualitatively explicated by Kittel's ferromagnetic resonance model.more » The asymmetric resonant frequency at positive and negative magnetic field is verified by the numerical simulation considering the in-plane anisotropy. The DC voltage dependence is interpreted through evaluating the misalignment angle between the magnetization of the free layer and the reference layer. The tunability of the detector performance by the magnetic field angle is evaluated through characterizing the sensitivity and bandwidth under 3D magnetic field. The frequency bandwidth up to 9.8 GHz or maximum sensitivity up to 154 mV/mW (after impedance mismatch correction) can be achieved by tuning the angle of the applied magnetic field. The results show that the bandwidth and sensitivity can be controlled and adjusted through optimizing the orientation of the magnetic field for various applications and requirements.« less

Structural, morphological, dielectric and impedance spectroscopy of lead-free Bi(Zn2/3Ta1/3)O3 electronic material

NASA Astrophysics Data System (ADS)

Halder, S.; Bhuyan, S.; Das, S. N.; Sahoo, S.; Choudhary, R. N. P.; Das, P.; Parida, K.

2017-12-01

A lead-free dielectric material [Bi(Zn2/3Ta1/3)O3] has been prepared using a solid state reaction technique at high-temperature. The resistive, conducting and capacitive characteristics of the prepared electronic material have been studied in different experimental conditions. The determination of basic crystal parameters and reflection indices confirm the development of polycrystalline compound with orthorhombic crystal structure. The study of frequency-temperature dependence of ac conductivity illustrates the nature and conduction mechanism of the material. On the basis of observed impedance data and detailed dielectric analysis, the existence of non-Debye type relaxation has been affirmed. The electronic charge carriers of compound have short range order that has been validated from the complex modulus and impedance spectrum. The detailed studies of resistive, capacitive, microstructural characteristics of the prepared material provide some useful data for considering the material as an electronic component for fabrication of devices.

Effect of Cu-doping on structural and electrical properties of Ni0.4-xCu0.3+xMg0.3Fe2O4 ferrites prepared using sol-gel method

NASA Astrophysics Data System (ADS)

Dhaou, Mohamed Houcine

2018-06-01

Ni0.4-xCu0.3+xMg0.3Fe2O4 spinel ferrites were prepared by sol-gel technique. X-ray diffraction results indicate that ferrite samples have a cubic spinel-type structure with ? space group. The electrical properties of the studied samples using complex impedance spectroscopy technique have been investigated as a function of frequency at different temperatures. We found that the addition of copper in Ni0.4-xCu0.3+xMg0.3Fe2O4 ferrite system can improve its conductivity. Dielectric properties have been discussed in terms of hopping of charge carriers between Fe2+ and Fe3+ ions. For all samples, frequency dependence of the imaginary part of impedance (Z") shows the existence of relaxation phenomenon. The appropriate equivalent circuit configuration for modeling the Nyquist plots of impedance is of the type of (Rg + Rgb//Cgb).

Multifrequency impedance measurement technique for wireless characterization of microbiological cell cultures

NASA Astrophysics Data System (ADS)

Wissenwasser, J.; Vellekoop, M. J.; Kapferer, W.; Lepperdinger, G.; Heer, R.

2011-11-01

An impedance measurement system with probe signal frequencies up to 50 kHz with AC-probe voltages below 30 mV rms was integrated for wireless and battery-free monitoring of microbiological cell cultures. The here presented modular design and the use of state-of-the-art components greatly eases adoptions to a wide range of biotechnological applications without the need of bulky LCR-meters or potentiostats. The device had a power consumption of less than 2.5 mA at a 3.3 V single power supply and worked trouble-free within the humid environment of a cell culture incubator. Measurements on lumped RC-elements showed an error of less than 1% for absolute values and less than 1° regarding the phase of the complex impedance. The performance of sensor devices with interdigitated electrode structures for the measurement of adherent cell cultures was tested in the presence of phosphate-buffered saline solution in the humid atmosphere of an incubator for biological cell cultures.

Characteristic impedance of a microchannel with two immiscible microfluids

NASA Astrophysics Data System (ADS)

Jaramillo Raquejo, Daniela

2014-05-01

Consider the case of a microcapillary of radius R with two microfluidic immiscible. The micro-capillary region 0 < r < R1 is occupied by the microfluidic less dense and less viscous; while the microcapillary region R1 <0 < R is occupied by the microfluidic more dense and more viscous. Determine the characteristic impedance of the microcapillary in this case when both microfluidics are driven by the same pressure gradient as the boundary condition at the wall of the microcapillary is of the non-Newtonian slip. The Navier Stokes equation is solved for both microfluidic methods using the Laplace transform. The velocity profiles are expressed in terms of Bessel functions. Similarly, the characteristic impedance of the microcapillary is expressed by a complex formula Bessel functions. Obtain the analytical results are important for designing engineering microdevices with applications in pharmaceutical, food engineering, nanotechnology and biotechnology in general in particular. For future research it is interesting to consider the case of boundary conditions with memory effects.

The development of the miniaturized waveform receiver with the function measuring Antenna Impedance in space plasmas

NASA Astrophysics Data System (ADS)

Ishii, H.; Kojima, H.; Fukuhara, H.; Okada, S.; Yamakawa, H.

2012-04-01

Plasma wave is one of the most essential physical quantities in the solar terrestrial physics. The role of plasma wave receiver onboard satellites is to detect plasma waves in space with a good signal to noise ratio. There are two types of plasma wave receivers, the sweep frequency analyzer and the waveform capture. While the sweep frequency analyzer provides plasma wave spectra, the waveform capture obtains waveforms with phase information that is significant in studying nonlinear phenomena. Antenna sensors to observe electric fields of the plasma waves show different features in plasmas from in vacuum. The antenna impedances have specific characteristics in the frequency domain because of the dispersion of plasmas. These antenna impedances are expressed with complex number. We need to know not only the antenna impedances but also the transfer functions of plasma wave receiver's circuits in order to calibrate observed waveforms precisely. The impedances of the electric field antennas are affected by a state of surrounding plasmas. Since satellites run through various regions with different plasma parameters, we precisely should measure the antenna impedances onboard spacecraft. On the contrary, we can obtain the plasma density and by measuring the antenna impedances. Several formulas of the antenna impedance measurement system were proposed. A synchronous detection method is used on the BepiColombo Mercury Magnetospheric Orbiter (MMO), which will be launched in 2014. The digital data are stored in the onboard memory. They are read out and converted to the analog waveforms by D/A converter. They are fed into the input of the preamplifiers of antenna sensors through a resistor. We can calculate a transfer function of the circuit by applying the synchronous detection method to the output waveform from waveform receivers and digital data as a signal source. The size of this system is same as an A5 board. In recent years, Application Specific Integrated Circuit (ASIC) is in attention which is a technique to integrate large scale and complicated circuits. Lots of ASICs have been applied to high energy astrophysics. In this paper, we show our attempt to miniaturize the antennas impedances measurement system and Waveform Capture using the analogue ASIC. We design 8bits segment D/A converter that is implemented inside the waveform receiver ASIC chip. We improve input logic of the D/A converter to generate very weak signals accurately. The designed chip realizes the measurement of the antenna impedance as well as the waveform observation in the board size of business cards.

Manned Versus Unmanned Risk and Complexity Considerations for Future Midsized X-Planes

NASA Technical Reports Server (NTRS)

Lechniak, Jason A.; Melton, John E.

2017-01-01

The objective of this work was to identify and estimate complexity and risks associated with the development and testing of new low-cost medium-scale X-plane aircraft primarily focused on air transport operations. Piloting modes that were evaluated for this task were manned, remotely piloted, and unmanned flight research programs. This analysis was conducted early in the data collection period for X-plane concept vehicles before preliminary designs were complete. Over 50 different aircraft and system topics were used to evaluate the three piloting control modes. Expert group evaluations from a diverse set of pilots, engineers, and other experts at Aeronautics Research Mission Directorate centers within the National Aeronautics and Space Administration provided qualitative reasoning on the many issues surrounding the decisions regarding piloting modes. The group evaluations were numerically rated to evaluate each topic quantitatively and were used to provide independent criteria for vehicle complexity and risk. An Edwards Air Force Base instruction document was identified that emerged as a source of the effects found in our qualitative and quantitative data. The study showed that a manned aircraft was the best choice to align with test activities for transport aircraft flight research from a low-complexity and low-risk perspective. The study concluded that a manned aircraft option would minimize the risk and complexity to improve flight-test efficiency and bound the cost of the flight-test portion of the program. Several key findings and discriminators between the three modes are discussed in detail.

Time-ordered exponential on the complex plane and Gell-Mann—Low formula as a mathematical theorem

DOE Office of Scientific and Technical Information (OSTI.GOV)

Futakuchi, Shinichiro; Usui, Kouta

2016-04-15

The time-ordered exponential representation of a complex time evolution operator in the interaction picture is studied. Using the complex time evolution, we prove the Gell-Mann—Low formula under certain abstract conditions, in mathematically rigorous manner. We apply the abstract results to quantum electrodynamics with cutoffs.

Acoustic response of Helmholtz dampers in the presence of hot grazing flow

NASA Astrophysics Data System (ADS)

Ćosić, B.; Wassmer, D.; Terhaar, S.; Paschereit, C. O.

2015-01-01

Thermoacoustic instabilities are high amplitude instabilities of premixed gas turbine combustors. Cooled passive dampers are used to attenuate or suppress these instabilities in the combustion chamber. For the first time, the influence of temperature differences between the grazing flow in the combustor and the cross-flow emanating from the Helmholtz damper is comprehensively investigated in the linear and nonlinear amplitude regime. The flow field inside the resonator and in the vicinity of the neck is measured with high-speed particle image velocimetry for various amplitudes and at different momentum-flux ratios of grazing and purging flow. Seeding is used as a tracer to qualitatively assess the mixing of the grazing and purging flow as well as the ingestion into the neck of the resonator. Experimentally, the acoustic response for various temperature differences between grazing and purging flow is investigated. The multi-microphone method, in combination with two microphones flush-mounted in the resonator volume and two microphones in the plane of the resonator entrance, is used to determine the impedance of the Helmholtz resonator in the linear and nonlinear amplitude regime for various temperatures and different momentum-flux ratios. Additionally, a thermocouple was used to measure the temperature in the neck. The acoustic response and the temperature measurements are used to obtain the virtual neck length and the effective area jump from a detailed impedance model. This model is extended to include the observed acoustic energy dissipation caused by the density gradients at the neck vicinity. A clear correlation between temperature differences and changes of the mass end-correction is confirmed. The capabilities of the impedance model are demonstrated.

Jet-noise reduction through liquid-base foam injection.

NASA Technical Reports Server (NTRS)

Manson, L.; Burge, H. L.

1971-01-01

An experimental investigation has been made of the sound-absorbing properties of liquid-base foams and of their ability to reduce jet noise. Protein, detergent, and polymer foaming agents were used in water solutions. A method of foam generation was developed to permit systematic variation of the foam density. The investigation included measurements of sound-absorption coefficents for both plane normal incidence waves and diffuse sound fields. The intrinsic acoustic properties of foam, e.g., the characteristic impedance and the propagation constant, were also determined. The sound emitted by a 1-in.-diam cold nitrogen jet was measured for subsonic (300 m/sec) and supersonic (422 m/sec) jets, with and without foam injection. Noise reductions up to 10 PNdB were measured.

Numerical Simulation on the Dynamic Splitting Tensile Test of reinforced concrete

NASA Astrophysics Data System (ADS)

Zhao, Zhuan; Jia, Haokai; Jing, Lin

2018-03-01

The research for crack resistance was of RC was based on the split Hopkinson bar and numerical simulate software LS-DYNA3D. In the research, the difference of dynamic splitting failure modes between plane concrete and reinforced concrete were completed, and the change rule of tensile stress distribution with reinforcement ratio was studied; also the effect rule with the strain rate and the crack resistance was also discussed by the radial tensile stress time history curve of RC specimen under different loading speeds. The results shows that the reinforcement in the concrete can impede the crack extension, defer the failure time of concrete, increase the tension intensity of concrete; with strain rate of concrete increased, the crack resistance of RC increased.

Design of modified pentagonal patch antenna on defective ground for Wi-Max/WLAN application

NASA Astrophysics Data System (ADS)

Rawat, Sanyog; Sharma, K. K.

2016-04-01

This paper presents the design and performance of a modified pentagonal patch antenna with defective ground plane. A pentagonal slot is inserted in the pentagonal patch and slot loaded ground through optimized dimensions is used in the antenna to resonate it at dual frequency. The geometry operates at two resonant frequencies (2.5 GHz and 5.58 GHz) and offers impedance bandwidth of 864 MHz and 554 MHz in the two bands of interest. The proposed antenna covers the lower band (2.45 to 2.484/2.495 to 2.695 GHz) and upper band (5.15 to 5.825 GHz/5.25 to 5.85 GHz) allocated for Wi-Max and WLAN communication systems.

Electrical properties of Ba(Dy{sub 1/2}Nb{sub 1/2})O{sub 3} ceramic

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nath, K. Amar, E-mail: karn190@gmail.com; Chandra, K. P., E-mail: kpchandra23@gmail.com; Dubey, K., E-mail: kirandubey45@yahoo.com

2016-05-06

Polycrystalline Ba(Dy{sub 1/2}Nb{sub 1/2})O{sub 3} was prepared using a high-temperature solid-state reaction method. X-ray diffraction analysis indicated the formation of a single-phase cubic structure having space group Pm3m. AC impedance plots as a function of frequency at different temperatures were used to analyse the electrical behaviour of the sample, which indicated the negative temperature coefficient of resistance character. Complex impedance analysis targeted non-Debye type dielectric relaxation. Frequency dependent ac conductivity data obeyed Jonscher’s power law. The apparent activation energy was estimated to be 0.97 eV at 1 kHz.

Aircraft panel with sensorless active sound power reduction capabilities through virtual mechanical impedances

NASA Astrophysics Data System (ADS)

Boulandet, R.; Michau, M.; Micheau, P.; Berry, A.

2016-01-01

This paper deals with an active structural acoustic control approach to reduce the transmission of tonal noise in aircraft cabins. The focus is on the practical implementation of the virtual mechanical impedances method by using sensoriactuators instead of conventional control units composed of separate sensors and actuators. The experimental setup includes two sensoriactuators developed from the electrodynamic inertial exciter and distributed over an aircraft trim panel which is subject to a time-harmonic diffuse sound field. The target mechanical impedances are first defined by solving a linear optimization problem from sound power measurements before being applied to the test panel using a complex envelope controller. Measured data are compared to results obtained with sensor-actuator pairs consisting of an accelerometer and an inertial exciter, particularly as regards sound power reduction. It is shown that the two types of control unit provide similar performance, and that here virtual impedance control stands apart from conventional active damping. In particular, it is clear from this study that extra vibrational energy must be provided by the actuators for optimal sound power reduction, mainly due to the high structural damping in the aircraft trim panel. Concluding remarks on the benefits of using these electrodynamic sensoriactuators to control tonal disturbances are also provided.

Evaluation of Novel Liner Concepts for Fan and Airframe Noise Reduction

NASA Technical Reports Server (NTRS)

Jones, M. G.; Howerton, B. M.

2016-01-01

This paper presents a review of four novel liner concepts: soft vanes, over-the-rotor liners, external liners, and flap side-edge liners. A number of similarities in the design and evaluation of these concepts emerged during these investigations. Since these were the first attempts to study these particular liner concepts, there was limited information to guide the design process. In all cases, the target frequencies (or frequency range) were known, but the optimum acoustic impedance and optimum liner placement were typically not known. For these cases, the maximum available surface was used and a c-impedance was targeted based on the assumption the sound field impinges on the surface at normal incidence. This choice proved fruitful for every application. An impedance prediction model was used to design variable-depth liner configurations, and a graphical design code (ILIAD) was developed to aid in this process. The ability to build increasingly complex liner configurations via additive manufacturing was key, such that multiple designs could quickly be tested in a normal incidence impedance tube. The Two-Thickness Method was used to evaluate available bulk materials, such that bulk liners could also be considered for each application. These novel liner concepts provide sufficient noise reduction to warrant further investigations.

Transition operators in acoustic-wave diffraction theory. I - General theory. II - Short-wavelength behavior, dominant singularities of Zk0 and Zk0 exp -1

NASA Technical Reports Server (NTRS)

Hahne, G. E.

1991-01-01

A formal theory of the scattering of time-harmonic acoustic scalar waves from impenetrable, immobile obstacles is established. The time-independent formal scattering theory of nonrelativistic quantum mechanics, in particular the theory of the complete Green's function and the transition (T) operator, provides the model. The quantum-mechanical approach is modified to allow the treatment of acoustic-wave scattering with imposed boundary conditions of impedance type on the surface (delta-Omega) of an impenetrable obstacle. With k0 as the free-space wavenumber of the signal, a simplified expression is obtained for the k0-dependent T operator for a general case of homogeneous impedance boundary conditions for the acoustic wave on delta-Omega. All the nonelementary operators entering the expression for the T operator are formally simple rational algebraic functions of a certain invertible linear radiation impedance operator which maps any sufficiently well-behaved complex-valued function on delta-Omega into another such function on delta-Omega. In the subsequent study, the short-wavelength and the long-wavelength behavior of the radiation impedance operator and its inverse (the 'radiation admittance' operator) as two-point kernels on a smooth delta-Omega are studied for pairs of points that are close together.

A LabVIEW model incorporating an open-loop arterial impedance and a closed-loop circulatory system.

PubMed

Cole, R T; Lucas, C L; Cascio, W E; Johnson, T A

2005-11-01

While numerous computer models exist for the circulatory system, many are limited in scope, contain unwanted features or incorporate complex components specific to unique experimental situations. Our purpose was to develop a basic, yet multifaceted, computer model of the left heart and systemic circulation in LabVIEW having universal appeal without sacrificing crucial physiologic features. The program we developed employs Windkessel-type impedance models in several open-loop configurations and a closed-loop model coupling a lumped impedance and ventricular pressure source. The open-loop impedance models demonstrate afterload effects on arbitrary aortic pressure/flow inputs. The closed-loop model catalogs the major circulatory waveforms with changes in afterload, preload, and left heart properties. Our model provides an avenue for expanding the use of the ventricular equations through closed-loop coupling that includes a basic coronary circuit. Tested values used for the afterload components and the effects of afterload parameter changes on various waveforms are consistent with published data. We conclude that this model offers the ability to alter several circulatory factors and digitally catalog the most salient features of the pressure/flow waveforms employing a user-friendly platform. These features make the model a useful instructional tool for students as well as a simple experimental tool for cardiovascular research.

Direct correlation between potentiometric and impedance biosensing of antibody-antigen interactions using an integrated system

NASA Astrophysics Data System (ADS)

Tsai, Meng-Yen; Creedon, Niamh; Brightbill, Eleanor; Pavlidis, Spyridon; Brown, Billyde; Gray, Darren W.; Shields, Niall; Sayers, Ríona; Mooney, Mark H.; O'Riordan, Alan; Vogel, Eric M.

2017-08-01

A fully integrated system that combines extended gate field-effect transistor (EGFET)-based potentiometric biosensors and electrochemical impedance spectroscopy (EIS)-based biosensors has been demonstrated. This integrated configuration enables the sequential measurement of the same immunological binding event on the same sensing surface and consequently sheds light on the fundamental origins of sensing signals produced by FET and EIS biosensors, as well as the correlation between the two. Detection of both the bovine serum albumin (BSA)/anti-BSA model system in buffer solution and bovine parainfluenza antibodies in complex blood plasma samples was demonstrated using the integrated biosensors. Comparison of the EGFET and EIS sensor responses reveals similar dynamic ranges, while equivalent circuit modeling of the EIS response shows that the commonly reported total impedance change (ΔZtotal) is dominated by the change in charge transfer resistance (Rct) rather than surface capacitance (Csurface). Using electrochemical kinetics and the Butler-Volmer equation, we unveil that the surface potential and charge transfer resistance, measured by potentiometric and impedance biosensors, respectively, are, in fact, intrinsically linked. This observation suggests that there is no significant gain in using the FET/EIS integrated system and leads to the demonstration that low-cost EGFET biosensors are sufficient as a detection tool to resolve the charge information of biomolecules for practical sensing applications.

Prediction for potential landslide zones using seismic amplitude in Liwan gas field, northern South China Sea

NASA Astrophysics Data System (ADS)

Li, Xishuang; Liu, Baohua; Liu, Lejun; Zheng, Jiewen; Zhou, Songwang; Zhou, Qingjie

2017-12-01

The Liwan (Lw) gas field located in the northern slope of the South China Sea (SCS) is extremely complex for its sea-floor topograghy, which is a huge challenge for the safety of subsea facilities. It is economically impractical to obtain parameters for risk assessment of slope stability through a large amount of sampling over the whole field. The linkage between soil shear strength and seabed peak amplitude derived from 2D/3D seismic data is helpful for understanding the regional slope-instability risk. In this paper, the relationships among seabed peak, acoustic impedance and shear strength of shallow soil in the study area were discussed based on statistical analysis results. We obtained a similar relationship to that obtained in other deep-water areas. There is a positive correlation between seabed peak amplitude and acoustic impedance and an exponential relationship between acoustic impedance and shear strength of sediment. The acoustic impedance is the key factor linking the seismic amplitude and shear strength. Infinite slope stability analysis results indicate the areas have a high potential of shallow landslide on slopes exceeding 15° when the thickness of loose sediments exceeds 8 m in the Lw gas field. Our prediction shows that they are mainly located in the heads and walls of submarine canyons.

A three-plane architectonic atlas of the rat hippocampal region.

PubMed

Boccara, Charlotte N; Kjonigsen, Lisa J; Hammer, Ingvild M; Bjaalie, Jan G; Leergaard, Trygve B; Witter, Menno P

2015-07-01

The hippocampal region, comprising the hippocampal formation and the parahippocampal region, has been one of the most intensively studied parts of the brain for decades. Better understanding of its functional diversity and complexity has led to an increased demand for specificity in experimental procedures and manipulations. In view of the complex 3D structure of the hippocampal region, precisely positioned experimental approaches require a fine-grained architectural description that is available and readable to experimentalists lacking detailed anatomical experience. In this paper, we provide the first cyto- and chemoarchitectural description of the hippocampal formation and parahippocampal region in the rat at high resolution and in the three standard sectional planes: coronal, horizontal and sagittal. The atlas uses a series of adjacent sections stained for neurons and for a number of chemical marker substances, particularly parvalbumin and calbindin. All the borders defined in one plane have been cross-checked against their counterparts in the other two planes. The entire dataset will be made available as a web-based interactive application through the Rodent Brain WorkBench (http://www.rbwb.org) which, together with this paper, provides a unique atlas resource. © 2014 Wiley Periodicals, Inc.

FRIEDA: Flexible Robust Intelligent Elastic Data Management Framework

DOE PAGES

Ghoshal, Devarshi; Hendrix, Valerie; Fox, William; ...

2017-02-01

Scientific applications are increasingly using cloud resources for their data analysis workflows. However, managing data effectively and efficiently over these cloud resources is challenging due to the myriad storage choices with different performance, cost trade-offs, complex application choices and complexity associated with elasticity, failure rates in these environments. The different data access patterns for data-intensive scientific applications require a more flexible and robust data management solution than the ones currently in existence. FRIEDA is a Flexible Robust Intelligent Elastic Data Management framework that employs a range of data management strategies in cloud environments. FRIEDA can manage storage and data lifecyclemore » of applications in cloud environments. There are four different stages in the data management lifecycle of FRIEDA – (i) storage planning, (ii) provisioning and preparation, (iii) data placement, and (iv) execution. FRIEDA defines a data control plane and an execution plane. The data control plane defines the data partition and distribution strategy, whereas the execution plane manages the execution of the application using a master-worker paradigm. FRIEDA also provides different data management strategies, either to partition the data in real-time, or predetermine the data partitions prior to application execution.« less

FRIEDA: Flexible Robust Intelligent Elastic Data Management Framework

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghoshal, Devarshi; Hendrix, Valerie; Fox, William

Scientific applications are increasingly using cloud resources for their data analysis workflows. However, managing data effectively and efficiently over these cloud resources is challenging due to the myriad storage choices with different performance, cost trade-offs, complex application choices and complexity associated with elasticity, failure rates in these environments. The different data access patterns for data-intensive scientific applications require a more flexible and robust data management solution than the ones currently in existence. FRIEDA is a Flexible Robust Intelligent Elastic Data Management framework that employs a range of data management strategies in cloud environments. FRIEDA can manage storage and data lifecyclemore » of applications in cloud environments. There are four different stages in the data management lifecycle of FRIEDA – (i) storage planning, (ii) provisioning and preparation, (iii) data placement, and (iv) execution. FRIEDA defines a data control plane and an execution plane. The data control plane defines the data partition and distribution strategy, whereas the execution plane manages the execution of the application using a master-worker paradigm. FRIEDA also provides different data management strategies, either to partition the data in real-time, or predetermine the data partitions prior to application execution.« less

Molecular dynamics simulations of cesium adsorption on illite nanoparticles.

PubMed

Lammers, Laura N; Bourg, Ian C; Okumura, Masahiko; Kolluri, Kedarnath; Sposito, Garrison; Machida, Masahiko

2017-03-15

The charged surfaces of micaceous minerals, especially illite, regulate the mobility of the major radioisotopes of Cs ( 134 Cs, 135 Cs, 137 Cs) in the geosphere. Despite the long history of Cs adsorption studies, the nature of the illite surface sites remains incompletely understood. To address this problem, we present atomistic simulations of Cs competition with Na for three candidate illite adsorption sites - edge, basal plane, and interlayer. Our simulation results are broadly consistent with affinities and selectivities that have been inferred from surface complexation models. Cation exchange on the basal planes is thermodynamically ideal, but exchange on edge surfaces and within interlayers shows complex, thermodynamically non-ideal behavior. The basal planes are weakly Cs-selective, while edges and interlayers have much higher affinity for Cs. The dynamics of NaCs exchange are rapid for both cations on the basal planes, but considerably slower for Cs localized on edge surfaces. In addition to new insights into Cs adsorption and exchange with Na on illite, we report the development of a methodology capable of simulating fully-flexible clay mineral nanoparticles with stable edge surfaces using a well-tested interatomic potential model. Copyright © 2016 Elsevier Inc. All rights reserved.

Microplasma generating array

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hopwood, Jeffrey A.; Wu, Chen; Hoskinson, Alan R.

A microplasma generator includes first and second conductive resonators disposed on a first surface of a dielectric substrate. The first and second conductive resonators are arranged in line with one another with a gap defined between a first end of each resonator. A ground plane is disposed on a second surface of the dielectric substrate and a second end of each of the first and second resonators is coupled to the ground plane. A power input connector is coupled to the first resonator at a first predetermined distance from the second end chosen as a function of the impedance ofmore » the first conductive resonator. A microplasma generating array includes a number of resonators in a dielectric material substrate with one end of each resonator coupled to ground. A micro-plasma is generated at the non-grounded end of each resonator. The substrate includes a ground electrode and the microplasmas are generated between the non-grounded end of the resonator and the ground electrode. The coupling of each resonator to ground may be made through controlled switches in order to turn each resonator off or on and therefore control where and when a microplasma will be created in the array.« less

Dispersion, dissipation and refraction of shock waves in acoustically treated turbofan inlets

NASA Astrophysics Data System (ADS)

Prasad, Dilip; Li, Ding; A. Topol, David

2015-09-01

This paper describes a numerical investigation of the effects of the inlet duct liner on the acoustics of a high-bypass ratio turbofan rotor operating at supersonic tip relative flow conditions. The near field of the blade row is then composed of periodic shocks that evolve spatially both because of the varying mean flow and because of the presence of acoustic treatment. The evolution of this shock system is studied using a Computational Fluid Dynamics-based method incorporating a wall impedance boundary condition. The configuration examined is representative of a fan operating near the takeoff condition. The behavior of the acoustic power and the associated waveforms reveal that significant dispersion occurs to the extent that there are no shocks in the perturbation field leaving the entrance plane of the duct. The effect of wave refraction due to the high degree of shear in the mean flow near the entrance plane of the inlet is examined, and numerical experiments are conducted to show that the incorporation of liners in this region can be highly beneficial. The implications of these results for the design of aircraft engine acoustic liners are discussed.

A method to determine the acoustic reflection and absorption coefficients of porous media by using modal dispersion in a waveguide.

PubMed

Prisutova, Jevgenija; Horoshenkov, Kirill; Groby, Jean-Philippe; Brouard, Bruno

2014-12-01

The measurement of acoustic material characteristics using a standard impedance tube method is generally limited to the plane wave regime below the tube cut-on frequency. This implies that the size of the tube and, consequently, the size of the material specimen must remain smaller than a half of the wavelength. This paper presents a method that enables the extension of the frequency range beyond the plane wave regime by at least a factor of 3, so that the size of the material specimen can be much larger than the wavelength. The proposed method is based on measuring of the sound pressure at different axial locations and applying the spatial Fourier transform. A normal mode decomposition approach is used together with an optimization algorithm to minimize the discrepancy between the measured and predicted sound pressure spectra. This allows the frequency and angle dependent reflection and absorption coefficients of the material specimen to be calculated in an extended frequency range. The method has been tested successfully on samples of melamine foam and wood fiber. The measured data are in close agreement with the predictions by the equivalent fluid model for the acoustical properties of porous media.

Efficient reduction of defects in (1120) non-polar and (1122) semi-polar GaN grown on nanorod templates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bai, J.; Gong, Y.; Xing, K.

2013-03-11

(1120) non-polar and (1122) semi-polar GaNs with a low defect density have been achieved by means of an overgrowth on nanorod templates, where a quick coalescence with a thickness even below 1 {mu}m occurs. On-axis and off-axis X-ray rocking curve measurements have shown a massive reduction in the linewidth for our overgrown GaN in comparison with standard GaN films grown on sapphire substrates. Transmission electron microscope observation demonstrates that the overgrowth on the nanorod templates takes advantage of an omni-directional growth around the sidewalls of the nanostructures. The dislocations redirect in basal planes during the overgrowth, leading to their annihilationmore » and termination at voids formed due to a large lateral growth rate. In the non-polar GaN, the priority <0001> lateral growth from vertical sidewalls of nanorods allows basal plane stacking faults (BSFs) to be blocked in the nanorod gaps; while for semi-polar GaN, the propagation of BSFs starts to be impeded when the growth front is changed to be along inclined <0001> direction above the nanorods.« less

The Effect of Military Load Carriage on Postural Sway, Forward Trunk Lean, and Pelvic Girdle Motion

PubMed Central

STRUBE, EILEEN M.; SUMNER, ANDREA; KOLLOCK, ROGER; GAMES, KENNETH E.; LACKAMP, MARIE A.; MIZUTANI, MASAHIRO; SEFTON, JOELLEN M.

2017-01-01

Musculoskeletal injuries are a common occurrence in military service members. It is believed that the load carried by the service member impedes stability and alters back and pelvis kinematics, increasing their susceptibility to musculoskeletal injuries, specifically in the lower extremities. The purpose of this study was to examine the effects of two different loads on postural sway, forward trunk lean, and pelvic girdle motion in United States Army Cadets. Twenty male Army Reserve Officers’ Training Corps Cadets participated in this study. Each participant performed the Modified Clinical Testing of Sensory Interaction (mCTSIB) Protocol and the Unilateral Stance (ULS) Protocol under three different rucksack load conditions (unloaded, 16.0 kg, and 20.5 kg loads). Mean postural sway velocity was recorded along with 2-D kinematics of the trunk in the sagittal plane and the pelvis in the frontal and sagittal planes. External loads of 16.0 kg (p < 0.001) and 20.5 kg (p ≤ 0.003) significantly increased mean sway velocity by 16% to 52% depending on stance and visual condition, but did not produce significant changes in trunk and pelvic kinematics. PMID:28479946

Continuous-wave operation of m-plane GaN-based vertical-cavity surface-emitting lasers with a tunnel junction intracavity contact

NASA Astrophysics Data System (ADS)

Forman, Charles A.; Lee, SeungGeun; Young, Erin C.; Kearns, Jared A.; Cohen, Daniel A.; Leonard, John T.; Margalith, Tal; DenBaars, Steven P.; Nakamura, Shuji

2018-03-01

We have achieved continuous-wave (CW) operation of an optically polarized m-plane GaN-based vertical-cavity surface-emitting laser (VCSEL) with an ion implanted current aperture, a tunnel junction intracavity contact, and a dual dielectric distributed Bragg reflector design. The reported VCSEL has 2 quantum wells, with a 14 nm quantum well width, 1 nm barriers, a 5 nm electron-blocking layer, and a 23 λ total cavity thickness. The thermal performance was improved by increasing the cavity length and using Au-In solid-liquid interdiffusion bonding, which led to lasing under CW operation for over 20 min. Lasing wavelengths under pulsed operation were observed at 406 nm, 412 nm, and 419 nm. Only the latter two modes appeared under CW operation due to the redshifted gain at higher temperatures. The peak output powers for a 6 μm aperture VCSEL under CW and pulsed operation were 140 μW and 700 μW, respectively. The fundamental transverse mode was observed without the presence of filamentary lasing. The thermal impedance was estimated to be ˜1400 °C/W for a 6 μm aperture 23 λ VCSEL.

Low-energy Structural Dynamics of Multiferroic Domain Walls in Hexagonal Rare-earth Manganites

NASA Astrophysics Data System (ADS)

Wu, Xiaoyu; Petralanda, Urko; Zheng, Lu; Ren, Yuan; Hu, Rongwei; Cheong, Sang-Wook; Artyukhin, Sergey; Lai, Keji

Multiferroic domain walls (DWs), the natural interfaces between domains with different order parameters, usually exhibit unconventional functionalities. For instance, recent discovery of the ferroelectric DW conduction highlights its extraordinary electronic structure that is absent in bulk domains. The structural dynamics of individual DWs in the microwave regime, however, have not been fully explored due to the lack of spatially resolved studies. Here, we report the broadband (106-1010 Hz) scanning impedance microscopy results on the interlocked anti-phase boundaries and ferroelectric DWs in hexagonal rare-earth manganites. Surprisingly, the effective conductivity of the (001) DWs displays a 106-fold increase from dc to GHz frequencies, while the effect is absent on surfaces with in-plane polarized domains. First-principles and model calculations indicate that the frequency range and selection rules are consistent with the periodic sliding of the DW around its equilibrium position. This DW acoustic-wave-like mode, which is associated with the synchronized oscillation of local polarization and apical oxygen atoms, is localized perpendicular to the DW but free to propagate along the DW plane. Our results break the ground to understand structural DW dynamics and exploit new interfacial phenomena for novel devices.

Tunable impedance matching network fundamental limits and practical considerations

NASA Astrophysics Data System (ADS)

Allen, Wesley N.

As wireless devices continue to increase in utility while decreasing in dimension, design of the RF front-end becomes more complex. It is common for a single handheld device to operate on a plethora of frequency bands, utilize multiple antennae, and be subjected to a variety of environments. One complexity in particular which arises from these factors is that of impedance mismatch. Recently, tunable impedance matching networks have begun to be implemented to address this problem. This dissertation presents the first in-depth study on the frequency tuning range of tunable impedance matching networks. Both the fundamental limitations of ideal networks as well as practical considerations for design and implementation are addressed. Specifically, distributed matching networks with a single tuning element are investigated for use with parallel resistor-capacitor and series resistor-inductor loads. Analytical formulas are developed to directly calculate the frequency tuning range TR of ideal topologies. The theoretical limit of TR for these topologies is presented and discussed. Additional formulas are developed which address limitations in transmission line characteristic impedance and varactor range. Equations to predict loss due to varactor quality factor are demonstrated and the ability of parasitics to both increase and decrease TR are shown. Measured results exemplify i) the potential to develop matching networks with a small impact from parasitics, ii) the need for accurate knowledge of parasitics when designing near transition points in optimal parameters, iii) the importance of using a transmission line with the right characteristic impedance, and iv) the ability to achieve extremely low loss at the design frequency with a lossy varactor under the right conditions (measured loss of -0.07 dB). In the area of application, tunable matching networks are designed and measured for mobile handset antennas, demonstrating up to a 3 dB improvement in power delivered to a planar inverted-F antenna and up to 4--5.6 dB improvement in power delivered to the iPhone(TM) antenna. Additionally, a single-varactor matching network is measured to achieve greater tuning range than a two-varactor matching network (> 824--960 MHz versus 850--915 MHz) and yield higher power handling. Addressing miniaturization, an accurate model of metal loss in planar integrated inductors for low-loss substrates is developed and demonstrated. Finally, immediate future research directions are suggested: i) expanding the topologies, tuning elements, and loads analyzed; ii) performing a deep study into parasitics; and iii) investigating power handling with various varactor technologies.

3D-Printed Detector Band for Magnetic Off-Plane Flux Measurements in Laminated Machine Cores

PubMed Central

Pfützner, Helmut; Palkovits, Martin; Windischhofer, Andreas; Giefing, Markus

2017-01-01

Laminated soft magnetic cores of transformers, rotating machines etc. may exhibit complex 3D flux distributions with pronounced normal fluxes (off-plane fluxes), perpendicular to the plane of magnetization. As recent research activities have shown, detections of off-plane fluxes tend to be essential for the optimization of core performances aiming at a reduction of core losses and of audible noise. Conventional sensors for off-plane flux measurements tend to be either of high thickness, influencing the measured fluxes significantly, or require laborious preparations. In the current work, thin novel detector bands for effective and simple off-plane flux detections in laminated machine cores were manufactured. They are printed in an automatic way by an in-house developed 3D/2D assembler. The latter enables a unique combination of conductive and non-conductive materials. The detector bands were effectively tested in the interior of a two-package, three-phase model transformer core. They proved to be mechanically resilient, even for strong clamping of the core. PMID:29257063

3D-Printed Detector Band for Magnetic Off-Plane Flux Measurements in Laminated Machine Cores.

PubMed

Shilyashki, Georgi; Pfützner, Helmut; Palkovits, Martin; Windischhofer, Andreas; Giefing, Markus

2017-12-19

Laminated soft magnetic cores of transformers, rotating machines etc. may exhibit complex 3D flux distributions with pronounced normal fluxes (off-plane fluxes), perpendicular to the plane of magnetization. As recent research activities have shown, detections of off-plane fluxes tend to be essential for the optimization of core performances aiming at a reduction of core losses and of audible noise. Conventional sensors for off-plane flux measurements tend to be either of high thickness, influencing the measured fluxes significantly, or require laborious preparations. In the current work, thin novel detector bands for effective and simple off-plane flux detections in laminated machine cores were manufactured. They are printed in an automatic way by an in-house developed 3D/2D assembler. The latter enables a unique combination of conductive and non-conductive materials. The detector bands were effectively tested in the interior of a two-package, three-phase model transformer core. They proved to be mechanically resilient, even for strong clamping of the core.

Small scale exact coherent structures at large Reynolds numbers in plane Couette flow

NASA Astrophysics Data System (ADS)

Eckhardt, Bruno; Zammert, Stefan

2018-02-01

The transition to turbulence in plane Couette flow and several other shear flows is connected with saddle node bifurcations in which fully three-dimensional, nonlinear solutions to the Navier-Stokes equation, so-called exact coherent states (ECS), appear. As the Reynolds number increases, the states undergo secondary bifurcations and their time-evolution becomes increasingly more complex. Their spatial complexity, in contrast, remains limited so that these states cannot contribute to the spatial complexity and cascade to smaller scales expected for higher Reynolds numbers. We here present families of scaling ECS that exist on ever smaller scales as the Reynolds number is increased. We focus in particular on two such families for plane Couette flow, one centered near the midplane and the other close to a wall. We discuss their scaling and localization properties and the bifurcation diagrams. All solutions are localized in the wall-normal direction. In the spanwise and downstream direction, they are either periodic or localized as well. The family of scaling ECS localized near a wall is reminiscent of attached eddies, and indicates how self-similar ECS can contribute to the formation of boundary layer profiles.

Synthesis, characterization and in vitro antimicrobial studies of Co(II), Ni(II) and Cu(II) complexes derived from macrocyclic compartmental ligand

NASA Astrophysics Data System (ADS)

El-Gammal, O. A.; Bekheit, M. M.; El-Brashy, S. A.

2015-02-01

New Co(II), Ni(II) and Cu(II) complexes derived from tetradentate macrocyclic nitrogen ligand, (1E,4E,8E,12E)-5,8,13,16-tetramethyl-1,4,9,12-tetrazacyclohexadeca-4,8,12,16-tetraene (EDHDH) have been synthesized. The complexes have been characterized by elemental analysis, spectral (IR, UV-Vis, 1H NMR and ESR (for Cu(II) complex)) mass, and magnetic as well as thermal analysis measurements. The complexes afforded the formulae: [Cu(EDHDH)Cl2]·2EtOH and [M(EDHDH)X2]·nH2O where M = Co(II) and Ni(II), X = Cl- or OH-, n = 1,0, respectively. The data revealed an octahedral arrangement with N4 tetradentate donor sites in addition to two Cl atoms occupying the other two sites. ESR spectrum of Cu2+ complex confirmed the suggested geometry with values of a α2and β2 indicating that the in-plane σ-bonding and in-plane π-bonding are appreciably covalent, and are consistent with very strong σ-in-plane bonding in the complexes. The molecular modeling is drawn and showed the bond length, bond angle, chemical reactivity, energy components (kcal/mol) and binding energy (kcal/mol) for all the title compounds using DFT method. Also, the thermal behavior and the kinetic parameters of degradation were determined using Coats-Redfern and Horowitz-Metzger methods. Moreover, the in vitro antibacterial studies of all compounds screened against pathogenic bacteria (two Gram +ve and two Gram -ve) to assess their inhibiting potential. The assay indicated that the inhibition potential is metal ion dependent. The ligand, EDHDH, Co(II) and Cu(II) complexes exhibited a remarkable antibacterial activity against Streptococcus Pyogenes as Gram +ve and Proteus vulgaris as Gram -ve bacterial strains. On the other hand, Ni(II) complex revealed a moderate antibacterial activity against both Gram +ve organisms and no activity against Gram -ve bacterial strain.

Traveling Wave Modes of a Plane Layered Anelastic Earth

DTIC Science & Technology

2016-05-20

dependent anelastic moduli. The anelastic moduli must be frequency dependent and satisfy the Kramers- Kronig relations to preserve causality. The...the complex, frequency dependent moduli satisfy the Kramers- Kronig relations. Stable, well-behaved numerical algorithms exist for solving the complex

Errors due to the truncation of the computational domain in static three-dimensional electrical impedance tomography.

PubMed

Vauhkonen, P J; Vauhkonen, M; Kaipio, J P

2000-02-01

In electrical impedance tomography (EIT), an approximation for the internal resistivity distribution is computed based on the knowledge of the injected currents and measured voltages on the surface of the body. The currents spread out in three dimensions and therefore off-plane structures have a significant effect on the reconstructed images. A question arises: how far from the current carrying electrodes should the discretized model of the object be extended? If the model is truncated too near the electrodes, errors are produced in the reconstructed images. On the other hand if the model is extended very far from the electrodes the computational time may become too long in practice. In this paper the model truncation problem is studied with the extended finite element method. Forward solutions obtained using so-called infinite elements, long finite elements and separable long finite elements are compared to the correct solution. The effects of the truncation of the computational domain on the reconstructed images are also discussed and results from the three-dimensional (3D) sensitivity analysis are given. We show that if the finite element method with ordinary elements is used in static 3D EIT, the dimension of the problem can become fairly large if the errors associated with the domain truncation are to be avoided.

Non-invasive estimation of middle-ear input impedance and efficiency.

PubMed

Lewis, James D; Neely, Stephen T

2015-08-01

A method to transform the impedance measured in the ear canal, ZEC, to the plane of the eardrum, ZED, is described. The portion of the canal between the probe and eardrum was modeled as a concatenated series of conical segments, allowing for spatial variations in its cross-sectional area. A model of the middle ear (ME) and cochlea terminated the ear-canal model, which permitted estimation of ME efficiency. Acoustic measurements of ZEC were made at two probe locations in 15 normal-hearing subjects. ZEC was sensitive to measurement location, especially near frequencies of canal resonances and anti-resonances. Transforming ZEC to ZED reduced the influence of the canal, decreasing insertion-depth sensitivity of ZED between 1 and 12 kHz compared to ZEC. Absorbance, A, was less sensitive to probe placement than ZEC, but more sensitive than ZED above 5 kHz. ZED and A were similarly insensitive to probe placement between 1 and 5 kHz. The probe-placement sensitivity of ZED below 1 kHz was not reduced from that of either A or ZEC. ME efficiency had a bandpass shape with greatest efficiency between 1 and 4 kHz. Estimates of ZED and ME efficiency could extend the diagnostic capability of wideband-acoustic immittance measurements.

Reconfigurable Wideband Circularly Polarized Stacked Square Patch Antenna for Cognitive Radios

NASA Technical Reports Server (NTRS)

Barbosa Kortright, Miguel A.; Waldstein, Seth W.; Simons, Rainee N.

2017-01-01

An almost square patch, a square patch and a stacked square patch with corner truncation for circular polarization (CP) are researched and developed at X-band for cognitive radios. Experimental results indicate, first, that the impedance bandwidth of a CP almost square patch fed from the edge by a 50 ohm line is 1.70 percent and second, that of a CP square patch fed from the ground plane side by a surface launch connector is 1.87 percent. Third, the impedance bandwidth of a CP stacked square patch fed by a surface launch connector is 2.22 percent. The measured center frequency for the CP square patch fed by a surface launch connector without and with an identical stacked patch is 8.45 and 8.1017 GHz, respectively. By stacking a patch, separated by a fixed air gap of 0.254 mm, the center frequency is observed to shift by as much as 348.3 MHz. The shift in the center frequency can be exploited to reconfigure the operating frequency by mechanically increasing the air gap. The results indicate that a tuning bandwidth of about 100 MHz can be achieved when the distance of separation between the driven patch and the stacked patch is increased from its initial setting of 0.254 to 1.016 mm.

Reconfigurable Wideband Circularly Polarized Stacked Square Patch Antenna for Cognitive Radios

NASA Technical Reports Server (NTRS)

Barbosa Kortright, Miguel A.; Waldstein, Seth W.; Simons, Rainee N.

2017-01-01

An almost square patch, a square patch and a stacked square patch with corner truncation for circular polarization (CP) are researched and developed at X-band for cognitive radios. Experimental results indicate, first, that the impedance bandwidth of a CP almost square patch fed from the edge by a 50 ohm line is 1.70% and second, that of a CP square patch fed from the ground plane side by a surface launch connector is 1.87%. Third, the impedance bandwidth of a CP stacked square patch fed by a surface launch connector is 2.22%. The measured center frequency for the CP square patch fed by a surface launch connector without and with an identical stacked patch is 8.45 and 8.1017 GHz, respectively. By stacking a patch, separated by a fixed air gap of 0.254 mm, the center frequency is observed to shift by as much as 348.3 MHz. The shift in center frequency, brought about by the reconfiguring of the physical layer antenna, can be exploited in a cognitive system since it expands the usable frequency spectrum for software reconfiguration in the presence of interference. In addition, varying the fixed air gap in the stacked antenna geometry by increments of 0.254 mm further expands the usable frequency spectrum.

Ventilation and perfusion imaging by electrical impedance tomography: a comparison with radionuclide scanning.

PubMed

Kunst, P W; Vonk Noordegraaf, A; Hoekstra, O S; Postmus, P E; de Vries, P M

1998-11-01

Electrical impedance tomography (EIT) is a technique that makes it possible to measure ventilation and pulmonary perfusion in a volume that approximates to a 2D plane. The possibility of using EIT for measuring the left-right division of ventilation and perfusion was compared with that of radionuclide imaging. Following routine ventilation (81mKr) and perfusion scanning (99mTc-MAA), EIT measurements were performed at the third and the sixth intercostal level in 14 patients with lung cancer. A correlation (r = 0.98, p < 0.005) between the left-right division for the ventilation measured with EIT and that with 81mKr was found. For the left-right division of pulmonary perfusion a correlation of 0.95 (p < 0.005) was found between the two methods. The reliability coefficient (RC) was calculated for estimating the left-right division with EIT. The RC for the ventilation measurements was 94% and 96% for the perfusion measurements. The correlation analysis for reproducibility of the EIT measurements was 0.95 (p < 0.001) for the ventilation and 0.93 (p < 0.001) for the perfusion measurements. In conclusion, EIT can be regarded as a promising technique to estimate the left-right division of pulmonary perfusion and ventilation.

A Minimized MIMO-UWB Antenna with High Isolation and Triple Band-Notched Functions

NASA Astrophysics Data System (ADS)

Kong, Yuanyuan; Li, Yingsong; Yu, Kai

2016-11-01

A compact high isolation MIMO-UWB antenna with triple frequency rejection bands is proposed for UWB communication applications. The proposed MIMO-UWB antenna consists of two identical UWB antennas and each antenna element has a semicircle ring shaped radiation patch fed by a bend microstrip feeding line for covering the UWB band, which operates from 2.85 GHz to 11.79 GHz with an impedance bandwidth of 122.1 %. By etching a L-shaped slot on the ground plane, and embedding an "anchor" shaped stub into the patch and integrating an open ring under the semicircle shaped radiation patch, three notch bands are realized to suppress WiMAX (3.3-3.6 GHz), WLAN(5.725-5.825 GHz) and uplink of X-band satellite (7.9-8.4 GHz) signals. The high isolation with S21<-20 dB in most UWB band is obtained by adding a protruded decoupling structure. The design procedure of the MIMO-UWB antenna is given in detail. The proposed MIMO-UWB antenna is simulated, fabricated and measured. Experimental results demonstrate that the proposed MIMO-UWB antenna has a stable gain, good impedance match, high isolation, low envelope correlation coefficient and good radiation pattern at the UWB operating band and it can provide three designated notch bands.

The symmetry of man.

PubMed

Ermolenko, Alexander E; Perepada, Elena A

2007-01-01

The paper contains a description of basic regularities in the manifestation of symmetry of human structural organization and its ontogenetic and phylogenetic development. A concept of macrobiocrystalloid with inherent complex symmetry is proposed for the description of the human organism in its integrity. The symmetry can be characterized as two-plane radial (quadrilateral), where the planar symmetry is predominant while the layout of organs of radial symmetry is subordinated to it. Out of the two planes of symmetry (sagittal and horizontal), the sagittal plane is predominant. The symmetry of the chromosome, of the embrio at the early stages of cell cleavage as well as of some organs and systems in their phylogenetic development is described. An hypothesis is postulated that the two-plane symmetry is formed by two mechanisms: a) the impact of morphogenetic fields of the whole crystalloid organism during embriogenesis and, b) genetic mechanisms of the development of chromosomes having two-plane symmetry.

Improving Reading and Social Studies Learning for Secondary Students with Reading Disabilities

ERIC Educational Resources Information Center

Capin, Philip; Vaughn, Sharon

2017-01-01

Significant numbers of adolescents and young adults do not adequately understand complex texts, impeding their school success, access to postsecondary learning, and opportunities within an increasingly competitive work environment. National data (National Assessment of Educational Progress [NAEP], 2015) have shown improvements among fourth- and…