Initial Transients Research Articles

Calibrating spectral estimation for the LISA Technology Package with multichannel synthetic noise generation

The scientific objectives of the Lisa Technology Package (LTP) experiment, on board of the LISA Pathfinder mission, demand for an accurate calibration and validation of the data analysis tools in advance of the mission launch. The levels of confidence required on the mission outcomes can be reached only with an intense activity on synthetically generated data. A flexible procedure allowing the generation of cross-correlated stationary noise time series was set-up. Multi-channel time series with the desired cross correlation behavior can be generated once a model for a multichannel cross-spectral matrix is provided. The core of the procedure is the synthesis of a noise coloring multichannel filter through a frequency-by-frequency eigendecomposition of the model cross-spectral matrix and a Z-domain fit. The common problem of initial transients in noise time series is solved with a proper initialization of the filter recursive equations. The noise generator performances were tested in a two dimensional case study of the LTP dynamics along the two principal channels of the sensing interferometer.

A two-liquid electroosmotic pump using low applied voltage and power

We report the development and experimental analysis of a two-liquid electroosmotic (EO) pump. The pump uses a collapsible and impermeable membrane to separate the liquid delivered from a working electrolyte solution optimized for EO pumping. To achieve high pressures at low voltages, we use a porous glass substrate with 450 nm mean diameter pores and a 1 mM sodium borate electrolyte. Results show that the membranes add negligible pressure load and that the pump can deliver adequately stable flow rates after an initial transient period. At flow rates and pressures suitable for drug delivery (order 10 μl/min and a few kPa), the pump requires an applied voltage and power of less than 3 V and 75 μW, respectively. Based on the relative scaling of flow rate, current, and time, we hypothesize that distinct initial transients in flow rate are attributable to concentration polarization and its effects on the spatiotemporal ionic strength of the working fluid.

Microwave Power Enhancement in the Simulation of a Resonant Coaxial Vircator

Cavity resonance effect is a useful concept in beam-wave interaction for enhancing the conversion efficiency. It is shown that an interplay between the growth of field energy inside the cavity and its extraction can be used judiciously to extract a larger power after the initial transients. Cavity parameters in a coaxial virtual-cathode oscillator have thus been optimized to allow field energy inside the cavity to grow initially. This growth is limited by the energy that leaves the cavity through the extraction region so that the field strength inside the cavity saturates optimally at a maximum value. The energy lost by the beam to the field can then be directly extracted at a high conversion efficiency. The peak cycle-averaged power efficiency obtained thus in particle-in-cell simulation exceeds 9%, while the efficiency over several cycles is found to be 7.5%.

The determination of activity of the enzyme Rubisco in cell extracts of the dinoflagellate alga Symbiodinium sp. by manganese chemiluminescence and its response to short‐term thermal stress of the alga

The dinoflagellate alga Symbiodinium sp., living in symbiosis with corals, clams and other invertebrates, is a primary producer in coral reefs and other marine ecosystems. The function of the carbon-fixing enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) in dinoflagellates is difficult to study because its activity is rapidly lost after extraction from the cell. We report procedures for the extraction of Rubisco from Symbiodinium cells and for stable storage. We describe a continuous assay for Rubisco activity in these crude cell extracts using the Mn(2+) chemiluminescence of Rubisco oxygenase. Chemiluminescence time courses exhibited initial transients resembling bacterial Form II Rubisco, followed by several minutes of linearly decreasing activity. The initial activity was determined from extrapolation of this linear section of the time course. The activity of fast-frozen cell extracts was stable at -80 degrees C and, after thawing and storage on ice, remained stable for up to 1 h before declining non-linearly. Crude cell extracts bound [(14)C] 2-carboxy-D-arabitinol 1,5-bisphosphate to a high molecular mass fraction separable by gel filtration chromatography. After pre-treatment of Symbiodinium cell cultures in darkness at temperatures above 30 degrees C, the extracted Rubisco activities decreased, with almost complete loss of activity above 36 degrees C. The implications for the sensitivity to elevated temperature of Symbiodinium photosynthesis are assessed.

Masking interrupts figure-ground signals in V1

In a backward masking paradigm, a target stimulus is rapidly (<100 msec) followed by a second stimulus. This typically results in a dramatic decrease in the visibility of the target stimulus. It has been shown that masking reduces responses in V1. It is not known, however, which process in V1 is affected by the mask. In the past, we have shown that in V1, modulations of neural activity that are specifically related to figure–ground segregation can be recorded. Here, we recorded from awake macaque monkeys, engaged in a task where they had to detect figures from background in a pattern backward masking paradigm. We show that the V1 figure–ground signals are selectively and fully suppressed at target–mask intervals that psychophysically result in the target being invisible. Initial response transients, signalling the features that make up the scene, are not affected. As figure–ground modulations depend on feedback from extrastriate areas, these results suggest that masking selectively interrupts the recurrent interactions between V1 and higher visual areas.

On the temporal response of active load control devices

AbstractFlow around airfoils with deploying microtabs and microflaps (or dynamic Gurney flap) have been numerically simulated by solving the unsteady turbulent compressible 2‐D Navier‐Stokes equations with the OVERFLOW 2 solver. Microtabs and microflaps on the order of 1%c were installed in the trailing edge region of the symmetric NACA 0012 airfoil using a Chimera or overset grid topology. The devices were deployed on the order of one characteristic time unit, and the unsteady aerodynamic responses of both devices were compared. The two devices appear to affect the flow similarly by creating a low pressure region aft of the device and changing the Kutta condition. While initial transients varied, the post‐deployment aerodynamic response showed a very similar temporal evolution towards a mean asymptotic solution. Both devices reached 90% of mean steady‐state lift values by approximately nine characteristic time units from the onset of deployment. Drag and pitching moments evolved significantly faster. The temporal development of these devices is not governed by near‐body effects, and instead is an advection driven process. Microflap deployment times of 0.25, 0.50 and 1.00 characteristic time units were also examined. The corresponding mean aerodynamic coefficients for the three deployment times were comparable by one characteristic time unit after deployment. Validation studies with experimental results comparing shedding frequencies and Strouhal numbers for static, deployed microtabs and microflaps were also performed to ensure accurate temporal resolution and convergence of the numerical simulations. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Stretching and twisting of the DNA duplexes in coarse-grained dynamical models

Three coarse-grained molecular dynamics models of the double-stranded DNA are proposedand compared in the context of single molecule mechanical manipulation such as twistingand various schemes of stretching—unzipping, shearing, two-strand stretching andstretching of only one strand. The models differ in the number of effective beads (betweentwo and five) representing each nucleotide. They all show similar behaviour, but the biggerthe resolution, the more details in the force patterns. The models incorporate the effectiveLennard-Jones potentials in the couplings between two strands and harmonicpotentials to describe the structure of a single strand. The force patterns are shown todepend on the sequence studied. In particular, both shearing and unzipping for anall-AT sequence lead to lower forces than for an all-CG sequence. The unzippingpatterns and the corresponding scenario diagrams for the contact rupture eventsare found to reflect the sequential information if the temperature is moderateand initial transients are discarded. The derived torque–force phase diagram isfound to be qualitatively consistent with experiments and all-atom simulations.

Absolute stability mechanism of a swept cylinder laminar boundary layer with imposed spanwise periodic conditions

The linear impulse response of a laminar three-dimensional boundary layer with imposed spanwise periodic conditions is theoretically analyzed. Because of the imposed spanwise periodicity, a unidirectional absolute instability is physically significant. The base flow is obtained through a direct numerical simulation of the flow along a swept cylinder, with periodic boundary conditions enforced at the spanwise boundaries. It is shown that this flow is absolutely stable. However, it exhibits crossflow modes of zero group velocity whose damping rate in time is quite slow. Moreover, these crossflow modes are spatially amplified. A direct numerical simulation of the same configuration but in the presence of surface roughness has enabled the observation of these traveling crossflow waves. The introduction of the roughness element in the computation creates initial transients that play the role of an impulselike forcing, which generates the traveling crossflow waves as predicted by the theoretical analysis. Depending on the roughness chordwise location, the frequency and damping rate in time of the crossflow waves change in agreement with the theoretical results.

Role of Phosphorylation and Basic Residues in the Catalytic Domain of Cytosolic Phospholipase A2α in Regulating Interfacial Kinetics and Binding and Cellular Function

Group IVA cytosolic phospholipase A(2) (cPLA(2)alpha) is regulated by phosphorylation and calcium-induced translocation to membranes. Immortalized mouse lung fibroblasts lacking endogenous cPLA(2)alpha (IMLF(-/-)) were reconstituted with wild type and cPLA(2)alpha mutants to investigate how calcium, phosphorylation, and the putative phosphatidylinositol 4,5-bisphosphate (PIP(2)) binding site regulate translocation and arachidonic acid (AA) release. Agonists that elicit distinct modes of calcium mobilization were used. Serum induced cPLA(2)alpha translocation to Golgi within seconds that temporally paralleled the initial calcium transient. However, the subsequent influx of extracellular calcium was essential for stable binding of cPLA(2)alpha to Golgi and AA release. In contrast, phorbol 12-myristate 13-acetate induced low amplitude calcium oscillations, slower translocation of cPLA(2)alpha to Golgi, and much less AA release, which were blocked by chelating extracellular calcium. AA release from IMLF(-/-) expressing phosphorylation site (S505A) and PIP(2) binding site (K488N/K543N/K544N) mutants was partially reduced compared with cells expressing wild type cPLA(2)alpha, but calcium-induced translocation was not impaired. Consistent with these results, Ser-505 phosphorylation did not change the calcium requirement for interfacial binding and catalysis in vitro but increased activity by 2-fold. Mutations in basic residues in the catalytic domain of cPLA(2)alpha reduced activation by PIP(2) but did not affect the concentration of calcium required for interfacial binding or phospholipid hydrolysis. The results demonstrate that Ser-505 phosphorylation and basic residues in the catalytic domain principally act to regulate cPLA(2)alpha hydrolytic activity.

Effects of pretreatment on the aluminium etch pit formation

The effect of chemical pretreatments on the electrochemical etching behavior of aluminium was investigated with the topographic studies of surface and the analysis of initial potential transients. Two-step pretreatments with H 3PO 4 and H 2SiF 6 result in a high density of pre-etch pits on aluminium surface by the incorporation of phosphate ion inside the oxide film and the removal of surface layer by aggressive fluorosilicic acid solution. It generates a high density of etch pits during electrochemical etching and results in the capacitance increase of etched Al electrode by expanding the surface area, up to 61.3 μF/cm 2 with the pretreatment solution of 0.5 M H 3PO 4 at 65 °C and 10 mM H 2SiF 6 at 45 °C.

Fenton's oxidation of pentachlorophenol

The combination of H 2O 2 and Fe(II) (Fenton's reaction) has been demonstrated to rapidly degrade many organics via hydroxyl radicals. However, few studies have related hydroxyl radical generation rates with measured organic chemical degradation data. The goals of this work were to investigate the kinetics, stoichiometry, and intermediates of pentachlorophenol (PCP) degradation in the Fenton's reaction and to develop a mathematical model of this reaction system. Batch reaction experiments were performed to assess both initial transients and steady states, and special attention was given to the analysis of intermediates. Solutions of PCP (55 μM) and Fe(II) (200 μM) were treated with variable levels of H 2O 2 (<850 μM), and the concentrations of these reactants and their products were measured. Partial PCP degradation and near stoichiometric dechlorination were observed at low initial H 2O 2 concentrations. Higher H 2O 2 doses achieved at most 70% dechlorination even though nearly all of the PCP was degraded. The reaction intermediates tetrachlorohydroquinone and dichloromaleic acid accounted for up to 5% of the PCP degraded. Organic carbon mineralization (transformation to CO 2) was not observed. The OH scavenging effects of the PCP-by-products mixture were characterized as a lumped parameter in the reaction kinetics model, which provided reasonable predictions of experimental results at different oxidant concentrations and reaction time.

Nonparametric Preprocessing in System Identification: a Powerful Tool

In this paper we study the properties of existing non-parametric methods for estimating the plant and noise transfer functions of a linear dynamic system. The analysis is based on the recent insight that leakage errors in the frequency domain have a smooth nature that is completely similar to the initial transients in the time domain. This not only allows us to understand better the existing classic methods, but also opens the road to new better performing algorithms. The paper includes the output error setup, the errors-in-variables setup, and measurements under feedback conditions. Eventually, some of the methods are illustrated in the analysis of a vibrating metal beam.

Acoustic holography of musical instruments using radiation directivity method.

Static and time-dependent acoustic holography is applied to the radiation of musical instruments using the acoustic camera developed at the Institute of Musicology consisting of 128 microphones simultaneously recording at a 48-kHz sample rate. Here a radiation directivity method was developed suiting the great amount of microphones as well as the high sampling frequency. It uses not only the radiation strength but also the radiation directivity pattern of 128 points on the geometry as a dependent variable. This does not only allow for a precise reconstruction of the vibration of the instruments but also results in a detailed description of the radiation directivity for the overall geometry or for each radiating point individually. Furthermore the time-dependent reconstruction avoids any temporal integration and reconstructs the vibration of the geometry with the samplerate precision. With this method the different role and strength instrument parts have in the overall body radiation, scattering effects caused by geometrical inhomogeneities, and time-dependent initial transients reconstructed as radiation patterns were investigated. The material as well as the air parts of the instrument are considered simultaneously, i.e., with guitars or violins, the enclosed air radiating through the sound holes is investigated in relation to the surrounding plates.

Superfluid spherical Couette flow

We solve numerically for the first time the two-fluid Hall–Vinen–Bekarevich–Khalatnikov (HVBK) equations for an He-II-like superfluid contained in a differentially rotating spherical shell, generalizing previous simulations of viscous spherical Couette flow (SCF) and superfluid Taylor–Couette flow. The simulations are conducted for Reynolds numbers in the range 1 × 102≤Re≤3 × 104, rotational shear 0.1≤ΔΩ/Ω≤0.3, and dimensionless gap widths 0.2≤δ≤0.5. The system tends towards a stationary but unsteady state, where the torque oscillates persistently, with amplitude and period determined by δ and ΔΩ/Ω. In axisymmetric superfluid SCF, the number of meridional circulation cells multiplies as Re increases, and their shapes become more complex, especially in the superfluid component, with multiple secondary cells arising for Re &gt; 103. The torque exerted by the normal component is approximately three times greater in a superfluid with anisotropic Hall–Vinen (HV) mutual friction than in a classical viscous fluid or a superfluid with isotropic Gorter–Mellink (GM) mutual friction. HV mutual friction also tends to ‘pinch’ meridional circulation cells more than GM mutual friction. The boundary condition on the superfluid component, whether no slip or perfect slip, does not affect the large-scale structure of the flow appreciably, but it does alter the cores of the circulation cells, especially at lower Re. As Re increases, and after initial transients die away, the mutual friction force dominates the vortex tension, and the streamlines of the superfluid and normal fluid components increasingly resemble each other. In non-axisymmetric superfluid SCF, three-dimensional vortex structures are classified according to topological invariants. For misaligned spheres, the flow is focal throughout most of its volume, except for thread-like zones where it is strain-dominated near the equator (inviscid component) and poles (viscous component). A wedge-shaped isosurface of vorticity rotates around the equator at roughly the rotation period. For a freely precessing outer sphere, the flow is equally strain- and vorticity-dominated throughout its volume. Unstable focus/contracting points are slightly more common than stable node/saddle/saddle points in the viscous component, but not in the inviscid component. Isosurfaces of positive and negative vorticity form interlocking poloidal ribbons (viscous component) or toroidal tongues (inviscid component) which attach and detach at roughly the rotation period.

Fluid and Thermal Dynamics of Cryogen Sprays Impinging on a Human Tissue Phantom

Cryogen spray cooling (CSC) protects the epidermis from unintended heating during cutaneous laser surgery. The present work investigated the time-dependent flow characteristics of cryogen sprays and correspondent thermal dynamics at the surface of a human tissue phantom. First, a numerical analysis was carried out to evaluate an epoxy block substrate as a human tissue phantom. Next, the velocity and diameter of cryogen droplets were measured simultaneously and correlated with surface temperature of the human tissue phantom during CSC. Finally, velocity and diameter measurements were used to compute the spray number, mass, and kinetic energy fluxes, and temperature measurements were used to compute the surface heat flux. Numerical modeling showed that the thermal response of our phantom was qualitatively similar to that of human stratum corneum and epidermis; quantitatively, thermal responses differed. A simple transformation to map the temperature response of the phantom to that of tissue was derived. Despite the relatively short spurt durations (10 ms, 30 ms, and 50 ms), cryogen delivery is mostly a steady state process with initial and final fluid transients mainly due to the valve dynamics. Thermal transients (16 ms) are longer than fluid transients (4 ms) due to the low thermal diffusivity of human tissues; steady states are comparable in duration ( approximately 10 ms, 30 ms, and 50 ms) although there is an inherent thermal delay ( approximately 12 ms). Steady state temperatures are the lowest surface temperatures experienced by the substrate, independent of spurt duration; hence, longer spurt durations result in larger exposures of the tissue surface to the same lower, steady state temperature as in shorter spurts. Temperatures in human tissue during CSC for the spray system and parameters used herein are estimated to be approximately -19 degrees C at the stratum corneum surface and >0 degrees C across the epidermis.

Frequency and phase characteristics of the edge tone

Extensive experimental and computational work was performed to characterize the edge tone phenomenon. The dependence of the oscillating frequency on some of the main parameters of the configuration including the nozzle‐wedge distance and the profile and the mean velocity of the jet was measured. The frequency was obtained from the FFT of a pressure sensor signal. The measured and computed frequencies are compared and show a very good agreement. For both the CFD simulations and the experiments the phase of the oscillation and the pressure at specified points on the wedge are correlated. For the experiments the phase of the flow oscillation is determined with the help of flow visualization pictures obtained by a high speed digital camera. From the CFD results spatial distribution of acoustical sources are also observed and correlated with pressure distribution on the wedge and with the phase of the oscillating flow. Some aspects of the initial transients are also presented.

DWT-Based Detection and Transient Power Direction-Based Location of High-Impedance Faults Due to Leaning Trees in Unearthed MV Networks

Electrical faults due to leaning trees are common in Nordic countries. This fault type has been studied in and it was found that the initial transients in the electrical network due to the associated arc reignitions are behavioral traits. In this paper, these features are extracted using the discrete wavelet transform (DWT) to localize this fault event. Wireless sensors are considered for processing the DWTs on a residual voltage of different measuring nodes that are distributed in the network. Therefore, the fault detection is confirmed by numerous DWT processors over a wide area of the network. The detection security is also enhanced because the DWT responded to a periodicity of the initial transients. The term for locating the faulty section is based on the polarity of a specific frequency bandpower computed by multiplying the DWT detail coefficient of the residual current and voltage at each measuring node. The fault due to a leaning tree occurring at different locations in an unearthed 20-kV network is simulated by the alternate transients program/electromagnetic transients program and the arc model is implemented using the universal arc representation. Test cases provide evidence of the efficacy of the proposed technique.

Characteristics of the Transition from Grain-Boundary Sliding to Solute Drag Creep in Superplastic AA5083

Superplastic tensile ductility has been attained when specially-processed AA5083 materials are strained in tension at relatively high strain rates, in the range of the transition from grain-boundary sliding (GBS) to solute drag creep (SDC) control of deformation. Quick plastic forming (QPF) technology involves deformation at such strain rates, and the relative contributions of GBS and SDC to the strain during deformation in this strain rate regime have been examined in this investigation. The additive, independent contributions of GBS and SDC to the elevated temperature deformation of fine-grained materials are reviewed. The transition from GBS to SDC in grain-refined AA5083 materials was evaluated by several methods, including the assessment of initial transients during straining and of transients during strain-rate change tests; the strain-rate dependence of the flow stress; the dependence of ductility on strain rate; flow localization behavior and fracture mode; cavitation growth; the evolution of microstructure and microtexture during deformation; and comparison with phenomenological models for the GBS-to-SDC transition.

Reproducible Te-doped InSb experiments in Microgravity Science Glovebox at the International Space Station

Four Te-doped InSb crystals were directionally solidified under microgravity conditions at the International Space Station (ISS). Three Te-doped InSb crystals were grown at R=5 mm/h. One crystal was grown at R=3.33 mm/h. The distribution of Te was measured using secondary ion mass spectroscopy (SIMS). The initial transients in Te concentration were found to be consistent, yielding a diffusivity of Te in InSb melts of D=1×10 −5 cm 2/s. One experiment revealed a diffusion controlled final transient. In all experiments, the charge was pressurized by a piston and spring device, to prevent de-wetting.

Electrolyte effects on charge, polarization, and conduction in thin anodic Al2O3 films. I. Initial charge and temperature-dependent polarization

A sequence of three current-voltage (I-V) curves of Al–Al2O3–Au capacitors has been used to study the effect of anodizing electrolyte on Qin, the initial charge introduced into Al2O3 during anodization and the temperature dependence of polarization of anodic Al2O3. The first I-V curve, with VA&amp;lt;0V, polarizes the Al2O3 film; the difference between the next two I-V curves is a measure of polarization induced by the negative voltage. Two aqueous electrolytes, 0.1M ammonium pentaborate (bor-H2O) and 0.1M ammonium citrate (citrate), and one nonaqueous electrolyte, 0.1M ammonium pentaborate per liter of ethylene glycol (bor-gly), are used for anodizing; Al2O3 thicknesses are between 12 and 54nm. The galvanostatic anodizing rate is the same for anodizing in bor-H2O and bor-gly electrolytes after initial transients. The anodizing rate in citrate electrolyte is constant but is 0.7 times the rate in the other two electrolytes. Qin for Al2O3 films formed in bor-H2O and bor-gly is proportional to Al2O3 thickness; it is distributed throughout the film. The magnitude of Qin is ∼100 times greater for Al2O3 films formed in the aqueous electrolyte. Qin for Al2O3 films formed in citrate is nearly constant with thickness. Qin anneals out when I-V curves are measured. Two quantities are measured that depend on polarization of anodic Al2O3, QPK, and Qmax. QPK is due solely to polarization produced by negative bias. Both polarization and conduction currents contribute to Qmax. Both QPK and Qmax depend exponentially on the polarizing field. Maximum values of QPK for samples anodized in bor-H2O or citrate are ∼13 times larger than for Al2O3 formed in bor-gly; maximum values of Qmax are more than 100 times larger for anodic Al2O3 formed in aqueous electrolytes. The temperature dependence of Qmax is also less for Al2O3 films formed in bor-gly than for Al2O3 formed in bor-H2O or citrate.