Change In Phase Shift Research Articles

The Vertical Structure of Low-Frequency Motions in the Nearshore. Part II: Theory

AbstractField observations from a vertical stack of two-component current meters obtained from the 1994 Duck94 nearshore field experiment (presented in a companion paper by Lippmann, et al.) show significant vertical structure in energy, phase, and rotation of motions at low frequencies around 0.005 Hz. Low-frequency motions are typically modeled in the surfzone with the shallow-water (depth averaged) momentum equations that do not allow for any vertical structure. Following work from the shelf tidal community (Prandle), this study shows that the observations are consistent with the depth-varying momentum equations including shear stresses induced by a bottom boundary layer described by a constant eddy viscosity νt and bottom friction given by a constant drag coefficient and depth-averaged velocity . The bidirectional flow field is solved over arbitrary depth profiles varying only in the cross-shore direction h(x) in the presence of a vertically uniform mean alongshore current with cross-shore shear structure V(x). Analytic solutions are found to depend on νt, cd, h, ∂V/∂x, and the parameter , where σ and k are the radian frequency and alongshore wavenumber of the oscillating motion. Model behavior is explored by plotting solutions for a given parameter space as functions of the nondimensional depth H = λh and dimensionless friction parameter that combines the effects of bottom drag and vertical mixing. The behavioral changes in amplitude, phase shift, and rotational structure over the water column are qualitatively similar to those observed in the field.

Performance of an adjustable, threaded inertance tube

The performance of the Stirling type pulse tube cryocooler depends strongly on the design of the inertance tube. The phase angle produced by the inertance tube is very sensitive to its diameter and length. Recent developments are reported here regarding an adjustable inertance device that can be adjusted in real time. The inertance passage is formed by the root of a concentric cylindrical threaded device. The depth of the threads installed on the outer screw varies. In this device, the outer screw can be rotated four and half turns. At the zero turn position the length of the passage is 1.74 m and the hydraulic diameter is 7 mm. By rotating the outer screw, the inner threaded rod engages with additional, larger depth threads. Therefore, at its upper limit of rotation, the inertance passage includes both the original 1.74 m length with 7mm hydraulic diameter plus an additional 1.86 m length with a 10 mm hydraulic diameter. A phase shift change of 24° has been experimentally measured by changing the position of outer screw while operating the device at a frequency of 60 Hz. This phase angle shift is less than the theoretically predicted value due to the presence of a relatively large leak through the thread clearance. Therefore, the distributed component model of the inertance tube was modified to account for the leak path causing the data to agree with the model. Further, the application of vacuum grease to the threads causes the performance of the device to improve substantially.

Bioreactance is a reliable method for estimating cardiac output at rest and during exercise

Bioreactance is a novel noninvasive method for cardiac output measurement that involves analysis of blood flow-dependent changes in phase shifts of electrical currents applied across the thorax. The present study evaluated the test-retest reliability of bioreactance for assessing haemodynamic variables at rest and during exercise. 22 healthy subjects (26 (4) yrs) performed an incremental cycle ergometer exercise protocol relative to their individual power output at maximal O2 consumption (Wmax) on two separate occasions (trials 1 and 2). Participants cycled for five 3 min stages at 20, 40, 60, 80 and 90% Wmax. Haemodynamic and cardiorespiratory variables were assessed at rest and continuously during the exercise protocol. Cardiac output was not significantly different between trials at rest (P=0.948), or between trials at any stage of the exercise protocol (all P>0.30). There was a strong relationship between cardiac output estimates between the trials (ICC=0.95, P<0.001) and oxygen consumption (ICC=0.99, P<0.001). Stroke volume was also not significantly different between trials at rest (P=0.989) or during exercise (all P>0.15), and strong relationships between trials were found (ICC=0.83, P<0.001). The bioreactance method demonstrates good test-retest reliability for estimating cardiac output at rest and during different stages of graded exercise testing including maximal exertion.

Influence of rubbing-alignment on microwave modulation induced by liquid crystal

The microwave modulation induced by liquid crystal is decided by the liquid crystal director distribution under an external applied voltage. The rubbing-alignment of substrate has an effect on the liquid crystal director, which must result in the change of microwave phase-shift. To illustrate the influence of rubbing-alignment on the microwave phase-shift, the microwave modulation property of twisted nematic liquid crystal is researched adopting the elastic theory of liquid crystal and the finite-difference iterative method. The variations of microwave phase-shift per unit-length for different pre-tilt and pre-twist angles of liquid crystal on the substrate surface and anchoring energy strengths with the applied voltage are numerically simulated. The result indicates that with the increase of pre-tilt angle and with the decrease of anchoring energy strength the weak anchoring twisted cell with pre-twisted angle 90° relative to the strong anchoring non-twisted cell can increase the microwave phase-shift per unit-length. As a result, for achieving the maximum microwave modulation, the weak anchoring twisted cell with pre-tilt angle 5° and anchoring energy strength 1×10−5J/m2 should be selected, which provides a reliably theoretical foundation for the design of liquid crystal microwave modulator.

Detection of cerebral hemorrhage in rabbits by time-difference magnetic inductive phase shift spectroscopy.

Cerebral hemorrhage, a difficult issue in clinical practice, is often detected and studied with computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET). However, these expensive devices are not readily available in economically underdeveloped regions, and hence are unable to provide bedside and emergency on-site monitoring. The magnetic inductive phase shift (MIPS) is an emerging technology that may become a new tool to detect cerebral hemorrhage and to serve as an inexpensive partial substitute to medical imaging. In order to study a wider band of cerebral hemorrhage MIPS and to provide more useful information for measuring cerebral hemorrhage, we established a cerebral hemorrhage magnetic induction phase shift spectroscopy (MIPSS) detection system. Thirteen rabbits with five cerebral hemorrhage states were studied using a single coil-coil within a 1 MHz-200 MHz frequency range in linear sweep. A feature band (FB) with the highest detection sensitivity and the greatest stability was selected for further analysis and processing. In addition, a maximum conductivity cerebrospinal fluid (CSF) MRI was performed to verify and interpret the MIPSS result. The average phase shift change induced by a 3 ml injection of autologous blood under FB was -7.7503° ± 1.4204°, which was considerably larger than our previous work. Data analysis with a non-parametric statistical Friedman M test showed that in the FB, MIPSS could distinguish the five states of cerebral hemorrhage in rabbits, with a statistical significance of p<0.05. A B-F distribution profile was designed according to the MIPSS under FB that can provide instantaneous diagnostic information about the cerebral hemorrhage severity from a single set of measurements. The results illustrate that the MIPSS detection method is able to provide a new possibility for real-time monitoring and diagnosis of the severity of cerebral hemorrhage.

Effect of magnetic spins flipping process on the dielectric properties of α-Fe1.6Ga0.4O3 system

The α-Fe1.6Ga0.4O3 (Ga doped α-Fe2O3) sample has been stabilized in rhombohedral structure. The sample is a canted ferromagnet at 300 K and above. The spins structure starts flipping from in-plane direction to out of plane direction of the rhombohedral structure to exhibit an antiferromagnetic order below a typical temperature ∼ 215 K, known as Morin transition. The magnetic and dielectric properties of α-Fe1.6Ga0.4O3 system have been discussed in the temperature range 123 K to 350 K to examine the effect of magnetic spins flipping process on dielectric properties. The dielectric constant has shown an anomalous peak at ∼ 310 K, followed by a rapidly decrease of dielectric constant with temperature and becomes weakly temperature dependent below Morin transition. The temperature dependent dielectric constant is accompanied with the changes in electrical conductivity, dielectric loss and phase shift of the current with respect to applied ac voltage across the material. The magnetization and dielectric constant showed a linear relation over a wide range of temperature across the Morin transition. The dielectric constant at room temperature decreases under magnetic field, which indicates magneto-dielectric effect in the system. The signature of magneto-dielectric effect reveals a coupling between spins degrees of freedom (magnetic order) and charge degrees of freedom (electric polarization) in corundum structured non-traditional ferroelectric systems.

Optical Measurements by Phase Shift Based Technique for High Sensitivity and High Resolution Detection of Chemical/Biological Substances

In this work we demonstrate that the phase shift detection technique can be applied to reveal, with very high sensitivity and resolution, concentrations of chemical/biological substances optically detectable by measuring power variations of a light source. The system is based on the synchronous demodulation technique and employs a Si photodiode (PD) operating in photovoltaic regime biased through a small modulating sinusoidal waveform. The phase shift variations are measured between this biasing voltage and that one generated by the Si PD illuminated by the light, that interacts with the chemical/biological sample under analysis, providing the phase shift change. Experimental results demonstrate that is possible to achieve phase detection sensitivity, with respect to light power variations, up to 3100°/μW as a function of the Si PD settable operating conditions. By using a commercial lock-in amplifier with a 0.01° phase resolution, a light power variation resolution of about 3pW has been achieved. As a case-example, variations of the molar concentration of a methylene blue solution are detected by performing optical absorption standard measurements. Despite the phase resolution limitation of the used lock-in amplifier, the comparison between the data obtained through the proposed technique and those ones achieved by conventional amplitude measurements demonstrates a high improvement of the detection sensitivity. As a consequence, the measurement of molar concentration variations with a resolution of 80pM is achieved resulting 33 times higher than that one obtained with the amplitude detection.

The effectiveness of melatonin for promoting healthy sleep: a rapid evidence assessment of the literature.

A systematic review was conducted using Samueli Institute’s Rapid Evidence Assessment of the Literature (REAL©) process to determine the evidence base for melatonin as an agent to optimize sleep or improve sleep quality, and generalize the results to a military, civilian, or other healthy, active, adult population. Multiple databases were searched yielding 35 randomized controlled trials (RCTs) meeting the review’s inclusion criteria, which were assessed for methodological quality as well as for melatonin effectiveness. The majority of included studies were high quality (83.0%). Overall, according to Grading Recommendations, Assessment Development and Evaluation (GRADE) methodology, weak recommendations were made for preventing phase shifts from jet lag, for improving insomnia in both healthy volunteers and individuals with a history of insomnia, and for initiating sleep and/or improving sleep efficacy. Based on the literature to date, no recommendations for use in shift workers or to improve hormonal phase shift changes in healthy people can be made at this time. Larger and longer-duration RCTs utilizing well characterized products are needed to warrant melatonin recommendations in young, healthy adults.

PHOTOVOLTAIC BASED BALANCING LOAD DISTRIBUTION FEEDERS USING LOOP POWER CONTROLLERS

Balancing load of distribution feeders is significant for falling of power loss and mitigating power flow. As the loop power controller is implanting for the active power and reactive power flows by change in voltage ratio and phase shift. So that the balancing of the load distribution feeders can be achieved. However it can include photovoltaic power producing in feeder balancing load, as a Taipower distribution feeder consisting of two feeders with large amount of photovoltaic equipment considered. The balancing load can be determine in distribution feeders with photovoltaic set up by using the loop power controllers as the changing of solar energy and power loading of feeders. With implanting the control algorithm in MATLAB for loop power controller by changing the voltage ratio and phase shift connecting to the feeder the proper amount of active power and reactive power can be change from the heavily loading feeder to the lightly loading feeder. When system power loss decreases, Photovoltaic balancing the load for loop power controller has been investigated.

The tropicalization of temperate marine ecosystems: climate-mediated changes in herbivory and community phase shifts.

Climate-driven changes in biotic interactions can profoundly alter ecological communities, particularly when they impact foundation species. In marine systems, changes in herbivory and the consequent loss of dominant habitat forming species can result in dramatic community phase shifts, such as from coral to macroalgal dominance when tropical fish herbivory decreases, and from algal forests to 'barrens' when temperate urchin grazing increases. Here, we propose a novel phase-shift away from macroalgal dominance caused by tropical herbivores extending their range into temperate regions. We argue that this phase shift is facilitated by poleward-flowing boundary currents that are creating ocean warming hotspots around the globe, enabling the range expansion of tropical species and increasing their grazing rates in temperate areas. Overgrazing of temperate macroalgae by tropical herbivorous fishes has already occurred in Japan and the Mediterranean. Emerging evidence suggests similar phenomena are occurring in other temperate regions, with increasing occurrence of tropical fishes on temperate reefs.

Modeling the interaction of microbubbles: Effects of proximity, confinement, and excitation amplitude

The interaction of closely spaced microbubbles (MBs) exposed to a transient external pressure field is relevant for a variety of industrial and medical applications. We present a computational framework employing an interface tracking approach to model the transient dynamics of multiple, interacting, insonated MBs in arbitrary settings. In particular, this technique allows studying the effects of mutual proximity, confinement, and variations in excitation amplitude on the translatory motion of pairs of differently sized MBs. Domains of mutual repulsion or attraction are observed for closely spaced MBs in the investigated range of excitation frequencies. The repulsion domain widens and shifts to lower frequencies with increasing excitation pressure amplitude. When the MBs are confined in rigid tubes of decreasing diameters, we observe a shift of the translatory patterns towards lower frequencies, accompanied by a change in relative strength of the two translation modes. This effect is correlated to a decrease of the resonance frequency due to confinement which causes changes in oscillation amplitude and phase shift between the bubble vibrations. Coupling to the viscous host liquid gives rise to phenomena such as collective MB drift, non-symmetric attraction or repulsion, and reversal of translation direction. A system comprising six MBs inside a narrow tube highlights the potential of the computational framework to treat complex setups with multiple bubbles.

Multi-parametric monitoring and assessment of high-intensity focused ultrasound (HIFU) boiling by harmonic motion imaging for focused ultrasound (HMIFU): an ex vivo feasibility study

Harmonic motion imaging for focused ultrasound (HMIFU) is a recently developed high-intensity focused ultrasound (HIFU) treatment monitoring method with feasibilities demonstrated in vitro and in vivo. Here, a multi-parametric study is performed to investigate both elastic and acoustics-independent viscoelastic tissue changes using the Harmonic Motion Imaging (HMI) displacement, axial compressive strain and change in relative phase shift during high energy HIFU treatment with tissue boiling. Forty three (n = 43) thermal lesions were formed in ex vivo canine liver specimens (n = 28). Two-dimensional (2D) transverse HMI displacement maps were also obtained before and after lesion formation. The same method was repeated in 10 s, 20 s and 30 s HIFU durations at three different acoustic powers of 8, 10, and 11 W, which were selected and verified as treatment parameters capable of inducing boiling using both thermocouple and passive cavitation detection (PCD) measurements. Although a steady decrease in the displacement, compressive strain, and relative change in the focal phase shift (Δϕ) were obtained in numerous cases, indicating an overall increase in relative stiffness, the study outcomes also showed that during boiling, a reverse lesion-to-background displacement contrast was detected, indicating potential change in tissue absorption, geometrical change and/or, mechanical gelatification or pulverization. Following treatment, corresponding 2D HMI displacement images of the thermal lesions also mapped consistent discrepancy in the lesion-to-background displacement contrast. Despite the expectedly chaotic changes in acoustic properties with boiling, the relative change in phase shift showed a consistent decrease, indicating its robustness to monitor biomechanical properties independent of the acoustic property changes throughout the HIFU treatment. In addition, the 2D HMI displacement images confirmed and indicated the increase in the thermal lesion size with treatment duration, which was validated against pathology. In conclusion, multi-parametric HMIFU was shown capable of monitoring and mapping tissue viscoelastic response changes during and after HIFU boiling, some of which were independent of the acoustic parameter changes.

Stochastic Soliton Solutions of the High-Order Nonlinear Schrödinger Equation in the Optical Fiber with Stochastic Dispersion and Nonlinearity

In this paper, the high-order nonlinear Schrödinger (HNLS) equation driven by the Gaussian white noise, which describes the wave propagation in the optical fiber with stochastic dispersion and nonlinearity, is studied. With the white noise functional approach and symbolic computation, stochastic one- and two-soliton solutions for the stochastic HNLS equation are obtained. For the stochastic one soliton, the energy and shape keep unchanged along the soliton propagation, but the velocity and phase shift change randomly because of the effects of Gaussian white noise. Ranges of the changes increase with the increase in the intensity of Gaussian white noise, and the direction of velocity is inverted along the soliton propagation. For the stochastic two solitons, the effects of Gaussian white noise on the interactions in the bound and unbound states are discussed: In the bound state, periodic oscillation of the two solitons is broken because of the existence of the Gaussian white noise, and the oscillation of stochastic two solitons forms randomly. In the unbound state, interaction of the stochastic two solitons happens twice because of the Gaussian white noise. With the increase in the intensity of Gaussian white noise, the region of the interaction enlarges.

Overcoming Patch-Potential Effects on the Surfaces of Tem Phase-Contrast Devices

A Focused-Ion Beam (FIB) tool is used to fabricate thin-foil apertures that have an electron-opaque half-circle at the center, suspended by a beam extending from the outer edge. The opaque half-circle produces single-sideband contrast (also known as schlieren, or Foucault knife-edge contrast) at low spatial frequencies, while still allowing one to use Scherzer defocus to provide optimal contrast transfer at intermediate and high spatial frequencies. While a requirement for such an aperture to be effective is that the electrostatic equipotential surface must conform closely to the physical surface of the device, this requirement is not well satisfied on the vacuum-side of any polycrystalline material, due to variation of the work function of difference crystal facets. We thus coat newly fabricated apertures with graphitic a-C to provide a surface with a uniform work function. We now report that heating such apertures to ∼650 °C during use is effective in real-time annealing of the radiation damage that otherwise causes a local (patchy) change in phase shift to build up at the edge of the opaque half-circle. While this represents a significant advance, there remains an as-yet unsolved problem in achieving consistent fabrication of apertures that retain the desired uniformity of electrostatic potential when they are heated to ∼650 °C. Current work is focused in two directions: (1) taking steps to enhance bonding of the a-C coating (i.e. prevent delamination), and (2) investigating other materials that may not need to be coated with a-C but that will (like a-C) be rad-hard, at least when heated to ∼650 °C or less.

Tunable phase-shifted fiber Bragg grating based on femtosecond laser fabricated in-grating bubble

We present a type of phase-shifted fiber Bragg gratings based on an in-grating bubble fabricated by femtosecond (fs) laser ablation together with a fusion-splicing technique. A microchannel vertically crossing the bubble is drilled by fs laser to allow liquid to flow in or out. By filling different refractive index (RI) liquid into the bubble, the phase-shift peak is found to experience a linear red shift with the increase of RI, while little contribution to the change of phase shift comes from the temperature and axial strain. Therefore, such a PS-FBG could be used to develop a promising tunable optical filter and sensor.

Assessment of Dynamic Cerebral Autoregulation in Patients with Basilar Artery Stenosis

Background and AimsPrevious studies have shown impaired cerebral autoregulation (CA) in carotid and middle cerebral artery (MCA) stenosis/occlusion. Little is known about CA in patients with basilar artery (BA) stenosis. We therefore investigated dynamic CA patterns in BA stenosis using transfer function analysis (TFA).MethodsWe measured spontaneous oscillations of blood flow velocity (CBFV) in the right posterior cerebral artery (PCA), and left MCA and mean arterial pressure (ABP) continuously in 25 patients with BA stenosis (moderate n=16 with 50-69% occlusion and severe n=9 with ≥70% occlusion) and 22 healthy volunteers in supine position during 6 circles per minute deep breath. Analysis was based on the ‘black-box’ model of transfer function deriving phase and gain in both PCA and MCA.ResultsThough changes of phase shift and gain between the patients and healthy controls were observed in MCA, the differences are however not significant. Phase shift in PCA was significantly decreased in severe stenosis when comparing with healthy controls and moderate stenosis (4.2±34.2° VS 41.1±40.4°, 4.2±34.2° VS 34.2±27.2°, both p<0.05), whilst the gain in PCA is increased for moderate BA stenosis and decreased for severe BA stenosis. Furthermore, we found that phase shift were almost abolished in patients with ischemic stroke who developed unfavorable clinical outcome (mRs>2) on the 90 days after stroke onset.ConclusionDynamic CA in PCA reduces in patients with severe BA stenosis and those with ischemic stroke who present poor outcome in 90 days after stroke onset. Phase shift might be a sensitive index prompting impaired CA in posterior circulation.

Transmissive liquid crystal light-valve for near-infrared applications

An optical valve is realized by associating a nematic liquid crystal layer with a Cr-doped gallium arsenide as a photoconductive substrate. The light-valve is shown to efficiently operate in transmission at 1.06 μm optical wavelength. The optical phase shift and refractive index change are measured as a function of the incident light intensity and of the voltage applied. Additionally, the light-valve is shown to act as a self-defocusing medium. Combining transmissive properties and nonlinear features, applications for dynamic holography in the near-infrared region of the spectrum can be envisaged.

TU‐C‐108‐04: Interferometric Phase Shift Measurements to Determine the Absorbed Dose to Water

Purpose: To investigate the feasibility of using phase shift measurements of visible light to determine the absorbed dose to water. To determine the minimum resolution of the optical system of a Michelson interferometer for measuring radiation induced changes in the temperature of water and to quantify the additional heating produced by the light. Methods: A Michelson interferometer was modeled with a water‐filled cell in one of its arms. The anticipated phase shift and temperature change was calculated for a 2 Gy irradiation. The observed change in intensity incident on the detector was calculated for different volumes of water and different doses. The heating of water caused by the laser was also estimated. Results: The refractive index of water is related to the dose delivered with a proportionality constant of 2.14E‐8 (λ=532 nm). For the modeled interferometer, the central spot signal in the detector arm is a function of the irradiated length of water and the dose delivered. Changes in intensity of 20 percent would be observed after a 2 Gy irradiation of a 20 cm long cell. Water heating due to the light beam is proportional to the laser power and the decadic absorption coefficient. For a 5 mW laser this would represent about 7.5 percent of the heating rate produced by a dose rate of 1 Gy/min. Conclusion: We showed that visible light phase shift measurements are a reasonable approach to determine the absorbed dose to water. Heating due to the light could be reduced using higher dose rates and/or a pulsed laser. This model provides a measure of the average dose over the beam path and a tomographic reconstruction can be used to ascertain the dose to a point. The reconstructed 2D dose distribution can be useful for small fields in radiation therapy.

On the computation of the magnetic phase shift for magnetic nano-particles of arbitrary shape using a spherical projection model

The magnetic phase shift of an electron wave traveling through a magnetized object is computed by considering the object to be made up of a collection of uniformly magnetized spheres arranged on the nodes of a cubic grid. In the limit of vanishing grid size, this approach becomes equivalent to other numerical approaches. Update equations are derived for the change of the magnetic phase shift when the magnetization of a single object voxel is modified. Example phase shift calculations are presented for a uniformly magnetized sphere, circular disks with an infinitely sharp vortex core and a smooth core, and an oval disk with a pair of vortices and an antivortex.

The interaction of two nonplanar solitary waves in electron-positron-ion plasmas: An application in active galactic nuclei

In the present research paper, the effect of bounded nonplanar (cylindrical and spherical) geometry on the interaction between two nonplanar electrostatic solitary waves (NESWs) in electron–positron–ion plasmas has been studied. The extended Poincaré–Lighthill–Kuo method is used to obtain nonplanar phase shifts after the interaction of the two NESWs. This study is a first attempt to investigate nonplanar phase shifts and trajectories for NESWs in a two-fluid plasma (a pair-plasma) consisting of electrons and positrons, as well as immobile background positive ions in nonplanar geometry. The change of phase shifts and trajectories for NESWs due to the effect of cylindrical geometry, spherical geometry, the physical processes (either isothermal or adiabatic), and the positions of two NESWs are discussed. The present investigation may be beneficial to understand the interaction between two NESWs that may occur in active galactic nuclei.