Phase Shift Difference Research Articles

Computational Modeling of the Mechanical Behavior of the Cerebrospinal Fluid System

A computational fluid dynamics (CFD) model of the cerebrospinal fluid system was constructed based on a simplified geometry of the brain ventricles and their connecting pathways. The flow is driven by a prescribed sinusoidal motion of the third ventricle lateral walls, with all other boundaries being rigid. The pressure propagation between the third and lateral ventricles was examined and compared to data obtained from a similar geometry with a stenosed aqueduct. It could be shown that the pressure amplitude in the lateral ventricles increases in the presence of aqueduct stenosis. No difference in phase shift between the motion of the third ventricle walls and the pressure in the lateral ventricles because of the aqueduct stenosis could be observed. It is deduced that CFD can be used to analyze the pressure propagation and its phase shift relative to the ventricle wall motion. It is further deduced that only models that take into account the coupling between ventricles, which feature a representation of the original geometry that is as accurate as possible and which represent the ventricle boundary motion realistically, should be used to make quantitative statements on flow and pressure in the ventricular space.

New Measurement ofΞ−→Λπ−Decay Parameters

A study on the measurement of φ≡ using a sample of 144×106 ≡- →λπ- decays having an average polarization of 3.7% was presented. The polarized ≡-'s were produced by directing an 800 geV÷c proton beam onto a 2 mm ×2 mm× 60 mm cu target at angles of +3 and -3 mrad. The results were shown to be a 2.9× improvement over the best previous mesurements. It was shown that CP violation in charged ≡→λπ decays are not suppressed by a vanishing final phase shift difference.

D-type fiber optic sensor used as a refractometer based on total-internal reflection heterodyne interferometry

A new type of fiber optic sensor (FOS) based on total-internal reflection heterodyne interferometry (TIRHI) is proposed. It can be used as a liquid refractometer. The phase shift difference due to the TIR effects between the P- and S-polarizations is measured using heterodyne interferometry with a D-type fiber optic sensor. Substituting the phase shift difference into Fresnel’s equations, the refractive index can be calculated. It has some merits, such as, high sensitivity and stability, small size and real-time measurement.

D-type fiber optic sensor used as a refractometer based on total-internal reflection heterodyne interferometry

A new type of fiber optic sensor (FOS) based on total-internal reflection heterodyne interferometry (TIRHI) is proposed. It can be used as a liquid refractometer. The phase shift difference due to the TIR effects between the P- and S-polarizations is measured using heterodyne interferometry with a D-type fiber optic sensor. Substituting the phase shift difference into Fresnel’s equations, the refractive index can be calculated. It has some merits, such as, high sensitivity and stability, small size and real-time measurement.

Optical characterization of hexagonal CdS layers grown on GaAs(111) by MBE: application of phase‐shift‐difference spectroscopy

Excitonic properties of hexagonal CdS epilayers grown on GaAs(111)A and B substrates by MBE have been investigated by means of a phase-shift-difference (PSD) spectroscopy in which the phase-shift of light upon reflection was measured. It is confirmed that the peak energy positions of the PSD spectrum correspond to the excitonic resonance energies by using CdS bulk crystal. The distinct transitions of A- and B-excitons were observed in the PSD spectra for the hexagonal CdS epilayers. Furthermore, new excitonic transition was found for the epilayers at the energy slightly below the resonance energy of the A-exciton. This transition was observed clearly for the epilayer on GaAs(111)A compared with that on GaAs(111)B, and was not observed for CdS bulk. Thus the new transition can be explained by a model of the exciton bound to staking faults that form a quantum well of cubic structure in the hexagonal epilayer. It is shown that stacking faults are potential well for electrons and potential barriers for holes. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Tests for a Difference in Timing of Physiological Response Between Two Brain Regions Measured by Using Functional Magnetic Resonance Imaging

Summary Functional magnetic resonance imaging (FMRI) measures the physiological response of the human brain to experimentally controlled stimulation. In a periodically designed experiment it is of interest to test for a difference in the timing (phase shift) of the response between two anatomically distinct brain regions. We suggest two tests for an interregional difference in phase shift: one based on asymptotic theory and one based on bootstrapping. Whilst the two procedures differ in some of their assumptions, both tests rely on employing the large number of voxels (three-dimensional pixels) in non-activated brain regions to take account of spatial autocorrelation between voxelwise phase shift observations within the activated regions of interest. As an example we apply both tests, and their counterparts assuming spatial independence, to FMRI phase shift data that were acquired from a normal young woman during performance of a periodically designed covert verbal fluency task. We conclude that it is necessary to take account of spatial autocovariance between voxelwise FMRI time series parameter estimates such as the phase shift, and that the most promising way of achieving this is by modelling the spatial autocorrelation structure from a suitably defined base region of the image slice.

Age-related changes in motor control during articulator visuomotor tracking.

The present study provides normative data on changes in visuomotor control of the oral-facial system across the lifespan. Control of the lower lip, jaw, and larynx (i.e., fundamental frequency) was examined using a nonspeech visuomotor tracking (VMT) task, where subjects move the articulator of interest to track a moving target on an oscilloscope screen. This task examines articulator motor control during movements that are similar to speech but that do not impose linguistic units or the demands of coordinating multiple structures. Accuracy and within- and between-subject variability in tracking performance were measured by cross correlation, gain ratio, phase shift, and target-tracker amplitude difference. Cross-correlation analyses indicated that performance of children (aged 8;2 to 17;0 [years;months]) and older adults (aged 45;1 to 84;3) is poorer than that of younger adults (aged 17;1 to 45;0). Accuracy of movement amplitude tended to increase during development and decline with aging, whereas age did not appear to influence accuracy of temporal parameters in lip and jaw tracking. In contrast, age tended to influence individual variability in temporal but not amplitude parameters. Differences were noted between articulators. The data complement previous studies that considered accuracy and variability of articulator movement during speech. The VMT method and the data provided may be applied to assessment of impairments in the motor speech system and to differential diagnosis of motor speech versus linguistically based disorders.

Bireflectance thin film in a high beat frequency laser

This paper investigates a kind of bireflectance thin film on the window plate of a 633 nm He–Ne laser. The film is coated on the substrate with the application of external load on it. The load on the substrate is removed after the coating has been accomplished, then the strain on the substrate will be transferred to the multilayer coatings. Due to photoelastic effect, the multilayer film becomes an anisotropic film. Selecting appropriate film structure and suitable center wavelength, a high phase dispersion with nearly constant reflectivity around the working wavelength will be obtained. For normal incidence, a sufficient phase shift difference between the two orthogonal polarization states of the reflected wave will be produced. As a result, a dual-frequency laser with a beat frequency of 5 MHz can be carried out by using this kind of multilayer film. The theory of designing such a film is emphasized and an example of bireflectance thin film is proposed.

Study of the single-beam reflection technique for measuring the linear electro-optic coefficient of the nonlinear optical polymer films

The single-beam reflection technique is usually used to measure the linear electro-optic (EO) coefficient (Pockels coefficient) in development of the EO polymer thin films. But there are some problems in the determination of the phase-shift difference between the s and p waves of a laser beam waveguided into the polymer film while a modulating voltage is applied across the electrodes in some articles, and different expressions of the linear EO coefficient have been deduced in these articles. In our research, more accurate expression of the linear EO coefficient was deduced by reasonably considering the phase shift between the s and p waves. The linear EO coefficients of several polymer thin films were measured by the reflection technique, and the results of the linear EO coefficient calculated by different expressions were compared. The limit of the single-beam reflection technique for measuring the linear EO coefficient of the polymer thin films was discussed.

Near threshold photoionization of excited alkali atoms Ak(np) (Ak = Na, K, Rb, Cs; n = 3-6)

The effect of the polarization of the atomic core by the outer electron on near threshold photoionization of excited alkali atoms Ak(np) (Ak = Na-Cs; n=3-6) is investigated. Partial and total cross-sections for photo-ionization of the np-electron were computed utilizing the configuration interaction technique with Pauli-Fock atomic orbitals (CIPF) and including the long range core polarization potential (CP). To calculate the core polarization potential the variational principle is applied. Comparison with previous theoretical results and with available experimental data is made for the total cross-section , for the electron angular distribution parameter , for the ratio of the reduced electric dipole matrix elements and for the phase shift difference , associated with the d-wave and s-wave continua, respectively. In the comparison, new experimental results for , , and , measured for laser-excited, polarized 39K(4p 3/2) atoms, have been included.

Molecular frame photoelectron angular distributions in inner valence photoionisation of CO

The velocity imaging photoionisation coincidence (VIPCO) technique is applied to the photoionisation of CO into the inner-valence 4 2Σ+ state of CO+, and the molecular frame photoelectron angular distributions are measured on the high energy side of the known σ* shape resonance. The angular distributions at 40.8 and 48.4 eV show that partial waves with the angular momentum l⩽3 provide the dominant contribution to both parallel and perpendicular transitions, and the contributions from the l4 partial waves are relatively negligible. By restricting the partial wave expansion to l⩽3, eight and four sets of dipole matrix elements and phase shift difference are extracted from the measured angular distributions for parallel and perpendicular transitions, respectively. Although it is not possible to choose unambiguously among these sets, combined enhancement among the l⩽3 partial waves for the parallel transition is obvious at the shape resonance.

市販振動加速度ピックアップの位相特性

In recent vibration and acceleration pickup applications, for example in modal analysis, active control of vibration isolation, and inertial navigation, the phase shift evaluation of pickup has become important. However, the frequency-phase characteristics of the pickup has not been reported quantitatively from the production makers in the past. In this report, the phase shift evaluation results of three types (piezoelectric-type, servo-type and capacitance-type) of commercially available vibration and acceleration pickups are presented. The evaluations were performed using the sine-approximation method, which will be adopted in the updated ISO standards. The phase shift and the uncertainty of each pickup have been elucidated. Expanded uncertainties of less than ±6×10-3 rad in phase shift evaluation at 5 kHz have been obtained. Three piezoelectric type pickups manufactured by different makers are also evaluated and compared. We observed a phase shift difference of up to 4×10-2 rad in each sensor.

Measurements of gas preionization for plasma radiation sources

Azimuthally symmetric ultraviolet (UV) preionization of the outer periphery of a gas puff z pinch, prior to current initiation, may reduce the growth of magnetically driven Rayleigh–Taylor instabilities or other nonuniformities affecting the final implosion stage of the pinch, leading to an improvement in K-shell x-ray yield. We report on measurements of a flashover UV photoionization scheme, capable of ionizing the periphery of argon gas puffs to 1%–10% of the initial gas density. Measurements are made with a two-color, (1064 and 532 nm), high sensitivity (∼10−5λ), Mach–Zehnder type interferometer. Two methods of measuring preionization are investigated. The first uses a single laser wavelength, 1064 nm, to probe a chord of the cylindrical gas puff. The gas density is measured first without preionization and then with the UV flashover discharge. The difference in phase shift determines the free electron density. The second technique uses both wavelengths to simultaneously probe the same line of sight, determining neutral and free electron densities using only one gas puff event. Gas preionization may introduce refractive species that complicate the conversion of phase shift to density. However, single-color interferometry with the IR and green beams indicates that it is sufficient to consider only two species, neural argon and free electrons for times of interest.

Computational investigation of experimental interaction impedance obtained by perturbation for helical traveling-wave tube structures

Conventional methods used to measure the cold-test interaction impedance of helical slow-wave structures involve perturbing a helical circuit with a cylindrical dielectric rod placed on the central axis of the circuit. It has been shown that the difference in resonant frequency or axial phase shift between the perturbed and unperturbed circuits can be related to the interaction impedance. However, because of the complex configuration of the helical circuit, deriving this relationship involves several approximations. With the advent of accurate three-dimensional (3-D) helical circuit models, these standard approximations can be fully investigated. This paper addresses the most prominent approximations made in the analysis for measured interaction impedance by Lagerstrom (1957) and investigates their accuracy using the 3-D simulation code MAFIA. It is shown that a more accurate value of interaction impedance can be obtained by using 3-D computational methods rather than performing costly and time consuming experimental cold-test measurements.

Heterodyne interferometric measurement of the thermo-optic coefficients of potassium niobate

A heterodyne interferometric technique is applied to determine the thermo-optic coefficients of a potassium niobate crystal with a GaAlAs diode laser. The heterodyne beats signal, resulting from the beating of the carrier and two side-band frequencies, is related to the phase shift difference between the carrier and the side-bands. This phase shift difference is determined with a phase sensitive detection technique and is found to be temperature dependent. From the temperature dependence, the thermo-optic coefficients of the potassium niobate crystal along the b and c crystallographic axes are determined to be −4.5×10−5 and 6.7×10−5 °C−1, respectively.

Rotating-compensator multichannel ellipsometry: Applications for real time Stokes vector spectroscopy of thin film growth

A multichannel spectroscopic ellipsometer based on the rotating-compensator principle was developed and applied to measure the time evolution of spectra (1.5–4.0 eV) in the normalized Stokes vector of the light beam reflected from the surface of a growing film. With this instrument, a time resolution of 32 ms for full spectra is possible. Several advantages of the rotating-compensator multichannel ellipsometer design over the simpler rotating-polarizer design are demonstrated here. These include the ability to: (i) determine the sign of the p-s wave phase-shift difference Δ, (ii) obtain accurate Δ values for low ellipticity polarization states, and (iii) deduce spectra in the degree of polarization of the light beam reflected from the sample. We have demonstrated the use of the latter spectra to characterize instrument errors such as stray light inside the spectrograph attached to the multichannel detector. The degree of polarization of the reflected beam has also been applied to characterize the time evolution of light scattering during the nucleation of thin film diamond by plasma-enhanced chemical vapor deposition, as well as the time evolution of thickness nonuniformities over the probed area of the growing diamond film. In this article, a detailed description of calibration and data reduction for the new instrument is provided. Future applications of this instrument are expected for real time characterization of film growth and etching on patterned surfaces for microelectronics and on thick transparent substrates for large area displays and photovoltaics.

PENGUIN CORRECTIONS AND STRONG PHASES IN A TIME-DEPENDENT ANALYSIS OF $\overline{B^0}(B^0)r\to \pi^+\pi^-$

From a time-dependent analysis of the decay [Formula: see text] and using a model-dependent AP/AT ratio of the penguin-to-tree amplitudes contributing to the decay, both the weak phase α and the strong phase shift difference δ can be extracted from the data. The value of the weak phase β expected to be measured from the decay [Formula: see text], is used to parametrize the value of AP/AT and the corresponding penguin correction to the observed asymmetry in [Formula: see text].

Performance of time delay estimation methods for small time shifts in ultrasonic signals.

In this study several time delay estimation (TDE) methods were investigated for estimation of time shifts of less than 10 ns at a frequency of 30 MHz. Using simulated and experimental echosignals we investigated the performance of five methods: two phase related methods (phase shift and phase difference method); two correlation methods (cross-correlation and correlation interpolation method); and a demodulation method. The results showed that the correlation interpolation method is by far the most accurate for all time delays. With this method, estimation errors of about 200 ps are achievable with an signal-to-noise ratio (SNR) of 40 dB (f0 = 30 MHz, bandwidth = 20 MHz) for time shifts of up to 10 ns.

Rotating-Compensator Multichannel Ellipsometry: Applications in Process Development for Nanocrystalline Diamond Thin Films

ABSTRACTA multichannel spectroscopic ellipsometer based on the rotating-compensator principle was developed and applied to characterize nanocrystalline diamond thin film growth processes by plasma-enhanced chemical vapor deposition (PECVD). With the newly-designed instrument, a time resolution of 32 ms is possible for spectra (1.5˜4.0 eV) in the Stokes vector of the light beam reflected from the surface of the growing film. Several advantages of the rotating-compensator over the simpler rotating-polarizer multichannel ellipsometer design are demonstrated here for diamond thin film growth. These include the ability to: (i) resolve the sign ambiguity in the p–s wave phase-shift difference Δ, (ii) obtain accurate Δ values for low ellipticity polarization states, and (iii) deduce spectra in the degree of polarization of the light beam reflected from the film/substrate. The degree of polarization has been applied to characterize the time evolution of light scattering during the nucleation of the diamond, as well as the time evolution of thickness non-uniformity over the probed area of the growing film. In this paper, a brief description of calibration and data reduction for the new instrument is also provided.

Elastic ππ scattering to two loops

We evaluate analytically the elastic ππ scattering amplitude to two loops in chiral perturbation theory and give numerical values for the two S-wave scattering lengths and for the phase shift difference δ 0 0 - δ 1 1.