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At least 523 records · Page 29Linked to original sources
PubMed2003

Least-squares modal estimation of wrapped phases: application to phase unwrapping.

Phase unwrapping continues to be an important step in those techniques that obtain the phase from Fourier transforms. We propose a fast two-dimensional phase-unwrapping algorithm that has been specially designed to be used as part of an iterative algorithm. It can be used also as a final step of a phase retrieval process with other unwrapping techniques. The algorithm consists of a modal least-squares estimation of the wrapped phase by using as inputs to the linear estimation the derivative of the wrapped phase. A theoretical description of the method, simulations, and experimental validations are presented.

Journal Article↗
PubMed2000

Phase-shift calibration algorithm for phase-shifting interferometry.

We propose a novel phase-shift calibration algorithm. With this technique we determine the unknown phase shift between two interferograms by examining the sums and differences of the intensities on each interferogram at the same spatial location, i.e., I1(x, y) +/- I2(x, y). These intensities are normalized so that they become sinusoidal in form. A uniformly illuminated region of the interferograms that contains at least a 2pi variation in phase is examined. The extrema of these sums and differences are found in this region and are used to find the unknown phase shift. An error analysis of the algorithm is provided. In addition, an error-correction algorithm is implemented. The method is tested by numerical simulation and implemented experimentally. The numerical tests, including digitization error, indicate that the phase step has a root-mean-square (RMS) phase error of less than 10(-6) deg. Even in the presence of added intensity noise (5% amplitude) the RMS error does not exceed 1 deg. The accuracy of the technique is not sensitive to nonlinearity in the interferogram.

Journal Article↗
PubMed2003

Least-squares phase estimation with multiple parameters in phase-shifting electronic speckle pattern interferometry.

We have developed an accurate and robust phase-estimation method in phase-shifting electronic speckle pattern interferometry. Unlike other methods that assume a constant phase within a fitting window, our method treats the phase variation with a gradient. A cost function that can utilize the information of pixel positions is formulated on the basis of a least-squares criterion. Powell's iteration method is applied to it to derive the phase and its gradient. An automatic consistency-checking routine and an algorithm that improves the initial guess of the iteration are developed for severe situations with large noise and steep phase variations.

Journal Article↗
PubMed2004

Phase-space interpretation of deterministic phase retrieval.

Deterministic phase retrieval is reinterpreted in terms of phase-space optics. A novel derivation of the transport-of-intensity equation is presented based on the Wigner distribution function and the ambiguity function. The phase retrieval problem is formulated as estimating the local first-order moment of the Wigner function from intensity information. A comparison with phase-space tomography suggests a generalization of deterministic phase retrieval that provides larger flexibility for signal recovery. In addition, one particular numerical implementation of generalized deterministic phase retrieval is presented. Simulated intensity data are used to validate the method.

Journal Article↗
PubMed2006

Phase-shifting interferometry in the presence of nonlinear phase steps, harmonics, and noise.

A phase-shifting piezo device commonly employed in phase-shifting interferometry exhibits a nonlinear response to applied voltage. Hence, a method for estimation of phase distribution in the presence of nonlinear phase steps is presented. The proposed method compensates for the harmonics present in the intensity fringe, allows the use of arbitrary phase-step values between 0 and tau rad, and does not impose constraints on the selection of particular phase-step values for minimizing nonlinearity and compensating for the harmonics. The comparison of the proposed method with other well-known benchmarking algorithms shows that our method is highly efficient and also works well in the presence of noise.

Journal Article↗
PubMed2005

Phase I and Phase II oxygen uptake kinetics during atrioventricular dyssynchrony in chronotropically competent pacemaker patients.

OBJECTIVE: To elucidate the effects of atrioventricular (AV) dyssynchrony on phase I and phase II oxygen uptake (V(O2)) kinetics in chronotropically competent pacemaker patients during exercise of an intensity comparable to activities of daily living. DESIGN: Blinded patients completed sub-ventilatory threshold (VT) work rate (WR) cycle ergometry exercise in random order during asynchronous AV pacing (AV OFF) and synchronous AV pacing. SETTING: Tertiary care hospital in a major city. SUBJECTS: Six chronotropically competent male pacemaker patients (mean [+/- SD] age, 68 +/- 10 years) with high-degree AV block and varying cardiac histories. RESULTS: The phase I and phase II V(O2) amplitude response and gain (deltaV(O2)/WR ratio) were lower (p < 0.05) and the time course of phase II was slower (p < 0.05) during AV OFF; however, the O2 deficit was similar (p > 0.05) across pacing modes. The stroke volume index (SVI) was consistently lower (p < 0.05) during AV OFF pacing and was significantly correlated with the time course of phase II V(O2). A significant compensatory amplitude response in heart rate (HR) was observed in addition to a higher (p < 0.05) deltaHR/V(O2) ratio during AV OFF. Ventilatory responses were consistent with ventilatory-perfusion mismatching and perceived exertion was higher during asynchronous pacing. CONCLUSION: This study demonstrated that the contribution of SVI affects V(O2) kinetics and underscores the importance of the atrial contribution to ventricular filling and, consequently, to metabolic and hemodynamic responses. This study supports the theory of an O2 transport limitation and further implicates SV as a potential limiting factor during sub-VT exercise intensities that are comparable to those encountered in activities of daily living.

Activities of Daily Living↗
PubMed1998

Photoperiod-induced phase-shifts of the endogenous clock controlling reproduction in the rainbow trout: a circannual phase-response curve.

Different groups of winter-spawning female rainbow trout that had been maintained under seasonally changing daylength and temperature were exposed to 2 months of continuous light at different times of the year. The same photoperiod produced advances in the time of spawning of up to 232 days and delays of up to 80 days, depending upon the timing of exposure in relation to the phase of the reproductive cycle. The proportion of fish spawning in each group varied from 18% to 100%, again dependent on the timing of exposure to continuous light. The photoperiod-induced changes in spawning time can be interpreted as phase-dependent phase-shifts of an endogenous circannual clock controlling maturation. It is proposed that long days, occurring earlier or later than they would under a natural photoperiod, were perceived as indications that the clock was running slow or fast, thus initiating corrective forward adjustments (advance phase-shifts) or backward adjustments (delay phase-shifts), respectively. Collectively, these responses can be described in the form of a circannual phase-response curve.

Animals↗
PubMedDate not supplied

Human optokinetic afternystagmus. Slow-phase characteristics and analysis of the decay of slow-phase velocity.

Events following the extinction of lights after 1-minute exposures of naive, normal subjects to an optokinetic stimulus at 40 deg/sec have been closely examined and quantified. Mean eye displacement in each slow phase decreased from 10.12 +/- 1.61 deg during optokinetic nystagmus (OKN) to 3.36 +/- 2.32 deg during optokinetic afternystagmus (OKAN). Slow-phase duration increased from 0.26 +/- 0.03 sec during OKN to 0.45 +/- 0.195 sec during OKAN. Eye displacement per slow phase remained fairly constant during OKAN, suggesting a spatial reference for the resetting of gaze. OKAN decay is a two-component process which can be closely approximated by a sum of two exponentials, one with a short time constant of 1.15 sec and the other with a long time constant of 48.8 sec. OKAN decay commenced at a time after lights out which depended upon the presence and timing of an intervening fast phase. When a fast phase intervened, OKAN decay commenced about 230 msec after it, and about 460 msec after lights out. When lights out occurred during the fast phase, OKAN decay commenced about 340 msec later.

Adult↗
PubMed2000

[Dependence of the kinetics of forming phases of a two-phase polymeric system on actin state].

New analytical possibilities of biological macromolecule partition in a two-phase polymer system (dextran-500/polyethyleneglycol-6000) were investigated. The technical principles were based on the fact that optical density of the system changes during phase formation. Various actin forms were investigated. Unlike G-actin, F-actin increases the speed of phase formation. Different actin isoforms exert different influence on this process. The kinetics of the partition system into phases makes it possible to figure out the picture of native G-actin damage. The two-phase polymer system has been shown to be capable of supporting the native properties of actin for not less than 6 days at 20 degrees C. An assumption is made that two-phase systems can be used for imitating the intracellular medium in studies on actin functional characteristics.

Actins↗
PubMed2000

[Features of formation of phases of dual-phase polymeric system in the presence of collagen I, laminin I, and their mixtures].

A study was made of the phase formation kinetics of a two-phase aqueous polymer system, consisting of 7.8% (w/w) dextran-500 and 4.6% (w/w) polyethylene glycol-6000, in the presence of various concentrations of collagen (0.07-0.20 mg/ml), laminin I (0.01-0.03 mg/ml) and their mixture. The phase formation was evaluated by registration of its optical density on a spectrophotometer. The obtained two-phase polymer system optical density curves and also the partitioning coefficients for the studied objects depend on surface properties of these objects. It has been shown that the surface properties of collagen I and laminin I differ according to differences in their molecules conformations, and that the phase formation kinetics points to their interaction during a mutual partitioning of these proteins in the system. The authors made a conclusion that collagen I and laminin I in the two-phase polymer system conditions could make complexes.

Biopolymers↗
PubMed2002

[Fast optimization of stepwise gradient conditions for ternary mobile phase in reversed-phase high performance liquid chromatography].

In high performance liquid chromatography, it is necessary to apply multi-composition gradient elution for the separation of complex samples such as environmental and biological samples. Multivariate stepwise gradient elution is one of the most efficient elution modes, because it combines the high selectivity of multi-composition mobile phase and shorter analysis time of gradient elution. In practical separations, the separation selectivity of samples can be effectively adjusted by using ternary mobile phase. For the optimization of these parameters, the retention equation of samples must be obtained at first. Traditionally, several isocratic experiments are used to get the retention equation of solute. However, it is time consuming especially for the separation of complex samples with a wide range of polarity. A new method for the fast optimization of ternary stepwise gradient elution was proposed based on the migration rule of solute in column. First, the coefficients of retention equation of solute are obtained by running several linear gradient experiments, then the optimal separation conditions are searched according to the hierarchical chromatography response function which acts as the optimization criterion. For each kind of organic modifier, two initial linear gradient experiments are used to obtain the primary coefficients of retention equation of each solute. For ternary mobile phase, only four linear gradient runs are needed to get the coefficients of retention equation. Then the retention times of solutes under arbitrary mobile phase composition can be predicted. The initial optimal mobile phase composition is obtained by resolution mapping for all of the solutes. A hierarchical chromatography response function is used to evaluate the separation efficiencies and search the optimal elution conditions. In subsequent optimization, the migrating distance of solute in the column is considered to decide the mobile phase composition and sustaining time of the latter steps until all the solutes are eluted out. Thus the first stepwise gradient elution conditions are predicted. If the resolution of samples under the predicted optimal separation conditions is satisfactory, the optimization procedure is stopped; otherwise, the coefficients of retention equation are adjusted according to the experimental results under the previously predicted elution conditions. Then the new stepwise gradient elution conditions are predicted repeatedly until satisfactory resolution is obtained. Normally, the satisfactory separation conditions can be found only after six experiments by using the proposed method. In comparison with the traditional optimization method, the time needed to finish the optimization procedure can be greatly reduced. The method has been validated by its application to the separation of several samples such as amino acid derivatives, aromatic amines, in which satisfactory separations were obtained with predicted resolution.

Amino Acids↗
PubMed2003

Time and dose-dependent modulation of phase 1 and phase 2 gene expression in response to treatment of MCF-7 cells with a natural anti-cancer agent.

Several known anti-cancer agents have been shown to lead to increased expression of phase 2 metabolic enzymes without affecting phase 1 enzymes. Phase 1 cytochrome P450 (CYP) enzymes are relevant in cancer studies in that they are involved in oxidative metabolism, biotransformation and detoxification, whereas phase 2 enzyme catalysis leads to clearance. In this study, we obtained semi-quantitative measurements of cytochrome P450 (phase 1) and phase 2 microsomal epoxide hydrolase (mEH) gene expression levels in response to treatment of MCF-7 breast cancer cells with water-soluble Vernonia amygdalina (V.A.) extract. V.A., a vegetable grown in Nigeria, has potential as an anti-cancer agent. The results of Western blot and RT-PCR analyses show that V.A. extract acts as a monofunctional inducer within exposure times ranging from 2-16 hr and dose ranges from 3-100 microg/ml of V.A. Exposure of cells to low doses of V.A. did not affect expression levels of CYP1A1/1A2 mRNA, but lead to induction of mEH, thus supporting the chemotherapeutic potential of VA. However, in parallel studies, CYP3A4 gene expression was also induced, suggesting potential intermediates which influence drug-drug interactions. These data are useful toward further validating V.A. extract as a potential clinically useful natural anti-cancer agent and provide some support for the concept that modulation in CYP3A4 expression in response to treatment is relevant to prognosis.

Breast Neoplasms↗
PubMed2005

[Optimal phase of dynamic CT for detecting hypervascular hepatocellular carcinoma: evaluation of double arterial phases].

PURPOSE: To investigate the appropriate time of arterial phase for the detection of hypervascular hepatocellular carcinoma (HCC). MATERIALS AND METHODS: Fifty-two hypervascular HCCs of 36 patients were evaluated on double arterial-phase images of the liver. The first and second arterial-phase images were obtained 10 sec after aortic peak enhancement time as determined by test bolus injection. Patients received a low or high concentration of contrast medium, according to their body weight, that was administered intravenously at a rate of 4 mL/sec and injection duration of 23 sec. Three radiologists evaluated the images separately. RESULTS: Sensitivity in detecting hypervascular HCCs was higher in the first arterial phase than in the second arterial phase (p = 0.039). HCCs were not detected as hypervascular nodules in one of 20 cases during 31 or fewer sec, or in 8 of 19 cases during 48 or more sec after the initiation of contrast medium injection. All nodules were detected as hypervascular lesions between 32 and 47 sec after the initiation of contrast medium injection. CONCLUSION: When a single arterial phase is obtained to detect hypervascular HCCs with a 23-sec injection time and an injection rate of 4 mL/sec, a protocol is recommended in which scanning is started at 35 sec and ended within 47 sec after initiating the injection of contrast medium.

Aged↗
PubMed1989

Review of the phase I and phase II teaching programmes in the School of Medical Sciences, Universiti Sains Malaysia.

The Phase I and Phase II undergraduate teaching programmes of the School of Medical Sciences were reviewed at the end of the 1985/86 academic year. It was found that deviations from the School's philosophy had crept into the implementation process. Modifications were therefore made in Phase I and Phase II programmes with a view to:--(i) reducing content, (ii) promoting integration, (iii) improving clinical examination skills of students, and (iv) providing more opportunities to students for self learning, reinforcement and application of knowledge. The number of assessment items in Phase I and the frequency of assessment in Phase II were also found to be inappropriate and so modifications in assessment were made to rectify this situation.

Curriculum↗
PubMed1984

Detection of phospholipid phase separation. A multifrequency phase fluorimetry study of 1,6-diphenyl-1,3,5-hexatriene fluorescence.

Using multifrequency phase and modulation fluorometry and a nonlinear least-squares analysis of lifetime data, we were able to determine the complex decay of 1,6-diphenyl-1,3,5-hexatriene (DPH) in synthetic phospholipid bilayers. Our results showed a monoexponential decay of DPH in the pure isotropic solvents studied, over a wide temperature range, and a double-exponential decay of DPH in phospholipids, both above and below the transition. During the transition, and in mixed-phase phospholipids, a three-component analysis was successfully accomplished, and the pre-exponential factors of the two main components have been shown to be quantitatively representative of the gel and liquid-crystalline phases of the bilayer. The fractional intensity of the shorter lifetime component depends on the modalities of the sample preparation. The factors affecting this component are discussed. From the DPH fluorescence lifetime and from the anisotropy data in L-alpha-dimyristoyl-phosphatidylcholine/L-alpha-dipalmitoyl-phosphatidyl choline mixtures, a phase diagram was independently constructed. Conclusions about the sensitivity and the partition of the probe between gel and the liquid-crystalline phases of the bilayer are derived. Lifetime experiments on DPH in a L-alpha-dilauroyl-phosphatidylcholine/L-alpha-dipalmitoyl-phosphatidylch oline mixture suggested a general method for the determination and quantitation of the two different phases in the bilayer.

Dimyristoylphosphatidylcholine↗
PubMed1980

[Correlation between the loss of plasmid DNA and the transition from virulent phase I to avirulent phase II in Shigella sonnei].

Transition from virulent phase I to non virulent phase II in five strains of Shigella sonnei was studied by immunofluorescence and plasmid electrophoresis. High frequency loss of phase I specific antigens was observed by use of fluorescent phase specific antibodies. Agarose gel electrophoresis of bacterial lysates showed that transition from phase I to phase II is associated with the loss of extrachromosomal DNA.

Animals↗
PubMed1995

Energy cost during ambulation in transfemoral amputees: a knee joint with a mechanical swing phase control vs a knee joint with a pneumatic swing phase control.

The aim of the study was (i) to evaluate the preference of transfemoral amputees for a 4-bar linked knee joint with either a mechanical swing phase control or a pneumatic swing phase control, and (ii) to compare the energy expenditure in transfemoral amputees using a prosthesis with a mechanical swing phase control with that of the same amputees using a prosthesis with a pneumatic swing phase control. The study included 28 unilateral transfemoral amputees amputated for reasons other than chronic vascular disease. All patients had a prosthesis with a knee joint with mechanical swing phase control (the Otto Bock 3R20) before entering the study. The amputees changed their knee joint to one with pneumatic swing phase control (the Tehlin knee joint) at random either after the first or second assessment. The amputees were asked for their preference at the second and third assessments. The energy expenditure while walking at speeds of 2 and 3 km/h was measured at each assessment. After having tried both knee joints, 19 patients preferred the Tehlin knee, 6 patients preferred the Otto Bock 3R20, and 3 patients had no preference. The energy expenditure measurement showed that walking with the Tehlin knee required more energy than walking with Otto Bock 3R20. Because of the limited number of patients included in the study and the fact that a double-blind design was impossible to achieve, conclusions should be drawn with caution.

Adolescent↗
PubMed1996

Stimulus specificity of phase-locked and non-phase-locked 40 Hz visual responses in human.

Considerable interest has been raised by non-phase-locked episodes of synchronization in the gamma-band (30-60 Hz). One of their putative roles in the visual modality is feature-binding. We tested the stimulus specificity of high-frequency oscillations in humans using three types of visual stimuli: two coherent stimuli (a Kanizsa and a real triangle) and a noncoherent stimulus ("no-triangle stimulus"). The task of the subject was to count the occurrences of a curved illusory triangle. A time-frequency analysis of single-trial EEG data recorded from eight human subjects was performed to characterize phase-locked as well as non-phase-locked high-frequency activities. We found in early phase-locked 40 Hz component, maximal at electrodes Cz-C4, which does not vary with stimulation type. We describe a second 40 Hz component, appearing around 280 msec, that is not phase-locked to stimulus onset. This component is stronger in response to a coherent triangle, whether real or illusory: it could reflect, therefore, a mechanism of feature binding based on high-frequency synchronization. Because both the illusory and the real triangle are more target-like, it could also correspond to an oscillatory mechanism for testing the match between stimulus and target. At the same latencies, the low-frequency evoked response components phase-locked to stimulus onset behave differently, suggesting that low- and high-frequency activities have different functional roles.

Adult↗