SEARCH · PubMed Health

Results for “phase variation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,135 records · Page 63Linked to original sources

PubMed1997

Comparison of DNA bending by Fos-Jun and phased A tracts by multifactorial phasing analysis.

Studies of DNA bending by Fos and Jun using different methods have yielded contradictory results. Whereas gel electrophoretic phasing analysis indicates that Fos and Jun bend DNA, results obtained through X-ray crystallography and ligase-catalyzed cyclization suggest that they do not. To test the assumptions underlying phasing analysis and to examine DNA bending by Fos and Jun, a multifactorial phasing analysis approach based on the distinct electrophoretic mobilities of DNA fragments of diverse shapes was developed. In this approach, the spacing between the bends, the length of sequences flanking the bends, and the acrylamide concentration in the gel are varied. Two closely spaced intrinsic bends with long flanking sequences had the same effect on electrophoretic mobility as a single bend corresponding to the sum of the bends when they were arranged in phase, and the difference between the bends when they were arranged out of phase. Based on the phase-dependent electrophoretic mobility variation of fragments containing intrinsic DNA bends of different magnitudes, three criteria for determination whether the phase-dependent mobility variation of protein-DNA complexes is caused by DNA bending were adopted. Complexes formed by the bZIP domains of Fos and Jun fulfilled each of these criteria. First, the electrophoretic mobility variation induced by Fos and Jun was proportional to that caused by an intrinsic bend over a broad range of acrylamide concentrations. Second, the mobility difference between fragments containing in phase and out of phase bends was reduced by an increase in the separation between the bends. The separation between the bends had the same effect on the electrophoretic mobility variation caused by Fos and Jun as well as intrinsic bends on long DNA fragments at low acrylamide concentrations. Third, on short DNA fragments analyzed at high acrylamide concentrations, two intrinsic bends separated by long spacers caused a larger decrease in electrophoretic mobility when they were out of phase than when they were in phase. This reversal of the phase dependence of the electrophoretic mobility variation was also observed for complexes formed by truncated Fos and Jun. Thus, the phase-dependent mobility variation of Fos and Jun complexes is due to DNA bending.

Animals↗

PubMed2001

Early brain damage and the development of motor behavior in children: clues for therapeutic intervention?

The Neuronal Group Selection Theory (NGST) could offer new insights into the mechanisms directing motor disorders, such as cerebral palsy and developmental coordination disorder. According to NGST, normal motor development is characterized by two phases of variability. Variation is not at random but determined by criteria set by genetic information. Development starts with the phase of primary variability, during which variation in motor behavior is not geared to external conditions. At function-specific ages secondary variability starts, during which motor performance can be adapted to specific situations. In both forms, of variability, selection on the basis of afferent information plays a significant role. From the NGST point of view, children with pre- or perinatally acquired brain damage, such as children with cerebral palsy and part of the children with developmental coordination disorder, suffer from stereotyped motor behavior, produced by a limited repertoire or primary (sub)cortical neuronal networks. These children also have problems in selecting the most efficient neuronal activity, due to deficits in the processing of sensory information. Therefore, NGST suggests that intervention in these children at early age should aim at an enlargement of the primary neuronal networks. With increasing age, the emphasis of intervention could shift to the provision of ample opportunities for active practice, which might form a compensation for the impaired selection.

Brain Damage, Chronic↗

PubMed1989

Gastric emptying of liquid meals. A study in 88 normal persons.

Using a gamma camera, gastric emptying of a nutrient liquid meal labelled with 99m-Tc-DTPA has been studied in 88 normal subjects in order to assess reproducibility and to establish the range for gastric emptying under standardized conditions. The emptying patterns were visualized as time-activity curves. The early phase (0-15 min) was characterized by a rapid emptying taking place during the first minutes and a subsequent period of almost no emptying (plateau) lasting for up to 20 minutes, followed by an almost constant emptying in the later phase (15-60 min). In the early and later phase mean percentages emptied were 13% (range, 0-30) and 49% (range, 9-79), respectively. The intraindividual variation was larger for repeated tests of months' than of days' intervals, the coefficients of variation in the early phase being on the average 72% (range, 29-175) and 37% (range, 13-128), respectively. During the later phase less variation was seen. Irregular deviations from the standard pattern were observed in the curves, indicating gastric contractions and duodenogastric reflux. Serial scintifotos revealed that the radionuclide labelled gastric content was not uniformly distributed within the stomach. This activity distribution, affected by the subject's position during emptying, seemed to occur instantaneously and to be completed within a few minutes. These findings allow the standardized radioisotope technique to be used for physiological, pathophysiological and pharmacological studies, when performing consecutive studies in the same individual within days or a few weeks. The wide reference interval for gastric emptying of this liquid meal invalidates the method as a clinical diagnostic tool.

Adult↗

PubMed2003

Effects of cross-phase modulation on phase jitter in soliton systems with constant dispersion.

In wavelength-division-multiplexed communication systems phase jitter is driven by amplifier noise and mediated by cross-phase modulation. The variational method is used to derive formulas for the absolute phase variance of an ensemble of solitons and the relative phase variance of ensembles of neighboring solitons. The predictions of these formulas are consistent with the results of numerical simulations.

Journal Article↗

PubMed2006

Theory of stepwise gradient elution in reversed-phase liquid chromatography coupled with flow rate variations: application to retention prediction and separation optimization of a set of amino acids.

The coupling of stepwise mobile phase gradient elution and flow programming is proposed as an integrated approach to the general elution problem in reversed-phase liquid chromatography. A model is developed to describe the above separation process performed under simultaneous programming of two separation parameters by extending our previous work on the rigorous derivation of the fundamental equation governing the concentration gradient of organic modifier in the mobile phase, that is, a single gradient elution mode (Anal. Chem. 2005, 77, 5670-5677). The theory was tested in the retention prediction and separation optimization of 18 o-phthalaldehyde derivatives of amino acids in eluting systems modified by acetonitrile or methanol. The retention prediction obtained for all solutes under all dual-mode gradient conditions was excellent. In addition, it has been shown that the combination of mobile phase and flow rate programming modes is particularly favorable, whereas the separations among the analytes were considerably improved by using the acetonitrile eluting system, as compared to those obtained by the methanol system.

Amino Acids↗

PubMed1999

Evaluation of the macrocyclic antibiotic LY333328 as a chiral selector when used as a mobile phase additive in narrow bore HPLC.

The macrocyclic antibiotic LY333328 has been evaluated as a chiral selector for the enantioseparation of nine dansylated amino acids. This macrocyclic glycopeptide was used as a chiral mobile phase additive (CMPA) in conjunction with narrow bore high-performance liquid chromatography (HPLC). The key mobile phase parameters of LY333328 concentration and buffer pH were varied, along with variations in stationary phases consisting of C8, phenyl, cyano, and silica. After observing and plotting changes in retention and resolution based on corresponding variation in these parameters, a better understanding of the behavior of this chiral selector was obtained. The pKa values of the dansyl amino acid analytes and LY333328 were measured and used to gain a better understanding of the microenvironment in which these enantioseparations occur. Optimized conditions resulted in the baseline separation of eight of nine dansyl amino acids.

Amino Acids↗

PubMed1977

Electromyographic study of duration of muscle activity in sit-up variations.

The external oblique, rectus abdominis, and rectus femoris muscles of 17 college women were studied electromyographically in 8 sit-up variations to determine the best variation for maximizing abdominal muscle activity and minimizing hip flexor activity. Integrated action potentials and movement phases of each variation were recorded simultaneously. The duration of muscle activity within the movement phases was analyzed. The variables of hook-lying/long-lying, feet supported/feet unsupported, and slow/fast speed of performance were examined. The hook-lying unsupported slow and fast variations were best for maximizing abdominal muscle duration of activity and for minimizing rectus femoris muscle duration of activity. Greatest duration of activity for all muscles occurred in the long-lying supported fast variation. Supporting the feet in both hook and long-lying fast variations was more effective for increasing activity duration of all muscles than the slow supported variations. Speed of performance seemed to be as important as support of the feet or leg position in increasing duration of muscle activity.

Abdominal Muscles↗

PubMed1975

Levels of prostaglandins F-2alpha and E-2 in human endometrium during the menstrual cycle.

A comparison between the prostaglandins found in proliferative and secretory endometrium in normal and tumor-bearing tissues is reported. The content of prostaglandins F-2alpha and E-2 is related to the three phases of the menstrual cycle and correlates with cyclic ovarian hormone variations. The menstrual phase is characterized by a high content of PGF-2alpha. High prostaglandin levels are found in tissues from patients with pathologic diseases such as adenocarcinoma of the endometrium when compared to normal tissues.

Adenocarcinoma↗

PubMed2001

The role of the medial wall and its anatomical variations for bimanual antiphase and in-phase movements.

The medial wall of the frontal cortex is thought to play an important role for bimanual coordination. However, there is uncertainty regarding the exact neuroanatomical regions involved. We compared the activation patterns related to bimanual movements using functional magnetic resonance imaging in 12 healthy right-handed subjects, paying special attention to the anatomical variability of the frontal medial wall. The subjects performed unimanual right and left and bimanual antiphase and in-phase flexion and extension movements of the index finger. Activation of the right supplementary motor area (SMA) proper, right and left caudal cingulate motor area (CMA), and right and left premotor cortices was significantly stronger during bimanual antiphase than bimanual in-phase movements, indicating an important function of these areas with bimanual coordination. A frequent anatomical variation is the presence of the paracingulate sulcus (PCS), which might be an anatomical landmark to determine the location of activated areas. Seven subjects had a bilateral, three a unilateral right, and two a unilateral left PCS. Because the area around the PCS is functionally closer coupled to the CMA than to the SMA, activation found in the area around the PCS should be attributed to the CMA. With anatomical variations such as the presence of a PCS or a vertical branch of the cingulate sulcus, normalization and determination of the activation with the help of stereotaxic coordinates can cause an incorrect shift of CMA activation to the SMA. This might explain some of the discrepancies found in previous studies.

Adult↗

PubMed2002

[Relationship between acute phase reactant proteins (APRP) and fatigue during post-operative convalescence].

Surgery originates an inflammatory state which triggers an acute phase response (APR). In this study, variations in the acute phase reactant proteins (APRP) and their relationship with fatigue were assessed. A total of 58 candidate patients for elective abdominal surgery participated in this study. In the preoperative period (PRE) and in the post-operative period (9 days [9-P], 27 days [27-P] and 45 days [45-P]), variations in serum APRP and fatigue were analyzed. In the post-operative period (9-P), a significant decrease in PT, ALB, PAB, TRF, and an increase in CER were observed. In 27-P, significant decreases were observed in PAB and PBR, with increased PT and CER, and without significant variations in ALB ad TRF. In the 45-P day, a concomitant increase in PT and CER was observed. Dynamometric parameters also decreased significantly in the post-operative period (9-P). In conclusion, our results demonstrate the existence of changes in serum proteins and in APRP after an elective abdominal surgical intervention, which are associated with fatigue, evaluated both by subjective and objective (dynamometry) means and the use of a mathematical model that considers weight, proteins and APRP.

Acute-Phase Proteins↗

PubMed2006

Cell surface acid-base properties of Escherichia coli and Bacillus brevis and variation as a function of growth phase, nitrogen source and C:N ratio.

Potentiometric titration has been conducted to systematically examine the acid-base properties of the cell surfaces of Escherichia coli K-12 and Bacillus brevis as a function of growth phase, nitrogen source (ammonium or nitrate), and carbon to nitrogen (C:N) ratio of the growth substrate. The two bacterial species revealed four distinct proton binding sites, with pK(a) values in the range of 3.08-4.05 (pK(1)), 4.62-5.57 (pK(2)), 6.47-7.30 (pK(3)), and 9.68-10.89 (pK(4)) corresponding to phosphoric/carboxylic, carboxylic, phosphoric, and hydroxyl/amine groups, respectively. Two general observations in the data are that for B. brevis the first site concentration (N(1)), corresponding to phosphoric/carboxylic groups (pK(1)), varied as a function of nitrogen source, while for E. coli the fourth site concentration (N(4)), corresponding to hydroxyl/amine groups (pK(4)), varied as a function of C:N ratio. Correspondingly, it was found that N(1) was the highest of the four site concentrations for B. brevis and N(4) was the highest for E. coli. The concentrations of the remaining sites showed little variation. Finally, comparison between the titration data and a number of cell surface compositional studies in the literature indicates one distinct difference between the two bacteria is that pK(4) of the Gram-negative E. coli can be attributed to hydroxyl groups while that of the Gram-positive B. brevis can be attributed to amine groups.

Acid-Base Equilibrium↗

PubMed2000

Mesoscopic microwave dispersion in ferroelectric thin films

The microwave dielectric response of a ferroelectric thin film is measured locally using time-resolved confocal scanning optical microscopy. Measurements performed on an ensemble of nanometer-scale regions show a well-defined phase shift between the paraelectric and ferroelectric response at 2-4 GHz. Application of a static electric field produces large local variations in the phase of the ferroelectric response. These variations are attributed to the growth of in-plane ferroelectric nanodomains whose size-dependent relaxation frequencies lead to strong dielectric dispersion at mesoscopic scales.

Journal Article↗

PubMed1997

Localized reversible frameshift mutation in an adhesin gene confers a phase-variable adherence phenotype in mycoplasma.

The variable adherence-associated (Vaa) antigen of Mycoplasma hominis is an abundant surface lipoprotein adhesin that may mediate important interactions of this wall-less prokaryotic pathogen with the human host. Extensive mutational variation of Vaa size, as well as sequence and antigenic divergence, has been described previously. Using a series of clonal isolates representing an isogenic lineage of variants oscillating in Vaa expression, Vaa is further shown in this study to undergo high-frequency phase variation in expression, which correlated precisely with the ability of M. hominis to adhere to cultured human cells. Although no DNA rearrangements or sequence differences in the 5' regions flanking vaa alleles were detected between Vaa+ and Vaa variants, intragenic vaa sequences from this lineage revealed an oscillating mutation involving a single nucleotide deletion/insertion in a short tract of adenine residues near the 5' end of the mature Vaa coding sequence, which created a translational frameshift resulting in either a complete Vaa ORF or an in-frame UAG stop codon immediately downstream of the poly-A tract. Evidence for the occurrence of this high-frequency frameshift mutation in vivo was obtained from analysis of PCR-generated vaa sequences amplified from the joint synovial fluid of a patient with M. hominis-associated arthritis, which indicated that Vaa phase variation occurs during M. hominis infection in the natural host. These results identify a distinctive frameshift mutator element in the vaa gene that governs M. hominis adherence and highlight the importance of mutational alteration of primary gene products on the mycoplasma surface as a means of generating and maintaining functional diversity in the host.

Adhesins, Bacterial↗

PubMed1982

Diurnal variations of plasma thyrotropin, thyroxine, and triiodothyronine in female rats are phase shifted after inversion of the photoperiod.

The present study examined plasma TSH, T4, and T3 concentrations in rats throughout the day to determine if diurnal variations of these hormones occurred. Female rats on a 12-h light, 12-h dark cycle (onset of light, 0730 h) were sampled by cardiac puncture at 2-h intervals throughout the day on 2 days, 1 week apart. Significant diurnal variations of plasma TSH, T4, and T3 were detected (P less than 0.01), Peak TSH concentrations occurred soon after the onset of light, whereas T4 and T3 concentrations peaked 3-4 h later. After these variations were detected, the effect of inverting the photoperiod was examined. Female rats were placed on 12-h light,, 12-h dark cycles, with the onset of light at 0730 h (LD) or 1930 h (DL). After 3 weeks, rats from each group were killed by decapitation at 4-h intervals throughout the day, and trunk blood was collected. Diurnal variations in plasma TSH, T4, and T3 (P less than 0.01) were similar to those found with 2-h sampling intervals in the previous experiment, and plasma corticosterone and PRL rhythms peaked near the onset of darkness (P less than 0.05). Inversion of the photoperiod phase shifted all diurnal variations, such that they maintained a similar phase relationship to the light-dark cycle on both LD and DL photoperiods. These results indicated that diurnal variations of plasma TSH, T4, and T3 concentrations could be repeatedly detected with different sampling protocols. These variations were phase shifted by inverting the photoperiod, which indicated that some aspect of the light-dark cycle can act to set the phase of these diurnal variations in the pituitary-thyroid axis.

Animals↗

PubMed1976

A solid-phase radioimmunoassay for the measurement of lactoferrin in human plasma: variations with age, sex, and disease.

A solid-phase radioimmunoassay is described for measuring lactoferrin levels in normal human plasma. The sensitivity of the assay was 6 ng. per milliliter with an intraassay coefficient of variation of 4 per cent and an interassay value of 9 per cent. Healthy adult males had a mean plasma level of 1.62 mug per milliliter which was significantly higher than adult females, 1.07 mug per milliliter. Postmenopausal females had levels similar to men, 1.74 mug per milliliter, while younger women had a significantly lower mean value, 0.75 mug per milliliter. Two menstruating women and 2 pregnant women had moderately elevated levels. Consistently elevated levels were found in patients with untreated or relapsing chronic myeloid leukemia--all over 12.0 mug per milliliter, while patients on marrow suppressant therapy tended to have subnormal levels. The collection of serum specimens as opposed to plasma, resulted in inconsistently elevated levels: EDTA was the anticoagulant of choice, as heparin interfered in the radioimmunoassay system.

Adult↗

PubMed1990

Cardiac phase-related variability of border detection or densitometric quantitation of postangioplasty lumens.

We applied an automated computer program capable of simultaneous geometric (through border detection) and densitometric quantitation of digital angiograms for evaluation of the results of percutaneous transluminal coronary angioplasty (PTCA) in different phases of the same cardiac cycle. Digital subtraction coronary angiograms (DSA) of 28 patients who had undergone PTCA to a total of 30 lesions, were analyzed in diastole, in systole, and in the middle of the cardiac cycle to test the variability in coronary quantitation resulting from random frame selection relative to cardiac phase. Before PTCA there was a low degree of variation between measurements obtained from the same lesion in different phases of the cardiac cycle, in both geometric (coefficient of variation between cardiac phases = 4.2%) and densitometric (coefficient of variation between cardiac phases = 5.1%) quantitation. After PTCA, however, there was a wider variation of values in different cardiac phases, which predominated in the densitometric measurements (coefficient of variation between cardiac phases = 33.6%, compared to 20.6% for geometric measurements). There was less agreement between different post-PTCA phases in densitometry, and discrepancies as large as 47% could occur in densitometric evaluation of the stenotic areas when different phases of the cycle were used. We concluded that border detection or densitometric quantitation of the postangioplasty lumens is subject to greater variation resulting from random frame selection relative to cardiac phase, as compared to preangioplasty assessment. This variation predominates in densitometric quantitation, which seems to be dependent not only on the radiographic projection but also on the cardiac phase. The usefulness of densitometric techniques for the evaluation of PTCA results appears to be questionable.

Angiography, Digital Subtraction↗

PubMed2000

Cavity phase engineering for stable enhanced terahertz pulse trains.

We show that the cavity round-trip Gouy phase leads to pulse-to-pulse variation of the absolute phase and temporal profile of circulating few- or single-cycle pulses in empty resonators. This pulse-to-pulse variation can be eliminated by the proper insertion of a lens into the cavity. An application to terahertz resonators with phase-locked feedback is discussed.

Journal Article↗

PubMed1998

A secondary ion mass spectroscopic study of the elemental composition pattern in rat incisor dental enamel during different stages of ameloblast differentiation.

In most earlier studies on the elemental composition pattern of dental enamel, a picture is presented which describes a limited region. In this study, estimates of the incorporation of some critical elements into enamel were correlated with the differentiation stages of the ameloblasts through out the whole tooth. Elemental analyses of rat incisor dental enamel during the secretory, transitional and maturation phases were performed using two different modes of secondary ion mass spectrometry (SIMS). The results were presented as ion images and three-dimensional spatial resolution graphs. In the elemental images of 23Na, 26CN, 35Cl and 39K, counts were detected during the secretory and maturation phases of amelogenesis. Variations were interpreted as resulting from secretion of elements during the secretory phase and resorption during the maturation phase. In line scans the ion yield from enamel during different stages of differentiation of the ameloblasts was analysed. The elements investigated were 12C, 19F, 23Na, 31P, 39K and 77CaCl. As seen in the images, most elements exhibited a higher ion yield during the earlier stages of secretion, and lower yields during the maturation-phase resorption. Cl, together with P, increased during the phases of maturation. In the most apical portions of the teeth, corresponding to a presecretory phase, an inverse pattern was seen for most of the elements. If the surface yield was high at the onset of the secretory phase, the presecretory yields were lower, and vice versa.

Amelogenesis↗