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PubMed2006

Linear free energy relationship as a tool for characterization of three teicoplanin-based chiral stationary phases under various mobile phase compositions.

Teicoplanin, teicoplanin aglycon, and methylated teicoplanin aglycon chiral stationary phases (CSPs) have been compared on the basis of the regression coefficients calculated from the linear free energy relationship (LFER) equation. The parameters have been obtained from the measurements of a set of 34 structurally diverse solutes. Influence of mobile phase composition - variation of methanol (MeOH) content - on the participation of different interactions types in the retention mechanism has been evaluated. Retention of the various interaction forces in analytes differs with both the CSP and the mobile phase composition. Hydrophobic interactions play a major role in mobile phases for high buffer contents. The more hydrophobic the CSP, the more important are they in the retention mechanism. With increase of MeOH contents in the mobile phase the major role in the interaction mechanism is shifted to more polar forces in which basicity and dipolarity/polarizability dominate. Although the LFER model does not address chiral aspects, we have attempted to explore the importance of the individual interactions in chiral discrimination of amino acids and their N-tert-butyloxycarbonyl derivatives.

Amino Acids↗

PubMed1991

Contrast/color card procedure: a new test of young infants' color vision.

We have developed a new test which can rapidly evaluate basic color vision in individual infants. The test consists of a series of large cards constructed with Munsell Hues. It uses a modified preferential looking procedure (FPL) and, to control brightness cues, incorporates a two-phase systematic variation of luminance. First, we evaluate an infant's ability to discriminate 9.5 by 16 degrees achromatic patches of varying luminance from a 26 by 65 degrees achromatic background of midrange luminance. In the second phase the test patch is chromatic and its luminance, relative to the background, is varied over a range of about 1.0 log cd/m2. The number of relative luminances chosen for each infant depends upon his/her performance in phase 1. Seventy 2- and 3-month-olds were tested with 4 broad-band chromatic patches, a red (dominant lambda = 660 nm), a yellow (dominant lambda = 580 nm), a green (dominant lambda = 520 nm), and a blue (dominant lambda = 475 nm). Results showed that 3-month-olds had little difficulty making any of the chromatic-achromatic discriminations but many 2-month-olds appeared to fail to discriminate the yellow and green from the background at relative luminances close to an adult brightness match. Most importantly, the test shows promise as a relatively simple, time-efficient, and portable tool for the assessment of early color vision.

Color Perception Tests↗

PubMed2000

Observation of Scholte-like waves on the liquid-loaded surfaces of periodic structures

The observation of Scholte-like ultrasonic waves travelling along the water-loaded surfaces of solids with periodically varying properties is reported. Results are presented for two 2D superlattices that intersect the surface normally: a laminated solid of alternating 0.5 mm thick layers of aluminium and a polymer, and a hexagonal array of polymer rods of lattice spacing 1 mm in an aluminium matrix. The surface waves are generated and detected by line-focus acoustic lenses aligned parallel to each other, and separated by varying distances. For homogeneous solids, phase matching constraints do not allow the Scholte wave to be coupled into with an experimental configuration of this type, and this is demonstrated with results on a uni-directional carbon-fibre/epoxy composite. These constraints are relaxed for a periodic solid, where coupling takes place through Umklapp processes. In our experiments, the source pulse is fairly broadband, extending up to about 6 MHz, whereas the spectrum of the observed Scholte arrival is peaked at around 4 MHz. We attribute this to a resonance in the surface response of the solid associated with the superlattice structure. On rotating the solid about its surface normal, the Scholte wave displays a characteristic variation in phase arrival time and, to a lesser extent, also group arrival time. This variation is well accounted for with a model that incorporates Umklapp processes in the solid's surface response.

Journal Article↗

PubMed2000

Prediction of retention indices. V. Influence of electronic effects and column polarity on retention index.

The retention index increment for addition of a methylene group to an analyte molecule is shown for 1-halo-n-alkanes to be different from 100 i.u., a value that is customarily assigned according to the current convention in retention index prediction. In temperature-programmed gas chromatography using linearly interpolated retention index I, a linear regression equation, I=AZ+(GRF), with the number of atoms (Z) in the molecule as variable can describe the retention of 16 homologous series of organic compounds on non-polar and polar columns with characteristic A (linear regression coefficient) and (GRF) (group retention factor) values. A molecular model of retention on the basis of electron density and electron density distribution relative to that of n-alkane is proposed. This model brings out the inter- and intramolecular electronic effects in the analyte molecule and its dipole-dipole interaction with the stationary liquid phases, as variations in the A value. The (GRF) value varies with the connectivity ability of a functional group for extended conjugation, substitution, etc., but is most influenced by hydrogen bonding (H-bonding) with the stationary liquid phase. One can estimate the sequence of elution of a mixture of organic compounds from any two of the three parameters on the right-hand side of the above equation or retrieve the retention indexes of an entire homologous series from its A and (GRF) values. The fact that each analyte molecule has its own A value on different columns makes column difference (deltaI) compound-specific rather than column-specific, a departure from previous assumptions.

Chromatography, Gas↗

PubMed1978

The role of phospholipids in the reduction of ubiquinone analogues by the mitochondrial reduced nicotinamide-adenine dinucleotide-ubiquinone oxidoreductase complex.

The isolated NADH-ubiquinone oxidoreductase complex of bovine heart mitochondria reduces ubiquinone analogues by two pathways. One pathway is inhibited by rotenone, and reduction of quinones takes place in the lipid phase of the system. The other pathway is insensitive to rotenone and reduction takes place in the aqueous phase. The variation of rates of electron transpport with the chemical nature of the quinone analogue and the concentrations of both quinone and phospholipid can be rationalized in terms of partition of the quinone between the aqueous and lipid phases of the system. Thus one function of phospholipid associated with the enzyme appears to be to act as solvent for ubiquinone reduced by the rotenone-sensitive pathway. This proposal is supported by the kinetic behaviour of enzyme whose endogenous lipids have been replaced by (1,2)-dimyristoylsn-glycero-3-phosphocholine. Thus, under certain circumstances, the rotenone-sensitive reduction of ubiquinone-1 exhibited a substantial increase in activation energy below the phase-transition temperature of the synthetic lipid, whereas the reduction of other acceptors was unaffected.

Animals↗

PubMed2005

Structure solution in binary systems under high pressure: phase decomposition and phase synthesis.

There are binary systems (compounds) for which no structural solution can be found for a new high-pressure state by assuming a single phase. In accordance with Gibb's phase rule, an additional variable--composition--leads to an additional degree of freedom for a binary system (one more than in a one-component system). Although the bulk composition of a system may remain fixed, compositional variation between phases should be taken into account when considering phase transitions under pressure in binary compounds. This approach allows for a binary system the following kinds of phase transitions that are not possible in a one-component system: (i) phase (compound) decomposition into two phases with different compositions; (ii) phase synthesis from two initial phases; and (iii) phase separation from an initial phase into phases of different compositions. Examples of these kinds of high-pressure transformations and structure solution are given for the following binary systems: In-Bi, In-Sn, Hg-Sn, Cd-Sb and Sn-Bi.

Journal Article↗

PubMed1992

Variation in ocular modulation and phase transfer functions with grating orientation.

For circular pupils of diameters < or = 2 mm the optical performance of the eye in monochromatic light is effectively diffraction-limited, so that its modulation transfer function (MTF) is essentially independent of grating orientation and its phase transfer function (PTF) is close to zero. For larger pupils, however, the wave aberration of the eye usually exceeds the Rayleigh quarter-wavelength limit. It is shown that the monochromatic MTF may then display marked variation with orientation and the associated PTFs can be non-zero. The exact effects vary markedly with the individual subject. In white light additional asymmetries may occur due to transverse chromatic aberration.

Contrast Sensitivity↗

PubMed1993

Search for functional significance of peptidylarginine deiminase in rat pituitaries: variation during pregnancy and ultrastructural localization in prolactin cells.

We have studied the expression of peptidylarginine deiminase in rat pituitaries during pregnancy. Both the enzyme protein and its mRNA decreased to low levels after the onset of gestation. Both started to increase markedly during mid pregnancy reaching their maxima on day 18 and declined thereafter. The early phase of variations were accompanied with a progressive decrease in the pituitary prolactin content, an abrupt decrease in the prolactin mRNA content, and a small but significant increase in the serum estrogen. We also performed an immunoelectron microscopic study of the enzyme, and showed its scattered localization in the cytoplasm of prolactin cells.

Animals↗

PubMed2005

Ectodomain shedding of membrane-anchored heparin-binding EGF like growth factor and subcellular localization of the C-terminal fragment in the cell cycle.

Heparin-binding EGF-like growth factor (HB-EGF) is initially synthesized as a type I transmembrane protein (proHB-EGF). The proHB-EGF is shed by specific metalloproteases, releasing the N-terminal fragment into the extracellular space as a soluble growth factor (HB-EGF) and the C-terminal fragment (HB-EGF-C) into the intracellular space, where it prevents transcriptional repression by the promyelocytic leukemia zinc finger protein (PLZF). The goal of the present study was to characterize regulation of proHB-EGF shedding and study its temporal variations in HB-EGF-C localization throughout the cell cycle. Quantitative combination analyses of cell surface proHB-EGF and HB-EGF in conditioned medium showed that proHB-EGF shedding occurred during the G(1) cell cycle phase. Laser scanning cytometry (LSC) revealed that HB-EGF-C was internalized into the cytoplasm during the late G1 phase and accumulated in the nucleus beginning in the S phase. Subsequent nuclear export of PLZF occurred during the late S phase. Further, HB-EGF-C was localized around the centrosome following breakdown of the nuclear envelope and was localized to the interzonal space with chromosome segregation in the late M phase. Temporal variations in HB-EGF localization throughout the cell cycle were also characterized by time-lapse imaging of cells expressing YFP-tagged proHB-EGF, and these results were consistent with those obtained in cytometry studies. These results indicate that proHB-EGF shedding and subsequent HB-EGF-C signaling are related with progression of the cell cycle and may provide a clue to understand the unique biological significance of non-receptor-mediated signaling of proHB-EGF in cell growth.

Animals↗

PubMed1986

The effect of ovariectomy on lipoprotein metabolism during a period of one year.

In a follow-up study over one year the influence of sex hormones on lipoprotein metabolism in women after ovariectomy was investigated. During this relatively long period we could observe several changes of lipid and apolipoprotein levels in serum which may be caused by adaptive processes after withdrawal of sex hormones. The first phase of variation of lipids and apolipoproteins (2 weeks after ovariectomy) is strongly influenced by the operation trauma and characterized by a decrease of apo A-I, apo A-II, TC levels and an increase of the triglyceride level. The second phase (6-18 weeks after operation) shows an increase of the levels of apolipoprotein of HDL (apo A-I and apo A-II) and also apo C-II and apo C-III. The pattern in the third phase (one year after operation) differs from that of the two earlier phases and is similar to that in the natural postmenopausal state (elevation of apo B, TC, nonsignificant elevation of apo A-I and significant elevation of apo A-II). It seems that ovariectomy causes permanent changes of the LDL-level whereas the fluctuation of HDL is temporary. The late changes in the lipoprotein spectrum following ovariectomy in the reported direction may be important for the increase of ischemic heart disease observed by many investigators.

Adult↗

PubMed1995

Effects of flicker adaptation and temporal gain control on the flicker ERG.

The flicker electroretinogram (ERG) to stimuli varying in temporal frequency and modulation depth was recorded to investigate retinal gain control. With increasing modulation of a sinusoidal flickering stimulus, the flicker ERG shows an amplitude compression and a phase retardation (of the fundamental component) at 16 Hz, an amplitude expansion and a phase advance around 40-48 Hz, and an approximately linear response at 72 Hz. With sum-of-two-sinusoids stimuli, the second stimulus enhances the fundamental response to a 40 or 48 Hz test stimulus at low modulations, and reduces the variation in phase with modulation. This interaction depends primarily on the amplitude of the response to the second stimulus, but not its frequency. With temporally alternating stimuli, a similar but smaller interaction effect is measured. The results suggest that there is an active nonlinear gain control mechanism in the outer retina and this gain control works by adjusting the phase delay of the retinal response. The phase control mechanism is set by the amplitude of the outer retinal response integrated over time.

Adaptation, Ocular↗

PubMed1998

Annual and diurnal variations in, and effects of altered photoperiod and temperature, ovariectomy, and estradiol-17 beta replacement on catechol-O-methyltransferase level in brain regions of the catfish, Heteropneustes fossilis.

The annual data show that catechol-O-methyltransferase (COMT) content increases with the progress of ovarian recrudescence in all the brain regions (telencephalon, hypothalamus, thalamus + tegmentum, and medulla oblongata) and declines after spawning to low values in quiescent phase. Diurnal variation in enzyme concentration with peak values at 24 hr was noticed in the hypothalamus throughout the reproductive cycle; in other brain regions, it was observed only in February and March. The stimulatory response of the enzyme to photoperiod and temperature alterations was differential and region-specific; an effect of photoperiod change was noticed only in the hypothalamus and was less in magnitude compared to the temperature effect. The response of the enzyme to ovariectomy (OVX) and E2 supplementation was region-specific (hypothalamus only), season-specific (prespawning phase), and varied:inhibitory at 3 and 4 weeks, stimulatory at 6-week of OVX and after 0.05, 0.1, 5, and 10 micrograms/g doses of E2, and none at week 2 and 5 of OVX and after 0.5 and 1 microgram/g doses of E2. The season-specific changes in hypothalamic COMT may be indicative of its involvement in catecholamine (and possibly catecholestrogen)-mediated neuroendocrine control of gonadotropin.

Animals↗

PubMed1979

Phase separations in membranes of Anacystis nidulans grown at different temperatures.

Freeze fracture electron microscopy studies were performed on samples of Anacystis nidulans quenched from different temperatures. Membrane lipid phase separations were observed to take place over the ranges 15--30 degrees C, 5--25 degrees C and -5--15 degrees C for cultures grown at 38, 28 and 18 degrees C, respectively. Differential scanning calorimetry heating curves showed endotherms which coincided with these temperature ranges. Variations of phase separation temperatures with growth temperature, and hysteresis effects in the calorimetric measurements, were related to changes in the fatty acid composition of membrane lipids.

Cell Fractionation↗

PubMed2004

Cellular and molecular characterization of a murine non-union model.

PURPOSE: We have developed a method to study the molecular and cellular events underlying delayed skeletal repair in a model that utilizes distraction osteogenesis. METHODS: The clinical states of delayed union and non-union were reproduced in this murine model by altering distraction parameters such as the inclusion and exclusion of a latency phase and variations in the rate and rhythm of distraction. Radiographic, cellular, and molecular analyses were performed on the distraction tissues. RESULTS: Eliminating the latency period delayed bony union, but did not appreciably alter the extent of platelet endothelial cell adhesion marker (PECAM) immunostaining. Following elimination of a latency phase and a threefold increase in the rate of distraction, there was a further delay in bone regeneration and a higher rate of non-union (60%). Instead of bone, the distraction gap was comprised of adipose or fibrous tissue. Once again, despite the rigorous distraction protocol, we detected equivalent PECAM staining within the distraction gap. In a minority of cases, cartilage and osseous tissues occupied the distraction gap likely by a prolonged process of endochondral ossification. CONCLUSIONS: Here, we have altered the mechanical environment in such a way to reproducibly create delays in skeletal regeneration. These delays in skeletal tissue regeneration appear to develop even in the presence of endothelial cells, which suggests that mechanisms other than a disruption to the vascular network can account for some cases of non-union.

Animals↗

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↗

PubMed1985

Use of acute phase protein changes to assess the effects of a nonsteroidal antiinflammatory drug (niflumic acid) on the inflammation process induced by limited plastic surgery.

Serum levels of acute phase proteins (C-reactive protein, alpha 1 acid glycoprotein, and haptoglobin) have been measured to assess the effects of a nonsteroidal antiinflammatory drug (niflumic acid). Thirty patients undergoing plastic surgery have been studied. The results obtained from this surgical model prove that nonsteroidal antiinflammatory drugs can modify acute phase response and especially acute phase proteins levels. The participation of prostaglandins in the acute phase protein variations is discussed. The authors conclude that haptoglobin could provide a convenient tool for studying some aspects of prostaglandin action in vivo.

Acute-Phase Proteins↗

PubMed2002

Phase and gain measurements in a distributed-loss cyclotron-resonance maser amplifier.

The control of gain and phase delay in a cyclotron-resonance maser (CRM) amplifier is essential for a variety of applications. In this experiment, the gain and phase-delay variations are measured with respect to controlling parameters; the electron-beam current and the axial magnetic field. Following Chu et al. [Phys. Rev. Lett. 74, 1103 (1995)], the CRM amplifier comprises of a distributed-loss waveguide to enable high gain without oscillations. Our experiment yields an amplification up to 26 dB, and a phase-delay control range of 360 degrees. In order to keep a fixed gain with the varying phase delay, the two controlling parameters (i.e., the solenoid field and the beam current) are operated together in a compensating mode. The experiment is conducted in a frequency of 7.3 GHz, with an electron beam of 18-kV voltage and 0.25-0.4-A current. The experimental results are compared with a theoretical model. Practical implementations of gain and phase control in CRM devices are discussed.

Journal Article↗

PubMed2006

The phase-dependent infrared brightness of the extrasolar planet upsilon Andromedae b.

The star upsilon Andromedae is orbited by three known planets, the innermost of which has an orbital period of 4.617 days and a mass at least 0.69 that of Jupiter. This planet is close enough to its host star that the radiation it absorbs overwhelms its internal heat losses. Here, we present the 24-micrometer light curve of this system, obtained with the Spitzer Space Telescope. It shows a variation in phase with the orbital motion of the innermost planet, demonstrating that such planets possess distinct hot substellar (day) and cold antistellar (night) faces.

Astronomical Phenomena↗