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At least 433 records · Page 24Linked to original sources
PubMed2005

Full-capillary sample stacking/sweeping-MEKC for the separation of naphthalene-2,3-dicarboxaldehyde-derivatized tryptophan and isoleucine.

In an attempt to improve the sensitivity of detection in capillary electrophoresis (CE), a novel online sample-concentration method, full-capillary sample stacking (FCSS)/sweeping-micellar electrokinetic chromatography (sweeping-MEKC) mode, is proposed. Naphthalene-2,3-dicarboxaldehyde (NDA)-derivatized tryptophan and isoleucine were selected as model compounds. In the initial step, the weakly acidic compounds, dissolved in a low-conductivity buffer (35.1 microS/cm; apparent ph (pH*) in a mixed solution of acetonitrile/methanol/water, 4.6), fill the entire capillary, two vials of a high-conductivity buffer (2.06 mS/cm; pH* 2.0) are placed on each end, and a negative polarity is then applied. Under these conditions, the direction of the electroosmotic flow (EOF) is toward the inlet. Meanwhile, the anionic analytes move in the reverse direction and are neutralized and stacked at the boundary of a dynamic pH-junction (between the sample matrix and the nonmicellar background solution (BGS)). When the sample concentration is completed, the BGS is quickly changed to solutions containing SDS-BGS for the subsequent separation. Since the mobility of SDS-analytes is then greater than the EOF, the following steps occur by the sweeping (for focusing) and MEKC (for separation) mode. Using these steps, a full-capillary sample injection/separation can be achieved.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed2000

Stripping/sweeping the membranes for inducing labour or preventing post-term pregnancy.

BACKGROUND: Stripping or sweeping of the membranes aims to initiate labour through a cascade of physiological events. These may reduce pregnancy duration or pre-empt formal induction of labour with either oxytocin, prostaglandins or amniotomy. OBJECTIVES: The objective of this review was to assess the effects of membrane sweeping to promote or induce labour on maternal and perinatal outcomes. SEARCH STRATEGY: We searched the Cochrane Pregnancy and Childbirth Group trials register and the Cochrane Controlled Trials Register (last searched April 1998). SELECTION CRITERIA: Adequately controlled trials of digital separation of the membranes from the lower uterine segment for inducing labour or for preventing post-term pregnancy, compared to either no vaginal examination or vaginal examination for cervical assessment only without the intention to detach the membranes. DATA COLLECTION AND ANALYSIS: Two reviewers assessed trial quality and extracted data. MAIN RESULTS: Fourteen trials were included. Sweeping of the membranes, performed as a general policy in women at term, was associated with reduced duration of pregnancy and the frequency of pregnancy continuing beyond 41 weeks (relative risk 0.42, 95% confidence interval 0.19 to 0.93, random effects model) and 42 weeks. After sweeping of the membranes, there was a 17% risk reduction (confidence interval 6 to 29%, random effects model) in the use of more formal methods for labour induction. There was no difference in the mode of delivery or in the risk of infection. Discomfort during vaginal examination and other adverse effects (bleeding, irregular contractions) were more frequently reported by women allocated to sweeping. REVIEWER'S CONCLUSIONS: Routine use of sweeping of membranes from 38 weeks of pregnancy onwards does not seem to produce clinically important benefits. When used as a means for induction of labour, the reduction in the use of more formal methods of induction needs to be balanced against women's discomfort and other adverse effects.

Extraembryonic Membranes↗
PubMed2001

Discovering the sweeping power of point mutations using a GIRAFF.

In pathogenic bacteria, point and other simple mutations can provide a strong selective advantage during the course of a single infection. Our understanding of the importance of these randomly occurring mutations has been hampered by a lack of technologies allowing mutation scanning on a genomic scale. Here, a novel technology is described that makes it possible to scan, in a single Southern blot experiment, the sequence identity of genomic regions with a combined length of hundreds of kilobases.

Animals↗
PubMed1999

Single cortical neurons serve both echolocation and passive sound localization.

The pallid bat uses passive listening at low frequencies to detect and locate terrestrial prey and reserves its high-frequency echolocation for general orientation. While hunting, this bat must attend to both streams of information. These streams are processed through two parallel, functionally specialized pathways that are segregated at the level of the inferior colliculus. This report describes functionally bimodal neurons in auditory cortex that receive converging input from these two pathways. Each brain stem pathway imposes its own suite of response properties on these cortical neurons. Consequently, the neurons are bimodally tuned to low and high frequencies, and respond selectively to both noise transients used in prey detection, and downward frequency modulation (FM) sweeps used in echolocation. A novel finding is that the monaural and binaural response properties of these neurons can change as a function of the sound presented. The majority of neurons appeared binaurally inhibited when presented with noise but monaural or binaurally facilitated when presented with the echolocation pulse. Consequently, their spatial sensitivity will change, depending on whether the bat is engaged in echolocation or passive listening. These results demonstrate that the response properties of single cortical neurons can change with behavioral context and suggest that they are capable of supporting more than one behavior.

Animals↗
PubMed1996

Receptive field asymmetries and sensitivity to random dot stereograms.

The differences between the two monocular receptive fields of cortical cells were measured and compared to their disparity tuning in the awake behaving monkey. Several receptive field properties (direction selectivity, orientation preference, eye preference and response modulation) were determined for each eye using sweeping bright bars. The disparity sensitivity of these cells was also assessed by plotting their response profile, determined for each cell under strictly binocular cyclopean stimulation (dynamic random dot stereograms, RDS). We have found that large differences between the two monocular receptive fields were infrequent and, apparently, not related with the disparity sensitivity profile. We conclude that the monocular asymmetries tested in this study and the sensitivity to positional binocular disparities present in RDS, might be linked to different mechanisms involved in depth perception in the visual system.

Animals↗
PubMed1994

Conflict between aftereffects of retinal sweep and looming motion.

Observers looked monocularly into a tunnel, with gratings on the left and right sides drifting toward the head. An exposure period was followed by a test with fixed gratings. With fixation points, left and right retinal fields could be stimulated selectively. When exposure and test were on the same retinal fields, but fixation was on opposite sides of the tunnel during exposure and test periods, aftereffects of retinal sweep and of perceived looming were in opposite directions. The two effects tended to cancel, yielding no perceived aftereffect. When they did occur, aftereffects in the retinal and the looming directions were equally likely. Cancellation was significantly more likely in the experimental conditions than in the control, when fixation always remained on the same side. When areas of retinal stimulation in the exposure and test periods did not overlap, cancellation was less frequent and aftereffects of looming were more frequent. Results were not significantly different for left and right visual fields, indicating that cortical vs. subcortical OKN pathways do not influence the illusion. Vection resulted for 16 of 20 observers under one or another of our conditions.

Adult↗
PubMed2002

Micellar electrokinetic chromatography: current developments and future.

This review highlights recent methodological and instrumental advances in micellar electrokinetic chromatography (MEKC). Enhancements in sensitivity and selectivity of the technique through the use of on-line preconcentration approaches (stacking and sweeping) and nonconventional pseudostationary phases, namely nonionic and zwitterionic surfactants, mixed micelles and polymers, are discussed in detail. Laser-induced fluorescence and mass spectrometry, as alternatives to UV-absorption detection, have been covered to evaluate their advantages and limitations when applied to analysis in an MEKC format. Some thoughts on future directions in this area such as in-capillary reactions, coated capillaries and MEKC on microchips are also presented.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed1996

Responses to exponential frequency modulations in the rat inferior colliculus.

We examined responses to pure tones and exponentially frequency-modulated (FM) stimuli in the inferior colliculus of ketamine anesthetized rats. All units responded to both pure-tone and FM stimulation: units responding selectively to FM stimuli were not found. The comparison between responses to many different FM sweeps revealed that activity was elicited when the instantaneous frequency of a FM sweep entered the unit's pure-tone tuning curve. Units were tuned to the rate of frequency modulation. Most modulation rate transfer functions had bandpass characteristics. Best modulation rates covered a range from 4.8 to 1904 octaves/s with more than 90% between 10 and 400 octaves/s. In contrast to previous studies, modulation direction was not coded in unit responses and only few units demonstrated a weak change in response strength when sweep direction was altered. This is at least partly attributable to the FM stimulus design which, in the present study, was adapted to the logarithmic frequency representation in the rat auditory system and carefully matched to the units' pure-tone responses area. In spite of the close relationship between pure tone and FM response behavior, modulation rate tuning cannot be completely explained on the basis of the units' pure-tone responses.

Acoustic Stimulation↗
PubMedDate not supplied

Improved gas chromatographic analysis of organophosphorus pesticides with pulsed splitless injection.

Gas chromatographic (GC) analysis of 6 organophosphorus pesticides (methamidophos, acephate, omethoate, diazinon, dimethoate, and chlorpyrifos) was performed with cool on-column, splitless, and pulsed splitless injections and with nitrogen-phosphorus or mass-selective detection. The pulsed splitless technique uses a high column flow rate during injection to sweep the sample out of the inlet rapidly, reducing analyte loss due to adsorption or thermal decomposition. After injection, the column flow rate is automatically reduced to normal values for chromatographic analysis. Pesticide recoveries for splitless and pulsed splitless injections were determined by comparison of GC peak areas with those obtained with cool on-column injection. With conventional splitless injection at a column flow rate of 5 mL/min, recoveries of acephate, omethoate, and methamidophos were only 57, 63, and 71%, respectively. Pulsed splitless methods with very fast injection flow rates dramatically improved recoveries, with all 6 pesticides falling in the 97-102% range. Because column flow rates are much less for GC with mass spectral detection (GC/MS), recoveries with splitless injection were lower and improvements with pulsed splitless injection were less dramatic for GC/MS. When splitless injection was used, recoveries of the 6 pesticides spiked into a green bean matrix were better than those of pesticides dissolved in pure solvent, presumably because matrix compounds compete with pesticides for active sites in the inlet. By using pulsed splitless injection of solvent standards with very fast initial column flow rates, systematic analyte losses in the inlet were eliminated, making recoveries of pesticides from solvent and green bean matrix very similar.

Chromatography, Gas↗
PubMed2004

Auditory sensitivity and frequency selectivity in greater spear-nosed bats suggest specializations for acoustic communication.

We investigated the relationship between auditory sensitivity, frequency selectivity, and the vocal repertoire of greater spear-nosed bats ( Phyllostomus hastatus). P. hastatus commonly emit three types of vocalizations: group-specific foraging calls that range from 6 to 11 kHz, low amplitude echolocation calls that sweep from 80 to 40 kHz, and infant isolation calls from 15 to 100 kHz. To determine if hearing in P. hastatus is differentially sensitive or selective to frequencies in these calls, we determined absolute thresholds and masked thresholds using an operant conditioning procedure. Both absolute and masked thresholds were lowest at 15 kHz, which corresponds with the peak energy of isolation calls. Auditory and masked thresholds were higher at sound frequencies used for group-specific foraging calls and echolocation calls. Isolation calls meet the requirements of individual signatures and facilitate parent-offspring recognition. Many bat species produce isolation calls with peak energy between 10 and 25 kHz, which corresponds with the frequency region of highest sensitivity in those species for which audiogram data are available. These findings suggest that selection for accurate offspring recognition exerts a strong influence on the sensory system of P. hastatus and likely on other species of group-living bats.

Acoustic Stimulation↗
PubMedDate not supplied

The backprojection method applied to classical tomography.

A method based upon backprojection of projection images which allows six degrees of freedom in the selection of the plane to be tomosynthesized is described. Data can be collected with any type of classical tomographic apparatus, including linear, circular, or other complex motion unit, which has been modified by the addition of a digital imaging chain. A set of projection images can be acquired in a single sweep, although, in principle, they could be acquired simultaneously. In addition, C-arms can also be used with no limitations of the selection of tomosynthesized planes.

Biometry↗
PubMed2000

Two-dimensional pulsed TRIPLE at 95 GHz

The one-dimensional (1D) pulsed TRIPLE resonance experiment, introduced by Mehring et al. (M. Mehring, P. Hofer, and A. Grupp, Ber. Bunseges. Phys. Chem. 91, 1132-1137 (1987)) is a modification of the standard Davies ENDOR experiment where an additional RF pi-pulse is applied during the mixing time. While the first RF pulse is set to one of the ENDOR transitions, the frequency of the second RF pulse is scanned to generate the TRIPLE spectrum. The difference between this spectrum and the ENDOR spectrum yields the difference TRIPLE spectrum, which exhibits only ENDOR lines that belong to the same M(S) manifold as the one selected by the first RF pulse. We have extended this experiment in two dimensions (2D) by sweeping the frequencies of both RF pulses. This experiment is particularly useful when the spectrum is congested and consists of signals originating from different paramagnetic centers. The connectivities between the peaks in the 2D spectrum enable a straightforward assignment of the signals to their respective centers and M(S) manifolds, thus providing the relative signs of hyperfine couplings. Carrying out the experiment at high fields has the additional advantage that nuclei with different nuclear gyromagnetic ratios are well separated. This is particularly true for protons which appear at significantly higher frequencies than other nuclei. The feasibility and effectiveness of the experiment is demonstrated at W-band (94.9 GHz) on a crystal of Cu(2+)-doped l-histidine. Homonuclear (1)H-(1)H, (14)N/(35)Cl-(14)N/(35)Cl and heteronuclear (1)H-(14)N/(35)Cl 2D TRIPLE spectra were measured and from the various connectivities in the 2D map the (1)H, (14)N, and (35)Cl signals that belong to two different Cu(2+) centers were identified and grouped according to their M(S) manifolds. Copyright 2000 Academic Press.

Journal Article↗
PubMed1976

Effect of early exposure to patterned sound on unit activity in rat inferior colliculus.

1. Young rats were exposed to one of two patterns of sounds for 5 h daily during the first 4 mo of life. The up pattern consisted of a tone swept from 6 to 9 kHz in 1 s alternated with a 1-s noise burst. The down pattern differed in that the sweeps were from 9 to 6 kHz. 2. A pattern evoked more spikes, on the average, from units in the inferior colliculus of rats exposed to that pattern than from units in animals exposed to the other pattern. 3. The exposure effect was most pronounced in the unit responses to the noise-burst segment within a pattern suggesting a long-lasting, malleable influence of the tone sweep which defined the pattern. Responses to pattern noise components were less for both exposed groups than for the unexposed controls, suggesting that inhibitory mechanisms were responsible for the pattern discrimination evident in the responses of the exposed unit population. 4. Unit responses in unexposed rats were somewhat more selective for the down pattern so that the resulting shift in response selectivity was relatively more apparent for exposure to the up pattern. 5. While control and down-exposed units generally responded more to both the tone sweep and noise burst in one pattern, a large proportion of the up-exposed unit population continued to favor the down over the up-swept tone, but responded more to the up-pattern noise bursts. This suggests that the unit responses to the noise bursts did not simply reflect prolonged responses to the tone sweeps. 6. No similar effects were seen for units from mothers similarly exposed to the same patterns.

Acoustic Stimulation↗
PubMed1988

Does adjuvant radiotherapy have a role in the postmastectomy management of patients with operable breast cancer--revisited.

About 2 decades ago, "routine" adjunctive postmastectomy radiotherapy, especially for axillary node-positive patients, was the norm and uncriticized standard against which adequate treatment was measured in most centers. With the advent of cyclic, aggressive, multi-agent chemotherapy and anti-hormones used as adjuvants, especially within the last decade, there has been tremendous reduction in patients referred to the radiation oncologist for consideration of adjunctive postmastectomy radiotherapy. This presentation will attempt to define a role for radiotherapy in at least selected subsets of patients who undergo modified radical mastectomy, based upon published series in the literature. Breast cancer is a protean disease and deserves a multidisciplinary approach to evaluation and treatment. "Routine" adjunctive postmastectomy radiotherapy for all patients with operable breast cancer obviously is not indicated, but there appear to be groups of patients who benefit from radiotherapy, both from the standpoint of disease-free survival and improved quality of life, and . . . in very narrow subsets, absolute survival. In some of these subsets the benefit clinically may be greater than that resulting from chemotherapy or anti-hormone therapy, although, because of sample size, falling short of statistical verification. In response to the posed question, while this remains a controversial issue, there appears to be a role for selective adjunctive postmastectomy radiotherapy in specific subsets of patients, and physicians administering adjunctive breast cancer therapy with sweeping applications of chemotherapy or anti-hormones alone do not appear to be offering their patients optimal therapy.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1996

Instrumentation for multiwavelengths excitation imaging.

We have developed a fluorescence ratio-imaging system which is based on a 12 bit, 2 MHz slow scan CCD camera and a patented (patent number P 42 28 366.3-52) polychromatic illumination system. The latter produces monochromatic light (12 nm bandwidth) of high intensity (> 3 mW between 300 and 500 nm) and allows one to switch to any wavelength between 260 and 680 nm in less than 3.5 ms in a computer-controlled fashion. The possibility to execute complex wavelength protocols facilitates multiple dye measurements with optimal exposure time for a given wavelength and the return to a dark phase in between exposures. Moreover, it allows sweeping over extended spectral regions in order to determine optimal experimental conditions for a given task. Wavelength selection is performed by a diffraction grating which is mounted onto a galvanometric scanner. The grating is illuminated by white light from a 75 W xenon lamp, using exclusively reflective optics, and the diffracted monochromatic light is coupled into the microscope by means of a single fibre quartz light guide. The epifluorescence optics, a special, achromatic, aplanatic UV condensor, image the exit face plate of the fibre into the specimen plane of an inverted microscope. This 'critical illumination' yields better homogeneity in the specimen plane than the classical Köhler illumination. Thus, with the Zeiss Fluar objective 40 x, NA = 1.3, fluence rates close to 10(23) photons m2 s-1 may be achieved at 340 nm. A DOS programme has been written in 'C' which controls both the monochromator and slow scan imaging system. It can acquire up to 13 full frames per s, and in its binning and skipping mode up to 100 subframes per s may be acquired. The frame-transfer structure of the chip allows one to acquire images at wavelength 'B' while simultaneously writing image data previously acquired at wavelength 'A' into the computer.

Animals↗
PubMed2006

Brian J. Scholl: award for distinguished scientific early career contributions to psychology.

Presents the citation for Brian J. Scholl, who received the Award for Distinguished Scientific Early Career Contributions to Psychology "for his brilliantly creative and sweepingly broad research program that addresses the hard questions in cognitive science." A brief profile and a selected bibliography accompany the citation. ((c) 2006 APA, all rights reserved).

Awards and Prizes↗
PubMed2000

Models of experimental evolution: the role of genetic chance and selective necessity.

We present a theoretical framework within which to analyze the results of experimental evolution. Rapidly evolving organisms such as viruses, bacteria, and protozoa can be induced to adapt to laboratory conditions on very short human time scales. Artificial adaptive radiation is characterized by a list of common observations; we offer a framework in which many of these repeated questions and patterns can be characterized analytically. We allow for stochasticity by including rare mutations and bottleneck effects, demonstrating how these increase variability in the evolutionary trajectory. When the product Np, the population size times the per locus error rate, is small, the rate of evolution is limited by the chance occurrence of beneficial mutations; when Np is large and selective pressure is strong, the rate-limiting step is the waiting time while existing beneficial mutations sweep through the population. We derive the rate of divergence (substitution rate) and rate of fitness increase for the case when Np is large and illustrate our approach with an application to an experimental data set. A minimal assumption of independent additive fitness contributions provides a good fit to the experimental evolution of the bacteriophage phiX174.

Animals↗
PubMedDate not supplied

Evaluation of local gas exchange in a pulsating respiratory support catheter.

An intravenous respiratory support catheter, the next generation of artificial lungs, is being developed in our laboratory to potentially support acute respiratory failure or patients with chronic obstructive pulmonary disease with acute exacerbations. A rapidly pulsating 25 ml balloon inside a bundle of hollow fiber membranes facilitates supplemental oxygenation and CO2 removal. In this study, we hypothesized that non-uniform gas exchange in different regions of this fiber bundle was present because of asymmetric balloon collapse and the interaction of longitudinal flow. Four quarter regions and two rings around the central balloon were selectively perfused to evaluate local gas exchange in a 3.18 cm test section using helium as the sweep gas. Quarter region CO2 exchange rates at 400 beats per minute were 156.8 +/- 0.8, 162.5 +/- 1.8, 157.2 +/- 0.2, and 196.6 +/- 0.8 ml/min/m2 (top, front, bottom, and back, respectively). The back section, adjacent to convex balloon collapse, had 17-20% higher exchange than the other sections caused by higher relative velocities past its stationary fibers. Inner and outer ring maximum pulsation gas exchange rates were 174.4 +/- 1.8 and 174.6 +/- 0.9 ml/min/m2, respectively, showing that fluid flow was equally distributed throughout the fiber bundle.

Artificial Organs↗