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PubMed2003

Plasma electron capture dissociation for the characterization of large proteins by top down mass spectrometry.

For the backbone dissociation of large (29 kDa) multiply charged protein ions in the gas phase by electron capture, the main experimental challenges are juxtaposition of the electron and ion for efficient capture, dissociation of tertiary noncovalent bonds that prevent product separation, and minimization of secondary electron capture that destroys larger product ions. A simple alternative methodology is described in which electrons (0.03-100 microA, 0.1-15 eV) are first impinged on a gas pulse in the ion cell of a Fourier transform mass spectrometer, followed by ion beam introduction. For carbonic anhydrase, the resulting plasma conditions produce 87% efficiency for electron capture; a single spectrum yields 512 product ions of 237 different masses from cleavage of 183 of the 258 interresidue bonds, while two spectra cleave 197 of these bonds. The problem of secondary dissociation of product ions is reduced by plasma conditions in which product ions are formed near electrons whose velocities are unfavorable and whose capture cross sections no longer have a square dependence on charge. One plasma ECD spectrum of ubiquitin provides its sequence de novo except for two residue pairs. ECD of casein identifies 126 of 208 interresidue cleavages, providing direct and specific characterization of all its 26 Ser/Thr/Tyr phosphorylation sites.

Amino Acid Sequence↗

PubMed1999

Effects of pressure on the kinetics of capture by yeast alcohol dehydrogenase.

High pressure causes biphasic effects on the oxidation of benzyl alcohol by yeast alcohol dehydrogenase as expressed in the kinetic parameter V/K which measures substrate capture. Moderate pressure increases the rate of capture of benzyl alcohol by activating the hydride transfer step. This means that the transition state for hydride transfer has a smaller volume than the free alcohol plus the capturing form of enzyme, with a DeltaV of -39 +/- 1 mL/mol, a value that is relatively large. This is the first physical property of an enzymatic transition state thus characterized, and it offers new possibilities for structure-activity analyses. Pressures of >1.5 kbar decrease the rate of capture of benzyl alcohol by favoring a conformation of the enzyme which binds nicotinamide adenine dinucleotide (NAD+) less tightly. This means that the ground state for tight binding, E-NAD+, has a larger volume than the collision complex, E-NAD+, with a DeltaV of 73 +/- 2 mL/mol. The equilibrium constant of the conformational change Keq is 75 +/- 13 at 1 atm. The effects of pressure on the capture of NAD+ have no activation phase because the conformational change is now being expressed kinetically instead of thermodynamically, together with but in opposition to hydride transfer, causing the effects to cancel. For yeast alcohol dehydrogenase, this conformational change had not been detected previously, but similar conformational changes have been found by spectroscopic means in other dehydrogenases, and some of them are also sensitive to pressure. The opposite signs for the volume change of tighter binding and hydride transfer run contrary to Pauling's hypothesis that substrates are bound more tightly in the transition state than in the Michaelian reactant state.

Alcohol Dehydrogenase↗

PubMedDate not supplied

Directed capture of enzymes and bacteria on bioplastic films.

The development of smart coatings for a variety of uses depends on the ability of the coating material to perform specific functions. We have used water dispersible polyurethane preparations for the immobilization of binding proteins under mild conditions. In these experiments, antibodies against the enzyme beta-galactosidase or the bacterium Escherichia coli were immobilized in polyurethane coatings and then used to effectively capture their cognate antigen. Further, a second, more general, capture protocol was developed which involves the incorporation of the protein avidin in the plastics. This system efficiently captures biotinylated beta-galactosidase. Biotinylated anti-E. coli antibody captured by avidin bioplastics resulted in a nearly 5-fold increase in the number of bound bacteria when compared to blank polyurethane. The use of avidin in a bioplastic allows any biotinylated antibody to be applied to all or part of the surface resulting in a patterning of capture agents on a preformed surface.

Antibodies, Bacterial↗

PubMedDate not supplied

Capture of bacteria from fermentation broth by body feed filtration: a solved problem?

The direct capture of bacteria produced in high cell density fermentation by filtration is not possible once the milliliter-scale has been surpassed. Filtration in the presence of a filter aid (body feed filtration) constitutes a putative and scalable alternative, but only if conditions proposed by industry for large-scale filtration processes, namely, flow rates (for aqueous solutions) in the range of 500-1,500 L/(m(2) x h) and a filter aid concentration of <or=20 g/L, can be met. To this end several filter aids (grades of cellulose, diatomaceous earth, mixes thereof) were tested, albeit with no success. Capture and retention of bacteria was low (not possible in the case of cellulose), and the produced filter cakes were unstable and of low permeability. In the case of the diatomaceous earth close to 100% bacterial capture was possible, but only with filter aid concentrations that were 1 order of magnitude above the proposed limit. By using flocculating agents (Fe(3+)/Al(3+), PEI) either alone or in combination with diatomaceous earth and also the use of positively charged cellulose, bacteria capture could be achieved from several liters of cell suspension (OD(600) <or= 15) in filtration experiments adhering to the industrial recommendations. However, the bacteria were only weakly retained in such cakes and easily released by sudden pressure pulses. Satisfactory results were only obtained by filtration of the bacteria suspension at slightly alkaline pH (8.0, 50 mM Tris buffer) after treatment with sodium-activated bentonite (5 g/L) and PEI (50 mg/L) in the presence of 250 mM NaCl. In such cases 100% of the bacteria could reproducibly be captured in a filtration using 20 g/L of diatomaceous earth as filter aid. The thus produced filter cakes strongly retained the bacteria and showed good filtration performance. The procedure is at present limited to E. coli culture with biomass contents of OD(600) <or= 15. Cultures with higher OD(600) have to be diluted prior to filtration.

Bentonite↗

PubMed2006

Gyroscopic effect in low-energy classical capture of a rotating quadrupolar diatom by an ion.

The low-energy capture of homonuclear diatoms by ions is due mainly to the long-range part of the interpartner potential with leading terms that correspond to charge-quadrupole interaction and charge-induced dipole interaction. The capture dynamics is described by the perturbed-rotor adiabatic potentials and the Coriolis interaction between manifold of states that belong to a given value of the intrinsic angular momentum. When the latter is large enough, it can noticeably affect the capture cross section calculated in the adiabatic channel approximation due to the gyroscopic property of a rotating diatom. This paper presents the low-energy (low-temperature) state-selected partial and mean capture cross sections (rate coefficients) for the charge-quadrupole interaction that include the gyroscopic effect (decoupling of intrinsic angular momentum from the collision axis), quantum correction for the diatom rotation, and the correction for the charge-induced dipole interaction. These results complement recent studies on the gyroscopic effect in the quantum regime of diatom-ion capture (Dashevskaya, E. I.; Litvin, I.; Nikitin, E. E.; Troe, J. J. Chem. Phys. 2004, 120, 9989-9997).

Coriolis Force↗

PubMed1993

Stimulus-driven attentional capture and attentional control settings.

Jonides and Yantis (1988) found that abrupt-onset singletons capture attention in visual search when onset is orthogonal to the target's defining and reported attributes and that color and brightness singletons do not. They concluded that abrupt onset may be unique in capturing visual attention. Folk, Remington, and Johnston (1992) challenge this conclusion and argue that (a) the occurrence of attentional capture is contingent on the adoption of an appropriate attentional control setting by the observer and (b) properties other than onset (in particular, color) can capture attention involuntarily. In this article, each of these claims is critically evaluated, and it is argued that the results reported by Folk et al., though important, do not definitively corroborate either one. The available evidence concerning stimulus-driven attentional capture is summarized, and 3 empirical generalizations that characterize the evidence are advanced.

Attention↗

PubMed2005

What you see is what you set: sustained inattentional blindness and the capture of awareness.

This article reports a theoretical and experimental attempt to relate and contrast 2 traditionally separate research programs: inattentional blindness and attention capture. Inattentional blindness refers to failures to notice unexpected objects and events when attention is otherwise engaged. Attention capture research has traditionally used implicit indices (e.g., response times) to investigate automatic shifts of attention. Because attention capture usually measures performance whereas inattentional blindness measures awareness, the 2 fields have existed side by side with no shared theoretical framework. Here, the authors propose a theoretical unification, adapting several important effects from the attention capture literature to the context of sustained inattentional blindness. Although some stimulus properties can influence noticing of unexpected objects, the most influential factor affecting noticing is a person's own attentional goals. The authors conclude that many--but not all--aspects of attention capture apply to inattentional blindness but that these 2 classes of phenomena remain importantly distinct.

Adult↗

PubMed2003

Attentional capture in singleton-detection and feature-search modes.

Six experiments were conducted to determine the circumstances under which an irrelevant singleton captures attention. Subjects searched for a target while ignoring a salient distractor that appeared at different stimulus onset asynchronies (SOAs) prior to each search display. Spatial congruency and interference effects were measured. The strategies available to find the target were controlled (only singleton-detection mode, only feature-search mode, or both search strategies available). An irrelevant abrupt onset captured attention in search for a color target, across SOAs, whatever strategies were available. In contrast, in search for a shape target, an irrelevant color singleton captured attention in the singleton-detection condition but delayed response at its location in the feature-search condition, across SOAs. When both strategies were available, capture was short lived (50- to 100-msec SOAs). The theoretical implications of these findings in relation to current views on attentional capture are discussed. ((c) 2003 APA, all rights reserved)

Adult↗

PubMed2004

Capturing attention when attention blinks.

Four experiments addressed the question of whether attention may be captured when the visual system is in the midst of an attentional blink (AB). Participants identified 2 target letters embedded among distractor letters in a rapid serial visual presentation sequence. In some trials, a square frame was inserted between the targets; as the only geometric object in the sequence, it constituted a singleton. Capture effects obtained when the AB was most severe and when it was over were compared. There were 3 main results. First, capture occurred even when the AB was crippling, suggesting that a singleton exogenously engaged attention even when processing of a previous target was continuing apace. Second, when the singleton contained the key target feature, capture effects were clearly manifest. Third, even when the singleton did not possess the key target feature, it still succeeded in capturing attention, although the effects were both feeble and fleeting.

Attention↗

PubMed2004

Immunomagnetic T cell capture from blood for PCR analysis using microfluidic systems.

A one-step immunomagnetic separation technique was performed on a microfluidic platform for the isolation of specific cells from blood samples. The cell isolation and purification studies targeted T cells, as a model for low abundance cells (about 1:10,000 cells), with more dilute cells as the ultimate goal. T cells were successfully separated on-chip from human blood and from reconstituted blood samples. Quantitative polymerase chain reaction analysis of the captured cells was used to characterize the efficiency of T cell capture in a variety of flow path designs. Employing many (4-8), 50 microm deep narrow channels, with the same overall cross section as a single, 3 mm wide channel, was much more effective in structuring dense enough magnetic bead beds to trap cells in a flowing stream. The use of 8-multiple bifurcated flow paths increased capture efficiencies from approximately 20 up to 37%, when compared to a straight 8-way split design, indicating the value of ensuring uniform flow distribution into each channel in a flow manifold for effective cell capture. Sample flow rates of up to 3 microL min(-1) were evaluated in these capture beds.

Blood Cell Count↗

PubMed2006

A multifunctional micro-fluidic system for dielectrophoretic concentration coupled with immuno-capture of low numbers of Listeria monocytogenes.

In this study, we demonstrated a micro-fluidic system with multiple functions, including concentration of bacteria using dielectrophoresis (DEP) and selective capture using antibody recognition, resulting in a high capture efficiency of bacterial cells. The device consisted of an array of oxide covered interdigitated electrodes on a flat silicon substrate and a approximately 16 microm high and approximately 260 microm wide micro-channel within a PDMS cover. For selective capture of Listeria monocytogenes from the samples, the channel surface was functionalized with a biotinylated BSA-streptavidin-biotinylated monoclonal antibody sandwich structure. Positive DEP (at 20 V(pp) and 1 MHz) was used to concentrate bacterial cells from the fluid flow. DEP could collect approximately 90% of the cells in a continuous flow at a flow rate of 0.2 microl min(-1) into the micro-channel with concentration factors between 10(2)-10(3), in sample volumes of 5-20 microl. A high flow rate of 0.6 microl min(-1) reduced the DEP capture efficiency to approximately 65%. Positive DEP attracts cells to the edges of the electrodes where the field gradient is the highest. Cells concentrated by DEP were captured by the antibodies immobilized on the channel surface with efficiencies of 18 to 27% with bacterial cell numbers ranging from 10(1) to 10(3) cells. It was found that DEP operation in our experiments did not cause any irreversible damage to bacterial cells in terms of cell viability. In addition, increased antigen expression (antigens to C11E9 monoclonal antibody) on cell membranes was observed following the exposure to DEP.

Antibodies, Monoclonal↗

PubMed2005

Measurement of white lesions surrounding orthodontic brackets: captured slides vs digital camera images.

Digital images provide an efficient means of processing and storing clinical images and are increasingly being used in orthodontic practice. However, for research purposes it must be shown that measurements from digital images are as reliable as those from captured slides, particularly in the area of postorthodontic demineralization. The aim of this in vitro study was to compare the assessment of demineralized white lesions surrounding orthodontic brackets using images produced from captured slides with those from a digital camera. Thirty teeth with orthodontic brackets and a systematic arrangement of artificially induced demineralization were used. Standardized images of the teeth were taken in 35-mm slide format and using a digital camera. The slides were scanned and saved as digital images. All the images were numbered, recoded in a random order, and assessed by a second investigator. The image was examined for the presence or absence of demineralization. This was compared with the actual demineralization pattern, and the positive and negative predictive values were calculated. Twenty images from each group were randomly chosen and duplicated for an assessment of measurement error. The positive and negative predictive values were better from the digital images (0.92 and 0.81) than from the captured slides (0.88 and 0.74). The percentage agreements for the repeat assessments of the same slide were similar (96% for the captured slides and 93% for the digital images). Measurements of enamel demineralization using images from a digital camera are as accurate and reproducible as images captured from a photographic slide.

Dental Enamel↗

PubMed2001

The utility of ultrasound to determine ventricular capture in external cardiac pacing.

Determining electrical capture when using an external cardiac pacemaker is often difficult and confusing, especially when the resulting clinical signs of an effective blood pressure and pulse are inadequate or nondetectable. The objective of this study was to determine the efficacy of using 2-dimensional ultrasound (US) in determining the presence of ventricular capture of an external cardiac pacemaker in a swine model. Five anesthetized swine underwent external cardiac pacing (ECP) at variable levels of energy output while concurrent US images and electrocardiograph monitoring were recorded on videotape. Determinations of capture/no capture were made in the laboratory. Segments of videotape were selected to be reviewed by 2 physicians blinded to these laboratory determinations of capture and to each other. Kappa levels of agreement were determined among the 3 pairs of comparisons. Seventeen segments were reviewed. Kappa levels of agreement were 0.76 for Reviewer A versus Laboratory determination, 0.88 for Reviewer B versus Laboratory determination, and 0.88 for Reviewer A versus Reviewer B. All P values were <.001. These excellent levels of agreement show that 2D US in this animal model is highly effective in determining the presence of ventricular capture in ECP.

Animals↗

PubMed2003

Separation and capture of CO2 from large stationary sources and sequestration in geological formations--coalbeds and deep saline aquifers.

The topic of global warming as a result of increased atmospheric CO2 concentration is arguably the most important environmental issue that the world faces today. It is a global problem that will need to be solved on a global level. The link between anthropogenic emissions of CO2 with increased atmospheric CO2 levels and, in turn, with increased global temperatures has been well established and accepted by the world. International organizations such as the United Nations Framework Convention on Climate Change (UNFCCC) and the Intergovernmental Panel on Climate Change (IPCC) have been formed to address this issue. Three options are being explored to stabilize atmospheric levels of greenhouse gases (GHGs) and global temperatures without severely and negatively impacting standard of living: (1) increasing energy efficiency, (2) switching to less carbon-intensive sources of energy, and (3) carbon sequestration. To be successful, all three options must be used in concert. The third option is the subject of this review. Specifically, this review will cover the capture and geologic sequestration of CO2 generated from large point sources, namely fossil-fuel-fired power gasification plants. Sequestration of CO2 in geological formations is necessary to meet the President's Global Climate Change Initiative target of an 18% reduction in GHG intensity by 2012. Further, the best strategy to stabilize the atmospheric concentration of CO2 results from a multifaceted approach where sequestration of CO2 into geological formations is combined with increased efficiency in electric power generation and utilization, increased conservation, increased use of lower carbon-intensity fuels, and increased use of nuclear energy and renewables. This review covers the separation and capture of CO2 from both flue gas and fuel gas using wet scrubbing technologies, dry regenerable sorbents, membranes, cryogenics, pressure and temperature swing adsorption, and other advanced concepts. Existing commercial CO2 capture facilities at electric power-generating stations based on the use of monoethanolamine are described, as is the Rectisol process used by Dakota Gasification to separate and capture CO2 from a coal gasifier. Two technologies for storage of the captured CO2 are reviewed--sequestration in deep unmineable coalbeds with concomitant recovery of CH4 and sequestration in deep saline aquifers. Key issues for both of these techniques include estimating the potential storage capacity, the storage integrity, and the physical and chemical processes that are initiated by injecting CO2 underground. Recent studies using computer modeling as well as laboratory and field experimentation are presented here. In addition, several projects have been initiated in which CO2 is injected into a deep coal seam or saline aquifer. The current status of several such projects is discussed. Included is a commercial-scale project in which a million tons of CO2 are injected annually into an aquifer under the North Sea in Norway. The review makes the case that this can all be accomplished safely with off-the-shelf technologies. However, substantial research and development must be performed to reduce the cost, decrease the risks, and increase the safety of sequestration technologies. This review also includes discussion of possible problems related to deep injection of CO2. There are safety concerns that need to be addressed because of the possibilities of leakage to the surface and induced seismic activity. These issues are presented along with a case study of a similar incident in the past. It is clear that monitoring and verification of storage will be a crucial part of all geological sequestration practices so that such problems may be avoided. Available techniques include direct measurement of CO2 and CH4 surface soil fluxes, the use of chemical tracers, and underground 4-D seismic monitoring. Ten new hypotheses were formulated to describe what happens when CO2 is pumped into a coal seam. These hypotheses provide significant insight into the fundamental chemical, physical, and thermodynamic phenomena that occur during coal seam sequestration of CO2.

Carbon Dioxide↗

PubMed2002

A capture-recapture model to estimate prevalence of children born in Scotland with developmental eye defects.

BACKGROUND: Microphthalmia, anophthalmia and coloboma (MAC) are closely related structural developmental eye defects that have caused public concern in the UK following media reports of apparent clusters of cases. An extensive search was carried out to identify potential cases, and diagnoses were confirmed by ophthalmological review. Despite this effort, it was recognised that some cases would remain unidentified. Capture-recapture methods could improve the accuracy of the study's birth prevalence estimate. METHODS: A register of all children born with the developmental eye defects of MAC in Scotland (1981-96) was compiled. This identified 188 cases from eight national ascertainment sources. The methods described by Hook and Regal were used to determine possible estimates for each source. A log-linear method of capture-recapture was used to fit a model to the number of children identified by the different combinations of the eight national sources, and the individual sources were included in the model as main effects. RESULTS: Maximum-likelihood estimates were calculated for tables of captured/not captured by one source versus any other source. The estimated number of unobserved cases for the most complete source, the register of congenital anomalies for Scotland, and the seven others combined is 78 (95% CI 53-115). Estimates calculated from two different log-linear models of the numbers of cases unobserved by all sources were 61 (95% CI 43-86) and 175 (95% CI 106-287). An external check with an independent congenital-anomalies register in one region, which is known to have high completeness, gave an estimate of 120. The study found a birth prevalence of MAC in Scotland of 1.9/10000, based on total live births during the study period. The capture-recapture analysis suggests that the true birth prevalence lies between 2.4/10 000 and 3.5/10000. DISCUSSION: Our experience shows that, even with multiple sources of ascertainment and considerable resources directed at case identification, a considerable level of under-ascertainment of congenital eye-anomalies still results, and suggests that the use of capture-recapture analysis would be a useful addition to congenital anomalies registers for needs assessment, disease-burden estimates and health-service planning.

Eye Abnormalities↗

PubMed1983

Capture efficiency of local exhaust ventilation systems.

A new technique to measure the performance of local exhaust ventilation systems has been developed and tested in both the laboratory and the field. The technique involves the measurement of the capture efficiency of exterior hoods, defined to be the fraction of contaminants given off by a process captured by the exhaust system serving that process. Capture efficiency measurement can be a powerful tool in the evaluation of local exhaust systems, since it is a direct, quantitative measure of system performance; in contrast, indices of performance now in use are either qualitative or measure quantities which may not be related directly to system performance. A basic theory for capture efficiency has been developed, and a prototype system for measuring capture efficiency has been constructed and tested. Preliminary laboratory and field measurements using the system have demonstrated the power of the method, which should find widespread use in the design of new ventilation systems and the evaluation of existing ones.

Air Pollutants, Occupational↗

PubMed2006

Dynamic microtubules are essential for efficient chromosome capture and biorientation in S. cerevisiae.

Attachment of chromosomes to the mitotic spindle has been proposed to require dynamic microtubules that randomly search three-dimensional space and become stabilized upon capture by kinetochores. In this study, we test this model by examining chromosome capture in Saccharomyces cerevisiae mutants with attenuated microtubule dynamics. Although viable, these cells are slow to progress through mitosis. Preanaphase cells contain a high proportion of chromosomes that are attached to only one spindle pole and missegregate in the absence of the spindle assembly checkpoint. Measurement of the rates of chromosome capture and biorientation demonstrate that both are severely decreased in the mutants. These results provide direct evidence that dynamic microtubules are critical for efficient chromosome capture and biorientation and support the hypothesis that microtubule search and capture plays a central role in assembly of the mitotic spindle.

Chromosomes, Fungal↗

PubMed1992

Transport calculations of depth-dose distributions for gadolinium neutron capture therapy.

Depth-dose distributions were calculated for thermal and epithermal neutron fluence and capture gamma ray dose rates using a two-dimensional neutron-coupled gamma-ray transport code (DOT 3.5) for gadolinium neutron capture therapy. The results show that (i) a capture gamma-ray dose rate of 10 Gy h-1 was obtained with a thermal neutron fluence rate of 1.5 x 10(9) cm-2 s-1 in a simulated tumour containing 5000 PPM gadolinium placed near the surface of a water phantom, (ii) deep-seated tumours may be treated with epithermal neutrons, and (iii) gadolinium neutron capture therapy appears to achieve comparable dose distributions to those of boron neutron capture therapy.

Gadolinium↗