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PubMed2006

Polydispersed O/W emulsions in porous media: segregation at low-tension conditions.

The segregation of polydispersed oil was studied in theoretical models, sand packs, and plugs from consolidated cores at low tension and atmospheric conditions. The height of the oil belt formed at the top of the porous column and its change in time were measured. The analysis of the segregation curves indicates the subsequent appearance and rise of three pseudo-phases. The primary phase, which contains the dominant fraction of oil in the system, rises with a relatively high steady state velocity. Unsteady state and decreasing velocity characterize the transitional secondary phase which is a lean emulsion left behind. The ternary phase, which follows it with a semi-steady state low velocity, is a lean emulsion of the smallest oil blobs present in low concentration. The process terminates at the segregation of the mobile oil particles in the subsequent phases where a small fraction of the total oil content remains in the porous bed, mainly from the last stage of segregation due to the entrapment in suitable microstructures. According to the postulated mechanism, the decreasing probability of the repeated coalescence in pore bodies and dispersion at the connecting pore throats are responsible for the development of the mobile phases at the sufficiently low-tension conditions. The structure of the pore network, the size-distribution of the oil droplets, the density of their population, and the length of paths affect the mechanism, properties, and behaviour of the systems.

Journal Article↗
PubMed2004

Unbiased analysis of bulk axonal segregation patterns.

The projection of retinal ganglion cell axons to the dorsal lateral geniculate nucleus of the thalamus (dLGN) is organized into eye-specific layers, which are macroscopic structures that reflect the bulk organization of thousands of axons. The processes that underlie the formation of these layers is the focus of research in several laboratories. The recent advent of fluorescently tagged tracers allows for the simultaneous visualization of axons from both eyes in the same dLGN section and therefore the analysis of axonal segregation patterns. However, the techniques traditionally used to quantify eye-specific segregation are far from standardized. Here we present an analysis method that objectively quantifies the extent of segregation. We apply this analyses to dLGN images from mice with normal retinogeniculate projection patterns and genetically altered mice with dramatically altered projection patterns. In addition, we compare dLGN images acquired at different optical resolutions to measure the spatial scale over which we can determine segregation unambiguously.

Animals↗
PubMed2005

Optical imaging in cat area 18: strabismus does not enhance the segregation of ocular dominance domains.

While early-onset strabismus leads to clearly segregated domains of the left and the right eye in cat primary visual cortex (area 17), far less is known about experience-dependent plasticity of ocular dominance in area 18. We therefore used optical imaging of intrinsic signals to analyze the influence of strabismus on cortical maps in cat area 18. Monocular visual stimulation of the left and right eye with moving square wave gratings of four different orientations induced patchy activity maps. Unlike our previous observations in cat area 17, the monocular activity maps in area 18 of strabismic cats were rather similar so that functional ocular dominance domains were not clearly segregated. Imaging of the 17/18 border region confirmed this observation and revealed a sudden change in the segregation of the left and right eye domains across the border. Our results demonstrate that modified visual input can have different consequences for different visual areas: while the decorrelation of activity between the two eyes (as induced by strabismus) clearly enhances the segregation of ocular dominance domains in cat area 17, area 18 does not show this effect although electrophysiological studies have confirmed that the percentage of binocularly driven neurons is as reduced as in area 17.

Animals↗
PubMed2004

Perceptual-binding and persistent surface segregation.

Visual input is segregated in the brain into subsystems that process different attributes such as motion and color. At the same time, visual information is perceptually segregated into objects and surfaces. Here we demonstrate that perceptual segregation of visual entities based on a transparency cue precedes and affects perceptual binding of attributes. Adding an irrelevant transparency cue paradoxically improved the pairing of color and motion for rapidly alternating surfaces. Subsequent experiments show: (1) Attributes are registered over the temporal window defined by the perceptual persistence of segregation, resulting in asynchrony in binding, and (2) attention is necessary for correct registration of attributes in the presence of ambiguity.

Attention↗
PubMed2004

Incineration of healthcare wastes: management of atmospheric emissions through waste segregation.

The amount of atmospheric pollutants emitted through the incineration of healthcare wastes can be estimated using emission factors. Emission factors have been published without including sufficient information about the types of wastes incinerated. This paper reports the first emission factors estimated for the incineration of wastes segregated into different types according to the Portuguese legislation. One controlled-air incinerator without air pollution control devices was used in the research. The main objectives of the study were: (i) to estimate the emission factors for particulate matter, dioxins, heavy metals and gaseous pollutants, according to the type of waste incinerated; (ii) to evaluate the quality of atmospheric emissions; and (iii) to define a methodology for the management of atmospheric emissions, evaluating the influence of type of waste incinerated and of the segregation method used on the emitted amounts. It was concluded that: (i) when emission factors are not associated with the type of incinerated mixture, the utility of the emission factors is highly doubtful; (ii) without appropriate equipment to control atmospheric pollution, incineration emissions exceed legal limits, neglecting the protection of human health (the legal limit for pollutant concentrations could only be met for NO(x), all other concentrations were higher than the maximum allowed: dioxins, 93-710 times; Hg, 1.3-226 times; CO, 11-24 times; SO(2), 2-5 times; and HCl, 9-200 times); (iii) rigorous segregation methodologies must be used to minimize atmospheric emissions, and incinerate only those wastes that should be incinerated according to the law. A rigorous segregation program can result in a reduction of the amount of waste that should be incinerated by 80%. A reduction in the quantity of waste incinerated results in a reduction on the amounts of pollutants emitted: particulate matter, 98%; dioxins, 99.5%; As, Cd, Cr, Mn and Ni, respectively, 90%, 92%, 84%, 77% and 92%; Hg and Pb, practically eliminated; SO(2) and NO(x), 93%; and CO and HCl, more than 99%.

Air Pollution↗
PubMed2003

Segregation of the photosystems in thylakoids depends on their size.

Lateral segregation of two types of photosystems in thylakoid membranes of green plants is one of the key factors that provide the stability and fine-tuning of the light quanta supply by pigment proteins and non-cyclic electron transport. Due to this specific feature of the membrane structural organization, the photosynthetic units function in the green plants with optimal performance. In this report a mesoscopic theory is outlined to address the physical aspects of segregation phenomenon. Results of theoretical studies and computer simulations suggest that charge mismatch and the size difference between two photosystems in grana are most responsible for their lateral segregation, which is driven by the screened electrostatic and lipid-induced interactions. Comparative simulations of photosystems of different sizes show the crucial dependence of their ordering on a geometrical parameter. It seems that the size effect alone may prevent photosystems from segregated arrangement in cyanobacterial thylakoids.

Computer Simulation↗
PubMed2001

Cholesterol does not induce segregation of liquid-ordered domains in bilayers modeling the inner leaflet of the plasma membrane.

A fluorescence-quenching method has been used to assess the potential formation of segregated liquid-ordered domains in lipid bilayers combining cholesterol with mixtures of amino and choline phospholipids like those found in the cytoplasmic leaflet of the mammalian cell plasma membrane. When present in proportions >20-30 mol %, different saturated phospholipids show a strong proclivity to form segregated domains when combined with unsaturated phospholipids and cholesterol, in a manner that is only weakly affected by the nature of the phospholipid headgroups. By contrast, mixtures containing purely unsaturated phospholipids and cholesterol do not exhibit detectable segregation of domains, even in systems whose components differ in headgroup structure, mono- versus polyunsaturation and/or acyl chain heterogeneity. These results indicate that mixtures of phospholipids resembling those found in the inner leaflet of the plasma membrane do not spontaneously form segregated liquid-ordered domains. Instead, our findings suggest that factors extrinsic to the inner-monolayer lipids themselves (e.g., transbilayer penetration of long sphingolipid acyl chains) would be essential to confer a distinctive, more highly ordered organization to the cytoplasmic leaflet of "lipid raft" structures in animal cell membranes.

Animals↗
PubMed1985

A model of bacterial DNA segregation based upon helical geometry.

A new mechanism to segregate daughter genomes in bacterial cells is suggested that is based upon the rules of geometry governing the helix clock (Mendelson, 1982a). The reorientation of cell surface string arrays used as a timing reference in the helix clock is capable of drawing apart the initial products of DNA replication. Physically linking the sister DNA replication origins to the ends of the initial cell surface string inserted into the cell surface at the start of a helix clock cycle, and linking the DNA terminus to a point along the length of the same string provides a means to mark the locations to which the genomes will segregate as well as the place where cell division will occur. The parallel packing of additional cell surface strings into an array which includes the string to which DNA is attached provides the necessary spatial rearrangements. The helical segregation model can account for the precise registration of cell divisions with the completion of replication forks in a multifork replication system, provides a basis for determining the relationship of sister cell sizes at division, and can also accommodate the asymmetrical divisions associated with minicell production and sporulation. Examination of the helical segregation theory under multifork DNA replication conditions moreover reveals that adjacent helical clocks are physically linked to one another although totally independent in terms of their progression through the clock cycle. A relationship between the initiation of DNA replication forks and the insertion of the first cell surface string associated with the start of a helix clock cycle is predicted by the model.

Cell Division↗
PubMed2003

Preserved use of spatial cues for sound segregation in a case of spatial deafness.

Auditory spatial cues contribute to sound localisation and to sound object segregation. We have investigated these capacities in a patient (NM) who complained having difficulties to localise sounds in everyday life after a right temporo-parieto-frontal ischemic lesion. Two groups of tasks were used, in which spatial dimension was simulated by interaural time differences (ITD): (i) active localisation of stationary or moving sound targets, and (ii) sound segregation on the basis of spatial cues. This latter included a spatial release from masking paradigm and two ITD diotic tasks. NM failed to localise stationary and moving sounds: she perceived all the stimuli at the centre of the head, and could not differentiate stationary from moving targets. In contrast, NM was able to use ITD cues to segregate simultaneous sound sources in the spatial-release-from-masking paradigm and in ITD diotic tasks.These results suggest that sound localisation and sound object segregation based on spatial cues do not rely on the same mechanisms.

Adult↗
PubMed2002

Asymmetric segregation of mitochondria and mortalin correlates with the multi-lineage potential of inner ear sensory cell progenitors in vitro.

The sensory epithelia of the inner ear include hair cells and supporting cells that share a common precursor. One possible mechanism involved in the genesis of these cell types is through asymmetric cell division. In this work we have studied asymmetric division of inner ear sensory cell progenitors in vitro in an attempt to understand how the different cell phenotypes are generated. In the search for molecules that will segregate asymmetrically we have found that mitochondria in general, and a mitochondrial protein named mortalin in particular, are asymmetrically segregated during certain cell divisions. In one conditionally immortal cell line (UB/OC-1), which represents a population of committed hair cell precursors, mortalin is uniformly distributed in the cytoplasm and shared equally between sibling cells during division. In another cell line (UB/UE-1), which represents a bipotent, vestibular supporting cell that can produce both neonatal hair cells as well as supporting cells, mortalin segregates asymmetrically. In UB/UE-1, approximately 12% of the cells display an asymmetric distribution of mortalin and mitochondria. The proportion of asymmetric cells increases immediately after the release of the immortalizing gene and before the onset of differentiation. The asymmetric segregation of mortalin in the bipotent cell line and its uniform distribution in a committed, lineage-restricted cell line raises the possibility that it may play a role in cell fate determination.

Animals↗
PubMed1999

Visual texture segregation by the chimpanzee (Pan troglodytes).

One adult male chimpanzee (Pan troglodytes) was trained to detect a target area consisting of texture elements from the background texture made of the different elements from the target area. The subject was given eight different stimulus conditions. In Condition 1, segregation was based on the difference of local feature of elements but not on global similarity. Conditions 2-3 investigated the effects of the number of terminators, which was considered as 'textons' in human texture perception. The chimpanzee showed better performance when the discrimination can be based on the difference of the number of terminators. This tendency, however, was reversed when the local salient feature (length of shorter lines) was enhanced, as in Enns' [15] study with humans as subjects. The subject showed asymmetries in segregation performance when discriminating based on gap (Conditions 4-5), line length (Condition 6), and regularity of line arrangement (Condition 7). Observed asymmetries were consistent with humans and with visual search asymmetries. The performance of texture segregation by the chimpanzee was consistent with humans, and the texture segregation is one of the useful tasks for comparative study of early vision as well as visual search task.

Animals↗
PubMed2001

Nanometer-scale solute segregation at heterophase interfaces and microstructural evolution of molybdenum nitride precipitates.

The interrelationship between coherency and solute segregation at metal/metal-nitride heterophase interfaces is studied on a subnanometer scale by both atom-probe field-ion and electron microscopies for molybdenum nitride precipitates in Fe-2 at% Mo-X, where X = 0.4 at% Sb or 0.5 at% Sn. Internal nitridation at 550 degrees C generates thin platelet-shaped molybdenum nitride precipitates, while nitridation at 600 degrees C produces, in addition to the small-scale structure with precipitates of the thin-platelet type, a much coarser structure of thick plates and spheroidal precipitates. The solute species Sn and Sb segregate at the heterophase interfaces of the coarse precipitates and Gibbsian interfacial excesses of up to 7 x 10(18) M(-2) are measured. The segregation is related to the presence of misfit dislocations at the interfaces of the coarse preciptitates, while the thin plates remain coherent with no detectable segregation.

Journal Article↗
PubMed2001

Magnetic resonance imaging investigation of the mixing-segregation process in a pharmaceutical blender.

Magnetic Resonance Imaging (MRI) was used to study the mixing process of binary mixtures of free flowing sugar beads in a Turbula mixer. In order to make particles MRI-sensitive, some reference beads were doped with an organic oil. Doped and undoped particles were mixed and MRI was used to non-destructively image the particle bed for a given number of mixer rotations (NR), bead diameter ratio (R=d(ref)/d(i)) and rotation speed (V). All the results were quantified on the basis of image analysis to characterise the degree of mixing. Studies showed that for binary mixtures of identical particle size, the mixing was complete after 30 rotations, whereas for beads of different size (R=2.8) a segregated steady state was obtained after nearly 10 rotations. Experiments revealed that segregation appeared as soon as R=0.9. Moreover, the lower the rotation speed, the more segregated the final state was. It appeared that for a filling level greater than 80%, dead regions appeared in the centre of the powder bed. In conclusion, when the particles are non-cohesive, the Turbula blender perfectly mixes identical beads but segregation occurs for beads of different size after just a few rotations.

Carbohydrates↗
PubMed2004

V-blender segregation patterns for free-flowing materials: effects of blender capacity and fill level.

Stable segregation patterns are shown to form in V-blenders over a wide range of vessel capacities, fill levels, and rotation rates. Slight changes in either rotation rate or fill level induce changes in pattern formation. Trajectory segregation in two regions of the flow, accumulating over many flow periods, drives segregation pattern formation. Scaling criteria derived to relate particle velocities to vessel size and rotation rate in rotating cylinders successfully predict the rotation rate for the transition between patterns across V-blenders of 0.8-26.5 quart total capacity. This agreement suggests that pattern formation is governed by the magnitude of particle velocities. Regardless of vessel size, when particle velocities at specific regions of the blender are below a certain value, one particular pattern appears, and when they increase beyond that speed (i.e. by changing the rotation rate or the vessel size), a different pattern emerges. A scaling relation between segregation pattern formation and blender fill level was not identified because the complex flow patterns in the V-blender (the length of the flowing layer and the mixture center of mass relative to the blender are constantly oscillating) preclude the determination of a relationship between blender fill level and particle velocities.

Chemical Phenomena↗
PubMed2001

Neural correlates of auditory stream segregation in primary auditory cortex of the awake monkey.

An important feature of auditory scene analysis is the perceptual organization of sequential sound components, or 'auditory stream segregation'. Auditory stream segregation can be demonstrated by presenting a sequence of high and low frequency tones in an alternating pattern, ABAB. When the tone presentation rate (PR) is slow or the frequency separation (DeltaF) between the tones is small (<10%), a connected alternating sequence ABAB is perceived. When the PR is fast or the DeltaF is large, however, the alternating sequence perceptually splits into two parallel auditory streams, one composed of interrupted 'A' tones, and the other of interrupted 'B' tones. The neurophysiological basis of this perceptual phenomenon is unknown. Neural correlates of auditory stream segregation were examined in A1 of the awake monkey using neuronal ensemble techniques (multiunit activity and current source density). Responses evoked by alternating frequency sequences of tones, ABAB, were studied as a function of PR (5, 10, 20 and 40 Hz). 'A' tones corresponded to the best frequency (BF) of the cortical site, while 'B' tones were situated away from the BF by an amount DeltaF. At slow PRs, 'A' and 'B' tones evoked responses that generated an overall pattern of activity at the stimulus PR. In contrast, at fast PRs, 'B' tone responses were differentially suppressed, resulting in a pattern of activity consisting predominantly of 'A' tone responses at half the PR. The magnitude of 'B' tone response suppression increased with DeltaF. Differential suppression of BF and non-BF tone responses at high PRs can be explained by physiological principles of forward masking. The effect of DeltaF is explained by the hypothesis that responses to tones distant from the BF are more susceptible to suppression by BF tones than responses to tones near the BF. These results parallel human psychoacoustics of auditory stream segregation and suggest a cortical basis for the perceptual phenomenon.

Acoustic Stimulation↗
PubMed2001

Auditory stream segregation processes operate similarly in school-aged children and adults.

Our previous research with adults suggests that pre-attentive (bottom-up) brain processes govern auditory stream segregation [Sussman et al., 1998. Brain Res. 789, 130--138; Sussman et al., 1999. Psychophysiology 36, 22--34; Winkler et al., submitted for publication]. We investigated whether the pre-attentive mechanisms underlying auditory stream segregation operate similarly in school-aged (7--10 years of age) children and adults. We used an electrophysiological index of auditory change detection that does not require the experimental participant to focus on the sounds to be evoked. In Experiment 1, children were presented with mixtures of high and low frequency tones in different conditions and were instructed to watch a silent video and ignore the sounds. In Experiment 2, children were asked to listen to the same sets of sounds as presented in Experiment 1 and tell whether they heard one or two auditory streams. The pre-attentive processing of the mixture of sounds as one or two auditory streams (Experiment 1), matched with the perception of the sounds as one or two distinct streams (Experiment 2). Our results demonstrate that the mechanisms for auditory stream segregation operate similarly in school-aged children and adults when frequency proximity is the cue for segregation.

Acoustic Stimulation↗
PubMed1994

Segregation variance after hybridization of isolated populations.

We develop a model to predict the increase in genetic variance of a quantitative character in a hybrid population produced by crossing two previously isolated populations of the same species. The increase in variance in the F2 hybrids, the 'segregation variance', is caused by differences in the average allelic effects at each locus and by linkage disequilibrium among loci. We focus on the case in which the character is additively based and the average value of the character does not differ in the two populations. In that case the predicted segregation variance depends strongly on what is assumed about the genetic basis of the character. If the genetic variance of the character in each population is attributable to loci with numerous alleles of small effect that are in moderate frequency, as in Lande's (1975) model, the segregation variance should increase linearly with time since the populations were isolated, at a rate determined by the inverse of the effective population size. If the genetic variance is attributable to loci with alleles in very low frequency, as in Turelli's (1984) house-of-cards model or in Barton's (1990) model of pleiotropic, deleterious alleles, then the segregation variance in the hybrid population increases at a much lower rate.

Genetic Variation↗
PubMed1992

Effect of doxorubicin on the order of the acyl chains of anionic and zwitterionic phospholipids in liquid-crystalline mixed model membranes: absence of drug-induced segregation of lipids into extended domains.

We investigated the effect of the antineoplastic drug doxorubicin on the order of the acyl chains in liquid-crystalline mixed bilayers consisting of dioleoylphosphatidylserine (DOPS) or -phosphatidic acid (DOPA), and dioleoylphosphatidylcholine (DOPC) or -phosphatidylethanolamine (DOPE). Previous 2H-NMR studies on bilayers consisting of a single species of di[11,11-2H2]oleoyl-labeled phospholipid showed that doxorubicin does not affect the acyl chain order of pure zwitterionic phospholipid but dramatically decreases the order of anionic phospholipid [de Wolf, F. A., et al. (1991) Biochim. Biophys. Acta 1096, 67-80]. In the present work, we studied mixed bilayers in which alternatively the anionic or the zwitterionic phospholipid component was 2H-labeled so as to monitor its individual acyl chain order. Doxorubicin decreased the order parameter of the mixed anionic and zwitterionic lipids by approximately the same amount and did not induce a clear segregation of the lipid components into extended, separate domains. The drug had a comparable disordering effect on mixed bilayers of unlabeled cardiolipin and 2H-labeled zwitterionic phospholipid, indicating the absence of extensive segregation also in that case. Upon addition of doxorubicin to bilayers consisting of 67 mol% DOPE and 33 mol% anionic phospholipid, a significant part of the lipid adopted the inverted hexagonal (HII) phase at 25 degrees C. This bilayer destabilization, which occurred only in mixtures of anionic phospholipid and sufficient amounts of DOPE, might be of physiological importance. Even upon formation of extended HII-phase domains, lipid segregation was not clearly detectable, since the relative distribution of 2H-labeled anionic phospholipid and [2H]DOPE between the bilayer phase and HII phase was very similar. Our findings argue against a role of extensive anionic/zwitterionic lipid segregation in the mechanism of action and toxicity of doxorubicin.

Doxorubicin↗