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At least 793 records · Page 44Linked to original sources
PubMed2002

Predicted distribution and ecological risk assessment of a "segregated" hydrofluorrother in the Japanese environment.

An assessment of HFE-7500, a 'segregated' hydrofluoroether, was conducted to evaluate the potential for exposure to and subsequent effects on humans and wildlife in Japan. The segregated hydrofluoroethers belong to a class of fluorochemicals currently being proposed as replacements for traditional fluorochemicals (CFCs and PFCs) that are currently being used in several industries, in particular, the semiconductor industry. These traditional compounds have been implicated as ozone-depleting or potent "greenhouse gases". The segregated hydrofluoroethers have useful physical and chemical properties, but do not contribute to ozone depletion and have lower "global warming potential" (GWP) indices. Although the physical properties of these materials (low H2O solubility and high vapor pressure) suggest there would be a very low level of risk to aquatic systems, a thorough analysis had not been previously performed. Predicted environmental concentrations (PECs) of HFE-7500 in Japan were determined with the Higashino model, a Gausian puff and plume model that used an approximation of environmental releases to the atmosphere as input to the model. Allowable concentrations to protect aquatic life, wildlife, and humans from noncancer effects were determined as detailed in USEPA's final Water Quality Guidance for the Great Lakes Systems. Potential risk to ecological receptors and humans was determined by calculating hazard quotients and margins of safety. The results of the risk assessment indicate that HFE-7500 poses no significant risk to either aquatic or terrestrial wildlife species or humans living in the Japanese environment. The least margin of safety for any ecological receptor was 100,000, and a margin of safety greater than 100,000,000 for most receptors indicated that HFE-7500 poses no threat to human health. Because of a scarcity of toxicity and exposure data, the risk assessment was based on very conservative assumptions. Therefore, the actual margins of safety for both humans and wildlife could have been 100- to 1,000-fold greater if additional data were available such that less stringent uncertainty factors could be applied. These results suggest that the environmental impact of HFE-7500 should be inconsequential based on the marked improvement in its atmospheric properties relative to the traditional compounds currently in use. Given the short atmospheric lifetime and low global warming potential of this material, its replacement of CFCs and PFCs would result in a net improvement of environmental health and safety.

Animals↗
PubMed2005

In situ study of water-induced segregation of bromide in bromide-doped sodium chloride by scanning polarization force microscopy.

The adsorption of water on Br-doped NaCl crystals has been studied in situ using scanning polarization force microscopy, a noncontact electrostatic atomic force microscopy operation mode. Both topography and contact potential images were acquired as a function of relative humidity at room temperature, from 0% to more than 55%. It was found that the surface of the freshly cleaved crystal has an inhomogeneous electrical surface potential distribution with the steps more negative than the terraces below 40% relative humidity. This difference disappears when the humidity reaches 40% and higher. Below 40% the step morphology experiences only small changes due to water adsorption; however, above 40% major changes take place due to solvation, segregation, and redistribution of lattice ions. Bromide-rich islands and crystallites segregate to the surface above 40% relative humidity followed by drying. These islands and crystallites have a negative surface potential relative to the rest of the surface. These effects are attributed to the preferential solvation and segregation of Br- ions.

Journal Article↗
PubMed2005

Entropically mediated polyolefin blend segregation at buried sapphire and air interfaces investigated by infrared-visible sum frequency generation vibrational spectroscopy.

The segregation behavior of binary polymer blends at hydrophilic solid sapphire and air interfaces was investigated by infrared-visible sum frequency generation (SFG) vibrational spectroscopy. SFG spectra were collected from a bulk miscible blend consisting of identical molecular weight (approximately 54,000) and similar surface free energy (29-35 dyn/cm) components of atactic polypropylene (aPP) and aspecific poly(ethylene-co-propylene) rubber (aEPR). Characteristic CH resonances of the blend were contrasted with those of the individual components at both buried (sapphire/polymer) and free (air/polymer) interfaces. Preferential segregation of the aPP component was observed after annealing at both air/polymer and sapphire/polymer interfaces. SFG spectra revealed ordering of the polymer backbone segments with the methylene (CH2) groups perpendicular to the surface at the sapphire interface and the methyl (CH3) groups upright at the air interface. The SFG results indicate that the surface composition can be determined from the peak intensities that are characteristic of each component and that conformational entropy played a likely role in surface segregation. aPP occupied a smaller free volume at the surface because of a statistically smaller segment length (aPP is more flexible and has a shorter length). In addition, the high density of the ordered CH3 side branches enhanced the surface activity by allowing the long-chain backbone segments of aPP to order at the surface.

Journal Article↗
PubMed2006

Promotion of the electrochemical activity of a bimetallic platinum-ruthenium catalyst by oxidation-induced segregation.

An alloy catalyst of 15 wt % Pt(50)Ru(50)/C was prepared by the method of incipient wetness impregnation and activated by hydrogen reduction at 620 K. Physical characterization of the freshly reduced catalyst indicated that bimetallic crystallites, Pt rich in the shell and Ru rich in the core, were finely dispersed in a diameter of dPtRu approximately 2 nm on carbon support. The reduced catalyst was subsequently modified by oxidization in air. On increasing the temperature of oxidation (T(o)), atoms of Ru in the core were found segregated to the surface of bimetallic crystallites and oxidized to amorphous RuO(2). Crystalline RuO(2) (RucO(2)) was formed on extensive segregation at To > 520 K. Catalytic activity of the alloy catalyst for electro-oxidation of methanol was examined by cyclic voltammetry. Electrochemical activity of the Pt-Ru/C catalyst was found to be significantly enhanced by oxidation treatments. The enhancement was, therefore, attributed to the segregation of Ru and the formation of RucO(2). Extensive oxidation treatment at elevated temperatures of To > 600 K, however, caused the deactivation of the electroactivity. The deactivation should be the result of excessive oxidation of the carbon support.

Journal Article↗
PubMed2006

Phase segregation in AlInP shells on GaAs nanowires.

We have studied morphology and phase segregation of AlInP shells on GaAs nanowires. Photoluminescence measurements on single core-shell nanowires indicated variations in the shell composition, and phase segregation was confirmed by cross-sectional scanning transmission electron microscopy on 30 nm thin slices of the wires. It was discovered that Al-rich domains form in the <112> directions where two {110} shell facets meet during growth. We propose that the mechanism behind this phase segregation is a variation in the chemical potential along the circumference of the nanowire together with a difference in diffusion lengths for the different growth species. From the morphology of the core and the shell, we conclude that the side facet growth is temperature dependent forming {112}facets at low growth temperature and {110} facets at high growth temperature.

Journal Article↗
PubMedDate not supplied

Electrophysiological correlates of human texture segregation, an overview.

'Texture segregation' results from parallel processing in the visual cortex. It occurs when the stimulus contains spatial gradients within a visual dimension. We here present an introductory overview of the field, concentrating on electrophysiological correlates in the human EEG ('tsVEPs') of the neuronal processes underlying texture segregation. We describe the isolation of the tsVEP from the background EEG, give examples of the correlation between saliency and tsVEP amplitude and compare texture segregation between visual dimensions.

Animals↗
PubMed2003

A cluster of autosomal recessive spondylocostal dysostosis caused by three newly identified DLL3 mutations segregating in a small village.

In 1982, one of us reported a cluster of eight individuals affected by spondylocostal dysostosis (SD, MIM 277300) in four nuclear families indigenous to a village from eastern Switzerland. We tested the hypothesis that the molecular basis for this cluster was segregation of a single mutation in the DLL3 gene, recently linked to SD. Marker haplotypes around the DLL3 locus contradicted this hypothesis as three different haplotypes were seen in affected individuals, but sequence analysis showed that three unreported DLL3 mutations were segregating: a duplication of 17 bp in exon 8 (c.1285-1301dup), a single-nucleotide deletion in exon 5 (c.615delC), and a R238X nonsense mutation in exon 6. Contrary to our initial assumption of a single allele segregating in this small community, three different pathogenic alleles were observed, with a putative founder mutation occurring at the homozygous state but also compounding with, and thus revealing, two other independent mutations. As all three mutations predict truncation of the DLL3 protein and loss of the membrane-attaching domain, the results confirm that autosomal recessive spondylocostal dysostosis represents the null phenotype of DLL3, with remarkable phenotypic consistency across families.

Dysostoses↗
PubMed1976

Stream segregation and the illusion of overlap.

When two different sounds continuously alternate at high speed, they segregate into two perceptual streams. The present article shows that this segregation produces a loss of information regarding the sequential relations of the sounds so that they seem perceptually to be overlapped in time. The segregation (and its contribution to perceived overlap) is shown to increase with the perceptual difference between the sounds. The mapping from perceptual difference to perceived overlap is not simple, however, since perceived overlap can also be affected by "perceived auditory continuity," another perceptual effect that responds differently to the perceptual difference between the two sounds.

Acoustic Stimulation↗
PubMedDate not supplied

Conservative segregation of nucleosome core histones.

Density labelling studies have shown that nascent histones are not mixed with parental histones during the assembly of nucleosome cores. However, experiments in other laboratories, examining histone deposition with respect to newly synthesized DNA, have been interpreted as suggesting that a substantial proportion of core histones (greater than 15%) are randomized at each chromatin replication. The data presented here support our previous results in showing that conservatively assembled nucleosome core histone octamers are conservatively segregated over successive cell generations. It is also shown that the nucleosome cores assembled during 1-beta-D-arabinofuranosylcytosine inhibition of DNA synthesis are conservatively segregated for a minimum of five or six cell generations. These results suggest that the nonrandom assembly of nucleosome cores is not merely a coincidence of the mechanism of histone transport into the nucleus and that the conservative mode of nucleosome segregation is a fundamental feature of chromatin replication, one which is stable to modulations in chromatin packaging.

Animals↗
PubMedDate not supplied

Prenatal development of individual retinogeniculate axons during the period of segregation.

When connections are first formed during the development of the vertebrate nervous system, inputs from different sources are frequently intermixed and the specific adult pattern then emerges as the different inputs segregate from each other. During the prenatal development of connections between retina and lateral geniculate nucleus (LGN) in the cat, the projections from the two eyes initially overlap with each other within the LGN. Over the next 3 weeks a reduction in the amount of overlap occurs so that by birth, a segregated pattern similar to the adult is present. We report here that during the period of overlap, individual retinogeniculate axons are simple in shape and restricted in extent without any widespread branches. Further, the appearance of the segregated pattern of eye input is accompanied by the elaboration of extensive new axonal arbors within appropriate LGN territory accompanied by retraction of only a limited number of minor branches. This developmental strategy contrasts with that in other regions of the vertebrate central nervous system in which the orderly adult pattern of connections within a target is achieved by a relative reduction in the overall extent of the axon arbor.

Animals↗
PubMed1990

The Drosophila claret segregation protein is a minus-end directed motor molecule.

A product encoded at the claret locus in Drosophila is needed for normal chromosome segregation in meiosis in females and in early mitotic divisions of the embryo. The predicted amino-acid sequence of the segregation protein was shown recently to be strikingly similar to Drosophila kinesin heavy chain. We have expressed the claret segregation protein in bacteria and have found that the bacterially expressed protein has motor activity in vitro with several novel features. The claret motor is slow (4 microns min-1), unlike either kinesin or dyneins. It has the directionality, the ability to generate torque and the sensitivity to inhibitors reported previously for dyneins. The finding of minus-end directed motor activity for a protein with sequence similarity to kinesin suggests that the dynein and kinesin motor domains are ancestrally related. The minus-end directed motor activity of the claret motor is consistent with a role for this protein in producing chromosome movement along spindle microtubules during prometaphase and/or anaphase.

Adenosine Triphosphatases↗
PubMed1991

Disruption of retinogeniculate afferent segregation by antagonists to NMDA receptors.

Afferent activity has an important role in the formation of connections in the developing mammalian visual system. But the extent to which the activity of target neurons shapes patterns of afferent termination and synaptic contact is not known. In the ferret's visual pathway, retinal ganglion cell axons from each eye segregate early in development into eye-specific laminae in the lateral geniculate nucleus (LGN). The dorsal laminae (termed laminae A and A1) then segregate further into inner and outer sublaminae that retain input from on-centre and off-centre retinal axons, respectively. Thus, individual retinogeniculate axons form terminal arbors within laminae A and A1 that are restricted to one inner or outer sublamina. We report here that blockade of N-methyl-D-aspartate (NMDA) receptors on LGN cells with specific antagonists during the period of sublamina formation prevents retinal afferents from segregating into 'On' and 'Off' sublaminae. Retinogeniculate axons have arbors that are not restricted appropriately, or are restricted in size but inappropriately positioned within the eye-specific laminae. NMDA receptor antagonists may specifically disrupt a mechanism by which LGN neurons detect correlated afferent and target activity, and have been shown to reduce retinogeniculate transmission more generally, causing LGN cells to have markedly reduced levels of activity. These results therefore indicate that the activity of postsynaptic cells can significantly influence the patterning of inputs and the structure of presynaptic afferents during development.

2-Amino-5-phosphonovalerate↗
PubMed1991

Basal body movements as a mechanism for mitochondrial genome segregation in the trypanosome cell cycle.

The mitochondrial genome of Trypanosoma brucei is organized in the form of a complex catenated network of circular DNA molecules. This mass of DNA, known as the kinetoplast, is present at a unique site in the single mitochondrion, and is replicated in a discrete, periodic S phase of the cell cycle. The single-copy nature of the kinetoplast suggests that there is a mechanism ensuring segregation fidelity of replicated copies to each daughter cell. Historically, speculation regarding the nature of this mechanism has often attributed significance to the close association between the kinetoplast and the flagellum basal body. We provide here direct evidence that this mitochondrial DNA complex is indeed linked to the basal body, and segregation of the kinetoplast DNA is dependent on a microtubule-mediated separation of the new and old flagellar basal bodies during the cell cycle. This unique system may represent the remnants of an evolutionarily archaic mechanism for genome segregation.

Animals↗
PubMed1995

Asymmetric segregation of Numb and Prospero during cell division.

A cell can divide asymmetrically by specifically segregating a determinant into one of its daughter cells. The Numb protein is a candidate for such a determinant in the asymmetric cell divisions of the developing Drosophila nervous system. Numb is a membrane-associated protein that localizes asymmetrically during cell division and segregates into one daughter cell, where it is required for the specification of the correct cell fate. Here we show that a nuclear protein, Prospero, translocates to the membrane at the beginning of cell division and colocalizes with Numb throughout mitosis, suggesting a common mechanism for asymmetric segregation. Numb and Prospero localization is coupled to mitosis and tightly correlated with the position of one of the two centrosomes. In contrast to centrosome positioning, however, Numb and Prospero localization is independent of microtubules. Cytochalasin D treatment suggests that the process is also independent of actin. We propose that there is an organizer of asymmetric cell division which provides positional information for both the orientation of the mitotic spindle and asymmetric localization of Numb and Prospero.

Actins↗
PubMed1997

A segregation analysis of testicular cancer based on Norwegian and Swedish families.

Clustering of testicular cancer cases in families is well known, although the aetiology is not. We present the results of a segregation analysis performed with the algorithm Pointer on familial data on 978 Scandinavian patients with testicular cancer. The segregation analysis favoured the involvement of major gene effects over models incorporating solely polygenic effects in testicular cancer aetiology. Overall, a recessive model best fits the family observations with an estimated gene frequency of 3.8% and a lifetime risk for homozygous men of developing the disease of 43%. This implies that 7.6% of men in the general population will be carriers of the mutant allele and that 0.1% would be homozygote and are, therefore, at high risk of developing the cancer. The testicular cancer incidence has changed greatly during the last generation. Also, the lethality of the disease has changed because of the introduction of new therapy. As failure to take account of such time trends might lead to inappropriate evidence for a recessive model, the analyses were repeated under different assumptions. The analyses favoured a recessive model of inheritance under all assumptions tested. However, the assumptions underlying the analyses are complex and, as this is the first segregation analysis of testicular cancer, the results must be interpreted cautiously.

Adolescent↗
PubMed1993

Identification of RAPD markers linked to a Rhynchosporium secalis resistance locus in barley using near-isogenic lines and bulked segregant analysis.

Three hundred random sequence 10-mer primers were used to screen a pair of near-isogenic lines of barley and their donor parent for markers linked to genes conferring resistance to Rhynchosporium secalis. One primer was identified which reproducibly generated a product, SC10-65-H400, from the donor parent and the Rhynchosporium-resistant near-isogenic line but not from the recurrent parent. Segregation analysis on a barley doubled haploid population and examination of a further three near-isogenic lines, their donor and recurrent parents confirmed that this marker was linked to the Rhynchosporium resistance locus (Rh) on chromosome 3L. The presence or absence of SC10-65-H400 was subsequently used along with the resistance phenotype to identify two groups of individuals in the doubled haploid population which possessed alternative alleles at both loci and defined a genetic interval between these two markers. Based on that information two bulked DNA samples were constructed by combining equal amounts of DNA from five individuals from each group. The two bulks and doubled haploid parental lines were screened with 700 10-mer primers. Seven products were identified which were present in the 'resistant' bulk and parent and were absent in the susceptible samples. Segregation analysis established their association with Rh. In addition co-segregation of the linked markers with a set of chromosome arm specific RFLPs confirmed the location of the Rh locus on the long arm of barley chromosome 3.

Base Sequence↗
PubMed1997

Sensitivity of segregation analysis to data structure and transformation: a case study of trypanotolerance in mice.

Sensitivity of segregation analysis for data structure and data transformation was studied using data from two trials in which mice were challenged at three months of age with a cloned isolate of Trypanosoma congolense and survival time was recorded. Data included records from three inbred strains (C57BL/6 (tolerant), A/J, and BALB/c (both susceptible)) and their crosses. Data were standardized and normalized using a modified power transformation. Segregation analysis was applied to both untransformed and transformed data to determine the genetic inheritance of trypanotolerance in these mice. Data from the two trials were analysed separately and combined. Four genetic models were compared; a one locus model, a polygenic model, a mixed model with common variance, and a mixed model with different variances for each major genotype. Even though the separate data sets and the combined data set all supported the hypothesis of a major gene (or a tightly linked cluster of genes) with different variances within each genotype, parameter estimates were highly sensitive to data transformation and several sets of parameter estimates gave similar likelihood values because of high dependency between parameters. Based on the results segregation analysis can be very sensitive to data structure in a crossbreeding design and to data transformation. Interpretation of the results can be misleading if the entire parameter space is not studied carefully.

Animals↗
PubMed1996

Random genetic drift in the female germline explains the rapid segregation of mammalian mitochondrial DNA.

Mitochondrial DNA (mtDNA) is maternally inherited in mammals. Despite the high genome copy number in mature oocytes (10(5)) and the relatively small number of cell divisions in the female germline, mtDNA sequence variants segregate rapidly between generations. To investigate the molecular basis for this apparent paradox we created lines of heteroplasmic mice carrying two mtDNA genotypes. We show that the pattern of segregation can be explained by random genetic drift occurring in early oogenesis, and that the effective number of segregating units for mtDNA is approximately 200 in mice. These results provide the basis for estimating recurrence risks for mitochondrial disease due to pathogenic mtDNA mutations and for predicting the rate of fixation of neutral mtDNA mutations in maternal lineages.

Animals↗