Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Cortical phase changes measured using 7-T MRI in subjects with subjective cognitive impairment, and their association with cognitive function
Rooden, Sanneke van; Buijs, Mathijs ; Vliet, Marjolein E. van; Versluis, Maarten J. ; Webb, Andrew G. ; Oleksik, Ania M. ; Wiel, Lotte van de; Middelkoop, Huub A.M. ; Blauw, Gerard Jan ; Weverling-Rynsburger, Annelies W.E. ; Goos, Jeroen D.C. ; Flier, Wiesje M. van der; Koene, Ted ; Scheltens, Philip ; Barkhof, Frederik ; Nieuwerth-van de Rest, Ondine ; Slagboom, P.E. ; Buchem, Mark A. van; Grond, Jeroen van der - \ 2016
NMR in Biomedicine 29 (2016)9. - ISSN 0952-3480 - p. 1289 - 1294.
AD pathology - Alzheimer's disease - brain imaging - cognition - human 7-T MRI - phase - subjective cognitive impairment

Studies have suggested that, in subjects with subjective cognitive impairment (SCI), Alzheimer's disease (AD)-like changes may occur in the brain. Recently, an in vivo study has indicated the potential of ultra-high-field MRI to visualize amyloid-beta (Aβ)-associated changes in the cortex in patients with AD, manifested by a phase shift on T2*-weighted MRI scans. The main aim of this study was to investigate whether cortical phase shifts on T2*-weighted images at 7 T in subjects with SCI can be detected, possibly implicating the deposition of Aβ plaques and associated iron. Cognitive tests and T2*-weighted scans using a 7-T MRI system were performed in 28 patients with AD, 18 subjects with SCI and 27 healthy controls (HCs). Cortical phase shifts were measured. Univariate general linear modeling and linear regression analysis were used to assess the association between diagnosis and cortical phase shift, and between cortical phase shift and the different neuropsychological tests, adjusted for age and gender. The phase shift (mean, 1.19; range, 1.00–1.35) of the entire cortex in AD was higher than in both SCI (mean, 0.85; range, 0.73–0.99; p <0.001) and HC (mean, 0.94; range, 0.79–1.10; p <0.001). No AD-like changes, e.g. increased cortical phase shifts, were found in subjects with SCI compared with HCs. In SCI, a significant association was found between memory function (Wechsler Memory Scale, WMS) and cortical phase shift (β = –0.544, p = 0.007). The major finding of this study is that, in subjects with SCI, an increased cortical phase shift measured at high field is associated with a poorer memory performance, although, as a group, subjects with SCI do not show an increased phase shift compared with HCs. This increased cortical phase shift related to memory performance may contribute to the understanding of SCI as it is still unclear whether SCI is a sign of pre-clinical AD.

New insights into the liquid crystal behaviour of hydrogen-bonded mixtures provided by temperature-dependent FTIR spectroscopy
Paterson, D.A. ; Martínez-Felipe, A. ; Jansze, S.M. ; Marcelis, A.T.M. ; Storey, J.M.D. ; Imrie, C.T. - \ 2015
Liquid Crystals 42 (2015)5-6. - ISSN 0267-8292 - p. 928 - 939.
low molar-mass - side-chain - carboxylic-acids - benzoic-acid - amorphous polymers - pyridyl moieties - ir-spectra - dimers - phase - complexes
The phase behaviour of equimolar mixtures of 6-(4'-cyanobiphenyl-4-yl)hexyloxybenzoic acid (CB6OBA) with either 1-(4-butylazobenzene-4'-oxy)-5-(4-oxypyridine)pentane (BuABO5OPyr) or 1-(4-butylazobenzene-4'-oxy)-6-(4-oxypyridine)hexane (BuABO6OPyr) is reported. CB6OBA shows a monotropic twist-bend nematic phase and an enantiotropic nematic phase whereas the two pyridyl-based components do not exhibit liquid crystallinity. Both equimolar mixtures (CB6OBA/BuABOnOPyr) show enantiotropic nematic phases. The nematic-isotropic transition temperature and associated entropy change are higher for the CB6OBA/BuABO6OPyr mixture than for the CB6OBA/BuABO5OPyr mixture. This may be accounted for in terms of the average shapes of the hydrogen-bonded 1:1 complexes formed between the two differing components in the mixtures. However, Fourier transform infrared spectroscopy reveals that this complex is not formed quantitatively, but instead a complex mixture exists over the complete temperature range studied, involving the 1:1 complex, both cyclic and open acid dimers, free acid and hence, free BuABOnOPyr molecules.
Multiscale analysis of structure development in expanded starch snacks
Sman, R.G.M. van der; Broeze, J. - \ 2014
Journal of Physics-Condensed Matter 26 (2014)46. - ISSN 0953-8984
mass-transfer - food materials - bubble-growth - porous-media - systems - polymer - phase - model - simulation - extrusion
In this paper we perform a multiscale analysis of the food structuring process of the expansion of starchy snack foods like keropok, which obtains a solid foam structure. In particular, we want to investigate the validity of the hypothesis of Kokini and coworkers, that expansion is optimal at the moisture content, where the glass transition and the boiling line intersect. In our analysis we make use of several tools, (1) time scale analysis from the field of physical transport phenomena, (2) the scale separation map (SSM) developed within a multiscale simulation framework of complex automata, (3) the supplemented state diagram (SSD), depicting phase transition and glass transition lines, and (4) a multiscale simulation model for the bubble expansion. Results of the time scale analysis are plotted in the SSD, and give insight into the dominant physical processes involved in expansion. Furthermore, the results of the time scale analysis are used to construct the SSM, which has aided us in the construction of the multiscale simulation model. Simulation results are plotted in the SSD. This clearly shows that the hypothesis of Kokini is qualitatively true, but has to be refined. Our results show that bubble expansion is optimal for moisture content, where the boiling line for gas pressure of 4 bars intersects the isoviscosity line of the critical viscosity 10(6) Pa.s, which runs parallel to the glass transition line.
Consequences of splitting whole-genome sequencing effort over multiple breeds on imputation accuracy
Bouwman, A.C. ; Veerkamp, R.F. - \ 2014
BMC Genetics 15 (2014). - ISSN 1471-2156 - 9 p.
genotype imputation - cattle breeds - linkage disequilibrium - phase - populations - jersey - values
The aim of this study was to determine the consequences of splitting sequencing effort over multiple breeds for imputation accuracy from a high-density SNP chip towards whole-genome sequence. Such information would assist for instance numerical smaller cattle breeds, but also pig and chicken breeders, who have to choose wisely how to spend their sequencing efforts over all the breeds or lines they evaluate. Sequence data from cattle breeds was used, because there are currently relatively many individuals from several breeds sequenced within the 1,000 Bull Genomes project. The advantage of whole-genome sequence data is that it carries the causal mutations, but the question is whether it is possible to impute the causal variants accurately. This study therefore focussed on imputation accuracy of variants with low minor allele frequency and breed specific variants. Results Imputation accuracy was assessed for chromosome 1 and 29 as the correlation between observed and imputed genotypes. For chromosome 1, the average imputation accuracy was 0.70 with a reference population of 20 Holstein, and increased to 0.83 when the reference population was increased by including 3 other dairy breeds with 20 animals each. When the same amount of animals from the Holstein breed were added the accuracy improved to 0.88, while adding the 3 other breeds to the reference population of 80 Holstein improved the average imputation accuracy marginally to 0.89. For chromosome 29, the average imputation accuracy was lower. Some variants benefitted from the inclusion of other breeds in the reference population, initially determined by the MAF of the variant in each breed, but even Holstein specific variants did gain imputation accuracy from the multi-breed reference population. Conclusions This study shows that splitting sequencing effort over multiple breeds and combining the reference populations is a good strategy for imputation from high-density SNP panels towards whole-genome sequence when reference populations are small and sequencing effort is limiting. When sequencing effort is limiting and interest lays in multiple breeds or lines this provides imputation of each breed.
Selection of SNP from 50K and 777K arrays to predict breed of origin in cattle
Hulsegge, B. ; Calus, M.P.L. ; Windig, J.J. ; Hoving, A.H. ; Maurice - Van Eijndhoven, M.H.T. ; Hiemstra, S.J. - \ 2013
Journal of Animal Science 91 (2013)11. - ISSN 0021-8812 - p. 5128 - 5134.
single-nucleotide polymorphisms - population divergence - informative markers - assignment - ancestry - individuals - inference - holstein - jersey - phase
Reliable breed assignment can be performed with SNP. Currently, high density SNP chips are available with large numbers of SNP from which the most informative SNP can be selected for breed assignment. Several methods have been published to select the most informative SNP to distinguish among breeds. In this study, we evaluated Delta, Wright's FST, and Weir and Cockerham's FST, and extended these methods by adding a rule to avoid selection of sets of SNP in high linkage disequilibrium (LD) providing the same information. The SNP that had a r2 value>0.3 with any of the SNP already selected were discarded. The different selection methods were evaluated for both the 50K SNP and 777K Bovine BeadChip. Animals from 4 cattle breeds (989 Holstein Friesian, 97 Groningen White headed, 137 Meuse-Rhine-Yssel, and 64 Dutch Friesian) were genotyped. After editing 30,447 and 452,525 SNP were available for the 50K and 777K SNP chip, respectively. All selection methods showed that only a small set of SNP is needed to differentiate among the 4 Dutch cattle breeds, whereas comparison of the selection methods showed only small differences. In general, the 777K performed marginally better than the 50K BeadChip, especially at higher confidence thresholds. The rule to avoid selection of SNP in high LD reduced the required number of SNP to achieve correct breed assignment. The Global Weir and Cockerham's FST performed marginally better than other selection methods. There was little overlap in the SNP selected from the 2 BeadChips, whereas the number of SNP selected was about the same.
Pickering emulsions: Wetting and colloidal stability of hairy particles - A self-consistent field theory
Salari, J.W.O. ; Leermakers, F.A.M. ; Klumperman, B. - \ 2011
Langmuir 27 (2011)11. - ISSN 0743-7463 - p. 6574 - 6583.
oil-water interface - interacting chain molecules - statistical-theory - solid particles - stabilization - adsorption - polymer - phase - microcapsules - surfactants
The assembly of sterically stabilized colloids at liquid–liquid interfaces is studied with the self-consistent field (SCF) theory using the discretization scheme that was developed by Scheutjens, Fleer, and co-workers. The model is based on a poly(methyl methacrylate) (pMMA) particle with poly(isobutylene) (pIB) grafted to the surface. The stabilizing groups on the particle surface have a significant effect on the interfacial assembly and, therefore, also on the formation and properties of Pickering emulsions. The wetting behavior of the particle is altered by the presence of the stabilizing groups, which affects the equilibrium position of the particles at the interface. The stabilizing groups can also lead to an activation barrier before interfacial adsorption, analogous to the steric repulsion between two particles. These effects are numerically solved with the SCF theory. It is commonly known that flocculating conditions enhance the interfacial adsorption and yield stable Pickering emulsions, which is confirmed in this work. Additionally, it is concluded that those conditions are not an absolute requirement. There is a window of stabilizer concentrations GpIB, 2.2–3.3 mg/m2 pIB, that shows both partial wetting and colloidal stability. The activation barrier for interfacial assembly is 140–550 kBT and is an order of magnitude higher than the colloidal stability. The difference can be attributed to the unfavorable interaction of pIB with water and a difference in geometry (plate–sphere vs sphere–sphere). This study demonstrates the interplay and provides a quantitative comparison between the wetting behavior and the colloidal stability, and it gives a better understanding of the colloidal assembly at soft interfaces and formation of Pickering emulsions in general
A simple McGowan specific volume correction for branching in hydrocarbons and its consequences for some other solvation parameter values
Noort, P.C.M. van; Haftka, J.J.H. ; Parsons, J.R. - \ 2011
Chemosphere 84 (2011). - ISSN 0045-6535 - p. 1102 - 1107.
energy relationship lser - organic-compounds - acyclic alkanes - phase - water - chromatography - descriptors
Differences in molecular properties between linear and branched alkanes as well as between compounds with branched alkyl groups is of relevance due to the large number of branched isomers of environmentally relevant compounds (e.g. fuels, fuel additives, surfactants). For branched alkane vapor pressures, the McGowan specific volume is a poor predictor. Therefore, in this study a correction on the McGowan specific volume is derived in terms of the number of branches and the number of pairs of vicinal branches to improve the prediction of branched alkane vapor pressures. This branching correction also brought branched /alkane solvent accessible volumes, octanol/water partition coefficients, air/hexadecane partition coefficients, and aqueous solubilities as well as alkyl-branched substituted aliphatic hydrocarbon air/hexadecane partition coefficients more in line with corresponding linear hydrocarbon properties when compared on a McGowan specific volume basis. Even for air–hexadecane partition coefficients of substituted aliphatic hydrocarbons with substituents at non-terminal carbons, application of the branching correction to the carbon bearing the substituent caused these partition coefficients to be more in line with those for linear compounds. Values for the Abraham A and B solvation parameters for nonlinear aliphatic ethers, amines, and alcohols, recalculated using branching corrected McGowan specific volumes, turned out to be closer to chemical expectations based on linear aliphatic ether, amine and alcohol values compared to previously reported experimental values obtained using uncorrected McGowan specific volumes. A comparison of alkylbenzene and alkene partition coefficient estimates from two different linear solvation energy relations, one containing a McGowan specific volume term and one without such a term, suggests that no branching correction is needed for alkyl groups at sp2 carbons. The main advantage of using branching corrected McGowan specific volumes is that the values of other solvation parameters become chemically more consistent.
Imputation of missing single nucleaotide polymorphism genotypes using multivariate mixed model framework
Calus, M.P.L. ; Veerkamp, R.F. ; Mulder, H.A. - \ 2011
Journal of Animal Science 89 (2011)7. - ISSN 0021-8812 - p. 2042 - 2049.
breeding value estimation - genomic selection - gene content - prediction - accuracy - populations - animals - cattle - phase
The objective of this paper was to investigate, for various scenarios at low and high marker density, the accuracy of imputing genotypes when using a multivariate mixed model framework using information from 2, 4, or 10 surrounding markers. This model predicts genotypes at a locus, using genotypes at nearby loci as correlated traits, and the additive genetic relationship matrix to use information from genotyped relatives. For 2 scenarios this method was compared with the population-based imputation algorithms FastPHASE and Beagle. Accuracies of imputation were obtained with Monte Carlo simulation and predicted with selection index theory, using input from the simulated data. Five different scenarios of missing genotypes were considered: 1) genotypes of some loci are missing due to genotyping errors, 2) juvenile selection candidates are genotyped using a smaller SNP panel, 3) some animals in the pedigree of a breeding population are not genotyped, 4) juvenile selection candidates are not genotyped, and 5) 1 generation of animals in the top of the pedigree are not genotyped. Surrounding marker information did not improve accuracy of imputation when animals whose genotypes were imputed were not genotyped for those surrounding markers. When those animals were genotyped for surrounding markers, results indicated a limited gain when linkage disequilibrium (LD) between SNP was low, but a substantial increase in accuracy when LD between SNP was high. For scenario 1, using 1 vs. 11 SNP, accuracy was respectively 0.75 and 0.81 at low, and 0.75 and 0.93 at high density. For scenario 2, using 1 vs. 11 SNP, accuracy was, respectively, 0.70 and 0.73 at low, and 0.71 and 0.84 at high density. Beagle outperformed the other methods at high SNP density, whereas the multivariate mixed model was clearly superior when SNP density was low and animals where genotyped with a reduced SNP panel. The results showed that extending the univariate gene content method to a multivariate BLUP model with inclusion of surrounding marker information only yields greater imputation accuracy when the animals with imputed loci are at least genotyped for some SNP that are in LD with the SNP to be imputed. The equation derived from selection index theory accurately predicted the accuracy of imputation using the multivariate mixed model framework.
Updated Abraham solvation parameters for polychlorinated biphenyls
Noort, P.C.M. van; Haftka, J.J.H. ; Parsons, J.R. - \ 2010
Environmental Science and Technology 44 (2010)18. - ISSN 0013-936X - p. 7037 - 7042.
carbon/water partition-coefficients - polycyclic aromatic-hydrocarbons - sodium dodecyl-sulfate - henrys law constants - physicochemical properties - aqueous solubilities - energy relationships - water - phase - gas
This study shows that the recently published polychlorinated biphenyl (PCB) Abraham solvation parameters predict PCB air-n-hexadecane and n-octanol-water partition coefficients very poorly, especially for highly ortho-chlorinated congeners. Therefore, an updated set of PCB solvation parameters was derived from four PCB properties and associated Abraham solvation equations. Additionally, the influence of ortho-chlorination on PCB solvent accessible volume and surface area was investigated. The updated PCB solvation parameters were tested on partitioning between five other phase combinations. Compared to the original PCB solvation parameter set, the updated PCB solvation parameters resulted in substantially improved estimates from Abraham solvation equations for (subcooled) liquid vapor pressures, aqueous solubilities, HPLC capacity factors, and for coefficients of air-n-hexadecane, air-water, organic carbon-water, and n-octanol-water partitioning. For water to polydimethyl siloxane and sodium dodecylsulphate (SDS) partitioning, the updated PCB solvation parameters yielded no improvement compared to the original data set. The main difference between the updated and the original parameter set is that updated PCB McGowan specific volumes depend on the degree of ortho-chlorination, which is qualitatively confirmed by trends in the PCB solvent accessible volumes and surface areas. The use of the updated PCB solvation parameters instead of the original values is therefore recommended
Modeling Logistic Performance in Quantitative Microbial Risk Assessment
Rijgersberg, H. ; Tromp, S.O. ; Jacxsens, L. ; Uyttendaele, M. - \ 2010
Risk Analysis 30 (2010)1. - ISSN 0272-4332 - p. 20 - 31.
equilibrium-modified atmosphere - listeria-monocytogenes growth - fresh-cut produce - exposure assessment - iceberg lettuce - microbiological quality - deli meats - food - phase - vegetables
In quantitative microbial risk assessment (QMRA), food safety in the food chain is modeled and simulated. In general, prevalences, concentrations, and numbers of microorganisms in media are investigated in the different steps from farm to fork. The underlying rates and conditions (such as storage times, temperatures, gas conditions, and their distributions) are determined. However, the logistic chain with its queues (storages, shelves) and mechanisms for ordering products is usually not taken into account. As a consequence, storage times—mutually dependent in successive steps in the chain—cannot be described adequately. This may have a great impact on the tails of risk distributions. Because food safety risks are generally very small, it is crucial to model the tails of (underlying) distributions as accurately as possible. Logistic performance can be modeled by describing the underlying planning and scheduling mechanisms in discrete-event modeling. This is common practice in operations research, specifically in supply chain management. In this article, we present the application of discrete-event modeling in the context of a QMRA for Listeria monocytogenes in fresh-cut iceberg lettuce. We show the potential value of discrete-event modeling in QMRA by calculating logistic interventions (modifications in the logistic chain) and determining their significance with respect to food safety.
Seasonal variation of total and biochemically available concentrations of PAHs in a floodplain lake sediment has no effect on the benthic invertebrate community
Lange, H.J. de; Peeters, E.T.H.M. ; Harmsen, J. ; Maas, H. ; Jonge, J. de - \ 2009
Chemosphere 75 (2009)3. - ISSN 0045-6535 - p. 319 - 326.
contaminated sediments - organic-compounds - toxicity - estuary - phase - rhine - bioavailability - netherlands - extraction - abundance
Floodplain areas in the Netherlands are moderately to heavily contaminated with trace metals and organic contaminants. The impact of this sediment pollution on benthic invertebrates is best described with so-called ‘bioavailable’ concentrations instead of total concentrations. Studies into the effect of contaminants on biota are usually a snapshot in time, with one or two samples in a year. In such studies, effect of seasonal variation cannot be detected. Objective of this study was to investigate the temporal variation of sediment PAH contamination in one floodplain lake, and possible consequences for the benthic invertebrate community. This was done by sampling biota, abiotic variables and sediment contaminants every four weeks during one year. We observed a limited seasonal variation in total and bioavailable concentrations of PAHs. Multivariate analysis revealed that the PAH contamination is not a significant factor for the benthic invertebrate community in this floodplain lake. Bioavailable concentrations of PAHs were low and no effects could be expected based on the measured values. No increase of available PAHs was observed in periods where conditions for degradation were absent (low temperature, anaerobic). These results also indicate that in such floodplain lake systems, with historical pollution, the timing of sampling to assess sediment contamination with organic pollutants is of limited importance. This can be useful for planning sampling in risk assessment studies
Modelling the level of the major glucosinolates in broccoli as affected by controlled atmosphere and temperature
Schouten, R.E. ; Zhang, X. ; Verkerk, R. ; Verschoor, J.A. ; Otma, E.C. ; Tijskens, L.M.M. ; Kooten, O. van - \ 2009
Postharvest Biology and Technology 53 (2009)1-2. - ISSN 0925-5214 - p. 1 - 10.
oleracea var. italica - gas-exchange - postharvest - storage - glucoraphanin - quality - heads - transport - period - phase
This study describes the effects of controlled atmosphere (CA) and temperature on glucosinolate (GLS) levels in broccoli. Gas exchange rates were measured in three climate rooms with twelve containers each holding 20 randomly selected broccoli (cv `1997¿) taken from one large batch of broccoli during a three-week period. Broccoli heads were stored at three temperatures and subjected to four levels of O2 and three levels of CO2. GLS were measured on individual broccoli heads using a HPLC-based protocol. Information about the GLS development over time was extracted by analysing `replicate¿ broccoli containers (containers stored at the same temperature and gas conditions) that were removed periodically during the storage period. The most striking feature was the large variation in GLS concentrations at harvest with the propagation of variation over time clearly affected by CA and temperature. Decay of the four most important GLS over time was described by a sigmoid model based on the decompartmentalisation of the enzyme myrosinase that hydrolyses GLS. Gas exchange parameters were estimated using the standard gas exchange model; the parameters of the GLS decay were estimated using a batch model that describes the propagation of the GLS variation as function of O2, CO2, time, temperature, the average biological age and biological variation ( 88%). This approach was used to study the effect of regular and modified atmosphere conditions on GLS keeping quality. Storage under regular atmosphere during chain simulation showed that the keeping quality for all four GLS is between four and seven days, while storage under 1.5 kPa O2 and 15 kPa CO2 showed a keeping quality of at least 14 d, indicating that to preserve the nutritional quality of broccoli, MA packaging is a viable option
Partial coalescence as a tool to control sensory perception of emulsions
Benjamins, J. ; Vingerhoeds, M.H. ; Zoet, F.D. ; Hoog, E.H.A. de; Aken, G.A. van - \ 2009
Food Hydrocolloids 23 (2009)1. - ISSN 0268-005X - p. 102 - 115.
in-water emulsions - protein-stabilized emulsions - fat-content - destabilization - aggregation - temperature - crystals - phase - films - shear
This study evaluates the role of partial coalescence of whey protein-stabilized emulsions on sensory perception. The selection of fats was restricted to vegetable fats that are essentially melted at oral temperatures. The sensitivity to partial coalescence was controlled by a variation in the fat melting curve and by addition of unsaturated monoglyceride. Most fat-related sensory attributes appear to be well-correlated to an increase in viscosity and coalescence in the mouth due to partial coalescence. Moreover, it was found that in-mouth aeration induces extra coalescence, which increases the perception of fat-related sensory attributes significantly. Monoglyceride addition induces a shift of the sensory perception of fattiness and other fat-related attributes. There are clear indications that monoglyceride addition affects sensory perception not only by promoting partial coalescence, but also by an additional effect such as its surface activity.
Detection of mastitis pathogens by analysis of volatile bacterial metabolites
Hettinga, K.A. ; Valenberg, H.J.F. van; Lam, T.J.G.M. ; Hooijdonk, A.C.M. van - \ 2008
Journal of Dairy Science 91 (2008). - ISSN 0022-0302 - p. 3834 - 3839.
electronic nose - staphylococcus-aureus - bovine mastitis - milk - culture - system - network - pattern - phase
The ability to detect mastitis pathogens based on their volatile metabolites was studied. Milk samples from cows with clinical mastitis, caused by Staphylococcus aureus, coagulase-negative staphylococci, Streptococcus uberis, Streptococcus dysgalactiae, and Escherichia coli were collected. In addition, samples from cows without clinical mastitis and with low somatic cell count (SCC) were collected for comparison. All mastitis samples were examined by using classical microbiological methods, followed by headspace analysis for volatile metabolites. Milk from culture-negative samples contained a lower number and amount of volatile components compared with cows with clinical mastitis. Because of variability between samples within a group, comparisons between pathogens were not sufficient for classification of the samples by univariate statistics. Therefore, an artificial neural network was trained to classify the pathogen in the milk samples based on the bacterial metabolites. The trained network differentiated milk from uninfected and infected quarters very well. When comparing pathogens, Staph. aureus produced a very different pattern of volatile metabolites compared with the other samples. Samples with coagulase-negative staphylococci and E. coli had enough dissimilarity with the other pathogens, making it possible to separate these 2 pathogens from each other and from the other samples. The 2 streptococcus species did not show significant differences between each other but could be identified as a different group from the other pathogens. Five groups can thus be identified based on the volatile bacterial metabolites: Staph. aureus, coagulase-negative staphylococci, streptococci (Strep. uberis and Strep. dysgalactiae as one group), E. coli, and uninfected quarters
Dimer Biphenyl Liquid Crystals with Trisiloxane-Containing Spacers
Achten, R. ; Koudijs, A. ; Giesbers, M. ; Marcelis, A.T.M. ; Sudhölter, E.J.R. - \ 2007
Molecular Crystals and Liquid Crystals 477 (2007)1. - ISSN 1542-1406 - p. 169 - 176.
mesogenic fluorinated organosiloxanes - polar order - phase - chirality - systems - series
Dimeric biphenyl liquid crystals with trisiloxane containing spacers were studied. Both the tail lengths and the spacer lengths to a central hexamethyltrisiloxane group were varied. In most cases a SmC-phase was found with an anticlinic interlayer relation. One of the compounds appears to have a SmA-phase, which could be a de Vries SmA-phase. A few other compounds show liquid crystalline polymorphism. X-ray diffraction experiments show that the smectic layers are strongly interdigitated. The thickness of the layers is mainly dependent on the length of the spacers. The length of the terminal alkyl chains hardly influences the smectic layer thickness.
A simple relation for the concentration dependence of osmotic pressure and depletion thickness in polymer solutions
Fleer, G.J. ; Skvortsov, A.M. ; Tuinier, R. - \ 2007
Macromolecular Theory and Simulations 16 (2007)5. - ISSN 1022-1344 - p. 531 - 540.
mean-field - chains - polystyrene - potentials - simulation - mixtures - equation - solvent - dilute - phase
We propose simple expressions II/IIo = 1 + and (omega/omega(ex))(3 alpha-1) and (delta(0)/delta)(2) = 1 + (omega/omega(ex))(2 alpha) for the osmotic pressure II and the depletion thickness 6 as a function of the polymer concentration omega. Here, IIo and delta 0 correspond to the dilute limit, and omega(ex) is an extrapolation concentration which is of the order of the overlap concentration omega(ov). The De Gennes exponent a describes the concentration dependence of the semidilute correlation length xi similar to omega(-alpha) it is related to the Flory exponent nu through alpha = nu/(3 nu - 1.). The quantity omega(ex) is experimentally accessible by extrapolating the semidilute limit towards II = IIo or delta = delta(o). These expressions are exact in mean field, where the ratio omega(ex)/omega(ov) (0.49 for II, 0.41 for delta) follows from established models. For excluded-volume chains they describe simulation data excellently: in this case omega(ex)/omega(ov) is 0.69 for II and again 0.41 for delta. We find also very good agreement with experimental data.
Wormlike aggregates from a supramolecular coordination polymer and a diblock copolymer
Yan, Y. ; Besseling, N.A.M. ; Keizer, A. de; Drechsler, M. ; Fokkink, R.G. ; Cohen Stuart, M.A. - \ 2007
The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 111 (2007)40. - ISSN 1520-6106 - p. 11662 - 11669.
block-copolymers - polyelectrolyte solutions - integral-equations - multivalent salts - micelles - complexes - delivery - phase - gene
The formation of wormlike micelles in mixed systems of a supramolecular coordination polymer Zn-L2EO4 and a diblock copolymer P2MVP41-b-PEO205 is investigated by light scattering and Cryo-TEM. By direct mixing at a stoichiometric charge ratio, the above mixtures proved to be capable of formation of spherical micelles with a radius of about 25 nm (Yan et al. Angew. Chem., Int. Ed.; 2007, 46, 1807-1809). Lately, we find wormlike micelles with a hydrodynamic radius >150 nm in a mixture with excess positive charge, that is, a negative charge fraction f- <0.5. The transformation between wormlike and spherical micelles can be realized by variation of the mixing ratio through different protocols. Upon addition of negatively charged Zn-L2EO4 to a mixture with excess positively charged P2MVP41-b-PEO205, most of the wormlike micelles are transformed into spherical ones; upon addition of positively charged P2MVP41-b-PEO205 to a mixture of pure spherical micelles, wormlike micelles can be produced again. The effect of sample preparation protocol, sample history, and concentration on this transformation process is systematically reported in this article. A possible mechanism for the formation of wormlike micelles is proposed.
Liquid crystalline dimers with bent-core mesogenic units
Achten, R. ; Koudijs, A. ; Giesbers, M. ; Marcelis, A.T.M. ; Sudhölter, E.J.R. ; Schroeder, M.W. ; Weissflog, W. - \ 2007
Liquid Crystals 34 (2007)1. - ISSN 0267-8292 - p. 59 - 64.
polar order - achiral molecules - chirality - antiferroelectricity - ferroelectricity - mesophases - spacer - phase
Two series of dimers, in which two identical aromatic bent core mesogenic units are connected via an organosiloxane or an alkylene spacer, have been investigated. The dimers with a spacer consisting of a trisiloxane central group and relatively long alkylene groups show an intercalated tilted smectic structure. The layer spacings appear to be very weakly dependent on the terminal chain lengths. In these dimers the smectic phase is stabilized for the compounds with a short terminal chain. Dimers with an aliphatic alkylene spacer are liquid crystalline only when the spacer is relatively short and the terminal chains are long. For these dimers a monolayer tilted smectic phase is observed.
H-Bond-Stabilized Triphenylene-Based Columnar Discotic Liquid Crystals
Paraschiv, I. ; Giesbers, M. ; Lagen, B. van; Grozema, F.C. ; Abellon, R.D. ; Siebbeles, L.D.A. ; Marcelis, A.T.M. ; Zuilhof, H. ; Sudhölter, E.J.R. - \ 2006
Chemistry of materials 18 (2006)4. - ISSN 0897-4756 - p. 968 - 974.
charge-carrier mobilities - organic gels - pr-trmc - mesophases - transport - chemistry - stacking - energy - phase - order
A 1,3,5-benzenetrisamide with three pending hexaalkoxytriphenylene groups has been synthesized as an example of an interesting class of intermolecular H-bond-stabilized columnar discotic liquid crystalline materials. The material forms a plastic hexagonal discotic phase that does not crystallize on cooling from the isotropic phase, even after annealing for a few days at room temperature. X-ray and computational studies provide a detailed model for the organization of this material. The charge carrier mobility, 0.12 cm2 V-1 s-1 at 180 C, is the highest ever reported for liquid crystalline triphenylene systems, and even increases with temperature. The factors responsible for this behavior are discussed.
DNA psi-condensation and reentrant decondensation: Effect of the PEG degree of polymerization
Ramos, J.E.B. ; Vries, R.J. de; Neto, J.R. - \ 2005
The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 109 (2005)49. - ISSN 1520-6106 - p. 23661 - 23665.
circular-dichroism - osmotic-stress - transition - forces - phase
¿-Condensation of DNA fragments of about 4 kbp was induced by poly(ethylene glycol) (PEG), with degrees of polymerization ranging from 45 to 182, and univalent salt (NaCl). Using circular dichroism spectroscopy, we were able to accurately determine the critical amount of PEG needed to induce condensation, as a function of the NaCl concentration. A significant dependence on the PEG degree of polymerization was found. Phase boundaries determined for the multimolecular condensation were very similar to those observed previously for the monomolecular collapse, with two asymptotic regimes at low and high salt concentrations. We analyze our data using a theoretical model that properly takes into account both the polyelectrolyte nature of the DNA and the liquid crystallinity of the condensed phase. The model assumes that all PEG is excluded from the condensates and shows reentrant decondensation only at low salt. We also systematically study reentrant decondensation and find a very strong dependence on PEG molecular weight. At low PEG molecular weight, decondensation occurs at relatively low concentrations of PEG, and over a wide range of salt concentrations. This suggests that in the reentrant decondensation the flexible polymers used are not completely excluded from the condensed phase
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