Home About us Contact
|
Home About us Contact | ||
|
|
||
Density Gradient (density + gradient)
Terms modified by Density Gradient Selected AbstractsFabrication of Density Gradients of Biodegradable Polymer Microparticles and Their Use in Guiding Neurite OutgrowthADVANCED FUNCTIONAL MATERIALS, Issue 10 2010Xiaoran Li Abstract A new method for generating both continuous and discrete density gradients in microparticles of biodegradable polymers via an electrospray technique is reported. The gradients are generated by spatially varying the deposition time of electrosprayed microparticles. The substrate coated with a density gradient of microparticles has varying surface roughness, offering a unique system for studying the effect of physical cues on neurite outgrowth from dorsal root ganglia. An optimal surface roughness for promoting neuron adhesion and neurite extension in vitro is obtained. Furthermore, this capability of approach is extended to generate a gradient of fluorescein isothiocyanate labeled bovine serum albumin by encapsulating it in the polymer microparticles in situ during electrospray. Taken together, this new class of substrates with gradients of microparticle density can potentially be used in various biomedical applications such as neural tissue engineering. [source] Density gradients in Galactic planetary nebulaeMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2007J. P. Phillips ABSTRACT Certain hydrodynamic models of planetary nebulae (PNe) suggest that their shells possess appreciable radial density gradients. However, the observational evidence for such gradients is far from clear. On the one hand, Taylor et al. claim to find evidence for radio spectral indices 0.6 < , < 1.8, a trend which is taken to imply a variation ne,r,2 in most of their sample of PNe. On the other hand, Siódmiak & Tylenda find no evidence for any such variations in density; shell inhomogeneities, where they occur, are primarily attributable to ,blobs or condensations'. It will be suggested that both of these analyses are unreliable, and should be treated with a considerable degree of caution. A new analysis within the log(F(5 GHz)/F(1.4 GHz)),log(TB(5 GHz)) plane will be used to show that at least 10,20 per cent of PNe are associated with strong density gradients. We shall also show that the ratio F(5 GHz)/F(1.4 GHz) varies with nebular radius; an evolution that can be interpreted in terms of varying shell masses, and declining electron densities. [source] Measurements of Directional Flow Using a Directional Langmuir Probe in Weakly Magnetized PlasmasCONTRIBUTIONS TO PLASMA PHYSICS, Issue 5-6 2006T. Shikama Abstract Measurement of flow directed with respect to the magnetic field is performed using a directional Langmuir probe (DLP). A previously proposed practical formula for measurement of the Mach number under a weakly magnetized condition is modified for application to the directional flow field which consists of parallel and azimuthal flow components. The effect of density gradient caused by the rotational DLP measurement in the measurement of the radial profile of ion current angular distribution is modified. For the verification of the DLP measurement, parallel flow velocity is measured from the Doppler shift of HeII emission, while azimuthal flow velocity is calculated from E × B and diamagnetic drifts. It is revealed that this method provides plausible Mach numbers in the parallel and azimuthal directions with inclusion of the effect of density gradient. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Microcystin-LR modulates selected immune parameters and induces necrosis/apoptosis of carp leucocytes,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2010Anna Rymuszka Abstract Microcystins (MCs) are potent hepatotoxins acting by the inhibition of protein phosphatase 1 and 2A, and may promote liver tumors. Moreover, studies also suggest they are nephrotoxic. The aim of the present study was to assess possible in vitro effects of microcystin-LR (which contains the amino acids leucine and arginine, the most widely studied and distributed variant of all microcystins) on the selected immune functions of the cells isolated from the head kidney of carp. In the experiments, pure microcystin-LR (MC-LR), was used at concentrations of 0.01, 0.1, 0.5, and 1,µg/ml RPMI-1640 medium. Leucocytes (lymphocytes and phagocytes) were isolated by centrifugation on a density gradient. Lymphocyte proliferation, intracellular production of reactive oxygen species by phagocytes, and the presence of apoptotic and/or necrotic cells were assessed. The respiratory burst activity of phagocytic cells was increased at the lowest toxin concentration used in the study, but it was decreased at higher concentrations. Using a sensitive luminescent immunoassay, MC-LR was observed to have no influence on the T-cell proliferation but decreased the proliferation of B lymphocytes. Moreover, it was noted that MC-LR induced necrosis to a higher degree than apoptosis in fish leucocytes. The results of the present study suggest the modulatory potency of microcystin-LR on fish leucocytes. Environ. Toxicol. Chem. 2010;29:569,574. © 2009 SETAC [source] Tracing salmon-derived nutrients and contaminants in freshwater food webs across a pronounced spawner density gradientENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2007Irene Gregory-Eaves Abstract Many have demonstrated that anadromous Pacific salmon are significant vectors of nutrients from the ocean to freshwaters. Recently, however, it has been recognized that salmon spawners also input significant quantities of contaminants. The objectives of this paper are to delineate the extent to which salmon-derived nutrients are integrated into the freshwater food web using ,15N and ,13C and to assess the influence of the salmon pathway in the accumulation of contaminants in rainbow trout (Oncorhynchus mykiss). We found that the ,15N and ,13C of food web components were related positively and significantly to sockeye salmon (Oncorhynchus nerka) spawner density. Contaminant concentrations in rainbow trout also positively and significantly were related to sockeye salmon spawner density. These data suggest that the anadromous salmon nutrient and contaminant pathways are related and significantly impact the contaminant burden of resident fish. [source] PLASTICITY IN QUEEN NUMBER AND SOCIAL STRUCTURE IN THE INVASIVE ARGENTINE ANT (LINEPITHEMA HUMILE)EVOLUTION, Issue 10 2002Krista K. Ingram Abstract., In many polygynous social insect societies, ecological factors such as habitat saturation promote high queen numbers by increasing the cost of solitary breeding. If polygyny is associated with constrained environments, queen number in colonies of invasive social insects should increase as saturation of their new habitat increases. Here I describe the variation in queen number, nestmate relatedness, and nest size along a gradient of time since colonization in an invading population of Argentine ants (Linepithema humile) in Haleakala, Hawaii. Nest densities in this population increase with distance from the leading edge of the invasion, reaching a stable density plateau approximately 80 m from the edge (> 2 years after colonization). Although the number of queens per nest in Haleakala is generally lower than previously reported for Argentine ants, there is significant variation in queen number across this population. Both the observed and effective queen numbers increase across the density gradient, and nests in the center of the population contain queen numbers three to nine times higher than those on the edge of the invasion. The number of workers per nest is correlated with queen number, and nests in the center are six times larger than nests at the edge. Microsatellite analysis of relatedness among nestmates reveals that all nests in the Haleakala population are characterized by low relatedness and have evidence of multiple reproducing queens. Relatedness values are significantly lower in nests in the center of the population, indicating that the number of reproducing queens is greater in areas of high nest density. The variation in queen number and nestmate relatedness in this study is consistent with expectations based on changes in ecological constraints during the invasion of a new habitat, suggesting that the social structure of Argentine ant populations is strongly influenced by ecological factors. Flexibility in social structure may facilitate persistence in variable environments and may also confer significant advantages to a species when introduced into new areas. [source] Fabrication of Density Gradients of Biodegradable Polymer Microparticles and Their Use in Guiding Neurite OutgrowthADVANCED FUNCTIONAL MATERIALS, Issue 10 2010Xiaoran Li Abstract A new method for generating both continuous and discrete density gradients in microparticles of biodegradable polymers via an electrospray technique is reported. The gradients are generated by spatially varying the deposition time of electrosprayed microparticles. The substrate coated with a density gradient of microparticles has varying surface roughness, offering a unique system for studying the effect of physical cues on neurite outgrowth from dorsal root ganglia. An optimal surface roughness for promoting neuron adhesion and neurite extension in vitro is obtained. Furthermore, this capability of approach is extended to generate a gradient of fluorescein isothiocyanate labeled bovine serum albumin by encapsulating it in the polymer microparticles in situ during electrospray. Taken together, this new class of substrates with gradients of microparticle density can potentially be used in various biomedical applications such as neural tissue engineering. [source] Transplantation of an acutely isolated bone marrow fraction repairs demyelinated adult rat spinal cord axonsGLIA, Issue 1 2001Masanori Sasaki Abstract The potential of bone marrow cells to differentiate into myelin-forming cells and to repair the demyelinated rat spinal cord in vivo was studied using cell transplantation techniques. The dorsal funiculus of the spinal cord was demyelinated by x-irradiation treatment, followed by microinjection of ethidium bromide. Suspensions of a bone marrow cell fraction acutely isolated from femoral bones in LacZ transgenic mice were prepared by centrifugation on a density gradient (Ficoll-Paque) to remove erythrocytes, platelets, and debris. The isolated cell fraction contained hematopoietic and nonhematopoietic stem and precursor cells and lymphocytes. The cells were transplanted into the demyelinated dorsal column lesions of immunosuppressed rats. An intense blue ,-galactosidase reaction was observed in the transplantation zone. The genetically labeled bone marrow cells remyelinated the spinal cord with predominately a peripheral pattern of myelination reminiscent of Schwann cell myelination. Transplantation of CD34+ hematopoietic stem cells survived in the lesion, but did not form myelin. These results indicate that bone marrow cells can differentiate in vivo into myelin-forming cells and repair demyelinated CNS. GLIA 35:26,34, 2001. © 2001 Wiley-Liss, Inc. [source] Generation of Arbitrary Lagrangian,Eulerian (ALE) velocities, based on monitor functions, for the solution of compressible fluid equationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10-11 2005B. V. Wells Abstract A moving mesh method is outlined based on the use of monitor functions. The method is developed from a weak conservation principle. From this principle a conservation law for the mesh position is derived. Using the Helmholtz decomposition theorem, this conservation law can be converted into an elliptic equation for a mesh velocity potential. The moving mesh method is discretized using standard finite elements. Once the mesh velocities are obtained an arbitrary Lagrangian,Eulerian (ALE) (Journal of Computational Physics 1974; 14:227) fluid solver is used to update the solution on the adaptive mesh. Results are shown for the compressible Euler equations of gas dynamics in one and two spatial dimensions. Two monitor functions are used, the fluid density (which corresponds to a Lagrangian description), and a function which includes the density gradient. A variety of test problems are considered. Copyright © 2005 John Wiley & Sons, Ltd. [source] Length Fractionation of Carbon Nanotubes Using Centrifugation,ADVANCED MATERIALS, Issue 9 2008Jeffrey A. Fagan Scalable separation of single-walled carbon nanotubes (SWCNTs)by length and chirality is critical to the adaptation of these materials for applications. Ultracentrifugation of SWCNTs within a density gradient produces chiral separation of the NTs, and it is shown here that ultracentrifugation can also be used to produce length fractionated SWCNTs by exploiting their transient motion in response to applied centripetal acceleration. [source] Entropy-based metrics in swarm clusteringINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 9 2009Bo Liu Ant-based clustering methods have received significant attention as robust methods for clustering. Most ant-based algorithms use local density as a metric for determining the ants' propensities to pick up or deposit a data item; however, a number of authors in classical clustering methods have pointed out the advantages of entropy-based metrics for clustering. We introduced an entropy metric into an ant-based clustering algorithm and compared it with other closely related algorithms using local density. The results strongly support the value of entropy metrics, obtaining faster and more accurate results. Entropy governs the pickup and drop behaviors, while movement is guided by the density gradient. Entropy measures also require fewer training parameters than density-based clustering. The remaining parameters are subjected to robustness studies, and a detailed analysis is performed. In the second phase of the study, we further investigated Ramos and Abraham's (In: Proc 2003 IEEE Congr Evol Comput, Hoboken, NJ: IEEE Press; 2003. pp 1370,1375) contention that ant-based methods are particularly suited to incremental clustering. Contrary to expectations, we did not find substantial differences between the efficiencies of incremental and nonincremental approaches to data clustering. © 2009 Wiley Periodicals, Inc. [source] Structural analysis of thin films of novel polynorbornene derivatives by grazing incidence X-ray scattering and specular X-ray reflectivity along with ellipsometryJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Taek Joon Lee In the present study, structural analyses using synchrotron grazing incidence X-ray scattering, specular reflectivity and ellipsometry were performed on thin films of two novel polynorbornene derivatives, chiral poly(norbornene acid methyl ester) and racemic poly(norbornene acid n -butyl ester), which are potential low dielectric constant materials for advanced microelectronic and display applications. These analyses provided important information on the structure, electron density gradient across the film thickness, chain orientation, refractive index and thermal expansion characteristics of the polymers in substrate-supported thin films. The structural characteristics and properties of the thin films depended on the tacticity of the polymer chain and were further influenced by the film thickness and thermal annealing history. [source] Radioiodinated clioquinol as a biomarker for ,-amyloid: Zn2+ complexes in Alzheimer's diseaseAGING CELL, Issue 1 2006Carlos Opazo Summary Neocortical ,-amyloid (A,) aggregates in Alzheimer's disease (AD) are enriched in transition metals that mediate assembly. Clioquinol (CQ) targets metal interaction with A, and inhibits amyloid pathology in transgenic mice. Here, we investigated the binding properties of radioiodinated CQ ([125I]CQ) to different in vitro and in vivo Alzheimer models. We observed saturable binding of [125I]CQ to synthetic A, precipitated by Zn2+ (Kd = 0.45 and 1.40 nm for A,1-42 and A,1-40, respectively), which was fully displaced by free Zn2+, Cu2+, the chelator DTPA (diethylene triamine pentaacetic acid) and partially by Congo red. Sucrose density gradient of post-mortem AD brain indicated that [125I]CQ concentrated in a fraction enriched for both A, and Zn, which was modulated by exogenous addition of Zn2+ or DTPA. APP transgenic (Tg2576) mice injected with [125I]CQ exhibited higher brain retention of tracer compared to non-Tg mice. Autoradiography of brain sections of these animals confirmed selective [125I]CQ enrichment in the neocortex. Histologically, both thioflavine-S (ThS)-positive and negative structures were labeled by [125I]CQ. A pilot SPECT study of [123I]CQ showed limited uptake of the tracer into the brain, which did however, appear to be more rapid in AD patients compared to age-matched controls. These data support metallated A, species as the neuropharmacological target of CQ and indicate that this drug class may have potential as in vivo imaging agents for Alzheimer neuropathology. [source] Effect of density homogeneity on the dynamic response of powder bedsAICHE JOURNAL, Issue 8 2003T. Yanagida Homogeneous and inhomogeneous powder beds subjected to low-magnitude vibration are compared in terms of the dynamic response. The inhomogeneous samples were segregated into two phases: loose and dense phases, layering the two phases horizontally or vertically. An apparent mass, defined as a ratio of the base force to base acceleration, was measured. Comparison of homogeneous and segregated data demonstrated a significant density gradient dependence on the apparent mass data. First, homogeneous systems showed a resonant peak, which gave the longitudinal elastic modulus of the bed via the velocity of longitudinal stress wave propagation. Second, vertically segregated systems exhibited two significant peaks at low frequencies, corresponding to the resonance of each phase. In addition, the apparent mass values at the two peaks were related to the quantity of each phase. Third, horizontally segregated systems exhibited a resonant peak, whose frequency was approximately equal to homogeneous data, but the apparent mass value at the peak differed from homogeneous data. A model based on the fourth-power scaling law, two-phase theory and Rayleigh's energy method gave an interpretation for the insensitivity of the peak frequency to the density gradient in the vertical direction. [source] Thermal expansion of organic crystals and precision of calculated crystal density: A survey of Cambridge Crystal DatabaseJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2007Changquan Calvin Sun Abstract True density is a physical property of both fundamental and practical importance to the study of pharmaceutical powders. True density may be calculated from crystal structure. However, precision of such calculated density is not well understood. Furthermore, thermal expansion properties of organic crystals have rarely been characterized. A survey of Cambridge Crystal Database is conducted to assess (1) precision of calculated crystal density from crystal structure; (2) thermal expansion properties of organic crystals. It is shown that calculated crystal density exhibits, on average, a relative standard deviation (RSD) of ,0.4%. It is found that crystal density generally increases linearly with decreasing temperature provided no phase change occurs. Slope of the line, termed thermal density gradient, of organic crystals ranges between 0.04 and 1.74 mg,cm,3,K,1 with an average of ,0.2 mg,cm,3,K,1. It is shown that majority polymorph pairs exhibit significantly different thermal expansion behavior and their density,temperature lines can cross. This likely contributes to the less than perfect prediction of relative stability of polymorphs at ambient temperature using the density rule. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96: 1043,1052, 2007 [source] Dendrimer complexes: Fine control of metal assembly in macromoleculesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2005Kimihisa Yamamoto Abstract New phenylazomethine dendrimers have been developed, with each dendrimer having a unique single structure. From ultraviolet,visible absorption spectra, we determined that stannous chloride added to dendritic polyphenylaz omethine (DPA) was assembled in a stepwise manner from the core shell to the periphery. The selective binding was achieved by the electron density gradient formed in the dendrimer, and it was confirmed by shell-selective imine reduction, transmission electron microscopy, and NMR measurements. The complex formation constants of the respective shells were estimated to be considerably different by a simulation analysis of ultraviolet,visible absorption spectra. The reversible assembly and release of iron into and out of the dendrimer were possible by electrochemical oxidation and reduction, respectively. DPA with a porphyrin at the core was found to function as an effective reduction catalyst of carbon dioxide. DPA with aryl amine at the core was demonstrated to function as a hole-transporting material in electroluminescent devices. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3719,3727, 2005 [source] Derivated fetal haemoglobin as a marker for red cell age in the human fetus reflecting stimulated or impaired red blood cell productionPRENATAL DIAGNOSIS, Issue 7 2001Margriet Huisman Abstract We have determined whether derivated fetal haemoglobin (dHbF, consisting of glycated and acetylated HbF) can be used as a cell age marker for fetal red blood cells (RBCs). Cord blood was obtained between 19 and 39 weeks of gestation from 28 alloimmunised anaemic fetuses (23 RhD+ and 5,Kell) and from 20 non-anaemic fetuses and newborns (controls). Density gradient centrifugation was applied to 36 samples (20 RhD+, 15 controls and 1,Kell) to obtain fractions of increasing cell age. Blood samples were used for measurements of mean cellular volume (MCV), mean cell haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), pyruvate kinase activity (PK) and derivated fetal haemoglobin (dHbF) by cation-exchange HPLC. Reticulocytes were counted only in the whole blood samples. In all density gradient separated RBC fractions, the values for MCV, MCH and PK activity decreased and those of MCHC and dHbF increased with increasing density (equivalent to increasing cell age). The mean density was lower for RBCs of the anaemic RHD group (1.072±0.007,g/ml) than for the non-anaemic controls (1.077±0.005,g/ml) (p<0.05) The RBC density of the Kell sensitised fetus did not differ from those of the controls. In the control group, the values of the cell age markers in whole blood changed significantly with the gestational age, showing an increase of mean age of the erythrocyte population. The best linear relationship was found for dHbF (y=6.28+0.17*weeks; r=0.84; p<0.001). In the anaemic RhD+ fetuses, the RBC age markers did not change with gestational age; the dHbF percentages were lower, and the MCV, MCH, PK values and the reticulocyte counts were higher than in the controls (0.05 Protamine ratio and the level of histone retention in sperm selected from a density gradient preparationANDROLOGIA, Issue 2 2009S. Hammoud Summary Fertile males express two forms of sperm nuclear proteins, protamine 1 (P1) and protamine 2 (P2), in roughly equal quantities, whereas some infertile men have been shown to have a reduction in protamine content and an increase in the level of histones retained in mature sperm. In this study, we assessed histone and protamine levels in spermatozoa isolated from different layers of a density gradient centrifugation column to evaluate the nuclear protein content of the sperm population selected. Protamine levels were measured using acid gel electrophoresis and immunofluorescence, and the percentage of cells retaining histones was evaluated using aniline staining and immunofluorescence. Our data suggests that there is an inverse correlation between P1/P2 ratio and the level of histone expression in the different layers of the density gradient. Paradoxically, the 90% layer had a lower P1/P2 ratio, which corresponded with an increase in histone expression. It is concluded that although the sperm population selected in the 90% layer of the density gradient columns had a lower P1/P2 ratio, it was yet similar to the P1/P2 ratio observed in previously screened fertile donors. [source] Metal enrichment of the intracluster medium: SN-driven galactic windsASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009V. Baumgartner Abstract We investigate the role of supernova (SN)-driven galactic winds in the chemical enrichment of the intracluster medium (ICM). Such outflows on galactic scales have their origin in huge star forming regions and expel metal enriched material out ofthe galaxies into their surroundings as observed, for example, in the nearby starburst galaxy NGC 253. As massive stars in OB-associations explode sequentially, shock waves are driven into the interstellar medium (ISM) of a galaxy and merge, forming a superbubble (SB). These SBs expand in a direction perpendicular to the disk plane following the density gradient of the ISM. We use the 2D analytical approximation by Kompaneets (1960) to model the expansion of SBs in an exponentially stratified ISM. This is modified in order to describe the sequence of SN-explosions as a time-dependent process taking into account the main-sequence life-time of the SN-progenitors and using an initial mass function to get the number of massive stars per mass interval. The evolution of the bubble in space and time is calculated analytically, from which the onset of Rayleigh-Taylor instabilities in the shell can be determined. In its further evolution, the shell will break up and high-metallicity gas will be ejected into the halo ofthe galaxy and even into the ICM. We derive the number of stars needed for blow-out depending on the scale height and density ofthe ambient medium, as well as the fraction of alpha- and iron peak elements contained in the hot gas. Finally, the amount of metals injected by Milky Way-type galaxies to the ICM is calculated confirming the importance ofthis enrichment process (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The unconventional myosin-VIIa associates with lysosomesCYTOSKELETON, Issue 1 2005Lily E. Soni Abstract Mutations in the myosin-VIIa (MYO7a) gene cause human Usher disease, characterized by hearing impairment and progressive retinal degeneration. In the retina, myosin-VIIa is highly expressed in the retinal pigment epithelium, where it plays a role in the positioning of melanosomes and other digestion organelles. Using a human cultured retinal pigmented epithelia cell line, ARPE-19, as a model system, we have found that a population of myosin-VIIa is associated with cathepsin D- and Rab7-positive lysosomes. Association of myosin-VIIa with lysosomes was Rab7 independent, as dominant negative and dominant active versions of Rab7 did not disrupt myosin-VIIa recruitment to lysosomes. Association of myosin-VIIa with lysosomes was also independent of the actin and microtubule cytoskeleton. Myosin-VIIa copurified with lysosomes on density gradients, and fractionation and extraction experiments suggested that it was tightly associated with the lysosome surface. These studies suggest that myosin-VIIa is a lysosome motor. Cell Motil. Cytoskeleton 62:13,26, 2005. © 2005 Wiley-Liss, Inc. [source] Effects of methylcyclodextrin on lysosomesFEBS JOURNAL, Issue 5 2001Michel Jadot The cholesterol complexing agent methyl-cyclodextrin (MCD) provides an efficient mean for the removal of cholesterol from biological membranes. In order to study the effects of this agent on the lysosomal membrane in situ, we treated HepG2 cells with MCD and studied the effects of this treatment on lysosomes in isolated fractions. We found that lysosomes prepared from treated cells are more sensitive to various membrane perturbing treatments such as: incubation of lysosomes in isotonic glucose, in hypotonic sucrose or in the presence of the lytic agent glycyl- l -phenylalanine 2-naphthylamide. The lysosomal membrane is also less resistant to increased hydrostatic pressure. Centrifugation methods were used to analyse the effect of MCD on lysosomes. Isopycnic centrifugation in sucrose density gradients demonstrates that the drug induces a reversible density increase of the lysosomes. Our study indicates that extracellularly added MCD can modify the properties of the lysosomal membrane in living cells. It suggests that MCD could be an effective tool to modulate the physical properties of lysosomes within intact cells and to monitor the cellular responses to such modifications. [source] Fabrication of Density Gradients of Biodegradable Polymer Microparticles and Their Use in Guiding Neurite OutgrowthADVANCED FUNCTIONAL MATERIALS, Issue 10 2010Xiaoran Li Abstract A new method for generating both continuous and discrete density gradients in microparticles of biodegradable polymers via an electrospray technique is reported. The gradients are generated by spatially varying the deposition time of electrosprayed microparticles. The substrate coated with a density gradient of microparticles has varying surface roughness, offering a unique system for studying the effect of physical cues on neurite outgrowth from dorsal root ganglia. An optimal surface roughness for promoting neuron adhesion and neurite extension in vitro is obtained. Furthermore, this capability of approach is extended to generate a gradient of fluorescein isothiocyanate labeled bovine serum albumin by encapsulating it in the polymer microparticles in situ during electrospray. Taken together, this new class of substrates with gradients of microparticle density can potentially be used in various biomedical applications such as neural tissue engineering. [source] Uniform Nonspherical Colloidal Particles with Tunable Shapes,ADVANCED MATERIALS, Issue 15 2007J.-W. Kim A framework for large-scale synthesis of a variety of uniform nonspherical particle types (see figure) is introduced. The technique involves controlling the directionality of phase separations in the seeded-polymerization technique by manipulating the crosslinking density gradients of the dimer seed particles, thus allowing the obtainment of novel nonspherical particle shapes and the production of sufficient quantities to characterize their bulk properties. [source] Anticipating bipedalism: trabecular organization in the newborn iliumJOURNAL OF ANATOMY, Issue 6 2009Craig A. Cunningham Abstract Trabecular bone structural organization is considered to be predominantly influenced by localized temporal forces which act to maintain and remodel the trabecular architecture into a biomechanically optimal configuration. In the adult pelvis, the most significant remodelling forces are believed to be those generated during bipedal locomotion. However, during the fetal and neonatal period the pelvic complex is non-weight bearing and, as such, structural organization of iliac trabecular bone cannot reflect direct stance-related forces. In this study, micro-computed tomography scans from 28 neonatal ilia were analysed, using a whole bone approach, to investigate the trabecular characteristics present within specific volumes of interest relevant to density gradients highlighted in a previous radiographic study. Analysis of the structural indices bone volume fraction, trabecular thickness, trabecular spacing and trabecular number was carried out to quantitatively investigate structural composition. Quantification of the neonatal trabecular structure reinforced radiographic observations by highlighting regions of significant architectural form which grossly parallel architectural differences in the adult pattern but which have previously been attributed to stance-related forces. It is suggested that the seemingly organized rudimentary scaffold observed in the neonatal ilium may be attributable to other non-weight bearing anatomical interactions or even to a predetermined genetic blueprint. It must also be postulated that whilst the observed patterning may be indicative of a predetermined inherent template, early non-weight bearing and late stance-related locomotive influences may subsequently be superimposed upon this scaffolding and perhaps reinforced and likely remodelled at a later age. Ultimately, the analysis of this fundamental primary pattern has core implications for understanding the earliest changes in pelvic trabecular architecture and provides a baseline insight into future ontogenetic development and bipedal capabilities. [source] Myosins II and V in chromaffin cells: myosin V is a chromaffin vesicle molecular motor involved in secretionJOURNAL OF NEUROCHEMISTRY, Issue 2 2003Sergio D. Rosé Abstract The presence of myosin II and V in chromaffin cells and their subcellular distribution is described. Myosin II and V distribution in sucrose density gradients showed only a strong correlation between the distribution of myosin V and secretory vesicle markers. Confocal microscopy images demonstrated colocalization of myosin V with dopamine ,-hydroxylase, a chromaffin vesicle marker, whereas myosin II was present mainly in the cell cortex. Cell depolarization induced, in a Ca2+ and time-dependent manner, the dissociation of myosin V from chromaffin vesicles suggesting that this association was not permanent but determined by secretory cycle requirements. Myosin II was also found in the crude granule fraction, however, its distribution was not affected by cell depolarization. Myosin V head antibodies were able to inhibit secretion whereas myosin II antibodies had no inhibitory effect. The pattern of inhibition indicated that these treatments interfered with the transport of vesicles from the reserve to the release-ready compartment, suggesting the involvement of myosin V and not myosin II in this transport process. The results described here suggest that myosin V is a molecular motor involved in chromaffin vesicle secretion. However, these results do not discard an indirect role for myosin II in secretion through its interaction with F-actin networks. [source] Determination of particle heterogeneity and stability of recombinant adenovirus by analytical ultracentrifugation in CsCl gradientsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2008Xiaoyu Yang Abstract Recombinant adenoviruses (rAd), widely used as vectors for gene therapy, are generally purified by column chromatography and frequently contain empty capsids and other aberrant forms of virus particles. To determine particle heterogeneity we utilized analytical ultracentrifugation (AUC) in CsCl density gradients. Preparations of three different rAd vectors were assessed. AUC was able to resolve multiple density forms including two empty capsid types in various virus preparations. One unusual density form (form V), was noninfectious and lacked protein VI. AUC was able to quantify empty capsids and monitor their removal during process development. Their relative concentrations were reduced by either addition of an immobilized zinc affinity chromatography (IZAC) step or by extension of the infection time. The Adenovirus Reference Material (ARM), a wild-type Ad5, had 2.2% empty capsids and no other detectable minor particle forms. Finally, AUC was utilized to monitor the thermal instability of the three rAd vectors via the transformations of different density forms. The vector and empty capsids containing protein IX were more stable than those without IX. Together, these results exemplify AUC in CsCl density gradients as a valuable technique for evaluating product particle heterogeneity and stability. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:746,763, 2008 [source] Density gradients in Galactic planetary nebulaeMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2007J. P. Phillips ABSTRACT Certain hydrodynamic models of planetary nebulae (PNe) suggest that their shells possess appreciable radial density gradients. However, the observational evidence for such gradients is far from clear. On the one hand, Taylor et al. claim to find evidence for radio spectral indices 0.6 < , < 1.8, a trend which is taken to imply a variation ne,r,2 in most of their sample of PNe. On the other hand, Siódmiak & Tylenda find no evidence for any such variations in density; shell inhomogeneities, where they occur, are primarily attributable to ,blobs or condensations'. It will be suggested that both of these analyses are unreliable, and should be treated with a considerable degree of caution. A new analysis within the log(F(5 GHz)/F(1.4 GHz)),log(TB(5 GHz)) plane will be used to show that at least 10,20 per cent of PNe are associated with strong density gradients. We shall also show that the ratio F(5 GHz)/F(1.4 GHz) varies with nebular radius; an evolution that can be interpreted in terms of varying shell masses, and declining electron densities. [source] MHD waves in the solar north polar coronal holeASTRONOMISCHE NACHRICHTEN, Issue 7 2010E. Devlen Abstract The effects, hitherto not treated, of the temperature and the number density gradients, both in the parallel and the perpendicular direction to the magnetic field, of O VI ions, on the MHD wave propagation characteristics in the solar North Polar Coronal Hole are investigated. We investigate the magnetosonic wave propagation in a resistive MHD regime where only the thermal conduction is taken into account. Heat conduction across the magnetic field is treated in a non-classical approach wherein the heat is assumed to be conducted by the plasma waves emitted by ions and absorbed at a distance from the source by other ions. Anisotropic temperature and the number density distributions of O VI ions revealed the chaotic nature of MHD standing wave, especially near the plume/interplume lane borders. Attenuation length scales of the fast mode is shown not to be smoothly varying function of the radial distance from the Sun (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Human thiopurine methyltransferase activity varies with red blood cell ageBRITISH JOURNAL OF CLINICAL PHARMACOLOGY, Issue 5 2001L. Lennard Aims, Inherited differences in thiopurine methyltransferase (TPMT) activity are an important factor in the wide interindividual variations observed in the clinical response to thiopurine chemotherapy. The aim of this study was to establish a population range for red blood cell (RBC) TPMT activity in children with acute lymphoblastic leukaemia (ALL) at disease diagnosis. An additional aim was to investigate factors that can influence TPMT activity within the RBC. Methods,Blood samples were collected from children with ALL at disease diagnosis, prior to any blood transfusions, as part of the nationwide UK MRC ALL97 therapeutic trial. RBC TPMT activity was measured by h.p.l.c. RBCs were age-fractionated on Percoll density gradients. Results,Pretreatment blood samples were received from 570 children within 3 days of venepuncture. TPMT activities at disease diagnosis ranged from 1.6 to 23.6 units/ml RBCs (median 7.9) compared with 0.654,18.8 units (median 12.9), in 111 healthy control children (median difference 4.5 units, 95% CI 3.9, 5.1 units, P < 0.001). A TPMT quality control sample, aliquots of which were assayed in 60 analytical runs over a 12 month period, contained a median of 11.98 units with a CV of 11.6%. Seven children had their RBCs age-fractionated on density gradients. TPMT activities in the top gradient (young cells) ranged from 4.2 to 14.1 units (median 7.5) and in the bottom gradient (old cells) 1.5,12.6 units (median 4.7 units), median difference 2.3 units, 95% CI 0.7, 4.1, P = 0.035. Conclusions,Circulating RBCs do not constitute a homogeneous population. They have a life span of around 120 days and during that time undergo a progressive ageing process. The anaemia of ALL is due to deficient RBC production. The results of this study indicate that RBC TPMT activities are significantly lower in children with ALL at disease diagnosis. This may be due, at least in part, to a relative excess of older RBCs. [source] Evidence of in vivo basophil activation in chronic idiopathic urticariaCLINICAL & EXPERIMENTAL ALLERGY, Issue 6 2006K. Vasagar Summary Background Approximately 40% of chronic idiopathic urticaria (CIU) subjects have autoantibodies to either Fc,RI, or IgE. The effect of such autoantibodies on circulating basophil activation status is unknown. Objective The expression of cell surface activation markers on basophils from CIU, non-allergic, and allergic subjects were compared. Further, the relationship between marker expression and serum factors reported in CIU, such as histamine-releasing activity (HRA) and immunoreactivity to Fc,RI, were examined. Methods Peripheral blood was obtained from CIU, allergic, and non-allergic donors and fractionated by density gradients. Enriched basophils (1,12%) were analysed by flow cytometry for expression of activation markers including CD63, CD69, and CD203c. Dilutions of serum (5,50%) were analysed for HRA on basophils from a normal donor. Serum was tested for immunoreactivity by western blotting to a standard cell lysate prepared from an RBL-SX38 cell line transfected with human Fc,RI,. Results CIU subjects (n=9) and allergic subjects (n=8) exhibited enhanced expression of CD63 and CD69, as compared with non-allergic subjects (n=7); however, no difference was seen among groups for CD203c expression. Five CIU and two non-allergic subjects had evidence of significant serum HRA (>20%), whereas two CIU, two allergic, and three non-allergic subjects had evidence of serum immunoreactivity to Fc,RI,. Serum HRA and serum immunoreactivity to Fc,RI, were not associated with enhanced surface marker expression. Conclusion Basophil activation marker expression is increased in CIU subjects and is not associated with serum factors. In addition, serum HRA and Fc,RI, immunoreactivity are not unique to CIU, or related to enhanced circulating basophil marker expression. [source]
| | ||||||||||||||||||||||||