The Highly Flattened Dark Matter Halo of NGC 4244

In a previous paper (Olling 1995, \aj, 110, 591; astro-ph/9505002) a method was developed to determine the shapes of dark matter halos of spiral galaxies from an accurate determination of the rotation curve, the flaring of the gas layer and the velocity dispersion in the HI. Here this method is applied to the almost edge-on Scd galaxy NGC 4244 for which the necessary parameters are determined in the accompanying paper (AJ, Aug. 1996; astro-ph/9605110). The observed flaring of the HI beyond the optical disk puts significant constraints on the shape of the dark matter halo, which are almost independent of the stellar mass-to-light ratio. NGC 4244's dark matter halo is found to be highly flattened with a shortest-to-longest axis ratio of 0.2 (-0.1)(+0.3). If the dark matter is disk-like, the data presented in this paper imply that the vertical velocity dispersion of the dark matter must be 10% - 30% larger than the measured tangential dispersion in the HI. Alternatively, the measured flaring curve is consistent with a round halo if the gaseous velocity dispersion ellipsoid is anisotropic. In that case the vertical dispersion of the gas is 50 - 70% of the measured tangential velocity dispersion.Comment: 16 pages LaTeX, uses aaspptwo style (357kByte). Includes 3 figures. Complete paper, is also available at http://www.astro.soton.ac.uk/~olling/PrePrints/Paper_03/ or via anonymous ftp at ftp.astro.soton.ac.uk, cd pub/olling/Paper_03 To be published in the Aug. 1996 issue of the Astronomical Journa

Addendum: "The Dynamics of M15: Observations of the Velocity Dispersion Profile and Fokker-Planck Models" (ApJ, 481, 267 [1997])

It has recently come to our attention that there are axis scale errors in three of the figures of Dull et al. (1997, hereafter D97). D97 presented Fokker-Planck models for the collapsed-core globular cluster M15 that include a dense, centrally concentrated population of neutron stars and massive white dwarfs, but do not include a central black hole. In this Addendum, we present corrected versions of Figures 9, 10, and 12, and an expanded version of Figure 6. This latter figure, which shows the full run of the velocity dispersion profile, indicates that the D97 model predictions are in good agreement with the moderately rising HST-STIS velocity dispersion profile for M15 reported by Gerssen et al. (2002, astro-ph/0209315). Thus, a central black hole is not required to fit the new STIS velocity measurements, provided that there is a sufficient population of neutron stars and massive white dwarfs. This conclusion is consistent with the findings of Gerssen et al. (2002, astro-ph/0210158), based on a reapplication of their Jeans equation analysis using the corrected mass-to-light profile (Figure 12) for the D97 models.Comment: 4 pages, 4 figures, submitted to Ap

Preparation and characterization of spray-dried valsartan-loaded Eudragit® E PO solid dispersion microparticles

AbstractThe purpose of this study was to develop the immediate release stomach-specific spray-dried formulation of valsartan (VAL) using Eudragit® E PO (EPO) as the carrier for enhancing dissolution rate in a gastric environment. Enhanced solubility and dissolution in gastric pH was achieved by formulating the solid dispersion using a spray drying technique. Different combinations of drug–polymer–surfactant were dissolved in 10% ethanol solution and spray-dried in order to obtain solid dispersion microparticles. Use of the VAL–EPO solid dispersion microparticles resulted in significant improvement of the dissolution rate of the drug at pH 1.2 and pH 4.0, compared to the free drug powder and the commercial product. A hard gelatin capsule was filled with the VAL–EPO solid dispersion powder prior to the dissolution test. The increased dissolution of VAL from solid dispersion microparticles in gastric pH was attributed to the effect of EPO and most importantly the transformation of crystalline drugs to amorphous solid dispersion powder, which was clearly shown by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and powder X-ray diffraction (P-XRD) studies. Thus, VAL, a potential antihypertensive drug in the form of a solid dispersion microparticulate powder, can be effectively delivered in the immediate release dosage form for stomach-specific drug delivery

Preparation and characterization of spray-dried valsartan-loaded Eudragit® E PO solid dispersion microparticles

AbstractThe purpose of this study was to develop the immediate release stomach-specific spray-dried formulation of valsartan (VAL) using Eudragit® E PO (EPO) as the carrier for enhancing dissolution rate in a gastric environment. Enhanced solubility and dissolution in gastric pH was achieved by formulating the solid dispersion using a spray drying technique. Different combinations of drug–polymer–surfactant were dissolved in 10% ethanol solution and spray-dried in order to obtain solid dispersion microparticles. Use of the VAL–EPO solid dispersion microparticles resulted in significant improvement of the dissolution rate of the drug at pH 1.2 and pH 4.0, compared to the free drug powder and the commercial product. A hard gelatin capsule was filled with the VAL–EPO solid dispersion powder prior to the dissolution test. The increased dissolution of VAL from solid dispersion microparticles in gastric pH was attributed to the effect of EPO and most importantly the transformation of crystalline drugs to amorphous solid dispersion powder, which was clearly shown by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and powder X-ray diffraction (P-XRD) studies. Thus, VAL, a potential antihypertensive drug in the form of a solid dispersion microparticulate powder, can be effectively delivered in the immediate release dosage form for stomach-specific drug delivery

CO Methanation over NiO-CeO2 Mixed-Oxide Catalysts Prepared by a Modified Co-Precipitation Method: Effect of the Preparation pH on the Catalytic Performance

In this study, a series of NiO-CeO2 mixed-oxide catalysts have been prepared by a modified co-precipitation method similar to the one used for the synthesis of hydrotalcites. The syntheses were carried out at different pH values (8, 9 and 10), in order to determine the influence of this synthetic variable on the properties of the obtained materials. These materials were characterized by using different techniques, such as TGA, XRD, ICP, N-2 adsorption-desorption isotherms, H-2 temperature-programmed reduction (H-2-TPR), and electron microscopy, including high-angle annular dark-field transmission electron microscopy (HAADF-TEM) and EDS. The characterization results revealed the influence of the preparation method, in general, and of the pH value, in particular, on the textural properties of the oxides, as well as on the dispersion of the Ni species. The catalyst prepared at a higher pH value (pH = 10) was the one that exhibited better behavior in the CO methanation reaction (almost 100% CO conversion at 235 degrees C), which is attributed to the achievement, under these synthetic conditions, of a combination of properties (metal dispersion, specific surface area, porosity) more suitable for the reaction

Reducing skim milk powder dispersion turbidity by dissociation of casein micelles at acidic and neutral pH: Physicochemical properties and possible mechanisms

Casein micelles comprise 80% of dairy proteins. However, casein micelles as the source for protein fortification in beverages are limited due to its contribution to dispersion turbidity. On the other hand, protein beverages are experiencing substantial market growth and what follows is the demand for new protein ingredients. At acidic conditions, like those commonly found in lots of beverages, dispersions of skim milk powder (SMP) have high turbidity and readily precipitate. In order to circumvent these problems, the dissociation of casein micelles is required to reduce turbidity and improve dispersion stability during storage. Additionally, beverages with neutral pH are preferred to consumers suffering dental problems such as tooth erosion. The objectives of the present study were 1) to reduce turbidity of SMP dispersions and 2) characterize their physicochemical properties after treatment at acidic and neutral pH. To acidify SMP dispersions to pH 2.4-3.0, citric acid or glucono delta-lactone was added, followed by subsequent heating at 60, 70, 80, or 90 °C for 2, 5, 10, 30, or 60 min. A lower pH (i.e., pH 2.4) was more effective than pH 3.0 to reduce the dispersion turbidity (e.g., 223 vs 861 NTU) and the hydrodynamic diameter (e.g., 115 vs 265 nm) after heating at 90 °C for 10 min. At neutral pH, translucent dispersions were obtained with the addition of calcium chelators; sodium tripolyphosphate, trisodium citrate, or sodium hexametaphosphate. Higher concentrations of calcium chelators in SMP dispersions resulted in significant reduction in turbidity values compared to the control (e.g., 230 NTU vs \u3e4000). The amount of dissolved calcium in the SMP serum phase apart from the casein micelles increased from ~150 to more than 500 mg/L after treatments at both acidic and neutral pH, indicating the dissociation of casein micelles due to the disruption of colloidal calcium phosphate. The SMP dispersions with modified casein structures can be utilized to produce novel types of beverages

Low aggregation stability of industrial nanopowders in surfactant solutions

The effect of the dispersion of aqueous suspensions on the dispersion properties of industrial Al2O3 nanopowders with an average particle size of 50, 140 and 250 nm was investigated. Using ultrasound and/or with the addition of citric and aminoacetic acids (0,5, 5 and 10 g・L-1), it has been shown the low aggregation stability of chosen particles in watering medium. The aggregative stability of the particles increased with decreasing particle size. Regardless of surfactant type and the initial particle size, concentration increase of carboxylic acids under the selected conditions had little effect on the degree of particle dispersion. Reducing the acidity of the medium (from 10 to 3 of pH units) contributed to the enhanced aggregation of nanoparticles