Successful topical dissolution of cholesterol gallbladder stones using ethyl propionate.

PubMed

Hofmann, A F; Amelsberg, A; Esch, O; Schteingart, C D; Lyche, K; Jinich, H; Vansonnenberg, E; D'Agostino, H B

1997-06-01

Topical dissolution of cholesterol gallbladder stones using methyl tert-butyl ether (MTBE) is useful in symptomatic patients judged too ill for surgery. Previous studies showed that ethyl propionate (EP), a C5 ester, dissolves cholesterol gallstones rapidly in vitro, but differs from MTBE in being eliminated so rapidly by the liver that blood levels remain undetectable. Our aim was to test EP as a topical dissolution agent for cholesterol gallbladder stones. Five high-risk patients underwent topical dissolution of gallbladder stones by EP. In three patients, the solvent was instilled via a cholecystostomy tube placed previously to treat acute cholecystitis; in two patients, a percutaneous transhepatic catheter was placed in the gallbladder electively. Gallstone dissolution was assessed by chromatography, by gravimetry, and by catheter cholecystography. Total dissolution of gallstones was obtained in four patients after 6-10 hr of lavage; in the fifth patient, partial gallstone dissolution facilitated basketing of the stones. In two patients, cholesterol dissolution was measured and averaged 30 mg/min. Side effects were limited to one episode of transient hypotension and pain at the infusion site; no patient developed somnolence or nausea. Gallstone elimination was associated with relief of symptoms. EP is an acceptable alternative to MTBE for topical dissolution of cholesterol gallbladder stones in high-risk patients. The lower volatility and rapid hepatic extraction of EP suggest that it may be preferable to MTBE in this investigational procedure.

Role of dispersion on the onset of convection during CO2 sequestration

NASA Astrophysics Data System (ADS)

Hidalgo, J. J.; Carrera Ramirez, J.

2009-12-01

CO2 sequestration in geological formations containing saline water has been proposed as a solution to reduce gas emission to the atmosphere. Dissolution of CO2 takes place at the interphase with the brine as the CO2 migrates. The CO2-rich brine is denser than the resident one and tends to sink. This creates an unstable configuration that leads to a fingering sinking plume and convection to dominate diffusion. Understanding how instability fingers develop has received much attention because they accelerate dissolution trapping, which favors long term sequestration. The time for the onset of convection as the dominant transport mechanism has been traditionally studied by neglecting dispersion and treating the CO2 interface as a prescribed concentration boundary by analogy to a thermal convection problem. This work presents a more realistic representation of CO2 dissolution into brine. The proposed conceptual model acknowledges fluid and porous medium compressibility, hydrodynamic dispersion is included as a transport mechanism and the Boussinesq simplification is not assumed. Finally, boundary conditions include the CO2 mass flux across the top boundary. Results show that accounting for the CO2 mass flux across the prescribed concentration boundary has little effect on the onset of convection. However, accounting for dispersion causes a reduction of up to two orders of magnitude on the onset time. This implies that CO2 dissolution can be accelerated by activating dispersion as a transport mechanism, which can be achieved adopting a fluctuating injection scheme.

Dissolution of Nickel Ferrite in Aqueous Solutions Containing Oxalic Acid and Ferrous Salts.

PubMed

Figueroa, Carlos A.; Sileo, Elsa E.; Morando, Pedro J.; Blesa, Miguel A.

2000-05-15

The dissolution of nickel ferrite in oxalic acid and in ferrous oxalate-oxalic acid aqueous solution was studied. Nickel ferrite was synthesized by thermal decomposition of a mixed tartrate; the particles were shown to be coated with a thin ferric oxide layer. Dissolution takes place in two stages, the first one corresponding to the dissolution of the ferric oxide outer layer and the second one being the dissolution of Ni(1.06)Fe(1.96)O(4). The kinetics of dissolution during this first stage is typical of ferric oxides: in oxalic acid, both a ligand-assisted and a redox mechanism operates, whereas in the presence of ferrous ions, redox catalysis leads to a faster dissolution. The rate dependence on both oxalic acid and on ferrous ion is described by the Langmuir-Hinshelwood equation; the best fitting corresponds to K(1)(ads)=25.6 mol(-1) dm(-3) and k(1)(max)=9.17x10(-7) mol m(-2) s(-1) and K(2)(ads)=37.1x10(3) mol(-1) dm(-3) and k(2)(max)=62.3x10(-7) mol m(-2) s(-1), respectively. In the second stage, Langmuir-Hinshelwood kinetics also describes the dissolution of iron and nickel from nickel ferrite, with K(1)(ads)=20.8 mol(-1) dm(3) and K(2)(ads)=1.16x10(5) mol(-1) dm(3). For iron, k(1)(max)=1.02x10(-7) mol of Fe m(-2) s(-1) and k(2)(max)=2.38x10(-7) mol of Fe m(-2) s(-1); for nickel, the rate constants k(1)(max) and k(2)(max) are 2.4 and 1.79 times smaller, respectively. The factor 1.79 agrees nicely with the stoichiometric ratio, whereas the factor 2.4 implies the accumulation of some nickel in the residual particles. The rate of nickel dissolution in oxalic acid is higher than that in bunsenite by a factor of 8, whereas hematite is more reactive by a factor of 9 (in the absence of Fe(II)) and 27 (in the presence of Fe (II)). It may be concluded that oxalic acid operates to dissolve iron, and the ensuing disruption of the solid framework accelerates the release of nickel. Copyright 2000 Academic Press.

Chalcopyrite dissolution: Scanning photoelectron microscopy examination of the evolution of sulfur species with and without added iron or pyrite

NASA Astrophysics Data System (ADS)

Li, Yubiao; Qian, Gujie; Brown, Paul L.; Gerson, Andrea R.

2017-09-01

Dissolution and oxidation of sulfide minerals play key roles in both acid and metalliferous rock drainage and supergene enrichment. Surface speciation heterogeneity, critical to understanding mechanisms of mineral sulfide dissolution, has to date largely not been considered. To this end synchrotron scanning photoelectron microscopy (SPEM) was employed to examine freshly fractured and partially dissolved chalcopyrite (CuFeS2) surfaces (pH 1.0 HClO4 solution, redox potential 650 mV relative to a standard hydrogen electrode, 75 °C). S2- (bulk), S22- and Sn2- were found to be present on all samples at varying concentrations. Oxidation was observed to take place heterogeneously at the sub-micron scale. As compared to chalcopyrite partially dissolved for 5 days, extended dissolution to 10 days did not show appreciably enhanced oxidation of surface species; however surface roughness increased markedly due to the growth/overlap of oxidised sulfur species. On addition of 4 mM iron both S0 and SO42- were observed but not SO32-, indicating that the greater Fe3+ activity/concentration promotes heterogeneous sulfur oxidation. On contact of pyrite (FeS2) with chalcopyrite, significantly greater chalcopyrite surface oxidation was observed than for the other systems examined, with S0, SO32- and SO42- being identified heterogeneously across the surface. It is proposed that chalcopyrite oxidative dissolution is enhanced by increasing its cathodic area, e.g. contacting with pyrite, while increased Fe3+ activity/concentration also contributes to increased dissolution rates. The high degree of surface heterogeneity of these surface products indicates that these surfaces are not passivated by their formation. These results suggest that chalcopyrite dissolution will be accelerated when in contact with pyrite at solution redox potential intermediate between the rest potentials of chalcopyrite and pyrite (560 mV and 660 mV, respectively) and/or iron rich acidic waters with resulting enhanced formation of secondary sulfur containing species and release of copper and iron. This in turn suggests accelerated supergene formation and enhanced metalliferous drainage under these conditions.

Revisiting classical silicate dissolution rate laws under hydrothermal conditions

NASA Astrophysics Data System (ADS)

Pollet-Villard, Marion; Daval, Damien; Saldi, Giuseppe; Knauss, Kevin; Wild, Bastien; Fritz, Bertrand

2015-04-01

In the context of geothermal energy, the relative intensities of primary mineral leaching and secondary mineral precipitation can affect porosity and permeability of the reservoir, thereby influencing its hydraulic performance and the efficiency of the geothermal power station. That is why the prediction of reaction kinetics of fluid/rock interactions represents a critical issue in this context. Moreover, in several geothermal systems such as the one of Soultz-sous-Forêts (Alsace, France), the circulation of aqueous fluids induces only modest modifications of their chemical composition. Therefore, fluid-rock interactions take place at close-to-equilibrium conditions, where the rate-affinity relations are poorly known and intensively debated [1]. To describe more precisely the dissolution processes, our strategy consists in investigating the dissolution of the main cleavages of K-spar minerals (one of the prevalent primary minerals in the reservoir of Soultz-sous-Forêts geothermal system) over a wide range of Gibbs free energy (ΔG) conditions. The aims are to decipher the impact of crystallographic orientation and microstructural surface modifications on the dissolution kinetics and to propose a relation between K-spar dissolution rate and ΔG. Our experimental work relies on a coupled approach which combines classical experiments of K-spar dissolution monitored by aqueous chemical analyses (ICP-AES) and innovative techniques of nm- to μm-scale characterization of solid surface (SEM, AFM, VSI) [2]. Our results confirm that K-spar dissolution is an anisotropic process: we measure a tenfold factor between the slowest and the fastest-dissolving surfaces. Moreover, the formation of etch pits on surfaces during their alteration has been evidenced on all of the different faces that have been studied. This complex evolution of the surface topography casts doubt of the relevance of a surface model based on shrinking particles and represents a possible cause of an apparent modification of silicate dissolution rate over time. In addition, we evidenced that the relation between K-spar dissolution rate and ΔG depends on the crystallographic orientation of the altered surface, and differs from the transition state theory currently implemented into geochemical codes. Importantly, this theoretical curve overestimates the dissolution rates measured in close-to-equilibrium conditions. Taken together, the new findings show promise as a means for improving the accuracy of geochemical simulations. [1] Schott, J., Pokrovsky, O. S., and Oelkers, E. H., 2009. The Link Between Mineral Dissolution/Precipitation Kinetics and Solution Chemistry. Rev Mineral Geochem 70, 207-258. [2] Daval, D., Hellmann, R., Saldi, G. D., Wirth, R., and Knauss, K. G., 2013. Linking nm-scale measurements of the anisotropy of silicate surface reactivity to macroscopic dissolution rate laws: New insights based on diopside. Geochim Cosmochim Acta 107, 121-134.

Reactive transport modelling to infer changes in soil hydraulic properties induced by non-conventional water irrigation

NASA Astrophysics Data System (ADS)

Valdes-Abellan, Javier; Jiménez-Martínez, Joaquín; Candela, Lucila; Jacques, Diederik; Kohfahl, Claus; Tamoh, Karim

2017-06-01

The use of non-conventional water (e.g., treated wastewater, desalinated water) for different purposes is increasing in many water scarce regions of the world. Its use for irrigation may have potential drawbacks, because of mineral dissolution/precipitation processes, such as changes in soil physical and hydraulic properties (e.g., porosity, permeability), modifying infiltration and aquifer recharge processes or blocking root growth. Prediction of soil and groundwater impacts is essential for achieving sustainable agricultural practices. A numerical model to solve unsaturated water flow and non-isothermal multicomponent reactive transport has been modified implementing the spatio-temporal evolution of soil physical and hydraulic properties. A long-term process simulation (30 years) of agricultural irrigation with desalinated water, based on a calibrated/validated 1D numerical model in a semi-arid region, is presented. Different scenarios conditioning reactive transport (i.e., rainwater irrigation, lack of gypsum in the soil profile, and lower partial pressure of CO2 (pCO2)) have also been considered. Results show that although boundary conditions and mineral soil composition highly influence the reactive processes, dissolution/precipitation of carbonate species is triggered mainly by pCO2, closely related to plant roots. Calcite dissolution occurs in the root zone, precipitation takes place under it and at the soil surface, which will lead a root growth blockage and a direct soil evaporation decrease, respectively. For the studied soil, a gypsum dissolution up to 40 cm depth is expected at long-term, with a general increase of porosity and hydraulic conductivity.

Experimental Study on the Behavior of TiN and Ti2O3 Inclusions in Contact with CaO‐Al2O3‐SiO2‐MgO Slags

PubMed Central

Bernhard, C.

2017-01-01

TiN and Ti2O3 are the predominant inclusion types in Ti-alloyed ferritic chromium stainless steels. In order to ensure the required steel cleanness level, an effective removal of such inclusions in the slag during secondary metallurgy is essential. This inclusion removal predominantly takes place via dissolution of the inclusion in the slag. The dissolution behavior of TiN and Ti2O3 in CaO-SiO2-Al2O3-MgO slags as well as their agglomeration behavior in the liquid steel is investigated using High Temperature Laser Scanning Confocal Microscopy and Tammann Furnace experiments. Thermodynamic calculations are performed using FactSage 7.0. The behavior of TiN is observed to be completely different to that of oxides. Ti2O3 dissolves quickly in slags, and its dissolution behavior is comparable to that of other already well examined oxides. In contrast, TiN shows a very intense gas reaction which is attributed to the release of nitrogen during contact with slag. Slags with higher SiO2 content show a significantly higher ability for the dissolution of TiN as compared to Al2O3-rich slags. The gas reaction is found to also significantly influence the final steel cleanness. Despite the easy absorption of TiN in the slag, the formed nitrogen supports the formation of pinholes in the steel. PMID:29109805

Dissolution-resistance of glass-added hydroxyapatite composites

NASA Astrophysics Data System (ADS)

Seo, Dong Seok; Lee, Jong Kook

2009-04-01

Hydroxyapatite (HA) has generated a great deal of interest as a promising implant material. However, its poor mechanical properties induced by severe dissolution in biological milieu limit medical applications and lead to clinical failure. In this study, HA ceramics with 30P2O5-30CaO-40Na2O glass (1.0 wt.% and 2.5 wt.%) were prepared to improve the resistance of monophase HA. The monophase HA sintered body showed microstructural degradation due to grain boundary dissolution in buffered water. However, the dissolution-resistance of HA/glass composites was significantly improved and showed no apparent evidence of dissolution. This suggests that a less soluble glass phase should be placed at grain boundaries to protect HA from dissolution.

Internal oxidation phenomenon in pure copper

NASA Astrophysics Data System (ADS)

Rudolf, Rebeka; Anžel, Ivan

2009-04-01

This paper presents two special kinds of internal oxidation phenomenon that can take place in pure metals containing a high concentration of non-equilibrium defects. These processes are Internal Oxidation (IO) and Internal Carbonisation (IC). Both processes start with the dissolution of oxidant (O or C) into the pure metal at the free surfaces, and continue with the diffusion of oxidant atoms into the metal matrix volume, where they are trapped at numerous defects within the crystal lattice. Increasing oxidant activity at these places causes local oxidation of the matrix and, consequently, precipitation of fine oxide or graphite particles. The IO and IC processes were tested on the rapidly solidified pure copper which was produced by the Chill-Block Melt Spinning Technique. Analysis of the IO process showed the formation of Cu-Cu2O, and the formation of Cu-C composite from the IC process.

Topical Lime Application for the Management of Munitions Constituents Following Blow-in-Place Operations

DTIC Science & Technology

2010-06-01

disposable glass pipettes with a small piece of glass wool at the bottom. On top of the glass wool was placed 0.5 g of Florisil, and 0.5 g of neutral...particles have a relatively slow dissolution rate (Lynch et al. 2003). Sufficient hydrated lime to effect complete destruction of the RDX particle...K. Hatfield, and J. J. Delfino. 2003. An exploratory approach to modeling explosive compound persistence and flux using dissolution kinetics

Organic matter and modeling redox reactions during river bank filtration in an alluvial aquifer of the Lot River, France.

PubMed

Kedziorek, Monika A M; Geoffriau, Stephane; Bourg, Alain C M

2008-04-15

A 3 year study of the infiltration of Lot River water into a well field located in an adjacent gravel and clay alluvial aquifer was conducted to assess the importance of organic matter regarding the redox processes which influence groundwater quality in a positive (denitrification) or negative (Mn dissolution) manner. Chloride was used to quantify the mixing of river water with groundwater. According to modeling with PHREEQC, the biodegradation of the infiltrated dissolved organic carbon (DOCi) is not sufficient to explain the observed consequences of the redox reactions (dissolved O2 depletion, denitrification, Mn dissolution). Another electron donor source must therefore be involved: we propose solid organic carbon (SOC) as a likely candidate, if made available for degradation by prior hydrolysis. Its contribution to redox reactions could be significant (30-80% of the total organic carbon consumed by redox reactions during river bank filtration). We show here also that even though the first few meters of infiltration are highly reactive, significant redox reactions can take place further in the aquifer, possibly affecting groundwater quality away from the river bank.

Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS): A rapid test for enteric coating thickness and integrity of controlled release pellet formulations.

PubMed

Alfarsi, Anas; Dillon, Amy; McSweeney, Seán; Krüse, Jacob; Griffin, Brendan; Devine, Ken; Sherry, Patricia; Henken, Stephan; Fitzpatrick, Stephen; Fitzpatrick, Dara

2018-06-10

There are no rapid dissolution based tests for determining coating thickness, integrity and drug concentration in controlled release pellets either during production or post-production. The manufacture of pellets requires several coating steps depending on the formulation. The sub-coating and enteric coating steps typically take up to six hours each followed by additional drying steps. Post production regulatory dissolution testing also takes up to six hours to determine if the batch can be released for commercial sale. The thickness of the enteric coating is a key factor that determines the release rate of the drug in the gastro-intestinal tract. Also, the amount of drug per unit mass decreases with increasing thickness of the enteric coating. In this study, the coating process is tracked from start to finish on an hourly basis by taking samples of pellets during production and testing those using BARDS (Broadband Acoustic Resonance Dissolution Spectroscopy). BARDS offers a rapid approach to characterising enteric coatings with measurements based on reproducible changes in the compressibility of a solvent due to the evolution of air during dissolution. This is monitored acoustically via associated changes in the frequency of induced acoustic resonances. A steady state acoustic lag time is associated with the disintegration of the enteric coatings in basic solution. This lag time is pH dependent and is indicative of the rate at which the coating layer dissolves. BARDS represents a possible future surrogate test for conventional USP dissolution testing as its data correlates directly with the thickness of the enteric coating, its integrity and also with the drug loading as validated by HPLC. Copyright © 2018 Elsevier B.V. All rights reserved.

Hydrogen suppresses UO 2 corrosion

NASA Astrophysics Data System (ADS)

Carbol, Paul; Fors, Patrik; Gouder, Thomas; Spahiu, Kastriot

2009-08-01

Release of long-lived radionuclides such as plutonium and caesium from spent nuclear fuel in deep geological repositories will depend mainly on the dissolution rate of the UO 2 fuel matrix. This dissolution rate will, in turn, depend on the redox conditions at the fuel surface. Under oxidative conditions UO 2 will be oxidised to the 1000 times more soluble UO 2.67. This may occur in a repository as the reducing deep groundwater becomes locally oxidative at the fuel surface under the effect of α-radiolysis, the process by which α-particles emitted from the fuel split water molecules. On the other hand, the groundwater corrodes canister iron generating large amounts of hydrogen. The role of molecular hydrogen as reductant in a deep bedrock repository is questioned. Here we show evidence of a surface-catalysed reaction, taking place in the H 2-UO 2-H 2O system where molecular hydrogen is able to reduce oxidants originating from α-radiolysis. In our experiment the UO 2 surface remained stoichiometric proving that the expected oxidation of UO 2.00 to UO 2.67 due to radiolytic oxidants was absent. As a consequence, the dissolution of UO 2 stopped when equilibrium was reached between the solid phase and U 4+ species in the aqueous phase. The steady-state concentration of uranium in solution was determined to be 9 × 10 -12 M, about 30 times lower than previously reported for reducing conditions. Our findings show that fuel dissolution is suppressed by H 2. Consequently, radiotoxic nuclides in spent nuclear fuel will remain immobilised in the UO 2 matrix. A mechanism for the surface-catalysed reaction between molecular hydrogen and radiolytic oxidants is proposed.

Electrochemical Applications in Metal Bioleaching.

PubMed

Tanne, Christoph Kurt; Schippers, Axel

2017-12-10

Biohydrometallurgy comprises the recovery of metals by biologically catalyzed metal dissolution from solids in an aqueous solution. The application of this kind of bioprocessing is described as "biomining," referring to either bioleaching or biooxidation of sulfide metal ores. Acidophilic iron- and sulfur-oxidizing microorganisms are the key to successful biomining. However, minerals such as primary copper sulfides are recalcitrant to dissolution, which is probably due to their semiconductivity or passivation effects, resulting in low reaction rates. Thus, further improvements of the bioleaching process are recommendable. Mineral sulfide dissolution is based on redox reactions and can be accomplished by electrochemical technologies. The impact of electrochemistry on biohydrometallurgy affects processing as well as analytics. Electroanalysis is still the most widely used electrochemical application in mineralogical research. Electrochemical processing can contribute to bioleaching in two ways. The first approach is the coupling of a mineral sulfide to a galvanic partner or electrocatalyst (spontaneous electron transfer). This approach requires only low energy consumption and takes place without technical installations by the addition of higher redox potential minerals (mostly pyrite), carbonic material, or electrocatalytic ions (mostly silver ions). Consequently, the processed mineral (often chalcopyrite) is preferentially dissolved. The second approach is the application of electrolytic bioreactors (controlled electron transfer). The electrochemical regulation of electrolyte properties by such reactors has found most consideration. It implies the regulation of ferrous and ferric ion ratios, which further results in optimized solution redox potential, less passivation effects, and promotion of microbial activity. However, many questions remain open and it is recommended that reactor and electrode designs are improved, with the aim of finding options for simplified biohydrometallurgical processing. This chapter focuses on metal sulfide dissolution via bioleaching and does not include other biohydrometallurgical processes such as microbial metal recovery from solution.

Rock-magnetic changes with reduction diagenesis in Japan Sea sediments and preservation of geomagnetic secular variation in inclination during the last 30,000 years

NASA Astrophysics Data System (ADS)

Yamazaki, T.; Abdeldayem, A. L.; Ikehara, K.

2003-06-01

A rock-magnetic and paleomagnetic study was conducted on a sediment core of about 4.4 m long taken from the northeastern part of the Japan Sea. The core covers the last about 30 kyrs, which was dated by nineteen radiocarbon (14C) ages. Remanent magnetization is carried dominantly by magnetite. Reductive dissolution of magnetic minerals occurs between 1.2 and 1.6 m in depth (about 5-8 ka in age). A rapid downcore decrease of anhysteretic remanent magnetization (ARM) begins at the shallowest depth. Saturation isothermal remanent magnetization (SIRM) follows, and a decrease of magnetic susceptibility (k) takes place at the deepest. Within this zone, coercivity of natural remanent magnetization (NRM) and the ratios of ARM to k and SIRM to k also decreases with depth. These observations indicate that finer magnetic grains were lost earlier than larger grains. A decrease of S ratios, wasp-waisted hysteresis curves, and a deviation from a mixing trend of single-domain and multi-domain grains in a Day plot occur as the dissolution proceeds, which suggests that high coercivity minerals like hematite are more resistive to dissolution than low coercivity minerals like magnetite. The start of the dissolution at 1.2 m in depth is synchronous with increases in organic-carbon and total-sulfur contents, but the horizon does not coincide with the present Fe-redox boundary at about 0.02 m below the sediment-water interface. From low-temperature magnetometry, it is estimated that magnetites with maghemite skin are reduced to pure magnetites prior to dissolution. There is no evidence for precipitation of secondary magnetic phases and acquisition of chemical remanent magnetization (CRM). Neither pyrrhotite nor greigite was detected. Information of paleomagnetic directions have survived the reductive dissolution. Inclination variations of this core resembles closely to the secular variation records available around Japan. Well-dated records older than 10 ka are still very rare, and hence our new record could be useful for establishing regional secular variations.

Caveats when Analyzing Ultra-high Molar Mass Polymers by SEC

USDA-ARS?s Scientific Manuscript database

The analysis of ultra-high molar mass (M > 1 million g/mol) polymers via size-exclusion chromatography (SEC) presents a number of non-trivial challenges. Dissolution and full solvation may take days, as is the case for cellulose dissolution in non-complexing non degrading solvents; very low concent...

Transient changes in shallow groundwater chemistry during the MSU ZERT CO2 injection experiment

USGS Publications Warehouse

Apps, J.A.; Zheng, Lingyun; Spycher, N.; Birkholzer, J.T.; Kharaka, Y.; Thordsen, J.; Kakouros, E.; Trautz, R.

2011-01-01

Food-grade CO2 was injected into a shallow aquifer through a perforated pipe placed horizontally 1-2 m below the water table at the Montana State University Zero Emission Research and Technology (MSU-ZERT) field site at Bozeman, Montana. The possible impact of elevated CO2 levels on groundwater quality was investigated by analyzing 80 water samples taken before, during, and following CO2 injection. Field determinations and laboratory analyses showed rapid and systematic changes in pH, alkalinity, and conductance, as well as increases in the aqueous concentrations of trace element species. The geochemical data were first evaluated using principal component analysis (PCA) in order to identify correlations between aqueous species. The PCA findings were then used in formulating a geochemical model to simulate the processes likely to be responsible for the observed increases in the concentrations of dissolved constituents. Modeling was conducted taking into account aqueous and surface complexation, cation exchange, and mineral precipitation and dissolution. Reasonable matches between measured data and model results suggest that: (1) CO2 dissolution in the groundwater causes calcite to dissolve. (2) Observed increases in the concentration of dissolved trace metals result likely from Ca+2-driven ion exchange with clays (smectites) and sorption/desorption reactions likely involving Fe (hydr)oxides. (3) Bicarbonate from CO2 dissolution appears to compete for sorption with anionic species such as HAsO4-2, potentially increasing dissolved As levels in groundwater. ?? 2011 Published by Elsevier Ltd.

Behaviour of F82H mod. stainless steel in lead-bismuth under temperature gradient

NASA Astrophysics Data System (ADS)

Gómez Briceño, D.; Martín Muñoz, F. J.; Soler Crespo, L.; Esteban, F.; Torres, C.

2001-07-01

Austenitic steels can be used in a hybrid system in contact with liquid lead-bismuth eutectic if the region of operating temperatures is not beyond 400°C. For higher temperatures, martensitic steels are recommended. However, at long times, the interaction between the structural material and the eutectic leads to the dissolution of some elements of the steel (Ni, Cr and Fe, mainly) in the liquid metal. In a non-isothermal lead-bismuth loop, the material dissolution takes place at the hot leg of the circuit and, due to the mass transfer, deposition occurs at the cold leg. One of the possible ways to improve the performance of structural materials in lead-bismuth is the creation of an oxide layer. Tests have been performed in a small natural convection loop built of austenitic steel (316L) that has been operating for 3000 h. This loop contains a test area in which several samples of F82Hmod. martensitic steel have been tested at different times. A gas with an oxygen content of 10 ppm was bubbled in the hot area of the circuit during the operation time. The obtained results show that an oxide layer is formed on the samples introduced in the loop at the beginning of the operation and this layer increases with time. However, the samples introduced at different times during the loop operation, are not protected by oxide layers and present material dissolution in some cases.

The geochemical evolution of aqueous sodium in the Black Creek Aquifer, Horry and Georgetown counties, South Carolina

USGS Publications Warehouse

Zack, Allen L.; Roberts, Ivan

1988-01-01

The Black Creek aquifer contains dilute seawater near the North Carolina State line, probably the result of incomplete flushing of ancient seawater. Data do not indicate that the dilute seawater has migrated toward areas of fresh ground-water withdrawals. The concentration of chloride in ground-water samples ranges from 5 to 720 milligrams per liter and that of sodium from 160 to 690 milligrams per liter. Ion-exchange reactions (sodium for calcium and fluoride for hydroxyl) occur with the calcium carbonate dissolution reaction which produces calcium, bicarbonate, and hydroxyl ions. The reaction sequence and stoichiometry result in an aqueous solution in which the sum of bicarbonate and chloride equivalents per liter is equal to the equivalents per liter of sodium. Calcium ions are exchanged for sodium ions derived from sodium-rich clays upgradient of the dilute seawater. The cation-exchange reaction equilibrates at a sodium concentration of 280 milligrams per liter. Amounts of sodium greater than 280 milligrams per liter are contributed from dilute seawater. The cation-exchange reaction approaches an equilibrium which represents a mass-action limit in terms of the ratio of sodium to calcium in solution versus the ratio of exchangeable sodium to calcium on clay surfaces. Where the limit of calcium carbonate solubility is approached and dissolution ceases, some precipitation of calcite probably takes place. The dissolution of calcite exposes fossil shark teeth which release fluoride ions to the ground water through anion exchange with aqueous hydroxyl ions.

Theoretical and Numerical Investigation of the Cavity Evolution in Gypsum Rock

NASA Astrophysics Data System (ADS)

Li, Wei; Einstein, Herbert H.

2017-11-01

When water flows through a preexisting cylindrical tube in gypsum rock, the nonuniform dissolution alters the tube into an enlarged tapered tube. A 2-D analytical model is developed to study the transport-controlled dissolution in an enlarged tapered tube, with explicit consideration of the tapered geometry and induced radial flow. The analytical model shows that the Graetz solution can be extended to model dissolution in the tapered tube. An alternative form of the governing equations is proposed to take advantage of the invariant quantities in the Graetz solution to facilitate modeling cavity evolution in gypsum rock. A 2-D finite volume model was developed to validate the extended Graetz solution. The time evolution of the transport-controlled and the reaction-controlled dissolution models for a single tube with time-invariant flow rate are compared. This comparison shows that for time-invariant flow rate, the reaction-controlled dissolution model produces a positive feedback between the tube enlargement and dissolution, while the transport-controlled dissolution does not.

Mercury-free dissolution of aluminum-clad fuel in nitric acid

DOEpatents

Christian, Jerry D.; Anderson, Philip A.

1994-01-01

A mercury-free dissolution process for aluminum involves placing the aluminum in a dissolver vessel in contact with nitric acid-fluoboric acid mixture at an elevated temperature. By maintaining a continuous flow of the acid mixture through the dissolver vessel, an effluent containing aluminum nitrate, nitric acid, fluoboric acid and other dissolved components are removed.

Mercury-free dissolution of aluminum-clad fuel in nitric acid

DOEpatents

Christian, J.D.; Anderson, P.A.

1994-11-15

A mercury-free dissolution process for aluminum involves placing the aluminum in a dissolver vessel in contact with nitric acid-fluoboric acid mixture at an elevated temperature. By maintaining a continuous flow of the acid mixture through the dissolver vessel, an effluent containing aluminum nitrate, nitric acid, fluoboric acid and other dissolved components are removed. 5 figs.

A possible application of magnetic resonance imaging for pharmaceutical research.

PubMed

Kowalczuk, Joanna; Tritt-Goc, Jadwiga

2011-03-18

Magnetic resonance imaging (MRI) is a non-destructive and non-invasive method, the experiment can be conducted in situ and allows the studying of the sample and the different processes in vitro or in vivo. 1D, 2D or 3D imaging can be undertaken. MRI is nowadays most widely used in medicine as a clinical diagnostic tool, but has still seen limited application in the food and pharmaceutical sciences. The different imaging pulse sequences of MRI allow to image the processes that take place in a wide scale range from ms (dissolution of compact tablets) to hours (hydration of drug delivery systems) for mobile as well as for rigid spins, usually protons. The paper gives examples of MRI application of in vitro imaging of pharmaceutical dosage based on hydroxypropyl methylcellulose which have focused on water-penetration, diffusion, polymer swelling, and drug release, characterized with respect to other physical parameters such as pH and the molecular weight of polymer. Tetracycline hydrochloride was used as a model drug. NMR imaging of density distributions and fast kinetics of the dissolution behavior of compact tablets is presented for paracetamol tablets. Copyright © 2010 Elsevier B.V. All rights reserved.

Using a Word Association Test for the Assessment of High School Students' Cognitive Structures on Dissolution

ERIC Educational Resources Information Center

Derman, Aysegul; Eilks, Ingo

2016-01-01

Understanding students' cognitive structures in a specific knowledge domain helps to determine the ''what, how and why'' features of such knowledge, so that we can take these structures into consideration in teaching. The purpose of the present study was to identify students' cognitive structures about solution and dissolution concepts. The study…

The long-term dissolution characteristics of a residually trapped BTX mixture in soil

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rixey, W.G.

1996-12-31

A mass transfer limited model is presented to describe the long-term dissolution of organic compounds from a benzene, toluene, and xylenes (BTX) mixture residually trapped in a sandy soil. The model is an extension of a previously presented equilibrium dissolution model which takes into consideration mass transfer limitations that develop later in the leaching process and is similar to that presented by Borden and Kao for modeling BTX dissolution from residually trapped gasoline. The residual nonaqueous phase liquid (NAPL) is divided into multiple regions: one region which undergoes equilibrium dissolution and additional regions in which mass transfer is progressively limited.more » Application of the model to BTX column effluent data indicates that the initial dissolution (exponential decay region) of BTX can be effectively described by equilibrium dissolution. When applied to later dissolution times (Asymptotic region) a multiple-region model is required to rationalize the data for all three components. This explanation of the observed tailing in leaching experiments form residually trapped hydrocarbons if offered as an alternative to the explanation of tailing due to rate-limited desorption from soils. 16 refs., 5 figs., 2 tabs.« less

The use of ordered mixtures for improving the dissolution rate of low solubility compounds.

PubMed

Nyström, C; Westerberg, M

1986-03-01

The dissolution rate of micronized griseofulvin has been investigated, both for the agglomerated raw material and the material formulated as an ordered mixture, by means of the USP XX paddle method. During the experiments, which were performed at sink condition and constant temperature, the effects of adding a surfactant and of agitation were tested. The ordered mixture with sodium chloride gave a fast dissolution rate, practically independent of the test parameters. Micronized griseofulvin alone gave dissolution profiles that were improved by adding polysorbate 80 and by increased agitation, but the dissolution rates obtained were much lower than those for the ordered mixture. It was concluded that the rate limiting step in the dissolution of griseofulvin as the raw material is the penetration of the dissolution medium into the agglomerates. With an ordered mixture, these agglomerates were deaggregated during the mixing process, producing a system in which the entire external surface area of the primary particles was exposed to the dissolution medium. This conclusion was supported by calculation of the contact surface areas taking part in the dissolution process for the systems tested. The procedure developed in this study could be applied to preformulation work where a cohesive, low solubility drug of hydrophobic nature is to be formulated.

Is the core top modern? Observations from the eastern equatorial Pacific

NASA Astrophysics Data System (ADS)

Mekik, Figen; Anderson, Robert

2018-04-01

A compilation of ages from 67 core tops in the eastern equatorial Pacific (EEP) does not display an easily discernible regional pattern. The ages range from 790 to over 15,000 years. The youngest core tops with the highest sediment focusing factors are located in the Panama Basin. There are weak but statistically significant inverse relationships between core top age and age-model based mass accumulation rates, bioturbation depth, linear sedimentation rate and sediment focusing factors. However, we found no statistically significant relationship between core top age and calcite dissolution in sediments or 230Th-normalized mass accumulation rates. We found evidence suggesting that greater amount of sediment focusing helps to preserve the carbonate fraction of the sediment where focusing is taking place. When focusing factors are plotted against percent calcite dissolved, we observe a strong inverse relationship, and core tops younger than 4500 years tend to occur where focusing factors are high and percent calcite dissolved values are low. Using labile organic carbon fluxes to estimate bioturbation depth in the sediments results in the observation that where bioturbation depth is shallow (<4 cm), the core top age has a strong, inverse relationship with sediment accumulation rate. We used the Globorotalia menardii Fragmentation Index (MFI) as an indicator of percent calcite dissolved in deep sea sediments. There is a distinct pattern to core top calcite dissolution in the EEP which delineates bands of high surface ocean productivity as well as the clear increase in dissolution downward on the flanks of the East Pacific Rise.

Electrochemical polishing of thread fastener test specimens of nickel-chromium iron alloys

DOEpatents

Kephart, Alan R.

1991-01-01

An electrochemical polishing device and method for selective anodic dissolution of the surface of test specimens comprised, for example, of nickel-chromium-iron alloys, which provides for uniform dissolution at the localized sites to remove metal through the use of a coiled wire electrode (cathode) placed in the immediate proximity of the working, surface resulting in a polished and uniform grain boundary.

Dependence of the electronic absorption spectra of aqueous solutions of iodine monochloride on the conditions of dilution and storage time

NASA Astrophysics Data System (ADS)

Klyubin, V. V.; Klyubina, K. A.; Makovetskaya, K. N.

2017-04-01

The electronic absorption spectra of aqueous solutions of iodine monochloride ICl are studied. The spectra of as-prepared solutions display the absorption band associated with hydrated ICl molecules. An additional band indicating that molecular iodine was formed in the solution emerges in the spectrum as dissolution takes place. Only the band belonging to iodine monochloride remains in the absorption spectra, and no additional bands appear after chloride anions Cl- are added to the solution. The absorption spectrum becomes more complex when ICl is dissolved in an alkaline medium. The band belonging to molecular iodine emerges in the spectra at low alkali concentrations, while being transformed to other shorter-wavelength bands at high alkali concentrations (pH ≥ 12).

Scaling theory in a model of corrosion and passivation.

PubMed

Aarão Reis, F D A; Stafiej, Janusz; Badiali, J-P

2006-09-07

We study a model for corrosion and passivation of a metallic surface after small damage of its protective layer using scaling arguments and simulation. We focus on the transition between an initial regime of slow corrosion rate (pit nucleation) to a regime of rapid corrosion (propagation of the pit), which takes place at the so-called incubation time. The model is defined in a lattice in which the states of the sites represent the possible states of the metal (bulk, reactive, and passive) and the solution (neutral, acidic, or basic). Simple probabilistic rules describe passivation of the metal surface, dissolution of the passive layer, which is enhanced in acidic media, and spatially separated electrochemical reactions, which may create pH inhomogeneities in the solution. On the basis of a suitable matching of characteristic times of creation and annihilation of pH inhomogeneities in the solution, our scaling theory estimates the average radius of the dissolved region at the incubation time as a function of the model parameters. Among the main consequences, that radius decreases with the rate of spatially separated reactions and the rate of dissolution in acidic media, and it increases with the diffusion coefficient of H(+) and OH(-) ions in solution. The average incubation time can be written as the sum of a series of characteristic times for the slow dissolution in neutral media, until significant pH inhomogeneities are observed in the dissolved cavity. Despite having a more complex dependence on the model parameters, it is shown that the average incubation time linearly increases with the rate of dissolution in neutral media, under the reasonable assumption that this is the slowest rate of the process. Our theoretical predictions are expected to apply in realistic ranges of values of the model parameters. They are confirmed by numerical simulation in two-dimensional lattices, and the expected extension of the theory to three dimensions is discussed.

Is the Core Top Really Modern? A Story of Chemical Erosion, Bioturbation, and Lateral Sediment Redistribution from the Eastern Equatorial Pacific

NASA Astrophysics Data System (ADS)

Mekik, F.

2016-12-01

Paleoceanographic work is based on calibrating paleo-environmental proxies using well-preserved core top sediments which represent the last one thousand years or less. However, core top sediments may be in places as old as 9000 years due to various sedimentary and diagenetic processes, such as chemical erosion, bioturbation and lateral sediment redistribution. We hypothesize that in regions with high surface ocean productivity, high organic carbon to calcite ratios reaching the seabed promote calcite dissolution in sediments, even in regions above the lysocline. This process may lead to chemical erosion of core tops which in turn may result in core top aging. The eastern equatorial Pacific (EEP), a popular site for calibration of paleoceanographic proxies, is such a place. Better understanding the relationship between core top age and dissolution will help correct biases inherent in proxy calibration because dissolution of foraminifers alters shell chemistry, and wholesale dissolution of sediments leads to core top aging and loss. We present both new and literature-based core top data of radiocarbon ages from the EEP. We created regional maps of both core top radiocarbon age and calcite preservation measured with the Globorotalia menardii Fragmentation Index (MFI; over 100 core tops). Our maps show a clear pattern of deep sea sedimentary calcite dissolution mimicking the pattern of surface ocean productivity observed from satellites and sediment traps in the EEP. Core top radiocarbon ages generally parallel the dissolution patterns observed in the region. Where this relationship does not hold true, bioturbation and/or lateral sediment redistribution may play a role. Down core radiocarbon and 230Th-normalized sediment accumulation rate data from several cores in the EEP support this hypothesis. Better understanding the role of diagenesis promotes the development of more reliable paleo-environmental proxies.

Students' Understanding of Salt Dissolution: Visualizing Animation in the Chemistry Classroom

NASA Astrophysics Data System (ADS)

Malkoc, Ummuhan

The present study explored the effect of animation implementation in learning a chemistry topic. 135 high school students taking chemistry class were selected for this study (quasi-experimental groups = 67 and control groups = 68). Independent samples t-tests were run to compare animation and control groups between and within the schools. The over-arching finding of this research indicated that when science teachers used animations while teaching salt dissolution phenomena, students will benefit the application of animations. In addition, the findings informed the TPACK framework on the idea that visual tools are important in students' understanding of salt dissolution concepts.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Li-Fang; Ou, Chin-Ching; Striebel, Kathryn A.

The goal of this research was to measure Mn dissolution from a thin porous spinel LiMn{sub 2}O{sub 4} electrode by rotating ring-disk collection experiments. The amount of Mn dissolution from the spinel LiMn{sub 2}O{sub 4} electrode under various conditions was detected by potential step chronoamperometry. The concentration of dissolved Mn was found to increase with increasing cycle numbers and elevated temperature. The dissolved Mn was not dependent on disk rotation speed, which indicated that the Mn dissolution from the disk was under reaction control. The in situ monitoring of Mn dissolution from the spinel was carried out under various conditions.more » The ring currents exhibited maxima corresponding to the end-of-charge (EOC) and end-of-discharge (EOD), with the largest peak at EOC. The results suggest that the dissolution of Mn from spinel LiMn{sub 2}O{sub 4} occurs during charge/discharge cycling, especially in a charged state (at >4.1 V) and in a discharged state (at <3.1 V). The largest peak at EOC demonstrated that Mn dissolution took place mainly at the top of charge. At elevated temperatures, the ring cathodic currents were larger due to the increase of Mn dissolution rate.« less

Effect of Food Thickener on Dissolution and Laxative Activity of Magnesium Oxide Tablets in Mice.

PubMed

Tomita, Takashi; Goto, Hidekazu; Yoshimura, Yuya; Kato, Kazushige; Yoshida, Tadashi; Tanaka, Katsuya; Sumiya, Kenji; Kohda, Yukinao

2016-01-01

The present study examined the dissolution of magnesium oxide (MgO) from MgO tablets placed in a food thickening agent (food thickener) and its effects on laxative activity. We prepared mixtures of MgO tablets suspended in an aqueous suspension and food thickeners in order to evaluate the dissolution of MgO. The results of the dissolution tests revealed that agar-based food thickeners did not affect the MgO dissolution. In contrast, some xanthan gum-based food-thickener products show dissolution rates with certain mixtures containing disintegrated MgO tablets suspended in a food thickener that decrease over time. However, other xanthan gum-based food-thickener products show dissolution rates that decrease immediately after mixing, regardless of the time they were allowed to stand. In order to investigate the laxative activity of MgO, we orally administered a mixture of MgO suspension and food thickener to mice and observed their bowel movements. The animal experiments showed that when agar-based food thickeners were used, the laxative activity of MgO was not affected, but it decreased when xanthan gum-based food thickeners were used.

Kinetics of scheelite dissolution in groundwater: defining the release rate of tungsten contamination from a natural source

NASA Astrophysics Data System (ADS)

Montgomery, S. D.; Mckibben, M. A.

2011-12-01

Tungsten, an emerging contaminant, has no EPA standard for its permissible levels in drinking water. At sites in California, Nevada, and Arizona there may be a correlation between elevated levels of tungsten in drinking water and clusters of childhood acute lymphocytic leukemia (ALL). Developing a better understanding of how tungsten is released from rocks into surface and groundwaters is therefore of growing environmental interest. Knowledge of tungstate ore mineral weathering processes, particularly the rates of dissolution of scheelite (CaWO4) in groundwater, could improve models of how tungsten is released and transported in natural waters. Our research is focusing on experimental determination of the rates and products of tungstate mineral dissolution in synthetic groundwater, as a function of temperature, pH and mineral surface area. The initial rate method is being used to develop rate laws. Batch reactor experiments are conducted within constant temperature circulation baths over a pH range of 2-9. Cleaned scheelite powder with grain diameters of 106-150um is placed between two screens in a sample platform and then placed inside a two liter Teflon vessel filled with synthetic groundwater. Ports on the vessel allow sample extraction, temperature and pH measurement, gas inflow, and water circulation. Aliquots of solution are taken periodically for product analysis by ICP -MS. Changes in mineral surface characteristics are monitored using SEM and EDS methods. Results so far reveal that the dissolution of scheelite is incongruent at both neutral and low pH. Solid tungstic acid forms on scheelite mineral surfaces under acidic conditions, implying that this phase controls the dissolution rate in acidic environments. The influence of dissolved CO2 and resultant calcium carbonate precipitation on the dissolution of scheelite at higher pH is also being investigated. The rate law being developed for scheelite dissolution will be useful in reactive-transport computer codes designed to model tungsten contamination in a variety of surface and groundwater settings.

Quality-by-design case study: investigation of the role of poloxamer in immediate-release tablets by experimental design and multivariate data analysis.

PubMed

Kaul, Goldi; Huang, Jun; Chatlapalli, Ramarao; Ghosh, Krishnendu; Nagi, Arwinder

2011-12-01

The role of poloxamer 188, water and binder addition rate, on retarding dissolution in immediate-release tablets of a model drug from BCS class II was investigated by means of multivariate data analysis (MVDA) combined with design of experiments (DOE). While the DOE analysis yielded important clues into the cause-and-effect relationship between the responses and design factors, multivariate data analysis of the 40+ variables provided additional information on slowdown in tablet dissolution. A steep dependence of both tablet dissolution and disintegration on the poloxamer and less so on other design variables was observed. Poloxamer was found to increase dissolution rates in granules as expected of surfactants in general but retard dissolution in tablets. The unexpected effect of poloxamer in tablets was accompanied by an increase in tablet-disintegration-time-mediated slowdown of tablet dissolution and by a surrogate binding effect of poloxamer at higher concentrations. It was additionally realized through MVDA that poloxamer in tablets either acts as a binder by itself or promotes binder action of the binder povidone resulting in increased intragranular cohesion. Additionally, poloxamer was found to mediate tablet dissolution on stability as well. In contrast to tablet dissolution at release (time zero), poloxamer appeared to increase tablet dissolution in a concentration-dependent manner on accelerated open-dish stability. Substituting polysorbate 80 as an alternate surfactant in place of poloxamer in the formulation was found to stabilize tablet dissolution.

On the present and future of dissolution-DNP

NASA Astrophysics Data System (ADS)

Ardenkjaer-Larsen, Jan Henrik

2016-03-01

Dissolution-DNP is a method to create solutions of molecules with nuclear spin polarization close to unity. The many orders of magnitude signal enhancement have enabled many new applications, in particular in vivo MR metabolic imaging. The method relies on solid state dynamic nuclear polarization at low temperature followed by a dissolution to produce the room temperature solution of highly polarized spins. This work describes the present and future of dissolution-DNP in the mind of the author. The article describes some of the current trends in the field as well as outlines some of the areas where new ideas will make an impact. Most certainly, the future will take unpredicted directions, but hopefully the thoughts presented here will stimulate new ideas that can further advance the field.

Matrimonial Causes Act 1989 (No. 2 of 1989), 6 January 1989.

PubMed

1989-01-01

This document contains a summary of major portions of Jamaica's Matrimonial Causes Act of 1989 which replaced the Divorce Act of 1879. The 1989 Act allows divorce after two years of marriage on the sole ground of irretrievable breakdown of marriage, evidenced by the continuous separation of the parties for the year previous to the petition. This separation does not guaranteed that a divorce will be granted; a judge may believe that the marriage can be saved and may refer the parties to a marriage counselor. Separation can be effected by only one party, and the separated couple may continue to reside in the same household. In addition to clarifying the law regarding annulments, the new Act introduced new remedies for cases of domestic violence, including court-ordered injunctions. Dissolution of marriage can take place upon presumption of death after the partner has been presumed dead for seven years. The Act contains sections which lay out the grounds for the jurisdiction of the court and the recognition of foreign decrees as well as sections which change the law relating to domicile. The Act also contains child and spousal support provisions which are effective during a marriage and upon the dissolution or nullity of a marriage.

Corrosion of Mg alloy AZ91D in the presence of living cells.

PubMed

Seuss, F; Seuss, S; Turhan, M C; Fabry, B; Virtanen, S

2011-11-01

Mg and Mg alloys are of interest for biodegradable implants as they readily corrode in biological fluids, and dissolved Mg ions are nontoxic. Even though it is well known that Mg dissolution leads to pH increase in the surroundings, the effect of the corrosion-induced alkalization on the biological environment has not been studied in detail. We therefore explored the interactions between corrosion-induced pH increase and cell growth on Mg alloy AZ91D surface. Cell adhesion and spreading on the alloy surface is unimpeded initially. However, with time a large fraction of cells de-adhere. We attribute this to the observed increase of the pH in the cell culture medium in the process of alloy dissolution. Cytotoxicity tests with HeLa cells grown on glass surfaces confirm that cell death increases with increasing alkalinity of the cell culture medium. We also show that a the cells that adhere on the Mg alloy surface act as a corrosion-blocking surface layer. In consequence, a slower pH increase in the medium takes place when the alloy surface is covered with cells. Electrochemical impedance spectroscopy measurements (EIS) verify that a cell layer slows down the corrosion process. 2011 Wiley Periodicals, Inc.

Detailed Modelling of Kinetic Biodegradation Processes in a Laboratory Mmicrocosm

NASA Astrophysics Data System (ADS)

Watson, I.; Oswald, S.; Banwart, S.; Mayer, U.

2003-04-01

Biodegradation of organic contaminants in soil and groundwater usually takes places via different redox processes happening sequentially as well as simultaneously. We used numerical modelling of a long-term lab microcosm experiment to simulate the dynamic behaviour of fermentation and respiration in the aqueous phase in contact with the sandstone material, and to develop a conceptual model describing these processes. Aqueous speciation, surface complexation, mineral dissolution and precipitation were taken into account also. Fermentation can be the first step of the degradation process producing intermediate species, which are subsequently consumed by TEAPs. Microbial growth and substrate utilisation kinetics are coupled via a formulation that also includes aqueous speciation and other geochemical reactions including surface complexation, mineral dissolution and precipitation. Competitive exclusion between TEAPs is integral to the conceptual model of the simulation, and the results indicate that exclusion is not complete, but some overlap is found between TEAPs. The model was used to test approaches like the partial equilibrium approach that currently make use of hydrogen levels to diagnose prevalent TEAPs in groundwater. The observed pattern of hydrogen and acetate concentrations were reproduced well by the simulations, and the results show the relevance of kinetics, lag times and inhibition, and especially that intermediate products play a key role.

Can we get a better knowledge on dissolution processes in chalk by using microfluidic chips?

NASA Astrophysics Data System (ADS)

Neuville, Amélie; Minde, Mona; Renaud, Louis; Vinningland, Jan Ludvig; Dysthe, Dag Kristian; Hiorth, Aksel

2017-04-01

This work has been initiated in the context of research on improving the oil recovery in chalk bedrocks. One of the methods to improve the oil recovery is to inject "smart water" (acidic water/brines). Experiments on core scale and field tests that have been carried out the last decade have clearly shown that water chemistry affects the final oil recovery. However, there is generally no consensus in the scientific community of why additional oil is released, and it is also still not understood what are the mineralogical and structural changes. Direct in situ observation of the structural changes that occur when chalk is flooded with brines could resolve many of the open questions that remain. One of the highlights of this work is thus the development of an innovative methodology where fluid/rock interactions are observed in-situ by microscopy. To do so, we create several types of custom-made microfluidic systems that embeds reactive materials like chalk and calcite. The methodology we develop can be applied to other reactive materials. We will present an experiment where a calcite window dissolves with a fluid, where we observe in-situ the topography features of the calcite window, as well as the dissolution rate [1]. The injected fluid circulates at controlled flowrates in a channel which is obtained by xurography: double sided tape is cut out with a cutter plotter and placed between the reactive window and a non-reactive support. While the calcite window reacts, its topography is measured in situ every 10 s using an interference microscope, with a pixel resolution of 4.9 μm and a vertical resolution of 50 nm. These experiments are also compared with reactive flow simulations done with Lattice Boltzmann methods. Then, we will present a dissolution experiment done with a microfluidic system that embeds chalk. In this experiment, the main flow takes place at the chalk surface, in contact with fluid flowing in a channel above the chalk sample. Thus the reaction mostly occurs at the surface of the sample. The reacting chalk surface is observed in situ by stereomicroscopy and by interferometry. The dissolution velocities are highly heterogeneous. To identify the mineral change of the surface, a posteriori measurements using field emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray spectroscopy (EDS). [1] Neuville et al, 2016, Xurography for microfluidics on a reactive solid, Lab on Chip, DOI: 10.1039/c6lc01253a

Dissolution of pulp tissue by aqueous solution of chlorhexidine digluconate and chlorhexidine digluconate gel.

PubMed

Okino, L A; Siqueira, E L; Santos, M; Bombana, A C; Figueiredo, J A P

2004-01-01

To evaluate the activity of various root canal irrigants on bovine pulp tissue. The irrigants tested were: 0.5, 1.0 and 2.5% sodium hypochlorite; 2% aqueous solution of chlorhexidine digluconate; 2% chlorhexidine digluconate gel (Natrosol); and distilled water as control. Bovine pulp fragments were weighed and placed in contact with 20 mL of each tested substance in a centrifuge at 150 r.p.m. until total dissolution. Dissolution speed was calculated by dividing pulp weight by dissolution time. Statistical analysis was performed using the Kruskal-Wallis test. Distilled water and both solutions of chlorhexidine did not dissolve the pulp tissue within 6 h. Mean dissolution speeds for 0.5, 1.0 and 2.5% sodium hypochlorite solutions were 0.31, 0.43 and 0.55 mg min(-1), respectively. The solvent ability of chlorhexidine solutions was similar to that of distilled water. The results for sodium hypochlorite solutions, chlorhexidine solutions and distilled water were statistically different (P>0.01). Both chlorhexidine preparations and distilled water were not able to dissolve pulp tissue. All sodium hypochlorite solutions were efficient in dissolving pulp tissue; the dissolution speed varied with the concentration of the solution.

Coupled multiphase reactive flow and mineral dissolution-precipitation kinetics: Examples of long-term CO2 sequestration in Utsira Sand, Norway and Mt. Simon Formation, Midwest USA

NASA Astrophysics Data System (ADS)

Zhang, Y.; Zhang, G.; Lu, P.; Hu, B.; Zhu, C.

2017-12-01

The extent of CO2 mineralization after CO2 injection into deep saline aquifers is a result of the complex coupling of multiphase fluid flow, mass transport, and brine-mineral reactions. The effects of dissolution rate laws and groundwater flow on the long-term fate of CO2 have been seriously overlooked. To investigate these effects, we conducted multiphase (CO2 and brine) coupled reactive transport modeling of CO2 storage in two sandy formations (Utsira Sand, Norway1,2 and Mt. Simon formation, USA 3) using ToughReact and simulated a series of scenarios. The results indicated that: (1) Different dissolution rate laws for feldspars can significantly affect the amount of CO2 mineralization. Increased feldspar dissolution will promote CO2 mineral trapping through the coupling between feldspar dissolution and carbonate mineral precipitation at raised pH. The predicted amount of CO2 mineral trapping when using the principle of detailed balancing-based rate law for feldspar dissolution is about twice as much as that when using sigmoidal rate laws in the literature. (2) Mineral trapping is twice as much when regional groundwater flow is taken into consideration in long-term simulations (e.g., 10,000 years) whereas most modeling studies neglected the regional groundwater flow back and effectively simulated a batch reactor process. Under the influence of regional groundwater flow, the fresh brine from upstream continuously dissolves CO2 at the tail of CO2 plume, generating a large acidified area where large amount of CO2 mineralization takes place. The upstream replenishment of groundwater results in ˜22% mineral trapping at year 10,000, compared to ˜4% when this effect is ignored. Refs: 1Zhang, G., Lu, P., Wei, X., Zhu, C. (2016). Impacts of Mineral Reaction Kinetics and Regional Groundwater Flow on Long-Term CO2 Fate at Sleipner. Energy & Fuels, 30(5), 4159-4180. 2Zhu, C., Zhang, G., Lu, P., Meng, L., Ji, X. (2015). Benchmark modeling of the Sleipner CO2 plume: Calibration to seismic data for the uppermost layer and model sensitivity analysis. International Journal of Greenhouse Gas Control, 43, 233-246. 3Zhang, G., Lu, P., Zhang, Y., Wei, X., Zhu, C. (2015). Effects of rate law formulation on predicting CO2 sequestration in sandstone formations. International Journal of Energy Research, 39(14), 1890-1908.

Fate of manufactured nanoparticles in environmental systems

NASA Astrophysics Data System (ADS)

Gelabert, A.; Sivry, Y.; Siron, V.; Akrout, A.; Ferrari, R.; Juillot, F.; Menguy, N.; Benedetti, M. F.

2009-12-01

Because of their specific physico-chemical properties, engineered nanoparticles (NPs) have become largely widespread in numerous industrial fields such as biomedicine, cosmetics, and material sciences. However, their growing use could possibly result in the release of various NPs amounts in environmental settings. Thus, an accurate understanding of their behaviour in natural systems is required, and of first importance is an estimation of their persistence and/or physico-chemical modifications since they can greatly alter their fate and bioavailability in the biogeosphere. The present study focuses on dissolution rate estimations for commercial NPs ZnO and TiO2 in natural waters (i.e. filtered Seine river water and seawater). Both NPs were used uncoated and coated with an organic polymer. Native NPs size and shape were investigated using TEM, and appeared as 20-50 nm spheroids, with an associated specific surface area of 37.5 and 57.6 m2/g for ZnO and TiO2, respectivelly. NPs dissolution rates were determined using both ultrafiltration (UF) and Donnan Membrane Techniques (DMT, [1]). The latter method allows a direct in-situ measurement of the free metal ion concentration only (here Zn2+), while the UF membrane small nominal pore size (approx. 2 nm) results in the separation of small inorganic complexes in addition to free metal ions. After a fast dissolution step reaching 1% of total zinc within the first hour for uncoated ZnO NPs in Seine water, precipitation of new mineral phases occurred with the formation of smithonite and hydrozincite as observed by XRD and TEM and confirmed by thermodynamic calculations (Visual Minteq). Interestingly, the behaviour of the coated ZnO NPs is slightly different since the initial dissolution step takes place during the first 72 hours, to reach up to 10% of the total zinc in our system. However, despite this difference in dissolution kinetics, both systems evolve similarly after 3 days, and they reach a steady state after approximatively 3 months of interaction. Moreover, to assess the influence of external parameters to NPs dissolution kinetics, two different pH (7.8 and 8.3) were tested. The obtained results demonstrate a strong dependence on pH, with the slower dissolution rates associated to the higher pH. XPS measurements performed on native uncoated ZnO NPs evidenced the presence of a layer of Zn(OH)2 which accounts for almost 20% of the total Zn in the NPs. This Zn(OH)2 phase, which is more soluble than ZnO, may control the early dissolution steps of the NPs in our systems. This study constitutes an important step for the understanding of the manufactured NPs fate in natural systems. [1] E. J. M. Temminghoff, A. C. C. Plette, R. Van Eck, W. H. Van Riemsdijk, (2000), Anal. Chim. Acta., 417, 149-157

Determination of the dissolution slowness surface by study of etched shapes I. Morphology of the dissolution slowness surface and theoretical etched shapes

NASA Astrophysics Data System (ADS)

Leblois, T.; Tellier, C. R.

1992-07-01

We propose a theoretical model for the anisotropic etching of crystals, in order to be applied in the micromachining. The originality of the model is due to the introduction of dissolution tensors to express the representative surface of the dissolution slowness. The knowledge of the equation of the slowness surface allows us to determine the trajectories of all the elements which compose the starting surface. It is then possible to construct the final etched shape by numerical simulation. Several examples are given in this paper which show that the final etched shapes are correlated to the extrema of the dissolution slowness. Since the slowness surface must be determined from experiments, emphasis is placed on difficulties encountered when we correlate theory to experiments. Nous avons modélisé le processus de dissolution anisotrope des cristaux en vue d'une application à la simulation des formes obtenues par photolithogravure chimique. La principale originalité de ce modèle tient à l'introduction de tenseurs de dissolution pour exprimer la surface représentative de la lenteur de dissolution. La connaissance de l'équation de la lenteur de dissolution permet de calculer les trajectoires des différents éléments constituant la surface de départ puis de reconstituer par simulation la forme dissoute. Les simulations démontrent que les formes limites des cristaux dissous sont corrélées aux extrema de la lenteur de dissolution. La détermination de la surface de la lenteur se faisant à partir de mesures expérimetales, nous nous sommes efforcés de montrer toutes les difficultés attachées à cette analyse.

The effect of fission-energy Xe ion irradiation on the structural integrity and dissolution of the CeO2 matrix

NASA Astrophysics Data System (ADS)

Popel, A. J.; Le Solliec, S.; Lampronti, G. I.; Day, J.; Petrov, P. K.; Farnan, I.

2017-02-01

This work considers the effect of fission fragment damage on the structural integrity and dissolution of the CeO2 matrix in water, as a simulant for the UO2 matrix of spent nuclear fuel. For this purpose, thin films of CeO2 on Si substrates were produced and irradiated by 92 MeV 129Xe23+ ions to a fluence of 4.8 × 1015 ions/cm2 to simulate fission damage that occurs within nuclear fuels along with bulk CeO2 samples. The irradiated and unirradiated samples were characterised and a static batch dissolution experiment was conducted to study the effect of the induced irradiation damage on dissolution of the CeO2 matrix. Complex restructuring took place in the irradiated films and the irradiated samples showed an increase in the amount of dissolved cerium, as compared to the corresponding unirradiated samples. Secondary phases were also observed on the surface of the irradiated CeO2 films after the dissolution experiment.

Arsenic release and speciation during the oxidative dissolution of arsenopyrite by O2 in the absence and presence of EDTA.

PubMed

Wang, Shaofeng; Jiao, BeiBei; Zhang, Mingmei; Zhang, Guoqing; Wang, Xin; Jia, Yongfeng

2018-03-15

The oxidative decomposition of arsenopyrite is an important source of As in surface environment. This study investigated the oxidative dissolution of arsenopyrite by O 2 and aqueous arsenic transformation at different pHs, dissolved oxygen (DO) contents, and temperatures in the absence and presence of EDTA. The oxidative dissolution was greatly inhibited at neutral and alkaline pH in the absence of EDTA. However, in the presence of EDTA, the oxidative dissolution rate increased linearly from pH 4 to 7. The highest dissolution rate was 3-4 times higher than that at pH 4 and 1-2 orders of magnitude higher than that at pH 7 in the absence of EDTA. This is possibly due to the lack of Fe oxyhydroxides on the surface of arsenopyrite. In the pH range of 7-10, the oxidative dissolution rate decreased linearly, possibly due to the formation of goethite and/or hematite coating. The oxidation of released arsenite (As III ) to arsenate (As V ) took place simultaneously during the oxidative dissolution of arsenopyrite in the presence of dissolved Fe without EDTA, while no obvious aqueous As III oxidation was observed in the presence of EDTA, indicating that aqueous Fe species play an important role in As III oxidation. Copyright © 2017 Elsevier B.V. All rights reserved.

Enhanced ferrihydrite dissolution by a unicellular, planktonic cyanobacterium: a biological contribution to particulate iron bioavailability.

PubMed

Kranzler, Chana; Kessler, Nivi; Keren, Nir; Shaked, Yeala

2016-12-01

Iron (Fe) bioavailability, as determined by its sources, sinks, solubility and speciation, places severe environmental constraints on microorganisms in aquatic environments. Cyanobacteria are a widespread group of aquatic, photosynthetic microorganisms with especially high iron requirements. While iron exists predominantly in particulate form, little is known about its bioavailability to cyanobacteria. Some cyanobacteria secrete iron solubilizing ligands called siderophores, yet many environmentally relevant strains do not have this ability. This work explores the bioavailability of amorphous synthetic Fe-oxides (ferrihydrite) to the non-siderophore producing, unicellular cyanobacterium, Synechocystis sp PCC 6803. Iron uptake assays with 55 ferrihydrite established dissolution as a critical prerequisite for iron transport. Dissolution assays with the iron binding ligand, desferrioxamine B, demonstrated that Synechocystis 6803 enhances ferrihydrite dissolution, exerting siderophore-independent biological influence on ferrihydrite bioavailability. Dissolution mechanisms were studied using a range of experimental conditions; both cell-particle physical proximity and cellular electron flow were shown to be important determinants of bio-dissolution by Synechocystis 6803. Finally, the effects of ferrihydrite stability on bio-dissolution rates and cell physiology were measured, integrating biological and chemical aspects of ferrihydrite bioavailability. Collectively, these findings demonstrate that Synechocystis 6803 actively dissolves ferrihydrite, highlighting a significant biological component to mineral phase iron bioavailability in aquatic environments. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

Controlled release formulations of risperidone antipsychotic drug in novel aliphatic polyester carriers: Data analysis and modelling.

PubMed

Siafaka, Panoraia I; Barmpalexis, Panagiotis; Lazaridou, Maria; Papageorgiou, George Z; Koutris, Efthimios; Karavas, Evangelos; Kostoglou, Margaritis; Bikiaris, Dimitrios N

2015-08-01

In the present study a series of biodegradable and biocompatible poly(ε-caprolactone)/poly(propylene glutarate) (PCL/PPGlu) polymer blends were investigated as controlled release carriers of Risperidone drug (RISP), appropriate for transdermal drug delivery. The PCL/PPGlu carriers were prepared in different weight ratios. Miscibility studies of blends were evaluated through differential scanning calorimetry (DSC) and X-ray diffractometry (XRD). Hydrolysis studies were performed at 37°C using a phosphate buffered saline solution. The prepared blends have been used for the preparation of RISP patches via solvent evaporation method, containing 5, 10 and 15wt% RISP. These formulations were characterized using FT-IR spectroscopy, DSC and WAXD in order to evaluate interactions taking place between polymer matrix and drug, as well as the dispersion and the physical state of the drug inside the polymer matrix. In vitro drug release studies were performed using as dissolution medium phosphate buffered saline simulating body fluids. It was found that in all cases controlled release formulations were obtained, while the RISP release varies due to the properties of the used polymer blend and the different levels of drug loading. Artificial Neural Networks (ANNs) were used for dissolution behaviour modelling showing increased correlation efficacy compared to Multi-Linear-Regression (MLR). Copyright © 2015 Elsevier B.V. All rights reserved.

Replacement processes in crystalline rocks

NASA Astrophysics Data System (ADS)

John, Timm; Putnis, Andrew

2010-05-01

A substantial question in metamorphism is what is the mechanism that dominates the conversion of one mineral assemblage to another in response to a change in the ambient physical and/or chemical conditions. Petrological, microstructural, and isotopic data indicate that aqueous fluids must be involved even in the reequilibration of large-scale systems. Fluid-mineral reactions take place by dissolution - precipitation processes, but converting one solid rock to another requires pervasive, either dominantly advective or diffusive fluid-mediated transport through the entire rock. The generation of reaction-induced porosity and the spatial and temporal coupling of dissolution and precipitation can account for fluid and element transport through rocks and the replacement of one mineral assemblage by another. To determine the mechanism of metamorphic reactions we refer to examples of interfaces and reaction textures which contain both the "before" (precursor) and "after" mineral assemblages - case studies where the process of conversion is frozen in. We will illustrate some aspects of the role of fluids in metamorphic reactions and discuss how reactive fluids can pervasively infiltrate a rock. The examples we will use are focussed on crystalline rocks and include reactions from the lower continental crust, the subducting oceanic crust, and the continental upper crust to show that except at very high-temperature conditions, essentially the same mechanisms are responsible for converting rocks to thermodynamically more stable mineral assemblages for given Pressure-Temperature-fluid composition (P-T-X) conditions.

Performance Enhancement and Side Reactions in Rechargeable Nickel-Iron Batteries with Nanostructured Electrodes.

PubMed

Lei, Danni; Lee, Dong-Chan; Magasinski, Alexandre; Zhao, Enbo; Steingart, Daniel; Yushin, Gleb

2016-01-27

We report for the first time a solution-based synthesis of strongly coupled nanoFe/multiwalled carbon nanotube (MWCNT) and nanoNiO/MWCNT nanocomposite materials for use as anodes and cathodes in rechargeable alkaline Ni-Fe batteries. The produced aqueous batteries demonstrate very high discharge capacities (800 mAh gFe(-1) at 200 mA g(-1) current density), which exceed that of commercial Ni-Fe cells by nearly 1 order of magnitude at comparable current densities. These cells also showed the lack of any "activation", typical in commercial batteries, where low initial capacity slowly increases during the initial 20-50 cycles. The use of a highly conductive MWCNT network allows for high-capacity utilization because of rapid and efficient electron transport to active metal nanoparticles in oxidized [such as Fe(OH)2 or Fe3O4] states. The flexible nature of MWCNTs accommodates significant volume changes taking place during phase transformation accompanying reduction-oxidation reactions in metal electrodes. At the same time, we report and discuss that high surface areas of active nanoparticles lead to multiple side reactions. Dissolution of Fe anodes leads to reprecipitation of significantly larger anode particles. Dissolution of Ni cathodes leads to precipitation of Ni metal on the anode, thus blocking transport of OH(-) anions. The electrolyte molarity and composition have a significant impact on the capacity utilization and cycling stability.

Activity–stability relationship in the surface electrochemistry of the oxygen evolution reaction

DOE PAGES

Chang, Seo Hyoung; Connell, Justin G.; Danilovic, Nemanja; ...

2014-07-25

Understanding the functional links between the stability and reactivity of oxide materials during the oxygen evolution reaction (OER) is one key to enabling a vibrant hydrogen economy capable of competing with fossil fuel-based technologies. In this work, by focusing on the surface chemistry of monometallic Ru oxide in acidic and alkaline environments, we found that the kinetics of the OER are almost entirely controlled by the stability of the Ru surface atoms. The same activity–stability relationship was found for more complex, polycrystalline and single-crystalline SrRuO 3 thin films in alkaline solutions. We propose that the electrochemical transformation of either watermore » (acidic solutions) or hydroxyl ions (alkaline solutions) to di-oxygen molecules takes place at defect sites that are inherently present on every electrode surface. During the OER, surface defects are also created by the corrosion of the Ru ions. The dissolution is triggered by the potential-dependent change in the valence state ( n) of Ru: from stable but inactive Ru 4+ to unstable but active Ru n>4+. We conclude that if the oxide is stable then it is completely inactive for the OER. As a result, a practical consequence is that the best materials for the OER should balance stability and activity in such a way that the dissolution rate of the oxide is neither too fast nor too slow.« less

Modeling Remineralization of Desalinated Water by Micronized Calcite Dissolution.

PubMed

Hasson, David; Fine, Larissa; Sagiv, Abraham; Semiat, Raphael; Shemer, Hilla

2017-11-07

A widely used process for remineralization of desalinated water consists of dissolution of calcite particles by flow of acidified desalinated water through a bed packed with millimeter-size calcite particles. An alternative process consists of calcite dissolution by slurry flow of micron-size calcite particles with acidified desalinated water. The objective of this investigation is to provide theoretical models enabling design of remineralization by calcite slurry dissolution with carbonic and sulfuric acids. Extensive experimental results are presented displaying the effects of acid concentration, slurry feed concentration, and dissolution contact time. The experimental data are shown to be in agreement within less than 10% with theoretical predictions based on the simplifying assumption that the slurry consists of uniform particles represented by the surface mean diameter of the powder. Agreement between theory and experiment is improved by 1-8% by taking into account the powder size distribution. Apart from the practical value of this work in providing a hitherto lacking design tool for a novel technology. The paper has the merit of being among the very few publications providing experimental confirmation to the theory describing reaction kinetics in a segregated flow system.

Mineral replacement reactions and element mobilization

NASA Astrophysics Data System (ADS)

Putnis, Christine V.; Ruiz-Agudo, Encarnacion; King, Helen E.; Hövelmann, Jörn; Renard, François

2016-04-01

When a mineral is out of equilibrium with an aqueous fluid, reactions will take place in an attempt to reach a new equilibrium. Commonly in the Earth dissolution at a mineral-fluid interface initiates a coupled reaction involving dissolution and precipitation (Ruiz-Agudo et al., 2014). This is a ubiquitous reaction during such processes as metamorphism, metasomatism and weathering. When rock-forming minerals such as feldspars, olivine, pyroxenes are in contact with aqueous fluids (typically NaCl-rich) resultant new phases are formed and elements present in the parent mineral are released to the fluid and therefore mobilized for transport elsewhere. This has been shown in a number of systems such as the albitisation of feldspars (Hövelmann et al., 2010) when a Ca-bearing plagioclase is replaced by albite (NaAlSi3O8). However during this reaction not only is Ca released to the fluid but most other minor elements, such as Mg, Pb, rare earth elements amongst others, are almost totally mobilized and removed in solution. This interface-coupled dissolution-precipitation reaction has many implications for the redistributon of elements in the crust of the Earth. It is also of note that albitisation occurs often in areas of high mineralization, such as in the Curnamona Province in S. Australia (Au-Cu and Ag-Pb-Zn deposits) and the Bamble District of S. Norway. Secondly atomic force microscopy (AFM) has been used to image these reactions at a nanoscale, especially at the calcite-fluid interface, such as the formation of apatite from phosphate-bearing solutions, and the sequestration of toxic elements, eg., Se and As. References Ruiz-Agudo E., Putnis C.V., Putnis A. (2014) Coupled dissolution and precipitation at mineral-fluid interfaces. Chemical Geology, 383, 132-146. Putnis C.V. and Ruiz-Agudo E. (2013) The mineral-water interface: where minerals react with the environment. Elements, 9, 177-182. Hövelmann J., Putnis A., Geisler T., Schmidt B.C., Golla-Schindler U. (2009) The replacement of plagioclase feldspars by albite: observations from hydrothermal experiments. Contrib. Min. and Pet. 159, 43-59.

Hydrothermal alteration of deep fractured granite: Effects of dissolution and precipitation

NASA Astrophysics Data System (ADS)

Nishimoto, Shoji; Yoshida, Hidekazu

2010-03-01

This paper investigates the mineralogical effects of hydrothermal alteration at depth in fractures in granite. A fracture accompanied by an alteration halo and filled with clay was found at a depth of 200 m in a drill core through Toki granite, Gifu, central Japan. Microscopic observation, XRD, XRF, EPMA and SXAM investigations revealed that the microcrystalline clays consist of illite, quartz and pyrite and that the halo round the fracture can be subdivided into a phyllic zone adjacent to the fracture, surrounded by a propylitic zone in which Fe-phyllosilicates are present, and a distinctive outer alteration front characterized by plagioclase breakdown. The processes that result in these changes took place in three successive stages: 1) partial dissolution of plagioclase with partial chloritization of biotite; 2) biotite dissolution and precipitation of Fe-phyllosilicate in the dissolution pores; 3) dissolution of K-feldspar and Fe-phyllosilicate, and illite precipitation associated with development of microcracks. These hydrothermal alterations of the granite proceed mainly by a dissolution-precipitation process resulting from the infiltration of hydrothermal fluid along microcracks. Such infiltration causes locally high mobility of Al and increases the ratio of fluid to rock in the alteration halo. These results contribute to an understanding of how granitic rock becomes altered in orogenic fields such as the Japanese island arc.

Viscous fingering with partially miscible fluids

NASA Astrophysics Data System (ADS)

Fu, Xiaojing; Cueto-Felgueroso, Luis; Juanes, Ruben

2017-10-01

Viscous fingering—the fluid-mechanical instability that takes place when a low-viscosity fluid displaces a high-viscosity fluid—has traditionally been studied under either fully miscible or fully immiscible fluid systems. Here we study the impact of partial miscibility (a common occurrence in practice) on the fingering dynamics. Through a careful design of the thermodynamic free energy of a binary mixture, we develop a phase-field model of fluid-fluid displacements in a Hele-Shaw cell for the general case in which the two fluids have limited (but nonzero) solubility into one another. We show, by means of high-resolution numerical simulations, that partial miscibility exerts a powerful control on the degree of fingering: fluid dissolution hinders fingering while fluid exsolution enhances fingering. We also show that, as a result of the interplay between compositional exchange and the hydrodynamic pattern-forming process, stronger fingering promotes the system to approach thermodynamic equilibrium more quickly.

Alternative Manufacturing Concepts for Solid Oral Dosage Forms From Drug Nanosuspensions Using Fluid Dispensing and Forced Drying Technology.

PubMed

Bonhoeffer, Bastian; Kwade, Arno; Juhnke, Michael

2018-03-01

Flexible manufacturing technologies for solid oral dosage forms with a continuous adjustability of the manufactured dose strength are of interest for applications in personalized medicine. This study explored the feasibility of using microvalve technology for the manufacturing of different solid oral dosage form concepts. Hard gelatin capsules filled with excipients, placebo tablets, and polymer films, placed in hard gelatin capsules after drying, were considered as substrates. For each concept, a basic understanding of relevant formulation parameters and their impact on dissolution behavior has been established. Suitable matrix formers, present either on the substrate or directly in the drug nanosuspension, proved to be essential to prevent nanoparticle agglomeration of the drug nanoparticles and to ensure a fast dissolution behavior. Furthermore, convection and radiation drying methods were investigated for the fast drying of drug nanosuspensions dispensed onto polymer films, which were then placed in hard gelatin capsules. Changes in morphology and in drug and matrix former distribution were observed for increasing drying intensity. However, even fast drying times below 1 min could be realized, while maintaining the nanoparticulate drug structure and a good dissolution behavior. Copyright © 2018 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

Experimental observation and modelling of rock - water interaction in a landslide-prone loess area of Hungary

NASA Astrophysics Data System (ADS)

Udvardi, Beatrix; Szabó, Zsuzsanna; Freiler, Ágnes; Kónya, Péter; Jerabek, Csaba; Pálfi, Éva; Kovács, István; Nagy, Péter; Halupka, Gábor

2017-04-01

It is well known that water from precipitation or other sources (e.g. groundwater, river) contributes to the triggering of landslides by means of infiltration into the slope, which causes an increase in the pore pressure and a reduction in the strength of the involved material. The physical failure is commonly coupled with chemical changes in landslides due the fact that soluble components dissolve in the pore water and others precipitate during rock-water interaction. Thus the composition of sediments and water chemistry are used jointly as indicators of the development of landslides. Rock-water interaction, however, takes a long time, and depends on hydrology and geochemistry of the landslide area; therefore, many researchers have focused on numerical simulation and laboratory experiment for setting up a landslide early warning system. Since water chemistry can change over time in landslides due to the seasonal rainfall pattern, groundwater fluctuation and flood events, the intensity of rock-water interaction (e.g. dissolution, precipitation) may also vary. Thus, the physicochemical processes cannot be elucidated precisely without understanding both the solution evolution and the mineral alteration in landslides. From this aspect, field survey, mineralogical (XRD, FTIR, DTG) and chemical measurements (ICP-OES), and geochemical modelling (PHREEQC) were conducted in a landslide-prone loess area along the River Danube (Hungary). Water from the River Danube and three springs were sampled during four field campaigns at Kulcs over a year. Additionally, landslide deposits including sliding surface and secondary precipitations were collected at Kulcs and Dunaújváros. In combination with previous hydrochemical analyses of the area and average rainfall composition of Hungary, it is possible to model the kinetic dissolution and precipitation of minerals during rainfall events and flooding periods of the river. The chemistry of springs shows that the Mg-Ca-HCO3 facies with high electrical conductivity (898 - 1227 µS/cm) may occur due to the dissolution of carbonates and silicates throughout the year. During occasional rainstorms in summer, however, it is found that the pH of the springs slightly increased while their electrical conductivity decreased tenfold. This can be attributed to the rapid infiltration of rainwater through fractures and holes of the loess deposit. Similar process can take place at Dunaújváros, however, larger subsidence happened there than at Kulcs. The secondary precipitations indicate that dissolved components in groundwater precipitate as calcite at the foot of the Dunaújváros landslide. Furthermore, the comparison between model of loess-river water and loess-spring water interaction suggests that the dissolution of dolomite, Ca-montmorillonite and chlorite is stronger during flooding than during low water level of the river. Therefore, frequency and duration of rainstorms and floodings may have deeper consequences for loess landslides.

Discoloration of the wetted surface in the 6.1D dissolver

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rudisill, T.; Mickalonis, J.; Crapse, K.

During a camera inspection of a failed coil in the 6.1D dissolver, an orange discoloration was observed on a portion of the dissolver wall and coils. At the request of H-Canyon Engineering, the inspection video of the dissolver was reviewed by SRNL to assess if the observed condition (a non-uniform, orange-colored substance on internal surfaces) was a result of corrosion. Although the dissolver vessel and coil corrode during dissolution operations, the high acid conditions are not consistent with the formation of ferrous oxides (i.e., orange/rust-colored corrosion products). In a subsequent investigation, SRNL performed dissolution experiments to determine if residues frommore » the nylon bags used for Pu containment could have generated the orange discoloration following dissolution. When small pieces of a nylon bag were placed in boiling 8 M nitric acid solutions containing other components representative of the H-Canyon process, complete dissolution occurred almost immediately. No residues were obtained even when a nylon mass to volume ratio greater than 100 times the 6.1D dissolver value was used. Degradation products from the dissolution of nylon bags are not responsible for the discoloration observed in the dissolver.« less

A Numerical Evaluation on the Viability of Heap Thermophilic Bioleaching of Chalcopyrite

NASA Astrophysics Data System (ADS)

Vilcaez, J.; Suto, K.; Inoue, C.

2007-03-01

The present numerical evaluation explores into the interactions among the many variables governing the mass and heat transport processes that take place in a heap thermophilic bioleaching system. The necessity of using mesophiles together with thermophiles is proved by tracing the activity of both microorganisms individually at each point throughout the heap. The role of key variables such as the fraction of FeS2 per CuFeS2 leached was quantified and its importance highlighted. In this evaluation, the heat transfer process plays the main role because of the heat accumulation required to maintain the heap temperature within the range of 60 °C to 80 °C where thermophilic microorganisms are capable of completing the unfinished dissolution of copper started by mesophilic microorganisms at 30 °C. The evaluation was done taking into consideration: biological activity as function of the temperature in the heap, heat loss due to conduction and advection from the top and bottom of the heap, and mass transfer between the gas and liquid phases as a function of temperature. The exothermic nature of the leaching reactions of CuFeS2 and FeS2 makes the system auto-thermal.

Gallstone dissolution using mono-octanoin infusion through an endoscopically placed nasobiliary catheter.

PubMed

Venu, R P; Geenen, J E; Toouli, J; Hogan, W J; Kozlov, N; Stewart, E T

1982-04-01

Endoscopic sphincterotomy is widely being used for the treatment of common bile duct stones. In a small group of patients the gallstones are large in size and, hence, difficult to be extracted after a successful endoscopic sphincterotomy. We used a constant infusion of mono-octanoin through a nasobiliary catheter in nine such patients. This method was successful in partial or complete dissolution of the stones in 74% of the patients. In the remaining 36% of the patients, the stones were noted to be soft allowing easy extraction by crushing.

Use of glancing angle X-ray powder diffractometry to depth-profile phase transformations during dissolution of indomethacin and theophylline tablets.

PubMed

Debnath, Smita; Predecki, Paul; Suryanarayanan, Raj

2004-01-01

The purpose of this study was (i) to develop glancing angle x-ray powder diffractometry (XRD) as a method for profiling phase transformations as a function of tablet depth; and (ii) to apply this technique to (a) study indomethacin crystallization during dissolution of partially amorphous indomethacin tablets and to (b) profile anhydrate --> hydrate transformations during dissolution of theophylline tablets. The intrinsic dissolution rates of indomethacin and theophylline were determined after different pharmaceutical processing steps. Phase transformations during dissolution were evaluated by various techniques. Transformation in the bulk and on the tablet surface was characterized by conventional XRD and scanning electron microscopy, respectively. Glancing angle XRD enabled us to profile these transformations as a function of depth from the tablet surface. Pharmaceutical processing resulted in a decrease in crystallinity of both indomethacin and theophylline. When placed in contact with the dissolution medium, while indomethacin recrystallized, theophylline anhydrate rapidly converted to theophylline monohydrate. Due to intimate contact with the dissolution medium, drug transformation occurred to a greater extent at or near the tablet surface. Glancing angle XRD enabled us to depth profile the extent of phase transformations as a function of the distance from the tablet surface. The processed sample (both indomethacin and theophylline) transformed more rapidly than did the corresponding unprocessed drug. Several challenges associated with the glancing angle technique, that is, the effects of sorbed water, phase transformations during the experimental timescale, and the influence of phase transformation on penetration depth, were addressed. Increased solubility, and consequently dissolution rate, is one of the potential advantages of metastable phases. This advantage is negated if, during dissolution, the metastable to stable transformation rate > dissolution rate. Glancing angle XRD enabled us to quantify and thereby profile phase transformations as a function of compact depth. The technique has potential utility in monitoring surface reactions, both chemical decomposition and physical transformations, in pharmaceutical systems.

Development of an automated experimental setup for the study of ionic-exchange kinetics. Application to the ionic adsorption, equilibrium attainment and dissolution of apatite compounds.

PubMed

Thomann, J M; Gasser, P; Bres, E F; Voegel, J C; Gramain, P

1990-02-01

An ion-selective electrode and microcomputer-based experimental setup for the study of ionic-exchange kinetics between a powdered solid and the solution is described. The equipment is composed of easily available commercial devices and a data acquisition and regularization computer program is presented. The system, especially developed to investigate the ionic adsorption, equilibrium attainment and dissolution of hard mineralized tissues, provides good reliable results by taking into account the volume changes of the reacting solution and the electrode behaviour under different experimental conditions, and by avoiding carbonation of the solution. A second computer program, using the regularized data and the experimental parameters, calculates the quantities of protons consumed and calcium released in the case of equilibrium attainment and dissolution of apatite-like compounds. Finally, typical examples of ion-exchange and dissolution kinetics under constant pH of enamel and synthetic hydroxyapatite are examined.

Defining level A IVIVC dissolution specifications based on individual in vitro dissolution profiles of a controlled release formulation.

PubMed

González-García, I; García-Arieta, A; Merino-Sanjuan, M; Mangas-Sanjuan, V; Bermejo, M

2018-07-01

Regulatory guidelines recommend that, when a level A IVIVC is established, dissolution specification should be established using averaged data and the maximum difference between AUC and C max between the reference and test formulations cannot be greater than 20%. However, averaging data assumes a loss of information and may reflect a bias in the results. The objective of the current work is to present a new approach to establish dissolution specifications using a new methodology (individual approach) instead of average data (classical approach). Different scenarios were established based on the relationship between in vitro-in vivo dissolution rate coefficient using a level A IVIVC of a controlled release formulation. Then, in order to compare this new approach with the classical one, six additional batches were simulated. For each batch, 1000 simulations of a dissolution assay were run. C max ratios between the reference formulation and each batch were calculated showing that the individual approach was more sensitive and able to detect differences between the reference and the batch formulation compared to the classical approach. Additionally, the new methodology displays wider dissolution specification limits than the classical approach, ensuring that any tablet from the new batch would generate in vivo profiles which its AUC or C max ratio will be out of the 0.8-1.25 range, taking into account the in vitro and in vivo variability of the new batches developed. Copyright © 2018 Elsevier B.V. All rights reserved.

Dissolution of Biogenic and Synthetic UO2 under Varied Reducing Conditions

PubMed Central

ULRICH, KAI – UWE; SINGH, ABHAS; SCHOFIELD, ELEANOR J.; BARGAR, JOHN R.; VEERAMANI, HARISH; SHARP, JONATHAN O.; LATMANI, RIZLAN BERNIER -; GIAMMAR, DANIEL E.

2008-01-01

The chemical stability of biogenic UO2, a nanoparticulate product of environmental bioremediation, may be impacted by the particles’ surface free energy, structural defects, and compositional variability in analogy to abiotic UO2+x (0 ≤ x ≤ 0.25). This study quantifies and compares intrinsic solubility and dissolution rate constants of biogenic nano-UO2 and synthetic bulk UO2.00, taking molecular-scale structure into account. Rates were determined under anoxic conditions as a function of pH and dissolved inorganic carbon in continuous-flow experiments. The dissolution rates of biogenic and synthetic UO2 solids were lowest at near neutral pH and increased with decreasing pH. Similar surface area-normalized rates of biogenic and synthetic UO2 suggest comparable reactive surface site densities. This finding is consistent with the identified structural homology of biogenic UO2 and stoichiometric UO2.00. Compared to carbonate-free anoxic conditions, dissolved inorganic carbon accelerated the dissolution rate of biogenic UO2 by 3 orders of magnitude. This phenomenon suggests continuous surface oxidation of U(IV) to U(VI), with detachment of U(VI) as the rate-determining step in dissolution. Although reducing conditions were maintained throughout the experiments, the UO2 surface can be oxidized by water and radiogenic oxidants. Even in anoxic aquifers, UO2 dissolution may be controlled by surface U(VI) rather than U(IV) phases. PMID:18754482

Physiological Parameters for Oral Delivery and In vitro Testing

PubMed Central

Mudie, Deanna M.; Amidon, Gordon L.; Amidon, Gregory E.

2010-01-01

Pharmaceutical solid oral dosage forms must undergo dissolution in the intestinal fluids of the gastrointestinal tract before they can be absorbed and reach the systemic circulation. Therefore, dissolution is a critical part of the drug-delivery process. The rate and extent of drug dissolution and absorption depend on the characteristics of the active ingredient as well as properties of the dosage form. Just as importantly, characteristics of the physiological environment such as buffer species, pH, bile salts, gastric emptying rate, intestinal motility, and hydrodynamics can significantly impact dissolution and absorption. While significant progress has been made since 1970 when the first compendial dissolution test was introduced (USP Apparatus 1), current dissolution testing does not take full advantage of the extensive physiologic information that is available. For quality control purposes, where the question is one of lot-to-lot consistency in performance, using nonphysiologic test conditions that match drug and dosage form properties with practical dissolution media and apparatus may be appropriate. However, where in vitro – in vivo correlations are desired, it is logical to consider and utilize knowledge of the in vivo condition. This publication critically reviews the literature that is relevant to oral human drug delivery. Physiologically relevant information must serve as a basis for the design of dissolution test methods and systems that are more representative of the human condition. As in vitro methods advance in their physiological relevance, better in vitro - in vivo correlations will be possible. This will, in turn, lead to in vitro systems that can be utilized to more effectively design dosage forms that have improved and more consistent oral bioperformance. PMID:20822152

A model for interpretation of brine-dependent spontaneous imbibition experiments

NASA Astrophysics Data System (ADS)

Evje, S.; Hiorth, A.

2011-12-01

Previous experimental results for spontaneous imbibition experiments in the context of chalk cores have revealed a rather puzzling behavior: the oil recovery curves, both the shape as well as the steady state level which is reached, depend strongly on the brine composition. In particular, it has been demonstrated that Mg,SO42-, and Ca 2+ play a central role in this physico-chemical system. A good theoretical understanding of these experimental results, in terms of mathematical models that can suggest possible explanations of the lab experiments as well as predict behavior not yet tested in the lab, seems to still be lacking. The purpose of this paper is to try to shed light on some important modeling aspects. The model we propose is an extended version of the classical Buckley-Leverett (BL) equation for two-phase spontaneous imbibition where the water saturation equation has been coupled to a system of reaction-diffusion (RD) equations describing water-rock chemistry relevant for chalk core plugs. As far as water-rock chemistry is concerned we focus in this work on the combined effect of transport and dissolution/precipitation of calcite, magnesite, and anhydrite. The line we pursue is to couple changes of the wetting state, expressed in terms of the relative permeability and capillary pressure functions, to the water-rock chemistry behavior. More precisely, we build into the model the mechanism that the rock surface will become more water-wet at the places where dissolution of calcite takes place. In particular, we illustrate and analyze how different compositions of the imbibing brine then lead to different water-rock interaction scenarios which in turn gives qualitative and quantitative differences in the solution of the saturation equation describing spontaneous imbibition. Comparison with relevant experimental behavior is included as well as illustration of some possible interesting and non-trivial characteristic features of the model reflecting the nonlinear coupling mechanisms between the RD model for the water-rock chemistry and the BL equation for the water-oil transport.

Bioglass implant-coating interactions in synthetic physiological fluids with varying degrees of biomimicry

PubMed Central

Popa, AC; Stan, GE; Husanu, MA; Mercioniu, I; Santos, LF; Fernandes, HR; Ferreira, JMF

2017-01-01

Synthetic physiological fluids are currently used as a first in vitro bioactivity assessment for bone grafts. Our understanding about the interactions taking place at the fluid–implant interface has evolved remarkably during the last decade, and does not comply with the traditional International Organization for Standardization/final draft International Standard 23317 protocol in purely inorganic simulated body fluid. The advances in our knowledge point to the need of a true paradigm shift toward testing physiological fluids with enhanced biomimicry and a better understanding of the materials’ structure-dissolution behavior. This will contribute to “upgrade” our vision of entire cascades of events taking place at the implant surfaces upon immersion in the testing media or after implantation. Starting from an osteoinductive bioglass composition with the ability to alleviate the oxidative stress, thin bioglass films with different degrees of polymerization were deposited onto titanium substrates. Their biomineralization activity in simulated body fluid and in a series of new inorganic–organic media with increasing biomimicry that more closely simulated the human intercellular environment was compared. A comprehensive range of advanced characterization tools (scanning electron microscopy; grazing-incidence X-ray diffraction; Fourier-transform infrared, micro-Raman, energy-dispersive, X-ray photoelectron, and surface-enhanced laser desorption/ionization time-of-flight mass spectroscopies; and cytocompatibility assays using mesenchymal stem cells) were used. The information gathered is very useful to biologists, biophysicists, clinicians, and material scientists with special interest in teaching and research. By combining all the analyses, we propose herein a step forward toward establishing an improved unified protocol for testing the bioactivity of implant materials. PMID:28176941

Bioglass implant-coating interactions in synthetic physiological fluids with varying degrees of biomimicry.

PubMed

Popa, A C; Stan, G E; Husanu, M A; Mercioniu, I; Santos, L F; Fernandes, H R; Ferreira, Jmf

2017-01-01

Synthetic physiological fluids are currently used as a first in vitro bioactivity assessment for bone grafts. Our understanding about the interactions taking place at the fluid-implant interface has evolved remarkably during the last decade, and does not comply with the traditional International Organization for Standardization/final draft International Standard 23317 protocol in purely inorganic simulated body fluid. The advances in our knowledge point to the need of a true paradigm shift toward testing physiological fluids with enhanced biomimicry and a better understanding of the materials' structure-dissolution behavior. This will contribute to "upgrade" our vision of entire cascades of events taking place at the implant surfaces upon immersion in the testing media or after implantation. Starting from an osteoinductive bioglass composition with the ability to alleviate the oxidative stress, thin bioglass films with different degrees of polymerization were deposited onto titanium substrates. Their biomineralization activity in simulated body fluid and in a series of new inorganic-organic media with increasing biomimicry that more closely simulated the human intercellular environment was compared. A comprehensive range of advanced characterization tools (scanning electron microscopy; grazing-incidence X-ray diffraction; Fourier-transform infrared, micro-Raman, energy-dispersive, X-ray photoelectron, and surface-enhanced laser desorption/ionization time-of-flight mass spectroscopies; and cytocompatibility assays using mesenchymal stem cells) were used. The information gathered is very useful to biologists, biophysicists, clinicians, and material scientists with special interest in teaching and research. By combining all the analyses, we propose herein a step forward toward establishing an improved unified protocol for testing the bioactivity of implant materials.

Suitability of Palestine salt dome, Anderson Co. , Texas for disposal of high-level radioactive waste

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patchick, P.F.

1980-01-01

The suitability of Palestine salt dome, in Anderson County, Texas, is in serious doubt for a repository to isolate high-level nuclear waste because of abandoned salt brining operations. The random geographic and spatial occurrence of 15 collapse sinks over the dome may prevent safe construction of the necessary surface installations for a repository. The dissolution of salt between the caprock and dome, from at least 15 brine wells up to 500 feet deep, may permit increased rates of salt dissolution long into future geologic time. The subsurface dissolution is occurring at a rate difficult, if not impossible, to assess ormore » to calculate. It cannot be shown that this dissolution rate is insignificant to the integrity of a future repository or to ancillary features. The most recent significant collapse was 36 feet in diameter and took place in 1972. The other collapses ranged from 27 to 105 feet in diameter and from 1.5 to more than 15 feet in depth. ONWI recommends that this dome be removed from consideration as a candidate site.« less

Fused deposition modeling provides solution for magnetic resonance imaging of solid dosage form by advancing design quickly from prototype to final product.

PubMed

Charest, Ken; Mak-Jurkauskas, Melody L; Cinicola, Daniel; Clausen, Andrew M

2013-02-01

The release profile of active pharmaceutical ingredient (API) from its solid dosage form is an important aspect of drug development as it is often used to predict potential drug release characteristics of a product in vivo. In recent years, magnetic resonance imaging has emerged as a nondestructive technique that captures the physical changes of solid dosage forms during dissolution. An example that highlights this application is in the dissolution of modified-release tablet studies. As the tablet dissolves, API disperses in a hydrogel matrix within the tablet, and swelling of the hydrogel layer eventually leads to release of API over time. To achieve optimum signal-to-noise ratios, the tablet should be placed in the most homogeneous region of the magnet and remain there throughout the dissolution experiment. Moreover, the tablet holder must maintain the tablet position without interfering with the natural dissolution process, such as by crushing the softened tablet. This can be difficult because the size, shape, and rigidity of the tablet change during dissolution. This article describes the process, material, and manufacture of a novel device that meets these challenges, with emphasis on how additive manufacturing on a 3D printer enabled an efficient and inexpensive process of design improvements.

Kinetics and mechanism of natural fluorapatite dissolution at 25 °C and pH from 3 to 12

NASA Astrophysics Data System (ADS)

Chaïrat, Claire; Schott, Jacques; Oelkers, Eric H.; Lartigue, Jean-Eric; Harouiya, Najatte

2007-12-01

The dissolution rates of natural fluorapatite (FAP), Ca 10(PO 4) 6F 2, were measured at 25 °C in mixed-flow reactors as a function of pH from 3.0 to 11.7, and aqueous calcium, phosphorus, and fluoride concentration. After an initial preferential Ca and/or F release, stoichiometric Ca, P, and F release was observed. Measured FAP dissolution rates decrease with increasing pH at 3 ⩽ pH ⩽ 7, FAP dissolution rates are pH independent at 7 ⩽ pH ⩽ 10, and FAP dissolution rates again decrease with increasing pH at pH ⩾ 10. Measured FAP dissolution rates are independent of aqueous Ca, P, and F concentration at pH ≈ 3 and pH ≈ 10. Apatite dissolution appears to be initiated by the relatively rapid removal from the near surface of F and the Ca located in the M1 sites, via proton for Ca exchange reactions. Dissolution rates are controlled by the destruction of this F and Ca depleted surface layer. The destruction of this layer is facilitated by the adsorption/penetration of protons into the surface at acidic conditions, and by surface hydration at neutral and basic conditions. Taking into account these two parallel mechanisms, measured fluorapatite forward dissolution rates can be accurately described using r+(molms)=6.61×10-6{aK}/{1+aK+aCa4aF1.4aOH0.6aH6K}+3.69×10-8[tbnd CaOH2+] where ai refers to the activity of the ith aqueous species, [tbnd CaOH2+] denotes the concentration of hydrated calcium sites at the surface of the leached layer (mol m -2), and Kex and Kads stand for the apparent stability constants of the Ca 2+/H + exchange and adsorption/penetration reactions, respectively.

A comparative study of spray-dried and freeze-dried hydrocortisone/polyvinyl pyrrolidone solid dispersions.

PubMed

Dontireddy, Rakesh; Crean, Abina M

2011-10-01

Poor water solubility of new chemical entities (NCEs) is one of the major challenges the pharmaceutical industry currently faces. The purpose of this study was to investigate the feasibility of freeze-drying as an alternative technique to spray-drying to produce solid dispersions of poorly water-soluble drugs. Also investigated was the use of aqueous solvent mixtures in place of pure solvent for the production of solid dispersions. Aqueous solvent systems would reduce the environmental impact of pure organic solvent systems. Spray-dried and freeze-dried hydrocortisone/polyvinyl pyrrolidone solid dispersions exhibited differences in dissolution behavior. Freeze-dried dispersions exhibited faster dissolution rates than the corresponding spray-dried dispersions. Spray-dried systems prepared using both solvent systems (20% v/v and 96% v/v ethanol) displayed similar dissolution performance despite displaying differences in glass transition temperatures (T(g)) and surface areas. All dispersions showed drug/polymer interactions indicated by positive deviations in T(g) from the predicted values calculated using the Couchman-Karasz equation. Fourier transform infrared (FTIR) spectroscopic results confirmed the conversion of crystalline drug to the amorphous in the dispersions. Stability studies were preformed at 40°C and 75% relative humidity to investigate the physical stability of prepared dispersions. Recrystallization was observed after a month and the resultant dispersions were tested for their dissolution performance to compare with the dissolution performance of the dispersions prior to the stability study. The dissolution rate of the freeze-dried dispersions remained higher than both spray-dried dispersions after storage.

Automation of preparation of nonmetallic samples for analysis by atomic absorption and inductively coupled plasma spectrometry

NASA Technical Reports Server (NTRS)

Wittmann, A.; Willay, G.

1986-01-01

For a rapid preparation of solutions intended for analysis by inductively coupled plasma emission spectrometry or atomic absorption spectrometry, an automatic device called Plasmasol was developed. This apparatus used the property of nonwettability of glassy C to fuse the sample in an appropriate flux. The sample-flux mixture is placed in a composite crucible, then heated at high temperature, swirled until full dissolution is achieved, and then poured into a water-filled beaker. After acid addition, dissolution of the melt, and filling to the mark, the solution is ready for analysis. The analytical results obtained, either for oxide samples or for prereduced iron ores show that the solutions prepared with this device are undistinguished from those obtained by manual dissolutions done by acid digestion or by high temperature fusion. Preparation reproducibility and analytical tests illustrate the performance of Plasmasol.

Atomistic simulation of damage accumulation and amorphization in Ge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gomez-Selles, Jose L., E-mail: joseluis.gomezselles@imdea.org; Martin-Bragado, Ignacio; Claverie, Alain

2015-02-07

Damage accumulation and amorphization mechanisms by means of ion implantation in Ge are studied using Kinetic Monte Carlo and Binary Collision Approximation techniques. Such mechanisms are investigated through different stages of damage accumulation taking place in the implantation process: from point defect generation and cluster formation up to full amorphization of Ge layers. We propose a damage concentration amorphization threshold for Ge of ∼1.3 × 10{sup 22} cm{sup −3} which is independent on the implantation conditions. Recombination energy barriers depending on amorphous pocket sizes are provided. This leads to an explanation of the reported distinct behavior of the damage generated by different ions.more » We have also observed that the dissolution of clusters plays an important role for relatively high temperatures and fluences. The model is able to explain and predict different damage generation regimes, amount of generated damage, and extension of amorphous layers in Ge for different ions and implantation conditions.« less

Lipid-based nanocarriers as an alternative for oral delivery of poorly water- soluble drugs: peroral and mucosal routes.

PubMed

Silva, A C; Santos, D; Ferreira, D; Lopes, C M

2012-01-01

The hydrophobic character of most drug molecules and their potential for degradation under the hostile environment of the gastrointestinal tract (GIT) constitutes the main obstacle in the development of a successful oral drug delivery system, since these are related to limitations of bioavailability and absorption processes. However, according to the advantages of the oral route, alternative ways of drug administration in the oral cavity should be considered. In this context, it is essential to have a systematic knowledge of the GIT and the oral cavity components, for a better understanding of the processes taking place during the oral administration of drugs. This review gives an overview of those anatomical and physiological features and elucidates about the current approaches employed to enhance the bioavailability of oral poorly water-soluble drugs. Strategies including the uses of lipid-based nanocarriers, such as nanoemulsions, liposomes and lipid nanoparticles are discussed, considering their ability to improve solubility, dissolution kinetics, absorption and, consequently, biopharmaceutical properties. Some toxicological concerns are also highlighted.

Reduction of liquid metal embrittlement in copper-brazed stainless steel joints

NASA Astrophysics Data System (ADS)

Uhlig, T.; Fedorov, V.; Elßner, M.; Wagner, G.; Weis, S.

2017-03-01

Due to its very good formability and the low raw material cost, pure copper in form of foils is commonly used to braze plate heat exchangers made of stainless steel. The difference in the electrochemical potentials of brazing filler and base material leads to corrosion effects in contact with electrolytes. This may lead to leakages, which decrease the reliability of the heat exchanger during service in potable water. The dissolution of the emerging corrosion products of brazing filler and base material induces the migration of heavy metal ions, such as Cu2+ and Ni2+, into the potable water. The so-called liquid metal embrittlement, which takes place during the brazing process, may intensify the corrosion. The brazing filler infiltrates the stainless steel along the grain boundaries and causes an embrittlement. This paper deals with the determination of the grain boundary erosion dependent on the degree of deformation and heat treatment of the stainless steel AISI 316L.

How does low-molecular-weight polystyrene dissolve: osmotic swelling vs. surface dissolution.

PubMed

Marcon, Valentina; van der Vegt, Nico F A

2014-12-07

By means of multiscale hierarchical modeling we study the real time evolution of low-molecular-weight polystyrene, below the glass transition temperature, in contact with its solvent, toluene. We observe two concurrent phenomena taking place: (1) the solvent diffuses into the polymer by a Case II mechanism, leading to osmotic driven swelling and progressive chain dilution (inside-out mechanism); (2) polymer chains are solvated, detach from the interface and move into the solvent before the film is completely swollen (outside-in mechanism). From our simulations we conclude that, below the entanglement length, a thin swollen layer, also observed in previous experiments, forms almost instantaneously, which allows for the outside-in mechanism to start a few tens of nanoseconds after the polymer-solvent initial contact. After this initial transient time the two mechanisms are concurrent. We furthermore observe that the presence of the solvent significantly enhances the mobility of the polymer chains of the surface layer, but only in the direction parallel to the interface.

Ultrasound assisted combustion synthesis of TiC in Al-Ti-C system.

PubMed

Liu, Zhiwei; Rakita, Milan; Xu, Wilson; Wang, Xiaoming; Han, Qingyou

2015-11-01

This research investigated the effects of high-intensity ultrasound on the combustion synthesis of TiC particles in Al-Ti-C system. The process involved that high-intensity ultrasound was applied on the surface of a compacted Al-Ti-C pellet directly through a Nb probe during the thermal explosion reaction. By comparing with the sample without ultrasonic treatment, it was found that the thermal explosion reaction for synthesizing TiC phase could take place thoroughly in the ultrasonically treated sample. During the process of synthesizing TiC phase, the dissolution of solid graphite particles into the Al-Ti melt, as well as the nucleation and growth of TiC particles could be promoted effectively due to the effects of ultrasound, leading to an enhancement of the formation of TiC particles. Ultrasound assisted combustion synthesis as a simple and effective approach was proposed for synthesizing materials in this research. Copyright © 2015 Elsevier B.V. All rights reserved.

Exhumation rates of high pressure metamorphic rocks in subduction channels: The effect of Rheology

NASA Astrophysics Data System (ADS)

Gerya, T. V.; Stöckhert, B.

2002-04-01

Exhumation of high-pressure metamorphic rocks can take place with typical plate velocities of cm/year. This is consistent with a model of forced flow in a subduction channel. The (micro)structural record of exhumed metamorphic rocks indicates that stresses are generally too low to drive deformation of the bulk material by dislocation creep, according to a power-law rheology. Instead deformation appears to be localized in low-strength shear zones, and is dominated by dissolution precipitation creep or fluid assisted granular flow, implying a Newtonian rheology. 1D modeling shows that the effective rheology of the material in the subduction channel has a significant influence on the rate of exhumation. When the subduction flux either equals or exceeds the return flux, the maximum exhumation rate for Newtonian behavior of the material is at least twice as high (~1/3 of the subduction burial rate) compared to that for power-law creep (~1/6 of the subduction burial rate).

Evidence for Rhythmicity Pacemaker in the Calcification Process of Scleractinian Coral

NASA Astrophysics Data System (ADS)

Gutner-Hoch, Eldad; Schneider, Kenneth; Stolarski, Jaroslaw; Domart-Coulon, Isabelle; Yam, Ruth; Meibom, Anders; Shemesh, Aldo; Levy, Oren

2016-02-01

Reef-building scleractinian (stony) corals are among the most efficient bio-mineralizing organisms in nature. The calcification rate of scleractinian corals oscillates under ambient light conditions, with a cyclic, diurnal pattern. A fundamental question is whether this cyclic pattern is controlled by exogenous signals or by an endogenous ‘biological-clock’ mechanism, or both. To address this problem, we have studied calcification patterns of the Red Sea scleractinian coral Acropora eurystoma with frequent measurements of total alkalinity (AT) under different light conditions. Additionally, skeletal extension and ultra-structure of newly deposited calcium carbonate were elucidated with 86Sr isotope labeling analysis, combined with NanoSIMS ion microprobe and scanning electron microscope imaging. Our results show that the calcification process persists with its cyclic pattern under constant light conditions while dissolution takes place within one day of constant dark conditions, indicating that an intrinsic, light-entrained mechanism may be involved in controlling the calcification process in photosymbiotic corals.

Hydrogeomorphic and ecological control on carbonate dissolution in a patterned landscape in South Florida

NASA Astrophysics Data System (ADS)

Dong, X.; Heffernan, J. B.; Murray, A. B.; Cohen, M. J.; Martin, J. B.

2016-12-01

The evolution of the critical zone both shapes and reflects hydrologic, geochemical, and ecological processes. These interactions are poorly understood in karst landscapes with highly soluble bedrock. In this study, we used the regular-dispersed wetland basins of Big Cypress National Preserve in Florida as a focal case to model the hydrologic, geochemical, and biological mechanisms that affect soil development in karst landscapes. We addressed two questions: (1) What is the minimum timescale for wetland basin development, and (2) do changes in soil depth feed back on dissolution processes and if so by what mechanism? We developed an atmosphere-water-soil model with coupled water-solute transport, incorporating major ion equilibria and kinetic non-equilibrium chemistry, and biogenic acid production via roots distributed through the soil horizon. Under current Florida climate, weathering to a depth of 2 m (a typical depth of wetland basins) would take 4000 6000 yrs, suggesting that landscape pattern could have origins as recent as the most recent stabilization of sea level. Our model further illustrates that interactions between ecological and hydrologic processes influence the rate and depth-dependence of weathering. Absent inundation, dissolution rate decreased exponentially with distance from the bedrock to groundwater table. Inundation generally increased bedrock dissolution, but surface water chemistry and residence time produced complex and non-linear effects on dissolution rate. Biogenic acidity accelerated the dissolution rate by 50 and 1,000 times in inundated and exposed soils. Phase portrait analysis indicated that exponential decreases in bedrock dissolution rate with soil depth could produce stable basin depths. Negative feedback between hydro-period and total basin volume could stabilize the basin radius, but the lesser strength of this mechanism may explain the coalescence of wetland basins observed in some parts of the Big Cypress Landscape.

Tissue dissolution by a novel multisonic ultracleaning system and sodium hypochlorite.

PubMed

Haapasalo, Markus; Wang, Zhejun; Shen, Ya; Curtis, Allison; Patel, Payal; Khakpour, Mehrzad

2014-08-01

This study aimed to evaluate the effectiveness of a novel Multisonic Ultracleaning System (Sonendo Inc, Laguna Hills, CA) in tissue dissolution in comparison with conventional irrigation devices. Pieces of bovine muscle tissue (68 ± 2 mg) were placed in 0.7-mL test tubes (height: 23.60 mm, inner diameter: 6.00 mm, outer diameter: 7.75 mm) and exposed to 5 minutes of irrigation by different devices. Endodontic devices included the Multisonic Ultracleaning System, the Piezon Master 700 (EMS, Dallas, TX) ultrasonic system with agitation, the EndoVac negative-pressure irrigation system (SybronEndo, Orange, CA), and a conventional positive-pressure 27-G irrigation needle at a flow rate of 10 mL/min. The systems were tested with 0.5%, 3%, and 6% sodium hypochlorite (NaOCl) at room temperature (21°C) as well as 40°C. Irrigation with sterile water was used as a control. The mass of tissue specimens was measured and recorded before and after the use of each device, and if the specimen was completely dissolved visually within 5 minutes, the dissolution time was recorded. The rate of tissue dissolution (%/s) was then calculated. The Multisonic Ultracleaning System had the fastest rate of tissue dissolution (P < .05), at 1.0% ± 0.1% per second using 0.5% NaOCl, 2.3% ± 0.9% per second using 3% NaOCl, and 2.9% ± 0.7% per second using 6% NaOCl. This tissue dissolution rate was more than 8 times greater than the second fastest device tested (P < .01), the Piezon Master 700 ultrasonic system, which resulted in a tissue dissolution rate of 0.328% ± 0.002% per second using 6% NaOCl at 40°C. For all irrigation devices tested, the rate of tissue dissolution increased with a higher concentration and temperature of the NaOCl solution. The novel Multisonic Ultracleaning System achieved a significantly faster tissue dissolution rate when compared with the other systems examined in vitro. Copyright © 2014 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Artificial Neural Network Modeling of Pt/C Cathode Degradation in PEM Fuel Cells

NASA Astrophysics Data System (ADS)

Maleki, Erfan; Maleki, Nasim

2016-08-01

Use of computational modeling with a few experiments is considered useful to obtain the best possible result for a final product, without performing expensive and time-consuming experiments. Proton exchange membrane fuel cells (PEMFCs) can produce clean electricity, but still require further study. An oxygen reduction reaction (ORR) takes place at the cathode, and carbon-supported platinum (Pt/C) is commonly used as an electrocatalyst. The harsh conditions during PEMFC operation result in Pt/C degradation. Observation of changes in the Pt/C layer under operating conditions provides a tool to study the lifetime of PEMFCs and overcome durability issues. Recently, artificial neural networks (ANNs) have been used to solve, predict, and optimize a wide range of scientific problems. In this study, several rates of change at the cathode were modeled using ANNs. The backpropagation (BP) algorithm was used to train the network, and experimental data were employed for network training and testing. Two different models are constructed in the present study. First, the potential cycles, temperature, and humidity are used as inputs to predict the resulting Pt dissolution rate of the Pt/C at the cathode as the output parameter of the network. Thereafter, the Pt dissolution rate and Pt ion diffusivity are regarded as inputs to obtain values of the Pt particle radius change rate, Pt mass loss rate, and surface area loss rate as outputs. The networks are finely tuned, and the modeling results agree well with experimental data. The modeled responses of the ANNs are acceptable for this application.

Calorimetric Investigation of Thermal Stability of 304H Cu (Fe-17.7Cr-9.3Ni-2.95Cu-0.91Mn-0.58Nb-0.24Si-0.1C-0.12N-Wt Pct) Austenitic Stainless Steel

NASA Astrophysics Data System (ADS)

Tripathy, Haraprasanna; Subramanian, Raju; Hajra, Raj Narayan; Rai, Arun Kumar; Rengachari, Mythili; Saibaba, Saroja; Jayakumar, Tammana

2016-12-01

The sequence of phase instabilities that take place in a Fe-17.7Cr-9.3Ni-0.58Nb-2.95Cu-0.12N (wt pct) austenitic stainless steel (304H Cu grade) as a function of temperature has been investigated using dynamic calorimetry. The results obtained from this investigation are supplemented by Thermocalc-based equilibrium and Scheil-Gulliver nonequilibrium solidification simulation. The following phase transformation sequence is found upon slow cooling from liquid: L → L + γ → L + γ + MX → γ + MX + δ → γ +MX + M23C6 → γ + MX + M23C6 + Cu. Under slow cooling, the solidification follows austenite + ferrite (AF) mode, which is in accordance with Thermocalc prediction and Scheil-Gulliver simulation. However, higher cooling rates result in skeletal δ-ferrite formation, due to increased segregation tendency of Nb and Cr to segregate to interdendritic liquid. The solidification mode is found to depend on combined Nb + Cu content. Experimental estimates of enthalpy change associated with melting and secondary phase precipitation are also obtained. In addition a semi-quantitative study on the dissolution kinetics of M23C6 type carbides has also been investigated. The standard solution treatment at 1413 K (1140 °C) is found to be adequate to dissolve both Cu and M23C6 into γ-austenite; but the complete dissolution of MX type carbonitrides occurs near the melting region.

ARSENIC SORUCE IDENTIFICATION AT THE GROUND WATER-SURFACE WATER INTERACTION ZONE AT A CONTAMINATED SITE

EPA Science Inventory

One of the challenges in assessing the current impact of the discharge of arsenic contaminated ground water into a surface water body is differentiating the arsenic ground-water flux versus dissolution of in-place contaminated sediments. A field investigation has been carried ou...

Atmospheric Dissolved Iron Depostiion to the Global Oceans: Effects of Oxalate-Promoted Fe Dissolution, Photochemical Redox Cycling, and Dust Mineralogy

NASA Technical Reports Server (NTRS)

Johnson, M. S.; Meskhidze, N.

2013-01-01

Mineral dust deposition is suggested to be a significant atmospheric supply pathway of bioavailable iron (Fe) to Fe-depleted surface oceans. In this study, mineral dust and dissolved Fe (Fed) deposition rates are predicted for March 2009 to February 2010 using the 3-D chemical transport model GEOS-Chem implemented with a comprehensive dust-Fe dissolution scheme. The model simulates Fed production during the atmospheric transport of mineral dust taking into account inorganic and organic (oxalate)-promoted Fe dissolution processes, photochemical redox cycling between ferric (Fe(III)) and ferrous (Fe(II)) forms of Fe, dissolution of three different Fe-containing minerals (hematite, goethite, and aluminosilicates), and detailed mineralogy of windblown dust from the major desert regions. Our calculations suggest that during the yearlong simulation is approximately 0.26 Tg (1 Tg = 1012 g) of Fed was deposited to global oceanic regions. Compared to simulations only taking into account proton-promoted Fe dissolution, the addition of oxalate to the dust-Fe mobilization scheme increased total annual model-predicted Fed deposition to global oceanic regions by approximately 75%. The implementation of Fe(II)/Fe(III) photochemical redox cycling in the model allows for the distinction between different oxidation states of deposited Fed. Our calculations suggest that during the daytime, large fractions of Fed deposited to the global oceans is likely to be in Fe(II) form, while nocturnal fluxes of Fed are largely in Fe(III) form. Model simulations also show that atmospheric fluxes of Fed can be strongly influenced by the mineralogy of Fe-containing compounds. This study shows that Fed deposition to the oceans is controlled by total dust-Fe mass concentrations, mineralogy, the surface area of dust particles, atmospheric chemical composition, cloud processing, and meteorological parameters and exhibits complex and spatiotemporally variable patterns. Our study suggests that the explicit model representation of individual processes leading to Fed production within mineral dust are needed to improve the understanding of the atmospheric Fe cycle, and quantify the effect of dust-Fe on ocean biological productivity, carbon cycle, and climate.

49 CFR 40.221 - Where does an alcohol test take place?

Code of Federal Regulations, 2011 CFR

2011-10-01

... 49 Transportation 1 2011-10-01 2011-10-01 false Where does an alcohol test take place? 40.221... WORKPLACE DRUG AND ALCOHOL TESTING PROGRAMS Testing Sites, Forms, Equipment and Supplies Used in Alcohol Testing § 40.221 Where does an alcohol test take place? (a) A DOT alcohol test must take place at an...

26 CFR 1.924(d)-1 - Requirement that economic processes take place outside the United States.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 26 Internal Revenue 10 2011-04-01 2011-04-01 false Requirement that economic processes take place... Citizens of United States § 1.924(d)-1 Requirement that economic processes take place outside the United... any transaction only if economic processes with respect to such transaction take place outside the...

Dissolution of bedded rock salt: A seismic profile across the active eastern margin of the Hutchinson Salt Member, central Kansas

USGS Publications Warehouse

Anderson, N.L.; Hopkins, J.; Martinez, A.; Knapp, R.W.; Macfarlane, P.A.; Watney, W.L.; Black, R.

1994-01-01

Since late Tertiary, bedded rock salt of the Permian Hutchinson Salt Member has been dissolved more-or-less continuously along its active eastern margin in central Kansas as a result of sustained contact with unconfined, undersaturated groundwater. The associated westward migration of the eastern margin has resulted in surface subsidence and the contemporaneous sedimentation of predominantly valley-filling Quarternary alluvium. In places, these alluvium deposits extend more than 25 km to the east of the present-day edge of the main body of contiguous rock salt. The margin could have receded this distance during the past several million years. From an environmental perspective, the continued leaching of the Hutchinson Salt is a major concern. This predominantly natural dissolution occurs in a broad zone across the central part of the State and adversely affects groundwater and surface-water quality as nonpoint source pollution. Significant surface subsidence occurs as well. Most of these subsidence features have formed gradually; others developed in a more catastrophic manner. The latter in particular pose real threats to roadways, railways, and buried oil and gas pipelines. In an effort to further clarify the process of natural salt dissolution in central Kansas and with the long-term goal of mitigating the adverse environmental affects of such leaching, the Kansas Geological Survey acquired a 4-km seismic profile across the eastern margin of the Hutchinson Salt in the Punkin Center area of central Kansas. The interpretation of these seismic data (and supporting surficial and borehole geologic control) is consistent with several hypotheses regarding the process and mechanisms of dissolution. More specifically these data support the theses that: 1. (1) Dissolution along the active eastern margin of the Hutchinson Salt Member was initiated during late Tertiary. Leaching has resulted in the steady westward migration of the eastern margin, surface subsidence, and the contemporaneous deposition of predominantly valley-filling Quarternary alluvium. 2. (2) Along the active eastern margin, the rock salt has been leached vertically from the top down, and horizontally along the uppermost remnant bedded soluble layer(s). As a result, the eastern margin thickens gradually (up to 90 m) and in a stepwise manner from east to west for distances on the order 5-15 km. 3. (3) In places, the Hutchinson Salt Member has been leached locally along NNE-trending paleoshear zones situated to the west of the present-day edge of the main body of contiguous rock salt. Leaching at these sites initiated when the main dissolution front impinged upon preexisting shear zones. ?? 1994.

Cidaroids spines facing ocean acidification.

PubMed

Dery, Aurélie; Tran, Phuong Dat; Compère, Philippe; Dubois, Philippe

2018-07-01

When facing seawater undersaturated towards calcium carbonates, spines of classical sea urchins (euechinoids) show traces of corrosion although they are covered by an epidermis. Cidaroids (a sister clade of euechinoids) are provided with mature spines devoid of epidermis, which makes them, at first sight, more sensitive to dissolution when facing undersaturated seawater. A recent study showed that spines of a tropical cidaroid are resistant to dissolution due to the high density and the low magnesium concentration of the peculiar external spine layer, the cortex. The biofilm and epibionts covering the spines was also suggested to take part in the spine protection. Here, we investigate the protective role of these factors in different cidaroid species from a broad range of latitude, temperature and depth. The high density of the cortical layer and the cover of biofilm and epibionts were confirmed as key protection against dissolution. The low magnesium concentration of cidaroid spines compared to that of euechinoid ones makes them less soluble in general. Copyright © 2018 Elsevier Ltd. All rights reserved.

Dynamic Pore-scale Reservoir-condition Imaging of Reaction in Carbonates Using Synchrotron Fast Tomography

PubMed Central

Menke, Hannah P.; Andrew, Matthew G.; Vila-Comamala, Joan; Rau, Christoph; Blunt, Martin J.; Bijeljic, Branko

2017-01-01

Underground storage permanence is a major concern for carbon capture and storage. Pumping CO2 into carbonate reservoirs has the potential to dissolve geologic seals and allow CO2 to escape. However, the dissolution processes at reservoir conditions are poorly understood. Thus, time-resolved experiments are needed to observe and predict the nature and rate of dissolution at the pore scale. Synchrotron fast tomography is a method of taking high-resolution time-resolved images of complex pore structures much more quickly than traditional µ-CT. The Diamond Lightsource Pink Beam was used to dynamically image dissolution of limestone in the presence of CO2-saturated brine at reservoir conditions. 100 scans were taken at a 6.1 µm resolution over a period of 2 hours. The images were segmented and the porosity and permeability were measured using image analysis and network extraction. Porosity increased uniformly along the length of the sample; however, the rate of increase of both porosity and permeability slowed at later times. PMID:28287529

Dynamic Pore-scale Reservoir-condition Imaging of Reaction in Carbonates Using Synchrotron Fast Tomography.

PubMed

Menke, Hannah P; Andrew, Matthew G; Vila-Comamala, Joan; Rau, Christoph; Blunt, Martin J; Bijeljic, Branko

2017-02-21

Underground storage permanence is a major concern for carbon capture and storage. Pumping CO2 into carbonate reservoirs has the potential to dissolve geologic seals and allow CO2 to escape. However, the dissolution processes at reservoir conditions are poorly understood. Thus, time-resolved experiments are needed to observe and predict the nature and rate of dissolution at the pore scale. Synchrotron fast tomography is a method of taking high-resolution time-resolved images of complex pore structures much more quickly than traditional µ-CT. The Diamond Lightsource Pink Beam was used to dynamically image dissolution of limestone in the presence of CO2-saturated brine at reservoir conditions. 100 scans were taken at a 6.1 µm resolution over a period of 2 hours. The images were segmented and the porosity and permeability were measured using image analysis and network extraction. Porosity increased uniformly along the length of the sample; however, the rate of increase of both porosity and permeability slowed at later times.

An immersed boundary-lattice Boltzmann model for biofilm growth and its impact on the NAPL dissolution in porous media

NASA Astrophysics Data System (ADS)

Benioug, M.; Yang, X.

2017-12-01

The evolution of microbial phase within porous medium is a complex process that involves growth, mortality, and detachment of the biofilm or attachment of moving cells. A better understanding of the interactions among biofilm growth, flow and solute transport and a rigorous modeling of such processes are essential for a more accurate prediction of the fate of pollutants (e.g. NAPLs) in soils. However, very few works are focused on the study of such processes in multiphase conditions (oil/water/biofilm systems). Our proposed numerical model takes into account the mechanisms that control bacterial growth and its impact on the dissolution of NAPL. An Immersed Boundary - Lattice Boltzmann Model (IB-LBM) is developed for flow simulations along with non-boundary conforming finite volume methods (volume of fluid and reconstruction methods) used for reactive solute transport. A sophisticated cellular automaton model is also developed to describe the spatial distribution of bacteria. A series of numerical simulations have been performed on complex porous media. A quantitative diagram representing the transitions between the different biofilm growth patterns is proposed. The bioenhanced dissolution of NAPL in the presence of biofilms is simulated at the pore scale. A uniform dissolution approach has been adopted to describe the temporal evolution of trapped blobs. Our simulations focus on the dissolution of NAPL in abiotic and biotic conditions. In abiotic conditions, we analyze the effect of the spatial distribution of NAPL blobs on the dissolution rate under different assumptions (blobs size, Péclet number). In biotic conditions, different conditions are also considered (spatial distribution, reaction kinetics, toxicity) and analyzed. The simulated results are consistent with those obtained from the literature.

Porosity developed during mineral replacement reactions: implications for fluid flux in the Earth

NASA Astrophysics Data System (ADS)

Putnis, Christine V.; Trindade Pedrosa, Elisabete; Hövelmann, Jörn; Renard, François; Ruiz-Agudo, Encarnacion

2017-04-01

Aqueous fluids, that are ubiquitous in the crust of the Earth, will move through possible pathways in rocks. Rocks characteristically have low permeability but fractures can provide fast fluid channels. Mineral grain boundaries also present easy fluid pathways. However, porosity within minerals forms when a mineral is out of equilibrium with an aqueous fluid and reactions take place in an attempt to reach a new equilibrium. Commonly, dissolution at a mineral-fluid interface initiates one or several coupled reactions involving dissolution and precipitation (Putnis C.V. and Ruiz-Agudo E., 2013; Ruiz-Agudo et al., 2014). In pseudomorphic volume-deficit reactions, a new phase forms while porosity is created, and thereby reactive fluid flow through the originally solid mineral is enhanced. These coupled dissolution-replacement reactions therefore will constrain the flux of material carried by the fluid. These reactions are common during such processes as metamorphism, metasomatism, and weathering. When rock-forming minerals such as feldspars, olivine, pyroxenes and carbonates are in contact with aqueous fluids (typically NaCl-rich) porosity is formed during the interfacial replacement reactions. Elements present in the parent mineral are released to the fluid and therefore mobilized for transport elsewhere. Porosity formation has been shown in a number of systems, such as during the albitisation of feldspars (Hövelmann et al., 2009) and the replacement of carbonates by apatite phases (Pedrosa et al., 2016). Some of these examples will be presented as well as examples from atomic force microscopy (AFM) experiments used to image these reactions at a nanoscale, especially at the calcite-fluid interface, when new phases can be directly observed forming. This mechanism has also been shown as a means of carbon and phosphorus sequestration and for the removal of toxic elements from superficial waters, such as Se and As. References Ruiz-Agudo E., Putnis C.V., Putnis A. (2014) Coupled dissolution and precipitation at mineral-fluid interfaces. Chem. Geol., 383, 132-146. Putnis C.V. and Ruiz-Agudo E. (2013) The mineral-water interface: where minerals react with the environment. Elements, 9, 177-182. Hövelmann J., Putnis A., Geisler T., Schmidt B.C., Golla-Schindler U. (2009) The replacement of plagioclase feldspars by albite: observations from hydrothermal experiments. Contrib. Min. and Pet. 159, 43-59. Pedrosa E.T., Putnis C.V., Putnis A. (2016) The pseudomorphic replacement of marble by apatite: the role of fluid composition. Chem. Geol., 425, 1-11.

40 CFR 264.256 - Special requirements for ignitable or reactive waste.

Code of Federal Regulations, 2010 CFR

2010-07-01

..., AND DISPOSAL FACILITIES Waste Piles § 264.256 Special requirements for ignitable or reactive waste. Ignitable or reactive waste must not be placed in a waste pile unless the waste and waste pile satisfy all... immediately after placement in the pile so that: (1) The resulting waste, mixture, or dissolution of material...

Electrochemical Deburring

NASA Technical Reports Server (NTRS)

Burley, R. K.

1983-01-01

Electrochemical deburring removes burrs from assembled injector tubes. Since process uses liquid anodic dissolution in liquid electrolyte to proide deburring action, smoothes surfaces and edges in otherwise inaccessible areas. Tool consists of sleeve that contains metallic ring cathode. Sleeve is placed over tube, and electrolytic solution is forced to flow between tube and sleeve. The workpiece serves an anode.

DISSOLUTION OF ZIRCONIUM-CONTAINING FUEL ELEMENTS

DOEpatents

Horn, F.L.

1961-12-12

Uranium is recovered from spent uranium fuel elements containing or clad with zirconium. These fuel elements are placed in an anhydrous solution of hydrogen fluoride and nitrogen dioxide. Within this system uranium forms a soluble complex and zirconium forms an insoluble complex. The uranium can then be separated, treated, and removed from solution as uranium hexafluoride. (AEC)

Nanoparticle toxicity by the gastrointestinal route: evidence and knowledge gaps

PubMed Central

Bergin, Ingrid L.; Witzmann, Frank A.

2013-01-01

The increasing interest in nanoparticles for advanced technologies, consumer products, and biomedical applications has led to great excitement about potential benefits but also concern over the potential for adverse human health effects. The gastrointestinal tract represents a likely route of entry for many nanomaterials, both directly through intentional ingestion or indirectly via nanoparticle dissolution from food containers or by secondary ingestion of inhaled particles. Additionally, increased utilisation of nanoparticles may lead to increased environmental contamination and unintentional ingestion via water, food animals, or fish. The gastrointestinal tract is a site of complex, symbiotic interactions between host cells and the resident microbiome. Accordingly, evaluation of nanoparticles must take into consideration not only absorption and extraintestinal organ accumulation but also the potential for altered gut microbes and the effects of this perturbation on the host. The existing literature was evaluated for evidence of toxicity based on these considerations. Focus was placed on three categories of nanomaterials: nanometals and metal oxides, carbon-based nanoparticles, and polymer/dendrimers with emphasis on those particles of greatest relevance to gastrointestinal exposures. PMID:24228068

Use of bauxite as packing material in steam injection wells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scoglio, J.; Joubert, G.; Gallardo, B.

1995-12-31

Cyclic steam injection, also known as steam soak, has proven to be the most efficient method for producing heavy crude oil and bitumen from unconsolidated sands. The application of steam injection may, however, generate sand production, causing, among other things, a decrease in production. The gravel pack technique is the most efficient way to prevent fines production from cold producing wells. But, once they are steam stimulated, a dissolution of quartz containing gravel material takes place reducing greatly the packing permeability and eventually sand production. Different types of packing material have been used to avoid sand production after cyclic steammore » injection, such as gravel, ceramics, bauxite, coated resin, and American sand. This paper presents the results of field test, using sinterized bauxite as a packing material, carried out in Venezuela`s heavy oil operations as a part of a comprehensive program aimed at increasing the packing durability and reducing sand production. This paper also verify the results of laboratory tests in which Bauxite was found to be less soluble than other packing material when steam injected.« less

Manufacturing of Dysprosium-Iron Alloys by Electrolysis in Fluoride-Based Electrolytes: Oxide Solubility Determinations

NASA Astrophysics Data System (ADS)

Martinez, Ana Maria; Støre, Anne; Osen, Karen Sende

2018-04-01

Electrolytic production of light rare earth elements and alloys takes place in a fluoride-based electrolyte using rare earth oxides as raw material. The optimization of this method, mainly in terms of the energy efficiency and environmental impact control, is rather challenging. Anode effects, evolution of fluorine-containing compounds, and side cathode reactions could largely be minimized by a good control of the amount of rare earth oxide species dissolved in the fluoride-based electrolyte and their dissolution rate. The oxide content of the fluoride melts REF3-LiF (RE = Nd, Dy) at different compositions and temperatures were experimentally determined by carbothermal analysis of melt samples. The highest solubility values of oxide species, added as Dy2O3 and Dy2(CO3)3, were obtained to be of ca. 3 wt pct (expressed as Dy2O3) in the case of the equimolar DyF3-LiF melt at 1323 K (1050 °C). The oxide saturation values increased with the amount of REF3 present in the molten bath and the working temperature.

Kinetics of brucite dissolution at 25°C in the presence of organic and inorganic ligands and divalent metals

NASA Astrophysics Data System (ADS)

Pokrovsky, Oleg S.; Schott, Jacques; Castillo, Alain

2005-02-01

Brucite (Mg(OH) 2) dissolution rate was measured at 25°C in a mixed-flow reactor at various pH (5 to 11) and ionic strengths (0.01 to 0.03 M) as a function of the concentration of 15 organic and 5 inorganic ligands and 8 divalent metals. At neutral and weakly alkaline pH, the dissolution is promoted by the addition of the following ligands ranked by decreasing effectiveness: EDTA ≥ H 2PO 4- > catechol ≥ HCO 3- > ascorbate > citrate > oxalate > acetate ˜ lactate and it is inhibited by boric acid. At pH >10.5, it decreases in the presence of PO 43-, CO 32-, F -, oxine, salicylate, lactate, acetate, 4-hydroxybenzoate, SO 42- and B(OH) 4- with orthophosphate and borate being the strongest and the weakest inhibitor, respectively. Xylose (up to 0.1 M), glycine (up to 0.05 M), formate (up to 0.3 M) and fulvic and humic acids (up to 40 mg/L DOC) have no effect on brucite dissolution kinetics. Fluorine inhibits dissolution both in neutral and alkaline solutions. From F sorption experiments in batch and flow-through reactors and the analysis of reacted surfaces using X-ray Photoelectron Spectroscopy (XPS), it is shown that fluorine adsorption is followed by its incorporation in brucite lattice likely via isomorphic substitution with OH. The effect of eight divalent metals (Sr, Ba, Ca, Pb, Mn, Fe, Co and Ni) studied at pH 4.9 and 0.01 M concentration revealed brucite dissolution rates to be correlated with the water molecule exchange rates in the first hydration sphere of the corresponding cation. The effect of investigated ligands on brucite dissolution rate can be modelled within the framework of the surface coordination approach taking into account the adsorption of ligands on dissolution-active sites and the molecular structure of the surface complexes they form. The higher the value of the ligand sorption constant, the stronger will be its catalyzing or inhibiting effect. As for Fe and Al oxides, bi- or multidentate mononuclear surface complexes, that labilize Mg-O bonds and water coordination to Mg atoms at the surface, enhance brucite dissolution whereas bi- or polynuclear surface complexes tend to inhibit dissolution by bridging two or more metal centers and extending the cross-linking at the solid surface. Overall, results of this study demonstrate that very high concentrations of organic ligands (0.01-0.1 M) are necessary to enhance or inhibit brucite dissolution. As a result, the effect of extracellular organic products on the weathering rate of Mg-bearing minerals is expected to be weak.

How to Justify Teaching False Science

ERIC Educational Resources Information Center

Slater, Matthew H.

2008-01-01

We often knowingly teach false science. Such a practice conflicts with a prima facie pedagogical value placed on teaching only what is true. I argue that only a partial dissolution of the conflict is possible: the proper aim of instruction in science is not to provide an armory of facts about what things the world contains, how they interact, and…

Me After You: Partner Influence and Individual Effort Predict Rejection of Self-Aspects and Self-Concept Clarity After Relationship Dissolution.

PubMed

Slotter, Erica B; Emery, Lydia F; Luchies, Laura B

2014-07-01

Individuals in ongoing romantic relationships incorporate attributes from their partner into their own self-concepts. However, little research has investigated what happens to these attributes should the relationship end. Across three studies, the present research sought to examine factors that predicted whether individuals retain or reject attributes from their self-concept that they initially gained during a relationship. We predicted that individuals would be more likely to reject attributes from their self post-dissolution if their ex-partner was influential in them adding those attributes to the self in the first place. However, we expected this effect to be moderated such that individuals who exerted greater, versus lesser, effort in maintaining relevant attributes would retain them as part of the self, regardless of whether the attribute originated from the partner. In addition, in two of our three studies, we explored the roles of partner influence, effort, and attribute rejection on individuals' post-dissolution self-concept clarity. © 2014 by the Society for Personality and Social Psychology, Inc.

A New Experimental Design to Study the Kinetics of Solid Dissolution into Liquids at Elevated Temperature

NASA Astrophysics Data System (ADS)

Wang, Huijun; White, Jesse F.; Sichen, Du

2018-04-01

A new method was developed to study the dissolution of a solid cylinder in a liquid under forced convection at elevated temperature. In the new design, a rotating cylinder was placed concentrically in a crucible fabricated by boring four holes into a blank material for creating an internal volume with a quatrefoil profile. A strong flow in the radial direction in the liquid was created, which was evidently shown by computational fluid dynamic (CFD) calculations and experiments at both room temperature and elevated temperature. The new setup was able to freeze the sample as it was at experimental temperature, particularly the interface between the solid and the liquid. This freezing was necessary to obtain reliable information for understanding the reaction mechanism. This was exemplified by the study of dissolution of a refractory in liquid slag. The absence of flow in the radial direction in the traditional setup using a symmetrical cylinder was also discussed. The differences in the findings by past investigators using the symmetrical cylinder are most likely due to the extent of misalignment of the cylinder in the containment vessel.

Laboratory Experiments and Modeling of Pooled NAPL Dissolution in Porous Media

NASA Astrophysics Data System (ADS)

Copty, N. K.; Sarikurt, D. A.; Gokdemir, C.

2017-12-01

The dissolution of non-aqueous phase liquids (NAPLs) entrapped in porous media is commonly modeled at the continuum scale as the product of a chemical potential and an interphase mass transfer coefficient, the latter expressed in terms of Sherwood correlations that are related to flow and porous media properties. Because of the lack of precise estimates of the interface area separating the NAPL and aqueous phase, numerous studies have lumped the interfacial area into the interphase mass transfer coefficient. In this paper controlled dissolution experiments from a pooled NAPL were conducted. The immobile NAPL mass is placed at the bottom of a flow cell filled with porous media with water flowing on top. Effluent aqueous phase concentrations were measured for a wide range of aqueous phase velocities and for two types of porous media. To interpret the experimental results, a two-dimensional pore network model of the NAPL dissolution was developed. The well-defined geometry of the NAPL-water interface and the observed effluent concentrations were used to compute best-fit mass transfer coefficients and non-lumped Sherwood correlations. Comparing the concentrations predicted with the pore network model to simple previously used one-dimensional analytic solutions indicates that the analytic model which ignores the transverse dispersion can lead to over-estimation of the mass transfer coefficient. The predicted Sherwood correlations are also compared to previously published data and implications on NAPL remediation strategies are discussed.

Bioavailability of indomethacin-saccharin cocrystals.

PubMed

Jung, Min-Sook; Kim, Jeong-Soo; Kim, Min-Soo; Alhalaweh, Amjad; Cho, Wonkyung; Hwang, Sung-Joo; Velaga, Sitaram P

2010-11-01

Pharmaceutical cocrystals are new solid forms with physicochemical properties that appear promising for drug product development. However, the in-vivo bioavailability of cocrystals has rarely been addressed. The cocrystal of indomethacin (IND), a Biopharmaceutical Classification System class II drug, with saccharin (SAC) has been shown to have higher solubility than IND at all pH. In this study, we aimed to evaluate the in-vitro dissolution and in-vivo bioavailability of IND-SAC cocrystals in comparison with IND in a physical mixture and the marketed product Indomee. Scale-up of the cocrystals was undertaken using cooling batch crystallisation without seeding. The chemical and physical purity of the up-scaled material was verified using high-performance liquid chromatography, differential scanning calorimetry and powder X-ray diffraction. The IND-SAC cocrystals and IND plus SAC were mixed with lactose and the formulations were placed into gelatin capsules. In-vitro dissolution studies were then performed using the rotating basket dissolution method. The intrinsic dissolution rate of IND and IND-SAC cocrystals was also determined. Finally, a bioavailability study for the formulations was conducted in beagle dogs. The plasma samples were analysed using high-performance liquid chromatography and the pharmacokinetic data were analysed using standard methodologies.   The bulk cocrystals (i.e. scaled-up material) were chemically and physically pure. The in-vitro dissolution rate of the cocrystals was higher than that of IND and similar to that of Indomee at pH 7.4 and pH 1.2. The in-vivo bioavailability of the IND-SAC cocrystals in dogs was significantly higher (ANOVA, P<0.05) than that of IND but not significantly different from Indomee (ANOVA, P>0.05). The study indicates that the improved aqueous solubility of the cocrystals leads to improved bioavailability of IND. Thus, the cocrystals are a viable alternative solid form that can improve the dissolution rate and bioavailability of poorly soluble drugs. © 2010 The Authors. JPP © 2010 Royal Pharmaceutical Society of Great Britain.

Dissolution of Si in Molten Al with Gas Injection

NASA Astrophysics Data System (ADS)

Seyed Ahmadi, Mehran

Silicon is an essential component of many aluminum alloys, as it imparts a range of desirable characteristics. However, there are considerable practical difficulties in dissolving solid Si in molten Al, because the dissolution process is slow, resulting in material and energy losses. It is thus essential to examine Si dissolution in molten Al, to identify means of accelerating the process. This thesis presents an experimental study of the effect of Si purity, bath temperature, fluid flow conditions, and gas stirring on the dissolution of Si in molten Al, plus the results of physical and numerical modeling of the flow to corroborate the experimental results. The dissolution experiments were conducted in a revolving liquid metal tank to generate a bulk velocity, and gas was introduced into the melt using top lance injection. Cylindrical Si specimens were immersed into molten Al for fixed durations, and upon removal the dissolved Si was measured. The shape and trajectory of injected bubbles were examined by means of auxiliary water experiments and video recordings of the molten Al free surface. The gas-agitated liquid was simulated using the commercial software FLOW-3D. The simulation results provide insights into bubble dynamics and offer estimates of the fluctuating velocities within the Al bath. The experimental results indicate that the dissolution rate of Si increases in tandem with the melt temperature and bulk velocity. A higher bath temperature increases the solubility of Si at the solid/liquid interface, resulting in a greater driving force for mass transfer, and a higher liquid velocity decreases the resistance to mass transfer via a thinner mass boundary layer. Impurities (with lower diffusion coefficients) in the form of inclusions obstruct the dissolution of the Si main matrix. Finally, dissolution rate enhancement was observed by gas agitation. It is postulated that the bubble-induced fluctuating velocities disturb the mass boundary layer, which increases the mass transfer rate. Correlations derived for mass transfer from solids in liquids under various operating conditions were applied to the Al--Si system. A new correlation for combined natural and forced convection mass transfer from vertical cylinders in cross flow is presented, and a modification is proposed to take into account free stream turbulence in a correlation for forced convection mass transfer from vertical cylinders in cross flow.

Effects of sinker shapes on dissolution profiles.

PubMed

Soltero, R A; Hoover, J M; Jones, T F; Standish, M

1989-01-01

In dissolution testing, according to the U.S. Pharmacopeia, a nonreactive stainless steel wire helix is typically used to sink dosage forms that would otherwise float. The objective of this investigation was to determine if other sinker shapes will influence the rate, extent, or variability of dissolution. Criteria for the optimal sinker were defined. Various new sinker designs were fabricated, tested, and classified. Four classes of sinker shapes were defined: longitudinal, lateral, screen enclosures, and internal weights. Longitudinal sinkers contact the dosage forms on the long axis. Lateral sinkers either wrap around or contact capsule dosage forms in the middle, such as the line where the top and bottom halves of a capsule shell come together. Screen enclosures are of two types: either a wire cage, which holds the entire capsule, or a circular piece of wire screen placed on top of the capsule. Internal weights consist of two steel ball bearings, one inserted into each end of the capsule. The investigation consisted of four studies: (1) visual observation of the dissolution performance using 12 different sinkers; (2) the effect on drug release from nine classified sinkers on two different capsule formulations; (3) side-by-side comparison between the selected optimal longitudinal U clip and the wire helix lateral type sinkers; and (4) hydrodynamic effects caused by the use of the longitudinal U clip and the wire helix lateral type sinkers in the absence of capsule shells. We concluded that capsules sunk with either of the two longitudinal sinkers, the U clip or the paper clip, have faster, more complete dissolution and less variable results than did lateral type sinkers.(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue dissolution by sodium hypochlorite: effect of concentration, temperature, agitation, and surfactant.

PubMed

Stojicic, Sonja; Zivkovic, Slavoljub; Qian, Wei; Zhang, Hui; Haapasalo, Markus

2010-09-01

Sodium hypochlorite is the most commonly used endodontic irrigant because of its antimicrobial and tissue-dissolving activity. The aim of this study was to evaluate and compare the effects of concentration, temperature, and agitation on the tissue-dissolving ability of sodium hypochlorite. In addition, a hypochlorite product with added surface active agent was compared with conventional hypochlorite solutions. Three sodium hypochlorite solutions from two different manufacturers in concentrations of 1%, 2%, 4%, and 5.8% were tested at room temperature, 37 degrees C, and 45 degrees C with and without agitation by ultrasonic and sonic energy and pipetting. Distilled and sterilized tap water was used as controls. Pieces of bovine muscle tissue (68 +/- 3 mg) were placed in 10 mL of each solution for five minutes. In selected samples, agitation was performed for one, two, or four 15-second periods per each minute. The tissue specimens were weighed before and after treatment, and the percentage of weight loss was calculated. The contact angle on dentin of the three solutions at concentrations of 1% and 5.8% was measured. Weight loss (dissolution) of the tissue increased almost linearly with the concentration of sodium hypochlorite. Higher temperatures and agitation considerably enhanced the efficacy of sodium hypochlorite. The effect of agitation on tissue dissolution was greater than that of temperature; continuous agitation resulted in the fastest tissue dissolution. Hypochlorite with added surface active agent had the lowest contact angle on dentin and was most effective in tissue dissolution in all experimental situations. Optimizing the concentration, temperature, flow, and surface tension can improve the tissue-dissolving effectiveness of hypochlorite even 50-fold. Copyright 2010 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Comparative evaluation of human pulp tissue dissolution by different concentrations of chlorine dioxide, calcium hypochlorite and sodium hypochlorite: An in vitro study

PubMed Central

Taneja, Sonali; Mishra, Neha; Malik, Shubhra

2014-01-01

Introduction: Irrigation plays an indispensable role in removal of tissue remnants and debris from the complicated root canal system. This study compared the human pulp tissue dissolution by different concentrations of chlorine dioxide, calcium hypochlorite and sodium hypochlorite. Materials and Methods: Pulp tissue was standardized to a weight of 9 mg for each sample. In all,60 samples obtained were divided into 6 groups according to the irrigating solution used- 2.5% sodium hypochlorite (NaOCl), 5.25% NaOCl, 5% calcium hypochlorite (Ca(OCl)2), 10% Ca(OCl)2, 5%chlorine dioxide (ClO2) and 13% ClO2. Pulp tissue was placed in each test tube carrying irrigants of measured volume (5ml) according to their specified subgroup time interval: 30 minutes (Subgroup A) and 60 minutes (Subgroup B). The solution from each sample test tube was filtered and was left for drying overnight. The residual weight was calculated by filtration method. Results: Mean tissue dissolution increases with increase in time period. Results showed 5.25% NaOCl to be most effective at both time intervals followed by 2.5% NaOCl at 60 minutes, 10%Ca(OCl)2 and 13% ClO2 at 60 minutes. Least amount of tissue dissolving ability was demonstrated by 5% Ca(OCl)2 and 5% ClO2 at 30 minutes. Distilled water showed no pulp tissue dissolution. Conclusion: Withinthe limitations of the study, NaOCl most efficiently dissolved the pulp tissue at both concentrations and at both time intervals. Mean tissue dissolution by Ca(OCl)2 and ClO2 gradually increased with time and with their increase in concentration. PMID:25506141

Tissue dissolution ability of sodium hypochlorite activated by photon-initiated photoacoustic streaming technique.

PubMed

Guneser, Mehmet Burak; Arslan, Dilara; Usumez, Aslihan

2015-05-01

The aim of this study was to evaluate the effect of the photon-initiated photoacoustic streaming (PIPS) technique on the pulp tissue-dissolving capacity of sodium hypochlorite (NaOCl) and compare it with the EndoActivator System (Dentsply Tulsa Dental Specialties, Tulsa, OK) and the Er:YAG laser with an endodontic fiber tip. Bovine pulp tissue samples (45 ± 15 mg) and dentin powder (10 mg) were placed in 1.5-mL Eppendorf tubes with 1 mL 5.25% NaOCl (Wizard; Rehber Kimya, Istanbul, Turkey) or distilled water (control) for 5 minutes with activation by the EndoActivator System, the Er:YAG laser with an endodontic fiber tip, and the PIPS technique. Nonactivated NaOCl served as the positive control. All testing procedures were performed at room temperature. The tissue samples were weighed before and after treatment, and the percentage of weight loss was calculated. The differences were statistically analyzed. The highest rate of tissue dissolution was observed in the NaOCl + Er:YAG group (P < .05). The NaOCl + PIPS group dissolved more bovine pulp tissue than the nonactivated NaOCl group (P < .05). There was no statistically significant difference between the rates of tissue dissolution of the NaOCl + EA and the nonactivated NaOCl groups (P > .05). NaOCl activation with the Er:YAG laser with an endodontic fiber tip was the most effective in bovine pulp tissue dissolution. The PIPS technique also promoted superior tissue-dissolving effects when compared with no activation. However, the EndoActivator System had no direct effect on tissue dissolution. Copyright © 2015 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Low temperature dissolution creep induced B-type olivine fabric during serpentinization and deformation in mantle wedge

NASA Astrophysics Data System (ADS)

Liu, W.; Zhang, J.

2017-12-01

The B-type olivine fabric (i.e., the [010]ol axes subnormal to foliation and the [001]ol axes subparallel to the lineation) has been regarded as an important olivine fabric for interpreting global trench-parallel S-wave polarization in fore-arc regions. However, strong serpentinization and cold temperature environment in the mantle wedge should inhibit development of the B-type olivine fabric that requires high temperature to activate solid-state plastic deformation. Here we report fabrics of olivine and antigorite generated at low temperatures (300-370 oC) during serpentinization in a fossil mantle wedge of the Val Malenco area, Central Alps. Olivine in the serpentine matrix develops a pronounced B-type fabric, while antigorite in the same matrix displays a strong crystallographic orientation (CPO) with the (001) and the [010] subparallel to foliation and lineation, respectively. The following evidence leads to the conclusion that the B-type olivine fabric is resulted from dissolution creep assisted by grain boundaries sliding (GBS) and grain rotation, rather than solid-state plastic deformation: (1) serpentinization took place at low temperatures and a fluid-enriched environment, ideal for dissolution-precipitation creep; (2) the voids and zigzag boundaries along the interface between antigorite and olivine suggest a fluid dissolution reaction; (3) the primary coarse olivine develops a nearly random fabric, indicating the B-type fabrics in the fine-grained olivine can't be inherited fabrics. These results document for the first time the B-type olivine CPO formed by dissolution creep at low temperatures during serpentinization and provide a mechanism to reconcile petrofabric observations with geophysical observations of trench parallel fast S-wave seismic anisotropy in fore-arc mantle wedge regions.

B-type olivine fabric induced by low temperature dissolution creep during serpentinization and deformation in mantle wedge

NASA Astrophysics Data System (ADS)

Liu, Wenlong; Zhang, Junfeng; Barou, Fabrice

2018-01-01

The B-type olivine fabric (i.e., the [010] axes subnormal to foliation and the [001] axes subparallel to the lineation) has been regarded as an important olivine fabric for interpreting global trench-parallel S-wave polarization in fore-arc regions. However, strong serpentinization and cold temperature environment in the mantle wedge should inhibit development of the B-type olivine fabric that requires high temperature to activate solid-state plastic deformation. Here we report fabrics of olivine and antigorite generated at low temperatures (300-370 °C) during serpentinization in a fossil mantle wedge of the Val Malenco area, Central Alps. Olivine in the serpentine matrix develops a pronounced B-type fabric, while antigorite in the same matrix displays a strong crystallographic preferred orientation (CPO) with the (001) planes and the [010] axes subparallel to foliation and lineation, respectively. The following evidence leads to the conclusion that the B-type olivine fabric results from dissolution creep assisted by grain boundary sliding (GBS) and grain rotation, rather than solid-state plastic deformation: (1) serpentinization took place at low temperatures and a fluid-enriched environment, ideal for dissolution-precipitation creep; (2) the voids and zigzag boundaries along the interface between antigorite and olivine suggest a fluid dissolution reaction; (3) the primary coarse olivine develops a nearly random fabric, indicating the B-type fabrics in the fine-grained olivine may not be inherited fabrics. These results document for the first time the B-type olivine CPO formed by dissolution creep at low temperatures during serpentinization and provide a mechanism to reconcile petrofabric observations with geophysical observations of trench parallel fast S-wave seismic anisotropy in fore-arc mantle wedge regions.

Extreme conditions in a dissolving air nanobubble

NASA Astrophysics Data System (ADS)

Yasui, Kyuichi; Tuziuti, Toru; Kanematsu, Wataru

2016-07-01

Numerical simulations of the dissolution of an air nanobubble in water have been performed taking into account the effect of bubble dynamics (inertia of the surrounding liquid). The presence of stable bulk nanobubbles is not assumed in the present study because the bubble radius inevitably passes the nanoscale in the complete dissolution of a bubble. The bubble surface is assumed to be clean because attachment of hydrophobic materials on the bubble surface could considerably change the gas diffusion rate. The speed of the bubble collapse (the bubble wall speed) increases to about 90 m/s or less. The shape of a bubble is kept nearly spherical because the amplitude of the nonspherical component of the bubble shape is negligible compared to the instantaneous bubble radius. In other words, a bubble never disintegrates into daughter bubbles during the dissolution. At the final moment of the dissolution, the temperature inside a bubble increases to about 3000 K due to the quasiadiabatic compression. The bubble temperature is higher than 1000 K only for the final 19 ps. However, the Knudsen number is more than 0.2 for this moment, and the error associated with the continuum model should be considerable. In the final 2.3 ns, only nitrogen molecules are present inside a bubble as the solubility of nitrogen is the lowest among the gas species. The radical formation inside a bubble is negligible because the probability of nitrogen dissociation is only on the order of 10-15. The pressure inside a bubble, as well as the liquid pressure at the bubble wall, increases to about 5 GPa at the final moment of dissolution. The pressure is higher than 1 GPa for the final 0.7 ns inside a bubble and for the final 0.6 ns in the liquid at the bubble wall. The liquid temperature at the bubble wall increases to about 360 K from 293 K at the final stage of the complete dissolution.

Continental Subduction: Mass Fluxes and Interactions with the Wider Earth System

NASA Astrophysics Data System (ADS)

Cuthbert, S. J.

2011-12-01

Substantial parts of ultra-high pressure (UHP) terrains probably represent subducted passive continental margins (PCM). This contribution reviews and synthesises research on processes operating in such systems and their implication for the wider Earth system. PCM sediments are large repositories of volatiles including hydrates, nitrogen species, carbonates and hydrocarbons. Sediments and upper/ mid-crustal basement are rich in incompatible elements and are fertile for melting. Lower crust may be more mafic and refractory. Juvenile rift-related mafic rocks also have the potential to generate substantial volumes of granitoid melts, especially if they have been hydrated. Exposed UHP terrains demonstrate the return of continental crust from mantle depths, show evidence for substantial fluxes of aqueous fluid, anatexis and, in entrained orogenic peridotites, metasomatism of mantle rocks by crust- derived C-O-H fluids. However, substantial bodies of continental material may never return to the surface as coherent masses of rock, but remain sequestered in the mantle where they melt or become entrained in the deeper mantle circulation. Hence during subduction, PCM's become partitioned by a range of mechanisms. Mechanical partitioning strips away weaker sediment and middle/upper crust, which circulate back up the subduction channel, while denser, stronger transitional pro-crust and lower crust may "stall" near the base of the lithosphere or be irreversibly subducted to join the global mantle circulation. Under certain conditions sediment and upper crustal basement may reach depths for UHPM. Further partitioning takes place by anatexis, which either aids stripping and exhumation of the more melt-prone rock-masses through mechanical softening, or separates melt from residuum so that melt escapes and is accreted to the upper plate leading to "undercrusting", late-orogenic magmatism and further refinement of the crust. Melt that traverses sections of mantle will interact with it causing metasomatism and refertilisation. Partitioning also takes place by solid-fluid and melt-fluid partitioning. Dehydration may take place both during subduction and exhumation, and fluxes between dehydrating and hydrating rock masses influence the internal fluid budget of the orogen (essential for eclogitisation and densification of mafic lithologies). Ascending granitic melts advect dissolved water to shallow levels, or even the atmosphere. Irreversible subduction of PCM sediment carries water plus nitrogen species to the deeper mantle. Decarbonation of voluminous PCM carbonates depends on thermal regime and may release a pulse of CO2 to the atmosphere, but is limited in colder subduction zones hence transferring large volumes of carbon to the deep mantle. This may ultimately be mobilised by melting or dissolution to form fluid media for diamond formation.

Vinasse application to sugar cane fields. Effect on the unsaturated zone and groundwater at Valle del Cauca (Colombia).

PubMed

Ortegón, Gloria Páez; Arboleda, Fernando Muñoz; Candela, Lucila; Tamoh, Karim; Valdes-Abellan, Javier

2016-01-01

Extensive application of vinasse, a subproduct from sugar cane plantations for bioethanol production, is currently taking place as a source of nutrients that forms part of agricultural management in different agroclimatic regions. Liquid vinasse composition is characterised by high variability of organic compounds and major ions, acid pH (4.7), high TDS concentration (117,416-599,400mgL(-1)) and elevated EC (14,350-64,099μScm(-1)). A large-scale sugar cane field application is taking place in Valle del Cauca (Colombia), where monitoring of soil, unsaturated zone and the aquifer underneath has been made since 2006 to evaluate possible impacts on three experimental plots. For this assessment, monitoring wells and piezometers were installed to determine groundwater flow and water samples were collected for chemical analysis. In the unsaturated zone, tensiometers were installed at different depths to determine flow patterns, while suction lysimeters were used for water sample chemical determinations. The findings show that in the sandy loam plot (Hacienda Real), the unsaturated zone is characterised by low water retention, showing a high transport capacity, while the other two plots of silty composition presented temporal saturation due to La Niña event (2010-2011). The strong La Niña effect on aquifer recharge which would dilute the infiltrated water during the monitoring period and, on the other hand dissolution of possible precipitated salts bringing them back into solution may occur. A slight increase in the concentration of major ions was observed in groundwater (~5% of TDS), which can be attributed to a combination of factors: vinasse dilution produced by water input and hydrochemical processes along with nutrient removal produced by sugar cane uptake. This fact may make the aquifer vulnerable to contamination. Copyright © 2015 Elsevier B.V. All rights reserved.

Effect of solvent on in vitro dissolution: Summary of results for uranium, americium, and cobalt aerosols

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guilmette, R.A.; Hoover, M.D.

1995-12-01

The revised 10 CFR Part 20 has adopted the ICRP Publication 30 method for calculating the committed effective dose equivalent from intakes of radionuclides. This dosimetry scheme requires knowledge or assumptions about the chemical form of the radionuclide, its particle size, and its known or assumed solubility. The solubility is classified as being either D (relatively soluble), W, or Y (relatively insoluble), depending on whether the material dissolves over periods of days, weeks, or years. Although Nuclear Regulatory Commission licensees may wish to take advantage of material-specific knowledge in order to adjust annual limits on intake and derived air concentrations,more » relatively few radioactive materials to which workers and the general population may be exposed have been adequately characterized either in terms of physicochemical form or solubility. Experimental measurement of solubility using some type of in vitro dissolution measurement system is therefore needed. However, there is currently no clear consensus regarding the appropriate design of in vitro dissolution systems, particularly when considering the range of different radionuclides to be studied, and the complexity of the biological mechanisms involved in the retention and clearance of inhaled deposited radioactive particles. The purpose of this study was to evaluate the effect of the several solvents on the dissolution of four test aerosols ({sup 57}Co{sub 3}O{sub 4}, {sup 241}AmO{sub 2}, ammonium diuranate [ADU], and U{sub 3}O{sub 8}) selected to encompass a variety of chemical and biochemical properties in vivo. The results of this study provide some guidance on the usefulness of in vitro dissolution tests for estimating the solubility of unknown radionuclide particles within the context of a simple model such as the class D, W, and Y formulation of ICRP 30.« less

Multiscale Computational Modeling of the Nanostructure of Solid Dispersions of Hydroxypropyl Methylcellulose Acetate Succinate (HPMCAS) and Phenytoin.

PubMed

Huang, Wenjun; Mandal, Taraknath; Larson, Ronald G

2017-10-02

We recently developed coarse-grained (CG) force fields for hydroxypropyl methylcellulose acetate succinate (HPMCAS) polymers and the model drug molecule phenytoin, and a continuum transport model to study the polymer-drug nanostructures presented during a dissolution test after solvation of solid dispersion particles. We model the polymer-drug interactions that contribute to suppression of drug aggregation, release, and crystal growth during the dissolution process, and we take these as indicators of polymer effectiveness. We find that the size and the intermolecular interaction strength of the functional group and the drug loading concentration are the major factors that impact the effectiveness of the polymeric excipient. The hydroxypropyl acetyl group is the most effective functional group, followed by the acetyl group, while the deprotonated succinyl group is the least effective functional group, except that the deprotonated succinyl group at the 6-position is very effective in slowing down the phenytoin crystal growth. Our simulation results thus suggest HPMCAS with higher acetyl and lower succinyl content is more effective in promoting phenytoin solubility in dissolution media, and polymers become less effective when drug loading becomes high (i.e., 50% of the mass of the polymer/drug solid dispersion), agreeing with previous experimental studies. In addition, our transport model indicates that the drug release time from a solid dispersion particle of 2 μm diameter is less than 10 min, correlating well with the experimental time scale for a typical dissolution profile to reach maximum peak concentration. Our modeling effort, therefore, provides new avenues to understand the dissolution behavior of complex HPMCAS-phenytoin solid dispersions and offers a new design tool to optimize the formulation. Moreover, the systematic and robust approach used in our computational models can be extended to other polymeric excipients and drug candidates.

"On-command" dissolvable tympanostomy tube in the chinchilla model: A proof of concept.

PubMed

Wiedermann, Joshua P; Mai, Johnny P; Dumont, Matthieu; Jenkins, Audrey; Cleary, Kevin; Reilly, Brian K

2017-10-01

To prove the concept that a dissolvable "on-command" tympanostomy tube placed into the tympanic membrane of a chinchilla can dissolve when a benign solution is applied and result in a well healed tympanic membrane without histologic evidence of injury. Prospective Randomized Single-Subject Controlled Trial. Prototype tympanostomy tubes were fabricated from poly(butyl methacrylate-co-(2-dimethylaminoethyl) methacrylate-co- methyl methacrylate) (PBM). "In vitro" dissolution studies were performed with applications of the benign chemical, hydrogen peroxide (HP). PBM tubes were placed into ten chinchilla tympanic membranes matched with standard plastic tubes placed into the contralateral side. All 20 tubes were exposed to HP for 21 days with serial endoscopic examinations. In vitro PBM tubes were weighed before and after interventions and compared to control tubes. In vivo photo documentation was used to show progression of dissolution and histologic slides were obtained to show the effect of the PBM on surrounding tissues. Compared to control tubes, all those exposed to hydrogen peroxide had a statistically significant reduction in weight (p < 0.01). After placement into the tympanic membrane of chinchillas, all PBM tubes dissolved within 21 days of hydrogen peroxide treatment leaving behind histologically normal, intact tympanic membranes. Our PBM tubes dissolve "on-command" in a chinchilla model when exposed to treatment with a benign chemical. Dissolvable "on-command" tympanostomy tubes may reduce significant complications related to pediatric tympanostomy tube use. Copyright © 2017 Elsevier B.V. All rights reserved.

Impact of polymers on the crystallization and phase transition kinetics of amorphous nifedipine during dissolution in aqueous media.

PubMed

Raina, Shweta A; Alonzo, David E; Zhang, Geoff G Z; Gao, Yi; Taylor, Lynne S

2014-10-06

The commercial and clinical success of amorphous solid dispersions (ASD) in overcoming the low bioavailability of poorly soluble molecules has generated momentum among pharmaceutical scientists to advance the fundamental understanding of these complex systems. A major limitation of these formulations stems from the propensity of amorphous solids to crystallize upon exposure to aqueous media. This study was specifically focused on developing analytical techniques to evaluate the impact of polymers on the crystallization behavior during dissolution, which is critical in designing effective amorphous formulations. In the study, the crystallization and polymorphic conversions of a model compound, nifedipine, were explored in the absence and presence of polyvinylpyrrolidone (PVP), hydroxypropylmethyl cellulose (HPMC), and HPMC-acetate succinate (HPMC-AS). A combination of analytical approaches including Raman spectroscopy, polarized light microscopy, and chemometric techniques such as multivariate curve resolution (MCR) were used to evaluate the kinetics of crystallization and polymorphic transitions as well as to identify the primary route of crystallization, i.e., whether crystallization took place in the dissolving solid matrix or from the supersaturated solutions generated during dissolution. Pure amorphous nifedipine, when exposed to aqueous media, was found to crystallize rapidly from the amorphous matrix, even when polymers were present in the dissolution medium. Matrix crystallization was avoided when amorphous solid dispersions were prepared, however, crystallization from the solution phase was rapid. MCR was found to be an excellent data processing technique to deconvolute the complex phase transition behavior of nifedipine.

Bioavailability and stability of erythromycin delayed release tablets.

PubMed

Ogwal, S; Xide, T U

2001-12-01

Erythromycin is available as the free base, ethylsuccinate, estolate, stearate, gluceptate, and lactobionate derivatives. When given orally erythromycin and its derivatives except the estolate are inactivated to some extent by the gastric acid and poor absorption may result. To establish whether delayed release erythromycin tablets meet the bioequivalent requirement for the market. Sectrophotometric analysis was used to determine the dissolution percentage of the tablets in vitro. High performance liquid chromatography and IBM/XT microcomputer was used to determine the bioavailability and pharmacokinetic parameters in vivo. Dissolution percentage in thirty minutes reached 28.9% and in sixty minutes erythromycin was completely released. The parameters of the delayed release tablets were Tlag 2.3 hr, Tmax.4.5 hr, and Cmax 2.123 g/ml Ka 0.38048 hr(-1) T (1/2) 1.8 hr, V*C/F 49.721 AUC 12.9155. The relative bioavailability of erythromycin delayed release tablet to erythromycin capsules was 105.31% The content, appearance, and dissolution bioavailability of delayed release erythromycin tablets conforms to the United States pharmacopoeia standards. The tablets should be stored in a cool and dry place in airtight containers and the shelf life is temporarily assigned two years.

Porous Carriers for Controlled/Modulated Drug Delivery

PubMed Central

Ahuja, G.; Pathak, K.

2009-01-01

Considerable research efforts have been directed in recent years towards the development of porous carriers as controlled drug delivery matrices because of possessing several features such as stable uniform porous structure, high surface area, tunable pore size and well-defined surface properties. Owing to wide range of useful properties porous carriers have been used in pharmaceuticals for many purposes including development of floating drug delivery systems, sustained drug delivery systems. Various types of pores like open, closed, transport and blind pores in the porous solid allow them to adsorb drugs and release them in a more reproducible and predictable manner. Pharmaceutically exploited porous adsorbents includes, silica (mesoporous), ethylene vinyl acetate (macroporous), polypropylene foam powder (microporous), titanium dioxide (nanoporous). When porous polymeric drug delivery system is placed in contact with appropriate dissolution medium, release of drug to medium must be preceded by the drug dissolution in the water filled pores or from surface and by diffusion through the water filled channels. The porous carriers are used to improve the oral bioavailability of poorly water soluble drugs, to increase the dissolution of relatively insoluble powders and conversion of crystalline state to amorphous state. PMID:20376211

Microbial and diagenetic steps leading to the mineralisation of Great Salt Lake microbialites

NASA Astrophysics Data System (ADS)

Pace, Aurélie; Bourillot, Raphaël; Bouton, Anthony; Vennin, Emmanuelle; Galaup, Serge; Bundeleva, Irina; Patrier, Patricia; Dupraz, Christophe; Thomazo, Christophe; Sansjofre, Pierre; Yokoyama, Yusuke; Franceschi, Michel; Anguy, Yannick; Pigot, Léa; Virgone, Aurélien; Visscher, Pieter T.

2016-08-01

Microbialites are widespread in modern and fossil hypersaline environments, where they provide a unique sedimentary archive. Authigenic mineral precipitation in modern microbialites results from a complex interplay between microbial metabolisms, organic matrices and environmental parameters. Here, we combined mineralogical and microscopic analyses with measurements of metabolic activity in order to characterise the mineralisation of microbial mats forming microbialites in the Great Salt Lake (Utah, USA). Our results show that the mineralisation process takes place in three steps progressing along geochemical gradients produced through microbial activity. First, a poorly crystallized Mg-Si phase precipitates on alveolar extracellular organic matrix due to a rise of the pH in the zone of active oxygenic photosynthesis. Second, aragonite patches nucleate in close proximity to sulfate reduction hotspots, as a result of the degradation of cyanobacteria and extracellular organic matrix mediated by, among others, sulfate reducing bacteria. A final step consists of partial replacement of aragonite by dolomite, possibly in neutral to slightly acidic porewater. This might occur due to dissolution-precipitation reactions when the most recalcitrant part of the organic matrix is degraded. The mineralisation pathways proposed here provide pivotal insight for the interpretation of microbial processes in past hypersaline environments.

Numerical simulation of phase transition problems with explicit interface tracking

DOE PAGES

Hu, Yijing; Shi, Qiangqiang; de Almeida, Valmor F.; ...

2015-12-19

Phase change is ubiquitous in nature and industrial processes. Started from the Stefan problem, it is a topic with a long history in applied mathematics and sciences and continues to generate outstanding mathematical problems. For instance, the explicit tracking of the Gibbs dividing surface between phases is still a grand challenge. Our work has been motivated by such challenge and here we report on progress made in solving the governing equations of continuum transport in the presence of a moving interface by the front tracking method. The most pressing issue is the accounting of topological changes suffered by the interfacemore » between phases wherein break up and/or merge takes place. The underlying physics of topological changes require the incorporation of space-time subscales not at reach at the moment. Therefore we use heuristic geometrical arguments to reconnect phases in space. This heuristic approach provides new insight in various applications and it is extensible to include subscale physics and chemistry in the future. We demonstrate the method on applications such as simulating freezing, melting, dissolution, and precipitation. The later examples also include the coupling of the phase transition solution with the Navier-Stokes equations for the effect of flow convection.« less

Generic Pharmaceutical Association (GPhA) - 2015 CMC Workshop (June 9-10, 2015 - Bethesda, Maryland, USA).

PubMed

Komlos, D

2015-07-01

Nearly 400 professionals attended the 2-day Generic Pharmaceutical Association (GPhA) workshop dedicated to fostering discussions on the FDA's chemistry, manufacturing and controls (CMC) expectations for abbreviated new drug applications (ANDAs), enhanced regulatory filing requirements, and other topics, as CMC takes root in the Office of Pharmaceutical Quality (OPQ). Following the keynote address by Janet Woodcock, Director of the FDA's Center for Drug Evaluation and Research (CDER) and Acting Director of OPQ, and an update from the Office of Generic Drugs (OGD) by Ted Sherwood, Acting Director of the OGD's Office of Regulatory Operations, plenary sessions took place covering OPQ updates, management plans, Generic Drug User Fee Amendments of 2012 (GDUFA) backlog, year 1 and 2 cohorts, drug substance, defining starting materials, quality related refuse-to-receive standards, risk and team-based integrated quality assessment, deficiencies and information requests - CMC submissions, emerging technologies, compliance and inspection, lifecycle management of drug products, quality metrics, pharmaceutically relevant dissolution specifications, and communication and project management. This report will provide a summary of conference highlights. Copyright 2015 Prous Science, S.A.U. or its licensors. All rights reserved.

Deep reaching fluid flow in the North East German Basin: origin and processes of groundwater salinisation

NASA Astrophysics Data System (ADS)

Tesmer, M.; Möller, P.; Wieland, S.; Jahnke, C.; Voigt, H.; Pekdeger, A.

2007-11-01

Major element chemistry, rare-earth element distribution, and H and O isotopes are conjointly used to study the sources of salinisation and interaquifer flow of saline groundwater in the North East German Basin. Chemical analyses from hydrocarbon exploration campaigns showed evidence of the existence of two different groups of brines: halite and halite Ca-Cl brines. Residual brines and leachates are identified by Br-/Cl- ratios. Most of the brines are dissolution brines of Permian evaporites. New analyses show that the pattern of rare-earth elements and yttrium (REY) are closely linked to H and O isotope distribution. Thermal brines from deep wells and artesian wells indicate isotopically evaporated brines, which chemically interacted with their aquifer environment. Isotopes and rare-earth element patterns prove that cross flow exists, especially in the post-Rupelian aquifer. However, even at depths exceeding 2,000 m, interaquifer flow takes place. The rare-earth element pattern and H and O isotopes identify locally ascending brines. A large-scale lateral groundwater flow has to be assumed because all pre-Rupelian aquifer systems to a depth of at least 500 m are isotopically characterised by Recent or Pleistocene recharge conditions.

Experimental investigation of the brittle-viscous transition in mafic rocks - Interplay between fracturing, reaction, and viscous deformation

NASA Astrophysics Data System (ADS)

Marti, Sina; Stünitz, Holger; Heilbronner, Renée; Plümper, Oliver; Drury, Martyn

2017-12-01

Rock deformation experiments are performed on fault gouge fabricated from 'Maryland Diabase' rock powder to investigate the transition from dominant brittle to dominant viscous behaviour. At the imposed strain rates of γ˙ = 3 ·10-5 - 3 ·10-6 s-1, the transition is observed in the temperature range of (600 °C < T < 800 °C) at confining pressures of (0.5 GPa ≤ Pc ≤ 1.5 GPa). The transition thereby takes place by a switch from brittle fracturing and cataclastic flow to viscous dissolution-precipitation creep and grain boundary sliding. Mineral reactions and resulting grain size refinement by nucleation are observed to be critical processes for the switch to viscous deformation, i.e., grain size sensitive creep. In the transitional regime, the mechanical response of the sample is a mixed-mode between brittle and viscous rheology and microstructures associated with both brittle and viscous deformation are observed. As grain size reduction by reaction and nucleation is a time dependent process, the brittle-viscous transition is not only a function of T but to a large extent also of microstructural evolution.

Isotopic analysis for degradation diagnosis of calcite matrix in mortar.

PubMed

Dotsika, E; Psomiadis, D; Poutoukis, D; Raco, B; Gamaletsos, P

2009-12-01

Mortar that was used in building as well as in conservation and restoration works of wall paintings have been analysed isotopically (delta(13)C and delta(18)O) in order to evaluate the setting environments and secondary processes, to distinguish the structural components used and to determine the exact causes that incurred the degradation phenomena. The material undergoes weathering and decay on a large proportion of its surface and in depth, due to the infiltration of water through the structural blocks. Mineralogical analysis indicated signs of sulphation and dissolution/recrystallisation processes taking place on the material, whereas stable isotopes provided information relative to the origin of the CO(2) and water during calcite formation and degradation processes. Isotopic change of the initial delta(13)C and delta(18)O in carbonate matrix was caused by alteration of the primary source of CO(2) and H(2)O in mortar over time, particularly by recrystallisation of calcite with porewater, evaporated or re-condensed water, and CO(2) from various sources of atmospheric and biogenic origin. Human influence (surface treatment) and biological growth (e.g. fungus) are major exogenic processes which may alter delta(18)O and delta(13)C in lime mortar.

A Bayesian, multivariate calibration for Globigerinoides ruberMg/Ca

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khider, D.; Huerta, G.; Jackson, C.

The use of Mg/Ca in marine carbonates as a paleothermometer has been challenged by observations that implicate salinity as a contributing influence on Mg incorporation into biotic calcite and that dissolution at the sea-floor alters the original Mg/Ca. Yet, these factors have not yet been incorporated into a single calibration model. In this paper, we introduce a new Bayesian calibration for Globigerinoides ruber Mg/Ca based on 186 globally distributed core top samples, which explicitly takes into account the effect of temperature, salinity, and dissolution on this proxy. Our reported temperature, salinity, and dissolution (here expressed as deep-water ΔCO 2- 3)more » sensitivities are (±2σ) 8.7±0.9%/°C, 3.9±1.2%/psu, and 3.3±1.3%/μmol.kg -1 below a critical threshold of 21 μmol/kg in good agreement with previous culturing and core-top studies. We then perform a sensitivity experiment on a published record from the western tropical Pacific to investigate the bias introduced by these secondary influences on the interpretation of past temperature variability. This experiment highlights the potential for misinterpretations of past oceanographic changes when the secondary influences of salinity and dissolution are not accounted for. Finally, multiproxy approaches could potentially help deconvolve the contributing influences but this awaits better characterization of the spatio-temporal relationship between salinity and δ 18O sw over millennial and orbital timescales.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Woodroffe, Jesse; Jordanova, Vania; Toth, Gabor

Extreme weather happens worldwide and it takes place in the magnetosphere. The magnetosphere is the place where the majority of earth’s satellites reside. These satellites provide weather forecasting and serve as national defense. When solar storms take place, they can damage satellites.

Nanoparticulate strategies for effective delivery of poorly soluble therapeutics.

PubMed

Gokce, Evren H; Ozyazici, Mine; Souto, Eliana B

2010-07-01

The pharmacological activity of a drug molecule depends on its ability to dissolve and interact with its biological target, either through dissolution and absorption, or through dissolution and receptor interaction. The low bioavailability that characterizes poorly water-soluble drugs is usually attributed to the dissolution kinetic profile. Novel strategies to effectively deliver these drugs include nanoparticulate approaches that either increase the surface area of the drug or improve the solubility characteristics of the drug. Nanosizing approaches are based on the production of drug nanocrytals dispersed in an aqueous surfactant solution, whereas other possibilities include drug loading in nanoparticles. Promising nanoparticulate approaches include the development of lipid-based nanocarriers to increase drug solubility followed by enhanced bioavailability. To select the best approach there are, however, some critical considerations to take into account, for example the physicochemical properties of the drug, the possibility to scale-up the production process, the toxicological considerations of the use of solvents and cosolvents, the selection of an environmentally sustainable methodology and the development of a more patient-friendly dosage form. This article addresses these relevant questions and provides feasible examples of novel strategies with respect to relevant administration routes.

Morphological Features of Diamond Crystals Dissolved in Fe0.7S0.3 Melt at 4 GPa and 1400°C

NASA Astrophysics Data System (ADS)

Sonin, V. M.; Zhimulev, E. I.; Pomazanskiy, B. S.; Zemnuhov, A. L.; Chepurov, A. A.; Afanasiev, V. P.; Chepurov, A. I.

2018-01-01

An experimental study of the dissolution of natural and synthetic diamonds in a sulfur-bearing iron melt (Fe0.7S0.3) with high P-T parameters (4 GPa, 1400°C) was performed. The results demonstrated that under these conditions, octahedral crystals with flat faces and rounded tetrahexahedral diamond crystals are transformed into rounded octahedroids, which have morphological characteristics similar to those of natural diamonds from kimberlite. It was suggested that, taking into account the complex history of individual natural diamond crystals, including the dissolution stages, sulfur-bearing metal melts up to sulfide melts were not only diamond-forming media during the early evolution of the Earth, but also natural solvents of diamond in the mantle environment before the formation of kimberlitic melts.

49 CFR 40.41 - Where does a urine collection for a DOT drug test take place?

Code of Federal Regulations, 2014 CFR

2014-10-01

... 49 Transportation 1 2014-10-01 2014-10-01 false Where does a urine collection for a DOT drug test... in DOT Urine Collections § 40.41 Where does a urine collection for a DOT drug test take place? (a) A urine collection for a DOT drug test must take place in a collection site meeting the requirements of...

49 CFR 40.41 - Where does a urine collection for a DOT drug test take place?

Code of Federal Regulations, 2013 CFR

2013-10-01

... 49 Transportation 1 2013-10-01 2013-10-01 false Where does a urine collection for a DOT drug test... in DOT Urine Collections § 40.41 Where does a urine collection for a DOT drug test take place? (a) A urine collection for a DOT drug test must take place in a collection site meeting the requirements of...

49 CFR 40.41 - Where does a urine collection for a DOT drug test take place?

Code of Federal Regulations, 2012 CFR

2012-10-01

... 49 Transportation 1 2012-10-01 2012-10-01 false Where does a urine collection for a DOT drug test... in DOT Urine Collections § 40.41 Where does a urine collection for a DOT drug test take place? (a) A urine collection for a DOT drug test must take place in a collection site meeting the requirements of...

49 CFR 40.41 - Where does a urine collection for a DOT drug test take place?

Code of Federal Regulations, 2011 CFR

2011-10-01

... 49 Transportation 1 2011-10-01 2011-10-01 false Where does a urine collection for a DOT drug test... in DOT Urine Collections § 40.41 Where does a urine collection for a DOT drug test take place? (a) A urine collection for a DOT drug test must take place in a collection site meeting the requirements of...

Genesis and shape of natural solution cavities within salt deposits

NASA Astrophysics Data System (ADS)

Gechter, Daniel; Huggenberger, Peter; Ackerer, Philippe; Waber, H. Niklaus

2008-11-01

Since the genesis and shape of natural deep-seated cavities within a salt body are insufficiently understood, the current study tries to shed some light on this topic. To this end, freshwater was pumped slowly through a horizontal borehole in rock salt cores. Owing to fast halite dissolution kinetics, high solubility, and slow inflow rate, halite dissolution took place only in the inflow of the rock salt cylinder. The shape of the created cavities is an approximately symmetrical half cone with a horizontal base facing upward. A conceptual model is presented that is inspired by the experimental results and based on theoretical hydraulic-geochemical considerations, as well as on field observations. It proposes that triangular prism or conically shaped cavities develop within salt under confined conditions, where aggressive water flows upward along a fracture/conduit from an insoluble aquifer into the soluble stratum. Such cavity enlargements may cause land subsidence and structure collapse.

The effect of sodium chloride on the dissolution of calcium silicate hydrate gels.

PubMed

Hill, J; Harris, A W; Manning, M; Chambers, A; Swanton, S W

2006-01-01

The use of cement based materials will be widespread in the long-term management of radioactive materials in the United Kingdom. One of the applications could be the Nirex reference vault backfill (NRVB) as an engineered barrier within a deep geological repository. NRVB confers alkaline conditions, which would provide a robust chemical barrier through the control of the solubility of some key radionuclides, enhanced sorption and minimised corrosion of steel containers. An understanding of the dissolution of C-S-H gels in cement under the appropriate conditions (e.g., saline groundwaters) is necessary to demonstrate the expected evolution of the chemistry over time and to provide sufficient cement to buffer the porewater conditions for the required time. A programme of experimental work has been undertaken to investigate C-S-H gel dissolution behaviour in sodium chloride solutions and the effect of calcium/silicon ratio (C/S), temperature and cation type on this behaviour. Reductions in calcium concentration and pH values were observed with samples equilibrated at 45 degrees C compared to those prepared at 25 degrees C. The effect of salt cation type on salt-concentration dependence of the dissolution of C-S-H gels was investigated by the addition of lithium or potassium chloride in place of sodium chloride for gels with a C/S of 1.0 and 1.8. With a C/S of 1.0, similar increases in dissolved calcium concentration with increasing ionic strength were recorded for the different salts. However, at a C/S of 1.8, anomalously high calcium concentrations were observed in the presence of lithium.

Stable isotope reactive transport modeling in water-rock interactions during CO2 injection

NASA Astrophysics Data System (ADS)

Hidalgo, Juan J.; Lagneau, Vincent; Agrinier, Pierre

2010-05-01

Stable isotopes can be of great usefulness in the characterization and monitoring of CO2 sequestration sites. Stable isotopes can be used to track the migration of the CO2 plume and identify leakage sources. Moreover, they provide unique information about the chemical reactions that take place on the CO2-water-rock system. However, there is a lack of appropriate tools that help modelers to incorporate stable isotope information into the flow and transport models used in CO2 sequestration problems. In this work, we present a numerical tool for modeling the transport of stable isotopes in groundwater reactive systems. The code is an extension of the groundwater single-phase flow and reactive transport code HYTEC [2]. HYTEC's transport module was modified to include element isotopes as separate species. This way, it is able to track isotope composition of the system by computing the mixing between the background water and the injected solution accounting for the dependency of diffusion on the isotope mass. The chemical module and database have been expanded to included isotopic exchange with minerals and the isotope fractionation associated with chemical reactions and mineral dissolution or precipitation. The performance of the code is illustrated through a series of column synthetic models. The code is also used to model the aqueous phase CO2 injection test carried out at the Lamont-Doherty Earth Observatory site (Palisades, New York, USA) [1]. References [1] N. Assayag, J. Matter, M. Ader, D. Goldberg, and P. Agrinier. Water-rock interactions during a CO2 injection field-test: Implications on host rock dissolution and alteration effects. Chemical Geology, 265(1-2):227-235, July 2009. [2] Jan van der Lee, Laurent De Windt, Vincent Lagneau, and Patrick Goblet. Module-oriented modeling of reactive transport with HYTEC. Computers & Geosciences, 29(3):265-275, April 2003.

Mechanism of dissolution of a lithium salt in an electrolytic solvent in a lithium ion secondary battery: a direct ab initio molecular dynamics (AIMD) study.

PubMed

Tachikawa, Hiroto

2014-06-06

The mechanism of dissolution of the Li(+) ion in an electrolytic solvent is investigated by the direct ab initio molecular dynamics (AIMD) method. Lithium fluoroborate (Li(+)BF4(-)) and ethylene carbonate (EC) are examined as the origin of the Li(+) ion and the solvent molecule, respectively. This salt is widely utilized as the electrolyte in the lithium ion secondary battery. The binding of EC to the Li(+) moiety of the Li(+)BF4(-) salt is exothermic, and the binding energies at the CAM-B3LYP/6-311++G(d,p) level for n=1, 2, 3, and 4, where n is the number of EC molecules binding to the Li(+) ion, (EC)n(Li(+)BF4(-)), are calculated to be 91.5, 89.8, 87.2, and 84.0 kcal mol(-1) (per EC molecule), respectively. The intermolecular distances between Li(+) and the F atom of BF4(-) are elongated: 1.773 Å (n=0), 1.820 Å (n=1), 1.974 Å (n=2), 1.942 Å (n=3), and 4.156 Å (n=4). The atomic bond populations between Li(+) and the F atom for n=0, 1, 2, 3, and 4 are 0.202, 0.186, 0.150, 0.038, and 0.0, respectively. These results indicate that the interaction of Li(+) with BF4(-) becomes weaker as the number of EC molecules is increased. The direct AIMD calculation for n=4 shows that EC reacts spontaneously with (EC)3(Li(+)BF4(-)) and the Li(+) ion is stripped from the salt. The following substitution reaction takes place: EC+(EC)3(Li(+)BF4(-))→(EC)4Li(+)-(BF4(-)). The reaction mechanism is discussed on the basis of the theoretical results. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Molybdenum isotope fractionation during acid leaching of a granitic uranium ore

NASA Astrophysics Data System (ADS)

Migeon, Valérie; Bourdon, Bernard; Pili, Eric; Fitoussi, Caroline

2018-06-01

As an attempt to prevent illicit trafficking of nuclear materials, it is critical to identify the origin and transformation of uranium materials from the nuclear fuel cycle based on chemical and isotope tracers. The potential of molybdenum (Mo) isotopes as tracers is considered in this study. We focused on leaching, the first industrial process used to release uranium from ores, which is also known to extract Mo depending on chemical conditions. Batch experiments were performed in the laboratory with pH ranging from 0.3 to 5.5 in sulfuric acid. In order to span a large range in uranium and molybdenum yields, oxidizers such as nitric acid, hydrogen peroxide and manganese dioxide were also added. An enrichment in heavy Mo isotopes is produced in the solution during leaching of a granitic uranium ore, when Mo recovery is not quantitative. At least two Mo reservoirs were identified in the ore: ∼40% as Mo oxides soluble in water or sulfuric acid, and ∼40% of Mo hosted in sulfides soluble in nitric acid or hydrogen peroxide. At pH > 1.8, adsorption and/or precipitation processes induce a decrease in Mo yields with time correlated with large Mo isotope fractionations. Quantitative models were used to evaluate the relative importance of the processes involved in Mo isotope fractionation: dissolution, adsorption, desorption, precipitation, polymerization and depolymerization. Model best fits are obtained when combining the effects of dissolution/precipitation, and adsorption/desorption onto secondary minerals. These processes are inferred to produce an equilibrium isotope fractionation, with an enrichment in heavy Mo isotopes in the liquid phase and in light isotopes in the solid phase. Quantification of Mo isotope fractionation resulting from uranium leaching is thus a promising tool to trace the origin and transformation of nuclear materials. Our observations of Mo leaching are also consistent with observations of natural Mo isotope fractionation taking place during chemical weathering in terrestrial environments where the role of secondary processes such as adsorption is significant.

Sulfur Cycling Mediates Calcium Carbonate Geochemistry in Modern Marine Stromatolites

NASA Technical Reports Server (NTRS)

Visscher, P. T.; Hoeft, S. E.; Bebout, B. M.; Reid, R. P.

2004-01-01

Modem marine stromatolites forming in Highborne Cay, Exumas (Bahamas), contain microbial mats dominated by Schizothrix. Although saturating concentrations of Ca2+ and CO32- exist, microbes mediate CaCO3 precipitation. Cyanobacterial photosynthesis in these stromatolites aids calcium carbonate precipitation by removal of HS+ through CO2 use. Photorespiration and exopolymer production predominantly by oxygenic phototrophs fuel heterotrophic activity: aerobic respiration (approximately 60 umol/sq cm.h) and sulfate reduction (SR; 1.2 umol SO42-/sq cm.h) are the dominant C- consuming processes. Aerobic microbial respiration and the combination of SR and H2S oxidation both facilitate CaCO3 dissolution through H+ production. Aerobic respiration consumes much more C on an hourly basis, but duel fluctuating O2 and H2 depth profiles indicate that overall, SR consumes only slightly less (0.2-0.5) of the primary production. Moreover, due to low O2 concentrations when SR rates are peaking, reoxidation of the H2S formed is incomplete: both thiosulfate and polythionates are formed. The process of complete H2S oxidation yields H+. However, due to a low O2 concentration late in the day and relatively high O2 concentrations early in the following morning, a two-stage oxidation takes place: first, polythionates are formed from H2S, creating alkalinity which coincides with CaCO3 precipitation; secondly, oxidation of polythionates to sulfate yields acidity, resulting in dissolution, etc. Vertical profiles confirmed that the pH peaked late in the afternoon (greater than 8.8) and had the lowest values (less than 7.4) early in the morning. Thus, the effect of this S-cycling through alkalinity production, followed by acidification during H2S oxidation, results in a six times stronger fluctuation in acidity than photosynthesis plus aerobic respiration accomplish. This implies that anaerobic processes play a pivotal role in stromatolite formation.

Verifying Dissolution Of Wax From Hardware Surfaces

NASA Technical Reports Server (NTRS)

Montoya, Benjamina G.

1995-01-01

Wax removed by cleaning solvent revealed by cooling solution with liquid nitrogen. Such improved procedure and test needed in case of hardware that must be protected by wax during machining or plating but required to be free of wax during subsequent use. Improved cleaning procedure and test take less than 5 minutes. Does not require special skill or equipment and performs at cleaning site. In addition, enables recovery of all cleaning solvent.

Evaluation of In-Use Stability of Anticoagulant Drug Products: Warfarin Sodium.

PubMed

Nguyenpho, Agnes; Ciavarella, Anthony B; Siddiqui, Akhtar; Rahman, Ziyaur; Akhtar, Sohail; Hunt, Robert; Korang-Yeboah, Maxwell; Khan, Mansoor A

2015-12-01

The objective of the study was to evaluate the stability of warfarin products during use by patients or caregivers. For evaluation, three commercial products manufactured by different processes were selected and placed at 30°C/75%RH to simulate in use condition. Samples were withdrawn up to 12 weeks and analyzed for the physicochemical changes. Scanning electron microscopy demonstrated increasing holes and craters in the tablets over the timeframe. Near-infrared chemical imaging and powder X-ray powder diffraction corroborated the change arising from conversion of crystalline to amorphous forms of the drug. Hardness and disintegration time of the tablets were found to increase progressively. With increasing time, moisture contents of the products were found to increase and consequent decrease in isopropyl alcohol content of the product. Dissolution of the tablets in media at pH 4.5 demonstrated discrimination between crystalline and amorphous drug products. Overall, percent drug dissolved in each product at 30 min was found to decrease with increasing exposure time. Dissolution of drug decreased from 54% to 38% and 82% to 54% for the two products while the third product maintained consistently high level of dissolution. These results suggest that the drug product quality attributes can change during use. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.

Dissolution behavior and early bone apposition of calcium phosphate-coated machined implants

PubMed Central

Hwang, Ji-Wan; Lee, Eun-Ung; Lee, Jung-Seok; Jung, Ui-Won; Lee, In-Seop

2013-01-01

Purpose Calcium phosphate (CaP)-coated implants promote osseointegration and survival rate. The aim of this study was to (1) analyze the dissolution behavior of the residual CaP particles of removed implants and (2) evaluate bone apposition of CaP-coated machined surface implants at the early healing phase. Methods Mandibular premolars were extracted from five dogs. After eight weeks, the implants were placed according to drilling protocols: a nonmobile implant (NI) group and rotational implant (RI) group. For CaP dissolution behavior analysis, 8 implants were removed after 0, 1, 2, and 4 weeks. The surface morphology and deposition of the coatings were observed. For bone apposition analysis, block sections were obtained after 1-, 2-, and 4-week healing periods and the specimens were analyzed. Results Calcium and phosphorus were detected in the implants that were removed immediately after insertion, and the other implants were composed mainly of titanium. There were no notable differences between the NI and RI groups in terms of the healing process. The bone-to-implant contact and bone density in the RI group showed a remarkable increase after 2 weeks of healing. Conclusions It can be speculated that the CaP coating dissolves early in the healing phase and chemically induces early bone formation regardless of the primary stability. PMID:24455442

Reaction processes and permeability changes during CO2-rich brine flow through fractured Portland cement

NASA Astrophysics Data System (ADS)

Abdoulghafour, H.; Luquot, L.; Gouze, P.

2012-12-01

So far, cement alteration was principally studied experimentally using batch reactor (with static or renewed fluid). All exhibit similar carbonation mechanisms. The acidic solution, formed by the dissolution of the CO2 into the pore water or directly surrounding the cement sample, diffuses into the cement and induces dissolution reactions of the cement hydrates in particular portlandite and CSH. The calcium released by the dissolution of these calcium bearing phases combining with carbonate ions of the fluid forms calcium carbonates. The cement pH, initially around 13, falls to values where carbonate ion is the most dominant element (pH ~ 9), then CaCO3 phases can precipitate. These studies mainly associate carbonation process with a reduction of porosity and permeability. Indeed an increase of volume (about 10%) is expected during the formation of calcite from portlandite (equation 2) assuming a stoichiometric reaction. Here we investigated the cement alteration mechanisms in the frame of a controlled continuous renewal of CO2-rich fluid in a fracture. This situation is that expected when seepage is activated by the mechanical failure of the cement material that initially seals two layers of distinctly different pressure: the storage reservoir and the aquifer above the caprock, for instance. We study the effect of flow rates from quasi-static flow to higher flow rates for well-connected fractures. In the quasi-static case we observed an extensive conversion of portlandite (Ca(OH)2) to calcite in the vicinity of the fracture similar to that observed in the published batch experiments. Eventually, the fracture was almost totally healed. The experiments with constant flow revealed a different behaviour triggered by the continuous renewing of the reactants and withdrawal of reaction products. We showed that calcite precipitation is more efficient for low flow rate. With intermediate flow rate, we measured that permeability increases slowly at the beginning of the experiment and then remains constant due to calcite precipitation in replacement of CSH and CH into fracture border. With higher flow rate, we measured a constant permeability which can be explained by the development of a highly hydrated Si-rich zone which maintains the initial fracture aperture during all over the experiment while noticeable mass is released from the sample. These preliminary results emphasize that more complex behaviours than that envisaged from batch experiments may take place in the vicinity of flowing fractures. We demonstrated that if only micro-cracks appear in the cement well, carbonation reaction may heal these micro-cracks and mitigate leakage whereas conductive fractures allowing high flow may represent a risk of perennial leakage because the net carbonation process, including the calcite precipitation and its subsequent re-dissolution, is sufficiently to heal the fracture. However, the precipitation of Si-rich amorphous phases may maintain the initial fracture aperture and limit the leakage rate. Keywords: leakage, cement alteration, flow rate, fracture, permeability changes, reaction processes.

Fractured cement reactivity during CO2-rich brine leakage: Consequences on hydrodynamic and structural properties

NASA Astrophysics Data System (ADS)

abdelghafour, H.; Luquot, L.; Gouze, P.

2013-12-01

So far, cement alteration was principally studied experimentally using batch reactor (with static or renewed fluid). All exhibit similar carbonation mechanisms. The acidic solution, formed by the dissolution of the CO2 into the pore water or directly surrounding the cement sample, diffuses into the cement and induces dissolution reactions of the cement hydrates in particular portlandite and CSH. The calcium released by the dissolution of these calcium bearing phases combining with carbonate ions of the fluid forms calcium carbonates. The cement pH, initially around 13, falls to values where carbonate ion is the most dominant element (pH ~ 9), then CaCO3 phases can precipitate. These studies mainly associate carbonation process with a reduction of porosity and permeability. Indeed an increase of volume (about 10%) is expected during the formation of calcite from portlandite assuming a stoichiometric reaction. Here we investigated the cement alteration mechanisms in the frame of a controlled continuous renewal of CO2-rich fluid in a fracture. This situation is that expected when seepage is activated by the mechanical failure of the cement material that initially seals two layers of distinctly different pressure: the storage reservoir and the aquifer above the caprock, for instance. We study the effect of flow rates from quasi-static flow to higher flow rates for well-connected fractures. In the quasi-static case we observed an extensive conversion of portlandite (Ca(OH)2) to calcite in the vicinity of the fracture similar to that observed in the published batch experiments. Eventually, the fracture was almost totally healed. The experiments with constant flow revealed a different behavior triggered by the continuous renewing of the reactants and withdrawal of the reaction products. We showed that calcite precipitation is more efficient for low flow rate. With intermediate flow rate, we measured that permeability increases slowly at the beginning of the experiment and then remains constant due to calcite precipitation in replacement of CSH and CH into fracture border. With higher flow rate, we measured a constant permeability which can be explained by the development of a highly hydrated Si-rich zone which maintains the initial fracture aperture during all over the experiment while noticeable mass is released from the sample. These results emphasize that more complex behaviors than that envisaged from batch experiments may take place in the vicinity of flowing fractures. We demonstrated that if only micro-cracks appear in the cement well, carbonation reaction may heal these micro-cracks and mitigate leakage whereas conductive fractures allowing high flow may represent a risk of perennial leakage because the net carbonation process, including the calcite precipitation and its subsequent re-dissolution, is sufficiently to heal the fracture. However, the precipitation of Si-rich amorphous phases may maintain the initial fracture aperture and limit the leakage rate.

Nanoparticle-in-microparticle oral drug delivery system of a clinically relevant darunavir/ritonavir antiretroviral combination.

PubMed

Augustine, Robin; Ashkenazi, Dana Levin; Arzi, Roni Sverdlov; Zlobin, Vita; Shofti, Rona; Sosnik, Alejandro

2018-05-01

Nanonizationhas been extensively investigated to increase theoral bioavailability of hydrophobicdrugsin general andantiretrovirals(ARVs)used inthe therapy of the human immunodeficiency virus (HIV) infection in particular. Weanticipatedthatin the caseofprotease inhibitors, a family of pH-dependent ARVsthatdisplay high aqueous solubility undertheacidconditionsof thestomach andextremely low solubilityunder the neutral ones ofthe small intestine, this strategy might failowing to an uncontrolled dissolution-re-precipitation process that will take place along the gastrointestinal tract.To tackle thisbiopharmaceutical challenge, in this work, wedesigned, produced and fully characterized a novelNanoparticle-in-MicroparticleDelivery System(NiMDS)comprised of pure nanoparticlesofthefirst-line protease inhibitor darunavir(DRV) and itsboosting agentritonavir (RIT) encapsulated within film-coated microparticles.For this, a clinically relevant combination of pure DRV and RIT nanoparticles wassynthesized by a sequential nanoprecipitation/solvent diffusion and evaporation method employing sodium alginateas viscosity stabilizer. Then, pure nanoparticles were encapsulated within calcium alginate/chitosanmicroparticlesthat were film-coated with a series ofpoly(methacrylate) copolymers with differential solubility in the gastrointestinal tract. This coating ensured full stability under gastric-like pH and sustained drug release under intestinal one. PharmacokineticstudiesconductedinalbinoSpragueDawleyratsshowed that DRV/RIT-loadedNiMDSs containing 17% w/w drug loading based on dry weight significantlyincreasedthe oral bioavailabilityof DRVby 2.3-foldwith respect to both theunprocessedandthenanonized DRV/RIT combinations that showed statistically similar performance. Moreover, they highlighted the limited advantage of only drugnanonizationto improve the oral pharmacokinetics of protease inhibitors and the potential of our novel delivery approach to improve the oral pharmacokinetics of nanonized poorly water-soluble drugs displaying pH-dependent solubility. Protease inhibitors (PIs) are gold-standard drugs in many ARV cocktails. Darunavir (DRV) is the latest approved PI and it is included in the 20th WHO Model List of Essential Medicines. PIs poorly-water soluble at intestinal pH and more soluble under gastric conditions. Drug nanonization represents one of the most common nanotechnology strategies to increase dissolution rate of hydrophobic drugs and thus, their oral bioavailability. For instance, pure drug nanosuspensions became the most clinically relevant nanoformulation. However, according to the physicochemical properties of PIs, nanonization does not appear as a very beneficial strategy due to the fast dissolution rate anticipated under the acid conditions of the stomach and their uncontrolled recrystallization and precipitation in the small intestine that might result in the formation of particles of unpredictable size and structure (e.g., crystallinity and polymorphism) and consequently, unknown dissolution rate and bioavailability. In this work, we developed a sequential nanoprecipitation method for the production of pure nanoparticles of DRV and its boosting agent ritonavir in a clinically relevant 8:1 wt ratio using alginate as viscosity stabilizer and used this nanosuspension to produce a novel kind of nanoparticle-in-microparticle delivery system that was fully characterized and the pharmacokinetics assessed in rats. The most significant points of the current manuscript are. Copyright © 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Bioleaching mechanism of Co and Li from spent lithium-ion battery by the mixed culture of acidophilic sulfur-oxidizing and iron-oxidizing bacteria.

PubMed

Xin, Baoping; Zhang, Di; Zhang, Xian; Xia, Yunting; Wu, Feng; Chen, Shi; Li, Li

2009-12-01

The bioleaching mechanism of Co and Li from spent lithium-ion batteries by mixed culture of sulfur-oxidizing and iron-oxidizing bacteria was investigated. It was found that the highest release of Li occurred at the lowest pH of 1.54 with elemental sulfur as an energy source, the lowest occurred at the highest pH of 1.69 with FeS(2). In contrast, the highest release of Co occurred at higher pH and varied ORP with S + FeS(2), the lowest occurred at almost unchanged ORP with S. It is suggested that acid dissolution is the main mechanism for Li bioleaching independent of energy matters types, however, apart from acid dissolution, Fe(2+) catalyzed reduction takes part in the bioleaching process as well. Co(2+) was released by acid dissolution after insoluble Co(3+) was reduced into soluble Co(2+) by Fe(2+) in both FeS(2) and FeS(2) + S systems. The proposed bioleaching mechanism mentioned above was confirmed by the further results obtained from the experiments of bioprocess-stimulated chemical leaching and from the changes in structure and component of bioleaching residues characterized by XPS, SEM and EDX.

Convective Instability and Mass Transport of the Diffusion Layer in CO2 Sequestration

NASA Astrophysics Data System (ADS)

Backhaus, S.

2011-12-01

The long-term fate of supercritical (sc) CO2 in saline aquifers is critical to the security of carbon sequestration, an important option for eliminating or reducing the emissions of this most prevalent greenhouse gas. scCO2 is less dense than brine and floats to the top of the aquifer where it is trapped in a metastable state by a geologic feature such as a low permeability cap rock. Dissolution into the underlying brine creates a CO2-brine mixture that is denser than brine, eliminating buoyancy and removing the threat of CO2 escaping back to the atmosphere. If molecular diffusion were the only dissolution mechanism, the CO2 waste stream from a typical large coal-fired electrical power plant may take upward of 10,000 years to no longer pose a threat, however, a convective instability of the dense diffusion boundary layer between the scCO2 and the brine can dramatically increase the dissolution rates, shortening the lifetime of the scCO2 waste pool. We present results of 2D and 3D similitude-correct, laboratory-scale experiments using an analog fluid system. The experiments and flow visualization reveal the onset of the convective instability, the dynamics of the fluid flows during the convective processes, and the long-term mass transfer rates.

Combined application of mixture experimental design and artificial neural networks in the solid dispersion development.

PubMed

Medarević, Djordje P; Kleinebudde, Peter; Djuriš, Jelena; Djurić, Zorica; Ibrić, Svetlana

2016-01-01

This study for the first time demonstrates combined application of mixture experimental design and artificial neural networks (ANNs) in the solid dispersions (SDs) development. Ternary carbamazepine-Soluplus®-poloxamer 188 SDs were prepared by solvent casting method to improve carbamazepine dissolution rate. The influence of the composition of prepared SDs on carbamazepine dissolution rate was evaluated using d-optimal mixture experimental design and multilayer perceptron ANNs. Physicochemical characterization proved the presence of the most stable carbamazepine polymorph III within the SD matrix. Ternary carbamazepine-Soluplus®-poloxamer 188 SDs significantly improved carbamazepine dissolution rate compared to pure drug. Models developed by ANNs and mixture experimental design well described the relationship between proportions of SD components and percentage of carbamazepine released after 10 (Q10) and 20 (Q20) min, wherein ANN model exhibit better predictability on test data set. Proportions of carbamazepine and poloxamer 188 exhibited the highest influence on carbamazepine release rate. The highest carbamazepine release rate was observed for SDs with the lowest proportions of carbamazepine and the highest proportions of poloxamer 188. ANNs and mixture experimental design can be used as powerful data modeling tools in the systematic development of SDs. Taking into account advantages and disadvantages of both techniques, their combined application should be encouraged.

45 CFR 501.5 - Depositions.

Code of Federal Regulations, 2012 CFR

2012-10-01

... is expected the witness will testify, and the time and place proposed for the taking of the... served upon all parties at least 10 days prior to the date of the taking of the deposition. (b) Who may... the time and place specified in the Commission's order, the officer taking the deposition will permit...

45 CFR 501.5 - Depositions.

Code of Federal Regulations, 2013 CFR

2013-10-01

... is expected the witness will testify, and the time and place proposed for the taking of the... served upon all parties at least 10 days prior to the date of the taking of the deposition. (b) Who may... the time and place specified in the Commission's order, the officer taking the deposition will permit...

45 CFR 501.5 - Depositions.

Code of Federal Regulations, 2014 CFR

2014-10-01

... is expected the witness will testify, and the time and place proposed for the taking of the... served upon all parties at least 10 days prior to the date of the taking of the deposition. (b) Who may... the time and place specified in the Commission's order, the officer taking the deposition will permit...

Optimal Vaccination in a Stochastic Epidemic Model of Two Non-Interacting Populations

DTIC Science & Technology

2015-02-17

of diminishing returns from vacci- nation will generally take place at smaller vaccine allocations V compared to the deterministic model. Optimal...take place and small r0 values where it does not is illustrat- ed in Fig. 4C. As r0 is decreased, the region between the two instances of switching...approximately distribute vaccine in proportion to population size. For large r0 (r0 ≳ 2.9), two switches take place . In the deterministic optimal solution, a

Consumer vinegar test for determining calcium disintegration.

PubMed

Mason, N A; Patel, J D; Dressman, J B; Shimp, L A

1992-09-01

A consumer test and standardized methods were compared for measuring the disintegration of calcium tablets, and the disintegration results were compared with results of dissolution testing to determine the ability of the consumer test of disintegration to predict bioavailability of calcium. Disintegration of 17 calcium supplement products, in tablet form, was studied in Simulated Gastric Fluid Test Solution, USP, without pepsin (GF), in distilled water, and in white distilled vinegar. For disintegration testing with GF and with distilled water, six tablets of each product were placed in an apparatus and immersed in the solution at 37 degrees C for 60 minutes. Six tablets of each product were tested in 200 mL of vinegar at room temperature for 30 minutes. Disintegration was determined by visual observation. Seven products were tested for dissolution in GF or water. Three samples of each product were tested at intervals over 120 minutes for calcium content. Results of testing with an ion-selective electrode were converted to milligrams and compared with the calcium content of the tablets (as claimed on the package label). The mean disintegration times of various calcium products in vinegar ranged from 1.8 to greater than 30 minutes. The mean time in distilled water and GF ranged from 1.6 to greater than 60 minutes and from 1.0 to greater than 60 minutes, respectively. Results were in agreement in 87% to 93% of cases between the consumer vinegar test and the standardized disintegration test methods, a significant correlation. No correlation was found between disintegration time and the extent of dissolution. The disintegration and dissolution of commercially available calcium tablets was highly variable.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulp tissue dissolution capacity of QMix 2in1 irrigation solution.

PubMed

Arslan, Dilara; Guneser, Mehmet Burak; Kustarci, Alper; Er, Kursat; Siso, Seyda Herguner

2015-01-01

The aim of this study was to evaluate the tissue dissolution efficacy of four root canal irrigation solutions (sodium hypochlorite [NaOCl], chlorhexidine gluconate [CHX], Octenidine [OCT], and QMix 2in1) on bovine pulp tissue. Fifty bovine pulp tissue samples, each weighing 6.55 mg, were prepared and randomly divided into four experimental groups and one control group (n = 10) according to the dissolution irrigants used: (1) 5.25% NaOCl group; (2) 2% CHX group; (3) OCT group; (4) QMix 2in1 group; and (5) control group (saline solution). These samples were then placed into special bovine dentin reservoir models and immersed for 1 h with each test solution (0.1 mL of each) at room temperature. The pulp samples were then blotted dry and weighed again. The percentage of weight loss was calculated. Statistically analyzed with one-way analysis of variance and post-hoc Tukey tests (P = 0.05). Saline solution did not dissolve the bovine pulp tissue. All groups, except OCT, dissolved pulp samples more effectively than the control group (P < 0.05). The highest tissue dissolution was observed in 5.25% NaOCl group (P < 0.05). No statistically significant difference was found between the tissue-dissolving effect between QMix 2in1 and those of 2% CHX. Within the limitations of this in vitro study, NaOCl exhibited the best tissue-dissolving effect out of all solutions tested. CHX and QMix 2in1 were able to dissolve pulp tissue but less than NaOCl. OCT and saline solutions could not exhibit significantly tissue-dissolving effectiveness. This study shown that QMix 2in1 has little capacity to dissolve pulp tissue therefore used alone is not sufficient for this purpose.

Weathering profiles in soils and rocks on Earth and Mars

NASA Astrophysics Data System (ADS)

Hausrath, E.; Adcock, C. T.; Bamisile, T.; Baumeister, J. L.; Gainey, S.; Ralston, S. J.; Steiner, M.; Tu, V.

2017-12-01

Interactions of liquid water with rock, soil, or sediments can result in significant chemical and mineralogical changes with depth. These changes can include transformation from one phase to another as well as translocation, addition, and loss of material. The resulting chemical and mineralogical depth profiles can record characteristics of the interacting liquid water such as pH, temperature, duration, and abundance. We use a combined field, laboratory, and modeling approach to interpret the environmental conditions preserved in soils and rocks. We study depth profiles in terrestrial field environments; perform dissolution experiments of primary and secondary phases important in soil environments; and perform numerical modeling to quantitatively interpret weathering environments. In our field studies we have measured time-integrated basaltic mineral dissolution rates, and interpreted the impact of pH and temperature on weathering in basaltic and serpentine-containing rocks and soils. These results help us interpret fundamental processes occurring in soils on Earth and on Mars, and can also be used to inform numerical modeling and laboratory experiments. Our laboratory experiments provide fundamental kinetic data to interpret processes occurring in soils. We have measured dissolution rates of Mars-relevant phosphate minerals, clay minerals, and amorphous phases, as well as dissolution rates under specific Mars-relevant conditions such as in concentrated brines. Finally, reactive transport modeling allows a quantitative interpretation of the kinetic, thermodynamic, and transport processes occurring in soil environments. Such modeling allows the testing of conditions under longer time frames and under different conditions than might be possible under either terrestrial field or laboratory conditions. We have used modeling to examine the weathering of basalt, olivine, carbonate, phosphate, and clay minerals, and placed constraints on the duration, pH, and solution chemistry of past aqueous alteration occurring on Mars.

Salt precipitation and dissolution in the late Quaternary Dead Sea: Evidence from chemical and δ37Cl composition of pore fluids and halites

NASA Astrophysics Data System (ADS)

Levy, Elan J.; Yechieli, Yoseph; Gavrieli, Ittai; Lazar, Boaz; Kiro, Yael; Stein, Mordechai; Sivan, Orit

2018-04-01

The chemical composition and δ37Cl of pore fluids from the ICDP core drilled in the deepest floor of the terminal and hypersaline Dead Sea, and halites from the adjacent Mount Sedom salt diapir, are used to establish the dynamics of halite precipitation and dissolution during the last interglacial and glacial periods. Between ∼132 and 116 thousand years ago (ka) halites precipitated in the lake resulting in the expulsion of Na+ and Cl- from the residual solution. Over 50% of the Cl- reservoir was removed, resulting in a decrease in the Na/Cl ratio from 0.57 to 0.19. This process was accompanied by a decrease in δ37Cl values in the precipitating halites and the associated residual Cl- in the lake. The observed decrease fits a Rayleigh distillation curve with a fractionation factor of Δ(NaCl-Dead Sea solution) = +0.32‰ (±0.12) determined in the present study. This behavior implies negligible contribution of external sources of Cl- to the lake during the main peak of the last interglacial, MIS5e. Subsequently, during the last glacial (ca. 117 to 17 ka) dissolution of halite took place, the Na+ and Cl- inventory were replenished, accompanied by an increase in Na/Cl from 0.21 to 0.55 and in the δ37Cl values from -0.46‰ to -0.12‰. While the lake underwent significant dilution during that time, the decrease in salinity was somewhat suppressed by the dissolution of the halite which was mostly derived from Mount Sedom salt diapir.

Pulp tissue dissolution capacity of QMix 2in1 irrigation solution

PubMed Central

Arslan, Dilara; Guneser, Mehmet Burak; Kustarci, Alper; Er, Kursat; Siso, Seyda Herguner

2015-01-01

Objective: The aim of this study was to evaluate the tissue dissolution efficacy of four root canal irrigation solutions (sodium hypochlorite [NaOCl], chlorhexidine gluconate [CHX], Octenidine [OCT], and QMix 2in1) on bovine pulp tissue. Materials and Methods: Fifty bovine pulp tissue samples, each weighing 6.55 mg, were prepared and randomly divided into four experimental groups and one control group (n = 10) according to the dissolution irrigants used: (1) 5.25% NaOCl group; (2) 2% CHX group; (3) OCT group; (4) QMix 2in1 group; and (5) control group (saline solution). These samples were then placed into special bovine dentin reservoir models and immersed for 1 h with each test solution (0.1 mL of each) at room temperature. The pulp samples were then blotted dry and weighed again. The percentage of weight loss was calculated. Statistically analyzed with one-way analysis of variance and post-hoc Tukey tests (P = 0.05). Results: Saline solution did not dissolve the bovine pulp tissue. All groups, except OCT, dissolved pulp samples more effectively than the control group (P < 0.05). The highest tissue dissolution was observed in 5.25% NaOCl group (P < 0.05). No statistically significant difference was found between the tissue-dissolving effect between QMix 2in1 and those of 2% CHX. Conclusions: Within the limitations of this in vitro study, NaOCl exhibited the best tissue-dissolving effect out of all solutions tested. CHX and QMix 2in1 were able to dissolve pulp tissue but less than NaOCl. OCT and saline solutions could not exhibit significantly tissue-dissolving effectiveness. This study shown that QMix 2in1 has little capacity to dissolve pulp tissue therefore used alone is not sufficient for this purpose. PMID:26430374

Speleothems in a wave-cut notch, Cayman Brac, British West Indies: The integrated product of subaerial precipitation, dissolution, and microbes

NASA Astrophysics Data System (ADS)

Jones, Brian

2010-12-01

A wave-cut notch that is deeply incised into the vertical cliff faces of Cayman Brac is adorned with stalactites, stalagmites, and columns. The prefix "notch" is applied to each type of speleothem in order to distinguish them from cave speleothems. These speleothemic deposits must have formed since the highstand, ~ 125,000 years ago, which was responsible for the development of the notch. The laminated notch speleothems are formed largely of aragonite (small and large crystals) and calcite (columnar, fiber, and grain-coating mats) along with minor amounts of dolomite, a Mg-Si precipitate (kerolite?), gypsum, and halite. Laminae, typically < 2 mm thick, are commonly bounded by dissolution discontinuities that truncate the older laminae and their formative aragonite and calcite crystals. The patchy tan, grey, to green surface coloration of the notch speleothems reflects the random distribution of the subaerial biofilms, which are formed of a diverse array of filamentous and non-filamentous microbes. The notch speleothems are the integrated product of precipitation and dissolution that was, in some places, microbially mediated. Interpretations based on their mineralogy and internal structures indicate that the composition of the formative waters must have temporally fluctuated with periods of precipitation being interrupted by periods of dissolution. The microbes that formed the subaerial biofilms may have influenced some of these processes. The aragonite, calcite, and kerolite (?) probably formed as evaporation and loss of Ca through precipitation progressively increased the Mg:Ca and the Si/(Ca + Mg) ratios. The dolomite, gypsum, and halite probably formed during early diagenesis during the evaporation of seawater that percolated into the interiors of the notch speleothems.

Colloid-associated plutonium aged at room temperature: evaluating its transport velocity in saturated coarse-grained granites

NASA Astrophysics Data System (ADS)

Xie, Jinchuan; Lin, Jianfeng; Wang, Yu; Li, Mei; Zhang, Jihong; Zhou, Xiaohua; He, Yifeng

2015-01-01

The fate and transport of colloidal contaminants in natural media are complicated by physicochemical properties of the contaminants and heterogeneous characteristics of the media. Size and charge exclusion are two key microscopic mechanisms dominating macroscopic transport velocities. Faster velocities of colloid-associated actinides than that of 3H2O were consistently indicated in many studies. However, dissociation/dissolution of these sorbed actinides (e.g., Pu and Np), caused by their redox reactions on mineral surfaces, possibly occurred under certain chemical conditions. How this dissolution is related to transport velocities remains unanswered. In this study, aging of the colloid-associated Pu (pseudo-colloid) at room temperature and transport through the saturated coarse-grained granites were performed to study whether Pu could exhibit slower velocity than that of 3H2O (UPu/UT < 1). The results show that oxidative dissolution of Pu(IV) associated with the surfaces of colloidal granite particles took place during the aging period. The relative velocity of UPu/UT declined from 1.06 (unaged) to 0.745 (135 d) over time. Size exclusion limited to the uncharged nano-sized particles could not explain such observed UPu/UT < 1. Therefore, the decline in UPu/UT was ascribed to the presence of electrostatic attraction between the negatively charged wall of granite pore channels and the Pu(V)O2+, as evidenced by increasing Pu(V)O2+ concentrations in the suspensions aged in sealed vessels. As a result of this attraction, Pu(V)O2+ was excluded from the domain closer to the centerline of pore channels. This reveals that charge exclusion played a more important role in dominating UPu than the size exclusion under the specific conditions, where oxidative dissolution of colloid-associated Pu(IV) was observed in the aged suspensions.

Synchrotron-Based In Situ Characterization of Carbon-Supported Platinum and Platinum Monolayer Electrocatalysts

DOE PAGES

Sasaki, Kotaro; Marinkovic, Nebojsa; Isaacs, Hugh S.; ...

2015-11-17

Understanding oxidation/dissolution mechanisms of Pt is critical in designing durable catalysts for the oxygen reduction reaction (ORR), but exact mechanisms remain unclear. Our present work explores the oxidation/dissolution of Pt and Pt monolayer (ML) electrocatalysts over a wide range of applied potentials using cells that facilitate in situ measurements by combining X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) measurements. Furthermore, the X-ray absorption near edge structure (XANES) measurement demonstrated that Pt nanoparticle surfaces were oxidized from metallic Pt to α-PtO 2-type oxide during the potential sweep from 0.41 to 1.5 V, and the transition state of O or OHmore » adsorption on Pt and the onset of the place exchange process were revealed by the delta mu (Δμ) method. Only the top layers of Pt nanoparticles were oxidized, while the inner Pt atoms remained intact. At a higher potential over 1.9 V, α-PtO 2-type surface oxides dissolve due to local acidification caused by the oxygen evolution reaction and carbon corrosion. Pt oxidation of Pt ML on the Pd nanoparticle electrocatalyst is considerably hampered compared with the Pt/C catalyst, presumably because preferential Pd oxidation proceeds at the defects in Pt MLs up to 0.91 V and through O penetrated through the Pt MLs by the place exchange process above 1.11 V.« less

Anticrack inclusion model for compaction bands in sandstone

NASA Astrophysics Data System (ADS)

Sternlof, Kurt R.; Rudnicki, John W.; Pollard, David D.

2005-11-01

Detailed observations of compaction bands exposed in the Aztec Sandstone of southeastern Nevada indicate that these thin, tabular, bounded features of localized porosity loss initiated at pervasive grain-scale flaws, which collapsed in response to compressive tectonic loading. From many of these Griffith-type flaws, an apparently self-sustaining progression of collapse propagated outward to form bands of compacted grains a few centimeters thick and tens of meters in planar extent. These compaction bands can be idealized as highly eccentric ellipsoidal bodies that have accommodated uniform uniaxial plastic strain parallel to their short dimension within a surrounding elastic material. They thus can be represented mechanically as contractile Eshelby inclusions, which generate near-tip compressive stress concentrations consistent with self-sustaining, in-plane propagation. The combination of extreme aspect ratio (˜10-4) and significant uniaxial plastic strain (˜10%) also justifies an approximation of the bands as anticracks: sharp boundaries across which a continuous distribution of closing mode displacement discontinuity has been accommodated. This anticrack interpretation of compaction bands is analogous to that of pressure solution surfaces, except that porosity loss takes the place of material dissolution. We find that displacement discontinuity boundary element modeling of compaction bands as anticracks within a two-dimensional linear elastic continuum can accurately represent the perturbed external stress fields they induce.

Size and shape tunability of self-assembled InAs/GaAs nanostructures through the capping rate

NASA Astrophysics Data System (ADS)

Utrilla, Antonio D.; Grossi, Davide F.; Reyes, Daniel F.; Gonzalo, Alicia; Braza, Verónica; Ben, Teresa; González, David; Guzman, Alvaro; Hierro, Adrian; Koenraad, Paul M.; Ulloa, Jose M.

2018-06-01

The practical realization of epitaxial quantum dot (QD) nanocrystals led before long to impressive experimental advances in optoelectronic devices, as well as to the emergence of new technological fields. However, the necessary capping process is well-known to hinder a precise control of the QD morphology and therefore of the possible electronic structure required for certain applications. A straightforward approach is shown to tune the structural and optical properties of InAs/GaAs QDs without the need for any capping material different from GaAs or annealing process. The mere adjust of the capping rate allows controlling kinetically the QD dissolution process induced by the surface In-Ga intermixing taking place during overgrowth, determining the final metastable structure. While low capping rates make QDs evolve into more thermodynamically favorable quantum ring structures, increasing capping rates help preserve the QD height and shape, simultaneously improving the luminescence properties. Indeed, a linear relationship between capping rate and QD height is found, resulting in a complete preservation of the original QD geometry for rates above ∼2.0 ML s-1. In addition, the inhibition of In diffusion from the QDs top to the areas in between them yields thinner WLs, what could improve the performance of several QD-based optoelectronic devices.

Roughness evolution of metallic implant surfaces under contact loading and nanometer-scale chemical etching.

PubMed

Ryu, J J; Letchuman, S; Shrotriya, P

2012-10-01

Surface damage of metallic implant surface at taper lock and clamped interfaces may take place through synergistic interactions between repeated contact loading and corrosion. In the present research, we investigated the influence of surface roughness and contact loading on the mechanical and chemical damage phenomena. Cobalt-chromium (CoCrMo) specimens with two different roughness configurations created by milling and grinding process were subjected to normal and inclined contact loading. During repeated contact loading, amplitude of surface roughness reached a steady value after decreasing during the first few cycles. During the second phase, the alternating experiment of rough surface contact and micro-etching was conducted to characterize surface evolution behavior. As a result, surface roughness amplitude continuously evolved-decreasing during contact loading due to plastic deformation of contacting asperities and increasing on exposure to corrosive environment by the preferential corrosion attack on stressed area. Two different instabilities could be identified in the surface roughness evolution during etching of contact loaded surfaces: increase in the amplitude of dominant wavenumber and increase in amplitude of a small group of roughness modes. A damage mechanism that incorporates contact-induced residual stress development and stress-assisted dissolution is proposed to elucidate the measured instabilities in surface roughness evolution. Copyright © 2012 Elsevier Ltd. All rights reserved.

Anisotropic Shape Changes of Silica Nanoparticles Induced in Liquid with Scanning Transmission Electron Microscopy.

PubMed

Zečević, Jovana; Hermannsdörfer, Justus; Schuh, Tobias; de Jong, Krijn P; de Jonge, Niels

2017-01-01

Liquid-phase transmission electron microscopy (TEM) is used for in-situ imaging of nanoscale processes taking place in liquid, such as the evolution of nanoparticles during synthesis or structural changes of nanomaterials in liquid environment. Here, it is shown that the focused electron beam of scanning TEM (STEM) brings about the dissolution of silica nanoparticles in water by a gradual reduction of their sizes, and that silica redeposites at the sides of the nanoparticles in the scanning direction of the electron beam, such that elongated nanoparticles are formed. Nanoparticles with an elongation in a different direction are obtained simply by changing the scan direction. Material is expelled from the center of the nanoparticles at higher electron dose, leading to the formation of doughnut-shaped objects. Nanoparticles assembled in an aggregate gradually fuse, and the electron beam exposed section of the aggregate reduces in size and is elongated. Under TEM conditions with a stationary electron beam, the nanoparticles dissolve but do not elongate. The observed phenomena are important to consider when conducting liquid-phase STEM experiments on silica-based materials and may find future application for controlled anisotropic manipulation of the size and the shape of nanoparticles in liquid. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Experimental investigation of cavitation induced air release

NASA Astrophysics Data System (ADS)

Kowalski, Karoline; Pollak, Stefan; Hussong, Jeanette

Variations in cross-sectional areas may lead to pressure drops below a critical value, such that cavitation and air release are provoked in hydraulic systems. Due to a relatively slow dissolution of gas bubbles, the performance of hydraulic systems will be affected on long time scales by the gas phase. Therefore predictions of air production rates are desirable to describe the system characteristics. Existing investigations on generic geometries such as micro-orifice flows show an outgassing process due to hydrodynamic cavitation which takes place on time scales far shorter than diffusion processes. The aim of the present investigation is to find a correlation between global, hydrodynamic flow characteristics and cavitation induced undissolved gas fractions generated behind generic flow constrictions such as an orifice or venturi tube. Experimental investigations are realised in a cavitation channel that enables an independent adjustment of the pressure level upstream and downstream of the orifice. Released air fractions are determined by means of shadowgraphy imaging. First results indicate that an increased cavitation activity leads to a rapid increase in undissolved gas volume only in the choking regime. The frequency distribution of generated gas bubble size seems to depend only indirectly on the cavitation intensity driven by an increase of downstream coalescence events due to a more densely populated bubbly flow.

Propagation mode of Portevin-Le Chatelier plastic instabilities in an aluminium-magnesium alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zeghloul, A.; Mliha-Touati, M.; Bakir, S.

1996-11-01

The Portevin-Le Chatelier (PLC) effect is characterized by the appearance of serrations in load (hard tensile machine for constant strain rate tests) or by steps (soft tensile machine for constant stress rate tests) or by steps (soft tensile machine for constant stress rate tests) on the stress-strain curves. It is now widely accepted that the PLC propagative instability stems from the dynamic interaction between diffusing solute atoms and mobile dislocations in the temperature and strain rate ranges where dynamic strain ageing (DSA) takes place. This competition results in a negative strain-rate sensitivity. However, in some alloys, like concentrated solid solutions,more » shearing of precipitates accompanied by their dissolution and subsequent reprecipitation during tensile test may also lead to a negative strain rate sensitivity. In view of the renewed theoretical interest in propagative instabilities, it is important that the experimental features of band propagation be well characterized. In this work the authors present experimental results that are obtained from the investigation of the PLC bands associated with discontinuous yielding. These results show that the band strain, the band velocity and the propagation mode of the bands depend on the stress rate when the test is carried out on a soft tensile machine.« less

Chemical weathering in a tropical watershed, Luquillo Mountains, Puerto Rico III: Quartz dissolution rates

USGS Publications Warehouse

Schulz, M.S.; White, A.F.

1999-01-01

The paucity of weathering rates for quartz in the natural environment stems both from the slow rate at which quartz dissolves and the difficulty in differentiating solute Si contributed by quartz from that derived from other silicate minerals. This study, a first effort in quantifying natural rates of quartz dissolution, takes advantage of extremely rapid tropical weathering, simple regolith mineralogy, and detailed information on hydrologic and chemical transport. Quartz abundances and grain sizes are relatively constant with depth in a thick saprolite. Limited quartz dissolution is indicated by solution rounding of primary angularity and by the formation of etch pits. A low correlation of surface area (0.14 and 0.42 m2 g-1) with grain size indicates that internal microfractures and pitting are the principal contributors to total surface area. Pore water silica concentration increases linearly with depth. On a molar basis, between one and three quarters of pore water silica is derived from quartz with the remainder contributed from biotite weathering. Average solute Si remains thermodynamically undersaturated with respect to recently revised estimates of quartz solubility (17-81 ??M). Etch pitting is more abundant on grains in the upper saprolite and is associated with pore waters lower in dissolved silica. Rate constants describing quartz dissolution increase with decreasing depth (from 10-14.5-10-15.1 mol m-2 s-1), which correlate with both greater thermodynamic undersaturation and increasing etch pit densities. Unlike for many aluminosilicates, the calculated natural weathering rates of quartz fall slightly below the rate constants previously reported for experimental studies (10-12.4-10-14.2 mol m-2 s-1). This agreement reflects the structural simplicity of quartz, dilute solutes, and near-hydrologic saturation.

2012 CCCC Chair's Address: Stories Take Place--A Performance in One Act

ERIC Educational Resources Information Center

Powell, Malea

2012-01-01

This is a written version of the address that Malea Powell gave at the Conference on College Composition and Communication (CCCC) Convention in St. Louis, Missouri, on Thursday, March 22, 2012. This address is a collection of stories. According to her, stories take place. Stories practice place into space. Stories produce habitable spaces. She…

Lithium Assisted “Dissolution–Alloying” Synthesis of Nanoalloys from Individual Bulk Metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barkholtz, Heather M.; Gallagher, James R.; Li, Tao

2016-04-12

We report new fundamental chemistry involved in the synthesis of bimetallic nanoalloys via dissolving the pure bulk transition metals in molten lithium. It is revealed at the atomic level that when two pure bulk transition metals such as Pd and Pt are placed in molten lithium (similar to 200 degrees C), they undergo a dissolution process in which the metal-metal bonds in pure bulk transition metals are completely ruptured, which results in the existence of individual Pd and Pt atoms surrounded by lithium atoms, as is evident by synchrotron X-ray adsorption techniques. Then, upon the conversion of metal lithium tomore » LiOH in humid air, the Pd and Pt atoms undergo an alloying process to aggregate into nanoalloys. This method was further expanded to include PdZn, which is notoriously difficult to prepare via traditional nanoalloy synthesis methods due to the easily oxidizable Zn component. The constantly reducing environment of metallic Li allowed for preparation of PdZn nanoalloys with minimal Zn oxidation via dissolution-alloying of individual bulk transition metals in molten lithium. Additionally, this lithium assisted "dissolution-alloying" method bypasses many complications intrinsic to conventional ion reduction-based nanoalloy synthesis including the necessity of ligated metal ions, the use of proper reducing agents and dispersing surfactants, and the presence of segregated phases due to different reduction potentials of the constituent metal ions.« less

Evaluation of Influence of Various Polymers on Dissolution and Phase Behavior of Carbamazepine-Succinic Acid Cocrystal in Matrix Tablets.

PubMed

Ullah, Majeed; Ullah, Hanif; Murtaza, Ghulam; Mahmood, Qaisar; Hussain, Izhar

2015-01-01

The aim of current study was to explore the influence of three commonly used polymers, that is, cellulosics and noncellulosics, for example, Methocel K4M, Kollidon VA/64, and Soluplus, on the phase disproportionation and drug release profile of carbamazepine-succinic acid (CBZ-SUC) cocrystal at varying drug to polymer ratios (1 : 1 to 1 : 0.25) in matrix tablets. The polymorphic phase disproportionation during in-depth dissolution studies of CBZ-SUC cocrystals and its crystalline properties were scrutinized by X-ray powder diffractrometry and Raman spectroscopy. The percent drug release from HPMC formulations (CSH) showed inverse relation with the concentration of polymer; that is, drug release increased with decrease in polymer concentration. On contrary, direct relation was observed between percent drug release and polymer concentrations of Kollidon VA 64/Soluplus (CSK, CSS). At similar polymer concentration, drug release from pure carbamazepine was slightly lower with HPMC formulations than that of cocrystal; however, opposite trend in release rate was observed with Kollidon VA/64 and Soluplus. The significant increase in dissolution rate of cocrystal occurred with Kollidon VA/64 and Soluplus at higher polymer concentration. Moreover, no phase change took place in Methocel and Kollidon formulations. No tablet residue was left for Soluplus formulation so the impact of polymer on cocrystal integrity cannot be predicted.

Evaluation of Influence of Various Polymers on Dissolution and Phase Behavior of Carbamazepine-Succinic Acid Cocrystal in Matrix Tablets

PubMed Central

Ullah, Majeed; Ullah, Hanif; Mahmood, Qaisar; Hussain, Izhar

2015-01-01

The aim of current study was to explore the influence of three commonly used polymers, that is, cellulosics and noncellulosics, for example, Methocel K4M, Kollidon VA/64, and Soluplus, on the phase disproportionation and drug release profile of carbamazepine-succinic acid (CBZ-SUC) cocrystal at varying drug to polymer ratios (1 : 1 to 1 : 0.25) in matrix tablets. The polymorphic phase disproportionation during in-depth dissolution studies of CBZ-SUC cocrystals and its crystalline properties were scrutinized by X-ray powder diffractrometry and Raman spectroscopy. The percent drug release from HPMC formulations (CSH) showed inverse relation with the concentration of polymer; that is, drug release increased with decrease in polymer concentration. On contrary, direct relation was observed between percent drug release and polymer concentrations of Kollidon VA 64/Soluplus (CSK, CSS). At similar polymer concentration, drug release from pure carbamazepine was slightly lower with HPMC formulations than that of cocrystal; however, opposite trend in release rate was observed with Kollidon VA/64 and Soluplus. The significant increase in dissolution rate of cocrystal occurred with Kollidon VA/64 and Soluplus at higher polymer concentration. Moreover, no phase change took place in Methocel and Kollidon formulations. No tablet residue was left for Soluplus formulation so the impact of polymer on cocrystal integrity cannot be predicted. PMID:26380301

Influence of oxidation state on water solubility of Si nanoparticles prepared by laser ablation in water

NASA Astrophysics Data System (ADS)

Ryabchikov, Yu. V.; Al-Kattan, A.; Chirvony, V.; Sanchez-Royo, J. F.; Sentis, M.; Timoshenko, V. Yu.; Kabashin, A. V.

2017-02-01

Femtosecond laser fragmentation from preliminarily prepared water-dispersed Si microcolloids was used to synthesize bare (ligand-free) spherical silicon nanoparticles (Si-NPs) with low size dispersion and controllable mean size from a few nm to several tens of nm. In order to control the oxidation state of Si-NPs, the fragmentation was performed in normal oxygen-saturated water (oxygen-rich conditions) or in water disoxygenated by pumping with noble gases (Ag, He) before and during the experiment (oxygen-free conditions). XPS and TEM studies revealed that Si-NPs were composed of Si nanocrystals with inclusions of silicon oxide species, covered by SiOx (1 < x < 2) shell, while the total oxide content depended whether Si-NPs were prepared in oxygen-rich or oxygen-free conditions. When placed into a dialysis box, waterdispersed Si-NPs rapidly dissolved, which was evidenced by TEM data. In this case, NPs prepared under oxygen-rich conditions demonstrated much faster dissolution kinetics and their complete disappearance after 7-10 days, while the dissolution process of less oxidized counterparts could last much longer (25-30 days). Much fast dissolution kinetics of more oxidized Si-NPs was attributed to more friable structure of nanoparticle core due to the presence of numerous oxidation-induced defects. Laser-synthesized Si-NPs are of paramount importance for biomedical applications.

Preparation of amorphous solid dispersions by rotary evaporation and KinetiSol Dispersing: approaches to enhance solubility of a poorly water-soluble gum extract.

PubMed

Bennett, Ryan C; Brough, Chris; Miller, Dave A; O'Donnell, Kevin P; Keen, Justin M; Hughey, Justin R; Williams, Robert O; McGinity, James W

2015-03-01

Acetyl-11-keto-β-boswellic acid (AKBA), a gum resin extract, possesses poor water-solubility that limits bioavailability and a high melting point making it difficult to successfully process into solid dispersions by fusion methods. The purpose of this study was to investigate solvent and thermal processing techniques for the preparation of amorphous solid dispersions (ASDs) exhibiting enhanced solubility, dissolution rates and bioavailability. Solid dispersions were successfully produced by rotary evaporation (RE) and KinetiSol® Dispersing (KSD). Solid state and chemical characterization revealed that ASD with good potency and purity were produced by both RE and KSD. Results of the RE studies demonstrated that AQOAT®-LF, AQOAT®-MF, Eudragit® L100-55 and Soluplus with the incorporation of dioctyl sulfosuccinate sodium provided substantial solubility enhancement. Non-sink dissolution analysis showed enhanced dissolution properties for KSD-processed solid dispersions in comparison to RE-processed solid dispersions. Variances in release performance were identified when different particle size fractions of KSD samples were analyzed. Selected RE samples varying in particle surface morphologies were placed under storage and exhibited crystalline growth following solid-state stability analysis at 12 months in comparison to stored KSD samples confirming amorphous instability for RE products. In vivo analysis of KSD-processed solid dispersions revealed significantly enhanced AKBA absorption in comparison to the neat, active substance.

Dissolution of fine particle fraction from truncated Anderson cascade impactor with an enhancer cell.

PubMed

Tay, Justin Yong Soon; Liew, Celine Valeria; Heng, Paul Wan Sia

2018-04-22

Dissolution testing for inhalers were previously conducted either on unfractionated drug-carrier powders or drug of specific aerodynamic particle size. In this study, the collection of the full fine particle fraction (FPF) was attempted on a single stage. Capsules containing 30 mg of 2% salbutamol sulfate (SS) was tested to have a FPF of 9 ± 1% using the full set of Andersen cascade impactor (ACI) and a modified Rotahaler® capable of achieving 4.0 kPa pressure drop at 60 L/min air flow rate. A truncated ACI comprising the USP throat, pre-separator, stage 0, stage 4, stage F, polytetrafluoroethylene funnel (TF) and small collection plate (sCP) was found to be capable of achieving a FPF of 9% collected on TF and sCP. An adhesive tape was used to collect the FPF from the TF and sCP and held in place by an enhancer cell in a 200 mL round bottom vessel containing 50 mL Gamble's solution with 0.2 v/v, % Tween 80. Dissolution testing of SS and Seretide® showed burst release of SS and salmeterol while sustained release of fluticasone. This study demonstrated a reproducible method which may be used for evaluation of the full FPF of orally inhaled products. Copyright © 2018 Elsevier B.V. All rights reserved.

[Chang of cognitions and feelings during the process of procrastination].

PubMed

Kohama, Shun

2010-10-01

This study investigated change of cognitions and feelings before, during, and after the process of procrastination. A questionnaire was administered to 358 undergraduate students asking them to recall and rate their experience of procrastinating. The results revealed that negative feelings which take place during procrastination interfere with task performance. Planning before procrastination is associated with positive feelings after procrastination, and these positive feelings assist task performance. Optimistic thinking is positively related to both positive and negative feelings; the former take place during procrastination, and the latter take place after procrastination.

Relationship of Technological Properties with Dynamic Recrystallization of Quartz on the Example of Objects of the Karelian-Kola Region

NASA Astrophysics Data System (ADS)

Skamnitskaya, Lubov; Rakov, Leonid; Bubnova, Tatyana; Shchiptsov, Vladimir

2017-12-01

Despite the significant reserves of quartz raw materials, there is a deficit of high purity quartz. It is due to the strict technical requirements imposed by standards for this type of raw materials and technological properties of quartz, which are determined by the features of the crystal structure. The crystalline structure is of particular importance for the technological properties of quartz, since such important characteristics as the limit of raw material enrichment, dissolution rate in acid, melting point of quartz, etc., are determined. The formation of the crystal structure of quartz under natural conditions is associated with the successive dynamic recrystallization of the mineral. The degree of dynamic recrystallization of quartz reflects the distribution of dispersed impurities. If it is weakly manifested, the dispersed impurities are not displaced from one zone to another, and all quartz microblocks contain approximately the same concentration. In this case, more or less uniform dissolution of various regions of quartz is observed, and the pattern of distribution of submicroscopic inhomogeneities is monotonic. If intensive dynamic recrystallization of quartz takes place, then it causes a significant redistribution of the scattered impurities. Then the treatment in HF leads to the appearance of a contrast pattern of the distribution of submicroscopic inhomogeneities. The details of the crystal structure of quartz in this work were investigated by the electron paramagnetic resonance (EPR) method using the ER-420 “Bruker” spectrometer. In the selected samples of quartz, the concentrations of isomorphic impurities Al and Ti were measured, and the degree of crystallinity D of the mineral was estimated from the EPR spectra of each of them. Thus, the technological properties of quartz are determined by various geological processes. The results of the studies show that when evaluating the prospects of quartz raw materials, it is necessary to take into account the staged dynamic dynamical recrystallization of quartz in natural conditions. This factor can play both a positive and a negative role at various stages of mineral formation. Its influence is reflected in the state of the crystal structure of quartz, which should be taken into account when developing effective technologies for its enrichment. The intermediate stage of dynamic recrystallization corresponding to the end of the second stage-the beginning of the third stage of quartz recrystallization-is optimal for the formation of high-purity quartz. When choosing a site for the first-stage quartz mining at large deposits in the Karelian-Kola region, one should be guided by the stage of dynamic recrystallization.

Pyroprocess for processing spent nuclear fuel

DOEpatents

Miller, William E.; Tomczuk, Zygmunt

2002-01-01

This is a pyroprocess for processing spent nuclear fuel. The spent nuclear fuel is chopped into pieces and placed in a basket which is lowered in to a liquid salt solution. The salt is rich in ZrF.sub.4 and containing alkali or alkaline earth fluorides, and in particular, the salt chosen was LiF-50 mol % ZrF.sub.4 with a eutectic melting point of 500.degree. C. Prior to lowering the basket, the salt is heated to a temperature of between 550.degree. C. and 700.degree. C. in order to obtain a molten solution. After dissolution the oxides of U, Th, rare earth and other like oxides, the salt bath solution is subject to hydro-fluorination to remove the oxygen and then to a fluorination step to remove U as gaseous UF.sub.6. In addition, after dissolution, the basket contains PuO.sub.2 and undissolved parts of the fuel rods, and the basket and its contents are processed to remove the Pu.

Investigation of structural resorption behavior of biphasic bioceramics with help of gravimetry, μCT, SEM, and XRD.

PubMed

de Wild, Michael; Amacher, Fabienne; Bradbury, Christopher R; Molenberg, Aart

2016-04-01

Resorbable bone substitute materials are widely used for bone augmentation after tumor resection, parallel to implant placement, or in critical size bone defects. In this study, the structural dissolution of a biphasic calcium phosphate bone substitute material with a hydroxyapatite (HA)/tricalcium phosphate (β-TCP) ratio of 60/40 was investigated by repeatedly placing porous blocks in EDTA solution at 37 °C. At several time points, the blocks were investigated by SEM, µCT, and gravimetry. It was found that always complete 2-3 µm sized grains were removed from the structure and that the β-TCP is dissolved more rapidly. This selective dissolution of the β-TCP grains was confirmed by XRD measurements. The blocks were eroded from the outside toward the center. The structure remained mechanically stable because the central part showed a delayed degradation and because the slower dissolving HA grains preserved the integrity of the structure. © 2015 Wiley Periodicals, Inc.

Questa baseline and pre-mining ground-water quality investigation. 19. Leaching characteristics of composited materials from mine waste-rock piles and naturally altered areas near Questa, New Mexico

USGS Publications Warehouse

Smith, Kathleen S.; Hageman, Philip L.; Briggs, Paul H.; Sutley, Stephen J.; McCleskey, R. Blaine; Livo, K. Eric; Verplanck, Philip L.; Adams, Monique G.; Gemery-Hill, Pamela A.

2007-01-01

The goal of this study is to compare and contrast the leachability of metals and the acidity from individual mine waste-rock piles and natural erosional scars in the study area near Questa, New Mexico. Surficial multi-increment (composite) samples less than 2 millimeters in diameter from five waste-rock piles, nine erosional-scar areas, a less-altered site, and a tailings slurry-pipe sample were analyzed for bulk chemistry and mineralogy and subjected to two back-to-back leaching procedures. The first leaching procedure, the U.S. Geological Survey Field Leach Test (FLT), is a short-duration leach (5-minute shaking and 10-minute settling) and is intended to leach readily soluble materials. The FLT was immediately followed by an 18-hour, end-over-end rotation leaching procedure. Comparison of results from the back-to-back leaching procedures can provide information about reactions that may take place upon migration of leachates through changing geochemical conditions (for example, pH changes), both within the waste-rock and scar materials and away from the source materials. For the scar leachates, the concentrations of leachable metals varied substantially between the scar areas sampled. The scar leachates have low pH (pH 3.2-4.1). Under these low-pH conditions, cationic metals are solubilized and mobile, but anionic species, such as molybdenum, are less soluble and less mobile. Generally, metal concentrations in the waste-rock leachates did not exceed the upper range of those metal concentrations in the erosional-scar leachates. One exception is molybdenum, which is notably higher in the waste-rock leachates compared with the scar leachates. Most of the waste-rock leachates were at least mildly acidic (pH 3.0-6.2). The pH values in the waste-rock leachates span a large pH range that includes some pH-dependent solubility and metal-attenuation reactions. An increase in pH with leaching time and agitation indicates that there is pH-buffering capacity in some of the waste-rock piles. As pH increased in the waste-pile leachates, concentrations of several metals decreased with increasing time and agitation. Similar pH-dependent reactions may take place upon migration of the leachates in the waste-rock piles. Bulk chemistry, mineralogy, and leachate sulfur-isotope data indicate that the Capulin and Sugar Shack West waste-rock piles are compositionally different from the younger Sugar Shack South, Sugar Shack Middle, and Old Sulphur Gulch piles. The Capulin and Sugar Shack West piles have the lowest-pH leachates (pH 3.0-4.1) of the waste-pile samples, and the source material for the Capulin and Sugar Shack West piles appears to be similar to the source material for the erosional-scar areas. Calcite dissolution, in addition to gypsum dissolution, appears to produce the calcium and sulfate concentrations in leachates from the Sugar Shack South, Sugar Shack Middle, and Old Sulphur Gulch piles.

77 FR 12353 - U.S. Department of State Advisory Committee on Private International Law (ACPIL): Notice of...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-29

... Conference on Private International Law. The public meeting will take place on Tuesday, April 3, 2012 from 10... Place: The meeting will take place in Room 1205, Harry S Truman Building, 2201 C Street, NW., Washington... purpose of the collection is to validate the identity of individuals who enter Department facilities. The...

4D XMT of Reaction in Carbonates: Reactive Transport Dynamics at Multiples Scales

NASA Astrophysics Data System (ADS)

Menke, H. P.; Reynolds, C. A.; Andrew, M. G.; Nunes, J. P. P.; Bijeljic, B.; Blunt, M. J.

2016-12-01

Upscaling pore scale rock-fluid interaction processes for predictive modelling poses a challenge to underground carbon storage. We have completed experiments and flow modelling to investigate the impact of pore-space heterogeneity and scale on the dissolution of two limestones at both the mm and cm scales. Two samples were reacted with reservoir condition CO2-saturated brine at both scales and scanned dynamically as dissolution took place. First, 1-cm long 4-mm diameter micro cores were scanned during reactive flow at a 4-μm resolution between 4 and 40 times using 4D X-ray micro-tomography over the course of 1.5 hours using a laboratory μ-CT. Second, 3.8-cm diameter, 8-cm long macro cores were reacted at the same conditions inside a reservoir condition flow rig and imaged using a medical CT scanner. Each sample was imaged 10 times over the course of 1.5 hours at a 250 x 250 x 500-μm resolution. The reacted macro cores were then scanned inside a μ-CT at a 27-μm resolution to assess the alteration in pore-scale reaction-induced heterogeneity. It was found that both limestones showed channel formation at the pore-scale and progressive high porosity pathway dissolution at the core-scale with the more heterogeneous rock having dissolution progressing along direction of flow more quickly. Additionally, upon analysis of the high-resolution macro core images it was found that the dissolution pathways contained a distinct microstructure that was not visible at the resolution of the medical CT, where the reactive fluid had not completely dissolved the internal pore-structure. Flow was modelled in connected pathways, the flow streamlines were traced and streamline density for each voxel was calculated. It was found that the streamline density was highest in the most well-connected pathways and that density increased with increasing heterogeneity as the number of connected pathways decreased and flow was consolidated along fewer pathways. This work represents the first study of scale dependency using reservoir condition 4D X-ray tomography and provides insight into the mechanisms that control local reaction rates at multiple scales.

Automated Dissolution for Enteric-Coated Aspirin Tablets: A Case Study for Method Transfer to a RoboDis II.

PubMed

Ibrahim, Sarah A; Martini, Luigi

2014-08-01

Dissolution method transfer is a complicated yet common process in the pharmaceutical industry. With increased pharmaceutical product manufacturing and dissolution acceptance requirements, dissolution testing has become one of the most labor-intensive quality control testing methods. There is an increased trend for automation in dissolution testing, particularly for large pharmaceutical companies to reduce variability and increase personnel efficiency. There is no official guideline for dissolution testing method transfer from a manual, semi-automated, to automated dissolution tester. In this study, a manual multipoint dissolution testing procedure for an enteric-coated aspirin tablet was transferred effectively and reproducibly to a fully automated dissolution testing device, RoboDis II. Enteric-coated aspirin samples were used as a model formulation to assess the feasibility and accuracy of media pH change during continuous automated dissolution testing. Several RoboDis II parameters were evaluated to ensure the integrity and equivalency of dissolution method transfer from a manual dissolution tester. This current study provides a systematic outline for the transfer of the manual dissolution testing protocol to an automated dissolution tester. This study further supports that automated dissolution testers compliant with regulatory requirements and similar to manual dissolution testers facilitate method transfer. © 2014 Society for Laboratory Automation and Screening.

[A Case of Intestinal Obstruction Caused by a Bezoar after Pylous-Preserving Gastrectomy].

PubMed

Yamazato, Yuzo; Kosuga, Toshiyuki; Ichikawa, Daisuke; Kubota, Takeshi; Okamoto, Kazuma; Konishi, Hirotaka; Shiozaki, Atsushi; Fujiwara, Hitoshi; Arita, Tomohiro; Morimura, Ryo; Murayama, Yasutoshi; Kuriu, Yoshiaki; Ikoma, Hisashi; Nakanishi, Masayoshi; Otsuji, Eigo

2017-11-01

A 65-year-old woman with a history of pylorus-preserving gastrectomy(PPG)for early gastric cancer visited our hospital because of vomiting. Gastrointestinal endoscopy revealed a large bezoar in the anastomotic site of the stomach. Because the bezoar was too large to be collected orally, the dissolution therapy with taking Coca-Cola®was continued. On the 3rd day after hospitalization, she felt acute abdominal pain with vomiting. Computed tomography revealed intestinal obstruction by a mass with air bubbles inside in the ileum. Emergency operation was performed under a diagnosis of intestinal obstruction due to the bezoar. The black brown bezoar sized 80×35×30mm was extracted through an ileotomy. The delayed gastric empty is considered to involve in the bezoar formation. Therefore, the appropriate education of diet and periodic endoscopic screening are necessary for patients with large amounts of gastric residues especially after PPG. In the dissolution therapy, physicians need to be careful of intestinal obstruction by a bezoar.

Different Material States of Pub1 Condensates Define Distinct Modes of Stress Adaptation and Recovery.

PubMed

Kroschwald, Sonja; Munder, Matthias C; Maharana, Shovamayee; Franzmann, Titus M; Richter, Doris; Ruer, Martine; Hyman, Anthony A; Alberti, Simon

2018-06-12

How cells adapt to varying environmental conditions is largely unknown. Here, we show that, in budding yeast, the RNA-binding and stress granule protein Pub1 has an intrinsic property to form condensates upon starvation or heat stress and that condensate formation is associated with cell-cycle arrest. Release from arrest coincides with condensate dissolution, which takes minutes (starvation) or hours (heat shock). In vitro reconstitution reveals that the different dissolution rates of starvation- and heat-induced condensates are due to their different material properties: starvation-induced Pub1 condensates form by liquid-liquid demixing and subsequently convert into reversible gel-like particles; heat-induced condensates are more solid-like and require chaperones for disaggregation. Our data suggest that different physiological stresses, as well as stress durations and intensities, induce condensates with distinct physical properties and thereby define different modes of stress adaptation and rates of recovery. Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.

76 FR 73996 - Special Local Regulations; Orange Bowl International Youth Regatta, Biscayne Bay, Miami, FL

Federal Register 2010, 2011, 2012, 2013, 2014

2011-11-30

..., a series of sailboat races. The Orange Bowl International Youth Regatta is scheduled to take place... take place at four separate race courses. Over 600 sailboats are expected to participate in the regatta...

Dissolution on Saturn's Moon Titan: A 3D Karst Landscape Evolution Model

NASA Astrophysics Data System (ADS)

Cornet, Thomas; Fleurant, Cyril; Seignovert, Benoît; Cordier, Daniel; Bourgeois, Olivier; Le Mouélic, Stéphane; Rodriguez, Sebastien; Lucas, Antoine

2017-04-01

Titan is an Earth-like world possessing a nitrogen-rich atmosphere that covers a surface with signs of lacustrine (lakes, seas, depressions), fluvial (channels, valleys) and aeolian (dunes) activity [1]. The chemistry implied in the geological processes is, however, strikingly different from that on Earth. Titan's extremely cold environment (T -180°C) allows water to exist only under the form of icy "bedrock". The presence of methane as the second major constituent in the atmosphere, as well as an active nitrogen-methane photochemistry, allows methane and ethane to drive a hydrocarbon cycle similar to the terrestrial hydrological cycle. A plethora of organic solids, more or less soluble in liquid hydrocarbons, is also produced in the atmosphere and can lead, by atmospheric sedimentation over geological timescales, to formation of some kind of organic geological sedimentary layer. Based on comparisons between Titan's landscapes seen in the Cassini spacecraft data and terrestrial analogues, karstic-like dissolution and evaporitic crystallization have been suggested in various instances to take part in the landscape development on Titan. Dissolution has been invoked, for instance, for the development of the so-called "labyrinthic terrain", located at high latitudes and resembling terrestrial cockpit or polygonal karst terrain. In this work, we aim at testing this hypothesis by comparing the natural landscapes visible in the Cassini/RADAR images of Titan's surface, with those inferred from the use of a 3D Landscape Evolution Model (LEM) based on the Channel-Hillslope Integrated Landscape Development (CHILD) [2] modified to include karstic dissolution as the major geological process [3]. Digital Elevation Models (DEMs) are generated from an initial quasi-planar surface for a set of dissolution rates, diffusion coefficients (solute transport), and sink densities of the mesh. The landscape evolves over millions of years. Synthetic SAR images are generated from these DEMs in order to be compared with Titan's landforms seen in the Cassini SAR data. Inference on the possible thickness and degree of maturation of the Titan karst will be discussed. [1] Lopes R.M.C. et al. (2010), Icarus ; [2] Tucker et al. (2001), Computers Geosciences ; [3] Fleurant C. et al. (2008), Geomorph., Rel., Proc., Envir.

Does the dose-solubility ratio affect the mean dissolution time of drugs?

PubMed

Lánský, P; Weiss, M

1999-09-01

To present a new model for describing drug dissolution. On the basis of the new model to characterize the dissolution profile by the distribution function of the random dissolution time of a drug molecule, which generalizes the classical first order model. Instead of assuming a constant fractional dissolution rate, as in the classical model, it is considered that the fractional dissolution rate is a decreasing function of the dissolved amount controlled by the dose-solubility ratio. The differential equation derived from this assumption is solved and the distribution measures (half-dissolution time, mean dissolution time, relative dispersion of the dissolution time, dissolution time density, and fractional dissolution rate) are calculated. Finally, instead of monotonically decreasing the fractional dissolution rate, a generalization resulting in zero dissolution rate at time origin is introduced. The behavior of the model is divided into two regions defined by q, the ratio of the dose to the solubility level: q < 1 (complete dissolution of the dose, dissolution time) and q > 1 (saturation of the solution, saturation time). The singular case q = 1 is also treated and in this situation the mean as well as the relative dispersion of the dissolution time increase to infinity. The model was successfully fitted to data (1). This empirical model is descriptive without detailed physical reasoning behind its derivation. According to the model, the mean dissolution time is affected by the dose-solubility ratio. Although this prediction appears to be in accordance with preliminary application, further validation based on more suitable experimental data is required.

Effects of Bacillus subtilis endospore surface reactivity on the rate of forsterite dissolution

NASA Astrophysics Data System (ADS)

Harrold, Z.; Gorman-Lewis, D.

2013-12-01

Primary mineral dissolution products, such as silica (Si), calcium (Ca) and magnesium (Mg), play an important role in numerous biologic and geochemical cycles including microbial metabolism, plant growth and secondary mineral precipitation. The flux of these and other dissolution products into the environment is largely controlled by the rate of primary silicate mineral dissolution. Bacteria, a ubiquitous component in water-rock systems, are known to facilitate mineral dissolution and may play a substantial role in determining the overall flux of dissolution products into the environment. Bacterial cell walls are complex and highly reactive organic surfaces that can affect mineral dissolution rates directly through microbe-mineral adsorption or indirectly by complexing dissolution products. The effect of bacterial surface adsorption on chemical weathering rates may even outweigh the influence of active processes in environments where a high proportion of cells are metabolically dormant or cell metabolism is slow. Complications associated with eliminating or accounting for ongoing metabolic processes in long-term dissolution studies have made it challenging to isolate the influence of cell wall interactions on mineral dissolution rates. We utilized Bacillus subtilis endospores, a robust and metabolically dormant cell type, to isolate and quantify the effects of bacterial surface reactivity on forsterite (Mg2SiO4) dissolution rates. We measured the influence of both direct and indirect microbe-mineral interactions on forsterite dissolution. Indirect pathways were isolated using dialysis tubing to prevent mineral-microbe contact while allowing free exchange of dissolved mineral products and endospore-ion adsorption. Homogenous experimental assays allowed both direct microbe-mineral and indirect microbe-ion interactions to affect forsterite dissolution rates. Dissolution rates were calculated based on silica concentrations and zero-order dissolution kinetics. Additional analyses including Mg concentrations, microprobe and BET analyses support mineral dissolution rate calculations and stoichiometry considerations. All experimental assays containing endospores show increased forsterite dissolution rates relative to abiotic controls. Forsterite dissolution rates increased by approximately one order of magnitude in dialysis bound, biotic experiments relative to abiotic assays. Homogenous biotic assays exhibited a more complex dissolution rate profile that changes over time. All microbially mediated forsterite dissolution rates returned to abiotic control rates after 10 to 15 days of incubation. This shift in dissolution rate likely corresponds to maximum endospore surface adsorption capacity. The Bacillus subtilis endospore surface serves as a first-order proxy for studying the effect of metabolizing microbe surfaces on silicate dissolution rates. Comparisons with published abiotic, microbial, and organic acid mediated forsterite dissolution rates will provide insight on the importance of bacterial surfaces in primary mineral dissolution processes.

A novel determination of calcite dissolution kinetics in seawater

NASA Astrophysics Data System (ADS)

Subhas, Adam V.; Rollins, Nick E.; Berelson, William M.; Dong, Sijia; Erez, Jonathan; Adkins, Jess F.

2015-12-01

We present a novel determination of the dissolution kinetics of inorganic calcite in seawater. We dissolved 13 C -labeled calcite in unlabeled seawater, and traced the evolving δ13 C composition of the fluid over time to establish dissolution rates. This method provides sensitive determinations of dissolution rate, which we couple with tight constraints on both seawater saturation state and surface area of the dissolving minerals. We have determined dissolution rates for two different abiotic calcite materials and three different grain sizes. Near-equilibrium dissolution rates are highly nonlinear, and are well normalized by geometric surface area, giving an empirical dissolution rate dependence on saturation state (Ω) of: This result substantiates the non-linear response of calcite dissolution to undersaturation. The bulk dissolution rate constant calculated here is in excellent agreement with those determined in far from equilibrium and dilute solution experiments. Plots of dissolution versus undersaturation indicates the presence of at least two dissolution mechanisms, implying a criticality in the calcite-seawater system. Finally, our new rate determination has implications for modeling of pelagic and seafloor dissolution. Nonlinear dissolution kinetics in a simple 1-D lysocline model indicate a possible transition from kinetic to diffusive control with increasing water depth, and also confirm the importance of respiration-driven dissolution in setting the shape of the calcite lysocline.

UFO's in the Classroom?

ERIC Educational Resources Information Center

Coleman, William

1980-01-01

This article is in response to the Scientific-Study of Unidentified Flying Objects (UFOs) by the University of Colorado which stated that miseducation was taking place in schools that allowed children to read UFO books. The author encourages the aerospace teacher to allow UFO studies to take place. (SA)

28 CFR 543.13 - Visits by attorneys.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 28 Judicial Administration 2 2013-07-01 2013-07-01 false Visits by attorneys. 543.13 Section 543.13 Judicial Administration BUREAU OF PRISONS, DEPARTMENT OF JUSTICE INSTITUTIONAL MANAGEMENT LEGAL... ordinarily take place during regular visiting hours. Attorney visits shall take place in a private conference...

28 CFR 543.13 - Visits by attorneys.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 28 Judicial Administration 2 2014-07-01 2014-07-01 false Visits by attorneys. 543.13 Section 543.13 Judicial Administration BUREAU OF PRISONS, DEPARTMENT OF JUSTICE INSTITUTIONAL MANAGEMENT LEGAL... ordinarily take place during regular visiting hours. Attorney visits shall take place in a private conference...

28 CFR 543.13 - Visits by attorneys.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 28 Judicial Administration 2 2012-07-01 2012-07-01 false Visits by attorneys. 543.13 Section 543.13 Judicial Administration BUREAU OF PRISONS, DEPARTMENT OF JUSTICE INSTITUTIONAL MANAGEMENT LEGAL... ordinarily take place during regular visiting hours. Attorney visits shall take place in a private conference...

Effects of selective handling of pyritic, acid-forming materials on the chemistry of pore gas and ground water at a reclaimed surface coal mine in Clarion County, PA, USA

USGS Publications Warehouse

Cravotta,, Charles A.; Dugas, Diana L.; Brady, Keith; Kovalchuck, Thomas E.

1994-01-01

A change from dragline to “selective handling” mining methods at a reclaimed surface coal mine in western Pennsylvania did not significantly affect concentrations of metals in ground water because oxidation of pyrite and dissolution of siderite were not abated. Throughout the mine, placement of pyritic material near the land surface facilitated the oxidation of pyrite, causing the consumption of oxygen (O2) and release of acid, iron, and sulfate ions. Locally in the unsaturated zone, water sampled within or near pyritic zones was acidic, with concentrations of sulfate exceeding 3,000 milligrams per liter (mg/L). However, acidic conditions generally did not persist below the water table because of neutralization by carbonate minerals. Dissolution of calcite, dolomite, and siderite in unsaturated and saturated zones produced elevated concentrations of carbon dioxide (CO2), alkalinity, calcium, magnesium, iron, and manganese. Alkalinity concentrations of 600 to 800 mg/L as CaCO3 were common in water samples from the unsaturated zone in spoil, and alkalinities of 100 to 400 mg/L as CaCO3 were common in ground-water samples from the underlying saturated zone in spoil and bedrock. Saturation indices indicated that siderite could dissolve in water throughout the spoil, but that calcite dissolution or precipitation could occur locally. Calcite dissolution could be promoted as a result of pyrite oxidation, gypsum precipitation, and calcium ion exchange for sodium. Calcite precipitation could be promoted by evapotranspiration and siderite dissolution, and corresponding increases in concentrations of alkalinity and other solutes. Partial pressures of O2 (Po2) and CO2 (Pco2) in spoil pore gas indicated that oxidation of pyrite and precipitation of ferric hydroxide, coupled with dissolution of calcite, dolomite, and siderite were the primary reactions affecting water quality. Highest vertical gradients in Po2, particularly in the near-surface zone (0-1 m), did not correlate with concentrations of total sulfur in spoil. This lack of correlation could indicate that total sulfur concentrations in spoil do not reflect the amount of reactive pyrite or that oxidation rates can be controlled more by rates of O2 diffusion than the amount of pyrite. Hence, if placed in O2-rich zones near the land surface, even small amounts of disseminated pyritic material can be relatively significant sources of acid and mineralized water.

Improved sonothrombolysis from a modified diagnostic transducer delivering impulses containing a longer pulse duration.

PubMed

Wu, Juefei; Xie, Feng; Kumar, Tanmay; Liu, Jinjin; Lof, John; Shi, William; Everbach, E Carr; Porter, Thomas R

2014-07-01

Although guided high-mechanical-index (MI) impulses from a diagnostic ultrasound transducer have been used in preclinical studies to dissolve coronary arterial and microvascular thrombi in the presence of intravenously infused microbubbles, it is possible that pulse durations (PDs) longer than that used for diagnostic imaging may further improve the effectiveness of this approach. By use of an established in vitro model flow system, a total of 90 occlusive porcine arterial thrombi (thrombus age: 3-4 h) within a vascular mimicking system were randomized to 10-min treatments with two different PDs (5 and 20 μs) using a Philips S5-1 transducer (1.6-MHz center frequency) at a range of MIs (from 0.2 to 1.4). All impulses were delivered in an intermittent fashion to permit microbubble replenishment within the thrombosed vessel. Diluted lipid-encapsulated microbubbles (0.5% Definity) were infused during the entire treatment period. A tissue-mimicking phantom 5 cm thick was placed between the transducer and thrombosed vessel to mimic transthoracic attenuation. Two 20-MHz passive cavitation detection systems were placed confocal to the insonified vessel to assess for inertial cavitational activity. Percentage thrombus dissolution was calculated by weighing the thrombi before and after each treatment. Percentage thrombus dissolution was significantly higher with a 20-μs PD already at the 0.2 and 0.4 MI therapeutic impulses (54 ± 12% vs. 33 ± 17% and 54 ± 22% vs. 34 ± 17%, p < 0.05 compared with the 5-μs PD group, respectively), and where passive cavitation detection systems detected only low intensities of inertial cavitation. At higher MI settings and 20-μs PDs, percentage thrombus dissolution decreased most likely from high-intensity cavitation shielding of the thrombus. Slightly prolonging the PD on a diagnostic transducer improves the degree of sonothrombolysis that can be achieved without fibrinolytic agents at a lower mechanical index. Copyright © 2014 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Effect of Mineral Dissolution/Precipitation and CO2 Exsolution on CO2 transport in Geological Carbon Storage.

PubMed

Xu, Ruina; Li, Rong; Ma, Jin; He, Di; Jiang, Peixue

2017-09-19

Geological carbon sequestration (GCS) in deep saline aquifers is an effective means for storing carbon dioxide to address global climate change. As the time after injection increases, the safety of storage increases as the CO 2 transforms from a separate phase to CO 2 (aq) and HCO 3 - by dissolution and then to carbonates by mineral dissolution. However, subsequent depressurization could lead to dissolved CO 2 (aq) escaping from the formation water and creating a new separate phase which may reduce the GCS system safety. The mineral dissolution and the CO 2 exsolution and mineral precipitation during depressurization change the morphology, porosity, and permeability of the porous rock medium, which then affects the two-phase flow of the CO 2 and formation water. A better understanding of these effects on the CO 2 -water two-phase flow will improve predictions of the long-term CO 2 storage reliability, especially the impact of depressurization on the long-term stability. In this Account, we summarize our recent work on the effect of CO 2 exsolution and mineral dissolution/precipitation on CO 2 transport in GCS reservoirs. We place emphasis on understanding the behavior and transformation of the carbon components in the reservoir, including CO 2 (sc/g), CO 2 (aq), HCO 3 - , and carbonate minerals (calcite and dolomite), highlight their transport and mobility by coupled geochemical and two-phase flow processes, and consider the implications of these transport mechanisms on estimates of the long-term safety of GCS. We describe experimental and numerical pore- and core-scale methods used in our lab in conjunction with industrial and international partners to investigate these effects. Experimental results show how mineral dissolution affects permeability, capillary pressure, and relative permeability, which are important phenomena affecting the input parameters for reservoir flow modeling. The porosity and the absolute permeability increase when CO 2 dissolved water is continuously injected through the core. The MRI results indicate dissolution of the carbonates during the experiments since the porosity has been increased after the core-flooding experiments. The mineral dissolution changes the pore structure by enlarging the throat diameters and decreasing the pore specific surface areas, resulting in lower CO 2 /water capillary pressures and changes in the relative permeability. When the reservoir pressure decreases, the CO 2 exsolution occurs due to the reduction of solubility. The CO 2 bubbles preferentially grow toward the larger pores instead of toward the throats or the finer pores during the depressurization. After exsolution, the exsolved CO 2 phase shows low mobility due to the highly dispersed pore-scale morphology, and the well dispersed small bubbles tend to merge without interface contact driven by the Ostwald ripening mechanism. During depressurization, the dissolved carbonate could also precipitate as a result of increasing pH. There is increasing formation water flow resistance and low mobility of the CO 2 in the presence of CO 2 exsolution and carbonate precipitation. These effects produce a self-sealing mechanism that may reduce unfavorable CO 2 migration even in the presence of sudden reservoir depressurization.

24 CFR 903.17 - What is the process for obtaining public comment on the plans?

Code of Federal Regulations, 2011 CFR

2011-04-01

... hearing is to take place, the PHA must: (1) Make the proposed PHA plan(s), the required attachments and..., and that a public hearing will take place on the plan, and the date, time and location of the hearing...

Learning: An Evolutionary Analysis

ERIC Educational Resources Information Center

Swann, Joanna

2009-01-01

This paper draws on the philosophy of Karl Popper to present a descriptive evolutionary epistemology that offers philosophical solutions to the following related problems: "What happens when learning takes place?" and "What happens in human learning?" It provides a detailed analysis of how learning takes place without any direct transfer of…

Negotiated Boundaries: Conceptual Locations of Pregnancy and Childbirth

ERIC Educational Resources Information Center

Houvouras, Shannon

2006-01-01

Dominant notions of reproduction perceive childbearing as physical processes that take place within womens bodies. This perception undermines non-physical components and removes men from the process. This project uses social constructionism to explore the locations women describe pregnancy and childbirth taking place in their childbearing…

Discriminative Dissolution Method for Benzoyl Metronidazole Oral Suspension.

PubMed

da Silva, Aline Santos; da Rosa Silva, Carlos Eduardo; Paula, Fávero Reisdorfer; da Silva, Fabiana Ernestina Barcellos

2016-06-01

A dissolution method for benzoyl metronidazole (BMZ) oral suspensions was developed and validated using a high-performance liquid chromatography (HPLC) method. After determination of sink conditions, dissolution profiles were evaluated using different dissolution media and agitation speeds. The sample insertion mode in dissolution media was also evaluated. The best conditions were obtained using a paddle, 50 rpm stirring speed, simulated gastric fluid (without pepsin) as the dissolution medium, and sample insertion by a syringe. These conditions were suitable for providing sink conditions and discriminatory power between different formulations. Through the tested conditions, the results can be considered specific, linear, precise, accurate, and robust. The dissolution profiles of five samples were compared using the similarity factor (f 2) and dissolution efficiency. The dissolution kinetics were evaluated and described by the Weibull model. Whereas there is no monograph for this pharmaceutical formulation, the dissolution method proposed can be considered suitable for quality control and dissolution profile comparison of different commercial formulations.

Evolution of strength and physical properties of carbonate and ultramafic rocks under hydrothermal conditions

NASA Astrophysics Data System (ADS)

Lisabeth, Harrison Paul

Interaction of rocks with fluids can significantly change mineral assemblage and structure. This so-called hydrothermal alteration is ubiquitous in the Earth's crust. Though the behavior of hydrothermally altered rocks can have planet-scale consequences, such as facilitating oceanic spreading along slow ridge segments and recycling volatiles into the mantle at subduction zones, the mechanisms involved in the hydrothermal alteration are often microscopic. Fluid-rock interactions take place where the fluid and rock meet. Fluid distribution, flux rate and reactive surface area control the efficiency and extent of hydrothermal alteration. Fluid-rock interactions, such as dissolution, precipitation and fluid mediated fracture and frictional sliding lead to changes in porosity and pore structure that feed back into the hydraulic and mechanical behavior of the bulk rock. Examining the nature of this highly coupled system involves coordinating observations of the mineralogy and structure of naturally altered rocks and laboratory investigation of the fine scale mechanisms of transformation under controlled conditions. In this study, I focus on fluid-rock interactions involving two common lithologies, carbonates and ultramafics, in order to elucidate the coupling between mechanical, hydraulic and chemical processes in these rocks. I perform constant strain-rate triaxial deformation and constant-stress creep tests on several suites of samples while monitoring the evolution of sample strain, permeability and physical properties. Subsequent microstructures are analyzed using optical and scanning electron microscopy. This work yields laboratory-based constraints on the extent and mechanisms of water weakening in carbonates and carbonation reactions in ultramafic rocks. I find that inundation with pore fluid thereby reducing permeability. This effect is sensitive to pore fluid saturation with respect to calcium carbonate. Fluid inundation weakens dunites as well. The addition of carbon dioxide to pore fluid enhances compaction and partial recovery of strength compared to pure water samples. Enhanced compaction in CO2-rich fluid samples is not accompanied by enhanced permeability reduction. Analysis of sample microstructures indicates that precipitation of carbonates along fracture surfaces is responsible for the partial restrengthening and channelized dissolution of olivine is responsible for permeability maintenance.

JPRS Report, East Europe

DTIC Science & Technology

1990-04-10

Limbach, member SPD by Bettina Herzog [Limbach] One could take the standpoint of the precon- and Siegfried Kusior; place and date not given: "Is the ...what transpired in the GDR prior to 9 November andSPD--that such a legal conformation can also take place afterwards. only step by step and that it must... place in the pluralisticThis last group, and each group numbers about the same, political scene. Structural reorganizations, personnel includes persons

Reactive Transport Models with Geomechanics to Mitigate Risks of CO2 Utilization and Storage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deo, Milind; Huang, Hai; Kweon, Hyukmin

2016-03-28

Reactivity of carbon dioxide (CO 2), rocks and brine is important in a number of practical situations in carbon dioxide sequestration. Injectivity of CO 2 will be affected by near wellbore dissolution or precipitation. Natural fractures or faults containing specific minerals may reactivate leading to induced seismicity. In this project, we first examined if the reactions between CO 2, brine and rocks affect the nature of the porous medium and properties including petrophysical properties in the timeframe of the injection operations. This was done by carrying out experiments at sequestration conditions (2000 psi for corefloods and 2400 psi for batchmore » experiments, and 600°C) with three different types of rocks – sandstone, limestone and dolomite. Experiments were performed in batch mode and corefloods were conducted over a two-week period. Batch experiments were performed with samples of differing surface area to understand the impact of surface area on overall reaction rates. Toughreact, a reactive transport model was used to interpret and understand the experimental results. The role of iron in dissolution and precipitation reactions was observed to be significant. Iron containing minerals – siderite and ankerite dissolved resulting in changes in porosity and permeability. Corefloods and batch experiments revealed similar patterns. With the right cationic balance, there is a possibility of precipitation of iron bearing carbonates. The results indicate that during injection operations mineralogical changes may lead to injectivity enhancements near the wellbore and petrophysical changes elsewhere in the system. Limestone and dolomite cores showed consistent dissolution at the entrance of the core. The dissolution led to formation of wormholes and interconnected dissolution zones. Results indicate that near wellbore dissolution in these rock-types may lead to rock failure. Micro-CT images of the cores before and after the experiments revealed that an initial high-permeability pathway facilitated the formation of wormholes. The peak cation concentrations and general trends were matched using Toughreact. Batch reactor modeling showed that the geometric factors obtained using powder data that related effective surface area to the BET surface area had to be reduced for fractured samples and cores. This indicates that the available surface area in consolidated samples is lower than that deduced from powder experiments. Field-scale modeling of reactive transport and geomechanics was developed in parallel at Idaho National Laboratory. The model is able to take into account complex chemistry, and consider interactions of natural fractures and faults. Poroelastic geomechanical considerations are also included in the model.« less

[Dissolution behavior of Fuzi Lizhong pill based on simultaneous determination of two components in Glycyrrhizae Radix et Rhizoma].

PubMed

Jiang, Mao-Yuan; Zhang, Zhen; Shi, Jin-Feng; Zhang, Jin-Ming; Fu, Chao-Mei; Lin, Xia; Liu, Yu-Mei

2018-03-01

To preliminarily investigate the dissolution behavior of Fuzi Lizhong pill, provide the basis for its quality control and lay foundation for in vivo dissolution behavior by determining the dissolution rate of liquiritin and glycyrrhizic acid. High-performance liquid chromatography (HPLC) method for simultaneous content determination of the two active ingredients of liquiritin and glycyrrhizic acid in Fuzi Lizhong pill was established; The dissolution amount of these two active ingredients in fifteen batches of Fuzi Lizhong pill from five manufacturers was obtained at different time points, and then the cumulative dissolution rate was calculated and cumulative dissolution curve was drawn. The similarity of cumulative dissolution curve of different batches was evaluated based on the same factory, and the similarity of cumulative dissolution curve of different factories was evaluated based on the same active ingredients. The dissolution model of Fuzi Lizhong pill based on two kinds of active ingredients was established by fitting with the dissolution data. The best dissolution medium was 0.25% sodium lauryl sulfate. The dissolution behavior of liquiritin and glycyrrhizic acid in Fuzi Lizhong pill was basically the same and sustained release in 48 h. Three batches of the factories (factory 2, factory 3, factory 4 and factory 5) appeared to be similar in dissolution behavior, indicating similarity in dissolution behavior in most factories. Two of the three batches from factory 1 appeared to be not similar in dissolution behavior of liquiritin and glycyrrhizic acid. The dissolution data of the effective ingredients from different factories were same in fitting, and Weibull model was the best model in these batches. Fuzi Lizhong pill in 15 batches from 5 factories showed sustained release in 48 h, proving obviously slow releasing characteristics "pill is lenitive and keeps a long-time efficacy". The generally good dissolution behavior also suggested that quality of different batches from most factories was stable. The dissolution behavior of liquiritin and glycyrrhizic acid in different factories was different, suggesting that the source of medicinal materials and preparation technology parameters in five factories were different. Copyright© by the Chinese Pharmaceutical Association.

Optimization of Dissolution Compartments in a Biorelevant Dissolution Apparatus Golem v2, Supported by Multivariate Analysis.

PubMed

Stupák, Ivan; Pavloková, Sylvie; Vysloužil, Jakub; Dohnal, Jiří; Čulen, Martin

2017-11-23

Biorelevant dissolution instruments represent an important tool for pharmaceutical research and development. These instruments are designed to simulate the dissolution of drug formulations in conditions most closely mimicking the gastrointestinal tract. In this work, we focused on the optimization of dissolution compartments/vessels for an updated version of the biorelevant dissolution apparatus-Golem v2. We designed eight compartments of uniform size but different inner geometry. The dissolution performance of the compartments was tested using immediate release caffeine tablets and evaluated by standard statistical methods and principal component analysis. Based on two phases of dissolution testing (using 250 and 100 mL of dissolution medium), we selected two compartment types yielding the highest measurement reproducibility. We also confirmed a statistically ssignificant effect of agitation rate and dissolution volume on the extent of drug dissolved and measurement reproducibility.

Geochemical and stable isotopic evolution of the Guarani Aquifer System in the state of São Paulo, Brazil

NASA Astrophysics Data System (ADS)

Sracek, Ondra; Hirata, Ricardo

2002-09-01

The purpose of this report is to explain geochemical and stable isotopes trends in the Brazilian unit of the Guarani Aquifer System (Botucatu and Piramboia aquifers) in São Paulo State, Brazil. Trends of dissolved species concentrations and geochemical modeling indicated a significant role of cation exchange and dissolution of carbonates in downgradient evolution of groundwater chemistry. Loss of calcium by the exchange for sodium drives dissolution of carbonates and results in Na-HCO3 type of groundwater. The cation-exchange front moves downgradient at probably much slower rate compared to the velocity of groundwater flow and at present is located near to the cities of Sertãozinho and Águas de Santa Barbara (wells PZ-34 and PZ-148, respectively) in a shallow confined area, 50-70 km from the recharge zone. Part of the sodium probably enters the Guarani Aquifer System. together with chloride and sulfate from the underlying Piramboia Formation by diffusion related to the dissolution of evaporates like halite and gypsum. High concentrations of fluorine (up to 13.3 mg/L) can be explained by dissolution of mineral fluoride also driven by cation exchange. However, it is unclear if the dissolution takes place directly in the Guarani Aquifer System or in the overlying basaltic Serra Geral Formation. There is depletion in δ2H and δ18O values in groundwater downgradient. Values of δ13C(DIC) are enriched downgradient, indicating dissolution of calcite under closed system conditions. Values of δ13C(DIC) in deep geothermal wells are very high (>-6.0‰) and probably indicate isotopic exchange with carbonates with δ13C about -3.0‰. Future work should be based on evaluation of vertical fluxes and potential for penetration of contamination to the Guarani Aquifer System. Résumé. Cet article a pour objet d'expliquer l'évolution de la géochimie et des isotopes stables dans l'unité brésilienne du système aquifère du Guarani (aquifères de Botucatu et Piramboia), dans l'État de Sao Paulo (Brésil). L'évolution des concentrations des espèces dissoutes et la modélisation géochimique ont fait apparaître le rôle notable des échanges de cations et de la dissolution des carbonates de l'amont vers l'aval des nappes. La perte de calcium par échange de cation avec le sodium pilote la dissolution des carbonates et donne naissance à des eaux souterraines à faciès Na-HCO3. Le front d'échange de cation se déplace vers l'aval probablement plus lentement que la vitesse d'écoulement de l'eau souterraine et est actuellement situé à proximité des villes de Sertaozinho et de Aguas de Santa Barbara (respectivement puits PZ-34 et PZ-148), dans une zone captive proche de la surface, à 50-70 km de la zone de recharge. Une partie du sodium provient probablement du système aquifère du Guarani, associée aux chlorures et aux sulfates de la formation Piramboia sous-jacente, par diffusion liée à la dissolution d'évaporites comme la halite et le gypse. De fortes concentrations en fluorures (jusqu'à 13,3 mg/L) peuvent être expliquées par la dissolution d'un minéral fluoré également pilotée par l'échange de cations. Cependant, on ne sait pas bien si la dissolution intervient directement dans le système aquifère du Guarani ou dans la formation basaltique sus-jacente de Serra Geral. Les valeurs de δ2H et δ18O décroissent vers l'aval de la nappe. Les valeurs de δ13C du carbone minéral dissous sont enrichies vers l'aval, indiquant qu'il se produit une dissolution de calcite en système fermé. Les valeurs de δ13C du carbone minéral dissous dans les puits géothermaux profonds sont très élevées (supérieures à -6,0‰) et rendent probablement compte d'échanges isotopiques avec des carbonates possédant un δ13C d'environ -3,0‰. De prochaines études devront s'attacher à évaluer les flux verticaux et le potentiel de pénétration de contamination du système aquifère du Guarani. Resumen. El propósito de este informe es explicar las tendencias geoquímicas y de los isótopos estables en la unidad brasileña del Sistema Acuífero Guaraní (acuíferos de Botucatu y Piramboya), en el Estado de Sao Paulo. Las concentraciones de especies disueltas y los resultados de modelaciones geoquímicas indican que el intercambio catiónico y la disolución de carbonatos desempeñan un papel importante en la evolución aguas abajo del acuífero. La disminución de calcio por el intercambio con sodio origina la disolución de carbonatos, dando lugar a aguas subterráneas de tipo bicarbonatado sódico. El frente de intercambio catiónico se desplaza a una velocidad probablemente mucho más lenta que la del flujo de agua; actualmente, se halla cerca de las ciudades de Sertaozinho y Aguas de Santa Bárbara (pozos PZ-34 y PZ-148, respectivamente), en una zona confinada somera que dista entre 50 y 70 km del área de recarga. Parte del sodio entra probablemente en el Sistema Acuífero Guaraní junto con el cloruro y el sulfato procedentes de la Formación Piramboia inferior, debido a la difusión relacionada con la disolución de evaporitas como la halita y los yesos. Se puede explicar las elevadas concentraciones de flúor (hasta 13,3 mg/L) por la disolución de fluoruro mineral, que sucede también por intercambio catiónico. Sin embargo, no está claro si la disolución ocurre directamente en el Sistema Acuífero Guaraní o en la Formación basáltica superior de Serra Geral. Hay una reducción de δ2H y de δ18O a favor del gradiente hidráulico. Hay un enriquecimiento en δ13C inorgánico aguas abajo, lo que indica que la calcita se disuelve en condiciones de sistema cerrado. Los valores de δ13C inorgánico en pozos geotérmicos profundos son muy altos (mayores que -6,0‰), y probablemente apuntan a un intercambio isotópico con carbonatos de δ13C que tiene un valor del orden del -3,0‰. Las líneas de investigación deberían centrarse en evaluar los flujos verticales y el potencial de penetración de contaminantes en el Sistema Acuífero Guaraní.

Inconvenient Truths about Teacher Learning: Towards Professional Development 3.0

ERIC Educational Resources Information Center

Korthagen, Fred

2017-01-01

Based on recent findings about teacher learning, a critical analysis of traditional and new approaches to professional development is presented. To a large degree, teacher learning takes place unconsciously and involves cognitive, emotional and motivational dimensions. Moreover, teacher learning takes place at various levels. Although these…

Environmental Flux and Locally Focused College Writing

ERIC Educational Resources Information Center

Shepley, Nathan

2014-01-01

This article reviews insights from place-based education and ecological models of writing to show how these theories can work together to shape locally focused composition pedagogies. From place-based education, the researcher takes an emphasis on physical specificity, and from ecological models of writing, the researcher takes an emphasis on…

Automated Information Services in Education.

ERIC Educational Resources Information Center

Cantoni, Mary

While most information dissemination activity in education is taking place at the national level within systems that emphasize documents, such as ERIC, the most important developments for individual teachers should take place at the state and local levels. SEEKER III, a local automated system in Michigan, is tied in with the Michigan Department of…

Etching of semiconductor cubic crystals: Determination of the dissolution slowness surfaces

NASA Astrophysics Data System (ADS)

Tellier, C. R.

1990-03-01

Equations of the representative surface of dissolution slowness for cubic crystals are determined in the framework of a tensorial approach of the orientation-dependent etching process. The independent dissolution constants are deduced from symmetry considerations. Using previous data on the chemical etching of germanium and gallium arsenide crystals, some possible polar diagrams of the dissolution slowness are proposed. A numerical and graphical simulation method is used to obtain the derived dissolution shapes. The influence of extrema in the dissolution slowness on the successive dissolution shapes is also examined. A graphical construction of limiting shapes of etched crystals appears possible using the tensorial representation of the dissolution slowness.

Coherent anti-Stokes Raman Scattering (CARS) Microscopy Visualizes Pharmaceutical Tablets During Dissolution

PubMed Central

Fussell, Andrew L.; Kleinebudde, Peter; Herek, Jennifer; Strachan, Clare J.; Offerhaus, Herman L.

2014-01-01

Traditional pharmaceutical dissolution tests determine the amount of drug dissolved over time by measuring drug content in the dissolution medium. This method provides little direct information about what is happening on the surface of the dissolving tablet. As the tablet surface composition and structure can change during dissolution, it is essential to monitor it during dissolution testing. In this work coherent anti-Stokes Raman scattering microscopy is used to image the surface of tablets during dissolution while UV absorption spectroscopy is simultaneously providing inline analysis of dissolved drug concentration for tablets containing a 50% mixture of theophylline anhydrate and ethyl cellulose. The measurements showed that in situ CARS microscopy is capable of imaging selectively theophylline in the presence of ethyl cellulose. Additionally, the theophylline anhydrate converted to theophylline monohydrate during dissolution, with needle-shaped crystals growing on the tablet surface during dissolution. The conversion of theophylline anhydrate to monohydrate, combined with reduced exposure of the drug to the flowing dissolution medium resulted in decreased dissolution rates. Our results show that in situ CARS microscopy combined with inline UV absorption spectroscopy is capable of monitoring pharmaceutical tablet dissolution and correlating surface changes with changes in dissolution rate. PMID:25045833

Evaluation of a biphasic in vitro dissolution test for estimating the bioavailability of carbamazepine polymorphic forms.

PubMed

Deng, Jia; Staufenbiel, Sven; Bodmeier, Roland

2017-07-15

The purpose of this study was to discriminate three crystal forms of carbamazepine (a BCS II drug) by in vitro dissolution testing and to correlate in vitro data with published in vivo data. A biphasic dissolution system (phosphate buffer pH6.8 and octanol) was used to evaluate the dissolution of the three polymorphic forms and to compare it with conventional single phase dissolution tests performed under sink and non-sink conditions. Similar dissolution profiles of three polymorphic forms were observed in the conventional dissolution test under sink conditions. Although a difference in dissolution was seen in the single phase dissolution test under non-sink conditions as well as in the aqueous phase of the biphasic test, little relevance for in vivo data was observed. In contrast, the biphasic dissolution system could discriminate between the different polymorphic forms in the octanol phase with a ranking of form III>form I>dihydrate form. This was in agreement with the in vivo performance. The dissolved drug available for oral absorption, which was dominated by dissolution and solution-mediated phase transformation, could be reflected in the biphasic dissolution test. Moreover, a good correlation was established between in vitro dissolution in the octanol phase of the biphasic test and in vivo pharmacokinetic data (R 2 =0.99). The biphasic dissolution method is a valuable tool to discriminate between different crystal forms in the formulations of poorly soluble drugs. Copyright © 2017. Published by Elsevier B.V.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Newell, J; Miller, D; Stone, M

The Savannah River National Laboratory (SRNL) was tasked to provide an assessment of the downstream impacts to the Defense Waste Processing Facility (DWPF) of decisions regarding the implementation of Al-dissolution to support sludge mass reduction and processing. Based on future sludge batch compositional projections from the Liquid Waste Organization's (LWO) sludge batch plan, assessments have been made with respect to the ability to maintain comparable projected operating windows for sludges with and without Al-dissolution. As part of that previous assessment, candidate frits were identified to provide insight into melt rate for average sludge batches representing with and without Al-dissolution flowsheets.more » Initial melt rate studies using the melt rate furnace (MRF) were performed using five frits each for Cluster 2 and Cluster 4 compositions representing average without and with Al-dissolution. It was determined, however, that the REDOX endpoint (Fe{sup 2+}/{Sigma}Fe for the glass) for Clusters 2 and 4 resulted in an overly oxidized feed which negatively affected the initial melt rate tests. After the sludge was adjusted to a more reduced state, additional testing was performed with frits that contained both high and low concentrations of sodium and boron oxides. These frits were selected strictly based on the ability to ascertain compositional trends in melt rate and did not necessarily apply to any acceptability criteria for DWPF processing. The melt rate data are in general agreement with historical trends observed at SRNL and during processing of SB3 (Sludge Batch 3)and SB4 in DWPF. When MAR acceptability criteria were applied, Frit 510 was seen to have the highest melt rate at 0.67 in/hr for Cluster 2 (without Al-dissolution), which is compositionally similar to SB4. For Cluster 4 (with Al-dissolution), which is compositionally similar to SB3, Frit 418 had the highest melt rate at 0.63 in/hr. Based on this data, there appears to be a slight advantage of the Frit 510 based system without Al-dissolution relative to the Frit 418 based system with Al-dissolution. Though the without aluminum dissolution scenario suggests a slightly higher melt rate with frit 510, several points must be taken into consideration: (1) The MRF does not have the ability to assess liquid feeds and, thus, rheology impacts. Instead, the MRF is a 'static' test bed in which a mass of dried melter feed (SRAT product plus frit) is placed in an 'isothermal' furnace for a period of time to assess melt rate. These conditions, although historically effective in terms of identifying candidate frits for specific sludge batches and mapping out melt rate versus waste loading trends, do not allow for assessments of the potential impact of feed rheology on melt rate. That is, if the rheological properties of the slurried melter feed resulted in the mounding of the feed in the melter (i.e., the melter feed was thick and did not flow across the cold cap), melt rate and/or melter operations (i.e., surges) could be negatively impacted. This could affect one or both flowsheets. (2) Waste throughput factors were not determined for Frit 510 and Frit 418 over multiple waste loadings. In order to provide insight into the mission life versus canister count question, one needs to define the maximum waste throughput for both flowsheets. Due to funding limitations, the melt rate testing only evaluated melt rate at a fixed waste loading. (3) DWPF will be processing SB5 through their facility in mid-November 2008. Insight into the over arching questions of melt rate, waste throughput, and mission life can be obtained directly from the facility. It is recommended that processing of SB5 through the facility be monitored closely and that data be used as input into the decision making process on whether to implement Al-dissolution for future sludge batches.« less

Syrian bean-caper (Zygophyllum fabago L.) improves organic matter and other properties of mine wastes deposits.

PubMed

Kabas, S; Arocena, J M; Acosta, J A; Faz, A; Martínez-Martínez, S; Zornoza, R; Carmona, D M

2014-01-01

The omni-presence of Zygophyllum fabago L. (Syrian bean-caper) natural colonies in post mining areas prompted us to investigate its contributions to reclamation of mine wastes deposits in southeast Spain. Select plant-related (edaphic) characteristics and bio- and water soluble-Cd, Cu, Pb and Zn in rhizosphere of Z. fabago were compared to deposits one year since application of pig slurry and marble waste. Total N in rhizosphere increased up to a factor of 20X (339 vs 17 mg N kg(-1)) in El Gorguel and 27X (85 vs 3.1 mg N kg(-1)) in El Lirio sites. Organic matter accumulation in rhizosphere from litter and roots of Z. fabago increased organic C from 6.6 to 19.5 g kg(-1) in El Gorguel and from 2.1 to 5.7 g kg(-1) in El Lirio in one year. Dissolution of inorganic C takes place due to organic acids from root exudates of Z. fabago. Reduction in bio-available Cd, Cu, Pb, and Zn in rhizosphere of Z. fabago at El Lirio is attributed to increase in pH from 5.3 to 7.7 through marble waste addition, although increased cation exchange capacity may also have played a role. Addition of marble waste to encourage colonization by Z. fabago in acidic mine wastes deposits was recommended.

Ultrastructural differentiation of sperm tail region in Diplometopon zarudnyi (an amphisbaenian reptile)

PubMed Central

Al-Dokhi, O.; Mukhtar, Ahmed; Al-Dosary, A.; Al-Sadoon, M.K.

2015-01-01

Diplometopon zarudnyi, a worm lizard belongs to amphisbaenia under trogonophidae family. This species exists in limited areas of the Arabian Peninsula and is an oscillating digger found in sub-surface soils. The present study aimed to investigate the sperm tail differentiation in D. zarudnyi. Ten male adults of D. zarudnyi were collected from Riyadh during April–May 2011. To study the sperm tail at the ultrastructural level the testes were fixed in 3% glutaraldehyde, than post fixed in 1% osmium tetaroxide followed by dehydration in ethanol grades; samples were cleared in propylene oxide and embedded in resin. Tail formation begins by the moving of centrioles and mitochondria towards the posterior pole of sperm head. Simultaneously many microtubules of the midpiece axoneme were enclosed by a thick layer of granular material. Mitochondria of midpiece lie alongside the proximal centriole which forms a very short neck region and possess tubular cristae internally and concentric layers of cristae superficially. During this course a fibrous sheath surrounds the axoneme of mid and principal piece. At the end dissolution of longitudinal manchette takes place. The mitochondria then rearrange themselves around the proximal and distal centrioles to form a neck region. Later, the fibrous sheath surrounds the proximal portion of the flagella. This part along with sperm head of D. zarudnyi provides a classical model that could be used in future for evolutionary and phylogenetic purposes of class reptilia. PMID:26155090

All-atomistic molecular dynamics (AA-MD) studies and pharmacokinetic performance of PAMAM-dendrimer-furosemide delivery systems.

PubMed

Otto, Daniel P; de Villiers, Melgardt M

2018-06-13

Improvement of problematic dissolution and solubility properties of a model drug, furosemide, was investigated for poly(amidoamine) (PAMAM) dendrimer complexes of the drug. Full and half generation dendrimers with amino and ester terminals respectively, were studied. In vitro release performance of these complexes was investigated at drug loads ranging 5-60% using simulated gastric fluids. Full generation dendrimers accommodated higher drug loads, outperformed half-generation complexes, and free drug. Pharmacokinetic studies in rats indicated that the dendrimer complexes markedly improved in the bioavailability of the drug compared to the unformulated drug. The G3.0-PAMAM dendrimer complex showed a two-fold increase in C max and a 1.75-fold increase in AUC over the free drug. Additionally, T max was shortened from approximately 25 to 20 min. One of the first all-atomistic molecular dynamics (AA-MD) simulation studies was performed to evaluate low-generation dendrimer-drug complexes as well as its pharmacokinetic performance. AA-MD provided insight into the intermolecular interactions that take place between the dendrimer and drug. It is suggested that the dendrimer not only encapsulates the drug, but can also orientate the drug in stabilized dispersion to prevent drug clustering which could impact release and bioavailability negatively. AA-MD can be a useful tool to develop dendrimer-based drug delivery systems. Copyright © 2018. Published by Elsevier B.V.

Wetting Behavior and Reactivity of Molten Silicon with h-BN Substrate at Ultrahigh Temperatures up to 1750 °C

NASA Astrophysics Data System (ADS)

Polkowski, Wojciech; Sobczak, Natalia; Nowak, Rafał; Kudyba, Artur; Bruzda, Grzegorz; Polkowska, Adelajda; Homa, Marta; Turalska, Patrycja; Tangstad, Merete; Safarian, Jafar; Moosavi-Khoonsari, Elmira; Datas, Alejandro

2017-12-01

For a successful implementation of newly proposed silicon-based latent heat thermal energy storage systems, proper ceramic materials that could withstand a contact heating with molten silicon at temperatures much higher than its melting point need to be developed. In this regard, a non-wetting behavior and low reactivity are the main criteria determining the applicability of ceramic as a potential crucible material for long-term ultrahigh temperature contact with molten silicon. In this work, the wetting of hexagonal boron nitride (h-BN) by molten silicon was examined for the first time at temperatures up to 1750 °C. For this purpose, the sessile drop technique combined with contact heating procedure under static argon was used. The reactivity in Si/h-BN system under proposed conditions was evaluated by SEM/EDS examinations of the solidified couple. It was demonstrated that increase in temperature improves wetting, and consequently, non-wetting-to-wetting transition takes place at around 1650 °C. The contact angle of 90° ± 5° is maintained at temperatures up to 1750 °C. The results of structural characterization supported by a thermodynamic modeling indicate that the wetting behavior of the Si/h-BN couple during heating to and cooling from ultrahigh temperature of 1750 °C is mainly controlled by the substrate dissolution/reprecipitation mechanism.

Reviews and Syntheses: Ocean acidification and its potential impacts on marine ecosystems

NASA Astrophysics Data System (ADS)

Mostofa, Khan M. G.; Liu, Cong-Qiang; Zhai, WeiDong; Minella, Marco; Vione, Davide; Gao, Kunshan; Minakata, Daisuke; Arakaki, Takemitsu; Yoshioka, Takahito; Hayakawa, Kazuhide; Konohira, Eiichi; Tanoue, Eiichiro; Akhand, Anirban; Chanda, Abhra; Wang, Baoli; Sakugawa, Hiroshi

2016-03-01

Ocean acidification, a complex phenomenon that lowers seawater pH, is the net outcome of several contributions. They include the dissolution of increasing atmospheric CO2 that adds up with dissolved inorganic carbon (dissolved CO2, H2CO3, HCO3-, and CO32-) generated upon mineralization of primary producers (PP) and dissolved organic matter (DOM). The aquatic processes leading to inorganic carbon are substantially affected by increased DOM and nutrients via terrestrial runoff, acidic rainfall, increased PP and algal blooms, nitrification, denitrification, sulfate reduction, global warming (GW), and by atmospheric CO2 itself through enhanced photosynthesis. They are consecutively associated with enhanced ocean acidification, hypoxia in acidified deeper seawater, pathogens, algal toxins, oxidative stress by reactive oxygen species, and thermal stress caused by longer stratification periods as an effect of GW. We discuss the mechanistic insights into the aforementioned processes and pH changes, with particular focus on processes taking place with different timescales (including the diurnal one) in surface and subsurface seawater. This review also discusses these collective influences to assess their potential detrimental effects to marine organisms, and of ecosystem processes and services. Our review of the effects operating in synergy with ocean acidification will provide a broad insight into the potential impact of acidification itself on biological processes. The foreseen danger to marine organisms by acidification is in fact expected to be amplified by several concurrent and interacting phenomena.

Reviews and Syntheses: Ocean acidification and its potential impacts on marine ecosystems

NASA Astrophysics Data System (ADS)

Mostofa, K. M. G.; Liu, C.-Q.; Zhai, W. D.; Minella, M.; Vione, D.; Gao, K.; Minakata, D.; Arakaki, T.; Yoshioka, T.; Hayakawa, K.; Konohira, E.; Tanoue, E.; Akhand, A.; Chanda, A.; Wang, B.; Sakugawa, H.

2015-07-01

Ocean acidification, a complex phenomenon that lowers seawater pH, is the net outcome of several contributions. They include the dissolution of increasing atmospheric CO2 that adds up with dissolved inorganic carbon (dissolved CO2, H2CO3, HCO3-, and CO32-) generated upon mineralization of primary producers (PP) and dissolved organic matter (DOM). The aquatic processes leading to inorganic carbon are substantially affected by increased DOM and nutrients via terrestrial runoff, acidic rainfall, increased PP and algal blooms, nitrification, denitrification, sulfate reduction, global warming (GW), and by atmospheric CO2 itself through enhanced photosynthesis. They are consecutively associated with enhanced ocean acidification, hypoxia in acidified deeper seawater, pathogens, algal toxins, oxidative stress by reactive oxygen species, and thermal stress caused by longer stratification periods as an effect of GW. We discuss the mechanistic insights into the aforementioned processes and pH changes, with particular focus on processes taking place with different time scales (including the diurnal one) in surface and subsurface seawater. This review also discusses these collective influences to assess their potential detrimental effects to marine organisms, and of ecosystem processes and services. Our review of the effects operating in synergy with ocean acidification will provide a broad insight into the potential impact of acidification itself on biological processes. The foreseen danger to marine organisms by acidification is in fact expected to be amplified by several concurrent and interacting phenomena.

Analysis of minerals containing dissolved traces of the fluid phase components water and carbon dioxide

NASA Technical Reports Server (NTRS)

Freund, Friedemann

1991-01-01

Substantial progress has been made towards a better understanding of the dissolution of common gas/fluid phase components, notably H2O and CO2, in minerals. It has been shown that the dissolution mechanisms are significantly more complex than currently believed. By judiciously combining various solid state analytical techniques, convincing evidence was obtained that traces of dissolved gas/fluid phase components undergo, at least in part, a redox conversion by which they split into reduced H2 and and reduced C on one hand and oxidized oxygen, O(-), on the other. Analysis for 2 and C as well as for any organic molecules which may form during the process of co-segregation are still impeded by the omnipresent danger of extraneous contamination. However, the presence of O(-), an unusual oxidized form of oxygen, has been proven beyond a reasonable doubt. The presence of O(-) testifies to the fact that a redox reaction must have taken place in the solid state involving the dissolved traces of gas/fluid phase components. Detailed information on the techniques used and the results obtained are given.

Pharmaceutical cocrystals: a novel approach for oral bioavailability enhancement of drugs.

PubMed

Chadha, Renu; Saini, Anupam; Arora, Poonam; Bhandari, Swati

2012-01-01

Solid dosage forms are by far the preferred drug delivery systems. However, these often face the problem of poor and erratic bioavailability during the drug development process. Numerous formulation strategies for drug delivery are currently under development, among which the solid forms such as polymorphs, solvates, salts, and cocrystals have been considered to be the most important for improving dissolution rate and bioavailability. Cocrystallization is a fairly new approach in pharmaceutical industry that can improve the solubility and, consequently, the bioactivity of the active pharmaceutical ingredient (API) without compromising its structural integrity. Pharmaceutical cocrystals have found their place in drug delivery, primarily due to their ability to produce alternative, viable solid forms when a more standard approach of salt and polymorph formation fails to deliver the desired objectives. Over the past few years, a number of papers have been published focusing on a broad range of subjects, from traditional crystal engineering to structure-property relationships of cocrystals. The present review, however, illustrates how the cocrystalline forms of APIs have improved their in vitro dissolution rate and in vivo bioavailability, often correlating well with their improved solubility as well.

Effects of drug-carrier interactions on drug dissolution from binary and ternary matrices

NASA Astrophysics Data System (ADS)

Iqbal, Zafar

For nearly five decades, pharmaceutical researchers have studied solid solutions of drugs in polymers as a potential means to enhance the dissolution of drugs with poor aqueous solubility. This has become of greater importance in recent years because most new potential drug compounds (new chemical entities) exhibit poor water solubility and present great challenges to scientists who must design dosage forms from which the drugs are bioavailable. During the formulation of a solid solution, the drug undergoes physical but not chemical alterations that increase its chemical potential in the formulation relative to that of the pure drug in its stable form. This increased chemical potential is responsible for enhanced dissolution as well as physical instabilities, such as amorphous to crystalline conversions and precipitation within the solid state. The chemical potential is derived from the Gibbs free energy, so it is reasonable to explain the behavior of solid solution systems in terms of thermodynamics. Solid solutions and dispersions have been extensively studied by pharmaceutical scientists, both with regard to manufacturing aspects and the proposal of various models in attempts to explain the physical bases for how these systems work. Recently, Dave and Bellantone proposed a model based on the thermodynamic changes resulting from the formulation of binary solid solutions of a drug in the polymer PVP. Their model introduced a modification of the F-H theory, which was used to quantify the drug-polymer interaction energies and calculate the entropy of mixing of the drug and polymer. In this work, the model of Dave and Bellantone was extended to include three-component systems, consisting of one drug mixed in a carrier matrix consisting of mixture of two polymers or a polymer and a surfactant. For this research, solid solutions were formed using various drug weight fractions in the formulations. The study focused on the following points: (1) Prepare solid solution formulations and perform appropriate physical characterizations. (2) Characterize the increase in drug dissolution rates resulting from solid solution formulations. (3) Relate the initial dissolution rates to the drug solubility. (4) Explain the solubility enhancement from solid solution dosage in terms of the drug polymer interactions using the extended thermodynamic model. Two poorly water soluble drugs, levonorgestrel (LEVO) and ethinyl estradiol (EE) were formulated in seven solid solution preparations comprised of four carrier systems. Materials used as carriers included various combinations of the polymers PVP K-30, Copovidone (COP), Poloxamer 182, and the surfactant TweenRTM 20. Additionally, ibuprofen (IBU) was used in three formulations consisting of various combinations of PVP K-30, Copovidone and TweenRTM 20. Formulations with various drug weight fractions (0.5%--30%) were prepared using the solvent evaporation technique. Each formulation was tested for dissolution using intrinsic dissolution apparatus (USP). The solid solutions were compressed into tablets into the sample die that maintained a constant surface area during the dissolution process. DSC, XRD and NIRS scans identified that the crystalline peaks of the drug disappeared with the addition of the polymer for all ratios of EE, indicating the formation of solid solutions (to within the limits of detection of the equipment). This was also observed for the LEVO dispersions up to 10% drug loading. At higher drug loading, solutions were formed but some small degree crystallinity was also present. For each experiment, the initial dissolution rates were obtained from the slope of the mass dissolved vs. time plots taken at early times, and volume normalized initial dissolution rates RV were calculated by dividing the initial dissolution rate by the volume fraction of the drug in the formulation. Comparison of the RV values for the various formulations with a reference RV (typically that of the pure drug or of the formulation with the highest polymer content) allowed calculation of relative volume normalized dissolution rates (RNV). The various RNV were used in the thermodynamic model for data analyses and to determine the interactions between the drug and carrier molecules. It was generally seen that RNV increased with decreased drug fraction, and was adequately modeled by the equations derived from the extended thermodynamic model. It was concluded that the model proposed for the binary and ternary systems successfully represented the mechanism of drug-polymer interaction and the energy changes taken place within the dispersion systems. The dissolution data analysis and subsequent understanding of physical modifications in the dispersion systems characterized by XRD, NIRS and DSC further substantiated the findings. The understanding of the fundamental physical might help scientists to predict the effects of mixing various drugs and polymers, and the effects of varying ratios.

5 CFR 2634.410 - Dissolution.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 5 Administrative Personnel 3 2014-01-01 2014-01-01 false Dissolution. 2634.410 Section 2634.410..., QUALIFIED TRUSTS, AND CERTIFICATES OF DIVESTITURE Qualified Trusts § 2634.410 Dissolution. Within thirty days of dissolution of a qualified trust, the interested party shall file a report of the dissolution...

5 CFR 2634.410 - Dissolution.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 5 Administrative Personnel 3 2013-01-01 2013-01-01 false Dissolution. 2634.410 Section 2634.410..., QUALIFIED TRUSTS, AND CERTIFICATES OF DIVESTITURE Qualified Trusts § 2634.410 Dissolution. Within thirty days of dissolution of a qualified trust, the interested party shall file a report of the dissolution...

High temperature dissolution of chromium substituted nickel ferrite in nitrilotriacetic acid medium

NASA Astrophysics Data System (ADS)

Sathyaseelan, V. S.; Chandramohan, P.; Velmurugan, S.

2016-12-01

High temperature (HT) dissolution of chromium substituted nickel ferrite was carried out with relevance to the decontamination of nuclear reactors by way of chemical dissolution of contaminated corrosion product oxides present on stainless steel coolant circuit surfaces. Chromium substituted nickel ferrites of composition, NiFe(2-x)CrxO4 (x ≤ 1), was synthetically prepared and characterized. HT dissolution of these oxides was carried out in nitrilotriacetic acid medium at 160 °C. Dissolution was remarkably increased at 160 °C when compared to at 85 °C in a reducing decontamination formulation. Complete dissolution could be achieved for the oxides with chromium content 0 and 0.2. Increasing the chromium content brought about a marked reduction in the dissolution rate. About 40 fold decrease in rate of dissolution was observed when chromium was increased from 0 to 1. The rate of dissolution was not very significantly reduced in the presence of N2H4. Dissolution of oxide was found to be stoichiometric.

Accelerating the dissolution of enteric coatings in the upper small intestine: evolution of a novel pH 5.6 bicarbonate buffer system to assess drug release.

PubMed

Varum, Felipe J O; Merchant, Hamid A; Goyanes, Alvaro; Assi, Pardis; Zboranová, Veronika; Basit, Abdul W

2014-07-01

Despite rapid dissolution in compendial phosphate buffers, gastro resistant (enteric coated) products can take up to 2 h to disintegrate in the human small intestine, which clearly highlights the inadequacy of the in vitro test method to predict in vivo behaviour of these formulations. The aim of this study was to establish the utility of a novel pH 5.6 bicarbonate buffer, stabilized by an Auto pH™ System, as a better surrogate of the conditions of the proximal small intestine to investigate the dissolution behaviour of standard and accelerated release enteric double coating formulations. Prednisolone tablets were coated with 3 or 5 mg/cm(2) of partially neutralized EUDRAGIT(®) L 30 D-55, HP-55 or HPMC adjusted to pH 6 or 8. An outer layer of EUDRAGIT(®) L 30 D-55 was applied at 5mg/cm(2). For comparison purposes, a standard single layer of EUDRAGIT(®) L 30 D-55 was applied to the tablets. Dissolution was carried out using USP II apparatus in 0.1 M HCl for 2 h, followed by pH 5.6 bicarbonate buffer. EUDRAGIT(®) L 30 D-55 single-coated tablets showed a slow drug release with a lag time of 75 min in buffer, whereas release from the EUDRAGIT(®) L 30 D-55 double-coated tablets was accelerated. These in vitro lag times closely match the in vivo disintegration times for these coated tablets reported previously. Drug release was further accelerated from modified double coatings, particularly in the case of coatings with a thinner inner layer of HP-55 or HPMC (pH 8 and KH2PO4). This study confirms that the pH 5.6 bicarbonate buffer system offers significant advantages during the development of dosage forms designed to release the drug in the upper small intestine. Copyright © 2014. Published by Elsevier B.V.

Evolution of supersaturation of amorphous pharmaceuticals: the effect of rate of supersaturation generation.

PubMed

Sun, Dajun D; Lee, Ping I

2013-11-04

The combination of a rapidly dissolving and supersaturating "spring" with a precipitation retarding "parachute" has often been pursued as an effective formulation strategy for amorphous solid dispersions (ASDs) to enhance the rate and extent of oral absorption. However, the interplay between these two rate processes in achieving and maintaining supersaturation remains inadequately understood, and the effect of rate of supersaturation buildup on the overall time evolution of supersaturation during the dissolution of amorphous solids has not been explored. The objective of this study is to investigate the effect of supersaturation generation rate on the resulting kinetic solubility profiles of amorphous pharmaceuticals and to delineate the evolution of supersaturation from a mechanistic viewpoint. Experimental concentration-time curves under varying rates of supersaturation generation and recrystallization for model drugs, indomethacin (IND), naproxen (NAP) and piroxicam (PIR), were generated from infusing dissolved drug (e.g., in ethanol) into the dissolution medium and compared with that predicted from a comprehensive mechanistic model based on the classical nucleation theory taking into account both the particle growth and ripening processes. In the absence of any dissolved polymer to inhibit drug precipitation, both our experimental and predicted results show that the maximum achievable supersaturation (i.e., kinetic solubility) of the amorphous solids increases, the time to reach maximum decreases, and the rate of concentration decline in the de-supersaturation phase increases, with increasing rate of supersaturation generation (i.e., dissolution rate). Our mechanistic model also predicts the existence of an optimal supersaturation rate which maximizes the area under the curve (AUC) of the kinetic solubility concentration-time profile, which agrees well with experimental data. In the presence of a dissolved polymer from ASD dissolution, these observed trends also hold true except the de-supersaturation phase is more extended due to the crystallization inhibition effect. Since the observed kinetic solubility of nonequilibrium amorphous solids depends on the rate of supersaturation generation, our results also highlight the underlying difficulty in determining a reproducible solubility advantage for amorphous solids.

Dissolution of solid dosage form. II. Equations for the dissolution of nondisintegrating tablet under the sink condition.

PubMed

Yonezawa, Y; Shirakura, K; Otsuka, A; Sunada, H

1991-03-01

An equation for dissolution from the whole surface of a nondisintegrating single component tablet under the sink condition was derived. Also, equations for several dissolution manners of the tablet under the sink condition were derived in the postulation of the dominant dissolution rate constant which determines the dissolution manner. The applicability or validity of these equations were examined by the dissolution measurements with nondisintegrating single component tablets. About one-tenth the amount of the amount needed to saturate the solution was used to prepare a tablet, and dissolution measurements were carried out with the tablet whose flat or side surface was masked with an adhesive tape in accordance with the conditions for derivation of equations. Among the derived equations, dissolution from the whole surface of a tablet was expressed by a form similar to the cube root law equation for particles. Hence, a single component tablet compressed by the use of a suitable amount was thought to behave like a single crystal. Also, equations derived for several dissolution manners were thought to be applicable for the dissolution of a nonspherical particle and crystal concerning the crystal's habit and its dissolution property, and the extended applicability was examined by converting the crystal into a simplified or idealized form, i.e., rectangle or plate.

Justification of disintegration testing beyond current FDA criteria using in vitro and in silico models.

PubMed

Uebbing, Lukas; Klumpp, Lukas; Webster, Gregory K; Löbenberg, Raimar

2017-01-01

Drug product performance testing is an important part of quality-by-design approaches, but this process often lacks the underlying mechanistic understanding of the complex interactions between the disintegration and dissolution processes involved. Whereas a recent draft guideline by the US Food and Drug Administration (FDA) has allowed the replacement of dissolution testing with disintegration testing, the mentioned criteria are not globally accepted. This study provides scientific justification for using disintegration testing rather than dissolution testing as a quality control method for certain immediate release (IR) formulations. A mechanistic approach, which is beyond the current FDA criteria, is presented. Dissolution testing via United States Pharmacopeial Convention Apparatus II at various paddle speeds was performed for immediate and extended release formulations of metronidazole. Dissolution profile fitting via DDSolver and dissolution profile predictions via DDDPlus™ were performed. The results showed that Fickian diffusion and drug particle properties (DPP) were responsible for the dissolution of the IR tablets, and that formulation factors (eg, coning) impacted dissolution only at lower rotation speeds. Dissolution was completely formulation controlled if extended release tablets were tested and DPP were not important. To demonstrate that disintegration is the most important dosage form attribute when dissolution is DPP controlled, disintegration, intrinsic dissolution and dissolution testing were performed in conventional and disintegration impacting media (DIM). Tablet disintegration was affected by DIM and model fitting to the Korsmeyer-Peppas equation showed a growing effect of the formulation in DIM. DDDPlus was able to predict tablet dissolution and the intrinsic dissolution profiles in conventional media and DIM. The study showed that disintegration has to occur before DPP-dependent dissolution can happen. The study suggests that disintegration can be used as performance test of rapidly disintegrating tablets beyond the FDA criteria. The scientific criteria and justification is that dissolution has to be DPP dependent, originated from active pharmaceutical ingredient characteristics and formulations factors have to be negligible.

Justification of disintegration testing beyond current FDA criteria using in vitro and in silico models

PubMed Central

Uebbing, Lukas; Klumpp, Lukas; Webster, Gregory K; Löbenberg, Raimar

2017-01-01

Drug product performance testing is an important part of quality-by-design approaches, but this process often lacks the underlying mechanistic understanding of the complex interactions between the disintegration and dissolution processes involved. Whereas a recent draft guideline by the US Food and Drug Administration (FDA) has allowed the replacement of dissolution testing with disintegration testing, the mentioned criteria are not globally accepted. This study provides scientific justification for using disintegration testing rather than dissolution testing as a quality control method for certain immediate release (IR) formulations. A mechanistic approach, which is beyond the current FDA criteria, is presented. Dissolution testing via United States Pharmacopeial Convention Apparatus II at various paddle speeds was performed for immediate and extended release formulations of metronidazole. Dissolution profile fitting via DDSolver and dissolution profile predictions via DDDPlus™ were performed. The results showed that Fickian diffusion and drug particle properties (DPP) were responsible for the dissolution of the IR tablets, and that formulation factors (eg, coning) impacted dissolution only at lower rotation speeds. Dissolution was completely formulation controlled if extended release tablets were tested and DPP were not important. To demonstrate that disintegration is the most important dosage form attribute when dissolution is DPP controlled, disintegration, intrinsic dissolution and dissolution testing were performed in conventional and disintegration impacting media (DIM). Tablet disintegration was affected by DIM and model fitting to the Korsmeyer–Peppas equation showed a growing effect of the formulation in DIM. DDDPlus was able to predict tablet dissolution and the intrinsic dissolution profiles in conventional media and DIM. The study showed that disintegration has to occur before DPP-dependent dissolution can happen. The study suggests that disintegration can be used as performance test of rapidly disintegrating tablets beyond the FDA criteria. The scientific criteria and justification is that dissolution has to be DPP dependent, originated from active pharmaceutical ingredient characteristics and formulations factors have to be negligible. PMID:28442890

Planning for the Business of Education.

ERIC Educational Resources Information Center

Nutt, Andy

There are two levels of planning: strategic and operational. Strategic planning takes place at the upper levels of management and relates to the longrange objectives of an organization. Operational planning takes place at the middle, or lower, management echelon and deals with the implementation of strategic plans. It is the task of the chief…

An Overview of Sexual Harassment

ERIC Educational Resources Information Center

Stier, William F., Jr.

2005-01-01

Sexual harassment, according to the Equal Employment Opportunity Commission (EEOC), is when any unwelcome sexual advances for sexual favors, and other verbal or physical conduct of a sexual nature takes place. For sexual harassment to take place there must be some type of behavior, language, or material of a sexual nature, which is offensive.…

14 CFR 11.53 - What takes place at a public meeting?

Code of Federal Regulations, 2014 CFR

2014-01-01

... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false What takes place at a public meeting? 11.53 Section 11.53 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... invite interested persons to attend and to present their views to the agency on specific issues. There...

14 CFR 11.53 - What takes place at a public meeting?

Code of Federal Regulations, 2012 CFR

2012-01-01

... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false What takes place at a public meeting? 11.53 Section 11.53 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... invite interested persons to attend and to present their views to the agency on specific issues. There...

Rotating Solids and Flipping Instruction

ERIC Educational Resources Information Center

Grypp, Lynette; Luebeck, Jennifer

2015-01-01

Technology is causing educators to rethink the entire notion of classroom learning, not only with respect to what learning should take place but also where it should take place. One such innovation is flipped instruction, broadly defined by Staker and Horn (2012) as an instructional model in which students learn partly through online delivery and…

12 CFR 208.85 - Where insurance activities may take place.

Code of Federal Regulations, 2010 CFR

2010-01-01

... SYSTEM MEMBERSHIP OF STATE BANKING INSTITUTIONS IN THE FEDERAL RESERVE SYSTEM (REGULATION H) Consumer Protection in Sales of Insurance § 208.85 Where insurance activities may take place. (a) General rule. A bank... transactions are routinely conducted in the bank may refer a consumer who seeks to purchase an insurance...

12 CFR 14.50 - Where insurance activities may take place.

Code of Federal Regulations, 2010 CFR

2010-01-01

....50 Section 14.50 Banks and Banking COMPTROLLER OF THE CURRENCY, DEPARTMENT OF THE TREASURY CONSUMER PROTECTION IN SALES OF INSURANCE § 14.50 Where insurance activities may take place. (a) General rule. A bank... transactions are routinely conducted in the bank may refer a consumer who seeks to purchase an insurance...

12 CFR 536.50 - Where insurance activities may take place.

Code of Federal Regulations, 2010 CFR

2010-01-01

....50 Section 536.50 Banks and Banking OFFICE OF THRIFT SUPERVISION, DEPARTMENT OF THE TREASURY CONSUMER PROTECTION IN SALES OF INSURANCE § 536.50 Where insurance activities may take place. (a) General rule. A... savings association may refer a consumer who seeks to purchase an insurance product or annuity to a...

33 CFR 13.01-5 - Gold and Silver Lifesaving Medals.

Code of Federal Regulations, 2010 CFR

2010-07-01

... GENERAL DECORATIONS, MEDALS, RIBBONS AND SIMILAR DEVICES Gold and Silver Lifesaving Medals, Bars, and... order for a person to be eligible for a Lifesaving Medal the rescue or attempted rescue must take place... attempted rescue takes place outside such waters, one or the other of the parties must be a citizen of the...

78 FR 72141 - Aviation Rulemaking Advisory Committee; Meeting

Federal Register 2010, 2011, 2012, 2013, 2014

2013-12-02

... Standard Time. Arrange oral presentations by December 12, 2013. ADDRESSES: The meeting will take place at... Act (5 U.S.C. App. 2), we are giving notice of a meeting of the ARAC taking place on December 19, 2013... includes: 1. Recommendation Report a. Flight Controls Harmonization Working Group (Transport Airplane and...

78 FR 50138 - Aviation Rulemaking Advisory Committee; Meeting

Federal Register 2010, 2011, 2012, 2013, 2014

2013-08-16

... Standard Time. Arrange oral presentations by September 12, 2013. ADDRESSES: The meeting will take place at... Act (5 U.S.C. App. 2), we are giving notice of a meeting of the ARAC taking place on September 19... Agenda includes: 1. Recommendation Report a. Airman Testing Standards and Training Working Group (ARAC) 2...

Knowledge Transfer among Projects Using a Learn-Forget Model

ERIC Educational Resources Information Center

Tukel, Oya I.; Rom, Walter O.; Kremic, Tibor

2008-01-01

Purpose: The purpose of this paper is to analyze the impact of learning in a project-driven organization and demonstrate analytically how the learning, which takes place during the execution of successive projects, and the forgetting that takes place during the dormant time between the project executions, can impact performance and productivity in…

Mutual understanding: a communication model for general practice.

PubMed

Hantho, Arne; Jensen, Lena; Malterud, Kirsti

2002-12-01

To present our pursuits towards development of a simple model for clinical communication intended for application by the practitioner as a tool for enhancing mutual understanding. Inspired by theories about patient-centredness and interactive modes of understanding, and supported by the perspectives of the Danish philosopher Niels Thomassen, we reviewed audiotapes from our own consultations. Recognising four dimensions assumed to be essential for mutual understanding in the transcripts, we explored these dimensions further. We present a communication model consisting of the following dimensions: The Framework, within which the communication takes place; The Subject, about which the communication takes place; The Persons, between whom the communication takes place; and The Action, verbally and non-verbally, through which communication takes place. We describe these dimensions in detail. The nature of the dimensions indicates that there is an interrelationship between them, implying that the character of the communication may change if one of the factors is changed. Analysis of an ongoing or recent consultation completed in accordance with these four dimensions allows the doctor to refocus the communication, thus leading to a more extensive mutual understanding and perhaps enhanced freedom of action.

12 CFR 546.4 - Voluntary dissolution.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 12 Banks and Banking 6 2014-01-01 2012-01-01 true Voluntary dissolution. 546.4 Section 546.4 Banks... ASSOCIATIONS-MERGER, DISSOLUTION, REORGANIZATION, AND CONVERSION § 546.4 Voluntary dissolution. A Federal savings association's board of directors may propose a plan for dissolution of the association. The plan...

12 CFR 546.4 - Voluntary dissolution.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 12 Banks and Banking 6 2013-01-01 2012-01-01 true Voluntary dissolution. 546.4 Section 546.4 Banks... ASSOCIATIONS-MERGER, DISSOLUTION, REORGANIZATION, AND CONVERSION § 546.4 Voluntary dissolution. A Federal savings association's board of directors may propose a plan for dissolution of the association. The plan...

12 CFR 546.4 - Voluntary dissolution.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 12 Banks and Banking 5 2010-01-01 2010-01-01 false Voluntary dissolution. 546.4 Section 546.4... ASSOCIATIONS-MERGER, DISSOLUTION, REORGANIZATION, AND CONVERSION § 546.4 Voluntary dissolution. A Federal savings association's board of directors may propose a plan for dissolution of the association. The plan...

12 CFR 146.4 - Voluntary dissolution.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 12 Banks and Banking 1 2014-01-01 2014-01-01 false Voluntary dissolution. 146.4 Section 146.4... ASSOCIATIONS-MERGER, DISSOLUTION, REORGANIZATION, AND CONVERSION § 146.4 Voluntary dissolution. (a) A Federal savings association's board of directors may propose a plan for dissolution of the association. The plan...

12 CFR 146.4 - Voluntary dissolution.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 12 Banks and Banking 1 2013-01-01 2013-01-01 false Voluntary dissolution. 146.4 Section 146.4... ASSOCIATIONS-MERGER, DISSOLUTION, REORGANIZATION, AND CONVERSION § 146.4 Voluntary dissolution. (a) A Federal savings association's board of directors may propose a plan for dissolution of the association. The plan...

12 CFR 546.4 - Voluntary dissolution.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 12 Banks and Banking 5 2011-01-01 2011-01-01 false Voluntary dissolution. 546.4 Section 546.4... ASSOCIATIONS-MERGER, DISSOLUTION, REORGANIZATION, AND CONVERSION § 546.4 Voluntary dissolution. A Federal savings association's board of directors may propose a plan for dissolution of the association. The plan...

12 CFR 546.4 - Voluntary dissolution.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 12 Banks and Banking 6 2012-01-01 2012-01-01 false Voluntary dissolution. 546.4 Section 546.4... ASSOCIATIONS-MERGER, DISSOLUTION, REORGANIZATION, AND CONVERSION § 546.4 Voluntary dissolution. A Federal savings association's board of directors may propose a plan for dissolution of the association. The plan...

12 CFR 146.4 - Voluntary dissolution.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 12 Banks and Banking 1 2012-01-01 2012-01-01 false Voluntary dissolution. 146.4 Section 146.4... ASSOCIATIONS-MERGER, DISSOLUTION, REORGANIZATION, AND CONVERSION § 146.4 Voluntary dissolution. (a) A Federal savings association's board of directors may propose a plan for dissolution of the association. The plan...

Interface dissolution control of the 14C profile in marine sediment

USGS Publications Warehouse

Keir, R.S.; Michel, R.L.

1993-01-01

The process of carbonate dissolution at the sediment-water interface has two possible endmember boundary conditions. Either the carbonate particles dissolve mostly before they are incorporated into the sediment by bioturbation (interface dissolution), or the vertical mixing is rapid relative to their extermination rate (homogeneous dissolution). In this study, a detailed radiocarbon profile was determined in deep equatorial Pacific sediment that receives a high rate of carbonate supply. In addition, a box model of sediment mixing was used to simulate radiocarbon, carbonate content and excess thorium profiles that result from either boundary process following a dissolution increase. Results from homogeneous dissolution imply a strong, very recent erosional event, while interface dissolution suggests that moderately increased dissolution began about 10,000 years ago. In order to achieve the observed mixed layer radiocarbon age, increased homogeneous dissolution would concentrate a greater amount of clay and 230Th than is observed, while for interface dissolution the predicted concentrations are too small. These results together with small discontinuities beneath the mixed layer in 230Th profiles suggest a two-stage increase in interface dissolution in the deep Pacific, the first occurring near the beginning of the Holocene and the second more recently, roughly 5000 years ago. ?? 1993.

Copper recovery and gold enrichment from waste printed circuit boards by mediated electrochemical oxidation.

PubMed

Fogarasi, Szabolcs; Imre-Lucaci, Florica; Imre-Lucaci, Arpád; Ilea, Petru

2014-05-30

The present study aims to develop an eco-friendly chemical-electrochemical process for the simultaneous recovery of copper and separation of a gold rich residue from waste printed circuit boards (WPCBs). The process was carried out by employing two different types of reactors coupled in series: a leaching reactor with a perforated rotating drum, for the dissolution of base metals and a divided electrochemical reactor for the regeneration of the leaching solution with the parallel electrowinning of copper. The process performances were evaluated on the basis of the dissolution efficiency, current efficiency and specific energy consumptions. Finally a process scale up was realized taking into consideration the optimal values of the operating parameters. The laboratory scale leaching plant allowed the recovery of a high purity copper deposit (99.04wt.%) at a current efficiency of 63.84% and specific energy consumption of 1.75kWh/kg cooper. The gold concentration in the remained solid residue was 25 times higher than the gold concentration in the initial WPCB samples. Copyright © 2014 Elsevier B.V. All rights reserved.

Significance of a Shelf-wide Dissolution Event during the Paleocene-Eocene Thermal Maximum, Maryland and New Jersey, USA

NASA Astrophysics Data System (ADS)

Bralower, T. J.; Kump, L. R.; Robinson, M. M.; Self-Trail, J. M.; Zachos, J. C.

2016-12-01

Continental-shelf sediments of the US Atlantic margin experienced a brief episode of carbonate dissolution during the onset of the Paleocene-Eocene Thermal Maximum (PETM). Dissolution is represented by reduced percentages of carbonate, and calcareous microfossil distribution and preservation trends, in cores from Maryland and New Jersey. The base and the top of the dissolution zone are abrupt compared to the gradual nature of the onset of the carbon isotope excursion (CIE). The thickness of the dissolution zone varies from 9 cm in the Bass River core (outer paleoshelf) to 1.6 m in the CamDor core (middle paleoshelf). The decrease in %CaCO3 suggests dissolution locally removed 83 to 100% of the initial biogenic carbonate. Shelf-wide dissolution during the onset of the PETM may be a regional event, associated, for example, with eutrophication. Samples from across the paleoshelf contain abundant fine-grained framboidal pyrite, which suggests photic-zone euxinia occurred before, during, and after the dissolution event. Dissolution may also be associated with oxidation of this pyrite during later exposure to oxidizing groundwaters, although the restricted duration of the dissolution interval argues against this. Alternatively, the dissolution event may have global significance related to surface ocean-water acidification or shoaling of the calcite compensation depth (CCD) to shelf depths. The event began near the onset of the CIE on the shelf, whereas dissolution in deep-sea sections began later. Earlier shelf dissolution is consistent with surface ocean acidification while later deep-sea dissolution is thought to be associated with shoaling of the CCD. In our presentation, we weigh evidence for each of these possibilities and test them using the global dataset.

26 CFR 301.6501(d)-1 - Request for prompt assessment.

Code of Federal Regulations, 2014 CFR

2014-04-01

... which is contemplating dissolution, is in the process of dissolution, or has been dissolved, may be... that the corporation contemplates dissolution at or before the expiration of such 18-month period; the dissolution is in good faith begun before the expiration of such 18-month period; and the dissolution so begun...

27 CFR 70.74 - Request for prompt assessment.

Code of Federal Regulations, 2014 CFR

2014-04-01

... contemplating dissolution, is in the process of dissolution, or has been dissolved, may be liable, shall be... dissolution at or before the expirationof such 18-month period; the dissolution is in good faith begun before the expiration of such 18-month period; and the dissolution so begun is completed either before or...

27 CFR 70.74 - Request for prompt assessment.

Code of Federal Regulations, 2012 CFR

2012-04-01

... contemplating dissolution, is in the process of dissolution, or has been dissolved, may be liable, shall be... dissolution at or before the expirationof such 18-month period; the dissolution is in good faith begun before the expiration of such 18-month period; and the dissolution so begun is completed either before or...

27 CFR 70.74 - Request for prompt assessment.

Code of Federal Regulations, 2010 CFR

2010-04-01

... contemplating dissolution, is in the process of dissolution, or has been dissolved, may be liable, shall be... dissolution at or before the expirationof such 18-month period; the dissolution is in good faith begun before the expiration of such 18-month period; and the dissolution so begun is completed either before or...

27 CFR 70.74 - Request for prompt assessment.

Code of Federal Regulations, 2013 CFR

2013-04-01

... contemplating dissolution, is in the process of dissolution, or has been dissolved, may be liable, shall be... dissolution at or before the expirationof such 18-month period; the dissolution is in good faith begun before the expiration of such 18-month period; and the dissolution so begun is completed either before or...

26 CFR 301.6501(d)-1 - Request for prompt assessment.

Code of Federal Regulations, 2012 CFR

2012-04-01

... which is contemplating dissolution, is in the process of dissolution, or has been dissolved, may be... that the corporation contemplates dissolution at or before the expiration of such 18-month period; the dissolution is in good faith begun before the expiration of such 18-month period; and the dissolution so begun...

26 CFR 301.6501(d)-1 - Request for prompt assessment.

Code of Federal Regulations, 2011 CFR

2011-04-01

... which is contemplating dissolution, is in the process of dissolution, or has been dissolved, may be... that the corporation contemplates dissolution at or before the expiration of such 18-month period; the dissolution is in good faith begun before the expiration of such 18-month period; and the dissolution so begun...

27 CFR 70.74 - Request for prompt assessment.

Code of Federal Regulations, 2011 CFR

2011-04-01

... contemplating dissolution, is in the process of dissolution, or has been dissolved, may be liable, shall be... dissolution at or before the expirationof such 18-month period; the dissolution is in good faith begun before the expiration of such 18-month period; and the dissolution so begun is completed either before or...

26 CFR 301.6501(d)-1 - Request for prompt assessment.

Code of Federal Regulations, 2013 CFR

2013-04-01

... which is contemplating dissolution, is in the process of dissolution, or has been dissolved, may be... that the corporation contemplates dissolution at or before the expiration of such 18-month period; the dissolution is in good faith begun before the expiration of such 18-month period; and the dissolution so begun...

26 CFR 301.6501(d)-1 - Request for prompt assessment.

Code of Federal Regulations, 2010 CFR

2010-04-01

... which is contemplating dissolution, is in the process of dissolution, or has been dissolved, may be... that the corporation contemplates dissolution at or before the expiration of such 18-month period; the dissolution is in good faith begun before the expiration of such 18-month period; and the dissolution so begun...

Dry powder inhalers: An overview of the in vitro dissolution methodologies and their correlation with the biopharmaceutical aspects of the drug products.

PubMed

Velaga, Sitaram P; Djuris, Jelena; Cvijic, Sandra; Rozou, Stavroula; Russo, Paola; Colombo, Gaia; Rossi, Alessandra

2018-02-15

In vitro dissolution testing is routinely used in the development of pharmaceutical products. Whilst the dissolution testing methods are well established and standardized for oral dosage forms, i.e. tablets and capsules, there are no pharmacopoeia methods or regulatory requirements for testing the dissolution of orally inhaled powders. Despite this, a wide variety of dissolution testing methods for orally inhaled powders has been developed and their bio-relevance has been evaluated. This review provides an overview of the in vitro dissolution methodologies for dry inhalation products, with particular emphasis on dry powder inhalers, where the dissolution behavior of the respirable particles can have a role on duration and absorption of the drug. Dissolution mechanisms of respirable particles as well as kinetic models have been presented. A more recent biorelevant dissolution set-ups and media for studying inhalation biopharmaceutics were also reviewed. In addition, factors affecting interplay between dissolution and absorption of deposited particles in the context of biopharmaceutical considerations of inhalation products were examined. Copyright © 2017 Elsevier B.V. All rights reserved.

Developing a quality by design approach to model tablet dissolution testing: an industrial case study.

PubMed

Yekpe, Ketsia; Abatzoglou, Nicolas; Bataille, Bernard; Gosselin, Ryan; Sharkawi, Tahmer; Simard, Jean-Sébastien; Cournoyer, Antoine

2018-07-01

This study applied the concept of Quality by Design (QbD) to tablet dissolution. Its goal was to propose a quality control strategy to model dissolution testing of solid oral dose products according to International Conference on Harmonization guidelines. The methodology involved the following three steps: (1) a risk analysis to identify the material- and process-related parameters impacting the critical quality attributes of dissolution testing, (2) an experimental design to evaluate the influence of design factors (attributes and parameters selected by risk analysis) on dissolution testing, and (3) an investigation of the relationship between design factors and dissolution profiles. Results show that (a) in the case studied, the two parameters impacting dissolution kinetics are active pharmaceutical ingredient particle size distributions and tablet hardness and (b) these two parameters could be monitored with PAT tools to predict dissolution profiles. Moreover, based on the results obtained, modeling dissolution is possible. The practicality and effectiveness of the QbD approach were demonstrated through this industrial case study. Implementing such an approach systematically in industrial pharmaceutical production would reduce the need for tablet dissolution testing.

Coupled Thermo-Hydro-Chemical (THC) Modeling of Hypogene Karst Evolution in a Prototype Mountain Hydrologic System

NASA Astrophysics Data System (ADS)

Chaudhuri, A.; Rajaram, H.; Viswanathan, H. S.; Zyvoloski, G.

2011-12-01

Hypogene karst systems are believed to develop when water flowing upward against the geothermal gradient dissolves limestone as it cools. We present a comprehensive THC model incorporating time-evolving fluid flow, heat transfer, buoyancy effects, multi-component reactive transport and aperture/permeability change to investigate the origin of hypogene karst systems. Our model incorporates the temperature and pressure dependence of the solubility and dissolution kinetics of calcite. It also allows for rigorous representation of temperature-dependent fluid density and its influence on buoyancy forces at various stages of karstification. The model is applied to investigate karstification over geological time scales in a prototype mountain hydrologic system. In this system, a high water table maintained by mountain recharge, drives flow downward through the country rock and upward via a high-permeability fault/fracture. The pressure boundary conditions are maintained constant in time. The fluid flux through the fracture remains nearly constant even though the fracture aperture and permeability increase by dissolution, largely because the permeability of the country rock is not altered significantly due to slower dissolution rates. However, karstification by fracture dissolution is not impeded even though the fluid flux stays nearly constant. Forced and buoyant convection effects arise due to the increased permeability of the evolving fracture system. Since in reality the aperture varies significantly within the fracture plane, the initial fracture aperture is modeled as a heterogeneous random field. In such a heterogeneous aperture field, the water initially flows at a significant rate mainly through preferential flow paths connecting the relatively large aperture zones. Dissolution is more prominent at early time along these flow paths, and the aperture grows faster within these paths. With time, the aperture within small sub-regions of these preferential flow paths grows to a point where the permeability is large enough for the onset of buoyant convection. As a result, a multitude of buoyant convection cells form that take on a two-dimensional (2D) maze-like appearance, which could represent a 2D analog of the three-dimensional (3D) mazework pattern widely thought to be characteristic of hypogene cave systems. Although computational limitations limited us to 2D, we suggest that similar process interactions in a 3D network of fractures and faults could produce a 3D mazework.

A new method for evaluating the dissolution of orodispersible films.

PubMed

Xia, Yiran; Chen, Fang; Zhang, Huiping; Luo, Chunlin

2015-05-01

The aim of this research was to develop and assess a new dissolution apparatus for orodispersible films (ODFs). The new apparatus was based on a flow-through cell design which requires only a limited amount of dissolution medium and can automatically collect samples in short-time intervals. Compared with the dissolution method in Chinese Pharmacopeia, our method simulated the flow condition of the oral cavity and resulted in reproducible dissolution data and remarkably discriminating capability. Therefore, we concluded that the proposed dissolution method was particularly suitable for evaluating the dissolution of ODFs and should also be applicable to other fast-dissolving solid dosage forms.

78 FR 8644 - Self-Regulatory Organizations; BOX Options Exchange LLC; Notice of Filing and Immediate...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-02-06

... when the Exchange deems it necessary to maintain an orderly market, to meet customer demand, or when... customer demand, or when certain price movements take place in the underlying market. The Exchange proposes..., to meet customer demand, or when certain price movements take place in the underlying market. The...

Learning for You and Learning for Me: Mentoring as Professional Development for Mentor Teachers

ERIC Educational Resources Information Center

Smith, Janette; Nadelson, Louis

2016-01-01

Professional development (PD) opportunities for teachers most commonly take place outside the classroom and are typically designed to address specific components of teachers' instruction or curriculum. However, there are other activities that take place within the classroom that may have a profound impact on the PD of a teacher. We sought to gain…

ALA Salary Survey: Personal Members

ERIC Educational Resources Information Center

American Libraries, 1971

1971-01-01

A survey of the members of the American Library Association revealed that the principal salary determinants are academic degree, type of employer and sex. The obvious differences in the earnings of men and women is not only found in the early experience years but any narrowing which does take place in the wage gap seems to take place at the…

49 CFR 40.221 - Where does an alcohol test take place?

Code of Federal Regulations, 2013 CFR

2013-10-01

... 49 Transportation 1 2013-10-01 2013-10-01 false Where does an alcohol test take place? 40.221 Section 40.221 Transportation Office of the Secretary of Transportation PROCEDURES FOR TRANSPORTATION WORKPLACE DRUG AND ALCOHOL TESTING PROGRAMS Testing Sites, Forms, Equipment and Supplies Used in Alcohol Testing § 40.221 Where does an alcohol test...

"Trying to Push Things through": Forms and Bounds of Agency in Transitions of School-Age Young People

ERIC Educational Resources Information Center

Aaltonen, Sanna

2013-01-01

The conventional approach to youth transitions has focused on particular transitional points taking place after the completion of compulsory education. This paper focuses on the ways in which institutional regulations, individual agency, and emotions are related in bringing about such significant transitions that take place outside the traditional…

Why It Takes Prevention, Not Detection, to Fight Bioterrorism

ERIC Educational Resources Information Center

Janata, Jiri (Art)

2005-01-01

Following the events which took place on September 11, 2001, and the anthrax attacks which occurred after that date, US authorities became concerned with the idea that an assault with chemical or biological weapons could take place on American territory or in American ships or planes. A worrisome model for such an assault was the 1995 terrorist…

Disrupting Adult and Community Education: Teaching, Learning, and Working in the Periphery

ERIC Educational Resources Information Center

Mizzi, Robert C., Ed.; Rocco, Tonette S., Ed.; Shore, Sue, Ed.

2016-01-01

This groundbreaking book critiques the boundaries of where adult education takes place through a candid examination of teaching, learning, and working practices in the social periphery. Lives in this context are diverse and made through complex practices that take place in the shadows of formal systems: on streetscapes and farms, in vehicles and…

The Effect of Flipped Learning (Revised Learning) on Iranian Students' Learning Outcomes

ERIC Educational Resources Information Center

Yousefzadeh, Malahat; Salimi, Asghar

2015-01-01

The purpose of this study was to investigate whether the flipped (revised) learning had effect on student learning outcome. Lage et al (2000) describes the flipped classroom as " Inverting the classroom means that events that have traditionally take place inside the classroom now take place outside the class and vice versa" (p.32). The…

26 CFR 1.924(d)-1 - Requirement that economic processes take place outside the United States.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 26 Internal Revenue 10 2014-04-01 2013-04-01 true Requirement that economic processes take place outside the United States. 1.924(d)-1 Section 1.924(d)-1 Internal Revenue INTERNAL REVENUE SERVICE... otherwise constitute advertising (such as sending sales literature to a customer or potential customer) will...

Using a Flying Thing in the Sky to See How Much Water is in the Cover of Tiny Ice Pieces in the High Places

NASA Astrophysics Data System (ADS)

Skiles, M.

2016-12-01

Groups of tiny ice pieces fall from the sky in the cold times and cover the high places. Later, the tiny ice pieces become water that moves to the lower places, where people can use it for drinking and stuff. The time when the tiny ice pieces turn to water is controlled by the sun. New tiny ice pieces from the sky, which are very white and don't take up much sun, group up and grow tall. When they become dark from getting old and large, and from getting covered in tiny dark bits from the sky, they take up more sun and turn to water. The more tiny dark bits, the faster they become water. Using a flying thing over the high places we can see how much water will come from the cover of tiny ice pieces by using ground looking things to see how tall it is, and and when it will become water by using picture taking things to see how much sun is taken up. The low places are happy to know how much water is in the high places.

General solution for diffusion-controlled dissolution of spherical particles. 1. Theory.

PubMed

Wang, J; Flanagan, D R

1999-07-01

Three classical particle dissolution rate expressions are commonly used to interpret particle dissolution rate phenomena. Our analysis shows that an assumption used in the derivation of the traditional cube-root law may not be accurate under all conditions for diffusion-controlled particle dissolution. Mathematical analysis shows that the three classical particle dissolution rate expressions are approximate solutions to a general diffusion layer model. The cube-root law is most appropriate when particle size is much larger than the diffusion layer thickness, the two-thirds-root expression applies when the particle size is much smaller than the diffusion layer thickness. The square-root expression is intermediate between these two models. A general solution to the diffusion layer model for monodispersed spherical particles dissolution was derived for sink and nonsink conditions. Constant diffusion layer thickness was assumed in the derivation. Simulated dissolution data showed that the ratio between particle size and diffusion layer thickness (a0/h) is an important factor in controlling the shape of particle dissolution profiles. A new semiempirical general particle dissolution equation is also discussed which encompasses the three classical particle dissolution expressions. The success of the general equation in explaining limitations of traditional particle dissolution expressions demonstrates the usefulness of the general diffusion layer model.

Development and Validation of Discriminating and Biorelevant Dissolution Test for Lornoxicam Tablets

PubMed Central

Anumolu, P. D.; Sunitha, G.; Bindu, S. Hima; Satheshbabu, P. R.; Subrahmanyam, C. V. S.

2015-01-01

The establishment of biorelevant and discriminating dissolution procedure for drug products with limited water solubility is a useful technique for qualitative forecasting of the in vivo behavior of formulations. It also characterizes the drug product performance in pharmaceutical development. Lornoxicam, a BCS class-II drug is a nonsteroidal antiinflammatory drug of the oxicam class, has no official dissolution media available in the literature. The objective of present work was to develop and validate a discriminating and biorelevant dissolution test for lornoxicam tablet dosage forms. To quantify the lornoxicam in dissolution samples, UV spectrophotometric method was developed using 0.01M sodium hydroxide solution as solvent at λma×376 nm. After evaluation of saturation solubility, dissolution, sink conditions and stability of lornoxicam bulk drug in different pH solutions and biorelevant media, the dissolution method was optimized using USP paddle type apparatus at 50 rpm rotation speed and 500 ml simulated intestinal fluid as discriminating and biorelevant dissolution medium. The similarity factor (f2) were investigated for formulations with changes in composition and manufacturing variations, values revealed that dissolution method having discriminating power and method was validated as per standard guidelines. The proposed dissolution method can be effectively applied for routine quality control in vitro dissolution studies of lornoxicam in tablets and helpful to pharmacopoeias. PMID:26180277

Development and Validation of Discriminating and Biorelevant Dissolution Test for Lornoxicam Tablets.

PubMed

Anumolu, P D; Sunitha, G; Bindu, S Hima; Satheshbabu, P R; Subrahmanyam, C V S

2015-01-01

The establishment of biorelevant and discriminating dissolution procedure for drug products with limited water solubility is a useful technique for qualitative forecasting of the in vivo behavior of formulations. It also characterizes the drug product performance in pharmaceutical development. Lornoxicam, a BCS class-II drug is a nonsteroidal antiinflammatory drug of the oxicam class, has no official dissolution media available in the literature. The objective of present work was to develop and validate a discriminating and biorelevant dissolution test for lornoxicam tablet dosage forms. To quantify the lornoxicam in dissolution samples, UV spectrophotometric method was developed using 0.01M sodium hydroxide solution as solvent at λma×376 nm. After evaluation of saturation solubility, dissolution, sink conditions and stability of lornoxicam bulk drug in different pH solutions and biorelevant media, the dissolution method was optimized using USP paddle type apparatus at 50 rpm rotation speed and 500 ml simulated intestinal fluid as discriminating and biorelevant dissolution medium. The similarity factor (f2) were investigated for formulations with changes in composition and manufacturing variations, values revealed that dissolution method having discriminating power and method was validated as per standard guidelines. The proposed dissolution method can be effectively applied for routine quality control in vitro dissolution studies of lornoxicam in tablets and helpful to pharmacopoeias.

Clinical pharmacokinetic study for the effect of glimepiride matrix tablets developed by quality by design concept.

PubMed

Ahmed, Tarek A; Suhail, Mohammad A A; Hosny, Khaled M; Abd-Allah, Fathy I

2018-01-01

Implementation of a new pharmaceutical technique to improve aqueous solubility and thus dissolution, enhancement of drug permeation, and finally formulation of a controlled release tablet loaded with glimepiride (GLMP). Improve GLMP bioavailability and pharmacokinetics in type II diabetic patients. Different polymers were used to enhance aqueous GLMP solubility of which a saturated polymeric drug solution was prepared and physically adsorbed onto silica. An experimental design was employed to optimize the formulation parameters affecting the preparation of GLMP matrix tablets. A compatibility study was conducted to study components interactions. Scanning electron microscope (SEM) was performed before and after the tablets were placed in the dissolution medium. An in vivo study in human volunteers was performed with the optimized GLMP tablets, which were compared to pure and marketed drug products. Enhancement of GLMP aqueous solubility, using the polymeric drug solution technique, by more than 6-7 times when compared with the binary system. All the studied formulation factors significantly affected the studied variables. No significant interaction was detected among components. SEM illustrated the surface and inner tablet structure, and confirmed the drug release which was attributed to diffusion mechanism. The volunteer group administered the optimized GLMP tablet exhibited higher drug plasma concentration (147.4 ng/mL), longer time to reach maximum plasma concentration (4 h) and longer t 1/2 (7.236 h) compared to other groups. Matrix tablet loaded with a physically modified drug form could represent a key solution for drugs with inconsistent dissolution and absorption profiles.

Rapid tissue dissolution efficiency of electrically-activated sodium hypochlorite on bovine muscle.

PubMed

Ertugrul, Ihsan Furkan; Maden, Murat; Orhan, Ekim Onur; Ozkorucuklu, Sabriye Percin; Aglarca, Ali Vasfi

2014-10-01

Sodium hypochlorite (NaOCl) is a common antimicrobial and tissue-dissolving irrigant. The aim of this in vitro study is to evaluate and compare dissolution capacities of sodium hypochlorite solutions after electrically activation (E-NaOCl) on bovine muscle specimens at various time periods and concentrations. Three sodium hypochlorite solutions of 1.25%, 2.5%, and 5% were tested at 3-min. and 5-min. with and without activation by electrically. Distilled water and NaOCl solutions without electrically activation were used as controls. Pieces of bovine muscle tissue (34 ± 2 mg) were placed in 10 mL of each solution at room temperature. In the group of E-NaOCl, electrically activation was performed through the potentiostat. The tissue specimens were weighed before and after treatment, and the percentage of weight loss was calculated. Weight loss of the tissue increased with the concentration of E-NaOCl and NaOCl. Higher concentration and electrically activation considerably enhanced the efficacy of sodium hypochlorite. The effect of electrically activation on tissue dissolution was much greater than that of same concentrations in the groups of NaOCl (P < 0.001). Tissue weight loss was significantly higher in 2.5% and 5% E-NaOCl at 3 min. than in 2.5% and 5% NaOCl at 5 min. (P < 0.05). There were not any significant differences between the 2.5% E-NaOCl and 5% NaOCl at 5 min. (P > 0.05). Electrically activation can improve the tissue-dissolving effectiveness of sodium hypochlorite.

In Situ Salt Formation during Melt Extrusion for Improved Chemical Stability and Dissolution Performance of a Meloxicam-Copovidone Amorphous Solid Dispersion.

PubMed

Haser, Abbe; Cao, Tu; Lubach, Joseph W; Zhang, Feng

2018-03-05

As the pipeline for poorly soluble compounds continues to grow, drug degradation during melt extrusion must be addressed. We present a novel method for stabilizing a thermally labile drug substance while preserving its physical stability and even improving its dissolution performance. In a previous study, we found that incorporating meglumine during extrusion of meloxicam results in chemical stabilization that cannot be achieved using process optimization alone. The purpose of this study is to understand the mechanism behind this stabilization and its impact on the performance of a meloxicam-Kollidon VA64 amorphous solid dispersion. The meloxicam concentration was maintained at 10% (w/w) for blends with and without meglumine. The optimal meglumine blend contained an equimolar amount of meloxicam to meglumine with the remainder consisting of Kollidon VA64. Both formulations were processed with optimized extrusion conditions and analyzed by HPLC for purity. Meglumine at a 1:1 molar ratio with meloxicam results in 100% purity of meloxicam after melt extrusion. Solid-state NMR revealed a proton transfer between the meloxicam and meglumine indicating an in situ salt formation. During non-sink dissolution, the meglumine ASD enables meloxicam to maintain supersaturatation (≅50 times more than meloxicam free acid) for >7.25 h. The ASD without meglumine began precipitating 2.25 h following the pH shift. The ASDs were placed at 40 °C/75% RH for 6 months, and their stability was assessed. No significant chemical degradation, recrystallization, or significant moisture uptake was observed after six months' storage at 40 °C/75% RH.

The influence of co-formers on the dissolution rates of co-amorphous sulfamerazine/excipient systems.

PubMed

Gniado, Katarzyna; Löbmann, Korbinian; Rades, Thomas; Erxleben, Andrea

2016-05-17

A comprehensive study on the dissolution properties of three co-amorphous sulfamerazine/excipient systems, namely sulfamerazine/deoxycholic acid, sulfamerazine/citric acid and sulfamerazine/sodium taurocholate (SMZ/DA, SMZ/CA and SMZ/NaTC; 1:1 molar ratio), is reported. While all three co-formers stabilize the amorphous state during storage, only co-amorphization with NaTC provides a dissolution advantage over crystalline SMZ and the reasons for this were analyzed. In the case of SMZ/DA extensive gelation of DA protects the amorphous phase from crystallization upon contact with buffer, but at the same time prevents the release of SMZ into solution. Disk dissolution studies showed an improved dissolution behavior of SMZ/CA compared to crystalline SMZ. However, enhanced dissolution properties were not seen in powder dissolution testing due to poor dispersibility. Co-amorphization of SMZ and NaTC resulted in a significant increase in dissolution rate, both in powder and disk dissolution studies. Copyright © 2016. Published by Elsevier B.V.

Estimation of dissolution rate from in vivo studies of synthetic vitreous fibers.

PubMed

Eastes, W; Potter, R M; Hadley, J G

2000-11-01

Although the dissolution rate of a fiber was originally defined by a measurement of dissolution in simulated lung fluid in vitro, it is feasible to determine it from animal studies as well. The dissolution rate constant for a fiber may be extracted from the decrease in long fiber diameter observed in certain intratracheal instillation experiments or from the observed long fiber retention in short-term biopersistence studies. These in vivo dissolution rates agree well with those measured in vitro for the same fibers. For those special types of fibers, the high-alumina rock wool fibers that could not be measured in vitro, the method provides a way of obtaining a chemical dissolution rate constant from an animal study. The inverse of the in vivo dissolution rate, the fiber dissolution time, correlates well with the weighted half life of long fibers in a biopersistence study, and the in vivo dissolution rate may be estimated accurately from this weighted half-life.

Uranium carbide dissolution in nitric solution: Sonication vs. silent conditions

NASA Astrophysics Data System (ADS)

Virot, Matthieu; Szenknect, Stéphanie; Chave, Tony; Dacheux, Nicolas; Moisy, Philippe; Nikitenko, Sergey I.

2013-10-01

The dissolution of uranium carbide (UC) in nitric acid media is considered by means of power ultrasound (sonication) or magnetic stirring. The induction period required to initiate UC dissolution was found to be dramatically shortened when sonicating a 3 M nitric solution (Ar, 20 kHz, 18 W cm-2, 20 °C). At higher acidity, magnetic stirring offers faster dissolution kinetics compared to sonication. Ultrasound-assisted UC dissolution is found to be passivated after ∼60% dissolution and remains incomplete whatever the acidity which is confirmed by ICP-AES, LECO and SEM-EDX analyses. In general, the kinetics of UC dissolution is linked to the in situ generation of nitrous acid in agreement with the general mechanism of UC dissolution; the nitrous acid formation is reported to be faster under ultrasound at low acidity due to the nitric acid sonolysis. The carbon balance shared between the gaseous, liquid, and solid phases is strongly influenced by the applied dissolution procedure and HNO3 concentration.

Arsenic in Holocene aquifers of the Red River floodplain, Vietnam: Effects of sediment-water interactions, sediment burial age and groundwater residence time

NASA Astrophysics Data System (ADS)

Sø, Helle Ugilt; Postma, Dieke; , Mai Lan, Vi; Pham, Thi Kim Trang; Kazmierczak, Jolanta; Dao, Viet Nga; Pi, Kunfu; Koch, Christian Bender; Pham, Hung Viet; Jakobsen, Rasmus

2018-03-01

Water-sediment interactions were investigated in arsenic contaminated Holocene aquifers of the Red River floodplain, Vietnam, in order to elucidate the origin of the spatial variability in the groundwater arsenic concentration. The investigated aquifers are spread over an 8 × 13 km field area with sediments that varied in burial age from <1 kyr to 11 kyr. The groundwater age ranged from less than 2 yr, up to a maximum near 90 yr. Groundwater As concentrations are between 0 and 6.5 μM and there are no simple correlations between the As concentration and groundwater age or aquifer sediment burial age. The aquifers are anoxic with up to 2 mM CH4 and up to 0.5 mM DOC. The downward advective DOC flux is too small to support both methanogenesis and the reduction of As-containing Fe-oxides and sedimentary carbon is therefore considered the main carbon source for the redox processes. The groundwater H2 concentration ranged between 0.1 and 4 nM. These values are intermediate between ranges characteristic for Fe-oxide reduction and methanogenesis and suggest that both processes take place simultaneously. The groundwater pe was calculated from the H2/H+ and CH4/CO2 redox couples, giving almost similar results that apparently reflects the pe of the bulk groundwater. The pe calculated for the As(III)/As(V) redox couple was found in disequilibrium with the other redox couples. Using the pe calculated from the CH4/CO2 redox couple we show that the groundwater has a reducing potential towards Fe-oxides ranging from ferrihydrite to poorly crystalline goethite, but not for well crystalline goethite or hematite. Hematite and poorly crystalline goethite were identified as the Fe-oxides present in the sediments. Reductive dissolution experiments identify two phases releasing Fe(II); one rapidly dissolving that also contains As and a second releasing Fe(II) more slowly but without As. The initial release of Fe and As occurs at a near constant As/Fe ratio that varied from site to site between 1.2 and 0.1 mmol As/mol Fe. Siderite (FeCO3) is the main sink for Fe(II), based on saturation calculations as well as the identification of siderite in the sediment. Most of the carbonate incorporated in siderite originates from the dissolution of sedimentary CaCO3. Over time the CaCO3 content of the sediments diminishes and FeCO3 appears instead. No specific secondary phases that incorporate arsenite could be identified. Alternatively, the amount of arsenic mobilized during the dissolution of reactive phases can be contained in the pool of adsorbed arsenite. Combining groundwater age with aquifer sediment age allows the calculation of the total number of pore volumes flushed through the aquifer. Comparison with groundwater chemistry shows the highest arsenic concentration to be present within the first 200 pore volumes flushed through the aquifer. These results agree with reactive transport modeling combining a kinetic description of reductive dissolution of As-containing Fe-oxide with adsorption and desorption of arsenite. Understanding variability in groundwater arsenic concentration requires appreciating the coupling of the chemical processes to both sedimentary and hydrogeological cycling.

Clustered Single Cellulosic Fiber Dissolution Kinetics and Mechanisms through Optical Microscopy under Limited Dissolving Conditions.

PubMed

Mäkelä, Valtteri; Wahlström, Ronny; Holopainen-Mantila, Ulla; Kilpeläinen, Ilkka; King, Alistair W T

2018-05-14

Herein, we describe a new method of assessing the kinetics of dissolution of single fibers by dissolution under limited dissolving conditions. The dissolution is followed by optical microscopy under limited dissolving conditions. Videos of the dissolution were processed in ImageJ to yield kinetics for dissolution, based on the disappearance of pixels associated with intact fibers. Data processing was performed using the Python language, utilizing available scientific libraries. The methods of processing the data include clustering of the single fiber data, identifying clusters associated with different fiber types, producing average dissolution traces and also extraction of practical parameters, such as, time taken to dissolve 25, 50, 75, 95, and 99.5% of the clustered fibers. In addition to these simple parameters, exponential fitting was also performed yielding rate constants for fiber dissolution. Fits for sample and cluster averages were variable, although demonstrating first-order kinetics for dissolution overall. To illustrate this process, two reference pulps (a bleached softwood kraft pulp and a bleached hardwood pre-hydrolysis kraft pulp) and their cellulase-treated versions were analyzed. As expected, differences in the kinetics and dissolution mechanisms between these samples were observed. Our initial interpretations are presented, based on the combined mechanistic observations and single fiber dissolution kinetics for these different samples. While the dissolution mechanisms observed were similar to those published previously, the more direct link of mechanistic information with the kinetics improve our understanding of cell wall structure and pre-treatments, toward improved processability.

Dissolution of Uranium Oxides Under Alkaline Oxidizing Conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Steven C.; Peper, Shane M.; Douglas, Matthew

2009-11-01

Bench scale experiments were conducted to determine the dissolution characteristics of uranium oxide powders (UO2, U3O8, and UO3) in aqueous peroxide-carbonate solutions. Experimental parameters included H2O2 concentration, carbonate counter cation (NH4+, Na+, K+, and Rb+), and pH. Results indicate the dissolution rate of UO2 in 1 M (NH4)2CO3 increases linearly with peroxide concentration ranging from 0.05 – 2 M. The three uranium oxide powders exhibited different dissolution patterns however, UO3 exhibited prompt complete dissolution. Carbonate counter cation affected the dissolution kinetics. There is minimal impact of solution pH, over the range 8.8 to 10.6, on initial dissolution rate.

Enacting a Place-Responsive Research Methodology: Walking Interviews with Educators

ERIC Educational Resources Information Center

Lynch, Jonathan; Mannion, Greg

2016-01-01

Place-based and place-responsive approaches to outdoor learning and education are developing in many countries but there is dearth of theoretically-supported methodologies to take a more explicit account of place in research in these areas. In response, this article outlines one theoretical framing for place-responsive methodologies for…

Place and Being

ERIC Educational Resources Information Center

Cannatella, Howard

2007-01-01

Do places matter educationally? When Edward Casey remarks: "The world is, minimally and forever, a place-world", we might take this statement as presupposing without argument that places exist as a given, that we know what a place is, a point that Aristotle would have never taken for granted and in fact neither does Casey. I find Casey's remark…

Estimating the time for dissolution of spent fuel exposed to unlimited water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leider, H.R.; Nguyen, S.N.; Stout, R.B.

1991-12-01

The release of radionuclides from spent fuel cannot be precisely predicted at this point because a satisfactory dissolution model based on specific chemical processes is not yet available. However, preliminary results on the dissolution rate of UO{sub 2} and spent fuel as a function of temperature and water composition have recently been reported. This information, together with data on fragment size distribution of spent fuel, are used to estimate the dissolution response of spent fuel in excess flowing water within the framework of a simple model. In this model, the reaction/dissolution front advances linearly with time and geometry is preserved.more » This also estimates the dissolution rate of the bulk of the fission products and higher actinides, which are uniformly distributed in the UO{sub 2} matrix and are presumed to dissolve congruently. We have used a fuel fragment distribution actually observed to calculate the time for total dissolution of spent fuel. A worst-case estimate was also made using the initial (maximum) rate of dissolution to predict the total dissolution time. The time for total dissolution of centimeter size particles is estimated to be 5.5 {times} 10{sup 4} years at 25{degrees}C.« less

Mechanism of Urea Crystal Dissolution in Water from Molecular Dynamics Simulation.

PubMed

Anand, Abhinav; Patey, G N

2018-01-25

Molecular dynamics simulations are used to determine the mechanism of urea crystal dissolution in water under sink conditions. Crystals of cubic and tablet shapes are considered, and results are reported for four commonly used water models. The dissolution rates for different water models can differ considerably, but the overall dissolution mechanism remains the same. Urea dissolution occurs in three stages: a relatively fast initial stage, a slower intermediate stage, and a final stage. We show that the long intermediate stage is well described by classical rate laws, which assume that the dissolution rate is proportional to the active surface area. By carrying out simulations at different temperatures, we show that urea dissolution is an activated process, with an activation energy of ∼32 kJ mol -1 . Our simulations give no indication of a significant diffusion layer, and we conclude that the detachment of molecules from the crystal is the rate-determining step for dissolution. The results we report for urea are consistent with earlier observations for the dissolution of NaCl crystals. This suggests that the three-stage mechanism and classical rate laws might apply to the dissolution of other ionic and molecular crystals.

Initial dissolution kinetics of cocrystal of carbamazepine with nicotinamide.

PubMed

Hattori, Yusuke; Sato, Maiko; Otsuka, Makoto

2015-11-01

Objectives of this study are investigating the initial dissolution kinetics of the cocrystal of carbamazepine (CBZ) with nicotinamide (NIC) and understanding its initial dissolution process. Cocrystal solids of CBZ with NIC were prepared by co-milling and solvent evaporation methods. The formation of cocrystal solid was verified via X-ray diffraction measurement. Dissolution tests of the solids were performed using an original flow cell and ultraviolet-visible spectroscopic detector. The spectra monitored in situ were analyzed to determine the dissolved compounds separately using the classical least squares regression method. The initial dissolution profiles were interpreted using simultaneous model of dissolution and phase changes. In the initial dissolution, CBZ in the cocrystal structure dissolved in water and it was suggested that CBZ reached a metastable intermediate state simultaneously with dissolution. The cocrystal solid prepared by solvent evaporation provided a higher rate constant of the phase change than that prepared by co-milling. Our results thus support the use of evaporation as the method of choice to produce ordered cocrystal structures. We suggest that CBZ forms dihydrate during the dissolution process; however, during the initial phase of dissolution, CBZ changes to a metastable intermediate phase. © 2015 Royal Pharmaceutical Society.

Justification of Drug Product Dissolution Rate and Drug Substance Particle Size Specifications Based on Absorption PBPK Modeling for Lesinurad Immediate Release Tablets.

PubMed

Pepin, Xavier J H; Flanagan, Talia R; Holt, David J; Eidelman, Anna; Treacy, Don; Rowlings, Colin E

2016-09-06

In silico absorption modeling has been performed, to assess the impact of in vitro dissolution on in vivo performance for ZURAMPIC (lesinurad) tablets. The dissolution profiles of lesinurad tablets generated using the quality control method were used as an input to a GastroPlus model to estimate in vivo dissolution in the various parts of the GI tract and predict human exposure. A model was set up, which accounts for differences of dosage form transit, dissolution, local pH in the GI tract, and fluid volumes available for dissolution. The predictive ability of the model was demonstrated by confirming that it can reproduce the Cmax observed for independent clinical trial. The model also indicated that drug product batches that pass the proposed dissolution specification of Q = 80% in 30 min are anticipated to be bioequivalent to the clinical reference batch. To further explore the dissolution space, additional simulations were performed using a theoretical dissolution profile below the proposed specification. The GastroPlus modeling indicates that such a batch will also be bioequivalent to standard clinical batches despite having a dissolution profile, which would fail the proposed dissolution specification of Q = 80% in 30 min. This demonstrates that the proposed dissolution specification sits comfortably within a region of dissolution performance where bioequivalence is anticipated and is not near an edge of failure for dissolution, providing additional confidence to the proposed specifications. Finally, simulations were performed using a virtual drug substance batch with a particle size distribution at the limit of the proposed specification for particle size. Based on these simulations, such a batch is also anticipated to be bioequivalent to clinical reference, demonstrating that the proposed specification limits for particle size distribution would give products bioequivalent to the pivotal clinical batches.

MEANS AND METHOD FOR PRODUCING A VACUUM

DOEpatents

Otavka, M.A.

1960-08-01

A new method is given for starting the operation of evapor-ion vacuum pumps. Ordinarily this type of pump is started by inducing an electric field with the vacuum chamber; however, by placing such an electric field in the chamber at the outset, a glow discharge may be initiated which is harmful to the pump. The procedure consists of using a negative electric field during which time only gettering action takes place; subsequently when the field reverses after a sufficient reduction of the number of gaseous particles in the chamber both gettering and ionizing takes place.

Cognitive processing in the aftermath of relationship dissolution: Associations with concurrent and prospective distress and posttraumatic growth.

PubMed

Del Palacio-González, Adriana; Clark, David A; O'Sullivan, Lucia F

2017-12-01

Non-marital romantic relationship dissolution is amongst the most stressful life events experienced by young adults. Yet, some individuals experience posttraumatic growth following relationship dissolution. Little is known about the specific and differential contribution of trait-like and event-specific cognitive processing styles to each of these outcomes. A longitudinal design was employed in which trait-like (brooding and reflection) and dissolution-specific (intrusive and deliberate) cognitive processing was examined as predictors of growth (Posttraumatic Growth Inventory) and distress (Breakup Distress Scale) following a recent relationship dissolution. Initially, 148 participants completed measures of trait-like and dissolution-specific cognitive processing, growth, and distress (T1). A subsample completed a seven-month follow-up (T2). Higher frequency of relationship-dissolution intrusive thoughts predicted concurrent distress after accounting for brooding and relationship characteristics. Further, higher brooding and lower reflection predicted higher distress prospectively. Concurrent growth was predicted by both higher brooding and more deliberate relationship-dissolution thoughts. Prospectively, T1 dissolution intrusive thoughts predicted higher T2 deliberate thoughts, and the interaction between these two constructs predicted higher T2 growth. Therefore, deliberately thinking of the dissolution was related to positive psychological outcomes. In contrast, intrusive dissolution cognitions and a tendency for brooding had a mixed (paradoxical) association with psychological adjustment. Copyright © 2016 John Wiley & Sons, Ltd.

76 FR 13226 - Meeting of the Department of Justice Global Justice Information Sharing Initiative Federal...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-03-10

... . DATES: The meeting will take place on Wednesday, April 20, 2011, from 8:30 a.m. to 4 p.m. ET. ADDRESSES: The meeting will take place at the Embassy Suites Washington, DC--Convention Center Hotel, 900 Tenth... priorities. The GAC will guide and monitor the development of the Global information sharing concept. It will...

Faculty Perspectives on the "3+3+4" Curriculum Reform in Hong Kong: A Case Study

ERIC Educational Resources Information Center

Chan, Cecilia K. Y.; Luk, Lillian Y. Y.

2013-01-01

Curriculum reform in higher education has been taking place in many countries, with much attention paid to many such as the national-level Bologna process in Europe, institutional-level Melbourne Model in Australia and discipline-level Engineering Criteria 2000 (EC2000). This paper gives a detailed account of the reform initiatives taking place in…

To Resist or Not to Resist? The Effect of Context and Crime Characteristics on Sex Offenders' Reaction to Victim Resistance

ERIC Educational Resources Information Center

Balemba, Samantha; Beauregard, Eric; Mieczkowski, Tom

2012-01-01

Circumstances under which a sexual assault takes place and how these circumstances affect offenders' reactions to victim resistance are not well understood. Previous studies have not thoroughly examined the interactions that take place between situational factors and resistance. Using a combination of logistic regression and Chi-square Automatic…

Music Education through Popular Music Festivals: A Study of the "OM Music Festival" in Ontario, Canada

ERIC Educational Resources Information Center

Snell, Karen

2005-01-01

Most people think of the teaching and learning of music as taking place in formal, institutional contexts like schools and universities. This study looks at the transmission of music teaching and learning that takes place in a more informal, musical environment, namely at a "popular music festival." In particular, it discusses the OM…

Root Metaphors, Paradigm Shifts, and Democratically Shared Values: Community Service-Learning as a Bridge-Building Endeavor

ERIC Educational Resources Information Center

Sheffield, Eric C.

2007-01-01

This paper claims that community service-learning (CSL) projects in schools and universities, if done well, might very well take us--all of us--to important new places. Under the conception of community service and democratic education more generally, CSL projects in schools and universities can take us to "the" most important place: a…

Lifelong Learning between "East" and "West": Confucianism and the Reflexive Project of the Self

ERIC Educational Resources Information Center

Zhao, Kang; Biesta, Gert J. J.

2011-01-01

Current theory, policy, and practice of lifelong learning are strongly influenced by ideas about the transformations that are taking place in contemporary societies. One influential set of ideas emphasizes that because of the rapid changes that are taking place in the (late-) modern world and because of the erosion of traditions, there is a…

Development of a biphasic dissolution test for Deferasirox dispersible tablets and its application in establishing an in vitro-in vivo correlation.

PubMed

Al Durdunji, Amal; AlKhatib, Hatim S; Al-Ghazawi, Mutasim

2016-05-01

In a biphasic dissolution medium, the integration of the in vitro dissolution of a drug in an aqueous phase and its subsequent partitioning into an organic phase is hypothesized to simulate the in vivo drug absorption. Such a methodology is expected to improve the probability of achieving a successful in vitro-in vivo correlation. Dissolution of Dispersible tablets of Deferasirox, a biopharmaceutics classification system type II compound, was studied in a biphasic dissolution medium using a flow-through dissolution apparatus coupled to a paddle apparatus. The experimental parameters associated with dissolution were optimized to discriminate between Deferasirox dispersible tablets of different formulations. The dissolution profiles obtained from this system were subsequently used to construct a level A in vitro-in vivo correlation. Copyright © 2016 Elsevier B.V. All rights reserved.

The use of the trendelenburg position in the surgical treatment of extreme cerebellar slump.

PubMed

Dewaele, Frank; Kalmar, Alain F; Baert, Edward; Van Haver, Annemieke; Hallaert, Giorgio; De Mets, Frank; Williams, Leonie; Kalala Okito, Jean Pierre; Paemeleire, Koen; Caemaert, Jacques; Van Roost, Dirk

2016-01-01

State-of-the-art treatment for Chiari Malformation I (CM-I) consists of decompression by posterior fossa craniectomy. A rare but severe complication that develops over months to years after this procedure is cerebellar slump. Treatment options for this condition are limited. We present a new and promising approach to treat this rare condition. The patients were placed in the Trendelenburg position to facilitate ascent of the cerebellum. After almost complete dissolution of neurologic symptoms, surgical reconstruction was performed by tonsillar resection and the creation of a new structural support using a bone graft. Both patients experienced good clinical and morphological outcomes immediately after surgery, and for two years thereafter. Neurological symptoms related to cerebellar or brainstem slump can be adequately reversed by placing the patient in the Trendelenburg position. After uneventful gravitational reversal of the slump, safe surgical reconstruction of the cerebellar support can be performed to securely preserve the anatomical reversal.

Comparison on Response and Dissolution Rates Between Ursodeoxycholic Acid Alone or in Combination With Chenodeoxycholic Acid for Gallstone Dissolution According to Stone Density on CT Scan: Strobe Compliant Observation Study.

PubMed

Lee, Jae Min; Hyun, Jong Jin; Choi, In Young; Yeom, Suk Keu; Kim, Seung Young; Jung, Sung Woo; Jung, Young Kul; Koo, Ja Seol; Yim, Hyung Joon; Lee, Hong Sik; Lee, Sang Woo; Kim, Chang Duck

2015-12-01

Medical dissolution of gallstone is usually performed on radiolucent gallstones in a functioning gallbladder. However, absence of visible gallstone on plain abdominal x-ray does not always preclude calcification. This study aims to compare the response and dissolution rates between ursodeoxycholic acid (UDCA) alone or in combination with chenodeoxycholic acid (CDCA) according to stone density on computed tomography (CT) scan. A total of 126 patients underwent dissolution therapy with either UDCA alone or combination of CDCA and UDCA (CNU) from December 2010 to March 2014 at Korea University Ansan Hospital. In the end, 81 patients (CNU group = 44, UDCA group = 37) completed dissolution therapy for 6 months. Dissolution rate (percentage reduction in the gallstone volume) and response to therapy (complete dissolution or partial dissolution defined as reduction in stone volume of >50%) were compared between the 2 groups. Dissolution and response rates of sludge was also compared between the 2 groups. The overall response rate was 50.6% (CNU group 43.2% vs UDCA group 59.5%, P = 0.14), and the overall dissolution rate was 48.34% (CNU group 41.5% vs UDCA group 56.5%, P = 0.13). When analyzed according to stone density, response rate was 33.3%, 87.1%, 30.0%, and 6.2% for hypodense, isodense, hyperdense, and calcified stones, respectively. Response rate (85.7% vs 88.2%, P = 0.83) and dissolution rate (81.01% vs 85.38%, P = 0.17) of isodense stones were similar between CNU and UDCA group. When only sludge was considered, the overall response rate was 87.5% (CNU group 71.4% vs UDCA group 94.1%, P = 0.19), and the overall dissolution rate was 85.42% (CNU group 67.9% vs UDCA group 92.7%, P = 0.23). Patients with isodense gallstones and sludge showed much better response to dissolution therapy with CNU and UDCA showing comparable efficacy. Therefore, CT scan should be performed before medication therapy if stone dissolution is intended.

Calcite Dissolution Kinetics

NASA Astrophysics Data System (ADS)

Berelson, W.; Subhas, A.; Dong, S.; Naviaux, J.; Adkins, J. F.

2016-12-01

A geological buffer for high atmospheric CO2 concentrations is neutralization via reaction with CaCO3. We have been studying the dissolution kinetics of carbonate minerals using labeled 13C calcite and Picarro-based measurements of 13C enrichments in solution DIC. This methodology has greatly facilitated our investigation of dissolution kinetics as a function of water carbonate chemistry, temperature and pressure. One can adjust the saturation state Omega by changing the ion activity product (e.g. adjusting carbonate ion concentration), or by changing the solubility product (e.g. adjusting temperature or pressure). The canonical formulation of dissolution rate vs. omega has been refined (Subhas et al. 2015) and shows distinct non-linear behavior near equilibrium and rates in sea water of 1-3 e-6 g/cm2day at omega = 0.8. Carbonic anhydrase (CA), an enzyme that catalyzes the hydration of dissolved CO2 to carbonic acid, was shown (in concentrations <=0.04 g/L) to enhance the dissolution rate at low degrees of undersaturation by >500x. This result points to the importance of carbonic acid in enhancing dissolution at low degrees of undersaturation. CA activity and abundance in nature must be considered regarding the role it plays in catalyzing dissolution. We also have been investigating the role of temperature on dissolution kinetics. An increase of 16C yields an order of magnitude increase in dissolution rate. Temperature (and P) also change Omega critical, the saturation state where dissolution rates change substantially. Increasing pressure (achieved in a pressure reaction chamber we built) also shifts Omega critical closer to equilibrium and small pressure increases have large impact on dissolution kinetics. Dissolution rates are enhanced by an order of magnitude for a change in pressure of 1500 psi relative to the dissolution rate achieved by water chemistry effects alone for an omega of 0.8. We've shown that the thermodynamic determination of saturation state does not adequately describe the kinetics of dissolution. The interplay of mineral composition and surface area, solution carbonate chemistry, temperature and pressure are factors the impact carbonate dissolution rates in natural settings. We suggest that these parameters be considered in CO2 mitigation strategies.

Comparison and analysis of theoretical models for diffusion-controlled dissolution.

PubMed

Wang, Yanxing; Abrahamsson, Bertil; Lindfors, Lennart; Brasseur, James G

2012-05-07

Dissolution models require, at their core, an accurate diffusion model. The accuracy of the model for diffusion-dominated dissolution is particularly important with the trend toward micro- and nanoscale drug particles. Often such models are based on the concept of a "diffusion layer." Here a framework is developed for diffusion-dominated dissolution models, and we discuss the inadequacy of classical models that are based on an unphysical constant diffusion layer thickness assumption, or do not correctly modify dissolution rate due to "confinement effects": (1) the increase in bulk concentration from confinement of the dissolution process, (2) the modification of the flux model (the Sherwood number) by confinement. We derive the exact mathematical solution for a spherical particle in a confined fluid with impermeable boundaries. Using this solution, we analyze the accuracy of a time-dependent "infinite domain model" (IDM) and "quasi steady-state model" (QSM), both formally derived for infinite domains but which can be applied in approximate fashion to confined dissolution with proper adjustment of a concentration parameter. We show that dissolution rate is sensitive to the degree of confinement or, equivalently, to the total concentration C(tot). The most practical model, the QSM, is shown to be very accurate for most applications and, consequently, can be used with confidence in design-level dissolution models so long as confinement is accurately treated. The QSM predicts the ratio of diffusion layer thickness to particle radius (the Sherwood number) as a constant plus a correction that depends on the degree of confinement. The QSM also predicts that the time required for complete saturation or dissolution in diffusion-controlled dissolution experiments is singular (i.e., infinite) when total concentration equals the solubility. Using the QSM, we show that measured differences in dissolution rate in a diffusion-controlled dissolution experiment are a result of differences in the degree of confinement on the increase in bulk concentration independent of container geometry and polydisperse vs single particle dissolution. We conclude that the constant diffusion-layer thickness assumption is incorrect in principle and should be replaced by the QSM with accurate treatment of confinement in models of diffusion-controlled dissolution.

Geotechnical studies associated with decommissioning the strategic petroleum reserve facility at Weeks Island, Louisiana: A case history

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bauer, S.J.; Ehgartner, B.L.; Neal, J.T.

1997-05-01

The first sinkhole at the Weeks Island Strategic Petroleum Reserve (SPR) site was initially observed in May 1992. Concurrent with the increasing dissolution of salt over the mined oil storage area below, it has gradually enlarged and deepened. Beginning in 1994 and continuing to the present, the injection of saturated brine directly into the sinkhole throat some 76 m beneath the ground surface essentially arrested further dissolution, providing time to make adequate preparation for the safe and orderly transfer of crude oil to other storage facilities. This mitigation measure marked the first time that such a control procedure has beenmore » used in salt mining; previously all control has been achieved by either in-mine or from-surface grouting. A second and much smaller sinkhole was noticed in early 1995 on an opposite edge of the SPR mine, but with a very similar geological and mine mechanics setting. Both sinkholes occur where the edges of upper 152 m and lower 213 m mined storage levels are nearly vertically aligned. Such coincidence maximizes the tensional stress development, leading to fracturing in the salt. This cracking takes 20 or more years to develop. The cracks then become flow paths for brine incursion, which after time progress into the mined openings. Undersaturated ground water gradually enlarges the cracks in salt through dissolution, leading to eventual collapse of the overlying sand to form sinkholes. Other geologic conditions may also be secondary factors in controlling both mining extent and sinkhole location.« less

Catalysis and chemical mechanisms of calcite dissolution in seawater.

PubMed

Subhas, Adam V; Adkins, Jess F; Rollins, Nick E; Naviaux, John; Erez, Jonathan; Berelson, William M

2017-07-18

Near-equilibrium calcite dissolution in seawater contributes significantly to the regulation of atmospheric [Formula: see text] on 1,000-y timescales. Despite many studies on far-from-equilibrium dissolution, little is known about the detailed mechanisms responsible for calcite dissolution in seawater. In this paper, we dissolve 13 C-labeled calcites in natural seawater. We show that the time-evolving enrichment of [Formula: see text] in solution is a direct measure of both dissolution and precipitation reactions across a large range of saturation states. Secondary Ion Mass Spectrometer profiles into the 13 C-labeled solids confirm the presence of precipitated material even in undersaturated conditions. The close balance of precipitation and dissolution near equilibrium can alter the chemical composition of calcite deeper than one monolayer into the crystal. This balance of dissolution-precipitation shifts significantly toward a dissolution-dominated mechanism below about [Formula: see text] Finally, we show that the enzyme carbonic anhydrase (CA) increases the dissolution rate across all saturation states, and the effect is most pronounced close to equilibrium. This finding suggests that the rate of hydration of [Formula: see text] is a rate-limiting step for calcite dissolution in seawater. We then interpret our dissolution data in a framework that incorporates both solution chemistry and geometric constraints on the calcite solid. Near equilibrium, this framework demonstrates a lowered free energy barrier at the solid-solution interface in the presence of CA. This framework also indicates a significant change in dissolution mechanism at [Formula: see text], which we interpret as the onset of homogeneous etch pit nucleation.

Contact Angle Measurements: an Alternative Approach Towards Understanding the Mechanism of Increased Drug Dissolution from Ethylcellulose Tablets Containing Surfactant and Exploring the Relationship Between Their Contact Angles and Dissolution Behaviors.

PubMed

Liu, Tiaotiao; Hao, Jingqiang; Yang, Baixue; Hu, Beibei; Cui, Zhixiang; Li, Sanming

2018-05-01

The addition of surfactant in tablet was a well-defined approach to improve drug dissolution rate. While the selected surfactant played a vital role in improving the wettability of tablet by medium, it was equally important to improve the dissolution rate by permeation effect due to production of pores or the reduced inter-particle adhesion. Furthermore, understanding the mechanism of dissolution rate increased was significant. In this work, contact angle measurement was taken up as an alternative approach for understanding the dissolution rate enhancement for tablet containing surfactant. Ethylcellulose, as a substrate, was used to prepare tablet. Four surfactants, sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), dodecyltrimethylammonium bromide (DTAB), and sodium lauryl sulfonate (SLS), were used. Berberine hydrochloride, metformin hydrochloride, and rutin were selected as model drugs. The contact angle of tablet in the absence and presence of surfactant was measured to explore the mechanism. The dissolution test was investigated to verify the mechanism and to establish a correlation with the contact angle. The result showed that the mechanism was the penetration effect rather than the wetting effect. The dissolution increased with a reduction in the contact angle. DTAB was found to obtain the highest level of dissolution enhancement and the lowest contact angle, while SDS, SDBS, and SLS were found to be the less effective in both dissolution enhancement and contact angle decrease. Therefore, contact angle was a good indicator for dissolution behavior besides exploring the mechanism of increased dissolution, which shows great potential in formula screening.

In situ dissolution analysis of pharmaceutical dosage forms using coherent anti-Stokes Raman scattering (CARS) microscopy

NASA Astrophysics Data System (ADS)

Fussell, A. L.; Garbacik, E. T.; Löbmann, K.; Offerhaus, H. L.; Kleinebudde, P.; Strachan, C. J.

2014-02-01

A custom-built intrinsic flow-through dissolution setup was developed and incorporated into a home-built CARS microscope consisting of a synchronously pumped optical parametric oscillator (OPO) and an inverted microscope with a 20X/0.5NA objective. CARS dissolution images (512×512 pixels) were collected every 1.12s for the duration of the dissolution experiment. Hyperspectral CARS images were obtained pre- and postdissolution by rapidly imaging while sweeping the wavelength of the OPO in discrete steps so that each frame in the data stack corresponds to a vibrational frequency. An image-processing routine projects this hyperspectral data into a single image wherein each compound appears with a unique color. Dissolution was conducted using theophylline and cimetidine-naproxen co-amorphous mixture. After 15 minutes of theophylline dissolution, hyperspectral imaging showed a conversion of theophylline anhydrate to the monohydrate, confirmed by a peak shift in the CARS spectra. CARS dissolution images showed that monohydrate crystal growth began immediately and reached a maximum with complete surface coverage at about 300s. This result correlated with the UV dissolution data where surface crystal growth on theophylline compacts resulted in a rapidly reducing dissolution rate during the first 300s. Co-amorphous cimetidinenaproxen didn't appear to crystallize during dissolution. We observed solid-state conversions on the compact's surface in situ during dissolution. Hyperspectral CARS imaging allowed visual discrimination between the solid-state forms on the compact's surface. In the case of theophylline we were able to correlate the solid-state change with a change in dissolution rate.

Low temperature dissolution flowsheet for Pu metal

DOE PAGES

Daniel, Jr., William E.; Almond, Philip M.; Rudisill, Tracy S.

2017-06-30

The Savannah River National Laboratory was requested to develop a Pu metal dissolution flowsheet at two reduced temperature ranges for implementation in the Savannah River Site H-Canyon facility. The dissolution and H 2 generation rates during Pu metal dissolution were investigated using a dissolving solution at ambient temperature (20–30°C) and for an intermediate temperature of 50–60°C. The Pu metal dissolution rate measured at 57°C was approximately 20 times slower than at boiling (112–116°C). As a result, the dissolution rate at ambient temperature (24°C) was approximately 80 times slower than the dissolution rate at boiling. Hydrogen concentrations were less than detectablemore » (<0.1 vol%).« less

Evaluation and selection of bio-relevant dissolution media for a poorly water-soluble new chemical entity.

PubMed

Tang, L; Khan, S U; Muhammad, N A

2001-11-01

The purpose of this work is to develop a bio-relevant dissolution method for formulation screening in order to select an enhanced bioavailable formulation for a poorly water-soluble drug. The methods used included a modified rotating disk apparatus for measuring intrinsic dissolution rate of the new chemical entity (NCE) and the USP dissolution method II for evaluating dissolution profiles of the drug in three different dosage forms. The in vitro dissolution results were compared with the in vivo bioavailability for selecting a bio-relevant medium. The results showed that the solubility of the NCE was proportional to the concentration of sodium lauryl sulfate (SLS) in the media. The apparent intrinsic dissolution rate of the NCE was linear to the rotational speed of the disk, which indicated that the dissolution of the drug is a diffusion-controlled mechanism. The apparent intrinsic dissolution rate was also linear to the surfactant concentration in the media, which was interpreted using the Noyes and Whitney Empirical Theory. Three formulations were studied in three different SLS media using the bulk drug as a reference. The dissolution results were compared with the corresponding bioavailability results in dogs. In the 1% SLS--sink conditions--the drug release from all the formulations was complete and the dissolution results were discriminative for the difference in particle size of the drug in the formulations. However, the data showed poor IVIV correlation. In the 0.5% SLS medium--non-sink conditions--the dissolution results showed the same rank order among the tested formulations as the bioavailability. The best IVIV correlation was obtained from the dissolution in 0.25% SLS medium, an over-saturated condition. The conclusions are: a surfactant medium increases the apparent intrinsic dissolution rate of the NCE linearly due to an increase in solubility. A low concentration of surfactant in the medium (0.25%) is more bio-relevant than higher concentrations of surfactant in the media for the poorly water-soluble drug. Creating sink conditions (based on bulk drug solubilities) by using a high concentration of a surfactant in the dissolution medium may not be a proper approach in developing a bio-relevant dissolution method for a poorly water-soluble drug.

Anion-Dependent Potential Precycling Effects on Lithium Deposition/Dissolution Reaction Studied by an Electrochemical Quartz Crystal Microbalance.

PubMed

Smaran, Kumar Sai; Shibata, Sae; Omachi, Asami; Ohama, Ayano; Tomizawa, Eika; Kondo, Toshihiro

2017-10-19

The electrochemical quartz crystal microbalance technique was employed to study the initial stage of the electrodeposition and dissolution of lithium utilizing three kinds of electrolyte solutions such as LiPF 6 , LiTFSI, or LiFSI in tetraglyme. The native-SEI (solid-electrolyte interphase) formed by a potential prescan before lithium deposition/dissolution in all three solutions. Simultaneous additional SEI (add-SEI) deposition and its dissolution with lithium deposition and dissolution, respectively, were observed in LiPF 6 and LiTFSI. Conversely, the add-SEI dissolution with lithium deposition and its deposition with lithium dissolution were observed in LiFSI. Additional potential precycling resulted in the accumulation of a "pre-SEI" layer over the native-SEI layer in all of the solutions. With the pre-SEI, only lithium deposition/dissolution were significantly observed in LiTFSI and LiFSI. On the basis of the potential dependences of the mass and resistance changes, the anion-dependent effects of such a pre-SEI layer presence/absence on the lithium deposition/dissolution processes were discussed.

Development and validation of a discriminating in vitro dissolution method for a poorly soluble drug, olmesartan medoxomil: comparison between commercial tablets.

PubMed

Bajerski, Lisiane; Rossi, Rochele Cassanta; Dias, Carolina Lupi; Bergold, Ana Maria; Fröehlich, Pedro Eduardo

2010-06-01

A dissolution test for tablets containing 40 mg of olmesartan medoxomil (OLM) was developed and validated using both LC-UV and UV methods. After evaluation of the sink condition, dissolution medium, and stability of the drug, the method was validated using USP apparatus 2, 50 rpm rotation speed, and 900 ml of deaerated H(2)O + 0.5% sodium lauryl sulfate (w/v) at pH 6.8 (adjusted with 18% phosphoric acid) as the dissolution medium. The model-independent method using difference factor (f(1)) and similarity factor (f(2)), model-dependent method, and dissolution efficiency were employed to compare dissolution profiles. The kinetic parameters of drug release were also investigated. The obtained results provided adequate dissolution profiles. The developed dissolution test was validated according to international guidelines. Since there is no monograph for this drug in tablets, the dissolution method presented here can be used as a quality control test for OLM in this dosage form, especially in a batch to batch evaluation.

Development and Validation of New Discriminative Dissolution Method for Carvedilol Tablets

PubMed Central

Raju, V.; Murthy, K. V. R.

2011-01-01

The objective of the present study was to develop and validate a discriminative dissolution method for evaluation of carvedilol tablets. Different conditions such as type of dissolution medium, volume of dissolution medium and rotation speed of paddle were evaluated. The best in vitro dissolution profile was obtained using Apparatus II (paddle), 50 rpm, 900 ml of pH 6.8 phosphate buffer as dissolution medium. The drug release was evaluated by high-performance liquid chromatographic method. The dissolution method was validated according to current ICH and FDA guidelines using parameters such as the specificity, accuracy, precision and stability were evaluated and obtained results were within the acceptable range. The comparison of the obtained dissolution profiles of three different products were investigated using ANOVA-based, model-dependent and model-independent methods, results showed that there is significant difference between the products. The dissolution test developed and validated was adequate for its higher discriminative capacity in differentiating the release characteristics of the products tested and could be applied for development and quality control of carvedilol tablets. PMID:22923865

Modelling and shadowgraph imaging of cocrystal dissolution and assessment of in vitro antimicrobial activity for sulfadimidine/4-aminosalicylic acid cocrystals.

PubMed

Serrano, Dolores R; Persoons, Tim; D'Arcy, Deirdre M; Galiana, Carolina; Dea-Ayuela, Maria Auxiliadora; Healy, Anne Marie

2016-06-30

The aim of this work was to evaluate the influence of crystal habit on the dissolution and in vitro antibacterial and anitiprotozoal activity of sulfadimidine:4-aminosalicylic acid cocrystals. Cocrystals were produced via milling or solvent mediated processes. In vitro dissolution was carried out in the flow-through apparatus, with shadowgraph imaging and mechanistic mathematical models used to observe and simulate particle dissolution. In vitro activity was tested using agar diffusion assays. Cocrystallisation via milling produced small polyhedral crystals with antimicrobial activity significantly higher than sulfadimidine alone, consistent with a fast dissolution rate which was matched only by cocrystals which were milled following solvent evaporation. Cocrystallisation by solvent evaporation (ethanol, acetone) or spray drying produced flattened, plate-like or quasi-spherical cocrystals, respectively, with more hydrophobic surfaces and greater tendency to form aggregates in aqueous media, limiting both the dissolution rate and in vitro activity. Deviation from predicted dissolution profiles was attributable to aggregation behaviour, supported by observations from shadowgraph imaging. Aggregation behaviour during dissolution of cocrystals with different habits affected the dissolution rate, consistent with in vitro activity. Combining mechanistic models with shadowgraph imaging is a valuable approach for dissolution process analysis. Copyright © 2016 Elsevier B.V. All rights reserved.

Effects of Pump Pulsation on Hydrodynamic Properties and Dissolution Profiles in Flow-Through Dissolution Systems (USP 4).

PubMed

Yoshida, Hiroyuki; Kuwana, Akemi; Shibata, Hiroko; Izutsu, Ken-Ichi; Goda, Yukihiro

2016-06-01

To clarify the effects of pump pulsation and flow-through cell (FTC) dissolution system settings on the hydrodynamic properties and dissolution profiles of model formulations. Two FTC systems with different cell temperature control mechanisms were used. Particle image velocimetry (PIV) was used to analyze the hydrodynamic properties of test solutions in the flow-through dissolution test cell. Two pulsation pumps (semi-sine, full-sine) and a non-pulsatile pump were used to study the effects of varied flows on the dissolution profiles of United States Pharmacopeia standard tablets. PIV analysis showed periodic changes in the aligned upward fluid flow throughout the dissolution cell that was designed to reduce the temperature gradient during pump pulsation (0.5 s/pulse). The maximum instantaneous flow from the semi-sine pump was higher than that of the full-sine pump under all conditions. The flow from the semi-sine wave pump showed faster dissolution of salicylic acid and prednisone tablets than those from other pumps. The semi-sine wave pump flow showed similar dissolution profiles in the two FTC systems. Variations in instantaneous fluid flow caused by pump pulsation that meets the requirements of pharmacopoeias are a factor that affects the dissolution profiles of tablets in FTC systems.

Nonlinear dynamics and instability of aqueous dissolution of silicate glasses and minerals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Yifeng; Jove-Colon, Carlos F.; Kuhlman, Kristopher L.

2016-07-22

Aqueous dissolution of silicate glasses and minerals plays a critical role in global biogeochemical cycles and climate evolution. The reactivity of these materials is also important to numerous engineering applications including nuclear waste disposal. The dissolution process has long been considered to be controlled by a leached surface layer in which cations in the silicate framework are gradually leached out and replaced by protons from the solution. This view has recently been challenged by observations of extremely sharp corrosion fronts and oscillatory zonings in altered rims of the materials, suggesting that corrosion of these materials may proceed directly through congruentmore » dissolution followed by secondary mineral precipitation. Here we show that complex silicate material dissolution behaviors can emerge from a simple positive feedback between dissolution-induced cation release and cation-enhanced dissolution kinetics. This self-accelerating mechanism enables a systematic prediction of the occurrence of sharp dissolution fronts (vs. leached surface layers), oscillatory dissolution behaviors and multiple stages of glass dissolution (in particular the alteration resumption at a late stage of a corrosion process). In conclusion, our work provides a new perspective for predicting long-term silicate weathering rates in actual geochemical systems and developing durable silicate materials for various engineering applications.« less

Ferrihydrite dissolution by pyridine-2,6-bis(monothiocarboxylic acid) and hydrolysis products

NASA Astrophysics Data System (ADS)

Dhungana, Suraj; Anthony, Charles R.; Hersman, Larry E.

2007-12-01

Pyridine-2,6-bis(monothiocarboxylate) (pdtc), a metabolic product of microorganisms, including Pseudomonas putida and Pseudomonas stutzeri was investigated for its ability of dissolve Fe(III)(hydr)oxides at pH 7.5. Concentration dependent dissolution of ferrihydrite under anaerobic environment showed saturation of the dissolution rate at the higher concentration of pdtc. The surface controlled ferrihydrite dissolution rate was determined to be 1.2 × 10 -6 mol m -2 h -1. Anaerobic dissolution of ferrihydrite by pyridine-2,6-dicarboxylic acid or dipicolinic acid (dpa), a hydrolysis product of pdtc, was investigated to study the mechanism(s) involved in the pdtc facilitated ferrihydrite dissolution. These studies suggest that pdtc dissolved ferrihydrite using a reduction step, where dpa chelates the Fe reduced by a second hydrolysis product, H 2S. Dpa facilitated dissolution of ferrihydrite showed very small increase in the Fe dissolution when the concentration of external reductant, ascorbate, was doubled, suggesting the surface dynamics being dominated by the interactions between dpa and ferrihydrite. Greater than stoichiometric amounts of Fe were mobilized during dpa dissolution of ferrihydrite assisted by ascorbate and cysteine. This is attributed to the catalytic dissolution of Fe(III)(hydr)oxides by the in situ generated Fe(II) in the presence of a complex former, dpa.

The Relationship Between the Evolution of an Internal Structure and Drug Dissolution from Controlled-Release Matrix Tablets.

PubMed

Kulinowski, Piotr; Hudy, Wiktor; Mendyk, Aleksander; Juszczyk, Ewelina; Węglarz, Władysław P; Jachowicz, Renata; Dorożyński, Przemysław

2016-06-01

In the last decade, imaging has been introduced as a supplementary method to the dissolution tests, but a direct relationship of dissolution and imaging data has been almost completely overlooked. The purpose of this study was to assess the feasibility of relating magnetic resonance imaging (MRI) and dissolution data to elucidate dissolution profile features (i.e., kinetics, kinetics changes, and variability). Commercial, hydroxypropylmethyl cellulose-based quetiapine fumarate controlled-release matrix tablets were studied using the following two methods: (i) MRI inside the USP4 apparatus with subsequent machine learning-based image segmentation and (ii) dissolution testing with piecewise dissolution modeling. Obtained data were analyzed together using statistical data processing methods, including multiple linear regression. As a result, in this case, zeroth order release was found to be a consequence of internal structure evolution (interplay between region's areas-e.g., linear relationship between interface and core), which eventually resulted in core disappearance. Dry core disappearance had an impact on (i) changes in dissolution kinetics (from zeroth order to nonlinear) and (ii) an increase in variability of drug dissolution results. It can be concluded that it is feasible to parameterize changes in micro/meso morphology of hydrated, controlled release, swellable matrices using MRI to establish a causal relationship between the changes in morphology and drug dissolution. Presented results open new perspectives in practical application of combined MRI/dissolution to controlled-release drug products.

Disintegration of highly soluble immediate release tablets: a surrogate for dissolution.

PubMed

Gupta, Abhay; Hunt, Robert L; Shah, Rakhi B; Sayeed, Vilayat A; Khan, Mansoor A

2009-01-01

The purpose of the work was to investigate correlation between disintegration and dissolution for immediate release tablets containing a high solubility drug and to identify formulations where disintegration test, instead of the dissolution test, may be used as the acceptance criteria based on International Conference on Harmonization Q6A guidelines. A statistical design of experiments was used to study the effect of filler, binder, disintegrating agent, and tablet hardness on the disintegration and dissolution of verapamil hydrochloride tablets. All formulation variables, i.e., filler, binder, and disintegrating agent, were found to influence tablet dissolution and disintegration, with the filler and disintegrating agent exerting the most significant influence. Slower dissolution was observed with increasing disintegration time when either the filler or the disintegrating agent was kept constant. However, no direct corelationship was observed between the disintegration and dissolution across all formulations due to the interactions between different formulation components. Although all tablets containing sodium carboxymethyl cellulose as the disintegrating agent, disintegrated in less than 3 min, half of them failed to meet the US Pharmacopeia 30 dissolution criteria for the verapamil hydrochloride tablets highlighting the dependence of dissolution process on the formulation components other than the disintegrating agent. The results identified only one formulation as suitable for using the disintegration test, instead of the dissolution test, as drug product acceptance criteria and highlight the need for systematic studies before using the disintegration test, instead of the dissolution test as the drug acceptance criteria.

Evaluation of extemporaneous oral itraconazole suspensions by dissolution profiles mapping.

PubMed

Tong, Henry H Y; Chan, Hokman; Du, Zhen; Zheng, Ying

2010-01-01

The objective of this study was to evaluate by dissolution profiles mapping five extemporaneous oral itraconazole suspensions reported in the literature. Dissolution profiles of the extemporaneous oral itraconazole preparations were mapped and correlated with their reported clinical data therein. Four out of five extemporaneous preparations had either too early or insufficient release of itraconazole during the dissolution study, potentially limiting the in vivo oral bioavailability in patients. Dissolution profiles in the remaining extemporaneous preparation was closely similar to that in commercial itraconazole capsules. Based on the reported clinical data and dissolution results in this study, the extemporaneous preparation proposed in a study by Ong and Fobes seems to be the most reasonable choice for our patients. Dissolution profile evaluation is an important quality-control parameter during the evaluation of extemporaneous preparations by pharmacists.

A reaction limited in vivo dissolution model for the study of drug absorption: Towards a new paradigm for the biopharmaceutic classification of drugs.

PubMed

Macheras, Panos; Iliadis, Athanassios; Melagraki, Georgia

2018-05-30

The aim of this work is to develop a gastrointestinal (GI) drug absorption model based on a reaction limited model of dissolution and consider its impact on the biopharmaceutic classification of drugs. Estimates for the fraction of dose absorbed as a function of dose, solubility, reaction/dissolution rate constant and the stoichiometry of drug-GI fluids reaction/dissolution were derived by numerical solution of the model equations. The undissolved drug dose and the reaction/dissolution rate constant drive the dissolution rate and determine the extent of absorption when high-constant drug permeability throughout the gastrointestinal tract is assumed. Dose is an important element of drug-GI fluids reaction/dissolution while solubility exclusively acts as an upper limit for drug concentrations in the lumen. The 3D plots of fraction of dose absorbed as a function of dose and reaction/dissolution rate constant for highly soluble and low soluble drugs for different "stoichiometries" (0.7, 1.0, 2.0) of the drug-reaction/dissolution with the GI fluids revealed that high extent of absorption was found assuming high drug- reaction/dissolution rate constant and high drug solubility. The model equations were used to simulate in vivo supersaturation and precipitation phenomena. The model developed provides the theoretical basis for the interpretation of the extent of drug's absorption on the basis of the parameters associated with the drug-GI fluids reaction/dissolution. A new paradigm emerges for the biopharmaceutic classification of drugs, namely, a model independent biopharmaceutic classification scheme of four drug categories based on either the fulfillment or not of the current dissolution criteria and the high or low % drug metabolism. Copyright © 2018. Published by Elsevier B.V.

Quantification of the resist dissolution process: an in situ analysis using high speed atomic force microscopy

NASA Astrophysics Data System (ADS)

Santillan, Julius Joseph; Shichiri, Motoharu; Itani, Toshiro

2016-03-01

This work focuses on the application of a high speed atomic force microscope (HS-AFM) for the in situ visualization / quantification of the resist dissolution process. This technique, as reported in the past, has provided useful pointers on the formation of resist patterns during dissolution. This paper discusses about an investigation made on the quantification of what we refer to as "dissolution unit size" or the basic units of patterning material dissolution. This was done through the establishment of an originally developed analysis method which extracts the difference between two succeeding temporal states of the material film surface (images) to indicate the amount of change occurring in the material film at a specific span of time. Preliminary experiments with actual patterning materials were done using a positive-tone EUV model resist composed only of polyhydroxystyrene (PHS)-based polymer with a molecular weight of 2,500 and a polydispersity index of 1.2. In the absence of a protecting group, the material was utilized at a 50nm film thickness with post application bake of 90°C/60s. The resulting film is soluble in the alkali-based developer even without exposure. Results have shown that the dissolution components (dissolution unit size) of the PHS-based material are not of fixed size. Instead, it was found that aside from one constantly dissolving unit size, another, much larger dissolution unit size trend also occurs during material dissolution. The presence of this larger dissolution unit size suggests an occurrence of "polymer clustering". Such polymer clustering was not significantly present during the initial stages of dissolution (near the original film surface) but becomes more persistently obvious after the dissolution process reaches a certain film thickness below the initial surface.

An Experimental Investigation of the Process of Isotope Exchange that Takes Place when Heavy Water Is Exposed to the Atmosphere

ERIC Educational Resources Information Center

Deeney, F. A.; O'Leary, J. P.

2009-01-01

We have used the recently developed method for rapid measurement of maximum density temperature to determine the rate at which hydrogen and deuterium isotope exchange takes place when a sample of heavy water is exposed to the atmosphere. We also provide a simple explanation for the observed linear rate of transition. (Contains 2 figures.)

Roles of Community Education in the Management and Sustainability of Universal Basic Education in Nigeria

ERIC Educational Resources Information Center

Oyebamiji, M. A.; Animasahun, M. Olaitan

2012-01-01

Education is seen as the bedrock of a nation's development and for any sustainable programme to take place, human factor, especially the community where the programme is taking place has to be considered. The inputs of the school are from the community and the products of the school service or engineer the community. It is in this context that,…

76 FR 53829 - Safety Zone; ESI Ironman 70.3 Augusta Triathlon, Savannah River, Augusta, GA

Federal Register 2010, 2011, 2012, 2013, 2014

2011-08-30

... participants, participant vessels, spectators, and the general public during the 1.1 mile swim portion of the... scheduled to take place in Augusta, Georgia. This event includes a 1.1 mile swim that will take place on the waters of the Savannah River. The swim starts at the 6th Street Railroad Bridge and finishes at Mile Post...

The Kinetics of Dissolution Revisited

NASA Astrophysics Data System (ADS)

Antonel, Paula S.; Hoijemberg, Pablo A.; Maiante, Leandro M.; Lagorio, M. Gabriela

2003-09-01

An experiment analyzing the kinetics of dissolution of a solid with cylindrical geometry in water is presented. The dissolution process is followed by measuring the solid mass and its size parameters (thickness and diameter) as a function of time. It is verified that the dissolution rate follows the Nernst model. Data treatment is compared with the dissolution of a spherical solid previously described. Kinetics, diffusion concepts, and polynomial fitting of experimental data are combined in this simple experiment.

Interactions between a poorly soluble cationic drug and sodium dodecyl sulfate in dissolution medium and their impact on in vitro dissolution behavior.

PubMed

Huang, Zongyun; Parikh, Shuchi; Fish, William P

2018-01-15

In the pharmaceutical industry, in vitro dissolution testing ofsolid oral dosage forms is a very important tool for drug development and quality control. However, ion-pairing interaction between the ionic drugand surfactants in dissolution medium often occurs, resulting in inconsistent and incomplete drug release. The aim of this study is toevaluate the effects ofsodium dodecyl sulfate (SDS) mediated medium onthe dissolution behaviors of a poorly soluble cationic drug (Drug B). The study was carried out by measuring solubility of Drug B substance and dissolution rate of Drug B product in media containing SDS.Desolubilization of Drug B substance was observed at pH 4.5 in the presence of SDS at concentrations below critical micelle concentration (CMC) which is attributed to the formation of an insoluble di-dodecyl sulfate salt between SDS and Drug B. This ion-pairing effect is less significant with increasing medium pH where Drug B is less ionized and CMC of SDS is lower. In medium at pH 4.5, dissolution of Drug B product was found incomplete with SDS concentration below CMC due to the desolubilization of Drug B substance. In media with SDS level above CMC, the dissolution rate is rather slower with higher inter-vessel variations compared to that obtained in pH 4.5 medium without SDS. The dissolution results demonstrate that the presence of SDS in medium generates unexpected irregular dissolution profiles for Drug B which are attributed to incompatible dissolution medium for this particular drug. Therefore, non-ionic surfactant was selected for Drug B product dissolution method and ion-pairing effect in SDS mediated medium should be evaluated when developing a dissolution method for any poorly soluble cationic drugs. Copyright © 2017 Elsevier B.V. All rights reserved.

A novel lipid nanoemulsion system for improved permeation of granisetron.

PubMed

Doh, Hea-Jeong; Jung, Yunjin; Balakrishnan, Prabagar; Cho, Hyun-Jong; Kim, Dae-Duk

2013-01-01

A new lipid nanoemulsion (LNE) system containing granisetron (GRN) was developed and its in vitro permeation-enhancing effect was evaluated using Caco-2 cell monolayers. Particle size, polydispersity index (PI) and stability of the prepared GRN-loaded LNE systems were also characterized. The mean diameters of prepared LNEs were around 50 nm with PI<0.2. Developed LNEs were stable at 4°C in the dark place over a period of 12 weeks. In vitro drug dissolution and cytotoxicity studies of GRN-loaded LNEs were performed. GRN-loaded LNEs exhibited significantly higher drug dissolution than GRN suspension at pH 6.8 for 2h (P<0.05). In vitro permeation study in Caco-2 cell monolayers showed that the LNEs significantly enhanced the drug permeation compared to GRN powder. The in vivo toxicity study in the rat jejunum revealed that the prepared GRN-loaded LNE was as safe as the commercial formulation (Kytril). These results suggest that LNE could be used as a potential oral liquid formulation of GRN for anti-emetic treatment on the post-operative and chemotherapeutic patients. Copyright © 2012 Elsevier B.V. All rights reserved.

Meeting report: applied biopharmaceutics and quality by design for dissolution/release specification setting: product quality for patient benefit.

PubMed

Selen, Arzu; Cruañes, Maria T; Müllertz, Anette; Dickinson, Paul A; Cook, Jack A; Polli, James E; Kesisoglou, Filippos; Crison, John; Johnson, Kevin C; Muirhead, Gordon T; Schofield, Timothy; Tsong, Yi

2010-09-01

A biopharmaceutics and Quality by Design (QbD) conference was held on June 10-12, 2009 in Rockville, Maryland, USA to provide a forum and identify approaches for enhancing product quality for patient benefit. Presentations concerned the current biopharmaceutical toolbox (i.e., in vitro, in silico, pre-clinical, in vivo, and statistical approaches), as well as case studies, and reflections on new paradigms. Plenary and breakout session discussions evaluated the current state and envisioned a future state that more effectively integrates QbD and biopharmaceutics. Breakout groups discussed the following four topics: Integrating Biopharmaceutical Assessment into the QbD Paradigm, Predictive Statistical Tools, Predictive Mechanistic Tools, and Predictive Analytical Tools. Nine priority areas, further described in this report, were identified for advancing integration of biopharmaceutics and support a more fundamentally based, integrated approach to setting product dissolution/release acceptance criteria. Collaboration among a broad range of disciplines and fostering a knowledge sharing environment that places the patient's needs as the focus of drug development, consistent with science- and risk-based spirit of QbD, were identified as key components of the path forward.

Solidification of nanosuspensions for the production of solid oral dosage forms and inhalable dry powders.

PubMed

Malamatari, Maria; Somavarapu, Satyanarayana; Taylor, Kevin M G; Buckton, Graham

2016-01-01

Nanosuspensions combine the advantages of nanotherapeutics (e.g. increased dissolution rate and saturation solubility) with ease of commercialisation. Transformation of nanosuspensions to solid oral and inhalable dosage forms minimises the physical instability associated with their liquid state, enhances patient compliance and enables targeted oral and pulmonary drug delivery. This review outlines solidification methods for nanosuspensions. It includes spray and freeze drying as the most widely used techniques. Fluidised-bed coating, granulation and pelletisation are also discussed as they yield nanocrystalline formulations with more straightforward downstream processing to tablets or capsules. Spray-freeze drying, aerosol flow reactor and printing of nanosuspensions are also presented as promising alternative solidification techniques. Results regarding the solid state, in vitro dissolution and/or aerosolisation efficiency of the nanocrystalline formulations are given and combined with available in vivo data. Focus is placed on the redispersibility of the solid nanocrystalline formulations, which is a prerequisite for their clinical application. A few solidified nanocrystalline products are already on the market and many more are in development. Oral and inhalable nanoparticle formulations are expected to have great potential especially in the areas of personalised medicine and delivery of high drug doses (e.g. antibiotics) to the lungs, respectively.

Dissolution mechanism of calcium apatites in acids: A review of literature

PubMed Central

Dorozhkin, Sergey V

2012-01-01

Eight dissolution models of calcium apatites (both fluorapatite and hydroxyapatite) in acids were drawn from the published literature, analyzed and discussed. Major limitations and drawbacks of the models were conversed in details. The models were shown to deal with different aspects of apatite dissolution phenomenon and none of them was able to describe the dissolution process in general. Therefore, an attempt to combine the findings obtained by different researchers was performed which resulted in creation of the general description of apatite dissolution in acids. For this purpose, eight dissolution models were assumed to complement each other and provide the correct description of the specific aspects of apatite dissolution. The general description considers all possible dissolution stages involved and points out to some missing and unclear phenomena to be experimentally studied and verified in future. This creates a new methodological approach to investigate reaction mechanisms based on sets of affine data, obtained by various research groups under dissimilar experimental conditions. PMID:25237611

Dissolution corrosion of 316L austenitic stainless steels in contact with static liquid lead-bismuth eutectic (LBE) at 500 °C

NASA Astrophysics Data System (ADS)

Lambrinou, Konstantina; Charalampopoulou, Evangelia; Van der Donck, Tom; Delville, Rémi; Schryvers, Dominique

2017-07-01

This work addresses the dissolution corrosion behaviour of 316L austenitic stainless steels. For this purpose, solution-annealed and cold-deformed 316L steels were simultaneously exposed to oxygen-poor (<10-8 mass%) static liquid lead-bismuth eutectic (LBE) for 253-3282 h at 500 °C. Corrosion was consistently more severe for the cold-drawn steels than the solution-annealed steel, indicating the importance of the steel thermomechanical state. The thickness of the dissolution-affected zone was non-uniform, and sites of locally-enhanced dissolution were occasionally observed. The progress of LBE dissolution attack was promoted by the interplay of certain steel microstructural features (grain boundaries, deformation twin laths, precipitates) with the dissolution corrosion process. The identified dissolution mechanisms were selective leaching leading to steel ferritization, and non-selective leaching; the latter was mainly observed in the solution-annealed steel. The maximum corrosion rate decreased with exposure time and was found to be inversely proportional to the depth of dissolution attack.

Dissolution rate enhancement of gliclazide by ordered mixing.

PubMed

Saharan, Vikas A; Choudhury, Pratim K

2011-09-01

The poorly water soluble antidiabetic drug gliclazide was selected to study the effect of excipients on dissolution rate enhancement. Ordered mixtures of micronized gliclazide with lactose, mannitol, sorbitol, maltitol and sodium chloride were prepared by manual shaking of glass vials containing the drug and excipient(s). Different water soluble excipients, addition of surfactant and superdisintegrant, drug concentration and carrier particle size influenced the dissolution rate of the drug. Dissolution rate studies of the prepared ordered mixtures revealed an increase in drug dissolution with all water soluble excipients. The order of dissolution rate improvement for gliclazide was mannitol > lactose > maltitol > sorbitol > sodium chloride. Composite granules of the particle size range 355-710 μm were superior in increasing the drug dissolution rate from ordered mixtures. Reducing the carrier particle size decreased the dissolution rate of the drug as well as the increase in drug concentration. Kinetic modeling of drug release data fitted best the Hixson-Crowell model, which indicates that all the ordered mixture formulations followed the cube root law fairly well.

Spontaneous dissolution of a guaifenesin stone.

PubMed

Nguyen, Thai T; Fallon, Bernard; Winfield, Howard N

2005-08-01

Guaifenesin is a commonly used expectorant whose use may lead to the occasional formation of guaifenesin urinary stones. We herein describe a patient who was taking 2400 mg Guaifenesin per day as part of his treatment for asthma. He had a past history of a guaifenesin stone removed ureteroscopically. His current presentation was with a 9 mm by 6 mm stone in the upper left ureter, seen on CT scan, and treated initially with a ureteral stent and hydration. After 3 weeks, the stone had disappeared, as confirmed by repeat CT scan. The genesis and treatment of guaifenesin stones is discussed.

The differences between the branded and generic medicines using solid dosage forms: In-vitro dissolution testing

PubMed Central

Al Ameri, Mubarak Nasser; Nayuni, Nanda; Anil Kumar, K.G.; Perrett, David; Tucker, Arthur; Johnston, Atholl

2011-01-01

Introduction Dissolution is the amount of substance that goes into solution per unit time under standardised conditions of liquid/solid interface, solvent composition and temperature. Dissolution is one of the most important tools to predict the in-vivo bioavailability and in some cases to determine bioequivalence and assure interchangeability. Aim To compare the differences in dissolution behaviour of solid dosage forms between innovators (reference products) and their generic counterparts (tested products). Methods Four replicates for each batch of 37 tested medicines was carried out using A PT-DT70 dissolution tester from Pharma Test. A total of 13 branded medicines and 24 generic counterparts were obtained locally and internationally to detect any differences in their dissolution behaviour. They were tested according to the British Pharmacopeia, European Pharmacopeia and the US Pharmacopeia with the rate of dissolution determined by ultra-violet Spectrophotometery. Results Most tested medicines complied with the pharmacopoeial specifications and achieved 85% dissolution in 60 min. However, some generic medicines showed significant differences in dissolution rate at 60 and 120 min. Many generic medicines showed a slower dissolution rate than their branded counterparts such as the generic forms of omeprazole 20 mg. Some showed an incomplete dissolution such as the generic form of nifedipine 10 mg. Other generics showed faster dissolution rate than their branded counterpart such as the generic forms of meloxicam 15 mg. Moreover, some generics from different batches of the same manufacturer showed significant differences in their dissolution rate such as the generic forms of meloxicam 7.5 mg. Nevertheless, some generic medicines violated the EMA and the FDA guidelines for industry when they failed to achieve 85% dissolution at 60 min, such as the generic form of diclofenac sodium 50 mg. Conclusion Most medicines in this study complied with the pharmacopeial limits. However, some generics dissolved differently than their branded counterparts. This can clearly question the interchangeability between the branded and its generic counterpart or even among generics. PMID:25755988

Environment of ore deposition in the Creede mining district, San Juan Mountains, Colorado: Part VI. Maximum duration for mineralization of the OH vein

USGS Publications Warehouse

Campbell, W.R.; Barton, P.B.

2005-01-01

The rate at which ore deposits form is one of the least well established parameters in all of economic geology. However, increased detail in sampling, improved technology of dating, and sophistication in modeling are reducing the uncertainties and establishing that ore formation, at least for the porphyry copper-skarn-epithermal base and precious metals deposit package, may take place in surprisingly brief intervals. This contribution applies another approach to examine the duration of mineralization. The degree to which compositional gradients within single crystals has flattened through solid-state diffusion offers a measure of the thermal dose (that is temperature combined with time) that the crystals have been subjected to since deposition. Here we examine the steepness of gradients in iron content within individual single sphalerite crystals from the epithermal silver-lead-zinc deposit in the OH vein at Creede, Colorado. Two initial textures are considered: growth-banded crystals and compositionally contrasting overgrowths that succeed crosscutting dissolution or fractured surfaces. The model used estimates the maximum possible time by assuming a perfectly sharp original compositional step, and it asks how long it would take at a known temperature for the gradient measured today to have formed. Applying the experimentally determined diffusion rates of Mizuta (1988a) to compositional gradients (ranging from 0.4-2.2 mol % FeS/??m) measured by the electron microprobe in 2-??m steps on banded sphalerite formed early in the paragenetic history yields a maximum duration of less than ???10,000 yr. Sphalerite from a solution unconformity in a position midway through the paragenetic sequence is indistinguishable from instantaneous deposition, supporting the conclusion of rapid ore formation. While this formation interval seems very brief, it is consistent with less well constrained estimates using entirely different criteria. ?? 2005 Society of Economic Geologists, Inc.

Influence of oxalic acid on the dissolution kinetics of manganese oxide

NASA Astrophysics Data System (ADS)

Godunov, E. B.; Artamonova, I. V.; Gorichev, I. G.; Lainer, Yu. A.

2012-11-01

The kinetics and electrochemical processes of the dissolution of manganese oxides with various oxidation states in sulfuric acid solutions containing oxalate ion additives is studied under variable conditions (concentration, pH, temperature). The parameters favoring a higher degree of the dissolution of manganese oxides in acidic media are determined. The optimal conditions are found for the dissolution of manganese oxides in acidic media in the presence of oxalate ions. The mechanism proposed for the dissolution of manganese oxides in sulfuric acid solutions containing oxalic acid is based on the results of kinetic and electrochemical studies. The steps of the dissolution mechanism are discussed.

Effect of sodium lauryl sulfate in dissolution media on dissolution of hard gelatin capsule shells.

PubMed

Zhao, Fang; Malayev, Vyacheslav; Rao, Venkatramana; Hussain, Munir

2004-01-01

Sodium lauryl sulfate (SLS) is a commonly used surfactant in dissolution media for poorly water soluble drugs. However, it has occasionally been observed that SLS negatively impacts the dissolution of drug products formulated in gelatin capsules. This study investigated the effect of SLS on the dissolution of hard gelatin capsule shells. The USP paddle method was used with online UV monitoring at 214 nm (peptide bond). Empty size #0 capsule shells were held to the bottom of the dissolution vessel by magnetic three-prong sinkers. SLS significantly slowed down the dissolution of gelatin shells at pH < 5. Visually, the gelatin shells transformed into some less-soluble precipitate under these conditions. This precipitate was found to contain a higher sulfur content than the gelatin control sample by elemental analysis, indicating that SLS is part of the precipitate. Additionally, the slowdown of capsule shell dissolution was shown to be dependent on the SLS concentration and the ionic strength of the media. SLS interacts with gelatin to form a less-soluble precipitate at pH < 5. The use of SLS in dissolution media at acidic pH should be carefully evaluated for gelatin capsule products.

Influence of Heterogamy by Religion on Risk of Marital Dissolution: A Cohort Study of 20,000 Couples.

PubMed

Wright, David M; Rosato, Michael; O'Reilly, Dermot

2017-01-01

Heterogamous marriages, in which partners have dissimilar attributes (e.g. by socio-economic status or ethnicity), are often at elevated risk of dissolution. We investigated the influences of heterogamy by religion and area of residence on risk of marital dissolution in Northern Ireland, a country with a history of conflict and residential segregation along Catholic-Protestant lines. We expected Catholic-Protestant marriages to have elevated risks of dissolution, especially in areas with high concentrations of a single religious group where opposition to intermarriage was expected to be high. We estimated risks of marital dissolution from 2001 to 2011 for 19,791 couples drawn from the Northern Ireland Longitudinal Study (a record linkage study), adjusting for a range of compositional and contextual factors using multilevel logistic regression. Dissolution risk decreased with increasing age and higher socio-economic status. Catholic-Protestant marriages were rare (5.9 % of the sample) and were at increased risk of dissolution relative to homogamous marriages. We found no association between local population composition and dissolution risk for Catholic-Protestant couples, indicating that partner and household characteristics may have a greater influence on dissolution risk than the wider community.

Dissolution enhancement of tadalafil by liquisolid technique.

PubMed

Lu, Mei; Xing, Haonan; Yang, Tianzhi; Yu, Jiankun; Yang, Zhen; Sun, Yanping; Ding, Pingtian

2017-02-01

This study aimed to enhance the dissolution of tadalafil, a poorly water-soluble drug by applying liquisolid technique. The effects of two critical formulation variables, namely drug concentration (17.5% and 35%, w/w) and excipients ratio (10, 15 and 20) on dissolution rates were investigated. Pre-compression tests, including particle size distribution, flowability determination, Fourier transform infrared (FT-IR), differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and scanning electron microscopy (SEM), were carried out to investigate the mechanism of dissolution enhancement. Tadalafil liquisolid tablets were prepared and their quality control tests, dissolution study, contact angle measurement, Raman mapping, and storage stability test were performed. The results suggested that all the liquisolid tablets exhibited significantly higher dissolution rates than the conventional tablets and pure tadalafil. FT-IR spectrum reflected no drug-excipient interactions. DSC and XRD studies indicated reduction in crystallinity of tadalafil, which was further confirmed by SEM and Raman mapping outcomes. The contact angle measurement demonstrated obvious increase in wetting property. Taken together, the reduction of particle size and crystallinity, and the improvement of wettability were the main mechanisms for the enhanced dissolution rate. No significant changes were observed in drug crystallinity and dissolution behavior after storage based on XRD, SEM and dissolution results.

Regulatory Perspectives on Strength-Dependent Dissolution Profiles and Biowaiver Approaches for Immediate Release (IR) Oral Tablets in New Drug Applications.

PubMed

Suarez-Sharp, Sandra; Delvadia, Poonam R; Dorantes, Angelica; Duan, John; Externbrink, Anna; Gao, Zongming; Ghosh, Tapash; Miksinski, Sarah Pope; Seo, Paul

2016-05-01

Dissolution profile comparisons are used by the pharmaceutical industry to assess the similarity in the dissolution characteristics of two formulations to decide whether the implemented changes, usually minor/moderate in nature, will have an impact on the in vitro/in vivo performance of the drug product. When similarity testing is applied to support the approval of lower strengths of the same formulation, the traditional approach for dissolution profile comparison is not always applicable for drug products exhibiting strength-dependent dissolution and may lead to incorrect conclusions about product performance. The objective of this article is to describe reasonable biopharmaceutic approaches for developing a biowaiver strategy for low solubility, proportionally similar/non-proportionally similar in composition immediate release drug products that exhibit strength-dependent dissolution profiles. The paths highlighted in the article include (1) approaches to address biowaiver requests, such as the use of multi-unit dissolution testing to account for sink condition differences between the higher and lower strengths; (2) the use of a single- vs. strength-dependent dissolution method; and (3) the use of single- vs. strength-dependent dissolution acceptance criteria. These approaches are cost- and time-effective and can avoid unnecessary bioequivalence studies.

The effect of a new formaldehyde-free binder on the dissolution rate of glass wool fibre in physiological saline solution.

PubMed

Potter, Russell M; Olang, Nassreen

2013-04-12

The in-vitro dissolution rate of fibres is a good predictor of the in-vivo behavior and potential health effects of inhaled fibres. This study examines the effect of a new formaldehyde-free carbohydrate-polycarboxylic acid binder on the in-vitro dissolution rate of biosoluble glass fibres. Dissolution rate measurements in pH 7.4 physiological saline solution show that the presence of the binder on wool insulation glass fibres has no effect on their dissolution. There is no measurable difference between the dissolution rates of continuous draw fibres before and after binder was applied by dipping. Nor is there a measurable difference between the dissolution rates of a production glass wool sample with binder and that same sample after removal of the binder by low-temperature ashing. Morphological examination shows that swelling of the binder in the solution is at least partially responsible for the development of open channels around the glass-binder interface early in the dissolution. These channels allow fluid to reach the entire glass surface under the binder coating. There is no evidence of any delay in the dissolution rate as a result of the binder coating.

The effect of a new formaldehyde-free binder on the dissolution rate of glass wool fibre in physiological saline solution

PubMed Central

2013-01-01

The in-vitro dissolution rate of fibres is a good predictor of the in-vivo behavior and potential health effects of inhaled fibres. This study examines the effect of a new formaldehyde-free carbohydrate-polycarboxylic acid binder on the in-vitro dissolution rate of biosoluble glass fibres. Dissolution rate measurements in pH 7.4 physiological saline solution show that the presence of the binder on wool insulation glass fibres has no effect on their dissolution. There is no measurable difference between the dissolution rates of continuous draw fibres before and after binder was applied by dipping. Nor is there a measurable difference between the dissolution rates of a production glass wool sample with binder and that same sample after removal of the binder by low-temperature ashing. Morphological examination shows that swelling of the binder in the solution is at least partially responsible for the development of open channels around the glass-binder interface early in the dissolution. These channels allow fluid to reach the entire glass surface under the binder coating. There is no evidence of any delay in the dissolution rate as a result of the binder coating. PMID:23587247

20 CFR 404.1219 - Dissolution of political subdivision.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 20 Employees' Benefits 2 2013-04-01 2013-04-01 false Dissolution of political subdivision. 404... Agreements Is Obtained and Continues § 404.1219 Dissolution of political subdivision. If a political... satisfactory evidence of its dissolution or nonexistence. The evidence must establish that the entity is not...

20 CFR 404.1219 - Dissolution of political subdivision.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 20 Employees' Benefits 2 2012-04-01 2012-04-01 false Dissolution of political subdivision. 404... Agreements Is Obtained and Continues § 404.1219 Dissolution of political subdivision. If a political... satisfactory evidence of its dissolution or nonexistence. The evidence must establish that the entity is not...

20 CFR 404.1219 - Dissolution of political subdivision.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 20 Employees' Benefits 2 2010-04-01 2010-04-01 false Dissolution of political subdivision. 404... Agreements Is Obtained and Continues § 404.1219 Dissolution of political subdivision. If a political... satisfactory evidence of its dissolution or nonexistence. The evidence must establish that the entity is not...

20 CFR 404.1219 - Dissolution of political subdivision.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 20 Employees' Benefits 2 2014-04-01 2014-04-01 false Dissolution of political subdivision. 404... Agreements Is Obtained and Continues § 404.1219 Dissolution of political subdivision. If a political... satisfactory evidence of its dissolution or nonexistence. The evidence must establish that the entity is not...

20 CFR 404.1219 - Dissolution of political subdivision.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 20 Employees' Benefits 2 2011-04-01 2011-04-01 false Dissolution of political subdivision. 404... Agreements Is Obtained and Continues § 404.1219 Dissolution of political subdivision. If a political... satisfactory evidence of its dissolution or nonexistence. The evidence must establish that the entity is not...

Development of weathering profile of a forest hillslope in clay-rich sedimentary system

NASA Astrophysics Data System (ADS)

Nicklas, R. W.; Kim, H.; Bishop, J. K.; Rempe, D. M.

2012-12-01

Hillslopes are an essential element to the understanding of landscape evolution, storm flow generation and biogeochemical processes. Since 2008, extensive studies of climate variables, vegetation, soil moisture, subsurface hydrology, and water chemistry have taken place at a small forested hillslope, "Rivendell", at the Angelo Coast Range Reserve located at the headwaters of the Eel River, California. Here we report on the signature of weathering processes through analysis of core and soil samples collected during well drilling campaigns. Core samples from multiple depths at four wells (at creek edge, mid-slope, up-slope, and ridge-top) were selected and include 1) soil; 2) unsaturated fractured/ weathered zone; 3) zone of seasonal water table fluctuation within weathered bedrock; and 4) chronically saturated fresh bedrock zone. We also include soil samples from a groundwater seep located at the toe of the slope. The mineralogy of these samples was identified using X-ray diffraction. Samples were analyzed for salt and Ca(Mg)CO3 concentrations, and cation exchange capacity using Milli-Q water and acetic acid extraction and BaCl2-NH4Cl treatments, respectively. To further quantify the mineral dissolution and secondary mineral precipitation, a sequential extraction of trace metals were conducted - 1) exchangeable using MgCl2; 2) bound to carbonates using NaOAc; 3) bound to Fe-Mn oxides using NH2OH HCl; and 4) bound to organic matters using H2O2 and HNO3. The total elemental contents were determined using HF-HNO3-HClO4 dissolution. The mineralogy of the fresh bedrock zone showed similar patterns throughout the site -for clay minerals, chlorite, illite, interstratified illite/smectite were dominant; K-feldspar dominated the primary minerals. Shallow (<30 cm) soils had kaolinite, and chlorite was absent in some samples. CaCO3 was also predominantly found in the fresh bedrock zone and progressively increased with depth. The depletion profile of major cations (Ca, Na, Mg, K, and Si) and trace metals (Fe, Mn and Al) show the mineral dissolution fronts. K-feldspar, chlorite and CaCO3 dissolution and secondary mineral precipitation are thus the major processes that are critical to the interpretation of groundwater chemistry.

Re(Place) Your Typical Writing Assignment: An Argument for Place-Based Writing

ERIC Educational Resources Information Center

Jacobs, Elliot

2011-01-01

Place-based writing affords students an opportunity to write meaningfully about themselves, grounded in a place that they know. Place-based writing is versatile and can be additive--taking just a week or two within a semester of different projects--or transformative, if positioned as the theme for an entire course. If students can learn to write…

Synergistic effect of reductive and ligand-promoted dissolution of goethite.

PubMed

Wang, Zimeng; Schenkeveld, Walter D C; Kraemer, Stephan M; Giammar, Daniel E

2015-06-16

Ligand-promoted dissolution and reductive dissolution of iron (hydr)oxide minerals control the bioavailability of iron in many environmental systems and have been recognized as biological iron acquisition strategies. This study investigated the potential synergism between ligands (desferrioxamine B (DFOB) or N,N'-Di(2-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid (HBED)) and a reductant (ascorbate) in goethite dissolution. Batch experiments were performed at pH 6 with ligand or reductant alone and in combination, and under both oxic and anoxic conditions. Goethite dissolution in the presence of reductant or ligand alone followed classic surface-controlled dissolution kinetics. Ascorbate alone does not promote goethite dissolution under oxic conditions due to rapid reoxidation of Fe(II). The rate coefficients for goethite dissolution by ligands are closely correlated with the stability constants of the aqueous Fe(III)-ligand complexes. A synergistic effect of DFOB and ascorbate on the rate of goethite dissolution was observed (total rates greater than the sum of the individual rates), and this effect was most pronounced under oxic conditions. For HBED, macroscopically the synergistic effect was hidden due to the inhibitory effect of ascorbate on HBED adsorption. After accounting for the concentrations of adsorbed ascorbate and HBED, a synergistic effect could still be identified. The potential synergism between ligand and reductant for iron (hydr)oxide dissolution may have important implications for iron bioavailability in soil environments.

Potential Dependence of Pt and Co Dissolution from Platinum-Cobalt Alloy PEFC Catalysts Using Time-Resolved Measurements

DOE PAGES

Ahluwalia, Rajesh K.; Papadias, Dionissios D.; Kariuki, Nancy N.; ...

2018-02-09

An electrochemical flow cell system with catalyst-ionomer ink deposited on glassy carbon is used to investigate the aqueous stability of commercial PtCo alloys under cyclic potentials. An on-line inductively coupled plasma-mass spectrometer, capable of real-time measurements, is used to resolve the anodic and cathodic dissolution of Pt and Co during square-wave and triangle-wave potential cycles. We observe Co dissolution at all potentials, distinct peaks in anodic and cathodic Pt dissolution rates above 0.9 V, and potential-dependent Pt and Co dissolution rates. The amount of Pt that dissolves cathodically is smaller than the amount that dissolves anodically if the upper potentialmore » limit (UPL) is lower than 0.9 V. At the highest UPL investigated, 1.0 V, the cathodic dissolution greatly exceeds the anodic dissolution. A non-ideal solid solution model indicates that the anodic dissolution can be associated with the electrochemical oxidation of Pt and PtOH to Pt 2+, and the cathodic dissolution to electrochemical reduction of a higher Pt oxide, PtO x (x > 1), to Pt 2+. Pt also dissolves oxidatively during the cathodic scans but in smaller amounts than due to the reductive dissolution of PtO x. The relative amounts Pt dissolving oxidatively as Pt and PtOH depend on the potential cycle and UPL.« less

Effect of guest drug character encapsulated in the cavity and intermolecular spaces of γ-cyclodextrins on the dissolution property of ternary γ-cyclodextrin complex.

PubMed

Liu, Nan; Higashi, Kenjirou; Ueda, Keisuke; Moribe, Kunikazu

2017-10-15

Various ternary Guest 2/(Guest 1/γ-cyclodextrin (CD)) complexes were prepared using a cogrinding and subsequent heating method, wherein Guest 1 was incorporated in the cavity of γ-CD and Guest 2 was incorporated into the intermolecular spaces between γ-CD columns. Dissolution fluxes of Guest 1 and Guest 2 from all ternary complexes were almost identical. The dissolution flux of flurbiprofen (Guest 1) from the ternary complexes depended on the solubility of Guest 2 drugs (naproxen

Assessment of oral bioavailability enhancing approaches for SB-247083 using flow-through cell dissolution testing as one of the screens.

PubMed

Perng, Cherng-Yih; Kearney, Albert S; Palepu, Nagesh R; Smith, Brian R; Azzarano, Leonard M

2003-01-02

SB-247083 is a potent, nonpeptidic, orally active, ETA-selective, endothelin receptor antagonist. The diacid form and three salts (monoarginine, diarginine and disodium) of SB-247083 were evaluated during the pre-clinical phase of development. The developability attributes (i.e. hygroscopicity, thermal behavior, aqueous solubility, and drug-excipient compatibility) of these compounds were evaluated. In addition to these attributes, the flow-through cell (FTC) dissolution testing (using USP Apparatus 4) was used as a screening technique to evaluate several SB-247083 formulations of the diacid and its salts. FTC dissolution testing offers two distinct advantages over the more traditional static-condition dissolution testing: (1) maintenance of sink conditions; and (2) the ability to change the dissolution medium during a dissolution run. The former advantage is especially important for poorly aqueous soluble drugs having associated dissolution-rate-limitations, and the latter advantage allows one to more closely simulate the pH gradient associated with transit through the GI tract. Based on the comparative dissolution data, three formulations were chosen for oral dosing in dogs. The reasonable correlation found between the FTC dissolution results and the oral bioavailability data demonstrate that FTC dissolution testing can be a valuable tool for aiding in salt (solid-state form) and formulation selection in the early stages of development of drug candidates.

Dissolution of man-made vitreous fibers in rat alveolar macrophage culture and Gamble's saline solution: influence of different media and chemical composition of the fibers.

PubMed Central

Luoto, K; Holopainen, M; Karppinen, K; Perander, M; Savolainen, K

1994-01-01

The effect of different chemical compositions of man-made vitreous fibers (MMVF) on their dissolution by alveolar macrophages (AM) in culture and in Gamble's solution was studied. The fibers were exposed to cultured rat AMs, culture medium alone; or Gamble's saline solution for 2, 4, or 8 days. The dissolution of the fibers was studied by measuring the amount of silicon (Si), iron (Fe), and aluminum (Al) in each medium. The AMs in culture dissolved Fe and Al from the fibers but the dissolution of Si was more marked in the cell culture medium without cells and in the Gamble's solution. The dissolution of Si, Fe, and Al was different for different fibers, and increased as a function of time. The Fe and Al content of the fibers correlated negatively with the dissolution of Si by AMs from the MMVF, i.e., when the content of Fe and Al of the fibers increased the dissolution of Si decreased. These results suggest that the chemical composition of MMVFs has a marked effect on their dissolution. AMs seem to affect the dissolution of Fe and Al from the fibers. This suggests that in vitro models with cells in the media rather than only culture media or saline solutions would be preferable in dissolution studies of MMVFs. PMID:7882911

Potential Dependence of Pt and Co Dissolution from Platinum-Cobalt Alloy PEFC Catalysts Using Time-Resolved Measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahluwalia, Rajesh K.; Papadias, Dionissios D.; Kariuki, Nancy N.

An electrochemical flow cell system with catalyst-ionomer ink deposited on glassy carbon is used to investigate the aqueous stability of commercial PtCo alloys under cyclic potentials. An on-line inductively coupled plasma-mass spectrometer, capable of real-time measurements, is used to resolve the anodic and cathodic dissolution of Pt and Co during square-wave and triangle-wave potential cycles. We observe Co dissolution at all potentials, distinct peaks in anodic and cathodic Pt dissolution rates above 0.9 V, and potential-dependent Pt and Co dissolution rates. The amount of Pt that dissolves cathodically is smaller than the amount that dissolves anodically if the upper potentialmore » limit (UPL) is lower than 0.9 V. At the highest UPL investigated, 1.0 V, the cathodic dissolution greatly exceeds the anodic dissolution. A non-ideal solid solution model indicates that the anodic dissolution can be associated with the electrochemical oxidation of Pt and PtOH to Pt 2+, and the cathodic dissolution to electrochemical reduction of a higher Pt oxide, PtO x (x > 1), to Pt 2+. Pt also dissolves oxidatively during the cathodic scans but in smaller amounts than due to the reductive dissolution of PtO x. The relative amounts Pt dissolving oxidatively as Pt and PtOH depend on the potential cycle and UPL.« less

A Quality by Design approach to investigate tablet dissolution shift upon accelerated stability by multivariate methods.

PubMed

Huang, Jun; Goolcharran, Chimanlall; Ghosh, Krishnendu

2011-05-01

This paper presents the use of experimental design, optimization and multivariate techniques to investigate root-cause of tablet dissolution shift (slow-down) upon stability and develop control strategies for a drug product during formulation and process development. The effectiveness and usefulness of these methodologies were demonstrated through two application examples. In both applications, dissolution slow-down was observed during a 4-week accelerated stability test under 51°C/75%RH storage condition. In Application I, an experimental design was carried out to evaluate the interactions and effects of the design factors on critical quality attribute (CQA) of dissolution upon stability. The design space was studied by design of experiment (DOE) and multivariate analysis to ensure desired dissolution profile and minimal dissolution shift upon stability. Multivariate techniques, such as multi-way principal component analysis (MPCA) of the entire dissolution profiles upon stability, were performed to reveal batch relationships and to evaluate the impact of design factors on dissolution. In Application II, an experiment was conducted to study the impact of varying tablet breaking force on dissolution upon stability utilizing MPCA. It was demonstrated that the use of multivariate methods, defined as Quality by Design (QbD) principles and tools in ICH-Q8 guidance, provides an effective means to achieve a greater understanding of tablet dissolution upon stability. Copyright © 2010 Elsevier B.V. All rights reserved.

Use of partial dissolution techniques in geochemical exploration

USGS Publications Warehouse

Chao, T.T.

1984-01-01

Application of partial dissolution techniques to geochemical exploration has advanced from an early empirical approach to an approach based on sound geochemical principles. This advance assures a prominent future position for the use of these techniques in geochemical exploration for concealed mineral deposits. Partial dissolution techniques are classified as single dissolution or sequential multiple dissolution depending on the number of steps taken in the procedure, or as "nonselective" extraction and as "selective" extraction in terms of the relative specificity of the extraction. The choice of dissolution techniques for use in geochemical exploration is dictated by the geology of the area, the type and degree of weathering, and the expected chemical forms of the ore and of the pathfinding elements. Case histories have illustrated many instances where partial dissolution techniques exhibit advantages over conventional methods of chemical analysis used in geochemical exploration. ?? 1984.

Automated potentiometric procedure for studying dissolution kinetics acidic drugs under sink conditions.

PubMed

Underwood, F L; Cadwallader, D E

1978-08-01

An automated potentiometric procedure was used for studying in vitro dissolution kinetics of acidic drugs. Theoretical considerations indicated that the pH-stat method could be used to establish approximate sink conditions or, possibly, a perfect sink. Data obtained from dissolution studies using the pH-stat method were compared with data obtained from known sink and nonsink conditions. These comparisons indicated that the pH-stat method can be used to establish a sink condition for dissolution studies. The effective diffusion layer thicknesses for benzoic and salicylic acids dissolving in water were determined, and a theoretical dissolution rate was calculated utilizing these values. The close agreement between the experimental dissolution rates obtained under pH-stat conditions and theoretical dissolution rates indicated that perfect sink conditions were established under the experimental conditions used.

In Vitro Model Simulating Gastro-Intestinal Digestion in the Pediatric Population (Neonates and Young Infants).

PubMed

Kamstrup, Danna; Berthelsen, Ragna; Sassene, Philip Jonas; Selen, Arzu; Müllertz, Anette

2017-02-01

The focus on drug delivery for the pediatric population has been steadily increasing in the last decades. In terms of developing in vitro models simulating characteristics of the targeted pediatric population, with the purpose of predicting drug product performance after oral administration, it is important to simulate the gastro-intestinal conditions and processes the drug will encounter upon oral administration. When a drug is administered in the fed state, which is commonly the case for neonates, as they are typically fed every 3 h, the digestion of the milk will affect the composition of the fluid available for drug dissolution/solubilization. Therefore, in order to predict the solubilized amount of drug available for absorption, an in vitro model simulating digestion in the gastro-intestinal tract should be utilized. In order to simulate the digestion process and the drug solubilization taking place in vivo, the following aspects should be considered; physiologically relevant media, media volume, use of physiological enzymes in proper amounts, as well as correct pH and addition of relevant co-factors, e.g., bile salts and co-enzymes. Furthermore, physiological transit times and appropriate mixing should be considered and mimicked as close as possible. This paper presents a literature review on physiological factors relevant for digestion and drug solubilization in neonates. Based on the available literature data, a novel in vitro digestion model simulating digestion and drug solubilization in the neonate and young infant pediatric population (2 months old and younger) was designed.

The Disintegration Process in Microcrystalline Cellulose Based Tablets, Part 1: Influence of Temperature, Porosity and Superdisintegrants

PubMed Central

Yassin, Samy; Goodwin, Daniel J; Anderson, Andrew; Sibik, Juraj; Wilson, D Ian; Gladden, Lynn F; Zeitler, J Axel

2015-01-01

Disintegration performance was measured by analysing both water ingress and tablet swelling of pure microcrystalline cellulose (MCC) and in mixture with croscarmellose sodium using terahertz pulsed imaging (TPI). Tablets made from pure MCC with porosities of 10% and 15% showed similar swelling and transport kinetics: within the first 15 s, tablets had swollen by up to 33% of their original thickness and water had fully penetrated the tablet following Darcy flow kinetics. In contrast, MCC tablets with a porosity of 5% exhibited much slower transport kinetics, with swelling to only 17% of their original thickness and full water penetration reached after 100 s, dominated by case II transport kinetics. The effect of adding superdisintegrant to the formulation and varying the temperature of the dissolution medium between 20°C and 37°C on the swelling and transport process was quantified. We have demonstrated that TPI can be used to non-invasively analyse the complex disintegration kinetics of formulations that take place on timescales of seconds and is a promising tool to better understand the effect of dosage form microstructure on its performance. By relating immediate-release formulations to mathematical models used to describe controlled release formulations, it becomes possible to use this data for formulation design. © 2015 The Authors. Journal of Pharmaceutical Sciences published by Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 104:3440–3450, 2015 PMID:26073446

Electrochemical corrosion and modeling studies of types 7075 and 2219 aluminum alloys in a nitric acid + ferric sulfate deoxidizer solution

NASA Astrophysics Data System (ADS)

Savas, Terence P.

The corrosion behavior of types 7075-T73 and 2219-T852 high strength aluminum alloys have been investigated in a HNO3 + Fe2(SO 4)3 solution. The materials are characterized in the time domain using the electrochemical noise resistance parameter (Rn) and in the frequency-domain using the spectral noise impedance parameter ( Rsn). The Rsn parameter is derived from an equivalent electrical circuit model that represents the corrosion test cell schematic used in the present study. These calculated parameters are correlated to each other, and to corresponding scanning electron microscopy (SEM) examinations of the corroded surfaces. In addition, energy dispersive spectroscopy (EDS) spectra are used in conjunction with SEM exams for particle mapping and identification. These constituent particles are characterized with respect to their size and composition and their effect on the localized corrosion mechanisms taking place. Pitting mechanisms are identified as 'circumferential' where the particles appeared noble with respect to the aluminum matrix and by 'selective dissolution' where they are anodic to the aluminum matrix. The electrochemical data are found to be in good agreement with the surface examinations. Specifically, the electrochemical parameters Rn and Rsn were consistent in predicting the corrosion resistance of 7075-T73 to be lower than for the 2219-T852 alloy. Other characteristic features used in understanding the corrosion mechanisms include the open circuit potential (OCP) and coupling-current time records.

Manufacturing of Dysprosium-Iron Alloys by Electrolysis in Fluoride-Based Electrolytes. Electrolysis in a Laboratory-Scale Cell

NASA Astrophysics Data System (ADS)

Martinez, Ana Maria; Osen, Karen Sende; Støre, Anne; Gudbrandsen, Henrik; Kjos, Ole Sigmund; Solheim, Asbjørn; Wang, Zhaohui; Oury, Alexandre; Namy, Patrick

2018-04-01

Electrolytic production of light rare earth elements and rare earth alloys with transition elements takes place in a fluoride-based electrolyte using rare earth oxides as raw material. The optimization of this method, mainly in terms of the energy efficiency and environmental impact control, is rather challenging. Anode effects, evolution of fluorine-containing compounds and side cathode reactions could largely be minimized by good control of the amount of rare earth oxide species dissolved in the fluoride-based electrolyte and their dissolution rate. The Dy2O3 feed rate needed for stable cell operation was studied by following up the anode voltage and gas analysis. On-line analysis of the cell off-gases by FTIR showed that the electrochemical reaction for the formation of Dy-Fe alloy gives mainly CO gas and that CF4 is starting to evolve gradually at anode voltages of ca. 3.25 V. The limiting current density for the discharge of the oxide ions at the graphite anode was in the range of 0.1 to 0.18 A cm-2 at dissolved Dy2O3 contents of ca. 1 wt pct. Modeling of the laboratory cell reactor was also carried out by implementing two models, i.e., an electrical model simulating the current density distribution at the electrodes and a laminal bubbly flow model that explains the electrolyte velocity induced by gas bubble production at the anode.

The electrochemical reduction processes of solid compounds in high temperature molten salts.

PubMed

Xiao, Wei; Wang, Dihua

2014-05-21

Solid electrode processes fall in the central focus of electrochemistry due to their broad-based applications in electrochemical energy storage/conversion devices, sensors and electrochemical preparation. The electrolytic production of metals, alloys, semiconductors and oxides via the electrochemical reduction of solid compounds (especially solid oxides) in high temperature molten salts has been well demonstrated to be an effective and environmentally friendly process for refractory metal extraction, functional materials preparation as well as spent fuel reprocessing. The (electro)chemical reduction of solid compounds under cathodic polarizations generally accompanies a variety of changes at the cathode/melt electrochemical interface which result in diverse electrolytic products with different compositions, morphologies and microstructures. This report summarizes various (electro)chemical reactions taking place at the compound cathode/melt interface during the electrochemical reduction of solid compounds in molten salts, which mainly include: (1) the direct electro-deoxidation of solid oxides; (2) the deposition of the active metal together with the electrochemical reduction of solid oxides; (3) the electro-inclusion of cations from molten salts; (4) the dissolution-electrodeposition process, and (5) the electron hopping process and carbon deposition with the utilization of carbon-based anodes. The implications of the forenamed cathodic reactions on the energy efficiency, chemical compositions and microstructures of the electrolytic products are also discussed. We hope that a comprehensive understanding of the cathodic processes during the electrochemical reduction of solid compounds in molten salts could form a basis for developing a clean, energy efficient and affordable production process for advanced/engineering materials.

Does the stepwave model predict mica dissolution kinetics?

NASA Astrophysics Data System (ADS)

Kurganskaya, Inna; Arvidson, Rolf S.; Fischer, Cornelius; Luttge, Andreas

2012-11-01

The micas are a unique class of minerals because of their layered structure. A frequent question arising in mica dissolution studies is whether this layered structure radically changes the dissolution mechanism. We address this question here, using data from VSI and AFM experiments involving muscovite to evaluate crystallographic controls on mica dissolution. These data provide insight into the dissolution process, and reveal important links to patterns of dissolution observed in framework minerals. Under our experimental conditions (pH 9.4, 155 °C), the minimal global rate of normal surface retreat observed in VSI data was 1.42 × 10-10 mol/m2/s (σ = 27%) while the local rate observed at deep etch pits reached 416 × 10-10 mol/m2/s (σ = 49%). Complementary AFM data clearly show crystallographic control of mica dissolution, both in terms of step advance and the geometric influence of interlayer rotation (stacking periodicity). These observations indicate that basal/edge surface area ratios are highly variable and change continuously over the course of reaction, thus obviating their utility as characteristic parameters defining mica reactivity. Instead, these observations of overall dissolution rate and the influence of screw dislocations illustrate the link between atomic step movement and overall dissolution rate defined by surface retreat normal to the mica surface. Considered in light of similar observations available elsewhere in the literature, these relationships provide support for application of the stepwave model to mica dissolution kinetics. This approach provides a basic mechanistic link between the dissolution kinetics of phyllosilicates, framework silicates, and related minerals, and suggests a resolution to the general problem of mica reactivity.

Comparison of Dissolution Similarity Assessment Methods for Products with Large Variations: f2 Statistics and Model-Independent Multivariate Confidence Region Procedure for Dissolution Profiles of Multiple Oral Products.

PubMed

Yoshida, Hiroyuki; Shibata, Hiroko; Izutsu, Ken-Ichi; Goda, Yukihiro

2017-01-01

The current Japanese Ministry of Health Labour and Welfare (MHLW)'s Guideline for Bioequivalence Studies of Generic Products uses averaged dissolution rates for the assessment of dissolution similarity between test and reference formulations. This study clarifies how the application of model-independent multivariate confidence region procedure (Method B), described in the European Medical Agency and U.S. Food and Drug Administration guidelines, affects similarity outcomes obtained empirically from dissolution profiles with large variations in individual dissolution rates. Sixty-one datasets of dissolution profiles for immediate release, oral generic, and corresponding innovator products that showed large variation in individual dissolution rates in generic products were assessed on their similarity by using the f 2 statistics defined in the MHLW guidelines (MHLW f 2 method) and two different Method B procedures, including a bootstrap method applied with f 2 statistics (BS method) and a multivariate analysis method using the Mahalanobis distance (MV method). The MHLW f 2 and BS methods provided similar dissolution similarities between reference and generic products. Although a small difference in the similarity assessment may be due to the decrease in the lower confidence interval for expected f 2 values derived from the large variation in individual dissolution rates, the MV method provided results different from those obtained through MHLW f 2 and BS methods. Analysis of actual dissolution data for products with large individual variations would provide valuable information towards an enhanced understanding of these methods and their possible incorporation in the MHLW guidelines.

Catalysis and chemical mechanisms of calcite dissolution in seawater

PubMed Central

Adkins, Jess F.; Rollins, Nick E.; Naviaux, John; Erez, Jonathan; Berelson, William M.

2017-01-01

Near-equilibrium calcite dissolution in seawater contributes significantly to the regulation of atmospheric CO2 on 1,000-y timescales. Despite many studies on far-from-equilibrium dissolution, little is known about the detailed mechanisms responsible for calcite dissolution in seawater. In this paper, we dissolve 13C-labeled calcites in natural seawater. We show that the time-evolving enrichment of 𝜹13C in solution is a direct measure of both dissolution and precipitation reactions across a large range of saturation states. Secondary Ion Mass Spectrometer profiles into the 13C-labeled solids confirm the presence of precipitated material even in undersaturated conditions. The close balance of precipitation and dissolution near equilibrium can alter the chemical composition of calcite deeper than one monolayer into the crystal. This balance of dissolution–precipitation shifts significantly toward a dissolution-dominated mechanism below about Ω= 0.7. Finally, we show that the enzyme carbonic anhydrase (CA) increases the dissolution rate across all saturation states, and the effect is most pronounced close to equilibrium. This finding suggests that the rate of hydration of CO2 is a rate-limiting step for calcite dissolution in seawater. We then interpret our dissolution data in a framework that incorporates both solution chemistry and geometric constraints on the calcite solid. Near equilibrium, this framework demonstrates a lowered free energy barrier at the solid–solution interface in the presence of CA. This framework also indicates a significant change in dissolution mechanism at Ω= 0.7, which we interpret as the onset of homogeneous etch pit nucleation. PMID:28720698

Mindful Place-Based Education: Mapping the Literature

ERIC Educational Resources Information Center

Deringer, S. Anthony

2017-01-01

Place-based education and mindfulness are not new concepts, but the idea of combining the two bodies of work to explore what mindful place-based education might look like may provide a useful new perspective. The purpose of the literature review is to take place-based pedagogical methods and examine how mindfulness might influence the experience…

25 CFR 11.605 - Dissolution.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 25 Indians 1 2013-04-01 2013-04-01 false Dissolution. 11.605 Section 11.605 Indians BUREAU OF... Domestic Relations § 11.605 Dissolution. (a) The Court of Indian Offenses shall enter a decree of dissolution of marriage if: (1) The court finds that the marriage is irretrievably broken, if the finding is...

25 CFR 11.606 - Dissolution proceedings.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 25 Indians 1 2012-04-01 2011-04-01 true Dissolution proceedings. 11.606 Section 11.606 Indians... ORDER CODE Domestic Relations § 11.606 Dissolution proceedings. (a) Either or both parties to the marriage may initiate dissolution proceedings. (b) If a proceeding is commenced by one of the parties, the...

32 CFR 202.10 - RAB adjournment and dissolution.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 32 National Defense 2 2013-07-01 2013-07-01 false RAB adjournment and dissolution. 202.10 Section... dissolution. (a) RAB adjournment—(1) Requirements for RAB adjournment. An Installation Commander may adjourn a... Commander decides to adjourn the RAB. (b) RAB dissolution—(1) Requirements for RAB dissolution. An...

25 CFR 11.605 - Dissolution.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 25 Indians 1 2011-04-01 2011-04-01 false Dissolution. 11.605 Section 11.605 Indians BUREAU OF... Domestic Relations § 11.605 Dissolution. (a) The Court of Indian Offenses shall enter a decree of dissolution of marriage if: (1) The court finds that the marriage is irretrievably broken, if the finding is...

12 CFR 710.8 - Certificate of dissolution and liquidation.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 12 Banks and Banking 7 2014-01-01 2014-01-01 false Certificate of dissolution and liquidation. 710... UNIONS VOLUNTARY LIQUIDATION § 710.8 Certificate of dissolution and liquidation. Within 120 days after the final distribution of assets to members is started, a duly executed Certificate of Dissolution and...

25 CFR 11.605 - Dissolution.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 25 Indians 1 2014-04-01 2014-04-01 false Dissolution. 11.605 Section 11.605 Indians BUREAU OF... Domestic Relations § 11.605 Dissolution. (a) The Court of Indian Offenses shall enter a decree of dissolution of marriage if: (1) The court finds that the marriage is irretrievably broken, if the finding is...

32 CFR 202.10 - RAB adjournment and dissolution.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 32 National Defense 2 2011-07-01 2011-07-01 false RAB adjournment and dissolution. 202.10 Section... dissolution. (a) RAB adjournment—(1) Requirements for RAB adjournment. An Installation Commander may adjourn a... Commander decides to adjourn the RAB. (b) RAB dissolution—(1) Requirements for RAB dissolution. An...

25 CFR 11.606 - Dissolution proceedings.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 25 Indians 1 2013-04-01 2013-04-01 false Dissolution proceedings. 11.606 Section 11.606 Indians... ORDER CODE Domestic Relations § 11.606 Dissolution proceedings. (a) Either or both parties to the marriage may initiate dissolution proceedings. (b) If a proceeding is commenced by one of the parties, the...

25 CFR 11.606 - Dissolution proceedings.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 25 Indians 1 2011-04-01 2011-04-01 false Dissolution proceedings. 11.606 Section 11.606 Indians... ORDER CODE Domestic Relations § 11.606 Dissolution proceedings. (a) Either or both parties to the marriage may initiate dissolution proceedings. (b) If a proceeding is commenced by one of the parties, the...

32 CFR 202.10 - RAB adjournment and dissolution.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 32 National Defense 2 2012-07-01 2012-07-01 false RAB adjournment and dissolution. 202.10 Section... dissolution. (a) RAB adjournment—(1) Requirements for RAB adjournment. An Installation Commander may adjourn a... Commander decides to adjourn the RAB. (b) RAB dissolution—(1) Requirements for RAB dissolution. An...

32 CFR 202.10 - RAB adjournment and dissolution.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 32 National Defense 2 2014-07-01 2014-07-01 false RAB adjournment and dissolution. 202.10 Section... dissolution. (a) RAB adjournment—(1) Requirements for RAB adjournment. An Installation Commander may adjourn a... Commander decides to adjourn the RAB. (b) RAB dissolution—(1) Requirements for RAB dissolution. An...

12 CFR 710.8 - Certificate of dissolution and liquidation.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 12 Banks and Banking 6 2011-01-01 2011-01-01 false Certificate of dissolution and liquidation. 710... UNIONS VOLUNTARY LIQUIDATION § 710.8 Certificate of dissolution and liquidation. Within 120 days after the final distribution of assets to members is started, a duly executed Certificate of Dissolution and...

12 CFR 710.8 - Certificate of dissolution and liquidation.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 12 Banks and Banking 7 2013-01-01 2013-01-01 false Certificate of dissolution and liquidation. 710... UNIONS VOLUNTARY LIQUIDATION § 710.8 Certificate of dissolution and liquidation. Within 120 days after the final distribution of assets to members is started, a duly executed Certificate of Dissolution and...

12 CFR 710.8 - Certificate of dissolution and liquidation.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 12 Banks and Banking 7 2012-01-01 2012-01-01 false Certificate of dissolution and liquidation. 710... UNIONS VOLUNTARY LIQUIDATION § 710.8 Certificate of dissolution and liquidation. Within 120 days after the final distribution of assets to members is started, a duly executed Certificate of Dissolution and...

25 CFR 11.606 - Dissolution proceedings.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 25 Indians 1 2014-04-01 2014-04-01 false Dissolution proceedings. 11.606 Section 11.606 Indians... ORDER CODE Domestic Relations § 11.606 Dissolution proceedings. (a) Either or both parties to the marriage may initiate dissolution proceedings. (b) If a proceeding is commenced by one of the parties, the...

12 CFR 710.8 - Certificate of dissolution and liquidation.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 12 Banks and Banking 6 2010-01-01 2010-01-01 false Certificate of dissolution and liquidation. 710... UNIONS VOLUNTARY LIQUIDATION § 710.8 Certificate of dissolution and liquidation. Within 120 days after the final distribution of assets to members is started, a duly executed Certificate of Dissolution and...

25 CFR 11.605 - Dissolution.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 25 Indians 1 2012-04-01 2011-04-01 true Dissolution. 11.605 Section 11.605 Indians BUREAU OF... Domestic Relations § 11.605 Dissolution. (a) The Court of Indian Offenses shall enter a decree of dissolution of marriage if: (1) The court finds that the marriage is irretrievably broken, if the finding is...

Sherwood correlation for dissolution of pooled NAPL in porous media

NASA Astrophysics Data System (ADS)

Aydin Sarikurt, Derya; Gokdemir, Cagri; Copty, Nadim K.

2017-11-01

The rate of interphase mass transfer from non-aqueous phase liquids (NAPLs) entrapped in the subsurface into the surrounding mobile aqueous phase is commonly expressed in terms of Sherwood (Sh) correlations that are expressed as a function of flow and porous media properties. Because of the lack of precise methods for the estimation of the interfacial area separating the NAPL and aqueous phases, most studies have opted to use modified Sherwood expressions that lump the interfacial area into the interphase mass transfer coefficient. To date, there are only two studies in the literature that have developed non-lumped Sherwood correlations; however, these correlations have undergone limited validation. In this paper controlled dissolution experiments from pooled NAPL were conducted. The immobile NAPL mass is placed at the bottom of a flow cell filled with porous media with water flowing horizontally on top. Effluent aqueous phase concentrations were measured for a wide range of aqueous phase velocities and for two different porous media. To interpret the experimental results, a two-dimensional pore network model of the NAPL dissolution kinetics and aqueous phase transport was developed. The observed effluent concentrations were then used to compute best-fit mass transfer coefficients. Comparison of the effluent concentrations computed with the two-dimensional pore network model to those estimated with one-dimensional analytical solutions indicates that the analytical model which ignores the transport in the lateral direction can lead to under-estimation of the mass transfer coefficient. Based on system parameters and the estimated mass transfer coefficients, non-lumped Sherwood correlations were developed and compared to previously published data. The developed correlations, which are a significant improvement over currently available correlations that are associated with large uncertainties, can be incorporated into future modeling studies requiring non-lumped Sh expressions.

Pavement Subsidence in the Cumberland Gap Tunnel, USA: A Story of Groundwater Chemistry

NASA Astrophysics Data System (ADS)

Zhu, J.; Currens, J. C.; Webb, S. E.; Rister, B. W.

2014-12-01

Cumberland Gap Tunnel was constructed in 1996 to improve highway travel between southeastern Kentucky and northeastern Tennessee and to restore Cumberland Gap to its historical appearance. About five years after construction, the concrete pavement in the tunnel began to exhibit noticeable signs of subsidence. Ground penetrating radar surveys detected voids in many areas of the limestone roadbed aggregate beneath the pavement. Field investigations conducted by the Kentucky Geological Survey and Kentucky Transportation Center from 2006 to 2008 discovered that groundwater was flowing from the bedrock invert into the aggregate along many parts of the tunnel. Average groundwater discharge from the tunnel was measured at approximately 1700 m3/d. We analyzed 265 groundwater samples collected from aggregate in different parts of the tunnel roadbed during low and high flow conditions. Calculated calcite saturation indices indicated that the groundwater was geochemically aggressive and capable of continuously dissolving calcite in the limestone aggregate although pH values of these water samples were near neutral. We also conducted an in-situ dissolution experiment by placing eight baskets filled with limestone aggregate beneath the roadbed in different locations in the tunnel for 178 days. At the end of the experiment, the limestone aggregate in contact with groundwater exhibited visual signs of dissolution and lost mass, and the highest mass loss recorded was 3.4 percent. Mass loss calculations based on kinetic models of calcite mineral and water samples taken near the baskets matched well with the actual measured mass losses, confirming that dissolution of calcite by the groundwater was the primary cause of the roadbed subsidence problem. Based on these findings, we suggested the limestone aggregate be replaced with noncarbonate (granite) aggregate to mitigate future road subsidence. The suggestion was adopted, and the repair was completed in early 2014.

Young People Take Their Rightful Places as Full and Contributing Members of a World Class Workforce: Philadelphia Youth Network Annual Report 2006

ERIC Educational Resources Information Center

Philadelphia Youth Network, 2006

2006-01-01

The title of this year's annual report has particular meaning for all of the staff at the Philadelphia Youth Network. The phrase derives from Philadelphia Youth Network's (PYN's) new vision statement, developed as part of its recent strategic planning process, which reads: All of our city's young people take their rightful places as full and…

Dissolution kinetics of soluble nondisintegrating disks.

PubMed

de Blaey, C J; van der Graaff, H

1977-12-01

An equation describing the isotropical dissolution of soluble nondisintegrating disks was developed. It was equivalent to the cube root law only if the height and diameter of the disk were equal. The dissolution kinetics of sodium chloride disks were examined, using a beaker equipped with a centrifugal stirrer as the dissolution chamber. The fit of the experimental data to the cube root law had a coefficient of variation of about 4-5%. It was demonstrated statistically that a fit to a square root of mass versus time relation was significantly better. With increasing porosity, the dissolution process proceeded faster than predicted on the basis of the diffusion-convection model. An explanation is proposed by assuming an increased effective dissolution surface.

Dissolution of quartz in aqueous basic solution, 106-236 C - Surface kinetics of 'perfect' crystallographic faces

NASA Technical Reports Server (NTRS)

Gratz, Andrew J.; Bird, Peter; Quiro, Glenn B.

1990-01-01

A highly accurate method, called the negative crystal method, for determining the rate of dissolution on specific crystallographic faces of crystals was developed, in which the dissolution rates of nominally perfect crystal faces are obtained by measuring the size of individual negative crystals during a sequence of dissolution steps. The method was applied to determine the apparent activation energy and rate constants for the dissolution of quartz in 0.01 M KOH solutions at temperatures from 106 to 236 C. Also investigated were the effects of hydroxyl activity and ionic strength. The apparent activation energies for the dissolution of the prism and of the rhomb were determined.

Substandard Antimalarials Available in Afghanistan: A Case for Assessing the Quality of Drugs in Resource Poor Settings

PubMed Central

Lalani, Mirza; Kaur, Harparkash; Mohammed, Nader; Mailk, Naiela; van Wyk, Albert; Jan, Sakhi; Kakar, Rishtya Meena; Mojadidi, Mohammed Khalid; Leslie, Toby

2015-01-01

Good-quality antimalarials are crucial for the effective treatment and control of malaria. A total of 7,740 individual and packaged tablets, ampoules, and syrups were obtained from 60 randomly selected public (N = 35) and private outlets (N = 25) in Afghanistan. Of these, 134 samples were screened using the Global Pharma Health Fund (GPHF) MiniLab® in Kabul with 33/126 (26%) samples failing the MiniLab® disintegration test. The quality of a subsample (N = 37) of cholorquine, quinine, and sulfadoxine/pyrimethamine tablets was assessed by in vitro dissolution testing following U.S. Pharmacopeia (USP) monographs at a bioanalytical laboratory in London, United Kingdom. Overall, 12/32 (32%) samples of sulfadoxine/pyrimethamine and quinine were found not to comply with the USP tolerance limits. Substandard antimalarials were available in Afghanistan demonstrating that continuous monitoring of drug quality is warranted. However, in Afghanistan as in many low-income countries, capacity to determine and monitor drug quality using methods such as dissolution testing needs to be established to empower national authorities to take appropriate action in setting up legislation and regulation. PMID:25897070

Influence of mass transfer on bubble plume hydrodynamics.

PubMed

Lima Neto, Iran E; Parente, Priscila A B

2016-03-01

This paper presents an integral model to evaluate the impact of gas transfer on the hydrodynamics of bubble plumes. The model is based on the Gaussian type self-similarity and functional relationships for the entrainment coefficient and factor of momentum amplification due to turbulence. The impact of mass transfer on bubble plume hydrodynamics is investigated considering different bubble sizes, gas flow rates and water depths. The results revealed a relevant impact when fine bubbles are considered, even for moderate water depths. Additionally, model simulations indicate that for weak bubble plumes (i.e., with relatively low flow rates and large depths and slip velocities), both dissolution and turbulence can affect plume hydrodynamics, which demonstrates the importance of taking the momentum amplification factor relationship into account. For deeper water conditions, simulations of bubble dissolution/decompression using the present model and classical models available in the literature resulted in a very good agreement for both aeration and oxygenation processes. Sensitivity analysis showed that the water depth, followed by the bubble size and the flow rate are the most important parameters that affect plume hydrodynamics. Lastly, dimensionless correlations are proposed to assess the impact of mass transfer on plume hydrodynamics, including both the aeration and oxygenation modes.

Microenvironmental pH measurement during sodium naproxenate dissolution in acidic medium by UV/vis imaging.

PubMed

Østergaard, Jesper; Jensen, Henrik; Larsen, Susan W; Larsen, Claus; Lenke, Jim

2014-11-01

Variable dissolution from sodium salts of drugs containing a carboxylic acid group after passing the acidic environment of the stomach may affect oral bioavailability. The aim of the present proof of concept study was to investigate pH effects in relation to the dissolution of sodium naproxenate in 0.01M hydrochloric acid. For this purpose a UV/vis imaging-based approach capable of measuring microenvironmental pH in the vicinity of the solid drug compact as well as monitoring drug dissolution was developed. Using a pH indicating dye real-time spatially resolved measurement of pH was achieved. Sodium naproxenate, can significantly alter the local pH of the dissolution medium, is eventually neutralized and precipitates as the acidic species naproxen. The developed approach is considered useful for detailed studies of pH dependent dissolution phenomena in dissolution testing. Copyright © 2014 Elsevier B.V. All rights reserved.

Dissolution of Platinum in the Operational Range of Fuel Cells

PubMed Central

Keeley, Gareth P.; Geiger, Simon; Zeradjanin, Aleksandar R.; Hodnik, Nejc; Kulyk, Nadiia

2015-01-01

Abstract One of the most important practical issues in low‐temperature fuel‐cell catalyst degradation is platinum dissolution. According to the literature, it initiates at 0.6–0.9 VRHE, whereas previous time‐ and potential‐resolved inductively coupled plasma mass spectrometry (ICP–MS) experiments, however, revealed dissolution onset at only 1.05 VRHE. In this manuscript, the apparent discrepancy is addressed by investigating bulk and nanoparticulated catalysts. It is shown that, given enough time for accumulation, traces of platinum can be detected at potentials as low as 0.85 VRHE. At these low potentials, anodic dissolution is the dominant process, whereas, at more positive potentials, more platinum dissolves during the oxide reduction after accumulation. Interestingly, the potential and time dissolution dependence is similar for both types of electrode. Dissolution processes are discussed with relevance to fuel‐cell operation and plausible dissolution mechanisms are considered. PMID:27525206

12 CFR 16.9 - Securities offered and sold in holding company dissolution.

Code of Federal Regulations, 2014 CFR

2014-01-01

... dissolution. 16.9 Section 16.9 Banks and Banking COMPTROLLER OF THE CURRENCY, DEPARTMENT OF THE TREASURY SECURITIES OFFERING DISCLOSURE RULES § 16.9 Securities offered and sold in holding company dissolution. Offers and sales of bank issued securities in connection with the dissolution of the holding company of...

26 CFR 301.6043-1 - Returns regarding liquidation, dissolution, termination, or contraction.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 26 Internal Revenue 18 2012-04-01 2012-04-01 false Returns regarding liquidation, dissolution... and Returns Returns and Records § 301.6043-1 Returns regarding liquidation, dissolution, termination... liquidations, dissolutions, terminations, or contracts, see §§ l.6043-1, 1.6043-2, and 1.6043-3 of this chapter...

26 CFR 1.6043-1 - Return regarding corporate dissolution or liquidation.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 26 Internal Revenue 13 2013-04-01 2013-04-01 false Return regarding corporate dissolution or... corporate dissolution or liquidation. (a) Requirement of returns. Within 30 days after the adoption of any resolution or plan for or in respect of the dissolution of a corporation or the liquidation of the whole or...

12 CFR 16.9 - Securities offered and sold in holding company dissolution.

Code of Federal Regulations, 2013 CFR

2013-01-01

... dissolution. 16.9 Section 16.9 Banks and Banking COMPTROLLER OF THE CURRENCY, DEPARTMENT OF THE TREASURY SECURITIES OFFERING DISCLOSURE RULES § 16.9 Securities offered and sold in holding company dissolution. Offers and sales of bank issued securities in connection with the dissolution of the holding company of...

12 CFR 16.9 - Securities offered and sold in holding company dissolution.

Code of Federal Regulations, 2011 CFR

2011-01-01

... dissolution. 16.9 Section 16.9 Banks and Banking COMPTROLLER OF THE CURRENCY, DEPARTMENT OF THE TREASURY SECURITIES OFFERING DISCLOSURE RULES § 16.9 Securities offered and sold in holding company dissolution. Offers and sales of bank issued securities in connection with the dissolution of the holding company of...

Examining Two Types of Best Friendship Dissolution during Early Adolescence

ERIC Educational Resources Information Center

Bowker, Julie C.

2011-01-01

This study examined young adolescents' experiences with best friendship dissolution. Participants were 77 sixth-grade students (M age = 11.63 years, SD = 0.36; 11.00-12.69 age range) who reported on past experiences with (1) "complete dissolutions" (when friendship ties are completely severed), and (2) "downgrade dissolutions"…

26 CFR 1.6043-1 - Return regarding corporate dissolution or liquidation.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 26 Internal Revenue 13 2012-04-01 2012-04-01 false Return regarding corporate dissolution or... corporate dissolution or liquidation. (a) Requirement of returns. Within 30 days after the adoption of any resolution or plan for or in respect of the dissolution of a corporation or the liquidation of the whole or...

42 CFR 412.331 - Determining hospital-specific rates in cases of hospital merger, consolidation, or dissolution.

Code of Federal Regulations, 2012 CFR

2012-10-01

... hospital merger, consolidation, or dissolution. 412.331 Section 412.331 Public Health CENTERS FOR MEDICARE... cases of hospital merger, consolidation, or dissolution. (a) New hospital merger or consolidation. If... dissolution. If a hospital separates into two or more hospitals that are subject to capital payments under...

12 CFR 16.9 - Securities offered and sold in holding company dissolution.

Code of Federal Regulations, 2010 CFR

2010-01-01

... dissolution. 16.9 Section 16.9 Banks and Banking COMPTROLLER OF THE CURRENCY, DEPARTMENT OF THE TREASURY SECURITIES OFFERING DISCLOSURE RULES § 16.9 Securities offered and sold in holding company dissolution. Offers and sales of bank issued securities in connection with the dissolution of the holding company of...

26 CFR 301.6043-1 - Returns regarding liquidation, dissolution, termination, or contraction.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 26 Internal Revenue 18 2011-04-01 2011-04-01 false Returns regarding liquidation, dissolution... and Returns Returns and Records § 301.6043-1 Returns regarding liquidation, dissolution, termination... liquidations, dissolutions, terminations, or contracts, see §§ l.6043-1, 1.6043-2, and 1.6043-3 of this chapter...

12 CFR 16.9 - Securities offered and sold in holding company dissolution.

Code of Federal Regulations, 2012 CFR

2012-01-01

... dissolution. 16.9 Section 16.9 Banks and Banking COMPTROLLER OF THE CURRENCY, DEPARTMENT OF THE TREASURY SECURITIES OFFERING DISCLOSURE RULES § 16.9 Securities offered and sold in holding company dissolution. Offers and sales of bank issued securities in connection with the dissolution of the holding company of...

42 CFR 412.331 - Determining hospital-specific rates in cases of hospital merger, consolidation, or dissolution.

Code of Federal Regulations, 2014 CFR

2014-10-01

... hospital merger, consolidation, or dissolution. 412.331 Section 412.331 Public Health CENTERS FOR MEDICARE... cases of hospital merger, consolidation, or dissolution. (a) New hospital merger or consolidation. If... dissolution. If a hospital separates into two or more hospitals that are subject to capital payments under...

42 CFR 412.331 - Determining hospital-specific rates in cases of hospital merger, consolidation, or dissolution.

Code of Federal Regulations, 2011 CFR

2011-10-01

... hospital merger, consolidation, or dissolution. 412.331 Section 412.331 Public Health CENTERS FOR MEDICARE... cases of hospital merger, consolidation, or dissolution. (a) New hospital merger or consolidation. If... dissolution. If a hospital separates into two or more hospitals that are subject to capital payments under...

26 CFR 301.6043-1 - Returns regarding liquidation, dissolution, termination, or contraction.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 26 Internal Revenue 18 2013-04-01 2013-04-01 false Returns regarding liquidation, dissolution... and Returns Returns and Records § 301.6043-1 Returns regarding liquidation, dissolution, termination... liquidations, dissolutions, terminations, or contracts, see §§ l.6043-1, 1.6043-2, and 1.6043-3 of this chapter...

26 CFR 301.6043-1 - Returns regarding liquidation, dissolution, termination, or contraction.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 26 Internal Revenue 18 2014-04-01 2014-04-01 false Returns regarding liquidation, dissolution... and Returns Returns and Records § 301.6043-1 Returns regarding liquidation, dissolution, termination... liquidations, dissolutions, terminations, or contracts, see §§ l.6043-1, 1.6043-2, and 1.6043-3 of this chapter...

26 CFR 301.6043-1 - Returns regarding liquidation, dissolution, termination, or contraction.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 26 Internal Revenue 18 2010-04-01 2010-04-01 false Returns regarding liquidation, dissolution... and Returns Returns and Records § 301.6043-1 Returns regarding liquidation, dissolution, termination... liquidations, dissolutions, terminations, or contracts, see §§ l.6043-1, 1.6043-2, and 1.6043-3 of this chapter...

42 CFR 412.331 - Determining hospital-specific rates in cases of hospital merger, consolidation, or dissolution.

Code of Federal Regulations, 2013 CFR

2013-10-01

... hospital merger, consolidation, or dissolution. 412.331 Section 412.331 Public Health CENTERS FOR MEDICARE... cases of hospital merger, consolidation, or dissolution. (a) New hospital merger or consolidation. If... dissolution. If a hospital separates into two or more hospitals that are subject to capital payments under...

26 CFR 1.6043-1 - Return regarding corporate dissolution or liquidation.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 26 Internal Revenue 13 2014-04-01 2014-04-01 false Return regarding corporate dissolution or... corporate dissolution or liquidation. (a) Requirement of returns. Within 30 days after the adoption of any resolution or plan for or in respect of the dissolution of a corporation or the liquidation of the whole or...

26 CFR 1.6043-1 - Return regarding corporate dissolution or liquidation.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 26 Internal Revenue 13 2011-04-01 2011-04-01 false Return regarding corporate dissolution or... corporate dissolution or liquidation. (a) Requirement of returns. Within 30 days after the adoption of any resolution or plan for or in respect of the dissolution of a corporation or the liquidation of the whole or...

Development and evaluation of methods for starch dissolution using asymmetrical flow field-flow fractionation. Part II: Dissolution of amylose.

PubMed

Perez-Rea, Daysi; Bergenståhl, Björn; Nilsson, Lars

2016-02-01

In this paper, we investigate whether dissolution in water under autoclaving conditions (140 °C, 20 min) or in dimethyl sulfoxide, DMSO (100 °C, 1 h), is preferable for characterization of amylose. Two types of amylose, potato and maize, were dissolved either in water using an autoclave or in DMSO. On the aqueous solutions obtained, the extent of molecular dissolution of the sample (referred to as the dissolution yield) was determined by enzymatic analysis as well as the molecular properties, such as molar mass and root-mean-square radius, obtained with asymmetrical flow field-flow fractionation coupled to multi-angle light scattering and differential refractive index detection (AF4-MALS-dRI). The results showed that both dissolution methods are efficient at dissolving amylose. However, AF4-MALS-dRI analysis revealed substantial differences. Amylose aqueous solutions obtained by dissolution in DMSO were relatively stable over time, but the dissolution method in autoclave caused some degradation of the molecules, and their solutions display a high tendency to retrograde.

Glass fiber dissolution in simulated lung fluid and measures needed to improve consistency and correspondence to in vivo dissolution.

PubMed Central

Mattson, S M

1994-01-01

The dissolution of a range of glass fibers including commercial glass and mineral wools has been studied using a modification of Gamble's solution in a flow system at pH 7.4 and 37 degrees C. Dissolution has been followed by weight loss, effluent analysis, and morphology change of fibers and bulk glass. Flow per glass surface area can strongly affect both dissolution rate and morphology due to the effect of the dissolution process on the fluid. Effluent pH is shown to be a guide for choice of optimum flow/area conditions. These conditions provide measurable concentrations of dissolved glass in the effluent while maintaining their concentrations below the point at which they significantly affect the dissolution process. SiO2 and Al2O3 vary widely in the extent to which they are involved in the leaching process, which removes alkalis, alkaline earths, and B2O3. This makes analysis of a single component in the effluent unsuitable as a means of comparing the dissolution rates of a wide range of compositions. PMID:7882963

Basic processes and factors determining the evolution of collapse sinkholes: a sensitivity study

NASA Astrophysics Data System (ADS)

Romanov, Douchko; Kaufmann, Georg

2017-04-01

Collapse sinkholes appear as closed depressions at the surface. The origin of these karst features is related to the continuous dissolution of the soluble rock caused by a focussed sub-surface flow. Water flowing along a preferential pathway through fissures and fractures within the phreatic part of a karst aquifer is able to dissolve the rock (limestone, gypsum, anhydrite). With time, the dissolved void volume increases and part of the ceiling above the stream can become unstable, collapses, and accumulates as debris in the flow path. The debris partially blocks the flow and thus activates new pathways. Because of the low compaction of the debris (high hydraulic conductivity), the flow and the dissolution rates within this crushed zone remain high. This allows a relatively fast dissolutional and erosional removal of the crushed material and the development of new empty voids. The void volume expands upwards towards the surface until a collapse sinkhole is formed. The collapse sinkholes exhibit a large variety of shapes (cylindrical, cone-, bowl-shaped), depths (from few to few hundred meters) and diameters (meters up to hundreds of meters). Two major processes are responsible for this diversity: a) the karst evolution of the aquifer - responsible for the dissolutional and erosional removal of material; b) the mechanical evolution of the host rock and the existence of structural features, faults for example, which determine the stability and the magnitude of the subsequent collapses. In this work we demonstrate the influence of the host rock type, the hydrological and geological boundary conditions, the chemical composition of the flowing water, and the geometry and the scale of the crushed zone, on the location and the evolution of the growing sinkhole. We demonstrate the ability of the karst evolution models to explain, at least qualitatively, the growth and the morphology of the collapse sinkholes and to roughly predict their shape and location. Implementing simple rules that describe the mechanical collapse, we come to the conclusion that a complete quantitative and qualitative description of a collapse sinkhole is possible, but for this it is necessary to take into account also the mechanical properties of the rock and the processes determining the mechanics of the collapses.

Evaluating the role of re-adsorption of dissolved Hg 2+ during cinnabar dissolution using isotope tracer technique

DOE PAGES

Jiang, Ping; Li, Yanbin; Liu, Guangliang; ...

2016-06-02

Cinnabar dissolution is an important factor controlling mercury (Hg) cycling. Recent studies have suggested the co-occurrence of re-adsorption of the released Hg during the course of cinnabar dissolution. However, there is a lack of feasible techniques that can quantitatively assess the amount of Hg re-adsorbed on cinnabar when investigating cinnabar dissolution. In this study, a new method, based on isotope tracing and dilution techniques, was developed to study the role of Hg re-adsorption in cinnabar dissolution. The developed method includes two key components: (1) accurate measurement of both released and spiked Hg in aqueous phase and (2) estimation of re-adsorbedmore » Hg on cinnabar surface via the reduction in spiked 202Hg 2+. By adopting the developed method, it was found that the released Hg for trials purged with oxygen could reach several hundred g L –1, while no significant cinnabar dissolution was detected under anaerobic condition. Cinnabar dissolution rate when considering Hg re-adsorption was approximately 2 times the value calculated solely with the Hg detected in the aqueous phase. Lastly, these results suggest that ignoring the Hg re-adsorption process can significantly underestimate the importance of cinnabar dissolution, highlighting the necessity of applying the developed method in future cinnabar dissolution studies.« less

A comparative pH-dissolution profile study of selected commercial levothyroxine products using inductively coupled plasma mass spectrometry.

PubMed

Pabla, Dimple; Akhlaghi, Fatemeh; Zia, Hossein

2009-05-01

Levothyroxine (T4) is a narrow therapeutic index drug with classic bioequivalence problem between various available products. Dissolution of a drug is a crucial step in its oral absorption and bioavailability. The dissolution of T4 from three commercial solid oral dosage forms: Synthroid (SYN), generic levothyroxine sodium by Sandoz Inc. (GEN) and Tirosint (TIR) was studied using a sensitive ICP-MS assay. All the three products showed variable and pH-dependent dissolution behaviors. The absence of surfactant from the dissolution media decreased the percent T4 dissolved for all the three products by 26-95% (at 30 min). SYN dissolution showed the most pH dependency, whereas GEN and TIR showed the fastest and highest dissolution, respectively. TIR was the most consistent one, and was minimally affected by pH and/or by the presence of surfactant. Furthermore, dissolution of T4 decreased considerably with increase in the pH, which suggests a possible physical interaction in patients concurrently on T4 and gastric pH altering drugs, such as proton pump inhibitors. Variable dissolution of T4 products can, therefore, impact the oral absorption and bioavailability of T4 and may result in bioequivalence problems between various available products.

Formulation and evaluation of a montelukast sodium orally disintegrating tablet with a similar dissolution profile as the marketed product.

PubMed

Chen, Yong; Feng, Tingting; Li, Yong; Du, Bin; Weng, Weiyu

2017-03-01

A major challenge of orally disintegrating tablet (ODT) development is predicting its bioequivalence to its corresponding marketed product. Therefore, comparing ODT dissolution profiles to those of the corresponding marketed product is very important. The objective of this study was to develop a 5.2-mg montelukast sodium (MS) ODT with a similar dissolution profile to that of the marketed chewable tablet. Dissolution profiles were examined in different media to screen each formulation. We found that MS dissolution from ODTs in acidic medium heavily depended on manufacturing methods. All MS ODTs prepared using direct compression rapidly disintegrated in acidic medium. However, dispersed MS powders aggregated into sticky masses, resulting in slow dissolution. In contrast, MS ODTs prepared using wet granulation had much faster dissolution rates in acidic medium with no obvious aggregation. Additionally, the optimized formulation, prepared using wet granulation, displayed similar dissolution profiles to the marketed reference in all four types of media examined (f 2  >   50). The in vitro disintegration time of the optimized ODT was 9.5 ± 2.4 s, which meets FDA requirements. In conclusion, the wet granulation preparation method of MS ODTs resulted in a product with equivalent dissolution profiles as those of the marketed product.

Dissolution Failure of Solid Oral Drug Products in Field Alert Reports.

PubMed

Sun, Dajun; Hu, Meng; Browning, Mark; Friedman, Rick L; Jiang, Wenlei; Zhao, Liang; Wen, Hong

2017-05-01

From 2005 to 2014, 370 data entries of dissolution failures of solid oral drug products were assessed with respect to the solubility of drug substances, dosage forms [immediate release (IR) vs. modified release (MR)], and manufacturers (brand name vs. generic). The study results show that the solubility of drug substances does not play a significant role in dissolution failures; however, MR drug products fail dissolution tests more frequently than IR drug products. When multiple variables were analyzed simultaneously, poorly water-soluble IR drug products failed the most dissolution tests, followed by poorly soluble MR drug products and very soluble MR drug products. Interestingly, the generic drug products fail dissolution tests at an earlier time point during a stability study than the brand name drug products. Whether the dissolution failure of these solid oral drug products has any in vivo implication will require further pharmacokinetic, pharmacodynamic, clinical, and drug safety evaluation. Food and Drug Administration is currently conducting risk-based assessment using in-house dissolution testing, physiologically based pharmacokinetic modeling and simulation, and post-market surveillance tools. At the meantime, this interim report will outline a general scheme of monitoring dissolution failures of solid oral dosage forms as a pharmaceutical quality indicator. Published by Elsevier Inc.

Impact of dissolution on the sedimentary record of the Paleocene-Eocene thermal maximum

NASA Astrophysics Data System (ADS)

Bralower, Timothy J.; Kelly, D. Clay; Gibbs, Samantha; Farley, Kenneth; Eccles, Laurie; Lindemann, T. Logan; Smith, Gregory J.

2014-09-01

The input of massive amounts of carbon to the atmosphere and ocean at the Paleocene-Eocene Thermal Maximum (PETM; ˜55.53 Ma) resulted in pervasive carbonate dissolution at the seafloor. At many sites this dissolution also penetrated into the underlying sediment column. The magnitude of dissolution at and below the seafloor, a process known as chemical erosion, and its effect on the stratigraphy of the PETM, are notoriously difficult to constrain. Here, we illuminate the impact of dissolution by analyzing the complete spectrum of sedimentological grain sizes across the PETM at three deep-sea sites characterized by a range of bottom water dissolution intensity. We show that the grain size spectrum provides a measure of the sediment fraction lost during dissolution. We compare these data with dissolution and other proxy records, electron micrograph observations of samples and lithology. The complete data set indicates that the two sites with slower carbonate accumulation, and less active bioturbation, are characterized by significant chemical erosion. At the third site, higher carbonate accumulation rates, more active bioturbation, and possibly winnowing have limited the impacts of dissolution. However, grain size data suggest that bioturbation and winnowing were not sufficiently intense to diminish the fidelity of isotopic and microfossil assemblage records.

Stirring effect on kaolinite dissolution rate

NASA Astrophysics Data System (ADS)

Metz, Volker; Ganor, Jiwchar

2001-10-01

Experiments were carried out measuring kaolinite dissolution rates using stirred and nonstirred flow-through reactors at pHs 2 to 4 and temperatures of 25°C, 50°C, and 70°C. The results show an increase of kaolinite dissolution rate with increasing stirring speed. The stirring effect is reversible, i.e., as the stirring slows down the dissolution rate decreases. The effect of stirring speed on kaolinite dissolution rate is higher at 25°C than at 50°C and 70°C and at pH 4 than at pHs 2 and 3. It is suggested that fine kaolinite particles are formed as a result of stirring-induced spalling or abrasion of kaolinite. These very fine particles have an increased ratio of reactive surface area to specific surface area, which results in enhancement of kaolinite dissolution rate. A balance between production and dissolution of the fine particles explains both the reversibility and the temperature and pH dependence of the stirring effect. Since the stirring effect on kaolinite dissolution rate varies with temperature and pH, measurement of kinetic parameters such as activation energy may be influenced by stirring. Therefore, standard use of nonagitated reaction vessels for kinetic experiments of mineral dissolution and precipitation is recommended, at least for slow reactions that are surface controlled.

Secondary calcification and dissolution respond differently to future ocean conditions

NASA Astrophysics Data System (ADS)

Silbiger, N. J.; Donahue, M. J.

2015-01-01

Climate change threatens both the accretion and erosion processes that sustain coral reefs. Secondary calcification, bioerosion, and reef dissolution are integral to the structural complexity and long-term persistence of coral reefs, yet these processes have received less research attention than reef accretion by corals. In this study, we use climate scenarios from RCP 8.5 to examine the combined effects of rising ocean acidity and sea surface temperature (SST) on both secondary calcification and dissolution rates of a natural coral rubble community using a flow-through aquarium system. We found that secondary reef calcification and dissolution responded differently to the combined effect of pCO2 and temperature. Calcification had a non-linear response to the combined effect of pCO2 and temperature: the highest calcification rate occurred slightly above ambient conditions and the lowest calcification rate was in the highest temperature-pCO2 condition. In contrast, dissolution increased linearly with temperature-pCO2 . The rubble community switched from net calcification to net dissolution at +271 μatm pCO2 and 0.75 °C above ambient conditions, suggesting that rubble reefs may shift from net calcification to net dissolution before the end of the century. Our results indicate that (i) dissolution may be more sensitive to climate change than calcification and (ii) that calcification and dissolution have different functional responses to climate stressors; this highlights the need to study the effects of climate stressors on both calcification and dissolution to predict future changes in coral reefs.

Secondary calcification and dissolution respond differently to future ocean conditions

NASA Astrophysics Data System (ADS)

Silbiger, N. J.; Donahue, M. J.

2014-09-01

Climate change threatens both the accretion and erosion processes that sustain coral reefs. Secondary calcification, bioerosion, and reef dissolution are integral to the structural complexity and long-term persistence of coral reefs, yet these processes have received less research attention than reef accretion by corals. In this study, we use climate scenarios from RCP8.5 to examine the combined effects of rising ocean acidity and SST on both secondary calcification and dissolution rates of a natural coral rubble community using a flow-through aquarium system. We found that secondary reef calcification and dissolution responded differently to the combined effect of pCO2 and temperature. Calcification had a non-linear response to the combined effect of pCO2-temperature: the highest calcification rate occurred slightly above ambient conditions and the lowest calcification rate was in the highest pCO2-temperature condition. In contrast, dissolution increased linearly with pCO2-temperature. The rubble community switched from net calcification to net dissolution at +272 μatm pCO2 and 0.84 °C above ambient conditions, suggesting that rubble reefs may shift from net calcification to net dissolution before the end of the century. Our results indicate that dissolution may be more sensitive to climate change than calcification, and that calcification and dissolution have different functional responses to climate stressors, highlighting the need to study the effects of climate stressors on both calcification and dissolution to predict future changes in coral reefs.

Insight into Flufenamic Acid Cocrystal Dissolution in the Presence of a Polymer in Solution: from Single Crystal to Powder Dissolution.

PubMed

Guo, Minshan; Wang, Ke; Qiao, Ning; Fábián, László; Sadiq, Ghazala; Li, Mingzhong

2017-12-04

Effects of three polymers, polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), and copolymer of vinylpyrrolidone/vinyl acetate (PVP-VA), on the dissolution behavior of the cocrystals of flufenamic acid with theophylline (FFA-TP CO) and nicotinamide (FFA-NIC CO) were investigated at multiple length scales. At the molecular level, the interactions of crystal surfaces with a polymer were analyzed by observing etching pattern changes using atomic force microscopy. At the macroscopic scale, dissolution rates of particular faces of a single crystal were determined by measurement of the physical retreat velocities of the faces using optical light microscopy. In the bulk experiments, the FFA concentration in a dissolution medium in the absence or presence of a polymer was measured under both sink and nonsink conditions. It has been found that the dissolution mechanisms of FFA-TP CO are controlled by the defect sites of the crystal surface and by precipitation of the parent drug FFA as individual crystals in the bulk fluid. In contrast, the dissolution mechanisms of FFA-NIC CO are controlled by surface layer removal and by a surface precipitation mechanism, where the parent drug FFA precipitates directly onto the surface of the dissolving cocrystals. Through controlling the dissolution environment by predissolving a polymer, PVP or PVP-VA, which can interact with the crystal surface to alter its dissolution properties, improved solubility, and dissolution rates of FFA-TP CO and FFA-NIC CO have been demonstrated.

Impact of vibration and agitation speed on dissolution of USP prednisone tablets RS and various IR tablet formulations.

PubMed

Seeger, Nicole; Lange, Sigrid; Klein, Sandra

2015-08-01

Dissolution testing is an in vitro procedure which is widely used in quality control (QC) of solid oral dosage forms and, given that real biorelevant test conditions are applied, can also be used as a predictive tool for the in vivo performance of such formulations. However, if a dissolution method is intended to be used for such purposes, it has to deliver results that are only determined by the quality of the test product, but not by other variables. In the recent past, more and more questions were arising on how to address the effects of vibration on dissolution test results. The present study was performed to screen for the correlation of prednisone dissolution of USP Prednisone Tablets RS with vibration caused by a commercially available vibration source as well as to investigate how drug release from a range of immediate release formulations containing class 1-4 drugs of the biopharmaceutical classification scheme is affected by vibration when performing dissolution experiments at different agitation rates. Results of the present study show that the dissolution process of oral drug formulations can be affected by vibration. However, it also becomes clear that the degree of which a certain level of vibration impacts dissolution is strongly dependent on several factors such as drug properties, formulation parameters, and the design of the dissolution method. To ensure the establishment of robust and predictive dissolution test methods, the impact of variation should thus be considered in method design and validation.

How does natural groundwater flow affect CO2 dissolution in saline aquifers?

NASA Astrophysics Data System (ADS)

Rosenzweig, R.; Michel-Meyer, I.; Tsinober, A.; Shavit, U.

2017-12-01

The dissolution of supercritical CO2 in aquifer brine is one of the most important trapping mechanisms in CO2 geological storage. Diffusion-limited dissolution is a very slow process. However, since the CO2-rich water is slightly denser than the CO2-free water, when CO2-free water is overlaid by heavier CO2-rich water, convective instability results in fingers of dense CO2-rich water that propagate downwards, causing CO2-unsaturated water to move upwards. This convection process significantly accelerates the dissolution rate of CO2 into the aquifer water.Most previous works have neglected the effect of natural groundwater flow and assumed it has no effect on the dissolution dynamics. However, it was found that in some of the saline aquifers groundwater flow rate, although small, is not zero. In this research, we study the effect of groundwater flow on dissolution by performing laboratory experiments in a bead pack cell using a mixture of methanol and ethylene-glycol as a CO2 analog while varying the water horizontal flow rate. We find that water horizontal flow decreases the number of fingers, their wavelength and their propagation velocity. When testing high water flow rates, no fingers were developed and the dissolution process was entirely diffusive. The effect of water flow on the dissolution rate did not show a clear picture. When increasing the horizontal flow rate the convective dissolution flux slightly decreased and then increased again. It seems that the combination of density-driven flow, water horizontal flow, mechanical dispersion and molecular diffusion affect the dissolution rate in a complex and non-monotonic manner. These intriguing dynamics should be further studied to understand their effect on dissolution trapping.

Investigating the Impact of Drug Crystallinity in Amorphous Tacrolimus Capsules on Pharmacokinetics and Bioequivalence Using Discriminatory In Vitro Dissolution Testing and Physiologically Based Pharmacokinetic Modeling and Simulation.

PubMed

Purohit, Hitesh S; Trasi, Niraj S; Sun, Dajun D; Chow, Edwin C Y; Wen, Hong; Zhang, Xinyuan; Gao, Yi; Taylor, Lynne S

2018-05-01

Delivering a drug in amorphous form in a formulated product is a strategy used to enhance the apparent solubility of a drug substance and its oral bioavailability. Drug crystallization in such products may occur during the manufacturing process or on storage, reducing the solubility advantage of the amorphous drug. However, the impact of partial drug crystallization in the drug product on the resulting bioavailability and pharmacokinetics is unknown. In this study, dissolution testing of commercial tacrolimus capsules (which are formulated to contain amorphous drug), both fresh and those containing different amounts of crystalline drug, was conducted using both United States Pharmacopeia and noncompendial dissolution tests with different dissolution media and volumes. A physiologically based pharmacokinetic (PBPK) absorption model was developed to predict the impact of crystallinity extent on the oral absorption of the products and to evaluate the discriminatory ability of the different dissolution methods. Virtual bioequivalence simulations between partially crystallized tacrolimus capsules versus fresh Prograf or generic tacrolimus capsules were performed using the PBPK model and in vitro dissolution data of the various fresh and partially crystallized capsules under United States Pharmacopeia and noncompendial dissolution conditions. The results suggest that compendial dissolution tests may not be sufficiently discriminatory with respect to the presence of crystallinity in an amorphous formulation. Nonsink dissolution tests using lower dissolution volumes generate more discriminatory profiles that predict different pharmacokinetics of tacrolimus capsules containing different extents of drug crystallinity. In conclusion, the PBPK modeling approach can be used to assess the impact of partial drug crystallinity in the formulated product and to guide the development of appropriate dissolution methods. Copyright © 2018 American Pharmacists Association®. All rights reserved.

Diatom species abundance and morphologically-based dissolution proxies in coastal Southern Ocean assemblages

NASA Astrophysics Data System (ADS)

Warnock, Jonathan P.; Scherer, Reed P.

2015-07-01

Taphonomic processes alter diatom assemblages in sediments, thus potentially negatively impacting paleoclimate records at various rates across space, time, and taxa. However, quantitative taphonomic data is rarely included in diatom-based paleoenvironmental reconstructions and no objective standard exists for comparing diatom dissolution in sediments recovered from marine depositional settings, including the Southern Ocean's opal belt. Furthermore, identifying changes to diatom dissolution through time can provide insight into the efficiency of both upper water column nutrient recycling and the biological pump. This is significant in that reactive metal proxies (e.g. Al, Ti) in the sediments only account for post-depositional dissolution, not the water column where the majority of dissolution occurs. In order to assess the range of variability of responses to dissolution in a typical Southern Ocean diatom community and provide a quantitative guideline for assessing taphonomic variability in diatoms recovered from core material, a sediment trap sample was subjected to controlled, serial dissolution. By evaluating dissolution-induced changes to diatom species' relative abundance, three preservational categories of diatoms have been identified: gracile, intermediate, and robust. The relative abundances of these categories can be used to establish a preservation grade for diatom assemblages. However, changes to the relative abundances of diatom species in sediment samples may reflect taphonomic or ecological factors. In order to address this complication, relative abundance changes have been tied to dissolution-induced morphological change to the areolae of Fragilariopsis curta, a significant sea-ice indicator in Southern Ocean sediments. This correlation allows differentiation between gracile species loss to dissolution versus ecological factors or sediment winnowing. These results mirror a similar morphological dissolution index from a parallel study utilizing Fragilariopsis kerguelensis, suggesting that results are applicable to a broad spectrum of diatoms typically preserved in the sediments.

Dissolution behavior of MgO based inert matrix fuel for the transmutation of minor actinides

NASA Astrophysics Data System (ADS)

Mühr-Ebert, E. L.; Lichte, E.; Bukaemskiy, A.; Finkeldei, S.; Klinkenberg, M.; Brandt, F.; Bosbach, D.; Modolo, G.

2018-07-01

This study explores the dissolution properties of magnesia-based inert matrix nuclear fuel (IMF) containing transuranium elements (TRU). Pure MgO pellets as well as MgO pellets containing CeO2, as surrogate for TRU oxides, and are considered as model systems for genuine magnesia based inert matrix fuel were fabricated. The aim of this study is to identify conditions at which the matrix material can be selectively dissolved during the head-end reprocessing step, allowing a separation of MgO from the actinides, whereas the actinides remain undissolved. The dissolution behavior was studied in macroscopic batch experiments as a function of nitric acid concentration, dissolution medium volume, temperature, stirring velocity, and pellet density (85, 90, 96, and 99%TD). To mimic pellets with various burn-ups the density of the here fabricated pellets was varied. MgO is soluble even under mild conditions (RT, 2.5 mol/L HNO3). The dissolution rates of MgO at different acid concentrations are rather similar, whereas the dissolution rate is strongly dependent on the temperature. Via a microscopic approach, a model was developed to describe the evolution of the pellet surface area during dissolution and determine a surface normalized dissolution rate. Moreover, dissolution rates of the inert matrix fuel containing CeO2 were determined as a function of the acid concentration and temperature. During the dissolution of MgO/CeO2 pellets the MgO dissolves completely, while CeO2 (>99%) remains undissolved. This study intends to provide a profound understanding of the chemical performance of magnesia based IMF containing fissile material. The feasibility of the dissolution of magnesia based IMF with nitric acid is discussed.

Dissolution of cinnabar (HgS) in the presence of natural organic matter

USGS Publications Warehouse

Waples, J.S.; Nagy, K.L.; Aiken, G.R.; Ryan, J.N.

2005-01-01

Cinnabar (HgS) dissolution rates were measured in the presence of 12 different natural dissolved organic matter (DOM) isolates including humic, fulvic, and hydrophobic acid fractions. Initial dissolution rates varied by 1.3 orders of magnitude, from 2.31 ?? 10-13 to 7.16 ?? 10-12 mol Hg (mg C)-1 m-2 s-1. Rates correlate positively with three DOM characteristics: specific ultraviolet absorbance (R2 = 0.88), aromaticity (R2 = 0.80), and molecular weight (R2 = 0.76). Three experimental observations demonstrate that dissolution was controlled by the interaction of DOM with the cinnabar surface: (1) linear rates of Hg release with time, (2) significantly reduced rates when DOM was physically separated from the surface by dialysis membranes, and (3) rates that approached constant values at a specific ratio of DOM concentration to cinnabar surface area, suggesting a maximum surface coverage by dissolution-reactive DOM. Dissolution rates for the hydrophobic acid fractions correlate negatively with sorbed DOM concentrations, indicating the presence of a DOM component that reduced the surface area of cinnabar that can be dissolved. When two hydrophobic acid isolates that enhanced dissolution to different extents were mixed equally, a 20% reduction in rate occurred compared to the rate with the more dissolution-enhancing isolate alone. Rates in the presence of the more dissolution-enhancing isolate were reduced by as much as 60% when cinnabar was prereacted with the isolate that enhanced dissolution to a lesser extent. The data, taken together, imply that the property of DOM that enhances cinnabar dissolution is distinct from the property that causes it to sorb irreversibly to the cinnabar surface. Copyright ?? 2005 Elsevier Ltd.

What controls silicon isotope fractionation during dissolution of diatom opal?

NASA Astrophysics Data System (ADS)

Wetzel, F.; de Souza, G. F.; Reynolds, B. C.

2014-04-01

The silicon isotope composition of opal frustules from photosynthesising diatoms is a promising tool for studying past changes in the marine silicon cycle, and indirectly that of carbon. Dissolution of this opal may be accompanied by silicon isotope fractionation that could disturb the pristine silicon isotope composition of diatom opal acquired in the surface ocean. It has previously been shown that dissolution of fresh and sediment trap diatom opal in seawater does fractionate silicon isotopes. However, as the mechanism of silicon isotope fractionation remained elusive, it is uncertain whether opal dissolution in general is associated with silicon isotope fractionation considering that opal chemistry and surface properties are spatially and temporally (i.e. opal of different age) diverse. In this study we dissolved sediment core diatom opal in 5 mM NaOH and found that this process is not associated with significant silicon isotope fractionation. Since no variability of the isotope effect was observed over a wide range of dissolution rates, we can rule out the suggestion that back-reactions had a significant influence on the net isotope effect. Similarly, we did not observe an impact of temperature, specific surface area, or degree of undersaturation on silicon isotope partitioning during dissolution, such that these can most likely also be ruled out as controlling factors. We discuss the potential impacts of the chemical composition of the dissolution medium and age of diatom opal on silicon isotope fractionation during dissolution. It appears most likely that the controlling mechanism of silicon isotope fractionation during dissolution is related to the reactivity, or potentially, aluminium content of the opal. Such a dependency would imply that silicon isotope fractionation during dissolution of diatom opal is spatially and temporally variable. However, since the isotope effects during dissolution are small, the silicon isotope composition of diatom opal appears to be robust against dissolution in the deep sea sedimentary environment.

Evaluation of various dissolution media for predicting in vivo performance of class I and II drugs.

PubMed

Galia, E; Nicolaides, E; Hörter, D; Löbenberg, R; Reppas, C; Dressman, J B

1998-05-01

In this paper we seek to verify the differences in dissolution behavior between class I and class II drugs and to evaluate the suitability of two new physiologically based media, of Simulated Gastric Fluid (SGF) and of milk for their ability to forecast trends in the in vivo performance of class II compounds and their formulations. Dissolution behavior of two class I drugs, i.e. acetaminophen and metoprolol, and of three class II drugs, i.e. danazol, mefenamic acid and ketoconazole, was studied with USP Apparatus 2 in water, SGF, milk, Simulated Intestinal Fluid without pancreatin (SIFsp) and in two media simulating the small intestinal contents in the fed (FeSSIF) and fasted (FaSSIF) states, respectively. Class I powders dissolved rapidly in all media tested. Acetaminophen dissolution in milk was slow from one tablet formulation, in all other cases dissolution was more than 85% complete in 15 minutes. The dissolution rate of metoprolol was shown to be dependent on formulation and manufacturing method, and one of the three tablet formulations did not meet compendial specifications (80%/30 minutes). Dissolution behavior of class II drugs was greatly affected by choice of medium. Dissolution from a capsule formulation of danazol proved to be dependent on the concentration of solubilizing agents, with a the 30-fold increase in percentage dissolved within 90 minutes upon changing from aqueous media without surfactants to FaSSIF. Use of FeSSIF or milk as the dissolution medium resulted in an even greater increase in percentage dissolved, 100 and 180-fold respectively. Dissolution of the weak acid mefenamic acid from a capsule formulation is dependent on both pH and bile salt concentration, which leads to an offset between increased bile salt concentration and lower pH in the fed state compared to the fasted state medium. The weak base ketoconazole showed complete dissolution from a tablet formulation in Simulated Gastric Fluid without pepsin (SGFsp) within 30 minutes, 70% dissolution in 2 hours under fed state simulated upper jejunal conditions but only 6% dissolution in 2 hours under fasted state conditions. As predicted, dissolution of class II drugs proved to be in general much more dependent on the medium than class I drugs. With the array of compendial and physiological media available, it should be possible to design a suitable set of tests to predict the in vivo dissolution of both class I and II drugs from immediate release formulations.

Experimental studies of alunite: II. Rates of alunite-water alkali and isotope exchange

USGS Publications Warehouse

Stoffregen, R.E.; Rye, R.O.; Wasserman, M.D.

1994-01-01

Rates of alkali exchange between alunite and water have been measured in hydrothermal experiments of 1 hour to 259 days duration at 150 to 400??C. Examination of run products by scanning electron microscope indicates that the reaction takes place by dissolution-reprecipitation. This exchange is modeled with an empirical rate equation which assumes a linear decrease in mineral surface area with percent exchange (f) and a linear dependence of the rate on the square root of the affinity for the alkali exchange reaction. This equation provides a good fit of the experimental data for f = 17% to 90% and yields log rate constants which range from -6.25 moles alkali m-2s-1 at 400??C to - 11.7 moles alkali m-2s-1 at 200??C. The variation in these rates with temperature is given by the equation log k* = -8.17(1000/T(K)) + 5.54 (r2 = 0.987) which yields an activation energy of 37.4 ?? 1.5 kcal/mol. For comparison, data from O'Neil and Taylor (1967) and Merigoux (1968) modeled with a pseudo-second-order rate expression give an activation energy of 36.1 ?? 2.9 kcal/mol for alkali-feldspar water Na-K exchange. In the absence of coupled alkali exchange, oxygen isotope exchange between alunite and water also occurs by dissolution-reprecipitation but rates are one to three orders of magnitude lower than those for alkali exchange. In fine-grained alunites, significant D-H exchange occurs by hydrogen diffusion at temperatures as low as 100??C. Computed hydrogen diffusion coefficients range from -15.7 to -17.3 cm2s-1 and suggest that the activation energy for hydrogen diffusion may be as low as 6 kcal/mol. These experiments indicate that rates of alkali exchange in the relatively coarse-grained alunites typical of hydrothermal ore deposits are insignificant, and support the reliability of K-Ar age data from such samples. However, the fine-grained alunites typical of low temperature settings may be susceptible to limited alkali exchange at surficial conditions which could cause alteration of their radiometric ages. Furthermore, the rapid rate of hydrogen diffusion observed at 100-150??C suggests that fine-grained alunites are susceptible to rapid D-H re-equilibration even at surficial conditions. ?? 1994.

Accounting for the Effect of Noncondensing Gases on Interphasic Heat and Mass Transfer in the Two-Fluid Model Used in the KORSAR Code

NASA Astrophysics Data System (ADS)

Yudov, Yu. V.

2018-03-01

A model is presented of the interphasic heat and mass transfer in the presence of noncondensable gases for the KORSAR/GP design code. This code was developed by FGUP NITI and the special design bureau OKB Gidropress. It was certified by Rostekhnadzor in 2009 for numerical substantiation of the safety of reactor installations with VVER reactors. The model is based on the assumption that there are three types of interphasic heat and mass transfer of the vapor component: vapor condensation or evaporation on the interphase under any thermodynamic conditions of the phases, pool boiling of the liquid superheated above the saturation temperature at the total pressure, and spontaneous condensation in the volume of gas phase supercooled below the saturation temperature at the vapor partial pressure. Condensation and evaporation on the interphase continuously occur in a two-phase flow and control the time response of the interphase heat and mass transfer. Boiling and spontaneous condensation take place only at the metastable condition of the phases and run at a quite high speed. The procedure used for calculating condensation and evaporation on the interphase accounts for the combined diffusion and thermal resistance of mass transfer in all regimes of the two-phase flow. The proposed approach accounts for, in a natural manner, a decrease in the rate of steam condensation (or generation) in the presence of noncondensing components in the gas phase due to a decrease (or increase) in the interphase temperature relative to the saturation temperature at the vapor partial pressure. The model of the interphase heat transfer also accounts for the processes of dissolution or release of noncondensing components in or from the liquid. The gas concentration at the interphase and on the saturation curve is calculated by the Henry law. The mass transfer coefficient in gas dissolution is based on the heat and mass transfer analogy. Results are presented of the verification of the interphase heat and mass transfer used in the KORSAR/GP code based on the data on film condensation of steam-air flows in vertical pipes. The proposed model was also tested by solving a problem of nitrogen release from a supersaturated water solution.

Simulation of acid mine drainage generation around Küre VMS Deposits, Northern Turkey

NASA Astrophysics Data System (ADS)

Demirel, Cansu; Kurt, Mehmet Ali; Çelik Balci, Nurgül

2015-04-01

This study investigated comparative leaching characteristics of acidophilic bacterial strains under shifting environmental conditions at proposed two stages as formation stage or post acidic mine drainage (AMD) generation. At the first stage, initial reactions associated with AMD generation was simulated in shaking flasks containing massive pyritic chalcopyrite ore by using a pure strain Acidithiobacillus ferrooxidans and a mixed culture of Acidithiobacillus sp. mostly dominated by A. ferrooxidans and A. thiooxidans at 26oC. At the second stage, long term bioleaching experiments were carried out with the same strains at 26oC and 40oC to investigate the leaching characteristics of pyritic chalcopyrite ore under elevated heavy metal and temperature conditions. During the experiments, physicochemical characteristics (e.i. Eh, pH, EC) metal (Fe, Co, Cu, Zn) and sulfate concentration of the experimental solution were monitored during 180 days. Significant acid generation and sulfate release were determined during bioleaching of the ore by mixed acidophilic cultures containing both iron and sulfur oxidizers. In the early stage of the experiments, heavy metal release from the ore was caused by generation of acid due to accelerated bacterial oxidation of the ore. Generally high concentrations of Co and Cu were released into the solution from the experiments conducted by pure cultures of Acidithiobacillus ferrooxidans whereas high Zn and Fe was released into the solution from the mixed culture experiments. In the later stage of AMD generation and post AMD, chemical oxidation is accelerated causing excessive amounts of contamination, even exceeding the amounts resulted from bacterial oxidation by mixed cultures. Acidithibacillus ferrooxidans was found to be more effective in leaching Cu, Fe and Co at higher temperatures in contrary to mixed acidophiles that are more prone to operate at optimal moderate conditions. Moreover, decreasing Fe values are noted in bioleaching experiments with mixed acidophiles at higher temperatures. Further depleted Fe(III) values coinciding with decreasing pH may point to precipitation of secondary phases (i.e. jarosite). This study revealed that the metals (Fe, Cu, Co and Zn) released during short term leaching of the ore (34 days) are generally caused by acid produced by dissolution reactions rather than oxidation. In the long term experiments a more complex biogeochemical reactions (oxidation and dissolution) take place in conjunction. Key words: Bioleaching, AMD, heavy metal release, environment, acidophilic bacteria, Küre copper ore deposits, volcanogenic massive sulfide deposits

Privileged Girls: The Place of Femininity and Femininity in Place

ERIC Educational Resources Information Center

Fahey, Johannah

2014-01-01

Constructions of femininity and attendant notions of feminism are being produced in different ways in different places around the world. This is a complicated global process that cannot be reduced to analyses that take place in nation states. This paper seeks to respond to and enhance Angela McRobbie's compelling argument about understandings of…

In vitro results with special plastics for biodegradable endoureteral stents.

PubMed

Schlick, R W; Planz, K

1998-10-01

Internal ureteral stents are widely used in urologic practice for temporary urinary diversion, but all double-J catheters to date exhibit the same disadvantage; that is, they have to be removed endoscopically, necessitating further intervention. We tested different materials (designated G100X-15xLB and G100X-20xLB) to develop a biodegradable (biodissolvable) endoureteral stent that can be held in place without functional loss yet could be dissolved by changing the environment. The principle of the biochemical background is based on the physiological milieu of the urine. The plastics tested are stable in acidic and dissolve in alkaline conditions. In a first step, specimens of two polymers were placed in artificial urine of different pH over a period of 60 days and monitored for integrity (solution trial). In a second step, artificial urine was set in motion (744 mL/24 hours) an infusion pump (Volumed microVP 5000; Fresenius AG, Bad Homburg vdH, Germany) through an infusion set in which a 30-cm piece of the materials to test had been placed (ureter model). Below the inserted specimen, the lumen of the infusion tube was minimized to make obstruction by fragments more possible. In the solution trial, all specimens remained stable under physiologic conditions (pH 5.2) over a period of at least 30 days. The specimens dissolved completely when the pH was adjusted to an alkaline one (pH 7.9). In the ureter model, with pH values of 7.9, all specimens were decomposed after 20 hours, and no occlusion of the model occurred. Using acidic artificial urine, the specimens remained stable with a smooth consistent surface. The dissolution was not a standard chemical one; the materials broke into microscopically small pieces, with fragments of G100X-20xLB being smaller than those of G100X-15xLB. Our first in vitro results show that the tested materials are suitable for further development of biodissolvable endoureteral stents, dissolution of which can be steered by changing the urinary pH.

Evaluating Primary Dendrite Trunk Diameters in Directionally Solidified Al-Si Alloys

NASA Technical Reports Server (NTRS)

Grugel, R. N.; Tewari, S. N.; Poirier, D. R.

2014-01-01

The primary dendrite trunk diameters of Al-Si alloys that were directionally solidified over a range of processing conditions have been measured. These data are analyzed with a model based primarily on an assessment of secondary dendrite arm dissolution in the mushy zone. Good fit with the experimental data is seen and it is suggested that the primary dendrite trunk diameter is a useful metric that correlates well with the actual solidification processing parameters. These results are placed in context with the limited results from the aluminium - 7 wt. % silicon samples directionally solidified aboard the International Space Station as part of the MICAST project.

Redox buffered hydrofluoric acid etchant for the reduction of galvanic attack during release etching of MEMS devices having noble material films

DOEpatents

Hankins, Matthew G [Albuquerque, NM

2009-10-06

Etchant solutions comprising a redox buffer can be used during the release etch step to reduce damage to the structural layers of a MEMS device that has noble material films. A preferred redox buffer comprises a soluble thiophosphoric acid, ester, or salt that maintains the electrochemical potential of the etchant solution at a level that prevents oxidation of the structural material. Therefore, the redox buffer preferentially oxidizes in place of the structural material. The sacrificial redox buffer thereby protects the exposed structural layers while permitting the dissolution of sacrificial oxide layers during the release etch.

31 CFR 353.83 - Reissue or payment on dissolution of corporation or partnership.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 31 Money and Finance:Treasury 2 2011-07-01 2011-07-01 false Reissue or payment on dissolution of... Reissue or payment on dissolution of corporation or partnership. (a) Corporations. A bond registered in the name of a private corporation which is in the process of dissolution will be paid to the...

31 CFR 315.83 - Reissue or payment on dissolution of corporation or partnership.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 31 Money and Finance: Treasury 2 2014-07-01 2014-07-01 false Reissue or payment on dissolution of... and Officers § 315.83 Reissue or payment on dissolution of corporation or partnership. (a) Corporations. A bond registered in the name of a private corporation which is in the process of dissolution...

31 CFR 353.83 - Reissue or payment on dissolution of corporation or partnership.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 31 Money and Finance:Treasury 2 2013-07-01 2013-07-01 false Reissue or payment on dissolution of... Reissue or payment on dissolution of corporation or partnership. (a) Corporations. A bond registered in the name of a private corporation which is in the process of dissolution will be paid to the...

31 CFR 315.83 - Reissue or payment on dissolution of corporation or partnership.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 31 Money and Finance: Treasury 2 2010-07-01 2010-07-01 false Reissue or payment on dissolution of... and Officers § 315.83 Reissue or payment on dissolution of corporation or partnership. (a) Corporations. A bond registered in the name of a private corporation which is in the process of dissolution...

31 CFR 353.83 - Reissue or payment on dissolution of corporation or partnership.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 31 Money and Finance:Treasury 2 2012-07-01 2012-07-01 false Reissue or payment on dissolution of... Reissue or payment on dissolution of corporation or partnership. (a) Corporations. A bond registered in the name of a private corporation which is in the process of dissolution will be paid to the...

5 CFR 2634.408 - Special filing requirements for qualified trusts.

Code of Federal Regulations, 2011 CFR

2011-01-01

... with § 2634.301(d). (3) Dissolution of the trust. Within thirty days of the dissolution of a qualified trust: (i) File a report of the dissolution with the Director of the Office of Government Ethics; and (ii) File with the Director a list of assets of the trust at the time of the dissolution, categorized...

31 CFR 353.83 - Reissue or payment on dissolution of corporation or partnership.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 31 Money and Finance: Treasury 2 2010-07-01 2010-07-01 false Reissue or payment on dissolution of... Reissue or payment on dissolution of corporation or partnership. (a) Corporations. A bond registered in the name of a private corporation which is in the process of dissolution will be paid to the...

26 CFR 1.6043-1 - Return regarding corporate dissolution or liquidation.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 26 Internal Revenue 13 2010-04-01 2010-04-01 false Return regarding corporate dissolution or... dissolution or liquidation. (a) Requirement of returns. Within 30 days after the adoption of any resolution or plan for or in respect of the dissolution of a corporation or the liquidation of the whole or any part...

31 CFR 315.83 - Reissue or payment on dissolution of corporation or partnership.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 31 Money and Finance:Treasury 2 2011-07-01 2011-07-01 false Reissue or payment on dissolution of... and Officers § 315.83 Reissue or payment on dissolution of corporation or partnership. (a) Corporations. A bond registered in the name of a private corporation which is in the process of dissolution...

31 CFR 315.83 - Reissue or payment on dissolution of corporation or partnership.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 31 Money and Finance:Treasury 2 2012-07-01 2012-07-01 false Reissue or payment on dissolution of... and Officers § 315.83 Reissue or payment on dissolution of corporation or partnership. (a) Corporations. A bond registered in the name of a private corporation which is in the process of dissolution...

31 CFR 353.83 - Reissue or payment on dissolution of corporation or partnership.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 31 Money and Finance: Treasury 2 2014-07-01 2014-07-01 false Reissue or payment on dissolution of... Reissue or payment on dissolution of corporation or partnership. (a) Corporations. A bond registered in the name of a private corporation which is in the process of dissolution will be paid to the...

31 CFR 315.83 - Reissue or payment on dissolution of corporation or partnership.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 31 Money and Finance:Treasury 2 2013-07-01 2013-07-01 false Reissue or payment on dissolution of... and Officers § 315.83 Reissue or payment on dissolution of corporation or partnership. (a) Corporations. A bond registered in the name of a private corporation which is in the process of dissolution...

5 CFR 2634.408 - Special filing requirements for qualified trusts.

Code of Federal Regulations, 2012 CFR

2012-01-01

... with § 2634.301(d). (3) Dissolution of the trust. Within thirty days of the dissolution of a qualified trust: (i) File a report of the dissolution with the Director of the Office of Government Ethics; and (ii) File with the Director a list of assets of the trust at the time of the dissolution, categorized...

Taking the metabolic pulse of the world's coral reefs.

PubMed

Cyronak, Tyler; Andersson, Andreas J; Langdon, Chris; Albright, Rebecca; Bates, Nicholas R; Caldeira, Ken; Carlton, Renee; Corredor, Jorge E; Dunbar, Rob B; Enochs, Ian; Erez, Jonathan; Eyre, Bradley D; Gattuso, Jean-Pierre; Gledhill, Dwight; Kayanne, Hajime; Kline, David I; Koweek, David A; Lantz, Coulson; Lazar, Boaz; Manzello, Derek; McMahon, Ashly; Meléndez, Melissa; Page, Heather N; Santos, Isaac R; Schulz, Kai G; Shaw, Emily; Silverman, Jacob; Suzuki, Atsushi; Teneva, Lida; Watanabe, Atsushi; Yamamoto, Shoji

2018-01-01

Worldwide, coral reef ecosystems are experiencing increasing pressure from a variety of anthropogenic perturbations including ocean warming and acidification, increased sedimentation, eutrophication, and overfishing, which could shift reefs to a condition of net calcium carbonate (CaCO3) dissolution and erosion. Herein, we determine the net calcification potential and the relative balance of net organic carbon metabolism (net community production; NCP) and net inorganic carbon metabolism (net community calcification; NCC) within 23 coral reef locations across the globe. In light of these results, we consider the suitability of using these two metrics developed from total alkalinity (TA) and dissolved inorganic carbon (DIC) measurements collected on different spatiotemporal scales to monitor coral reef biogeochemistry under anthropogenic change. All reefs in this study were net calcifying for the majority of observations as inferred from alkalinity depletion relative to offshore, although occasional observations of net dissolution occurred at most locations. However, reefs with lower net calcification potential (i.e., lower TA depletion) could shift towards net dissolution sooner than reefs with a higher potential. The percent influence of organic carbon fluxes on total changes in dissolved inorganic carbon (DIC) (i.e., NCP compared to the sum of NCP and NCC) ranged from 32% to 88% and reflected inherent biogeochemical differences between reefs. Reefs with the largest relative percentage of NCP experienced the largest variability in seawater pH for a given change in DIC, which is directly related to the reefs ability to elevate or suppress local pH relative to the open ocean. This work highlights the value of measuring coral reef carbonate chemistry when evaluating their susceptibility to ongoing global environmental change and offers a baseline from which to guide future conservation efforts aimed at preserving these valuable ecosystems.

Impact and oxidation of single silver nanoparticles at electrode surfaces: one shot versus multiple events† †Electronic supplementary information (ESI) available: Summary of previous studies; Ag NP characterization: TEM and DLS; event duration histogram; maximum current histogram. See DOI: 10.1039/c6sc04483b Click here for additional data file.

PubMed Central

Kang, Minkyung; Bullions, Erin

2017-01-01

Single nanoparticle (NP) electrochemical impacts is a rapidly expanding field of fundamental electrochemistry, with applications from electrocatalysis to electroanalysis. These studies, which involve monitoring the electrochemical (usually current–time, I–t) response when a NP from solution impacts with a collector electrode, have the scope to provide considerable information on the properties of individual NPs. Taking the widely studied oxidative dissolution of individual silver nanoparticles (Ag NPs) as an important example, we present measurements with unprecedented noise (< 5 pA) and time resolution (time constant 100 μs) that are highly revealing of Ag NP dissolution dynamics. Whereas Ag NPs of diameter, d = 10 nm are mostly dissolved in a single event (on the timescale of the measurements), a wide variety of complex processes operate for NPs of larger diameter (d ≥ 20 nm). Detailed quantitative analysis of the I–t features, consumed charge, event duration and impact frequency leads to a major conclusion: Ag NPs undergo sequential partial stripping (oxidative dissolution) events, where a fraction of a NP is electrochemically oxidized, followed by the NP drifting away and back to the tunnelling region before the next partial stripping event. As a consequence, analysis of the charge consumed by single events (so-called “impact coulometry”) cannot be used as a general method to determine the size of colloidal NPs. However, a proper analysis of the I–t responses provides highly valuable information on the transient physicochemical interactions between NPs and polarized surfaces. PMID:28553474

Taking the metabolic pulse of the world’s coral reefs

PubMed Central

Andersson, Andreas J.; Langdon, Chris; Albright, Rebecca; Bates, Nicholas R.; Caldeira, Ken; Carlton, Renee; Corredor, Jorge E.; Dunbar, Rob B.; Enochs, Ian; Erez, Jonathan; Eyre, Bradley D.; Gattuso, Jean-Pierre; Gledhill, Dwight; Kayanne, Hajime; Kline, David I.; Koweek, David A.; Lantz, Coulson; Lazar, Boaz; Manzello, Derek; McMahon, Ashly; Meléndez, Melissa; Page, Heather N.; Santos, Isaac R.; Schulz, Kai G.; Shaw, Emily; Silverman, Jacob; Suzuki, Atsushi; Teneva, Lida; Watanabe, Atsushi; Yamamoto, Shoji

2018-01-01

Worldwide, coral reef ecosystems are experiencing increasing pressure from a variety of anthropogenic perturbations including ocean warming and acidification, increased sedimentation, eutrophication, and overfishing, which could shift reefs to a condition of net calcium carbonate (CaCO3) dissolution and erosion. Herein, we determine the net calcification potential and the relative balance of net organic carbon metabolism (net community production; NCP) and net inorganic carbon metabolism (net community calcification; NCC) within 23 coral reef locations across the globe. In light of these results, we consider the suitability of using these two metrics developed from total alkalinity (TA) and dissolved inorganic carbon (DIC) measurements collected on different spatiotemporal scales to monitor coral reef biogeochemistry under anthropogenic change. All reefs in this study were net calcifying for the majority of observations as inferred from alkalinity depletion relative to offshore, although occasional observations of net dissolution occurred at most locations. However, reefs with lower net calcification potential (i.e., lower TA depletion) could shift towards net dissolution sooner than reefs with a higher potential. The percent influence of organic carbon fluxes on total changes in dissolved inorganic carbon (DIC) (i.e., NCP compared to the sum of NCP and NCC) ranged from 32% to 88% and reflected inherent biogeochemical differences between reefs. Reefs with the largest relative percentage of NCP experienced the largest variability in seawater pH for a given change in DIC, which is directly related to the reefs ability to elevate or suppress local pH relative to the open ocean. This work highlights the value of measuring coral reef carbonate chemistry when evaluating their susceptibility to ongoing global environmental change and offers a baseline from which to guide future conservation efforts aimed at preserving these valuable ecosystems. PMID:29315312

Dissolution of realgar by Acidithiobacillus ferrooxidans in the presence and absence of zerovalent iron: Implications for remediation of iron-deficient realgar tailings.

PubMed

Fan, Lijun; Zhao, Fenghua; Liu, Jing; Hudson-Edwards, Karen A

2018-06-06

Realgar (As 4 S 4 )-rich tailings are iron-deficient arsenical mine wastes. The mechanisms and products of the dissolution of realgar by Acidithiobacillus ferrooxidans (A. ferrooxidans) in the presence (0.2 g and 2 g) and absence of zerovalent iron (ZVI) are investigated for three stages (each of 7 d with fresh A. ferrooxidans medium addition between the stages). SEM-EDX, FTIR, XPS and selective extraction analysis are used to characterize the solid-phase during the experiments. ZVI addition causes the systems to become more acid-generating, although pH increases are observed in the first day due to ZVI dissolution. Arsenic is released to solution due to realgar oxidation (∼30 mg L -1 in the 0 g ZVI system in Stage I), but low concentrations are observed in the ZVI-added systems (<5 mg L -1 ) and in Stages II and III of the 0 g ZVI system. As(III) dominates the released As(T) at day 1 (83-89% of As(T)), but is largely oxidized to As(V) at day 7 of each stage (53-98% of As(T)). Arsenic attenuation is attributed to the formation of mixed As-Fe oxyhydroxides and oxyhydroxy sulfates that take up released arsenic and are abundant in the 2.0 g ZVI system, and to passivation of the realgar surface. Consequently, a new strategy that combines A. ferrooxidans and exogenous ZVI addition for treating in-situ iron-deficient realgar-rich tailings is proposed, although its long-term effects need to be monitored. Copyright © 2018 Elsevier Ltd. All rights reserved.

Lyophilic matrix method for dissolution and release studies of nanoscale particles.

PubMed

Pessi, Jenni; Svanbäck, Sami; Lassila, Ilkka; Hæggström, Edward; Yliruusi, Jouko

2017-10-25

We introduce a system with a lyophilic matrix to aid dissolution studies of powders and particulate systems. This lyophilic matrix method (LM method) is based on the ability to discriminate between non-dissolved particles and the dissolved species. In the LM method the test substance is embedded in a thin lyophilic core-shell matrix. This permits rapid contact with the dissolution medium while minimizing dispersion of non-dissolved particles without presenting a substantial diffusion barrier. The method produces realistic dissolution and release results for particulate systems, especially those featuring nanoscale particles. By minimizing method-induced effects on the dissolution profile of nanopowders, the LM method overcomes shortcomings associated with current dissolution tests. Copyright © 2017 Elsevier B.V. All rights reserved.

Carbon in oxides and silicates - Dissolution versus exsolution

NASA Technical Reports Server (NTRS)

Freund, F.

1986-01-01

A theory of CO2 dissolution in the solid state is developed, using the idea proposed by Freund (1983) concerning dissolution of CO/CO2 in MgO on the basis of their experimental results obtained with an MgO-containing carbon impurity. It is shown that the dissolution mechanism may be linked to an internal redox reaction by which a certain number of lattice oxygens change their formal oxidation state from -2 to -1, while the carbon becomes reduced. The similarities between the mechanisms of CO and/or CO2 dissolution and that of H2O dissolution are pointed out. A hypothesis is proposed concerning the exsolution of reduced carbon from supersaturated solid solutions under conditions which permit C-C bond formation.

Designing for Inter-Organizational Coordination in Indonesia’s Maritime Domain

DTIC Science & Technology

2014-12-01

the-week distribution (Figure 24), the concentration of accidents appears to take place Tuesday tln·ough Saturday, with the percentage well above 13...incidents. Meanwhile, the peak takes place on Tuesday to Thursday as shown in the Figure 51 below. Figure 51. Violations at sea time wheel (Data from...outlook: Southeast Asia 2008–2009. Singapore: ISEAS Publishing. Larsen, Richard J. & Marx, Morris L. (1981). An introduction to mathematical

Thermodynamics of water intrusion in nanoporous hydrophobic solids.

PubMed

Cailliez, Fabien; Trzpit, Mickael; Soulard, Michel; Demachy, Isabelle; Boutin, Anne; Patarin, Joël; Fuchs, Alain H

2008-08-28

We report a joint experimental and molecular simulation study of water intrusion in silicalite-1 and ferrerite zeolites. The main conclusion of this study is that water condensation takes place through a genuine first-order phase transition, provided that the interconnected pores structure is 3-dimensional. In the extreme confinement situation (ferrierite zeolite), condensation takes place through a continuous transition, which is explained by a shift of both the first-order transition line and the critical point with increasing confinement. The present findings are at odds with the common belief that conventional phase transitions cannot take place in microporous solids such as zeolites. The most important features of the intrusion/extrusion process can be understood in terms of equilibrium thermodynamics considerations. We believe that these findings are very general for hydrophobic solids, i.e. for both nonwetting as well as wetting water-solid interface systems.

Cabbage Patch Chemistry.

ERIC Educational Resources Information Center

Journal of Chemical Education, 2000

2000-01-01

This activity takes students through the process of fermentation. Requires an entire month for the full reaction to take place. The reaction, catalyzed by bacterial enzymes, produces lactic acid from glucose. (SAH)

In-life pteropod shell dissolution as an indicator of past ocean carbonate saturation

NASA Astrophysics Data System (ADS)

Wall-Palmer, Deborah; Smart, Christopher W.; Hart, Malcolm B.

2013-12-01

Recent concern over the effects of ocean acidification upon calcifying organisms has highlighted the aragonitic shelled thecosomatous pteropods as being at a high risk. Both in-situ and laboratory studies have shown that an increased dissolved CO2 concentration, leading to decreased water pH and low carbonate concentration, causes reduced calcification rates and enhanced dissolution in the shells of living pteropods. In fossil records unaffected by post-depositional dissolution, this in-life shell dissolution can be detected. Here we present the first evidence of variations of in-life pteropod shell dissolution due to variations in surface water carbonate concentration during the Late Pleistocene by analysing the surface layer of pteropod shells in marine sediment cores from the Caribbean Sea and Indian Ocean. In-life shell dissolution was determined by applying the Limacina Dissolution Index (LDX) to the sub-tropical pteropod Limacina inflata. Average shell size information shows that high in-life dissolution is accompanied by smaller shell sizes in L. inflata, which may indicate a reduction in calcification rate. Comparison of the LDX profile to Late Pleistocene Vostok atmospheric CO2 concentrations, shows that in-life pteropod dissolution is closely associated to variations in past ocean carbonate saturation. This study confirms the findings of laboratory studies, showing enhanced shell dissolution and reduced calcification in living pteropods when surface ocean carbonate concentrations were lower. Results also demonstrate that oceanic pH levels that were less acidic and changing less rapidly than those predicted for the 21st Century, negatively affected pteropods during the Late Pleistocene.

Insight into the Development of Dissolution Media for BCS Class II Drugs: A Review from Quality Control and Prediction of In Vivo Performance Perspectives.

PubMed

Wu, Chunnuan; Liu, Yan; He, Zhonggui; Sun, Jin

2016-01-01

To assess in vivo behavior through in vitro method, the dissolution test is mostly used, both for quality control (QC) and for development purpose. In view of the fact that a dissolution test can hardly achieve two goals at the same time, the design of dissolution testing generally varies along with the development stage of drug products and therefore the selection of dissolution media may change with the goals of the dissolution test. To serve the QC purpose, a dissolution medium is designed to provide a sink condition; for development purpose, the dissolution medium is required to simulate the physiological conditions in the gastrointestinal tract as far as possible. In this review, we intended to provide an initial introduction to the various dissolution media applied for QC and formulation development purposes for poorly water soluble drugs. We focused on these methods like addition of cosolvents, surfactants and utilization of biphasic media, applied to provide sink conditions which are difficult to be achieved by simple aqueous buffers for lipophilic drugs, and introduced the development of physiologically relevant media for human and animals like dog and rat with respect to the choice of buffers, bile salts, lipids and so on. In addition, we further discussed the influence of biorelevant dissolution media on the modification of drug Biopharmaceutical Classification System (BCS) classification, especially for BCS class II drugs with low solubility and high permeability, the solubility of which is relatively sensitive to the presence of bile salts and lipids.

Acoustic activation of water-in-oil microemulsions for controlled salt dissolution.

PubMed

Baxamusa, Salmaan; Ehrmann, Paul; Ong, Jemi

2018-06-18

The dynamic nature of the oil-water interface allows for sequestration of material within the dispersed domains of a microemulsion. Microstructural changes should therefore change the dissolution rate of a solid surface in a microemulsion. We hypothesize that microstructural changes due to formulation and cavitation in an acoustic field will enable control over solid dissolution rates. Water-in-oil microemulsions were formulated using cyclohexane, water, Triton X-100, and hexanol. The microstructure and solvation properties of Winsor Type IV formulations were characterized. Dissolution rates of KH 2 PO 4 (KDP), were measured. A kinetic analysis isolated the effect of the microstructure, and rate enhancements due to cavitation effects on the microstructure were characterized by measuring dissolution rates in an ultrasonic field. Dispersed aqueous domains of 2-6 nm radius dissolve a solid block of KDP at 0-10 nm/min. Dissolution rate is governed not by the domain-surface collision frequency but rather by a dissolution probability per domain-surface encounter. Higher probabilities are correlated with larger domains. Rapid and reversible dissolution rate increases of up to 270× were observed under ultrasonic conditions, with <20% of the increase due to bulk heating effects. The rest is attributed to cavitation-induced changes to the domain microstructure, providing a simple method for remotely activating and de-activating dissolution. Copyright © 2018 Elsevier Inc. All rights reserved.

Upper Cretaceous Shannon Sandstone Reservoirs, Powder River Basin, Wyoming: Evidence for organic acid diagenesis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hansley, P.L.; Nuccio, V.F.

Comparison of the petrology of shallow and deep oil reservoirs in the Upper Cretaceous Shannon Sandstone Beds of the Steele Member of the Cody Shale strongly suggests that organic acids have had a more significant impact on the diagenetic alteration of aluminosilicate grains and carbonate cements in the deep reservoirs than in the shallow reservoirs. In shallow reservoirs, detrital grains exhibit minor dissolution, sparse and small overgrowths, and secondary porosity created by dissolution of early calcite cement. However, deeper sandstones are characterized by extensive dissolution of detrital K-feldspar and detrital glauconite grains, and precipitation of abundant, large quartz and feldsparmore » overgrowths. Throughout the Shannon and Steele, dissolution of glauconite and degradation of kerogen were probably aided by clay mineral/organic catalysis, which caused simultaneous reduction of iron and oxidation of kerogen. This process resulted in release of ferrous iron and organic acids and was promoted in the deep reservoirs by higher formation temperatures accounting for more extensive dissolution of aluminosilicate grains. Carbonic acid produced from the dissolution of early calcite cement, decarboxylation of organic matter, and influx of meteoric water after Laramide uplift produced additional dissolution of cements and grains. Dissolution by organic acids and complexing by organic acid anions, however, best explain the intensity of diagenesis and absence of dissolution products in secondary pores and on etched surfaces of framework grains in deep reservoirs.« less

Effect of oxalate on the dissolution rates of oligoclase and tremolite (journal version)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mast, M.A.; Drever, J.I.

1987-01-01

The effect of oxalate, a strong chelator for Al and other cations, on the dissolution rates of oligoclase feldspar and tremolite amphibole was investigated in a flow-through reactor at 22 deg C. Oxalate at concentrations of 0.5 and 1 mM has essentially no effect on the dissolution rate of tremolite, nor on the steady-state rate of release of Si from oligoclase. The fact that oxalate has no effect on dissolution rate suggests that detachment of Si rather than Al or Mg is the rate-limiting step. At pH 4 and 9, oxalate has no effect on the steady-state rate of releasemore » of Al, and dissolution is congruent. At pH 5 and 7, oligoclase dissolution is congruent in the presence of oxalate, but in the absence of oxalate Al is preferentially retained in the solid relative to Si. The rate of dissolution of tremolite is independent of pH over the pH range 2-5, and decreases at higher pH. The rate of dissolution of oligoclase was independent of pH over the pH range 4-9. Since the dissolution rate of these minerals is independent of pH and organic ligand concentration, the effect of acid deposition from the atmosphere on the rate of supply of cations from weathering of granitic rocks should be minor.« less

Dissolution properties of co-amorphous drug-amino acid formulations in buffer and biorelevant media.

PubMed

Heikkinen, A T; DeClerck, L; Löbmann, K; Grohganz, H; Rades, T; Laitinen, R

2015-07-01

Co-amorphous formulations, particularly binary drug-amino acid mixtures, have been shown to provide enhanced dissolution for poorly-soluble drugs and improved physical stability of the amorphous state. However, to date the dissolution properties (mainly intrinsic dissolution rate) of the co-amorphous formulations have been tested only in buffers and their supersaturation ability remain unexplored. Consequently, dissolution studies in simulated intestinal fluids need to be conducted in order to better evaluate the potential of these systems in increasing the oral bioavailability of biopharmaceutics classification system class II drugs. In this study, solubility and dissolution properties of the co-amorphous simvastatin-lysine, gibenclamide-serine, glibenclamide-threonine and glibenclamide-serine-threonine were studied in phosphate buffer pH 7.2 and biorelevant media (fasted and fed state simulated intestinal fluids (FaSSIF and FeSSIF, respectively)). The co-amorphous formulations were found to provide a long-lasting supersaturation and improve the dissolution of the drugs compared to the crystalline and amorphous drugs alone in buffer. Similar improvement, but in lesser extent, was observed in biorelevant media suggesting that a dissolution advantage observed in aqueous buffers may overestimate the advantage in vivo. However, the results show that, in addition to stability advantage shown earlier, co-amorphous drug-amino acid formulations provide dissolution advantage over crystalline drugs in both aqueous and biorelevant conditions.

Citrate, not phosphate, can dissolve calcium oxalate monohydrate crystals and detach these crystals from renal tubular cells.

PubMed

Chutipongtanate, Somchai; Chaiyarit, Sakdithep; Thongboonkerd, Visith

2012-08-15

Dissolution therapy of calcium oxalate monohydrate (COM) kidney stone disease has not yet been implemented due to a lack of well characterized COM dissolution agents. The present study therefore aimed to identify potential COM crystal dissolution compounds. COM crystals were treated with deionized water (negative control), 5 mM EDTA (positive control), 5 mM sodium citrate, or 5mM sodium phosphate. COM crystal dissolution activities of these compounds were evaluated by phase-contrast and video-assisted microscopic examinations, semi-quantitative analysis of crystal size, number and total mass, and spectrophotometric oxalate-dissolution assay. In addition, effects of these compounds on detachment of COM crystals, which adhered tightly onto renal tubular cell surface, were also investigated. The results showed that citrate, not phosphate, had a significant dissolution effect on COM crystals as demonstrated by significant reduction of crystal size (approximately 37% decrease), crystal number (approximately 53% decrease) and total crystal mass (approximately 72% decrease) compared to blank and negative controls. Spectrophotometric oxalate-dissolution assay successfully confirmed the COM crystal dissolution property of citrate. Moreover, citrate could detach up to 85% of the adherent COM crystals from renal tubular cell surface. These data indicate that citrate is better than phosphate for dissolution and detachment of COM crystals. Copyright © 2012 Elsevier B.V. All rights reserved.

Understanding and predicting the impact of critical dissolution variables for nifedipine immediate release capsules by multivariate data analysis.

PubMed

Mercuri, A; Pagliari, M; Baxevanis, F; Fares, R; Fotaki, N

2017-02-25

In this study the selection of in vivo predictive in vitro dissolution experimental set-ups using a multivariate analysis approach, in line with the Quality by Design (QbD) principles, is explored. The dissolution variables selected using a design of experiments (DoE) were the dissolution apparatus [USP1 apparatus (basket) and USP2 apparatus (paddle)], the rotational speed of the basket/or paddle, the operator conditions (dissolution apparatus brand and operator), the volume, the pH, and the ethanol content of the dissolution medium. The dissolution profiles of two nifedipine capsules (poorly soluble compound), under conditions mimicking the intake of the capsules with i. water, ii. orange juice and iii. an alcoholic drink (orange juice and ethanol) were analysed using multiple linear regression (MLR). Optimised dissolution set-ups, generated based on the mathematical model obtained via MLR, were used to build predicted in vitro-in vivo correlations (IVIVC). IVIVC could be achieved using physiologically relevant in vitro conditions mimicking the intake of the capsules with an alcoholic drink (orange juice and ethanol). The multivariate analysis revealed that the concentration of ethanol used in the in vitro dissolution experiments (47% v/v) can be lowered to less than 20% v/v, reflecting recently found physiological conditions. Copyright © 2016 Elsevier B.V. All rights reserved.

Evaluating the role of re-adsorption of dissolved Hg(2+) during cinnabar dissolution using isotope tracer technique.

PubMed

Jiang, Ping; Li, Yanbin; Liu, Guangliang; Yang, Guidi; Lagos, Leonel; Yin, Yongguang; Gu, Baohua; Jiang, Guibin; Cai, Yong

2016-11-05

Cinnabar dissolution is an important factor controlling mercury (Hg) cycling. Recent studies have suggested the co-occurrence of re-adsorption of the released Hg during the course of cinnabar dissolution. However, there is a lack of feasible techniques that can quantitatively assess the amount of Hg re-adsorbed on cinnabar when investigating cinnabar dissolution. In this study, a new method, based on isotope tracing and dilution techniques, was developed to study the role of Hg re-adsorption in cinnabar dissolution. The developed method includes two key components: (1) accurate measurement of both released and spiked Hg in aqueous phase and (2) estimation of re-adsorbed Hg on cinnabar surface via the reduction in spiked (202)Hg(2+). By adopting the developed method, it was found that the released Hg for trials purged with oxygen could reach several hundred μgL(-1), while no significant cinnabar dissolution was detected under anaerobic condition. Cinnabar dissolution rate when considering Hg re-adsorption was approximately 2 times the value calculated solely with the Hg detected in the aqueous phase. These results suggest that ignoring the Hg re-adsorption process can significantly underestimate the importance of cinnabar dissolution, highlighting the necessity of applying the developed method in future cinnabar dissolution studies. Copyright © 2016 Elsevier B.V. All rights reserved.