Dissolution Constants Research Articles

Molecular and Functional Characterization of Three General Odorant-Binding Protein 2 Genes in Cydia pomonella (Lepidoptera: Tortricidae).

General odorant-binding proteins (GOBPs) play a crucial role in the detection of host plant volatiles and pheromones by lepidopterans. Previous studies identified two duplications in the GOBP2 gene in Cydia pomonella. In this study, we employed qRT-PCR, protein purification, and fluorescence competitive binding assays to investigate the functions of three GOBP2 genes in C. pomonella. Our findings reveal that CpomGOBP2a and CpomGOBP2b are specifically highly expressed in antennae, while CpomGOBP2c exhibits high specific expression in wings, suggesting a potential divergence in their functions. Recombinant proteins of CpomGOBP2a, CpomGOBP2b, and CpomGOBP2c were successfully expressed and purified, enabling an in-depth exploration of their functions. Competitive binding assays with 20 host plant volatiles and the sex pheromone (codlemone) demonstrated that CpomGOBP2a exhibits strong binding to four compounds, namely butyl octanoate, ethyl (2E,4Z)-deca-2,4-dienoate (pear ester), codlemone, and geranylacetone, with corresponding dissolution constants (Ki) of 8.59993 μM, 9.14704 μM, 22.66298 μM, and 22.86923 μM, respectively. CpomGOBP2b showed specific binding to pear ester (Ki = 17.37481 μM), while CpomGOBP2c did not exhibit binding to any tested compounds. In conclusion, our results indicate a functional divergence among CpomGOBP2a, CpomGOBP2b, and CpomGOBP2c. These findings contribute valuable insights for the development of novel prevention and control technologies and enhance our understanding of the evolutionary mechanisms of olfactory genes in C. pomonella.

A thin-film modeling approach for analysis of carbon capture sorbent-based devices

The threat of climate change has driven scientists and engineers to develop new methods reducing carbon emitted as well as capturing CO2 from the atmosphere and other point sources. Carbon capture technology is still in its infancy and requires significant system efficiency improvements before commercial or industrial adoption is not cost prohibitive. Contactor designs must optimize capture efficiency while minimizing pumping losses through this stage, and typical contactors employ a packing material that is wetted with a fluid spray to create a film. The capture efficiency is determined by a complex relationship of operating parameters, contactor geometry, and the chemical kinetics of the CO2 and chosen capture fluid. Due in part to the large parameter space, as well as the physical difficulty of accurately determining capture efficiency, numerical modeling has become an important tool in research and development of contactors for carbon capture. Historically, modeling approaches used for CO2 capture simulations have been too computationally intensive for design work. This work examines the effectiveness of using a thin-film approximation approach to model the reacting fluid, thus avoiding the expensive grid resolution requirements of the volume-of-fluid (VOF) method. Results showed that changes in the reaction model and dissolution constants have a significant impact in the capture efficiency predictions. CO2 capture was largely dictated by the supply of MEA in the film, with capture efficiency reductions as MEA was depleted. Changes in gas temperatures and velocities also had some impact in the CO2 mass transfer. Overall the results validation shows that in a non-flooded contactor, the thin-film approximation is capable of predicting experimental results with sufficient accuracy. Therefore, this model can be used to quickly evaluate contactor designs.

Corrosion Rate of Steel in Liquid Zn, Zn-Bi and Zn-Sn Baths

In the hot dip galvanizing process, steel products are immersed in a liquid zinc bath. The contact of steel with liquid zinc causes the corrosion of the steel as a result of Fe dissolution processes in the liquid. If the dissolution process is carried out in a controlled manner, it results in the formation of a coating. Uncontrolled dissolution leads to the degradation of the steel surface. This article presents the results of research into the influence of Bi and Sn additions to zinc baths on the corrosion of steel in liquid zinc. Corrosion tests were carried out under conditions of kinetic dissolution using the rotating disc method. The kinetic dissolution constants of steel with different Si contents in Zn, Zn-0.5Bi and Zn-2Sn baths were determined. It was found that the addition of Bi and Sn lowers the value of the dissolution constant and may act as an inhibitor of Fe dissolution in liquid zinc. Based on the measurements and the determined value of the dissolution constant, the activation energy of kinetic dissolution was determined. It was found that in the temperature range of 440–480 °C, the addition of Bi and Sn increases the value of dissolution activation energy, which reduces the intensity of Fe transfer to the zinc bath.

Reactive Transport Modeling during Uranium In Situ Leaching (ISL): The Effects of Ore Composition on Mining Recovery

Unconsolidated sandstone uranium deposits exploited by the in situ leaching (ISL) method, contain complex tetravalent and hexavalent uranium compounds, mostly as UO2 and UO3 oxides that have different dissolution rates in sulfuric acid solutions. This work investigates a reactive transport model that takes into account the dissolution of both UO2 and UO3 in sulfuric acid solution together with possible interactions with rock minerals during the ISL uranium extraction. Several empirical reaction rate constants were determined during lab experiments on uranium extraction assays, including dissolution rates of tetravalent and hexavalent uranium oxides, and the dissolution rate of rock components by sulfuric acid solution. Effects on the recovery of solution flow rates and ratios between tetravalent and hexavalent uranium compounds are also investigated. The experimental dissolution constants were then used in the proposed reactive transport model to be applied to a real case study in Kazakhstan for comparing the 16 months history matching of an exploitation block consisting of 18 well injectors and 4 producers. The obtained numerical results show good agreement with empirical data gathered during exploitation.

Chemosensory protein 4 is required for Bradysia odoriphaga to be olfactory attracted to sulfur compounds released from Chinese chives.

Bradysia odoriphaga (Diptera: Sciaridae) is a serious pest of Chinese chives cultivated in China. Chemosensory proteins (CSPs) are important components of insect olfactory systems that capture and bind environmental semiochemicals which are then transported to olfactory receptors. Despite their importance, the mechanism of olfaction and related behavioral processes in B. odoriphaga have not been characterized. Here, we found that BodoCSP4 has an important olfactory function. RT-qPCR indicated that BodoCSP4 expression was highest in the heads (antennae removed) of adult males, followed by the antennae of adult males. Competitive binding assays with 33 ligands indicated that BodoCSP4 binds well with methyl allyl disulfide, diallyl disulfide, and n-heptadecane; the corresponding dissolution constants (Ki) were as high as 5.71, 5.71, and 6.85 μM, respectively. 3D-structural and molecular docking indicated that BodoCSP4 has five α-helices and surrounds the ligand with certain hydrophobic residues including Leu60, Leu63, Leu64, Ala67, Val28, Ile30, Ile33, Leu34, and Val86, suggesting these residues help BodoCSP4 bind to ligands. Silencing of BodoCSP4 significantly decreased the attraction of B. odoriphaga males to diallyl disulfide and n-heptadecane but not to methyl allyl disulfide in Y-tube olfaction assays. These results increase our understanding of how BodoCSP4 contributes to host and female localization by B. odoriphaga males.

Influence of Agitator Geometry in the Dissolution Kinetics of a Spherical Solid

An experimental study has been performed in order to establish both the effect of the agitator geometry and the agitation rate onthe dissolution kinetics of spherical candies. To do so, the dissolution constants were determined in aqueous solution by way ofthe Hixson-Crowell model on three types of agitators, namely, a paddle agitator of two blades, and two turbine agitators of four andsix blades respectively. Subsequently, for a fixed agitation rate the temperature was varied in order to experimentally determine theactivation energy for each agitator. It was found that while the geometry of the agitator has an effect on the pre-exponential factorsof the dissolution constant, the activation energy remains constant. Finally, differences on the dissolution constants as a functionof the angular frequency of the agitator were also found.

Function and Characterization Analysis of BodoOBP8 from Bradysia odoriphaga (Diptera: Sciaridae) in the Recognition of Plant Volatiles and Sex Pheromones.

Simple SummaryBradysia odoriphaga (Diptera: Sciaridae) is an important underground pest in Chinese chives. Chemical pesticides are the main prevention and control method, however, but this method not only leads to the increase of the insect’s resistance, but also causes pesticide residues and pollutes the environment. Previous studies have shown that olfaction plays a crucial role in the recognition of plant volatiles and sex pheromones, but the mechanism of olfactory action is still unclear. In the present study, Real-time PCR (qRT-PCR) analysis revealed that BodoOBP8 was highly expressed in the antennae of both sexes, and speculated that it is very likely to participate in the olfactory process. Then we used prokaryotic expression, fluorescence competitive binding, homology modeling, and molecular docking to prove its olfactory function. The results of this study increase our understanding of the binding of BodoOBP8 with plant volatiles and sex pheromone, facilitating the development of novel ways to control B. odoriphaga.The belowground pest Bradysia odoriphaga (Diptera: Sciaridae) has a sophisticated and sensitive olfactory system to detect semiochemical signals from the surrounding environment. In particular, odorant-binding proteins (OBPs) are crucial in capturing and transporting these semiochemical signals across the sensilla lymph to the corresponding odorant receptors. In this study, we cloned a full-length cDNA sequence of BodoOBP8 from B. odoriphaga. Real-time PCR (qRT-PCR) analysis revealed that BodoOBP8 has the highest expression levels in males, with more pronounced expression in the male antennae than in other tissues. In this study, the recombinant protein BodoOBP8 was successfully expressed by a bacterial system to explore its function. Competitive binding assays with 33 host plant volatiles and one putative sex pheromone (n-heptadecane) revealed that purified BodoOBP8 strongly bound to two sulfur compounds (methyl allyl disulfide and diallyl disulfide) and to n-heptadecane; the corresponding dissolution constants (Ki) were 4.04, 6.73, and 4.04 μM, respectively. Molecular docking indicated that Ile96, Ile103, Ala107, and Leu111, located in the hydrophobic cavity of BodoOBP8, are the key residues mediating the interaction of BodoOBP8 with two sulfur compounds (methyl allyl disulfide and diallyl disulfide) and n-heptadecane. These results show that BodoOBP8 plays a role in the recognition of plant volatiles and sex pheromones, suggesting its application as a molecular target for the screening of B. odoriphaga attractants and repellents and facilitating a new mechanism of B. odoriphaga control.

Molecular and Binding Characteristics of OBP5 of Bradysia odoriphaga (Diptera: Sciaridae).

Odorant-binding proteins (OBPs) capture and transport semiochemicals to olfactory receptors (OR) and function in the first step in insect olfaction. In the present study, we cloned a full-length cDNA sequence of BodoOBP5 from the insect pest Bradysia odoriphaga (Diptera: Sciaridae). Real-time PCR (qRT-PCR) analysis revealed that BodoOBP5 was expressed at higher levels in female adults than in other developmental stages. In the different tissues, BodoOBP5 was highly expressed in the female antennae, whereas low levels were expressed in the head and the male antennae, expression was negligible in other tissues. The recombinant protein of BodoOBP5 was successfully expressed with a bacterial system. Competitive binding assays with nine host plant volatiles and a putative sex pheromone revealed that purified BodoOBP5 strongly bound to two sulfur compounds (methyl allyl disulfide and diallyl disulfide); the corresponding dissolution constants (Ki) were 10.38 and 9.23 μM, respectively. Molecular docking indicated that Leu99, Leu103, Ala143, Tyr107, Phe142, and Trp144 in the hydrophobic cavity of BodoOBP5 are the key residues mediating the interaction of BodoOBP5 with methyl allyl disulfide and diallyl disulfide. RNAi-based Y-tube olfactometer assay indicated that there is no significant difference in methyl allyl disulfide and diallyl disulfide. The results of this study increase our understanding of the binding of BodoOBP5 with plant volatiles, facilitating the development of novel ways to control B. odoriphaga.

Zero Stress Aging of Glass and Carbon Fibers in Water and Oil—Strength Reduction Explained by Dissolution Kinetics

Understanding the strength degradation of glass and carbon fibers due to exposure to liquids over time is important for structural applications. A model has been developed for glass fibers that links the strength reduction in water to the increase of the Griffith flaw size of the fibers. The speed of the increase is determined by regular chemical dissolution kinetics of glass in water. Crack growth and strength reduction can be predicted for several water temperatures and pH, based on the corresponding dissolution constants. Agreement with experimental results for the case of water at 60 °C with a pH of 5.8 is reasonably good. Carbon fibers in water and toluene and glass fibers in toluene do not chemically react with the liquid. Subsequently no strength degradation is expected and will be confirmed experimentally. All fiber strength measurements are carried out on bundles. The glass fibers are R-glass.

Long-term Water-rock Interaction in the Bohemian Cretaceous Basin (Central Europe): Field Evidence and Modelling

Two models of reversible and irreversible water – mineral interaction are developed to simulate geochemical evolution of old groundwater in the Cenomanian and Turonian sandstone aquifers in the Bohemian Cretaceous Basin in Central Europe. The kinetic constants of dissolution and equilibrium constants of reversible reactions are results of laboratory experiments published in literature. Reactive surface areas of minerals are calculated. The model simulates the evolution of the chemical composition of groundwater whose age was derived from isotopic data. The results are compared to the chemical composition of groundwater along the trajectory of the prevailing flow. The model represents the interaction between groundwater and sandstones containing quartz, amorphous silica, a mixture of clay minerals, calcite and traces of residual feldspars. The three processes of water rock interaction are the irreversible dissolution of feldspars and carbonate, aluminium and silica equilibrium. The composition of groundwater in the Cenomanian aquifer with a confined water table is a result of geochemical evolution during the last 26,000 years, while the groundwater in the Turonian aquifer with a free water table is a mixture of old groundwater and recent water infiltrated from the surface. The proposed models are applicable to confined aquifers with residual rock matrix derived from granitic rocks decomposed by weathering without mixing of waters of different ages.

Development of multifunctional films for peripheral nerve regeneration.

This manuscript focuses on the development of multifunctional degradable polymer films that provide topographic cues for guided growth, surface gradients of growth factors as well as nanoparticles in the films for tunable release of growth factors to enable peripheral nerve regeneration. The combination of cues was designed to overcome limitations of current strategies to facilitate peripheral nerve regeneration. These multifunctional films successfully provided high protein loading capacities while persevering activity, protein gradients on the surface, and tunable release of bioactive nerve growth factor that promoted directional and guided neurite extension of PC12 cells of up to 10μm in 2days. These multifunctional films can be made into conduits for peripheral nerve regeneration.

Effect of trace metal‐limited growth on the postmortem dissolution of the marine diatom Pseudo‐nitzschia delicatissima

AbstractWe investigated the effects of iron (Fe) and copper (Cu) limitations on biogenic silica (bSiO2) dissolution kinetics of the marine diatom Pseudo‐nitzschia delicatissima during a 3 week batch dissolution experiment. The dissolution of this species was faster during the first week than thereafter. Modeling results from four dissolution models and scanning electron microcopy images suggested the successive dissolution of two phases of bSiO2, with two different dissolution constants. Micronutrient limitation during growth affected the respective proportion of the two phases and their dissolution constants. After 3 weeks of dissolution, frustules from micronutrient‐limited diatoms were better preserved than those of replete cells. Our results also confirm that micronutrient‐limited cells may export more Si relative to N than replete cells and may increase the silicate pump: This may not only be due to a higher degree of silicification of the live cells but also to a decoupling between the recycling of Si and N during dissolution. We suggest that a mechanistic understanding of the evolution of the dissolution constant during dissolution is needed. This would improve the parameterization of dissolution in ecosystem models, and ultimately their predictions on the amount of bSiO2 that dissolves in the photic zone, and the amount of bSiO2 that is exported to the seafloor.

Enhanced Lithium-Sulfur Battery By Amine-Functionalized Cathode and Kinetic Study of Polysulfides Dissolution

Lithium-Sulfur battery is very attractive due to its high energy density of 2500 Wh/kg or 2800 Wh/L. The low cost of Sulfur ($0.02/g) provides a significant driving force to obtain a commercial Li-S battery. But their practical use is still hindered by several issues including capacity fading, short lifespan, and low efficiency. The dissolution of long-chain lithium polysulfides (Li2Sx, 2 < x < 8) (LiPS) into the electrolyte and the shuttling of polysulfides between cathode and anode have been generally considered responsible for the capacity degradation. A variety of methods have been applied to prevent the dissolution of LiPS, most of which focus on physical trapping by using carbon matrix as barrier materials. However, the effect of barrier materials is kinetics; LiPS physically trapped in carbon host will eventually leach into the electrolyte. Also, the nonpolar carbon matrix will facilitate the detachment of LiPS, which is highly polar, from the cathode, resulting in loss of active materials. Thus thermal sequestering of LiPS via chemical binding and a polar cathode surface is desired. Herein, we report a facile approach towards high-performance sulfur-carbon cathodes by stabilizing LiPS on amine-functionalized cathode. Specifically, Polyethylenimine (PEI) is chosen for the reason that it possesses a large amount of amine groups within a molecular. PEI is attached to the cathode by reacting with hydroxyl functionalized carbon nanotubes (Figure 1). The strong affinity of LiPS to PEI-functionalized CNT is verified by DFT calculation, showing high binding energy of 1.23 eV, while it is 0.34eV between LiPS and graphene and 0.83eV between LiPS and PVDF. The interaction is also confirmed by FTIR, XPS, and other characterization techniques. With the merits of CNT such as good conductivity and robust mechanical properties, the nanocomposite of amine-functionalized CNT and sulfur exhibits stable cycling performance with high capacities (Figure 1). Furthermore, the kinetic study of polysulfides dissolution is carefully carried out. The dissolution constant k is determined by the method described in Figure 2. k is obtained for cathodes with various compositions: (1) Li2S4 without PEI; (2) Li2S4 with PEI; (3) Li2S9 without PEI; (4) Li2S9 with PEI. By comparing dissolution constants in each case, the much stronger affinity of PEI with the LiPS can be observed with smaller k. Also, the higher solubility and dissolution rate are found with increasing chain length of LiPS. The equilibrium concentration (ceq) of LiPS in the electrolyte is found, where LiPS has equal chemical potential in the electrolyte and cathode. This guides us in adding LiPS with concentration of ceqto the electrolyte when designing Li-S batteries. In this case, LiPS will not leach into the electrolyte since there is no driving force in the condition of equilibrium. The battery performance will be presented in the talk. In summary, the new method takes advantage of the numerous amine groups in PEI and the strong affinity with LiPS to realize a high performance Li-S battery. The systematical kinetic study also reveals the working mechanism and paves the way to further rational design of Li-S battery. Figure 1

Impact of sodium dodecyl sulphate on the dissolution of poorly soluble drug into biorelevant medium from drug-surfactant discs

The purpose was to elucidate the mechanism of action of sodium dodecyl sulphate (SDS) on drug dissolution from discs under physiologically relevant conditions. The effect of incorporating SDS (4-30%, w/w) and drug into discs on the dissolution constant and solubility were evaluated for the poorly soluble drugs griseofulvin and felodipine in a biorelevant dissolution medium (BDM). Dissolution constants from dissolution profiles of drug discs with and without SDS were measured using miniaturized rotating disc dissolution. Solid state changes were investigated by X-ray diffraction. Solubility was determined using HPLC-UV. The interaction between micelles in BDM and SDS was investigated by isothermal titration calorimetry and dynamic light scattering. Isothermal titration calorimetry showed that SDS formed mixed micelles with bile salt:phospholipid (BS:PC) micelles in BDM. Dynamic light scattering showed that the addition of SDS made the BS:PC micelles grow up to 2.5 times in volume. As a function of SDS addition, the dissolution constant showed an apparent exponential increase, while drug solubility showed a weak linear dependence. The pronounced effect on dissolution constant with SDS in the discs is not caused by an increased surface area as SDS dissolves, micelles in the bulk medium or changes in the solid state properties of the drugs. The proposed mechanism involves a high local concentration of SDS at the solid-liquid interface as SDS dissolves and this solubilizes the drug. The improved solubility at the solid-liquid interface provided a much steeper concentration gradient resulted in a faster dissolution. The total amount of SDS in the discs only gave a minor increase in total surfactant concentration in the dissolution medium and did therefore not to any large extent affect the drug solubility in the bulk.

Release mechanism and parameter estimation in drug-eluting stent systems: analytical solutions of drug release and tissue transport

Drug-eluting stents have significantly improved the treatment of coronary artery disease. They offer reduced rates of restenosis compared with their bare-metal predecessors and are the current gold standard in percutaneous coronary interventions. Drug-eluting stents have been approved for use in humans since 2002 and yet, despite the intensive research activity over the past decade, the drug release mechanism(s) and the uptake into the arterial wall are still poorly understood. While stent manufacturers have focussed primarily on empirical methods, several mathematical models have appeared in the literature considering the release problem, the uptake problem and also the coupled problem. However, two significant challenges that remain are in understanding the drug release mechanism(s) and also the determination of the various parameters characterizing the system. These include drug diffusion coefficients and dissolution constants in the stent polymer coating as well as drug diffusion coefficients, binding/uptake rates and the magnitude of the transmural convection in the arterial wall. In this paper we attempt to address these problems. We provide analytical solutions which, when compared with appropriate experiments, may allow the various parameters of the system to be estimated via the inverse problem. The analytical solutions which we provide here for drug release in vitro may thus be used as a tool for providing insights into the mechanism(s) of release.

Ni Enrichment and Stability of Al-Free Garnierite Solid-Solutions: A Thermodynamic Approach

AbstractGarnierites represent significant Ni ore minerals in the many Ni-laterite deposits worldwide. The occurrence of a variety of garnierite minerals with variable Ni content poses questions about the conditions of their formation. From an aqueous-solution equilibrium thermodynamic point of view, the present study examines the conditions that favor the precipitation of a particular garnierite phase and the mechanism of Ni-enrichment, and gives an explanation to the temporal and spatial succession of different garnierite minerals in Ni-laterite deposits. The chemical and structural characterization of garnierite minerals from many nickel laterite deposits around the world show that this group of minerals is formed essentially by an intimate intermixing of three Mg-Ni phyllosilicate solid solutions: serpentine-népouite, kerolite-pimelite, and sepiolite-falcondoite, without or with very small amounts of Al in their composition. The present study deals with garnierites which are essentially Al-free. The published experimental dissolution constants for Mg end-members of the above solid solutions and the calculated constants for pure Ni end-members were used to calculate Lippmann diagrams for the three solid solutions, on the assumption that they are ideal. With the help of these diagrams, congruent dissolution of Ni-poor primary minerals, followed by equilibrium precipitation of Ni-rich secondary phyllosilicates, is proposed as an efficient mechanism for Ni supergene enrichment in the laterite profile. The stability fields of the solid solutions were constructed using [log aSiO2(aq), log ((aMg2+aNi2+)/(aH+)2)] (predominance) diagrams. These, combined with Lippmann diagrams, give an almost complete chemical characterization of the solution and the precipitating phase(s) in equilibrium. The temporal and spatial succession of hydrous Mg- Ni phyllosilicates encountered in Ni-laterite deposits is explained by the small mobility of silica and the increase in its activity.

GaAs micromachining in the 1 H2SO4:1 H2O2:8 H2O system. From anisotropy to simulation

The bulk micromachining on (010), (110) and (111)A GaAs substrates in the 1 H 2 SO 4 :1 H 2 O 2 :8 H 2 O system is investigated. Focus is placed on anisotropy of 3D etching shapes with a special emphasis on convex and concave undercuts which are of prime importance in the wet micromachining of mechanical structures. Etched structures exhibit curved contours and more and less rounded sidewalls showing that the anisotropy is of type 2. This anisotropy can be conveniently described by a kinematic and tensorial model. Hence, a database composed of dissolution constants is further determined from experiments. A self-elaborated simulator which works with the proposed database is used to derive theoretical 3D shapes. Simulated shapes agree well with observed shapes of microstructures. The successful simulations open up two important applications for MEMS: CAD of mask patterns and meshing of simulated shapes for FEM simulation tools.

Effect of metal ions on the in vitro availability of enoxacin, its in vivo implications, kinetic and antibacterial studies

The present paper describes the effect of metals ions on the in vitro availability of enoxacin (a second generation quinolone antibiotic) owing to drug-metal interaction. These interaction studies were performed at 37 °C in different pH environments simulating human body compartments and were studied by UV spectroscopic technique. In order to determine the probability of these reactions different kinetic parameters (dissolution constants (K) and free energy change (ΔG)) for these reactions were also calculated. It is proposed that the structure of enoxacin contains various electron donating sites which facilitate its binding with metallic cations forming chelates. Hence taking food products, nutritional supplements or multivitamins containing multivalent cations at the same time as enoxacin, could reduce the absorption of the drug into the circulation and thus would decrease the effectiveness of the drug. In addition, the MIC of enoxacin for various microorganisms before and after interaction with metal ions was calculated which in most cases was increased which possibly could impair the clinical efficacy of the drug.

Factors Influencing Drug Dissolution Characteristic from Hydrophilic Polymer Matrix Tablet

The aim of this work was to investigate the factors influencing the dissolution characteristics of drug substances from hydrophilic polymer matrix tablets. Various kinds of cellulose derivative polymers were used in for matrix formation. Their swelling propertiesy waswere measured. The effects on drug release was firstly carried were studiedout in comparison with lactose. Results showedindicate that drug release characteristics from polymer matrix tablets followed a Higuchi square root time kinetics. It was found that the polymers could retard the release of drugs in both simulated gastric fluid (SGF) and simulated intestinal fluid (SIF), but at different levels. The dissolution constants of drugs exhibitedwere higher when the pH of the dissolution medium was increased. Results also demonstratedindicate a the linear correlation between the proportions of matrix-forming structures in the tablets and the extent of dissolution retardation. It was found that not only the swelling property of the polymer but also its hydrophobicity and the hardness of the tablet played an important role onin the retardation of drug release. Results also revealedindicate that PVP K30 could supports cellulose polymers so as to improve the release behavior in order keep a better control to maintain a constant drug release in each time interval.in order to better keep drug release constant in each time interval.

Micromachining of GaAs structures with an acidic hydrogen peroxide solution: Experimental and theoretical 3D etching shapes

A study was made on the micromachining of various GaAs substrates in a H2SO4:H2O2:H2O solution with composition 1:8:1. In the first part the anisotropy etching behaviour was studied. Etch rates and morphologies produced by the acidic solution were evaluated. The second part was devoted to the determination of a database (dissolution constants) for the GaAs crystal. Theoretical 3D etching shapes were derived from the simulator TENSOSIM using this database. Comparison of theoretical 3D etching shapes with experimental shapes supports the validity of the proposed database. So this study opens up new applications in the field of GaAs micromechanical devices.