Small Retardation Research Articles

Use of cellulose ether containing excipients with microcrystalline cellulose for the production of pellets containing metformin hydrochloride by the process of extrusion-spheronization

The project is concerned mainly with the evaluation of two cellulose ether containing excipients, Aquacoat WG and Avicel 955 MCC for the improved extrusion-spheronization of metformin hydrochoride. Factorially designed experiments subject to statistical analyses were employed and products obtained were evaluated by sieve, packing density and image analysis, scanning electron microscopy and dissolution testing at pH 6.8. Aquacoat WG did not improve the ease of spheronization of drug mixes containing microcrystalline cellulose wetted with the optimum level of water. However, Avicel 955 MCC, which is a new experimental excipient containing 95% microcrystalline cellulose and 5% methylcellulose, did aid ease of spheronization facilitating acceptable yield of good spheres with high drug loadings (70%). Avicel 955 MCC containing drug mixes were more tolerant to minor alterations in level of hydration and yielded spheres which showed a small retardation of drug release despite the very high solubility of metformin hydrochloride.

Use of Transport Coefficients to Calculate Properties of Electrode Sheaths of Electric Arcs

Particle conservation equations for electrons and positive ions, together with Poisson"s equation to account for space-charge effects on the electric field, have been solved for the electrode sheath regions of electric arcs. For thermionic cathodes and the anode, we find that the ambipolar diffusion approximation is generally valid. At the surface of the anode we find that there is generally a small retarding electric field. For non-thermionic cathodes and no ionisation due to the electric field in the sheath, we calculate unrealistically high sheath voltages and even then, find that the electric fields at the cathode surface are insufficient for field emission. It is suggested that photoionisation in the region close to the cathode may be a principal source of electrons for non-thermionic cathodes.

9‐Substituted acridines. Demethoxylation of 9‐methoxyacridine and dechlorination of 9‐chloroacridine in hydroxylic solvents

AbstractIn methanol‐water mixtures containing sodium or potassium hydroxide (up to 2.00M) the demethoxylation of 9‐methoxyacridine to 9‐acridone is of first order in both the free form of 9‐methoxyacridine and the hydroxyl ion. The rate of the reaction is increased with an increase in the concentration of water. Sodium perchlorate has a small retarding effect on the reaction. In methanol‐water mixtures containing perchloric or hydrochloric acid (up to 3.45M) the demethoxylation is of first order with respect to the protonated form of 9‐methoxyacridine. The rate of the reaction decreases with an increase in the concentration of the acid or of sodium perchlorate, but when the concentration of water is increased (≈︁1.7 to 50M) and that of the acid is not changed, it reaches a maximum value in mixtures containing 8 to 10M‐water. The dechlorination of 9‐chloroacridine to 9‐methoxyacridine in methanol containing sodium hydroxide or methoxide (up to 0.31 M) is of first order in both the 9‐chloroacridine and the hydroxyl or methoxyl ions.

Colloid-facilitated radionuclide transport in fractured porous rock

Numerical methods have been applied for the prediction of colloid-facilitated radionuclide transport through water-saturated fractured porous rock. The presence of colloids may enhance the transport of radionuclides in groundwater by reducing retardation effects. The colloids existing in the groundwater act as carriers, adsorbing radionuclides in their large surface area and moving faster than the average water velocity. With colloids present, the system consists of three phases, i.e. an aqueous phase, a carrier phase and a stationary solid phase. In the basic model, one-dimensional advection in a single planar fracture of infinite extent is coupled with diffusion in the rock matrix perpendicular to the fracture. In this study, a full-equilibrium model was developed to describe the transport and fate of the radionuclides in the fracture. Sorption onto the rock matrix, fracture surface and sorption onto mobile and immobile colloids are included. The effect of colloidal particle size was also considered. Mass partition mechanisms between the colloids and solid matrix and between colloid and contaminant are represented by local equilibrium. In the three-phase system, the three parameters, the retardation coefficient, the hydrodynamic dispersion coefficient and fracture width, are modified to include the equilibrium distribution coefficient of a contaminant with a carrier. In the three-phase model, much smaller retardation and hydrodynamic dispersion coefficients are obtained and the effect of the fracture width is larger. Much faster transport of contaminant has resulted mainly because the radionuclides attached to colloidal particles are not subject to retardation by diffusion into the rock matrix. With the additional consideration of colloidal particle sizes, these effects become ever larger. Numerical solutions for the model were obtained using a fully implicit finite difference scheme. A significant sensitivity to model parameters was discovered, and, in particular, the equilibrium distribution coefficients between a contaminant and the carrier were found to be the most important factors.

Development of Scanning Stress Measurement Method Using Laser Photoelasticity.

We have developed an optical equipment which possesses high detection sensitivity for measuring small optical retardation induced by stress by means of laser photoelasticity. A He-Ne laser is used as a light source to measure small stress in transparent materials. We explain the theory and process of the measurement of optical retardation in the materials. The magnitude of principal stress difference as well as the direction of the principal stress are obtained simultaneously and quantitatively using our equipment. In order to evaluate the performance of the optical retardation measurement equipment, the stress distribution of a pulled rectangular glass plate with notches at both sides was measured using the equipment. The results of stress distribution agreed with the analytical results. Stress at many points can be determined quickly using the equipment and scanning stress distribution measurement has been realized.

MICROSTRUCTURAL EFFECTS ON SMALL FATIGUE CRACK INITIATION AND GROWTH IN Ti6A14V ALLOYS

Abstract— The nucleation and growth of small naturally initiated cracks have been investigated on Ti 6 Al 4V alloys, with bimodal or globular microstructures. Tests have been performed in air at a stress amplitude near 0.75 of the yield stress. The influence of microstructure on fatigue damage is described and the differences in fatigue life of some titanium alloys are explained. The effect of microstructure on fatigue resistance is mainly related to the early stages of damage including initiation and small crack growth. Coalescence processes favoured by a high density of initiated surface microcracks in fine α grain material, or rapid initiation of large cracks in coarse α colonies, explains low fatigue resistance or lifetime scattering in globular alloys. Small crack growth retardation due to α/β barriers associated with a low surface crack density, limiting coalescence processes, explains the highest resistance of bimodal structures.

Spectrophotometric Determination of 6-Aminopenicillanic and 7-Aminocephalosporanic Acids as the Schiff Bases with para-Dimethylaminobenzaldehyde in the Presence of Sodium Dodecyl Sulfate Micelles

Yields of colored Schiff base products of the reversible condensation of 6-aminopenicillanic and 7-aminocephalosporanic acids with para-dimethylaminobenzaldehyde in a weakly acid aqueous solution strongly increase in the presence of micelles of sodium dodecyl sulfate. The binding constants of reactants and products of both reactions to micelles were calculated from the concentration profiles of micellar effects on rates and equilibrium of the condensation reactions. The observed micellar-induced shifts of equilibrium are accompanied by strong acceleration of the forward and small retardation of backward processes. Some deviations from the theoretical profiles due to saturation of micelles with reactants were observed. The colored form of the reaction product was found to be the protonated Schiff base. Its stability in time is strongly enhanced in the micellar medium. The spectrophotometric determination of title compounds under optimum micellar conditions possesses ca. 300 times higher sensitivity than the standard procedure.

Flow birefringence in axisymmetric geometries

Flow birefringence has become increasingly popular as a tool in non‐Newtonian fluid mechanics, where it provides a means of measuring stress distributions in complex polymer flows. In order to access a wider range of kinematic complexity in the testing of constitutive models, we explore the application of flow birefringence in axisymmetric geometries. Unlike traditional applications of flow birefringence in two‐dimensional flows, there is no direct relationship between measured optical properties and stresses in the material. Rather, the optical properties reflect the cumulative effect of the axisymmetric refractive index (and hence stress) tensor on the polarization state of light. Since a typical goal of flow birefringence studies is comparison between experiment and computation, we propose that optical property distributions could serve as the basis for comparison rather than attempting to invert optical data to yield radial stress distributions. In the limit of small total retardance, there are particularly simple relationships between experimental observables and integrals of the stress distributions. Experiments are performed on an index‐matched Newtonian test fluid in a prototype axisymmetric geometry (tube flow past an obstruction with a hemispherical cap) in order to illustrate the principles of the technique.

Circularly polarized undulator radiation from the new double crossed undulator beamline at BESSY and its first use for spin resolved Auger electron emission spectroscopy

The new beamline U2-FSGM at BESSY provides now circularly polarized radiation of high flux for photon energies between 20 eV and 200 eV. For users working at this beamline it is essential to measure the photon polarization. We have developed a new apparatus consisting of a Rabinovitch detector for analyzing the photon polarization, a 90° spherical electron spectrometer and a small retarding spherical Mott polarimeter (45 keV) for determining the electron spin polarization. As a first application we have measured the M 3VV Auger emission from Cu(100) spin resolved after photo excitation by means of circularly polarized radiation of 76 eV.

Photoelastic study of the durability of interfacial bonding of carbon fibre-epoxy resin composites

The physical techniques of polarizing microscopy, including the quantitative measurements of small optical retardations, have been used to investigate elastic fields adjacent to short carbon fibres in epoxy resin composites. The elastic fields associated with shear stress distribution along the fibre-matrix interface have been employed to monitor the initiation of interface debonding during hot (100 °C) water uptake. By examining the development of stress birefringence during resin swelling in the resin adjacent to individual fibres, the differences in the durability of interfacial bonding and the fibre failure modes for differently coated fibres have been obtained. The results show that the state of self-stress in model composites, comprising a single carbon fibre in a film of epoxy resin, can, by immersion in hot distilled water, be enhanced to such an extent that the axial tension in the fibre can be sufficient to initiate fibre fracture. The results also show that, for fibres that have been given certain proprietary surface treatments, the fibre fractures by different failure modes.

Retardation of Tritium and Cesium in Brine‐Saturated Mudstone, Halite, and Carbonate Porous Media

AbstractBatch and column sorption/desorption experiments were conducted to quantify the retardation of tritium and cesium in brine‐saturated mudstone, halite, and carbonate rocks from Palo Duro Basin, Texas, one of the three sites originally nominated by the U.S. Department of Energy for construction of a civilian nuclear waste repository. Retardation factors (R) were determined using six different methods, including batch sorption equilibrium, fitting of two transport models, breakthrough area integration, and pore volume displacement at C/C0= 0.5, for both the sorption and desorption parts of the breakthrough curves. The breakthrough area integration method resulted in R values consistently lower than the other methods, which were in reasonable agreement. The data indicated very small retardation for cesium in all the media, except mudstone, which exhibited moderate retardation (R < 3.5). It was shown that the small extent of cesium retardation was most possibly caused by the strong competition for sorption sites of the components of the saturated brine, which were several orders of magnitude higher in concentration than cesium. Tritium breakthrough curves for all media tested were accurately simulated by the local equilibrium advection‐dispersion model (model I). With the exception of mudstone, cesium breakthrough curves were also adequately simulated by model I. The cesium breakthrough curve for mudstone exhibited considerable tailing on the desorption side of the curve, which was best described by the two‐site kinetic sorption model II. This was attributed to chemical nonequilibrium (two types of sorption sites). Predicted breakthrough curves for cesium using model I were in good to reasonable agreement with measured breakthrough curves.

Pesticide leaching in heterogeneous soils with oscillating flow: approximations

Pesticide screening models are used to assess which pesticides may leach in significant amounts into ground water. In this paper we consider the effects of transient flow and spatial variability of soil properties on the leached fraction of pesticides. Transient flow is approximated with sinusoidal variations of the flow velocity. We show that the main effect is due to the difference with respect to the residence time in soil, compared with the case of steady flow. The effect is most profound for pesticides with small retardation factors. Spatial variability of physical and (bio)chemical parameters is shown to lead to larger leached fractions that in the case of a homogeneous flow domain. Several effects are illustrated with analytical approximations.

Matrix-assisted laser desorption fourier transform mass spectrometry for the structural examination of modified nucleic acid constituents

Laser desorption Fourier transform mass spectrometry (LDFTMS) can be used for the structural characterization of modified nucleic acid constituents. Laser desorption of these polar non-volatile compounds generates characteristic negative ions including abundant (M—H) − ions in most cases. The accurate mass measurement and ion manipulation techniques available with FTMS provide detailed structural information for the identification of modified nucleic acid constituents such as amino-polycyclic aromatic hydrocarbon adducts of guanine at the isomeric level. Matrix-assisted laser desorption was required for the generation of abundant (M—H) − ions as well as fragment ions of modified nucleotides and oligonucleotides. Examination of fragment ions from these compounds provided not only adduct identification and location but also sequence information and isomeric differentiation for most small oligonucleotides. In order to investigate the application of this instrumental technique to larger oligonucleotides, experiments were designed to examine the kinetic energy distributions of ions generated by matrix-assisted laser desorption and to evaluate methods of improving the trapping efficiencies. Initial experiments indicated that ions at m/z < 600 have kinetic energies less than 5eV; however, the use of simple retarding fields did not significantly affect trapping efficiencies, implying that the space-charged ion could generated by matrix-assisted laser desorption was relatively unaffected by small retarding fields (less than 10 V)

Visualization of the Wing-Tip Vortex in Temporal and Spatial Pressure Gradients

The evolution of the longitudinal vortex in the near field of a rectangular wing has been visualized using smoke and laser light sheet. The smoke photographs have been used to obtain qualitative and some quantitative information on the effect of small temporal and spatial pressure gradients on the evolution of the vortex in this region. The experiments indicate that even small temporal retardation of the flow can produce a significant increase in the vortex size. This effect becomes larger with increase in retardation, angle of incidence and distance downstream from the trailing edge. Also, vortex “breakdown” was found to occur in many temporal-deceleration experiments. The vortex evolution was, however, found to be relatively insensitive to the presence of small spatial adverse pressure gradients along the flow direction. The study is preliminary in nature and needs to be supported by more extensive quantitative measurements.

Auto-ignition temperatures of binary mixtures of alkanes in a closed vessel: Comparisons between experimental measurements and numerical predictions

Autoignition temperatures of the binary mixtures methane+ethane and methane+ n -butane in air were measured at atmospheric pressure in a 0.56 dm 3 spherical reaction vessel. The method followed that for standard ASTM and BS tests for gaseous fuels. Fixed proportions by volume of the total fuel in air were studied, which corresponded at the extreme of each composition range for methane, ethane and butane to the equivalence ratios of =0.93, 1.63 and 3.04 respectively. Supplementary experiments were carried out on n -butane alone in air in the range 0<<3.04. The autoignition temperature (T a,cr ) in binary mixtures was reduced by 40 K from that for pure methane (T a,cr =900 K) when ethane was present at up to 10% of the total fuel. Similar proportions of butane added to methane caused T a,cr to be decreased by 90 K. The effects were not linearly dependent on the proportion of additive. There was an additional sensitive region when n -butane was present in the proportion 50–70% of the methane/butane mixture. The autoignition temperatures of mixtures containing n -butane alone matched very closely the autoignition temperatures of the equivalent methane/butane compositions except at the leanest mixtures ( butane <0.5). Numerical simulations of spontaneous ignition based on a comprehensive kinetic model yielded predicted autoignition temperatures that were in very satisfactory agreement with the measured values throughout all ranges of composition. The same regions of high sensitivity to composition change were distinguished. Alkylperoxy isomerisation and decomposition reactions were found to control the reactivity of butane at the lowest temperatures. Reactions of dialkylperoxy radicals seemed not to be especially important. The rates of H atom abstraction by OH governed the relative reactivity of methane to that of butane. The competition by methane for OH radicals caused a small retarding effect on the overall rate of butane oxidation.

Collapse of conical cavities in aluminium metal under shock wave impact

Under shock wave impact the conical free surface of the metal collapses and a metallic jet with a velocity exceeding 10 km/s is squirted out of the metallic target. Variation in the jet tip velocity when the cavity half angle ranges from 60 down to 7.5° has been studied over three different shock pressures. The jet velocity has been found to increase with the decrease in the angle of the conical free surface and as the angle approaches zero the jet tip velocity attains a value near to the limit set by hydrodynamic theory for non-compressible fluids. The effect of aerodynamic drag on this type of jet has been studied and it has been found that the jet formed by the collapse of a small angle conical cavity quickly slows down while travelling in air, whereas the jet coming out of large angle cavity suffers a small retardation. Theoretical explanation and experimental evidence in support of this fact are also presented.

Genome imprinting phenomena on mouse chromosome 7

Heterozygotes for the reciprocal translocation T(7;15)9H were intercrossed, with albino (c) and underwhite (uw) as genetic markers, in order to study genetic complementation in mouse chromosome 7. Chromosome 15 is known to show normal complementation. Neither reciprocal cross in which one parent was c/c and the other wild type yielded albino progeny at birth although about 17% would be expected, but albino foetuses were recovered when the mother was c/c and father wild type. These products of maternal duplication/paternal deficiency for distal 7 were markedly retarded with small placentae. No albino foetuses were found when the father was c/c and mother wild type, which suggested earlier lethality. Equivalent crosses with uw (chromosome 15) as proximal marker gave normal underwhite progeny when the mother was uw/uw but small placentae, retardation and neonatal death of presumptive underwhites in the reciprocal cross. These abnormal newborn would have had a maternal duplication/paternal deficiency for proximal 7. These and other findings indicate that one region of defective complementation probably lies distal to the breakpoint of T(7;18)50H at 7E2-F2, while another is between the centromere and 7B3. Examination of man-mouse homologies suggests that the loci for three pathological human conditions (Beckwith-Weidemann syndrome, dystrophia myotonia and rhabdomyosarcoma) with differential parental transmission may be located in homologous regions to those affected by imprinting phenomena on mouse chromosome 7.

Response to Growth Hormone Treatment and Final Height after Cranial or Craniospinal Irradiation

Growth hormone (GH) deficiency (GHD) induced by cranial irradiation has become a frequent indication of hGH substitutive therapy. This study analyses the growth response to hGH therapy and the factors involved in the decrease in growth velocity observed after cranial irradiation. One hundred children (61 boys and 39 girls) given cranial radiation for pathology distant from the hypothalamo-pituitary area were studied. Fifty-six of them received hGH therapy for GHD resulting in decreased growth velocity. The initial annual height gain in the cranial-irradiated group was comparable to that of patients treated for idiopathic GHD; additional spinal irradiation significantly reduced the growth response. Twenty-eight hGH-treated patients reached final heights which were compared to those of 2 untreated irradiated groups, one with GHD (n = 27) and the other with normal GH secretion (n = 17). The height SD score changes observed in hGH therapy were +0.3 in the cranial (n = 10) and -1.2 SD in the craniospinal (n = 18) groups. GH deficiency had contributed to a mean height loss of 1 SD and spinal irradiation to a loss of 1.4 SD. The small effect of hGH therapy on final height is probably linked to the small bone age retardation at onset of hGH therapy and to the fact that irradiated children entered puberty at a younger age in terms of chronological age (10.6 +/- 0.3 yr in girls and 11.0 +/- 0.3 yr in boys) and bone age (9.6 +/- 0.4 yr in girls and 12.6 +/- 0.3 in boys) than the idiopathic GHD patients. These data suggest that the results of hGH therapy in irradiated children might be improved with higher and more fractionated hGH doses and, in some patients, by delaying puberty using luteinizing hormone releasing hormone analogs.

Micellar effects upon the reactions of complex ions in solution. Part 4.—Kinetics of aquation and base hydrolysis of some cis-(chloro)(amine)bis(ethylenediamine)cobalt(III) complexes in the presence of neutral and anionic surfactants in an aqueous medium

The binding of the substrates cis-[Co(en)2BCl]2+(en = 1,2-diaminoethane, B = alkylamines, imidazole, N-methylimidazole) to the micellar surface of sodium dodecyl sulphate resulted in the retardation of their dissociative aquation rates, the effect being sensitive to the hydrophobicity of the nonlabile amine ligand B. A contrastingly small rate acceleration for the corresponding ethanolamine and propan-2-ol amine complexes was observed under similar conditions. Triton X-100 (0.02 ⩽[Triton X]T/mol dm–3⩽ 0.1) had virtually no effect on the aquation rates of such complexes except for cis-[Co(en)2(C6H11NH2)Cl]2+, in which case a small rate retardation was also observed. The rates of base hydrolysis of the cobalt(III) substrates were strongly retarded by the anionic micelles of SDS; the neutral micelles of Triton X-100 were effective in decelerating the rate of base hydrolysis of the cyclohexylamine complex cis-[Co(en)2(C6H11NH2)Cl]2+ only. The pseudo-phase ion-exchange equilibrium model satisfactorily explained the binding of the cationic substrates to the anionic micellar pseudo-phase of SDS. The values of the ion-exchange equilibrium constant and the relative base hydrolysis rates (kW/kM) indicated that both micellar binding and retardation of hydrolysis are governed by hydrophobic and electrostatic interactions.

Modeling the Transport of Chromium (VI) in Soil Columns

AbstractMiscible displacement experiments were conducted to describe chromium [Cr(VI)] mobility and interactions in six different soils. For Calciorthid, Webster, and Norwood soils Cr breakthrough curves (BTCs) indicated that the interactions with the soil matrix were similar to those for a nonreactive solute where no or small retardation of the equilibrium type was observed. These observations are in support of earlier kinetic batch results where little retention was observed for a wide range of Cr concentrations in these (high pH) soils. The BTCs from Olivier, Cecil, and Windsor soils indicated high Cr retention capacity as indicated by increased retardation, low peak concentrations, irreversible sorption and extensive effluent tailing during desorption (leaching). A nonlinear retention/release model is proposed for the purpose of describing Cr(VI) reactions during transport in soils. The model is incorporated into the convection‐dispersion transport equation for reactive solute in uniform soils. The model was capable of providing a good description of the Cr BTCs for all soils where model parameters were obtained using a nonlinear least squares (best fit) parameter optimization scheme. The model grossly underestimated effluent concentrations for Olivier and Windsor BTCs when independently measured retention/release rate coefficients from the batch data sets were used. Model predictions overestimated the amount irreversibly retained by Cecil soil. Model predictions indicated that a unique set of independently measured rate coefficients was not capable of providing an adequate description of Cr BTCs for these soils.