The influence of sodium chloride on the crystallization rate of gypsum

The growth kinetics of gypsum was studied in supersaturated solutions both in pure water and in the presence of NaCl, using a seeded growth technique. Radioactive tracer techniques were employed to follow the growth process.The mean linear growth rate R was plotted against the relative supersaturation σ. For low σ values the relation between R and σ is given by a linear law, for higher σ values by a parabolic law and for the highest σ values by a growth “order” higher than two.It was shown that the addition of sodium chloride increased the crystallization rate remarkably. The higher the NaCl concentration the higher the growth rate.     

Effect of dose and dose rate of gamma radiation on catalytic activity of catalase

Catalytic activity of gamma irradiated catalase from bovine liver was studied for hydrogen peroxide decomposition at constant temperature and pressure. The measurement was performed at temperatures 27, 32, 37, 42 and 47 °C. Solutions containing 1 and 0.01 g dm⁻³ of catalase in phosphate buffer were used for the study. Repeatability of both sample preparation and kinetics measurement was experimentally verified. Rate constants of the reaction were determined for all temperatures and the activation energy was evaluated from Arrhenius plot. Gamma irradiation was performed using ⁶⁰Co radionuclide source Gammacell 220 at two different dose rates 5.5 and 70 Gy h⁻¹, with doses ranging from 10 to 1000 Gy. The observed reaction of irradiated and non-irradiated catalase with hydrogen peroxide is of the first order. Irradiation significantly decreases catalytic activity of catalase, but the activation energy does not depend markedly on the dose. The effect of irradiation is more significant at higher dose rate.     

The influence of hydroxyl groups on the ultraviolet spectra of substituted aromatic molecules adsorbed on silica surfaces

Infrared and uv spectroscopy have been used to study the interactions of a series of mono and di-substituted benzene molecules on both porous and nonporous high surface area silicas. It is confirmed that the strength of adsorption depends upon the presence and type of surface hydroxyl group but shown that the uv spectral shifts are not necessarily related to bond strength. Thus, when the surface OH groups reduce the effect of the electron donating side groups, stronger hydrogen bonds produce larger blue shifts in π-π* transitions. When n-π* transitions are involved, however, it is a dipole-dipole interaction which determines the magnitude of the red shift and not the strength of the hydrogen bond.     

Effect of dose rate on emulsion and microemulsion polymerization of styrene

Emulsion and microemulsion polymerization of styrene were initiated with a gamma ray to study the effect of dose rate on polymerization. In both systems, there is an apparent plateau of polymerization rate in the curve of reaction rate vs. conversion. It was shown that emulsion polymerization conformed to the Smith–Ewart theory very well. Changing the dose rate in interval 2 had no great influence on polymerization rate, but it changed the average lifetime of radicals in polymer particles and affected the molecular weight of polymer produced. For microemulsion polymerization it was assumed that in the plateau it is the number of growing polymer particles being kept constant, not the number of polymer particles. When the dose rate was changed while the polymerization came into the constant period, the polymerization rate and the molecular weight of the polymer varied with the dose rate. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 257–262, 1998     

Effect of photosensitizer dose on fluence rate responses to photodynamic therapy

Photodynamic therapy (PDT) regimens that conserve tumor oxygenation are typically more efficacious, but require longer treatment times. This makes them clinically unfavorable. In this report, the inverse pairing of fluence rate and photosensitizer dose is investigated as a means of controlling oxygen depletion and benefiting therapeutic response to PDT under conditions of constant treatment time. Studies were performed for Photofrin-PDT of radiation-induced fibrosarcoma tumors over fluence rate and drug dose ranges of 25-225 mW cm(-2) and 2.5-10 mg kg(-1), respectively, for 30 min of treatment. Tumor response was similar among all inverse regimens tested, and, in general, tumor hemoglobin oxygen saturation (SO2) was well conserved during PDT, although the highest fluence rate regimen (225 mWx2.5 mg) did lead to a modest but significant reduction in SO2. Regardless, significant direct tumor cell kill (>1 log) was detected during 225 mWx2.5 mg PDT, and minimal normal tissue toxicity was found. PDT effect on tumor oxygenation was highly associated with tumor response at 225 mWx2.5 mg, as well as in all other regimens tested. These data suggest that high fluence rate PDT can be carried out under oxygen-conserving, efficacious conditions at low photosensitizer dose. Clinical confirmation and application of these results will be possible through use of minimally invasive oxygen and photosensitizer monitoring technologies, which are currently under development.     

Effect of dose rate on radiation-induced polymerization of styrene adsorbed on silica gel

The effect of dose rate on the rate of polymerization and molecular weight distribution of radiation-induced polymerization of styrene adsorbed on silica gel was studied in a wide dose rate range of 4.4 × 10⁴ to 3 × 10⁸ rad/hr by γ rays of ⁶⁰Co and electron beams with a Cockcroft-Walton-type accelerator. Dose rate dependence on the initial rate of polymerization was about 1 below 3 × 10⁷ rad/hr, and it decreased gradually at high dose rates. Throughout the dose rate range, graft polymerizations and homopolymerizations by cationic and radical mechanisms proceeded simultaneously. Dose rate dependence of the cationic polymerization was 1 below 3 × 10⁷ rad/hr, while dose rate dependence of the radical polymerization was 0.65 below 3 × 10⁷ rad/hr. At high dose rates, molecular weight and fraction of graft polymer decreased, and fraction of cationic polymerization increased. A very high-molecular-weight graft polymer was formed above 4.4 × 10⁵ rad/hr at the initial stage of the polymerization. The dose rate dependence of this polymerization was larger than 1 and decreased with increase in dose rate. The polymerization seems to be related to an excitation of monomer or growing chain.     

The influence of inhibitors on the normal rate of combustion of rich near-limit hydrogen-containing mixtures

The normal rate of combustion S _ui of rich near-limit hydrogen-oxidizing medium-retarder mixtures was determined experimentally. The oxidizing medium was a mixture of nitrogen and oxygen with oxygen contents of 15, 20.6, and 25 vol%; the retarding agents were trifluoromethane CF₃H, pentafluoroethane C₂F₅H, and perfluorobutane C₄F₁₀, and the inhibitor was AKM. Deviations from the empirical rule of approximately constant normal rate of combustion of near-limit mixtures were observed. In the presence of pentafluoroethane, the dependence of S _ui on the content of the retarder contained a pronounced maximum. The AKM inhibitor was found to be highly effective with respect to the combustion of near-limit mixtures in oxidizing media enriched in oxygen.     

The influence of α-trialkylsilyloxy groups on the rate of ring opening of cyclopropylmethyl radicals

The rate of ring opening of α-trialkylsilyloxycyclopropylmethyl radicals is about ten times slower than of the cyclopropylmethyl radical at 298K.     

The influence of elongational flow on association rate and phase behaviour of binary polymer blends

Flow‐induced phase separation in binary blends of end‐associating polymers is studied analytically. To describe the conformational and orientational properties of a polymer chain a simple dumbbell model is applied. It is demonstrated that the association rate for formation of associated diblock copolymer‐like chains decreases with an increase of flow rate. This is due to the extra‐stretching of the associated chain compared with the two initial homopolymer chains. The decrease in the fraction of associated diblock copolymer‐like chains makes the homogeneous state less stable, so the effect of flow manifests itself in the enhancement of the segregation tendency in these kind of associated polymer blends.     

Terrestrial gamma dose rate in Pahang state Malaysia

Environmental terrestrial gamma radiations (TGR) were measured in Pahang state Malaysia between January and April 2013. The TGR dose rates ranged from 26 to 750 nGy h^?1. The measurements were done based on geology and soil types of the area. The mean TGR dose rate was found to be 176 ± 5 nGy h^?1. Few areas of relatively enhanced activity were located in Raub, Temerloh, Bentong and Rompin districts. These areas have external gamma dose rates of between 500 and 750 nGy h^?1. An Isodose map of the state was produced using ArcGIS9 software version 9.3. To evaluate the radiological hazard due to terrestrial gamma dose, the annual effective dose equivalent and the mean population weighted dose rate were calculated and found to be 0.22 mSv year^?1 and 168 nGy h^?1 respectively.     

The influence of shear rate, temperature and chain conformation on the critical concentration c

 When viscometry is used, a crossover phenomenon is observed separating the dilute solutions into extremely dilute solutions and dilute solutions. The critical concentration c ^**, determined from this crossover phenomenon, strongly depends on the shear rate in the solution. At very high values of shear rate the critical concentration c ^** becomes very low and depends only on the contour length of the elongated chains of different polymers. An increase of the temperature induces an increase of c ^** because the relaxation time of the chains decreases. If a polymer adopts a rodlike conformation (in a given solvent at a given temperature) the excluded volume of its chains increases and its critical concentration c ^** decreases. Received: 14 October 1996 Accepted: 3 March 1997     

Use of the dichromate solution as a dosimeter for high dose and high dose rate

The radiolytic reduction of Cr(VI) in N₂O-saturated aqueous solutions has been investigated over a large range of pH by steady state radiolysis. At pH 3 in the presence of formate as scavenger for ·OH, G(−Cr(VI)) is higher than the expected yield and a strong dose rate effect is observed. The solution cannot be used for dosimetry at this pH. The proposed mechanism to explain the enhanced response and the dose rate dependence involves the reduction of the unstable radiolytically produced Cr(IV) by HCO₂⁻. At pH 9.2 the reaction between Cr(IV) and formate is absent and no dose rate effect was observed up to 70 kGy min⁻¹, which makes this system particularly attractive as a dosimeter in the 0.1–10 kGy dose range. Radiation chemical aspects relating to the use of this system as a high-dose and high-dose rate chemical dosimeter are discussed.     

Effect of dose rate on the radiation-induced polymerization of ethylene in tert-butyl alcohol

The dependence of the dose rate on the rate of radiation-induced polymerization of ethylene in tert-butyl alcohol containing 5 vol-% water was studied. The reaction was carried out by use of a reactor with a capacity of 100 ml under the following conditions: pressure, 200 kg/cm²; temperature, 24 ± 3°C; dose rate, 3.7 × 10⁴?1.6 × 10⁵ rad/hr; amount of medium, 70 ml. The dose rate exponents for rate of the polymerization, the molecular weight, and the number of polymer chain were found to be about 0.8, ?0.1, and 0.9, respectively. These results were well explained with kinetic results (obtained by a novel analytical method) for the polymerization which contain both first-order and second-order terminations for the concentrations of propagating radical. The individual values of the rate constants in each elementary reaction were also obtained.     

Effect of dose rate on degradation of 2,6-dichlorophenol by electron beam irradiation

The effects of different dose rates on the degradation of 2,6-dichlorophenol (2,6-DCP) in aqueous solution were investigated at about 2?×?10⁴ Gy absorbed dose, using a 10 MeV electron beam accelerator. It was found that the removal efficiency decreased with increasing dose rate at all initial concentrations of 0.5, 1 and 2 g L^?1, and the effect was significantly diminished by addition of P25 TiO₂ nanoparticles. Alkaline medium were unfavorable for degradation of 2,6-DCP. Hydrogen peroxide (H₂O₂) could promote the removal efficiency at a lower dose rate rather than at a higher one.

     

The influence of a magnetic field on the fluorescence and photolysis rate of carbon disulfide vapour

The effect of a magnetic field on the fluorescence of carbon disulphide vapour under stationary excitation by light with λ = 3130±30 Å has been investigated at 0.014–165.1 Torr. Over the whole range of pressure, the magnetic effect does not depend on the gas pressure. A magnetic field has been found to affect the photolysis rate of carbon disulphide vapour in light with λ>2900 Å. The magnetic effect does not vary with pressure from 2.6–90 Torr.     

On the influence of solvents on the rate of ion-transfer reactions

The literature data on the kinetics of cation electrodeposition on mercury in different solvents were analysed. For all cations considered in different solvents there was a linear decrease of the logarithm of the standard charge-transfer rate constant with increasing basicity of solvent and with more negative formal potential of the electrode reaction expressed in the scale of a solvent-independent electrode, as well as a linear dependence of the activation energy on the Gibbs energy of cation transfer. No dependence of the logarithm of the heterogeneous rate constant on the rate of exchange of solvent molecules from the first solvation sphere was observed. For the different electrode systems studied in one solvent, the dependences of the activation energy on (i) the cation solvation energy, (ii) the Gibbs energy of metal amalgamation, and (iii) metal solubility in mercury were analysed.     

Dependence of ultraviolet absorbers' performance on ultraviolet wavelength

So far, ultraviolet absorbers (UVA) have been discussed mainly on the basis of the extinction coefficient (?), and the light degradation of polymeric materials is explained by photolysis of hydroperoxides and Norrish reactions of ketones. This study focuses on the photo-antioxidant ability as characteristic which UVA must possess for the light stabilization, and examines the dependence of the photo-initiation by oxidation products on UV wavelength range. As a result, it has been made clear that UV rays ranging 290-320 nm trigger photo-oxidation (degradation) by photolysis of hydroperoxides and Norrish reactions of ketones, and α-diketone derived from further oxidation of the ketones, for example, initiates photo-oxidation at a surprisingly higher velocity under UV rays above 350 nm. UV rays in the range of 320-350 nm participate in the photo-initiation by an enone (CCCO) structure in addition to the above-mentioned oxidation products, in which the initiation velocity is the medium between the velocities for the above two wavelength ranges. That is to say, the longer the UV rays wavelength range, the faster the photo-initiation velocity. Finally, it is concluded that excellent UVA are judged based on λ_max rather than ?, and that UVA absorbing longer wavelength UV rays can more control the photo-oxidation.