The effects of ionising radiation on polypropylene

The interaction of ionising radiation with polymers is described and the literature relating; to the effects on polypropylene is reviewed. Oxidative and free radical reactions are discussed with particular reference to post-irradiationeffects.Isotactic and atactic polypropylene were δ and electron irradiated to doses of up to 20 megarad. Irradiations weremainly made in air. A series of other polymers were also irradiated in a preliminary survey. Molar mass measurements are used to measure the radiationyield for chain scission G (s). Irradiation at room temperature causes significantly more chain scission than at 195K. Additional chain scission occurs on storage following irradiation at 195 K. Free radical concentrations are determined by electron spin resonance, and the decay rates measured. The radical formed in air is a peroxy radical and in vacuo is a hydrocarbon radical. At77K in vacuo the radical is -CH2 - C* (CH3) - CH2 - but additional radicals are produced on warning to room temperature. The effects of increasing tenparature on radicals formed in air are described. Electron spin resonance studies on atactic polypropylene,and isotactic polypropylene in hydrogen, sulphur dioxide and nitric oxide are reported.. The melting temperatures, spherulite growth rates, and isothermal crystallisation rates of irradiated polypropylene are compared to those of the non-irradiated polymer. Crystallisation is found to proceed with an Avrami integer n = 2. At a given crystallisation temperature, the overall crystallisation rate of irradiated polymer is less than the non-irradiated, but spherulite growth rates are identical. Thermogravimetric analysis is used to assess the thermal stability of irradiated polypropylene in nitrogen, air and oxygen. Hydroperoxide analysis is used to show that several molecules of oxygen are absorbed for each initial radical, and that hydroperoxides continue to be formed for a long period following irradiation. Possible solutions for minimising irradiation and post-irradiation degradation are suggested, together with some problems for further study.

The effects of solar radiation pressure on the motion of an artificial satellite

This thesis documents an investigation of the effect of solar radiation pressure on the motion of an artificial satellite. Consideration is given to the methods required for the inclusion of the discontinuous effect of the Earth's shadow. The analysis resulting from the description of a deformed diffusely reflecting balloon satellite and an algorithm describing the effects of Earth reflected solar radiation pressure are developed, culminating in the application of the derived theory to the orbital data of the balloon satellite, Explorer 19.

Dynamic analysis of submerged microscale plates:the effects of acoustic radiation and viscous dissipation

The aim of this paper is to study the dynamic characteristics of micromechanical rectangular plates used as sensing elements in a viscous compressible fluid. A novel modelling procedure for the plate- fluid interaction problem is developed on the basis of linearized Navier-Stokes equations and noslip conditions. Analytical expression for the fluidloading impedance is obtained using a double Fourier transform approach. This modelling work provides us an analytical means to study the effects of inertial loading, acoustic radiation and viscous dissipation of the fluid acting on the vibration of microplates. The numerical simulation is conducted on microplates with different boundary conditions and fluids with different viscosities. The simulation results reveal that the acoustic radiation dominates the damping mechanism of the submerged microplates. It is also proved that microplates offer better sensitivities (Q-factors) than the conventional beam type microcantilevers beingmass sensing platforms in a viscous fluid environment. The frequency response features of microplates under highly viscous fluid loading are studied using the present model. The dynamics of the microplates with all edges clamped are less influenced by the highly viscous dissipation of the fluid than the microplates with other types of boundary conditions.

Combined effects of solar UV radiation and CO2-induced seawater acidification on photosynthetic carbon fixation of phytoplankton assemblages in the South China Sea, 2010

We carried out short term pCO2/pH perturbation experiments in the coastal waters of the South China Sea to evaluate the combined effects of seawater acidification (low pH/high pCO2) and solar UV radiation (UVR, 280-400 nm) on photosynthetic carbon fixation of phytoplankton assemblages. Under photosynthetically active radiation (PAR) alone treatments, reduced pCO2 (190 ppmv) with increased pH resulted in a significant decrease in the photosynthetic carbon fixation rate (about 23%), while enriched pCO2 (700 ppmv) with lowered pH had no significant effect on the photosynthetic performance compared to the ambient level. The apparent photosynthetic efficiency decreased under the reduced pCO2 level, probably due to C-limitation as well as energy being diverged for up-regulation of carbon concentrating mechanisms (CCMs). In the presence of UVR, both UV-A and UV-B caused photosynthetic inhibition, though UV-A appeared to enhance the photosynthetic efficiency under lower PAR levels. UV-B caused less inhibition of photosynthesis under the reduced pCO2 level, probably because of its contribution to the inorganic carbon (Ci)-acquisition processes. Under the seawater acidification conditions (enriched pCO2), both UV-A and UV-B reduced the photosynthetic carbon fixation to higher extents compared to the ambient pCO2 conditions. We conclude that solar UV and seawater acidification could synergistically inhibit photosynthesis.

Boosting the CD4 Count in HIV Infection: Comparative Effects of Highly Active Anti-retroviral therapy (HAART) and Different Modalities of Physical Exercise on Biomarkers of Immunity

A decline in the CD4 count is a common feature in HIV/AIDS, suggesting a compromise in immunity of patients. In response, highly active antiretroviral therapy (HAART) is prescribed to slow-down a diminution in the CD4 count and risk of AIDS-related malignancies. However, exercise may improve both the utility and population of innate immune cell components, and may be beneficial for patients with HIV infection. Comparing the effects of different exercises against HAART, on CD4 count, helps in understanding the role and evidence-based application of exercises to ameliorate immune deficiency.

Study of the ecophysiological stress effects on HPG and HPI axes, immunity system and reproduction processes in Persian sturgeon (Acipenser persicus)

The ecophysiological effects of stress in female Persian sturgeon, Acipenser persicus brood fishes during catch, transport and their confinement in the Kurenski ponds at the Shahid Dr. Beheshti Fish Propagation and Rearing Center were studied. The brood fishes under study were caught at three catch stations located at the Sefidrud River, Sefidrud River estuary and Gorganrud River estuary and were held in ponds at the Shahid Marjani Fish Propagation and Rearing Center.

Effects of gamma radiation in mycotoxin descontamination of Aloysia citrodora Paláu

The interest and demand for aromatic and medicinal plants have been growing due to their combined organoleptic and bioactive properties. However, in general these plants suffer natural contamination by fungi and associated toxins during growth as also in harvesting, storage and drying processes, which represents a threat to public health. The rigorous standards required by the industrial sector in terms of good quality of raw materials demand efficient decontamination procedures (1-3). Gamma radiation is assumed as an accredited methodology for the decontamination of medicinal and aromatic plants, with numerous advantages not only to the product itself but also to the consumer and the environment (4). In this study, efficient methods for detecting aflatoxins (AFB" AFB2, AFG1 and AFG2) and ocratoxin A (OTA), were optimized and validated, and afterwards, applied to spiked samples of Aloysia citrodora Pahiu submitted to gamma radiation treatment at different doses (I , 5 and I 0 kGy ), to evaluate the effectiveness of irradiation as a decontamination technique for dry plants. Mycotoxin levels were determined by reversed-phase high-performance liquid chromatography (HPLC) with fluorescence detection, after immunoaffinity column (lAC) cleanup. All the applied gamma radiation doses conducted to a degradation of the studied mycotoxins. In relation to the control sample (0 kGy), the reduction rates in the irradiated samples ranged from 4.9 and 5.2% in OTA, 5.3 and 9.6% in AFBt. 12.3 and 13.5 in AFB2, 16.4 and 23.6 in AFG1 and, finally, 52.6 and 62.7% in AFG2. The gamma radiation dose of 5 kGy stood out as the best decontamination dose for AFB1 and AFG1, which are the most significant aflatoxins naturally found in food commodities. For OTA, AFG2 and AFB2 there was no significant difference in decontamination between doses. In conclusion, the extraction and analysis methods proved to be suitable for detection of aflatoxins and ocratoxin A in A. citrodora. Gamma radiation seems to be an effective technique for reducing aflatoxins G in A. citrodora, and eventually oth~r medicinal and aromatic plants. On the other hand, aflatoxins B and OTA are less affected by this treatment.

CHARACTERIZATION OF THE ATMOSPHERIC EFFECTS ON THE TRANSMISSION OF THERMAL RADIATION

Atmospheric scattering plays a crucial rule in degrading the performance of electro optical imaging systems operating in the visible and infra-red spectral bands, and hence limits the quality of the acquired images, either through reduction of contrast or increase of image blur. The exact nature of light scattering by atmospheric media is highly complex and depends on the types, orientations, sizes and distributions of particles constituting these media, as well as wavelengths, polarization states and directions of the propagating radiation. Here we follow the common approach for solving imaging and propagation problems by treating the propagating light through atmospheric media as composed of two main components: a direct (unscattered), and a scattered component. In this work we developed a detailed model of the effects of absorption and scattering by haze and fog atmospheric aerosols on the optical radiation propagating from the object plane to an imaging system, based on the classical theory of EM scattering. This detailed model is then used to compute the average point spread function (PSF) of an imaging system which properly accounts for the effects of the diffraction, scattering, and the appropriate optical power level of both the direct and the scattered radiation arriving at the pupil of the imaging system. Also, the calculated PSF, properly weighted for the energy contributions of the direct and scattered components is used, in combination with a radiometric model, to estimate the average number of the direct and scattered photons detected at the sensor plane, which are then used to calculate the image spectrum signal to- noise ratio (SNR) in the visible near infra-red (NIR) and mid infra-red (MIR) spectral wavelength bands. Reconstruction of images degraded by atmospheric scattering and measurement noise is then performed, up to the limit imposed by the noise effective cutoff spatial frequency of the image spectrum SNR. Key results of this research are as follows: A mathematical model based on Mie scattering theory for how scattering from aerosols affects the overall point spread function (PSF) of an imaging system was developed, coded in MATLAB, and demonstrated. This model along with radiometric theory was used to predict the limiting resolution of an imaging system as a function of the optics, scattering environment, and measurement noise. Finally, image reconstruction algorithms were developed and demonstrated which mitigate the effects of scattering-induced blurring to within the limits imposed by noise.