Gas breakthrough and emission through unsaturated compacted clay in landfill final cover.

Determination of gas transport parameters in compacted clay plays a vital role for evaluating the effectiveness of soil barriers. The gas breakthrough pressure has been widely studied for saturated swelling clay buffer commonly used in high-level radioactive waste disposal facility where the generated gas pressure is very high (in the order of MPa). However, compacted clay in landfill cover is usually unsaturated and the generated landfill gas pressure is normally low (typically less than 10 kPa). Furthermore, effects of clay thickness and degree of saturation on gas breakthrough and emission rate in the context of unsaturated landfill cover has not been quantitatively investigated in previous studies. The feasibility of using unsaturated compacted clay as gas barrier in landfill covers is thus worthwhile to be explored over a wide range of landfill gas pressures under various degrees of saturation and clay thicknesses. In this study, to evaluate the effectiveness of unsaturated compacted clay to minimize gas emission, one-dimensional soil column tests were carried out on unsaturated compacted clay to determine gas breakthrough pressures at ultimate limit state (high pressure range) and gas emission rates at serviceability limit state (low pressure range). Various degrees of saturation and thicknesses of unsaturated clay sample were considered. Moreover, numerical simulations were carried out using a coupled gas-water flow finite element program (CODE-BRIGHT) to better understand the experimental results by extending the clay thickness and varying the degree of saturation to a broader range that is typical at different climate conditions. The results of experimental study and numerical simulation reveal that as the degree of saturation and thickness of clay increase, the gas breakthrough pressure increases but the gas emission rate decreases significantly. Under a gas pressure of 10 kPa (the upper bound limit of typical landfill gas pressure), a 0.6m or thicker compacted clay is able to prevent gas breakthrough at degree of saturation of 60% or above (in humid regions). Furthermore, to meet the limit of gas emission rate set by the Australian guideline, a 0.6m-thick clay layer may be sufficient even at low degree of saturation (i.e., 10% like in arid regions).

Pulmonary perfusion during lung transplant rejection and experimental pneumonia.

Six left lung allotransplants were performed in healthy mongrel dogs. Immunosuppression was established with cyclosporine (15 mg/kg/day p.o.) from the day of transplantation for 30 days. Another group of animals (n = 3) was used to produce acute experimental pneumonia by instilling 4-6 ml of a 10(8) CFU suspension of Pseudomonas aeruginosa into the right lower lobe. Dynamic perfusory lung scintigraphy (DPLS) was performed before transplant/pneumonia (control), during acute rejection/pneumonia as detected radiologically, and after treatment with methylprednisolone (1 g/day for 3 days i.v.) (transplant group) or antibiotics (pneumonia group). Seroalbumin macroaggregates (5-8 McI) marked with 99-mTc were injected into the cephalic vein and the percentage of perfusion to each lung was determined. Eight acute rejection episodes were detected. DPLS showed similar perfusion to each lung, whereas during acute rejection perfusion was significantly reduced by almost 30%. Perfusion was reestablished to control levels after treatment with methylprednisolone. Reduction in perfusion correlated with radiological rejection grading. No reduction in left lung perfusion was detected in pneumonia animals. In conclusion, acute rejection reduces perfusion to the transplanted lung as measured by DPLS. Treatment restores normal perfusion.

The pharmacokinetic characteristics of a hepatobiliary 99mTc-radiopharmaceutical: comparison of the imported and national kits.

In nuclear medicine, the search for the perfect hepatobiliary agent started in 1955 with the rose bengal dye labeled with 131I. With the advent of technetium-99m, many ligands were labeled and Tc-99m-PG and 99mTc-HIDA were among the best suited for this purpose. Both were synthesized at the radiopharmacy laboratory during 1977-1980 and have been used at INNSZ for clinical studies. For the last three years, a new ligand with a bromine atom and an extra methyl radical has been reported as being one of the best third generation HIDAs. We received the gift of several kits of trimethyl-Br-IDA from Sorin Biomedica, Italy, (A) and of Mebrofenin from ININ, Mexico, (B) to be labeled and tested in order to select one of them for clinical work. For a comparative study on the radiopharmacodynamic characteristics of the two labeled ligands, six healthy women volunteered to undergo two tests with a 72 hour hour rest period to assure complete washout. After the I.V. dose of 111 MBq (3 mCi) the dynamic study was started and a total of 127 16-second images were acquired with a Siemens Digitrac 750 scintillation camera coupled to a Scintiview computer. Static images were taken at the end of the dynamic study and after breakfast. Blood and urine samples were collected for 24 hours and the amount of radioactivity was measured with a well type scintillation detector. The radiopharmacokinetic results are listed in tables 1-4.(ABSTRACT TRUNCATED AT 250 WORDS)

[Total water content in cardiac patients]. / Contenido de agua total en cardiopatas.

In the present study total body water was determined in a group of cardiac patients, using titriated water. The study was performed in a service of internal medicine of an important hospital in Mexico City. Of the 30 patients originally evaluated, only 23 could be considered cardiacs; of these 47.83% had an excess of water, 39.13% had a normal amount and 13.04% were dehidrated. The patients belonged to both sexes and their ages were anywhere between 14 and 82 years. Very often, other aliments or conditions were present which had a bearing on the total body water. The test is innocuous and the bother to the patient is minimal constituting a valuable auxiliary to the clinician.