Set Of Experiments In Order Research Articles

Comparison of Chars Obtained under Oxy-Fuel and Conventional Pulverized Coal Combustion Atmospheres

The combustion of coal in conventional power plants produces large amounts of CO2 which contributes to the greenhouse effect. One of the ways to approach the CO2 emissions abatement is to burn the coal in an O2/CO2 atmosphere which eliminates the need of a separation step. In this study, two coals of different rank (a high volatile and a low volatile bituminous) have been burned in a drop tube reactor using O2/N2 and O2/CO2 mixtures with increasing oxygen content from 0 to 21%. Various oxygen concentrations have been selected for each set of experiments in order to follow both the progress of combustion and the influence of oxygen content in the devolatilization behavior of coal. Results show that a higher amount of O2 in CO2 than in N2 is needed to achieve similar burnout levels. Significant differences were found in the influence of oxygen content on the devolatilization behavior of the lower and higher rank coal. The limited amount of oxygen in the reacting atmosphere resulted in volatile release inhib...

Post-irradiation annealing of small defect clusters

Post-irradiation annealing studies indicate small defect clusters may be a potential contributor to IASCC. In this study, small defect clusters and their behavior during annealing are examined. A CP-304 SS alloy was irradiated with 3.2 MeV protons to 0.17 dpa at <75°C. The increase in hardness after 0.17 dpa at <75°C was greater than that after 0.55 dpa at 360°C, but dropped significantly after annealing at 350°C for short times, although, no dislocation damage was observed using transmission electron microscopy (TEM). For samples irradiated in a previous study at 360°C, the smallest dislocation loops and clusters were removed preferentially during annealing at 500°C for 45 minutes. Computer simulations of the annealing behavior were performed for the data from both sets of experiments in order to gain further insight into the nature of small clusters.

Ex-situ post-deposition processing for large area Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ films and coated tapes

Ex-situ post-deposition reaction processing is considered a promising alternative to in-situ physical vapor deposition techniques for coated Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ conductor development. It was reported recently that attempts at ex-situ processing of long Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ precursor tapes resulted in an inhomogeneous growth rate over the tape length and rather poor properties for the whole sample. We performed a set of experiments in order to clarify the mechanisms for the ex-situ processing of large area films and estimate properties of long coated conductors manufactured by the ex-situ technique. It was found that rate limiting step of ex-situ growth of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ is removal of the reaction product, hydrofluoric acid, by both gas diffusion and convection in the reaction atmosphere. We report on a quantitative model that well describes the observed growth rates for films with various areas.

Differential suppression of the human mixed epidermal cell lymphocyte reaction (MECLR) and mixed lymphocyte reaction (MLR) by cis-urocanic acid.

Cis-urocanic acid (UCA), formed in the stratum corneum by UV irradiation of trans-UCA has been proposed as a mediator of UV-induced immunosuppression in the skin. In this study, we examined the in vitro effect of cis-UCA (6-100 micrograms/mL) on the human mixed lymphocyte reaction (MLR) and the mixed epidermal cell lymphocyte reaction (MECLR). Addition of cis-UCA (purified or in a mixture with trans-UCA) did not affect the MLR but was able to induce a 20% suppression of the MECLR responses. Because this effect of cis-UCA on the MECLR was not as strong as could be expected from previous in vivo results, we designed a set of experiments in order to enhance the in vitro immunosuppressive capacity of cis-UCA. Firstly, we preincubated epidermal cells with UCA (50 micrograms/mL). for 3 or 6 days before culture in the MECLR because in vivo repeated UV exposure can lead to a photostationary state, where cis-UCA may be present for several weeks. This pretreatment with cis-UCA resulted in a maximal decrease of the MECLR response of 27%, whereas trans-UCA had no effect. Secondly, we investigated whether UVB irradiation of epidermal cells could make cells more sensitive to cis-UCA. However, addition of trans- or cis-UCA did not potentiate the reduced alloactivating capacity of UVB-irradiated cells. Finally, we examined the possibility of a synergistic effect of cis-UCA with histamine. Addition of histamine suppressed the MLR and MECLR responses, but neither cis- nor trans-UCA were able to modulate this decrease. We conclude that cis-UCA can partly downregulate the human MECLR but not the MLR. The mechanism involved in this differential downregulation is not known. In this respect it is striking that cis-UCA dose not potentiate the UVB- or histamine-induced suppression of the MECLR.

Interactions between nitrate and ammonium during uptake by carob seedlings and the effect of the form of earlier nitrogen nutrition

Seedlings of carob (Ceratonia siliqua L. cv. Mulata) were used in two sets of experiments in order to evaluate; (1) the reciprocal effects of each nitrogen form on net uptake of nitrate and ammonium, and (2) the effect of earlier nitrogen nutrition on ammonium versus nitrate uptake. In the former group of experiments we studied the kinetics of nitrate and ammonium uptake as well as the interference of each of the two forms with net uptake of ammonium and nitrate by both nitrogen depleted and nitrogen fed carob seedlings. On the whole, nitrogen depletion led to increase in both affinity and Vmax of the system for both forms of nitrogen, at the same time as the effects of nitrate on uptake of ammonium and vice versa were concentration dependent. In the second group of experiments the effects of earlier nitrogen nutrition on nitrate and ammonium uptake were characterized, and in this case we observed that: (a) if only one form of N was supplied, ammonium was taken up in greater amounts than nitrate; (b) the presence of ammonium enhanced nitrate uptake; (c) ammonium uptake was inhibited by nitrate; (d) there was a significant effect of the earlier nitrogen nutrition on the response of the plants to a different nitrogen source. The latter was evident mainly as regards ammonium uptake by plants grown in ammonium nitrate. The interactions between nitrate and ammonium uptake systems are discussed on the basis of the adaptation to the nitrogen source during early growth.

Cardiac and vascular effects of chronic angiotensin converting enzyme inhibition at subantihypertensive doses

We performed two sets of experiments in order to prevent or to regress cardiac and vascular hypertrophy, using antihypertensive and subantihypertensive doses of the angiotensin converting enzyme inhibitor zabicipril. Spontaneously hypertensive rats (SHR) begin to develop hypertension at less than 4 weeks of age and reach stable hypertension levels after 12-14 weeks. The blood pressure increase is accompanied by the development of cardiac and vascular hypertrophy. Treatment of SHR in utero and up to the age of 20 weeks with an antihypertensive dose of zabicipril (1 mg/kg per day) not only prevented the development of high blood pressure but also the development of cardiac and vascular hypertrophy. This effect was demonstrated by a significant decrease in left ventricular weight and the number of smooth muscle cell layers in the vascular media, media thickness and the media:lumen ratio in mesenteric arteries. In contrast, antihypertensive treatment with the Ca2+ antagonist verapamil (100 mg/kg per day) and the subantihypertensive dose of zabicipril (0.01 mg/kg per day) did not affect the development of cardiac and vascular hypertrophy. We found a significant increase in the length and surface density of myocardial capillaries after treatment with zabicipril at 1 mg/kg per day, indicating that the capillary density had improved and therefore that the oxygen supply of the heart was improved. Similar findings were observed with the low dose of zabicipril in SHR, although these rats had high blood pressure and cardiac and vascular hypertrophy. Treatment of adult SHR for 16 weeks with zabicipril at 1 mg/kg per day completely normalized their blood pressure levels. This effect was accompanied by a regression of left ventricular but not of vascular hypertrophy. Treatment with an antihypertensive dose of verapamil or with a subantihypertensive dose of zabicipril had no effect on cardiac and vascular hypertrophy.

An integrated modeling-experimental strategy for the analysis of metabolic pathways

An inherent problem in studying the behavior of a metabolic pathway is the impossibility of developing a complete, detailed model that includes all the cellular processes that have an impact on the set of fluxes in such a pathway. Lacking this, one requires some means of modeling the interactions between a metabolic pathway and other cellular processes for the purpose of analyzing pathway characteristics within the cell (e.g., determining sensitivity coefficients for various steps in the pathway) with a minimal amount of time and effort. A general framework is developed for studying these issues in a rigorous manner. Using this framework, detailed knowledge about a metabolic pathway (i.e., a set of rate expressions for steps in the pathway) can be combined with the results from a relatively simple set of experiments in order to obtain estimates for the sensitivity of the pathway to enzyme activities, inhibition constants, and other parameters that determine the pathway's behavior, while accounting for the pathway's interaction with the rest of the cellular metabolism. A model system representing amino acid production is used to illustrate the problem and to provide results based on computational experiments. The modeling strategy described here should be useful in genetic design to improve pathway fluxes and metabolic network selectivity.

Pulsed laser heating profile width and changes in total coupling with pulse length and pressure

Thermal coupling involves the heat absorbed by a surface in air under irradiation by a laser beam. At high incident intensities plasmas are ignited and there is an enhancement of total thermal coupling. Part of this occurs as some energy is transferred to the region outside of the laser beam spot because of plasma growth with increasing energy. The diameter of disk-shaped targets was used as a parameter in one set of experiments in order to determine the width of the radial heating profile. Second, when the axial temperatures of thin targets were measured as a function of time, there was a relationship for those and the assumed radial heating profiles which allowed the use of the Laplace inversion technique to obtain their widths. When the laser pulse length was varied over the range 1–25 μsec, the thermal coupling peak and threshold showed only small changes. No real optimization was seen when an initial spike was present. Thermal coupling at 0.1 Torr air pressure was found to lack the normal 1-atm enhanced regime. No abrupt intensity or fluence threshold was seen for either aluminum or titanium and the variation of thermal coupling with fluence was material dependent. Total thermal coupling maxima at 0.1 Torr were lower than those seen at 1 atm.

Electrophysiological demonstration of an excitatory subthalamonigral pathway in the rat

The subthalamonigral projection was studied with extracellular techniques in the rat. Orthodromic and antidromic stimulations of this pathway were performed in different sets of experiments in order to exclude the possible activation of passing fibers. A majority of the recorded cells in the subthalamic nucleus (STN) were antidromically activated by nigral stimulation. It was furthermore shown that the subthalamofugal fibers are excitatory to cells located in the pars compacta as well as in the pars reticulata of the substantia nigra. The possible existence of another descending STN pathway is also discussed.