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We have developed a new numerical technique, called Green’s-function reaction dynamics (GFRD), that makes it possible to simulate biochemical networks at the particle level and in both time and space. In this scheme, a maximum time step is chosen such that only single particles or pairs of particles have to be considered. For these particles, the Smoluchowski equation can be solved analytically using Green’s functions. The main idea of GFRD is to exploit the exact solution of the Smoluchoswki equation to set up an event-driven algorithm, which combines in one step the propagation of the particles in space with the reactions between them. The event-driven nature allows GFRD to make large jumps in time and space when the particles are far apart from each other. Here, we apply the technique to a simple model of gene expression. The simulations reveal that spatial fluctuations can be a major source of noise in biochemical networks. The calculations also show that GFRD is highly efficient. Under biologically relevant conditions, GFRD is up to five orders of magnitude faster than conventional particle-based techniques for simulating biochemical networks in time and space. GFRD is not limited to biochemical networks. It can also be applied to a large number of other reaction-diffusion problems. [ABSTRACT FROM AUTHOR]

In the present study, polyethersulfone (PES) membranes on a macroporous alumina support was prepared by solvent-deposition method to separate H2/CH4 mixture. The membrane solution viscosities were determined in order to understand the effect of PES concentration on the formation of selective membranes over a support. Supported PES membranes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and single gas permeability measurements of H2 and CH4. The membrane casting solution with 20% PES concentration provided the formation of defectless single-layer supported membrane. At lower concentrations, the penetration of membrane casting solution into the pores of support was prevented by using intermediate layer, hence the prepared 2-layered membrane performance was improved. H2/CH4 ideal selectivity of best membrane exhibited is 73 at 35 °C, which shows promise for H2/Hydrocarbon separation. [ABSTRACT FROM AUTHOR]

Waste mineral oil pollution causes serious environmental damages in long term. It affects the availability of nutrients in top layer of soil which is rich in organic matter and prevents the entrance of water and oxygen to the soil. In this study, two different mineral oil (1% and 5%) doses were amended to soil-soil+wastewater sludge samples and then an incubation study was performed during three months. Ammonium nitrogen, nitrate nitrogen, total nitrogen and hydrolysable (H) nitrogen forms (HO-amino nitrogen, HO-amide nitrogen, HO-hexozamine nitrogen, HO-rest nitrogen) were analyzed in samples. The results of the study indicated that total nitrogen concentrations in mineral oil containing soils were decreased at the end of the incubation period. It is determined that nitrogen mineralization and nitrification processes were inhibited in soils contaminated with high doses of mineral oil. The magnitude of hydrolysable nitrogen forms was found to be as H-amino-nitrogen>H-rest nitrogen=H-amide-nitrogen>H-heksozamine nitrogen. It was found that the percentages of hyrolysable nitrogen in total nitrogen varied between 94% and 96%. The results have indicated the faster mineralization of amino acids and accumulation of mineral nitrogen as amid N fraction, as well as the preferential use of mineral oil C as carbon source by microorganisms during the process. [ABSTRACT FROM AUTHOR]

In the study, it was described the process of development and application a diagnostic test identifying and documenting students' alternative conceptions related to diffusion and osmosis. The test development procedure had three general steps: defining the content boundaries of the test, identifying students' alternative conceptions, and instrument development. Alternative conceptions were derived from a multiple-choice test which also required free responses in addition to literature. This first draft of the test was applied to 119 ninth graders from three different high schools. The alternative conceptions gathered from this administration and literature was used for developing second tiers of the items. In this way, the final version of the test was clarified and applied to 90 ninth and 73 tenth graders at Erzurum Anatolian High School. The reliability coefficient for the whole test is 0.62, average difficulty index is 0.55, and average discrimination power is 0.41. According to the results revealed from application of the test, high school students had many alternative conceptions on diffusion and osmosis. [ABSTRACT FROM AUTHOR]

The presence of heavy metals such as cadmium(II), chromium(III), zinc(II), and copper(II), etc. in water and wastewater has been of great public concern. Heavy metals are frequently discharged into the environment from a number of industrial processes, including extractive metallurgy processes, electroplating, refining, leather tanning, metal finishing, printed circuit board manufacturing, and dyeing. Heavy metals are not biodegradable and tend to build up in living organisms, causing several diseases and disorder. It has been shown that copper deposited in human skin, liver, pancreas, brain, and myocardium may result in Wilson's disease. The maximum contaminant level goal under the Lead and Copper Rule, promulgated by the U.S. EPA in 1991 to limit the concentration of lead and copper in public drinking water at the consumer's tap, is 1.3 mg/L of copper. A wide range of methods have been used to remove heavy metals from aqueous solutions, such as electro- chemical precipitation, ultra-filtration, ion exchange, reverse osmosis, and sorption onto solid substrates such as activated carbon. Each of these methods has some significant drawbacks in practice. A major disadvantage of precipitation is the production of sludge. Ion exchange is considered a better alternative than precipitation. But, it is not economically feasible due to high operational cost. Adsorption using commercial activated carbon (CAC) can remove heavy metals from wastewater, such as Cd, Ni, Cr, Zn, and Cu. However, CAC is an expensive material for heavy metal removal. As a result, researchers have focused on finding low-cost adsorbents and investigated several absorbents such as bagasse sugar, starch xanthate, sawdust of pinus sylvestris, chitosan, bentonite, and discarded automobile tires. Discarded tires are an interesting and inexpensive medium for the sorption of toxic metals from aqueous solutions. In this study, crumb rubber was chosen for the removal of copper from aqueous solution and used for the pre-concentration/separation of copper prior to its determination by flame atomic absorption spectrometry (FAAS). At first the adsorption properties of crumb rubber were investigated by batch technique using inductively coupled plasma-optical emission spectrometry (ICP-OES). The effects of pH, contact time and initial metal concentration on the removal of Cu(II) were studied. Experiments with solution pH as a variable were conducted to determine the optimum pH range for maximum Cu adsorption by crumb rubber at different initial Cu(II) ion concentrations. In all cases, it was found that the uptake increased as the initial pH increased from 1.5 to 6 and slightly changed at the pH value of 7. Therefore, the following experiments were performed in the solution pH of 6. The effect of contact time on the removal of copper by crumb rubber at different initial Cu(II) ion concentrations was studied. In all cases, the removal increases with time and attains equilibrium in 72 hr. The metal uptakes versus time curves are single, smooth and continuously leading to saturation, suggesting the possible monolayer coverage of metal ions on the surface of the adsorbent. The removal of Cu(II) by adsorption on crumb rubber has been shown to take place rapidly for all initial concentrations.… [ABSTRACT FROM AUTHOR]