The 20S proteasome is the catalytic core of the 26S proteasome. It comprises four stacked rings of seven subunits each, a 1-7 b 1-7 b 1-7 a 1-7 . Recent studies indicated that proteasome-specific chaperones and b-subunit appendages assist in the formation of a-rings and dimerization of halfproteasomes, but the process involved in the assembly of b-rings is poorly understood. Here, we clarify the mechanism of b-ring formation on a-rings by characterizing assembly intermediates accumulated in cells depleted of each b-subunit. Starting from b2, incorporation of b-subunits occurs in an orderly manner dependent on the propeptides of b2 and b5, and the C-terminal tail of b2. Unexpectedly, hUmp1, a chaperone functioning at the final assembly step, is incorporated as early as b2 and is required for the structural integrity of early assembly intermediates. We propose a model in which b-ring formation is assisted by both intramolecular and extrinsic chaperones, whose roles are partially different between yeast and mammals.
This paper presents an array of deformation-dependent flow models of various porosities and permeabilities relevant to the characterization of naturally fractured reservoirs. A unified multiporosity multipermeability formulation is proposed as a generalization of the porosity-or permeability-oriented models of specific degree. Some new relationships are identified in the parametric investigation for both single-porosity and dual-porosity models. A formula is derived to express Skempton's constant B by Biot's coefficient H and relative compressibility •b*. It is found that the recovery of the original expression for Skempton's constant B is largely dependent on the choice of 0', representing relative compressibility. The dual-porosity/dual-permeability model is evaluated through an alternative finite element approximation. The deformation-dependent fracture flow mechanism is introduced where the rock matrix possesses low permeability and fracture flow is dominant. A preliminary study of the reservoir simulation identifies the strong coupling between the fluid flow and solid deformation. curve where the important fluid interchange between fractures and matrix blocks occurs. In general, interporosity flow has been described by two mechanisms. The first is the simple quasi-steady state model proposed by Warren and Root [1963], followed by the more sophisticated unsteady state models of various versions [Kazemi, 1969; deSwaan-O., 1976; Duguid and Lee, 1977; Kucuk and Sawyer, 1980; Najurieta, 1980; Chen et al., 1985]. Some noticeable differences in terms of pressure distributions in the transition period result from the two different mechanisms. The transient flow and deformation behavior in a porous medium may result from changes in either the fluid pressure or total stress boundary conditions applied to the system. It is the admissibility of changes in total stress within the system (which may result from natural tectonic changes or human activities) that describes the essence of coupled deformation-dependent flow behavior within porous media and sets it apart from decoupled diffusive (flow) systems. Comprehensive coupling between stresses and pore pressures was first rationalized by Biot [1941] and later adopted in many applications to specific deformation flow systems [Ghaboussi and Wilson, 1973; Zienkiewicz et aI., 1977; Simon et al., 1984; Lewis and Schrefier, 1987; Detournay and Cheng, 1988]. In naturally fractured reservoirs where the medium consists of discrete fractions of varying solid compressibilities and permeabilities, a multiporosity/ multipermeability approach appears more appropriate.It is important to correctly characterize the behavior of naturally fractured reservoirs. For example, the exceptionally high oil rate recovered in the initial stages of reservoir production may lead to overestimating well production by assuming a higher storage to exist than exists in reality. It was assumed that the high matrix block storage would 1621
The synthesis of ammonia has been studied in methane-nitrogen plasmas using a micro-gap discharge under an environmentally friendly condition. The effects of some parameters such as the specific input energy, the discharge gap, the volume ratio of CH 4 / N 2 , the residence time, and the gas temperature on the yield of NH 3 and conversion rate of CH 4 are discussed in the paper. The results show that the highest yield of NH 3 is 8000 ppm for a residence time of 1.6 s. In addition, the yield and generating rate of H 2 are 9.1% (v/v) and 1879.8 lmol/min, respectively. Therefore, the micro-gap discharge is an efficient method for NH 3 synthesis and H 2 generation from CH 4.
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