Distinct element codes

The mechanical phase of the computation has made use of the 3DEC distinct element code, which relies upon an explicit solution of motion equations based on small lime steps the ensuing computation cycles lead to achieving equilibrium. The blocks separated by discontinuities were considered as elastic in the FEBEX case. Joints respect the Coulomb slip criterion characterised by normal and shear stiffnesses, as well as friction, cohesion and tensile strength properties assigned to each joint. 

The two-dimensional distinct element code, UDEC (Itasca, 2000) is applied for the modeling of mechanical and hydraulic behaviours. UDEC simulates the response of a fractured rock mass represented as an assemblage of discrete deformable blocks, subjected to the mechanical stress and hydraulic pressure boundary condition. Numerical experiment consists of 1) generation of a Discrete Fracture Network (DFN) as a geometric model, 2) application of various stress conditions, and 3) application of fluid boundary condition and calculation of equivalent permeability. 

Itasca Consulting Group, Inc., 1994. 3DEC 3-Dimensional Distinct Element Code. Minneapolis, Minnesota ICG. 

Itasca Consulting Group (1998) 3DEC - universal distinct element code, Minneapolis... 

To take care of the first two points we can drop the use of the macro USE from subroutine scfGR and simply write down the decisions necessary to evaluate the contributions to the distinct elements of the G matrix, using the equalities amongst the labels to decide whether or not to double the relevant contribution. This leads to some very unappealing looking code but it is a good deal more efficient than the original. 

A replication-deficient adenovirus has been used to deliver a gene construct, which contains within its promoter region a radiation-responsive element. Upon irradiation with conventional doses of X rays, this construct initiates transcription of the gene coding for the toxic cytokine, tumor necrosis factor-a (35). The above is an exquisite example of how emerging delivery and gene therapies are fast blurring the distinction between an active and an excipient (Fig. 3D). 

Fig. 1. Control regions that regulate transcription of a typical eukaryotic protein-coding gene. Although shown as distinct entities here for clarity, in vivo the different regulatory proteins bound to the control elements and distant enhancers interact with each other and with the general transcription factors of the transcription initiation complex to modulate the rate of transcriptional initiation.

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