3 research outputs found
Tekuk Torsi Lateral Balok I Kantilever Non Prismatis
. This paper presents the results of a study about elastic lateral torsional buckling of web tapered cantilever I beams. Elastic buckling analysis was carried out on a number of web tapered cantilever I beam. Beam parameters are expressed in term of dimensionless parameter for lateral torsional buckling and the slope of the side of the tapered web. The analysis is performed using finite element method and the SAP 2000 v 14 program is used to do the analysis. The finite element formulation is based on bifurcation theory. This theory leads to Eigen Value Problem. Critical moment is the lowest Eigen value. The load to be considered is point load at the free end of the beam and uniformly distributed load. Three location of load are considered. The first is at shear center, the second is at top flange and the third is at the bottom flange.From this study, it can be concluded that the slope of the side of tapered web has little influence on the critical moment. But the influence of load height on critical moment is strongly influenced by the slope of the side of the tapered web. Equations for estimating the critical moment has been obtained by regression of the data results of the finite element method
Hydrolysis of the E2P Phosphoenzyme of the Ca<sup>2+</sup>-ATPase: A Theoretical Study
Dephosphorylation of the E2P phosphoenzyme
intermediate of the
sarcoplasmic reticulum Ca<sup>2+</sup>-ATPase was studied using density
functional theory. The hydrolysis reaction proceeds via a nucleophilic
attack on the phosphorylated residue Asp351 by a water molecule, which
is positioned by the nearby residue Glu183 acting as a base. The activation
barrier was calculated to be 14.3 kcal/mol, which agrees well with
values of 15β17 kcal/mol derived from experimentally observed
rates. The optimized structure of the transition state reveals considerable
bond breakage between phosphorus and the Asp351 oxygen (distance 2.19 Γ
)
and little bond formation to the attacking water oxygen (distance
2.26 Γ
). Upon formation of the singly protonated phosphate product,
Glu183 becomes protonated. The bridging aspartyl phosphate oxygen
approaches Lys684 progressively when proceeding from the reactant
state (distance 1.94 Γ
) via the transition state (1.78 Γ
)
to the product state (1.58 Γ
). This stabilizes the negative charge
that develops on the leaving group. The reaction was calculated to
be slightly endergonic (+0.9 kcal/mol) and therefore reversible, in
line with experimental findings. It is catalyzed by a preorganized
active site with little movement of the nonreacting groups except
for a rotation of Thr625 toward the phosphate group