Generalized Haldane Equation and Fluctuation Theorem in the Steady State Cycle Kinetics of Single Enzymes

Enyzme kinetics are cyclic. We study a Markov renewal process model of single-enzyme turnover in nonequilibrium steady-state (NESS) with sustained concentrations for substrates and products. We show that the forward and backward cycle times have idential non-exponential distributions: \QQ_+(t)=\QQ_-(t). This equation generalizes the Haldane relation in reversible enzyme kinetics. In terms of the probabilities for the forward ($p_+$) and backward ($p_-$) cycles, $k_BT\ln(p_+/p_-)$ is shown to be the chemical driving force of the NESS, $\Delta\mu$. More interestingly, the moment generating function of the stochastic number of substrate cycle $\nu(t)$, follows the fluctuation theorem in the form of Kurchan-Lebowitz-Spohn-type symmetry. When $\lambda$ = $\Delta\mu/k_BT$, we obtain the Jarzynski-Hatano-Sasa-type equality: $\equiv$ 1 for all $t$, where $\nu\Delta\mu$ is the fluctuating chemical work done for sustaining the NESS. This theory suggests possible methods to experimentally determine the nonequilibrium driving force {\it in situ} from turnover data via single-molecule enzymology.Comment: 4 pages, 3 figure

Calorimetric Evidence of Strong-Coupling Multiband Superconductivity in Fe(Te0.57Se0.43) Single Crystal

We have investigated the specific heat of optimally-doped iron chalcogenide superconductor Fe(Te0.57Se0.43) with a high-quality single crystal sample. The electronic specific heat Ce of this sample has been successfully separated from the phonon contribution using the specific heat of a non-superconducting sample (Fe0.90Cu0.10)(Te0.57Se0.43) as a reference. The normal state Sommerfeld coefficient gamma_n of the superconducting sample is found to be ~ 26.6 mJ/mol K^2, indicating intermediate electronic correlation. The temperature dependence of Ce in the superconducting state can be best fitted using a double-gap model with 2Delta_s(0)/kBTc = 3.92 and 2Delta_l(0)/kBTc = 5.84. The large gap magnitudes derived from fitting, as well as the large specific heat jump of Delta_Ce(Tc)/gamma_n*Tc ~ 2.11, indicate strong-coupling superconductivity. Furthermore, the magnetic field dependence of specific heat shows strong evidence for multiband superconductivity

Relative Entropy: Free Energy Associated with Equilibrium Fluctuations and Nonequilibrium Deviations

Using a one-dimensional macromolecule in aqueous solution as an illustration, we demonstrate that the relative entropy from information theory, $\sum_k p_k\ln(p_k/p_k^*)$, has a natural role in the energetics of equilibrium and nonequilibrium conformational fluctuations of the single molecule. It is identified as the free energy difference associated with a fluctuating density in equilibrium, and is associated with the distribution deviate from the equilibrium in nonequilibrium relaxation. This result can be generalized to any other isothermal macromolecular systems using the mathematical theories of large deviations and Markov processes, and at the same time provides the well-known mathematical results with an interesting physical interpretations.Comment: 5 page

Progressive Collapse Resistance of Precast Concrete Beam-Column Sub-assemblages with High-Performance Dry Connections

Due to its relatively lower integrity, precast concrete structures are considered to be more vulnerable to progressive collapse than cast-in-place concrete structures. However, to date, majority of existing studies on progressive collapse focused on cast-in-place concrete structures, little attentions were paid to precast concrete structures. Among existing precast concrete structures, unbonded post-tensioning precast concrete structure is one of innovation dry connection structural systems, which no casting at the connections on site. Its excellent seismic performance was recognized by many studies, while studies on its progressive collapse resistance were very few. To fill this knowledge gaps, in this paper, eight half-scaled unbonded post-tensioning precast concrete beam-column sub-assemblages with different connection configurations were tested through pushdown tests to investigate their capacities and resistance mechanisms to prevent progressive collapse. The test results demonstrated various behaviors of beam-column sub-assemblages with different connection types. It was found that, as the longitudinal reinforcements were discontinuous across the beam-column joint region in the beams, flexural action observed in the cast-in-place concrete frames was not mobilized for the specimens with purely unbonded post-tensioning connections. When the specimens installed top-seat angles at the beam-column interfaces, considerable flexural action capacity could be mobilized for load resistance. Moreover, it was found that the failure modes of the specimens are distinctly different to that of conventional reinforced concrete frames or precast concrete frames with cast-in-place joints. The characteristic of compressive arch action and tensile catenary action in tested specimens is quite different to that of conventional reinforced concrete frames

Oxygen content variation and cation doping dependence of (La)1.4(Sr1-yCay)1.6Mn2O7 (y = 0, 0.25, 0.5) bilayered manganites properties

The results of the synthesis and characterization of the optimally doped (La)1.4(Sr1-yCay)1.6Mn2O7 solid solution with y=0, 0.25 and 0.5 are reported. By progressively replacing the Sr with the smaller Ca, while keeping fixed the hole-concentration due to the divalent dopant, the 'size effect' of the cation itself on the structural, transport and magnetic properties of the bilayered manganite has been analysed. Two different annealing treatments of the solid solution, in pure oxygen and in pure argon, allowed also to study the effect of the oxygen content variation. Structure and electronic properties of the samples have been investigated by means of X-ray powder diffraction and X-ray absorption spectroscopy measurements. Magnetoresistivity and static magnetization measurements have been carried out to complete the samples characterization. Oxygen annealing of the solid solution, that showed a limit for about y=0.5, induces an increase of the Mn average valence state and a transition of the crystal structure from tetragonal to orthorhombic while the argon annealing induces an oxygen under-stoichiometry and, in turn, a reduction of the Mn average valence state. Along with the Ca substitution, the Jahn-Teller distortion of the MnO6 octahedra is reduced. This has been directly connected to a general enhancement of the transport properties induced by the Ca-doping. For the same cation composition, oxygen over-stoichiometry leads to higher metal-insulator transition temperatures and lower resistivity values. Curie temperatures (TC) reduce by increasing the Ca-doping. The lower TC for all the annealed samples with respect to the 'as prepared' ones are connected to the strong influence on the magnetic interaction of the point defects due to the oxygen content variation.Comment: 49 pages, 13 figure