Macroscopic Kinetic Effect of Cell-to-Cell Variation in Biochemical Reactions

Genetically identical cells under the same environmental conditions can show strong variations in protein copy numbers due to inherently stochastic events in individual cells. We here develop a theoretical framework to address how variations in enzyme abundance affect the collective kinetics of metabolic reactions observed within a population of cells. Kinetic parameters measured at the cell population level are shown to be systematically deviated from those of single cells, even within populations of homogeneous parameters. Because of these considerations, Michaelis-Menten kinetics can even be inappropriate to apply at the population level. Our findings elucidate a novel origin of discrepancy between in vivo and in vitro kinetics, and offer potential utility for analysis of single-cell metabolomic data

Impacts of Water Supply Changes on the Rice Market of Lao PDR: Stochastic Analysis of Supply and Demand Model

Laotian rice producers in upland areas experience highly fluctuating yields and production and producers in wet season rice areas in the southern region face high price risk. This paper examines the exposure to risk of producers in both regions facing changes in water supplies. A supply and demand model of rice in Laos, considering water supply changes, is developed and stochastic elements are added to the model to represent uncertainty in climatic variables. Furthermore, the risks associated with price and production fluctuation are evaluated by using the differences between market and certainty equivalent prices. The results show that the coefficient of variation of production is higher in upland rice than wet and dry season rice, i.e., 0.3226, and if the fluctuation of water supply increases 20%, the coefficient of variation of production will increase about 20% for all type of rice cultivation. In the case of expanding water supply fluctuations, potentially due to climatic change, the price risk of wet season rice will increase from 48.5 kip to 150.8 kip while that of upland and dry season rice will increase from 66.4 kip to 94.9 kip and 14.3 kip to 20.5 kip respectively. Examining provincial price risk of wet season rice, the differences between market and certainty equivalent prices are 56.3 kip and 33.9 kip in Champasack and Attapeu provinces. The regions or provinces which suffer highly fluctuating production and price risk may need to consider alternative water management and harvesting methods.water supply change, rice supply and demand model, stochastic model, Lao PDR, Q11, Q25, Crop Production/Industries, Resource /Energy Economics and Policy,

Precision Test of Mass Ratio Variations with Lattice-Confined Ultracold Molecules

We propose a precision measurement of time variations of the proton-electron mass ratio using ultracold molecules in an optical lattice. Vibrational energy intervals are sensitive to changes of the mass ratio. In contrast to measurements that use hyperfine-interval-based atomic clocks, the scheme discussed here is model-independent and does not require separation of time variations of different physical constants. The possibility of applying the zero-differential-Stark-shift optical lattice technique is explored to measure vibrational transitions at high accuracy.Comment: 4 pages, 4 figure

Non-Hermitian dynamics of slowly-varying Hamiltonians

We develop a theoretical description of non-Hermitian time evolution that accounts for the break- down of the adiabatic theorem. We obtain closed-form expressions for the time-dependent state amplitudes, involving the complex eigen-energies as well as inter-band Berry connections calculated using basis sets from appropriately-chosen Schur decompositions. Using a two-level system as an example, we show that our theory accurately captures the phenomenon of "sudden transitions", where the system state abruptly jumps from one eigenstate to another.Comment: 12 pages, 4 figure

Going Overboard? On Busy Directors and Firm Value

Abstract The literature disagrees on the link between so-called busy boards (where many independent directors hold multiple board seats) and firm performance. Some argue that busyness certifies a director’s ability and that such directors are value enhancing. Others argue that “over-boarded” directors are ineffective and detract from firm value. We find evidence that (1) the disparate results in prior work stem from differences in both sample composition and empirical design, (2) on balance the results suggest a negative association between board busyness and firm performance, and (3) the inclusion of firm fixed effects dramatically affects the conclusions drawn from, and the explanatory power of, multivariate analyses. We also explore alternative empirical definitions of what constitutes a busy director and find that commonly used proxies for busyness perform well relative to more complex alternatives. Highlights ► The disparate busy director findings result from different samples and methodology. ► Including firm fixed effects results in a constant negative relation. ► The common busy director definition is as informative as more intense alternatives