The volatility characteristics of Vietnamese coffee export price and transmission mechanism of influencing factors: a Markov switching approach

Purpose This study aims to examine the transmission mechanism of factors on the characteristic fluctuation of Vietnamese coffee bean export price (PVN). Design/methodology/approach Applying Markov switching–vector autoregressive model. Findings Significantly, the empirical results showed that the transmission of independent variables on PVN is non-linear, and the fluctuation of PVN is affected by many factors, especially PVN in the previous period. In addition, the effect of Robusta coffee price was the greatest with coefficient is 0.28785, and the correlation between PVN and it was also the highest in both regimes with coefficients are 0.5317 and 0.3959, respectively. Originality/value These obtained results are in accordance with reality, as Vietnam is the largest exporter of Robusta coffee in the world.

Physical limit to concentration sensing in a changing environment

Cells adapt to changing environments by sensing ligand concentrations using specific receptors. The accuracy of sensing is ultimately limited by the finite number of ligand molecules bound by receptors. Previously derived physical limits to sensing accuracy have assumed that the concentration was constant and ignored its temporal fluctuations. We formulate the problem of concentration sensing in a strongly fluctuating environment as a non-linear field-theoretic problem, for which we find an excellent approximate Gaussian solution. We derive a new physical bound on the relative error in concentration c which scales as δc/c ~ (Dacτ)−1/4 with ligand diffusivity D, receptor cross-section a, and characteristic fluctuation time scale τ, in stark contrast with the usual Berg and Purcell bound δc/c ~ (DacT)−1/2 for a perfect receptor sensing concentration during time T. We show how the bound can be achieved by a simple biochemical network downstream the receptor that adapts the kinetics of signaling as a function of the square root of the sensed concentration.