No Maxwell’s Demon at work in Ranque-Hilsch vortex tubes

PRL - The long-standing problem of how a vortex tube simultaneously produces hot and cold  air streams with nothing more than the injection of a high-speed peripheral air stream has been unravelled in this paper by simplification of the device to its lowest single element – a duct rotating about a central outlet delivering air from its periphery.  This simple case shows unequivocally that a pressure gradient driving air flow against a centrifugal gravitational field results in the air giving up kinetic and internal energy as angular propulsion, resulting in a temperature reduction at the central outlet.  The theory presented is based on thermodynamic principles and shows that the maximum temperature drop is a function of the velocity of the gas at the periphery of the tube.  The article also shows that the effect is easily scaled up.

Studying the Light Response of Living Photoreceptor Cells

LN12705 -  Eyes of living organisms represent advanced light harvesting systems, developed through hundreds of millions years of evolution. Some of their features are comparable or even superior to existing man-made photodetection devices. For example, rod photoreceptor cells of the retina, which are responsible for night vision and form the focus of the present study, represent miniaturized photodetectors containing a photosensitive element (rhodopsin pigment) along with a ‘‘built-in’’ chemical power supply (ATP produced by mitochondria). They have sensitivity down to single-photon level, and demonstrate a remarkable low noise operation. Understanding such properties of nature-given photodetectors stimulates considerable interest in interfacing them with sources of nonclassical light, such as light with a ‘‘fixed’’ number of photons, and ‘‘squeezed’’ light. We analyzed the electrophysiological response of an isolated rod photoreceptor of the  African Clawed Frog (Xenopus laevis) under stimulation by coherent and pseudothermal light sources. Using the suction-electrode technique for single cell recordings and a fiber optics setup for light delivery allowed measurements of the major statistical characteristics of the rod response. The results indicate differences in average responses of rod cells to coherent and pseudothermal light of the same intensity and also differences in signal-to-noise ratios and second-order intensity correlation functions. These findings should be relevant for interdisciplinary studies seeking applications of quantum optics in biology.

Proteins in cell membranes studied using string theory to help unravel the mystery of sneezing

LQ13362  - We see how forces arising from thermal fluctuations could affect proteins embedded in cellular membranes by applying conformal field theory methods originally developed by string theorists.  Our research is inspired by an astonishing recent discovery that cell membranes can separate into two fluid regions (the way oil and water separate, but in two dimensions), forming microscopic fractal puddles of each in the membranes of living cells. We find that fluctuations in this complicated two-dimensional soup lead to long-range attractive forces between proteins preferring the same type of puddle, and repulsion between proteins preferring dissimilar puddles. These forces could help explain many mysteries in the experimentally observed behavior of membrane proteins.  For example, they may be important in clumping together the proteins that detect and respond to allergens in pollen, initiating a complex sequence of events that eventually makes you sneeze.