What is special about water as a matrix of life?

What dominates the time dependence of diffusion transverse to axons: Intra- or extra-axonal water?

Brownian motion of water molecules provides an essential length scale, the diffusion length, commensurate with cell dimensions in biological tissues. Measuring the diffusion coefficient as a function of diffusion time makes in vivo diffusion MRI uniquely sensitive to the cellular features about three orders of magnitude below imaging resolution. However, there is a longstanding debate, regarding which contribution --- intra- or extra-cellular --- is more relevant in the overall time-dependence of the diffusion metrics. Here we resolve this debate in the human brain white matter. By varying not…

Schrödinger's "What is Life?" at 75

2019 marked the 75th anniversary of the publication of Erwin Schrödinger's "What is Life?", a short book described by Roger Penrose in his preface to a reprint of this classic as "among the most influential scientific writings of the 20th century." In this article, I review the long argument made by Schrödinger as he mused on how the laws of physics could help us understand "the events in space and time which take place within the spatial boundary of a living organism." Though Schrödinger's book is often hailed for its influence on some of the titans who founded molecular biology, this article…

物理学基本常数告诉我们关于生命的什么？

What do the fundamental constants of physics tell us about life?

本文用Weisskopf式论证和量纲分析，展示如何用物理学基本常数定量估计化学自复制体的生长产率、倍增时间和休眠功耗，揭示物理定律对地球及宇宙生命的约束。

Water Movement in Vascular Plants: A Primer

The origin of land plants was one of the most important events in evolutionary history of earth in terms of its broad impact on metazoan life and the biotic environment. Because vascular tissues enabled land plants to meet the challenges of terrestrial life, it is important to understand the mechanistic basis of water transport through these tissues from soil to the canopy of trees, in some cases almost 100 meters high. The answers to these questions involve not only the biology of plant vasculature, but also the physical properties of water that enable such transport. Although early researche…

Brillouin microscopy, what is it really measuring?

Brillouin microscopy measures compressibility, but is being increasingly used to assess stiffness of cells and tissues. Using hydrogels with tunable properties, we demonstrate that Brillouin microscopy is insensitive to stiffness of hydrated materials, but depends strongly on water content, consistent with a theoretical model of biphasic compressibility. Empirical correlations between Brillouin measurements and stiffness arise due to their mutual dependence on water content, but correlations vanish once hydration is controlled.

生命之树在生长时是什么样子？演化与时间的多重分形性

What does the tree of life look like as it grows? Evolution and the multifractality of time

本文统一系统发育的嵌套性、二元性和随机性，将动态生命之树建模为随机迭代函数系统，证明其与时间均具有多重分形性而非超度量结构。

Whilst this Planet Has Gone Cycling On: What Role for Periodic Astronomical Phenomena in Large Scale Patterns in the History of Life?

One of the longstanding debates in the history of paleontology focuses on the issue of whether or not there have been long term cycles (operating over tens of millions of years) in biodiversity and extinction. Here we consider the history of this debate by connecting the skein from Grabau up to 2008. We focus on the evidence for periodicity that has emerged thus far, and conclude that there is indeed some evidence that periodicity may be real, though of course more work is needed. We also comment on possible causal mechanisms, focusing especially on the motion of our solar system in the Galaxy…