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Showing posts from February, 2014

Why Biological Systems Suddenly Change State: An Intuitive Guide to Freidlin–Wentzell Theory

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  Stochasticity is ubiquitous in biology and neuroscience, manifesting in various forms, including ion channel noise, synaptic variability, gene regulatory fluctuations, noisy population dynamics, and more. Many biological systems spend long periods in a stable “state” and only rarely transition to another state due to noise. For instance, a neuron typically remains inactive but may occasionally trigger a spontaneous spike. Similarly, a gene can switch from the OFF state to the ON state due to rare bursts of transcription factors. Cells can also transition out of metabolic or epigenetic states, populations might shift between different ecological equilibria, and a viral infection can fluctuate between phases of control and uncontrollability. Freidlin–Wentzell theory provides a mathematically rigorous framework to study these phenomena when noise is small but nonzero . It tells you, firstly, h ow likely rare transitions are,    secondly,   h ow fast they occ...

Global cooling. The crazy winter 2013-2014

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Another wave of frost is hitting the United States. The bad weather has caused paralysis of road traffic (with at least 13 deaths from traffic accidents) and the cancellation of about 6,000 flights in the last two days. The more dramatic  situation  is reported in North Carolina, where  because snow and ice have created an immense traffic jam in both directions of  the highway , with thousands of people trapped and hundreds of abandoned cars in the middle of the roadway . Just as had happened two weeks ago near Atlanta , Georgia. Over half a million homes and businesses were left without electricity due to power outage caused by snow and ice. President Barack Obama has declared a state of natural disaster in Georgia and South Carolina, sending federal aid. And the spate of bad weather is moving to the northeast, where heavy snowfalls are expected in Boston, the capital Washington and New York. The scenario is rather catastrophic . In the capital all federal offi...

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