# Archive | flotsam

## cyclicity and meditation

Ben Zimmerman, a neuroscientist working with us on the Slow Cortical Waves project, published a wonderful medium post reflecting on this work and much much more.

…for some reason the “default-mode” of the brain, what the mind automatically does at rest, seems to be to imagine and plan — to linger in the future or the past. This requires processing information from high-level semantic representations backwards to their constituent sensory components…

## taxes and incentives at work

For some reason I remembered yesterday that opinion by Greg Mankiw from 2010 where he warned us that the (then feared) tax hikes by Obama admin would diminish his personal incentives to work. He was talking very directly about his output as articles which we would miss: to quote, “I [would] supply less of my services[…;] because you are reading this article, you are one of my customers.”

I thought it would be interesting to check what the 2017′ Tax Cuts and Jobs Act did to Mankiw’s productivity.…

## more on matrix-tree formula

Fix a weighted graph $$\Gamma=(V,E), w:E\to \mathbb{R}$$.

The Laplacian $$L$$ of $$\Gamma$$ is the symmetric matrix

$$L_{u,v}=\left\{ \begin{array}{ll} -w(uv)&\mbox{ if }u\neq v,\\ \sum_{u’\neq u} w(uu’)& \mbox{ if }u=v\\ \end{array}\right..$$

(Here we view the weights $$w$$ as formal variables.)

As we all know, any principal minor of $$L$$ equals the sum of the weights of spanning trees of $$\Gamma$$.

Another way to define the principal minor is as the determinant of the restriction the quadratic form given by $$L$$ to any of the coordinate hyperplanes.…

## alons enfants de la patrie

In collaboration with Cynthia Sung, Daniel Feshbach and bloodthirsty French people……

## damping covid

This plot, from the Apple mobility site, reminded me of the standard paradigm of linear controlled systems: playing with your gains in linear control systems can affect damping behavior of your system.

It is intuitively clear from the picture, that something separates the NYC, Chicago, LA from Houston: one sees oscillations in Houston, not in the other three metropolises, – so reminiscent of the transition from overdamped to underdamped systems.

What is it? Here’s a toy model which accounts for this phenomenon.…

## simulating the opening

### Will the campus reopen in Fall?

Whether the schools will reopen in Fall is now a matter of prediction markets bets, but the planning at UofI is already underway.

The focus of the planning is, understandably, on the students, staff and faculty safety. Yet there is an aspect of the process going beyond the campus.

Indeed, UIUC is a primary campus of a large state school with a significant fraction of the students from Illinois, and, more to the point, students returning home on a regular basis.…

## misusing this crisis

This Monday, the University Senate Executive Committee (SEC) met in a special meeting and “voted unanimously to exercise its emergency powers to take” Resolution RS2003 on the University’s Response to COVID-19.

The process asks for giving the Members of the Academic Senate 3 days, till 5 p.m. of Thursday, March 26 to express their views, so that SEC can adopt a resolution and recommend a course of actions to the administration on Friday, March 27th.

This is a fast track action, if one ever saw one.…

## Introduction

As Covid-19 takes over the country, many organizations move their teams to work from home. Often, it is necessary to keep an office presence. This can be done in various ways: split your team into smaller units and let them alternate days, or weeks, or do completely random assignments (essentially, toss a coin for who will be in the office three days from now), etc. Or, one can abandon the fixed teams, and shuffle employees, again on a random or periodic basis…

These scenarios are apriori quite different in terms of their impact on infection propagation. …