Facebook, Dunbar’s Number and Geometry

Closest Packing of Spheres with Umbrella Light Camera
Closest Packing of Spheres with Umbrella Light Camera

NPR says: Don’t Believe Facebook; You Only Have 150 Friends and discusses Dunbar’s number.

Dunbar says there are some neurological mechanisms in place to help us cope with the ever-growing amount of social connections life seems to require. Humans have the ability, for example, to facially recognize about 1,500 people. Now that would be an impressive number of Facebook friends.
Yet the problem with such a large number of “friends,” Dunbar says, is that “relationships involved across very big units then become very casual — and don’t have that deep meaning and sense of obligation and reciprocity that you have with your close friends.”
One solution to that problem, he adds, can be seen in the modern military. Even as they create “supergroups” — battalions, regiments, divisions — most militaries are nonetheless able to maintain the sense of community felt at the 150-person company level.
“The answer has to come out of that,” Dunbar says, “trying to create a greater sense of community.

Wikipedia says of Dunbar’s number

Dunbar’s number is a theoretical cognitive limit to the number of people with whom one can maintain stable social relationships. These are relationships in which an individual knows who each person is, and how each person relates to every other person. Proponents assert that numbers larger than this generally require more restrictive rules, laws, and enforced norms to maintain a stable, cohesive group. No precise value has been proposed for Dunbar’s number. It has been proposed to lie between 100 and 230, with a commonly used value of 150. Dunbar’s number states the number of people one knows and keeps social contact with, and it does not include the number of people known personally with a ceased social relationship, a number which might be much higher and likely depends on long-term memory size.
Dunbar’s number was first proposed by British anthropologist Robin Dunbar, who theorized that “this limit is a direct function of relative neocortex size, and that this in turn limits group size … the limit imposed by neocortical processing capacity is simply on the number of individuals with whom a stable inter-personal relationship can be maintained.” On the periphery, the number also includes past colleagues such as high school friends with whom a person would want to reacquaint oneself if they met again.[3]

Christopher Allen writes about “The Dunbar Number as a Limit to Group Sizes“, and posits various sizes are stable, and others unstable, focusing on online communities.
In 2-dimensions, one penny can be surrounded by exactly 6 pennies (of equal size) that it touches. A group of eight pennies will not be as stable as a group of seven (six plus one), since the eighth orbits the close packing of pennies. However if you can fill the second ring, then you can add 12 more pennies (for a total of 19).
Closest packing of circles, spheres, cubes, pyramids, etc, provides a certain number of linkages at degree 0, another number at degree 1, and so on. This is like the valence number of electrons around the nucleus of an atom. Some numbers are stable, others are + or – and less stable.
Does the Dunbar number correspond to any particular physical shape that is stable around 150, but falls apart if larger? This might help explain the limits and network topology of our neurology.

How Affordable is Transportation? A Context-Sensitive Framework

A new report from CTS: How Affordable is Transportation? A Context-Sensitive Framework

Yingling Fan, Arthur Huang
May 2011
Report no. CTS 11-12, Series: Transitway Impacts Research Program
Projects: How Affordable is Transportation? An Accessibility-Based Evaluation
Topics: Modes, Transit
Transportation affordability refers to the financial burden households bear in purchasing transportation services. Traditional measures, which focus on what share of household disposable income or total budget goes to transportation services, often fail to consider the wide variation in households’ transportation needs and locational settings. In this project, we propose a contextualized transportation affordability analysis framework that differentiates population groups based upon their socio-demographics, the built environment, and the policy environment. The necessity of such a context-sensitive framework is demonstrated via a case study of the Twin Cities metropolitan area, which shows heterogeneity among different population groups in terms of their transportation needs and resource availability. The proposed context-sensitive framework points to two dilemmas associated with transportation affordability. First, the socio-economically disadvantaged group has the lowest auto ownership rate, yet its transportation needs are better served by automobiles. Second, while automobiles can reduce transportation hardship for the socio-economically disadvantaged, the existing auto-oriented urban landscape in the U.S. requires more travel for access to destinations, which leads to higher transportation costs. The dilemmas call for a multi-modal transportation solution: reducing societal auto dependence and providing financial subsidies for car access among disadvantaged populations are equally important to enhance transportation affordability and social welfare.


Heat buckles pavement, snarling Twin Cities traffic | Minnesota Public Radio News

A couple of days ago from MPR (back when it was summer, not winter), but more fodder for the asphalt vs. concrete war: Heat buckles pavement, snarling Twin Cities traffic

“Heat buckles pavement, snarling Twin Cities traffic
by Nancy Lebens, Minnesota Public Radio
June 6, 2011
St. Paul, Minn. — The Minnesota Department of Transportation is warning motorists to watch out for roads that might buckle without warning.
MnDOT spokesman Kent Barnard said the heat and humidity had caused pavement to heave on some Twin Cities metro highways.
Monday afternoon lanes were closed in I-94 in Minneapolis and St. Paul. Barnard said heat damaged roads in more than 20 places.
Barnard said he has not heard of accidents associated with buckling pavement. But he’d heard reports of damage to cars.
Older concrete highways are more prone to heave up, as debris fills the cracks between the panels, leaving no place for the pavement to expand.
‘The natural expansion places are filled up and so there is no place for that pavement to expand,’ Barnard said. ‘And the stress of that expansion looks for the weakest area. It could be another crack in the pavement or it could happen real close to where the expansion joint actually is.’
There’s no way to predict exactly where pavement will heave. Barnard said motorists should watch the road and not tailgate.
While the roads are still prone to buckle yet through the evening, Barnard said they should be better by the Tuesday morning commute.”