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The Dubious Power of Power Laws

Submitted by jdp on Wed, 09/23/2015 - 11:23 am


Everyone knows the classic normal distribution—the “bell curve,” where most observations cluster around the mean, and the frequency falls off toward either end, with well known statistical properties. Lots of things in nature are more-or-less normally distributed, but lots of things are not. In some cases distributions are “heavy-tailed,” such that for example there are many of the small ones, and increasingly fewer as size increases. Famous examples are the distribution of earthquake magnitudes, rank-size distributions of cities, and the distribution of wealth in societies.

Models of avalanche size distributions in (mathematically-simulated) sand piles were seminal in developing ideas about self-organized criticality and power laws, both in geomorphology and in general. Unfortunately even real sandpiles, much less more complex systems, are not necessarily well described by the models.

Convergence, Divergence & Reverse Engineering Power Laws

Submitted by jdp on Sun, 09/20/2015 - 05:18 pm

Landform and landscape evolution may be convergent, whereby initial differences and irregularities are (on average) reduced and smoothed, or divergent, with increasing variation and irregularity. Convergent and divergent evolution are directly related to dynamical (in)stability. Unstable interactions among geomorphic system components tend to dominate in earlier stages of development, while stable limits often become dominant in later stages. This results in mode switching, from unstable, divergent to stable, convergent development. Divergent-to-convergent mode switches emerge from a common structure in many geomorphic systems: mutually reinforcing or competitive interrelationships among system components, and negative self-effects limiting individual components. When the interactions between components are dominant, divergent evolution occurs. As threshold limits to divergent development are approached, self-limiting effects become more important, triggering a switch to convergence. The mode shift is an emergent phenomenon, arising from basic principles of threshold modulation and gradient selection.

Circular Reasoning

Submitted by jdp on Fri, 09/18/2015 - 05:11 pm

Scientists, including geographers and geoscientists, are easily seduced by repeated forms and patterns in nature. This is not surprising, as our mission is to detect and explain patterns in nature, ideally arising from some unifying underlying law or principle. Further, in the case of geography and Earth sciences, spatial patterns and form-process relationships are paramount.

Unfortunately, the recurrence of similar shapes, forms, or patterns may not tell us much. Over the years we have made much of, e.g. logarithmic spirals, Fibonacci sequences, fractal geometry, and power-law distributions—all of which recur in numerous phenomena—only to learn that they don’t necessarily tell us anything, other than that several different phenomena or causes can lead to the same form or pattern. The phenomenon whereby different processes, causes, or histories can lead to similar outcomes is called equifinality.

Center pivot irrigation in Kansas, USA (USGS photo).

Faculty Poster Presentation

Submitted by lajo234 on Mon, 09/14/2015 - 08:25 am

The Department of Chemistry hosted a Faculty Poster Presentation on Friday, September 4, 2015.  This annual event is an opportunity for new graduate students to meet Chemistry faculty members and learn about their current research projects.Each of the 30 new graduate students needs to choose a research group by December, and the poster Presentation is designed them find a project that aligns with their interests.  This choice is critical, because the research group a student chooses this semester will determine the course of his or her academic career.

Disturbing Foundations

Submitted by jdp on Thu, 09/10/2015 - 04:55 pm

Some comments from a reviewer on a recent manuscript of mine dealing with responses to disturbance in geomorphology got me to thinking about the concept of disturbance in the environmental sciences. Though the paper is a geomorphology paper (hopefully to be) in a geomorphology journal, the referee insisted that I should be citing some of the “foundational” ecological papers on disturbance. These, according to the referee, turned out to be papers from the 1980s and 1990s that are widely cited in the aquatic ecology and stream restoration literature, but are hardly foundational in general.

Consideration of the role of disturbance goes back to the earliest days of ecology, and is a major theme in the classic papers of, e.g., Warming, Cowles, and Clements in the late 19th and early 20th centuries. A general reconsideration (“reimagining” is the term many would use, but I’ve grown to hate that overused word) of the role of disturbance in ecological systems was well underway by the 1970s, and the last five years or so have seem some very interesting syntheses of these emerging ideas (two I especially like are Mori, 2011 and Pulsford et al., 2014).

Meet Aaron Vaught

Submitted by asvaug2 on Thu, 09/10/2015 - 01:26 pm

I grew up in Somerset, KY and came to Lexington in 2006 to attend UK. I graduated with a BA in Geography in 2009 and an MS in Education Policy in 2012. As an undergraduate, I helped out in a preschool classroom at Booker T. Washington Elementary. I was also an Arts & Sciences Ambassador my senior year. In graduate school, I worked in the Center for Student Involvement and was the advisor to the Center for Community Outreach programs.  Along the way I met my wife Ashley and we have been married 4 years.


1.       What is your favorite movie or book? I tend to read more periodicals/newspapers than books. I am usually reading a combination of The Economist, BusinessWeek, National Geographic, and Mental Floss.

2.       What is your favorite animal? Definitely a dog person. My wife and I have a goldendoodle named Luna (of Harry Potter fame).

Meet John Haas!

Submitted by UK01682 on Wed, 09/09/2015 - 12:38 pm

John is a sophomore from Louisville, Kentucky. John is new to the College of Arts & Sciences, and is a student office assistant in the Department of Chemistry.

John finds that working in the College of Arts & Sciences has been very useful for a career in accounting or finance. He has already gained some helpful insights regarding his own communications skills and has increased his knowledge and proficiency in using the Microsoft Office Suite of products.

Currently, John and one other student worker in the Chemistry Department are working on a project to help redo the classroom signs around the Chemistry-Physics building. He feels that he is an important part of the process and that their insight on what would be most helpful for the students will be taken into account and potentially implemented.

When he isn’t hard at work in Arts & Sciences, John is an avid sports fan and loves to attend UK football and basketball games. He also enjoys professional sports and follows the Green Bay Packers, Arsenal and Bayern Munich football clubs. John spends his free time either reading or being in nature, and enjoys fishing, canoeing, and exploring.


Welcome to A&S, John.

Bank Full Of It

Submitted by jdp on Wed, 08/26/2015 - 04:38 pm

Fluvial geomorphologists, along with hydrologists and river engineers, have long been concerned with the flows or discharges that are primarily responsible for forming and shaping river channels. In the mid-20th century it was suggested that this flow is associated with bankfull stage—the stage right at the threshold of overflowing the channel—and that this occurs, on average, about every year or two in humid-climate perennial streams. If you have to choose just one flow to fixate on—and sometimes you do, for various management, design, and assessment purposes—and have no other a priori information about the river, bankfull is indeed the best choice. But, of course, nature is not that simple.

Meet Cheryl Edwards

Submitted by cledwa2 on Thu, 08/20/2015 - 08:28 am
Hi Everyone!  My name is Cheryl Edwards.  I work in the POT IBU in the College of Arts & Sciences.  I’ve worked at UK since August 2001.  I worked in the Biology Dept. for about 12 years before the reorganization.  I worked at the Hardin County Clerk’s Office/Vehicle Registration in Hardin County (Elizabethtown) for 15 ½ years before moving to Lexington.  I grew up military, mostly between Ft. Knox and Germany.  My mother is German and I was born there.  I have one sister and two brothers.
Random/fun fact about myself:  I have an unusual hobby that some people at UK know about.  I’m a sweepstaker!  By that, I mean that I enter sweepstakes and contests.  I’ve been doing it for about 25 years.  I’ve won many things over the years—small things like t-shirts, Xbox, cash, a trip to New York and the biggest thing of all—my Jeep Wrangler!  I just love it.  But, just like any other hobby, it takes a lot of time, money and work.