Archive for September, 2020

Engineer detects “soul crushing” patterns in “A Million Random Digits”

Posted by mark in Basic stats & math, Uncategorized on September 27, 2020

Randomization provides an essential hedge against time-related lurking variables, such as increasing temperature and humidity. It made all the difference for me succeeding with my first designed experiment on a high-pressure reactor placed outdoors for safety reasons.

Back then I made use of several methods for randomization:

  • Flipping open a telephone directory and reading off the last four digits of listings
  • Pulling out number from pieces of paper put in my hard hat (easiest approach)
  • Using a table of random numbers.

All of these methods seem quaint with the ubiquity of random-number generators.* However, this past spring at the height of the pandemic quarantine, a software engineer Gary Briggs of Rand combatted boredom by bearing down on his company’s landmark 1955 compilation of “A Million Random Digits with 100,000 Normal Deviates”.**

“Rand legend has it that a submarine commander used the book to set unpredictable courses to dodge enemy ships.”

Wall Street Journal

As reported here by the Wall Street Journal (9/24/20), Briggs discovered “soul crushing” flaws.

No worries, though, Rand promises to remedy the mistakes in their online edition of the book — worth a look if only for the enlightening foreword.

* Design-Expert® software generates random run orders via code based on the Mersenne Twister. For a view of leading edge technology, see the report last week (9/21/20) by HPC Wire on IBM, CQC Enable Cloud-based Quantum Random Number Generation.

**For a few good laughs, see these Amazon customer reviews.

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Magic of multifactor testing revealed by fun physics experiment: Part Three—the details and data

Posted by mark in design of experiments, Education, Uncategorized on September 2, 2020

Detail on factors:

  1. Ball type (bought for $3.50 each from Five Below (www.fivebelow.com)):
    • 4 inch, 41 g, hollow, licensed (Marvel Spiderman) playball from Hedstrom (Ashland, OH)
    • 4 inch, 159 g, energy high bounce ball from PPNC (Yorba Linda, CA)
  2. Temperature (equilibrated by storing overnight or longer):
    • Freezer at about -4 F
    • Room at 72 to 76 F with differing levels of humidity
  3. Drop height (released by hand):
    • 3 feet
    • 6 feet
  4. Floor surface:
    • Oak hardwood
    • Rubber, 3/4″ thick, Anti Fatigue Comfort Floor Mat by Sky Mats (www.skymats.com)

Measurement:

Measurements done with Android PhyPhox app “(In)Elastic”. Record T1 and H1, time and height (calculated) of first bounce. As a check note H0, the estimated drop height—this is already known (specified by factor C low and high levels).

Data:

Std   # Run   # A: Ball type B: Temp deg F C: Height feet D: Floor type Time seconds Height centimeters
1 16 Hollow Room 3 Wood 0.618 46.85
2 6 Solid Room 3 Wood 0.778 74.14
3 3 Hollow Freezer 3 Wood 0.510 31.91
4 12 Solid Freezer 3 Wood 0.326 13.02
5 8 Hollow Room 6 Wood 0.829 84.33
6 14 Solid Room 6 Wood 1.119 153.54
7 1 Hollow Freezer 6 Wood 0.677 56.17
8 4 Solid Freezer 6 Wood 0.481 28.34
9 5 Hollow Room 3 Rubber 0.598 43.92
10 10 Solid Room 3 Rubber 0.735 66.17
11 2 Hollow Freezer 3 Rubber 0.559 38.27
12 7 Solid Freezer 3 Rubber 0.478 28.03
13 15 Hollow Room 6 Rubber 0.788 76.12
14 11 Solid Room 6 Rubber 0.945 109.59
15 9 Hollow Freezer 6 Rubber 0.719 63.43
16 13 Solid Freezer 6 Rubber 0.693 58.96

Observations:

  • Run 7: First drop produced result >2 sec with height of 494 cm. This is >16 feet! Obviously something went wrong. My guess is that the mic on my phone is having trouble picking up the sound of the softer solid ball and missed a bounce or two. In any case, I redid the bounce.
    • Starting run 8, I will record Height 0 in Comments as a check against bad readings.
  • Run 8: Had to drop 3 times to get time registered due to such small, quiet and quick bounces.
    • Could have tried changing setting for threshold provided by the (In)Elastic app.
  • Run 14: Showing as outlier for height so it was re-run. Results came out nearly the same 1.123 s (vs 1.119 s) and 154.62 cm (vs 153.54). After transforming by square root these results fell into line. This makes sense by physics being that distance for is a function of time squared.

Suggestions for future:

  • Rather than drop the balls by eye from a mark on the wall, do so from a more precise mechanism to be more consistent and precise for height
  • Adjust up for 3/4″ loss in height of drop due to thickness of mat
  • Drop multiple times for each run and trim off outliers before averaging (or use median result)
  • Record room temp to nearest degree

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