Author Archives: mathscinotes

Everest Climbers With No Supplemental Oxygen

I recently have seen pictures on the news of a line of people preparing to summit Mount Everest (Figure 1), which got me thinking about the difficulty of waiting in line under low-pressure conditions.The vast majority of the people who climb Everest use supplemental oxygen. The air pressure at the summit of Everest is about 0.3 atmosphere, which is not enough to support human life for an extended period of time. But a relatively small number of people have climbed Everest with No Supplemental Oxygen (NSO). In this post, I will look at this very select group of people. Continue reading

 
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My Robot Lawn Mowers

I am working today in my garage office at my cabin in northern Minnesota. From the office window, I can see a Worx Landroid robot mowing the lawn (Figure 1). I installed two of these mowers  (one for garage and one for cabin) because I am not regularly at the cabin and wanted to ensure the lawn was mowed even when I could not be there. Continue reading

 
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US Dairy Industry Stats

Early in my life, I spent quite a bit of time around cows on small farms with about 160 to 200 acres of land, and 40 to 50 cows. I never saw a corporate farm. Three years ago, I spent quite a bit of time in Iowa working on a number of fiber optic deployments in rural areas populated with a large number of dairy operations. While performing fiber installation inspections, I noticed that many of the old farmhouses were occupied by renters and the land was being farmed by corporations. As I looked around both Iowa and Minnesota, I realized that the number of dairy farms is dropping fast (Figure 1).  Continue reading

 
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Using Excel to Convert a Number List to Dashed String of Ranges

While working on a test report for an aircraft manufacturer this week, I needed to convert a large number of number lists to strings of dashed ranges. For example, suppose you are given a list {1, 2, 3, 5, 6, 7, 8, 10}. Converting this list to a dashed set of ranges means generating the string "1-3, 5, 6-8, 10." Figure 1 shows another example with an optional prefix added to each number. Continue reading

 
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US Iron and Aluminum Mining During WW2

My vacation/retirement cabin is in the iron mining region of Minnesota. The rock throughout the area shows the reddish hue of iron. I recently heard some old-timers talking about how the intensity of mining operations during WW2 took the last of the high-grade iron ore (hematite –Figure 1) and left only low-grade ore (taconite). This comment made me curious about mining during WW2. Continue reading

 
Posted in History Through Spreadsheets | 2 Comments

Estimating Exponential Time Constants

I have been presented with a large amount of experimental data from which I need to determine many exponential time constants. There are so many time constants to calculate that I need to automate the process. Continue reading

 
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Determining RMS Acceleration for a Vibration Acceleration Spectral Density

I was asked last week to write a vibration test plan for a mobile electronic product. I am used to writing vibration test plans that follow canned procedures in standards like MIL-STD-810F or SAE J1455, but this case is different because the customer has specified a non‑standard random vibration acceleration profile, which is also called a Power Spectral Density (PSD). I need to determine the RMS g level for this profile. This post shows how I go about this calculation. I am not going to showing the customer's vibration PSD because it is proprietary. Instead, I will use a well‑known US Navy vibration PSD as a computation example (Figure 1). Continue reading

 
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Let's Grow Some Oats

I am going to grow and process some oats this year. This is a project that I have been interested in doing for a while because one of my sons is now in the oat business and he has shown some interest in working through the entire oat processing cycle. As a boy, I used to mill oats on the family farm, but I remember very little of that time. Continue reading

 
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Age of Supreme Court Justices at Confirmation with Power Query

I was listening to a political pundit mention that both US political parties want to confirm young Supreme Court justices to ensure that their judicial philosophies endure. I was curious as to whether that was true over time. I went to the Wikipedia and saw that they had a list of all the justices since the founding of the US and web pages for each justice. Sounds like a perfect opportunity for a bit of web scraping! Continue reading

 
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Power Query DATEDIF Function

I have been using Excel's DATEDIF function for years to determine the age of items in years, months, and days. I did not know that the function was unsupported and had issues until I ran into a bug last week. Because much of my personal work involves dates, I need to have an accurate age calculation function for use in Excel and Power Query. In this post, I will discuss a DATEIF workaround that I found online (Figure 1) and a Power Query age calculation function that I wrote based on a concept from Imke Feldmann. My workbook is available here for those who are interested. The workbook shows how I tested the routine by comparing it with the DATEDIF workaround results. I tested the boundary conditions and then random dates. The results agreed with the DATEDIF workaround of Figure 1 and an online date calculator. Continue reading

 
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