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“You can’t manipulate someone with candor and truth. That is called enlightenment.”

– (slightly paraphrased) from the book Changes by Jim Butcher

I had to stay home sick. Blah. Just lots of mild “blah” symptoms all over my person. I’m laying low so I feel better for my trip to Florida over Thanksgiving break!

Hypothetically, if you had three student loans totaling about $100,000 at different interest rates… say $3%, 5%, and 6%, would you push to pay them off or invest the “extra” money in the stock market?

My first thought was that the stock market generally pays 7% interest so I should pay down the 6% loan and put all the rest of the money into the stock market, but now I’m second-guessing myself. Thoughts?

Of course, first priority is to make a rainy day fund and pay into any matching 401(k) programs.

…

I found some answers for myself….

Look at this cool chart (via) (local copy). This chart shows how the S&P 500 index performed over the past hundred years. There is a “20 year” diagonal line, I highlighted it in red in the image to the right. Read the numbers on that line. For investments put in from 1930 until today, the S&P 500 has made pretty reliable 7% interest (as low as 4%, as high as 14%) per year. If you can wait 30+ years (highlighted in yellow in the image to the right), it’s a VERY reliable 7-9% interest rate, you can see that by looking at the far right side of the chart. Looking at the 10 year diagonal, the interest rates are more variable, -4% to 14%.

I’ve got about 20 years to retirement. With a 20 year window, the S&P 500 should always beat a 4% loan. Everything else is a crap-shoot. For example, with a 10 year window, $100,000 could balloon into $370,000 (that’s 14%, compounded yearly) woo hoo! That’s a nice nest-egg to retire on!   Or, it could eviscerate $100,000 into $66,000 (4% loss, compounded yearly). [sad trombone] enough to get me into a chichi cardboard-box retirement community.

So what to do?

Since I’ve got 20 years left, invest in the stock market (claiming my 4 – 14%), making sure to diversify enough to match the S&P 500. But in 5 years, it’ll be time to switch to the safer (3 – 6%) investing of paying down student loans instead of continuing to invest in a riskier 10 year plan that pays (-4% – 14%).

There was this awful noise that I’d sometimes hear in my room at school. It sounded like a machine in the walls suddenly turning on. Sometimes for a half a second, sometimes for a minute. On and off, on and off! It’d come on a bit more around 11am or so so I thought it might be related to kids going to the nearby bathroom. When it was happening and I had the opportunity, I’d run around the building looking for the source. It wasn’t the air conditioning, wasn’t the bathrooms, wasn’t the heaters, wasn’t the neighboring classrooms playing with power tools. I talked to the school custodian, to the neighboring teachers. But they all thought I was mad. I wasn’t mad! I wasn’t! I swear it!

Then, a few days ago, more than a YEAR after first noticing the sound, I found it! A water hammer in the sink of the classroom two doors down. So simple! When the kids were cleaning up from morning work, they’d turn on the water. Curiously, it was quieter in the room with the offending sink than in mine.

I got the most joy when Ms. S. the teacher one door down told me how for the last DECADE she was explaining-away that horrible sound to her students. We were both beaming!

I went to the custodian and explained what was going on. We wrote up a work order for the plumber together. And 3 days later, with one gentle turn of a wrench, the problem dissolved into the mists!

My in-laws’ two homes are each about 1 mile away from the flames of the Kincaid fire in Santa Rosa. Please send good wishes!

TL;DNR: Keeping the humidity at 40-60% dramatically decreases airborne infection rates!

Here are snippets from an article in Forbes, shown to me by Winnie Chen.

Oct 17, 2019, 09:30am
This Inexpensive Action Lowers Hospital Infections And Protects Against Flu Season
Leah Binder
Healthcare

“Harvard Medical School graduate and lecturer, Stephanie Taylor” heads this research…

“The one factor most associated with infection was (drum roll): dry air.”

“Taylor finds one of the most interesting studies from a team at the Mayo Clinic, which humidified half of the classrooms in a preschool and left the other half alone over three months during the winter. Influenza-related absenteeism in the humidified classrooms was two-thirds lower than in the standard classrooms–a dramatic difference.”

“They used to assume the microbes in desiccated droplets were dead, but advances in the past several years changed that thinking.”

In looking up hand research for work, I came across this super-cool machine learning article. In brief: a computer can read an X-Ray and tell if a person is a boy or girl really accurately and (at least some) doctors can’t! Maybe by paying attention to what the computer sees, doctors can figure out how to determine the gender of the hand in the X-ray.

https://link.springer.com/article/10.1007/s10278-018-0148-x

Abstract
Despite the well-established impact of sex and sex hormones on bone structure and density, there has been limited description of sexual dimorphism in the hand and wrist in the literature. We developed a deep convolutional neural network (CNN) model to predict sex based on hand radiographs of children and adults aged between 5 and 70 years. Of the 1531 radiographs tested, the algorithm predicted sex correctly in 95.9% (κ = 0.92) of the cases. Two human radiologists achieved 58% (κ = 0.15) and 46% (κ = − 0.07) accuracy. The class activation maps (CAM) showed that the model mostly focused on the 2nd and 3rd metacarpal base or thumb sesamoid in women, and distal radioulnar joint, distal radial physis and epiphysis, or 3rd metacarpophalangeal joint in men. The radiologists reviewed 70 cases (35 females and 35 males) labeled with sex along with heat maps generated by CAM, but they could not find any patterns that distinguish the two sexes. A small sample of patients (n = 44) with sexual developmental disorders or transgender identity was selected for a preliminary exploration of application of the model. The model prediction agreed with phenotypic sex in only 77.8% (κ = 0.54) of these cases. To the best of our knowledge, this is the first study that demonstrated a machine learning model to perform a task in which human experts could not fulfill.

Problem: At my school, I often want to keep my heavy, automatically-locking door open just a crack so I and the kids can get back in. Using a traditional wedge door-stop works but it often gets stepped on, kicked or misplaced. Now I use these pinch guards. When not in use, I use Velcro (AKA hook and loop fasteners) on the wall to keep them close-by. All-in, they cost less than $4 per door and they work very well!

Pinch-guard

Self Adhesive Hook and Loop Tape (Velcro)

Some tips and notes:

• Use long pieces of Velcro on both the pinch-guard and the doorway, it makes it easier to stick them to the wall quickly.
• For the Velcro, remember to put the “soft on the surface“. It makes it easier to feel the rough part on the pinch guard and it’s good to establish that as the norm in your room, you can stick objects onto fabric (a good stand-in for soft Velcro).
• The glue on the velcro didn’t hold to the pinch guard perfectly so I added staples.
• I had tried similar, popular horseshoe-shaped pinch guards but they didn’t work well on my thick door with a strong closer.
• It’s nice that this white pinch guard is easy to see on the door from a distance. Regular doorstops can be hard to see.

Update 10-29-19: These pinch guards are standing up to normal use but not rough abuse from my students in my classrooms. A student doesn’t have to be strong to tear it apart. I’ve come across a very sturdy rubber-plastic door pinch-guard but I don’t know where to buy more! Where can I buy more of these? They were apparently provided for all the classrooms when one of my schools was renovated in ~2007. See the photo to the right. This doorstop would be too heavy to hold in place with velcro so maybe the solution above is best.

The problem: In some of the classrooms I work in, students sometimes interrupt computer presentations on the teacher’s computer by randomly hitting the the keyboard.

The solution: A free Windows software utility. With it, the keyboard and mouse can be easily locked and unlocked with a special key combination, for example: Ctrl-Alt-F. This makes their computer immune to “fly-by” keyboard tapping. When the behavior doesn’t get the frustrated attention it used to, it is quickly extinguished.

You can find the software here: BlueLife KeyFreeze v1.4

Just in case, here is a local copy of the Bluelife KeyFreeze 1.4.

I tried several other keyboard & mouse lockers and this one was clearly the best. KeyFreeze is free software. It works great “out of the box” but you may want to change a few options from the icon on the system tray. I turned off the cute lock/unlock music and customized it a little.

Installing it takes a couple steps (I’m not complaining, it’s totally free software!), I’ll walk you through it.

1 – Download and unzip BlueLife  KeyFreeze

2 – It doesn’t run an installation program, it just runs when you double-click on it. It’s not good practice to run the program from my “Downloads” folder so I copied all the files to a new folder named C:\Programs\Keyfreeze

3 – You should make it start automatically when Windows starts. Here’s how to do that: Go to the C:\Programs\Keyfreeze folder and create a shortcut to KeyFreeze_x64.exe by right-clicking on it. Hit Win+R. Type “shell:startup” to open up the Windows startup folder. Drag the shortcut you just made into that folder. Done!

Now, when you want to freeze the keyboard and mouse, just hit Ctrl-Alt-F. To unfreeze, do it again.

For difficult classroom situations, you might want to disable the touch-screen and the “turn computer off when closing the lid” features. Here’s how:

– On my computer, to disable the touch-screen I hit the Windows key, type “Device manager”, find “Human Interface Devices”, find the “HID Compliant touch screen”, click the “driver” tab, click “Disable Device”. You can re-enable the touch screen by coming back to this page and clicking “Enable Device”

– To disable the “Turn off the computer when closing the lid” feature, hit the Windows key, type “change what closing the lid does”, change “When I close the lid” to “Do nothing”.

I’d love to hear in the comments if this software was useful in your classroom!

I’ve become an enthusiastic yet strangely melancholic fan of the band This Will Destroy You, this post-ambient, syncopated, instrumental rock band. Their music makes me feel like I’m being gently smothered by a giant tabby cat while sleeping, only for me to leap up, gasping for the most delicious breath of my life. Oh yeah.

Let’s see them together on February 8th in Berkeley, CA at The Cornerstone!

Here’s one of their cat-breath-stealing hits https://www.youtube.com/watch?v=fbszJJr9I9U