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2022 March 30

Secret Walks: Koi-to-koi

Filed under: Uncategorized — gasstationwithoutpumps @ 11:01
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On Saturday 27 March 2022, my wife and I took a long walk that visited two koi ponds: one on campus and one just off campus in the Pogonip.  The originally planned walk was 4.59 miles, but we had a few mistakes that increased it to 7.27 miles.  A koi-to-koi walk that started at the Rachel Carson bus stop, went without detours from the Porter koi pond to the Pogonip koi pond, then back to the Cowell/Stevenson bus stop would be about 2.6 miles.  Most of this walk was in the detours and walking home from the Pogonip.


(Click map for high-resolution version) We started by taking the 19 bus to the Rachel Carson College stop, then went to Porter College to view the koi pond there. Then we walked across campus to Quarry Plaza, where we had lunch from a food truck, then over to Stevenson college (the red route on the map). We had planned to go across the parking lot to McLaughlin and to the trailhead to the Pogonip (yellow route), but my wife had left her hiking pole at Quarry Plaza, so we went back there (pink path), then over to the Chadwick Garden, with the intention of going through the garden and out the lower gate. Unfortunately the lower gate was padlocked, so we had to retrace our steps out of the garden (brown route). We walked on McLaughlin to get to the Pogonip, but I misjudged the distance on the map and went past the turnoff to the koi pond. Instead we continued all the way to Fern Trail, where I realized we’d made a mistake and got out my phone (cheating!) and went down Spring Trail (purple path) to the other end of the route to the koi pond (olive path). We walked up that path, while the original plan had been to walk down it. My wife did not like the idea of walking back down it, preferring the extra ⅔ mile of redoing the purple route. We then headed down Spring Trail to Kalkar Quarry (green route) and took an alternative route back from the quarry (blue route).


This lamp post at Porter College has a rather creepy Big-Brother vibe.


The koi pond at Porter can be identified by this fountain, which circulates the water and keeps it aerated.


Here is one of the large koi in the pond.


Two more of the koi.


This one has particularly fancy fins.


Although people are not supposed to feed the koi, the koi do come to investigate any visitors, and swim away again when no food is forthcoming.


Porter has a long tradition of student -painted murals. The current crop seem to be advertisements for Porter—less witty than some of the ones from decades ago. Perhaps the approval process for them has gotten more bureaucratic or committee-based?


A door mural, again with the advertising theme.


A mural that seems a little more artist-directed and less “Porter ad”.


Forget-me-nots were blooming in the woods.


This covered bike parking at Kerr Halls has almost never been used—it does not help that you would have to manage a flight of stairs to get to it, and almost no one knows the parking is there.


When the path was redone, these bike parking posts at Kerr Hall were rendered unusable.


I think that this nettle-like flower is a California hedge nettle (Stachys bullata).


This wild turkey was unusual in being alone, rather than in a large flock.


Violets were also blooming.


There is a fine flannel bush (Fremontodendron californicum) next to the parking lot by the Bay Tree Bookstore (which has been officially renamed the Bay Tree Campus Store, as they no longer sell books). We ate our lunch under the flannel bush.


At Cowell College the dogwood trees were blooming. I liked the shape of this particular blossom, though it is not the characteristic shape for dogwood blossoms.


The entrance to Stevenson College has this rhododendron in a ceramic pot—I think that it has outgrown the pot and needs to be repotted.


The Chadwick Garden is looking a bit weedy, though some beds have clearly been cleared and planted for spring crops.


There is a nice arbor covered with Lady Banks’ roses at the east end of the Chadwick Garden.


This berry seems out of season—I would not expect the flowers for another month yet.


The jasmine was blooming next to the road below the Chadwick Garden.


In the Pogonip, past where we had planned to turn, there is a very Romanic ruin of a limekiln. It is not a folly, though it is is maintained like one.


An adjacent limekiln.


I was a little surprised to see a red columbine (Aquilegia canadensis) in the woods, as it is native to the northeast US and Canada, not to California.


These are the steps that we took from Spring Trail up (and up) to the koi pond—our original plan had been to come down that path from the pond.


The koi in the Pogonip were hard to photograph, because there was a lot of sunlight on the surface and the water was not very clear. This impressionistic painterly shot was the best I could do.


This tree seems to have a bit of a cave under its roots (too small for anything bigger than an opossum).


This wire fence along Spring Trail has an unusual mesh, but seems to be in good shape, so I doubt that it is very old.


This flower at the end of a tall, smooth stem seems to be “blue dicks” (Dipterostemon capitatus). I don’t remember ever seeing it before.


I thought these were morning glory, but (based on the leaf shape), I think my wife is right that these are the invasive bindweed.


This appears to be some sort of lupine.


There were fields of California poppies in bloom also.


I always have trouble getting closeups of California poppies, as my camera wants to overexpose the petals. This is the best I’ve managed so far (and it took some exposure correction in Photoshop Elements).

The alternative route back from Kalkar Quarry involved going through the opening in the fence off Limestone Lane into the UCSC faculty housing, then along that fence down to the Peace United Church of Christ property, and down a concrete drainage swale.  When we were there, there was a concert r rehearsal going on in the church, with what sounded like a brass ensemble—it made for a very dramatic soundtrack to our walking down the drainage swale.

2022 March 29

Better heartbeat detection

Filed under: Circuits course — gasstationwithoutpumps @ 14:37
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In Lower PVC frequency, I promised “I’ll report on the algorithms when I get something a little better than I have now.”

I’ve played with three algorithms this week:

  • Doing spike detection, then measuring the time for 2n periods by looking at the time between the spikes n before andafter the current spike.  This gives a fine resolution both in time and frequency, and provides smoothing because adjacent measurements overlap by 2(n-1) periods. It is, however, very susceptible to errors due to miscalling the spikes.  Missed spikes result in too low a frequency, and extraneous spikes result in too high a frequency. I could increase n to reduce the effect of miscounts, but at some loss of time resolution when pulse rate changed.
  • Taking FFT of a block of samples (say 4096, which is about 17 seconds at 240 Hz) and looking for a high energy frequency.  Temporal resolution is poor (even with 50% overlapping blocks we get one measurement every 8.5s) and frequency resolution also poor (bins are about 3.5 bpm wide). I tried improving the frequency resolution by looking at the phase change for the peak between adjacent windows, but that didn’t solve the main problem, which was that choosing the right peak in the spectrum was often difficult.  The simple algorithms I tried for choosing the peak often failed. I eventually gave up on this technique.
  • Taking the autocorrelation of a block of samples (using rfft and irfft) and looking for a peak. The time for that peak is the period, which can be inverted to get the frequency.  This method provides the same coarse time resolution as the FFT method (same size blocks), but has much better frequency resolution, as even the fastest reasonable pulse rate (240bpm or 4Hz) has 60 samples at a sampling rate of 240Hz. I tried accentuating peaks “of the right width” in the autocorrelation by doing some filtering of the autocorrelation, and I tried looking for harmonic errors (where 150bpm might result in a larger peak in the autocorrelation at 75bpm, 50bpm, or 37.5bpm). Even with all the tweaks I could think of, I still had a number of way-off estimates, though median filtering removed most of the anomalies.  Of course, median-of-5 filter makes the time resolution even worse, as median could have come from any of 5 windows (with 50% overlap, that means a time range of 12288 samples or 51.2 seconds!).

I did most of my algorithm testing on one data set (the exercise set from 23 March 2022), and the algorithm is almost certainly overtrained on that data.


Here are both algorithms applied to the two data sets from 23 March. On the exercise set, the autocorrelation method did an excellent job (except right at the end of the run), but the 12-period measure clearly shows missing and extra peaks. On the resting set, the 12-period measurements were very good, but the autocorrelation ones failed at one point, even with median-of-five filtering. The autocorrelation measurements were also consistently somewhat low.


To try to figure out why the autocorrelation estimates of the pulse rate were low, I tried superimposing the filtered ECG signal on the plot. The PVCs are visible as large downward spikes. Having one or more PVCs in the window seems to make the autocorrelation estimates somewhat too low. I still have no explanation for why the autocorrelation measure fails so badly around 50 seconds.

Although the autocorrelation measure makes a nice smooth plot on the exercise data set, I sacrificed a lot of temporal resolution to get that. I think that I would do better to make a more robust spike detector to improve the period-based measurements.

2022 March 25

Secret Walks: Wilder Ranch Coastal Loop

Filed under: Uncategorized — gasstationwithoutpumps @ 23:30
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On Friday March 25, I went for a walk with a friend.  She drove us to Wilder Ranch, where we did the short coastal loop (about 2.15 miles). The route could be extended by scrambling down to Little Strawberry Beach, or by going around Old Dairy Gulch along the railway tracks—there is quite a bit more coastal trail to the west (which Santa Cruz people will think of as “north”).


We did about the shortest coastal loop that is possible, as the fields are still being farmed.Click the image for a higher-resolution map.

There was a lot of scenery and wildlife along the route, so I took a lot of pictures. I think that the tide was low, so that the rocks and sea caves were unusually visible.


There are some nice views of sea caves.


The telephoto lens lets me get a good view of the sea cave in the previous picture without getting wet.


The little black oval about a third of the way up the cliff is a cormorant, I believe. The man on top of the cliff provides scale.


Another sea cave.


My wife and I regard a walk near water as well-formed if we see an egret. This one was a bit far away, and some of the zoom here is from Photoshop Elements, but it is clearly an egret.


These were also way too far away to get a good picture, but I believe that they are black guillemots.


I believe that this is Erigeron glaucus, known as seaside daisy or seaside fleabane.


I believe that this handsome gull is a western gull, but I have a hard time identifying gulls.


The cormorants here look like they are members of a gang.


Another western gull.


A convention of cormorants


Sea lions Seals on a beach and yet another sea cave


I believe that this is a galucous-winged gull hanging out with the cormorants.


This rabbit was a bit cautious and would not let us get close.


This rabbit with the notched ear was closer, but behind plants that made it hard for me to get a good photo.


I don’t know what mechanism makes all the holes in this cliff be at the same height.


The holes continue around the cliffs at the same level.


This sea lion seal was a loner, not sharing the beach with most of the others.


The canada goose was right at the edge of the cliff—probably for easy take-off and good views.


Some of the sea lions seals on the beach watched us, but most just napped on their sides.


One of the alert sea lions seals.


The patterns on the fur vary quite a bit.


This one seemed to be particularly relaxed.


A view of the beach with sea lions seals from the landward end.


A california quail.

2022 March 24

Lower PVC frequency

Filed under: Circuits course — gasstationwithoutpumps @ 09:58
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In PVC: Premature Ventricular Contraction, PVC and pulse, PVC again, and No PVC while exercising I posted some ECG recordings of my heart to show the premature ventricular complexes. Yesterday I tried recording the ECGs again, this time using only 2 electrodes using Lead I (LA–RA) and connecting the bias wire to right-arm electrode.  When I’ve tried that in the past it has not worked well, but with the new amplifier I got reasonably good recording, with only a bit more noise than I usually get with a 3-electrode configuration.  I did not do direct comparisons of the 2-electrode and 3-electrode configurations—I’ll have to try that sometime soon.

The interesting result is that my PVCs seem to be much less frequent now.  In a fairly long (454-second) recording, I had 355 normal spikes and 13 PVCs—a PVC burden of only 3.5%, with a pulse rate of 48.5 bpm.


The resting pulses looked pretty much like other recordings I made (averaged over all the pulses.

I also made a recording while on the bicycle ergometer: 100s just sitting, 400s pedaling moderately hard, and 500s recovering.  There were very few PVCs in that recording also (only 13 detected, for a PVC burden of 0.9%).  The averaging of waveforms across the entire recording did not produce a very useful result, as the heart rate varied from around 45bpm to around 154bpm.  I probably should modify the software to produce averages over just a dozen or so beats, to get the noise reduction without the confounding effect of variation in rate.

My attempt to produce a bpm vs time graph was not very successful—the signal was noisy enough that the spike detection algorithm was occasionally missing a spike or picking up an extra one, so that the method I was using of just inverting the time for n periods resulted in a very noisy graph at the higher heart rates.  I spent most of yesterday looking at two other ways of determining the period—one using the peak in an FFT and phase changes at that peak between overlapping windows and one using peaks in autocorrelation.  None of the three techniques worked well enough to produce a smooth graph, so I’ll probably work on them some more to try to come up with a more robust pulse finder.

I’ll report on the algorithms when I get something a little better than I have now.

2022 March 21

NY Times is really out of touch

Filed under: Uncategorized — gasstationwithoutpumps @ 19:57
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I try to buy one issue of the New York Times each week—the Tuesday issue that has the Science Times section.  You can’t subscribe to just Tuesdays, so I have to bike down to Bookshop Santa Cruz in the morning to buy a copy (they’ve usually sold out by the afternoon, and even CVS sells out when the bookshop has run out).

It often takes a week or more for me to get to the less interesting sections (like the business section), so I only today got around to reading “Apple’s New SE Is the iPhone Built, and Priced,  for the Anti-Consumer” (which is available online as 

In the article, Brian X. Chen makes some truly ridiculous statements, which either he was paid to do by Apple or because he has absolutely no understanding of anti-consumerism.  He claims that the iPhone SE is “a no-frills phone … for a reasonable price” and that it is “a budget phone”—oops, that is “a budget iPhone”, which is not at all the same thing. 

The phone costs $430, which is not a budget phone by any stretch of the imagination.  A budget phone is a $24 Cricket burner phone from Walmart.  But let’s say you want a decent, no-frills smartphone—for $49 you can get a Moto G Play (2021 model) from Google Fi, and get a cheap Google Fi phone plan as well (we pay about $43/month for two phones, including taxes). An anti-consumerist mobile phone would be a flip phone for <$10 from Goodwill. Under no stretch of the definition is any iPhone anti-consumerist—the iPhone brand is built entirely on consumerism and conspicuous consumption, with even their “budget” models 5 to 10 times the price of the competition.

Brian does, grudgingly, mention Google’s Pixel 5A, which is a similarly over-priced “low-end” phone ($300 with Google Fi, $400 otherwise).

It seems like the editors of the business section of the NY Times are so out of touch that they let Brian’s piece pass uncorrected.  I’d already given up on the opinion page as being so right-wing it hurt to read, and I knew that the business section was unapologetically addressing the wealthiest 5% in most of their articles, but pretending that an iPhone is anti-consumerist is going way beyond the bounds of responsible journalism.


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