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2021 November 27

Secret Walks: Neary Lagoon

Filed under: Uncategorized — gasstationwithoutpumps @ 18:41
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On Saturday 27 November, my wife and I  walked the Neary Lagoon loop from Secret Walks & Staircases in Santa Cruz, by Debbie Bulger and Richard Stover.  The walk in the book is 1.3 miles, but we rotated and reversed the walk to start at the California Ave entrance to Neary Lagoon and do the floating dock first, added a side trip to Laurel Creek by the Cypress Point Apartments (where lived when I first moved to Santa Cruz, 35 years ago),adding about 0.8 miles, and had 2.3 miles for getting to and from the start, making a total of 4.4 miles—one of our shortest walks so far.  The floating docks were open this time, even though the some of the signs saying they were closed have still not been taken down.


Before leaving on the walk, I saw this marvelous cobweb behind the piano—I’ll have to do a little cleaning!


The settling tank at the sewage-treatment plant is always popular with the mallard ducks.


Here are a male and female mallard in Neary Lagoon.


We saw this bird on a rock just past the end of the Neary Lagoon Pier. We did not get too close, to avoid scaring it away. It appears to be a juvenile double-crested cormorant.


The tule removal this Fall in the lagoon has revealed a few trees that were previously completely hidden by the tule reeds.


There is still enough tule left for the mallards to have comfortable resting places.


There are quite a few American coots in Neary Lagoon, though not nearly as many as the mallard ducks.


I’m not sure what species this bird house is intended for (maybe marsh wrens?). We saw two of the bird houses, but this one has a decided problem with tilt—perhaps it is copying San Francisco’s Millenium Tower?


A landscape of tule and open water—it is rather surprising how well the city is hidden from Neary Lagoon.


Much of the path is boardwalk—even when it is not floating on the Lagoon. I liked the way the trees grew over the path here.

When we got back to dry land, we did not immediately finish the loop, but took a side trip (recommended in the book) to walk along the lagoon on the sanctuary access path by Cypress Point Apartments. We also spent a little time looking for the apartment building I lived in 35 years ago (133 Felix Street). The paint job on the building has changed since then and looks a little more cheerful (though Shelter Lagoon Condominiums seem to have kept the same paint scheme for the 35 years).


I took another picture of the lychee on Neary Street. Most of the fruit seems to have fallen now, but there are still a few high up in the tree.


The mallards like Laurel Creek where it is still narrow and fast flowing (when it has water, that is).


Laurel Creek widens out and slows way down as it enters Neary Lagoon.


We saw a black phoebe on a branch by Cypress Point Apartments and the Shelter Lagoon Condominiums. I could not get close enough to get a really clear shot.

When we got to the end of the path, we did not retrace the path through along the lagoon, but exited through the Shelter Lagoon parking lot, returning to Neary Lagoon Park and continuing the loop around the lagoon.


Here is the path across a field, along the northeast edge of the park.


As we approach the sewage-treatment plant again at the end of the loop, we can look back and see the Dream Inn sticking up above the park.


The path between sewage-treatment plant and the lagoon on the southwest side of the park has nice views of the tule marsh.


I managed to catch another black phoebe flying, showing off its white belly.


We walked past Spring Hill School on the way home, to see the new signage. My wife and I agree that the “SCHOOL” lettering is much too light and won’t be visible from cars driving by. The California poppy is replacing the previous dolphin as the school’s symbol, and the school is being repainted in green and orange to match the colors.


We saw this succulent in flower on Van Ness near California Avenue, but we had no idea what it is. Using Google image search, we have tentatively identified it as Calandrinia spectabilis (rock purslane), a common garden plant originally from Chile.


This Little Free Library on Van Ness Ave often has books my wife finds interesting.


This Little Free Library (on a different block of Van Ness Ave) matches the house nicely, but my wife does not find the book selection as useful.


We often have crows on Van Ness, so I thought I’d round out the bird pictures with ones from outside the park.

We did not stop for lunch on this walk, though I suggested trying the sushi place at Mission and Van Ness (one of the few places along this stretch that has outdoor seating), but my wife had had a late breakfast and the walk was not really long enough to make us very hungry, so we just went home.

2021 November 25

PVC and pulse

Filed under: Circuits course — gasstationwithoutpumps @ 15:17
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In PVC: Premature Ventricular Contraction, I posted some ECG recordings of my heart to show the premature ventricular contractions.  But that post brought up two questions for me:

  1. Do the PVCs pump blood around, or do they do nothing?
  2. How are PVCs affected by exercise?

In this post, I’ll try to answer the first question, by simultaneously recording both a Lead I ECG signal and a fingertip pulse with an optical pulse monitor.  The amplifier for the optical pulse monitor has a 0.35Hz–5.6Hz filter on it, there is some rounding and delay of the pulse waveform, but I was too lazy to build a new log-transimpedance amplifier without that filter.

I recorded for about 209 seconds, and I got 119 spikes and 56 PVCs.  The overall pulse rate was 50.0bpm, but the sinus rhythm was only about 33.9bpm with 15.8 PVCs/min.  That is a very high rate of PVCs.

I wrote a program that bandpass-filtered  (0.2–50Hz, 4th-order Bessel filter, both forwards and backwards in time) the signal and then identified where all the R spikes were. The program also separated the normal pulses from the PVCs.  This program was specific to my recordings of Lead I—it does not attempt to identify PVCs from an arbitrary ECG!  I also had the program average all the normal waveforms and all the PVC waveforms, lining them up by the detected peak of the R spike.


The solid lines are the ECG signals (in mV) and the dashed lines are the optical pulse signal (in dB, because I was using a log-transimpedance amplifier).

So what can I determine from this plot?

First, the P-spike is missing from the PVCs—this is part of the definition of a premature ventricular contraction, so is hardly surprising.

Second, the T-spike that represents the repolarization wave seems to happen at about the same time for both normal and PVC events, though the shape of the waveforms is different.

Third, my pulse is slow enough and irregular enough that the averaging does not show adjacent ECG signals within this 1.4-second window, but the optical pulse signal shows that the PVC is happening sooner relative to the recovery from the previous pressure pulse than a normal beat. (Again what we would expect from a premature contraction.)

The optical pulse at the fingertip had about the same delay from the R spike for both PVCs and normal pulses—the difference may be due to my defining the R spike as happening at the positive peak, when a more accurate time for the R spike on the PVC would be slightly later.  The PVC pulses were definitely weaker at the fingertips than the normal pulses, but were still fairly strong, so the premature ventricular contractions are pumping blood, but not as much as a normal heartbeat.

In a subsequent post, I’ll try looking at what exercise does to the PVCs.

2021 November 24

Contract signed with publisher!

Filed under: Circuits course,Uncategorized — gasstationwithoutpumps @ 10:31
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I’ve just signed a contract with World Scientific Publishing to publish my Applied Analog Electronics textbook.  They first contacted me on 2021 Oct 7 expressing an interest in the book, we met on Zoom on Oct 20, and they had a proposed contract to me by Oct 26, and we had a few back-and-forth rounds of negotiations.  The final contract was sent to me on Nov 19, I signed Nov 21, and they signed Nov 24. So the full process took about 48 days.

Here is the contract:

The most surprising thing in the contract is that they are continuing to let me sell the PDF through Leanpub (and my own web site, if I ever create one).  The royalties per book for Leanpub sales are higher than I’ll get from World Scientific Publishing, and the price will most likely be lower.

I did not use a lawyer in negotiating the contract—I contacted 4 lawyers who specialize in book contracts, but even the cheapest of them was too expensive, as I don’t really expect to make much money on this publishing deal.  I did use two online books:

Now I just have to get the 250MB of source files to the publisher and fill out the promotional questionnaire.  They may want me to make some small changes (like changing the title page).  When they are ready to publish, I’ll have to register the copyright also.

I’ll post here again when the book becomes available in paper.

2021 November 23

Secret Walks: Riverwalk

Filed under: Uncategorized — gasstationwithoutpumps @ 21:34
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On Saturday 20 November, I  walked the Riverwalk loop from Secret Walks & Staircases in Santa Cruz, by Debbie Bulger and Richard Stover.  The walk in the book is 3.8 miles, but I walked another 1.4 miles on each end, totalling 6.6 miles.My wife did not accompany me for this walk—her hip was bothering her, she had been exposed to Covid at work and had not had a second negative test yet, and she does not like walking by the homeless encampment on the river.


Pacific Avenue downtown was block by this large crane, which was replacing the HVAC equipment on the top of Cooper House.


Here is a view of the crane with one of the old pieces of duct work.


An unidentified bird under Water Street bridge.


The levee on the west side of the San Lorenzo river, looking north. There are a lot of young trees in the flood plain.


Large old logs between the levees have been cut up—probably so that they don’t jam against the bridges and cause flooding if we ever get enough rain to float them again.


There are a number of public exercise machines on the Riverwalk by Gateway Plaza, just a little downstream of Highway 1.


The pedestrian bridge across the river just below Highway is fairly heavily used, both by homeless people and by people living in houses on the east side of the river.


Here is the view upstream from the pedestrian bridge, showing how little water there is in the river and how much traffic there is on Highway 1.


The view looking south (downstream) along the levee on the east side of the river.


In San Lorenzo Park, which is just across the river from where the loop started, there is a bowling green. This used to have lawn bowling, but the lawn has been replaced by an artificial surface, so now it is more like indoor-outdoor carpet bowling.


There are hundreds of tents for homeless people on the benchlands of San Lorenzo Park, making a rather stark contrast to the bowling green, duck pond, and play structures of the rest of the park. This picture shows only a small fraction of the homeless encampment, which fills the benchlands next to the river below the levee. The encampment is at serious risk of flooding if we get a heavy rain.


The duck pond in San Lorenzo Park has a small stage in the middle (which used to be used a lot for free concerts). Ducks can be seen resting in the shade under the stage.


The mallard on the left is the most commonly seen duck in Santa Cruz—I think that this is the first time I’ve seen a merganser (the duck on the right) in Santa Cruz, though they are also supposed to be fairly common.


Here is the merganser again, surrounded by mallards (there were another 20–50 mallards not in the frame here).


This concrete play structure has been in San Lorenzo Park for at least 20 years, but all the other play structures that were there when my son was of an age to visit playgrounds have since been replaced.


I have always liked speaking tubes in playgrounds—here are the two ends of the one in San Lorenzo Park.


Ground squirrels are very common in open fields throughout Santa Cruz—including in the river bed.


Coots on the river.


There were a lot of gulls on the river, but they suddenly took off, wheeled around a few times, and settled back on the river. It was hard photographing them, because of where the sun was.


Crossing back to the west side of the river on the pedestrian path on the railway trestle gives a nice view of the log ride at Santa Cruz Boardwalk. As seems to be the standard every time I cross this bridge, there was a Chinese tour group crossing the other way.


Here is part of the flock of gulls I showed earlier, now from the west side of the river, with the light behind me.


I’m not 100% sure, but I think that this is a female goldeneye. Even at max zoom, I could not get a clear view of the bird. (I’m seriously thinking of getting a camera with much more zoom.)


There is another set of public exercise equipment just below the Laurel Street bridge.

After finishing the Rivierwalk loop, I had lunch downtown: a grilled-cheese sandwich at Central Coast Creamery in Abbot Square, followed by an ice-cream cone at The Penny Ice Creamery (pecan pie and crême fraiche with dates). I had to wait in line for 15 minutes at the Penny, because the weather was so nice that everyone was getting ice cream, and they only had one person working the counter (staffing retail and restaurants has been difficult lately).

2021 November 17

Secret Walks: Lighthouse-Whale Museum

Filed under: Uncategorized — gasstationwithoutpumps @ 20:26
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On Saturday 13 November, my wife and I did the Walton Lighthouse-Natural History Museum loop from Secret Walks & Staircases in Santa Cruz, by Debbie Bulger and Richard Stover.  The walk in the book is 3.4 miles, but we walked another 2.4 miles to get to the start and another 3 miles to get home, totaling 8.8 miles.


This small mosaic is embedded in a stucco garden wall of a private home.


This slightly larger mosaic is in the same garden wall.


This pathway connects the end of Harbor Drive to Frederick Street Park.


This couple on one of boat-launch ramps have just thrown a stick to their dog (not in the photo).


The path to the Walton lighthouse was popular with pedestrians, as we had very nice weather.


The “Coastal Access Pier” does not really provide access to anything but views, as there is no way down to the water from the pier.


The huge cleats on the “Coastal Access Pier” are purely decorative, as nothing ties up to the rather high deck of the pier.


The birds seem to like the floating pipe that is the outlet of the dredger.


Here is the dredger itself, though I don’t think it was operating on the weekend.


The Walton lighthouse is not an old one, but it is rather picturesque.


We love these “jetty jacks”, though we prefer to call them “caltrops”, after a medieval weapon of roughly the same shape.


The caltrops do a good job of breaking up the waves that would otherwise wash the jetty away.


The breaking waves were a bit hard to photographs, as the sun was behind them.


Mosaics seem to be popular in Santa Cruz—this one was added to the end of one of the caltrops


I have no idea what this plant growing on the beach is—I think we saw the same species at Natural Bridges State Beach also.


This seems to be another beach plant we couldn’t identify.


This plant, growing on the cliff by the stairs, looks a lot like dusty miller, but I don’t think it is.


The Walton lighthouse from the stairs, showing the jumble of caltrops around the jetty.


A view of the cliff from the stairs. Note the pink flags at the bottom right, marking where native plants have been added to try to stabilize the cliff. You can also see at the top where there used to be a walkway that is now just an asphalt overhang.


My wife and I admire this stone chimney. The house looks like it should be a hexagon, but it is just a half hexagon on the end of a rectangular house.


This life-size whale sculpture in front of the Santa Cruz Museum of Natural History leads some locals to refer to it as the “whale museum”, though it does not have that much about whales.


This artwork replaces one of the windows of the museum.


The main entrance of the museum.


I think that this Little Free Library is on Seabright.


This sign on Seabright accurately points away from the beach.

About 3/4 of the way through the walk, we stopped for lunch at Java Junction—one of several places to eat near Murray and Seabright.  We had thought to Betty’s Burgers, but the line was too long, and we thought of Seabright Social (which used to be Seabright Brewery), but neither of us wanted beer.  I was a little disturbed that none of the staff at Java Junction were wearing masks—COVID rates in the county are low, but they are nudging back up due to carelessness like that.

My wife and I are planning to replace our Wednesday night dinners out with Saturday lunches out—it is getting too dark and chilly for eating outdoors and walking home at night to be much fun.  We may switch back in March, when Daylight Savings Time returns.  If COVID rates drop a lot at the students at my wife’s elementary school all get vaccinated, we might start eating indoors at restaurants again.


The playful cutouts in this fence overlook Murray, which is rather busy here.


The dredger pipes that aren’t currently attached to the dredger are laid out beside the harbor. Based on the vegetation, some of them have been here for a while. We were somewhat surprised to see that there were several different diameters of the pipe, though that is not evident in this photo.


The boats in the harbor always look picturesque, though they now represent a lot of surplus money, as there are almost no working boats any more.


I rather like the elegance of this fence, which is almost certainly custom made. The vertical bars seem to be copper tubing for plumbing and the horizontal bars are simple cuts. I think that the panel consists of 12 copper tubes, not 3, with holes drilled about ⅓ of the way through the wood to hold the tubes.


Another Little Free Library. I think this one was on Windsor near Frederick.

Coming back, we walked along Windsor instead of Broadway from Frederick Street to Ocean View.  The street is much quieter and more pleasant. I think it is probably worth detouring a block when bicycling or walking across town—I don’t know why I’ve never taken Windsor before.


Creative sidewalk patching.


This one is on Windsor and Branciforte.


This one is on Roosevelt Terrace, overlooking the Broadway Playhouse where my son had so many acting classes.


I’m always rather fascinated by the way that old houses get jacked up (by Fresno House Movers) to build a foundation under the house. I wonder how they drill the holes in the sill plate to line up with the bolts cast into the new concrete foundation. Is it careful measurement or eyeball estimates? Do they drill the holes extra large and then use large washers? Or do they put in a new sill plate and the lower the house onto it?


This turtle mosaic is the first one you come to on the Laurel Street bridge coming from the east. Each of the uprights has a mosaic but the sidewalk is too narrow on the bridge to get far enough away for good pictures of most of them.

On Sunday, I got a little more exercise by bicycling up to my office to fetch the purple beans that I had bought at the farmstand on Friday, but left in the refrigerator in the grad-student office by mistake.  Monday and Tuesday, I mowed the lawn (front yard on Monday, back yard on Tuesday).

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