Gas station without pumps

2017 July 22

Logos no more

Filed under: Uncategorized — gasstationwithoutpumps @ 11:19
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On Thursday this week, I spent most of my afternoon waiting in line to check out at a bookstore.  The main used-book store in town, Logos, is going out of business after 48 years and they have started their closing sales (which will probably last another month or two).  Thursday was the first day of their sale, and though prices were not particularly low (20% off their usual prices), a lot of people wanted to mourn the passing of the bookstore (and use up their store credit before all the “good” books were gone).  The result was so many people wanting in that the fire marshal insisted on a rule that a person could only enter the store when one left.  But the wait to get in was not all that bad (about 30 minutes)—the delays were in checking out, as the store had only four registers in operation and none of the cashiers had ever been trained for speed (bookstores gain more from social interaction at the register than from high-speed transactions).  I was in line to check out for about an hour, and my wife, waiting in the other line, was in line for about 3 hours.  Most of the 125 people that the fire marshal permitted were waiting in one or the other checkout lines.

Here is how the Sentinel started their article  Logos, a beloved Santa Cruz bookstore, falls victim to a changing retail economy:

For the first time since the summer of the moon landing, Santa Cruz will soon be without Logos, the used-book emporium that has been part of the downtown landscape since the days of the Pacific Garden Mall.

In about six weeks, after a long everything-must-go liquidating sale, Logos will shut its Pacific Avenue doors for good.

John Livingston, the store’s owner and operator for its entire 48-year run, said that he put the store up for sale a year ago. Facing little interest and no serious offers, as well as sharply declining revenues, he has decided to close his business.

Since the rebuilding after the 1989 Loma Prieta earthquake, the anchor businesses downtown have been Bookshop Santa Cruz near the north end of Pacific Avenue and Logos near the middle.  (More recently, Cinema 9 has also drawn a lot of people downtown.)  The rest of the businesses are mostly a mix of surf shops, boutiques, gift shops, and eateries.  (After dark, only the restaurants and bars are open, and the highest crime rate in the city seems to be about closing time for the bars downtown.)

For a while around the turn of the century, Santa Cruz was the chief battleground between independent bookstores and chains (the owner of Bookshop Santa Cruz was the president of the Independent Booksellers Association and both Crown Books and Borders opened stores in downtown Santa Cruz with the avowed intent of crushing Bookshop Santa Cruz—both are gone, but Bookshop Santa Cruz remains).  Logos was mostly ignored in this fight, as there were no large chains trying to get into the used-book business, which has long relied on customer browsing, impulse purchases, and store owners who know both their customers and their stock—not a business that scales well.

Between a third and a half of my over 3000 books have come from Logos, and they have been where I’ve sold back my surplus and duplicate volumes.  A bookstore that primarily sells new books (like Bookshop Santa Cruz) may be better for authors, but browsing the stacks of a used bookstore for books that are long out of print or undeservedly forgotten is a pleasure that cannot be duplicated by on-line shopping.  I’ve bought a few books online, when I knew precisely what I wanted and it wasn’t available locally, and I’ve bought new books from Bookshop Santa Cruz, but most of my purchases have been used paperbacks from Logos.

These purchases were a result of browsing—I needed a book (or 10) for bedtime reading, and I had only vague ideas about what I wanted: usually science fiction or fantasy, with characters I could identify with and decent world building (both of which are rarer than they should be in the genre). Browsing is very difficult in on-line purchasing, and new bookstores tend to be too stuffed with the latest fad books (where they make what little profit they get) to have much that I’m interested in reading and haven’t already read. (OK, that may be more a commentary on the narrowness of my tastes than on the contents of the store.)

I mourn the passing of an era—soon there will be no places left to browse through stacks of paperbacks, looking for treasures amongst the dross.  Logos had decent book buyers, so the ratio of treasure to recyclable paper was higher than at many bookstores (though it always irked me that they would buy back only about a quarter of my surplus books—they’d sold the books once, why did they think they couldn’t sell them again?).

My wife has even more cause to mourn Logos than me, as about half the books she acquired for her school library were from Logos. Almost as many were from Friends of the Library books sales, but that source is much less reliable and requires very fast decision making for children’s books, as they are snapped up quickly.

For those, like me, who appreciated the pleasures of finding strange and wonderful books and being able to buy them for very low prices, take a little time in the next couple of weeks to visit Logos for remembrance’s sake.

2017 July 15

More recent theater events

I haven’t been posting about theater I’ve seen since the post Recent theater events, which was back in April.  Here is a list of things we’ve seen since then:

Date title produced by
2017 May 13 Great Expectations WEST performing arts
2017 May 19 Avenue Q Santa Cruz High School
2017 May 20 Sylvia Jewel Theatre
2017 June 3 Zoot Suit UCSC Theater Department
2017 June 5 Two Gentlemen of Verona UCSC Shakes To Go
2017 June 10–11 Midsummer Night’s Dream UCSB Shakespeare in the Park
2017 June 17 Merry Wives of Windsor Silicon Valley Shakespeare
2017 July 14 The 39 Steps Santa Cruz Shakespeare

The WEST teen production for the spring, Great Expectations, was fairly well done, though there were a few actors who were too quiet, even in the small Broadway Playhouse.  The teen productions have a mix of first-time-on-stage actors and experienced ones, so can be a bit hit-and-miss.  Their WEST Esemble players are their more experienced teen troupe—I did not get to see their production this Spring, though my wife did—they had an adaptation of Robin Hood that they performed at some local schools, including the one where my wife is the librarian.

The Santa Cruz High production of Avenue Q was good—we went because it included an actress who has also performed (at WEST) with our son (she’s also the daughter of one of my former students—we found out that she was in the Avenue Q production when we ran into her and her father at a local eatery).  The biggest problem with the Avenue Q production was that the singers were miked, but the mikes did not work consistently. I’m not a big fan of musicals, but Avenue Q seemed better written than most.

The next evening after Avenue Q we went to see Sylvia by the Jewel Theatre. The acting and production were good, but the script was rather weak material, so the production as a whole was not very satisfying.  It was quite a contrast to Avenue Q the night before, which had much weaker production values but better material. It showed that even a professional production can’t rescue a weak script.

Zoot Suit at UCSC was an amazing production, combining first-rate acting, superb costuming, and a first-rate script. The script was updated by the author (Luis Valdez) last year for a production in Los Angeles, and this production was directed by his son, Kinan Valdez. Because Luis Valdez is a local author, he attended the performance the same night we were there and was available after the show for Q&A (we did not stay for that, because we needed to catch a bus home). This was probably the best student production I’ve seen, at UCSC or elsewhere.

My wife and I saw the Shakes to Go production of Two Gentlemen of Verona at the elementary school where my wife works, as I was unable to get to any of the performances that they did on the UCSC campus. As always, the Shakes to Go production was fast-paced and simplified for school children to be able to follow, but well done within the constraints of a production that has to be finished in 50 minutes and needs to be portable enough to be set up on in an unfamiliar location in about half an hour.

We traveled down to Santa Barbara to see our son in Midsummer Night’s Dream, where he played Peter Quince (the leader of the play within a play). I made a video recording of both performances, but haven’t yet rendered it to put it up on YouTube.  The play was difficult to film, as they had a lot of the action in the audience, and I had a hard time panning the camera fast enough to catch what was going on.  I liked the production, but I never know how much of that is just my bias towards anything my son is in.

After my son got home from Santa Barbara, all three of us took the bus to San Jose to see Merry Wives of Windsor in Willow Street Park. The performance space in Willow Street Park is quite nice—a very large stage area with a steeply raked bowl for the audience and a wooded backdrop. It was a fun production, but not quite at the high standards of Santa Cruz Shakespeare (more at the level of good student productions).  The performance was free (suggested $10 donation at the end), subsidized in part by the San Jose City Council, I believe.  We spent as much on getting to the performance as we did on the show. Unfortunately, we probably won’t be able to go to the other Silicon Valley Shakespeare productions this summer, as they are in Sanborn Park, which is inaccessible by public transportation. (We might be able to use Lyft to and from the Lawrence Expressway train station, but that makes for a fairly long trip, and catching the last Highway 17 bus home could be difficult.)

Last night we went to see Santa Cruz Shakespeare’s production of The 39 Steps, a farce based on Hitchcock’s movie of the same name. The production is amazing, with the 4 actors playing dozens of roles (well, one actor has 1 role, the actress has 3 roles, and the remaining roles are all played by the 2 remaining actors). The costumes and costume changes were perfect. The show was hilarious and has been getting good reviews—I was surprised to see that Grove had not been sold out and that there was a lot of groundling space still available.

All four actors in the Scottish inn scene, photo from the SCS media page

Santa Cruz Shakespeare is doing only comedies this summer (the other two are Measure for Measure and Two Gentlemen of Verona). Their interns are doing Candide, and the company will be doing two staged readings: A Most Dangerous Woman and The Night that Never Existed. We, of course, are planning to see it all.

We took public transit to the Audrey Stanley Grove last night, which really meant about 2.4 miles by bus and 2 miles walking.  It would have been almost as fast to walk the whole way, as we could have gone a slightly more direct route. We took the newly built path from Park Way Trail (at the end of Park Way) up to the Audrey Stanley Grove. It is a very steep path that my wife was willing to do uphill, but not downhill—I’d be a little reluctant to take it in the dark also. The trail is definitely a hiking trail and not for bicycles. We ended up taking Lyft home, which for the three of us was not much more expensive than the bus and much more convenient.

2017 July 13

Analog Discovery 2 oscilloscope input impedance fixed

Filed under: Circuits course,Data acquisition — gasstationwithoutpumps @ 23:25
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This morning in Analog Discovery 2 oscilloscope input impedance, I wrote

I cannot fit a model based on the input divider circuit to the data—I keep getting a negative capacitance for C9 or C8, so that they can cancel each other.  These models also make C1 around 50pF.

So I can reconcile the DC behavior (1.044MΩ is well within the ±2% measurement error of the nominal 1.04MΩ), but not the AC behavior of the scope inputs.

I must be missing something, but what?  Any useful suggestions (which don’t involve modifying the Analog Discovery 2) are welcome.

This evening I figured out what I was missing. The model I was trying to fit was the following one for the oscilloscope, with a 2MΩ resistor in series as the reference impedance:

There is a natural, internal split into an 820kΩ and 220kΩ resistance in the input voltage divider (component numbers here are for channel 1, but channel 2 is identically designed).

What I was missing was parasitic capacitance from the breadboard and scope wiring. If I model a capacitor (Cref) in parallel with the 2MΩ resistor and another capacitor (Cextra) in parallel with the scope, I can get a good fit.  I can leave all the internal resistors and capacitors at their nominal values, and fit for several different values for the trim capacitor C8:

I can get an excellent fit with Rref being only a little over 1% off and reasonable parasitic capacitance values.

Analog Discovery 2 oscilloscope input impedance

Filed under: Circuits course,Data acquisition — gasstationwithoutpumps @ 11:43
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I have been blindly trusting the documentation for the Analog Discovery 2 that claims that the input impedance of the differential oscilloscope channels is 1MΩ || 24pF.  Yesterday, when my son was measuring the input impedance of the reference inputs of a sigma-delta ADC, we had reason for a while to doubt that claim, so I measured the input impedance in a simple way:  I put a 2MΩ 1% resistor in series with one input channel and used the other input channel to measure the voltage across the series pair. I swept the network analyzer from 10Hz to 1MHz, and recorded the voltage gain (and the phase).  The voltage gain is not well-fit by a simple (1MΩ || 24 pF) model, as the impedance does not keep decreasing.  It seems to be well modeled by a model with Rs+(Cp||Rp), though.

The reported voltage gain for Channel 2/Channel 1 is well fit by a voltage divider.

Because the Analog Discovery 2 reports gain for Channel 2/Channel 1, I had to invert the data to get it in the form I wanted for my model (I could, alternatively, have swapped the legs of the voltage divider in the model).

The phases were also well fit by the models, though I did not use the phase information in the fitting. (I tried refitting using just the phase information, but that did not change the parameters by much, nor did it visibly improve the fit of the measured phases, so I left the parameters with just the amplitude fit.)

The DC impedances are both 1.044MΩ, very close to the specified value, but the capacitor is over twice the specified value, and not directly in parallel with the resistance.  The reference resistor I used is supposed to be a 2MΩ±1% resistor, but it was part of a cheap assortment, and we’ve found these cheap assortments to often be slightly out of spec, so I’d not trust it to be better than ±2%.

The 200kΩ/800kΩ split is not very surprising, when we look at the circuit for the input divider of the oscilloscope (from the hardware reference manual):

There is a natural, internal split into an 820kΩ and 220kΩ resistance in the input voltage divider (component numbers here are for channel 1, but channel 2 is identically designed).

The appearance of the 200kΩ/800kΩ split in the model for the input impedance suggests that the trimmer capacitor C8 is not properly adjusted.  If all capacitance and resistance values were nominal, then C8 should be set to 39.59pF, to provide a flat response from the voltage divider (at the high-gain setting), producing an input impedance of (1.04MΩ || 26pF).  But C8 only has a 5–20pF range, so perhaps there are some other, parasitic capacitances that change the desired trimming.

I cannot fit a model based on the input divider circuit to the data—I keep getting a negative capacitance for C9 or C8, so that they can cancel each other.  These models also make C1 around 50pF.

So I can reconcile the DC behavior (1.044MΩ is well within the ±2% measurement error of the nominal 1.04MΩ), but not the AC behavior of the scope inputs.

I must be missing something, but what?  Any useful suggestions (which don’t involve modifying the Analog Discovery 2) are welcome.

2017 July 12

UCSC iGEM crowd-funding 2017

Filed under: Uncategorized — gasstationwithoutpumps @ 18:30
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Each year a group of UCSC bioengineering engages in a summer research project in synthetic biology as part of the iGEM synthetic biology competition.  Although they get some support from the University, they have to raise the money for going to the iGEM jamboree (the conference where every team presents its results) by crowd-funding.

The UCSC iGEM team has opened their crowd-funding site for this summer:
UC Santa Cruz | UCSC iGEM 2017: Bugs without Borders

UCSC iGEM 2017: Bugs without Borders

What is iGEM?

The iGEM (International Genetically Engineered Machine) competition is an international symposium dedicated to the advancement of synthetic biology. For over 10 years, iGEM has been encouraging students to work together to solve real-world challenges by building genetically engineered biological systems with standard, interchangeable parts. Student teams design, build and test their projects over the summer and gather to present their work and compete at the annual Jamboree.

The epitome of undergraduate research, iGEM provides an unparalleled opportunity for talented students to administer their own projects, advocate for their research and procure resources for funding. In doing so, the competition promotes creativity, collaboration and curiosity as students develop the critical, analytical, and independent real-world problem solving skills that are difficult to cultivate within the classroom.

Our Project: Bugs Without Borders

UCSC’s 2017 iGEM team is focused on the shortage of supplements and essential vitamins in third world countries. Affectionately dubbed “Bugs without Borders”, this year’s project aims to engineer a Generally Regarded As Safe (GRAS) microorganism capable of producing a target supplement or essential vitamin in a safe and efficient manner.

Go to their crowd-funding site and watch their video to see what they are planning for this year.

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