Gas station without pumps

2014 September 12

Power supply test

Filed under: Uncategorized — gasstationwithoutpumps @ 12:22
Tags: , ,

Earlier this summer, I bought a beefy power supply from Jameco (1952361 PWR SPLY,TBL,REG,9V@6A,F2). One warning: the power supply does not come with a power cord, which must be purchased separately. The online catalog makes this clear, but in my comparison shopping for power supplies I somehow missed that. The nice people at Jameco sent me a power cord when I pointed out that their competitors were including the power cords with the power supplies, even though I admitted the oversight was entirely my fault. With the cost of the power cord, the prices at Jameco are about the same as other reputable sources of power supplies (like Pololu).

now that I have some power resistors, I finally got around to testing it. Because I have 3 different size resistors, I can test the voltage drop across many different load resistances: ∞, R1, R2, R3, R1||R2, R1||R3, R2||R3, R1||R2||R3, R1+R2, R1+R3, R2+R3, R1+R2+R3, R1||(R2+R3), R2||(R1+R3), R3||(R2+R1), R1+(R2||R3), R2+(R1||R3), R3+(R1||R2). But many of those are very similar resistances and won’t tell me much. I was mainly interested in how the power supply behaved when near the top of its power range, so I only tested the first 8 resistances on that list (no load and the various parallel arrangements).

Current vs. voltage curve for the Jameco 1952361 power supply.

Current vs. voltage curve for the Jameco 1952361 power supply.

The current is computed by measuring the voltage and the resistance and dividing. Because the resistance values are so low (1.34Ω to 10.17Ω), the repeatability of the measurements is not great (about ±0.04Ω), possibly due to differences in the attachment of the clip leads. This variation in the resistance probably accounts for most of the deviation of the points from the fitted load line, though the ±0.005V variation in the voltage measurements probably also contributes.

I made the measurements at the barrel jack that I plugged the power supply into, as that is the relevant point in the circuit for designing around. The output impedance of the power supply is 47mΩ, which is probably due mainly to the resistance of the cable from the power supply to the barrel connector. The cable is 1m long, and 47mΩ for 2m of copper wire is 23.5Ω/km, which is about the resistance of 18-gauge copper wire (20.9Ω/km), which is consistent with the diameter of the cable and what I would expect a 6A supply to use.

The supply delivered 6.647A at 8.907V (59.2W), comfortably above the specification of 54W. I did not detect any increase in temperature of the power supply at this power output, even after a few minutes (during which time the resistors got quite warm). So it seems that the power supply is indeed what it claims to be.

2014 September 11

JanSport warranty works

Filed under: Uncategorized — gasstationwithoutpumps @ 18:35
Tags: , ,

As I reported in Testing JanSport warranty, I sent my worn-out JanSport backpack in to their warranty service a month ago, as it was no longer usable (hole in the leather bottom, main zipper fails frequently, shoulder straps fraying where they join the body of the pack) to try out the JanSport warranty:

JanSport engineers quality, durable, and reliable products. So, if your pack ever breaks down, simply return it to our warranty center. We’ll fix it or if we can’t we’ll replace it or refund it. We stand by our packs for a lifetime and since we’ve been making packs since 1967, that’s a guarantee you can stand by.  []

Shipping the pack to San Leandro, CA only cost me $5.32, which seemed like a better deal than $55 for a new backpack.  The replacement pack came today (as I expected, they figured it would be cheaper to replace rather than repair the pack), a month later than when I sent the old one in.

The new pack is a different color (they no longer make a brown pack), and they have gone cheap on some aspects of the design—the old pack had an organizer that held 4 or more pens and pencils, plus a checkbook or two.  The new one barely holds 3 pencils and credit card, and the material for the organizer seems flimsy.  They’ve added a new feature—a laptop sleeve that adds weight to the pack while not adding anything I find useful, just making the main compartment more cluttered. I’ll use this one for a while, but I’ll probably be looking for a pack that has a decent organizer, since that was the feature that drew me to the old JanSport pack, and they have abandoned the one feature that made it stand out from a bunch of similar packs.

So the new pack is not as useful for me as the old one was when it was new, but better than the worn-out pack.  At least the zipper works and the shoulder straps aren’t in danger of falling off. The JanSport warranty works, if you don’t mind that they no longer make their sturdy pack with a decent organizer.

2014 September 9

Why are students going to for-profit colleges?

Filed under: Uncategorized — gasstationwithoutpumps @ 18:03
Tags: , , , ,

Faculty in public colleges are often mystified why students would choose to take out enormous loans to attend for-profit colleges whose degrees are mostly not respected either by industry or other colleges. In Confessions of a Community College Dean: Corinthian Learner “Dean Dad” explains why for-profit colleges managed to attract students, despite the low quality and ripoff financing:

Put simply, for-profits rushed in to fill the void left by the publics.  Decades of relative neglect of public higher education, combined with a certain (ahem) narcissism within the sector itself, left entire populations underserved.  Perhaps for impure reasons, for-profits figured out how to reach students nobody else bothered to reach.  They pioneered evening, weekend, and online delivery.  They built schedules around student needs.  They focused on a few distinct majors that both students and employers could understand.  And for a while, in some sectors, some of them got decent results.  In the late 90’s, you could do a lot worse than graduating with a degree in CIS.

For-profits filled a void. If you want to prevent the next catastrophe, tend to the void.

That means consciously and aggressively using the public sector—both community colleges and four-year regional campuses—as hedges against future disaster. It means making a dramatic and sustained turn away from the long-term trend of austerity for the publics and an open spigot for for-profits. When you include the cost of bailouts, the “efficient” for-profits wind up inflicting a far greater fiscal burden on the public than more generously funded publics would have. That’s even more true when you factor in student loan debt from students who never graduated, or who graduated but never earned salaries commensurate with their debts.

If dampening demand isn’t really an option, and diverting demand to the private sector leads to financial catastrophe, maybe…stay with me…we could fund the public sector well enough to meet the demand itself. Keep student cost down, get quality up, and learn some valuable lessons from for-profits about meeting students where they actually are. Prevent the next wave of for-profit megagrowth by choking off its air supply.

That means getting away from flat or declining operating budgets supplemented by “targeted” grants that fade away in three years, and instead pouring a fraction of what a for-profit bailout would cost into the public sector. When I was at DeVry, I didn’t see fear of the government or fear of lawyers. I saw fear of the nearby community college. There was a reason for that.

As long as for-profits are considered in isolation, we’ll continue to miss the point. Yes, close loopholes, prosecute liars, and enforce regulations, but those amount to fighting the last war. If you want to prevent the next bailout instead of the last one, you have to address the demand side. Give community and state colleges the resources—and, yes, the flexibility—to flood the zone. It’ll cost some money upfront, but it’s cheaper, more humane, and far more productive than bailouts and legal fees after the next collapse. We don’t have a great record of learning from catastrophes, but this one should be easy.

His post was made in response to the failure of the Corinthian Colleges chain, where the investors had siphoned off all they could get away with and the federal government was not allowing them to be the recipients of student loan money any more.  Other for-profit chains (Anthem Education, for example) are also on the ropes, now that the Federal spigot of infinite loans is being turned back a tiny bit. No attempt is expected to claw back the money from the “investors” who ripped off the students tricking them into taking out enormous loans for a fake education.

I think that his message is indeed correct. It is a lot cheaper to fund public universities well than to clean up the mess left by a completely unregulated for-profit education “industry”.  Students should not need to take out enormous loans to get an education, particularly not the inferior one that the for-profits provided.  Society is better served by having an educated populace that is not hugely in debt.


First-generation students

Filed under: Uncategorized — gasstationwithoutpumps @ 14:27
Tags: , , , ,

There were a couple of blog posts by in The Academe Blog in August 2014 pointing to articles about first-generation college students: students whose parents did not graduate from college with 4-year degrees.  This is a particularly important topic for University of California campuses, as UC admissions puts a high premium on being a first-generation student, resulting in large numbers of first-generation students.  (In Fall 2013, 44% of the freshmen at UCSC were first-generation students.)

In the first post First Generation Students Part I: Difference-Education, Walter Breau quotes from an  interview published in the Stanford Report:

“Closing the Social-Class Achievement Gap,” offers a new approach to help [first-generation students] advance in college: discuss class differences rather than ignore them. The research showed that when incoming first-generation students saw and heard stories from junior and senior students with different social-class backgrounds tell stories about their struggles and successes in college, they gained a framework to understand how their backgrounds shaped their own experiences and how to see this as an asset,”

(How’s that for 4 levels of indirection: me quoting Breau quoting an interview with Hamidani about a paper by Hamidani, Stephens, and Westin.)

The abstract of the paper itself sums up the research fairly well:

College students who do not have parents with 4-year degrees (first-generation students) earn lower grades and encounter more obstacles to success than do students who have at least one parent with a 4-year degree (continuing-generation students). In the study reported here, we tested a novel intervention designed to reduce this social-class achievement gap with a randomized controlled trial (N = 168). Using senior college students’ real-life stories, we conducted a difference-education intervention with incoming students about how their diverse backgrounds can shape what they experience in college. Compared with a standard intervention that provided similar stories of college adjustment without highlighting students’ different backgrounds, the difference-education intervention eliminated the social-class achievement gap by increasing first-generation students’ tendency to seek out college resources (e.g., meeting with professors) and, in turn, improving their end-of-year grade point averages. The difference-education intervention also improved the college transition for all students on numerous psychosocial outcomes (e.g., mental health and engagement).

The do not identify the private university at which they did the study, and I believe that the details of the university make a huge difference.  The adjustments needed when first-generation students are an insignificant minority (as they are at most elite private colleges) and when they are 44% of the incoming class are likely quite different, and so the interventions needed may differ not just in scale but in kind.  Since all the authors are at private research universities (Stanford and Northwestern), they likely did their study at either Stanford or Northwestern, neither of which has many first-generation students, and both of which have large numbers of rather wealthy students.  I question somewhat how well the results of studies on such campuses generalizes to the public universities which may soon be majority first-generation students (or already are in some cases), and where social class is not so skewed toward the wealthy.

In First Generation Students Part II: Cultural Fit, Walter Breau points to an article about cultural fit:

“Unseen Disadvantage: How American Universities’ Focus on Independence Undermines the Academic Performance of First-Generation College Students,” published in 2012 in the Journal of Personality and Social Psychology, concluded:

“That the seemingly positive middle-and upper-class cultural norms that pervade traditional American universities—norms that emphasize independent values such as ‘do your own thing,’ ‘pave your own path,’ and ‘express yourself’—can undermine the academic performance of first-generation students.”

The distinction that the article makes between “middle-class” and “working-class” values is independence vs. interdependence.  They found that college administrators at top-ranked colleges valued independent decision making much more than they valued interdependence, but that there were not significant differences between responses to questions about about independent vs. collaborative work.  Lower ranked colleges had less of a skew toward valuing independent decision making, but were otherwise fairly similar.

The study looked at a modest sample of student surveys and grades (245 first-generation, 1179 continuing-generation) to see whether independent/interdependent motive predicted cumulative GPA at the end of 2 years.  The effect sizes they saw were tiny—only coming out larger than race because they lumped all non-white race categories together, which makes some sense for looking at independent/interdependent, but not for looking at GPA, since Asian student typically perform quite differently from black and Latino students.  SAT scores alone were a much better predictor of grades than any of the sociological variables they looked at, and the only really good predictor of 2-year GPA was the 1-year GPA. So, while their results were statistically significant, it is not clear that they were really large enough to justify any conclusions about whether the “American Universities’ Focus on Independence Undermines the Academic Performance of First-Generation College Students”.  I certainly would not want to base policy decisions on such small effects.

Their study was done at schools with only about 17% first-generation students (based on the participant numbers in their study), which may be typical of US colleges as a whole, but is nothing like the UC system.  Even UCB, with the lowest ratio of first-generation students of any UC campus, had 23% first-generation students in 2010 (the latest for which I could find UC-wide data), and some campus were majority first-generation even in 2010 (Merced and Riverside).

Although it is important for UC to figure out how to help first-generation college students succeed, it is not clear to me that either of the studies that Breau reported on have much relevance for UC.


2014 September 1

Where PhDs get their Bachelors’ degrees

Last year I wrote about a study that looked at where CS PhD students got their bachelors’ degrees. Now Reed College has extended that question to other fields as well: Doctoral Degree Productivity.  Their point was to show how high Reed ranked on the standard they chose: the number of students who went on to get PhDs divided by the number of students getting bachelor’s degrees.  I quote the tables and accompanying text below, but I take no credit or blame for the data—this is directly from Reed’s site:

Undergraduate Origins of Doctoral Degrees

Percentage ranking of doctorates, by academic field, conferred upon graduates of listed institutions.

Rank All Disciplines Science and Math Social Sciences Humanities and Arts
1 Calif. Inst. of Tech. Calif. Inst. of Tech. Swarthmore New England Conserv. of Music
2 Harvey Mudd Harvey Mudd Grinnell Curtis Institute of Music
3 Swarthmore Reed Reed Juilliard
4 Reed MIT Bryn Mawr Cleveland Inst. of Music
5 Carleton NM Institute Mining & Tech. Spelman St. John’s College
6 MIT Carleton Oberlin Reed
7 Grinnell Wabash Wesleyan Hellenic College-Holy Cross Greek Orthodox Sch. of Theology
8 Princeton Rice St. Joseph Seminary Swarthmore
9 Harvard Univ. of Chicago Harvard Oberlin
10 Oberlin Grinnell Pomona Amherst

Percentage Ranking by Specific Fields of Study

Rank Life Sciences Physical Sciences Psychology Other Social Sciences* Humanities
1 Calif. Inst. of Tech. Calif. Inst. of Tech. Univ. Puerto Rico – Aguadilla Swarthmore St. John’s, MD
2 Reed Harvey Mudd Wellesley Reed Reed
3 Swarthmore Reed Vassar Harvard Amherst
4 Carleton MIT Hendrix Grinnell Swarthmore
5 Grinnell NM Institute Mining/Tech. Pontifical Coll. Josephinum Univ. of Chicago Carleton
6 Harvey Mudd Carleton Grinnell Bryn Mawr Yale
7 Univ. of Chicago Wabash Swarthmore Thomas More College of Lib. Arts Thomas More College of Lib. Arts
8 Haverford Rice Barnard Oberlin Bryn Mawr
9 MIT Univ. of Chicago St. Joseph Seminary Coll. Bard College at Simon’s Rock St. John’s, NM
10 Earlham Grinnell Pomona Wesleyan Wesleyan
11 Harvard Haverford Reed Amherst Princeton
12 Cornell Univ. Swarthmore Wesleyan Pomona Bard College at Simon’s Rock

*Does not include psychology, education, or communications and librarianship.

Source: National Science Foundation and Integrated Postsecondary Education Data System. The listing shows the top institutions in the nation ranked by estimated percentage of graduates who went on to earn a doctoral degree in selected disciplines between 2001-2010.

All the schools listed are private schools except Univ. Puerto Rico—Aguadilla and NM Institute Mining/Tech., but seeing dominance by expensive private schools is not very surprising—grad school is expensive, and students who can afford expensive private schools are more likely to be able to afford expensive grad school and are less likely to need to work immediately after getting their B.S. or B.A. A PhD is not a working-class degree—it is prepares one for only a small number of jobs, mainly in academia or national labs, so for many it is just an elite status symbol.  What is more surprising is how poorly the Ivy League schools do on this list—perhaps those who get their elite status conferred by their bachelor’s institution see no need to continue on to get higher degrees.

Reed does not report numbers directly comparable with the ones in the Computing Research Association report, which reports only on computer science PhDs, where

Only one institution (MIT) had an annual average production of 15 or more undergraduates.   Three other institutions (Berkeley, CMU, and Cornell) had an average production of more than 10 but less than 15.  Together, these four baccalaureate institutions accounted for over 10% of all Ph.D.’s awarded to domestic students.   The next 10% of all Ph.D.’s in that period came from only eight other baccalaureate institutions (Harvard, Brigham Young, Stanford, UT Austin, UIUC, Princeton, University of Michigan, and UCLA). 

Note that five of the top producers of bachelor’s in CS who went on to get PhDs were public schools.  The CRA does not report PhD/BS numbers for individual institutions, probably because the numbers are too small to be meaningful for most colleges—you have to aggregate either across many colleges or across many fields before the denominators are big enough to avoid just reporting noise.  Reed did the aggregating across fields, while the CRA report aggregated across colleges, finding that research universities sent about 2.5% of their CS graduates on to get PhDs, 4-year colleges about 0.9% and masters-granting institutions about 0.6%.  They did have one finding that supports Reed’s analysis:

The top 25 liberal arts colleges (using the U.S. News and World Reports ranking) collectively enroll slightly less than 50,000 students per year in all majors and were the origins of 190 Ph.D. degrees between 2000 and 2010, collectively ranking ahead of any single research university.

Reed’s findings are also consistent with the NSF report that put the “Oberlin 50″ colleges highest at over 5% of their science and engineering graduates going on to get PhDs, compared to about 3% for research universities.  The NSF report supports somewhat the analysis that socio-economic status is important in determining who goes on to grad school—private research universities match the Oberlin 50, but public research universities have only about half as large a fraction of their graduates go on to grad school.

I found out about this site from The Colleges Where PhD’s Get Their Start, which has a copy of the tables that probably came from an earlier, buggy  version of the site, because Lynn O’Shaughnessy wrote

I bet most families assume that attending a public flagship university or a nationally known private research university is the best ticket to graduate school. If you look at the following lists of the most successful PhD feeder schools for different majors, you will see a somewhat different story. Not a single public university makes any of the lists. The entire Cal State system, however, is considered the No. 1 producer of humanities PhD’s.

I could believe that the Cal State system had the largest raw numbers of students going on to get PhDs in humanities, as they are a huge 4-year college, enrolling about 438,000 students [], with about 76,000 bachelor’s degrees per year []. Are there any other colleges in the US graduating so many BS or BA students per year? But the fact remains that Cal State is not the flagship university of California, and the University of California probably has a much higher percentage of its alumni go on to get PhDs.

In fact, one of the big problems with these lists is the question of scale—most of the colleges that come up high on Reed’s lists (which means high on NSF’s lists) do so by having very small denominators—they don’t graduate many students, though a high percentage of those go on to get PhDs.  In terms of raw numbers of students who go on to get PhDs, the public research universities produce many more than the private research universities, and the liberal arts schools are just a drop in the bucket. Of the top 25 schools in terms of raw numbers who go on to get PhDs in science and engineering, 19 are public research universities and 6 are private research universities—of the top 50 only 17 are private research universities.

When you are looking for a cohort of similarly minded students, you get slightly higher enrichment at some very selective private schools, but there are actually more peers at a large public research university—if you can find them.

Next Page »

The Rubric Theme. Blog at


Get every new post delivered to your Inbox.

Join 268 other followers

%d bloggers like this: