Author: admin

Links for November 2021

Designing a Workflow For Thinking by Steven Johnson
Easy Focus Stack in Linux
Who Goes Fascist? A Political Psychologist Explains. Kristen Renwick Monroe looks at rescuers, bystanders, and perpetrators to understand why people do unspeakable acts. by Linda Mannheim

Reuters unmasks Trump supporters who terrified U.S. election officials by LINDA SO and JASON SZEP. Reporters track down criminals who made violent threats who police ignored.

GO client for linux, Sabaki

The ultra-wealthy have made full use of Roth individual retirement accounts. Here’s how you can do the same.

This Is How Many Calories You Burn on a Hilly Hike

60 Minutes Helps Andrew Sullivan’s Whitewashing: The blogger gets some prime time help with rewriting history
by Jeet Heer

Raccoon Was Once a Thanksgiving Feast Fit for a President. Calvin Coolidge refused to cook the raccoon sent to him, but the critter was a beloved staple for many Americans. by Jason Daley

Flourless chocolate cake recipe

I’m Confused Why All These People Are Quitting Jobs That Pay No Money and Make Them Want to Die by Chas Gillespie

Chicago Tool Library, South side

Plan C, information on access to mifepristone and misoprostol

Links for October 2021

Typical Employee Equity Levels
The 10 commandments of salary negotiation

Why $15 minimum wage is pretty safe. And why economists changed their minds on the minimum wage. by Noah Smith

Frank Wilhoit: The Travesty of Liberalism: “There is only conservatism. No other political philosophy actually exists; by the political analogue of Gresham’s Law, conservatism has driven every other idea out of circulation. There might be, and should be, anti-conservatism; but it does not yet exist. What would it be? In order to answer that question, it is necessary and sufficient to characterize conservatism. Fortunately, this can be done very concisely. Conservatism consists of exactly one proposition, to wit: There must be in-groups whom the law protects but does not bind, alongside out-groups whom the law binds but does not protect.

Coqz Heaumez, or Helmeted Cock

The Methods of Moral Panic Journalism: Scare stories on “left-wing illiberalism” display a familiar pattern. by Michael Hobbes

Multi-color 3D print head idea

Saw this paper, “Voxelated soft matter via multimaterial multinozzle 3D printing“, pdf. Two or more fluids come together at bend, and static pressure is enough to keep the current printing liquid moving towards the outlet, not backing up into the second material source tube. And the pressure of the current print liquid keeps the other fluids back.

There is effectively no mix chamber, so the change from one fluid to the other is quite quick, and there is little mixing after a switch.

This works because of the size and orientation of the fluid tubes in relation to the viscosity and other properties of the liquids. The authors make the print heads out of plastic and print with silicon and wax.

To use this for 3D printing plastic, the print head should be made out of a material with better heat resistance, such are metal or ceramic.

Make a print head like this out of ceramic (alumina, or similar ‘technical ceramic’). 1) 3D print the flow chamber and nozzle geometry out of a thermoplastic (or wax), then 2) slip cast ceramic around this. 3) When the ceramic is fired, the plastic will melt out or vaporize, leaving the desired nozzle geometry.

Idea 2
The geometry needed is simple, at least for two inputs. The thin join can be a very short segment, a few mm in length. The lead in tube can be drilled 2-3mm wide, then the 0.5 or 0.25 mm join tubes can be drilled out. Drill the outlet from the bottom, then drill the inlets from the bottom of the lead in holes. This would require precision to make the segments join up correctly, but the drill holes would be short.

Glass cutting w/ short laser pulses

Filamentation cutting
The output of an ultrashort pulse (< 15 picoseconds) laser is focused to a small spot within the substrate. The very high laser intensity achieved produces self-focusing of the beam (due to the Kerr optical effect) within the glass. This self-focusing further increases power density, until, at a certain threshold, a low-density plasma is created in the material. This plasma lowers the material refractive index in the center of the beam path and causes the beam to defocus. If the beam focusing optics are properly configured, this focusing/defocusing effect can be balanced to repeat periodically and self-sustain. This forms a stable filament, that is, a line of tiny voids, which extends over several millimeters in depth into the glass. The typical filament diameter is in the range of 0.5 µm to 1 μm.

Example system: 50 W of average output power at a wavelength of 1064 nm, 100 mm/s – 2 m/s.

Selective laser-induced etching (SLE)
An ultra-short pulsed laser (Satsuma HP2, Amplitude Systèmes, Pessac, France) with a central wavelength of 1030 nm and the maximum output power of 20 W was used. The maximum laser pulse energy was 40 μJ at the pulse repetition rate of 500 kHz and the pulse width variation was from 370 fs to 10 ps. The pulse repetition rate was variable up to 2000 kHz. For 3D fabrication machine, the laser amplifier was integrated with a 2-axis (XY) galvano scanner (DynAXIS, ScanLab, Puchheim, Germany) and an air bearing 3-axis(XYZ) servo motion stage with a controller (A3200, Aerotech, pittsburgh, USA). A focusing objective lens (NA = 0.4, model No. 378-867-5, Mitutoyo, Kawasaki, JAPAN) was assembled with the galvano scanner for high scan speed. The focused laser beam size is estimated about 2 μm. The combined scan speed of the scanner and 3D stage is up to 200 mm/s and the field size is 100 mm × 100 mm. After laser modification process, the exposed glass substrate was etched using 8 mol potassium hydroxide (KOH) at 85 °C in an ultrasonic bath for uniform concentration control. (Kim et al, 2019)

Possible laser: Osram SPL PL90 3 pulsed laser diode. It is constructed from three epitaxially stacked emitters with a laser aperture of 200 μm by 10 μm and has a peak output power of 75 W, a wavelength of 905 nm, and a maximum pulse width of 100 ns. The rated duty cycle is 0.1%, but this has been exceeded without damage to the diode. $20. datasheet, (Parziale_et_al, 2015)

Diodes with ps pulses are low energy mW or less, so coupling and amplification through a fiber laser is needed.

Can a waterjet be made from a centrifuge?

A waterjet is fast moving water:
waterjet water speed at 40,000 psi = 680 m/s
waterjet water speed at 60,000 psi = 1021 m/s

A pressure washer gives water a speed of 110 m/s.

How fast can a centrifuge spin? Ultracentrifuge speed:
centrifuge spins at 1e5 rpm, has a 10 cm radius rotor.
This give a speed at the rim of:
45 cm rotor circumference at the bottom of the tube
1e5/60 rotations / sec
0.45m/60 x 1e5 = 7.5e2 m/s
So a centrifuge does get water moving fast enough to act as a waterjet.

To turn the rotor spin into a line of water drops, open a door in the bottom of the rotor as the rotor passes a certain point in every spin (1000-2000 times / sec).

If the door is open for 10 us, the rotor will spin 1.5mm.
If the door is open for 1 us, the rotor will spin 0.15 mm.
The water stream will come out in a line, so the resolution in the other dimension can be finer, with the waterjet spread out along the direction of the cut.

A door can’t be mechanically opened and closed that fast, 1 ms is likely the limit.

But a reasonable solution is a rotating (or vibrating) plate with a hole, say spinning 1000/s (or 100/s, opening only every tenth pass), and synchronized with the main rotor spin so opening appeared at the same point along the edge. This would tend to torque the main rotor, but it might be tolerable.

This would give a waterjet with slower cutting–the drop density is 1:1000 or 1:10,000 of a stream.

The rotor would need to be refilled and have enough power to accelerate the new water, and solidly built enough to overcome vibration/torque. And fast centrifuges are expensive.

A micofuge will only give a water speed of 125 m/s.

Using cron to mute sound in Ubuntu 20.04

I wanted to turn off audio at night automatically using cron.

I saw suggestions to use amixer:
export DISPLAY=:0 && /usr/bin/amixer -D pulse sset Master,0 0%
but this gave an error:

ALSA lib pulse.c:242:(pulse_connect) PulseAudio: Unable to connect: Connection refused
amixer: Mixer attach pulse error: Connection refused

This works, add this line to /etc/crontab:

* 23<tab>* * *<tab>jiml<tab>DISPLAY=:0.0 pactl --server unix:/run/user/1000/pulse/native set-sink-mute @DEFAULT_SINK@ true

and restart cron:
service cron restart

jiml is the user with the open desktop.
‘1000’ is the uid of user ‘jiml’, this can be found by:

ls /run/user
id -u jiml

and restart cron:
service cron restart

jiml is the user with the open desktop.
‘1000’ is the uid of user ‘jiml’, this can be found by:

ls /run/user
id -u jiml