Scientific Computing

To disable Bluetooth on Ubuntu persistently (stays off after reboot too):

systemctl disable bluetooth.service

To manually re-enable Bluetooth if desired:

systemctl enable bluetooth.service

Some Linux distros in the past set the APM default very aggressively, leading your hard drive to hundreds and thousands of load/unload cycles in too short period of time. Typically HDD are only rated for 600,000 load/unload cycles, so it might be beneficial to reduce this cycling, at the expense of some additional power consumption.

The procedure below is informational, and may or may not provide benefit.

You can slow down the cycling manually, but the system will FORGET this setting upon reboot.

Make HDParm setting semi-permanent:

make line hdparm -B 250 /dev/sda, where /dev/sda is the HDD you’re wanting to stop cycling.

geany /etc/pm/power.d/90_hdparm

type

chmod +x /etc/pm/power.d/90_hdparm

cp /etc/pm/power.d/90_hdparm /etc/pm/sleep.d

Reboot, and check that your setting “stayed”

hdparm -B /dev/sda

This setting allows the drive to unload after an extended period without use, perhaps helping the HDD run a bit cooler without excessive wear. Instead of 250 you could use 254, which is thought to disallow unloading altogether. Try 254 and monitor HDD temperature–100 degrees Fahrenheit is possible.

To check how many load/unload cycles you’re using, go into Disk Utility, SMART data, and scroll down to Load/Unload cycle count.

similar procedure

WINE users may experience:

Failed reading JPEG because unable to find libjpeg.so.62

Fix by installing the Windows codecs:

winetricks windowscodecs

The Seagate Momentus XT 500GB hybrid hard drive (4GB SSD, 500GB HDD) is a useful way to speedup system boot and execution. However, on brand new files the speed is the same as a typical hard drive. A USB 3.0 drive adapter shows what the drive could do over a USB 3.0 link, using Disk Utility on Ubuntu.

Average read speed: 90MB/sec. Average write speed: 97MB/sec.

magnetic bottle: pitch angle distribution vs. mirror height equipotential lines -> parallel E-field (Stephen Knight 1970) -> Large scale, dull auroral arc

• inertial alfven wave connection to parallel E-field

fine scale arcs assosciated with Farley-Buneman instabilities, GPS scintillation

energy to produce electron-ion pair ionization potential ~ 18 eV takes on average ~ 35 eV

energy deposition physics

single particle motion, 3 adiabatic invariants, Debye length, two fluid vector potential

Alfven wave can couple to whistler mode

Auroral emissions: Bohr model of atom. have to release energy gap between orbitals (work function). Vibrational modes

Ions: closure current electrons: field aligned current

Inertial alfven wave: electron mass matters due to phase speed > speed of light F=ma inertial limit inerital lag – prevents group velocity from exceeding speed of light

λ_e = c / ω_pe electron skin depth confines wave

Auroral emissions:

Björn Gustavsson Ph.D. thesis discusses briefly specifics of four major auroral emission lines.

Thesis on kinetic reactions resulting in auroral emissions.

Auroral width:

• Borovsky 1993 “Auroral arc thicknesses as predicted by various theories”, JGR: Space Physics.
• Chaston 2003 “Width and brightness of auroral arcs driven by inertial Alfven waves”, JGR: Space Physics.

Books:

• Chen
• Kivelson and Russell
• Cravens
• Nagey

Do NOT do this if you have an encrypted partition, as you’ll lose access to all that data!! reference on forgotten password vis ecryptfs.

1. Reboot
2. at GRUB, choose Recovery Mode, then root.
3. reset password

mount -o remount,rw /

passwd myusername

With the spectre of the Positive Train Control mandate looming over small railroads, it’s not only the short-line railroads impacted. Long-distance rural lines can have considerable dark territory. Such railroads may have substantial cost added to their capital budget by PTC. Without radio contact, such railroads have been limited in dark territory to restricted speed 10-25 mph instead of the 49 mph they might otherwise run in dark territory.

Possible solutions for radio contact in rural areas

• microwave links - much too expensive for distance, terrain vs. low train count
• leased (dedicated) phone line - same as microwave–too expensive
• PSTN/POTS - use a typical “interconnect” for two-way radio.

The latter option may be much more economically feasible for many rural railroads. This option has not been evaluated for compliance with federal railroad regulations. Railroads in the Rocky Mountains, with vast individual tower coverage areas, have long used DTMF selective calling of dispatch to avoid dispatchers being overwhelmed with constant train chatter.

CONOPS of POTS-linked rural dark territory railroad radio: dispatch has multiple phone lines, all ringing for the same number dedicated to inbound radio calls. Different branches dispatched by distinct dispatchers could obviously have separate phone numbers. The caller ID of the individual interconnect into dispatch identifies the approximate subdivision the train is on (not for legal purposes but for convenience). Cell phones could be used in place of POTS if more economical.

Train to dispatch: train keys up mic, dials dispatch phone number like a standard two-way radio interconnect call. Train engineer uses standard radio message protocol to talk to dispatch, then train hangs up via DTMF. Can use single frequency for network to keep any other trains advised, although dark territory and long distances imply long blocks.

Dispatch to train: dispatch calls phone number of interconnect they believe train is in range of. Train engineer answers via DTMF, uses standard radio protocol to talk. Dispatch hangs up phone, train engineer sends DTMF to close link if phone line hangup not detected.

Besides the typical radio base station tower and antenna, selected with sufficient overlap in 49 mph-desired territory, the Zetron Model 30 is about $600. Cost of power and phone connection trenching might be mitigated by sharing with cellular towers or power utility company where feasible. Naturally, a more advanced interconnect could be used to control and monitor railroad switches and the like, also enhancing railway safety. In regions hauling relatively benign cargo with a single train per day, some in the industry have felt PTC requirements were two stringent. If it’s not too late, some waivers might be obtained for a time at least by using ideas as above, pending compliance with all applicable regulations.

I tried honestly to use the HP 50g, and here are a few objections that put me back to the TI-89. The low resolution (blocky/grainy) HP 50g display detracts from its usefulness as a high-end graphing calculator. Low resolution limits length of equations and number of equations on the screen. One of the major reasons for having a high-end calculator is to allow entering long equations on the screen.

That being said, the HP 50g has a dedicated core of aficionados. HP 50g advocates will present a list of counterpoints–and their arguments have merits.

Given the feature set and the inevitable eventual sunsetting of the 15+ year old TI-89 series, a new user considering what high-end calculator to purchase should look to the TI Nspire CX CAS.

In closing, I will give strong admonition to students. DO NOT rely heavily on calculators in math courses. This will only cause suffering in later courses. Even if the last math class in college will be Calculus I or II, you will never gain the true richness of understanding if constantly using a calculator for homework.

A better approach is to do the problems manually, and on occasion check with the calculator.

Legacy auroral video acquisition has been plagued with several problems including

1. camera sensitivity
2. data storage
3. video time synchronization
4. software instability

An example of such a system was deployed last winter to Poker Flat Research Range. The results of this work won “Honorable Mention” at the CEDAR 2011 Workshop. A two camera system observed the aurora from Poker Flat Research Range (Chatanika, AK) and Ester, AK.

Notice the hardware synchronization connections on the camera are not being used. This makes the system reliant on the vagaries of software timing of the OS, which in Windows case can account for order 100 ms. When one wants 33 ms cadence video, this means such video will be roughly syntonized, but poorly synchronized.

Timing error due to non-hardware synchronization: error for a single frame, the error will accumulate in general due to error bias, quickly leading the cameras to be taking pictures at different times (no video frame overlap in time).

The software trigger error is not predictable and can reach up to 1/2 second. Aurora has apparent motion of kilometers per second, and so a camera designed for 10..100 m scale width observations needs to have timing error commensurate with the physical phenomenon. Hopes of a tomographic solution are dashed if the pictures are taken at times distant enough such that the feature of interest changes on timescale less than the error.

Observational Solution for Auroral Tomography: the ill-conditioned, ill-posed nature of the high-resolution auroral tomography problem dictates attention to detail of all aspects of cross-site registration. We will have to ensure:

1. images are accurately registered.
2. Absolute and relative timing are synchronized to at least 2 orders of magnitude better than the frame cadence (< 1 % timing error)
3. If the data writing becomes overwhelmed, the system should discard a bit of video and recover rather than stutter the recording.

Notes

Plant, G., Semeter, J., Marshall, R., Dahlgren, H., Goenka, C., and Hampton, D. (2011). A high-speed tomographic imaging system for studying dynamic aurora. In Instruments or Techniques for Ionospheric or Thermospheric Observation. CEDAR Workshop, Santa Fe, NM. ITIT-06.

When you view the aurora, whether by camera or by being outside with your eyes, what you see is a line integral of the line-of-sight brightness of the optically thin aurora. Mathematically, this is

I = ∫_0 ∞ p(ℓ) dℓ

where:

• I is the intensity seen by your eye or camera pixel
• p(ℓ) is the volume intensity rate of the aurora at each differential point along ℓ

Volume emission rate of aurora is created when particles (electrons or ions) strike the cold gas of the ionosphere, typically N_2, N_2+ or O. As altitude increases above a couple hundred kilometers, oxygen starts to become the dominant gas instead of nitrogen. This affects the color of the aurora, and is part of why aurora appears as green below red.

Unfortunately, many of the images taken of aurora with digital cameras have incorrect white balance, and completely non-physical colors are seen. Yes, there is purple aurora, but it is quite faint and below the green emissions in altitude. So a sky full of purple, yellow, and orange is not believable, it’s an artifact of incorrect white balance.

That’s a big part of why it’s good to save auroral photos in RAW format from your camera so you can fix the images in post-processing.