Posts about sciblog (old posts, page 12)

2013-11-08 homebrew cask (level 0): contributing a new cask

Read more…


2013-11-04 SparkleShare on a QNAP

  • SparkleShare is a great alternative to DropBox

  • Fetch the Dazzle script on

    curl   --output /usr/bin/dazzle && chmod +x /usr/bin/dazzle
  • set-up variables:

    export DAZZLE_USER=admin
    export DAZZLE_HOME=/share/Multimedia/dazzle
  • do it:

    dazzle setup
    dazzle create pool # a first project
    dazzle create-encrypted passwords # this one is completely encrypted on the server side and before the files leave the client


2013-10-26 Meshnet


2013-07-08 Useful numbers


  • Radiometric units represent physical energy (e.g., radiance has units of watts sr-1 . m-2 )
  • Colorimetric units adjust radiometric units for visual wavelength sensitivity (e.g. luminance has units of cd m-2 ); scotopic units are proportional to rod absorptions; photopic luminance units are proportional to a weighted sum of the L and M cone absorptions
  • Typical ambient luminance levels (in cd m-2): starlight 10-3; moonlight 10-1 ; indoor lighting 102 ; sunlight 105; max intensity of common CRT monitors, 102
  • One Troland (Td) of retinal illumination is produced on the retina when the eye looks at a surface of 1 cd / m2 through a pupil of area 1 mm2.
  • Lens focal length: f (meters); lens power = 1/f (diopters)
  • Conversion of linear units (X) to decibels: Y = 20 log10(X); a change of 0.3 log10 units is a factor of 2, or 6 dB

Image Formation

  • The eyes are 6 cm apart and half-way down the head
  • Visual angle of the sun or moon = 0.5 deg
  • At arm’s length: thumbnail = 1.5 deg; thumb joint= 2.0 deg; fist = 8-10 deg; index's thumbnail = 1 deg
  • Monocular visual field measured from central fixation: 160 deg (w) x 175 deg (h)
  • Binocular visual field measured from central fixation: 200 deg (w) x 135 deg (h)
  • Region of binocular overlap: 120 deg (w) x 135 deg (h)
  • Range of pupil diameters: 2mm -8mm.
  • Refractive indices: air 1.000; glass 1.520; water 1.333; cornea 1.376
  • Optical power (diopters): cornea, 43; lens, 20 (relaxed); whole eye, 60
  • Change in power due to accommodation, 8 diopters
  • Axial chromatic aberration over the visible spectrum: 2 diopters


  • Retinal size: 5 cm x 5 cm; 0.4 mm thick
  • One degree of visual angle = 0.3 mm on the retina
  • Number of cones in each retina: 5 x 10^6
  • Number of rods in each retina: 10^8
  • Diameter of the fovea: 1.5 mm (5.2 deg); rod-free fovea: 0.5 mm (1.7 deg); foveola (rod-free, capillary-free fovea): 0.3 mm (1 deg); size of the optic nerve head: 1.5 mm x 2.1 mm (5 deg (w) x 7 deg (h)) location of the optic nerve head: 15 deg nasal
  • Peak cone density: 1.6 x 105 cones/mm2;
  • Foveal cone size: 1-4 mu (diameter) x 50-80 mu (length); extrafoveal cone size: 4-10 mu (diameter) x 40 mu (length)
  • Size of rods near fovea: 1 mu (diameter) x 60 mu (length)
  • S cone spacing (foveal): 10 arc min
  • L and M cone spacing (foveal): 0.5 arc min
  • Number of (L + M) cones / Number of S cones = 14 (though the ratio may be higher in the foveola)
  • 1.5 10^6 optic nerve fibers/retina; ratio of receptors to ganglion cell in fovea 1:3; ratio of receptors to ganglion cells for whole retina, 125:1


  • Area of entire cortex: 1.3 x 105 mm2; 1.7 mm thick
  • Total number of cortical neurons: 1010; density: 105 neurons / mm3
  • Synapses: 5 x 108 synapses / mm3 4 x 103^ synapses/neuron;
  • Axons: 3 kilometers / mm^3
  • Number of corpus callosum fibers: 5 x 108
  • Number of macaque visual areas: 30
  • Size of each area V1: 3cm by 8 cm
  • Half of area V1 represents the central 10 deg (2% of the visual field)
  • Width of a human ocular dominance column 0.5-1.0 mm; width of a macaque ocular dominance column 0.3 mm”>.


  • Minimum number of absorptions for: scotopic detection 1-5; detectable electrical excitation of a rod 1; photopic detection 10-15
  • The number of photoisomerisations per rod (per sec?) required to saturate the retinal rod circuit.
  • Following exposure to a sunny day, dark adaptation to a moonless night involves: 10 minutes (photopic); 40 minutes (scotopic); change in visual sensitivity 6 log10 units
  • Highest detectable spatial frequency at high ambient light levels, 50-60 cpd; low ambient light levels, 20-30 cpd
  • The contrast threshold (Delta L / L) for a static edge at photopic luminances is 1%.
  • Highest detectable temporal frequency: high ambient large field, 80 Hz; low ambient, large field 40 Hz.
  • Typical localization threshold: 6 arc sec (0.5 mu on the retina)
  • Minimum temporal separation needed to discriminate two small, brief light pulses from a single equal-energy pulse: 15-20 ms
  • Stereoscopic depth discrimination: step threshold, 3 arc sec; point threshold, 30 arc sec


  • Visible spectrum: 370-730 nm
  • Peak wavelength sensitivity: 507nm (scotopic) and 555 nm (photopic)
  • Spectral equilibrium hues: 475 nm (blue), 500 nm (green), 575 nm (yellow), no spectral equilibrium red
  • Number of basic English color names: 11
  • Incidence of: anomalous trichromacy, 10-2 (male), 10-4 (female); protanopia and deuteranopia, 10-2 (male), 10-4 (female); tritanopia, 10-4; rod monochromacy, 10-4; cone monochromacy, 10-5


2013-06-12 updating to mactex (texlive for mac), version 2013

  • mactex is not there yet, but pre-relaeses are.

  • you can install the package from this script, or more simply

    wget # pre-release of TexLive 2013
    sudo installer -pkg mactex-2013.pkg -target /
  • to update your resource location to update packages, use

    sudo tlmgr option location
  • to upgrade

    sudo tlmgr update --self
    sudo tlmgr update --all


2013-05-14 dropping owncloud

  • since about 6 months, I was using ownCloud as a remplacement of dropbox, but I had unfortunately lots of problems and finally decided to drop wasting time on maintaining it.
  • it is certainly a useful service, but there are certainly simpler things to use to sync files accross computers and implement "your own cloud". here, I give some reasons for my choice and hope they may be useful for further developpment of owncloud or any other alternative to dropbox:
    • first of all, you need an efficient file syncing. it is dangerously buggy in owncloud:
      1. generates zillions of conflict files, takes ages to sync a folder with lots of files.
      2. the client happened to delete some files with no warning
      3. gives little feedback on how things are processed (the info dialog in client 1.2.5 is not functional). it took me a while to find a way to get some logfile (by calling the client with the --logfile argument) - but it is not documented elsewhere. the icons and error codes are not always informative.
      4. does not compile on snow leopard / 32-bit.
    • the server is simple to install but is too shiny over-the-top compared to its raw functionality.
      1. the upgrade process was rarely smooth due to "maintenance problems" related to the database (one day wasted for 5.0.4 > 5.0.5). this hints me that there may be security issues that are unresolved.
      2. the media server / photo gallery is merely useless
    • I bought the apps for iOS and android, and they are a joke
      1. you need to synchronize all your files, no choice is possible - thus it is just not useful and I could never access any file off-line
      2. uploading photos is buggy, videos are ignored
    • the ecosystem:
      1. based on a set of developers (some part of a company) and a set of users complaining about bugs that get closed is not reassuring
      2. the motto "you have a dropbox problem" is not pushing issues forward. certainly when comparing to the quality of the dropbox service
  • alert everything I say here is with a QNAP server (and I am not a sysdamin), so it is certainly partly my fault.


2013-03-25 using tabs in vim

  • call vim to open more files

    vim -p file1 file2 file3
  • or open one in your editing session

    :tabf <pattern>

    (will find the file corresponding to <pattern>)

  • to switch tab, use gt