症状: touch pad is too sensitive
方法：编辑 /etc/X11/xorg.conf
Section "InputDevice"
Identifier "Synaptics Touchpad"
Driver "synaptics"
Option "SendCoreEvents" "true"
Option "Device" "/dev/psaux"
Option "Protocol" "auto-dev"
Option "MaxTapMove" "10"
Option "SHMConfig" "on"
EndSection
Section "ServerLayout"
Identifier "Default Layout"
Screen "Default Screen"
InputDevice "Generic Keyboard"
InputDevice "Synaptics Touchpad"
InputDevice "Configured Mouse"
InputDevice "stylus" "SendCoreEvents"
InputDevice "cursor" "SendCoreEvents"
InputDevice "eraser" "SendCoreEvents"
EndSection
7/28/2008
天文距离单位Parsec (pc)
How Distances are Measured in Astronomy
Dealing with the numbers involved with the distances to the stars or even with those found in the solar system can be hard going. Astronomers make their lives easier by using a number of rulers (units of distance) for the distances and although they have some strange names they can be very useful for comparing the distances to stars, other galaxies and even the planets in our solar system.
AU (astronomical units)
One AU is the distance that the average distance that the Earth orbits the Sun at. The AUis most commonly used for the distances of objects with in our solar system. Pluto, the last planet in the solar system is found at an average distance of 39.47 au from the Sun. Sedna the new body nearly as large as a planet found beyond Pluto is never nearer to the Sun than 76AU and then goes to 880AU from the Sun in its giant elliptical orbit.
Light Years
One of the most common rulers is the light year. The light year is is the distance that light travel in one year (365 1/4 days). It is most commonly used for the distances to stars and other galaxies.
The nearest star is 4.2 light years away from our sun. We are 8.3 light minutes away form the Sun. the distance to the outer most planet Pluto is about 13 light hours.
Some other interesting distances in light years:
| Object | Distance in light years |
| Nearest Star (Proxima Centuri) | 4.2 |
| Sirius the dog star (the brightest star in the sky) | 8.6 |
| centre of the galaxy | approximately 30 000 |
| Andromeda (one of our nearest neighbouring galaxies) | approximately 2 million |
| The stars of Orion. (Betelgeuse and Rigel) | 1400 light years |
Parsec (pc)
Astronomers started measuring distances from the amount that a star moves as the Earth goes from one side of the Sun to the other. Try moving your head and you will see that the postion of everything around you changes. One parsec is derived from the smallest angle measurement of 1/3,600th of a degree or an arc second that is the angle that a star at this distance would appear to move in 6 months as the Earth journeys around the Sun. A parsec is 3.2616 light years or 30,857,000,000,000 km.. Two parsecs is 6.5532 light years or twice the distance, it is not a measure of change in angles of the stars. Due to the massive distance in the universe astronomers often use multiples of parsec commonly found are kiloparsec (kpc) a 1000 parsecs or a megaparsec (Mpc) 1,000,000 parsecs.
Below is a conversion table for some useful astronomical distance units
| kilometres (km) | Astronomical units (AU) | Light Years (l.y.) | Parsec (pc) | |
| kilometres (km) | 1 | 149.6 million | 9,460,000,000,000 | 30,857,000,000,000 |
| Astronomical units (AU) | 0.0000000067 | 1 | 63,240 | 206,263 |
| Light Years (l.y.) | 0.00000000000011 | 0.000016 | 1 | 3.2616 |
| Parsec (pc) | 0.000000000000033 | 0.0000048 | 0.3066 | 1 |
7/23/2008
7/22/2008
7/21/2008
mathematica 字体 透明 问题
在linux有时mathematica会有 字体透明问题，起根本原因是x文件冲突
解决办法是
在运行 mathematica 之前运行
解决办法是
在运行 mathematica 之前运行
export XLIB_SKIP_ARGB_VISUALS=1
很无奈但是没别的办法。
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