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User: egede

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  1. Virtual environment in all cases on Ask Slashdot: Choosing a Laptop To Support Physics Research? · · Score: 1

    As a senior academic in particle physics I run linux on a Lenovo laptop at the moment. However, this is mainly out of habit as I have been running linux on my desktop/laptops for the last 18 years. If you have linux on your laptop, it is highly unlikely that you will anyway install a version that is compatible with the software used in particle physics (the standard platform will stay as a RHEL 6 at CERN until the end of RUN II at the LHC, so another 4 years or so). For this reason I anyway run the particle physics code inside a virtual machine.

    Running code locally can have many advantages. You are not for running big simulations, but lots of the data analysis takes place with datasets that have been reduced to 1 GB or less in size. To not rely on a shared file system and not waiting for X-windows to show up from the other side of the globe is a big advantage.

    All papers and reports are written in LaTeX which is supported everywhere. Presentations are written in many different ways (Latex, PowerPoint, LibreOffice, ...). and converted into PDF. In this area you can just do what you are most comfortable with. For communication, skype is used a lot (working fine on all platforms) and CERN is a partner in the Vidyo conference call system that again is supported everywhere.

    Conclusion from this is that the system on the machine is not an important choice. For developing and running code you will anyway use a virtualised linux environment, and for the rest, it is a matter of taste.

  2. Re:To *have* such problems... on Multi-Threaded SSH/SCP · · Score: 5, Informative

    The limitations of transfer rates for scp is often the round trip time that consumes time for confirmation of received packages. This is a serious issue for transfers from the Europe to the US West Coast (around 200 ms) or to Australia (around 400 ms). Having several parallel TCP streams can solve this problem and has been in use for many years for transfer of data in High Energy Physics. An example of such a solution is GridFTP http://www.globus.org/toolkit/docs/4.0/data/gridftp/.

  3. Re:Aerogel Facts on The Amazing Properties of Aerogel · · Score: 1

    There is nothing fantastic about the "faster than speed of light here". The speed of light is lower than in vacuum in all materials. As an example in quartz the speed of light is around 200000 km/s compared to the speed of light in vacuum which is 300000 km/s. So a particle travelling at 290000 km/s travels faster than the speed of light in quartz (and thus emits cherenkov radiation) but slower than the speed of light in vacuum.

    Einsteins theory of special relativity says that particles cannot travel faster than the speed of light in vacuum so no "warp" factors are required here.

  4. Re:Aerogel Facts on The Amazing Properties of Aerogel · · Score: 3, Informative

    Aerogel is also used within particle physics for telling different types of particles apart in Cherenkov detectors.

    In any transparent material particles will emit light in a cone around their trajectory when they are travelling faster than the speed of light in that material (analogous to sonic boom produced by plane going faster than speed of sound). From measuring the angle the light is emitted at we can work out the velocity. The range of velocities we are sensitive to depends on the refractive index of the material which is where aerogel comes into the game. We have gasses with refractive indices very close to one (n = 1.0005 for CF4) or glass with large refractive index (n=1.47 for quartz) but no normal material in between. Aerogel with a refractive index around 1.03 gives us new possibilities.

    Within a particle physics experiment we can use a magnetic field to determine the momentum of a particle from the curvature of its trajectory. If we put this together with the measurement of its velocity from the Cherenkov detector we can work out the mass. This allows us to distinguish pions and kaons in an experiment like LHCb which is currently under construction. Here CF4 (gas), C4F10 (heavier gas) and aerogel are used to give coverage of a wide velocity range.