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SSH has a great feature. It allows you to setup a private and public key pair with which you can SSH into the server without requiring a password. There are various reasons why you should want that. For example, you might be lazy (and you don't like typing it in). Another possibility is that you may want to have scripts which automatically login into the server (and fetch or place data). Setting it up is easy.

Often, I find myself having to surf the web through my employer. The main reason is that the library subscriptions for online journals recognizes the IP. For some strange reason, my ISP doesn't buy those subscriptions, but my university does.

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Cosmic Rays and Climate

This is the second of the three part article on the climatic role of the sun.

With the exception of those who have been living in a dark cave, it is well known that Earth has warmed over the 20^th century. Anyone who reads papers or watches TV knows that it is humans who are those responsible for this warming.

What is climate sensitivity?

The equilibrium climate sensitivity refers to the equilibrium change in average global surface air temperature following a unit change in the radiative forcing. This sensitivity (often denoted as λ) therefore has units of °C/(W/m²).

Often, instead &\lambda;, the sensitivity is expressed through the temperature change &Delta T_x2, in response to a doubled atmospheric CO₂ content, which is equivalent to a radiative forcing of 3.8 W/m². Thus, &Delta T_x2 = 3.8 W/m² λ

General Remarks

The manuscript submitted by Jahnke is an attempt to repeat analyses previously carried by myself (Shaviv PRL, 2002, New Astronomy, 2003). Although Jahnke raises a few interesting aspects, his analysis excludes several critical problems, because of which he obtains his negative result, that is, that there is no statistically significant periodicity in the data. By far, the most notable problem is that Jahnke's analysis does not consider the measurement errors. In his analysis, poorly dated meteorites were given the same weight as those with better exposure age determinations. As I show below, this has a grave effect on the signal to noise ratio (S/N) and consequently, on the statistical significance of any result.

My colleague and friend, Prof. Jan Veizer of the University of Ottawa, has written a review on the climatic role of carbon dioxide, cosmic rays and solar variability over different time scale. Unlike other material you will find on this web site, which was written with my subjective physicist's point of view, this review was written by one of the world's leading geochemists. Originally, Prof. Veizer set out to collect the most comprehensive geochemical data set, to reconstruct the paleoclimate variations over Phanerozoic (the past 550 Million years over which there are multicellular fossils to work with). His goal was to find the climatic signature of carbon dioxide in the data. To his disappointment, there was no clear correlation between his paleoclimatic reconstruction and the CO2 reconstruction (e.g.,

Ever wondered whether it was sufficiently cold for sufficiently long to allow you to stand on ice, without falling in? I once did. Here is an estimate for the duration required to reach a given thickness. Actually, it is a lower limit, since we assume a few simplifying assumptions.

Many physical systems have a tendency to equilibrate the energy between different subcomponents. Sometimes it is exact, and sometimes not. For example, in an acoustic wave, the wave's energy is on average half kinetic (motion of the gas) and half internal (pressure). In the interstellar medium, there is roughly the same energy in the different components, such as internal energy, turbulent energy, magnetic field and energy of the cosmic rays. Stars are no different. In the sun, there is roughly the same binding energy (which is negative) as there is thermal energy. This can also be shown using the virial theorem. In white dwarfs, the thermal energy is unimportant, instead, there the degenergy energy of the electrons is comparable to the binding energy. We can use this tendency for equipartition to estimate different stellar parameters.

Did you ever wonder how can it snow at above freezing temperatures? Well, the naive explanation is that it simple takes time for the snowflakes to melt once they penertrate above freezing air, as they descent downwards to the ground. As it turns out, this is the reaons why hail can fall in warm weather. The hail stones simple fall fast, too fast to let the warm air melt the hail.

With snow flakes, this isn't the case. The flakes fall very slowly and the large surface to volume ratio ensure that the flakes can reach thermal equilibrium with the environment on time scales much shorter than their descend time. So, how can the flakes remain frozen as they fall?

Water Rockets are simple homemade invensions that model their chemically fueled cousins. Unlike the latter, water rockets operate using water propulsion and hand-pump generated air pressure. Here we describe the equations of the problem. They are also solved numerically in the water rocket calculator.

How do you setup TeXShop to work with hebrew?

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