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Fig. 3.13.1. Constraints on the relation between Vo and Kh in a convection-diffusion model from the observed CR grammage X and the observed abundance f of radioactive isotope 10Be. Results are shown for different extent of the halo zh . According to Bloemen et al. (1993).

Fig. 3.13.1 shows that the best fit of Vo and kh that can explain simultaneously X

= 6-8 g cm-2 and f = 0.2-0.3 are Kh = 1028cm2sec-1 and Vo = 10km.sec-1kpc-1 At a distance 30 kpc from the disk the velocity of galactic wind is expected to be 300 km/sec. This result shows that the galactic wind plays an important role for CR propagation and formation of the chemical composition. Moreover, this result can be considered as some additional evidence of existence of galactic wind.

3.13.2. The geometry of galactic wind and possible role of CR

The model of galactic wind driven by CR was proposed by Ipavich (1975). Recently we have had some radio-astronomical evidence for the existence of galactic wind (Reich and Reich, 1988; Hummel et al., 1988; Hummel and Dettmar, 1990; Pohl et al., 1991). In Section 3.13.1 we considered the importance of the existence of galactic wind for CR propagation and formation of chemical composition. One-dimensional Cartesian geometry of galactic wind (which is valid near the center and for distances z < 10 kpc from the disk) was considered by Breitschwerdt et al.(1991) and Fichtner et al. (1991). On the other hand, one-

dimensional spherical symmetric geometry, considered by Ipavich (1975) and Zank (1989), is applicable only for very large galacto-centric distances >15 kpc. A multidimensional model for ellipsoidal geometry (contains planar and spherical regimes as asymptotic cases) was considered by Fichtner et al. (1991), Vormbrock and Fichtner (1993).

3.13.3. Expected distribution of galactic wind velocity and CR density in the halo (ellipsoidal geometry model)

Vormbrock and Fichtner (1993) considered ellipsoidal geometry for the model of galactic wind driving by CR for our Galaxy and for NGC 4631 with about the same mass 2.75 x 1011 MSun and about the same dimensions of disk r^ = 15 kpc, hd = 1 kpc. The basic set of hydrodynamic equations is:

u pu

- uf - Ai + A2 = 0, V((YcPc -KVPc) - (Yc - l)(uV) = 0,

where f is the gravitational force, A1 reflects the heating processes (Coulomb interaction, ionization by CR), A2 takes into account cooling processes (bremsstrahlung, recombination, collision induced line emission). Fig. 3.13.2 shows the expected distribution of directions and values of galactic wind velocity in assuming that it has only one cause: driving by CR. The expected full mass loss rate is = 0.8 MSun/year, in good agreement with observations.

Let us note that the calculated values for galactic wind must be considered as a lower limit because there are at least several additional sources (supernova explosions, stellar winds etc.). In Fig. 3.13.3 the expected distribution of CR pressure Pc in the dynamical halo is shown (according to Vormbrock and Fichtner, 1993).

Fig. 3.13.2. Expected galactic wind velocity field: 1 - 25, 2 - 75, 3 -150, 4 - 225, 5 - 300 and 6 - 350 km/s. According to Vormbrock and Fichtner (1993).

r [kpcj

Fig. 3.13.2. Expected galactic wind velocity field: 1 - 25, 2 - 75, 3 -150, 4 - 225, 5 - 300 and 6 - 350 km/s. According to Vormbrock and Fichtner (1993).

Fig. 3.13.3. Expected distribution of CR pressure: 1 - 0.001, 2 - 0.003, 3 - 0.015, 4 - 0.075, and 5-0.2 eV/cm3. According to Vormbrock and Fichtner (1993).

Fig. 3.13.3. Expected distribution of CR pressure: 1 - 0.001, 2 - 0.003, 3 - 0.015, 4 - 0.075, and 5-0.2 eV/cm3. According to Vormbrock and Fichtner (1993).

3.14. Self-consistent problem for dynamic halo in rotating Galaxy

3.14.1. Solution for galactic wind and magnetic field

The self-consistent problem of CR propagation in the expanded halo, taking into account the rotation of the Galaxy, was considered by Zirakashvili et al. (1993), Ptuskin and Zirakashvili (1993). In the frame of axisymmetrical model it was supposed that plasma moved along some surface of rotation S (according to Weber and Davis, 1967; Yeh, 1976). The vectors u (galactic wind velocity) and H (frozen magnetic field) are coplanar to S. It is assumed that d/ds is the derivative in meridian direction (symbolized by ' ) and the cross section of the tube is B(s, ro). The basic steady state MHD equations which include CR pressure Pc (and under the assumption of the smooth transition of the solution through the possible critical points) will be:

Bpu = const, BH = const, p(y<-uru%¬°ur)= -(pg + Pc) -(r2H<| )/8nr2 + pf ',(3.14.1)

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Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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