Uji Daya Hambat Ekstrak Daun Bawang Merah ( Allium Cepa L.) Terhadap Pertumbuhan Bakteri Escherichia Coli

: Backround - Shallots (Allium cepa L) is one of the plant that can be used as a traditional medicine. Method - This study was performed by using onion leaf to determine the inhibitory against the growth of Escherichia coli. Onion leafs extracted by maceration using 95% alcohol. The extract of the Onion leaves was diluted with distilled water to reach concentration of 1000 ppm, 3000 ppm, and 10,000 ppm. The test of inhibition effect of the extract of onion leaves was performed by using the papper disc method. Results - The results showed all the leaves of onion extract concentration did not produce a clear zone on the media. Conclusion - onion leaf extract has no inhibition on the growth of the bacterium Escherichia coli

How magnetic helicity ejection helps large scale dynamos

There is mounting evidence that the ejection of magnetic helicity from the solar surface is important for the solar dynamo. Observations suggest that in the northern hemisphere the magnetic helicity flux is negative. We propose that this magnetic helicity flux is mostly due to small scale magnetic fields; in contrast to the more systematic large scale field of the 11 year cycle, whose helicity flux may be of opposite sign, and may be excluded from the observational interpretation. Using idealized simulations of MHD turbulence as well as a simple two-scale model, we show that shedding small scale (helical) field has two important effects. (i) The strength of the large scale field reaches the observed levels. (ii) The evolution of the large scale field proceeds on time scales shorter than the resistive time scale, as would otherwise be enforced by magnetic helicity conservation. In other words, the losses ensure that the solar dynamo is always in the near-kinematic regime. This requires, however, that the ratio of small scale to large scale losses cannot be too small, for otherwise the large scale field in the near-kinematic regime will not reach the observed values.Comment: 10 pages, 5 figures, to appear in Adv. Space Sci. (Cospar 2002, ed. Buchner

The supernova-regulated ISM. I. The multi-phase structure

We simulate the multi-phase interstellar medium randomly heated and stirred by supernovae, with gravity, differential rotation and other parameters of the solar neighbourhood. Here we describe in detail both numerical and physical aspects of the model, including injection of thermal and kinetic energy by SN explosions, radiative cooling, photoelectric heating and various transport processes. With 3D domain extending 1 kpc^2 horizontally and 2 kpc vertically, the model routinely spans gas number densities 10^-5 - 10^2 cm^-3, temperatures 10-10^8 K, local velocities up to 10^3 km s^-1 (with Mach number up to 25). The thermal structure of the modelled ISM is classified by inspection of the joint probability density of the gas number density and temperature. We confirm that most of the complexity can be captured in terms of just three phases, separated by temperature borderlines at about 10^3 K and 5x10^5 K. The probability distribution of gas density within each phase is approximately lognormal. We clarify the connection between the fractional volume of a phase and its various proxies, and derive an exact relation between the fractional volume and the filling factors defined in terms of the volume and probabilistic averages. These results are discussed in both observational and computational contexts. The correlation scale of the random flows is calculated from the velocity autocorrelation function; it is of order 100 pc and tends to grow with distance from the mid-plane. We use two distinct parameterizations of radiative cooling to show that the multi-phase structure of the gas is robust, as it does not depend significantly on this choice.Comment: 28 pages, 22 figures and 8 table

Galactic dynamos with captured magnetic flux and an accretion flow

We examine the behaviour of an axisymmetric galactic dynamo model with a radial accretion flow in the disc. We also introduce a vertical magnetic flux through the galactic midplane, to simulate the presence of a large scale magnetic field trapped by the galaxy when forming. The trapped vertical flux is conserved and advected towards the disc centre by the radial flow. We confirm that accretion flows of magnitude several km/s through a significant part of the galactic disc can markedly inhibit dynamo action. Moreover, advection of the vertical flux in general results in mixed parity galactic fields. However, the effect is nonlinear and non-additive -- global magnetic field energies are usually significantly smaller that the sum of purely dynamo generated and purely advected field energies. For large inflow speeds, a form of `semi-dynamo' action may occur. We apply our results to the accumulation and redistribution, by a radial inflow, of a vertical magnetic flux captured by the Galactic disc. Taking representative values, it appears difficult to obtain mean vertical fields near the centre of the Milky Way that are much in excess of 10 microgauss, largely because the galactic dynamo and turbulent magnetic diffusion modify the external magnetic field before it can reach the disc centre.Comment: 18 pages, 12 figures, LaTE