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Flaxer E.,Afeka Academic College of Engineering
Review of Scientific Instruments | Year: 2014

We present a new design of a compact, ultra fast, high resolution and high-powered, pulse generator for inductive load, using power MOSFET, dedicated gate driver and a digital signal controller. This design is an improved circuit of our old version controller. We demonstrate the performance of this pulse generator as a driver for a new generation of high-pressure supersonic pulsed valves. © 2014 AIP Publishing LLC.

Flaxer E.,Afeka Academic College of Engineering
Review of Scientific Instruments | Year: 2011

In electron ionization source, electrons are produced through thermionic emission by heating a wire filament, accelerating the electrons by high voltage, and ionizing the analyzed molecules. In such a system, one important parameter is the filament emission current that determines the ionization rate; therefore, one needs to regulate this current. On the one hand, fast responses control is needed to keep the emission current constant, but on the other hand, we need to protect the filament from damage that occurs by large filaments current transients and overheating. To control our filament current and emission current, we developed a digital circuit based on a digital signal processing controller that has several modes of operation. We used a smart algorithm that has a fast response to a small signal and a slow response to a large signal. In addition, we have several protective measures that prevent the current from reaching unsafe values. © 2011 American Institute of Physics.

Goldman I.,Afeka Academic College of Engineering
Acta Physica Polonica B | Year: 2011

We study the implications of asymmetric Dark Matter on neutron stars. We construct a "mixed neutron star" model composed of ordinary baryons and of asymmetric Dark Matter baryons. We derive the general relativistic structure equations for each specie, the equation for the mass within a given radius, and the redshift as function of radius. We present one specific numerical model as an illustrative example. In this example, the mass of the dark neutron equals half that of the ordinary neutron. The main results are: a total mass of 3:74M, a total mass within the neutron-sphere equaling 1:56M, the neutrons mass is 1:34M, the star radius is 31:9 km, the neutron-sphere radius is 11:1 km, and the redshifts from the neutronsphere and from the star surface are 0:72, 0:25, respectively. We comment briefly on possible astrophysical implications.

Drory A.,Afeka Academic College of Engineering
Foundations of Physics | Year: 2013

A recent paper suggested that if Galilean covariance was extended to signals and interactions, the resulting theory would contain such anomalies as would have impelled physicists towards special relativity even without empirical prompts. I analyze this claim. Some so-called anomalies turn out to be errors. Others have classical analogs, which suggests that classical physicists would not have viewed them as anomalous. Still others, finally, remain intact in special relativity, so that they serve as no impetus towards this theory. I conclude that Galilean covariance is insufficient to derive special relativity. © 2013 Springer Science+Business Media New York.

Contini M.,Tel Aviv University | Goldman I.,Afeka Academic College of Engineering
Monthly Notices of the Royal Astronomical Society | Year: 2011

The spectra emitted from clouds near the Galactic Centre (GC) are investigated calculating the UV-optical-IR lines using the physical parameters and the element abundances obtained by the detailed modelling of mid-IR observations. Graphical representation of the spectra reveals strong lines. Characteristic line ratios calculated at the nebula provide information about the dereddened spectra emitted from regions near the GC. These line ratios are compared with those observed in active galaxies. We have found that the physical conditions in the nebulae near the GC are different from those of starburst galaxies and active galactic nuclei, namely, gas velocities and densities as well as the photoionization fluxes are relatively low. The geometrical thickness of the emitting filaments is particularly small suggesting that matter is strongly fragmented by instabilities leading to an underlying shock-generated turbulence. This is revealed by the power spectra of the radial velocities, of the mid-IR continuum flux and of the computed Si/H relative abundances. Moreover, turbulence could amplify the initial magnetic fields. © 2010 The Authors. Journal compilation © 2010 RAS.

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