Question: Acta Crystallographica and Journal of Synchrotron Radiation are defined as what?

<P0-S0> Acta Crystallographica is a series of peer-reviewed scientific journals, with articles centred on crystallography, published by the International Union of Crystallography (IUCr). <P0-S1>  Originally established in 1948 as a single journal called "Acta Crystallographica", there are now six independent "Acta Crystallographica" titles: "", "", "", "", "" and "". <P0-S2>  "Acta Crystallographica" has been noted for the high quality of the papers that it produces, as well as the large impact that its papers have had on the field of crystallography. <P0-S3>  The current six journals form part of the journal portfolio of the IUCr, which is completed by the "Journal of Applied Crystallography", the "Journal of Synchrotron Radiation", the open-access "IUCrJ" and the open-access data publication "IUCr Data". <SEP> <P1-S0> Cyclotron turnover is one of two phenomena due to which the power spectrum of synchrotron radiation decreases at very low frequencies. <P1-S1>  The other is synchrotron self-absorption. <P1-S2>  While the synchrotron self-absorption is determined from detailed balance, cyclotron turnover occurs when the assumptions of synchrotron radiation are violated. <P1-S3>  We recall that when a charged particle moves in a magnetic field its orbit is a helix, and its velocities can be divided into two independent components: uniform velocity parallel to the axis of the helix, and rotation about the axis. <P1-S4>  Synchrotron radiation requires that both velocities be ultra-relativistic, but if the velocity parallel to the axis is relativistic and the rotation is not, then the spectrum would simply be that of a Doppler shifted cyclotron radiation, and this behavior is called cyclotron turnover. <P1-S5>  In real systems there would be a competition between these two phenomena, so the only one that sets in at higher frequencies will be observed. <P1-S6>  An interesting feature about the cyclotron turnover is that it allows emission at frequencies lower that the cyclotron frequency, if the particle is moving away from the observer. <SEP> <P2-S0> The Journal of Synchrotron Radiation is a peer-reviewed scientific journal published by Wiley-Blackwell on behalf of the International Union of Crystallography. <P2-S1>  It was established in 1994 and covers research on synchrotron radiation and its applications. <P2-S2>  The editor-in-chief is S. Samar Hasnain (University of Liverpool). <SEP> <P3-S0> Synchrotron radiation (also known as magnetobremsstrahlung) is the electromagnetic radiation emitted when charged particles are accelerated radially, i.e., when they are subject to an acceleration perpendicular to their velocity (a ⊥ v ). <P3-S1>  It is produced, for example, in synchrotrons using bending magnets, undulators and/or wigglers. <P3-S2>  If the particle is non-relativistic, then the emission is called cyclotron emission. <P3-S3>  If, on the other hand, the particles are relativistic, sometimes referred to as ultrarelativistic, the emission is called synchrotron emission. <P3-S4>  Synchrotron radiation may be achieved artificially in synchrotrons or storage rings, or naturally by fast electrons moving through magnetic fields. <P3-S5>  The radiation produced in this way has a characteristic polarization and the frequencies generated can range over the entire electromagnetic spectrum which is also called continuum radiation.