Question: Acta Crystallographica and Journal of Synchrotron Radiation are defined as what?
Context: The Journal of Synchrotron Radiation is a peer-reviewed scientific journal published by Wiley-Blackwell on behalf of the International Union of Crystallography.  It was established in 1994 and covers research on synchrotron radiation and its applications.  The editor-in-chief is S. Samar Hasnain (University of Liverpool). Cyclotron turnover is one of two phenomena due to which the power spectrum of synchrotron radiation decreases at very low frequencies.  The other is synchrotron self-absorption.  While the synchrotron self-absorption is determined from detailed balance, cyclotron turnover occurs when the assumptions of synchrotron radiation are violated.  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.  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.  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.  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. 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 ).  It is produced, for example, in synchrotrons using bending magnets, undulators and/or wigglers.  If the particle is non-relativistic, then the emission is called cyclotron emission.  If, on the other hand, the particles are relativistic, sometimes referred to as ultrarelativistic, the emission is called synchrotron emission.  Synchrotron radiation may be achieved artificially in synchrotrons or storage rings, or naturally by fast electrons moving through magnetic fields.  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. Acta Crystallographica is a series of peer-reviewed scientific journals, with articles centred on crystallography, published by the International Union of Crystallography (IUCr).  Originally established in 1948 as a single journal called "Acta Crystallographica", there are now six independent "Acta Crystallographica" titles: "", "", "", "", "" and "".  "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.  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". The Synchrotron Radiation Center (SRC), located in Stoughton, Wisconsin and operated by the University of Wisconsin–Madison, was a national synchrotron light source research facility, operating the Aladdin storage ring.  From 1968-1987 SRC was the home of Tantalus, the first storage ring dedicated to the production of synchrotron radiation. SPring-8 (an acronym of Super Photon Ring – 8 GeV) is a synchrotron radiation facility located in Hyōgo Prefecture, Japan, which was developed jointly by RIKEN and the Japan Atomic Energy Research Institute.  It is owned and managed by RIKEN, and run under commission by the Japan Synchrotron Radiation Research Institute.  The machine consists of a storage ring containing an 8 GeV electron beam.  On its path around the storage ring, the beam passes through insertion devices to produce synchrotron radiation with energies ranging from soft X-rays (300 eV) up to hard X-rays (300 keV).  The synchrotron radiation produced at SPring-8 is used for materials analysis and biochemical protein characterization by many Japanese manufacturers and universities. The Hiroshima Synchrotron Radiation Center, also known as Hiroshima Synchrotron Orbital Radiation (HiSOR), at Hiroshima University is a national user research facility in Japan.  It was founded in 1996 by the University Science Council at Hiroshima University initially as a combined educational and research facility before opening to users in Japan and across the world in 2002.  It is the only synchrotron radiation experimental facility located at a national university in Japan. The Stanford Synchrotron Radiation Lightsource (formerly Stanford Synchrotron Radiation Laboratory), a division of SLAC National Accelerator Laboratory, is operated by Stanford University for the Department of Energy.  SSRL is a National User Facility which provides synchrotron radiation, a name given to electromagnetic radiation in the x-ray, ultraviolet, visible and infrared realms produced by electrons circulating in a storage ring (Stanford Positron Electron Asymmetric Ring - SPEAR) at nearly the speed of light.  The extremely bright light that is produced can be used to investigate various forms of matter ranging from objects of atomic and molecular size to man-made materials with unusual properties.  The obtained information and knowledge is of great value to society, with impact in areas such as the environment, future technologies, health, and education. The Synchrotron Radiation Source (SRS) at the Daresbury Laboratory in Cheshire, England was the first second-generation synchrotron radiation source to produce X-rays.  The research facility provided synchrotron radiation to a large number of experimental stations and had an operating cost of approximately £20 million per annum. The Canadian Synchrotron Radiation Facility (CSRF) (French: "Institut canadien du rayonnement synchrotron – ICRS" ) was Canada's national synchrotron facility from 1983–2005.  Eventually consisting of three beamlines at the Synchrotron Radiation Center at the University of Wisconsin–Madison, USA, it served the Canadian synchrotron community until the opening of the Canadian Light Source in Saskatoon, Saskatchewan, finally ceasing operations in 2008.
Answer: peer-reviewed scientific journal